Continuum observations at 350um are presented of seven nearby elliptical galaxies, for which CO-gas disks have recently been resolved with interferometry mapping. These SHARCII mapping results provide the first clearly resolved far-infrared(FIR) to submillimeter(submm) continuum emission from cold dust (with temperatures 32K > T > 22K) of any elliptical galaxy at a distance >40Mpc. The measured FIR excess shows that the most likely and dominant heating source of this dust is not dilute stellar radiation or cooling flows, but rather star-formation, that could have been triggered by an accretion or merger event and fueled by dust-rich material that has settled in a dense region co-spatial with the central CO-gas disks. The dust is detected even in two cluster ellipticals that are deficient in HI, showing that, unlike the HI, cold dust and CO in ellipticals can survive in the presence of hot X-ray gas, even in galaxy clusters. No dust cooler than 20K, either distributed outside the CO disks, or co-spatial with and heated by the entire dilute stellar optical galaxy (or very extended HI), is currently evident.
Simple one-zone homogeneous synchrotron self-Compton models have severe difficulties in explaining the TeV emission observed in the radiogalaxy M87. Also the site of the TeV emission region is uncertain: it could be the unresolved jet close to the nucleus, analogously to what proposed for blazars, or an active knot, called HST-1, tens of parsec away. We explore the possibility that the TeV emission of M87 is produced in the misaligned subpc scale jet. We base our modelling on a structured jet, with a fast spine surrounded by a slower layer. In this context the main site responsible for the emission of the TeV radiation is the layer, while the (debeamed) spine accounts for the emission from the radio to the GeV band: therefore we expect a more complex correlation with the TeV component than that expected in one-zone scenarios, in which both components are produced by the same region. Observed from small angles, the spine would dominate the emission, with an overall Spectral Energy Distribution close to those of BL Lac objects with a synchrotron peak located at low energy (LBLs).
Aims: We present J, H, K interferometry with a spectral resolution of 35 for
the Mira variable S Orionis. We aim at measuring the diameter variation as a
function of wavelength that is expected due to molecular layers lying above the
continuum-forming photosphere.
Methods: Visibility data of S Ori were obtained at phase 0.78 with the
VLTI/AMBER instrument using the fringe tracker FINITO at 29 spectral channels
between 1.29 and 2.32 mu. Apparent uniform disk (UD) diameters were computed
for each spectral channel. In addition, the visibility data were directly
compared to predictions by recent self-excited dynamic model atmospheres.
Results: S Ori shows significant variations in the visibility values as a
function of spectral channel that can only be described by a clear variation in
the apparent angular size with wavelength. The closure phase values are close
to zero at all spectral channels, indicating the absence of asymmetric
intensity features. The apparent UD angular diameter is smallest at about 1.3
and 1.7 mu and increases by a factor of ~1.4 around 2.0 mu. The minimum UD
angular diameter is 8.1 pm 0.5 mas, corresponding to ~420 R_sun. The S Ori
visibility data and the apparent UD variations can be explained reasonably well
by a dynamic atmosphere model that includes molecular layers.
Conclusions: The measured visibility and UD diameter variations with
wavelength resemble and generally confirm the predictions by recent dynamic
model atmospheres. [abridged]
We consider the effect of mass segregation on the observable integrated properties of star clusters. The measurable properties depend on a combination of the dynamical age of the cluster and the physical age of the stars in the cluster. To investigate all possible combinations of these two quantities we propose an analytical model for the mass function of segregated star clusters that agrees with the results of N-body simulations, in which any combination can be specified. For a realistic degree of mass segregation and a fixed density profile we find with increasing age an increase in the measured core radii and a central surface brightness that decreases in all filters more rapidly than what is expected from stellar evolution alone. Within a Gyr the measured core radius increases by a factor of two and the central surface density in all filters of a segregated cluster will be overestimated by a similar factor when not taking into account mass segregation in the conversion from light to mass. We find that the $V-I$ colour of mass segregated clusters decreases with radius by about 0.1-0.2 mag, which could be observable. From recent observations of partially resolved extra-galactic clusters a decreasing half-light radius with increasing wavelength was observed, which was attributed to mass segregation. These observations can not be reproduced by our models. We find that the differences between measured radii in different filters are always smaller than 5%.
In this contribution, I present a simplified overview of the evolution of the disk galaxy population since z=1, and a brief discussion of a few open questions. Galaxy evolution surveys have found that the disk galaxy population forms stars intensely at intermediate redshift. In particular, they dominate the cosmic star formation rate at z<1 -- the factor of ten drop in cosmic average comoving star formation rate in the last 8 Gyr is driven primarily by disk physics, not by a decreasing major merger rate. Despite this intense star formation, there has been little change in the stellar mass density in disk galaxies since z=1; large numbers of disk galaxies are being transformed into non-star-forming spheroid-dominated galaxies by galaxy interactions, AGN feedback, environmental effects, and other physical processes. Finally, despite this intense activity, the scaling relations of disk galaxies appear to evolve little. In particular, as individual galaxies grow in mass through the formation of stars, they appear to grow in radius (on average, the population grows inside-out), and they appear to evolve towards somewhat higher rotation velocity (i.e., mass is added at both small and large radii during this inside-out growth).
A simple explicit example of a Roberts-type dynamo is given in which the alpha-effect of mean-field electrodynamics exists in spite of point-wise vanishing kinetic helicity of the fluid flow. In this way it is shown that alpha-effect dynamos do not necessarily require non-zero kinetic helicity. A mean-field theory of Roberts-type dynamos is established within the framework of the second-order correlation approximation. In addition numerical solutions of the original dynamo equations are given, that are independent of any approximation of that kind. Both theory and numerical results demonstrate the possibility of dynamo action in the absence of kinetic helicity.
Context: Over the last decade, several groups of young (mainly low-mass) stars have been discovered in the solar neighbourhood (closer than ~100 pc), thanks to cross-correlation between X-ray, optical spectroscopy and kinematic data. These young local associations -- including an important fraction whose members are Hipparcos stars -- offer insights into the star formation process in low-density environments, shed light on the substellar domain, and could have played an important role in the recent history of the local interstellar medium. Aims: To study the kinematic evolution of young local associations and their relation to other young stellar groups and structures in the local interstellar medium, thus casting new light on recent star formation processes in the solar neighbourhood. Methods: We compiled the data published in the literature for young local associations. Using a realistic Galactic potential we integrated the orbits for these associations and the Sco-Cen complex back in time. Results: Combining these data with the spatial structure of the Local Bubble and the spiral structure of the Galaxy, we propose a recent history of star formation in the solar neighbourhood. We suggest that both the Sco-Cen complex and young local associations originated as a result of the impact of the inner spiral arm shock wave against a giant molecular cloud. The core of the giant molecular cloud formed the Sco-Cen complex, and some small cloudlets in a halo around the giant molecular cloud formed young local associations several million years later. We also propose a supernova in young local associations a few million years ago as the most likely candidate to have reheated the Local Bubble to its present temperature.
We present an approach to describe the nonlinear matter power spectrum for a mixed dark matter (cold dark matter plus neutrinos having total mass of ~0.1eV) model based on cosmological perturbation theory. The suppression of the power spectrum amplitude caused by massive neutrinos is enhanced in the weakly nonlinear regime where standard linear theory ceases to be accurate. Due to this enhanced effect and the gain in the applicable range of the model prediction, the nonlinear model may enable a precision of sigma(m_tot)~0.09eV in constraining the total neutrino mass for the planned galaxy redshift survey, a factor 2.5 improvement compared to the linear regime. The refined model prescription thus offers a vital opportunity to determine the neutrino masses.
We used the Submillimeter Array to map the angular distribution of the H30$\alpha$ recombination line (231.9 GHz) in the circumstellar region of the peculiar star MWC349A. The resolution was $1\farcs2$, but because of high signal-to-noise ratio we measured the positions of all maser components to accuracies better than $0\farcs01$, at a velocity resolution of $1 kms$. The two strongest maser components (called high velocity components) at velocities near -14 and $32 kms$ are separated by $0\farcs048 \pm 0\farcs001$ (60 AU) along a position angle of $102 \pm 1\arcdeg$. The distribution of maser emission at velocities between and beyond these two strongest components were also provided. The continuum emission lies at the center of the maser distribution to within 10 mas. The masers appear to trace a nearly edge-on rotating disk structure, reminiscent of the water masers in Keplerian rotation in the nuclear accretion disk of the galaxy NGC4258. However, the maser components in MWC349A do not follow a simple Keplerian kinematic prescription with $v \sim r^{-1/2}$, but have a larger power law index. We explore the possibility that the high velocity masers trace spiral density or shock waves. We also emphasize caution in the interpretation of relative centroid maser positions where the maser is not clearly resolved in position or velocity, and we present simulations that illustrate the range of applicability of the centroiding method.
In 1996, a major radio flux-density outburst occured in the broad-line radio galaxy 3C111. It was followed by a particularly bright plasma ejection associated with a superluminal jet component, which has shaped the parsec-scale structure of 3C111 for almost a decade. Here, we present results from 18 epochs of Very Long Baseline Array (VLBA) observations conducted since 1995 as part of the VLBA 2 cm Survey and MOJAVE monitoring programs. This major event allows us to study a variety of processes associated with outbursts of radio-loud AGN in much greater detail than has been possible in other cases: the primary perturbation gives rise to the formation of a leading and a following component, which are interpreted as a forward and a backward-shock. Both components evolve in characteristically different ways and allow us to draw conclusions about the work flow of jet-production events; the expansion, acceleration and recollimation of the ejected jet plasma in an environment with steep pressure and density gradients are revealed; trailing components are formed in the wake of the primary perturbation possibly as a result of coupling to Kelvin-Helmholtz instability pinching modes from the interaction of the jet with the external medium. The interaction of the jet with its ambient medium is further described by the linear-polarization signature of jet components traveling along the jet and passing a region of steep pressure/density gradients.
The origin of both the diffuse high-latitude MeV gamma-ray emission and the 511 keV line flux from the Galactic bulge are uncertain. Previous studies have invoked dark matter physics to independently explain these observations, though as yet none has been able to explain both of these emissions within the well-motivated framework of Weakly-Interacting Massive Particles (WIMPs). Here we use an unstable WIMP dark matter model to show that it is in fact possible to simultaneously reconcile both of these observations, and in the process show a remarkable coincidence: decaying dark matter with MeV mass splittings can explain both observations if positrons and photons are produced with similar branching fractions. We illustrate this idea with an unstable branon, which is a standard WIMP dark matter candidate appearing in brane world models with large extra dimensions. We show that because branons decay via three-body final states, they are additionally unconstrained by searches for Galactic MeV gamma-ray lines. As a result, such unstable long-lifetime dark matter particles provide novel and distinct signatures that can be tested by future observations of MeV gamma-rays.
The size distribution of the mini-filaments in voids has been derived from the Millennium Run halo catalogs at redshifts z=0,0.5,1 and 2. It is assumed that the primordial tidal field originated anisotropy in the distribution of the void halos which resulted in the presence of the mini-filaments in the void regions and that the mini-filaments in the voids are pristine without being modified severely in the evolutionary stages. Applying the filament-finding-algorithm based on the minimal spanning technique to the Millennium voids, we identify the mini-filaments connecting the void halos and measure their sizes at each redshift. Then, we calculate the comoving number density of the void mini-filaments as a function of their sizes, S, in the logarithmic interval and determine an analytic fitting function for it. It is found that the size distribution of the void mini-filaments in the logarithmic interval has an almost universal shape, insensitive to the redshift: In the short-size section it is well approximated as a power-law, S, while in the long-size section it decreases exponentially as exp[-S^2/(2S^{2}_0)], with S_0 ~11 Mpc/h . We expect that the universal size distribution of the void filaments may provide a useful cosmological probe without resorting to the rms density fluctuation.
Recent astronomical observations indicate that the Universe is in the phase of accelerated expansion. There are many cosmological models which explain this phenomenon, but should we prefer those models over the simplest one -- $\Lambda$CDM model? According to the Occam's razor principle if all models describe the observations equally well we should prefer the simplest one. We consider the model comparison methods which involve such rules: the Akaike information criterion (AIC), Bayesian information criterion (BIC) and Bayesian evidence to compare the $\Lambda$CDM model with its generalisation where the interaction between dark matter and dark energy is allowed. The analyses based on the AIC and Bayesian evidence indicate that there is only a weak evidence in favour of the $\Lambda$CDM model over its generalisation, while those based on BIC quantity indicate the strong evidence in favour the simpler model. We also calculate some quantity which measure the effective number of model parameters that the given data can constrain. This value is used to compare the concordance LCDM model with its generalization basing on the extended interpretation of continuity condition-interacting $\Lambda$CDM cosmology. We conclude that data set are not enough informative to constrain all parameters allows to vary in the models.
We cross-correlate large scale structure (LSS) observations from a number of surveys with CMB anisotropies from WMAP to investigate the Integrated Sachs-Wolfe (ISW) effect as a function of redshift, covering z~0.1-2.5. Our main goal is to go beyond reporting detections towards developing a reliable likelihood analysis that allows one to determine cosmological constraints from ISW observations. With this in mind we spend a considerable amount of effort in determining the redshift-dependent bias and redshift distribution b(z)*dN/dz of these samples by matching with spectroscopic observations where available, and analyzing auto-power spectra and cross-power spectra between the samples. The data sets we use are 2-Micron All Sky Survey (2MASS) samples, Sloan Digital Sky Survey (SDSS) photometric Luminous Red Galaxies, SDSS photometric quasars and NRAO VLA Sky Survey (NVSS) radio sources. We make a joint analysis of all samples constructing a full covariance matrix, which we subsequently use for cosmological parameter fitting. We report a 3.7 sigma detection of ISW combining all the datasets. We combine the ISW likelihood function with weak lensing of CMB and CMB power spectrum to constrain the equation of state of dark energy and the curvature of the Universe. While ISW does not significantly improve the constraints in the simplest 6-parameter flat Lambda CDM model, it improves constraints on 7-parameter models with curvature by a factor of 2.5 (relative to WMAP alone) to Omega_K=-0.006^{+0.017}_{-0.028}, and with dark energy equation of state by 15% to w=-1.01^{+0.37}_{-0.40}. (Abridged.)
We investigate the correlation of gravitational lensing of the cosmic microwave background (CMB) with several tracers of large-scale structure, including luminous red galaxies (LRGs), quasars, and radio sources. The lensing field is reconstructed based on the CMB maps from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite; the LRGs and quasars are observed by the Sloan Digital Sky Survey (SDSS); and the radio sources are observed in the NRAO VLA Sky Survey (NVSS). Combining all three large-scale structure samples, we find evidence for a positive cross-correlation at the $2.5\sigma$ level ($1.8\sigma$ for the SDSS samples and $2.1\sigma$ for NVSS); the cross-correlation amplitude is $1.06\pm 0.42$ times that expected for the WMAP cosmological parameters. Our analysis extends other recent analyses in that we carefully determine bias weighted redshift distribution of the sources, which is needed for a meaningful cosmological interpretation of the detected signal. We investigate contamination of the signal by Galactic emission, extragalactic radio and infrared sources, thermal and kinetic Sunyaev-Zel'dovich effects, and the Rees-Sciama effect, and find all of them to be negligible.
Observations from the Space Telescope Imaging Spectrograph define the flux of the DBQ4 star LDS749B from 0.12-1.0 \mu m with an uncertainty of ~1% relative to the three pure hydrogen WD primary HST standards. With T_{eff}=13575 K, log g=8.05, and a trace of carbon at <1x10^{-6} of solar, a He model atmosphere fits the measured STIS fluxes within the observational noise, except in a few spectral lines with uncertain physics of the line broadening theory. Upper limit to the atmospheric hydrogen and oxygen fractions by number are 1x10^{-7} and 7x10^{-10}, respectively. The excellent agreement of the model flux distribution with the observations lends confidence to the accuracy of the modeled IR fluxes beyond the limits of the STIS spectrophotometry. The estimated precision of ~1% in the predicted IR absolute fluxes at 30 \mu m should be better than the model predictions for Vega and should be comparable to the absolute accuracy of the three primary WD models.
Results: The two Wolf-Rayet stars WR20a (WN6ha+WN6ha) and WR20b (WN6ha) were analyzed in detail. They are both very luminous and display very hard spectra, but WR20b does not seem to vary. On the contrary, WR20a, a known eclipsing, colliding-wind binary, brightens in the X-ray domain during the eclipses, i.e. when the collision is seen face-on. This can be explained by the properties of the wind-wind collision zone, whose high density leads to a large absorbing column (2 10^24 cm^-2).All twelve O-type stars previously classified spectroscopically, two eclipsing binaries previously identified and nine newly identified O-type star candidates are detected in the high energy domain; ten of them could be analyzed spectroscopically. Four are overluminous, but the others present typical L_X/L_BOL ratios, suggesting that several O-type objects are actually binaries. Variability at the ~2sigma level was detected for a majority of the sources, of unknown origin for the putatively single objects. Faint, soft, diffuse emission pervades the entire field-of-view but no clear structure can be identified, even at the position of a blister proposed to be at the origin of the TeV source HESS J1023-575. Finally, the X-ray properties of PMS objects were also investigated, in particular the brightest flaring ones. They provided an additional argument in favor of a large distance (~8kpc) for the cluster.
We conducted a search for brown dwarfs (BDs) and very low mass (VLM) stars in the 625 Myr-old Hyades cluster in order to derive the cluster's mass function across the stellar-substellar boundary. We performed a deep (I=23, z=22.5) photometric survey over 16 sq.deg. around the cluster center, followed up with K-band photometry to measure the proper motion of candidate members, and optical and near-IR spectroscopy of probable BD and VLM members. We report the discovery of the first 2 brown dwarfs in the Hyades cluster. The 2 objects have a spectral type early-T and their optical and near-IR photometry as well as their proper motion are consistent with them being cluster members. According to models, their mass is 50 Jupiter masses at an age of 625 Myr. We also report the discovery of 3 new very low mass stellar members of the cluster, and confirm the membership of 16 others. We combine these results with a list of previously known cluster members to build the present-day mass function (PDMF) of the Hyades cluster from 50 Jupiter masses to 3Mo. We find the Hyades PDMF to be strongly deficient in very low mass objects and brown dwarfs compared to the IMF of younger open clusters such as the Pleiades. We interpret this deficiency as the result of dynamical evolution over the past few 100 Myr, i.e., the preferential evaporation of low mass cluster members due to weak gravitational encounters. We thus estimate that the Hyades cluster currently hosts about 10-15 brown dwarfs, while its initial substellar population may have amounted up to 150-200 members.
We provide a new interpretation of ultraviolet transition region emission line widths observed by the SUMER instrument on the Solar and Heliospheric Observatory (SOHO). This investigation is prompted by observations of the chromosphere at unprecedented spatial and temporal resolution from the Solar Optical Telescope (SOT) on Hinode revealing that all chromospheric structures above the limb display significant transverse (Alfvenic) perturbations. We demonstrate that the magnitude, network sensitivity and apparent center-to-limb isotropy of the measured line widths (formed below 250,000K) can be explained by an observationally constrained forward-model in which the line width is caused by the line-of-sight superposition of longitudinal and Alfvenic motions on the small-scale (spicular) structures that dominate the chromosphere and low transition region.
context: The spectrum of IRAS 16594-4656 shows shock excited H_2 emission and collisionally excited emission lines such as[O I],[C I],and [Fe II]. aim: The goal is to determine the location of the H_2 and [Fe II] shock emission, to determine the shock velocities,and constrain the physical properties in the shock. methods: High resolution spectra of the H_2 1-0 S(1),H_2 2-1 S(1), [Fe II], and Pa$\beta$ emission lines were obtained with the near infrared spectrograph Phoenix on Gemini South. results: The position-velocity diagrams of H_2 1-0 S(1), H_2 2-1 S(1), and [Fe II] are presented. The H_2 and [Fe II] emission is spatially extended. The collisionally excited [O I] and [C I] optical emission lines have a similar double peaked profile compared to the extracted H_2 profile and appear to be produced in the same shock. They all indicate an expansion velocity of ~8 km/s and the presence of a neutral, very high density region with $n_{\rm e}$ about 3 x 10^6 to 5 x10^7 cm$^{-3}$. The [Fe II] emission however is single peaked. It has a gaussian FWHM of 30 km/s and a total width of 62 km/s at 1% of the peak. The Pa$\beta$ profile is even wider with a gaussian FWHM of 48 km/s and a total width of 75 km/s at 1% of the peak. conclusions: The H$_2$ emission is excited in a slow 5 to 20 km/s shock into dense material at the edge of the lobes, caused by the interaction of the AGB ejecta and the post-AGB wind. The 3D representation of the H_2 data shows a hollow structure with less H_2 emission in the equatorial region. The [Fe II] emission is not present in the lobes, but originates close to the central star in fast shocks in the post-AGB wind or in a disk. The Pa$\beta$ emission also appears to originate close to the star.
Context: Several approaches to estimate frequency, phase and amplitude errors in time series analyses were reported in the literature, but they are either time consuming to compute, grossly overestimating the error, or are based on empirically determined criteria. Aims: A simple, but realistic estimate of the frequency uncertainty in time series analyses. Methods: Synthetic data sets with mono- and multi-periodic harmonic signals and with randomly distributed amplitude, frequency and phase were generated and white noise added. We tried to recover the input parameters with classical Fourier techniques and investigated the error as a function of the relative level of noise, signal and frequency difference. Results: We present simple formulas for the upper limit of the amplitude, frequency and phase uncertainties in time-series analyses. We also demonstrate the possibility to detect frequencies which are separated by less than the classical frequency resolution and that the realistic frequency error is at least 4 times smaller than the classical frequency resolution.
We present the strategies adopted in the relative and absolute calibration of two different data sets: U,B,V,I-band images collected with the Wide Field Imager (WFI) mosaic camera mounted on the 2.2m ESO/MPI Telescope and u,v,b,y Stroemgren images collected with the 1.54m Danish Telescope (ESO, La Silla). In the case of the WFI camera we adopted two methods for the calibration, one for images collected before 2002, with the ESO filters U/38_ESO841 and B/99_ESO842, and a different one for data secured after 2002, with the filters U/50_ESO877 and B/123_ESO878. The positional and color effects turned out to be stronger for images collected with the old filters. The eight WFI chips of these images were corrected one by one, while in the case of images secured with the new filters, we corrected the entire mosaic in a single step. In the case of the Danish data set, we compared point-spread function (PSF) and aperture photometry for each frame, finding a trend in both the X and Y directions of the chip. The corrections resulted in a set of first and second order polynomials to be applied to the instrumental magnitudes of each individual frame as a function of the star position.
An asymptotic treatment of thin accretion disks, introduced by Klu\'zniak & Kita (2000) for a steady-state disk flow, is extended to a time-dependent problem. Transient growth of axisymmetric disturbances is analytically shown to occur on the global disk scale. The implications of this result on the theory of hydrodynamical thin accretion disks, as well as future prospects, are discussed.
We study the visibility of sunspots and its influence on observed values of sunspot region parameters. We use Virtual Observatory tools provided by AstroGrid to analyse a sample of 6862 sunspot regions. By studying the distributions of locations where sunspots were first and last observed on the solar disk, we derive the visibility function of sunspots, the rate of magnetic flux emergence and the ratio between the durations of growth and decay phases of solar active regions. We demonstrate that the visibility of small sunspots has a strong center-to-limb variation, far larger than would be expected from geometrical (projection) effects. This results in a large number of young spots being invisible: 44% of new regions emerging in the West of the Sun go undetected. For sunspot regions that are detected, large differences exist between actual locations and times of flux emergence, and the apparent ones derived from sunspot data. The duration of the growth phase of solar regions has been up to now underestimated.
Neither standard model SEDs nor truncated standard model SEDs fit observed spectra of QU Carinae with acceptable accuracy over the range 900\AA to 3000\AA. Non-standard model SEDs fit the observation set accurately. The non-standard accretion disk models have a hot region extending from the white dwarf to $R=1.36R_{\rm wd}$,a narrow intermediate temperature annulus, and an isothermal remainder to the tidal cutoff boundary. The models include a range of $\dot{M}$ values between $1.0{\times}10^{-7}M_{\odot} {\rm yr}^{-1}$ and $1.0{\times}10^{-6}M_{\odot} {\rm yr}^{-1}$ and limiting values of $M_{\rm wd}$ between $0.6M_{\odot}$ and $1.2M_{\odot}$. A solution with $M_{\rm wd}=1.2M_{\odot}$ is consistent with an empirical mass-period relation. The set of models agree on a limited range of possible isothermal region $T_{\rm eff}$ values between 14,000K and 18,000K. The model-to-model residuals are so similar that it is not possible to choose a best model. The Hipparcos distance, 610 pc, is representative of the model results. The orbital inclination is between $40\arcdeg$ and $60\arcdeg$.
Early universe equations of state including realistic interactions between constituents are built up. Under certain reasonable assumptions, these equations are able to generate an inflationary regime prior to the nucleosynthesis period. The resulting accelerated expansion is intense enough to solve the flatness and horizon problems. In the cases of curvature parameter \kappa equal to 0 or +1, the model is able to avoid the initial singularity and offers a natural explanation for why the universe is in expansion.
Swift has revealed features in GRB early light curves, such as steep decays and X-ray flares, whose properties are consistent with an internal origin though they are far from understood. The steep X-ray decay is often explained using the curvature effect; however a significant number of GRBs display strong spectral evolution during this phase, and a new mechanism must be invoked to explain this. Of particular interest are the longest duration GRBs in which the early emission can be studied in most detail. Here we present data for GRB 070616, in which the prompt emission shows a complex multipeaked structure, leading to one of the longest prompt emission durations ever recorded. We take advantage of extensive coverage of such a long burst by all Swift instruments. Combining data from Swift and Suzaku we study the evolution of the prompt emission spectrum, following the temporal variability of the peak energy and spectral slope.
The distribution of eccentricities e of extra-solar planets with semi-major axes a > 0.2 AU is very uniform, and values for e are relatively large, averaging 0.3 and broadly distributed up to near 1. For a < 0.2 AU, eccentricities are much smaller (most e < 0.2), a characteristic widely attributed to damping by tides after the planets formed and the protoplanetary gas disk dissipated. Most previous estimates of the tidal damping considered the tides raised on the planets, but ignored the tides raised on the stars. Most also assumed specific values for the planets' poorly constrained tidal dissipation parameter Qp. Perhaps most important, in many studies, the strongly coupled evolution between e and a was ignored. We have now integrated the coupled tidal evolution equations for e and a over the estimated age of each planet, and confirmed that the distribution of initial e values of close-in planets matches that of the general population for reasonable Q values, with the best fits for stellar and planetary Q being ~10^5.5 and ~10^6.5, respectively. The accompanying evolution of a values shows most close-in planets had significantly larger a at the start of tidal migration. The earlier gas disk migration did not bring all planets to their current orbits. The current small values of a were only reached gradually due to tides over the lifetimes of the planets. These results may have important implications for planet formation models, atmospheric models of "hot Jupiters", and the success of transit surveys.
Orbifold branes in string theory are investigated, and the general field equations of the branes are found explicitly for type II and heterotic string. It is shown that the effective cosmological constant on the branes can be easily lowered to its current observational value, using large extra dimensions. This is also true for type I string. Thus, brane world of string theory provides a viable and built-in mechanism of solving the long-standing cosmological constant problem. Applying the formulas to cosmology, we obtain the generalized Friedmann equations on the branes.
We solve exactly the classical non-relativistic Landau-Lifshitz equations of motion for a charged particle moving in a Coulomb potential, including radiation damping. The general solution involves the Painleve transcendent of type II. It confirms our physical intuition that a negatively charged classical particle will spiral into the nucleus, supporting the the validity of the Landau-Lifshitz equation.
