In this letter we present ground-based subarcsecond mid-infrared imaging and spectroscopy of young super star clusters in the overlap region of the merging galaxies NGC4038/4039 (the Antennae) obtained with the VLT Imager and Spectrometer for mid-Infrared (VISIR). With its unprecedented spatial resolution VISIR begins to resolve the HII/PDR complexes around the star-forming regions for the first time. In the N-band spectra of two young star clusters unexpectedly low polycyclic aromatic hydrocarbon (PAH) emission is observed, compared to what is seen with the Infrared Space Observatory (ISO) and with the Spitzer Space Telescope. We conclude that a large fraction of the PAH emission cannot directly be associated with the super star clusters, but originate from an extended region of at least 215 pc radius around the clusters. In the distribution of [NeII] 12.81 micron emission a highly obscured cluster is discovered that does not have an optical or near-infrared counterpart.
We find that the size-luminosity relation of early-type Brightest Cluster Galaxies (BCGs), Re ~ L^0.92, is steeper than that for the bulk of the early-type galaxy population, for which Re ~ L^0.62. This is true if quantities derived from either deVaucouleur or Sersic fits to the surface brightness profiles are used. This difference is not due to contamination from intra-cluster light. In addition, when placed on the Fundamental Plane defined by the bulk of the early-type population, early-type BCGs show only a small offset, but considerably smaller scatter. The larger than expected sizes of BCGs, and the increased homogeneity, are qualitatively consistent with models which seek to explain the colors of the most massive galaxies by invoking dry dissipationless mergers, since dissipation tends to reduce the sizes of galaxies, and wet mergers would tend to increase the scatter in luminosity at fixed size and velocity dispersion. Dry merger models also suggest slightly bluer colors for BCGs; this is not seen in our data, suggesting that if BCGs formed from dry mergers, then their progenitors hosted redder stellar populations than typical for their luminosities. Despite following a steeper size-luminosity relation, BCGs tend to define a tight relation between dynamical mass sigma^2 Re/G and luminosity. As a result, they define a shallower sigma-L relation than the bulk of the early-type galaxy population. This shallower relation suggests there may be curvature in the correlation between black hole mass and velocity dispersion; simple extrapolation of the M_bh-sigma relation to large sigma will underestimate M_bh.
We present new numerical simulations in the thin-disk approximation which characterize the burst mode of protostellar accretion. The burst mode begins upon the formation of a centrifugally balanced disk around a newly formed protostar. It is comprised of prolonged quiescent periods of low accretion rate (typically $\la 10^{-7} \Msun$ yr$^{-1}$) which are punctuated by intense bursts of accretion (typically $\ga 10^{-4} \Msun$ yr$^{-1}$, with duration $\la 100$ yr) during which most of the protostellar mass is accumulated. The accretion bursts are associated with the formation of dense protostellar/protoplanetary embryos, which are later driven onto the protostar by the gravitational torques that develop in the disk. Gravitational instability in the disk, driven by continuing infall from the envelope, is shown to be an effective means of transporting angular momentum outward, and mass inward to the protostar. We show that the disk mass always remains significantly less than the central protostar mass throughout this process. The burst phenomenon is robust enough to occur for a variety of initial values of rotation rate, frozen-in (supercritical) magnetic field, and density-temperature relations. Even in cases where the bursts are nearly entirely suppressed, a moderate increase in cloud size or rotation rate can lead to vigorous burst activity. We conclude that most (if not all) protostars undergo a burst mode of evolution during their early accretion history, as inferred empirically from observations of FU Orionis variables.
By combining data from four different sets of published 3-D simulations of Keplerian shearing boxes unstable to the magnetorotational instability (MRI), we highlight tight anti-correlations between the total effective inferred angular momentum transport parameter, $\alpha_{tot}$, its separate Maxwell and Reynolds contributions $\alpha_{mag}$ and $\alpha_{kin}$, and the kinetic to magnetic pressure ratio $\beta$. Plots of $Log (\alpha_{kin}), Log (\alpha_{mag})$, and $Log (\alpha_{tot})$ vs $Log (\beta)$ are straight lines even as $\alpha_{kin}$, $\alpha_{mag}$,and $\alpha_{tot}$ vary by four orders of magnitude for the full range of simulations included. The ratio $\alpha_{kin}/\alpha_{mag}$ and the product $\alpha_{tot}\beta$ are therefore remarkably constant over this range, the latter maintining a value between $0.4-0.5$ independent of the presence or absence of weak mean fields, the simulation method, and the choice of initial and boundary conditions, with possibly a slight dependence on polytropic index. Although more work is needed to derive $\alpha_{tot}\beta$ from first principles, the simulations tightly constrain this product even though they do not strongly constrain $\alpha_{tot}$ and $\beta$ separately.
The shape of the angular power spectrum of galaxies in the linear regime is defined by the horizon size at the matter-radiation equality. When calibrated by cosmic microwave background measurements, the shape of the clustering spectrum can be used as a standard ruler to estimate angular diameter distance as a function of redshift at which galaxy clustering is measured. We apply the proposed cosmological test of Cooray et al. (2001) to a recent set of luminous red galaxy angular clustering spectra from the Sloan Digital Sky Survey between redshifts of 0.2 and 0.6. Using the overall shape of the clustering power spectrum in the linear regime, w e measure comoving angular diameter distances to eight redshift bins by marginalizing over the bias factors that determine the overall amplitude of the clustering spectrum in each of the bins. The Hubble constant consistent with these distance estimates is 68.5^+6.7_-6.1 km s^-1 Mpc-1 at the 68% confidence level. We comment on the expected improvements with future surveys and the potential to measure dark energy parameters with this method.
In addition to a smooth component of WIMP dark matter in galaxies, there may be streams of material; the effects of WIMP streams on direct detection experiments is examined in this paper. The contribution to the count rate due to the stream cuts off at some characteristic energy. Near this cutoff energy, the stream contribution to the annual modulation of recoils in the detector is comparable to that of the halo, even if the stream represents only a small portion of the local halo density. Consequently the total modulation may be quite different than would be expected for the standard halo model alone: it may not be cosine-like and can peak at a different date than expected. The effects of speed, direction, density, and velocity dispersion of a stream on the modulation are examined. We describe how the observation of a modulation can be used to determine these stream parameters. Alternatively, the presence of a dropoff in the recoil spectrum can be used to determine the WIMP mass if the stream speed is known. The annual modulation of the cutoff energy together with the annual modulation of the overall signal provide a "smoking gun" for WIMP detection.
We explore the requirements for a Lyman-alpha forest (LyaF) survey designed to measure the angular diameter distance and Hubble parameter at 2~<z~<4 using the standard ruler provided by baryonic acoustic oscillations (BAO). The goal would be to obtain a high enough density of sources to probe the three-dimensional density field on the scale of the BAO feature. A percent-level measurement in this redshift range can almost double the Dark Energy Task Force Figure of Merit, relative to the case with only a similar precision measurement at z~1, if the Universe is not assumed to be flat. This improvement is greater than the one obtained by doubling the size of the z~1 survey, with Planck and a weak SDSS-like z=0.3 BAO measurement assumed in each case. Galaxy BAO surveys at z~1 may be able to make an effective LyaF measurement simultaneously at minimal added cost, because the required number density of quasars is relatively small. We discuss the constraining power as a function of area, magnitude limit (density of quasars), resolution, and signal-to-noise of the spectra. For example, a survey covering 2000 sq. deg. and achieving S/N=1.8 per Ang. at g=23 (~40 quasars per sq. deg.) with an R~>250 spectrograph is sufficient to measure both the radial and transverse oscillation scales to 1.4% from the LyaF (or better, if fainter magnitudes and possibly Lyman-break galaxies can be used). At fixed integration time and in the sky-noise-dominated limit, a wider, noisier survey is generally more efficient; the only fundamental upper limit on noise being the need to identify a quasar and find a redshift. Because the LyaF is much closer to linear and generally better understood than galaxies, systematic errors are even less likely to be a problem.
The supermassive black hole in the center of our Galaxy, Sgr A*, is unique because the angular size of the black hole is the largest in the sky thus providing detailed boundary conditions on, and much less freedom for, accretion flow models. In this paper I review advection-dominated accretion flow (ADAF; another name is radiatively inefficient accretion flow) models for Sgr A*. This includes the developments and dynamics of ADAFs, and how to explain observational results including the multi-waveband spectrum, radio polarization, IR and X-ray flares, and the size measurements at radio wavebands.
Spectral state transitions in neutron star LMXB systems have been widely observed yet not well understood. Here we report an abrupt spectral change in 4U 1608-52, a typical atoll source, during its decay phase of the 2004 outburst. The source is found to undergo sudden changes in its spectral hardness and other properties. The transition occurred when its luminosity is between (3.3-5.3) E36 ergs/s, assuming a distance of 3.6 kpc. Interpreting this event in terms of the propeller effect, we infer the neutron star surface magnetic field as (1.4-1.8) E8 Gauss. We also briefly discuss similarities and differences between the spectral states of neutron star and black hole binary systems.
Multi-object spectroscopy (MOS) instruments, such as the Two-degree Field (2dF) facility of the Anglo-Australian Observatory (AAO), have facilitated large-scale redshift surveys. Yet despite their acclaim, instrument design has been suspected of introducing subtle selection effects into surveys. Investigation into these selection effects has been overshadowed by instrument complexity. We identify the field configuration algorithm (FCA) used to select targets for observation as mainly responsible for such effects. A FCA can imprint artificial structure on observed target distributions, which may accrue over large angular scales, potentially to the detriment of statistical analyses applied to such surveys. We present here a new FCA developed for 2dF that is based on simulated annealing (SA), a generic method commonly used to solve constrained optimisation problems. We generate synthetic fields and utilise mock 2dF volumes to contrast the behaviour of previous strategies with the SA FCA. The angular two-point correlation function and other sensitive techniques reveal that the new FCA achieves unprecedented sampling uniformity and target yield with improved target priority handling and observational flexibility over current FCAs. The SA FCA is generic enough to be used by current 2dF-like and potentially next-generation MOS instruments with little modification.
Several observational constraints are imposed on the interacting holographic model of Dark Energy and Dark Matter. First we use the age parameter today, as given by the WMAP results. Subsequently, we explained the reason why it is possible, as recently observed, for an old quasar to be observed in early stages of the universe. We discuss this question in terms of the evolution of the age parameter as well as in terms of the structure formation. Finally, we give a detailed discussion of the constraints implied by the observed CMB low $\ell$ suppression. As a result, the interacting holographic model has been proved to be robust and with reasonable bounds predicts a non vanishing interaction of Dark Energy and Dark Matter.
We present our proposal for a small X-ray mission DIOS (Diffuse Intergalactic Oxygen Surveyor), consisting of a 4-stage X-ray telescope and an array of TES microcalorimeters, cooled with mechanical coolers, with a total weight of about 400 kg. The mission will perform survey observations of warm-hot intergalactic medium using OVII and OVIII emission lines, with the energy coverage up to 1.5 keV. The wide field of view of about 50' diameter, superior energy resolution close to 2 eV FWHM, and very low background will together enable us a wide range of science for diffuse X-ray sources. We briefly describe the design of the satellite, performance of the subsystems and the expected results.
The number of binary asteroids in the near-Earth region might be significantly higher than expected. While Bottke and Melosh (1996) suggested that about 15% of the NEAs are binaries, as indicated from the frequency of double craters, and Pravec and Harris (2000) suggested that half of the fast-rotating NEAs are binaries, our recent study of Aten NEA lightcurves shows that the fraction of binary NEAs might be even higher than 50%. We found two asteroids with asynchronous binary characteristics such as two additive periods and fast rotation of the primary fragment. We also identified three asteroids with synchronous binary characteristics such as amplitude higher than one magnitude, U-shaped lightcurve maxima and V-shaped lightcurve minima. These five binaries were detected out of a sample of eight asteroids observed, implying a 63% binarity frequency. Confirmation of this high binary population requires the study of a larger representative sample. However, any mitigation program that requires the deflection or demise of a potential impactor will have to factor in the possibility that the target is a binary or multiple asteroid system.
Diffuse interstellar bands (DIBs) still await an explanation. One expects that some progress in this field will be possible when all the known DIBs are divided into families in such a way that only one carrier is responsible for all bands belonging to the given family. Analysing high resolution optical spectra of reddened stars we try to find out spectroscopic families for two prominent DIBs, at 5780 and 5797 angstroms. Among the DIBs, observed in the spectral range from 5590 to 6830 angstroms, we have found 8 candidates to belong to 5780 spectroscopic family and the other 12 DIBs candidating to family of 5797 structure.
This paper presents the cosmological applications of the quasispherical Szekeres model. The quasispherical Szekeres model is an exact solution of the Einstein field equations, which represents a time-dependent mass dipole superposed on a monopole and therefore is suitable for modelling double structures such as voids and adjourning galaxy superclusters. Moreover, as the Szekeres model is an exact solution of the Einstein equations it enables tracing light and estimation of the impact of cosmic structures on light propagation. This paper presents the evolution of a void and adjourning supercluster and also reports on how the Szekeres model might be employed either for the estimation of mass of galaxies clusters or for the estimation of the luminosity distance.
The Friedman equation is solved for a universe contains hotdark matter and cold dark matter. In this scenario, hot-dark matter drives an accelerating universe no cold dark matter.
We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuum observations toward one of the strongest mm-wave sources in OMC-3, MMS 7, with the Nobeyama Millimeter Array (NMA) and the Nobeyama 45 m telescope. With the NMA, we detected centrally-condensed 3.3 mm dust-continuum emission which coincides with the MIR source and the free-free jet. Our combined H13CO+ observations have revealed a disk-like envelope. The size and the mass of the disk-like envelope are 0.15 times 0.11 pc and 5.1 - 9.1 M_sun, respectively. The combined map also shows that the outer portion of the disk-like envelope has a fan-shaped structure which delineates the rim of the CO(1-0) outflow observed with the NMA. The position-velocity (P-V) diagrams in the H13CO+ (1-0) emission show that the velocity field in the disk-like envelope is composed of a dispersing gas motion and a possible rigid-like rotation. The mass dispersing rate is estimated to be (3.4 - 6.0) times 10^-5 M_sun/yr, which implies that MMS 7 has an ability to disperse ~10 M_sun during the protostellar evolutional time of a few times 10^5 yr. The specific angular momentum of the possible rotation in the disk-like envelope is nearly two orders of magnitude larger than that in low-mass cores. The turn-over point of the power law of the angular momentum distribution in the disk-like envelope (< 0.007 pc), which is likely to be related to the outer radius of the central mass accretion, is similar to the size of the 3.3 mm dust condensation. The intermediate-mass protostar MMS 7 is in the last stage of the main accretion phase and that the substantial portion of the outer gas has already been dispersed, while the mass accretion may still be on-going at the innermost region traced by the dusty condensation.
We have searched for microlensing variability in the light curves of five gravitationally lensed quasars with well-determined time delays: SBS 1520+530, FBQ 0951+2635, RX J0911+0551, B1600+434 and HE 2149-2745. By comparing the light curve of the leading image with a suitably time offset light curve of a trailing image we find that two (SBS 1520+530 and FBQ 0951+2635) out of the five quasars have significant long-term (years) and short-term (100 days) brightness variations that may be attributed to microlensing.The short-term variations may be due to nanolenses, relativistic hot or cold spots in the quasar accretion disks, or coherent microlensing at large optical depth.
We present the first systematic search for microlensing events with variability in their baselines using data from the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). A total of 137 candidates (88 new) was discovered toward the Galactic bulge. Among these, 21 have periodic oscillations in their baselines, 111 are irregular variables and 5 are potential long period detached eclipsing binaries. This is about 10% of the total number of constant baseline events. They are hence quite common and can be regarded as a new type of exotic events, which allow the determination of extra parameters of the events. We show that microlensing of variable stars may allow us to break the degeneracy between the blending parameter and magnification. We note that in some cases variability hidden in the baseline due to strong blending may be revealed in highly magnified events and resemble other exotic microlensing behavior, including planetary deviation. A new system (VEWS) for detecting ongoing variable baseline microlensing events is presented.
We analyze X-ray sources detected over 4.2 pseudo-contiguous sq. deg. in the 0.5-2 keV and 2-10 keV bands down to fluxes of 2x10^{-15} and 8x10^{-15} erg/s/cm^2 respectively, as part of the XMM Large Scale Structure Survey. The logN-logS in both bands shows a steep slope at bright fluxes, but agrees well with other determinations below ~2x10^{-14} erg/s/cm^2. The detected sources resolve close to 30 per cent of the X-ray background in the 2-10 keV band. We study the two-point angular clustering of point sources using nearest neighbours and correlation function statistics and find a weak, positive signal for ~1130 sources in the 0.5-2 keV band, but no correlation for ~400 sources in the 2-10 keV band below scales of 100 arcsec. A sub-sample of ~200 faint sources with hard X-ray count ratios, that is likely to be dominated by obscured AGN, does show a positive signal with the data allowing for a large scaling of the angular correlation length, but only at the ~2 (3) sigma level, based on re-sampling (Poisson) statistics. We discuss possible implications and emphasize the importance of wider, complete surveys in order to fully understand the large scale structure of the X-ray sky.
It has long been speculated that the observed periodic radial velocity pattern for the K giant Pollux might be explained in terms of an orbiting planetary companion. We have collected 80 high-resolution spectra for Pollux at Lick Observatory yielding precise radial velocities with a mean error of 3.8 m/s, providing the most comprehensive and precise data set available for this star. Our data confirm the periodicity previously seen in the radial velocities. We derive a period of 589.7+/-3.5 days and, assuming a primary mass of 1.86 M_Sun, a minimum companion mass of 2.9+/-0.3 M_Jup, consistent with earlier determinations. No evidence for any periodicities is visible in our analysis of the shapes of the spectral lines via the bisector method, so that we conclude that evidence is accumulating and compelling for a planet around Pollux. However, some last doubt remains about this interpretation, because non-radial pulsations which might be present in giant stars could in principle also explain the observed radial velocities, while the accompanying bisector variations might be too small to be detectable with current data.
WSRT observations have been used to investigate the presence of neutral hydrogen in extremely young radio galaxies. These objects were selected from a sample of High-Frequency Peakers (HFPs). We detect 2 of the 6 observed galaxies confirming previous detection of HI in these objects. In the case of OQ 208 - for which discrepant results were available - we confirm the presence of a broad (~ 1800 km/s), blue-shifted and shallow HI absorption. No significant changes in the HI profile have been found between the two epochs of the observations. The intriguing result is that the derived HI column densities and upper limits obtained for the most compact sources, do not follow the inverse correlation between the column density and the linear size found for CSS/GPS sources. This can be explained - assuming the gas is already in a torus/disk structure - by a combination of the orientation and the extreme compactness of the sources. In this scenario, our line of sight to the source would intersect the torus in its inner region with low optical depth due to high spin and kinetic temperatures. There is no evidence, with the exception of OQ 208, of unsettled, high column density gas still enshrouding the young radio sources. This can be due to the low filling factor of such a medium.
The optical-UV and X-ray instruments on-board XMM-Ndewton provide an excellent opportunity to perform simultaneous observations of violently variable objects over a broad wavelength range. The UV and X-ray bright BL Lac object PKS 2155-304 has been repeatedly observed with XMM-Ndewton about twice per year. In this paper, we present a detailed analysis of the simultaneous multiwavelength variability of the source from optical to X-rays, based on the currently available XMM-Ndewton observations. These observations probed the intra-day multiwavelength variability at optical-UV and X-ray wavelengths of the source. The UV variability amplitude is substantially smaller than the X-ray one, and the hardness ratios of the UV to X-rays correlates with the X-ray fluxes: the brighter the source, the flatter the UV-X-ray spectra. On 2000 May 30-31 the UV and X-ray light curves were weakly correlated, while the UV variations followed the X-ray ones with no detectable lags on 2000 November 19-21. On 2001 November 30 the source exhibited a major X-ray flare that was not detected in the optical. The intra-day UV and X-ray variability presented here is not similar to the inter-day UV and X-ray variability obtained from the previous coordinated extensive multiwavelength campaigns on the source, indicating that different ``modes'' of variability might be operating in PKS 2155-304 on different timescales or from epoch to epoch.
We explore the angular distribution of two samples of satellite galaxies orbiting isolated hosts extracted from the Sloan Digital Sky Survey Data Release 4. We find a clear alignment of the satellites along the major axis of their hosts when restricting the analysis to red hosts. The anisotropy is most pronounced for red satellites of red hosts. We find that the distribution of the satellites about blue, isolated hosts is consistent with isotropy. We show that under the assumption that the true, underlying distribution of satellites of blue hosts exhibits the same anisotropy as the satellites of red hosts, the sample of blue hosts is too small to measure this anisotropy at a statistically-significant level. The anisotropy that we detect for satellites about red primaries is independent of the projected radius. In particular, it is evident at large projected distances from primaries (300 < r_p < 500 kpc).
