To date, all of the reported high velocity stars (HVSs), which are believed to be ejected from the Galactic center, are blue and therefore almost certainly young. Old-population HVSs could be much more numerous than the young ones that have been discovered, but still have escaped detection because they are hidden in a much denser background of Galactic halo stars. Discovery of these stars would shed light on star formation at the Galactic center, the mechanism by which they are ejected from it, and, if they prove numerous, enable detailed studies of the structure of the dark halo. We analyze the problem of finding these stars and show that the search should be concentrated around the main-sequence turnoff (0.3<g-i<1.1) at relatively faint magnitudes (19.5<g<21.5). If the ratio of turnoff stars to B stars is the same for HVSs as it is in the local disk, such a search would yield about 1 old-population HVS per 10 deg^2. A telescope similar to the Sloan 2.5m could search about 20 deg^2 per night, implying that in short order such a population, should it exist, would show up in interesting numbers.
We study the relation between black hole (BH) mass and host galaxy properties in simulations of major galaxy mergers. We show that the simulations predict the existence of a BH fundamental plane (BHFP), of the form M_BH ~ sigma^3 R_e^0.5 (~ M_stellar^0.5 sigma^2), analogous to the FP of ellipticals. Comparing with existing BH measurements, observed systems indeed follow an identical BHFP relation, favoring such a BHFP over a simple relation between M_BH and any of sigma, M_stellar, M_dyn, or R_e alone at >99.9% significance. This can be roughly understood as a 'tilted' correlation between BH mass and spheroid binding energy, or from the condition for feedback to power a pressure-driven outflow. While changes in halo circular velocity, merger orbital parameters, progenitor disk redshifts and gas fractions, ISM gas pressurization, and other parameters can drive changes in e.g. sigma at fixed M_stellar, and therefore changes in the M_BH-sigma or M_BH-M_stellar relations, the BHFP is robust. Given the empirical trend of decreasing R_e at fixed stellar mass at high redshift, the BHFP predicts BHs will be more massive at fixed M_stellar, in agreement with recent observations. This evolution is driven by the fact that disks (merger progenitors) have larger gas fractions at high redshifts. Adopting the observed evolution of disk f_gas with redshift, our simulations predict the observed trends in both R_e(M_stellar) and M_BH(M_stellar). We discuss the implications of this BHFP for the masses of the largest BHs and apparent 'outliers' in the M_BH-sigma and M_BH-M_stellar relations.
Sub-arcsecond scale Keck images of the young A1V star, 49 Ceti, resolve emission at lambda = 12.5 and 17.9 microns from a disk with long axis at PA 125 pm 10 degrees and inclination phi = 60 pm 15 degrees . At 17.9 microns, the emission is brighter and more extended toward the NW than the SE. Modeling of the mid-infrared images combined with flux densities from the literature indicate that the bulk of the mid-infrared emission comes from very small grains (a ~ 0.1 microns) confined between 30 and 60 AU from the star. This population of dust grains contributes negligibly to the significant excess observed in the spectral energy distribution. Most of the non- photospheric energy is radiated at longer wavelengths by an outer disk of larger grains (a ~ 15 microns), inner radius ~ 60 AU, and outer radius ~ 900 AU. Global properties of the 49 Cet disk show more affinity with the Beta Pic and HR 4796A disks than with other debris disks. This may be because they are all very young (t < 20 Myr), adding strength to the argument that they are transitional objects between Herbig Ae and "Vega-like" A stars with more tenuous circumstellar disks.
In this paper we investigate quintom cosmologies with arbitrary potentials from the dynamical systems perspective. The dynamical systems analysis is complete in the sense that it includes the asymptotic regime where both scalar fields diverge, which proves to be particularly relevant in connection with the existence of tracking phases. The results of the present study indicate that the existence of phantom attractors is not generic: for quintom models there may exist either de Sitter attractors associated with the saddle points of the potential, or tracking attractors in the asymptotic regime where the scalar fields diverge.
In McCarthy et al. (2007, astro-ph/0701335) we present an analysis of entropy generation during cluster mergers, using SPH simulations. This conference proceeding contribution summarizes some of the most important findings of that paper, without all the technical details. Our main result is that during cluster mergers, entropy is generated in two major shock episodes, that heat the gas from the inside-out, in a way that distributes most of the energy within the more massive clump. This is different from the "onion-skin" model adopted in many simple analytic models of cluster formation.
We present deep IRAC images that highlight the scattered light emission around many of the youngest protostars, the so-called Class 0 sources, in L1448. By comparison of the data with a Monte Carlo radiative transfer code \citep{whitney2003a}, we demonstrate for the first time that the observed infrared light from these objects is consistent with scattered light from the central protostar. The scattered light escapes out the cavity, carved by molecular outflows, in the circumstellar envelope. In particular, we observe prominent scattered light nebulae associated with the Class 0 sources: L1448-mm, L1448 IRS 2, and 3B, as well as a Class I source: IRS 3A. We use a grid of models with probable protostellar properties to generate model spectral energy distributions (SEDs) and images for bands sensitive to this scattered light: J, H, Ks, and \textit{Spitzer} IRAC bands. By simultaneously fitting SEDs and images of the outflow cavities, we are able to model geometric parameters, i.e. inclination angle and opening angle, and loosely constrain physical parameters. The opening angle may be an important indicator of the evolutionary state of a source. We compare our results for Class 0 sources to similar studies of Class I sources. There may be a transition phase from Class 0 to Class I when a source has an opening angle between 20$^o$ to 30$^o$. It is important to note that while the best fit model image and SED do not fully describe the sources, the fits generally describe the circumstellar structure of Class 0 sources in L1448.
We present accurate V-band photometry for a planetary transit of OGLE-TR-111 acquired with VIMOS at the ESO Very Large Telescope. The measurement of this transit allows to refine the planetary radius, obtaining R_p= 1.01 +/- 0.06 R_J. Given the mass of M_p = 0.53 M_J previously measured from radial velocities, we confirm that the density is rho_p= 0.6 +/- 0.2 g/cm^3. We also revise the ephemeris for OGLE-TR-111-b, obtaining an accurate orbital period P= 4.014484 +/- 0.000014 days, and predicting that the next observable transits would occur around December 2006, and after that only in mid-2008. Even though this period is different from previously published values, we cannot yet rule out a constant period.
Rotational invariance is a well-established feature of low-energy physics. Violations of this symmetry must be extremely small today, but could have been larger in earlier epochs. In this paper we examine the consequences of a small breaking of rotational invariance during the inflationary era when the primordial density fluctuations were generated. Assuming that a fixed-norm vector picked out a preferred direction during the inflationary era, we explore the imprint it would leave on the cosmic microwave background anisotropy, and provide explicit formulas for the expected amplitudes $<a_{lm}a_{l'm'}^*>$ of the spherical-harmonic coefficients. We suggest that it is natural to expect that the imprint on the primordial power spectrum of a preferred spatial direction is approximately scale-invariant, and examine a simple model in which this is true.
The total number of degrees of freedom of a d-dimensional body in n-space is derived so that equipartition of energy may be applied to a possibly n-dimensional early universe. A comparison is made of a range of proposals to include free and bound black holes as either a small component or the dominant constituent of dark matter in the universe. The hypothesis that dark matter consists in part of atomic gravitationally bound primordial black holes is closely examined in 3-space, as well as in n-space; and the Chavda and Chavda holeum hypothesis is found to be flawed. Blackbody and Hawking radiation are generalized to n-space, and Hawking radiation is shown to be simply proportional to the black hole density. The importance of quantum gravity in understanding the role of early universe dark matter is undermined because present approaches to a theory of quantum gravity violate the equivalence principle. A novel approach to the accelerated expansion of the universe is discussed. An anomalous surprising aspect of 4-space is demonstrated.
The energy released in a solar flare is partitioned between thermal and non-thermal particle energy and lost to thermal conduction and radiation over a broad range of wavelengths. It is difficult to determine the conductive losses and the energy radiated at transition region temperatures during the impulsive phases of flares. We use UVCS measurements of O VI photons produced by 5 flares and subsequently scattered by O VI ions in the corona to determine the 5.0 < log T < 6.0 transition region luminosities. We compare them with the rates of increase of thermal energy and the conductive losses deduced from RHESSI and GOES X-ray data using areas from RHESSI images to estimate the loop volumes, cross-sectional areas and scale lengths. The transition region luminosities during the impulsive phase exceed the X-ray luminosities for the first few minutes, but they are smaller than the rates of increase of thermal energy unless the filling factor of the X-ray emitting gas is ~ 0.01. The estimated conductive losses from the hot gas are too large to be balanced by radiative losses or heating of evaporated plasma, and we conclude that the area of the flare magnetic flux tubes is much smaller than the effective area measured by RHESSI during this phase of the flares. For the 2002 July 23 flare, the energy deposited by non-thermal particles exceeds the X-ray and UV energy losses and the rate of increase of the thermal energy.
We are using the Australia Telescope Compact Array to image about six square degrees surrounding the Chandra Deep Field South and European Large Area ISO Survey - South 1 regions, with the aim of producing the widest deep radio survey ever attempted, in fields with deep optical, infrared, and X-ray data. Our goal is to penetrate the heavy dust extinction which is found in active galaxies at all redshifts, and study the star formation activity and active galactic nuclei buried within. Although we are only about half-way through the survey, our data are proving remarkably fruitful. For example, we have discovered a new and unexpected class of object (the Infrared-Faint Radio Sources), we have found that the radio-FIR correlation extends to low flux densities, and we havefound powerful AGN-like radio objects in galaxies with a star-forming SED.
Astronomy is one of the most data-intensive of the sciences. Data technology is accelerating the quality and effectiveness of its research, and the rate of astronomical discovery is higher than ever. As a result, many view astronomy as being in a 'Golden Age', and projects such as the Virtual Observatory are amongst the most ambitious data projects in any field of science. But these powerful tools will be impotent unless the data on which they operate are of matching quality. Astronomy, like other fields of science, therefore needs to establish and agree on a set of guiding principles for the management of astronomical data. To focus this process, we are constructing a 'data manifesto', which proposes guidelines to maximise the rate and cost-effectiveness of scientific discovery.
The abundances of iron and oxygen are homogeneously determined in a sample of 523 nearby (d<150 pc) FGK disk and halo stars with metallicities in the range -1.5<[Fe/H]<0.5. The oxygen abundances were inferred from a restricted non-LTE analysis of the 777 nm O I triplet. We use the stellar kinematics to compute the probabilities of our sample stars to be members of the thin disk, thick disk, or halo of the Galaxy. We find that the majority of the kinematically-selected thick-disk stars show larger [O/Fe] ratios compared to thin-disk stars. A close examination of this pattern for disk stars with ambiguous probabilities shows that an intermediate population with properties between those of the thin and thick disks does not exist. Excluding the stars with unusual kinematics, we find that thick-disk stars show slowly decreasing [O/Fe] ratios from about 0.5 to 0.4 in the -0.8<[Fe/H]<-0.3 range. Using a simple model for the chemical evolution of the thick disk we show that this trend results directly from the metallicity dependence of the Type II supernova yields. At [Fe/H]>-0.3, we find no obvious indication of a sudden decrease (i.e., a 'knee') in the [O/Fe] vs. [Fe/H] pattern of thick-disk stars that would connect the thick and thin disk trends at a high metallicity. We conclude that Type Ia supernovae (SN Ia) did not contribute significantly to the chemical enrichment of the thick disk. [Abridged]
In a hierarchical picture of galaxy formation virialization continually transforms gravitational potential energy into kinetic energies in the baryonic and dark matter. For the gaseous component the kinetic, turbulent energy is transformed eventually into internal thermal energy through shocks and viscous dissipation. Traditionally this virialization and shock heating has been assumed to occur instantaneously allowing an estimate of the gas temperature to be derived from the the virial temperature defined from the embedding dark matter halo velocity dispersion. As the mass grows the virial temperature of a halo grows. Mass accretion hence can be translated into a heating term. We derive this heating rate from the extended Press Schechter formalism and demonstrate its usefulness in semi-analytical models of galaxy formation. Our method is preferable to the traditional approaches in which heating from mass accretion is only modeled implicitly through an instantaneous change in virial temperature. Our formalism can trivially be applied in all current semi-analytical models as the heating term can be computed directly from the underlying merger trees. Our analytic results for the first cooling halos and the transition from cold to hot accretion are in agreement with numerical simulations.
Nuclear ``pasta'', nonspherical nuclei in dense matter, is predicted to occur in collapsing supernova cores. We show how pasta phases affect the neutrino transport cross section via weak neutral current using several nuclear models. This is the first calculation of the neutrino opacity of the phases with rod-like and slab-like nuclei taking account of finite temperature effects, which are well described by the quantum molecular dynamics. We also show that pasta phases can occupy 10--20% of the mass of supernova cores in the later stage of the collapse.
We study weak gravitational lensing of galaxy clusters in terms of the relativistic MOND (MOdified Newtonian Dynamics) theory proposed by Bekenstein (2004). We calculate shears and magnifications of background galaxies for three clusters (A1689, CL0024+1654, CL1358+6245) and 42 SDSS (Sloan Digital Sky Survey) clusters and compare them with observational data. The mass profile is modeled as a sum of X-ray gas, galaxies and dark halo. For the shear as a function of the angle from the lens center, MOND predicts a shallower slope than the data irrespective of the critical acceleration parameter $g_0$. The dark halo is necessary to explain the data for any $g_0$. If the dark halo is composed of massive neutrinos, its mass should be heavier than 2-3 eV. However, it is still difficult to explain a small core (100-300 kpc) determined by the lensing data in the neutrino halo model.
In a disk around DM Tau, previous observation of 13CO (J=2-1 and 1-0 transitions) derived the 13CO gas temperature of \sim 13-20K, which is lower than the sublimation temperature of CO (20 K). We argue that the existence of such cold CO can be explained by a vertical mixing of disk material. As the gas is transported from a warm layer to a cold layer, CO is depleted onto dust grains with a timescale of \sim 10^3 yr. Because of the steep temperature gradient in the vertical direction, an observable amount of CO is still in the gas phase when the fluid parcel reaches the layer of \sim 13 K. Apparent temperature of CO decreases as the maximum grain size increases from micron-size to mm-size.
In this thesis I present measurements of the physical properties of the
nuclei of Jupiter Family comets (JFCs), based on time-series observations. From
the time-series photometry rotation rates and elongations were measured, and
from these constraints were placed on the bulk density and porosity of nuclei.
Multi-filter imaging was performed to enable measurement of their surface
colours. In addition, a large amount of `snap-shot' imaging was performed
during the observing runs, and taken with the time-series data is used to
measure nuclei sizes. These results are compared with other data from the
literature to study the general properties of JFC nuclei.
(Abridged)
The evolution of an X2.7 solar flare, that occurred in a complex $\beta\gamma\delta$ magnetic configuration region on 2003 November 3, is discussed utilizing a multi-wavelength data set. The H$\alpha$ images taken from the solar tower telescope at ARIES, Nainital, reveal well-defined footpoint (FP) and loop-top (LT) sources. As the flare evolves, the LT source moves upward and the separation between the two FP sources increases which is consistent with reconnection models of solar flares. The co-alignment of H$\alpha$ with hard X-ray (HXR) images obtained from RHESSI shows spatial correlation between H$\alpha$ and HXR footpoints, while the rising LT source in HXR is always located above the LT source seen in H$\alpha$. The EUV images of the flaring region at 195 {\AA} taken from SOHO/EIT reveal intense emission from low-lying loops near the active region during the impulsive phase. On the other hand, two bright loops are seen well outside the active region which undergo large scale reorganization during the flare. In radio wavelengths, type III radio bursts are observed few minutes prior to the start of HXR emission at the LT indicating pre-flare coronal activity. Slow drifting type IV bursts, which are observed at lower coronal heights at two time intervals along the flare period, are likely to be associated with the reconnection processes at two different coronal heights. Further, the intense type II radio burst at time inbetween these type IV bursts, but at a relatively larger height indicates the onset of CME and its associated coronal shock wave. The results of this study support the `break-out' scenario observed in multipole magnetic configuration of a flaring region.
We present a model with a complex and a real scalar fields and a potential whose symmetry is explicitly broken by Planck-scale physics. For exponentially small breaking, the model accounts for the period of inflation in the early universe and for the period of acceleration of the late universe or for the dark matter, depending on the smallness of the explicit breaking.
We present a model based on the idea that Planck-scale effects may produce a small explicit breaking of global symmetries. The model contains a new complex scalar field $\Psi$, charged under a certain global U(1) symmetry, interacting with a new real scalar field $\chi$, neutral under U(1). For exponentially small breaking, the model accounts for both {\em early} and {\em late} periods of acceleration of the universe.