We show that the internal stationary state of a black hole for massless Dirac fields can be represented by an entangled state of collapsing matter and infalling Hawking radiation. This implies that the Horowitz-Maldacena conjecture for the black hole final state originally proposed for the massless scalar fields is also applicable to fermionic fields as well. For an initially mixed state we find that the measure of mixedness is expected to decrease under evaporation.
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Supermassive black hole binaries (BHBs) produced in galaxy mergers recoil at the time of their coalescence due to the emission of gravitational waves (GWs). We simulate the response of a thin, 2D disk of collisionless particles, initially on circular orbits around a 10^6 M_sun BHB, to kicks that are either parallel or perpendicular to the initial orbital plane. Typical kick velocities (v_k) can exceed the sound speed in a circumbinary gas disk. While the inner disk is strongly bound to the recoiling binary, the outer disk is only weakly bound or unbound. This leads to differential motions in the disturbed disk that increase with radius and can become supersonic at ~700 Schwarzschild radii for v_k ~500 km/s, implying that shocks form beyond this radius. We indeed find that kicks in the disk plane lead to immediate strong density enhancements (within weeks) in a tightly wound spiral caustic, propagating outward at the speed v_k. Concentric density enhancements are also observed for kicks perpendicular to the disk, but are weaker and develop into caustics only after a long delay (>1 year). Unless both BH spins are low or precisely aligned with the orbital angular momentum, a significant fraction (> several %) of kicks are sufficiently large and well aligned with the orbital plane for strong shocks to be produced. The shocks could result in an afterglow whose characteristic photon energy increases with time, from the UV (~10eV) to the soft X-ray (~100eV) range, between one month and one year after the merger. This could help identify EM counterparts to GW sources discovered by LISA.
We investigate a scenario where the recently discovered non-thermal hard X-ray emission from the Ophiuchus cluster originates from inverse Compton scattering of energetic electrons and positrons produced in weakly interacting dark matter pair annihilations. We show that this scenario can account for both the X-ray and the radio emission, provided the average magnetic field is of the order of 0.1 microGauss. We demonstrate that GLAST will conclusively test the dark matter annihilation hypothesis. Depending on the particle dark matter model, GLAST might even detect the monochromatic line produced by dark matter pair annihilation into two photons.
Since 1999, we have been conducting a radial velocity survey of 179 K giants using the CAT at UCO/Lick observatory. At present ~20-100 measurements have been collected per star with a precision of 5 to 8 m/s. Of the stars monitored, 145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43 exhibit significant periodicities. Our aim is to investigate possible mechanism(s) that cause these observed RV variations. We intend to test whether these variations are intrinsic in nature, or possibly induced by companions, or both. In addition, we aim to characterise the parameters of these companions. A relation between log g and the amplitude of the RV variations is investigated for all stars in the sample. Furthermore, the hypothesis that all periodic RV variations are caused by companions is investigated by comparing their inferred orbital statistics with the statistics of companions around main sequence stars. A strong relation is found between the amplitude of the RV variations and log g in K giant stars, as suggested earlier by Hatzes & Cochran (1998). However, most of the stars exhibiting periodic variations are located above this relation. These RV variations can be split in a periodic component which is not correlated with log g and a random residual part which does correlate with log g. Compared to main-sequence stars, K giants frequently exhibit periodic RV variations. Interpreting these RV variations as being caused by companions, the orbital param eters are different from the companions orbiting dwarfs. Intrinsic mechanisms play an important role in producing RV variations in K giants stars, as suggested by their dependence on log g. However, it appears that periodic RV variations are additional to these intrinsic variations, consistent with them being caused by companions.
If inflation is to be considered in an unbiased way, as possibly originating from one of a wide range of underlying theories, then observations need not be simply applied to reconstructing the inflaton potential, V(\phi), or a specific kinetic term, as in DBI inflation, but rather to reconstruct the inflationary action in its entirety. We discuss the constraints that can be placed on a general single field action from measurements of the primordial scalar and tensor fluctuation power spectra and non-Gaussianities. We also present the flow equation formalism for reconstructing a general inflationary Lagrangian, L(X,\phi), with X={1/2}\partial_\mu\phi\partial^\mu\phi, in a general gauge, that reduces to canonical and DBI inflation in the specific gauge \partial L/\partial X = c_s^{-1}.
Chemically peculiar stars define a class of stars that show unusual elemental abundances due to stellar photospheric effects and not due to natal variations. In this paper, we compare the elemental abundance patterns of the ultra metal-poor stars with metallicities [Fe/H] $\sim -5 $ to those of a subclass of chemically peculiar stars. These include post-AGB stars, RV Tauri variable stars, and the Lambda Bootis stars, which range in mass, age, binarity, and evolutionary status, yet can have iron abundance determinations as low as [Fe/H] $\sim -5$. These chemical peculiarities are interpreted as due to the separation of gas and dust beyond the stellar surface, followed by the accretion of dust depleted-gas. Contrary to this, the elemental abundances in the ultra metal-poor stars are thought to represent yields of the most metal-poor supernova and, therefore, observationally constrain the earliest stages of chemical evolution in the Universe. The abundance of the elements in the photospheres of the ultra metal-poor stars appear to be related to the condensation temperature of that element; if so, then their CNO abundances suggest true metallicities of [X/H]~ -2 to -4, rather than their present metallicities of [Fe/H] < -5.
We use Vector Spectromagnetograph (VSM) chromospheric full-disk magnetograms, from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) project, to study the distribution of magnetic field flux concentrations within the polar caps. We find that magnetic flux elements preferentially appear toward lower latitudes within the polar caps away from the poles. This has implications on numerous solar phenomena such as the formation and evolution of fine polar coronal structures (i.e., polar plumes). Our results also have implications for the processes carrying the magnetic flux from low to high latitudes (e.g., meridional circulation).
We study the relationship between different wave phenomena associated with a coronal mass ejection (CME) observed on 05 Mar. 2000. EIT waves were observed in the images recorded by EIT at 195 {\AA}. The white-light LASCO/C2 images show clear deflection and propagation of a kink along with the CME. Spectroscopic observations recorded by the UVCS reveals excessive line broadening in the two O {\sc{vi}} lines (1032 and 1037 {\AA}). Moreover very hot lines such as Si {\sc{xii}} and Mg {\sc{x}} were observed. Interestingly, the EIT wave, the streamer deflection and the intensity modulation along the slit were all propagating North-East. Spatial and temporal correlations show that the streamer deflection and spectral line broadening are highly likely to be due to a CME-driven shock wave and that the EIT wave is the signature of a CME-driven shock wave in the lower corona.
Although it is acknowledged that the host galaxy of GRB is the source of GRB at present, but it is in fact not obtained a reliable confirmation. However, the fact is still unclear because the host is possibly a background galaxy that has no physical affiliation to the GRB. Here, I show a series of evidences, including three methods, to identify the status of hosts. The correlation analysis shows that there is no correlation between the distance of GRBs and the redshift of hosts although there is a significant correlation between the apparent magnitude of hosts and the redshift; the deductive reasoning shows that many wrong conclusions that violate to the basic principle of physics would inevitably be obtained if the redshift indicates the distance; and the variables separation test proves directly that, however, the distance is independent from the redshift and the values of the fluence and the photon flux can be accurately forecasted for the GRB with higher redshift. On the other hand, the three statistical laws of GRBs have been deduced theoretically based on the observed fact; and a precise background galaxy theory can explain all the observed laws of GRBs and provides a new method with the least uncertain factors for determining the deceleration parameter that contains the contribution of the dark matter, and obtain q0 = 0.148.
Asteroid 3200 Phaethon resembles a comet in some ways, including a highly-eccentric orbit (e=0.89) and a strong associated meteor shower (the Geminids). Yet this object has never been observed to exhibit any cometary activity, i.e., gas production. We observed 3200 Phaethon with the Caltech Submillimeter Observatory on two occasions, once while it was near its closest approach to Earth as it neared perihelion, and another while it was further from Earth post-perihelion. Observations of the J=2-1 and J=3-2 rotational transitions of 12CO, typically strong lines in comets and indicative of gas production, yielded no detection. Upper limits on the 12CO production of 1.8e28 molecules/s and 7.6e28 molecules/s for Phaethon were determined on these two occasions.
The 6dF Galaxy Survey provides a very large sample of galaxies with reliable measurements of Lick line indices and velocity dispersions. This sample can be used to explore the correlations between mass and stellar population parameters such as age, metallicity and [alpha/Fe]. Preliminary results from such an analysis are presented here, and show that age and metallicity are significantly anti-correlated for both passive and star-forming galaxies. Passive galaxies have strong correlations between mass and metallicity and between age and alpha-element over-abundance, which combine to produce a downsizing relation between age and mass. For old passive galaxies, the different trends of M/L with mass and luminosity in different passbands result from the differential effect of the mass-metallicity relation on the luminosities in each passband. Future work with this sample will examine the Fundamental Plane of bulge-dominated galaxies and the influence of environment on relations between stellar population parameters and mass.
The 6dF Galaxy Survey (6dFGS) and the 2MASS Redshift Survey (2MRS) provide the most complete maps of the large-scale structures and motions in the nearby universe. These maps have been used to reconstruct the density field in the local volume, and to predict the corresponding velocity field and the dipole of the Local Group motion.
OH absorption against PSR B1718-35 at (l,b) =351.688,+0.671 has been discovered at 1665 and 1667 MHz using the Green Bank Telescope. The absorption appears to arise at the interface of an HII region and a molecular cloud which are likely associated with the high mass star forming region NGC 6334. Beam dilution is found to be the cause of differences in the opacity of the OH against the Galactic background continuum emission and against the pulsar. The OH cloud is approximately 3 by 1.3 pc and is located behind the HII region.
We present results from a pilot HST ACS deep imaging study in broad-band V of five low-redshift QSO host galaxies classified in the literature as ellipticals. The aim of our study is to determine whether these early-type hosts formed at high redshift and have since evolved passively, or whether they have undergone relatively recent mergers that may be related to the triggering of the nuclear activity. We perform two-dimensional modeling of the light distributions to analyze the host galaxies' morphology. We find that, while each host galaxy is reasonably well fitted by a de Vaucouleurs profile, the majority of them (4/5) reveal significant fine structure such as shells and tidal tails. These structures contribute between ~5% and 10% to the total V-band luminosity of each host galaxy within a region of r ~ 3 r_eff and are indicative of merger events that occurred between a few hundred Myr and a Gyr ago. These timescales are comparable to starburst ages in the QSO hosts previously inferred from Keck spectroscopy. Our results thus support a consistent scenario in which most of the QSO host galaxies suffered mergers with accompanying starbursts that likely also triggered the QSO activity in some way, but we are also left with considerable uncertainty on physical mechanisms that might have delayed this triggering for several hundred Myr after the merger.
We discuss a cosmology in which cold dark matter begins to decay into relativistic particles at a recent epoch (z < 1). We show that the large entropy production and associated bulk viscosity from such decays leads to an accelerating cosmology as required by observations. We investigate the effects of decaying cold dark matter in a Lambda = 0, flat, initially matter dominated cosmology. We show that this model satisfies the cosmological constraint from the redshift-distance relation for type Ia supernovae. The age in such models is also consistent with the constraints from the oldest stars and globular clusters. Possible candidates for this late decaying dark matter are suggested along with additional observational tests of this cosmological paradigm.
In this Letter, we propose that a microphysical process takes a vital role in the shocked region in which the prompt emission of GRBs is emitted. The turbulent energy is included in the internal energy transferred by the kinetic energy of the shock. It dissipates through stochastic acceleration for the electrons to supply the early X-ray emission in the phase of shallow decay. We put the constraints on the time evolution of microphysical parameters. The early X-ray fluxes can be obtained by this scenario and these results are consistent with the Swift observation
In this paper, we investigate the structures of galaxies which either have or have had three BHs using $N$-body simulations, and compare them with those of galaxies with binary BHs. We found that the cusp region of a galaxy which have (or had) triple BHs is significantly larger and less dense than that of a galaxy with binary BHs of the same mass. Moreover, the size of the cusp region depends strongly on the evolution history of triple BHs, while in the case of binary BHs, the size of the cusp is determined by the mass of the BHs. In galaxies which have (or had) three BHs, there is a region with significant radial velocity anisotropy, while such a region is not observed in galaxies with binary BH. These differences come from the fact that with triple BHs the energy deposit to the central region of the galaxy can be much larger due to multiple binary-single BH scatterings. Our result suggests that we can discriminate between galaxies which experienced triple BH interactions with those which did not, through the observable signatures such as the cusp size and velocity anisotropy.
Aims. Despite photometry and spectroscopy of its oscillations obtained over
the past 25 years, the pulsation frequency spectrum of the rapidly oscillating
Ap (roAp) star gamma Equ has remained poorly understood. Better time-series
photometry, combined with recent advances to incorporate interior magnetic
field geometry into pulsational models, enable us to perform improved
asteroseismology of this roAp star.
Methods. We obtained 19 days of continuous high-precision photometry of gamma
Equ with the MOST (Microvariability & Oscillations of STars) satellite. The
data were reduced with two different reduction techniques and significant
frequencies were identified. Those frequencies were fitted by interpolating a
grid of pulsation models which include dipole magnetic fields of various polar
strengths.
Results. We identify 7 frequencies in gamma Equ which we associate with 5
high-overtone p-modes and 1st and 2nd harmonics of the dominant p-mode. One of
the modes and both harmonics are new discoveries for this star. Our best model
solution (1.8 M_sun, log T_eff ~ 3.882; polar field strength ~8.1 kG) leads to
unique mode identifications for these frequencies (ell = 0, 1, 2 and 4). This
is the first purely asteroseismic fit to a grid of magnetic models. We measure
amplitude and phase modulation of the primary frequency due to beating with a
closely spaced frequency which had never been resolved. This casts doubts on
theories that such modulation - unrelated to the rotation of the star - is due
to a stochastic excitation mechanism.
Context. On October 24, 2007 the periodic comet 17P/Holmes underwent an astonishing outburst that increased its apparent total brightness from magnitude V\sim17 up to V\sim2.5 in roughly two days. We report on Wendelstein 0.8 m telescope (WST) photometric observations of the early evolution stages of the outburst. Aims. We studied the evolution of the structure morphology, its kinematic, and estimated the ejected dust mass. Methods. We analized 126 images in the BVRI photometric bands spread between 26/10/2007 and 20/11/2007. The bright comet core appeared well separated from that one of a quickly expanding dust cloud in all the data, and the bulk of the latter was contained in the field of view of our instrument. The ejected dust mass was derived on the base of differential photometry on background stars occulted by the moving cloud. Results. The two cores were moving apart from each other at a relative projected constant velocity of (9.87 +/- 0.07) arcsec/day (0.135 +/-0.001 km/sec). In the inner regions of the dust cloud we observed a linear increase in size at a mean constant velocity of (14.6+/-0.3) arcsec/day (0.200+/-0.004 km/sec). Evidence of a radial velocity gradient in the expanding cloud was also found. Our estimate for the expanding coma's mass was of the order of 10^{-2}-1 comet's mass implying a significant disintegration event. Conclusions. We interpreted our observations in the context of an explosive scenario which was more probably originated by some internal instability processes, rather than an impact with an asteroidal body. Due to the peculiar characteristics of this event, further observations and investigations are necessary in order to enlight the nature of the physical processes that determined it.
I present a method to deproject the observed intensity profile of an
axisymmetric bulge with arbitrary flattening to derive the 3D luminosity
density profile and to calculate the contribution of the bulge to the rotation
curve. I show the rotation curves for a family of fiducial bulges with Sersic
surface brightness profiles and with various concentrations and intrinsic axis
ratios. Both parameters have a profound impact on the shape of the rotation
curve. In particular, I show how the peak rotation velocity, as well as the
radius where it is reached, depend on both parameters.
I also discuss the implications of the flattening of a bulge for the
decomposition of a rotation curve and use the case of NGC 5533 to show the
errors that result from neglecting it. For NGC 5533, neglecting the flattening
of the bulge leads to an overestimate of its mass-to-light ratio by
approximately 30% and an underestimate of the contributions from the stellar
disc and dark matter halo in the regions outside the bulge-dominated area.
Fitting whole spectra at intermediate spectral resolution (R = 1000 -- 3000), to derive physical properties of stellar populations, appears as an optimized alternative to methods based on spectrophotometric indices: it uses all the redundant information contained in the signal. This paper addresses the validation of the method and it investigates the quality of the population models together with the reliability of the fitting procedures. We are using two algorithms: STECKMAP, a non-parametric regularized program and NBURSTS a parametric non-linear minimization. We compare three spectral synthesis models for single stellar populations: Pegase-HR, Galaxev (BC03) and Vazdekis/Miles, and we analyse spectra of Galactic clusters whose populations are known from studies of color-magnitude diagrams (CMD) and spectroscopy of individual stars. We find that: (1) The quality of the models critically depends on the stellar library they use. Pegase-HR and Vazdekis/Miles are consistent, while the comparison between Pegase-HR and BC03 shows some systematics reflecting the limitations of the stellar library (STELIB) used to generate the latter models; (2) The two fitting programs are consistent; (3) For globular clusters and M67 spectra, the method restitutes metallicities in agreement with spectroscopy of stars within 0.14 dex; (4) The spectroscopic ages are very sensitive to the presence of a blue horizontal branch (BHB) or of blue stragglers. A BHB morphology results in a young SSP-equivalent age. Fitting a free amount of blue stars in addition to the SSP model to mimic the BHB improves and stabilizes the fit and restores ages in agreement with CMDs studies. This method is potentially able to disentangle age or BHB effects in extragalactic clusters.
We present medium resolution spectropolarimetry and long term photo-polarimetry of two massive post-red supergiants, IRC +10420 and HD 179821. The data provide new information on their circumstellar material as well as their evolution. In IRC +10420, the polarization of the Halpha line is different to that of the continuum, which indicates that the electron-scattering region is not spherically symmetric. The observed long term changes in the polarimetry can be associated with an axi-symmetric structure, along the short axis of the extended reflection nebulosity. Long term photometry reveals that the star increased in temperature until the mid-nineties, after which the photospheric flux in the optical levelled off. As the photometric changes are mostly probed in the red, they do not trace high stellar temperatures sensitively. And so, it is not obvious whether the star has halted its increase in temperature or not. For HD 179821 we find no polarization effects across any absorption or emission lines, but observe very large polarization changes of order 5% over 15 years. Unexpectedly, during the same period, the optical photometry displayed modest variability at the 0.2 magnitude level. Several explanations for this puzzling fact are discussed. Most of which, involving asymmetries in the circumstellar material, seem to fail as there is no evidence for the presence of hot, dusty material close to the star. Alternatively, the variations can be explained by the presence of a non-radially pulsating photosphere. Changes in the photometry hint at an increase in temperature corresponding to a change through two spectral subclasses over the past ten years.
Model of supermassive black holes formation inside the clusters of primordial black holes is developed. Namely, it is supposed, that some mass fraction of the universe ~10^-3 is composed of the compact clusters of primordial (relic) black holes, produced during phase transitions in the early universe. These clusters are the centers of dark matter condensation. We model the formation of protogalaxies with masses about 2*10^8M_sun at the redshift z=15. These induced protogalaxies contain central black holes with mass ~10^5M_sun and look like dwarf spheroidal galaxies with central density spike. The subsequent merging of induced protogalaxies and ordinary dark matter haloes corresponds to the standard hierarchical clustering scenario of large-scale structure formation. The coalescence of primordial black holes results in formation of supermassive black holes in the galactic centers. As a result, the observed correlation between the masses of central black holes and velocity dispersion in the galactic bulges is reproduced.
We present a deep [O III] 4959,5007 image of the northern filamentary jet in the Crab Nebula taken with the 8.2m Subaru telescope. Using this image and an image taken with the KPNO 4m in 1988 (Fesen & Staker 1993), we have computed proper motions for 35 locations in the jet. The results suggest that when compared to the main body of the remnant, the jet experienced less outward acceleration from the central pulsar's rapidly expanding synchrotron nebula. The jet's apparent expansion rate yields an undecelerated explosion date for the Crab Nebula of 1055 plus or minus 24 C.E., a date much closer to the appearance of the historic 1054 C.E. guest star than the 1120 - 1140 C.E. dates estimated in previous studies using filaments located within the remnant's main nebula. Our proper motion measurements suggest the jet likely formed during the 1054 supernova explosion and represents the remnant's highest velocity knots possibly associated with a suspected N-S bipolar outflow from the supernova explosion.
On 10 March 2001 the active region NOAA 9368 produced an unusually impulsive solar flare in close proximity to the solar limb. This flare has previously been studied in great detail, with observations classifying it as a type 1 white-light flare with a very hard spectrum in hard X-rays. The flare was also associated with a type II radio burst and coronal mass ejection. The flare emission characteristics appeared to closely correspond with previous instances of seismic emission from acoustically active flares. Using standard local helioseismic methods, we identified the seismic signatures produced by the flare that, to date, is the least energetic (in soft X-rays) of the flares known to have generated a detectable acoustic transient. Holographic analysis of the flare shows a compact acoustic source strongly correlated with the impulsive hard X-ray, visible continuum, and radio emission. Time-distance diagrams of the seismic waves emanating from the flare region also show faint signatures, mainly in the eastern sector of the active region. The strong spatial coincidence between the seismic source and the impulsive visible continuum emission reinforces the theory that a substantial component of the seismic emission seen is a result of sudden heating of the low photosphere associated with the observed visible continuum emission. Furthermore, the low-altitude magnetic loop structure inferred from potential--field extrapolations in the flaring region suggests that there is a significant inverse correlation between the seismicity of a flare and the height of the magnetic loops that conduct the particle beams from the corona.
We study dust accumulation by photophoresis in optically thin gas disks. Using formulae of the photophoretic force that are applicable for the free molecular regime and for the slip-flow regime, we calculate dust accumulation distances as a function of the particle size. It is found that photophoresis pushes particles (smaller than 10 cm) outward. For a Sun-like star, these particles are transported to 0.1-100 AU, depending on the particle size, and forms an inner disk. Radiation pressure pushes out small particles (< 1 mm) further and forms an extended outer disk. Consequently, an inner hole opens inside ~0.1 AU. The radius of the inner hole is determined by the condition that the mean free path of the gas molecules equals the maximum size of the particles that photophoresis effectively works on (100 micron - 10 cm, depending on the dust property). The dust disk structure formed by photophoresis can be distinguished from the structure of gas-free dust disk models, because the particle sizes of the outer disks are larger, and the inner hole radius depends on the gas density.
This study reports pulse variation analysis results for the forth discovered accretion-powered millisecond pulsar XTE J1807-294 during its 2003 outburst observed by {\it Rossi X-ray Timing Explorer}. The pulsation is significantly detected only in the first $\sim$90d out of $\sim$150d observations. The pulse phase variation is too complex to be described as an orbital motion plus a simple polynomial model. The precise orbital parameters with $P_{orb}=40.073601(8)$ min and ${\it a_x}\sin {\it i}=4.823(5)$ lt-ms were obtained after applying the trend removal to the daily observed 150s segments pulse phases folded with a constant spin frequency without Keplerian orbit included. The binary barycenter corrected pulse phases show smooth evolution and clear negative phase shifts coincident with the flares seen on the light curve and the enhancements of fractional pulse amplitude. The non-flare pulse phases for the first $\sim$60d data are well described as a fourth order polynomial implying that the neutron star was spun-up during the first $\sim$60d with a rate $\dot \nu=(1.7\pm0.3) \times 10^{-13}$ Hz/s at the beginning of the outburst. Significant soft phase lags up to $\sim$500 $\mu s$ ($\sim$10% cycle) between 2 to 20 keV were detected for the nonflare pulse phases. We conclude that the anomalous phase shifts are unlikely due to the accretion torque but could result from the ``hot spot'' moving on the surface of neutron star.
We present here near-infrared spectroscopy in the H and K bands of a
selection of nearly 80 stars that belong to various AGB types, namely S type, M
type and SR type. This sample also includes 16 Post-AGB (PAGB) stars. From
these spectra, we seek correlations between the equivalent widths of some
important spectral signatures and the infrared colors that are indicative of
mass loss. Repeated spectroscopic observations were made on some PAGB stars to
look for spectral variations. We also analyse archival SPITZER mid-infrared
spectra on a few PAGB stars to identify spectral features due to PAH molecules
providing confirmation of the advanced stage of their evolution. Further, we
model the SEDs of the stars (compiled from archival data) and compare
circumstellar dust parameters and mass loss rates in different types.
Our near-infrared spectra show that in the case of M and S type stars, the
equivalent widths of the CO(3-0) band are moderately correlated with infrared
colors, suggesting a possible relationship with mass loss processes. A few PAGB
stars revealed short term variability in their spectra, indicating episodic
mass loss: the cooler stars showed in CO first overtone bands and the hotter
ones showed in HI Brackett lines. Our spectra on IRAS 19399+2312 suggest that
it is a transition object. From the SPITZER spectra, there seems to be a
dependence between the spectral type of the PAGB stars and the strength of the
PAH features. Modelling of SEDs showed among the M and PAGB stars that the
higher the mass loss rates, the higher the [K-12] colour in our sample.
We review the possible mechanisms for production of non-thermal electrons which are responsible for non-thermal radiation in clusters of galaxies. Our primary focus is on non-thermal Bremsstrahlung and inverse Compton scattering, that produce hard X-ray emission. We briefly review acceleration mechanisms and point out that in most astrophysical situations, and in particular for the intracluster medium, shocks, turbulence and plasma waves play a crucial role. We consider two scenarios for production of non-thermal radiation. The first is hard X-ray emission due to non-thermal Bremsstrahlung by nonrelativistic particles. Non-thermal tails are produced by accelerating electrons from the background plasma with an initial Maxwellian distribution. However, these tails are accompanied by significant heating and they are present for a short time of <10^6 yr, which is also the time that the tail will be thermalised. Such non-thermal tails, even if possible, can only explain the hard X-ray but not the radio emission which needs GeV or higher energy electrons. For these and for production of hard X-rays by the inverse Compton model, we need the second scenario where there is injection and subsequent acceleration of relativistic electrons. It is shown that a steady state situation, for example arising from secondary electrons produced from cosmic ray proton scattering by background protons, will most likely lead to flatter than required electron spectra or it requires a short escape time of the electrons from the cluster. An episodic injection of relativistic electrons, presumably from galaxies or AGN, and/or episodic generation of turbulence and shocks by mergers can result in an electron spectrum consistent with observations but for only a short period of less than one billion years.
We present deep I and z' imaging of the colour-selected cluster RzCS 052 and study the color-magnitude relation of this cluster, its scatter, the morphological distribution on the red sequence, the luminosity and stellar mass functions of red galaxies and the cluster blue fraction. We find that the stellar populations of early type galaxies in this cluster are uniformly old and that their luminosity function does not show any sign of evolution other than the passive evolution of their stellar populations. We rule out a significant contribution from mergers in the buildup of the red sequence of RzCS 052. The cluster has a large (~30%) blue fraction and and we infer that the evolution of the blue galaxies is faster than an exponentially declining star formation model and that these objects have probably experienced starburst episodes. Mergers are unlikely to be the driver of the observed colour evolution, because of the measured constancy of the mass function, as derived from near-infrared photometry of 32 clusters, including RzCS 052, presented in a related paper. Mechanisms with clustercentric radial dependent efficiencies are disfavored as well, because of the observed constant blue fraction with clustercentric distance.
We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT.
During the last few years a class of enigmatic sub-luminous accreting neutron stars has been found in our Galaxy. They have peak X-ray luminosities (2-10 keV) of a few times 1E34 erg/s to a few times 1E35 erg/s, and both persistent and transient sources have been found. I present a short overview of our knowledge of these systems and what we can learn from them.
