We study the evolution of the scaling relations between maximum circular velocity, stellar mass and optical half-light radius of star-forming disk-dominated galaxies in the context of LCDM-based galaxy formation models. Using data from the literature combined with new data from the DEEP2 and AEGIS surveys we show that there is a consistent observational and theoretical picture for the evolution of these scaling relations from z\sim 2 to z=0. The evolution of the observed stellar scaling relations is weaker than that of the virial scaling relations of dark matter haloes, which can be reproduced, both qualitatively and quantitatively, with a simple, cosmologically-motivated model for disk evolution inside growing NFW dark matter haloes. In this model optical half-light radii are smaller, both at fixed stellar mass and maximum circular velocity, at higher redshifts. This model also predicts that the scaling relations between baryonic quantities evolve even more weakly than the corresponding stellar relations. We emphasize, though, that this weak evolution does not imply that individual galaxies evolve weakly. On the contrary, individual galaxies grow strongly in mass, size and velocity, but in such a way that they move largely along the scaling relations. Finally, recent observation have claimed surprisingly large sizes for a number of star-forming disk galaxies at z \sim 2, which has caused some authors to suggest that high redshift disk galaxies have abnormally high spin parameters. However, we argue that the disk scale lengths in question have been systematically overestimated by a factor \sim 2, and that there is an offset of a factor \sim 1.4 between H\alpha sizes and optical sizes. Taking these effects into account, there is no indication that star forming galaxies at high redshifts (z\sim 2) have abnormally high spin parameters.
Cosmological shocks are a critical part of large-scale structure formation, and are responsible for heating the intracluster medium in galaxy clusters. In addition, they are also capable of accelerating non-thermal electrons and protons. In this work, we focus on the acceleration of electrons at shock fronts, which is thought to be responsible for radio relics - extended radio features in the vicinity of merging galaxy clusters. By combining high resolution AMR/N-body cosmological simulations with an accurate shock finding algorithm and a model for electron acceleration, we calculate the expected synchrotron emission resulting from cosmological structure formation. We produce synthetic radio maps of a large sample of galaxy clusters and present luminosity functions and scaling relationships. With upcoming long wavelength radio telescopes, we expect to see an abundance of radio emission associated with merger shocks in the intracluster medium. By producing observationally motivated statistics, we provide predictions that can be compared with observations to further our understanding of magnetic fields and electron shock acceleration.
We present a statistically robust mass-metallicity (M-Z) relation for long-duration gamma-ray burst (LGRB) host galaxies at z < 1. By comparing the LGRB host M-Z relation to samples representative of the general star-forming galaxy population, we conclude that LGRBs occur in host galaxies with lower metallicities than the general population, and that this trend extends to z ~ 1, with an average offset of -0.50 +/- 0.19 from the M-Z relation for star-forming galaxies. Our sample in this work includes new spectroscopic data for 6 LGRB host galaxies obtained at the Keck and Magellan telescopes, as well as 2 new host galaxies from the literature. Combined with data from our previous work, this yields a total sample of 6 LGRB host galaxies at z < 0.3 and 10 host galaxies at 0.3 < z < 1. We have determined a number of interstellar medium properties for our host galaxies using optical emission-line diagnostics, including metallicity, ionization parameter, young stellar population age, and star formation rate. Across our full sample of 16 LGRB hosts we find an average metallicity of log(O/H) + 12 = 8.4 +/- 0.3. Notably, we also measure a comparatively high metallicity of log(O/H) + 12 = 8.83 +/- 0.1 for the z = 0.296 host galaxy of GRB 050826. We also determine stellar masses (M*) for our LGRB host galaxy sample, finding a mean stellar mass of log(M*/Msun) = 9.25 (+0.19,-0.23).
We present an estimate of the black hole mass function (BHMF) of broad line quasars (BLQSOs) that self-consistently corrects for incompleteness and the statistical uncertainty in the mass estimates, based on a sample of 9886 quasars at 1 < z < 4.5 drawn from the Sloan Digital Sky Survey. We find evidence for `cosmic downsizing' of black holes in BLQSOs, where the peak in their number density shifts to higher redshift with increasing black hole mass. The cosmic mass density for black holes seen as BLQSOs peaks at z ~ 2. We estimate the completeness of the SDSS as a function of black hole mass and Eddington ratio, and find that at z > 1 it is highly incomplete at M_BH < 10^9 M_Sun and L / L_Edd < 0.5. We also estimate a lower limit on the lifetime of a single BLQSO phase and we place constraints on the maximum mass of a black hole in a BLQSO. Our estimated distribution of BLQSO Eddington ratios peaks at L / L_Edd ~ 0.05 and has a dispersion of ~ 0.4 dex, implying that most BLQSOs are not radiating at or near the Eddington limit; however the location of the peak is subject to considerable uncertainty. The steep increase in number density of BLQSOs toward lower Eddington ratios is expected if the BLQSO accretion rate monotonically decays with time. Furthermore, our estimated lifetime and Eddington ratio distributions imply that the majority of the most massive black holes spend a significant amount of time growing in an earlier obscured phase, a conclusion which is independent of the unknown obscured fraction. These results are consistent with models for self-regulated black hole growth, at least for massive systems at z > 1, where the BLQSO phase occurs at the end of a fueling event when black hole feedback unbinds the accreting gas, halting the accretion flow.
We study the short-term effects of an intermediate mass black hole (IBH) on the orbit of star S2 (S02), the shortest period star known to orbit the supermassive black hole (SBH) in the centre of the Milky Way. Near-infrared imaging and spectroscopic observations allow an accurate determination of the orbit of the star. Given S2's short orbital period and large eccentricity, general relativity (GR) needs to be taken into account, and its effects are potentially measurable with current technology. We show that perturbations due to an IBH in orbit around the SBH can produce a shift in the apoapsis of S2 that is as large or even larger than the GR shift. An IBH will also induce changes in the plane of S2's orbit at a level as large as one degree per period. We apply observational orbital fitting techniques to simulations of the S-cluster in the presence of an IBH and find that an IBH more massive than about 1000 solar masses at the distance of the S-stars will be detectable at the next periapse passage of S2, which will occur in 2018.
In this letter we develop a common theoretical framework for the dynamics of thin featureless interfaces. We explicitly demonstrate that the same phase field and velocity-dependent one-scale models characterizing the dynamics of relativistic domain walls, in a cosmological context, can also successfully describe, in a friction dominated regime, the dynamics of non-relativistic interfaces in a wide variety of material systems. We further show that a statistical version of the von-Neumman's law applies in the case of scaling relativistic interface networks implying that, although relativistic and non-relativistic interfaces have very different dynamics, a single simulation snapshot is not able to clearly distinguish the two regimes. We highlight that crucial information characterizing an interface network is contained in a single simulation snapshot and explain why laboratory tests with non-relativistic interfaces can be used to rule out cosmological domain walls as a significant dark energy source.
We describe the effect of AGN light on host galaxy optical and UV-optical colours, as determined from X-ray-selected AGN host galaxies at z~1, and compare the AGN host galaxy colours to those of a control sample matched to the AGN sample in both redshift and stellar mass. We identify as X-ray-selected AGN 8.7 +4/-3 per cent of the red-sequence control galaxies, 9.8 +/-3 per cent of the blue-cloud control galaxies, and 14.7 +4/-3 per cent of the green-valley control galaxies. The nuclear colours of AGN hosts are generally bluer than their outer colours, while the control galaxies exhibit redder nuclei. AGN in blue-cloud host galaxies experience less X-ray obscuration, while AGN in red-sequence hosts have more, which is the reverse of what is expected from general considerations of the interstellar medium. Outer and integrated colours of AGN hosts generally agree with the control galaxies, regardless of X-ray obscuration, but the nuclear colours of unobscured AGN are typically much bluer, especially for X-ray luminous objects. Visible point sources are seen in many of these, indicating that the nuclear colours have been contaminated by AGN light and that obscuration of the X-ray radiation and visible light are therefore highly correlated. Red AGN hosts are typically slightly bluer than red-sequence control galaxies, which suggests that their stellar populations are slightly younger. We compare these colour data to current models of AGN formation. The unexpected trend of less X-ray obscuration in blue-cloud galaxies and more in red-sequence galaxies is problematic for all AGN feedback models, in which gas and dust is thought to be removed as star formation shuts down. A second class of models involving radiative instabilities in hot gas is more promising for red-sequence AGN but predicts a larger number of point sources in red-sequence AGNs than is observed. [See paper for full abstract.]
We present single-dish (sub)millimeter observations of gas and dust in the Galactic high-mass star-forming region G19.61-0.23, with the aim of studying the large-scale properties and physical conditions of the molecular gas across the region. The final aim is to compare the large-scale (about 100 pc) properties with the small-scale (about 3 pc) properties and to consider possible implications for extragalactic studies. We have mapped CO isotopologues in the J=1-0 transition using the FCRAO-14m telescope and the J=2-1 transition using the IRAM-30m telescope. We have also used data from the ATLASGAL survey and from the BU-FCRAO Galactic Ring Survey, as well as the Spitzer infrared Galactic plane surveys GLIMPSE and MIPSGAL to characterize the star-formation activity within the molecular clouds. We reveal a population of molecular clumps in the 13CO(1-0) emission. Our analysis of the 13CO suggests that the virial parameter (ratio of kinetic to gravitational energy) varies over an order of magnitude between clumps that are unbound and some that are apparently "unstable". This conclusion is independent of whether they show evidence of ongoing star formation. We find that the majority of ATLASGAL sources have MIPSGAL counterparts with luminosities in the range 10^4 - 5 10^4 Lsun and are presumably forming relatively massive stars. We compare our results with previous extragalactic studies of the nearby spiral galaxies M31 and M33; and the blue compact dwarf galaxy Henize2-10. We find that the main giant molecular cloud surrounding G19.61-0.23 has physical properties typical for Galactic GMCs and which are comparable to the GMCs in M31 and M33. However, the GMC studied here shows smaller surface densities and masses than the clouds identified in Henize2-10 and associated with super star cluster formation.
Knowledge of the supernova (SN) delay time distribution (DTD) - the SN rate versus time that would follow a hypothetical brief burst of star formation - can shed light on SN progenitors and physics. We compile recent measurements of the Type-Ia SN (SN Ia) rate in galaxy clusters at redshifts z=0-1.45. Together with the observed iron-to-stellar mass ratio in clusters, which constrains the time-integrated number of SN Ia events in clusters, we recover the DTD of SNe Ia in cluster environments. The DTD peaks at the shortest time-delay interval we probe, 0<t<2.2 Gyr, with a low tail out to delays of ~10 Gyr, and is remarkably consistent with several recent DTD reconstructions based on different methods, in different environments. We test DTD models from the literature, requiring that they simultaneously reproduce the observed cluster SN rates and the observed iron-to-stellar mass ratios. A power-law DTD of the form t^{-1.1+/-0.1}, extending to a Hubble time, can satisfy both constraints. Shallower power laws, such as t^{-1/2} cannot, assuming a single DTD, and a single star-formation burst (either brief or extended) at high z. This implies 50-85% of SNe Ia explode within 1 Gyr of star formation. DTDs from double-degenerate (DD) models, which generically have ~t^{-1} shapes over a wide range of timescales, match the data, but only if their predictions are scaled up by factors of 5-10. Single degenerate (SD) DTDs always give poor fits to the data, due to a lack of delayed SNe and overall low numbers of SNe. The observations also permit a combination of two SN Ia populations - prompt (e.g. SD) SNe Ia that explode within a few Gyr of star formation, and produce about 60% of the iron mass in clusters, and a DD population that contributes the events seen at z<1.4. Our results support the existence of a DD progenitor channel for SNe Ia, if the overall predicted numbers can be suitably increased.
Recent wide-field near-infrared surveys have uncovered a large number of cool brown dwarfs, extending the temperature sequence down to less than 500 K and constraining the faint end of the luminosity function. One interesting implication of the derived luminosity function is that the brown dwarf census in the immediate (<10 pc) solar neighborhood is still largely incomplete, and some bright (J<16) brown dwarfs remain to be identified in existing surveys. These objects are especially interesting as they are the ones that can be studied in most detail, especially with techniques that require large fluxes (e.g. time-variability, polarimetry, high-resolution spectroscopy) that cannot realistically be applied to objects uncovered by deep surveys. By cross-matching the DENIS and the 2MASS point-source catalogs, we have identified an overlooked brown dwarf -DENIS J081730.0-615520- that is the brightest field mid-T dwarf in the sky (J = 13.6). We present astrometry and spectroscopy follow-up observations of this brown dwarf. Our data indicate a spectral type T6 and a distance -from parallax measurement- of 4.9\pm0.3 pc, placing this mid-T dwarf among the 3 closest isolated brown dwarfs to the Sun.
We analyzed the full Stokes spectra using simultaneous measurements of the photospheric (FeI 630.15 and 630.25 nm) and chromospheric (MgI b2 517.27 nm) lines. The data were obtained with the HAO/NSO Advanced Stokes Polarimeter, about a near disc center sunspot region, NOAA AR 9661. We compare the characteristics of Stokes profiles in terms of Doppler shifts and asymmetries among the three spectral lines, which helps us to better understand the chromospheric lines and the magnetic and flow fields in different magnetic regions. The main results are: (1) For penumbral area observed by the photospheric FeI lines, Doppler velocities derived from Stokes I (Vi) are very close to those derived from linear polarization profiles (Vlp) but significantly different from those derived from Stokes V profiles (Vzc), which provides direct and strong evidence that the penumbral Evershed flows are magnetized and mainly carried by the horizontal magnetic component. (2) The rudimentary inverse Evershed effect observed by the MgI b2 line provides a qualitative evidence on its formation height that is around or just above the temperature minimum region. (3) Vzc and Vlp in penumbrae and Vzc in pores generally approach their Vi observed by the chromospheric MgI line, which is not the case for the photospheric FeI lines. (4) Outer penumbrae and pores show similar behavior of the Stokes V asymmetries that tend to change from positive values in the photosphere (FeI lines) to negative values in the low chromosphere (MgI line). (5) The Stokes V profiles in plage regions are highly asymmetric in the photosphere and more symmetric in the low chromosphere. (6) Strong red shifts and large asymmetries are found around the magnetic polarity inversion line within the common penumbra of the Delta spot. This study thus emphasizes the importance of spectro-polarimetry using chromospheric lines.
We present here three transit observations of HAT-P-9b taken on 14 February 2010, 18 February 2010, and 05 April 2010 UT from the University of Arizona's 1.55 meter Kuiper telescope on Mt. Bigelow. Our transit light curves were obtained in the I filter for all our observations, and underwent the same reduction process. All three of our transits deviated significantly (approximately 24 minutes earlier) from the ephemeris of Shporer et al. (2008). However, due to the large time span between our observed transits and those of Shporer et al. (2008), a 6.5 second (2 sigma) shift downwards in orbital period from the value of Shporer et al. (2008) is sufficient to explain all available transit data. We find a new period of 3.922814 +/- 0.000002 days for HAT-P-9b with no evidence for significant nonlinearities in the transit period.
Information about the three-dimensional structure of solar magnetic fields is encoded in the polarized spectra of solar radiation by a host of physical processes. To extract this information, solar spectra must be obtained in a variety of magnetically sensitive spectral lines at high spatial, spectral, and temporal resolution with high precision. The need to observe many different spectral lines drives the development of Stokes polarimeters with a high degree of wavelength diversity. We present a new paradigm for the design of polarization modulators that operate over a wide wavelength range with near optimal polarimetric efficiency and are directly applicable to the next generation of multi-line Stokes polarimeters. These modulators are not achromatic in the usual sense because their polarimetric properties vary with wavelength, but they do so in an optimal way. Thus we refer to these modulators as polychromatic. We present here the theory behind polychromatic modulators, illustrate the concept with design examples, and present the performance properties of a prototype polychromatic modulator.
Using the \textit{Hyperz} code (Bolzonella et al. 2000) we present photometric redshift estimates for a random sample of galaxies selected from the SDSS/DR7 and GALEX/DR4, for which spectroscopic redshifts are also available. We confirm that the inclusion of ultraviolet photometry improves the accuracy of photo-$z$s for those galaxies with $g^\star-r^\star \le 0.7$ and $z_{\rm spec} \le 0.2$. We also address the problem of how binary interactions can affect photo-$z$ estimates, and find that their effect is negligible.
We present the integrated $J, H, K, L, M$ and $N$ magnitudes and the colours involving infrared bands, for an extensive set of instantaneous-burst binary stellar populations (BSPs) by using evolutionary population synthesis (EPS). By comparing the results for BSPs {\it WITH} and {\it WITHOUT} binary interactions we show that the inclusion of binary interactions makes the magnitudes of populations larger (fainter) and the integrated colours smaller (bluer) for $\tau \ge 1$ Gyr. Also, we compare our model magnitudes and colours with those of Bruzual & Charlot (2003, hereafter BC03) and Maraston (2005, hereafter M05). At last, we compare these model broad colours with Magellanic Clouds globular clusters (GCs) and Milky Way GCs. In $(V-R)-$[Fe/H] and $(V-I)-$[Fe/H] diagrams it seems that our models match the observations better than those of BC03 and M05.
Using Yunnan evolutionary population synthesis (EPS) models, we present
integrated colours, integrated spectral energy distributions (ISEDs) and
absorption-line indices defined by the Lick Observatory image dissector scanner
(Lick/IDS) system, for an extensive set of instantaneous-burst binary stellar
populations (BSPs) with interactions. By comparing the results for populations
with and without interactions we show that {\it the inclusion of binary
interactions makes the appearance of the population substantially bluer}. This
effect raises the derived age and metallicity of the population.
To be used in the studies of modern spectroscopic galaxy surveys at
intermediate/high spectral resolution, we also present intermediate- (3\,\AA)
and high-resolution ($\sim 0.3$\,\AA) ISEDs and Lick/IDS absorption-line
indices for BSPs. To directly compare with observations the Lick/IDS absorption
indices are also presented by measuring them directly from the ISEDs.
We determined the silicon abundances of 253 metal-poor stars in the metallicity range $-4<\mathrm{[Fe/H]} <-1.5$, based on non-local thermodynamic equilibrium (NLTE) line formation calculations of neutral silicon and high-resolution spectra obtained with VLT-UT2/UVES. The $T_{\mathrm{eff}}$ dependence of [Si/Fe] noticed in previous investigation is diminished in our abundance analysis due to the inclusion of NLTE effects. An increasing slope of [Si/Fe] towards decreasing metallicity is present in our results, in agreement with Galactic chemical evolution models. The small intrinsic scatter of [Si/Fe] in our sample may imply that these stars formed in a region where the yields of type II supernovae were mixed into a large volume, or that the formation of these stars was strongly clustered, even if the ISM was enriched by single SNa II in a small mixing volume. We identified two dwarfs with $\mathrm{[Si/Fe]}\sim +1.0$: HE 0131$-$3953, and HE 1430$-$1123. These main-sequence turnoff stars are also carbon-enhanced. They might have been pre-enriched by sub-luminous supernovae.
We study the observational constraints on the Phantom Crossing DGP model. We demonstrate that the crossing of the phantom divide does not occur within the framework of the original Dvali-Gabadadze-Porrati (DGP) model or the DGP model developed by Dvali and Turner. By extending their model in the framework of an extra dimension scenario, we construct a model that realizes crossing of the phantom divide. We investigate the cosmological constraints obtained from the recent observational data of Type Ia Supernovae, Cosmic Microwave Background anisotropies, and Baryon Acoustic Oscillations. The best fit values of the parameters with 1$\sigma$ (68\%) errors for the Phantom Crossing DGP model are $\Omega_{m,0}=0.27^{+0.02}_{-0.02}$, $\beta=0.54^{+0.24}_{-0.30}$. We find that the Phantom Crossing DGP model is more compatible with the observations than the original DGP model or the DGP model developed by Dvali and Turner. Our model can realize late-time acceleration of the universe, similar to that of $\Lambda$CDM model, without dark energy due to the effect of DGP gravity. In our model, crossing of the phantom divide occurs at a redshift of $z \sim 0.2$.
Supernova remnant (SNR) RX J0852.0-4622 is one of the youngest and is most likely the closest among known galactic supernova remnants (SNRs). It was detected in X-rays, the 44Ti gamma-line, and radio. We obtain and analyze medium-resolution spectra of 14 stars in the direction towards the SNR RX J0852.0-4622 in an attempt to detect broad absorption lines of unshocked ejecta against background stars. Spectral synthesis is performed for all the stars in the wavelength range of 3740-4020AA to extract the broad absorption lines of Ca II related to the SNR RX J0852.0-4622. We do not detect any broad absorption line and place a 3-sigma upper limit on the relative depths of <0.04 for the broad Ca II absorption produced by the SNR. We detect narrow low and high velocity absorption components of Ca II. High velocity |V(LSR)|=100-140 km/s components are attributed to radiative shocks in clouds engulfed by the old Vela SNR. The upper limit to the absorption line strength combined with the width and flux of the 44Ti gamma-ray line 1.16 MeV lead us to conclude that SNR RX J0852.0-4622 was probably produced by an energetic SN Ic explosion.
We want to estimate the distance to molecular clouds in the solar vicinity in
a statistically precise way. Clouds are recognized as extinction
discontinuities. The extinction is estimated from the $(H-K) \ vs. \ (J-H)$
diagram and distances from a $(J-K)_0 \ vs. \ M_J$ relation based on Hipparcos.
The stellar sample of relevance for the cloud distance is confined by the FWHM
of the $A_V / D_{\star}(pc)$ or of its derivative. The cloud distance is
estimated from fitting a function to the $(A_V, 1/ \pi_{JHK})$ pairs in this
sample with a function like $arctanh^p (D_\star /D_{cloud})$ where the power
$p$ and $D_{cloud}$ both are estimated. The fit follows the $(A_V,
1/\pi_{JHK})_{cloud}$ data rather well. Formal standard deviations less than a
few times 10 pc seem obtainable implying that cloud distances are estimated on
the $\lesssim$10$\%$ level. Such a precision allows estimates of the depths of
cloud complexes in some cases. As examples of our results we present distances
for $\sim$25 molecular clouds in Table ~\ref{t2}.
$Keywords$: interstellar medium: molecular cloud distances
We report detections of three z ~ 2.5 submillimeter-selected galaxies (SMGs) in the lowest rotational transition of the carbon monoxide molecule (CO J = 1-0) and one nondetection. For the three galaxies we detected, we find a line-integrated brightness temperature ratio of 0.53 +/- 0.08. The ratio is lower than the frequent assumption of unity, suggesting that mass estimates for SMGs based on J = 3-2 observations and J = 1-0 column density or mass conversion factors should should be multiplied by a factor of 1.8. Comparison of the 1-0 line intensities with intensities of higher-J transitions indicates that single-component models for the interstellar media in SMGs are incomplete. The small dispersion, along with published detections of CO lines with upper J > 3 in most of the sources, indicates that the molecules are not subthermally excited in most galaxies, but that the emission is from a multi-component interstellar medium with physical structure common to many classes of galaxies. This result tends to rule out the lowest scaling factors between CO luminosity and molecular gas mass and further increases molecular mass estimates calibrated against observations of galaxies in the local universe. We also describe and demonstrate a statistically sound method for finding weak lines in broadband spectra, which will find application in searches for molecular lines from sources at unknown redshifts.
Cool white dwarf stars are usually found to have an outer atmosphere that is practically pure in hydrogen or helium. However, a small fraction have traces of heavy elements that must originate from the accretion of extrinsic material, most probably circumstellar matter. Upon examining thousands of Sloan Digital Sky Survey spectra, we discovered that the helium-atmosphere white dwarf SDSS J073842.56+183509.6 shows the most severe metal pollution ever seen in the outermost layers of such stars. We present here a quantitative analysis of this exciting star by combining high S/N follow-up spectroscopic and photometric observations with model atmospheres and evolutionary models. We determine the global structural properties of our target star, as well as the abundances of the most significant pollutants in its atmosphere, i.e., H, O, Na, Mg, Si, Ca, and Fe. The relative abundances of these elements imply that the source of the accreted material has a composition similar to that of Bulk Earth. We also report the signature of a circumstellar disk revealed through a large infrared excess in JHK photometry. Combined with our inferred estimate of the mass of the accreted material, this strongly suggests that we are witnessing the remains of a tidally disrupted extrasolar body that was as large as Ceres.
The prospects for accomplishing X-ray polarization measurements appear to have grown in recent years after a more than 35-year hiatus. Unfortunately, this long hiatus has brought with it some confusion over the statistical uncertainties associated with polarization measurements of astronomical sources. The heart of this confusion stems from a misunderstanding (or potential misunderstanding) of a standard figure of merit-the minimum detectable polarization (MDP)-that one of us introduced many years ago. We review the relevant statistics, and quantify the differences between the MDP and the uncertainty of an actual polarization measurement. We discuss the implications for future missions.
Among other things, studies of the formation and evolution of planetary systems currently draw on two important observational resources: the precise characterization available for planets that transit their parent stars and the frequency and nature of systems with multiple planets. Thus far, the study of transiting exoplanets has focused almost exclusively on systems with only one planet, except for considering the influence of additional planets on the transit light curve, mostly through transit timing variations (TTVs). This work considers systems where multiple planets are seen to transit the same star and concludes that such "multi-transiting" systems will be the most information-rich planetary systems besides our own solar system. Five new candidate multi-transiting systems from \emph{Kepler} have been announced in Steffen et al. 2010, though these candidates have not yet been fully confirmed as planets. In anticipation of the likely confirmation of multi-transiting systems, we discuss the value of these systems in detail. For example, proper interpretation of transit timing variations is significantly improved in multi-transiting systems. The true mutual inclination, a valuable probe of planetary formation, can also be well determined in certain systems, especially through Rossiter-McLaughlin measurements of each planet. In addition, such systems may undergo predictable and observable mutual events, where one planet crosses over the other, which allow for unique constraints on various physical and orbital parameters, particularly the mutual inclination.
We present a three-dimensional simulation of the corona of an FK Com-type rapidly rotating G giant using a magnetohydrodynamic model that was originally developed for the solar corona in order to capture the more realistic, non-potential coronal structure. We drive the simulation with surface maps for the radial magnetic field obtained from a stellar dynamo model of the FK Com system. This enables us to obtain the coronal structure for different field topologies representing different periods of time. We find that the corona of such an FK Com-like star, including the large scale coronal loops, is dominated by a strong toroidal component of the magnetic field. This is a result of part of the field being dragged by the radial outflow, while the other part remains attached to the rapidly rotating stellar surface. This tangling of the magnetic field,in addition to a reduction in the radial flow component, leads to a flattening of the gas density profile with distance in the inner part of the corona. The three-dimensional simulation provides a global view of the coronal structure. Some aspects of the results, such as the toroidal wrapping of the magnetic field, should also be applicable to coronae on fast rotators in general, which our study shows can be considerably different from the well-studied and well-observed solar corona. Studying the global structure of such coronae should also lead to a better understanding of their related stellar processes, such as flares and coronal mass ejections, and in particular, should lead to an improved understanding of mass and angular momentum loss from such systems.
We present and analyse integral-field observations of six type-II QSOs with z=0.3-0.4, selected from the Sloan Digital Sky Survey (SDSS). Two of our sample are found to be surrounded by a nebula of warm ionized gas, with the largest nebula extending across 8" (40 kpc). Some regions of the extended nebulae show kinematics that are consistent with gravitational motion, while other regions show relatively perturbed kinematics: velocity shifts and line widths too large to be readily explained by gravitational motion. We propose that a ~20 kpc x20 kpc outflow is present in one of the galaxies. Possible mechanisms for triggering the outflow are discussed. In this object, we also find evidence for ionization both by shocks and the radiation field of the AGN.
Supernova (SN) rates are potentially powerful diagnostics of metal enrichment and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials and relatively simple star-formation histories. We have carried out a survey for supernovae (SNe) in galaxy clusters, at a redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We reimaged a sample of 15 clusters that were previously imaged by ACS, thus obtaining two to three epochs per cluster, in which we discovered five likely cluster SNe, six possible cluster SNe Ia, two hostless SN candidates, and several background and foreground events. Keck spectra of the host galaxies were obtained to establish cluster membership. We conducted detailed efficiency simulations, and measured the stellar luminosities of the clusters using Subaru images. We derive a cluster SN rate of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01 (systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM +0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic) [where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of cluster SN rates, the uncertainties are dominated by small-number statistics. The SN rate in this redshift bin is consistent with the SN rate in clusters at lower redshifts (to within the uncertainties), and shows that there is, at most, only a slight increase of cluster SN rate with increasing redshift. The low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron mass in clusters was already in place by z~1. The recently observed doubling of iron abundances in the intracluster medium between z=1 and 0, if real, is likely the result of redistribution of existing iron, rather than new production of iron.
The recent detection (Jee etal 2009) of the massive cluster XMMU J2235.3-2557 at a redshift z = 1.4, with an estimated mass M = 6.4 +- 1.2 X 10^14 M_sol, has been claimed to be a possible challenge to the standard LCDM cosmological model. More specifically, the probability to detect such a cluster has been estimated to be 0.005 if a LCDM model with gaussian initial conditions is assumed, resulting in a 3 sigma discrepancy from the standard cosmological model. In this paper we propose to use high redshift clusters as the one detected in Jee etal 2009 to compare the cosmological constant scenario with interacting dark energy models. We show that coupled dark energy models, where an interaction is present between dark energy and cold dark matter, can significantly enhance the probability to observe very massive clusters at high redshift.
Low-order, non-axisymmetric p-modes (also referred as inertial-acoustic modes) trapped in the inner-most region of hydrodynamic accretion discs around black holes, are plausible candidates for high-frequency quasi-periodic oscillations (QPOs) observed in a number of accreting black-hole systems. These modes are subject to global instabilities due to wave absorption at the corotation resonance (where the wave pattern frequency $\omega/m$ equals the disc rotation rate $\Omega$), when the fluid vortensity, $\zeta=\kappa^2/(2\Omega\Sigma)$ (where $\kappa$ and $\Sigma$ are the radial epicyclic frequency and disc surface density, respectively), has a positive gradient. We investigate the effects of disc magnetic fields on the wave absorption at corotation and the related wave super-reflection of the corotation barrier, and on the overstability of disc p-modes. For discs with a pure toroidal field, the corotation resonance is split into two magnetic resonances, where the wave frequency in the corotating frame of the fluid, $\tomega=\omega-m\Omega$, matches the slow magnetosonic wave frequency. Significant wave energy/angular momentum absorption occurs at both magnetic resonances, but with opposite signs. The combined effect of the two magnetic resonances is to reduce the super-reflection and the growth rate of the overstable p-modes. We show that even a subthermal toroidal field may suppress the overstability of hydrodynamic ($B=0$) p-modes. For accretion discs with mixed (toroidal and vertical) magnetic fields, two additional Alfven resonances appear, where $\tomega$ matches the local Alfven wave frequency. They further reduce the growth rate of p-modes. Our results suggest that in order for the non-axisymmetric p-modes to be a viable candidate for the observed high-frequency QPOs, the disc magnetic field must be appreciably subthermal, or other mode excitation mechanisms are at work.
