We investigate the secular resonances for massless small bodies and Earth-like planets in several planetary systems. We further compare the results with those of Solar System. For example, in the GJ 876 planetary system, we show that the secular resonances $\nu_1$ and $\nu_2$ (respectively, resulting from the inner and outer giant planets) can excite the eccentricities of the Earth-like planets with orbits 0.21 AU $\leq a <$ 0.50 AU and eject them out of the system in a short timescale. However, in a dynamical sense, the potential zones for the existence of Earth-like planets are in the area 0.50 AU $\leq a \leq$ 1.00 AU, and there exist all stable orbits last up to $10^5$ yr with low eccentricities. For other systems, e.g., 47 UMa, we also show that the Habitable Zones for Earth-like planets are related to both secular resonances and mean motion resonances in the systems.
We show that positive averaged acceleration obtained in LTB models through spatial averaging can require integration over a region beyond the event horizon of the central observer. We provide an example of a LTB model with positive averaged acceleration in which the luminosity distance does not contain information about the entire spatially averaged region, making the averaged acceleration unobservable. Since the cosmic acceleration is obtained from fitting the observed luminosity distance to a FRW model we conclude that in general a positive averaged acceleration in LTB models does not imply a positive FRW cosmic acceleration.
We investigate the evolution over the last 6.3 Gyr of cosmic time (i.e., since z ~ 0.7) of the average X-ray properties of early-type galaxies within the Extended Chandra Deep Field-South (E-CDF-S). Our early-type galaxy sample includes 539 objects with red-sequence colors and Sersic indices larger than n = 2.5, which were selected jointly from the COMBO-17 (Classifying Objects by Medium-Band Observations in 17 Filters) and GEMS (Galaxy Evolution from Morphologies and SEDs) surveys. We utilize the deep Chandra observations over the E-CDF-S and X-ray stacking analyses to constrain primarily the average X-ray emission from "normal" early-type galaxies (i.e., those that are not dominated by luminous active galactic nuclei [AGNs]). In our analyses, we study separately optically luminous (L_B ~ 10^[10-11] L_B,sol) and faint (L_B ~ 10^[9.3-10] L_B,sol) galaxy samples, which we expect to have soft (0.5-2.0 keV) X-ray emission dominated by hot (~1 keV) interstellar gas and low mass X-ray binary (LMXB) populations, respectively. We detect individually 49 (~9%) of our galaxies in the X-ray band, and classify these sources as either normal early-type galaxies (17 galaxies) or AGN candidates (32 galaxies). The AGN fraction of our optically luminous samples evolves with redshift in a manner consistent with the (1+z)^3 evolution observed in other investigations of X-ray-selected AGNs. After removing potential AGNs from our samples, we find that the X-ray-to-B-band mean luminosity ratio (L_X/L_B) for optically luminous early-type galaxies does not evolve significantly over the redshift range z~0.0-0.7. This lack of X-ray evolution implies a general balance between the heating and cooling of the hot interstellar gas [Abridged].
We investigate the suppression of the baryon density fluctuations compared to the dark matter in the linear regime. Previous calculations predict that the suppression occurs up to a characteristic mass scale of ~ 1,000,000 solar masses, which suggests that pressure has a central role in determining the properties of the first luminous objects at early times. We show that the expected characteristic mass scale is in fact substantially lower (by a factor of ~ 3-10, depending on redshift), and thus the effect of baryonic pressure on the formation of galaxies up to reionization is only moderate. This result is due to the influence on perturbation growth of the high pressure that prevailed in the period from cosmic recombination to z ~ 200, when the gas began to cool adiabatically and the pressure then dropped. At z ~ 10 the suppression of the baryon fluctuations is still sensitive to the history of pressure in this high-redshift era. We calculate the fraction of the cosmic gas that is in minihalos and find that it is substantially higher than would be expected with the previously-estimated characteristic mass. Expanding our investigation to the non-linear regime, we calculate in detail the spherical collapse of high-redshift objects in a Lambda-CDM universe. We include the gravitational contributions of the baryons and radiation and the memory of their kinematic coupling before recombination. We use our results to predict a more accurate halo mass function as a function of redshift.
We investigate the uncertainty in surface abundances and yields of asymptotic giant branch (AGB) stars. We apply three different mass loss laws to a 1.5 solar mass star of metallicity Z=0.008 at the beginning of the thermally pulsing asymptotic giant branch (TP-AGB) phase. Efficient third dredge-up is found even at very low envelope mass, contrary to previous simulations with other evolution codes. We find that the yield of carbon is uncertain by about 15% and for most other light elements the yield is uncertain at the level of 20-80%. For iron group elements the uncertainty varies from around 30% for the more abundant species to over a factor of two for the less abundant radioactive species, like iron-60. The post-AGB surface abundances for this mass and metallicity are much more uncertain due to the dilution of dredged-up material in differing envelope masses in the later stages of the models. Our results are compared to known planetary nebula (PN) and post-AGB abundances. We find that the models are mostly consistent with observations but we are unable to reproduce observations of some of the isotopes.
We consider the effects on the primordial power spectrum of a period of radiation-dominated expansion prior to the inflationary era. If inflation lasts a total of only 60 e-folds or so, the boundary condition for quantum modes cannot be taken in the short-wavelength limit as in the standard perturbation calculation. Instead, the boundary condition is set by the vacuum state of the prior radiation-dominated epoch, which only corresponds to the inflationary vacuum state in the ultraviolet limit. This altered vacuum state results in a modulation of the inflationary power spectrum. We calculate the modification to a best-fit model from the WMAP3 data set, and find that power is suppressed at large scales. The modified power spectrum is favored only very weakly by the data.
We present results of a multi-wavelength program to study the faint discrete X-ray source population discovered by Chandra in the Galactic Centre (GC). From IR imaging obtained with the VLT we identify candidate K-band counterparts to 75% of the X-ray sources in our sample. By combining follow-up VLT K-band spectroscopy of a subset of these candidate counterparts with the magnitude limits of our photometric survey, we suggest that only a small percentage of the sources are HMXBs, while the majority are likely to be canonical LMXBs and CVs at the distance of the GC. In addition, we present our discovery of highly structured small-scale (5-15") extinction towards the Galactic Centre. This is the finest-scale extinction study of the Galactic Centre to date. Finally, from these VLT observations we are able to place constraints on the stellar counterpart to the ``bursting pulsar'' GRO J1744-28.
We present Hubble Space Telescope (HST) images of new planetary nebulae (PNe) that were discovered in the Reid-Parker AAO/UKST H-alpha survey of the Large Magellanic Cloud. These serendipitous observations from various HST programs yield independent confirmations of 6 PNe; one other detected nebula may also be a PN, and one appears to be a region of diffuse emission. The high resolution HST archival images enable us to determine the physical sizes, the nebular morphology, and related features of these new PNe in detail for the first time. In a few cases we were also able to identify the central star, which was impossible with the lower resolution, wide-field discovery data. The confirmation of faint, extended halos surrounding many PNe in the RP catalog must await the acquisition of new deep, high-resolution, narrow-band imagery.
We present results from a survey of nearby AGN using the near infrared adaptive optics integral field spectrograph SINFONI. These data enable us to probe the distribution and kinematics of the gas and stars at spatial resolutions as small as 0.085arcsec. We find strong evidence for recent but short lived starbursts residing in very dense nuclear disks. On scales of less than 10pc these would have reached Eddington-limited luminosities when active, perhaps accounting for their short duration. In addition, for NGC1068 at a resolution of 6pc, we present direct observations of molecular gas close around the AGN which we identify with the obscuring torus.
Self-consistency of interaction models QGSJET 01, SIBYLL 2.1, NEXUS 3.97 and QGSJET II is checked in terms of their ability to reproduce simultaneously experimental data on fluxes of muons and hadrons. From this point of view SIBYLL 2.1 gives the most acceptable, though not quite satisfactory, results. Analysis of the situation for muons supports our previous conclusions, that high-energy muon deficit is due both to underestimation of primary light nuclei fluxes in direct emulsion chamber experiments and to softness of $p+A\to\pi^\pm,K^\pm+X$ inclusive spectra in fragmentation region, especially prominent in case of QGSJET 01 model.
In this work the vacuum inflation with a boundary condition specified at a short-distance scale in a generally primeval non-flat Universe, and implications of the correspondingly modified primordial power spectrum via the WMAP three year data are investigated. We obtain a general form of the modified primordial power spectrum including the effects of both possibly new physics and the curvature term. The modulation of the primordial power spectrum due to new physics is of the order $H/\Lambda$, where $H$ is the Hubble parameter during inflation and $\Lambda$ is the new physics scale that is key to inflation, while the modulation from the curvature term is of the order $K/k^2$, where $K$ is the space curvature before inflation and $k$ is the comoving wave number. We add two more parameters, which describe the effects from new physics scale and the curvature term respectively, into the six-parameter standard model of cosmology and make a fitting analysis with the WMAP data sets. The result shows that new physics would appear around the GUT scale and a closed Universe before inflation is slightly favored by the data fittings.
Is there a stellar upper mass limit? Recent statistical work seems to indicate that there is and that it is in the vicinity of 150 solar masses. In this paper we use HST and ground-based data to investigate the brightest members of the cluster Pismis 24, which was previously inferred to have a mass greater than 200 solar masses, in apparent disagreement with that limit. We determine that Pismis 24-1 is composed of at least three objects, the resolved Pismis 24-1SW and the unresolved spectroscopic binary Pismis 24-1NE. The evolutionary zero-age masses of those two objects and that of the nearby Pismis 24-17 are all approximately 100 solar masses, very large but under the stellar upper mass limit.
The known encounter velocity (6.1kms-1) and particle incidence angle (perpendicular) between the Stardust spacecraft and the dust emanating from the nucleus of comet Wild 2 fall within a range that allows simulation in laboratory light gas gun experiments designed to validate analytical methods for the interpretation of dust impacts on the aluminum foil components of the Stardust collector. Buckshot of a wide size, shape and density range of mineral, glass, polymer and metal grains, have been fired to impact perpendicularly upon samples of Stardust Al1100 foil, tightly wrapped onto aluminium alloy plate as an analogue of foil on the spacecraft collector. We have not yet been able to produce laboratory impacts by projectiles with weak and porous aggregate structure, as may occur in some cometary dust grains. In this report we present information on crater gross morphology and its dependence on particle size and density, the pre-existing major and trace element composition of the foil, geometrical issues for energy dispersive X-ray analysis of the impact residues in scanning electron microscopes, and the modification of dust chemical composition during creation of impact craters as revealed by analytical transmission electron microscopy. Together, these observations help to underpin the interpretation of size, density and composition for particles impacted upon the Stardust aluminum foils.
Microlensing has recently proven to be a valuable tool to search for extrasolar planets of Neptune- to super-Earth-mass planets at orbits of few AU. Since planetary signals are of very short duration, an intense and continuous monitoring is required, which is achieved by PLANET : ``Probing Lensing Anomalies NETwork''. Up to now the detection number amounts to four, one of them being OGLE 2005-BLG-390Lb, an extrasolar planet of only ~5.5 M_earth orbiting its M-dwarf host star at ~2.6 AU. For non-planetary microlensing events observed from 1995 to 2006, we compute detection efficiency diagrams which can then be used to derive an estimate of the limit on the Galactic abundance of sub-Jupiter-mass planets, as well as relative abundance of Neptune-like planets.
We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae, which will affect the dynamical evolution of their remnants. The ejecta of mergers consist of very neutron rich nuclei. Some of these neutron rich nuclei will produce observational signatures in form of gamma ray lines during their decay. The composition of the ejecta might even give interesting constraints about the internal structure of the neutron star. We further discuss the possibility that merger remnants appear as recently discovered 'dark accelerators' which are extended TeV sources which lack emission in other bands.
The detection of fast variations of the TeV (10^12 eV) gamma-ray flux, on time-scales of days, from the nearby radio galaxy M 87 is reported. These variations are ~10 times faster than that observed in any other waveband and imply a very compact emission region with a dimension similar to the Schwarzschild radius of the central black hole. We thus can exclude several other sites and processes of the gamma-ray production. The observations confirm that TeV gamma-rays are emitted by extragalactic sources other than blazars, where jets are not relativistically beamed towards the observer.
We present specific Star Formation Rate (sSFR) radial profiles for a sample
of 161 relatively face-on spiral galaxies from the GALEX Atlas of Nearby
Galaxies. The sSFR profiles are derived from GALEX & 2MASS (FUV-K) color
profiles after a proper SFR calibration of the UV luminosity and K-band
mass-to-light ratio are adopted. The (FUV-K) profiles were first corrected for
foreground Galactic extinction and later for internal extinction using the
ratio of the total-infrared (TIR) to FUV emission. For those objects where
TIR-to-FUV-ratio radial profiles were not available, the (FUV-NUV) color
profiles as a measure of the UV slope. The sSFR radial gradients derived from
these profiles allow us to quantify the inside-out scenario for the growth of
spiral disks for the first time in the local Universe.
We find a large dispersion in the slope of the sSFR profiles with a slightly
positive mean value, which implies a moderate inside-out disk formation. There
is also a strong dependency of the value of this slope on the luminosity and
size of the disks, with large systems showing a uniform, slightly positive
slope in almost all cases and low-luminosity small disks showing a large
dispersion with both positive and negative large values. While a majority of
the galaxies can be interpreted as forming stars gradually either from inside
out or from outside in, a few disks require episodes of enhanced recent growth
with scale lengths of the SFR (or gas infall) being significantly larger at
present than in the past. We do not find any clear dependence of the sSFR
gradient on the environment (local galaxy density or presence of close
neighbors).
We have identified 7824 radio sources from the 1.4GHz NRAO VLA Sky Survey
(NVSS) with galaxies brighter than K=12.75 mag. in the Second Incremental Data
Release of the 6dF Galaxy Survey (6dFGS DR2). The resulting sample of redshifts
and optical spectra for radio sources over an effective sky area of 7076 square
degrees (about 17% of the celestial sphere) is the largest of its kind ever
obtained. NVSS radio sources associated with galaxies in the 6dFGS span a
redshift range 0.003<z<0.3 and have median z=0.043. Through visual examination
of 6dF spectra we have identified the dominant mechanism for radio emission
from each galaxy. 60% are fuelled by star-formation and 40% are fuelled by an
active galactic nucleus powered by a supermassive black hole. We have
accurately determined the local radio luminosity function at 1.4GHz for both
classes of radio source and have found it to agree well with other recent
determinations. From the radio luminosity function of star-forming galaxies we
derive a local star formation density of 0.022+/-0.001 M_sun/yr/Mpc^3, in broad
agreement with recent determinations at radio and other wavelengths.
We have split the radio luminosity function of radio-loud AGN into bins of
absolute K-band magnitude (M_K) and compared this with the underlying K-band
galaxy luminosity function of all 6dFGS galaxies to determine the bivariate
radio-$K$-band luminosity function. We verify that radio-loud AGN
preferentially inhabit the brightest and hence most massive host galaxies and
show that the fraction of all galaxies which host a radio-loud AGN scales as
L_K^2.1, indicative of a similarly strong scaling with black hole mass and
stellar mass.
We have combined optical data from the 2dF-SDSS Luminous Red Galaxy and QSO
(2SLAQ) redshift survey with radio measurements from the 1.4 GHz VLA FIRST and
NVSS surveys to identify a volume-limited sample of 391 radio galaxies at
redshift 0.4<z<0.7. By determining an accurate radio luminosity function for
early-type galaxies in this redshift range, we can investigate the cosmic
evolution of the radio-galaxy population over a wide range in radio luminosity.
We find that low-power radio galaxies (those with 1.4 GHz radio luminosities
in the range 10^{24} to 10^{25} W/Hz, corresponding to FR I radio galaxies in
the local universe) undergo significant cosmic evolution over the redshift
range 0<z<0.7, consistent with pure luminosity evolution of the form (1+z)^k,
where k=2.0+/-0.3. Our results appear to rule out (at the 6-7 sigma level)
models in which low-power radio galaxies undergo no cosmic evolution. The most
powerful radio galaxies in our sample (with radio luminosities above 10^{26}
W/Hz) appear to undergo more rapid evolution over the same redshift range.
The evolution seen in the low-power radio-galaxy population implies that the
total energy input into massive early-type galaxies from AGN heating increases
with redshift, and was roughly 50% higher at z~0.55 (and up to a factor of two
higher at z~1) than in the local universe.
In this paper we study the infall, by dynamical friction, of rigid
"satellites" taken in a variety of initial configurations and models. We thus
measure how dynamical friction depends on the density concentration and on the
pressure anisotropy of the host galaxy and, separately, the response of the
galaxy during the process.
The investigation is carried out by using a numerical laboratory set up in
previous papers of this series.
We find that the pressure anisotropy present in the host galaxy has little
effect on dynamical friction. Instead, the shape of the galaxy density profile
is very important. The classical idealized description appears to be applicable
to galaxy models characterized by a small density gradient but not to
concentrated models. In contrast to the behavior found in small density
gradient models, the orbits of satellites captured in concentrated models are
not circularized by dynamical friction.
The induced evolution in the host galaxy reflects the initial conditions
adopted for the captured satellite. Satellites spiraling in on quasi-circular
orbits tend to modify the pressure tensor of the host galaxy in the tangential
direction and the galaxy shape from spherical to oblate, while satellites
captured along quasi-radial orbits tend to induce pressure anisotropy in the
radial direction and to generate a prolate shape. This result suggests that the
shape of early-type galaxies may result from occasional mergers rather than
being directly related to the effectiveness of the radial-orbit instability
during the process of formation via collisionless collapse, as often argued in
the past.
We have analyzed the two longest (elapsed time > 3 days) BeppoSAX
observations of the X-ray brightest Seyfert galaxy, NGC 4151, to search for
spectral variability on time-scales from a few tens of ksec to years. We found
in both cases highly significant spectral variability below ~ 6 keV down to the
shortest time-scales investigated. These variations can be naturally explained
in terms of variations in the low energy cut-off due to obscuring matter along
the line of sight. If the cut-off is modeled by two neutral absorption
components, one fully covering the source and the second covering only a
fraction of the source, the shortest time-scale of variability of a few days
constrains the location of the obscuring matter to within 3.4 X 10^4
Schwarzschild radii from the central X-ray source. This is consistent with the
distance of the Broad Emission Line Region, as inferred from reverberation
mapping, and difficult to reconcile with the parsec scale dusty molecular torus
of Krolik & Begelman (1988). We have also explored a more complex absorption
structure, namely the presence of an ionized absorber. Although the behaviour
of the ionization parameter is nicely consistent with the expectations, the
results are not completely satisfactory from the statistical point of view.
The overall absorption during the 2001 December observation is lower than in
all other historical observations with similar 2-10 keV flux. This suggests
that absorption variability plays a crucial role in the observed flux
variability of this source.
A light scalar field, minimally or not-minimally coupled to the metric field, is a well-defined candidate for the dark energy, overcoming the coincidence problem intrinsic to the cosmological constant and avoiding the difficulties of parameterizations. We present a general description of the weak gravitational lensing valid for every metric theory of gravity, including vector and tensor perturbations for a non-flat spatial metric. Based on this description, we investigate two minimally-coupled scalar field quintessence models using VIRMOS-Descart and CFHTLS cosmic shear data, and forecast the constraints for the proposed space-borne wide-field imager DUNE.
(Abridged) We present the results of the photometric and spectroscopic identification of 110 hard X-ray selected sources (6e-15<F(2-10 keV)<4e-14 cgs) from 5 additional XMM-Newton fields, nearly doubling the original HELLAS2XMM sample. We spectroscopically identified 59 new sources, bringing the completeness of the full HELLAS2XMM sample to ~70%. We found optical counterparts for 214 out of the 232 X-ray sources of the full sample down to R~25. We measure the flux and luminosity of the [OIII](5007) emission line for 59 such sources. Results. We use the full HELLAS2XMM and the CDF samples to estimate the LogN-LogS and the obscured QSO surface densities down to F(2-10 keV)~1e-14 and 1e-15 cgs. At these flux limits the fraction of X-ray selected obscured and unobscured QSO turns out to be similar. Since X-ray selection misses most Compton thick AGN, the number of obscured QSO may well outnumber that of unobscured QSOs. We find that hard X-ray selected AGNs with detected [OIII] emission span a wide range of L(2-10 keV)/L[OIII] with a median higher than that of optically selected AGNs, suggesting that optically selected samples are at least partly incomplete, and/or [OIII] emission is not a perfect isotropic indicator of the nuclear power. Differently from narrow-line AGNs in the same z interval, the 7 XBONGs candidates in the sample have L(2-10 keV)/L[OIII]> 1000, while their Lx, L(R) and Nh are similar. This suggests that while the central engine of narrow-line AGNs and XBONGs looks similar, the narrow-line region in XBONGs could be strongly inhibited or obscured.