We study inflation and late-time acceleration in the expansion of the universe in non-minimal electromagnetism, in which the electromagnetic field couples to the scalar curvature function. It is shown that power-law inflation can be realized due to the non-minimal gravitational coupling of the electromagnetic field, and that large-scale magnetic fields can be generated due to the breaking of the conformal invariance of the electromagnetic field through its non-minimal gravitational coupling. Furthermore, it is demonstrated that both inflation and the late-time acceleration of the universe can be realized in a modified Maxwell-$F(R)$ gravity which is consistent with solar system tests and cosmological bounds and free of instabilities. At small curvature typical for current universe the standard Maxwell theory is recovered. We also consider classically equivalent form of non-minimal Maxwell-$F(R)$ gravity, and propose the origin of the non-minimal gravitational coupling function based on renormalization-group considerations.
The success of the SWIFT/BAT and INTEGRAL missions has definitely opened a new window for follow-up and deep study of the transient gamma-ray sky. This now appears as the access key to important progresses in the area of cosmological research and deep understanding of the physics of compact objects. To detect in near real-time explosive events like Gamma-Ray bursts, thermonuclear flashes from Neutron Stars and other types of X-ray outbursts we have developed a concept for a wide-field gamma-ray coded mask instrument working in the range 8-200 keV, having a sensitivity of 0.4 ph cm-2 s-1 in 1s (15-150 keV) and arcmin location accuracy over a sky region as wide as 3sr. This scientific requirement can be achieved by means of two large area, high spatial resolution CZT detection planes made of arrays of relatively large (~1cm2) crystals, which are in turn read out as matrices of smaller pixels. To achieve such a wide Field-Of-View the two units can be placed at the sides of a S/C platform serving a payload with a complex of powerful X-ray instruments, as designed for the EDGE mission. The two units will be equipped with powerful signal read out system and data handling electronics, providing accurate on-board reconstruction of the source positions for fast, autonomous target acquisition by the X-ray telescopes.
We collected the parameters (position, absorption, spin, orbital period, etc..), when known, of all Galactic sources detected by INTEGRAL during its four first years of activity. We use these parameters to test theoretical predictions. For example, it is clear that HMXBs tend to be found mostly in the tangential direction of the Galactic arms, while LMXBs tend to be clustered in the Galactic bulge. We then focus on HMXBs and present two possible new tools, in addition to the well-known ``Corbet-diagram'', to distinguish between Be-HMXBs and Sg-HMXBs
We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the "missing baryon" problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations.
As part of a large survey of halo and thick disc stars, we found one halo star, HD 106038, exceptionally overabundant in beryllium. In spite of its low metallicity, [Fe/H] = -1.26, the star has log(Be/H) = -10.60, which is similar to the solar meteoritic abundance, log(Be/H) = -10.58. This abundance is more than ten times higher the abundance of stars with similar metallicity and cannot be explained by models of chemical evolution of the Galaxy that include the standard theory of cosmic-ray spallation. No other halo star exhibiting such a beryllium overabundance is known. In addition, overabundances of Li, Si, Ni, Y, and Ba are also observed. We suggest that all these chemical peculiarities, but the Ba abundance, can be simultaneously explained if the star was formed in the vicinity of a hypernova.
Clusters of galaxies are self-gravitating systems of mass ~10^14-10^15 Msun. They consist of dark matter (~80 %), hot diffuse intracluster plasma (< 20 %) and a small fraction of stars, dust, and cold gas, mostly locked in galaxies. In most clusters, scaling relations between their properties testify that the cluster components are in approximate dynamical equilibrium within the cluster gravitational potential well. However, spatially inhomogeneous thermal and non-thermal emission of the intracluster medium (ICM), observed in some clusters in the X-ray and radio bands, and the kinematic and morphological segregation of galaxies are a signature of non-gravitational processes, ongoing cluster merging and interactions. In the current bottom-up scenario for the formation of cosmic structure, clusters are the most massive nodes of the filamentary large-scale structure of the cosmic web and form by anisotropic and episodic accretion of mass. In this model of the universe dominated by cold dark matter, at the present time most baryons are expected to be in a diffuse component rather than in stars and galaxies; moreover, ~50 % of this diffuse component has temperature ~0.01-1 keV and permeates the filamentary distribution of the dark matter. The temperature of this Warm-Hot Intergalactic Medium (WHIM) increases with the local density and its search in the outer regions of clusters and lower density regions has been the quest of much recent observational effort. Over the last thirty years, an impressive coherent picture of the formation and evolution of cosmic structures has emerged from the intense interplay between observations, theory and numerical experiments. Future efforts will continue to test whether this picture keeps being valid, needs corrections or suffers dramatic failures in its predictive power.
Aims: By performing a detailed radiative transfer analysis, we determine
fractional abundances of circumstellar H2O in the envelopes around six M-type
asymptotic giant branch stars. The models are also used to predict H2O spectral
line emission for the upcoming Herschel/HIFI mission.
Methods: We use Infrared space observatory long wavelength spectrometer
spectra to constrain the circumstellar fractional abundance distribution of
ortho-H2O, using a non-local thermal equilibrium, and non-local, radiative
transfer code based on the accelerated lambda iteration formalism. The
mass-loss rates and kinetic temperature structures for the sample stars are
determined through radiative transfer modelling of CO line emission based on
the Monte-Carlo method. The density and temperature profiles of the
circumstellar dust grains are determined through spectral energy distribution
modelling using the publicly available code Dusty.
Results: The determined ortho-H2O abundances lie between 1e-4 and 1.5e-3
relative to H2, with the exception of WX Psc, which has a much lower estimated
ortho-H2O abundance of only 2e-6, possibly indicating H_2O adsorption onto dust
grains or recent mass-loss-rate modulations. The estimated abundances are
uncertain by, at best, a factor of a few.
Conclusions: The high water abundance found for the majority of the sources
suggests that either the `normal' chemical processes are very effective in
producing H2O, or else non-local thermal equilibrium atmospheric chemistry,
grain surface reactions, or a release of H_2O (e.g. from icy bodies like Kuiper
belt objects) play a role. We provide predictions for ortho-H2O lines in the
spectral window of Herschel/HIFI.
We investigate the effects of ambipolar diffusion and the Hall effect on the stability of weakly-ionized, magnetized planar shear flows. Employing a local approach similar to the shearing-sheet approximation, we solve for the evolution of linear perturbations in both streamwise-symmetric and non-streamwise-symmetric geometries using WKB techniques and/or numerical methods. We find that instability arises from the combination of shear and non-ideal magnetohydrodynamic processes, and is a result of the ability of these processes to influence the free energy path between the perturbations and the shear. They turn what would be simple linear-in-time growth due to current and vortex stretching from shear into exponentially-growing instabilities. Our results aid in understanding previous work on the behaviour of weakly-ionized accretion discs. In particular, the recent finding that the Hall effect and ambipolar diffusion destabilize both positive and negative angular velocity gradients acquires a natural explanation in the more general context of this paper. We construct a simple toy model for these instabilities based upon transformation operators (shears, rotations, and projections) that captures both their qualitative and, in certain cases, exact quantitative behaviour.
The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas collapsing in large-scale filaments and probably harbours a substantial fraction of the baryons in the local Universe. Absorption-line measurements in the ultraviolet (UV) and in the X-ray band currently represent the best method to study the WHIM at low redshifts. We here describe the physical properties of the WHIM and the concepts behind WHIM absorption line measurements of H I and high ions such as O VI, O VII, and O VIII in the far-ultraviolet and X-ray band. We review results of recent WHIM absorption line studies carried out with UV and X-ray satellites such as FUSE, HST, Chandra, and XMM-Newton and discuss their implications for our knowledge of the WHIM.
An excess over the extrapolation to the extreme ultraviolet and soft X-ray ranges of the thermal emission from the hot intracluster medium has been detected in a number of clusters of galaxies. We briefly present each of the satellites (EUVE, ROSAT PSPC and BeppoSAX, and presently XMM-Newton, Chandra and Suzaku) and their corresponding instrumental issues, which are responsible for the fact that this soft excess remains controversial in a number of cases. We then review the evidence for this soft X-ray excess and discuss the possible mechanisms (thermal and non-thermal) which could be responsible for this emission.
Recent observations of high energy (> 20 keV) X-ray emission in a few clusters of galaxies broaden our knowledge of physical phenomena in the intracluster space. This emission is likely to be nonthermal, probably resulting from Compton scattering of relativistic electrons by the cosmic microwave background (CMB) radiation. Direct evidence for the presence of relativistic electrons in some 50 clusters comes from measurements of extended radio emission in their central regions. We briefly review the main results from observations of extended regions of radio emission, and Faraday rotation measurements of background and cluster radio sources. The main focus of the review are searches for nonthermal X-ray emission conducted with past and currently operating satellites, which yielded appreciable evidence for nonthermal emission components in the spectra of a few clusters. This evidence is clearly not unequivocal, due to substantial observational and systematic uncertainties, in addition to virtually complete lack of spatial information. If indeed the emission has its origin in Compton scattering of relativistic electrons by the CMB, then the mean magnetic field strength and density of relativistic electrons in the cluster can be directly determined. Knowledge of these basic nonthermal quantities is valuable for the detailed description of processes in intracluster gas and for the origin of magnetic fields.
We review observations of extended regions of radio emission in clusters; these include diffuse emission in `relics', and the large central regions commonly referred to as `halos'. The spectral observations, as well as Faraday rotation measurements of background and cluster radio sources, provide the main evidence for large-scale intracluster magnetic fields and significant densities of relativistic electrons. Implications from these observations on acceleration mechanisms of these electrons are reviewed, including turbulent and shock acceleration, and also the origin of some of the electrons in collisions of relativistic protons by ambient protons in the (thermal) gas. Improved knowledge of non-thermal phenomena in clusters requires more extensive and detailed radio measurements; we briefly review prospects for future observations.
We have used the RXTE and INTEGRAL satellites simultaneously to observe the High Mass X-ray binary IGR J19140+0951. The spectra obtained in the 3-80 keV range have allowed us to perform a precise spectral analysis of the system along its binary orbit. The spectral evolution confirms the supergiant nature of the companion star and the neutron star nature of the compact object. Using a simple stellar wind model to describe the evolution of the photoelectric absorption, we were able to restrict the orbital inclination angle in the range 37-75 degrees. This analysis leads to a wind mass-loss rate from the companion star of ~ 10e-7 Msun/year, consistent with its expected spectral type. We have detected a soft excess in at least three observations, for the first time for this source. Such soft excesses have been reported in several HMXBs in the past. We discuss the possible origin of this excess, and suggest, based on its spectral properties and occurrences prior to the superior conjunction, that it may be explained as the reprocessing of the X-ray emission originating from the neutron star by the surrounding ionised gas.
(Abridged) We demonstrate that the tenet of hierarchical structure growth leads directly to a robust, falsifiable prediction for the correlation between stellar fraction (fstar) and total system mass (M500) of galaxy groups and clusters. This prediction is relatively insensitive to the details of baryonic physics or cosmological parameters. In particular, if the fstar-M500 relation is fixed and does not evolve with redshift, CDM models predict the logarithmic slope of this relation to be b>-0.3. This constraint can be weakened if the fstar-M500 relation evolves strongly, but this implies more stars must be formed in situ in groups at low redshift. Conservatively requiring that at least half the stars in groups were formed by z=1, the constraint from evolution models is b>-0.35. Since the most massive clusters (M500=1E15 Msun) are observed to have fstar=0.01, this means that groups with M500=5E13 Msun must have fstar<0.03. Recent observations by Gonzalez et al. (2007) indicate a much steeper relation, with fstar>0.04 in groups, leading to b=-0.64. If confirmed, this would rule out hierarchical structure formation models: today's clusters could not have been built from today's groups, or even from the higher-redshift progenitors of those groups. We perform a careful analysis of these and other data to identify the most important systematic uncertainties in their measurements. Although correlated uncertainties on stellar and total masses might explain the steep observed relation, the data are only consistent with theory if the observed group masses are systematically underestimated.
Attempts have been made to parameterise the thermoacoustic emission of particle cascades induced by EeV neutrinos interacting in the sea. Understanding the characteristic radiation from such an event allows us to predict the pressure pulse observed by underwater acoustic sensors distributed in kilometre scale arrays. We find that detectors encompassing thousands of cubic kilometres are required, with a minimum of 100 hydrophones per kilometre cubed, in order to observe the flux of neutrinos predicted by the attenuation of ultra high energy cosmic rays on cosmic microwave background photons. The pressure threshold of such an array must be in the range 5-10 mPa and the said detector will have to operate for five years or more. Additionally a qualitative analysis of the first acoustic data recorded by the Rona hydrophone array off the north-west coast of Scotland is reported.
Large-scale structure formation, accretion and merging processes, AGN activity produce cosmological gas shocks. The shocks convert a fraction of the energy of gravitationally accelerated flows to internal energy of the gas. Being the main gas-heating agent, cosmological shocks could amplify magnetic fields and accelerate energetic particles via the multi-fluid plasma relaxation processes. We first discuss the basic properties of standard single-fluid shocks. Cosmological plasma shocks are expected to be collisionless. We then review the plasma processes responsible for the microscopic structure of collisionless shocks. A tiny fraction of the particles crossing the shock is injected into the non-thermal energetic component that could get a substantial part of the ram pressure power dissipated at the shock. The energetic particles penetrate deep into the shock upstream producing an extended shock precursor. Scaling relations for postshock ion temperature and entropy as functions of shock velocity in strong collisionless multi-fluid shocks are discussed. We show that the multi-fluid nature of collisionless shocks results in excessive gas compression, energetic particle acceleration, precursor gas heating, magnetic field amplification and non-thermal emission. Multi-fluid shocks provide a reduced gas entropy production and could also modify the observable thermodynamic scaling relations for clusters of galaxies.
The Warm-Hot Intergalactic Medium (WHIM) is thought to contribute about 40-50 % to the baryonic budget at the present evolution stage of the universe. The observed large scale structure is likely to be due to gravitational growth of density fluctuations in the post-inflation era. The evolving cosmic web is governed by non-linear gravitational growth of the initially weak density fluctuations in the dark energy dominated cosmology. Non-linear structure formation, accretion and merging processes, star forming and AGN activity produce gas shocks in the WHIM. Shock waves are converting a fraction of the gravitation power to thermal and non-thermal emission of baryonic/leptonic matter. They provide the most likely way to power the luminous matter in the WHIM. The plasma shocks in the WHIM are expected to be collisionless. Collisionless shocks produce a highly non-equilibrium state with anisotropic temperatures and a large differences in ion and electron temperatures. We discuss the ion and electron heating by the collisionless shocks and then review the plasma processes responsible for the Coulomb equilibration and collisional ionisation equilibrium of oxygen ions in the WHIM. MHD-turbulence produced by the strong collisionless shocks could provide a sizeable non-thermal contribution to the observed Doppler parameter of the UV line spectra of the WHIM.
We discuss the different physical processes that are important to understand the thermal X-ray emission and absorption spectra of the diffuse gas in clusters of galaxies and the warm-hot intergalactic medium. The ionisation balance, line and continuum emission and absorption properties are reviewed and several practical examples are given that illustrate the most important diagnostic features in the X-ray spectra.
In this paper we review the possible radiation mechanisms for the observed non-thermal emission in clusters of galaxies, with a primary focus on the radio and hard X-ray emission. We show that the difficulty with the non-thermal, non-relativistic Bremsstrahlung model for the hard X-ray emission, first pointed out by Petrosian (2001) using a cold target approximation, is somewhat alleviated when one treats the problem more exactly by including the fact that the background plasma particle energies are on average a factor of 10 below the energy of the non-thermal particles. This increases the lifetime of the non-thermal particles, and as a result decreases the extreme energy requirement, but at most by a factor of three. We then review the synchrotron and so-called inverse Compton emission by relativistic electrons, which when compared with observations can constrain the value of the magnetic field and energy of relativistic electrons. This model requires a low value of the magnetic field which is far from the equipartition value. We briefly review the possibilities of gamma-ray emission and prospects for GLAST observations. We also present a toy model of the non-thermal electron spectra that are produced by the acceleration mechanisms discussed in an accompanying paper.
An implicit algorithm for solving the equations of general relativistic
hydrodynamics in conservative form in three-dimensional axi-symmetry is
presented. This algorithm is a direct extension of the pseudo-Newtonian
implicit radiative magnetohydrodynamical solver -IRMHD- into the general
relativistic regime.
We adopt the Boyer-Lindquist coordinates and formulate the hydrodynamical
equations in the fixed background of a Kerr black hole. The set of equations
are solved implicitly using the hierarchical solution scenario (HSS). The HSS
is efficient, robust and enables the use of a variety of solution procedures
that range from a purely explicit up to fully implicit schemes. The
discretization of the HD-equations is based on the finite volume formulation
and the defect-correction iteration strategy for recovering higher order
spatial and temporal accuracies. Depending on the astrophysical problem, a
variety of relaxation methods can be applied. In particular the vectorized
black-white Line-Gauss-Seidel relaxation method is most suitable for modeling
accretion flows with shocks, whereas the Approximate Factorization Method is
for weakly compressible flows.
The results of several test calculations that verify the accuracy and
robustness of the algorithm are shown. Extending the algorithm to enable
solving the non-ideal MHD equations in the general relativistic regime is the
subject of our ongoing research.
We study the effects of rotation on the outer convective zones of massive stars. We examine the effects of rotation on the thermal gradient and on the Solberg--Hoiland term by analytical developments and by numerical models. Writing the criterion for convection in rotating envelopes, we show that the effects of rotation on the thermal gradient are much larger and of opposite sign to the effect of the Solberg-Hoiland criterion. On the whole, rotation favors convection in stellar envelopes at the equator and to a smaller extent at the poles. In a rotating 20 Msun star at 94% of the critical angular velocity, there are two convective envelopes, with the bigger one having a thickness of 13.2% of the equatorial radius. In the non-rotating model, the corresponding convective zone has a thickness of only 4.6% of the radius. The occurrence of outer convection in massive stars has many consequences.
Modern cosmological observations allow us to study in great detail the evolution and history of the large scale structure hierarchy. The fundamental problem of accurate constraints on the cosmological parameters, within a given cosmological model, requires precise modelling of the observed structure. In this paper we briefly review the current most effective techniques of large scale structure simulations, emphasising both their advantages and shortcomings. Starting with basics of the direct N-body simulations appropriate to modelling cold dark matter evolution, we then discuss the direct-sum technique GRAPE, particle-mesh (PM) and hybrid methods, combining the PM and the tree algorithms. Simulations of baryonic matter in the Universe often use hydrodynamic codes based on both particle methods that discretise mass, and grid-based methods. We briefly describe Eulerian grid methods, and also some variants of Lagrangian smoothed particle hydrodynamics (SPH) methods.
We present a phase-coherent timing analysis of the intermittent accreting millisecond pulsar SAX J1748.9-2021. A new timing solution for the pulsar spin period and the Keplerian binary orbital parameters was achieved by phase connecting all episodes of intermittent pulsations visible during the 2001 outburst. We investigate the pulse profile shapes, their energy dependence and the possible influence of Type I X-ray bursts on the time of arrival and fractional amplitude of the pulsations. We find that the timing solution of SAX J1748.9-2021 shows an erratic behavior when selecting different subsets of data, that is related to substantial timing noise in the timing post-fit residuals. The pulse profiles are very sinusoidal and their fractional amplitude increases linearly with energy and no second harmonic is detected. The reason why this pulsar is intermittent is still unknown but we can rule out a one-to-one correspondence between Type I X-ray bursts and the appearance of the pulsations.
Modern hydrodynamical simulations offer nowadays a powerful means to trace the evolution of the X-ray properties of the intra-cluster medium (ICM) during the cosmological history of the hierarchical build up of galaxy clusters. In this paper we review the current status of these simulations and how their predictions fare in reproducing the most recent X-ray observations of clusters. After briefly discussing the shortcomings of the self-similar model, based on assuming that gravity only drives the evolution of the ICM, we discuss how the processes of gas cooling and non-gravitational heating are expected to bring model predictions into better agreement with observational data. We then present results from the hydrodynamical simulations, performed by different groups, and how they compare with observational data. As terms of comparison, we use X-ray scaling relations between mass, luminosity, temperature and pressure, as well as the profiles of temperature and entropy. The results of this comparison can be summarised as follows: (a) simulations, which include gas cooling, star formation and supernova feedback, are generally successful in reproducing the X-ray properties of the ICM outside the core regions; (b) simulations generally fail in reproducing the observed ``cool core'' structure, in that they have serious difficulties in regulating overcooling, thereby producing steep negative central temperature profiles. This discrepancy calls for the need of introducing other physical processes, such as energy feedback from active galactic nuclei, which should compensate the radiative losses of the gas with high density, low entropy and short cooling time, which is observed to reside in the innermost regions of galaxy clusters.
Using extremely deep (rms 3.3 microJy/bm) 1.4GHz sub-arcsecond resolution MERLIN + VLA radio observations of a 8'.5 by 8'.5 field centred upon the Hubble Deep Field North, in conjunction with Spitzer 24 micron data we present an investigation of the radio-MIR correlation at very low flux densities. By stacking individual sources within these data we are able to extend the MIR-radio correlation to the extremely faint (~microJy and even sub-microJy) radio source population. Tentatively we demonstrate a small deviation from the correlation for the faintest MIR sources. We suggest that this small observed change in the gradient of the correlation is the result of a suppression of the MIR emission in faint star-forming galaxies. This deviation potentially has significant implications for using either the MIR or non-thermal radio emission as a star-formation tracer at low luminosities.
In this paper we investigate the radio-MIR correlation at very low flux densities using extremely deep 1.4 GHz sub-arcsecond angular resolution MERLIN+VLA observations of a 8'.5 by 8'.5 field centred upon the Hubble Deep Field North, in conjunction with Spitzer 24micron data. From these results the MIR-radio correlation is extended to the very faint (~microJy) radio source population. Tentatively we detect a small deviation from the correlation at the faintest IR flux densities. We suggest that this small observed change in the gradient of the correlation is the result of a suppression of the MIR emission in faint star-forming galaxies. This deviation potentially has significant implications for using either the MIR or non-thermal radio emission as a star-formation tracer of very low luminosity galaxies.
In this paper we review the current predictions of numerical simulations for the origin and observability of the warm hot intergalactic medium (WHIM), the diffuse gas that contains up to 50 per cent of the baryons at z~0. During structure formation, gravitational accretion shocks emerging from collapsing regions gradually heat the intergalactic medium (IGM) to temperatures in the range T~10^5-10^7 K. The WHIM is predicted to radiate most of its energy in the ultraviolet (UV) and X-ray bands and to contribute a significant fraction of the soft X-ray background emission. While O VI and C IV absorption systems arising in the cooler fraction of the WHIM with T~10^5-10^5.5 K are seen in FUSE and HST observations, models agree that current X-ray telescopes such as Chandra and XMM-Newton do not have enough sensitivity to detect the hotter WHIM. However, future missions such as Constellation-X and XEUS might be able to detect both emission lines and absorption systems from highly ionised atoms such as O VII, O VIII and Fe XVII.
Non-thermal components are key ingredients for understanding clusters of galaxies. In the hierarchical model of structure formation, shocks and large-scale turbulence are unavoidable in the cluster formation processes. Understanding the amplification and evolution of the magnetic field in galaxy clusters is necessary for modelling both the heat transport and the dissipative processes in the hot intra-cluster plasma. The acceleration, transport and interactions of non-thermal energetic particles are essential for modelling the observed emissions. Therefore, the inclusion of the non-thermal components will be mandatory for simulating accurately the global dynamical processes in clusters. In this review, we summarise the results obtained with the simulations of the formation of galaxy clusters which address the issues of shocks, magnetic field, cosmic ray particles and turbulence.
We present spectra of accretion discs around white-dwarfs calculated with an improved and updated version of the Shaviv & Wehrse (1991) model. The new version includes line opacities and convective energy transport and can be used to calculate spectra of hot discs in bright systems (nova--like variables or dwarf novae in outburst) as well as spectra of cold accretion discs in quiescent dwarf novae.
Because of their deep gravitational potential wells, clusters of galaxies retain all the metals produced by the stellar populations of the member galaxies. Most of these metals reside in the hot plasma which dominates the baryon content of clusters. This makes them excellent laboratories for the study of the nucleosynthesis and chemical enrichment history of the Universe. Here we review the history, current possibilities and limitations of the abundance studies, and the present observational status of X-ray measurements of the chemical composition of the intra-cluster medium. We summarise the latest progress in using the abundance patterns in clusters to put constraints on theoretical models of supernovae and we show how cluster abundances provide new insights into the star-formation history of the Universe.
There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment. Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and environmental properties.
The study of the metal enrichment of the intra-cluster and inter-galactic media (ICM and IGM) represents a direct means to reconstruct the past history of star formation, the role of feedback processes and the gas-dynamical processes which determine the evolution of the cosmic baryons. In this paper we review the approaches that have been followed so far to model the enrichment of the ICM in a cosmological context. While our presentation will be focused on the role played by hydrodynamical simulations, we will also discuss other approaches based on semi-analytical models of galaxy formation, also critically discussing pros and cons of the different methods. We will first review the concept of the model of chemical evolution to be implemented in any chemo-dynamical description. We will emphasise how the predictions of this model critically depend on the choice of the stellar initial mass function, on the stellar life-times and on the stellar yields. We will then overview the comparisons presented so far between X-ray observations of the ICM enrichment and model predictions. We will show how the most recent chemo-dynamical models are able to capture the basic features of the observed metal content of the ICM and its evolution. We will conclude by highlighting the open questions in this study and the direction of improvements for cosmological chemo-dynamical models of the next generation.
We briefly review capabilities and requirements for future instrumentation in UV- and X-ray astronomy that can contribute to advancing our understanding of the diffuse, highly ionised intergalactic medium.
Strong selection effects are present in observational samples of cataclysmic variables (CVs), complicating comparisons to theoretical predictions. The selection criteria used to define most CV samples discriminate heavily against the discovery of short-period, intrinsically faint systems. The situation can be improved by selecting CVs for the presence of emission lines. For this reason, we have constructed a homogeneous sample of CVs selected on the basis of Halpha emission. We present discovery observations of the 14 CVs and 2 additional CV candidates found in this search. The orbital periods of 11 of the new CVs were measured; all are above 3 h. There are two eclipsing systems in the sample, and one in which we observed a quasi-periodic modulation on a \sim 1000 s time-scale. We also detect the secondary star in the spectrum of one system, and measure its spectral type. Several of the new CVs have the spectroscopic appearance of nova-like variables (NLs), and a few display what may be SW Sex star behaviour. In a companion paper, we discuss the implications of this new sample for CV evolution.
We present CCD photometric and mass function study of 9 young Large Magellanic Cloud star clusters namely NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2006, SL 538, NGC 2011, NGC 2098 and NGC 2136. The BVRI data reaching down to V ~ 21 mag, are collected from 3.5-meter NTT/EFOSC2 in sub-arcsec seeing conditions. For NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2011 and NGC 2136, broad band photometric CCD data are presented for the first time. Seven of the 9 clusters have ages between 16 to 25 Myr while remaining two clusters have ages $32\pm4$ Myr (NGC 2098) and $90\pm10$ Myr (NGC 2136). For 7 younger clusters, the age estimates based on a recent model and the integrated spectra are found to be systematically lower ($\sim$ 10 Myr) from the present estimate. In the mass range of $\sim 2 - 12$ $M_{\odot}$, the MF slopes for 8 out of nine clusters were found to be similar with the value of $\gamma$ ranging from $-1.90\pm0.16$ to $-2.28\pm0.21$. For NGC 1767 it is flatter with $\gamma = -1.23\pm0.27$. Mass segregation effects are observed for NGC 2002, NGC 2006, NGC 2136 and NGC 2098. This is consistent with the findings of Kontizas et al. for NGC 2098. Presence of mass segregation in these clusters could be an imprint of star formation process as their ages are significantly smaller than their dynamical evolution time. Mean MF slope of $\gamma = -2.22\pm0.16$ derived for a sample of 25 young ($\le 100$ Myr) dynamically unevolved LMC stellar systems provide support for the universality of IMF in the intermediate mass range $\sim 2-12 M_{\odot}$.