We study the topology of cosmic large-scale structure through the genus statistics, using galaxy catalogues generated from the Millennium Simulation and observational data from the latest Sloan Digital Sky Survey Data Release (SDSS DR7). We introduce a new method for constructing galaxy density fields and for measuring the genus statistics of its isodensity surfaces. It is based on a Delaunay tessellation field estimation (DTFE) technique that allows the definition of a piece-wise continuous density field and the exact computation of the topology of its polygonal isodensity contours, without introducing any free numerical parameter. Besides this new approach, we also employ the traditional approaches of smoothing the galaxy distribution with a Gaussian of fixed width, or by adaptively smoothing with a kernel that encloses a constant number of neighboring galaxies. Our results show that the Delaunay-based method extracts the largest amount of topological information. Unlike the traditional approach for genus statistics, it is able to discriminate between the different theoretical galaxy catalogues analyzed here, both in real space and in redshift space, even though they are based on the same underlying simulation model. In particular, the DFTE approach detects with high confidence a discrepancy of one of the semi-analytic models studied here compared with the SDSS data, while the other models are found to be consistent.
I demonstrate that an effect similar to the Roemer delay, familiar from timing radio pulsars, should be detectable in the first eclipsing double white dwarf (WD) binary, NLTT 11748. By measuring the difference of the time between the secondary and primary eclipses from one-half period (4.6 s), one can determine the physical size of the orbit and hence constrain the masses of the individual WDs. A measurement with uncertainty <0.1 s---possible with modern large telescopes---will determine the individual masses to +/-0.02 Msun when combined with good-quality (<1 km/s) radial velocity data, although the eccentricity must also be known to high accuracy (+/- 1e-3). Mass constraints improve as P^{-1/2} (where P is the orbital period), so this works best in wide binaries and should be detectable even for non-degenerate stars, but such constraints require the mass ratio to differ from one and undistorted orbits.
Bolometric corrections based on the optical-to-ultraviolet continuum spectrum of quasars are widely used to quantify their radiative output, although such estimates are affected by a myriad of uncertainties, such as the generally unknown line-of-sight angle to the central engine. In order to shed light on these issues, we investigate the state-of-the-art models of Hubeny et al. that describe the continuum spectrum of thin accretion discs and include relativistic effects. We explore the bolometric corrections as a function of mass accretion rates, black hole masses and viewing angles, restricted to the parameter space expected for type-1 quasars. We find that a nonlinear relationship log L_bol=A + B log(lambda L_lambda) with B<=0.9 is favoured by the models and becomes tighter as the wavelength decreases. We calculate from the model the bolometric corrections corresponding to the wavelengths lambda = 1450A, 3000A and 5100A. In particular, for lambda=3000A we find A=9.24 +- 0.77 and B=0.81 +- 0.02. We demonstrate that the often-made assumption that quasars emit isotropically may lead to severe systematic errors in the determination of L_bol, when using the method of integrating the "big blue bump" spectrum. For a typical viewing angle of ~30 degrees to the quasar central engine, we obtain that the value of L_bol resulting from the isotropy assumption has a systematic error of ~30% high compared to the value of L_bol which incorporates the anisotropic emission of the accretion disc. These results are of direct relevance to observational determinations of the bolometric luminosities of quasars, and may be used to improve such estimates.
The Laser Interferometer Space Antenna's (LISA's) observation of supermassive binary black holes (SMBBH) could provide a new tool for precision cosmography. Inclusion of sub-dominant signal harmonics in the inspiral signal allows for high-accuracy sky localization, dramatically improving the chances of finding the host galaxy and obtaining its redshift. A SMBBH merger can potentially have component masses from a wide range ($10^5 - 10^8\,\Ms$) over which parameter accuracies vary considerably. We perform an in-depth study in order to understand (i) what fraction of possible SMBBH mergers allow for sky localization, depending on the parameters of the source, and (ii) how accurately $w$ can be measured when the host galaxy can be identified. We also investigate how accuracies on all parameters improve when a knowledge of the sky position can be folded into the estimation of errors. We find that $w$ can be measured to within a few percent in most cases, if the only error in measuring the luminosity distance is due to LISA's instrumental noise and the confusion background from Galactic binaries. However, weak lensing-induced errors will severely degrade the accuracy with which $w$ can be obtained, emphasizing that methods to mitigate weak lensing effects would be required to take advantage of LISA's full potential.
We investigate the formation of caustics in Dirac-Born-Infeld type scalar field systems for generic classes of potentials, viz., massive rolling scalar with potential, $V(\phi)=V_0e^{\pm \frac{1}{2} M^2 \phi^2}$ and inverse power-law potentials with $V(\phi)=V_0/\phi^n,~0<n<2$. We find that in the case of\texttt{} exponentially decreasing rolling massive scalar field potential, there are multi-valued regions and regions of likely to be caustics in the field configuration. However there are no caustics in the case of exponentially increasing potential. We show that the formation of caustics is inevitable for the inverse power-law potentials under consideration in Minkowski space time whereas caustics do not form in this case in the FRW universe.
Collective flavor oscillations are known to bring multiple splits in the supernova (SN) neutrino and antineutrino spectra. These spectral splits depend not only on the mass hierarchy of the neutrinos but also on the initial relative flux composition. Observation of spectral splits in a future galactic supernova signal is expected to throw light on the mass hierarchy pattern of the neutrinos. However, since the Diffuse Supernova Neutrino Background (DSNB) comprises of a superposition of neutrino fluxes from all past supernovae, and since different SN are expected to have slightly different initial fluxes, it is pertinent to check if the hierarchy dependent signature of collective oscillations can survive this averaging of the flux spectra. Since the actual distribution of SN with initial relative flux spectra of the neutrinos and antineutrinos is unknown, we assume a log-normal distribution for them. We find that it will be hard, if not nearly impossible, to acertain the neutrino mass hierarchy from observation of the DSNB once this distribution of the initial spectra over all past supernovae are taken into account. We show that our conclusions are rather robust against the choice of the initial flux distribution function.
The sensitivity of the stellar moment of inertia to the neutron-star matter equation of state is examined using accurately-calibrated relativistic mean-field models. We probe this sensitivity by tuning both the density dependence of the symmetry energy and the high density component of the equation of state, properties that are at present poorly constrained by existing laboratory data. Particularly attractive is the study of the fraction of the moment of inertia contained in the solid crust. Analytic treatments of the crustal moment of inertia reveal a high sensitivity to the transition pressure at the core-crust interface. This may suggest the existence of a strong correlation between the density dependence of the symmetry energy and the crustal moment of inertia. However, no correlation was found. We conclude that constraining the density dependence of the symmetry energy - through, for example, the measurement of the neutron skin thickness in 208Pb - will place no significant bound on either the transition pressure or the crustal moment of inertia.
The Laser Interferometer Space Antenna (LISA) is designed to detect gravitational wave signals from astrophysical sources, including those from coalescing binary systems of compact objects such as black holes. Colliding galaxies have central black holes that sink to the center of the merged galaxy and begin to orbit one another and emit gravitational waves. Some galaxy evolution models predict that the binary black hole system will enter the LISA band with significant orbital eccentricity, while other models suggest that the orbits will already have circularized. Using a full seventeen parameter waveform model that includes the effects of orbital eccentricity, spin precession and higher harmonics, we investigate how well the source parameters can be inferred from simulated LISA data. Defining the reference eccentricity as the value one year before merger, we find that for typical LISA sources, it will be possible to measure the eccentricity to an accuracy of parts in a thousand. The accuracy with which the eccentricity can be measured depends only very weakly on the eccentricity, making it possible to distinguish circular orbits from those with very small eccentricities. LISA measurements of the orbital eccentricity can provide strong constraints on theories of galaxy mergers in the early universe.
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We hydrodynamically explore the dependence on spatial dimension of the viability of the neutrino heating mechanism of core-collapse supernova explosions. We find that the tendency to explode is a monotonically increasing function of dimension, with 3D requiring $\sim$40$-$50\% lower driving neutrino luminosity than 1D and $\sim$15$-$25\% lower driving neutrino luminosity than 2D. Moreover, we find that the delay to explosion for a given neutrino luminosity is always shorter in 3D than 2D, sometimes by many hundreds of milliseconds. The magnitude of this dimensional effect is much larger than the purported magnitude of a variety of other effects, such as nuclear burning, inelastic scattering, or general relativity, which are sometimes invoked to bridge the gap between the current ambiguous and uncertain theoretical situation and the fact of robust supernova explosions in Nature. Since Nature is 3D, our finding may be an important step towards unraveling one of the most problematic puzzles in stellar astrophysics. In addition, even though in 3D we do see pre-explosion instabilities and blast asymmetries, unlike the situation in 2D, we do not see an obvious axially-symmetric dipolar shock oscillation. Rather, the free energy available to power instabilites seems to be shared by more and more degrees of freedom as the dimension increases. Hence, the strong dipolar axisymmetry seen in 2D and previously identified as a fundamental characteristic of the shock hydrodynamics may not survive in 3D as a prominent feature.
Quillen et al. and O'Dea et al. carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT Brightest Cluster Sample chosen based on their elevated H-alpha flux. We present Hubble Space Telescope Advanced Camera for Surveys (ACS) far ultraviolet (FUV) images of the Ly-alpha and continuum emission of the luminous emission-line nebulae in 7 BCGs found to have an infrared excess. We confirm that the BCGs are actively forming stars suggesting that the IR excess seen in these BCGs is indeed associated with star formation. The FUV continuum emission extends over a region of ~7-28 kpc (largest linear size) and even larger in Ly-alpha. The young stellar population required by the FUV observations would produce a significant fraction of the ionizing photons required to power the emission line nebulae. Star formation rates estimated from the FUV continuum range from ~3 to ~14 times lower than those estimated from the IR, however both the Balmer decrement in the central few arcseconds and detection of CO in most of these galaxies imply that there are regions of high extinction that could have absorbed much of the FUV continuum. Analysis of archival VLA observations reveals compact radio sources in all 7 BCGs and kpc scale jets in Abell 1835 and RXJ 2129+00. The four galaxies with archival deep Chandra observations exhibit asymmetric X-ray emission, the peaks of which are offset from the center of the BCGs by ~10 kpc on average. A low feedback state for the AGN could allow increased condensation of the hot gas into the center of the galaxy and the feeding of star formation.
Variation in high energy cosmic rays (HECRs) has been proposed to explain a 62 My periodicity in terrestrial fossil biodiversity. It has been suggested that the infall of our galaxy toward the Virgo cluster could generate an extragalactic shock, accelerating charged particles and exposing the earth to a flux of high energy cosmic rays (HECRs). The oscillation of the Sun perpendicular to the galactic plane could induce 62 My periodicity in the HECR flux on the Earth, with a magnitude much higher than the Galactic cosmic ray change we see in a solar cycle. This mechanism could potentially explain the observed 62 My periodicity in terrestrial biodiversity over the past 500 My. In addition to direct effects on life from secondaries, HECRs induced air showers ionize the atmosphere leading to changes in atmospheric chemistry and microphysical processes that can lead to cloud formation including low altitude cloud cover. An increase in ionization changes the global electric circuit which could enhance the formation of cloud condensation nuclei (CCN) through microphysical processes such as electroscavenging and ion mediated nucleation, leading to an increase in the cloud cover. This could increase the albedo and reduce the solar flux reaching the ground, reducing the global temperature. Using an existing model, we have calculated the enhancement in atmospheric ionization at low altitudes resulting from exposure to HECRs. We use a conservative model to estimate the change in low altitude cloud cover from this increased ionization.
The measurement of Baryonic Acoustic Oscillations from galaxy surveys is well known to be a robust and powerful tool to constrain dark energy. This method relies on the knowledge of the size of the acoustic horizon at radiation drag derived from Cosmic Microwave Background Anisotropy measurements. In this paper we quantify the effect of non-standard initial conditions in the form of an isocurvature component on the determination of dark energy parameters from future BAO surveys. In particular, if there is an isocurvature component (at a level still allowed by present data) but it is ignored in the CMB analysis, the sound horizon and cosmological parameters determination is biased, and, as a consequence, future surveys may incorrectly suggest deviations from a cosmological constant. In order to recover an unbiased determination of the sound horizon and dark energy parameters, a component of isocurvature perturbations must be included in the model when analyzing CMB data. Fortunately, doing so does not increase parameter errors significantly.
I look at the growth of weak density inhomogeneities of nonrelativistic matter, in bimetric-MOND (BIMOND) cosmology. I concentrate on matter-twin-matter-symmetric versions of BIMOND, and assume that, on average, the universe is symmetrically populated in the two sectors. MOND effects are absent in an exactly symmetric universe, apart from the appearance of a cosmological constant, Lambda~(a0/c)^2. MOND effects--local and cosmological--do enter when density inhomogeneities that differ in the two sectors appear and develop. MOND later takes its standard form in systems that are islands dominated by pure matter. I derive the nonrelativistic equations governing small-scale fluctuation growth. The equations split into two uncoupled systems, one for the sum, the other for the difference, of the fluctuations in the two sectors. The former is governed strictly by Newtonian dynamics. The latter is governed by MOND dynamics, which entails stronger gravity, and nonlinearity even for the smallest of perturbations. These cause the difference to grow faster than the sum, conducing to matter-twin-matter segregation. The nonlinearity also causes interaction between nested perturbations on different scales. Because matter and twin matter repel each other in the MOND regime, matter inhomogeneities grow not only by their own self gravity, but also through shepherding by flanking TM overdensitie. The relative importance of gravity and pressure in the MOND system depends also on the strength of the perturbation. The development of structure in the universe, in either sector, thus depends crucially on two initial fluctuation spectra: that of matter alone and that of the matter-TM difference. I also discuss the back reaction on cosmology of BIMOND effects that appear as ``phantom matter'' resulting from inhomogeneity differences between the two sectors. (abridged)
Highly ionized species such as C IV, N V, and O VI, are commonly observed in diffuse gas in various places in the universe, such as in our Galaxy's disk and halo, high velocity clouds (HVCs), external galaxies, and the intergalactic medium. One possible mechanism for producing high ions is turbulent mixing of cool gas with hotter gas in locations where these gases slide past each other. By using hydrodynamic simulations with radiative cooling and non-equilibrium ionization (NEI) calculations, we investigate the physical properties of turbulent mixing layers and the production of high ions. We find that most of the mixing occurs on the hot side of the hot/cool interface and that the mixed region separates into a tepid zone containing radiatively cooled, C IV-rich gas and a hotter zone which is rich in C IV, N V, and O VI. Mixing occurs faster than ionization or recombination, making the mixed gas a better source of C IV, N V, and O VI in our NEI simulations than in our collisional ionization equilibrium (CIE) simulations. In addition, the gas radiatively cools faster than the ions recombine, which also allows large numbers of high ions to linger in the NEI simulations. For these reasons, our NEI calculations predict more high ions than our CIE calculations predict. We also simulate various initial configurations of turbulent mixing layers and discuss their results. We compare the results of our simulations with observations and other models, including other turbulent mixing calculations. The ratios of C IV to N V and N V to O VI are in reasonable agreement with the averages calculated from observations of the halo. There is a great deal of variation from sightline to sightline and with time in our simulations. Such spatial and temporal variation may explain some of the variation seen among observations.
NGC6611 and its parental cloud, the Eagle Nebula (M16), are well-studied star-forming regions, thanks to their large content of both OB stars and stars with disks and the observed ongoing star formation. We identified 834 disk-bearing stars associated with the cloud, after detecting their excesses in NIR bands from J band to 8.0 micron. In this paper, we study in detail the nature of a subsample of disk-bearing stars that show peculiar characteristics. They appear older than the other members in the V vs. V-I diagram, and/or they have one or more IRAC colors at pure photospheric values, despite showing NIR excesses, when optical and infrared colors are compared. We confirm the membership of these stars to M16 by a spectroscopic analysis. The physical properties of these stars with disks are studied by comparing their spectral energy distributions (SEDs) with the SEDs predicted by models of T-Tauri stars with disks and envelopes. We show that the age of these stars estimated from the V vs. V-I diagram is unreliable since their V-I colors are altered by the light scattered by the disk into the line of sight. Only in a few cases their SEDs are compatible with models with excesses in V band caused by optical veiling. Candidate members with disks and photospheric IRAC colors are selected by the used NIR disk diagnostic, which is sensitive to moderate excesses, such as those produced by disks with low masses. In 1/3 of these cases, scattering of stellar flux by the disks can also be invoked. The photospheric light scattered by the disk grains into the line of sight can affect the derivation of physical parameters of ClassII stars from photometric optical and NIR data. Besides, the disks diagnostic we defined are useful for selecting stars with disks, even those with moderate excesses or whose optical colors are altered by veiling or photospheric scattered light.
Deep near-infrared images recorded with NICI on Gemini South are used to investigate the evolved stellar content in the outer regions of the south east quadrant of the spiral galaxy M83. A diffuse population of asymptotic giant branch (AGB) stars is detected outside of the previously identified young and intermediate age star clusters in the outer disk. The brightest AGB stars have M_K > -8, and the AGB luminosity function (LF) is well-matched by model LFs that assume ages < 1 Gyr. The specific star formation rate (SFR) during the past few Gyr estimated from AGB star counts is consistent with that computed from mid-infrared observations of star clusters at similar radii, and it is concluded that the disruption timescale for star clusters in the outer disk is << 1 Gyr. The luminosity function and specific frequency of AGB stars varies with radius, in a manner that is indicative of lower luminosity-weighted ages at larger radii. Modest numbers of red supergiants are also found, indicating that there has been star formation during the past 100 Myr, while the ratio of C stars to M giants is consistent with that expected for a solar metallicity system that has experienced a constant SFR for the past few Gyrs.
The core accretion mechanism is presently the most widely accepted cause of the formation of giant planets. For simplicity, most models presently assume that the growth of planetary embryos occurs in isolation. We explore how the simultaneous growth of two embryos at the present locations of Jupiter and Saturn affects the outcome of planetary formation. We model planet formation on the basis of the core accretion scenario and include several key physical ingredients. We consider a protoplanetary gas disk that exponentially decays with time. For planetesimals, we allow for a distribution of sizes from 100~m to 100~km with most of the mass in the smaller objects. We include planetesimal migration as well as different profiles for the surface density $\Sigma$ of the disk. The core growth is computed in the framework of the oligarchic growth regime and includes the viscous enhancement of the planetesimal capture cross-section. Planet migration is ignored. By comparing calculations assuming formation of embryos in isolation to calculations with simultaneous embryo growth, we find that the growth of one embryo generally significantly affects the other. This occurs in spite of the feeding zones of each planet never overlapping. The results may be classified as a function of the gas surface density profile $\Sigma$: if $\Sigma \propto r^{-3/2}$ and the protoplanetary disk is rather massive, Jupiter's formation inhibits the growth of Saturn. If $\Sigma \propto r^{-1}$ isolated and simultaneous formation lead to very similar outcomes; in the the case of $\Sigma \propto r^{-1/2}$ Saturn grows faster and induces a density wave that later acclerates the formation of Jupiter. Our results indicate that the simultaneous growth of several embryos impacts the final outcome and should be taken into account by planet formation models.
Hot accretion tori around a compact object are known to be susceptible to a global hydrodynamical instability, the so-called Papaloizou-Pringle (PP) instability, arising from the interaction of non-axisymmetric waves across the corotation radius, where the wave pattern speed matches the fluid rotation rate. However, accretion tori produced in various astrophysical situations (e.g., collapsars and neutron star binary mergers) are likely to be highly magnetized. We study the effect of magnetic fields on the PP instability in incompressible tori with various magnetic strengths and structures. In general, toroidal magnetic fields have significant effects on the PP instability: For thin tori (with the fractional width relative to the outer torus radius much less than unity), the instability is suppressed at large field strengths with the corresponding toroidal Alfven speed $v_{A\phi}\go 0.2r\Omega$ (where $\Omega$ is the flow rotation rate). For thicker tori (with the fractional width of order 0.4 or larger), which are hydrodynamically stable, the instability sets in for sufficiently strong magnetic fields (with $v_{A\phi}\go 0.2 r\Omega$). Our results suggest that highly magnetized accretion tori may be subjected to global instability even when it is stable against the usual magneto-rotational instability.
We investigate the ability of spectroscopic techniques to yield realistic star formation histories (SFHs) for the bulges of spiral galaxies based on a comparison with their observed broadband colors. Full spectrum fitting to optical spectra indicates that recent (within ~1 Gyr) star formation activity can contribute significantly to the V-band flux, whilst accounting for only a minor fraction of the stellar mass budget which is made up primarily of old stars. Furthermore, recent implementations of stellar population (SP) models reveal that the inclusion of a more complete treatment of the thermally pulsating asymptotic giant branch (TP-AGB) phase to SP models greatly increases the NIR flux for SPs of ages 0.2-2 Gyr. Comparing the optical--NIR colors predicted from population synthesis fitting, using models which do not include all stages of the TP-AGB phase, to the observed colors reveals that observed optical--NIR colors are too red compared to the model predictions. However, when a 1 Gyr SP from models including a full treatment the TP-AGB phase is used, the observed and predicted colors are in good agreement. This has strong implications for the interpretation of stellar populations, dust content, and SFHs derived from colors alone.
Exoplanets are often found with short periods or high eccentricities, and multiple-planet systems are often in resonance. They require dynamical theories that describe more extreme motions than those of the relatively placid planetary orbits of the Solar System. We describe the most important dynamical processes in fully-formed planetary systems and how they are modeled. Such methods have been applied to detect the evolution of exoplanet orbits in action and to infer dramatic histories from the dynamical properties of planetary systems.
This study investigates Parker instability in an interstellar medium (ISM) near the Galactic plane using three-dimensional magneto-hydrodynamic simulations. Parker instability arises from the presence of a magnetic field in a plasma, wherein the magnetic buoyant pressure expels the gas and cause the gas to move along the field lines. The process is thought to induce the formation of giant molecular clouds in the Galaxy. In this study, the effects of cosmic-ray (CR) diffusion are examined. The ISM at equilibrium is assumed to comprise a plasma fluid and a CR fluid at various temperatures, with a uniform magnetic field passing through it in the azimuthal direction of the Galactic disk. After a small perturbation, the unstable gas aggregates at the footpoint of the magnetic fields and forms dense blobs. The growth rate of the instability increases with the strength of the CR diffusion. The formation of dense clouds is enhanced by the effect of cosmic rays (CRs), whereas the shape of the clouds depends sensitively on the initial conditions of perturbation.
Both Uranus and Neptune are thought to have strong zonal winds with velocities of several hundred meters per second. These wind velocities, however, assume solid-body rotation periods based on Voyager 2 measurements of periodic variations in the planets' radio signals and of fits to the planets' magnetic fields; 17.24h and 16.11h for Uranus and Neptune, respectively. The realization that the radio period of Saturn does not represent the planet's deep interior rotation and the complexity of the magnetic fields of Uranus and Neptune raise the possibility that the Voyager 2 radio and magnetic periods might not represent the deep interior rotation periods of the ice giants. Moreover, if there is deep differential rotation within Uranus and Neptune no single solid-body rotation period could characterize the bulk rotation of the planets. We use wind and shape data to investigate the rotation of Uranus and Neptune. The shapes (flattening) of the ice giants are not measured, but only inferred from atmospheric wind speeds and radio occultation measurements at a single latitude. The inferred oblateness values of Uranus and Neptune do not correspond to bodies rotating with the Voyager rotation periods. Minimization of wind velocities or dynamic heights of the 1 bar isosurfaces, constrained by the single occultation radii and gravitational coefficients of the planets, leads to solid-body rotation periods of ~16.58h for Uranus and ~17.46h for Neptune. Uranus might be rotating faster and Neptune slower than Voyager rotation speeds. We derive shapes for the planets based on these rotation rates. Wind velocities with respect to these rotation periods are essentially identical on Uranus and Neptune and wind speeds are slower than previously thought. Alternatively, if we interpret wind measurements in terms of differential rotation on cylinders there are essentially no residual atmospheric winds.
The main atmospheric parameters and abundances of the iron group elements (vanadium, chromium, iron, cobalt and nickel) are determined for 62 red giant "clump" stars revealed in the Galactic field by the Hipparcos orbiting observatory. The stars form a homogeneous sample with the mean value of temperature T=4750 +- 160K, of surface gravity log g = 2.41 +- 0.26 and the mean value of metallicity [Fe/H] = -0.04 +- 0.15 dex. A Gaussian fit to the [Fe/H] distribution produces the mean [Fe/H] = -0.01 dex and dispersion of [Fe/H] = 0.08 dex. The near-solar metallicity and small dispersion of [Fe/H] of clump stars of the Galaxy obtained in this work confirm the theoretical model of the Hipparcos clump by Girardi & Salaris (2001). This suggests that nearby clump stars are (in the mean) relatively young objects, reflecting mainly the near-solar metallicities developed in the local disk during the last few Gyrs of its history. We find iron group element to iron abundance ratios in clump giants to be close to solar.
Galaxy cluster surveys based on the Sunyaev-Zeldovich effect (SZE) mapping are expected from ongoing experiments. Such surveys are anticipated to provide a significant amount of information relevant to cosmology from the number counts redshift distribution. We carry out an estimation of predicted SZE counts and their redshift distribution taking into account the current cosmological constraints and the X-ray cluster temperature distribution functions. Comparison between local and distant cluster temperature distribution functions provides evidence for an evolution in the abundance of X-ray clusters that is not consistent with the use of standard scaling relations of cluster properties in the framework of the current concordance model. The hypothesis of some evolution of the scaling law driven by non-gravitational processes is a natural solution to this problem. We perform a MCMC statistical study using COSMOMC, combining current CMB observations from WMAP, the SNIa Hubble diagram, the galaxy power spectrum data from SDSS and X-ray clusters temperature distributions to predict SZE cluster number counts. Models reproducing well the X-ray cluster temperature distribution function evolution lead to a significantly lower SZE clusters number counts with a distinctive redshift distribution. Ongoing microwave SZE surveys will therefore shed new light on intracluster gas physics and greatly help to identify the role of possible non-gravitational physics in the history of the hot gas component of x-ray clusters.
Rotational velocity, lithium abundance, and the mass depth of the outer convective zone are key parameters in the study of the processes at work in the stellar interior, in particular when examining the poorly understood processes operating in the interior of solar-analog stars. We investigate whether the large dispersion in the observed lithium abundances of solar-analog stars can be explained by the depth behavior of the outer convective zone masses, within the framework of the standard convection model based on the local mixing-length theory. We also aims to analyze the link between rotation and lithium abundance in solar-analog stars. We computed a new extensive grid of stellar evolutionary models, applicable to solar-analog stars, for a finely discretized set of mass and metallicity. From these models, the stellar mass, age, and mass depth of the outer convective zone were estimated for 117 solar-analog stars, using Teff and [Fe/H] available in the literature, and the new HIPPARCOS trigonometric parallax measurements. We determine the age and mass of the outer convective zone for a bona fide sample of 117 solar-analog stars. No significant on-to-one correlation is found between the computed convection zone mass and published lithium abundance, indicating that the large A(Li) dispersion in solar analogs cannot be explained by the classical framework of envelope convective mixing coupled with lithium depletion at the bottom of the convection zone. These results illustrate the need for an extra-mixing process to explain lithium behavior in solar-analog stars, such as, shear mixing caused by differential rotation. To derive a more realistic definition of solar-analog stars, as well as solar-twin, it seems important to consider the inner physical properties of stars, such as convection, hence rotation and magnetic properties.
Spider is a balloon-borne array of six telescopes that will observe the Cosmic Microwave Background. The 2624 antenna-coupled bolometers in the instrument will make a polarization map of the CMB with approximately one-half degree resolution at 145 GHz. Polarization modulation is achieved via a cryogenic sapphire half-wave plate (HWP) skyward of the primary optic. We have measured millimeter-wave transmission spectra of the sapphire at room and cryogenic temperatures. The spectra are consistent with our physical optics model, and the data gives excellent measurements of the indices of A-cut sapphire. We have also taken preliminary spectra of the integrated HWP, optical system, and detectors in the prototype Spider receiver. We calculate the variation in response of the HWP between observing the CMB and foreground spectra, and estimate that it should not limit the Spider constraints on inflation.
Motivated by the solar composition problem and by using the recently developed Linear Solar Model approach, we analyze the role of opacity and metals in the sun. After a brief discussion of the relation between the effects produced by a variation of composition and those produced by a modification of the radiative opacity, we calculate numerically the opacity kernels that, in a linear approximation, relate an arbitrary opacity variation to the corresponding modification of the solar observable properties. We use these opacity kernels to discuss the present constraints on opacity (and composition) provided by helioseismic and solar neutrino data.
Using the Very Large Array (VLA) at 3.6~cm we identify four new compact radio sources in the vicinity of the cometary HII region G78.4+2.6 (VLA~1). The four compact radio sources (named VLA~2 to VLA~5), have near-infrared counterparts, as seen in the 3.6 $\mu$m Spitzer image. One of them (VLA~5) clearly shows evidence of radio variability in a timescale of hours. We explore the possibility that these radio sources are associated with pre-main sequence (PMS) stars in the vicinity of the UC HII region G78.4+2.6. Our results favor the smaller distance value of 1.7 kpc for G78.4+2.6. In addition to the detection of the radio sources in the vicinity of G78.4+2.6, we detected another group of five sources which appear located about 3' to the northwest of the HII region. Some of them exhibit extended emission.
High-energy photons emitted from gamma-ray bursts (GRBs) are subject to pair-production interactions with lower energy photons, leading to an effective optical depth. In this Letter, we estimate the opacity resulting from photon fields located at various distances from long GRB sites: that of the binary companion to the massive stellar progenitor, that of the star-forming molecular cloud containing the GRB, and the total photon field of the host galaxy. The first two photon fields are found to be transparent for most reasonable sets of assumptions about these systems. In the case of galactic radiation fields, we have performed several numerical simulations to calculate the expected opacities for different line-of-sight geometries through the host galaxy, and include a full accounting of the infrared radiation produced by the absorption and re-radiation of starlight by dust. The optical depth for GeV gamma-rays, due to direct starlight is less than unity for all host galaxies. At higher energies, $>$10 TeV, a spectral cutoff can occur due to the rapidly increasing number of mid- to far-IR intra-galactic photons reradiated by dust. Photons in the extragalactic background light therefore remain the only relevant source of photon-photon opacity for ongoing GRB observations with Fermi LAT, and potential future detections with ground-based gamma-ray telescopes.
