We discuss in the framework of the excursion set formalism a recent discovery from N-body simulations that the clustering of haloes of given mass depends on their formation history. We review why the standard implementation of this formalism is unable to explain such dependencies, and we show that this can, in principle, be rectified by implementing in full an ellipsoidal collapse model where collapse depends not only on the overdensity but also on the shape of the initial density field. We also present an alternative remedy for this deficiency, namely the inclusion of collapse barriers for pancakes and filaments, together with the assumption that formation history depends on when these barriers are crossed. We implement both these extensions in a generalised excursion set method, and run large Monte Carlo realisations to quantify the effects. Our results suggest that effects as large as those found in simulations can only arise in the excursion set formalism if the formation history of a halo does indeed depend on the size of its progenitor filaments and pancakes. We also present conditional distributions of progenitor pancakes and filaments for low-mass haloes identified at present epoch, and discuss a recent claim by Mo et.al. that most low-mass haloes were embedded in massive pancakes at $z\sim 2$.
The accelerating expansion of the universe presents an exciting, fundamental challenge to the standard models of particle physics and cosmology. I highlight some of the outstanding challenges in both developing theoretical models and interpreting without bias the observational results from precision cosmology experiments in the next decade that will return data to help reveal the nature of the new physics. Examples given focus on distinguishing a new component of energy from a new law of gravity, and the effect of early dark energy on baryon acoustic oscillations.
We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics to study the formation of the first luminous objects in the LCDM cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from z~10 to z~50 and cover an order of magnitude in halo mass, including one within 1 Gpc^3 volume. We find that the physical properties of the central star-forming clouds are very similar in all of the simulated objects despite significant differences in formation redshift and environment. The physical properties of the clouds have little correlation with spin, mass, or assembly history of the host halo. The collapse of protostellar objects at higher redshifts progresses much more rapidly due to the higher densities, which accelerates the formation of molecular hydrogen, enhances initial cooling and shortens the dynamical timescales. The mass of the star-forming clouds cover a broad range, from a few hundred to a few thousand solar masses, and exhibit various morphologies: some of have disk-like structures nearly rotational supported; others form flattened spheroids; still others form bars. All of them develop a single proto-stellar `seed' which does not fragment into multiple objects up to the moment that the central gas becomes optically thick to H2 cooling lines. At this time, the instantaneous mass accretion rate onto the centre varies significantly from object to object, with disk-like structuress have the smallest mass accretion rates. The formation epoch and properties of the star-forming clouds are sensitive to the values of cosmological parameters.
In the context of 2D, axisymmetric, multi-group, radiation/hydrodynamic simulations of core-collapse supernovae over the full 180$^{\circ}$ domain, we present an exploration of the progenitor dependence of the acoustic mechanism of explosion. All progenitor models we have tested with our Newtonian code explode. We investigate the roles of the Standing-Accretion-Shock-Instability (SASI), the excitation of core g-modes, the generation of core acoustic power, the ejection of matter with r-process potential, the wind-like character of the explosion, and the fundamental anisotropy of the blasts. We find that the breaking of spherical symmetry is central to the supernova phenomenon and the blasts, when top-bottom asymmetric, are self-collimating. We see indications that the initial explosion energies are larger for the more massive progenitors, and smaller for the less massive progenitors, and that the neutrino contribution to the explosion energy may be an increasing function of progenitor mass. The degree of explosion asymmetry we obtain is completely consistent with that inferred from the polarization measurements of Type Ic supernovae. Furthermore, we calculate for the first time the magnitude and sign of the net impulse on the core due to anisotropic neutrino emission and suggest that hydrodynamic and neutrino recoils in the context of our asymmetric explosions afford a natural mechanism for observed pulsar proper motions. [abridged]
We report on our further analysis of the expanded and revised sample of potential BL Lac objects (the 2BL) optically identified from two catalogues of blue-selected (UV excess) point sources, the 2dF and 6dF QSO Redshift Surveys (2QZ and 6QZ). The 2BL comprises 52 objects with no apparent proper motion, over the magnitude range 16.0 < bj< 20.0. Follow-up high signal-to-noise spectra of 36 2BL objects and NIR imaging of 18 objects, together with data for 19 2BL objects found in the Sloan Digital Sky survey (SDSS), show 17 objects to be stellar, while a further 16 objects have evidence of weak, broad emission features, although for at least one of these the continuum level has clearly varied. Classification of three objects remains uncertain,with NIR results indicating a marked reduction in flux as compared to SDSS optical magnitudes. Seven objects have neither high signal-to-noise spectra nor NIR imaging. Deep radio observations of 26 2BL objects at the VLA resulted in only three further radio-detections, however none of the three is classed as a featureless continuum object. Seven 2BL objects with a radio detection are confirmed as candidate BL Lac objects while one extragalactic (z=0.494) continuum object is undetected at radio frequencies. One further radio-undetected object is also a potential BL Lac candidate. However it would appear that there is no significant population of radio-quiet BL Lac objects.
We systematically analyze the prompt emission and the early afterglow data of a sample of 31 GRBs detected by {\em Swift} before September 2005, and estimate the GRB radiative efficiency. BAT's narrow band inhibits a precise determination of the GRB spectral parameters, and we have developed a method to estimate these parameters with the hardness ratio information. The shallow decay component commonly existing in early X-ray afterglows, if interpreted as continuous energy injection in the external shock, suggests that the GRB efficiency previously derived from the late-time X-ray data were not reliable. We calculate two radiative efficiencies using the afterglow kinetic energy E_K derived at the putative deceleration time t_{dec}) and at the break time (t_b) when the energy injection phase ends, respectively. At t_b XRFs appear to be less efficient than normal GRBs. However, when we analyze the data at t_{dec} XRFs are found to be as efficient as GRBs. Short GRBs have similar radiative efficiencies to long GRBs despite of their different progenitors. Twenty-two bursts in the sample are identified to have the afterglow cooling frequency below the X-ray band. Assuming \epsilon_e = 0.1, we find \eta_\gamma(t_b) usually <10% and \eta_\gamma (t_{dec}) varying from a few percents to > 90%. Nine GRBs in the sample have the afterglow cooling frequency above the X-ray band for a very long time. This suggests a very small \epsilon_B and/or a very low ambient density n.
Fine-scale structure in the corona appears not to be well resolved by current imaging instruments. Assuming this to be true offers a simple geometric explanation for several current puzzles in coronal physics, including: the apparent uniform cross-section of bright threadlike structures in the corona; the low EUV contrast (long apparent scale height) between the top and bottom of active region loops; the inconsistency between loop densities derived by spectral and photometric means; the rapid time scale of active region loop evolution; and the presence of tall, cool, FUV-bright loops in active regions and post-flare arcades. Treating coronal loops as a mixture of diffuse background and very dense, unresolved filamentary structures address these problems with a combination of high plasma density within the structures, shortening the radiative time and greatly increasing the emissivity of the structures, and geometric effects that attenuate the apparent brightness of the feature at low altitudes. Using the low-beta character of the coronal plasma and a self-similarity argument, I derive an estimate of the fundamental length scale of strong heating events at the base of the corona (10-100 km). I also suggest a potential explanation for the surprisingly high contrast of coronal loops as seen with EUV telescopes, and the uniform ``typical'' height of the bright portion of the corona (about 0.3 R_s) in full-disk EUV images.
We report precise Doppler measurements of GJ849 (M3.5V) that reveal the presence of a planet with a minimum mass of 0.82 Mjup in a 5.16 year orbit. At a = 2.35 AU, GJ849b is the first planet discovered around an M dwarf to orbit beyond 0.21 AU, and is only the second Jupiter mass planet discovered around a star less massive than 0.5 Msun. This detection brings to 4 the number of M stars known to harbor planets. Based on the results of our survey of 1300 FGKM main--sequence stars we find that giant planets within 2.5 AU are ~3 times more common around GK stars than around M stars. Due to the GJ849's proximity of 8.8 pc, the planet's angular separation is 0."27, making this system a prime target for high--resolution imaging using adaptive optics and future space--borne missions such as the Space Interferometry Mission. We also find evidence of a linear trend in the velocity time series, which may be indicative of an additional planetary companion.
16O/17O and 12C/13C ratios in 23 M giants are determined from high resolution IR spectra observed with the KPNO FTS. The masses of our sample are estimated with the use of the evolutionary tracks by Claret (2004), which could account for only about half of our sample. The resulting rather large variation of 16O/17O in low mass stars is well consistent with the prediction of the evolutionary models, but quite low 16O/17O ratios observed in some higher mass stars cannot be explained with the model prediction. The observed 12C/13C ratios are mostly around 10, in contradiction with the predict 12C/13C ratios of about 20. Thus we confirm a long-standing 12C/13C puzzle, and it appears that this dilemma may not be resolved yet even with extra mixing such as "cool bottom processing" expected only in low mass stars.
We fit the Doppler profiles of the He-like triplet complexes of \ion{O}{7} and \ion{N}{6} in the X-ray spectrum of the O star $\zeta$ Puppis, using XMM-Newton RGS data collected over $\sim 400$ ks of exposure. We find that they cannot be well fit if the resonance and intercombination lines are constrained to have the same profile shape. However, a significantly better fit is achieved with a model incorporating the effects of resonance scattering, which causes the resonance line to become more symmetric than the intercombination line for a given characteristic continuum optical depth $\tau_*$. We discuss the plausibility of this hypothesis, as well as its significance for our understanding of Doppler profiles of X-ray emission lines in O stars.
We calculate axisymmetric oscillations of rotating neutron stars composed of the surface fluid ocean, solid crust, and fluid core, taking account of a dipole magnetic field as strong as $B_S\sim 10^{15}$G at the surface. The adiabatic oscillation equations for the solid crust threaded by a dipole magnetic field are derived in Newtonian dynamics, on the assumption that the axis of rotation is aligned with the magnetic axis so that perturbations on the equilibrium can be represented by series expansions in terms of spherical harmonic functions $Y_l^m(\theta,\phi)$ with different degrees $l$ for a given azimuthal wave number $m$ around the the magnetic axis. Although the three component models can support a rich variety of oscillation modes, axisymmetric ($m=0$) toroidal $_{l}t_n$ and spheroidal $_ls_n$ shear waves propagating in the solid crust are our main concerns, where $l$ and $n$ denote the harmonic degree and the radial order of the modes, respectively. In the absence of rotation, axisymmetric spheroidal and toroidal modes are completely decoupled, and we consider the effects of rotation on the oscillation modes only in the limit of slow rotation. We find that the oscillation frequencies of the fundamental toroidal torsional modes $_{l}t_n$ in the crust are hardly affected by the magnetic field as strong as $B_S\sim 10^{15}$G at the surface. As the radial order $n$ of the shear modes in the crust becomes higher, however, both spheroidal and toroidal modes become susceptible to the magnetic field and their frequencies in general get higher with increasing $B_S$. We also find that the surface $g$ modes and the crust/ocean interfacial modes are suppressed by a strong magnetic field, and that there appear magnetic modes in the presence of a strong magnetic field.
A new method for separating intensity variations of a source's radio emission having various physical natures is proposed. The method is based on a joint analysis of the structure function of the intensity variations and the asymmetry function, which is a generalization of the asymmetry coefficient and characterizes the asymmetry of the distribution function of the intensity fluctuations on various scales for the inhomogeneities in the diffractive scintillation pattern. Relationships for the asymmetry function in the cases of a logarithmic normal distribution of the intensity fluctuations and a normal distribution of the field fluctuations are derived. Theoretical relationships and observational data on interstellar scintillations of pulsars (refractive, diffractive, and weak scintillations) are compared. Pulsar scintillations match the behavior expected for a normal distribution of the field fluctuations (diffractive scintillation) or logarithmic normal distribution of the intensity fluctuations (refractive and weak scintillation). Analysis of the asymmetry function is a good test for distinguishing scintillations against the background of variations that have different origins.
We study the virialization of the cosmic structures in the framework of flat cosmological models where the dark energy component plays an important role in the global dynamics of the universe. In particular, our analysis focuses on the study of the spherical matter perturbations, as the latter decouple from the background expansion and start to ``turn around'' and finally collapse. We generalize this procedure taking into account models with an equation of state which vary with time, and provide a complete formulation of the cluster virialization attempting to address the nonlinear regime of structure formation. In particular, assuming that clusters have collapsed prior to the epoch of $z_{\rm f}\simeq 1.4$, in which the most distant cluster has been found, we show that the behavior of the spherical collapse model depends on the functional form of the equation of state.
Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28~ks (but over a gross time span of 90~ks), both objects varied in intensity by about 50~%. The 0.4--10 keV X-ray luminosity of X-1 and X-2 was measured as $2.5 \times 10^{40}~{\rm erg~s^{-1}}$ and $5.8 \times 10^{39}~{\rm erg~s^{-1}}$, respectively, with the former the highest ever reported for this ULX. The spectrum of X-1 can be explained by a sum of a strong and variable power-law component with a high energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of $\sim 0.2$ keV. These results suggest that X-1 was in a ``very high'' state, where the disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with the innermost disk temperature of 1.2--1.3 keV, and becomes flatter as the source becomes brighter. Hence X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of a few tens to a few hundreds solar masses.
We present wide-field near-infrared images of the DR21/W75 high-mass star forming region, obtained with the Wide Field Camera, WFCAM, on the United Kingdom Infrared Telescope. Broad-band JHK and narrow-band H2 1-0S(1) images are compared to archival mid-IR images from the Spitzer Space Telescope, and 850 micron dust-continuum maps obtained with the Submillimeter Common User Bolometer Array (SCUBA). Together these data give a complete picture of dynamic star formation across this extensive region, which includes at least four separate star forming sites in various stages of evolution. The H2 data reveal knots and bow shocks associated with more than 50 individual flows. Most are well collimated, and at least five qualify as parsec-scale flows. Most appear to be driven by embedded, low-mass protostars. The orientations of the outflows, particularly from the few higher-mass sources in the region (DR21, DR21(OH), W75N and ERO~1), show some degree of order, being preferentially orientated roughly orthogonal to the chain of dusty cores that runs north-south through DR21. Clustering may inhibit disk accretion and therefore the production of outflows; we certainly do not see enhanced outflow activity from clusters of protostars. Finally, although the low-mass protostellar outflows are abundant and widely distributed, the current generation does not provide sufficient momentum and kinetic energy to account for the observed turbulent motions in the DR21/W75 giant molecular clouds. Rather, multiple epochs of outflow activity are required over the million-year timescale for turbulent decay.
A microscopic analysis of the viscous energy gain of energetic particles in (gradual) non-relativistic shear flows is presented. We extend previous work and derive the Fokker-Planck coefficients for the average rate of momentum change and dispersion in the general case of a momentum-dependent scattering time $\tau(p) \propto p^{\alpha}$ with $\alpha \geq 0$. We show that in contrast to diffusive shock acceleration the characteristic shear acceleration timescale depends inversely on the particle mean free path which makes the mechanism particularly attractive for high energy seed particles. Based on an analysis of the associated Fokker-Planck equation we show that above the injection momentum $p_0$ power-law differential particle number density spectra $n(p) \propto p^{-(1+ \alpha)}$ are generated for $\alpha >0$ if radiative energy losses are negligible. We discuss the modifications introduced by synchrotron losses and determine the contribution of the accelerated particles to the viscosity of the background flow. Possible implications for the plasma composition in mildly relativistic extragalactic jet sources (WATs) are addressed.
We calculate energy release associated with a first order phase transition at the center of a rotating neutron star. The results are based on precise numerical 2-D calculations, in which both the polytropic equations of state (EOS) as well as realistic EOS of the normal phase are used. Presented results are obtained for a broad range of metastability of initial configuration and size of the new superdense phase core in the final configuration. For small radii of the superdense phase core analytical expressions for the energy release are obtained. For a fixed "overpressure" dP (the relative excess of central pressure of collapsing metastable star over the pressure of equilibrium first-order phase transition) the energy release remarkably does not depend on the stellar angular momentum and coincides with that for nonrotating stars with the same dP. The energy release is proportional to dP^2.5 for small dPs, when sufficiently precise brute force 2-D numerical calculations are out of question. For higher dPs, results of 1-D calculations of energy release for non-rotating stars are shown to reproduce, with very high precision, the exact 2-D results for rotating stars.
Aims : We study an unknown, or very poorly known, interstellar HII component
in the Magellanic Clouds. This is the first study ever devoted to this class of
objects, which we call Low-excitation blobs (LEBs).
Methods : We used low-dispersion spectroscopy carried out at ESO to obtain
emission line intensities of Ha, Hb, and [OIII] (4959+5007) for 15 objects in
the Large Magellanic Cloud and 14 objects in the Small Magellanic Cloud.
Results are displayed in excitation ([oiii]/Hb ratio) versus Hb luminosity
diagrams.
Results : We show the presence of an LEB component in the Magellanic Clouds
and study its relationship with the already known class of high-excitation
blobs (HEBs). The newly found LEBs are lower excitation counterparts of HEBs
and are powered by less massive exciting stars. Further study of LEBs is
expected to provide new pieces of information for a better understanding the
low mass end of the upper initial mass function in the Magellanic Clouds.
Astrocladistics, a methodology borrowed from biology, is an objective way of understanding galaxy diversity through evolutionary relationships. It is based on the evolution of all the available parameters describing galaxies and thus integrates the complexity of these objects. Through the formalization of the concepts around galaxy formation and evolution, and the identification of the processes of diversification (build up, secular evolution, interaction, merging/accretion, sweeping/ejection), galaxy diversity can be expected to organize itself in a hierarchy. About 500 galaxies described by about 40 observables have now been analysed and several robust trees found. For instance, we show that the Dwarf Galaxies of the Local Group all derive from a common ancestral kind of objects. We identify three evolutionary groups, each one having its own characteristics and own evolution. The Virgo galaxies present a relatively regular diversification, with rather few violent events such as major mergers. Diversification in another sample made of gas-poor galaxies in different environments appears to be slightly more complicated with several diverging evolutionary groups. Work on a large sample of galaxies at non-zero redshifts is in progress and is pioneering a brand new approach to exploit data from the big extragalactic surveys.
The First Data Release (DR1) of the UKIRT Infrared Deep Sky Survey (UKIDSS) took place on 2006 July 21. UKIDSS is a set of five large near-infrared surveys, covering a complementary range of areas, depths, and Galactic latitudes. DR1 is the first large release of survey-quality data from UKIDSS and includes 320 sq degs of multicolour data to (Vega) K=18, complete (depending on the survey) in three to five bands from the set ZYJHK, together with 4 sq degs of deep JK data to an average depth K=21. In addition the release includes a similar quantity of data with incomplete filter coverage. In JHK, in regions of low extinction, the photometric uniformity of the calibration is better than 0.02 mag. in each band. The accuracy of the calibration in ZY remains to be quantified, and the same is true of JHK in regions of high extinction. The median image FWHM across the dataset is 0.82 arcsec. We describe changes since the Early Data Release in the implementation, pipeline and calibration, quality control, and archive procedures. We provide maps of the areas surveyed, and summarise the contents of each of the five surveys in terms of filters, areas, and depths. DR1 marks completion of 7 per cent of the UKIDSS 7-year goals.
In this brief summary I describe our recent work on superfluid neutron star dynamics. I review results on shear viscosity, hyperon bulk viscosity, vortex mediated mutual friction and the modelling of multifluid systems in general. For each problem I provide a set of questions that need to be addressed by future work.
We present a simple method to constrain the total mass of groups of galaxies. Tidal theory predicts that a limit to the mass of bound groups of galaxies can be obtained by using the fact that the tidal forces due to the external mass distributions are insufficient to disrupt the groups. To illustrate how the method works, we find tidal limits on the mass of eleven nearby galaxy groups. In most cases, tidal limits placed on these groups show that mass estimations obtained from methods based either on the application of the virial theorem or moments of the projected mass are underestimated by a factor of about 2 even if, in many cases, errors are large. Three groups show virial parameters fully concordant with the tidal constraints while two outlier groups show anomalous results. The irregular state of the latter suggests that the reliability of the method depends on the physical properties of the test groups, which should match the fundamental assumptions of spherical symmetry and dynamical equilibrium state.
A new observational study of the Herbig Ae star VV Ser has been performed in order to detect and accurately measure pulsation frequencies in the $\delta$ Scuti range. As it belongs to the continuous field of view of the asteroseismological satellite COROT, this study also aims at characterizing the properties of VV Ser as a potential ``COROT additional program'' candidate. CCD time series photometry in the Johnson V filter has been obtained during three consecutive years. The resulting light curves have been subject to detailed frequency analysis and the derived frequencies have been compared to model predictions. Seven pulsation frequencies have been measured on the basis of the best dataset obtained in 2004, ranging from $\sim$ 31 to $\sim$ 118 $\mu Hz$, with an accuracy of the order of 0.5 $\mu Hz$. The comparison with an extensive set of asteroseismological models shows that all the observed periodicities can be reproduced if the stellar mass is close to $4 M_{\odot}$. Conversely, the measured frequencies can be associated to $p$ modes only if the effective temperature is significantly lower than that obtained from the spectral type conversion. The present results seem to suggest that more accurate spectral type determination is necessary in order to discriminate the best fit model solution. In any case, the stellar mass of VV Ser is close to the upper mass limit ($\sim 4 M_{\odot}$) for this class of pulsators.
Our knowledge of the high-energy universe will change dramatically over the next several years as new astronomical detectors of high-energy radiation reach their design sensitivities. Besides Swift and HESS, which are already making important discoveries, these include the ground-based imaging air-Cherenkov telescopes VERITAS and MAGIC, the gamma-ray space telescopes GLAST and AGILE, and the particle observatories IceCube and Auger. A formalism for calculating statistical properties of cosmological gamma-ray sources is presented. Application is made to model calculations of the statistical distributions of gamma-ray and neutrino emission from beamed sources, specifically, long-duration GRBs, blazars, and extagalactic microquasars, and unbeamed sources, including normal galaxies, starburst galaxies and clusters. Expressions for the integrated intensities of faint beamed and unbeamed high-energy radiation sources are also derived. A toy model for the background intensity of radiation from dark-matter annihilation taking place in the early universe is constructed. Estimates for the gamma-ray fluxes of local group galaxies, starburst, and infrared luminous galaxies are briefly reviewed. Because the brightest extragalactic gamma-ray sources are flaring sources, and these are the best targets for sources of PeV -- EeV neutrinos and ultra-high energy cosmic rays, rapidly slewing all-sky telescopes like MAGIC and an all-sky gamma-ray observatory beyond Milagro will be crucial for optimal science return in the multi-messenger age.