We present Very Large Array 21-cm observations of the massive edge-on spiral galaxy NGC 5746. This galaxy has recently been reported to have a luminous X-ray halo, which has been taken as evidence of residual hot gas as predicted in galaxy formation scenarios. Such models also predict that some of this gas should undergo thermal instabilities, leading to a population of warm clouds falling onto the disk. If so, then one might expect to find a vertically extended neutral layer. We detect a substantial high-latitude component, but conclude that almost all of its mass of 1.2-1.6 billion solar masses most likely resides in a warp. Four features far from the plane containing about 100 million solar masses are found at velocities distinct from this warp. These clouds may be associated with the expected infall, although an origin in a disk-halo flow cannot be ruled out, except for one feature which is counter-rotating. The warp itself may be a result of infall according to recent models. But clearly this galaxy lacks a massive, lagging neutral halo as found in NGC 891. The disk HI is concentrated into two rings of radii 1.5 and 3 arcminutes. Radial inflow is found in the disk, probably due to the bar in this galaxy. A nearby member of this galaxy group, NGC 5740, is also detected. It shows a prominent one-sided extension which may be the result of ram pressure stripping.
We use an independent new sample of cataclysmic variables (CVs), constructed by selecting objects for Halpha emission, to constrain the properties of the intrinsic CV population. This sample is restricted to systems that are likely to be non-magnetic and unevolved; it consists of 17 CVs, of which at least 10 have orbital periods above 3 h. We find that even very generous allowance for selection effects is not sufficient to reconcile the large ratio of short- to long-period CVs predicted by standard CV evolution theory with the observed sample, possibly implying that short-period systems evolve faster than predicted by the disrupted magnetic braking model. This would require that an angular momentum loss mechanism, besides gravitational radiation, acts on CVs with orbital periods below the period gap. To bring the model into agreement with observations, the rate of angular momentum loss below the period gap must be increased by a factor of at least 3, unless the model also over estimates the angular momentum loss rate of long-period CVs.
We summarize and discuss recent work (Fregeau 2007) that presents the confluence of three results suggesting that most Galactic globular clusters are still in the process of core contraction, and have not yet reached the thermal equilibrium phase driven by binary scattering interactions: that 1) the three clusters that appear to be overabundant in X-ray binaries per unit encounter frequency are observationally classified as "core-collapsed," 2) recent numerical simulations of cluster evolution with primordial binaries show that structural parameters of clusters in the binary-burning phase agree only with "core-collapsed" clusters, and 3) a cluster in the binary-burning phase for the last few Gyr should have about 5 times more dynamically formed X-ray sources than if it were in the core contraction phase for the same time.
In this paper we present the results of two detailed N-body simulations of the interaction of a sample of four massive globular clusters in the inner region of a triaxial galaxy. A full merging of the clusters takes place, leading to a slowly evolving cluster which is quite similar to observed Nuclear Clusters. Actually, both the density and the velocity dispersion profiles match qualitatively, and quantitatively after scaling, with observed features of many nucleated galaxies. In the case of dense initial clusters, the merger remnant shows a density profile more concentrated than that of the progenitors, with a central density higher than the sum of the central progenitors central densities. These findings support the idea that a massive Nuclear Cluster may have formed in early phases of the mother galaxy evolution and lead to the formation of a nucleus, which, in many galaxies, has indeed a luminosity profile similar to that of an extended King model. A correlation with galactic nuclear activity is suggested.
We report on next phase of our study of rotating accretion flows onto black holes. We consider hydrodynamical (HD) accretion flows with a spherically symmetric density distribution at the outer boundary but with spherical symmetry broken by the introduction of a small, latitude-dependent angular momentum. We study accretion flows by means of numerical two-dimensional, axisymmetric, HD simulations for variety of the adiabatic index, $\gamma$ and the gas temperature at infinity, $c_\infty$. Our work is an extension of work done by Proga & Begelman who consider models for only $\gamma=5/3$. Our main result is that the flow properties such as the topology of the sonic surface and time behavior strongly depend on $\gamma$ but little on $c_\infty$. In particular, for $1 < \gamma < 5/3$, the mass accretion rate shows large amplitude, slow time-variability which is a result of mixing between slow and fast rotating gas. This temporal behavior differs significantly from that in models with $\gamma\simless 5/3$ where the accretion rate is relatively constant and from that in models with $\gamma\simgreat 1$ where the accretion exhibits small amplitude quasi-periodic oscillations. The key parameter responsible for the differences is the sound speed of the accretion flow which in turn determines whether the flow is dominated by gas pressure, radiation pressure or rotation. Despite these differences the time-averaged mass accretion rate in units of the corresponding Bondi rate is a weak function of $\gamma$ and $c_\infty$.
The line-of-sight velocities and [OIII] 5007 AA expansion velocities are measured for 11 planetary nebulae (PNs) in the Virgo cluster core, at 15 Mpc distance, with the FLAMES spectrograph on the ESO VLT. These PNs are located about halfway between the two giant ellipticals M87 and M86. From the [OIII] 5007 AA line profile widths, the average half-width at half maximum expansion velocity for this sample of 11 PNs is v_HWHM = 16.5 km/s (RMS=2.6 km/s). We use the PN subsample bound to M87 to remove the distance uncertainties, and the resulting [OIII] 5007 AA luminosities to derive the central star masses. We find these masses to be at least 0.6 M_sun and obtain PN observable life times t_PN < 2000 yrs, which imply that the bright PNs detected in the Virgo cluster core are compact, high density nebulae. We finally discuss several scenarios for explaining the high central star masses in these bright M87 halo PNs.
The colour-magnitude diagrams of resolved single stellar populations, such as open and globular clusters, have provided the best natural laboratories to test stellar evolution theory. Whilst a variety of techniques have been used to infer the basic properties of these simple populations, systematic uncertainties arise from the purely geometrical degeneracy produced by the similar shape of isochrones of different ages and metallicities. Here we present an objective and robust statistical technique which lifts this degeneracy to a great extent through the use of a key observable: the number of stars along the isochrone. Through extensive Monte Carlo simulations we show that, for instance, we can infer the four main parameters (age, metallicity, distance and reddening) in an objective way, along with robust confidence intervals and their full covariance matrix. We show that systematic uncertainties due to field contamination, unresolved binaries, initial or present-day stellar mass function are either negligible or well under control. This technique provides, for the first time, a proper way to infer with unprecedented accuracy the fundamental properties of simple stellar populations, in an easy-to-implement algorithm.
We present high- and medium-resolution spectroscopic observations of the cataclysmic variable BF Eri during its low and bright states. The orbital period of this system was found to be 0.270881(3) days. The secondary star is clearly visible in the spectra through absorption lines of the neutral metals MgI, FeI and CaI. Its spectral type was found to be K3+-0.5. A radial velocity study of the secondary yielded a semi-amplitude of K_2=182.5+-0.9 km/s. The radial velocity semiamplitude of the white dwarf was found to be K_1=74+-3 km/s from the motion of the wings of the Halpha and Hbeta emission lines. From these parameters we have obtained that the secondary in BF Eri is an evolved star with a mass of 0.50-0.59 Msun, whose size is about 30 per cent larger than a zero-age main-sequence single-star of the same mass. We also show that BF Eri contains a massive white dwarf (M1>1.23 Msun), allowing us to consider the system as a SN Ia progenitor. BF Eri also shows a high gamma-velocity (gamma=-94 km/s) and substantial proper motion. With our estimation of the distance to the system (d~700+-200 pc), this corresponds to a space velocity of ~350 km/s with respect to the dynamical local standard of rest. The cumulative effect of repeated nova eruptions with asymmetric envelope ejection might explain the high space velocity of the system. We analyze the outburst behaviour of BF Eri and question the current classification of the system as a dwarf nova. We propose that BF Eri might be an old nova exhibiting "stunted" outbursts.
I study the joint effect of dynamical friction, tidal torques and cosmological constant on clusters of galaxies formation I show that within high-density environments, such as rich clusters of galaxies, both dynamical friction and tidal torques slows down the collapse of low-? peaks producing an observable variation in the time of collapse of the perturbation and, as a consequence, a reduction in the mass bound to the collapsed perturbation Moreover, the delay of the collapse produces a tendency for less dense regions to accrete less mass, with respect to a classical spherical model, inducing a biasing of over-dense regions toward higher mass I show how the threshold of collapse is modified if dynamical friction, tidal torques and a non-zero cosmological constant are taken into account and I use the Extended Press Schecter (EPS) approach to calculate the effects on the mass function Then, I compare the numerical mass function given in Reed et al (2003) with the theoretical mass function obtained in the present paper I show that the barrier obtained in the present paper gives rise to a better description of the mass function evolution with respect to other previous models (Sheth & Tormen 1999, MNRAS, 308, 119 (hereafter ST); Sheth & Tormen 2002, MNRAS, 329, 61 (hereafter ST1))
Most of multi-planetary systems detected until now are characterized by hot-Jupiters close to their central star and moving on eccentric orbits. Hence, from a dynamical point of view, compact multi-planetary systems form a particular class of the general N-body problem (with N >3). Moreover, extrasolar planets are up to now found in prograde orbital motions about their host star and often in mean motion resonances (MMR). In the present paper, we investigate theoretically in a first step a new stabilizing mechanism particularly suitable for compact two-planet systems. Such a mechanism involves counter-revolving orbits forming a retrograde MMR. In a second step, we study the feasibility of planetary systems to host counter-revolving planets. In order to characterize dynamical behaviors of multi-dimensional planetary systems in the vicinity of observations, we apply our technique of global dynamics analysis based on the MEGNO indicator (Mean Exponential Growth factor of Nearby Orbits) that provides the fine structure of the phase space. We also fit a few examples involving counter-revolving configurations by using the Pikaia genetic algorithm. Studying and fitting a particular case, namely the HD73526 planetary system, we find that counter-revolving configurations may be consistent with the observational data. We also point up the novel fine and characteristic structure of retrograde MMRs. We show that retrograde resonances and their resources open a family of stabilizing mechanisms involving new behaviors of apsidal precessions. Considering two possible mechanisms of formation (free-floating planets and the Slingshot model), we may conclude that counter-revolving configurations may be considered as feasible.
This paper provides a review of the variants of dark matter which are thought to be fundamental components of the universe and their role in origin and evolution of structures and some new original results concerning improvements to the spherical collapse model. In particular, I show how the spherical collapse model is modified when we take into account dynamical friction and tidal torques.
In this paper I show how the statistics of the gravitational field is changed when the system is characterized by a non-uniform distribution of particles. I show how the distribution functions W(dF/dt) giving the joint probability that a test particle is subject to a force F and an associated rate of change of F given by dF/dt, are modified by inhomogeneity. Then I calculate the first moment of dF/dt to study the effects of inhomogenity on dynamical friction. Finally I test, by N-Body simulations, that the theoretical W(F) and dF/dt describes correctly the experimental data and I find that the stochastic force distribution obtained for the evolved system is in good agreement with theory. Moreover, I find that in an inhomogeneous background the friction force is actually enhanced relative to the homogeneous case.
We used chemical equilibrium calculations to model thermal metamorphism of ordinary chondritic material as a function of temperature, pressure, and trace element abundance and use our results to discuss volatile mobilization during thermal metamorphism of ordinary chondrite parent bodies. The calculations include ~1,700 solids and gases of 40 elements. We compiled trace element abundances in H-, L-, and LL-chondrites for the elements Ag, As, Au, Bi, Cd, Cs, Cu, Ga, Ge, In, Pb, Rb, Sb, Se, Sn, Te, Tl, and Zn, and identified abundance trends as a function of petrographic type within each class. We found that abundance patterns within the H- and L- chondrites are consistent with mobilization of volatile elements in an onionshell-type parent body. LL-chondrites have more complex abundance patterns that may support a rubble-pile model for the LL-chondrite parent body. We calculated volatility sequences for the trace elements in the ordinary chondritic material, which differs significantly from the solar nebula volatility sequence.
Core-collapse supernovae (CC-SNe) are the explosion following the death of massive stars. Some of them are linked to long-duration gamma-ray bursts (GRBs). One important question is whether all CC-SNe share common features in their explosion mechanism. Here we present late-time spectra for a number of stripped-envelope CC-SNe, and use them to explore any asphericity generated in the inner part of the exploding star, near the site of collapse. A variety of oxygen emission-line profiles is observed, including a high incidence of double-peaked profiles, a distinct signature of an aspherical explosion. Our results suggest that all stripped-envelope CC-SNe are aspherical, perhaps jet-driven explosions, and that SNe accompanied by GRBs exhibit the highest degree of asphericity.
Motivated by the recently discovered class of faint (10^34-10^35 ergs/s) X-ray transients in the Galactic Center region, we investigate the 2-10 keV properties of classical and recurrent novae. Existing data are consistent with the idea that all classical novae are transient X-ray sources with durations of months to years and peak luminosities in the 10^34-10^35 ergs/s range. This makes classical novae a viable candidate class for the faint Galactic Center transients. We estimate the rate of classical novae within a 15 arcmin radius region centered on the Galactic Center (roughly the field of view of XMM-Newton observations centered on Sgr A*) to be ~0.1 per year. Therefore, it is plausible that some of the Galactic Center transients that have been announced to date are unrecognized classical novae. The continuing monitoring of the Galactic Center region carried out by Chandra and XMM-Newton may therefore provide a new method to detect classical novae in this crowded and obscured region, where optical surveys are not, and can never hope to be, effective. Therefore, X-ray monitoring may provide the best means of testing the completeness of the current understanding of the nova populations.
We study the development of entropy fluctuations in brane inflation in a warped throat, including the brane-antibrane tachyon as the waterfall field. We find that there is a period at the end of inflation during which the entropy mode associated with the tachyon field increases exponentially. In turn, the induced entropy seeds a contribution to the curvature fluctuation on cosmological scales which grows rapidly and exceeds the primordial curvature perturbation. We identify parameter values for which the induced curvature fluctuations are larger than the primordial adiabatic ones. This demonstrates that the study of the development of entropy fluctuations at the end of the period of inflation can lead to important constraints on models of brane inflation and also suggests that the curvaton mechanism may contribute significantly.
We study the dynamics and evolution of Nambu-Goto strings in a warped spacetime, where the warp factor is a function of the internal coordinates giving rise to a `throat' region. The microscopic equations of motion for strings in this background include potential and friction terms, which attract the strings towards the bottom of the warping throat. However, by considering the resulting macroscopic equations for the velocities of strings in the vicinity of the throat, we note the absence of enough classical damping to guarantee that the strings actually reach the warped minimum and stabilise there. Instead, our classical analysis supports a picture in which the strings experience mere deflections and bounces around the tip, rather than strongly damped oscillations. Indeed, 4D Hubble friction is inefficient in the internal dimensions and there is no other classical mechanism known, which could provide efficient damping. These results have potentially important implications for the intercommuting probabilities of cosmic superstrings.
The 5-dimensional (5d) Birkhoff theorem gives the class of 5d vacuum space-times containing spatial hypersurfaces with cosmological symmetries. This theorem is violated by the 5d vacuum Gergely-Maartens (GM) space-time, which is not a representant of the above class, but contains the static Einstein brane as embedded hypersurface. We prove that the 5d Birkhoff theorem is still satisfied in a weaker sense: the GM space-time is related to the degenerated horizon metric of certain black-hole space-times of the allowed class. This result resembles the connection between the Bertotti-Robinson space-time and the horizon region of the extremal Reissner-Nordstrom space-time in general relativity.
This work tabulates experimental results for coefficients for Lorentz and CPT violation in the minimal Standard-Model Extension. Summary tables are provided listing attained sensitivities in the matter and photon sectors.
We consider cosmological consequences of a heavy axino, decaying to the neutralino in R-parity conserving models. The importance and influence of the axino decay on the resultant abundance of neutralino dark matter depends on the lifetime and the energy density of axino. For a high reheating temperature after inflation, copiously produced axinos dominate the energy density of the universe and its decay produces a large amount of entropy. As a bonus, we obtain that the upper bound on the reheating temperature via gravitino decay after inflation can be moderated, because the entropy production by the axino decay more or less dilutes the gravitinos.
We show that, within Palatini modified gravity, the non-linear nature of the field equations implies that the usual naive averaging procedure (replacing the microscopic energy-momentum by its cosmological average) is invalid. As a consequence, we find the relative motion of particles in Palatini theories is indistinguishable from that predicted by General Relativity with a cosmological constant. Moreover, there is no WEP violation. It follows that the late time cosmology and astrophysics predicted by these two theories are the same. Palatini gravity does however predict alterations to particle physics laws e.g. corrections to the hydrogen energy levels. Measurements of transitions between those energy levels place strong constraints on the magnitude of such corrections and on the properties of viable Palatini gravities.
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We investigate the properties of one--dimensional flux ``voids'' (connected regions in the flux distribution above the mean flux level) by comparing hydrodynamical simulations of large cosmological volumes with a set of observed high--resolution spectra at z ~ 2. After addressing the effects of box size and resolution, we study how the void distribution changes when the most significant cosmological and astrophysical parameters are varied. We find that the void distribution in the flux is in excellent agreement with predictions of the standard LCDM cosmology, which also fits other flux statistics remarkably well. We then model the relation between flux voids and the corresponding one--dimensional gas density field along the line--of--sight and make a preliminary attempt to connect the one--dimensional properties of the gas density field to the three--dimensional dark matter distribution at the same redshift. This provides a framework that allows statistical interpretations of the void population at high redshift using observed quasar spectra, and eventually it will enable linking the void properties of the high--redshift universe with those at lower redshifts, which are better known.
E+A galaxies have been interpreted as post-starburst galaxies based on the
presence of strong Balmer absorption lines combined with the absence of major
emission lines ([OII] nor H$\alpha$). As a population of galaxies in the midst
of the transformation, E+A galaxies has been subject to an intense research
activity. It has been, however, difficult to investigate E+A galaxies
statistically since E+A galaxies are an extremely rare population of galaxies
($<$1% of all galaxies in the local Universe).
Here, we present a large catalog of 564 E+A (post-starburst) galaxies
carefully selected from half million spectra of the Sloan Digital Sky Survey
Data Release 5. We define E+A galaxies as those with H$\delta$ equivalent width
$>$5\AA and no detectable emission in [OII] $and$ H$\alpha$. The catalog
contains 564 E+A galaxies, and thus, is one of the largest of the kind to date.
In addition, we have included the H$\alpha$ line in the selection to remove
dusty star-forming galaxies, which could have contaminated previous [OII]-based
samples of E+A galaxies up to 52%. Thus, the catalog is one of the most
homogeneous, let alone its size. The catalog presented here can be used for
follow-up observations and statistical analyses of this rare population of
galaxies.
A white dwarf (WD) gains substantial angular momentum during the accretion process that grows it toward a Chandrasekhar mass. It is therefore expected to be quickly rotating when it ignites as a Type Ia supernova. The thermal and shearing profile are important for subsequent flame propagation. We highlight processes that could affect the WD shear, during accretion as well as during the ~1000 years of pre-explosive simmering. Baroclinic instabilities and/or the shear growth of small magnetic fields provide sufficient torque to bring the WD very close to solid body rotation during accretion. The lack of significant shear makes it difficult to grow a WD substantially past the typical Chandrasekhar mass. Once carbon ignites, a convective region spreads from the WD's center. This phase occurs regardless of progenitor scenario, and therefore it is of great interest for understanding how the WD interior is prepared before the explosive burning begins. We summarize some of the key properties of the convective region, which includes demonstrating that the mass enclosed by convection at any given time depends most sensitively on a single parameter that can be expressed as either the ratio of temperatures or densities at the top and bottom of the convection zone. At low Rossby numbers the redistribution of angular momentum by convection may result in significant shearing at the convective/non-convective boundary.
Passive spiral galaxies, despite their spiral morphological appearance, do not have any emission lines indicative of ongoing star formation in their optical spectra. Previous studies have suggested that passive spiral galaxies preferentially exist in infall regions of galaxy clusters, suggesting that the cluster environment is likely to be responsible for creating these galaxies. By carrying out spatially resolved long-slit spectroscopy on four nearby passive spiral galaxies with the Apache Point Observatory 3.5-m telescope, we investigated the stellar populations of passive spiral galaxies separately for their inner and outer regions. In the two unambiguously passive spiral galaxies among the four observed galaxies, H$\delta$ absorption lines are more prominent in the outer regions of the galaxies, whereas the 4000-{\AA} breaks (D$_{4000}$) are strongest in the inner regions of the galaxies. A comparison with a simple stellar population model for the two passive spiral galaxies indicates that the outer regions of the galaxies tend to harbour younger populations of stars. The strong H$\delta$ absorption observed in the outer regions of the sample galaxies is consistent with that of galaxies whose star formation ceased a few Gyrs ago. Because of the large uncertainty in the absorption indices in our samples, further observations are needed in order to place constraints on the mechanisms that quench star formation in passive spiral galaxies.
We have performed a two-dimensional spectroscopy of three nearby E+A (post-starburst) galaxies with the Kyoto3DII integral field spectrograph. In all the cases, Hdelta absorption is stronger at the centre of the galaxies, but significantly extended in a few kpc scale. For one galaxy (J1656), we found a close companion galaxy at the same redshift. The galaxy turned out to be a star-forming galaxy with a strong emission in Hgamma. For the other two galaxies, we have found that the central post-starburst regions possibly extend toward the direction of the tidal tails. Our results are consistent with the merger/interaction origin of E+A galaxies, where the infalling-gas possibly caused by a galaxy-galaxy merging creates a central-starburst, succeeded by a post-starburst (E+A) phase once the gas is depleted.
Using the Gemini Near-InfraRed Spectrograph (GNIRS), we have completed a near-infrared spectroscopic survey for K-bright galaxies at z~2.3, selected from the MUSYC survey. We derived spectroscopic redshifts from emission lines or from continuum features and shapes for all 36 observed galaxies. The continuum redshifts are driven by the Balmer/4000 Angstrom break, and have an uncertainty in dz/(1+z) of <0.019. We use this unique sample to determine, for the first time, how accurately redshifts and other properties of massive high-redshift galaxies can be determined from broadband photometric data alone. We find that the photometric redshifts of the galaxies in our sample have a systematic error of 0.08 and a random error of 0.13 in dz/(1+z). The systematic error can be reduced by using optimal templates and deep photometry; the random error, however, will be hard to reduce below 5%. The spectra lead to significantly improved constraints for stellar population parameters. For most quantities this improvement is about equally driven by the higher spectral resolution and by the much reduced redshift uncertainty. Properties such as the age, A_V, current star formation rate, and the star formation history are generally very poorly constrained with broadband data alone. Interestingly stellar masses and mass-to-light ratios are among the most stable parameters from broadband data. Nevertheless, photometric studies may overestimate the number of massive galaxies at 2<z<3, and thus underestimate the evolution of the stellar mass density. Finally,the spectroscopy supports our previous finding that red galaxies dominate the high-mass end of the galaxy population at z=2-3.
As first Paper of a series devoted to study the old stellar population in clusters and fields in the Small Magellanic Cloud, we present deep observations of NGC121 in the F555W and F814W filters, obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. The resulting color-magnitude diagram reaches ~3.5 mag below the main-sequence turn-off; deeper than any previous data. We derive the age of NGC121 using both absolute and relative age-dating methods. Fitting isochrones in the ACS photometric system to the observed ridge line of NGC121, gives ages of 11.8 +- 0.5 Gyr (Teramo), 11.2 +- 0.5 Gyr (Padova) and 10.5 +- 0.5 Gyr (Dartmouth). The cluster ridge line is best approximated by the alpha-enhanced Dartmouth isochrones. Placing our relative ages on an absolute age scale, we find ages of 10.9 +- 0.5 Gyr (from the magnitude difference between the main-sequence turn-off and the horizontal branch) and 11.5 +- 0.5 Gyr (from the absolute magnitude of the horizontal branch), respectively. These five different age determinations are all lower by 2 - 3 Gyr than the ages of the oldest Galactic globular clusters of comparable metallicity. Therefore we confirm the earlier finding that the oldest globular cluster in the Small Magellanic Cloud, NGC121, is a few Gyr younger than its oldest counterparts in the Milky Way and in other nearby dwarf galaxies such as the Large Magellanic Cloud, Fornax, and Sagittarius. If it were accreted into the Galactic halo, NGC121 would resemble the ''young halo globulars'', although it is not as young as the youngest globular clusters associated with the Sagittarius dwarf. The young age of NGC121 could result from delayed cluster formation in the Small Magellanic Cloud or result from the random survival of only one example of an initially small number star clusters.
Type 2 quasars are luminous active galactic nuclei (AGN) whose central regions are obscured by large amounts of gas and dust. In this paper, we present a catalog of type 2 quasars from the Sloan Digital Sky Survey (SDSS), selected based on their optical emission lines. The catalog contains 887 objects with redshifts z < 0.83; this is six times larger than the previous version and is by far the largest sample of type 2 quasars in the literature. We derive the [OIII]5008 luminosity function for 10^8.3 Lsun < L[OIII] < 10^10 Lsun (corresponding to intrinsic luminosities up to M[2400A]~-28 mag or bolometric luminosities up to 4x10^47 erg/sec). This luminosity function provides strong lower limits to the actual space density of obscured quasars, due to our selection criteria, the details of the spectroscopic target selection, as well as other effects. We derive the equivalent luminosity function for the complete sample of type 1 (unobscured) quasars; then, we determine the ratio of type 2/type 1 quasar number densities. Our best data constrain this ratio to be at least 1.5:1 for 10^8.3 Lsun < L[OIII] < 10^9.5 Lsun at z < 0.3, and at least 1.2:1 for L[OIII]=10^10 Lsun at 0.3 < z < 0.83. Type 2 quasars are at least as abundant as type 1 quasars in the relatively nearby Universe (z < 0.8) for the highest luminosities.
We investigate the evolution of $\sim$ 3 Myr-old MIPS-detected circumstellar disks in IC 348 that may be in an intermediate stage between primordial, optically-thick disks of gas/dust and debris disks characteristic of the final stages of planet formation. We demonstrate that these \textit{anemic} disks are not a homogenous class of objects corresponding to a unique evolutionary state. Rather, such disks around early (B/A) spectral type stars are most likely warm, terrestrial zone debris disks; MIPS-detected anemic disks around later (M) stars are likely \textit{evolved primordial disks} such as transition disks in their mid-IR colors, accretion signatures, and disk luminosities. Anemic disks surrounding G and K stars contain both populations. The difference in evolutionary states between anemic disks surrounding early type vs. late-type stars is consistent with a mass-dependent evolution of circumstellar disks from the primordial disk phase through the debris disk phase. Specifically, disks characteristically get to the debris disk phase faster for early-type stars; debris disks dominate the disk population of early-type stars by $\sim$ 3--5 Myr. Debris disks take $\sim$ 13--30 Myr to dominate the disk population around late-type stars.