We analyse observed fractions of core-collapse SN types from the Lick Observatory SN Search, and we discuss corresponding implications for massive star evolution. For a standard IMF, observed fractions of SN types cannot be reconciled with expectations of single-star evolution. The mass range of WR stars that shed their H envelopes via their own mass loss accounts for less than half the observed fraction of SNeIbc. Progenitors of SNeIbc must extend to a much lower range of initial masses than classical WR stars, and we argue that most SNIbc and SNIIb progenitors must arise from binary Roche-lobe overflow. SNeIc still trace higher mass and metallicity, because line-driven winds in the WR stage remove the He layer and propel the transition from SNIb to Ic. Less massive progenitors of SNeIb and IIb may not be classical WR stars; they may be underluminous with weak winds, possibly hidden by overluminous mass-gainer companions that appear as B[e] supergiants or related objects having aspherical circumstellar material. The remaining SN types (II-P, II-L, and IIn) are redistributed across the full range of initial mass. We consider direct collapse to black holes without visible SNe, but find this problematic. Major areas of remaining uncertainty are (1) the influence of binary separation, rotation, and metallicity, (2) mass differences in progenitors of SNeIIn compared to SNeII-L and II-P, and (3) SNeIc arising from single stars with eruptive mass loss, its dependence on metallicity, and how it relates to diversity within the SNIc subclass. (abridged)
In this second paper of two analysis, we present near-infrared morphological and asymmetry studies perfomed in sample of 92 galaxies found in different density environments: galaxies in Compact Groups (HCGs), Isolated Pairs of Galaxies (KPGs), and Isolated Galaxies (KIGs). Both studies have proved useful to identify the effect of interactions on galaxies. In the NIR, the properties of the galaxies in HCGs, KPGs and KIGs are more similar than in the optical. This is because the NIR band traces the older stellar populations, which formed earlier and are more relaxed than the younger populations. However, we found asymmetries related to interacions in both, KPG and HCG samples. In HCGs, the fraction of asymmetric galaxies is even higher than what we found in the optical. In the KPGs, the interactions look like very recent events, while in the HCGs, galaxies are more morphologically evolved and show properties suggesting they suffered more frequent interactions. The key difference seems to be the absence of star formation in the HCGs: while interactions produce intense star formation in the KPGs we do not see this effect in the HCGs. This is consistent with the dry merger hypothesis (Coziol & Plauchu-Frayn 2007): the interaction between galaxies in compact groups, (CG), are happening without the presence of gas. If the gas was spent in stellar formation (to build the bulge of the numerous early-type galaxies), then the HCGs possibly started interacting sometime before the KPGs. On the other hand, the dry interaction condition in CGs suggests the galaxies are on merging orbits, and consequently such system cannot be that much older either. [abridge]
We present the first observations of diffuse radiation in the far ultraviolet (1000 -- 1150 \AA) from the Large Magellanic Cloud based on observations made with the {\it Far Ultraviolet Spectroscopic Explorer}. The fraction of the total radiation in the field emitted as diffuse radiation is typically 5 -- 20\% with a high of 45\% near N70 where there are few exciting stars, indicating that much of the emission is not due to nearby stars. Much less light is scattered in the far ultraviolet than at longer wavelengths with the stellar radiation going into heating the interstellar dust.
The new 1-m f/4 fast-slew Zadko Telescope was installed in June 2008 about 70 km north of Perth, Western Australia. It is the only metre-class optical facility at this southern latitude between the east coast of Australia and South Africa, and can rapidly image optical transients at a longitude not monitored by other similar facilities. We report on first imaging tests of a pilot program of minor planet searches, and Target of Opportunity observations triggered by the Swift satellite. In 12 months, 6 gamma-ray burst afterglows were detected, with estimated magnitudes; two of them, GRB 090205 (z = 4.65) and GRB 090516 (z = 4.11), are among the most distant optical transients imaged by an Australian telescope. Many asteroids were observed in a systematic 3-month search. In September 2009, an automatic telescope control system was installed, which will be used to link the facility to a global robotic telescope network; future targets will include fast optical transients triggered by highenergy satellites, radio transient detections, and LIGO gravitational wave candidate events. We also outline the importance of the facility as a potential tool for education, training, and public outreach.
We present a novel exact solution to Einstein's General Relativity equations for an ideal fluid and explore the possibility that it could describe the patch of the universe observable to us. We consider a Lorentzian manifold whose metric can be parameterized as $g_{\mu \nu} = diag\left(1, -a^2(t) r_0^2/r^2, -a^2(t) r_0^2/r^2, -a^2(t) r_0^2/r^2\right)$ in a cartesian comoving grid $(t,x,y,z)$ in which the fluid is assumed to be at rest $u^{\mu}=(1,0,0,0)$, $t$ denotes cosmological time, $r=\sqrt{x^2+y^2+z^2}$ is a radial comoving coordinate and $r_0$ is a characteristic $length$ scale. This novel class of solutions fits well with the observational pillars upon which relies the standard FLRW cosmology and, furthermore, it naturally solves some of its most outstanding problems.
Pulsar timing array projects are carrying out high precision observations of millisecond pulsars with the aim of detecting ultra-low frequency (~ 10^{-9} to 10^{-8} Hz) gravitational waves. We show how unambiguous detections of such waves can be obtained by identifying a signal that is correlated between the timing of different pulsars. Here we describe the ongoing observing projects, the expected sources of gravitational waves, the processing of the data and the implications of current results.
Subdwarf B stars (sdBs) can significantly change the ultraviolet spectra of
populations at age $t\sim$1\,Gyr, and have been even included in the
volutionary population synthesis (EPS) models by Han et al. (2007). In this
study we present the spectral energy distributions (SEDs) of binary stellar
populations (BSPs) by combining the EPS models of Han et al. (2007) and those
of { the} Yunnan group (Zhang et al. 2004, 005), which have included various
binary interactions (except sdBs) in EPS models. This set { of} SEDs { is}
available { upon} request from the authors.
Using this set { of} SEDs of BSPs we build the spectra of Burst, E, S0-Sd and
Irr types of galaxies by using the package of Bruzual \& Charlot { (2003,
BC03)}. { Combined} with the photometric data (filters and magnitudes), we
obtain the photometric redshifts and morphologies of 1502 galaxies by using the
\textit{Hyperz} code of Bolzonella et al. { (2000)}. This sample of galaxies is
obtained by removing those objects, { mismatched} with {\sl the} SDSS/DR7 and
GALEX/DR4, from the catalogue of Fukugita et al. { (2007)}. By comparison the
results with the SDSS spectroscopic redshifts and the morphological index of
Fukugita et al. { (2007)}, we find that the photo-$z$s fluctuate with the SDSS
spectroscopic redshifts, while the Sa-Sc galaxies in the catalogue of Fukugita
et al. { (2007)} are classified earlier as Burst-E galaxies.
Studies of galactic circumnuclear environments is important to our understanding of the feeding and feedback of the central super-massive black hole and in turn the global evolution of the host galaxy. We present an observational overview of the circumnuclear environment in M31 and a tentative understanding of its regulation. Notes on selected open issues, as well as on a comparison with the Galactic Center and other extragalactic circumnuclear environments, are also presented.
We report the discovery of the likely orbital period of the ultracompact low-mass X-ray binary (LMXB) 2S 0918-549. Using time-resolved optical photometry carried out with the 8-m Gemini South Telescope, we obtained a 2.4-hr long, Sloan r' light curve of 2S 0918-549 and found a periodic, sinusoidal modulation at 17.4+/-0.1 min with a semiamplitude of 0.015+/-0.002 mag. We identify the modulation as the binary period. In addition to 4U 0513-40 in the globular cluster NGC 1851 and the Galactic disk source 4U 1543-624, 2S 0918-549 is the third member of the ultracompact LMXBs that have orbital periods around 18 min. Our result verifies the suggestion of 2S 0918-549 as an ultracompact binary based on its X-ray and optical spectroscopic properties. Given that the donor in 2S 0918-549 has been suggested to be either a C-O or He white dwarf, its likely mass and radius are around 0.024--0.029 M_sun and 0.03--0.032 R_sun, respectively, for the former case and 0.034--0.039 M_sun and 0.033--0.035 R_sun for the latter case. If the optical modulation arises from X-ray heating of the mass donor, its sinusoidal shape suggests that the binary has a low inclination angle, probably around 10 deg.
In our evolutionary population synthesis models, the samples of binaries are
reproduced by the '{\sl patched}' Monte Carlo simulation and the stellar
masses, integrated $J, H, K, L, L2$ and $M$ magnitudes, mass-to-light ratios
and broad colours involving infrared bands are presented, for an extensive set
of instantaneous-burst binary stellar populations. In addition, the
fluctuations in the integrated colours, which have been given by
\citet{zha05a}, are reduced.
By comparing the results for binary stellar populations with (Model A) and
without (Model B) binary interactions we show that the inclusion of binary
interactions makes the stellar mass of a binary stellar population smaller
($\sim$\,3.6-4.5\,\% during the past 15\,Gyr); magnitudes greater (except $U$,
$\sim$\,0.18\,mag at the most); colours smaller ($\sim$\,0.15\,mag for $V-K$ at
the most); the mass-to-light ratios greater ($\sim$\,0.06 for $K$-band) except
those in the $U$ and $B$ passbands at higher metallicities. And, Binary
interactions make the $V$ magnitude less sensitive to age, $R$ and $I$
magnitudes more sensitive to metallicity.
Given an age, the absolute values of the differences in the stellar mass,
magnitudes, mass-to-light ratios (except those in the $U$ and $B$ bands)
between Models A and B reach the maximum at $Z=0.0001$, i.e., the effects of
binary interactions on these parameters reach the maximum, while the
differences in some colours reach the maximum at $Z \sim$\,0.01-0.0004. On the
contrary, the absolute value of the difference in the stellar mass is minimal
at $Z=0.03$, those in the $U,B,V$ magnitudes and the mass-to-light ratios in
the $U$ and $B$ bands reach the minimum at $Z \sim$\,0.01-0.004.
To investigate the metallicity distribution function (MDF) of the Galactic halo, a metal-poor main-sequence turnoff-star (MSTO) sample was selected from the Hamburg/ESO objective-prism survey (HES) database. Corresponding follow-up moderate-resolution observations (R ~ 2000) of some 682 stars (among which 617 were accepted program stars) were carried out with the 2.3m telescope at the Siding Spring Observatory (SSO). Corrections for the survey volume covered by the sample stars were quantitatively estimated and applied to the observed MDF. The corrections are quite small, when compared with those for a previously studied sample of metal-poor giants. The corrected observational MDF of the turnoff sample was then compared with that of the giants, as well as with a number of theoretical predictions of Galactic chemical evolution, including the mass-loss modified simple model. We show that, though the survey-volume corrected MDFs of the metal-poor turnoff and the halo giants notably differ in the region of [Fe/H] > -2.0, in the region of [Fe/H] < -2.0, i.e., the most important region in this work, both MDFs show a sharp drop at [Fe/H] ~ -3.6 and present rather similar distributions in the low-metallicity tail. Theoretical models can fit part of the observed MDF, but none is found to simultaneously reproduce the peak and features in the metal-poor region with [Fe/H] between -2.0 to -3.6. Among the models tested, only the GAMETE model, with Z_{cr} = 10^{-3.4}Z_{\odot}, is able to predict the sharp drop at [Fe/H] ~ -3.6, when fit to the tail of the observed MDF below [Fe/H] ~ -3.0.
The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (>1/2) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton scattered relic radiation from the cosmic microwave background (CMB), with additional contribution at higher energies from the infrared-to-optical extragalactic background light (EBL). These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, and a promising method to probe the cosmic relic photon fields.
Bayesian methods are becoming more widely used in asteroseismic analysis. In particular, they are being used to determine oscillation frequencies, which are also commonly found by Fourier analysis. It is important to establish whether the Bayesian methods provide an improvement on Fourier methods. We compare, using simulated data, the standard iterative sine-wave fitting method against a Markov Chain Monte Carlo (MCMC) code that has been introduced to infer purely the frequencies of oscillation modes (Brewer et al. 2007). A uniform prior probability distribution function is used for the MCMC method. We find the methods do equally well at determining the correct oscillation frequencies, although the Bayesian method is able to highlight the possibility of a misidentification due to aliasing, which can be useful. In general, we suggest that the least computationally intensive method is preferable.
We comment on the recent arguments by Senatore and Zaldarriaga that loop corrections to the zeta-zeta correlator cannot grow with time after first horizon crossing. We first emphasize the need to search for such secular dependence in corrections whose in-out matrix elements are infrared singular on an infinite spatial manifold. Then we give examples of such time dependence from pure quantum gravity and from scalar potential models. Finally, we point out that this time dependence arises from inflationary particle production and is therefore unlikely to endanger the preservation of super-horizon correlations as a record of inflation.
A numerical model of the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect for objects defined in terms of a triangular mesh is described. The algorithm requires that each surface triangle can be handled independently, which implies the use of a 1D thermal model. Insolation of each triangle is determined by an optimized ray-triangle intersection search. Surface temperature is modeled with a spectral approach; imposing a quasi-periodic solution we replace heat conduction equation by the Helmholtz equation. Nonlinear boundary conditions are handled by an iterative, FFT based solver. The results resolve the question of the YORP effect in rotation rate independence on conductivity within the nonlinear 1D thermal model regardless of the accuracy issues and homogeneity assumptions. A seasonal YORP effect in attitude is revealed for objects moving on elliptic orbits when a nonlinear thermal model is used.
We present a study of the motion of compact jet components in quasar B3 1633+382. Through analyzing 14 epochs of VLBI observations of three components (B1, B2, and B3) at 22 GHz, we find two different possibilities of component classification. Thus two corresponding kinematical models can be adopted to explain the evolutionary track of components. One is a linear motion, while another is a helical model. Future observations are needed to provide new kinematical constraints for the motion of these components in this source.
We demonstrate novel features in the behavior of the second and third order non-linearity parameters of the curvature perturbation, namely, $f_{NL}$ and $g_{NL}$, arising from non-linear motion of curvaton field. We investigate two classes of potentials for the curvaton - the first has tiny oscillations super-imposed upon the quadratic potential. The second is characterized by a single 'feature' separating two quadratic regimes with different mass scales. The feature may either be a bump or a flattening of the potential. In the case of the oscillatory potential we find that as the width and height of superimposed oscillations increase, both $f_{NL}$ and $g_{NL}$ deviate strongly from their expected values from a quadratic potential. $f_{NL}$ changes sign from positive to negative as the oscillations in the potential become more prominent. Hence, this model can be severely constrained by convincing evidence from observations that $f_{NL}$ is positive. $g_{NL}$, on the other hand, acquires very large negative values. For the the single feature potential, we find that $f_{NL}$ and $g_{NL}$ exhibit oscillatory behavior as a function of the parameter that controls the feature.
Measurements of the interplanetary magnetic field (IMF) over several solar cycles do not agree with computed values of open magnetic flux from potential field extrapolations. The discrepancy becomes greater around solar maximum in each cycle, when the IMF can be twice as strong as predicted by the potential field model. Here we demonstrate that this discrepancy may be resolved by allowing for electric currents in the low corona (below 2.5 solar radii). We present a quasi-static numerical model of the large-scale coronal magnetic evolution, which systematically produces these currents through flux emergence and shearing by surface motions. The open flux is increased by 75%-85% at solar maximum, but only 25% at solar minimum, bringing it in line with estimates from IMF measurements. The additional open flux in the non-potential model arises through inflation of the magnetic field by electric currents, with super-imposed fluctuations due to coronal mass ejections. The latter are modelled by the self-consistent ejection of twisted magnetic flux ropes.
Observations of the A5p star KIC 8677585 obtained during the Kepler 10-d commissioning run with 1-min time resolution show that it is a roAp star with several frequencies with periods near 10 min. In addition, a low frequency at 3.142 cycles/day is also clearly present. Multiperiodic gamma Doradus and delta Scuti pulsations, never before seen in any Ap star, are present in Kepler observations of at least three other Ap stars. Since gamma Doradus pulsations are seen in Ap stars, it is likely that the low-frequency in KIC 8677585 is also a gamma Doradus pulsation. The simultaneous presence of both gamma Doradus and roAp pulsations and the unexpected detection of delta Scuti and gamma Doradus pulsations in Ap stars present new opportunities and challenges for the interpretation of these stars.
We describe a method of determining the V magnitude of an asteroid using differential photometry, with the magnitudes of comparison stars derived from Carlsberg Meridian Catalogue 14 (CMC14) data. The availability of a large number of suitable CMC14 stars enables a reasonably accurate magnitude (\pm0.05 mag) to be found without having to resort to more complicated absolute or all-sky photometry. An improvement in accuracy to \pm0.03 mag is possible if an ensemble of several CMC14 stars is used. This method is expected to be less accurate for stars located within \pm10deg of the galactic equator owing to excessive interstellar reddening and stellar crowding.
A photometric method is described for accurately quantifying the brightness of short-period comets far from perihelion. The method utilizes the Sloan Digital Sky Survey Catalog (Data Release 7) as a homogeneous source of reference star magnitudes. Results are based on SDSS-r' filtered images taken using 2.0-m aperture telescopes for which the exposure time was adjusted to achieve a constant motion-blur of 2.0 pixels (0.56 arcsec) on the CCD chip. Aperture photometry using circular and tilted elliptical apertures was performed on images, which were stacked to increase signal to noise. Magnitude dependence on 'seeing' was determined, and this calibration was used to normalize photometry to constant seeing thereby maximizing photometric accuracy. From observations of comet 17P/Holmes between 2008 October and 2009 March, a very significant outburst of 17P was found to have occurred on 2009 Jan 4.7 (\pm0.5 day). Night-to-night measurements of the brightness of the inner coma (3000-km radius) exhibited a scatter of only 0.015-0.019 mag. No short time-scale (<36 hr) periodicity was found in the fading lightcurve. From literature data, it was estimated that reflected light from the nucleus contributed 7-11% of the signal within the inner coma and it is concluded that either the nucleus of 17P must be relatively spherical (projected axial ratio of <1.25), or, if its shape is more typical of other comet nuclei, it has a rotational period in excess of 10 days (assuming the observations were not made with the nucleus 'pole-on' to the Earth). Evidence from intermittent activity displayed by the nucleus is indicative of a possible 44-day rotation period.
Several lines of evidence suggest that fine silicate crystals observed in primitive meteorite and interplanetary dust particles (IDPs) nucleated in a supersaturated silicate vapor followed by crystalline growth. We investigated evaporation of $\mu$m-sized silicate particles heated by a bow shock produced by a planetesimal orbiting in the gas in the early solar nebula and condensation of crystalline silicate from the vapor thus produced. Our numerical simulation of shock-wave heating showed that these {\mu}m-sized particles evaporated almost completely when the bow shock is strong enough to cause melting of chondrule precursor dust particles. We found that the silicate vapor cools very rapidly with expansion into the ambient unshocked nebular region; the cooling rate is estimated, for instance, to be as high as 2000 K s$^{-1}$ for a vapor heated by a bow shock associated with a planetesimal of radius 1 km. The rapid cooling of the vapor leads to nonequilibrium gas-phase condensation of dust at temperatures much lower than those expected from the equilibrium condensation. It was found that the condensation temperatures are lower by a few hundred K or more than the equilibrium temperatures. This explains the results of the recent experimental studies of condensation from a silicate vapor that condensation in such large supercooling reproduces morphologies similar to those of silicate crystals found in meteorites. Our results suggest strongly that the planetesimal bow shock is one of the plausible sites for formation of not only chondrules but also other cosmic crystals in the early solar system.
A black hole accretion may have both the Keplerian and the sub-Keplerian component. In the so-called Chakrabarti-Titarchuk scenario, the Keplerian component supplies low energy (soft) photons while the sub-Keplerian component supplies hot electrons which exchange their energy with the soft photons through Comptonization or inverse Comptonization processes. In the sub-Keplerian component, a shock is generally produced due to the centrifugal force. The postshock region is known as the CENtrifugal pressure-supported BOundary Layer (CENBOL). In this paper, we compute the effects of the thermal and the bulk motion Comptonization on the soft photons emitted from a Keplerian disk by the CENBOL, the preshock sub-Keplerian disk and the outflowing jet. We study the emerging spectrum when the converging inflow and the diverging outflow (generated from the CENBOL) are simultaneously present. From the strength of the shock, we calculate the percentage of matter being carried away by the outflow and determine how the emerging spectrum depends on the outflow rate. The preshock sub-Keplerian flow is also found to Comptonize the soft photons significantly. The interplay between the up-scattering and down-scattering effects determines the effective shape of the emerging spectrum. By simulating several cases with various inflow parameters, we conclude that whether the preshock flow, or the postshock CENBOL or the emerging jet is dominant in shaping the emerging spectrum depends strongly on the geometry of the flow and the strength of the shock in the sub-Keplerian flow.
We present an analysis of stellar population gradients in 4,546 Early-Type Galaxies with photometry in $grizYHJK$ along with optical spectroscopy. A new approach is described which utilizes color information to constrain age and metallicity gradients. Defining an effective color gradient, $\nabla_{\star}$, which incorporates all of the available color indices, we investigate how $\nabla_{\star}$ varies with galaxy mass proxies, i.e. velocity dispersion, stellar (M_star) and dynamical (M_dyn) masses, as well as age, metallicity, and alpha/Fe. ETGs with M_dyn larger than 8.5 x 10^10, M_odot have increasing age gradients and decreasing metallicity gradients wrt mass, metallicity, and enhancement. We find that velocity dispersion and alpha/Fe are the main drivers of these correlations. ETGs with 2.5 x 10^10 M_odot =< M_dyn =< 8.5 x 10^10 M_odot, show no correlation of age, metallicity, and color gradients wrt mass, although color gradients still correlate with stellar population parameters, and these correlations are independent of each other. In both mass regimes, the striking anti-correlation between color gradient and alpha-enhancement is significant at \sim 4sigma, and results from the fact that metallicity gradient decreases with alpha/Fe. This anti-correlation may reflect the fact that star formation and metallicity enrichment are regulated by the interplay between the energy input from supernovae, and the temperature and pressure of the hot X-ray gas in ETGs. For all mass ranges, positive age gradients are associated with old galaxies (>5-7 Gyr). For galaxies younger than \sim 5 Gyr, mostly at low-mass, the age gradient tends to be anti-correlated with the Age parameter, with more positive gradients at younger ages.
We present high resolution images of the bipolar outflow in W51e2, which are produced from the Submillimeter Array archival data observed for CO(3-2) and HCN(4-3) lines with angular resolutions of 0.8" x 0.6" and 0.3" x 0.2", respectively. The images show that the powerful outflow originates from the protostellar core W51e2-E rather than from the ultracompact HII region W51e2-W. The kinematic timescale of the outflow from W51e2-E is about 1000 yr, younger than the age (~5000 yr) of the ultracompact HII region W51e2-W. A large mass loss rate of ~1 x 10^{-3} M_sun yr^{-1} and a high mechanical power of 120 L_sun are inferred, suggesting that an O star or a cluster of B stars are forming in W51e2-E. The observed outflow activity along with the inferred large accretion rate indicates that at present W51e2-E is in a rapid phase of star formation.
While QCD appears not to be accurately solvable in the regime of interest for neutron star physics, microscopic calculations are feasible at both low and very high densities. In this work, we propose using the most realistic calculations in these two regimes of nuclear physics and perturbative QCD, and construct equations of state by matching the results requiring thermodynamic consistency. We find that the resulting equations of state --- in contrast to several hadronic ones --- are able to reproduce current observational data on neutron stars without any fine tuning, and allow stable hybrid stars with masses up to 2.1M_{sun}. Using recent observations of star radii, we perform a maximum likelihood analysis to further constrain the equation of state, and in addition show that the effects of rotation on radii and masses should not be neglected in future precision studies.
Temporal analysis of radiation from Astrophysical sources like Active Galactic Nuclei, X-ray Binaries and Gamma-ray bursts provide information on the geometry and sizes of the emitting regions. Robustly establishing that two light-curves in different energy bands are correlated and measuring the phase and time-lag between them is an important and frequently used temporal diagnostic. Analytical expressions to estimate the errors on the cross-correlation, phase and time-lag between two light-curves are presented. Earlier estimates depended upon numerically expensive simulations or on dividing the light-curves in large number of segments to find the variance. Thus, the analytical estimates presented here allow for analysis of light-curves with relatively small (~ 1000) number of points, as well as to obtain information on the longest time-scales available. The error estimation is verified using simulations of light-curves derived from both white and 1/f stochastic processes with measurement errors. As a demonstration, we apply this technique to the XMM-Newton light-curves of the Active Galactic Nucleus, Akn 564.
We analyze the chemical abundances of planetary nebulae and HII regions in the M81 disk for insight on galactic evolution, and compare it with that of other galaxies, including the Milky Way. We acquired Hectospec/MMT spectra of 39 PNe and 20 HII regions, with 33 spectra viable for temperature and abundance analysis. Our PN observations represent the first PN spectra in M81 ever published, while several HII region spectra have been published before, although without a direct electron temperature determination. We determine elemental abundances of helium, nitrogen, oxygen, neon, sulfur, and argon in PNe and HII regions, and determine their averages and radial gradients. The average O/H ratio of PNe compared to that of the HII regions indicates a general oxygen enrichment in M81 in the last ~10 Gyr. The PN metallicity gradient in the disk of M81 is -0.055+-0.02 dex/kpc. Neon and sulfur in PNe have a radial distribution similar to that of oxygen, with similar gradient slopes. If we combine our HII sample with the one in the literature we find a possible mild evolution of the gradient slope, with results consistent with gradient steepening with time. Additional spectroscopy is needed to confirm this trend. There are no Type I PNe in our M81 sample, consistently with the observation of only the brightest bins of the PNLF, the galaxy metallicity, and the evolution of post-AGB shells. Both the young and the old populations of M81 disclose shallow but detectable negative radial metallicity gradient, which could be slightly steeper for the young population, thus not excluding a mild gradients steepening with the time since galaxy formation. During its evolution M81 has been producing oxygen; its total oxygen enrichment exceeds that of other nearby galaxies.
We present high- and intermediate resolution radio observations of the central region in the spiral galaxy IC 2497, performed using the European VLBI Network (EVN) at 18 cm, and the Multi-Element Radio Linked Interferometer Network (MERLIN) at 18 cm and 6 cm. We detect two compact radio sources, with brightness temperatures above 10e5 K, suggesting that they are related to AGN activity. We show that the total 18 cm radio emission from the galaxy is dominated neither by these compact sources nor large-scale emission, but extended emission confined within a sub-kpc central region. IC 2497 therefore appears as a typical luminous infrared galaxy that exhibits a nuclear starburst with a massive star formation rate (M > 5M_solar) of 12.4 M_solar/yr. These results are in line with the hypothesis that the ionisation nebula "Hanny's Voorwerp" at a distance of approx. 15-25 kpc from the galaxy is ionised by the radiation cone of the AGN.
We study the effect of massive neutrinos on the evolution of the early mini-halos (M~10^{6} M_{\odot} at z~20) where the first stars may have formed. In the framework of the extended Press-Schechter formalism, we evaluate analytically the rates of merging of the mini-halos into zero-dimensional larger halos and one dimensional mini-filaments. It is shown that the halo-to-filament merging rate increases sharply with the neutrino mass fraction f_{\nu} while the halo-to-halo merging rate decreases with f_{\nu}. For f_{\nu}\le 0.04, the halo-to-filament merging rate is negligibly low at all filament mass scales while for f_{\nu}\ge0.07 the halo- to-filament merging rate exceeds the halo-to-halo merging rate at the characteristic filament mass scales of 10^{9}-10^{10} M_{\odot}. The distribution of the epochs of the longest-axis collapse of these first filaments is also derived and found to reach a sharp maximum at z~8-9. Once the first mini-filaments form, they would provide bridges along which the matter and gas more rapidly accrete onto the constituent halos, causing the early formation of the first galaxies and rapid growth of their central blackholes. Furthermore, the longest axis collapse of these first mini-filaments would spur the supermassive blackholes to power the ultraluminous high-$z$ quasars. In this scenario, the mass estimate ~3x10^{9}M_{\odot} for the supermassive blackholes in the Sloan quasar detected at $z\approx 6.4$ by Willott et al. in 2003 corresponds to an upper limit of the neutrino neutrino mass, m_{\nu}\le 0.22 eV.
In strict analogy to prompt pulses, X-ray flares observed by Swift-XRT in long Gamma-Ray Bursts define a lag-luminosity relation: L_p,iso \propto t_lag^{-0.95+/-0.23}. The lag-luminosity is proven to be a fundamental law extending 5 decades in time and 5 in energy. This is direct evidence that GRB X-ray flares and prompt gamma-ray pulses are produced by the same mechanism.
Angular momentum loss in ultracompact binaries, such as the AM Canum Venaticorum stars, is usually assumed to be due entirely to gravitational radiation. Motivated by the outflows observed in ultracompact binaries, we investigate whether magnetically coupled winds could in fact lead to substantial additional angular momentum losses. We remark that the scaling relations often invoked for the relative importance of gravitational and magnetic braking do not apply, and instead use simple non-empirical expressions for the braking rates. In order to remove significant angular momentum, the wind must be tied to field lines anchored in one of the binary's component stars; uncertainties remain as to the driving mechanism for such a wind. In the case of white dwarf accretors, we find that magnetic braking can potentially remove angular momentum on comparable or even shorter timescales than gravitational waves over a large range in orbital period. We present such a solution for the 17-minute binary AM CVn itself which admits a cold white dwarf donor and requires that the accretor have surface field strength ~6E4 G. Such a field would not substantially disturb the accretion disk. Although the treatment in this paper is necessarily simplified, and many conditions must be met in order for a wind to operate as proposed, it is clear that magnetic braking cannot easily be ruled out as an important angular momentum sink. We finish by highlighting observational tests that in the next few years will allow an assessment of the importance of magnetic braking.
Aims: We investigated the X-ray emission from young stars and brown dwarfs in the sigma Orionis cluster (tau~3 Ma, d~385 pc) and its relation to mass, presence of circumstellar discs, and separation to the cluster centre by taking advantage of the superb spatial resolution of the Chandra X-ray Observatory. Methods: We used public HRC-I/Chandra data from a 97.6 ks pointing towards the cluster centre and complemented them with X-ray data from IPC/Einstein, HRI/ROSAT, EPIC/XMM-Newton, and ACIS-S/Chandra together with optical and infrared photometry and spectroscopy from the literature and public catalogues. On our HRC-I/Chandra data, we measured count rates, estimated X-ray fluxes, and searched for short-term variability. We also looked for long-term variability by comparing with previous X-ray observations. Results: Among the 107 detected X-ray sources, there were 70 cluster stars with known signposts of youth, two young brown dwarfs, 12 cluster member candidates, four field dwarfs, and two galaxies with optical-infrared counterpart. The remaining sources had extragalactic nature. Based on a robust Poisson-chi^2 analysis, nine cluster stars displayed flares or rotational modulation during the HRC-I observations, while other eight stars and one brown dwarf showed long-term X-ray flux variations. We constructed a cluster X-ray luminosity function from O9.5 (~18 Msol) to M6.5 (~0.06 Msol). We found: a tendency of early-type stars in multiple systems or with spectroscopic peculiarities to display X-ray emission, that the two detected brown dwarfs and the least-massive star are among the sigma Orionis objects with the highest L_X/L_J ratios, and that a large fraction of known classical T Tauri stars in the cluster are absent in this and other X-ray surveys. We concluded that dozens X-ray sigma Orionis stars and brown dwarfs are still to be detected [abridged].
