The formation of disk galaxies is one of the most outstanding problems in modern astrophysics and cosmology. We review the progress made by numerical simulations carried out on large parallel supercomputers. Recent progress stems from a combination of increased resolution and improved treatment of the astrophysical processes modeled in the simulations, such as the phenomenological description of the interstellar medium and of the process of star formation. High mass and spatial resolution is a necessary condition in order to obtain large disks comparable with observed spiral galaxies avoiding spurious dissipation of angular momentum. A realistic model of the star formation history. gas-to-stars ratio and the morphology of the stellar and gaseous component is instead controlled by the phenomenological description of the non-gravitational energy budget in the galaxy. We show that simulations of gas collapse within cold dark matter halos including a phenomenological description of supernovae blast-waves allow to obtain stellar disks with nearly exponential surface density profiles as those observed in real disk galaxies, counteracting the tendency of gas collapsing in such halos to form cuspy baryonic profiles. However, the ab-initio formation of a realistic rotationally supported disk galaxy with a pure exponential disk in a fully cosmological simulation is still an open problem. We argue that the suppression of bulge formation is related to the physics of galaxy formation during the merger of the most massive protogalactic lumps at high redshift, where the reionization of the Universe likely plays a key role. A sufficiently high resolution during this early phase of galaxy formation is also crucial to avoid artificial angular momentum loss (Abridged).
We describe the design and implementation of an autonomous adaptive software agent that addresses the practical problem of observing undersampled, periodic, time-varying phenomena using a network of HTN-compliant robotic telescopes. The algorithm governing the behaviour of the agent uses an optimal geometric sampling technique to cover the period range of interest, but additionally implements proactive behaviour that maximises the optimality of the dataset in the face of an uncertain and changing operating environment.
We study the degeneracies between dark energy dynamics, dark matter and curvature using a non-parametric and non-perturbative approach. This allows us to examine the knock-on bias induced in the reconstructed dark energy equation of state, w(z), when there is a bias in the cosmic curvature or dark matter content, without relying on any specific parameterisation of w. Even assuming perfect Hubble, distance and volume measurements, we show that for z > 1, the bias in w(z) is up to two orders of magnitude larger than the corresponding errors in Omega_k or Omega_m. This highlights the importance of obtaining unbiased estimators of all cosmic parameters in the hunt for dark energy dynamics.
I review recent progresses in the dynamics and the evolution of self-gravitating accretion discs. Accretion discs are a fundamental component of several astrophysical systems on very diverse scales, and can be found around supermassive black holes in Active Galactic Nuclei (AGN), and also in our Galaxy around stellar mass compact objects and around young stars. Notwithstanding the specific differences arising from such diversity in physical extent, all these systems share a common feature where a central object is fed from the accretion disc, due to the effect of turbulence and disc instabilities, which are able to remove the angular momentum from the gas and allow its accretion. In recent years, it has become increasingly apparent that the gravitational field produced by the disc itself (the disc's self-gravity) is an important ingredient in the models, especially in the context of protostellar discs and of AGN discs. Indeed, it appears that in many cases (and especially in the colder outer parts of the disc) the development of gravitational instabilities can be one of the main agents in the redistribution of angular momentum. In some cases, the instability can be strong enough to lead to the formation of gravitationally bound clumps within the disc, and thus to determine the disc fragmentation. As a result, progress in our understanding of the dynamics of self-gravitating discs is essential to understand the processes that lead to the feeding of both young stars and of supermassive black holes in AGN. At the same time, understanding the fragmentation conditions is important to determine under which conditions AGN discs would fragment and form stars and whether protostellar discs might form giant gaseous planets through disc fragmentation.
Recent work has suggested that the fraction of obscured AGN declines with increasing luminosity, but it has been difficult to quantify this trend. Here, we attempt to measure this fraction as a function of luminosity by studying the ratio of mid-infrared to intrinsic nuclear bolometric luminosity in unobscured AGN. Because the mid-infrared is created by dust reprocessing of shorter wavelength nuclear light, this ratio is a diagnostic of f_obsc, the fraction of solid angle around the nucleus covered by obscuring matter. In order to eliminate possible redshift-dependences while also achieving a large dynamic range in luminosity, we have collected archival 24 micron MIPS photometry from objects with z~1 in the Sloan Digital Sky Survey (SDSS), the Great Observatories Origins Deep Survey (GOODS) and the Cosmic Evolution Survey (COSMOS). To measure the bolometric luminosity for each object, we used archival optical data supplemented by GALEX data. We find that the mean ratio of 24 microns to bolometric luminosity decreases by a factor of ~3 in the L_bol=10^44-3x10^47 ergs s^-1 range, but there is also a large scatter at constant L_bol. Using radiation transfer solutions for model geometries, we show how the IR/bolometric ratio relates to f_obsc and compare these values with those obtained obtained from samples of X-ray selected AGN. Although we find approximate agreement, our method indicates somewhat higher values of f_obsc, particularly in the middle range of luminosities, suggesting that there may be a significant number of heavily obscured AGN missed by X-ray surveys.
We present photometry and spectroscopy of the suspected cataclysmic variable (CV) Lanning 386. We confirm that it is a CV, and observe deep eclipses, from which we determine the orbital period Porb to be 0.1640517 +- 0.0000001 d (= 3.94 h). Photometric monitoring over two observing seasons shows a very active system with frequent outbursts of variable amplitude, up to approx. 2 mag. The spectrum in quiescence is typical of dwarf novae, but in its high state the system shows strong HeII emission and a broad CIV Wolf-Rayet feature. This is unusual for dwarf novae in outburst and indicates a high excitation. In its high state the system shows some features reminiscent of an SW Sextantis-type CV, but lacks others. We discuss the classification of this puzzling object.
We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum of the single G-type giant HR 9024 during a large flare. In analogy to solar X-ray observations, we interpret the observed Fe K$\alpha$ line as being produced by illumination of the photosphere by ionizing coronal X-rays, in which case, for a given Fe photospheric abundance, its intensity depends on the height of the X-ray source. The HETGS observations, together with 3D Monte Carlo calculations to model the fluorescence emission, are used to obtain a direct geometric constraint on the scale height of the flaring coronal plasma. We compute the Fe fluorescent emission induced by the emission of a single flaring coronal loop which well reproduces the observed X-ray temporal and spectral properties according to a detailed hydrodynamic modeling. The predicted Fe fluorescent emission is in good agreement with the observed value within observational uncertainties, pointing to a scale height $\lesssim 0.3$\rstar. Comparison of the HR 9024 flare with that recently observed on II Peg by Swift indicates the latter is consistent with excitation by X-ray photoionization.
Supergiant Fast X-ray Transients are obviously related to persistent Supergiant X-ray Binaries. Any convincing explanation for their behaviour must consistently take into account all types of X-ray sources powered by wind accretion. Here we present a common framework for wind accreting sources, within the context of clumpy wind models, that allows a coherent interpretation of their different behaviours as an immediate consequence of diverse orbital geometries.
We calculate the advances in near-infrared astronomy made possible through
the use of fibre Bragg gratings to selectively remove hydroxyl emission lines
from the night sky spectrum. Fibre Bragg gratings should remove OH lines at
high resolution (R=10,000), with high suppression (30dB) whilst maintaining
high throughput (~90 per cent) between the lines. Devices currently under
construction should remove 150 lines in each of the J and H bands, effectively
making the night sky surface brightness ~4 magnitudes fainter. This background
reduction is greater than the improvement adapative optics makes over natural
seeing; photonic OH suppression is at least as important as adaptive optics for
the future of cosmology.
We present a model of the NIR sky spectrum, and show that the interline
continuum is very faint (~80 ph/s/m^s/arcsec/micron on the ecliptic plane). We
show that OH suppression by high dispersion, i.e. `resolving out' the skylines,
cannot obtain the required level of sensitivity to reach the interline
continuum due to scattering of light. The OH lines must be suppressed prior to
dispersion.
We have simulated observations employing fibre Bragg gratings of first light
objects, high redshift galaxies and cool, low-mass stars. The simulations are
of complete end-to-end systems from object to detector. The results demonstrate
that fibre Bragg grating OH suppression will significantly advance our
knowledge in many areas of astrophysics, and in particular will enable
rest-frame ultra-violet observations of the Universe at the time of first light
and reionisation.
This report is based on a rapporteur talk presented at the 30th International Cosmic Ray Conference held in Merida, Mexico (July 2007), and covers three of the OG sessions devoted to neutrino, gravitational wave, and gamma-ray detection.
We derive an analytic model for the redshift evolution of linear-bias, allowing for interactions and merging of the mass-tracers, by solving a second order differential equation based on linear perturbation theory and the Friedmann-Lemaitre solutions of the cosmological field equations. We then study the halo-mass dependence of the bias evolution, using the dark matter halo distribution in a $\Lambda$CDM simulation in order to calibrate the free parameters of the model. Finally, we compare our theoretical predictions with available observational data and find a good agreement. In particular, we find that the bias of optical QSO's evolve differently than those selected in X-rays and that their corresponding typical dark matter halo mass is $\sim 10^{13} h^{-1} M_{\odot}$ and $\magcir 5 \times 10^{13} h^{-1} M_{\odot}$, respectively.
This paper presents the sixth part to the Very Long Baseline Array (VLBA) Calibrator Survey. It contains the positions and maps of 264 sources of which 169 were not previously observed with very long baseline interferometry (VLBI). This survey, based on two 24 hour VLBA observing sessions, was focused on 1) improving positions of 95 sources from previous VLBA Calibrator surveys that were observed either with very large a priori position errors or were observed not long enough to get reliable positions and 2) observing the remaining new flat-spectrum sources with predicted correlated flux density in the range 100-200 mJy that were not observed in previous surveys. Source positions were derived from astrometric analysis of group delays determined at the 2.3 and 8.6 GHz frequency bands using the Calc/Solve software package. The VCS6 catalogue of source positions, plots of correlated flux density versus projected baseline length, contour plots and fits files of naturally weighted CLEAN images, as well as calibrated visibility function files are available on the Web at this http URL
The Be/X-ray binary 1A 0535+262 was discovered in 1975 during a giant outburst. Afterwards it has shown periods of quiescence (flux below 10 mCrab), normal outbursts (10 mCrab-1Crab) and occasionally giant outbursts (several Crab). Ending 11 years of quiescence, the last giant outburst took place in May/June 2005, but the source was too close to the Sun to be observed by most satellites. A subsequent normal outburst took place in August 2005, which was observed by INTEGRAL and RXTE TOO observations. Based on INTEGRAL data, we present results on the long term pulse period history of the source, on their energy dependent pulse profiles and on phase resolved spectra.
We analyze the H-alpha spectral variability of the rapidly-rotating K1-dwarf LQ Hya using high-resolution H-alpha spectra recorded during April-May 2000. Chromospheric parameters were computed from the H-alpha profile as a function of rotational phase. We find that all these parameters vary in phase, with a higher chromospheric electron density coinciding with the maximum H-alpha emission. We find a clear rotational modulation of the H-alpha emission that is better emphasized by subtracting a reference photospheric template built up with a spectrum of a non-active star of the same spectral type. A geometrical plage model applied to the H-alpha variation curve allows us to derive the location of the active regions that come out to be close in longitude to the most pronounced photospheric spots found with Doppler imaging applied to the photospheric lines in the same spectra. Our analysis suggests that the H-alpha features observed in LQ Hya in 2000 are a scaled-up version of the solar plages as regards dimensions and/or flux contrast. No clear indication of chromospheric mass motions emerges.
We have studied a sample of 415 associated (z_ab z_em; relative velocity with respect to QSO <3000km/s) Mg II absorption systems with 1.0<=z_ab<=1.86, in the spectra of SDSS DR3 QSOs, to determine the dust content and ionization state in the absorbers. We studied the dependence of these properties on the properties of the QSOs and also, compared the properties with those of a similarly selected sample of 809 intervening systems (apparent relative velocity with respect to the QSO of >3000km/s), so as to understand their origin. From the analysis of the composite spectra, as well as from the comparison of measured equivalent widths in individual spectra, we conclude that the associated Mg II absorbers have higher apparent ionization, measured by the strength of the C IV absorption lines compared to the Mg II absorption lines, than the intervening absorbers. The ionization so measured appears to be related to apparent ejection velocity, being lower as the apparent ejection velocity is more and more positive. There is clear evidence, from the composite spectra, for SMC like dust attenuation in these systems; the 2175AA absorption feature is not present. The extinction is almost twice that observed in the similarly selected sample of intervening systems. We reconfirm that QSOs with non-zero FIRST radio flux are intrinsically redder than the QSOs with no detection in the FIRST survey. The incidence of associated Mg II systems in QSOs with non-zero FIRST radio flux is 1.7 times that in the QSOs with no detection in the FIRST survey. The associated absorbers in radio-detected QSOs which comprise about 12% of our sample, cause 3 times more reddening than the associated absorbers in radio-undetected QSOs. This excess reddening possibly suggests an intrinsic nature for the associated absorbers in radio-detected QSOs.
We present a comparison of the properties of a giant radio galaxy and the ambient intergalactic medium, whose properties are inferred from the large-scale distribution in galaxies. The double lobes of the radio galaxy MSH 05-22 are giant--1.8 Mpc projected linear size--and interacting with the environment outside the interstellar medium and coronal halo associated with the host galaxy. The radio lobes appear to be relicts and the double structure is asymmetric. We have examined the large-scale structure in the galaxy distribution surrounding the radio source. The host galaxy of MSH 05-22 is associated with a small group that lies close to the boundary of sheet-like and filamentary density enhancements, and adjacent to a void. Assuming that the galaxies trace gas, the asymmetries in the radio morphology in this case study appear related to the anisotropy in the medium. However, the observed overdensities and structure formation models for the heating of the intergalactic medium (IGM) suggest a density-temperature product for the IGM environment that is an order of magnitude below that expected from the properties of the radio source. The discordance suggests that even sources like MSH 05-22, which are observed in the relatively low-density IGM environment associated with the filamentary large-scale structure and have multiple signatures of being relicts, may be overpressured and evolving towards an equilibrium relaxed state with the ambient IGM. Alternately, it is speculated that astrophysical feedback originating in galaxy overdensities observed 1-2 Mpc to the N and NE of MSH 05-22 might be the mechanism for the heating of the ambient IGM gas.
In this paper we present the first results of a detailed spectroscopic and photometric analysis of the V = 11.7m eclipsing binary ASAS J052821+0338.5. With the FIES spectrograph at the Nordic Optical Telescope we have obtained a series of high-resolution spectra (R=47000) covering the entire orbit of the system. In addition we obtained simultaneous broadband photometry from three small aperture telescopes. From these spectroscopic and photometric data we have derived the system's orbital parameters and determined the fundamental stellar parameters of the two components. Our results indicate that ASAS J052821+0338.5 is a K1/K3 pre-main-sequence eclipsing binary, with component masses of 1.38 M_sun and 1.33 M_sun and a period of 3.87 days, located at a distance of 280 +/- 30 pc. The kinematics, physical location and the evolutionary status of the two stars suggest that ASAS J052821+0338.5 is a member of the approximately 11 Myr old Orion OB1a subassociation. The systems also exhibits smooth 0.15m out-of-eclipse variations that are similar to those found in RS CVn binaries. Furthermore the parameters we derived are consistent with the 10-13 Myr isochrones of the popular Baraffe stellar evolutionary models.
By using most of the present CMB and LSS measurements and the BBN constraints on the primordial helium abundance, Y_p, we set bounds on the radiation content of the Universe and neutrino properties. We consider lepton asymmetric cosmological models parametrized by the neutrino degeneracy parameter \xi_{\nu} and the variation of the relativistic degrees of freedom, \Delta N_{oth}^{eff}, due to possible other physical processes that occurred between BBN and structure formation epoch. We found that present CMB and LSS data constraints the neutrino degeneracy parameter at \xi_{\nu} \leq 0.722, implying a lepton asymmetry of the neutrino background {\cal L}_{\nu} \leq 0.614 (2-\sigma). We also found \Delta N^{eff}_{oth}=0.572^{+1.972}_{-1.780}, the contribution to the effective number of relativistic neutrino species N^{eff}=3.058^{+1.971}_{-1.178} and a primordial helium abundance Y_p=0.249^{+0.014}_{-0.016} (2-\sigma errors). These results bring an important improvement over the similar ones obtained by using WMAP~1-year and older LSS data or the WMAP~3-year data alone and the standard primordial helium abundance value Y_p=0.24, relaxing the stringent BBN constraint on the neutrino degeneracy parameter (\xi_{\nu} \leq 0.07). We forecast that the CMB temperature and polarization maps observed with high angular resolutions and sensitivity by the future Planck Mission will constraint the primordial primordial helium abundance at Y_p=0.247 \pm 0.002 (2-\sigma errors) in agreement with the most stringent limits on Y_p given by the BBN and the neutrino degeneracy parameter at \xi_{\nu} \leq 0.280 (2-\sigma), not excluding the possibility of larger lepton asymmetry. This work has been done on behalf of Planck-LFI activities.
We study the dynamics of 2D and 3D barred galaxy analytical models, focusing on the distinction between regular and chaotic orbits with the help of the Smaller ALigment Index (SALI), a very powerful tool for this kind of problems. We present briefly the method and we calculate the fraction of chaotic and regular orbits in several cases. In the 2D model, taking initial conditions on a Poincar\'{e} $(y,p_y)$ surface of section, we determine the fraction of regular and chaotic orbits. In the 3D model, choosing initial conditions on a cartesian grid in a region of the $(x, z, p_y)$ space, which in coordinate space covers the inner disc, we find how the fraction of regular orbits changes as a function of the Jacobi constant. Finally, we outline that regions near the $(x,y)$ plane are populated mainly by regular orbits. The same is true for regions that lie either near to the galactic center, or at larger relatively distances from it.
The dynamical mass of a star cluster can be derived from the virial theorem, using the measured half-mass radius and line-of-sight velocity dispersion of the cluster. However, this dynamical mass may be a significant overestimation of the cluster mass if the contribution of the binary orbital motion is not taken into account. In these proceedings we describe the mass overestimation as a function of cluster properties and binary population properties, and briefly touch the issue of selection effects. We find that for clusters with a measured velocity dispersion of sigma > 10 km/s the presence of binaries does not affect the dynamical mass significantly. For clusters with sigma < 1 km/s (i.e., low-density clusters), the contribution of binaries to sigma is significant, and may result in a major dynamical mass overestimation. The presence of binaries may introduce a downward shift of Delta log(L/Mdyn) = 0.05-0.4 in the log(L/Mdyn) vs. age diagram.
In 1981, a faint radio source (G') was detected near the center of the lensing galaxy of the famous "twin quasar" Q0957+561. It is still unknown whether this central radio source is a third quasar image or an active nucleus of the lensing galaxy, or a combination of both. In an attempt to resolve this ambiguity, we observed Q0957+561 at radio wavelengths of 13cm, 18cm, and 21cm, using the Very Long Baseline Array in combination with the phased Very Large Array and the Green Bank Telescope. We measured the spectrum of G' for the first time and found it to be significantly different from the spectra of the two bright quasar images. This finding suggests that the central component is primarily or entirely emission from the foreground lens galaxy, but the spectrum is also consistent with the hypothesis of a central quasar image suffering free-free absorption. In addition, we confirm the previously-reported VLBI position of G' just north of the optical center of the lens galaxy. The position slightly favors the hypothesis that G' originates in the lens, but is not conclusive. We discuss the prospects for further clarification of this issue.
We demonstrate the ability to measure precise stellar barycentric radial velocities with the dispersed fixed-delay interferometer technique using the Exoplanet Tracker (ET), an instrument primarily designed for precision differential Doppler velocity measurements using this technique. Our barycentric radial velocities, derived from observations taken at the KPNO 2.1 meter telescope, differ from those of Nidever et al. by 0.047 km/s (rms) when simultaneous iodine calibration is used, and by 0.120 km/s (rms) without simultaneous iodine calibration. Our results effectively show that a Michelson interferometer coupled to a spectrograph allows precise measurements of barycentric radial velocities even at a modest spectral resolution of R ~ 5100. A multi-object version of the ET instrument capable of observing ~500 stars per night is being used at the Sloan 2.5 m telescope at Apache Point Observatory for the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS), a wide-field radial velocity survey for extrasolar planets around TYCHO-2 stars in the magnitude range 7.6<V<12. In addition to precise differential velocities, this survey will also yield precise barycentric radial velocities for many thousands of stars using the data analysis techniques reported here. Such a large kinematic survey at high velocity precision will be useful in identifying the signature of accretion events in the Milky Way and understanding local stellar kinematics in addition to discovering exoplanets, brown dwarfs and spectroscopic binaries.
We present some results obtained from the synthesis of Stokes profiles in small-scale flux tubes with propagating MHD waves. To that aim, realistic flux tubes showing internal structure have been excited with 5 min period drivers, allowing non-linear waves to propagate inside the magnetic structure. The observational signatures of these waves in Stokes profiles of several spectral lines that are commonly used in spectropolarimetric measurements are discussed.
We describe Monte Carlo models for the dynamical evolution of the nearby globular cluster M4. The code includes treatments of two-body relaxation, three- and four-body interactions involving primordial binaries and those formed dynamically, the Galactic tide, and the internal evolution of both single and binary stars. We arrive at a set of initial parameters for the cluster which, after 12Gyr of evolution, gives a model with a satisfactory match to the surface brightness profile, the velocity dispersion profile, and the luminosity function in two fields. We describe in particular the evolution of the core, and find that M4 (which has a classic King profile) is actually a post-collapse cluster, its core radius being sustained by binary burning. We also consider the distribution of its binaries, including those which would be observed as photometric binaries and as radial-velocity binaries. We also consider the populations of white dwarfs, neutron stars, black holes and blue stragglers, though not all channels for blue straggler formation are represented yet in our simulations.
Spectroscopic observations of three lenticular (S0) galaxies (NGC 1167, NGC 4150, and NGC 6340) and one SBa galaxy (NGC 2273) have been taken with the 6-m telescope of the Special AstrophysicalObservatory of the Russian Academy of Sciences aimed to study the structure and kinematic properties of early-type disk galaxies. The radial profiles of the stellar radial velocities and the velocity dispersion are measured. N-body simulations are used to construct dynamical models of galaxies containing a stellar disk, bulge, and halo. The masses of individual components are estimated formaximum-mass disk models. A comparison of models with estimated rotational velocities and the stellar velocity dispersion suggests that the stellar disks in lenticular galaxies are "overheated"; i.e., there is a significant excess velocity dispersion over the minimum level required to maintain the stability of the disk. This supports the hypothesis that the stellar disks of S0 galaxies were subject to strong gravitational perturbations. The relative thickness of the stellar disks in the S0 galaxies considered substantially exceed the typical disk thickness of spiral galaxies.
V5116 Sgr (Nova Sgr 2005 No. 2), discovered on 2005 July 4, was observed with XMM-Newton in March 2007, 20 months after the optical outburst. The X-ray spectrum shows that the nova had evolved to a pure supersoft X-ray source, with no significant emission at energies above 1 keV. The X-ray light-curve shows abrupt decreases and increases of the flux by a factor ~8. It is consistent with a periodicity of 2.97 h, the orbital period suggested by Dobrotka et al. (2007), although the observation lasted just a little more than a whole period. We estimate the distance to V5116 Sgr to be 11+/-3 kpc. A simple blackbody model does not fit correctly the EPIC spectra, with reduced chi^2>4. In contrast, ONe rich white dwarf atmosphere models provide a good fit, with nH=1.3(+/-0.1)e21 cm^-2, T=6.1(+/-0.1)e5 K, and L=3.9(+/-0.8)e37(D/10kpc)^2 erg/s (during the high-flux periods). This is consistent with residual hydrogen burning in the white dwarf envelope. The white dwarf atmosphere temperature is the same both in the low and the high flux periods, ruling out an intrinsic variation of the X-ray source as the origin of the flux changes. We speculate that the X-ray light-curve may result from a partial coverage by an asymmetric accretion disk in a high inclination system.
Observations in polarized emission reveal the existence of large-scale coherent magnetic fields in a wide range of spiral galaxies. Radio-polarization data show that these fields are strongly inclined towards the radial direction, with pitch angles up to $35\degr$ and thus cannot be explained by differential rotation alone. Global dynamo models describe the generation of the radial magnetic field from the underlying turbulence via the so called $\alpha$-effect. However, these global models still rely on crude assumptions about the small-scale turbulence. To overcome these restrictions we perform fully dynamical MHD simulations of interstellar turbulence driven by supernova explosions. From our simulations we extract profiles of the contributing diagonal elements of the dynamo $\alpha$-tensor as functions of galactic height. We also measure the coefficients describing vertical pumping and find that the ratio $\hat{\gamma}$ between these two effects has been overestimated in earlier analytical work, where dynamo action seemed impossible. In contradiction to these models based on isolated remnants we always find the pumping to be directed inward. In addition we observe that $\hat{\gamma}$ depends on whether clustering in terms of super-bubbles is taken into account. Finally, we apply a test field method to derive a quantitative measure of the turbulent magnetic diffusivity which we determine to be ~ 2 kpc km/s.
I summarize the highlights of the conference. First I provide a brief history of the beach symposia series our massive star community has been organizing. Then I use most of my allocated space discussing what I believe are the main answered and open questions in the field. Finally I conclude with a perspective of the future of massive star research.
We present multi-waveband optical imaging data obtained from observations of the Subaru/XMM-Newton Deep Survey (SXDS). The survey field, centered at R.A.=02:18:00, decl.=-05:00:00, has been the focus of a wide range of multi-wavelength observing programs spanning from X-ray to radio wavelengths. A large part of the optical imaging observations are carried out with Suprime-Cam on Subaru Telescope at Mauna Kea in the course of Subaru Telescope Observatory Projects. This paper describes our optical observations, data reduction and analysis procedures employed, and the characteristics of the data products. A total area of 1.22 sqdeg is covered in five contiguous sub-fields, each of which corresponds to a single Suprime-Cam field of view (34'x27'), in five broad-band filters B, V, Rc, i', z' to the depths of B=28.4, V=27.8, Rc=27.7, i'=27.7 and z'=26.6 (AB, 3-sigma, 2-arcsec aperture). The data are reduced and compiled into five multi-waveband photometric catalogs, separately for each Suprime-Cam pointing. The i'-band catalogs contain about 900,000 objects, making the SXDS catalogs one of the largest multi-waveband catalogs in corresponding depth and area coverage. The SXDS catalogs can be used for an extensive range of astronomical applications such as the number density of the Galactic halo stars to the large scale structures at the distant universe. The number counts of galaxies are derived and compared with those of existing deep extragalactic surveys. The optical data, the source catalogs, and configuration files used to create the catalogs are publicly available via the SXDS web page (this http URL)
An evaporating black hole in the presence of an extra spatial dimension would undergo an explosive phase of evaporation. We show that such an event, involving a primordial black hole, can produce a detectable electromagnetic pulse, signaling the existence of an extra dimension of size $L\sim10^{-18}-10^{-20}$~m. We derive a generic relationship between the Lorentz factor of a pulse-producing "fireball" and the TeV energy scale. For a toroidally compactified extra dimension, transient radio-pulse searches probe the electroweak energy scale ($\sim$0.1 TeV), enabling comparison with the Large Hadron Collider. The enormous challenges of detecting quantum gravitational effects, and exploring electroweak-scale physics, make this a particularly attractive possibility.
The role of the isoscalar hyperon Lambda in probing the density dependence of the nuclear symmetry energy is studied in multi-Lambda hypernuclei, hyperon-rich matter and neutron stars in relativistic models. Relationships between the properties of three types of objects and the neutron thickness in 208Pb are established with respect to the isoscalar-isovector coupling that modifies the density dependence of the symmetry energy. The exotic isotopes far from the neutron drip line can be stabilized by filling in considerable Lambda hyperons. The difference of the binding energy of multi-Lambda hypernuclei from different models is attributed to different symmetry energies. The isovector potential together with the neutron thickness in multi-Lambda hypernuclei investigated is very sensitive to the isoscalar-isovector coupling. The large sensitivity of the Lambda hyperon fraction to the isoscalar-isovector coupling occurs at about 2-3 rho_0 in beta equilibrated hyperon-rich matter. In neutron stars with hyperonization, an on-off effect with respect to the isoscalar-isovector coupling exists for the neutron star radius.
Models with varying cosmical parameters, which were earlier regarded constant, are getting attention. However, different models are usually invoked to explain the evolution of different parameters. We argue that whatever physical process is responsible for the evolution of one parameter, should also be responsible for the evolution of others. This means that the different parameters are coupled together somehow. Based on this guiding principle, we investigate a Bianchi type I model with variable $\Lambda$ and $G$, in which $\Lambda$, $G$ and the shear parameter $\sigma^2$, all are coupled. It is interesting that the resulting model reduces to the FLRW model for large $t$ with $G$ approaching a constant.
