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New submissions for Mon, 22 Feb 10

[1]  arXiv:1002.3611 [ps, pdf, other]
Title: Connections Between Local and Global Turbulence in Accretion Disks
Comments: 8 Pages, 7 Figures ApJ, In Press
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We analyze a suite of global magnetohydrodynamic (MHD) accretion disk simulations in order to determine whether scaling laws for turbulence driven by the magnetorotational instability, discovered via local shearing box studies, are globally robust. The simulations model geometrically-thin disks with zero net magnetic flux and no explicit resistivity or viscosity. We show that the local Maxwell stress is correlated with the self-generated local vertical magnetic field in a manner that is similar to that found in local simulations. Moreover, local patches of vertical field are strong enough to stimulate and control the strength of angular momentum transport across much of the disk. We demonstrate the importance of magnetic linkages (through the low-density corona) between different regions of the disk in determining the local field, and suggest a new convergence requirement for global simulations -- the vertical extent of the corona must be fully captured and resolved. Finally, we examine the temporal convergence of the average stress, and show that an initial long-term secular drift in the local flux-stress relation dies away on a time scale that is consistent with turbulent mixing of the initial magnetic field.

[2]  arXiv:1002.3614 [pdf, other]
Title: Measuring the "Reduced" Shear
Authors: Jun Zhang (UT Austin, UC Berkeley)
Comments: 10 pages, 3 figures, submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We show that cosmic shear measurement can be made accurate to the second order in shear in the presence of a PSF and photon noise using an extension of the method of Zhang (2008). The sign of the second order correction is opposite to what is conventionally assumed. Neglecting the second order corrections can lead to a few percent uncertainties on cosmic shears, and becomes more important for cluster lensing mass reconstructions. Our shear measurement method is well defined mathematically. It does not require assumptions on the morphologies of galaxies and the point spread function. Contaminations to the shear signals from the background photon noise can be removed also in a well defined way. Using a large ensemble (10^7) of mock galaxies of unrestricted morphologies, we demonstrate that the shear recovery accuracy in this method reaches at least sub-percent levels even in the presence of large and correlated background noise. The recovery accuracy of shear-shear correlations are also tested under general conditions.

[3]  arXiv:1002.3615 [ps, pdf, other]
Title: Ideal Cosmic Shear Estimators Do Not Exist
Authors: Jun Zhang (UT Austin, UC Berkeley)
Comments: 10 pages, submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)

A long standing problem in weak lensing is about how to construct a cosmic shear estimator from galaxy images. Ideally, for each shear component, one wants a single quantity from each galaxy image, whose ensemble average is equal to the true shear value. We prove that such ideal shear estimators do not exist in the presence of the point spread function. Alternatively, from each galaxy image, one can construct two quantities for each shear component, and use the ratio of the ensemble averages of the two quantities to recover the shear in an unbiased way. We show that the later is achievable using the shear measurement method of Zhang (2008). We also demonstrate that with the new but less ideal shear estimator, weak lensing statistics such as n-point correlations should be carried out in a slightly different way, but with little additional cost.

[4]  arXiv:1002.3618 [ps, pdf, other]
Title: The AGN fraction of submm-selected galaxies and contributions to the submm/mm-wave extragalactic background light
Comments: Accepted for Astronomy and Astrophysics AKARI special issue
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

We present a comparison of the SCUBA Half Degree Extragalactic Survey (SHADES) at 450, 850 and 1100 microns with deep guaranteed time 15 microns AKARI FU-HYU survey data and Spitzer guaranteed time data at 3.6-24 microns in the Lockman Hole East. The AKARI data was analysed using bespoke software based in part on the drizzling and minimum-variance matched filtering developed for SHADES, and was cross calibrated against Infrared Space Observatory (ISO) fluxes. Our stacking analyses find AKARI 15um galaxies with >~200 microJy contribute >10% of the 450 micron background, but only <4% of the 1100 micron background, suggesting that different populations contribute at mm-wavelengths. We confirm our earlier result that the ultra-deep 450 micron SCUBA-2 Cosmology Survey will be dominated by populations already detected by AKARI and Spitzer mid-infrared surveys. The superb mid-infrared wavelength coverage afforded by combining Spitzer and AKARI photometry is an excellent diagnostic of AGN contributions, and we find that (23-52)% of submm-selected galaxies have AGN bolometric fractions f_AGN>0.3.

[5]  arXiv:1002.3619 [pdf, other]
Title: AMUSE-Virgo II. Down-sizing in black hole accretion
Comments: Version submitted to ApJ after addressing referee's comments
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

(Abridged) We complete the census of nuclear X-ray activity in 100 early type Virgo galaxies observed by the Chandra X-ray Telescope as part of the AMUSE-Virgo survey, down to a (3sigma) limiting luminosity of 3.7E+38 erg/s over 0.5-7 keV. The stellar mass distribution of the targeted sample, which is mostly composed of formally `inactive' galaxies, peaks below 1E+10 M_Sun, a regime where the very existence of nuclear super-massive black holes (SMBHs) is debated. Out of 100 objects, 32 show a nuclear X-ray source, including 6 hybrid nuclei which also host a massive nuclear cluster as visible from archival HST images. After carefully accounting for contamination from nuclear low-mass X-ray binaries based on the shape and normalization of their X-ray luminosity function, we conclude that between 24-34% of the galaxies in our sample host a X-ray active SMBH (at the 95% C.L.). This sets a firm lower limit to the black hole occupation fraction in nearby bulges within a cluster environment. At face value, the active fraction -down to our luminosity limit- is found to increase with host stellar mass. However, taking into account selection effects, we find that the average Eddington-scaled X-ray luminosity scales with black hole mass as M_BH^(0.62^{+0.13}_{-0.12}), with an intrinsic scatter of 0.46^({+0.08}_{-0.06}) dex. This finding can be interpreted as observational evidence for `down-sizing' of black hole accretion in local early types, that is, low mass black holes shine relatively closer to their Eddington limit than higher mass objects. As a consequence, the fraction of active galaxies, defined as those above a fixed X-ray Eddington ratio, decreases with increasing black hole mass.

[6]  arXiv:1002.3620 [ps, pdf, other]
Title: Surface appearance of dynamo-generated large-scale fields
Authors: J. Warnecke (1,2), A. Brandenburg (1,2) ((1) Nordita (2), Stockholm University)
Comments: 7 pages, 10 figs, submitted to A&amp;A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Twisted magnetic fields are frequently seen to emerge above the visible surface of the Sun. This emergence is usually associated with the rise of buoyant magnetic flux structures. Here we address the question about magnetic field structures that are generated by a turbulent large-scale dynamo just beneath the surface. The computational domain is split into two parts. In the lower part, which we refer to as the turbulence zone, the flow is driven by an adopted helical forcing function leading to dynamo action. Above this region, which we refer to as the exterior, a nearly force-free magnetic field is computed at each time step using the stress-and-relax method. A twisted arcade-like field structure is found to emerge in the exterior above the turbulence zone. Strong current sheets tend to be formed above the neutral line, where the vertical field component vanishes. The degree to which the exterior field is force-free is estimated as the ratio of the dot product of current density and field strength to their respective rms values. This ratio reaches values of up to 95% in the exterior. A weak outward wind is driven by the residual Lorentz force.

[7]  arXiv:1002.3625 [ps, pdf, other]
Title: Chandra and Swift Follow-up Observations of the Intermediate Mass Black Hole in ESO243-49
Authors: N. A. Webb, D. Barret, O. Godet (CESR), M. Servillat (CfA), S. A. Farrell (U. Leicester), S. R. Oates (MSSL)
Comments: 10 pages, 3 figures, accepted for publication in ApJL on 12/02/2010
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The brightest Ultra-Luminous X-ray source HLX-1 in the galaxy ESO 243-49 provides strong evidence for the existence of intermediate mass black holes. As the luminosity and thus the mass estimate depend on the association of HLX-1 with ESO 243-49, it is essential to confirm its affiliation. This requires follow-up investigations at wavelengths other than X-rays, which in-turn needs an improved source position. To further reinforce the intermediate mass black hole identification, it is necessary to determine HLX-1's environment to establish whether it could potentially form and nourish a black hole at the luminosities observed. Using the High Resolution Camera onboard Chandra, we determine a source position of RA=01h10m28.3s and Dec=-46d04'22.3". A conservative 95% error of 0.3" was found following a boresight correction by cross-matching the positions of 3 X-ray sources in the field with the 2MASS catalog. Combining all Swift UV/Optical Telescope uvw2 images, we failed to detect a UV source at the Chandra position down to a 3sigma limiting magnitude of 20.25 mag. However, there is evidence that the UV emission is elongated in the direction of HLX-1. This is supported by archival data from GALEX and suggests that the far-UV emission is stronger than the near-UV. This could imply that HLX-1 may be situated near the edge of a star forming region. Using the latest X-ray observations we deduce the mass accretion rate of a 500 Msun black hole with the observed luminosity and show that this is compatible with such an environment.

[8]  arXiv:1002.3626 [ps, pdf, other]
Title: The TAOS Project: Statistical Analysis of Multi-Telescope Time Series Data
Comments: 15 pages, 14 figures. Submitted to PASP
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The Taiwanese-American Occultation Survey (TAOS) monitors fields of up to ~1000 stars at 5 Hz simultaneously with four small telescopes to detect occultation events from small (~1 km) Kuiper Belt Objects (KBOs). The survey presents a number of challenges, in particular the fact that the occultation events we are searching for are extremely rare and are typically manifested as slight flux drops for only one or two consecutive time series measurements. We have developed a statistical analysis technique to search the multi-telescope data set for simultaneous flux drops which provides a robust false positive rejection and calculation of event significance. In this paper, we describe in detail this statistical technique and its application to the TAOS data set.

[9]  arXiv:1002.3637 [ps, pdf, other]
Title: Sky Variability in the y Band at the LSST Site
Comments: 8 pages, 5 figures, submitted to PASP
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We have measured spatial and temporal variability in the y band sky brightness over the course of four nights above Cerro Tololo near Cerro Pachon, Chile, the planned site for the Large Synoptic Survey Telescope (LSST). Our wide-angle camera lens provided a 41 deg field of view and a 145 arcsec pixel scale. We minimized potential system throughput differences by deploying a deep depletion CCD and a filter that matches the proposed LSST y_3 band (970 to 1030 nm). Images of the sky exhibited coherent wave structure, attributable to atmospheric gravity waves at 90 km altitude, creating 3 to 4% root mean square spatial sky flux variability on scales of about 2 degrees and larger. Over the course of a full night the y_3 band additionally showed highly coherent temporal variability of up to a factor of 2 in flux. We estimate the mean absolute sky level to be approximately y_3 = 17.8 mag (Vega), or y_3 = 18.3 mag (AB). While our observations were made through a y_3 filter, the relative sky brightness variability should hold for all proposed y bands, whereas the absolute levels should more strongly depend on spectral response. The spatial variability presents a challenge to wide-field cameras that require illumination correction strategies that make use of stacked sky flats. The temporal variability may warrant an adaptive y band imaging strategy for LSST, to take advantage of times when the sky is darkest.

[10]  arXiv:1002.3648 [pdf, other]
Title: Local Benchmarks for the Evolution of Major-Merger Galaxies -- Spitzer Observations of a K-Band Selected Sample
Comments: 73 pages; accpected by ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present Spitzer observations for a sample of close major-merger galaxy pairs (KPAIR sample) selected from 2MASS/SDSS-DR3 cross-matches. The goals are to study the star formation activity in these galaxies and to set a local bench mark for the cosmic evolution of close major mergers. The Spitzer KPAIR sample (27 pairs, 54 galaxies) includes all spectroscopically confirmed S+S and S+E pairs in a parent sample that is complete for primaries brighter than K=12.5 mag, projected separations of 5< s < 20 kpc/h, and mass ratios<2.5. The Spitzer data consist of images in 7 bands (3.6, 4.5, 5.8, 8, 24, 70, 160 um). Compared to single spiral galaxies in a control sample, only spiral galaxies in S+S pairs show significantly enhanced specific star formation rate (sSFR=SFR/M), whereas spiral galaxies in S+E pairs do not. Furthermore, the SFR enhancement of spiral galaxies in S+S pairs is highly mass-dependent. Only those with $\rm M \gsim 10^{10.5} M_\sun$ show significant enhancement. Relatively low mass ($\rm M \sim 10^{10} M_\sun$) spirals in S+S pairs have about the same SFR/M compared to their counterparts in the control sample. There is evidence for a correlation between the global star formation activities (but not the nuclear activities) of the component galaxies in massive S+S major-merger pairs (the "Holmberg effect"). There is no significant difference in the SFR/M between the primaries and the secondaries, nor between spirals of SEP<1 and those of SEP.1. The contribution of KPAIR galaxies to the cosmic SFR density in the local universe is only 1.7%.

[11]  arXiv:1002.3650 [pdf, other]
Title: Inflating Hot Jupiters With Ohmic Dissipation
Comments: 6 pages, 3 figures, 1 table. Submitted to Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We present a new, magnetohydrodynamic mechanism for inflation of close-in giant extrasolar planets. The idea behind the mechanism is that current, which is induced through interaction of atmospheric winds and the planetary magnetic field, results in significant Ohmic dissipation of energy in the interior. We develop an analytical model for computation of interior Ohmic dissipation, with a simplified treatment of the atmosphere. We apply our model to HD209458b, Tres-4b and HD189733b. With conservative assumptions for wind speed and field strength, our model predicts a generated power that appears to be large enough to maintain the transit radii, opening an unexplored avenue towards solving a decade-old puzzle of extrasolar gas giant radius anomalies.

[12]  arXiv:1002.3651 [ps, pdf, other]
Title: Ellipsoidal Variability and the Difference between Sequence D and E Red Giants
Comments: 7 pages, 5 figures. Accepted to MNRAS 2010 February 18
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We have studied a sample of Large Magellanic Cloud red giant binaries that lie on sequence E in the period--luminosity plane. We show that their combined light and velocity curves unambiguously demonstrate that they are binaries showing ellipsoidal variability. By comparing the phased light and velocity curves of both sequence D and E variables, we show that the sequence D variation -- the Long Secondary Period -- is not caused by ellipsoidal variability. We also demonstrate several further differences between stars on sequences D and E. These include differences in velocity amplitude, in the distribution of eccentricity, and in the correlations of velocity amplitude with luminosity and period. We also show that the sequence E stars, unlike stars on sequence D, do not show any evidence of a mid-infrared excess that would indicate circumstellar dust.

[13]  arXiv:1002.3654 [ps, pdf, other]
Title: Polycyclic aromatic hydrocarbon (PAH) luminous galaxies at z~1
Comments: Accepted to A&amp;A, 15 pages, 14 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

Using an AKARI multi-wavelength mid-infrared (IR) survey, we identify luminous starburst galaxies at z> 0.5 based on the PAH luminosity, and investigate the nature of these PAH-selected starbursts. An extragalactic survey with AKARI towards the north ecliptic pole (NEP), the NEP-Deep survey, is unique in terms of a comprehensive wavelength coverage from 2 to 24um using all 9 photometric bands of the InfraRed Camera (IRC). This survey allows us to photometrically identify galaxies whose mid-IR emission is clearly dominated by PAHs. We propose a single colour selection method to identify such galaxies, using two mid-IR flux ratios at 11-to-7um and 15-to-9um (PAH-to-continuum flux ratio in the rest-frame), which are useful to identify starburst galaxies at z~0.5 and 1, respectively. We perform a fitting of the spectral energy distributions (SEDs) from optical to mid-IR wavelengths, using an evolutionary starburst model with a proper treatment of radiative transfer (SBURT), in order to investigate their nature. The SBURT model reproduces observed optical-to-mid-IR SEDs of more than a half of PAH-selected galaxies. Based on the 8um luminosity, we find ultra luminous infrared galaxies (ULIRGs) among PAH-selected galaxies. Their PAH luminosity is higher than local ULIRGs with a similar luminosity, and the PAH-to-total IR luminosity ratio is consistent with that of less luminous starburst galaxies. They are a unique galaxy population at high redshifts and we call these PAH-selected ULIRGs "PAH-luminous" galaxies. Although they are not as massive as submillimetre galaxies at z~2, they have the stellar mass of >3x10^{10} Msun and therefore moderately massive.

[14]  arXiv:1002.3656 [ps, pdf, other]
Title: Spectroscopic Studies of Limb Spicules. I. Radial and Turbulent Velocities
Comments: 13 pages, 12 figures, to be published in Publications of the Astronomical Society of Japan
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We made high-resolution spectroscopic observations of limb-spicules in H-alpha using the Vertical Spectrograph of Domeless Solar Telescope at Hida Observatory. While more than half of the observed spicules have Gaussian line-profiles, some spicules have distinctly asymmetric profiles which can be fitted with two Gaussian components. The faster of these components has radial velocities of 10 - 40 km/s and Doppler-widths of about 0.4 A which suggest that it is from a single spicule oriented nearly along the line-of-sight. Profiles of the slower components and the single-Gaussian type show very similar characteristics. Their radial velocities are less than 10 km/s and the Doppler-widths are 0.6 - 0.9 A. Non-thermal "macroturbulent" velocities of order 30 km/s are required to explain these width-values.

[15]  arXiv:1002.3660 [ps, pdf, other]
Title: Halos and galaxies in the standard cosmological model: results from the Bolshoi simulation
Comments: 26 pages, 22 figures, submitted to ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present the first results from the new Bolshoi N-body cosmological LCDM simulation that uses cosmological parameters favored by current observations. The Bolshoi simulation was done in a volume 250Mpc on a side using 8billion particles with mass and force resolution adequate to follow subhalos down to a completeness limit of Vcirc=50km/ s circular velocity. Using excellent statistics of halos and subhalos (10M at every moment and 50M over the whole history) we present accurate approximations for statistics such as the halo mass function, the concentrations for distinct halos and subhalos, abundance of halos as function of their circular velocity, the abundance and the spatial distribution of subhalos. We find that at high redshifts the concentration falls to a minimum of about 3.8 and then rises slightly for higher values of halo mass. We find that while the Sheth-Tormen approximation for the mass function of halos found by spherical overdensity is accurate at low redshifts, it over-predicts the abundance of halos by nearly an order of magnitude by z=10. We find that the number of subhalos scales with the circular velocity of the host halo as Vhost**0.5, and that subhalos have nearly the same radial distribution as dark matter particles at radii 0.3-2 times the host halo virial radius. The subhalo velocity function n(>V) behaves as V**(-3). We give normalization of this relation for different masses and redshifts. Finally, we use an abundance-matching procedure to assign r-band luminosities to dark matter halos as a function of halo Vcirc, and find that the luminosity-velocity relation is in remarkably good agreement with the observed Tully-Fisher relation for galaxies in the range 50-200km/s.

[16]  arXiv:1002.3662 [ps, pdf, other]
Title: On the trigger mechanisms for SGR giant flares
Comments: 7 pages, 1 figure, submitted to MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We examine two trigger mechanisms, one internal and the other external to the neutron star, that give rise to the intense soft gamma-ray repeater (SGR) giant flares. So far, three giant flares have been observed from the three out of the four confirmed SGRs on March 5, 1979, August 27, 1998, and December 27, 2004. The last two events were found to be much more powerful than the first, and both showcased the existence of a precursor, that we show to have had initiated the main flare. In the internal mechanism, we propose that the strongly wound up poloidal magnetic field develops tangential discontinuities and dissipates its torsional energy in heating the crust. The timescale for the instability to develop coincides with the duration of the quiescent state that followed the precursor. Alternatively, we develop a reconnection model based on the hypothesis that shearing motion of the footpoints causes the materialization of a Sweet-Parker current layer in the magnetosphere. The thinning of this macroscopic layer due to the development of an embedded super-hot turbulent current layer switches on the impulsive Hall reconnection, which powers the giant flare. Again, we show that the thinning time is on the order of the preflare quiescent time. Our model naturally explains the origin of the observed nonthermal radiation during the flares, as well as the post flare radio afterglows.

[17]  arXiv:1002.3668 [ps, pdf, other]
Title: Suzaku Discovery of a Hard X-Ray Tail in the Persistent Spectra from the Magnetar 1E 1547.0-5408 during its 2009 Activity
Authors: Enoto Teruaki (1), Nakazawa Kazuhiro (1), Makishima Kazuo (1 and 2), Nakagawa E. Yujin (2), Sakamoto Takanori (3), Ohno Masanori (4), Takahashi Tadayuki (4), Terada Yukikatsu (5), Yamaoka Kazutaka (6), Murakami Toshio (7), Takahashi Hiromitsu (8) ((1) Department of Physics, University of Tokyo, (2) Cosmic Radiation Laboratory, Institute of Physical and Chemical Research, (3) GoddardSpaceFlight Center, NASA, (4) Department of High Energy Astrophysics, Institute of Space and Astronautical Science, (5) Department of Physics, Saitama University, (6) Department of Physics and Mathematics, Aoyama Gakuin University, (7) Department of Physics, Kanazawa University, (8) Department of Physical Science, Hiroshima University)
Comments: 12 pages, 7 figures, PASJ Vol.62 No.2 accepted
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

The fastest-rotating magnetar 1E 1547.0-5408 was observed in broad-band X-rays with Suzaku for 33 ks on 2009 January 28-29, 7 days after the onset of its latest bursting activity. After removing burst events, the absorption-uncorrected 2-10 keV flux of the persistent emission was measured with the XIS as 5.7e-11 ergs cm-2 s-1, which is 1-2 orders of magnitude higher than was measured in 2006 and 2007 when the source was less active. The persistent emission was also detected significantly with the HXD in >10 keV up to at least ~110 keV, with an even higher flux of 1.3e-10 ergs cm-2 s-1 in 20-100 keV. The pulsation was detected at least up to 70 keV at a period of 2.072135+/-0.00005 s, with a deeper modulation than was measured in a fainter state. The phase-averaged 0.7-114 keV spectrum was reproduced by an absorbed blackbody emission with a temperature of 0.65+/-0.02 keV, plus a hard power-law with a photon index of ~1.5. At a distance of 9 kpc, the bolometric luminosity of the blackbody and the 2-100 keV luminosity of the hard power-law are estimated as (6.2+/-1.2)e+35 ergs s-1 and 1.9e+36 ergs s-1, respectively, while the blackbody radius becomes ~5 km. Although the source had not been detected significantly in hard X-rays during the past fainter states, a comparison of the present and past spectra in energies below 10 keV suggests that the hard component is more enhanced than the soft X-ray component during the persistent activity.

[18]  arXiv:1002.3673 [pdf]
Title: Formation and Dynamical Evolution of the Neptune Trojans - the Influence of the Initial Solar System Architecture
Comments: 17 pages, 2 figures, MNRAS (in press). Abstract slightly reduced in size, but in original form in the PDF file
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

In this work, we investigate the dynamical stability of pre-formed Neptune Trojans under the gravitational influence of the four giant planets in compact planetary architectures, over 10 Myr. In our modelling, the initial orbital locations of Uranus and Neptune (aN) were varied to produce systems in which those planets moved on non-resonant orbits, or in which they lay in their mutual 1:2, 2:3 and 3:4 mean-motion resonances (MMRs). In total, 420 simulations were carried out, examining 42 different architectures, with a total of 840000 particles across all runs. In the non-resonant cases, the Trojans suffered only moderate levels of dynamical erosion, with the most compact systems (those with aN less than or equal 18 AU) losing around 50% of their Trojans by the end of the integrations. In the 2:3 and 3:4 MMR scenarios, however, dynamical erosion was much higher with depletion rates typically greater than 66% and total depletion in the most compact systems. The 1:2 resonant scenarios featured disruption on levels intermediate between the non-resonant cases and other resonant scenarios, with depletion rates of the order of tens of percent. Overall, the great majority of plausible pre-migration planetary architectures resulted in severe levels of depletion of the Neptunian Trojan clouds. In particular, if Uranus and Neptune formed near their mutual 2:3 or 3:4 MMR and at heliocentric distances within 18 AU (as favoured by recent studies), we found that the great majority of pre-formed Trojans would have been lost prior to Neptune's migration. This strengthens the case for the great bulk of the current Neptunian Trojan population having been captured during that migration.

[19]  arXiv:1002.3674 [ps, pdf, other]
Title: Detection of the Cosmic Far-Infrared Background in the AKARI Deep Field South
Comments: 50 pages, 15 figures, submitted to ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

We report the detection and measurement of the absolute brightness and spatial fluctuations of the cosmic infrared background (CIB) with the AKARI satellite. We have carried out observations at 65, 90, 140 and 160 um as a cosmological survey in AKARI Deep Field South (ADF-S), which is one of the lowest cirrus regions with contiguous area on the sky. After removing bright galaxies and subtracting zodiacal and Galactic foregrounds from the measured sky brightness, we have successfully measured the CIB brightness and its fluctuations across a wide range of angular scales from arcminutes to degrees. The measured CIB brightness is consistent with previous results reported from COBE data but significantly higher than the lower limits at 70 and 160 um obtained with the Spitzer satellite from the stacking analysis of 24-um selected sources. The discrepancy with the Spitzer result is possibly due to a new galaxy population at high redshift obscured by hot dust. From power spectrum analysis at 90 um, three components are identified: shot noise due to individual galaxies; Galactic cirrus emission dominating at the largest angular scales of a few degrees; and an additional component at an intermediate angular scale of 10-30 arcminutes, possibly due to galaxy clustering. The spectral shape of the clustering component at 90 um is very similar to that at longer wavelengths as observed by Spitzer and BLAST. Moreover, the color of the fluctuations indicates that the clustering component is as red as Ultra-luminous infrared galaxies (ULIRGs) at high redshift, These galaxies are not likely to be the majority of the CIB emission at 90 um, but responsible for the clustering component. Our results provide new constraints on the evolution and clustering properties of distant infrared galaxies.

[20]  arXiv:1002.3701 [pdf, other]
Title: Photometric Response Functions of the SDSS Imager
Comments: 54 pages, 18 figures, 7 tables, accepted for publication in AJ
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The monochromatic illumination system is constructed to carry out in situ measurements of the response function of the mosaicked CCD imager used in the Sloan Digital Sky Survey (SDSS). The system is outlined and the results of the measurements, mostly during the first 6 years of the SDSS, are described. We present the reference response functions for the five colour passbands derived from these measurements, and discuss column to column variations and variations in time, and also their effects on photometry. We also discuss the effect arising from various, slightly different response functions of the associated detector systems that were used to give SDSS photometry. We show that the calibration procedures of SDSS remove these variations reasonably well with the resulting final errors from variant response functions being unlikely to be larger than 0.01 mag for g, r, i, and z bands over the entire duration of the survey. The considerable aging effect is uncovered in the u band, the response function showing a 30% decrease in the throughput in the short wavelength side during the survey years, which potentially causes a systematic error in photometry. The aging effect is consistent with variation of the instrumental sensitivity in u-band, which is calibrated out. The expected colour variation is consistent with measured colour variation in the catalog of repeated photometry. The colour variation is delta (u-g) ~ 0.01 for most stars, and at most delta (u-g) ~ 0.02 mag for those with extreme colours. We verified in the final catalogue that no systematic variations in excess of 0.01 mag are detected in the photometry which can be ascribed to aging and/or seasonal effects except for the secular u-g colour variation for stars with extreme colours.

[21]  arXiv:1002.3703 [pdf, other]
Title: On the possibility of braneworld quintessential inflation
Comments: 11 pages RevTex file with 13 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We examine the possibility of achieving quintessential inflation, where the same field serves as both inflaton and quintessence, in the context of a five-dimensional braneworld. Braneworld cosmology provides an appropriate environment as it permits inflation with much steeper potentials than the conventional scenario, which is favourable to a late-time quintessence. We explore a wide space of models, together with contemporary observational data, to determine in which contexts such a picture is possible. We find that such a scenario, although attractive, is in fact impossible to achieve for the potentials studied due to the restrictiveness of current data.

[22]  arXiv:1002.3729 [ps, pdf, other]
Title: Evidence for a compact jet dominating the broadband spectrum of the black hole accretor XTE J1550-564
Authors: D. M. Russell (1), D. Maitra (1,2), R. J. H. Dunn (3), S. Markoff (1) ((1) University of Amsterdam (2) University of Michigan (3) Excellence Cluster Universe)
Comments: MNRAS accepted, 12 pages, 9 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

[abridged] The black hole X-ray binary XTE J1550-564 was monitored extensively at X-ray, optical and infrared wavelengths throughout its outburst in 2000. We show that it is possible to separate the optical/near-infrared (OIR) jet emission from the OIR disc emission. Focussing on the jet component, we find that as the source fades in the X-ray hard state, the OIR jet emission has a spectral index consistent with optically thin synchrotron emission (alpha ~ -0.6 to -0.7, where F_nu \propto nu^alpha). This jet emission is tightly and linearly correlated with the X-ray flux; L_OIR,jet \propto L_X^(0.98 +- 0.08) suggesting a common origin. This is supported by the OIR, X-ray and OIR to X-ray spectral indices being consistent with a single power law (alpha = -0.73). Ostensibly the compact, synchrotron jet could therefore account for ~ 100 % of the X-ray flux at low luminosities in the hard state. At the same time, (i) an excess is seen over the power law decay of the X-ray flux at the point in which the jet would start to dominate, (ii) the X-ray spectrum slightly softens, which seems to be due to a high energy cut-off or break shifting to a lower energy, and (iii) the X-ray rms variability increases. This may be the strongest evidence to date of synchrotron emission from the compact, steady jet dominating the X-ray flux of an X-ray binary. For XTE J1550-564, this is likely to occur within the luminosity range ~ (2 e-4 - 2 e-3) L_Edd on the hard state decline of this outburst. However, on the hard state rise of the outburst and initially on the hard state decline, the synchrotron jet can only provide a small fraction (~ a few per cent) of the X-ray flux. Both thermal Comptonization and the synchrotron jet can therefore produce the hard X-ray power law in accreting black holes.

[23]  arXiv:1002.3740 [ps, pdf, other]
Title: The intriguing nature of the high energy gamma ray source XSSJ12270-4859
Comments: 12 pages, 11 figures, 3 tables; Accepted for publication in Astronomy &amp; Astrophysics Main Journa
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The nature of the hard X-ray source XSSJ12270-4859 is still unclear though it was claimed to be a magnetic Cataclysmic Variable. We here present a broad-band X-ray and gamma ray study based on a recent XMM-Newton observation and archival INTEGRAL and RXTE data. From the Fermi/LAT 1-year point source catalogue, we tentatively associate XSSJ12270-4859 with 1FGLJ1227.9-4852, a source of high energy gamma rays with emission up to 10GeV. We complement the study with UV photometry from XMM-Newton and ground-based optical and near-IR photometry. The X-ray emission is highly variable showing flares and intensity dips. The X-ray flares consist of flare-dip pairs. Flares are also detected in the UV range but not the dips. Aperiodic dipping behaviour is also observed during X-ray quiescence but not in the UV. The 0.2-100keV spectrum is featureless and described by a power law model with Gamma=1.7. The 100MeV-10GeV spectrum is instead represented by a power law index of 2.45. The luminosity ratio between 0.1-100GeV and 0.2--100keV is ~0.8, hence the GeV emission is a significant component of the total energy output. Furthermore, the X-ray spectrum does not greatly change during flares, quiescence and the dips seen in quiescence but it hardens during the post-flare dips. Optical photometry reveals a period of 4.32hr likely related to the binary orbit. Near-IR, possibly ellipsoidal, variations are detected. Large amplitude variability on shorter (tens mins) timescales are found to be non-periodic. The observed variability at all wavelengths and the spectral characteristics strongly favour a low-mass atypical low-luminosity X-ray binary and are against a Cataclysmic Variable nature. The association with a Fermi/LAT high energy gamma ray source further strengths this interpretation.

[24]  arXiv:1002.3742 [ps, pdf, other]
Title: Type III migration in a low viscosity disc
Comments: 20 pages, 20 figures, accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We study the type III migration of a Saturn mass planet in low viscosity discs. The planet is found to experience cyclic episodes of rapid decay in orbital radius, each amounting to a few Hill radii. We find this to be due to the scattering of large- scale vortices present in the disc. The origin and role of vortices in the context of type III migration is explored. It is shown through numerical simulations and semi- analytical modelling that spiral shocks induced by a sufficiently massive planet will extend close to the planet orbital radius. The production of vortensity across shock tips results in thin high vortensity rings with a characteristic width of the local scale height. For planets with masses equal to and above that of Saturn, the rings are co-orbital features extending the entire azimuth. Linear stability analysis show there exists unstable modes that are localised about local vortensity minima which coincide with gap edges. Simulations show that vortices are non-linear a outcome. We used hydrodynamic simulations to examine vortex-planet interactions. Their effect is present in discs with kinematic viscosity less than about an order of magnitude smaller than the typically adopted value of \nu = 10^{-5}\Omega_pr_p(0)^2, where r_p(0) and \Omega_p are the initial orbital radius and angular velocity of the planet respectively. We find that the magnitude of viscosity affects the nature of type III migration but not the extent of the orbital decay. The role of vortices as a function of initial disc mass is also explored and it is found that the amount of orbital decay during one episode of vortex-planet interaction is independent of initial disc mass. We incorporate the concept of the co-orbital mass deficit in the analysis of our results and link it to the presence of vortices at gap edges.

[25]  arXiv:1002.3750 [ps, pdf, other]
Title: Resistive double-diffusive instability in the dead-zones of protostellar disks
Comments: 15 pages, 5 figures. MNRAS Accepted
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We outline a novel linear instability that may arise in the dead-zones of protostellar disks, and possibly the fluid interiors of planets and protoplanets. In essence it is an axisymmetric buoyancy instability, but one that would not be present in a purely hydrodynamical gas. The necessary ingredients for growth include a negative radial entropy gradient (of any magnitude), weak magnetic fields, and efficient resistive diffusion (in comparison with thermal diffusion). The character of the instability is local, axisymmetric, and double-diffusive, and it attacks lengths much shorter than the resistive scale. Like the axisymmetric convective instability, it draws its energy from the negative radial entropy gradient; but by utilising the diffusing magnetic field, it can negate the stabilising influence of rotation. Its nonlinear saturated state, while not transporting appreciable angular momentum, could drive radial and vertical mixing, which may influence the temperature structure of the disk, dust dynamics and, potentially, planet formation.

[26]  arXiv:1002.3759 [ps, pdf, other]
Title: Second-order matter perturbations in a LambdaCDM cosmology and non-Gaussianity
Authors: N. Bartolo, S. Matarrese, O. Pantano (Padova University), A. Riotto (INFN, Padova and CERN)
Comments: 15 pages. LaTeX file. Invited article for CQG issue on non-linear cosmology
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We obtain exact expressions for the effect of primordial non-Gaussianity on the matter density perturbation up to second order in a LambdaCDM cosmology, fully accounting for the general relativistic corrections arising on scales comparable with the Hubble radius. We present our results both in the Poisson gauge and in the comoving and synchronous gauge, which are relevant for comparison to different cosmological observables.

[27]  arXiv:1002.3775 [ps, pdf, other]
Title: New method for the time calibration of an interferometric radio antenna array
Comments: 9 pages, 9 figures, 1 table, pre-print of article published in Nuclear Inst. and Methods in Physics Research, A, available at: this http URL
Journal-ref: F.G. Schroeder, et al., Nucl. Instr. and Meth. A (2010), doi:10.1016/j.nima.2010.01.072
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE)

Digital radio antenna arrays, like LOPES (LOFAR PrototypE Station), detect high-energy cosmic rays via the radio emission from atmospheric extensive air showers. LOPES is an array of dipole antennas placed within and triggered by the KASCADE-Grande experiment on site of the Karlsruhe Institute of Technology, Germany. The antennas are digitally combined to build a radio interferometer by forming a beam into the air shower arrival direction which allows measurements even at low signal-to-noise ratios in individual antennas. This technique requires a precise time calibration. A combination of several calibration steps is used to achieve the necessary timing accuracy of about 1 ns. The group delays of the setup are measured, the frequency dependence of these delays (dispersion) is corrected in the subsequent data analysis, and variations of the delays with time are monitored. We use a transmitting reference antenna, a beacon, which continuously emits sine waves at known frequencies. Variations of the relative delays between the antennas can be detected and corrected for at each recorded event by measuring the phases at the beacon frequencies.

[28]  arXiv:1002.3787 [ps, pdf, other]
Title: The Future of Stellar Populations Studies in the Milky Way and the Local Group
Comments: 12 pages, 0 figures, IAU Symposium No. 262, Stellar Populations - Planning for the Next Decade
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The last decade has seen enormous progress in understanding the structure of the Milky Way and neighboring galaxies via the production of large-scale digital surveys of the sky like 2MASS and SDSS, as well as specialized, counterpart imaging surveys of other Local Group systems. Apart from providing snaphots of galaxy structure, these "cartographic" surveys lend insights into the formation and evolution of galaxies when supplemented with additional data (e.g., spectroscopy, astrometry) and when referenced to theoretical models and simulations of galaxy evolution. These increasingly sophisticated simulations are making ever more specific predictions about the detailed chemistry and dynamics of stellar populations in galaxies. To fully exploit, test and constrain these theoretical ventures demands similar commitments of observational effort as has been plied into the previous imaging surveys to fill out other dimensions of parameter space with statistically significant intensity. Fortunately the future of large-scale stellar population studies is bright with a number of grand projects on the horizon that collectively will contribute a breathtaking volume of information on individual stars in Local Group galaxies.