We are conducting the first systematic 3D spectroscopic imaging survey to quantify the properties of the atomic gas (HI) in a distance-limited sample of 28 Seyfert galaxies and a sample of 28 inactive control galaxies with well-matched optical properties (the VHIKINGS survey). This study aims to address the role of the host galaxy in nuclear activity and confront outstanding controversies in optical/IR imaging surveys. Early results show possible relationships between Seyfert activity and HI extent, content and the prevalence of small, nearby gas-rich dwarf galaxies (M(HI)~10^7 Msun); results will be tested via rigorous comparison with control galaxies. Initial results from our optical followup study of 15 of our galaxies using the SAURON integral field unit on the WHT suggest a possible difference between Seyfert and inactive stellar and gaseous kinematics that support the conclusion that internal kinematics of galaxies are the key to nuclear activity.
Perturbation theory within Newtonian approximation is presented for cosmological models with varying physical constants. Analytical solutions for perturbations dynamics are obtained for each Gurzadyan-Xue model with pressureless matter and radiation. We found that perturbations grow during entire expansion within GX models, including curvature- and vacuum-dominated stage when they cease to grow in the standard cosmological model.
Be stars, which are characterised by intermittent emission in their hydrogen lines, are known to be fast rotators. This fast rotation is a requirement for the formation of a Keplerian disk, which in turn gives rise to the emission. However, the pulsating, magnetic B1IV star $\beta$ Cephei is a very slow rotator that still shows H$\alpha$ emission episodes like in other Be stars, contradicting current theories. We investigate the hypothesis that the H$\alpha$ emission stems from the spectroscopically unresolved companion of $\beta$ Cep. Spectra of the two unresolved components have been separated in the 6350-6850\AA range with spectro-astrometric techniques, using 11 longslit spectra obtained with ALFOSC at the Nordic Optical Telescope, La Palma. We find that the H$\alpha$ emission is not related to the primary in $\beta$ Cep, but is due to its 3.4 magnitudes fainter companion. This companion has been resolved by speckle techniques, but it remains unresolved by traditional spectroscopy. The emission extends from about $-$400 to +400 km s$^{-1}$. The companion star in its 90-year orbit is likely to be a classical Be star with a spectral type around B6-8. By identifying its Be-star companion as the origin of the H$\alpha$ emission behaviour, the enigma behind the Be status of the slow rotator $\beta$ Cep has been resolved.
Modeling type Ia supernova (SN Ia) explosions in three dimensions allows to eliminate any undetermined parameters and provides predictive power to simulations. This is necessary to improve the understanding of the explosion mechanism and to settle the question of the applicability of SNe Ia in cosmological distance measurements. Since the models contain no tunable parameters, it is also possible to directly assess their validity on the basis of a comparison with observations. Here, we describe the modeling of SNe Ia as thermonuclear explosions in which the flame after ignition near the center of the progenitor white dwarf star propagates outward in the sub-sonic deflagration mode accelerated by the interaction with turbulence. We explore the capabilities of this model by comparison with observations and show in a preliminary approach, how such a model can be applied to study the origin of the diversity of SNe Ia.
We performed sub-arcsecond high-sensitivity nterferometric observations of the thermal dust emission at 1.4 mm and 2.8 mm in the disks surrounding LkCa 15 and MWC 480, with the new 750 m baselines of the IRAM PdBI array. This provides a linear resolution of about 60 AU at the Taurus distance. We report the existence of a cavity of about 50 AU radius in the inner disk of LkCa 15. Whereas LkCa 15 emission is optically thin, the optically thick core of MWC 480 is resolved at 1.4 mm with a radius of about 35 AU, constraining the dust temperature. In MWC 480, the dust emission is coming from a colder layer than the CO emission, most likely the disk mid-plane. These observations provide direct evidence of an inner cavity around LkCa 15. Such a cavity most probably results from the tidal disturbance created by a low mass companion or large planet at about 30 AU from the star. These results suggest that planetary system formation is already at work in LkCa 15. They also indicate that the classical steady-state viscous disk model is a too simplistic description of the inner 50 AU of ''proto-planetary'' disks, and that the disk evolution is coupled to the planet formation process. The MWC 480 results indicate that a proper estimate of the dust temperature and size of the optically thick core are essential to determine the dust emissivity index.
In this paper, we use high-resolution smoothed particle hydrodynamics (SPH) simulations to investigate the response of a marginally stable self-gravitating protostellar disc to a close parabolic encounter with a companion discless star. Our main aim is to test whether close brown dwarfs or massive planets can form out of the fragmentation of such discs. We follow the thermal evolution of the disc by including the effects of heating due to compression and shocks and a simple prescription for cooling and find results that contrast with previous isothermal simulations. In the present case we find that fragmentation is inhibited by the interaction, due to the strong effect of tidal heating, which results in a strong stabilization of the disc. A similar behaviour was also previously observed in other simulations involving discs in binary systems. As in the case of isolated discs, it appears that the condition for fragmentation ultimately depends on the cooling rate.
New and previously published observations of the bright eclipsing binary VV Orionis are analyzed. We present new radial velocities and interstellar reddening measurements from high-resolution spectra of this detached, short-period (P=1.48 d) binary. We discuss the validity of prior claims for the existence of a third body and show that our new velocities and light curve solution cast doubt on them. The components of VV Ori are shown to be a B1 V primary with a mass $M{_1}=10.9 \pm 0.1 M_{\sun}$ and a radius $R_{1}=4.98 \pm 0.02 R_{\sun}$ and a B4.5 V secondary with a mass $M{_2}=4.09 \pm 0.05 M_{\sun}$ and a radius $R_{2}=2.41 \pm 0.01 R_{\sun}$.
We present initial results from a survey of nearby AGN using the near infrared adaptive optics integral field spectrograph SINFONI. These data enable us to probe the distribution and kinematics of the gas and stars at spatial resolutions as small as 0.085arcsec, corresponding in some cases to less than 10pc. In this contribution we present results concerning (1) the molecular gas in the nucleus of NGC1068 and its relation to the obscuring torus; and (2) the stars which exist on spatial scales of a few tens of parsecs around the AGN, the evidence for their remarkably young age and extreme intensities, and their relation to the AGN.
We describe briefly a novel interpretation of the physical nature of dark energy (DE), based on the vacuum fluctuations model by Gurzadyan & Xue, and describe an internally consistent solution for the behavor of DE as a function of redshift. A key choice is the nature of the upper bound used for the computation of energy density contributions by vacuum modes. We show that use of the comoving horizon radius produces a viable model, whereas use of the proper horizon radius is inconsistent with the observations. After introduction of a single phenomenological parameter, the model is consistent with all of the curently available data, and fits them as well as the standard cosmological constant model, while making testable predictions. While some substantial interpretative uncertainties remain, future developments of this model may lead to significant new insights into the physical nature of DE.
Proper motions with values >10 mas/yr or <-10 mas/yr have been extracted from the USNO-B1.0 and Tycho II catalogues for all Lanning UV-bright sources identified in the Sandage Two-color Survey of the Galactic Plane and presented in Papers I-VI. Of the 572 sources examined, we find at least 213 which exhibit a significantly large proper motion. Based on the location of the sources in a reduced proper motion diagram, we demonstrate that about two thirds of the high proper motion sources are likely or very likely to be heretofore unidentified white dwarfs.
Planetary nebulae (PN) represent the evolutionary fate of the asymptotic giant branch (AGB) stellar envelopes, thus are ideally suited to study the chemical impact of AGB stars. Stellar evolution predict elemental enrichment through the AGB evolution, and convective dredge-up episodes allow the products of stellar evolution to reach the stellar outer layers. Planetary nebulae are probes of these processes, and are also probes of the environment at the time of formation of their progenitors, through the elements not affected by AGB evolution. Ultimately PN may be used to test AGB stars as actors and probes. Planetary nebulae are easily identified and detected in the galaxy, the Magellanic Clouds, and beyond, thus they are probes of AGB evolution an stellar populations in different environments as well.
Current and future ground-based interferometers require knowledge of the
atmospheric time constant t_0, but this parameter has diverse definitions.
Moreover, adequate techniques for monitoring t_0 still have to be implemented.
We derive a new formula for the structure function of the fringe phase
(piston) in a long-baseline interferometer, and review available techniques for
measuring the atmospheric time constant and the shortcomings.
It is shown that the standard adaptive-optics atmospheric time constant is
sufficient for quantifying the piston coherence time, with only minor
modifications. The residual error of a fast fringe tracker and the loss of
fringe visibility in a finite exposure time are calculated in terms of the same
parameter. A new method based on the fast variations of defocus is proposed.
The formula for relating the defocus speed to the time constant is derived.
Simulations of a 35-cm telescope demonstrate the feasibility of this new
technique for site testing.
Loeb and Waxman have argued that high energy neutrinos from the decay of pions produced in interactions of cosmic rays with interstellar gas in starburst galaxies would be produced with a large enough flux to be observable. Here we obtain an upper limit to the diffuse neutrino flux from starburst galaxies which is a factor of $\sim$5 lower than the flux which they predict. Compared with predicted fluxes from other extragalactic high energy neutrino sources, starburst neutrinos with $\sim$ PeV energies would have a flux considerably below that predicted for AGN models. We also estimate an upper limit for the diffuse GeV $\gamma$-ray flux from starbust galaxies to be $\cal{O}$$(10^{-2})$ of the observed $\gamma$-ray background, much less than the component from unresolved blazars.
An improved formulation for the X-factor is proposed. The statement that the velocity-integrated radiation temperature of the $\COone$ line, $I(\CO)$, ``counts'' optically thick clumps is quantified using the formalism of \citet{Martin84} for line emission in a clumpy cloud. Adopting the simplifying assumptions of thermalized $\COone$ line emission and isothermal gas, an effective optical depth, $\tef$, is defined as the product of the clump filling factor within each velocity interval and the clump effective optical depth as a function of the optical depth on the clump's central sightline, $\tau_0$. The clump effective optical depth is well approximated as a power law in $\tau_0$ with power-law index, $\epsilon$, referred to here as the clump ``fluffiness,'' and has values between zero and unity. While the $\COone$ line is optically thick within each clump (i.e., high $\tau_0$), it is optically thin ``to the clumps'' (i.e., low $\tef$). Thus the dependence of $I(CO)$ on $\tef$ is linear, resulting in an X-factor that depends only on clump properties and {\it not} directly on the entire cloud. Assuming virialization of the clumps yields an expression for the X-factor whose dependence on physical parameters like density and temperature is ``softened'' by power-law indices of less than unity that depend on the fluffiness parameter, $\epsilon$. The X-factor provides estimates of gas column density because each sightline within the beam has optically thin gas within certain narrow velocity ranges. Determining column density from the optically thin gas is straightforward and parameters like $\epsilon$ then allow extrapolation of the column density of the optically thin gas to that of all the gas.
We calculate the trispectrum of the primordial curvature perturbation generated by an epoch of slow-roll inflation in the early universe, and demonstrate that the non-gaussian signature imprinted at horizon crossing is unobservably small, of order tau_NL < r/10, where r < 1 is the tensor-to-scalar ratio. Therefore any primordial non-gaussianity observed in future microwave background experiments is likely to have been synthesized by gravitational effects on superhorizon scales. We discuss the application of Maldacena's consistency condition to the trispectrum.
We investigate the cosmological Fisher information in the non-linear dark-matter power spectrum in the context of the halo model. We find that there is a plateau in information content on translinear scales which is generic to all cosmological parameters we tried. There is a rise in information on smaller scales, but we find that it is quite degenerate among different cosmological parameters (except, perhaps, the tilt). This suggests that the non-linear regime of the dark-matter power spectrum could be of little practical use to constrain cosmological parameters. Finally, we suggest ways to get around this problem, such as removing the largest haloes from consideration in survey analysis.
We present a re-analysis of our H- and K-band photometry and light-curves for GCIRS 16SW, a regular periodic source near the Galactic center. These data include those presented by DePoy et al. (2004); we correct a sign error in their reduction, finding GCIRS 16SW to be an eclipsing binary with no color variations. We find the system to be an equal mass overcontact binary (both stars overfilling their Roche lobes) with a period P=19.4513 days, an inclination angle i=71 degrees, and zero eccentricity. This confirms and strengthens the findings of Martins et al. (2006) that GCIRS 16SW is an eclipsing binary composed of two ~50 Msun stars, implying that there has been recent star formation very close to the Galactic center. Finally, the calculated luminosity of each component is close to the Eddington luminosity, implying that the temperature of 24400 K given by Najarro et al. (1997) might be too high for these evolved stars.
We modify the public PM code developed by Anatoly Klypin and Jon Holtzman to
simulate cosmology with arbitrary initial power spectrum and equation of state
of dark energy. With this tool in hand, we perform the following studies on the
matter power spectrum.
With an artificial sharp peak at k~0.2 h/Mpc in the initial power spectrum,
we find that the position of the peak is not shifted by nonlinear evolution. We
also find that the existence of a peak in the linear power spectrum would boost
the nonlinear power at all scales evenly. This is contrary to what HKLM scaling
relation predicts, but roughly consistent with that of halo model.
We construct two dark energy models with the same linear power spectra today
but different linear growth histories. We demonstrate that their nonlinear
power spectra differ at the level of the maximum deviation of the corresponding
linear power spectra in the past. Similarly, two constructed dark energy models
with the same growth histories result in consistent nonlinear power spectra.
This is hinting, not a proof, that linear power spectrum together with linear
growth history uniquely determine the nonlinear power spectrum. Based on these
results, we propose that linear growth history be included in the next
generation fitting formulas of nonlinear power spectrum. (abridged)
We present new L' (3.75 um) photometry of six L and T dwarfs, and M' (4.70 um) photometry of ten L and T dwarfs, observed at Gemini Observatory, and new 3.55, 4.49, 5.73 and 7.87 um photometry of nine L and T dwarfs, obtained with the Spitzer Space Telescope. The sample includes unusually blue and red dwarfs from our near-infrared studies. The data are combined with published L', M' and Spitzer photometry of L and T dwarfs, and trends of colors with spectral type and other colors are examined. Model atmospheres by Marley and Saumon are used to generate synthetic colors for ranges of effective temperature, gravity, grain sedimentation efficiency, metallicity and vertical mixing efficiency. We explore how these parameters affect the mid-infrared colors of L and T dwarfs and find that the data are modelled satisfactorily only if substantial vertical mixing occurs in both L- and T-dwarf atmospheres. The location and range of the L and T dwarf sequences in IRAC color-color and color - magnitude diagrams is also only reproduced if this mixing occurs, with a range of efficiency described by K_zz ~ 10^2-10^6 cm^2/s. The colors of the unusually red dwarfs are best reproduced by non-equilibrium models with low sedimentation efficiency, i.e. thick cloud decks, and those of the unusually blue dwarfs by non-equilibrium models with high sedimentation efficiency, i.e. thin cloud decks. The K-L' and Spitzer [3.55]-[4.49] colors can be used as indicators of effective temperature for L and T dwarfs, but care must be taken to include gravity and metallicity effects for late-T dwarfs and vertical mixing for both late-L and T dwarfs.
Recent observational literature suggests that only a small number of colliding galaxies show substantial star formation enhancements before merging. Most have SFRs comparable to those of late-type field galaxies. Preliminary Spitzer studies (with data from the Spirals, Bridges and Tails and SINGs projects) generally confirm this, though with some caveats. If star formation in isolated disks is self-regulated, while collisions disequilibrate much of the disk, then the similarity to star-formation in isolated disks is surprising. Comparisons of observations and dynamical models suggest some resolutions to this paradox, including the role of downsizing. The interesting example of the Arp 82 system is presented.
Astronomers traditionally find steep, open-ended functions difficult: the log N - log S curve for example, or the probability-area-radius relation in making cross-waveband identifications. The debate over the existence of a redshift cutoff for RQSOs (radio-loud QSOs; Jarvis and Rawlings 2000, Wall et al. 2005) is a case in point: an instance in which a second-order effect involving radio-variable QSOs, initially selected by survey from a population with a steep source count, leads to discrepant results from different analyses. A redshift cutoff is present in optically-selected QSOs of the SDSS and in X-ray selected QSOs of XMM, ROSAT and CHANDRA. A similar cutoff for radio-loud QSOs is important to establish, because if present, no known type of obscuration can be responsible. Such a space-density diminution then defines an epoch of creation for galaxy hosts of massive black holes powering AGN, a datum for galaxy formation. I discuss the resolution of the debate: the issue is highly relevant to modern surveys and their follow-up observations.
Selected results from recent studies of star formation in galaxies at different stages of interaction are reviewed. Recent results from the Spitzer Space Telescope are highlighted. Ideas on how large-scale driving of star formation in interacting galaxies might mesh with our understanding of star formation in isolated galaxies and small scale mechanisms within galaxies are considered. In particular, there is evidence that on small scales star formation is determined by the same thermal and turbulent processes in cool compressed clouds as in isolated galaxies. If so, this affirms the notion that the primary role of large-scale dynamics is to gather and compress the gas fuel. In gas-rich interactions this is generally done with increasing efficiency through the merger process.
We present spectra taken with the Infrared Spectrograph on Spitzer covering the 5-38 micron region of the ten Ultraluminous Infrared Galaxies (ULIRGs) found in the IRAS Bright Galaxy Sample. Among the BGS ULIRGs, we find a factor of 50 spread in the rest-frame mid to far-infrared spectral slope. The 9.7 micron silicate optical depths range from less than 0.4 more than 4.2, implying line of sight extinctions of A(V) ~ 8 - 78 mag. There is evidence for water ice and hydrocarbon absorption and C2H2 and HCN absorption features in four and possibly six of the 10 BGS ULIRGs, indicating shielded molecular clouds and a warm, dense ISM. We have detected [NeV] emission in three of the ten BGS ULIRGs, at flux levels of 5-18E-14 erg/cm^2/sec and [NeV] 14.3/[NeII] 12.8 line flux ratios of 0.12-0.85. The remaining BGS ULIRGs have limits on their [NeV]/[NeII] line flux ratios which range from less than 0.15 to less than 0.01. Among the BGS ULIRGs, the AGN fractions implied by either the [NeV]/[NeII] or [OIV]/[NeII] line flux ratios (or their upper limits) are significantly lower than implied by the MIR slope or EQW of the 6.2 micron PAH feature. Fitting the SEDs, we see evidence for hot (T > 300K) dust in five of the BGS ULIRGs, with the fraction of hot dust to total dust luminosity ranging from ~1-23%, before correcting for extinction. When integrated over the IRAC-8, IRS blue peakup, and MIPS-24 filter bandpasses, the IRS spectra imply very blue colors for some ULIRGs at z ~ 1.3. This is most extreme for sources with significant amounts of warm dust and deep silicate absorption.
Despite the wealth of solar data currently available, the explicit connection between coronal streamers and features on the solar disk remains unresolved. An empirical three-dimensional model, which reproduces the evolution of the large-scale coronal structure starting from the solar surface, is presented. The model is based on the view that the source of the large-scale coronal structure, namely streamers, is a consequence of the evolution of twisted sheet-like structures originating from prominences (or, equivalently, filaments) at the base of the corona. The high-density sheets evolve and merge with height into a final radial configuration constrained by the oberved position of streamers stalks higher up in the corona. The observational constraints are provided by white light observations from the LASCO/C2 data during the declining phase of solar activity, spanning the end of Carrington Rotation (CR) 2005 and the start of CR 2006, i.e. July-August 2003, and the position of filaments from the corresponding H$\alpha$ synoptic maps of the Paris-Meudon Observatory. The 3D model thus derived yields a reasonable agreement with the observed large-scale coronal structure, in particular the shape of large helmet streamers. These results give confidence in the underlying assumption that large helmet streamers can be the result of the convergence of two or more sheet-like structures originating from a distribution of prominences on the solar disk. The model supports the view that streamers, during that time of the solar cycle, are often associated with multiple current sheets.
In addition to density perturbations, inflationary models of the early universe generally predict a stochastic background of gravitational waves or tensor fluctuations. By making use of the inflationary flow approach for single field models and fitting the models with Monte-Carlo techniques to cosmic microwave background (CMB) data from the {\it Wilkinson Microwave Anisotropy Probe} (WMAP), we discuss the expected properties of the gravitational wave background from inflation at scales corresponding to direct detection experiments with laser interferometers in space. We complement the Monte-Carlo numerical calculations by including predictions expected under several classes of analytical inflationary models. We find that an improved version of {\it Big Bang Observer} (BBO-grand) can be used to detect a gravitational wave background at 0.1 Hz with a corresponding CMB tensor-to-scalar ratio above 10$^{-4}$. Even if the CMB tensor-to-scalar ratio were to be above 10$^{-2}$, we suggest that BBO-grand will be useful to study inflationary models as the standard version of BBO, with a sensitivity to a stochastic gravitational wave background $\Omega_{\rm GW}h^2 > 10^{-17}$, will only allow a marginal detection of the amplitude while leaving the tensor spectral index at 0.1 Hz unconstrained. We also discuss the extent to which CMB measurements can be used to predict the gravitational wave background amplitude in a direct detection experiment and how any measurement of the amplitude and the spectral tilt of the gravitational wave background at direct detection frequencies together with the CMB tensor-to-scalar ratio can be used to establish slow-roll inflation.
Helioseismology has revealed many details of solar differential rotation and also its time variation, known as torsional oscillations. So far there is no generally accepted theoretical explanation for torsional oscillations, even though a close relation to the solar activity cycle is evident. On the theoretical side non-kinematic dynamo models (including the Lorentz force feedback on differential rotation) have been used to explain torsional oscillations. In this paper we use a slightly different approach by forcing torsional oscillations in a mean field differential rotation model. Our aim is not a fully self-consistent model but rather to point out a few general properties of torsional oscillations and their possible origin that are independent from a particular dynamo model. We find that the poleward propagating high latitude branch of the torsional oscillations can be explained as a response of the coupled differential rotation / meridional flow system to periodic forcing in mid-latitudes, of either mechanical (Lorentz force) or thermal nature. The speed of the poleward propagation sets constraints on the value of the turbulent viscosity in the solar convection zone to be less than 3x10^8 m^2/s. We also show that the equatorward propagating low latitude branch is very unlikely a consequence of mechanical forcing (Lorentz force) alone, but rather of thermal origin due to the Taylor-Proudman theorem.