The Relativistic Motion Integrator (RMI) consists in integrating numerically
the EXACT relativistic equations of motion, with respect to the appropriate
gravitational metric, instead of Newtonian equations plus relativistic
corrections. The aim of the present paper is to validate the method, and to
illustrate how RMI can be used for space missions to produce relativistic
ephemerides of satellites. Indeed, nowadays, relativistic effects have to be
taken into account, and comparing a RMI ephemeris with a classical keplerian
one helps to quantify such effects.
LISA is a relevant example to use RMI. This mission is an interferometer
formed by three spacecraft which aims at the detection of gravitational waves.
Precise ephemerides of LISA spacecraft are needed not only for the sake of the
orbitography but also to compute the photon flight time in laser links between
spacecraft, required in LISA data pre-processing in order to reach the
gravitational wave detection level.
Relativistic effects in LISA orbitography needed to be considered and
quantified. Using RMI, we show that the numerical classical model for LISA
orbits in the gravitational field of a non-rotating spherical Sun without
planets can be wrong, with respect to the numerical relativisitic version of
the same model, by as much as about 9 km in radial distance during a year and
up to 59 km in along track distance after a year... with consequences on
estimated photon flight times.
We validated RMI numerical results with an analytical developpement. Finally,
the RMI relativistic numerical approach is soon more efficient than the
analytical development. Moreover, RMI can be applied to other space missions.
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We present deep, wide-field g and r photometry of the transition type dwarf galaxy Leo T, obtained with the blue arm of the Large Binocular Telescope. The data confirm the presence of both very young (<1 Gyr) as well as much older (>5 Gyr) stars. We study the structural properties of the old and young stellar populations by preferentially selecting either population based on their color and magnitude. The young population is significantly more concentrated than the old population, with half-light radii of 148+-16 and 104+-8 pc respectively, and their centers are slightly offset. Approximately 10% of the total stellar mass is estimated to be represented by the young stellar population. Comparison of the color-magnitude diagram (CMD) with theoretical isochrones as well as numerical CMD-fitting suggest that star formation began over 10 Gyr ago and continued in recent times until at least a few hundred Myr ago. The CMD-fitting results are indicative of two distinct star formation bursts, with a quiescent period around 3 Gyr ago, albeit at low significance. The results are consistent with no metallicity evolution and [Fe/H]~-1.5 over the entire age of the system. Finally, the data show little if any sign of tidal distortion of Leo T.
We present the results from a multiwavelength campaign on the TeV blazar 1ES 1959+650, performed in May, 2006. Data from the optical, UV, soft- and hard-X-ray and very high energy (VHE) gamma-ray (E > 100 GeV) bands were obtained with the SUZAKU and SWIFT satellites, with the MAGIC telescope and other ground based facilities. The source spectral energy distribution (SED), derived from SUZAKU and MAGIC observations at the end of May 2006, shows the usual double hump shape, with the synchrotron peak at a higher flux level than the Compton peak. With respect to historical values, during our campaign the source exhibited a relatively high state in X-rays and optical, while in the VHE band it was at one of the lowest level so far recorded. We also monitored the source for flux-spectral variability on a time window of 10 days in the optical-UV and X-ray bands and 7 days in the VHE band. The source varies more in the X-ray, than in the optical band, with the 2-10 keV X-ray flux varying by a factor of ~2. The synchrotron peak is located in the X-ray band and moves to higher energies as the source gets brighter, with the X-ray fluxes above it varying more rapidly than the X-ray fluxes at lower energies. The variability behaviour observed in the X-ray band cannot be produced by emitting regions varying independently, and suggests instead some sort of ``standing shock'' scenario. The overall SED is well represented by an homogeneous one-zone synchrotron inverse Compton emission model, from which we derive physical parameters that are typical of high energy peaked blazars.
(Abridged) We model the X-ray properties of millisecond pulsars (MSPs) by considering hot spot emission from a weakly magnetized rotating neutron star (NS) covered by an optically-thick hydrogen atmosphere. We investigate the limitations of using the thermal X-ray pulse profiles of MSPs to constrain the mass-to-radius ($M/R$) ratio of the underlying NS. The accuracy is strongly dependent on the viewing angle and magnetic inclination. For certain systems, the accuracy is ultimately limited only by photon statistics implying that future X-ray observatories could, in principle, achieve constraints on $M/R$ and hence the NS equation of state to better than $\sim$5%. We demonstrate that valuable information regarding the basic properties of the NS can be extracted even from X-ray data of fairly limited photon statistics through modeling of archival spectroscopic and timing observations of the nearby isolated PSRs J0030+0451 and J2124--3358. The X-ray emission from these pulsars is consistent with the presence of a hydrogen atmosphere and a dipolar magnetic field configuration, in agreement with previous findings for PSR J0437--4715. For both MSPs, the favorable geometry allows us to place interesting limits on the allowed $M/R$ of NSs. Assuming 1.4 M$_{\odot}$, the stellar radius is constrained to be $R > 9.4$ km and $R > 7.8$ km (68% confidence) for PSRs J0030+0451 and J2124--3358, respectively. We explore the prospects of using future observatories such as \textit{Constellation-X} and \textit{XEUS} to conduct blind X-ray timing searches for MSPs not detectable at radio wavelengths due to unfavorable viewing geometry. Using the observational constraints on the pulsar obliquities we are also able to place strong constraints on the magnetic field evolution model proposed by Ruderman.
We revisit the distant future of the Sun and the solar system, based on
stellar models computed with a thoroughly tested evolution code. For the solar
giant stages, mass-loss by the cool (but not dust-driven) wind is considered in
detail. Using the new and well-calibrated mass-loss formula of Schroder & Cuntz
(2005, 2007), we find that the mass lost by the Sun as an RGB giant (0.332
M_Sun, 7.59 Gy from now) potentially gives planet Earth a significant orbital
expansion, inversely proportional to the remaining solar mass.
According to these solar evolution models, the closest encounter of planet
Earth with the solar cool giant photosphere will occur during the tip-RGB
phase. During this critical episode, for each time-step of the evolution model,
we consider the loss of orbital angular momentum suffered by planet Earth from
tidal interaction with the giant Sun, as well as dynamical drag in the lower
chromosphere. We find that planet Earth will not be able to escape engulfment,
despite the positive effect of solar mass-loss. In order to survive the solar
tip-RGB phase, any hypothetical planet would require a present-day minimum
orbital radius of about 1.15 AU.
Furthermore, our solar evolution models with detailed mass-loss description
predict that the resulting tip-AGB giant will not reach its tip-RGB size. The
main reason is the more significant amount of mass lost already in the RGB
phase of the Sun. Hence, the tip-AGB luminosity will come short of driving a
final, dust-driven superwind, and there will be no regular solar planetary
nebula (PN). But a last thermal pulse may produce a circumstellar (CS) shell
similar to, but rather smaller than, that of the peculiar PN IC 2149 with an
estimated total CS shell mass of just a few hundredths of a solar mass.
We prove that static fluid stars can stably support magnetic fields (within the ideal MHD approximation).
We have examined the fate of impact ejecta liberated from the surface of
Mercury due to impacts by comets or asteroids, in order to study (1) meteorite
transfer to Earth, and (2) re-accumulation of an expelled mantle in
giant-impact scenarios seeking to explain Mercury's large core. In the context
of meteorite transfer, we note that Mercury's impact ejecta leave the planet's
surface much faster (on average) than other planet's in the Solar System
because it is the only planet where impact speeds routinely range from 5-20
times the planet's escape speed. Thus, a large fraction of mercurian ejecta may
reach heliocentric orbit with speeds sufficiently high for Earth-crossing
orbits to exist immediately after impact, resulting in larger fractions of the
ejecta reaching Earth as meteorites. We calculate the delivery rate to Earth on
a time scale of 30 Myr and show that several percent of the high-speed ejecta
reach Earth (a factor of -3 less than typical launches from Mars); this is one
to two orders of magnitude more efficient than previous estimates. Similar
quantities of material reach Venus.
These calculations also yield measurements of the re-accretion time scale of
material ejected from Mercury in a putative giant impact (assuming gravity is
dominant). For mercurian ejecta escaping the gravitational reach of the planet
with excess speeds equal to Mercury's escape speed, about one third of ejecta
re-accretes in as little as 2 Myr. Thus collisional stripping of a silicate
proto-mercurian mantle can only work effectively if the liberated mantle
material remains in small enough particles that radiation forces can drag them
into the Sun on time scale of a few million years, or Mercury would simply
re-accrete the material.
The fitting of the observed redshifts and magnitudes of type Ia supernovae to what we would see in homogeneous cosmological models has led to constraints on cosmological parameters. However, in doing such fits it is assumed that the sampled supernovae are moving with the Hubble flow, i.e. that their peculiar velocities are zero. In reality, peculiar velocities will modify supernova data in a way that can impact best-fit cosmological parameters. We theoretically quantify this effect in the nonlinear regime with a Monte-Carlo analysis, using data from semi-analytic galaxy catalogs that are built from the Millennium N-body simulation. We find scaling relations for the errors in best-fit parameters resulting solely from peculiar velocities, as a function of the total number of sources in a supernova survey N and its maximum redshift z_max. For low redshift surveys, we find that these errors can be of the same order of magnitude as the errors due to an intrinsic magnitude scatter of 0.1 mag. For a survey with N=2000 and z_max=1.7, we estimate the expected errors in the best-fit cosmological constant density and equation of state can be sigma_Lambda ~ 0.009 and sigma_w ~ 0.01, respectively. We further find that throwing away supernova data below a redshift z ~ 0.01-0.02 can reduce the combined error, due to peculiar velocities and the intrinsic scatter, but by only about 10%.
Observations of local X-ray absorbers, high-velocity clouds, and distant quasar absorption line systems suggest that a significant fraction of baryons may reside in multi-phase, low-density, extended, ~100 kpc, gaseous halos around normal galaxies. We present a pair of high-resolution SPH (smoothed particle hydrodynamics) simulations that explore the nature of cool gas infall into galaxies, and the physical conditions necessary to support the type of gaseous halos that seem to be required by observations. The two simulations are identical other than their initial gas density distributions: one is initialized with a standard hot gas halo that traces the cuspy profile of the dark matter, and the other is initialized with a cored hot halo with a high central entropy, as might be expected in models with early pre-heating feedback. Galaxy formation proceeds in dramatically different fashions in these two cases. While the standard cuspy halo cools rapidly, primarily from the central region, the cored halo is quasi-stable for ~4 Gyr and eventually cools via the fragmentation and infall of clouds from ~100 kpc distances. After 10 Gyr of cooling, the standard halo's X-ray luminosity is ~100 times current limits and the resultant disk galaxy is twice as massive as the Milky Way. In contrast, the cored halo has an X-ray luminosity that is in line with observations, an extended cloud population reminiscent of the high-velocity cloud population of the Milky Way, and a disk galaxy with half the mass and ~50% more specific angular momentum than the disk formed in the low-entropy simulation. These results suggest that the distribution and character of halo gas provides an important testing ground for galaxy formation models and may be used to constrain the physics of galaxy formation.
Normal field stars located behind dense clouds are a valuable resource in interstellar astrophysics, as they provide continua in which to study phenomena such as gas-phase and solid-state absorption features, interstellar extinction and polarization. This paper reports the results of a search for highly reddened stars behind the Taurus Dark Cloud complex. We use the Two Micron All Sky Survey (2MASS) Point Source Catalog to survey a 50 sq deg area of the cloud to a limiting magnitude of K = 10.0. Photometry in the 1.2-2.2 micron passbands from 2MASS is combined with photometry at longer infrared wavelengths (3.6-12 micron) from the Spitzer Space Telescope and the Infrared Astronomical Satellite to provide effective discrimination between reddened field stars and young stellar objects (YSOs) embedded in the cloud. Our final catalog contains 248 confirmed or probable background field stars, together with estimates of their total visual extinctions, which span the range 2-29 mag. We also identify the 2MASS source J04292083+2742074 (IRAS 04262+2735) as a previously unrecognized candidate YSO, based on the presence of infrared emission greatly in excess of that predicted for a normal reddened photosphere at wavelengths >5 microns.
A brief review of various methods to calculate radiative accelerations for stellar evolution and an analysis of their limitations are followed by applications to Pop I and Pop II stars. Recent applications to Horizontal Branch (HB) star evolution are also described. It is shown that models including atomic diffusion satisfy Schwarzschild's criterion on the interior side of the core boundary on the HB without the introduction of overshooting. Using stellar evolution models starting on the Main Sequence and calculated throughout evolution with atomic diffusion, radiative accelerations are shown to lead to abundance anomalies similar to those observed on the HB of M15.
Using the OGLE catalogue of eclipsing binaries, 15 contact binaries were identified towards the SMC and the LMC at vertical distances from the Galactic plane between 300 pc and 10 kpc. Based on the luminosity function calculated for these contact binaries, we estimated a frequency of occurrence relative to Main Sequence stars in the thick disk at roughly 1/600. This estimate suffers from the small number statistics, but is consistent with the value previously found for the solar neighbourhood.
We use several main-sequence models to derive distances (and extinctions), with statistically meaningful uncertainties for 11 star-forming-regions and young clusters. The model dependency is shown to be small, allowing us to adopt the distances derived using one model. Using these distances we have revised the age order for some of the clusters of Mayne et al (2007). The new (approximate) nominal ages are: 2 Myrs for NGC6530 and the ONC, 3 Myrs for Lambda Orionis, NGC2264 and Sigma Orionis, 4-5 Myrs for NGC2362, 13 Myrs for h and chi Per, 20 Myrs for NGC1960 and 40 Myrs for NGC2547. In cases of significantly variable extinction we have derived individual extinctions using a revised Q-method (Johnson and Morgan, 1953). These new data show that the largest remaining uncertainty in deriving an age ordering (and necessarily ages) is metallicity. We also discuss the use of a feature we term the R-C gap overlap to provide a diagnostic of isochronal age spreads or varying accretion histories within a given star-formation-region. Finally, recent derivations of the distance to the ONC lie in two groups. Our new more precise distance of 391(+12,-9) pc allows us to decisively reject the further distance, we adopt 400 pc as a convenient value.
We have conducted an optical and infrared imaging in the neighbourhoods of 4 triplets of quasars. R, z', J and Ks images were obtained with MOSAIC II and ISPI at Cerro Tololo Interamerican Observatory. Accurate relative photometry and astrometry were obtained from these images for subsequent use in deriving photometric redshifts. We analyzed the homogeneity and depth of the photometric catalog by comparing with results coming from the literature. The good agreement shows that our magnitudes are reliable to study large scale structure reaching limiting magnitudes of R = 24.5, z' = 22.5, J = 20.5 and Ks = 19.0. With this catalog we can study the neighbourhoods of the triplets of quasars searching for galaxy overdensities such as groups and galaxy clusters.
Evolution of global morphology of galaxy clusters as seen in the X-rays was measured, using a variety of morphological measures at different radii, and by accounting for Poisson noise in images. Ellipticities and the multipole-moment power ratios of Buote & Tsai (1995,1996), were used. The power ratios $PR_2$, $PR_3$, $PR_4$, and $PR_1^{\rm (pk)}$ served to quantify morphology. A sample of 143 galaxy clusters at redshifts $0.1028 < z < 1.273$ was assembled using Chandra X-Ray Observatory archive data as of August, 2006. Multiple observations of sources were merged, when available, for enhanced signal-to-noise. Galaxy cluster morphologies were probed in circular apertures whose radii were $300h_{70}^{-1}$ kpc and $500h_{70}^{-1}$ kpc. We find significant evolution of cluster morphology with redshift, as measured by $PR_3$, $PR_4$, and $PR_1^{\rm (pk)}$ at the 3-4$\sigma$ level at both scales, with $PR_3$ exhibiting a sensitivity to noise-correction at $300h_{70}^{-1}$ kpc. Results for ellipticity and $PR_2$ are consistent with no evolution. We find that $PR_1^{\rm (pk)}$ is an ideal statistic to use for probing morphology evolution as it sees evolution at both scales, regardless of whether noise-correction is applied. Our results for evolution of $PR_2$, $PR_3$, and $PR_4$ are fully consistent with previous observational work. Jeltema et al. (2005) see no consistency of $PR_4$ at $500h_{70}^{-1}$ kpc with evolution when they apply their noise-correction, which is in disagreement with our results. Furthermore, our results for the evolution of cluster ellipticity with redshift fail to explain away, e.g., the predictions of Ho et al. (2006).
The ratio of the Bondi and Jeans lengths is used to develop a cloud-accretion model that describes both an inner Bondi-type regime where gas pressure is balanced by the gravity of a central star and an outer Jeans-type regime where gas pressure is balanced by gas self-gravity. The gas density profile provided by this model makes a smooth transition from a wind-type inner solution to a Bonnor-Ebert type outer solution. It is shown that high-velocity dust impinging on this cloud will tend to pile-up due to having a different velocity profile than gas so that the dust-to-gas ratio is substantially enriched above the 1% ISM level.
We present new high resolution (R=18,000) near-infrared spectroscopic observations of a sample of classical FU Orionis stars (FUors) and other young stars with FUor characteristics that are sources of Herbig-Haro flows. Spectra are presented for the region 2.203 - 2.236 microns which is rich in absorption lines sensitive to both effective temperatures and surface gravities of stars. Both FUors and FUor-like stars show numerous broad and weak unidentified spectral features in this region. Spectra of the 2.280 - 2.300 micron region are also presented, with the 2.2935 micron v=2-0 CO absorption bandhead being clearly the strongest feature seen in the spectra all FUors and Fuor-like stars. A cross-correlation analysis shows that FUor and FUor-like spectra in the 2.203 - 2.236 micron region are not consistent with late-type dwarfs, giants, nor embedded protostars. The cross-correlations also show that the observed FUor-like Herbig-Haro energy sources have spectra that are substantively similar to those of FUors. Both object groups also have similar near-infrared colors. The large line widths and double-peaked nature of the spectra of the FUor-like stars are consistent with the established accretion disk model for FUors, also consistent with their near-infrared colors. It appears that young stars with FUor-like characteristics may be more common than projected from the relatively few known classical FUors.
To constrain the equation of state of super-nuclear density matter and probe the interior composition of the X-ray pulsar in SAX J1808.4-3658. In our estimation, we consider both its persistent 2.49 ms X-ray pulsations discovered by Wijnands and van der Klis from using the Rossi X-ray Timing Explorer, which is interpreted to come from an accreting-powered millisecond X-ray pulsar in the low mass X-ray binaries, and the corresponding mass-radius data analyzed of the light curves of SAX J1808.4-3685 during its 1998 and 2005 outbursts by Leahy et al. from assuming a hot spot model where the X-rays are originated from the surface of the neutron star.
We present high precision, time-resolved visible and near infrared photometry of the large (diameter ~ 2500 km) Kuiper belt object (136108) 2003 EL61. The new data confirm rapid rotation at period P = 3.9155+/-0.0001 hr with a peak-to-peak photometric range (Delta m_R) = 0.29+/-0.02 mag and further show subtle but reproducible color variations with rotation. Rotational deformation of 2003 EL61 alone would give rise to a symmetric lightcurve free of color variations. The observed photometric deviations from the best-fit equilibrium model show the existence of a large surface region with an albedo and color different from the mean surface of 2003 EL61. We explore constraints on the nature of this anomalous region set by the existing data.
The Bekenstein-Milgrom gravity theory with a modified Poisson equation is tested here for the existence of triaxial equilibrium solutions. Using the non-negative least square method, we show that self-consistent triaxial galaxies exist for baryonic models with a mild density cusp $\rho \sim {\Sigma \over r}$. Self-consistency is achieved for a wide range of central concentrations, $\Sigma \sim 10-1000\mathrm{M_{\odot}pc^{-2}}$, representing low-to-high surface brightness galaxies. Our results demonstrate for the first time that the orbit superposition technique is fruitful for constructing galaxy models beyond Newtonian gravity, and triaxial cuspy galaxies might exist without the help of Cold dark Matter.
(Abridged) Classification schemes for YSOs are based on evaluating the degree
of dissipation of the surrounding envelope, whose main effects are the
extinction of the optical radiation from the central YSO and re-emission in the
far-infrared. Since extinction is a property of column density along the line
of sight, the presence of a protoplanetary disk may lead to a misclassification
when the system is viewed edge-on.
We performed radiative transfer calculations, using the axysimmetric 3D
radiative transfer codes RADMC and RADICAL, to show the effects of different
geometries on the main indicators of YSO evolutionary stage, like the slope of
the flux between 2 and 24mum, the bolometric temperature and the optical depth
of silicates and ices.
We show that for systems viewed at intermediate angles the 'classical'
indicators of evolution accurately trace the envelope column density, and they
all agree with each other. On the other hand, edge-on system are misclassified
for inclinations larger than ~65deg. In particular, silicate emission, typical
of pre-main sequence stars with disks, turns into absorption when the disk
column density reaches 1e22cm-2, corresponding e.g. to a 5e-3 Msun flaring disk
viewed at 64deg. A similar effect is noticed in all the other classification
indicators studied alpha, Tbol, and the H2O and CO2 ices absorption strengths.
This misclassification has a big impact on the nature of the flat-spectrum
sources (alpha ~0), whose number can be explained by simple geometrical
arguments without invoking evolution. A reliable classification scheme using a
minimal number of observations is constituted by observations of the mm-flux
with both a single dish and an interferometer.
We study the effect of noncommutativty on single field inflation including slow-roll, DBI and K-inflation. We derive the general form of modified power spectrum and the running spectral index and make some model testing. We find that the modified parts can well be realized as the origin of the running spectral index from WMAP3 which implies a negative running spectral.
We report observations of the nova RS Ophiuchi (RS Oph) using the Keck Interferometer Nuller (KIN), approximately 3.8 days following the most recent outburst that occurred on 2006 February 12. These observations represent the first scientific results from the KIN, which operates in N-band from 8 to 12.5 microns in a nulling mode. By fitting the unique KIN data, we have obtained an angular size of the mid-infrared continuum of 6.2, 4.0, or 5.4 mas for a disk profile, gaussian profile (FWHM), and shell profile respectively. The data show evidence of enhanced neutral atomic hydrogen emission and atomic metals including silicon located in the inner spatial regime near the white dwarf (WD) relative to the outer regime. There are also nebular emission lines and evidence of hot silicate dust in the outer spatial region, centered at ! 17 AU from the WD, that are not found in the inner regime. Our evidence suggests that these features have been excited by the nova flash in the outer spatial regime before the blast wave reached these regions. These identifications support a model in which the dust appears to be present between outbursts and is not created during the outburst event. We further discuss the present results in terms of a unifying model of the system that includes an increase in density in the plane of the orbit of the two stars created by a spiral shock wave caused by the motion of the stars through the cool wind of the red giant star. These data show the power and potential of the nulling technique which has been developed for the detection of Earth-like planets around nearby stars for the Terrestrial Planet Finder Mission and Darwin missions.
New solar wind data from the Voyager 1 and Voyager 2 spacecraft, together with the SOHO SWAN measurements of the direction that neutral hydrogen enters into the inner heliosheath and neutral helium measurements provided by multiple observations are expected to provide more reliable constraints on the ionization ratio of the local interstellar medium (LISM) and the direction and magnitude of the interstellar magnetic field (ISMF). In this paper we use currently the most sophisticated numerical model of the heliospheric interface, which is based on an MHD treatment of the ion flow and kinetic modeling of neutral particles, to analyze an ISMF-induced asymmetry of the heliosphere in the presence of the interplanetary magnetic field and neutral particles. It is shown that secondary hydrogen atoms modify the LISM properties leading to its shock-free deceleration at the heliopause. We determine the deflection of hydrogen atoms from their original trajectory in the unperturbed LISM and show that it occurs not only in the plane defined by the ISMF and LISM velocity vectors, but also, to a lesser extent, perpendicular to this plane. We also consider the possibility of using 2-3 kHz radio emission data to further constrain the ISMF direction.
SWIFT J1756.9-2508 is one of the few accreting millisecond pulsars (AMPs) discovered to date. We report here the results of our analysis of its aperiodic X-ray variability, as measured with the Rossi X-ray Timing Explorer during the 2007 outburst of the source. We detect strong (~35%) flat-topped broadband noise throughout the outburst with low characteristic frequencies (~0.1 Hz). This makes SWIFT J1756.9-2508 similar to the rest of AMPs and to other low luminosity accreting neutron stars when they are in their hard states, and enables us to classify this AMP as an atoll source in the extreme island state. We also find a hard tail in its energy spectrum extending up to 100 keV, fully consistent with such source and state classification.
The Newtonian solid-mechanical theory of non-compressional spheroidal and torsional nodeless elastic vibrations in the homogenous crust model of a quaking neutron star is developed and applied to the modal classification of the quasi-periodic oscillations (QPOs) of X-ray luminosity in the aftermath of giant flares in SGR 1806-20 and SGR 1900+14. Particular attention is given to the low-frequency QPOs in the data for SGR 1806-20 whose physical origin has been called into question. Our calculations suggest that unspecified QPOs are due to nodeless dipole torsional and dipole spheroidal elastic shear vibrations.
Over the past ten years, there has been a revolution in our understanding of massive young stellar clusters in the Galaxy. Initially, there were no known examples having masses $>10^4$, yet we now know that there are at least a half dozen such clusters in the Galaxy. In all but one case, the masses have been determined through infrared observations. Several had been identified as clusters long ago, but their massive natures were only recently determined. Presumably, we are just scratching the surface, and we might look forward to having statistically significant samples of coeval massive stars at all important stages of stellar evolution in the near future. I review the efforts that have led to this dramatic turn of events and the growing sample of young massive clusters in the Galaxy.
The dynamic spectrum of a radio pulsar is an in-line digital hologram of the ionised interstellar medium. It has previously been demonstrated that such holograms permit image reconstruction, in the sense that one can determine an approximation to the complex electric field values as a function of Doppler-shift and delay, but to date the quality of the reconstructions has been poor. Here we report a substantial improvement in the method which we have achieved by simultaneous optimisation of the thousands of coefficients that describe the electric field. For our test spectrum of PSR B0834+06 we find that the model provides an accurate representation of the data over the full 63 dB dynamic range of the observations: residual differences between model and data are noise-like. The advent of interstellar holography enables detailed quantitative investigation of the interstellar radio-wave propagation paths for a given pulsar at each epoch of observation; we illustrate this using our test data which show the scattering material to be structured and highly anisotropic. The temporal response of the medium exhibits a scattering tail out to beyond 100 microsec and a pulse arrival time measurement at this frequency and this epoch of observation would be affected by a mean delay of 15 microsec due to multipath propagation in the interstellar medium.
The Stokes V parameter characterizes asymmetry of amplitudes between right- and left-handed waves, and non-vanishing value of the V parameter yields a circularly polarized signal. Cosmologically, V parameter may be a direct probe for parity violation in the universe. In this paper, we theoretically investigate a measurement of this parameter, particularly focusing on the gravitational-wave backgrounds observed via ground-based interferometers. In contrast to the traditional analysis that only considers the total amplitude (or equivalently $\Omega_{GW}$), the signal analysis including a circular-polarized mode has a rich structure due to the multi-dimensionality of target parameters. We show that, by using the network of next-generation detectors, separation between polarized and unpolarized modes can be performed with small statistical loss induced by their correlation.
The chemical compositions of seven Carbon-Enhanced Metal-Poor (CEMP) turn-off stars are determined from high-resolution spectroscopy. Five of them are selected from the SDSS/SEGUE sample of metal-poor stars. The effective temperatures of these objects are all higher than 6000 K, while their metallicities, parametrized by [Fe/H], are all below -2. Six of our program objects exhibit high abundance ratios of barium ([Ba/H]> +1), suggesting large contributions of the products of former AGB companions via mass transfer across binary systems. Combining our results with previous studies provides a total of 20 CEMP main-sequence turn-off stars for which the abundances of carbon and at least some neutron-capture elements are determined. Inspection of the [C/H] ratios for this sample of CEMP turn-off stars show that they are generally higher than those of CEMP giants; their dispersion in this ratio is also smaller. We take these results to indicate that the carbon-enhanced material provided from the companion AGB star is preserved at the surface of turn-off stars with no significant dilution. In contrast, a large dispersion in the observed [Ba/H] is found for the sample of CEMP turn-off stars, suggesting that the efficiency of the s-process in very metal-poor AGB stars may differ greatly from star to star. Four of the six stars from the SDSS/SEGUE sample exhibit kinematics that are associated with membership in the outer-halo population, a remarkably high fraction.
We consider the impact of thermal inflation -- a short, secondary period of inflation that can arise in supersymmetric scenarios -- on the stochastic gravitational wave background. We show that while the primordial inflationary gravitational wave background is essentially unchanged at CMB scales, it is massively diluted at solar system scales and would be unobservable by a BBO style experiment. Conversely, bubble collisions at the end of thermal inflation can generate a new stochastic background. We calculate the likely properties of the bubbles created during this phase transition, and show that the expected amplitude and frequency of this signal would fall within the BBO range.