[29]  arXiv:1002.3788 [ps, pdf, other]
Title: The ugrizYJHK luminosity distributions and densities from the combined MGC, SDSS and UKIDSS LAS datasets
Comments: 17 pages, 13 figures, Accepted in MNRAS: 2010 January 18; in original form 2009 August 17
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

We combine data from the MGC, SDSS and UKIDSS LAS surveys to produce ugrizYJHK luminosity functions and densities from within a common, low redshift volume (z<0.1, ~71,000 h_1^-3 Mpc^3 for L* systems) with 100 per cent spectroscopic completeness. In the optical the fitted Schechter functions are comparable in shape to those previously reported values but with higher normalisations (typically 0, 30, 20, 15, 5 per cent higher phi*-values in u, g, r, i, z respectively over those reported by the SDSS team). We attribute these to differences in the redshift ranges probed, incompleteness, and adopted normalisation methods. In the NIR we find significantly different Schechter function parameters (mainly in the M* values) to those previously reported and attribute this to the improvement in the quality of the imaging data over previous studies. This is the first homogeneous measurement of the extragalactic luminosity density which fully samples both the optical and near-IR regimes. Unlike previous compilations that have noted a discontinuity between the optical and near-IR regimes our homogeneous dataset shows a smooth cosmic spectral energy distribution (CSED). After correcting for dust attenuation we compare our CSED to the expected values based on recent constraints on the cosmic star-formation history and the initial mass function.

[30]  arXiv:1002.3789 [ps, pdf, other]
Title: The young open cluster Trumpler 3
Subjects: Galaxy Astrophysics (astro-ph.GA)

We present a photometric and spectroscopic study of the poorly investigated open cluster Trumpler~3. Basic parameters such as the age of $70\pm10$ Myr, the color excess $E(B-V)=0.30\pm0.02$ mag, the distance of $0.69\pm0.03$ kpc and the limiting radius of 12' were redetermined and compared with previous preliminary studies. The distance of $0.65\pm0.09$ kpc was determined independently by spectral parallaxes. Simultaneously, our analysis allowed us to estimate a total number of members to be $N_{\rm{tot}}=570\pm90$ and a total mass of the cluster to be $M_{\rm{tot}}=270\pm40$ $\rm{M}_{\odot}$. We also determined a state of cluster's dynamical evolution. We conclude that Trumpler~3 is a young low-massive stellar ensemble with a typical mass function slope, located near to the outer edge of the Galaxy's Orion Spur. As a result of a wide-field search for short period variable stars, 24 variables were discovered in the cluster's area. Only one of them -- a variable of the $\gamma$-Dor type -- was found to be a likely cluster member.

[31]  arXiv:1002.3791 [ps, pdf, other]
Title: Observation of magnetocoriolis waves in a liquid metal Taylor-Couette experiment
Journal-ref: Phys. Rev. Lett. 104, 074501 (2010)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Fluid Dynamics (physics.flu-dyn)

The first observation of fast and slow magnetocoriolis (MC) waves in a laboratory experiment is reported. Rotating nonaxisymmetric modes arising from a magnetized turbulent Taylor-Couette flow of liquid metal are identified as the fast and slow MC waves by the dependence of the rotation frequency on the applied field strength. The observed slow MC wave is damped but the observation provides a means for predicting the onset of the Magnetorotational Instability.

[32]  arXiv:1002.3792 [ps, pdf, other]
Title: Microflare Activity driven by Forced Magnetic Reconnection
Comments: 2 Figures, accepted as an ApJ Letter
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

High cadence, multiwavelength, optical observations of a solar active region are presented, obtained with the Swedish Solar Telescope. Two magnetic bright points are seen to separate in opposite directions at a constant velocity of 2.8km/s. After a separation distance of approximately 4400km is reached, multiple Ellerman bombs are observed in both H-alpha and Ca-K images. As a result of the Ellerman bombs, periodic velocity perturbations in the vicinity of the magnetic neutral line, derived from simultaneous MDI data, are generated with amplitude +/- 6km/s and wavelength 1000km. The velocity oscillations are followed by an impulsive brightening visible in H-alpha and Ca-K, with a peak intensity enhancement of 63%. We interpret these velocity perturbations as the magnetic field deformation necessary to trigger forced reconnection. A time delay of approximately 3min between the H-alpha wing and Ca-K observations indicate that the observed magnetic reconnection occurs at a height of 200km above the solar surface. These observations are consistent with theoretical predictions and provide the first observational evidence of microflare activity driven by forced magnetic reconnection.

[33]  arXiv:1002.3799 [ps, pdf, other]
Title: Detection of Voigt Spectral Line Profiles of Hydrogen Radio Recombination Lines toward Sagittarius B2(N)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We report the detection of Voigt spectral line profiles of radio recombination lines (RRLs) toward Sagittarius B2(N) with the 100-m Green Bank Telescope (GBT). At radio wavelengths, astronomical spectra are highly populated with RRLs, which serve as ideal probes of the physical conditions in molecular cloud complexes. An analysis of the Hn(alpha) lines presented herein shows that RRLs of higher principal quantum number (n>90) are generally divergent from their expected Gaussian profiles and, moreover, are well described by their respective Voigt profiles. This is in agreement with the theory that spectral lines experience pressure broadening as a result of electron collisions at lower radio frequencies. Given the inherent technical difficulties regarding the detection and profiling of true RRL wing spans and shapes, it is crucial that the observing instrumentation produce flat baselines as well as high sensitivity, high resolution data. The GBT has demonstrated its capabilities regarding all of these aspects, and we believe that future observations of RRL emission via the GBT will be crucial towards advancing our knowledge of the larger-scale extended structures of ionized gas in the interstellar medium (ISM).

[34]  arXiv:1002.3820 [pdf, other]
Title: Conservative Constraints on Dark Matter from the Fermi-LAT Isotropic Diffuse Gamma-Ray Background Spectrum
Comments: 10 pages
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We examine the constraints on final state radiation from Weakly
Interacting Massive Particle (WIMP) dark matter candidates annihilating into various standard model final states, as imposed by the measurement of the isotropic diffuse gamma-ray background by the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope. The expected isotropic diffuse signal from dark matter annihilation has contributions from the local Milky Way (MW) as well as from extragalactic dark matter. While the signal from the MW is very insensitive to the adopted dark matter profile of the halos, the signal from extragalactic halos is sensitive to the low mass cut-off of the halo mass function. We adopt a conservative model for the low halo mass survival cut-off, and only consider the primary final state radiation. This provides robust constraints which reach the thermal production cross-section for low mass WIMPs annihilating into hadronic modes. We also reanalyze limits from HESS observations of the Galactic Ridge region using a conservative model for the dark matter halo profile. When combined with the HESS constraint, the isotropic diffuse spectrum rules out all interpretations of the PAMELA positron excess based on dark matter annihilation into two lepton final states. Annihilation into four leptons through new intermediate states, although constrained by the data, is not excluded.

Cross-lists for Mon, 22 Feb 10

[35]  arXiv:1002.2979 (cross-list from hep-ph) [ps, pdf, other]
Title: Atomic Ionization by keV-scale Pseudoscalar Dark Matter Particles
Comments: 4.5 pages, 3 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Experiment (hep-ex); Atomic Physics (physics.atom-ph)

Using the relativistic Hartree-Fock approximation, we calculate the rates of atomic ionization by absorption of pseudoscalar particles in the mass range from 10 to $\sim$ 50 keV. We present numerical results for atoms relevant for the direct dark matter searches (e.g. Ar, Ge, I and Xe), as well as the analytical formula which fits numerical calculations with few per cent accuracy and may be used for multi-electron atoms, molecules and condensed matter systems.

[36]  arXiv:1002.3373 (cross-list from hep-th) [ps, pdf, other]
Title: Overall observational constraints on the running parameter $\lambda$ of Hořava-Lifshitz gravity
Comments: 10 pages, 2 figures
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

We use observational data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB), along with requirements of Big Bang Nucleosynthesis (BBN), to constrain the running parameter $\lambda$ of Ho\v{r}ava-Lifshitz gravity, which determines the flow between the Ultra-Violet and the Infra-Red. We consider both the detailed and non-detailed balance versions of the gravitational sector, and we include the matter and radiation sectors. Allowing for variation of all the parameters of the theory, we construct the likelihood contours and we conclude that in $1\sigma$ confidence $\lambda$ is restricted to $|\lambda-1|\lesssim0.02$, while its best fit value is $|\lambda_{b.f}-1|\approx0.0006$. Although this observational analysis restricts the running parameter $\lambda$ very close to its IR value 1, it does not enlighten the discussion about the theory's possible conceptual and theoretical problems.

[37]  arXiv:1002.3527 (cross-list from hep-ph) [pdf, other]
Title: 13th International Conference on Elastic and Diffractive Scattering (Blois Workshop) - Moving Forward into the LHC Era
Comments: 514 pages. Proceedings of the 13th International Conference on Elastic and Diffractive Scattering, CERN, Geneva, June-July 2009. DESY-PROC-2010-XXX to appear
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)

Proceedings of the 13th International Conference on Elastic and Diffractive Scattering (Blois Workshop) - Moving Forward into the LHC Era

[38]  arXiv:1002.3678 (cross-list from physics.atm-clus) [ps, pdf, other]
Title: Dielectronic recombination data for astrophysical applications: Plasma rate-coefficients for Fe^q+ (q=7-10, 13-22) and Ni^25+ ions from storage-ring experiments
Comments: submitted for publication in the International Review of Atomic and Molecular Physics, 8 figures, 3 tables, 68 references
Subjects: Atomic and Molecular Clusters (physics.atm-clus); Instrumentation and Methods for Astrophysics (astro-ph.IM); Atomic Physics (physics.atom-ph)

This review summarizes the present status of an ongoing experimental effort to provide reliable rate coefficients for dielectronic recombination of highly charged iron ions for the modeling of astrophysical and other plasmas. The experimental work has been carried out over more than a decade at the heavy-ion storage-ring TSR of the Max-Planck-Institute for Nuclear Physics in Heidelberg, Germany. The experimental and data reduction procedures are outlined. The role of previously disregarded processes such as fine-structure core excitations and trielectronic recombination is highlighted. Plasma rate coefficients for dielectronic recombination of Fe^q+ ions (q=7-10, 13-22) and Ni^25+ are presented graphically and in a simple parameterized form allowing for easy use in plasma modeling codes. It is concluded that storage-ring experiments are presently the only source for reliable low-temperature dielectronic recombination rate-coefficients of complex ions.

Replacements for Mon, 22 Feb 10

[39]  arXiv:0909.0404 (replaced) [pdf]
Title: Origin and Dynamical Evolution of Neptune Trojans - I: Formation and Planetary Migration
Comments: 25 pages, 6 figures
Journal-ref: MNRAS 398, 1715-1729 (2009)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[40]  arXiv:0911.2798 (replaced) [ps, pdf, other]
Title: Brightest Cluster Galaxies and Core Gas Density in REXCESS Clusters
Comments: 16 pages, 8 figures, accepted Astrophysical Journal
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[41]  arXiv:0911.4967 (replaced) [ps, pdf, other]
Title: Galaxy rotation curves from General Relativity with Renormalization Group corrections
Comments: 33 pages, 12 figures. v2: ref's added. v3: Small changes to clarify our paper, including: new figure on the mass-to-light ratios, new table on the free parameters, more comments on the stellar masses and on LCDM
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)
[42]  arXiv:0911.4972 (replaced) [ps, pdf, other]
Title: Precision cluster mass determination from weak lensing
Comments: 27 pages, 7 figures, submitted to MNRAS; v2 has expanded explanation for clarity, no change in results or conclusions
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[43]  arXiv:0912.1668 (replaced) [pdf]
Title: Dark matter redistribution explains how galaxies grow in size and develop characteristic rotation curves
Comments: 11 pages, 1 table, 4 figures
Subjects: General Physics (physics.gen-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[44]  arXiv:1001.5435 (replaced) [ps, pdf, other]
Title: Dynamical Models of the Galactic Center
Authors: David Merritt
Comments: To appear in "The Galactic Center: A Window on the Nuclear Environment of Disk Galaxies", ed. Mark Morris, Daniel Q. Wang and Feng Yuan
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[45]  arXiv:1002.1346 (replaced) [pdf]
Title: Difference in the wind speeds required for initiation versus continuation of sand transport on Mars: Implications for dunes and dust storms
Authors: Jasper F. Kok
Comments: 4 pages, 3 figures, published in Physical Review Letters
Journal-ref: J. F. Kok, Phys. Rev. Lett., 104, 074502 (2010)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[46]  arXiv:1002.2022 (replaced) [pdf]
Title: The Neptune Trojans - a new source for the Centaurs?
Comments: 16 pages, 7 figures
Journal-ref: MNRAS 402, 13-20 (2010)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[47]  arXiv:1002.2220 (replaced) [ps, pdf, other]
Title: Muon Fluxes and Showers from Dark Matter Annihilation in the Galactic Center
Comments: 13 pages, 14 figures, 3 tables; Fig. 14 replaced and references added
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE)
[48]  arXiv:1002.2951 (replaced) [ps, pdf, other]
Title: Gamma-ray excess from a stacked sample of high-frequency peaked blazars observed with the MAGIC telescope
Authors: MAGIC Collaboration: J. Aleksić (1), L. A. Antonelli (2), P. Antoranz (3), M. Backes (4), C. Baixeras (5), J. A. Barrio (6), D. Bastieri (7), J. Becerra González (8), W. Bednarek (9), A. Berdyugin (10), K. Berger (10), E. Bernardini (11), A. Biland (12), O. Blanch (1), R. K. Bock (13,7), G. Bonnoli (2), P. Bordas (14), D. Borla Tridon (13), V. Bosch-Ramon (14), D. Bose (6), I. Braun (12), T. Bretz (15), D. Britzger (13), M. Camara (6), E. Carmona (13), A. Carosi (2), P. Colin (13), S. Commichau (12), J. L. Contreras (6), J. Cortina (1), M. T. Costado (8,16), S. Covino (2), F. Dazzi (17,26), A. De Angelis (17), E. De Cea del Pozo (18), R. De los Reyes (6,28), B. De Lotto (17), M. De Maria (17), F. De Sabata (17), C. Delgado Mendez (8,27), M. Doert (4), A. Domínguez (19), D. Dominis Prester (20), et al. (105 additional authors not shown)
Comments: 13 pages, 4 figures, submitted to ApJ, reference added
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
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New submissions for Tue, 23 Feb 10

[1]  arXiv:1002.3825 [ps, pdf, other]
Title: The Mass and Radius of the Neutron Star in 4U 1820-30
Comments: in review for the Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

We report on the measurement of the mass and radius of the neutron star in the low-mass X-ray binary 4U 1820-30. The analysis of the spectroscopic data on multiple thermonuclear bursts yields well-constrained values for the apparent emitting area and the Eddington flux, both of which depend in a distinct way on the mass and radius of the neutron star. The distance to the source is that of the globular cluster NGC 6624, where the source resides. Combining these measurements, we uniquely determine the probability density over the stellar mass and radius. We find the mass to be M = 1.58 +/- 0.06 M_sun and the radius to be R = 9.11 +/- 0.40 km.

[2]  arXiv:1002.3826 [ps, pdf, other]
Title: The faint outskirts of the blue compact galaxy Haro 11: is there a red excess?
Comments: This paper contains 8 figures and 2 tables
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Previous studies of the low surface brightness host of the blue compact galaxy (BCG) Haro 11 have suggested an abnormally red color of V-K=4.2+-0.8 for the host galaxy. This color is inconsistent with any normal stellar population over a wide range of stellar metallicities (Z=0.001-0.02). Similar though less extreme host colors have been measured for other BCGs and may be reconciled with population synthesis models, provided that the stellar metallicity of the host is higher than that of the ionized gas in the central starburst. We present the deepest V and K band observations to date of Haro 11 and derive a new V-K color for the host galaxy. Our new data suggest a far less extreme colour of V-K=2.3+-0.2, which is perfectly consistent with the expectations for an old host galaxy with the same metallicty as that derived from nebular emission lines in the star-forming center.

[3]  arXiv:1002.3827 [ps, pdf, other]
Title: Evolution of massive black hole spins
Authors: Marta Volonteri
Comments: 10 pages. To appear in the proceedings of the conference "Accretion and ejection in AGN: a global view" (Como, 22-26 June 2009)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Black hole spins affect the efficiency of the "classical" accretion processes, hence the radiative output from quasars. Spins also determine how much energy is extractable from the hole itself. Recently it became clear that massive black hole spins also affect the retention of black holes in galaxies, be cause of the impulsive "gravitational recoil", up to thousands km/s, due to anisotropic emission of gravitational waves at merger. I discuss here the evolution of massive black hole spins along the cosmic history, due to the combination of mergers and accretion events. I describe recent simulations of accreting black holes in merger remnants, and discuss the implication for the spins of black holes in quasars.

[4]  arXiv:1002.3830 [ps, pdf, other]
Title: Two confirmed compact elliptical galaxies in the Antlia cluster
Comments: 4 pages, 2 figures, accepted for publication in 52 BAAA
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We confirm the existence of two compact elliptical (cE) galaxies in the central region of the Antlia cluster through MAGELLAN-MIKE and GEMINI-GMOS spectra. Only about a dozen galaxies of this rare type are known today up to a distance of 100 Mpc. With this finding, Antlia becomes the nearest galaxy cluster harbouring more than one cE galaxy among its galaxy population. One of these galaxies shows evidence of interaction with one of the giant ellipticals that dominate the central region of the cluster.

[5]  arXiv:1002.3832 [ps, pdf, other]
Title: SDSS J094604.90+183541.8: A Gravitationally Lensed Quasar at z=4.8
Authors: Ian D. McGreer (1), Patrick B. Hall (2), Xiaohui Fan (1), Fuyan Bian (1), Naohisa Inada (3), Masamune Oguri (4), Michael A. Strauss (5), Donald P. Schneider (6), Kara Farnsworth (1) ((1)Steward Observatory, (2)York University, (3) Cosmic Radiation Laboratory, (4) National Astronomical Observatory of Japan, (5)Princeton University Observatory, (6)Pennsylvania State University)
Comments: Submitted to AJ, 8 pages, 5 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We report the discovery of a gravitationally lensed quasar identified serendipitously in the Sloan Digital Sky Survey (SDSS). The object, SDSS J094604.90+183541.8, was initially targeted for spectroscopy as a luminous red galaxy, but the SDSS spectrum has the features of both a z=0.388 galaxy and a z=4.8 quasar. We have obtained additional imaging that resolves the system into two quasar images separated by 3.06 arcsec and a bright galaxy that is strongly blended with one of the quasar images. We confirm spectroscopically that the two quasar images represent a single lensed source at z=4.8 with a total magnification of 3.2, and we derive a model for the lensing galaxy. This is the highest redshift lensed quasar currently known. We examine the issues surrounding the selection of such an unusual object from existing data and briefly discuss implications for lensed quasar surveys.

[6]  arXiv:1002.3838 [ps, pdf, other]
Title: Imaging the molecular gas in a submm galaxy at z = 4.05: cold mode accretion or a major merger?
Authors: C.L. Carilli (NRAO), E. Daddi (CEA), D. Riechers (CIT), F. Walter (MPIA), A. Weiss (MPIfR), H. Dannerbauer (CEA), G.E. Morrison (UH), J. Wagg (ESO), Romeel Dave (UA), D. Elbaz (CEA), D. Stern (JPL), M. Dickinson (NOAO), M. Krips (IRAM), M. Aravena (NRAO)
Comments: 33 pages, 8 figures, submitted to the ApJ, aas latex format
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present a high resolution (down to 0.18"), multi-transition imaging study of the molecular gas in the z = 4.05 submillimeter galaxy GN20. GN20 is one of the most luminous starburst galaxy known at z > 4, and is a member of a rich proto-cluster of galaxies at z = 4.05 in GOODS-North. We have observed the CO 1-0 and 2-1 emission with the VLA, the CO 6-5 emission with the PdBI Interferometer, and the 5-4 emission with CARMA. The H_2 mass derived from the CO 1-0 emission is 1.3 \times 10^{11} (\alpha/0.8) Mo. High resolution imaging of CO 2-1 shows emission distributed over a large area, appearing as partial ring, or disk, of ~ 10kpc diameter. The integrated CO excitation is higher than found in the inner disk of the Milky Way, but lower than that seen in high redshift quasar host galaxies and low redshift starburst nuclei. The VLA CO 2-1 image at 0.2" resolution shows resolved, clumpy structure, with a few brighter clumps with intrinsic sizes ~ 2 kpc. The velocity field determined from the CO 6-5 emission is consistent with a rotating disk with a rotation velocity of ~ 570 km s^{-1} (using an inclination angle of 45^o), from which we derive a dynamical mass of 3 \times 10^{11} \msun within about 4 kpc radius. The star formation distribution, as derived from imaging of the radio synchrotron and dust continuum, is on a similar scale as the molecular gas distribution. The molecular gas and star formation are offset by ~ 1" from the HST I-band emission, implying that the regions of most intense star formation are highly dust-obscured on a scale of ~ 10 kpc. The large spatial extent and ordered rotation of this object suggests that this is not a major merger, but rather a clumpy disk accreting gas rapidly in minor mergers or smoothly from the proto-intracluster medium. ABSTRACT TRUNCATED

[7]  arXiv:1002.3848 [ps, pdf, other]
Title: Using Gamma-Ray Burst Prompt Emission to Probe Relativistic Shock Acceleration
Comments: 15 pages, 2 figures. Accepted for publication in Advances of Space Research
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

It is widely accepted that the prompt transient signal in the 10 keV - 10 GeV band from gamma-ray bursts (GRBs) arises from multiple shocks internal to the ultra-relativistic expansion. The detailed understanding of the dissipation and accompanying acceleration at these shocks is a currently topical subject. This paper explores the relationship between GRB prompt emission spectra and the electron (or ion) acceleration properties at the relativistic shocks that pertain to GRB models. The focus is on the array of possible high-energy power-law indices in accelerated populations, highlighting how spectra above 1 MeV can probe the field obliquity in GRB internal shocks, and the character of hydromagnetic turbulence in their environs. It is emphasized that diffusive shock acceleration theory generates no canonical spectrum at relativistic MHD discontinuities. This diversity is commensurate with the significant range of spectral indices discerned in prompt burst emission. Such system diagnostics are now being enhanced by the broadband spectral coverage of bursts by the Fermi Gamma-Ray Space Telescope; while the Gamma-Ray Burst Monitor (GBM) provides key diagnostics on the lower energy portions of the particle population, the focus here is on constraints in the non-thermal, power-law regime of the particle distribution that are provided by the Large Area Telescope (LAT).

[8]  arXiv:1002.3849 [ps, pdf, other]
Title: Spectral Lag Relations in GRB Pulses Detected with HETE-2
Comments: 13 pages, 9 figures, accepted for the publication in PASJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Using a pulse-fit method, we investigate the spectral lags between the traditional gamma-ray band (50-400 keV) and the X-ray band (6-25 keV) for 8 GRBs with known redshifts (GRB 010921, GRB 020124, GRB 020127, GRB 021211, GRB 030528, GRB 040924, GRB 041006, GRB 050408) detected with the WXM and FREGATE instruments aboard the HETE-2 satellite. We find several relations for the individual GRB pulses between the spectral lag and other observables, such as the luminosity, pulse duration, and peak energy (Epeak). The obtained results are consistent with those for BATSE, indicating that the BATSE correlations are still valid at lower energies (6-25 keV). Furthermore, we find that the photon energy dependence for the spectral lags can reconcile the simple curvature effect model. We discuss the implication of these results from various points of view.

[9]  arXiv:1002.3854 [ps, pdf, other]
Title: Electron fraction constraints based on Nuclear Statistical Equilibrium with beta equilibrium
Comments: 8 pages, 8 figures, submitted to Astronomy and Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The electron-to-nucleon ratio or electron fraction is a key parameter in many astrophysical studies. Its value is determined by weak-interaction rates that are based on theoretical calculations subject to unknown uncertainties. Consequently, it is important to have a model independent way of constraining the electron fraction value in different astrophysical environments. Here we show that nuclear statistical equilibrium combined with beta equilibrium can provide such a constraint. We test the validity of this approximation in presupernova models and give lower limits for the electron fraction that is expected in type Ia supernova and accretion-induced collapse.

[10]  arXiv:1002.3855 [ps, pdf, other]
Title: Analytic formulae for CMB anisotropy in LTB cosmology
Comments: 4 pages, 1 figure. For proceedings of JGRG19 (Rikkyo U, Japan, 30 November - 4 December 2009)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The local void model has lately attracted considerable attention since it can explain the present apparent accelerated expansion of the universe without introducing dark energy. However, in order to justify this model as an alternative cosmological model to the standard $\Lambda$CDM model (FLRW universe plus dark energy), one has to test the model by various observations, such as CMB temperature anisotropy, other than the distance-redshift relation of SNIa. For this purpose, we derive some analytic formulae that can be used to rigorously compare consequences of this model with observations of CMB anisotropy and to place constraints on the position of observers in the void model.

[11]  arXiv:1002.3867 [ps, pdf, other]
Title: Statefinder diagnosis for the Palatini $f(R)$ gravity theories
Comments: 11 pages, 5 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The Palatini $f(R)$ gravity, is able to probably explain the late time cosmic acceleration without the need for dark energy, is studied. In this paper, we investigate a number of $f(R)$ gravity theories in Palatini formalism by means of statefinder diagnosis. We consider two types of $f(R)$ theories: (i) $f(R)=R+\alpha R^{m}-\beta R^{-n}$ and (ii) $f(R)=R+\alpha ln R+\beta$. We find that the evolutionary trajectories in the $s-r$ and $q-r$ planes for various types of the Palatini $f(R)$ theories reveal different evolutionary properties of the universe. Additionally, we use the observational $H(z)$ data to constrain models of $f(R)$ gravity.

[12]  arXiv:1002.3869 [ps, pdf, other]
Title: Closing the gap in the solutions of the strong explosion problem: An expansion of the family of second-type self-similar solutions
Authors: Doron Kushnir, Eli Waxman (Weizmann)
Comments: 9 pages, 9 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Shock waves driven by the release of energy at the center of a cold ideal gas sphere of initial density rho\propto r^{-omega} approach a self-similar (SLS) behavior, with velocity \dot{R}\propto R^delta, as R->\infty. For omega>3 the solutions are of the second type, i.e. delta is determined by the requirement that the flow should include a sonic point. No solution satisfying this requirement exists, however, in the 3\leq omega\leq omega_{g}(gamma) "gap" (omega_{g}=3.26 for adiabatic index gamma=5/3). We argue that second type solutions should not be required in general to include a sonic point. Rather, it is sufficient to require the existence of a characteristic line r_c(t), such that the energy in the region r_c(t)<r<R approaches a constant as R->\infty, and an asymptotic solution given by the SLS solution at r_c(t)<r<R and deviating from it at r<r_c may be constructed. The two requirements coincide for omega>omega_g, and the latter identifies delta=0 solutions as the asymptotic solutions for 3\leq omega\leq omega_{g} (as suggested by Gruzinov 2003). In these solutions, r_c is a C_0 characteristic. It is difficult to check, using numerical solutions of the hydrodynamic equations, whether the flow indeed approaches a delta=0 SLS behavior as R->\infty, due to the slow convergence to SLS for omega~3. We show that in this case the flow may be described by a modified SLS solution, d\ln\dot{R}/d\ln R=delta with slowly varying delta(R), eta\equiv d delta/d\ln R<<1, and spatial profiles given by a sum of the SLS solution corresponding to the instantaneous value of delta and a SLS correction linear in eta. The modified SLS solutions provide an excellent approximation to numerical solutions obtained for omega~3 at large R, with delta->0 (and eta\neq0) for 3\leq omega\leq omega_{g}.

[13]  arXiv:1002.3872 [ps, pdf, other]
Title: Asymptotic self-similar solutions with a characteristic time-scale
Comments: 5 pages, 2 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

For a wide variety of initial and boundary conditions, adiabatic one dimensional flows of an ideal gas approach self-similar behavior when the characteristic length scale over which the flow takes place, $R$, diverges or tends to zero. It is commonly assumed that self-similarity is approached since in the $R\to\infty(0)$ limit the flow becomes independent of any characteristic length or time scales. In this case the flow fields $f(r,t)$ must be of the form $f(r,t)=t^{\alpha_f}F(r/R)$ with $R\propto(\pm t)^\alpha$. We show that requiring the asymptotic flow to be independent only of characteristic length scales imply a more general form of self-similar solutions, $f(r,t)=R^{\delta_f}F(r/R)$ with $\dot{R}\propto R^\delta$, which includes the exponential ($\delta=1$) solutions, $R\propto e^{t/\tau}$. We demonstrate that the latter, less restrictive, requirement is the physically relevant one by showing that the asymptotic behavior of accelerating blast-waves, driven by the release of energy at the center of a cold gas sphere of initial density $\rho\propto r^{-\omega}$, changes its character at large $\omega$: The flow is described by $0\le\delta<1$, $R\propto t^{1/(1-\delta)}$, solutions for $\omega<\omega_c$, by $\delta>1$ solutions with $R\propto (-t)^{1/(\delta-1)}$ diverging at finite time ($t=0$) for $\omega>\omega_c$, and by exponential solutions for $\omega=\omega_c$ ($\omega_c$ depends on the adiabatic index of the gas, $\omega_c\sim8$ for $4/3<\gamma<5/3$). The properties of the new solutions obtained here for $\omega\ge\omega_c$ are analyzed, and self-similar solutions describing the $t>0$ behavior for $\omega>\omega_c$ are also derived.

[14]  arXiv:1002.3873 [ps, pdf, other]
Title: Cherenkov radio pulses from electromagnetic showers in the time-domain
Comments: 10 pages, 4 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The electric field of the Cherenkov radio pulse produced by a single charged particle track in a dielectric medium is derived from first principles. An algorithm is developed to obtain the pulse in the time domain for numerical calculations. The algorithm is implemented in a Monte Carlo simulation of electromagnetic showers in dense media (specifically designed for coherent radio emission applications) as might be induced by interactions of ultra-high energy neutrinos. The coherent Cherenkov radio emission produced by such showers is obtained simultaneously both in the time and frequency domains. A consistency check performed by Fourier-transforming the pulse in time and comparing it to the frequency spectrum obtained directly in the simulations yields, as expected, fully consistent results. The reversal of the time structure inside the Cherenkov cone and the signs of the corresponding pulses are addressed in detail. The results, besides testing algorithms used for reference calculations in the frequency domain, shed new light into the properties of the radio pulse in the time domain. The shape of the pulse in the time domain is directly related to the depth development of the excess charge in the shower and its width to the observation angle with respect to the Cherenkov direction. This information can be of great practical importance for interpreting actual data.

[15]  arXiv:1002.3882 [ps, pdf, other]
Title: Modelling the chemical evolution
Authors: Gerhard Hensler, Simone Recchi (Institute of Astronomy, University of Vienna)
Comments: 12 pages, 3 figures, to appear in the proceedings of "Chemical Abundances in the Universe: Connecting First Stars to Planets". IAU Symposium No. 265, 2009. K. Cunha, M. Spite &amp; B. Barbuy, eds
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Advanced observational facilities allow to trace back the chemical evolution of the Universe, on the one hand, from local objects of different ages and, secondly, by direct observations of redshifted objects. The chemical enrichment serves as one of the cornerstones of cosmological evolution. In order to understand this chemical evolution in morphologically different astrophysical objects models are constructed based on analytical descriptions or numerical methods. For the comparison of their chemical issues, as there are element abundances, gradients, and ratios, with observations not only the present-day values are used but also their temporal evolution from the first era of metal enrichment. Here we will provide some insight into basics of chemical evolution models, highlight advancements, and discuss a few applications.

[16]  arXiv:1002.3888 [ps, pdf, other]
Title: The relativistic jet of Cygnus X-3 in gamma rays
Comments: 5 pages, 4 figures, accepted for publication in MNRAS Letters
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

High energy gamma-rays have been detected from Cygnus X-3, a system composed of a Wolf-Rayet star and a black hole or neutron star. The gamma-ray emission is linked to the radio emission from the jet launched in the system. The flux is modulated with the 4.8 hr orbital period, as expected if high energy electrons are upscattering photons emitted by the Wolf-Rayet star to gamma-ray energies. This modulation is computed assuming that high energy electrons are located at some distance along a relativistic jet of arbitrary orientation. Modeling shows that the jet must be inclined and that the gamma ray emitting electrons cannot be located within the system. This is consistent with the idea that the electrons gain energy where the jet is recollimated by the stellar wind pressure and forms a shock. Jet precession should strongly affect the gamma-ray modulation shape at different epochs. The power in non-thermal electrons represents a small fraction of the Eddington luminosity only if the inclination is low i.e. if the compact object is a black hole.

[17]  arXiv:1002.3889 [pdf, other]
Title: Imaging and burst location with the EXIST high-energy telescope
Journal-ref: Proc. SPIE Volume 7435, 2009, pp 0B1-0B12
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The primary instrument of the proposed EXIST mission is a coded mask high energy telescope (the HET), that must have a wide field of view and extremely good sensitivity. It will be crucial to minimize systematic errors so that even for very long total integration times the imaging performance is close to the statistical photon limit. There is also a requirement to be able to reconstruct images on-board in near real time in order to detect and localize gamma-ray bursts. This must be done while the spacecraft is scanning the sky. The scanning provides all-sky coverage and is key to reducing systematic errors. The on-board computational problem is made even more challenging for EXIST by the very large number of detector pixels. Numerous alternative designs for the HET have been evaluated. The baseline concept adopted depends on a unique coded mask with two spatial scales. Monte Carlo simulations and analytic analysis techniques have been used to demonstrate the capabilities of the design and of the proposed two-step burst localization procedure.

[18]  arXiv:1002.3912 [ps, pdf, other]
Title: Multi-scale cosmology and structure-emerging Dark Energy: a plausibility analysis
Comments: 24 pages, 27 figures, submitted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Cosmological backreaction suggests a link between structure formation and the expansion history of the Universe. In order to quantitatively examine this connection we dynamically investigate a volume partition of the Universe into over- and underdense regions. This allows to trace structure formation using the volume fraction of the overdense regions $\lambda_{\CM}$ as its characterizing parameter. Employing results from cosmological perturbation theory and extrapolating the leading mode into the nonlinear regime, we construct a three-parameter model for the effective cosmic expansion history, involving $\lambda_{\CM_{0}}$, the matter density $\Omega_{m}^{\CD_{0}}$ and the Hubble rate $H_{\CD_{0}}$ of today's Universe. Taking standard values for $\Omega_{m}^{\CD_{0}}$ and $H_{\CD_{0}}$ as well as a reasonable value for $\lambda_{\CM_{0}}$, that we derive from $N$--body simulations, we determine the corresponding amounts of backreaction and spatial curvature. We find that the obtained values that are sufficient to generate today's structure also lead to a $\Lambda$CDM-like behavior of the scale factor, parametrized by the same parameters $\Omega_{m}^{\CD_{0}}$ and $H_{\CD_{0}}$, but without a cosmological constant. However, the temporal behavior of $\lambda_{\CM}$ does not faithfully reproduce the structure formation history. Surprisingly, however, the model matches with structure formation with the assumption of a low matter content, $\Omega_{m}^{\CD_{0}}\approx 3%$, a result that hints to a different interpretation of part of the backreaction effect as kinematical Dark Matter. (truncated)

[19]  arXiv:1002.3928 [ps, pdf, other]
Title: Large scale directional anomalies in the WMAP 5yr ILC map
Comments: 12 pages, 10 figures, 3 tables. Accepted for publication in JCAP
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We study the alignments of the low multipoles of CMB anisotropies with specific directions in the sky (i.e. the dipole, the north Ecliptic pole, the north Galactic pole and the north Super Galactic pole). Performing $10^5$ random extractions we have found that: 1) separately quadrupole and octupole are mildly orthogonal to the dipole but when they are considered together, in analogy to \cite{Copi2006}, we find an unlikely orthogonality at the level of 0.8% C.L.; 2) the multipole vectors associated to $\ell=4$ are unlikely aligned with the dipole at $99.1 %$ C.L.; 3) the multipole vectors associated to $\ell=5$ are mildly orthogonal to the dipole but when we consider only maps that show exactly the same correlation among the multipoles as in the observed WMAP 5yr ILC, these multipole vectors are unlikely orthogonal to the dipole at $99.7 %$ C.L..

[20]  arXiv:1002.3952 [ps, pdf, other]
Title: Cluster Weak Gravitational Lensing
Authors: Keiichi Umetsu (ASIAA)
Comments: Lectures given at the International School of Physics Enrico Fermi, Course CLXXII - "Astrophysics of Galaxy Clusters", Varenna, Italy, July 2008, ed. by A. Cavaliere and Y. Rephaeli; 31 pages, 14 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Weak gravitational lensing of background galaxies is a unique, direct probe of the distribution of matter in clusters of galaxies. We review several important aspects of cluster weak gravitational lensing together with recent advances in weak lensing techniques for measuring cluster lensing profiles and constraining cluster structure parameters.

[21]  arXiv:1002.3953 [ps, pdf, other]
Title: Why Are Halo Coronal Mass Ejections Faster?
Comments: 12 pages, 10 figures, to be published in RAA
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Halo coronal mass ejections (CMEs) were found to be significantly faster than normal CMEs, which was a long-standing puzzle. In order to solve the puzzle, we first investigate the observed properties of 31 limb CMEs that display clearly loop-shaped frontal loops. The observational results show a strong tendency that slower CMEs are weaker in the white-light intensity. Then, we perform a Monte Carlo simulation of 20 000 artificial limb CMEs that have average velocity of $\sim$523 km s$^{-1}$. The Thomson scattering of these events is calculated when they are assumed to be observed as limb and halo events, respectively. It is found that the white-light intensity of many slow CMEs becomes remarkably reduced as they turn from being viewed as a limb event to as a halo event. When the intensity is below the background solar wind fluctuation, it is assumed that they would be missed by coronagraphs. The average velocity of "detectable" halo CMEs is $\sim$922 km s$^{-1}$, very close to the observed value. It also indicates that wider events are more likely to be recorded. The results soundly suggest that the higher average velocity of halo CMEs is due to that a majority of slow events and a part of narrow fast events carrying less material are so faint that they are blended with the solar wind fluctuations, and therefore are not observed.

