Using the Sloan Digital Sky Survey, Data Release 5, we survey proximate damped Lya systems (PDLAs): absorption line systems with HI column density N(HI)> 2x10^20 cm^{-2} at velocity separation dv < 3000 km/s from their background quasar. These absorbers are physically associated with their background quasars, and their statistics allow us to study quasar environments out to z~5. However, the large ionizing flux emitted by a quasar can ionize the neutral gas in a nearby galaxy possibly giving rise to a ``proximity effect'', analogous to the similar effect observed in the Lya forest. From a sample of 111 PDLAs, we measure the HI frequency distribution f(N), incidence, and gas mass density of the PDLAs near luminous quasars over the redshift interval z= 2.2 to 5. The incidence and mass density of PDLAs at z~3 is approximately twice that of intervening DLAs, but at z<2.5 and z>3.5 the f(N) distribution is consistent with the intervening population. We interpret the observed enhancement of PDLAs around quasars in terms of quasar-galaxy clustering, and compare the strength of the clustering signal to the expectation from independent measures of the respective clustering strengths of DLAs and quasars, as well as a complementary analysis of the clustering of absorbers around quasars in the transverse direction. We find that there are a factor of 5-10 fewer PDLAs around quasars than expected and interpret this result as evidence for the hypothesis that the ionizing flux from the quasars photoevaporates HI in nearby DLA galaxies, thus reducing their cross-section for DLA absorption. This constitues the first detection of a ``proximity effect'' for DLAs.
From a Chandra survey of nine interacting galaxy systems the evolution of X-ray emission during the merger process has been investigated. It is found that the X-ray luminosity peaks ~300 Myr before nuclear coalescence, and then dips, even though we know that rapid and increasing activity is still taking place at this time. It is likely that this drop in X-ray luminosity is a consequence of outflows breaking out of the galactic discs of these systems. In this work it is also shown that, for the systems close to the point of nuclear coalescence, Lfir becomes massively enhanced compared to the X-ray luminosity of these systems. We suggest that this enhancement may indicate a `top heavy' IMF, with an enhanced fraction of massive stars. At a time ~1 Gyr after coalescence, the merger-remnants in our sample are X-ray faint when compared to typical mature elliptical galaxies. However, we do see evidence that these systems will start to resemble typical elliptical galaxies at a greater dynamical age, given the properties of the 3 Gyr system within our sample, supporting the idea that halo regeneration will take place within low Lx merger-remnants. Also as a part of this survey, detailed Chandra observations for the double nucleus merger system Mkn 266 and the merger-remnant Arp 222 are presented for the first time.
We show that radiative feedback due to reionization has a profound effect on the extent of mechanical feedback due to galactic outflows. The photoionization of the Intergalactic Medium (IGM) suppresses low-mass galaxy formation by photoheating the gas and limiting atomic line cooling. The number of low-mass galaxies is central for the enrichment of the IGM as these objects have the capacity to enrich a significant fraction of the Universe. We use a modified version of our galactic outflow model, combined with a simple criterion for suppression, to investigate the potential impact upon the IGM. We find that this suppression strongly reduces the enrichment of the IGM and is sensitive to the reionization history. This history is expressed by a step-like reionization at z_r and we consider a best value of z_r = 11 and a conservative value of z_r = 6. We find that the extent of enrichment is strongly dependent on this parameter. While low-mass galaxies appear to be strongly suppressed, the lowest mass galaxies which dominate mechanical feedback are largely unaffected by suppression using z_r = 6 and relatively weakly affected using z_r = 11.
This paper presents results from axisymmetric simulations of magneto-rotational stellar core collapse to neutron stars in general relativity. These simulations are performed using a new general relativistic numerical code specifically designed to study this astrophysical scenario. The code is based on the conformally-flat approximation of Einstein's field equations and conservative formulations of the magneto-hydrodynamics equations. The code has been recently upgraded to incorporate a tabulated, microphysical equation of state and an approximate deleptonization scheme. This allows us to perform the most realistic simulations of magneto-rotational core collapse to date, which are compared with simulations employing a simplified (hybrid) equation of state, widely used in the relativistic core collapse community. Furthermore, state-of-the-art (unmagnetized) initial models from stellar evolution are used. In general, stellar evolution models predict weak magnetic fields in the progenitors, which justifies our simplification of performing the computations under the approach that we call the passive field approximation for the magnetic field. Our results show that for the core collapse models with microphysics the saturation of the magnetic field cannot be reached within dynamical time scales by winding up the poloidal magnetic field into a toroidal one. We estimate the effect of other amplification mechanisms including the magneto-rotational instability (MRI) and several types of dynamos.
Presence of a cool multicolor disk component with an inner disk temperature kT=0.1~0.3 keV at a luminosity L>10^40 erg/s has been interpreted as evidence that the ultraluminous X-ray source NGC 1313 X-2 harbors an intermediate-mass black hole (IMBH). The temperature of a disk component should vary with luminosity as $L\propto T^4$. However, upon investigating the spectral evolution with multiple XMM-Newton observations, we found that the cool disk component failed to follow this relation with a confidence level of 1-3.6x10^-5. Indeed, the luminosity decreases as the temperature increases, and the luminosities at high temperatures are more than an order of magnitude less than expected from the $L\propto T^4$ extrapolation of luminosities at low temperatures. This places a strong constraint against the validity of modeling the X-ray spectra of NGC 1313 X-2 as emission from the accretion disk of an IMBH. The decrease of luminosity with increasing temperature of the soft component follows the trend suggested by a model in which the soft emission arises from an outflow from a stellar-mass black hole with super-Eddington accretion viewed along the symmetry axis. Alternatively, the spectra can be adequately fitted by a p-free disk model with kT=~2 keV and p=~0.5. The spectral evolution is consistent with the $L\propto T^4$ relation and appears to be a high luminosity extension of the L-kT relation of Galactic black holes. This, again, would suggest that the emission is from a super-Eddington accreting stellar-mass black hole.
We use a 3-D relativistic SPH (Smoothed Particle Hydrodynamics) code to study mergers of black hole -- neutron star (BH--NS) binary systems with low mass ratios, adopting $M_{NS}/M_{BH} \simeq 0.1$ as a representative case. The outcome of such mergers depends sensitively on both the magnitude of the BH spin and its obliquity (i.e., the inclination of the binary orbit with respect to the equatorial plane of the BH). In particular, only systems with sufficiently high BH spin parameter $a$ and sufficiently low orbital inclinations allow any NS matter to escape or to form a long-lived disk outside the BH horizon after disruption. Mergers of binaries with orbital inclinations above $\sim60^o$ lead to complete prompt accretion of the entire NS by the BH, even for the case of an extreme Kerr BH. We find that the formation of a significant disk or torus of NS material around the BH always requires a near-maximal BH spin and a low initial inclination of the NS orbit just prior to merger.
Propagating star formation in a collisional ring galaxy Arp10 is investigated by a complex approach, which includes the broad- and narrow-band photometry, long- slit spectroscopy, and scanning Fabry-Perot spectroscopy. The ionized gas velocity field obtained with best spatial resolution to date indicates a non- isotropic expansion of the outer ring with a maximum velocity 110km/s. Strong vertical and non-circular motions are also seen in the vicinity of the inner ring. Our kinematic data suggest that Arp10 has a small inclination i=22\degr and high total (luminous plus dark matter) mass of about $10^{12} M_{\odot}$ within a 50 kpc radius.The abundance of oxygen 12 + log(O/H) in both star- forming rings is about 8.6.The analysis of spectral indices provides an estimate on the propagation velocities of both rings and metallicity of the pre-collision stellar population.A small "knot" near the nucleus of Arp10,which was previously suspected as a possible candidate for collision, is now unambiguously identified as the "intruder" of at least 1/4 of the total mass of Arp~10.We use a simplified two-dimensional hydrodynamic modeling of galaxy collisions to test a collisional origin of Arp10. We confirm that the sizes of the inner and outer rings, maximum expansion velocity of the outer ring, and radial profile of the gas circular velocity can be reproduced by a near-central collision with the intruder galaxy, which occurred approximately 85Myr ago. We acknowledge that an apparent crescent- shaped distribution of H$\alpha$ emission in the outer ring is caused by a star formation threshold in the gas disk of Arp10.
We compare the predictions of the Pe\~narrubia et al. (2005) model for the Monoceros stellar ring around the Milky Way with new observational constraints that provide deeper insights on its origin. Recently, Grillmair (2006) found a coherent sub-structure in a panoramic analysis of SDSS data, spanning 5x65 deg^2 above the Galactic plane towards the anticenter. We show here that this structure strikingly matches the prior model predictions in projected position on the sky and the distance (~10 kpc) to within 20%. Newly measured velocities within this sub-structure also match the model predictions perfectly. This match suggests that the model assumptions are correct, namely, that the Monoceros Ring corresponds to a tidal stream wrapping the Milky Way that results from a single disruption event of a satellite (M~5x10e8 M_sun) with a prograde, low-inclination, low-eccentric orbit. Further support for the external origin of the Mon Ring comes from new metalicity measurements of the Mon Ring, which show that this system is much more metal poor than star clusters in the outer Galactic disk at the same radius, and independent detections of RRLyr over-densities in the area that are in excellent agreement with the model predictions. That these observational data can be comprehensively explained by alternative disk heating scenarios seems not likely, but would need to be checked by detailed modeling.
We include the effect of neutrino free streaming into the spectrum of relic gravitational waves (RGWs) in the currently accelerating universe. For the realistic case of a varying fractional neutrino energy density and a non-vanishing derivative of mode function at the neutrino decoupling, the integro-differential equation of RGWs is solved by a perturbation method for the period from the neutrino decoupling to the matter-dominant stage. Incorporating it to the analytic solution of the whole history of expansion of the universe, the analytic solution of GRWs is obtained, evolving from the inflation up to the current acceleration. The resulting spectrum of GRWs covers the whole range of frequency $(10^{-19}\sim 10^{10})$Hz, and improves the previous results. It is found that the neutrino free-streaming causes a reduction of the spectral amplitude by $\sim 20%$ in the range $(10^{-16}\sim 10^{-10})$ Hz, and leaves the other portion of the spectrum almost unchanged. This agrees with the earlier numerical calculations. Examination is made on the difference between the accelerating and non-accelerating models, and our analysis shows that the ratio of the spectral amplitude in accelerating $\Lambda$CDM model over that in CDM model is $\sim 0.7$, and within the various accelerating models of $\Omega_{\Lambda}> \Omega_m $ the spectral amplitude is proportional to $ \Omega_m/\Omega_{\Lambda}$ for the whole range of frequency. Comparison with LIGO S5 Runs Sensitivity shows that RGWs are not yet detectable by the present LIGO, and in the future LISA may be able to detect RGWs in some inflationary models.
We show that the gravitational potential in the plane of an axisymmetrical flat disk where the surface density varies as a power of the radius obeys an inhomogeneous first-order Ordinary Differential Equation (ODE) solvable by standard techniques. The potential being exactly known at the origin for any power index (and at infinity as well), the search for solutions consists of a Two-point Boundary Value Problem (TBVP) with Dirichlet conditions. The computating time is then linear with the number of grid points, instead of quadratic from direct summation methods. Complex mass distributions which can be decomposed into a mixture of power law surface density profiles are easily accessible through the superposition principle. This ODE definitively takes the place of the untractable bidimensional Poisson equation for planar calculations. It opens new horizons to investigate various aspects related to self-gravity in astrophysical disks (force calculations, stability analysis, etc.).
Scalar and tensorial cosmological perturbations generated in warm inflationary scenarios whose matter-radiation fluid is endowed with a viscous pressure are considered. Recent observational data from the WMAP experiment are employed to restrict the parameters of the model. Although the effect of this pressure on the matter power spectrum is of the order of a few percent, it may be detected in future experiments.
ALBUM is a general-purpose tool to visualize and screen large amounts of slitless spectra. It was developed for a search for emission-line stars in SMC and LMC clusters. The observations were obtained with ESO's Wide Field Imager (WFI) and comprise ~8 million low-resolution spectra. The tool as well as the results of its application to the SMC part of the database are presented. The inferred frequency of Be stars is compared to the one in the higher-metallicity environment of the Milky Way.
The Coma cluster is the richest and most compact of the nearby clusters, yet there is growing evidence that its formation is still on-going. A sensitive probe of this evolution is the dynamics of intracluster stars, which are unbound from galaxies while the cluster forms, according to cosmological simulations. With a new multi-slit imaging spectroscopy technique pioneered at the 8.2 m Subaru telescope and FOCAS, we can now detect and measure the line-of-sight velocities of the intracluster planetary nebulae which are associated with the diffuse stellar population of stars, at 100 Mpc distance. We detect significant velocity substructures within a 6 arcmin diameter field, centred on the Coma X-ray cluster emission. One substructure ispresent at ~5000 km/s, probably from infall of a galaxy group, while the main intracluster stellar component moves at ~ 6500 km/s. Hence the ICPNs associated with the diffuse light at the position of the MSIS field are not bound to the nearby cD galaxy NGC 4874, whose radial velocity is ~ 700 km/s greater.
[Abridged] The giant molecular clouds (GMCs) of external galaxies can be mapped with sub-arcsecond resolution using multiband observations in the near-infrared. However, the interpretation of the observed features, and their transformation into physical quantities, is greatly hampered by the effects arising from the unknown geometry and the scattering of light by dust particles. We examine the relation between the observed NIR reddening and the column density of the dust clouds. In this paper we particularly assess the feasibility of deriving the mass function of GMCs from NIR color-excess data. We perform Monte Carlo radiative transfer simulations with 3D models of stellar radiation and clumpy dust distributions. We include the scattered light in the models and calculate NIR color maps from the simulated data. We extract clumps from the color maps and compare the observed mass function to the true mass function. For the physical configuration chosen in this study, essentially a face-on geometry, the observed mass function is a non-trivial function of the true mass function. The dynamical range of the observed mass function is confined to ~10^3.5... 10^5.5 M_\odot regardless of the dynamical range of the true mass function. The color maps are more sensitive in detecting the high-mass end of the mass function, and on average the masses of clouds are underestimated by a factor of ~10. The simulations show that the cloud mass function derived from JHK color excess data using simple foreground screening geometry cannot be regarded as a one-to-one tracer of the underlying mass function.
In this paper a simple analytical model for the steady-state evolution of debris disks due to collisions is confronted with Spitzer observations of main sequence A stars. All stars are assumed to have planetesimal belts with a distribution of initial masses and radii. In the model disk mass is constant until the largest planetesimals reach collisional equilibrium whereupon the mass falls off oc 1/t. We find that the detection statistics and trends seen at both 24 and 70um can be fitted well by the model. While there is no need to invoke stochastic evolution or delayed stirring to explain the statistics, a moderate rate of stochastic events is not ruled out. Potentially anomalous systems are identified by a high dust luminosity compared with the maximum permissible in the model (HD3003, HD38678, HD115892, HD172555). Their planetesimals may have unusual properties (high strength or low eccentricity) or this dust could be transient. While transient phenomena are also favored for a few systems in the literature, the overall success of our model, which assumes planetesimals in all belts have the same strength, eccentricity and maximum size, suggests a large degree of uniformity in the outcome of planet formation. The distribution of planetesimal belt radii, once corrected for detection bias, follows N(r) oc r^{-0.8+-0.3} for 3-120AU. Since the inner edge is often attributed to an unseen planet, this provides a unique constraint on the planetary systems of A stars. It is also shown that P-R drag may sculpt the inner edges of A star disks close to the Spitzer detection threshold (HD2262, HD19356, HD106591, HD115892). This model can be readily applied to the interpretation of future surveys, and predictions are made for the upcoming SCUBA-2 survey, including that >17% of A stars should be detectable at 850um.
We investigate a new approach to the detection of companions to extrasolar
planets beyond the transit method. We discuss the possibility of the existence
of binary planets.
We develop a method based on the imaging of a planet-companion as an
unresolved system (but resolved from its parent star). It makes use of
planet-companion mutual phenomena, namely mutual transits and mutual shadows.
We show that companions can be detected and their radius measured down to
lunar sizes.
To detect changes in repeated astronomical images of the same field of view (FOV), a common practice is to stroboscopically switch between the images. Using this method, objects that are changing in location or intensity between images are easier to see because they are constantly changing. A novel display method, called arrival time color intensity projections (CIPs), is presented that combines any number of grayscale images into a single color image on a pixel by pixel basis. Any values that are unchanged over the grayscale images look the same in the color image. However, pixels that change over the grayscale image have a color saturation that increases with the amount of change and a hue that corresponds to the timing of the changes. Thus objects moving in the grayscale images change from red to green to blue as they move across the color image. Consequently, moving objects are easier to detect and assess on the color image than on the grayscale images. A sequence of images of a comet plunging into the sun taken by the SOHO satellite (NASA/ESA) and Hubble Space Telescope images of a trans-Neptunian object (TNO) are used to demonstrate the method.
Simulations of the chemical enrichment histories of ten Local Group (LG) dwarf galaxies are presented, employing empirically-derived star formation histories (SFHs), a rich network of isotopic and elemental nucleosynthetic yields, and a range of prescriptions for supernova (SN)-driven outflows. Our main conclusions are that (i) neutron-capture element patterns (particularly that of Ba/Y) suggest a strong contribution from low- and intermediate-mass stars, (ii) neutron star mergers may play a relatively larger role in the nucleosynthesis of dwarfs, (iii) SN feedback alone can explain the observed gas fraction in dwarf irregulars (dIrrs), but dwarf spheroidals (dSphs) require almost all their gas to be removed via ram pressure and/or tidal stripping, (iv) the predicted heavy Mg isotope enhancements in the interstellar medium of dwarfs may provide an alternate solution to claims of a varying fine structure (v) the gas lost from dwarfs have O,Si/C abundances in broad agreement with intergalactic medium abundances at redshifts 2<z<4, and (vi) the chemical properties of dSphs are well-matched by preventing galactic winds from re-accreting, whilst those of dIrrs are better-matched by incorporating metallicity-dependent cooling and re-accretion of hot winds. Finally, doubts are cast upon a claimed association between LG dSph UMaII and High-Velocity Cloud Complex A.
Aims: To calculate the power budget for electron acceleration and the efficiency of the plasma emission mechanism in a post-flare decimetric continuum source. Methods: We have imaged a high brightness temperature ($\sim 10^{9}$K) post-flare source at 1060 MHz with the Giant Metrewave Radio Telescope (GMRT). We use information from these images and the dynamic spectrum from the Hiraiso spectrograph together with the theoretical method described in Subramanian & Becker (2006) to calculate the power input to the electron acceleration process. The method assumes that the electrons are accelerated via a second-order Fermi acceleration mechanism. Results: We find that the power input to the nonthermal electrons is in the range $3\times 10^{25}$--$10^{26}$ erg/s. The efficiency of the overall plasma emission process starting from electron acceleration and culminating in the observed emission could range from $2.87\times 10^{-9}$ to $2.38 \times 10^{-8}$.
We present the properties of spectrum of radiation emitted during gravitational collapse in which electromagnetic field strengths rise over the critical value for $e^+e^-$ pair creation. A drift from soft to a hard energy and a high energy cut off have been found; a comparison with a pure black body spectrum is outlined.
As a result of the search among about 11 000 stars from the public ASAS-3 database, we report detection of pulsating components in eleven eclipsing binaries. In particular, we have found three classical Algols, MX Pav, IZ Tel, and VY Mic, with $\delta$ Sct-type primary components. In six other eclipsing binaries, the short-period variability can also be interpreted in terms of $\delta$ Sct-type pulsations, but in these systems both components are probably main-sequence stars. In HD 99612, the pulsation mode shows significant amplitude decrease during the time interval covered by observations. In addition, we find variability in one of the components of the eclipsing and double-lined spectroscopic O-type binary ALS 1135 which we interpret as a $\beta$ Cep-type pulsation. Finally, we find Y Cir to be a good candidate for an SPB star in an eclipsing binary system.