Fluorescence light is induced by extensive air showers while developing in the Earth's atmosphere. The number of emitted fluorescence photons depends on the conditions of the air and on the energy deposited by the shower particles at every stage of the development. In a previous model calculation, the pressure and temperature dependences of the fluorescence yield have been studied on the basis of kinetic gas theory, assuming temperature-independent molecular collision cross-sections. In this work we investigate the importance of temperature-dependent collision cross-sections and of water vapour quenching on the expected fluorescence yield. The calculations will be applied to simulated air showers while using actual atmospheric profiles to estimate the influence on the reconstructed energy of extensive air showers.
We discuss a Lagrangian reconstruction method of the velocity field from galaxy redshift catalog that takes its root in the Euler equation. This results in a ``functional'' of the velocity field which must be minimized. This is helped by an algorithm solving the minimization of cost-flow problems. The results obtained by applying this method to cosmological problems are shown and boundary effects happening in real observational cases are then discussed. Finally, a statistical model of the errors made by the reconstruction method is proposed.
Improving our understanding of the initial conditions and earliest stages of star formation is crucial to gain insight into the origin of stellar masses, multiple systems, and protoplanetary disks. We review the properties of low-mass dense cores as derived from recent millimeter/submillimeter observations of nearby molecular clouds and discuss them in the context of various contemporary scenarios for cloud core formation and evolution. None of the extreme scenarios can explain all observations. Pure laminar ambipolar diffusion has relatively long growth times for typical ionization levels and has difficulty satisfying core lifetime constraints. Purely hydrodynamic pictures have trouble accounting for the inefficiency of core formation and the detailed velocity structure of individual cores. A possible favorable scenario is a mixed model involving gravitational fragmentation of turbulent molecular clouds close to magnetic criticality. The evolution of the magnetic field and angular momentum in individual cloud cores after the onset of gravitational collapse is also discussed. In particular, we stress the importance of radiation-magnetohydrodynamical processes and resistive MHD effects during the protostellar phase. We also emphasize the role of the formation of the short-lived first (protostellar) core in providing a chance for sub-fragmentation into binary systems and triggering MHD outflows. Future submillimeter facilities such as Herschel and ALMA will soon provide major new observational constraints in this field. On the theoretical side, an important challenge for the future will be to link the formation of molecular clouds and prestellar cores in a coherent picture.
We review the impact of global helioseismology on key questions concerning the internal structure and dynamics of the Sun, and consider the exciting challenges the field faces as it enters a fourth decade of science exploitation. We do so with an eye on the past, looking at the perspectives global helioseismology offered in its earlier phases, in particular the mid-to-late 1970s and the 1980s. We look at how modern, higher-quality, longer datasets coupled with new developments in analysis, have altered, refined, and changed some of those perspectives, and opened others that were not previously available for study. We finish by discussing outstanding challenges and questions for the field.
We present an extension to our XMM-Newton X-ray source catalogue of M 31,
containing 39 newly found sources. In order to classify and identify more of
the sources we search for X-ray time variability in XMM-Newton archival data of
the M 31 centre field.
As a source list we used our extended catalogue based on observations
covering the time span from June 2000 to July 2004. We then determined the flux
or at least an upper limit at the source positions for each observation.
Deriving the flux ratios for the different observations and searching for the
maximum flux difference we determined variability factors. We also calculated
the significance of the flux ratios.
Using hardness ratios, X-ray variability and cross correlations with
catalogues in the X-ray, optical, infrared and radio regimes, we detected three
super soft source candidates, one supernova remnant and six supernova remnant
candidates, one globular cluster candidate, three X-ray binaries and four X-ray
binary candidates. Additionally we identified one foreground star candidate and
classified fifteen sources with hard spectra, which may either be X-ray
binaries or Crab-like supernova remnants in M 31 or background active galactic
nuclei. The remaining five sources stay unidentified or without classification.
Based on the time variability results we suggest six sources, which were
formerly classified as "hard", to be X-ray binary candidates. The
classification of one other source (XMMM31 J004236.7+411349) as a supernova
remnant, has to be rejected due to the distinct time variability we found. We
now classify this source as a foreground star.
We examine the effects of all possible phenomenological interactions between dark energy and dark matter on cosmological parameters and their efficiency in solving the coincidence problem. We work with two simple parameterizations of the dynamical dark energy equation of state and the constant dark energy equation of state. Using observational data coming from the new 182 Gold type Ia supernova samples, the shift parameter of the Cosmic Microwave Background given by the three-year Wilkinson Microwave Anisotropy Probe observations, and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, we perform a statistical joint analysis of different forms of phenomenological interactions between dark energy and dark matter.
Aims. We report the discovery of a peculiar object observed serendipitously with XMM-Newton. We present its timing and spectral properties and investigate its optical counterpart. Methods. The light curve of the X-ray source, its spectrum, and the spectrum of the best optical counterpart are presented and analyzed. Results. The X-ray flux decreases by a factor of 6.5 within 1 h and stays in a low state for at least 10 h, thereby suggesting the presence of an eclipse. The spectrum is very soft, a power law with a slope of Gamma~2.8, and does not change significantly before and after the flux drop. The source is spatially coincident within few arc-seconds with a Seyfert~2 galaxy belonging to a galaxy pair. Conclusions. Although the background AGN seems the best counterpart, neither the temporal nor the spectral properties of the X-ray source are compatible with it. We investigate the possibility of having a foreground low-mass X-ray binary in quiescence, where the companion is not detected in the optical wavelength.
The dissipation of energy from sound waves and weak shocks is one of the most
promising mechanisms for coupling AGN activity to the surrounding intracluster
medium (ICM), and so offsetting cooling in cluster cores. We present a detailed
analysis of the weak shock found in deep Chandra observations of the Perseus
cluster core. A comparison of the spectra either side of the shock front shows
that they are very similar. By performing a deprojection analysis of a sector
containing the shock, we produce temperature and density profiles across the
shock front. These show no evidence for a temperature jump coincident with the
density jump. To understand this result, we model the shock formation using 1D
hydrodynamic simulations including models with thermal conduction and gamma <
5/3 gas. These models do not agree well with the data, suggesting that further
physics is needed to explain the shock structure. We suggest that an
interaction between the shock and the H-alpha filaments could have a
significant effect on cooling the post-shock gas.
We also calculate the thermal energy liberated by the weak shock. The total
energy in the shocked region is about 3.5 times the work needed to inflate the
bubbles adiabatically, and the power of the shock is around 6x10^44 erg/s per
bubble, just over 10^45 erg/s in total.
The inversion of a gravitational lens system is, as is well known, plagued by the so-called mass-sheet degeneracy: one can always rescale the density distribution of the lens and add a constant-density mass-sheet such that the, also properly rescaled, source plane is projected onto the same observed images. For strong lensing systems, it is often claimed that this degeneracy is broken as soon as two or more sources at different redshifts are available. This is definitely true in the strict sense that it is then impossible to add a constant-density mass-sheet to the rescaled density of the lens without affecting the resulting images. However, often one can easily construct a more general mass distribution -- instead of a constant-density sheet of mass -- which gives rise to the same effect: a uniform scaling of the sources involved without affecting the observed images. We show that this can be achieved by adding one or more circularly symmetric mass distributions, each with its own center of symmetry, to the rescaled mass distribution of the original lens. As it uses circularly symmetric distributions, this procedure can lead to the introduction of ring shaped features in the mass distribution of the lens. In this paper, we show explicitly how degenerate inversions for a given strong lensing system can be constructed. It then becomes clear that many constraints are needed to effectively break this degeneracy.
The light-time effect method, its limitations and applications were studied. A powerful combined method of simultaneous analysis of the O-C diagrams and astrometric orbit in triple eclipsing-astrometric binaries was presented. Eleven eclipsing systems were studied in detail according to their O-C diagrams (RY Aqr, BF CMi, RW Cap, TY Cap, SS Cet, RR Dra, TY Del, TZ Eri, RV Per, UZ Sge, and BO Vul). The introduced method for studying the astrometric-eclipsing binaries was applied to QS Aql, VW Cep, Zeta Phe, V505 Sgr, HT Vir, and V2388 Oph. The algorithm for such an analysis was introduced and the its limitations were discussed. The catalogue of another systems, which contain eclipsing binaries in astrometric binaries, was presented. Such systems could be useful for prospective analysis. The method itself could be easily modified for estimation of the parallax of the individual systems.
Thermal wind emission in the form of free-free and free-bound emission is known to show up in the infrared and radio continuum of hot and massive stars. For OB supergiants with moderate mass loss rates and a wind velocity distribution with \beta = 0.8...1.0, no influence of the wind to the optical continuum, i.e. for \lambda < 1 micron, is expected. Investigations of stellar and wind parameters of OB supergiants over the last few years suggest, however, that for many objects \beta is much higher than 1.0, reaching values up to 3.5. We investigate the influence of the free-free and free-bound emission on the emerging radiation, especially at optical wavelengths, from OB supergiants having wind velocity distributions with \beta > 1. For the case of a spherically symmetric, isothermal wind in local thermodynamical equilibrium (LTE) we calculate the free-free and free-bound processes and the emerging wind and total continuum spectra. We localize the generation region of the optical wind continuum and especially focus on the influence of a \beta-type wind velocity distribution with \beta > 1 on the formation of the wind continuum at optical wavelengths. The optical wind continuum is found to be generated within about 2 R_* which is exactly the wind region where \beta strongly influences the density distribution. We find that for \beta > 1, the continuum of a typical OB supergiant can indeed be contaminated with thermal wind emission, even at optical wavelengths. The strong increase in the optical wind emission is dominantly produced by free-bound processes.
We present results from Hubble Space Telescope UV spectroscopy of the massive X-ray binary system, HD226868 = Cyg X-1. The spectra were obtained at both orbital conjunction phases in two separate runs in 2002 and 2003 when the system was in the X-ray high/soft state. The stellar wind lines suffer large reductions in strength when the black hole is in the foreground due to the X-ray ionization of the wind ions. A comparison of HST and archival IUE spectra shows that similar photoionization effects occur in both the X-ray states. We constructed model UV wind line profiles assuming that X-ray ionization occurs everywhere in the wind except the zone where the supergiant blocks the X-ray flux. The good match between the observed and model profiles indicates that the wind ionization extends to near to the hemisphere of the supergiant facing the X-ray source. The H-alpha emission strength is generally lower in the high/soft state compared to the low/hard state, but the He II 4686 emission is relatively constant between states. The results suggest that mass transfer in Cyg X-1 is dominated by a focused wind flow that peaks along the axis joining the stars and that the stellar wind contribution is shut down by X-ray photoionization effects. The strong stellar wind from the shadowed side of the supergiant will stall when Coriolis deflection brings the gas into the region of X-ray illumination. This stalled gas component may be overtaken by the orbital motion of the black hole and act to inhibit accretion from the focused wind. The variations in the strength of the shadow wind component may then lead to accretion rate changes that ultimately determine the X-ray state.
We undertake an optical and ultraviolet spectroscopic analysis of a sample of 20 Galactic B0 - B5 supergiants of luminosity classes Ia, Ib, Iab and II. Fundamental stellar parameters are obtained from optical diagnostics and a critical comparison of the model predictions to observed UV spectral features is made. These parameters are derived for individual stars using CMFGEN, the nLTE, line-blanketed model atmosphere code of Hillier et al., 1998. The B supergiant temperature scale derived here shows a reduction of 1000 - 3000 K compared to previous results obtained using unblanketed codes. Mass loss rate estimates are in good agreement with predicted theoretical values and all of the 20 B0 - B5 supergiants analysed show evidence for CNO processing. The observed WLR values calculated for B0 - B0.7 supergiants are larger than predicted values, whereas the reverse is true for B1 - B5 supergiants. This means that the discrepancy between observed and theoretical values cannot be resolved by adopting clumped (i.e., lower) mass loss rates, as for O stars. The most surprising result is that, although CMFGEN succeeds in reproducing the optical spectrum accurately, it fails to reproduce key UV diagnostics, such as NV and CIV P Cygni profiles, precisely. This problem arises because the models are not ionised enough and fail to reproduce the full extent of the observed absorption trough of the P Cygni profiles. These findings add further support to the need to revise the standard model of massive star winds.
We describe the results of a radio continuum survey of the central 4x1deg with the 100 m Green Bank Telescope (GBT) at wavelengths of 3.5, 6, 20, and 90 cm. The 3.5 and 6 cm surveys are the most sensitive and highest resolution single dish surveys made of the central degrees of our Galaxy. We present catalogs of compact and extended sources in the central four degrees of our Galaxy, including detailed spectral index studies of all sources. The analysis covers star-forming regions such as Sgr B and Sgr C where we find evidence of a mixture of thermal and nonthermal emission. The analysis quantifies the relative contribution of thermal and nonthermal processes to the radio continuum flux density toward the GC region. In the central 4x1deg of the GC, the thermal and nonthermal flux fractions for all compact and diffuse sources are 28%/72% at 3.5 cm and 19%/81% at 6 cm. The total flux densities from these sources are 783+-52 Jy and 1063+-93 Jy at 3.5 and 6 cm, respectively, excluding the contribution of Galactic synchrotron emission.
The coming Planck and Herschel missions will survey the sky at unprecedented
angular scales and sensitivities. Simulations are needed for better
interpretating the results of the surveys and for testing new methods of, e.g.,
source extraction and component separation. We present new simulations of the
infrared and submillimeter cosmic background, including the correlation between
infrared galaxies. The simulations were used to quantify the source-detection
thresholds for Herschel/SPIRE and Planck/HFI, as well as to study the
detectability of the cosmic infrared background correlated fluctuations.
The simulations are based on an empirical model of IR galaxy evolution. For
the correlations, we only included the linear clustering, assuming that
infrared galaxies are biased tracers of the dark-matter fluctuation density
field. We used the simulations with different bias parameters to predict the
confusion noise for Herschel/SPIRE and Planck/HFI and the completeness levels.
We also discuss the detectability of the linear clustering in Planck/HFI power
spectra, including the foreground and backgrounds components.
Simulated maps and catalogs are publicly available online at
this http URL
We present an analysis of the 5-8 micron Spitzer-IRS spectra of a sample of 68 local Ultraluminous Infrared Galaxies (ULIRGs). Our diagnostic technique allows a clear separation of the active galactic nucleus (AGN) and starburst (SB) components in the observed mid-IR emission, and a simple analytic model provides a quantitative estimate of the AGN/starburst contribution to the bolometric luminosity. We show that AGNs are ~30 times brighter at 6 micron than starbursts with the same bolometric luminosity, so that even faint AGNs can be detected. Star formation events are confirmed as the dominant power source for extreme infrared activity, since ~85% of ULIRG luminosity arises from the SB component. Nonetheless an AGN is present in the majority (46/68) of our sources.
We present a new method for the reconstruction of the longitudinal profile of extensive air showers induced by ultra-high energy cosmic rays. In contrast to the typically considered shower size profile, this method employs directly the ionization energy deposit of the shower particles in the atmosphere. Due to universality of the energy spectra of electrons and positrons, both fluorescence and Cherenkov light can be used simultaneously as signal to infer the shower profile from the detected light. The method is based on an analytic least-square solution for the estimation of the shower profile from the observed light signal. Furthermore, the extrapolation of the observed part of the profile with a Gaisser-Hillas function is discussed and the total statistical uncertainty of shower parameters like total energy and shower maximum is calculated.
X-ray emission due to inverse-Compton scattering of microwave background photons by electrons in the lobes of powerful radio galaxies has now been seen in a large number of objects. Combining an inverse-Compton model for the lobe X-ray emission with information obtained from radio synchrotron emission provides a method of constraining the electron population and magnetic field energy density, which cannot be accomplished using the radio data alone. Using six frequencies of new and archival radio data and new XMM-Newton observations of the Fanaroff & Riley class II radio galaxy 3C353, we show that inverse-Compton emission is detected in the radio lobes of this source at a level consistent with what is seen in other objects. We argue that variations in the X-ray/radio ratio in the brighter eastern lobe require positionally varying magnetic field strength. We also examine the X-ray nucleus and the cluster, Zw 1819.1-0108, spatially and spectrally.
We report millimeter interferometric observations of polarized continuum and line emission from the massive star forming region G34.4. Polarized thermal dust emission at 3 mm wavelength and CO $J=1 \to 0$ line emission were observed using the Berkeley-Illinois-Maryland Association (BIMA) array. Our results show a remarkably uniform polarization pattern in both dust and in CO J=$1 \to 0$ emission. In addition, the line emission presents a consistent uniform polarization pattern over most of the velocity channel maps. These uniform polarization patterns are aligned with the north-south main axis of the filament between the main millimeter source (MM) and the ultra-compact H {\scriptsize II} region, which are the central sources in G34.4, suggesting a magnetic field orthogonal to this axis. This morphology is consistent with a magnetically supported disk seen roughly edge-on.
Almost 50 radio SNR objects were selected from Green's catalogue for continuum and polarization observations. We present preliminary results of this observational campaign at 4.7 GHz carried out with Torun 32-metre radio telescope.
We describe and discuss the spectral and temporal characteristics of the prompt emission and X-ray afterglow emission of X-ray flashes (XRFs) and X-ray-rich gamma-ray bursts (XRRs) detected and observed by Swift between December 2004 and September 2006. We compare these characteristics to a sample of conventional classical gamma-ray bursts (C-GRBs) observed during the same period. We confirm the correlation between Epeak_obs and fluence noted by others and find further evidence that XRFs, XRRs and C-GRBs form a continuum. We also confirm that our known redshift sample is consistent with the correlation between the peak energy in the GRB rest frame (Epeak_src) and the isotropic radiated energy (Eiso), so called the Epeak_src-Eiso relation. The spectral properties of X-ray afterglows of XRFs and C-GRBs are similar, but the temporal properties of XRFs and C-GRBs are quite different. We found that the light curves of C-GRB afterglows show a break to steeper indices (shallow-to-steep break) at much earlier times than do XRF afterglows. Moreover, the overall luminosity of XRF X-ray afterglows is systematically smaller by a factor of two or more compared to that of C-GRBs. These distinct differences between the X-ray afterglows of XRFs and C-GRBs may be the key to understanding not only the mysterious shallow-to-steep break in X-ray afterglow light curves, but also the unique nature of XRFs.
We analyze the hitherto available space-based X-ray data as well as ground-based optical data of the X-ray transient 080109/SN2008D. From the data we suggest that (i) The initial transient (\lesssim 800 sec) is attributed to the reverse shock emission of a mildly relativistic (\Gamma \sim a few) outflow stalled by the dense stellar wind. (ii) The subsequent X-ray afterglow (\lesssim 2\times 10^4 sec) can be ascribed to the forward shock emission of the outflow, with a kinetic energy \sim 10^{46} erg, when sweeping up the stellar wind medium. (iii) The late X-ray flattening (\gtrsim 2\times 10^4$ sec) is powered by the fastest non-decelerated component of SN2008D's ejecta. (iv) The local event rate of X-ray transient has a lower limit of \sim 1.6\times 10^4 yr^{-1} Gpc^{-3}, indicating a vast majority of X-ray transients have a wide opening angle of \gtrsim 100 degree. The off-axis viewing model is less likely. (v) Transient 080109/SN2008D may lead to a continuum from GRB-SN to under-luminous GRB-/XRF-SN to X-ray transient-SN and to ordinary Ibc SN (if not every Ibc SN has a relativistic jet), as shown in Figure 2 of this Letter.
Using archival spectroscopic and photometric data, we searched for massive stars with Balmer-emission consistent with magnetically confined circumstellar material. HR 7355 is a formerly unknown He-strong star showing Balmer emission. At V=6.02 mag, it is one of the brightest objects simultaneously showing anomalous helium absorption and hydrogen emission. Among similar objects, only sigma Ori E has so far been subjected to any systematic analysis of the circumstellar material responsible for the emission. We argue that the double-wave photometric period of 0.52d corresponds to the rotation period. In tandem with the high projected equatorial velocity, v sin i=320 km/s, this short period suggests that HR 7355 is the most rapidly rotating He-strong star known to date; a class that was hitherto expected to host stars with slow to moderate rotation only.
We investigate how well the 3D density field of neutral hydrogen in the Intergalactic Medium (IGM) can be reconstructed using the Lyman-alpha absorptions observed along lines of sight to quasars separated by arcmin distances in projection on the sky. We use cosmological hydrodynamical simulations to compare the topologies of different fields: dark matter, gas and neutral hydrogen optical depth and to investigate how well the topology of the IGM can be recovered from the Wiener interpolation method implemented by Pichon et al. (2001). The global statistical and topological properties of the recovered field are analyzed quantitatively through the power-spectrum, the probability distribution function (PDF), the Euler characteristics, its associated critical point counts and the filling factor of underdense regions. The local geometrical properties of the field are analysed using the local skeleton by defining the concept of inter-skeleton distance. At scales larger than ~1.4 <d_LOS>, where <d_LOS> is the mean separation between lines of sight, the reconstruction accurately recovers the topological features of the large scale density distribution of the gas, in particular the filamentary structures. At scales larger than the intrinsic smoothing length of the inversion procedure, the power spectrum of the recovered HI density field matches well that of the original one and the low order moments of the PDF are well recovered as well as the shape of the Euler characteristic. The integral errors on the PDF and the critical point counts are indeed small, less than 20% for <d_LOS>~2.5 arcmin. The small deviations between the reconstruction and the exact solution mainly reflect departures from the log-normal behaviour that are ascribed to highly non-linear objects in overdense regions.
The $BeppoSAX$ archive is currently the largest reservoir of high sensitivity simultaneous soft and hard-X ray data of Seyfert galaxies. From this database all the Seyfert galaxies (105 objects of which 43 are type I and 62 are type II) with redshift lower than 0.1 have been selected and analyzed in a homogeneous way (Dadina 2007). The X-ray data so collected allow to infer the average spectral properties of nearby Seyfert galaxies included in the original sample and, most notably: the photon index ($\Gamma$$\sim$1.8), the high-energy cut-off (Ec$\sim$290 keV), and the relative amount of reflection (R$\sim$1.0). The data have been also used to test some assumptions of the unified scheme for the AGN. The distributions of the isotropic indicators (photon index, relative amount of reflection, high-energy cut-off and narrow FeK$\alpha$ energy centroid) are similar in type I and type II objects while the absorbing column and the iron line equivalent width significantly differ between the two classes of active galactic nuclei. Confirming previous results, the narrow FeK$\alpha$ line is consistent, in Seyfert 2, with being produced in the same matter responsible for the observed obscuration. These results, thus, support the basic picture of the unified model. Moreover, the presence of a X-ray Baldwin effect in Seyfert 1 has been here measured using the 20-100 keV luminosity (EW$\propto$L(20-100)$^{-0.22\pm0.05}$). Finally, the possible presence of a correlation between the photon index and the amount of reflection is confirmed thus indicating thermal Comptonization as the most likely origin of the high energy emission for the active galactic nuclei included in the original sample.
The operational conditions found by $BeppoSAX$ in observing nearby (z$\leq$0.1) Seyferts were reproduced for $Simbol$-$X$ in order to simulate a realistic final database of the mission. The results indicate that, even in the worst conditions, the $Simbol$-$X$ archive of pointings will allow to fully characterize the high-energy spectrum of nearby Seyferts and, most importantly, to obtain solid results on R and Ec (fundamental to model the cosmic X-Ray background, CXB). The measurement of the inclination angle of the accretion disk will be possible for $\sim$15 objects allowing to directly test the unified models for AGN. Finally, the time-dependent characteristics of the reflected component will be studied in at least $\sim$25 objects.
We present the latest results on CIB fluctuations from early epochs from deep Spitzer data. The results show the existence of significant CIB fluctuations at the IRAC wavelengths (3.6 to 8 mic) which remain after removing galaxies down to very faint levels. These fluctuations must arise from populations with a significant clustering component, but only low levels of the shot noise. There are no correlations between the source-subtracted IRAC maps and the corresponding fields observed with the HST ACS at optical wavelengths. Taken together, these data imply that 1) the sources producing the CIB fluctuations are individually faint with S_\nu< a few nJy at 3.6 and 4.5 mic; 2) have different clustering pattern than the more recent galaxy populations; 3) are located within the first 0.7 Gyr (unless these fluctuations can somehow be produced by - so far unobserved - local galaxies of extremely low luminosity and with the unusual for local populations clustering pattern), 4) produce contribution to the net CIB flux of at least 1-2 nW/m^2/sr at 3.6 and 4.5 mic and must have mass-to-light ratio significantly below the present-day populations, and 5) they have angular density of ~ a few per arcsec^2 and are in the confusion of the present day instruments, but can be individually observable with JWST.
We discuss how rotation and binary interactions may be related to the diversity of type Ibc supernovae and long gamma-ray bursts. After presenting recent evolutionary models of massive single and binary stars including rotation, the Tayler-Spruit dynamo and binary interactions, we argue that the nature of SNe Ibc progenitors from binary systems may not significantly differ from that of single star progenitors in terms of rotation, and that most long GRB progenitors may be produced via the quasi-chemically homogeneous evolution at sub-solar metallicity. We also briefly discuss the possible role of magnetic fields generated in the convective core of a massive star for the transport of angular momentum, which is potentially important for future stellar evolution models of supernova and GRB progenitors.
Both core accretion and disk instability appear to be required as formation mechanisms in order to explain the entire range of giant planets found in extrasolar planetary systems. Disk instability is based on the formation of clumps in a marginally-gravitationally unstable protoplanetary disk. These clumps can only be expected to contract and survive to become protoplanets if they are able to lose thermal energy through a combination of convection and radiative cooling. Here we present several new three dimensional, radiative hydrodynamics models of self-gravitating protoplanetary disks, where radiative transfer is handled in the flux-limited diffusion approximation. We show that while the flux-limited models lead to higher midplane temperatures than in a diffusion approximation model without the flux-limiter, the difference in temperatures does not appear to be sufficiently high to have any significant effect on the formation of self-gravitating clumps. Self-gravitating clumps form rapidly in the models both with and without the flux-limiter. These models suggest that the reason for the different outcomes of numerical models of disk instability by different groups cannot be attributed solely to the handling of radiative transfer, but rather appears to be caused by a range of numerical effects and assumptions. Given the observational imperative to have disk instability form at least some extrasolar planets, these models imply that disk instability remains as a viable giant planet formation mechanism.
This paper is the first in a series aimed at understanding the long-term evolution of neutron star magnetic fields. We model the stellar matter as an electrically neutral and lightly ionized plasma composed of three moving particle species: neutrons, protons, and electrons, which can be converted into each other by weak interactions (beta decays), suffer binary collisions, and be affected by each other's macroscopic electromagnetic fields. Since the evolution of the magnetic field occurs over thousands of years or more, compared to dynamical time scales (sound and Alfv\'en) of milliseconds to seconds, we use a slow-motion approximation in which we neglect the inertial terms in the equations of motion for the particles. We restrict ourselves to a one-dimensional geometry in which the magnetic field points in one Cartesian direction but varies only along an orthogonal direction. We study the evolution of the system in three different ways: (i) estimating time scales directly from the equations, guided by physical intuition; (ii) a normal-mode analysis in the limit of a nearly uniform system; and (iii) a finite-difference numerical integration of the equations of motion. We find good agreement between our analytical normal-mode solutions and the numerical simulations. We show that the magnetic field and the particles evolve through successive quasi-equilibrium states, on time scales that can be understood by physical arguments. Depending of the parameter values the magnetic field can evolve by ohmic diffusion or by ambipolar diffusion, the latter being limited either by interparticle collisions or by relaxation to chemical equilibrium through beta decays. The numerical simulations are further validated by verifying that they satisfy the known conservation laws also in highly non-linear situations.
We discuss recent models on the evolution of massive stars at very low metallicity including the effects of rotation, magnetic fields and binarity. Very metal poor stars lose very little mass and angular momentum during the main sequence evolution, and rotation plays a dominant role in their evolution. In rapidly rotating massive stars, the rotationally induced mixing time scale can be even shorter than the nuclear time scale throughout the main sequence. The consequent quasi-chemically homogeneous evolution greatly differs from the standard massive star evolution that leads to formation of red giants with strong chemical stratification. Interesting outcomes of such a new mode of evolution include the formation of rapidly rotating massive Wolf-Rayet stars that emit large amounts of ionizing photons, the formation of a long gamma-ray bursts and a hypernovae, and the production of large amounts of primary nitrogen. We show that binary interactions can further enhance the effects of rotation, as mass accretion in a close binary spins up the secondary.
The linear instability that induces a relativistic electron beam passing through a return plasma current to filament transversely is often related to some filamentation mode with wave vector normal to the beam or confused with Weibel modes. We show that these modes may not be relevant in this matter and identify the most unstable mode on the two-stream/filamentation branch as the main trigger for filamentation. This sets both the characteristic transverse and longitudinal filamentation scales in the non-resistive initial stage.