EF Eri is a magnetic cataclysmic variable that has been in a low accretion state for the past nine years. Low state optical spectra reveal the underlying Zeeman-split white dwarf absorption lines. These features are used to determine a value of 13-14 MG as the white dwarf field strength. Recently, 5-7 years into the low state, Balmer and other emission lines have appeared in the optical. An analysis of the H$\alpha$ emission line yields the first radial velocity solution for EF Eri, leading to a spectroscopic ephemeris for the binary and, using the best available white dwarf mass of 0.6M${\odot}$, a mass estimate for the secondary of 0.055M${\odot}$. For a white dwarf mass of 0.95M${\odot}$, the average for magnetic white dwarfs, the secondary mass increases to 0.087M${\odot}$. At EF Eri's orbital period of 81 minutes, this higher mass secondary could not be a normal star and still fit within the Roche lobe. The source of the Balmer and other emission lines is confirmed to be from the sub-stellar secondary and we argue that it is due to stellar activity. We compare EF Eri's emission line spectrum and activity behavior to that recently observed in AM Her and VV Pup and attributed to stellar activity. We explore observations and models originally developed for V471 Tau, for the RS CVn binaries, and for extra-solar planets. We conclude that irradiation of the secondary in EF Eri and similar systems is unlikely and, in polars, the magnetic field interaction between the two stars (with a possible tidal component) is a probable mechanism which would concentrate chromospheric activity on the secondary near the sub-stellar point of the white dwarf.
[Abridged] The nature and evolutionary properties of the faint radio population, responsible for the steepening observed in the 1.4 GHz source counts below 1 milliJy, are not yet entirely clear. Radio spectral indices may help to constrain the origin of the radio emission in such faint radio sources and may be fundamental in understanding eventual links to the optical light. We study the spectral index behaviour of sources that were found in the 1.4 GHz ATESP survey (Prandoni et al. 2000a,b). Using the Australia Telescope Compact Array we observed at 5 GHz part of the region covered by the sub-mJy ATESP survey. In particular we imaged a one square degree area for which deep optical imaging in UBVRIJK is available. In this paper we present the 5 GHz survey and source catalogue, we derive the 5 GHz source counts and we discuss the 1.4-5 GHz spectral index properties of the ATESP sources. The analysis of the optical properties of the sample will be the subject of a following paper. The 5 GHz survey has produced a catalogue of 111 radio sources, complete down to a (6 sigma) limit S_lim(5 GHz)~0.4 mJy. We take advantage of the better spatial resolution at 5 GHz (~2 arcsec compared to ~8 arcsec at 1.4 GHz) to infer radio source structures and sizes. The 5 GHz source counts derived by the present sample are consistent with those reported in the literature, but improve significantly the statistics in the flux range 0.4< S(5 GHz)<1 mJy. The ATESP sources show a flattening of the 1.4-5 GHz spectral index with decreasing flux density, which is particularly significant for the 5 GHz selected sample. Such a flattening confirm previous results coming from smaller samples and is consistent with a flattening of the 5 GHz source counts occurring at fluxes <=0.5 mJy.
The widely accepted dark matter hypothesis offers a seductive solution to missing mass problems (galaxies, clusters of galaxies, gravitational collapse in structure formation,...). However the physical nature of the Dark Matter itself is still unknown. Alternatively, it has been proposed that apparent dynamical evidence of dark matter is due to a modification of Newtons's law of gravitation. Here we revisit the Modified Newtonian Dynamics (MOND) theories at the scale of galaxy clusters. Using hydrodynamical simulations, we derived quantities such as the density and the temperature of the ICM. We compared those MOND simulated predictions to high quality X-ray density and temperature profiles observed down to ~0.5 the virial radius. If the density profiles seems in acceptable agreement, the simulated temperature show a constant increase with the radius whereas the observed profiles show a flat to a mild decrease shape down to ~0.5 Rvirial . We also computed the dynamical MOND mass for 8 X-ray clusters observed with XMM-Newton. If the MOND mass helps to lower the discrepancy with the baryonic mass by ~20%, still ~80% of the mass in clusters is unaccounted by baryons. In order to solve this problem and to reconcile MOND with clusters observations, we investigated the possibility of an added dark baryonic component. We assumed a component of massive neutrinos to fill the remaining discrepancy between the observed MOND dynamical mass and the baryonic mass. This led us to derive a tied observational lower limit for the neutrino mass, m_nu > 1.06 eV.
Aimes: We intend to use the current data on large deep fields to look for high-redshift galaxies in the rest-frame UV wavelength range and study the evolution of the cosmic star-formation density at z~7. Methods: Deep HST/ACS and VLT/ISAAC data of the GOODS-South field were used to survey 130 sq.arcmin down to a limiting magnitude of about (J+Ks)AB=25.5 looking for drop-out objects in the z' ACS filter. The large sampled area would allow for the detection of galaxies which are 20 times less numerous and 1-2 magnitudes brighter than similar studies using HST/NICMOS near-IR data. Results: Two objects were initially selected as promising candidates of galaxies at z~7, but have subsequently been dismissed and identified as Galactic brown dwarfs through a detailed analysis of their morphology and Spitzer colors, as well as through spectroscopic information. As a consequence, we conclude that there are no galaxies at z~7 down to our limiting magnitude in the field we investigated. Our non detection of galaxies at z~7 provides clear evidence for a strong evolution of the luminosity function between z=6 and z=7, i.e. over a time interval of only ~170Myr. Our constraints also provide evidence for a significant decline of the total star formation rate at z=7, which must be less than 40% of that at z=3 and 40-80% of that at z=6. We also derive an upper limit to the ionizing flux at z=7, which is only marginally consistent with that required to completely ionize the Universe. This result suggests that at z=7 we are approaching the beginning of the star formation epoch.
BD+303639, the brightest planetary nebula at X-ray energies, was observed with Suzaku, an X-ray observatory launched on 2005 July 10. Using the X-ray Imaging Spectrometer, the K-lines from C VI, O VII, and O VIII were resolved for the first time, and C/O, N/O, and Ne/O abundance ratios determined. The C/O and Ne/O abundance ratios exceed the solar value by a factor of at least 30 and 5, respectively. These results indicate that the X-rays are emitted mainly by helium shell-burning products.
We calculate the structure of accretion disks around Kerr black holes for accretion rates 0.001 - 10 M_sun/s. Such disks are plausible candidates for the central engine of gamma-ray bursts. Our disk model is fully relativistic and treats accurately microphysics of the accreting matter: neutrino emissivity, opacity, electron degeneracy, and nuclear composition. The neutrino-cooled disk forms above a critical accretion rate that depends on the black hole spin. The disk has the ``ignition'' radius r_ign where neutrino flux rises dramatically, cooling becomes efficient, and the proton-to-nucleon ratio Y_e drops. Other characteristic radii are r_alpha where most of alpha-particles are disintegrated, r_nu where the disk becomes neutrino-opaque, and r_trap where neutrinos get trapped and advected into the black hole. We find r_alpha, r_ign, r_nu, r_trap and show their dependence on the accretion rate. We discuss the qualitative picture of accretion and present sample numerical models of the disk structure. All neutrino-cooled disks regulate themselves to a characteristic state such that: (1) electrons are mildly degenerate, (2) Y_e ~ 0.1, and (3) neutrons dominate the pressure in the disk.
Sensitive measurements of the interstellar gas-phase oxygen abundance have revealed a slight oxygen deficiency ($\sim$ 15%) toward stars within 500 pc of the Sun as compared to more distant sightlines. Recent $FUSE$ observations of the interstellar gas-phase nitrogen abundance indicate larger variations, but no trends with distance were reported due to the significant measurement uncertainties for many sightlines. By considering only the highest quality ($\geq$ 5 $\sigma$) N/O abundance measurements, we find an intriguing trend in the interstellar N/O ratio with distance. Toward the seven stars within $\sim$ 500 pc of the Sun, the weighted mean N/O ratio is 0.217 $\pm$ 0.011, while for the six stars further away the weighted mean value (N/O = 0.142 $\pm$ 0.008) is curiously consistent with the current Solar value (N/O = 0.138$^{+0.20}_{-0.18}$). It is difficult to imagine a scenario invoking environmental (e.g., dust depletion, ionization, etc.) variations alone that explains this abundance anomaly. Is the enhanced nitrogen abundance localized to the Solar neighborhood or evidence of a more widespread phenomenon? If it is localized, then recent infall of low metallicity gas in the Solar neighborhood may be the best explanation. Otherwise, the N/O variations may be best explained by large-scale differences in the interstellar mixing processes for AGB stars and Type II supernovae.
We present first results of a campaign to find and identify new compact objects in the Galactic Center. Selecting candidates from a combination of Chandra and 2MASS survey data, we search for accretion disk signatures via infrared spectroscopy. We have found the infrared counterpart to the Chandra source CXO J174536.1-285638, the spectrum of which has strong Br-gamma and HeI emission. The presence of CIII, NIII, and HeII indicate a binary system. We suspect that the system is some form of high-mass binary system, either a high-mass X-ray binary or a colliding wind binary.
The gamma-ray burst GRB060218 is an important event because of its very low redshift z = 0.0331, its low isotropic-equivalent radiated energy Eiso 7 x 1049 erg and its clear association with a supernova (SN) event (SN2006aj). Under these respects, GRB060218 is the event most similar to GRB980425, the proto-type event of the GRB/SN connection. However, while the peak energy Ep,i and Eiso values of GRB980425 are inconsistent with the Ep,i - Eiso (Amati) correlation olding for long GRBs/XRFs, GRB060218 is fully consistent with it. Given that one of the most popular explanations of the inconsistency of GRB980425 with the Ep,i - Eiso correlation is that it is a 'normal' GRBs seen at very high off-axis angles, our result implies that GRB060218 is not an off-axis event, as also suggested by the 'chromatic' behavior of afterglow light curves measured by Swift. In this letter we discuss some implications of our finding on the present understanding of the GRB/SN connection.
We use 211 galaxy spectra from our survey for Lyman break galaxies (LBGs)
associated with 11 damped Lyman alpha systems (DLAs) to measure the
three-dimensional LBG auto-correlation and DLA-LBG cross-correlation functions
with the primary goal of inferring the mass of DLAs at z~3. Conventional
binning of the data while varying both r_0 and gamma parameters of the fiducial
model of the correlation function xi(r)=(r/r_0)^{-gamma} resulted in the best
fit values and 1 sigma uncertainties of r_0=2.65+/-0.48, gamma=1.55+/-0.40 for
the LBG auto-correlation and r_0=3.32+/-1.25, gamma=1.74+/-0.36 for DLA-LBG
cross-correlation function. To circumvent shortcomings found in binning small
datasets, we perform a maximum likelihood analysis based on Poisson statistics.
The best fit values and 1 sigma confidence levels from this analysis were
found to be r_0=2.91(+1.0,-1.0), gamma=1.21(+0.6,-0.3) for the LBG
auto-correlation and r_0=2.81(+1.4,-2.0), gamma=2.11(+1.3,-1.4) for the DLA-LBG
cross-correlation function. We report a redshift spike of five LBGs with Delta
z = 0.015 of the z=2.936 DLA in the PSS0808+5215 field and find that the
DLA-LBG clustering signal survives when omitting this field from the analysis.
Using the correlation functions measurements and uncertainties, we compute the
z~3 LBG galaxy bias b_LBG to be 1.5<b_LBG<3 corresponding to an average halo
mass of 10^(9.7)<M_LBG<10^(11.6) M_odot and the z~3 DLA galaxy bias b_DLA to be
1.3<b_DLA<4 corresponding to an average halo mass of 10^(9)<M_LBG<10^(12)
M_odot. Lastly, two of the six QSOs discovered in this survey were found to lie
within Delta z = 0.0125 of two of the survey DLAs. We estimate the probability
of this occurring by chance is 1 in 940 and may indicate a possible
relationship between the distribution of QSOs and DLAs at z~3.
We use an array of high-resolution N-body simulations to determine the mass function of dark matter haloes at redshifts 10-30. We develop a new method for compensating for the effects of finite simulation volume that allows us to find an approximation to the true ``global'' mass function. By simulating a wide range of volumes at different mass resolution, we calculate the abundance of haloes of mass 10^{5-12} Msun/h. The enables us to predict accurately the abundance of the haloes that host the sources that reionize the universe. In particular, we focus on the small mass haloes (>~10^{5.5-6} Msun/h) likely to harbour population III stars where gas cools by molecular hydrogen emission, early galaxies in which baryons cool by atomic hydrogen emission at virial temperature of ~10^4K (~10^{7.5-8} Msun/h), and massive galaxies that may be observable at redshift ~10. When we combine our data with simulations that include high mass halos at low redshift, we find that the best fit to the halo mass function depends not only on linear overdensity, as is commonly assumed in analytic models, but also upon the slope of the linear power spectrum at the scale of the halo mass. The Press-Schechter model gives a poor fit to the halo mass function at all epochs; the Sheth-Tormen model gives a better match to the simulations, but still underpredicts the abundance of rare objects at all times by up to 50%. Finally, we consider the consequences of the recently released WMAP 3-year cosmological parameters. These lead to much less structure at high redshift, reducing the number of z=10 ``mini-haloes'' by about one third and the number of z=30 galaxy hosts by nearly three orders of magnitude.
We present near-infrared $JHK_s$ photometry and light curves of the candidate magnetic white dwarf+brown dwarf binary SDSS J121209.31+013627.7 and report on the detection of near-infrared excess and variability in the $K_s-$band. The observed near-infrared excess can be explained by the presence of an L7 brown dwarf and an extra emission source. The $J$ and $H$ light curves appear flat, which rules out eclipses deeper than 0.2 mag and the presence of an accretion hot spot on the white dwarf. From the variable $K_s$ lightcurve, we get a refined period for the system of 88$\pm$1 minutes. We show that the observed variability in $K_s-$band can be explained by cyclotron emission, which can be modeled by a small spot on the surface of the white dwarf. SDSS 1212 exhibits similarities to the ultra-short period polar EF Eridani, however the lack of evidence for Roche-lobe overflow accretion suggests it may be a pre-polar.
It is now well established that many young brown dwarfs exhibit characteristics similar to classical T Tauri stars, including infrared excess from disks and emission lines related to accretion. Whether the same holds true for even lower mass objects, namely those near and below the Deuterium-burning limit, is an important question. Here we present optical spectra of six isolated planetary mass candidates in Chamaeleon II, Lupus I and Ophiuchus star-forming regions, recently identified by Allers and collaborators to harbor substantial mid-infrared excesses. Our spectra, from ESO's Very Large Telescope and New Technology Telescope, show that four of the targets have spectral types in the ~M9-L1 range, and three of those also exhibit H_alpha. Their luminosities are consistent with masses of ~5-15 M_{Jupiter} according to models of Chabrier, Baraffe and co-workers, thus placing these four objects among the lowest mass brown dwarfs known to be surrounded by circum-sub-stellar disks. Our findings bolster the idea that free-floating planetary mass objects could have infancies remarkably similar to those of Sun-like stars and suggest the intriguing possibility of planet formation around primaries whose masses are comparable to those of extra-solar giant planets. Another target appears to be a brown dwarf (~M8) with prominent H_alpha emission, possibly arising from accretion. The sixth candidate is likely a background source, underlining the need for spectroscopic confirmation.
We examine statistical isotropy of large scale anisotropies of the Internal Linear Combination (ILC) map, based on three year WMAP data. Our study reveals no significant deviation from statistical isotropy on large angular scales of 3-year ILC map. Comparing statistical isotropy of 3-year ILC map and 1-year ILC map, we find a significant improvement in 3-year ILC map which can be due to the gain model, improved ILC map processing and foreground minimization.
We present preliminary results from the first X-ray gratings spectrometer observations of a planetary nebula (PN). We have used the Chandra X-ray Observatory Low Energy Transmission Gratings Spectrometer (LETGS) to observe the bright, diffuse X-ray source within the well-studied BD +30 3639. The LETGS spectrum of BD +30 3639 displays prominent and well-resolved emission lines of H-like C, O, and Ne and He-like O and Ne. Initial modeling indicates a plasma temperature T_x ~ 2.5x10^6 K and abundance ratios of C/O ~ 20, N/O <~ 1, Ne/O ~ 4, and Fe/O <~ 0.1. These results suggest that the X-ray-emitting plasma is dominated by the shocked fast wind from the emerging PN core, where this wind gas likely originated from the intershell region of the progenitor asymptotic giant branch star.
The increase of computational resources has recently allowed high resolution, three dimensional calculations of planets embedded in gaseous protoplanetary disks. They provide estimates of the planet migration timescale that can be compared to analytical predictions. While these predictions can result in extremely short migration timescales for cores of a few Earth masses, recent numerical calculations have given an unexpected outcome: the torque acting on planets with masses between 5 M_Earth and 20 M_Earth is considerably smaller than the analytic, linear estimate. These findings motivated the present work, which investigates existence and origin of this discrepancy or ``offset'', as we shall call it, by means of two and three dimensional numerical calculations. We show that the offset is indeed physical and arises from the coorbital corotation torque, since (i) it scales with the disk vortensity gradient, (ii) its asymptotic value depends on the disk viscosity, (iii) it is associated to an excess of the horseshoe zone width. We show that the offset corresponds to the onset of non-linearities of the flow around the planet, which alter the streamline topology as the planet mass increases: at low mass the flow non-linearities are confined to the planet's Bondi sphere whereas at larger mass the streamlines display a classical picture reminiscent of the restricted three body problem, with a prograde circumplanetary disk inside a ``Roche lobe''. This behavior is of particular importance for the sub-critical solid cores (M <~ 15 M_Earth) in thin (H/r <~0.06) protoplanetary disks. Their migration could be significantly slowed down, or reversed, in disks with shallow surface density profiles.
We have measured non-zero closure phases for about 29% of our sample of 56 nearby Asymptotic Giant Branch (AGB) stars, using the 3-telescope Infrared Optical Telescope Array (IOTA) interferometer at near-infrared wavelengths (H band) and with angular resolutions in the range 5-10 milliarcseconds. These nonzero closure phases can only be generated by asymmetric brightness distributions of the target stars or their surroundings. We discuss how these results were obtained, and how they might be interpreted in terms of structures on or near the target stars. We also report measured angular sizes and hypothesize that most Mira stars would show detectable asymmetry if observed with adequate angular resolution.
The classical nova V4743 Sgr was observed with XMM-Newton for about 10 hours on April 4 2003, 6.5 months after optical maximum. At this time, this nova had become the brightest supersoft X-ray source ever observed. We present the results of a time series analysis performed on the X-ray light curve obtained in this observation, and in a previous shorter observation done with Chandra 16 days earlier. Intense variability, with amplitude as large as 40% of the total flux, was observed both times. Similarities can be found between the two observations in the structure of the variations. Most of the variability is well represented as a combination of oscillations at a set of discrete frequencies lower than 1.7 mHz. At least five frequencies are constant over the 16 day time interval between the two observations. We suggest that a periods in the power spectrum of both light curves at the frequency of 0.75 mHz and its first harmonic are related to the spin period of the white dwarf in the system, and that other observed frequencies are signatures of nonradial white dwarf pulsations. A possible signal with a 24000 sec period is also found in the XMM-Newton light curve: a cycle and a half are clearly identified. This period is consistent with the 24278 s periodicity discovered in the optical light curve of the source and thought to be the orbital period of the nova binary system.
We report on multi-epoch optical and near-infrared spectroscopy around the first overtone ro-vibrational band of CO in the pulsating yellow hypergiant Rho Cas, one of the most massive stars in the Galaxy and a candidate SN II progenitor. We argue that the double cores of the CO absorption lines, that have previously been attributed to separate circumstellar shells expelled during its recurrent outbursts, result in fact from a superposition of a wide absorption line and a narrow central emission line. The CO line doubling returns over subsequent pulsation cycles, where the superposed line emission assumes its largest intensity near phases of maximum light. We find that the morphology and behavior of the CO band closely resemble the remarkable "line-splitting phenomenon" also observed in optical low-excitation atomic lines. Based on radiative transport calculations we present a simplified model of the near-IR CO emission emerging from cooler atmospheric layers in the immediate vicinity of the photosphere. We speculate that the kinetic temperature minimum in our model results from a periodical pulsation-driven shock wave. We further discuss a number of alternative explanations for the origin of the ubiquitous emission line spectrum, possibly due to a quasi-chromosphere or a steady shock wave at the interface of a fast expanding wind and the ISM. We present a number of interesting spectroscopic similarities between Rho Cas and other types of cool variable supergiants such as the RV Tau and R CrB stars. We further propose a possibly common mechanism for the enigmatic outburst behavior of these luminous pulsating cool stars.
We present results from Chandra and XMM-Newton observations of the bright group of galaxies HCG 62. There are two cavities at about 30'' northeast and 20'' southwest of the central galaxy in the Chandra image. The energy spectrum shows no significant change in the cavity compared with that in the surrounding region. The radial X-ray profile is described by a sum of 3-beta components with core radii about 2, 10, and 160 kpc, respectively. We studied radial distributions of temperature and metal abundance with joint spectral fit for the Chandra and XMM-Newton data, and two temperatures were required in the inner r< 2' (35 kpc) region. The sharp drop of temperature at r about 5' implies the gravitational mass density even lower than the gas density, suggesting the gas may not be in hydrostatic equilibrium. Fe and Si abundances are 1-2 solar at the center and drop to about 0.1 solar at r about 10'. O abundance is less than 0.5 solar and shows a flatter profile. Observed metal distribution supports the view that iron and silicon are produced by type Ia supernova in the central galaxy, while galactic winds by type II supernova have caused wide distribution of oxygen. The supporting mechanism of the cavity is discussed. Pressure for the sum of electrons and magnetic field is too low to displace the hot group gas, and the required pressure due to high energy protons are nearly 700 times higher than the electron pressure. This leaves the origin of the cavities a puzzle, and we discuss other possible origins of the cavities.
Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data confirm the ellipticity of anisotropies of Cosmic Microwave Background (CMB) maps, found previously for Boomerang and WMAP 1-year high sensitivity maps. The low noise level of the WMAP latter data enable also to show that, the ellipticity is a property not described by the conventional cosmological model fitting the power spectrum of CMB. As a large scale anomaly, the ellipticity characteristics are consistent with the effect of geodesics mixing occurring in hyperbolic Universe. Its relation to other large scale effects, i.e. to suppressed low multipoles, as well as to dark energy if the latter is due to vacuum fluctuations, is then an arising issue.
We investigate the global transition from a turbulent state of superfluid vorticity to a laminar state, and vice versa, in the outer core of a neutron star. By solving numerically the hydrodynamic Hall-Vinen-Bekarevich-Khalatnikov equations for a rotating superfluid in a differentially rotating spherical shell, we find that the meridional counterflow driven by Ekman pumping exceeds the Donnelly-Glaberson threshold throughout most of the outer core, exciting unstable Kelvin waves which disrupt the rectilinear vortex array, creating a vortex tangle. In the turbulent state, the torque exerted on the crust oscillates, and the crust-core coupling is weaker than in the laminar state. This leads to a new scenario for the rotational glitches observed in radio pulsars: a vortex tangle is sustained in the differentially rotating outer core by the meridional counterflow, a sudden spin-up event brings the crust and core into corotation, the vortex tangle relaxes back to a rectilinear vortex array, then the crust spins down electromagnetically until enough meridional counterflow builds up to reform a vortex tangle. The turbulent-laminar transition can occur uniformly or in patches; the associated time-scales are estimated from vortex filament theory. We calculate numerically the global structure of the flow with and without an inviscid superfluid component, for Hall-Vinen and Gorter-Mellink forms of the mutual friction. We also calculate the post-glitch evolution of the angular velocity of the crust and its time derivative, and compare the results with radio pulse timing data, predicting a correlation between glitch activity and Reynolds number.
We re-investigate the gravitationally lensed system Q2237+0305 data record to quantify the probability of having a caustic crossing in the A component. Several works assume that this is the case, but no quantitative analysis is available in the literature. We combine the datasets from the OGLE and GLITP collaborations to accurately trace the prominent event in the lightcurve for the A component of the system. Then the observed event is compared with synthetic light curves derived from trajectories in magnification maps. These maps are generated using a ray-tracing technique. We take more than 10^9 trajectories and test a wide range of different physical properties of the lensing galaxy and the source quasar (lens transverse velocity, microlens mass, source intensity profile and source size). We found that around 75% of our good trajectories (i.e. that are consistent with the observations) are caustic crossings. In addition, a high transverse velocity exceeding 300 km/s, a microlens mass of about 0.1 M_sun and a small standard accretion disk is the best parameter combination. The results justify the interpretation of the OGLE-GLITP event in Q2237+0305A as a caustic crossing. Moreover, the physical properties of the lens and source are in very good agreement with previous works. We also remark that a standard accretion disk is prefered to those simpler approaches, and that the former should be used in subsequent simulations.
We investigate in details the kinematics and morphology of the Seyfert galaxy NGC6104 in order to identify the mechanism of gas transportation to the active galactic nucleus (AGN). Our observational data were obtained at the 6-m Special Astrophysical Observatory telescope with the MPFS integral-field spectrograph and the SCORPIO universal device in three modes: direct imaging, a scanning Fabry-Perot interferometer, and long-slit spectroscopy. Images from the HST archive were invoked to study the structure of the circumnuclear region. An analysis of deep images has revealed that NGC6104 is in the phase of active merging with a companion galaxy. We have been able to study the detailed picture of ionized gas motions up to galactocentric distances of 14 kpc and to construct the stellar velocity field for the inner region. The radial gas motions toward the AGN along the central bar play a significant role at galactocentric distances of 1-5 kpc. In addition, we have detected an outflow of ionized gas from the nucleus that presumably resulted from the intrusion of a radio jet into the ambient interstellar medium. Using diagnostic diagrams, we estimate the contributions from the AGN and star formation to the galactic gas ionization. We estimate the bar pattern speed by the Tremaine-Weinberg method and show that the inner ring observed in the galactic images has a resonant nature. Two possible ring formation scenarios (before and during the interaction with a companion) are discussed.
Instabilities in magnetic fields wound up by differential rotation as reviewed in Spruit (1999) are discussed with some detail and new developments added. In stellar models which include magnetic torques, the differential rotation tends to accumulate in the gradients in composition. In view of this, instability in a $\mu$-gradient is studied in more detail here, resulting in the detection of a second instability. Its relevance for angular momentum transport is uncertain, however, since it requires high horizontal field gradients and would not operate near the pole. Finally, the possibility is discussed that magnetic instability in a $\mu$-gradient will lead to {\em layer formation}: the gradients breaking up into small steps of uniform composition and rotation rate. This would enhance the angular momentum transport across inhomogeneous zones, and decrease the rotation rates of the end products of stellar evolution. A recent {\tt astro-ph} submission by Dennisenkov and Pinsonneault proposing a modification of the instability conditions is shown to contain a mathematical error.
Here we briefly report on results of self-consistent numerical modeling of a differentially rotating force-free magnetosphere of an aligned rotator. We show that differential rotation of the open field line zone is significant for adjusting of the global structure of the magnetosphere to the current density flowing through the polar cap cascades.
We present new ab initio calculations of the electronic structure of various atoms and molecules in strong magnetic fields ranging from B=10^12 G to 2x10^15 G, appropriate for radio pulsars and magnetars. For these field strengths, the magnetic forces on the electrons dominate over the Coulomb forces, and to a good approximation the electrons are confined to the ground Landau level. Our calculations are based on the density functional theory, and use a local magnetic exchange-correlation function which is tested to be reliable in the strong field regime. Numerical results of the ground-state energies are given for H_N (up to N=10), He_N (up to N=8), C_N (up to N=5) and Fe_N (up to N=3), as well as for various ionized atoms. Fitting formulae for the B-dependence of the energies are also given. In general, as N increases, the binding energy per atom in a molecule, |E_N|/N, increases and approaches a constant value. For all the field strengths considered in this paper, hydrogen, helium, and carbon molecules are found to be bound relative to individual atoms (although for B less than a few x 10^12 G, the relative binding between C and C_2 is small). Iron molecules are not bound at B<10^13 G, but become energetically more favorable than individual atoms at larger field strengths.
The results of long-term spectral observations were used to search for changes in planetary nebulae and emission-line stars. Significant increase of excitation degree is found in two objects: M1-6 and M1-11.
Theoretical modeling of surface emission from magnetized neutron stars (NSs) requires proper treatment of QED effects, in particular the effect of photon mode conversion due to the ``vacuum resonance'' between plasma and vacuum polarization. Previous NS atmosphere models incorporated this effect approximately, using transfer equations for the photon modes which are inadequate near the vacuum resonance, particularly for field strengths around $B_l\simeq 7\times 10^{13}$ G, where the vacuum resonance occurs near the photosphere. In this paper, we provide an accurate treatment of the QED-induced mode conversion effect in NS atmosphere models, employing both the modal radiative transfer equations, coupled with an accurate mode conversion probability at the resonance, and the full evolution equations for the photon Stokes parameters. In doing so, we are able to quantitatively calculate the effects of vacuum polarization on the atmosphere emission spectra, beam patterns, and polarizations for the entire range of field strengths, $B=10^{12}-10^{15}$ G. We find that for NSs with $B\ga 2 B_l$, vacuum polarization reduces the widths of spectral features, and softens the hard spectral tail typical of magnetized atmosphere models. For $B\la B_l/2$, vacuum polarization does not change the emission spectra, but can significantly affect the polarization signals. We show that vacuum polarization induces a unique energy-dependent linear polarization signature, and that circular polarization can be generated in the magnetospheres of rapidly rotating NSs. We discuss the implications of our results for recent observations of thermally emitting isolated NSs and magnetars, as well as the prospects for future spectral and polarization observations.
Primordial magnetic fields possibly generated in the very early universe are one of the candidates for the origin of magnetic fields observed in many galaxies and galaxy clusters. After recombination, the dissipation process of the primordial magnetic fields increases the baryon temperature. The Lorentz force acts on the residual ions and electrons to generate density fluctuations. These effects are imprinted on the cosmic microwave background (CMB) brightness temperature fluctuations produced by the neutral hydrogen 21cm line. We calculate the angular power spectrum of brightness temperature fluctuations for the model with the primordial magnetic fields of a several nano Gauss strength and a power-law spectrum. It is found that the overall amplitude and the shape of the brightness temperature fluctuations depend on the strength and the spectral index of the primordial magnetic fields. Therefore, it is expected that the observations of the CMB brightness temperature fluctuations give us a strong constraint on the primordial magnetic fields.
We present the XMM-LSS cluster catalogue corresponding to the CFHTLS D1 area. The list contains 13 spectroscopically confirmed, X-ray selected galaxy clusters over 0.8 deg2 to a redshift of unity and so constitutes the highest density sample of clusters to date. Cluster X-ray bolometric luminosities range from 0.03 to 5x10^{44} erg/s. In this study, we describe our catalogue construction procedure: from the detection of X-ray cluster candidates to the compilation of a spectroscopically confirmed cluster sample with an explicit selection function. The procedure further provides basic X-ray products such as cluster temperature, flux and luminosity. We detected slightly more clusters with a (0.5-2.0 keV) X-ray fluxes of >2x10^{-14} erg/s/cm^{-2} than we expected based on expectations from deep ROSAT surveys. We also present the Luminosity-Temperature relation for our 9 brightest objects possessing a reliable temperature determination. The slope is in good agreement with the local relation, yet compatible with a luminosity enhancement for the 0.15 < z< 0.35 objects having 1 < T < 2 keV, a population that the XMM-LSS is identifying systematically for the first time. The present study permits the compilation of cluster samples from XMM images whose selection biases are understood. This allows, in addition to studies of large-scale structure, the systematic investigation of cluster scaling law evolution, especially for low mass X-ray groups which constitute the bulk of our observed cluster population. All cluster ancillary data (images, profiles, spectra) are made available in electronic form via the XMM-LSS cluster database.
We report the serendipitous discovery of the Sloan Digital Sky Survey star, SDSS J160043.6+074802.9 to be a very rapid pulsator. The variation is dominated by a frequency near 8380 microHz (period = 119.33 s) with a large amplitude (0.04 mag) and its first harmonic at 16760 microHz (59.66 s; 0.005 mag). In between these frequencies, we find at least another 8 variations with periods between 62 and 118 seconds and amplitudes between about 0.007 and 0.003 mag; weaker oscillations might also be present. Preliminary spectrograms from the performance verification phase of the Southern African Large Telescope indicate that SDSS J160043.6+074802.9 is a spectroscopic binary consisting of an sdO star and a late-type main-sequence companion. This makes it the first unambiguous detection of such an sdO star to pulsate, and certainly the first found to exhibit multi-frequency variations.
We present results of fitting the 50-day time series of photometry of alpha
Cen A taken by the WIRE satellite in 1999. Both power spectrum and
autocovariance function (ACF) fitting techniques were used in an attempt to
determine mode frequencies, rotational splittings, lifetimes and amplitudes of
low-l p-modes. In all, using both techniques, we managed to fit 18 modes (seven
l = 0, eight l = 1 and three l = 2) with frequencies determined to within 1 - 2
micro-Hz. These estimates are shown to be 0.6 +/- 0.3 micro-Hz lower, on
average, than the frequencies determined from two other more recent studies
(Bouchy & Carrier, 2002; Bedding et al. 2004) which used data gathered about 19
months after the WIRE observations. This could be indicative of an activity
cycle, although due to the large uncertainty, more data would be needed to
confirm this.
Over a range of 1700 to 2650 micro-Hz we were also able to use the ACF
fitting to determine an average lifetime of 3.9 +/- 1.4 days, and an average
rotational splitting of 0.54 +/- 0.22 micro-Hz, which is the first ever
reliable estimate of this parameter. In contrast to the ACF, the power spectrum
fitting was shown to return significantly biased results for these parameters.
Observations with the Newton X-ray Multimirror Mission (XMM) show a strong periodic modulation at 6.67+/-0.03 hours of the X-ray source at the centre of the 2,000-year-old supernova remnant RCW 103. No fast pulsations are visible. If genetically tied to the supernova remnant, the source could either be an X-ray binary, comprising a compact object and a low-mass star in an eccentric orbit, or an isolated neutron star. In the latter case, its age-period combination would point to a peculiar magnetar, dramatically slowed-down, possibly by a supernova debris disc. Both scenarios require non-standard assumptions on the formation and evolution of compact objects in supernova explosions.
In the presence of a strong $m=2$ component in a rotating galaxy, the phase space structure near corotation is shaped to a large extent by the {\it invariant manifolds} of the short period family of unstable periodic orbits terminating at L$_1$ or L$_2$. The main effect of these manifolds is to create robust {\it phase correlations} among a number of chaotic orbits large enough to support a {\it spiral} density wave outside corotation. The phenomenon is described theoretically by soliton-like solutions of a Sine-Gordon equation. Numerical examples are given in an N-Body simulation of a barred spiral galaxy. In these examples, we demonstrate how the projection of unstable manifolds in configuration space reproduces essentially the entire observed bar-spiral pattern.
Since the discovery of the first giant planet outside the solar system in 1995 (Mayor & Queloz 1995), more than 180 extrasolar planets have been discovered. With improving detection capabilities, a new class of planets with masses 5-20 times larger than the Earth, at close distance from their parent star is rapidly emerging. Recently, the first system of three Neptune-mass planets has been discovered around the solar type star HD69830 (Lovis et al. 2006). Here, we present and discuss a possible formation scenario for this planetary system based on a consistent coupling between the extended core accretion model and evolutionary models (Alibert et al. 2005a, Baraffe et al. 2004,2006). We show that the innermost planet formed from an embryo having started inside the iceline is composed essentially of a rocky core surrounded by a tiny gaseous envelope. The two outermost planets started their formation beyond the iceline and, as a consequence, accrete a substantial amount of water ice during their formation. We calculate the present day thermodynamical conditions inside these two latter planets and show that they are made of a rocky core surrounded by a shell of fluid water and a gaseous envelope.
One of the most intriguing spectral features of WR binary stars is the presence of time-dependent line profiles. Long term observations of several systems revealed the periodicity of this variability, synchronized with the orbital movement. Several partially successful models have been proposed to reproduce the observed data. The most promising assume that the origin of the emission is the wind-wind interaction zone. In this scenario, two high velocity and dense winds produce a strong shock layer, responsible for most of the X-rays observed from these systems. As the secondary star moves along its orbital path, the shock region of conical shape, changes its position with relation to the line of sight. As a consequence, the stream measured Doppler shift presents time variations resulting in position changes of the spectral line. In our work, we present an alternative model, introducing turbulence in the shock layer to account for the line broadening and opacity effects for the asymmetry in the line profiles. We showed that the gas turbulence avoids the need of an unnaturally large contact layer thickness to reproduce line broadening. Also, we demonstrated that if the emission from the opposing cone surface is absorbed, the result is a single peaked profile. This result fully satisfies the recent data obtained from massive binary systems, and can help on the determination of both winds and orbital parameters. We successfully applied this model to the Br22 system and determined its orbital parameters.
We present the X-ray pipeline developed for the purpose of the cluster search in the XMM-LSS survey. It is based on a two-stage procedure via a dedicated handling of the Poisson nature of the signal: (1) source detection on multi-resolution wavelet filtered images; (2) source analysis by means of a maximum likelihood fit to the photon images. The source detection efficiency and characterisation are studied through extensive Monte-Carlo simulations. This led us to define two samples of extended sources: the C1 class that is uncontaminated, and the less restrictive C2 class that allows for 50% contamination. The resulting predicted selection function is presented and the comparison to the current XMM-LSS confirmed cluster sample shows very good agreement. We arrive at average predicted source densities of about 7 C1 and 12 C2 per deg2, which is higher than any available wide field X-ray survey. We finally notice a substantial deviation of the predicted redshift distribution for our samples from the one obtained using the usual assumption of a flux limited sample.
We present the results of XMM-Newton observations of two AM CVn systems - V396 Hya and SDSS J1240-01. Both systems are detected in X-rays and in the UV: neither shows coherent variability in their light curves. We compare the rms variability of the X-ray and UV power spectra of these sources with other AM CVn systems. Apart from ES Cet, AM CVn sources are not strongly variable in X-rays, while in the UV the degree of variability is related to the systems apparent brightness. The X-ray spectra of V396 Hya and SDSS J1240-01 show highly non-solar abundances, requiring enhanced nitrogen to obtain good fits. We compare the UV and X-ray luminosities for 7 AM CVn systems using recent distances. We find that the X-ray luminosity is not strongly dependent upon orbital period. However, the UV luminosity is highly correlated with orbital period with the UV luminosity decreasing with increasing orbital period. We expect that this is due to the accretion disk making an increasingly strong contribution to the UV emission at shorter periods. The implied luminosities are in remarkably good agreement with predictions.
Recent observations of near-infrared and X-ray flares from Sagittarius A*, which is believed to be a supermassive black hole at the Galactic center, show that the source exhibits about 20-minute periodic variability. Here we provide arguments based on a quantitative analysis that supermassive objects at galactic centers are bubbles of dark matter axions, rather then black holes. An oscillating axion bubble can explain periodic variability of Sagittarius A* and with no free parameters yields the axion mass about 1 meV in agreement with our previous findings obtained from quasar observations. The bubble scenario naturally explains lack of supermassive "black holes" with M<10^6M_{Sun}. Low-mass bubbles decay fast and as a result are very rare. We also found that the mass of an axion bubble can not exceed 2.5\times 10^9M_{Sun}, in agreement with the largest supermassive "black hole" masses measured for active galactic nuclei. Our finding, if confirmed, suggests that Einstein general relativity is invalid for strong gravity and the gravitational force effectively becomes repulsive at large potential. Imaging a shadow of the "black hole" at the Galactic center with VLBI within the next few years will be capable to distinguish between the black hole and the oscillating axion bubble scenarios. In the case of axion bubble, a steady shadow will not be observed. Instead, the shadow will appear and disappear periodically with a period of about 20 min.
It has long been suggested that fission cycling may play an important role in the r-process. Fission cycling can only occur in a very neutron rich environment. In traditional calculations of the neutrino driven wind of the core-collapse supernova, the environment is not sufficiently neutron rich to produce the r-process elements. However, we show that with a reduction of the electron neutrino flux coming from the supernova, fission cycling does occur and furthermore it produces an abundance pattern which is consistent with observed r-process abundance pattern in halo stars. Such a reduction can be caused by active-sterile neutrino oscillations or other new physics.}
(abridged) We suggest here that the large scale coherent fields $\sim \mu$G, observed in galaxies at high and low redshifts, have their origin in the electromagnetic fluctuations that naturally occur in the dense hot plasmas that existed in the early Universe. This scenario avoids the general problem of primordial MF generation, which creates small MFs on small comoving scales at low redshifts. Dense hot plasmas in equilibrium create large fluctuations of the magnetic field, $\sim 10^{16}$ G, immediately after the quark-hadron phase transition (QHPT), as predicted by the Fluctuation-Dissipation Theorem. We evolve the predicted fields to the present time. The size of the coherent region increases due to the fusion (polymerization) of smaller regions. It is found that MFs of much stronger intensity are obtained over much larger comoving regions than previous suggested by mechanisms whose origin is the QHPT. We obtain $\sim 0.1 \mu G$ over a comoving $\sim 0.1$ pc region. A statistical average is made over a protogalactic $\sim 1$ Mpc comoving region. Magnetic fields $\sim$ $10^{-8}$ $\mu$G - $10^{-1}$ $\mu$G are obtained at a redshift z $\sim$ 10. In the collapse to a galaxy at this redsihft, the fields are amplified to $10^{-5} \mu G - 10 \mu G$. This indicates that the MFs created immediately after the QHPT, predicted by the Fluctuation-Dissipation Theorem, could be the origin of the $\sim \mu G$ fields observed today in galaxies at high and low redshifts.
A method of the calculation of optical parameters of the nonisothermal giant planet atmospheres was developed using detailed intensity data of Raman scattering. We have used the model of Morozhenko (A.V. Morozhenko, 1997) as a baseline. In such a way, using observational data of Uranus and Neptune (E.Karkoschka, 1994), the spectral values of ratio of optical depth components: aerosol and gas components \tau a/ \tau R, absorbing and scattering components \tau a/ \tau R, and also single scattering albedo of aerosol component corrected for Raman scattering \omega were obtained (where \tau a, \tau R are aerosol and gas components, and \tau ? is absorbing components of effective optical depths of the formation of diffusely reflected irradiation). The averaged value of ratio \tau a/ \tau R is 0.96 but it slowly decreases in the spectral range of 350-450nm for Uranus and \tau a/ \tau R is 1.35 for Neptune.
We present the light curve variations of the two active binaries with hot subdwarf component. According to the brightness variations outside of the eclipses, the giant components of the systems are chromospherically active stars. The dark and cool active structures on this components cause the variations of the total light of the systems.