We investigate the effect of dust on the observed rotation rate of a stellar bar. The only direct way to measure this quantity relies on the Tremaine & Weinberg method which requires that the tracer satisfies the continuity equation. Thus it has been applied largely to early-type barred galaxies. We show using numerical simulations of barred galaxies that dust attenuation factors typically found in these systems change the observed bar pattern speed by 20-40 percent. We also address the effect of star formation on the TW method and find that it does not change the results significantly. The results presented here suggest that applications of the TW method can be extended to include barred galaxies covering the full range of Hubble type.
We report the detection of [Ne II] emission at 12.81 micron in four out of the six optically thick dust disks observed as part of the FEPS Spitzer Legacy program. In addition, we detect a H I(7-6) emission line at 12.37 micron from the source RXJ1852.3-3700. Detections of [Ne II] lines are favored by low mid-infrared excess emission. Both stellar X-rays and extreme UV (EUV) photons can sufficiently ionize the disk surface to reproduce the observed line fluxes, suggesting that emission from Ne+ originates in the hot disk atmosphere. On the other hand, the H I(7-6) line is not associated with the gas in the disk surface and magnetospheric accretion flows can account only for at most ~30% of the observed flux. We conclude that accretion shock regions and/or the stellar corona could contribute to most of the H I(7-6)emission. Finally, we discuss the observations necessary to identify whether stellar X-rays or EUV photons are the dominant ionization mechanism for Ne atoms. Because the observed [Ne II] emission probes very small amounts of gas in the disk surface (~10^{-6} Jupiter masses) we suggest using this gas line to determine the presence or absence of gas in more evolved circumstellar disks.
Clumping in hot star winds can significantly affect estimates of mass-loss rates, the inferred evolution of the star and the environmental impact of the wind. A hydrodynamical simulation of a colliding winds binary (CWB) with clumpy winds reveals that the clumps are rapidly destroyed after passing through the confining shocks of the wind-wind collision region (WCR) for reasonable parameters of the clumps if the flow in the WCR is adiabatic. Despite large density and temperature fluctuations in the post-shock gas, the overall effect of the interaction is to smooth the existing structure in the winds. Averaged over the entire interaction region, the resulting X-ray emission is very similar to that from the collision of smooth winds. The insensitivity of the X-ray emission to clumping suggests it is an excellent diagnostic of the stellar mass-loss rates in wide CWBs, and may prove to be a useful addition to existing techniques for deriving mass-loss rates, many of which are extremely sensitive to clumping. Clumpy winds also have implications for a variety of phenomena at the WCR: particle acceleration may occur throughout the WCR due to supersonic MHD turbulence, re-acceleration at multiple shocks, and re-connection; a statistical description of the properties of the WCR may be required for studies of non-equilibrium ionization and the rate of electron heating; and the physical mixing of the two winds will be enhanced, as seems necessary to trigger dust formation.
Massive WR+O star systems produce high-temperature, shock-heated plasma where the wind of the WR star and that of its binary companion collide - the wind-collision region (WCR). The WCR is a source of thermal (e.g. hard X-rays) and non-thermal (e.g. synchrotron) emission, the latter arising from electrons and ions accelerated to relativistic energies. These colliding wind binaries provide an excellent laboratory for the study of particle acceleration at higher mass, photon and magnetic energy densities than exist in SNRs. Recent models of the non-thermal emission from WR 140 have provided insight into this process.
We obtain contemporaneous observations of the surface and corona of AB Dor
using ground-based circularly polarised spectra from the Anglo-Australian
Telescope and X-ray data from the Chandra satellite. The ground-based data are
used to construct surface magnetic field maps, which are extrapolated to
produce detailed models of the quiescent corona. The X-ray data serve as a new
test for the validity of these coronal models.
The high coronal density and complex multi-polar magnetic field indicate a
compact X-ray corona, which is concentrated close to the surface, with a
height, H~0.3-0.4R*. There is also significant correlation between the surface
and coronal active region locations. At this epoch AB Dor appears to possess
one very large active longitude region; displaying enhanced activity in the
form of large dark spots, strong magnetic fields and chromospheric emission.
Finally, the level of rotational modulation and shape of the X-ray lightcurve
depend on the distribution of magnetic field in the obscured hemisphere. The
models that best reproduce the rotational modulation observed in the
contemporaneous Chandra X-ray lightcurve and spectra require the magnetic field
in the obscured hemisphere to be of the same polarity as that in the observed
hemisphere. The Sun shows different behaviour, with the leading polarity
reversed in the opposite hemisphere. The X-ray observations provide a unique
constraint on the magnetic structure in the obscured hemisphere.
The baryonic acoustic signature in the large-scale clustering pattern of galaxies has been detected in the two-point correlation function. Its precise spatial scale has been forwarded as a rigid-rod ruler test for the space-time geometry, and hence as a probe for tracking the evolution of Dark Energy. Percent-level shifts in the measured position can bias such a test and erode its power to constrain cosmology. This paper addresses some of the systematic effects that might induce shifts: namely non-linear corrections from matter evolution, redshift space distortions and biasing. We tackle these questions through analytic methods and through a large battery of numerical simulations, with total volume of the order 105 [Gpc/h]^3. A toy-model calculation shows that if the non-linear corrections simply smooth the acoustic peak, then this gives rise to an `apparent' shifting to smaller scales. However if tilts in the broad band power spectrum are induced, then this gives rise to more pernicious `physical' shift. Our numerical simulations show evidence of both: in real space and at z=0, we find that for the dark matter the shift is of order a few percent; for haloes the shifts depend on halo mass, with larger shifts being found for the most biased samples, roughly 3-5%. In redshift space these effects are exacerbated, but at higher redshifts are slightly alleviated. We develop an analytical model to understand this, based on solutions to the pair conservation equation using characteristic curves. When combined with modeling of pairwise velocities the model reproduces the main trends found in the data. The model may also help to unbias the acoustic peak.
E+A galaxies are characterized as a galaxy with strong Balmer absorption
lines but without any [OII] or H$\alpha$ emission lines. The existence of
strong Balmer absorption lines means that E+A galaxies have experienced a
starburst within the last $<$1-1.5 gigayear. However, the lack of [OII] or
H$\alpha$ emission lines indicates that E+A galaxies do not have any on-going
star formation. Therefore, E+A galaxies are interpreted as a post-starburst
galaxy.
Morphologically, E+A galaxies appear as early-type galaxies, implying E+A
galaxies may be one of the progenitors of present-day elliptical galaxies.
However, there remained other possibilities such as the dusty starburst
scenario, where E+A galaxies have on-going star formation, but optical emission
lines are invisible due to the heavy obscuration by dust. Therefore, an
additional evidence of the post-starburst phenomena has been eagerly awaited.
Using one of the largest samples of 451 E+A galaxies carefully selected from
the Sloan Digital Sky Survey Data Release 4, here we show the abundance
diagnosis of E+A galaxies using Mg and Fe lines. Our findings are as follows
:(i) E+A galaxies has enhanced $\alpha$-element abundance ratio compared to the
star-forming galaxies with similar Balmer absorption strength. Since the
truncation of strong starburst is required to enhance the alpha element ratio,
this is an additional evidence that E+A galaxies are in the post-starburst
phase; (ii) the metallicity and $\alpha$-element abundance of E+A galaxies are
consistent with those of elliptical galaxies, suggesting that E+A galaxies
could be one of the progenitors of present-day elliptical galaxies in terms of
chemical abundances.
We describe a possible new technique for precise wavelength calibration of high-resolution astronomical spectrographs using femtosecond-pulsed mode-locked lasers controlled by stable oscillators such as atomic clocks. Such `frequency combs' provide a series of narrow modes which are uniformly spaced according to the laser's pulse repetition rate and whose absolute frequencies are known a priori with relative precision better than 10^{-12}. Simulations of frequency comb spectra show that the photon-limited wavelength calibration precision achievable with existing echelle spectrographs should be ~1 cm/s when integrated over a 4000A range. Moreover, comb spectra may be used to accurately characterise distortions of the wavelength scale introduced by the spectrograph and detector system. The simulations show that frequency combs with pulse repetition rates of 5-30GHz are required, given the typical resolving power of existing and possible future echelle spectrographs. Achieving such high repetition rates, together with the desire to produce all comb modes with uniform intensity over the entire optical range, represent the only significant challenges in the design of a practical system. Frequency comb systems may remove wavelength calibration uncertainties from all practical spectroscopic experiments, even those combining data from different telescopes over many decades.
Echelle spectrographs currently provide some of the most precise and detailed spectra in astronomy, the interpretation of which sometimes depends on the wavelength calibration accuracy. In some applications, such as constraining cosmological variations in the fundamental constants from quasar absorption lines, the wavelength calibration is crucial. Here we detail an algorithm for selecting thorium-argon (ThAr) emission lines for wavelength calibration which incorporates the properties of both a new laboratory wavelength list and the spectrograph of interest. We apply the algorithm to the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (UVES) and demonstrate a factor of >3 improvement in the wavelength calibration residuals (i.e. random errors) alone. It is also found that UVES spectra calibrated using a previous, widely distributed line-list contain systematic +/-30-75 m/s distortions of the wavelength scale over both short and long wavelength ranges. These distortions have important implications for current UVES constraints on cosmological variations in the fine-structure constant. The induced systematic errors are most severe for Mg/FeII quasar absorbers in the redshift range 1.2 < z < 2.3, with individual absorbers studied by recent authors containing systematic errors up to 4 times larger than quoted statistical errors.
In concordance cosmology, dark matter density perturbations generated by inflation lead to nonlinear, virialized minihalos, into which baryons collapse at redshift $z \sim 20$. We survey here novel baryon evolution produced by a modification of the power spectrum from white noise density perturbations at scales below $k \sim 10 h {Mpc}^{-1}$ (the smallest scales currently measured with the Lyman-$\alpha$ forest). Exotic dark matter dynamics, such as would arise from scalar dark matter with a late phase transition (similar to an axion, but with lower mass), create such an amplification of small scale power. The dark matter produced in such a phase transition collapses into minihalos, with a size given by the dark matter mass within the horizon at the phase transition. If the mass of the initial minihalos is larger than $\sim 10^{-3} M_\odot$, the modified power spectrum is found to cause widespread baryon collapse earlier than standard $\Lambda$CDM, leading to earlier gas heating. It also results in higher spin temperature of the baryons in the 21 cm line relative to $\Lambda$CDM at redshifts $z > 20$ if the mass of the minihalo is larger than $1 M_\odot$. It is estimated that experiments probing 21 cm radiation at high redshift will contribute a significant constraint on dark matter models of this type for initial minihalos larger than $\sim 10 M_\odot$. Early experiments reaching to $z\approx 15$ will constrain minihalos down to $\sim 10^3 M_\odot$.
We derive some new constraints on single-field inflation from the WMAP 3-year data combined with the Sloan Luminous Red Galaxy survey (SDSS-LRG). Our work differs from previous analyses by focusing only on the observable part of the inflaton potential, or in other words, by making absolutely no assumption about extrapolation of the potential from its observable region to its minimum (i.e., about the branch of the potential responsible for the last ~50 inflationary e-folds). We only assume that inflation starts a few e-folds before the observable Universe leaves the Hubble radius, and that the inflaton rolls down a monotonic and regular potential, with no sharp features or phase transitions. We Taylor-expand the inflaton potential at order v=2, 3 or 4 in the vicinity of the pivot scale, compute the primordial spectra of scalar and tensor perturbations numerically and fit the data. For v > 2, a large fraction of the allowed models is found to produce a large negative running of the scalar tilt, and to fall in a region of parameter space where the second-order slow-roll formalism is strongly inaccurate. We release a code for the computation of inflationary perturbations which is compatible with CosmoMC.
We present results from SMA observations of the star forming region Cepheus A-East at ~340 GHz (875 micron) with 0.7'' - 2'' resolution. At least four compact submm continuum sources have been detected, as well as a rich forest of hot core line emission. Two kinematically, chemically, and thermally distinct regions of molecular emission are present in the vicinity of the HW2 thermal jet, both spatially distinct from the submm counterpart to HW2. We propose that this emission is indicative of multiple protostars rather than a massive disk as reported by Patel et al. (2005).
Coronal mass ejections (CMEs) observed near the Sun via LASCO coronographic imaging are the most important solar drivers of geomagnetic storms. ICMEs, their interplanetary, near-Earth counterparts, can be detected in-situ, for example, by the Wind and ACE spacecraft. An ICME usually exhibits a complex structure that very often includes a magnetic cloud (MC). They can be commonly modelled as magnetic flux ropes and there is observational evidence to expect that the orientation of a halo CME elongation corresponds to the orientation of the flux rope. In this study, we compare orientations of elongated CME halos and the corresponding MCs, measured by Wind and ACE spacecraft. We characterize the MC structures by using the Grad-Shafranov reconstruction technique and three MC fitting methods to obtain their axis directions. The CME tilt angles and MC fitted axis angles were compared without taking into account handedness of the underlying flux rope field and the polarity of its axial field. We report that for about 64% of CME-MC events, we found a good correspondence between the orientation angles implying that for the majority of interplanetary ejecta their orientations do not change significantly (less than 45 deg rotation) while travelling from the Sun to the near Earth environment.
In this article we study closed inflationary universe models by using a tachyonic field theory. We determine and characterize the existence of an universe with $\Omega > 1$, and which describes a period of inflation. We find that considered models are less restrictive compared to the standard ones with a scalar field. We use recent astronomical observations to constraint the parameters appearing in the model. Obtained results are compared to those found in the standard scalar field inflationary universes.
We develop a method to measure the strength of the absorption features in Type Ia supernova (SN Ia) spectra and use it to make a quantitative comparison between the spectra of Type Ia supernovae at low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 < z < 0.912) SNe Ia observed by the Supernova Cosmology Project . Through measurements of the strengths of these features and of the blueshift of the absorption minimum in Ca II H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z < 0.15). One supernova in our high redshift sample, SN 2002fd at z=0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like supernovae.
We apply the Statefinder diagnostic to the Modified Polytropic Cardassian Universe in this work. We find that the Statefinder diagnostic is quite effective to distinguish Cardassian models from a series of other cosmological models. The $s-r$ plane is used to classify the Modified Polytropic Cardassian models into six cases. The evolutionary trajectories in the $s-r$ plane for the cases with different $n$ and $\beta$ reveal different evolutionary properties of the universe. In addition, we combine the observational $H(z)$ data, the Cosmic Microwave Background (CMB) data and the Baryonic Acoustic Oscillation (BAO) data to make a joint analysis. We find that \textbf{Case 2} can be excluded at the 68.3% confidence level and any case is consistent with the observations at the 95.4% confidence level.
Current sheets formed in magnetic reconnection events are found to be unstable to high-wavenumber perturbations. The instability is very fast: its maximum growth rate scales as S^{1/4} L/v_A, where L is the length of the sheet, v_A the Alfven speed and S the Lundquist number. As a result, a chain of plasmoids (secondary islands) is formed, whose number scales as S^{3/8}.
We have searched for emission from the 557 GHz ortho-water line in the interstellar medium of six nearby starburst galaxies. We used the Odin satellite to observe the 1_10-1_01 transition of o-H2O in the galaxies NGC253, IC342, M82, NGC4258, CenA, and M51. None of the galaxies in our sample was detected. We derive three sigma upper limits to the H2O abundance relative to H2 ranging from 2e-9 to 1e-8. The best of these upper limits are comparable to the measured abundance of H$_2$O in the Galactic star forming region W3. However, if only 10% of the molecular gas is in very dense cores, then the water abundance limits in the cores themselves would be larger by a factor of 10 i.e. 2e-8 to 1e-7. These observations suggest that detections of H2O emission in galaxies with the upcoming Herschel Space Observatory are likely to require on-source integration times of a few hours even in the most promising extragalactic targets.
We discuss the differences induced by the assumed composition of extragalactic sources on the predicted UHECR spectrum and the energy evolution of the cosmic-ray shower <X_{\max}>. We show that different assumptions for the source power evolution do not modify our earlier finding that in the case of a mixed composition the ankle can be interpreted as the end of the transition from galactic to extragalactic cosmic rays. We show that the <X_{\max}> features associated with this transition in each cosmic-ray source model are essentially independent of the assumed hadronic model. In the mixed composition cases, a signature of the interactions of nuclei with the photon backgrounds is also expected above $10^{19}$ eV. The comparisons with Stereo HiRes and Fly's Eye data favour an extragalactic mixed composition and the corresponding interpretation of the ankle. Confrontation of model predictions with future data at the highest energies will allow a better determination of the transition features and of the cosmic-ray source composition, independently of hadronic models. We also emphasize that in the pure proton case, a combined analysis of the spectrum and composition below the ankle could lead to constraints on the source power evolution with redshift.
We present the most precise light curve ever obtained of a detached eclipsing binary star and use it investigate the inclusion of non-linear limb darkening laws in eclipsing binary light curve models. This light curve, of the bright system beta Aurigae, was obtained using the star tracker aboard the WIRE satellite and contains 30000 datapoints with a scatter of 0.3 mmag. We analyse it using a version of the EBOP code modified to include non-linear limb darkening and to directly incorporate observed times of minimum light and spectroscopic light ratios into the solution as individual observations. We also analyse the dataset with the WD code to ensure that the two models give consistent results. EBOP provides an excellent fit to the WIRE data. Whilst the fractional radii are only defined to a precision of 5%, including an accurate published spectroscopic light ratio improves this dramatically to 0.5%. Using non-linear limb darkening improves the quality of the fit significantly and causes the measured radii to increase by 0.4%. It is possible to derive all of the limb darkening coefficients from the light curve, although they are strongly correlated with each other, and they agree with theoretical predictions. The radii and masses of the components of beta Aur are R_A = 2.762 +/- 0.017 Rsun, R_B = 2.568 +/- 0.017 Rsun, M_A = 2.376 +/- 0.027 Msun and M_B = 2.291 +/- 0.027 Msun. Theoretical stellar models can match these parameters for a solar metal abundance and an age of 450-500 Myr. The Hipparcos trigonometric parallax and an interferometrically-derived orbital parallax give distances to beta Aur which are in excellent agreement with each other and with distances derived using surface brightness relations and several sets of empirical and theoretical bolometric corrections (abridged).
Massive tori with $\approx 10^{8-9}M_{\odot}$ are predicted to extend on $\sim $100 pc scale around the centre of elliptical galaxy progenitors by a model of a supermassive black hole (SMBH) growth coeval to the spheroidal population of the host galaxy. Direct detection of such massive tori would cast light on a key physical condition that allows the rapid growth of SMBHs and the appearance of QSOs at high redshift. For this reason, we examine the detectability of such structures at substantial redshift with the Atacama Large Millimeter Array (ALMA). We propose that submillimeter galaxies (SMGs) are the best targets to test our predictions. In order to assess the observational feasibility, we estimate the expected number counts of SMGs with massive tori and check the detectability with the ALMA instrument, the unique facility which can resolve the central region of high redshift objects. Our work shows that ALMA will be able to resolve and detect high-$J$ ($J >$ 4) CO emissions from $\sim$100 pc scale extended massive tori up to $z\approx2$. Observations of lensed SMGs will yield excellent spatial resolution, allowing even to resolve their massive tori at higher redshift. We discuss further the detectability of the HCN molecule, as a better tracer of the high density gas expected in such tori. The final goal of these kind of observations is to pinpoint possible physical mechanisms that storage in the very central galactic regions very large amount gas on timescale of several 10$^{8}$ yr.