The high energy proton beams expected when the Large Hadron Collider (LHC) comes online should provide a pass/fail test for a gravity-related explanation of ultrahigh energy cosmic rays. The model predicts that particles have two kinds energies, equal for null gravitational potentials and, in the potential at the Earth, differing significantly above one TeV. If correct, a 7 TeV trajectory energy proton at the LHC would deliver a 23.5 TeV particle state energy in a collision.
The behavior of spin-half particles is discussed in the 3 + 1-dimensional constant curvature black hole (CCBH) spacetime. We use Schwarzschild-like coordinates, valid outside the black hole event horizon. The constant time surfaces corresponding to the time-like Killing vector are degenerate at the black hole event horizon and also along an axis. We write down the Dirac equation in this spacetime using Newman-Penrose formalism which is not easily separable unlike that in the Kerr metric. However, with a particular choice of basis system the equation is separable and we obtain the solutions. We discuss the structural difference in the Dirac equation in the CCBH spacetime with that in the Kerr geometry, due to difference in the corresponding spacetime metric, resulting complexity arised in separation in the earlier case.
Several examples are known where quantum gravity effects resolve the classical big bang singularity by a bounce. The most detailed analysis has probably occurred for loop quantum cosmology of isotropic models sourced by a free, massless scalar. Once a bounce has been realized under fairly general conditions, the central questions are how strongly quantum it behaves, what influence quantum effects can have on its appearance, and what quantum space-time beyond the bounce may look like. This, then, has to be taken into account for effective equations which describe the evolution properly and can be used for further phenomenological investigations. Here, we provide the first analysis with interacting matter with new effective equations valid for weak self-interactions or small masses. They differ from the free scalar equations by crucial terms and have an important influence on the bounce and the space-time around it. Especially the role of squeezed states, which have often been overlooked in this context, is highlighted. The presence of a bounce is proven for uncorrelated states, but as squeezing is a dynamical property and may change in time, further work is required for a general conclusion.
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I give a concise introduction into high energy cosmic ray physics, including also few related aspects of high energy gamma-ray and neutrino astrophysics. The main emphasis is placed on astrophysical questions, and the level of the presentation is kept basic.
We studied the geometry of the inner (AU-scale) circumstellar environment
around the Herbig Be star MWC 147. Combining, for the first time, near- (NIR, K
band) and mid-infrared (MIR, N band) spectro-interferometry on a Herbig star,
our VLTI/MIDI and AMBER data constrain not only the geometry of the brightness
distribution, but also the radial temperature distribution in the disk.
For our detailed modeling of the interferometric data and the spectral energy
distribution, we employ 2-D radiation transfer simulations, showing that
passive irradiated Keplerian dust disks can easily fit the SED, but predict
much lower visibilities than observed. Models of a Keplerian disk with emission
from an optically thick inner gaseous accretion disk (inside the dust
sublimation zone), however, yield a good fit of the SED and simultaneously
reproduce the observed NIR and MIR visibilities. We conclude that the NIR
continuum emission from MWC 147 is dominated by accretion luminosity emerging
from an optically thick inner gaseous disk, while the MIR emission also
contains strong contributions from the outer dust disk.
We find that the fraction of Broad Absorption line quasars (BALQSOs) among the FIRST radio sources in the Sloan Data Release 3, is about 45.5^{+7.6}_{-7.5}% at the faintest radio powers detected (L_{1.4 GHz}~10^{32} erg/s), and rapidly drops to 23.9^{+3.4}_{-3.1}% at L_{1.4 GHz}~3*10^{33} erg/s. While the high fraction at low radio power is consistent with the recent near-IR estimate by Dai et al. (2007), the lower fraction at high radio powers is intriguing. The trend is independent of the redshift limits, the optical and radio flux selection limits, the exact definition of a BALQSO, or the exact definition of a radio match. The absorption index decreases with the radio luminosity while the mean maximum wind velocity is roughly a constant at all radio powers. We also find that at fixed optical magnitude, the highest bins of radio luminosity are preferentially populated by non-BALQSOs, consistent with the overall trend. These results are difficult to reconcile with a strictly evolutionary model for the BALQSO and radio emission phases, while a simple geometric model where the apparent radio luminosity function is partly due to beamed, non-BALQSOs can reproduce the results.
We present a global measurement of the integrated Sachs-Wolfe (ISW) effect obtained by cross-correlating all relevant large scale galaxy data sets with the cosmic microwave background radiation map provided by the Wilkinson Microwave Anisotropy Probe. With these measurements, the overall ISW signal is detected at the 4 - 4.5 sigma level. We also examine the cosmological implications of these measurements, particularly the dark energy equation of state w, its sound speed, and the overall curvature of the Universe. The flat LCDM model is a good fit to the data and, assuming this model, we find that the ISW data constrain Omega_m = 0.20 +0.12 -0.08 at the 95% confidence level. When we combine our ISW results with the latest BAO measurements, we find that the peak of the likelihood is shifted, by 1 sigma, towards phantom energy models (w < -1). The result obtained combining our ISW data with the SN data is instead consistent with w = -1.
AIMS: We have compiled one of the largest normal-galaxy samples ever to probe
X-ray luminosity function evolution separately for early and late-type systems.
METHODS: We selected 207 normal galaxies up to redshift z~1.4, with data from
four major Chandra X-ray surveys, namely the Chandra deep fields (north, south
and extended) and XBootes, and a combination of X-ray and optical criteria. We
used template spectral energy-distribution fitting to obtain separate early-
and late-type sub-samples, made up of 101 and 106 systems, respectively. For
the full sample, as well as the two sub-samples, we obtained luminosity
functions using both a non-parametric and a parametric, maximum-likelihood
method.
RESULTS: For the full sample, the non-parametric method strongly suggests
luminosity evolution with redshift. The maximum-likelihood estimate shows that
this evolution follows ~(1+z)^k_total, k_total=2.2+-0.3. For the late-type
sub-sample, we obtained k_late=2.4^+1.0_-2.0. We detected no significant
evolution in the early-type sub-sample. The distributions of early and
late-type systems with redshift show that late types dominate at z>~0.5 and
hence drive the observed evolution for the total sample.
CONCLUSIONS: Our results support previous results in X-ray and other
wavebands, which suggests luminosity evolution with k=2-3.
We are conducting a search for supermassive black holes (SMBHs) with masses below 10^7 M_sun by looking for signs of extremely low-level nuclear activity in nearby galaxies that are not known to be AGNs. Our survey has the following characteristics: (a) X-ray selection using the Chandra X-ray Observatory, since x-rays are a ubiquitous feature of AGNs; (b) Emphasis on late-type spiral and dwarf galaxies, as the galaxies most likely to have low-mass SMBHs; (c) Use of multiwavelength data to verify the source is an AGN; and (d) Use of the highest angular resolution available for observations in x-rays and other bands, to separate nuclear from off-nuclear sources and to minimize contamination by host galaxy light. Here we show the feasibility of this technique to find AGNs by applying it to six nearby, face-on spiral galaxies (NGC 3169, NGC 3184, NGC 4102, NGC 4647, NGC 4713, NGC 5457) for which data already exist in the Chandra archive. All six show nuclear x-ray sources. The data as they exist at present are ambiguous regarding the nature of the nuclear x-ray sources in NGC 4713 and NGC 4647. We conclude, in accord with previous studies, that NGC 3169 and NGC 4102 are almost certainly AGNs. Most interestingly, a strong argument can be made that NGC 3184 and NGC 5457, both of type Scd, host AGNs.
We compile one of the largest ever samples to probe the X-ray normal galaxy luminosity function and its evolution with cosmic time. In particular, we select 207 galaxies (106 late and 101 early-type systems) from the Chandra Deep Field North and South surveys, the Extended Chandra Deep Field South and the XBOOTES survey. We derive the luminosity function separately for the total (early+late), the early and the late-type samples using both a parametric maximum likelihood method, and a variant of the non-parametric 1/V_m method. Although the statistics is limited, we find that the total (early+late) galaxy sample is consistent with a Pure Luminosity evolution model where the luminosity evolves according to L(z) ~ (1+z)^2.2. The late-type systems appear to drive this trend while the early-type systems show much weaker evidence for evolution. We argue that the X-ray evolution of late-type systems is consistent with that of blue galaxies in the optical. In contrast there is a mismatch between the X-ray evolution of early-type systems and that of red galaxies at optical wavelengths.
Studies of nearby elliptical and S0 galaxies reveal that roughly half of the low mass X-ray binaries (LMXBs), which are luminous tracers of accreting neutron star or black hole systems, are in clusters. There is a surprising tendency of LMXBs to be preferentially associated with metal-rich globular clusters (GCs), with metal-rich GCs hosting three times as many LMXBs as metal-poor ones. There is no convincing evidence of a correlation with GC age so far. In some galaxies the LMXB formation rate varies with GC color even within the metal-rich peak of the typical bimodal cluster metallicity distribution. This provides some of the strongest evidence to date that there are metallicity variations within the metal-rich GC peak, as is expected in hierarchical galaxy formation scenarios. We also note that apparent correlations between the interaction rates in GCs and LMXB frequency may not be reliable because of the uncertainties in some GC parameters. We argue in fact that there are considerable uncertainties in the integrated properties of even the Milky Way clusters that are often overlooked.
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons has different properties than synchrotron radiation which assumes a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
We use the Spitzer Space Telescope to search for infrared excess at 24, 70, and 160 micron due to debris disks around a sample of 45 FGK-type members of the Hyades cluster. We supplement our observations with archival 24 and 70 micron Spitzer data of an additional 22 FGK-type and 11 A-type Hyades members in order to provide robust statistics on the incidence of debris disks at 625 Myr of age an era corresponding to the late heavy bombardment in the Solar System. We find that none of the 67 FGK-type stars in our sample show evidence for a debris disk, while 2 out of the 11 A-type stars do so. This difference in debris disk detection rate is likely to be due to a sensitivity bias in favor of early-type stars. The fractional disk luminosity, L_dust/L*, of the disks around the two A-type stars is ~4x10E-5, a level that is below the sensitivity of our observations toward the FGK-type stars. However, our sensitivity limits for FGK-type stars are able to exclude, at the 2-sigma level, frequencies higher than 12% and 5% of disks with L_dust/L* > 10E-4 and L_dust/L* > 5x10E-4, respectively. We also use our sensitivity limits and debris disk models to constrain the maximum mass of dust, as a function of distance from the stars, that could remain undetected around our targets.
We calculate the contribution of cosmic strings arising from a phase transition in the early universe, or cosmic superstrings arising from brane inflation, to the cosmic 21 cm power spectrum at redshifts z > 30. Future experiments can exploit this effect to constrain the cosmic string tension Gu and probe virtually the entire brane inflation model space allowed by current observations. Although current experiments with a collecting area of ~ 1 km^2 will not provide any useful constraints, future experiments with a collecting area of 10^4-10^6 km^2 covering the cleanest 10% of the sky can in principle constrain cosmic strings with tension Gu > 10^(-10) to 10^(-12) (superstring/phase transition mass scale >10^13 GeV).
We investigate the tidal interaction between a low-mass planet and a self-gravitating protoplanetary disk, by means of two-dimensional hydrodynamic simulations. We first show that considering a planet freely migrating in a disk without self-gravity leads to a significant overestimate of the migration rate. The overestimate can reach a factor of two for a disk having three times the surface density of the minimum mass solar nebula. Unbiased drift rates may be obtained only by considering a planet and a disk orbiting within the same gravitational potential. In a second part, the disk self-gravity is taken into account. We confirm that the disk gravity enhances the differential Lindblad torque with respect to the situation where neither the planet nor the disk feels the disk gravity. This enhancement only depends on the Toomre parameter at the planet location. It is typically one order of magnitude smaller than the spurious one induced by assuming a planet migrating in a disk without self-gravity. We confirm that the torque enhancement due to the disk gravity can be entirely accounted for by a shift of Lindblad resonances, and can be reproduced by the use of an anisotropic pressure tensor. We do not find any significant impact of the disk gravity on the corotation torque.
We present an analysis of the Suzaku observation of the northeastern rim of the Cygnus Loop supernova remnant. The high detection efficiency together with the high spectral resolution of the Suzaku X-ray CCD camera enables us to detect highly-ionized C and N emission lines from the Cygnus Loop. Given the significant plasma structure within the Suzaku field of view, we selected the softest region based on ROSAT observations. The Suzaku spectral data are well characterized by a two-component non-equilibrium ionization model with different best-fit values for both the electron temperature and ionization timescale. Abundances of C to Fe are all depleted to typically 0.23 times solar with the exception of O. The abundance of O is relatively depleted by an additional factor of two compared with other heavy elements. We found that the resonance-line-scattering optical depth for the intense resonance lines of O is significant and, whereas the optical depth for other resonance lines is not as significant, it still needs to be taken into account for accurate abundance determination.
Astrometric observations of resolved binaries provide estimates of orbital
periods and will eventually lead to measurement of dynamical masses. Only a few
very low mass star and brown dwarf masses have been measured to date, and the
mass-luminosity relation still needs to be calibrated.
We have monitored 14 very low mass multiple systems for several years to
confirm their multiplicity and, for those with a short period, derive accurate
orbital parameters and dynamical mass estimates.
We have used high spatial resolution images obtained at the Paranal, Lick and
HST observatories to obtain astrometric and photometric measurements of the
multiple systems at several epochs. The targets have periods ranging from 5 to
200 years, and spectral types in the range M7.5 - T5.5.
All of our 14 multiple systems are confirmed as common proper motion pairs.
One system (2MASSW J0920122+351742) is not resolved in our new images, probably
because the discovery images were taken near maximum elongation. Six systems
have periods short enough to allow dynamical mass measurements within the next
15 to 20years. We estimate that only 8% of the ultracool dwarfs in the solar
neighborhood are binaries with separations large enough to be resolved, and yet
periods short enough to derive astrometric orbital fits over a reasonable time
frame with current instrumentation. A survey that doubles the number of
ultracool dwarfs observed with high angular resolution is called for to
discover enough binaries for a first attempt to derive the mass-luminosity
relationship for very low-mass stars and brown dwarfs.
The proposed design for PILOT is a general-purpose, wide-field 1 degree 2.4m, f/10 Ritchey-Chretien telescope, with fast tip-tilt guiding, for use 0.5-25 microns. The design allows both wide-field and diffraction-limited use at these wavelengths. The expected overall image quality, including median seeing, is 0.28-0.3" FWHM from 0.8-2.4 microns. Point source sensitivities are estimated.
Cosmic shear offers a remarkbly clean way to measure the equation of state of
the Universe and its evolution. Resolution over a wide field is paramount, and
Antarctica offers unique possibilities in this respect. There is an order of
magnitude gain in speed over temperate sites, or a factor three in surface
density. This means that PILOT outperforms much larger telescopes elsewhere,
and can compete with the proposed DUNE space mission.
Keywords: Antarctic astronomy, Surveys, Adaptive optics, Weak lensing
The millimeter-wave rotational emission lines (4(04)-3(03) and 5(05)-4(04)) of protonated carbon dioxide, HCO2+(HOCO+), has been detected toward the low-mass class 0 protostar IRAS 04368+2557 in L1527 with the IRAM 30 m telescope. This is the first detection of HCO2+ except for the Galactic Center clouds. The column density of HCO2+ averaged over the beam size (29") is determined to be 7.6x10^10 cm^-2, assuming the rotational temperature of 12.3 K. The fractional abundance of gaseous CO2 relative to H2 is estimated from the column density of HCO2+ with an aid of a simplified chemical model. If the HCO2+ emission only comes from the evaporation region of CO2 near the protostar (T>50 K), the fractional abundance of CO2 is estimated to be higher than 6.6x10^-4. This is comparable to the elemental abundance of carbon in interstellar clouds, and hence, the direct evaporation of CO2 from dust grain is unrealistic as a source of gaseous CO2 in L1527. A narrow line width of HCO2+ also supports this. On the other hand, the fractional abundance of CO2 is estimated to be 2.9x10^-7, if the source size is comparable to the beam size. These results indicate that gaseous CO2 is abundant even in the low-mass star-forming region. Possible production mechanisms of gaseous CO2 are discussed.
A clear detection of excess of power, providing a substantial evidence for solar-like oscillations in the G5 subgiant \muher{}, is presented. This star was observed over seven nights with the SARG echelle spectrograph operating with the 3.6-m Italian TNG Telescope, using an iodine absorption cell as a velocity reference. A clear excess of power centered at 1.2 mHz, with peak amplitudes of about 0.9 \ms in the amplitude spectrum is present. Fitting the asymptotic relation to the power spectrum, a mode identification for the $\ell=0,1,2,3$ modes in the frequency range $900-1600 \muHz$ is derived. The most likely value for the large separation turns out to be 56.5 \muHz, consistent with theoretical expectations. The mean amplitude per mode ($l=0,1$) at peak power results to be $0.63 \rm m s^{-1}$, almost three times larger than the solar one.
At the surface of the Sun, acoustic waves appear to be affected by the presence of strong magnetic fields in active regions. We explore the possibility that the inclined magnetic field in sunspot penumbrae may convert primarily vertically propagating acoustic waves into elliptical motion. We use helioseismic holography to measure the modulus and phase of the correlation between incoming acoustic waves and the local surface motion within two sunspots. These correlations are modeled assuming the surface motion is elliptical, and we explore the properties of the elliptical motion on the magnetic field inclination. We also demonstrate that the phase shift of the outward propagating waves is opposite to the phase shift of the inward propagating waves in stronger, more vertical fields, but similar to the inward phase shifts in weaker, more inclined fields.
The planets Uranus and Neptune with small apparent diameters are primary calibration standards. We investigate their variability at ~90 GHz using archived data taken at the IRAM 30m telescope during the 20 years period 1985 to 2005. We calibrate the planetary observations against non-variable secondary standards (NGC7027, NGC7538, W3OH, K3-50A) observed almost simultaneously. Between 1985 and 2005, the viewing angle of Uranus changed from south-pole to equatorial. We find that the disk brightness temperature declines by almost 10% (~2sigma) over this time span indicating that the south-pole region is significantly brighter than average. Our finding is consistent with recent long-term radio observations at 8.6 GHz by Klein & Hofstadter (2006). Both data sets do moreover show a rapid decrease of the Uranus brightness temperature during the year 1993, indicating a temporal, planetary scale change. We do not find indications for a variation of Neptune's brightness temperature at the 8% level. If Uranus is to be used as calibration source, and if accuracies better than 10% are required, the Uranus sub-earth point latitude needs to be taken into account.
We report on a correlation between virial mass M and spin parameter lambda for dark matter halos forming at redshifts z > 10. We find that the spin parameter decreases with increasing halo mass. Interestingly, our analysis indicates that halos forming at later times do not exhibit such a strong correlation, in agreement with the findings of previous studies. We briefly discuss the implications of this correlation for galaxy formation at high redshifts and the galaxy population we observe today.
A variety of magnetohydrodynamic mechanisms that may play a role in magnetic, chemically peculiar (mCP) stars is reviewed. These involve dynamo mechanisms in laminar flows as well as turbulent environments, and magnetic instabilities of poloidal and toroidal fields as well as combinations of the two. While the proto-stellar phase makes the survival of primordial fields difficult, the variety of magnetic field configurations on mCP stars may be an indication for that they are instability remnants, but there is no process which is clearly superior in explaining the strong fields.
Context: Hyper-velocity stars move so fast that only a supermassive black hole (SMBH) seems to be capable to accelerate them. Hence the Galactic centre (GC) is their only suggested place of origin. Edelmann et al. (2005) found the early B-star HE0437-5439 to be too short-lived to have reached its current position in the Galactic halo if ejected from the GC, except if being a blue straggler. Its proximity to the LMC suggested an origin from this galaxy. Aims: The chemical signatures of stars at the GC are significantly different from those in the LMC. Hence, an accurate measurement of the abundance pattern of HE0437-5439 will yield a new tight constraint on the place of birth of this star. Methods: High-resolution spectra obtained with UVES on the VLT are analysed using state-of-the-art non-LTE modelling techniques. Results: We measured abundances of individual elements to very high accuracy in HE0437-5439 as well as in two reference stars, from the LMC and the solar neighbourhood. The abundance pattern is not consistent at all with that observed in stars near the GC, ruling our an origin from the GC. However, there is a high degree of consistency with the LMC abundance pattern. Our abundance results cannot rule out an origin in the outskirts of the Galactic disk. However, we find the life time of HE0437-5439 to be more than 3 times shorter than the time of flight to the edge of the disk, rendering a Galactic origin unlikely. Conclusions: Only one SMBH is known to be present in Galaxy and none in the LMC. Hence the exclusion of an GC origin challenges the SMBH paradigm. We conclude that there must be other mechanism(s) to accelerate stars to hyper-velocity speed than the SMBH. We draw attention to dynamical ejection from dense massive clusters, that has recently been proposed by Gvaramadze et al. (2008).
Since GRBs fade rapidly, it is important to publish accurate, precise positions at early times. For Swift-detected bursts, the best promptly available position is most commonly the X-ray Telescope (XRT) position. We present two processes, developed by the Swift team at Leicester, which are now routinely used to improve the precision and accuracy of the XRT positions reported by the Swift team. Both methods, which are fully automated, make use of a PSF-fitting approach which accounts for the bad columns on the CCD. The first method yields positions with 90% error radii <4.4" 90% of the time, within 10--20 minutes of the trigger. The second method astrometrically corrects the position using UVOT field stars and the known mapping between the XRT and UVOT detectors, yielding enhanced positions with 90% error radii of <2.8" 90% of the time, usually ~2 hours after the trigger.
Published data for large amplitude asymptotic giant branch variables in the
Large Magellanic Cloud are re-analysed to establish the constants for an
infrared (K) period-luminosity relation of the form: Mk=rho[log P-2.38] +
delta. A slope of rho=-3.51+/-0.20 and a zero point of delta=-7.15+/-0.06 are
found for oxygen-rich Miras (if a distance modulus of 18.39+/-0.05 is used for
the LMC). Assuming this slope is applicable to Galactic Miras we discuss the
zero-point for these stars using the revised Hipparcos parallaxes together with
published VLBI parallaxes for OH Masers and Miras in Globular Clusters. These
result in a mean zero-point of delta=-7.25+/-0.07 for O-rich Galactic Miras.
The zero-point for Miras in the Galactic Bulge is not significantly different
from this value.
Carbon-rich stars are also discussed and provide results that are consistent
with the above numbers, but with higher uncertainties. Within the uncertainties
there is no evidence for a significant difference between the period-luminosity
relation zero-points for systems with different metallicity.
Formation of circumstellar lines of Na I and Ca II in type Ia supernovae is studied for the case, when supernova explodes in a binary system with a red giant. The model suggests a spherically-symmetric wind and takes into account ionization and heating of the wind by X-rays from the shock wave and by gamma-quanta of ^{56}Ni radioactive decay. For the wind density typical of the red giant the expected optical depth of the wind in Na I lines turnes out too low (\tau<0.001}) to detect the absorption. For the same wind densities the predicted optical depth of Ca II 3934 \AA is sufficient for the detection (\tau>0.1). I conclude that the absorption lines detected in SN 2006X cannot form in the red giant wind; they are rather related to clouds at distances larger than the dust evaporation radius (r>10^{17} cm). From the absence in SN 2006X of Ca II absorption lines not related with the similar Na I components I derive the upper limit of the mass loss rate by the wind with velocity u: \dot{M}<10^{-8}(u/10 km/s) M_{\odot} yr^{-1}.
We consider the influence of microlensing on different spectral bands of lensed QSOs. We assumed that the emitting X-ray, UV and optical regions are different in size, but that the continuum emission in these spectral bands is originating from an accretion disc. Estimations of the time scales for microlensing and flux amplification in different bands are given. We found that the microlensing duration should be shorter in the X-ray (several months) than in UV/optical emitting region (several years). This result indicates that monitoring of the X-ray variations in lensed QSOs that show a 'flux anomaly' can clarify the source of this anomaly.
We report on 2MASS J01542930+0053266, a faint eclipsing system composed of two M dwarfs. The variability of this system was originally discovered during a pilot study of the 2MASS Calibration Point Source Working Database. Additional photometry from the Sloan Digital Sky Survey yields an 8-passband lightcurve, from which we derive an orbital period of 2.6390157 +/- 0.0000016 days. Spectroscopic followup confirms our photometric classification of the system, which is likely composed of M0 and M1 dwarfs. Radial velocity measurements allow us to derive the masses (M_1 = 0.66 +/- 0.03 M_sun; M_2 = 0.62 +/- 0.03 M_sun) and radii (R_1 = 0.64 +/- 0.08 R_sun; R_2 = 0.61 +/- 0.09 R_sun) of the components, which are consistent with empirical mass-radius relationships for low-mass stars in binary systems. We perform Monte Carlo simulations of the lightcurves which allow us to uncover complicated degeneracies between the system parameters. Both stars show evidence of H-alpha emission, something not common in early-type M dwarfs. This suggests that binarity may influence the magnetic activity properties of low-mass stars; activity in the binary may persist long after the dynamos in their isolated counterparts have decayed, yielding a new potential foreground of flaring activity for next generation variability surveys.
The Alpha Magnetic Spectrometer (AMS) to be installed on the International Space Station (ISS) will be equipped with a proximity Ring Imaging Cherenkov (RICH) detector for measuring the velocity and electric charge of the charged cosmic particles. This detector will contribute to the high level of redundancy required for AMS as well as to the rejection of albedo particles. Charge separation up to iron and a velocity resolution of the order of 0.1% for singly charged particles are expected. A RICH protoptype consisting of a detection matrix with 96 photomultiplier units, a segment of a conical mirror and samples of the radiator materials was built and its performance was evaluated. Results from the last test beam performed with ion fragments resulting from the collision of a 158 GeV/c/nucleon primary beam of indium ions (CERN SPS) on a lead target are reported. The large amount of collected data allowed to test and characterize different aerogel samples and the sodium fluoride radiator. In addition, the reflectivity of the mirror was evaluated. The data analysis confirms the design goals.
We have studied the non-resonant streaming instability of charged energetic particles moving through a background plasma, discovered by Bell (2004). We confirm his numerical results regarding a significant magnetic field amplification in the system. A detailed physical picture of the instability development and of the magnetic field evolution is given.
We investigate the diffusive shock acceleration in the presence of the non-resonant streaming instability introduced by Bell (2004). The numerical MHD simulations of the magnetic field amplification combined with the analytical treatment of cosmic ray acceleration permit us to calculate the maximum energy of particles accelerated by high-velocity supernova shocks. The estimates for Cas A, Kepler, SN1006, and Tycho historical supernova remnants are given. We also found that the amplified magnetic field is preferentially oriented perpendicular to the shock front downstream of the fast shock. This explains the origin of the radial magnetic fields observed in young supernova remnants.
Evolutionary models for massive stars, accounting for rotational mixing effects, do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. Contrary to theoretical expectations, we present a detailed and fully-homogeneous, NLTE abundance analysis of 20 early B-type dwarfs and (sub)giants that reveals the existence of a population of nitrogen-rich and boron-depleted, yet intrinsically slowly-rotating objects. The low-rotation rate of several of these stars is firmly established, either from the occurrence of phase-locked UV wind line-profile variations, which can be ascribed to rotational modulation, or from theoretical modelling in the pulsating variables. The observational data presently available suggest a higher incidence of chemical peculiarities in stars with a (weak) detected magnetic field. This opens the possibility that magnetic phenomena are important in altering the photospheric abundances of early B dwarfs, even for surface field strengths at the one hundred Gauss level. However, further spectropolarimetric observations are needed to assess the validity of this hypothesis.
Chandra and XMM surveys show that the fraction of obscured AGN decreases rapidly with increasing luminosity. Although this is usually explained by assuming that the covering factor of the central engine is much smaller at luminous QSOs, the exact origin of this effect remains unknown. We perform toy simulations to test whether photo-ionisation of the obscuring screen in the presence of a strong radiation field can reproduce this effect. In particular, we create X-ray spectral simulations using a warm absorber model assuming a range of input column densities and ionization parameters. We fit instead the simulated spectra with a simple cold absorption power-law model that is the standard practice in X-ray surveys. We find that the fraction of absorbed AGN should fall with luminosity as $L^{-0.16\pm0.03}$ in rough agreement with the observations. Furthermore, this apparent decrease in the obscuring material is consistent with the dependence of the FeK$\alpha$ narrow-line equivalent width on luminosity, ie. the X-ray Baldwin effect.