We analyse the presence of nonradial oscillations in Cepheids, a problem which has not been theoretically revised since the work of Dziembowsky (1977) and Osaki (1977). Our analysis is motivated by a work of Moskalik et al. (2004) which reports the detec tion of low amplitude periodicities in a few Cepheids of the large Magellanic cloud. These newly discovered periodicities were interpreted as nonradial modes.} {Based on linear nonadiabatic stability analysis, our goal is to reanalyse the presence and stability of nonradial modes, taking into account improvement in the main input phys ics required for the modelling of Cepheids.} {We compare the results obtained from two different numerical methods used to solve the set of differential equations: a matrix method and the Ricatti method.} {We show the limitation of the matrix method to find low order p-modes ($l<6$), because of their dual character in evolved stars such as Cepheids. For higher order p-modes, we find an excellent agreement between the two methods.} {No nonradial instability is found below $l=5$, whereas many unstable nonradial modes exist for higher orders. We also find that nonradial modes remain unstable, even at hotter effective temperatures than the blue edge of the Cepheid instability strip, where no radial pulsations are expected.
Gravitational lensing and stellar dynamics are two independent methods, based solely on gravity, to study the mass distributions of galaxies. Both methods suffer from degeneracies, however, that are difficult to break. In this paper, we present a new framework that self-consistently unifies gravitational lensing and stellar dynamics. This approach breaks some of classical degeneracies that have limited their individual usage, in particular in the study of high-redshift galaxies. The methodology is based on the premise that, for any given galaxy potential, the mapping of both the unknown lensed source brightness distribution and the stellar phase-space distribution function on to the photometric and kinematic observables, can be cast as a single set of coupled linear equations. This set of linear equations is solved, maximizing the likelihood penalty function. The evidence penalty function, as derived from Bayesian statistics, subsequently allows the best potential-model parameters to be found and potential-model families, or other model assumptions (e.g. PSF), to be quantitatively ranked. We have implemented a fast algorithm that solves for the maximum-likelihood pixelized lensed source brightness distribution and the two-integral stellar phase-space distribution function f(E, L_z), assuming axisymmetric potentials. To make the method practical, we have devised a new Monte-Carlo approach to Schwarzschild's orbital superposition method, based on the superposition of two-integral (E and L_z) toroidal components, to find the maximum-likelihood two-integral distribution function in a matter of seconds in any axisymmetric potential. The non-linear parameters of the potential are subsequently found through a hybrid MCMC and Simplex optimization of the evidence. (Abridged)
Rather weak fossil magnetic fields in the radiative core can produce the solar tachocline if the field is poloidal and almost horizontal in the tachocline region, i.e. if the field is confined within the core. This particular field geometry is shown to result from a shallow (<~1Mm) penetration of the meridional flow existing in the convection zone into the radiative core. I.e., two conditions are crucial for a magnetic tachocline theory: (i) the presence of meridional flow of a few meters per second at the base of the convection zone, and (ii) a magnetic diffusivity inside the tachocline smaller than 10^8 cm^2s^-1. Numerical solutions for both confined poloidal fields and the resulting tachocline structures are presented. We find that the tachocline thickness runs as <I>B</I>_p^-1/2 with the poloidal field amplitude falling below 5% of the solar radius for <I>B</I>^p > 5 mG. The resulting toroidal field amplitude inside the tachocline of about 100 G does not depend on the <I>B</I>^p. The hydromagnetic stability of the tachocline is only briefly discussed. For the hydrodynamic stability of latitudinal differential rotation we found that the critical 29% of the 2D theory of Watson (1981) are reduced to only 21% in 3D for marginal modes of about 6 Mm radial scale.
We show some of the most important reasons why the likely fate of the merger of a neutron star with another compact object may be to yield a short gamma-ray burst (sGRB). Emphasis is made on some robust results that general relativistic (magneto)hydrodynamic simulations have established regarding the aforementioned subject.
On basis of modification of Einstein's gravitational equations by adding the term $f(R)\propto \beta R^n$, a geometric model of quintessence is proposed. The evolution equation for the scale factor $a$ of the Universe is analyzed for the two parameters $n=2$ and $n=4/3$, which were preferred by previous studies of the early Universe. Another choice of parameters $n$ and $\beta$ is proposed from the following reasons: the exponent $n$ close to 1.2953 follows from the request for the evolution of the Universe after recombination to be close to the evolution of the flat FRW model with cold dark matter and reasonable age of the Universe defines the value of the coefficient $\beta$. Such a model corresponding to the evolution of the Universe with the dynamical $\Lambda$-term describes well enough the observational data.
Over the next few years the new radio telescopes, such as the Low Frequency Array (LOFAR) will greatly enhance our knowledge of the active history of the Universe. Large-area surveys with these new telescopes will no longer be dominated by the powerful active galactic nuclei, but by radio-quiet quasars and star-forming galaxies over all cosmic epochs. Further in the future (~2014) the Square Kilometre Array (SKA) will take studies in the radio regime to a whole new level, with the ability to detect neutral hydrogen via the 21cm transition over the majority of cosmic time. This will enable both the detailed study of individual galaxies and the use of these galaxies as probes Dark Energy. In these proceedings I give an overview of the science goals behind these new radio telescopes, with particular emphasis on galaxy evolution and cosmology. Finally I briefly discuss the SKA science simulation effort.
The results of study of the gravitational fragmentation in the interstellar medium (ISM) by clump-clump collisions are presented. We suggest, that collision of clumps, that are subparts of Giant Molecular Clouds (GMC) may be on of the basic mechanism, which result to ISM fragmentation and define the dynamical as well as statistical characteristics (e.g. the mass spectra) of protostellar condensation. In the present paper, we describe our 3D SPH-modeling, in isothermal approximation, of supersonic collisions of two identical clumps with a few variants of initial impact parameters ($\beta$), that cover the wide range. Our results shown, that at all $\beta$ in system began intensive fragmentation. The resulting fragments mass function depend from initial impact parameter. The obtained mass spectra have the slopes in a good enough agreement with observational data for our Galaxy -- especially for large impact parameters, which are more realistic as for large clumps ensembles.
We acquired radial velocities of a significant number of globular clusters (GCs) on wide fields between galaxies in the nearby Fornax cluster of galaxies, in order to derive their velocity dispersion radial profile and to probe the dynamics of the cluster. We used FLAMES on the VLT to obtain accurate velocities for 149 GCs, within a ~500x150 kpc strip centered on NGC 1399, the Fornax central galaxy. These objects are at the very bright tail (M_V < -9.5) of the GC luminosity function, overlapping the so-called ``ultra-compact dwarfs'' magnitude range. Eight of the brightest FLAMES-confirmed members indeed show hints of resolution in the subarcsecond pre-imaging data we used for selecting the ~500 targets for FLAMES spectroscopy. Ignoring the GCs around galaxies by applying 3d_25 diameter masks, we find 61 GCs of 20.0 < V < 22.2 lying in the intra-cluster (IC) medium. The velocity dispersion of the population of ICGCs is 200 km/s at ~150 kpc from the central NGC 1399 and rises to nearly 400 km/s at 200 kpc, a value which compares with the velocity dispersion of the population of dwarf galaxies, thought to be infalling from the surroundings of the cluster.
DOT high-resolution imagery suggests that only internetwork-spanning H-alpha "mottles" constitute the quiet-sun chromosphere, whereas more upright network "straws" in "hedge rows" reflect transition-region conditions.
We revisit the problem of constraining steps in the inflationary potential with cosmological data. We argue that a step in the inflationary potential produces qualitatively similar oscillations in the primordial power spectrum, independently of the details of the inflationary model. We propose a phenomenological description of these oscillations and constrain these features using a selection of cosmological data including the baryonic peak data from the correlation function of luminous red galaxies in the Sloan Digital Sky Survey. Our results show that degeneracies of the oscillation with standard cosmological parameters are virtually non-existent. The inclusion of new data severely tightens the constraints on the parameter space of oscillation parameters with respect to older work. This confirms that extensions to the simplest inflationary models can be successfully constrained using cosmological data.
We perform hydrodynamical and nucleosynthesis calculations of core-collapse supernovae (SNe) and hypernovae (HNe) of Population (Pop) III stars. We provide new yields for the main-sequence mass of $M_{\rm MS}=13-50$ $M_{\odot}$ and the explosion energy of $E=1-40\times10^{51}$ ergs to apply for chemical evolution studies. Our HN yields based on the mixing-fallback model of explosions reproduce the observed abundance patterns of extremely metal-poor (EMP) stars ($-4< {\rm [Fe/H]}< -3$), while those of very metal-poor (VMP) stars ($-3<{\rm [Fe/H]} < -2$) are reproduced by the normal SN yields integrated over the Salpeter initial mass function. Moreover, the observed trends of abundance ratios [X/Fe] against [Fe/H] with small dispersions for the EMP stars can be reproduced as a sequence resulting from the various combination of $M_{\rm MS}$ and $E$. This is because we adopt the empirical relation that a larger amount of Fe is ejected by more massive HNe. Our results imply that the observed trends with small dispersions do not necessarily mean the rapid homogeneous mixing in the early galactic halo at [Fe/H] $< -3$, but can be reproduced by the ``inhomogeneous'' chemical evolution model. In addition, we examine how the modifications of the distributions of the electron mole fraction $Y_{\rm e}$ and the density in the presupernova models improve the agreement with observations. In this connection, we discuss possible contributions of nucleosynthesis in the neutrino-driven wind and the accretion disk.
Why do plants reflect in the green and have a 'red edge' in the red, and should extrasolar photosynthesis be the same? We provide: 1) a brief review of how photosynthesis works; 2) an overview of the diversity of photosynthetic organisms, their light harvesting systems, and environmental ranges; 3) a synthesis of photosynthetic surface spectral signatures; 4) evolutionary rationales for photosynthetic surface reflectance spectra with regard to utilization of photon energy and the planetary light environment. Given the surface incident photon flux density spectrum and resonance transfer in light harvesting, we propose some rules with regard to where photosynthetic pigments will peak in absorbance: a) the wavelength of peak incident photon flux; b) the longest available wavelength for core antenna or reaction center pigments; and c) the shortest wavelengths within an atmospheric window for accessory pigments. That plants absorb less green light may not be an inefficient legacy of evolutionary history, but may actually satisfy the above criteria.
We present the results of a search for gravitationally-lensed giant arcs conducted on a sample of 825 SDSS galaxy clusters. Both a visual inspection of the images and an automated search were performed and no arcs were found. This result is used to set an upper limit on the arc probability per cluster. We present selection functions for our survey, in the form of arc detection efficiency curves plotted as functions of arc parameters, both for the visual inspection and the automated search. The selection function is such that we are sensitive only to long, high surface brightness arcs with g-band surface brightness mu_g < 24.8 and length-to-width ratio l/w > 10. Our upper limits on the arc probability are compatible with previous arc searches. Lastly, we report on a serendipitous discovery of a giant arc in the SDSS data, known inside the SDSS Collaboration as Hall's arc.
New observations are reported of J-band spectra (1.04micron -- 1.4 micron) of three Seyfert 2 galaxies, Mkn 34, Mkn 78 and NGC 5929. In each case the spectral range includes the near-infrared lines of [FeII], [PII], HeI and Pa beta. Each Seyfert galaxy has a known radio jet, and we investigate the infrared line ratios of the nuclear and extended regions of each galaxy compared to the radio structure. In Mkn 34 there is a clear indication of an extranuclear region, probably coincident with a shock induced by the radio jet, in which [FeII] is considerably enhanced, although the nuclear emission is almost certainly the result of photoionization by the continuum of the active nucleus. Similar effects in extranuclear regions are seen in the other objects, in the case of Mkn 78 confirming recent studies by Ramos Almeida et al. A possible detection of extranuclear [PII] emission suggests, if real, that photoionization by the active nucleus is the dominant line excitation mechanism over the whole source, including the regions coincident with the radio jet.
Planetary formation is an efficient process now thought to take place on a relatively short astronomical time scale. Recent observations have shown that the dust surrounding a protostar emits more efficiently at longer wavelengths as the protoplanetary disk evolves, suggesting that the dust particles are coagulating into fluffy aggregates, "much as dust bunnies form under a bed." One poorly understood problem in this coagulation process is the manner in which micron-sized, charged grains form the fractal aggregate structures now thought to be the precursors of protoplanetary disk evolution. This study examines the characteristics of such fractal aggregates formed by the collision of spherical monomers and aggregates where the charge is distributed over the aggregate structure. The aggregates are free to rotate due to collisions and dipole-dipole electrostatic interactions. Comparisons are made for different precursor size distributions and like-charged, oppositelycharged, and neutral grains.
We report on the results of an analysis of XMM-Newton observations of MS0735+7421, the galaxy cluster which hosts the most energetic AGN outburst currently known. The previous Chandra image shows twin giant X-ray cavities (~200 kpc diameter) filled with radio emission and surrounded by a weak shock front. XMM data are consistent with these findings. The total energy in cavities and shock (~6 \times 10^{61} erg) is enough to quench the cooling flow and, since most of the energy is deposited outside the cooling region (~100 kpc), to heat the gas within 1 Mpc by ~1/4 keV per particle. The cluster exhibits an upward departure (factor ~2) from the mean L-T relation. The boost in emissivity produced by the ICM compression in the bright shells due to the cavity expansion may contribute to explain the high luminosity and high central gas mass fraction that we measure. The scaled temperature and metallicity profiles are in general agreement with those observed in relaxed clusters. Also, the quantities we measure are consistent with the observed M-T relation. We conclude that violent outbursts such as the one in MS0735+7421 do not cause dramatic instantaneous departures from cluster scaling relations (other than the L-T relation). However, if they are relatively common they may play a role in creating the global cluster properties.
The origin of magnetic fields in intermediate-mass and high-mass stars is fundamentally a mystery. Clues toward solving this basic astrophysical problem can likely be found at the pre-main sequence (PMS) evolutionary stage. With this work, we perform the largest and most sensitive search for magnetic fields in pre-main sequence Herbig Ae/Be (HAeBe) stars. Sixty-eight observations of 50 HAeBe stars have been obtained in circularly polarised light using the FORS1 spectropolarimeter at the ESO VLT. An analysis of both Balmer and metallic lines reveals the possible presence of weak longitudinal magnetic fields in photospheric lines of two HAeBe stars, HD 101412 and BF Ori. The intensity of the longitudinal fields detected in HD 101412 and BF Ori suggest that they correspond to globally-ordered magnetic fields with surface intensities of order 1 kG. Monte Carlo simulations of the longitudinal field measurements of the undetected stars allow us to place an upper limits of about 300 G on the general presence of aligned magnetic dipole magnetic fields, and of about 500 G on perpendicular dipole fields. We find that the observed bulk incidence of magnetic HAeBe stars in our sample is 8-12%, in good agreement with that of magnetic main sequence stars of similar masses. We also find that the rms longitudinal field intensity of magnetically-detected HAeBe stars is similar to that of Ap stars and consistent with magnetic flux conservation during stellar evolution. These results are all in agreement with the hypothesis that the magnetic fields of main sequence Ap/Bp stars are fossils, which already exist within the stars at the pre-main sequence stage. Finally, we explore the ability of our new magnetic data to constrain magnetospheric accretion in Herbig Ae/Be stars.
We show how the complex-shift method introduced by Appell in gravity to the case of a point mass (and applied among others in electrodynamics by Newman, Carter, Lynden-Bell, and Kaiser to determine remarkable properties of the electromagnetic field of rotating charged configurations), can be extended to obtain new and explicit density-potential pairs for self-gravitating systems departing significantly from spherical symmetry. The rotational properties of two axysimmetric baroclinic gaseous configurations derived with the proposed method are illustrated.
We are conducting a transit survey of the open cluster M37 using the Megacam instrument on the 6.5 m Multiple-Mirror Telescope. We have obtained ~4500 images of this cluster over 18.5 nights and have achieved the precision necessary to detect planets smaller than Saturn. In this presentation we provide an overview of the project, describe the ongoing data reduction/analysis and present some of our preliminary results.
We report the discovery with XMM-Newton of quasiperiodic variability in the 0.2 - 10 keV X-ray flux from the ultraluminous X-ray source NGC 5408 X-1. The average power spectrum of all EPIC-pn data reveals a strong 20 mHz QPO with an average amplitude (rms) of 9%, and a coherence of Q~6. In a 33 ksec time interval when the 20 mHz QPO is strongest we also find evidence for a 2nd QPO peak at 15 mHz. This is the first indication for a close pair of QPOs in a ULX source. Interestingly, the frequency ratio of this QPO pair is inconsistent with 3:2 at the 3sigma level, but is consistent with a 4:3 ratio. A powerlaw noise component with slope near 1.5 is also present below 0.1 Hz with evidence for a break to a flatter slope at about 3 mHz. The source shows substantial broadband variability, with a total amplitude (rms) of about 30% in the 0.1 - 100 mHz frequency band, and there is strong energy dependence to the variability. We discuss the implications of these findings in the context of models for ULXs, and their implications for the object's mass.