[22]  arXiv:1002.3955 [ps, pdf, other]
Title: The dependence of the EIT wave velocity on the magnetic field strength
Comments: 11 pages, 8 figures, accepted for publication in Solar Phys
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

"EIT waves" are a wavelike phenomenon propagating in the corona, which were initially observed in the extreme ultraviolet (EUV) wavelength by the EUV Imaging Telescope (EIT). Their nature is still elusive, with the debate between fast-mode wave model and non-wave model. In order to distinguish between these models, we investigate the relation between the EIT wave velocity and the local magnetic field in the corona. It is found that the two parameters show significant negative correlation in most of the EIT wave fronts, {\it i.e.}, EIT wave propagates more slowly in the regions of stronger magnetic field. Such a result poses a big challenge to the fast-mode wave model, which would predict a strong positive correlation between the two parameters. However, it is demonstrated that such a result can be explained by the fieldline stretching model, \emph{i.e.,} that "EIT waves" are apparently-propagating brightenings, which are generated by successive stretching of closed magnetic field lines pushed by the erupting flux rope during coronal mass ejections (CMEs).

[23]  arXiv:1002.3966 [pdf, other]
Title: Why all these prejudices against a constant?
Comments: 9 pages, 4 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations. Arguments are commonly presented to the effect that this simple explanation is not viable or not sufficient, and therefore we are facing the "great mystery" of the "nature of a dark energy". We argue that these arguments are unconvincing, or ill-founded.

[24]  arXiv:1002.3980 [ps, pdf, other]
Title: Very-High-Energy Gamma-Ray Signal from Nuclear Photodisintegration as a Probe of Extragalactic Sources of Ultrahigh-Energy Nuclei
Comments: 4 pages, 2 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Detecting gamma rays and neutrinos is crucial for studying the unknown nature of the ultrahigh-energy cosmic-ray (UHECR) sources. Recent results from the Pierre Auger Observatory favor a heavy nuclear composition for the UHECRs. Under the requirement that heavy nuclei survive in these sources, using gamma-ray bursts as an example, we predict a diagnostic gamma-ray signal, unique to nuclei -- the emission of de-excitation gamma rays following photodisintegration. These gamma rays, boosted from MeV to TeV-PeV energies, would be detectable by gamma-ray telescopes such as VERITAS, HESS, and MAGIC, and especially the next-generation CTA and AGIS.

[25]  arXiv:1002.4017 [ps, pdf, other]
Title: A nonlinear theory of the parallel firehose and gyrothermal instabilities in a weakly collisional plasma
Authors: M. S. Rosin (Cambridge), A. A. Schekochihin (Oxford), F. Rincon (Toulouse), S. C. Cowley (CCFE)
Comments: 33 pages, submitted to MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Plasmas have a natural tendency to develop pressure anisotropies with respect to the local direction of the magnetic field. These anisotropies trigger plasma instabilities at scales just above the ion Larmor radius with growth rates of a fraction of the ion cyclotron frequency - much faster than either the global dynamics or local turbulence. The instabilities can dramatically modify the macroscopic dynamics of the plasma. Nonlinear evolution of these instabilities is expected to drive pressure anisotropies towards marginal stability values, controlled by the plasma beta. This nonlinear evolution is worked out in an ab initio kinetic calculation for the simplest analytically tractable example - the parallel firehose instability in a high-beta plasma. A closed nonlinear equation for the firehose turbulence is derived and solved. In the nonlinear regime, the instability leads to secular (~t) growth of magnetic fluctuations. The fluctuations develop a k^{-3} spectrum, extending from scales somewhat larger than rho_i to the maximum scale that grows secularly with time (~t^{1/2}); the relative pressure anisotropy tends to the marginal value -2/beta. When a parallel ion heat flux is present, the firehose mutates into the new gyrothermal instability (GTI), which continues to be unstable up to pressure anisotropies that can be positive and are limited by the magnitude of the heat flux. Its nonlinear evolution also involves secular growth of the magnetic energy, but the fluctuation spectrum is eventually dominated by modes around a maximal scale ~ rho_i l_T/lambda_mfp, where l_T is the scale of the parallel temperature variation. Implications for momentum and heat transport are speculated about. This study is motivated the dynamics of the intracluster medium, but its relevance to solar wind and accretion flows is also discussed.

[26]  arXiv:1002.4021 [ps, pdf, other]
Title: Feeding the AGN with backflows
Authors: V. Antonuccio-Delogu (INAF, Italy), J. Silk (Oxford)
Comments: 6 pages, 4 figures. Oral contributed talk to "Accretion and Ejection in AGN: A global view", Como, Italy, May 22-26, 2009
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We study the internal circulation within the cocoon carved out by a relativistic jet emanating from an AGN, first developing model and then validating it using a series of numerical simulations. We notice that a significant increase of in this flow arises because gradients in the density and entropy develop near the hot spot, as a consequence of Crocco vorticity theorem. We find simple solutions for the streamlines, and we use them to predict the mass inflow rates towards the central regions. The 2D simulations we perform span a rather wide range of mechanical jet's input power and Black Hole masses, and we show that the predicted nuclear mass inflows are in good agreement with the theoretical model.

[27]  arXiv:1002.4023 [pdf]
Title: Chandra Observations of Comets 8P/Tuttle and 17P/Holmes during Solar Minimum
Comments: 37 Pages, 8 Tables, 11 Figures; Accepted in Astrophysical Journal Supplements
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present results for Chandra observations of comets, 17P/Holmes (17P) and 8P/Tuttle (8P). 17P was observed for 30 ksec right after its major outburst, on 31 Oct 2007 (10:07 UT) and comet 8P/Tuttle was observed in 2008 January for 47 ksec. During the two Chandra observations, 17P was producing at least 100 times more water than 8P but was 2.2 times further away from the Sun. Also, 17P is the first comet observed at high latitude (+19.1 degrees) during solar minimum, while 8P was observed at a lower solar latitude (3.4 degrees). The X-ray spectrum of 17P is unusually soft with little significant emission at energies above 500 eV. Depending on our choice of background, we derive a 300 to 1000 eV flux of 0.5 to 4.5 x 10^-13 ergs/cm2/sec, with over 90% of the emission in the 300 to 400 eV range. This corresponds to an X-ray luminosity between 0.4 to 3.3 x 10^15 ergs/sec. 17P's lack of X-rays in the 400 to 1000 eV range, in a simple picture, may be attributed to the polar solar wind, which is depleted in highly charged ions. 8P/Tuttle was much brighter, with an average count rate of 0.20 counts/s in the 300 to 1000 eV range. We derive an average X-ray flux in this range of 9.4 x 10^-13 ergs/cm2/sec and an X-ray luminosity for the comet of 1.7 x 10^14 ergs/sec. The light curve showed a dramatic decrease in flux of over 60% between observations on January 1st and 4th. When comparing outer regions of the coma to inner regions, its spectra showed a decrease in ratios of CVI/CV, OVIII/OVII, as predicted by recent solar wind charge exchange emission models. There are remarkable differences between the X-ray emission from these two comets, further demonstrating the qualities of cometary X-ray observations, and solar wind charge exchange emission in more general as a means of remote diagnostics of the interaction of astrophysical plasmas.

[28]  arXiv:1002.4025 [pdf]
Title: Common Radial Velocity vs. Rare Microlensing: Difficulties and Futures
Comments: 21 figures, 3 tables; Prepublished version
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)

In this paper, effective factors for success of Microlensing and Radial Velocity methods were choose. A semi-Delphi process applied on the factors to evaluating them and finding the most important factors for present situation of ML and RV, with help from about 100 experts, in or related exoplanets detection. I found the public definition on "success of exoplanets detection methods" is not correct and we should change it, as some experts did it, in the form of fundamental questions in planetary science. Also, the views of "Special Experts" are different from other experts that help us to choose the right way in evaluating. The next step was choosing the best strategy for future and finally, from SWOT landscape and with a new objective of ML method (New Game Board Strategy) I suggested four critical future strategies for completing current strategic directions.

[29]  arXiv:1002.4027 [ps, pdf, other]
Title: Pulsar Observations with the Fermi Large Area Telescope
Authors: Damien Parent
Comments: Ph. D. Thesis; Universite de Bordeaux 1; Centre d'Etudes Nucleaires de Bordeaux-Gradignan
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

The Large Area Telescope (LAT) on Fermi, launched on 2008 June 11, is a space telescope to explore the high energy gamma-ray universe. The instrument covers the energy range from 20 MeV to 300 GeV with greatly improved sensitivity and ability to localize gamma-ray point sources. It detects gamma-rays through conversion to electron-positron pairs and measurement of their direction in a tracker and their energy in a calorimeter.
This thesis presents the gamma-ray light curves and the phase-resolved spectral measurements of radio-loud gamma-ray pulsars detected by the LAT. The measurement of pulsar spectral parameters (i.e. integrated flux, spectral index, and energy cut-off) depends on the instrument response functions (IRFs). A method developed for the on-orbit validation of the effective area is presented using the Vela pulsar. The cut efficiencies between the real data and the simulated data are compared at each stage of the background rejection. The results are then propagated to the IRFs, allowing the systematic uncertainties of the spectral parameters to be estimated.
The last part of this thesis presents the discoveries, using both the LAT observations and the radio and X ephemeredes, of new individual gamma-ray pulsars such as PSR J0205+6449, and the Vela-like pulsars J2229+6114 and J1048-5832. Timing and spectral analysis are investigated in order to constrain the gamma-ray emission model. In addition, we discuss the properties of a large population of gamma-ray pulsars detected by the LAT, including normal pulsars, and millisecond pulsars.

[30]  arXiv:1002.4029 [pdf, other]
Title: CMB polarization as a probe of the anomalous nature of the Cold Spot
Comments: 7 pages, 3 figures, submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

One of the most interesting explanations for the non-Gaussian Cold Spot detected in WMAP data by Vielva et al. 2004 is that it arises from the interaction of the CMB radiation with a cosmic texture (Cruz et al. 2007b). In this case, a lack of polarization is expected in the area of the spot as compared to the typical values associated to large fluctuations of a Gaussian and isotropic random field. In this work we characterize the polarization properties of the Cold Spot, under both hypotheses: a large Gaussian fluctuation and an anomalous feature. We propose as well a methodology to distinguish between them, and we discuss the discrimination power as a function of the instrumental noise level. In particular, we address the cases of current experiments, like WMAP and Planck, and others in development as QUIJOTE. We find that for an ideal experiment with a very high sensitivity in polarization, the Gaussian hypothesis could be rejected at a significance level lower than 0.8%. Whereas WMAP is quite far form providing us any useful information in this respect, we find that Planck will be able to provide a significance of around 7%; in addition, we show that the ground-based experiment QUIJOTE could provide a good significance of around 1%. If these numbers are used in combination with the already reported significance level of the Cold Spot from non-Gaussian analyses that only consider temperature studies, then the capability of QUIJOTE and Planck to reject the alternative hypothesis becomes 0.025% and 0.124%, respectively.

[31]  arXiv:1002.4030 [ps, pdf, other]
Title: INTEGRAL and Swift/XRT observations of the source PKS 0208-512
Comments: accepted for publication in A&amp;A
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

The active galaxy PKS 0208-512, detected at lower energies by COMPTEL, has been claimed to be a MeV blazar from EGRET. We report on the most recent INTEGRAL observations of the blazar PKS 0208-512, which are supplemented by Swift ToO observations. The high energy X-ray and gamma-ray emission of PKS 0208-512 during August - December 2008 has been studied using 682 ks of INTEGRAL guest observer time and ~ 56 ks of Swift/XRT observations. These data were collected during the decay of a gamma-ray flare observed by Fermi/LAT. At X-ray energies (0.2 - 10 keV) PKS 0208-512 is significantly detected by Swift/XRT, showing a power-law spectrum with a photon index of ~ 1.64. Its X-ray luminosity varied by roughly 30% during one month. At hard X-/soft gamma-ray energies PKS 0208-512 shows a marginally significant (~ 3.2 sigma) emission in the 0.5-1 MeV band when combining all INTEGRAL/SPI data. Non-detections at energies below and above this band by INTEGRAL/SPI may indicate intrinsic excess emission. If this possible excess is produced by the blazar, one possible explanation could be that its jet consists of an abundant electron-positron plasma, which may lead to the emission of an annihilation radiation feature. Assuming this scenario, we estimate physical parameters of the jet of PKS 0208-512.

[32]  arXiv:1002.4050 [ps, pdf, other]
Title: The Vela Pulsar: Results from the First Year of Fermi LAT Observations
Authors: A. A. Abdo etc. (Fermi-LAT Collaboration)
Comments: 35 pages, 12 figures, accepted for publication in Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

We report on analysis of timing and spectroscopy of the Vela pulsar using eleven months of observations with the Large Area Telescope on the Fermi Gamma-Ray Space Telescope. The intrinsic brightness of Vela at GeV energies combined with the angular resolution and sensitivity of the LAT allow us to make the most detailed study to date of the energy-dependent light curves and phase-resolved spectra, using a LAT-derived timing model. The light curve consists of two peaks (P1 and P2) connected by bridge emission containing a third peak (P3). We have confirmed the strong decrease of the P1/P2 ratio with increasing energy seen with EGRET and previous Fermi LAT data, and observe that P1 disappears above 20 GeV. The increase with energy of the mean phase of the P3 component can be followed with much greater detail, showing that P3 and P2 are present up to the highest energies of pulsation. We find significant pulsed emission at phases outside the main profile, indicating that magnetospheric emission exists over 80% of the pulsar period. With increased high-energy counts the phase-averaged spectrum is seen to depart from a power- law with simple exponential cutoff, and is better fit with a more gradual cutoff. The spectra in fixed-count phase bins are well fit with power-laws with exponential cutoffs, revealing a strong and complex phase dependence of the cutoff energy, especially in the peaks. By combining these results with predictions of the outer magnetosphere models that map emission characteristics to phase, it will be possible to probe the particle acceleration and the structure of the pulsar magnetosphere with unprecedented detail.

[33]  arXiv:1002.4073 [pdf, other]
Title: Aperiodic optical variability of intermediate polars - cataclysmic variables with truncated accretion disks
Authors: M. Revnivtsev (1,2), R. Burenin (2), I. Bikmaev (3), A. Kniazev (4,5), D.A.H. Buckley (4,5), M.L. Pretorius (6,4,5), I. Khamitov (7), T. Ak (7,8), Z. Eker (7), S. Melnikov (3), S. Crawford (4), M. Pavlinsky (2) ((1)Excellence Cluster Universe, (2)IKI, (3)KSU, (4)SAAO, (5)SALT Foundation, (6)ESO, (7)TUBITAK, (8)Istanbul University)
Comments: Accepted for publication in A&amp;A
Subjects: Galaxy Astrophysics (astro-ph.GA)

We study the power spectra of the variability of seven intermediate polars containing magnetized asynchronous accreting white dwarfs, XSS J00564+4548,IGR J00234+6141, DO Dra, V1223 Sgr, IGR J15094-6649, IGR J16500-3307 and IGR J17195-4100, in the optical band and demonstrate that their variability can be well described by a model based on fluctuations propagating in a truncated accretion disk. The power spectra have breaks at Fourier frequencies, which we associate with the Keplerian frequency of the disk at the boundary of the white dwarfs' magnetospheres. We propose that the properties of the optical power spectra can be used to deduce the geometry of the inner parts of the accretion disk, in particular: 1) truncation radii of the magnetically disrupted accretion disks in intermediate polars, 2) the truncation radii of the accretion disk in quiescent states of dwarf novae

[34]  arXiv:1002.4077 [ps, pdf, other]
Title: Bacterial survival in Martian conditions
Comments: 5 pages, 3 figures, special issue of Planetary and Space science on Methane on Mars discovery. Topics: Astrobiology - Methods: laboratory - Mars - Panspermia
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We shortly discuss the observable consequences of the two hypotheses about the origin of life on Earth and Mars: the Lithopanspermia (Mars to Earth or viceversa) and the origin from a unique progenitor, that for Earth is called LUCA (the LUCA hypothesis). To test the possibility that some lifeforms similar to the terrestrial ones may survive on Mars, we designed and built two simulators of Martian environments where to perform experiments with different bacterial strains: LISA and mini-LISA. Our LISA environmental chambers can reproduce the conditions of many Martian locations near the surface trough changes of temperature, pressure, UV fluence and atmospheric composition. Both simulators are open to collaboration with other laboratories interested in performing experiments on many kind of samples (biological, minerals, electronic) in situations similar to that of the red planet. Inside LISA we have studied the survival of several bacterial strains and endospores. We verified that the UV light is the major responsible of cell death. Neither the low temperature, nor the pressure, nor the desiccation or the atmospheric changes were effective in this sense. We found that some Bacillus strains have a particular capability to survive for some hours in Martian conditions without being screened by dust or other shields. We also simulated the coverage happening on a planet by dust transported by the winds, blowing on the samples a very small quantity of volcanic ash grains or red iron oxide particles. Samples covered by these dust grains have shown a high percentage of survival, indicating that under the surface dust, if life were to be present on Mars in the past, some bacteria colonies or cells could still be present.

[35]  arXiv:1002.4091 [ps, pdf, other]
Title: CP and related phenomena in the context of Stellar Evolution
Authors: J. Braithwaite (1,2), T. Akgün (3), E. Alecian (4), A. F. Kholtygin (5), J. D. Landstreet (6,7), S. Mathis (8), G. Michaud (9), J. Portnoy (10), G. Alecian (4), V. D. Bychkov (11), L. V. Bychkova (11), N. Drake (5), S. N. Fabrika (11), A. Reisenegger (3), R. Steinitz (12), M. Vick (9) ((1)CITA, (2)Uni Bonn, (3)Universidad Católica Santiago, (4)Observatoire de Paris, (5)Saint-Petersburg State University, (6)University of Western Ontario, (7)Armagh Observatory, (8)CEA-Saclay, (9)Université de Montréal, (10)Sami Shamoon College of Engineering, (11)Special Astrophysical Observatory Russia, (12)Ben Gurion University)
Comments: Proceedings of IAU GA in Rio, JD4 on Ap stars; 10 pages, 7 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We review the interaction in intermediate and high mass stars between their evolution and magnetic and chemical properties. We describe the theory of Ap-star `fossil' fields, before touching on the expected secular diffusive processes which give rise to evolution of the field. We then present recent results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that magnetic fields of the kind seen on the main-sequence already exist during the pre-main sequence phase, in agreement with fossil field theory, and that the origin of the slow rotation of Ap/Bp stars also lies early in the pre-main sequence evolution; we also present results confirming a lack of stars with fields below a few hundred gauss. We then seek which macroscopic motions compete with atomic diffusion in determining the surface abundances of AmFm stars. While turbulent transport and mass loss, in competition with atomic diffusion, are both able to explain observed surface abundances, the interior abundance distribution is different enough to potentially lead to a test using asterosismology. Finally we review progress on the turbulence-driving and mixing processes in stellar radiative zones.

[36]  arXiv:1002.4092 [ps, pdf, other]
Title: The occultation events of the Herbig Ae/Be star V1247 Ori
Comments: A&amp;A Letters, in press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Aims: I study new deep (DeltaV ~ 1.20-1.65 mag) occultation events of the delta Scuti, Herbig Ae/Be star V1247 Ori in the Ori OB1 b association. Methods: I use the V-band ASAS light curve of V1247 Ori, which covers the last nine years, together with photometric data in the near-ultraviolet, visible, near-, and far-infrared taken from the literature. I carry out a periodogram analysis of the "cleaned" light curve and construct the spectral energy distribution of the star. Results: The star V1247 Ori is interesting for the study of the UX Orionis phenomenon, in which Herbig Ae/Be stars are occulted by their protoplanetary discs, for three reasons: brightness (V ~ 9.85 mag), large infrared excess at 20-100 mum (F_60 ~ 10 Jy), and photometric stability out of occultation (sigma(V) ~ 0.02 mag), which may help to determine the location and spatial structure of the occulting disc clumps.

[37]  arXiv:1002.4101 [ps, pdf, other]
Title: No evidence for dust extinction in GRB 050904 at z ~ 6.3
Authors: Tayyaba Zafar (1), Darach J. Watson (1), Daniele Malesani (1), Paul M. Vreeswijk (1), Johan P.U. Fynbo (1), Jens Hjorth (1), Andrew J. Levan (2), Michał J. Michałowski (1,3) ((1) DARK, (2) Univ. Warwick., (3) Univ. Edinburgh)
Comments: 7 pages, 3 figures; accepted for publication in A&amp;A
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

Context: GRB afterglows are excellent probes of gas and dust in star-forming galaxies at all epochs. It has been posited that dust in the early Universe must be different from dust at lower z. To date two reports directly support this contention, one of which is based on the spectral shape of GRB 050904 at z = 6.295. Aims: We reinvestigate the afterglow to understand dust at high z. We address the claimed evidence for unusual (SN-origin) dust in its host galaxy by simultaneously examining the X-ray and optical/NIR spectrophotometric data. Methods: We derive the intrinsic SED of the afterglow at 0.47, 1.25 and 3.4 days, by re-reducing the Swift X-ray data, the 1.25 days FORS2 z-Gunn photometric data, the spectroscopic and z'-band photometric data at ~3 days from the Subaru telescope, as well as the critical UKIRT Z-band photometry at 0.47 days, upon which the claim of dust detection largely relies. Results: We find no evidence of dust extinction in the SED. We compute flux densities at lambda_rest = 1250 AA directly from the observed counts at all epochs. In the earliest epoch, 0.47 days, the Z-band suppression is found to be smaller (0.3 +- 0.2 mag) than previously reported and statistically insignificant (<1.5 sigma). Furthermore we find that the photometry of this band is unstable and difficult to calibrate. Conclusions: From the afterglow SED we demonstrate that there is no evidence for dust extinction -- the SED at all times can be reproduced without dust, and at 1.25 days in particular, significant extinction can be excluded, with A(3000 AA) < 0.27 mag at 95% confidence using the SN-type extinction curve. We conclude that there is no evidence of any extinction in the afterglow of GRB 050904 and that the presence of SN-origin dust in the host of GRB 050904 must be viewed skeptically. [abridged]

[38]  arXiv:1002.4113 [pdf, other]
Title: Planetary eclipse mapping of CoRoT-2a. Evolution, differential rotation, and spot migration
Comments: Paper accepted by A&amp;A 17/02/2010. For a better resolution paper please visit my homepage: this http URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The lightcurve of CoRoT-2 shows substantial rotational modulation and deformations of the planet's transit profiles caused by starspots. We consistently model the entire lightcurve, including both rotational modulation and transits, stretching over approximately 30 stellar rotations and 79 transits. The spot distribution and its evolution on the noneclipsed and eclipsed surface sections are presented and analyzed, making use of the high resolution achievable under the transit path.
We measure the average surface brightness on the eclipsed section to be (5\pm1) % lower than on the noneclipsed section. Adopting a solar spot contrast, the spot coverage on the entire surface reaches up to 19 % and a maximum of almost 40 % on the eclipsed section. Features under the transit path, i.e. close to the equator, rotate with a period close to 4.55 days. Significantly higher rotation periods are found for features on the noneclipsed section indicating a differential rotation of $\Delta \Omega > 0.1$. Spotted and unspotted regions in both surface sections concentrate on preferred longitudes separated by roughly 180 deg.

[39]  arXiv:1002.4122 [ps, pdf, other]
Title: A sub-resolution multiphase interstellar medium model of star formation and SNe energy feedback
Authors: Giuseppe Murante (INAF- Osservatorio di Torino), Pierluigi Monaco (Universita' di Trieste), Martina Giovalli (Universita' di Torino), Stefano Borgani (Universita' di Trieste), Antonaldo Diaferio (Universita' di Torino)
Comments: 23 pages, 26 figures, MNRAS accepted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present a new multi-phase sub-resolution model for star formation and feedback in SPH numerical simulations of galaxy formation. Our model, called MUPPI (MUlti-Phase Particle Integrator), describes each gas particle as a multi-phase system, with cold and hot gas phases, coexisting in pressure equilibrium, and a stellar component. Cooling of the hot tenuous gas phase feeds the cold gas phase. Stars are formed out of molecular gas with a given efficiency, which scales with the dynamical time of the cold phase. Our prescription for star formation is not based on imposing the Schmidt-Kennicutt relation, which is instead naturally produced by MUPPI. Energy from supernova explosions is deposited partly into the hot phase of the gas particles, and partly to that of neighboring particles. Mass and energy flows among the different phases of each particle are described by a set of ordinary differential equations which we explicitly integrate for each gas particle, instead of relying on equilibrium solutions. This system of equations also includes the response of the multi-phase structure to energy changes associated to the thermodynamics of the gas. We apply our model to two isolated disk galaxy simulations and two spherical cooling flows. MUPPI is able to reproduce the Schmidt-Kennicutt relation for disc galaxies. It also reproduces the basic properties of the inter-stellar medium in disc galaxies, the surface densities of cold and molecular gas, of stars and of star formation rate, the vertical velocity dispersion of cold clouds and the flows connected to the galactic fountains. Quite remarkably, MUPPI also provides efficient stellar feedback without the need to include a scheme of kinetic energy feedback. [abridged]

[40]  arXiv:1002.4125 [ps, pdf, other]
Title: The outflow in Mrk 509: A method to calibrate XMM-Newton EPIC-pn and RGS
Comments: 11 pages, 9 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We have analyzed three XMM-Newton observations of the Seyfert 1 galaxy Mrk 509, with the goal to detect small variations in the ionized outflow properties. Such measurements are limited by the quality of the cross-calibration between RGS, the best instrument to characterize the spectrum, and EPIC-pn, the best instrument to characterize the variability. For all three observations we are able to improve the relative calibration of RGS and pn consistently to 4 %. In all observations we detect three different outflow components and, thanks to our accurate cross-calibration we are able to detect small differences in the ionization parameter and column density in the highest ionized component of the outflow. This constrains the location of this component of the outflow to within 0.5 pc of the central source. Our method for modeling the relative effective area is not restricted to just this source and can in principle be extended to other types of sources as well.

[41]  arXiv:1002.4134 [ps, pdf, other]
Title: Ultra High Energy Cosmic Rays: Anisotropies and Spectrum
Comments: 12 pages, 5 eps figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The recent results of the Pierre Auger Observatory on the possible correlation of Ultra High Energy Cosmic Rays events and several nearby discrete sources could be the starting point of a new era with charged particles astronomy. In this paper we introduce a simple model to determine the effects of any local distribution of sources on the expected flux. We consider two populations of sources: faraway sources uniformly distributed and local point sources. We study the effects on the expected flux of the local distribution of sources, referring, in particular, to the set of astrophysical objects whose correlation with the Auger events seems experimentally confirmed.

[42]  arXiv:1002.4160 [ps, pdf, other]
Title: The Quasar Accretion Disk Size -- Black Hole Mass Relation
Authors: Christopher W. Morgan (1), C.S. Kochanek (2), Nicholas D . Morgan (2), Emilio E. Falco (3) ((1)Department of Physics, U.S. Naval Academy, (2)Department of Astronomy, The Ohio State University, (3)Harvard-Smithsonian Center for Astrophysics)
Comments: 19 pages, 4 figures, accepted by The Astrophysical Journal
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We use the microlensing variability observed for eleven gravitationally lensed quasars to show that the accretion disk size at a rest-frame wavelength of 2500 Angstroms is related to the black hole mass by log(R_{2500}/cm)=(15.78\pm0.12) + (0.80\pm0.17)\log(M_BH/10^9M_sun). This scaling is consistent with the expectation from thin disk theory (R ~ M_BH^{2/3}), but when interpreted in terms of the standard thin disk model (T ~ R^{-3/4}), it implies that black holes radiate with very low efficiency, log(eta) = -1.77\pm0.29 + log(L/L_E) where eta=L/(Mdot*c^2). Only by making the maximum reasonable shifts in the average inclination, Eddington factors and black hole masses can we raise the efficiency estimate to be marginally consistent with typical efficiency estimates (eta ~ 10%). With one exception, these sizes are larger by a factor of ~4 than the size needed to produce the observed 0.8 micron quasar flux by thermal radiation from a thin disk with the same T ~ R^{-3/4} temperature profile. While scattering a significant fraction of the disk emission on large scales or including a large fraction of contaminating line emission can reduce the size discrepancy, resolving it also appears to require that accretion disks have flatter temperature/surface brightness profiles.

[43]  arXiv:1002.4177 [ps, pdf, other]
Title: Foregrounds for observations of the cosmological 21 cm line: II. Westerbork observations of the fields around 3C196 and the North Celestial Pole
Comments: 20 pages, 22 figures, A&amp;A submitted. A version with full resolution figures is available at this http URL
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

In the coming years a new insight into galaxy formation and the thermal history of the Universe is expected to come from the detection of the highly redshifted cosmological 21 cm line. The cosmological 21 cm line signal is buried under Galactic and extragalactic foregrounds which are likely to be a few orders of magnitude brighter. Strategies and techniques for effective subtraction of these foreground sources require a detailed knowledge of their structure in both intensity and polarization on the relevant angular scales of 1-30 arcmin. We present results from observations conducted with the Westerbork telescope in the 140-160 MHz range with 2 arcmin resolution in two fields located at intermediate Galactic latitude, centred around the bright quasar 3C196 and the North Celestial Pole. They were observed with the purpose of characterizing the foreground properties in sky areas where actual observations of the cosmological 21 cm line could be carried out. The polarization data were analysed through the rotation measure synthesis technique. We have computed total intensity and polarization angular power spectra. Total intensity maps were carefully calibrated, reaching a high dynamic range, 150000:1 in the case of the 3C196 field. [abridged]

[44]  arXiv:1002.4178 [ps, pdf, other]
Title: The ACS LCID Project. II. Faint Variable Stars in the Isolated Dwarf Irregular Galaxy IC1613
Comments: 20 pages, 17 figures, in emulateapj format. Accepted for publication in ApJ. Several figures degraded. See this http URL for a version with full resolution figures
Subjects: Galaxy Astrophysics (astro-ph.GA)

(Abridged) We present the results of a new search for variable stars in the Local Group (LG) isolated dwarf galaxy IC1613, based on 24 orbits of F475W and F814W photometry from the ACS camera onboard the HST. We detected 259 candidate variables in this field, of which only 13 (all of them bright Cepheids) were previously known. Out of the confirmed variables, we found 90 RR Lyrae stars, 49 classical Cepheids (including 36 new discoveries), and 38 eclipsing binary stars for which we could determine a period. The RR Lyrae include 61 fundamental (RRab) and 24 first-overtone (RRc) pulsators, and 5 pulsating in both modes simultaneously (RRd). As for the majority of LG dwarfs, the mean periods of the RRab and RRc (0.611 and 0.334 day, respectively) as well as the fraction of overtone pulsators (f_c=0.28) place this galaxy in the intermediate regime between the Oosterhoff types. From their position on the period-luminosity diagram and light-curve morphology, we can unambiguously classify 25 and 14 Cepheids as fundamental and first-overtone mode pulsators, respectively. Another two are clearly second-overtone Cepheids, the first ones to be discovered beyond the Magellanic Clouds. We estimate the distance to IC1613 using various methods based on the photometric and pulsational properties of the Cepheids and RR Lyrae stars. The values we find are in very good agreement with each other and with previous estimates based on independent methods. When corrected to a common reddening of E(B-V)=0.025 and true LMC distance modulus of (m-M)_{LMC,0}=18.515+-0.085, we find that all the distance determinations from the literature converge to a common value of (m-M)_0=24.400+-0.014 (statistical), or 760 kpc.

[45]  arXiv:1002.4179 [ps, pdf, other]
Title: Gauss-Seidel and Successive Overrelaxation Methods for Radiative Transfer with Partial Frequency Redistribution
Comments: 39 pages, 9 figures, accepted for publication in the Astrophysical Journal (2010)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The linearly-polarized solar limb spectrum that is produced by scattering processes contains a wealth of information on the physical conditions and magnetic fields of the solar outer atmosphere, but the modeling of many of its strongest spectral lines requires solving an involved non-LTE radiative transfer problem accounting for partial redistribution (PRD) effects. Fast radiative transfer methods for the numerical solution of PRD problems are also needed for a proper treatment of hydrogen lines when aiming at realistic time-dependent magnetohydrodynamic simulations of the solar chromosphere. Here we show how the two-level atom PRD problem with and without polarization can be solved accurately and efficiently via the application of highly convergent iterative schemes based on the Gauss-Seidel (GS) and Successive Overrelaxation (SOR) radiative transfer methods that had been previously developed for the complete redistribution (CRD) case. Of particular interest is the Symmetric SOR method, which allows us to reach the fully converged solution with an order of magnitude of improvement in the total computational time with respect to the Jacobi-based local ALI (Accelerated Lambda Iteration) method.

[46]  arXiv:1002.4185 [pdf, other]
Title: EM counterparts of recoiling black holes: general relativistic simulations of non-Keplerian discs
Comments: 17 pages, 11 figures, submitted to MNRAS, movies available at this http URL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We investigate the dynamics of a circumbinary disc that responds to the loss of mass and to the recoil velocity of the black hole produced by the merger of a binary system of supermassive black holes. More specifically, we perform the first two-dimensional general relativistic hydrodynamics simulations of \textit{extended} non-Keplerian discs and employ a new technique to construct a "shock detector", thus determining the precise location of the shocks produced in the accreting disc by the recoiling black hole. In this way we can study how the properties of the system, such as the spin, mass and recoil velocity of the black hole, affect the mass accretion rate and are imprinted on the electromagnetic emission from these sources. In contrast with what done in similar works, we here question the estimates of the bremsstrahlung luminosity when computed without properly taking into account the radiation transfer, thus yielding cooling times that are unrealistically short. At the same time we show, through an approximation based on the relativistic analogue of the isothermal evolution of \citet{Corrales2009}, that the luminosity produced can reach a peak value above $L \simeq 10^{43} {\rm erg/s} $ at about $\sim 20 {\rm d}$ after the merger of a binary with total mass $M\simeq 10^6 M_\odot$ and persist for several days at values which are a factor of a few smaller. If confirmed by more sophisticated calculations such a signal could indeed lead to an electromagnetic counterpart of the merger of binary black-hole system.

Cross-lists for Tue, 23 Feb 10

[47]  arXiv:1002.2257 (cross-list from nucl-th) [ps, pdf, other]
Title: Exact Analytical Solutions in Three-Body Problems and Model of Neutrino Generator
Comments: 12 pages, 19th International IUPAP Conference on Few-Body Problems in Physics, 30Aug - 05 Sep 2009, Bonn,Germany
Subjects: Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)

Exact analytic solutions are obtained in three-body problem for the scattering of light particle on two fixed centers in the case when pair potentials have a separable form. Solutions show an appearance of new three-body resonance states that depend on distance between two fixed centers. In the case when two-body neutron-nucleus amplitudes have the Breit-Wigner's form and heavy nuclei fixed in nodes of crystalline lattice widths of new resonance states can be equal to zero at certain values of the distance. It gives the possibility of transitions between three-body resonance states connected with process of electron capture by proton with formation of neutron and emission of neutrino. This exoenergic process leading to the cooling of star without nuclear reactions is discussed.

[48]  arXiv:1002.3101 (cross-list from hep-th) [ps, pdf, other]
Title: Cosmological perturbations in a healthy extension of Horava gravity
Comments: 9 pages, 4 figures
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

In Horava's theory of gravity, Lorentz symmetry is broken in exchange for renormalizability, but the original theory has been argued to be plagued with problems associated with a new scalar mode stemming from the very breaking of Lorentz symmetry. Recently, Blas, Pujolas, and Sibiryakov have proposed a healthy extension of Ho\v{r}ava gravity, in which the behavior of the scalar mode is improved. In this paper, we study scalar modes of cosmological perturbations in extended Horava gravity. The evolution of metric and density perturbations is addressed analytically and numerically. It is shown that for vanishing non-adiabatic pressure of matter the large scale evolution of cosmological perturbations converges to that described by a single constant, $\zeta$, which is an analog of a curvature perturbation on the uniform-density slicing commonly used in usual gravitational theories. The subsequent evolution is thus determined completely by the value of $\zeta$.

[49]  arXiv:1002.3705 (cross-list from nucl-th) [ps, pdf, other]
Title: Unified description of neutron superfluidity in the neutron-star crust with analogy to anisotropic multi-band BCS superconductors
Comments: 15 pages, 31 figures, accepted for publication in Physical Review C
Subjects: Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Superconductivity (cond-mat.supr-con)

The neutron superfluidity in the inner crust of a neutron star has been traditionally studied considering either homogeneous neutron matter or only a small number of nucleons confined inside the spherical Wigner-Seitz cell. Drawing analogies with the recently discovered multi-band superconductors, we have solved the anisotropic multi-band BCS gap equations with Bloch boundary conditions, thus providing a unified description taking consistently into account both the free neutrons and the nuclear clusters. Calculations have been carried out using the effective interaction underlying our recent Hartree-Fock-Bogoliubov nuclear mass model HFB-16. We have found that even though the presence of inhomogeneities lowers the neutron pairing gaps, the reduction is much less than that predicted by previous calculations using the Wigner-Seitz approximation. We have studied the disappearance of superfluidity with increasing temperature. As an application we have calculated the neutron specific heat, which is an important ingredient for modeling the thermal evolution of newly-born neutron stars. This work provides a new scheme for realistic calculations of superfluidity in neutron-star crusts.