We investigate the IR spectral features of a sample of D-type symbiotic stars. Analyzing unexploited ISO-SWS data, deriving the basic observational parameters of dust bands and comparing them with respect to those observed in other astronomical sources, we try to highlight the effect of environment on grain chemistry and physic. We find strong amorphous silicate emission bands at 10 micron and 18 micron in a large fraction of the sample. The analysis of the 10 micron band, along with a direct comparison with several astronomical sources, reveals that silicate dust in symbiotic stars shows features between the characteristic circumstellar environments and the interstellar medium. This indicates an increasing reprocessing of grains in relation to specific symbiotic behavior of the objects. A correlation between the central wavelength of the 10 and 18 micron dust bands is found. By the modeling of IR spectral lines we investigate also dust grains conditions within the shocked nebulae. Both the unusual depletion values and the high sputtering efficiency might be explained by the formation of SiO moleculae, which are known to be a very reliable shock tracer. We conclude that the signature of dust chemical disturbance due to symbiotic activity should be looked for in the outer, circumbinary, expanding shells where the environmental conditions for grain processing might be achieved. Symbiotic stars are thus attractive targets for new mid-infrared and mm observations.
This review is split into two parts: one on chromospheric line formation in answer to the frequent question "where is my line formed", and one presenting state-of-the-art imagery of the chromosphere. In the first part I specifically treat the formation of the Na D lines, Ca II H & K, and Halpha. In the second I show DOT, IBIS, VAULT, and TRACE images as evidence that the chromosphere consists of fibrils of intrinsically different types. The straight-up ones are hottest. The slanted ones are filled by shocks and likely possess thin transition sheaths to coronal plasma. The ones hovering horizontally over "clapotispheric" cell interiors outline magnetic canopies and are buffeted by shocks, most violently in the quietest regions. In the absence of integral-field ultraviolet spectrometry, H$\alpha$ remains the principal chromosphere diagnostic. The required fast-cadence profile-sampling imaging is an important quest for new telescope technology.
This paper is an invitation to the international community to participate in
the usage and a substantial upgrade of the Dutch Open Telescope on La Palma
(DOT, \url{this http URL}).
We first give a brief overview of the approach, design, and current science
capabilities of the DOT.
The DOT database (\url{this http URL}) now contains many
tomographic image sequences with 0.2-0.3 arcsec resolution and up to multi-hour
duration. You are welcome to pull them over for analysis.
The main part of this contribution outlines DOT upgrade designs implementing
larger aperture. The motivation for aperture increase is the recognition that
optical solar physics needs the substantially larger telescope apertures that
became useful with the advent of adaptive optics and viable through the DOT's
open principle, both for photospheric polarimetry at high resolution and high
sensitivity and for chromospheric fine-structure diagnosis at high cadence and
full spectral sampling.
Realization of an upgrade requires external partnership(s). This report about
DOT upgrade options therefore serves also as initial documentation for
potential partners.
The goal is to build up a simple dynamical model for the out-flowing circumstellar envelope around AGB stars in a wide binary system to explore the parameter dependence of the geometrical characteristics of column density patterns. An AGB star in a wide binary system is considered as a 3-D piston model that can induce a 3-D quasi-spherical density structure in the circumstellar envelope by orbital motion of the AGB star. The column density pattern only depends on two parameters: eccentricity of the orbit e and the terminal outflow velocity to mean orbital velocity ratio gamma. When viewed perpendicular to the orbital plane, spiral, broken spiral, and incomplete concentric shell patterns can be seen, while when viewed along the orbital plane, alternative concentric half-shell, egg-shell, and half-shell half-gap patterns will develop. Non-zero eccentricity causes asymmetry, while larger gamma makes a weaker pattern and helps bring out asymmetry. A spiral pattern may becomes broken when e > 0.4. The spiral center is always less than 12% of spiral pitch away from the orbit center. One should have more chances (~ 80%) seeing spiral-like patterns than seeing concentric shells (~ 20%) in the circumstellar envelope of wide binary AGB stars.
The predicted infrared brightness temperature of Mars using the 1976 model of Wright is tabulated here for the period 1983 to 2103. This model was developed for far-infrared calibration, and is still being used for JCMT calibration.
The rare and conspicuous flux density variations of some radio sources
(extragalactic and pulsars) for periods of weeks to months have been denoted
Extreme Scattering Events (ESE's) by Fiedler et al. (1987). Presently, there is
no astrophysical mechanism that satisfactorily produces this phenomenon. In
this paper, we conjecture that inhomogeneities of the electronic density in the
turbulent interstellar medium might be the origin of this phenomenon. We have
tested this conjecture by a simulation of the scintillation of the pulsar
B1937+21 at 1.4 GHz and 1.7 GHz for a period of six months. To this end, we
have constructed a large square Kolmogorov phase screen made of 131k x 131k
pixels with electron inhomogeneity scales ranging from 6 x $10^6$ m to
$10^{12}$ m and used the Kirchhoff-Fresnel integral to simulate dynamic spectra
of a pulsar within the framework of Physical Optics.
The simulated light curves exhibit a 10 day long variation simultaneously at
1.41 and 1.7 GHz that is alike the ``ESE'' observed with the Nancay
radiotelescope toward the pulsar B1937+21 in October 1989. Consequently, we
conclude that ``ESE'' toward pulsars can be caused naturally by the turbulence
in the ionized interstellar medium instead of invoking the crossing of discrete
over pressured ionized clouds on the line of sight as in the model of Fiedler
et al. (1987). We suggest that longer events could occur in a simulation of
scintillation, if larger electron inhomogeneities > $10^{12}$ m were included
in the construction of the Kolmogorov phase screen. This next step requires a
supercomputer.
Pre-main sequence evolutionary theory is not well-calibrated to observations. With care, the observed quantities can be converted into effective temperature and luminosity (i.e. the Hertzsprung-Russell diagram) which the theoretical calculations also predict as a function of stellar mass and age. For a sample of nearby young stellar clusters and associations ranging in age from <1 Myr to >100 Myr, we have tested the loci of luminosity as a function of effective temperature against various sets of predicted pre-main sequence isochrones. As we found in Hillenbrand & White (2004) which tested stellar masses, here for the stellar ages there are two conclusions: some evolutionary calculations fare better than others in reproducing the empirical sequences, and systematic differences between all pre-main sequence evolutionary calculations and the data are apparent. We also simulate hypothetical clusters of varying star formation history and compare the resulting HR diagram predictions to observed clusters. Our efforts are directed towards quantitative assessment of **apparent** luminosity spreads in star forming regions and young clusters, which are often erroneously interpreted as **true** luminosity spreads indicative of **true** age spreads.
Environment plays an important role in the evolution of the gas contents of galaxies. Gas deficiency of cluster spirals and the role of the hot intracluster medium (ICM) in stripping gas from these galaxies is a well studied subject. Loose groups with diffuse X-ray emmision from the intragroup medium (IGM) offer an intermediate environment between clusters and groups without a hot IGM. These X-ray bright groups have smaller velocity dispersion and lower temperature than clusters, but higher IGM density than loose groups without diffuse X-ray emission. A single dish comparative study of loose groups with and without diffuse X-ray emission from the IGM, showed that the galaxies in X-ray bright groups have lost more gas on average than the galaxies in non X-ray bright groups. In this paper we present GMRT HI observations of 13 galaxies from 4 X-ray bright groups: NGC5044, NGC720, NGC1550 and IC1459. The aim of this work is to study the morphology of HI in these galaxies and to see if the hot IGM has in any way affected their HI content or distribution. In addition to disturbed HI morphology, we find that most galaxies have shrunken HI disks compared to the field spirals. This indicates that IGM assisted stripping processes like ram pressure may have stripped gas from the outer edges of the galaxies.
The strict analogy between scalar-tensor theories of gravity and high order gravity is well known in literature. In this paper it is shown that, from a particular high order gravity theory known in literature, it is possible to produce, in the linearized approch, particles which can be seen like massive scalar modes of gravitational waves and the response of interferometers to this type of particles is analyzed. The presence of the mass generates a longitudinal force in addition of the transverse one which is proper of the massless gravitational waves and the response of an arm of an interferometer to this longitudinal effect in the frame of a local observer is computed. This longitudinal response function is directly connected with the function of the Ricci scalar in the particular action of this high order theory. Important conseguences from a theoretical point of view could arise from this approach, because it opens to the possibility of using the signals seen from interferometers to understand which is the correct theory of gravitation.
Up to now, Dark Energy evidences are based on the dynamics of the universe on very large scales, above 1 Gpc. Assuming it continues to behave like a cosmological constant $\Lambda$ on much smaller scales, I discuss its effects on the motion of non-relativistic test-particles in a weak gravitational field and I propose a way to detect evidences of $\Lambda \neq 0$ at the scale of about 1 Mpc: the main ingredient is the measurement of galaxy cluster masses.
Photometry of galaxies has typically focused on small, faint systems due to
their interest for cosmological studies. Large angular size galaxies, on the
other hand, offer a more detailed view into the properties of galaxies, but
bring a series of computational and technical difficulties that inhibit the
general astronomer from extracting all the information found in a detailed
galaxy image. To this end, a new galaxy photometry system has been developed
(mostly building on tools and techniques that have existed in the community for
decades) that combines ease of usage with a mixture of pre-built scripts. The
audience for this system is a new user (graduate student or non-optical
astronomer) with a fast, built-in learning curve to offer any astronomer, with
imaging data, a suite of tools to quickly extract meaningful parameters from
decent data. The tools are available either by a client/server web site or by
tarball for personal installation. The tools also provide simple scripts to
interface with various on-line datasets (e.g. 2MASS, Sloan, DSS) for data
mining capability of imaged data.
As a proof of concept, we preform a re-analysis of the 2MASS Large Galaxy
Atlas to demonstrate the differences in an automated pipeline, with its
emphasis on speed, versus this package with an emphasis on accuracy. This
comparison finds the structural parameters extracted from the 2MASS pipeline is
seriously flawed with scale lengths that are too small by 50% and central
surface brightness that are, on average, 1 to 0.5 mags too bright. A cautionary
tale on how to reduce information-rich data such as surface brightness
profiles. This document and software can be found at
this http URL
The property of the spectrum of large-scale magnetic fields generated due to the breaking of the conformal invariance of the Maxwell theory through some mechanism in inflationary cosmology is studied. It is shown that the spectrum of the generated magnetic fields should not be perfectly scale-invariant but be slightly red so that the amplitude of large-scale magnetic fields can be stronger than $\sim 10^{-12}$G at the present time. This analysis is performed by assuming the absence of amplification due to the late-time action of some dynamo (or similar) mechanism.
We have performed time-dependent numerical simulations of the interstellar medium (ISM) which account for galactic shear and magnetic fields, vertical gravity, and a radiative cooling function for atomic gas. This allows us to study the magnetorotational instability (MRI) in cloudy, vertically-stratified disks. As in previous unstratified models, we find that thermal instability interacts with MRI-driven turbulence and galactic shear to produce a network of cold, dense, filamentary clouds embedded in a warm diffuse ambient medium. This structure strongly resembles the morphology of HI gas observed in the 21 cm line. There is significant thermally-unstable gas, but the density and temperature distributions retain the twin peaks of the classical two-phase ISM. We analyze the vertical distributions of density and various pressure terms, and address what supports the ISM vertically. Turbulent velocities of the cold gas increase as the cold mass fraction decreases, but are generally low ~1-3 km/s near the midplane; they increase to > 5 km/s at high z. Finally, we argue that in the outer parts of galactic disks, MRI is likely able to prevent the development of self-gravitating instabilities and hence suppress star formation, even if cold gas is present.
In this work we present a detailed explanation of the construction of an appropriate equation of state (EoS) for nuclear astrophysics. We use a relativistic model in order to obtain an EoS for neutrally charged matter that extends from very low to high densities, from zero temperature to 100 MeV with proton fractions ranging from 0 (no protons) to 0.6 (asymmetric matter with proton excess). For the achievement of complete convergence, the Sommerfeld approximation is used at low temperatures and the Boltzman distribution for relativistic particles is used in the calculation of the electron properties at very low densities. Photons are also incorporated as blackbody radiation. An extension of this EoS is also presented with the inclusion of strangeness by taking into account the sigma minus hyperon only. Strangeness fractions range from 0.02 to 0.3.
The theory of moving reversing layers for hot stars is updated to include an extensive line list, a radiative boundary condition from static model atmospheres, line transfer by scattering, and continuation to supersonic velocities. A Monte Carlo technique determines the theory's eigenvalue J, the mass flux, and the derived J's are in good agreement with the wind models of Pauldrach et al. (2001). The solutions' sensitivity to the photospheric microturbulent velocity reveals that this parameter has a throttling effect on J: turbulent line-broadening in the quasi-static layers reduces the radiation force available to accelerate matter through the sonic point. If photospheric turbulence approaches sonic velocities, this mechanism reduces mass loss rates by factors > 3, which would partly account for the reduced rates found observationally for clumpy winds.
Weakly interacting massive particles (WIMPs) are one of the leading candidates for dark matter. Currently, the most promising method to detect many different WIMP candidates is the direct detection of the recoil energy deposited in a low--background laboratory detector due to elastic WIMP--nucleus scattering. So far the usual procedure has been to predict the event rate of direct detection of WIMPs based on some model(s) of the galactic halo. The aim of our work is to invert this process. That is, we study what future direct detection experiment can teach us about the WIMP halo. As the first step we consider a time--averaged recoil spectrum, assuming that no directional information exists. We develop a method to construct the (time--averaged) one--dimensional velocity distribution function from this spectrum. Moments of this function, such as the mean velocity and velocity dispersion of WIMPs, can also be obtained directly from the recoil spectrum. The only input needed in addition to a measured recoil spectrum is the mass of the WIMP; no information about the scattering cross section or WIMP density is required.
We investigate the impact of 3D hydrodynamical model atmospheres of red giant stars at different metallicities on the formation of spectral lines of a number of ions and molecules. We carry out realistic 3D simulations of surface convection in red giant stars with varying stellar parameters. We use the simulations as time-dependent hydrodynamical model stellar atmospheres to compute atomic (Li, O, Na, Mg, Ca, Fe) and molecular (CH, NH, OH) spectral lines under the assumption of local thermodynamic equilibrium (LTE). We compare the line strengths computed in 3D with the results of analogous line formation calculations for 1D, hydrostatic, plane-parallel MARCS model atmospheres in order to estimate the impact of 3D models on the derivation of elemental abundances. The temperature and density inhomogeneities and correlated velocities in 3D models, as well as the differences between the 1D and mean 3D structures significantly affect the predicted line strengths. Under the assumption of LTE, the low atmospheric temperatures of very metal-poor 3D model atmospheres cause the lines from neutral species and molecules to appear stronger than in 1D. Therefore, elemental abundances derived from these lines using 3D models are significantly lower than according to 1D analyses. Differences between 3D and 1D abundances of C, N, and O derived from CH, NH, and OH weak low-excitation lines are found to be in the range -0.5 dex to -1.0 dex for the the red giant stars at [Fe/H]=-3 considered here. At this metallicity, large negative corrections (about -0.8 dex) are also found for weak low-excitation Fe I lines. We caution, however, that departures from LTE might be significant for these and other elements and comparable to the effects due to stellar granulation.
We study the relationship between the local environment of galaxies and their star formation rate (SFR) in the Great Observatories Origins Deep Survey, GOODS, at z~1, from ultradeep imaging at 24 microns with the MIPS camera onboard Spitzer. We show that the star formation-density relation observed locally was reversed at z~1. The average SFR of an individual galaxy increased with local galaxy density when the universe was less than half its present age. Hierarchical galaxy formation models (simulated lightcones from the Millennium model) do expect a reversal but at a lower level and only at earlier epochs (z>2). We present a remarkable structure at z~1.016, containing X-ray traced galaxy concentrations, which will eventually merge into a Virgo-like cluster. This structure illustrates how the individual SFR of galaxies increases with density and shows that it is the ~1-2 Mpc scale that affects most the star formation in galaxies at z ~ 1. There is a correlation between the SFR and stellar mass of galaxies at z ~ 1 but the specific SFR (=SFR/M*) increases with galaxy density hence favoring the interpretation that the environment does directly affect the star formation activity of galaxies. Nearly half of the z ~ 1 LIRGs present the HST-ACS morphology of spirals, while only a third present a clear signature of major mergers, the remaining galaxies are divided into compact (9%) and irreguliar (14%) galaxies. The specific SFR of major mergers is only marginally stronger than that of spirals, hence major mergers appear not to be the major cause for the reversal of the star formation-density relation at z ~ 1. Reproducing the SFR-density relation at z ~ 1 is a new challenge for models, requiring a correct balance between mass assembly through mergers and in-situ star formation at early epochs.
We report the optical polarization of a gamma ray burst (GRB) afterglow, obtained 203 seconds after the initial burst of gamma rays from GRB 060418, using a ring polarimeter on the robotic Liverpool Telescope. Our robust (2-sigma) upper limit on the percentage of polarization, less than 8%, coincides with the fireball deceleration time at the onset of the afterglow. The combination of the rate of decay of the optical brightness and the low polarization at this critical time constrains standard models of GRB ejecta, ruling out the presence of a large-scale ordered magnetic field in the emitting region.
This paper gives a simple and original presentation of various coronagraphs inherited from the Lyot coronagraph. We first present the Lyot and Roddier phase mask coronagraphs and study their properties as a function of the focal mask size. We show that the Roddier phase mask can be used to produce an apodization for the star. Optimal coronagraphy can be obtained from two main approaches, using prolate spheroidal pupil apodization and a finite-size focal mask, or using a clear aperture and an infinite mask of variable transmission.
We present spectra of six Type Ia and two Type II supernovae obtained in June 2002 at the William Herschel Telescope during a search for Type Ia supernovae (SNIa) at intermediate redshift. Supernova type identification and phase determination are performed using a fitting technique based on a Xi2 minimization against a series of model templates. The spectra range from z=0.033 to z=0.328, including one spectroscopically underluminous SNIa at z=0.033. This set of spectra significantly increases the sample of well-observed type SNIa supernovae available in the range 0.15< z <0.35. Together with the twelve supernovae observed by our team in 1999 in the same redshift range, they form an homogeneous sample of seventeen type Ia supernovae with comparable signal-to-noise ratio and regular phase sampling in a still largely unexplored region of the redshift space.
We investigate the correlation between the bulge effective radius (r_e) and disk scale length (r_d), in the near-infrared K band for lenticular galaxies in the field and in clusters. We find markedly different relations between the two parameters as a function of luminosity. Lenticulars with total absolute magnitude fainter than M_T = -24.5 show a positive correlation, in line with predictions of secular formation processes for the pseudo bulges of late-type disk galaxies. But brighter lenticulars with M_T < -24.5 show an anti-correlation, indicating that they formed through a different mechanism. The available data is insufficient to reliably determine the effect of galaxy environment on these correlation.
We present ELODIE.3.1, an updated release of the library published in
Prugniel & Soubiran (2001, 2004).
The library includes 1962 spectra of 1388 stars obtained with the ELODIE
spectrograph at the Observatoire de Haute-Provence 193cm telescope in the
wavelength range 390 to 680 nm. It provides a wide coverage of atmospheric
parameters : T_eff from 3100 K to 50000 K, log g from -0.25 to 4.9 and [Fe/H]
from -3 to +1. The library is given at two resolutions: R~42000, with the flux
normalized to the pseudo-continuum, FWHM=0.55\AA (R~10000) calibrated in
physical flux
(reduced above earth atmosphere) with a broad-band photometric precision of
2.5% and narrow-band precision of 0.5%.
In this new release the data-reduction (flux calibration, reconnection of the
echelle orders) has been improved, and in particular the blue region, between
390 and 400 nm has been added.
The FITS files for each spectra, and the measured atmospheric parameters are
publicly available.