The analysis of the density and brightness of big planets satellites, main asteroid belt objects, Kuiper belt objects and centaurs has been carried out as well as the analysis of suspected unseen satellites of the stars. According to the date on the first of January 2006 the catalogue of planetary objects has been compiled.
One of the goals of the Hubble Space Telescope program to observe periodic comet 9P/Tempel 1 in conjunction with NASA's Deep Impact mission was to study the generation and evolution of the gaseous coma resulting from the impact. For this purpose, the Solar Blind Channel of the Advanced Camera for Surveys was used with the F140LP filter which is sensitive primarily to the ultraviolet emission (>1400 A) from the CO Fourth Positive system. Following the impact we detected an increase in brightness, which if all due to CO corresponds to 1.5 x 10^31 molecules or a mass of 6.6 x 10^5 kg, an amount that would normally be produced by 7-10 hours of quiescent outgassing from the comet. This number is less than or equal to 10% of the number of water molecules excavated, and suggests that the volatile content of the material excavated by the impact did not differ significantly from the surface or near sub-surface material responsible for the quiescent outgassing of the comet.
We present a preliminary statistical analysis of a period change of eclipsing binaries from the ASAS Catalog of Variable Stars. For each contact and semidetached system brighter than 13.3$mag$ (in V) with a period shorter than 0.4 days and at least 300 observation points we have found an angular velocity $\omega$ and its time derivative $\frac{d\omega}{dt}$. According to our accuracy there is no evidence that average $\frac{d\omega}{dt}$ differs from 0. Light curves for selected stars are presented.
Data of 23-years of Jupiter polarimetric observations (1981- 2004) have been reprocessed using new improved technique. The data from other observers have been added to the analysis (1971-74). Anticorrelation between asymmetry of polarization and insolation has been found. The mechanism of influence of seasons changing (through temperature variations) on north-south asymmetry of polarization formation has been proposed. Also a possibility of existence of influence of solar cosmic rays flux on polarization value is noted.
We present analysis of extensive monitoring of SS433 by the RXTE observatory collected over the period 1996-2005. The difference between energy spectra taken at different precessional and orbital phases shows the presence of a strong photoabsorption near the optical star, probably due to its powerful dense wind. Assuming that a precessing accretion disk is thick, we recover the temperature profile in the X-ray emitting jet that best fits the observed precessional variations of the X-ray emission temperature. The hottest visible part of the X-ray jet is located at a distance of $l_0/a\sim0.06-0.09$, or $\sim2-3\times10^{11}$cm from the central compact object and has a temperature of about $T_{\rm max}\sim30$ keV. We discovered appreciable orbital X-ray eclipses at the ``crossover'' precessional phases (jets are in the plane of the sky, disk is edge-on) which put a lower limit on the size of the optical component $R/a\ga0.5$ and an upper limit on a mass ratio of binary companions $q=M_{\rm x}/M_{\rm opt}\la0.3-0.35$. The size of the eclipsing region can be larger than secondary's Roche lobe because of substantial photoabsorption by dense stellar wind. This must be taken into account when evaluating the mass ratio from analysis of X-ray eclipses.
We investigate spherical accretion to a rotating magnetized star in the "propeller" regime using axisymmetric resistive magnetohydrodynamic simulations. The regime is predicted to occur if the magnetospheric radius is larger than the corotation radius and smaller than the light cylinder radius. The simulations show that accreting matter is expelled from the equatorial region of the magnetosphere and that it moves away from the star in a supersonic, disk-shaped outflow. At larger radial distances the outflow slows down and becomes subsonic. The equatorial matter outflow is initially driven by the centrifugal force, but at larger distances the pressure gradient force becomes significant. We find the fraction of the Bondi accretion rate which accretes to the surface of the star.
We present the V band variability analysis of the point sources in the Faint Sky Variability Survey on time scales from 24 minutes to tens of days. We find that about one percent of the point sources down to V = 24 are variables. We discuss the variability detection probabilities for each field depending on field sampling, amplitude and timescale of the variability. The combination of colour and variability information allows us to explore the fraction of variable sources for different spectral types. We find that about 50 percent of the variables show variability timescales shorter than 6 hours. The total number of variables is dominated by main sequence sources. The distribution of variables with spectral type is fairly constant along the main sequence, with 1 per cent of the sources being variable, except at the blue end of the main sequence, between spectral types F0--F5, where the fraction of variable sources increases to about 2 percent. For bluer sources, above the main sequence, this percentage increases to about 3.5. We find that the combination of the sampling and the number of observations allows us to determine the variability timescales and amplitudes for a maximum of 40 percent of the variables found. About a third of the total number of short timescale variables found in the survey were not detected in either B or/and I. These show a similar variability timescale distribution to that found for the variables detected in all three bands.
We have developed an interactive program which shows the solar energetic particle (SEP) intensity-time profile as observed by SOHO/ERNE, simultaneously with the associated coronal mass ejection in optical imaging movies taken by LASCO coronagraph, soft X-ray by YOHKOH, ultraviolet by EIT, DH radio emission by WAVE/Wind, and the H$\alpha$ location for the solar flare and spectral radio emission from the journal of geophysical data. The whole set of data will provide increased scientific knowledge on the solar energetic particle events and the solar phenomena associated with them, because in this program one can see easily the temporal associations of each phenomenon during the evolution of the particle intensity. The (SEP) intensity-time profile will give a clear view to detect the velocity dispersion in the events, if it exists. The ERNE data are commented in order to follow of phenomena associated with changes of the intensity-time profiles. We introduce this set of data as an index for the ERNE/SOHO solar energetic particle events. The interactive program is applied for statistical, correlative study of SEP events observed on board SOHO.
New observations of LS 5039, a High Mass X-ray Binary comprising a massive star and compact object, were carried out with the High Energy Stereoscopic System of Cherenkov Telescopes (H.E.S.S.) in 2005 at very high energy (VHE) gamma-ray energies. These observations reveal that its flux and energy spectrum are modulated with the 3.9 day orbital period of the binary system. This is the first time in gamma-ray astronomy that orbital modulation has been observed, and periodicity clearly established using ground-based gamma-ray detectors. The VHE gamma-ray emission is largely confined to half of the orbit, peaking around the inferior conjunction epoch of the compact object. For this epoch, there is also a hardening of the energy spectrum in the energy range between 0.2 TeV and a few TeV. The flux vs. orbital phase profile provides the first clear indication of gamma-ray absorption via pair production within an astrophysical source, a process which is expected to occur if the gamma-ray production site is situated within ~1 AU of the compact object. Moreover the production region size must be not significantly greater than the binary separation (~0.15 AU). Notably, these constraints are also considerably smaller than the collimated outflows or jets (extending out to ~1000 AU) observed in LS 5039. The spectral hardening could arise from variations with phase in the maximum electron energies, and/or the dominant VHE gamma-ray production mechanism.
The carriers of diffuse interstellar bands are still mysterious species. There exist many arguments that diffuse bands at 5797 and 5850 angstroms have the same carrier. Using high-resolution spectra of few dozens of reddened stars we have searched mutual correlation between intensities of considered bands. Results of our analysis indicate that 5797 and 5850 really tend to have the same carrier.
Carbon chains are sometimes considered as possible carriers of some diffuse interstellar bands. Spectroscopic observations in UV band carried by spectrometer STIS fed with HST, give us the possibility to detect many interstellar molecules. We focused our attention on C2 molecule and we detected it in spectra of three reddened stars (HD27778, HD147933, HD207198). Interstellar molecule C2 was detected as a set of absorption lines around 2313 angstroms.
The energy output in the gamma-ray burst (GRB) prompt emission and afterglow phase is expected to photoionize the surrounding medium out to large radii. Cooling of this gas produces line emission, particularly strong in the optical, whose variability is a strong diagnostics of the gas density and geometry in the close environment of the burst. We present the results of a spectral time series analysis of the host galaxy of GRB 990712 observed up to ~6 years after the burst. We analyze the emission line fluxes together with those of the previous observations of the same GRB, in search for photoionization signatures. We find that the emission line fluxes show no variation within the uncertainities up to 6 years after the burst, and we use the measured line intensities to set a limit on the density of the gas within a few parsecs of the burst location. This is the first time that emission from cooling GRB remnants is probed on years time scales.
The presumed Wolf-Rayet star progenitors of Type Ib/c supernovae have fast, low density winds and the shock waves generated by the supernova interaction with the wind are not expected to be radiative at typical times of observation. The injected energy spectrum of radio emitting electrons typically has an observed index p=3, which is suggestive of acceleration in cosmic ray dominated shocks. The early, absorbed part of the radio light curves can be attributed to synchrotron self-absorption, which leads to constraints on the magnetic field in the emitting region and on the circumstellar density. The range of circumstellar densities inferred from the radio emission is somewhat broader than that for Galactic Wolf-Rayet stars, if similar efficiencies of synchrotron emission are assumed in the extragalactic supernovae. For the observed and expected ranges of circumstellar densities to roughly overlap, a high efficiency of magnetic field production in the shocked region is required (epsilon_B ~ 0.1). For the expected densities around a Wolf-Rayet star, a nonthermal mechanism is generally required to explain the observed X-ray luminosities of Type Ib/c supernovae. Although the inverse Compton mechanism can explain the observed X-ray emission from SN 2002ap if the wind parameters are taken from the radio model, the mechanism is not promising for other supernovae unless the postshock magnetic energy density is much smaller than the electron energy density. In some cases another mechanism is definitely needed and we suggest that it is X-ray synchrotron emission in a case where the shock wave is cosmic ray dominated so that the electron energy spectrum flattens at high energy. More comprehensive X-ray observations of a Type Ib/c supernova are needed to determine whether this suggestion is correct.
Loeb and Waxman have argued that high energy neutrinos from the decay of pions produced in interactions of cosmic rays with interstellar gas in starburst galaxies would be produced with a large enough flux to be observable. Their model is reexamined here and it is shown that the the neutrino flux from starburst galaxies, even given the various assumptions made by them, is more than an order of magnitude lower than the flux which they predict. The predicted neutrino flux would be below the atmospheric neutrino foreground flux at energies below 300 TeV and therefore would be unobservable. PeV neutrinos from starburst galaxies are also unlikely to be detected. Compared with predicted fluxes from other extragalactic high energy neutrino sources, PeV starburst neutrinos would have a flux considerably below that predicted for AGN models.
The luminosities and effective temperatures, as well as the whole bolometric lightcurves of nonlinear convective RR Lyrae models with 0.0001<Z<0.006 are transformed into the SDSS photometric system. The obtained ugriz lightcurves, mean magnitudes and colors, pulsation amplitudes and color-color loops are shown and analytical relations connecting pulsational to intrinsic stellar parameters, similarly to the ones currently used in the Johnson-Cousins filters, are derived. Finally the behaviour in the color-color planes is compared with available observations in the literature and possible systematic uncertainties affecting this comparison are discussed.
I review some important aspects of the structural and statistical properties of the nearby X-ray galaxy cluster population, discussing the new constraints on mass profiles, the mass-temperature relation, and the entropy of the intracluster medium which have become available from recent X-ray observations.
In this paper we report on a new study of the SNR Puppis A based on VLA observations at 1425 MHz; the improvement represents a factor of two in angular resolution and almost ten times in sensitivity compared to the best previous image of Puppis A. This new image is used to compare with re-processed 327 MHz data and ROSAT and Chandra images to investigate morphological and spectral characteristics.
This paper reviews the Serret-Andoyer (SA) canonical formalism in rigid-body dynamics and presents some new results. As well known, the problem of unsupported and unperturbed rigid rotator can be reduced. The availability of this reduction is offered by the underlying symmetry, which stems from conservation of the angular momentum and rotational kinetic energy. When a perturbation is turned on, these quantities are no longer preserved. Nonetheless, the language of reduced description remains extremely instrumental even in the perturbed case. We describe the canonical reduction performed by the Serret-Andoyer (SA) method, and discuss its applications to attitude dynamics and to the theory of planetary rotation. Specifically, we consider the case of angular-velocity-dependent torques, and discuss the variation-of-parameters inherent antinomy between canonicity and osculation. Finally, we address the transformation of the Andoyer variables into the action-angle ones, using the method of Sadov.
The B-Mode of the Cosmic Microwave Background Polarization (CMBP) promises to detect the gravitational wave background left by Inflation and explore this very early period of the Universe. In spite of its importance, however, the cosmic signal is tiny and can be severely limited by astrophysical foregrounds. In this contribution we discuss about one of the main contaminant, the diffuse synchrotron emission of the Galaxy. We briefly report about recent deep observations at high Galactic latitudes, the most interesting for CMB purposes because of the low emission, and discuss the contraints in CMBP investigations. The contamination competes with CMB models with T/S = 10^{-2}--10^{-3}, close to the intrinsic limit for a 15% portion of the sky (which is T/S ~ 10^{-3}). If confirmed by future surveys with larger sky coverage, this gives interesting perpectives for experiments, that, targeting selected low emission regions, could reach this theoretical limit.
A residual planetesimal disk of mass 10-100 Earth masses remained in the outer solar system following the birth of the giant planets, as implied by the existence of the Oort cloud, coagulation requirements for Pluto, and inefficiencies in planet formation. Upon gravitationally scattering planetesimal debris, planets migrate. Orbital migration can lead to resonance capture, as evidenced here in the Kuiper and asteroid belts, and abroad in extra-solar systems. Finite sizes of planetesimals render migration stochastic ("noisy"). At fixed disk mass, larger (fewer) planetesimals generate more noise. Extreme noise defeats resonance capture.
A residual planetesimal disk of mass 10-100 Earth masses remained in the outer solar system following the birth of the giant planets, as implied by the existence of the Oort cloud, coagulation requirements for Pluto, and inefficiencies in planet formation. Upon gravitationally scattering planetesimal debris, planets migrate. Orbital migration can lead to resonance capture, as evidenced here in the Kuiper and asteroid belts, and abroad in extra-solar systems. Finite sizes of planetesimals render migration stochastic ("noisy"). At fixed disk mass, larger (fewer) planetesimals generate more noise. Extreme noise defeats resonance capture. We employ order-of-magnitude physics to construct an analytic theory for how a planet's orbital semi-major axis fluctuates in response to random planetesimal scatterings. To retain a body in resonance, the planet's semi-major axis must not random walk a distance greater than the resonant libration width. We translate this criterion into an analytic formula for the retention efficiency of the resonance as a function of system parameters, including planetesimal size. We verify our results with tailored numerical simulations. Application of our theory reveals that capture of Resonant Kuiper belt objects by a migrating Neptune remains effective if the bulk of the primordial disk was locked in bodies having sizes < O(100) km and if the fraction of disk mass in objects with sizes > 1000 km was less than a few percent. Coagulation simulations produce a size distribution of primordial planetesimals that easily satisfies these constraints. We conclude that stochasticity did not interfere with, nor modify in any substantive way, Neptune's ability to capture and retain Resonant Kuiper belt objects during its migration.
We measure the evolution in the virial mass-to-light ratio (M_{200}/L_B) and virial-to-stellar mass ratio (M_{200}/M_\ast) for isolated ~ L* galaxies between z~1 and z~0 by combining data from the DEEP2 Galaxy Redshift Survey and the Sloan Digital Sky Survey. Utilizing the motions of satellite galaxies around isolated galaxies, we measure line-of-sight velocity dispersions and derive dark matter halo virial masses for these host galaxies. At both epochs the velocity dispersion of satellites correlates with host galaxy stellar mass, \sigma\propto M_\ast^{0.4+/-0.1}, while the relation between satellite velocity dispersion and host galaxy B-band luminosity may grow somewhat shallower from \sigma\propto L_B^{0.6+/-0.1} at z~1 to \sigma\propto L_B^{0.4+/-0.1} at z~0. The evolution in M_200/M_\ast from z~1 to z~0 displays a bimodality insofar as host galaxies with stellar mass below M_\ast ~10^{11} M_Sun/h maintain a constant ratio (the intrinsic increase is constrained to a factor of 1.1+/-0.7) while host galaxies above M_\ast ~10^{11} M_Sun/h experience a factor of 4+/-3 increase in their virial-to-stellar mass ratio. This result can be easily understood if galaxies below this stellar mass scale continue to form stars while star formation in galaxies above this scale is quenched and the dark matter halos of galaxies both above and below this scale grow in accordance with LCDM cosmological simulations. Host galaxies that are red in U-B color have larger satellite dispersions and hence reside on average in more massive halos than blue galaxies at both z~1 and z~0. The redshift and host galaxy stellar mass dependence of M_200/M_\ast agrees qualitatively with the Millennium Run semi-analytic model of galaxy formation. (ABRIDGED)
We estimate the optical depth distribution of dust present in absorption systems along the line of sight of high redshift galaxies and the resulting reddening. We characterize the probability distribution of the transmission to a given redshift and the shape of the effective mean extinction law by means of analytical estimates and Monte Carlo simulations. We present our results in a format useful for applications to present samples of high redshift galaxies and discuss the implications for observations with the James Webb Space Telescope. Our most realistic model takes into account the metallicity evolution of Damped Lyman Alpha absorbers and predicts that the effects of dust absorption are modest: at redshift z \gtrsim 5 the transmission is above 0.8 at an emitted wavelength \lambda_e = 0.14 \mu m with probability 90%. Therefore dust obscuration along the line of sight will affect only marginally observations at very high redshift.
We present some results from a UVI photometric study of a field in the young open cluster NGC 2264 aimed, in part, at testing whether accretion in pre-main sequence stars is linked to rotation. We confirm that U-V excess is well correlated with H-alpha equivalent width for the stars in our sample. We show that for the more massive stars in the cluster sample (roughly 0.4-1.2 M_sun) there is also a significant association between U-V excess and rotation, in the sense that slow rotators are more likely to show excess U-band emission and variability. This constitutes significant new evidence in support of the disk-locking paradigm.
The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called ``machos'') could be a major component of the dark matter halo of the Milky Way galaxy. To this end, EROS-2 monitored millions of stars in the Magellanic clouds for microlensing events caused by such objects. About $33\times10^6$ Magellanic stars were observed over a period of 6.7 years. Unlike all previous studies of Magellanic microlensing, we use only a subsample of $7\times10^6$ bright stars. This strategy minimizes backgrounds due to variable stars and ensures accurate determination of lensing parameters by minimizing source confusion (blending). Using this sample of bright stars, only one candidate event was found, whereas $\sim42$ events would have been expected if the Halo were entirely populated by objects of mass $M\sim0.4M_{\odot}$. Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud (\object{LMC}) due to such lenses is $\tau<0.36\times10^{-7}$ (95%CL), corresponding to a fraction of the halo mass of less than 7%. This result is at variance with the measurement of the MACHO collaboration. More generally, machos in the mass range $10^{-7}M_\odot<M<5M_{\odot}$ are ruled out as the primary occupants of the Milky Way Halo.
We review current observational constraints on the polarization of the Cosmic Microwave Background (CMB), with a particular emphasis on detecting the signature of primordial gravitational waves. We present an analytic solution to the Polanarev approximation for CMB polarization produced by primordial gravitational waves. This simplifies the calculation of the curl, or B-mode power spectrum associated with gravitational waves during the epoch of cosmological inflation. We compare our analytic method to existing numerical methods and also make predictions for the sensitivity of upcoming CMB polarization observations to the inflationary gravitational wave background. We show that upcoming experiments should be able either detect the relic gravitational wave background or completely rule out whole classes of inflationary models.
We present the first calculation of the kinetic Sunyaev-Zel'dovich (kSZ) effect due to the inhomogeneus reionization of the universe based on detailed large-scale radiative transfer simulations of reionization. The resulting sky power spectra peak at l=2000-8000 with maximum values of l(l+1)C_l/(2pi)_{max}~4-7x10^{-13}. The scale roughly corresponds to the typical ionized bubble sizes observed in our simulations, of ~5-20 Mpc. The kSZ anisotropy signal from reionization dominates the primary CMB signal above l=3000. At large scales the patchy kSZ signal depends only on the source efficiencies. It is higher when sources are more efficient at producing ionizing photons, since such sources produce larger ionized regions, on average, than less efficient sources. The introduction of sub-grid gas clumping in the radiative transfer simulations produce significantly more power at small scales, but has little effect at large scales. The patchy reionization kSZ signal is dominated by the post-reionization signal from fully-ionized gas, but the two contributions are of similar order at scales l~3000-10^4, indicating that the kSZ anisotropies from reionization are an important component of the total kSZ signal at these scales.
Two types of stability boundaries exist for any planetary system consisting of one star and two planets. Lagrange stability requires that the planets remain bound to the star, conserves the ordering of the distance from the star, and limits the variations of orbital elements like semi-major axis and eccentricity. Hill stability only requires that the ordering of the planets remain constant; the outer planet may escape to infinity. A simple formula defines a region in orbital element space that is guaranteed to be Hill stable, although Hill stable orbits may lie outside the region as well. No analytic criteria describe Lagrange stability. We compare the results of 1000 numerical simulations of planetary systems similar to 47 UMa and HD 12661 with these two types of boundaries. All cases are consistent with the analytic criterion for Hill stability. Moreover, the numerically determined Lagrange boundary lies close to the analytic boundary for Hill stability. This result suggests an analytic formulation that may describe the criterion for Lagrange stability.