Replacements for Tue, 23 Feb 10

[50]  arXiv:0903.2271 (replaced) [ps, pdf, other]
Title: Nonthermal emission from clusters of galaxies
Authors: Doron Kushnir, Eli Waxman (Weizmann)
Comments: 22 pages, 16 figures, somewhat revised, published in JCAP
Journal-ref: JCAP 0908:002,2009
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[51]  arXiv:0903.2275 (replaced) [ps, pdf, other]
Title: Magnetic fields and cosmic rays in clusters of galaxies
Authors: Doron Kushnir, Boaz Katz, Eli Waxman (Weizmann)
Comments: 7 pages, 2 figures, somewhat revised, published in JCAP
Journal-ref: JCAP 0909:024,2009
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[52]  arXiv:0905.1950 (replaced) [ps, pdf, other]
Title: Hard X-ray emission from accretion shocks around galaxy clusters
Authors: Doron Kushnir, Eli Waxman (Weizmann)
Comments: 7 pages, 3 figures, somewhat revised, published in JCAP
Journal-ref: JCAP 1002:025,2010
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[53]  arXiv:0907.3885 (replaced) [ps, pdf, other]
Title: The Nucleosynthetic Imprint of 15-40 Solar Mass Primordial Supernovae on Metal-Poor Stars
Comments: 16 pages, 11 figures; submitted to ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
[54]  arXiv:0909.2683 (replaced) [ps, pdf, other]
Title: Interpreting Power Anisotropy Measurements in Plasma Turbulence
Comments: 5 pages, 3 figures, published version
Journal-ref: Astrophysical Journal Letters 711 (2010) L79-L83
Subjects: Plasma Physics (physics.plasm-ph); Earth and Planetary Astrophysics (astro-ph.EP); Space Physics (physics.space-ph)
[55]  arXiv:0910.0842 (replaced) [ps, pdf, other]
Title: A new tool to determine masses and mass profiles using gravitational flexion
Comments: 14 pages, 11 figures, 4 tables, MNRAS accepted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[56]  arXiv:0911.0687 (replaced) [ps, pdf, other]
Title: Semi-Analytic Calculation of the Gravitational Wave Signal From the Electroweak Phase Transition for General Quartic Scalar Effective Potentials
Comments: accepted by JCAP, revisions: removed turbulence contribution, minor changes to experimental sensitivity, fixed various minor typos and text revisions, made it clear we consider only detonations; 17 pages, 4 figures, revtex4
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
[57]  arXiv:0911.1129 (replaced) [ps, pdf, other]
Title: Dynamical difference between the cD galaxy and the stellar diffuse component in simulated galaxy clusters
Comments: 15 pages, 18 figures, MNRAS in press
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[58]  arXiv:0911.1213 (replaced) [pdf, other]
Title: Inflation with racetrack superpotential and matter field
Authors: Marcin Badziak, Marek Olechowski (Warsaw U.)
Comments: 40 pages, 13 figures, references added, typos corrected, version to be published
Journal-ref: JCAP1002:026, 2010
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)
[59]  arXiv:0911.1241 (replaced) [ps, pdf, other]
Title: CMB temperature trispectrum of cosmic strings
Comments: 9 pages, 3 figures, uses RevTeX. Misprints corrected, matches published version
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
[60]  arXiv:0911.2234 (replaced) [ps, pdf, other]
Title: Black Holes and Galactic Density Cusps II Spherically Symmetric Anisotropic Cusps
Authors: Morgan Le Delliou (IFT), Richard N. Henriksen (QUARG), Joseph D. Macmillan (FScUOIT)
Comments: 9 pp, 3 figs
Subjects: Galaxy Astrophysics (astro-ph.GA)
[61]  arXiv:0911.2776 (replaced) [ps, pdf, other]
Title: Very High Gas Fractions and Extended Gas Reservoirs in z=1.5 Disk Galaxies
Comments: Accepted for publication in Astrophysical Journal, 22 pages, 18 figures, minor revisions
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[62]  arXiv:0911.3550 (replaced) [ps, pdf, other]
Title: Non-Gaussianity constrains hybrid inflation
Comments: 26pp, 2 figs v2: note added (see abstract)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
[63]  arXiv:0912.3449 (replaced) [ps, pdf, other]
Title: Galactic tide and secular orbital evolution
Comments: 15 pages, 6 figures, corrected exponent in equation of motion, corrected program for numerical solution
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[64]  arXiv:1001.0155 (replaced) [ps, pdf, other]
Title: Singularities in Horava-Lifshitz theory
Comments: Revtex4, six figures. Version to appear in Phys. Lett. B
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
[65]  arXiv:1001.1875 (replaced) [ps, pdf, other]
Title: Recessional velocities and Hubble's law in Schwarzschild-de Sitter space
Comments: This article extends the results of, and replaces, a previous paper by the same authors entitled: "Superluminal velocities in Schwarzschild-de Sitter space," arXiv:0910.5254v1
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[66]  arXiv:1001.3652 (replaced) [ps, pdf, other]
Title: Stars and brown dwarfs in the sigma Orionis cluster. II. A proper motion study
Comments: A&amp;A, in press (v2: language edited)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)
[67]  arXiv:1001.4605 (replaced) [ps, pdf, other]
Title: Metallicity of high stellar mass galaxies with signs of merger events
Authors: M. S. Alonso (ICATE), L. Michel-Dansac (CRAL), D. G. Lambas (IATE)
Comments: Astronomy &amp; Astrophysics, in press
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
[68]  arXiv:1001.5107 (replaced) [ps, pdf, other]
Title: Outflow - Core Interaction in Barnard 1
Authors: Masaaki Hiramatsu (1,2), Naomi Hirano (1), Shigehisa Takakuwa (1) ((1)ASIAA, (2)NTHU)
Comments: 34 pages, 8 figures, accepted for the publication in ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA)
[69]  arXiv:1001.5432 (replaced) [ps, pdf, other]
Title: Reaching the boundary between stellar kinematic groups and very wide binaries. II. alpha Lib + KU Lib: a common proper motion system in Castor separated by 1.0 pc
Comments: A&amp;A, in press (v2: language edited)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)
[70]  arXiv:1002.0071 (replaced) [ps, pdf, other]
Title: The LABOCA survey of the Extended Chandra Deep Field South: Two modes of star formation in AGN hosts?
Comments: 39 manuscript pages, 6 figures, accepted for publication in ApJ (no changes to text wrt v1)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[71]  arXiv:1002.2132 (replaced) [ps, pdf, other]
Title: Sensitivity of the g-mode frequencies to pulsation codes and their parameters
Comments: 10 pages, 5 figures, accepted in Solar Physics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[72]  arXiv:1002.2223 (replaced) [ps, pdf, other]
Title: Deep Chandra observations of TeV binaries I: LSI +61 303
Authors: N. Rea (CSIC-IEEC), D. F. Torres (CSIC-IEEC, ICREA), M. van der Klis (Amsterdam), P. G. Jonker (SRON), M. Mendez (Groningen), A. Sierpowska-Bartosik (Lodz)
Comments: 9 pages, 6 figures, submitted to MNRAS on 06/12/2009, referee comments included
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)
[73]  arXiv:1002.3529 (replaced) [ps, pdf, other]
Title: Electronic spectroscopy of medium-sized polycyclic aromatic hydrocarbons: Implications for the carriers of the 2175 Å UV bump
Comments: 6 pages, 4 Postscript figures, accepted for publication in Astrophys. J. Lett. (2010)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
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New submissions for Wed, 24 Feb 10

[1]  arXiv:1002.4192 [ps, pdf, other]
Title: HI 21 cm opacity fluctuations power spectra towards Cassiopeia A
Comments: 5 pages, 3 figures. Accepted for publication in MNRAS Letters. The definitive version will be available at this http URL
Subjects: Galaxy Astrophysics (astro-ph.GA)

The angular power spectrum of HI 21 cm opacity fluctuations is a useful statistic for quantifying the observed opacity fluctuations as well as for comparing these with theoretical models. We present here the HI 21 cm opacity fluctuation power spectrum towards the supernova remnant Cas A from interferometric data with spacial resolution of 5" and spectral resolution of 0.4 km/s. The power spectrum has been estimated using a simple but robust visibility based technique. We find that the power spectrum is well fit by a power law P_tau(U) = U^{alpha} with a power law index of alpha ~ -2.86 +/- 0.10 (3 sigma error) over the scales of 0.07 - 2.3 pc for the gas in the Perseus spiral arm and 0.002 - 0.07 pc (480 - 15730 au) for that in the Local arm. This estimated power law index is consistent with earlier observational results based on both HI emission over larger scales and absorption studies over a similar range of scales. We do not detect any statistically significant change in the power law index with the velocity width of the frequency channels. This constrains the power law index of the velocity structure function to be beta = 0.2 +/- 0.6 (3 sigma error).

[2]  arXiv:1002.4193 [ps, pdf, other]
Title: The merger-driven evolution of massive galaxies
Comments: Submitted to ApJ. Referee's comments included
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We explore the rate and impact of galaxy mergers on the massive galaxy population using the amplitude of the two-point correlation function on small scales for M > 5e10 M_sun galaxies from the COSMOS and COMBO-17 surveys. Using a pair fraction derived from the Sloan Digital Sky Survey as a low-redshift benchmark, the large survey area at intermediate redshifts allows us to determine the evolution of the close pair fraction with unprecedented accuracy for a mass-selected sample: we find that the fraction of galaxies more massive than 5e10M_sun in pairs separated by less than 30 kpc in 3D space evolves as F(z) = (0.0130+/-0.0019)x(1+z)^1.21+/-0.25 between z = 0 and z = 1.2. Assuming a merger time scale of 0.5 Gyrs, the inferred merger rate is such that galaxies with mass in excess of 1e11 M_sun have undergone, on average, 0.5 (0.7) mergers involving progenitor galaxies both more massive than 5e10 M_sun since z = 0.6 (1.2). We also study the number density evolution of massive red sequence galaxies using published luminosity functions and constraints on the M/L evolution from the fundamental plane. Moreover, we demonstrate that the measured merger rate of massive galaxies is sufficient to explain this observed number density evolution in massive red sequence galaxies since z = 1.

[3]  arXiv:1002.4194 [ps, pdf, other]
Title: GRB 090323 and GRB 090328: two long high-energy GRBs detected with Fermi
Comments: 6 pages, 4 figures, 1 table, Proceedings for "The Shocking Universe - Gamma-Ray Bursts and High Energy Shock phenomena", Venice (Italy), September 14-18, 2009
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present the analysis of two long Gamma-Ray Bursts, GRB 090323 and GRB 090328, which triggered the Fermi Gamma-Ray Burst Monitor (GBM) and generated an Autonomous Repoint Request to the Fermi Large Area Telescope. The GBM light curves show multi-peaked structures for both events. Here, we present time-integrated and time-resolved burst spectra fitted with different models by the GBM detectors.

[4]  arXiv:1002.4195 [ps, pdf, other]
Title: Abundances and density structure of the inner circumstellar ring around SN 1987A
Authors: Seppo Mattila (1,2), Peter Lundqvist (2), Per Groeningsson (2), Peter Meikle (3), Raylee Stathakis (4), Claes Fransson (2,5), Russell Cannon (4) ((1) Tuorla Observatory; (2) Stockholm Observatory; (3) Imperial College London; (4) AAO; (5) Oskar Klein Centre)
Comments: 17 pages, 8 figures, submitted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present optical spectroscopic data of the inner circumstellar ring around SN 1987A from the Anglo-Australian Telescope (AAT) and the Very Large Telescope (VLT) between ~1400 and ~5000 days post-explosion. We also assembled the available optical and near-infrared line fluxes from the literature between ~300 and ~2000 days. These line light curves were fitted with a photoionization model to determine the density structure and the elemental abundances for the inner ring. We found densities ranging from 1x10^3 to 3x10^4 atoms cm^-3 and a total mass of the ionized gas of 0.058 Msun within the inner ring. Abundances inferred from the optical and near-infrared data were also complemented with estimates of Lundqvist & Fransson (1996) based on ultraviolet lines. This way we found an He/H-ratio (by number of atoms) of 0.17+-0.06, N/O-ratio of 1.5+-0.7, and the total (C+N+O)/(H+He) abundance about 1.6 times its LMC value or roughly 0.6 times the most recent solar value. An iron abundance of 0.20+-0.11 times solar was found which is within the range of the estimates for the LMC. We also present late time (~5000-7500 days) line light curves of [O III], [Ne III], [Ne IV], [Ar III], [Ar IV], and [Fe VII] from observations with the VLT. We compared these with model fluxes and found that an additional 10^2 atoms cm^-3 component was required to explain the data of the highest ionization lines. Such low density gas is expected in the H II-region interior to the inner ring which likely extends also to larger radii at higher latitudes. At epochs later than ~5000 days our models underproduce the emission of most of these lines as expected due to the contribution from the interaction of the SN ejecta with the ring.

[5]  arXiv:1002.4196 [pdf, other]
Title: A dark energy view of inflation
Comments: 5 pages, 4 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Traditionally, inflationary models are analyzed in terms of parameters such as the scalar spectral index ns and the tensor to scalar ratio r, while dark energy models are studied in terms of the equation of state parameter w. Motivated by the fact that both deal with periods of accelerated expansion, we study the evolution of w during inflation, in order to derive observational constraints on its value during an earlier epoch likely dominated by a dynamic form of dark energy. We find that the cosmic microwave background and large-scale structure data is consistent with w_inflation=-1 and provides an upper limit of 1+w <~ 0.02. Nonetheless, an exact de Sitter expansion with a constant w=-1 is disfavored since this would result in ns=1.

[6]  arXiv:1002.4197 [ps, pdf, other]
Title: Current constraints on the cosmic growth history
Comments: 14 pages, 10 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present constraints on the cosmic growth history with recent cosmological data, allowing for deviations from Lambda CDM as might arise if cosmic acceleration is due to modifications to GR or inhomogeneous dark energy. We combine measures of the cosmic expansion history, from Type 1a supernovae, baryon acoustic oscillations and the CMB, with constraints on the growth of structure from recent galaxy, CMB and weak lensing surveys along with ISW-galaxy cross-correlations. Deviations from Lambda CDM are parameterized by phenomenological modifications to the Poisson equation and the relationship between the two Newtonian potentials. We find modifications that are present at the time the CMB is formed are tightly constrained through their impact on the well-measured CMB acoustic peaks. By contrast, constraints on late-time modifications to the growth history, as might arise if modifications are related to the onset of cosmic acceleration, are far weaker, but remain consistent with Lambda CDM at the 95% confidence level. For these late-time modifications we find that differences in the evolution on large and small scales could provide an interesting signature by which to search for modified growth histories with future wide angular coverage, large scale structure surveys.

[7]  arXiv:1002.4198 [ps, pdf, other]
Title: A galaxy populations study of a radio-selected protocluster at z~3.1
Comments: 19 pages, 20 figures, accepted for publication in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present a population study of several types of galaxies within the protocluster surrounding the radio galaxy MRC0316-257 at z~3.1. In addition to the known population of Ly_alpha emitters (LAEs) and [OIII] emitters, we use colour selection techniques to identify protocluster candidates that are Lyman break galaxies (LBG) and Balmer break galaxies (BBGs). The radio galaxy field contains an excess of LBG candidates, with a surface density 1.6\pm0.3 times larger than found for comparable blank fields. This surface overdensity corresponds to an LBG volume overdensity of ~8\pm4. The BBG photometric redshift distribution peaks at the protocluster's redshift, but we detect no significant surface overdensity of BBG. This is not surprising because a volume overdensity similar to the LBGs would have resulted in a surface density of ~1.2 that found in the blank field. This could not have been detected in our sample. Masses and star formation rates of the candidate protocluster galaxies are determined using SED fitting. These properties are not significantly different from those of field galaxies. The galaxies with the highest masses and star formation rates are located near the radio galaxy, indicating that the protocluster environment influences galaxy evolution at z~3. We conclude that the protocluster around MRC0316-257 is still in the early stages of formation.

[8]  arXiv:1002.4200 [ps, pdf, other]
Title: Dissecting Galaxy Formation: II. Comparing Substructure in Pure Dark Matter and Baryonic Models
Authors: Emilio Romano-Diaz (UK Lexington), Isaac Shlosman (UK Lexington), Clayton Heller (Georgia SU), Yehuda Hoffman (Hebrew University, Israel)
Comments: 11 pages, 9 figures, submitted to the Astrophysical Journal
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We compare the substructure evolution in pure dark matter (DM) halos with those in the presence of baryons (PDM and BDM). The prime halos have been analyzed by Romano-Diaz et al (2009). Models have been evolved from identical initial conditions using Constrained Realizations, including star formation and feedback. A comprehensive catalog of subhalos has been compiled and properties of subhalos analyzed in the mass range of 10^8 Mo - 10^11 Mo. We find that subhalo mass functions are consistent with a single power law, M_sbh^{-alpha}, but detect a nonnegligible shift between these functions, alpha -0.86 for the PDM, and -0.98 for the BDM. Overall, alpha const. with intrinsic scatter of +-15%. Second, we find that the radial mass distribution of subhalos can be approximated by a power law, R^{-gamma} with a steepening around the radius of a maximal circular velocity, Rvmax, in the prime halos. Gamma -1.5 for the PDM and -1 for the BDM, inside Rvmax, and is steeper outside. We detect little spatial bias between the subhalo populations and the DM of the main halos. The subhalo population exhibits much less triaxiality with baryons, in tandem with the prime halo. Finally, we find that, counter-intuitively, the BDM population is depleted at a faster rate than the PDM one within the central 30kpc of the prime. Although the baryons provide a substantial glue to the subhalos, the main halos exhibit the same trend. This assures a more efficient tidal disruption of the BDM subhalos. This effect can be reversed for a more efficient feedback from stellar evolution and supermassive black holes, which will expel baryons from the center and decrease the concentration of the prime halo.

[9]  arXiv:1002.4201 [ps, pdf, other]
Title: Ellipsoidal primary of the RS CVn binary zeta And: Investigation using high-resolution spectroscopy and optical interferometry
Authors: H. Korhonen (ESO), M. Wittkowski (ESO), Zs. Kovari (Konkoly), Th. Granzer (AIP), T. Hackman (Helsinki), K.G. Strassmeier (AIP)
Comments: 9 pages, 9 figures, accepted for A&amp;A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We have obtained high-resolution spectroscopy, optical interferometry, and long-term broad band photometry of the ellipsoidal primary of the RS CVn-type binary system zeta And. Based on the optical interferometry the apparent limb darkened diameter of zeta And is 2.55 +/- 0.09 mas using a uniform disk fit. The Hipparcos distance and the limb-darkened diameter obtained with a uniform disk fit give stellar radius of 15.9 +/- 0.8 Rsolar, and combined with bolometric luminosity, it implies an effective temperature of 4665 +/- 140 K. The temperature maps obtained from high resolution spectra using Doppler imaging show a strong belt of equatorial spots and hints of a cool polar cap. The equatorial spots show a concentration around the phase 0.75. This spot configuration is reminiscent of the one seen in the earlier published temperature maps of zeta And. Investigation of the Halpha line reveals both prominences and cool clouds in the chromosphere. Long-term photometry spanning 12 years shows hints of a spot activity cycle, which is also implied by the Doppler images, but the cycle length cannot be reliably determined from the current data.

[10]  arXiv:1002.4205 [ps, pdf, other]
Title: Revealing the nature of unidentified INTEGRAL sources through optical spectroscopy: an overview
Authors: P. Parisi, N. Masetti, for the IBIS Team
Comments: 6 pages, 2 figures; Contributed talk. To be published in the proceedings of "The Extreme sky: Sampling the Universe above 10 keV", October 13-17, 2009, Otranto (LE), Italy
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Thanks to the INTEGRAL satellite the way of looking at the hard X-ray sky above 20 keV has changed substantially. Through the unique imaging and spectroscopy capabilities of the IBIS instrument that has formed the basis of the INTEGRAL surveys, this satellite has improved the knowledge on hard X-ray sources in terms of sensitivity and positional accuracy. Many of the sources belonging to these surveys are however of unidentified nature, but the combined use of available information at longer wavelengths (mainly soft X-rays and radio) and above all optical spectroscopy on the putative counterparts of these hard X-ray objects can reveal their exact nature. Since 2004 our group identified more than 100 it INTEGRAL sources, reducing drastically the percentage of unidentified objects in the various IBIS surveys and allowing statistical studies on them. Here we present a summary of this identification work and an outlook of our preliminary results on identification of newly-discovered sources belonging to the 4th IBIS catalog.

[11]  arXiv:1002.4212 [pdf, other]
Title: Radio galaxy feedback in X-ray selected groups from COSMOS: the effect on the ICM
Authors: S. Giodini (1), V. Smolcic (2), A. Finoguenov (1 and 3), H. Boehringer (1), L. Birzan (5), G. Zamorani (9), A. Oklopcic (6), D. Pierini (1), G.W. Pratt (4), E. Schinnerer (8), R. Massey (2), A.M. Koekemoer (7), M. Salvato (12), D.B. Sanders (10), J. S. Kartaltepe (10), D. Thompson (11) ((1) MPE Garching, (2) Caltech, (3) University of Maryland, Baltimore, (4) CEA-Saclay, France, (5) Leiden Observatory, (6) University of Zagreb, (7) Space Telescope Science Institute, Baltimore, (8) MPIA, Heidelberg, (9) INAF Osservatorio Astronomico di Bologna, (10) IfA Honolulu, (11) LBT Observatory, Tucson, (12) Excellence Cluster Universe/ IPP, Garching)
Comments: Accepted for publication in the Astrophysical Journal. 12 Pages
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We quantify the importance of the mechanical energy released by radio-galaxies inside galaxy groups. We use scaling relations to estimate the mechanical energy released by 16 radio-AGN located inside X-ray detected galaxy groups in the COSMOS field. By comparing this energy output to the host groups' gravitational binding energy, we find that radio galaxies produce sufficient energy to unbind a significant fraction of the intra-group medium. This unbinding effect is negligible in massive galaxy clusters with deeper potential wells. Our results correctly reproduce the breaking of self-similarity observed in the scaling relation between entropy and temperature for galaxy groups.

[12]  arXiv:1002.4213 [ps, pdf, other]
Title: Pulsar electrons detection in AMS-02 experiment. Model status and discovery potential
Authors: Jonathan Pochon
Comments: 14 pages, 18 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The measurements of electrons from cosmic rays have begun a new era a few years ago with high precision experiments like PAMELA and Fermi-LAT. The positron fraction seems to indicate an unknown component above the standard background described in the last 40 years, mostly by HEAT. In the last few years, the PAMELA satellite has confirmed the positron fraction excess above 10 GeV, and studying Fermi-LAT data, the electron flux seems to be steeper than expected. While these new measurements have not closed the debate, results from AMS-02 are expected to reach the accuracy needed to determine a full description of this excess and possibly give some evidence on the possible source. We will present in this note, the AMS-02 capacity in the case of positrons produced by pulsars.

[13]  arXiv:1002.4229 [ps, pdf, other]
Title: Birthrates and delay times of Type Ia supernovae
Comments: 11 pages, 2 figures, accepted by Science in China Series G (Dec.30, 2009)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclear. In this paper, according to a detailed binary population synthesis study, we obtained SN Ia birthrates and delay times from different progenitor models, and compared them with observations. We find that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those inferred from observations, while the birthrate from the single-degenerate (SD) model accounts for only about 1/2-2/3 of the observations. If a single starburst is assumed, the distribution of the delay times of SNe Ia from the SD model is a weak bimodality, where the WD + He channel contributes to the SNe Ia with delay times shorter than 100Myr, and the WD + MS and WD + RG channels to those with age longer than 1Gyr.

[14]  arXiv:1002.4244 [ps, pdf, other]
Title: Testing circumstellar disk lifetimes in young embedded clusters associated with the Vela Molecular Ridge
Authors: Fabrizio Massi (1), Elisa Di Carlo (2), Claudio Codella (1), Leonardo Testi (1 and 3), Leonardo Vanzi (4), Joana Gomes (5 and 6) ((1) INAF-Arcetri, (2) INAF-Teramo, (3) ESO, (4) Department of Astronomy and Astrophysics, Pontificia Universidad Católica de Chile, (5) Centro de Astronomia e Astrofisica da Universidade de Lisboa, (6) Centre for Astrophysics Research, University of Hertfordshire)
Comments: 13 pages, 11 figures, accepted for publication in Astronomy and Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)

Context. The Vela Molecular Ridge hosts a number of young embedded star clusters in the same evolutionary stage. Aims. The main aim of the present work is testing whether the fraction of members with a circumstellar disk in a sample of clusters in the cloud D of the Vela Molecular Ridge, is consistent with relations derived for larger samples of star clusters with an age spread. Besides, we want to constrain the age of the young embedded star clusters associated with cloud D. Methods. We carried out L (3.78 microns) photometry on images of six young embedded star clusters associated with cloud D of the Vela Molecular Ridge, taken with ISAAC at the VLT. These data are complemented with the available HKs photometry. The 6 clusters are roughly of the same size and appear to be in the same evolutionary stage. The fraction of stars with a circumstellar disk was measured in each cluster by counting the fraction of sources displaying a NIR excess in colour-colour (HKsL) diagrams. Results. The L photometry allowed us to identify the NIR counterparts of the IRAS sources associated with the clusters. The fraction of stars with a circumstellar disk appears to be constant within errors for the 6 clusters. There is a hint that this is lower for the most massive stars. The age of the clusters is constrained to ~1-2 Myr. Conclusions. The fraction of stars with a circumstellar disk in the observed sample is consistent with the relations derived from larger samples of star clusters and with other age estimates for cloud D. The fraction may be lower for the most massive stars. Our results agree with a scenario where all intermediate and low-mass stars form with a disk, whose lifetime is shorter for higher mass stars.

[15]  arXiv:1002.4245 [ps, pdf, other]
Title: Anisotropic radiation field and trapped photons around the Kerr black hole
Comments: Accepted for publication in A&amp;A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Aims. In order to understand the anisotropic properties of local radiation field in the curved spacetime around a rotating black hole, we investigate the appearance of a black hole seen by an observer located near the black hole. When the black hole is in front of a source of illumination the black hole cast shadow in the illumination. Accordingly, the appearance of the black hole is called the black hole shadow.
Methods. We first analytically describe the shape of the shadow in terms of constants of motion for a photon seen by the observer in the locally non-rotating reference frame (LNRF). Then, we newly derive the useful equation for the solid angle of the shadow. In a third step, we can easily plot the apparent image of the black hole shadow. Finally, we also calculate the ratio of the photon trapped by the hole and the escape photon to the distant region for photons emitted near the black hole.
Results. From the shape and the size of the black hole shadow, we can understand the signatures of the curved spacetime; i.e., the mass and spin of the black hole. Our equations for the solid angle of the shadow has technical advantages in calculating the photon trapping ratio. That is, this equation is computationally very easy, and gives extremely precise results. This is because this equation is described by the one-parameter integration with given values of the spin and location for the black hole considered. After this, the solid angle can be obtained without numerical calculations of the null geodesics for photons.

[16]  arXiv:1002.4268 [ps, pdf, other]
Title: Accurate fundamental parameters for 23 bright solar-type stars
Comments: Accepted by MNRAS. Abstract abridged
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We combine results from interferometry, asteroseismology and spectroscopy to determine accurate fundamental parameters of 23 bright solar-type stars, from spectral type F5 to K2 and luminosity classes III to V. For some stars we can use direct techniques to determine the mass, radius, luminosity and effective temperature, and we compare with indirect methods that rely on photometric calibrations or spectroscopic analyses. We use the asteroseismic information available in the literature to infer an indirect mass with an accuracy of 4-15 percent. From indirect methods we determine luminosity and radius to 3 percent. For Teff we find a slight offset of -40+-20 K between the spectroscopic method and the direct method, meaning the spectroscopic temperatures are too high.
From the spectroscopic analysis we determine the detailed chemical composition for 13 elements, including Li, C and O. We find no significant offset between the spectroscopic surface gravity and the value from combining asteroseismology with radius estimates. From the spectroscopy we also determine vsini and we present a new calibration of macro- and microturbulence. From the comparison between the results from the direct and spectroscopic methods we claim that we can determine Teff, log g, and [Fe/H] with absolute accuracies of 80 K, 0.08 dex, and 0.07 dex. The indirect methods are important to obtain reliable estimates of the fundamental parameters of relatively faint stars when interferometry cannot be used. Our study is the first to compare direct and indirect methods for a large sample of stars, and we conclude that indirect methods are valid, although slight corrections may be needed.

[17]  arXiv:1002.4274 [ps, pdf, other]
Title: Magnetic Fields and Velocity Structures around a Cancellation Site
Comments: 18 pages, 5 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

A cancellation is thought to be a basic process of the photospheric magnetic field and plays an important role in magnetic flux budget and in various solar activities. There are two major theoretical scenarios for this phenomena, i.e. the "U-loop emergence" and the Omega-loop submergence models. It is important to clarify which is the dominant process during the cancellation for the estimation of the solar magnetic flux transport through the surface. We study the vector magnetic field and velocity structures around a quiet Sun cancellation by using the Solar Optical Telescope on board Hinode satellite. Transverse magnetic field connecting the canceling magnetic features and strong long-lasting Doppler red-shift signal are found. The transverse field is observed in the first spectropolarimetric observation after the occurrence of the cancellation while the red-shift clearly delayed to the cancellation by 20 minutes. These results indicate that the observed cancellation is an Omega-loop submergence.

[18]  arXiv:1002.4299 [ps, pdf, other]
Title: Ultraluminous X-ray sources out to z~0.3 in the COSMOS field
Comments: 10 pages, 9 figures, accepted for publication in Astronomy &amp; Astrophysics
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

Using Chandra observations we have identified a sample of seven off-nuclear X-ray sources, in the redshift range z=0.072-0.283, located within optically bright galaxies in the COSMOS Survey. Using the multi-wavelength coverage available in the COSMOS field, we study the properties of the host galaxies of these ULXs. In detail, we derived their star formation rate from H_alpha measurements and their stellar masses using SED fitting techniques with the aim to compute the probability to have an off-nuclear source based on the host galaxy properties. We divide the host galaxies in different morphological classes using the available ACS/HST imaging. We find that our ULXs candidates are located in regions of the SFR versus M$_star$ plane where one or more off-nuclear detectable sources are expected. From a morphological analysis of the ACS imaging and the use of rest-frame colours, we find that our ULXs are hosted both in late and early type galaxies. Finally, we find that the fraction of galaxies hosting a ULX ranges from ~0.5% to ~0.2% going from L[0.5-2 keV]=3 x 10^39 erg s^-1 to L[0.5-2 keV]= 2 x 10^40 erg s^-1.

[19]  arXiv:1002.4300 [ps, pdf, other]
Title: The ACS LCID project. III. The star formation history of the Cetus dSph galaxy: a post-reionization fossil
Comments: 24 pages, 23 figures in emulateapj format. Submitted of ApJ. Several figures degraded. See this http URL for a version with full resolution figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We use deep HST/ACS observations to calculate the star formation history (SFH) of the Cetus dwarf spheroidal (dSph) galaxy. Our photometry reaches below the oldest main sequence turn-offs, which allows us to estimate the age and duration of the main episode of star formation in Cetus. This is well approximated by a single episode that peaked roughly 12+/-0.5 Gyr ago and lasted no longer than about 1.9+/-0.5 Gyr (FWHM). Our solution also suggests that essentially no stars formed in Cetus during the past 8 Gyrs. This makes Cetus' SFH comparable to that of the oldest Milky Way dSphs. Given the current isolation of Cetus in the outer fringes of the Local Group, this implies that Cetus is a clear outlier in the morphology-Galactocentric distance relation that holds for the majority of Milky Way dwarf satellites. Our results also show that Cetus continued forming stars through z ~ 1, long after the Universe was reionized, and that there is no clear signature of the epoch of reionization in Cetus' SFH. We discuss briefly the implications of these results for dwarf galaxy evolution models. Finally, we present a comprehensive account of the data reduction and analysis strategy adopted for all galaxies targeted by the LCID (Local Cosmology from Isolated Dwarfs) project. We employ two different photometry codes (DAOPHOT/ALLFRAME and DOLPHOT), three different SFH reconstruction codes (IAC-pop/MinnIAC, MATCH, COLE), and two stellar evolution libraries (BaSTI and Padova/Girardi), allowing for a detailed assessment of the modeling and observational uncertainties.

[20]  arXiv:1002.4301 [ps, pdf, other]
Title: Age and metallicity of star clusters in the Small Magellanic Cloud from integrated spectroscopy
Authors: Bruno Dias (1), Paula Coelho (2), Beatriz Barbuy (1), Leandro Kerber (1 and 3), Thais Idiart (1) ((1) IAG, Universidade de São Paulo, (2) NAT, Universidade Cruzeiro do Sul, (3) Universidade Estadual de Santa Cruz)
Comments: 17 pages, 8 figures + 34 figures as appendix, submitted to A&amp;A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context: Analysis of ages and metallicities of star clusters in the Magellanic Clouds bring information for studies on the chemical evolution of the Clouds and other dwarf Irregular galaxies. Aims: The aim is to derive ages and metallicities from integrated spectra of 14 star clusters in the Small Magellanic Cloud. We are seeking at identifying, in particular, intermediate/old age star clusters. Methods: Making use of a full spectrum fitting technique, we compared the integrated spectra of the sample clusters to three different sets of single stellar population models, using two fitting codes available in the literature. Results: We derive the ages and metallicities of 9 intermediate/old age clusters, some of them previously unstudied, and 5 young clusters. Conclusions: We point out the interest of the newly identified as intermediate/old age clusters HW1, NGC 152, Lindsay 3, Lindsay 11 and Lindsay 113. We also confirm the old ages of NGC 361, NGC 419, Kron 3, and of the very well-known oldest SMC cluster NGC 121.

[21]  arXiv:1002.4339 [ps, pdf, other]
Title: HR 7355 - another rapidly braking He-strong CP star?
Comments: 4 printed pages, 2 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)

Strong meridional mixing induced by rapid rotation is one reason why all hot main-sequence stars are not chemically peculiar. However, the finding that the He-strong CP star HR 7355 is a rapid rotator complicates this concept. Our goal is to explain the observed behaviour of HR 7355 based on period analysis of all available photometry. Over two years, we acquired 114 new BV observations of HR 7355 at observatories in Arizona, U.S.A and Cape Town, South Africa. We performed period analyses of the new observations along with new analyses of 732 archival measurements from the Hipparcos and ASAS projects. We find that the light curves of HR 7355 in various filters are quite similar, with amplitudes 0.035(4), 0.036(4), and 0.038(3) mag in B, Hp and V, respectively. The light curves are double-peaked, with unevenly deep minima. We substantially refine the rotational period to be P=0.5214410(4) d, indicating that HR 7355 is the most rapidly rotating CP star known. Our period analyses reveal a possible lengthening of the rotational period with dP/dt/P = 2.4(8)x 10^-6/yr. We conclude that the shape and amplitude of HR 7355 light curves are typical of magnetic He-strong CP stars, for which light variations are the result of photospheric spots on the surface of a rotating star. We hypothesise that the light variations are caused mainly by an uneven distribution of overabundant helium on the star's surface. We briefly describe and discuss the cause of the rapid rotational braking of the star.

[22]  arXiv:1002.4355 [ps, pdf, other]
Title: Magnetic Field Structures in a Facular Region Observed by THEMIS and Hinode
Comments: 20 pages, 9 figures, 3 tables, accepted for publication in Solar Physics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The main objective of this paper is to build and compare vector magnetic maps obtained by two spectral polarimeters, i.e. THEMIS/MTR and Hinode SOT/SP, using two inversion codes (UNNOFIT and MELANIE) based on the Milne-Eddington solar atmosphere model. To this end, we used observations of a facular region within active region NOAA 10996 on 23 May 2008, and found consistent results concerning the field strength, azimuth and inclination distributions. Because SOT/SP is free from the seeing effect and has better spatial resolution, we were able to resolve small magnetic polarities with sizes of 1" to 2", and we could detect strong horizontal magnetic fields, which converge or diverge in negative or positive facular polarities. These findings support models which suggest the existence of small vertical flux tube bundles in faculae. A new method is proposed to get the relative formation heights of the multi-lines observed by MTR assuming the validity of a flux tube model for the faculae. We found that the Fe 1 6302.5 \AA line forms at a greater atmospheric height than the Fe 1 5250.2 \AA line.

[23]  arXiv:1002.4356 [ps, pdf, other]
Title: Searching for the earliest galaxies in the 21 cm forest
Comments: 8 pages, 3 figures. Accepted for publication in Science in China Series G
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We use a model developed by Xu et al. (2010) to compute the 21 cm line absorption signatures imprinted by star-forming dwarf galaxies (DGs) and starless minihalos (MHs). The method, based on a statistical comparison of the equivalent width (W_\nu) distribution and flux correlation function, allows us to derive a simple selection criteria for candidate DGs at very high (z >= 8) redshift. We find that ~ 18% of the total number of DGs along a line of sight to a target radio source (GRB or quasar) can be identified by the condition W_\nu < 0; these objects correspond to the high-mass tail of the DG distribution at high redshift, and are embedded in large HII regions. The criterion W_\nu > 0.37 kHz instead selects ~ 11% of MHs. Selected candidate DGs could later be re-observed in the near-IR by the JWST with high efficiency, thus providing a direct probe of the most likely reionization sources.

[24]  arXiv:1002.4357 [pdf, other]
Title: The Long-term Evolution of the Galactic Disk Traced by Dissolving Star Clusters
Comments: ApJ, in press; 15 pages, 9 figures (ApJ format)
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The Galactic disk retains a vast amount of information about how it came to be, and how it evolved over cosmic time. However, we know very little about the secular processes associated with disk evolution. One major uncertainty is the extent to which stars migrate radially through the disk, thereby washing out signatures of their past (e.g. birth sites). Recent theoretical work finds that such "blurring" of the disk can be important if spiral arms are transient phenomena. Here we describe an experiment to determine the importance of diffusion from the Solar circle with cosmic time. Consider a star cluster that has been placed into a differentially rotating, stellar fluid. We show that all clusters up to ~10^4 solar masses, and a significant fraction of those up to ~10^5 solar masses, are expected to be chemically homogeneous, and that clusters of this size can be assigned a unique "chemical tag" by measuring the abundances of <~10 independent element groups, with better age and orbit determinations allowing fewer abundance measurements. The star cluster therefore acts like a "tracer dye", and the present-day distribution of its stars provides a strong constraint on the rate of radial diffusion or migration in the Galactic disk. Sellwood & Binney have argued for strong radial transport driven by transient spiral perturbations: in principle, we could measure the strength of this migration directly.