At the frontier of most areas in science, computer simulations play a central role. The traditional division of natural science into experimental and theoretical investigations is now completely outdated. Instead, theory, simulation, and experimentation form three equally essential aspects, each with its own unique flavor and challenges. Yet, education in computational science is still lagging far behind, and the number of text books in this area is minuscule compared to the many text books on theoretical and experimental science. As a result, many researchers still carry out simulations in a haphazard way, without properly setting up the computational equivalent of a well equipped laboratory. The art of creating such a virtual laboratory, while providing proper extensibility and documentation, is still in its infancy. A new approach is described here, Open Knowledge, as an extension of the notion of Open Source software. Besides open source code, manuals, and primers, an open knowledge project provides simulated dialogues between code developers, thus sharing not only the code, but also the motivations behind the code.
I provide some background about recent efforts made in modeling dense stellar systems, within the context of the MODEST initiative. During the last four years, we have seen more than fifteen MODEST workshops, with an attendance between twenty and a hundred participants, and topics ranging from very specialized discussions to rather general overviews.
General Relativity effects (gravitational redshift, light bending, ...) strongly modify the characteristics of the lines emitted close to the Black Hole in Active Galactic Nuclei and Galactic Black Hole systems. These effects are reviewed and illustrated, with particular emphasis on line emission from the accretion disc. Methods, based on the iron line, to measure the two astrophysically relevant parameters of a Black Hole, the mass and spin, are briefly discussed.
We report the discovery of a new detached eclipsing binary known as NSVS01031772 with component masses M_1= 0.5428 +/- 0.0027Msun, M_2= 0.4982 +/- 0.0025Msun, and radii R_1= 0.5260 +/- 0.0028Rsun, R_2= 0.5088 +/- 0.0030Rsun. The system has an orbital period of 0.3681414(3) days and an apparent magnitude V ~ 12.6. The estimated effective temperatures of the stars are T_eff1 = 3615 +/- 72K and T_eff2 = 3513 +/- 31K. The space velocities of the system suggest that it is a main sequence binary and with a metallicity that is approximately solar. The two stars in this binary are located in a region of the Mass-Radius relation where no accurate observational data were previously available. Similarly to other low-mass binaries recently studied, the radius of each star in NSVS01031772 exceeds the best evolutionary model predictions by about 8.5% on average.
UHE cosmic neutrino interaction with the cosmic neutrino background (CnuB) is expected to produce absorption dips in the UHE neutrino flux at energies above the threshold for Z-boson resonant production. The observation of these dips would constitute an evidence for the existence of the CnuB; they could also be used to determine the value of the relic neutrino masses as well as some features of the population of UHE neutrino sources. After breafly discussing the current prospects for relic neutrino spectroscopy, we present a calculation of the UHE neutrino transmission probability based on finite-temperature field theory which takes into account the thermal motion of the relic neutrinos. We then compare our results with the approximate expressions existing in the literature and discuss the influence of thermal effects on the absorption dips in the context of realistic UHE neutrino fluxes and favoured neutrino mass schemes.
We reported the result of long term optical variability of the blazar 4C 29.45 (QSO 1156+295, Ton 599), carried out optical photometric observations in Johnson V, Cousins RI passbands during April 1997 to March 2002 using the 1.56 meter telescope of the Shanghai Astronomical Observatory (SHAO) at Sheshan, China, compiled the post-1974 optical photometric data of the blazar by combining our new observations with the published optical data, and found maximum variations in different passbands: $\Delta$U = 4.41 mag, $\Delta$B = 5.55 mag, $\Delta$V = 4.53 mag, $\Delta$R = 5.80 mag, and $\Delta$I = 5.34 mag. The average color indices are: U$-$B = $-0.54\pm$0.18 mag, B$-$V = 0.56$\pm$0.21 mag, B$-$R = 0.93$\pm$0.18 mag, B$-$I = 1.51$\pm$0.24 mag, V$-$R = 0.44$\pm$0.15 mag and V$-$I = 1.03$\pm$0.23 mag. The post-1974 data give us an excellent opportunity to search for the existence of possible periodicity in the light curve. In search for periodicity in the R passband light curve, we performed Jurkevich test and power spectral (Fourier) analysis methods, and CLEANest algorithms to remove false signals. We found possible periods of 3.55 and 1.58 years. The possible mechanism for the periodic variability was discussed.
Supernova (SN) rates are a potentially powerful diagnostic of star formation history (SFH), metal enrichment, and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials, and simple SFH. However, a low-redshift cluster SN rate has never been published. We derive the SN rate in galaxy clusters at 0.06<z<0.19, based on type Ia supernovae (SNe Ia) that were discovered by the Wise Observatory Optical Transient Survey. As described in a separate paper, a sample of 140 rich Abell clusters was monitored, in which six cluster SNe Ia were found and confirmed spectroscopically. Here, we determine the SN detection efficiencies of the individual survey images, and combine the efficiencies with the known spectral properties of SNe Ia to calculate the effective visibility time of the survey. The cluster stellar luminosities are measured from the Sloan Digital Sky Survey (SDSS) database in the griz SDSS bands. Uncertainties are estimated using Monte-Carlo simulations in which all input parameters are allowed to vary over their known distributions. We derive SN rates normalized by stellar luminosity, in units of SNe (century 10^10 L_sun)^-1 in five photometric bandpasses, of 0.27+/-(0.16,0.11)+/-0.02 (B), 0.259+/-(0.155,0.103)+/-0.015 (g), 0.215+/-(0.128,0.085)+/-0.013 (r), 0.172+/-(0.103,0.068)+/-0.009 (i), 0.140+/-(0.084,0.056)+/-0.007 (z), where the quoted errors are statistical and systematic, respectively. The SN rate per stellar mass unit, derived using a color-luminosity-mass relation, is 0.074+/-(0.044,0.029)+/-0.021 SNe (century 10^10 M_sun)^-1. The low cluster SN rates we find are similar to, and consistent with, the SN Ia rate in local elliptical galaxies.
Unexpected in the AGN unified scheme, there exists a population of broad-line z~2 QSOs which have heavily absorbed X-ray spectra. These objects constitute 10% of the population at luminosities and redshifts characteristic of the main producers of QSO luminosity in the Universe. Our follow up observations in the submm show that these QSOs are often embedded in ultraluminous starburst galaxies, unlike most QSOs at the same redshifts and luminosities. The radically different star formation properties between the absorbed and unabsorbed QSOs implies that the X-ray absorption is unrelated to the torus invoked in AGN unification schemes. Instead, these results suggest that the objects represent a transitional phase in an evolutionary sequence relating the growth of massive black holes to the formation of galaxies. The most puzzling question about these objects has always been the nature of the X-ray absorber. We present our study of the X-ray absorbers based on deep (50-100ks) XMM-Newton spectroscopy. We show that the absorption is most likely due to a dense ionised wind driven by the QSO. This wind could be the mechanism by which the QSO terminates the star formation in the host galaxy, and ends the supply of accretion material, to produce the present day black hole/spheroid mass ratio.
The ONC appears to be unusual on two grounds: The observed constellation of the OB stars of the entire Orion Nebula cluster and its Trapezium at its centre implies a time-scale problem given the age of the Trapezium, and an IMF problem for the whole OB star population in the ONC. Given the estimated crossing time of the Trapezium, it ought to have totally dynamically decayed by now. Furthermore, by combining the lower limit of the ONC mass with a standard IMF it emerges that the ONC should have formed at least about 40 stars heavier than 5 M_sun while only ten are observed. Using N-body experiments we (i) confirm the expected instability of the trapezium and (ii) show that beginning with a compact OB-star configuration of about 40 stars the number of observed OB stars after 1 Myr within 1 pc radius and a compact trapezium configuration can both be reproduced. These two empirical constraints thus support our estimate of 40 initial OB stars in the cluster. Interestingly, a more-evolved version of the ONC resembles the Upper Scorpius OB association. The N-body experiments are performed with the new C-code CATENA by integrating the equations of motion using the chain-multiple-regularisation method. In addition, we present a new numerical formulation of the initial mass function.
Recent Chandra observations of an outflowing gas in GRO J1655-40 resulted in a suggestion by Miller et al. (2006) that the wind in this system must be powered by a magnetic process that can also drive accretion through the disk around the black hole. The alternative explanations, of radiation pressure or thermally driven flows, were considered unsatisfactory because of the highly ionized level of the gas and because of the derived small distance from the black hole, well inside the minimum distance required for an efficient X-ray heated wind. The present paper shows that there is a simple photoionized wind solution for this system where the gas is much further out than assumed by Miller et al., at r/r_g = 10^(4.7-5.7). The expected wind velocity, as well as the computed equivalent widths of more than 50 absorption lines in this single-component 1D model, are all in good agreement with the Chandra observations.
We compare the supernova data on the acceleration of the universe with a particular modification of gravity, the DGP 5-dimensional theory. We show the parameters of the theory are now very tightly constrained and at very reasonable values. For example, the curvature parameter, $\Omega_k$, in contrast to an earlier analysis which used a smaller data set, is now consistent with zero, and the redshift at which the universe starts to accelerate is near unity.
We present the results of the analysis of the hard band XMM-Newton spectra of the luminous, L(2-10keV)~3.4E+45 erg/s, radio-quiet quasar, E1821+643. Two emission features were observed in the 6-7 keV rest frame band, confirming previous Chandra detection of these structures. We interpret these features as two single emission lines, one consistent with the neutral Fe K-alpha line at 6.4 keV and the other most likely due to FeXXVI. If related to the quasar, the high-energy emission line should originate in highly ionised matter, i.e. the accretion disc or the clouds of the emission line regions. Alternatively, it may be related to the intergalactic medium of the rich galaxy cluster in which E1821+643 is embedded. A composite broad emission line in combination with an absorption line model, however, also fits the data well. We discuss the possible physical interpretations of the origin of these features.
The primordial magnetic field (PMF) can strongly affect the cosmic microwave background (CMB) power spectrum and the formation of large scale structure. In this presentation, we calculate the CMB temperature anisotropies generated by including a power-law magnetic field at the photon last scattering surface (PLSS). We then deduce an upper limit on the primordial magnetic field based upon our theoretical analysis of the power excess on small angular scales. We have taken into account several important effects such as the modified matter sound speed in the presence of a magnetic field. An upper limit to the field strength of $|B_\lambda|\lesssim$ 4.7 nG at the present scale of 1 Mpc is deduced. This is obtained by comparing the calculated theoretical result including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the small scale CMB anisotropies from the Wilkinson Microwave Anisotropy Probe (WMAP), the Cosmic Background Imager (CBI) and the Arcminute Cosmology Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for the generation and evolution of the PMF before, during and after the BBN.
Hard X-ray INT observations of SS 433 carried out during 2003-2005 years with an analysis of precessional and orbital variability is presented. The width of X-ray eclipse in the 25-50 keV range at the precessional phase $\psi=0.1$ (accretion disk is open to observer) is higher than that in the Ginga 18.4-27.6 keV range. This fact suggests existance the presence of hot extended corona around the supercritical accretion disk. Spectrum of hard X-rays in the range 10-200 keV does not change with the precessional phase which also suggests that hard X-ray flux is generated in the hot extended corona around the accretion disk. The parameters of this hot corona are: kT=23-25 keV, \tau = 1.8-2.8. Mass ratio estimated from the analysis of the ingress part of the eclipse light curve is in the range q=m_x/m_v=0.3-0.5.
Bright emission nebulae, or HII regions, around hot stars are readily seen in H-alpha light. However, the all-pervasive faint H-alpha emission has only recently been detected and mapped over the whole sky. Mostly the H-alpha emission observed along a line of sight is produced by ionised gas in situ. There are, however, cases where all or most of the H-alpha radiation is due to scattering by electrons or dust particles which are illuminated by an H-alpha emitting source off the line of sight. Here we demonstrate that diffuse, translucent and dark dust clouds at high galactic latitudes are in many cases observed to have an excess of diffuse H-alpha surface brightness, i.e. they are brighter than the surrounding sky. We show that the majority of this excess surface brightness can be understood as light scattered off the interstellar dust grains. The source of incident photons is the general Galactic H-alpha background radiation impinging on the dust clouds from all over the sky.
It is shown that nuggets of strange quark matter may be extracted from the surface of pulsars and accelerated by strong electric fields to high energies if pulsars are strange stars with the crusts, comprised of nuggets embedded in a uniform electron background. Such high energy nuggets called usually strangelets give an observable contribution into galactic cosmic rays and may be detected by the upcoming cosmic ray experiment Alpha Magnetic Spectrometer AMS-02 on the International Space Station.
We propose a model for rotating current patterns within radiopulsar polar cap
accelerators which has observational consequences that mimic those which have
been attributed to neutron star free precession. The model is a simple
extension of a canonical one for the origin of the "drifting subpulses" often
observed within the pulse envelope of radiopulsars.
The new model's current pattern rotation period (with respect to the neutron
star) is estimated to be of order a year. Associated with that rotation are
small oscillations in spin-down torque, pulse arrival time, and radiobeam
direction with this same period. These have estimated magnitudes which support
a reinterpretation of free precession "observations" which could resolve the
severe problem of obtaining anywhere near the otherwise required precession
parameters with canonical neutron star models.
We discuss the results of the MEGA microlensing campaign towards M31. Our analysis is based on an analytical evaluation of the microlensing rate, taking into account the observational efficiency as given by the MEGA collaboration. In particular, we study the spatial and time duration distributions of the microlensing events for several mass distribution models of the M31 bulge. We find that only for extreme models of the M31 luminous components it is possible to reconcile the total observed MEGA events with the expected self-lensing contribution. Nevertheless, the expected spatial distribution of self-lensing events is more concentrated and hardly in agreement with the observed distribution. We find it thus difficult to explain all events as being due to self-lensing alone. On the other hand, the small number of events does not yet allow to draw firm conclusions on the halo dark matter fraction in form of MACHOs.
Context. Abundance analysis of post-AGB objects as probes of AGB nucleosynthesis. Aims. A detailed photospheric abundance study is performed on the carbon-rich post-AGB candidate MACHO47.2496.8 in the LMC. Methods. High-resolution, high signal-to-noise ESO VLT-UVES spectra of MACHO47.2496.8 are analysed by performing detailed spectrum synthesis modelling using state-of-the-art carbon-rich MARCS atmosphere models. Results. The spectrum of MACHO47.2496.8 is not only dominated by bands of carbon bearing molecules, but also by lines of atomic transitions of s-process elements. The metallicity of [Fe/H]=-1.4 is surprisingly low for a field LMC star. The C/O ratio, however difficult to quantify, is greater than 2, and the s-process enrichment is large: the light s-process elements are enhanced by 1.2 dex compared to iron ([ls/Fe]=+1.2), while for the heavy s-process elements an even stronger enrichment is measured: [hs/Fe]=+2.1. The lead abundance is comparable to the [hs/Fe]. With its low intrinsic metallicity and its luminosity at the low end of the carbon star luminosity function, the star represents likely the final stage of a low initial mass star. Conclusions. The LMC RV Tauri star MACHO47.2496.8 is highly carbon and s-process enriched, and is most probable a genuine post-C(N-type) AGB star. This is the first detailed abundance analysis of an extragalactic post-AGB star to date.
We present the morphological analysis based on HST-NIC2 (0.075 arcsec/pixel) images in the F160W filter of a sample of 9 massive field (> 10^{11} M_\odot) galaxies spectroscopically classified as early-types at 1.2<z<1.7. Our analysis shows that all of them are bulge dominated systems. In particular, 6 of them are well fitted by a de Vaucouleurs profile (n=4) suggesting that they can be considered pure elliptical galaxies. The remaining 3 galaxies are better fitted by a Sersic profile with index 1.9<n<2.3 suggesting that a disk-like component could contribute up to 30% to the total light of these galaxies. We derived the effective radius R_e and the mean surface brightness <mu_e> within R_e of our galaxies and we compared them with those of early-types at lower redshifts. We find that the surface brightness <mu_e> of our galaxies should get fainter by 2.5 mag from z~1.5 to z~0 to match the surface brightness of the local ellipticals with comparable R_e, i.e. the local Kormendy relation. Luminosity evolution without morphological changes can only explain half of this effect, as the maximum dimming expected for an elliptical galaxy is ~1.6 mag in this redshift range. Thus, other parameters, possibly structural, may undergo evolution and play an important role in reconciling models and observations. Hypothesizing an evolution of the effective radius of galaxies we find that R_e should increase by a factor 1.5 from z~1.5 to z~0.
We describe a powerful signal processing method, the continuous wavelet
transform, and use it to analyze radial structure in Cassini ISS images of
Saturn's rings. Wavelet analysis locally separates signal components in
frequency space, causing many structures to become evident that are difficult
to observe with the naked eye. Density waves, generated at resonances with
saturnian satellites orbiting outside (or within) the rings, are particularly
amenable to such analysis. We identify a number of previously unobserved weak
waves, and demonstrate the wavelet transform's ability to isolate multiple
waves superimposed on top of one another. We also present two wave-like
structures that we are unable to conclusively identify.
In a multi-step semi-automated process, we recover four parameters from
clearly observed weak spiral density waves: the local ring surface density, the
local ring viscosity, the precise resonance location (useful for pointing
images, and potentially for refining saturnian astrometry), and the wave
amplitude (potentially providing new constraints upon the masses of the
perturbing moons). Our derived surface densities have less scatter than
previous measurements that were derived from stronger non-linear waves, and
suggest a gentle linear increase in surface density from the inner to the mid-A
Ring. We show that ring viscosity consistently increases from the Cassini
Division outward to the Encke Gap. Meaningful upper limits on ring thickness
can be placed on the Cassini Division (3.0 m at r~118,800 km, 4.5 m at
r~120,700 km) and the inner A Ring (10 to 15 m for r<127,000 km).
The cross-correlation between the ROSAT all-sky survey (~150000 sources) and the Tycho mission (~1000000 stars) catalogs has selected about 14000 stellar X-ray sources (RasTyc sample, Guillout et al. 1999). About 200-300 stars have been spectroscopically observed at high resolution both in the Halpha and LiI lambda-6708 regions with Elodie and Aurelie spectrographs of the OHP (Observatoire de l'Haute Provence, France). The aim was to classify the RasTyc star sample in terms of age and chromospheric activity level and to detect eventual binary systems. Photometric and spectroscopic follow-up observations of a RasTyc sub-sample composed of particularly interesting objects (binaries and very young stars) has been performed with the 91-cm telescope of the Catania Astrophysical Observatory. In this work we present some results of this monitoring. In particular, we have obtained good radial velocity curves and solved for the orbits of three SB2 and three SB1 spectroscopic binaries. In addition, for near all sources we have detected a photometric modulation ascribable to photospheric surface inhomogeneities and chromospheric Halpha line variation.
Gaia is a fully-approved all-sky astrometric and photometric survey due for launch in 2011. It will measure accurate parallaxes and proper motions for everything brighter than G=20 (ca. 10^9 stars). Its primary objective is to study the composition, origin and evolution of our Galaxy from the 3D structure, 3D velocities, abundances and ages of its stars. In some respects it can be considered as a cosmological survey at redshift zero. Several other upcoming space-based surveys, in particular JWST and Herschel, will study star and galaxy formation in the early (high-redshift) universe. In this paper I briefly describe these missions, as well as SIM and Jasmine, and explain why they need to observe from space. I then discuss some Galactic science contributions of Gaia concerning dark matter, the search for substructure, stellar populations and the mass--luminosity relation. The Gaia data are complex and require the development of novel analysis methods; here I summarize the principle of the astrometric processing. In the last two sections I outline how the Gaia data can be exploited in connection with other observational and theoretical work in order to build up a more comprehensive picture of galactic evolution.
Aims. This study aims to determine the level and constancy of the Spite plateau as definitively as possible from homogeneous high-quality VLT-UVES spectra of 19 of the most metal-poor dwarf stars known. Methods. Our high-resolution (R ~ 43000), high S/N spectra are analysed with OSMARCS 1D LTE model atmospheres and turbospectrum synthetic spectra to determine effective temperatures, surface gravities, and metallicities as well as Li abundances for our stars. Results. Eliminating a cool subgiant and a spectroscopic binary, we find 8 stars to have -3.5 < [Fe/H] < -3.0 and 9 stars with -3.0 < [Fe/H] < -2.5. Our best value for the mean level of the plateau is A(Li) =2.10 +- 0.09. The scatter around the mean is entirely explained by our estimate of the observational error and does not allow for any intrinsic scatter in the Li abundances. In addition, we conclude that a systematic error of the order of 200 K in any of the current temperature scales remains possible. The iron excitation equilibria in our stars support our adopted temperature scale, which is based on a fit to wings of the Halpha line, and disfavour hotter scales, which would lead to a higher Li abundance, but fail to achieve excitation equilibrium for iron. Conclusions. We confirm the previously noted discrepancy between the Li abundance measured in extremely metal-poor turnoff stars and the primordial Li abundance predicted by standard Big-Bang nucleosynthesis models adopting the baryonic density inferred from WMAP. We discuss recent work explaining the discrepancy in terms of diffusion and find the uncertain temperature scales to remain a major question mark. (abridged)
The present lecture notes are an introduction to selected topics of {\it Galactic Dynamics}. The focus is on topics that we consider more relevant to the main theme of this workshop, {\it Celestial Mechanics}. This is not intended to be a review article. In fact, any of the topics below could be the subject of a separate review. Only the main ideas and notions are introduced, as well as some important currently open problems in each topic. Some relevant results from our own research are also presented. We discuss topics related mostly to the so-called {\it ellipsoidal components} of galaxies. These are \textbf{a)} the dark halos of both elliptical and disk galaxies, \textbf{b)} the luminous matter in elliptical galaxies, and \textbf{c)} the bulges of disk galaxies. We shall only occasionally refer to the dynamics of disks, bars or spiral structure.