Aims: We investigated in detail the system WDS 19312+3607, whose primary is an active M4.5Ve star previously thought to be young (tau ~ 300-500 Ma) based on high X-ray luminosity. Methods: We collected intermediate- and low-resolution optical spectra taken with 2 m-class telescopes, photometric data from the $B$ to 8 mum bands, and eleven astrometric epochs with a time baseline of over 56 years for the two components in the system, G 125-15 and G 125-14. Results: We derived M4.5V spectral types for both stars, confirmed their common proper motion, estimated the heliocentric distance and projected physical separation, determined the galactocentric space velocities, and deduced a most-probable age older than 600 Ma. We discovered that the primary, G 125-15, is in turn an inflated, double-lined, spectroscopic binary with a short period of photometric variability of P ~ 1.6 d, which we associated to orbital synchronisation. The observed X-ray and Halpha emissions, photometric variability, and abnormal radius and effective temperature of G 125-15 AB indicate strong magnetic activity, possibly due to fast rotation. Besides, the estimated projected physical separation between G 125-15 AB and G 125-14 of about 1200 AU makes WDS 19312+3607 to be one of the widest systems with intermediate M-type primaries. Conclusions: G 125-15 AB is a nearby (d ~ 26 pc), bright (J ~ 9.6 mag), active spectroscopic binary with a single proper-motion companion of the same spectral type at a wide separation. They are thus ideal targets for specific follow-ups to investigate wide and close multiplicity or stellar expansion and surface cooling due to reduced convective efficiency.
We present a radiative magnetohydrodynamics simulation of the formation of an Active Region on the solar surface. The simulation models the rise of a buoyant magnetic flux bundle from a depth of 7.5 Mm in the convection zone up into the solar photosphere. The rise of the magnetic plasma in the convection zone is accompanied by predominantly horizontal expansion. Such an expansion leads to a scaling relation between the plasma density and the magnetic field strength such that $B\propto\varrho^{1/2}$. The emergence of magnetic flux into the photosphere appears as a complex magnetic pattern, which results from the interaction of the rising magnetic field with the turbulent convective flows. Small-scale magnetic elements at the surface first appear, followed by their gradual coalescence into larger magnetic concentrations, which eventually result in the formation of a pair of opposite polarity spots. Although the mean flow pattern in the vicinity of the developing spots is directed radially outward, correlations between the magnetic field and velocity field fluctuations allow the spots to accumulate flux. Such correlations result from the Lorentz-force driven, counter-streaming motion of opposite-polarity fragments. The formation of the simulated Active Region is accompanied by transient light bridges between umbrae and umbral dots. Together with recent sunspot modeling, this work highlights the common magnetoconvective origin of umbral dots, light bridges and penumbral filaments.
We present the first results from a survey of SDSS quasars selected for strong H I damped Lyman-{\alpha} (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g. C II {\lambda}1334 and Si II {\lambda}1260). These metal-poor DLA candidates were selected from the SDSS DR5 quasar spectroscopic database, and comprise a large new sample for probing low metallicity galaxies. Medium-resolution echellette spectra from the Keck ESI spectrograph for an initial sample of 35 systems were obtained to explore the metal-poor tail of the DLA distribution and to investigate the nucleosynthetic patterns at these metallicities. We have estimated saturation corrections for the moderately under-resolved spectra, and systems with very narrow Doppler parameter (b \le 5 km s-1) will likely have underestimated abundances. For those systems with Doppler parameters b > 5 km s-1, we have measured low metallicity DLA gas with [X/H] < -2.4 for at least one of C, O, Si, or Fe. Assuming non-saturated components, we estimate that several DLA systems have [X/H] < -2.8, including five DLA systems with both low equivalent widths and low metallicity in transitions of both C II and O I. All of the measured DLA metallicities, however, exceed or are consistent with a metallicity of at least 1/1000 of solar, regardless of the effects of saturation in our spectra. Our results indicate that the metal-poor tail of galaxies at z \sim 3 drops exponentially at [X/H]< -3. The observed ratio of [C/O] for values of [O/H] < -2.5 exceeds values seen in moderate metallicity DLA systems, and also exceeds theoretical nucleosynthesis predictions for higher mass Population III stars.
The stellar rotation periods of ten exoplanet host stars have been determined using newly analysed Ca II H & K flux records from Mount Wilson Observatory and Stromgren b, y photometric measurements from Tennessee State University's automatic photometric telescopes (APTs) at Fairborn Observatory. Five of the rotation periods have not previously been reported, with that of HD 130322 very strongly detected at Prot = 26.1 \pm 3.5 d. The rotation periods of five other stars have been updated using new data. We use the rotation periods to derive the line-of-sight inclinations of the stellar rotation axes, which may be used to probe theories of planet formation and evolution when combined with the planetary orbital inclination found from other methods. Finally, we estimate the masses of fourteen exoplanets under the assumption that the stellar rotation axis is aligned with the orbital axis. We calculate the mass of HD 92788 b (28 MJ) to be within the low-mass brown dwarf regime and suggest that this object warrants further investigation to confirm its true nature.
The polarization effect of the 20 reflections within the Coude mirror train of an auxiliary telescope of the Very Large Telescope Interferometer is calculated as a function of pointing direction and rotator angle. With a rough estimate of the mean complex index of refraction of the reflecting surfaces, their Jones matrices are concatenated while tracing a ray from M1 up to the delay line tunnel. The net effect is summarized in terms of the axis ratio of the polarization ellipse of star light that was circularly polarized before hitting the primary.
We present results on modeling solar pores and sunspots using 2D axisymmetric magneto-hydrodynamic (MHD) simulations. These models are helpful for understanding the mechanisms of magnetic field concentration in sunspots, and the large-scale flow patterns associated with them. The simulations provide consistent, self-maintained, although not fully realistic, models of concentrated magnetic field near the solar surface. In this paper, we explore under which conditions the associated flows are converging or diverging near the surface. We find that in most cases in which a stable, pore-like concentration of magnetic field forms, a configuration with converging over diverging flow is established.
The phase transition from hadronic to quark matter may take place already during the early post-bounce stage of core collapse supernovae when matter is still hot and lepton rich. If the phase transition is of first order and exhibits a barrier, the formation of the new phase occurs via the nucleation of droplets. We investigate the thermal nucleation of a quark phase in supernova matter and calculate its rate for a wide range of physical parameters. We show that the formation of the first droplet of a quark phase might be very fast and therefore the phase transition to quark matter could play an important role in the mechanism and dynamics of supernova explosions.
Two field 2-forms on the space-time manifold, in a relationship of duality, are presented and applied to derive the equations of motion for relativistic particles having both electric and magnetic charges. By exterior derivatives, these forms yield the two groups of Maxwell equations, while specific integrality conditions ensure magnetic monopole or electric charge quantization. Some properties of the common characteristic vector of the dual 2-forms are discussed. It is shown that the coupled energy-density continuity equation and the eikonal equation represent a classical, infinite-dimensional Hamiltonian system.
We perform a global analysis of cosmological observables in generalized cosmologies which depart from $\Lambda$CDM models by allowing non-vanishing curvature $\Omega_k\neq 0$, dark energy with equation of state with $\omega\neq -1$, the presence of additional relativistic degrees of freedom $\Delta N_{\rm rel}$, and neutrino masses $\Omega_\nu\neq 0$. By combining the data from cosmic microwave background (CMB) experiments (in particular the latest results from WMAP-7), the present day Hubble constant (H0) measurement, the high-redshift Type-I supernovae (SN) results and the information from large scale structure (LSS) surveys, we determine the parameters in the 10-dimensional parameter space for such models. We present the results from the analysis when the full shape information from the LSS matter power spectrum (LSSPS) is included versus when only the corresponding distance measurement from the baryon acoustic oscillations (BAO) is accounted for. We compare the bounds on the neutrino mass scale in these generalized scenarios with those obtained for the 6+1 parameter analysis in $\Lambda{\rm CDM}+m_\nu$ models and we also study the dependence of those on the set of observables included in the analysis. Finally we combine these results with the information on neutrino mass differences and mixing from the global analysis of neutrino oscillation experiments and derive the presently allowed ranges for the two laboratory probes of the absolute scale of neutrino mass: the effective electron neutrino mass in single beta decay and the effective Majorana neutrino mass in neutrinoless $\beta\beta$ decay.
We use the Fock-Ivanenko formalism to obtain the Dirac equation which describes the interaction of a massless 1/2-spin neutral fermion with a gravitational field around a Schwarzschild black hole (BH). We obtain approximated analytical solutions for eigenvalues of energy (quasi-normal frequencies) and their corresponding eigenstates (quasi-normal states). The interesting result is that all the excited states [and their supersymmetric (SUSY) partners] has a purely imaginary frequency, which can be expressed in terms of the Hawking temperature. Furthermore, as one expects for SUSY Hamiltonians, the isolated bottom state has a real null-stable-eigenvalue of energy.
This work deals with $F(T)$ gravity models driven by real scalar fields with usual and phantom dynamics. We illustrate the results with examples of current interest, and we find some analytical solutions for scale factors and scalar fields. The results indicate that torsion-scalar models also admit the accelerated expansion of the universe.
We investigate strong nonlinear damping effects which occur during high amplitude oscillations of neutron stars, and the gravitational waves they produce. For this, we use a general relativistic nonlinear hydrodynamics code in conjunction with a fixed spacetime (Cowling approximation) and a polytropic equation of state (EOS). Gravitational waves are estimated using the quadrupole formula. Our main interest are $l=m=2$ $f$-modes subject to the CFS (Chandrasekhar, Friedman, Schutz) instability, but we also investigate axisymmetric and quasi-radial modes. We study various models to determine the influence of rotation rate and EOS. We find that axisymmetric oscillations at high amplitudes are predominantly damped by shock formation, while the non-axisymmetric $f$-modes are mainly damped by wave breaking and, for rapidly rotating models, coupling to non-axisymmetric inertial modes. From the observed nonlinear damping, we derive upper limits for the saturation amplitude of CFS-unstable $f$-modes. Finally, we estimate that the corresponding gravitational waves for an oscillation amplitude at the upper limit should be detectable with the advanced LIGO and VIRGO interferometers at distances above $10\usk\mega\parsec$. This strongly depends on the stellar model, in particular on the mode frequency.
We demonstrate that there exists a large class of action functionals of the scalar curvature and of the Gauss-Bonnet invariant which are able to relax dynamically a large cosmological constant (CC), whatever it be its starting value in the early universe. Hence, it is possible to understand, without fine-tuning, the very small current value of the CC as compared to its theoretically expected large value in quantum field theory and string theory. In our framework, this relaxation appears as a pure gravitational effect, where no ad hoc scalar fields are needed. The action involves a positive power of a characteristic mass parameter, M, whose value can be, interestingly enough, of the order of a typical particle physics mass of the Standard Model of the strong and electroweak interactions or extensions thereof, including the neutrino mass. The model universe emerging from this scenario (the ``Relaxed Universe'') falls within the class of the so-called LXCDM models of the cosmic evolution. Therefore, there is a ``cosmon'' entity X (represented by an effective object, not a field), which in this case is generated by the effective functional and is responsible for the dynamical adjustment of the cosmological constant. This model universe successfully mimics the essential past epochs of the standard (or ``concordance'') cosmological model (LCDM). Furthermore, it provides interesting clues to the coincidence problem and it may even connect naturally with primordial inflation.
An exact de Sitter solution of scalar-tensor gravity is found, in which the non-minimal coupling scalar is rolling along a non-constant potential. Based on this solution, a dust-filled FRW universe is explored in frame of scalar-tensor gravity. The effective dark energy induced by the sole non-minimal scalar can be quintessence-like, phantom-like, and more significantly, can cross the phantom divide. The rich and varied properties of scalar-tensor gravity even with only one scalar is shown in this article.
We show that most of cutoff measures of the multiverse violate some of the basic properties of probability theory when applied repeatedly to predict the results of local experiments. Starting from minimal assumptions, such as Markov property, we derive a correspondence between cosmological measures and quantum field theories in one lesser dimension. The correspondence allows us to replace the picture of an infinite multiverse with a finite causally connected region accessible by a given observer in conjunction with a Euclidean theory defined on its past boundary.
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We used archival multi-band Hubble Space Telescope observations obtained with the Wide-Field Camera 3 in the UV-optical channel to present new important observational findings on the color-magnitude diagram (CMD) of the Galactic globular cluster omega Centauri. The ultraviolet WFC3 data have been coupled with available WFC/ACS optical-band data. The new CMDs, obtained from the combination of colors coming from eight different bands, disclose an even more complex stellar population than previously identified. This paper discusses the detailed morphology of the CMDs.
The helicity of a photon traversing a magnetized plasma can flip when the B-field along the trajectory slowly reverses. Broderick and Blandford have recently shown that this intriguing effect can profoundly change the usual Faraday effect for radio waves. We study this phenomenon in a formalism analogous to neutrino flavor oscillations: the evolution is governed by a Schroedinger equation for a two-level system consisting of the two photon helicities. Our treatment allows for a transparent physical understanding of this system and its dynamics. In particular, it allows us to investigate the nature of transitions at intermediate adiabaticities.
This paper presents applications of weighted meshless scheme for conservation laws to the Euler equations and the equations of ideal magnetohydrodynamics. The divergence constraint of the latter is maintained to the truncation error by a new meshless divergence cleaning procedure. The physics of the interaction between the particles is described by an one-dimensional Riemann problem in a moving frame. As a result, necessary diffusion which is required to treat dissipative processes is added automatically. As a result, our scheme has no free parameters that controls the physics of inter-particle interaction, with the exception of the number of the interacting neighbours which control the resolution and accuracy. The resulting equations have the form similar to SPH equations, and therefore existing SPH codes can be used to implement the weighed particle scheme. The scheme is validated in several hydrodynamic and MHD test cases. In particular, we demonstrate for the first time the ability of a meshless MHD scheme to model magneto-rotational instability in accretion disks.
We present the final results from a high sampling rate, multi-month, spectrophotometric reverberation mapping campaign undertaken to obtain either new or improved Hbeta reverberation lag measurements for several relatively low-luminosity AGNs. We have reliably measured thetime delay between variations in the continuum and Hbeta emission line in six local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) R-L relationship, where our results remove outliers and reduce the scatter at the low-luminosity end of this relationship. We also present velocity-resolved Hbeta time delay measurements for our complete sample, though the clearest velocity-resolved kinematic signatures have already been published.
We show that stars with transiting planets for which the stellar obliquity is large are preferentially hot (T_eff > 6250 K). This could explain why small obliquities were observed in the earliest measurements, which focused on relatively cool stars drawn from Doppler surveys, as opposed to hotter stars that emerged later from transit surveys. The observed trend could be due to differences in planet formation and migration around stars of varying mass. Alternatively, we speculate that hot-Jupiter systems begin with a wide range of obliquities, but the photospheres of cool stars realign with the orbits due to tidal dissipation in their convective zones, while hot stars cannot realign because of their thinner convective zones. This in turn would suggest that hot Jupiters originate from few-body gravitational dynamics, and that disk migration plays at most a supporting role.
We report the discovery of a six-month-long mid-infrared transient, SDWFS-MT-1, in the Spitzer Deep, Wide-Field Survey of the NOAO Deep Wide-Field Survey Bootes field. The transient, located in a z=0.19 low luminosity (M_[4.5]~-18.6 mag, L/L_MilkyWay~0.01) metal-poor (12+log(O/H)~7.8) irregular galaxy, peaked at a mid-infrared absolute magnitude of M_[4.5]~-24.2 in the 4.5 micron Spitzer/IRAC band and emitted a total energy of at least 10^51 ergs. The optical emission was likely fainter than the mid-infrared, although our constraints on the optical emission are poor because the transient peaked when the source was "behind" the Sun. The Spitzer data are consistent with emission by a modified black body with a temperature of ~1350 K. We rule out a number of scenarios for the origin of the transient such as a Galactic star, AGN activity, GRB, tidal disruption of a star by a black hole and gravitational lensing. The most plausible scenario is a supernova exploding inside a massive, optically thick circumstellar medium, composed of multiple shells of previously ejected material. If the proposed scenario is correct, then a significant fraction (~10%) of the most luminous supernova may be self-enshrouded by dust not only before but also after the supernova occurs. The spectral energy distribution of the progenitor of such a supernova would be a slightly cooler version of eta Carina, peaking at 20-30 microns.
J113924.74+164144.0 is an interesting galaxy at z = 0.0693, i.e. D_L ~ 305 Mpc, with tidal-tail-like extended optical features on both sides. There are two neighbouring galaxies, a spiral galaxy J113922.85+164136.3 which has a strikingly similar 'tidal' morphology, and a faint galaxy J113923.58+164129.9. We report HI 21 cm observations of this field to search for signatures of possible interaction. Narrow HI emission is detected from J113924.74+164144.0, but J113922.85+164136.3 shows no detectable emission. The total HI mass detected in J113924.74+164144.0 is 7.7 x 10^9 M_solar. The HI emission from the galaxy is found to be extended and significantly offset from the optical position of the galaxy. We interpret this as signature of possible interaction with the neighbouring spiral galaxy. There is also a possible detection of HI emission from another nearby galaxy J113952.31+164531.8 at z = 0.0680 at a projected distance of 600 kpc, and with a total HI mass of 5.3 x 10^9 M_solar, suggesting that all these galaxies form a loose group at z ~ 0.069.
Indirect detection of high-energy particles from dark matter interactions is a promising avenue for learning more about dark matter, but is hampered by the frequent coincidence of high-energy astrophysical sources of such particles with putative high-density regions of dark matter. We calculate the boost factor and gamma-ray flux from dark matter associated with two shell-like caustics of luminous tidal debris recently discovered around the Andromeda galaxy, under the assumption that dark matter is its own supersymmetric antiparticle. These shell features are a good candidate for indirect detection of dark matter via gamma rays because they are located far from the primary confusion sources at the galaxy's center, and because the shapes of the shells indicate that most of the mass has piled up near apocenter. Using a numerical estimator specifically calibrated to estimate densities in N-body representations with sharp features and a previously determined N-body model of the shells, we find that the largest boost factors do occur in the shells but are only a few percent, and that the gamma-ray flux is an order of magnitude too low to be detected with Fermi for likely dark matter parameters. We further show that the radial density profiles and relative radial spacing of the shells, in either dark or luminous matter, is relatively insensitive to the details of the potential of the host galaxy but depends in a predictable way on the velocity dispersion of the progenitor galaxy.
Models that lead to a cosmological stiff fluid component, with a density $\rho_S$ that scales as $a^{-6}$, where $a$ is the scale factor, have been proposed recently in a variety of contexts. We calculate numerically the effect of such a stiff fluid on the primordial element abundances. Because the stiff fluid energy density decreases with the scale factor more rapidly than radiation, it produces a relatively larger change in the primordial helium-4 abundance than in the other element abundances, relative to the changes produced by an additional radiation component. We show that the helium-4 abundance varies linearly with the density of the stiff fluid at a fixed fiducial temperature. Taking $\rho_{S10}$ and $\rho_{R10}$ to be the stiff fluid energy density and the standard density in relativistic particles, respectively, at $T = 10$ MeV, we find that the change in the primordial helium abundance is well-fit by $\Delta Y_p = 0.00024(\rho_{S10}/\rho_{R10})$. The changes in the helium-4 abundance produced by additional radiation or by a stiff fluid are identical when these two components have equal density at a ``pivot temperature", $T_*$, where we find $T_* = 0.55$ MeV. Current estimates of the primordial $^4$He abundance give the constraint on a stiff fluid energy density of $\rho_{S10}/\rho_{R10} < 30$.
Motivated by the strong discrepancy between the main sequence turn-off age and the white dwarf cooling age in the metal-rich open cluster NGC 6791, we compute a grid of white dwarf evolutionary sequences that incorporates for the first time the energy released by the processes of 22Ne sedimentation and of carbon/oxygen phase separation upon crystallization. The grid covers the mass range from 0.52 to 1.0 Msun, and it is appropriate for the study of white dwarfs in metal-rich clusters. The evolutionary calculations are based on a detailed and self-consistent treatment of the energy released from these two processes, as well as on the employment of realistic carbon/oxygen profiles, of relevance for an accurate evaluation of the energy released by carbon/oxygen phase separation. We find that 22Ne sedimentation strongly delays the cooling rate of white dwarfs stemming from progenitors with high metallicities at moderate luminosities, whilst carbon/oxygen phase separation adds considerable delays at low luminosities. Cooling times are sensitive to possible uncertainties in the actual value of the diffusion coefficient of 22Ne. Changing the diffusion coefficient by a factor of 2, leads to maximum age differences of approx. 8-20% depending on the stellar mass. We find that the magnitude of the delays resulting from chemical changes in the core is consistent with the slow down in the white dwarf cooling rate that is required to solve the age discrepancy in NGC 6791.
We present a novel method for computing the Minkowski Functionals from isodensity surfaces extracted directly from the Delaunay tessellation of a point distribution. This is an important step forward compared to the previous cosmological studies when the isodensity surface was built in the field on a uniform cubic grid and therefore having a uniform spatial resolution. The density field representing a particular interest in cosmology is the density of galaxies which is obtained from the highly nonuniform distribution of the galaxy positions. Therefore, the constraints caused by the spatially uniform grid put severe limitations on the studies of the geometry and shapes of the large-scale objects: superclusters and voids of galaxies. Our technique potentially is able to eliminate most of these limitations. The method is tested with some simple geometric models and an application to the density field from an N-body simulation is shown.
A new effect is described by which primordial gravity waves leave a permanent signature in the large scale structure of the Universe. The effect occurs at second order in perturbation theory and is sensitive to the order in which perturbations on different scales are generated. We derive general forecasts for the detectability of the effect with future experiments, and consider observations of the pre-reionization gas through the 21 cm line. It is found that the Square Kilometre Array will not be competitive with current cosmic microwave background constraints. However, a more futuristic experiment could, through this effect, provide the highest ultimate sensitivity to tensor modes and possibly even measure the tensor spectral index. It is thus a potentially quantitative probe of the inflationary paradigm.
We present a Spitzer InfraRed Spectrometer search for 10-36 micron molecular emission from a large sample of protoplanetary disks, including lines from H2O, OH, C2H2, HCN and CO2. This paper describes the sample and data processing and derives the detection rate of mid-infrared molecular emission as a function of stellar mass. The sample covers a range of spectral type from early M to A, and is supplemented by archival spectra of disks around A and B stars. It is drawn from a variety of nearby star forming regions, including Ophiuchus, Lupus and Chamaeleon. In total, we identify 22 T Tauri stars with strong mid-infrared H2O emission. Integrated water line luminosities, where water vapor is detected, range from 5x10^-4 to 9x10^-3 Lsun, likely making water the dominant line coolant of inner disk surfaces in classical T Tauri stars. None of the 5 transitional disks in the sample show detectable gaseous molecular emission with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios (apart from H2). We find a strong dependence on detection rate with spectral type; no disks around our sample of 25 A and B stars were found to exhibit water emission, down to 1-2% line-to-continuum ratios, in the mid-infrared, while almost 2/3 of the disks around K stars show sufficiently intense water emission to be detected by Spitzer. Some Herbig Ae/Be stars show tentative H2O/OH emission features beyond 20 micron at the 1-2 level, however, and one of them shows CO2 in emission. We argue that the observed differences between T Tauri disks and Herbig Ae/Be disks is due to a difference in excitation and/or chemistry depending on spectral type and suggest that photochemistry may be playing an important role in the observable characteristics of mid-infrared molecular line emission from protoplanetary disks.
In the Friedmann cosmology the deceleration of the expansion $q$ plays a fundamental role. We derive the deceleration as a function of redshift $q(z)$ in two scenarios: $\Lambda$CDM model and modified Chaplygin gas ($MCG$) model. The function for the $MCG$ model is then fitted to the cosmological data in order to obtain the cosmological parameters that minimize $\chi^2$. We use the Fisher matrix to construct the covariance matrix of our parameters and reconstruct the q(z) function. We use Supernovae Ia, WMAP5 and BAO measurements to obtain the observational constraints. We determined the present acceleration as $q_0=-0.60 \pm 0.12$ for the $MCG$ model using the Constitution dataset of SNeIa and BAO, and $q_0=-0.63 \pm 0.17$ for the Union dataset and BAO. The transition redshift from deceleration to acceleration was found to be around $0.6$ for both datasets. We have also determined the dark energy parameter for the $MCG$ model: $\Omega_{X0}=0.834 \pm 0.028$ for the Constitution dataset and $\Omega_{X0}=0.854 \pm 0.036$ using the Union dataset.
In accelerating dark energy models, the estimates of H0 from Sunyaev-Zel'dovich effect (SZE) and X-ray surface brightness of galaxy clusters may depend on the matter content (Omega_M), the curvature (Omega_K) and the equation of state parameter (w). In this article, by using a sample of 25 angular diameter distances from galaxy clusters obtained through SZE/X-ray technique, we constrain H_0 in the framework of a general LCDM models (free curvature) and a flat XCDM model with equation of state parameter, w=p_x/\rho_x (w=constant). In order to broke the degeneracy on the cosmological parameters, we apply a joint analysis involving the baryon acoustic oscillations (BAO) and the CMB Shift Parameter signature. By neglecting systematic uncertainties, for nonflat LCDM cosmologies we obtain $H_0=73.2^{+4.3}_{-3.7}$ km s$^{-1}$ Mpc$^{-1}$ (1sigma) whereas for a flat universe with constant equation of state parameter we find $H_0=71.4^{+4.4}_{-3.4}$ km s$^{-1}$ Mpc$^{-1}$ (1$\sigma$). Such results are also in good agreement with independent studies from the Hubble Space Telescope key project and recent estimates based on Wilkinson Microwave Anisotropy Probe, thereby suggesting that the combination of these three independent phenomena provides an interesting method to constrain the Hubble constant. In particular, comparing these results with a recent determination for a flat LCDM model using only the SZE technique and BAO [Cunha et al. MNRAS 379, L1 2007], we see that the geometry has a very weak influence on H0 estimates for this combination of data.
The structural parameters of the disk of the Large Magellanic Cloud (LMC) are estimated.We used the red clump stars from the VI photometric data of the Optical Gravitational Lensing Experiment (OGLE III) survey and from the Magellanic Cloud Photometric Survey (MCPS) for the estimation of inclination and position angle of line of nodes of the LMC disk. The dereddened peak I magnitude of the red clump stars in each subregion is used to obtain the relative distances and hence the z coordinate. The RA and Dec of each sub-region is converted into x & y cartesian coordinates. A weighted least square plane fitting method is applied to this x,y,z data to estimate the structural parameters of the LMC disk. We find an inclination of i =23.0 plus or minus 0.8 and PAlon = 163.7 plus or minus 1.5 for the LMC disk using the OGLE III data and an inclination of i=37.4 plus or minus 2.3 and PAlon= 141.2 plus or minus 3.7 for the LMC disk using the MCPS data. Extra-planar features which are in front as well as behind the fitted plane are seen in both the data sets. The effect of choice of center, reddening and area covered on the estimated parameters are discussed. Regions in the north west, south west and south east of the LMC disk are warped with respect to the fitted plane. We also identify a symmetric but offcentered warp in the inner LMC.We identify that the structure of the LMC disk inside the 3 degree radius is different from the outside disk such that the inner LMC has relatively less inclination and relatively large PAlon. The 3D plot of the LMC disk suggests an offcentered increase in the inclination for the north-eastern regions which might be due to tidal effects. We suggest that the variation in the planar parameters estimated by various authors as well as in this study is because of the difference in coverage and the complicated inner structure of the LMC disk. In the inner LMC, the stellar and HI disk are found to have similar properties.
We report measurement of the trigonometric parallax of W51 Main/South using the Very Long Baseline Array (VLBA). We measure a value of 0.185 +/- 0.010 mas, corresponding to a distance of 5.41 (+0.31/-0.28) kpc. W51 Main/South is a well-known massive star-forming region near the tangent point of the Sagittarius spiral arm of the Milky Way. Our distance to W51 yields an estimate of the distance to the Galactic center of Ro = 8.3 +/- 0.46 (statistical) +/- 1.0 kpc by simple geometry. Combining the parallax and proper motion measurements for W51, we obtained the full-space motion of this massive star forming region. We find W51 is in a nearly circular orbit about the Galactic center. The H2O masers used for our parallax measurements trace four powerful bipolar outflows within a 0.4 pc size region, some of which are associated with dusty molecular hot cores and/or hyper- or ultra-compact HII regions.
A new concept of bolometer arrays is used for the imager of PACS, one of the three instruments aboard the future Herschel space observatory. Within the framework of PACS photometer characterization, irradiation tests were performed on a dedicated bolometer array in order to study long-term and short-term radiation effects. The main objective was to study particles impacts on the detectors applicable to future observations in orbit and possible hard and/or soft curing to restore its performances. Cobalt-60 gamma ray irradiations did not show significant degradation, so we mainly focused on single events effects (SEE). Protons and alphas irradiations were then performed at the Van de Graaf tandem accelerator at the Institut de Physique Nucleaire (IPN, Orsay, France), respectively at 20MeV and 30MeV. Observation showed that the shape of signal perturbations clearly depends on the location of the impacts either on the detector itself or the read-out circuit. Software curing has then to be anticipated in order to deglitch the signal. This test gives also a unique opportunity to measure some parameters of the detector: electrical crosstalk and thermo- electrical time constant. However a detailed bolometer model is necessary to understand the contribution of the thermal response in relation with the electrical response. It will be the second step of our study. Finally the complete radiation evaluation proved that this detector can be used in spatial experiments.
Primordial magnetic fields could provide an explanation for the galactic magnetic fields observed today, in which case they may also leave interesting signals in the CMB and the small-scale matter power spectrum. We discuss how to approximately calculate the important non-linear magnetic effects within the guise of linear perturbation theory, and calculate the matter and CMB power spectra including the SZ contribution. We then use various cosmological datasets to constrain the form of the magnetic field power spectrum. Using solely large-scale CMB data (WMAP7, QUaD and ACBAR) we find a 95% CL on the variance of the magnetic field at 1 Mpc of B_\lambda < 6.4 nG. When we include SPT data to constrain the SZ effect, we find a revised limit of B_\lambda < 4.1 nG. The addition of SDSS Lyman-alpha data lowers this limit even further, roughly constraining the magnetic field to B_\lambda < 1.3 nG.
(Abreviated) Continued radial velocity monitoring of the nearby M4V red dwarf star GJ~876 with Keck/HIRES has revealed the presence of a Uranus-mass fourth planetary companion in the system. The new planet has a mean period of $P_e=126.6$ days (over the 12.6-year baseline of the radial velocity observations), and a minimum mass of $m_e\sin{i_e}=12.9\pm 1.7\,M_{\oplus}$. Self-consistent, N-body fits to the radial velocity data set show that the four-planet system has an invariable plane with an inclination relative to the plane of the sky of $i=59.5^{\circ}$. The fit is not significantly improved by the introduction of a mutual inclination between the planets ``b'' and ``c,'' but the new data do confirm a non-zero eccentricity, $e_d=0.207\pm0.055$ for the innermost planet, ``d.'' In our best-fit coplanar model, the mass of the new component is $m_e=14.6\pm1.7\,M_{\oplus}$. Our best-fitting model places the new planet in a 3-body resonance with the previously known giant planets (which have mean periods of $P_c=30.4$ and $P_b=61.1$ days). The critical argument, $\varphi_{\rm Laplace}=\lambda_c-3\lambda_b+2\lambda_e$, for the Laplace resonance librates with an amplitude of $\Delta\varphi_{\rm Laplace}=40\pm13^{\circ}$ about $\varphi_{\rm Laplace}=0^{\circ}$. Numerical integration indicates that the four-planet system is stable for at least a billion years (at least for the coplanar cases). This resonant configuration of three giant planets orbiting an M-dwarf primary differs from the well-known Laplace configuration of the three inner Galilean satellites of Jupiter, which are executing very small librations about $\varphi_{\rm Laplace}=180^{\circ}$, and which never experience triple conjunctions. The GJ~876 system, by contrast, comes close to a triple conjunction between the outer three planets once per every orbit of the outer planet, ``e.''