[25]  arXiv:1002.4370 [ps, pdf, other]
Title: Photometric scaling relations of lenticular and spiral galaxies
Comments: Accepted to MNRAS, includes a big figure in electronic form, not included here
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Photometric scaling relations are studied for S0 galaxies and compared with those for spirals. New 2D K_s-band multi-component decompositions are presented for 122 early-type disk galaxies. Combining with our previous decompositions, the final sample consists of 175 galaxies. As a comparison sample we use the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS), for which similar decompositions have previously been made by us. Our main results are: (1) Important scaling relations are present, indicating that the formative processes of bulges and disks in S0s are coupled like has been previously found for spirals. (2) We obtain median r_{eff}/h_r = 0.20, 0.15 and 0.10 for S0, S0/a-Sa and Sab-Sc galaxies: these are smaller than predicted by simulation models in which bulges are formed by galaxy mergers. (3) The properties of bulges of S0s are different from the elliptical galaxies, which is manifested in the M_K(bulge) vs r_{eff} relation, in the photometric plane, and to some extent also in the Kormendy relation. The bulges of S0s are similar to bulges of spirals with M_K(bulge) < -20 mag. Some S0s have small bulges, but their properties are not compatible with the idea that they could evolve to dwarfs by galaxy harassment. (4) The relative bulge flux B/T for S0s covers the full range found in the Hubble sequence. (5) The values and relations of the parameters of the disks of the S0 galaxies in NIRS0S are similar to those obtained for spirals in the OSUBSGS. Overall, our results support the view that spiral galaxies with bulges brighter than -20 mag in the K-band can evolve directly into S0s, due to stripping of gas followed by truncated star formation.

[26]  arXiv:1002.4381 [ps, pdf, other]
Title: HST Spectrophotometry and Models for Solar Analogs
Authors: R. C. Bohlin (Space Telescope Science Institute)
Comments: 19 pages, 2 tables, 7 figures; to appear in AJ 2010 April
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Absolute flux distributions for seven solar analog stars are measured from 0.3 to 2.5 \mu m by HST spectrophotometry.In order to predict the longer wavelength mid-IR fluxes that are required for JWST calibration, the HST SEDs are fit with Castelli & Kurucz model atmospheres; and the results are compared with fits from the MARCS model grid. The rms residuals in 10 broad band bins are all <0.5% for the best fits from both model grids. However, the fits differ systematically: The MARCS fits are 40-100 K hotter in T_{eff}, 0.25-0.80 higher in log g, 0.01-0.10 higher in log z, and 0.008-0.021 higher in the reddening E(B-V), probably because their specifications include different metal abundances. Despite these differences in the parameters of the fits, the predicted mid-IR fluxes differ by only ~1%; and the modeled flux distributions of these G stars have an estimated ensemble accuracy of 2% out to 30 \mu m.

[27]  arXiv:1002.4383 [ps, pdf, other]
Title: Fermi Large Area Telescope observations of the Vela-X Pulsar Wind Nebula
Comments: 21 pages, 5 figures, accepted for publication in Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

We report on gamma-ray observations in the off-pulse window of the Vela pulsar PSR B0833-45, using 11 months of survey data from the Fermi Large Area Telescope (LAT). This pulsar is located in the 8 degree diameter Vela supernova remnant, which contains several regions of non-thermal emission detected in the radio, X-ray and gamma-ray bands. The gamma-ray emission detected by the LAT lies within one of these regions, the 2*3 degrees area south of the pulsar known as Vela-X. The LAT flux is signicantly spatially extended with a best-fit radius of 0.88 +/- 0.12 degrees for an assumed radially symmetric uniform disk. The 200 MeV to 20 GeV LAT spectrum of this source is well described by a power-law with a spectral index of 2.41 +/- 0.09 +/- 0.15 and integral flux above 100 MeV of (4.73 +/- 0.63 +/- 1.32) * 10^{-7} cm^{-2} s^{-1}. The first errors represent the statistical error on the fit parameters, while the second ones are the systematic uncertainties. Detailed morphological and spectral analyses give strong constraints on the energetics and magnetic field of the pulsar wind nebula (PWN) system and favor a scenario with two distinct electron populations.

[28]  arXiv:1002.4391 [ps, pdf, other]
Title: Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter
Authors: R. Martinez-Arnaiz (1), J. Maldonado (2), D. Montes (1), C. Eiroa (2), B. Montesinos (3), ((1) Universidad Complutense de Madrid, (2) Universidad Autonoma de Madrid, (3) LAEX, CAB (CSIC-INTA))
Comments: Accepted for publication in Astronomy &amp; Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)

Context: Chromospheric activity produces both photometric and spectroscopic variations that can be mistaken as planets. Large spots crossing the stellar disc can produce planet-like periodic variations in the light curve of a star. These spots clearly affect the spectral line profiles and their perturbations alter the line centroids creating a radial velocity jitter that might contaminate" the variations induced by a planet. Precise chromospheric activity measurements are needed to estimate the activity-induced noise that should be expected for a given star. Aims: We obtain precise chromospheric activity measurements and projected rotational velocities for nearby (d < 25 pc) cool (spectral types F to K) stars, to estimate their expected activity-related jitter. As a complementary objective, we attempt to obtain relationships between fluxes in different activity indicator lines, that permit a transformation of traditional activity indicators, i.e, CaII H & K lines, to others that hold noteworthy advantages. Methods: We used high resolution (~50000) echelle optical spectra. To determine the chromospheric emission of the stars in the sample, we used the spectral subtraction technique. Rotational velocities were determined using the cross-correlation technique. To infer activity-related radial velocity (RV) jitter, we used empirical relationships between this jitter and the R'_HK index. Results: We measured chromospheric activity, as given by different indicators throughout the optical spectra, and projected rotational velocities for 371 nearby cool stars. We have built empirical relationships among the most important chromospheric emission lines. Finally, we used the measured chromospheric activity to estimate the expected RV jitter for the active stars in the sample.

[29]  arXiv:1002.4397 [ps, pdf, other]
Title: Where do long-period comets come from? 26 comets from the non-gravitational Oort spike
Comments: Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The apparent source region (or regions) of long-period comets as well as the definition of the dynamically new comet are still open questions.The aim of this investigation is to look for the apparent source of selected long period comets and to refine the definition of dynamically new comets. We show that incorporation of the non-gravitational forces into the orbit determination process significantly changes the situation. We determined precise non-gravitational orbits of all investigated comets and next followed numerically their past and future motion during one orbital period. Applying ingenious Sitarski's method of creating swarms of virtual comets compatible with observations, we were able to derive the uncertainties of original and future orbital elements, as well as the uncertainties of the previous and next perihelion distances. We concluded that the past and future evolution of cometary orbits under the Galactic tide perturbations is the only way to find which comets are really dynamically new. We also have shown that a significant percentage of long-period comets can visit the zone of visibility during at least two or three consecutive perihelion passages.

[30]  arXiv:1002.4399 [ps, pdf, other]
Title: The Parker Magnetostatic Theorem
Authors: B. C. Low
Comments: 13 pages, no figure
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We demonstrate the Parker Magnetostatic Theorem in terms of a small neighborhood in solution space containing continuous force-free magnetic fields in small deviations from the uniform field. These fields are embedded in a perfectly conducting fluid bounded by a pair of rigid plates where each field is anchored, taking the plates perpendicular to the uniform field. Those force-free fields obtainable from the uniform field by continuous magnetic footpoint displacements at the plates have field topologies that are shown to be a restricted subset of the field topologies similarly created without imposing the force-free equilibirum condition. The theorem then follows from the deduction that a continuous nonequilibrum field with a topology not in that subset must find a force-free state containing tangential discontinuities.

[31]  arXiv:1002.4401 [pdf, other]
Title: Properties of hierarchically forming star clusters
Authors: Th. Maschberger (1,2), C.J. Clarke (1), I.A. Bonnell (3), P. Kroupa (2) ( (1) Institute of Astronomy, Cambridge (2) Argelander-Institut, Bonn (3) School of Physics and Astronomy, St. Andrews)
Comments: 21 Pages, 25 Figures
Subjects: Galaxy Astrophysics (astro-ph.GA)

We undertake a systematic analysis of the early (< 0.5 Myr) evolution of clustering and the stellar initial mass function in turbulent fragmentation simulations. These large scale simulations for the first time offer the opportunity for a statistical analysis of IMF variations and correlations between stellar properties and cluster richness. The typical evolutionary scenario involves star formation in small-n clusters which then progressively merge; the first stars to form are seeds of massive stars and achieve a headstart in mass acquisition. These massive seeds end up in the cores of clusters and a large fraction of new stars of lower mass is formed in the outer parts of the clusters. The resulting clusters are therefore mass segregated at an age of 0.5 Myr, although the signature of mass segregation is weakened during mergers. We find that the resulting IMF has a smaller exponent (alpha=1.8-2.2) than the Salpeter value (alpha=2.35). The IMFs in subclusters are truncated at masses only somewhat larger than the most massive stars (which depends on the richness of the cluster) and an universal upper mass limit of 150 Msun is ruled out. We also find that the simulations show signs of the IGIMF effect proposed by Weidner & Kroupa, where the frequency of massive stars is suppressed in the integrated IMF compared to the IMF in individual clusters. We identify clusters through the use of a minimum spanning tree algorithm which allows easy comparison between observational survey data and the predictions of turbulent fragmentation models. In particular we present quantitative predictions regarding properties such as cluster morphology, degree of mass segregation, upper slope of the IMF and the relation between cluster richness and maximum stellar mass. [abridged]

[32]  arXiv:1002.4402 [ps, pdf, other]
Title: Looking into the heart of a beast: the black hole binary LS 5039
Comments: 6 pages, 2 figures (with 8 panels); Proceedings of the 5th Workshop of Young Researchers in Astronomy and Astrophysics, Budapest, 2009; to be published in J. Phys.: Conf. Series (JPCS)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

LS 5039 is a relatively close microquasar consisting of a late O-type star and a compact object (very possibly a black hole) on a highly eccentric orbit with a period of 3.9 days. The high X-ray, gamma-ray and radio luminosity indicate light-matter interaction, which arise from the stellar wind of the primary star accreting toward the black hole. Former examinations suggest that LS 5039 could be a prototype of wind-fed high mass X-ray binaries (WXBs) with diskless main sequence O primaries. Now there is a great chance to better understand the configuration and the physical processes in the exotic system. In July 2009 LS 5039 was followed by the Canadian MOST space telescope to get ultraprecise photometric data in a month-long semi-continuous time series. Parallel to this, we have taken simultaneous high-resolution optical spectra using the 2.3m ANU telescope of the Siding Spring Observatory, supplemented with further data obtained in early August 2009 with the same instrument. Here we present the first results from the new echelle spectra, which represent the best optical spectroscopy ever obtained for this intriguing system. We determined fundamental orbital and physical parameters of LS 5039 and examined the configuration and the circumstellar environment of the system via radial velocity measurements and detailed line-profile analysis of H-Balmer, He I and He II lines.

Cross-lists for Wed, 24 Feb 10

[33]  arXiv:1002.3478 (cross-list from gr-qc) [ps, pdf, other]
Title: Quintessence and phantom cosmology with non-minimal derivative coupling
Comments: 8 pages, 8 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

We investigate cosmological scenarios with a non-minimal derivative coupling between the scalar field and the curvature, examining both the quintessence and the phantom cases in zero and constant potentials. In general, we find that the universe transits from one de Sitter solution to another, determined by the coupling parameter. Furthermore, according to the parameter choices and without the need for matter, we can obtain a Big Bang, an expanding universe with no beginning, a cosmological turnaround, an eternally contracting universe, a Big Crunch, a Big Rip avoidance and a cosmological bounce. This variety of behaviors reveals the capabilities of the present scenario.

[34]  arXiv:1002.3828 (cross-list from hep-ph) [ps, pdf, other]
Title: Non-WIMP Candidates
Authors: Jonathan L. Feng
Comments: 20 pages, published as Chapter 10, pp. 190-204, in Particle Dark Matter: Observations, Models and Searches, edited by Gianfranco Bertone (Cambridge University Press, 2010), available at this http URL
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Non-WIMP dark matter candidates include particles motivated by minimality, candidates motivated by experimental anomalies, and exotic possibilities motivated primarily by the desire of clever iconoclasts to highlight how truly ignorant we are about the nature of dark matter. In this review, I discuss candidates that are not WIMPs, but nevertheless share the same theoretical motivations as WIMPs and also naturally have the correct relic density. There are two classes: superWIMP dark matter, where the desired relic density is inherited through decays, and WIMPless dark matter, where the dark matter's mass and couplings scale together to maintain the desired thermal relic density.

[35]  arXiv:1002.4044 (cross-list from hep-ph) [ps, pdf, other]
Title: Inflation and Dynamical Compactification
Comments: 8 pages
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

We consider a $4+N$ dimensional Einstein gravity coupled to a non-linear sigma model. This theory admits a solution in which the $N$ extra dimensions contract exponentially while the ordinary space expand exponentially. Physically, the non-linear sigma fields induce the dynamical compactification of the extra dimensions, which in turn drives inflation. No inflatons are required.

[36]  arXiv:1002.4138 (cross-list from hep-th) [ps, pdf, other]
Title: Bouncing inflation in nonlinear $R^2+R^4$ gravitational model
Comments: RevTex 13 pages, 13 figures
Subjects: High Energy Physics - Theory (hep-th); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

We study a gravitational model with curvature-squared $R^2$ and curvature-quartic $R^4$ nonlinearities. The effective scalar degree of freedom $\phi$ (scalaron) has a multi-valued potential $U(\phi)$ consisting of a number of branches. These branches are fitted with each other in the branching and monotonic points. In the case of four-dimensional space-time, we show that the monotonic points are penetrable for scalaron while in the vicinity of the branching points scalaron has the bouncing behavior and cannot cross these points. Moreover, there are branching points where scalaron bounces an infinite number of times with decreasing amplitude and the Universe asymptotically approaches the de Sitter stage. Such accelerating behavior we call bouncing inflation. For this accelerating expansion there is no need for original potential $U(\phi)$ to have a minimum or to check the slow-roll conditions. A necessary condition for such inflation is the existence of the branching points. This is a new type of inflation. We show that bouncing inflation takes place both in the Einstein and Brans-Dicke frames.

[37]  arXiv:1002.4155 (cross-list from hep-ph) [ps, pdf, other]
Title: SO(10) SUSY GUTs with mainly axion cold dark matter: implications for cosmology and colliders
Authors: Howard Baer
Comments: 6 pages plus 2 .eps figures; invited talk given at Axions 2010 meeting, University of Florida, Jan. 15-17, 2010
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Experiment (hep-ex)

Supersymmetric grand unified theories based on the gauge group SO(10) are highly motivated. In the simplest models, one expects t-b-\tau Yukawa coupling unification, in addition to gauge, matter and Higgs unification. Yukawa unification only occurs with very special GUT scale boundary conditions, leading to a spectra with ~10 TeV first and second generation scalars, TeV-scale third generation scalars, and light gauginos. The relic density of neutralino cold dark matter is calculated to be 10^2-10^4 times higher than observation. If we extend the theory with the PQWW solution to the strong CP problem, then instead a mixture of axions and axinos comprises the dark matter, with the measured abundance. Such a solution solves several cosmological problems. We predict a rather light gluino with m(gluino)~300-500 GeV that should be visible in either Tevatron or forthcoming LHC run 1 data. We would also expect ultimately a positive result from relic axion search experiments.

Replacements for Wed, 24 Feb 10

[38]  arXiv:0902.1433 (replaced) [ps, pdf, other]
Title: Chemical stratification in the Orion Bar: JCMT Spectral Legacy Survey observations
Authors: Matthijs H. D. van der Wiel (1 and 2), Floris F. S. van der Tak (2 and 1), Volker Ossenkopf (3 and 2), Marco Spaans (1), Helen Roberts (4), Gary A. Fuller (5), René Plume (6) ((1) Kapteyn, Groningen, NL, (2) SRON, Groningen, NL, (3) Köln, DE, (4) Belfast, UK, (5) Manchester, UK, (6) Calgary, CA)
Comments: Published in A&amp;A 498, 161-165 (2009); v2: updated with correct line strengths after corrigendum in A&amp;A 510, C1 (2010)
Subjects: Galaxy Astrophysics (astro-ph.GA)
[39]  arXiv:0903.0092 (replaced) [ps, pdf, other]
Title: Topological aspects in a two component Bose condensed system in neutron star
Authors: Heng Guo, Ji-Rong Ren
Comments: 9 pages, no figures
Journal-ref: Chinese Phys. B 18 (2009)3379-3383
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[40]  arXiv:0905.0730 (replaced) [ps, pdf, other]
Title: Analytic solution for matter density perturbations in a class of viable cosmological f(R) models
Comments: 11 pages; More discussion and references added, results unchanged, matches the version to be published in IJMPD; A typo in eq. (25) is fixed
Journal-ref: Int.J.Mod.Phys.D18:1731-1740,2009
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
[41]  arXiv:0906.1181 (replaced) [pdf, other]
Title: Measurement of Cosmic Microwave Background Polarization Power Spectra from Two Years of BICEP Data
Comments: Updated to reflect published version
Journal-ref: Astrophysical Journal 711 (2010) 1123-1140
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[42]  arXiv:0909.3517 (replaced) [ps, pdf, other]
Title: The Stellar Mass Density and Specific Star Formation Rate of the Universe at z~7
Authors: Valentino Gonzalez (UCSC), Ivo Labbe (OCIW), Rychard J. Bouwens (UCSC/Leiden Observatory), Garth Illingworth (UCSC), Marijn Franx (Leiden Observatory), Mariska Kriek (Princeton University), Gabriel B. Brammer (Yale University)
Comments: 17 pages, 7 figures, 5 tables, accepted for publication in the Astrophysical Journal, updated to match version in press
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[43]  arXiv:0910.5705 (replaced) [ps, pdf, other]
Title: An HI absorbing circumnuclear disk in Cygnus A
Authors: Christian Struve (1,2), John E. Conway (3) ((1) Netherlands Foundation for Research in Astronomy (2) Kapteyn Institute, University of Groningen (3) Onsala Space Observatory)
Comments: 9 pages, 4 figures; A&amp;A, in press
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
[44]  arXiv:0911.1592 (replaced) [pdf, other]
Title: A Simultaneous Stacking and Deblending Algorithm for Astronomical Images
Comments: accepted to The Astronomical Journal. 18 pages, 6 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[45]  arXiv:0911.2244 (replaced) [ps, pdf, other]
Title: Full-sky lensing shear at second order
Comments: 29 pages, discussion about the first-order convergence added, matches published version
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[46]  arXiv:0911.3709 (replaced) [ps, pdf, other]
Title: Simulating X-ray Supercavities and Their Impact on Galaxy Clusters
Authors: Fulai Guo, William G. Mathews (UC Santa Cruz)
Comments: Slightly revised version, accepted for publication in ApJ. 11 pages, 6 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
[47]  arXiv:0911.5178 (replaced) [ps, pdf, other]
Title: Spherical Collapse and the Halo Model in Braneworld Gravity
Comments: 20 pages, 16 figures; v2: minor addition to appendix; matches published version
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[48]  arXiv:0912.1751 (replaced) [ps, pdf, other]
Title: Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments
Comments: Accepted for publication in A&amp;A, 9 pages, 4 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
[49]  arXiv:0912.2866 (replaced) [ps, pdf, other]
Title: Can the cosmological constant be mimicked by smooth large-scale inhomogeneities for more than one observable?
Comments: 1 pages
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
[50]  arXiv:0912.3998 (replaced) [ps, pdf, other]
Title: An Indication for the Binarity of P Cygni from Its Seventeenth Century Eruption
Authors: Amit Kashi
Comments: Accepted to MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[51]  arXiv:1001.0648 (replaced) [ps, pdf, other]
Title: Exploring mass loss, low-Z accretion, and convective overshoot in solar models to mitigate the solar abundance problem
Comments: Submitted to the Astrophysical Journal;Revised version that includes preliminary exploration of solar models using CO^5BOLD abundances and model with early main sequence mass loss
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[52]  arXiv:1001.0780 (replaced) [ps, pdf, other]
Title: LoCuSS: A Comparison of Cluster Mass Measurements from XMM-Newton and Subaru - Testing Deviation from Hydrostatic Equilibrium and Non-Thermal Pressure Support
Comments: ApJ (2010), 711, 1033-1043, 5 figures and 6 tables
Journal-ref: Zhang et al, 2010, ApJ, 711, 1033-1043
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
[53]  arXiv:1001.3715 (replaced) [pdf, other]
Title: The dark secrets of gaseous nebulae -- highlights from deep spectroscopy
Authors: Xiaowei Liu
Comments: 34 pages, 8 figures. A review on photoionized gaseous nebulae. To appear in New Vision 400: Engaging Big Questions in Astronomy and Cosmology Four Hundred Years after the Invention of the Telescope, eds. D. G. York, O. Gingerich, S.-N. Zhang, C. L. Harper, Jr
Subjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
[54]  arXiv:1001.5041 (replaced) [ps, pdf, other]
Title: The Presence of Weak Active Galactic Nuclei in High Redshift Star Forming Galaxies
Comments: 15 pages, 4 figures, ApJ Accepted, new version to be published (updated text, figures, and table)
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[55]  arXiv:1001.5318 (replaced) [ps, pdf, other]
Title: Hidden Double-Peaked Emitters in Seyfert 2 Galaxies
Authors: Hien D. Tran (W. M. Keck Observatory)
Comments: 11 pages in emulateapj; ApJ vol. 711, 2010 March 10; v2: minor corrections to text for consistency with published version
Journal-ref: Astrophysical Journal 711 (2010) 1174-1184
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
[56]  arXiv:1002.0462 (replaced) [ps, pdf, other]
Title: Phantom behaviour and growth index anomalous evolution in viable f(R) gravity models
Comments: 7 pages, 6 figures. To be published in the Proceedings of 19th Workshop in General Relativity and Gravitation in Japan (JGRG19); Figures 2 and 3 are replaced
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[57]  arXiv:1002.2312 (replaced) [ps, pdf, other]
Title: Rotation Measure Synthesis of Galactic Polarized Emission with the DRAO 26-m Telescope
Comments: Accepted for publication in The Astronomical Journal
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Galaxy Astrophysics (astro-ph.GA)
[58]  arXiv:1002.4021 (replaced) [ps, pdf, other]
Title: Feeding the AGN with backflows
Authors: V. Antonuccio-Delogu (INAF, Italy), J. Silk (Oxford)
Comments: 6 pages, 4 figures. Oral contributed talk to "Accretion and Ejection in AGN: A global view", Como, Italy, May 22-26, 2009. Corrected few typos
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
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New submissions for Thu, 25 Feb 10

[1]  arXiv:1002.4405 [pdf, other]
Title: Distinguishing standard reionization from dark matter models
Comments: 15 pages, 5 figures, submitted to Physical Review D
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The WMAP experiment has detected reionization at the $5.5 \sigma$ level and has reported a mean optical depth of $0.088 \pm 0.015$. A powerful probe of reionization is the large-angle $EE$ polarization power spectrum, which is now (since the first five years of data from WMAP) cosmic variance limited for $2\le l \le6$. Here we consider partial reionization caused by WIMP dark matter annihilation, and calculate the expected polarization power spectrum. We compare the dark matter models with a standard 2-step reionization theory, and examine whether the models may be distinguished using current, and future CMB observations. We consider dark matter annihilation at intermediate redshifts ($z<60$) due to halos, as well as annihilation at higher redshifts due to free particles. In order to study the effect of high redshift dark matter annihilation on CMB power spectra, it is essential to include the contribution of residual electrons (left over from recombination) to the ionization history. Dark matter halos at redshifts $z<60$ influence the low multipoles $l<20$ in the $EE$ power spectrum, while the annihilation of free particle dark matter at high redshifts $z>100$ mainly affects multipoles $l>10$.

[2]  arXiv:1002.4406 [ps, pdf, other]
Title: p3d: a general data-reduction tool for fiber-fed integral-field spectrographs
Comments: 18 pages, 15 figures, 3 tables, accepted for publication in A&amp;A
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The reduction of integral-field spectrograph (IFS) data is demanding work. Many repetitive operations are required in order to convert raw data into, typically a large number of, spectra. This effort can be markedly simplified through the use of a tool or pipeline, which is designed to complete many of the repetitive operations without human interaction. Here we present our semi-automatic data-reduction tool p3d that is designed to be used with fiber-fed IFSs. Important components of p3d include a novel algorithm for automatic finding and tracing of spectra on the detector, and two methods of optimal spectrum extraction in addition to standard aperture extraction. p3d also provides tools to combine several images, perform wavelength calibration and flat field data. p3d is at the moment configured for four IFSs. In order to evaluate its performance we have tested the different components of the tool. For these tests we used both simulated and observational data. We demonstrate that for three of the IFSs a correction for so-called cross-talk due to overlapping spectra on the detector is required. Without such a correction spectra will be inaccurate, in particular if there is a significant intensity gradient across the object. Our tests showed that p3d is able to produce accurate results. p3d is a highly general and freely available tool. It is easily extended to include improved algorithms, new visualization tools and support for additional instruments. The program code can be downloaded from the p3d-project web site this http URL

[3]  arXiv:1002.4412 [ps, pdf, other]
Title: A NLTE analysis of boron abundances in metal-poor stars
Comments: accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The non-local thermodynamic equilibrium (NLTE) line formation of neutral boron in the atmospheres of cool stars are investigated. Our results confirm that NLTE effects for the B I resonance lines, which are due to a combination of overionization and optical pumping effects, are most important for hot, metalpoor, and low-gravity stars; however, the amplitude of departures from LTE found by this work are smaller than that of previous studies. In addition, our calculation shows that the line formation of B I will get closer to LTE if the strength of collisions with neutral hydrogen increases, which is contrary to the result of previous studies. The NLTE line formation results are applied to the determination of boron abundances for a sample of 16 metal-poor stars with the method of spectrum synthesis of the B I 2497 A resonance lines using the archived HST/GHRS spectra. Beryllium and oxygen abundances are also determined for these stars. The abundances of the nine stars which are not depleted in Be or B show that, no matter the strength of collisions with neutral hydrogen may be, both Be and B increase with O quasi-linearly in the logarithmic plane, which confirms the conclusions that Be and B are mainly produced by primary process in the early Galaxy. The most noteworthy result of this work is that B increases with Fe or O at a very similar speed as, or a bit faster than Be does, which is in accord with the theoretical models. The B/Be ratios remain almost constant over the metallicity range investigated here. Our average B/Be ratio falls in the interval [13+-4, 17+-4], which is consistent with the predictions of spallation process. The contribution of B from the nu-process may be required if the 11B/10B isotopic ratios in metal-poor stars are the same as the meteoric value.

[4]  arXiv:1002.4413 [ps, pdf, other]
Title: AGN activity: Self-regulation from backflow
Authors: V. Antonuccio-Delogu (INAF), J. Silk (Oxford)
Comments: 13 pages, 11 figures. Accepted for publication by MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We study the internal circulation within the cocoon carved out by the relativistic jet emanating from an AGN within the ISM of its host galaxy. Firstly, we develop a model for the origin of the internal flow, noticing that a significant increase of large scale velocity circulation within the cocoon arises as significant gradients in the density and entropy are created near the hot spot (a consequence of Crocco's vorticity generation theorem). We find simple and accurate approximate solutions for the large scale flow,showing that a backflow towards the few inner parsec region develops. We solve the appropriate fluid dynamic equations, and we use these solutions to predict the mass inflow rates towards the central regions. We then perform a series of 2D simulations of the propagation of jets using FLASH 2.5, in order to validate the predictions of our model. The backflows which arise supply the central AGN region with very low angular momentum gas, at average rates of the order of $0.1-0.8 \rm{M}_{\odot} \rm{yr.}^{-1}$, the exact value seen to be strongly dependent on the central ISM density (for fixed input jet power). The time scales of these inflows are apparently weakly dependent on the jet/ISM parameters, and are of the order of $3-5\times 10^{7} \rm{yrs}$. We then argue that these backflows could (at least partially) feed the AGN, and provide a self-regulatory mechanism of AGN activity, that is not directly controlled by, but instead controls, the star formation rate within the central circumnuclear disk.

[5]  arXiv:1002.4414 [ps, pdf, other]
Title: The mass assembly of galaxy groups and the evolution of the magnitude gap
Comments: 16 pages, 11 figures, 2 tables. Accepted for publication in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We investigate the assembly of groups and clusters of galaxies using the Millennium dark matter simulation and the associated gas simulations and semi-analytic catalogues of galaxies. In particular, in order to find an observable quantity that could be used to identify early-formed groups, we study the development of the difference in magnitude between their brightest galaxies to assess the use of magnitude gaps as possible indicators. We select galaxy groups and clusters at redshift z=1 with dark matter halo mass M(R200) > 1E13/h Msun, and trace their properties until the present time (z=0). We consider only the systems with X-ray luminosity L_X> 0.25E42/h^2 erg/s at z=0. While it is true that a large magnitude gap between the two brightest galaxies of a particular group often indicates that a large fraction of its mass was assembled at an early epoch, it is not a necessary condition. More than 90% of fossil groups defined on the basis of their magnitude gaps (at any epoch between 0<z<1) cease to be fossils within 4 Gyr, mostly because other massive galaxies are assembled within their cores, even though most of the mass in their haloes might have been assembled at early times. We show that, compared to the conventional definition of fossil galaxy groups based on the magnitude gap Delta m(12)> 2 (in the R-band, within 0.5R200 of the centre of the group), an alternative criterion Delta m(14)>2.5 (within the same radius) finds 50% more early-formed systems, and those that on average retain their fossil phase longer. However, the conventional criterion performs marginally better at finding early-formed groups at the high-mass end of groups. Nevertheless, both criteria fail to identify a majority of the early-formed systems.

[6]  arXiv:1002.4415 [pdf, other]
Title: Constraints on Cosmological Dark Matter Annihilation from the Fermi-LAT Isotropic Diffuse Gamma-Ray Measurement
Comments: 29 pages, 7 figures, to be published in JCAP. Corresponding authors: Jan Conrad, Michael Gustafsson, Alexander Sellerholm, Gabrijela Zaharijas
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

The first published Fermi large area telescope (Fermi-LAT) measurement of the isotropic diffuse gamma-ray emission is in good agreement with a single power law, and is not showing any signature of a dominant contribution from dark matter sources in the energy range from 20 to 100 GeV. We use the absolute size and spectral shape of this measured flux to derive cross section limits on three types of generic dark matter candidates: annihilating into quarks, charged leptons and monochromatic photons. Predicted gamma-ray fluxes from annihilating dark matter are strongly affected by the underlying distribution of dark matter, and by using different available results of matter structure formation we assess these uncertainties. We also quantify how the dark matter constraints depend on the assumed conventional backgrounds and on the Universe's transparency to high-energy gamma-rays. In reasonable background and dark matter structure scenarios (but not in all scenarios we consider) it is possible to exclude models proposed to explain the excess of electrons and positrons measured by the Fermi-LAT and PAMELA experiments. Derived limits also start to probe cross sections expected from thermally produced relics (e.g. in minimal supersymmetry models) annihilating predominantly into quarks. For the monochromatic gamma-ray signature, the current measurement constrains only dark matter scenarios with very strong signals.

[7]  arXiv:1002.4418 [ps, pdf, other]
Title: Galaxy Pairs in the Sloan Digital Sky Survey - II: The Effect of Environment on Interactions
Comments: Submitted to MNRAS, 16 pages
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We use a sample of close galaxy pairs selected from the SDSS DR4 to investigate in what environments galaxy mergers occur and how the results of these mergers depend on differences in local galaxy density. Lower density environments have fractionally more galaxy pairs with small projected separations (r_p) and relative velocities (Delta V), but even high density environments contain significant populations of pairs with parameters that should be conducive to interactions. The connection between environment and Delta V also implies that the velocity selection of a pairs sample affects (biases) the environment from which the pairs are selected. Metrics of asymmetry and colour are used to identify merger activity and triggered star formation. The location of star formation is inferred by distinguishing bulge and disk colours and calculating bulge fractions from the SDSS images. Considering only pairs with Delta V < 200 km/s, we show that the asymmetry of galaxies with a close companion increases at all local densities at r_p < 30 kpc. However, of these closely separated pairs, galaxies in the lowest density environments exhibit the most significant trends towards increased star formation rates and bluer bulge colours. We interpret these results as evidence that whilst interactions occur at all densities, triggered star formation is seen only in low-to-intermediate density environments. We argue that this is likely due to the typically higher gas fractions of galaxies in low density environments. Finally, by cross-correlating our sample of galaxy pairs with a cluster catalogue, we find evidence for galaxy-galaxy interactions only at the cluster periphery.

[8]  arXiv:1002.4421 [ps, pdf, other]
Title: A Catalog of MIPSGAL Disk and Ring Sources
Authors: D.R. Mizuno (1), K. E. Kraemer (2), N. Flagey (3), N. Billot (4), S. Shenoy (5), R. Paladini (3), E. Ryan (6), A. Noriega-Crespo (3), S. J. Carey (3). ((1) Institute for Scientific Research, (2) Air Force Research Laboratory, (3) Spitzer Science Center, (4) NASA Herschel Science Center, (5) Ames Research Center, (6) University of Minnesota)
Subjects: Galaxy Astrophysics (astro-ph.GA)

We present a catalog of 416 extended, resolved, disk- and ring-like objects as detected in the MIPSGAL 24 micron survey of the Galactic plane. This catalog is the result of a search in the MIPSGAL image data for generally circularly symmetric, extended "bubbles" without prior knowledge or expectation of their physical nature. Most of the objects have no extended counterpart at 8 or 70 micron, with less than 20% detections at each wavelength. For the 54 objects with central point sources, the sources are nearly always seen in all IRAC bands. About 70 objects (16%) have been previously identified, with another 35 listed as IRAS sources. Among the identified objects, those with central sources are mostly listed as emission-line stars, but with other source types including supernova remnants, luminous blue variables, and planetary nebulae. The 57 identified objects (of 362) without central sources are nearly all PNe (~90%).which suggests that a large fraction of the 300+ unidentified objects in this category are also PNe. These identifications suggest that this is primarily a catalog of evolved stars. Also included in the catalog are two filamentary objects that are almost certainly SNRs, and ten unusual compact extended objects discovered in the search. Two of these show remarkable spiral structure at both 8 and 24 micron. These are likely background galaxies previously hidden by the intervening Galactic plane.

[9]  arXiv:1002.4434 [pdf, other]
Title: Magnetic Field Effects near the launching region of Astrophysical Jets
Comments: 9 pages, 3 figures, invited paper for the Procs. of the Conference on High Energy Phenomena in Relativistic Outflows II, Buenos Aires, October 2009. Submitted to International Journal of Modern Physics D
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

One of the fundamental properties of astrophysical magnetic fields is their ability to change topology through reconnection and in doing so, to release magnetic energy, sometimes violently. In this work, we review recent results on the role of magnetic reconnection and associated heating and particle acceleration in jet/accretion disk systems, namely young stellar objects (YSOs), microquasars, and active galactic nuclei (AGNs).

[10]  arXiv:1002.4447 [ps, pdf, other]
Title: Interior structure models of GJ 436b
Comments: submitted to A&amp;A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

GJ436b is the first extrasolar planet discovered that resembles Neptune in mass and radius, two more are known (HAT-P-11b and Kepler-4b), and many more are expected to be found in the upcoming years. The particularly interesting property of Neptune-sized planets is that their mass Mp and radius Rp are close to theoretical M-R relations of water planets. Given Mp, Rp, and equilibrium temperature however, various internal compositions are possible. A broad set of interior structure models is presented here that illustrates the dependence of internal composition and possible phases of water in presumably water-rich planets such as GJ436b on the uncertainty in atmospheric temperature profile and mean density. We model the interior by assuming either three layers (hydrogen-helium envelope, water layer, rock core) or two layers (H/He/H2O envelope, rocky core). For water we use the equation of state H2O-REOS based on FT-DFT-MD. Some admixture of H/He appears mandatory for explaining the measured radius. In case of the warmest models considered, the H/He mass fraction can reduce to 0.1%, yet extending over 0.7 Rearth. If water occurs, it will be essentially in the plasma phase or in the superionic phase, but not in an ice phase. Metal-free envelope models have 0.02<k2<0.2, and the core mass cannot be determined from a measurement of the tidal Love number k2. In contrast, models with 0.3<k2<0.82 require large outer envelope metallicities Z1<0.89. The uncertainty in core mass decreases to 0.4 Mp, if k2>0.3, and further to 0.2 Mp, if k2>0.5, and core mass and Z1 become a sensitive function of k2.

[11]  arXiv:1002.4469 [ps, pdf, other]
Title: Can cold quark matter be solid?
Authors: Renxin Xu (PKU)
Comments: Submitted to Proceedings of IWARA2009
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

The state of cold quark matter really challenges both astrophysicists and particle physicists, even many-body physicists. It is conventionally suggested that BCS-like color superconductivity occurs in cold quark matter; however, other scenarios with a ground state rather than of Fermi gas could still be possible. It is addressed that quarks are dressed and clustering in cold quark matter at realistic baryon densities of compact stars, since a weakly coupling treatment of the interaction between constituent quarks would not be reliable. Cold quark matter is conjectured to be in a solid state if thermal kinematic energy is much lower than the interaction energy of quark clusters, and such a state could be relevant to different manifestations of pulsar-like compact stars.