Hubble Space Telescope observations of the nearby (3.22 pc), K2 V star epsilon Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, \eps b, we extend our astrometric coverage to a total of 14.94 years (including the three year span of the \HST data) by including lower-precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8 -- 2006.3. We obtain a perturbation period, P = 6.85 +/- 0.03 yr, semi-major axis, alpha =1.88 +/- 0.20 mas, and inclination i = 30.1 +/- 3.8 degrees. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M_* = 0.83 M_{\sun}, we obtain a companion mass M = 1.55 +/- 0.24 M_{Jup}. Given the relatively young age of epsilon Eri (~800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct imaging attempts. We predict the next periastron at 2007.3 with a total separation, rho = 0.3 arcsec at position angle, p.a. = -27 degrees. Orbit orientation and geometry dictate that epsilon Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 years indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 years, possibly responsible for one feature of the dust morphology, the inner cavity.
Gamma Ray Bursts (GRBs) are among the most powerful sources in the Universe: they emit up to 10^54 erg in the hard X-ray band in few tens of seconds. The cosmological origin of GRBs has been confirmed by several spectroscopic measurements of their redshifts, distributed in the range 0.1-6.3. These two properties make GRBs very appealing to investigate the far Universe. The energetics implied by the observed fluences and redshifts span at least four orders of magnitudes. Therefore, at first sight, GRBs are all but standard candles. But there are correlations among some observed quantities which allow us to know the total energy or the peak luminosity emitted by a specific burst with a great accuracy. Through these correlations, GRBs become "known" candles to constrain the cosmological parameters. One of these correlation is between the rest frame peak spectral energy E_peak and the total energy emitted in gamma--rays E_gamma, properly corrected for the collimation factor. Another correlation, discovered very recently, relates the total GRB luminosity L_iso, its peak spectral energy E_peak and a characteristic timescale T_0.45, related to the variability of the prompt emission. It is based only on prompt emission properties, it is completely phenomenological, model independent and assumption--free. The constraints found through these correlations on the Omega_M and Omega_Lambda parameters are consistent with the concordance model. The present limited sample of bursts and the lack of low redshift events, necessary to calibrate these correlations, makes the cosmological constraints obtained with GRBs still large compared to those obtained with other cosmological probes (e.g. SNIa or CMB). However, the newly born field of GRB--cosmology is very promising for the future.
The MMF technique is used to segment the cosmic web as seen in a cosmological N-body simulation into wall-like and filament-like structures. We find that the spins and shapes of dark matter haloes are significantly correlated with each other and with the orientation of their host structures. The shape orientation is such that the halo minor axes tend to lie perpendicular to the host structure, be it a wall or filament. The orientation of the halo spin vector is mass dependent. Low mass haloes in walls and filaments have a tendency to have their spins oriented within the parent structure, while higher mass haloes in filaments have spins that tend to lie perpendicular to the parent structure.
ecent observations of type Ia supernovae indicate that the Universe is in an accelerating phase of expansion. The fundamental quest in theoretical cosmology is to identify the origin of this phenomenon. In principle there are two possibilities: 1) the presence of matter which violates the strong energy condition (a substantial form of dark energy), 2) modified Friedmann equations (Cardassian models -- a non-substantial form of dark matter). We classify all these models in terms of 2-dimensional dynamical systems of the Newtonian type. We search for generic properties of the models. It is achieved with the help of Peixoto's theorem for dynamical system on the Poincar{\'e} sphere. We find that the notion of structural stability can be useful to distinguish the generic cases of evolutional paths with acceleration. We find that, while the $\Lambda$CDM models and phantom models are typical accelerating models, the cosmological models with bouncing phase are non-generic in the space of all planar dynamical systems. We derive the universal shape of potential function which gives rise to presently accelerating models. Our results show explicitly the advantages of using a potential function (instead of the equation of state) to probe the origin of the present acceleration. We argue that simplicity and genericity are the best guide in understanding our Universe and its acceleration.
Relativistic shocks provide an efficient method for high-energy particle acceleration in many astrophysical sources. Multiple shock systems are even more effective and of importance, for example, in the internal shock model of gamma-ray bursts. We investigate the reacceleration of pre-existing energetic particles at such relativistic internal shocks by the first order Fermi process of pitch angle scattering. We use a well established eigenfunction method to calculate the resulting spectra for infinitely thin shocks. Implications for GRBs and relativistic jets are discussed.
(abridged) We investigate biases in cluster ages and [Fe/H] estimated from the (V-K)-(V-I) diagram, arising from inconsistent Horizontal Branch morphology, metal mixture, treatment of core convection between observed clusters and the theoretical colour grid employed for age and metallicity determinations. We also study the role played by statistical fluctuations of the observed colours, caused by the low total mass of typical globulars. Horizontal Branch morphology is potentially the largest source of uncertainty. A single-age system harbouring a large fraction of clusters with an HB morphology systematically bluer than the one accounted for in the theoretical colour grid, can simulate a bimodal population with an age difference as large as 8 Gyr. When only the redder clusters are considered, this uncertainty is almost negligible, unless there is an extreme mass loss along the Red Giant Branch phase. The metal mixture affects mainly the redder clusters; the effect of colour fluctuations becomes negligible for the redder clusters, or when the integrated Mv is brighter than -8.5 mag. The treatment of core convection is relevant for ages below ~4 Gyr. The retrieved [Fe/H] distributions are overall only mildly affected. Colour fluctuations and convective core extension have the largest effect. When 1sigma photometric errors reach 0.10 mag, all biases found in our analysis are erased, and bimodal age populations with age differences of up to ~8 Gyr go undetected. The use of both (U-I)-(V-K) and (V-I)-(V-K) diagrams may help disclosing the presence of blue HB stars unaccounted for in the theoretical colour calibration.
Recent observations and theoretical investigations of neutron stars indicate that their atmospheres consist not of hydrogen or iron but possibly heavier elements such as helium. We calculate the ionization and dissociation equilibrium of helium in the conditions found in the atmospheres of magnetized neutron stars. For the first time this investigation includes the internal degrees of freedom of the helium molecule. We found that at the temperatures and densities of neutron star atmospheres the rotovibrational excitations of helium molecules are populated. Including these excitations increases the expected abundance of molecules by up to two orders of magnitude relative to calculations that ignore the internal states of the molecule; therefore, if the atmospheres of neutron stars indeed consist of helium, helium molecules and possibly polymers will make the bulk of the atmosphere and leave signatures on the observed spectra from neutron stars.
We examine new methods of producing and analyzing the empirical initial-final mass relation for open cluster white dwarfs (WDs). We re-determine initial and final masses for the complete sample of published cluster WDs and then pare this sample using stringent criteria. We create an empirical initial-final mass relation by binning all WDs in individual clusters to a single point. Despite potentially significant systematics arising from this approach, we are comfortable concluding that, to within current observational constraints, the initial-final mass relation is linear, any intrinsic scatter in the relation is <~0.05 solar masses, and there is no metallicity dependence. More exploration of these issues is clearly warranted.
We report early follow-up observations of the error box of the short burst 050813 using the telescopes at Calar Alto and at Observatorio Sierra Nevada (OSN), followed by deep VLT/FORS2 $I$-band observations obtained under very good seeing conditions 5.7 and 11.7 days after the event. No evidence for a GRB afterglow was found in our Calar Alto and OSN data, no rising supernova component was detected on our FORS2 images. A potential host galaxy can be identified on our FORS2 images, even though we cannot state with certainty its association with GRB 050813. In any case, the optical afterglow of GRB 050813 was very faint, well in agreement with what is known so far about the optical properties of afterglows of short bursts. We conclude that all optical data support the interpretation that GRB 050813 was a \emph{bona-fide} short burst.
We examine faint infrared emission features detected in Spitzer Space Telescope images of M51, which are associated with atomic hydrogen in the outer disk and tidal tail at R greater than R_25 (4.9', ~14 kpc at d=9.6 Mpc). The infrared colors of these features are consistent with the colors of dust associated with star formation in the bright disk. However, the star formation efficiency (as a ratio of star formation rate to neutral gas mass) implied in the outer disk is lower than that in the bright disk of M51 by an order of magnitude, assuming a similar relationship between infrared emission and star formation rate in the inner and outer disks.
The non-Gaussianity of initial perturbations provides information on the mechanism that generated primordial density fluctuations. The expected non-Gaussianity for slow-roll inflationary models is well below the ultimate detection level with cosmic microwave background (CMB) anisotropies or large-large structure at low redshifts. We find that 21-cm background anisotropies of the low-frequency radio sky due to inhomogeneous neutral Hydrogen distribution at redshifts between 30 and 100 captures information on primordial non-Gaussianity better than any other cosmological probe. An all-sky 21-cm experiment over the frequency range from 14 MHz to 40 MHz using a bandwidth of 1 MHz and with angular information out to a multipole of 10^5 can limit the primordial non-Gaussianity parameter f_nl < 0.01. The 21-cm background should eventually reveal the non-Gaussianity associated with single field slow-roll inflation.
We make use of hydrodynamical simulations of the intergalactic medium (IGM) to create model quasar absorption spectra. We compare these model spectra with the observed Keck spectra of three z>6.2 quasars with full Gunn-Peterson troughs: SDSS J1148+5251 (z=6.42), SDSS J1030+0524 (z=6.28), and SDSS J1623+3112 (z=6.22). We fit the probability density distributions (PDFs) of the observed Ly alpha optical depths with those generated from the simulation, by exploring a range of values for the size of the quasar's surrounding HII region, R_S, the volume-weighted mean neutral hydrogen fraction in the ambient IGM, x_H, and the quasar's ionizing photon emissivity, N_Q. In order to avoid averaging over possibly large sightline-to-sightline fluctuations in IGM properties, we analyze each observed quasar independently. We find the following results for J1148+5251, J1030+0524, and J1623+3112: The best-fit sizes R_S are 40, 41, and 29 (comoving) Mpc, respectively. These constraints are tight, with only ~ 10% uncertainties, comparable to those caused by redshift--determination errors. The best-fit values of N_Q are 2.1, 1.3, and 0.9 x 10^{57} s^{-1}, respectively, with a factor of ~ 2 uncertainty in each case. Finally, the best--fit values of x_H are 0.16, 1.0, and 1.0, respectively. The uncertainty in the case of J1148+5251 is large, and x_H is not well constrained. However, for both J1030+0524 and J1623+3112, we find a significant lower limit of x_H >~ 0.033. Our method is different from previous analyses of the GP absorption spectra of these quasars, and our results strengthen the evidence that the rapid end--stage of reionization is occurring near z ~ 6.
Surface brightness maps for the young K0 dwarf AB Doradus are reconstructed from archival data sets for epochs spanning 1988 to 1994. By using the signal-to-noise enhancement technique of Least-Squares Deconvolution, our results show a greatly increased resolution of spot features than obtained in previously published surface brightness reconstructions. These images show that for the exception of epoch 1988.96, the starspot distributions are dominated by a long-lived polar cap, and short-lived low to high latitude features. The fragmented polar cap at epoch 1988.96 could indicate a change in the nature of the dynamo in the star. For the first time we measure differential rotation for epochs with sufficient phase coverage (1992.05, 1993.89, 1994.87). These measurements show variations on a timescale of at least one year, with the strongest surface differential rotation ever measured for AB Dor occurring in 1994.86. In conjunction with previous investigations, our results represent the first long-term analysis of the temporal evolution of differential rotation on active stars.
Magnetic perturbations to the frequencies of low degree, high radial order,
axisymmetric pulsations in stellar models permeated by large scale magnetic
fields are presented. Magnetic fields with dipolar, quadrupolar and a
superposition of aligned dipolar and quadrupolar components are considered.
The results confirm that the magnetic field may produce strong anomalies in
the power spectra of roAp stars. It is shown for the first time that anomalies
may result both from a sudden decrease or a sudden increase of a mode
frequency. Moreover, the results indicate that the anomalies depend essentially
on the geometry of the problem, i.e., on the configuration of the magnetic
field and on the degree of the modes. This dependence opens the possibility of
using these anomalies as a tool to learn about the magnetic field configuration
in the magnetic boundary layer of pulsating stars permeated by large scale
magnetic fields.
Spectra of galaxies contain an enormous amount of information about the relative mixture of ages and metallicities of constituent stars. We present a comprehensive study designed to extract the maximum information from spectra of data quality typical in large galaxy surveys. We test fitting techniques using the Bruzual-Charlot 2003 high resolution simple stellar population synthesis models to simultaneously estimate the ages and metallicities of 101 globular clusters in M31 and the Magellanic Clouds. The clusters cover a wide range of ages and metallicities, 4 Myr to 20 Gyr and -1.6 < [Fe/H] < +0.3, estimated by other methods in the literature. We compare results from model fits to both the spectra and photometry and find that fits to continuum-normalized (CN) spectra over the entire range available, typically 350-1000 nm for this sample, provides the best results. For clusters older than 1 Gyr we agree with literature ages to 0.16 dex (35%) and [Fe/H] to 0.12 dex. For younger clusters we agree with literature ages to 0.3 dex (63%), but cannot constrain the metallicity. It is particularly important to use the entire CN spectrum to avoid problems with model continua for young objects and to break age-metallicity degeneracies of broadband photometry. Our required S/N = 15-30 for 20% age uncertainties and 30-55 for 10% uncertainties over spectral resolutions of 5-25 Angstroms. This technique should work well for the age-metallicity parameter space expected for early-type galaxies at z~1, although individual galaxy spectral S/N may require the coaddition of a few like objects.
The use of polarimetric techniques is nowadays widespread among solar and stellar astronomers. However, notwithstanding the recommandations that have often been made about the publication of polarimetric results in the astronomical literature, we are still far from having a standard protocol on which to conform. In this paper we review the basic definitions and the physical significance of the Stokes parameters, and we propose a standardization of the measurement of polarized radiation.
Observations suggest that the properties of dust in the obscuring regions (``tori'') of active galactic nuclei (AGN) are different from those of normal galaxies, with most of the grains being significantly larger. We argue that, for luminous AGN, the presence of nuclear obscuration may be intimately linked to these modified dust properties. On $\sim$ parsec scales, the conditions in thin accretion disks in AGN allow most dust grains to grow to sizes of $\sim 1\micron$. These micron-sized grains significantly enhance the far infrared opacity in the disk. For luminous AGN, the X-ray and UV flux illuminating the outer parsec-scale disk is super-Eddington with respect to the local dust opacity. The outer disk may thus puff up to $h\sim R$. This provides a mechanism for generating a geometrically thick obscuring region from an intrinsically thin disk. We find obscuring columns $\sim 10^{22} - 10^{23} {\rm cm}^{-2}$, in reasonable agreement with observations.
Using the extended J, H and K magnitudes provided by the 2MASS data archive, we have considered the position of brightest cluster galaxies (BCGs) in the observed relations between supermassive black hole (SMBH) mass and the host galaxy properties, as well as their position in the stellar velocity dispersion and luminosity (sigma-L) relation, compared to E and S0 galaxies. We find that SMBH masses (M) derived from near-infrared (NIR) magnitudes do not exceed ~ 3E9Msun and that these masses agree well with the SMBH mass predictions made from stellar velocity dispersions. In the NIR, there is no evidence that BCGs depart from the sigma-L relation defined by less luminous early-type galaxies. The higher SMBH masses predicted from V-band luminosities (M ~ 3.2E10Msun) are attributed to the presence of extended blue envelopes around the BCGs.
We present commissioning data from the OSIRIS integral field spectrograph (IFS) on the Keck II 10 m telescope that demonstrate the utility of adaptive optics IFS spectroscopy in studying faint close-in sub-stellar companions in the haloes of bright stars. Our R~2000 J- and H-band spectra of the sub-stellar companion to the 1-10 Myr-old GQ Lup complement existing K-band spectra and photometry, and improve on the original estimate of its spectral type. We find that GQ Lup B is somewhat hotter (M6-L0) than reported in the discovery paper by Neuhauser and collaborators (M9-L4), mainly due to the surface-gravity sensitivity of the K-band spectral classification indices used by the discoverers. Spectroscopic features characteristic of low surface gravity objects, such as lack of alkali absorption and a triangular H-band continuum, are indeed prominent in our spectrum of GQ Lup B. The peculiar shape of the H-band continuum and the difference between the two spectral type estimates is well explained in the context of the diminishing strength of H2 collision induced absorption with decreasing surface gravity, as recently proposed for young ultra-cool dwarfs by Kirkpatrick and collaborators. Using our updated spectroscopic classification of GQ Lup B and a re-evaluation of the age and heliocentric distance of the primary, we perform a comparative analysis of the available sub-stellar evolutionary models to estimate the mass of the companion. We find that the mass of GQ Lup B is 0.010-0.040 Msun. Hence, it is unlikely to be a wide-orbit counterpart to the known radial-velocity extrasolar planets, whose masses are < 0.015 Msun. Instead, GQ Lup A/B is probably a member of a growing family of very low mass ratio widely separated binaries discovered through high-contrast imaging.
The tachyon field in cosmology is studied by applying the generating function method to obtain exact solutions. As special cases of the generating function, i.e. the constant, the power-law, and the exponential functions we can obtain the general form solutions to interesting physical cosmology quantities. The equation of state parameter of the tachyon field is derived as $w=-1+\epsilon\dot{\phi^2}$, which can be expressed as a function in terms of the redshift $z$. Based on these solutions, we propose some tachyon-inspired dark energy models to explore the properties of the corresponding cosmological evolution. The explicit relations between Hubble parameter and redshift enable us to test the models with SNe Ia data sets easily. In the current work we employ the SNe Ia data with the parameter $\mathcal{A}$ measured from the SDSS and the shift parameter $\mathcal{R}$ from WMAP observations to constrain the parameters in our models. The results show that the tachyon field with a power-law-like potential is a good candidate for dark energy, and the phantom in this case is slightly favored though the cosmological constant is still most economic and globally consistent so far.
We propose that the presence of additional planets in extrasolar planetary systems can be detected by long-term transit timing studies. If a transiting planet is on an eccentric orbit then the presence of another planet causes a secular advance of the transiting planet's pericenter over and above the effect of general relativity. Although this secular effect is impractical to detect over a small number of orbits, it causes long-term differences in when future transits occur, much like the long-term decay observed in pulsars. Measuring this transit-timing delay would thus allow the detection of either one or more additional planets in the system or the first measurements of non-zero oblateness ($J_2$) of the central stars.
The CANGAROO-II telescope observed sub-TeV gamma-ray emission from the nearby starburst galaxy NGC 253. The emission region was extended with a radial size of 0.3-0.6 degree. On the contrary, H.E.S.S could not confirm this emission and gave upper limits at the level of the CANGAROO-II flux. In order to resolve this discrepancy, we analyzed new observational results for NGC 253 by CANGAROO-III and also assessed the results by CANGAROO-II. Observation was made with three telescopes of the CANGAROO-III in October 2004. We analyzed three-fold coincidence data by the robust Fisher Discriminant method to discriminate gamma ray events from hadron events. The result by the CANGAROO-III was negative. The upper limit of gamma ray flux was 5.8% Crab at 0.58 TeV for point-source assumption. In addition, the significance of the excess flux of gamma-rays by the CANGAROO-II was lowered to less than 4 sigma after assessing treatment of malfunction of photomultiplier tubes.
Recent observations have shown that most of the warps in the disk galaxies are asymmetric. However there exists no generic mechanism to generate these asymmetries in warps. We have shown that a rich variety of possible asymmetries in the z-distribution of the spiral galaxies can naturally arise due to a dynamical wave interference between the first two bending modes i.e. bowl-shaped mode(m=0) and S-shaped warping mode(m=1) in the galactic disk embedded in a dark matter halo. We show that the asymmetric warps are more pronounced when the dark matter content within the optical disk is lower as in early-type galaxies.
Simultaneous observations of Mkn~421 were taken in very high energy gamma -rays (>200 GeV, CAT experiment), X-rays (RXTE) and optical (KVA). Multi -day RXTE observations are also presented, allowing for detailed modelling of the spectral variability.
n this paper we present the first results of an ongoing project devoted to the search of giant radio halos in galaxy clusters located in the redshift range z=0.2--0.4. One of the main goals of our study is to measure the fraction of massive galaxy clusters in this redshift interval hosting a radio halo, and to constrain the expectations of the particle re--acceleration model for the origin of non--thermal radio emission in galaxy clusters. We selected 27 REFLEX clusters and here we present Giant Metrewave Radio Telescope (GMRT) observations at 610 MHz for 11 of them. The sensitivity (1$\sigma$) in our images is in the range 35--100 $\mu$Jy b$^{-1}$ for all clusters. We found three new radio halos, doubling the number of halos known in the selected sample. In particular, a giant radio halo was found in A209 and RXCJ2003.5--2323, and one halo (of smaller size) was found in RXCJ1314.4--2515. Candidate extended emission on smaller scale was found around the central galaxy in A3444 which deserves further investigation. Furthermore, a radio relic was found in A521, and two relics were found in RXCJ1314.5--2515. The remaining six clusters observed do not host extended emission of any kind.
We present Keck K-band photometry and low-resolution H & K-band spectroscopy of the X-ray nova GRO J0422+32 obtained while the system was in the quiescent state. No clear ellipsoidal modulation is present in the light curve, which is instead dominated by a strong flickering component. In the K-band we observe strong Br_gamma emission, with an equivalent width of 38 +/- 5 Angstroms. From this we conclude that the accretion disc is the most likely source of the observed photometric contamination, and that previous infrared-based attempts to constrain the mass of the putative black hole in this system are prone to considerable uncertainty. We finally proceed to show how it is possible to place meaningful constraints on some of the binary parameters of this system, even in the presence of a relatively high level of contamination from the disc.
We have used the Australia Telescope Compact Array to conduct a search for the simplest amino acid, glycine (conformers I and II), and the simple chiral molecule propylene oxide at 3-mm in the Sgr B2 LMH. We searched 15 portions of spectrum between 85 and 91 GHz, each of 64 MHz bandwidth, and detected 58 emission features and 21 absorption features, giving a line density of 75 emission lines and 25 absorption lines per GHz stronger than the 5 sigma level of 110 mJy. Of these, 19 are transitions previously detected in the interstellar medium, and we have made tentative assignments of a further 23 features to molecular transitions. However, as many of these involve molecules not previously detected in the ISM, these assignments cannot be regarded with confidence. Given the median line width of 6.5 km/s in Sgr B2 LMH, we find that the spectra have reached a level where there is line confusion, with about 1/5 of the band being covered with lines. Although we did not confidently detect either glycine or propylene oxide, we can set 3 sigma upper limits for most transitions searched. We also show that if glycine is present in the Sgr B2 LMH at the level of N = 4 x 10^{14} cm^{-2} found by Kuan et al. (2003) in their reported detection of glycine, it should have been easily detected with the ATCA synthesized beam size of 17.0 x 3.4 arcsec^{2}, if it were confined to the scale of the LMH continuum source (< 5 arcsec). This thus puts a strong upper limit on any small-scale glycine emission in Sgr B2, for both of conformers I and II.