See the ELODIE.3.1 page for more details:
this http URL
We present results of the near-infrared (IR) spectroscopy of six quasars whose redshifts ranging from 0.158 to 1.084. Combined with the satellite ultraviolet data, it is given the relative line strengths of OI1304, 8446, and 11287, and near-IR CaII triplet. In addition, corresponding OI line strengths measured in Seyfert 1s and narrow-line Seyfert 1s are collected from literature. These lines are thought to emerge from the same gas with FeII lines, so are good tracers of the FeII emission region within a broad-emission-line region (BELR) in active galactic nuclei. In order to reveal the physical condition within the relevant emission region, we performed photoionized model calculations and compared them to the observations. It suggests that a rather dense gas with density nH ~ 10^(11.5) cm-3 is present at an outer portion of the BELR, illuminated by the ionizing radiation corresponding to an ionization parameter U ~ 10^(-2.5), and is dominantly responsible for the observed OI, CaII, and FeII lines based on the resemblance of their profiles. The three OI lines are proved to be formed through Ly beta fluorescence and collisional excitation. We also show that the l1304 bump typically observed in AGN spectra consists of the comparable contributions of OI and SiII multiplets, and discuss the origin of such a strong SiII emission. The results are interpreted in the context of the locally optimally emitting cloud (LOC) scenario to find the most plausible distribution functions of the BELR gas of distance from the central source and density.
We present 3.6 - 160 micron infrared images of Kepler's supernova remnant (SN1604) obtained with the IRAC and MIPS instruments on the Spitzer Space Telescope. We also present MIPS SED low resolution spectra in the 55 - 95 micron region. The observed emission in the MIPS 24 micron band shows the entire shell. Emission in the MIPS 70 micron and IRAC 8 micron bands is seen only from the brightest regions of 24 micron emission, which also correspond to the regions seen in optical Halpha images. Shorter wavelength IRAC images are increasingly dominated by stars, although faint filaments are discernible. The SED spectrum of shows a faint continuum dropping off to longer wavelengths and confirms that strong line emission does not dominate the mid-IR spectral region. The emission we see is due primarily to warm dust emission from dust heated by the primary blast wave; no excess infrared emission is observed in regions where supernova ejecta are seen in X-rays. We use models of the dust to interpret the observed 70/24 micron ratio and constrain the allowed range of temperatures and densities. We estimate the current mass of dust in the warm dust component to be 5.4 x 10^{-4} solar masses, and infer an original mass of about 3 x 10^{-3} solar masses before grain sputtering. The MIPS 160 micron band shows no emission belonging to the remnant. We place a conservative but temperature dependent upper limit on any cold dust component roughly a factor of 10 below the cold dust mass inferred from SCUBA observations. Finally, we comment on issues relevant to the possible precursor star and the supernova type.
We present detailed comparisons of the intracluster medium (ICM) in cosmological Eulerian cluster simulations with deep Chandra observations of nearby relaxed clusters. To assess the impact of galaxy formation, we compare two sets of simulations, one performed in the non-radiative regime and another with radiative cooling and several physical processes critical to various aspects of galaxy formation: star formation, metal enrichment and stellar feedback. We show that the observed ICM properties outside cluster cores are well-reproduced in the simulations that include cooling and star formation, while the non-radiative simulations predict an overall shape of the ICM profiles inconsistent with observations. In particular, we find that the ICM entropy in our runs with cooling is enhanced to the observed levels at radii as large as half of the virial radius. We also find that outside cluster cores entropy scaling with the mean ICM temperature in both simulations and Chandra observations is consistent with self-similar within current errorbars. We find that the pressure profiles of simulated clusters are also close to self-similar and exhibit little cluster-to-cluster scatter. The X-ray observable-total mass relations for our simulated sample agree with the Chandra measurements to \~10%-20% in normalization. We show that this systematic difference could be caused by the subsonic gas motions, unaccounted for in X-ray hydrostatic mass estimates. The much improved agreement of simulations and observations in the ICM profiles and scaling relations is encouraging and the existence of tight relations of X-ray observables, such as Yx, and total cluster mass and the simple redshift evolution of these relations hold promise for the use of clusters as cosmological probes.
We present an accurate X-ray position of the massive globular cluster G1 by using XMM-Newton and the Hubble Space Telescope (HST). The X-ray emission of G1 has been detected recently with XMM-Newton. There are two possibilities for the origin of the X-ray emission. It can be either due to accretion of the central intermediate-mass black hole, or by ordinary low-mass X-ray binaries. The precise location of the X-ray emission might distinguish between these two scenarios. By refining the astrometry of the XMM-Newton and HST data, we reduced the XMM-Newton error circle to 1.5". Despite the smaller error circle, the precision is not sufficient to distinguish an intermediate-mass black hole and luminous low-mass X-ray binaries. This result, however, suggests that future Chandra observations may reveal the origin of the X-ray emission.
The death of massive stars produces a variety of supernovae, which are linked to the structure of the exploding stars. The detection of several precursor stars of Type II supernovae have been reported, however we do not yet have direct information on the progenitors of the hydrogen deficient Type Ib and Ic supernovae. Here we report that the peculiar Type Ib supernova SN2006jc is spatially coincident with a bright optical transient that occurred in 2004. Spectroscopic and photometric monitoring of the supernova leads us to suggest that the progenitor was a carbon-oxygen Wolf-Rayet star embedded within a helium-rich circumstellar medium. There are different possible explanations for this pre-explosion transient. It appears similar to the giant outbursts of Luminous Blue Variables (LBV) of 60-100 solar mass stars, however the progenitor of SN2006jc was helium and hydrogen deficient. An LBV-like outburst of a Wolf-Rayet star could be invoked, but this would be the first observational evidence of such a phenomenon. Alternatively a massive binary system composed of an LBV which erupted in 2004, and a Wolf-Rayet star exploding as SN2006jc, could explain the observations.
We present a sample of 40 Ultra Steep Spectrum (USS, $\alpha \leq -1.3$, $S_{\nu}\propto \nu^{\alpha}$) radio sources selected from the Westerbork in the Southern Hemisphere (WISH) catalog. The USS sources have been imaged in K--band at the Cerro Tololo Inter-American Observatory (CTIO) and with the Very Large Telescope at Cerro Paranal. We also present VLT, Keck and Willian Herschel Telescope(WHT) optical spectroscopy of 14 targets selection from 4 different USS samples. For 12 sources, we have been able to determine the redshifts, including 4 new radio galaxies at z > 3. We find that most of our USS sources have predominantly small (6'') radio sizes and faint magnitudes (K~18). The mean K-band counterpart magnitude is $\bar{K}$=18.6. The expected redshift distribution estimated using the Hubble K-z diagram has a mean of $\bar{z}_{exp}$$\sim$2.13, which is higher than the predicted redshift obtained for the SUMSS-NVSS sample and the expected redshift obtained in the 6C$^{**}$ survey. The compact USS sample analyzed here may contain a higher fraction of galaxies which are high redshift and/or are heavily obscured by dust. Using the 74, 352 and 1400 MHz flux densities of a sub-sample, we construct a radio colour-colour diagram. We find that all but one of our USS sources have a strong tendency to flatten below 352 MHz. We also find that the highest redshift source from this paper (at z=3.84) does not show evidence for spectral flattening down to 151 MHz. This suggests that very low frequency selected USS samples will likely be more efficient to find high redshift galaxies.
We study the chemical abundances of the interstellar medium surrounding high z gamma-ray bursts (GRBs) through analysis of the damped Lya systems (DLAs) identified in afterglow spectra. These GRB-DLAs are characterized by large HI column densities N(HI) and metallicities [M/H] spanning 1/100 to nearly solar, with median [M/H]>-1. The majority of GRB-DLAs have [M/H] values exceeding the cosmic mean metallicity of atomic gas at z>2, i.e. if anything, the GRB-DLAs are biased to larger metallicity. We also observe (i) large [Zn/Fe] values (>+0.6) and sub-solar Ti/Fe ratios which imply substantial differential depletion, (ii) large a/Fe ratios suggesting nucleosynthetic enrichment by massive stars, and (iii) low C^0/C^+ ratios (<10^{-4}). Quantitatively, the observed depletion levels and C^0/C^+ ratios of the gas are not characteristic of cold, dense HI clouds in the Galactic ISM. We argue that the GRB-DLAs represent the ISM near the GRB but not gas directly local to the GRB (e.g. its molecular cloud or circumstellar material). We compare these observations with DLAs intervening background quasars (QSO-DLAs). The GRB-DLAs exhibit larger N(HI) values, higher a/Fe and Zn/Fe ratios, and have higher metallicity than the QSO-DLAs. We argue that the differences primarily result from galactocentric radius-dependent differences in the ISM: GRB-DLAs preferentially probe denser, more depleted, higher metallicity gaslocated in the inner few kpc whereas QSO-DLAs are more likely to intersect the less dense, less enriched, outer regions of the galaxy. Finally, we investigate whether dust obscuration may exclude GRB-DLA sightlines from QSO-DLA samples; we find that the majority of GRB-DLAs would be recovered which implies little observational bias against large N(HI) systems.
We examine the abundance of molecular hydrogen (H2) in the spectra of gamma ray burst afterglows (GRBs). In nearby galaxies H2 traces the cold neutral medium (CNM) and dense molecular star-forming interstellar gas. Though H2 is detected in at least half of all sightlines towards hot stars in the Magellanic Clouds and in ~25% of damped Lya systems toward quasars, it is not detected in any of the five GRB environments with a similar range of neutral hydrogen column and metallicity. We detect no vibrationally-excited H2 that would imply the GRB itself has photodissociated its parent molecular cloud, so such models are ruled out unless the parent cloud was <~4 pc in radius and was fully dissociated prior to the spectroscopic observations, or the star escaped its parent cloud during its main-sequence lifetime. The low molecular fractions for the GRBs are mysterious in light their large column densities of neutral H and expectations based on local analogs, i.e. 30 Doradus in the LMC. This surprising lack of H2 in GRB-DLAs indicates that the destruction processes that suppress molecule formation in the LMC and SMC are more effective in the GRB hosts, most probably a combination of low metallicity and an FUV radiation field 10--100 times the Galactic mean field. These inferred conditions place strong constraints on the star forming regions in these early galaxies.
Lyman-alpha forest absorption spectra towards quasars at z ~ 6 show regions of enhanced transmission close to their source. Several authors have argued that the apparently small sizes of these regions indicate that quasar ionization fronts at z >~ 6 expand into a largely or partly neutral intergalactic medium (IGM). Assuming that the typical region in the IGM is reionized by z <= 6, as is suggested by Ly-a forest observations, we argue that at {\em least} 50% of the volume of the IGM was reionized before the highest redshift quasars turned on. Further, even if the IGM is as much as 50% neutral at quasar turn-on, the quasars are likely born into large galaxy-generated HII regions. The HII regions during reionization are themselves clustered, and using radiative transfer simulations, we find that long skewers through the IGM towards quasar progenitor halos pass entirely through ionized bubbles, even when the IGM is half neutral. These effects have been neglected in most previous analyses of quasar proximity zones, which assumed a spatially {\em uniform} neutral fraction. We model the subsequent ionization from a quasar, and construct mock Ly-a forest spectra. Our mock absorption spectra are more sensitive to the level of small-scale structure in the IGM than to the volume-averaged neutral fraction, and suggest that existing proximity-zone size measurements are compatible with a fully ionized IGM. However, we mention several improvements in our modeling that are necessary to make more definitive conclusions.
We explore the evolution of the morphology density relation using the COSMOS-ACS survey and previous cluster studies. The Gini parameter measured in a Petrosian aperture is found to be an effective way of selecting early-type galaxies free from systematic effects with redshift. We find galaxies are transformed from late (spiral and irregular) to early (E+S0) type galaxies more rapidly in dense than sparse regions. At a given density, the early-type fraction grows constantly with cosmic time, but the growth rate increases with density as a power law of index $0.29\pm0.02$. However, at densities below 100 galaxies per Mpc$^{2}$ no evolution is found at $z>0.4$. In contrast the star-formation-density relation shows strong evolution at all densities and redshifts, suggesting different physical mechanisms are responsible for the morphological and star formation transformation. We show photometric redshifts can measure local galaxy environment, but the present results are limited by photometric redshift error to densities above $\Sigma=3$ galaxies per Mpc$^{2}$.
We hereby report on a sensitive search for radio continuum observations from a sample of 34 Mira and semi-regular variable stars. The main aim of this survey was to search for thermal free-free emission from post-shock ionised gas. Thirty-four stars were observed at 3- and 6-cm using the Australia Telescope Compact Array. Radio continuum emission was detected from one source only, the symbiotic Mira R Aqr. No continuum emission was detected from the other sources, with three-sigma upper limits of typically 0.3 mJy. From the upper limits to the radio flux densities, we have found upper limits to the gas brightness temperatures near two stellar radii at a characteristic size of $5\times10^{13}$ cm. Upper limits to shock velocities have been estimated using a shock model. For the 11 nearest sources in our sample we obtain brightness temperatures below 6 000 K and shock velocities below 13 km s$^{-1}$. For 11 out of 14 sources with previously published detections, the radio brightness temperatures are below 4 000 K. For an upper limit of 4 000 K, we estimate that the shock velocities at two stellar radii are below 10 km s$^{-1}$.
In the last few years the realization has emerged that the universal baryons are almost equally distributed by mass in three components: (1) galactic concentrations, (2) a warm-hot intergalactic medium (WHIM) and (3) a diffuse intergalactic medium. These three components are predicted by hydrodynamical simulations and are probed by QSO absorption lines. To observe the WHIM in neutral hydrogen, observations are needed which are deeper than log(N$_{HI}$)=18. The WHIM should appear as a Cosmic Web, underlying the galaxies with higher column densities. We have used the WSRT, to simulate a filled aperture by observing at very high hour angles, to reach very high column density sensitivity. To achieve even higher image fidelity, an accurate model of the WSRT primary beam was developed. This will be used in the joint deconvolution of the observations. To get a good overview of the distribution and kinematics of the Cosmic Web, a deep survey of 1500 square degrees of sky was undertaken, containing the galaxy filament extending between the Local Group and the Virgo Cluster. The auto-correlation data has been reduced and has an RMS of $\Delta N_{HI} = 4.2\times10^{16}$ cm$^{-2}$ over 20 kms$^{-1}$. Several sources have been tentatively detected, which were previously unknown, as well as an indication for diffuse intergalactic filaments.
The study of magnetic connectivity in the solar corona reveals a need to
generalize the field line mapping technique to arbitrary geometry of the
boundaries and systems of coordinates. Indeed, the global description of the
connectivity in the corona requires the use of the photospheric and solar wind
boundaries. Both are closed surfaces and therefore do not admit a global
regular system of coordinates. At least two overlapping regular systems of
coordinates for each of the boundaries are necessary in this case to avoid
spherical-pole-like singularities in the coordinates of the footpoints. This
implies that the basic characteristic of magnetic connectivity - the squashing
degree or factor $Q$ of elemental flux tubes (Titov et al., 2002) - must be
rewritten in covariant form. Such a covariant expression of $Q$ is derived in
this work. The derived expression is very flexible and highly efficient for
describing the global magnetic connectivity in the solar corona.
In addition, a general expression for a new characteristic $Q_\perp$ which
defines a squashing of the flux tubes in the directions perpendicular to the
field lines is determined. This new quantity makes it possible to filter out
the quasi-separatrix layers whose large values of $Q$ are caused by a
projection effect at the field lines nearly touching the photosphere. Thus, the
value $Q_\perp$ provides a much more precise description of the volumetric
properties of the magnetic field structure. The difference between $Q$ and
$Q_\perp$ is illustrated by comparing their distributions for two
configurations, one of which is the Titov-Demoulin (1999) model of a twisted
magnetic field.
Context: For the past 3 years we have been monitoring a sample of 62 K giant stars using precise stellar radial velocity measurements taken at the Thueringer Landessternwarte Tautenburg. Aims: To search for sub-stellar companions to giant stars and to understand the nature of the diverse radial velocity variations exhibited by K giant stars. Methods: We present precise stellar radial velocity measurements of the K1III giant star 4 UMa (HD 73108). These were obtained using the coude echelle spectrograph of 2-m Alfred Jensch Telescope. The wavelength reference for the radial velocity measurements was provided by an iodine absorption cell. Results: Our measurements reveal that the radial velocity of 4 UMa exhibits a periodic variation of 269.3 days with a semiamplitude K = 216.8 m/s. A Keplerian orbit with an eccentricity, e = 0.43 +/- 0.02 is the most reasonable explanation for the radial velocity variations. The orbit yields a mass function, f(m) = (2.05 +/- 0.24) x 10^(- 7) M_sun. From our high resolution spectra we calculate a metallicity of -0.25 +/- 0.05 and derive a stellar mass of 1.23 M_sun +/- 0.15 for the host star. Conclusions: The K giant star 4 UMa hosts a substellar companion with minimum mass m sin i = 7.1 +/- 1.6 M_Jupiter.
An extension of the Standard Model by three right-handed neutrinos with masses smaller than the electroweak scale (the $\nu$MSM) can explain simultaneously dark matter and baryon asymmetry of the Universe, being consistent with the data on neutrino oscillations. A dark matter candidate in this theory is the sterile neutrino with the mass in keV range. We discuss the constraints on the properties of this particle and mechanisms of their cosmological production. Baryon asymmetry generation in this model is reviewed. Crucial experiments that can confirm or rule out the $\nu$MSM are briefly discussed.
Aims. Motivated by the new determination of the distance to the microquasar GRO J1655-40 by Foellmi et al. (2006), we conduct a detailed study of the distribution of the atomic and molecular gas, and dust around the open cluster NGC 6242, the possible birth place of the microquasar. The proximity and relative height of the cluster on the galactic disk provides a unique opportunity to study SNR evolution and its possible physical link with microquasar formation. Methods. We search in the interstellar atomic and molecular gas around NGC 6242 for traces that may have been left from a supernova explosion associated to the formation of the black hole in GRO J1655-40. Furthermore, the 60/100 mu IR color is used as a tracer of shocked-heated dust. Results. At the kinematical distance of the cluster the observations have revealed the existence of a HI hole of 1.5*1.5 degrees in diameter and compressed CO material acumulated along the south-eastern internal border of the HI cavity. In this same area, we found extended infrared emission with characteristics of shocked-heated dust. Based on the HI, CO and FIR emissions, we suggest that the cavity in the ISM was produced by a supernova explosion occured within NGC 6242. The lower limit to the kinematic energy transferred by the supernova shock to the surrounding interstellar medium is ~ 10^{49} erg and the atomic and molecular mass displaced to form the cavity of ~ 16.500 solar masses. The lower limit to the time elapsed since the SN explosion is ~ 2.2*10^{5} yr, which is consistent with the time required by GRO J1655-40 to move from the cluster up to its present position. The observations suggest that GRO J1655-40 could have been born inside NGC 6242, being one of the nearest microquasars known so far.
We support, with new fitting instruments and the analysis of more recent experimental data, the proposal of a relationship between the mass of a Supermassive Black Hole (SMBH) and the kinetic energy of random motions in the host elliptical galaxy. The first results obtained in a previous paper with 13 elliptical galaxies are now confirmed by the new data and an enlarged sample. We find $M_{BH} \propto (M_{G} \sigma^{2}/c^2)^\beta$ with $0.8 \leq \beta \leq 1$ depending on the different fitting methods and samples used. The meaningful case $\beta = 1$ is carefully analyzed. Furthermore, we test the robustness of our relationship including in the sample also lenticular and spiral galaxies and we show that the result does not change. Finally we find a stronger correlation between the mass of the galaxy and the corresponding velocity dispersion that allows to connect our relationship to the $M_{BH} \propto \sigma^\alpha$ law. With respect to this law, our relationship has the advantage to have a smaller scatter.
A few tight correlations linking several properties of gamma-ray bursts (GRBs), namely the spectral peak energy, the total radiated energy, and the afterglow break time, have been discovered with pre-Swift GRBs. They were used to constrain the cosmological parameters together with type-Ia supernovae. However, the tightness of these correlations is a challenge to GRB models. We explore the effect of the addition of Swift bursts to the Ghirlanda and Liang-Zhang relations. Although are still both valid, they become significantly weakened. This is mostly due to the presence of significant outliers, which are otherwise apparently normal GRBs, and thus difficult to discriminate. The increased dispersion of the relations makes them less reliable for precision cosmology purposes.