As photosynthesis on Earth produces the primary signatures of life that can be detected astronomically at the global scale, a strong focus of the search for extrasolar life will be photosynthesis, particularly photosynthesis that has evolved with a different parent star. We take planetary atmospheric compositions simulated by Segura, et al. (2003, 2005) for Earth-like planets around observed F2V and K2V stars, modeled M1V and M5V stars, and around the active M4.5V star AD Leo; our scenarios use Earth's atmospheric composition as well as very low O2 content in case anoxygenic photosynthesis dominates. We calculate the incident spectral photon flux densities at the surface of the planet and under water. We identify bands of available photosynthetically relevant radiation and find that photosynthetic pigments on planets around F2V stars may peak in absorbance in the blue, K2V in the red-orange, and M stars in the NIR, in bands at 0.93-1.1 microns, 1.1-1.4 microns, 1.5-1.8 microns, and 1.8-2.5 microns. In addition, we calculate wavelength restrictions for underwater organisms and depths of water at which they would be protected from UV flares in the early life of M stars. We estimate the potential productivity for both surface and underwater photosynthesis, for both oxygenic and anoxygenic photosynthesis, and for hypothetical photosynthesis in which longer wavelength, multi-photosystem series are used.
(ABRIDGED) We present a study of the highly ionized gas (plasma) associated with damped Lyman-alpha (DLA) systems at z=2.1-3.1. We search for O VI absorption and corresponding Si IV, C IV, and N V in a Very Large Telescope/Ultraviolet-Visible Echelle Spectrograph (VLT/UVES) sample of 35 DLA systems with data covering O VI at S/N>10. We report twelve DLAs (nine intervening and three at <5000 km/s from the QSO redshift) with detections of O VI absorption. There are no clear O VI non-detections, so the incidence of O VI in DLAs is between 34% (12/35) and 100%. Analysis of the line widths together with photoionization modelling suggests that two phases of DLA plasma exist: a hot, collisionally ionized phase (seen in broad O VI components), and a warm, photoionized phase (seen just in narrow C IV and Si IV components). We find tentative evidence (98% confidence) for correlations between the DLA metallicity (measured in the neutral gas) and high-ion column density, and between the DLA metallicity and high-ion line width, as would be expected if supernova-driven galactic outflows rather than accretion produced the high ions. Using conservative ionization corrections, we find lower limits to the total hydrogen column densities in the hot (O VI-bearing) and warm (C IV-bearing) phases in the range log N(Hot H II) >19.5 to >21.1, and log N(Warm H II) >19.4 to >20.9. On average, the hot and warm phases thus contain >40% and >20% of the baryonic mass of the neutral phase in DLAs, respectively. If the temperature in the O VI phase is ~10^6 K and so f(O VI)=O VI/O<<0.2 the plasma can make a significant contribution to the metal budget at high redshift.
Constraining cosmological parameters from measurements of the Integrated Sachs-Wolfe effect requires developing robust and accurate methods for computing statistical errors in the cross-correlation between maps. This paper presents a detailed comparison of such error estimation applied to the case of cross-correlation of Cosmic Microwave Background (CMB) and large-scale structure data. We compare theoretical models for error estimation with montecarlo simulations where both the galaxy and the CMB maps vary around a fiducial auto-correlation and cross-correlation model which agrees well with the current concordance LCDM cosmology. Our analysis compares estimators both in harmonic and configuration (or real) space, quantifies the accuracy of the error analysis and discuss the impact of partial sky survey area and the choice of input fiducial model on dark-energy constraints. We show that purely analytic approaches yield accurate errors even in surveys that cover only 10% of the sky and that parameter constraints strongly depend on the fiducial model employed. Alternatively, we discuss the advantages and limitations of error estimators that can be directly applied to data. In particular, we show that errors and covariances from the Jack-Knife method agree well with the theoretical approaches and simulations. We also introduce a novel method in real space that is computationally efficient and can be applied to real data and realistic survey geometries. Finally, we present a number of new findings and prescriptions that can be useful for analysis of real data and forecasts, and present a critical summary of the analyses done to date.
The astrophysical processes that led to the formation of the first seed black holes and to their growth into the supermassive variety that powers bright quasars at redshift 6 are poorly understood. In standard LCDM hierarchical cosmologies, the earliest massive holes (MBHs) likely formed at redshift z~15 at the centers of low-mass (M>5e5 solar masses) dark matter ``minihalos'', and produced hard radiation by accretion. FUV/X-ray photons from such ``miniquasars'' may have permeated the universe more uniformly than EUV radiation, reduced gas clumping, and changed the chemistry of primordial gas. The role of accreting seed black holes in determining the thermal and ionization state of the intergalactic medium depends on the amount of cold and dense gas that forms and gets retained in protogalaxies after the formation of the first stars. The highest resolution N-body simulation to date of Galactic substructure shows that subhalos below the atomic cooling mass were very inefficient at forming stars.
We investigate the conditions under which the first low-mass stars formed in the universe by confronting theoretical predictions governing the transition from massive Population III to low-mass Population II stars with recent observational C and/or O abundance data of metal-poor Galactic stars. We introduce a new function, the transition discriminant D_trans, which allows powerful comparisons between samples of halo stars and theoretical predictions of the formation of the first low-mass stars (< 1 M_sun). Specifically, we test the theory that fine-structure lines of C and O dominate the transition from Pop III to Pop II in the early universe. We find the observational data for halo stars as well as for dSph galaxies and globular clusters to be consistent with this theory. An explanation for the observed lack of metal-poor stars in dSph galaxies and globular clusters is also suggested. Finally, we predict that any star to be found with [Fe/H]<-4 should have enhanced C and/or O abundances. The high C and O abundances of the two most iron-poor stars are in line with our prediction.
We report a three year, 18 epoch, VLBI monitoring study of H2O masers in the sub-parsec, warped, accretion disk within the NGC4258 AGN. Our immediate goals are to trace the geometry of the underlying disk, track rotation via measurement of proper motion, and ascertain the radii of masers for which centripetal acceleration may be measured separately. The monitoring includes ~ 4 times as many epochs, ~ 3 times denser sampling, and tighter control over sources of systematic error than earlier VLBI investigations. Coverage of a ~ 2400 km/s bandwidth has also enabled mapping of molecular material ~ 30% closer to the black hole than accomplished previously, which will strengthen geometric and dynamical disk models. Through repeated observation we have also measured for the first time a 5 microarsecond (1 sigma) thickness of the maser medium. Assuming this corresponds to the thickness of the accretion disk, hydrostatic equilibrium requires a disk plane temperature of ~ 600 K. Our long-term goal is a geometric distance to NGC4258 that is accurate to ~ 3%, a ~ 2 times improvement over the current best estimate. A geometric estimate of distance can be compared to distances obtained from analysis of Cepheid light curves, with the intent to recalibrate the extragalactic distance scale with reduced systematic uncertainties. This is the first paper in a series. We present here VLBI observations, data reduction, and temporal and spatial characteristics of the maser emission. Later papers will report estimation of orbital acceleration and proper motion, modeling of disk 3-D geometry and dynamics, and estimation of a "maser distance." Estimation of a "Cepheid distance" is presented in a parallel paper series.
The luminous, oxygen-rich supernova remnant, J1228+441, is located in the irregular galaxy NGC 4449 and has been observed at radio wavelengths for thirty years. An analysis of recent VLA observations of NGC 4449, combined with VLA archive data and previously published VLA and WSRT observations, yields light curves at 6 and 20 cm from 1972 to 2002. The light curves at all radio frequencies exhibit a marked decline in radio emission, confirming past findings. This paper presents and discusses the radio light curves and spectral index, alpha, variations from 1972 to 2002 where nu propto nu^(-alpha) and compares J1228+441 with other radio supernovae. The spectral index of J1228+441 appears to have steepened in the last five years at higher frequencies from alpha=0.64 +- 0.02 in 1996 to alpha=1.01 +- 0.02 in 2001-2002.
We present 10 - 19 um moderate resolution spectra of ten M dwarfs, one L dwarf, and two T dwarf systems obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The IRS allows us to examine molecular spectroscopic features/lines at moderate spectral resolution in a heretofore untapped wavelength regime. These R~600 spectra allow for a more detailed examination of clouds, non-equilibrium chemistry, as well as the molecular features of H2O, NH3, and other trace molecular species that are the hallmarks of these objects. A cloud-free model best fits our mid-infrared spectrum of the T1 dwarf epsilon Indi Ba, and we find that the NH3 feature in epsilon Indi Bb is best explained by a non-equilibrium abundance due to vertical transport in its atmosphere. We examined a set of objects (mostly M dwarfs) in multiple systems to look for evidence of emission features, which might indicate an atmospheric temperature inversion, as well as trace molecular species; however, we found no evidence of either.
The recent three-year WMAP data selects large-field models with certain power-law potentials and small-field models for all power-law potentials as consistent inflation models. We study the large-field and small-field inflation model with a quadratic and a quartic potential within the framework of quantum field theory in an expanding Friedmann-Robertson-Walker universe. We find that quantum fluctuations in the small-field model lead to a significant contribution to the effective potential and may have non-negligible effects on the slow-roll parameters predicted by classical theory.
Aims. We derive simple estimates of the maximum efficiency with which matter can be ejected by the propeller mechanism in disk-fed, rotating magnetic neutron stars. Some binary evolution scenarios envisage that this mechanism is responsible for expelling to infinity the mass inflowing at a low rate from the companion star, therefore limiting the total amount of mass that can be accreted by the neutron star. Methods. We demonstrate that, for typical neutron star parameters, a maximum of \eta_{pro} < 5.7 (P_{-3})^{1/3} times more matter than accreted can be expelled through the propeller mechanism at the expenses of the neutron star rotational energy (P_{-3} is the NS spin period in unit of 10E-3 s). Approaching this value, however, would require a great deal of fine tuning in the system parameters and the properties of the interaction of matter and magnetic field at the magnetospheric boundary. Results. We conclude that some other mechanism must be invoked in order to prevent that too much mass accretes onto the neutron stars of some low mass X-ray binaries.
In this paper we investigate the dependence of umbral core brightness, as well as the mean umbral and penumbral brightness on the phase of the solar cycle and on the size of the sunspot. Albregtsen & Maltby (1978) reported an increase in umbral core brightness from the early to the late phase of solar cycle from the analysis of 13 sunspots which cover solar cycles 20 and 21. Here we revisit this topic by analysing continuum images of more than 160 sunspots observed by the MDI instrument on board the SOHO spacecraft for the period between 1998 March to 2004 March, i.e. a sizable part of solar cycle 23. The advantage of this data set is its homogeneity, with no seeing fluctuations. A careful stray light correction, which is validated using the Mercury transit of 7th May, 2003, is carried out before the umbral and penumbral intensities are determined. The influence of the Zeeman splitting of the nearby NiI spectral line on the measured 'continuum' intensity is also taken into account. We did not observe any significant variation in umbral core, mean umbral and mean penumbral intensities with solar cycle, which is in contrast to earlier findings for the umbral core intensity. We do find a strong and clear dependence of the umbral brightness on sunspot size, however. The penumbral brightness also displays a weak dependence. The brightness-radius relationship has numerous implications, some of which, such as those for the energy transport in umbrae, are pointed out.
In recent years evidence has accumulated that nearby spiral galaxies are surrounded by massive haloes of neutral and ionised gas. These gaseous haloes rotate more slowly than the disks and show inflow motions. They are clearly analogous to the High Velocity Clouds of the Milky Way. We show that these haloes cannot be produced by a galactic fountain process (supernova outflows from the disk) where the fountain gas conserves its angular momentum. Making this gas interact with a pre-existing hot corona does not solve the problem. These results point at the need for a substantial accretion of low angular momentum material from the IGM.
Several studies of nearby active galaxies indicate significantly higher HCN-to-CO intensity ratios in AGN than in starburst (SB) environments. HCN enhancement can be caused by many different effects, such as higher gas densities/temperatures, UV/X-ray radiation, and non-collisional excitation. As active galaxies often exhibit intense circumnuclear SB, high angular resolution/sensitivity observations are of paramount importance to disentangling the influence of SB from that of nuclear activity on the chemistry of the surrounding molecular gas. The tight relation of HCN enhancement and nuclear activity may qualify HCN as an ideal tracer of molecular gas close to the AGN, providing complementary and additional information to that gained via CO. NGC6951 houses nuclear and SB activity, making it an ideal testbed in which to study the effects of different excitation conditions on the molecular gas. We used the new ABCD configurations of the IRAM PdBI to observe HCN(1-0) in NGC6951 at high angular resolution (1''). We detect very compact (<50pc) HCN emission in its nucleus, supporting previous hints of nuclear gas structure. Our observations also reveal HCN emission in the SB ring and resolve it into several peaks, leading to a higher coincidence between the HCN and CO distributions than previously reported. We find a significantly higher HCN-to-CO intensity ratio (>0.4) in the nucleus than in the SB ring (0.02-0.05). As for NGC1068, this might result from a higher HCN abundance in the centre due to an X-ray dominated gas chemistry, but a higher gas density/temperature or additional non-collisional excitation of HCN cannot be entirely ruled out, based on these observations. The compact HCN emission is associated with rotating gas in a circumnuclear disk/torus.
We investigate the dynamics of the nebula around the symbiotic star Hen 2-147, determine its expansion parallax, and compare it with the distance obtained via the Period-Luminosity relation for its Mira variable. The geometry of the nebula is found to be that of a knotty annulus of ionized gas inclined to the plane of sky and expanding with a velocity of ~90 km/s. A straightforward application of the expansion parallax method provides a distance of 1.5+-0.4 kpc, which is a factor of two lower than the distance of 3.0+-0.4 kpc obtained from the Period-Luminosity relationship for the Mira (which has a pulsation period of 373 days). The discrepancy is removed if, instead of expanding matter, we are observing the expansion of a shock front in the plane of the sky. This shock interpretation is further supported by the broadening of the nebular emission lines.
The holographic dark energy model is proposed by Li as an attempt for probing the nature of dark energy within the framework of quantum gravity. The main characteristic of holographic dark energy is governed by a numerical parameter $c$ in the model. The parameter $c$ can only be determined by observations. Thus, in order to characterize the evolving feature of dark energy and to predict the fate of the universe, it is of extraordinary importance to constrain the parameter $c$ by using the currently available observational data. In this paper, we derive constraints on the holographic dark energy model from the latest observational data including the gold sample of 182 Type Ia supernovae (SNIa), the shift parameter of the cosmic microwave background (CMB) given by the three-year {\it Wilkinson Microwave Anisotropy Probe} ({\it WMAP}) observations, and the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS). The joint analysis gives the fit results in 1-$\sigma$: $c=0.91^{+0.26}_{-0.18}$ and $\Omega_{\rm m0}=0.29\pm 0.03$. That is to say, though the possibility of $c<1$ is more favored, the possibility of $c>1$ can not be excluded in one-sigma error range, which is somewhat different from the result derived from previous investigations using earlier data. So, according to the new data, the evidence for the quintom feature in the holographic dark energy model is not as strong as before.
Assuming a naive star formation history, we construct the synthetic X-ray source populations for comparison with the X-ray luminosity function (XLF) of the interacting galaxies NGC 4038/4039 using a population synthesis code. We have considered high- and intermediate-mass X-ray binaries, young rotation-powered pulsars and fallback disc-fed black holes in modelling the bright X-ray sources detected. To examine the effects of the input parameters on the calculated results we produce a series of hybrid models. We find that for typical binary evolution parameters, it is difficult to match the observed XLF shape, and the predicted XLFs seem to be steeper than those of starburst and late type spiral galaxies. We note that the shape of the XLFs depends critically on the existence of XLF break for young populations, which seems to be a popular feature in theoretical population synthesis works. We discuss possible reasons and implications on the discrepancy of the calculated and observational XLFs.
We present results of a new feedback scheme implemented in the Munich galaxy formation model. The new scheme includes a dynamical treatment of galactic winds powered by supernovae explosions and stellar winds and is an excellent alternative to empirically-motivated recipes for feedback in galaxy formation. Model results are in good agreement with the observed luminosity function and stellar mass function for galaxies in the local Universe. In particular, the new scheme predicts a number density of dwarfs that is lower than in previous models. The model is also able to reproduce the observed mass--stellar metallicity and luminosity-gas metallicity relations. This demonstrates that our scheme provides a significant improvement in the treatment of the feedback in dwarf galaxies. A new feature of the model allows an estimate of the amount of mass and metals that haloes can permanently deposit into the IGM. It is this loss of material that leads to a suppression of star formation in small haloes and therefore to a decrease in the number density of dwarf galaxies. Despite its successes, our model does not reproduce the observed bimodality in galaxy colours. Finally, we investigate the efficiency of mass and metal injections in winds and in the intergalactic medium. We find that galaxies that reside in haloes with M_vir < 10^12.5 M_sun may deposit most of their metal mass into the intergalactic medium, while groups and clusters at z=0 have lost at most a few percent of their metals before the bulk of the halo mass was accreted.
We report interstellar FeII and SiII column densities toward six translucent sight lines (A_V >~ 1) observed with the Space Telescope Imaging Spectrograph (STIS). The abundances were determined from the absorption of SiII] at 2335 Angstroms, and several weak Fe transitions including the first reported detections of the 2234 Angstrom line. We derive an empirical f-value for the FeII 2234 Angstrom transition of log(f lambda) = -1.54 +/- 0.05. The observed sight lines sample a variety of extinction characteristics as indicated by their R_V values, which range from 2.6 - 5.8. The dust-phase abundances of both Si and Fe are positively correlated with the small-grain population (effective radii smaller than a few hundred micron) toward the targets. The physical conditions along the sight lines suggest that this relationship may be due to differences in the survival of small particles in some interstellar environments. The chemical composition of the small grains could either resemble dust mantles or be silicate rich.