We present a comprehensive description of the theory and practice of opacity calculations from the infrared to the ultraviolet needed to generate models of the atmospheres of brown dwarfs and extrasolar giant planets. Methods for using existing line lists and spectroscopic databases in disparate formats are presented and plots of the resulting absorptive opacities versus wavelength for the most important molecules and atoms at representative temperature/pressure points are provided. Electronic, ro-vibrational, bound-free, bound-bound, free-free, and collision-induced transitions and monochromatic opacities are derived, discussed, and analyzed. The species addressed include the alkali metals, iron, heavy metal oxides, metal hydrides, $H_2$, $H_2O$, $CH_4$, $CO$, $NH_3$, $H_2S$, $PH_3$, and representative grains. [Abridged]
The high density of the close-in extrasolar planet HD149026b suggests the presence of a huge core in the planet, which challenges planet formation theory. We first derive constraints on the amount of heavy elements and hydrogen/helium present in the planet: We find that preferred values of the core mass are between 50 and 80 M_E. We then investigate the possibility of subcritical core accretion as envisioned for Uranus and Neptune and find that the subcritical accretion scenario is unlikely in the case of HD149026b for at least two reasons: (i) Subcritical planets are such that the ratio of their core mass to their total mass is above ~0.7, in contradiction with constraints for all but the most extreme interior models of HD149026b; (ii) High accretion rates and large isolation mass required for the formation of a subcritical core of 30 M_E are possible only at specific orbital distances in a disk with a surface density of dust equal to at least 10 times that of the minimum mass solar nebula. This value climbs to 30 when considering a 50 M_E core. These facts point toward two main routes for the formation of this planet: (i) Gas accretion that is limited by a slow viscous inflow of gas in an evaporating disk; (ii) A significant modification of the composition of the planet after as accretion has stopped. These two routes are not mutually exclusive. Illustrating the second route, we show that for a wide range of impact parameters, giant impacts lead to a loss of the gas component of the planet and thus may lead to planets that are highly enriched in heavy elements. In the giant impact scenario, we expect an outer giant planet to be present. Observational studies by imaging, astrometry and long term interferometry of this system are needed to better narrow down the ensemble of possibilities.
We analysed Rossi X-ray Timing Explorer observations of the accretion-powered
401 Hz pulsar SAX J1808.4-3658, in order to precisely determine the source
distance. While the fluences for the five transient outbursts observed from
1996 were constant to within the uncertainties, the outburst interval varied
signficantly, so that the time-averaged flux (and accretion rate) decreased by
around 40%. By equating the time-averaged X-ray flux with the expected mass
transfer rate from gravitational radiation, we derived a lower limit on the
distance of 3.4 kpc. Combined with an upper limit from assuming that the four
radius-expansion thermonuclear bursts observed during the 2002 October outburst
reached at most the Eddington limit for a pure He atmosphere, we found that the
probable distance range for the source is 3.4-3.6 kpc. The implied inclination,
based on the optical/IR properties of the counterpart, is i<~30 degrees.
We compared the properties of the bursts with an ignition model. The time
between bursts was long enough for hot CNO burning to significantly deplete the
accreted hydrogen, so that ignition occurred in a pure helium layer underlying
a stable hydrogen burning shell. This is the first time that this burning
regime has been securely observationally identified. The observed energetics of
the bursts give a mean hydrogen fraction at ignition of <X> approx. 0.1, and
require that the accreted hydrogen fraction X_0 and the CNO metallicity Z_CNO
are related by Z_CNO approx. 0.03(X_0/0.7)^2. We show that in this burning
regime, a measurement of the burst recurrence time and energetics allows the
local accretion rate onto the star to be determined independently of the
accreted composition, giving a new method for estimating the source distance
which is in good agreement with our other estimates.
Matter accreting onto the magnetic poles of a neutron star spreads under gravity towards the magnetic equator, burying the polar magnetic field and compressing it into a narrow equatorial belt. Steady-state, Grad-Shafranov calculations with a self-consistent mass-flux distribution (and a semi-quantitative treatment of Ohmic diffusion) show that, for $\Ma \gtrsim 10^{-5}\Msun$, the maximum field strength and latitudinal half-width of the equatorial magnetic belt are $B_{\rm max} = 5.6\times 10^{15} (\Ma/10^{-4}\Msun)^{0.32}$ G and $\Delta\theta = \max[3^{\circ} (\Ma/10^{-4}\Msun)^{-1.5},3^{\circ} (\Ma/10^{-4}\Msun)^{0.5}(\dot{M}_{\rm a}/10^{-8}\Msun {\rm yr}^{-1})^{-0.5}]$ respectively, where $\Ma$ is the total accreted mass and $\dot{M}_{\rm a}$ is the accretion rate. It is shown that the belt prevents north-south heat transport by conduction, convection, radiation, and ageostrophic shear. This may explain why millisecond oscillations observed in the tails of thermonuclear (type I) X-ray bursts in low-mass X-ray binaries are highly sinusoidal: the thermonuclear flame is sequestered in the magnetic hemisphere which ignites first. The model is also consistent with the occasional occurrence of closely spaced pairs of bursts. Time-dependent, ideal-magnetohydrodynamic simulations confirm that the equatorial belt is not disrupted by Parker and interchange instabilities.
We estimate the strength of the induced magnetic field due to the total induced magnetic moment of the anisotropic ($^3PF^2$) neutron superfluid interior of neutron stars. The induced magnetic field of the neutron stars is found as follows. $B^{(in)} = \frac{\eta}{{T_7 - \eta}}B^{(0)} ,\begin{array}{*{20}c}{} & {\eta =} \ \end{array}\frac{{m(^3 P_2 )}}{{0.1m_{Sun}}}R_{NS,6}^{- 3} $ ($T_7$ denotes the interior temperature of the neutron star in unit of 10$^7$ K). The induced magnetic field will gradually increase with the temperature of the neutron star decreasing in their late evolutionary stage. A magnetar may appear in a condition when $T_7 \to \eta$. The upper limit of the induced magnetic field of $^3P^2$ superfluid is $3.35 \time 10^{14} \eta$.
This is a doctorate level lecture on the physics of accretion discs driving magnetically self-confined jets, usually referred to in the literature as disc winds. I will first review the governing magnetohydrodynamic equations and then discuss their physical content. At that level, necessary conditions to drive jets from keplerian accretion discs can already be derived. These conditions are validated with self-similar calculations of accretion-ejection structures. In a second part, I will critically discuss the biases introduced when using self-similarity as well as some other questions such as: Are these systems really unstable? Can a standard accretion disc provide the conditions to launch jets in its innermost parts? What is the difference between X-winds and disc-winds? Finally, the magnetic interaction between a protostar and its circumstellar disc will be discussed with a focus on stellar spin down.
Most population I Wolf-Rayet (WR) stars are the He-rich descendants of the most massive stars (M_i = 25 - 100 M_sun). Evidence has been accumulating over the years that among all pop I WR stars, those of the relatively cool, N-rich subtype "WN8" are among the most peculiar: 1. They tend to be runaways, with large space velocity and/or avoid clusters. 2. Unlike their equally luminous WN6,7 cousins, only a very small number of WN8 stars are known to belong to a close binary with an OB companion. 3. They are the systematically most highly stochastically variable among all (single) WR stars. Taken together, these suggest that many WN8 stars may originally have been in close binaries (like half of all stars), in which the original primary exploded as a supernova, leaving behind a very close binary containing a massive star with a neutron star/black hole companion (like Cyg X-3). When the massive remaining star evolved in turn, it engulfed and eventually swallowed the compact companion, leading to the presently puffed-up, variable WN8 star. Such stars could fall in the realm of the exotic Thorne-Zytkow objects.
The determinations of element abundances in red-giant stars and in particular in AGB stars are reviewed and the resulting abundances are compared with those obtained for planetary nebulae in the Galaxy and in nearby galaxies. The problems, possibilities and implications of such comparisons when estimating yields from low-mass and intermediate-mass stars are illustrated and commented on.
Extrasolar planets as light as a few Earths are now being detected. Such planets are likely not gas or ice giants. Here, we present a study on the possible properties of the small and cold extrasolar planets, applied to the case of the recently discovered planet OGLE-2005-BLG-390Lb (Beaulieu et al. 2006). This planet (5.5[+5.5/-2.7] Earth masses) orbits 2.6[+1.5/-0.6]-astronomical units away from an old M-type star of the Galactic Bulge. The planet should be entirely frozen given the low surface temperature (35 to 47 K). However, depending on the rock-to-ice mass ratio in the planet, the radiogenic heating could be sufficient to make the existence of liquid water within an icy crust possible. This possibility is estimated as a function of the planetary mass and the illumination received from the parent star, both being strongly related by the observational constraints. The results are presented for water-poor and water-rich planets. We find that no oceans can be present in any cases at 9-10 Gyr, a typical age for a star of the Bulge. However, we find that, in the past when the planet was < 5-billion-years old, liquid water was likely present below an icy surface. Nevertheless, the planet is now likely to be entirely frozen.
NLTE spectral analyses of high-gravity central stars by means of state-of-the-art model atmosphere techniques provide information about the precursor AGB stars. The hydrogen-deficient post-AGB stars allow investigations on the intershell matter which is apparently exhibited at the stellar surface. We summarize recent results from imaging, spectroscopy, and spectropolarimetry.
We present the results from adaptive optics (AO) assisted imaging in the Ks band of an area of 15 arcmin^2 for SWAN (Survey of a Wide Area with NACO). We derive the high resolution near-IR morphology of ~400 galaxies up to Ks~23.5 in the first 21 SWAN fields around bright guide stars, carefully taking into account the survey selection effects and using an accurate treatment of the anisoplanatic AO PSF. The detected galaxies are sorted into two morphological classes according to their Sersic index. The extracted morphological properties and number counts of the galaxies are compared with the predictions of different galaxy formation and evolution models, both for the whole galaxy population and separately for late-type and early-type galaxies. This is one of the first times such a comparison has been done in the near-IR, as AO observations and accurate PSF modeling are needed to obtain reliable morphological classification of faint field galaxies at these wavelengths. For early-type galaxies we find that a pure luminosity evolution model, without evidence for relevant number and size evolution, better reproduces the observed properties of our Ks-selected sample than current semi-analytic models based on the hierarchical picture of galaxy formation. In particular, we find that the observed flattening of elliptical galaxy counts at Ks~20 is quantitatively in good agreement with the prediction of the pure luminosity evolution model that was calculated prior to the observation. For late-type galaxies, while both models are able to reproduce the number counts, we find some hints of a possible size growth. These results demonstrate the unique power of AO observations to derive high resolution details of faint galaxies' morphology in the near-IR and drive studies of galaxy evolution.
Disk material has been observed around both components of some young close binary star systems. It has been shown that if planets form at the right places within such disks, they can remain dynamically stable for very long times. Herein, we numerically simulate the late stages of terrestrial planet growth in circumbinary disks around 'close' binary star systems with stellar separations between 0.05 AU and 0.4 AU and binary eccentricities up to 0.8. In each simulation, the sum of the masses of the two stars is 1 solar mass, and giant planets are included. Our results are statistically compared to a set of planet formation simulations in the Sun-Jupiter-Saturn system that begin with essentially the same initial disk of protoplanets. The planetary systems formed around binaries with apastron distances less than ~ 0.2 AU are very similar to those around single stars, whereas those with larger maximum separations tend to be sparcer, with fewer planets, especially interior to 1 AU. We also provide formulae that can be used to scale results of planetary accretion simulations to various systems with different total stellar mass, disk sizes, and planetesimal masses and densities.
Starting with the first detection of an afterglow from a short-duration hard-spectrum gamma-ray burst (SHB) by Swift last year, a growing body of evidence has suggested that SHBs are associated with an older and lower-redshift galactic population than long-soft GRBs and, in a few cases, with large (>~ 10 kpc) projected offsets from the centers of their putative host galaxies. Here we present observations of the field of GRB 060502B, a SHB detected by Swift and localized by the X-ray Telescope (XRT). We find a massive red galaxy at a redshift of z=0.287 at an angular distance of 17.5" from our revised XRT position. Using associative and probabilistic arguments we suggest that this galaxy hosted the progenitor of GRB 060502B. If true, this offset would correspond to a physical displacement of 73 +/- 15 kpc in projection, about twice the largest offset inferred for any SHB to date and almost an order of magnitude larger than a typical long-soft burst offset. Spectra and modeling of the star-formation history of this possible host show it to have undergone a large ancient starburst. If the progenitor of GRB 060502B was formed in this starburst episode, this would be the first direct constraint on the age and minimum kick velocity of a SHB progentior from its birthsite. In particular, tau = 1.3 +- 0.2 Gyr and v_kick_min = 55 +- 15 km/s.
We perform long-term two dimensional axisymmetric simulations in the
postbounce phase of core-collapse supernovae to study how the asphericities
induced by the growth of the standing accretion shock instability (SASI)
produce the gravitational waveforms. To obtain the neutrino-driven explosions,
we parameterize the neutrino fluxes emitted from the central protoneutron star
and approximate the neutrino transfer by a light-bulb scheme. We find that the
waveforms due to the anisotropic neutrino emissions show the monotonic increase
with time, whose amplitudes are up to two order-of-magnitudes larger than the
ones from the convective matter motions outside the protoneutron stars.
We point out that the amplitudes begin to become larger when the growth of the
SASI enters the nonlinear phase, in which the deformation of the shocks and the
neutrino anisotropy become large.
From the spectrum analysis of the waveforms, we find that the amplitudes from
the neutrinos are dominant over the ones from the matter motions at the
frequency below $\sim 100$ Hz, which are suggested to be within the detection
limits of the detectors in the next generation such as LCGT and the advanced
LIGO for a supernova at 10 kpc.
As a contribution to the gravitational wave background, we show that the
amplitudes from this source could be larger at the frequency above $\sim$ 1 Hz
than the primordial gravitational wave backgrounds, but unfortunately,
invisible to the proposed space-based detectors.
The assertion that there is an intrinsic excess of binaries with mass ratios q \simeq 1 - the twin hypothesis - is investigated. A strong version of this hypothesis (H_s), due to Lucy & Ricco (1979) and Tokovinin (2000), refers to a narrow peak in the distribution function psi(q) for q \ga 0.95. A weak version (H_w), due to Halbwachs et al. (2003), refers to a broad peak for q \ga 0.8. Current data on SB2's is analysed and H_s is found to be statistically significant for a sample restricted to orbits of high precision. But claims that H_s is significant for binaries with special characteristics are not confirmed since the sample sizes are well below the minimum required for a reliable test. With regard to H_w, additional observational evidence is not presented, but evidence to the contrary in the form of Hogeveen's (1992b) model of biased sampling with psi \propto q^{-2} is criticized. Specifically, his success in thus fitting catalogued data depends on implausible assumptions about the research methodologies of binary-star spectroscopists.
Double-peaked Balmer-line profiles originate in the accretion disks of a few percent of optically selected AGN. The reasons behind the strong low-ionization line emission from the accretion disks of these objects is still uncertain. In this paper, we characterize the X-ray properties of 39 double-peaked Balmer line AGN, 29 from the Sloan Digital Sky Survey and 10 low optical-luminosity double-peaked emitters from earlier radio-selected samples. We find that the UV-to-X-ray slope of radio-quiet (RQ) double-peaked emitters as a class does not differ substantially from that of normal RQ AGN with similar UV monochromatic luminosity. The radio-loud (RL) double-peaked emitters, with the exception of LINER galaxies, are more luminous in the X-rays than RQ AGN, as has been observed for other RL AGN with single-peaked profiles. The X-ray spectral shapes of double-peaked emitters, measured by their hardness ratios or power-law photon indices, are also largely consistent with those of normal AGN of similar radio-loudness. In practically all cases studied here, external illumination of the accretion disk is necessary to produce the Balmer-line emission, as the gravitational energy released locally in the disk by viscous stresses is insufficient to produce lines of the observed strength. In the Appendix we study the variability of Mrk 926, a double-peaked emitter with several observations in the optical and X-ray bands.
We revisit anthropic arguments purporting to explain the measured value of the cosmological constant. We argue that different ways of assigning probabilities to candidate universes lead to totally different anthropic predictions. As an explicit example, we show that weighting different universes by the total number of possible observations leads to an extremely small probability for observing a value of Lambda equal to or greater than what we now measure. We conclude that anthropic reasoning within the framework of probability as frequency is ill-defined and that it cannot be used to explain the value of Lambda, nor, likely, any other physical parameters.
This review focuses on the X-ray emission processes of extra-galactic jets on scales resolvable by the sub arcsec resolution of the Chandra X-ray Observatory. It is divided into 4 parts. The introductory chapter reviews the classical problems for jets, as well as those associated directly with the X-ray emission. Throughout this section, we deal with the dualisms of low powered radio sources versus high powered radio galaxies and quasars; synchrotron models versus inverse Compton models; and the distinction between the relativistic plasma responsible for the received radiation and the medium responsible for the transport of energy down the jet. The second part collects the observational and inferred parameters for the currently detected X-ray jets and attempts to put their relative sizes and luminosities in perspective. In part 3, we first give the relevant radio and optical jet characteristics, and then examine the details of the X-ray data and how they can be related to various jet attributes. The last section is devoted to a critique of the two non-thermal emission processes and to prospects for progress in our understanding of jets.
We report the results of analyzing Swift, RossiXTE, and INTEGRAL data of Swift J1922.7-1716, a likely transient X-ray source discovered by Swift/BAT. Both the fast variability measured by the RXTE/PCA and the combined Swift/XRT, RXTE/PCA, and INTEGRAL/ISGRI (0.5-100 keV) energy spectrum suggest that the system is a neutron-star low-mass X-ray binary or a black-hole candidate at low accretion levels. The non-simultaneous spectra are consistent with the same spectral shape and flux, suggesting little variability over the period July to October 2005, but the analysis of archival INTEGRAL data shows that the source was not detected in 2003-2004, suggesting a transient or strongly variable behavior.
In this paper, we present a new method to perform numerical simulations of astrophysical MHD flows using the Adaptive Mesh Refinement framework and Constrained Transport. The algorithm is based on a previous work in which the MUSCL--Hancock scheme was used to evolve the induction equation. In this paper, we detail the extension of this scheme to the full MHD equations and discuss its properties. Through a series of test problems, we illustrate the performances of this new code using two different MHD Riemann solvers (Lax-Friedrich and Roe) and the need of the Adaptive Mesh Refinement capabilities in some cases. Finally, we show its versatility by applying it to two completely different astrophysical situations well studied in the past years: the growth of the magnetorotational instability in the shearing box and the collapse of magnetized cloud cores. We have implemented this new Godunov scheme to solve the ideal MHD equations in the AMR code RAMSES. It results in a powerful tool that can be applied to a great variety of astrophysical problems, ranging from galaxies formation in the early universe to high resolution studies of molecular cloud collapse in our galaxy.
We report on a uniform comparative analysis of the fundamental parameters of early--type galaxies at z~1 down to M_B \leq -20, both in the field and in the clusters. The changes in the M/L_B ratio from z~1 to today are larger for lower mass galaxies in all environments, and are larger in the field than in the clusters for galaxies with the same mass. By deriving ages from the M/L_B ratio, we estimate the formation redshift for early-type galaxies as a function of galaxy mass and environment. We find that (1) the age of early-type galaxies increases with galaxy mass (downsizing) in all environments, (2) cluster galaxies are older than field galaxies at any given galaxy mass, and (3) this age difference increases with galaxy mass. The first two results confirm similar ones obtained by other means, while the third one is new. The most recent incarnation of the hierarchical models of galaxy formation and evolution is capable of explaining the first two results, but predicts the opposite of our third result. We also find a total lack of massive early--type galaxies M>3 10^{11} solar masses with a formation redshift smaller than 2, which cannot be due to selection effects.
We present high resolution 0.45" x 0.32" observations from the BIMA array toward the Herbig Ae system MWC 480 in the lambda = 1.4 mm dust continuum. We resolve a circumstellar disk of radius ~170 AU and constrain the disk parameters by comparing the observations to flat disk models. These results show that the typical fit parameters of the disk, such as the mass, Md ~ 0.04-0.18 Mo, and the surface density power law index, p=0.5 or 1, are comparable to those of the lower mass T Tauri stars. The dust in the MWC 480 disk can be modeled as processed dust material (beta ~ 0.8), similar to the Herbig Ae star CQ Tau disk; the fitted disk parameters are also consistent with less-evolved dust (beta ~ 1.2). The possibility of grain growth in the MWC 480 circumstellar disk is supported by the acceptable fits with beta ~ 0.8. The surface density power-law profiles of p=0.5 and p=1 can be easily fit to the MWC 480 disk; however, a surface density power-law profile similiar to the minimum mass solar nebula model p=1.5 is ruled out at an 80% confidence level.
On December 27th 2004, a giant gamma flare from the Soft Gamma-ray Repeater 1806-20 saturated many satellite gamma-ray detectors. This event was by more than two orders of magnitude the brightest cosmic transient ever observed. If the gamma emission extends up to TeV energies with a hard power law energy spectrum, photo-produced muons could be observed in surface and underground arrays. Moreover, high-energy neutrinos could have been produced during the SGR giant flare if there were substantial baryonic outflow from the magnetar. These high-energy neutrinos would have also produced muons in an underground array. AMANDA-II was used to search for downgoing muons indicative of high-energy gammas and/or neutrinos. The data revealed no significant signal. The upper limit on the gamma flux at 90% CL is dN/dE < 0.05 (0.5) TeV^-1 m^-2 s^-1 for gamma=-1.47 (-2). Similarly, we set limits on the normalization constant of the high-energy neutrino emission of 0.4 (6.1) TeV^-1 m^-2 s^-1 for gamma=-1.47 (-2).