A review on acoustic mode damping and excitation in solar-type stars is presented. Current models for linear damping rates are discussed in the light of recent low-degree solar linewidth measurements with emphasis on the frequency-dependence of damping rates of low-order modes. Recent developments in stochastic excitation models are reviewed and tested against the latest high-quality data of solar-like oscillations, such as from alpha Cen A, and against results obtained from hydrodynamical simulations.
We present an improved model for an asteroseismic diagnostic contained in the frequency spacing of low-degree acoustic modes. By modelling in a realistic manner regions of rapid variation of dynamically relevant quantities, which we call acoustic glitches, we can derive signatures of the gross properties of those glitches. In particular, we are interested in measuring properties that are related to the helium ionization zones and to the rapid variation in the background state associated with the lower boundary of the convective envelope. The formula for the seismic diagnostic is tested against a sequence of theoretical models of the Sun, and is compared with seismic diagnostics published previously by Monteiro & Thompson (1998, 2005) and by Basu et al. (2004).
We have studied the stellar main sequence (MS) of the globular cluster NGC2298 using deep HST/ACS observations in the F606W and F814W bands covering an area of 3.4' x 3.4' around the cluster centre or about twice the cluster's half-mass radius. The colour-magnitude diagram that we derive in this way reveals a narrow and well defined MS extending down to the 10 sigma detection limit at m_606~26.5, m_814~25, corresponding to stars of ~0.2 Msolar. The luminosity function (LF) obtained with these data, once corrected for the limited effects of photometric incompleteness, reveals a remarkable deficiency of low-mass stars as well as a radial gradient, in that the LF becomes progressively steeper with radius. Using the mass-luminosity relation appropriate for the metallicity of NGC2298, we derive the cluster's global mass function (GMF) by using a multi-mass Michie-King model. Over the range 0.8 - 0.2 Msolar, the number of stars per unit mass decreases following a power-law distribution of the type dN/dm \propto m^(0.5), where, for comparison, typical halo clusters have dN/dm \propto m^(-1.5). If the IMF of NGC2298 was similar to that of other metal poor halo clusters, like e.g. NGC6397, the present GMF that we obtain implies that this object must have lost of order 85% of its original mass, at a rate much higher than that suggested by current models based on the available cluster orbit. The latter may, therefore, need revision.
We present studies of a massive protocluster AFGL5142 in the J=2-1 transition
of the CO isotopologues, SO, CH_3OH and CH_3CN lines, as well as continuum at
225 GHz and 8.4 GHz. The 225 GHz continuum emission reveals three prominent
peaks MM-1, MM-2 and MM-3. MM-1 and MM-2 are associated with strong CH_3CN
emission with temperatures of 90 \pm 20 and 250 \pm 40 K, respectively, while
both MM-1 and MM-3 are associated with faint continuum emission at 8.4 GHz.
Additional dust continuum peaks MM-4 and MM-5 appear to be associated with \h2O
masers. With many continuum sources at cm and mm wavelengths, and those already
identified in the infrared, this region is forming a cluster of stars.
The CO and SO emission reveals at least three molecular outflows originating
from the center of the dust core. The outflows are well collimated, with
terminal velocities up to 50 \kms-1 from the cloud velocity. Outflow A
coincides with the SiO jet identified previously by Hunter et al. (1999). Since
jet-like outflows and disk-mediated accretion process are physically connected,
the well collimated outflows indicate that even in this cluster environment,
accretion is responsible for the formation of individual stars in the cluster.
We present statistical and monitoring results of narrow absorption lines that are physically related to quasars (i.e., intrinsic NALs). We use Keck/HIRES spectra of 37 optically bright quasars at z=2-4, and identify 150 NAL systems that contain 124 C IV, 12 N V, and 50 Si IV doublets. Among them, 39 are classified as intrinsic systems based on partial coverage analysis. At least 50% of quasars host intrinsic NALs. We identify two families of intrinsic systems based on their ionization state. Some intrinsic systems have detectable low-ionization NALs at similar velocities as higher-ionization NALs, although such low-ionization lines are rare in broad absorption line (BAL) systems. We also have observed an optically bright quasar, HS1603+3820, eight times with Subaru/HDS and HET/MRS over an interval of 4.2 years (1.2 years in the quasar rest frame), for the purpose of monitoring a variable C IV mini-BAL system. We find that all the troughs of the system vary in concert. However, no other correlations are seen between the variations of different profile parameters. We propose that the observed variations are either (i) a result of rapid continuum fluctuations, caused by a clumpy screen of variable optical depth located between the continuum source and the mini-BAL gas, or (ii) a result of variable scattering of continuum photons around the absorber.
We observed 69 A3-F8 main sequence binary star systems using the Multiband Imaging Photometer for Spitzer onboard the Spitzer Space Telescope. We find emission significantly in excess of predicted photospheric flux levels for 9(+4/-3)% and 40(+7/-6)% of these systems at 24 and 70 microns, respectively. Twenty two systems total have excess emission, including four systems that show excess emission at both wavelengths. A very large fraction (nearly 60%) of observed binary systems with small (<3 AU) separations have excess thermal mission. We interpret the observed infrared excesses as thermal emission from dust produced by collisions in planetesimal belts. The incidence of debris disks around main sequence A3-F8 binaries is marginally higher than that for single old AFGK stars. Whatever combination of nature (birth conditions of binary systems) and nurture (interactions between the two stars) drives the evolution of debris disks in binary systems, it is clear that planetesimal formation is not inhibited to any great degree. We model these dust disks through fitting the spectral energy distributions and derive typical dust temperatures in the range 100--200 K and typical fractional luminosities around 10^-5, with both parameters similar to other Spitzer-discovered debris disks. Our calculated dust temperatures suggest that about half the excesses we observe are derived from circumbinary planetesimal belts and around one third of the excesses clearly suggest circumstellar material. Three systems with excesses have dust in dynamically unstable regions, and we discuss possible scenarios for the origin of this short-lived dust.
We investigate the influence of the ionization of helium on the low-degree acoustic oscillation frequencies in model solar-type stars. The signature in the oscillation frequencies characterizing the ionization-induced depression of the first adiabatic exponent $\gamma$ is a superposition of two decaying periodic functions of frequency $\nu$, with `frequencies' that are approximately twice the acoustic depths of the centres of the Helium I and Helium II ionization regions. That variation is probably best exhibited in the second frequency difference $\Delta_2\nu_{n,l}\equiv\nu_{n-1,l}-2\nu{n,l}+\nu_{n+1,l}$. We show how an analytic approximation to the variation of $\gamma$ leads to a simple representation of this oscillatory contribution to $\Delta_2\nu$ which can be used to characterize the $\gamma$ variation, our intention being to use it as a seismic diagnostic of the helium abundance of the star. We emphasize that the objective is to characterize $\gamma$, not merely to find a formula for $\Delta_2\nu$ that reproduces the data.
We show that all X-ray decay curves of GRBs measured by Swift can be fitted
using one or two components both of which have exactly the same functional form
comprised of an early falling exponential phase followed by a power law decay.
The 1st component contains the prompt gamma-ray emission and the initial X-ray
decay. The 2nd component appears later, has a much longer duration and is
present for ~80% of GRBs. It most likely arises from the external shock which
eventually develops into the X-ray afterglow. In the remaining ~20% of GRBs the
initial X-ray decay of the 1st component fades more slowly than the 2nd and
dominates at late times to form an afterglow but it is not clear what the
origin of this emission is.
The temporal decay parameters and gamma/X-ray spectral indices derived for
107 GRBs are compared to the expectations of the standard fireball model
including a search for possible "jet breaks". For ~50% of GRBs the observed
afterglow is in accord with the model but for the rest the temporal and
spectral indices do not conform to the expected closure relations and are
suggestive of continued, late, energy injection. We identify a few possible jet
breaks but there are many examples where such breaks are predicted but are
absent.
The time, T_a, at which the exponential phase of the 2nd component changes to
a final powerlaw decay afterglow is correlated with the peak of the gamma-ray
spectrum, E_peak. This is analogous to the Ghirlanda relation, indicating that
this time is in some way related to optically observed break times measured for
pre-Swift bursts.
Double-black-hole binaries are among the most important sources of gravitational radiation for ground-based detectors such as LIGO or Virgo. Even if formed with lower efficiency than double-neutron-star binaries, they can dominate the predicted detection rates, since black holes are more massive than neutron stars and therefore could be detected at greater distances. Here we discuss a new binary evolution process that can very significantly limit the formation of close double-black-hole binaries: the vast majority of their potential progenitors undergo a common-envelope (CE) phase while the donor, one of the massive binary components, is evolving through the Hertzsprung gap. Our latest theoretical understanding of the CE process suggests that this will always leads to a merger, preventing the double-black-hole formation. Using population synthesis calculations, we find that the corresponding reduction in the merger rate of double black holes formed in galactic fields is so great (by \~500) that their contribution to inspiral detection rates for ground-based detectors could become relatively small (~ 1 in 20) compared to double-neutron-star binaries. Our predicted detection rates for Advanced LIGO are now much lower for double black holes (~2 per yr), but are still high for double neutron stars (~40 per yr). If double black holes were found to be dominant in the detected inspiral signals, this could indicate that they mainly originate from dense star clusters (not included here) or that our theoretical modeling of the CE phase needs significant revision.
NICMOS observations of the resolved object fluxes in the Hubble Deep Field North and the Hubble Ultra Deep Field are significantly below the fluxes attributed to a 1.4 - 1.8 microns Near InfraRed Background Excess (NIRBE) from previous low spatial resolution NIRS measurements. Tests placing sources in the NICMOS image with fluxes sufficient to account for the NIRBE indicate that the NIRBE flux must be either flat on scales greater than 100 arc second or clumped on scales of several arc minutes to avoid detection in the NICMOS image. A fluctuation analysis of the new NICMOS data shows a fluctuation spectrum consistent with that found at the same wavelength in deep 2MASS calibration images. The fluctuation analysis shows that the majority of the fluctuation power comes from resolved galaxies at redshifts of 1.5 and less and that the fluctuations observed in the earlier deep 2MASS observations can be completely accounted for with normal low redshift galaxies. Neither the NICMOS direct flux measurements nor the fluctuation analysis require an additional component of near infrared flux other than the flux from normal resolved galaxies in the redshift range between 0 and 7. The residual fluctuations in the angular range between 1 and 10 arc seconds is 1-2 nW m-2 sr-1 which is at or above several predictions of fluctuations from high redshift population III objects, but inconsistent with attributing the entire NIRBE to high redshift galaxies.
We calculate the transformation from the Sloan Digital Sky Survey (SDSS) photometric system to the Johnson-Morgan-Cousins System in the HK Survey. This research was done in late 2001, so the SDSS photometry was taken from the database prior to the release of DR1. This paper is being posted because it is referenced in other papers in the literature, but will not be submitted to a refereed journal because it uses unpublished versions of the catalogs.
A photoionized gas in thermal equilibrium can display a thermal instability, with 3 or more solutions in the multi-branch region of the S-shape curve giving the temperature versus the radiation-to-gas-pressure ratio. Many studies have been devoted to this curve and to its dependence on different parameters, always in the optically thin case. The purpose of our study is the thermal instability in optically thick, stratified media, in total pressure equilibrium. We have developped a new algorithm to select the hot/cold stable solution, and thereof to compute a fully consistent photoionization model. We have implemented it in the TITAN code and computed a set of models encompassing the range of conditions valid for the Warm Absorber in Active Galactic Nuclei. We have demonstrated that the thermal instability problem is quite different in thin or thick media. In thick media the spectral distribution changes as the radiation progresses inside the ionized gas. This has observational implications in the emitted/absorbed spectra, ionization states, and variability. However impossible to know what solution the plasma will adopt when attaining the multi-solutions regime, we expect the emitted/absorbed spectrum to be intermediate between those resulting from pure cold and hot models. Large spectral fluctuations corresponding to the onset of a cold/hot solution could be observed in timescales of the order of the dynamical time. A strong turbulence implying supersonic velocities should permanently exist in the multi-branch region of thick, stratified, pressure equilibrium media.
We assess the claim that Ultra-luminous X-ray sources (ULXs) host intermediate-mass black holes (BH) by comparing the cool disc-blackbody model with a range of other models, namelly a more complex physical model based on a power-law component slightly modified at various energies by smeared emission/absorption lines from highly-ionized gas. Our main conclusion is that the presence of a soft excess, or a soft deficit, depends entirely on the energy range to which we choose to fit the ``true'' power-law continuum; hence, we argue that those components should not be taken as evidence for accretion disc emission, nor used to infer BH masses. We speculate that bright ULXs could be in a spectral state similar to (or an extension of) the steep-power-law state of Galactic BH candidates, in which the disc is completely comptonized and not directly detectable, and the power-law emission may be modified by the surrounding, fast-moving, ionized gas.
We have studied the thermal instabilities in the context of Active Galactic Nuclei (AGN), addressing the cases of thin and thick (stratified) X-ray illuminated media. For that, we have compared the behaviour of different models in pressure equilibrium. Ionized gas in pressure equilibrium show temperature discontinuities which, however difficult to tackle, can be modelled with the transfer-photoionization code TITAN. Our code allows to choose between the hot and the cold stable solutions in the multi-branch regime of the S-curve, and then to compute a fully consistent photoionisation model with the chosen solution. For the first time, it is now possible to compare the true stable solution models with the approximate solution model normally used. Our studies may be applied to media in any pressure equilibrium conditions, e.g. constant gas pressure, constant total pressure, or hydrostatic pressure equilibrium; they can be used to model irradiated accretion discs in AGN, the Warm Absorber in type 1 AGN, or the X-ray line-emitting gas in type 2 AGN.
We propose a new Monte Carlo method to study extended X-ray sources with the European Photon Imaging Camera (EPIC) aboard XMM Newton. The Smoothed Particle Inference (SPI) technique, described in a companion paper, is applied here to the EPIC data for the clusters of galaxies Abell 1689, Centaurus and RXJ 0658-55 (the ``bullet cluster''). We aim to show the advantages of this method of simultaneous spectral-spatial modeling over traditional X-ray spectral analysis. In Abell 1689 we confirm our earlier findings about structure in temperature distribution and produce a high resolution temperature map. We also confirm our findings about velocity structure within the gas. In the bullet cluster, RXJ 0658-55, we produce the highest resolution temperature map yet to be published of this cluster allowing us to trace what looks like the motion of the bullet in the cluster. We even detect a south to north temperature gradient within the bullet itself. In the Centaurus cluster we detect, by dividing up the luminosity of the cluster in bands of gas temperatures, a striking feature to the north-east of the cluster core. We hypothesize that this feature is caused by a subcluster left over from a substantial merger that slightly displaced the core. We conclude that our method is very powerful in determining the spatial distributions of plasma temperatures and very useful for systematic studies in cluster structure.
We present a new model-independent method of comparison of NIR visibility data of YSOs. The method is based on scaling the measured baseline with the YSO's distance and luminosity, which removes the dependence of visibility on these two variables. We use this method to compare all available NIR visibility data and demonstrate that it distinguishes YSOs of luminosity >1000L_sun (low-L) from YSOs of <1000L_sun (high-L). This confirms earlier suggestions, based on fits of image models to the visibility data, for the difference between the NIR sizes of these two luminosity groups. When plotted against the ``scaled'' baseline, the visibility creates the following data clusters: low-L Herbig Ae/Be stars, T Tauri stars, and high-L Herbig Be stars. The T Tau cluster is similar to the low-L Herbig Ae/Be cluster, which has ~7 times smaller ``scaled'' baselines than the high-L Herbig Be cluster. We model the shape and size of clusters with different image models and find that low-L Herbig stars are the best explained by the uniform brightness ring and the halo model, T Tauri stars with the halo model, and high-L Herbig stars with the accretion disk model. However, the plausibility of each model is not well established. Therefore, we try to build a descriptive model of the circumstellar environment consistent with various observed properties of YSOs. We argue that low-L YSOs have optically thick disks with the optically thin inner dust sublimation cavity and an optically thin dusty outflow above the inner disk regions. High-L YSOs have optically thick accretion disks with high accretion rates enabling gas to dominate the NIR emission over dust. Although observations would favor such a description of YSOs, the required dust distribution is not supported by our current understanding of dust dynamics.
We present an indirect dynamical evidence, based on the measure of the core to half mass radius ratio (rc/rh), that a significant fraction of globular clusters in our galaxy with an age greater than 10 half-mass relaxation times (t_rh) host an intermediate mass black hole (IMBH). In fact, after a few t_rh much of the memory about the details of initial conditions is erased and rc/rh is determined solely by the balance of the stellar encounters energy production in the core with the dissipation due to global expansion of the cluster. Here we compare the observed values of rc/rh from a sample of 57 galactic globular cluster, selected to be dynamically old and not strongly influenced by tidal forces, with the theoretical expectation for the rc/rh ratio based on analytical models and detailed numerical simulations. The simulations of the evolution of star clusters considered include combinations of single stars, primordial binaries and IMBH. For at least half of the clusters in our sample the observed rc/rh ratio appears to be too large to be explained without invoking the presence of an IMBH at the center of the system.
In this letter we consider the evolution of a planetary system around a star inside a wide binary. We simulate numerically the evolution of the planetary orbits for both co-planar and highly-inclined systems. We find that the Kozai mechanism operates in the latter case. This produces a highly eccentric outer planet whose orbit crosses those of some of the inner planets. Strong planet-planet interactions then follow resulting in the ejection of one or more planets. We note that planetary systems resembling our solar system, formed around single stars in stellar clusters may exchange into binaries and thus will be vulnerable to planet stripping. This process will reduce the number of solar-system like planetary systems, and may produce at least some of the observed extra-solar planets.
In order to investigate the dependence of quasar variability on fundamental physical parameters like black hole mass, we have matched quasars from the QUEST1 Variability Survey with broad-lined objects from the Sloan Digital Sky Survey. The matched sample contains approximately 100 quasars, and the Sloan spectra are used to estimate black hole masses and bolometric luminosities. Variability amplitudes are measured from the QUEST1 light curves. We find that black hole mass correlates with several measures of the variability amplitude at the 99% significance level or better. The correlation does not appear to be caused by obvious selection effects inherent to flux-limited quasar samples, host galaxy contamination or other well-known correlations between quasar variability and luminosity/redshift. We evaluate variability as a function of rest-frame time lag using structure functions, and find further support for the variability--black hole mass correlation. The correlation is strongest for time lags of the order a few months up to the QUEST1 maximum temporal resolution of approximately 2 years, and may provide important clues for understanding the long-standing problem of the origin of quasar optical variability. We discuss whether our result is a manifestation of a relation between characteristic variability timescale and black hole mass, where the variability timescale is typical for accretion disk thermal timescales, but find little support for this. Our favoured explanation is that more massive black holes have larger variability amplitudes, and we highlight the need for larger samples with more complete temporal sampling to test the robustness of this result.
Although the Sloan Digital Sky Survey has permitted the discovery of an increasing number of new ZZ Ceti stars, recent published analyses have shown that there are still many relatively bright (V < 17) ZZ Ceti stars waiting to be found. We will discuss the discovery of several such objects in addition to a number of DA stars in which we detected no photometric variations. These were uncovered as part of an ongoing spectroscopic survey of DA white dwarfs from the McCook & Sion Catalog. By determining the atmospheric parameters of a large sample of DA stars, we were able to identify objects placed within or near the empirical boundaries of the ZZ Ceti instability strip. By establishing the photometric status of these stars, we can use them in an effort to conclusively pin down the empirical boundaries of the ZZ Ceti instability strip.