This paper analyzes the performance of observatories based on the so-called h-index (Hirsch 2005), a new, easy-to-use parameter that quantifies scientists' research impact and relevance. Compared to other bibliometric criteria, like total number of publications or citations, the h-index is less biased. Using NASA's Astrophysics Data System (ADS), we investigate the performance of selected observatories, taking into account their specific number of years of operation.
Identification of Fraunhofer lines with the known atomic and molecular absorbers and predictions leading to such an effort has been a challenging area of study crowned with occasional success. Such studies have also lead, amongst other things to (i) a determination of abundances of elements and that of their isotopes (ii) valuable information on model atmospheres and (iii) use of Sun as a laboratory source. We summarize and review here the work done in the last four decades in the area of solar spectroscopy at Aryabhatta Research Institute of observational sciencES (ARIES in short) with a view to pick up new and interesting areas for future investigations in the light of the tremendous progress made elsewhere in observations of the sun and in the laboratory studies.
We calculated pre-supernova evolution models of single rotating massive
stars. These models reproduce observations during the early stages of the
evolution very well, in particular Wolf--Rayet (WR) populations and ratio
between type II and type Ib,c supernovae at different metallicities (Z). Using
these models we found the following results concerning long and soft gamma--ray
burst (GRB) progenitors:
- GRBs coming from WO--type (SNIc) WR stars are only produced at low Z (LMC
or lower).
- The upper metallicity limit for GRBs is reduced to Z ~ 0.004 (SMC) when the
effects of magnetic fields are included.
- GRBs are predicted from the second (and probably the first) stellar
generation onwards.
We performed a detailed analysis of the Chandra and HST images of the Seyfert 2 galaxy, NGC7582. The dust lane, as mapped by the HST NIR and optical images, strongly influences the morphology of the soft X-ray emission, being spatially coincident with excess of X-ray absorption. Two 'hot spots', i.e. regions where emission from higher ionization stages of O and Ne is stronger, are observed in the soft X-ray image. They can be tracers of variations of the ionization parameter, even if, at least for one of them, absorption may be the dominant effect. The positions of the `hot spots' suggest that they are not affected by the star-formation regions observed with HST, being located far away from them. Therefore, the starburst does not seem to play an important role in the photoionization of the soft X-ray emitting gas. The resulting picture is consistent with modified unification scenarios, where the Compton-thick torus coexists with a large-scale Compton-thin material associated with the dust lane and circumnuclear gas is photoionized by the AGN along torus-free lines of sight.
Large differences between the properties of the known sample of cataclysmic variable stars (CVs) and the predictions of the theory of binary star evolution have long been recognised. However, because all existing CV samples suffer from strong selection effects, observational biases must be taken into account before it is possible to tell whether there is an inconsistency. In order to address this problem, we have modelled the impact of selection effects on observed CV samples using a Monte Carlo approach. By simulating the selection criteria of the Palomar-Green (PG) Survey, we show that selection effects cannot reconcile the predictions of standard CV evolution theory with the observed sample. More generally, we illustrate the effect of the biases that are introduced by magnitude limits, selection cuts in U-B, and restrictions in galactic latitude.
We present and analyze the first high-resolution X-ray images ever obtained of the Eagle Nebula star-forming region. On 2001 July 30 the Chandra X-ray Observatory obtained a 78 ks image of the Eagle Nebula (M 16) that includes the core of the young galactic cluster NGC 6611 and the dark columns of dust and cold molecular gas in M 16 known as the Pillars of Creation. We find a total of 1101 X-ray sources in the 17'x17' ACIS-I field of view. Most of the X-ray sources are low mass pre-main-sequence or high-mass main-sequence stars in this young cluster. A handful of hard X-ray sources in the pillars are spatially coincident with deeply embedded young stellar objects seen in high-resolution near-infrared images recently obtained with the VLT (McCaughrean & Andersen 2002). In this paper, we focus on the 40 X-ray sources in and around Pillars 1-4 at the heart of the Eagle Nebula. None of the X-ray sources are associated with the evaporating gaseous globules (EGGs) first observed by Hester et al. (1996) in HST WFPC2 images of M 16, implying that either the EGGs do not contain protostars or that the protostars have not yet become X-ray active. Eight X-ray counts are coincident with the Herbig-Haro object HH216, implying log L_X~30.0.
Using a series of high-resolution N-body simulations of the concordance cosmology we investigate how the formation histories, shapes and angular momenta of dark-matter haloes depend on environment. We first present a classification scheme that allows to distinguish between haloes in clusters, filaments, sheets and voids in the large-scale distribution of matter. This method is based on a local-stability criterion for the orbits of test particles and closely relates to the Zel'dovich approximation. Applying this scheme to our simulations we then find that: i) Mass assembly histories and formation redshifts strongly depend on environment for haloes of mass M<M* (haloes of a given mass tend to be older in clusters and younger in voids) and are independent of it for larger masses; ii) Low-mass haloes in clusters are generally less spherical and more oblate than in other regions; iii) Low-mass haloes in clusters have a higher median spin than in filaments and present a more prominent fraction of rapidly spinning objects; we identify recent major mergers as a likely source of this effect. For all these relations, we provide accurate functional fits as a function of halo mass and environment. We also look for correlations between halo-spin directions and the large-scale structures: the strongest effect is seen in sheets where halo spins tend to lie within the plane of symmetry of the mass distribution. Finally, we measure the spatial auto-correlation of spin directions and the cross-correlation between the directions of intrinsic and orbital angular momenta of neightbouring haloes. While the first quantity is always very small, we find that spin-orbit correlations are rather strong especially for low-mass haloes in clusters and high-mass haloes in filaments.
A series of fast rotating models at very low metallicity (Z=1e-8) was
computed in order to explain the surface abundances observed at the surface of
CEMP stars, in particular for nitrogen. The main results are the following:
- Strong mixing occurs during He--burning and leads to important primary
nitrogen production.
- Important mass loss takes place in the RSG stage for the most massive
models. The 85 solar mass model loses about three quarter of its initial mass,
becomes a WO star and could produce a GRB.
- The CNO elements of HE1327-2326 could have been produced in massive
rotating stars and ejected by their stellar winds.
We present coordinates and available photometric information (either from previous or recent broadband UBV observations, and near-infrared photometry from the 2MASS Point Source Catalog) for 12056 stars (11516 of which are unique) identified in the HK Survey of Beers and colleagues as candidate field horizontal-branch or A-type stars. These stars, in the apparent magnitude range 10 <= B <= 16.0, were selected using an objective-prism/interference-filter survey technique. The availability of 2MASS information permits assembly of a cleaned version of this catalog, comprising likely blue horizontal-branch (BHB) stars or blue stragglers in the color interval -0.2 <= (B-V)o <= +0.2, which are of particular interest for investigation of the structure, kinematics, and dynamics of the thick disk and inner halo of the Milky Way, the total mass and mass profile of the Galaxy, and as potential foreground/background objects in efforts to bracket distances to high velocity clouds of H I. A comparison of the stars classified as high-likelihood BHB candidates with previous classifications based on UBV photometry and medium-resolution spectroscopy indicates that this class contains 78% correct identifications.
We present the second XMM-Newton observation (85 ks) of the narrow-line Seyfert 1 galaxy (NLS1) I Zw 1 and describe its mean spectral and timing characteristics. On average, I Zw 1 is ~35 per cent dimmer in 2005 than in the shorter (20 ks) 2002 observation. Between the two epochs the intrinsic absorption column density diminished, but there were also subtle changes in the continuum shape. Considering the blurred ionised reflection model, the long-term changes can be associated with a varying contribution of the power law component relative to the total spectrum. Examination of normalised light curves indicates that the high-energy variations are quite structured and that there are delays, but only in some parts of the light curve. Interestingly, a hard X-ray lag first appears during the most-distinct structure in the mean light curve, a flux dip ~25 ks into the observation. The previously discovered broad, ionised Fe Ka line shows significant variations over the course of the 2005 observation. The amplitude of the variations is 25-45 per cent and they are unlikely due to changes in the Fe ka-producing region, but perhaps arise from orbital motion around the black hole or obscuration in the broad iron line-emitting region. The 2002 data are re-examined for variability of the Fe Ka line at that epoch. There is evidence of energy and flux variations that are associated with a hard X-ray flare that occurred during that observation.
We present the first application of the 3D cosmic shear method developed in Heavens et al. (2006) and the geometric shear-ratio analysis developed in Taylor et al. (2006), to the COMBO-17 data set. 3D cosmic shear has been used to analyse galaxies with redshift estimates from two random COMBO-17 fields covering 0.52 square degrees in total, providing a conditional constraint in the ($\sigma_8$, $\Omega_m$) plane as well as a conditional constraint on the equation of state of dark energy, parameterised by a constant $w\equiv p/\rho c^2$. The ($\sigma_8$, $\Omega_m$) plane analysis constrained the relation between $\sigma_8$ and $\Omega_m$ to be $\sigma_8(\Omega_m/0.3)^{0.57\pm 0.19}=1.06^{+0.17}_{-0.16}$, in agreement with a 2D cosmic shear analysis of COMBO-17. The 3D cosmic shear conditional constraint on $w$ using the two random fields is $w=-1.27^{+0.64}_{-0.70}$. The geometric shear-ratio analysis has been applied to the A901/2 field, which contains three small galaxy clusters. Combining the analysis from the A901/2 field, using the geometric shear-ratio analysis, and the two random fields, using 3D cosmic shear, $w$ is conditionally constrained to $w=-1.08^{+0.63}_{-0.58}$. The errors presented in this paper are shown to agree with Fisher matrix predictions made in Heavens et al. (2006) and Taylor et al. (2006). When these methods are applied to large datasets, as expected soon from surveys such as Pan-STARRS and VST-KIDS, the dark energy equation of state could be constrained to an unprecedented degree of accuracy.
The angular and the radial parts of the dynamics of the perturbed Kepler motion are separable in many important cases. In this paper we study the radial motion and its parametrizations. We develop in detail a generalized eccentric anomaly parametrization and a procedure of computing a generic class of integrals based on the residue theorem. We apply the formalism to determine various contributions to the luminosity of a compact binary.
We discuss the thermal evaporation of tiny HI clouds in the interstellar medium. Cold neutral clouds will take ~10^6 - 10^7 yr to evaporate if they are embedded in warm neutral gas and about half as long if embedded in hot gas. Heat flux saturation effects severely reduce the evaporation rate of tiny cold neutral medium (CNM) clouds into hot gas. For CNM clouds embedded in warm neutral medium (WNM) the much lower conductivity results in slower evaporation. This mass loss rate could still be significant, however, if the environment is relatively quiescent. Partial ionization of the WNM gas would substantially reduce the conductivity and lengthen the lifetime of the tiny HI clouds. The ultimate importance of thermal conduction to cloud evolution will depend on the role of turbulence and the characteristics of the medium in which the clouds are embedded.
In this work we consider compact binaries on eccentric orbit under the spin-spin interaction. Using the post-Newtonian formalism, the binaries undergo a perturbed Keplerian motion. Here we investigate only the radial motion and derive the contribution of the second post-Newtonian order spin-spin effect to the solution.
In this paper we apply and discuss a method for the determination of the
magnetic field (H) evolution in supernova remnants (SNRs) from radio luminosity
at given frequency nu to diameter (L_{nu}-D) correlation. We assumed that H
evolves as H = D^{-delta}, where D is the diameter of the remnant.
Value delta=1.2 is obtained under the equipartition assumption from the
equations for revised equipartition calculation (REC) and by using the data
sample from the nearby starburst galaxy M82. We try to investigate whether or
not SNRs in M82 are in the equipartition state. The implication is that M82
SNRs are likely to be in equipartition state. In addition, we calculate H for
SNRs from M82, our Galaxy and some nearby galaxies. The magnetic field H is
obtained by using REC. We also discuss the accuracy of H values obtained under
REC assumptions, by comparing values obtained from REC with the more reliable
ones available in literature (found for few SNRs from Large Magellanic Cloud
and our Galaxy), and by relying on the fact that SNR luminosity is mainly
determined by the density of environment in which they evolve. We found that
our REC values for H are overestimated by a factor of 2 and accurate to an
order of magnitude.
We have used a set of archived Hubble Space Telescope/ACS images to probe the evolved populations of the globular cluster 47 Tucanae. We find an excess of Asymptotic Giant Branch (AGB) stars in the cluster core. We interpret this feature as the signature of an extra-population likely made by the progeny of massive stars originated by the evolution of binary systems. Indeed the comparison with theoretical tracks suggests that the AGB population of 47 Tuc can be significantly contaminated by more massive stars currently experiencing the first ascending Red Giant Branch.
We present here a complete list of contributions to the gravitational wave frequency evolution from compact binaries on circular orbits up to the second post-Newtonian order by including the interaction of magnetic dipole moments, quadrupole-monopole interactions together with the spin-orbit, the spin-spin and the self-interaction spin contributions. We apply our results to the Manchester et al. model of the J0737-3039A-B double pulsar.
Type Ia Supernovae (SNe Ia) are the best standard candles known today. At high redshift ($z\sim1$) SNe Ia are used to determine the Cosmological Constant Lambda with great success. However the most serious concern is raised by thepossible luminosity evolution of the SNe Ia explosion itself, i.e., that their intrinsic luminosity might vary with the look-back time. It is unknown to which extent high-redshift SNe Ia can directly be compared to near SNe Ia in order to determine Lambda. A possibility to circumvent this problem is to restrict the analysis to nearby SNe Ia situated preferably in E/S0 galaxies. Since the signal will be much smaller, we have to consider an substantial sample. As there are not enough data yet available, we conducted our analysis based on 200 synthetic SNe Ia with a luminosity scatter $\sigma_{\mathrm{m}}=0.^{\mathrm{m}}12$ (derived from observations) assuming a homogeneous space distribution and a limiting distance of $z\leq0.16$. We show that this kind of data, which we expect from future observations, will allow us to distinguish between a matter dominated or Lambda-dominated ($\Omega_{\mathrm{M}}=0.3$, $\Omega_{\mathrm{\Lambda}}=0.7$) universe with a significance of up to 2-3 sigma.
This paper investigates evolution of cosmic structures in different environments. For this purpose the quasispherical Szekeres model is employed. The Szekeres model is an exact solution of the Einstein field equations within which it is possible to describe more than one structure. In this way investigations of the evolution of the cosmic structures presented here can be freed from such assumptions as small amplitude of the density contrast. Also, studying the evolution of two or three structures within one framework enables us to follow the interaction between these structures and their impact on the evolution. Main findings include a conclusion that small voids surrounded by large overdensities evolve slower than large, isolated voids do. On the other hand, large voids enhance the evolution of adjourning galaxy clusters which evolve much faster than isolated clusters.
The abundances of O, Mg, Si and Fe in the intracluster medium of the Centaurus cluster are derived. The Fe abundance has a negative radial gradient. In solar units, the Si abundance is close to the Fe abundance, while the O and Mg abundances are much smaller. The high Fe/O and Si/O ratio indicate that metal supply from supernovae Ia is important and supernovae Ia synthesize Si as well as Fe. Within 2$'$, the O and Mg abundances are consistent with the stellar metallicity of the cD galaxy derived from the Mg$_2$ index. This result indicates that the central gas is dominated by the gas from the cD galaxy. The observed abundance pattern of the Centaurus cluster resembles to those observed in center of other clusters and groups of galaxies. However, the central Fe abundance and the Si/Fe ratio are 40 % higher and 30% smaller than those of M 87, respectively. Since the accumulation timescale of the supernovae Ia is higher in the Centaurus cluster, these differences imply a time dependence of nucleosynthesis by supernovae Ia.
We investigate the possibility of probing dark energy by measuring the isotropy of the galaxy cluster autocorrelation function (an Alcock-Paczynski test). The correlation function is distorted in redshift space because of the cluster peculiar velocities, but if these are known and can be subtracted, the correlation function measurement becomes in principle a pure test of cosmic geometry. Galaxy cluster peculiar velocities can be measured using the kinetic Sunyaev Zel'dovich (kSZ) effect. Upcoming CMB surveys, e.g., ACT, SPT, Planck, are expected to do this with varying levels of accuracy, dependent on systematic errors due to cluster temperature measurements, radio point sources, and the primary CMB anisotropy. We use the Hubble volume N-body simulation and the hydrodynamic simulation results of Nagai et. al (2003) to simulate various kSZ surveys. We find by model fitting that a measurement of the correlation function distortion can be used to recover the cosmological parameters that have been used to generate the simulation. However, the low space density of galaxy clusters requires larger surveys than are taking place at present to place tight constraints on cosmology. For example, with the SPT and ACT surveys, Omega_Lambda could be measured to within 0.1 and 0.2 respectively at one sigma, but only upper limits on the equation of state parameter w will be possible. Nevertheless, with accurate measurements of the kSZ effect, this test can eventually be used to probe the dark energy equation of state and its evolution with redshift, with different systematic errors than other methods.
We search data from the Energetic Gamma Ray Experiment Telescope (EGRET) for a gamma-ray line in the energy range 0.1-10 GeV from the 10 X 10 degree region around the Galactic center. Our null results lead to upper limits to the line flux from the Galactic center. Such lines may have appeared if the dark matter in the Galactic halo is composed of weakly-interacting massive particles (WIMPs) in the mass range 0.1-10 GeV. For a given dark-matter-halo model, our null search translates to upper limits to the WIMP two-photon annihilation cross section as a function of WIMP mass. We show that for a toy model in which Majorana WIMPs in this mass range annihilate only to electron-positron pairs, these upper limits supersede those derived from measurements of the 511-keV line and continuum photons from internal bremsstrahlung at the Galactic center.
We compute the amplitude of the non-Gaussianities in inflationary models with multiple, uncoupled scalar fields. This calculation thus applies to all models of assisted inflation, including N-flation, where inflation is driven by multiple axion fields arising from shift symmetries in a flux stabilized string vacuum. The non-Gaussianities are associated with nonlinear evolution of the field (and density) perturbations, characterized by the parameter $f_{NL}$. We derive a general expression for the nonlinear parameter, incorporating the evolution of perturbations after horizon-crossing. This is valid for arbitrary separable potentials during slow roll. To develop an intuitive understanding of this system and to demonstrate the applicability of the formalism we examine several cases with quadratic potentials: two-field models with a wide range of mass ratios, and a general N-field model with a narrow mass spectrum. We uncover that $f_{NL}$ is suppressed as the number of e-foldings grows, and that this suppression is increased in models with a broad spectrum of masses. On the other hand, we find no enhancement to $f_{NL}$ that increases with the number of fields. We thus conclude that the production of a large non-Gaussian signal in multi-field models of inflation is thus very unlikely. Finally, we compute a spectrum for the scalar spectral index that incorporates the nonlinear corrections to the fields' evolution.
We consider the competition of the different physical processes that can affect the evolution of a flame bubble in a Type Ia supernovae -- burning, turbulence and buoyancy. Even in the vigorously turbulent conditions of a convecting white dwarf, thermonuclear burning that begins at a point near the center (within 100 km) of the star is dominated by the spherical laminar expansion of the flame, until the burning region reaches kilometers in size. Consequently flames that ignite in the inner ~20 km promptly burn through the center, and flame bubbles anywhere must grow quite large--indeed, resolvable by large-scale simulations of the global system--for significant motion or deformation occur. As a result, any hot-spot that successfully ignites into a flame can burn a significant amount of white dwarf material. This potentially increases the stochastic nature of the explosion compared to a scenario where a simmering progenitor can have small early hot-spots float harmlessly away. Further, the size where the laminar flame speed dominates other relevant velocities sets a characteristic scale for fragmentation of larger flame structures, as nothing--by definition--can easily break the burning region into smaller volumes. This makes possible the development of semi-analytic descriptions of the earliest phase of the propagation of burning in a Type Ia supernovae, which we present here. Our analysis is supported by fully resolved numerical simulations of flame bubbles.
We study the kinematics of dark matter using the massive cluster of galaxies 1E0657-56. The velocity of the "bullet" subcluster has been measured by X-ray emission from the shock front, and the masses and separation of the main and sub-clusters have been measured by gravitational lensing. The velocity with gravity alone is calculated in a variety of models of the initial conditions, mass distribution and accretion history; it is much higher than expected, by at least 2.4 sigma. The probability of so large a subcluster velocity in cosmological simulations is <~ 10^{-7}. A long range force with strength ~ 0.4 - 0.8 times that of gravity would provide the needed additional acceleration.
We present an analysis of Chandra ACIS observations of the field of TeV J2032+4130, the first unidentified TeV source, detected serendipitously by HEGRA. This deep (48.7 ksec) observation of the field follows up on an earlier 5 ksec Chandra director's discretionary observation. Of the numerous point-like X-ray sources in the field, the brightest are shown to be a mixture of early and late-type stars. We find that several of the X-ray sources are transients, exhibiting rapid increases in count rates by factors 3-10, and similar in nature to the one, hard absorbed transient source located in the earlier Chandra observation of the field. None of these transient sources are likely to correspond to the TeV source. Instead, we identify a region of diffuse X-ray emission within the error circle of the TeV source and consider its plausible association.
We study the size of BLRs of low luminosity Active Galactic Nuclei, also called 'dwarf AGN', defined as having ($L_{H\alpha}\le10^{41}{\rm erg\cdot s^{-1}}$)). We more than double the sample size analyzed previously (Wang & Zhang 2003, hereafter Paper I). In this study we first confirm our previous result that the sizes of BLRs of low luminosity AGN are larger than the ones expected from the empirical relation $R_{BLRs} - L_{H\alpha}$ valid for 'normal' AGN: Seyfert 1s and quasars, except for the objects with accretion rate $\dot{m_{H\alpha}}>10^{-5.5}$. Second, we find a positive correlation between the line width of the narrow emission line (as tracer of velocity dipersion and thus bulge and black hole mass) and the size of BLRs for both normal and low luminosity AGN. In this paper we find a non-linear dependence of the BLRs sizes of low luminosity AGN on BH masses. We also show that their sizes of BLRs are more strongly dominated by the 'specific accretion rate' $\dot{m_{H\alpha}}$ defined as $\dot{m_{H\alpha}} = L_{H\alpha}/L_{Edd}$, than by the masses of their cetral black holes. As an expected result, the distance of emission regions of low-ionization broad H$\alpha$ of NGC 4395 should be consistent with the value from the empirical relation of $R_{BLRs} - L_{H\alpha}$, according to the high accretion rate.