The study of the dominant population of high redshift IR-luminous galaxies (10^11 - 10^12 Lsun at 1<z<3), requires observation of sources at the ~0.1 mJy level in the mid-IR. We present the deepest spectra taken to date with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. We targeted two faint (f24~0.15 mJy) sources in the Southern GOODS field at z=1.09 and z=2.69. Spectra of the lower redshift target were taken in the observed-frame 8--21 micron range, while the spectrum of the higher redshift target covered 21--37 microns. We also present the spectra of two secondary sources within the slit. We detect strong PAH emission in all four targets, and compare the spectra to those of local galaxies observed by the IRS. The z=1.09 source appears to be a typical, star-formation dominated IR-luminous galaxy, while the z=2.69 source is a composite source with strong star formation and a prominent AGN. The IRAC colors of this source show no evidence of rest-frame near-infrared stellar photospheric emission. We demonstrate that an AGN which contributes only a small (~10%) fraction of the bolometric luminosity can produce enough hot dust emission to overwhelm the near-IR photospheric emission from stars. Such sources would be excluded from photometric surveys which rely on the near-IR bump to identify starbursts, leading to an underestimate of the star formation rate density.
The soft excess seen in many AGN is most probably due to partially ionized material moving at relativistic speeds close to the black hole. There are currently two potential geometries for this material, one where it is out of the line of sight, seen via reflection, e.g. the accretion disc, the other where it is in the line of sight, seen in absorption e.g. a wind above the disc. Both models require apparent fine tuning of the ionization parameter of this material in order to produce the large jump in opacity at ~0.7 keV associated with OVII/VIII, as required to make the soft excess. However, Chevalier et al (2006) show that these states rather naturally dominate the absorption spectrum for soft X-ray spectra if the illuminated material is (at least approximately) in pressure balance. Here we explore whether hydrostatic pressure equilibrium in a disc can likewise naturally select the required ionization states in reflection. We find the opposite. The soft excess X-ray excess is much weaker in the hydrostatic models than it is in the constant density models. Since even the constant density models cannot fit the largest soft excesses seen without the intrinsic continuum being hidden from view, this means that reflection from a hydrostatic disc cannot realistically match the data. Even if the disc structure is instead more like constant density atmosphere, the required fine-tuning of the ionization parameter still remains a problem, making this also an unlikely explanation for the soft excess.
We compare the hot star wind models calculated assuming older solar abundance determination with models calculated using the recently published values derived from 3D hydrodynamical model atmospheres. We show that the use of new abundances with lower metallicity improves the agreement between wind observation and theory in several aspects: (1) The predicted wind mass-loss rates are lower by a factor of 0.76. This leads to a better agreement with mass-loss rate determinations derived from observations with account of clumping. (2) As a result of the lowering of mass-loss rates, there is a better agreement between predicted modified wind momentum-luminosity relationship and that derived from observations with account of clumping. (3) Both the lower mass fraction of heavier elements and lower mass-loss rates lead to a decrease of the opacity in the X-ray region. This has influence on the prediction of the X-ray line profile shapes. (4) There is a better agreement between predicted PV ionization fractions and those derived from observations.
We have observed the micro-quasar V4641 Sgr (SAX J1819.3-2525) at the time of flare during May 2002, using the Giant Metrewave Radio Telescope at low radio frequencies (244 and 610 MHz). This is the lowest frequency radio detection of the source. The source showed clear signature of spectral evolution from optically thick to thin state. We model the spectral evolution of the source to obtain some of the source parameters. Assuming the value of magnetic field strength to be in the range of 0.1 to 1 Gauss, we obtain the initial velocity of expansion of the jet to be in the range $\sim$ 0.45c to 0.25c. This is consistent with the known expansion velocities of the jet with other microquasars.
We present broad band optical afterglow observations of a long duration GRB 060124 using the 1.04-m Sampurnanand Telescope at ARIES, Nainital and the 2.01-m HCT at IAO, Hanle, including the earliest ground based observations in R band for this GRB. We determine the decay slope of the light curve at different bands and examine the reality of a proposed jet break. We use data from our observations as well as others reported in the literature to construct light curves in different bands and make power law fits to them. The spectral slope of the afterglow emission in the optical band is estimated. Our first R-band observations were taken $\sim 0.038$~d after burst. We find that all available optical data after this epoch are well fit by a single power law, with a temporal flux decay index $\alpha\sim 0.94$. We do not find any evidence of a jet break within our data, which extend till $\sim 2$~d after the burst. The X-ray light curve, however, shows a distinct break around 0.6 day. We attribute this break to a steepening of the electron energy spectrum at high energies. We conclude that the above measurements are consistent with the picture of a standard fireball evolution with no jet break within $t\sim 2$~days after the burst. This sets a lower limit of $3\times 10^{50}$~erg to the total energy released in the explosion.
We present a methodological study to find out how far back and to what precision star formation histories of galaxies can be reconstructed from CMDs, from integrated spectra and Lick indices, and from integrated multi-band photometry. Our evolutionary synthesis models GALEV allow to describe the evolution of galaxies in terms of all three approaches and we have assumed typical observational uncertainties for each of them and then investigated to what extent and accuracy different star formation histories can be discriminated. For a field in the LMC bar region with both a deep CMD from HST observations and a trailing slit spectrum across exactly the same field of view we could test our modelling results against real data.
The Galactic open cluster Westerlund 1 was found only a few years ago to be
much more massive than previously thought, with evidence suggesting its mass to
be in excess of ~10^5 Msun, in the range spanned by young extragalactic star
clusters. Unlike those clusters its proximity makes spatially resolved studies
of its stellar population feasible. It is therefore the ultimate template for a
young, massive star cluster, permitting direct comparison of its properties
with measurements of velocity dispersion and dynamical mass for spatially
unresolved extragalactic clusters.
To this end, we used the long slit near-infrared spectrograph VLT/ISAAC to
observe the CO bandhead region near 2.29 micron scanning the slit across the
cluster centre during the integration. Spatially collapsing the spectra along
the slit results in a single co-added spectrum of the cluster, comparable to
what one would obtain in the extragalactic cluster context.
This spectrum was analysed the same way as the spectra of almost point-like
extragalactic clusters, using red superiant cluster members as velocity
templates.
We detected four red supergiants which are included in the integrated
spectrum, and our measured velocity dispersion is 5.8 km/s. Together with the
cluster size of 0.86 pc, derived from archival near-infrared SOFI-NTT images,
this yields a dynamical mass of 6.3x10^4 Msun. While this value is not to be
considered the final word, there is at least so far no sign for rapid expansion
or collapse.
In thermonuclear supernovae, intermediate mass elements are mostly produced by distributed burning provided that a deflagration to detonation transition does not set in. Apart from the two-dimensional study by Roepke & Hillebrandt (2005), very little attention has been payed so far to the correct treatment of this burning regime in numerical simulations. In this article, the physics of distributed burning is reviewed from the literature on terrestrial combustion and differences which arise from the very small Prandtl numbers encountered in degenerate matter are pointed out. Then it is shown that the level set method continues to be applicable beyond the flamelet regime as long as the width of the flame brush does not become smaller than the numerical cutoff length. Implementing this constraint with a simple parameterisation of the effect of turbulence onto the energy generation rate, the production of intermediate mass elements increases substantially compared to previous simulations, in which the burning process was stopped once the mass density dropped below 10^7 g/cm^3. Although these results depend on the chosen numerical resolution, an improvement of the constraints on the the total mass of burning products in the pure deflagration scenario can be achieved.
We present near-infrared imaging with ESO VLT+ISAAC of the host galaxies of low luminosity quasars in the redshift range 1 < z < 2, aimed at investigating the relationship between the nuclear and host galaxy luminosities at high redshift. This work complements our previous study to trace the cosmological evolution of the host galaxies of high luminosity quasars (Falomo et al. 2004). The new sample includes 15 low luminosity quasars, nine radio-loud (RLQ) and six radio-quiet (RQQ). They have similar distribution of redshift and optical luminosity, and together with the high luminosity quasars they cover a large range (~4 mag) of the quasar luminosity function. The host galaxies of both types of quasars are in the range of massive inactive ellipticals between L* and 10 L*. RLQ hosts are systematically more luminous than RQQ hosts by a factor of ~2. This difference is similar to that found for the high luminosity quasars. This luminosity gap appears to be independent of the rest-frame U-band luminosity but clearly correlated with the rest-frame R-band luminosity. The color difference between the RQQs and the RLQs is likely a combination of an intrinsic difference in the strength of the thermal and nonthermal components in the SEDs of RLQs and RQQs, and a selection effect due to internal dust extinction. For the combined set of quasars, we find a reasonable correlation between the nuclear and the host luminosities. This correlation is less apparent for RQQs than for RLQs. If the R-band luminosity is representative of the bolometric luminosity, and assuming that the host luminosity is proportional to the black hole mass, as observed in nearby massive spheroids, quasars emit with a relatively narrow range of power with respect to their Eddington luminosity and with the same distribution for RLQs and RQQs.
Dissipationless collapses in Modified Newtonian Dynamics (MOND) are studied by using a new particle-mesh N-body code based on our numerical MOND potential solver. We found that low surface-density end-products have shallower inner density profile, flatter radial velocity-dispersion profile, and more radially anisotropic orbital distribution than high surface-density end-products. The projected density profiles of the final virialized systems are well described by Sersic profiles with index m~4, down to m~2 for a deep-MOND collapse. Consistently with observations of elliptical galaxies, the MOND end-products, if interpreted in the context of Newtonian gravity, would appear to have little or no dark matter within the effective radius. However, we found impossible (under the assumption of constant mass-to-light ratio) to simultaneously place the resulting systems on the observed Kormendy, Faber-Jackson and Fundamental Plane relations of elliptical galaxies. Finally, the simulations provide strong evidence that phase mixing is less effective in MOND than in Newtonian gravity.
We use the Hubble Ultra Deep Field to study the galaxy luminosity-size (M-Re) distribution. With a careful analysis of selection effects due to both detection completeness and measurement reliability we identify bias-free regions in the M-Re plane for a series of volume-limited samples. By comparison to a nearby survey also having well defined selection limits, namely the Millennium Galaxy Catalogue, we present clear evidence for evolution in surface brightness since z ~ 0.7. Specifically, we demonstrate that the mean, rest-frame B-band surface brightness for galaxies in a sample spanning 8 magnitudes in luminosity between M = -22 and -14 mag increases by ~1.0 mag/arcsec^2 from z ~ 0.1 to z ~ 0.7. We also highlight the importance of considering surface brightness dependent measurement biases in addition to incompleteness biases. In particular, the increasing, systematic under-estimation of Kron fluxes towards low surface brightnesses may cause diffuse, yet luminous, systems to be mistaken for faint, compact objects.
New data and results on the optical behaviour of the blazar PKS 0735+178 are presented. In addition the whole historical light curve, and a new photometric calibration of comparison stars are reported. Optical spectral indexes are calculated and studied on years scales, while several methods for time-series analysis are applied to the whole historical series and to each observing season of our data set. This allowed to search and identify optical variability modes, characteristic timescales and the signal power spectrum over 3 decades in time. In the last 10 years the optical flux of PKS 0735+178 exhibited a rather achromatic long-term behaviour and a variability mode resembling the shot-noise. The brightness level was in an intermediate/low state with a mild flaring activity and a superimposition/succession of rapid and slower flares, with no extraordinary/isolated outbursts but, at any rate, characterized by 1 major active phase in 2001. Several mid-term scales (days, weeks) were found, the more common falling into values of about 27-28 days, 50-56 days and 76-79 days. The rapid variability in the historical curve appear to be modulated by a general, slower and rather oscillating trend, where typical timescales of about 4.5, 8.5 and 11-13 years can be identified. This spectral and temporal analysis, accompanying our data publication, suggests the occurrence of distinctive variability signatures at days/weeks scales, that can likely be of transitory nature. On the other hand the possible pseudo-cyclical or multi-component modulations at long times could be more stable, recurrent and correlated to the bimodal radio flux behaviour and the twisted radio structure observed by many years in this blazar.
This online dictionary presents the definition of classical as well as advanced concepts of modern astronomy. Moreover, each English entry is accompanied by its French and Persian equivalents. The dictionary is intended to be helpful to professional as well as amateur astronomers. As a notable particularity, it also provides a detailed etymology of English and Persian terms. The etymological material contained in this work may interest linguists, in particular those concerned with the evolution of Indo-European languages, especially with that of their Iranian branch. Apart from educational and outreach objectives in the field of astronomy, one of the main aims of this work is to contribute to the Persian language by creating a comprehensive dictionary of astronomy and astrophysics.
The Taurus-Auriga star-forming complex hosts the only population of T Tauri stars in which an anticorrelation of X-ray activity and rotation period has been observed. We have used XMM-Newton's European Photon Imaging Cameras to perform the most sensitive survey to date of X-ray emission (0.3-10 keV) from young stars in Taurus-Auriga and investigate the dependences of X-ray activity measures -- X-ray luminosity, Lx, its ratio with the stellar luminosity, Lx/Lstar, and the surface-averaged X-ray flux, Fxs -- on rotation period. We tested for differences in the distributions of Lx/Lstar of fast and slow rotators, accretors and non-accretors, and compared the dependence of Lx/Lstar on the ratio of the rotation period and the convective turnover timescale, the Rossby number, with that of late-type main-sequence stars. We found significant anticorrelations of Lx and Fxs with rotation period, but these could be explained by the typically higher stellar luminosity and effective temperature of fast-rotators in Taurus-Auriga and a near-linear dependence of Lx on Lstar. We found no evidence for a dependence of Lx/Lstar on rotation period, but for accretors to have lower Lx/Lstar than non-accretors at all rotation periods. The Rossby numbers of accretors and non-accretors were found to be the same as those of late-type main-sequence stars showing saturated X-ray emission. We conclude that non-accreting T Tauri stars show X-ray activity entirely consistent with the saturated activity of late-type main-sequence stars. Accreting T Tauri stars show lower X-ray activity, which cannot be attributed to their slower rotation.
We report on the development of an innovative CdTe detector plane (DPIX) optimized for the detection and localization of gamma-ray bursts in the X-ray band (below 100 keV). DPIX is part of an R&D program funded by the French Space Agency (CNES). DPIX builds upon the heritage of the ISGRI instrument, currently operating with great success on the ESA INTEGRAL mission. DPIX is an assembly of 200 elementary modules (XRDPIX) equipped with 32 CdTe Schottky detectors (4x4 mm2, 1 mm thickness) produced by ACRORAD Co. LTD. in Japan. These detectors offer good energy response up to 100 keV. Each XRDPIX is readout by the very low noise front-end electronics chip IDeF-X, currently under development at CEA/DSM/DAPNIA. In this paper, we describe the design of XRDPIX, the main features of the IDeF-X chip, and will present preliminary results of the reading out of one CdTe Schottky detector by the IDeF-X V1.0 chip. A low-energy threshold around 2.7 keV has been measured. This is to be compared with the 12-15 keV threshold of the ISGRI-INTEGRAL and BAT-SWIFT instruments, which both use similar detector material.
We study the locus of dwarf and giant early and late-type galaxies on the Tully-Fisher relation (TFR), the stellar mass Tully-Fisher relation (sTFR) and the so-called baryonic or HI gas+stellar mass Tully-Fisher relation (gsTFR). We show that early-type and late-type galaxies, from dwarfs to giants, trace different yet approximately parallel TFRs. Surprisingly, early-type and late-type galaxies trace a single yet curved sTFR over a range of 3.5 orders of magnitude in stellar mass. Moreover, all galaxies trace a single, linear gsTFR, over 3.5 orders of magnitude in HI gas+stellar mass. Dwarf ellipticals, however, lie slightly below the gsTFR. This may indicate that early-type dwarfs, contrary to the late-types, have lost their gas, e.g. by galactic winds or ram-pressure stripping. Overall, environment only plays a secondary role in shaping these relations, making them a rather ``clean'' cosmological tool. LCDM simulations predict roughly the correct slopes for these relations.
We report sub-arcsec CO observations of the disks around MWC 480, LkCa 15 and DM Tau, and simultaneous measurements of HCO+ J=1-0. We derive the disk properties by fitting a standard disk model, with all parameters power laws of the distance to the star. Biases are explained and discussed. We find evidence for vertical temperature gradient in the disks of MWC 480 and DM Tau, as in AB Aur, but not in LkCa 15. The disks temperature increase with stellar effective temperature. Most of the CO gas is at temperatures smaller than 17 K, the condensation temperature on grains. The scale height of the CO distribution appears larger (by 50%) than the hydrostatic scale height. The more UV luminous stars have more CO, but there is no simple dependency of CO abundance and isotopologue ratio with stellar type. The 13CO/HCO+ ratio is around 600. The temperature behaviour is consistent with expectations, but published chemical models have difficulty reproducing the observed CO quantities. Vertical mixing and photo-dissociation at the disk outer edge seem important chemical agents. The CO data suggest a more complex surface density distribution than assumed in models.