Eccentricity or obliquity tides have been proposed as the missing energy source that may explain the anomalously large radius of some transiting ``hot Jupiters''. To maintain a non-zero and large obliquity, it was argued that the planets can be locked in a Cassini state, i.e. a resonance between spin and orbital precessions. We compute the tidal heating within ``inflated'' close-in giant planets with a non-zero eccentricity or obliquity. We further inspect whether the spin of a ``hot Jupiter'' could have been trapped and maintained in a Cassini state during its early despinning and migration. We estimate the capture probability in a spin-orbit resonance between $\sim$ 0.5 AU (a distance where tidal effects become significant) and 0.05 AU for a wide range of secular orbital frequencies and amplitudes of gravitational perturbations. Numerical simulations of the spin evolution are performed to explore the influence of tidal despinning and migration processes on the resonance stability. We find that tidal heating within a non-synchronous giant planet is about twice larger than previous estimates based on the hypothesis of synchronization. Chances of capture in a spin-orbit resonance are very good around 0.5 AU but they decrease dramatically with the semi-major axis. Furthermore, even if captured, both tidal despinning and migration processes cause the tidal torque to become large enough that the obliquity ultimately leaves the resonance and switches to near $0^{\circ}$. Locking a ``hot Jupiter'' in an isolated spin-orbit resonance is unlikely at 0.05 AU but could be possible at larger distances. Another mechanism is then required to maintain a large obliquity and create internal heating through obliquity tides
The mid-IR flux ratios F_A/F_B = 2.84 +/- 0.06 of the two images of the gravitationally lensed quasar HE 1104-1805 show no wavelength dependence to within 3% across 3.6-8.0 um, no time dependence over 6 months and agree with the broad emission line flux ratios. This indicates that the mid-IR emission likely comes from scales large enough to be little affected by microlensing and that there is little differential extinction between the images. We measure a revised time-delay between these two images of 152.2 +2.8-3.0 days from R and V-band data covering 1997 to 2006. This time-delay indicates that the lens has an approximately flat rotation curve over scales of 1-2 R_e. We also observed uncorrelated variations of ~0.05 mag/yr which we attribute to microlensing of the optical emission from the accretion disk. The optical colors have also changed significantly in the sense that image A is now redder than image B, rather than bluer as it was in 1993.
We present the general notions and observational consequences of the "Supercritical Pile" GRB model; the fundamental feature of this model is a detailed process for the conversion of the energy stored in relativistic protons in the GRB Relativistic Blast Waves (RBW) into relativistic electrons and then into radiation. The conversion is effected through the $p \gamma \to p e^+e^-$ reaction, whose kinematic threshold is imprinted on the GRB spectra to provide a peak of their emitted luminosity at energy \Ep $\sim 1$ MeV in the lab frame. We extend this model to include, in addition to the (quasi--)thermal relativistic post-shock protons an accelerated component of power law form. This component guarantees the production of $e^+e^- -$pairs even after the RBW has slowed down to the point that its (quasi--)thermal protons cannot fulfill the threshold of the above reaction. We suggest that this last condition marks the transition from the prompt to the afterglow GRB phase. We also discuss conditions under which this transition is accompanied by a significant drop in the flux and could thus account for several puzzling, recent observations. Finally, we indicate that the same mechanism applied to the late stages of the GRB evolution leads to a decrease in \Ep $\propto \Gamma^2(t)\propto t^{-3/4}$, a feature amenable to future observational tests.
The study of the ages of early-type galaxies and their dependence on galaxy mass and environment is crucial for understanding the formation and early evolution of galaxies. We review recent works on the M/L ratio evolution, as derived from an analysis of the Fundamental Plane of early-type galaxies at z~1 both in the field and in the clusters environment. We use the M/L ratio to derive an estimate of the galaxy age. We also use a set of high-S/N intermediate-resolution VLT spectra of a sample of early-type galaxies with 0.88<z<1.3 from the K20 survey to derive an independent estimate of their age by fitting SSP model spectra. Taking advantage of the good leverage provided by the high sample redshift, we analyse the results in comparison with the ages obtained for the same sample from the analysis of the M/L ratio, and with the predictions of the current hierarchical models of galaxy formation.
Table 1 in our paper, ApJ 648, 774 (2006) entitled "Intergalactic Photon Spectra from the Far IR to the UV Lyman Limit for 0 < z < 6 and the Optical Depth of the Universe to High Energy Gamma-Rays" had erroneous numbers for the coefficients fitting the parametric form for the optical depth of the universe to gamma-rays. The correct values for these parameters as described in the original text are given here in a corrected table for various redshifts for the baseline model (upper row) and fast evolution (lower row) for each individual redshift.
I present a review of chemical evolution models of the solar neighborhood. I give special attention to the necessary ingredients to reproduce the observed [Xi/Fe] ratios in nearby metal and super metal rich stars, and to the chemical properties of the solar vicinity focusing on [Fe/H] > -0.1. I suggest that the observed abundance trends are due to material synthesized and ejected by intermediate mass stars with solar metallicity in the AGB stage, and also by massive stars with (super) solar metallicity in the stellar wind and supernovae stages. The required tool to build chemical evolution models that reach super-solar metallicities is the computation of stellar yields for stellar metallicities higher than the initial solar value. Based on these models it might be possible to estimate the importance of merger events in the recent history of the Galactic disk as well as the relevance of radial stellar migration from the inner to the outer regions of the Galaxy. I also present a short review of the photospheric solar abundances and their relation with the initial solar abundances.
In recent years, an increasing number of proper motions have been measured for Galactic X-ray binaries. When supplemented with accurate determinations of the component masses, orbital period, and donor luminosity and effective temperature, these kinematical constraints harbor a wealth of information on the systems' past evolution. The constraints on compact object progenitors and kicks derived from this are of immense value for understanding compact object formation and exposing common threads and fundamental differences between black hole and neutron star formation. Here, we present the results of such an analysis for the black hole X-ray binary XTE J1118+480. We present results from modeling the mass transfer phase, following the motion in the Galaxy back to the birth site of the black hole, and examining the dynamics of symmetric and asymmetric core-collapses of the black hole progenitor.
Most cosmic-ray air shower arrays have focused on detecting electromagnetic shower particles and low energy muons. A few groups (most notably MACRO + EASTOP and SPASE + AMANDA) have studied the high energy muon component of showers. However, these experiments had small solid angles, and did not study muons far from the core. The IceTop + IceCube combination, with its 1 km$^2$ muon detection area can study muons far from the shower core. IceCube can measure their energy loss ($dE/dx$), and hence their energy. With the energy, and the known distribution of production heights, the transverse momentum ($p_T$) spectrum of high $p_T$ muons can be determined. The production of these muons is calculable in perturbative QCD, so the measured muon spectra can be used to probe the composition of incident cosmic-rays.
Some recent results on rotating self-gravitating configurations composed with Bosons and Fermions are reported. Given a star composed of both Bosons and Fermions without interaction, it is shown that it is possible to obtain stable slowly rotating configurations by using the same perturbative relativistic method that usually describes neutron stars.
We present multiwavelength observations of the very luminous "E+A" galaxy known as G515 (J152426.55+080906.7), including deep K_s imaging, spatially resolved H-alpha spectroscopy, and radio observations. The data, together with detailed spectral synthesis of the galaxy's integrated stellar population, show that G515 is a ~1 Gyr old post-merger, post-starburst galaxy. We detect no Balmer line emission in the galaxy, although there is a small amount of [NII]6548,6583A emission. The galaxy's H I mass has a 2-sigma upper limit of 1.0 * 10^9 solar masses. IRAS detections in the 60-micron and 100-micron bands indicate a far infrared luminosity of ~5.8 * 10^10 solar luminosities. A small amount (~3 mJy) of radio continuum flux, which appears to be variable, has been detected. The data suggest that G515 may have once been an ultraluminous infrared galaxy, and may harbor a weak, dust-obscured active nucleus.
A forefront area of research concerns the exploration of the properties of hadronic matter under extreme conditions of temperature and density, and the determination of the equation of state--the relation between pressure, temperature and density--of such matter. Experimentally, relativistic heavy-ion collision experiments enable physicists to cast a brief glance at hot and ultra-dense matter for times as little as about $10^{-22}$ seconds. Complementary to this, the matter that exists in the cores of neutron stars, observed as radio pulsars, X-ray pulsars, and magnetars, is at low temperatures but compressed permanently to ultra-high densities that may be more than an order of magnitude higher than the density of atomic nuclei. This makes pulsars superb astrophysical laboratories for medium and high-energy nuclear physics, as discussed in this paper.
With current terrestrial gravitational wave detectors working at initial design sensitivities, and upgrades and space missions planned, it is likely that in the next five to ten years gravitational radiation will be detected directly from a variety of classes of objects. The most confidently expected of these classes is compact binaries, involving neutron stars or black holes. Detection of their coalescence, or their long-term orbits, has the potential to inform us about the evolutionary history of compact binaries and possibly even star formation over the past several billion years. We review what is currently known about compact binaries as sources of gravitational radiation, as well as the current uncertainties and what we expect to learn from future detections of gravitational waves from these systems.
To be published in the proceedings of IAU Symposium 239 "Convection in Astrophysics" (ed. F. Kupka, I. W. Roxburgh, K. L. Chan). Content: 1. From Nice to Prague, 2. The triumph of 3-D simulations, 3. How to lower the cost - what else can be done? 4. A powerful tool to determine surface abundances, 5. The effects of convection are not confined to convection zones, 6. Towards a realistic model of the solar dynamo, 7. The moment of truth: facing observational tests, 8. On my wish-list.
We present sensitive, high angular resolution 1.3 cm and 7 mm observations of the massive core NGC 6334 I(N), a region known to be undergoing massive star formation. At 1.3 cm we detect three sources, of which two had been previously detected at centimeter or millimeter wavelengths. At 7 mm we detect four sources. We suggest that three of these sources are subcomponents of the millimeter source SMA 1, that at these wavelengths is the dominant source in the region. The fourth 7 mm source appears to be associated with the relatively isolated source SMA 6. In all four 7 mm sources, the continuum emission is arising from structures of dimensions in the order of 1000 AU for which we estimate masses of order a few solar masses. We interpret these 7 mm sources as massive circumstellar disks that, however, surround stars or compact small stellar groups that at present have masses comparable to those of the disks but that may be accreting on their way to become massive stars.
We present a Chandra survey of LMXBs in 24 early-type galaxies. Correcting for detection incompleteness, the X-ray luminosity function (XLF) of each galaxy is consistent with a powerlaw with negative logarithmic differential slope, beta~2.0. However, beta strongly correlates with incompleteness, indicating the XLF flattens at low-Lx. The composite XLF is well-fitted by a powerlaw with a break at (1.8^{+0.37}_{-0.32})\times 10^{38} erg/s and beta=0.99+/-0.15 and 2.82^{+0.30}_{-0.24} below and above it, respectively. The break is close to the Eddington limit for a 1.4Msun neutron-star, but the XLF shape rules out its representing the division between neutron-star and black-hole systems. Although the XLFs are similar, we find evidence of some variation between galaxies. The high-Lz XLF slope does not correlate with age, but may correlate with [alpha/Fe]. Matching the LMXBs with globular clusters (GCs) identified in HST observations of 19 of the galaxies, we find the probability a GC hosts an LMXB is proportional to {L_{GC}^\alpha Z_{Fe}^\gamma} where alpha=0.85+/-0.16 and gamma=0.30+/-0.11. Correcting for GC luminosity and colour effects, and detection incompleteness, we find no evidence that the fraction of LMXBs in GCs (41%), or the fraction of GCs hosting LMXBs (~5.3%) varies between galaxies. The spatial distribution of LMXBs resembles that of red GCs, and the specific frequency of LMXB is proportional to the GC specific luminosity, consistent with the hypothesis that all LMXB form in GCs. Our results imply ~1.1 LMXB are formed Gyr^{-1} per GC and we place an upper limit of 1 LMXB formed in the field per 1.9E9Lsun of V-band luminosity.
Aims: Study the high-mass X-ray binary X-7 in M33 using broad-band optical
data.
Methods: We used recently published CFHT r' and i' data for variable stars in
M33 to extract the light curve of the optical counterpart of X-7. We combined
these data with DIRECT B and V measurements in order to search for an
independent optical modulation with the X-ray periodicity. The periodic
modulation is modelled with the ellipsoidal effect. We used UBVRr'i' magnitudes
of the system to constrain the temperature and radius of the optical component.
Results: The optical data revealed a periodicity of 3.4530 +- 0.0014 days,
which is consistent with the known X-ray period. Double modulation, which we
attributed to ellipsoidal modulation, is clearly seen in four different optical
bands. The absolute magnitude in six optical bands is most consistent with a
stellar counterpart with 33000 < T_{eff} < 47000 K and 15 < R < 20 R_{\sun}. We
modelled the optical periodic modulation and derived the masses of the two
components as a function of the orbital inclination and the radius of the
stellar component. The resulting mass range for the compact object is 1.3 < M <
23 M_{\sun}.
Conclusions: The system is probably a black hole HMXB, similar to Cyg X-1,
LMC X-1 and LMC X-3.
In this paper we analyze the constraints on the property of dark energy from cosmological observations. We include 52 long Gamma-Ray Bursts (GRBs) data in our study. Together with SNe Ia Gold sample, WMAP, SDSS and 2dFGRS data, we perform global fitting using Markov Chain Monte Carlo (MCMC) technique. Dark energy perturbations are explicitly considered. We pay particular attention to the time evolution of the equation of state of dark energy parameterized as w_{DE}=w_o+w_a(1-a) with a the scale factor of the universe, emphasizing the complementarity of high redshift GRBs to other cosmological probes. It is found that the constraints on dark energy become stringent by taking into account high redshift GRBs, especially for w_a, which delineates the evolution of dark energy. The best fitting dark energy model has w_0=-1.09 and w_a=0.89. The cosmological constant with w_0=-1 and w_a=0 is well within 2\sigma range.
The recent discovery of burst oscillations at 1122 Hz in the x-ray transient XTE J1739-285, together with the measurement of the mass of the binary millisecond pulsar PSR J0751+1807 (2.1 +- 0.2 solar masses) can finally allow us to put strong, model-independent observational constraints to the equation of state of compact stars. We show that the measurement of the moment of inertia of PSR J0737+3039A, together with these constraints, could allow to discriminate further the details of the inner structure of neutron stars. Moreover, we show that if XTE J1739-285 is constituted of nucleonic matter, any equation of state allows only a narrow range of very high masses, and this could explain why up to now compact stars spinning faster than a millisecond have been so difficult to detect.
The high occurrence on Earth of ordinary chondrite meteorites and the making of models based upon arbitrary assumptions has led to some confusion about the origin of ordinary chondrites. Major element fractionation among chondrites has been discussed for decades as ratios relative to Si or Mg. Expressing ratios relative to Fe leads to a new relationship admitting the possibility that ordinary chondrite meteorites are derived from two components: one is a relatively undifferentiated, primitive component, oxidized like the CI or C1 chondrites; the other is a somewhat differentiated, planetary component, with oxidation state like the reduced enstatite chondrites. Such a picture would seem to explain for the ordinary chondrites, their major element compositions, their intermediate states of oxidation, and their ubiquitous defiencies of refractory siderophile elements. I suggest that the planetary component of ordinary chondrite formation consists of planet Mercury's missing complement of elements, presumably separated from protoplanetary Mercury during its formation.
We present JHK-band near-infrared photometry of star clusters in the dwarf irregular galaxy IC 5152. After excluding possible foreground stars, a number of candidate star clusters are identified in the near-infrared images of IC 5152, which include young populations. Especially, five young star clusters are identified in the (J-H, H-K) two color diagram and the total extinction values toward these clusters are estimated to be A_V =2 - 6 from the comparison with the theoretical values given by the Leitherer et al. (1999)'s theoretical star cluster model.
The influence of microlensing in the profiles of the emission lines generated in a biconical geometry is discussed. Microlensing amplification in this anisotropic model is not directly related to the bicone's intrinsic size but depends on the orientation of the bicone axis and on the cone aperture. The orientation of the projected bicone with respect to the shear of the magnification pattern can induce very interesting effects, like the quasi-periodic enhancements of the red/blue part of the emission line profile or the lack of correlation between the broad line region (BLR) and continuum light curves of QSOs. The emission line profiles of a BLR moving in a high caustic concentration exhibit sharp features that are well defined in wavelength. These features (spikes) correspond to the scanning of the kinematics of the BLR by the caustic clusters. The biconical model can qualitatively reproduce with a transversal (with respect to the shear) movement of the BLR, the recurrent blue-wing enhancement detected in the emission line profile of the A image of the quasar lensed system SDSS J1004+4112. The probability of observing this repetitive event is almost a 2% for a fraction of matter in stars of a 5%. This result would make plausible the detection of the spectral variability in SDSS J1004+4112 under the hypothesis of microlensing of a bicone.
During its first cycle of observations, the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescope has observed very high energy gamma-rays from fife galactic objects: the Crab Nebula, the SNRs HESS J1813-178 and HESS J1834-087, the Galactic Center and the gamma-ray binary LS I +61 303. After a short introduction to the MAGIC telescope and the data analysis procedure, the results of these fife sources are reviewed.
We have developed a method to calculate overdensities in multicolour surveys, facilitating a direct comparison of the local density contrast measured using galaxy samples that have different redshift error distributions, i.e. for red and blue, or bright and faint galaxies, respectively. We calculate overdensities for three COMBO-17 fields, and identify a region in the Chandra Deep Field South that is underdense by almost a factor 2 compared to the other two fields in the same redshift range (0.25< z < 0.4). This can be used for an investigation of the variation of the type-dependent luminosity function with environment: We calculate the luminosity function in this redshift range for red sequence and blue cloud galaxies in each of the fields separately. While the luminosity function of the blue galaxies remains unaffected by different density contrasts, the luminosity function of the red galaxies clearly has a more positive faint-end slope in the CDFS. The underdensity there is thus mainly due to a deficiency of faint red galaxies. This result is in qualitative agreement with the trends seen at z=0.1 in the 2dFGRS.
We present a quantitative study of the quantum decoherence of curvature perturbations during inflation in the presence of isocurvature modes. If the latter cannot be observed directly, tracing them out effectively decoheres the curvature perturbation even in the absence of a direct coupling between the scalar fields involved. We then calculate the entanglement entropy and argue that it provides a quantitative measure for decoherence.
We summarize multiwavelength properties of a sample of galaxies in the CDF-N and CDF-S whose Spectral Energy Distributions (SEDs) exhibit the characteristic power-law behavior expected for AGN in the Spitzer/IRAC 3.6-8micron bands. AGN selected this way tend to comprise the majority of high X-ray luminosity AGN, whereas AGN selected via other IRAC color-color criteria might contain more star-formation dominated galaxies. Approximately half of these IR power-law galaxies in the CDF-S are detected in deep (1Ms) Chandra X-ray imaging, although in the CDF-N (2Ms) about 77% are detected at the 3sigma level. The SEDs and X-ray upper limits of the sources not detected in X-rays are consistent with those of obscured AGN, and are significantly different from those of massive star-forming galaxies. About 40% of IR power-law galaxies detected in X-rays have SEDs resembling that of an optical QSO and morphologies dominated by bright point source emission. The remaining 60% have SEDs whose UV and optical continuum are much steeper (obscured) and more extended morphologies than those detected in X-rays. Most of the IR power-law galaxies not detected in X-rays have IR (8-1000micron above 10^12Lsun, and X-ray (upper limits) to mid-IR ratios similar to those of local warm (ie, hosting an AGN) ULIRGs. The SED shapes of power-law galaxies are consistent with the obscured fraction (4:1) as derived from the X-ray column densities, if we assume that all the sources not detected in X-rays are heavily absorbed. IR power-law galaxies may account for between 20% and 50% of the predicted number density of mid-IR detected obscured AGN. The remaining obscured AGN probably have rest-frame SEDs dominated by stellar emission.
A supermassive black hole in the nucleus of a galaxy will be revealed when a star passes close enough to be torn apart by tidal forces and a flare of radiation is emitted by the stream of stellar debris that plunges into the black hole. Since common active galactic nuclei have accreting black holes that can also produce flares, a convincing demonstration that a stellar tidal disruption has occurred generally begins with a ``normal'' galaxy that has no evidence of prior nuclear activity. Here we report a luminous UV flare from an elliptical galaxy at z = 0.37 in the Groth field of the GALEX Deep Imaging Survey that has no evidence of a Seyfert nucleus from optical spectroscopy and X-ray imaging obtained during the flare. Multiwavelength data collected at the time of the event, and for 2 years following, allow us to constrain, for the first time, the spectral energy distribution of a candidate tidal disruption flare from optical through X-rays. The luminosity and temperature of the radiation and the decay curve of the flare are in excellent agreement with theoretical predictions for the tidal disruption of a star, and provide the strongest empirical evidence for a stellar disruption event to date.