[12]  arXiv:1002.4472 [pdf, other]
Title: The Wide Field Spectrograph (WiFeS): Performance and Data Reduction
Comments: Accepted for publication in Astrophysics &amp; Space Science, 15pp, 11 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

This paper describes the on-telescope performance of the Wide Field Spectrograph (WiFeS). The design characteristics of this instrument, at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) and mounted on the ANU 2.3m telescope at the Siding Spring Observatory has been already described in an earlier paper (Dopita et al. 2007). Here we describe the throughput, resolution and stability of the instrument, and describe some minor issues which have been encountered. We also give a description of the data reduction pipeline, and show some preliminary results.

[13]  arXiv:1002.4474 [ps, pdf, other]
Title: Thick gas disks in faint dwarf galaxies
Comments: 5 pages, 4 figures. Accepted for publication in MNRAS Letters
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We determine the intrinsic axial ratio distribution of the 'gas' disks of extremely faint M_B < -14.5 dwarf irregular galaxies. We start with the measured (beam corrected) distribution of apparent axial ratios in the HI 21cm images of dwarf irregular galaxies observed as part of the Faint Irregular Galaxy GMRT Survey (FIGGS). Assuming that the disks can be approximated as oblate spheroids, the intrinsic axial ratio distribution can be obtained from the observed apparent axial ratio distribution. We use a variety of methods to do this, and our final results are based on using Lucy's deconvolution algorithm. This method is constrained to produce physically plausible distributions, and also has the added advantage of allowing for observational errors to be accounted for. While one might a priori expect that gas disks would be thin (because collisions between gas clouds would cause them to quickly settle down to a thin disk), we find that the HI disks of faint dwarf irregulars are quite thick, with mean axial ratio <q> ~ 0.6. While this is substantially larger than the typical value of ~ 0.2 for the 'stellar' disks of large spiral galaxies, it is consistent with the much larger ratio of velocity dispersion to rotational velocity (sigma/v_c) in dwarf galaxy HI disks as compared to that in spiral galaxies. Our findings have implications for studies of the mass distribution in and the Tully - Fisher relation for faint dwarf irregular galaxies, where it is often assumed that the gas is in a thin disk.

[14]  arXiv:1002.4475 [ps, pdf, other]
Title: Chemodynamical simulations with variable IMF
Authors: Chiaki Kobayashi
Comments: 4 pages, 3 figures, to appear in "Hunting for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista and C.C. Popescu, AIP Conf. Ser., in press
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

Using self-consistent chemodynamical simulations including star formation, supernova feedback, and chemical enrichment, I show the dependence of cosmic star formation and chemical enrichment histories on the initial mass function (IMF). The effects of Pop-III IMF can be only seen in the elemental abundance ratios at z>4 or [Fe/H]<-2. The preferable IMF has a flatter slope in the case of high star formation rate (SFR) and smaller upper-mass (~20Msun) in the case of low SFR, which is consistent with the observed elemental abundances of dwarf spheroidal galaxies. However, the [alpha/Fe] problem of elliptical galaxies may require other solutions.

[15]  arXiv:1002.4477 [ps, pdf, other]
Title: HD 209621: Abundances of neutron-capture elements
Authors: Aruna Goswami (1), Wako Aoki (2) ((1) Indian Institute of Astrophysics, Bangalore, (2) National Astronomical Observatory, Mitaka, Tokyo)
Comments: 16 pages,8 figures. Accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

High resolution spectra obtained from the Subaru Telescope High Dispersion Spectrograph have been used to update the stellar atmospheric parameters and metallicity of the star HD 209621. We have derived a metallicity of [Fe/H] = -1.93 for this star, and have found a large enhancement of carbon and of heavy elements, with respect to iron. Updates on the elemental abundances of four s-process elements (Y, Ce, Pr, Nd) along with the first estimates of abundances for a number of other heavy elements (Sr, Zr, Ba, La, Sm, Eu, Er, Pb) are reported. The stellar atmospheric parameters, the effective temperature, Teff, and the surface gravity, log g (4500 K, 2.0), are determined from LTE analysis using model atmospheres. Estimated [Ba/Eu] = +0.35, places the star in the group of CEMP-(r+s) stars; however, the s-elements abundance pattern seen in HD 209621 is characteristic of CH stars; notably, the 2nd-peak s-process elements are more enhanced than the first peak s-process elements. HD 209621 is also found to show a large enhancement of the 3rd-peak s-process element lead (Pb) with [Pb/Fe] = +1.88. The relative contributions of the two neutron-capture processes, r- and s- to the observed abundances are examined using a parametric model based analysis, that hints that the neutron-capture elements in HD 209621 primarily originate in s-process.

[16]  arXiv:1002.4479 [ps, pdf, other]
Title: On the coldness of the local Hubble flow: the role of baryons
Authors: Sébastien Peirani (IAP)
Comments: Submitted to MNRAS, 11 pages, 7 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

(Abridged) Our aim is to investigate whether the presence of baryons can have any significant influence on the properties of the local Hubble flow which has proved to be "cold". We use two cosmological zoom simulations in the standard LCDM cosmology with the same set of initial conditions to study the formation of a local group-like system within a sphere of ~7 Mpc/h. The first one is a pure dark matter simulation (runDM) while a complete treatment of the physics of baryons is introduced in the second one (runB). We found that galaxies identified in runB and their corresponding dark matter haloes in runDM have very similar spatial distributions and dynamical properties on large scales. Then, when analyzing the velocity field and the deviation from a pure Hubble flow in both simulations, namely when computing the dispersion of peculiar velocities of galaxies ?*(R) and those of their corresponding dark matter haloes in runDM, we found no particular differences for distances R=1 to 8 Mpc from the local group mass center. The results indicate that the "true" ?*(R) values can be estimated from the pure dark matter simulation with a mean error of 3 km/s when dark matter haloes are selected with maximum circular velocities of Vc?30 km/s, corresponding to a population of dark matter haloes in runB that host galaxies. By investigating the properties of the Hubble flow at distances R~0.7 to 3 Mpc, we also found that the estimation of the total mass enclosed at the radius of the zero-velocity surface R0, using the spherical infall model adapted to LCDM, can be underestimated by at least 50%.

[17]  arXiv:1002.4480 [ps, pdf, other]
Title: X-ray views of neutron star low-mass X-ray binaries
Authors: Sudip Bhattacharyya (TIFR, India)
Comments: 21 pages, 13 figures, An Invited Review, published in Current Science
Journal-ref: Current Science.97:804-820,2009
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

A neutron star low-mass X-ray binary is a binary stellar system with a neutron star and a low-mass companion star rotating around each other. In this system the neutron star accretes mass from the companion, and as this matter falls into the deep potential well of the neutron star, the gravitational potential energy is released primarily in the X-ray wavelengths. Such a source was first discovered in X-rays in 1962, and this discovery formally gave birth to the "X-ray astronomy". In the subsequent decades, our knowledge of these sources has increased enormously by the observations with several X-ray space missions. Here we give a brief overview of our current understanding of the X-ray observational aspects of these systems.

[18]  arXiv:1002.4497 [ps, pdf, other]
Title: On the maximum and minimum mass of protoneutron stars in the Brueckner theory
Authors: G.F. Burgio, H.-J. Schulze (INFN Catania, Italy)
Comments: 8 pages, 7 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We study the structure of protoneutron stars within the finite-temperature Brueckner-Bethe-Goldstone theoretical approach, paying particular attention to the joining with a low-density nuclear equation of state (EOS). We find a slight sensitivity of the minimum value of the protoneutron star mass on the low-density EOS, whereas the maximum mass is hardly affected.

[19]  arXiv:1002.4503 [ps, pdf, other]
Title: A statistical method to determine open cluster metallicities
Comments: 14 pages, 6 figures, accepted for publication in Astronomy &amp; Astrophysics
Subjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

The study of open cluster metallicities helps to understand the local stellar formation and evolution throughout the Milky Way. Its metallicity gradient is an important tracer for the Galactic formation in a global sense. Because open clusters can be treated in a statistical way, the error of the cluster mean is minimized. Our final goal is a semi-automatic statistical robust method to estimate the metallicity of a statistically significant number of open clusters based on Johnson BV data of their members, an algorithm that can easily be extended to other photometric systems for a systematic investigation. This method incorporates evolutionary grids for different metallicities and a calibration of the effective temperature and luminosity. With cluster parameters (age, reddening and distance) it is possible to estimate the metallicity from a statistical point of view. The iterative process includes an intrinsic consistency check of the starting input parameters and allows us to modify them. We extensively tested the method with published data for the Hyades and selected sixteen open clusters within 1000pc around the Sun with available and reliable Johnson BV measurements. In addition, Berkeley 29, with a distance of about 15kpc was chosen. For several targets we are able to compare our result with published ones which yielded a very good coincidence (including Berkeley 29).

[20]  arXiv:1002.4514 [ps, pdf, other]
Title: Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
Comments: Accepted for publication in A&amp;A as a four-page Letter with five pages of online material
Subjects: Galaxy Astrophysics (astro-ph.GA)

Precise abundance ratios are determined for 94 dwarf stars with 5200 < Teff < 6300 K, -1.6 < [Fe/H] < -0.4, and distances D < 335 pc. Most of them have halo kinematics, but 16 thick-disk stars are included. Equivalent widths of atomic lines are measured from VLT/UVES and NOT/FIES spectra with resolutions R = 55000 and R = 40000, respectively. An LTE abundance analysis based on MARCS models is applied to derive precise differential abundance ratios of Na, Mg, Si, Ca, Ti, Cr, and Ni with respect to Fe.
The halo stars fall into two populations, clearly separated in [alpha/Fe], where alpha refers to the average abundance of Mg, Si, Ca, and Ti. Differences in [Na/Fe] and [Ni/Fe] are also present with a remarkably clear correlation between these two abundance ratios. The `high-alpha' stars may be ancient disk or bulge stars `heated' to halo kinematics by merging satellite galaxies or they could have formed as the first stars during the collapse of a proto-Galactic gas cloud. The kinematics of the `low-alpha' stars suggest that they have been accreted from dwarf galaxies, and that some of them may originate from the omega Cen progenitor galaxy.

[21]  arXiv:1002.4521 [ps, pdf, other]
Title: Large-scale distributions of mid- and far-infrared emission from the center to the halo of M82 revealed with AKARI
Comments: 12 pages, 8 figures, accepted for publication in A&amp;A
Subjects: Galaxy Astrophysics (astro-ph.GA)

The edge-on starburst galaxy M82 exhibits complicated distributions of gaseous materials in its halo, which include ionized superwinds driven by nuclear starbursts, neutral materials entrained by the superwinds, and large-scale neutral streamers probably caused by a past tidal interaction with M81. We investigate detailed distributions of dust grains and polycyclic aromatic hydrocarbons (PAHs) around M82 to understand their interplay with the gaseous components. We performed mid- (MIR) and far-infrared (FIR) observations of M82 with the Infrared Camera and Far-Infrared Surveyor on board AKARI. We obtain new MIR and FIR images of M82, which reveal both faint extended emission in the halo and very bright emission in the center with signal dynamic ranges as large as five and three orders of magnitude for the MIR and FIR, respectively. We detect MIR and FIR emission in the regions far away from the disk of the galaxy, reflecting the presence of dust and PAHs in the halo of M82. We find that the dust and PAHs are contained in both ionized and neutral gas components, implying that they have been expelled into the halo of M82 by both starbursts and galaxy interaction. In particular, we obtain a tight correlation between the PAH and H$\alpha$ emission, which provides evidence that the PAHs are well mixed in the ionized superwind gas and outflowing from the disk.

[22]  arXiv:1002.4523 [ps, pdf, other]
Title: Have Cherenkov telescopes detected a new light boson?
Comments: 3 pages, 1 figure, Proceeding of the "Eleventh International Workshop on Topics in Astroparticle and Underground Physics" (TAUP), Roma, Italy, 1 - 5 July 2009 (to be published in the Proceedings)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Recent observations by H.E.S.S. and MAGIC strongly suggest that the Universe is more transparent to very-high-energy gamma rays than previously thought. We show that this fact can be reconciled with standard blazar emission models provided that photon oscillations into a very light Axion-Like Particle occur in extragalactic magnetic fields. A quantitative estimate of this effect indeed explains the observed data and in particular the spectrum of blazar 3C279.

[23]  arXiv:1002.4524 [ps, pdf, other]
Title: The compact radio structure of the high-redshift blazar J1430+4204 before and after a major outburst
Comments: Proceedings of the 5th Workshop of Young Researchers in Astronomy and Astrophysics, Budapest, 2009; to be published in J. Phys.: Conf. Series (JPCS); 4 pages, 3 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The high-redshift (z=4.72) blazar J1430+4204 produced an exceptional radio outburst in 2006. We analyzed 15-GHz radio interferometric images obtained with the Very Long Baseline Array (VLBA) before and after the outburst, to search for possible structural changes on milli-arcsecond angular scales and to determine physical parameters of the source.

[24]  arXiv:1002.4528 [ps, pdf, other]
Title: Varying Constants: Constraints from Seasonal Variations
Comments: 4 pages, 1 figure. Contribution to the proceedings of the Joint Discussion 9, XXVIIth IAU, General Assembly, Rio de Janeiro :"Are the fundamental constants varying with spacetime?"
Journal-ref: Memorie della Societa Astronomica Italiana, 80, 640-643, (2009)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Atomic Physics (physics.atom-ph)

We analyse the constraints obtained from new atomic clock data on the possible time variation of the fine structure `constant' and the electron-proton mass ratio and show how they are strengthened when the seasonal variation of Sun's gravitational field at the Earth's surface is taken into account.

[25]  arXiv:1002.4539 [ps, pdf, other]
Title: The evolution of galaxy cluster X-ray scaling relations
Authors: C. J. Short (1), P. A. Thomas (1), O. E. Young (1), F. R. Pearce (2), A. Jenkins (3), O. Muanwong (4) ((1)University of Sussex, UK, (2)University of Nottingham, UK, (3)University of Durham, UK, (4)Khon Kaen University, Thailand)
Comments: 21 pages, 13 figures, 3 tables. Submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We use numerical simulations to investigate, for the first time, the joint effect of feedback from supernovae (SNe) and active galactic nuclei (AGN) on the evolution of galaxy cluster X-ray scaling relations. Our simulations are drawn from the Millennium Gas Project and are some of the largest hydrodynamical N-body simulations ever carried out. Feedback is implemented using a hybrid scheme, where the energy input into intracluster gas by SNe and AGN is taken from a semi-analytic model of galaxy formation. This ensures that the source of feedback is a population of galaxies that closely resembles that found in the real universe. We show that our feedback model is capable of reproducing observed local X-ray scaling laws, at least for non-cool core clusters, but that almost identical results can be obtained with a simplistic preheating model. However, we demonstrate that the two models predict opposing evolutionary behaviour. We have examined whether the evolution predicted by our feedback model is compatible with observations of high-redshift clusters. Broadly speaking, we find that the data seems to favour the feedback model for z<0.5, and the preheating model at higher redshift. However, a statistically meaningful comparison with observations is impossible, because the large samples of high-redshift clusters currently available are prone to strong selection biases. As the observational picture becomes clearer in the near future, it should be possible to place tight constraints on the evolution of the scaling laws, providing us with an invaluable probe of the physical processes operating in galaxy clusters.

[26]  arXiv:1002.4555 [pdf]
Title: On the chains of star complexes and superclouds in spiral arms
Authors: Yuri N.Efremov
Comments: 20 pages, 12 figures, accepted for publication in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The relation is studied between occurrence of a regular chain of star complexes and superclouds in a spiral arm, and other properties of the latter. A regular string of star complexes is located in the north-western arm of M31; they have about the same size 0.6 kpc with spacing of 1.1 kpc. Within the same arm segment the regular magnetic field with the wavelength of 2.3 kpc was found by Beck et al. (1989). We noted that this wavelength is twice as large as the spacing between complexes and suggested that they were formed in result of magneto-gravitational instability developed along the arm. In this NW arm, star complexes are located inside the gas-dust lane, whilst in the south-western arm of M31 the gas-dust lane is upstream of the bright and uniform stellar arm. Earlier, evidence for the age gradient has been found in the SW arm. All these are signatures of a spiral shock, which may be associated with unusually large (for M31) pitch-angle of this SW arm segment. Such a shock may prevent the formation of the regular magnetic field, which might explain the absence of star complexes there. Anti-correlation between shock wave signatures and presence of star complexes is observed in spiral arms of a few other galaxies. Regular chains of star complexes and superclouds in spiral arms are rare, which may imply that a rather specific mechanism is involved in their formation, and the most probable one is the Parker-Jeans instability. The spiral pattern of our Galaxy is briefly discussed; it may be of M101 type in the outer parts. The regular bi-modal spacing of HI superclouds is found in Carina and Cygnus (Outer) arms, which may be an indirect evidence for the regular magnetic field along these arms.

[27]  arXiv:1002.4562 [ps, pdf, other]
Title: 3D simulations of wind-jet interaction in massive X-ray binaries
Comments: Accepted for publication in A&amp;A Letters
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

High-mass microquasars may produce jets that will strongly interact with surrounding stellar winds on binary system spatial scales. We study the dynamics of the collision between a mildly relativistic hydrodynamical jet of supersonic nature and the wind of an OB star. We performed numerical 3D simulations of jets that cross the stellar wind with the code Ratpenat. The jet head generates a strong shock in the wind, and strong recollimation shocks occur due to the initial overpressure of the jet with its environment. These shocks can accelerate particles up to TeV energies and produce gamma-rays. The recollimation shock also strengthens jet asymmetric Kelvin-Helmholtz instabilities produced in the wind/jet contact discontinuity. This can lead to jet disruption even for jet powers of several times $10^{36}$ erg s$^{-1}$. High-mass microquasar jets likely suffer a strong recollimation shock that can be a site of particle acceleration up to very high energies, but also eventually lead to the disruption of the jet.

[28]  arXiv:1002.4565 [ps, pdf, other]
Title: The Masses of the Milky Way and Andromeda galaxies
Authors: L.L. Watkins (1), N.W. Evans (1), J. An (2) ((1)IoA, Cambridge, (2)NAO, Beijing, China)
Comments: 15 pages, submitted to MNRAS
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present a family of robust tracer mass estimators to compute the enclosed mass of galaxy haloes from samples of discrete positional and kinematical data of tracers, such as halo stars, globular clusters and dwarf satellites. The data may be projected positions, distances, line of sight velocities or proper motions. Forms of the estimator tailored for the Milky Way galaxy and for M31 are given. Monte Carlo simulations are used to quantify the uncertainty as a function of sample size. For the Milky Way, the satellite sample consists of 26 galaxies with line-of-sight velocities. We find that the mass of the Milky Way within 300 kpc is ~ 0.9 x 10^12 solar masses assuming velocity isotropy. However, the mass estimate is sensitive to the anisotropy and could plausibly lie between 0.7 - 3.4 x 10^12 solar masses. Incorporating the proper motions of 6 Milky Way satellites into the dataset, we find ~ 1.4 x 10^12 solar masses. The range here if plausible anisotropies are used is still broader, from 1.2 - 2.7 x 10^12 solar masses. For M31, there are 23 satellite galaxies with measured line-of-sight velocities, but only M33 and IC 10 have proper motions. We use the line of sight velocities and distances of the satellite galaxies to estimate the mass of M31 within 300 kpc as ~ 1.4 x 10^12 solar masses assuming isotropy. There is only a modest dependence on anisotropy, with the mass varying between 1.3 -1.6 x 10^12 solar masses. Given the uncertainties, we conclude that the satellite data by themselves yield no reliable insights into which of the two galaxies is actually the more massive.

[29]  arXiv:1002.4578 [pdf, other]
Title: Spatial distribution of interstellar dust in the Sun vicinity, comparison with neutral sodium-bearing gas
Comments: 13 pages, 12 figures
Subjects: Galaxy Astrophysics (astro-ph.GA)

3D tomography of the interstellar dust and gas may be useful in many respects, from the physical and chemical evolution of the ISM itself to foreground decontamination of the CMB, or various studies of the environments of specific objects. Our goal here is to bring more precise information on the distance to nearby interstellar dust and gas clouds within 250 pc.
We apply the best available calibration methods to a carefully screened set of stellar Stromgren photometry data for targets possessing a Hipparcos parallax and spectral type classification. We combine the derived interstellar extinctions and the parallax distances for about 6,000 stars to build a 3D tomography of the local dust. We use an inversion method based on a regularized Bayesian approach and a least squares criterion. We obtain 3D maps of the opacity and the distance to the main dust-bearing clouds with 250 pc.
We calculate the integrated extinction between the Sun and the cube boundary and compare with the total galactic extinction derived from infrared 2D maps. We also compare the opacity distribution with the 3D distribution of interstellar neutral sodium resulting from the inversion of sodium columns towards about 1,700 target stars. Our maps show a larger high latitude dust opacity in the North compared to the South, while gas maps do not show the same asymmetry, suggesting a polar asymmetry of the dust to gas ratio at small distances.

[30]  arXiv:1002.4586 [pdf, other]
Title: Mathematical properties of the SimpleX algorithm
Comments: 18 pages, 17 figures, accepted for publication in A&amp;A
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Extragalactic Astrophysics (astro-ph.CO); Computational Physics (physics.comp-ph)

Context. Analytical and numerical analysis of the SimpleX radiative transfer algorithm, which features transport on a Delaunay triangulation. Aims. Verify whether the SimpleX radiative transfer algorithm conforms to mathematical expectations, to develop error analysis and present improvements upon earlier versions of the code. Methods. Voronoi-Delaunay tessellation, classical Markov theory. Results. Quantitative description of the error properties of the SimpleX method. Numerical validation of the method and verification of the analytical results. Improvements in accuracy and speed of the method. Conclusions. It is possible to transport particles such as photons in a physically correct manner with the SimpleX algorithm. This requires the use of weighting schemes or the modification of the point process underlying the transport grid. We have explored and applied several possibilities.

[31]  arXiv:1002.4588 [ps, pdf, other]
Title: Comment on Calculation of Positron Flux from Galactic Dark Matter
Comments: 18 pages, 6 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Energetic positrons produced in annihilation or decay of dark matter particles in the Milky Way can serve as an important indirect signature of dark matter. Computing the positron flux expected in a given dark matter model involves solving transport equations, which account for interaction of positrons with matter and galactic magnetic fields. Existing calculations solve the equations inside the diffusion zone, where galactic magnetic fields confine positrons, and assume vanishing positron density on the boundaries of this zone. However, in many models, a substantial fraction of the dark matter halo lies outside the diffusion zone. Positrons produced there can then enter the diffusion zone and get trapped, potentially reaching the Earth and increasing the expected flux. We calculate this enhancement for a variety of models. We also evaluate the expected enhancement of the flux of energetic photons produced by the inverse Compton scattering of the extra positrons on starlight and cosmic microwave background. We find maximal flux enhancements of order 20% in both cases.

[32]  arXiv:1002.4605 [pdf, other]
Title: Calculating the Hubble diagram by perturbation theory
Authors: Gyula Bene
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The effect of density fluctuations upon light propagation is calculated perturbatively in a matter dominated irrotational universe. The starting point is the perturbed metric (second order in the perturbation strength), while the output is the Hubble diagram. Density fluctuations cause this diagram to broaden to a strip. Moreover, the shift of the diagram mimics accelerated expansion.

[33]  arXiv:1002.4608 [ps, pdf, other]
Title: WASP-12b as a prolate, inflated and disrupting planet from tidal dissipation
Authors: Shu-lin Li (1,2), Neil Miller (3), Douglas N. C. Lin (1,3), Jonathan J. Fortney (3) ((1)Kavli Institude for Astronomy and Astrophysics, Peking University Beijing, (2)Department of Astronomy, Peking University, Beijing, (3)UCSC)
Comments: Accepted to Nature, 14 pages, 1 figure
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The class of exotic Jupiter-mass planets that orbit very close to their parent stars were not explicitly expected before their discovery. The recently found transiting planet WASP-12b has a mass Mp = 1.4(+/-0.1) Jupiter masses (MJ), a mean orbital distance of only 3.1 stellar radii (meaning it is subject to intense tidal forces), and a period of 1.1 days. Its radius 1.79(+/- 0.09) RJ is unexpectedly large and its orbital eccentricity 0.049(+/-0:015) is even more surprising as such close orbits are in general quickly circularized. Here we report an analysis of its properties, which reveals that the planet is losing mass to its host star at a rate ~ 10^-7 MJ yr^-1. The planets surface is distorted by the stars gravity and the light curve produced by its prolate shape will differ by about ten per cent from that of a spherical planet. We conclude that dissipation of the stars tidal perturbation in the planets convective envelope provides the energy source for its large volume. We predict up to 10mJy CO band-head (2.292 micron) emission from a tenuous disk around the host star, made up of tidally stripped planetary gas. It may also contain a detectable resonant super-Earth, as a hypothetical perturber that continually stirs up WASP-12b's eccentricity.

[34]  arXiv:1002.4610 [pdf, other]
Title: Accelerating expansion in the swisscheese model
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

A version of the swisscheese model is investigated. Nonoverlapping spheres are cut from a flat Friedmann-Robertson-Walker (FRW) universe. The mass they contained before is compressed within each sphere to a smaller sphere with homogeneous density distribution. Hence the inner spheres form sections of some closed FRW model. Between the outer and inner spheres there is a vacuum, where, due to spherical symmetry, the Schwarzschield metric describes the gravitational field. Within the inner spheres the closed FRW metric is valid, while outside the cut spheres the flat FRW metric is relevant. The metric and its first derivatives are continuous across the bordering surfaces of the different regions. We discuss this model in detail, and show that such a model universe can have a realistic density distribution on large scales, and exhibits accelerating expansion for a limited period of time. Especially, we determine the Hubble diagram and discuss its properties.

[35]  arXiv:1002.4611 [ps, pdf, other]
Title: Barred Galaxies in the Coma Cluster
Authors: Irina Marinova (UT Austin), Shardha Jogee (UT Austin), Neil Trentham (Cambridge), Henry C. Ferguson (STScI), Tim Weinzirl (UT Austin), Marc Balcells (Tenerife), David Carter (Liverpool), Mark den Brok (Kapteyn), Peter Erwin (MPIA), Alister W. Graham (Swinburne), Paul Goudfrooij (STScI), Rafael Guzman (Florida), Derek Hammer (Johns Hopkins), Carlos Hoyos (Florida), Reynier F. Peletier (Kapteyn), Avon P. Huxor (Bristol), Erik Peng (Peking University), Gijs Verdoes Kleijn (Kapteyn)
Comments: Proceedings of the Bash symposium, to appear in the Astronomical Society of the Pacific Conference Series, eds. L. Stanford, L. Hao, Y. Mao, J. Green
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We use ACS data from the HST Treasury survey of the Coma cluster (z~0.02) to study the properties of barred galaxies in the Coma core, the densest environment in the nearby Universe. This study provides a complementary data point for studies of barred galaxies as a function of redshift and environment.
From ~470 cluster members brighter than M_I = -11 mag, we select a sample of 46 disk galaxies (S0--Im) based on visual classification. The sample is dominated by S0s for which we find an optical bar fraction of 47+/-11% through ellipse fitting and visual inspection. Among the bars in the core of the Coma cluster, we do not find any very large (a_bar > 2 kpc) bars. Comparison to other studies reveals that while the optical bar fraction for S0s shows only a modest variation across low-to-intermediate density environments (field to intermediate-density clusters), it can be higher by up to a factor of ~2 in the very high-density environment of the rich Coma cluster core.

[36]  arXiv:1002.4612 [ps, pdf, other]
Title: Ionized gas, molecules, and dust in Sh2-132
Comments: 11 figures and 5 tables, accepted in MNRAS
Subjects: Galaxy Astrophysics (astro-ph.GA)

We analyze the various interstellar components of the HII region Sh2-132. The main stellar source is the double binary system that includes the Wolf-Rayet star WR153ab. We use radio continuum images at 408 and 1420 MHz, and HI 21cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO(1-0) line at 115 GHz from the Five College Radio Astronomy Observatory, and available mid and far IR observations obtained with the MSX and IRAS satellites, respectively.
Sh2-132 is composed of two shells showing radio continuum counterparts at both frequencies. The emission is thermal in nature. The estimated rms electron density and ionized mass of the nebula are n_e = 20 cm^{-3} and M_HII = 1500 Mo. The distribution of the CO emission shows molecular gas bordering the ionized nebula and interacting with it. The velocities of the molecular gas is in the range --38 to --53 km/s, similar to the velocity of the ionized gas. The emission at 8.3 mic. reveals a ring like feature of about 15' that encircles the bright optical regions. This emission is due to the PAHs and marks the location of photodissociation regions.
The gas distribution in the environs of Sh2-132 can be explained in a scenario where the massive stars in the region photodissociated, ionized, and swept-up the dense molecular material from the parental cloud through their strong stellar winds and intense UV photon flux.

[37]  arXiv:1002.4617 [ps, pdf, other]
Title: Coorbital Satellites of Saturn: Congenital Formation
Comments: 10 pages, 9 figures, 4 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Saturn is the only known planet to have coorbital satellite systems. In the present work we studied the process of mass accretion as a possible mechanism for coorbital satellites formation. The system considered is composed of Saturn, a proto-satellite and a cloud of planetesimals distributed in the coorbital region around a triangular Lagrangian point. The adopted relative mass for the proto-satellite was 10^-6 of Saturn's mass and for each planetesimal of the cloud three cases of relative mass were considered, 10^-14, 10^-13 and 10^-12 masses of Saturn. In the simulations each cloud of planetesimal was composed of 10^3, 5 x 10^3 or 10^4 planetesimals. The results of the simulations show the formation of coorbital satellites with relative masses of the same order of those found in the saturnian system (10^-13 - 10^-9). Most of them present horseshoe type orbits, but a significant part is in tadpole orbit around L_4 or L_5. Therefore, the results indicate that this is a plausible mechanism for the formation of coorbital satellites.

Cross-lists for Thu, 25 Feb 10

[38]  arXiv:0911.0288 (cross-list from gr-qc) [pdf, other]
Title: Classifying LISA gravitational wave burst signals using Bayesian evidence
Comments: 21 pages, 11 figures, accepted by CQG; v2 has minor changes for consistency with accepted version
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We consider the problem of characterisation of burst sources detected with the Laser Interferometer Space Antenna (LISA) using the multi-modal nested sampling algorithm, MultiNest. We use MultiNest as a tool to search for modelled bursts from cosmic string cusps, and compute the Bayesian evidence associated with the cosmic string model. As an alternative burst model, we consider sine-Gaussian burst signals, and show how the evidence ratio can be used to choose between these two alternatives. We present results from an application of MultiNest to the last round of the Mock LISA Data Challenge, in which we were able to successfully detect and characterise all three of the cosmic string burst sources present in the release data set. We also present results of independent trials and show that MultiNest can detect cosmic string signals with signal-to-noise ratio (SNR) as low as ~7 and sine-Gaussian signals with SNR as low as ~8. In both cases, we show that the threshold at which the sources become detectable coincides with the SNR at which the evidence ratio begins to favour the correct model over the alternative.

[39]  arXiv:1002.4230 (cross-list from gr-qc) [ps, pdf, other]
Title: A Couple of Issues Concerning Spinor Dark Energy
Authors: Hao Wei
Comments: 15 pages, 2 figures, revtex4
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

Recently, the so-called Elko spinor field has been proposed to be a candidate of dark energy. It is a non-standard spinor and has unusual properties. When the Elko spinor field is used in cosmology, its unusual properties could bring some interesting consequences. In the present work, we consider two different issues concerning the dark energy model described by the Elko spinor fields. Firstly, we discuss the cosmological coincidence problem in the spinor dark energy model by using the dynamical system method. Our results show that the coincidence problem should be taken to heart in the investigations of spinor dark energy models. Next, we turn to another issue. In this work, we propose a simple method to reconstruct spinor dark energy from the cosmological observations. We find that this reconstruction method works fairly well.

[40]  arXiv:1002.4278 (cross-list from hep-th) [pdf, other]
Title: Entropic Accelerating Universe
Comments: 10 pages, 1 figure
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

To accommodate the observed accelerated expansion of the universe, one popular idea is to invoke a driving term in the Friedmann-Lema\^{i}tre equation of dark energy which must then comprise 70% of the present cosmological energy density. We propose an alternative interpretation which takes into account the temperature intrinsic to the information holographically stored on the screen which is the surface of the universe. Dark energy is thereby obviated and the acceleration is due to an entropic force naturally arising from the information storage on a surface screen. We consider an additional quantitative approach based upon the entropy and surface terms usually neglected in General Relativity and show that this leads to the entropic accelerating universe.

[41]  arXiv:1002.4584 (cross-list from physics.gen-ph) [ps, pdf, other]
Title: On the Sackur-Tetrode equation of an expanding universe
Authors: S. H. Pereira
Comments: 7 pages
Subjects: General Physics (physics.gen-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

In this work we investigate the thermodynamic properties satisfied by an expanding universe filled with a monoatomic ideal gas. We show that the equations for the energy density, entropy density and chemical potential remain the same as the ideal gas.

Replacements for Thu, 25 Feb 10

[42]  arXiv:0810.4852 (replaced) [ps, pdf, other]
Title: Nearby Spiral Galaxy Globular Cluster Systems II: Globular Cluster Abundances in NGC 300
Comments: 36 pages, 15 figures, accepted to AJ; altered a second time according to referee-report so as to slightly change the criteria for GC selection
Subjects: Astrophysics (astro-ph)
[43]  arXiv:0903.5308 (replaced) [ps, pdf, other]
Title: Dynamical inference from a kinematic snapshot: The force law in the Solar System
Authors: Jo Bovy (NYU), Iain Murray (Toronto), David W. Hogg (NYU, MPIA)
Journal-ref: Astrophys.J.711:1157-1167,2010
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Galaxy Astrophysics (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); Classical Physics (physics.class-ph); Data Analysis, Statistics and Probability (physics.data-an)
[44]  arXiv:0906.4069 (replaced) [ps, pdf, other]
Title: Characterization of the BICEP Telescope for High-Precision Cosmic Microwave Background Polarimetry
Comments: 16 pages, 22 figures, updated to reflect published version
Journal-ref: Astrophysical Journal 711 (2010) 1141-1156
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[45]  arXiv:0907.2941 (replaced) [ps, pdf, other]
Title: Tracking Quintessence and Cold Dark Matter Candidates
Comments: Final version
Journal-ref: JCAP 0911:017,2009
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[46]  arXiv:0908.4091 (replaced) [ps, pdf, other]
Title: Star Cluster Candidates in M81
Comments: 35 pages, 11 figures, submitted to AJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[47]  arXiv:0909.2043 (replaced) [ps, pdf, other]
Title: Models of Neptune-Mass Exoplanets: Emergent Fluxes and Albedos
Authors: David S. Spiegel (1), Adam Burrows (1), Laurent Ibgui (1), Ivan Hubeny (2), John A. Milsom (3) ((1)Princeton University, (2)Steward Observatory, (3)The University of Arizona)
Comments: Accepted and Published in ApJ (2010 ApJ,709,149)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[48]  arXiv:0909.3026 (replaced) [ps, pdf, other]
Title: Cold Dark Matter in non-Standard Cosmologies, PAMELA, ATIC and Fermi LAT
Authors: C. Pallis
Comments: Final version
Journal-ref: Nucl.Phys.B831:217-247,2010
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[49]  arXiv:0909.4268 (replaced) [ps, pdf, other]
Title: A NLTE model atmosphere analysis of the pulsating sdO star SDSS J1600+0748
Comments: 4 pages, 4 figures, accepted in Astrophysics and Space Science (24/02/2010), Special issue Hot sudbwarf stars
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[50]  arXiv:0910.5218 (replaced) [ps, pdf, other]
Title: O-V-S-Z and friends: Non-Gaussianity from inhomogeneous reionization
Comments: Published version
Journal-ref: ApJ 711 (2010) 1310
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[51]  arXiv:0910.5248 (replaced) [ps, pdf, other]
Title: The Origin of Magnetic Fields in Galaxies
Comments: 10 pages, 3 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
[52]  arXiv:0911.0687 (replaced) [ps, pdf, other]
Title: Semi-Analytic Calculation of the Gravitational Wave Signal From the Electroweak Phase Transition for General Quartic Scalar Effective Potentials
Comments: accepted by JCAP, revisions: removed turbulence contribution, minor changes to experimental sensitivity, fixed various minor typos and text revisions, added references, made it clear we consider only detonations; 17 pages, 4 figures, revtex4
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
[53]  arXiv:0911.1274 (replaced) [ps, pdf, other]
Title: The importance of precession in modelling the direction of the final spin from a black-hole merger
Authors: Enrico Barausse
Comments: 6 pages, 2 figures. Panel added to fig 2, discussion extended to comply with referee's comments. Version accepted for publication as proceeding of the 8th Amaldi International Conference on Gravitational Waves, NYC, 21-26 June 2009
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
[54]  arXiv:0911.3327 (replaced) [ps, pdf, other]
Title: Simulating magnetic fields in the Antennae galaxies
Comments: 16 pages, 13 figures, resubmitted after referee report
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[55]  arXiv:0912.2094 (replaced) [ps, pdf, other]
Title: Cold Fronts from Shock Collisions
Comments: 5 pages, 4 figures, Revised version
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
[56]  arXiv:0912.2119 (replaced) [ps, pdf, other]
Title: Spectroscopy of M81 Globular Clusters
Comments: 46 pages, 15 figures, submitted to AJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[57]  arXiv:0912.3385 (replaced) [ps, pdf, other]
Title: Revised Results for Non-thermal Recombination Flare Hard X-Ray Emission
Comments: 6 pages, 8 figures, 1 table
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[58]  arXiv:1001.1171 (replaced) [ps, pdf, other]
Title: A time-dependent radiative model for the atmosphere of the eccentric exoplanets
Comments: Accepted for publication in the Astrophysical Journal (In Press)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[59]  arXiv:1001.3140 (replaced) [ps, pdf, other]
Title: The Simultaneous Optical-to-X-ray Spectral Energy Distribution of Soft X-ray Selected AGN observed by Swift
Authors: Dirk Grupe (PSU), S. Komossa (MPE), Karen M. Leighly (University of Oklahoma), Kim L. Page (University of Leicester)
Comments: 76 pages, 25 figures, 7 tables
Journal-ref: 2010, ApJ Suppl, 187, 64
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[60]  arXiv:1001.4580 (replaced) [ps, pdf, other]
Title: Quasar variability limits on cosmological density of cosmic strings
Authors: Artem Tuntsov (Sternberg Astronomical Institute), Maxim Pshirkov (Pushchino Radio Astronomy Observatory)
Comments: 7 pages, 2 figures, accepted to Phys.Rev.D, no essential changes from v1. Based on the referee's feedback, a paragraph is added that emphasizes the value of the obtained limits to constrain the abundance and reconnection probabilities of fundamental (rather than topological) strings
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
[61]  arXiv:1001.4742 (replaced) [ps, pdf, other]
Title: Searching for the inverse-Compton emission from bright cluster-centre radio galaxies
Comments: 10 pages, 1 figure. Accepted for MNRAS. Updated version provides some missing references, no change to paper content
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
[62]  arXiv:1002.0150 (replaced) [ps, pdf, other]
Title: The First Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
Comments: 68 pages, 28 figures; submitted to ApJ; electronic tables available by clicking the link in the top left of this http URL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[63]  arXiv:1002.0723 (replaced) [ps, pdf, other]
Title: A revision of the X-ray absorption nature of the BALQSOs
Comments: Accepted by A&amp;A. 12 pages, 8 figures. Added references and corrected typos
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)
[64]  arXiv:1002.1080 (replaced) [ps, pdf, other]
Title: J0454-0309: Evidence for a strong lensing fossil group falling into a poor galaxy cluster
Authors: Mischa Schirmer (1), Sherry Suyu (1), Tim Schrabback (2), Hendrik Hildebrandt (2), Aleksi Halkola (3,4), Thomas Erben (1) ((1)Argelander-Institut fuer Astronomie, (2)Leiden Observatory, (3)University of Tuorla Observatory, (4)Excellence Cluster Universe Technische Universitaet Muenchen)
Comments: 20 pages, 17 figures; Identical to the publication in A+A. Small language corrections. Minor additions: We check the influence of individual galaxy haloes to the external shear (Sect. 8.1.1). Alternative interpretation of the data: Galaxies ina filament projected along the l.o.s. fall into the fossil group (Section 8.1.2)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[65]  arXiv:1002.3966 (replaced) [pdf, other]
Title: Why all these prejudices against a constant?
Comments: 9 pages, 4 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
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New submissions for Fri, 26 Feb 10

[1]  arXiv:1002.4619 [ps, pdf, other]
Title: The jet/disk connection in blazars
Authors: Gabriele Ghisellini (INAF - Osservatorio Astronomico di Brera)
Comments: 12 pages, 10 figures, invited contribution for the meeting: Plasmas in the Laboratory and in the Universe: interactions, patterns, and turbulence. Como, December 2009
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

The new high energy data coming mainly from the Fermi and Swift satellites and from the ground based Cerenkov telescopes are making possible to study not only the energetics of blazar jets, but also their connection to the associated accretion disks. Furthermore, the black hole mass of the most powerful objects can be constrained through IR-optical emission, originating in the accretion disks. For the first time, we can evaluate jet and accretion powers in units of the Eddington luminosity for a large number of blazars. Firsts results are intriguing. Blazar jets have powers comparable to, and often larger than the luminosity produced by their accretion disk. Blazar jets are produced at all accretion rates (in Eddington units), and their appearance depends if the accretion regime is radiatively efficient or not. The jet power is dominated by the bulk motion of matter, not by the Poynting flux, at least in the jet region where the bulk of the emission is produced, at ~1000 Schwarzschild radii. The mechanism at the origin of relativistic jets must be very efficient, possibly more than accretion, even if accretion must play a crucial role. Black hole masses for the most powerful jets at redshift ~3 exceed one billion solar masses, flagging the existence of a very large population of heavy black holes at these redshifts.