A new revision of the gamma flux that we expect to detect in Imaging Atmospheric Cherenkov Telescopes (IACTs) from SUSY dark matter annihilation in the Draco dSph is presented using the dark matter density profiles compatible with the latest observations. This revision takes also into account the important effect of the Point Spread Function (PSF) of the telescope. We show that this effect is crucial in the way we will observe and interpret a possible signal detection. In particular, it could be impossible to discriminate between a cuspy and a cored dark matter density profile due to the fact that both density profiles may yield very similar flux profile observed by the telescope. Finally, we discuss the prospects to detect a possible gamma signal from Draco for current or planned experiments, i.e. MAGIC, GLAST and GAW.
We present the properties of a cosmic superstring network in the scenario of flux compactification. An infinite family of strings, the (p,q)-strings, are allowed to exist. The flux compactification leads to a string tension that is periodic in p. Monopoles, appearing here as beads on a string, are formed in certain interactions in such networks. This allows bare strings to become cosmic necklaces. We study network evolution in this scenario, outlining what conditions are necessary to reach a cosmologically viable scaling solution. We also analyze the physics of the beads on a cosmic necklace, and present general conditions for which they will be cosmologically safe, leaving the network's scaling undisturbed. In particular, we find that these conditions include requiring the average loop size to be large. Finally, we argue that loop formation will promote a scaling solution for the interbead distance in some situations.
Bimodality is a common feature of globular cluster (GC) color distributions in galaxies. Although it is well known that the GC system of the Milky Way is bimodal in metallicity, this has yet to be directly demonstrated for an elliptical galaxy. We use Lick index measurements from the literature to derive metallicities for 47 GCs in the giant Virgo elliptical galaxy NGC 4472. The resulting distribution shows clear evidence for two metallicity subpopulations of GCs.
From a quantitative analysis of 413 Virgo cluster early-type dwarf galaxies (dEs) with Sloan Digital Sky Survey imaging data, we find that the dE class can be divided into multiple subpopulations that differ significantly in their morphology and clustering properties. Three dE subclasses are shaped like thick disks and show no central clustering: (1) dEs with disk features like spiral arms or bars, (2) dEs with central star formation, and (3) ordinary, bright dEs that have no or only a weak nucleus. These populations probably formed from infalling progenitor galaxies. In contrast, ordinary nucleated dEs follow the picture of classical dwarf elliptical galaxies in that they are spheroidal objects and are centrally clustered like E and S0 galaxies, indicating that they have resided in the cluster since a long time, or were formed along with it. These results define a morphology-density relation within the dE class. We find that the difference in the clustering properties of nucleated dEs and dEs with no or only a weak nucleus is not caused by selection biases, as opposed to previously reported suggestions. The correlation between surface brightness and observed axial ratio favors oblate shapes for all subclasses, but our derivation of intrinsic axial ratios indicates the presence of at least some triaxiality. We discuss possible interrelations and formation mechanisms (ram-pressure stripping, tidally induced star formation, harassment) of these dE subpopulations.
The flat decay phase in the first 100-1e4 seconds of the X-ray light curve of Gamma Ray Bursts (GRBs) has not yet found a convincing explanation. The fact that the optical and X-ray lightcurves are often different, with breaks at different times, makes contrived any explanation based on the same origin for both the X-ray and optical fluxes. We here propose that the central engine can be active for a long time, producing shells of decreasing kinetic energy and bulk Lorentz factor Gamma The internal dissipation of these late shells, at radii similar to what occurs for the early prompt, can produce radiation most often dominant in the X-ray band, and sometimes even in the optical. When Gamma of the late shells is larger than 1/theta_j, where theta_j is the jet opening angle, we see only a portion of the emitting surface. Eventually, Gamma becomes smaller than 1/theta_j, and the entire emitting surface is visible. Thus there is a break in the light curve when Gamma=1/theta_j, which we associate to the time at which the plateau ends. After a few hundreds seconds since the onset of the burst, i.e. after the steeply decaying phase which follows the early prompt, we see the sum of two emission components: the "late--prompt" emission (due to late internal dissipation), and the "real afterglow" emission (due to external shocks). A variety of different optical and X-ray light curves are then possible, explaining why the X-ray and the optical light curves often do not track each other (but sometimes do), and often they do not have simultaneous breaks.
Far-infrared Spitzer observations of elliptical galaxies are inconsistent with simple steady state models of dust creation in red giant stars and destruction by grain sputtering in the hot interstellar gas at T ~ 10^7 K. The flux at 24 microns correlates with optical fluxes, suggesting that this relatively hot dust is largely circumstellar. But fluxes at 70 and 160 microns do not correlate with optical fluxes. Elliptical galaxies with similar L_B have luminosities at 70 and 160 microns (L_70 and L_160) that vary over a factor ~ 100, implying an additional source of dust unrelated to that produced by ongoing local stellar mass loss. Neither L_70/L_B nor L_160/L_B correlate with the stellar age or metallicity. Optical line fluxes from warm gas at T ~ 10^4 K correlate weakly with L_70 and L_160, suggesting that the dust may be responsible for cooling this gas. Many normal elliptical galaxies have emission at 70 microns that is extended to 5-10 kpc. Extended far-infrared emission with sputtering lifetimes of ~10^8 yrs is difficult to maintain by mergers with gas-rich galaxies. Instead, we propose that this cold dust is buoyantly transported from reservoirs of dust in the galactic cores which is supplied by mass loss from stars in the core. Intermittent energy outbursts from AGNs can drive the buoyant outflow.
We calculate the power spectrum of curvature perturbations when the inflaton field is rolling over the top of a local maximum of a potential. We show that the evolution of the field can be decomposed into a late-time attractor, which is identified as the slow roll solution, plus a rapidly decaying non-slow roll solution, corresponding to the field rolling ``up the hill'' to the maximum of the potential. The exponentially decaying transient solution can map to an observationally relevant range of scales because the universe is also expanding exponentially. We consider the two branches separately and we find that they are related through a simple transformation of the slow roll parameter $\eta$ and they predict identical power spectra. We generalize this approach to the case where the inflaton field is described by both branches simultaneously and find that the mode equation can be solved exactly at all times. Even though the slow roll parameter $\eta$ is evolving rapidly during the transition from the transient solution to the late-time attractor solution, the resultant power spectrum is an exact power-law spectrum. Such solutions may be useful for model-building on the string landscape.
We study the prospects for constraining dark energy at very high redshift with the Sandage-Loeb (SL) test - a measurement of the evolution of cosmic redshift obtained by taking quasar spectra at sufficiently separated epochs. This test is unique in its coverage of the ``redshift desert'', corresponding roughly to redshifts between 2 and 5, where other dark energy probes are unable to provide useful information about the cosmic expansion history. Extremely large telescopes planned for construction in the near future, with ultra high resolution spectrographs (such as the proposed CODEX), will indeed be able to measure cosmic redshift variations of quasar Lyman-alpha absorption lines over a period as short as ten years. We find that these measurements can constrain non-standard and dynamical dark energy models with high significance and in a redshift range not accessible with future dark energy surveys. As the cosmic signal increases linearly with time, measurements made over several decades by a generation of patient cosmologists may provide definitive constraints on the expansion history in the era that follows the dark ages but precedes the time when standard candles and rulers come into existence.
We apply a novel adaptive mesh refinement code, AMRVAC, to numerically investigate the various evolutionary phases in the interaction of a relativistic shell with its surrounding cold Interstellar Medium (ISM). We do this for both 1D isotropic as well as full 2D jetlike fireball models. This is relevant for Gamma Ray Bursts, and we demonstrate that, thanks to the AMR strategy, we resolve the internal structure of the shocked shell-ISM matter, which will leave its imprint on the GRB afterglow. We determine the deceleration from an initial Lorentz factor $\gamma=100$ up to the almost Newtonian $\gamma\sim{\cal O}(2)$ phase of the flow. We present axisymmetric 2D shell evolutions, with the 2D extent characterized by their initial opening angle. In such jetlike GRB models, we discuss the differences with the 1D isotropic GRB equivalents. These are mainly due to thermally induced sideways expansions of both the shocked shell and shocked ISM regions. We found that the propagating 2D ultrarelativistic shell does not accrete all the surrounding medium located within its initial opening angle. Part of this ISM matter gets pushed away laterally and forms a wide bow-shock configuration with swirling flow patterns trailing the thin shell. The resulting shell deceleration is quite different from that found in isotropic GRB models. As long as the lateral shell expansion is merely due to ballistic spreading of the shell, isotropic and 2D models agree perfectly. As thermally induced expansions eventually lead to significantly higher lateral speeds, the 2D shell interacts with comparably more ISM matter and decelerates earlier than its isotropic counterpart.
We present morphological and statistical results of a study of neutral hydrogen (HI) in a complete sample of nearby, non-cluster radio galaxies. We detect large-scale HI emission in the early-type host galaxies of 25% of our sample sources. The large-scale HI is mainly distributed in disk- and ring-like structures with sizes up to 190 kpc and masses up to 2 x 10^10 M_solar. All radio galaxies with M_HI >= 10^9 M_solar have a compact radio source. When we compare our sample of radio-loud early-type galaxies with samples of radio-quiet early-type galaxies there appears to be no significant difference in HI properties (mass, morphology and detection rate). This suggests that that the radio-loud phase could be just a short phase that occurs at some point during the life-time of many, or even all, early-type galaxies.
Long-running measurements of the solar radio flux density at 810 MHz were processed. Based on the least-squares method and using modified periodograms and an iterative technique of fitting and subtracting sinusoids in the time domain, frequency, amplitude, and phase characteristics of any analyzed time series were obtained. Solar cycles 20, 21, and 22 and shorter segments around solar minima and maxima were examined separately. Also, dynamic studies with 405, 810, and 1620 day windows were undertaken. The harmonic representations obtained for all these time series indicate large differences among solar cycles and their segments. We show that the solar radio flux at 810 MHz violates the Gnevyshev-Ohl rule for the pair of cycles 22-23. Analyzing the period 1957-2004, the following spectral periods longer than 1350 days were detected: 10.6, 8.0, 28.0, 5.3, 55.0, 3.9, 6.0, 4.4, and 14.6 yr. For spectral periods between 270 and 1350 days the 11 yr cycle is not recognized. We think that these harmonics form ``impulses of activity'' or a quasi-biennial cycle defined in the Benevolenskaya model of the ``double magnetic cycle.'' The value of about 0.09 is proposed for the interaction parameter (between the low- and high-frequency components) of this model. We confirm the intermittent behavior of the periodicity near 155 days. Correlation coefficients between the radio emission at 810 MHz and sunspot numbers, as well as the radio emission at 2800 MHz calculated for 540 day intervals, depend on the solar cycle phase.
The strong broad emission lines in the optical and UV spectra of Active Galactic Nuclei (AGN) are important for several reasons. Not only do they give us information about the structure of the AGN, their properties are now used to estimate black hole masses and metallicities in the vicinity of quasars, and these estimates are propagated widely throughout astronomy today. Photoionization codes such as Cloudy are invaluable for understanding the physical conditions of the gas emitting AGN broad lines. In this review, we discuss briefly the development of the historical ``standard'' model. We then review evidence that the following are important: 1.) the column density, in particular the presence of gas optically thin to the hydrogen continuum, influences the line emission; 2.) the BLR emission region is comprised of gas with a range of densities and ionization parameters; 3.) the spectral energy distribution of an individual AGN influences the line ratios in an observable way.
We present results of a study of neutral hydrogen (HI) in a complete sample of nearby non-cluster radio galaxies. We find that radio galaxies with large amounts of extended HI (M_HI >= 10^9 M_solar) all have a compact radio source. The host galaxies of the more extended radio sources, all of Fanaroff & Riley type-I, do not contain these amounts of HI. We discuss several possible explanations for this segregation. The large-scale HI is mainly distributed in disk- and ring-like structures with sizes up to 190 kpc and masses up to 2 x 10^10 M_solar. The formation of these structures could be related to past merger events, although in some cases it may also be consistent with a cold-accretion scenario.
High resolution spectroscopy with FUSE and STIS of atomic and molecular velocity stratification in the nebular outflow of M27 challenge models for the abundance kinematics in planetary nebulae. The simple picture of a very high speed (~ 1000 km/s), high ionization, radiation driven stellar wind surrounded by a slower (~ 10 km/s) mostly molecular outflow, with low ionization and neutral atomic species residing at the wind interaction interface, is not supported... We find ...there is a fast (33 -- 65 km/s) low ionization zone, surrounding a slower (<~ 33 km/s) high ionization zone and, at the transition velocity (33 km/s), vibrationally excited H_2 is intermixed with a predominately neutral atomic medium... Far-UV continuum fluorescence of H_2 is not detected, but Lyman alpha (Lya) fluorescence is present. The diffuse nebular medium is inhospitable to molecules and dust. Maintaining the modest equilibrium abundance of H_2 (N(H_2)/N(HI) << 1) in the diffuse nebular medium requires a source of H_2, mostly likely the clumpy nebular medium. The stellar SED shows no signs of reddening (E(B-V) < 0.01), but paradoxically measurements of Ha/Hb ... indicate E(B-V) ~ 0.1. ...the apparent enhancement of Ha/Hb in the absence of dust may result from a two step process of H_2 ionization by Lyman continuum (Lyc) photons followed by dissociative recombination (H_2 + gamma -> H_2^+ + e -> H(1s) + H (nl)), which ultimately produces fluorescence of Ha and Lya. In the optically thin limit at the inferred radius of the velocity transition we find dissociation of H_2 by stellar Lyc photons is an order of magnitude more efficient than spontaneous dissociation by far-UV photons. We suggest that the importance of this H_2 destruction process in HII regions has been overlooked.
Fast (~1000 km/s) outflows of neutral gas (from 21-cm HI absorption) are detected in strong radio sources. The outflows occur, at least in some cases, at distances from the radio core that range between few hundred parsecs and kpc. These HI outflows likely originate from the interaction between radio jets and the dense surrounding medium. The estimated mass outflow rates are comparable to those of moderate starburst-driven superwinds. The impact on the evolution of the host galaxies is discussed.
We describe IRAC 3.6-8 mu_m observations and ground-based near-IR JHKs photometry from Mimir and 2MASS of the massive double cluster h & chi Persei complete to J=15.5 (M ~ 1.3 Msun. Within 25' of the cluster centers we detect \~11,000 sources with J < 15.5, ~7,000 sources with [4.5] < 15, and ~ 5000 sources with [8] < 14.5. In both clusters, the surface density profiles derived from the 2MASS data decline with distance from the cluster centers as expected for a bound cluster. Within 15' of the cluster centers, ~ 50% of the stars lie on a reddened ~ 13 Myr isochrone; at 15'-25' from the cluster centers, ~ 40% lie on this isochrone. Thus, the optical/2MASS color-magnitude diagrams indicate that h & chi Per are accompanied by a halo population with roughly the same age and distance as the two dense clusters. The double cluster lacks any clear IR excess sources for J < 13.5 (~ 2.7 Msun). Therefore, disks around high-mass stars disperse prior to ~ 10^{7} yr. At least 2-3% of the fainter cluster stars have strong IR excess at both [5.8] and [8]. About 4-8% of sources slightly more massive than the Sun (~ 1.4 Msun) have IR excesses at [8]. Combined with the lack of detectable excesses for brighter stars, this result suggests that disks around lower-mass stars have longer lifetimes. The IR excess population also appears to be larger at longer IRAC bands ([5.8], [8]) than at shorter IRAC/2MASS bands ($K_{s}$, [4.5]), a result consistent with an inside-out clearing of disks.
We present models of temperature distribution in the crust of a neutron star in the presence of a strong toroidal component superposed to the poloidal component of the magnetic field. The presence of such a toroidal field hinders heat flow toward the surface in a large part of the crust. As a result, the neutron star surface presents two warm regions surrounded by extended cold regions and has a thermal luminosity much lower than in the case the magnetic field is purely poloidal. We apply these models to calculate the thermal evolution of such neutron stars and show that the lowered photon luminosity naturally extends their life-time as detectable thermal X-ray sources.
In the core accretion model, gas giant formation is a race between growth and migration; for a core to become a jovian planet, it must accrete its envelope before it spirals into the host star. We use a multizone numerical model to extend our previous investigation of the "window of opportunity" for gas giant formation within a disk. When the collision cross-section enhancement due to core atmospheres is taken into account, we find that a broad range of protoplanetary disks posses such a window.