Asymptotic Giant Branch (AGB) stars are typified by strong dust-driven, molecular outflows. For long, it was believed that the molecular setup of the circumstellar envelope of AGB stars is primarily determined by the atmospheric C/O ratio. However, recent observations of molecules such as HCN, SiO, and SO reveal gas-phase abundances higher than predicted by thermodynamic equilibrium (TE) models. UV-photon initiated dissociation in the outer envelope or non-equilibrium formation by the effect of shocks in the inner envelope may be the origin of the anomolous abundances. We aim at detecting (i.) a group of `parent' molecules (CO, SiO, HCN, CS), predicted by the non-equilibrium study of Cherchneff (2006) to form with almost constant abundances independent of the C/O ratio and the stellar evolutionary stage on the Asymptotic Giant Branch (AGB), and (ii.) few molecules, such as SiS and SO,which are sensitive to the O- or C-rich nature of the star. Several low and high excitation rotational transitions of key molecules are observed at mm and sub-mm wavelengths with JCMT and APEX in four AGB stars: the oxygen-rich Mira WX Psc, the S star W Aql, and the two carbon stars V Cyg and II Lup. A critical density analysis is performed to determine the formation region of the high-excitation molecular lines. We detect the four `parent' molecules in all four objects, implying that, indeed, these chemical species form whatever the stage of evolution on the AGB. High-excitation lines of SiS are also detected in three stars with APEX, whereas SO is only detected in the oxygen-rich star WX Psc. This is the first multi-molecular observational proof that periodically shocked layers above the photosphere of AGB stars show some chemical homogeneity, whatever the photospheric C/O ratio and stage of evolution of the star.
We consider axisymmetric relativistic jets with a toroidal magnetic field and an ultrarelativistic equation of state, with the goal of studying the lateral structure of jets whose pressure is matched to the pressure of the medium through which they propagate. We find all self-similar steady-state solutions of the relativistic MHD equations for this setup. One of the solutions is the case of a parabolic jet being accelerated by the pressure gradient as it propagates through a medium with pressure declining as p(z)\propto z^{-2}. As the jet material expands due to internal pressure gradients, it runs into the ambient medium resulting in a pile-up of material along the jet boundary, while the magnetic field acts to produce a magnetic pinch along the axis of the jet. Such jets can be in a lateral pressure equilibrium only if their opening angle \theta_j at distance z is smaller than about 1/\gamma, where \gamma is the characteristic bulk Lorentz-factor at this distance; otherwise, different parts of the jet cannot maintain causal contact. We construct maps of optically thin synchrotron emission from our self-similar models. We suggest that the boundary pile-up may be the reason for the limb-brightening of the sub-parsec jet of M87. We find that if the synchrotron emissivity falls with the distance from the jet axis, the polarization fraction rises toward the edge, as seen in 3C273 and Mkn501. Projection effects and the emissivity pattern of the jet have a strong effect on the observed polarization signal, so the interpretation of the polarization data in terms of the geometry of magnetic fields is rather uncertain. For example, jets with toroidal magnetic fields display the `spine-sheath' polarization angle pattern seen in some BL Lac objects.
We present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXB) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code (Belczynski et al., 2006), assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLF) of point sources in these galaxies. For the first time we explore the population XLF down to luminosities of 3X10^36 erg/s, as probed by the most recent observational results (Kim et al., 2006). We consider models for the formation and evolution of LMXBs in galactic fields with different CE efficiencies, stellar wind prescriptions, magnetic braking laws and initial mass functions. We identify models that produce an XLF in excellent agreement with the observations both in shape and absolute normalization. We also find that the treatment of the outburst luminosity of transient systems remains a crucial factor for the determination of the XLF since the modeled populations are dominated by transient X-ray systems.
We use numerical simulations to study the properties of substructure within galaxy-sized dark matter halos. Our study extends previous work by considering the whole population of subhalos physically associated with the main system; these are subhalos that have at some time been within the virial radius of the main progenitor and have survived as self-bound entities to z=0. We find that this population extends beyond three times the virial radius and contains objects on extreme orbits. We trace the origin of these unorthodox orbits to multiple-body interactions acting during the tidal dissociation of bound groups. Multiple-body interactions affect primarily low-mass subhalos and push them onto higher energy orbits, resulting in a strong mass-dependent bias in the spatial distribution and kinematics of associated subhalos: the lower the subhalo mass at accretion time, the less concentrated and kinematically hotter their descendant population. Our findings imply that subhalos identified within the virial radius represent an incomplete census of the substructure physically related to a halo: only about one half of all associated subhalos are found today within the virial radius of a halo, and many relatively isolated halos may have actually been ejected from a more massive system. These results may explain the age dependence of the clustering of low-mass halos, and has implications for (i) the interpretation of the structural parameters, and assembly histories of halos neighboring massive systems; (ii) the existence of dynamical outliers, such as Leo I and And XII in the Local Group; and (iii) the presence of evidence for evolutionary effects, such as tidal truncation or ram-pressure stripping, well outside the traditional virial boundary of a system.
We imaged a set of 15 intermediate redshift (z~0.8) luminous infrared galaxies (LIRGs) with the Keck Laser Guide Star (LGS) AO facility. These galaxies were selected from the GOODS-S field, allowing us to combine the high spatial resolution HST optical (B, V, i, and z-bands) images with our near-infrared (K'-band) images to study the LIRG morphologies and spatially resolved spectral energy distributions (SEDs). Two thirds of the LIRGs are disk galaxies, with only one third showing some evidence for interactions, minor, or major mergers. In contrast with local LIRG disks (which are primarily barred systems), only 10% of the LIRG disks in our sample contain a prominent bar. While the optical bands tend to show significant point-like substructure, indicating distributed star formation, the AO K-band images tend to be smooth. The SEDs of the LIRGs are consistent with distributed dusty star formation, as exhibited by optical to IR colors redder than allowed by old stellar populations alone. This effect is most pronounced in the galaxy cores, possibly indicating central star formation. We also observed a set of 11 intermediate redshift comparison galaxies, selected to be non-ellipticals with apparent K-band magnitudes comparable to the LIRGs. The "normal" (non-LIRG) systems tended to have lower optical luminosity, lower stellar mass, and more irregular morphology than the LIRGs. Half of the "normal" galaxies have SEDs consistent with intermediate aged stellar populations and minimal dust. The other half show evidence for some dusty star formation, usually concentrated in their cores. Our work suggests that the LIRG disk galaxies are similar to large disk systems today, undergoing self regulated star formation, only at 10 - 20 times higher rates. (Abridged)
We present a detailed measurement of the proper motion of the Crab pulsar, with the primary goal of comparing the direction of its proper motion with the projected axis of its pulsar wind nebula (the projected spin axis of the pulsar). We demonstrate that our measurement is robust and has an uncertainty of only +/-0.4 mas/yr on each component of the proper motion. We find mu_alpha = -11.7+/-0.4+/-0.5 mas/yr and mu_delta = +4.2+/-0.4+/-0.5 mas/yr relative to the pulsar's standard of rest, where the two uncertainties are from the measurement and the ncertainties in correcting the proper motion reference frame, respectively. Comparing this proper motion to the symmetry axis of the pulsar wind nebula, we must also consider the unknown velocity of the pulsar's progenitor (assumed to be ~10 km/s), and hence add an additional uncertainty of +/-2 mas/yr to each component of the proper motion, although this could be significantly larger. This implies a projected misalignment with the nebular axis of 14+/-2+/-9 degrees. We conclude that the precision of individual measurements which compare the direction of motion of a neutron star to a fixed axis will often be limited by fundamental uncertainties regarding reference frames and progenitor properties. The question of spin-kick (mis)alignment, and its implications for asymmetries and other processes during supernova core-collapse, is best approached by considering a statistical ensemble of such measurements, rather than detailed studies of individual sources. [abriged]
We describe a sample of thermally emitting neutron stars discovered in the ROSAT All-Sky Survey. We discuss the basic observational properties of these objects and conclude that they are nearby, middle-aged pulsars with moderate magnetic fields that we see through their cooling radiation. While these objects are potentially very useful as probes of matter at very high densities and magnetic fields, our lack of understanding of their surface emission limits their current utility. We discuss this and other outstanding problems: the spectral evolution of one sources and the relation of this population to the overall pulsar population.
A two-dimensional electrodynamic model is used to study particle acceleration
and non-thermal emission mechanisms in the pulsar magnetospheres.
We solve distribution of the accelerating electric field with the emission
process and the pair-creation process in meridional plane, which includes the
rotational axis and the magnetic axis. By solving the evolutions of the Lorentz
factor, and of the pitch angle, we calculate spectrum in optical through
$\gamma$-ray bands with the curvature radiation, synchrotron radiation, and
inverse-Compton process not only for outgoing particles, but also for ingoing
particles, which were ignored in previous studies. We apply the theory to the
Vela pulsar. We find that the curvature radiation from the outgoing particles
is the major emission process above 10 MeV bands. In soft $\gamma$-ray to hard
X-ray bands, the synchrotron radiation from the ingoing primary particles in
the gap dominates in the spectrum. Below hard X-ray bands, the synchrotron
emissions from both outgoing and ingoing particles contribute to the calculated
spectrum. The calculated spectrum is consistent with the observed
phase-averaged spectrum of the Vela pulsar. We show that the observed five-peak
pulse profile in the X-ray bands of the Vela pulsar is reproduced by the inward
and outward emissions, and the observed double-peak pulse profile in
$\gamma$-ray bands is explained by the outward emissions.
We continue our work on developing techniques for studying turbulence with spectroscopic data. We show that Doppler-broadened absorption spectral lines, in particularly, saturated absorption lines, can be used within the framework of the earlier-introduced technique termed the Velocity Coordinate spectrum (VCS). The VCS relates the statistics of fluctuations along the velocity coordinate to the statistics of turbulence, thus it does not require spatial coverage by sampling directions in the plane of the sky. We consider lines with different degree of absorption and show that for lines of optical depth less than one, our earlier treatment of the VCS developed for spectral emission lines is applicable, if the optical depth is used instead of intensity. This amounts to correlating the logarithms of absorbed intensities. For larger optical depths and saturated absorption lines, we show, that the amount of information that one can use is, inevitably, limited by noise. In practical terms, this means that only wings of the line are available for the analysis. In terms of the VCS formalism, this results in introducing an additional window, which size decreases with the increase of the optical depth. As a result, strongly saturated absorption lines carry the information only about the small scale turbulence. Nevertheless, the contrast of the fluctuations corresponding to the small scale turbulence increases with the increase of the optical depth, which provides advantages for studying turbulence combining lines with different optical depths. Combining different absorption lines one can tomography turbulence in the interstellar gas in all its complexity.
We present a high resolution dark matter reconstruction of the z=0.165 Abell 901/902 supercluster from a weak lensing analysis of the HST STAGES survey. We detect the four main structures of the supercluster at high significance, resolving substructure within and between the clusters. We find that the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. We also find a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group Abell 901alpha. We present mass, mass-to-light and mass-to-stellar mass ratio measurements of the structures and substructures that we detect. We find no evidence for variation of the mass-to-light and mass-to-stellar mass ratio between the different clusters. We compare our space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster to demonstrate the importance of space-based imaging for future weak lensing dark matter 'observations'.
We present K-band polarimetric images of several massive young stellar objects at resolutions $\sim$ 0.1-0.5 arcsec. The polarization vectors around these sources are nearly centro-symmetric, indicating they are dominating the illumination of each field. Three out of the four sources show elongated low-polarization structures passing through the centers, suggesting the presence of polarization disks. These structures and their surrounding reflection nebulae make up bipolar outflow/disk systems, supporting the collapse/accretion scenario as their low-mass siblings. In particular, S140 IRS1 show well defined outflow cavity walls and a polarization disk which matches the direction of previously observed equatorial disk wind, thus confirming the polarization disk is actually the circumstellar disk. To date, a dozen massive protostellar objects show evidence for the existence of disks; our work add additional samples around MYSOs equivalent to early B-type stars.
With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low luminosity YSOs using 3-38 um Spitzer and ground-based spectra. The long-known 6.0 and 6.85 um bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. In almost all sources the 6.0 um band is deeper than expected from the bending mode of pure solid H2O. The depth and shape variations of the remaining 5-7 um absorption indicate that it consists of 5 independent components, which, by comparison to laboratory studies, must be from at least 8 different carriers. Simple species are responsible for much of the absorption in the 5-7 um region, at abundances of 1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ~6% for H2CO, and ~0.3% for HCOO- with respect to solid H2O. The 6.85 um band likely consists of one or two carriers, of which one is less volatile than H2O because its abundance relative to H2O is enhanced at lower H2O/tau_9.7 ratios. It does not survive in the diffuse interstellar medium (ISM), however. The similarity of the 6.85 um bands for YSOs and background stars indicates that its carrier(s) must be formed early in the molecular cloud evolution. If an NH4+ salt is the carrier its abundance with respect to solid H2O is typically 7%, and low temperature acid-base chemistry or cosmic ray induced reactions must have been involved in its formation. Possible origins are discussed for the carrier of an enigmatic, very broad absorption between 5 and 8 um. Finally, all the phenomena observed for ices toward massive YSOs are also observed toward low mass YSOs, indicating that processing of the ices by internal ultraviolet radiation fields is a minor factor in the early chemical evolution of the ices. [abridged]
We examine the central-galaxy luminosity -- host-halo mass relation for 54 Brightest Group Galaxies (BGGs) and 92 Brightest Cluster Galaxies (BCGs) at z<0.1 and present the first measurement of this relation for a sample of known BCGs at 0.1<z<0.8 (average z~0.3). At z<0.1 we find L_K \propto M_{200}^{0.24\pm0.08} for the BCGs and the early-type BGGs in groups with extended X-ray emission and L_K \propto M_{200}^{0.11\pm0.10} for the BCGs alone. At 0.1<z<0.8 we find L_K \propto M_{200}^{0.28\pm0.11}. We conclude that there is no evidence for evolution in this relationship between z<0.1 and z<0.8: BCG growth appears to still be limited by the timescale for dynamical friction at these earlier times, not proceeding according to the predictions of current semi-analytic models.
$\Lambda$CDM numerical simulations predict that the "missing baryons" reside in a Warm-Hot gas phase in the over-dense cosmic filaments. However, there are now several theoretical and observational arguments that support the fact that galactic disks may be more massive than usually thought, containing a substantial fraction of the "missing baryons". Hereafter, we present new N-body simulations of galactic disks, where the gas content has been multiplied by a factor 5. The stability of the disk is ensured by assuming that the ISM is composed out of two partially coupled phases, a warm phase, corresponding the observed CO and HI gas and a cold collisionless phase corresponding to the unseen baryons.
We combine ultradeep optical spectroscopy from the GMASS project ("Galaxy Mass Assembly ultradeep Spectroscopic Survey") with GOODS multi-band photometry and HST imaging to study a sample of passive galaxiesat 1.39<z<1.99 selected at 4.5 microns. A stacked spectrum with an equivalent integration time of ~500 hours was obtained is publicly released. The spectral and photometric SED properties indicate very weak or absent star formation, moderately old stellar ages of ~1 Gyr (for solar metallicity) and stellar masses in the range of 10^{10-11} solar masses, thus implying that the major star formation and assembly processes for these galaxies occurred at z>2. These galaxies have morphologies that are predominantly compact and spheroidal.However, their sizes (R_e <~ 1 kpc) are much smaller than those of spheroids in the present--day Universe. Their stellar mass surface densities are consequently higher by ~1 dex if compared to spheroids at z~0 with the same mass. Their rest-frame B-band surface brightness scales with the effective radius, but the offset with respect to the surface brightness of the local Kormendy relation is too large to be explained by simple passive evolution. At z~1, a larger fraction of passive galaxies follows the z~0 size -- mass relation. Superdense relics with R_e~1 kpc are extremely rare at z~0 with respect to z>1, and absent if R_e<1 kpc. Because of the similar sizes and mass densities, we suggest that the superdense passive galaxies at 1<z<2 are the remnants of the powerful starbursts occurring in submillimeter--selected galaxies at z>2. The results are compared with theoretical models and the main implications discussed in the framework of massive galaxy formation and evolution.
Using our 3D Lya radiation transfer code, we compute the radiation transfer of Lya and UV continuum photons including dust. Observational constraints on the neutral gas (column density, kinematics, etc.) are taken from other analysis of this object. RESULTS: The observed Lya profile of MS 1512--cB58 is reproduced for the first time taking radiation transfer and all observational constraints into account. The observed absorption profile is found to result naturally from the observed amount of dust and the relatively high HI column density. Radiation transfer effects and suppresion by dust transform a strong intrinsic Lya emission with EW(Lya)>~ 60 Ang into the observed faint superposed Lya emission peak. We propose that the vast majority of LBGs have intrinsically EW(Lya)~60-80 Ang or larger, and that the main physical parameter responsible for the observed variety of Lya strengths and profiles in LBGs is N_H and the accompanying variation of the dust content. Observed EW(Lya) distributions, Lya luminosity functions, and related quantities must therefore be corrected for radiation transfer and dust effects. The implications from our scenario on the duty-cycle of Lya emitters are also discussed.
Post-starburst, or E+A galaxies, are the best candidates for galaxies in transition from being gas-rich and star-forming to gas-poor and passively-evolving via galaxy-galaxy mergers. To determine what E+A galaxies become after their young stellar populations fade away, we present the detailed morphologies of 21 E+As using HST images. We find that E+As are similar to early types in that they have large bulge fractions (median B/T = 0.59), high Sersic index (n > 4), and high concentration indices (C > 4.3). The large fraction (70%) of E+As with positive color gradients (i.e., bluer nuclei) indicates that the young stellar populations are more concentrated than the old populations. We show that these positive color gradients can evolve into the negative gradients typical in E/S0s if the central parts of these galaxies are metal enhanced. E+A galaxies stand apart from the E/S0s in the edge-on projection of the Fundamental Plane, implying that E+As have, on average, a M/L that is ~3.8 times smaller than that of E/S0s. The tilt of the E+A FP indicates that the variation among stellar populations in these galaxies is closely tied to their structural parameters such that smaller or less massive galaxies have smaller M/L. We find a population of unresolved compact sources in nine E+As (45%). Their colors and luminosities are consistent with the hypothesis that these are newly formed star clusters. The bright end of the cluster LF is fainter in redder E+A's, suggesting that the young star cluster systems have faded or been disrupted as the merger remnant aged. In summary, the morphologies, color profiles, scaling relations, and cluster populations are all consistent with the hypothesis that E+As galaxies are the results of mergers that evolve into early-type galaxies.
Context: Galaxy metallicities have been measured to redshift z~2 by gas-phase oxygen abundances of the interstellar medium using the R23 and N2 methods. Galaxy stellar metallicities provide crucial data for chemical evolution models but have not been assessed reliably much outside the local Universe. Aims: We determine the iron-abundance, stellar metallicity of star-forming galaxies (SFGs) at redshift z~2, observed as part of the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS). Methods: We compute the equivalent width of a rest-frame mid-ultraviolet, photospheric absorption-line index, the 1978 index found to vary monotonically with stellar metallicity by Rix and collaborators. We normalise and combine 75 SFG spectra from the GMASS survey to produce a spectrum corresponding to a total integration time 1652.5 hours (and a signal-to-noise ratio ~100 for our 1.5 angstrom binning) of FORS2 spectroscopic observations at the Very Large Telescope. Results: We measure an iron-abundance, stellar metallicity of log (Z/Zsolar) = -0.574+/-0.159 for our spectrum representative of a galaxy of stellar mass 9.4 x 10^9 Msolar assuming a Chabrier IMF. We find that the R04 model SFG spectrum for log (Z/Zsolar) = -0.699 solar metallicity provides the best description of our GMASS coadded spectrum. For similar galaxy stellar mass, our stellar metallicity is ~0.25 dex lower than the oxygen-abundance, gas-phase metallicity quantified by Erb and collaborators for UV-selected star-forming galaxies at z=2. Conclusions: We conclude that we are witnessing the establishment of a light-element overabundance in galaxies as they are being formed at redshift z~2. Our measurements are reminiscent of the alpha-element enhancement seen in low-redshift, galactic bulges and early-type galaxies. (Abridged)
If the gas in filaments and halos shares the same velocity field than the luminous matter, it will generate measurable temperature anisotropies due to the Kinematic Sunyaev-Zeldovich effect. We compute the distribution function of the KSZ signal produced by a typical filament and show it is highly non-gaussian. The combined contribution of the Thermal and Kinematic SZ effects of a filament of size $L\simeq 5$Mpc and electron density $n_e\simeq 10^3m^{-3}$ could explain the cold spots of $\delta\sim -200\mu$K on scales of 30' found in the Corona Borealis Supercluster by the VSA experiment. PLANCK, with its large resolution and frequency coverage, could provide the first evidence of the existence of filaments in this region. The KSZ contribution of the network of filaments and halo structures to the radiation power spectrum peaks around $l\sim 400$, a scale very different from that of clusters of galaxies, with a maximum amplitude $l(l+1)C_l/2\pi\sim 10-25 (\mu K)^2$, depending on model parameters, i.e., $\sigma_8$ and the Jeans length. About 80% of the signal comes from filaments with redshift $z\le 0.1$. Adding this component to the intrinsic Cosmic Microwave Background temperature anisotropies of the concordance model improves the fit to WMAP 3yr data by $\Delta\chi^2\simeq 1$. The improvement is not statistically significant but a more systematic study could demonstrate that gas could significantly contribute to the anisotropies measured by WMAP.
We study the dynamics of the closed scalar field FRW cosmological models in
the framework of the so called Unified Dark Matter (UDM) scenario. Performing a
theoretical as well as a numerical analysis we find that there is a strong
indication of chaos in agreement with previous studies. We find that a positive
value of the spatial curvature is essential for the appearance of chaoticity,
though the Lyapunov number seems to be independent of the curvature value.
Models that are close to flat exhibit a chaotic behavior after a long time
while pure flat models do not exhibit any chaos. Moreover, we find that some of
the semiflat models in the UDM scenario exhibit similar dynamical behavior with
the Lambda cosmology despite their chaoticity.
Finally, we compare the measured evolution of the Hubble parameter derived
from the differential ages of passively evolving galaxies with that expected in
the semiflat unified scalar field cosmology. Based on a specific set of initial
conditions we find that the UDM scalar field model matches well the
observational data.
Aims. We revisit the vicinity of the microquasar Cygnus X-3 at radio
wavelengths. We aim to improve our previous search for possible associated
extended radio features/hot spots in the position angle of the Cygnus X-3
relativistic jets focusing on shorter angular scales than previously explored.
Methods. Our work is mostly based on analyzing modern survey and archive
radio data, mainly including observations carried out with the Very Large Array
and the Ryle Telescopes. We also used deep near-infrared images that we
obtained in 2005.
Results. We present new radio maps of the Cygnus X-3 field computed after
combining multi-configuration Very Large Array archive data at 6 cm and
different observing runs at 2 cm with the Ryle Telescope. These are probably
among the deepest radio images of Cygnus X-3 reported to date at cm
wavelengths. Both interferometers reveal an extended radio feature within a few
arc-minutes of the microquasar position, thus making our detection more
credible. Moreover, this extended emission is possibly non-thermal, although
this point still needs confirmation. Its physical connection with the
microquasar is tentatively considered under different physical scenarios. We
also report on the serendipitous discovery of a likely Fanaroff-Riley type II
radio galaxy only 3 arc-minute away from Cygnus X-3.
We report results based on the monitoring of the BL Lac object Mrk 501 in the
optical (B, V and R) passbands from March to May 2000. Observations spread over
12 nights were carried out using 1.2 meter Mount Abu Telescope, India and 61 cm
Telescope at Sobaeksan Astronomy Observatory, South Korea. The aim is to study
the intra-day variability (IDV), short term variability and color variability
in the low state of the source. We have detected flux variation of 0.05 mag in
the R-band in time scale of 15 min in one night. In the B and V passbands, we
have less data points and it is difficult to infer any IDVs. Short term flux
variations are also observed in the V and R bands during the observing run. No
significant variation in color (B$-$R) has been detected but (V$-$R) shows
variation during the present observing run.
Assuming the shortest observed time scale of variability (15 min) to
represent the disk instability or pulsation at a distance of 5 Schwarschild
radii from the black hole (BH), mass of the central BH is estimated $\sim$ 1.20
$\times$ 10$^{8} M_{\odot}$.
We combine VLT/ISAAC NIR spectroscopy with archival HST/WFPC2 and HST/NICMOS imaging to study the central 20"x20" of M83. Our NIR indices for clusters in the circumnuclear star-burst region are inconsistent with simple instantaneous burst models. However, models of a single burst dispersed over a duration of 6 Myrs fit the data well and provide the clearest evidence yet of an age gradient along the star forming arc, with the youngest clusters nearest the north-east dust lane. The long slit kinematics show no evidence to support previous claims of a second hidden mass concentration, although we do observe changes in molecular gas velocity consistent with the presence of a shock at the edge of the dust lane.
We study clusters in the BCS cluster sample which are observed by Chandra and
are more distant than redshift, z>0.1. We select from this subsample the
clusters which have both a short central cooling time and a central temperature
drop, and also those with a central radio source. Six of the clusters have
clear bubbles near the centre. We calculate the heating by these bubbles and
express it as the ratio r_heat/r_cool=1.34+/-0.20. This result is used to
calculate the average size of bubbles expected in all clusters with central
radio sources. In three cases the predicted bubble sizes approximately match
the observed radio lobe dimensions.
We combine this cluster sample with the B55 sample studied in earlier work to
increase the total sample size and redshift range. This extended sample
contains 71 clusters in the redshift range 0<z<0.4. The average distance out to
which the bubbles offset the X-ray cooling in the combined sample is at least
r_heat/r_cool=0.92+/-0.11. The distribution of central cooling times for the
combined sample shows no clusters with clear bubbles and t_cool>1.2Gyr. An
investigation of the evolution of cluster parameters within the redshift range
of the combined samples does not show any clear variation with redshift.
We selected a sample of a dozen blazars which are the prime candidates for simultaneous multi-wavelength observing campaigns in their outburst phase. We searched for optical outbursts, intra-day variability and short term variability in these blazars. We carried out optical photometric monitoring of nine of these blazars in 13 observing nights during our observing run October 27, 2006 - March 20, 2007 by using the 1.02 meter optical telescope. From our observations, our data favor the hypothesis that three blazars were in the outburst state; one blazar was in the post outburst state; three blazars were in the pre/post outburst state; one blazar was in the low-state; and the state of one blazar was not known because there is not much optical data available for the blazar to compare with our observations. Out of three nights of observations of AO 0235+164, intra-day variability was detected in two nights. Out of five nights of observations of S5 0716+714, intra-day variability was detected in two nights. In one night of observations of PKS 0735+178, intra-day variability was detected. Out of six nights of observations of 3C 454.3, intra-day variability was detected in three nights. No intra-day variability was detected in S2 0109+224, OJ 287, ON 231, 3C 279 and 1ES 2344+514 in their 1, 4, 1, 2 and 1 nights of observations respectively. AO 0235+164, S5 0716+714, OJ 287, 3C 279 and 3C 454.3 were observed in more than one night and short term variations in all these blazars were also noticed. From our observations and the available data, we found that the predicted optical outburst with the time interval of ~ 8 years in AO 0235+164 and ~ 3 years in S5 0716+714 have possibly occurred.
Scaling relations for the mass, angular momentum and other properties of a wide range of self-similar structures in the universe are seen to have universal features. As a consequence of the ideas elaborated in earlier papers these relations can be connected to a background constant curvature given by the cosmological constant dominating cosmical dynamics.
CH4 is proposed to be the starting point of a rich organic chemistry. Solid CH4 abundances have previously been determined mostly toward high mass star forming regions. Spitzer/IRS now provides a unique opportunity to probe solid CH4 toward low mass star forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH4 abundance toward a large sample of low mass young stellar objects. 25 out of 52 ice sources in the $c2d$ (cores to disks) legacy have an absorption feature at 7.7 um, attributed to the bending mode of solid CH4. The solid CH4 / H2O abundances are 2-8%, except for three sources with abundances as high as 11-13%. These latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H2O column densities above 2E18 cm-2, the CH4 abundances (20 out of 25) are nearly constant at 4.7+/-1.6%. Correlation plots with solid H2O, CH3OH, CO2 and CO column densities and abundances relative to H2O reveal a closer relationship of solid CH4 with CO2 and H2O than with solid CO and CH3OH. The inferred solid CH4 abundances are consistent with models where CH4 is formed through sequential hydrogenation of C on grain surfaces. Finally the equal or higher abundances toward low mass young stellar objects compared with high mass objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH3OH and formation in gas phase with subsequent freeze-out.