Nebular spectra of Supernovae (SNe) offer an unimpeded view of the inner region of the ejecta, where most nucleosynthesis takes place. Optical spectra cover most, but not all of the emitting elements, and therefore offer only a partial view of the products of the explosion. Simultaneous optical-infrared spectra, on the other hand, contain emission lines of all important elements, from C and O through to the Intermediate Mass Elements (IME) Mg, Si, S, Ca, and to Fe and Ni. In particular, Si and S are best seen in the IR. The availability of IR data makes it possible to explore in greater detail the results of the explosion. SN\,2007gr is the first Type Ic SN for which such data are available. Modelling the spectra with a NLTE code reveals that the inner ejecta contain $\sim 1 \Msun$ of material within a velocity of $\approx 4500$\,\kms. %The spectrum is powered by \Nifs, in an amount ($0.076 \Msun$) consistent with that %derived from the early-time data. The same mass of \Nifs\ derived from the light curve peak ($0.076 \Msun$) was used to power the spectrum, yielding consistent results. Oxygen is the dominant element, contributing $\sim 0.8 \Msun$. The C/O ratio is $< 0.2$. IME account for $\sim 0.1 \Msun$. This confirms that SN\,2007gr was the explosion of a low-mass CO core, probably the result of a star of main-sequence mass $\approx 15 \Msun$. The ratios of the \CaII\ lines, and of those of \FeII, are sensitive to the assumed degree of clumping. In particular, the optical lines of [\FeII] become stronger, relative to the IR lines, for higher degrees of clumping.
It is commonly believed that millisecond radio pulsars have been spun up by transfer of matter and angular momentum from a low-mass companion during an X-ray active mass transfer phase. A subclass of low-mass X-ray binaries is that of the accreting millisecond X-ray pulsars, transient systems that show periods of X-ray quiescence during which radio emission could switch on. The aim of this work is to search for millisecond pulsations from three accreting millisecond X-ray pulsars, XTE J1751-305, XTE J1814-338, and SAX J1808.4-3658, observed during their quiescent X-ray phases at high radio frequencies (5 - 8 GHz) in order to overcome the problem of the free-free absorption due to the matter engulfing the system. A positive result would provide definite proof of the recycling model, providing the direct link between the progenitors and their evolutionary products. The data analysis methodology has been chosen on the basis of the precise knowledge of orbital and spin parameters from X-ray observations. It is subdivided in three steps: we corrected the time series for the effects of (I) the dispersion due to interstellar medium and (II) of the orbital motions, and finally (III) folded modulo the spin period to increase the signal-to-noise ratio. No radio signal with spin and orbital characteristics matching those of the X-ray sources has been found in our search, down to very low flux density upper limits. We analysed several mechanisms that could have prevented the detection of the signal, concluding that the low luminosity of the sources and the geometric factor are the most likely reasons for this negative result.
2M1938+4603 (KIC 9472174) displays a spectacular light curve dominated by a strong reflection effect and rather shallow, grazing eclipses. The orbital period is 0.126 days, the second longest period yet found for an eclipsing sdB+dM, but still close to the minimum 0.1-d period among such systems. The phase-folded light curve was used to detrend the orbital effects from the dataset, and the resulting amplitude spectrum shows a rich collection of pulsation peaks spanning frequencies from ~50 to 4500 uHz. The presence of a complex pulsation spectrum in both the p-mode and the g-mode regions has never been seen before in a compact pulsator. Eclipsing sdB+dM stars are very rare, with only seven systems known and only one with a pulsating primary. Pulsating stars in eclipsing binaries are especially important since they permit masses derived from seismological model fits to be cross checked with orbital mass constraints. We present a first analysis of this star based on the Kepler 9.7-day commissioning light curve and extensive ground-based photometry and spectroscopy that allow us to set useful bounds on the system parameters. We derive a radial-velocity amplitude K_1 = 65.7 +/- 0.6 km/s, inclination angle i = 69.45 +/- 0.20 degrees, and find that the masses of the components are M_1 = 0.48 +/- 0.03 and M_2 = 0.12 +/- 0.01 solar masses.
The deuterium fractionation, Dfrac, has been proposed as an evolutionary indicator in pre-protostellar and protostellar cores of low-mass star-forming regions. We investigate Dfrac, with high angular resolution, in the cluster environment surrounding the UCHII region IRAS 20293+3952. We performed high angular resolution observations with the IRAM Plateau de Bure Interferometer (PdBI) of the ortho-NH2D 1_{11}-1_{01} line at 85.926 GHz and compared them with previously reported VLA NH3 data. We detected strong NH2D emission toward the pre-protostellar cores identified in NH3 and dust emission, all located in the vicinity of the UCHII region IRAS 20293+3952. We found high values of Dfrac~0.1-0.8 in all the pre-protostellar cores and low values, Dfrac<0.1, associated with young stellar objects. The high values of Dfrac in pre-protostellar cores could be indicative of evolution, although outflow interactions and UV radiation could also play a role.
We investigate the scale on which the correlation arises between the 843 MHz radio and the 60 micron far-infrared (FIR) emission from star forming regions in the Milky way. The correlation, which exists on the smallest scales investigated (down to ~4 pc), becomes noticeably tight on fields of size 30', corresponding to physical scales of ~20-50 pc. The FIR to radio flux ratio on this scale is consistent with the radio emission being dominated by thermal emission. We also investigate the location dependence of q_mean, a parameter measuring the mean FIR to radio flux ratio, of a sample of star forming regions. We show that q_mean displays a modest dependence on galactic latitude. If this is interpreted as a dependence on the intensity of star formation activity, the result is consistent with studies of the Large Magellanic Cloud (LMC) and other nearby galaxies that show elevated values for q in regions of enhanced star formation.
Long timeseries of data increase the frequency resolution in the power spectrum. This allows for resolving stochastically excited modes with long mode lifetimes, as well as features that are close together in frequency. The CoRoT fields observed during the initial run and second long run partly overlap, and stars in this overlapping field observed in both runs are used to create timeseries with a longer timespan than available from the individual runs. We aim to measure the mode lifetimes of red giants and compare them with theoretical predictions. We also investigate the dependence of the mode lifetimes on frequency and the degree of the oscillation modes. We perform simulations to investigate the influence of the gap in the data between the initial and second long run, the total length of the run and the signal-to-noise ratio on the measured mode lifetime. This provides us with a correction factor to apply to the mode lifetimes measured from a maximum likelihood fit to the oscillation frequencies. We find that the length of the timeseries, the signal-to-noise ratio and possible gaps do have a non-negligible effect on the measurements of the mode lifetime of stochastically excited oscillation modes, but that we can correct for it. For the four stars for which we can perform a fit of the oscillation frequencies, we find that the mode lifetimes depend on frequency and on degree of the mode, which is in quantitative agreement with theoretical predictions.
Star formation is regulated through a variety of feedback processes. In this study, we treat feedback by metal injection and a UV background as well as by X-ray irradiation. Our aim is to investigate whether star formation is significantly affected when the ISM of a proto-galaxxy enjoys different metallicities and when a star forming cloud resides in the vicinity of a strong X-ray source. We perform cosmological Enzo simulations with a detailed treatment of non-zero metallicity chemistry and thermal balance. We also perform FLASH simulations with embedded Lagrangian sink particles of a collapsing molecular cloud near a massive, 10^{7} M\odot, black hole that produces X-ray radiation. We find that a multi-phase ISM forms for metallicites as small as 10^{-4} Solar at z = 6, with higher (10^{-2}Z\odot) metallicities supporting a cold (< 100 K) and dense (> 10^{3} cm^{-3}) phase at higher (z = 20) redshift. A star formation recipe based on the presence of a cold dense phase leads to a self-regulating mode in the presence of supernova and radiation feedback. We also find that when there is strong X-ray feedback a collapsing cloud fragments into larger clumps whereby fewer but more massive protostellar cores are formed. This is a consequence of the higher Jeans mass in the warm (50 K, due to ionization heating) molecular gas. Accretion processes dominate the mass function and a near-flat, non-Salpeter IMF results.
The Sun is a variable star whose magnetic activity varies most perceptibly on a timescale of approximately 11 years. However, significant variation is also observed on much shorter timescales. We observe a quasi-biennial (2 year) signal in the natural oscillation frequencies of the Sun. The oscillation frequencies are sensitive probes of the solar interior and so by studying them we can gain information about conditions beneath the solar surface. Our results point strongly to the 2 year signal being distinct and separate from, but nevertheless susceptible to the influence of, the main 11 year solar cycle.
We report on a scheme of incorporating vertical radiative energy transport into a fully relativistic, Kerr-metric model of optically thick, advective, transonic alpha disks. Our code couples the radial and vertical equations of the accretion disk. The flux is computed in the diffusion approximation, and convection is included in the mixing-length approximation. We present the detailed structure of this ``two-dimensional'' slim-disk model for $\alpha=0.01$. We then calculate the emergent spectra integrated over the disk surface. The values of surface density, radial velocity, and the photospheric height for these models differ by 20\%-30\% from those obtained in the polytropic, height-averaged slim disk model considered previously. However, the emission profiles and the resulting spectra are quite similar for both types of models. For high values of the alpha parameter, and for large accretion rates, the slim disk becomes effectively optically thin.
(Abridged) A numerical model of a circumstellar debris disk is developed and
applied to observations of the circumstellar dust orbiting beta Pictoris. The
model accounts for the rates at which dust is produced by collisions among
unseen planetesimals, and the rate at which dust grains are destroyed due to
collisions. The model also accounts for the effects of radiation pressure,
which is the dominant perturbation on the disk's smaller but abundant dust
grains. Solving the resulting system of rate equations then provides the dust
abundances versus grain size and over time. Those solutions also provide the
dust grains' collisional lifetime versus grain size, and the debris disk's
optical depth and surface brightness versus distance from the star. Comparison
to observations then yields estimates of the unseen planetesimal disk's radius,
and the rate at which the disk sheds mass due to planetesimal grinding.
The model is then applied to optical observations of the edge-on dust disk
orbiting beta Pictoris, and good agreement is achieved when the unseen
planetesimal disk is broad, with 75<r<150 AU. If it is assumed that the dust
grains are bright like Saturn's icy rings, then the cross section of dust in
the disk is A_d~2x10^20 km^2 and its mass is M_d~11 lunar masses. In this case
the planetesimal disk's dust production rate is quite heavy, dM_d/dt~9
earth-masses per Myr, implying that there is or was a substantial amount of
planetesimal mass there, at least 110 earth-masses. But if the dust grains are
darker than assumed, then the planetesimal disk's mass-loss rate and its total
mass are heavier. In fact, the apparent dearth of any major planets in this
region, plus the planetesimal disk's heavy mass-loss rate, suggests that the
75<r<150 AU zone at beta Pic might be a region of planetesimal destruction,
rather than a site of ongoing planet formation.
We use simulated images of star-forming regions to explore the effects of various image acquisition techniques on the derived clump mass function. In particular, we focus on the effects of finite image angular resolution, the presence of noise, and spatial filtering. We find that, even when the image has been so heavily degraded with added noise and lowered angular resolution that the clumps it contains clearly no longer correspond to pre-stellar cores, still the clump mass function is typically consistent with the stellar initial mass function within their mutual uncertainties. We explain this result by suggesting that noise, source blending, and spatial filtering all randomly perturb the clump masses, biasing the mass function toward a lognormal form whose high-mass end mimics a Salpeter power law. We argue that this is a consequence of the central limit theorem and that it strongly limits our ability to accurately measure the true mass function of the clumps. We support this conclusion by showing that the characteristic mass scale of the clump mass function, represented by the ``break mass'', scales as a simple function of the angular resolution of the image from which the clump mass function is derived. This strongly constrains our ability to use the clump mass function to derive a star formation efficiency. We discuss the potential and limitations of the current and next generation of instruments for measuring the clump mass function.
To investigate the present situation of the merging in the southern outer region of Abell 85, we carried out long (~100 ks) observations with Suzaku, and produced an X-ray hardness ratio map. We found a high hardness ratio peak in the east side of a subcluster located in the south of the cluster; an X-ray spectrum of the region including this peak indicates a high temperature of ~8.5 keV. This hot spot has not been reported so far. We consider that this hot spot is a postshock region produced by the infall of the subcluster from the southwest. By using the Rankine--Hugoniot jump conditions for shocks, the Mach number and the infall velocity of the subcluster are obtained as 1.5 +/- 0.2 and 1950^{+290}_{-280} km s^{-1}, respectively, in the case of merging with the subcluster from the southwest direction. By using the redshift difference between the A 85 and the subcluster obtained from optical observations, the angle between the line of sight and the direction of the motion of the subcluster is estimated to be 75^{+7}_{-8} degrees. We estimate the kinetic energy of the subcluster and the energy used for intracluster medium (ICM) heating to be ~10^{63} and \lesssim 8 \times 10^{60} erg, respectively. This shows that the deceleration of the subcluster by ICM heating has been negligibly small.
A rotational modulator (RM) gamma-ray imager is capable of obtaining significantly better angular resolution than the fundamental geometric resolution defined by the ratio of detector diameter to mask-detector separation. An RM imager consisting of a single grid of absorbing slats rotating ahead of an array of a small number of position-insensitive detectors has the advantage of fewer detector elements (i.e., detector plane pixels) than required by a coded aperture imaging system with comparable angular resolution. The RM therefore offers the possibility of a major reduction in instrument complexity, cost, and power. A novel image reconstruction technique makes it possible to deconvolve the raw images, remove sidelobes, reduce the effects of noise, and provide resolving power a factor of 6 - 8 times better than the geometric resolution. A 19-channel prototype RM developed in our laboratory at Louisiana State University features 13.8 deg full-angle field of view, 1.9 deg geometric angular resolution, and the capability of resolving sources to within 35' separation. We describe the technique, demonstrate the measured performance of the prototype instrument, and describe the prospects for applying the technique to either a high-sensitivity standoff gamma-ray imaging detector or a satellite- or balloon-borne gamma-ray astronomy telescope.
A common problem in astrophysics is determining how bright a source could be and still not be detected. Despite the simplicity with which the problem can be stated, the solution involves complex statistical issues that require careful analysis. In contrast to the confidence bound, this concept has never been formally analyzed, leading to a great variety of often ad hoc solutions. Here we formulate and describe the problem in a self-consistent manner. Detection significance is usually defined by the acceptable proportion of false positives (the TypeI error), and we invoke the complementary concept of false negatives (the TypeII error), based on the statistical power of a test, to compute an upper limit to the detectable source intensity. To determine the minimum intensity that a source must have for it to be detected, we first define a detection threshold, and then compute the probabilities of detecting sources of various intensities at the given threshold. The intensity that corresponds to the specified TypeII error probability defines that minimum intensity, and is identified as the upper limit. Thus, an upper limit is a characteristic of the detection procedure rather than the strength of any particular source and should not be confused with confidence intervals or other estimates of source intensity. This is particularly important given the large number of catalogs that are being generated from increasingly sensitive surveys. We discuss the differences between these upper limits and confidence bounds. Both measures are useful quantities that should be reported in order to extract the most science from catalogs, though they answer different statistical questions: an upper bound describes an inference range on the source intensity, while an upper limit calibrates the detection process. We provide a recipe for computing upper limits that applies to all detection algorithms.
The model accepted is one where during the Archean Eon the Earths climate was clement despite the weaker Sun. The observational evidence that supports this concept is: the emergence of life, the existence of evaporitic sediments and the presence of terrigenous sediments, all of which require liquid water and clement conditions. A theoretical argument used to support this idea is the so called ice-albedo feedback, which states that if the Earth was frozen, it would still be frozen.The aim of this document is to present an alternative scenario in which a frozen world, "snowball" style, with liquid water at the bottom of the sea, also allows for the emergence of life and evaporitic and terrigenous sedimentation. Archean climatic evidence, available at present, is discussed and can be reinterpreted to support the idea that, in Archean times, the surface of the Earth was frozen. Also, a mathematical model is being developed to demonstrate that the ice-albedo feedback is not an inevitable consequence of a frozen Archean Eon. Results: Reinterpretation of the evidence shows that life could appear within the oceanic depths and not necessarily on the surface. The evaporitic sediments could have formed by saline saturation of the water enclosed in the limited cavities of liquid water located at the bottom of the ocean. Also, the terrigenous sediments could have been formed by catastrophic currents of liquid water due to the fusion of the ice from the sub glacial volcanoes. From the mathematical model it is deduced that the defrosting moment of the Earth is towards the end of the Proterozoic, moment in which the evidence shows the "snowball" Earth ends.
We perform a numerical study of the evolution of a Coronal Mass Ejection (CME) and its interaction with the coronal magnetic field based on the May 12, 1997, CME event using a global MagnetoHydroDynamic (MHD) model for the solar corona. The ambient solar wind steady-state solution is driven by photospheric magnetic field data, while the solar eruption is obtained by superimposing an unstable flux rope onto the steady-state solution. During the initial stage of CME expansion, the core flux rope reconnects with the neighboring field, which facilitates lateral expansion of the CME footprint in the low corona. The flux rope field also reconnects with the oppositely orientated overlying magnetic field in the manner of the breakout model. During this stage of the eruption, the simulated CME rotates counter-clockwise to achieve an orientation that is in agreement with the interplanetary flux rope observed at 1 AU. A significant component of the CME that expands into interplanetary space comprises one of the side lobes created mainly as a result of reconnection with the overlying field. Within 3 hours, reconnection effectively modifies the CME connectivity from the initial condition where both footpoints are rooted in the active region to a situation where one footpoint is displaced into the quiet Sun, at a significant distance ($\approx 1R_\odot$) from the original source region. The expansion and rotation due to interaction with the overlying magnetic field stops when the CME reaches the outer edge of the helmet streamer belt, where the field is organized on a global scale. The simulation thus offers a new view of the role reconnection plays in rotating a CME flux rope and transporting its footpoints while preserving its core structure.
The emergence of tilted bipolar active regions and the dispersal of their flux, mediated via processes such as diffusion, differential rotation and meridional circulation is believed to be responsible for the reversal of the Sun's polar field. This process (commonly known as the Babcock-Leighton mechanism) is usually modeled as a near-surface, spatially distributed $\alpha$-effect in kinematic mean-field dynamo models. However, this formulation leads to a relationship between polar field strength and meridional flow speed which is opposite to that suggested by physical insight and predicted by surface flux-transport simulations. With this in mind, we present an improved double-ring algorithm for modeling the Babcock-Leighton mechanism based on active region eruption, within the framework of an axisymmetric dynamo model. Using surface flux-transport simulations we first show that an axisymmetric formulation -- which is usually invoked in kinematic dynamo models -- can reasonably approximate the surface flux dynamics. Finally, we demonstrate that our treatment of the Babcock-Leighton mechanism through double-ring eruption leads to an inverse relationship between polar field strength and meridional flow speed as expected, reconciling the discrepancy between surface flux-transport simulations and kinematic dynamo models.
Aims: The main goal of this study is to perform a sub-arcsecond resolution analysis of the high-mass star formation region G19.61-0.23, both in the continuum and molecular line emission. While the centimeter continuum images will be discussed in detail in a forthcoming paper, here we focus on the (sub)mm emission, devoting special attention to the hot molecular core. Results: Our observations resolve the HMC into three cores whose masses are on the order of 10^1-10^3 Msun. No submm core presents detectable free-free emission in the centimeter regime, but they appear to be associated with masers and thermal line emission from complex organic molecules. Towards the most massive core, SMA1, the CH3CN (18_K-17_K) lines reveal hints of rotation about the axis of a jet/outflow traced by H2O maser and H13CO+ (1--0) line emission. Inverse P-Cygni profiles of the 13CO (3--2) and C18O (3--2) lines seen towards SMA1 indicate that the central high-mass (proto)star(s) is (are) still gaining mass with an accretion rate $ge 3 ~10^{-3}$ Msun/yr. Due to the linear scales and the large values of the accretion rate, we hypothesize that we are observing an accretion flow towards a cluster in the making, rather than towards a single massive star.
We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles. We use two different statistical methods to determine the underlying nature of these flux-flux relationships. First, we use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second, we use signal theory to examine the flux-flux relationships for a temporal component. We find that a well-defined temporal component exists and accounts for some of the variance in the data. This temporal component arises because active regions with high magnetic field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux density. In most cases, the model reconstructions can account for 85-90% of the variability of the radiative flux from the chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures of solar and stellar variability.
We report new O isotopic data on 41 presolar oxide grains, 38 MgAl2O4 (spinel) and 3 Al2O3 from the CM2 meteorite Murray, identified with a recently developed automated measurement system for the NanoSIMS. We have also obtained Mg-Al isotopic results on 29 of the same grains (26 spinel and 3 Al2O3). The majority of the grains have O isotopic compositions typical of most presolar oxides, fall well into the four previously defined groups, and are most likely condensates from either red giant branch or asymptotic giant branch stars. We have also discovered several grains with more unusual O and Mg compositions suggesting formation in extreme astrophysical environments, such as novae and supernovae. One of these grains has massive enrichments in 17O, 25Mg, and 26Mg, which are isotopic signatures indicative of condensation from nova ejecta. Two grains of supernova origin were also discovered: one has a large 18O/16O ratio typical of Group 4 presolar oxides; another grain is substantially enriched in 16O, and also contains radiogenic 44Ca from the decay of 44Ti, a likely condensate from material originating in the O-rich inner zones of a Type II supernova. In addition, several Group 2 presolar spinel grains also have large 25Mg and 26Mg isotopic anomalies that are difficult to explain by standard nucleosynthesis in low-mass stars. Auger elemental spectral analyses were performed on the grains and qualitatively suggest that presolar spinel may not have higher-than- stoichiometric Al/Mg ratios, in contrast to SIMS results obtained here and reported previously.
We study a simple five-dimensional extension of the Standard Model, compactified on a flat line segment in which there propagate Higgs and gauge bosons of the Standard Model. We impose a Dirichlet boundary condition on the Higgs field to realize its vacuum expectation value. Since a flat Nambu-Goldstone zero-mode of the bulk Higgs is eliminated by the Dirichlet boundary condition, a superposition of the Higgs Kaluza-Klein modes play the role of the Nambu-Goldstone boson except at the boundaries. We discuss phenomenology of our model at the LHC, namely the top Yukawa deviation and the production and invisibly rapid decay of the physical Higgs field, as well as the constraints from the electroweak precision measurements.
The purpose of this paper is to explain clearly why nonlocality must be an essential part of the theory of relativity. In the standard local version of this theory, Lorentz invariance is extended to accelerated observers by assuming that they are pointwise inertial. This locality postulate is exact when dealing with phenomena involving classical point particles and rays of radiation, but breaks down for electromagnetic fields, as field properties in general cannot be measured instantaneously. The problem is corrected in nonlocal relativity by supplementing the locality postulate with a certain average over the past world line of the observer.
We study the stability properties of the Cauchy horizon for two different self-dual black hole solutions obtained in a model inspired by Loop Quantum Gravity. The self-dual spacetimes depend on a free dimensionless parameter called a polymeric parameter P. For the first metric the Cauchy horizon is stable for supermassive black holes only if this parameter is sufficiently small. For small black holes, however the stability is easily implemented. The second metric analyzed is not only self-dual but also "form-invariant" under the transformation r -> r*^2/r and r* = 2 m P. We find that this symmetry protects the Cauchy horizon for any value of the polymeric parameter.
The persistent discrepancy between observations of 7Li with putative primordial origin and its abundance prediction in Big Bang Nucleosynthesis (BBN) has become a challenge for the standard cosmological and astrophysical picture. We point out that the decay of GeV-scale metastable particles X may significantly reduce the BBN value down to a level at which it is reconciled with observations. The most efficient reduction occurs when the decay happens to charged pions and kaons, followed by their charge exchange reactions with protons. Similarly, if X decays to muons, secondary electron antineutrinos produce a similar effect. We consider the viability of these mechanisms in different classes of new GeV-scale sectors, and find that several minimal extensions of the Standard Model with metastable vector and/or scalar particles are capable of solving the cosmological lithium problem. Such light states can be a key to the explanation of recent cosmic ray anomalies and can be searched for in a variety of high-intensity medium-energy experiments.
Particles dropped into a rotating black hole can collide near the inner horizon with enormous energies. The entropy produced by these collisions can be several times larger than the increase in the horizon entropy due to the addition of the particles. In this paper entropy is produced by releasing large numbers of neutrons near the outer horizon of a rotating black hole such that they collide near the inner horizon at energies similar to those achieved at the Relativistic Heavy Ion Collider. The increase in horizon entropy is approximately 80 per dropped neutron pair, while the entropy produced in the collisions is 160 per neutron pair. The collision entropy is produced inside the horizon, so this excess entropy production does not violate Bousso's bound limiting the entropy that can go through the black hole's horizon. The generalized laws of black hole thermodynamics are obeyed. No individual observer inside the black hole sees a violation of the second law of thermodynamics
We give a novel description of the recently proposed theory of new massive gravity (NMG) in three dimensions. We show that in terms of a Dirac type differential operator acting on the traceless Ricci tensor, the field equations of the theory reduce to the massive Klein-Gordon type equation with a curvature-squared source term and to a constraint equation. Under a certain relation between the source tensor and the traceless Ricci tensor, fulfilled for constant scalar curvature, the field equations of topologically massive gravity (TMG) can be thought of as the ``square-root" of the massive Klein-Gordon type equation. Using this fact, we establish a simple framework for mapping all known algebraic types D and N solutions of TMG into NMG. We also present new exact solutions of algebraic types D and N that are only inherent in NMG.
We present the results of three-dimensional general relativistic hydrodynamic simulations of adiabatic and spherically symmetric accretion in Kerr space-time. We consider compact objects with spin parameter $|a_*| \le 1$ (black holes) and with $|a_*| > 1$ (super-spinars). Our full three-dimensional simulations confirm the formation of equatorial outflows for high values of $|a_*|$, as found in our previous work in 2.5 dimensions. We show that the critical value of $|a_*|$ determining the onset of powerful outflows depends mainly on the radius of the compact object. The phenomenon of equatorial outflows can hardly occur around a black hole and may thus be used to test the bound $|a_*| \le 1$ for astrophysical black hole candidates.
Based on the Hugenholtz-Van Hove theorem, it is shown that both the symmetry energy E$_{sym}(\rho)$ and its density slope $L(\rho)$ at normal density $\rho_0$ are completely determined by the global nucleon optical potentials that can be extracted directly from nucleon-nucleus scatterings, (p,n) charge exchange reactions and single-particle energy levels of bound states. Adopting a value of $m^*/m=0.7$ for the nucleon effective k-mass in symmetric nuclear matter at $\rho_0$ and averaging all phenomenological isovector nucleon potentials constrained by world data available in the literature since 1969, the best estimates of $E_{sym}(\rho_0)=31.3$ MeV and $L(\rho_0)=52.7$ MeV are simultaneously obtained. Uncertainties involved in the estimates are discussed.
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We present the 24 micron rest-frame luminosity function (LF) of star-forming galaxies in the redshift range 0.0 < z < 0.6 constructed from 4047 spectroscopic redshifts from the AGN and Galaxy Evolution Survey of 24 micron selected sources in the Bootes field of the NOAO Deep Wide-Field Survey. This sample provides the best available combination of large area (9 deg^2), depth, and statistically complete spectroscopic observations, allowing us to probe the evolution of the 24 micron LF of galaxies at low and intermediate redshifts while minimizing the effects of cosmic variance. In order to use the observed 24 micron luminosity as a tracer for star formation, active galactic nuclei (AGNs) that could contribute significantly at 24 micron are identified and excluded from our star-forming galaxy sample based on their mid-IR spectral energy distributions or the detection of X-ray emission. The evolution of the 24 micron LF of star-forming galaxies for redshifts of z < 0.65 is consistent with a pure luminosity evolution where the characteristic 24 micron luminosity evolves as (1+z)^(3.8+/-0.3). We extend our evolutionary study to encompass 0.0 < z < 1.2 by combining our data with that of the Far-Infrared Deep Extragalactic Legacy Survey. Over this entire redshift range the evolution of the characteristic 24 micron luminosity is described by a slightly shallower power law of (1+z)^(3.4+/-0.2). We find a local star formation rate density of (1.09+/-0.21) x 10^-2 Msun/yr/Mpc^-3, and that it evolves as (1+z)^(3.5+/-0.2) over 0.0 < z < 1.2. These estimates are in good agreement with the rates using optical and UV fluxes corrected for the effects of intrinsic extinction in the observed sources. This agreement confirms that star formation at z <~ 1.2 is robustly traced by 24 micron observations and that it largely occurs in obscured regions of galaxies. (Abridged)
(abridged) Using a Lyman-Break technique, we identify 66 z~7 and 47 z~8 candidate galaxies in the ultra-deep (~29 AB mag) WFC3/IR observations over the HUDF and two nearby HUDF09 fields (14 arcmin**2) and the deep (~27.5 AB mag), wide-area (~40 arcmin**2) ERS observations. This 26-29 AB mag sample of 113 galaxies in the reionization epoch is the largest currently available. A contamination rate of <=14% is found after thoroughly assessing the impact of lower redshift sources, photometric scatter, low mass stars, spurious sources, and transients on our selection. Carefully modelling the selection volumes for each of our search fields, we derive luminosity functions for galaxies at z~7 and z~8. The faint-end slopes alpha we find at z~7 and z~8 are alpha = -1.94+/-0.24 and alpha=-2.00+/-0.33, respectively. This provides increasingly strong evidence that the UV LF at z>~6 is at least as steep as at z~4 (alpha=-1.73+/-0.05), with alpha<~-1.7, and that lower luminosity galaxies dominate the galaxy luminosity density during the epoch of reionization. Luminosity densities and SFRs derived from these UV LFs are compared to those derived from recent stellar mass density determinations at z>~4. We find reasonable consistency, with the SFR densities implied from the stellar mass densities being only ~40% higher at z<7. This suggests that (1) the stellar mass densities inferred from the Spitzer IRAC photometry are reasonably accurate and (2) that the IMF at very high redshift may not be that different from later times. Extrapolating these LFs to lower luminosities and higher redshifts show that galaxies contribute substantially to the reionization. Thomson optical depths of 0.056 (0.075), within 2sigma (1sigma) of the latest WMAP values, are obtained for escape fractions of 20% (60%) and clumping factors of 3.