We discuss the origin of superluminal radio jets in Black hole X-ray binaries with relativistic radio jets in our Galaxy popularly known as microquasars. We classify the relativistic superluminal jet according to the radio emission in black hole X-ray binaries (transient or persistent) rather than the mass of the companion. The black hole X-ray binaries with transient radio emission (mostly LMXBs) produce superluminal jets with $\beta_{app} >$ 1 when the accretion rate, $\dot{m}_{accr}$ is high and the bolometric luminosity L$_{bol}$ approaches the Eddington Luminosity, L$_{Edd}$. On the other hand, the black hole X-ray binaries with persistent radio emission (mostly HMXBs) produce superluminal jets with $\beta_{app} <$ 1 at relatively low $\dot{m}_{accr}$. We specially discuss the case of V4641 Sgr, a HMXB with transient radio emission which produces superluminal radio jets like in LMXBs.
Our goal is to study the effects of the UV radiation from the first stars, quasars and hypothetical Super Heavy Dark Matter (SHDM) particle decays on the formation of primordial bound objects in the Universe. We trace the evolution of a spherically symmetric density perturbation in the Lambda Cold Dark Matter and MOND model, solving the frequency-dependent radiative transfer equation, non-equilibrium chemistry, and one-dimensional gas hydrodynamics. We concentrate on the destruction and formation processes of the $H_{2}$ molecule, which is the main coolant in the primordial objects.
Advances in our understanding and the modeling of stellar core-collapse and supernova explosions over the past 15 years are reviewed, concentrating on the evolution of hydrodynamical simulations, the description of weak interactions and nuclear equation of state effects, and new insights into the nucleosynthesis occurring in the early phases of the explosion, in particular the neutrino-p process. The latter is enabled by the proton-richness of the early ejecta, which was discovered because of significant progress has been made in the treatment of neutrino transport and weak interactions. This progress has led to a new generation of sophisticated Newtonian and relativistic hydrodynamics simulations in spherical symmetry. Based on these, it is now clear that the prompt bounce-shock mechanism is not the driver of supernova explosions, and that the delayed neutrino-heating mechanism can produce explosions without the aid of multi-dimensional processes only if the progenitor star has an ONeMg core inside a very dilute He-core, i.e., has a mass in the 8--10 solar mass range. Hydrodynamic instabilities of various kinds have indeed been recognized to occur in the supernova core and to be of potential importance for the explosion. Neutrino-driven explosions, however, have been seen in two-dimensional simulations with sophisticated neutrino transport so far only when the star has a small iron core and low density in the surrounding shells as being found in stars near 10--11 solar masses. The explosion mechanism of more massive progenitors is still a puzzle. It might involve effects of three-dimensional hydrodynamics or might point to the relevance of rapid rotation and magnetohydrodynamics, or to still incompletely explored properties of neutrinos and the high-density equation of state.
Coalescing binary black holes experience a ``kick'' due to anisotropic emission of gravitational waves with an amplitude as great as ~200 km/s. We examine the orbital evolution of black holes that have been kicked from the centers of triaxial galaxies. Time scales for orbital decay are generally longer in triaxial galaxies than in equivalent spherical galaxies, since a kicked black hole does not return directly through the dense center where the dynamical friction force is highest. We evaluate this effect by constructing self-consistent triaxial models and integrating the trajectories of massive particles after they are ejected from the center; the dynamical friction force is computed directly from the velocity dispersion tensor of the self-consistent model. We find return times that are several times longer than in a spherical galaxy with the same radial density profile, particularly in galaxy models with dense centers, implying a substantially greater probability of finding an off-center black hole.
Future optical interferometric instrumentation mainly relies on the availability of an efficient cophasing system: once available, what has so far postponed the relevance of direct imaging with an interferometer will vanish. This paper focuses on the actual limits of snapshot imaging, inherent to the use of a sparse aperture: the number of telescopes and the geometry of the array impose the maximum extent of the field of view and the complexity of the sources. A second limitation may arise from the beam combination scheme. Comparing already available solutions, we show that the so called hypertelescope mode (or densified pupil) is ideal. By adjusting the direct imaging field of view to the useful field of view offered by the array, the hypertelescope makes an optimal use of the collected photons. It optimizes signal to noise ratio, drastically improves the luminosity of images and makes the interferometer compatible with coronagraphy, without inducing any loss of useful field of view.
Deep combination radio observations at 1.4GHz with the VLA and MERLIN have imaged a region 10 arcminutes square surrounding the Hubble Deep Field North (HDF-N). Initial studies of the weak radio source population have shown that the proportion of starburst systems increases with decreasing radio flux density with more than 70% of radio sources being starburst in nature at flux densities less than S1.4GHz)~70microJy. The recently published GOODS ACS field overlaps this area, and here we present the results of a follow-up statistical study of the very weak radio sources (S(1.4GHz)<40microJy) in an 8.5 arcminute square field centred on the HDF-N which contains the region of overlap. Radio emission at the level of a few microJy are statistically detected associated with ACS galaxies brighter than a z-band magnitude of 25. These very faint radio sources are extended starburst systems with average radii in the range 0.6 to 0.8 arcseconds and for those with measured redshifts, radio luminosities typically several times that of the nearby well-studies starburst galaxy M82.
We present recent results from very deep MERLIN/VLA 1.4GHz observations of an 8.5-by-8.5 arcminute field centred on the the Hubble Deep Field North, in conjunction with BVIz catalogues of GOODS/ACS sources detected in this field. In an extension of work by Muxlow et al. (also presented at this conference) on the statistical properties of over 8000 sources, the results presented here take advantage of the deep (rms: 3.3 microJy/bm), sub-arcsecond radio imaging of this field to characterise the properties at 1.4GHz of a number of individual radio counterparts to GOODS/ACS sources.
We present recent and ongoing results from extremely deep 18 day MERLIN + VLA 1.4GHz observations (rms: 3.3microJy/bm) of an 8.5-by-8.5 arcminute field centred upon the Hubble Deep Field North. This area of sky has been the subject of some of the deepest observations ever made over a wide range of frequencies, from X-rays to the radio. The results presented here use our deep, sub-arcsecond radio imaging of this field to characterise the radio structures of the several hundred GOODS Spitzer MIR sources in this field. These MIR sources primarily trace the luminous starburst sources. A significant proportion of the MIR sources are detected and resolved by our radio observations, allowing these observations to trace the IR/Radio correlation for galaxies over ~7 orders of magnitude, extending it to ever lower luminosities.
We use Virtual Observatory methods to investigate the association between
radio and X-ray emission at high redshifts. Fifty-five of the 92 HDF(N) sources
resolved by combining
MERLIN+VLA data were detected by Chandra, of which 18 are hard enough and
bright enough to be obscured AGN. The high-z population of microJy radio
sources is dominated by starbursts an order of magnitude more active and more
extended than any found at z<1 and at least a quarter of these simultaneously
host highly X-ray-luminous obscured AGN.
A simple phenomenological description for the energy transfer between a variable cosmological constant (CC) and a gas of relic neutrinos in an expanding universe can account for a near coincidence between the neutrino and dark-energy densities to hold over a significant portion of the history of the universe. Although such a cosmological setup may promote neutrinos to mass-varying particles, both with slow and quick neutrino mass changing with the expansion of the universe naturally implemented in the model, it also works equally well for static neutrino masses. We also stress what sort of models for variable CC can potentially underpin the above scenario.
Fundamental properties of the extinction curve, like the slope in the rest-frame UV and the presence/absence of a broad absorption excess centred at 2175A (the UV bump), are investigated for a sample of 108 massive, star-forming galaxies at 1<z<2.5, selected from the FDF Spectroscopic Survey, the K20 survey, and the GDDS. These characteristics are constrained from a parametric description of the UV spectral energy distribution of a galaxy. It turns out that the sample galaxies host dust producing extinction curves with properties in between those of the Small and Large Magellanic Clouds (SMC and LMC, respectively). LMC-like extinction curves, which exhibit a UV bump, are mainly found among highly-reddened, UV-ultraluminous galaxies at z~2.4 and highly-reddened, near-IR-bright, star-forming galaxies at z~1.2. We discuss star-formation rates, total stellar masses, the morphology, and the chemical properties of our sample galaxies with respect to possible explanations for the different extinction curves.
Different types of observations, together with consistent and physical modelizations, suggest as realistic the hypothesis of enrichement of galactic nuclei by mean of massive globular clusters orbitally decayed and merged in the inner regions of early type galaxies. In this context, the scenario of globular cluster mergers and subsequent formation of a dense Super Star Cluster in the center of a triaxial galaxy is presented and discussed, together with its astrophysical implications, including that of massive black hole feeding and accretion in the center of a triaxial galaxy.
This note gives a short review of the statistical issues concerning upper limit calculation and claiming of discovery arising in the search for exotic physics with neutrino telescopes. Low sample sizes and significant instrumental uncertainties require special consideration. Methods for treating instrumental or theoretical uncertainties in the calculation of limits or discovery are described. Software implementing these methods is presented. The issue of optimization of analysis cuts and definition of sensitivity is briefly discussed.
Scientific output varies between research fields and between disciplines within a field such as astrophysics. Even in fields where publication is the primary output, there is considerable variation in publication and hence in citation rates. Data from the Smithsonian/NASA Astrophysics Data System is used to illustrate this problem and argue against a "one size fits all" approach to performance metrics, especially over the short time-span covered by the Research Assessment Exercise (soon underway in the UK).
We study the effect of rotation on sheared turbulence, due to differential rotation. By solving quasi-linear equations for the fluctuating fields, we derive turbulence amplitude and turbulent transport coefficients, taking into account the effects of shear and rotation on turbulence. We focus on the tachocline regions near the equator and the poles where the rotation and the shear are perpendicular and parallel, respectively. For parameters values typical of the tachocline, we show that the shear reduces both turbulence amplitude and transport, more strongly in the radial direction (parallel to the shear) than in the horizontal one, resulting in an anisotropic turbulence. The rotation further reduces turbulence amplitude and transport at the equator whereas it does not have much effect near the pole. The interaction between the shear and the rotation is shown to give rise to a novel non diffusive flux of angular momentum, possibly offering a mechanism for the occurrence of a strong shear region in the solar interior.
We investigate the confinement and long-term dynamics of the magnetised solar tachocline. Starting from first principles, we derive the values of turbulent transport coefficients and then explore the implications for the confinement and long-term dynamics of the tachocline. For reasonable parameter values, the turbulent eddy viscosity is found to be negative, with turbulence enhancing the radial shear in the tachocline. Both magnetic diffusivity and thermal diffusivity are severely quenched, with the values much smaller than the magnitude of the eddy viscosity. The effect of the meridional circulation on momentum transport via the hyperviscosity becomes important when the radial shear becomes large (larger than the presently inferred value) due to the negative viscosity.
We study the influence of the dimension of space on the thermodynamics of the classical and quantum self-gravitating gas. We consider Hamiltonian systems of self-gravitating particles described by the microcanonical ensemble and self-gravitating Brownian particles described by the canonical ensemble. We present a gallery of caloric curves in different dimensions of space and discuss the nature of phase transitions as a function of the dimension d. We also provide the general form of the Virial theorem in d dimensions and discuss the particularity of the dimension d=4 for Hamiltonian systems and the dimension d=2 for Brownian systems.
We analyse the attenuation properties of a sample of UV selected galaxies, with the use of the spectrophotometric model Grasil. In particular, we focus on the relation between dust attenuation and the reddening in the UV spectral region. We show that a realistic modelling of geometrical distribution of dust and of the different population of stars can explain the UV reddening of normal spiral galaxies also with a standard Milky Way dust. Our results clearly underline that it is fundamental to take into account that younger stars suffer a higher attenuation than older stars (the age-dependent extinction) because stars are born in more-than-average dusty environments. In this work we also find that the concentration of young stars on the galactic plane of spirals has a relevant impact on the expected UV colours, impact that has not been explored before this paper. Finally, we discuss the role of IMF in shaping the relation between UV reddening and dust attenuation, and we show that a Kroupa IMF is more consistent with observed data than the classical Salpeter IMF.
Context: Methanol masers at 6.7GHz are recognised markers of high-mass star formation regions. The study of their distribution in the Galaxy gives important insights into the star formation activity of the Milky Way. We present a statistical analysis on the General Catalogue of 6.7GHz methanol masers in the Galaxy with the aim of extracting global properties of the masers. Aims: We provide constraints on the luminosity function of 6.7GHz methanol masers and on their total number in the Galaxy. Methods: We model the spatial distribution of the masers in the Milky Way by using their distribution in galactocentric distance which is unambiguous once a rotation curve for the Galaxy is assumed. This is the starting point for determining the luminosity function of the masers. Results: The luminosity function of 6.7GHz methanol masers is modelled as a power-law with sharp cutoffs and having an index lying between -1.5 and -2. We also predict the number of detections of methanol masers assuming different sensitivity limits in the observations.
The desire to extend the Hubble Diagram to higher redshifts than the range of current Type Ia Supernovae observations has prompted investigation into spectral correlations in Gamma Ray Bursts, in the hope that standard candle-like properties can be identified. In this paper we discuss the potential of these new `cosmic rulers' and highlight their limitations by investigating the constraints that current data can place on an alternative Cosmological model in the form of Conformal Gravity. By fitting current Type 1a Supernovae and Gamma Ray Burst (GRB) data to the predicted luminosity distance redshift relation of both the standard Concordance Model and Conformal Gravity, we show that currently \emph{neither} model is strongly favoured at high redshift. The scatter in the current GRB data testifies to the further work required if GRBs are to cement their place as effective probes of the cosmological distance scale.
We have selected pre-main-sequence stars in 12 groups of notional ages ranging from 1 Myr to 35 Myrs, using heterogeneous membership criteria. Using these members we have constructed empirical isochrones in V, V-I colour magnitude diagrams (CMDs). This allows us to identify clearly the gap between the radiative main sequence and the convective pre-main-sequence (the R-C gap). We follow the evolution of this gap with age and show that it can be a useful age indicator for groups less than ~15 Myrs old. We also observe a reduction in absolute spreads about the sequences with age. Finally the empirical isochrones allow us to place the groups in order of age, independently of theory. The youngest groups can be collated into three sets of similar ages. The youngest set is the ONC, NGC6530 and IC5146 (nominally 1 Myrs); next Cep OB3b, NGC2362, Lambda Ori and NGC2264 (nominally 3 Myrs); and finally Sigma Ori and IC348 (nominally 4-5 Myrs). This suggests Cep OB3b is younger than previously thought, and IC348 older. For IC348 the stellar rotation rate distribution and fraction of stars with discs imply a younger age than we derive. We suggest this is because of the absence of O-stars in this cluster, whose winds and/or ionising radiation may be an important factor in the removal of discs in other clusters.
In the framework of renormalization-group improved cosmologies, we use the Noether symmetry approach to get exact and general integration of the matter-dominated cosmological equations. This is performed by using an expression of Lambda=Lambda(G) determined by the method itself. We also work out a comparison between such a model and the concordance LambdaCDM model as to the magnitude-redshift relationship, hence showing that no appreciable differences occur.
We introduce a new tool for 'unmasking' the composition of neutron star (NS) interiors which is based on the fact that the state of matter at high densities determines the statistics of both NS observables, the temperature-age (TA) data as well as the mass distribution. We use modern cooling simulations to extract distributions of NS masses required to reproduce those of the yet sparse data in the TA plane. By comparing the results with a mass distribution for young, nearby NSs from population synthesis we can sharpen two NS cooling problems. The direct Urca (DU) problem consists in a narrowing of the NS population at the mass value for which the DU process as the most effective cooling mechanism in the hadronic layer of the star can occur. The Vela mass problem is a broadening of the population beyond the range of the typical mass window of 1.1 - 1.5 M_sun. Applying this tool to modern EoS we discuss examples for pure hadronic stars which are in conflict with these constraints while hybrid stars with a color superconducting quark matter core can predict a satisfactory mass distribution, provided the smallest diquark pairing gap has a properly defined density dependence.
We present a timing analysis of the 2002 outburst of the accreting millisecond pulsar SAX J1808.4-3658. A study of the phase delays of the entire pulse profile shows a behavior that is surprising and difficult to interpret: superposed to a general trend, a big jump by about 0.2 in phase is visible, starting at day 14 after the beginning of the outburst. An analysis of the pulse profile indicates the presence of a significant first harmonic. Studying the fundamental and the first harmonic separately, we find that the phase delays of the first harmonic are more regular, with no sign of the jump observed in the fundamental. The fitting of the phase delays of the first harmonic with a model which takes into account the observed exponential decay of the X-ray flux (and therefore of the mass accretion rate onto the neutron star) gives important information on the torque acting on the neutron star during the outburst. We find that the source shows spin-up in the first part of the outburst, while a spin-down dominates at the end. From these results we derive an estimate of the neutron star magnetic field strength.
Archival HST/NICMOS-2 images of the Cloverleaf gravitational lens (H1413+117), a quadruply imaged quasar, have been analysed with a new method derived from the MCS deconvolution algorithm (Magain et al., 1998). This method is based on an iterative process which simultaneously allows to determine the Point Spread Function (PSF) and to perform a deconvolution of images containing several point sources plus extended structures. As such, it is well adapted to the processing of gravitational lens images, especially in the case of multiply imaged quasars. Two sets of data have been analysed : the first one, which has been obtained through the F160W filter in 1997, basically corresponds to a continuum image, while the second one, obtained through the narrower F180M filter in 2003, is centered around the forbidden [OIII] emission lines at the source redshift, thus probing the narrow-line region of the quasar. The deconvolution gives astrometric and photometric measurements in both filters and reveals the primary lensing galaxy as well as a partial Einstein ring. The high accuracy of the results is particularly important in order to model the lensing system and to reconstruct the source undergoing the strong lensing. The reliability of the method is checked on a synthetic image similar to H1413+117.
Below a threshold energy, gas in the constant density core of a triaxial galaxy can find no simple non-intersecting periodic orbit to act as an attractor for its trajectory. If a disc of gas arriving from further out in the galaxy dissipates sufficient energy to fall below this threshold, it will thereafter collapse into the very centre. Such a mechanism may be relevant to the early growth of super-massive black holes at the Eddington limit and the appearance of the quasar phenomenon at high redshift. This process is self-limiting in the sense that, when the black hole mass has grown to a significant fraction of the core mass, simple angular momentum conserving orbits are restored and accretion reverts to the slow viscous mode. The mechanism depends upon the pre-existence of constant density cores in triaxial spheroidal galaxies.
We present Spitzer IRAC and IRS observations of the dark cloud L1287. The mid-infrared (MIR) IRAC images show deeply embedded infrared sources in the vicinity of the FU Orionis objects RNO 1B and RNO 1C suggesting their association with a small young stellar cluster. For the first time we resolve the MIR point source associated with IRAS 00338+6312 which is a deeply embedded intermediate-mass protostar driving a known molecular outflow. The IRAC colors of all objects are consistent with young stars ranging from deeply embedded Class 0/I sources to Class II objects, part of which appear to be locally reddened. The two IRS spectra show strong absorption bands by ices and dust particles, confirming that the circumstellar environment around RNO 1B/1C has a high optical depth. Additional hydrogen emission lines from pure rotational transitions are superimposed on the spectra. Given the outflow direction, we attribute these emission lines to shocked gas in the molecular outflow powered by IRAS 00338+6312. The derived shock temperatures are in agreement with high velocity C-type shocks.
Context: In 2004 asteroid (2867) Steins has been selected as a flyby target for the Rosetta mission. Determination of its spin period and the orientation of its rotation axis are essential for optimization of the flyby planning. Aim: Measurement of the rotation period and light curve of asteroid (2867) Steins at a phase angle larger than achievable from ground based observations, providing a high quality data set to contribute to the determination of the orientation of the spin axis and of the pole direction. Methods: On March 11, 2006, asteroid (2867) Steins was observed continuously for 24 hours with the scientific camera system OSIRIS onboard Rosetta. The phase angle was 41.7 degrees, larger than the maximum phase angle of 30 degrees when Steins is observed from Earth. A total of 238 images, covering four rotation periods without interruption, were acquired. Results: The light curve of (2867) Steins is double peaked with an amplitude of $\approx$ 0.23 mag. The rotation period is 6.052 $\pm$ 0.007 hours. The continuous observations over four rotation periods exclude the possibility of period ambiguities. There is no indication of deviation from a principal axis rotation state. Assuming a slope parameter of G = 0.15, the absolute visual magnitude of Steins is 13.05 $\pm$ 0.03.
Black hole masses in Active Galactic Nuclei have been determined in 35
objects through reverberation mapping of the emission line region. I mention
some uncertainties of the method, such as the ``scale factor'' relating the
Virial Product to the mass, which depends on the unknown structure and dynamics
of the Broad Line Region.