The Milagro's observation shows that there is a strong diffuse multi-TeV $\gamma$-ray excess in the Cygnus region compared with the background estimated by GALPROP. While the GeV observation by EGRET shows no significant excess in this region (except the ``GeV excess''). It indicates that there exists high energy cosmic ray population to generate the very high energy $\gamma$-rays. We try to build theoretical models to account for this very high energy $\gamma$-ray emission from GeV to multi-TeV energy range in the Cygnus region. A diffuse source term of cosmic rays (either proton or electron), together with the background contribution from the average Galactic cosmic rays, is used to reproduce both the EGRET observational data in GeV energy range and the Milagro data in TeV range. The background is calculated using GALPROP. A dark matter contribution is introduced to account for the ``GeV excess'' problem of EGRET data. The neutrino emission associated with the hadronic interaction or the hard X-ray synchrotron radiation associated with the leptonic model is discussed as a discrimination of these scenarios. We find that both the hadronic and leptonic models can account for the current observational data. The further measurement of $\gamma$-rays to several hundred GeV by GLAST or the neutrino detection is expected to be helpful in understanding the diffuse emission mechanism of this region.
The ultraviolet spectra of all "weak emission line central stars of planetary nebulae" (WELS) with available IUE data is analyzed. We found that the WELS can be divided in three different groups regarding their UV: (1) Strong P-Cygni profiles (mainly in C IV 1549); (2) Weak P-Cygni features and (3) Absence of P-Cygni profiles. We have measured wind terminal velocities for all objects presenting P-Cygni profiles in N V 1238 and/or C IV 1549. The results obtained were compared to the UV data of the two prototype stars of the [WC]-PG 1159 class, namely, A30 and A78. They indicate that WELS are distinct from the [WC]-PG 1159 stars, in contrast to previous claims in the literature. In order to gain a better understanding about the WELS, we clearly need to determine their physical parameters and chemical abundances. First non LTE expanding atmosphere models (using the CMFGEN code) for the UV and optical spectra of the star Hen 2-12 are presented.
We derive new constraints on the mass of the Milky Way's dark matter halo, based on a set of halo stars from SDSS DR-6 as kinematic tracers. Our sample contains 2466 rigorously selected Blue Horizontal-Branch (BHB) halo stars distances from the Galactic center up to ~60 kpc. This sample enables construction of the full line-of-sight velocity distribution at different Galactocentric radii. To interpret these distributions, we compare them to matched mock observations drawn from two different cosmological galaxy formation simulations designed to resemble the Milky Way. Specifically, we select simulated halo stars in the same volume as the observations, and derive the distributions P(V_{l.o.s}/V_{cir}) of their line-of-sight velocities for different radii, normalized by the simulation's local circular velocity. We then determine which value of V_{cir}(r) brings the observed distribution into agreement with the corresponding distributions from the simulations; these values as adopted as observational estimates for V_{cir}(r) in the Milky Way's halo. This procedure results in an estimate of the Milky Way rotation curve to ~60 kpc, which is found to be slightly falling and implies M$_{\rm vir}=1.1\pm 0.2 \times 10^{12}$M$_\odot$. The radial dependence of the circular velocity is found to be consistent with the expectations from an NFW dark matter halo with the established stellar mass components at its center. If we assume an NFW halo profile of characteristic concentration holds, we can estimate the virial mass of the Milky Way's dark matter halo, M$_{vir}=1.1\pm 0.2 \times 10^{12}$M$_\odot$. This estimate implies that nearly 40% of the baryons within the virial radius of the Milky Way's dark matter halo reside in the stellar components of our Galaxy.
The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the radio and optical bands. Moreover, an extra emission component contributing to the UV and soft X-ray flux was detected, whose nature is not yet clear. A predicted optical outburst was observed in late 2006/early 2007. We here present the radio-to-optical WEBT light curves during the outburst, together with UV data acquired by Swift in the same period. We found the optical outburst to be as strong as the big outbursts of the past: starting from late September 2006, a brightness increase of 5 mag led to the outburst peak in February 19-21, 2007. We also observed an outburst at mm and then at cm wavelengths, with an increasing time delay going toward lower frequencies during the rising phase. Cross-correlation analysis indicates that the 1 mm and 37 GHz flux variations lagged behind the R-band ones by about 3 weeks and 2 months, respectively. These short time delays suggest that the corresponding jet emitting regions are only slightly separated and/or misaligned. In contrast, during the outburst decreasing phase the flux faded contemporaneously at all cm wavelengths. This abrupt change in the emission behaviour may suggest the presence of some shutdown mechanism of intrinsic or geometric nature. The behaviour of the UV flux closely follows the optical and near-IR one. By separating the synchrotron and extra component contributions to the UV flux, we found that they correlate, which suggests that the two emissions have a common origin.
Intrinsic stellar variability can hinder the detection of shallow transits, particularly in space-based data. Therefore, this variability has to be filtered out before running the transit search. Unfortunately, filtering out the low frequency signal of the stellar variability also modifies the transit shape. This results in errors in the measured transit depth and duration used to derive the planet radius, and orbital inclination. We present an evaluation of the magnitude of this effect based on 20 simulated light curves from the CoRoT blind exercise 2 (BT2). We then present an iterative filter which uses the strictly periodic nature of the transits to separate them from other forms of variability, so as to recover the original transit shape before deriving the planet parameters. On average with this filter, we improve the estimation of the transit depth and duration by 15% and 10% respectively.
Observations with the Hinode spectro-polarimeter have revealed strong horizontal internetwork magnetic fields in the quiet solar photosphere. We aim at interpreting the observations by means of results from numerical simulations. Radiative MHD simulations of dynamo action by near-surface convection are analyzed with respect to the relation between vertical and horizontal magnetic field components. The dynamo-generated fields show a clear dominance of the horizontal field in the height range where the spectral lines used for the observations are formed. The ratio between the averaged horizontal and vertical field components is consistent with the values derived from the observations. This behavior results from the intermittent nature of the dynamo field with polarity mixing on small scales in the surface layers. Our results provide further evidence that local near-surface dynamo action contributes significantly to the solar internetwork fields.
The nature of the extended hard X-ray source XMMU J061804.3+222732 and its surroundings is investigated using XMM-Newton, Chandra, and Spitzer observations. This source is located in an interaction region of the IC 443 supernova remnant with a neighboring molecular cloud. The X-ray emission consists of a number of bright clumps embedded in an extended structured non-thermal X-ray nebula larger than 30" in size. Some clumps show evidence for line emission at ~1.9 keV and ~3.7 keV at the 99% confidence level. Large-scale diffuse radio emission of IC 443 passes over the source region, with an enhancement near the source. An IR source of about 14" x 7" size is prominent in the 24 um, 70 um, and 2.2 um bands, adjacent to a putative Si K-shell X-ray line emission region. The observed IR/X-ray morphology and spectra are consistent with those expected for J/C-type shocks of different velocities driven by fragmented supernova ejecta colliding with the dense medium of a molecular cloud. The IR emission of the source detected by Spitzer can be attributed to both continuum emission from an HII region created by the ejecta fragment and line emission excited by shocks. This source region in IC 443 may be an example of a rather numerous population of hard X-ray/IR sources created by supernova explosions in the dense environment of star-forming regions. Alternative Galactic and extragalactic interpretations of the observed source are also discussed.
It is widely accepted that the large obliquity of Uranus is the result of a great tangential collision (GC) with an Earth size proto-planet at the end of the accretion. We attempt to constraint the GC scenario as the cause of Uranus' obliquity as well as on the mechanisms able to give origin to the Uranian irregulars. Different capture mechanisms for irregulars operate at different stages on the giant planets formation process. The mechanisms able to capture the uranian irregulars before and after the GC are analysed. Assuming that they were captured before the GC, we calculate the orbital transfer of the nine irregulars by the impulse imparted by the GC. If their orbital transfer results dynamically implausible, they should have originated after the GC. We investigate and discuss the dissipative mechanisms able to operate later. In particular Prospero could not exist at the time of the GC. Different capture mechanisms for Prospero after the GC are investigated. Gas drag by Uranus'envelope and pull-down capture are not plausible mechanisms. Capture of Prospero through a collisionless interaction seems to be difficult. The GC itself provides a mechanism of permanent capture. However, the capture of Prospero by the GC is a low probable event. Catastrophic collisions could be a possible mechanism for the birth of Prospero and the other irregulars after the GC. Orbital and physical clusterings should then be expected. Either Prospero had to originate after the GC or the GC did not occur. In the former case, the mechanism for the origin of Prospero after the GC remains an open question. In the latter case, another theory to account for Uranus' obliquity and the formation of the Uranian regular satellites on the equatorial plane of the planet would be needed.
In the present paper, we have reported the result of simultaneous multi-wavelength observations of the TeV blazar Mrk 421 during February $-$ March 2003. In this period, we have observed Mrk 421 using Pachmarhi Array of \v{C}erenkov Telescopes (PACT) of Tata Institute of Fundamental Research at Pachmarhi, India. Other simultaneous data were taken from the published literature and public data archives. We have analyzed the high quality X-ray (2-20 keV) observations from the NASA Rossi X-Ray Timing Explorer (RXTE). We have seen a possible correlated variability between X-ray and J band (1.25 $\mu$) near infrared (NIR) wavelength. This is the first case of X-ray and NIR correlated variability in Mrk 421 or any high energy peaked (HBL) blazar. The correlated variability reported here is indicating a similar origin for NIR and X-ray emission. The emission is not affected much by the environment of the surrounding medium around the central engine of the Mrk 421. The observations are consistent with the shock-in-jet model for the emission of radiations.
It is been known for more than a decade that BALQSOs (broad absorption line quasars) are highly attenuated in the X-ray regime compared to other quasars, especially in the soft band ($< $ 1 keV). Using X-ray selection techniques we have found "soft X-ray loud" BALQSOs that, by definition, have soft X-ray (0.3 keV) to UV ($3000 \AA$) flux density ratios that are higher than typical nonBAL radio quiet quasars. Our sample of 3 sources includes one LoBALQSO (low ionization BALQSO) which are generally considered to be the most highly attenuated in the X-rays. The three QSOs are the only known BALQSOs that have X-ray observations that are consistent with no intrinsic soft X-ray absorption. The existence of a large X-ray luminosity and the hard ionizing continuum that it presents to potential UV absorption gas is in conflict with the ionization states that are conducive to line driving forces within BAL winds (especially for the LoBALs).
Phase self-calibration (or selfcal) is an algorithm often used in the calibration of interferometric observations in astronomy. Although a powerful tool, this algorithm presents strong limitations when applied to data with a low signal-to-noise ratio. We analyze the artifacts that the phase selfcal algorithm produces when applied to extremely noisy data. We show how the phase selfcal may generate a spurious source in the sky from a distribution of completely random visibilities. This spurious source is indistinguishable from a real one. We numerically and analytically compute the relationship between the maximum spurious flux density generated by selfcal from noise and the particulars of the interferometric observations. Finally, we present two simple tests that can be applied to interferometric data for checking whether a source detection is real or whether the source is an artifact of the phase self-calibration algorithm.
We compare the X-ray spectra and luminosities, in the 2-8 keV band, of known and suspected cataclysmic variables (CVs) in different environments, assessing the nature of these source populations. These objects include nearby CVs observed with ASCA; the Galactic Center X-ray source population identified by Muno et al.; and likely CVs identified in globular clusters. Both of the latter have been suggested to be dominated by magnetic CVs. We find that the brighter objects in both categories are likely to be magnetic CVs, but that the fainter objects are likely to include a substantial contribution from normal CVs. The strangely hard spectra observed from the Galactic Center sources reflect the high and variable extinction, which is significantly greater than the canonical 6e22 /cm2 over much of the region, and the magnetic nature of many of the brightest CVs. The total numbers of faint Galactic Center sources are compatible with expectations of the numbers of CVs in this field.
In ESO period 65 (April-September 2000) the large programme 165.N-0276, led by Roger Cayrel, began making use of UVES at the Kueyen VLT telescope. Known within the Team and outside as ``First Stars'', it was aimed at obtaining high resolution, high signal-to-noise ratio spectra in the range 320 nm -- 1000 nm for a large sample of extremely metal-poor (EMP) stars identified from the HK objective prism survey.In this contribution we highlight the main results of the large programme.
Over a timescale of a few years, an observed change in the optically thick radio continuum flux can indicate whether an unresolved H II region around a newly formed massive star is changing in size. In this Letter we report on a study of archival VLA observations of the hypercompact H II region G24.78+0.08 A1 that shows a decrease of ~ 45 % in the 6-cm flux over a five year period. Such a decrease indicates a contraction of ~ 25 % in the ionized radius and could be caused by an increase in the ionized gas density if the size of the H II region is determined by a balance between photoionization and recombination. This finding is not compatible with continuous expansion of the H II region after the end of accretion onto the ionizing star, but is consistent with the hypothesis of gravitational trapping and ionized accretion flows if the mass-accretion rate is not steady.
We analyze the non-gaussian density perturbations generated in ekpyrotic/cyclic models based on heterotic M-theory. In this picture, two scalar fields produce nearly scale-invariant entropic perturbations during an ekpyrotic phase that are converted into curvature modes {\it after the ekpyrotic phase is complete} and just before the big bang. Both intrinsic non-linearity in the entropy perturbation and the conversion process contribute to non-gaussianity. The range of the non-gaussianity parameter $f_{NL}$ depends on how gradual the conversion process is and the steepness of the scalar field potential during the ekpyrotic phase. Although a wider range is possible, in principle, natural values of the ekpyrotic parameters combined with a gradual conversion process lead to values of $-50 \lesssim f_{NL} \lesssim +200$, typically much greater than slow-roll inflation but within the current observational bounds.
We build a minimal cosmological model in higher dimensions based on a hidden sector gauge theory, which is less constrained by the low energy experiments. In this model we introduce the minimal non-Abelian gauge symmetry SU(2) in the fifth spatial dimension. The inflaton field which is identified as a part of higher dimensional gauge boson is protected by the gauge symmetry. Thus the inflaton potential is fully radiatively generated by the gauge self interaction alone without introducing any ad hoc field. and is flat enough to drive slow-roll inflation. We find that in the regime of perturbative gauge interaction and large compactification radius the anticipated magnitude of the curvature perturbation power spectrum and the value of the corresponding spectral index are in perfect agreement with the recent observations in a wide range of the model parameters. The model also predicts a large fraction of the gravitational waves, negligible non-Gaussianity, and high enough reheating temperature.
We investigate early time inflationary scenarios in an Universe filled with a dilute noncommutative bosonic gas at high temperature. A noncommutative bosonic gas is a gas composed of bosonic scalar field with noncommutative field space on a commutative spacetime. Such noncommutative field theories was recently introduced as a generalization of quantum mechanics on a noncommutative spacetime. As key features of these theories are Lorentz invariance violation and CPT violation. In the present study we use a noncommutative bosonic field theory that besides the noncommutative parameter $\theta$ shows up a further parameter $\sigma$. This parameter $\sigma$ controls the range of the noncommutativity and acts as a regulator for the theory. Both parameters play a key role in the modified dispersion relations of the noncommutative bosonic field, leading to possible striking consequences for phenomenology. In this work we obtain an equation of state $p=\omega(\sigma,\theta;\beta)\rho$ for the noncommutative bosonic gas relating pressure $p$ and energy density $\rho$, in the limit of high temperature. We analyse possible behaviours for this gas parameters $\sigma$, $\theta$ and $\beta$, so that $-1\leq\omega<-1/3$, which is the region where the Universe enters an accelerated phase.
In this paper we determine the tidal distortion parameter k_m of the secondary partner (mass loser) of the semi-detached eclipsing binary system V621 Cen by comparing the phenomenologically determined orbital period P_b=3.683549(11) d to the Keplerian one P^Kep computed with the values of the relevant system's parameters determined independently of the third Kepler law itself. Our result is k_m = -1.5 +/- 0.6. Using the periastron precession, as traditionally done with other eclipsing binaries in eccentric orbits, would have not been possible because of the circularity of the V621 Cen path.
We construct an effective field theory (EFT) to derive the self-force on a compact object moving in the background spacetime of a supermassive black hole. The EFT approach utilizes the disparity between two length scales, the size of the compact object $r_m$ and the radius of curvature of the background spacetime $\cR$ such that $\mu \equiv r_m / \cR \ll 1$, to treat the orbital dynamics of the compact object, described as an effective point particle, separately from its tidal deformations. The equation of motion of an effective relativistic point particle coupled to the gravitational waves generated by its motion in a curved background spacetime can be derived without making a slow motion or weak field approximation, as was assumed in earlier EFT treatment of post-Newtonian binaries. Ultraviolet divergences are regularized using Hadamard's {\it partie finie} to isolate the non-local finite part from the quasi-local divergent part. The latter is constructed from a momentum space representation for the graviton retarded propagator and is evaluated using dimensional regularization in which only logarithmic divergences are relevant for renormalizing the parameters of the theory. As an important application of this framework we explicitly derive the first order self-force given by Mino, Sasaki, Tanaka, Quinn and Wald. Going beyond the point particle approximation, to account for the finite size of the object, we demonstrate that for extreme mass ratio inspirals the motion of a compact object is affected by tidally induced moments at $O(\mu^4)$, in the form of an Effacement Principle. This work provides a new foundation for further exploration of higher order self force corrections, gravitational radiation and spinning compact objects.
Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.
We determine the full post-Newtonian limit of theories of gravity that extend general relativity by replacing the Ricci scalar, R, in the generating Lagrangian by some analytic function, f(R). We restrict ourselves to theories that admit Minkowski space as a suitable background, and perform a perturbative expansion in the manner prescribed by the parameterised post-Newtonian formalism. Extra potentials are found to be present that are not accounted for in the usual treatment, and a discussion is provided on how they may be used to observationally distinguished these theories from general relativity at the post-Newtonian level.
We study the linear perturbations of multi-field inflationary models governed by a Lagrangian which is a general function of the scalar fields and of a global kinetic term combining their spacetime gradients with an arbitrary field space metric. Our analysis includes k-inflation, DBI inflation and its multi-field extensions which have been recently studied. For this general class of models, we calculate the action to second order in the linear perturbations. We decompose the perturbations into an (instantaneous) adiabatic mode, parallel to the background trajectory, and entropy modes. We show that all the entropy modes propagate with the speed of light whereas the adiabatic mode propagates with an effective speed of sound. We also identify the specific combination of entropy modes which sources the curvature perturbation on large scales. We then study in some detail the case of two scalar fields: we write explicitly the equations of motion for the adiabatic and entropy modes in a compact form and discuss their quantum fluctuations and primordial power spectra.
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Aims: To determine alpha effect and turbulent magnetic diffusivity for mean magnetic fields with profiles of different length scale from simulations of isotropic turbulence, and to relate these results to nonlocal formulations in which alpha and the turbulent magnetic diffusivity correspond to integral kernels. Methods: A set of evolution equations for magnetic fields is solved which gives the response to imposed test fields, that is, mean magnetic fields with various wavenumbers. Both an imposed fully helical steady flow consisting of a pattern of screw-like motions (Roberts flow) and time-dependent statistically steady isotropic turbulence are considered. In the latter case the aforementioned evolution equations are solved simultaneously with the momentum and continuity equations. The corresponding results for the electromotive force are used to calculate alpha and magnetic diffusivity tensors. Results: For both the Roberts flow under the second--order correlation approximation and isotropic turbulence alpha and turbulent magnetic diffusivity are largest at large scales and these values diminish toward smaller scales. In both cases the alpha effect and turbulent diffusion kernels are well approximated by exponentials, corresponding to Lorentzian profiles in Fourier space. For isotropic turbulence the turbulent diffusion kernel is half as wide as the alpha effect kernel. For the Roberts flow beyond the second--order correlation approximation the turbulent diffusion kernel becomes negative at large scales.
Following unstable ignition of carbon, but prior to explosion, a white dwarf (WD) in a Type Ia supernova (SN Ia) undergoes a simmering phase. During this time, a central convective region grows and encompasses ~1 Msun of the WD over a timescale of ~1000 yrs, which sets the thermal and turbulent profile for the subsequent explosion. We study this time-dependent convection and summarize some of the key features that differ from the traditional, steady-state case. We show that the long conductive timescale above the convective zone and the extraction of energy to heat the WD core leads to a decrease of the convective luminosity and characteristic velocities near the convective zone's top boundary. In addition, differences in the composition between the convective core and the conductive exterior will significantly alter the location of this boundary. In this respect, we find the biggest effect due to complete 22Ne sedimentation prior to carbon ignition. These effects add diversity to the possible WD models, which may alter the properties of the SN Ia explosion.
We study the afterglow phases of a GRB through relativistic magnetohydrodynamic simulations. The evolution of a relativistic shell propagating into a homogeneous external medium is followed. We focus on the effect of the magnetization of the ejecta on the initial phases of the ejecta-external medium interaction. In particular we are studying the condition for the existence of a reverse shock into the ejecta, the timescale for the transfer of the energy from the shell to the shocked medium and the resulting multiwavelength light curves. To this end, we have developed a novel scheme to include non-thermal processeses which is coupled to the relativistic magnetohydrodynamic code MRGENESIS in order to compute the non-thermal synchrotron radiation.
As part of an effort to understand the origin of open clusters, we present a statistical analysis of the currently observed Pleiades. Starting with a photometric catalog of the cluster, we employ a maximum likelihood technique to determine the mass distribution of its members, including single stars and both components of binary systems. We find that the overall binary fraction for unresolved pairs is 68%. Extrapolating to include resolved systems, this fraction climbs to about 76%, significantly higher than the accepted field-star result. Both figures are sensitive to the cluster age, for which we have used the currently favored value of 125 Myr. The primary and secondary masses within binaries are correlated, in the sense that their ratios are closer to unity than under the hypothesis of random pairing. We map out the spatial variation of the cluster's projected and three-dimensional mass and number densities. Finally, we revisit the issue of mass segregation in the Pleiades. We find unambiguous evidence of segregation, and introduce a new method for quantifying it.
The celestial phenomenon have always been a source of wonder and interest to people, even as long ago as the ancient Egyptians. While the ancient Egyptians did not know all the things about astronomy that we do now, they had a good understanding of the some celestial phenomenon. The achievements in astronomy of ancient Egyptians are relatively well known, but we know very little about the people who made these achievements. The goal of this paper is to bring some light on the life of Senenmut, the chief architect and astronomer during the reign of Queen Hatshepsut.
A review of theoretical results on cosmic ray first-order Fermi acceleration
at relativistic shock waves is presented, with recent results substantially
changing the existing knowledge on these processes. In particular one can not
expect such shocks to form particle distributions extending to very high
energies. Instead, distributions with the shock compressed injected component
followed by a more or less extended high energy tail are usually created.
Increasing the shock Lorentz factor leads to steepening of the energetic tail.
An observational check of real electron spectra in the Cyg A hot spots
provides results clearly deviating from the standard expectations. The spectrum
consist of a very flat low energy part (sigma ~1.5)up to electron energies ~1
GeV, and a much steeper part (sigma > 3)at higher energies. We conclude with
remarks on the Fermi second-order processes acting in relativistic plasmas,
possibly the main accelerating agent for very high energy cosmic rays.
We present recent results from several on-going studies: The first addresses the question of gas-density thresholds for star formation, as probed by the outer disks of normal nearby galaxies. The second concerns the observational evidence for the existence of gravitating non-luminous (GNL) galaxies, as predicted by most recent simulations of galaxy formation in Lambda-CDM cosmologies. We find that (1) If star formation is traced by far-ultraviolet light, then there is no evidence for a threshold to star formation at any gas density so far probed, and (2) there is no evidence for GNL galaxies gravitationally interacting with known optical systems based on the observations (a) that there are no ring galaxies without plausible optically visible intruders, (b) all peculiar galaxies in the Arp Atlas that are bodily distorted have nearby plausibly interacting companions, and (c) there are no convincingly distorted/peculiar galaxies within Karachentsev's sample of more than 1,000 apparently/optically isolated galaxies.
I investigate the discrepancy between the evolution and pulsation masses for Cepheid variables. A number of recent works have proposed that non-canonical mass-loss can account for the mass discrepancy. This mass-loss would be such that a 5Mo star loses approximately 20% of its mass by arriving at the Cepheid instability strip; a 14Mo star, none. Such findings would pose a serious challenge to our understanding of mass-loss. I revisit these results in light of the Padova stellar evolutionary models and find evolutionary masses are ($17\pm5$)% greater than pulsation masses for Cepheids between 5<M/Mo<14. I find that mild internal mixing in the main-sequence progenitor of the Cepheid are able to account for this mass discrepancy.
We present new observations of the white dwarf sequence of the old open cluster NGC 6791. The brighter peak previously observed in the white dwarf luminosity function (WDLF) is now better delineated, and the second, fainter peak that we suggested earlier is now confirmed. A careful study suggests that we have reached the end of the white dwarf sequence. The WDs that create the two peaks in the WDLF show a significant turn to the blue in the color-magnitude diagram. The discrepancy between the age from the WDs and that from the main sequence turnoff remains, and we have an additional puzzle in the second peak in the WDLF. Canonical WD models seem to fail --at least at ~25%-level-- in reproducing the age of clusters of this metallicity. We discuss briefly possible ways of arriving at a theoretical understanding of the WDLF.
The central star of this nebula has an observed intense magnetic field and the fast wind is no longer present, indicating that a back flow process has probably developed. Long-slit, spatially resolved echelle spectra have been obtained across the main body of NGC 1360 and over its system of bipolar jets. Deep images of the knotty structures of the jets have also been obtained. The data allow a detailed study of the structure and kinematics of this object and the results are modeled considering the effects of a magnetic collimation process in the development of the nebula and then switching off the fast stellar wind to follow its evolution to its current state. The model is able to successfully reproduce many of the key features of NGC 1360 under these premises.
In Roukema et al. 2004 it was suggested that the topology of the Universe as probed by the ``matched circles'' method in the first year release of the WMAP CMB data, might be that of the Poincare dodecahedral space (PDS) model. In that paper, an excess in the correlation of the ``identified circles'' was found, for the circles of angular radius of ~11 deg. for a relative phase twist -36 deg., hinting that this was due to a Clifford translation, if the hypothesized model was true. However in that work the statistical significance of the signal was not specified. In this paper we investigate the statistical significance of that result using Monte Carlo CMB simulations in a simply connected Universe, and also present the updated results from the extended search in the three year WMAP data. We find that both first and three year WMAP data are consistent with the simply connected space at confidence level as low as 68%.
Magnetars (SGRs and AXPs) are one of the most evolutionary paths of a neutron star. These objects have an ultra-strong magnetic field $B \sim 10^{15}$ G at their surface and show persistent X-ray pulsations and transient bursts. Till date there are 14 magnetars known: 5 SGRs (4 confirmed, 1 candidate) and 9 AXPs (7 confirmed, 2 candidates). It is an open puzzle that all these objects are isolated and none have been found in binaries. We discuss the formation scenario which can lead to such a situation.
We have investigated the formation of close-in extrasolar giant planets through a coupling effect of mutual scattering, Kozai mechanism, and tidal circularization, by orbital integrations. We have carried out orbital integrations of three planets with Jupiter-mass, directly including the effect of tidal circularization. We have found that in about 30% runs close-in planets are formed, which is much higher than suggested by previous studies. We have found that Kozai mechanism by outer planets is responsible for the formation of close-in planets. During the three-planet orbital crossing, the Kozai excitation is repeated and the eccentricity is often increased secularly to values close enough to unity for tidal circularization to transform the inner planet to a close-in planet. Since a moderate eccentricity can remain for the close-in planet, this mechanism may account for the observed close-in planets with moderate eccentricities and without nearby secondary planets. Since these planets also remain a broad range of orbital inclinations (even retrograde ones), the contribution of this process would be clarified by more observations of Rossiter-McLaughlin effects for transiting planets.