The reionization of the Universe, it is believed, occurred by the growth of ionized regions (bubbles) in the neutral intergalactic medium (IGM). We study the possibility of detecting these bubbles in radio-interferometric observations of redshifted neutral hydrogen (HI) 21 cm radiation. The signal (<1 mJy) will be buried in noise and foregrounds, the latter being at least a few orders of magnitude stronger than the signal. We develop a visibility based formalism that uses a filter to optimally combine the entire signal from a bubble while minimizing the noise and foreground contributions. This formalism makes definite predictions on the ability to detect an ionized bubble or conclusively rule out its presence in a radio-interferometric observation. We make predictions for the currently functioning GMRT and a forthcoming instrument, the MWA at a frequency of 150 MHz (corresponding to a redshift of 8.5). For both instruments, we show that it will be possible to detect a bubble of comoving radius R_b > 40 Mpc (assuming them to be spherical) in 100 hrs of observation and R_b > 22 Mpc in 1000 hrs of observation, provided the bubble is at the center of the field of view. In both these cases the filter effectively removes the expected foreground contribution so that it is below the signal, and the system noise is the deciding criteria. We find that there is a fundamental limitation on the smallest bubble that can be detected arising from the statistical fluctuations in the HI distribution. Assuming that the HI traces the dark matter we find that it will not be possible to detect bubbles with R_b < 8 Mpc using the GMRT and R_b < 16 Mpc using the MWA, however large be the integration time.
There is strong evidence that long duration gamma-ray bursts (GRBs) are produced during the collapse of a massive star. In the standard version of the Collapsar model, a broad-lined and luminous Type Ic core-collapse supernova (SN) accompanies the GRB. This association has been confirmed in observations of several nearby GRBs. Recent observations show that some long duration GRBs are different. No SN emission accompanied the long duration GRBs 060505 and 060614 down to limits fainter than any known Type Ic SN and hundreds of times fainter than the archetypal SN1998bw that accompanied GRB980425. Multi-band observations of the early afterglows, as well as spectroscopy of the host galaxies, exclude the possibility of significant dust obscuration. Furthermore, the bursts originated in star-forming galaxies, and in the case of GRBs060505 the burst was localised to a compact star-forming knot in a spiral arm of its host galaxy. We find that the properties of the host galaxies, the long duration of the bursts and, in the case of GRB060505 the location of the burst within its host, all imply a massive stellar origin. The absence of a SN to such deep limits therefore suggests a new phenomenological type of massive stellar death.
In the framework of an ongoing ACS@HST project (HST program #10586, PI: Aloisi) we have obtained deep multi-color imaging of the very metal-poor Blue Compact Dwarf galaxy IZw18. The data were acquired in time-series fashion to allow the identification of Classical Cepheids (CCs). The main aim of this project is to constrain both the distance and the Star Formation History of the galaxy. However, as a byproduct these data also provide new insights into the properties of CCs at very low metallicities. We have identified 24 candidate CCs in IZw18. New theoretical pulsation models of CCs specifically for the low metallicity of this primordial galaxy (Z=0.0004, Y=0.24) have been computed to interpret our results.
In this proceeding we present the procedure that we have adopted to obtain a dataset of Padova94 tracks interpolated in metallicity. The procedure requires special care to avoid spurious features in the resulting grid, thus we have subdivided tracks in evolutionary phases, we have chosen the suitable interpolation method and the transition masses. Finally, we have compared our interpolated dataset with a similar models, Girardi et al. 2000, obtaining a general good agreement.
Duration of the extended solar cycles is taken into the consideration. The beginning of cycles is counted from the moment of polarity reversal of large-scale magnetic field in high latitudes, occurring in the sunspot cycle n till the minimum of the cycle n+2. The connection between cycle duration and its amplitude is established. Duration of the "latent" period of evolution of extended cycle between reversals and a minimum of the current sunspot cycle is entered. It is shown, that the latent period of cycles evolution is connected with the next sunspot cycle amplitude and can be used for the prognosis of a level and time of a sunspot maximum. The 24-th activity cycle prognosis is done. Long-term behavior of extended cycle's lengths is considered.
The deuterium abundances inferred from observations of the interstellar medium within 1-2 kpc of the Sun range over a factor of three and the corresponding oxygen abundances show an even larger dispersion. While the lower D (and O) abundances likely result from depletion onto dust, the higher D abundances are consistent with the BBN-predicted primordial D abundance and chemical evolution models of the Galaxy with infall of primordial or nearly primordial material. The large ranges in deuterium and oxygen abundances suggest that the effects of depletion and/or infall have not been homogenized in the local interstellar medium.
Two scenarios of possible ion heating due to finite amplitude parallel propagating Alfv\'en waves in the solar atmosphere are investigated using a 1D test particle approach. 1. An finite amplitude Alfv\'en wave is instantly introduced into a plasma (or equivalently, new ions are instantly created). 2. New ions are constantly created. In both scenarios, ions will be picked up by the Alfv\'en wave. In case 1, the wave scatters ions in the transverse direction leading to a randomization (or heating) process. This process is complete when a phase shift of $\pm \pi$ in the ion gyro-speed is produced between particles with characteristic parallel thermal speed and particles with zero parallel speed. This corresponds to $t={\pi \over k v_{th}}$ ($k$ is the wave number and $v_{th}$ is the ion thermal speed). A ring velocity distribution can be produced for large wave amplitude. The process yields a mass-proportional heating in the transverse direction, a temperature anisotropy and a bulk flow along the background magnetic field. In case 2, continuous ion creation represents a continuing phase shift in the ion gyro-speed leading to heating. New particles are picked up by the Alfv\'en wave within one ion gyroperiod. It is speculated that the mechanism may operate in the chromosphere and active regions where transient events may generate finite amplitude Alfv\'en waves.
On September 21, 2006, an intense (~10^39 erg/s) and short (20 ms) burst was
detected by Swift BAT at a position consistent with that of the candidate
Anomalous X-ray Pulsar, CXOU J164710.2-455216, discovered by Chandra in 2005.
Swift follow-up observations began about 13 hours after the event and found the
source at a 1-10keV flux level of about 4.5 x 10^-11 erg/s/cm^2, i.e. ~300
times brighter than measured 5 days earlier by XMM. We report the results
obtained from Swift BAT observations of the burst and subsequent Swift XRT
observations carried out during the first four months after the burst. These
data are complemented with those from two XMM observations (carried out just
before and after the BAT event) and four archival Chandra observations carried
out between 2005 and 2007. We find a phase coherent solution for the source
pulsations after the burst. The evolution of the pulse phase comprises an
exponential component decaying with timescale of 1.4d which we interpret as the
recovery stage following a large glitch (Delta nu / nu about 6 x 10^-5). We
also detect a quadratic component corresponding to a spin-down rate of Pdot ~ 9
x 10^-13, implying a magnetic field strength of 10^14 Gauss.
During the first Swift XRT observation taken 0.6 days after the burst, the
spectrum showed a kT = 0.65keV blackbody (R_BB = 1.5km) plus a Gamma=2.3
power-law accounting for about 60% of the 1-10 keV observed flux. Analysis of
Chandra archival data, taken during 2005 when the source was in quiescence,
reveal that the modulation in quiescence is 100% pulsed at energies above 4 keV
and consistent with the (unusually small-sized) blackbody component being
occulted by the neutron star as it rotates.
We use the Cambridge stellar evolution code STARS to model the evolution and nucleosynthesis of zero-metallicity intermediate-mass stars. We investigate the effect of duplicity on the nucleosynthesis output of these systems and the potential abundances of the secondaries. The surfaces of zero-metallicity stars are enriched in CNO elements after second dredge up. During binary interaction, such as Roche lobe overflow or wind accretion, metals can be released from these stars and the secondaries enriched in CNO isotopes. We investigate the formation of the two most metal poor stars known, HE 0107-5240 and HE 1327-2326. The observed carbon and nitrogen abundances of HE 0107-5240 can be reproduced by accretion of material from the companion-enhanced wind of a seven solar star after second dredge-up, though oxygen and sodium are underproduced. We speculate that HE 1327-2326, which is richer in nitrogen and strontium, may similarly be formed by wind accretion in a later AGB phase after third dredge-up.
Effects of the neutrino trapping and symmetry energy behavior are investigated in the framework of the chiral Kaplan-Nelson model with kaon condensation. Decrease in the condensation threshold during deleptonization if found to be generic regardless uncertainties in the nucleon-kaon interactions and symmetry energy. Quantitatively however, differences are shown to be important
Cross-identifications for 14,574 intrinsically luminous galactic stars (mostly OB stars) to objects in the 2MASS survey have been determined using a search box of +/-0.0015 degrees (+/- 5.4 arcsec) in both RA and Dec. Instructions on obtaining the relevant files can be obtained at othello.alma.edu/~reed/OB-2MASS.doc.
We present a new procedure to fit non-axisymmetric flow patterns to 2-D velocity maps of spiral galaxies. We concentrate on flows caused by bar-like or oval distortions to the total potential that may arise either from a non-axially symmetric halo or a bar in the luminous disk. We apply our method to high-quality CO and Halpha data for the nearby, low-mass spiral NGC 2976 previously obtained by Simon et al., and find that a bar-like model fits the data at least as well as their model with large radial flows. We find supporting evidence for the existence of a bar in the baryonic disk. Our model suggests that the azimuthally averaged central attraction in the inner part of this galaxy is larger than estimated by these authors. It is likely that the disk is also more massive, which will limit the increase to the allowed dark halo density. Allowance for bar-like distortions in other galaxies may either increase or decrease the estimated central attraction.
New high-resolution spectropolarimetric observations of solar prominences require improved radiative modelling capabilities in order to take into account both multi-dimensional - at least 2D - geometry and complex atomic models. This makes necessary the use of very fast numerical schemes for the resolution of 2D non-LTE radiative transfer problems considering freestanding and illuminated slabs. The implementation of Gauss-Seidel and successive over-relaxation iterative schemes in 2D, together with a multi-grid algorithm, is thoroughly described in the frame of the short characteristics method for the computation of the formal solution of the radiative transfer equation in cartesian geometry. We propose a new test for multidimensional radiative transfer codes and we also provide original benchmark results for simple 2D multilevel atom cases which should be helpful for the further development of such radiative transfer codes, in general.
We have obtained quasi-simultaneous ultraviolet-optical spectra for 22 out of 23 quasars in the complete PG-X-ray sample with redshift, z<0.4, and M_B<-23. The spectra cover rest-frame wavelengths from at least Lyman-alpha to H-alpha. Here we provide a detailed description of the data, including careful spectrophotometry and redshift determination. We also present direct measurements of the continua, strong emission lines and features, including Lyman-alpha, SiIV+OIV], CIV, CIII], SiIII], MgII, H-beta, [OIII], He5876+NaI5890,5896, H-alpha, and blended iron emission in the UV and optical. The widths, asymmetries and velocity shifts of profiles of strong emission lines show that CIV and Lyman-alpha are very different from H-beta and H-alpha. This suggests that the motion of the broad line region is related to the ionization structure, but the data appears not agree with the radially stratified ionization structure supported by reverberation mapping studies, and therefore suggest that outflows contribute additional velocity components to the broad emission line profiles.
In recent years, the development of spectropolarimetric techniques deeply modified our knowledge of stellar magnetism. In the case of solar-type stars, the challenge is to measure a geometrically complex field and determine its evolution over very different time frames. In this article, I summarize some important observational results obtained in this field over the last two decades and detail what they tell us about the dynamo processes that orchestrate the activity of cool stars. I also discuss what we learn from such observations about the ability of magnetic fields to affect the formation and evolution of Sun-like stars. Finally, I evoke promising directions to be explored in the coming years, thanks to the advent of a new generation of instruments specifically designed to progress in this domain.
Using ISAAC on the VLT, we have detected 2 candidate counterparts to the bursting pulsar GRO J 1744-28, one bright and one faint, both within the X-ray error circles found using XMM-Newton and Chandra. Photometry and spectroscopy of the bright candidate indicate that it is most likely a G type giant. The spectrum does not show Brackett-gamma emission, a known indicator of accretion, and dynamical calculations and comparison with the X-ray mass-function indicate that this star is most likely not the true X-ray source counterpart. Photometry of the fainter candidate indicates it is a K5 V star at a distance of 4 kpc. This fits the LEdd distance and the measured infrared extinction. If this star is the IR counterpart, dynamical calculations would require the system to be at very low inclination; however this source cannot be excluded without follow-up spectroscopy to detect emission signatures. The mass-function remains the tightest constraint for this system. The true counterpart most likely has a mass M < 0.3Msol. Mass transfer in such a system will be by wind-accretion as the counterpart will not fill its Roche lobe given the observed Porb. In this case, the derived magnetic field strength of 2.4 x 10^11 G is sufficient to inhibit accretion of captured material by the propeller effect.
We present results of the CFHT adaptive optics (AO) search for companions of a homogeneous group of contact binary stars, as a contribution of our attempts to prove a hypothesis that these binaries require a third star to become so close as observed. The data were obtained on two nights in 1998 and two nights in 2005. In addition to companions directly discovered at separations of 1"-10" separations, we introduced a new method of AO image analysis to analyze distortions of the AO diffraction ring pattern at separations of 0.07"-1". Very close companions, with separations in the latter range were discovered in systems HV Aqr, OO Aql, CK Boo, XY Leo, BE Scl, and RZ Tau. More distant companions were detected in V402 Aur, AO Cam, V2082 Cyg. Our results provide a contribution to the mounting evidence that the presence of close companions is a very common phenomenon for very close binaries with orbital periods <1 day.
I propose a mechanism that would explain the near alignment of the low order multipoles of the cosmic microwave background (CMB). This mechanism supposes a large-scale cosmic magnetic field that tends to align the cyclotron orbit axes of electrons in hot plasmas along the same direction. Inverse Compton scattering of the CMB photons then imprints this pattern on the CMB, thus causing the low- multipoles to be generally aligned. The spins of the majority of spiral galaxies and that of our own Galaxy appear to be aligned along the cosmic magnetic field.
We modeled the HeII 4686 line profiles observed in the eta Carinae binary system close to the 2003.5 spectroscopic event, assuming that they were formed in the shocked gas that flows at both sides of the contact surface formed by wind-wind collision. We used a constant flow velocity and added turbulence in the form of a gaussian velocity distribution. We allowed emission from both the primary and secondary shocks but introduced infinite opacity at the contact surface, implying that only the side of the contact cone visible to the observer contributed to the line profile. Using the orbital parameters of the binary system derived from the 7 mm light curve during the last spectroscopic event (Paper II) we were able to reproduce the line profiles obtained with the HST at different epochs, as well as the line mean velocities obtained with ground based telescopes. A very important feature of our model is that the line profile depends on the inclination of the orbital plane; we found that to explain the latitude dependent mean velocity of the line, scattered into the line of sight by the Homunculus, the orbit inclination should be close to 90 degrees, meaning that it does not lie in the Homunculus equatorial plane, as usually assumed. This inclination, together with the relative position of the stars during the spectroscopic events, allowed us to explain most of the observational features, like the variation of the Purple Haze with the orbital phase, and to conciliate the X-ray absorption with the postulated shell effect used to explain the optical and UV light curves.
We present a new automatic code (ARES) for determining equivalent widths of
the absorption lines present in stellar spectra. We also describe its use for
determining fundamental spectroscopic stellar parameters.
The code is written in C++ based on the standard method of determining EWs
and is available for the community. The code automates the manual procedure
that the users normally carry out when using interactive routines such as the
splot routine implemented in IRAF.
We test the code using both simulated and real spectra with different levels
of resolution and noise and comparing its measurements to the manual ones
obtained in the standard way. The results shows a small systematic difference,
always below 1.5m\AA. This can be explained by errors in the manual
measurements caused by subjective continuum determination. The code works
better and faster than others tested before.
NGC1313 X-2 was among the first ultraluminous X-ray sources discovered, and has been a frequent target of X-ray and optical observations. Using the HST/ACS multi-band observations, this source is identified with a unique counterpart within an error circle of $0\farcs2$. The counterpart is a blue star on the edge of a young cluster of $\le10^7$ years amid a dominant old stellar population. Its spectral energy distribution is consistent with that for a Z=0.004 star with 8.5 $M_\odot$ about $5\times10^6$ years old, or for an O7 V star at solar metallicity. The counterpart exhibited significant variability of $\Delta m = 0.153\pm0.033$ mag between two F555W observations separated by three months, reminiscent of the ellipsoidal variability due to the orbital motion of this ULX binary.
The temperature distribution of the cosmic gas-phase oxygen at z~3 is
determined combining high resolution cosmological simulations with two
observationally based, V-band (rest-frame) galaxy LFs. The simulations invoke
three different stellar IMFs, a Kroupa (K98), a Salpeter (S) and an
Arimoto-Yoshii (AY), spanning a range of a factor of five in chemical yield and
specific SNII energy feedback.
Oxygen is found to be distributed over all T phases (cold: logT<~4, warm:
logT~4.5, hot: logT>~5), in particular for the (top-heavy) AY IMF. For the K98
and S IMFs, the most important phase is the cold one. Moreover, the cold phase
alone contains 1-3 times the mass of oxygen in galactic stars for the three
IMFs. The implications of this in relation to DLA studies are discussed.
In relation to ``missing metals'' it is found that the ratio of gas-phase to
stellar oxygen mass is 2-13, and the ratio of warm+hot to cold gas-phase oxygen
mass is 0.8-3.2 for the three IMFs (for the AY IMF, the hot phase contains more
oxygen than the cold+warm), so a large fraction of the cosmic metals may be
difficult to detect. Also, it is found that less than about 20-30% of the
cosmic oxygen is associated with galaxies brighter than M_V~-22, the faintest
LBGs allowing direct metallicity estimation at present.
From the LBG based, lambda~1500 AA UV luminosity density history at z>3, the
mean cosmic oxygen density at z=3 is inferred. Comparing this to the models, it
is found that the (solar neighbourhood type) K98 IMF is strongly excluded (too
small yield), the S is marginally excluded, and the AY matches the constraint
well. The optimal IMF has a yield between the S and AY. A similar conclusion is
reached on the basis of the C IV abundance of the moderate density IGM.
We present and discuss evolutionary synthesis models for massive stellar populations generated with the Starburst99 code in combination with a new set of stellar evolution models accounting for rotation. The new stellar evolution models were compiled from several data releases of the Geneva group and cover heavy-element abundances ranging from twice solar to one fifth solar. The evolution models were computed for rotation velocities on the zero-age main-sequence of 0 and 300 km/s and with the latest revision of stellar mass-loss rates. Since the mass coverage is incomplete, in particular at non-solar chemical composition, our parameter study is still preliminary and must be viewed as exploratory. Stellar population properties computed with Starburst99 and the new evolution models show some marked differences in comparison with models obtained using earlier tracks. Since individual stars now tend to be more luminous and bluer when on the blue side of the Hertzsprung-Russell diagram, the populations mirror this trend. For instance, increases by factors of two or more are found for the light-to-mass ratios at ultraviolet to near-infrared wavelengths, as well as for the output of hydrogen ionizing photons. If these results are confirmed once the evolution models have matured, recalibrations of certain star-formation and initial mass function indicators will be required.
We show that the mean values and distributions of the time ending the shallow decay of the light curve of the X-ray afterglow of long gamma ray bursts (GRBs), the equivalent isotropic energy in the X-ray afterglow up to that time and the equivalent isotropic GRB energy, as well as the correlations between them, are precisely those predicted by the cannonball (CB) model of GRBs. Correlations between prompt and afterglow observables are important in that they test the overall consistency of a GRB model. In the CB model, the prompt and afterglow spectra, the endtime, the complex canonical shape of the X-ray afterglows and the correlations between GRB observables are not surprises, but predictions.