We present time-series data on Jupiter Family Comets (JFCs) 17P/Holmes, 47P/Ashbrook-Jackson and 137P/Shoemaker-Levy 2. In addition we also present results from `snap-shot' observations of comets 43P/Wolf-Harrington, 44P/Reinmuth 2, 103P/Hartley 2 and 104P/Kowal 2 taken during the same run. The comets were at heliocentric distances of between 3 and 7 AU at this time. We present measurements of size and activity levels for the snap-shot targets. The time-series data allow us to constrain rotation periods and shapes, and thus bulk densities. We also measure colour indices (V-R) and (R-I) and reliable radii for these comets. We compare all of our findings to date with similar results for other comets and Kuiper Belt Objects (KBOs). We find that the rotational properties of nuclei and KBOs are very similar, that there is evidence for a cut-off in bulk densities at ~ 0.6 g cm^{-3} in both populations, and the colours of the two populations show similar correlations. For JFCs there is no observational evidence for the optical colours being dependant on either position in the orbit or on orbital parameters.
Aims: Using XMM-Newton data, we have aimed to study the nuclear outflow of the nearby starburst galaxy NGC 253 in X-rays with respect to its morphology and to spectral variations along the outflow. Methods: We analysed XMM-Newton RGS spectra, RGS brightness profiles in cross-dispersion direction, narrow band RGS and EPIC images and EPIC PN brightness profiles of the nuclear region and of the outflow of NGC 253. Results: We detect a diversity of emission lines along the outflow of NGC 253. This includes the He-like ions of Si, Mg, Ne and O and their corresponding ions in the next higher ionisation state. Additionally transitions from Fe XVII and Fe XVIII are prominent. The derived temperatures from line ratios along the outflow range from 0.21+/-0.01 to 0.79+/-0.06 keV and the ratio of Fe XVII lines indicates a predominantly collisionally ionised plasma. The RGS image in the O VIII line energy clearly shows the morphology of an outflow extending out to ~750 pc along the south-east minor axis, while the north-west part of the outflow is not seen in O VIII due to the heavy absorption by the galactic disc. This is the first time that the hot wind fluid has been detected directly. The limb brightening seen in Chandra and XMM-Newton EPIC observations is only seen in the energy range containing the Fe XVII lines (550-750 eV). In all other energy ranges between 400 and 2000 eV no clear evidence of limb brightening could be detected.
We present near-infrared spectra of late phase (>200 d) Type Ia supernovae (SNe Ia) taken at the Subaru telescope. The [Fe II] line of SN 2003hv shows a clear flat-topped feature, while that of SN 2005W show less prominent flatness. In addition, a large shift in their line center, varying from -3000 to 1000 (km/s) with respect to the host galaxies, is seen. Such a shift suggests the occurrence of an off-center, non-spherical explosion in the central region, and provides important, new constraints on the explosion models of SNe Ia.
I review recent observational progress on Anomalous X-ray Pulsars, with an emphasis on timing, variability, and spectra. Highlighted results include the recent timing and flux stabilization of the notoriously unstable AXP 1E 1048.1-5937, the remarkable glitches seen in two AXPs, the newly recognized variety of AXP variability types, including outbursts, bursts, flares, and pulse profile changes, as well as recent discoveries regarding AXP spectra, including their surprising hard X-ray and far-infrared emission, as well as the pulsed radio emission seen in one source. Much has been learned about these enigmatic objects over the past few years, with the pace of discoveries remaining steady. However additional work on both observational and theoretical fronts is needed before we have a comprehensive understanding of AXPs and their place in the zoo of manifestations of young neutron stars.
Based on the work of OPAL (Iglesias & Rogers 1996) and Alexander & Ferguson (1994), we construct a series of opacity tables for various metallicities Z=0, 0.00001, 0.00003, 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton's stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for ${\log}_{10}(T/{\rm K})> 3.95$ and Alexander's for ${\log}_{10}(T/{\rm K})< 3.95$. At ${\rm log}_{10}(T/{\rm K})=3.95$, the two groups' data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev & Urpin (1980). For different metallicities $1M_\odot$ models are constructed with the new opacity tables. Comparison of 1 and $5M\odot$ models constructed with the older OPAL tables (Iglesias & Rogers 1992) shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars.
Absorption spectra of high redshift quasars suggest that the reionisation of cosmic hydrogen was complete near z~6. The dominant sources of ionising photons responsible for this reionisation are generally thought to be stars and quasars. In this paper we make a quantitative estimate of the relative contributions made by these sources. Our approach is to compute the evolution of the post overlap ionising background radiation by combining semi-analytic descriptions of reionisation in a clumpy medium with a model for the quasar luminosity function. Our overall model has two free parameters, the star formation efficiency and the minimum quasar luminosity. By adjusting these parameters, we constrain the relative contributions made by stars and quasars through comparison with reported observations (Fan et al. 2005). We find that the relative quasar contribution (at z=5.7) to the ionising background was between 1.4% and 14.5%. The range of uncertainty is dominated by the unknown minimum quasar luminosity.
Young pulsars produce relativistic winds which interact with matter ejected during the supernova explosion and the surrounding interstellar gas. Particles are accelerated to very high energies somewhere in the pulsar winds or at the shocks produced in collisions of the winds with the surrounding medium. As a result of interactions of relativistic leptons with the magnetic field and low energy radiation (of synchrotron origin, thermal, or microwave background), the non-thermal radiation is produced with the lowest possible energies up to $\sim$100 TeV. The high energy (TeV) gamma-ray emission has been originally observed from the Crab Nebula and recently from several other objects. Recent observations by the HESS Cherenkov telescopes allow to study for the first time morphology of the sources of high energy emission, showing unexpected spectral features. They might be also interpreted as due to acceleration of hadrons. However, theory of particle acceleration in the PWNe and models for production of radiation are still at their early stage of development since it becomes clear that realistic modeling of these objects should include their time evolution and three-dimensional geometry. In this paper we concentrate on the attempts to create a model for the high energy processes inside the PWNe which includes existence not only relativistic leptons but also hadrons inside the nebula. Such model should also take into account evolution of the nebula in time. Possible high energy expectations based on such a model are discussed in the context of new observations.
Some arguments are brought that often active dwarf galaxies are the circumnuclear regions of LSB-galaxies in fact,rather than an ordinary galaxies.
We present 2D axisymmetric hydrodynamic simulations investigating the long term effect of FR II radio galaxies on the metal distribution of the surrounding intra-cluster medium (ICM). A light jet is injected into a cooling flow atmosphere for 10-30 Myr. We then follow the subsequent evolution for 3 Gyr on a spherical grid spanning 3 Mpc in radius. A series of passive tracer particles were placed in an annulus about the cluster core to simulate metal carrying clouds in order to calculate the metallicity (Z) as a function of time and radial distance from the cluster centre. The jet has a significant effect on the ICM over the entire 3 Gyr period. By the end of the simulations, the jets produced metallicities of ~10% of the initial metallicity of the cluster core throughout much of the cluster. The jets transport the metals not only in mixing regions, but also through upwelling ICM behind the jet, enriching the cluster over both long and short distances.
Big Bang nucleosynthesis produces only light elements and the very first generation stars are thus formed from metal-free clouds. They start the production of heavy elements during their life, and enrich the interstellar medium through their explosive death. Stellar evolution models show that the treatment of rotation has important effects on the evolution of those metal-free stars: for example, rotating models produce up to five orders of magnitude more primary nitrogen than non rotating models, due to internal mixing. This will have an impact in the composition of the second generation stars, some of which may now be observed in the Galactic halo. In the case Population III stars were very massive and would end up as direct black holes, rotation again have an interesting effect of enhancing mass loss through centrifugal force and surface enrichment. CNO composition patterns observed in ultra metal-poor halo stars may be explained by a 'wind only' contribution.
Comparing the asymmetry coefficients and scintillation indices for observed time variations of the intensity of the radiation of extragalactic sources and the predictions of theoretical models is a good test of the nature of the observed variations. Such comparisons can be used to determine whether flux-density variations are due to scintillation in the interstellar medium or are intrinsic to the source. In the former case, they can be used to estimate the fraction of the total flux contributed by the compact component (core) whose flux-density variations are brought about by inhomogeneities in the interstellar plasma. Results for the radio sources PKS 0405-385, B0917+624, PKS 1257-336, and J1819+3845 demonstrate that the scintillating component in these objects makes up from 50% to 100% of the total flux, and that the intrinsic angular sizes of the sources at 5 GHz is 10-40 microarcseconds. The characteristics of the medium giving rise to the scintillations are presented.
An elementary derivation of the fundamental relation $T/S=4\gamma$ between the tensor and scalar modes of cosmological perturbations in the early universe is given. Statements by L.P.Grishchuk on this problem are commented on.
We investigate the production of gamma-rays in the inverse Compton (IC) scattering process by leptons accelerated inside relativistic blobs in jets of active galactic nuclei. Leptons are injected homogeneously inside the spherical blob and initiate IC $e^\pm$ pair cascade in the synchrotron radiation (produced by the same population of leptons, SSC model), provided that the optical depth for gamma-rays is larger than unity. It is shown that for likely parameters internal absorption of gamma-rays has to be important. We suggest that new type of blazars might be discovered by the future simultaneous X-ray and $\gamma$-ray observations, showing peak emissions in the hard X-rays, and in the GeV $\gamma$-rays. Moreover, the considered scenario might be also responsible for the orphan X-ray flares recently reported from BL Lac type active galaxies.
We present a series of calculations aimed at examining how an inner system of planetesimals/protoplanets, undergoing terrestrial planet formation, evolves under the influence of a giant planet undergoing inward type II migration through the region bounded between 5 - 0.1 AU. We find that > 60% of the solids disk survives by being scattered by the giant planet into external orbits. Planetesimals are scattered outward almost as efficiently as protoplanets, resulting in the regeneration of a solids disk where dynamical friction is strong and terrestrial planet formation is able to resume. A simulation extended for a few Myr after the migration of the giant planet halted at 0.1 AU, resulted in an apparently stable planet of ~ 2 Earth masses forming in the habitable zone. Migration-induced mixing of volatile-rich material from beyond the `snowline' into the inner disk regions means that terrestrial planets that form there are likely to be water-rich. We predict that hot--Jupiter systems are likely to harbor water-rich terrestrial planets in their habitable zones. These planets may be detected by future planet search missions.
We study the acceleration and radiation of charged particles in the shock waves of supernova remnants using a recent version of the "box model". According to this, particles are accelerated in an energy-dependent region around the shock by the first order Fermi mechanism and lose energy through radiation. The particle distribution function is obtained from a spatially averaged kinetic equation that treats the energy losses self-consistently. There exists also a second population that consists of those particles that escape behind the shock where they also radiate. The energy distribution of this population is calculated in a similar manner. The application of the model to the supernova remnant RX J1713.7-3946, which was recently confirmed as a TeV source by H.E.S.S., shows that the X-ray emission can be attributed to electron synchrotron radiation while in gamma-rays there are contributions from both electrons and protons, with protons playing the dominant role. Additionally, there are strong indications that particles diffuse in turbulence that has a Kolmogorov spectrum.
We present a population synthesis study of NGC4435, an early-type Virgo galaxy interacting with NGC4438. We combine new spectroscopic observations obtained with the Spitzer Space Telescope IRS instrument with IRAC archival data and broad band data from the literature. The IRS spectrum shows prominent PAH features, low ionization emission lines and H_2 rotational lines arising from the dusty circumnuclear disk characterizing this galaxy. The central SED, from X-ray to radio, is well fitted by a model of an exponential burst superimposed on an old simple stellar population. From the lack of high excitation nebular lines, the [NeIII]15.5/[NeII]12.8 ratio, the temperature of molecular hydrogen, and the fit to the full X-ray to radio SED we argue that the present activity of the galaxy is driven by star formation alone. The AGN contribution to the ionizing flux is constrained to be less than 2%. The age of the burst is found to be around 190 Myr and it is fully consistent with the notion that the star formation process has been triggered by the interaction with NGC4438. The mass involved in the rejuvenation episode turns out to be less than 1.5% of the stellar galaxy mass sampled in a 5" central aperture. This is enough to render NGC4435 closely similar to a typical interacting early-type galaxy with inverted CaII[H+K] lines that will later turn into a typical cluster E+A galaxy and enforces the notion that these objects are the result of a recent rejuvenation episode rather than a genuine delayed formation.
Observatory libraries traditionally have maintained databases of publications resulting from usage of their facilities. In the era of electronic publication, the methodology of the creation of these databases has perforce changed as well. In this poster, we will compare a variety of methods for obtaining this information electronically and point out the advantages and shortcomings of each.
We report on our large scale search of 2MASS and SuperCOSMOS in the southern hemisphere for very widely separated white dwarf / L-dwarf binary systems and present our findings, including 8 widely separated candidate systems, and proper motion analysis confirming one of these as a widely separated white dwarf/ L-dwarf common proper motion binary candidate.
\integral and \sax observations of the neutron-star LMXB 4U~1705--44 have been analysed to deeply investigate the spectral state transitions nature. Its energy spectrum can be described as the sum of one or two blackbody, a 6.4-keV Fe line and a component due to thermal Comptonization. For the first time in this source, we find a strong signature of Compton reflection, presumably due to illumination of the optically-thick accretion disk by the Comptonized spectrum. Detection of two blackbody component in the soft states could originate in the disk and the neutron-star surface, and the Comptonized component arises from a hot inner flow with the seed photons coming from the disk and/or the neutron-star surface. The spectral transitions are shown to be associated with variations in the accretion rate, which changes in turn the temperature of the Comptonizing electrons and the strength of Compton reflection.
Recent INTEGRAL observations and archival BeppoSAX data have been analyzed to deeply investigate the hard X-ray behavior of the neutron star, atoll type, low mass X-ray Binary 4U1636-53. Our investigation in three different periods outline three corresponding different sates. Infact, the source was detected in both the canonical high and low state and moreover in one occasion \integral spectrum shows, for first time in this source, a hard tail dominating the emission above 30 keV. This spectrum is fitted as the sum of a Comptonized component similar to soft state and a power-law component ($\Gamma=2.76$), indicating the presence of a non thermal electron distribution of velocities.
Young galactic X-ray point sources (XPs) closely trace the ongoing star formation in galaxies. From measured XP number counts we extract the collective 2-10 keV luminosity of young XPs, L_yXP, which we use to gauge the current star-formation rate (SFR) in galaxies. We find that, for a sample of local star-forming galaxies (i.e., normal spirals and mild starbursts), L_yXP correlates linearly with the SFR over three decades in luminosity. A separate, high-SFR sample of starburst ULIRGs can be used to check the calibration of the relation. Using their (presumably SF-related) total 2-10 keV luminosities we find that these sources satisfy the SFR-L_yXP relation, as defined by the weaker sample, and extend it to span about 5 decades in luminosity. The SFR-L_yXP relation is likely to hold also for distant Hubble Deep Field North galaxies, especially so if these high-SFR objects are similar to the (more nearby) ULIRGs. It is argued that the SFR-L_yXP relation provides the most adequate X-ray estimator of instantaneous SFR by the phenomena characterizing massive stars from their birth (FIR emission from placental dust clouds) through their death as compact remnants (emitting X-rays by accreting from a close donor). For local, low/intermediate-SFR galaxies, the simultaneous existence of a correlation of the instantaneous SFR with the total 2-10 keV luminosity, which traces the SFR integrated over (approximately) the last Gyr, suggests that during such epoch the SF in these galaxies has been proceeding at a relatively constant rate.
We present a new mode of observations with VISIR, the mid-InfraRed (mid-IR) imager and spectrometer on the VLT (ESO, Chile): the so-called BURST mode. This mode allows to reach the diffraction limit of the telescope. To illustrate results obtained with this mode, we discuss observations of disks around Herbig Ae stars. These stars are the more massive analogues of T Tauri stars and are believed to harbour circumstellar disks. The 10-20 microns atmospheric windows are well-suited to study the extended emission of these objects. With a 8 m class telescope, in fair seeing conditions, the observations are diffraction-limited at 10 microns and the spatial resolution could reach the diffraction limit of 0.3 arcsec. As a result, it is possible to resolve disks with a typical size of 100 AU around objects at a distance of 100 pc. We present here a significant example, HD97048, for which a flared disk of 350 AU is resolved at 11.3 microns (PAH band).
We identify the radio-emitting shell-type supernova remnant G15.9+0.2 as a relatively young remnant containing an X-ray point source that may be its associated neutron star. The integrated spectrum of the remnant shell obtained from our 30 ks exploratory Chandra observation shows very strong lines that require elevated element abundances from ejecta, in particular of sulfur. A plane-shock model fit gives a temperature $kT = 0.9 (0.8, 1.0)$ keV, an ionization timescale $n_et = 6 (4, 9) \times 10^{10}$ cm$^{-3}$ s, and a sulfur abundance of 2.1 (1.7, 2.7) times solar (90% confidence limits). Two-component models with one solar and one enriched component are also plausible, but are not well constrained by the data. Various estimates give a remnant age of order $10^3$ yr, which would make G15.9+0.2 among the dozen or so youngest remnants in the Galaxy. The sparse point source spectrum is consistent with either a steep $\Gamma \sim$ 4 power law or a $kT \sim$ 0.4 keV blackbody. The spectrum is absorbed by a H column density $N_H \sim 4 \times 10^{22}$ cm$^{-2}$ similar to that required for the remnant shell. The implied 2--9.5 keV source luminosity is about $10^{33}$ ergs s$^{-1}$ for an assumed distance of 8.5 kpc consistent with the high absorption column. We suggest that the point source is either a rotation-powered pulsar or a compact central object (CCO).
The archival spectrum of SDSS J212531.92-010745.9 shows not only the typical signature of a PG1159 star, but also indicates the presence of a companion. With time-series photometry of SDSS J212531.92-010745.9 during 10 nights, spread over one month, with the T"ubingen 80cm and the G"ottingen 50cm telescopes, the binary nature of this object has recently been proven. An orbital period of 6.9h could be determined, and the observed light curve fitted with the nightfall program. A comparison of the spectrum of SDSS J212531.92-010745.9 with NLTE models further constrained the light curve solution. We emphasize that this is the first system of this kind which will allow a dynamical mass determination for a PG1159 star.
We report INTEGRAL/IBIS results on temporal and spectral behaviour of the Low Mass X-ray Binary XB 1832-330 located in the globular cluster NGC 6652. During the 2003-2005 monitoring of the Galactic Centre, the source shows a weak flux variability and an everage flux in the 20-150 keV of about 2*10^{-10} erg s^{-1} cm^{-2}. The overall energy spectrum extends up to 150 keV and is well described by a Comptonization model with an electrons temperature of $\sim$ 22 keV and a plasma optical depth of 1.8. We thus confirm the persistent nature of this burtser.
Nine quasar absorption spectra at 21-cm and UV rest-wavelengths are used to estimate possible variations in x=alpha^2 g_p mu, (alpha is the fine structure constant, g_p the proton g-factor and mu=me/mp the electron-to-proton mass ratio). We find <Delta x/x>^weighted_total(=Dxxwt)=(0.63+-0.99) 10^-5 over 0.23~<z_abs~<2.35 (2.7 to 10.5 Gyr, look-back time, t_lb). A linear best fit against t_lb, tied to Delta x/x=0 at z=0, gives (dot x)/x=(-0.6+-1.2) 10^-15 /yr. Our large sample demonstrates that intrinsic line-of-sight velocity differences between the 21-cm and UV absorption redshifts, (on average Delta_vlos~6km/s), with random sign and magnitude in each absorption system, limit our precision. Combining our Delta x/x measurement with absorption-line constraints on alpha-variation yields strong limits on the variation of mu. Our most conservative estimate, obtained by assuming no variations in alpha or g_p is Delta mu/mu(=Dmm)=Dxxwt. If we use only the four high-redshift absorbers in our sample, we obtain Dmm=(0.58+-1.95) 10^-5, which agrees (2sigma) with recent, more direct estimates from two absorption systems containing molecular hydrogen, also at high redshift, and which have hinted at a possible mu-variation, Dmm=(-2.0+-0.6) 10^-5. Our method of constraining Dmm is completely independent from the molecular hydrogen observations. If we include the low-redshift systems, our Dmm result differs significantly from the high-redshift molecular hydrogen results. We detect a dipole variation in mu across the sky, but this model is required by the data at only the 88 per cent confidence level. Clearly, much larger samples of 21-cm and molecular hydrogen absorbers are required to adequately resolve the issue of the variation of mu and x.(Abridged)
The chromosphere in internetwork regions of the quiet Sun was regarded as a static and homogeneous layer for a long time. Thanks to advances in observations and numerical modelling, the wave nature of these atmospheric regions received increasing attention during the last decade. Recent three-dimensional radiation magnetohydrodynamic simulations with CO5BOLD feature the chromosphere of internetwork regions as a dynamic and intermittent phenomenon. It is a direct product of interacting waves that form a mesh-like pattern of hot shock fronts and cool post-shock regions. The waves are excited self-consistently at the top of the convection zone. In the middle chromosphere above an average height of 1000 km, plasma beta gets larger than one and magnetic fields become more important. The model chromosphere exhibits a magnetic field that is much more homogeneous than in the layers below and evolves much faster. That includes fast propagating (MHD) waves. Further improvements of the simulations like time-dependent hydrogen ionisation are currently in progress. This class of models is capable of explaining apparently contradicting diagnostics such as carbon monoxide and UV emission at the same time.