APEX single-dish observations at sub-millimeter wavelengths toward a sample of massive star-forming regions reveal that C2H is almost omni-present toward all covered evolutionary stages from Infrared Dark Clouds via High-Mass Protostellar Objects to Ultracompact HII regions. High-resolution data from the Submillimeter Array toward one hot-core like High-Mass Protostellar Object show a shell-like distribution of C2H with a radius of ~9000AU around the central submm peak position. These observed features are well reproduced by a 1D cloud model with power-law density and temperature distributions and a gas-grain chemical network. The reactive C2H radical (ethynyl) is abundant from the onset of massive star formation, but later it is rapidly transformed to other molecules in the core center. In the outer cloud regions the abundance of C2H remains high due to constant replenishment of elemental carbon from CO being dissociated by the interstellar UV photons. We suggest that C2H may be a molecule well suited to study the initial conditions of massive star formation.
Archeops is a balloon-borne experiment, mainly designed to measure the Cosmic Microwave Background (CMB) temperature anisotropies at high angular resolution (~ 12 arcminutes). By-products of the mission are shallow sensitivity maps over a large fraction of the sky (about 30 %) in the millimetre and submillimetre range at 143, 217, 353 and 545 GHz. From these maps, we produce a catalog of bright submillimetre point sources. We present in this paper the processing and analysis of the Archeops point sources. Redundancy across detectors is the key factor allowing to sort out glitches from genuine point sources in the 20 independent maps. We look at the properties of the most reliable point sources, totalling 304. Fluxes range from 1 to 10,000 Jy (at the frequencies covering 143 to 545 GHz). All sources are either planets (2) or of galactic origin. Longitude range is from 75 to 198 degrees. Some of the sources are associated with well-known Lynds Nebulae and HII compact regions in the galactic plane. A large fraction of the sources have an IRAS counterpart. Except for Jupiter, Saturn, the Crab and CasA, all sources show a dust-emission-like modified blackbody emission spectrum. Temperatures cover a range from 7 to 27 K. For the coldest sources (T<10 K), a steep nu^beta emissivity law is found with a surprising beta ~ 3 to 4. An inverse relationship between T and beta is observed. The number density of sources at 353 GHz with flux brighter than 100 Jy is of the order of 1 per degree of Galactic longitude. These sources will provide a strong check for the calibration of the Planck HFI focal plane geometry in complement to planets. These very cold sources observed by Archeops should be prime targets for mapping observations by the Akari and Herschel space missions and ground--based observatories.
We present measurements with the VLBA of the variability in the centroid position of Sgr A* relative to a background quasar at 7-mm wavelength. We find an average centroid wander of 71 +/- 45 micro-arcsec for time scales between 50 and 100 min and 113 +/- 50 micro-arcsec for timescales between 100 and 200 min, with no secular trend. These are sufficient to begin constraining the viability of the hot-spot model for the radio variability of Sgr A*. It is possible to rule out hot spots with orbital radii above 15GM_SgrA*/c^2, which contribute more than 30% of the total 7-mm flux. However, closer or less luminous hot spots remain unconstrained. Since the fractional variability of Sgr A* during our observations was ~20% on time scales of hours, the hot-spot model for Sgr A*'s radio variability remains consistent with these limits. Improved monitoring of Sgr A*'s centroid position has the potential to place significant constraints upon the existence and morphology of inhomogeneities in a supermassive black hole accretion flow.
Context. Blue Stragglers Stars (BSSs) are thought to form in globular clusters by two main formation channels: i) mergers induced by stellar collisions and ii) coalescence or mass-transfer between companions in binary systems. The detailed study of the BSS properties is therefore crucial for understanding the binary evolution mechanisms, and the complex interplay between dynamics and stellar evolution in dense stellar systems. Aims. We present the first comparison between the BSS specific frequency and the binary fraction in the core of a sample of Galactic globular clusters, with the aim of investigating the relative efficiency of the two proposed formation mechanisms. Methods. We derived the frequency of BSSs in the core of thirteen low-density Galactic globular clusters by using deep ACS@HST observations and investigated its correlation with the binary fraction and various other cluster parameters. Results. We observed a correlation between the BSS specific frequency and the binary fraction. The significance of the correlation increases by including a further dependence on the cluster central velocity dispersion. Conclusions. We conclude that the unperturbed evolution of primordial binaries could be the dominant BSS formation process, at least in low-density environments.
We study the anisotropy signature which is expected if the sources of ultra high energy, >10^{19} eV, cosmic-rays (UHECRs) are extragalactic and trace the large scale distribution of luminous matter. Using the PSCz galaxy catalog as a tracer of the large scale structure (LSS), we derive the expected all sky angular distribution of the UHECR intensity. We define a statistic, that measures the correlation between the predicted and observed UHECR arrival direction distributions, and show that it is more sensitive to the expected anisotropy signature than the power spectrum and the two point correlation function. The distribution of the correlation statistic is not sensitive to the unknown redshift evolution of UHECR source density and to the unknown strength and structure of inter-galactic magnetic fields. We show, using this statistic, that recently published >5.7x10^{19} eV Auger data are inconsistent with isotropy at ~98% CL, and consistent with a source distribution that traces LSS, with some preference to a source distribution that is biased with respect to the galaxy distribution. The anisotropy signature should be detectable also at lower energy, >4x10^{19} eV. A few fold increase of the Auger exposure is likely to increase the significance to >99% CL, but not to >99.9% CL (unless the UHECR source density is comparable or larger than that of galaxies). In order to distinguish between different bias models, the systematic uncertainty in the absolute energy calibration of the experiments should be reduced to well below the current ~25%.
Models with dark energy decaying into dark matter have been proposed to solve the coincidence problem in cosmology. We study the effect of such coupling in the cosmic microwave background temperature anisotropies. The interaction changes the rate of evolution of the metric potentials, the growth rate of matter density perturbations and modifies the Integrated Sachs-Wolfe component of cosmic microwave background temperature anisotropies. We show that cross-correlation of galaxy catalogs with CMB maps provides a model independent test to constrain the interaction. We particularize our analysis for a specific interacting model and show that an all-sky galaxy catalog with a median redshift $z_m=0.1$ could provide an upper limit on the amplitude of the interaction at $c^2\le 0.1$ at the $4\sigma$ confidence level. We also show that the effect of the interaction is to increase the rate of evolution of matter density perturbations at low redshift. This change could provide an explanation to the discrepancy between the fraction of dark energy measured with WMAP 3yr data and this fraction obtained from the ISW effect.
We compare magnetic field extrapolations from a photospheric magnetogram with the observationally inferred structure of magnetic loops in a newly developed active region. This is the first time that the reconstructed 3D-topology of the magnetic field is available to test the extrapolations. We compare the observations with potential fields, linear force-free fields and non-linear force-free fields. This comparison reveals that a potential field extrapolation is not suitable for a reconstruction of the magnetic field in this young, developing active region. The inclusion of field-line-parallel electric currents, the so called force-free approach, gives much better results. Furthermore, a non-linear force-free computation reproduces the observations better than the linear force-free approximation, although no free parameters are available in the former case.
We report H-alpha observations of zeta Tauri, taken between late 2000 and early 2006. Next to extending existing long-term montioring of the disk state of this star we report an intermediate timescale of about 69 days to be present in the V/R variations of the Halpha line. The observational data will be published together with this manuscript.
This paper summarizes highlights of the OG1 session of the 30th International Cosmic Ray Conference, held in Merida (Yucatan, Mexico). The subsessions (OG1.1, OG1.2, OG1.3, OG1.4 and OG1.5) summarized here were mainly devoted to direct measurements, acceleration and propagation of cosmic rays.
We derive the SZ effect arising in radio-galaxy lobes that are filled with high-energy, non-thermal electrons. We provide here quantitative estimates for SZ effect expected from the radio galaxy lobes by normalizing it to the Inverse-Compton light, observed in the X-ray band, as produced by the extrapolation to low energies of the radio emitting electron spectrum in these radio lobes. We compute the spectral and spatial characteristics of the SZ effect associated to the radio lobes of two distant radio galaxies (3C294 and 3C432) recently observed by Chandra, and we further discuss its detectability with the next generation microwave and sub-mm experiments with arcsec and $\sim \mu$K sensitivity. We finally highlight the potential use of the SZE from radio-galaxy lobes in the astrophysical and cosmological context.
We present two-dimensional (radial velocity, orbital phase) spectroscopic results for the very low mass-ratio close binary AW UMa which strongly indicate that the spectroscopic mass ratio (q_sp = 0.10) does not agree with the photometrically derived one and that the widely adopted contact binary model appears to experience serious inconsistencies and limitations for this object. AW UMa is compared with V566 Oph (q_sp = 0.26) which we found to behave according to the contact model. Observed broadening functions of AW UMa can be interpreted by a very strong limb darkening and/or non-solid body rotation of the dominant primary component; the former assumption is unphysical while the differential rotation is not supported by an apparent stability of localized, dark features on the outer side of the primary. There are indications of the existence of an equatorial belt encompassing the whole system. All deficiencies in the interpretation and the discrepancy between the photometric and spectroscopic mass ratio of AW UMa can be solved within a new model of AW UMa where both components are detached and the system is submerged in a stream of hot, optically thick matter which mimics the stellar contact. While the masses and their ratio are correctly given by spectroscopy, the photometric picture is heavily modified by the matter engulfing both stars in the equatorial plane.
We report the discovery of a new open cluster (OC) in the Galaxy at $\ell=167.0^\circ$ and $b=-1.0^\circ$. Its field includes the planetary nebula (PN) PK 167-0.1. We study the possible associations of the PN/OC pairs NGC 2818/NGC 2818A, NGC 2438/M 46 (NGC 2437), PK 6+2.5/NGC 6469, as well as of the PN PK 167-0.1 with New Cluster 1. The analyses are based on near-infrared colour-magnitude diagrams (CMDs) and stellar radial density profiles (RDPs). NGC 6469 is located in a heavily contaminated bulge field. The CMD morphology, especially for the latter two cases, is defined with a field star decontamination algorithm applied to the 2MASS \jj, \hh, and \ks photometry. Field decontamination for the OCs NGC 2818A and M 46 produced better defined CMDs and more accurate cluster parameters than in the literature. Those pieces of evidence point to M 46 as physically associated with the PN NGC 2438. The same occurs for the OC NGC 2818A and the PN NGC 2818, however previous radial velocity arguments indicate that they are not associated. The OC NGC 6469 does not appear to be associated with the PN PK 6+2.5, which probably belongs to the bulge. Finally, the distance of the OC New Cluster 1 is consistent with a physical association with the PN PK 167-0.1.
This paper is the written version of the rapporteur talk on Section HE-2, muons and neutrinos, presented at the 30th International Cosmic Ray Conference, Merida, Yucatan, July 11, 2007. Topics include atmospheric muons and neutrinos, solar neutrinos and astrophysical neutrinos as well as calculations and instrumentation related to these topics.
The Roma International Conference on Astroparticle Physics covered gamma-ray astronomy, air shower experiments and neutrino astronomy on three successive days. I organize my brief summary comments into four topics that cut across these three techniques. They are detector calibration, galactic sources, extra-galactic sources and cosmology.
Massive hot stars produce dense ultraviolet (UV) photon fields in their surroundings. If a very high-energy (VHE) gamma-ray emitter is located close to the star, then gamma-rays are absorbed in the stellar photon field, creating secondary (electron-positron) pairs. We study the broadband emission of these secondary pairs in the stellar photon and magnetic fields. Under certain assumptions on the stellar wind and the magnetic field in the surroundings of a massive hot star, we calculate the steady state energy distribution of secondary pairs created in the system and its radiation from radio to gamma-rays. Under the ambient magnetic field, possibly high enough to suppress electromagnetic (EM) cascading, the energy of secondary pairs is radiated via synchrotron and single IC scattering producing radio-to-gamma-ray radiation. The synchrotron spectral energy distribution (SED) is hard, peaks around X-ray energies, and becomes softer. The IC SED is hard as well and peaks around 10 GeV, becoming also softer at higher energies due to synchrotron loss dominance. The radio emission from secondary pairs is moderate and detectable as a point-like and/or extended source. In X-rays, the secondary pair synchrotron component may be dominant. At energies <10 GeV, the secondary pair IC radiation may be the dominant primary gamma-ray emission and possibly detectable by the next generation of instruments.
The Cygnus X-ray Emission Spectroscopic Survey (CyXESS) sounding rocket payload was launched from White Sands Missile Range on 2006 November 20 and obtained a high resolution spectrum of the Cygnus Loop supernova remnant in the soft X-rays. The novel X-ray spectrograph incorporated a wire-grid collimator feeding an array of gratings in the extreme off-plane mount which ultimately dispersed the spectrum onto Gaseous Electron Multiplier (GEM) detectors. This instrument recorded 65 seconds of usable data between 43-49.5 \AA in two prominent features. The first feature near 45 \AA is dominated by the He-like triplet of \ion{O}{7} in second order with contributions from \ion{Mg}{10} and \ion{Si}{9}-\ion{Si}{12} in first order, while the second feature near 47.5 \AA is first order \ion{S}{9} and \ion{S}{10}. Fits to the spectra give an equilibrium plasma at $\log(T)=6.2$ ($kT_e=0.14$ keV) and near cosmic abundances. This is consistent with previous observations, which demonstrated that the soft x-ray emission from the Cygnus Loop is dominated by interactions between the initial blast wave with the walls of a precursor formed cavity surrounding the Cygnus Loop and that this interaction can be described using equilibrium conditions.
Motivated by Higgs Portal and Hidden Valley models, heavy particle dark matter that communicates with the supersymmetric Standard Model via pure Higgs sector interactions is considered. We show that a thermal relic abundance consistent with the measured density of dark matter is possible for masses up to $\sim$ 30 TeV. For dark matter masses above $\sim$ 1 TeV, non-perturbative Sommerfeld corrections to the annihilation rate are large, and have the potential to greatly affect indirect detection signals. For large dark matter masses, the Higgs-dark matter sector couplings are large and we show how such models may be given a UV completion within the context of so-called "Fat-Higgs" models. Higgs Portal dark matter provides an example of an attractive alternative to conventional MSSM neutralino dark matter that may evade discovery at the LHC, while still being within the reach of current and upcoming indirect detection experiments.
Applying the Thomas-Fermi approximation to renormalizable field theories, we construct ghost condensation models that are free of the instabilities associated with violations of the null-energy condition.
We show that hidden-sector dark matter is a generic feature of the type IIB string theory landscape and that its lifetime may allow for a discovery through the observation of very energetic gamma-rays produced in the decay. Throats or, equivalently, conformally sequestered hidden sectors are common in flux compactifications and the energy deposited in these sectors can be calculated if the reheating temperature of the standard model sector is known. Assuming that throats with various warp factors are available in the compact manifold, we determine which throats maximize the late-time abundance of sequestered dark matter. For such throats, this abundance agrees with cosmological data if the standard model reheating temperature was 10^10 - 10^11 GeV. In two distinct scenarios, the mass of dark matter particles, i.e. the IR scale of the throat, is either around 10^5 GeV or around 10^10 GeV. The lifetime and the decay channels of our dark matter candidates depend crucially on the fact that the Klebanov-Strassler throat is supersymmetric. Furthermore, the details of supersymmetry breaking both in the throat and in the visible sector play an essential role. We identify a number of scenarios where this type of dark matter can be discovered via gamma-ray observations.
We study the stability of the isotropic vacuum Friedmann universe in gravity theories with higher-order curvature terms of the form $(R_{ab}R^{ab})^{n}$ added to the Einstein-Hilbert Lagrangian of general relativity on approach to an initial cosmological singularity. Earlier, we had shown that, when $% n=1$, a special isotropic vacuum solution exists which behaves like the radiation-dominated Friedmann universe and is stable to anisotropic and small inhomogeneous perturbations of scalar, vector and tensor type. This is completely different to the situation that holds in general relativity, where an isotropic initial cosmological singularity is unstable in vacuum and under a wide range of non-vacuum conditions. We show that when $n\neq 1$, although a special isotropic vacuum solution found by Clifton and Barrow always exists, it is no longer stable when the initial singularity is approached. We find the particular stability conditions under the influence of tensor, vector, and scalar perturbations for general $n$ for both solution branches. On approach to the initial singularity, the isotropic vacuum solution with scale factor $a(t)=t^{P_{-}/3}$ is found to be stable to tensor perturbations for $0.5<n< 1.1309$ and stable to vector perturbations for $0.861425 < n \leq 1$, but is unstable as $t \to 0$ otherwise. The solution with scale factor $a(t)=t^{P_{+}/3}$ is not relevant to the case of an initial singularity for $n>1$ and is unstable as $t \to 0$ for all $n$ for each type of perturbation.
We argue that Einstein gravity coupled to a Born-Infeld theory provides an attractive candidate to represent dark matter and dark energy. For cosmological models, the Born-Infeld field has an equation of state which interpolates between matter, $p=0$ (small times), and a cosmological constant $p=-\rho$ (large times). On galactic scales, the Born-Infeld field predicts asymptotically flat rotation curves.
If the spontaneous breaking of Peccei-Quinn symmetry comes from soft supersymmetry breaking, the fermionic partners of the symmetry-breaking fields have mass of order the gravitino mass, and are called flatinos. The lightest flatino, called here the flaxino, is a CDM candidate if it is the lightest supersymmetric particle. We here explore flaxino dark matter assuming that the lightest ordinary supersymmetric particle is the stau, with gravity-mediated supersymmetry breaking. The decay of the stau to the flaxino is fast enough not to spoil the standard predictions of Big Bang Nucleosynthesis, and its track and decay can be seen in future colliders.
The reheating of the universe after hybrid inflation proceeds through the nucleation and subsequent collision of large concentrations of energy density in the form of bubble-like structures moving at relativistic speeds. This generates a significant fraction of energy in the form of a stochastic background of gravitational waves, whose time evolution is determined by the successive stages of reheating: First, tachyonic preheating makes the amplitude of gravity waves grow exponentially fast. Second, bubble collisions add a new burst of gravitational radiation. Third, turbulent motions finally sets the end of gravitational waves production. From then on, these waves propagate unimpeded to us. We find that the fraction of energy density today in these primordial gravitational waves could be significant for GUT scale models of inflation, although well beyond the frequency range sensitivity of gravitational wave observatories like LIGO, LISA or BBO. However, low-scale models could still produce a detectable signal at frequencies accessible to BBO or DECIGO. For comparison, we have also computed the analogous background from some chaotic inflation models and obtained similar results to those of other groups. The discovery of such a background would open a new observational window into the very early universe, where the details of the process of reheating could be explored. Thus, it could also serve as a new experimental tool for testing the Inflationary Paradigm.
The proton-proton fusion reaction, $pp\to de^+\nu$, is studied in pionless effective field theory (EFT) with di-baryon fields up to next-to leading order. With the aid of the di-baryon fields, the effective range corrections are naturally resummed up to the infinite order and thus the calculation is greatly simplified. Furthermore, the low-energy constant which appears in the axial-current-di-baryon-di-baryon contact vertex is fixed through the ratio of two- and one-body matrix elements which reproduces the tritium lifetime very precisely. As a result we can perform a parameter free calculation for the process. We compare our numerical result with those from the accurate potential model and previous pionless EFT calculations, and find a good agreement within the accuracy better than 1%.
Links to: arXiv, form interface, /find, astro-ph, /recent, /0801, /abs, contact, help (Access key information)
We present a survey of bright optical dropout sources in two deep, multiwavelength surveys comprising eleven widely-separated fields, aimed at constraining the galaxy luminosity function at z~7 for sources at 5-10L*(z=6). Our combined survey area is 225 arcmin^2 to a depth of J=24.2 (AB, 3 sigma) and 135 arcmin^2 to J=25.3 (AB, 4 sigma). We find that infrared data longwards of 2 microns is essential for classifying optical dropout sources, and in particular for identifying cool Galactic star contaminants. Our limits on the number density of high redshift sources are consistent with current estimates of the Lyman break galaxy luminosity function at z=6.
Narrow Line Seyfert 1 galaxies (NLS1s) are generally considered peculiar objects among the broad class of Type 1 active galactic nuclei, due to the relatively small width of the broad lines, strong X-ray variability, soft X-ray continua, weak [OIII], and strong FeII line intensities. The mass M_BH of the central massive black hole (MBH) is claimed to be lighter than expected from known MBH-host galaxy scaling relations, while the accretion rate onto the MBH larger than the average value appropriate to Seyfert 1 galaxies. In this Letter, we show that NLS1 peculiar M_BH and L/L_Edd turn out to be fairly standard, provided that the broad line region is allowed to have a disc-like, rather than isotropic, geometry. Assuming that NLS1s are rather ``normal'' Seyfert 1 objects seen along the disc axis, we could estimate the typical inclination angles from the fraction of Seyfert 1 classified as NLS1s, and compute the geometrical factor relating the observed FWHM of broad lines to the virial mass of the MBH. We show that the geometrical factor can fully account for the "black hole mass deficit" observed in NLS1s, and that L/L_Edd is (on average) comparable to the value of the more common broad line Seyfert 1 galaxies.
Planets embedded in optically thick passive accretion disks are expected to produce perturbations in the density and temperature structure of the disk. We calculate the magnitudes of these perturbations for a range of planet masses and distances. The model predicts the formation of a shadow at the position of the planet paired with a brightening just beyond the shadow. We improve on previous work on the subject by self-consistently calculating the temperature and density structures under the assumption of hydrostatic equilibrium and taking the full three-dimensional shape of the disk into account rather than assuming a plane-parallel disk. While the excursion in temperatures is less than in previous models, the spatial size of the perturbation is larger. We demonstrate that a self-consistent calculation of the density and temperature structure of the disk has a large effect on the disk model. In addition, the temperature structure in the disk is highly sensitive to the angle of incidence of stellar irradition at the surface, so accurately calculating the shape of the disk surface is crucial for modeling the thermal structure of the disk.
An arbitrary initial magnetic field in an A star evolves into a stable equilibrium. Simulations are presented of the formation of non-axisymmetric equilibria consisting of twisted flux tubes meandering under the surface of the star, and analytic arguments are given relating the stability and form of these equilibria. These results may help to explain observations of Ap stars with very non-dipolar fields. This work is also applicable to other essentially non-convective stars such as white dwarfs and neutron stars.
Galaxies are seen from different viewing angles and their observed properties change as a function of viewing angle. In many circumstances we would rather know the intrinsic properties of galaxies - those properties that do not depend on viewing angle. For a large sample of galaxies it is possible to recover the intrinsic properties of galaxies, statistically, by looking for correlations with galaxy inclination, and then applying a correction to remove those dependencies. Studying the intrinsic properties of galaxies can give a different impression of the galaxy population and help avoid the mistake of connecting observed properties to quantities that don't depend on inclination like halo mass.
In this paper we investigate the potential of 3D cosmic shear to constrain massive neutrino parameters. We find that if the total mass is substantial (near the upper limits from LSS, but setting aside the Ly alpha limit for now), then 3D cosmic shear + Planck is very sensitive to neutrino mass and one may expect that a next generation photometric redshift survey could constrain the number of neutrinos N_nu and the sum of their masses m_nu to an accuracy of dN_nu ~ 0.08 and dm_nu ~ 0.03 eV respectively. If in fact the masses are close to zero, then the errors weaken to dN_nu ~ 0.10 and dm_nu~0.07 eV. In either case there is a factor 4 improvement over Planck alone. We use a Bayesian evidence method to predict joint expected evidence for N_nu and m_nu. We find that 3D cosmic shear combined with a Planck prior could provide `substantial' evidence for massive neutrinos and be able to distinguish `decisively' between many competing massive neutrino models. This technique should `decisively' distinguish between models in which there are no massive neutrinos and models in which there are massive neutrinos with |N_nu-3| > 0.35 and m_nu > 0.25 eV. We introduce the notion of marginalised and conditional evidence when considering evidence for individual parameter values within a multi-parameter model.
Context: Isolated cooling neutron stars with thermal X-ray emission remain
rarely detected objects despite many searches investigating the ROSAT data.
Aims: We simulate the population of close-by young cooling neutron stars to
explain the current observational results. Given the inhomogeneity of the
neutron star distribution on the sky it is particularly interesting to identify
promising sky regions with respect to on-going and future searches.
Methods: Applying a population synthesis model the inhomogeneity of the
progenitor distribution and the inhomogeneity of the X-ray absorbing
interstellar medium are considered for the first time. The total number of
observable neutron stars is derived with respect to ROSAT count rates. In
addition, we present sky maps of neutron star locations and discuss age and
distance distributions of the simulated neutron stars. Implications for future
searches are discussed.
Results: With our advanced model we can successfully explain the observed
logN - logS distribution of close-by neutron stars. Cooling neutron stars will
be most abundant in the directions of rich OB associations. New candidates are
expected to be identified behind the Gould Belt, in particular in the
Cygnus-Cepheus region. They are expected to be on average younger and then
hotter than the known population of isolated cooling neutron stars. In
addition, we propose to use data on runaway stars to search for more
radio-quiet cooling neutron stars.
In the CDM cosmological framework structures grow from merging with smaller structures. Merging should have observable effects on galaxies including destroying disks and creating spheroids. This proceeding aims to give a brief overview of how mergers occur in cosmological simulations. In this regard it is important to understand that dark matter halo mergers are not galaxy mergers; a theory of galaxy formation is necessary to connect the two. Mergers of galaxies in hydrodynamical simulations show a stronger dependence on mass than halo mergers in N-body simulations. If one knows how to connect galaxies to dark matter halos then the halo merger rate can be converted into a galaxy merger rate. When this is done it becomes clear that major mergers are many times more common in more massive galaxies offering a possible explanation of why Hubble type depends on galaxy mass.
We carry out a comprehensive analysis of the behavior of the magnetorotational instability (MRI) in viscous, resistive plasmas. We find exact, non-linear solutions of the non-ideal magnetohydrodynamic (MHD) equations describing the local dynamics of an incompressible, differentially rotating background threaded by a vertical magnetic field when disturbances with wavenumbers perpendicular to the shear are considered. We provide a geometrical description of these viscous, resistive MRI modes and show how their physical structure is modified as a function of the Reynolds and magnetic Reynolds numbers. We demonstrate that when finite dissipative effects are considered, velocity and magnetic field disturbances are no longer orthogonal (as it is the case in the ideal MHD limit) unless the magnetic Prandtl number is unity. We generalize previous results found in the ideal limit and show that a series of key properties of the mean Reynolds and Maxwell stresses also hold for the viscous, resistive MRI. In particular, we show that the Reynolds stress is always positive and the Maxwell stress is always negative. Therefore, even in the presence of viscosity and resistivity, the total mean angular momentum transport is always directed outwards. We also find that, for any combination of the Reynolds and magnetic Reynolds numbers, magnetic disturbances dominate both the energetics and the transport of angular momentum and that the total mean energy density is an upper bound for the total mean stress responsible for angular momentum transport. The ratios between the Maxwell and Reynolds stresses and between magnetic and kinetic energy densities increase with decreasing Reynolds numbers for any magnetic Reynolds number; the lowest limit of both ratios is reached in the ideal MHD regime.
Circumstellar disks are an integral part of the star formation process and the sites where planets are formed. Understanding the physical processes that drive their evolution, as disks evolve from optically thick to optically thin, is crucial for our understanding of planet formation. Disks evolve through various processes including accretion onto the star, dust settling and coagulation, dynamical interactions with forming planets, and photo-evaporation. However, the relative importance and timescales of these processes are still poorly understood. In this review, I summarize current models of the different processes that control the evolution of primordial circumstellar disks around low-mass stars. I also discuss recent observational developments on circumstellar disk evolution with a focus on new Spitzer results on transition objects.
The structure of the solar corona is dominated by the magnetic field because the magnetic pressure is about four orders of magnitude higher than the plasma pressure. Due to the high conductivity the emitting coronal plasma (visible e.g. in SOHO/EIT) outlines the magnetic field lines. The gradient of the emitting plasma structures is significantly lower parallel to the magnetic field lines than in the perpendicular direction. Consequently information regarding the coronal magnetic field can be used for the interpretation of coronal plasma structures. We extrapolate the coronal magnetic field from photospheric magnetic field measurements into the corona. The extrapolation method depends on assumptions regarding coronal currents, e.g. potential fields (current free) or force-free fields (current parallel to magnetic field). As a next step we project the reconstructed 3D magnetic field lines on an EIT-image and compare with the emitting plasma structures. Coronal loops are identified as closed magnetic field lines with a high emissivity in EIT and a small gradient of the emissivity along the magnetic field.
We present mid-infrared spectroscopy of a sample of 16 optically faint infrared luminous galaxies obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. These sources were jointly selected from Spitzer and Chandra imaging surveys in the NDWFS Bootes field and were selected from their bright X-ray fluxes to host luminous AGN. None of the spectra show significant emission from polycyclic aromatic hydrocarbons (PAHs; 6.2um equivalent widths <0.2um), consistent with their infrared emission being dominated by AGN. Nine of the X-ray sources show 9.7um silicate absorption features. Their redshifts are in the range 0.9<z<2.6, implying infrared luminosities of log(L{IR})=12.5-13.6 solar luminosities. The average silicate absorption strength is not as strong as that of previously targeted optically faint infrared luminous galaxies with similar mid-infrared luminosities implying that the X-ray selection favors sources behind a smaller column of Si-rich dust than non-X-ray selection. Seven of the X-ray sources have featureless power-law mid-IR spectra. We argue that the featureless spectra likely result from the sources having weak or absent silicate and PAH features rather than the sources lying at higher redshifts where these features are shifted out of the IRS spectral window. We investigate whether there are any correlations between X-ray and infrared properties and find that sources with silicate absorption features tend to have fainter X-ray fluxes and harder X-ray spectra, indicating a weak relation between the amount of silicate absorption and column density of X-ray-absorbing gas.