Context: Supergranulation is a pattern of the velocity field at the surface
of the Sun, which has been known about for more than fifty years, however, no
satisfactory explanation of its origin has been proposed. Aims: New
observational constraints are therefore needed to guide theoretical approaches
which hesitate between scenarios that either invoke a large-scale instability
of the surface turbulent convection or a direct forcing by buoyancy. Method:
Using the 14-Mpixel CALAS camera at the Pic-du-Midi observatory, we obtained a
7.5h-long sequence of high resolution images with unprecedented field size.
Tracking granules, we have determined the velocity field at the Sun's surface
in great detail from a scale of 2.5Mm up to 250Mm.
Results: The kinetic energy density spectrum shows that supergranulation
peaks at 36Mm and spans on scales ranging between 20Mm and 75Mm. The decrease
of supergranular flows in the small scales is close to a $k^{-2}$-power law,
steeper than the equipartition Kolmogorov one. The probability distribution
function of the divergence field shows the signature of intermittency of the
supergranulation and thus its turbulent nature.
We discuss some implications of our recent detection of extragalactic H3O+: the location of the gas in M82, the origin of energetic radiation in M82, and the possible feedback effects of star formation on the cosmic ray flux in galaxies.
We present semi-analytic models of galactic outflows, constrained by available observations on high redshift star formation and reionization. Galactic outflows are modeled in a manner akin to models of stellar wind blown bubbles. Large scale outflows can generically escape from low mass halos (M<10^9 M_sun) for a wide range of model parameters but not from high mass halos (M> 10^{11} M_sun). The gas phase metallicity of the outflow and within the galaxy are computed. Ionization states of different metal species are calculated and used to examine the detectability of metal lines from the outflows. The global influence of galactic outflows is also investigated. Models with only atomic cooled halos significantly fill the IGM at z~3 with metals (with -2.5>[Z/Z_sun]>-3.7), the actual extent depending on the efficiency of winds, the IMF, the fractional mass that goes through star formation and the reionization history of the universe. In these models, a large fraction of outflows at z~3 are supersonic, hot (T> 10^5 K) and have low density, making metal lines difficult to detect. They may also result in significant perturbations in the IGM gas on scales probed by the Lyman-alpha forest. On the contrary, models including molecular cooled halos with a normal mode of star formation can potentially volume fill the universe at z> 8 without drastic dynamic effects on the IGM, thereby setting up a possible metallicity floor (-4.0<[Z/Z_sun]<-3.6). Interestingly, molecular cooled halos with a ``top-heavy'' mode of star formation are not very successful in establishing the metallicity floor because of the additional radiative feedback, that they induce. (Abridged)
We explore the importance of magnetic-field-oriented thermal conduction in the interaction of supernova remnant (SNR) shocks with radiative gas clouds and in determining the mass and energy exchange between the clouds and the hot surrounding medium. We perform 2.5D MHD simulations of a shock impacting on an isolated gas cloud, including anisotropic thermal conduction and radiative cooling; we consider the representative case of a Mach 50 shock impacting on a cloud ten-fold denser than the ambient medium. We consider different configurations of the ambient magnetic field and compare MHD models with or without the thermal conduction. The efficiency of the thermal conduction in the presence of magnetic field is, in general, reduced with respect to the unmagnetized case. The reduction factor strongly depends on the initial magnetic field orientation, and it is minimum when the magnetic field is initially aligned with the direction of shock propagation. The thermal conduction contributes to suppress hydrodynamic instabilities, reducing the mass mixing of the cloud and preserving the cloud from complete fragmentation. Depending on the magnetic field orientation, the heat conduction may determine a significant energy exchange between the cloud and the hot surrounding medium which, while remaining always at levels less than those in the unmagnetized case, leads to a progressive heating and evaporation of the cloud. This additional heating may contrast the radiative cooling of some parts of the cloud, preventing the onset of thermal instabilities.
8-Gsps 1-bit Analog-to-Digital Converters (ADCs) were newly developed toward the realization of the wideband observation. The development of the wideband ADCs is one of the most essential developments for the radio interferometer. To evaluate its performance in interferometric observations, the time (phase) stability and frequency response were measured with a noise source and a signal generator. The results of these measurements show that the developed ADCs can achieve the jitter time less than 0.05 psec at the time interval of 1 sec, the passband frequency response with the slope less than 0.73 dB/GHz and the ripple less than 1.8 dB, and the aperture time less than 20 psec. The details of the developed ADC design, the measurement methods, and the results of these measurements are presented in this paper.
We calculate the wavelength dependence of the ratio of the linear polarization degree to extinction (polarizing efficiency) $P(\lambda)/A(\lambda)$ from the ultraviolet to near-infrared. The prolate and oblate particles with aspect ratios from $a/b=1.1$ up to 10 are assumed to be rotating and partially aligned with the mechanism of paramagnetic relaxation (Davis--Greenstein). Size/shape/orientation effects are analyzed. It is found that the wavelength dependence of $P(\lambda)/A(\lambda)$ is mainly determined by the particle composition and size whereas the values of $P(\lambda)/A(\lambda)$ depend on the particle shape, degree and direction of alignment.
We study perturbation of holographic dark energy, and find it be stable. We make a simple and phenomenological classification of the interacting holographic dark energy. We also discussed the cosmic coincidence problem in the context of holographic dark energy.
In this short note I discuss the hypothesis that bursting activity of magnetars evolves in time analogously to the glitching activity of normal radio pulsars (i.e. sources are more active at smaller ages), and that the increase of the burst rate follows one of the laws established for glitching radio pulsars. If the activity of soft gamma repeaters decreases in time in the way similar to the evolution of core-quake glitches ($\propto t^{5/2}$), then it is more probable to find the youngest soft gamma repeaters, but the energy of giant flares from these sources should be smaller than observed $10^{44}$ --$10^{46}$ ergs as the total energy stored in a magnetar's magnetic field is not enough to support thousands of bursts similar to the prototype 5 March 1979 flare.
We present a spatially resolved 894 micron map of the circumstellar disk of the Butterfly star in Taurus (IRAS 04302+2247), obtained with the Submillimeter Array (SMA). The predicted and observed radial brightness profile agree well in the outer disk region, but differ in the inner region with an outer radius of ~80-120 AU. In particular, we find a local minimum of the radial brightness distribution at the center, which can be explained by an increasing density / optical depth combined with the decreasing vertical extent of the disk towards the center. Our finding indicates that young circumstellar disks can be optically thick at wavelengths as long as 894 micron. While earlier modeling lead to general conclusions about the global disk structure and, most importantly, evidence for grain growth in the disk (Wolf, Padgett, & Stapelfeldt 2003), the presented SMA observations provide more detailed constraints for the disk structure and dust grain properties in the inner, potentially planet-forming region (inside ~80-120 AU) vs. the outer disk region (~120-300 AU).
We perform a combined X-ray and strong lensing analysis of RX J1347.5-1145, one of the most luminous galaxy clusters at X-ray wavelengths. We show that evidence from strong lensing alone, based on published VLT and new HST data, strongly argues in favor of a complex structure. The analysis takes into account arc positions, shapes and orientations and is done thoroughly in the image plane. The cluster inner regions are well fitted by a bimodal mass distribution, with a total projected mass of $M_{tot} = (9.9 \pm 0.3)\times 10^{14} M_\odot/h$ within a radius of $360 \mathrm{kpc}/h$ ($1.5'$). Such a complex structure could be a signature of a recent major merger as further supported by X-ray data. A temperature map of the cluster, based on deep Chandra observations, reveals a hot front located between the first main component and an X-ray emitting South Eastern sub-clump. The map also unveils a filament of cold gas in the innermost regions of the cluster, most probably a cooling wake caused by the motion of the cD inside the cool core region. A merger scenario in the plane of the sky between two dark matter sub-clumps is consistent with both our lensing and X-ray analyses, and can explain previous discrepancies with mass estimates based on the virial theorem.
Frequencies, powers and damping rates of the solar p modes are all observed to vary over the 11-yr solar activity cycle. Here, we show that simultaneous variations of these parameters give rise to a subtle cross-talk effect, which we call the ``devil in the detail'', that biases p-mode frequencies estimated from analysis of long power frequency spectra. We also show that the resonant peaks observed in the power frequency spectra show small distortions due to the effect. Most of our paper is devoted to a study of the effect for Sun-as-a-star observations of the low-l p modes. We show that for these data the significance of the effect is marginal. We also touch briefly on the likely l dependence of the effect, and discuss the implications of these results for solar structure inversions.
This is a brief review on the history of the BEC or boson star model of galactic dark matter halos, where ultra-light scalar dark matter particles condense in a single BEC quantum state. The halos can be described as self-gravitating coherent scalar field, possibly self-interacting. On the scale larger than galaxies, dark matter behaves like cold dark matter, while below the scale quantum mechanical nature suppresses structure formation due to the minimum length scale determined by the mass $m\st{>}{\sim}10^{-24} eV$ and self-interaction among the particles. This property could alleviate the cusp problem and missing satellite problems of the $\Lambda$CDM model. Furthermore, this model well reproduces the observed rotation curves of spiral and dwarf galaxies, which makes the model very promising.
Gamma-Ray Burst (GRB) afterglow observations in the Swift era have a
perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift
era. Specifically, relatively few breaks, consistent with jet breaks, are
observed in the X-ray light curves of these bursts. If these breaks are truly
missing, it has serious consequences for the interpretation of GRB jet
collimation and energy requirements, and the use of GRBs as standard candles.
Here we address the issue of X-ray breaks which are possibly 'hidden' and
hence the light curves are misinterpreted as being single power-laws. We show
how a number of precedents, including GRB 990510 & GRB 060206, exist for such
hidden breaks and how, even with the well sampled light curves of the Swift
era, these breaks may be left misidentified. We do so by synthesising X-ray
light curves and finding general trends via Monte Carlo analysis. Furthermore,
in light of these simulations, we discuss how to best identify achromatic
breaks in afterglow light curves via multi-wavelength analysis.
This paper provides an analytical description of the transport of ultra-high energy cosmic rays in an inhomogeneously magnetized intergalactic medium. This latter is modeled as a collection of magnetized scattering centers such as radio cocoons, magnetized galactic winds, clusters or magnetized filaments of large scale structure, with negligible magnetic fields in between. Magnetic deflection is no longer a continuous process, it is rather dominated by scattering events. We study the interaction between high energy cosmic rays and the scattering agents. We then compute the optical depth of the Universe to cosmic ray scattering and discuss the phenomological consequences for various source scenarios. For typical parameters of the scattering centers, the optical depth is greater than unity at 5.10^{19}eV, but the total angular deflection is smaller than unity. One important consequence of this scenario is the possibility that the last scattering center encountered by a cosmic ray be mistaken with the source of this cosmic ray. In particular, we suggest that at least part of the correlation recently reported by the Pierre Auger Observatory may be affected by such delusion: this experiment may be observing the last scattering surface of ultra-high energy cosmic rays rather than their source population. Since the optical depth falls rapidly with increasing energy, one should probe the arrival directions of the highest energy events beyond 10^{20}eV on an event by event basis to circumvent this effect.
We predict how protoplanetary disks around low-mass young stars would appear in molecular lines observed with the ALMA interferometer. Our goal is to identify those molecules and transitions that can be used to probe and distinguish between chemical and physical disk structure and to define necessary requirements for ALMA observations. Disk models with and without vertical temperature gradient as well as with uniform abundances and those from a chemical network are considered. As an example, we show the channel maps of HCO$^+$(4-3) synthesized with a non-LTE line radiative transfer code and used as an input to the GILDAS ALMA simulator to produce noise-added realistic images. The channel maps reveal complex asymmetric patterns even for the model with uniform abundances and no vertical thermal gradient. We find that a spatial resolution of $0.2-0.5\arcsec$ and 0.5--10 hours of integration time will be needed to disentangle large-scale temperature gradients and the chemical stratification in disks in lines of abundant molecules.
We report on time-dependent axisymmetric simulations of an X-ray excited flow from a parsec-scale, rotating, cold torus around an active galactic nucleus. Our simulations account for radiative heating and cooling and radiation pressure force. The simulations follow the development of a broad bi-conical outflow induced mainly by X-ray heating. We compute synthetic spectra predicted by our simulations. The wind characteristics and the spectra support the hypothesis that a rotationally supported torus can serve as the source of a wind which is responsible for the warm absorber gas observed in the X-ray spectra of many Seyfert galaxies.
The backbone of double bars is made out of double-frequency orbits, and loops, their maps, indicate the bars' extent, morphology and dynamics.
We report on our attempts to achieve a nearly steady-state gas flow in hydrodynamical simulations of doubly barred galaxies. After exploring the parameter space, we construct two models, for which we evaluate the photometric and the kinematic integrals, present in the Tremaine-Weinberg method, in search of observational signatures of two rotating patterns. We show that such signatures are often present, but a direct fit to data points is likely to return incorrect pattern speeds. However, for a particular distribution of the tracer, presented here, the values of the pattern speeds can be retrieved reliably even with the direct fit.
We present the characteristics and some early scientific results of the first instrument at the Large Binocular Telescope (LBT), the Large Binocular Camera (LBC). Each LBT telescope unit will be equipped with similar prime focus cameras. The blue channel is optimized for imaging in the UV-B bands, the red channel is optimized for imaging in the VRIz bands. The corrected field of view for each camera is about 30 arcmin of diameter and the chip area is equivalent to a 23x23 arcmin2 field. In this paper we also present the commissioning results of the blue channel. Several measurements have been obtained to assess the technical and scientific performance of the blue camera. Among others, astrometric distortion, flat fielding, ghosts and photometric calibration. These measurements have been used as input to a data reduction pipeline applied to the science data selected for the commissioning of the instrument. The measurements obtained during the commissioning showed that the technical performance of the Blue camera is within the expectation of the original project. Since the red camera is very similar to the blue one we expect similar performances from the commissioning that will be performed in the following months in binocular configuration. From a deep UV image obtained during the commissioning of the Blue camera we derived very deep UV galaxy counts in a large sky area down to U(Vega)=26.5 showing that the Blue camera is the most powerful UV imager available at present and in the near future in terms of depth and large field of view. We have also emphasized the importance of LBC-Blue to increase the robustness of the UGR multicolour selection of Lyman break galaxies at redshift z~3.
We have investigated the correlation between the supermassive black holes (SMBHs) mass ($M_{\rm bh}$) and the stellar velocity dispersion ($\sigma_*$) in two types of host galaxies: the classical bulges (or elliptical galaxies), and pseudobulges. In the form $\log (M_{\rm bh}/{\rm M_\odot})=\alpha+\beta\log(\sigma_*/200 {\rm km s^{-1}})$, the best-fit results for the 41 classical bulges/elliptical galaxies are the slope $\beta=4.17\pm0.25$ and the normalization $\alpha=8.29\pm0.04$; the best-fit results for the 12 pseudobulges are $\beta=4.17\pm0.70$, $\alpha=7.49\pm0.13$. Both relations have intrinsic scatter in $\log M_{\rm bh}$ of $\lesssim0.25$ dex. The $M_{\rm bh}$-$\sigma_*$ relation for pseudobulges is different from the relation in the classical bulges over the 3$\sigma$ significance level. The contrasting relations indicate the formation and growth histories of SMBHs depend on their host type, the pseudobulges is relatively low efficient to fuel the central SMBHs. The discrepancy between the slope of the $M_{\rm bh}$-$\sigma_*$ relations using different definition of velocity dispersion vanishes in our sample, a uniform slope will constrain the coevolution theories of the SMBHs and their host galaxies more effectively. We also find the slope for the 13 ``core'' elliptical galaxies at the high mass range of the relation appears slightly steeper, which may be the imprint of their origin of dissipationless mergers.
In this work we show that the presence of a vector field on cosmological scales could explain the present phase of accelerated expansion of the universe. The proposed theory contains no dimensional parameters nor potential terms and does not require unnatural initial conditions in the early universe, thus avoiding the so called cosmic coincidence problem. In addition, it fits the data from high-redshift supernovae with excellent precision, making definite predictions for cosmological parameters. Upcoming observations will be able to clearly discriminate this model from standard cosmology with cosmological constant.
LS 5039 is one of a handful of X-ray binaries that have been recently detected at high-energy $\gamma$-rays, in this case, by the High-Energy Stereoscopy Array (H.E.S.S.). The nature of this system is unknown: both a black hole and a pulsar have been invoked as possible compact object companions. Here we work with a model of the high energy phenomenology of the system in which it is assumed that the companion object is a pulsar rotating around an O6.5V star in the $\sim 3.9$ days orbit. The model assumes two different sets of power-law spectral parameters of the interacting primary leptons corresponding to the two orbital phase intervals defined by H.E.S.S. as having different gamma-ray spectra and very-high-energy (VHE) cutoffs. We show the H.E.S.S. phenomenology is completely explained by this model. We present predictions for photons with lower energies (for $E>1 $ GeV), subject to test in the forthcoming months with the GLAST satellite. We find that GLAST is able to judge on this model within one year.
We present two-dimensional (2D) stellar and gaseous kinematics of the inner ~130x180 pc^2 of the Narrow Line Seyfert 1 galaxy NGC4051 at a sampling of 4.5 pc, from near-infrared K-band spectroscopic observations obtained with the Gemini's Near-infrared Integral Field Spectrograph (NIFS). The turnover of the stellar rotation curve at only ~55 pc from the nucleus, revealing a highly concentrated gravitational potential. The stellar velocity dispersion of the bulge is ~60 km/s -- implying on a nuclear black hole mass of ~10^6 M_sun -- within which patches of lower velocity dispersion suggest the presence of regions of more recent star formation. The Brgamma emission-line shows no rotation as well as no blueshifts or redshifts in excess of 30 km/s, and is thus not restricted to the galaxy plane. The [CaVIII] coronal region is compact but resolved, extending over the inner 75 pc. It shows the highest blueshifts -- of up to -250 km/s, and the highest velocity dispersions, interpreted as due to outflows from the active nucleus, supporting an origin close to the nucleus. Subtraction of the stellar velocity field from the gaseous velocity field has allowed us to isolate non-circular motions observed in the H_2 emitting gas. The most conspicuous kinematic structures are two nuclear spiral arms. We interpret these structures as inflows towards the nucleus, a result similar to those of previous studies in which we have found streaming motions along nuclear spirals in ionized gas using optical IFU observations. We have calculated the mass inflow rate along the nuclear spiral arms, obtaining $\dot{M}_{H_2} ~ 4x10^{-5} M_Sun/yr, value ~100 times smaller than the accretion rate necessary to power the active nucleus.
In this paper, we present results from the complete set of cosmic microwave background (CMB) radiation temperature anisotropy observations made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR) operating at 150 GHz. We include new data from the final 2005 observing season, expanding the number of detector-hours by 210% and the sky coverage by 490% over that used for the previous ACBAR release. As a result, the band-power uncertainties have been reduced by more than a factor of two on angular scales encompassing the third to fifth acoustic peaks as well as the damping tail of the CMB power spectrum. The calibration uncertainty has been reduced from 6% to 2.2% in temperature through a direct comparison of the CMB anisotropy measured by ACBAR with that of the dipole-calibrated WMAP3 experiment. The measured power spectrum is consistent with a spatially flat, LambdaCDM cosmological model. We see evidence for weak gravitational lensing of the CMB at >3-sigma significance by comparing the likelihood for the best-fit lensed/unlensed models to the ACBAR+WMAP3 data. On fine angular scales, there is weak evidence (1.7 sigma) for excess power above the level expected from primary anisotropies. The source of this power cannot be constrained by the ACBAR 150 GHz observations alone; however, if it is the same signal seen at 30 GHz by the CBI and BIMA experiments, then it has a spectrum consistent with the Sunyaev-Zel'dovich effect.
We report on interferometric observations of the CO J=1--0 and J=3--2 line emission from the controversial QSO/galaxy pair HE 0450--2958. {\it The detected CO J=1--0 line emission is found associated with the disturbed companion galaxy not the luminous QSO,} and implies $\rm M_{gal}(H_2)\sim (1-2)\times 10^{10} M_{\odot}$, which is $\ga 30% $ of the dynamical mass in its $\sim \rm 11 kpc\times 6 kpc$ CO-luminous region. Fueled by this large gas reservoir this galaxy is the site of an intense starburst with $\rm SFR\sim 370 M_{\odot} yr^{-1}$, placing it firmly on the upper gas-rich/star-forming end of Ultra Luminous Infrared Galaxies (ULIRGs, $\rm L_{IR}>10^{12} L_{\odot}$). This makes HE 0450--2958 the first case of extreme starburst and powerful QSO activity, intimately linked (triggered by a strong interaction) but not coincident. The lack of CO emission towards the QSO itself renews the controversy regarding its host galaxy by making a gas-rich spiral (the typical host of Narrow Line Seyfert 1 AGNs) less likely. Finally, the prominence of HE 0450--2958 and similar IR-warm QSOs as ULIRG$\to $QSO transition candidates raises the possibility that some may {\it simply be gas-rich/gas-poor (e.g. spiral/elliptical) galaxy interactions} ``activating'' an optically bright unobscured QSO in the gas-poor galaxy, and a starburst in the gas-rich one. We argue that such events may have gone largely unoticed even in the local Universe because the tools necessary to disentagle the progenitors, namely the combination of high S/N optical and CO imaging at high resolution, became available only~recently.
We report high-cadence time-series photometry of the recently-discovered transiting exoplanet system HD 17156, spanning the time of transit on UT 2007 October 1, from three separate observatories. We present a joint analysis of our photometry, previously published radial velocity measurements, and times of transit center for 3 additional events. Adopting the spectroscopically-determined values and uncertainties for the stellar mass and radius, we estimate a planet radius of Rp = 1.01 +/- 0.09 RJup and an inclination of i = 86.5 +1.1 -0.7 degrees. We find a time of transit center of Tc = 2454374.8338 +/- 0.0020 HJD and an orbital period of P = 21.21691 +/- 0.00071 days, and note that the 4 transits reported to date show no sign of timing variations that would indicate the presence of a third body in the system. Our results do not preclude the existence of a secondary eclipse, but imply there is only a 9.2% chance for this to be present, and an even lower probability (6.9%) that the secondary eclipse would be a non-grazing event. Due to its eccentric orbit and long period, HD 17156b is a fascinating object for the study of the dynamics of exoplanet atmospheres. To aid such future studies, we present theoretical light curves for the variable infrared emission from the visible hemisphere of the planet throughout its orbit.
Using Spitzer archival data from the SAGE (Surveying the Agents of a Galaxy's Evolution) program, we derive the Cepheid period-luminosity (P-L) relation at 3.6, 4.5, 5.8 and 8.0 microns for Large Magellanic Cloud (LMC) Cepheids. These P-L relations can be used, for example, in future extragalactic distance scale studies carried out with the James Webb Space Telescope. We also derive Cepheid period-color (P-C) relations in these bands and find that the slopes of the P-C relations are relatively flat. We test the nonlinearity of these P-L relations with the F statistical test, and find that the 3.6 micron, 4.5 micron and 5.8 micron P-L relations are consistent with linearity. However the 8.0 micron P-L relation presents possible but inconclusive evidence of nonlinearity.
I provide an incomplete inventory of the astronomical variability that will be found by next-generation time-domain astronomical surveys. These phenomena span the distance range from near-Earth satellites to the farthest Gamma Ray Bursts. The surveys that detect these transients will issue alerts to the greater astronomical community; this decision process must be extremely robust to avoid a slew of ``false'' alerts, and to maintain the community's trust in the surveys. I review the functionality required of both the surveys and the telescope networks that will be following them up, and the role of VOEvents in this process. Finally, I offer some ideas about object and event classification, which will be explored more thoroughly by other articles in these proceedings.
The origin of Big Bang singularity in 3+1 dimensions can be understood in an exact string theory background obtained by an analytic continuation of a cigar like geometry with a nontrivial dilaton. In a T-dual conformal field theory picture there exists a closed string tachyon potential which excises the singular space-time of a strongly coupled regime to ensure that a higher dimensional universe has no curvature singularity. However in 3+1 dimensions the universe exhibits all the pathology of a standard Big Bang cosmology. The emergence of a singularity now owes to a higher dimensional orbifold singularity which does not have a curvature singularity in higher dimensions, suggesting that close to the compactification scale an effective description of 3+1 dimensions breaks down and bouncing universe emerges in 5 and higher dimensions.
We study equilibrium conditions between a static, sphErically symmetric black hole and classical matter in terms of the radial pressure to density ratio p_r/\rho = w(u), where u is the radial coordinate. It is shown that such an equilibrium is possible in two cases: (i) the well-known case w\to -1 as $u\to u_h (the horizon), i.e., "vacuum" matter, for which \rho(u_h) can be nonzero; (ii) w \to -1/(1+2k) and \rho \sim (u-u_h)^k as u\to u_h, where k>0 is a positive integer (w=-1/3 in the generic case k=1). A non-interacting mixture of these two kinds of matter can also exist. The whole reasoning is local, hence the results do not depend on any global or asymptotic conditions. They mean, in particular, that a static black hole cannot live inside a star with nonnegative pressure and density. As an example, an exact solution for an isotropic fluid with w = -1/3 (that is, a fluid of disordered cosmic strings), with or without vacuum matter, is presented.
In this paper, we consider half-integer charged particles predicted by models of orbifold compactification of the $E_8\times E_8$ heterotic string theory. We find that it is possible for half-integer charged particles to exist in our universe, and the location of half-interger charged particles in a galaxy should be in the centers of the galaxy. By qualitative analysis, we find half-interger charged particles may be helpful in explaining the formation of SMBH at the large redshift and solving the UHECR puzzle.
In the present work, it is shown that a chameleon scalar field having a nonminimal coupling with dark matter can give rise to a smooth transition from a decelerated to an accelerated phase of expansion for the universe. It is surprising to note that the coupling with the chameleon scalar field hardly affects the evolution of the dark matter sector, which still redshifts as $a^{-3}$.
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A long standing problem for hierarchical disk galaxy formation models has been the simultaneous matching of the zero point of the Tully-Fisher relation and the galaxy luminosity function (LF). We illustrate this problem for a typical disk galaxy and discuss three solutions: low stellar mass-to-light ratios, low initial dark halo concentrations, and no halo contraction. We speculate that halo contraction may be reversed through a combination of mass ejection through feedback and angular momentum exchange brought about by dynamical friction between baryons and dark matter during the disk formation process.
The scaling relations between rotation velocity, size and luminosity form a benchmark test for any theory of disk galaxy formation. We confront recent theoretical models of disk formation to a recent large compilation of such scaling relations. We stress the importance of achieving a fair comparison between models and observations.
We report the discovery of WASP-4b, a large transiting gas-giant planet with an orbital period of 1.34 days. This is the first planet to be discovered by the SuperWASP-South observatory and CORALIE collaboration and the first planet orbiting a star brighter than 16th magnitude to be discovered in the Southern hemisphere. A simultaneous fit to high-quality lightcurves and precision radial-velocity measurements leads to a planetary mass of 1.27 +/- 0.1 MJup and a planetary radius of 1.45 +/- 0.08 RJup. The host star is USNO-B1.0 0479-0948995, a G7V star of visual magnitude 12.5. As a result of the short orbital period, the predicted surface temperature of the planet is 1776 K, making it an ideal candidate for detections of the secondary eclipse at infrared wavelengths.