Many models of early structure formation predict a period of heating immediately preceding reionization, when X-rays raise the gas temperature above that of the cosmic microwave background. These X-rays are often assumed to heat the intergalactic medium (IGM) uniformly, but in reality they will heat the gas more strongly closer to the sources. We develop a framework for calculating fluctuations in the 21 cm brightness temperature that originate from this spatial variation in the heating rate. High-redshift sources are highly clustered, leading to significant gas temperature fluctuations (with fractional variations ~40%, peaking on k~0.1 Mpc^{-1} scales). This induces a distinctive peak-trough structure in the angle-averaged 21 cm power spectrum, which may be accessible to the proposed Square Kilometre Array. This signal reaches the ~10 mK level, and is stronger than that induced by Lyman alpha flux fluctuations. As well as probing the thermal evolution of the IGM before reionization, this 21 cm signal contains information about the spectra of the first X-ray sources. Finally, we consider disentangling temperature, density and Lyman alpha flux fluctuations as functions of redshift.
We derive detailed theoretical models for 1074 nearby stars from the SPOCS (Spectroscopic Properties of Cool Stars) Catalog. The California and Carnegie Planet Search has obtained high-quality echelle spectra of over 1000 nearby stars taken with the Hamilton spectrograph at Lick Observatory, the HIRES spectrograph at Keck, and UCLES at the Anglo Australian Observatory. A uniform analysis of the high-resolution spectra has yielded precise stellar parameters, enabling systematic error analyses and accurate theoretical stellar modeling. We have created a large database of theoretical stellar evolution tracks using the Yale Stellar Evolution Code (YREC) to match the observed parameters of the SPOCS stars. Our very dense grids of evolutionary tracks eliminate the need for interpolation between stellar evolutionary tracks and allow precise determinations of physical stellar parameters (mass, age, radius, size and mass of the convective zone, etc.). Combining our stellar models with the observed stellar atmospheric parameters and uncertainties, we compute the likelihood for each set of stellar model parameters separated by uniform time steps along the stellar evolutionary tracks. The computed likelihoods are used for a Bayesian analysis to derive posterior probability distribution functions for the physical stellar parameters of interest. We provide a catalog of physical parameters for 1074 stars that are based on a uniform set of high quality spectral observations, a uniform spectral reduction procedure, and a uniform set of stellar evolutionary models. We explore this catalog for various possible correlations between stellar and planetary properties, which may help constrain the formation and dynamical histories of other planetary systems.
The Local Group galaxies constitute a fundamental step in the definition of cosmic distance scale. Therefore, obtaining accurate distance determinations to the galaxies in the Local Group, and notably to the Andromeda Galaxy (M31), is essential to determining the age and evolution of the Universe. With this ultimate goal in mind, we started a project to use eclipsing binaries as distance indicators to M31. Eclipsing binaries have been proved to yield direct and precise distances that are essentially assumption free. To do so, high-quality photometric and spectroscopic data are needed. As a first step in the project, broad band photometry (in Johnson B and V) has been obtained in a region (34'x34') at the North-Eastern quadrant of the galaxy over 5 years. The data, containing more than 250 observations per filter, have been reduced by means of the so-called difference image analysis technique and the DAOPHOT program. A catalog with 236238 objects with photometry in both B and V passbands has been obtained. The catalog is the deepest (V<25.5 mag) obtained so far in the studied region and contains 3964 identified variable stars, with 437 eclipsing binaries and 416 Cepheids. The most suitable eclipsing binary candidates for distance determination have been selected according to their brightness and from the modelling of the obtained light curves. The resulting sample includes 24 targets with photometric errors around 0.01 mag. Detailed analysis (including spectroscopy) of some 5-10 of these eclipsing systems should result in a distance determination to M31 with a relative uncertainty of 2-3% and essentially free from systematic errors, thus representing the most accurate and reliable determination to date.
We investigate the properties of satellite galaxies formed in N-body/SPH simulations of galaxy formation in the $\Lambda$CDM cosmology. The simulations include the main physical effects thought to be important in galaxy formation and, in several cases, produce realistic spiral discs. In total, a sample of 9 galaxies of luminosity comparable to the Milky Way was obtained. At magnitudes brighter than the resolution limit, $M_V=-12$, the luminosity function of the satellite galaxies in the simulations is in excellent agreement with data for the Local Group. The radial number density profile of the model satellites, as well as their gas fractions also match observations very well. In agreement with previous N-body studies, we find that the satellites tend to be distributed in highly flattened configurations whose major axis is aligned with the major axis of the (generally triaxial) dark halo. In 2 out of 3 systems with sufficiently large satellite populations, the satellite system is nearly perpendicular to the plane of the galactic disc, a configuration analogous to that observed in the Milk Way. The discs themselves are perpendicular to the minor axis of their host halos in the inner parts, and the correlation between the orientation of the galaxy and the shape of the halo persists even out to the virial radius. However, in one case the disc's minor axis ends up, at the virial radius, perpendicular to the minor axis of the halo. The angular momenta of the galaxies and their host halo tend to be well aligned.
We present the luminosity function to very faint magnitudes for the globular clusters in M87, based on a 30 orbit \textit{Hubble Space Telescope (HST)} WFPC2 imaging program. The very deep images and corresponding improved false source rejection allow us to probe the mass function further beyond the turnover than has been done before. We compare our luminosity function to those that have been observed in the past, and confirm the similarity of the turnover luminosity between M87 and the Milky Way. We also find with high statistical significance that the M87 luminosity function is broader than that of the Milky Way. We discuss how determining the mass function of the cluster system to low masses can constrain theoretical models of the dynamical evolution of globular cluster systems. Our mass function is consistent with the dependence of mass loss on the initial cluster mass given by classical evaporation, and somewhat inconsistent with newer proposals that have a shallower mass dependence. In addition, the rate of mass loss is consistent with standard evaporation models, and not with the much higher rates proposed by some recent studies of very young cluster systems. We also find that the mass-size relation has very little slope, indicating that there is almost no increase in the size of a cluster with increasing mass.
We report on the results of a visual search for galaxy-scale strong gravitational lenses over 650 arcmin^2 of HST/ACS imaging in the DEEP2-EGS field. In addition to a previously-known Einstein Cross (the "Cross," HST J141735+52264, with z_lens=0.8106 and a published z_source=3.40), we identify two new strong galaxy-galaxy lenses with multiple extended arcs. The first, HST J141820+52361 (the ``Dewdrop''; z_lens=0.5798, lenses two distinct extended sources into two pairs of arcs z_source=0.while), 9818 the second, HST J141833+52435 (the ``Anchor''; z_lens=0.4625), produces a single pair of arcs (source redshift not yet known). All three definite lenses are fit well by simple singular isothermal ellipsoid models including external shear. Using the three-dimensional line-of-sight (LOS) information on galaxies from the DEEP2 data, we calculate the convergence and shear contributions, assuming singular isothermal sphere halos truncated at 200 h^-1 kpc. These are also compared against three-dimensional local-density estimates. We find that even strong lenses in demonstrably underdense local environments may be considerably affected by LOS contributions, which in turn, may be underestimates of the effect of large scale structure.
We present a simultaneous analysis of 10 galaxy lenses having time-delay measurements. For each lens we derive a detailed free-form mass map, with uncertainties, and with the additional requirement of a shared value of the Hubble parameter across all the lenses. We test the prior involved in the lens reconstruction against a galaxy-formation simulation. Assuming a concordance cosmology, we obtain 1/H_0 = 13.5 (+2.5/-1.3) Gyr
We present a new, simple, fast algorithm to numerically evolve disks of inelastically colliding particles surrounding a central star. Our algorithm adds negligible computational cost to the fastest existing collisionless N-body codes, and can be used to simulate, for the first time, the interaction of planets with disks over many viscous times. Though the algorithm is implemented in two dimensions-i.e., the motions of bodies need only be tracked in a plane-it captures the behavior of fully three-dimensional disks in which collisions maintain inclinations that are comparable to random eccentricities. We subject the algorithm to a battery of tests for the case of an isolated, narrow, circular ring. Numerical simulations agree with analytic theory with regards to how particles' random velocities equilibrate; how the ring viscously spreads; and how energy dissipation, angular momentum transport, and material transport are connected. We derive and measure the critical value of the coefficient of restitution above which viscous stirring dominates inelastic damping and the particles' velocity dispersion runs away.
We use deep and wide near infrared (NIR) imaging from the Palomar telescope combined with DEEP2 spectroscopy and Hubble Space Telescope (HST) and Chandra Space Telescope imaging to investigate the nature of galaxies that are red in NIR colors. We locate these `distant red galaxies' (DRGs) through the color cut (J-K)_{vega} > 2.3 over 0.7 deg^{2}, where we find 1010 DRG candidates down to K_s = 20.5. We combine 95 high quality spectroscopic redshifts with photometric redshifts from BRIJK photometry to determine the redshift and stellar mass distributions for these systems, and morphological/structural and X-ray properties for 107 DRGs in the Extended Groth Strip. We find that many bright (J-K)_{vega}>2.3 galaxies with K_s<20.5 are at redshifts z<2, with 64% between 1<z<2. The stellar mass distributions for these galaxies is broad, ranging from 10^{9}-10^{12} M_solar, but with most z>2 systems massive with M_*>10^{11} M_solar. HST imaging shows that the structural properties and morphologies of DRGs are also diverse, with the majority elliptical/compact (57%), and the remainder edge-on spirals (7%), and peculiar galaxies (29%). The DRGs at z < 1.4 with high quality spectroscopic redshifts are generally compact, with small half light radii, and span a range in rest-frame optical properties. The spectral energy distributions for these objects differ from higher redshift DRGs: they are bluer by one magnitude in observed (I-J) color. A pure IR color selection of high redshift populations is not sufficient to identify unique populations, and other colors, or spectroscopic redshifts are needed to produce homogeneous samples.
We present a phenomenological model of imbalanced MHD turbulence in an incompressible magnetofluid. The steady-state cascades, of waves traveling in opposite directions along the mean magnetic field, carry unequal energy fluxes to small length scales, where they decay due to viscous and resistive dissipation. The inertial-range scalings are well-understood when both cascades are weak. We study the case when both cascades are, in a sense, strong. The inertial-range of this imbalanced cascade has the following properties: (i) the ratio of the r.m.s. Elsasser amplitudes is independent of scale, and is equal to the ratio of the corresponding energy fluxes; (ii) in common with the balanced strong cascade, the energy spectra of both Elsasser waves are of the anisotropic Kolmogorov form, with their parallel correlation lengths equal to each other on all scales, and proportional to the two-thirds power of the transverse correlation length; (iii) the equality of cascade time and waveperiod (critical balance) that characterizes the strong balanced cascade does not apply to the Elsasser field with the larger amplitude. Instead, the more general criterion that always applies to both Elsasser fields is that the cascade time is equal to the correlation time of the straining imposed by oppositely-directed waves. Our results are particularly relevant for turbulence in the solar wind. Spacecraft measurements have established that, in the inertial range of solar wind turbulence, waves travelling away from the sun have higher amplitudes than those travelling towards it. Result (i) allows us to infer the turbulent flux ratios from the amplitude ratios, thus providing insight into the origin of the turbulence.
Convection that develops behind the shock front during the first second of a core-collapse supernova explosion is believed to play a crucial role in the explosion mechanism. We demonstrate that the resulting turbulent density fluctuations may be directly observable in the neutrino signal starting at t>~ 3-4 s after the onset of the explosion. The effect comes from the modulation of the MSW flavor transformations by the turbulent density fluctuations. We derive a simple and general criterion for neutrino flavor depolarization in a Kolmogorov-type turbulence and apply it to the turbulence seen in modern numerical simulations. The turbulence casts a "shadow", by making other features, such as the shock front, unobservable in the density range covered by the turbulence.
Aliphatic hydrocarbons exhibit an absorption feature at 3.4 micron observed toward sources that sample diffuse regions of the interstellar medium. The absorbers responsible for this feature are assumed to reside in some component of interstellar dust, but the physical nature of the particles (size, shape, structure, etc.) is uncertain. Observations of interstellar polarization provide discrimination. Since the grains that carry the silicate absorption feature are known to be aligned, polarization across the 3.4 micron hydrocarbon feature can be used to test the silicate core-organic refractory mantle grain theory. Although the 3.4 micron feature has been observed to be devoid of polarization for one line of sight toward the Galactic center, a corresponding silicate polarization measurement for the same line of sight was not available. Here, we present spectropolarimetric observations toward GCS 3-II and GCS 3-IV toward the Galactic center, where the 9.7 micron silicate polarization has been previously observed. We show that polarization is not detected across the 3.4 micron feature to a limit of 0.06 +/- 0.13% (GCS 3-II) and 0.15 +/- 0.31% (GCS 3-IV), well below the lowest available prediction of polarization on the basis of the core-mantle model. We conclude that the hydrocarbons in the diffuse ISM do not reside on the same grains as the silicates and likely form a separate population of small grains.
The HII regions around quasars and galaxies at redshifts beyond the epoch of reionisation will provide prime targets for upcoming 21cm campaigns using a new generation of low-frequency radio observatories. Here we show that the boundaries of these HII regions will not be sharp. Rather, the clustering of sources near massive galaxies results in a neutral fraction that rises gradually towards large radii from an interior value near zero. A neutral fraction corresponding to the global background value is typically reached at a distance of 2-5 times the radius of the HII region around the central massive galaxy.
Three different analysis techniques for Atmospheric Imaging System are presented. The classical Hillas parameters based technique is shown to be robust and efficient, but more elaborate techniques can improve the sensitivity of the analysis. A comparison of the different analysis techniques shows that they use different information for gamma-hadron separation, and that it is possible to combine their qualities.
The pulsar B1822-09 (J1825-0935) experienced a series of five unusual slow glitches over the 1995-2004 interval. The results of further study of this unusual glitch phenomenon are presented. It is also reported the detection a new glitch of typical signature that occurred in the pulsar period in 2006 January.
We describe a simple procedure to estimate the high-energy neutrino flux from the observed gamma-ray spectra of galactic cosmic ray sources that are transparent to their gamma radiation. We evaluate in this way the neutrino flux from the supernova remnant RX J1713.7-3946, whose very high-energy gamma-ray spectrum (assumed to be of hadronic origin) is not a power law distribution according to H.E.S.S. observations. The corresponding muon signal in neutrino telescopes is found to be about 5 events per square kilometer per year in an ideal detector.
We carried out numerical experiments on the evaluation of the possibilities of obtaining the information about brightness distributions for the components of eclipsing variables from the data of high-precision photometry expected for planned satellites COROT and Kepler. We examined a simple model of the eclipsing binary with the spherical components on circular orbits and the linear law of the limb darkening. The solutions of light curves have been obtained as by fitting of the nonlinear model, into the number of parameters of which included the limb darkening coefficients, so also by the solution of the ill-posed inverse problem of restoration of brightness distributions across the disks of stars without rigid model constraints on the form of these functions. The obtained estimations show that if the observational accuracy amounts to 0.0001 then the limb darkening coefficients can be found with the relative error approximately 0.01 . The brightness distributions across the disks of components can be restored also nearly with the same accuracy.
The limited angular resolution of gamma-ray telescopes prevents a direct identification of the majority of sources detected so far. This is particularly true for the low latitude, probably galactic, ones only 10 % of which has been identified. Most counterparts of the identified low-latitude gamma-ray sources are Isolated Neutron Stars (INS), both radio-loud and radio-quiet (Geminga-like) objects, which are characterised by an extremely high value of the X-ray-to-optical flux ratio f_X/f_opt. Therefore, the systematic X-ray and optical coverage of low-latitude unidentified gamma-ray sources aiming at high f_X/f_opt sources seems one of the most promising ways to spot INS candidate counterparts. Since low latitude sources are heavily affected by the interstellar absorption at both X-ray and optical wavelengths, we have focussed on two middle-latitude, probably galactic, GRO/EGRET sources: 3EG J0616-3310 and 3EG J1249-8330. These two sources, which could belong to a local galactic population, have been selected owing to their relatively good positional accuracy, spectral shape and lack of candidate extragalactic radio counterparts. Here we report on X-ray observations of the two gamma-ray error boxes performed with XMM-Newton and on their optical follow-up carried on with the Wide Field Imager at the ESO/MPG 2.2m telescope. Less than half of the ~300 sources detected by the X-ray coverage have no optical counterparts. Among those, we have selected few interesting sources with f_X/f_opt > 100, which we consider promising INS candidates.
AIMS. We study and discuss the time-dependent X-ray emission predicted by
hydrodynamic modeling of the interaction of a SNR shock wave with an
interstellar gas cloud. The scope includes: 1) to study the correspondence
between modeled and X-ray emitting structures, 2) to explore two different
physical regimes in which either thermal conduction or radiative cooling plays
a dominant role, and 3) to investigate the effects of the physical processes at
work on the emission of the shocked cloud in the two different regimes.
METHODS. We use a detailed hydrodynamic model, including thermal conduction
and radiation, and explore two cases characterized by different Mach numbers of
the primary shock: M = 30 in which the cloud dynamics is dominated by radiative
cooling and M = 50 dominated by thermal conduction. From the simulations, we
synthesize the expected X-ray emission, using available spectral codes.
RESULTS. The morphology of the X-ray emitting structures is significantly
different from that of the flow structures originating from the shock-cloud
interaction. The hydrodynamic instabilities are never clearly visible in the
X-ray band. Shocked clouds are preferentially visible during the early phases
of their evolution. Thermal conduction and radiative cooling lead to two
different phases of the shocked cloud: a cold cooling dominated core emitting
at low energies and a hot thermally conducting corona emitting in the X-ray
band. The thermal conduction makes the X-ray image of the cloud smaller, more
diffuse, and shorter-lived than that observed when thermal conduction is
neglected.
In this work we study the physical and kinematical properties of the emission line region of Seyfert 1.5 galaxy Mrk 817 using three sets of observations, among which are high-resolution spectra obtained with the Isaac Newton Telescope on Canary Islands. We find that in Mrk 817 the Narrow (NEL) and Broad Emission Lines (BEL) are very complex, indicating that structure of both the Narrow (NLR) and Broad Line Region (BLR) is complex and consists of at least two sub-regions with different kinematical properties. We find that the BEL can be fitted with the two-component model, where the core of the line is coming from a spherical region with isotropic velocity distribution, and wings might be affected by a low inclined accretion disc (or disc-like emitting region). Also, we discuss the physical properties of the BLR. Moreover, we find that an outflow is present in the NLR, that may be driven by an approaching jet.
We apply the linear filter for the weak-lensing signal of dark-matter halos developed in Maturi et al. (2005) to the cosmic-shear data extracted from the Garching-Bonn-Deep-Survey (GaBoDS). We wish to search for dark-matter halos through weak-lensing signatures which are significantly above the random and systematic noise level caused by intervening large-scale structures. We employ a linear matched filter which maximises the signal-to-noise ratio by minimising the number of spurious detections caused by the superposition of large-scale structures (LSS). This is achieved by suppressing those spatial frequencies dominated by the LSS contamination. We confirm the improved stability and reliability of the detections achieved with our new filter compared to the commonly-used aperture mass (Schneider, 1996; Schneider et al., 1998) and to the aperture mass based on the shear profile expected for NFW haloes (see e.g. Schirmer et al., 2004; Hennawi & Spergel, 2005). Schirmer et al.~(2006) achieved results comparable to our filter, but probably only because of the low average redshift of the background sources in GaBoDS, which keeps the LSS contamination low. For deeper data, the difference will be more important, as shown by Maturi et al. (2005). We detect fourteen halos on about eighteen square degrees selected from the survey. Five are known clusters, two are associated with over-densities of galaxies visible in the GaBoDS image, and seven have no known optical or X-ray counterparts.
Measurements of CMB anisotropy and, more recently, polarization have played a very important role allowing precise determination of various parameters of the `standard' cosmological model. The expectation of the paradigm of inflation and the generic prediction of the simplest realization of inflationary scenario in the early universe have also been established -- `acausally' correlated initial perturbations in a flat, statistically isotropic universe, adiabatic nature of primordial density perturbations. Direct evidence for gravitational instability mechanism for structure formation from primordial perturbations has been established. In the next decade, future experiments promise to strengthen these deductions and uncover the remaining crucial signature of inflation -- the primordial gravitational wave background.
We evaluate the result of the recent pioneering numerical simulations in Spitkovsky~2006 on the spindown of an oblique relativistic magnetic dipole rotator. Our discussion is based on our experience from two idealized cases, that of an aligned dipole rotator, and that of an oblique split-monopole rotator. We conclude that the issue of electromagnetic pulsar spindown may not have been resolved yet.
Including loop corrections, black-body radiation in noncommutative space is anisotropic. A direct implication of possible space noncommutativity on the Cosmic Microwave Background map is argued.