We study the long term evolution of magnetic fields generated by an initially unmagnetized collisionless relativistic $e^+e^-$ shock. Our 2D particle-in-cell numerical simulations show that downstream of such a Weibel-mediated shock, particle distributions are approximately isotropic, relativistic Maxwellians, and the magnetic turbulence is highly intermittent spatially, nonpropagating, and decaying. Using linear kinetic theory, we find a simple analytic form for these damping rates. Our theory predicts that overall magnetic energy decays like $(\omega_p t)^{-q}$ with $q \sim 1$, which compares favorably with simulations, but predicts overly rapid damping of short wavelength modes. Magnetic trapping of particles within the magnetic structures may be the origin of this discrepancy. We conclude that initially unmagnetized relativistic shocks in electron-positron plasmas are unable to form persistent downstream magnetic fields. These results put interesting constraints on synchrotron models for the prompt and afterglow emission from GRBs.
White dwarfs (WDs) with carbon absorption features in their optical spectra are known as DQ WDs. The subclass of peculiar DQ WDs are cool objects (T_eff<6000 K) which show molecular absorption bands that have centroid wavelengths ~100-300 Angstroms shortward of the bandheads of the C_2 Swan bands. These "peculiar DQ bands" have been attributed to a hydrocarbon such as C_2H. We point out that C_2H does not show strong absorption bands with wavelengths matching those of the peculiar DQ bands and neither does any other simple molecule or ion likely to be present in a cool WD atmosphere. The most straightforward explanation for the peculiar DQ bands is that they are pressure-shifted Swan bands of C_2. While current models of WD atmospheres suggest that, in general, peculiar DQ WDs do not have higher photospheric pressures than normal DQ WDs do, that finding requires confirmation by improved models of WD atmospheres and of the behavior of C_2 at high pressures and temperatures. If it is eventually shown that the peculiar DQ bands cannot be explained as pressure-shifted Swan bands, the only explanation remaining would seem to be that they arise from highly rotationally excited C_2 (J_peak>45). In either case, the absorption band profiles can in principle be used to constrain the pressure and the rotational temperature of C_2 in the line-forming regions of normal and peculiar DQ WD atmospheres, which will be useful for comparison with models. Finally, we note that progress in understanding magnetic DQ WDs may require models which simultaneously consider magnetic fields, high pressures and rotational excitation of C_2.
We analyse the point-symmetric planetary nebula NGC 6309 in terms of its three-dimensional structure and of internal variations of the physical conditions to deduce the physical processes involved in its formation. We used VLA-D 3.6-cm continuum, ground-based, and HST-archive imaging as well as long slit high- and low-dispersion spectroscopy. The low-dispersion spectra indicate a high excitation nebula, with low to medium variations of its internal physical conditions. In the optical images, the point-symmetric knots show a lack of [NII] emission as compared with similar features previously known in other PNe. A rich internal structure of the central region is seen in the HST images, resembling a deformed torus. Long slit high-dispersion spectra reveal a complex kinematics in the central region. The spectral line profiles from the external regions of NGC 6309 indicate expanding lobes (~40 km/s) as those generally found in bipolar nebulae. Finally, we have found evidence for the presence of a faint halo, possibly related to the envelope of the AGB-star progenitor. Our data indicate that NGC 6309 is a quadrupolar nebula with two pairs of bipolar lobes whose axes are oriented PA=40 and PA=76. Equatorial and polar velocities for these two pairs of lobes are 29 and 86 km/s for the bipolar system at PA=40 and 25 and 75 km/s for the bipolar system at PA=76. There is also a central torus that is expanding at 25 km/s. Kinematical age for all these structures is around 3700 to 4000 yr. We conclude that NGC 6309 was formed by a set of well-collimated bipolar outflows (jets), which were ejected in the initial stages of its formation as a planetary nebula. These jets carved the bipolar lobes in the previous AGB wind and their remnants are now observed as the point-symmetric knots tracing the edges of the lobes.
The results from a Hubble Space Telescope (HST) snapshot survey of post-AGB objects are shown. The aim of the survey is to complement existing HST images of PPN and to connect various types of nebulosities with physical and chemical properties of their central stars. Nebulosities are detected in 15 of 33 sources. Images and photometric and geometric measurements are presented. For sources with nebulosities we see a morphological bifurcation into two groups, DUPLEX and SOLE, as previous studies have found. We find further support to the previous results suggesting that this dichotomy is caused by a difference in optical thickness of the dust shell. The remaining 18 sources are classified as stellar post-AGB objects, because our observations indicate a lack of nebulosity. We show that some stellar sources may in fact be DUPLEX or SOLE based on their infrared colors. The cause of the differences among the groups are investigated. We discuss some evidence suggesting that high progenitor-mass AGB stars tend to become DUPLEX post-AGB objects. Intermediate progenitor-mass AGB stars tend to be SOLE post-AGB objects. Most of the stellar sources probably have low mass progenitors and do not seem to develop nebulosities during the post-AGB phase and therefore do not become planetary nebulae.
We calculate the radiation spectrum and its time variability of the black hole accretion disk-corona system based on the three-dimensional magnetohydrodynamic simulation. In explaining the spectral properties of active galactic nuclei (AGNs), it is often assumed that they consist of a geometrically thin, optically thick disk and hot, optically thin corona surrounding the thin disk. As for a model of the corona, we adopt the simulation data of three-dimensional, non-radiative MHD accretion flows calculated by Kato and coworkers, while for a thin disk we assume a standard type disk. We perform Monte Carlo radiative transfer simulations in the corona, taking into account the Compton scattering of soft photons from the thin disk by hot thermal electrons and coronal irradiation heating of the thin disk, which emits blackbody radiation. By adjusting the density parameter of the MHD coronal flow, we can produce the emergent spectra which are consistent with those of typical Seyfert galaxies. Moreover, we find rapid time variability in X-ray emission spectra, originating from the density fluctuation produced by the magnetorotational instability in the MHD corona. The features of reflection component including iron fluorescent line emission are also briefly discussed.
In these proceedings I discuss various extragalactic surveys which will be undertaken over the next few years and which will be complementary to any HI and/or continuum surveys with the SKA-pathfinder telescopes. I concentrate on the near-infrared public surveys which will be undertaken with the Visible and Infrared Survey Telscope for Astronomy (VISTA), and in particular the VISTA Deep Extragalactic Observations (VIDEO) survey which will provide the ideal data set to combine with any deep SKA-pathfinder observations of the extragalactic sky. After highlighting the links that the SKA pathfinders have with the various VISTA surveys, I briefly describe an approved large area survey to be carried out with the Herschel Space Observatory which has a large scientific overlap with the SKA pathfinder telescopes.
Context: Rapid rotation modifies the structure of the frequency spectrum of
pulsating stars, thus making mode identification difficult.
Aims: We look for new forms of organisation for the frequency spectrum that
can provide a basis for mode identification at high rotation rates.
Methods: Acoustic modes in uniformly rotating polytropic models of stars are
computed using a numerical code that fully takes the effects of rotation
(centrifugal distortion and Coriolis acceleration) into account. All low-degree
modes, l=0 to 3, with radial orders n=1-10 and 21-25 for N=3 polytropic models
and n=1-10 for N=1.5 polytropic models are followed from a zero rotation rate
up to 59 % of the break-up velocity.
Results: We find an empirical formula that gives a good description of the
high-frequency range of the computed acoustic spectrum for high rotation rates.
Differences between this formula and complete eigenmode calculations are shown
to be substantially smaller than those obtained with a third order perturbative
method valid at low rotation rates.
This paper addresses the origin of the silicate emission observed in PG QSOs, based on observations with the Spitzer Space Telescope. Scenarios based on the unified model suggest that silicate emission in AGN arises mainly from the illuminated faces of the clouds in the torus at temperatures near sublimation. However, detections of silicate emission in Type 2 QSOs, and the estimated cool dust temperatures, argue for a more extended emission region.To investigate this issue we present the mid-infrared spectra of 23 QSOs. These spectra, and especially the silicate emission features at ~10 and ~18 mu can be fitted using dusty narrow line region (NLR) models and a combination of black bodies. The bolometric luminosities of the QSOs allow us to derive the radial distances and covering factors for the silicate-emitting dust. The inferred radii are 100-200 times larger than the dust sublimation radius, much larger than the expected dimensions of the inner torus. Our QSO mid-IR spectra are consistent with the bulk of the silicate dust emission arising from the dust in the innermost parts of the NLR.
We discuss short wavelength (inertial wave) instabilities present in the standard two-fluid neutron star model when there is sufficient relative flow along the superfluid neutron vortex array. We demonstrate that these instabilities may be triggered in precessing neutron stars, since the angular velocity vectors of the neutron and proton fluids are misaligned during precession. The presence of such an instability would render the standard, solid body rotation, model for free precession inconsistent. Our results suggest that the standard (Eulerian) slow precession that results for weak drag between the vortices and the charged fluid (protons and electrons) is not seriously constrained by the existence of the instability. In contrast, the fast precession, which results when vortices are strongly coupled to the charged component, is generally unstable. This implies that fast precession may not be realised in astrophysical systems
This is the fourth in a series of papers that deal with angular momentum transport by internal gravity waves in stellar interiors. Here, we want to examine the potential role of waves in other evolutionary phases than the main sequence. We study the evolution of a 3Msun Population I model from the pre-main sequence to the early-AGB phase and examine whether waves can lead to angular momentum redistribution and/or element diffusion at the external convection zone boundary. We find that, although waves produced by the surface convection zone can be ignored safely for such a star during the main sequence, it is not the case for later evolutionary stages. In particular, angular momentum transport by internal waves could be quite important at the end of the sub-giant branch and during the early-AGB phase. Wave-induced mixing of chemicals is expected during the early-AGB phase.
Almost all properties of a photodissociation region (PDR) depend on its metallicity. The heating and cooling efficiencies that determine the temperature of the gas and dust, the dust composition, as well as the elemental abundances that influence the chemical structure of the PDR are just three examples that demonstrate the importance of metallicity effects in PDRs. PDRs are often associated with sites of star formation. If we want to understand the star formation history of our own Galaxy and of distant low-metallicity objects we need to understanding how metallicity acts on PDR physics and chemistry.
The Alpha Magnetic Spectrometer (AMS) is a particle physics detector designed to measure charged cosmic ray spectra with energies up to the TeV region and with high energy photon detection capability up to few hundred GeV. It will be installed on the International Space Station (ISS) in 2008 and will operate for more than three years. Due to its large acceptance, the flight duration and the state-of-art of particle identification techniques, AMS will have a remarkable sensitivity on antimatter and dark matter searches. The addition of different detector systems provide AMS with complementary and redundant electric charge and velocity measurements. The velocity of singly charged particles is expected to be measured with a precision of 0.1% and charge separation up to iron is attainable. The AMS capability of measuring a large range of electric charges and accurate velocities, will largely contribute to a better understanding of cosmic ray production, acceleration and propagation mechanisms in the galaxy.
We report the discovery of a giant, low surface-brightness loop-like stellar structure around the edge-on spiral galaxy NGC 4013. This arcing feature extends 6 arcmin (~26 kpc in projected distance) northeast from the center; likely related features are also apparent on the southwest side of the disk, extending to 4 arcmin (~17 kpc). The detection of this loop-like structure is independently confirmed in three separate datasets from three different telescopes. We estimate a surface brightness of muB = 28.6+0.6-0.4 magsqarcsec and muR = 27.0+0.3-0.2 magsqarcsec. The significantly redder colour of the stream material compared to the outer parts of the disk of NGC 4013 suggests that this loop did not originate from the disk itself, but rather is the tidal stream of a dwarf galaxy being destroyed in NGC 4013's gravitational potential. Although its true three-dimensional geometry is unknown, the projected tidal loop displays a very good overall match with the external edge-on perspective of the Monoceros tidal stream in the Milky Way predicted by recent N-body simulations. Our results demonstrate that NGC 4013, previously considered a prototypical isolated disk galaxy, is in fact undergoing a tidal encounter with a low-mass satellite. In this sense NGC 4013, with one of the most prominent HI warped disks known but showing no previously obvious indication of tidal activity, could be a Rosetta Stone for understanding disks that appear almost pristine in the optical but warped in HI maps and may provide key insights into the formation of warps in general.
The Alpha Magnetic Spectrometer (AMS) to be installed on the International Space Station (ISS) will be equipped with a proximity focusing Ring Imaging Cerenkov detector (RICH). Reconstruction of the Cerenkov angle and the electric charge with RICH are discussed. A likelihood method for the Cerenkov angle reconstruction was applied leading to a velocity determination for protons with a resolution around 0.1%. The electric charge reconstruction is based on the counting of the number of photoelectrons and on an overall efficiency estimation on an event-by-event basis. The isotopic mass separation of helium and beryllium is presented.
We derive fundamental parameters of the embedded cluster DBSB48 in the southern nebula Hoffleit18 and the very young open cluster Trumpler14, by means of deep JHKs infrared photometry. We build colour-magnitude and colour-colour diagrams to derive reddening and age, based on main sequence and pre-main sequence distributions. Radial stellar density profiles are used to study cluster structure and guide photometric diagram extractions. Field-star decontamination is applied to uncover the intrinsic cluster sequences in the diagrams. Ages are inferred from K-excess fractions. A prominent pre-main-sequence population is present in DBSB48, and the K-excess fraction f_K=55+/-6% gives an age of 1.1+/-0.5Myr. A mean reddening of A_K_s=0.9+/-0.03 was found, corresponding to $A_V=8.2\pm0.3$. The cluster CMD is consistent with the far kinematic distance of 5 kpc for Hoffleit 18. For Trumpler 14 we derived similar parameters as in previous studies in the optical, in particular an age of $1.7\pm0.7$ Myr. The fraction of stars with infrared excess in Trumpler 14 is $f_K=28\pm4%$. Despite the young ages, both clusters are described by a King profile with core radii $\rc=0.46\pm0.05$ pc and $\rc=0.35\pm0.04$ pc, respectively for DBSB 48 and Trumpler 14. Such cores are smaller than those of typical open clusters. Small cores are probably related to the cluster formation and/or parent molecular cloud fragmentation. In DBSB 48, the magnitude extent of the upper main sequence is $\Delta \ks\approx2$ mag, while in Trumpler 14 it is $\Delta \ks\approx5$ mag, consistent with the estimated ages.
In this paper, we estimate the gamma-ray fluxes coming from dark matter annihilation in a complex Milky Way framework provided by a recent N-BODY HORIZON simulation. We first study the characteristics of the simulation and highlight the mass distribution within the galactic halo. The general dark matter density has a typical $r^{-3}$ power law for high radii but the inner behaviour is poorly constrained below the resolution of the simulation ($\sim 200$ pc). We identify clumps and subclumps and analyze their distribution as well as their internal structure. Inside the clumps, the power law is quite universal, $r^{-2.5}$ in the outer part with again strong uncertainties for smaller radii especially for light clumps. We show a full skymap of the astrophysical contribution to the gamma-ray fluxes in this N-BODY framework. Thanks to quite model independent and general assumptions for the high energy physics part, we evaluate the possible absolute fluxes and show some benchmark regions for the GLAST experiment. While individual clumps seem to be beyond detection reach, the galactic center region is promising and GLAST could be sensitive to the geometry and the structure of its dark matter distribution. We also point out that the lack of resolution leaves the inner structure of subhalos poorly constrained. Using the same clump spectrum and mass fraction, a clump luminosity boost of order ten can be achieved with a steeper profile in the inner part of the sub-halos.
We provide measurements of the neutral hydrogen fraction xHI at z~6, by comparing semi-analytical models of the Lyalpha forest with observations of high-z quasars and Gamma Ray Bursts absorption spectra. We analyze the transmitted flux in a sample of 17 QSOs spectra at 5.74<zem<6.42 studying separately the narrow transmission windows (peaks) and the wide dark portions (gaps) in the observed absorption spectra. By comparing the statistics of these spectral features with our models, we conclude that xHI evolves smoothly from 10^{-4.4} at z=5.3 to 10^{-4.2} at z=5.6, with a robust upper limit xHI<0.36 at z=6.3. We show the results of the first-ever detected transverse proximity effect in the HI Lyalpha forest, produced by the HII region of the faint quasar RD J1148+5253 at z=5.70 intervening along the LOS of SDSS J1148+5251 at z=6.42. Moreover, we propose a novel method to study cosmic reionization using absorption line spectra of high-redshift GRBs afterglows. We show that the time evolution and the statistics of gaps in the observed spectra represent exquisite tools to discriminate among different reionization models. By applying our methods to GRB 050904 detected at z=6.29, we show that the observation of this burst provides strong indications of a highly ionized intergalactic medium at z~6, with an estimated mean neutral hydrogen fraction xHI=7.0\pm 4.0\times 10^{-4} along that line of sight.
Aims. We present a 0.2--200 keV broad-band study of absorbed AGN observed with INTEGRAL, XMM-Newton, Chandra and ASCA to investigate the continuum shape and the absorbing/reflecting medium properties. Methods. The sources are selected in the INTEGRAL AGN sample to have a 20--100 keV flux below 8$\times10^{-11}$ $\flux$ (5 mCrab), and are characterized by a 2--10 keV flux in the range (0.8--10)$\times10^{-11}$ $\flux$. The good statistics allow us a detailed study of the intrinsic and reflected continuum components. In particular, the analysis performed on the combined broad-band spectra allow us to investigate the presence of Compton reflection features and high energy cut-off in these objects. Results. The column density of the absorbing gas establishes the Compton thin nature for three sources in which a measure of the absorption was still missing. The Compton thin nature of all the sources in this small sample is also confirmed by the diagnostic ratios F$x/F[OIII]. The Compton reflection components we measure, reflection continuum and iron line, are not immediately compatible with a scenario in which the absorbing and reflecting media are one and the same, i.e. the obscuring torus. A possible solution is that the absorption is more effective than reflection, e.g. under the hypothesis that the absorbing/reflecting medium is not uniform, like a clumpy torus, or that the source is observed through a torus with a very shallow opening angle. The high energy cut-off (a lower limit in two cases) is found in all sources of our sample and the range of values is in good agreement with that found in type 1 Seyfert galaxies. At lower energies there is clear evidence of a soft component (reproduced with a thermal and/or scattering model), in six objects.
A bright X-ray transient was seen during an XMM-Newton observation in the direction of the Small Magellanic Cloud (SMC) in October 2006. The EPIC data allow us to accurately locate the source and to investigate its temporal and spectral behaviour. X-ray spectra covering 0.2-10 keV and pulse profiles in different energy bands were extracted from the EPIC data. The detection of 6.85 s pulsations in the EPIC-PN data unambiguously identifies the transient with XTE J0103-728, discovered as 6.85 s pulsar by RXTE. The X-ray light curve during the XMM-Newton observation shows flaring activity of the source with intensity changes by a factor of two within 10 minutes. Modelling of pulse-phase averaged spectra with a simple absorbed power-law indicates systematic residuals which can be accounted for by a second emission component. For models implying blackbody emission, thermal plasma emission or emission from the accretion disk (disk-blackbody), the latter yields physically sensible parameters. The photon index of the power-law of ~0.4 indicates a relatively hard spectrum. The 0.2-10 keV luminosity was 2x10^{37} with a contribution of ~3% from the disk-blackbody component. A likely origin for the excess emission is reprocessing of hard X-rays from the neutron star by optically thick material near the inner edge of an accretion disk. From a timing analysis we determine the pulse period to 6.85401(1) s indicating an average spin-down of ~0.0017 s per year since the discovery of XTE J0103-728 in May 2003. The X-ray properties and the identification with a Be star confirm XTE J0103-728 as Be/X-ray binary transient in the SMC.
The nature and origin of the soft X-ray excess in radio quiet AGN is still an open issue. The interpretation in terms of thermal disc emission has been challanged by the discovery of the constancy of the effective temperature despite the wide range of Black Hole masses of the observed sources. Alternative models are reflection from ionized matter and absorption in a relativistically smeared wind. We analyzed XMM-Newton observations of four luminous radio quiet AGN with the aim of characterising their main properties and in particular the soft excess. Different spectral models for the soft excess were tried: thermal disc emission, Comptonization, ionized reflection, relativistically smeared winds. Comptonization of thermal emission and the smeared winds provide the best fits, but the other models also provide acceptable fits. All models, however, return parameters very similar from source to source, despite the large differences in luminosities, Black Hole masses and Eddington ratios. Moreover, the smeared wind model require very large smearing velocities. The UV to X-ray fluxes ratios are very different, but do not correlate with any other parameter. No fully satisfactory explanation for the soft X-ray excess is found. Better data, like e.g. observations in a broader energy band, are needed to make further progresses.
The problem of the resolution of turbulent flows in adaptive mesh refinement (AMR) simulations is investigated by means of 3D hydrodynamical simulations in an idealised setup, representing a moving subcluster during a merger event. AMR simulations performed with the usual refinement criteria based on local gradients of selected variables do not properly resolve the production of turbulence downstream of the cluster. Therefore we apply novel AMR criteria which are optimised to follow the evolution of a turbulent flow. We demonstrate that these criteria provide a better resolution of the flow past the subcluster, allowing us to follow the onset of the shear instability, the evolution of the turbulent wake and the subsequent back-reaction on the subcluster core morphology. We discuss some implications for the modelling of cluster cold fronts.
We present the results of a synthetic spectral analysis of HST STIS spectra of five long period dwarf novae obtained during their quiescence to determine the properties of their white dwarfs which are little known for systems above the CV period gap. The five systems, TU Men, BD Pav, SS Aur, TT Crt, and V442 Cen were observed as part of an HST Snapshot project. The spectra are described and fitted with combinations of white dwarf photospheres and accretion disks. We provide evidence that the white dwarfs in all five systems are at least partially exposed. We discuss the evolutionary implications of our model fitting results and compare these dwarf novae to previously analyzed FUV spectra of other dwarf novae above the period gap. The dispersion in CV WD temperatures above the period gap is substantially greater than one finds below the period gap where there is a surprisingly narrow dispersion in temperatures around 15,000K. There appears to be a larger spread of surface temperatures in dwarf novae above the period than is seen below the gap.
Some useful developments in the model physics are briefly presented, followed by model results on chemical enrichments and WR stars. We discuss the expected rotation velocities of WR stars. We emphasize that the (C+O)/He ratio is a better chemical indicator of evolution for WC stars than the C/He ratios. With or without rotation, at a given luminosity the (C+O)/He ratios should be higher in regions of lower metallicity Z. Also, for a given (C+O)/He ratio the WC stars in lower Z regions have higher luminosities. The WO stars, which are likely the progenitors of supernovae SNIc and of some GRBs, should preferentially be found in regions of low Z and be the descendants of very high initial masses. Finally, we emphasize the physical reasons why massive rotating low Z stars may also experience heavy mass loss
We compare the small-scale features visible in the Ne viii Doppler-shift map of an equatorial coronal hole (CH) as observed by SUMER with the small-scale structures of the magnetic field as constructed from a simultaneous photospheric magnetogram by a potential magnetic-field extrapolation. The combined data set is analysed with respect to the small-scale flows of coronal matter, which means that the Ne viii Doppler-shift used as tracer of the plasma flow is investigated in close connection with the ambient magnetic field. Some small closed-field regions in this largely open CH are also found in the coronal volume considered. The Doppler-shift patterns are found to be clearly linked with the field topology.
The development of turbulent gas flows in the intra-cluster medium and in the core of a galaxy cluster is studied by means of adaptive mesh refinement (AMR) cosmological simulations. A series of six runs was performed, employing identical simulation parameters but different criteria for triggering the mesh refinement. In particular, two different AMR strategies were followed, based on the regional variability of control variables of the flow and on the overdensity of subclumps, respectively. We show that both approaches, albeit with different results, are useful to get an improved resolution of the turbulent flow in the ICM. The vorticity is used as a diagnostic for turbulence, showing that the turbulent flow is not highly volume-filling but has a large area-covering factor, in agreement with previous theoretical expectations. The measured turbulent velocity in the cluster core is larger than 200 km/s, and the level of turbulent pressure contribution to the cluster hydrostatic equilibrium is increased by using the improved AMR criteria.
This is the third of a series of papers presenting the first attempt to analyze the growth of the bar instability in a consistent cosmological scenario. In the previous two articles we explored the role of the cosmology on stellar disks, and the impact of the gaseous component on a disk embedded in a cosmological dark matter halo. The aim of this paper is to point out the impact of the star formation on the bar instability inside disks having different gas fractions. We perform cosmological simulations of the same disk-to-halo mass systems as in the previous works where the star formation was not triggered. We compare the results of the new simulations with the previous ones to investigate the effect of the star formation by analysing the morphology of the stellar components, the bar strength, the behaviour of the pattern speed. We follow the gas and the central mass concentration during the evolution and their impact on the bar strength. In all our cosmological simulations a stellar bar, lasting 10 Gyr, is still living at z=0. The central mass concentration of gas and of the new stars has a mild action on the ellipticity of the bar but is not able to destroy it; at z=0 the stellar bar strength is enhanced by the star formation. The bar pattern speed is decreasing with the disk evolution.
The observed velocities of pulsars suggest the possibility that sterile neutrinos with mass of several keV are emitted from a cooling neutron star. The same sterile neutrinos could constitute all or part of cosmological dark matter. The neutrino-driven kicks can exhibit delays depending on the mass and the mixing angle, which can be compared with the pulsar data. We discuss the allowed ranges of sterile neutrino parameters, consistent with the latest cosmological and X-ray bounds, which can explain the pulsar kicks for different delay times.
The following problems are discussed. 1. Pulsars and close binaries. 2. Hulse-Taylor pulsar. 3. Disrupted pulsar pairs. 4. RP statistics. 5. Enhanced evaporation: formation of single RP. 6. General relativity effects: NS+NS. 7. A Double pulsar system. 8. Checking general relativity. 9. Variability of the gravitational constant. 10. Space Watch.
The future of ground based gamma ray astronomy lies in large arrays of Imaging Atmospheric Cherenkov Telescopes (IACT) with better capabilities: lower energy threshold, higher sensitivity, better resolution and background rejection. Currently, designs for the next generation of IACT arrays are being explored by various groups. We have studied possible configurations with a large number of telescopes of various sizes. Here, we present the precision of source, shower core and energy reconstruction for gamma rays in the GeV-TeV range for different altitudes of observation. These results were obtained through tools that we have developed in order to simulate any type of IACT configuration and evaluate its performance.
We present a systematic survey of the temporal and spectral properties of all GRB X-ray afterglows observed by Swift-XRT between January 2005 and July 2007. We have constructed a catalog of all light curves and spectra and investigate the physical origin of each afterglow segment in the framework of the forward shock models by comparing the data with the closure relations. We search for possible jet-like breaks in the lightcurves and try to explain some of the "missing" X-ray jet breaks in the lightcurves.
The intriguing observations of {Swift}/BAT GRB 060218 and CGRO/BATSE burst 980425, both with much lower luminosity and redshift compared to other observed bursts, lead naturally to the question whether these low-luminosity (LL) bursts constitute a separate population from high-luminosity (HL) bursts. Utilizing Monte Carlo simulations we compare various single-component luminosity function (LF)models (single power law or broken power law) with the two-component luminosity function model proposed by Liang et al. Using various criteria, we demonstrate that the single-component LF models have great difficulty in simultaneously reproducing both the high local LL-GRB rate and the oberved distributions of redshift, luminosity, and $\log N-\log P$ for HL-GRBs. We argue that the two-component LF model is necessary, and we use the observed BATSE and Swift $\log N-\log P$ distributions to add constrains to the LL and HL-LF parameters. The LL-LF can be modeled by a smoothed, broken power law with a break at around $10^{47}$ erg s$^{-1}$, dropping steeply above this luminosity. The local rate of LL-GRBs is $\sim$ 100 Gpc$^{-3}$ yr$^{-1}$ at the break luminosity, much larger than that of HL-GRBs. The recently discovered peculiar X-ray transient XRF 080109/SN 2008D strengthens this conclusion, and requires that the LL-population LF extends further down in luminosity with a probably even higher local rate at lower luminosities.