[2]  arXiv:1002.4620 [ps, pdf, other]
Title: Detection of 21-cm, H2 and Deuterium absorption at z>3 along the line-of-sight to J1337+3152
Comments: 14 pages, 11 figures, 4 tables, accepted for publication in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We report the detection of 21-cm and H2 absorption lines in the same DLA system (log N(HI)=21.36+-0.10) at zabs=3.17447 towards SDSSJ133724+315254 (z=3.174). We estimate the spin temperature of the gas to be, Ts~600 K, intermediate between the expected values for cold and warm neutral media. This suggests that the HI absorption originates from a mixture of different phases. The total molecular fraction is low, f=10^-7, and H2 rotational level populations are not in equilibrium. The average abundance of the alpha-elements is, [S/H]=-1.45. N and Fe are found underabundant with respect to alpha-elements by ~1.0 dex and ~0.5 dex respectively. Using photoionization models we conclude that the gas is located more than 270 kpc away from the QSO. While the position of 21-cm absorption line coincides with the H2 velocity profile, their centroid are shifted by 2.7+-1.0 km/s from each other. However, the position of the strongest metal absorption component matches the position of the 21-cm absorption line within 0.5 km/s. From this, we constrain the variation of the combination of fundamental constants x=alpha^2 Gp/mu, Delta x/x=-(1.7+-1.7)x10^-6. This system is unique as we can at the same time have an independent constrain on mu using H2 lines. However only Werner band absorption lines are seen and the range of sensitivity coefficients is too narrow to provide a stringent constraint: Delta mu/mu <= 4.0x10^-4. The VLT/UVES spectrum reveals another DLA at zabs=3.16768 with log N(HI)=20.41+-0.15 and low metallicity, [Si/H]=-2.68+-0.11. We derive log N(DI)/N(HI)=-(4.93+-0.15) in this system. This is a factor of two smaller than the value expected from the best fitted value of Omega_b from the WMAP 5 yr data. This confirms the presence of astration of deuterium even at very low metallicity. [abridged]

[3]  arXiv:1002.4621 [ps, pdf, other]
Title: On the angular momentum transport due to vertical convection in accretion discs
Authors: G. Lesur, G. I. Ogilvie (Cambridge)
Comments: 6 pages, 5 figures, accepted in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

The mechanism of angular momentum transport in accretion discs has long been debated. Although the magnetorotational instability appears to be a promising process, poorly ionized regions of accretion discs may not undergo this instability. In this letter, we revisit the possibility of transporting angular momentum by turbulent thermal convection. Using high-resolution spectral methods, we show that strongly turbulent convection can drive outward angular momentum transport at a rate that is, under certain conditions, compatible with observations of discs. We find however that the angular momentum transport is always much weaker than the vertical heat transport. These results indicate that convection might be another way to explain global disc evolution, provided that a sufficiently unstable vertical temperature profile can be maintained.

[4]  arXiv:1002.4623 [ps, pdf, other]
Title: Spitzer Spectroscopy of the Transition Object TW Hya
Comments: To appear in the Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)

We report sensitive Spitzer IRS spectroscopy in the 10-20 micron region of TW Hya, a nearby T Tauri star. The unusual spectral energy distribution of the source, that of a transition object, indicates that the circumstellar disk in the system has experienced significant evolution, possibly as a result of planet formation. The spectrum we measure is strikingly different from that of other classical T Tauri stars reported in the literature, displaying no strong emission features of water, acetylene, or HCN. The difference indicates that the inner planet formation region (within 5 AU) of the gaseous disk has evolved physically and/or chemically away from the classical T Tauri norm. Nevertheless, TW Hya does show a rich spectrum of emission features of atoms (HI, [NeII], and [NeIII]) and molecules (H2, OH, CO2, HCO+, and possibly CH3), some of which are also detected in classical T Tauri spectra. The properties of the neon emission are consistent with an origin for the emission in a disk irradiated by X-rays (with a possible role for additional irradiation by stellar EUV). The OH emission we detect, which also likely originates in the disk, is hot, arising from energy levels up to 23,000 K above ground, and may be produced by the UV photodissociation of water. The HI emission is surprisingly strong, with relative strengths that are consistent with case B recombination. While the absence of strong molecular emission in the 10-20 micron region may indicate that the inner region of the gaseous disk has been partly cleared by an orbiting giant planet, chemical and/or excitation effects may be responsible instead. We discuss these issues and how our results bear on our understanding of the evolutionary state of the TW Hya disk.

[5]  arXiv:1002.4626 [ps, pdf, other]
Title: Galaxy Counterparts of metal-rich Damped Lyman-$\alpha$ Absorbers - I: The case of the z=2.35 DLA towards Q2222$-0946
Comments: 9 pages, 7 figures. Submitted to MNRAS. Comments welcome
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Lyman-alpha absorbers (DLAs). Our rationale is that high-metallicity DLAs due to the luminosity-metallicity relation likely will have the most luminous galaxy counterparts. We have chosen DLAs where the strongest rest-frame optical lines ([OII], [OIII], Hbeta and Halpha) fall in the NIR atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the z_abs= 2.354 DLA towards the z=2.926 Q2222$-0946. This DLA is amongst the most metal-rich z>2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements onto dust grains. We measure metallicities from ZnII, SiII, NiII, MnII and FeII of -0.46+/-0.07, -0.51+/-0.06, -0.85+/-0.06, -1.23+/-0.06, and -0.99+/-0.06, respectively. The galaxy is detected in the Lyalpha, [OIII] 4960, 5008 and Halpha emission lines at an impact parameter of about 0.8 arcsec (6 kpc at z_abs = 2.354). Based on the Halpha line, we infer a star-formation rate of 10 M_sun yr^-1. Compared to the recently determined Halpha luminosity function for z=2.2 galaxies the DLA-galaxy counterpart is a dwarf galaxy (L~0.1L*). The emission-line ratios are 3.6 (Lyalpha/Halpha) and 1.6 ([OIII]/Halpha). In particular, the Lyalpha line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The properties of the galaxy counterpart of this DLA confirms the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts.

[6]  arXiv:1002.4627 [ps, pdf, other]
Title: Ultra- and Hyper-compact HII regions at 20 GHz
Authors: Tara Murphy (1), Martin Cohen (2), Ronald D. Ekers (3), Anne J. Green (1), Robin Wark (3), Vanessa Moss (1) ((1) The University of Sydney, (2) University of California, Berkeley, (3) The Australia Telescope National Facility)
Comments: 13 pages, 7 figures, accepted for publication in MNRAS
Subjects: Galaxy Astrophysics (astro-ph.GA)

We present radio and infrared observations of 4 hyper-compact HII regions and 4 ultra-compact HII regions in the southern Galactic plane. These objects were selected from a blind survey for UCHII regions using data from two new radio surveys of the southern sky; the Australia Telescope 20 GHz survey (AT20G) and the 2nd epoch Molonglo Galactic Plane Survey (MGPS-2) at 843 MHz. To our knowledge, this is the first blind radio survey for hyper- and ultra-compact HII regions.
We have followed up these sources with the Australia Telescope Compact Array to obtain H70-alpha recombination line measurements, higher resolution images at 20 GHz and flux density measurements at 30, 40 and 95 GHz. From this we have determined sizes and recombination line temperatures as well as modeling the spectral energy distributions to determine emission measures. We have classified the sources as hyper-compact or ultra-compact on the basis of their physical parameters, in comparison with benchmark parameters from the literature.
Several of these bright, compact sources are potential calibrators for the Low Frequency Instrument (30-70 GHz) and the 100-GHz channel of the High Frequency Instrument of the Planck satellite mission. They may also be useful as calibrators for the Australia Telescope Compact Array, which lacks good non-variable primary flux calibrators at higher frequencies and in the Galactic plane region. Our spectral energy distributions allow the flux densities within the Planck bands to be determined, although our high frequency observations show that several sources have excess emission at 95 GHz (3 mm) that can not be explained by current models.

[7]  arXiv:1002.4631 [ps, pdf, other]
Title: An XMM-Newton Survey of the Soft X-ray Background. I. The O VII and O VIII Lines Between l=120 and l=240
Authors: David B. Henley, Robin L. Shelton (University of Georgia)
Comments: 43 pages, 19 figures. Accepted for publication in the Astrophysical Journal Supplement Series
Subjects: Galaxy Astrophysics (astro-ph.GA)

We present measurements of the soft X-ray background (SXRB) O VII and O VIII intensity between $l = 120\degr$ and $l = 240\degr$, the first results of a survey of the SXRB using archival XMM-Newton observations. We do not restrict ourselves to blank-sky observations, but instead use as many observations as possible, removing bright or extended sources by hand if necessary. The oxygen intensities are typically ~0.5-10 photons/cm^2/s/sr (line units, L.U.) for O VII and ~0-5 L.U. for O VIII. Our dataset includes 69 directions with multiple observations, whose oxygen intensity variations can be used to constrain SWCX models. One observation exhibits an O VII enhancement of ~25 L.U. over 2 other observations of the same direction, although most SWCX enhancements are $\la 4$ L.U. for O VII and $\la 2$ L.U. for O VIII. We find no clear tendency for the O VII centroid to shift toward the forbidden line energy in observations with bright SWCX enhancements. There is also no universal association between enhanced SWCX emission and increased solar wind flux or the closeness of the sightline to the sub-solar region of the magnetosheath. After removing observations likely to be contaminated by heliospheric SWCX emission, we use our results to examine the Galactic halo. There is some scatter in the halo intensity about the predictions of a simple plane-parallel model, indicating a patchiness to the halo emission. The O VII/O VIII intensity ratio implies a halo temperature of ~2.0-2.5 MK, in good agreement with previous studies. (Abridged)

[8]  arXiv:1002.4644 [ps, pdf, other]
Title: The Multicolor "Lyra" Photometric System for Variable stars and Halo Studies
Comments: 7 pages, 5 Postscript figures, uses psfig.sty and vshalo.sty
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The space photometric project "Lyra" is developed now in Russia.The project purpose is determination of the photometric information and coordinates of the natural and artificial space objects, from the brightest ones to 16^m in visual lights. It is supposed to obtain the data for about 40-400 million objects from board of International Space Station, using an astronomical telescope with diameter of the main mirror of 0.5 m. The observations will be carried out in a scanning mode. Photometry will be obtained in 10 spectral bands. The expected uncertainty of magnitudes for objects of 16^m in the V-band is 0.001^m.
The main results of experiment should become:
1) creation of spatial model of the Galaxy on distances to 3 kpc from the Sun;
2) specification of physical parameters of stars and models of star evolution;
3) discovering of a huge number (to several millions) of variable stars and determination of their variability parameters.
The central wavelengths of the 10 bands of "Lyra" photometric system will be at 195, 218, 270, 350, 440, 550, 700, 825, 930 and 1000 nm. It is shown that combinations of various colour indices will allow to determine confidently both effective temperature and metallicity of stars. The presence of a 218 nm band allows to determine confidently interstellar extinction on stars of O-F spectral classes. The photometric system will make it possible to separate halo stars from disk stars and to define physical parameters of their atmospheres.

[9]  arXiv:1002.4653 [ps, pdf, other]
Title: Thermal Equilibria of Optically Thin, Magnetically Supported, Two-Temperature, Black Hole Accretion Disks
Comments: 24 pages, 10 figures,accepted for publication in Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We obtained thermal equilibrium solutions for optically thin, two-temperature black hole accretion disks incorporating magnetic fields. The main objective of this study is to explain the bright/hard state observed during the bright/slow transition of galactic black hole candidates. We assume that the energy transfer from ions to electrons occurs via Coulomb collisions. Bremsstrahlung, synchrotron, and inverse Compton scattering are considered as the radiative cooling processes. In order to complete the set of basic equations, we specify the magnetic flux advection rate. We find magnetically supported (low-beta), thermally stable solutions. In these solutions, the total amount of the heating via the dissipation of turbulent magnetic fields goes into electrons and balances the radiative cooling. The low-$\beta$ solutions extend to high mass accretion rates and the electron temperature is moderately cool. High luminosities and moderately high energy cutoffs in the X-ray spectrum observed in the bright/hard state can be explained by the low-beta solutions.

[10]  arXiv:1002.4663 [ps, pdf, other]
Title: The reanalysis of spectra of GRB 080913 to estimate the neutral fraction of the IGM at a redshift of 6.7
Comments: 4 pages, 4 figures, A&amp;A accepted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

Aims: We reanalyse optical spectra of the z=6.7 gamma-ray burst GRB 080913, adding hitherto unpublished spectra, in order to reassess the measurement of the neutral fraction of the IGM at high redshifts.
Methods: In the data reduction we take particular care to minimise systematic errors in the sky subtraction, which are evident in the published spectrum, and compromise the analysis. The final combined spectrum has a higher S/N than the previously published spectrum by a factor of 1.3.
Results: We find a single significant absorption line redward of the Ly-alpha continuum break, which we identify with the SII+SiII blend (rest wavelength of 0.1260 micron), at z=6.733. The sharp spectral break at Ly-alpha implies a comparatively low total column density of neutral hydrogen along the line of sight, log [N(HI)/cm^-2] < 20. We model the absorption with a host-galaxy DLA, surrounded by an ionised region of unknown size r, within the IGM of neutral fraction, x(HI). Despite knowing the source redshift, and the improved S/N of the spectrum, when fitting only over wavelengths redward of Ly-alpha, no useful constraints on x(HI) can be obtained. We consider the possibility of including the ionised region, blueward of Ly-alpha, in constraining the fit. For the optimistic assumption that the ionised region is transparent, tau_{GP} << 1, we find that the region is of small size r < 2 proper Mpc, and we obtain an upper limit to the neutral fraction of the IGM at z=6.7 of x(HI) < 0.73.

[11]  arXiv:1002.4667 [ps, pdf, other]
Title: Outflows from AGN: their Impact on Spectra and the Environment
Authors: Daniel Proga (UNLV), Ryuichi Kurosawa (UNLV, Cornell Univ.)
Comments: 8 pages, 6 figures, Proceedings of "Accretion and Ejection in AGN: a global view", Como (Italy) 06/22-26/2009, ASP Conference Series, Eds: L. Maraschi, G. Ghisellini, R. Della Ceca, and F. Tavecchio, invited talk
Subjects: Galaxy Astrophysics (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We present a brief summary of the main results from our multi-dimensional, time-dependent simulations of gas dynamics in AGN. We focus on two types of outflows powered by radiation emitted from the AGN: disk winds and winds driven from large-scale inflows. We show spectra predicted by the simulations and discuss their relevance to observations of broad- and narrow-line regions of the AGN. We finish with a few remarks on whether these outflows can have a significant impact on their environment and host galaxy.

[12]  arXiv:1002.4677 [ps, pdf, other]
Title: Detection of a white dwarf companion to the white dwarf binary SDSSJ125733.63+542850.5
Comments: 5 figures, submitted to ApJ Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

SDSSJ125733.63+542850.5 (hereafter SDSSJ1257+5428) is a white dwarf from the Sloan Digital Sky Survey recently shown to exhibit high-amplitude radial velocity variations on a period of 4.56 hours suggesting that it has either a neutron star or black-hole binary companion. At a distance of only 48 pc, this would make it the closest remnant of a supernova known and imply that such systems are common in our Galaxy and others. Here we present optical spectroscopy that shows that the companion star in SDSSJ1257+5428 is in fact another white dwarf. SDSSJ1257+5428's spectrum is thus a composite, with narrow line cores from a cool, low mass white dwarf (7000 K; 0.2 Msun), and broad wings from its hotter, high-mass companion (10,000 K; > 1 Msun). We present evidence that suggests that the high-mass star is rapidly rotating with v sin i = 500 to 1000 km/s. This suggests that the most recent phase of mass transfer was long-lasting and stable as against the usually-assumed common envelope phase. Within the constraints set by our data, SDSSJ1257+5428 could have a total mass greater than the Chandrasekhar limit and thus be a potential Type Ia supernova progenitor. However, its mass ratio, q < 0.2, is extreme enough to guarantee stable mass transfer on contact, and it is probably more likely to evolve into an accreting ultracompact binary star. In the light of our model we revise the distance to
SDSSJ1257+5428 to d = 100 pc.

[13]  arXiv:1002.4681 [ps, pdf, other]
Title: The Redshifted Excess in Quasar C IV Broad Emission Lines
Authors: Brian Punsly
Comments: To appear in ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

In this Letter, the Evans and Koratkar Atlas of Hubble Space Telescope Faint Object Spectrograph Spectra of Active Galactic Nuclei and Quasars is used to study the redward asymmetry in CIV broad emission lines (BELs). It is concluded that there is a highly significant correlation between the spectral index from 10 GHz to 1350 $\AA$ and the amount of excess luminosity in the red wing of the CIV BEL ($>99.9999%$ significance level for the full sample and the radio loud subsample independently, but no correlation is found for the radio quiet subsample). This is interpreted as a correlation between radio core dominance and the strength of the CIV redward asymmetry. The data implies that within the quasar environment there is BEL gas with moderately blueshifted emission associated with the purely radio quiet quasar phenomenon (the accretion disk) and the radio jet emission mechanism is associated with a redward BEL component that is most prominent for lines of sight along the jet axis. Thus, radio quiet quasars have CIV BELs that tend to show blueshifted excess and radio loud quasars show either a red or blue excess with the tendency for a dominant red excess increasing as the line of sight approaches the jet axis.

[14]  arXiv:1002.4691 [ps, pdf, other]
Title: Testing Strict Hydrostatic Equilibrium in Abell 1689
Authors: S. M. Molnar (1), I.-N. Chiu (2,3), K. Umetsu (1), P. Chen (2,3), N. Hearn (4), T. Broadhurst (5), G. Bryan (6), C. Shang (6) ((1) Institute of Astronomy & Astrophysics, Academia Sinica, (2) Department of Physics, Institute of Astrophysics, & Center for Theoretical Sciences, National Taiwan University (3) Leung center for Cosmology and Particle Astrophysics, National Taiwan University (4) School of Physics and Astronomy, Tel Aviv University (5) Computational & Information Systems Laboratory, National Center for Atmospheric Research (6) Department of Astronomy, Columbia University)
Comments: submitted to ApJL; 4 pages, 3 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Recent mass estimates of the well-studied massive galaxy cluster Abell 1689 based on X-ray observations and gravitational lensing, assuming spherical symmetry, still give discrepant results. Contamination by a cool component, substructure and triaxial gas distribution have been proposed to resolve this discrepancy. However, none of these solutions is fully consistent with all observations and predictions of cold dark matter models. A common assumption in all proposed solutions is strict hydrostatic equilibrium, i.e., the gas pressure is provided entirely by thermal pressure, P_he = P_th. We derive P_th and P_he from X-ray and gravitational lensing observations of A1689 in order to test the validity of this assumption. Assuming spherical symmetry, we find that P_th/P_he ~0.6 within the core region of this cluster. We analyze a sample of massive clusters of galaxies drawn from high resolution cosmological simulations, and find, in accord with previous studies, that there is a significant contribution from non-thermal pressure in the core region of relaxed clusters. Our results suggest an alternate explanation for the mass discrepancy in the core region of A1689: the assumption of strict hydrostatic equilibrium is not valid, i.e., P_th not = P_he, in this region.

[15]  arXiv:1002.4693 [ps, pdf, other]
Title: Forming Low Mass Stars and Brown Dwarfs in Protoplanetary Disks of Very Massive Stars
Comments: 13 pages, 1 figure
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We suggest that planets, brown dwarfs, and even low mass stars can be formed by fragmentation of protoplanetary disks around very massive stars (M>~100 solar masses). We discuss how fragmentation conditions make the formation of very massive planetary systems around very massive stars favorable. Such planetary systems are likely to be composed of brown dwarfs and low mass stars of ~ 0.1-0.3 solar masses, at orbital separations of ~ few 100 - 10^4 AU. Such fragmentation objects can be excellent targets for the James Webb Space Telescope and other large telescopes working in the IR bands. We predict that deep observations of very massive stars would reveal these fragmentation objects, orbiting in the same orbital plane in cases where there are more than one object.

[16]  arXiv:1002.4699 [pdf]
Title: 2001 QR322: a dynamically unstable Neptune Trojan?
Comments: 14 pages, 5 figures, MNRAS (in press)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Since early work on the stability of the first Neptunian Trojan, 2001 QR322, suggested that it was a dynamically stable, primordial body, it has been assumed this applies to both that object, and its more recently discovered brethren. However, it seems that things are no longer so clear cut. In this work, we present the results of detailed dynamical simulations of the orbital behaviour of 2001 QR322. Using an ephemeris for the object that has significantly improved since earlier works, we follow the evolution of 19683 test particles, placed on orbits within the observational error ellipse of 2001 QR322's orbit, for a period of 1 Gyr. We find that majority of these "clones" of 2001 QR322 are dynamically unstable, exhibiting a near-exponential decay from both the Neptunian Trojan cloud (decay halflife ~550 Myr) and the Solar system (decay halflife ~590 Myr). The stability of the object within Neptune's Trojan cloud is found to be strongly dependent on the initial semi-major axis used, with those objects located at semimajor axis equal or greater than 30.30 AU being significantly less stable than those interior to this value, as a result of their having initial libration amplitudes very close to a critical threshold dividing regular and irregular motion, located at ~70-75 deg (full extent of angular motion). This result suggests that, if 2001 QR322 is a primordial Neptunian Trojan, it must be a representative of a population that was once significantly larger than that we see today, and adds weight to the idea that the Neptune Trojans may represent a significant source of objects moving on unstable orbits between the giant planets (the Centaurs).

[17]  arXiv:1002.4702 [ps, pdf, other]
Title: Educated search for transiting habitable planets. Targetting M dwarfs with known transiting planets
Authors: M. Gillon (1,2), X. Bonfils (2,3), B.-O. Demory (4,2), S. Seager (4), D. Deming (5) ((1) University of Liege, Belgium, (2) Geneva Observatory, Switzerland, (3) University Joseph-Fourier, Grenoble, France, (4) MIT, Boston, USA, (5) NASA/Goddard SFC, Greenbelt, USA)
Comments: Submitted to A&amp;A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The photometric monitoring of stars known to host a transiting planet could thus reveal the transits of one or more other planets. Depending on several parameters, significantly enhanced transit probability could be expected for habitable planets. This approach is especially interesting for M dwarfs because these stars have close-in habitable zones and because their small radii make possible the detection of terrestrial planets down to Mars size. We investigate the potential of this approach for the two M dwarfs known to host a transiting planet, GJ 436 and GJ 1214. Contrary to GJ 436, GJ 1214 reveals to be a very promising target for the considered approach. Assuming a distribution of orbital inclinations similar to our solar system, a habitable planet orbiting around GJ 1214 would have a mean transit probability of ~25%, much better than the probability of 1.5% expected if the transits of GJ 1214b are not considered. Because of the small size of GJ 1214, a ground-based photometric monitoring of this star could detect the transit of a habitable planet as small as the Earth, while a space-based monitoring (e.g., with Warm Spitzer) could detect any transiting habitable planet down to the size of Mars. A dedicated high-precision photometric monitoring of M dwarfs known to harbor close-in transiting planets could thus be an efficient way to detect transiting habitable planets much smaller than our Earth that would be out of reach for existing Doppler and transit surveys.

[18]  arXiv:1002.4703 [ps, pdf, other]
Title: Results from a Search for Light-Mass Dark Matter with a P-type Point Contact Germanium Detector
Comments: 4 pages, 4 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We report on several features present in the energy spectrum from an ultra low-noise germanium detector operated at 2,100 m.w.e. By implementing a new technique able to reject surface events, a number of cosmogenic peaks can be observed for the first time. We discuss several possible causes for an irreducible excess of bulk-like events below 3 keVee, including a dark matter candidate common to the DAMA/LIBRA annual modulation effect, the hint of a signal in CDMS, and phenomenological predictions. Improved constraints are placed on a cosmological origin for the DAMA/LIBRA effect.

[19]  arXiv:1002.4707 [ps, pdf, other]
Title: The Spitzer search for the transits of HARPS low-mass planets - I. No transit for the super-Earth HD 40307b
Authors: M. Gillon (1,2), D. Deming (3), B.-O. Demory (4,2), C. Lovis (2), S. Seager (4), M. Mayor (2), F. Pepe (2), D. Queloz (2), D. Segransan (2), S. Udry (2), S. Delmelle (1), P. Magain (1) ((1) University of Liege, Belgium, (2) Geneva Observatory, Switzerland, (3) NASA/Goddard SFC, Greenbelt, USA, (4) MIT, Boston, USA)
Comments: Submitted to A&amp;A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We have used Spitzer and its IRAC camera to search for the transit of the super-Earth HD 40307b. The transiting nature of the planet could not be firmly discarded from our first photometric monitoring of a transit window because of the uncertainty coming from the modeling of the photometric baseline. To obtain a firm result, two more transit windows were observed and a global Bayesian analysis of the three IRAC time series and the HARPS radial velocities was performed. Unfortunately, any transit of the planet during the observed phase window is firmly discarded, while the probability that the planet transits but that the eclipse was missed by our observations is nearly negligible (0.26%).

[20]  arXiv:1002.4708 [pdf, other]
Title: Quantifying dwarf satellites through gravitational imaging: the case of SDSS J120602.09+514229.5
Authors: S. Vegetti, O. Czoske, L.V.E. Koopmans. (Kapteyn Astronomical Institute, RUG)
Comments: Submitted to MNRAS; Abstract abridged
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

SDSS J120602.09+514229.5 is a gravitational lens system formed by a group of galaxies at redshift z=0.422 lensing a bright background galaxy at redshift z=2.001. The main peculiarity of this system is the presence of a luminous satellite near the Einstein radius, that slightly deforms the giant arc. This makes SDSS J120602.09+514229.5 the ideal system to test our grid-based Bayesian lens modelling method, designed to detect galactic satellites independently from their mass-to-light ratio, and to measure the mass of this dwarf galaxy despite its high redshift. Thanks to the pixelized source and potential reconstruction technique of Vegetti and Koopmans 2009a we are able to detect the luminous satellite as a local positive surface density correction to the overall smooth potential. Assuming a truncated Pseudo-Jaffe density profile, the satellite has a mass M=(2.75+-0.04)10^10 M_sun inside its tidal radius of r_t=0.68". We determine for the satellite a luminosity of L_B=(1.6+-0.8)10^9 L_sun, leading to a total mass-to-light ratio within the tidal radius of (M/L)_B=(17.2+-8.5) M_sun/L_sun. The central galaxy has a sub-isothermal density profile as in general is expected for group members. From the SDSS spectrum we derive for the central galaxy a velocity dispersion of sigma_kinem=380+-60 km/s within the SDSS aperture of diameter 3". The logarithmic density slope of gamma=1.7+0.25-0.30 (68% CL), derived from this measurement, is consistent within 1-sigma with the density slope of the dominant lens galaxy gamma~1.6, determined from the lens model. This paper shows how powerful pixelized lensing techniques are in detecting and constraining the properties of dwarf satellites at high redshift.

[21]  arXiv:1002.4712 [ps, pdf, other]
Title: Re-evaluating the Local Compton-thick AGN Fraction
Comments: Comments: 8 pages, 4 figures. Accepted for publication on PoS (contribution PoS(extremesky2009)012), proceedings of "The Extreme sky: Sampling the Universe above 10 keV", held in Otranto (Italy), 13-17 October 2009
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We study the NH distribution in a complete sample of 88 AGN selected in the 20-40 keV band from INTEGRAL/IBIS observations. We find that the fraction of absorbed (NH > 10^22 cm^-2) sources is 43% while Compton thick AGN comprise 7% of the sample. While these estimates are fully compatible with previous soft gamma-ray surveys, they would appear to be in contrast with results reported from an optically selected sample. This apparent difference can be explained as being due to a selection bias caused by the reduction in high energy flux in Compton thick objects rendering them invisible at our sensitivity limit. Taking this into account we estimate that the fraction of highly absorbed sources is actually in close agreement with the optically selected sample. Furthermore we show that the measured fraction of absorbed sources in our sample decreases from 80% to ~20-30% as a function of redshift with all Compton thick AGN having z<0.015. We conclude that in the low redshift bin we are seeing almost the entire AGN population, from unabsorbed to at least mildly Compton thick objects, while in the total sample we lose the heavily absorbed 'counterparts' of distant and therefore dim sources with little or no absorption. Taking therefore this low z bin as the only one able to provide the 'true' distribution of absorption in type 1 and 2 AGN, we estimate the fraction of Compton thick objects to be >24%

[22]  arXiv:1002.4714 [ps, pdf, other]
Title: Latitude migration of solar filaments
Authors: K. J. Li
Comments: 15 pages,5figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The Carte Synoptique catalogue of solar filaments from March 1919 to December 1989, corresponding to complete cycles 16 to 21 is utilized to show latitudinal migration of filaments at low latitudes (less than 50 deg), and the latitudinal drift of solar filaments in each hemisphere in each cycle of the time interval is compared with the corresponding drift of sunspot groups. The physical implication behind the latitudinal drift of filaments is explored.

[23]  arXiv:1002.4715 [ps, pdf, other]
Title: Dark Matter and Dark Energy from Gravitational Symmetry Breaking
Authors: A. Fuzfa, J.-M. Alimi
Comments: 12 pages, 3 figures, to appear in the AIP proceedings of the 'Invisible Universe International Conference', UNESCO-Paris, June 29-July 3, 2009
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

We build a mechanism of gravitational symmetry breaking (GSB) of a global U(1) symmetry based on the relaxation of the equivalence principle due to the mass variation of pseudo Nambu-Goldstone dark matter (DM) particles. This GSB process is described by the modified cosmological convergence mechanism of the Abnormally Weighting Energy (AWE) Hypothesis previously introduced by the authors. Several remarkable constraints from the Hubble diagram of far-away supernovae are derived, notably on the explicit and gravitational symmetry breaking energy scales of the model. We then briefly present some consequences on neutrino masses when this mechanism is applied to the particular case of the breaking of lepton number symmetry.

[24]  arXiv:1002.4721 [ps, pdf, other]
Title: The Abnormally Weighting Energy Hypothesis: The origin of the cosmic acceleration
Authors: J.-M. Alimi, A. Fuzfa
Comments: 10 pages, 4 figures, to appear in the AIP proceedings of the 'Invisible Universe International Conference', UNESCO-Paris, June 29-July 3, 2009
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We generalize tensor-scalar theories of gravitation by the introduction of an abnormally weighting type of energy. This theory of tensor-scalar anomalous gravity is based on a relaxation of the weak equivalence principle that is now restricted to ordinary visible matter only. As a consequence, the convergence mechanism toward general relativity is modified and produces naturally cosmic acceleration as an inescapable gravitational feedback induced by the mass-variation of some invisible sector. The cosmological implications of this new theoretical framework are studied. This glimpses at an enticing new symmetry between the visible and invisible sectors, namely that the scalar charges of visible and invisible matter are exactly opposite.

[25]  arXiv:1002.4740 [ps, pdf, other]
Title: Measuring Unified Dark Matter with 3D cosmic shear
Comments: 12 pages, 5 figures, submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present parameter estimation forecasts for future 3D cosmic shear surveys for a class of Unified Dark Matter (UDM) models, where a single scalar field mimics both Dark Matter (DM) and Dark Energy (DE). These models have the advantage that they can describe the dynamics of the Universe with a single matter component providing an explanation for structure formation and cosmic acceleration. A crucial feature of the class of UDM models we use in this work is characterized by a parameter, c_inf (c=1), that is the value of the sound speed at late times and on which structure formation depends. We demonstrate that the properties of the DM-like behaviour of the scalar field can be estimated with very high precision with large-scale, fully 3D weak lensing surveys. We found that 3D weak lensing significantly constrains c_inf, and we find minimal errors 0.00013, for the fiducial value c_inf=0.0005, and 0.0004, for c_inf=0.05. Moreover, we compute the Bayesian evidence for UDM models over the LCDM model as a function of c_inf. For this purpose, we can consider the LCDM model as a UDM model with c_inf=0. We find an interesting maximum in the Bayes factor. This is due to the peculiar dynamics of UDM models. In fact, as the value of c_inf increases, its signature in the shear signal becomes more and more evident, until the sound speed is so high that the DM-like component of the scalar field can not cluster any more, thus the shear signal starts to be damped and the evidence decreases. Moreover, the expected evidence clearly shows that the survey data would unquestionably favour UDM models over the LCDM model, if c_inf>0.0001.

[26]  arXiv:1002.4742 [ps, pdf, other]
Title: Companion stars of Type Ia supernovae and single low-mass white dwarfs
Authors: Bo Wang, Zhanwen Han
Comments: 5 pages, 5 figures, accepted for publication in MNRAS Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Recent investigations of the WD + MS channel of Type Ia supernovae (SNe Ia) imply that this channel may be the main contribution to the old population (>1Gyr) of SNe Ia. In the WD + MS channel, the WD could accrete material from a main-sequence or a slightly evolved star until it reaches the Chandrasekhar mass limit. The companions in this channel would survive after SN explosion and show distinguishing properties. In this Letter, based on SN Ia production regions of the WD + MS channel and three formation channels of WD + MS systems, we performed a detailed binary population synthesis study to obtain the properties of the surviving companions. The properties can be verified by future observations. We find that the surviving companions of the old SNe Ia have a low mass, which provides a possible way to explain the formation of the population of single low-mass WDs (<0.45Msun).