Rectified diameters and albedo estimates of 1517 main belt asteroid selected from the IRAS and MSX asteroid photometry catalogues are derived from updated infrared thermal models, the Standard Thermal Model (STM) and the Near Earth Asteroid Thermal Model (NEATM), and Monte Carlo simulations, using new Minor Planet Center (MPC) compilations of absolute magnitudes (H-values) constrained by occultation and radar derived parameters. The NEATM approach produces a more robust estimate of albedos and diameters, yielding albedos of $p_{v}$(NEATM mean)$=0.081 \pm 0.064$. The asteroid beaming parameter ($\eta$) for the selected asteroids has a mean value of $1.07 \pm 0.27$, and the smooth distribution of $\eta$ suggests that this parameter is independent of asteroid properties such as composition. No trends in $\eta$ due to size-dependent rotation rates are evident. Comparison of derived $\eta$'s as a function of taxonomic type indicates the beaming parameter values for S-type and C-type asteroids are identical within the standard deviation of the population of beaming parameters.
For extrasolar planets discovered using the radial velocity method, the spectral characterization of the host star leads to a mass-estimate of the star and subsequently of the orbiting planet. In contrast, if also the orbital velocity of the planet would be known, the masses of both star and planet could be determined directly using Newton's law of gravity, just as in the case of stellar double-line eclipsing binaries. Here we report on the detection of the orbital velocity of extrasolar planet HD209458b. High dispersion ground-based spectroscopy during a transit of this planet reveals absorption lines from carbon monoxide produced in the planet atmosphere, which shift significantly in wavelength due to the change in the radial component of the planet orbital velocity. These observations result in a mass determination of the star and planet of 1.00+-0.22 Msun and 0.64+-0.09 Mjup respectively. A ~2 km/sec blueshift of the carbon monoxide signal with respect to the systemic velocity of the host star suggests the presence of a strong wind flowing from the irradiated dayside to the non-irradiated nightside of the planet within the 0.01-0.1 mbar atmospheric pressure range probed by these observations. The strength of the carbon monoxide signal suggests a CO mixing ratio of 1-3x10-3 in this planet's upper atmosphere.
Adiabatic contraction is frequently used to model the effects of baryon condensation on dark matter halos. However, it has recently been shown that this model is not always accurate; authors including Gnedin et al. (2004) and Gustafsson et al. (2006) have found it to be inaccurate at the level of tens of percent. We have analyzed high resolution N-body simulations of dark matter halos, focusing specifically on the evolution of angular momentum, to assess the accuracy of the assumptions of the adiabatic contraction model. We investigate the validity of the assumptions using dark-matter-only halos, in order to provide a limit on how accurate we may expect the adiabatic contraction model to be once baryons are included. In brief, we find that not only is individual particle angular momentum not conserved, but the radial profile and distribution of angular momentum also varies over the age of the Universe by up to factors of a few. We find that torques from external structure are the most likely cause for this distribution shift. This variation implies that there is a fundamental limit on the possible accuracy of the adiabatic contraction model in modeling the response of DM halos to the growth of galaxies.
We present results from new Chandra, GMRT, and SOAR observations of NGC 5813, the dominant central galaxy in a nearby galaxy subgroup. The system shows clear signatures from three distinct outbursts of the central AGN, with three pairs of roughly collinear cavities. The inner two cavity pairs are each associated with elliptical surface brightness edges, which we unambiguously identify as shocks with measured temperature jumps and with Mach numbers of M \approx 1.7 and M \approx 1.5 for the inner and outer shocks, respectively. Such clear signatures from three distinct AGN outbursts in an otherwise relaxed system provide a unique opportunity to study AGN feedback and outburst history. The mean power of the two most recent outbursts varies by an order of magnitude, indicating that the mean jet power varies significantly over long (~10^7 yr) timescales. The total energy output of the most recent outburst is also less than the total energy of the previous outburst, which may be a result of the lower mean power, or may indicate that the most recent outburst is ongoing. We directly measure the local heat input into the ICM at the shock fronts, and show that the shock heating balances radiative cooling of the gas locally. The outburst interval implied by both the shock and cavity ages (~10^7 yr) indicates that in this system shock heating alone is sufficient to balance radiative cooling close to the central AGN, which is the relevant region for regulating feedback between the ICM and the central SMBH.
We have measured redshifts for 243 z ~3 quasars in nine VLT VIMOS LBG redshift survey areas, each of which is centred on a known bright quasar. Using spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Lya forest and 1020 Lyman-break galaxies at z ~3. We find an increase in neutral hydrogen absorption within 5 h^-1 Mpc of a galaxy in agreement with the results of Adelberger et al. (2003, 2005). The Lya-LBG cross-correlation can be described by a power-law on scales larger than 3 h^-1 Mpc. When galaxy velocity dispersions are taken into account our results at smaller scales (<2 h^-1 Mpc) are also in good agreement with the results of Adelberger et al. (2005). There is little immediate indication of a region with a transmission spike above the mean IGM value which might indicate the presence of star-formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift space distortion measurements of Bielby et al. (2010). We find that the redshift-space transmission spike implied in the results of Adelberger et al. (2003) is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical fluke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Lya absorption surrounding LBGs which can mask the spike's presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 CIV systems in the quasar spectra and find an LBG-CIV correlation strength on scales of 10 h^-1 Mpc consistent with the relation measured at ~Mpc scales.
We report the identification of presolar silicates (~177 ppm), presolar oxides (~11 ppm), and one presolar SiO2 grain in the ALHA 77307 chondrite. Three grains having Si isotopic compositions similar to SiC X and Z grains were also identified, though the mineral phases are unconfirmed. Similar abundances of presolar silicates (~152 ppm) and oxides (~8 ppm) were also uncovered in the primitive CR chondrite QUE 99177, along with 13 presolar SiC grains and one presolar silicon nitride. The O isotopic compositions of the presolar silicates and oxides indicate that most of the grains condensed in low-mass red giant and asymptotic giant branch stars. Interestingly, unlike presolar oxides, few presolar silicate grains have isotopic compositions pointing to low-metallicity, low-mass stars (Group 3). The 18O-rich (Group 4) silicates, along with the few Group 3 silicates that were identified, likely have origins in supernova outflows. This is supported by their O and Si isotopic compositions. Elemental compositions for 74 presolar silicate grains were determined by scanning Auger spectroscopy. Most of the grains have non-stoichiometric elemental compositions inconsistent with pyroxene or olivine, the phases commonly used to fit astronomical spectra, and have comparable Mg and Fe contents. Non-equilibrium condensation and/or secondary alteration could produce the high Fe contents. Transmission electron microscopic analysis of three silicate grains also reveals non-stoichiometric compositions, attributable to non-equilibrium or multistep condensation, and very fine-scale elemental heterogeneity, possibly due to subsequent annealing. The mineralogies of presolar silicates identified in meteorites thus far seem to differ from those in interplanetary dust particles.
Over the past decade the study of solar-like oscillations in red-giant stars has developed significantly. Not only the number of red-giant stars for which solar-like oscillations have been observed has increased, but the quality of these observations has improved as well. These steps forward were possible thanks to the development of instrumentation to measure radial velocity variations with a precision of the order of m/s, as well as the launch of dedicated space missions, which provide timeseries of data with unprecedented photometric precision. Many more exciting discoveries are to be expected in the (near) future. This article provides an overview of the development of the field over the last decade, discusses difficulties encountered and overcome in interpreting the observational data, and addresses some challenges and opportunities for further research.
Type Ia supernovae are generally thought to be due to the thermonuclear explosions of carbon-oxygen white dwarfs with masses near the Chandrasekhar mass. This scenario, however, has two long-standing problems. First, the explosions do not naturally produce the correct mix of elements, but have to be finely tuned to proceed from sub-sonic deflagration to super-sonic detonation. Second, population models and observations give formation rates of near-Chandrasekhar white dwarfs that are far too small. Here, we suggest that type Ia supernovae instead result from mergers of roughly equal-mass carbon-oxygen white dwarfs, including those that produce sub-Chandrasekhar mass remnants. Numerical studies of such mergers have shown that the remnants consist of rapidly rotating cores that contain most of the mass and are hottest in the center, surrounded by dense, small disks. We argue that the disks accrete quickly, and that the resulting compressional heating likely ignites the carbon. This ignition occurs at densities for which pure detonations lead to events similar to type Ia supernovae. With this merger scenario, we can understand the type Ia rates, and have plausible reasons for the observed range in luminosity and for the bias of more luminous supernovae towards younger populations. We speculate that explosions of near-Chandrasekhar mass white dwarfs---which should also occur---are responsible for some of the "atypical" type Ia supernovae.
We present a model for plasma heating produced by time-dependent, spatially localized reconnection within a flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity which subsequently retract at Alfv\'enic speeds from the reconnection site. Heating occurs in gas-dynamic shocks which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of reconnected flux tubes, including pressure-driven parallel dynamics as well as temperature dependent, anisotropic viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions. Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong gas-dynamic shocks generated by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the tube, rendering the diffusive processes dominant. They determine the thickness of the shock that evolves up to a steady-state value, although this condition may not be reached in the short times involved in a flare. For realistic solar coronal parameters, this steady-state shock thickness might be as long as the entire flux tube. For strong shocks at low Prandtl numbers, typical of the solar corona, the gas-dynamic shock consists of an isothermal sub-shock where all the compression and cooling occur, preceded by a thermal front where the temperature increases and most of the heating occurs. We estimate the length of each of these sub-regions and the speed of their propagation.
The study of linear perturbation theory for general functions of the Ricci and Gauss-Bonnet scalars is done over an empty anisotropic universe, i.e. the Kasner-type background, in order to show that an anisotropic background in general has ghost degrees of freedom, which are absent on Friedmann-Lemaitre-Robertson-Walker (FLRW) backgrounds. The study of the scalar perturbation reveals that on this background the number of independent propagating degrees of freedom is four and reduces to three on FLRW backgrounds, as one mode becomes highly massive to decouple from the physical spectrum. When this mode remains physical, there is inevitably a ghost mode.
Our goal is to limit the redshifts of three blazars PG 1553+113, 3C 66A and PKS 1424+240, through the investigation of their Fermi and VHE (very high energy) $\gamma$-ray observations. We assume that the intrinsic spectra of PG 1553+113, 3C 66A, and PKS 1424+240 have not any cutoff across the Fermi and VHE $\gamma$-ray energy ranges. The intrinsic spectra of VHE $\gamma$-rays are obtained through the extrapolation of Fermi spectra. Comparing the measured and intrinsic VHE spectra due to extragalactic background light (EBL) absorption, we give the redshift upper limits of three blazars assuming a specific EBL model. The redshift upper limits of PG 1553+113, 3C 66A and PKS 1424+240 are 0.78, 0.58, and 1.19 respectively. Near the TeV energy the optical depth of VHE $\gamma$ photons might be overestimated by Franceschini (2008) EBL model, or the second emission component might be present in the VHE spectra and lead the intrinsic photon index harder than the Fermi ones.
Using the Hyperz code and a template spectral library which consists of 4
observed galaxy spectra from Coleman, Wu & Weedman (CWW, 1980) and 8 spectral
families built with evolutionary population synthesis models, we present
photometric redshift estimates (photo-z) for a spectroscopic sample of 6,531
galaxies, and morphologies for a morphological sample of 1,502 bright galaxies.
All galaxies are matched with the SDSS DR7 and GALEX DR4.
The inclusion of Fuv or Nuv or both photometry decreases the number of
catastrophic identifications (CIs, |z_phot -z_spec| > 1.0). If CIs are removed,
the inclusion of both Fuv and Nuv photometry mainly increases the number of
non-CIs in the low redshift, g-r < 0.8 and fainter r-magnitude regions. The
inclusion of binary interactions (BIs) mainly increases the number of non-CIs
and decreases the deviations in the 0.3 < g-r < 0.8 region in the case of only
using optical photometry.
The inclusion of UV photometry would decrease and increase the probability
that early types are classified as Burst and E types, respectively, and
increase that late types are classified as CWW-Sbc and CWW-Scd types. If CIs
are excluded, the inclusion of UV data mainly raises the identifications of
late types in all redshift, bluer g-r and r > 14 regions. Moreover, BIs mainly
affect the determinations of E and S0 types.
Nuv -u = 1.94 and 5.77-1.47(u-r) = Fuv discriminators can be used as
morphology selection indicators. These two criteria have comparable reliability
and completeness for selecting early- and late-type galaxies to C=2.6 criterion
and higher completeness for early-type selection than u-r=2.22 criterion.
We present the general properties of the far-ultraviolet (FUV; 1370-1720A) continuum background over most of the sky, obtained with the Spectroscopy of Plasma Evolution from Astrophysical Radiation instrument (SPEAR, also known as FIMS), flown aboard the STSAT-1 satellite mission. We find that the diffuse FUV continuum intensity is well correlated with N_{HI}, 100 $\mu$m, and H-alpha intensities but anti-correlated with soft X-ray. The strongest correlation is with the H-alpha emission, and the correlation of the diffuse background with the direct stellar flux is weaker than the correlation with other parameters. The continuum spectra are relatively flat. However, a weak softening of the FUV spectra toward some sight lines, mostly at high Galactic latitudes, is found not only in direct-stellar but also in diffuse background spectra. The diffuse background is relatively softer that the direct stellar spectrum. We also find that the diffuse FUV background averaged over the sky has about the same level as the direct-stellar radiation field in the statistical sense and a bit softer spectrum compared to direct stellar radiation. A map of the ratio of 1400-1510A to 1560-1660A shows that the sky is divided into roughly two parts. However, this map shows a lot of patchy structures on small scales. The spatial variation of the hardness ratio seems to be largely determined by the longitudinal distribution of spectral types of stars in the Galactic plane. A correlation of the hardness ratio with the FUV intensity at high intensities is found but an anti-correlation at low intensities. We also find evidence that the FUV intensity distribution is log-normal in nature.
The road to becoming an astronomer is exciting, but often fraught with danger and conflicting messages. A PhD student is inundated with catch-phrases such as "publish or perish" and "it's not about the quantity, but the quality of work". How do we know which advice to follow? How can we publish copious amounts of quality work in only three years so as to maximize our success in the future? How do we even know what "good quality" really is? With only a short time to prepare ourselves for the big wide world of Astronomy, what is the best way for a PhD student to maximize their research and ultimately maximize their success as a real astronomer? The PhD students of today are the astronomers of tomorrow, but their journey depends on a positive work environment in which they can thrive and improve. Here I present the results of a survey of current PhD students on how they believe they can maximize their success in science. I find that PhD students in Australia expect to write more papers during their PhD than is expected by their supervisors, but that they are generally happy with the quality of their supervision. Above all, students love telescopes, and hands-on observations are an important part of acquiring the knowledge and culture necessary to becoming a real astronomer.
Population III star formation during the dark ages shifted from minihalos (~10^6 Msun) cooled via molecular hydrogen to more massive halos (~10^8 Msun) cooled via Ly-alpha as Lyman-Werner backgrounds progressively quenched molecular hydrogen cooling. Eventually, both modes of primordial star formation were suppressed by the chemical enrichment of the IGM. We present a comprehensive model for following the modes of Population III star formation that is based on a combination of analytical calculations and cosmological simulations. We characterize the properties of the transition from metal-free star formation to the first Population II clusters for an average region of the Universe and for the progenitors of the Milky Way. Finally, we highlight the possibility of observing the explosion of Population III stars within Ly-alpha cooled halos at redshift z~6 in future deep all sky surveys such as LSST.
The presence of absorbing gas around the central engine of Active Galactic Nuclei (AGN) is a common feature of these objects. Recent work has looked at the effect of the dust component of the gas, and how it enhances radiation pressure such that dusty gas can have a lower effective Eddington limit than ionised gas. In this work, we use multi-wavelength data and X-ray spectra from the 2 Ms exposures of the Chandra Deep Field North and Chandra Deep Field South surveys, to characterise the AGN in terms of their Eddington ratio and hydrogen column density. Their distributions are then compared with what is predicted when considering the coupling between dust and gas. Our final sample consists of 234 objects from both fields, the largest and deepest sample of AGN for which this comparison has been made up to date. We find that most of the AGN in our sample tend to be found at low Eddington ratios (typically between 1e-4 and 1e-1) and high column density (>1e22 cm^-2), with black hole masses between ~1e8 and 1e9 solar masses. Their distribution is in agreement with that expected from the enhanced radiation pressure model, avoiding the area where we would predict the presence of outflows. We also investigate how the balance between AGN radiation pressure and gravitational potential influences the behaviour of clouds in the galactic bulge, and describe a scenario where an enhanced radiation pressure can lead to the fundamental plane of black hole/galaxy scaling relations.
This paper is the second in a series devoted to the hard X-ray (17-60 keV) whole sky survey performed by the INTEGRAL observatory over seven years. Here we present a catalog of detected sources which includes 521 objects, 449 of which exceed a 5 sigma detection threshold on the time-averaged map of the sky, and 53 were detected in various subsamples of exposures. Among the identified sources with known and suspected nature, 262 are Galactic (101 low-mass X-ray binaries, 95 high-mass X-ray binaries, 36 cataclysmic variables, and 30 of other types) and 219 are extragalactic, including 214 active galactic nuclei (AGNs), 4 galaxy clusters, and galaxy ESO 389-G 002. The extragalactic (|b|>5 deg) and Galactic (|b|<5 deg) persistently detected source samples are of high identification completeness (respectively ~96% and ~94%) and valuable for population studies.
I derive the physical properties of 30 transiting extrasolar planetary systems using a homogeneous analysis of published data. The light curves are modelled with the JKTEBOP code, with attention paid to limb darkening and eccentricity. The light from some systems is contaminated by faint nearby stars, which if ignored will systematically bias the results. I show that this must be accounted for using external measurements of the amount of contaminating light. A contamination of 5% is enough to make the measurement of a planetary radius 2% too low. The physical properties of the 30 transiting systems are obtained by interpolating in stellar model predictions to find the best match to their measured quantities. The error budgets are used to compile a list of systems which would benefit from additional observations. The systematic errors arising from the inclusion of stellar models are assessed by using five different theoretical models. This model dependence sets a lower limit on the accuracy of measurements of the system properties, and at worst is 1% for the stellar mass. The correlations of planetary surface gravity and mass with orbital period have significance levels of only 3.1 sigma and 2.3 sigma. The division of planets into two classes based on Safronov number is increasingly blurred. Most of the objects studied here would benefit from more photometry and/or spectroscopy, as well as a better understanding of low-mass stars.
We analyze temporal evolution of the number of accreting white dwarfs with shell hydrogen burning in semidetached and detached binaries. We consider a stellar system in which star formation lasts for 10 Gyr with a constant rate, as well as a system in which the same amount of stars is formed in a single burst lasting for 1 Gyr. Evolution of the number of white dwarfs is confronted to the evolution of occurrence rate of events that usually are identified with SN Ia or accretion-induced collapses, i.e. with accumulation of Chandrasekhar mass by a white dwarf or a merger of a pair of CO white dwarfs with total mass not lower than the Chandrasekhar one. In the systems with a burst of star formation, at $t=$10 Gyr observed supersoft X-ray sources, most probably, are not precursors of SN Ia. The same is true for an overwhelming majority of the sources in the systems with constant star formation rate. In the systems of both kinds mergers of white dwarfs is the dominant SN Ia scenario. In symbiotic binaries, accreting CO-dwarfs do not accumulate enough mass for SN Ia explosion, while ONeMg-dwarfs finish their evolution by an accretion-induced collapse with formation of a neutron star.
The IBIS imager on board INTEGRAL, with a sensitivity better than a mCrab in deep observations and a point source location accuracy of the order of few arcminutes, has localized so far 723 hard X-ray sources in the 17--100 keV energy band, of which a fraction of about 1/3 are still unclassified. The aim of this research is to provide sub-arcsecond localizations of the unidentified sources, necessary to pinpoint the optical and/or infrared counterpart of those objects whose nature is so far unknown. The cross-correlation between the new IBIS sources published within the fourth INTEGRAL/IBIS Survey catalogue and the CHANDRA/ACIS data archive resulted in a sample of 5 not yet identified objects. We present here the results of CHANDRA X-ray Observatory observations of these five hard X-ray sources discovered by the INTEGRAL satellite. We associated IGR J10447-6027 with IR source 2MASSJ10445192-6025115, IGR J16377-6423 with the cluster CIZA J1638.2-6420, IGR J14193-6048 with the pulsar with nebula PSR J1420-6048 and IGR J12562+2554 with the Quasar SDSSJ125610.42+260103.5. We suggest that the counterpart of IGR J12288+0052 may be an AGN/QSO type~2 at a confidence level of 90%.
We analyze the optical-near infrared spectra of 33 quasars with redshifts 3.9 < z < 6.4 with the aim of investigating the properties of dust extinction at these cosmic epochs. The SMC extinction curve has been shown to reproduce the dust reddening of most quasars at z < 2.2; the main goal of this work is to investigate whether this curve provides a good prescription for describing dust extinction also at higher redshifts or not. We fit the observed spectra with synthetic absorbed quasar templates obtained by varying the intrinsic slope (alpha), the absolute extinction (A3000) and by using grid of empirical and theoretical extinction curves. We find that seven quasars in our sample require substantial extinction (A3000 > 0.8), and are characterized by very steep intrinsic slopes (alpha < -2.3). All of the individual quasars require extinction curve deviating from the SMC, with a tendency to flatten at lambda < 2000 A (rest frame). We obtain a mean extinction curve at z>4, both by a simultaneous fit of all quasars and by averaging the extinction curves inferred for individual quasars. In the case of Broad Absorption Line quasars the mean extinction curve deviates from the SMC at a confidence level > 95%. The different extinction curves in quasars at z>4 relative to quasars at lower redshift suggest either a different dust production mechanism at high redshift, or a different mechanism of processing dust into the ISM. We suggest that the same transitions may also apply to normal, star forming galaxies at z>4. In particular, the observed change of the average spectral slope in galaxies at z>4 may be partially ascribed to a variation of the extinction curve, rather than a lower dust content at high redshift. In this scenario, the extinction curve inferred at z>4 would imply a corrected cosmic star formation rate at these epochs a factor of \sim 2 higher than estimated in the past.
We present high-precision photometry of three transits of the extrasolar planetary system WASP-2, obtained by defocussing the telescope, and achieving point-to-point scatters of between 0.42 and 0.73 mmag. These data are modelled using the JKTEBOP code, and taking into account the light from the recently-discovered faint star close to the system. The physical properties of the WASP-2 system are derived using tabulated predictions from five different sets of stellar evolutionary models, allowing both statistical and systematic errorbars to be specified. We find the mass and radius of the planet to be M_b = 0.847 +/- 0.038 +/- 0.024 Mjup and R_b = 1.044 +/- 0.029 +/- 0.015 Rjup. It has a low equilibrium temperature of 1280 +/- 21 K, in agreement with a recent finding that it does not have an atmospheric temperature inversion. The first of our transit datasets has a scatter of only 0.42 mmag with respect to the best-fitting light curve model, which to our knowledge is a record for ground-based observations of a transiting extrasolar planet.
We analyse the redshift dependence of space number density of quasars assuming that they are the short-lived active stages of the massive galaxies and arise immediately after the collapse of homogeneous central part of protogalaxy clouds. Obtained dependence fits the observational data ChaMP+CDF+ROSAT (Silverman et al. 2005) very well for protogalaxy clouds of mass $M\approx 8\cdot 10^{11}$ $h^{-1}M_{\odot}$ and ellipticity $e<0.4$. The lifetime of bright X-ray AGNs or QSOs with $L_X>10^{44.5}$ erg$\cdot s^{-1}$ in the range of energies $0.3-8$ keV is $\tau_{QSO}\sim 6\cdot10^6$ years when the mass of supermassive black hole is $M_{SMBH}\sim 10^{9}$ $M_{\odot}$ and the values of other quasar parameters are reasonable. The analysis and all calculations were carried out in the framework of $\Lambda$CDM-model with parameters determined from 5-years WMAP, SNIa and large scale structure data \cite{Komatsu09}. It is concluded, that the halo model of galaxy formation in the $\Lambda$CDM cosmological model matches well observational data on AGNs and QSOs number density coming from current optical and X-ray surveys.
Gamma-ray bursts are usually classified through their high-energy emission into short-duration and long-duration bursts, which presumably reflect two different types of progenitors. However, it has been shown on statistical grounds that a third, intermediate population is needed in this classification scheme, although an extensive study of the properties of this class has so far not been done. The large amount of follow-up studies generated during the Swift era allows us to have a suficient sample to attempt a study of this third population through the properties of their prompt emission and their afterglows. Our study is focused on a sample of GRBs observed by Swift during its first four years of operation. The sample contains those bursts with measured redshift since this allows us to derive intrinsic properties. Intermediate bursts are less energetic and have dimmer afterglows than long GRBs, especially when considering the X-ray light curves, which are on average one order of magnitude fainter than long bursts. There is a less significant trend in the redshift distribution that places intermediate bursts closer than long bursts. Except for this, intermediate bursts show similar properties to long bursts. In particular, they follow the Epeak vs. Eiso correlation and have, on average, positive spectral lags with a distribution similar to that of long bursts. Like long GRBs, they normally have an associated supernova, although some intermediate bursts have shown no supernova component. This study shows that intermediate bursts are different from short bursts and, in spite of sharing many properties with long bursts, there are some differences between them as well. We suggest that the physical difference between intermediate and long bursts could be that for the first the ejecta are thin shells while for the latter they are thick shells.
We present colour transformations from Two Micron All Sky Survey (2MASS) photometric system to Johnson-Cousins system and to Sloan Digital Sky Survey (SDSS) system for late-type giants and vice versa. The giant star sample was formed using surface gravity constraints ($2 < \log g \leq 3$) to Cayrel de Strobel et al.\rq s (2001) spectroscopic catalogue. 2MASS, SDSS and Johnson-Cousins photometric data was taken from Cutri et al. (2003), Ofek (2008) and van Leeuwen (2007), respectively. The final sample was refined applying the following steps: (1) the data were dereddened, (2) the sample stars selected are of the highest photometric quality. We give two--colour dependent transformations as a function of metallicity as well as independent of metallicity. The transformations provide absolute magnitudes and distance determinations which can be used in space density evaluations at relatively short distances where some or all of the SDSS magnitudes of late--type giants are saturated.
We perform a uniform, systematic analysis of a sample of 38 X-ray galaxy clusters with three different Chandra calibrations. The temperatures change systematically between calibrations. Cluster temperatures change on average by roughly ~6% for the smallest changes and roughly ~13% for the more extreme changes between calibrations. We explore the effects of the changing cluster spectral properties on Sunyaev-Zel'dovich effect (SZE) and X-ray determinations of the Hubble constant. The Hubble parameter changes by +10% and -13% between the current calibration and two previous Chandra calibrations, indicating that changes in the cluster temperature basically explain the entire change in H_0. Although this work focuses on the difference in spectral properties and resultant Hubble parameters between the calibrations, it is intriguing to note that the newer calibrations favor a lower value of the Hubble constant, H_0 ~ 60 km s-1 Mpc-1, typical of results from SZE/X-ray distances. Both galaxy clusters themselves and the details of the instruments must be known precisely to enable reliable precision cosmology with clusters, which will be feasible with combined efforts from ongoing observations and planned missions and observatories covering a wide range of wavelengths.
Abridged. In the double detonation scenario for Type Ia supernovae (SNe Ia) a detonation initiates in a shell of He-rich material accreted from a companion star by a sub-Chandrasekhar-mass White Dwarf (WD). This shell detonation drives a shock front into the carbon-oxygen (C/O) WD that triggers a secondary detonation in the core. The core detonation results in a complete disruption of the WD. Earlier studies concluded that this scenario has difficulties in accounting for the observed properties of SNe Ia since the explosion ejecta are surrounded by the products of explosive He burning in the shell. Recently, it was proposed that detonations might be possible for much less massive He shells than previously assumed. Moreover, it was shown that even detonations of these minimum He shell masses robustly trigger detonations of the C/O core. Here we present time-dependent multi-wavelength radiative transfer calculations for models with minimum He shell mass and derive synthetic observables for both the optical and {\gamma}-ray spectral regions. These differ strongly from those found in earlier simulations of sub-Chandrasekhar-mass explosions in which more massive He shells were considered. Our models predict light curves which cover both the range of brightnesses and the rise and decline times of observed SNe Ia. However, their colours and spectra do not match the observations. In particular, their B-V colours are generally too red. We show that this discrepancy is mainly due to the composition of the burning products of the He shell of our models which contain significant amounts of Ti and Cr. Using a toy model, we also show that the burning products of the He shell depend crucially on its initial composition. This leads us to conclude that good agreement between sub-Chandrasekhar-mass explosions and observed SNe Ia may still be feasible but further study of the shell properties is required.
(abridged) Hard X-ray surveys performed by the INTEGRAL satellite have discovered a conspicuous fraction (up to 30%) of unidentified objects among the detected sources. Here we continue our identification program by selecting probable optical candidates using positional cross-correlation with soft X-ray, radio, and/or optical archives, and performing optical spectroscopy on them. As a result, we identified or more accurately characterized 44 counterparts of INTEGRAL sources: 32 active galactic nuclei, with redshift 0.019 < z < 0.6058, 6 cataclysmic variables (CVs), 5 high-mass X-ray binaries (2 of which in the Small Magellanic Cloud), and 1 low-mass X-ray binary. This was achieved by using 7 telescopes of various sizes and archival data from two online spectroscopic surveys. The main physical parameters of these hard X-ray sources were also determined using the available multiwavelength information. AGNs are the most abundant population among hard X-ray objects, and our results confirm this tendency when optical spectroscopy is used as an identification tool. The deeper sensitivity of recent INTEGRAL surveys enables one to begin detecting hard X-ray emission above 20 keV from sources such as LINER-type AGNs and non-magnetic CVs.
The X-ray spectrum of the Seyfert 1.5 source NGC 6860 is among the most complex of the sources detected in the Swift Burst Alert Telescope all-sky survey. A short XMM-Newton follow-up observation of the source revealed a flat spectrum both above and below 2 keV. To uncover the complexity of the source, in this paper we analyze both a 40 ks Suzaku and a 100 ks XMM-Newton observation of NGC 6860. While the spectral state of the source changed between the newer observations presented here and the earlier short XMM-Newton spectrum - showing a higher flux and steeper power law component - the spectrum of NGC 6860 is still complex with clearly detected warm absorption signatures. We find that a two component warm ionized absorber is present in the soft spectrum, with column densities of about 10^20 and 10^21 cm$^-2, ionization parameters of xi = 180 and 45 ergs cm s^-1, and outflow velocities for each component in the range of 0-300 km s^-1. Additionally, in the hard spectrum we find a broad (approx 11000 km s^-1) Fe K-alpha emission line, redshifted by approx 2800 km s^-1.
We apply the light bending model of X-ray variability to Suzaku data of the Seyfert 1 galaxy MCG-6-30-15. We analyze the energy dependence of the root mean square (rms) variability, and discuss conditions necessary for the model to explain the characteristic decrease of the source variability around 5-8 keV. A model, where the X-ray source moves radially rather than vertically close to the disk surface, can indeed reproduce the reduced variability near the energy of the Fe Kalpha line, although the formal fit quality is poor. The model then predicts the energy spectra, which can be compared to observational data. The spectra are strongly reflection dominated, and do not provide a good fit to Suzaku spectral data of the source. The inconsistency of this result with some previous claims can be traced to our using data in a broader energy band, where effects of warm absorber in the spectrum cannot be neglected.