We analyze the gas kinematics of damped Lya systems (DLAs) hosting high z gamma-ray bursts (GRBs) and those toward quasars (QSO-DLAs) focusing on threestatistics: (1) dv, the velocity interval encompassing 90% of the totaloptical depth, (2,3) Wsi and Wciv, the rest equivalent widths of the SiII1526 and CIV1548 transitions. The dv distributions of the GRB-DLAs and QSO-DLAs are similar, each has median dv~80km/s and a significant tail to several hundred km/s. This suggests comparable galaxy masses for the parent populations of GRB-DLAs and QSO-DLAs and we infer the average dark matter halo mass of GRB galaxies is <~10^{12} Msol. The unique configuration of GRB-DLA sightlines and the presence (and absence) of fine-structure absorption together give special insight into the nature of high z, protogalactic velocity fields. The data support a scenario where the dv statistic reflects dynamics in the interstellar medium (ISM) and Wsi traces motions outside the ISM (e.g. halo gas, galactic-scale winds). The Wsi statistic and gas metallicity [M/H] are tightly correlated, especially for the QSO-DLAs: [M/H]=a + b log(Wsi/1A) with a=-0.92+/-0.05 and b=-1.41+/-0.10. We argue that the Wsi statistic primarily tracks dynamical motions in the halos of high z galaxies and interpret this correlation as a mass-metallicity relation with very similar slope to the trend observed in local, low-metallicity galaxies. Finally, the GRB-DLAs exhibit systematically larger Wsi values (>0.5A) than the QSO-DLAs (<Wsi>~ 0.5A) which may suggest galactic-scale outflows contribute to the largest observed velocity fields.
We study the cosmological evolution of two coupled scalar fields with an arbitrary interaction term V_T(\phi,\vp) in the presence of a barotropic fluid, which can be matter or radiation. The force between the barotropic fluid and the scalar fields is only gravitational. We show that the dynamics is completely determine by only three parameters L_i i=1,2,3. We determine all critical points and study their stability. We find six different attractor solutions depending on the values of L_i and we calculate the relevant cosmological parameters. We discuss the possibility of having one of the scalar fields as of dark energy while the other could be a scalar field redshifting as matter.
We present FUSE observations of the line of sight to WD0439+466 (LS V +46 21), the central star of the old planetary nebula Sh2-216. The FUSE data shows absorption by many interstellar and stellar lines, in particular D I, H2 (J = 0 - 9), HD (J = 0 - 1), and CO. Many other stellar and ISM lines are detected in the STIS E140M HST spectra of this sightline, which we use to determine N(HI). We derive, for the neutral gas, D/H=(0.76 +0.12 -0.11)E-5, O/H = (0.89 +0.15 -0.11)E-4 and N/H = (3.24 +0.61-0.55)E-5. We argue that most of the gas along this sightline is associated with the planetary nebula. The low D/H ratio is likely the result of this gas being processed through the star (astrated) but not mixed with the ISM. This would be the first time that the D/H ratio has been measured in predominantly astrated gas. The O/H and N/H ratios derived here are lower than typical values measured in other planetary nebulae likely due to unaccounted for ionization corrections.
The continuous infall of dark matter with low velocity dispersion from all directions in a galactic halo leads to the formation of caustics which are very small scale ($\sim$parsec) high density structures. If the dark matter is made up of SUSY neutralinos, the annihilation of these particles produces a characteristic spectrum of gamma rays which in principle, could be detected. The annihilation signal at different energy bands is computed and compared with the expected gamma ray background.
We present 31 bright eclipsing contact and semi-detached binaries that showed high period change rates in a 5 year interval in observations by the All-Sky Automated Survey (ASAS). The time-scales of these changes range from only 50 up to 400 kyr. The orbital periods of 10 binaries are increasing and of 21 are decreasing, and even a larger excess is seen in contact binaries, where the numbers are 5 and 17, respectively. Period change has previously been noticed for only two of these binaries; our observations confirmed a secular period drift for SV Cen and period oscillations for VY Cet. The spectroscopic quadruple system V1084 Sco shows both period change and brightness modulation. All investigated binaries were selected from a sample of 1711 (1135 contact and 576 semi-detached) that fulfilled all criteria of data quality. We also introduce a "branch" test to check if luminosity changes on part of the binary's photosphere has led to a spurious or poorly characterized period change detection.
(Abridged) The open cluster NGC 1893, illuminating the HII region IC410, contains a moderately large population of O-type stars and is one of the youngest clusters observable in the optical range. We have probed the stellar population of NGC 1893 in an attempt to determine its size and extent. We classify a large sample of cluster members with new intermediate resolution spectroscopy. We use H-alpha slitless spectroscopy of the field to search for emission line objects, identifying 18 emission-line PMS stars. We then combine existing optical photometry with 2MASS JHKs photometry to detect stars with infrared excesses, finding close to 20 more PMS candidates. While almost all stars earlier than B2 indicate standard reddening, all later cluster members show strong deviations from a standard reddening law, which we interpret in terms of infrared excess emission. Emission-line stars and IR-excess objects show the same spatial distribution, concentrating around two localised areas, the immediate vicinity of the pennant nebulae Sim 129 and Sim 130 and the area close to the cluster core where the rim of the molecular cloud associated with IC 410 is illuminated by the nearby O-type stars. In and around the emission nebula Sim 130 we find three Herbig Be stars with spectral types in the B1-4 range and several other fainter emission-line stars. We obtain a complete census of B-type stars by combining Stroemgren, Johnson and 2MASS photometry and find a deficit of intermediate mass stars compared to massive stars. We observe a relatively extended halo of massive stars surrounding the cluster without an accompanying population of intermediate-mass stars. The overall picture of star formation in NGC 1893 suggests a very complex process.
The TRACER instrument Transition Radiation Array for Cosmic Energetic Radiation is designed to measure the individual energy spectra of cosmic-ray nuclei in long-duration balloon flights The large geometric factor of TRACER 5 m 2 sr permits statistically significant measurements at particle energies well beyond 10 14 eV TRACER identifies individual cosmic-ray nuclei with single-element resolution and measures their energy over a very wide range from about 0 5 to 10 000 GeV nucleon This is accomplished with a gas detector system of 1600 single-wire proportional tubes and plastic fiber radiators that measure specific ionization and transition radiation signals combined with plastic scintillators and acrylic Cherenkov counters A two-week flight in Antarctica in December 2003 has led to a measurement of the nuclear species oxygen to iron O Ne Mg Si S Ar Ca and Fe up to about 3 000 GeV nucleon We shall present the energy spectra and relative abundances for these elements and discuss the implication of the results in the context of current models of acceleration and propagation of galactic cosmic rays The instrument has been refurbished for a second long-duration flight in the Northern hemisphere scheduled for summer 2006 For this flight the dynamic range of TRACER has been extended to permit inclusion of the lighter elements B C and N in the measurement.
Recent measurements of the temperature fluctuations of the cosmic microwave background (CMB) radiation from the WMAP satellite provide indication of a non-Gaussian behavior. Although the observed feature is small, it is detectable and analyzable. Indeed, the temperature distribution P^{CMB}(Delta T) of these data can be quite well fitted by the anomalous probability distribution emerging within nonextensive statistical mechanics, based on the entropy S_q = k (1 - \int dx [P(x)]^q)/(q - 1) (where in the limit case q -> 1 we obtain the Boltzmann-Gibbs entropy S_1 = - k \int dx P(x) ln[P(x)]). For the CMB frequencies analysed, \nu= 40.7, 60.8, and 93.5 GHz, P^{CMB}(Delta T) is well described by P_q(Delta T) \propto 1/[1 + (q-1) B(\nu) (Delta T)^2]^{1/(q-1)}, with q = 1.04 \pm 0.01, the strongest non-Gaussian contribution coming from the South-East sector of the celestial sphere. Moreover, Monte Carlo simulations exclude, at the 99% confidence level, P_1(Delta T) \propto e^{- B(\nu) (Delta T)^2} to fit the three-year WMAP data.
We have carried out the harmonic analysis of the atomic hydrogen (HI) surface density maps and the velocity fields for 11 galaxies belonging to the Ursa Major group, over a radial range of 4-6 disc scalelengths in each galaxy. This analysis gives the radial variation of spatial lopsidedness, quantified by the Fourier amplitude A$_1$ of the m=1 component normalised to the average value. The kinematical analysis gives a value for the elongation of the potential to be $\sim 10 % $. The mean amplitude of spatial lopsidedness is found to be $\sim 0.14$ in the inner disc, similar to the field galaxies, and is smaller by a factor of $\sim 2$ compared to the Eridanus group galaxies. It is also shown that the the average value of A$_1$ does not increase with the Hubble type, contrary to what is seen in field galaxies. We argue that the physical origin of lopsidedness in the Ursa Major group of galaxies is tidal interactions, albeit weaker and less frequent than in Eridanus. Thus systematic studies of lopsidedness in groups of galaxies can provide dynamical clues regarding the interactions and evolution of galaxies in a group environment.
We have made a comprehensive transit search for exoplanets down to about 2 Earth radii in the HD 209458 system, based on nearly uninterrupted broadband optical photometry obtained with the MOST (Microvariability and Oscillations of Stars) satellite, spanning 14 days in 2004 and 44 days in 2005. We have searched these data for limb-darkened transits at periods other than that of the known giant planet, from about 0.5 days to 2 weeks. Monte Carlo statistical tests of the data with synthetic transits inserted allow us to rule out additional close-in exoplanets with sizes ranging from about 0.20-0.36 RJ (Jupiter radii), or 2.2-4.0 RE (Earth radii) on orbits whose planes are near that of HD 209458b. These null results constrain theories that invoke lower mass planets in orbits similar to HD 209458b to explain its anomalously large radius, and those that predict "hot Earths" due to the inward migration of HD 209458b.
Some basic properties of the solar convection zone are considered and the use of helioseismology as an observational tool to determine its depth and internal angular velocity is discussed. Aspects of solar magnetism are described and explained in the framework of dynamo theory. The main focus is on mean field theories for the Sun's magnetic field and its differential rotation.
We consider the classical picture of three dimensional motion of charged particles in pulsar magnetosphere. We adopt a perturbative method to solve the equation of motion, and find the trajectory of particles as they move along the rotating dipolar magnetic field lines. Our aim is to study the influence of rotation on the pulsar radio emission by considering the constrained motion of particles along the open dipolar magnetic field lines. We find that the rotation induces a significant curvature into the particle trajectories. Our model predicts the intensity on leading side dominates over that of trailing side. We expect that if there is any curvature induced radio emission from the region close to the magnetic axis then it must be due to the rotation induced curvature. Our model predicts the radius--to--frequency mapping (RFM) in the core emissions.
We estimate the two-point correlation function in redshift space of the recently compiled HIPASS neutral hydrogen (HI) sources catalogue, which if modeled as a power law, $\xi(r)=(r_{0}/r)^{\gamma}$, the best-fitting parameters for the HI selected galaxies are found to be $r_{0}=3.3 \pm 0.3 h^{-1}$ Mpc with $\gamma=1.38 \pm 0.24$. Fixing the slope to its universal value $\gamma=1.8$, we obtain $r_{0}= 3.2\pm 0.2 h^{-1}$ Mpc. Comparing the measured two point correlation function with the predictions of the concordance cosmological model, we find that at the present epoch the HI selected galaxies are anti-biased with respect to the underlying matter fluctuation field with their bias value being $b_{0}\simeq 0.68$. Furthermore, dividing the HI galaxies into two richness subsamples we find that the low mass HI galaxies have a very low present bias factor ($b_{0}\simeq 0.48$), while the high mass HI galaxies trace the underlying matter distribution as the optical galaxies ($b_{0}\simeq 1$). Using our derived present-day HI galaxy bias we estimate their redshift space distortion parameter, and correct accordingly the correlation function for peculiar motions. The resulting real-space correlation length is $r^{\rm re}_{0}=1.8 \pm 0.2 h^{-1}$Mpc and $r^{\rm re}_{0}=3.9 \pm 0.6 h^{-1}$Mpc for the low and high mass HI galaxies, respectively. The low-mass HI galaxies appear to have the lowest correlation length among all extragalactic populations studied to-date. Also, we have correlated the IRAS-PSCz reconstructed density field, smoothed over scales of 5$h^{-1}$ Mpc, with the positions of the HI galaxies, to find that indeed the HI galaxies are typically found in negative overdensity regions ($\delta\rho/\rho_{\rm PSCz} \mincir 0$).
The recent revision of the solar chemical composition (Asplund, Grevesse and Sauval 2005)is characterized by about 40 per cent decrease of C, N, O, Ne, Ar abundances and by 20 percent decrease of Fe and some other metal abundances. We tested the effect of these modifications on the instability of Beta Cephei models. For the opacities, the newest OP data from the Opacity Project (Seaton 2005) were used. We show that the Beta Cephei instability domain in the Hertzsprung-Russel diagram, when computed with new data for Z=0.012 (revised solar value), is very similar to the instability domain computed earlier using the OPAL opacities for the older solar composition with Z=0.02. Almost all observed Beta Cephei variables are located within the instability domain. Two effects are responsible for stronger instability when using the new data: (i) Metal opacity bump in the OP case is located slightly deeper in the star than that in the OPAL case, which results in more effective driving; (ii) at a fixed Z value, the new Fe-group abundances are higher than the older ones because the Z value is determined mainly by the abundances of C, N, 0, and Ne.
For the Delta Scuti star 44 Tau 13 independent frequencies have been detected in previous studies. This star is unusual among the Delta Scuti stars because of its very low v sin i value of 2 +/- 1 km/s, indicating that it is either an extremely slow rotator or seen pole-on. 44 Tau shows unusually high amplitudes for a typical nonradially pulsating Delta Scuti star and is believed to be a connecting link between the high-amplitude Delta Scuti stars (HADS) and the low-amplitude Delta Scuti stars. We performed an asteroseimic study to find the appropriate theoretical model for this star. The fact that the radial fundamental and first overtone frequencies have been identified allows for reducing the number of possible solutions significantly. Standard post-main sequence models with inefficient convection in the envelope seem to be preferable in comparison with various models on the main sequence. They fit both observed global parameters of 44 Tau and most of identified radial and nonradial frequencies.
H2 formation in metal-free gas occurs via the intermediate H- or H2+ ions. Destruction of these ions by photodissociation therefore serves to suppress H2 formation. In this paper, I highlight the fact that several processes that occur in ionized primordial gas produce photons energetic enough to photodissociate H- or H2+ and outline how to compute the photodissociation rates produced by a particular distribution of ionized gas. I also show that there are circumstances of interest, such as during the growth of HII regions around the first stars, in which this previously overlooked form of radiative feedback is of considerable importance.
With the ongoing AKARI infrared sky survey, of much greater sensitivity than IRAS, a wealth of post-AGB objects may be discovered. It is thus time to organize our present knowledge of known post-AGB stars in th galaxy with a view to using it to search for new post-AGB objects among AKARI sources. We searched the literature available on the NASA Astrophysics Data System up to 1 October 2006, and defined criteria for classifying sources into three categories: "very likely", "possible" and "disqualified" post-AGB objects. The category of "very likely" post-AGB objects is made up of several classes. We have created an evolutionary, on-line catalogue of Galactic post-AGB objects, to be referred to as "The Torun catalogue of Galactic post-AGB and related objects". The present version of the catalogue contains 326 "very likely", 107 "possible" and 64 "disqualified" objects. For the very likely post-AGB objects, the catalogue gives the available optical and infrared photometry, infrared spectroscopy and spectral types, and links to finding charts and bibliography.
We aim to study the structure of the nebula around the post-AGB, binary star 89 Her. The presence of a rotating disk around this star had been proposed but not been yet confirmed by observations. We present high-resolution PdBI maps of CO J=2-1 and 1-0. Properties of the nebula are directly derived from the data and model fitting. We also present N-band interferometric data on the extent of the hot dust emission, obtained with the VLTI. Two nebular components are found: (a) an extended hour-glass-like structure, with expansion velocities of about 7 km/s and a total mass ~ 3 10$^{-3}$ Mo, and (b) an unresolved very compact component, smaller than ~ 0.4" and with a low total velocity dispersion of ~ 5 km/s. We cannot determine the velocity field in the compact component, but we argue that it can hardly be in expansion, since his would require too recent and too sudden an ejection of mass. On the other hand, assuming that this component is a keplerian disk, we derive disk properties that are compatible with expectations for such a structure; in particular, the size of the rotating gas disk should be very similar to the extent of the hot dust component from our VLTI data. Assuming that the equator of the extended nebula coincides with the binary orbital plane, we provide new results on the companion star mass and orbit.
We consider gamma-ray burst outflows with a substantial neutron component that are either dominated by thermal energy (fireballs) or by magnetic energy. In the latter case, we focus on the recently introduced `AC' model which relies on magnetic reconnection to accelerate the flow and power the prompt emission. For both the fireball and the AC model, we investigate the dynamical importance of neutrons on the outflow. We study particle creation in inelastic neutron - proton collisions and find that in both models the resulting neutrino emission is too weak to be detectable. The inelastic collisions also produce gamma-rays, which create pairs in interactions with soft photons carried with the flow. In magnetically driven outflows, the energy of these pairs is radiated away as synchrotron emission. The bulk of the emission takes place at a few hundred keV, which makes it difficult to disentangle this signal from the prompt emission. In fireballs, however, pair cascading leads to the emission of gamma-rays with observer energy in the range of 2 - 20 GeV and a fluence well above the GLAST threshold. Therefore this emission can be a useful diagnostic of the nature of the outflow.
SN 1987A in the Large Magellanic Cloud is close enough for a study of the very late time evolution of a supernova and its transition to a supernova remnant. Nearly two decades after explosion we are witnessing the supernova shock wave engaging the inner circumstellar ring, which had been fluorescing since being ionised by the soft X-ray flash from shock breakout. We follow the interaction of the supernova shock with the ring material. The spatially resolved information provides us with insight into the individual shock regions around the ring. Near-infrared integral field spectroscopy observations with SINFONI/VLT of the SN-ring interaction is presented. SINFONI's adaptive optics supported integral field spectrograph spatially resolves the ring and the data thus we obtain a better spatial understanding of the spectrum in different regions of the object. With a dynamical map of the interacting ring we determine parameters for its geometry. Since most of the IR emission lines originate behind the shock front we obtain an indication of the radial velocity of the shocked material after deconvolving the geometry. The ring geometry is consistent with a circle and we also derive a new, independent measurement of the systemic ring, and presumably also supernova, velocity. We find from the spatial distributions of the flux in the different emission lines the degree of cooling in the shocked material and follows the increases observed in the radio and X-rays. Emission from the ejecta is detected only in the strongest [Fe II] lines.
High frequency acoustic waves have been suggested as a source of mechanical heating in the chromosphere. In this work the radial component of waves in the frequency interval 22mHz to 1mHz are investigated. Observations were performed using 2D spectroscopy in the spectral lines of Fe I 543.45nm and Fe I 543.29nm at the Vacuum Tower Telescope, Tenerife, Spain. Speckle reconstruction has been applied to the observations. We have used Fourier and wavelet techniques to identify oscillatory power. The energy flux is estimated assuming that all observed oscillations are acoustics running waves. We find that the estimated energy flux is not sufficient to cover the chromospheric radiative losses.
According to recent general-relativistic simulations, the coalescence of two spinning black holes (BHs) could lead to recoil speeds of the BH remnant of up to thousands of km/s as a result of the emission of gravitational radiation. Such speeds would enable the merger product to escape its host galaxy. Here we examine the circumstances resulting from a gas-rich galaxy merger under which the ejected BH would carry an accretion disk with it and be observable. As the initial BH binary emits gravitational radiation and its orbit tightens, a hole is opened around it in the disk which delays the consumption of gas prior to the eventual BH ejection. The punctured disk remains bound to the ejected BH within the region where the gas orbital velocity is larger than the ejection speed. For a ~10^7 solar mass BH the ejected disk has a characteristic size of tens of thousands of Schwarzschild radii and an accretion lifetime of ~10^7 years. During that time, the ejected BH could traverse a considerable distance and appear as an off-center quasar with a feedback trail along the path it left behind. A small fraction of all quasars could be associated with an escaping BH.