During the last few years, considerable effort has been directed towards large-scale (>> $1 Billion US) missions to detect and characterize earth-like planets around nearby stars, such as the Terrestrial Planet Finder Interferometer (TPF-I) and Darwin missions. However, technological and budgetary issues as well as shifting science priorities will likely prevent these missions from entering Phase A until the next decade. The secondary eclipse technique using the Spitzer Space Telescope has been used to directly measure the temperature and emission spectrum of extrasolar planets. However, only a small fraction of known extrasolar planets are in transiting orbits. Thus, a simplified nulling interferometer, which produces an artificial eclipse or occultation, and operates in the near- to mid-infrared (e.g. ~ 3 to 8 or 10 microns), can characterize the atmospheres of this much larger sample of the known but non-transiting exoplanets. Many other scientific problems can be addressed with a system like this, including imaging debris disks, active galactic nuclei, and low mass companions around nearby stars. We discuss the rationale for a probe-scale mission in the $600-800 Million range, which we name here as the Small Prototype Planet Finding Interferometer (SPPFI).
We present a Very Long Baseline Interferometry image of the water maser emission in the nuclear region of NGC3393. The maser emission has a linear distribution oriented at a position angle of $\sim -34\degr$, perpendicular to both the kpc-scale radio jet and the axis of the narrow line region. The position-velocity diagram displays a red-blue asymmetry about the systemic velocity and the estimated dynamical center, and is thus consistent with rotation. Assuming Keplerian rotation in an edge-on disk, we obtain an enclosed mass of $(3.1\pm 0.2) \times 10^7 M_{\sun}$ within $0.36\pm 0.02$ pc ($1.48\pm 0.06$ mas), which corresponds to a mean mass density of $\sim10^{8.2} M_{\sun}$ pc$^{-3}$. We also report the measurement with the Green Bank Telescope of a velocity drift, a manifestation of centripetal acceleration within the disk, of $5\pm 1$ km s $^{-1}$ yr$^{-1}$ in the $\sim3880$ km s$^{-1}$ maser feature, which is most likely located along the line of sight to the dynamical center of the system. From the acceleration of this feature, we estimate a disk radius of $0.17\pm 0.02$ pc, which is smaller than the inner disk radius ($0.36\pm 0.02$ pc) of emission that occurs along the midline (i.e., the line of nodes). The emission along the line of sight to the dynamical center evidently occurs much closer to the center than the emission from the disk midline, contrary to the situation in the archetypal maser systems NGC4258 and NGC1068. The outer radius of the disk as traced by the masers along the midline is about 1.5 pc.
We examine numerically and qualitatively the Lema\^\i tre--Tolman--Bondi (LTB) inhomogeneous dust solutions as a 3--dimensional dynamical system characterized by six critical points. One of the coordinates of the phase space is an average density parameter, $<\Omega>$, which behaves as the ordinary $\Omega$ in Friedman-Lema\^\i tre--Robertson--Walker (FLRW) dust spacetimes. The other two coordinates, a shear parameter and a density contrast function, convey the effects of inhomogeneity. As long as shell crossing singularities are absent, this phase space is bounded or it can be trivially compactified. This space contains several invariant subspaces which define relevant particular cases, such as: ``parabolic'' evolution, FLRW dust and the Schwarzschild--Kruskal vacuum limit. We examine in detail the phase space evolution of several dust configurations: a low density void formation scenario, high density re--collapsing universes with open, closed and wormhole topologies, a structure formation scenario with a black hole surrounded by an expanding background, and the Schwarzschild--Kruskal vacuum case. Solution curves start expanding from a past attractor (source) in the plane $<\Omega>=1$, associated with self similar regime at an initial singularity. Depending on the initial conditions and specific configurations, the curves approach several saddle points as they evolve between this past attractor and other two possible future attractors: perpetually expanding curves terminate at a line of sinks at $<\Omega>=0$, while collapsing curves reach maximal expansion as $<\Omega>$ diverges and end up in sink that coincides with the past attractor and is also associated with self similar behavior.
We provide a new construction of the modes of the Poincare dodecahedral space S^3/I*. The construction uses the Hopf map, Maxwell's multipole vectors and orbifolds. In particular, the *235-orbifold serves as a parameter space for the modes of S^3/I* shedding new light on the geometrical significance of the dimension of each space of $k$-modes, as well as on the modes themselves.
In order for a modified gravity model to be a candidate for cosmological dark energy it has to pass stringent local gravity experiments. We find that a Brans-Dicke (BD) theory with well-defined second order corrections that include the Gauss-Bonnet term possess this feature. We construct the generic second order theory that gives, to linear order, a BD metric solution for a point-like mass source. We find that these theories interpolate between general relativity (GR) and BD gravity. In particular it is found that the relevant Eddington parameter, that is commonly heavily constrained by time delay experiments, can be arbitrarily close to the GR value of 1, with an arbitrary BD parameter. We find the region where the solution is stable to small timelike perturbations.
The annihilations of neutralino dark matter (or other dark matter candidate) generate, among other Standard Model states, electrons and positrons. These particles emit synchrotron photons as a result of their interaction with the Galactic Magnetic Field. In this letter, we use the measurements of the WMAP satellite to constrain the intensity of this synchrotron emission and, in turn, the annihilation cross section of the lightest neutralino. We find this constraint to be more stringent than that provided by any other current indirect detection channel. In particular, the neutralino annihilation cross section must be less than ~ 3 x 10^-26 cm^3/s (1 x 10^25 cm^3/s) for 100 GeV (500 GeV) neutralinos distributed with an NFW halo profile. For the conservative case of an entirely flat dark matter distribution within the inner 8 kiloparsecs of the Milky Way, the constraint is approximately a factor of 30 less stringent. Even in this conservative case, synchrotron measurements strongly constrain, for example, the possibility of wino or higgsino neutralino dark matter produced non-thermally in the early universe.
We investigate the influence of magnetic fields upon the dynamics of and resulting gravitational waves from a binary neutron star merger in full general relativity coupled to ideal magnetohydrodynamics (MHD). We consider two merger scenarios, one where the stars begin with initially aligned poloidal magnetic fields and one with no magnetic field. Both mergers result in a strongly differentially rotating object. In comparison to the non-magnetized scenario, the aligned magnetic fields delay the final merger of the two stars. During and after merger we observe phenomena driven by the magnetic field, including Kelvin-Helmholtz instabilities in shear layers, winding of the field lines, and transition from poloidal to toroidal fields. These effects not only produce electromagnetic radiation, but also can have a strong influence on the gravitational waves. Thus, there are promising prospects for studying such systems with both types of waves.
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HST ACS/HRC images in UV (F250W), V (F555W), and I (F814W) resolve three isolated OB associations that lie up to 30 kpc from the stellar disk of the S0 galaxy NGC 1533. Previous narrow-band Halpha imaging and optical spectroscopy showed these objects as unresolved intergalactic HII regions having Halpha luminosities consistent with single early-type O stars. These young stars lie in stripped HI gas with column densities ranging from 1.5 - 2.5 * 10^20 cm^-2 and velocity dispersions near 30 km s^-1. Using the HST broadband colors and magnitudes along with previously-determined Halpha luminosities, we place limits on the masses and ages of each association, considering the importance of stochastic effects for faint (M_V >-8) stellar populations. The upper limits to their stellar masses range from 600 M_sun to 7000 M_sun, and ages range from 2 - 6 Myrs. This analysis includes an updated calculation of the conversion factor between the ionizing luminosity and the total number of main sequence O stars contained within an HII region. The photometric properties and sizes of the isolated associations and other objects in the HRC fields are consistent with those of Galactic stellar associations, open clusters and/or single O and B stars. We interpret the age-size sequence of associations and clustered field objects as an indication that these isolated associations are most likely rapidly dispersing. Furthermore, we consider the possibility that these isolated associations represent the first generation of stars in the HI ring surrounding NGC 1533. This work suggests star formation in the unique environment of a galaxy's outermost gaseous regions proceeds similarly to that within the Galactic disk and that star formation in tidal debris may be responsible for building up a younger halo component.
We show that Gamma Ray Bursts (GRBs) of known redshift and rest frame optical extinction detected by the Swift satellite fully confirm earlier results concerning the distribution of the optical afterglow luminosity at 12 hours after trigger (rest frame time). This distribution is bimodal and relatively narrow, especially for the high luminosity branch. This is intriguing, given that Swift GRBs have, on average, a redshift larger than pre-Swift ones, and is unexpected in the common scenario explaining the GRB afterglow. We investigate if the observed distribution can be the result of selection effects affecting a unimodal parent luminosity distribution, and find that either the distribution is intrinsically bimodal, or most (60 per cent) of the bursts are absorbed by a substantial amount of grey dust. In both cases we suggest that most dark bursts should belong to the underluminous optical family.
We examine the dynamics and X-ray spectrum of the young Type Ia supernova remnant 0509-67.5 in the context of the recent results obtained from the optical spectroscopy of its light echo. Our goal is to estimate the kinetic energy of the supernova explosion using Chandra and XMM-Newton observations of the supernova remnant, thus placing the birth event of 0509-67.5 in the sequence of dim to bright Type Ia supernovae. We base our analysis on a standard grid of one-dimensional delayed detonation explosion models, together with hydrodynamic and X-ray spectral calculations of the supernova remnant evolution. From the remnant dynamics and the properties of the O, Si, S, and Fe emission in its X-ray spectrum we conclude that 0509-67.5 was originated ~400 years ago by a bright, highly energetic Type Ia explosion similar to SN 1991T. Our best model has a kinetic energy of 1.4x10E51 erg and synthesizes 0.97 Msun of 56Ni. These results are in excellent agreement with the age estimate and spectroscopy from the light echo. We have thus established the first connection between a Type Ia supernova and its supernova remnant based on a detailed quantitative analysis of both objects.
We report the successful identification of the type of the supernova responsible for the supernova remnant SNR 0509-675 in the Large Magellanic Cloud (LMC) using Gemini spectra of surrounding light echoes. The ability to classify outbursts associated with centuries-old remnants provides a new window into several aspects of supernova research and is likely to be successful in providing new constraints on additional LMC supernovae as well as their historical counterparts in the Milky Way Galaxy (MWG). The combined spectrum of echo light from SNR 0509-675 shows broad emission and absorption lines consistent with a supernova (SN) spectrum. We create a spectral library consisting of 26 SNe Ia and 6 SN Ib/c that are time-integrated, dust-scattered by LMC dust, and reddened by the LMC and MWG. We fit these SN templates to the observed light echo spectrum using $\chi^2$ minimization as well as correlation techniques, and we find that overluminous 91T-like SNe Ia with $\dm15<0.9$ match the observed spectrum best.
We investigate the apparent discrepancy between gas and dust outer radii derived from millimeter observations of protoplanetary disks. Using 230 and 345 GHz continuum and CO J=3-2 data from the Submillimeter Array for four nearby disk systems (HD 163296, TW Hydrae, GM Aurigae, and MWC 480), we examine models of circumstellar disk structure and the effects of their treatment of the outer disk edge. We show that for these disks, models described by power laws in surface density and temperature that are truncated at an outer radius are incapable of reproducing both the gas and dust emission simultaneously: the outer radius derived from the dust continuum emission is always significantly smaller than the extent of the molecular gas disk traced by CO emission. However, a simple model motivated by similarity solutions of the time evolution of accretion disks that includes a tapered exponential edge in the surface density distribution (and the same number of free parameters) does much better at reproducing both the gas and dust emission. While this analysis does not rule out the disparate radii implied by the truncated power-law models, a realistic alternative disk model, grounded in the physics of accretion, provides a consistent picture for the extent of both the gas and dust.
We use a set of high-resolution N-body simulations of binary galaxy mergers to show that the morphologies of the tidal features that are seen around a large fraction of nearby, massive ellipticals in the field, cannot be reproduced by equal-mass dissipationless mergers; rather, they are well explained by the accretion of disk-dominated galaxies. In particular, the arm- and loop-like morphologies of the observed tidal debris can only be produced by the kinematically-cold material of the disk components of the accreted galaxies. The tidal features that arise from such "cold-accretion" events onto a massive elliptical are visible for significantly longer timescales than the features produced by elliptical-elliptical mergers (about 1-2 Gyr vs. a few hundred million years). Mass ratios of order $1:10$ between the accreting elliptical and the accreted disk are sufficient to match the brightness of the observed debris. Furthermore, stellar population synthesis models and simple order of magnitude calculations indicate that the colors of the tidal features generated in such minor cold-accretion events are relatively red, in agreement with the observations. The minor cold-accretion events that explain the presence, brightness and structural and color properties of the tidal debris, cause only a modest mass and luminosity increase in the accreting massive elliptical. These results, coupled with the relative statistical frequencies of disk- and bulge-dominated galaxies in the field, imply that the most massive ellipticals assemble well before their tidal debris forms through the accretion of relatively little, kinematically-cold material, rather than in very recent, dissipationless major mergers.
We present results on the interstellar medium (ISM) properties of 29 galaxies based on a comparison of {\it Spitzer} far-infrared and Westerbork Synthesis Radio Telescope radio continuum imagery. Of these 29 galaxies, 18 are close enough to resolve at $\la$1 kpc scales at 70 $\micron$ and 22 cm. We extend the \citet{ejm06a,ejm06b} approach of smoothing infrared images to approximate cosmic-ray (CR) electron spreading and thus largely reproduce the appearance of radio images. Using a wavelet analysis we decompose each 70 $\micron$ image into one component containing the star-forming {\it structures} and a second one for the diffuse {\it disk}. The components are smoothed separately, and their combination compared to a free-free corrected 22 cm radio image; the scale-lengths are then varied to best match the radio and smoothed infrared images. We find that late-type spirals having high amounts of ongoing star formation benefit most from the two-component method. We also find that the disk component dominates for galaxies having low star formation activity, whereas the structure component dominates at high star formation activity. We propose that this result arises from an age effect rather than from differences in CR electron diffusion due to varying ISM parameters. The bulk of the CR electron population in actively star-forming galaxies is significantly younger than that in less active galaxies due to recent episodes of enhanced star formation; these galaxies are observed within $\sim10^{8}$ yr since the onset of the most recent star formation episode. The sample irregulars have anomalously low best-fit scale-lengths for their surface brightnesses compared to the rest of the sample spirals which we attribute to enhanced CR electron escape.
We present results of a study of large-scale neutral hydrogen (HI) gas in nearby radio galaxies. We find that the early-type host galaxies of different types of radio sources (compact, FR-I and FR-II) appear to contain fundamentally different large-scale HI properties: enormous regular rotating disks and rings are present around the host galaxies of a significant fraction of low power compact radio sources, while no large-scale HI is detected in low power, edge-darkened FR-I radio galaxies. Preliminary results of a study of nearby powerful, edge-brightened FR-II radio galaxies show that these systems generally contain significant amounts of large-scale HI, often distributed in tail- or bridge-like structures, indicative of a recent galaxy merger or collision. Our results suggest that different types of radio galaxies may have a different formation history, which could be related to a difference in the triggering mechanism of the radio source. If confirmed by larger studies with the next generation radio telescopes, this would be in agreement with previous optical studies that suggest that powerful FR-II radio sources are likely triggered by galaxy mergers and collisions, while the lower power FR-I sources are fed in other ways (e.g. through the accretion of hot IGM). The giant HI disks/rings associated with some compact sources could - at least in some cases - be the relics of much more advanced mergers.
We present the results of an experiment to image the interacting binary star beta Lyrae with data from the Navy Prototype Optical Interferometer (NPOI), using a differential phase technique to correct for the effects of the instrument and atmosphere on the interferometer phases. We take advantage of the fact that the visual primary of beta Lyrae and the visibility calibrator we used are both nearly unresolved and nearly centrally symmetric, and consequently have interferometric phases near zero. We used this property to detect and correct for the effects of the instrument and atmosphere on the phases of beta Lyrae and to obtain differential phases in the channel containing the Halpha emission line. Combining the Halpha-channel phases with information about the line strength, we recovered complex visibilities and imaged the Halpha emission using standard radio interferometry methods. We find that the results from our differential phase technique are consistent with those obtained from a more-standard analysis using squared visibilities (V^2's). Our images show the position of the Halpha emitting regions relative to the continuum photocenter as a function of orbital phase and indicate that the major axis of the orbit is oriented along p.a.=248.8+/-1.7 deg. The orbit is smaller than previously predicted, a discrepancy that can be alleviated if we assume that the system is at a larger distance from us, or that the contribution of the stellar continuum to the Halpha channel is larger than estimated. Finally, we also detected a differential phase signal in the channels containing HeI emission lines at 587.6 and 706.5nm, with orbital behavior different from that of the Halpha, indicating that it originates from a different part of this interacting system.
We analyze the mid-infrared (MIR) spectra of ultraluminous infrared galaxies (ULIRGs) observed with the Spitzer Space Telescope's Infrared Spectrograph. Dust emission dominates the MIR spectra of ULIRGs, and the reprocessed radiation that emerges is independent of the underlying heating spectrum. Instead, the resulting emission depends sensitively on the geometric distribution of the dust, which we diagnose with comparisons of numerical simulations of radiative transfer. Quantifying the silicate emission and absorption features that appear near 10 and 18um requires a reliable determination of the continuum, and we demonstrate that including a measurement of the continuum at intermediate wavelength (between the features) produces accurate results at all optical depths. With high-quality spectra, we successfully use the silicate features to constrain the dust chemistry. The observations of the ULIRGs and local sightlines require dust that has a relatively high 18/10um absorption ratio of the silicate features (around 0.5). Specifically, the cold dust of Ossenkopf et al. (1992) is consistent with the observations, while other dust models are not. We use the silicate feature strengths to identify two families of ULIRGs, in which the dust distributions are fundamentally different. Optical spectral classifications are related to these families. In ULIRGs that harbor an active galactic nucleus, the spectrally broad lines are detected only when the nuclear surroundings are clumpy. In contrast, the sources of lower ionization optical spectra are deeply embedded in smooth distributions of optically thick dust.
We report on variations in important X-ray emission lines in a series of Chandra grating spectra of the supermassive colliding wind binary star Eta Carinae, including key phases around the X-ray minimum/periastron passage in 2003.5. The X-rays arise from the collision of the slow, dense wind of Eta Car with the fast, low-density wind of an otherwise hidden companion star. The X-ray emission lines provide the only direct measure of the flow dynamics of the companion's wind along the wind-wind collision zone. We concentrate here on the silicon and sulfur lines, which are the strongest and best resolved lines in the X-ray spectra. Most of the line profiles can be adequately fit with symmetric Gaussians with little significant skewness. Both the silicon and sulfur lines show significant velocity shifts and correlated increases in line widths through the observations. The R = forbidden-to-intercombination ratio from the Si XIII and S XV triplets is near or above the low-density limit in all observations, suggesting that the line-forming region is >1.6 stellar radii from the companion star. We show that simple geometrical models cannot simultaneously fit both the observed centroid variations and changes in line width as a function of phase. We show that the observed profiles can be fitted with synthetic profiles with a reasonable model of the emissivity along the wind-wind collision boundary. We use this analysis to help constrain the line formation region as a function of orbital phase, and the orbital geometry.
OB stars with strong radiation-driven stellar winds and large-scale magnetic fields generate strong and hard X-ray emission via the Magnetically Channeled Wind Shock (MCWS) mechanism. In this brief paper, I describe four separate X-ray diagnostics of the MCWS mechanism in OB stars, with applications to the prototype young O star, theta-1 Ori C.
We present new HST optical imagery as well as new UV and IR spectroscopic data obtained with the Hubble and Spitzer Space Telescopes, respectively, of the halo planetary nebula DdDm-1. For the first time we present a resolved image of this object which indicates that the morphology of DdDm-1 can be described as two orthogonal elliptical components in the central part surrounded by an extended halo. The extent of the emission is somewhat larger than was previously reported in the literature. We combine the spectral data with our own previously published optical measurements to derive nebular abundances of He, C, N, O, Ne, Si, S, Cl, Ar, and Fe. Our abundance determinations include the use of the newly developed program ELSA for obtaining abundances directly from emission line strengths along with detailed photoionization models to render a robust set of abundances for this object. The metallicity, as gauged by oxygen, is found to be 0.46 dex below the solar value, confirming DdDm-1's status as a halo PN. In addition, we find that Si and Fe are markedly underabundant, suggesting their depletion onto dust. The very low (but uncertain) C/O ratio suggests that the chemistry of the nebula should be consistent with an oxygen-rich environment. We find that the sulfur abundance of DdDm-1 is only slightly below the value expected based upon the normal lockstep behavior between S and O observed in H II regions and blue compact galaxies. The central star effective temperature and luminosity are estimated to be 55,000 K and 1000 solar luminosities, respectively, implying an initial progenitor mass of <1 solar masses. Finally, we report on a new radial velocity determination from echelle observations.
The recently-discovered lack of close binaries, among extreme horizontal branch (EHB) stars in Galactic globular clusters, has thus far constituted a major puzzle, in view of the fact that blue subdwarf stars - the field counterparts of cluster EHB stars - are well-known to present a high binary fraction. In this Letter, we provide new results that confirm the lack of close EHB binaries in globular clusters, and present a first scenario to explain the difference between field and cluster EHB stars. First, in order to confirm that the lack of EHB binaries in globular clusters is a statistically robust result, we undertook a new analysis of 145 horizontal branch stars in NGC6752, out of which forty-one belong to the EHB. To search for radial-velocity variations as a function of time, we repeated high-resolution (R=18500) spectroscopy of all stars, four times during a single night of observations. We detected a single, hot (25000 K), radial-velocity variable star as a close-binary candidate. From these results, we estimate an upper-limit for the close (period P < 5 day) binary fraction f among NGC6752 EHB stars of 16% (95% confidence level), with the most probable value being f=4%. Thus our results clearly confirm the lack of close binaries among the hot HB stars in this cluster. We suggest that the confirmed discrepancy between the binary fractions for field and cluster EHB stars is the consequence of an f-age relation, with close binaries being more likely in the case of younger systems. We analyze theoretical and observational results available in the literature, which support this scenario. If so, an age difference between the EHB progenitors in the field and in clusters, the former being younger (on average) by up to several Gyr, would naturally account for the startling differences in binary fraction between the two populations.
We describe the construction of GROND, a 7-channel imager, primarily designed for rapid observations of gamma-ray burst afterglows. It allows simultaneous imaging in the Sloan g'r'i'z' and near-infrared $JHK$ bands. GROND was commissioned at the MPI/ESO 2.2m telescope at La Silla (Chile) in April 2007, and first results of its performance and calibration are presented.
(Abridged) S147 is a large faint shell-type supernova remnant (SNR). Its remarkable spectral break at cm-wavelengths is an important physical property to characterize the SNR evolution. However, the spectral break is based on radio observations with limited precision. We made new radio continuum and polarization observations of S147 at 11cm and at 6cm with the Effelsberg 100-m telescope and the Urumqi 25-m telescope, respectively. These new data were combined with published lower frequency data from the Effelsberg 100-m telescope and very high frequency data from WMAP to investigate the spectral turnover and polarization properties of S147. S147 consists of numerous filaments embedded in diffuse emission. We found that the integrated flux densities of S147 are 34.8+/-4.0 Jy at 11cm and 15.4+/-3.0Jy at 6cm. These new measurements confirm the known spectral turnover at ~1.5GHz, which can be entirely attributed to the diffuse emission component. The spectral index above the turnover is -1.35+/-0.20. The filamentary emission component has a constant spectral index over the entire wavelength range up to 40.7GHz of -0.35+/-0.15. The weak polarized emission of S147 is at the same level as the ambient diffuse Galactic polarization. The rotation measure of the eastern filamentary shell is about -70 rad/m2. The filamentary and diffuse emission components of S147 have different physical properties, which make S147 outstanding among shell type SNRs.The weak polarization of S147 at 11cm and at 6cm can be attributed to a section of the S147 shell showing a tangential magnetic field direction.
We report photometric observations of AL Com during its rare outburst in 2007. The light curve is reminiscent of its past superoutbursts in 1995 and 2001, except for the rebrightening phase after the main superoutburst. During the rebrightening phase in 2007, we found clear modulations between V=16.2-15.2. In conjunction with the lack of prominent superhumps in our time-series observations, the modulations can most naturally be interpreted as repetitive short rebrightenings with a cycle of 1-2 days. The rebrightening characteristics in 2007 are different from those in 1995 and 2001. This indicates that the type of rebrightenings in WZ Sge stars depends not on binary parameters of objects, but on the mass-accretion process for each outburst.
Infrared observations of hot massive stars and their environments provide a detailed picture of mass loss histories, dust formation, and dynamical interactions with the local stellar medium that can be unique to the thermal regime. We have acquired new infrared spectroscopy and imaging with the sensitive instruments onboard the Spitzer Space Telescope in guaranteed and open time programs comprised of some of the best known examples of hot stars with circumstellar nebulae, supplementing with unpublished Infrared Space Observatory spectroscopy. Here we present highlights of our work on the environment around the extreme P Cygni-type star HDE316285, revealing collisionally excited H2 for the first time in a hot star nebula, and providing some defining characteristics of the star's evolution and interactions with the ISM at unprecented detail in the infrared.
If a microlensing event is caused by a star, the event can exhibit change in color due to the light from the lens. In the previous and current lensing surveys, the color shift could not be used to constrain the lens population because the blended light responsible for the color shift is mostly attributed to nearby background stars rather than the lens. However, events to be observed in future space-based surveys do not suffer from blending and thus the color information can be used to constrain lenses. In this paper, we demonstrate the usefulness of future surveys in measuring color shifts. By conducting simulation of galactic lensing events based on the specification of a proposed space-based lensing survey, we estimate that the shift in the color of $R-H$ will be measured at 5$\sigma$ level for $\sim 12%$ of events that occur on source stars with apparent magnitudes brighter than $J=22.5$. Color-shifted events tend to have high magnifications and the lenses will have brightnesses equivalent to those of source stars. The time scales of the color-shifted events tend to be longer than those without color shifts. From the mass distribution of lenses, we find that most of the color-shifted events will be produced by stellar lenses with spectral types down to mid M-type main sequence stars.
It has long been know how to analytically relate the clustering properties of the collapsed structures (halos) to those of the underlying dark matter distribution for Gaussian initial conditions. Here we apply the same approach to physically motivated non-Gaussian models. The techniques we use were developed in the 1980s to deal with the clustering of peaks of non-Gaussian density fields. The description of the clustering of halos for non-Gaussian initial conditions has recently received renewed interest, motivated by the forthcoming large galaxy and cluster surveys. For inflationary-motivated non-Gaussianites, we find an analytic expression for the halo bias as a function of scale, mass and redshift, employing only the approximations of high-peaks and large separations.
We investigate clustering properties of Lyman-break galaxies (LBGs) at z~3 based on deep multi-waveband imaging data from optical to near-infrared wavelengths in the Subaru/XMM-Newton Deep Field. The LBGs are selected by U-V and V-z' colors in one contiguous area of 561 arcmin^2 down to z'=25.5. We study the dependence of the clustering strength on rest-frame UV and optical magnitudes, which can be indicators of star formation rate and stellar mass, respectively. The correlation length is found to be a strong function of both UV and optical magnitudes with brighter galaxies being more clustered than faint ones in both cases. Furthermore, the correlation length is dependent on a combination of UV and optical magnitudes in the sense that galaxies bright in optical magnitude have large correlation lengths irrespective of UV magnitude, while galaxies faint in optical magnitude have correlation lengths decreasing with decreasing UV brightness. These results suggest that galaxies with large stellar masses always belong to massive halos in which they can have various star formation rates, while galaxies with small stellar masses reside in less massive halos only if they have low star formation rates. There appears to be an upper limit to the stellar mass and the star formation rate which is determined by the mass of hosting dark halos.
Among more than 200 extrasolar planet candidates discovered to date, there is no known planet orbiting around normal binary stars. In this paper, we demonstrate that microlensing is a technique that can detect such planets. Microlensing discoveries of these planets are possible because the planet and host binary stars produce perturbations at a common region around center of mass of the binary stars and thus the signatures of both planet and binary can be detected in the light curves of high-magnification microlensing events. The ranges of the planetary and binary separations of systems for optimal detection vary depending on the planet mass. For a Jupiter-mass planet, we find that high detection efficiency is expected for planets located in the range of $\sim$ 1 AU -- 5 AU from the binary stars which are separated by $\sim$ 0.15 AU -- 0.5 AU
This paper investigates the possibility that UCD galaxies in the Fornax
cluster are formed by the threshing of nucleated, early-type dwarf galaxies
(hereafter dwarf galaxies).
Similar to the results of Cote et al. (2006) for the Virgo cluster, we show
that the Fornax Cluster observations are consistent with a single population in
which all dwarfs are nucleated, with a ratio of nuclear to total magnitude that
varies slowly with magnitude. Importantly, the magnitude distribution of the
UCD population is similar to that of the dwarf nuclei in the Fornax cluster.
The joint population of UCDs and the dwarfs from which they may originate is
modelled and shown to be consistent with an NFW profile with a characteristic
radius of 5 kpc. Furthermore, a steady-state dynamical model reproduces the
known mass profile of Fornax. However, there are a number of peculiarities in
the velocity dispersion data that remain unexplained.