[27]  arXiv:1002.4745 [ps, pdf, other]
Title: Power Asymmetries in the Cosmic Microwave Background Temperature and Polarization patterns
Comments: 8 pages, 13 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We test the asymmetry of the Cosmic Microwave Background anisotropy jointly in temperature and polarization. We study the hemispherical asymmetry, previously found only in the temperature field, with respect to the axis identified by Hansen et al. (2009). To this extent, we make use of the low resolution WMAP 5 year temperature and polarization Nside=16 maps and the optimal angular power spectrum estimator BolPol (Gruppuso et al. 2009). We consider two simple estimators for the power asymmetry and we compare our findings with Monte Carlo simulations which take into account the full noise covariance matrix. We confirm an excess of power in temperature angular power spectrum in the Southern hemisphere at a significant level, between 3 'sigma' and 4 'sigma' depending on the exact range of multipoles considered. We find a milder excess of power in the gradient (curl) component EE (BB) of polarized angular spectra in the Northern (Southern) hemisphere: this asymmetry is less significant level than the temperature one, and is evident only at low multipoles where the signal-to-noise ratio is larger. We do not find any significant hemispherical asymmetry in the cross-correlation power spectra, i.e. TE up to l=32, TB, EB for any multipoles. We also show that the Cold Spot found by Vielva et al. (2004) in the Southern Galactic hemisphere does not alter the significance of the hemispherical asymmetries on multipoles which can be probed by maps at resolution Nside=16. Although the origin of the hemispherical asymmetry in temperature remains unclear, the study of the polarization patter could add useful information on its explanation. We therefore forecast by Monte Carlo the Planck capabilities in probing polarization asymmetries.

[28]  arXiv:1002.4752 [ps, pdf, other]
Title: Pulsation Models for Ultra-Low (Z=0.0004) Metallicity Classical Cepheids
Comments: accepted for publication on ApJ. Table3 is in a separate file because it will appear only in electronic form. Figures 11 and 14 are separate gif files for size reasons
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Classical Cepheids are primary distance indicators playing a fundamental role in the calibration of the extragalactic distance scale. The possible dependence of their characteristic Period-Luminosity (PL) relation on chemical composition is still debated in the literature, and the behaviour of these pulsators at very low metallicity regimes is almost unexplored. In order to derive constraints on the application of the Period-Luminosity relation at low metal abundances, we investigate the properties of the few ultra-low metallicity (Z ~ 0.0004) Cepheids recently discovered in the Blue Compact Dwarf galaxy IZw18. To this purpose we have computed an updated and extended set of nonlinear convective models for Z=0.0004 and Y=0.24, spanning a wide range of stellar masses, and taking into account the evolutionary constraints for selected luminosity levels. As a result we are able to predict the topology of the instability strip, the variations of all the relevant quantities along the pulsation cycle, including the morphology of the light curves, the theoretical Period-Luminosity-Color, Period-Wesenheit and Period-Luminosity relations at such a low metallicity. For each of these relations we provide the appropriate coefficients for fundamental mode pulsators with Z=0.0004. By comparing these results with the properties of more metal rich Cepheids we find that the synthetic PL relations for Z=0.0004 are steeper than at higher Z, but similar to the Z=0.004 ones, thus suggesting a leveling off of the metallicity effect towards the lowest Zs.

[29]  arXiv:1002.4765 [ps, pdf, other]
Title: Non-Minimally Gravity-Coupled Inflationary Models
Authors: C. Pallis
Comments: 15 pages, 4 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

We consider the non-supersymmetric models of chaotic (driven by a quadratic potential) and hybrid inflation, taking into account the minimal possible radiative corrections to the inflationary potential. We show that two simple coupling functions $f(\sg)$ (with a parameter $\cR$ involved) between the inflaton field $\sg$ and the Ricci scalar curvature ensure, for sub-Planckian values of the inflaton field, observationally acceptable values for the spectral index, $\ns$, and sufficient reheating after inflation. In the case of chaotic inflation we take $625<\cR<2.1\cdot10^7$ resulting to $\ns=0.955$ and tensor-to-scalar ratio $r=0.2$. In the case of hybrid inflation, the selected $f(\sg)$ assists us to obtain hilltop-type inflation. For values of the relevant mass parameter, m, less than $10^6 \TeV$ and the observationally central value of $\ns$, we find $\cR=(0.015-0.078)$ with the relevant coupling constants $\lambda=\kappa$ and the symmetry breaking scale, $M$, confined in the ranges $(2\cdot 10^{-7}-0.001)$ and $(1-16.8)\cdot10^{17} \GeV$, respectively.

[30]  arXiv:1002.4777 [ps, pdf, other]
Title: The value of the fine structure constant over cosmological times
Comments: 22 pages, 10 figures. Accepted for publication in Astrophysical Journal
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The optical spectra of objects classified as QSOs in the SDSS DR6 are analyzed with the aim of determining the value of the fine structure constant in the past and then check for possible changes in the constant over cosmological timescales. The analysis is done by measuring the position of the fine structure lines of the [OIII] doublet (4959 and 5008) in QSO nebular emission. From the sample of QSOs at redshifts z < 0.8 a subsample was selected on the basis of the amplitude and width of the [OIII] lines. Two different method were used to determine the position of the lines of the [OIII] doublet, both giving similar results. Using a clean sample containing 1568 of such spectra, a value of Delta alpha /alpha=(+2.4 +-2.5) x 10^{-5} (in the range of redshifts 0-0.8) was determined. The use of a larger number of spectra allows a factor ~5 improvement on previous constraints based on the same method. On the whole, we find no evidence of changes in alpha on such cosmological timescales. The mean variation compatible with our results is 1/ <t> Delta alpha/alpha=(+0.7 +- 0.7) x 10^{-14} yr^{-1}. The analysis was extended to the [NeIII] and [SII] doublets, although their usefulness is limited due to the fact that all these doublets in QSOs tend to be fainter than [OIII], and that some of them are affected by systematics.

[31]  arXiv:1002.4778 [ps, pdf, other]
Title: Gamma ray flares from Mrk421 in 2008 observed with the ARGO-YBJ detector
Authors: G.Aielli et al. (ARGO-YBJ Collaboration)
Comments: Accepted for publication on ApJL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

In 2008 the blazar Markarian 421 entered a very active phase and was one of the brightest sources in the sky at TeV energies, showing frequent flaring episodes. Using the data of ARGO-YBJ, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at gamma ray energies E > 0.3 TeV during the whole year. The observed flux was variable, with the strongest flares in March and June, in correlation with X-ray enhanced activity. While during specific episodes the TeV flux could be several times larger than the Crab Nebula one, the average emission from day 41 to 180 was almost twice the Crab level, with an integral flux of (3.6 +-0.6) 10^-11 photons cm^-2 s^-1 for energies E > 1 TeV, and decreased afterwards.
This paper concentrates on the flares occurred in the first half of June. This period has been deeply studied from optical to 100 MeV gamma rays, and partially up to TeV energies, since the moonlight hampered the Cherenkov telescope observations during the most intense part of the emission. Our data complete these observations, with the detection of a signal with a statistical significance of 3.8 standard deviations on June 11-13, corresponding to a gamma ray flux about 6 times larger than the Crab one above 1 TeV. The reconstructed differential spectrum, corrected for the intergalactic absorption, can be represented by a power law with an index alpha = -2.1 extending up to several TeV. The spectrum slope is fully consistent with previous observations reporting a correlation between the flux and the spectral index, suggesting that this property is maintained in different epochs and characterizes the source emission processes.

[32]  arXiv:1002.4779 [ps, pdf, other]
Title: Applicability of the linearly perturbed FRW metric and Newtonian cosmology
Authors: Syksy Rasanen
Comments: 23 pages
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

It has been argued that the effect of cosmological structure formation on the average expansion rate is negligible, because the linear approximation to the metric remains applicable in the regime of non-linear density perturbations. We discuss why the arguments based on the linear theory are not valid. We emphasise the difference between Newtonian gravity and the weak field, small velocity limit of general relativity in the cosmological setting.

[33]  arXiv:1002.4782 [ps, pdf, other]
Title: Prospects for Very High Energy Blazar Survey by the Next Generation Cherenkov Telescopes
Authors: Yoshiyuki Inoue, Tomonori Totani (Kyoto), Masaki Mori (Ritsumeikan)
Comments: 11 pages, 11 figures, submitted to PASJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The prospects for future blazar surveys by next-generation very high energy (VHE) gamma-ray telescopes, such as Advanced Gamma-ray Imaging System (AGIS) and Cherenkov Telescope Array (CTA), are investigated using the latest model of blazar luminosity function and its evolution which is in good agreement with the flux and redshift distribution of observed blazars as well as the extragalactic gamma-ray background. We extend and improve the template of spectral energy distributions (SEDs) based on the blazar SED sequence paradigm, to make it reliable also in the VHE bands (above 100 GeV) by comparing with the existing VHE blazar data. Assuming the planned CTA sensitivities, a blind survey using a total survey time of ~100 hrs could detect ~3 VHE blazars, with larger expected numbers for wider/shallower surveys. We also discuss following-up of Fermi blazars. Detectability of VHE blazars in the plane of Fermi flux and redshift is presented, which would be useful for future survey planning. Prospects and strategies are discussed to constrain the extragalactic background light (EBL) by using the absorption feature of brightest blazar spectra, as well as cut-offs in the redshift distribution. We will be able to get useful constraints on EBL by VHE blazars at different redshifts ranging 0.3-1 TeV corresponding to z=0.10-0.36.

[34]  arXiv:1002.4785 [ps, pdf, other]
Title: Gravitons production in a new type of GCG
Comments: 3 pages, 2 figures. To appear in the proceedings of 12th Marcel Grossmann Meeting, Paris (France)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

A new scenario for the early era of the Universe is proposed. It corresponds to a smooth transition between a de Sitter-like phase and a radiation dominated era. We calculate the production of gravitons in this model.

[35]  arXiv:1002.4810 [ps, pdf, other]
Title: From super-charged nuclei to massive nuclear density cores
Authors: Vladimir Popov
Comments: To appear in the proceedings of the international conference "The Sun, the Stars, The Universe and General Relativity" in honor of Ya.B. Zeldovich 95th Anniversary, held in Minsk, Belarus on April 20-23, 2009. AIP Conf. Proc. Vol. 1205 (2010)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)

Due to $e^+e^-$-pair production in the field of supercritical $(Z \gg Z_{cr}\approx 170 $) nucleus an electron shell, created out of the vacuum, is formed. The distribution of the vacuum charge in this shell has been determined for super-charged nuclei $Ze^3 \ga 1$ within the framework of the Thomas-Fermi equation generalized to the relativistic case. For $Ze^3 \gg 1$ the electron shell penetrates inside the nucleus and almost completely screens its charge. Inside such nucleus the potential takes a constant value equal to $V_0=-(3\pi^2 n_p)^{1/3} \sim -2m_{\pi}c^2$, and super-charged nucleus represents an electrically neutral plasma consisting of $e,p$ and $n$. Near the edge of the nucleus a transition layer exists with a width $\lambda \approx \alpha^{-1/2} \hbar/m_{\pi} c\sim 15$ fm, which is independent of $Z~~ (\hbar/m_{\pi} c \ll \lambda \ll \hbar/m_e c)$. The electric field and surface charge are concentrated in this layer. These results, obtained earlier for hypothetical superheavy nuclei with $Z \sim A/2\la 10^4 \div 10^6$, are extrapolated to massive nuclear density cores having a mass number $A \approx (m_{Planck}/m_n)\sim 10^{57}$. The problem of the gravitational and electrodynamical stability of such objects is considered. It is shown that for $A \ga 0.04 (Z/A)^{1/2}(m_{Planck}/m_n)^3$ the Coulomb repulsion of protons, screened by relativistic electrons, can be balanced by gravitational forces. The overcritical electric fields $E\sim m^2_{\pi} c^3/e\hbar$ are present in the narrow transition layer near the core surface.

[36]  arXiv:1002.4811 [ps, pdf, other]
Title: Suzaku Observation of Abell 1689: Anisotropic Temperature and Entropy Distributions Associated with the Large-Scale Structure
Comments: 24 pages, 15 figures, 9 tables. Accepted for publication in ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

(Abridged) We present results of Suzaku observations of the intracluster medium (ICM) in Abell 1689, combined with complementary analysis of the SDSS data and weak and strong lensing analysis of Subaru/Suprime-Cam and HST/ACS observations. Faint X-ray emission from the ICM around the virial radius is detected at 4.0 sigma significance. We find anisotropic gas temperature and entropy distributions in cluster outskirts correlated with large-scale structure of galaxies. The high temperature and entropy region in the northeastern (NE) outskirts is connected to an overdense filamentary structure. The outskirt regions in contact with low density void environments have low gas temperatures and entropies, deviating from hydrostatic equilibrium. These results suggest that thermalization of the ICM occurs faster along the filamentary structures than the void regions. A joint X-ray and lensing analysis shows that the hydrostatic mass is $\sim60-90%$ of spherical lensing one but comparable to a triaxial halo mass within errors in $0.6r_{2500} \simlt r \simlt 0.8r_{500}$, and that it is significantly biased as low as $\simlt60%$ within $0.4r_{2500}$, irrespective of mass models. The thermal gas pressure within $r_{500}$ is, at most, $\sim50$--60% of the total pressure to balance fully the gravity of the spherical lensing mass, and $\sim30$--40% around the virial radius. Although these constitute lower limits when one considers the possible halo triaxiality, these small relative contributions of thermal pressure would require additional sources of pressure, such as bulk and/or turbulent motions.

[37]  arXiv:1002.4815 [pdf, other]
Title: A study of the interacting binary V 393 Scorpii
Comments: 13 pages, 14 figures, 7 tables. Accepted for publication in MNRAS, main journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present high resolution J-band spectroscopy of V 393 Sco obtained with the CRIRES at the ESO Paranal Observatory along with a discussion of archival IUE spectra and published broad band magnitudes. The best fit to the spectral energy distribution outside eclipse gives $T_{1}$= 19000 $\pm$ 500 $K$ for the gainer, $T_{2}$= 7250 $\pm$ 300 $K$ for the donor, $E(B-V)$= 0.13 $\pm$ 0.02 mag. and a distance of $d$= 523 $\pm$ 60 pc, although circumstellar material was not considered in the fit. We argue that V 393 Sco is not a member of the open cluster M7. The shape of the He I 1083 nm line shows orbital modulations that can be interpreted in terms of an optically thick pseudo-photosphere mimicking a hot B-type star and relatively large equatorial mass loss through the Lagrangian L3 point during long cycle minimum. IUE spectra show several (usually asymmetric) absorption lines from highly ionized metals and a narrow L$\alpha$ emission core on a broad absorption profile. The overall behavior of these lines suggests the existence of a wind at intermediate latitudes. From the analysis of the radial velocities we find $M_{2}/M_{1}$= 0.24 $\pm$ 0.02 and a mass function of $f$= 4.76 $\pm$ 0.24 M$\odot$. Our observations favor equatorial mass loss rather than high latitude outflows as the cause for the long variability.

[38]  arXiv:1002.4819 [ps, pdf, other]
Title: Impact regimes and post-formation sequestration processes: implications for the origin of heavy noble gases in terrestrial planets
Comments: Accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The difference between the measured atmospheric abundances of neon, argon, krypton and xenon for Venus, the Earth and Mars is striking. Because these abundances drop by at least two orders of magnitude as one moves outward from Venus to Mars, the study of the origin of this discrepancy is a key issue that must be explained if we are to fully understand the different delivery mechanisms of the volatiles accreted by the terrestrial planets. In this work, we aim to investigate whether it is possible to quantitatively explain the variation of the heavy noble gas abundances measured on Venus, the Earth and Mars, assuming that cometary bombardment was the main delivery mechanism of these noble gases to the terrestrial planets. To do so, we use recent dynamical simulations that allow the study of the impact fluxes of comets upon the terrestrial planets during the course of their formation and evolution. Assuming that the mass of noble gases delivered by comets is proportional to rate at which they collide with the terrestrial planets, we show that the krypton and xenon abundances in Venus and the Earth can be explained in a manner consistent with the hypothesis of cometary bombardment. In order to explain the krypton and xenon abundance differences between the Earth and Mars, we need to invoke the presence of large amounts of CO2-dominated clathrates in the Martian soil that would have efficiently sequestered these noble gases.

[39]  arXiv:1002.4823 [pdf]
Title: Revealing the First Stellar and Supermassive Black Holes to EXIST
Comments: 6 pages, 4 figures. Invited talk at conference "X-ray Astronomy 2009: Present status, multiwavelength approach and future perspectives", September 2009, Bologna. To appear in AIP Conf. Proc. (editors: A. Comastri, M. Cappi, L. Angelini)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)

The epochs of origin of the first stars and galaxies, and subsequent growth of the first supermassive black holes, are among the most fundamental questions. Observations of the highest redshift Gamma-Ray Bursts (GRBs) will be the most compelling in situ probe of the history of initial star formation and consequent epoch of reionization if their prompt and precise detection can be followed immediately by sensitive near-IR imaging and spectroscopy. Blazars are the persistent analogs of GRBs and for the same reason (beaming) can be observed at highest redshifts where they might best trace the high accretion rate-driven jets and growth of supermassive black holes in galaxies. The proposed EXIST mission can uniquely probe these questions, and many others, given its unparalled combination of sensitivity and spatial-spectral-temporal coverage and resolution. Here we provide a brief summary of the mission design, key science objectives, mission plan and readiness for EXIST, as proposed to Astro2010.

[40]  arXiv:1002.4840 [pdf]
Title: Cosmic Ray Accelerators in the Large Magellanic Cloud
Authors: Yousaf M. Butt
Comments: Research Note
Subjects: Galaxy Astrophysics (astro-ph.GA)

I point out a correlation between gamma-ray emissivity and the historical star formation rate in the Large Magellanic Cloud ~12.5 Myr ago. This correlation bolsters the view that CRs in the LMC are accelerated by conglomerations of supernova remnants: i.e. superbubbles and supergiant shells.

[41]  arXiv:1002.4849 [ps, pdf, other]
Title: Simulation of radio emission from air showers in atmospheric electric fields
Authors: S. Buitink (1 and 2), T. Huege (3), H. Falcke (2), J. Kuijpers (2) ((1) Lawrence Berkeley National Laboratory, (2) Radboud University Nijmegen, Netherlands, (3) Karlsruher Institut fuer Technologie, Germany)
Comments: 26 pages, 12 figures, accepted for publication in Astroparticle Physics
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We study the effect of atmospheric electric fields on the radio pulse emitted by cosmic ray air showers. Under fair weather conditions the dominant part of the radio emission is driven by the geomagnetic field. When the shower charges are accelerated and deflected in an electric field additional radiation is emitted. We simulate this effect with the Monte Carlo code REAS2, using CORSIKA-simulated showers as input. In both codes a routine has been implemented that treats the effect of the electric field on the shower particles. We find that the radio pulse is significantly altered in background fields of the order of ~100 V/cm and higher. Practically, this means that air showers passing through thunderstorms emit radio pulses that are not a reliable measure for the shower energy. Under other weather circumstances significant electric field effects are expected to occur rarely, but nimbostratus clouds can harbor fields that are large enough. In general, the contribution of the electric field to the radio pulse has polarization properties that are different from the geomagnetic pulse. In order to filter out radio pulses that have been affected by electric field effects, radio air shower experiments should keep weather information and perform full polarization measurements of the radio signal.

[42]  arXiv:1002.4856 [ps, pdf, other]
Title: The High-Density Ionized Gas in the Central Parsecs of the Galaxy
Comments: 4 pages, 2 figures
Subjects: Galaxy Astrophysics (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We report the results from observations of H30$\alpha$ line emission in Sgr A West with the Submillimeter Array at a resolution of 2\arcsec and a field of view of about 40\arcsec. The H30$\alpha$ line is sensitive to the high-density ionized gas in the minispiral structure. We compare the velocity field obtained from H30$\alpha$ line emission to a Keplerian model, and our results suggest that the supermassive black hole at Sgr A* dominates the dynamics of the ionized gas. However, we also detect significant deviations from the Keplerian motion, which show that the impact of strong stellar winds from the massive stars along the ionized flows and the interaction between Northern and Eastern arms play significant roles in the local gas dynamics.

[43]  arXiv:1002.4864 [ps, pdf, other]
Title: Photometric determination of the mass accretion rates of pre-main sequence stars. I. Method and application to the SN1987A field
Comments: 18 pages, 18 figures, accepted for publication in the Astrophysical Journal
Subjects: Galaxy Astrophysics (astro-ph.GA)

We have developed and successfully tested a new self-consistent method to reliably identify pre-main sequence (PMS) objects actively undergoing mass accretion in a resolved stellar population, regardless of their age. The method does not require spectroscopy and combines broad-band V and I photometry with narrow-band Halpha imaging to: (1) identify all stars with excess Halpha emission; (2) derive their Halpha luminosity L(Halpha); (3) estimate the Halpha emission equivalent width; (4) derive the accretion luminosity L_acc from L(Halpha); and finally (5) obtain the mass accretion rate M_acc from L_acc and the stellar parameters (mass and radius). By selecting stars with photometric accuracy in Halpha better than 15%, the statistical uncertainty on the derived M_acc is typically <17% and is dictated by the precision of the Halpha photometry. Systematic uncertainties, of up to a factor of 3 on the value of M_acc, are caused by our incomplete understanding of the physics of the accretion process and affect all determinations of the mass accretion rate, including those based on a spectroscopic Halpha line analysis.
As an application of our method, we study a field of 9.16 arcmin2 around SN1987A, using existing HST photometry. We identify as bona-fide PMS stars a total of 133 objects with a Halpha excess above the 4 sigma level and a median age of 13.5 Myr. Their median mass accretion rate of 2.6x10-8 Msolar/yr is in excellent agreement with previous determinations based on the U-band excess of the stars in this field, and with the value measured for G-type PMS stars in the Milky Way. Their L_acc shows a strong dependence on their distance from a group of hot massive stars in the field and suggests that the UV radiation of the latter is rapidly eroding the circumstellar discs around PMS stars.

[44]  arXiv:1002.4866 [ps, pdf, other]
Title: New Star Forming Galaxies at $z\approx 7$ from WFC3 Imaging
Comments: to be submitted to MNRAS, comments welcome
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The addition of Wide Field Camera 3 (WFC3) on the {\em Hubble Space Telescope} ({\em HST}) has led to a dramatic increase in our ability to study the $z>6$ Universe. The increase in the near-infrared (NIR) sensitivity of WFC3 over previous instruments has enabled us to reach apparent magnitudes approaching 29 (AB). This allows us to probe the rest-frame ultraviolet (UV) continuum, redshifted into the NIR at $z>6$. Taking advantage of the large optical depths at this redshift, resulting in the Lyman-$\alpha$ break, we use a combination of WFC3 imaging and pre-existing Advanced Camera for Surveys (ACS) imaging to search for $z\approx 7$ over 4 fields. Our analysis reveals 29 new $z\approx 7$ star forming galaxy candidates in addition to 16 pre-existing candidates already discovered in these fields. The improved statistics from our doubling of the robust sample of $z$-drop candidates confirms the previously observed evolution of the bright end of the luminosity function.

[45]  arXiv:1002.4869 [ps, pdf, other]
Title: Reconciliation of Waiting Time Statistics of Solar Flares Observed in Hard X-Rays
Comments: Preprint also available at this http URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We study the waiting time distributions of solar flares observed in hard X-rays with ISEE-3/ICE, HXRBS/SMM, WATCH/GRANAT, BATSE/CGRO, and RHESSI. Although discordant results and interpretations have been published earlier, based on relatively small ranges ($< 2$ decades) of waiting times, we find that all observed distributions, spanning over 6 decades of waiting times ($\Delta t \approx 10^{-3}- 10^3$ hrs), can be reconciled with a single distribution function, $N(\Delta t) \propto \lambda_0 (1 + \lambda_0 \Delta t)^{-2}$, which has a powerlaw slope of $p \approx 2.0$ at large waiting times ($\Delta t \approx 1-1000$ hrs) and flattens out at short waiting times $\Delta t \lapprox \Delta t_0 = 1/\lambda_0$. We find a consistent breakpoint at $\Delta t_0 = 1/\lambda_0 = 0.80\pm0.14$ hours from the WATCH, HXRBS, BATSE, and RHESSI data. The distribution of waiting times is invariant for sampling with different flux thresholds, while the mean waiting time scales reciprocically with the number of detected events, $\Delta t_0 \propto 1/n_{det}$. This waiting time distribution can be modeled with a nonstationary Poisson process with a flare rate $\lambda=1/\Delta t$ that varies as $f(\lambda) \propto \lambda^{-1} \exp{-(\lambda/\lambda_0)}$. This flare rate distribution represents a highly intermittent flaring productivity in short clusters with high flare rates, separated by quiescent intervals with very low flare rates.

[46]  arXiv:1002.4870 [ps, pdf, other]
Title: Jeans Instability of Palomar 5's Tidal Tail
Authors: Alice C. Quillen, Justin Comparetta (Rochester)
Comments: sumbmitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

Tidal tails composed of stars should be unstable to the Jeans instability and this can cause them to look like beads on a string. The Jeans wavelength and tail diameter determine the wavelength and growth rate of the fastest growing unstable mode. Consequently the distance along the tail to the first clump and spacing between clumps can be used to estimate the mass density in the tail and its longitudinal velocity dispersion. Clumps in the tidal tails of the globular cluster Palomar 5 could be due to Jeans instability. We find that their spacing is consistent with the fastest growing mode if the velocity dispersion in the tail is similar to that in the cluster itself. While all tidal tails should exhibit gravitational instability, we find that clusters or galaxies with low concentration parameters are most likely to exhibit short wavelength rapidly growing Jeans modes in their tidal tails.

Cross-lists for Fri, 26 Feb 10

[47]  arXiv:0906.2042 (cross-list from gr-qc) [ps, pdf, other]
Title: The Riemannian Penrose inequality and a virtual gravitational collapse
Comments: 4pages, minor changes, accepted for publication in Physical Review D
Journal-ref: Phys.Rev.D80:047501,2009
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th); Differential Geometry (math.DG)

We reinterpret the proof of the Riemannian Penrose inequality by H. Bray. The modified argument turns out to have a nice feature so that the flow of Riemannian metrics appearing Bray's proof gives a Lorentzian metric of a spacetime. We also discuss a possible extension of our approach to charged black holes.

[48]  arXiv:1002.4032 (cross-list from hep-ph) [ps, pdf, other]
Title: Formation of the Q ball in the thermal logarithmic potential and its properties
Authors: Shinta Kasuya
Comments: 5 pages, 3 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We investigate the Q-ball formation in the thermal logarithmic potential by means of the lattice simulation, and reconfirm qualitatively the relation between Q-ball charge and the amplitude of the Affleck-Dine field at the onset of its oscillation. We find time dependence of some properties of the Q ball, such as its size and the field value at its center. Since the thermal logarithmic potential decreases as the temperature falls down, the gravity-mediation potential will affect the properties of the Q ball. Even in the case when the gravity-mediation potential alone does not allow Q-ball solution, we find the transformation from the thich-wall type of the Q ball to the thin-wall type, contrary to the immediate destruction of the Q balls when the gravity-mediation potential becomes dominant at the center of the Q ball, mentioned in the literature.

[49]  arXiv:1002.4035 (cross-list from gr-qc) [ps, pdf, other]
Title: When scalar field is kinetically coupled to the Einstein tensor
Authors: Changjun Gao
Comments: 11 pages, 16 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

We explore the cosmic evolution of a scalar field when the kinetic term is coupled to the Einstein tensor. When the kinetic term is coupled to one Einstein tensor, we find that in the absence of other matter sources or in the presence of pressureless matter, the scalar would behave as the pressureless matter. This enables the scalar field to be the candidate of cold dark matter. By taking into account of a scalar potential in this case, we find the scalar field may play the role of both dark matter and dark energy. For sufficiently small exponential potential parameter $\zeta$, the equation of state of the scalar is $w\simeq -1$ in the total history of the Universe. We also find that the equation of state for the scalar can cross the phantom divide. But due to the kinetic energy is always positive, the scalar field is stable to classically perturbations. On the other hand, if the kinetic term is coupled to many more Einstein tensors, we find the equation of state is always approximately equals to -1 regardless whether the potential is flat or not. Thus the scalar may also be the candidate of inflaton field.

[50]  arXiv:1002.4568 (cross-list from hep-th) [ps, pdf, other]
Title: Gravity as Quantum Entanglement Force
Comments: 7 pages, 1 figure, revtex4-1
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); Quantum Physics (quant-ph)

We conjecture that quantum entanglement of matter and vacuum in the universe tend to increase with time, like entropy, and there is an effective force called quantum entanglement force associated with this tendency. It is also suggested that gravity and dark energy are types of the quantum entanglement force, similar to Verlinde's entropic force. If the entanglement entropy of the universe saturates the Bekenstein bound, this gives holographic dark energy with the equation of state consistent with current observational data. This connection between quantum information and gravity gives some new insights on the origin of gravity, dark energy, the holographic principle and arrow of time.

[51]  arXiv:1002.4585 (cross-list from gr-qc) [ps, pdf, other]
Title: Effects of standard and modified gravity on interplanetary ranges
Authors: Lorenzo Iorio
Comments: LaTex, 56 pages, 39 figures, no tables, 39 references. Abridged version: 5 figures not included for saving space. They are those on the action of Ceres, Pallas, Vesta on all the four ranges, and of X on Mercury
Subjects: General Relativity and Quantum Cosmology (gr-qc); Earth and Planetary Astrophysics (astro-ph.EP); High Energy Physics - Phenomenology (hep-ph)

We numerically investigate the impact on the two-body range by several Newtonian and non-Newtonian dynamical effects for some Earth-planet pairs in view of the expected cm-level accuracy in future planned or proposed interplanetary ranging operations. The general relativistic gravitomagnetic Lense-Thirring effect should be modeled and solved-for in future, accurate ranging tests of Newtonian and post-Newtonian gravity because it falls within their measurability domain. It could a-priori "imprint" the determination of some of the target parameters of the tests considered. Moreover, the ring of the minor asteroids, Ceres, Pallas, Vesta and the Trans-Neptunian Objects (TNOs) act as sources of non-negligible systematic uncertainty on the larger gravitoelectric post-Newtonian signals from which it is intended to determine the parameters \gamma and \beta of the Parameterized Post Newtonian (PPN) formalism with very high precision (orders of magnitude better than the current 10^-4-10^-5 levels). Also other putative, non-conventional gravitational effects like a violation of the Strong Equivalence Principle (SEP), a secular variation of the Newtonian constant of gravitation G, and the Pioneer anomaly are considered. The presence of a hypothetical, distant planetary-sized body X could be detectable with future high-accuracy planetary ranging. Our analysis can, in principle, be extended also to future interplanetary ranging scenarios in which one or more spacecraft in heliocentric orbits are involved.

[52]  arXiv:1002.4596 (cross-list from gr-qc) [ps, pdf, other]
Title: A-priori "imprinting" of General Relativity itself on some tests of it?
Authors: Lorenzo Iorio
Comments: LaTex, 11 pages, no figures, no tables. Accepted in Advances in Astronomy
Journal-ref: Advances in Astronomy Volume 2010 (2010), Article ID 735487
Subjects: General Relativity and Quantum Cosmology (gr-qc); Earth and Planetary Astrophysics (astro-ph.EP); High Energy Physics - Phenomenology (hep-ph); Space Physics (physics.space-ph)

We investigate the effect of possible a-priori "imprinting" effects of general relativity itself on satellite/spaceraft-based tests of it. We deal with some performed or proposed time-delay ranging experiments in the Sun's gravitational field. It turns out that the "imprint" of general relativity on the Astronomical Unit and the solar gravitational constant GM_{\odot}, not solved for in the so far performed spacecraft-based time-delay tests, induces an a-priori bias of the order of 10^-6 in typical solar system ranging experiments aimed to measuring the space curvature PPN parameter gamma. It is too small by one order of magnitude to be of concern for the performed Cassini experiment, but it would affect future planned or proposed tests aiming to reach a 10^-7-10^-9 accuracy in determining gamma.

[53]  arXiv:1002.4650 (cross-list from physics.gen-ph) [ps, pdf, other]
Title: Cahill's Cosmological Model Exacerbates The Primordial Lithium Problem And Creates New Problems For Primordial Deuterium And Helium
Authors: Gary Steigman
Comments: 3 pages, no figures
Subjects: General Physics (physics.gen-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

In a recent article R. T. Cahill claims that the cosmological model based on his "new physics of a dynamical 3-space" resolves the CMB-BBN Lithium-7 and Helium-4 abundance anomalies. In this note it is shown that this conclusion is wrong, resulting from a misunderstanding. In fact, primordial nucleosynthesis in this non-standard cosmological model exacerbates the LIthium-7 problem and creates new problems for primordial Helium-4 and Deuterium.

[54]  arXiv:1002.4655 (cross-list from hep-ph) [pdf]
Title: FLUKA as a new high energy cosmic ray generator
Comments: Presented by A.Margiotta at the Very Large Volume neutrino Telescope Workshop 2009 - VLVnT09, Athens, October 2009. 3 pages, 1 figure. To be published in NIM A
Subjects: High Energy Physics - Phenomenology (hep-ph); Instrumentation and Methods for Astrophysics (astro-ph.IM)

FLUKA is a multipurpose Monte Carlo code, which can transport particles over a wide range of energies in user-defined geometries. Here we present a new FLUKA library, which allows the interaction and propagation of high energy cosmic rays in the Earth atmosphere and the transport of high energy muons in underground/underwater environments

[55]  arXiv:1002.4670 (cross-list from physics.class-ph) [ps, pdf, other]
Title: Classical Scaling Symmetry Implies Useful Nonconservation Laws
Comments: 17 pages, 5 figures
Subjects: Classical Physics (physics.class-ph); Solar and Stellar Astrophysics (astro-ph.SR)

Scaling symmetries of the Euler-Lagrange equations are generally not variational symmetries of the action and do not lead to conservation laws. Nevertheless, by an extension of Noether's theorem, scaling symmetries lead to useful {\em nonconservation} laws, which still reduce the Euler-Lagrange equations to first order in terms of scale invariants. We illustrate scaling symmetry dynamically and statically. Applied dynamically to systems of bodies interacting via central forces, the nonconservation law is Lagrange's identity, leading to generalized virial laws. Applied to self-gravitating spheres in hydrostatic equilibrium, the nonconservation law leads to well-known properties of polytropes describing degenerate stars and chemically homogeneous nondegenerate stellar cores.

Replacements for Fri, 26 Feb 10

[56]  arXiv:0811.3979 (replaced) [ps, pdf, other]
Title: The Distance, Mass, and Radius of the Neutron Star in 4U 1608-52
Comments: ApJ in print. Resulting probability distributions of our measurements can be found at this http URL
Subjects: Astrophysics (astro-ph)
[57]  arXiv:0901.0915 (replaced) [ps, pdf, other]
Title: A top-heavy stellar initial mass function in starbursts as an explanation for the high mass-to-light ratios of ultra compact dwarf galaxies
Comments: 17 pages, 5 figures, accepted for publication in MNRAS. Typo in equation 14 corrected. No consequences for the rest of the paper
Subjects: Galaxy Astrophysics (astro-ph.GA)
[58]  arXiv:0902.3232 (replaced) [ps, pdf, other]
Title: Large-scale peculiar motions and cosmic acceleration
Comments: Revised approach, discussion and references. To appear in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
[59]  arXiv:0906.3681 (replaced) [ps, pdf, other]
Title: Gamma-ray detection from gravitino dark matter decay in the $\mu\nu$SSM
Comments: Final version to appear in JCAP, 13 pages, 3 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE)
[60]  arXiv:0907.3271 (replaced) [ps, pdf, other]
Title: High-Redshift Clumpy Disks and Bulges in Cosmological Simulations
Comments: improved version: more details added, main conclusions unchanged. 20 pages, 12 figures, accepted in MNRAS. Movies can be found at this http URL
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[61]  arXiv:0907.4192 (replaced) [src]
Title: Testing Radiation Pressure Corrections to Reverberation Mapping Masses
Authors: Christopher A. Onken (Mount Stromlo Observatory)
Comments: This paper has been withdrawn
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[62]  arXiv:0909.4145 (replaced) [ps, pdf, other]
Title: Formation and Evolution of Dust in Type IIb Supernova with Application to the Cassiopeia A Supernova Remnant
Comments: 50 pages, 17 figures, 3 tables. Accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[63]  arXiv:0911.5340 (replaced) [ps, pdf, other]
Title: $\nu$MSSM superpotential to 6th order - normalised and with no superfluous couplings
Authors: Anders Basboll
Comments: 10 pages. v2+v3+v4: typos corrected. v3: small expansion of section IIB
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[64]  arXiv:0912.0585 (replaced) [ps, pdf, other]
Title: Lepton Flavor Violation and Cosmological Constraints on R-parity Violation
Comments: 21 pages, 7 figures. v2: minor changes
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
[65]  arXiv:1001.4585 (replaced) [ps, pdf, other]
Title: Modified Entropic Force
Authors: Changjun Gao
Comments: 4 pages, 2 figures
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
[66]  arXiv:1002.2729 (replaced) [ps, pdf, other]
Title: Pulsating Components in Binary and Multiple Stellar Systems -- A Catalog of Oscillating Binaries
Authors: A.-Y. Zhou
Comments: Major updates. 38 pages, 3 figures. Extended contribution talk
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[67]  arXiv:1002.3529 (replaced) [ps, pdf, other]
Title: Electronic spectroscopy of medium-sized polycyclic aromatic hydrocarbons: Implications for the carriers of the 2175 Å UV bump
Comments: 6 pages, 4 Postscript figures, published in Astrophys. J. Lett. (2010)
Journal-ref: M. Steglich et al 2010 ApJ 712 L16-L20
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
[68]  arXiv:1002.3775 (replaced) [ps, pdf, other]
Title: New method for the time calibration of an interferometric radio antenna array
Comments: 9 pages, 9 figures, 1 table, pre-print of article published in Nuclear Inst. and Methods in Physics Research, A, available at: this http URL
Journal-ref: F.G. Schroeder, et al., Nucl. Instr. and Meth. A (2010)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE)
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