We present radio observations at frequencies ranging from 240 to 8460 MHz of the radio galaxy 4C29.30 (J0840+2949) using the Giant Metrewave Radio Telescope (GMRT), the Very Large Array (VLA) and the Effelsberg telescope. We report the existence of weak extended emission with an angular size of $\sim$520 arcsec (639 kpc) within which a compact edge-brightened double-lobed source with a size of 29 arcsec (36 kpc) is embedded. We determine the spectrum of the inner double from 240 to 8460 MHz and show that it has a single power-law spectrum with a spectral index of $\sim$0.8. Its spectral age is estimated to be $\lapp$33 Myr. The extended diffuse emission has a steep spectrum with a spectral index of $\sim$1.3 and a break frequency $\lapp$240 MHz. The spectral age is $\gapp$200 Myr, suggesting that the extended diffuse emission is due to an earlier cycle of activity. We reanalyse archival x-ray data from Chandra and suggest that the x-ray emission from the hotspots consists of a mixture of nonthermal and thermal components, the latter being possibly due to gas which is shock heated by the jets from the host galaxy.
A review is presented of some of the ingredients, assumptions and techniques that are used in the computation of the structure and evolution of low-mass stars. Emphasis is placed on several ingredients which are still subject to considerable uncertainty. An overview of the evolution of low-mass stars is also presented, from the cloud collapse phase all the way to the white dwarf cooling curve.
The discovery of the short-period giant exoplanet population, the so-called hot Jupiter population, and their link to brown dwarfs and low-mass stars challenges the conventional view of planet formation and evolution. We took advantage of the multi-fiber facilities GIRAFFE and FLAMES-UVES (VLT) to perform the first large radial velocity survey using a multi-fiber spectrograph, aiming at detecting planetary and brown dwarfs candidates and binaries. We observed during 5 consecutive half-nights 816 stars selected within one of the exoplanet field of the space mission CoRoT. We computed the radial velocities of these stars and shown that a systematic error of 30 m s$^{-1}$ has been reached over 5 consecutive nights. Over the whole sample the Doppler measurements allowed us to identify a sample of 50 binaries, 9 active or blended binary stars, 5 unsolved cases and 14 exoplanets and brown dwarf candidates. Further higher precision Doppler measurements are now necessary to confirm and better characterize these candidates. This study demonstrates the efficiency of such a multi-fiber approach for large radial velocity surveys in search for exoplanets as well as the follow-up of transiting exoplanet candidates of existing and future programs like the CoRoT space mission.
Most Type I X-ray bursts from accreting neutron stars have a lightcurve with a single peak, but there is a rare population of faint bursts that are double or even triple peaked. Suggested mechanisms include polar ignition with equatorial stalling, or multi-step energy release; the latter being caused by hydrodynamic instabilities or waiting points in the nuclear reaction sequence. We present an analysis of the accretion rate dependence of the multi-peak bursts, and discuss the consequences for the various models. The observations pose particular challenges for the polar ignition mechanism given current models of ignition latitude dependence.
We present a new multi-wavelength study of supernova remnant (SNR) B0513-692 in the Large Magellanic Cloud (LMC). The remnant also has a strong, superposed, essentially unresolved, but unrelated radio source at its north-western edge, J051324-691049. This is identified as a likely compact HII region based on related optical imaging and spectroscopy. We use the Australia Telescope Compact Array (ATCA) at 4790 and 8640 MHz to determine the large scale morphology, spectral index and polarization characteristics of B0513-692 for the first time. We detect a strongly polarized region (49%) in the remnant's southern edge. Interestingly we also detect a small (~40 arcsec) moderately bright, but distinct optical, circular shell in our Halpha imagery which is adjacent to the compact HII region and just within the borders of the NE edge of B0513-692. We suggest this is a separate new SNR candidate based on its apparently distinct character in terms of optical morphology in 3 imaged emission lines and indicative SNR optical spectroscopy (including enhanced optical [SII] emission relative to Halpha).
In this work, we want to find out if the IMF can be determined from colour images, integrated colours, or mass-to-light ratios, especially at high redshift, where galaxies cannot be resolved into individual stars, which would enable us to investigate dependencies of the IMF on cosmological epoch. We use chemo-dynamical models to investigate the influence of the Initial Mass Function (IMF) on the evolution of a Milky Way-type disk galaxy, in particular of its colours. We find that the effect of the IMF on the internal gas absorption is larger than its effect on the light from the stellar content. However, the two effects work in the opposite sense: An IMF with more high mass stars leads to brighter and bluer star-light, but also to more interstellar dust and thus to more absorption, causing a kind of "IMF degeneracy". The most likely wavelength region in which to detect IMF effects is the infrared (i. e., JHK). We also provide photometric absorption and inclination corrections in the SDSS ugriz and the HST WFPC2 and NICMOS systems.
We study star formation in a sample of 1204 galaxies in minor (| \Delta m_z | \geq 2) pairs and compact groups, drawn from the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). We analyze an analogous sample of 2409 galaxies in major (| \Delta m_z | < 2$) pairs and compact groups to ensure that our selection reproduces previous results, and we use a ``field'' sample of 65,570 galaxies for comparison. Our major and minor pairs samples include only galaxies in spectroscopically confirmed pairs, where the recessional velocity separation $\Delta V < 500$ km/s and the projected spatial separation $\Delta D < 50$ kpc/h. The relative magnitude (a proxy for the mass ratio) of the pair is an important parameter in the effectiveness of the tidally triggered star formation in minor interactions. As expected, the secondary galaxies in minor pairs show evidence for tidally triggered star formation, whereas the primary galaxies in the minor pairs do not. The galaxy color is also an important parameter in the effectiveness of triggered star formation in the major galaxy pairs. In the major pairs sample, there is a correlation between the specific H$\alpha$ star formation rate (SSFR) and $\Delta D$ in the blue primary and blue secondary galaxies; for the red primary and red secondary galaxies, there is none. Galaxies in pairs have a higher mean SSFR at every absolute magnitude compared to matched sets of field galaxies, and the relative increase in mean SSFR becomes larger with decreasing intrinsic luminosity. We also detect a significantly increased AGN fraction in the pair galaxies compared to matched sets of field galaxies.
The aim of these lectures is to introduce some basic problems arising in gravitation and modern cosmology. All along the discussion the guiding theme is provided by the phenomenological and theoretical properties of the Cosmic Microwave Background (CMB). These lectures have been prepared for a regular Phd course of the University of Milan-Bicocca.
Our knowledge of the phenomenology of accretion onto black holes has increased considerably thanks to ten years of observations with the RXTE satellite. However, only recently it has been possible to derive a scheme for the outburst evolution of transient systems on the basis of their spectral and timing properties, reaching a comprehensive definition of source states. These states are in turn linked to the ejection of relativistic jets as observed in the radio band. Here I concentrate on some specific aspects of this classification, concentrating on the properties of the aperiodic variability and on their link with jet ejection.
Vortices have been postulated at a range of size scales in the universe including at the stellar size-scale. Whilst hydrodynamically simulating the wind from an asymptotic giant branch (AGB) star moving through and sweeping up its surrounding interstellar medium (ISM), we have found vortices on the size scale of 10^-1 pc to 10^1 pc in the wake of the star. These vortices appear to be the result of instabilities at the head of the bow shock formed upstream of the AGB star. The instabilities peel off downstream and form vortices in the tail of AGB material behind the bow shock, mixing with the surrounding ISM. We suggest such structures are visible in the planetary nebula Sh 2-188.
We measure variations in orientation of fourteen dynamic fibrils as a function of time in a small isolated plage and nearby network using a 10-min time sequence of H-alpha filtergrams obtained by the Dutch Open Telescope. We found motions with average angular velocities of the order of 1 deg/min suggesting systematic turning from one limit position to another, particularly apparent in the case of fibrils with lifetimes of a few minutes. Shorter fibrils tend to turn faster than longer ones, which we interpret as due to vortex flows in the underlying granulation that twist magnetic fields.
In recent years there is increasing evidence for a thermal component in the gamma- and X-ray spectrum of the prompt emission phase in gamma-ray bursts. The temperature and flux of the thermal component show a characteristic break in the temporal behavior after few seconds. We show here, that measurements of the temperature and flux of the thermal component at early times (before the break) allow the determination of the values of two of the least restricted fireball model parameters: the size at the base of the flow and the outflow bulk Lorentz factor. Relying on the thermal emission component only, this measurement is insensitive to the inherent uncertainties of previous estimates of the bulk motion Lorentz factor. We give specific examples of the use of this method: for GRB970828 at redshift z=0.9578, we show that the physical size at the base of the flow is r_0 = (3.3+-2.1)*10^8 cm and the Lorentz factor of the flow is \Gamma = 305+-28, and for GRB990510 at z=1.619, r_0=(1.9+-2.0)*10^8 cm and \Gamma=384+-71.
We present new sensitive, high angular resolution 1.3, 2, and 6 cm observations of the continuum emission from the peculiar emission-line star MWC 349A, made with the Very Large Array. This radio emission is believed to originate in an ionized flow produced by the photoevaporation of a disk that surrounds the star. We determine for the first time the proper motion of this source, which is consistent with that expected for the location of the source in the galaxy. Our analysis of the images, that include the new observations as well as archive data covering a time interval of more than 20 years, indicates that the appearance of MWC 349A has been systematically changing over time. The well-defined ``hourglass'' shape that characterized the 2 and 1.3 cm appearance of the source in the early 1980's has disappeared to be replaced by a more ``square'' shape. We discuss if these changes can be accounted for by precession of the MWC 349A disk or by intrinsic changes in the parameters of the disk, but could not reach a satisfactory explanation.
We report spatially resolved, spectrally dispersed N-band observations of the
B[e] star Hen 3-1191 with the MIDI instrument of the Very Large Telescope
Interferometer. The object is resolved with a 40 m baseline and has an
equivalent uniform disc diameter ranging from 24 mas at 8 microns to 36 mas at
13 microns. The MIDI spectrum and visibilities show a curvature which can arise
from a weak silicate feature in which the object appears ~ 15% larger than in
the continuum, but this could result from a change in the object's geometry
within the band.
We then model Hen's 3-1191 spectral energy distribution (.4-60 microns) and
N-band visibilities. Because of the unknown nature for the object, we use a
wide variety of models for objects with IR excesses. We find the observations
to be consistent with a disc featuring an unusually high mass accretion and a
large central gap almost void of matter, an excretion disc, and a binary made
of two IR sources. We are unable to find a circumstellar shell model consistent
with the data.
At last, we review the different hypotheses concerning the physical nature of
the star and conclude that it is neither a Be supergiant nor a symbiotic star.
However, we could not discriminate between the scenario of a young stellar
object featuring an unusually strong FU Orionis-like outburst of mass accretion
(4 to 250 x 10^-4 solar mass per year) and that of a protoplanetary nebula with
an equatorial mass excretion rate (>~ 4 x 10^-5 solar mass per year). In both
cases, taking the additional presence of an envelope or wind into account would
result in lower mass flows.
Might stable energy species "lighter" than radiation, with $w > 1/3$, exist? A dimensional expansion of the cosmological Friedmann Equation of energy has a clear place for them. Such energies would affect the universe much differently than dark energies, and so are here dubbed "ultralight." As the universe expands, ultralight dilutes even faster than light. Although any specie of energy can be mimicked by a properly evolving scalar field, ultralight energy species are hypothesized here to be stable and not related to dynamics of a scalar field. Ultralight is not considered a candidate to make a significant contribution to the energy budget of the universe today, although ultralight might have affected the universe in the distant past. In particular, the $w=2/3$ ultralight energy specie appears to have relatively mundane physical attributes. A discussion of properties and falsifiable attributes of ultralight is given. The duration of primordial nucleosynthesis is extrapolated to limit the present density of $w=2/3$ ultralight to below one part in 100 billion of the critical density.
We describe a statistical reconstruction methodology for the GLAST LAT. The methodology incorporates in detail the statistics of the interactions of photons and charged particles with the tungsten layers in the LAT, and uses the scattering distributions to compute the full probability distribution over the energy and direction of the incident photons. It uses model selection methods to estimate the probabilities of the possible geometrical configurations of the particles produced in the detector, and numerical marginalization over the energy loss and scattering angles at each layer. Preliminary results show that it can improve on the tracker-only energy estimates for muons and electrons incident on the LAT.
The general relativistic cosmological Friedmann equations that describe how the scale factor of the universe evolves are expanded explicitly to include energy species not usually seen. The evolution of a universe as indicated by the Friedmann equations when dominated by a single, isotropic, stable, static, perfect-fluid energy species are discussed and compared. These energy species include phantom energy ($w<-1$), cosmological constant ($w=-1$), domain walls ($w = -2/3$), cosmic strings ($w = -1/3$), normal matter ($w = 0$), radiation and relativistic matter ($w = 1/3$), and a previously little-discussed specie of energy called "ultralight" ($w>1/3$). A very brief history and possible futures of Friedmann universes when dominated by stable energy species are discussed.
Cosmic reionization progresses as H II regions form around sources of ionizing radiation. Their average size grows continuously until they percolate and complete reionization. We demonstrate how this typical growth can be calculated around the largest, biased sources of UV emission such as quasars by further developing an analytical model based on the excursion set formalism. This approach allows us to calculate the sizes and growth of the HII regions created by the progenitors of any dark matter halo of given mass and redshift with a minimum of free parameters. Statistical variations in the size of these pre-existing HII regions are an additional source of uncertainty in the determination of very high redshift quasar properties from their observed HII region sizes. We use this model to demonstrate that the transmission gaps seen in very high redshift quasars can be understood from the radiation of only their progenitors and associated clustered small galaxies. The fit requires the epoch of overlap to be at z=5.8 +/- 0.1. This interpretation makes the transmission gaps independent of the age of the quasars observed. If this interpretation were correct it would raise the prospects of using radio interferometers currently under construction to detect the epoch of reionization.
We study the importance of baryonic physics on predictions of the matter power spectrum as it is relevant for forthcoming weak lensing surveys. We quantify the impact of baryonic physics using a set of three cosmological numerical simulations. Each simulation has the same initial density field, but models a different set of physical processes. The first simulation evolves the density field using gravity alone, the second includes non-radiative gasdynamics, and the third includes radiative heating and cooling of baryons, star formation, and supernova feedback. We find that baryonic processes alter predictions for the matter power spectrum significantly relative to models that include only gravitational interactions. Our results imply that future weak lensing experiments such as LSST and SNAP will be very sensitive to the poorly-understood physics governing the nonlinear evolution of the baryonic component of the universe. The net effect is significantly larger in the case of the model with cooling and star formation, in which case our results imply that contemporary surveys such as the CFHT Wide survey may also be sensitive to baryonic processes. In particular, this effect could be important for forecasts of the constraining power of future surveys if information from scales larger than l ~ 1000 is included in the analysis. We find that deviations are caused primarily by the rearrangement of matter within individual dark matter halos relative to the gravity-only case, rather than a large-scale rearrangement of matter. Consequently, we propose a simple model, based on the phenomenological halo model of dark matter clustering, for baryonic effects that can be used to aid in the interpretation of forthcoming weak lensing data.
Astrophysical relativistic flow problems require high resolution three-dimensional numerical simulations. In this paper, we describe a new parallel three-dimensional code for simulations of special relativistic hydrodynamics (SRHD) using both spatially and temporally structured adaptive mesh refinement (AMR). We used method of lines to discrete SRHD equations spatially and used a total variation diminishing (TVD) Runge-Kutta scheme for time integration. For spatial reconstruction, we have implemented piecewise linear method (PLM), piecewise parabolic method (PPM), third order convex essentially non-oscillatory (CENO) and third and fifth order weighted essentially non-oscillatory (WENO) schemes. Flux is computed using either direct flux reconstruction or approximate Riemann solvers including HLL, modified Marquina flux, local Lax-Friedrichs flux formulas and HLLC. The AMR part of the code is built on top of the cosmological Eulerian AMR code {\sl enzo}, which uses the Berger-Colella AMR algorithm and is parallel with dynamical load balancing using the widely available Message Passing Interface library. We discuss the coupling of the AMR framework with the relativistic solvers and show its performance on eleven test problems.
We present a catalog of spectro-photometric redshifts for 1308 galaxies from the GRism ACS Program for Extragalactic Science (GRAPES) observations with the Hubble Space Telescope. These low-resolution spectra between 6000 A and 9500 A are supplemented with U, J, H, and Ks from various facilities, resulting in redshifts computed with ~40 spectral bins per galaxy. For 81 galaxies between 0.5<z<1.5 with spectroscopic redshifts, the standard deviation in the fractional error in (1+z) is 0.046. With this catalog, we compute the B-band luminosity function in this redshift range from 72 galaxies. Owing to the depth of the GRAPES survey, we are able to accurately constrain the faint-end slope by going to M_B~-18 mag at 0.8<z<1.2, nearly two magnitudes fainter than previous studies. The faint-end slope is alpha=-1.32+-0.07. When compared to numerous published values at various redshifts, we find strong evidence for a steepening of the faint-end slope with redshift which is expected in the hierarchical formation scenario of galaxies.
We discuss the general framework for a perfect continuum medium in cosmology and show that an interesting generalization of the fluids normally used is for the medium to have rigidity and, hence, be analogous to an elastic solid. Such models can provide perfect, adiabatic fluids which are stable even when the pressure is negative, if the rigidity is sufficiently large, making them natural candidates to describe the dark energy. In fact, if the medium is adiabatic and isotropic, they provide the most general description of linearized perturbations. We derive the equations of motion and wave propagation speeds in the isotropic case. We point out that anisotropic models can also be incorporated within the same formalism and that they are classified by the standard Bravais Lattices. We identify the adiabatic and isocurvature modes allowed in both the scalar and vector sectors and discuss the predictions they make for CMB and matter power spectra. We comment on the relationship between these models and other fluid-based approaches to dark energy, and discuss a possible microphysical manifestation of this class of models as a continuum description of defect-dominated scenarios.
We investigate the plasma dynamics (outflow speed and turbulence) inside polar plumes. We compare line profiles (mainly of \ion{O}{6}) observed by the UVCS instrument on SOHO at the minimum of solar cycle 22-23 with model calculations. We consider Maxwellian velocity distributions with different widths in plume and inter-plume regions. Electron densities are assumed to be enhanced in plumes and to approach inter-plume values with increasing height. Different combinations of the outflow and turbulence velocity in the plume regions are considered. We compute line profiles and total intensities of the \ion{H}{1} Ly$\alpha$ and the \ion{O}{6} doublets. The observed profile shapes and intensities are reproduced best by a small solar wind speed at low altitudes in plumes that increases with height to reach ambient inter-plume values above roughly 3-4 $R_\sun$ combined with a similar variation of the width of the velocity distribution of the scattering atoms/ions. We also find that plumes very close to the pole give narrow profiles at heights above 2.5 $R_\sun$, which are not observed. This suggests a tendency for plumes to be located away from the pole. We find that the inclusion of plumes in the model computations provides an improved correspondence with the observations and confirms previous results showing that published UVCS observations in polar coronal holes can be roughly reproduced without the need for large temperature anisotropy. The latitude distributions of plumes and magnetic flux distributions are studied by analyzing data from different instruments on SOHO and with SOLIS.