The TeV-emitting BL Lac object Mkn 421 was observed with very long baseline interferometry (VLBI) at three closely-spaced epochs one-month apart in March-April 1998. The source was also monitored at very-high gamma-ray energies (TeV measurements) during the same period in an attempt to search for correlations between TeV variability and the evolution of the radio morphology on parsec scales. While the VLBI maps show no temporal changes in the Mkn 421 VLBI jet, there is strong evidence of complex variability in both the total and polarized fluxes of the VLBI core of Mkn 421 and in its spectrum over the two-month span of our data. The high-energy measurements indicate that the overall TeV activity of the source was rising during this period, with a gamma-ray flare detected just three days prior to our second VLBI observing run. Although no firm correlation can be established, our data suggest that the two phenomena (TeV activity and VLBI core variability) are connected, with the VLBI core at 22 GHz being the self-absorbed radio counterpart of synchrotron self-Compton (SSC) emission at high energies. Based on the size of the VLBI core, we could derive an upper limit of 0.1 pc (3 x 10**17 cm) for the projected size of the SSC zone. This determination is the first model-free estimate of the size of the gamma-ray emitting region in a blazar.
Adaptive optics (AO) allows one to derive the point spread function (PSF) simultaneously to the science image, which is a major advantage in post-processing tasks such as astrometry/photometry or deconvolution. Based on the algorithm of \citet{veran97}, PSF reconstruction has been developed for four different AO systems so far: PUEO, ALFA, Lick-AO and Altair. A similar effort is undertaken for NAOS/VLT in a collaboration between the group PHASE (Onera and Observatoire de Paris/LESIA) and ESO. In this paper, we first introduce two new algorithms that prevent the use of the so-called "$U\_{ij}$ functions" to: (1) avoid the storage of a large amount of data (for both new algorithms), (2) shorten the PSF reconstruction computation time (for one of the two) and (3) provide an estimation of the PSF variability (for the other one). We then identify and explain issues in the exploitation of real-time Shack-Hartmann (SH) data for PSF reconstruction, emphasising the large impact of thresholding in the accuracy of the phase residual estimation. Finally, we present the data provided by the NAOS real-time computer (RTC) to reconstruct PSF ({\em (1)} the data presently available, {\em (2)} two NAOS software modifications that would provide new data to increase the accuracy of the PSF reconstruction and {\em (3)} the tests of these modifications) and the PSF reconstruction algorithms we are developing for NAOS on that basis.
We have analyzed 5.5 years of timing observations of 7 'slowly' rotating radio pulsars, made with the Westerbork Synthesis Radio Telescope. We present improved timing solutions and 30, mostly small, new glitches. Particularly interesting are our results on PSR J1814-1744, which is one of the pulsars with similar rotation parameters and magnetic field strength to the Anomalous X-ray Pulsars (AXPs). Although the high-B radio pulsars do not show X-ray emission, and no radio emission is detected for AXPs, the roughly similar glitch parameters provide us with another tool to compare these classes of neutron stars. Furthermore, we were able to detect glitches one to two orders of magnitude smaller than before, for example in our well-sampled observations of PSR B0355+54. We double the total number of known glitches in PSR B1737-30, and improve statistics on glitch sizes for this pulsar individually and pulsars in general. We detect no significant variations in dispersion measure for PSRs B1951+32 and B2224+65, two pulsars located in high-density surroundings. We discuss the effect of small glitches on timing noise, and show it is possible to resolve timing-noise looking structures in the residuals of PSR B1951+32 by using a set of small glitches.
We present the results of a detailed analysis of 452 ground-based high-resolution high S/N spectroscopic measurements spread over 4.5 years for beta Canis Majoris with the aim to determine the pulsational characteristics of this star, and to use them to derive seismic constraints on the stellar parameters. We determine pulsation frequencies in the SiIII 4553 Angstrom line with Fourier methods. We identify the m-value of the modes by taking into account the photometric identifications of the degrees l. To this end we use the moment method together with the amplitude and phase variations across the line profile. The frequencies of the identified modes are used for a seismic interpretation of the structure of the star. We confirm the presence of the three pulsation frequencies already detected in previous photometric datasets: f_1 = 3.9793 c/d (46.057 microHz), f_2 = 3.9995 c/d (46.291 microHz) and f_3 = 4.1832 c/d (48.417 microHz). For the two modes with the highest amplitudes we unambiguously identify (l_1,m_1) = (2,2) and (l_2,m_2) = (0,0). We cannot conclude anything for the third mode identification, except that m_3 > 0. We also deduce an equatorial rotational velocity of 31 +/- 5 Km/s for the star. We show that the mode f_1 must be close to an avoided crossing. Constraints on the mass (13.5 +/- 0.5 Msun), age (12.4 +/- 0.7 Myr) and core overshoot (0.20 +/- 0.05 H_P) of beta CMa are obtained from seismic modelling using f_1 and f_2.
Recent data, including the three--year WMAP data, the full 2dF galaxy power spectrum and the first--year data of the Supernova Legacy Survey, are used to constrain model parameters in quintessence cosmologies. In particular, we discuss the inverse power--law (RP) and SUGRA potentials and compare parameter constraints with those for LCDM. Both potentials fit current observations with a goodness of fit comparable or better than LCDM. The constraints on the energy scale Lambda_DE appearing in both potential expressions are however different. For RP, only energy scales around the cosmological constant limit are allowed, making the allowed models quite similar to LCDM. For SUGRA, Lambda_DE values approximately up to Electroweak energy scale are still allowed, while other parameter intervals are slightly but significantly displaced. In particular a value of the primeval spectral index n_s = 1 is still allowed at the 95% c.l., and this can have an impact on constraints on possible inflationary potentials.
Compact groups are associations of a few galaxies in which the environment plays an important role in galaxy evolution. The low group velocity dispersion favors tidal interactions and mergers, which may bring stars from galaxies to the diffuse intragroup light. Numerical simulations of galaxy clusters in hierarchical cosmologies show that the amount of the diffuse light increases with the dynamical evolution of the cluster. We search for diffuse light in the galaxy group HCG 44 in order to determine its luminosity and luminosity fraction. Combining with literature data, we aim to constrain the dynamical status of Hickson compact groups. We use Intra Group planetary nebulae (IGPNe) as tracers of diffuse light. These are detected by the so-called on band-off band technique. We found 12 emission line objects in HCG 44, none of them associated with the galaxies of the group. 6/12 emission line objects are consistent with being IGPNe in HCG 44, but are also consistent with being Ly$\alpha$ background galaxies. Thus we derive an upper limit to the diffuse light fraction in HCG 44 of 4.7%. We find a correlation between the fraction of elliptical galaxies and the amount of diffuse light in Hickson compact groups. Those with large fraction of diffuse light are those with large fractions in number and luminosity of E/S0 galaxies. We propose an evolutionary sequence for Hickson compact groups in which the amount of diffuse light increases with the dynamical evolution of the group.
We present the results of a detailed NLTE abundance study of nine beta Cephei stars, all of them being prime targets for theoretical modelling: gamma Peg, delta Cet, nu Eri, beta CMa, xi1 CMa, V836 Cen, V2052 Oph, beta Cep and DD (12) Lac. The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S and Fe. Our abundance analysis is based on a large number of time-resolved, high-resolution optical spectra covering in most cases the entire oscillation cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four stars, three of which have severe constraints on their equatorial rotational velocity, \Omega R, from seismic or line-profile variation studies: beta Cep (\Omega R~26 km/s), V2052 Oph (\Omega R~56 km/s), delta Cet (\Omega R < 28 km/s) and xi1 CMa (\Omega R sin i < 10 km/s). The existence of core-processed material at the surface of such largely unevolved, slowly-rotating objects is not predicted by current evolutionary models including rotation. We draw attention to the fact that three stars in this subsample have a detected magnetic field and briefly discuss recent theoretical work pointing to the occurrence of diffusion effects in beta Cephei stars possibly capable of altering the nitrogen surface abundance. On the other hand, the abundances of all the other chemical elements considered are, within the errors, indistinguishable from the values found for OB dwarfs in the solar neighbourhood. Despite the mild nitrogen excess observed in some objects, we thus find no evidence for a significantly higher photospheric metal content in the studied beta Cephei stars compared to non-pulsating B-type stars of similar characteristics.
We present Spitzer Space Telescope images of the isolated dwarf galaxy UGC 10445. The galaxy is detected at all photometric bands (3.6-160um) as well as in the Multiband Imaging Photometer for Spitzer (MIPS) spectral energy distribution mode (55-95um). We derive a star formation rate of 0.25 M_sun/yr based on H-alpha and infrared flux densities. There is over 10^6 solar masses of cold dust (T~18K) in the galaxy, represented by 160um emission, that extends to a larger radius than the ultraviolet (UV), optical and near-infrared light. Such extended emission has been seen previously only in dwarf galaxies in cluster environments. We suggest the source of heating for this dust is UV light originating in star forming complexes. To produce the large quantity of dust requires a higher rate of star formation in the past than is observed currently.
We describe briefly the properties of the recently completed Southern African Large Telescope (SALT), along with its first light imager SALTICAM. Using this instrument, we present 4.3 hr of high speed unfiltered photometric observations of the eclipsing polar SDSSJ015543.40+002807.2 with time resolution as short as 112 ms, the highest quality observations of this kind of any polar to date. The system was observed during its high luminosity state. Two accreting poles are clearly seen in the eclipse light curve. The binary system parameters have been constrained: the white dwarf mass is at the low end of the range expected for cataclysmic variables. Correlations between the positions of the accretion regions on or near the surface of the white dwarf and the binary system parameters were established. The sizes of the accretion regions and their relative movement from eclipse to eclipse were estimated: they are typically 4-7 deg depending on the mass of the white dwarf. The potential of these observations will only fully be realised when low state data of the same kind are obtained and the contact phases of the eclipse of the white dwarf are measured.
We present a detection of [CI] line emission in the lensed quasar APM 08279+5255 at z=3.91 using the IRAM Plateau de Bure interferometer. The [CI] line velocity and width are similar to the values of previously detected high-J CO and HCN lines in this source, suggesting that the emission from all of these species arises from the same region. The apparent luminosity of the [CI] line is L'(CI) = (3.1 +/- 0.4)x10^10 K km/s pc^2, which implies a neutral carbon mass, M(CI) = (4.4+/-0.6)/m x10^7 M_sun, where m is the lensing magnification factor. The [CI] line luminosity is consistent with the large molecular gas mass inferred from the nuclear CO line luminosity ~10^11 /m M_sun. We also present an upper limit on the H2O line luminosity in APM 08279+5255 of, L'(H2O) < 1.8x10^10 K km/s pc^2 (3-sigma).
An unsolved issue in the standard core accretion model for gaseous planet formation is how kilometre-sized planetesimals form from, initially, micron-sized dust grains. Solid growth beyond metre sizes can be difficult both because the sticking efficiency becomes very small, and because these particles should rapidly migrate into the central star. We consider here how metre-sized particles evolve in self-gravitating accretion discs using simulations in which the gravitational influence of the solid particles is also included. Metre-sized particles become strongly concentrated in the spiral structures present in the disc and, if the solid to gas density ratio is sufficiently high, can fragment due to their own self-gravity to form planetesimals directly. This result suggests that planetesimal formation may occur very early in the star formation process while discs are still massive enough to be self-gravitating. The dependence of this process on the surface density of the solids is also consistent with the observation that extrasolar planets are preferentially found around high metallicity stars.
We report the first results from an imaging program with the ACS camera on HST designed to measure the structural characteristics of a wide range of globular clusters in NGC 5128, the nearest giant elliptical galaxy. From 12 ACS/WFC fields, we have measured a total of 62 previously known globular clusters and have discovered 69 new high-probability cluster candidates not found in any previous work. We present magnitudes and color indices for all of these, along with rough measurements of their effective diameters and ellipticities. The luminosity distribution of this nearly-uncontaminated sample of clusters matches well with the normal GCLF for giant elliptical galaxies, and the cluster scale size and ellipticity distributions are similar to those in the Milky Way system. The indication from this survey is that many hundreds of individual clusters remain to be found with carefully designed search techniques in the future. A very rough estimate of the total cluster population from our data suggests N_GC = 1500 in NGC 5128, over all magnitudes and within a projected radius R = 25' from the galaxy center.
We discuss the relationship between rest-frame color and optical luminosity for X-ray sources in the range 0.6<z<1.4 selected from the Chandra survey of the Extended Groth Strip (EGS). These objects are almost exclusively active galactic nuclei (AGN). While there are a few luminous QSOs, most are relatively weak or obscured AGN whose optical colors should be dominated by host galaxy light. The vast majority of AGN hosts at z~1 are luminous and red, with very few objects fainter than M_{B}=-20.5 or bluer than U-B=0.6. This places the AGN in a distinct region of color-magnitude space, on the ``red sequence'' or at the top of the ``blue cloud'', with many in between these two modes in galaxy color. A key stage in the evolution of massive galaxies is when star formation is quenched, resulting in a migration from the blue cloud to the red sequence. Our results are consistent with scenarios in which AGN either cause or maintain this quenching. The large numbers of red sequence AGN imply that strong, ongoing star formation is not a necessary ingredient for AGN activity, as black hole accretion appears often to persist after star formation has been terminated.
We describe AEGIS20 - a radio survey of the Extended Groth Strip (EGS) conducted with the Very Large Array (VLA) at 1.4GHz. The resulting catalog contains 1,123 emitters and is sensitive to ultraluminous starbursts to z<=1.1, well matched to the redshift range of the DEEP2 spectroscopic survey in this region. We use stacking techniques to explore the uJy-level emission from a variety of galaxy populations selected via conventional criteria - Lyman-break galaxies (LBGs), distant red galaxies (DRGs), UV-selected galaxies and extremely red objects (EROs) - determining their properties as a function of color, magnitude and redshift and their extinction-free contributions to the history of star formation. We confirm the familiar pattern that the star-formation-rate (SFR) density, SFRD, rises by at least ~10x from z=0-1, although we note highly discrepant UV- and radio-based SFR estimates. Our radio-based SFRs become more difficult to interpret at z>1 where correcting for contamination by radio-loud active galactic nuclei (AGN) comes at the price of rejecting luminous starbursts. Whilst stacking radio images is a useful technique, accurate radio-based SFRs for z>>1 galaxies require precise redshifts and extraordinarily high-fidelity radio data to identify and remove accretion-related emission.
Using data from the DEEP2 Galaxy Redshift Survey and HST/ACS imaging in the Extended Groth Strip, we select nearly 100 interacting galaxy systems including kinematic close pairs and morphologically-identified merging galaxies. Spitzer MIPS 24 micron fluxes of these systems reflect the current dusty star formation activity, and at fixed stellar mass (M_{*}) the median infrared luminosity (L_{IR}) among merging galaxies and close pairs of blue galaxies is twice (1.9 +/- 0.4) that of control pairs drawn from isolated blue galaxies. Enhancement declines with galaxy separation, being strongest in close pairs and mergers and weaker in wide pairs compared to the control sample. At z ~ 0.9, 7.1 +/- 4.3 % of massive interacting galaxies (M_{*} > 2*10^{10} M_{solar}) are found to be ULIRGs, compared to 2.6 +/- 0.7 % in the control sample. The large spread of IR luminosity to stellar mass ratio among interacting galaxies suggests that this enhancement may depend on the merger stage as well as other as yet unidentified factors (e.g., galaxy structure, mass ratio, orbital characteristics, presence of AGN or bar). The contribution of interacting systems to the total IR luminosity density is moderate (<= 36 %).
We analyse $u-r$ colour distributions for several samples of galaxies in groups drawn from the Fourth Data Release of the Sloan Digital Sky Survey. For all luminosity ranges and environments considered the colour distributions are well described by the sum of two Gaussian functions. We find that the fraction of galaxies in the red sequence is an increasing function of group virial mass. We also study the evolution of the galaxy colour distributions at low redshift, $z\le0.18$ in the field and in groups for galaxies brighter than $M_r-5\log(h)=-20$, finding significant evidence of recent evolution in the population of galaxies in groups. The fraction of red galaxies monotonically increases with decreasing redshift, this effect implies a much stronger evolution of galaxies in groups than in the field.
We explore the environment of z~1 AGN using a sample of 53 spectroscopically identified X-ray sources in the All-wavelength Extended Groth strip International Survey. We quantify the local density in the vicinity of an X-ray source by measuring the projected surface density of spectroscopically identified optical galaxies within a radius defined by the 3rd nearest neighbour. Our main result is that X-ray selected AGN at z~1 avoid underdense regions at the 99.89% confidence level. Moreover, although we find that the overall population shares the same (rich) environment with optical galaxies of similar U-B and M_B, there is also tentative evidence (96%) that AGN with blue colors (U-B<1) reside in denser environments compared to optical galaxies. We argue that the results above are a consequence of the whereabouts of massive galaxies, capable of hosting supermassive black holes at their centers, with available cold gas reservoirs, the fuel for AGN activity. At z~1 an increasing fraction of such systems are found in dense regions.
We use the three-year WMAP observations to determine the normalization of the matter power spectrum in inflationary cosmologies. In this context, the quantity of interest is not the normalization marginalized over all parameters, but rather the normalization as a function of the inflationary parameters n and r with marginalization over the remaining cosmological parameters. We compute this normalization and provide an accurate fitting function. The statistical uncertainty in the normalization is 3 percent, roughly half that achieved by COBE. We use the k-l relation for the standard cosmological model to identify the pivot scale for the WMAP normalization. We also quote the inflationary energy scale corresponding to the WMAP normalization.
This letter reports rich X-ray jet structures found in the Chandra observation of PKS 1055+201. In addition to an X-ray jet coincident with the radio jet we detect a region of extended X-ray emission surrounding the jet as far from the core as the radio hotspot to the North, and a similar extended X-ray region along the presumed path of the unseen counterjet to the Southern radio lobe. Both X-ray regions show a similar curvature to the west, relative to the quasar. We interpret this as the first example where we separately detect the X-ray emission from a narrow jet and extended, residual jet plasma over the entire length of a powerful FRII jet.
We present new, ab initio calculations of the electronic structure of one-dimensional infinite chains and three-dimensional condensed matter in strong magnetic fields ranging from B=10^12 G to 2x10^15 G, appropriate for observed magnetic neutron stars. At these field strengths, the magnetic forces on the electrons dominate over the Coulomb forces, and to a good approximation the electrons are confined to the ground Landau level. Our calculations are based on the density functional theory, and use a local magnetic exchange-correlation function appropriate in the strong field regime. The band structures of electrons in different Landau orbitals are computed self-consistently. Numerical results of the ground-state energies and electron work functions are given for one-dimensional chains of H, He, C, and Fe. Fitting formulae for the B-dependence of the energies are also provided. For all the field strengths considered in this paper, hydrogen, helium, and carbon chains are found to be bound relative to individual atoms (although for B less than a few x 10^12 G, the relative binding between C and C_infinity is small). Iron chains are significantly bound for B>10^14 G and are weakly bound if at all at B<10^13 G. We also study the cohesive property of three-dimensional condensed matter of H, He, C, and Fe at zero pressure, constructed from interacting chains in a body-centered tetragonal lattice. Such three-dimensional condensed matter is found to be bound relative to individual atoms, with the cohesive energy increasing rapidly with increasing B.
From examination of only 4 deg^2 of sky in the NOAO Deep Wide-Field Survey (NDWFS) region, we have identified the first radio-loud quasar at a redshift z>6. The object, FIRST J1427385+331241, was discovered by matching the FLAMEX IR survey to FIRST survey radio sources with NDWFS counterparts. One candidate z>6 quasar was found, and spectroscopy with the Keck II telescope confirmed its identification, yielding a redshift z=6.12. The object is a Broad Absorption Line (BAL) quasar with an optical luminosity of M_B ~ -26.9 and a radio-to-optical flux ratio ~ 60. Two MgII absorptions systems are present at redshifts of z=2.18 and z=2.20. We briefly discuss the implications of this discovery for the high-redshift quasar population.
Submilliarcsecond astrometry and imaging of the black hole Sgr A* at the Galactic Center may become possible in the near future at infrared and submillimetre wavelengths. This resolution is sufficient to observe the silhouette the supermassive black hole in the Galactic center casts upon background emission. However, more exciting is the prospect of observing ``hot spots'' in the accretion flow. Here we discuss how such measurements may be used to test not only the consistency of General Relativity, but also the validity of the Kerr metric in particular.
We present deep Hubble Space Telescope Advanced Camera for Surveys / High Resolution Channel U, narrow-V, and I images of nine "ultracompact" blue dwarf galaxies (UCBDs) selected from the Sloan Digital Sky Survey. We define UCBDs as local (z < 0.01) star-forming galaxies having angular diameters < 6" and physical sizes < 1 kpc. They are also among the most metal-poor galaxies known, and are found to reside within voids. Both the HST images and the objects' optical spectra reveal that they are composites of young (~1 Myr) populations that dominate their light, and older (~10 Gyr) populations that dominate their stellar masses, which we estimate to be ~10^7 - 10^8 Msol. An intermediate-age population is also indicated in most cases. The objects are not as dynamically disturbed as the prototype UCBD, POX 186, but the structure of several of them suggests that their current starbursts have been triggered by the collisions/mergers of smaller clumps of stars. In one case, HS 0822+3542, the ACS/HRC images resolve the object into two small (~100 pc) components which appear to have recently collided, supporting this interpretation. In six of the objects much of their star formation is concentrated in Young Massive Star clusters. The evidence that the galaxies consist mainly of ~10 Gyr old stars establishes that they are not protogalaxies; their low metallicities are more likely to be the result of the escape of supernova ejecta, as opposed to youth. These results are consistent with recent galaxy formation simulations which predict that cosmic re-ionization at z ~ 6 significantly limited the subsequent star formation of dwarf galaxies in voids due to the photo-evaporation of baryons from their cold dark matter halos (Abridged).