The 4-200 keV spectral and temporal behaviour of the low mass X-ray binary 4U 1820-30 has been studied with INTEGRAL during 2003-2005. This source as been observed in both the soft (banana) and hard (island) spectral states. A high energy tail above 50 keV in the hard state has been revealed for the first time. This places the source in the category of X-ray bursters showing high-energy emission. The tail can be modeled as a soft power law component, with the photon index of ~ 2.4, on top of thermal Comptonization emission from a plasma with the electron temperature of kT_e ~ 6 keV and optical depth of $\tau ~ 4. Alternatively, but at a lower goodness of the fit, the hard-state broad band spectrum can be accounted for by emission from a hybrid, thermal-nonthermal, plasma. During the observations, the source spent most of the time in the soft state, as previously reported and the $\ge$4 keV spectra can be represented by thermal Comptonization with kT_e ~ 3 keV and $\tau ~ 6-7.
We study, by means of dedicated simulations of massive black hole build-up, the possibility to constraint the existence and nature of the AGN population at z>6 with available and planned X-ray and near infrared space telescopes. We find that X-ray deep-field observations can set important constraints to the faint-end of the AGN luminosity function at very high redshift. Planned X-ray telescopes should be able to detect AGN hosting black holes with masses down to >10^5 Msun (i.e., X-ray luminosities in excess of 10^42 erg s^-1), and can constrain the evolution of the population of massive black hole at early times (6<z<10). We find that this population of AGN should contribute substantially (~25%) to the unresolved fraction of the cosmic X-ray background in the 0.5-10 keV range, and that a significant fraction (~3-4%) of the total background intensity would remain unaccounted even after future X-ray observations. As byproduct, we compute the expected UV background from AGN at z>6 and we discuss the possible role of AGN in the reionization of the Universe at these early epochs, showing that AGN alone can provide enough ionizing photons only in the (improbable) case of an almost completely homogeneous inter-galactic medium. Finally, we show that super-Eddington accretion, suggested by the observed QSOs at z>6, must be a very rare event, confined to black holes living in the highest density peaks.
Selection effects in cosmology are often invoked to "explain" why some of the fundamental constant of Nature, and in particular the cosmological constant, take on the value they do in our Universe. We briefly review this probabilistic "anthropic reasoning" and we argue that different (equally plausible) ways of assigning probabilities to candidate universes lead to totally different anthropic predictions, presenting an explicit example based on the total number of possible observations observers can carry out. We conclude that in absence of a fundamental motivation for selecting one weighting scheme over another the anthropic principle cannot be used to explain the value of Lambda. .
We have previously shown that spherically symmetric, inhomogeneous universe models can explain both the supernova data and the location of the first peak in the CMB spectrum without resorting to dark energy. In this work, we investigate whether it is possible to get an even better fit to the supernova data by allowing the observer to be positioned away from the origin in the spherically symmetric coordinate system. In such a scenario, the observer sees an anisotropic relation between redshifts and the luminosity distances of supernovae. The level of anisotropy allowed by the data will then constrain how far away from the origin the observer can be located, and possibly even allow for a better fit. Our analysis shows that the fit is indeed improved, but not by a significant amount. Furthermore, it shows that the supernova data do not place a rigorous constraint on how far off-center the observer can be located.
The interaction of optically emitting clouds with warm X-ray gas and hot, tenuous radio plasma in radio jet cocoons is modelled by 2D compressible hydrodynamic simulations. The initial setup is the Kelvin-Helmholtz instability at a contact surface of density contrast 10,000. The denser medium contains clouds of higher density. Optically thin radiation is realised via a cooling source term. The cool phase effectively extracts energy from the other gas which is both, radiated away and used for acceleration of the cold phase. This increases the system's cooling rate substantially and leads to a massively amplified cold mass dropout. We show that it is feasible, given small seed clouds of order 100 solar masses, that all of the optically emitting gas in a radio jet cocoon may be produced by this mechanism on the propagation timescale of the jet. The mass is generally distributed as T^-1/2 with temperature, with a prominent peak at 14,000 K. This peak is likely to be related to the counteracting effects of shock heating and a strong rise in the cooling function. The volume filling factor of cold gas in this peak is of the order 10^-5 to 10^-3 and generally increases during the simulation time. We find an isotropic scale free energy spectrum as expected for shock dominated turbulence and the same Mach-number density relation as Kritsuk & Norman (2004). We show that this relation may explain the velocity widths of emission lines associated with high redshift radio galaxies, if the environmental temperature is lower, or the jet-ambient density ratio is less extreme than in their low redshift counterparts.
We report on new results of our multiplicity study and present our follow-up observations of the recently detected faint companion HD3651B, the first directly imaged T dwarf companion of an exoplanet host star.
We report signal-to-noise ratio SNR ~ 100 optical spectra for four DA white dwarf stars acquired with the GMOS spectrograph of the 8m Gemini north telescope. These stars have 18<g<19 and are around Teff ~ 12000 K, were the hydrogen lines are close to maximum. Our purpose is to test if the effective temperatures and surface gravities derived from the relatively low signal-to-noise ratio (<SNR> ~ 21) optical spectra acquired by the Sloan Digital Sky Survey through model atmosphere fitting are trustworthy. Our spectra range from 3800A to 6000A, therefore including H beta to H9. The H8 line was only marginally present in the SDSS spectra, but is crucial to determine the gravity. When we compare the values published by Kleinman et al. (2004) and Eisenstein et al. (2006) with our line-profile (LPT) fits, the average differences are: Delta Teff ~ 320 K, systematically lower in SDSS, and Delta log g ~ 0.24 dex, systematically larger in SDSS. The correlation between gravity and effective temperature can only be broken at wavelengths bluer than 3800 A. The uncertainties in Teff are 60% larger, and in log g larger by a factor of 4, than the Kleinman et al. (2004) and Eisenstein et al. (2006) internal uncertainties.
We briefly review the properties of quasi-normal modes of neutron stars and black holes. We analyse the consequences of a possible detection of such modes via the gravitational waves associated with them, especially addressing our study to the Brazilian spherical antenna, on which a possible detection would occur at 3.0-3.4 kHz. A question related to any putative gravitational wave detection concerns the source that produces it. We argue that, since the characteristic damping times for the gravitational waves of neutron stars and black holes are different, a detection can distinguish between them, and also distinguish the neutron stars oscillating modes. Moreover, since the source can be identified by its characteristic damping time, we are able to extract information about the neutron star or black hole. This information would lead, for example, to a strong constraint in the nuclear matter equation of state, namely the compression modulus should be K=220 MeV.
There has been some recent activity in trying to understand the dark matter clustering properties in the quasilinear regime, through resummation of perturbative terms, otherwise known as the renormalized perturbation theory (astro-ph/0509418), or the renormalization group method (astro-ph/0606028). While it is not always clear why such methods should work so well, there is no reason for them to capture non-perturbative events such as shell-crossing. In order to estimate the magnitude of non-perturbative effects, we introduce a (hypothetical) model of sticky dark matter, which only differs from collisionless dark matter in the shell-crossing regime. This enables us to show that the level of non-perturbative effects in the dark matter power spectrum at k ~ 0.1 Mpc^{-1}, which is relevant for baryonic acoustic oscillations, is about a percent, but rises to order unity at k ~ 1 Mpc^{-1}.
We have obtained optical spectrophotometry of the evolution of comet 9P/Tempel 1 after the impact of the Deep Impact probe, using the Supernova Integral Field Spectrograph (SNIFS) at the UH 2.2m telescope, as well as simultaneous optical and infrared spectra using the Lick Visible-to-Near-Infrared Imaging Spectrograph (VNIRIS) spectrograph. The spatial distribution and temporal evolution of the "violet band" CN (0-0) emission and of the 630 nm [OI] emission was studied. We found that CN emission centered on the nucleus increased in the two hours after impact, but that this CN emission was delayed compared to the light curve of dust-scattered sunlight. The CN emission also expanded faster than the cloud of scattering dust. The emission of [OI] at 630 nm rose similarly to the scattered light, but then remained nearly constant for several hours after impact. On the day following the impact, both CN and [OI] emission concentrated on the comet nucleus had returned nearly to pre-impact levels. We have also searched for differences in the scattering properties of the dust ejected by the impact compared to the dust released under normal conditions. Compared to the pre-impact state of the comet, we find evidence that the color of the comet was slightly bluer during the post-impact rise in brightness. Long after the impact, in the following nights, the comet colors returned to their pre-impact values. This can be explained by postulating a change to a smaller particle size distribution in the ejecta cloud, in agreement with the findings from mid-infrared observatons, or by postulating a large fraction of clean ice particles, or by a combination of these two.
We have performed a set of high resolution, three dimensional simulations of a jetted AGN embedded in a relaxed cooling cluster. To the best of our knowledge, these are the first simulation to include both full jet dynamics and a feedback model. These ideal hydrodynamic simulations show that, although there is enough energy present to offset cooling on average, the jet heating is not spatially deposited in a way that can prevent catastrophic cooling of the cluster.
Warm inflationary universe models in a tachyon field theory are studied. General conditions required for these models to be realizable are derived and discussed. We describe scalar perturbations (in the longitudinal gauge) and tensor perturbations for these scenarios. We develop our models for a constant dissipation parameter $\Gamma$ in one case and one dependent on $\phi$ in the other case. We have been successful in describing such of inflationary universe models. We use recent astronomical observations for constraining the parameters appearing in our model. Also, our results are compared with their analogous found in the cool inflationary case.
It is shown how pair production itself would almost certainly prevent the astrophysical formation of macroscopic dyadospheres, hypothetical regions, extending many electron Compton wavelengths in all directions, where the electric field exceeds the critical value for microscopically rapid Schwinger pair production. Pair production is a self-regulating process that would discharge a growing electric field, in the example of a hypothetical collapsing charged stellar core, before it reached 6% of the minimum dyadosphere value, keeping the pair production rate more than 26 orders of magnitude below the dyadosphere value, and keeping the efficiency below 0.0002 (M/M_sun)^{1/2}.
A widely considered characteristic of extra-solar planetary systems has been a seeming tendency for major axes of adjacent orbits to librate in stable configurations. Based on a new catalog of extra-solar planets (Butler et al. 2006) and our numerical integrations, we find that such small amplitude oscillations are actually not common, but in fact quite rare; most pairs of planets' major axes a re consistenet with circulating relative to one another. However, the new result s are consistent with studies that find that two-planet systems tend to lie near a separatrix between libration and circulation. Similarly, in systems of more than two planets, many adjacent orbits lie near a separatrix that divides modes of circulation.
We present the first study of the dynamical evolution of an isolated star cluster that combines a significant population of primordial binaries with the presence of a central black hole. We use equal-mass direct N-body simulations, with N ranging from 4096 to 16384 and a primordial binary ratio of 0-10%; the black hole mass is about one percent of the total mass of the cluster. The evolution of the binary population is strongly influenced by the presence of the black hole, which gives the cluster a large core with a central density cusp. Starting from a variety of initial conditions (Plummer and King models), we first encounter a phase, that last approximately 10 half-mass relaxation times, in which binaries are disrupted faster compared to analogous simulations without a black hole. Subsequently, however, binary disruption slows down significantly, due to the large core size. The dynamical interplay between the primordial binaries and the black hole thus introduces new features with respect to the scenarios investigated so far, where the influence of the black hole and of the binaries have been considered separately. A large core to half mass radius ratio appears to be a promising indirect evidence for the presence of a intermediate-mass black hole in old globular clusters.
We study the simple-stellar-population-equivalent (SSP-equivalent) age and chemical composition measured from the Lick/IDS line-strength indices of composite stellar populations (CSP). We build two sets of ~30000 CSP models using stellar populations synthesis models, combining an old population and a young population with a range of ages and chemical compositions representative of early-type galaxies. We investigate how the SSP-equivalent stellar parameters of the CSP's depend on the stellar parameters of the two input populations; how they depend on V-band luminosity-weighted stellar parameters; and how SSP-equivalent parameters derived from different Balmer-line indices can be used to reveal the presence of a young population on top of an old one. We find that the SSP-equivalent age depends primarily on the age of the young population and on the mass fraction of the two populations, and that the SSP-equivalent chemical composition depends mainly on the chemical composition of the old population. Furthermore, while the SSP-equivalent chemical composition tracks quite closely the V-band luminosity weighted one, the SSP-equivalent age does not and is strongly biased towards the age of the young population. In this bias the age of the young population and the mass fraction between old and young population are degenerate. Finally, assuming typical error bars, we find that a discrepancy between the SSP-equivalent parameters determined with different Balmer-line indices can reveal the presence of a young stellar population on top of an old one as long as the age of the young population is less than ~2.5 Gyr and the mass fraction of young to old population is between 1% and 10%. Such disrepancy is larger at supersolar metallicities.
The high energy end of gamma-ray source spectra might provide important clues regarding the nature of the processes involved in gamma-ray emission. Several galactic sources with hard emission spectra extending up to more than 30TeV have already been reported. Measurements around 100TeV and above should be an important goal for the next generation of high energy gamma-ray astronomy experiments. Here we present several techniques providing the required exposure (100 km^2.h). We focus our study on three Imaging Atmospheric Cherenkov Technique (IACT) based approaches: low elevation observations, large field of view telescopes, and large telescope arrays. We comment on the advantages and disadvantages of each approach and report simulation based estimates of their energy ranges and sensitivities.
Many problems in astrophysics involve relativistic outflows. The plasma dynamics in these scenarios is critical to determine the conditions for the self-consistent evolution of the fields and particle acceleration. Advances in computer power now allow for kinetic plasma simulations, based on the particle-in-cell (PIC) paradigm, capable of providing information about the role of plasma instabilities in relativistic outflows. A discussion of the key issues associated with PIC simulations is presented, along with some the most important results and open questions, with a particular emphasis on the long time evolution of the filamentation, or Weibel, instability, and on the possible collisionless mechanisms for particle acceleration arising in the collision of relativistic plasma shells.
This paper investigates the peculiar behaviour of the light even (alpha-elements) and odd atomic number elements in red giants in the galactic bulge, both in terms of the chemical evolution of the bulge, and in terms of possible deep-mixing mechanisms in these evolved stars. Using UVES on VLT, we measure the abundances of the four light elements O, Na, Mg and Al in 13 red clump and 40 red giant branch stars in four fields spanning the bulge from b=-3 to -12\deg. We show that the resulting abundance patterns point towards a chemical enrichment dominated by massive stars at all metallicities. O, Mg and Al ratios with respect to iron are overabundant with respect to both galactic disks (thin and thick) for [Fe/H]$>-0.5$. A formation timescale for the galactic bulge shorter than for both the thin and thick disks is therefore inferred. Using Mg as a proxy for metallicity (instead of Fe) we further show that: (i) the bulge stars [O/Mg] ratio follows and extend to higher metallicities the decreasing trend of [O/Mg] found in the galactic disks. (ii) the [Na/Mg] ratio trend with increasing [Mg/H] is found to increase in three distinct sequences in the thin disk, the thick disk and the bulge. The bulge trend is well represented by the predicted metallicity-dependent yields of massive stars, whereas the galactic disks have too high Na/Mg ratios at low metallicities, pointing to an additional source of Na from AGB stars. (iii) Contrary to Na, there appears to be no systematic difference in the [Al/Mg] ratio between bulge and disk stars, and the theoretical yields by massive stars agree with the observed ratios, leaving no space for AGB contribution to Al.
We propose a new method of analysing a variable component for type 1 active galactic nuclei (AGNs) in the near-infrared wavelength region. This analysis uses a multiple regression technique and divides the variable component into two components originating in the accretion disk at the center of AGNs and from the dust torus that far surrounds the disk. Applying this analysis to the long-term $VHK$ monitoring data of MCG+08-11-011 that were obtained by the MAGNUM project, we found that the $(H-K)$-color temperature of the dust component is $T = 1635$K $\pm20$K, which agrees with the sublimation temperature of dust grains, and that the time delay of $K$ to $H$ variations is $\Delta t\approx 6$ days, which indicates the existence of a radial temperature gradient in the dust torus. As for the disk component, we found that the power-law spectrum of $f_\nu \propto \nu^\alpha$ in the $V$ to near-infrared $HK$ bands varies with a fixed index of $\alpha\approx -0.1$ -- +0.4, which is broadly consistent with the irradiated standard disk model. The outer part of the disk therefore extends out to a radial distance where the temperature decreases to radiate the light in the near-infrared.
We investigate polarization of high-energy emissions from the Crab pulsar in
the frame work of the outer gap accelerator, following previous works of Cheng
and coworkers. The recent version of the outer gap, which extends from inside
the null charge surface to the light cylinder, is used for examining the
synchrotron radiations from the secondary and the tertiary pairs, which are
produced outside the gap. We calculate the light curve, the spectrum and the
polarization characteristics, simultaneously, by taking into account gyration
motion of the particles. The polarization position angle curve and the
polarization degree are calculated to compare with the Crab optical data. We
demonstrate that the radiations from inside the null charge surface make
outer-wing and off-pulse emissions in the light curve, and the tertiary pairs
contribute to bridge emissions. The emissions from the secondary pairs explain
the main features of the observed light curve and spectrum.
On the other hand, both emissions from inside the null charge surface and from
the tertiary pairs are required to explain the optical polarization behavior of
the Crab pulsar. The energy dependence of the polarization features is expected
by the present model. For the Crab pulsar, the polarization position angle
curve indicates that the viewing angle of the observer measured from the
rotational axis is greater than $90^{\circ}$.
We use very deep near-infrared imaging data taken with Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the Subaru Telescope to investigate the number counts of Distant Red Galaxies (DRGs). We have observed a 4x7 arcmin^2 field in the Great Observatories Origins Deep Survey North (GOODS-N), and our data reach J=24.6 and K=23.2 (5sigma, Vega magnitude). The surface density of DRGs selected by J-K>2.3 is 2.35+-0.31 arcmin^-2 at K<22 and 3.54+-0.38 arcmin^-2 at K<23, respectively. These values are consistent with those in the GOODS-South and FIRES. Our deep and wide data suggest that the number counts of DRGs turn over at K~22, and the surface density of the faint DRGs with K>22 is smaller than that expected from the number counts at the brighter magnitude. The result indicates that while there are many bright galaxies at 2<z<4 with the relatively old stellar population and/or heavy dust extinction, the number of the faint galaxies with the similar red color is relatively small. Different behaviors of the number counts of the DRGs and bluer galaxies with 2<z_phot<4 at K>22 suggest that the mass-dependent color distribution, where most of low-mass galaxies are blue while more massive galaxies tend to have redder colors, had already been established at that epoch.
We present spectroscopic observations for quasars Q0107-025A, Q0107-025B, and Q0107-0232. For the first time, all data obtained with the Hubble Space Telescope's GHRS and FOS for these three quasars are combined. Ly-alpha absorbers selected from the spectra can be used to trace the coherence of the intergalactic medium (IGM) on scales of 1-2 h_{70}^{-1} Mpc over the redshift range 0.4 < z_a < 0.9. A new analysis of double and triple absorber coincidences derived from the improved spectra is performed. Automated line-selection algorithms were used to detect absorption lines in the QSO spectra; coincident absorbers were identified across two and three sight lines based on their proximity to each other in velocity space. A control simulation designed to generate artificial absorption-line spectra was used to gauge the significance of the coincidences. Four intervening metal line absorption systems are detected, with three of the four coincident to the A and B sight lines and one coincident across all three sight lines. This is evidence for substantial clustering among the objects responsible for the metal-enriched gas. By contrast, large scale coherence of the IGM gas is detectable but weak. Fewer than half of the absorbers are coincident on scales of 1-2 h_{70}^{-1} Mpc, a result that is significant at the 99% confidence level, and coherence arises preferentially in the higher column density gas. Triple absorber coincidences occur at a level that is significant at the 99% confidence level, which indicates that the higher column density gas has a planar geometry.
A machine capable of digitizing two 8 inch by 10 inch (203 mm by 254 mm) glass astrophotographic plates or a single 14 inch by 17 inch (356 mm by 432 mm) plate at a resolution of 11 microns per pixel or 2309 dots per inch (dpi) in 92 seconds is described. The purpose of the machine is to digitize the \~500,000 plate collection of the Harvard College Observatory in a five year time frame. The digitization must meet the requirements for scientific work in astrometry, photometry, and archival preservation of the plates. This paper describes the requirements for and the design of the subsystems of the machine that was developed specifically for this task.
The aim of this work is to identify the so far unknown low mass stellar population of the ~2Myr old Cygnus OB2 region, and to investigate the X-ray and near-IR stellar properties of its members. We analyzed a 97.7 ksec Chandra ACIS-I observation pointed at the core of the Cygnus OB2 region. X-ray variability ans spectral analysis of sources was characterized through the KS-test and XSPEC thermal models, respectively. We detected 1003 X-ray sources. Of these, 775 have near-IR counterparts associated with Cygnus OB2 members. We estimate a typical absorption toward Cygnus OB2 of Av~7.0 mag. Although the region is young, very few stars (~4.4 %) show disk-induced excesses in the near-IR. X-ray variability is detected in ~13 % of the sources. Flares account for at least 60 % of the variability. O- that early B-type stars are not significantly variable. Typical X-ray spectral parameters are log(Nh)~22.25 and kT~1.35 keV. Variable and flaring sources have harder spectra with median kT=3.3 and 3.8 keV, respectively. OB stars are typically softer (kT~0.75 keV). X-ray luminosities range between 1E+30 and 1E+31 erg/s for intermediate- and low-mass stars, and 2.5x10^30 and between 6.3E+33 erg/s for OB stars. The Cygnus OB2 region has a very rich population of low-mass X-ray emitting stars. Circumstellar disks seem to be very scarce.
The differential rotation of the F5V-IV star Procyon A is computed for a class of models which are consistent with recent astrometric and asteroseismic data. The rotation pattern is determined by solving the Reynolds equation for motion, including the convective energy transport, where the latter is anisotropic owing to the Coriolis force action which produces a horizontal temperature gradient between the poles and the equator. All the models show a decrease of the rotation rate with increasing radius and solar-type isorotation surfaces with the equator rotating faster than the poles, the horizontal rotational shear being much smaller for models with a less extended convective envelope. The meridional flow circulation can be either clockwise or counter-clockwise, and in some cases a double latitudinal cell appears. The rotational splittings are calculated for low degree $p$-modes with $l=1, m=1$ and $l=2, m=1,2$, and it is shown that, for modes with $m=1$, the stronger is the horizontal differential rotation shear the weaker the effect on the average rotational splitting expected, whilst the opposite happens for the mode with $m=2$. On the basis of the present study, a resolution of $10 \rm nHz$ in individual oscillation frequencies seems to be necessary to test the different dynamical behaviour of the proposed models, that appears barely achievable even in the forthcoming space missions. However, the average over several observed splittings could produce the required accuracy.