When the black hole masses are estimated indirectly using the empirical
size-luminosity relation deduced from this method, the uncertainties can be
larger, especially when the relation is extrapolated to high and low masses
and/or luminosities. In particular they lead to Eddington ratios of the order
of unity in samples of Narrow Line Seyfert 1. As the optical-UV luminosity is
provided by the accretion disk, the accretion rates can be determined and are
found to be much larger than the Eddington rates. So, accretion must be
performed at a super-critical rate through a slim disk, resulting in rapid
growth of the black holes. The alternative is that the mass determination is
wrong at this limit.
We report observations of the recurrent nova RS Oph using long-baseline near-IR interferometry. We are able to resolve emission from the nova for several weeks after the February 2006 outburst. The near-IR source initially expands to a size of approximately 5 milli-arcseconds. However, beginning around day 10 the IR source appears to begin to shrink, reaching approximately 2 milli-arcseconds by day 100. We combine our measured angular diameters with previously available interferometric and photometric data to derive an emission measure for the source, and hence are able to determine the mass-loss rate of the nova in the days following the outburst.
A 227 ksec Chandra Observatory X-ray image of the hot plasma in the Hydra A cluster has revealed an extensive cavity system. The system was created by a continuous outflow or a series of bursts from the nucleus of the central galaxy over the past 200-500 Myr. The cavities have displaced 10% of the plasma within a 300 kpc radius of the central galaxy, creating a swiss-cheese-like topology in the hot gas. The surface brightness decrements are consistent with empty cavities oriented within 40 degrees of the plane of the sky. The outflow has deposited upward of 10^61 erg into the cluster gas, most of which was propelled beyond the inner ~100 kpc cooling region. The supermassive black hole has accreted at a rate of approximately 0.1-0.25 solar masses per year over this time frame, which is a small fraction of the Eddington rate of a ~10^9 solar mass black hole, but is dramatically larger than the Bondi rate. Given the previous evidence for a circumnuclear disk of cold gas in Hydra A, these results are consistent with the AGN being powered primarily by infalling cold gas. The cavity system is shadowed perfectly by 330 MHz radio emission. Such low frequency synchrotron emission may be an excellent proxy for X-ray cavities and thus the total energy liberated by the supermassive black hole.
The s-process should occur in all but the lower mass progenitor stars of planetary nebulae, and this should be reflected in the chemical composition of the gas which is expelled to create the current planetary nebula shell. Weak forbidden emission lines are expected from several s-process elements in these shells, and have been searched for and in some cases detected in previous investigations. Here we extend these studies by combining very high signal-to-noise echelle spectra of a sample of PNe with a critical analysis of the identification of the emission lines of Z>30 ions. Emission lines of Br, Kr, Xe, Rb, Ba, and Pb are detected with a reasonable degree of certainty in at least some of the objects studied here, and we also tentatively identify lines from Te and I, each in one object. The strengths of these lines indicate enhancement of s-process elements in the central star progenitors, and we determine the abundances of Br, Kr, and Xe, elements for which atomic data relevant for abundance determination have recently become available. As representative elements of the ``light'' and ``heavy'' s-process peaks Kr and Xe exhibit similar enhancements over solar values, suggesting that PNe progenitors experience substantial neutron exposure.
The cosmological constant and many other possible origins for acceleration of the cosmic expansion possess variations in the dark energy properties slow on the Hubble time scale. Given that models with more rapid variation, or even phase transitions, are possible though, we examine the fineness in redshift with which cosmological probes can realistically be employed, and what constraints this could impose on dark energy behavior. In particular, we discuss various aspects of baryon acoustic oscillations, and their use to measure the Hubble parameter H(z). We find that cosmological probes have an innate resolution no finer than Delta z=0.2-0.3.
We present a new estimator, omega, of the small scale galaxy correlation function that is robust against the effects of redshift space distortions and large scale structures. The estimator is a weighted integral of the redshift space or angular correlation function and is a convolution of the real space correlation function with a localized filter. This allows a direct comparison with theory, without modeling redshift space distortions and the large scale correlation function. This has a number of advantages over the more traditional w_p estimator, including (i) an insensitivity to large scale structures and the details of the truncation of the line of sight integral, (ii) a compact kernel in xi(r), and (iii) being unbinned. We discuss how this estimator would be used in practice, applying it to a sample of mock galaxies selected from the Millennium simulation.
We remark on the utility of an observational relation between the absorption column density in excess of the Galactic absorption column density, Delta N_H = N_H,fit - N_H,gal, and redshift, z, determined from all 54 Swift-observed long bursts with spectroscopic redshifts as of 2006 November. The absorption column densities, N_H,fit, are determined from powerlaw fits to the X-ray spectra with the absorption column density left as a free parameter. We find that higher excess absorption column densities are only present in bursts with redshifts z<3. Low absorption column densities appear preferentially in high-redshift bursts. Our interpretation is that this relation between redshift and excess column density is an observational effect resulting from the shift of the source rest-frame energy range below 1 keV out of the XRT observable energy range. We found a clear anti-correlation between Delta N_H and z that can be used to limit the range of the maximum redshift of an afterglow. A critical application of our finding is that rapid X-ray observations can be used to optimize ground-based optical/NIR follow-up observations.
Submillimetre (sub-mm) galaxies have very high infrared (IR) luminosities and are thousands of times more numerous at z~2 than local ultra-luminous IR galaxies. They therefore represent a key phase in galaxy evolution which can be missed in optical surveys. Determining their contribution to the global star formation rate requires dissecting their IR emission into contributions from starbursts (SB) and active galactic nuclei (AGN). There are several examples of AGN systems which masquerade as SBs in either the IR or X-ray, and SBs can often look like AGN in some wavebands. A combination of SB and AGN emission is not unreasonable, given models of merger-driven evolution. To assess in detail what powers the intense IR luminosity of sub-mm galaxies it is important to obtain a complete multi-wavelength picture. Mid-IR spectroscopy is a particularly good probe of where the intense IR luminosity is coming from. We present the first results from a program to obtain Spitzer IRS spectroscopy of a sample of high redshift galaxies in the GOODS-N field, a large fraction of which are sub-mm galaxies. This field is already home to the deepest X-ray, optical, IR and radio data. We piece together the sub-mm data with the Spitzer photometry and IRS spectra to provide a well sampled IR spectral energy distribution (SED) of sub-mm galaxies and determine the contribution to the bolometric luminosity from the AGN and SB components.
We examine whether observations independent of type Ia supernova surveys are sufficient to imply the existence of dark energy. We find that best measurements of the age of the universe $t_0$, the Hubble parameter $H_0$ and the matter fraction $\Omega_m$ strongly favor the existence of a repulsive, acceleration-causing ($w < -1/3$) component of energy if the universe is nearly flat.
We report on observations of the stellar populations in twelve fields spanning the region between the Magellanic Clouds, made with the Mosaic-II camera on the 4-meter telescope at the Cerro-Tololo Inter-American Observatory. The two main goals of the observations are to characterize the young stellar population (which presumably formed in situ in the Bridge and therefore represents the nearest stellar population formed from tidal debris), and to search for an older stellar component (which would have been stripped from either Cloud as stars, by the same tidal forces which formed the gaseous Bridge). We determine the star-formation history of the young inter-Cloud population, which provides a constraint on the timing of the gravitational interaction which formed the Bridge. We do not detect an older stellar population belonging to the Bridge in any of our fields, implying that the material that was stripped from the Clouds to form the Magellanic Bridge was very nearly a pure gas.
We have measured the time dependence of scintillation light from electronic and nuclear recoils in liquid neon, finding a slow time constant of 15.4+-0.2 us. Pulse shape discrimination is investigated as a means of identifying event type in liquid neon. Finally, the nuclear recoil scintillation efficiency is measured to be 0.26+-0.03 for 387 keV nuclear recoils.
We have detected occasional, short-lived ``echoes'' of giant pulses from the Crab pulsar. These echo events remind us of previously reported echoes from this pulsar, but they differ significantly in detail. Our echo events last at most only a few days; the echo emission lags the primary emission by only 40-100 musec. The echoes are consistently weaker and broader than the primary emission, and appear only at the lower of our two simultaneous observing frequencies. We suggest that these echoes are created by refraction in small plasma structures -- plasma clouds or magnetic flux ropes -- deep within the Crab nebula. If this is true, our echoes provide a new probe of small-scale structures within the inner synchrotron nebula.
Most of the Ultra High Energy Cosmic Ray (UHECR) experiments and projects (HiRes, AUGER, TA, EUSO, TUS,...) use air fluorescence to detect and measure extensive air showers (EAS). The precise knowledge of the Fluorescence Light Yield (FLY) is of paramount importance for the reconstruction of UHECR. The MACFLY - Measurement of Air Cherenkov and Fluorescence Light Yield - experiment has been designed to perform such FLY measurements. In this paper we will present the results of FLY in the 290-440 nm wavelength range for dry air and pure nitrogen, both excited by electrons with energy of 1.5 MeV, 20 GeV and 50 GeV. The experiment uses a 90Sr radioactive source for low energy measurement and a CERN SPS electron beam for high energy. We find that the FLY is proportional to the deposited energy (E_d) in the gas and we show that the air fluorescence properties remain constant independently of the electron energy. At the reference point: atmospheric dry air at 1013 hPa and 23C, the ratio FLY/E_d=17.6 photon/MeV with a systematic error of 13.2%.
We have observed a new, complete, cooling-core sample with the VLA, in order to understand how the massive black hole in the central galaxy interacts with the local cluster plasma. We find that every cooling core is currently being energized by an active radio jet, which has probably been destabilized by its interaction with the cooling core. We argue that current models of cooling-core radio galaxies need to be improved before they can be used to determine the rate at which the jet is heating the cooling core. We also argue that the extended radio haloes we see in many cooling-core clusters need extended, in situ re-energization, which cannot be supplied solely by the central galaxy.
We present preliminary results on a single field observed by WHAT, a small-aperture short focal length automated telescope with an 8.2 deg x 8.2 deg field of view, located at the Wise Observatory. The system is similar to the members of HATNet (this http URL) and is aimed at searching for transiting extrasolar planets and variable objects. With 5 min integration time, the telescope achieved a precision of a few mmag for the brightest objects. We detect variables with peak-to-peak amplitudes less than 0.01 mag. All 152 periodic variables are presented at this http URL .
Considering that the universe is filled with the nonrelativistic matter and dark energy and each component is respectively satisfied with its conservation condition in the absence of their interaction, we give the change rate of the fractional density and the density of dark energy from the conservation condition. It is clear that the fractional density of dark energy will monotonously increase and gradually become the dominating contribution to the universe as the redshift becomes low. Combining the evolutional trend of the state equation of dark energy and the change rate of the density of dark energy we find that the density of dark energy will decrease up to a minimum and whereafter it will increase again as the redshift becomes low. This can be regarded as the phase transition of dark energy from the quintessence phase to the phantom phase.
We have obtained multi-object spectroscopy of luminous blue supergiants in NGC 3109, a galaxy at the periphery of the Local Group at ~1.3 Mpc. We present a detailed catalog including finding charts, V and I magnitudes, spectral classifications, and stellar radial velocities. The radial velocities are seen to trace the rotation curves obtained from studies of the HI gas. From quantitative analysis of eight B-type supergiants we find a mean oxygen abundance of 12+log(O/H) = 7.76 +/-0.07 (1-sigma systematic uncertainty), with a median result of 7.8. Given its distance, we highlight NGC 3109 as the ideal example of a low metallicity, dark-matter dominated, dwarf galaxy for observations with the next generation of ground-based extremely large telescopes (ELTs).
This paper aims to retrieve the ghost streams under the pre-assumption that all the globular clusters in our Galaxy were formed in the very early merge events. The results are based on two speculations: that the specific energy and angular momentum of the globular clusters after merge are not changed in process of evolution and that the globular clusters with common origin would stay in the same orbit plane as parent galaxy. In addition, taking into account the apo-galacticum distance of the orbits, five possible streams were suggested with a significant confidence. The number of streams is consistent with previous results. Three of the four well established members of the Sagittarius stream were found to be in one of our streams. Several other globular clusters in our result were also thought to come from accretion by previous research. Furthermore, the orbital parameters of the streams are derived, which provide a way to testify whether these streams are true with the help of the accurate measurement of proper motions of the globular clusters.
About 54% of radio galaxies at z>3 and 8% of radio galaxies at 2<z<3 show
unusually strong Ly-alpha emission, compared with the general population of
high redshift (z>2) radio galaxies. These Ly-alpha excess objects (LAEs) show
Ly-alpha/HeII values consistent with or above standard photoionization model
predictions.
We show that the most successful explanation is the presence of a young
stellar population which provides the extra supply of ionizing photons required
to explain the Ly-alpha excess in at least the most extreme LAEs (probably in
all of them).
The measurement of unusually high Ly-alpha ratios in the extended gas of some
high redshift radio galaxies suggests that star formation activity occurs in
spatial scales of tens of kpc.
We argue that, although the fraction of LAEs may be incompletely determined,
both at 2<z<3 and at z>3, the much larger fraction of LAEs found at z>3 is a
genuine redshift evolution and not due to selection effects. Therefore, our
results suggest that the radio galaxy phenomenon is more often associated with
a massive starburst at z>3 than at z<3.
We study the properties of very faint, sub-L* Lyman break galaxies at z~2-5 - thus far a largely neglected but numerically and energetically very important population. We find that the LBG luminosity function undergoes luminosity-dependent evolution: the number of luminous galaxies remains constant while the number of faint ones grows with time. The total UV luminosity density increases with cosmic time from at least z~5 until reaching a peak or a plateau around z~2 - behaviour that is governed by the sub-L* galaxies in the LF's "faint tail". Using broadband SED fitting we find a nearly-linear relationship between SFR and galaxy stellar mass at z~2. A typical L* LBG at z~2 shows a stellar mass of ~10^10M_sun, remarkably similar to the bimodality mass at low redshift. This similarity suggests that the mechanisms responsible for the galaxy bimodality at low-z may have also been at play at z~2.
We present a new cluster-finding algorithm based on a combination of the Voronoi Tessellation and Friends-Of-Friends methods. The algorithm utilises probability distribution functions derived from a photometric redshift analysis and is tested on simulated cluster-catalogues. We use a 9 band photometric catalogue over 0.5 square degrees in the Subaru XMM-Newton Deep Field. The photometry is comprised of UKIDSS Ultra Deep Survey infrared J and K data combined with 3.6 micro-m and 4.5 micro-m Spitzer bands and optical BVRi'z' imaging from the Subaru Telescope. The cluster catalogue contains 13 clusters at redshifts 0.61 <= z <= 1.39 with luminosities 10L* < L_tot < 50 L*.
We present a detailed stellar population analysis of 27 massive elliptical galaxies within 4 very rich clusters at redshift z~0.2: A115, A655, A963 and A2111. Using the new, high-resolution stellar populations models developed in our group, we obtained accurate estimates of the mean luminosity-weighted ages and relative abundances of CN, Mg and Fe. We have found that [CN/H] and [Mg/H] are correlated with sigma while [Fe/H] and Log(age) are not. In addition, both abundance ratios [CN/Fe] and [Mg/Fe] increase with sigma. Furthermore, the [CN/H]-sigma and [CN/Fe]-sigma slopes are steeper for galaxies in very rich clusters than those in the less dense Virgo and Coma clusters. On the other hand, [Mg/H]-sigma and [Mg/Fe]-sigma slopes keep constant as functions of the environment. Our results are compatible with a scenario in which the stellar populations of massive elliptical galaxies, independently of their environment and mass, had formation timescales shorter than ~1 Gyr. This result implies that massive elliptical galaxies have evolved passively since, at least, as long ago as z~2. For a given galaxy mass the duration of star formation is shorter in those galaxies belonging to more dense environments; whereas the mass-metallicity relation appears to be also a function of the cluster properties: the denser the environment is, the steeper are the correlations. Finally, we show that the abundance ratios [CN/Fe] and [Mg/Fe] are the key "chemical clocks" to infer the star formation history timescales in ellipticals. In particular, [Mg/Fe] provides an upper limit for those formation timescales, while [CN/Fe] apperars to be the most suitable parameter to resolve them in elliptical galaxies with sigma<300 km/s.
We investigate the redshift and luminosity evolution of the galaxy colour-density relation using the data from the First Epoch VIMOS-VLT Deep Survey (VVDS) on scales of R=5 h^(-1)Mpc up to redshift z ~ 1.5. While at lower redshift we confirm the existence of a steep colour-density relation, with the fraction of the reddest(/bluest) galaxies of the same luminosity increasing(/decreasing) as a function of density, this trend progressively disappears in the highest redshift bins investigated.Our results suggest the existence of an epoch (more remote for brighter galaxies) characterized by the absence of the colour-density relation on the R=5 h^(-1)Mpc scales investigated. The rest frame u*-g' colour-magnitude diagram shows a bimodal pattern in both low and high density environments up to redshift z ~ 1.5. We find that the bimodal distribution is not universal but strongly depends upon environment. Both the colour-density and colour-magnitude-density relations, on the R=5 h^(-1)Mpc scales, appear to be a transient, cumulative product of genetic and environmental factors that have been operating over at least a period of 9 Gyr. These findings support an evolutionary scenario in which star formation/gas depletion processes are accelerated in more luminous objects and in high density environments: star formation activity is progressively shifting with cosmic time towards lower luminosity galaxies (downsizing), and out of high density environments.
The detection of flares with the Swift satellite triggered a lot of bservational and theoretical interest in these phenomena. As a consequence a large analysis effort started within the community to characterize the phenomenon and at the same time a variety of theoretical speculations have been proposed to explain it. In this presentation we discuss part of the results we obtained analyzing a first statistical sample of GRBs observed with Swift. The first goal of this research is very simple: derive those observational properties that could distinguish between internal and external shock and between an ever active central engine and delayed shocks (refreshing) related to a very small initial Lorentz bulk factor. We discuss first the method of analysis and the morphology evidencing the similarities such flares have with the prompt emission pulses. We conclude that GRB flares are due to internal shocks and leave still open the question of whether or not the central engine is active for a time of the order of 105 seconds after the prompt emission.
We find that the HNC J=3-2 emission is brighter than the HCN 3-2 emission by factors of 1.5 to 2.3 in the ultraluminous mergers Arp220 and Mrk231 and the luminous IR galaxy NGC4418. We furthermore report the detection of HNC J=4-3 in Mrk231. Overluminous HNC emission is unexpected in warm molecular gas in ultraluminous galaxies since I(HNC)>I(HCN) is usually taken as a signature of cold (10 - 20 K) dark clouds. Since the molecular gas of the studied galaxies is warm (T_k > 40 K) we present two alternative explanations to the overluminous HNC: a) HNC excitation is affected by pumping of the rotational levels through the mid-infrared continuum and b) XDRs (X-ray Dominated Regions) influence the abundances of HNC. HNC may become pumped at 21.5 micron brightness temperatures of 50 K, suggesting that HNC-pumping could be common in warm, ultraluminous galaxies with compact IR-nuclei.On the other hand, all three galaxies are either suspected of having buried AGN - or the presence of AGN is clear (Mrk231) - indicating that X-rays may affect the ISM chemistry. We conclude that both the pumping and XDR alternatives imply molecular cloud ensembles distinctly different from those of typical starforming regions in the Galaxy, or the ISM of less extreme starburst galaxies. The HNC molecule shows the potential of becoming an additional important tracer of extreme nuclear environments.
Deep redshift surveys of the universe provide the basic ingredients to compute the probability distribution function (PDF) of galaxy fluctuations and to constrain its evolution with cosmic time. When this statistic is combined with analytical CDM predictions for the PDF of mass, useful insights into the biasing function relating mass and galaxy distributions can be obtained. In this paper, we focus on two issues: the shape of the biasing function and its evolution with redshift. We constrain these quantities by using a preliminary sample of galaxies spectroscopically surveyed by the Vimos-VLT Deep Survey in a deep cone 0.4<z<1.5 covering 0.4x0.4 sq. deg. We show that the ratio between the amplitude of galaxy fluctuations and the underlying mass fluctuations declines with cosmic time, and that its evolution rate is a function of redshift: biasing evolution is marginal up to z~0.8 and more pronounced for z > 0.8.
We describe a newly developed code for the extrapolation of nonlinear force-free coronal magnetic fields in spherical coordinates. The program uses measured vector magnetograms on the solar photosphere as input and solves the force-free equations in the solar corona. The method is based on an optimization principle and the heritage of the newly developed code is a corresponding method in Cartesian geometry. We test the newly developed code with the help of a semi-analytic solution and rate the quality of our reconstruction qualitatively by magnetic field line plots and quantitatively with a number of comparison metrics. We find that we can reconstruct the original test field with high accuracy. The method is fast if the computation is limited to low co-latitudes (say $30^\circ \leq \theta \leq 150^\circ$), but becomes significantly slower if the polar regions are included.