In this short contribution we consider what types of surveys might be optimally pursued with path-finding instruments of 1%, 10% and finally 100% of the projected SKA sensitivity from the perspective of scientific applications that utilize the red-shifted 21 cm emission line. Achieving interesting HI galaxy sample sizes with 1% SKA surveys requires very substantial survey durations, of about 1000 days. Good sampling (log(N)~5) down to below M_HI* can then be achieved out to z=0.2 over 8000 deg^2 of survey area or even to z=0.5 over 800 deg^2. The same surveys will permit the resolved imaging of order 1000 galaxies in each of several red-shift bins as well as detection of faint neutral filaments in the vicinity of galaxies with a column density of about 10^18 cm^-2. Once 10% SKA sensitivities are achieved, then ground-breaking surveys are possible with only 100 day duration. Sample sizes of log(N)~6 extending below M_HI* are possible over 800 deg^2 out to z=0.5 and over 80 deg^2 out to z=1. Such surveys will permit very competitive measurement of acoustic oscillations in the galaxy power spectrum. One can then envision a series of 10% SKA surveys probing different depths. With the 100% SKA sensitivity the capabilities are truly phenomenal. Survey sample sizes in the range log(N)=7-8 are feasible over the red-shift range of 0.2 to about 5. Precise tracking of potential time evolution of dark energy (via the baryonic acoustic oscillation signature) should be possible out to z~3. The local cosmic web will be imaged down to N_HI=10^16 cm^-2. What exactly will be seen at z > 3 ? This will depend crucially on the SKA sensitivity in the critical frequency window of 350 to 200 MHz.
We have observed oscillations in the nearby G2 subgiant star beta Hyi using high-precision velocity observations obtained over more than a week with the HARPS and UCLES spectrographs. The oscillation frequencies show a regular comb structure, as expected for solar-like oscillations, but with several l=1 modes being strongly affected by avoided crossings. The data, combined with those we obtained five years earlier, allow us to identify 28 oscillation modes. By scaling the large frequency separation from the Sun, we measure the mean density of beta Hyi to an accuracy of 0.6%. The amplitudes of the oscillations are about 2.5 times solar and the mode lifetime is 2.3 d. A detailed comparison of the mixed l=1 modes with theoretical models should allow a precise estimate of the age of the star.
Elliptical galaxies are modelled as homeoidally striated Jacobi ellipsoids where the peculiar velocity distribution is anisotropic, or equivalently as their adjoints configurations i.e. classical Jacobi ellipsoids of equal mass and axes, in real or imaginary rotation. Reasons for the coincidence of bifurcation points from axisymmetric to triaxial configurations in both the sequences, contrary to earlier findings, are presented and discussed. The effect of centrifugal support at the ends of the major equatorial axis, is briefly outlined. The existence of a lower limit to the flattening of elliptical galaxies is investigated in dealing with a number of limiting situations. More specifically, (i) elliptical galaxies are considered as isolated systems, and an allowed region within Ellipsoidland, related to the occurrence of bifurcation points from ellipsoidal to pear-shaped configurations, is shown to be consistent with observations; (ii) elliptical galaxies are considered as embedded within dark matter haloes and, under reasonable assumptions, it is shown that tidal effects from hosting haloes have little influence on the above mentioned results; (iii) dark matter haloes and embedded elliptical galaxies, idealized as a single homeoidally striated Jacobi ellipsoid, are considered in connection with the cosmological transition from expansion to relaxation, by generalizing an earlier model, and the existence of a lower limit to the flattening of relaxed (oblate-like) configurations, is established. On the other hand, no lower limit is found to the elongation of relaxed (prolate-like) configurations, and the existence of some sort of instability is predicted, owing to the observed lack of elliptical galaxies more flattened or elongated than E7.
Using Chandra X-ray, Spitzer mid-IR, and 1.5 GHz radio data, we examine the spatial structure of SNR 3C391. The X-ray surface brightness is generally anti-correlative with the IR and radio brightness. The multiband data clearly exhibit a heart-shaped morphology and show the multi-shell structure of the remnant. A thin brace-like shell on the south detected at 24 um is projected outside the radio border and confines the southern faint X-ray emission. The leading 24 um knot on the SE boundary appears to be partly surrounded by soft X-ray emitting gas. The mid-IR emission is dominated by the contribution of the shocked dust grains, which may have been partly destroyed by sputtering.
We present the preliminary results of a Chandra X-ray study of N132D, a young shell-like supernova remnant (SNR) in the Large Magellanic Cloud. The equivalent width maps of emissions from O, Ne, Mg, Si, and S are provided. Spatially resolved spectral analysis for the small-scale regions were tentatively performed. The X-ray spectra of the interior can be described with a single-thermal model. The faint interior regions have lower density and higher temperature (above 1keV) than those of bright interior regions. The X-ray spectra along the shell can be phenomenally fitted with either a double-vpshock model or a vpshock + powerlaw model. If the non-thermal component is true, N132D would be listed as another X-ray synchrotron SNR.
The various requirements on a consistent varying speed of light (`VSL') theory are surveyed, giving a short check-list of issues that should be satisfactorily handled by such theories.
We present images of quasi-simultaneous VLBI observations of the GHz-Peaked-Spectrum radio source OQ 208 with the Very Long Baseline Array at 1.4, 1.7, 2.3, 5.0, 8.4, 15.4 GHz and the European VLBI Network at 6.7 GHz. The low frequency (1.4, 1.7 and 2.3 GHz) observations reveal a weak and extended steep-spectrum component at about 30 mas away in the position angle of $- 110^\circ$ which may be a remnant emission. The radio structure of OQ 208 consists of two mini-lobes at 5.0, 6.7, 8.4 and 15.4 GHz. Our spectral analysis further confirms that the southwest lobe undergoes free-free absorption and finds that the free-free absorption is stronger in the inner region. By fitting the 8.4 GHz images from 1994 to 2005, we obtain a separation speed of 0.031 $\pm$ 0.006 mas yr$^{-1}$ between the two mini-lobes. This indicates a jet proper motion of 0.105 $\pm$ 0.020 $c$ and a kinematic age of 219 $\pm$ 42 yr for the radio source.
In this article we present the O-C diagram of the hot subdwarf B pulsating star HS2201+2610 after seven years of observations. A secular increase of the main pulsation period, Pdot=(1.3+-0.1)x10**(-12), is inferred from the data. Moreover, a further sinusoidal pattern suggests the presence of a low-mass companion (Msini=~3.5 Mjup), orbiting the hot star at a distance of about 1.7 AU with a period near 1140 days.
The frequency of planets in binaries is an important issue in the field of extrasolar planet studies, because of its relevance in estimating of the global planet population of our Galaxy and the clues it can give to our understanding of planet formation and evolution. However, only preliminary estimates are available in the literature. We analyze and compare the frequency of planets in multiple systems to the frequency of planets orbiting single stars. We also try to highlight possible connections between the frequency of planets and the orbital parameters of the binaries (such as the periastron and mass ratio.) A literature search was performed for binaries and multiple systems among the stars of the sample with uniform planet detectability defined by Fischer & Valenti (2005), and 202 of the 850 stars of the sample turned out to be binaries, allowing a statistical comparison of the frequency of planets in binaries and single stars and a study of the run of the planet frequency as a function of the binary separation. We found that the global frequency of planets in the binaries of the sample is not statistically different from that of planets in single stars. Even conservatively taking the probable incompleteness of binary detection in our sample into account, we estimate that the frequency of planets in binaries can be no more than a factor of three lower than that of planets in single stars. There is no significant dependence of planet frequency on the binary separation, except for a lower value of frequency for close binaries. However, this is probably not as low as required to explain the presence of planets in close binaries only as the result of modifications of the binary orbit after the planet formation.
We explore the possibility that large-scale convection be inhibited over some regions of giant planet interiors, as a consequence of a gradient of composition inherited either from their formation history or from particular events like giant impacts or core erosion during their evolution. Under appropriate circumstances, the redistribution of the gradient of molecular weight can lead to double diffusive layered or overstable convection. This leads to much less efficient heat transport and compositional mixing than large-scale adiabatic convection. We show that this process can explain the abnormally large radius of the transit planet HD209458b and similar objects, and may be at play in some giant planets, with short-period planets offering the most favorable conditions. Observational signatures of this transport mechanism are a large radius and a reduced heat flux output compared with uniformly mixed objects. If our suggestion is correct, it bears major consequences on our understanding of giant planet formation, structure and evolution, including possibly our own jovian planets.
With the development of new instrumentation providing measurements of solar photospheric vector magnetic fields, we need to develop our understanding of the effects of current density on coronal magnetic field configurations. The object is to understand the diverse and complex nature of coronal magnetic fields in active regions using a nonlinear force-free model. From the observed photospheric magnetic field we derive the photospheric current density for two active regions: one is a decaying active region with strong currents (AR8151), and the other is a newly emerged active region with weak currents (AR8210). We compare the three-dimensional structure of the magnetic fields for both active region when they are assumed to be either potential or nonlinear force-free. The latter is computed using a Grad-Rubin vector-potential-like numerical scheme. A quantitative comparison is performed in terms of the geometry, the connectivity of field lines, the magnetic energy and the magnetic helicity content. For the old decaying active region the connectivity and geometry of the nonlinear force-free model include strong twist and strong shear and are very different from the potential model. The twisted flux bundles store magnetic energy and magnetic helicity high in the corona (about 50 Mm). The newly emerged active region has a complex topology and the departure from a potential field is small, but the excess magnetic energy is stored in the low corona and is enough to trigger powerful flares.
The existence of a population of wandering Intermediate Mass Black Holes (IMBHs) is a generic prediction of scenarios that seek to explain the formation of Supermassive Black Holes in terms of growth from massive seeds. The growth of IMBHs may lead to the formation of DM overdensities called "mini-spikes", recently proposed as ideal targets for indirect DM searches. Current ground-based gamma-ray experiments, however, cannot search for these objects due to their limited field of view, and it might be challenging to discriminate mini-spikes in the Milky Way from the many astrophysical sources that GLAST is expected to observe. We show here that gamma-ray experiments can effectively search for IMBHs in the nearby Andromeda galaxy (also known as M31), where mini-spikes would appear as a distribution of point-sources, isotropically distributed in a \thickapprox 3^{\circ} circle around the galactic center. For a neutralino-like DM candidate with a mass m_{\chi}=150 GeV, up to 20 sources would be detected with GLAST (at 5\sigma, in 2 months). With Air Cherenkov Telescopes such as MAGIC and VERITAS, up to 10 sources might be detected, provided that the mass of neutralino is in the TeV range or above.
We present a detailed analysis of a large spectroscopic and photometric sample of DZ white dwarfs based on our latest model atmosphere calculations. We revise the atmospheric parameters of the trigonometric parallax sample of Bergeron, Leggett, & Ruiz (12 stars) and analyze 147 new DZ white dwarfs discovered in the Sloan Digital Sky Survey. The inclusion of metals and hydrogen in our model atmosphere calculations leads to different atmospheric parameters than those derived from pure helium models. Calcium abundances are found in the range from log (Ca/He) = -12 to -8. We also find that fits of the coolest objects show peculiarities, suggesting that our physical models may not correctly describe the conditions of high atmospheric pressure encountered in the coolest DZ stars. We find that the mean mass of the 11 DZ stars with trigonometric parallaxes, <M> = 0.63 Mo, is significantly lower than that obtained from pure helium models, <M> = 0.78 Mo, and in much better agreement with the mean mass of other types of white dwarfs. We determine hydrogen abundances for 27% of the DZ stars in our sample, while only upper limits are obtained for objects with low signal-to-noise ratio spectroscopic data. We confirm with a high level of confidence that the accretion rate of hydrogen is at least two orders of magnitude smaller than that of metals (and up to five in some cases) to be compatible with the observations. We find a correlation between the hydrogen abundance and the effective temperature, suggesting for the first time empirical evidence of a lower temperature boundary for the hydrogen screening mechanism. Finally, we speculate on the possibility that the DZA white dwarfs could be the result of the convective mixing of thin hydrogen-rich atmospheres with the underlying helium convection zone.
Regenerated high energy emissions from gamma-ray bursts (GRBs) are studied in detail. If the primary emission spectrum extends to TeV range, these very high energy photons will be absorbed by the cosmic infrared background (CIB). The created high energy electron-positron pairs up-scatter not only cosmic microwave background (CMB) photons but also CIB photons, and secondary photons are generated in the GeV-TeV range. These secondary delayed photons may be observed in the near future, and useful for a consistency check for the primary spectra and GRB physical parameters. The up-scattered CIB photons cannot be neglected for low redshift bursts and/or GRBs with a relatively low maximum photon energy. The secondary gamma-rays also give us additional information on the CIB, which is uncertain in observations so far.
Despite the many studies on stellar nucleosynthesis published so far, the scenario for the production of Cu in stars remains elusive. In particular, it is still debated whether copper originates mostly in massive stars or type Ia supernovae. To answer this question, we compute self-consistent chemical evolution models taking into account the results of updated stellar nucleosynthesis. By contrasting copper evolution in Omega Cen and the Milky Way, we end up with a picture where massive stars are the major responsible for the production of Cu in Omega Cen as well as the Galactic disc.
We trace the star formation regions in the SMC and study their properties. The size and spatial distribution of these regions is found to support the hierarchical scenario of star formation, whereas, the evaluation of their intensity, contributes to the understanding of the various stages of star formation. Their connection to the LMC-SMC close encounter, about $(0.9-2) \times 10^{8}$ years ago, is investigated as well. The SMC, being almost edge-on, does not easily reveal these areas, as is the case with the LMC. However, a study through multi-wavelength images such as optical, IR and radio has been proved very useful. A selection of areas, with enhanced 60 and 100-$\mu$m infrared flux and emission in all IRAS bands, identifies the star forming regions. All of the identified regions are dominated by early-type stars and considering their overall size (increasing order) a total of 24 aggregates, 23 complexes, and 3 super-complexes were found. We present their coordinates, dimensions, and IR fluxes. Moreover, we correlate their positions with known associations, SNRs, and \hii regions and discuss their activity.
In the slow-roll inflationary scenario, the amplitude of the curvature perturbations approaches a constant value soon after the modes leave the Hubble radius. However, relatively recently, it was shown that the amplitude of the curvature perturbations induced by the canonical scalar field can grow at super-Hubble scales if there is either a transition to fast roll inflation or if inflation is interrupted for some period of time. In this work, we extend the earlier analysis to the case of a scalar field described by the Dirac-Born-Infeld action. With the help of a specific example, we show that the amplitude of the tachyonic perturbations grows at super-Hubble scales when there is a transition from slow roll to fast roll inflation. We also illustrate as to how the growth of the entropy perturbations acts as the source for the amplification of the curvature perturbations during the period of fast roll inflation. Furthermore, following the earlier result for the canonical scalar field, we obtain a general criterion for the amplification of the tachyonic perturbations. Finally, we briefly comment on an application of this phenomenon.
We investigated the low state of the polar VV Pup by collecting high S/N time series spectra. We monitored VV Pup with VLT+FORS1 and analyzed the evolution of its spectroscopic features across two orbits. We report the first detection of photospheric Zeeman lines in VV Puppis. We argue that the photospheric field structure is inconsistent with the assumption that the accretion shocks are located close to the foot points of a closed field line in a dipolar field distribution. A more complex field structure and coupling process is implied making VV Puppis similar to other well studied AM Herculis type systems.
Motivated by recent models involving off-centre ignition of type Ia supernova explosions, we undertake three-dimensional time-dependent radiation transport simulations to investigate the range of bolometric light curve properties that could be observed from supernovae in which there is a lop-sided distribution of the products from nuclear burning. We consider both a grid of artificial toy models which illustrate the conceivable range of effects and a recent three-dimensional hydrodynamical explosion model. We find that observationally significant viewing angle effects are likely to arise in such supernovae and that these may have important ramifications for the interpretation of the observed diversity of type Ia supernova and the systematic uncertainties which relate to their use as standard candles in contemporary cosmology.
We present results on the X-ray and optical/UV emission from the type IIP SN 2006bp and the interaction of the SN shock with its environment, obtained with the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) on-board the Swift observatory. SN 2006bp is detected in X-rays at a 4.5 sigma level of significance in the merged XRT data from days 1 to 12 after the explosion. If the X-ray luminosity of (1.8+/-0.4)E39 ergs/s is caused by interaction of the SN shock with circumstellar material (CSM), deposited by a stellar wind from the progenitor's companion star, a mass-loss rate of ~E-05 M_sun/yr is inferred. The mass-loss rate is consistent with the non-detection in the radio with the VLA on days 2, 9, and 11 after the explosion and characteristic of a red supergiant progenitor with a mass around 12-15 M_sun prior to the explosion. In combination with a follow-up XMM-Newton observation obtained on day 21 after the explosion, an X-ray rate of decline with index 1.2+/-0.6 is inferred. Since no other SN has been detected in X-rays prior to the optical peak and since type IIP SNe have an extended 'plateau' phase in the optical, we discuss the scenario that the X-rays might be due to inverse Compton scattering of photospheric optical photons off relativistic electrons produced in circumstellar shocks. However, due to the high required value of the Lorentz factor (~10-100) we conclude that Inverse Compton scattering is an unlikely explanation for the observed X-ray emission. The fast evolution of the optical/ultraviolet spectral energy distribution and the spectral changes observed with Swift reveal the onset of metal line-blanketing and cooling of the expanding photosphere during the first few weeks after the outburst.
We use nearby K dwarf stars to measure the helium-to-metal enrichment ratio, a diagnostic of the chemical history of the Solar Neighbourhood. Our sample of K dwarfs has homogeneously determined effective temperatures, bolometric luminosities and metallicities, allowing us to fit each star to the appropriate stellar isochrone and determine its helium content indirectly. We use a newly computed set of Padova isochrones which cover a wide range of helium and metal content. Our theoretical isochrones have been checked against a congruous set of main sequence binaries with accurately measured masses, to discuss and validate their range of applicability. We find that the stellar masses deduced from the isochrones are usually in excellent agrement with empirical measurements. Good agreement is also found with empirical mass-luminosity relations. Despite fitting the masses of the stars very well, we find that anomalously low helium content (lower than primordial helium) is required to fit the luminosities and temperatures of the metal poor K dwarfs, while more conventional values of the helium content are derived for the stars around solar metallicity. We have investigated the effect of diffusion in stellar models and LTE assumption in deriving metallicities. Neither of these is able to resolve the low helium problem alone and only marginally if the cumulated effects are included, unless we assume a mixing-length which is strongly decreasing with metallicity. Further work in stellar models is urgently needed. The helium-to-metal enrichment ratio is found to be Delta Y / Delta Z = 2.2 +/- 1.1 around and above solar metallicity, consistent with previous studies, whereas open problems still remain at the lowest metallicities. Finally, we determine the helium content for a set of planetary host stars.
Accurate photometry with HST/ACS shows that the main sequence of the globular cluster NGC 2808 splits into three separate branches. The three MS branches may be associated with complexities of the cluster's horizontal branch and of its abundance distribution. We attribute the MS branches to successive rounds of star formation, with different helium abundances; we discuss possible sources of helium enrichment. Some other massive globulars also appear to have complex populations; we compare them with NGC 2808.
A simple algorithm is employed to deproject the two dimensional images of a pilot sample of 12 high-quality images of edge-on disk galaxies and to study their intrinsic 3 dimensional stellar distribution. We examine the radial profiles of the stars as a function of height above the plane and report a general trend within our sample of an increasing radial scalelength with height outside of the dustlane. This could be explained by the widespread presence of a thick disk component in these galaxies. In addition, the 3 dimensional view allows the study of the vertical distribution of the outer disk, beyond the break region, where we detect a significant increase in scalelength with vertical distance from the major axis for the truncated disks. This could be regarded as a weakening of the "truncation" with increasing distance from the plane. Furthermore, we conclude that the recently revised classification of the radial surface brightness profiles found for face-on galaxies is indeed independent of geometry. In particular, we find at least one example of each of the three main profile classes as defined in complete samples of intermediate to face-on galaxies: not-truncated, truncated and antitruncated. The position and surface brightness that mark the break location in the radial light distribution are found to be consistent with those of face-on galaxies.