The simplest possible threshing model is tested, in which dwarf galaxies move
on orbits in a static cluster potential and are threshed if they pass within a
radius at which the tidal force from the cluster exceeds the internal gravity
at the core of their dark matter halo. This fails to reproduce the observed
fraction of UCDs at radii greater than 30 kpc from the core of Fornax.
We review on the viability of $F(R)$-gravity. We show that recent cosmic acceleration, radiation/matter-dominated epoch and inflation could be realized in the framework of $F(R)$-gravity in the unified way. For some classes of $F(R)$-gravity, the correction to the Newton law is extremely small and there is no so-called matter instability (the very heavy positive mass for additional scalar degree of freedom is generated). The reconstruction program in modified gravity is also reviewed and it is demonstrated that {\it any} time-evolution of the universe expansion could be realized in $F(R)$-gravity. Special attention is paid to modified gravity which unifies inflation with cosmic acceleration and passes local tests. It turns out that such a theory may describe also dark matter.
We present numerical simulations of cold, axisymmetric, magnetically driven relativistic outflows. The outflows are initially sub-Alfv\'enic and Poynting flux-dominated, with total--to--rest-mass energy flux ratio up to $\mu \sim 620$. To study the magnetic acceleration of jets we simulate flows confined within a funnel with rigid wall of prescribed shape, which we take to be $z\propto r^a$ (in cylindrical coordinates, with $a$ ranging from 1 to 2). This allows us to eliminate the numerical dissipative effects induced by a free boundary with an ambient medium. We find that in all cases they converge to a steady state characterized by a spatially extended acceleration region. For the jet solutions the acceleration process is very efficient - on the outermost scale of the simulation more than half of the Poynting flux has been converted into kinetic energy flux, and the terminal Lorentz factor approached its maximum possible value ($\Gamma_\infty \simeq \mu$). The acceleration is accompanied by the collimation of magnetic field lines in excess of that dictated by the funnel shape. The numerical solutions are generally consistent with the semi-analytic self-similar jets solutions and the spatially extended acceleration observed in some astrophysical relativistic jets. In agreement with previous studies we also find that the acceleration is significantly less effective for wind solutions suggesting that pulsar winds may remain Poynting dominated when they reach the termination shock.
We show that as many as ~50 quasars with at least mJy-level expected flux density can be pre-selected as potential in-beam phase-reference targets for ASTRO-G. Most of them have never been imaged with VLBI. These sources are located around strong, compact calibrator sources that have correlated flux density >100 mJy on the longest VLBA baselines at 8.4 GHz. All the targets lie within 12' from the respective reference source. The basis of this selection is an efficient method to identify potential weak VLBI target quasars simply using optical and low-resolution radio catalogue data. The sample of these dominantly weak sources offers a good opportunity for a statistical study of their radio structure with unprecedented angular resolution at 8.4 GHz.
We studied the radio structure of high-redshift (z>3) quasars with VSOP at 1.6 and 5 GHz. These sources are the most distant objects ever observed with Space VLBI, at rest-frame frequencies up to ~25 GHz. Here we give an account of the observations and briefly highlight the most interesting cases and results. These observations allowed us, among other things, to estimate the mass of the central black holes powering these quasars, to identify large misalignments between the milli-arcsecond (mas) and sub-mas scale radio structures, and to detect apparent superluminal motion at sub-mas scale.
We construct self-consistent dynamical models for disk galaxies with triaxial, cuspy halos. We begin with an equilibrium, axisymmetric, disk-bulge-halo system and apply an artificial acceleration to the halo particles. By design, this acceleration conserves energy and thereby preserving the system's differential energy distribution even as its phase space distribution function is altered. The halo becomes triaxial but its spherically-averaged density profile remains largely unchanged. The final system is in equilibrium, to a very good approximation, so long as the halo's shape changes adiabatically. The disk and bulge are ``live'' while the halo is being deformed; they respond to the changing gravitational potential but also influence the deformation of the halo. We test the hypothesis that halo triaxiality can explain the rotation curves of low surface brightness galaxies by modelling the galaxy F568-3.
VIVA HI observations of the Virgo spiral galaxy NGC 4501 are presented. The HI disk is sharply truncated to the southwest, well within the stellar disk. A region of low surface-density gas, which is more extended than the main HI disk, is discovered northeast of the galaxy center. These data are compared to existing 6cm polarized radio continuum emission, Halpha, and optical broad band images. We observe a coincidence between the western HI and polarized emission edges, on the one hand, and a faint Halpha emission ridge, on the other. The polarized emission maxima are located within the gaps between the spiral arms and the faint Halpha ridge. Based on the comparison of these observations with a sample of dynamical simulations with different values for maximum ram pressure and different inclination angles between the disk and the orbital plane,we conclude that ram pressure stripping can account for the main observed characteristics. NGC 4501 is stripped nearly edge-on, is heading southwest, and is ~200-300 Myr before peak ram pressure, i.e. its closest approach to M87. The southwestern ridge of enhanced gas surface density and enhanced polarized radio-continuum emission is due to ram pressure compression. It is argued that the faint western Halpha emission ridge is induced by nearly edge-on ram pressure stripping. NGC 4501 represents an especially clear example of early stage ram pressure stripping of a large cluster-spiral galaxy.
Multi-frequency (4.6, 5, 5.5, 8, 8.8, 13, 15, 22 & 43 GHz) polarization observations of 6 "blazars" were obtained on the American Very Long Baseline Array (VLBA) over a 24-hr period on 2 July 2006. Observing at several frequencies, separated by short and long intervals, enabled reliable determination of the distribution of Faraday Rotation on a range of scales. In all cases the magnitude of the RM increases in the higher frequency observations, implying that the electron density and/or magnetic field strength is increasing as we get closer to the central engine. After correcting for Faraday rotation, the polarization orientation in the jet is either parallel or perpendicular to the jet direction. A transverse Rotation Measure (RM) gradient was detected in the jet of 0954+658, providing evidence for the presence of a helical magnetic field surrounding the jet. For three of the sources (0954+658, 1418+546, 2200+420), the sign of the RM in the core region changes in different frequency-intervals, indicating that the line-of-sight component of the magnetic field is changing with distance from the base of the jet. We suggest an explanation for this in terms of bends in a relativistic jet surrounded by a helical magnetic field; where there is no clear evidence for pc-scale bends, the same effect can be explained by an accelerating/decelerating jet.
We have investigated the temporal variability and statistics of the "instantaneous" Strehl ratio. The observations were carried out with the 3.63-m AEOS telescope equipped with a high-order adaptive optics system. In this paper Strehl ratio is defined as the peak intensity of a single short exposure. We have also studied the behaviour of the phase variance computed on the reconstructed wavefronts. We tested the Marechal approximation and used it to explain the observed negative skewness of the Strehl ratio distribution. The estimate of the phase variance is shown to fit a three-parameter Gamma distribution model. We show that simple scaling of the reconstructed wavefronts has a large impact on the shape of the Strehl ratio distribution.
We present a new public archive of light-motion curves in Sloan Digital Sky
Survey (SDSS) Stripe 82, covering 99 deg in right ascension from RA = 20.7 h to
3.3 h and spanning 2.52 deg in declination from Dec = -1.26 to 1.26 deg, for a
total sky area of ~249 sq deg. Stripe 82 has been repeatedly monitored in the
u, g, r, i and z bands over a seven-year baseline. Objects are cross-matched
between runs, taking into account the effects of any proper motion. The
resulting catalogue contains almost 4 million light-motion curves of stellar
objects and galaxies. The photometry are recalibrated to correct for varying
photometric zeropoints, achieving ~20 mmag and ~30 mmag root-mean-square (RMS)
accuracy down to 18 mag in the g, r, i and z bands for point sources and
extended sources, respectively. The astrometry are recalibrated to correct for
inherent systematic errors in the SDSS astrometric solutions, achieving ~32 mas
and ~35 mas RMS accuracy down to 18 mag for point sources and extended sources,
respectively.
For each light-motion curve, 229 photometric and astrometric quantities are
derived and stored in a higher-level catalogue. On the photometric side, these
include mean exponential and PSF magnitudes along with uncertainties, RMS
scatter, chi^2 per degree of freedom, various magnitude distribution
percentiles, object type (stellar or galaxy), and eclipse, Stetson and Vidrih
variability indices. On the astrometric side, these quantities include mean
positions, proper motions as well as their uncertainties and chi^2 per degree
of freedom. The here presented light-motion curve catalogue is complete down to
r~21.5 and is at present the deepest large-area photometric and astrometric
variability catalogue available.
We present the results of relic density calculations for cold dark matter candidates coming from a model of dark energy and dark matter, which is described by an asymptotically free gauge group SU(2)_Z (QZD) with a coupling constant alpha_Z ~ 1 at very low scale of Lambda_Z ~ 10^(-3) eV while alpha_Z ~ weak coupling at high energies. The dark matter candidates of QZD are two fermions in the form of weakly interacting massive particles. Our results show that for masses between 50 and 285 GeV, they can account for either a considerable fraction or the entire dark matter of the Universe.
We are using "broadband" (4.6 to 43 GHz) multi-frequency VLBA polarization observations of compact AGN to investigate the 3-D structure of their jet magnetic (B) fields. Observing at several frequencies, separated by short and long intervals, enables reliable determination of the distribution of Faraday Rotation, and thereby the intrinsic B field structure. Transverse Rotation Measure (RM) gradients were detected in the jets of 0954+658 and 1418+546, providing evidence for the presence of a helical B field surrounding the jet. The RM in the core regions of 2200+420 (BL Lac), 0954+658 and 1418+546 display different signs in different frequency-intervals (on different spatial scales); we suggest an explanation for this in terms of modest bends in a helical B field surrounding their jets. In future, polarization observations with a combination of VSOP-2 at 8, 22 and 43 GHz and ground arrays at frequencies with corresponding resolution will help map out the distributions of Faraday rotation, spectral index and the 3-D B field structure both across the jet and closer to the central engine, providing strong constraints for any jet B field models.
The recent interferometric study of Achernar, leading to the conclusion that its geometrical oblateness cannot be explained in the Roche approximation, has stirred substantial interest in the community, in view of its potential impact in many fields of stellar astrophysics. It is the purpose of this paper to reinterpret the interferometric observations with a fast rotating, gravity darkened central star surrounded by a small equatorial disk, whose presence is consistent with contemporaneous spectroscopic data. We find that we can only fit the available data assuming a critically rotating central star. We identified two different disk models that simultaneously fit the spectroscopic, polarimetric, and interferometric observational constraints: a tenuous disk in hydrostatic equilibrium (i.e., with small scaleheight) and a smaller, scaleheight enhanced disk. We believe that these relatively small disks correspond to the transition region between the photosphere and the circumstellar environment, and that they are probably perturbed by some photospheric mechanism. The study of this interface between photosphere and circumstellar disk for near-critical rotators is crucial to our understanding of the Be phenomenon, and the mass and angular momentum loss of stars in general. This work shows that it is nowadays possible to directly study this transition region from simultaneous multi-technique observations.
This paper proposes a new phenomenology for strong incompressible MHD turbulence with nonzero cross helicity. This phenomenology is then developed into a quantitative Fokker-Planck model that describes the time evolution of the anisotropic power spectra of the fluctuations propagating parallel and anti-parallel to the background magnetic field. It is found that in steady state the power spectra of the magnetic field and total energy are steeper than a Kolmogorov spectrum and become increasingly steep as C/E increases, where C is the cross helicity and E is the fluctuation energy. Increasing C with fixed E increases the time required for energy to cascade to smaller scales, reduces the cascade power, and increases the anisotropy of the small-scale fluctuations. The implications of these results for the solar wind and solar corona are discussed in some detail.
We have constructed a grid of photoionization models of spherical, elliptical and bipolar planetary nebulae. Assuming different velocity fields, we have computed line profiles corresponding to different orientations, slit sizes and positions. The atlas is meant both for didactic purposes and for the interpretation of data on real nebulae. As an application, we have shown that line profiles are often degenerate, and that recovering the geometry and velocity field from observations requires lines from ions with different masses and different ionization potentials. We have also shown that the empirical way to measure mass-weighted expansion velocities from observed line widths is reasonably accurate if considering the HWHM. For distant nebulae, entirely covered by the slit, the unknown geometry and orientation do not alter the measured velocities statistically. The atlas is freely accessible from internet. The Cloudy_3D suite and the associated VISNEB tool are available on request.
We analyze integral-field ionized gas and stellar line-of-sight kinematics in the context of determining the stellar velocity ellipsoid for spiral galaxies observed by the Disk-Mass Survey. Our new methodology enables us to measure, for the first time, a radial gradient in the ellipsoid ratio sigma_z / sigma_R. Random errors in this decomposition are 15% at two disk scale-lengths.
Solar observations with the Hinode space observatory led to the discovery of strong horizontal magnetic fields in the photosphere of quiet internetwork regions. Here we investigate realistic numerical simulations of the surface layers of the Sun with respect to horizontal magnetic fields and compute the corresponding responses in the Fe I 630 nm line pair. We analyze two simulation runs with greatly different initial and boundary conditions. Both show a local maximum in the mean flux density of the horizontal field component at a height of around 500 km in the photosphere, where the horizontal surpasses the vertical component by a factor of 2.0 or 5.6, depending on the initial and boundary conditions. From the synthesized Stokes profiles we derive a mean horizontal field component that is, respectively, 1.5 and 2.8 stronger than the vertical component. This is the consequence of both intrinsically stronger flux densities and the larger area fraction occupied by, the horizontal fields. It is shown that convective overshooting pumps horizontal fields in the vertical direction, leading to a positive vertical Poynting flux in the photosphere, while this quantity is negative in the convectively unstable layer below it so that the solar surface constitutes a separatrix for the vertical Poynting flux.
We review recent 3D cosmological hydrodynamic simulations of primordial star formation from cosmological initial conditions (Pop III.1) and from initial conditions that have been altered by radiative feedback from stellar sources (Pop III.2). We concentrate on simulations that resolve the formation of the gravitationally unstable cloud cores in mini-halos over the mass range $10^5 < M/\Msun < 10^7 $ and follow their evolution to densities of at least $10^{10} \cmm3$ and length scales of $<10^{-2}$ pc such that accretion rates can be estimated. The advent of ensembles of such simulations exploring a variety of conditions permits us to assess the robustness of the standard model for Pop III.1 star formation and investigate scatter in their formation redshifts and accretion rates, thereby providing much needed information about the Pop III IMF. The simulations confirm the prediction that Pop III.1 stars were massive ($\sim 100 \Msun$), and form in isolation in primordial mini-halos. Simulations of Pop III.2 star forming in relic HII regions suggest somewhat lower masses ($\sim 30 \Msun$) which may help explain the chemical abundances of extremely metal poor stars. We note that no 3D simulation at present has achieved stellar density let alone followed the entire accretion history of the star in any scenario, and thus the IMF of Pop III stars remains poorly determined theoretically.
This paper presents a mechanism that may modify the extinction law for SNIa
observed at higher redshift. Starting from the observations that (1) SNIa occur
predominantly in spiral galaxies, (2) star-formation ejects ISM out of the
plane of spirals, (3) star-formation alters the extinction properties of the
dust in the ISM, and (4) there is substantially more star-formation at higher
redshift, I propose that spiral galaxies have a dustier halo in the past than
they do now. The ejected material's lower value of $R_V$ will lead to a lower
average value ($\bar{R}_V$) for SNIa observed at higher redshift.
Two relations in SNIa observations indicate evolution of the average $R_V$:
the relation of observed $R_V$ with inclination of the host galaxy at low
redshift and the matching of the distribution of extinction values ($A_V$) for
SNIa in different redshift intervals. The inclination effect does point to a
halo with lower $R_V$ values. In contrast, the distributions of $A_V$ values
match best for a $\bar{R}_V(z)$ evolution that mimics the relation of SNIa
dimming with redshift attributed to the cosmological constant. However, even in
the worse case scenario, the evolution $\bar{R}_V$ can not fully explain the
dimming of SNIa: host galaxy extinction law evolution is not a viable
alternative to account for the dimming of SNIa.
Future observations of SNIa --multi-color lightcurves and spectra-- will
solve separately for values of $A_V$ and $R_V$ for each SNIa . Solving for
evolution of $\bar{R}_V$ (and $A_V$) with redshift will be important for the
coming generation of cosmological SNIa measurements and has the bonus science
of insight into the distribution of dust-rich ISM in the host galaxies in the
distant past.
The concordance Cold Dark Matter model for the formation of structure in the Universe, while remarkably successful at describing observations on large scales, has a number of problems on galaxy scales. The Milky Way and its satellite system provide a key laboratory for exploring dark matter (DM) in this regime, but some of the most definitive tests of local DM await microarcsecond astrometry, such as will be delivered by the Space Interferometry Mission (SIM Planetquest). I discuss several tests of Galactic DM enabled by future microarcsecond astrometry.
We implement an efficient method to quantify time-dependent orbital complexity in gravitational $N$-body simulations. The technique, which we name DWaTIM, is based on a discrete wavelet transform of velocity orbital time series. The wavelet power-spectrum is used to measure trends in complexity continuously in time. We apply the method to the test cases $N=3$ Pythagorean- and a perturbed $N=5$ Caledonian configurations. The method recovers the well-known time-dependent complexity of the dynamics in these small-$N$ problems. We then apply the technique to an equal-mass collisional $N=256$ body simulation ran through core-collapse. We find that a majority of stars evolve on relatively complex orbits up to the time when the first hard binary forms, whereas after core-collapse, less complex orbits are found on the whole as a result of expanding mass shells.
The variable star DZ Cru was thought to be a nova when it was discovered in eruption in 2003 August. This explanation was later challenged, however, when the first spectra of the object were reported. We present near infrared spectroscopy of DZ Cru obtained at the New Technology Telescope on 3 occasions, starting 1.5 years after outburst, with the aim of establishing the nature of the object. The spectra display H I, O I, [N I] emission lines, together with He I P Cygni lines superposed on a dust continuum. These observations suggest the "peculiar variable in Crux'' is a classical nova.
Following the recent abundance measurements of Mg, Al, Ca, Fe, and Ni in the black hole X-ray binary XTE J1118+480 using medium-resolution Keck II/ESI spectra of the secondary star (Gonz\'alez Hern\'andez et al. 2006), we perform a detailed abundance analysis including the abundances of Si and Ti. These element abundances, higher than solar, indicate that the black hole in this system formed in a supernova event, whose nucleosynthetic products could pollute the atmosphere of the secondary star, providing clues on the possible formation region of the system, either Galactic halo, thick disk, or thin disk. We explore a grid of explosion models with different He core masses, metallicities, and geometries. Metal-poor models associated with a formation scenario in the Galactic halo provide unacceptable fits to the observed abundances, allowing us to reject a halo origin for this X-ray binary. The thick-disk scenario produces better fits, although they require substantial fallback and very efficient mixing processes between the inner layers of the explosion and the ejecta, making quite unlikely an origin in the thick disk. The best agreement between the model predictions and the observed abundances is obtained for metal-rich progenitor models. In particular, non-spherically symmetric models are able to explain, without strong assumptions of extensive fallback and mixing, the observed abundances. Moreover, asymmetric mass ejection in a supernova explosion could account for the required impulse necessary to launch the system from its formation region in the Galactic thin disk to its current halo orbit.
We highlight the importance of transit observations on understanding the physics of planetary atmospheres and interiors. Transmission spectra and emission spectra allow us to characterize this exotic atmospheres, which possess TiO, VO, H2O, CO, Na, and K, as principal absorbers. We calculate mass-radius relations for water-rock-iron and gas giant planets and examine these relations in light of current and future transit observations. A brief review is given of mechanisms that could lead to the large radii observed for some transiting planets.
I discuss different theories of massive star formation: formation from massive cores, competitive Bondi-Hoyle accretion, and protostellar collisions. I summarize basic features of the Turbulent Core Model (TCM). I then introduce the Orion Kleinmann-Low (KL) region, embedded in the Orion Nebula Cluster (ONC) and one of the nearest regions of massive star formation. The KL region contains three principal radio sources, known as "I", "n" and "BN". BN is known to be a runaway star, almost certainly set in motion by dynamical ejection within the ONC from a multiple system of massive stars, that would leave behind a recoiling, hard, massive, probably eccentric binary. I review the debate about whether this binary is Theta^1C, the most massive star in the ONC, or source "I", and argue that it is most likely to be Theta^1C, since this is now known be a recoiling, hard, massive, eccentric binary, with properties that satisfy the energy and momentum constraints implied by BN's motion. Source "n" is a relatively low-mass protostar with extended radio emission suggestive of a bipolar outflow. Source "I", located near the center of the main gas concentration in the region, the Orion Hot Core, is the likely location of a massive protostar that is powering the KL region, and I discuss how its basic properties are consistent with predictions from the TCM. In this scenario, the radio emission from source "I" is the base of a bipolar outflow that is ionized by the massive protostar and should be elongated along the axis of the outflow.
The Alpha Magnetic Spectrometer (AMS) to be installed on the International
Space Station (ISS) will measure charged cosmic ray spectra of elements up to
iron, in the rigidity range from 1 GV to 1 TV, for at least three years. AMS is
a large angular spectrometer composed of different subdetectors, including a
proximity focusing Ring Imaging CHerenkov (RICH) detector. This will be
equipped with a mixed radiator made of aerogel and sodium fluoride (NaF), a
lateral conical mirror and a detection plane made of 680 photomultipliers
coupled to light guides. The RICH detector allows measurements of particle's
electric charge up to iron, and particle's velocity. Two possible methods for
reconstructing the Cherenkov angle and the electric charge with the RICH will
be discussed.
A RICH prototype consisting of a detection matrix with 96 photomultipliers, a
segment of a conical mirror and samples of the radiator materials was built and
its performance was evaluated using ion beam data. Results from the last test
beam performed with ion fragments resulting from the collision of a 158
GeV/c/nucleon primary beam of indium ions (CERN SPS) on a lead target are
reported. The large amount of collected data allowed to test and characterize
different aerogel samples and the NaF radiator. In addition, the reflectivity
of the mirror was evaluated. The data analysis confirms the design goals.
For more than fifty years, it has been believed that cosmic ray (CR) nuclei are accelerated to high energies in the rapidly expanding shockwaves created by powerful supernova explosions. Yet observational proof of this conjecture is still lacking. Recently, Uchiyama and collaborators reported the detection of small-scale X-ray flares in one such supernova remnant, dubbed 'RX J1713-3946' (a.k.a. G347.3-0.5), which also emits very energetic, TeV (10^12 eV) range, gamma-rays. They contend that the variability of these X-ray 'hotspots' implies that the magnetic field in the remnant is about a hundred times larger than normally assumed; and this, they say, means that the detected TeV range photons were produced in energetic nuclear interactions, providing 'a strong argument for acceleration of protons and nuclei to energies of 1 PeV (10^15 eV) and beyond in young supernova remnants.' We point out here that the existing multiwavelength data on this object certainly do not support such conclusions. Though intriguing, the small-scale X-ray flares are not the long sought-after 'smoking gun' of nucleonic CR acceleration in SNRs.
We present the results of a systematic study of mid-IR spectra of Galactic regions, Magellanic HII regions, and galaxies of various types (dwarf, spiral, starburst), observed by the satellites ISO and Spitzer. We study the relative variations of the 6.2, 7.7, 8.6 and 11.3 micron features inside spatially resolved objects (such as M82, M51, 30 Doradus, M17 and the Orion Bar), as well as among 90 integrated spectra of 50 objects. Our main results are that the 6.2, 7.7 and 8.6 micron bands are essentially tied together, while the ratios between these bands and the 11.3 micron band varies by one order of magnitude. This implies that the properties of the PAHs are remarkably universal throughout our sample, and that the relative variations of the band ratios are mainly controled by the fraction of ionized PAHs. In particular, we show that we can rule out both the modification of the PAH size distribution, and the mid-infrared extinction, as an explanation of these variations. Using a few well-studied Galactic regions (including the spectral image of the Orion Bar), we give an empirical relation between the I(6.2)/I(11.3) ratio and the ionization/recombination ratio G0/ne.Tgas^0.5, therefore providing a useful quantitative diagnostic tool of the physical conditions in the regions where the PAH emission originates. Finally, we discuss the physical interpretation of the I(6.2)/I(11.3) ratio, on galactic size scales.
The Alpha Magnetic Spectrometer (AMS) is a particle detector, designed to search for cosmic antimatter and dark matter and to study the elemental and isotopic composition of primary cosmic rays, that will be installed on the International Space Station (ISS) in 2008 to operate for at least three years. The detector will be equipped with a ring imaging Cherenkov detector (RICH) enabling measurements of particle electric charge and velocity with unprecedented accuracy. Physics prospects and test beam results are shortly presented.
Simultaneous observations by the large number of gamma-ray burst detectors operating in the GLAST era will provide the spectra, lightcurves and locations necessary for studying burst physics and testing the putative relations between intrinsic burst properties. The detectors' energy band and the accumulation timescale of their trigger system affect their sensitivity to hard vs. soft and long vs. short bursts. Coordination of the Swift and GLAST observing plans consistent with Swift's other science objectives could increase the detection rate of GLAST bursts with redshifts.
The Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS) has created a large homogeneous database of intermediate redshift (0.2 < z < 1.0) type Ia supernovae (SNe Ia). The SNLS team has shown that correlations exist between SN Ia rates, properties, and host galaxy star formation rates. The SNLS SN Ia database has now been combined with a photometric redshift galaxy catalog and an optical galaxy cluster catalog to investigate the possible influence of galaxy clustering on the SN Ia rate, over and above the expected effect due to the dependence of SFR on clustering through the morphology-density relation. We identify three cluster SNe Ia, plus three additional possible cluster SNe Ia, and find the SN Ia rate per unit mass in clusters at intermediate redshifts is consistent with the rate per unit mass in field early-type galaxies and the SN Ia cluster rate from low redshift cluster targeted surveys. We also find the number of SNe Ia in cluster environments to be within a factor of two of expectations from the two component SNIa rate model.
We develop a numerical formalism to examine the evolution of matter sources in modern cosmology under inhomogeneous conditions. These can include the Chaplygin gas and mixtures of cold dark matter (CDM) and dark energy (DE), taken as sources of a spherically symmetric Lemaitre--Tolman--Bondi (LTB) metric. Besides local energy density and pressure, non--local volume averaged density and pressure emerge naturally from the field and conservation equations. The latter equations can be reduced to a self--consistent system of evolution equations for the local and averaged variables, a suitable Hubble scale function and a shear factor. The evolution equations for the averaged variables are formally identical to those of an equivalent Friedman--Lemaitre--Robertson--Walker (FLRW) cosmology. This suggests that cosmic dynamics could be determined by these non--local variables, while local dynamics would follow from the more complicated evolution equations of local variables. The resulting models are sufficiently general to test a wide variety of physical assumptions and scenarios on modern cosmological sources: ``equations of state'', possible interactions between CDM and DE, black hole and structure formation, matchings with a FLRW background. At the same time, the models are sufficiently idealized so that evolution equations can be integrated with relatively simple numerical methods. In order to illustrate the formalism we briefly examine local gravitational collapse in an expanding Chaplygin gas and void formation in a simple interactive mixture of CDM and DE.
In cyclic cosmology based on phantom dark energy the requirement that our universe satisfy a CBE-condition ({\it Comes Back Empty}) imposes a lower bound on the number $N_{\rm cp}$ of causal patches which separate just prior to turnaround. This bound depends on the dark energy equation of state $w = p/\rho = -1 - \phi$ with $\phi > 0$. More accurate measurement of $\phi$ will constrain $N_{\rm cp}$. The critical density $\rho_c$ in the model has a lower bound $\rho_c \ge (10^9 {\rm GeV})^4$ or $\rho_c \ge (10^{18} {\rm GeV})^4$ when the smallest bound state has size $10^{-15}$m, or $10^{-35}$m, respectively.
We discuss models that can account for today's dark energy. The underlying cosmological constant may be Planck scale but starts as a redundant coupling which can be eliminated by a field redefinition. The observed vacuum energy arises when the redundancy is explicitly broken, say by a non-minimal coupling to curvature. We give a recipe for constructing models, including R + 1/R type models, that realize this mechanism and satisfy all solar system constraints on gravity. A similar model, based on Gauss-Bonnet gravity, provides a technically natural explanation for dark energy and exhibits an interesting see-saw behavior: a large underlying cosmological constant gives rise to both low and high curvature solutions. Such models could be statistically favored in the string landscape.
We investigate the modified gravity theories in terms of the effective dark energy models. We compare the cosmic expansion history and the linear growth in different models. We also study the evolution of linear cosmological perturbations in modified theories of gravity assuming the Palatini formalism. We find the stability of the superhorizon metric evolution depends on models. We also study the matter density fluctuation in the general gauge and show the differential equations in super and sub-horizon scales.
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