The Sagittarius dwarf Spheroidal galaxy is the nearest neighbor of the Milky Way. Moving along a short period quasi-polar orbit within the Halo, it is being destroyed by the tidal interaction with our Galaxy, losing its stellar content along a huge stellar stream. We study the detailed chemical composition of 12 giant stars in the Sagittarius dwarf Spheroidal main body, together with 5 more in the associated globular cluster Terzan 7 by means of high resolution VLT-UVES spectra. Abundances are derived for up to 21 elements from O to Nd, by fitting lines EW or line profiles against ATLAS 9 model atmospheres and SYNTHE spectral syntheses calculated ad-hoc. Temperatures are derived from (V-I)_0 or (B-V)_0 colors, gravities from Fe I - Fe II ionization equilibrium. The metallicity of the observed stars is between [Fe/H]=-0.9 and 0. We detected a highly peculiar ``chemical signature'', with undersolar alpha elements, Na, Al, Sc, V, Co, Ni, Cu and Zn among others, and overabundant La, Ce and Nd. Many of these abundance ratios (in particular light-odd elements and iron peak ones) are strongly at odds with what is observed within the Milky Way, they thus may be a very useful tool to recognize populations originated within the Sagittarius dwarf. This can be clearly seen in the case of the globular Palomar 12, which is believed to have been stripped from Sagittarius: the cluster shows precisely the same chemical ``oddities'', thus finally confirming its extragalactic origin.
Context: Stars form in the cold dense cores of interstellar molecular clouds and the detailed knowledge of the spectrum of masses of such cores is clearly a key for the understanding of the origin of the IMF. To date, observations have presented somewhat contradictory evidence relating to this issue. Aims: In this paper we propose to derive the mass function of a complete sample of dense molecular cores in a single cloud employing a robust method that uses uses extinction of background starlight to measure core masses and enables the reliable extension of such measurements to lower masses than previously possible. Methods: We use a map of near-infrared extinction in the nearby Pipe dark cloud to identify the population of dense cores in the cloud and measure their masses. Results: We identify 159 dense cores and construct the mass function for this population. We present the first robust evidence for a departure from a single power-law form in the mass function of a population of cores and find that this mass function is surprisingly similar in shape to the stellar IMF but scaled to a higher mass by a factor of about 3. This suggests that the distribution of stellar birth masses (IMF) is the direct product of the dense core mass function and a uniform star formation efficiency of 30%+/-10%, and that the stellar IMF may already be fixed during or before the earliest stages of core evolution. These results are consistent with previous dust continuum studies which suggested that the IMF directly originates from the core mass function. The typical density of ~10^4/cm^3 measured for the dense cores in this cloud suggests that the mass scale that characterizes the dense core mass function may be the result of a simple process of thermal (Jeans) fragmentation.
The narrow line QSO PG1211+143 has been a focus of recent attempts to understand the soft excess in AGN, while the 2001 XMM-Newton observation of this luminous AGN also provided evidence for a massive and energetic outflow. Here we consider a physical link between the energetic outflow and the variable soft excess.
We conduct Smoothed Particle Hydrodynamics simulations of the `collect and collapse' scenario (Elmegreen and Lada, 1977) for star formation triggered by an expanding HII region. We simulate the evolution of a spherical uniform molecular cloud with an ionising source at its centre. The gas in the cloud is self-gravitating, although the cloud is prevented from globally collapsing. We find that the shell driven by the HII region fragments to form numerous self--gravitating objects. We repeat our calculations at four numerical resolutions to ensure that they are converged. We compare our results to the analytical model of Whitworth et al, 1994 and show that our simulations and the predictions of Whitworth et al are in good agreement in the sense that the shell fragments at the time and radius predicted by Whitworth et al to within 20% and 25% respectively. Most of the fragments produced in our two highest resolution calculations are approximately half the mass of those predicted, but this conclusion is robust against both numerical resolution and the presence of random noise (local fluctuations in density of a factor of $\sim2$) in the initial gas distribution. We conclude that such noise has little impact on the fragmentation process.
Chang et al. (2006) reported millisecond duration dips in the X-ray intensity of Sco X-1 and attributed them to occultations of the source by small trans-Neptunian objects (TNOs). We have found evidence that these dips are in fact not astronomical in origin, but rather the result of high-energy charged particle events in the RXTE PCA detectors.
In the current paradigm of cosmic structure formation, dark matter plays a key role on the formation and evolution of galaxies through its gravitational influence. On microscopic scales, dark matter particles are expected to annihilate amongst themselves into different products, with some fraction of the energy being transferred to the baryonic component. It is the aim of the present work to show that, in the innermost regions of dark matter halos, heating by dark matter annihilation may be comparable to the cooling rate of the gas. We use analytical models of the dark matter and gas distributions in order to estimate the heating and cooling rates, as well as the energy available from supernova explosions. Depending on the model parameters and the precise nature of dark matter particles, the injected energy may be enough to balance radiative cooling in the cores of galaxy clusters. On galactic scales, it would inhibit star formation more efficiently than supernova feedback. Our results suggest that dark matter annihilation prevents gas cooling and star formation within at least $0.01-1$ per cent of the virial radius.
We collected data for two samples of normal and interacting galaxies for a total of 2953 galaxies having fluxes in one or more of the following wavebands: FIR, 21 cm line, CO(1-0) lines and soft X-ray. The large set of data obtained allowed us to revisit some of the already known relations between the different tracers of the interstellar medium (ISM), such as the link between the FIR flux and the CO line emission, the relation between X-ray emission and the blue or FIR luminosity. The relation lacking from observations for early-type galaxies has been discussed and explained in detail in the frame of a suitable theoretical model, obtained by coupling chemo-dynamical N-body simulations with a dusty spectrophotometric code of population synthesis.
There has been much recent progress in our understanding of quark matter, culminating in the discovery that if such matter exists in the cores of neutron stars it ought to be in a color superconducting state. This paper explores the impact of superconducting quark matter on the properties (e.g., masses, radii, surface gravity, photon emission) of compact stars.
Aims: We test the technique of spectro-astrometry as a potential method to
investigate the close environment of massive young stars.
Method: Archival VLT near infrared K band spectra (R=8900) of three massive
young stellar objects and one Wolf-Rayet star are examined for
spectro-astrometric signatures. The young stellar objects display emission
lines such as Brackett gamma, CO 2-0 and CO 3-1 that are characteristic of
ionised regions and molecular disks respectively. Two of the sample sources
also display emission lines such as NIII and MgII that are characteristic of
high temperatures.
Results: Most of the emission lines show spectro-astrometric signal at
various levels resulting in different positional displacements. The shapes and
magnitudes of the positional displacements imply the presence of large
disk/envelopes in emission and expanding shells of ionised gas. The results
obtained for the source 18006-2422nr766 in particular provide larger estimates
(> 300AU) on CO emitting regions indicating that in MYSOs CO may arise from
inner regions of extended dense envelopes as well.
Conclusions: The overall results from this study demonstrate the utility of
spectro-astrometry as a potential method to constrain the sizes of various
physical entities such as disks/envelopes, UCHII regions and/or ionised shells
in the close environment of a massive young star.
Discerning the exact nature of the faint (sub-mJy) radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep observations from Chandra/XMM-Newton/Spitzer and ground based follow up we are able to disentangle the AGN and star-forming populations for the first time in a deep multi-frequency GMRT/VLA/MERLIN Survey. The many diagnostics include radio luminosity, morphology, radio to mid-IR flux density ratios, radio to optical flux density ratios and radio spectral indices. Further diagnostics, e.g. optical spectra X-ray spectra/hardness ratios, IR colours indicate the presence of the AGN {\em independent} of whether the radio emission is powered by AGN or star-formation. We are able to examine the star-formation history of the universe up to z=2.5 in a unique way based on an unbiased star-formation rate indicator, radio luminosity. This work provides an alternative perspective on the distribution of star-formation by mass, ``downsizing'' and allows us to examine the prevalence of AGN in star-bursts.
Lambda Virginis (LamVir) is a well-known double-lined spectroscopic Am binary with the interesting property that both stars are very similar in abundance but one is sharp-lined and the other is broad-lined. We present combined interferometric and spectroscopic studies of LamVir. The small scale of the LamVir orbit (~20 mas) is well resolved by the Infrared Optical Telescope Array (IOTA), allowing us to determine its elements as well as the physical properties of the components to high accuracy. The masses of the two stars are determined to be 1.897 Msun and 1.721 Msun, with 0.7% and 1.5% errors respectively, and the two stars are found to have the same temperature of 8280 +/- 200 K. The accurately determined properties of LamVir allow comparisons between observations and current stellar evolution models, and reasonable matches are found. The best-fit stellar model gives LamVir a subsolar metallicity of Z=0.0097, and an age of 935 Myr. The orbital and physical parameters of LamVir also allow us to study its tidal evolution time scales and status. Although currently atomic diffusion is considered to be the most plausible cause of the Am phenomenon, the issue is still being actively debated in the literature. With the present study of the properties and evolutionary status of LamVir, this system is an ideal candidate for further detailed abundance analyses that might shed more light on the source of the chemical anomalies in these A stars.
We present Gemini optical spectroscopy of three young star clusters in the western tidal tail of \n3256. Compact star clusters (as opposed to dwarf-galaxy candidates) in tidal tails are rare, with these three clusters the first for which detailed quantitative spectroscopy has ever been obtained. We find that two of these clusters appear to be coeval, while the third is approximately two times older ($\sim$200 Myr vs. $\sim$80 Myr). All three clusters are massive (1--$3\times 10^5 \msun $) and appear to be of roughly solar metallicity. Additionally, the three clusters appear to be relatively large (R$_{\rm eff} = 10-20$ pc), possibly reflecting weak compression at the time of formation and/or the weak influence of the tidal field of the galaxy. All three clusters have velocities consistent with the general trend of the \ion{H}{1} velocities in the tidal tail. We conclude that if the loosely bound tail material of NGC 3256 gets stripped during future interactions of this galaxy within its group, these three clusters may become part of the intra-group medium.
We present a measurement of the velocity flow of the local universe relative to the CMB rest frame, based on the Jha, Riess & Kirshner (2007) sample of 133 low redshift type Ia supernovae. At a depth of 4500 km/s we find a dipole amplitude of 279+-68 km/s in the direction (l,b) = (285+-18,-10+-15), consistent with earlier measurements and with the assumption that the local velocity field is dominated by the Great Attractor region. At a larger depth of 5900 km/s we find a shift in the dipole direction towards the Shapley concentration. We also present the first measurement of the quadrupole term in the local velocity flow at these depths. Finally, we have performed detailed studies based on N-body simulations of the expected precision with which the lowest multipoles in the velocity field can be measured out to redshifts of order 0.1. Our mock catalogues are in good agreement with current observations, and demonstrate that our results are robust with respect to assumptions about the influence of local environment on the type Ia supernova rate.
We have used Aperture Masking Interferometry and Adaptive Optics (AO) at the Palomar 200'' to obtain precise mass measurements of the binary M dwarf GJ 623. AO observations spread over 3 years combined with a decade of radial velocity measurements constrain all orbital parameters of the GJ 623 binary system accurately enough to critically challenge the models. The dynamical masses measured are $m_{1}=0.360\pm0.014 M_{\sun}$ (4%) and $m_{2}=0.120\pm0.0023 M_{\sun}$ (2%) for the primary and the secondary respectively. Models are not consistent with color and mass, requiring very low metallicities.
Recent years have seen dramatic progress in the study of the core and nuclear properties of galaxies. The structure of the cores has been shown to vary methodically with global and nuclear properties, as cores respond to the mechanisms by which galaxies form/evolve. The dynamical centers of galaxies have been found capable of hosting two seemingly disparate objects: supermassive black holes (SBHs) and compact stellar nuclei. In a drastic departure from previous beliefs, it has been discovered that both structures are common: galaxies lacking SBHs and/or stellar nuclei are the exception, rather than the norm. This review explores the connection between cores, SBHs and stellar nuclei in early-type galaxies, as revealed by the ACS Virgo Cluster Survey. We find that, from parsec to kiloparsec scales, the surface brightness profiles of early-type galaxies are well described by a Sersic model -- a parametrization that is shown to be preferable to the so called `Nuker' model. Relative to the inward extrapolation of the best fitting Sersic model, the profiles within the inner few tens of parsecs transition from luminosity `deficits', in the brightest (M_B < ~-20) galaxies, to luminosity `excesses' in the faintest. The compact stellar nuclei responsible for such luminosity excesses comprise approximatively 0.2% of the total galactic mass. Remarkably, this is the same fraction believed to reside in the SBHs, which are predominantly found in the brightest galaxies showing luminosity deficits.
We study the ability of three-frequency, arcminute-resolution microwave measurements to detect galaxy clusters via their Sunyaev-Zel'dovich (SZ) distortion of the microwave background. For this purpose, we have constructed large-area simulations of the microwave sky, and we have made them publicly available to further investigations into optimal data reduction techniques for upcoming SZ cluster surveys. In these sky simulations, galaxy clusters are modeled using N-body simulated dark matter halos plus a gas prescription for the intracluster medium that allows the small scale cluster physics such as star formation and feedback to be realistically incorporated. We also model the primary microwave background, radio and infrared point sources, galactic dust emission, and the SZ flux including kinetic and relativistic contributions. We make use of these simulations to study the cluster scaling relation between integrated SZ flux and cluster mass and find our clusters fit a power-law well, with a power-law index that is steeper than that for self-similar cluster models. Some evolution of the power-law index and normalization with redshift is also observed. These simulations are also used to study cluster detection for the Atacama Cosmology Telescope (ACT). Using a multi-frequency Wiener filter to separate clusters from other microwave components, we find that ACT alone can recover a cluster sample that is ~90% complete above 3*10^{14} M_sun and ~85% pure.
The yields from transit surveys can be used to constrain the frequency and statistical properties of extrasolar planets. Conversely, planet frequencies can be used to estimate expected detection rates, which are critical for the planning and execution of these surveys. Here I review efforts to accomplish these two related goals, both of which generally require realistic simulations. Early attempts to predict planet yields generally resulted in overly optimistic detection rates that have not been realized. I point out where these estimates likely went wrong, and emphasize the strong biases and sensitivity to detection thresholds inherent in transit surveys. I argue that meaningful comparisons between observed and predicted detection rates require proper calibration of these biases and thresholds. In the few cases where this has been done, the observed rates agree with the results from radial velocity surveys for similar stellar environments. I then go on to describe recent, detailed calculations which should provide more accurate rates, which can be critically compared to observed yields. Finally, I discuss expectations for future all-sky synoptic surveys, which may have the sensitivity to detect hundreds or thousands of close-in transiting planets. Realizing the enormous potential of these surveys will require novel methods of coping with the overwhelming number of astrophysical false positives that will accompany the planet detections.
We at first introduce a novel photometric system, which consists of a Schmidt telescope, an objective prism, a CCD camera, and, especially, a multi-peak interference filter. The multi-peak interference filter enables light in multi passbands to pass through it simultaneously. The light in different passbands is differentially refracted by the objective prism and is focused on the CCD separately, so we have multi "images" for each object on the CCD frames. This system enables us to monitor blazars exactly simultaneously in multi wavebands on a single telescope, and to accurately trace the color change during the variation. We used this novel system to monitor the BL Lacertae object S5 0716+714 during 2006 January and February and achieved a very high temporal resolution. The object was very bright and very active during this period. Two strong flares were observed, with variation amplitudes of about 0.8 and 0.6 mags in the $V'$ band, respectively. Strong bluer-when-brighter correlations were found for both internight and intranight variations. No apparent time lag was observed between the $V'$- and $R'$-band variations, and the observed bluer-when-brighter chromatism may be mainly attributed to the larger variation amplitude at shorter wavelength. In addition to the bluer-when-brighter trend, the object also showed a bluer color when it was more active. The observed variability and its color behaviors are consistent with the shock-in-jet model.
We present the results of a radio polarimetric study of the high-redshift radio galaxy PKS B0529-549 (z=2.575), based on high-resolution 12 mm and 3 cm images obtained with the Australia Telescope Compact Array (ATCA). The source is found to have a rest-frame Faraday rotation measure of -9600 rad m^{-2}, the largest seen thus far in the environment of a z > 2 radio galaxy. In addition, the rest-frame Faraday dispersion in the screen responsible for the rotation is calculated to be 5800 rad m^{-2}, implying rotation measures as large as -15400 rad m^{-2}. Using supporting near-IR imaging from the Very Large Telescope (VLT), we suggest that the rotation measure originates in the Ly-alpha halo surrounding the host galaxy, and estimate the magnetic field strength to be ~10 microGauss. We also present a new optical spectrum of PKS B0529-549 obtained with the New Technology Telescope (NTT), and propose that the emission-line ratios are best described by a photoionization model. Furthermore, the host galaxy is found to exhibit both hot dust emission at 8.0 microns and significant internal visual extinction (~1.6 mag), as inferred from Spitzer Space Telescope near/mid-IR imaging.
Current observations of double neutron stars provide us with a wealth of information that we can use to investigate their evolutionary history and the physical conditions of neutron star formation. Understanding this history and formation conditions further allow us to make theoretical predictions for the formation of other double compact objects with one or two black hole components and assess the detectability of such systems by ground-based gravitational-wave interferometers. In this paper we summarize our group's body of work in the past few years and we place our conclusions and current understanding in the framework of other work in this area of astrophysical research.
RX J1856.5-3754 is one of the brightest nearby isolated neutron stars, and considerable observational resources have been devoted to it. However, current models are unable to satisfactorily explain the data. We show that our latest models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a condensed surface can fit the entire spectrum, from X-rays to optical, of RX J1856.5-3754, within the uncertainties. In our simplest model, the best-fit parameters are an interstellar column density N_H \approx 1x10^20 cm^-2 and an emitting area with R^infty \approx 17 km (assuming a distance to RX J1856.5-3754 of 140 pc), temperature T^infty \approx 4.3x10^5 K, gravitational redshift z_g \sim 0.22, atmospheric hydrogen column y_H \approx 1 g cm^-2, and magnetic field B \approx (3-4)x10^12 G; the values for the temperature and magnetic field indicate an effective average over the surface. We also calculate a more realistic model, which accounts for magnetic field and temperature variations over the neutron star surface as well as general relativistic effects, to determine pulsations; we find there exist viewing geometries that produce pulsations near the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Our model thus represents the most self-consistent picture to date for explaining all the observations of RX J1856.5-3754.
We propose to measure the weak cosmic shear using the spatial derivatives of the galaxy surface brightness field. The measurement should be carried out in Fourier space, in which the point spread function (PSF) can be transformed to a desired form with multiplications, and the spatial derivatives can be easily measured. This method is mathematically well defined regardless of the galaxy morphology and the form of the PSF, and involves simple procedures of image processing. Furthermore, with high resolution galaxy images, this approach allows one to probe the shape distortions of galaxy substructures, which can potentially provide much more independent shear measurements than the ellipticities of the whole galaxy. We demonstrate the efficiency of this method using computer-generated mock galaxy images.
We continue our study of the core helium flash using the three dimensional hydrodynamics code Djehuty. Continuing from earlier calculations, we now take relaxed 3D configurations and add various amounts of rotation. We find that rotation periods consistent with those observed in white dwarfs produce negligible changes in the structure and evolution of the core flash, at least for the very small timescales we have yet been able to investigate. There is no sign of any extra mixing due to the rotation. There is some inconclusive evidence for a slight change in the luminosity, at the 1% level.
A Gaussianity analysis using a goodness-of-fit test has been performed to
study the measured Archeops Cosmic Microwave Background (CMB) temperature
anisotropy data for a 143 GHz Archeops bolometer. We consider large angular
scales, greater than 1.8 degrees, and a large fraction of the North Galactic
hemisphere, around 16%, with a galactic latitude b > 15 degrees.
The considered goodness-of-fit test, first proposed by Rayner & Best (1989),
has been applied to the data after a signal-to-noise decomposition. The method
has been calibrated using simulations of Archeops data containing the CMB
signal and instrumental noise. Two kind of maps produced with two different
map-making techniques (coaddition and Mirage) have been analysed.
Archeops maps for both Mirage and coaddition map-making, have been found to
be compatible with Gaussianity. From these results we can exclude a dust and
atmospheric contamination larger than 11.5% (90% CL). For comparison, the same
method has been applied to data from the NASA WMAP satellite in the same region
of sky. The 1-year and 3-year releases have been used. Results are compatible
with those obtained with Archeops, implying a similar upper limit for $f_{nl}$
on degree angular scales.