Context. Hydrogen ionized by young, high-mass stars in starburst galaxies
radiates radio recombination lines (RRLs), whose strength can be used as a
diagnostic of the ionization rate, conditions and gas dynamics in the
starburst, without problems of dust obscuration. However, the lines are weak
and only few extragalactic starburst systems have been detected.
Aims. We aimed to increase the number of known starburst systems with
detectable RRLs for detailed studies.
Methods. We searched for the RRLs H91alpha and H92alpha at 8 GHz in the
nearby Seyfert galaxy NGC 4945 using the ATCA with resolution of 3". This
yielded a detection from which we derived conditions in the starburst.
Results. We detected RRLs from the nucleus of NGC 4945 with a peak strength
of 17.8 mJy, making it the strongest extragalactic RRL emitter known at this
frequency. The line emission from NGC 4945 can be matched by a model consisting
of a collection of 10 to 300 H II regions with temperatures of 5000 K,
densities of 10^3 cm^-3 to 10^4 cm^-3 and a total effective diameter of 2 pc to
100 pc. The Lyman continuum production rate required to maintain the ionization
requires 2000 to 10000 O5 stars to be produced in the starburst, inferring a
star formation rate of 2 Msun/yr to 8 Msun/yr. We resolved the rotation curve
within the central 70 pc region and this is well described by a set of rotating
rings that were coplanar and edge on with a simple flat rotation curve. The
rotation speed of 120 km/s within the central 1" (19 pc) radius infers an
enclosed mass of 3 x 10^7 Msun.
Conclusion. We discovered RRLs from NGC 4945. It is the strongest known
extragalactic RRL emitter and is suited to high-quality spectroscopic study. We
resolved the dynamics of the ionized gas in the central 70 pc and derived
conditions and star formation rates in the ionized gas.
We analyze how the orbital support of the inner bar in a double-barred galaxy (nested bars) depends on the angular velocity (i.e. pattern speed) of this bar. We study orbits in seven models of double bars using the method of invariant loops. The range of pattern speed is covered exhaustively. We find that not all pattern speeds are allowed when the inner bar rotates in the same direction as the outer bar. Below a certain minimum pattern speed orbital support for the inner bar abruptly disappears, while at high values of this speed the orbits indicate an increasingly round bar that looks more like a twist in the nuclear isophotes than a dynamically independent component. For values between these two extremes, orbits supporting the inner bar extend further out as the bar's pattern speed decreases, their corresponding loops become more eccentric, pulsate more, and their rotation becomes increasingly non-uniform, as they speed up and slow down in their motion. Lower pattern speeds also lead to a less coherent bar, as the pulsation and acceleration increasingly varies among the loops supporting the inner bar. The morphologies of fast and slow inner bars expected from the orbital structure studied here are recently recovered observationally by decomposition of double barred galaxies. Our findings allow us to link the observed morphology to the dynamics of the inner bar.
Stellar kinematics in the external regions of globular clusters can be used to probe the validity of Newton's law in the low acceleration regimes without the complication of non-baryonic dark matter. Indeed, in contrast with what happens when studying galaxies, in globular clusters a systematic deviation of the velocity dispersion profile from the expected Keplerian falloff would provide indication of a breakdown of Newtonian dynamics rather than the existence of dark matter. We perform a detailed analysis of the velocity dispersion in the globular cluster omega Centauri in order to investigate whether it does decrease monotonically with distance as recently claimed by Sollima et al. (2009), or whether it converges toward a constant value as claimed by Scarpa Marconi and Gilmozzi (2003B). We combine measurements from these two works to almost double the data available at large radii, in this way obtaining an improved determination of the velocity dispersion profile in the low acceleration regime. We found the inner region of omega Centauri is clearly rotating, while the rotational velocity tend to vanish, and is consistent with no rotation at all, in the external regions. The cluster velocity dispersion at large radii from the center is found to be sensibly constant. The main conclusion of this work is that strong similarities are emerging between globular clusters and elliptical galaxies, for in both classes of objects the velocity dispersion tends to remain constant at large radii. In the case of galaxies, this is ascribed to the presence of a massive halo of dark matter, something physically unlikely in the case of globular clusters. Such similarity, if confirmed, is best explained by a breakdown of Newtonian dynamics below a critical acceleration.
We use high spatial and spectral resolution observations obtained with the CRisp Imaging SpectroPolarimeter at the Swedish 1-m Solar Telescope to analyze the velocity profile of granular light bridges in a sunspot. We find upflows associated with the central dark lanes of the light bridges. From bisectors in the Fe I 630.15 nm line we find that the magnitude of the upflows varies with height with the strongest upflows being deeper in the atmosphere. Typical upflow velocities measured from the 70% bisector are around 500 m/s with peaks above 1 km/s. The upflows in the central dark lane are surrounded by downflows of weaker magnitude, sometimes concentrated in patches with enhanced velocities reaching up to 1.1 km/s. A small spatial offset between the upflows and the continuum dark lane is interpreted as a line-of-sight effect due to the elevated nature of the dark lane and the light bridge above the umbral surroundings. Our observations show that the central dark lane in granular light bridges is not equivalent to the intergranular lanes of normal photospheric granulation that host convective downflows. These results support recent MHD simulations of magneto-convection in sunspot atmospheres.
We use a collection of 14 well-measured neutron star masses to strengthen the case that a substantial fraction of these neutron stars was formed via electron-capture supernovae (SNe) as opposed to Fe-core collapse SNe. The e-capture SNe are characterized by lower resultant gravitational masses and smaller natal kicks, leading to lower orbital eccentricities when the e-capture SN has led to the formation of the second neutron star in a binary system. Based on the measured masses and eccentricities, we identify four neutron stars, which have a mean post-collapse gravitational mass of ~1.25 solar masses, as the product of e-capture SNe. We associate the remaining ten neutron stars, which have a mean mass of 1.35 solar masses, with Fe-core collapse SNe. If the e-capture supernova occurs during the formation of the first neutron star, then this should substantially increase the formation probability for double neutron stars, given that more systems will remain bound with the smaller kicks. However, this does not appear to be the case for any of the observed systems, and we discuss possible reasons for this.
The wavelet regression detrended fluctuations of the reconstructed temperature for the past three ice ages: approximately 340000 years (Antarctic ice cores isotopic data), exhibit clear evidences of the galactic turbulence modulation up to 2500 years time-scales. The observed strictly Kolmogorov turbulence features indicates the Kolmogorov nature of galactic turbulence, and provide explanation to random-like fluctuations of the global temperature on the millennial time scales.
We report the first extrasolar planet observations from the 10.4-m Gran Telescopio Canarias (GTC), currently the world's largest, fully steerable, single-aperture optical telescope. We used the OSIRIS tunable filter imager on the GTC to acquire high-precision, narrow-band photometry of the transits of the giant exoplanets, TrES-2b and TrES-3b. We obtained near-simultaneous observations in two near-infrared (NIR) wavebands (790.2 and 794.4 +/- 2.0 nm) specifically chosen to avoid water vapor absorption and skyglow so as to minimize the atmospheric effects that often limit the precision of ground-based photometry. Our results demonstrate a very-high photometric precision with minimal atmospheric contamination despite relatively poor atmospheric conditions and some technical problems with the telescope. We find the photometric precision for the TrES-2 observations to be 0.343 and 0.412 mmag for the 790.2 and 794.4 nm light curves, and the precision of the TrES-3 observations was found to be 0.470 and 0.424 mmag for the 790.2 and 794.4 nm light curves. We also discuss how future follow-up observations of transiting planets with this novel technique can contribute to the characterization of Neptune- and super-Earth-size planets to be discovered by space-based missions like CoRoT and Kepler, as well as measure atmospheric properties of giant planets, such as the strength of atmospheric absorption features.
The Brorfelde Schmidt CCD Catalog (BSCC) contains about 13.7 million stars, north of +49 deg Declination with precise positions and V, R photometry. The catalog has been constructed from the reductions of 18,667 CCD frames observed with the Brorfelde Schmidt Telescope between 2000 and 2007. The Tycho-2 catalog was used for astrometric and photometric reference stars. Errors of individual positions are about 20 to 200 mas for stars in the R = 10 to 18 mag range. External comparisons with 2MASS and SDSS reveal possible small systematic errors in the BSCC of up to about 30 mas. The catalog is supplemented with J, H, and K_s magnitudes from the 2MASS catalog. The catalog data file (about 550 MB ASCII, compressed) will be made available at the Strasbourg Data Center (CDS).
Understanding the infrared emission of galaxies is critical to observational and theoretical investigations of the condensation of galaxies out of the intergalactic medium and the conversion of gas into stars over cosmic time. From an observational perspective, about half of all photons emitted within galaxies are locally absorbed by dust grains, necessitating a self-consistent analysis of the panchromatic emission of galaxies to quantify star-formation and AGN activity as a function of epoch and environment. From a theoretical perspective, physical processes involving dust are expected to play a major role in regulating the accumulation of baryons in galaxies and their condensation into stars on scales ranging from Mpc down to sub-pc. All this requires a quantitative analysis of the interaction between dust, gas and radiation. Here we review progress in the modelling of some of these processes.
This is the first paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). We have obtained 2.3 million observations of 14,882 sample galaxies over an interval of 11 years (March 1998 through Dec. 2008). We considered 1036 SNe detected in our sample and used an optimal subsample of 726 SNe (274 SNe~Ia, 116 SNe~Ibc, 324 SNe~II) to determine our SN rates. This is the largest and most homogeneous set of nearby SNe ever assembled for this purpose, and ours is the first local SN rate analysis based on CCD imaging and modern image-subtraction techniques. In this paper, we lay the foundation of the study. We derive the recipe for the control-time calculation for SNe with a known luminosity function, and provide details on the construction of the galaxy and SN samples used in the calculations. Compared with a complete volume-limited galaxy sample, our sample has a deficit of low-luminosity galaxies but still provides enough statistics for a reliable rate calculation. There is a strong Malmquist bias, so the average size (luminosity or mass) of the galaxies increases monotonically with distance, and this trend is used to showcase a correlation between SN rates and galaxy sizes. Very few core-collapse SNe are found in early-type galaxies, providing strong constraints on the amount of recent star formation within these galaxies. The small average observation interval ($\sim 9$ days) of our survey ensures that our control-time calculations can tolerate a reasonable amount of uncertainty in the luminosity functions of SNe. We perform Monte Carlo simulations to determine the limiting magnitude of each image and the SN detection efficiency as a function of galaxy Hubble type ... (abridged)
This is the second paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). In this paper, a complete SN sample is constructed, and the observed (uncorrected for host-galaxy extinction) luminosity functions (LFs) of SNe are derived. These LFs solve two issues that have plagued previous rate calculations for nearby SNe: the luminosity distribution of SNe and the host-galaxy extinction. We select a volume-limited sample of 175 SNe, collect photometry for every object, and fit a family of light curves to constrain the peak magnitudes and light-curve shapes. The volume-limited LFs show that they are not well represented by a Gaussian distribution. There are notable differences in the LFs for galaxies of different Hubble types (especially for SNe Ia). We derive the observed fractions for the different subclasses in a complete SN sample, and find significant fractions of SNe II-L (10%), IIb (12%), and IIn (9%) in the SN II sample. Furthermore, we derive the LFs and the observed fractions of different SN subclasses in a magnitude-limited survey with different observation intervals, and find that the LFs are enhanced at the high-luminosity end and appear more "standard" with smaller scatter, and that the LFs and fractions of SNe do not change significantly when the observation interval is shorter than 10 days. We also discuss the LFs in different galaxy sizes and inclinations, and for different SN subclasses. Some notable results are ... (abridged).
This is the third paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). We have considered a sample of about 1000 SNe and used an optimal subsample of 726 SNe (274 SNe Ia, 116 SNe Ibc, and 324 SNe II) to determine our rates. We study the trend of the rates as a function of a few quantities available for our galaxy sample, such as luminosity in the B and K bands, stellar mass, and morphological class. We discuss different choices (SN samples, input SN luminosity functions, inclination correction factors) and their effect on the rates and their uncertainties. A comparison between our SN rates and the published measurements shows that they are consistent with each other to within uncertainties when the rate calculations are done in the same manner. Nevertheless, our data demonstrate that the rates cannot be adequately described by a single parameter using either galaxy Hubble types or B - K colours. A secondary parameter in galaxy "size", expressed by luminosity or stellar mass, is needed to adequately describe the rates in the rate-size relation: the galaxies of smaller sizes have higher SN rates per unit mass or per unit luminosity. The trends of the SN rates in galaxies of different Hubble types and colours are discussed. We examine possible causes for the rate-size relation. Physically, such a relation for the core-collapse SNe is probably linked to the correlation between the specific star-formation rate and the galaxy sizes, but it is not clear whether the same link can be established for SNe Ia. We discuss the two-component ("tardy" and "prompt") model for SN Ia rates, and find that the SN Ia rates in young stellar populations might have a strong correlation with the core-collapse SN rates. We derive volumetric and Milky Way rates ... (abridged)
Couplings between the inflaton and any additional fields can lead to isolated bursts of particle production during inflation (for example from parametric resonance or a phase transition). Inflationary particle production leaves localized features in the spectrum and bispectrum of the observable cosmological fluctuations, via the Infra-Red (IR) cascading mechanism. We focus on a simple prototype interaction g^2 (\phi-\phi_0)^2\chi^2 between the inflaton, \phi, and iso-inflaton, \chi; extending previous work on this model in two directions. First, we quantify the magnitude of the produced nongaussianity by extracting the moments of the probability distribution function from lattice field theory simulations. We argue that the bispectrum feature from particle production might be observable for reasonable values of the coupling, g^2. Second, we develop a detailed analytical theory of particle production and IR cascading during inflation, which is in excellent agreement with numerical simulations. Our formalism improves significantly on previous approaches by consistently incorporating both the expansion of the universe and also metric perturbations. We use this new formalism to estimate the shape of the bispectrum from particle production, showing this to be distinguishable from other mechanisms that predict large nongaussianity.
We present 3D numerical simulations of the early evolution of long-duration gamma-ray bursts in the collapsar scenario. Starting from the core-collapse of a realistic progenitor model, we follow the formation and evolution of a central black hole and centrifugally balanced disk. The dense, hot accretion disk produces freely-escaping neutrinos and is hydrodynamically unstable to clumping and to forming non-axisymmetric (m=1, 2) modes. We show that these spiral structures, which form on dynamical timescales, can efficiently transfer angular momentum outward and can drive the high required accretion rates (>=0.1-1 M_sun) for producing a jet. We utilise the smoothed particle hydrodynamics code, Gadget-2, modified to implement relevant microphysics, such as cooling by neutrinos, a plausible treatment approximating the central object and relativistic effects. Finally, we discuss implications of this scenario as a source of energy to produce relativistically beamed gamma-ray jets.
We construct and compare a variety of simple models for strange stars, namely, hypothetical self-bound objects made of a cold stable version of the quark-gluon plasma. Exact, quasi-exact and numerical models are examined to find the most economical description for these objects. A simple and successful parametrization of them is given in terms of the central density, and many differences among the models are explicitly shown and discussed.
We study superparticle spectra in the superconformal flavor scenario with non-universal gaugino masses. The non-universality of gaugino masses can lead to the wino-like or higgsino-like neutralino LSP. Furthermore, it is shown that the parameter space for the higgsino-like LSP includes the region where the fine-tuning problem can be improved. The degeneracy of soft scalar masses squared does not drastically change by taking ratios of gaugino masses of order one. The degeneracy of scalar masses for squarks and left-handed sleptons would be good to avoid the FCNC problem but that of right-handed slepton masses is weak. However, the overall size of right-handed slepton masses become larger when the bino becomes heavier. It is also pointed out that such region can be realized, and thus, that would be favorable to avoid the FCNC problem for soft scalar masses as well as A-terms.
Gamma ray source detection above 30TeV is an encouraging approach for finding galactic cosmic ray origins. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100GeV. To target the goals, the ARGO-YBJ experiment has been established. Significant progresses have been made in the experiment. A large air shower detector array in an area of 1km2 is proposed to boost the sensitivity. Hybrid detection with multi-techniques will allow a good discrimination between different types of primary particles, including photons and protons, thus enable an energy spectrum measurement for individual specie. Fluorescence light detector array will extend the spectrum measurement above 100PeV where the second knee is located. An energy scale determined by balloon experiments at 10TeV will be propagated to ultra high energy cosmic ray experiments.
Precision tests of gravity can be used to constrain the properties of hypothetical very light scalar fields, but these tests depend crucially on how macroscopic astrophysical objects couple to the new scalar field. We develop quasi-analytic methods for solving the equations of stellar structure using scalar-tensor gravity, with the goal of seeing how stellar properties depend on assumptions made about the scalar coupling at a microscopic level. We illustrate these methods by applying them to Brans-Dicke scalars, and their generalization in which the scalar-matter coupling is a weak function of the scalar field. The four observable parameters that characterize the fields external to a spherically symmetric star (the stellar radius, R, mass, M, scalar `charge', Q, and the scalar's asymptotic value, phi_infty) are subject to two relations because of the matching to the interior solution, generalizing the usual mass-radius, M(R), relation of General Relativity. We identify how these relations depend on the microscopic scalar couplings, agreeing with earlier workers when comparisons are possible. Explicit analytical solutions are obtained for the instructive toy model of constant-density stars, whose properties we compare to more realistic equations of state for neutron star models.
In hybrid inflation, initial field values leading to sufficiently long inflation were thought be fine-tuned in a narrow band along the inflationary valley. A re-analysis of this problem has shown that there exists a non negligible proportion of successful initial conditions exterior to the valley, organized in a complex structure with fractal boundaries, and whose origin has been explained. Their existence in a large part of the parameter space has been demonstrated using a bayesian Monte-Carlo-Markov-Chain (MCMC) method, and natural bounds on potential parameters have been established. Moreover, these results are shown to be valid not only for the original hybrid model, but also for other hybrid realizations in various frameworks.
We study analytically the relaxation dynamics of charged test fields left outside a newly born charged black hole. In particular, we obtain a simple analytic expression for the fundamental quasinormal resonances of near-extremal Reissner-Nordstr\"om black holes. The formula is expressed in terms of the black-hole physical parameters: $\omega=q\Phi-i2\pi T_{BH}(n+{1 \over 2})$, where $T_{BH}$ and $\Phi$ are the temperature and electric potential of the black hole, and $q$ is the charge of the field.
If neutrino mass is a function of the Higgs potential then minimum of the total thermodynamic potential $\Omega$ (which is the Higgs potential minus the neutrino pressure) can shift from the standard electro-weak vev $v=246.2$ GeV by a small amount which depends on the neutrino pressure. If the neutrino mass is a very steep function of the Higgs field then the equilibrium thermodynamic potential can act like the dark energy with $\omega \simeq -1$. Choosing the neutrino mass as logarithmic function of the Higgs field and a heavy mass scale, we find that the correct magnitude of the cosmological density of the present universe $\rho_\lambda \simeq (0.002 eV)^4$ is obtained by choosing the heavy mass at the GUT scale.
The characterization of a $m$-dimensional internal manifold with metric as having positive, zero or negative curvature is known to be one of the most important aspects of warped compactifications in $(4+m)$-dimensional supergravity models and hence that of matter content in an effective four-dimensional theory. In this context, Douglas and Kallosh in arXiv:1001.4008 argued that string compactifications using manifolds whose scalar curvature is everywhere negative must have significant warping or large stringy corrections, or both. Douglas-Kallosh argument may apply to some particular class of flux compactifications with strong constraints on the warp geometry or standard Kaluza-Klein compactifications (with constant warp factor), but perhaps not to a general class of warped solutions in curved manifolds. For clarity, we first present some explicit examples of 4D de Sitter solutions in ten and eleven dimensions, without source terms (fluxes or objects that violate positivity conditions), but with an arbitrary 6D curvature. We then explore the possibility of obtaining de Sitter solutions by using a 6-dimensional warped manifold ${\cal M}$ by introducing p-form gauge fields. We show that 4D de Sitter solutions can exist with almost any choice of internal space curvature, including manifolds whose 6D Ricci scalar curvature is negative.
By performing a bayesian Monte-Carlo-Markov-Chain analysis, it is shown that a large number of e-folds (more than 60) are generated classically during the waterfall after hybrid inflation in a large part of the parameter space of the model. As a result, the observable perturbation modes leave the Hubble radius during waterfall inflation. The power spectrum of adiabatic perturbations is red, possibly in agreement with CMB constraints. A particular attention has been given to study only the regions for which quantum backreactions do not affect the classical dynamics. Implications concerning the preheating and the absence of topological defects in our universe are discussed.
We expand the study of generalized brane cosmologies by allowing for an $f(\tilde{\cal R})$ gravity term on the brane, with $\tilde{\cal R}$ the curvature scalar derived from the induced metric. We also include arbitrary matter components on the brane and in the five-dimensional bulk. At low energies, the effect of the bulk on the brane evolution can be described through a mirage component, termed generalized dark radiation, in the effective four-dimensional field equations. Using the covariant formalism, we derive the exact form of these equations. We also derive an effective conservation equation involving the brane matter and the generalized dark radiation. At low energies the coupled brane-bulk system has a purely four-dimensional description. The applications of the formalism include generalizations of the Starobinsky model and the Dvali-Gabadadze-Porrati cosmology.
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We present new measurements of the coherent motion of galaxies based on observations of the large-scale redshift--space distortions seen in the two--dimensional two--point correlation function of Luminous Red Galaxies in Data Release Seven of the Sloan Digital Sky Survey. We have developed a new methodology for estimating these coherent motions, which is less dependent on the details of galaxy bias and of the cosmological model to explain the late--time acceleration of the expansion of the Universe. We measure a one--dimensional velocity dispersion of galaxies on large--scales of sigma_v=3.01^{+0.45}_{-0.46} Mpc/h and sigma_v=3.69^{+0.47}_{-0.47} Mpc/h at a mean redshift of z=0.25 and 0.38 respectively. These values are fully consistent with predictions for a WMAP7--normalised LCDM Universe and inconsistent (at >5 sigma) with a Dvali-Gabadadze-Porrati (DGP) model for the Universe. We can convert the units of these sigma_v measurements to 270^{+40}_{-41} km/s and 320^{+41}_{-41} km/s respectively (assuming a LCDM universe), which are much lower than that expected based on recent low redshift (z<0.2) measurements of the peculiar velocity field (or ``bulk flows"), i.e., we would have predicted motions of ~ 600 km/s over our redshift range (0.16<z<0.47) to be consistent with these local measurements. One possible explanation for such a large discrepancy is that our Galaxy is located in unusually over, or under, dense region of the Universe.
We present N2D+ 3-2 (IRAM) and H2D+ 1_11 - 1_10 and N2H+ 4-3 (JCMT) maps of the small cluster-forming Ophiuchus B2 core in the nearby Ophiuchus molecular cloud. In conjunction with previously published N2H+ 1-0 observations, the N2D+ data reveal the deuterium fractionation in the high density gas across Oph B2. The average deuterium fractionation R_D = N(N2D+)/N(N2H+) ~ 0.03 over Oph B2, with several small scale R_D peaks and a maximum R_D = 0.1. The mean R_D is consistent with previous results in isolated starless and protostellar cores. The column density distributions of both H2D+ and N2D+ show no correlation with total H2 column density. We find, however, an anticorrelation in deuterium fractionation with proximity to the embedded protostars in Oph B2 to distances >= 0.04 pc. Destruction mechanisms for deuterated molecules require gas temperatures greater than those previously determined through NH3 observations of Oph B2 to proceed. We present temperatures calculated for the dense core gas through the equating of non-thermal line widths for molecules (i.e., N2D+ and H2D+) expected to trace the same core regions, but the observed complex line structures in B2 preclude finding a reasonable result in many locations. This method may, however, work well in isolated cores with less complicated velocity structures. Finally, we use R_D and the H2D+ column density across Oph B2 to set a lower limit on the ionization fraction across the core, finding a mean x_e, lim >= few x 10^{-8}. Our results show that care must be taken when using deuterated species as a probe of the physical conditions of dense gas in star-forming regions.
One of the strongest arguments against the cosmological constant as an explanation of the current epoch of accelerated cosmic expansion is the existence of an earlier, dynamical acceleration, i.e. inflation. We examine the likelihood that acceleration is an occasional phenomenon, putting stringent limits on the length of any accelerating epoch between recombination and the recent acceleration; such an epoch must last less than 0.05 e-fold (at z>2) or the matter power spectrum is modified by more than 20%.
Continuous observations were performed of a quiescent prominence with the Solar Optical Telescope (SOT) on board the /emph{Hinode} satellite on 2006 December 23--24. A peculiar slowly-rising column of $/sim10^{4}$ K plasma develops from the lower atmosphere during the observations. The apparent ascent speed of the column is 2 km s$^{-1}$, while the fine structures of the column exhibit much faster motion of up to 20 km s$^{-1}$. The column eventually becomes a faint low-lying prominence. Associated with the appearance of the column, an overlying coronal cavity seen in the X-ray and EUV moves upward at $/sim$5 km s$^{-1}$. We discuss the relationship between these episodes, and suggest that they are due to the emergence of a helical flux rope that undergoes reconnection with lower coronal fields, possibly carrying material into the coronal cavity. Under the assumption of the emerging flux scenario, the lower velocity of 2 km s$^{-1}$ and the higher one of 20 km s$^{-1}$ in the column are attributed to the rising motion of the emerging flux and to the outflow driven by magnetic reconnection between the emerging flux and the pre-existing coronal field, respectively. The present paper gives a coherent explanation of the enigmatic phenomenon of the rising column with the emergence of the helical rope, and its effect on the corona. We discuss the implications that the emergence of such a helical rope has on the dynamo process in the convection zone.
We present a HST/STIS spectroscopic and optical/radio imaging study of the Seyfert NGC 2110 aiming to measure the dynamics and understand the nature of the nuclear outflow in the galaxy. Previous HST studies have revealed the presence of a linear structure in the Narrow-Line Region (NLR) aligned with the radio jet. We show that this structure is strongly accelerated, probably by the jet, but is unlikely to be entrained in the jet flow. The ionisation properties of this structure are consistent with photoionisation of dusty, dense gas by the active nucleus. We present a plausible geometrical model for the NLR, bringing together various components of the nuclear environment of the galaxy. We highlight the importance of the circum-nuclear disc in determining the appearance of the emission line gas and the morphology of the jet. From the dynamics of the emission line gas, we place constraints on the accelerating mechanism of the outflow and discuss the relative importance of radio source synchrotron pressure, radio jet ram pressure and nuclear radiation pressure in accelerating the gas. While all three mechanisms can account for the energetics of the emission line gas, gravitational arguments support radio jet ram pressure as the most likely source of the outflow.
The spectral energy distribution of galaxies is a complex function of the star formation history and geometrical arrangement of stars and gas in galaxies. The computation of the radiative transfer of stellar radiation through the dust distribution is time-consuming. This aspect becomes unacceptable in particular when dealing with the predictions by semi-analytical galaxy formation models populating cosmological volumes, to be then compared with multi-wavelength surveys. Mainly for this aim, we have implemented an artificial neural network algorithm into the spectro-photometric and radiative transfer code GRASIL in order to compute the spectral energy distribution of galaxies in a short computing time. This allows to avoid the adoption of empirical templates that may have nothing to do with the mock galaxies output by models. The ANN has been implemented to compute the dust emission spectrum (the bottleneck of the computation), and separately for the star-forming molecular clouds and the diffuse dust (due to their different properties and dependencies). We have defined the input neurons effectively determining their emission, which means this implementation has a general applicability and is not linked to a particular galaxy formation model. We have trained the net for the disc and spherical geometries, and tested its performance to reproduce the SED of disc and starburst galaxies, as well as for a semi-analytical model for spheroidal galaxies. We have checked that for this model both the SEDs and the galaxy counts in the Herschel bands obtained with the ANN approximation are almost superimposed to the same quantities obtained with the full GRASIL. We conclude that this method appears robust and advantageous, and will present the application to a more complex SAM in another paper.
We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state is not equal to -1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.
A key goal of radio and $\gamma-$ray observations of active galactic nuclei is to characterize their time variability in order to elucidate physical processes responsible for the radiation. I describe algorithms for relevant time series analysis tools -- correlation functions, Fourier and wavelet amplitude and phase spectra, structure functions, and time-frequency distributions, all for arbitrary data modes and sampling schemes. For example radio measurements can be cross-analyzed with data streams consisting of time-tagged gamma-ray photons. Underlying these methods is the Bayesian block scheme, useful in its own right to characterize local structure in the light curves, and also prepare raw data for input to the other analysis algorithms. One goal of this presentation is to stimulate discussion of these methods during the workshop.
We show here how Renormalized Perturbation Theory (RPT) calculations applied to the quasi-linear growth of the large-scale structure can be carried on in presence of primordial non-Gaussian (PNG) initial conditions. It is explicitly demonstrated that the series reordering scheme proposed in Bernardeau, Crocce and Scoccimarro (2008) is preserved for non-Gaussian initial conditions. This scheme applies to the power spectrum and higher order spectra and is based on a reorganization of the contributing terms into sum of products of multi-point propagators. In case of PNG new contributing terms appear, the importance of which is discussed in the context of current PNG models. The properties of the building blocks of such resummation schemes, the multi-point propagators, are then investigated. It is first remarked that their expressions are left unchanged at one-loop order irrespectively of statistical properties of the initial field. We furthermore show that the high-momemtum limit of each of these propagators can be explicitly computed even for arbitrary initial conditions. They are found to be damped by an exponential cutoff whose expression is directly related to the moment generating function of the one-dimensional displacement field. This extends what had been established for multi-point propagators for Gaussian initial conditions. Numerical forms of the cut-off are shown for the so-called local model of PNG.
Determining the type of matter that is inside a neutron star (NS) has been a long-standing goal of astrophysics. Despite this, most of the NS equations of state (EOS) that predict maximum masses in the range 1.4-2.8 solar masses are still viable. Most of the precise NS mass measurements that have been made to date show values close to 1.4 solar masses, but a reliable measurement of an over-massive NS would constrain the EOS possibilities. Here, we investigate how optical astrometry at the microarcsecond level can be used to map out the orbits of High-Mass X-ray Binaries (HMXBs), leading to tight constraints on NS masses. While previous studies by Unwin and co-workers and Tomsick and co-workers discuss the fact that the future Space Interferometry Mission should be capable of making such measurements, the current work describes detailed simulations for 6 HMXB systems, including predicted constraints on all orbital parameters. We find that the direct NS masses can be measured to an accuracy of 2.5% (1-sigma) in the best case (X Per), to 6.5% for Vela X-1, and to 10% for two other HMXBs.
We present results of performance modelling for METIS, the Mid-infrared European Extremely Large Telescope (E-ELT) Imager and Spectrograph. Designed by a consortium of NOVA (Netherlands), UK Astronomy Technology Centre (UK), MPIA Heidelberg (Germany), CEA Saclay (France) and KU Leuven (Belgium), METIS will cover the atmospheric windows in L, M and N-band and will offer imaging, medium-resolution slit spectroscopy (R~1000-3000) and high-resolution integral field spectroscopy (R~100,000). Our model uses a detailed set of input parameters for site characteristics and atmospheric profiles, optical design, thermal background and the most up-to-date IR detector specifications. We show that METIS will bring an orders-of-magnitude level improvement in sensitivity and resolution over current ground-based IR facilities, bringing mid-IR sensitivities to the micro-Jansky regime. As the only proposed E-ELT instrument to cover this entire spectral region, and the only mid-IR high-resolution integral field unit planned on the ground or in space, METIS will open up a huge discovery space in IR astronomy in the next decade.