We model the population characteristics of the sample of millisecond pulsars within a distance of 1.5kpc.We find that for a braking index n=3, the birth magnetic field distribution of the neutron stars as they switch on as radio MSPs can be represented by a Gaussian with mean $\log B(G)= 8.1$ and $\sigma_{\log B}=0.4$ and their birth spin period by a Gaussian with mean $P_0=4$ ms and $\sigma_{P_0}=1.3$ ms. Our study, which takes into consideration acceleration effects on the observed spin-down rate, shows that most MSPs are born with periods that are close to the currently observed values and with average characteristic ages typically larger by a factor 1.5 compared to the true age. The Galactic birth rate of the MSPs is deduced to be $\gsimeq 3.2 \times 10^{-6}$ yr$^{-1}$ near the upper end of previous estimates and larger than the semi-empirical birth rate $\sim 10^{-7}$ yr$^{-1}$ of the LMXBs. The mean birth spin period deduced by us for the radio MSPs is a factor 2 higher than the mean spin period observed for the accretion and nuclear powered X-ray pulsars, although this discrepancy can be resolved if we use a braking index $n=5$, the value appropriate to spin down caused by angular momentum losses by gravitational radiation or magnetic multipolar radiation. We discuss the arguments for and against the hypothesis that accretion induced collapse may constitute the main route to the formation of the MSPs, pointing out that on the AIC scenario the low magnetic fields of the MSPs may simply reflect the field distribution in isolated magnetic white dwarfs which has recently been shown to be bi-modal with a dominant component that is likely to peak at fields below $10^3$ G which would scale to neutron star fields below $10^9$ G.
Observations of planetary nebulae (PNe) by Sterling, Dinerstein and Bowers have revealed abundances in the neutron-capture element Germanium (Ge) from solar to factors of 3 -- 10 above solar. The enhanced Ge is an indication that the slow-neutron capture process (s process) operated in the parent star during the thermally-pulsing asymptotic giant branch (TP-AGB) phase. We compute the detailed nucleosynthesis of a series of AGB models to estimate the surface enrichment of Ge near the end of the AGB. A partial mixing zone of constant mass is included at the deepest extent of each dredge-up episode, resulting in the formation of a 13C pocket in the top ~1/10th of the He-rich intershell. All of the models show surface increases of [Ge/Fe] less than about 0.5, except the 2.5Msun, Z=0.004 case which produced a factor of 6 enhancement of Ge. Near the tip of the TP-AGB, a couple of extra TPs could occur to account for the composition of the most Ge-enriched PNe. Uncertainties in the theoretical modeling of AGB stellar evolution might account for larger Ge enhancements than we predict here. Alternatively, a possible solution could be provided by the occurrence of a late TP during the post-AGB phase. Difficulties related to spectroscopic abundance estimates also need to be taken into consideration. Further study is required to better assess how the model uncertainties affect the predictions and, consequently, if a late TP should be invoked.
The generalized Chaplygin gas (GCG), is studied in this paper by using the latest observational data including 182 gold sample type Ia supernovae (Sne Ia) data, the ESSENCE Sne Ia data and the distance ratio from $z=0.35$ to $z=1089$ (the redshift of decoupling). Our results rule out the Chaplygin gas model ($\alpha=1$) at the 99.7% confidence level and the $\lambda CDM$ model ($\alpha=0$) at the 68.3% confidence level. At a 95.4% confidence level, we obtain $w=-0.70_{-0.13}^{+0.12}$ and $\alpha=-0.27_{-0.30}^{+0.49}$. In addition, we find that the phase transition from deceleration to acceleration occurs at redshift $z_{q=0}\sim 0.89-1.0$ at a $1\sigma$ confidence level for the GCG model.
The workshop on Small Ionized and Neutral Structures in the Interstellar Medium featured many contributions on the theory of the objects which are responsible for ``Tiny Scale Atomic Structures'' (TSAS) and ``Extreme Scattering Events'' (ESE). The main demand on theory is accounting for objects that have the high densities and small sizes apparently required by the observations, but also persist over a sufficiently long time to be observable. One extensively-discussed mechanism is compressions by transonic turbulence in the warm interstellar medium, followed by thermal instabilities leading to an even more compressed state. In addressing the requirements for overpressured but persistent objects, workshop participants also discussed fundamental topics in the physics of the interstellar medium, such as the timescale for evaporation of cool dense clouds, the relevance of thermodynamically-defined phases of the ISM, the effect of magnetic fields, statistical effects, and the length and time scales introduced by interstellar processes.
I discuss the spectral properties of short GRBs detected by BATSE and compare them with long events. The detailed modeling of short GRB spectra shows that their being (on average) harder than long events (as it has been found by comparing their hardness ratios) is indeed due to a harder low energy spectral component (i.e. the powerlaw of the Band or cutoff-powerlaw model) in short GRBs which, instead, have a peak energy similar to long events. Another open issue is the distance scale to short GRBs. While the few redshift measurements suggests that they are at z<1, statistical studies (with local galaxies or X-ray selected clusters) suggest that they should be even more local.
A method is developed for fitting theoretically predicted astronomical spectra to an observed spectrum. Using a hierarchical Bayesian principle, the method takes both systematic and statistical measurement errors into account, which has not been done before in the astronomical literature. The goal is to estimate fundamental stellar parameters and their associated uncertainties. The non-availability of a convenient deterministic relation between stellar parameters and the observed spectrum, combined with the computational complexities this entails, necessitate the curtailment of the continuous Bayesian model to a reduced model based on a grid of synthetic spectra. A criterion for model selection based on the so-called predictive squared error loss function is proposed, together with a measure for the goodness-of-fit between observed and synthetic spectra. The proposed method is applied to the infrared 2.38--2.60 \mic ISO-SWS data (Infrared Space Observatory - Short Wavelength Spectrometer) of the star $\alpha$ Bootis, yielding estimates for the stellar parameters: effective temperature \Teff = 4230 $\pm$ 83 K, gravity $\log$ g = 1.50 $\pm$ 0.15 dex, and metallicity [Fe/H] = $-0.30 \pm 0.21$ dex.
We discuss some of the preliminary results and findings derived from the analysis of a first sample of flares detected by the XRT on board Swift. The analysis shows that the morphology of flares is the one we expect from the collision of ultra-relativistic shells as it happens during the internal shock model proposed by Rees and Meszaros in 1994. Furthermore the Delta(t)/t ratio and the decay-time to rise-time ratio have mean values that are in good agreement with the values observed in the prompt emission pulses that are believed to originate from internal shocks. The conclusion is that the flare analysis favors the internal shock as due to shells that have been ejected by the central engine after the prompt emission. The central engine seems to remain active and capable of generating large amounts of energy also at later times. More data are needed to establish whether or not some of the flares could be due to shells that have been emitted with small Lorentz factor at the time of the prompt emission and generate later time flares due to the catch up of these shells.
We review methodologies currently available to interprete time series of high-resolution high-S/N spectroscopic data of pulsating stars in terms of the kind of (non-radial) modes that are excited. We illustrate the drastic improvement of the detection treshold of line-profile variability thanks to the advancement of the instrumentation over the past two decades. This has led to the opportunity to interprete line-profile variations with amplitudes of order m/s, which is a factor 1000 lower than the earliest line-profile time series studies allowed for.
We present data probing the spatial and kinematical distribution of both the atomic (HI) and molecular (CO) gas in NGC 5218, the late-type barred spiral galaxy in the spiral-elliptical interacting pair, Arp 104. We consider these data in conjunction with far-infrared and radio continuum data, and N-body simulations, to study the galaxies interactions, and the star formation properties of NGC 5218. We use these data to assess the importance of the bar and tidal interaction on the evolution of NGC 5218, and the extent to which the tidal interaction may have been important in triggering the bar. The molecular gas distribution of NGC 5218 appears to have been strongly affected by the bar; the distribution is centrally condensed with a very large surface density in the central region. The N-body simulations indicate a timescale since perigalacticon of approximately 3 x 10**8 yr, which is consistent with the interaction having triggered or enhanced the bar potential in NGC 5218, leading to inflow and the large central molecular gas density observed. Whilst NGC 5218 appears to be undergoing active star formation, its star formation efficiency is comparable to a `normal' SBb galaxy. We propose that this system may be on the brink of a more active phase of star formation.
At a conference devoted to ever deeper surveys hunting for ever more distant galaxies, I posed a question for which a concensus view has been difficult to reach: `Is there evidence for, or can we rule out, a significant population of dust-obscured starbursts at z > 3?' If, as seems likely, submm-selected galaxies are proto-ellipticals, one of the biggest unanswered questions is whether a significant fraction form at very high redshift - perhaps by the collapse of single gas clouds - or whether the entire population forms over a range of redshifts, primarily via merging. The latter scenario is favoured strongly by existing data for the majority of bright submm galaxies - mergers are common; typical spectroscopic redshifts are in the range 1 to 3. However, our reliance on radio imaging to pinpoint submm galaxies leaves open the possibility of a significant population of very distant, massive starbursts. To rule out such a scenario requires a completely unbiased redshift distribution for submm-selected galaxies and this is unlikely to be forthcoming using conventional optical/infrared spectroscopic techniques. Here, I summarise recent attempts to close that door, or pass through to an early Universe inhabited by a significant population of collosal, dust-obscured starbursts. I conclude that the door is only barely ajar; however, the idea of galaxies forming, near instantaneously, on a collosal scale is not dead: I show an SMG imaged by MERLIN+VLA for >1Ms - the deepest high-resolution radio image so far obtained. The data reveal a galaxy-wide starburst covering >=10kpc. Thus interpreting SMGs in terms of compact ULIRG-like events may not always be appropriate, as one might expect when considering the Eddington limit for >~1000M(sun)/yr starbursts.
We consider the effect of toroidal magnetic fields on hydrodynamically stable Taylor-Couette differential rotation flows. For current-free magnetic fields a nonaxisymmetric m=1 magnetorotational instability arises when the magnetic Reynolds number exceeds O (100). We then consider how this `azimuthal magnetorotational instability' (AMRI) is modified if the magnetic field is not current-free, but also has an associated electric current throughout the fluid. This gives rise to current-driven Tayler instabilities (TI) that exist even without any differential rotation at all. The interaction of the AMRI and the TI is then considered when both electric currents and differential rotation are present simultaneously. The magnetic Prandtl number Pm turns out to be crucial in this case. Large Pm have a destabilizing influence, and lead to a smooth transition between the AMRI and the TI. In contrast, small Pm have a stabilizing influence, with a broad stable zone separating the AMRI and the TI. In this region the differential rotation is acting to stabilize the Tayler instabilities, with possible astrophysical applications (Ap stars). The growth rates of both the AMRI and the TI are largely independent of Pm, with the TI acting on the timescale of a single rotation period, and the AMRI slightly slower, but still on the basic rotational timescale. The azimuthal drift timescale is ~20 rotations, and may thus be a (flip-flop) timescale of stellar activity between the rotation period and the diffusion time.
M1-92 can be considered an archetype of bipolar pre-planetary nebulae. It shows a clear axial symmetry, along with the kinematics and momentum excess characteristic of this class of envelopes around post-AGB stars. By taking advantage of the new extended configuration of the IRAM Plateau de Bure interferometer, we wanted to study the morphology and velocity field of the molecular gas better in this nebula, particularly in its central part. We performed sub-arcsecond resolution interferometric observations of the J=2-1 rotational line 13CO M1-92. We found that the equatorial component is a thin flat disk, which expands radially with a velocity proportional to the distance to the center. The kinetic age of this equatorial flow is very similar to that of the two lobes. The small widths and velocity dispersion in the gas forming the lobe walls confirm that the acceleration responsible for the nebular shape could not last more than 100-120 yr. The present kinematics of the molecular gas can be explained as the result of a single brief acceleration event, after which the nebula reached an expansion velocity field with axial symmetry. In view of the similarity to other objects, we speculate on the possibility that the whole nebula was formed as a result of a magneto-rotational explosion in a common-envelope system.
Gamma-ray bursts can be divided into three groups ("short", "intermediate", "long") with respect to their durations. The third type of gamma-ray bursts - as known - has the intermediate duration. We show that the intermediate group is the softest one. An anticorrelation between the hardness and the duration is found for this subclass in contrast to the short and long groups.
The linear non homogeneous singular integral equation (LNSIE)derived from the nonlinear non homogeneous integral eauation (NNIE)of Chandrsasekhar's H- functions is considered here to develop a new form of H - functions.The Plemelj's formulae are applied to that equation to determine a new linear non homogeneous integral equation(LNIE)for H- functions in complex plane . The analytic properties of this new linear integral equation are assessed and compared with known linear integral equations satisfied by H- functions. The Cauchy integral formulae in complex plane are used to obtain this form of H- functions not dependent on H- function in the integral . This new form of H-function is represented as a simple integral in terms of known functions both for conservative and non conservative cases. This is identical with the form of H- functions derived by this author by application of Wiener HOpf technique. The equivalence of application of the theory of linear singular integral equation in Riemann Hilbert Problem and of the technique of Wiener- Hopf in linear integral in representing the H- functions is therefore eatablished .This new form may be used for solving the problems of radiative transfer in anisotropic and non coherent scattering by the method of Laplace Transform and Wiener -Hopf technique.
We present results from {\em Chandra}/ACIS-S, {\em Spitzer}, {\em XMM-Newton}, {\em HST}, and VLA observations of the radio hot spots, extended environment, and nucleus of the nearby ($z$=0.0597) FR II radio galaxy 3C 33. This is a relatively low-power FR II radio galaxy, and so we expect, {\it a priori}, to detect a significant X-ray synchrotron component to the emission from the hot spots. We detect X-ray emission coincident with the two knots of polarized optical emission from the southern hot spot (SHS), as well as along the northwest arm of this hot spot. We also detect X-ray emission from two compact regions of the northern hot spot (NHS), as well as diffuse emission behind the radio peak. The X-ray flux density of the region at the tip of the southern hot spot, the most compact radio feature of the southern lobe, is consistent with the synchrotron self-Compton (SSC) process. The X-ray flux densities of the other three regions of the SHS and the two compact regions of the NHS are an order of magnitude or more above the predictions from either the SSC and inverse-Compton scattering of the CMB (IC/CMB) mechanisms, thus strongly disfavoring these scenarios unless they are far from equipartition ($B$ $\sim$4-14 times smaller than the equipartition values). The X-ray flux from the diffuse region behind the NHS is consistent with the IC/CMB prediction assuming a small departure from equipartition. We conclude that the X-ray emission is synchrotron emission from multiple populations of ultrarelativistic electrons unless these regions are far from equipartition. There must therefore be unresolved substructure within each knot, similar to that which is found in Chandra observations of nearby FR I jets such as Centaurus A and 3C 66B.
In this review paper, we summarise the goals of asteroseismic studies of close binary stars. We first briefly recall the basic principles of asteroseismology, and highlight how the binarity of a star can be an asset, but also a complication, for the interpretation of the stellar oscillations. We discuss a few sample studies of pulsations in close binaries and summarise some case studies. This leads us to conclude that asteroseismology of close binaries is a challenging field of research, but with large potential for the improvement of current stellar structure theory. Finally, we highlight the best observing strategy to make efficient progress in the near future.
In this paper the linear non linear non homogenous integral equations of H- functions is considered to find a new form of H- function as its solution.The Wiener Hopf technique is used to express a known function into two functions with different zones of analyticity.The linear non homogenous integral equation is thereafter expressed into two different sets of function having different zones of regularity.The modified form of Lioville's theorem is used thereafter.Cauchy's integrl formulae are used to determine functional representation over the cut region in a complex plane.The new form off H function is derived both for conservative and non conservative cases.The exiatence of solution of linear nonhomogenous integral equations and its uniqueness are shown.For numerical calculation of this new H-function,a set of useful formulae are derived both for conservative and non conservative cases.
The present common view about GRB origin is related to cosmology, what is based on statistical analysis, and on measurements of the redshifts in the GRB optical afterglows of long GRB. Models of radiation, and models of the central machine for GRB are critically analyzed. Most of these models cannot produce the amount of energy required for the cosmological GRB. Collimation is needed to reduce GRB energy output. No correlation is found between redshifts, GRB spectrum, and total GRB fluence. Comparison of KONUS and BATSE data about statistics and hard X-ray lines is done, and some differences are noted. Hard gamma-ray afterglows, prompt optical spectra, hard X-ray lines measurements could be important for farther insight into GRB origin. Two bright optical afterglows had been detected, indicating that initial bright optical emission is directly connected with the GRB itself, and has a different origin from the subsequent faint optical emission. Results of these observations are represented. Observations indicate that GRB originate in star forming regions of galaxies with a high matter density. Interaction of the mighty gamma ray flux from the cosmological GRB with the dense surrounding molecular cloud lead to long optical afterglow, lasting up to 10 years, due to reradiation of the cloud. Results of numerical simulations of such reradiation for different forms of clouds are represented. Possible connection of short GRB with soft gamma repeaters is discussed.
The nature of the evolution of the magnetic field, and of current sheet formation, at three-dimensional (3D) magnetic null points is investigated. A kinematic example is presented which demonstrates that there is no possible choice of boundary conditions which renders the evolution of the field ideal at the null, when the ratios of the null eigenvalues are time-dependent. Resistive MHD simulations are described which demonstrate that this evolution is generic. A 3D null is subjected to boundary driving by shearing motions, and it is shown that a current sheet localised at the null is formed. The qualitative and quantitative properties of the current sheet are discussed. Accompanying the sheet development is the growth of a localised parallel electric field, one of the signatures of magnetic reconnection. Finally, the relevance of the results to a recent theory of turbulent reconnection are discussed.