Context: Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ltimately, how the energy is extracted from the central black hole in radio-loud active galactic nuclei. Aims: Crucial information is provided by broad-band spectral energy distributions (SEDs), their trends with luminosity and correlated multi-frequency variability. With this study we plan to obtain a database of contemporaneous radio-to-optical spectra of a sample of blazars, which are and will be observed by current and future high-energy satellites. Methods: Since December 2004 we are performing a monthly multi-frequency radio monitoring of a sample of 35 blazars at the antennas in Medicina and Noto. Contemporaneous near-IR and optical observations for all our observing epochs are organised. Results: Until June 2006 about 4000 radio measurements and 5500 near-IR and optical measurements were obtained. Most of the sources show significant variability in all observing bands. Here we present the multi-frequency data acquired during the first eighteen months of the project, and construct the SEDs for the best-sampled sources.
We discuss the present bounds on the relativistic energy density in the Universe parameterized in terms of the effective number of neutrinos N using the most recent cosmological data on Cosmic Microwave Background (CMB) temperature anisotropies and polarization, Large Scale galaxy clustering from the Sloan Digital Sky Survey (SDSS) and 2dF, luminosity distances of type Ia Supernovae, Lyman-alpha absorption clouds (Ly-alpha), the Baryonic Acoustic Oscillations (BAO) detected in the Luminous Red Galaxies of the SDSS and finally, Big Bang Nucleosynthesis (BBN) predictions for 4He and Deuterium abundances. We find N= 5.2+2.7-2.2 from CMB and Large Scale Structure data, while adding Ly-alpha and BAO we obtain N= 4.6+1.6-1.5 at 95 % c.l.. These results show some tension with the standard value N=3.046 as well as with the BBN range N= 3.1+1.4-1.2 at 95 % c.l., though the discrepancy is slightly below the 2-sigma level. We emphasize the impact of an improved upper limit (or measurement) of the primordial value of 3He abundance in clarifying the issue of whether the value of N at early (BBN) and more recent epochs coincide.
Backreaction of nonlinear inhomogeneities to the cosmic expansion is analyzed in the framework of general relativity with cosmological constant. By defining the spatially averaged matter energy density, cosmological constant induces a new type of backreaction whose equation of state is $P=-4/3 \rho$, where $\rho$ and $P$ are the effective energy density and effective pressure of the backreaction in the averaged Friedmann universe. However the effective density is negative so that it decreases the acceleration caused by the cosmological constant.
(Abbrev.) This paper prepares a series of papers analysing the Intermediate MAss Galaxy Evolution Sequence (IMAGES) up to z=1. Intermediate mass galaxies (MJ <=-20.3) are selected from the Chandra Deep Field South (CDFS) for which we identify a serious lack of spectroscopically determined redshifts..... We have spectroscopically identified 691 objects including 580 gal., 7 QSOs, and 104 stars. This study provides 531 new redshifts in the CDFS. It confirms the presence of several large scale structures in the CDFS. To test the impact of these structures in the GOODS-South field, we ... compare the evolution of rest-frame U, B, V and K galaxy luminosity densities to that derived from the CFRS. The CDFS field shows a significant excess of luminosity densities in the z=0.5-0.75 range, which increases with the wavelength, reaching up to 0.5 dex at 2.1 um. Stellar mass and specific star formation evolutions might be significantly affected by the presence of the peculiar large scale structures at z= 0.668 and at z= 0.735, that contain a significant excess of evolved, massive galaxies when compared to other fields. This leads to a clear warning to results based on the CDFS/GOODS South fields, especially those related to the evolution of red luminosity densities, i.e. stellar mass density and specific star formation rate. Photometric redshift techniques, when applied to that field, are producing quantities which are apparently less affected by cosmic variance (0.25 dex at 2.1 um), however at the cost of the difficulty in disentangling between evolutionary and cosmic variance effects.
The IX Russian-Finnish Symposium on Radio Astronomy was held in Special astrophysical observatory RAS in Nizhnij Arkhyz, Russia on 15-20 October 2006. It was dedicated to the two-side collaboration in the field of multi-wavelength investigations of solar radio emission, studies of polar regions of the Sun, studies of stellar activity, AGNs, quasars and BL Lac objects in radio bands from millimeter to decimetre wavelengths with RATAN-600, Metsahovi 14m, RT32m radio telescope and VLBI systems. Here abstracts of all forty papers are given. The Web-site of the Symposium is this http URL .
The results of a 3-dimensional SNSPH simulation of the core collapse of a 23 solar mass star are presented. This simulation did not launch an explosion until over 600ms after collapse, allowing an ideal opportunity to study the evolution and structure of the convection below the accretion shock to late times. This late-time convection allows us to study several of the recent claims in the literature about the role of convection: is it dominated by an l=1 mode driven by vortical-acoustic (or other) instability, does it produce strong neutron star kicks, and, finally, is it the key to a new explosion mechanism? The convective region buffets the neutron star, imparting a 150-200 km/s kick. Because the l=1 mode does not dominate the convection, the neutron star does not achieve large (>450 km/s) velocities. Finally, the neutron star in this simulation moves, but does not develop strong oscillations, the energy source for a recently proposed supernova engine. We discuss the implications these results have on supernovae, hypernovae (and gamma-ray bursts), and stellar-massed black holes.
The rather wide-spread belief that cosmological expansion of a flat 3D-space (with spatial curvature k=0) cannot be observationally distinguished from a kinematics of galaxies moving in a flat and non-expanding space is erroneous. We suggest that the error may have its source in a non relativistic intuition that imagines the Universe not as a spacetime but separates space from time and pictures the cosmological expansion as space evolving in time. The physical reality, however, is fundamentally different - the expanding Universe is necessarily a curved spacetime. We show here that the fact that the spacetime is curved implies that the interpretation of the observed cosmological redshift as being due to the expansion of the cosmological 3D-space is observationally verifiable. Thus it is impossible to mimic the true cosmological redshift by a Doppler effect caused by motion of galaxies in a non-expanding 3D-space, flat or curved. We summarize our points in simple spacetime diagrams that illustrate a gedanken experiment distinguishing between expansion of space and pure kinematics. We also provide all relevant mathematics. None of the previously published discussions of the issue, including a recent popular Scientific American article, offered a similarly clear way out of the confusion.
Sgr A* is considered to be a massive black hole at the Galactic center and is known to be variable in radio, millimeter, near-IR and X-rays. Recent multi-wavelength observing campaigns show a simultaneous X-ray and near-IR flare, as well as sub-millimeter and near-IR flares from Sgr A*. The flare activity is thought to be arising from the innermost region of Sgr A*. We have recently argued that the duration of flares in near-IR and submillimeter wavelengths implies that the burst of emission expands and cools on a dynamical time scale before the flares leave Sgr A*. The detection of radio flares with a time delay in the range of 20 and 40 minutes between 7 and 12mm peak emission implies adiabatic expansion of a uniform, spherical hot blob due to flare activity. We suspect that this simple outflow picture shows some of the characteristics that are known to take place in microquasars, thus we may learn much from comparative study of Sgr A* and its environment vs. microquasars.
The interpretation of extensive air shower (EAS) measurements is strongly dependent on the hadronic interaction models used for simulating reference showers. We study the importance of low-energy hadronic interactions in simulated air showers, generated with the simulation package CORSIKA, for the observed characteristics of extensive air showers. In particular we investigate in detail the energy and the phase space regions of secondary particle production which are most important for muon production. This phase space region is covered by fixed target experiments at CERN. In the second part of this work we present preliminary momentum spectra of secondary pi+ and pi- in p+C collisions at 12 GeV/c measured with the HARP spectrometer at the PS accelerator at CERN. In addition we use the new p+C NA49 data at 158 GeV/c to check the reliability of hadronic interaction models for muon production in EAS. Finally, possibilities to measure relevant quantities of hadron production in existing and planned accelerator experiments are discussed.
We report on the direct detection of a close companion to HD 160934, a young active star, SB1 spectroscopic binary, and suggested member of the AB Doradus moving group. High angular resolution at the Calar Alto 2.2m telescope was achieved by means of the Lucky Imaging technique, allowing direct imaging close to the diffraction limit in the SDSS z' band. Our results are combined with pre-discovery HST archive data, own UBVRI broadband photometry, published JHK magnitudes, and available radial velocity measurements to constrain the physical properties of the HD 160934 close binary. We suggest that the direct detection may be identical to the spectroscopically discovered companion.
Aim: The aim is to study the stellar content of the bar region to constrain its formation and evolution. Methods: Line-strength indices in the bar region of a sample of 6 barred galaxies were employed to derive age and metallicity gradients along the bars using stellar population models. Results: We find clear radial gradients in the line-strength indices for all the galaxies. We find positive gradients within the bar region in the metal indices in four of the six galaxies, and opposite trends in the other two. These latter two galaxies are classified as SAB and they present exponential bar light profiles. For all the galaxies we find a positive gradient in the Balmer indices. There is a clear correlation between the position of morphological features inside the bar region with changes in the slope and value of the indices, which indicate, using stellar population analysis, changes in the stellar populations. Therefore, it seems that the bar regions show a gradient in both age and metallicity, changing radially to younger and more metal rich populations for all the galaxies except for those two with exponential profiles.
We present a detailed chemical abundance analysis of HE 1300+0157, a subgiant with [Fe/H]=-3.9. From a high-resolution, high-S/N Subaru/HDS spectrum we find the star to be enriched in C ([C/Fe]_1D ~ +1.4) and O ([O/Fe]_1D ~ +1.8). With the exception of these species, HE 1300+0157 exhibits an elemental abundance pattern similar to that found in many other very and extremely metal-poor stars. The Li abundance is lower than the Spite-plateau value, in agreement with expectation for its evolutionary status. Of particular interest, no neutron-capture elements are detected in HE 1300+0157. This type of abundance pattern has been found by recent studies in several other metal-poor giants. We suggest that HE 1300+0157 is an unevolved example of this group of stars, which exhibit high C abundances together with low (or absent) abundances of neutron-capture elements. Several potential enrichment scenarios are presented. The low neutron-capture elements, including Sr, Ba, and Pb, suggests that the carbon excess observed in HE 1300+0157 is not due to mass transfer across a binary system. Such a scenario is applied to carbon-rich objects with excesses of s-process elements. The normal observed Li abundance supports this interpretation. Most likely, the high levels of C and O were produced prior to the birth of this star. It remains unclear whether a single hypernova is responsible for its overall chemical pattern, or whether one requires a superposition of yields from a massive Population III object and a normal Type II SN. These scenarios provide important information on the C production in the early Universe, and on the formation of C-rich stars in the early Galaxy.
M85OT2006-1 is the latest and most brilliant addition to the small group of known Luminous Red Novae (LRNe). An identifying characteristic of the previously detected events (M31 RV, V432 Sgr & V838 Mon) was a spectral red-ward evolution connected with an emerging infrared component following the optical decay. Here we report on the discovery of a similar feature in Keck/NIRC and Spitzer photometry of M85OT2006-1 six months post-eruption. We find that its 2.1-22 micrometer spectral energy distribution is best described by a black body with effective temperature T_eff=950+-150 K and bolometric luminosity L=2.9+-0.5x10^5 L_sun. Assuming spherical geometry, the black body effective radius, R=2.0+-0.5x10^4 R_sun, and corresponding expansion velocity, v=870+-260 km/s, are remarkably similar to the properties of M31 RV 70 days after its eruption. Furthermore, we propose a search strategy for LRNe in the local Universe making use of the longevity of their infrared excess emission and discuss the expected number of events in the Spitzer Nearby Galaxies Survey.
We present the initial results from our search for high redshift, z > 6, quasars using near infrared data from the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). Our analysis of the first 106 deg^2 of sky has resulted in the discovery of ULAS J020332.38+001229.2, a luminous (J_AB=20.0, J_Vega=19.1, M_1450=-26.2) quasar at z=5.86. Following candidate selection from the combined IR and optical catalogue data and stacking of multiple epoch Sloan Digital Sky Survey (SDSS) data, we have obtained optical spectroscopy for two candidates. The VLT FORS2 spectrum of ULAS J020332.38+001229.2 shows broad Ly alpha + NV1240 emission at ~8350 A and an abrupt continuum break due to absorption by the Ly alpha forest. The quasar is not present in the SDSS DR5 catalogue and the continuum spectral index of alpha=-1.4 (F_nu~nu^alpha) is redder than a composite of SDSS quasars at similar redshifts (alpha=-0.5). The discovery of one z~6 quasar in ~100 deg^2 down to Y_AB=20.4 (7 sigma) is consistent with existing SDSS results. ULAS J020332.38+001229.2 is the first quasar to be discovered from our programme to employ the planned 4000 deg^2 coverage of the UKIDSS LAS to detect quasars with z>6.5. We describe our survey methodology, including the use of optical data from the SDSS and the highly effective procedures developed to isolate the very small surface density of high-probability quasar candidates.
We study the spatial distribution of Galactic metal-free stars by combining an extremely high-resolution (7.8 X 10^5 solar masses per particle) Cold Dark Matter N-body simulation of the Milky-Way with a semi-analytic model of metal enrichment. This approach allows us to resolve halos with virial temperatures down to the 10^4K atomic cooling limit, and it is sufficiently flexible to make a number of robust conclusions, despite the extremely uncertain properties of the first stars. Galactic metal-free stars are formed over a large redshift range, which peaks at z~10, but continues down to z~5, contributing stars at wide range of Galactocentric radii. Stars containing only metals generated by primordial stars are similarly widespread. Neither changing the efficiency of metal dispersal by two orders of magnitude, nor drastically changing the approximations in our semi-analytical model can affect these result. Thus, if they have sufficiently long lifetimes, a significant number of stars formed in initially primordial star clusters should be found in the nearby Galactic halo regardless of the specifics of metal-free star formation. Observations of metal abundances in Galactic halo stars should be taken as directly constraining the properties of primordial stars, and the lack of metal-free halo stars today should be taken as strongly suggesting a 0.8 solar mass lower limit on the primordial initial mass function.
In the first two papers of this series, we determined the position of Sgr A* on infrared images, by aligning the positions of red giant stars with positions measured at radio wavelengths for their circumstellar SiO masers. In this paper, we report detections of 5 new stellar SiO masers within 50" (2 pc) of Sgr A* and new and/or improved positions and proper motions of 15 stellar SiO masers. The current accuracies are ~1 mas in position and ~0.3 mas/y in proper motion. We find that the proper motion of the central stellar cluster with respect to Sgr A* is less than 45 km/s. One star, IRS 9, has a three-dimensional speed of ~370 km/s at a projected distance of 0.33 pc from Sgr A*. If IRS 9 is bound to the inner parsec, this requires an enclosed mass that exceeds current estimates of the sum of the mass of Sgr A* and luminous stars in the stellar cusp by ~0.8 x 10^6 Msun. Possible explanations include i) that IRS 9 is not bound to the central parsec and has "fallen" from a radius greater than 9 pc, ii) that a cluster of dark stellar remnants accounts for some of the excess mass, and/or iii) that Ro is considerably greater than 8 kpc.
We present a reconstruction of the mass distribution of galaxy cluster Abell 1689 at z = 0.18 using detected strong lensing features from deep HST/ACS observations and extensive ground based spectroscopy. Earlier analyses have reported up to 32 multiply imaged systems in this cluster, of which only 3 were spectroscopically confirmed. In this work, we present a parametric strong lensing mass reconstruction using 24 multiply imaged systems with newly determined spectroscopic redshifts, which is a major step forward in building a robust mass model. In turn, the new spectroscopic data allows a more secure identification of multiply imaged systems. The resultant mass model enables us to reliably predict the redshifts of additional multiply imaged systems for which no spectra are currently available, and to use the location of these systems to further constrain the mass model. In particular, we have detected 5 strong galaxy-galaxy lensing systems just outside the Einstein ring region, further constraining the mass profile. Our strong lensing mass model is consistent with that inferred from our large scale weak lensing analysis derived using CFH12k wide field images. Thanks to a new method for reliably selecting a well defined background lensed galaxy population, we resolve the discrepancy found between the strong and weak lensing mass models reported in earlier work. [ABRIDGED]
This paper presents MoLUSC, a new method for generating mock galaxy catalogs from a large scale ($\approx 1000^3$ Mpc$^3$) dark matter simulation, that requires only modest CPU time and memory allocation. The method uses a small-scale ($\approx 256^3$ Mpc$^3$) dark matter simulation on which the \galics semi-analytic code has been run in order to define the transformation from dark matter density to galaxy density transformation using a probabilistic treatment. MoLUSC is then applied to a large-scale dark matter simulation in order to produce a realistic distribution of galaxies and their associated spectra. This permits the fast generation of large-scale mock surveys using relatively low-resolution simulations. We describe various tests which have been conducted to validate the method, and demonstrate a first application to generate a mock Sloan Digital Sky Survey redshift survey.
It is claimed that ultra-relativistic, magnetized, electron-ion shocks are, for most magnetic geometries, poor accelerators of non-thermal particles. The phenomenon of "missing" early X-ray afterglow observed in many of the Swift gamma-ray burst (GRB) afterglow data may simply be due to this fact. Rapid time variability of the X-ray emission could be produced by fluctuations in the orientation of the ambient magnetic field.
We make use of a flat, axisymmetric Bianchi I metric to investigate the effects of a magnetic field upon the dynamics of the universe for the previously unconsidered case when the accompanying fluid is a cosmological constant and derive two new solutions to the dynamical equations for this case. We examine the behaviour of the scale factor perpendicular and parallel to the field lines, A(t) and W(t) respectively, and find the expected behaviour. The field has the strongest effect when A(t) is small, decelerating collapse perpendicular to the field lines, due to magnetic pressure, and accelerating collapse along the field lines, due to magnetic tension, while the vacuum energy dominates at late time, driving accelerated expansion.
We use deep J and Ks images of the Antennae (NGC 4038/9) obtained with WIRC
on the Palomar 200-inch telescope, together with the Chandra X-ray source list
of Zezas et al. (2002a), to search for IR counterparts to X-ray point sources.
We establish an X-ray/IR astrometric frame tie with 0.5" rms residuals over a
\~4.3' field. We find 13 ``strong'' IR counterparts brighter than Ks = 17.8 mag
and < 1.0" from X-ray sources, and an additional 6 ``possible'' IR counterparts
between 1.0" and 1.5" from X-ray sources. The surface density of IR sources
near the X-ray sources suggests only ~2 of the ``strong'' counterparts and ~3
of the ``possible'' counterparts are chance superpositions of unrelated
objects.
Comparing both strong and possible IR counterparts to our photometric study
of ~220 Antennae, IR clusters, we find the IR counterparts to X-ray sources are
\~1.2 mag more luminous in Ks than average non-X-ray clusters. We also note
that the X-ray/IR matches are concentrated in the spiral arms and ``overlap''
regions of the Antennae. This implies that these X-ray sources lie in the most
``super'' of the Antennae's Super Star Clusters, and thus trace the recent
massive star formation history here. Based on the N_H inferred from the X-ray
sources without IR counterparts, we determine that the absence of most of the
``missing'' IR counterparts is because they are intrinsically less luminous in
the IR, implying that they trace a different (possibly older) stellar
population.
The X-ray light-curves of the GRB afterglows monitored by Swift display one
to four phases of power-law decay. In chronological order they are: the burst
tail, the "hump", the standard decay, and the post jet-break decay.
More than half of GRB tails can be identified with the large-angle emission
produced during the burst, but arriving at observer later. Several afterglows
exhibit a slow, unbroken power-law decay from burst end until 1 day, showing
that the forward shock emission is, sometimes, present from the earliest
afterglow observations. In fact, the decay of most GRB tails is also consistent
with that of the forward-shock emission from a narrow jet (half-angle less than
1 degree).
The X-ray light-curve hump may be due to an increase of the kinetic energy
per solid angle of the forward-shock region visible to the observer, caused by
either the transfer of energy from some incoming ejecta to the forward shock or
by the emergence of the emission from an outflow seen from a location outside
the outflow's opening. However, the correlations among the hump timing, flux,
and decay index expected in the latter model are not confirmed by observations.
We identify several afterglows whose X-ray light-curves show a second
steepening at 0.1-3 day that is consistent with a jet-break. Optical
observations for four of them indicate that the X-ray break is achromatic,
further strengthening their interpretation as jet-breaks. The decay of 75% of
the X-ray afterglows monitored for more than a few days do not exhibit a
steepening, implying jet half-angles larger than several degrees.