It is now generally agreed that multidimensional, multigroup, radiation hydrodynamics is an indispensable element of any realistic model of stellar-core collapse, core-collapse supernovae, and protoneutron star instabilities. We have developed a new, two-dimensional, multigroup algorithm that can model neutrino-radiation-hydrodynamic flows in core-collapse supernovae. Our algorithm uses an approach that is similar to the ZEUS family of algorithms, originally developed by Stone and Norman. However, we extend that previous work in three significant ways: First, we incorporate multispecies, multigroup, radiation hydrodynamics in a flux-limited-diffusion approximation. Our approach is capable of modeling pair-coupled neutrino-radiation hydrodynamics, and includes effects of Pauli blocking in the collision integrals. Blocking gives rise to nonlinearities in the discretized radiation-transport equations, which we evolve implicitly in time. We employ parallelized Newton-Krylov methods to obtain a solution of these nonlinear, implicit equations. Our second major extension to the ZEUS algorithm is inclusion of an electron conservation equation, which describes evolution of electron-number density in the hydrodynamic flow. This permits following the effects of deleptonization in a stellar core. In our third extension, we have modified the hydrodynamics algorithm to accommodate realistic, complex equations of state, including those having non-convex behavior. In this paper, >... <abstract continues>
We discuss non-self-gravitating hydrodynamic disks in the thin disk limit. These systems are stable according to the Rayleigh criterion, and yet there is some evidence that the dissipative and transport processes in these disks are hydrodynamic in nature at least some of the time. We draw on recent work on the hydrodynamics of laboratory shear flows. Such flows are often experimentally unstable even in the absence of a linear instability. The transition to turbulence in these systems, as well as the large linear transient amplification of initial disturbances, may depend upon the non-self-adjoint nature of the differential operator that describes the dynamics of perturbations to the background state. We find that small initial perturbations can produce large growth in accretion disks in the shearing sheet approximation with shearing box boundary conditions, despite the absence of any linear instability. Furthermore, the differential operator that propagates initial conditions forward in time is asymptotically close (as a function of Reynolds number) to possessing growing eigenmodes. The similarity to the dynamics of laboratory shear flows is suggestive that accretion disks might be hydrodynamically unstable despite the lack of any known instability mechanism.
The large majority of extragalactic star cluster studies performed to date essentially use multi-colour photometry, combined with theoretical stellar synthesis models, to derive ages, masses, extinction estimates, and metallicities. M31 offers a unique laboratory for studies of globular cluster (GC) systems. In this paper, we obtain new age estimates for 91 M31 globular clusters, based on improved photometric data, updated theoretical stellar synthesis models and sophisticated new fitting methods. In particular, we used photometric measurements from the Two Micron All Sky Survey (2MASS), which, in combination with optical photometry, can partially break the well-known age-metallicity degeneracy operating at ages in excess of a few Gyr. We show robustly that previous age determinations based on photometric data were affected significantly by this age-metallicity degeneracy. Except for one cluster, the ages of our other sample GCs are all older than 1 Gyr. Their age distribution shows populations of young and intermediate-age GCs, peaking at $\sim3$ and 8 Gyr respectively, as well as the "usual" complement of well-known old GCs, i.e., GCs of similar age as the majority of the Galactic GCs. Our results also show that although there is significant scatter in metallicity at any age, there is a noticeable lack of young metal-poor and old metal-rich GCs, which might be indicative of an underlying age-metallicity relationship among the M31 GC population.
We derive analytical formulae for the Minkowski Functions of the cosmic microwave background (CMB) and large-scale structure (LSS) from primordial non-Gaussianity. These formulae enable us to estimate a non-linear coupling parameter, f_NL, directly from the CMB and LSS data without relying on numerical simulations of non-Gaussian primordial fluctuations. One can use these formulae to estimate statistical errors on f_NL from Gaussian realizations, which are much faster to generate than non-Gaussian ones, fully taking into account the cosmic/sampling variance, beam smearing, survey mask, etc. We show that the CMB data from the Wilkinson Microwave Anisotropy Probe should be sensitive to |f_NL|\simeq 40 at the 68% confidence level. The Planck data should be sensitive to |f_NL|\simeq 20. As for the LSS data, the late-time non-Gaussianity arising from gravitational instability and galaxy biasing makes it more challenging to detect primordial non-Gaussianity at low redshifts. The late-time effects obscure the primordial signals at small spatial scales. High-redshift galaxy surveys at z>2 covering \sim 10Gpc^3 volume would be required for the LSS data to detect |f_NL|\simeq 100. Minkowski Functionals are nicely complementary to the bispectrum because the Minkowski Functionals are defined in real space and the bispectrum is defined in Fourier space. This property makes the Minksowski Functionals a useful tool in the presence of real-world issues such as anisotropic noise, foreground and survey masks. Our formalism can be extended to scale-dependent f_NL easily.
It has been recognized that magnetic reconnection process is of great importance in high-energy astrophysics. We develop a new two-dimensional relativistic resistive magnetohydrodynamic (R$^2$MHD) code, and carry out numerical simulations of magnetic reconnection. We find that outflow velocity reaches Alfv\'{e}n velocity in the inflow region, and that higher Alfv\'{e}n velocity provides higher reconnection rate. We also find Lorentz contraction plays an important role in enhancement of reconnection rate.
The recent progress made in galactic gamma-ray astronomy using the H.E.S.S. instrument provides for the first time a population of galactic TeV gamma-ray, and hence potential neutrino sources, for which the neutrino flux can be estimated. Using the energy spectra and source-morphologies measured by H.E.S.S., together with new parameterisations of pion production and decay in hadronic interactions, we estimate the signal and background rates expected for these sources in a first generation water Cherenkov detector (ANTARES) and a next generation neutrino telescope in the Mediterranean Sea, KM3NeT, with an instrumented volume of 1 km^3. We find that the brightest gamma-ray sources produce neutrino rates above 1 TeV comparable to the background from atmospheric neutrinos. The expected event rates of the brightest sources in the ANTARES detector make a detection unlikely. However, for a 1 km^3 KM3NeT detector, event rates of the order of one neutrino per year from these sources are expected and the detection of individual sources seems possible. Although, generally these estimates should be taken as flux upper limits, we discuss the conditions and type of gamma-ray sources for which the neutrino flux predictions can be considered as robust.
Abundances of 18 elements are determined for the common proper-motion pair, HD134439 and HD134440, which shows high [Mn/Fe] and low [\alpha/Fe] ratios as compared to normal halo stars. Moreover, puzzling abundances are indicated from elements whose origins are normally considered to be from the same nucleosynthesis history. Particularly, we have found that [Mg/Fe] and [Si/Fe] are lower than [Ca/Fe] and [Ti/Fe] by 0.1-0.3 dex. When elemental abundances are interpreted in term of their condensation temperatures (Tc), obvious trends of [X/Fe] vs. Tc for alpha elements and probably iron-peak elements as well are shown. The hypothesis that these stars have formed from a dusty environment in dSph galaxy provides a solution to the puzzling abundance pattern.
We study a possibility to use the octopole moment of gravitationally lensed images as a direct measure of the third-order weak gravitational lensing effect, or the gravitational flexion. It turns out that there is a natural relation between flexion and certain combinations of octopole moments which we call the Higher Order Lensing Image's Characteristics (HOLICs). This will allow one to measure directly flexion from observable octopole moments of background images. We show based on simulated observations how the use of HOLICs can improve the accuracy and resolution of a reconstructed mass map, in which we assume Gaussian uncertainties in the shape measurements estimated using deep $i'$-band data of blank fields observed with Suprime-Cam on the Subaru telescope.
We present photoionization calculations for the spatially-extended absorbers observed towards the extended emission line spectrum of two high-redshift radio galaxies: 0943-242 (z=2.922) and 0200+015 (z=2.230), with the aim of reproducing the absorber column ratio, N(CIV)/N(HI). We explore the effects of using different UV continua in the photoionization calculations. A comparison is drawn between the absorber in 0200+015 and the two absorbers in the lensed Lynx Arc Nebula at z=3.36, which present similar N(CIV)/N(HI) ratios. We find that hot stars from a powerful starburst, or a metagalactic background radiation (MBR) in which stars dominate over quasars, are equally successful in producing the observed N(CIV)/N(HI), assuming subsolar absorber metallicities. These softer SEDs eliminate the factor 1000 difference in metallicity between the two absorbers encountered in earlier work assuming a powerlaw SED. The detected level of continuum flux in 0943-242 is consistent with stellar ionization. If the MBR is responsible for the ionization of the radio galaxy absorbing shells, their radii (if spherical) would be large (> 100 kpc) and their mass would be huge (>1E12 M_Sun), implying that a feedback event within the radiogalaxy has expelled more baryonic material than left within it. If, as we believe more likely, stellar sources within the radiogalaxy are responsible for the absorber's ionization, smaller radii of ~25 kpc and much smaller masses (~1E8-1E10 M_Sun) are inferred. This radius is consistent with the observed transition in radio source size between smaller sources where strong HI absorption is almost ubiquitous, and the larger sources where it is mostly lacking. Finally, we outline additional absorption line diagnostics which could further constrain the properties of the haloes and their ionization sources.
We discuss recent evidence that currently accepted mass-loss rates may need to be revised downwards, as a consequence of previously neglected ``clumping'' of the wind. New results on the radial stratification of the corresponding clumping factors are summarized. We investigate the influence of clumping on the ionization equilibrium of phosphorus, which is of major relevance when deriving constraints on the clumping factors from an analysis of the FUV PV resonance lines.
VLTi Spectro-Imager (VSI) is a proposition for a second generation VLTI instrument which is aimed at providing the ESO community with the capability of performing image synthesis at milli-arcsecond angular resolution. VSI provides the VLTI with an instrument able to combine 4 telescopes in a baseline version and optionally up to 6 telescopes in the near-infrared spectral domain with moderate to high spectral resolution. The instrument contains its own fringe tracker in order to relax the constraints onto the VLTI infrastructure. VSI will do imaging at the milli-arcsecond scale with spectral resolution of: a) the close environments of young stars probing the initial conditions for planet formation; b) the surfaces of stars; c) the environment of evolved stars, stellar remnants and stellar winds, and d) the central region of active galactic nuclei and supermassive black holes. The science cases allowed us to specify the astrophysical requirements of the instrument and to define the necessary studies of the science group for phase A.
The present paper addresses some of the problems in the buildup of element
stratification in stellar magnetic atmospheres due to microscopic diffusion, in
particular the redistribution of momentum among the various ionisation stages
of a given element and the calculation of diffusion velocities in the presence
of inclined magnetic fields.
We have considerably modified and extended our CARAT code to provide
radiative accelerations, not only from bound-bound but also from bound-free
transitions. In addition, our code now computes ionisation and recombination
rates, both radiative and collisional. These rates are used in calculating the
redistribution of momentum among the various ionisation stages of the chemical
elements. A careful comparison shows that the two different theoretical
approaches to redistribution that are presently available lead to widely
discrepant results for some chemical elements, especially in the magnetic case.
In the absence of a fully satisfactory theory of redistribution, we propose to
use the geometrical mean of the radiative accelerations from both methods.
Diffusion velocities have been calculated for 28 chemical elements in a T_eff
= 12000K, log g = 4.00 stellar magnetic atmosphere with solar abundances.
Velocities and resulting element fluxes in magnetic fields are discussed; rates
of abundance changes are analysed for systematic trends with field strength and
field direction. Special consideration is given to the Si case and our results
are confronted in detail with well-known results derived more than two decades
ago.
We propose a new approach to measure differential radial velocities, mainly for single-lined spectroscopic binaries. The proposed procedure - TIRAVEL (Template Independent RAdial VELocities) - does not rely on a prior theoretical or observed template, but instead looks for a set of relative Doppler shifts that simultaneously optimizes the alignment of all the observed spectra. We suggest a simple measure to quantify this overall alignment and use its maximum to measure the relative radial velocities. As a demonstration, we apply TIRAVEL to the observed spectra of three known spectroscopic binaries, and show that in two cases TIRAVEL performs as good as the commonly used approach, while in one case TIRAVEL yielded a better orbital solution.
The birefringent effects of photon-pseudoscalar boson (Goldstone) particle mixing in intergalactic magnetic field are calculated for cosmological objects. We use the recent results of PVLAS collaboration that reported recently the observation of a rotation of the polarization plane of light propagating through a transverse static magnetic field. Such results which were interpretated as arising due to conversion of photon into pseudoscalar with coupling strength $g_{a\gamma}\sim 4\times 10^{-6} GeV^{-1}$ allows us to estimate the intergalactic magnetic field magnitude as $\sim 10^{-16} G$ based on Hatsemekers et al. observations of extreme-scale alignments of quasar polarization vectors. We have analyzed some additional results of astronomical observations that could be explained by axion interpretation of the PVLAS data: a sharp steepening of the QSO continuum short ward of $\simeq 1100$\AA, observed circular polarization of AGNs and QSOs, discrepancy between observed intrinsic polarization of stars in the Local Bubble and stellar spectral classification. The observed polarization of stars in the Local Bubble can't be explained by interstellar origin.
We have investigated the abundance anomalies of lithium for stars with planets in the temperature range of 5600--5900 K reported by Israelian and coworkers, as compared to 20 normal stars at the same temperature and metallicity ranges. Our result indicates a higher probability of lithium depletion for stars with planets in the main--sequence stage. It seems that stellar photospheric abundances of lithium in stars with planets may be somewhat affected by the presence of planets. Two possible mechanisms are considered to account for the lower Li abundances of stars with planets. One is related to the rotation-induced mixing due to the conservation of angular momentum by the protoplanetary disk, and the other is a shear instability triggered by planet migration. These results provide new information on stellar evolution and the lithium evolution of the Galaxy.
We consider the production of positrons in microquasars, i.e. X-ray binary systems that exhibit jets frequently, but not continuously. We estimate the production rate of positrons in microquasars, both by simple energy considerations and in the framework of various proposed models. We then evaluate the collective emissivity of the annihilation radiation produced by Galactic microquasars and we find that it might constitute a substantial contribution to the annihilation flux measured by INTEGRAL/SPI. We also discuss the possible spatial distribution of Galactic microquasars, on the basis of the (scarce) available data and the resulting morphology of the flux received on Earth. Finally, we consider nearby 'misaligned' microquasars, with jets occasionally hitting the atmosphere of the companion star; these would represent interesting point sources, for which we determine the annihilation flux and the corresponding light curve, as well as the line's spectral profile. We discuss the possibility of detection of such point sources by future instruments.
In this paper I summarize the science motivations, as well as a few mid-infrared spectroscopic methods used to identify the principal mechanisms of energy production in dust enshrouded galactic nuclei. The development of the various techniques is briefly discussed. Emphasis is given to the use of the data which are becoming available with the infrared spectrograph (IRS) on Spitzer, as well as the results which have been obtained by IRS over the past two years.
We study X-ray emission from young stars by analyzing deep XMM-Newton observations of two regions of the Upper Scorpius association, having an age of 5 Myr. Based on near infrared and optical photometry we identify 22 Upper Scorpius photometric members among the 224 detected X-ray sources. We derive coronal properties of Upper Scorpius stars by performing X-ray spectral and timing analysis. The study of four strong and isolated stellar flares allows us to derive the length of the flaring loops. Among the 22 Upper Scorpius stars, 13 are identified as Upper Scorpius photometric members for the first time. The sample includes 7 weak-line T Tauri stars and 1 classical T Tauri star, while the nature of the remaining sources is unknown. Except for the intermediate mass star HD 142578, all the detected USco sources are low mass stars of spectral type ranging from G to late M. The X-ray emission spectrum of the most intense Upper Scorpius sources indicates metal depleted plasma with temperature of ~10 MK, resembling the typical coronal emission of active main sequence stars. At least 59% of the detected members of the association have variable X-ray emission, and the flaring coronal structures appear shorter than or comparable to the stellar radii already at the Upper Scorpius age. We also find indication of increasing plasma metallicity (up to a factor 20) during strong flares. We identify a new galaxy cluster among the 224 X-ray source detected: the X-ray spectrum of its intra cluster medium indicates a redshift of 0.41+/-0.02.
The results of 27 hours of time series photometry of SDSS 121209.31+013627.7 are presented. The binary period established from spectroscopy is confirmed and refined to 0.061412 d (88.43 minutes). The photometric variations are dominated by a brightening of about 16 mmag, lasting a little less than half a binary cycle. The amplitude is approximately the same in V, R and white light. A secondary small brightness increase during each cycle may also be present. We speculate that SDSS 121209.31+013627.7 may be a polar in a low state.
The aim of the present analysis is to improve the knowledge of the statistical properties of the Galactic diffuse synchrotron emission, which constrains sensitive CMB anisotropy measurements. We have analysed the new DRAO 1.4 GHz polarization survey together with the Stockert 1.4 GHz total intensity survey and derived the angular power spectra (APSs) of the total intensity, the polarized emission, and their cross-correlation for the entire surveys and for three low-intensity regions. The APSs of the diffuse synchrotron emission are modelled by power laws. For the $E$ and $B$ modes, a slope of $\alpha \sim [-3.0,-2.5]$ for the multipole range $\sim [30,300]$ is found. By the extrapolation of these results to 70 GHz, we can estimate the Galactic synchrotron contamination of CMB anisotropies, and we find results that are compatible with the ones coming from WMAP 3-yr data. In the low-intensity regions, the cosmological primordial B~mode peak at $\ell \sim 100$ should be clearly observable for a tensor-to-scalar ratio $T/S \gsim 0.5$ and a synchrotron temperature spectral index $\beta \sim -3$. Its detection is also possible for $T/S \gsim 0.005$ and $\beta \sim -3$, in case a separation of the foreground from the CMB signal could be achieved with an accuracy of $\sim 5-10%$. For the TE mode, a mask excluding $|b_{gal}| \le 5^{\circ}$ (for $\beta\sim -3.0$) or $|b_{gal}| \le 20^{\circ}$ (for $\beta\sim -2.8$) from the surveys is sufficient to render the foreground contamination negligible, thus confirming the ability of WMAP to have a clear view of the temperature-polarization correlation peak and antipeak series.
We use the Simon, Verde, & Jimenez (2005) determination of the redshift dependence of the Hubble parameter to constrain cosmological parameters in three dark energy cosmological models. We consider the standard $\Lambda$CDM model, the XCDM parameterization of the dark energy equation of state, and a slowly rolling dark energy scalar field with an inverse power-law potential. The constraints are restrictive, consistent with those derived from Type Ia supernova redshift-magnitude data, and complement those from galaxy cluster gas mass fraction versus redshift data.
The next generation of weak gravitational lensing surveys is capable of generating good measurements of cosmological parameters, provided that, amongst other requirements, adequate redshift information is available for the background galaxies that are measured. It is frequently assumed that photometric redshift techniques provide the means to achieve this. Here we compare Bayesian and frequentist approaches to photometric redshift estimation, particularly at faint magnitudes. We identify and discuss the biases that are inherent in the various methods, and describe an optimum Bayesian method for extracting redshift distributions from photometric data.
We present the first results of the MIRIAD (MIPS [Multiband Imaging Photometer for Spitzer] Infra-Red Imaging of AGB [asymptotic giant branch] Dustshells) project using the Spitzer Space Telescope. The primary aim of the project is to probe the material distribution in the extended circumstellar envelopes (CSE) of evolved stars and recover the fossil record of their mass loss history. Hence, we must map the whole of the CSEs plus the surrounding sky for background subtraction, while avoiding the central star that is brighter than the detector saturation limit. With our unique mapping strategy, we have achieved better than one MJy/sr sensitivity in three hours of integration and successfully detected a faint (< 5 MJy/sr), extended (~400 arcsec) far-infrared nebula around the AGB star R Hya. Based on the parabolic structure of the nebula, the direction of the space motion of the star with respect to the nebula shape, and the presence of extended H alpha emission co-spatial to the nebula, we suggest that the detected far-IR nebula is due to a bow shock at the interface of the interstellar medium and the AGB wind of this moving star. This is the first detection of the stellar-wind bow-shock interaction for an AGB star and exemplifies the potential of Spitzer as a tool to examine the detailed structure of extended far-IR nebulae around bright central sources. \
WMAP's first year non-detection of the Sunyaev-Zel'dovich effect (SZE) among a sample of 31 rich Abell clusters is interpreted in terms of conventional physics. It is already widely believed that the central soft X-ray excess found in some clusters cannot be of thermal origin, due to problems with rapid gas cooling, but may arise from inverse-Compton scattering between intracluster relativistic electrons and the cosmic microwave background. We demonstrate that higher energy electrons drawn from the same power-law spectrum as that responsible for the soft excess may also synchrotron radiate in the intracluster magnetic field of strength B $\lesssim$ 1~$\mu$G to produce cluster microwave emissions in the WMAP passbands that account for the missing SZE flux. There is in fact no significant discrepancy between the model parameters that account for either phenomena. This strengthens the likelihood of prevailing non-thermal activities in at least some clusters. The key point is that by merely invoking an intracluster population of cosmic rays having the same properties as those of our Galaxy, the microwave synchrotron flux is already within a factor of five from the expected SZE flux. The electrons may originate from AGN jet injection, then distributed cluster-wide with accompanying {\it in situ} Fermi acceleration, by Alfven waves.