Observational arguments supporting the binary explanation of the long secondary periods (LSP) phenomenon in red giants are presented. Photometry of about 1200 semiregular variables with the LSP in the Large Magellanic Cloud are analyzed using the MACHO and OGLE photometry. For about 5% of these objects additional ellipsoidal-like or eclipsing-like modulation with the same periods as the LSP is detectable. These double-humped variations are usually shifted in phase comparing to the LSP light curves. I discuss the model of binary system with a red giant as the primary component and a low-mass object as the secondary one. The mass lost by the red giant through the wind follows the spiral pattern in the orbit around the primary star and obscures it causing the LSP variations.
We study the generation of parallel electric fields by virtue of propagation of ion cyclotron waves in the plasma with a transverse density inhomogeneity. Using two-fluid, cold plasma linearised equations, we show for the first time that $E_{\parallel}$ generation can be understood by an analytic equation that couples $E_{\parallel}$ to the transverse electric field. We prove that the minimal model required to reproduce previous kinetic results on $E_{\parallel}$ generation is the two-fluid, cold plasma approximation in the linear regime. In this simplified model, the generated $E_{\parallel}$ amplitude e.g. for plausible solar coronal parameters attains values of $10^4$ Vm$^{-1}$. By considering the numerical solutions we also show that the cause of $E_{\parallel}$ generation is the charge separation induced by the transverse density inhomogeneity. The model also correctly reproduces the previous kinetic results in that only electrons are accelerated (along the background magnetic field), while ions do not accelerate.
We present images for 36 galaxies of the M81 group obtained in the H-alpha
line. Estimates of the H-alpha flux and star formation rate, SFR, are avialable
now for all the known members of the group with absolute magnitudes down to M_B
= -10^m.
The character of distribution of the galaxies over three paremeters: M_B,
SFR, and total hydrogen mass permits us to draw the following conclusions as to
evolution status of the group population. a) Spiral and irregular type galaxies
would have time to generate their luminosity (baryon mass) during the
cosmological time T_0=13.7 Gyr, but dwarf spheroidal objects are capable of
reproducing only ~5% of their observed luminosity. b) S and Im,BCD galaxies
possess the supply of gas sufficient to maintain their observed SFRs during
only next (1/4 -
1/3)T_0 years, while dIr and dSph populations have the mean gas depletion
time about 3 T_0. c) There is indirect evidence that the star formation in Im,
BCD and dIr galaxies proceeds in a mode of vigorous burst activity rather than
in the form of a sluggish process. We note the dwarf tidal system near NGC
3077, the Garland, to have the highest SFR per unit luminosity among 150
galaxies of the Local volume with known SFRs.
Being averaged over the local "cell of homogeneity" of 4 Mpc in diameter
around M 81, the rate of star formation of the group, rho(SFR)= 0.165
M_sun/year*Mpc^3, proves to be 5-8 times higherthan, that of the average global
rate at Z =0.
We show that the rapid and large decrease in the intensity of high-ionization emission lines from the Eta Carinae massive binary system can be explained by the accretion model. These emission lines are emitted by material in the nebula around the binary system that is being ionized by radiation from the hot secondary star. The emission lines suffer three months long deep fading every 5.54 year, assumed to be the orbital period of the binary system. In the accretion model, for ~70 day the less massive secondary star is accreting mass from the primary wind instead of blowing its fast wind. The accretion event has two effects that substantially reduce the high-energy ionizing radiation flux from the secondary star. (1) The accreted mass absorbs a larger fraction of the ionizing flux. (2) The accreted mass forms a temporarily blanked around the secondary star that increases its effective radius, hence lowering its effective temperature and the flux of high energy photons. This explanation is compatible with the fading of the emission lines at the same time the X-ray is declining to its minimum, and with the fading being less pronounced in the polar directions.
Long baseline interferometry is now a mature technique in the optical domain. Current interferometers are however highly limited in number of sub apertures and concepts are being developed for future generations of very large optical arrays and especially with the goal of direct imaging. In this paper, we study the effects of introducing single-mode fibers in direct imaging optical interferometers. We show how the flexibility of optical fibers is well adapted to the pupil densification scheme. We study the effects of the truncation of the gaussian beams in the imaging process, either in the Fizeau mode or in the densified pupil mode or in the densified image mode. Finally, in the pupil densification configuration, we identify an optimum of the diaphragm width. This optimum maximizes the on-axis irradiance and corresponds to a trade-off between the loss of transmission and the efficiency of the densification.
The Millennium Galaxy Catalogue (MGC) provides a structural database comprising 10,095 well resolved galaxies drawn from a 37.5 sq. deg region of sky, with $B_{\tiny \sc mgc} < 20.0$ mag and 96.1 per cent spectroscopic completeness. The data are being used to investigate a number of diverse topics including: the nearby galaxy merger rate (via close pairs and asymmetry); dust attenuation; bulge and disc luminosity functions; the luminosity size relations; the supermassive black hole mass function; galaxy bimodality; the space-density of high and low surface brightness galaxies; blue spheroids; and the total $B$-band luminosity function. Plans to extend the MGC in area (200 sq. deg), depth ($K_{Vega}=16.5$ mag), resolution (0.5$''$) and wavelength $(u-K)$ are underway.
We report Spitzer Space Telescope photometry between 3.6 microns and 24 microns and spectroscopy between 5 microns and 15 microns of GD 362, a white dwarf with an effective temperature near 10,000 K that displays a remarkably high concentration of metals in its photosphere and a thermal infrared excess. We approximately reproduce both the infrared continuum and the very strong 10 micron silicate emission feature with a model of an orbiting dusty disk which is flat out to 50 stellar radii and warped between 50 and 70 stellar radii. The relatively small amount of cold material implied by the weak 24 mircon flux argues that the disk lies within the Roche radius of the star, and we may be witnessing a system where an asteroidal-size body has been tidally destroyed. If so, determination of the photospheric metal abundances may measure the bulk composition of an extrasolar minor planet.
We perform a comprehensive analysis of the superorbital modulation in the ultracompact X-ray source 4U 1820-303, consisting of a white dwarf accreting onto a neutron star. Based on XTE data, we measure the fractional amplitude of the source superorbital variability (with a 70-d quasi-period) in the folded and averaged light curves, and find it to be by a factor of 2. As proposed before, the superorbital variability can be explained by oscillations of the binary eccentricity. We now present detailed calculations of the eccentricity-dependent flow through the inner Lagrangian point, and find a maximum of the eccentricity of 0.004 is sufficient to explain the observed fractional amplitude. We then study hierarchical triple models yielding the required quasi-periodic eccentricity oscillations through the Kozai process. We find the resulting theoretical light curves to match well the observed ones. We constrain the ratio of the semimajor axes of the outer and inner systems, the component masses, and the inclination angle between the inner and outer orbits. Last but not least, we discover a remarkable and puzzling synchronization between the observed period of the superorbital variability (equal to the period of the eccentricity oscillations in our model) and the period of the general-relativistic periastron precession of the binary.
Increasing observational evidence gathered especially in X-rays and gamma-rays during the course of the last few years support the notion that Supernova remnants (SNRs) are Galactic particle accelerators up to energies close to the ``knee'' in the energy spectrum of Cosmic rays. This review summarises the current status of VHE gamma-ray observations of SNRs. Shell-type as well as plerionic type SNRs are addressed and prospect for observations of these two source classes with the upcoming GLAST satellite in the energy regime above 100 MeV are given.
We report the discovery, using XTE data, of a dependence of the X-ray orbital modulation depth on the X-ray spectral state in the ultracompact atoll binary 4U 1820-303. This state (measured by us by the position on the X-ray colour-colour diagram) is tightly coupled to the accretion rate, which, in turn, is coupled to the phase of the 170-d superorbital cycle of this source. The modulation depth is much stronger in the high-luminosity, so-called banana, state than in the low-luminosity, island, state. We find the X-ray modulation is independent of energy, which rules out bound-free X-ray absorption in an optically thin medium as the cause of the modulation. We also find a significant dependence of the offset phase of the orbital modulation on the spectral state, which favours the model in which the modulation is caused by scattering in hot gas around a bulge at the disc edge, which both size and the position vary with the accretion rate. Estimates of the source inclination appear to rule out a model in which the bulge itself occults a part of the accretion disc corona. We calculate the average flux of this source over the course of its superorbital variability (which has the period of 170 d), and find it to be fully compatible with the model of accretion as due to the angular momentum loss via emission of gravitational radiation. Also, we compare the dates of all X-ray bursts observed from this source by BeppoSAX and XTE with the XTE light curve, and find all of them to coincide with deep minima of the flux, confirming previous results based on smaller samples.
We have used the MHW2 filter to obtain estimates of the flux densities at the WMAP frequencies of a complete sample of 2491 sources, mostly brighter than 500 mJy at 5 GHz, distributed over the whole sky excluding a strip around the Galactic equator (b < 5 degrees). After having detected 933 sources above the 3 sigma level in the MHW2 filtered maps - our New Extragalactic WMAP Point Source (NEWPS_3sigma) Catalogue - we are left with 381 sources above 5 sigma in at least one WMAP channel, 369 of which constitute our NEWPS_5sigma catalogue. It is remarkable to note that 98 (i.e. 26%) sources detected above 5 sigma are `new', they are not present in the WMAP catalogue. Source fluxes have been corrected for the Eddington bias. Our flux density estimates before such correction are generally in good agreement with the WMAP ones at 23 GHz. At higher frequencies WMAP fluxes tend to be slightly higher than ours, probably because WMAP estimates neglect the deviations of the point spread function from a Gaussian shape. On the whole, above the estimated completeness limit of 1.1 Jy at 23 GHz we detected 43 sources missed by the blind method adopted by the WMAP team. On the other hand, our low-frequency selection threshold left out 25 WMAP sources, only 12 of which, however, are 5 sigma detections and only 3 have fluxes S at 23 GHz > 1.1 Jy. Thus, our approach proved to be competitive with, and complementary to the WMAP one.
Hubble Space Telescope (HST/ACS) images of the Helix Planetary Nebula (NGC 7293) are interpreted using the hydro-gravitational-dynamics theory (HGD) of Gibson 1996-2006. HGD predicts that baryonic-dark-matter (BDM) dominates the mass of galaxies (Schild 1996) as Jovian (promordial-fog-particle, PFP) Planets (JPPs) in proto-globular-star-cluster (PGC) clumps within galaxy halo diameters surrounding its stars. From HGD, supernova Ia (SNe Ia) events normally occur in planetary nebulae (PNe) within PGCs where binary clustering cascades of merging planets produce central binary star systems. As central stars of PNe, binaries exchange mass and accrete JPPs to grow white-dwarfs to $1.44 M_{\sun}$ instability within ionized (Oort cloud) cavities bounded by evaporating JPPs. SNe Ia events are thus intermittently obscured by radiation-inflated JPP atmospheres producing systematic SNe Ia distance errors, so the otherwise mysterious ``dark energy'' concept is unnecessary. HST/ACS and WFPC2 Helix images show $>7000$ cometary globules, here interpreted as gas-dust cocoons of JPPs evaporated by beamed radiation from its white-dwarf plus companion central binary star system. Mass for growing the stars, the PNe, and possibly a SNe Ia event, is accreted gravitationally from ambient BDM JPPs. Measured JPP masses $\approx 3 \times 10^{25}$ kg with spacing $\approx 10^{14}$ m support the HGD prediction that the density $\rho$ of galaxy star forming regions fossilize the density $\rho_{0} \approx (3-1) \times 10^{-17}$ kg m$^{-3}$ existing at 30,000 years in the plasma-epoch, when proto-superclusters fragmented in the expanding universe giving the first gravitational structures.
In the framework of the study of supernova remnants and their complex interaction with the interstellar medium and the circumstellar material, we focus on the galactic supernova remnant W49B. Its morphology exhibits an X-ray bright elongated nebula, terminated on its eastern end by a sharp perpendicular structure aligned with the radio shell. The X-ray spectrum of W49B is characterized by strong K emission lines from Si, S, Ar, Ca, and Fe. There is a variation of the temperature in the remnant with the highest temperature found in the eastern side and the lowest one in the western side. The analysis of the recent observations of W49B indicates that the remnant may be the result of an asymmetric bipolar explosion where the ejecta are collimated along a jet-like structure and the eastern jet is hotter and more Fe-rich than the western one. Another possible scenario associates the X-ray emission with a spherical explosion where parts of the ejecta are interacting with a dense belt of ambient material. To overcome this ambiguity we present new results of the analysis of an XMM-Newton observation and we perform estimates of the mass and energy of the remnant. We conclude that the scenario of an anisotropic jet-like explosion explains quite naturally our observation results, but the association of W49B with a hypernova and a gamma-ray burst, although still possible, is not directly supported by any evidence.
We report new Spitzer Space Telescope observations from the IRAC and MIPS instruments of the young (~ 3 Myr) sigma Orionis cluster. We identify 336 stars as members of the cluster using optical and near-infrared color magnitude diagrams. Using the spectral energy distribution (SED) slopes in the IRAC spectral range, we place objects in several classes: non-excess stars, stars with optically thick disks(like classical T Tauri stars), class I (protostellar) candidates, and stars with ``evolved disks''; the last exhibit smaller IRAC excesses than optically thick disk systems. In general, this classification agrees with the location expected in IRAC-MIPS color-color diagrams for these objects. We find that the evolved disk systems are mostly a combination of objects with optically thick but non-flared disks, suggesting grain growth and/or settling, and transition disks, systems in which the inner disk is partially or fully cleared of small dust. In all, we identify 7 transition disk candidates and 3 possible debris disk systems. As in other young stellar populations, the fraction of disks depends on the stellar mass, ranging from ~10% for stars in the Herbig Ae/Be mass range (>2 msun) to ~35% in the T Tauri mass range (1-0.1 msun). We find that the disk fraction does not decrease significantly toward the brown dwarf candidates (<0.1 msun). The IRAC infrared excesses found in stellar clusters and associations with and without central high mass stars are similar, suggesting that external photoevaporation is not very important in many clusters. Finally, we find no correlation between the X-ray luminosity and the disk infrared excess, suggesting that the X-rays are not strongly affected by disk accretion.
Observations of Halpha emission measures and pulsar dispersion measures at high Galactic latitude (|b| > 10 deg) provide information about the density and distribution of the diffuse warm ionized medium (WIM). The diffuse WIM has a lognormal distribution of EM sin |b|, which is consistent with a density structure established by isothermal turbulence. The H+ responsible for most of the emission along high-EM sin |b| sightlines is clumped in high density (> 0.1 cm^{-3}) regions that occupy only a few parsecs along the line of sight, while the H+ along low-EM sightlines occupies hundreds of parsecs with considerably lower densities.
We present a study of the morphological nature of redshift z~0.7 star-forming galaxies using a combination of HST/ACS, GALEX and ground-based images of the COSMOS field. Our sample consists of 8,146 galaxies, 5,777 of which are detected in the GALEX near-ultraviolet band down to a limiting magnitude of 25.5 (AB). We make use of the UV to estimate star formation rates, correcting for the effect of dust using the UV-slope, and compute, from the ACS F814W images, the C,A,S,G,M20 morphological parameters for all objects in our sample. We observe a morphological bimodality in the galaxy population and show that it has a strong correspondence with the FUV - g color bimodality. We conclude that UV-optical color predominantly evolves concurrently with morphology. We observe many of the most star-forming galaxies to have morphologies approaching that of early-type galaxies, and interpret this as evidence that strong starburst events are linked to bulge growth and constitute a process through which galaxies can be brought from the blue to the red sequence while simultaneously modifying their morphology accordingly. We conclude that the red sequence has continued growing at z~<0.7. We also observe z~0.7 galaxies to have physical properties similar to that of local galaxies, except for higher star formation rates. Whence we infer that the dimming of star-forming galaxies is responsible for most of the evolution in the star formation rate density of the Universe since that redshift, although our data are also consistent with a mild number evolution. [abridged]
We make a systematic study of the cosmological dynamics for a number of f(R) gravity theories in Palatini formalism. We find a number of interesting results: (i) models based on theories of the type (a) f(R)=R-beta R^n and (b) f(R)=R+alpha ln R -beta, unlike the metric formalism, are capable of producing the sequence of radiation-dominated, matter-dominated and de-Sitter periods, and (ii) models based on theories of the type (c) f(R)=R+alpha R^m -beta R^n can produce early as well as late accelerating phases. However for the classes of models considered here, we have been unable to find the sequence of all four dynamical epochs required to account for the complete cosmological dynamics, even though three out of four phases are possible. We also place observational constraints on these models using the recently released supernovae data (SNLS) as well as the baryon acoustic oscillation peak and the CMB shift parameter. The best-fit values are found to be n=0.027, alpha=4.63 for the models based on (a) and alpha=0.11, beta=4.62 for the models based on (b), neither of which are significantly preferred over the LCDM model. The models based on (c) are also consistent with the data with suitable choices of their parameters.