Small fractions of isocurvature perturbations correlated with the dominant adiabatic mode are shown to be a significant primordial systematic for future Baryon Acoustic Oscillation (BAO) surveys, distorting the standard ruler distance by broadening and shifting the peak in the galaxy correlation function. Untreated this systematic leads to biases that can exceed $10\sigma$ in the dark energy parameters even for Planck-level isocurvature constraints. Accounting for the isocurvature modes corrects for this bias but degrades the dark energy figure of merit by at least 50\%. The BAO data in turn provides extremely powerful new constraints on the nature of the primordial perturbations. Future large galaxy surveys will thus be powerful probes of the earliest phase of the universe in addition to helping pin down the nature of dark energy.
Galactic spiral shocks are dominant morphological features and believed to be responsible for substructure formation within spiral arms in disk galaxies. They can also contribute a substantial amount of kinetic energy to the interstellar gas by tapping the (differential) rotational motion. We use numerical hydrodynamic simulations to investigate dynamics and structure of spiral shocks with thermal instability in vertically stratified galactic disks, focusing on environmental conditions (of heating and the galactic potential) similar to the Solar neighborhood. We initially consider an isothermal disk in vertical hydrostatic equilibrium and let it evolve subject to interstellar cooling and heating as well as a stellar spiral potential. Due to thermal instability, a disk with surface density $\Sigma_0 \geq 6.7\Surf$ rapidly turns to a thin dense slab near the midplane sandwiched between layers of rarefied gas. The imposed spiral potential leads to a vertically curved shock that exhibits strong flapping motions in the plane perpendicular to the arm. The overall flow structure at saturation is comprised of arm, postshock expansion zone, and interarm regions that occupy typically 10\%, 20\%, and 70\% of the arm-to-arm distance, in which the gas resides for 15\%, 30\%, and 55\% of the arm-to-arm crossing time, respectively. The flows are characterized by transitions from rarefied to dense phases at the shock and from dense to rarefied phases in the postshock expansion zone, although gas with too-large postshock-density does not undergo this return phase transition, instead forming dense condensations. If self-gravity is omitted, the shock flapping drives random motions in the gas, but only up to $\sim 2-3 \kms$ in the in-plane direction and less than $2\kms$ in the vertical direction. Time-averaged shock profiles show... (abridged).
We investigate the dynamics of an Alfven surface (where the Alfven speed equals the advection velocity) in the context of core collapse supernovae during the phase of accretion on the proto-neutron star. Such a surface should exist even for weak magnetic fields because the advection velocity decreases to zero at the center of the collapsing core. In this decelerated flow, Alfven waves created by the standing accretion shock instability (SASI) or convection accumulate and amplify while approaching the Alfven surface. We study this amplification using one dimensional MHD simulations with explicit physical dissipation. In the linear regime, the amplification continues until the Alfven wavelength becomes as small as the dissipative scale. A pressure feedback that increases the pressure in the upstream flow is created via a non linear coupling. We derive analytic formulae for the maximum amplification and the non linear coupling and check them with numerical simulations to a very good accuracy. Interestingly, these quantities diverge if the dissipation is decreased to zero, scaling like the square root of the Reynolds number, suggesting large effects in weakly dissipative flows. We also characterize the non linear saturation of this amplification when compression effects become important, leading to either a change of the velocity gradient, or a steepening of the Alfven wave. Applying these results to core collapse supernovae shows that the amplification can be fast enough to affect the dynamics, if the magnetic field is strong enough for the Alfven surface to lie in the region of strong velocity gradient just above the neutrinosphere. An extrapolation of our analytic formula (taking into account the nonlinear saturation) suggests that the Alfven wave could reach an amplitude of B ~ 10^15 G, and that the pressure feedback could significantly contribute to the pressure below the shock.
The evolution of stars and planets is mostly controlled by the properties of their atmosphere. This is particularly true in the case of exoplanets close to their stars, for which one has to account both for an (often intense) irradiation flux, and from an intrinsic flux responsible for the progressive loss of the inner planetary heat. The goals of the present work are to help understanding the coupling between radiative transfer and advection in exoplanetary atmospheres and to provide constraints on the temperatures of the deep atmospheres. This is crucial in assessing whether modifying assumed opacity sources and/or heat transport may explain the inflated sizes of a significant number of giant exoplanets found so far. I use a simple analytical approach inspired by Eddington's approximation for stellar atmospheres to derive a relation between temperature and optical depth valid for plane-parallel static grey atmospheres which are both transporting an intrinsic heat flux and receiving an outer radiation flux. The model is parameterized as a function of mean visible and thermal opacities, respectively. The model is shown to reproduce relatively well temperature profiles obtained from more sophisticated radiative transfer calculations of exoplanetary atmospheres. It naturally explains why a temperature inversion (stratosphere) appears when the opacity in the optical becomes significant compared to that in the infrared. I further show that the mean equivalent flux (proportional to T^4) is conserved in the presence of horizontal advection on constant optical depth levels. This implies with these hypotheses that the deep atmospheric temperature used as outer boundary for the evolution models should be calculated from models pertaining to the entire planetary atmosphere, not from ones that are relevant to the day side or to the substellar point. In these conditions, present-day models yield deep temperatures that are ~1000K too cold to explain the present size of planet HD 209458b. An tenfold increase in the infrared to visible opacity ratio would be required to slow the planetary cooling and contraction sufficiently to explain its size. However, the mean equivalent flux is not conserved anymore in the presence of opacity variations, or in the case of non-radiative vertical transport of energy: The presence of clouds on the night side or a downward transport of kinetic energy and its dissipation at deep levels would help making the deep atmosphere hotter and may explain the inflated sizes of giant exoplanets.
Planet formation and migration in accretion discs is a very active topic. Among the many aspects related to that question, dead zones are of particular importance as they can influence both the formation and the migration of planetary embryos. The ionisation level in the disc is the key element in determining the existence and the location of the dead zone. This has been studied either within the Standard Accretion Disc (SAD) framework or using parametric discs. In this paper, we extend this study to the case of Jet Emitting Discs (JED), the structure of which strongly differ from SADs because of the new energy balance and angular momentum extraction imposed by the jets. We make use of the (r,z) density distributions provided by self-similar accretion-ejection models, along with the JED thermal structure derived in a previous paper, to create maps of the ionisation structure of JEDs. We compare the ionisation rates we obtain to the critical value required to trigger the magneto-rotational instability. It is found that JEDs have a much higher ionisation degree than SADs which renders very unlikely the presence of a dead zone in these discs. As JEDs are believed to occupy the inner regions of accretion discs, the extension of the dead zones published in the literature should be re-considered for systems in which a jet is present. Moreover, since JEDs require large scale magnetic fields close to equipartition, our findings raise again the question of magnetic field advection in circumstellar accretion discs.
The Galaxy Ultraviolet Explorer (GALEX) satellite has recently shown the presence of an extended, outer ring studded with UV-bright knots surrounding the lenticular galaxy NGC 4262. Such a structure---not detected in the optical---is coupled with a ring of atomic (HI) gas. We want to show that both star-forming and HI rings surrounding this SB0 galaxy share the same radial distance from the galaxy center and spatial orientation. We want also to model the kinematics of the ring(s) and of the galaxy body. We make use of archive FUV and NUV GALEX data plus HI observations from the literature. We confirm that the UV-bright and atomic gas rings of NGC 4262 have the same extent and projected spatial orientation. Their kinematics is not coupled with that of the galaxy stars. It is possible that NGC 4262 has undergone a major gas stripping event in the past which gave origin to the present "necklace" of UV-bright knots.
The disk masses of four low surface brightness galaxies (LSB) were estimated using marginal gravitational stability criterion and the stellar velocity dispersion data which were taken from Pizzella et al., 2008 [1]. The constructed mass models appear to be close to the models of maximal disk. The results show that the disks of LSB galaxies may be significantly more massive than it is usually accepted from their brightnesses. In this case their surface densities and masses appear to be rather typical for normal spirals. Otherwise, unlike the disks of many spiral galaxies, the LSB disks are dynamically overheated.
Using the exact Lemaitre-Bondi-Tolman solution with a non-vanishing cosmological constant $\Lambda$, we investigate how the presence of a local spherically-symmetric inhomogeneity can affect apparent cosmological observables, such as the deceleration parameter or the effective equation of state of dark energy (DE), derived from the luminosity distance under the assumption that the real space-time is exactly homogeneous and isotropic. The presence of a local underdensity is found to produce apparent phantom behavior of DE, while a locally overdense region leads to apparent quintessence behavior. Our study shows how observations in an inhomogeneous $\Lambda$CDM universe with initial conditions compatible with the inflationary beginning, if interpreted under the wrong assumption of homogeneity, can lead to the wrong conclusion about the presence of ``fake'' evolving dark energy instead of $\Lambda$.
We present hydrodynamic simulations of a major merger of disk galaxies, and study the ISM dynamics and star formation properties. High spatial and mass resolutions of 12pc and 4x10^4 M_sol allow to resolve cold and turbulent gas clouds embedded in a warmer diffuse phase. We compare to lower resolution models, where the multiphase ISM is not resolved and is modeled as a relatively homogeneous and stable medium. While merger-driven bursts of star formation are generally attributed to large-scale gas inflows towards the nuclear regions, we show that once a realistic ISM is resolved, the dominant process is actually gas fragmentation into massive and dense clouds and rapid star formation therein. As a consequence, star formation is more efficient by a factor of up to 10 and is also somewhat more extended, while the gas density probability distribution function (PDF) rapidly evolves towards very high densities. We thus propose that the actual mechanism of starburst triggering in galaxy collisions can only be captured at high spatial resolution and when the cooling of gas is modeled down to less than 10^3 K. Not only does our model reproduce the properties of the Antennae system, but it also explains the ``starburst mode'' revealed recently in high-redshift mergers compared to quiescent disks.
We investigate the potential of exploiting the Sunyaev-Zeldovich effect (SZE) to study the properties of hot gas in galaxy groups. It is shown that, with upcoming SZE surveys, one can stack SZE maps around galaxy groups of similar halo masses selected from large galaxy redshift surveys to study the hot gas in halos represented by galaxy groups. We use various models for the hot halo gas to study how the expected SZE signals are affected by gas fraction, equation of state, halo concentration, and cosmology. Comparing the model predictions with the sensitivities expected from the SPT, ACT and Planck surveys shows that a SPT-like survey can provide stringent constraints on the hot gas properties for halos with masses M ~> 10^{13} h^{-1}Msun. We also explore the idea of using the cross correlation between hot gas and galaxies of different luminosity to probe the hot gas in dark matter halos without identifying galaxy groups to represent dark halos. Our results show that, with a galaxy survey as large as the Sloan Digital Sky Survey and with the help of the conditional luminosity function (CLF) model, one can obtain stringent constraints on the hot gas properties in halos with masses down to 10^{13} h^{-1}Msun. Thus, the upcoming SZE surveys should provide a very promising avenue to probe the hot gas in relatively low-mass halos where the majority of L*-galaxies reside.
Primordial non-Gaussianity is a potentially powerful discriminant of the physical mechanisms that generated the cosmological fluctuations observed today. Any detection of significant non-Gaussianity would thus have profound implications for our understanding of cosmic structure formation. The large scale mass distribution in the Universe is a sensitive probe of the nature of initial conditions. Recent theoretical progress together with rapid developments in observational techniques will enable us to critically confront predictions of inflationary scenarios and set constraints as competitive as those from the Cosmic Microwave Background. In this paper, we review past and current efforts in the search for primordial non-Gaussianity in the large scale structure of the Universe.
We present two observational campaigns performed with the RXTE satellite on the black hole transient H 1743-322. The source was observed in outburst on two separate occasions between October-November 2008 and May-July 2009. We have carried out timing and spectral analysis of the data set, obtaining a complete state classification of all the observations. We find that all the observations are well described by using a spectral model consisting of a disk-blackbody, a powerlaw + reflection + absorption and a gaussian emission component. During the 2009 outburst the system followed the canonical evolution through all the states seen in black hole transients. In the 2008 outburst only the hard states were reached. The early evolution of the spectral parameters is consistent between the two epochs, and it does not provide clues about the subsequent behavior of the source. The variation of the flux associated to the two main spectral components (i.e. disk and powerlaw) allows us to set a lower limit to the orbital inclination of the system of >= 43{\deg}.
We are constructing the broadband SED catalog of the MOJAVE sample from the radio to the gamma-ray band using MOJAVE, Swift UVOT/XRT/BAT, and Fermi/LAT data, in order to understand the emission mechanism of extragalactic outflows and to investigate the site of high-energy emission in AGN. Since the launch of Fermi gamma-ray Space Telescope in August 2008, two thirds of the MOJAVE sources have been detected by Fermi/LAT. Combining the results of high-resolution VLBI, X-ray, and gamma-ray observations of the jet-dominated AGN sample, we want to pin down the origin of high-energy emission in relativistic jets. Here we present our overall project and preliminary results for 6 selected sources.
Disk galaxies at high redshift (z~2) are characterized by high fractions of cold gas, strong turbulence, and giant star-forming clumps. Major mergers should typically involve such galaxies. High-redshift merger simulations, however, have always modeled the ISM as stable, homogeneous, and thermally pressurized. We present the first high-redshift merger simulations with cold, turbulent, and clumpy gas, and we discuss the major new features of these models compared to models where the gas is artificially stabilized and warmed. Gas turbulence, which is already strong in high-redshift disks, is further enhanced in mergers. Some phases are dispersion-dominated, with most of the gas kinetic energy in the form of velocity dispersion and very chaotic velocity fields, unlike low-redshift mergers. High-redshift mergers are also characterized by highly dissipative gas collapse to the center of mass, with the stellar component following in a global contraction. The final galaxies are early-type with relatively small radii and high Sersic indices, like high-redshift compact spheroids. The mass fraction in a disk component that survives or re-forms after a merger is severely reduced compared to models with stabilized gas, which lends support to cold accretion as the main formation mechanism for massive disks at high redshift .
We present the results of hydrodynamic simulations of the growth and orbital evolution of giant planets embedded in a protoplanetary disk with a dead-zone. The aim is to examine to what extent the presence of a dead-zone affects the rates of mass accretion and migration for giant planets. We performed 3D numerical simulations using a grid-based hydrodynamics code. In these simulations of non-magnetised disks, the dead-zone is treated as a region where the vertical profile of the viscosity depends on the distance from the equatorial plane. We consider dead-zones with vertical sizes, H_dz, ranging from 0 to H_dz=2.3H, where H is the disk scale-height. For all models, the vertically integrated viscous stress, and the related mass flux through the disk, have the same value, such that the simulations test the dependence of planetary mass accretion and migration on the vertical distribution of the viscous stress. For each model, an embedded 30 earth-masses planet on a fixed circular orbit is allowed to accrete gas from the disk. Once the planet mass becomes equal to that of Saturn or Jupiter, we allow the planet orbit to evolve due to gravitational interaction with the disk. We find that the time scale over which a protoplanet grows to become a giant planet is essentially independent of the dead-zone size, and depends only on the total rate at which the disk viscously supplies material to the planet. For Saturn-mass planets, the migration rate depends only weakly on the size of the dead-zone for H_dz< 1.5H, but becomes slower when H_dz=2.3H. This effect is due to the desaturation of corotation torques which originate from residual material in the partial-gap region. For Jupiter-mass planets, there is a clear tendency for the migration to proceed more slowly as the size of the dead-zone increases.
The excitation of solar and solar-like g-modes in non-relativistic stars by arbitrary external gravitational wave fields is studied starting from the full field equations of general relativity. We develop a formalism that yields the mean-square amplitudes and surface velocities of global normal modes excited in such a way. The isotropic elastic sphere model of a star is adopted to demonstrate this formalism and for calculative simplicity. It is shown that gravitational waves solely couple to quadrupolar spheroidal eigenmodes and that normal modes are only sensitive to the spherical component of the gravitational waves having the same azimuthal order. The mean-square amplitudes in case of stationary external gravitational waves are given by a simple expression, a product of a factor depending on the resonant properties of the star and the power spectral density of the gravitational waves' spherical accelerations. Both mean-square amplitudes and surface velocities show a characteristic R^8-dependence (effective R^2-dependence) on the radius of the star. This finding increases the relevance of this excitation mechanism in case of stars larger than the Sun.
We analyzed the behavior of the rotational velocity in the parent stars of extrasolar planets. Projected rotational velocity v sin i and angular momentum were combined with stellar and planetary parameters, for a unique sample of 147 stars, amounting to 184 extrasolar planets, including 25 multiple systems. Indeed, for the present working sample we considered only stars with planets detected by the radial-velocity procedure. Our analysis shows that the v sin i distribution of stars with planets along the HR Diagram follows the well established scenario for the rotation of intermediate to low main sequence stars, with a sudden decline in rotation near 1.2 Msun. The decline occurs around Teff ~ 6000 K, corresponding to the late-F spectral region. A statistical comparison of the distribution of the rotation of stars with planets and a sample of stars without planets indicates that the v sin i distribution for these two families of stars is drawn from the same population distribution function. We also found that the angular momentum of extrasolar planet parent stars follows, at least qualitatively, Krafts relation J \alpha (M/Msun)^{\alpha}. The stars without detected planets show a clear trend of angular momentum deficit compared to the stars with planets, in particular for masses higher than about 1.25 Msun. Stars with the largest mass planets tend to have angular momentum comparable to or higher than the Sun.
We analyze interferometric measurements of the Luminous Blue Variable Eta Carinae with the goal of constraining the rotational velocity of the primary star and probing the influence of the companion. Using 2-D radiative transfer models of latitude-dependent stellar winds, we find that prolate wind models with a ratio of the rotational velocity (vrot) to the critical velocity (vcrit) of W=0.77-0.92, inclination angle of i=60-90 degrees, and position angle PA=108-142 degrees reproduce simultaneously K-band continuum visibilities from VLTI/VINCI and closure phase measurements from VLTI/AMBER. Interestingly, oblate models with W=0.73-0.90 and i=80-90 degrees produce similar fits to the interferometric data, but require PA=210-230 degrees. Therefore, both prolate and oblate models suggest that the rotation axis of the primary star is not aligned with the Homunculus polar axis. We also compute radiative transfer models of the primary star allowing for the presence of a cavity and dense wind-wind interaction region created by the companion star. We find that the wind-wind interaction has a significant effect on the K-band image mainly via free-free emission from the compressed walls and, for reasonable model parameters, can reproduce the VLTI/VINCI visibilities taken at phase 0.92-0.93. We conclude that the density structure of the primary wind can be sufficiently disturbed by the companion, thus mimicking the effects of fast rotation in the interferometric observables. Therefore, fast rotation may not be the only explanation for the interferometric observations. Intense temporal monitoring and 3-D modeling are needed to resolve these issues.
Context. Close binary supersoft X-ray sources (CBSS) are binary systems that contain a white dwarf with stable nuclear burning on its surface. These sources, first discovered in the Magellanic Clouds, have high accretion rates and near-Eddington luminosities (10^37 - 10^38 erg/s) with high temperatures (T = 2 - 7 x 10^5 K). Aims. The total number of known objects in the MC is still small and, in our galaxy, even smaller. We observed the field of the unidentified transient supersoft X-ray source RX J0527.8-6954 in order to identify its optical counterpart. Methods. The observation was made with the IFU-GMOS on the Gemini South telescope with the purpose of identifying stars with possible He II or Balmer emission or else of observing nebular extended jets or ionization cones, features that may be expected in CBSS. Results. The X-ray source is identified with a B5e V star that is associated with subarcsecond extended Halpha emission, possibly bipolar. Conclusions. If the primary star is a white dwarf, as suggested by the supersoft X-ray spectrum, the expected orbital period exceeds 21 h; therefore, we believe that the 9.4 h period found so far is not associated to this system.
RR Lyrae stars have been observed to improve the insight into the processes at work in their atmospheres. Simultaneous Stroemgren-photometry allows to obtain a rapid sequence of measurements in which photometric indices are unaffected by non-optimum observing conditions. The indices y, b-y, and c_1 are used with an established calibration to derive T_eff and to derive the gravity, log g_BJ from the Balmer jump, throughout the pulsation cycle. By employing the equations for stellar structure, additional parameters can be derived. Stroemgren photometry and its calibration in terms of T_eff and log g can be used to determine the run of R and the atmosphere pulsation velocity. We find that the Balmer-line strengths are correlated with T_eff and that the strength of the Ca_ii K line correlates well with the radius of the star and thus the pulsation-dependent density of the atmosphere. The density in the stellar atmosphere fluctuates as indicated by the changes in the gravity log g_BJ, derived from c_1, between 2.3 and 4.5 dex. Also the Stroemgren metal index, m_1, fluctuates. We find a disagreement between log g(T,L,M), the gravity calculated from T_eff, L, and the mass M,and the gravity log g_BJ. This can be used to reassess the mass and the absolute magnitude of an individual star.The curves derived for the pulsational velocity V_pul differ from curves obtained from spectra needed to apply the Baade-Wesselink method; we think these differences are due to phase dependent differences in the optical depth levels sampled in continuum photometry and in spectroscopy. We find an atmospheric oscillation in these fundamental mode RR Lyrae stars of periodicity P/7.
In this paper we present multiband optical polarimetric observations of the VHE blazar PKS 2155-304 made simultaneously with a H.E.S.S./Fermi high-energy campaign in 2008, when the source was found to be in a low state. The intense daily coverage of the dataset allowed us to study in detail the temporal evolution of the emission and we found that the particle acceleration timescales are decoupled from the changes in the polarimetric properties of the source. We present a model in which the optical polarimetric emission originates at the polarised mm-wave core and propose an explanation for the lack of correlation between the photometric and polarimetric fluxes. The optical emission is consistent with an inhomogeneous synchrotron source in which the large scale field is locally organised by a shock in which particle acceleration takes place. Finally, we use these optical polarimetric observations of PKS 2155-304 at a low state to propose an origin for the quiescent gamma-ray flux of the object, in an attempt to provide clues for the source of its recently established persistent TeV emission.
The High Energy Stereoscopic System (H.E.S.S.) is a southern hemisphere array of four Imaging Atmospheric Cherenkov Telescopes observing the sky in the very high energy gamma-ray range (E $>$ 100 GeV). VHE observations are an invaluable tool to study the acceleration and propagation of energetic particles in many astrophysical systems where relativistic outflows are the main drivers of the emission, such as AGNs and galactic binary systems. In this paper the main results of the H.E.S.S. observations of these objects will be reviewed, and the general picture that emerges from them will be presented. We will also comment on prospects for future investigations with H.E.S.S.-II.
(shortened) [...] Within the Fireshell model [...] a new family of disguised short bursts has been introduced: long bursts with a protracted low instantaneous luminosity due to a low density CircumBurst Medium (CBM). GRB 071227 presents, in the 15-150 keV energy band, a short duration (about 1.8s) spikelike emission followed by a very soft extended tail up to one hundred seconds after the trigger. It is a low luminous (E_{iso}=5.8x10^{50}) near GRB (z=0.383) and there is not an associated type Ib/c bright Supernova (SN). For these reasons GRB 071227 has been classified as a short burst not fulfilling the Amati relation holding for long burst. We check the classification of GRB 071227 within the fireshell model. In particular, we want to test if this burst is another example of disguised short burst, after GRB 970228 and GRB 060614 and, for this reason, it would indeed fulfill the Amati relation. MWe simulate GRB 071227 light curves in the Swift BAT 15-50 keV bandpass and in the XRT (0.3-10 keV) energy band within the fireshell model. We perform simulations of the tail in the 15-50 keV bandpass, as well as of the first part of the X-ray afterglow. This provides: E_{tot}^{e^\pm}= 5.04x10^{51} erg, B=2.0x10^{-4}, E_{P-GRB}/E_{aft} ~ 0.25 and <n_{cbm}> = 3.33 particles/cm^3. Such values are still well in the range of "long duration" GRBs. We interpret the observed energy of the first hard emission by identifying it with the P-GRB emission. The remaining long soft tail indeed fulfills the Amati relation. CONCLUSIONS: GRB 071227, classified in literature as a short burst, by the analysis made within the fireshell scenario results to be another example of disguised short bursts, after GRB 970228 and GRB 060614. A further confirmation of this result is that the soft tail of GRB 071227 fulfills the Amati relation.
We compare the model power spectrum, computed based on the perturbation theory (PT) of structure formation, with the power spectrum of luminous red galaxies (LRG) measured from the Sloan Digital Sky Survey Data Release 7 catalog, assuming a flat, cold dark matter-dominated cosmology. The model includes the effects of massive neutrinos, nonlinear matter clustering and nonlinear, scale-dependent galaxy bias in a self-consistent manner. Combining with the recent results from Wilkinson Microwave Background Anisotropy Probe (WMAP), we found that the PT model well matches the LRG power spectrum down to k=0.1 h/Mpc. We then derive a upper limit on the sum of neutrino masses, sigma(m_nu,tot) < 0.81 eV (95% C.L.), marginalized over other parameters including nonlinear bias parameters and dark energy equation of state parameter. The neutrino mass limit is improved by a factor of 1.85 compared to the limit from the WMAP5 alone.
This chapter reviews theoretical work on the stellar dynamics of galaxy disks. All the known collective global instabilities are identified, and their mechanisms described in terms of local wave mechanics. A detailed discussion of warps and other bending waves is also given. The structure of bars in galaxies, and their effect on galaxy evolution, is now reasonably well understood, but there is still no convincing explanation for their origin and frequency. Spiral patterns have long presented a special challenge, and ideas and recent developments are reviewed. Other topics include scattering of disk stars and the survival of thin disks.
We have used the Montage image mosaic engine to investigate the cost and performance of processing images on the Amazon EC2 cloud, and to inform the requirements that higher-level products impose on provenance management technologies. We will present a detailed comparison of the performance of Montage on the cloud and on the Abe high performance cluster at the National Center for Supercomputing Applications (NCSA). Because Montage generates many intermediate products, we have used it to understand the science requirements that higher-level products impose on provenance management technologies. We describe experiments with provenance management technologies such as the "Provenance Aware Service Oriented Architecture" (PASOA).
We analyze the occurrence frequency distributions of peak fluxes $P$, total fluxes $E$, and durations $T$ of solar flares over the last three solar cycles (during 1980-2010) from hard X-ray data of HXRBS/SMM, BATSE/CGRO, and RHESSI. From the synthesized data we find powerlaw slopes with mean values of $\alpha_P=1.75\pm0.05$ for the peak flux, $\alpha_E=1.61\pm0.04$ for the total flux, and $\alpha_T=2.08\pm0.10$ for flare durations. We find no evidence that these frequency distributions have significantly different slopes during the minima of the solar cycles, including the current anomalously extended solar minimum. The powerlaw distributions can be interpreted in terms of a nonlinear dissipative system in the state of self-organized criticality (SOC). The invariance of the powerlaw slopes during the solar cycles, despite of the nonstationarity of the flare rate by orders of magnitude, implies a universal behavior in the nonlinear growth evolution of magnetic instabilities in solar flares, independent of a slow or fast driving rate by the solar dynamo. We model the observed frequency distributions with a randomized exponential-growth process in a SOC state.
We perform a full perturbative stability analysis of the 6D cascading gravity model in the presence of 3-brane tension. We demonstrate that for sufficiently large tension on the (flat) 3-brane, there are no ghosts at the perturbative level, consistent with results that had previously only been obtained in a specific 5D decoupling limit. These results establish the cascading gravity framework as a consistent infrared modification of gravity.
Assuming that supernovae type Ia (SNe Ia) are standard candles one could use them to test cosmological theories. The Hubble Space Telescope team analyzed 186 SNe Ia\cite{Riess_04} to test the Standard Cosmological model (SC) associated with expanded lengths in the Universe and evaluate its parameters. We use the same sample to determine parameters of Conformal Cosmological model (CC) with relative reference units of intervals, so that conformal quantities of General Relativity are interpreted as observables. We concluded, that really the test is extremely useful and allows to evaluate parameters of the model. From a formal statistical point of view the best fit of the CC model is almost the same quality approximation as the best fit of SC model with $\Omega_\Lambda=0.72, \Omega_m=0.28$. As it was noted earlier, for CC models, a rigid matter component could substitute the $\Lambda$-term (or quintessence) existing in the SC model. We note that a free massless scalar field can generate such a rigid matter. We describe results of our analysis for more recent "gold" data (for 192 SNe Ia).
Assuming the lightest neutralino solely composes the cosmic dark matter, we examine the constraints of the CDMS II and XENON100 dark matter direct searches on the parameter space of the MSSM Higgs sector. We find that the current CDMS II and XENON100 limits can exclude some of the parameter space which survive the constraints from the dark matter relic density and various collider experiments. We also find that in the currently allowed parameter space, it is almost unlikely to discover any non-SM Higgs bosons (H^+-, H, A) at the LHC for an integrated luminosity of 30 fb^{-1}. The future XENON100 (6000 kg-days exposure) will further tighten the parameter space in case of nonobservation of dark matter, pushing the parameter space further below the LHC sensitivity for discovering the non-SM Higgs bosons. So, if the MSSM is the true story, the current constraints already prefer a lone SM-like Higgs boson (h) at the LHC and the future XENON100 limits (in case of nonobservation) will further strengthen this conclusion.
We consider the presence and evolution of primordial density perturbations in a cosmological model based on a simple ansatz which captures -- by providing a set of effective gravitational field equations -- the strength of the enhanced quantum loop effects that can arise during inflation. After deriving the general equations that perturbations obey, we concentrate on scalar perturbations and show that their evolution is quite different than that of conventional inflationary models but still phenomenologically acceptable. The main reason for this novel evolution is the presence of an oscillating regime after the end of inflation which makes all super-horizon scalar modes oscillate. The same reason allows for a natural and very fast reheating mechanism for the universe.
Evidence for an anomalous annual periodicity in certain nuclear decay data has led to speculation concerning a possible solar influence on nuclear processes. As a test of this hypothesis, we here search for evidence in decay data that might be indicative of a process involving solar rotation, focusing on data for 32Si and 36Cl decay rates acquired at the Brookhaven National Laboratory. Examination of the power spectrum over a range of frequencies (10 - 15 year^-1) appropriate for solar synodic rotation rates reveals several periodicities, the most prominent being one at 11.18 year^-1 with power 20.76. We evaluate the significance of this peak in terms of the false-alarm probability, by means of the shuffle test, and also by means of a new test (the "shake" test) that involves small random time displacements. The last two tests indicate that the peak at 11.18 year^-1 would arise by chance only once out of about 10^7 trials. Since there are several peaks in the search band, we also investigate the running mean of the power spectrum, and identify a major peak at 11.93 year^-1 with peak running-mean power 4.08. Application of the shuffle test and the shake test indicates that there is less than one chance in 10^11, and one chance in 10^15, respectively, finding by chance a value as large as 4.08.
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