In this study I present new K and L$'$-band infrared photometry and 2-4$\mu$m spectra of ten Class I and flat spectrum stars forming within the Taurus dark cloud complex. Nine sources have H$_2$ {\it v}=0-1 S(1) emission, and some show multiple H$_2$ emission features in their K-band spectra. Photospheric absorptions characteristic to low mass stars are detected in five of the targets, and these stars were fit with models to determine spectral type, infrared accretion excess veiling (r$_K$ and r$_{L'}$) and dust temperatures, estimates of visual extinction and characteristics of the 3$\mu$m water-ice absorption. On average, the models found high extinction values, infrared accretion excess emission with blackbody temperatures in the 900-1050K range, and 3$\mu$m absorption profiles best fit by water frozen onto cold grains rather than thermally processed ice. Five techniques were used to estimate the extinction toward the stellar photospheres; most gave vastly different results. Analysis of emission line ratios suggests that the effect of infrared scattered light toward some protostars should not be neglected. For stars that exhibited Br$\gamma$ in emission, accretion luminosities were estimated using relations between L$_{acc}$ and Br$\gamma$ luminosity. The young stars in this sample were preferentially chosen as variables, but they do not have the accretion dominated luminosities necessary to put them in their main stage of mass-building. The characteristics of the 2-4$\mu$m spectra are placed in the context of existing multi-wavelength data, and five of the stars are more consistent with reddened Class IIs or stars in transition between Class I and II, rather than protostars embedded within massive remnant envelopes.
We examine the relationship between the frequency of close companions (stellar and planetary companions with orbital periods < 5 years) and the metallicity of their Sun-like (~ FGK) hosts. We confirm and quantify a ~4 sigma positive correlation between host metallicity and planetary companions. We find little or no host-mass-dependence or distance-dependence in this correlation. In contrast to the metallicity dependence of planetary companions, stellar companions tend to be more abundant around low metallicity hosts. At the ~2 sigma level we find an anti-correlation between host metallicity and the presence of a stellar companion. Upon dividing our sample into FG and K sub-samples, we find a negligible anti-correlation in the FG sub-sample and a 3 sigma anti-correlation in the K sub-sample. A kinematic analysis suggests that this anti-correlation is produced by a combination of low-metallicity, high-binarity thick disk stars and higher-metallicity, lower-binarity thin disk stars.
We use Sloan Digital Sky Survey (SDSS) DR5 photometric data to explore the structure of the Galaxy halo and hope to discover new companions or substructures which may reveal the forming history of the halo. We study overdensities in a sky area where $\alpha=120^{\circ}\sim270^{\circ}$ and $\delta=25^{\circ}\sim70^{\circ}$ and pick out ten overdensity areas by comparing color-magnitude diagrams with known globular clusters or dwarf spheroidal galaxies. An automatic template matching method is developed to fit the color-magnitude diagram for each overdensities with a suitable stellar evolution isochronic line so that distance module and metalicity are roughly estimated. The performance test of the method indicates that our estimates on distance is acceptable. The 10 overdensities and three known objects, UMa I, UMa II and Willman 1 are found to be connected with a long arc substructure starts from $\sim8$kpc above the disk and spread to $\sim150$kpc into north galactic cap. Evidence also shows a relationship between metalicities and distance modules of the overdensities. C7, one of the 10 overdensities is most likely a dwarf spheroidal galaxy according to radial density profile study and its absolute magnitude. Other overdensties are not classified for poor information. The arc structure may either be a long tidal stream or be an intrinsic substructure of the halo. Follow-up study need to be done to clarify this problem.
The color-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud (LMC) star cluster NGC 2154 and its adjacent field, has been analyzed using Padova stellar models to determine the cluster's fundamental parameters and its Star Formation History (SFH). Deep $BR$ CCD photometry, together with synthetic CMDs and Integrated Luminosity Functions (ILFs), has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyrs, which began approximately 2.3 Gyr and ended 1.1 Gyr ago. The physical reality of such a prolonged period of star formation is however questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70%) seems to exist in NGC 2154.
I review recent work that goes beyond our model for the Low-Frequency Quasi-Periodic Oscillation of microquasars, based on the Accretion-Ejection Instability. I show that similar instabilities, which can be viewed as strongly unstable versions of the diskoseismologic modes, provide explanations for both the High-Frequency QPO and for the quasi-periodicity observed durng the flares of Sgr A*, the supermassive black hole at the Galactic Center.
The axion is just one from a general class of new particles -- called Light Pseudoscalar Bosons (LPBs) -- predicted by many realistic extensions of the Standard Model. We offer a somewhat pedagogical review of their main properties, with particular emphasis on the effects they induce in a light beam travelling in an external magnetic field, like photon-LPB oscillations, birefringence and dichroism. Moreover, we discuss a new strategy whereby LPBs can be discovered by high-precision observations of certain binary neutron-star systems. Basically, in a double pulsar seen almost edge-on, photon-LPB oscillations can give rise to a characteristic attenuation pattern of the light beam emitted by one of the pulsars when it goes through the magnetosphere of the companion. Depending on the actual values of the LPB mass and its two-photon coupling constant, the effect can be seen in the $\gamma$-ray band with the upcoming GLAST mission. We also shown that this method provides a remarkable cross-check for the recent claim by the PVLAS collaboration about the existence of a new LPB.
After nearly two decades at least five emission mechanisms can be found in SN 1987A. The ejecta continue to glow as a result of the radioactive decay of long-lived nuclei (mostly 44Ti), but is fading continuously because of the expansion and the reduced opacity. The nearly stationary rings around SN 1987A are still fluorescing from the recombination of matter originally excited by the soft X-ray emission from the shock breakout at explosion. The supernova shock reached the inner circumstellar ring about ten years ago and the forward shock is moving through the inner ring and leaves shocked material behind. This material is excited and accelerated. The reverse shock illuminates the fast-moving supernova ejecta as it catches up. And, finally light echoes in nearby interstellar matter can still be observed. We present here high resolution spectroscopy in the optical and integral-field spectroscopy in the near infrared of SN 1987A and its rings.
X-Ray Flashes (XRFs) are soft gamma-ray bursts whose nature is not clear. Their soft spectrum can be due to cosmological effects (high redshift), an off-axis view of the jet or can be intrinsic to the source. We use SWIFT observations to investigate different scenarios proposed to explain their origin.We have made a systematic analysis of the afterglows of XRFs with known redshift observed by SWIFT. We derive their redshift and luminosity distributions, and compare their properties with a sample of normal GRBs observed by the same instrument. The high distance hypothesis is ruled out by the redshift distribution of our sample of XRFs, indicating that, at least for our sample, the off-axis and sub-energetic hypotheses are preferred. Of course, this does not exclude that some XRFs without known redshift could be at high distance. However we find that taking into account the sensitivity of the BAT instrument, SWIFT XRFs cannot be detected beyond redshift ~ 3. The luminosity distribution of XRFs is similar to the GRB one. This would rule out most off-axis models, but for the homogeneous jet model. However this model predicts a GRB rate uncomfortably near the observed rate of supernovae. This may imply that XRFs, at least those of our sample, could be intrinsically soft.
We study the form of the luminosity distance as a function of redshift in the presence of large scale inhomogeneities, with sizes of order 10 Mpc or larger. We approximate the Universe through the Swiss-cheese model, with each spherical region described by the Tolman-Bondi metric. We study the propagation of light beams in this background, assuming that the locations of the source and the observer are random. We derive the optical equations for the evolution of the beam area and shear. Through their integration we determine the configurations that can lead to an increase of the luminosity distance relative to the homogeneous cosmology. We find that this can be achieved if the Universe is composed of spherical void-like regions, with matter concentrated near their surface. For inhomogeneities consistent with the observed large scale structure, the relative increase of the luminosity distance is of the order of a few percent at redshifts near 1, and falls short of explaining the substantial increase required by the supernova data. On the other hand, the effect we describe is important for the correct determination of the energy content of the Universe from observations.
Subcritical transition to turbulence in Keplerian accretion disks is still a controversial issue and some theoretical progress is required in order to determine whether or not this scenario provides a plausible explanation for the origin of angular momentum transport in non-magnetized accretion disks. Motivated by the recent discoveries of exact nonlinear steady self-sustaining solutions in linearly stable non-rotating shear flows, we attempt to compute similar solutions in Rayleigh-stable rotating plane Couette flows and to identify transition mechanisms in such flows by combining nonlinear continuation methods and asymptotic theory. We obtain exact nonlinear solutions for Rayleigh-stable cyclonic regimes but show that it is not possible to compute solutions for Rayleigh-stable anticyclonic regimes, including Keplerian flow, using similar techniques. We also present asymptotic descriptions of these various problems at large Reynolds numbers that provide some insight into the differences between the non-rotating and Rayleigh-stable anticyclonic regimes and derive some necessary conditions for mechanisms analogous to the non-rotating self-sustaining process to be present in flows on the Rayleigh line. Our results demonstrate that subcritical transition mechanisms cannot be identified in wall-bounded Rayleigh-stable anticyclonic shear flows by transposing directly the phenomenology of subcritical transition in cyclonic and non-rotating wall-bounded shear flows. Asymptotic developments, however, leave open the possibility that nonlinear self-sustaining solutions may exist in unbounded or periodic flows on the Rayleigh line. These could serve as a starting point to discover solutions in Rayleigh-stable flows, but the nonlinear stability of Keplerian accretion disks remains to be determined.
The EGRET results for gamma ray intensities in and near the Galactic Plane
have been analysed in some detail. Attention has been concentrated on energies
above 1 GeV and the individual intensities in a $4^{\circ}$ longitude bin have
been determined and compared with the large scale mean found from a nine-degree
polynomial fit. Comparison has been made of the observed standard deviation for
the ratio of these intensities with that expected from variants of our model.
The basic model adopts cosmic ray origin from supernova remnants, the particles
then diffusing through the Galaxy with our usual `anomalous diffusion'. The
variants involve the clustering of SN, a frequency distribution for supernova
explosion energies, and 'normal', rather than 'anomalous' diffusion.
It is found that for supernovae of unique energy, and our usual anomalous
diffusion, clustering is necessary, particularly in the Inner Galaxy. An
alternative, and preferred, situation is to adopt the model with a frequency
distribution of supernova energies. The results for the Outer Galaxy are such
that no clustering is required.
If their explosion energies are distributed then supernovae can be the origin
of UHECR.
We present initial results from our ongoing campaign of spectroscopic identifications of Lyman--break galaxies (LBGs) at z ~ 4, 5 and 6 with FORS2 at the ESO VLT. The sample of LBGs is selected from the HST/ACS images in the GOODS southern field (CDF--S), and here we discuss the spectroscopic properties of 103 LBGs that we have cofirmed in the redshift interval 3.5 < z < 6.3, of which 34 at z>5 and 27 between 5.5 and 6.3. As for LBGs at lower redshifts, we find that LBGs with LyA in emission are characterized by weaker intestellar absorption lines and bluer UV continua than galaxies whose LyA is observed in absorption. No correlation between the LyA properties and the apparent elongation of the UV morphology of the galaxies is observed, suggesting that geometrical effects are not the cause of the spectral differences. A trend of increasing LyA equivalent width with decreasing luminosity is also observed. We also present new measures of the UV luinosity function of LBGs.
We have studied variability of the spectral lines of the OB star $\delta $Ori A--the brightest component of the $\delta $Ori triple system. Forty spectra with signal-to-noise ratios $\approx$500--800 and a time resolution of four minutes were obtained. We detected variability in the HeII$ \lambda 4686$, HeI$ \lambda $4713 and H$\beta$ absorption and the CIII$ \lambda $5696 emission line profiles. The amplitude of the variability is $\approx$(0.5--1)% of the continuum intensity. The dynamical wavelet spectrum of the profile variations reveals large-scale components in the interval 25--50 km/s that move within the -$V\sin i$ to $V\sin i$ band for the primary star of the system, Aa$^1$, with a band crossing time of 4$^h$--5$^h$. However, some of the variable features go outside the band, presumably due to either imhomogeneities in the stellar wind from $\delta $Ori Aa$^1$ or non-radial pulsations of the weaker components of the system, Aa$^2$ or Ab. The detected variability may by cyclic with a period of $\approx 4^h$ . We suggest that it is associated with non-radial pulsations of the primary in the sector mode $(l, m)=(2,-2)$.
We present semi-analytical and numerical models, accounting for the impact of radiative cooling on the hydrodynamics of the matter reinserted as strong stellar winds and supernovae within the volume occupied by young, massive and compact superstellar clusters. First of all we corroborate the location of the threshold line in the mechanical energy input rate vs the cluster size plane, found by Silich et al. (2004). Such a line separates clusters able to drive a quasi-adiabatic or a strongly radiative wind from clusters in which catastrophic cooling occurs within the star cluster volume. Then we show that the latter, clusters above the threshold line, undergo a bimodal behavior in which the central densest zones cool rapidly and accumulate the injected matter to eventually feed further generations of star formation, while the outer zones are still able to drive a stationary wind. The results are presented into a series of universal dimensionless diagrams from which one can infer: the size of the two zones, the fraction of the deposited mass that goes into each of them and the luminosity of the resultant winds, for clusters of all sizes and energy input rates, regardless the assumed adiabatic terminal speed V_A.
The main component of the intracluster medium (ICM) in clusters of galaxies is represented by the X-ray emitting thermal plasma. In addition, the presence of relativistic electrons and large-scale magnetic fields in a fraction of galaxy clusters is demonstrated by the detection of large-scale synchrotron radio sources, which have no optical counterpart and no obvious connection to the cluster galaxies. Observational results provide evidence that these phenomena are related to cluster merger activity, which supplies the energy for the reacceleration of the radio emitting particles. The investigation of the halo-merger connection is of great importance to the knowledge of the formation and evolution of clusters of galaxies.
The origin of the magnetic fields of the chemically peculiar main sequence Ap/Bp stars is still matter of intense debate. The recent discoveries of magnetic fields in Herbig Ae/Be stars using high resolution data obtained with the spectropolarimeter ESPaDOnS at CFHT provide a strong argument in favour of the fossil field hypothesis. Using a simple oblique rotator model of a centered dipole, we fit the Stokes V LSD profiles of two of these magnetic HAeBe stars, HD 200775 and V380 Ori, as well as their variations on timescales from days to months. We find that in both cases the dipole hypothesis is acceptable and we determine the rotation period, the angle between rotation and magnetic axes and the intensity of the magnetic field at pole.
We study the potential of a large future weak-lensing survey to constrain dark energy properties by using both the number counts of detected galaxy clusters (sensitive primarily to density fluctuations on small scales) and tomographic shear-shear correlations (restricted to large scales). We use the Fisher matrix formalism, assume a flat universe and parameterize the equation of state of dark energy by w(a)=w_0+w_a(1-a), to forecast the expected statistical errors from either observable, and from their combination. We show that the covariance between these two observables is small, and argue that therefore they can be regarded as independent constraints. We find that when the number counts and the shear-shear correlations (on angular scales l < 1000) are combined, an LSST (Large Synoptic Survey Telescope)-like survey can yield statistical errors on (Omega_DE, w_0, w_a) as tight as (0.003, 0.03, 0.1). These values are a factor of 2-25 better than using either observable alone. The results are also about a factor of two better than those from combining number counts of galaxy clusters and their power spectrum.
While until recently they were often considered as exotic objects of dubious
existence, in the last decades there have been overwhelming observational
evidences for the presence of stellar mass black holes in binary systems,
supermassive black holes at the centers of galaxies, and possibly,
intermediate-mass black holes observed as ultraluminous X-ray sources in nearby
galaxies. Black holes are now widely accepted as real physical entities that
play an important role in several areas of modern astrophysics.
Here I review the concluding remarks of the IAU Sympposium No 238 on Black
Holes, with particular emphasis on the topical questions in this area of
research.
The measurements of pulsar frequency second derivatives have shown that they are $10^2-10^6$ times larger than expected for standard pulsar spin-down law, and are even negative for about half of pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters $\nu$, $\dot \nu$ and $\ddot \nu$ of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between $\ddot \nu$ and $\dot \nu$ for both $\ddot\nu > 0$ and $\ddot\nu < 0$, as well as between $\nu$ and $\dot\nu$. We interpret these dependencies as evolutionary ones due to $\dot\nu$ being nearly proportional to the pulsars' age. The derived statistical relations as well as "anomalous" values of $\ddot\nu$ are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore, consists of secular change of $\nu_{ev}(t)$, $\dot\nu_{ev}(t)$ and $\ddot\nu_{ev}(t)$ according to the power law with $n \approx 5$, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that timespan -- several tens of years.
Using ~300,000 photometrically classified quasars, by far the largest quasar sample ever used for such analyses, we study the redshift and luminosity evolution of quasar clustering on scales of ~50 kpc/h to ~20 Mpc/h from redshifts of z~0.75 to z~2.28. We parameterize our clustering amplitudes using realistic dark matter models, and find that a LCDM power spectrum provides a superb fit to our data with a redshift-averaged quasar bias of b_Q = 2.41+/-0.08 ($P_{<\chi^2}=0.847$) for $\sigma_8=0.9$. This represents a better fit than the best-fit power-law model ($\omega = 0.0493\pm0.0064\theta^ {-0.928\pm0.055}$; $P_{<\chi^2}=0.482$). We find b_Q increases with redshift. This evolution is significant at >99.6% using our data set alone, increasing to >99.9999% if stellar contamination is not explicitly parameterized. We measure the quasar classification efficiency across our full sample as a = 95.6 +/- ^{4.4}_{1.9}%, a star-quasar separation comparable with the star-galaxy separation in many photometric studies of galaxy clustering. We derive the mean mass of the dark matter halos hosting quasars as MDMH=(5.2+/-0.6)x10^{12} M_solar/h. At z~1.9 we find a $1.5\sigma$ deviation from luminosity-independent quasar clustering; this suggests that increasing our sample size by a factor of 1.8 could begin to constrain any luminosity dependence in quasar bias at z~2. Our results agree with recent studies of quasar environments at z < 0.4, which detected little luminosity dependence to quasar clustering on proper scales >50 kpc/h. At z < 1.6, our analysis suggests that b_Q is constant with luminosity to within ~0.6, and that, for g < 21, angular quasar autocorrelation measurements are unlikely to have sufficient statistical power at z < 1.6 to detect any luminosity dependence in quasars' clustering.
We study quasar clustering on small scales, modeling clustering amplitudes using halo-driven dark matter descriptions. From 91 pairs on scales <35 kpc/h, we detect only a slight excess in quasar clustering over our best-fit large-scale model. Integrated across all redshifts, the implied quasar bias is b_Q = 4.21+/-0.98 (b_Q = 3.93+/-0.71) at ~18 kpc/h (~28 kpc/h). Our best-fit (real-space) power index is ~-2 (i.e., $\xi(r) \propto r^{-2}$), implying steeper halo profiles than currently found in simulations. Alternatively, quasar binaries with separation <35 kpc/h may trace merging galaxies, with typical dynamical merger times t_d~(610+/-260)m^{-1/2} Myr/h, for quasars of host halo mass m x 10^{12} Msolar/h. We find UVX quasars at ~28 kpc/h cluster >5 times higher at z > 2, than at z < 2, at the $2.0\sigma$ level. However, as the space density of quasars declines as z increases, an excess of quasar binaries (over expectation) at z > 2 could be consistent with reduced merger rates at z > 2 for the galaxies forming UVX quasars. Comparing our clustering at ~28 kpc/h to a $\xi(r)=(r/4.8\Mpch)^{-1.53}$ power-law, we find an upper limit on any excess of a factor of 4.3+/-1.3, which, noting some caveats, differs from large excesses recently measured for binary quasars, at $2.2\sigma$. We speculate that binary quasar surveys that are biased to z > 2 may find inflated clustering excesses when compared to models fit at z < 2. We provide details of 111 photometrically classified quasar pairs with separations <0.1'. Spectroscopy of these pairs could significantly constrain quasar dynamics in merging galaxies.
It is shown that gravitational lensing by point masses arranged in an infinitely extended regular lattice can be studied (semi-)analytically. In particular, we draw the critical curves and the caustic networks for the lenses arranged in regular-polygonal -- square, equilateral triangle, regular hexagon -- grids. From this, the mean number of positive parity images as a function of the average optical depth is derived and compared to the case of the infinitely extended field of randomly distributed lenses. We find that the high degree of the symmetry in the lattice arrangement leads to a significant bias towards canceling of the shear caused by the neighboring lenses on a given lens position and lensing behaviour that is qualitatively distinct from the random star field. We also discuss some possible connections to more realistic lensing scenarios.