Context: The comparison of observed counts in a given sky direction with predictions by Galactic models yields constraints to the spatial distribution and the stellar birthrate of young stellar populations. In this work we present the results of the analysis of the stellar content of the XMM-Newton Bright Serendipitous Survey (XBSS). This unbiased survey includes a total of 58 stellar sources selected in the 0.5 -- 4.5 keV energy band, having a limiting sensitivity of $10^{-2}$ cnt s$^{-1}$ and covering an area of 28.10 sq. deg. Aims: Our main goal is to understand the recent star formation history of the Galaxy in the vicinity of the Sun. Methods: We compare the observations with the predictions obtained with XCOUNT, a model of the stellar X-ray content of the Galaxy. The model predicts the number and properties of the stars to be observed in terms of magnitude, colour, population and $f_\mathrm{x}/f_\mathrm{v}$ ratio distributions of the coronal sources detected with a given instrument and sensitivity in a specific sky direction. Results: As in other shallow surveys, we observe an excess of stars not predicted by our Galaxy model. Comparing the colours of the identified infrared counterparts with the model predictions, we observe that this excess is produced by yellow (G+K) stars. The study of the X-ray spectrum of each source reveals a main population of stars with coronal temperature stratification typical of intermediate-age stars. As no assumptions have been made for the selection of the sample, our results must be representative of the entire Solar Neighbourhood. Some stars show excess circumstellar absorption indicative of youth.
We present optical images of nearby 50 narrow-line Seyfert 1 galaxies (NLS1s) which cover all the NLS1s at z<0.0666 and $\delta \ge -25^{\circ}$ known at the time of 2001. Among the 50 NLS1s, 40 images are newly obtained by our observations and 10 images are taken from archive data. Motivated by the hypothesis that NLS1s are in an early phase of a super-massive black hole (BH) evolution, we present a study of NLS1 host galaxy morphology to examine trigger mechanism(s) of active galactic nuclei (AGNs) by seeing the early phase of AGN. With these images, we made morphological classification by eye inspection and by quantitative method, and found a high bar frequency of the NLS1s in the optical band; the bar frequency is $85 \pm 7% among disk galaxies ($64- 71$% in total sample) which is more frequent than that (40-70%) of broad-line Seyfert 1 galaxies (BLS1s) and normal disk galaxies, though the significance is marginal. Our results confirm the claim by Crenshaw et al. (2003) with a similar analysis for 19 NLS1s. The frequency is comparable to that of HII/starburst galaxies. We also examined the bar frequency against width of the broad H$\beta$ emission line, Eddington ratio, and black hole mass, but no clear trend is seen. Possible implications such as an evolutionary sequence from NLS1s to BLS1 are discussed briefly.
The striking broad emission line spectroscopic appearance of Wolf-Rayet stars have long defied analysis due to the extreme physical conditions of their line and continuum forming regions. Recently, model atmosphere studies have advanced sufficiently to enable the determination of stellar temperatures, luminosities, elemental abundances, ionizing fluxes and wind properties. The observed distribution of nitrogen (WN) and carbon (WC) sequence WR stars in the Milky Way and nearby star forming galaxies is discussed, from which lower limits to progenitor masses are 25, 40, 75 Msun for hydrogen-depleted (He-burning) WN, WC, and H-rich (H-burning) WN stars, respectively. WR stars in massive binaries permit studies of wind-wind interactions and dust formation in WC systems, plus current mass determinations, revealing typically 10-25 Msun, although extending up to 80Msun for H-rich WN stars. Theoretical and observational evidence in favour of a metallicity dependence of WR winds is presented, with implications for evolutionary models, ionizing fluxes, and the role of WR stars within the context of core-collapse supernovae and long-duration gamma ray bursts.
We present the results of some recent research on AM CVn systems. We present: X-ray/UV observations made using XMM-Newton; the X-ray grating spectrum of RX J1914+24; preliminary results of a search for radio emission from AM CVn binaries, and discuss the strategy and first results of the RATS project, whose main aim is to discover AM CVn systems.
In five years of operation, data from INTEGRAL has been used to discover a large number of gamma-ray sources, a substantial fraction of which have turned out to be active galactic nuclei (AGN). Recently Bassani et al. (2006) have presented a sample of around 60 AGNs of which some still lack optical identification or information in the X-ray band. In this work we present X-ray data for 8 objects acquired with the XRT telescope on-board Swift satellite. The XRT positioning has allowed us to identify the optical counterparts and to classify their types through follow-up measurements. Analysis of these data has also provided information on their spectra below 10 keV.
We constrain the spectral ages for two very asymmetric Compact Symmetric Objects (CSO) from the B3-VLA-CSS sample, and we investigate the role of the ambient medium potentially able to influence the individual source evolution. Multi-frequency VLBA observations have been carried out to study the distribution of the break frequency of the spectra across different regions of each source. From the analysis of synchrotron spectra and assuming an equipartition magnetic field, we find radiative ages of about 2x10^3 and 10^4 years for B0147+400 and B0840+424, respectively. The derived individual hot-spot advance speed is in the range between 0.03c and 0.3c, in agreement with kinematic studies carried out on other CSOs. The very asymmetric morphology found in both sources is likely related to an inhomogeneous ambient medium in which the sources are growing, rather than to different intrinsic hot-spot pressures on the two sides.
\abridged The nuclei of active galaxies harbor massive young stars, an accreting central black hole, or both. In order to determine the physical conditions that pertain to molecular gas close to the sources of radiation, numerical models are constructed. These models determine the thermal and chemical balance of molecular gas that is exposed to X-rays and far-ultraviolet radiation, as a function of depth. We present a grid of XDR and PDR models that span ranges in density, irradiation and column density. We find that the fine-structure line ratios of e.g. [SiII] 35mum/[CII] 158 mum are larger in XDRs than in PDRs, for a given density, column and irradiation strength. We find that the line ratios HCN/HCO+ and HNC/HCN, as well as the column density ratio CN/HCN, discriminate between PDRs and XDRs. The HCN/HCO+ 1-0 ratio is <1 (>1) for XDRs (PDRs) if the density exceeds 10^5 cm^-3 and if the column density is >10^23 cm^-2. For columns <10^ 22.5 cm^-2 the XDR HCN/HCO+ 1-0 ratio becomes larger than one, although the individual HCN 1-0 and HCO+ 1-0 line intensities are weaker. For modest densities, n=10^4-10^5 cm^-3, and strong radiation fields (>100 erg s^-1 cm^-2), HCN/HCO+ ratios can become larger in XDRs than PDRs as well. The HCN/CO 1-0 ratio is typically smaller in XDRs, and the HCN emission in XDRs is boosted with respect to CO only for columns >10^{23} cm^{-2} and densities <10^4 cm^-3. CO is typically warmer in XDRs than in PDRs, for the same total energy input. This leads to higher CO J=N+1-N/CO 1-0, N>=1, line ratios in XDRs. Lines with N>=10, like CO(16-15) and CO(10-9) observable with HIFI/Herschel, discriminate very well between XDRs and PDRs. Column density ratios indicate that CH, CH+, NO, HOC+ and HCO are good PDR/XDR discriminators.
We investigate the impact of instrumental systematic errors on the potential of cosmic microwave background polarization experiments targeting primordial B-modes. To do so, we introduce spin-weighted Muller matrix-valued fields describing the linear response of the imperfect optical system and receiver, and give a careful discussion of the behaviour of the induced systematic effects under rotation of the instrument. We give the correspondence between the matrix components and known optical and receiver imperfections, and compare the likely performance of pseudo-correlation receivers and those that modulate the polarization with a half-wave plate. The latter is shown to have the significant advantage of not coupling the total intensity into polarization for perfect optics, but potential effects like optical distortions that may be introduced by the quasi-optical wave plate warrant further investigation. A fast method for tolerancing time-invariant systematic effects is presented, which propagates errors through to power spectra and cosmological parameters. The method extends previous studies to an arbitrary scan strategy, and eliminates the need for time-consuming Monte-Carlo simulations in the early phases of instrument and survey design. We illustrate the method with both simple parametrized forms for the systematics and with beams based on physical-optics simulations. Example results are given in the context of next-generation experiments targeting tensor-to-scalar ratios r ~ 0.01.
AIMS: We present data from the CFHTLS Strong Lensing Legacy Survey (SL2S). Due to the unsurpassed combined depth, area and image quality of the Canada-France-Hawaii Legacy Survey it is becoming possible to uncover a large, statistically well-defined sample of strong gravitational lenses which spans the dark halo mass spectrum predicted by the concordance model from galaxy to cluster haloes. METHODS: We describe the development of several automated procedures to find strong lenses of various mass regimes in CFHTLS images. RESULTS: The preliminary sample of about 40 strong lensing candidates discovered in the CFHTLS T0002 release, covering an effective field of view of 28 deg$^2$ is presented. These strong lensing systems were discovered using an automated search and consist mainly of gravitational arc systems with splitting angles between 2 and 15 arcsec. This sample shows for the first time that it is possible to uncover a large population of strong lenses from galaxy groups with typical halo masses of about $10^{13}h^{-1}M_\odot$. We discuss the future evolution of the SL2S project and its main scientific aims for the next 3 years, in particular our observational strategy to extract the hundreds of gravitational rings also present in these fields.
We discuss preliminary results from our programme to map the fields of high-redshift AGN. In the context of the hierarchical models such fields are predicted to contain an over-density of young, luminous galaxies destined to evolve into the core of a rich cluster by the present epoch. We have thus imaged from submillimetre to X-ray wavelengths the few-arcmin scale fields of a small sample of high-redshift QSOs. We find that submillimetre wavelength data from SCUBA show striking over-densities of luminous star-forming galaxies over scales of ~500 kpc. Whilst many of these galaxies are undetected even in deep near-IR imaging almost all of them are detected by Spitzer at 4.5, 8.0 and 24 um, showing that they have extremely red colours. However, they are not detected in our XMM-Newton observations suggesting that any AGN must be highly obscured. Optical-through-mid-IR SEDs show the redshifted 1.6 um bump from star-light giving preliminary evidence that the galaxies lie at the same redshift, and thus in the same structure, as the QSO although this finding must be confirmed with photometric and/or spectroscopic redshifts.
We discuss the potential of high sensitivity mid-IR and far-IR spectroscopy to proof the physical properties of active nuclei and starburst regions of local and distant galaxies. For local galaxies, it will be possible to map the discs and ISM through the low ionization ionic lines and a variety of molecular tracers, such as OH, H2O and high-J CO. At increasing distance, most of the ionic nebular lines (typical of stars and AGNs) are shifted into the FIR, making possible to compare the observed spectra with those predicted by different evolutionary scenarios. At the very high redshift of 10-15, sensitive mid-to-far-IR spectrometers, such as those planned to be at the focal plane of the future SPICA mision, could be adequate to detect the H recombination lines excited in the HII regions around population III stars, if these stars happened to reside in large clusters of more than 10^5 members.
We present the first direct magnetic field measurements on M dwarfs cooler than spectral class M4.5. Utilizing a new method based on the effects of a field on the FeH band near 1 micron, we obtain information on whether the integrated surface magnetic flux (Bf) is low (well under 1 kilogauss), intermediate (between 1 and about 2.5 kG), or strong (greater than about 3 kG) on a set of stars ranging from M2 down to M9. We also measure the rotational broadening (vsini) and Halpha emission for more than 20 stars. Our goal is to advance the understanding of how dynamo field production varies with stellar parameters for very low-mass stars, how the field and emission activity are related, and whether there is a connection between the rotation and magnetic flux. We find that fields are produced throughout the M-dwarfs. Among the early M stars we have too few targets to yield conclusive results. In the mid-M stars, there is a clear connection between slow rotation and weak fields. In the late-M stars, rotation is always measureable, and the strongest fields go with the most rapid rotators. These very cool rapid rotators have the largest magnetic flux in the whole sample. Halpha emission is found to be a good general proxy for magnetic fields. The drop-off in fractional emission near the bottom of the main sequence is not accompanied by a drop-off in magnetic flux, lending credence to the hypothesis that it is due to atmospheric coupling to the field rather than changes in the field itself. It is clear that the methodology we have developed can be further applied to discover more about the behavior of magnetic dynamos and magnetic activity in cool and fully convective objects.
We present a reanalysis of the HeII Lyman alpha absorption towards the quasars HS1700+6416 and HE2347-4342 using new high S/N, optical observations. An alternative analysis method is applied, which fits the high quality, optical HI data directly to the HeII spectrum. The results are compared to those inferred from standard line profile analyses. This new method enables us to derive redshift scales characterizing the fluctuations of the column density ratio eta. We find eta changing smoothly with redshift on typical scales of Delta z ~ 0.01-0.03 corresponding to 8-24 h^-1 Mpc comoving. The real length scales of variations of the column density ratio might be even larger, since part of the fluctuations may be caused by noise in the HeII data and by effects due to the applied method. However, eta variations on small scales of a few Mpc with an amplitude of about +/- 1.5 dex cannot be ruled out completely. The data shows an apparent correlation between low eta regions and the presence of metal line absorbers, which corresponds to the more general correlation of low eta and strong HI absorption. Thermal line broadening is suggested as a probable explanation for this apparent correlation, since both fit methods would severely underestimate eta for absorbers with log N(HI) > 13 if the line width was dominated by thermal broadening. Indeed, lines located close to the cut-off of the b(N) distribution yield lower column density ratios compared to the whole sample, in particular if high density absorbers are considered. We argue that the apparent correlation of eta with the strength of the HI absorption is caused by insufficient consideration of thermal broadened lines by the standard analysis. As unbiased value of the column density ratio, we find eta ~80 in agreement with previous estimates.
$f(R)$-theories of gravity are reviewed in the context of the so called gravitational baryogenesis. The latter is a mechanism for generating the baryon asymmetry in the Universe, and relies on the coupling between the Ricci scalar curvature $R$ and the baryon current. Gravity Lagrangians of the form ${\cal L}(R)\sim R^n$, where $n$ differs from 1 (the case of the General Relativity) only for tiny deviations of a few percent, are consistent with the current bounds on the observed baryon asymmetry.
We have investigated the time scale for formation of molecular clouds by examining the conversion of HI to H2 using a time-dependent model. H2 formation on dust grains and cosmic ray and photo destruction are included in one-dimensional model slab clouds which incorporate time-independent density and temperature distributions. We calculate 21cm spectral line profiles seen in absorption against a background provided by general Galactic HI emission, and compare the model spectra with HI Narrow Self-Absorption, or HINSA, profiles absorbed in a number of nearby molecular clouds. The time evolution of the HI and H2 densities is dramatic, with the atomic hydrogen disappearing in a wave propagating from the central, denser regions which have a shorter H2 formation time scale, to the edges, where the density is lower and the time scale for H2 formation longer. The model 21cm spectra are characterized by very strong absorption at early times, when the HI column density through the model clouds is extremely large. The minimum time required for a cloud to have evolved to its observed configuration, based on the model spectra, is set by the requirement that most of the HI in the outer portions of the cloud, which otherwise overwhelms the narrow absorption, be removed. The characteristic time that has elapsed since cloud compression and initiation of the HI to H2 conversion is a few x 10^{14} s or ~ 10^7 yr. This sets a minimum time for the age of these molecular clouds and thus for the star formation that may take place within them.
(abridged) In this paper, we examined XMM Newton EPIC spectra of 14 ultra-luminous X-ray sources (ULXs)in addition to the XMM RGS spectra of two sources (Holmberg II X-1 and Holmberg IX X-1). We determined oxygen and iron abundances of the host galaxy's interstellar medium (ISM) using K-shell (O) and L-shell (Fe) X-ray photo-ionization edges towards these ULXs. We found that the oxygen abundances closely matched recent solar abundances for all of our sources, implying that ULXs live in similar local environments despite the wide range of galaxy host properties. Also, we compare the X-ray hydrogen column densities (n_H) for 8 ULX sources with column densities obtained from radio H I observations. The X-ray model n_H values are in good agreement with the H I n_H values, implying that the hydrogen absorption towards the ULXs is not local to the source (with the exception of the source M81 XMM1). In order to obtain the column density and abundance values, we fit the X-ray spectra of the ULXs with a combined power law and one of several accretion disk models. We tested the abundances obtained from the XSPEC models bbody, diskbb, grad, and diskpn along with a power law, finding that the abundances were independent of the thermal model used. We comment on the physical implications of these different model fits. We also note that very deep observations allow a breaking of the degeneracy noted by Stobbart et al. (2006) favoring a high mass solution for the absorbed grad + power law model.
We consider the consequences of applying general relativity to the description of the dynamics of a galaxy, given the observed flattened rotation curves. The galaxy is modeled as a stationary axially symmetric pressure-free fluid. In spite of the weak gravitational field and the non-relativistic source velocities, the mathematical system is still seen to be non-linear. It is shown that the rotation curves for various galaxies as examples are consistent with the mass density distributions of the visible matter within essentially flattened disks. This obviates the need for a massive halo of exotic dark matter. We determine that the mass density for the luminous threshold as tracked in the radial direction is $10^{-21.75}$ kg$\cdot$m$^{-3}$ for these galaxies and conjecture that this will be the case for other galaxies yet to be analyzed. We present a velocity dispersion test to determine the extent, if of any significance, of matter that may lie beyond the visible/HI region. Various comments and criticisms from colleagues are addressed.
[abridged] We report integral-field spectroscopic observations with CIRPASS mounted on the GEMINI South telescope of the nucleus of the nearby galaxy NGC 5128 (Centaurus A). We detect two-dimensional distributions of the following emission-lines: [PII], [FeII] and Paschen beta. We compare our observations with previously published radio observations (VLA) and archival space-based near-infrared imaging (HST/NICMOS) and find similar features, as well as a region of high continuum coinciding with the jet (and its N1 knot) at about 2 arcsec North-East of the nucleus, possibly related to jet-induced star formation. We use the [FeII]/[PII] ratio to probe the ionisation mechanism, which suggests that with increasing radius shocks play an increasingly important role. We extract spatially resolved 2D kinematics of Pa beta and [FeII] emission-lines. All emission-line regions are part of the same kinematic structure which shows a twist in the zero-velocity curve beyond ~1 arcsec (for both Pa beta and [FeII]). The kinematics of the two emission-lines are similar, but the Pa beta velocity gradient is steeper in the centre while the velocity dispersion is low everywhere. The velocity dispersion of the [FeII] emission is relatively high featuring a plateau, approximately oriented in the same way as the central part of the warped disk. We use 2D kinematic information to test the hypothesis that the ionised gas is distributed in a circularly rotating disk. We estimate the mass of the central black hole using Pa beta kinematics, which is consistent with being distributed in a circularly rotating disk. We obtain Mbh = 8.25^{+2.25}_{-4.25} * 10^7 Msun, for PA = -3 degr and i=25 degr, which is in good agreement with previous studies.
We discuss the possibility of observing ultra high energy cosmic ray sources inhigh energy gamma rays. Protons propagating away from their accelerators produce secondary electrons during interactions with cosmic microwave background photons. These electrons start an electromagnetic cascade that results in a broad band gamma ray emission. We show that in a magnetized Universe ($B \gtrsim 10^{-12}$ G) such emission is likely to be too extended to be detected above the diffusebackground. A more promising possibility comes from the detection of synchrotron photons from the extremely energetic secondary electrons. Although this emission is produced in a rather extended region of size $\sim 10Mpc$, it is expected to be point-like and detectable at GeV energies if the intergalactic magnetic field is at the nanogauss level.
Using galaxy clusters from the ESO Distant Cluster Survey, we study how the distribution of galaxies along the colour-magnitude relation has evolved since z~0.8. While red-sequence galaxies in all these clusters are well described by an old, passively evolving population, we confirm our previous finding of a significant evolution in their luminosity distribution as a function of redshift. When compared to galaxy clusters in the local Universe, the high redshift EDisCS clusters exhibit a significant "deficit" of faint red galaxies. Combining clusters in three different redshift bins, and defining as `faint' all galaxies in the range 0.4 > L/L* > 0.1, we find a clear decrease in the luminous-to-faint ratio of red galaxies from z~0.8 to z~0.4. The amount of such a decrease appears to be in qualitative agreement with predictions of a model where the blue bright galaxies that populate the colour-magnitude diagram of high redshift clusters, have their star formation suppressed by the hostile cluster environment. Although model results need to be interpreted with caution, our findings clearly indicate that the red-sequence population of high-redshift clusters does not contain all progenitors of nearby red-sequence cluster galaxies. A significant fraction of these must have moved onto the red-sequence below z~0.8.
The result of the recent publication [M. Kachelriess and D. V. Semikoz Astropart. Phys. 26, 10 (2006)] of a broad maximum around 25 degrees in the two-point autocorrelation function of ultra-high energy cosmic ray arrival directions has been intriguingly interpreted as the first imprint of the large scale structures (LSS) of baryonic matter in the near universe. We analyze this suggestion in light of the clustering properties expected from the PSCz astronomical catalogue of LSS. The chance probability of the signal is consistent within 2 sigma with our expectations. No evidence for a significant cross-correlation of the observed events with known overdensities in the LSS is found, which may be due to the role of the galactic and extragalactic magnetic fields, and is however consistent with the limited statistics. The larger statistics to be collected by the Pierre Auger Observatory is needed to answer definitely the question.
In the core of a canonical spinning magnetized neutron star(NS) a nearly uniform superfluid neutron vortex-array interacts strongly with a twisted array of magnetic flux-tubes threading the core's superconducting protons. One consequence is that changes in NS-spin alter both arrays and also the magnetic field distribution on the surface of the surrounding crust. Among predicted consequences for very young spinning-down NSs are "spin-down indices" increasing from 2 to 3, and a family of (Crab-like) spin-period "glitches" with permanent fractional jumps in spin-down torque 10E5 times greater than those in NS-spin. For older NSs, average spin-down indices increase to around 5, and an additional (Vela-like) family of giant glitches develops. NS spin-up to millesecond pulsars results in a high abundance of orthogonal and aligned rotators, and anomolously small polar cap areas. Observations do not conflict with these expectations. An epoch of NS magnetic field evolution between the onset of proton superconductivity (approx. yr) and neutron superfluidity (approx. 10E3 yrs ?) may be important for large surface magnetic field changes and needs further study. Observations generally considered evidence for NS precession seem to need reconsideration.