We demonstrate that gravitational lensing can be used to discover and study planets in the habitable zones of nearby dwarf stars. If appropriate software is developed, a new generation of monitoring programs will automatically conduct a census of nearby planets in the habitable zones of dwarf stars. In addition, individual nearby dwarf stars can produce lensing events at predictable times; careful monitoring of these events can discover any planets located in the zone of habitability. Because lensing can discover planets (1) in face-on orbits, and (2) in orbit around the dimmest stars, lensing techniques will provide complementary information to that gleaned through Doppler and/or transit investigations. The ultimate result will be a comprehensive understanding of the variety of systems with conditions similar to those that gave rise to life on Earth.
This paper is devoted to exploring how we can discover and study nearby (< 1-2 kpc) planetary and binary systems by observing their action as gravitational lenses. Lensing can extend the realm of nearby binaries and planets that can be systematically studied to include dark and dim binaries, and face-on systems. As with more traditional studies, which use light from the system, orbital parameters (including the total mass, mass ratio, and orbital separation) can be extracted from lensing data, Also in common with these traditional methods, individual systems can be targeted for study. We discuss the specific observing strategies needed in order to optimize the discovery and study of nearby planetary and binary systems by observing their actions as lenses.
In the synchrotron radiation model, the polarization property depends on both the configuration of the magnetic field and the geometry of the visible emitting region. Some peculiar behaviors in the X-ray afterglows of {\it Swift} gamma-ray bursts (GRBs), such as energetic flares and the plateau followed by a sharp drop, might by highly linearly-polarized because the outflows powering these behaviors may be Poynting-flux dominated. Furthermore, the broken-down of the symmetry of the visible emitting region may be hiding in current X-ray data and will give rise to interesting polarization signatures. In this work we focus on the polarization accompanying the very early sharp decline of GRB X-ray afterglows. We show that strong polarization evolution is possible in both the high latitude emission model and the dying central engine model which are used to interpret this sharp X-ray decline. It is thus not easy to efficiently probe the physical origin of the very early X-ray sharp decline with future polarimetry. Strong polarization evolution is also possible in the decline phase of X-ray flares and in the shallow decline phase of X-ray light curves characterized by chromatic X-ray VS. Optical breaks. An {\it XRT}-like detector but with polarization capability on board a {\em Swift}-like satellite would be suitable to test our predictions.
We report a dynamical measurement of the mass of the brown dwarf GJ 802B using aperture-masking interferometry and astrometry. In addition, we report the discovery that GJ 802A is itself a close spectroscopic non-eclipsing binary with a 19 hour period. We find the mass of GJ 802B to be $0.063\pm0.005$M$_\sun$. GJ 802 has kinematics inconsistent with a young star and more consistent with the thick disk population, implying a system age of $\sim$10 GYr. However, model evolutionary tracks for GJ 802B predict system ages of $\sim$2 GYr, suggesting that brown dwarf evolutionary models may be underestimating luminosity for old brown dwarfs.
We present a geometrical methodology to interpret the periodical light curves of Soft Gamma Repeaters based on the magnetar model and the numerical arithmetic of the three-dimensional magnetosphere model for the young pulsars. The hot plasma released by the star quake is trapped in the magnetosphere and photons are emitted tangent to the local magnetic field lines. The variety of radiation morphologies in the burst tails and the persistent stages could be well explained by the trapped fireballs on different sites inside the closed field lines. Furthermore, our numerical results suggests that the pulse profile evolution of SGR 1806-20 during the 27 December 2004 giant flare is due to a lateral drift of the emitting region in the magnetosphere.
There is an ongoing debate in the literature as to whether the effects of averaging out inhomogeneities (``backreaction'') in Cosmology can be large enough to account for the acceleration of the scale factor in the FLRW models. In particular, some simple models of structure formation studied in the literature seem to indicate that this is indeed possible, and it has also been suggested that the perturbed FLRW framework is no longer a good approximation during structure formation, when the density contrast becomes nonlinear. In this work we attempt to clarify the situation to some extent, using a fully relativistic model of pressureless spherical collapse. We find that whereas averaging during structure formation can lead to acceleration via a selective choice of averaging domains, the acceleration is not present when more generic domains are used for averaging. Further, we show that for most of the duration of the collapse, matter velocities remain small, and the perturbed FLRW form of the metric can be explicitly recovered, in the structure formation phase.
The residuals about the standard M-sigma relation correlate with the
effective radius, absolute magnitude, and Sersic index of the host bulge -
although, it is noted here that the elliptical galaxies do not partake in such
correlations. Moreover, it is revealed that barred galaxies (with their
relatively small, faint, and low stellar concentration bulges) can deviate from
the M-sigma relation by delta(log M) = -0.5 to -1.0 dex (in the sense that
their sigma values are too large) and generate much of the aforementioned
correlations. Removal of the seven barred galaxies from the Tremaine et al. set
of 31 galaxies results in a ``barless M-sigma'' relation with an intrinsic
scatter of 0.17 dex (cf. 0.27 dex for the 31 galaxies) and a total scatter of
0.25 dex (cf. 0.34 dex for the 31 galaxies). The introduction of third
parameters does not reduce the scatter of the barless M-sigma relation.
Furthermore, removal of the barred galaxies, or all the disk galaxies, from an
expanded and updated set of 40 galaxies with reliable black hole mass
measurements gives a consistent result, such that log(M_bh/M_sun) =
(8.25+/-0.05) + (3.68+/-0.25)log [sigma/200].
The "barless" sigma-L relation for galaxies with black hole mass measurements
is found to be consistent with that from the SDSS sample of early-type
galaxies. In addition, the barless M-sigma relation, the M-L relation, and the
M-n relation are all shown to yield SMBH masses less than 2-4 x 10^9 M_sun.
The kinematics of galactic rings were studied with a scanning Fabry-Perot interferometer mounted in the multi-mode focal reducer SCORPIO (Afanasiev & Moiseev 2005) at the SAO RAS 6-m telescope. The analysis of the ionized gas velocity fields allows us to understand the nature of the ring formation in several galaxies. The different types of the rings in the presented objects (resonanced, collisional, polar) were caused by the various sorts of interactions: merging, head-on collisions.
We have studied the kinematics of the ionized gas and stellar component in Mrk334 using methods of panoramic (3D) spectroscopy. The observations were performed at the prime focus of the SAO RAS 6-m telescope with the integral-field spectrograph MPFS (Afanasiev et al. 2001) and with a scanning Fabry-Perot interferometer (FPI), installed on the multimode device SCORPIO (Afanasiev & Moiseev 2005). Based on these data, the monochromatic maps and velocity fields in different emission lines of the ionized gas were constructed. The diagnostic diagrams have been made based on the emission lines ratios.
We report the discovery of two concentric Einstein rings around the gravitational lens SDSSJ0946+1006, as part of the Sloan Lens ACS Survey. The main lens is at redshift zl=0.222, while the inner ring (1) is at zs1=0.609 and Einstein radius $Re_1=1.43\pm0.01"$. The wider image separation ($Re_2=2.07\pm 0.02"$) of the outer ring (2) implies that it is at higher redshift. Its detection in the F814W filter implies zs2<6.9. The configuration can be well described by a total density profile $\rho_{tot} ~ r^-g'$ with $g'=2.00\pm0.03$ and velocity dispersion $\sigma_{SIE}=287\pm5\kms$. [...] We consider whether this configuration can be used to constrain cosmological parameters exploiting angular distance ratios entering the lens equations. Constraints for SDSSJ0946+1006, are uninteresting due to the sub-optimal lens and source redshifts. We then consider the perturbing effect of the mass associated with Ring 1 building a double lens plane compound lens model. This introduces minor changes to the mass of the main lens and allows to estimate the mass of Ring 1 $(\sigma_{SIE,s1}=94\pm30\kms)$. We examine the prospects of doing cosmography with a sample of 50 double lenses, expected from future space based surveys such as DUNE or JDEM. Taking full account of the model uncertainties, such a sample could be used to measure $\Omega_m$ and $w$ with 10% accuracy, for a flat cosmology.
An observational evidence for the tidal shear effect of the large-scale structure on the galaxy morphological type is presented. By analyzing a sample of 15,882 well-resolved nearby galaxies from the Tully Catalog and the real space tidal field reconstructed from the 2Mass Redshift Survey (2MRS), we investigate the dependence of galaxy morphological type on the shear of large-scale environment. We first divide the Tully galaxies into six subsamples according to their morphological types. Then, we calculate the density (delta), ellipticity (e), prolateness (p), and Q-factor of the regions where the subsample galaxies are located by interpolating the 2MRS tidal shear field. Here, the Q-factor differentiates among a void-like (Q=-1), a sheet-like (Q=-1/3), a filament-like (Q=1/3), and a halo-like (Q=1) environment. Averaging the four quantities over the six subsamples separately, we show how the mean values of $\delta$, $e$, $p$ and $Q$ change with the six subsamples. It is found that there exist systematic changes of <e>, <p> and <Q> with galaxy morphological type. We also calculate the conditional number densities of the subsample galaxies located in the void-like, sheet-like, filament-like, and halo-like environments and show how the relative abundances of the subsamples galaxies vary among different environments. Our result suggests that the galaxy morphological type is a strong function of not only the density but also the shear of large-scale environment. It is concluded that our work will provide a new insight in the formation and evolution of galaxies in the cosmic web.
We argue that supermassive black hole growth in AGN occurs via sequences of
randomly--oriented accretion discs with angular momentum limited by
self--gravity. These stably co-- or counter--align with the black hole spin
with almost equal frequency. Accretion from these discs very rapidly adjusts
the hole's spin parameter to average values $\bar a \sim 0.1-0.3$ (the precise
range depending slightly on the disc vertical viscosity coefficient $\alpha_2$)
from any initial conditions, but with significant fluctuations ($\Delta a\sim
\pm 0.2$) about these. We conclude (a) AGN black holes should on average spin
moderately, with the mean value $\bar a$ decreasing slowly as the mass
increases; (b) SMBH coalescences leave little long--term effect on $\bar a$;
(c) SMBH coalescence products in general have modest recoil velocities, so that
there is little likelihood of their being ejected from the host galaxy; (d)
black holes can grow even from stellar masses to $\sim 5\times 10^9 \msun$ at
high redshift $z\sim 6$; (e) jets produced in successive accretion episodes can
have similar directions, but after several episodes the jet direction deviates
significantly. Rare examples of massive holes with larger spin parameters could
result from prograde coalescences with SMBH of similar mass, and are most
likely to be found in giant ellipticals. We compare these results with
observation.
(abridged)
Globular clusters as $\omega$ Cen and NGC 2808 appear to have a population of very He-rich stars. From a theoretical point of view, one expects the presence of He-rich stars in all globular clusters showing an oxygen-sodium (O-Na) anticorrelation. In this paper, we briefly recall how fast rotating massive stars could be the main source of the material from which He-rich stars have formed. We speculate that the UV-upturn phenomenon observed in all elliptical galaxies might be due to He-rich stars. If this hypothesis is correct then fast rotating massive stars may have played in the early evolutionary phases of these systems a similar role as the one they played in the nascent globular clusters.
We investigated the nature of the hitherto unresolved elliptical infrared emission in the centre of the ~20000 AU circumstellar disc silhouette in M17. We combined high-resolution JHKLM band imaging carried out with NAOS/CONICA at the VLT with H2 and [Fe II] narrow band imaging using SOFI at the NTT. The analysis is supported by Spitzer/GLIMPSE archival data and by already published SINFONI/VLT Integral Field Spectroscopy data. For the first time, we resolve the elongated central infrared emission into a point-source and a jet-like feature that extends to the northeast in an opposite direction to a recently discovered collimated H2 jet. We interpret the point-like emission as to originate from an accreting intermediate to high-mass protostar. In addition, our images reveal a weak and curved southwestern lobe whose morphology resembles that of the previously detected northeastern one. Both are located at a distance of 1500 AU from the disc centre. Such a jet is strongly suggested by H2 emission emerging from the disc centre toward the southwest along an axis that is almost perpendicular to the disc plane. The protostar is embedded in circumstellar material producing a visual extinction of Av > 60. The observed Ks band magnitude is equivalent to a main-sequence star having a spectral type of at least B8 that corresponds to a stellar mass of ~2.8 Msun. Altogether, we suggest that the large M17 disc silhouette is associated with an intermediate to high-mass protostar that accretes material from the disc and expels part of it through a symmetric bipolar jet or outflow.
The existence of supermassive black holes lurking in the centers of galaxies and of stellar binary systems containing a black hole with a few solar masses has been established beyond reasonable doubt. The idea that black holes of intermediate masses ($\sim 1000$ \msun) may exist in globular star clusters has gained credence over recent years but no conclusive evidence has been established yet. An attractive feature of this hypothesis is the potential to not only disrupt solar-type stars but also compact white dwarf stars. In close encounters the white dwarfs can be sufficiently compressed to thermonuclearly explode. The detection of an underluminous thermonuclear explosion accompanied by a soft, transient X-ray signal would be compelling evidence for the presence of intermediate mass black holes in stellar clusters. In this paper we focus on the numerical techniques used to simulate the entire disruption process from the initial parabolic orbit, over the nuclear energy release during tidal compression, the subsequent ejection of freshly synthesized material and the formation process of an accretion disk around the black hole.
We present a comparison between the 2001 XMM-Newton and 2005 Suzaku observations of the quasar, PG1211+143 at z=0.0809. Variability is observed in the 7 keV iron K-shell absorption line (at 7.6 keV in the quasar frame), which is significantly weaker in 2005 than during the 2001 XMM-Newton observation. From a recombination timescale of <4 years, this implies an absorber density n>0.004 particles/cm3, while the absorber column is 5e22<N_H <1 1e24 particles/cm2. Thus the sizescale of the absorber is too compact (pc scale) and the surface brightness of the dense gas too high (by 9-10 orders of magnitude) to arise from local hot gas, such as the local bubble, group or Warm/Hot Intergalactic Medium (WHIM), as suggested by McKernan et al. (2004, 2005). Instead the iron K-shell absorption must be associated with an AGN outflow with mildly relativistic velocities. Finally we show that the the association of the absorption in PG1211+143 with local hot gas is simply a coincidence, the comparison between the recession and iron K absorber outflow velocities in other AGN does not reveal a one to one kinematic correlation.
We present a compilation of measurements of the stellar mass density as a function of redshift. Using this stellar mass history we obtain a star formation history and compare it to the instantaneous star formation history. For z<0.7 there is good agreement between the two star formation histories. At higher redshifts the instantaneous indicators suggest star formation rates larger than that implied by the evolution of the stellar mass density. This discrepancy peaks at z=3 where instantaneous indicators suggest a star formation rate around 0.6 dex higher than those of the best fit to the stellar mass history. We discuss a variety of explanations for this inconsistency, such as inaccurate dust extinction corrections, incorrect measurements of stellar masses and a possible evolution of the stellar initial mass function.
Neutrino telescopes are moving steadily toward the goal of detecting astrophysical neutrinos from the most powerful galactic and extragalactic sources. Here we describe analysis methods to search for high energy point-like neutrino sources using detectors deep in the ice or sea. We simulate an ideal cubic kilometer detector based on real world performance of existing detectors such as AMANDA, IceCube, and ANTARES. An unbinned likelihood ratio method is applied, making use of the point spread function and energy distribution of simulated neutrino signal events to separate them from the background of atmospheric neutrinos produced by cosmic ray showers. The unbinned point source analyses are shown to perform better than binned searches and, depending on the source spectral index, the use of energy information is shown to improve discovery potential by almost a factor of two.
The discovery of refractory grains amongst the particles collected from Comet 81P/Wild 2 by the Stardust spacecraft (Brownlee et al. 2006) provides the ground truth for large-scale transport of materials formed in high temperature regions close to the protosun outward to the comet-forming regions of the solar nebula. While accretion disk models driven by a generic turbulent viscosity have been invoked as a means to explain such large-scale transport, the detailed physics behind such an ``alpha'' viscosity remains unclear. We present here an alternative physical mechanism for large-scale transport in the solar nebula: gravitational torques associated with the transient spiral arms in a marginally gravitationally unstable disk, of the type that appears to be necessary to form gas giant planets. Three dimensional models are presented of the time evolution of self-gravitating disks, including radiative transfer and detailed equations of state, showing that small dust grains will be transported upstream and downstream (with respect to the mean inward flow of gas and dust being accreted by the central protostar) inside the disk on time scales of less than 1000 yr inside 10 AU. These models furthermore show that any initial spatial heterogeneities present (e.g., in short-lived isotopes such as 26Al) will be homogenized by disk mixing down to a level of ~10%, preserving the use of short-lived isotopes as accurate nebular chronometers, while simultaneously allowing for the spread of stable oxygen isotope ratios. This finite level of nebular spatial heterogeneity appears to be related to the coarse mixing achieved by spiral arms, with radial widths of order 1 AU, over time scales of ~1000 yrs.
Present and planned dark matter detection experiments search for WIMP-induced nuclear recoils in poorly known background conditions. In this environment, the maximum gap statistical method provides a way of setting more sensitive cross section upper limits by incorporating known signal information. We give a recipe for the numerical calculation of upper limits for planned directional dark matter detection experiments, that will measure both recoil energy and angle, based on the gaps between events in two-dimensional phase space.
We use 2MASS and MSX infrared observations, along with new molecular line (CO) observations, to examine the distribution of young stellar objects (YSOs) in the molecular cloud surrounding the halo HII region KR 140 in order to determine if the ongoing star-formation activity in this region is dominated by sequential star formation within the photodissociation region (PDR) surrounding the HII region. We find that KR 140 has an extensive population of YSOs that have spontaneously formed due to processes not related to the expansion of the HII region. Much of the YSO population in the molecular cloud is concentrated along a dense filamentary molecular structure, traced by C18O, that has not been erased by the formation of the exciting O star. Some of the previously observed submillimetre clumps surrounding the HII region are shown to be sites of recent intermediate and low-mass star formation while other massive starless clumps clearly associated with the PDR may be the next sites of sequential star formation.
Context: An analytical solution of the generalized diffusive and convective transport equation is derived to explain the transport of cosmic ray protons within elliptical galaxies. Aims: Cosmic ray transport within elliptical galaxies is an interesting element in understanding the origin of high energetic particles measured on Earth. As probable sources of those high energetic particles, elliptical galaxies show a dense interstellar medium as a consequence of activity in the galactic nucleus or merging events between galaxies. Thus it is necessary for an appropriate description of cosmic ray transport to take the diffusive and convective processes in a dense interstellar environment into account. Here we show that the transport equations can be solved analytically with respect to the given geometry and boundary conditions in position space, as well as in momentum space. Results: The spatial solution is shown using a generalized source of cosmic rays. Additionally, the special case of a jet-like source is illustrated. We present the solution in momentum space with respect to an escape term for cosmic ray protons depending on the spatial shape of the galaxy. For a delta-shape injection function, the momentum solution is obtained analytically. We find that the spectral index measured on Earth can be obtained by appropriately choosing of the strength of Fermi I and Fermi II processes. From these results we calculate the gamma-ray flux from pion decay due to proton-proton interaction to give connection to observations. Additionally we determine the escape-spectrum of cosmic rays. The results show that both spectra are harder than the intrinsic power-law spectrum for cosmic rays in elliptical galaxies.
We aim to characterise the morphology and the physical parameters governing the shock physics of the Herbig-Haro object HH99B. We have obtained SINFONI-SPIFFI IFU spectroscopy between 1.10 and 2.45 um detecting more than 170 emission lines, Most of them come from ro-vibrational transitions of H_2 and [FeII]. All the brightest lines appear resolved in velocity. Intensity ratios of ionic lines have been compared with predictions of NLTE models to derive bi-dimensional maps of extinction and electron density, along with estimates of temperature, fractional ionisation and atomic hydrogen post-shock density. H_2 line intensities have been interpreted in the framework of Boltzmann diagrams, from which we have derived maps of extinction and temperature of the molecular gas. From the intensity maps of bright lines the kinematical properties of the shock(s) at work in the region have been delineated. Finally, from selected [FeII] lines, constraints on the spontaneous emission coefficients of the 1.257, 1.321 and 1.644 um lines are provided. The kinematical properties derived for the molecular gas substantially confirm those published in Davis et al.(1999), while new information (e.g. v_shock ~115 km s^-1 is provided for the shock component responsible for the ionic emission. We also provide an indirect measure of the H_2 breakdown speed (between 70 and 90 km s^-1) and compute the inclination angle with respect to the line of sight. The map parameters, along with images of the observed line intensities, will be used to put stringent constraints on up-to-date shock models.
As Pr. Th. Henning said at the conference, cold precursors of high-mass stars are now "hot topics". We here propose some observational criteria to identify massive infrared-quiet dense cores which can host the high-mass analogs of Class 0 protostars and pre-stellar condensations. We also show how far-infrared to millimeter imaging surveys of entire complexes forming OB stars are starting to unveil the initial conditions of high-mass star formation.
We show, by means of a perturbative weakly nonlinear analysis, that the axisymmetric magneto-rotational instability (MRI) in a magnetic Taylor-Couette (mTC) flow in a thin-gap gives rise, for very small magnetic Prandtl numbers (P_m), to a real Ginzburg-Landau equation for the disturbance amplitude. The saturation amplitude A_s is found to scale in this regime as P^\delta, with 1/2<\delta<2/3 (depending on the boundary conditions adopted). The asymptotic results are shown to comply with numerical calculations performed by using a spectral code. They suggest that the transport due to the nonlinearly developed MRI may be vanishingly small for P_m << 1.
We detect 353 X-ray point sources, mostly low-mass X-ray binaries (LMXBs), in four Chandra observations of Centaurus A (NGC 5128), the nearest giant early-type galaxy, and correlate this point source population with the largest available ensemble of confirmed and likely globular clusters associated with this galaxy. Of the X-ray sources, 31 are coincident with 30 globular clusters that are confirmed members of the galaxy by radial velocity measurement (2 X-ray sources match one globular cluster within our search radius), while 1 X-ray source coincides with a globular cluster resolved by HST images. Another 36 X-ray point sources match probable, but spectroscopically unconfirmed, globular cluster candidates. The color distribution of globular clusters and cluster candidates in Cen A is bimodal, and the probability that a red, metal rich GC candidate contains an LMXB is at least 1.7 times that of a blue, metal poor one. If we consider only spectroscopically confirmed GCs, this ratio increases to ~3. We find that LMXBs appear preferentially in more luminous (massive) GCs. These two effects are independent, and the latter is likely a consequence of enhanced dynamical encounter rates in more massive clusters which have on average denser cores. The X-ray luminosity functions of the LMXBs found in GCs and of those that are unmatched with GCs reveal similar underlying populations, though there is some indication that fewer X-ray faint LMXBs are found in globular clusters than X-ray bright ones. Our results agree with previous observations of the connection of GCs and LMXBs in early-type galaxies and extend previous work on Centaurus A.
Prior to the explosion of a carbon-oxygen white dwarf in a Type Ia supernova there is a long "simmering," during which the 12C+12C reaction gradually heats the white dwarf on a long (~ 10^3 yr) timescale. Protons liberated by the 12C+12C->23Na+p branch capture onto 12C to make beta-unstable 13N, which in turn electron captures. Piro & Bildsten showed that, as a result of this electron capture, there is a maximum electron abundance Ye at the time of the explosion. We investigate the nuclear reactions during this simmering with a series of self-heating, at constant pressure, reaction network calculations. Unlike in AGB stars, p captures onto 22Ne and heavier trace nuclei do not play a significant role; at high concentrations of 22Ne (appropriate for progenitors with three times solar O/H), proton captures onto 22Ne reduce the production of 13N by < 10%. The reaction 13C(alpha,n)16O is a strong neutron source, but the 12C abundance is sufficiently high that the neutrons preferentially capture onto 12C, rather than iron group nuclei. As an aid to hydrodynamical simulations of the simmering phase, we present fits to the rates of heating, electron capture, change in mean atomic mass, and consumption of 12C in terms of the screened thermally averaged cross section for 12C+12C. Our evaluation of the net heating rate includes contributions from electron captures into the 3.68 MeV excited state of 13C. This results in a slightly larger energy release, per 12C consumed, than that found by Piro & Bildsten, but less than that released for a burn to only 20Ne and 23Na. We compare our one-zone results to more accurate integrations over the white dwarf structure to estimate the amount of 12C that must be consumed to raise the white dwarf temperature, and hence to determine the net reduction of Ye during simmering.
We have simulated the 3D emergence and interaction of two twisted flux tubes, which rise from the interior into the outer atmosphere of the Sun. We present evidence for the multiple formation and eruption of flux ropes inside the emerging flux systems and hot arcade-like structures in between them. Their formation is due to internal reconnection, occurring between oppositely directed, highly stretched and sheared fieldlines at photospheric heights. Most of the eruptions escape into the corona, but some are confined and fade away without leaving the low atmosphere. As these flux ropes erupt, new reconnected fieldlines accumulate around the main axis of the initial magnetic flux systems. We also show the complex 3D fieldline geometry and the structure of the multiple current sheets, which form as a result of the reconnection between the emerging flux systems.
Properties and structure of neutron stars are determined by the equation of state of stellar matter. Recent data on isospin-diffusion and isoscaling in heavy-ion collisions at intermediate energies as well as the size of neutron skin in $^{208}Pb$ have constrained considerably the density dependence of the nuclear symmetry energy and, in turn, the equation of state of neutron-rich nucleonic matter. These constraints could provide more reliable information about the neutron star moment of inertia. The moment of inertia of component A of the extremely relativistic double neutron star system PSR J0737-3039 will be measurable in the near future and this makes theoretical calculations of the moment of inertia very timely. We show that the moment of inertia of PSR J0737-3039A is between 1.30 and 1.63 $(\times10^{45}g$ $cm^2)$. The moment of inertia increases with rotational frequency at a rate strongly dependent upon the equation of state. Finally, we demonstrate that the transition density at the crust-core boundary is in the narrow range of $\rho_t=[0.091-0.093](fm^{-3})$.
We develop a framework for studying collective three-flavor neutrino oscillations based on the density matrix formalism. We show how techniques proven useful for collective two-flavor neutrino oscillations such as corotating frames can be applied readily to three-flavor mixing. Applying two simple assumptions and the conservation of two ``lepton numbers'' we use this framework to demonstrate how the adiabatic/precession solution emerges. We illustrate with a numerical example how two stepwise spectral swaps appear naturally if the flavor evolution of the neutrino gas can be described by such a solution. For the special case where mu and tau flavor neutrinos are equally mixed and are produced with identical energy spectra and total numbers, we find that one of the spectral swaps in the three-flavor scenario agrees with that in the two-flavor scenario when appropriate mixing parameters are used. Using the corotating frame technique we show how the adiabatic/precession solution can obtain even in the presence of a dominant ordinary matter background. With this solution we can explain why neutrino spectral swapping can be sensitive to deviations from maximal 23-mixing when the ``mu-tau'' matter term is significant.
The classical tests of general relativity (perihelion precession, deflection of light, and the radar echo delay) are considered for the Dadhich, Maartens, Papadopoulos and Rezania (DMPR) solution of the spherically symmetric static vacuum field equations in brane world models. For this solution the metric in the vacuum exterior to a brane world star is similar to the Reissner-Nordstrom form of classical general relativity, with the role of the charge played by the tidal effects arising from projections of the fifth dimension. The existing observational solar system data on the perihelion shift of Mercury, on the light bending around the Sun (obtained using long-baseline radio interferometry), and ranging to Mars using the Viking lander, constrain the numerical values of the bulk tidal parameter and of the brane tension.
We study a 5-dimensional $f({\cal R})$ brane gravity within the framework of scalar-tensor type theories. We show that such a model predicts, for a certain choice of $f({\cal R})$ and a spatially flat universe, an exponential potential, leading to an accelerated expanding universe driven solely by the curvature of the bulk space. This result is consistent with the observational data in the cosmological scale.
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