We present a three dimensional cosmic shear analysis of the Hubble Space Telescope COSMOS survey, the largest ever optical imaging program performed in space. We have measured the shapes of galaxies for the tell-tale distortions caused by weak gravitational lensing, and traced the growth of that signal as a function of redshift. Using both 2D and 3D analyses, we measure cosmological parameters Omega_m, the density of matter in the universe, and sigma_8, the normalization of the matter power spectrum. The introduction of redshift information tightens the constraints by a factor of three, and also reduces the relative sampling (or "cosmic") variance compared to recent surveys that may be larger but are only two dimensional. From the 3D analysis, we find sigma_8*(Omega_m/0.3)^-0.44=0.866+^0.085_-0.068 at 68% confidence limits, including both statistical and potential systematic sources of error in the total budget. Indeed, the absolute calibration of shear measurement methods is now the dominant source of uncertainty. Assuming instead a baseline cosmology to fix the geometry of the universe, we have measured the growth of structure on both linear and non-linear physical scales. Our results thus demonstrate a proof of concept for tomographic analysis techniques that have been proposed for future weak lensing surveys by a dedicated wide-field telescope in space.
We use model selection forecasting to assess the ability of the Planck satellite to make a positive detection of spectral index running. We simulate Planck data for a range of assumed cosmological parameter values, and carry out a three-way Bayesian model comparison of a Harrison-Zel'dovich model, a power-law model, and a model including running. We find that Planck will be able to strongly support running only if its true value satisfies |dn/d ln k| > 0.02.
We have identified a large-scale structure at z~0.73 in the COSMOS field, coherently described by the distribution of galaxy photometric redshifts, an ACS weak-lensing convergence map and the distribution of extended X-ray sources in a mosaic of XMM observations. The main peak seen in these maps corresponds to a rich cluster with Tx= 3.51+0.60/-0.46 keV and Lx=(1.56+/-0.04) x 10^{44} erg/s ([0.1-2.4] keV band). We estimate an X-ray mass within $r500$ corresponding to M500~1.6 x 10^{14} Msun and a total lensing mass (extrapolated by fitting a NFW profile) M(NFW)=(6+/-3) x 10^15 Msun. We use an automated morphological classification of all galaxies brighter than I_AB=24 over the structure area to measure the fraction of early-type objects as a function of local projected density Sigma_10, based on photometric redshifts derived from ground-based deep multi-band photometry. We recover a robust morphology-density relation at this redshift, indicating, for comparable local densities, a smaller fraction of early-type galaxies than today. Interestingly, this difference is less strong at the highest densities and becomes more severe in intermediate environments. We also find, however, local "inversions'' of the observed global relation, possibly driven by the large-scale environment. In particular, we find direct correspondence of a large concentration of disk galaxies to (the colder side of) a possible shock region detected in the X-ray temperature map and surface brightness distribution of the dominant cluster. We interpret this as potential evidence of shock-induced star formation in existing galaxy disks, during the ongoing merger between two sub-clusters.
We study the enviromental dependence and the morphological composition of the galaxy color-magnitude diagram at z~0.7, using a pilot sub-sample of ~2000 galaxies from the COSMOS surve, with I_AB<24, photometric redshift within 0.61<z<0.85 and galaxy morphologies based on the HST-ACS data. The C-M diagram shows a clear red-sequence dominated by early-type galaxies and also a remarkably well-defined "blue sequence'" described by late-type objects. While the percentage of objects populating the two sequences is a function of environment, with a clear morphology/color-density relation, their normalization and slope are independent of local density. We identify and study a number of objects with "anomalous'' colors, given their morphology. Red late-type galaxies are found to be mostly highly-inclined spiral galaxies, with colors dominated by internal reddening (33% contamination with respect to truly passive spheroidals). Conversely, the population of blue early-type galaxies is composed by objects of moderate luminosity and mass, concurring to only ~5% of the mass in spheroidal galaxies. The majority of them (~70%) occupy a position in the surface-brightness/effective-radius plane not consistent with them being precursors of current epoch elliptical galaxies. In a color-mass diagram, color sequences are even better defined, with red galaxies covering in general a wider range of masses at nearly constant color, and blue galaxies showing a more pronounced dependence of color on mass. While the red sequence is adequately reproduced by models of passive evolution, the blue sequence is better interpreted as a specific star-formation sequence. Its substantial invariance with respect to local density suggests that the overall, "secular'' star formation is driven more by galaxy mass than by environment. [...]
We present new models of the deuterium chemistry in protoplanetary disks,
including, for the first time, multiply deuterated species. We use these models
to explore whether observations in combination with models can give us clues as
to which desorption processes occur in disks. We find, in common with other
authors, that photodesorption can allow strongly bound molecules such as HDO to
exist in the gas phase in a layer above the midplane. Models including this
process give the best agreement with the observations. In the midplane, cosmic
ray heating can desorb weakly bound molecules such as CO and N$_2$. We find the
observations suggest that N$_2$ is gaseous in this region, but that CO must be
retained on the grains to account for the observed DCO$^+$/HCO$^+$. This could
be achieved by CO having a higher binding energy than N$_2$ (as may be the case
when these molecules are accreted onto water ice) or by a smaller cosmic ray
desorption rate for CO than assumed here, as suggested by recent theoretical
work.
For gaseous molecules the calculated deuteration can be greatly changed by
chemical processing in the disk from the input molecular cloud values. On the
grains singly deuterated species tend to retain the D/H ratio set in the
molecular cloud, whereas multiply deuterated species are more affected by the
disk chemistry. Consequently the D/H ratios observed in comets may be partly
set in the parent cloud and partly in the disk, depending on the molecule.
These notes provide an introduction to the theory of the formation and early evolution of planetary systems. Topics covered include the structure, evolution and dispersal of protoplanetary disks; the formation of planetesimals, terrestrial and gas giant planets; and orbital evolution due to gas disk migration, planetesimal scattering, and planet-planet interactions.
We report numerical evidence that self-organized criticality (SOC)and intermittent turbulence (IT) coexist in a current sheet model based on resistive magnetohydrodynamic (MHD) equations. The model also includes a local hysteretic switch to capture plasma physical processes outside of MHD, which are normally described as current-dependent resistivity. Results from numerical simulations show scale-free avalanches of magnetic energy dissipation characteristic of SOC, as well as multiscaling in the velocity field numerically indistinguishable from certain hierarchical turbulence theories. We argue that SOC and IT are complementary descriptions of dynamical states realized by driven current sheets -- which occur ubiquitously in astrophysical and space plasmas.
We present an X-ray study of the massive edge-on Sa galaxy, Sombrero (M~104; NGC 4594), based on XMM-Newton and Chandra observations. A list of 62 XMM-Newton and 175 Chandra discrete X-ray sources is provided. At energies above 2 keV, the source-subtracted X-ray emission is distributed similarly as the stellar K-band light and is primarily due to the residual emission from discrete sources. At lower energies, however, a substantial fraction of the source-subtracted emission arises from diffuse hot gas extending to ~20 kpc from the galactic center. The observed diffuse X-ray emission from the galaxy shows a steep spectrum that can be characterized by an optically-thin thermal plasma with temperatures of ~0.6-0.7 keV, varying little with radius. The diffuse emission has a total luminosity of ~3e39 erg/s in the 0.2-2 keV energy range. This luminosity is significantly smaller than the prediction by current numerical simulations for galaxies as massive as Sombrero. We argue that the stellar feedback likely plays an essential role in regulating the physical properties of hot gas. Indeed, the observed diffuse X-ray luminosity of Sombrero accounts for at most a few percent of the expected mechanical energy input from Type Ia supernovae. The inferred gas mass and metal content are also substantially less than those expected from stellar ejecta. We speculate that a galactic bulge wind, powered primarily by Type Ia supernovae, has removed much of the 'missing' energy and metal-enriched gas from regions revealed by the X-ray observations.
We present a direct detection of the gravitational lens that caused the microlensing event MACHO-95-BLG-37. This is the first fully resolved microlensing system involving a source in the Galactic bulge, and the second such system in general. The lens and source are clearly resolved in images taken with the High Resolution Channel of the Advanced Camera for Surveys on board the Hubble Space Telescope (HST) ~9 years after the microlensing event. Only one plausible scenario fits all currently available data without invoking unusual physics or geometry. The lens is most likely a 0.6 solar mass main-sequence star of spectral type K2 with a sub-solar metallicity and located at a distance of ~3.5 kpc. However, in the view of challenges and limitations of the present data combined with a natural scatter in the physical properties of stars in the Galaxy, it is possible that different solutions will be found with the addition of new observations.
We have carried out detailed analysis on the black hole candidate (BHC) X- ray transient Swift J1753.5-0127 observed by the Rossi X-Ray Timing Explorer (RXTE) during its outburst in 2005 {2006. The spectral analysis shows that the emissions are dominated by the hard X-rays, thus revealing the low/hard state of the source during the outburst. The peak luminosity is found lower than the typical value of balancing the mass flow and evaporation of the inner edge of disk (Meyer-Hofmeister 2004). As a result, the disk is prevented from extending inward to produce strong soft X-rays, corresponding to the so-called high/soft state. These are the typical characteristics for a small subset of BHCs, i.e. those soft X-ray transients stay at the low/hard state during the outburst. In most observational time, the QPO frequencies are found to vary roughly linearly with the fluxes and the spectral indices, while the deviation from this relationship at the peak luminosity might provide the first observational evidence of a partially evaporated inner edge of the accretion disk. The anti-correlation between the QPO frequency and spectral color suggests that the global disk oscillation model proposed by Titarchuk & Osherovich (2000) is not likely at work.
In this paper, a parameterized deceleration parameter $q(z)= 1/2 - a/(1 + z)^b$ is reconstructed from the latest type Ia supernovae gold dataset. It is found out that the transition redshift from decelerated expansion to accelerated expansion is at $z_T=0.35^{+0.14}_{-0.07}$ with $1\sigma$ confidence level in this parameterized deceleration parameter. And, the best fit values of parameters in $1\sigma$ errors are $a=1.56^{+0.99}_{-0.55}$ and $b=3.82^{+3.70}_{-2.27}$.
Chaotic dynamics essentially defines the global properties of gravitating systems, including, probably, the basics of morphology of galaxies. We use the Ricci curvature criterion to study the degree of relative chaos (exponential instability) in core-halo gravitating configurations. We show the existence of a critical core radius when the system is least chaotic, while systems with both smaller and larger core radius will typically possess stronger chaotic properties.
Lyman-$\alpha$ spheres, i.e. regions around the first stars which are illuminated by Lyman-$\alpha$ photons and show 21cm absorption feature against the CMB, are smoking guns at the dawn of the reionization epoch. Though overwhelming radio foreground makes their detections extremely difficult, we pointed out that, strong gravitational lensing can significantly improve their observational feasibility. Since Lyman-$\alpha$ spheres have ~10" sizes, comparable to the caustic size of galaxy clusters, individual images of each strongly lensed Lyman-$\alpha$ sphere often merge together and form single structures in the 21cm sky with irregular shapes. Using high-resolution N-body LCDM simulations, we found that the lensing probability to have magnification bigger than 10 is ~10^{-5}. This results in $\ga 10^6$ strongly lensed Lyman-$\alpha$ spheres across the sky, which should be the primary targets for first detections of Lyman-$\alpha$ spheres. Although the required total radio array collecting area for their detection is large (~100 km^2), the design of long fixed cylindrical reflectors can significantly reduce the total cost of such array to the level of the square kilometer array (SKA) and makes the detection of these very first objects feasible.
We analyse the 267 radio sources from our deep (flux limit of 42 microJy at the field center at 1.4 GHz) Chandra Deep Field South 1.4 and 5 GHz VLA survey. The radio population is studied by using a wealth of multi-wavelength information, including morphology and spectral types, in the radio, optical, and X-ray bands. The availability of redshifts for ~ 70% of our sources allows us to derive reliable luminosity estimates for the majority of the objects. Contrary to some previous results, we find that star-forming galaxies make up only a minority (~ 1/3) of sub-mJy sources, the bulk of which are faint radio galaxies, mostly of the Fanaroff-Riley I type.
We study the effect of wind anisotropies on the stellar evolution leading to collapsars. Rotating models of a 60 M$_\odot$ star with $\Omega/\Omega_{\rm crit}=0.75$ on the ZAMS, accounting for shellular rotation and a magnetic field, with and without wind anisotropies, are computed at $Z$=0.002 until the end of the core He-burning phase. Only the models accounting for the effects of the wind anisotropies retain enough angular momentum in their core to produce a Gamma Ray Burst (GRB). The chemical composition is such that a type Ic supernova event occurs. Wind anisotropies appear to be a key physical ingredient in the scenario leading to long GRBs.
We use the recent supernova data set from the ESSENCE collaboration combined with data from the Supernova Legacy Survey and nearby supernovae to test the DGP brane world model and its generalisations. Combination of this data with a flatness prior and the position of the peak of the CMB disfavours the DGP model slightly, although does not rule it out significantly. Inclusion of the baryon acoustic peak from the Sloan Digital Sky Survey would rule out the DGP model at the 3-sigma level, although it is not clear how self consistent this procedure would be without a re-analysis of the survey data in the framework of the DGP cosmology. Generalisations of the DGP model are tested and constraints on relevant parameters obtained.
Ghirlanda et al. (2004) derived the collimation-corrected energy E_gamma for a sample of 15 bursts under the assumption of a homogeneous circumburst density profile. They found a correlation (the so-called Ghirlanda correlation) between E_gamma and the rest frame peak energy of the nuF_nu prompt spectrum (E_p). Nava et al. (2006) showed that, assuming a circumburst density distribuited with a r^-2 wind profile, the Ghirlanda correlation remains tight and becomes linear. This implies that: i) it remains linear also in the comoving frame, no matter the distribution of bulk Lorentz factors, ii) it entails that different bursts have the same number of relevant photons. We have updated these findings including recently detected bursts (21 in total), stressing the two important implications.
In this paper, we examine numerically the difference between triggered and revealed star formation. We present Smoothed Particle Hydrodynamics (SPH) simulations of the impact on a turbulent 10^4 solar-mass molecular cloud of irradiation by an external source of ionising photons. In particular, using a control model, we investigate the triggering of star formation within the cloud. We find that, although feedback has a dramatic effect on the morphology of our model cloud, its impact on star formation is relatively minor. We show that external irradiation has both positive and negative effects, accelerating the formation of some objects, delaying the formation of others, and inducing the formation of some that would not otherwise have formed. Overall, the calculation in which feedback is included forms nearly twice as many objects over a period of \sim0.5 freefall times (\sim2.4 Myr), resulting in a star--formation efficiency approximately one third higher (\sim4% as opposed to \sim3% at this epoch) as in the control run in which feedback is absent. Unfortunately, there appear to be no observable characteristics which could be used to differentiate objects whose formation was triggered from those which were forming anyway and which were simply revealed by the effects of radiation, although this could be an effect of poor statistics.
The differential energy spectrum of cosmic rays exhibits a change of slope,
called "knee" of the spectrum, around the nominal energy of 3 x 10^15 eV, and
individual "knees" for single ions, at different energies. The present work
reports a detailed account of the characteristics and the origin of the knees
for Helium and Iron. Current observational data regarding the magnetic field,
the insterstellar matter density, the size of the Galaxy and the galactic wind,
are incorporated in appropriate algorithms which allow to simulate millions of
cosmic-ion trajectories in the disk. Bundles of ion trajectories define
galactic regions called basins utilized in the present analysis of the knees.
The fundamental role of the nuclear cross sections in the origin of the helium
and iron knees is demonstrated and highlighted.
The results of the calculation are compared with the experimental data in the
energy interval 10^12 eV - 5 x 10^17 eV. There is a fair agreement between the
computed and measured energy spectra of Helium and Iron; rather surprisingly
their relative intensities are also in accord with those computed here. The
results suggest that acceleration mechanisms in the disk are extraneous to the
origin of the "knees".
The recent introduction of high resolution/large spectral range spectrographs
provided the opportunity to investigate in detail the chemical composition of
classical Cepheids. This paper is focussed on new abundance determinations for
iron and 6 light metals (O, Na, Mg, Al, Si, Ca) in 30 Galactic Cepheids. We
also give a new estimate of the Galactic radial abundance gradient.
The stellar effective temperatures have been determined using the method of
line depth ratios, while the surface gravity and the microturbulent velocity
v$_{t}$ by imposing the ionization balance between Fe I and Fe II and the help
of the curves of growth. Abundances were calculated with classical LTE
atmosphere models.
Abundances are obtained with RMS accuracies of the order of 0.05-0.10 dex for
Fe, and 0.05-0.20 dex for the other elements. Cepheids in our sample have
solar-like abundances and current measurements agree quite-well with previous
determinations. We computed ``single zone'' Galactic radial abundance gradients
for the 8-12 kpc region and found a slope for iron of -0.061 dex kpc$^{-1}$.
We present a combined analysis of the kinematics of the Large Magellanic Cloud through its HI gas, carbon stars, and red supergiant stars. After correcting the line-of-sight velocities for the recent accurate measurement of the LMC's space motion, we find that each kinematic tracer clearly defines a flat rotation curve with similar shape but different amplitude for each tracer: 61 km/s for the carbon stars, 80 km/s for the HI, and 107 km/s for the red supergiants. Previously identified tidal HI features are seen to harbor numerous carbon stars, with the tidally disturbed stars comprising 7-15% of the total sample. This discovery implies that we cannot depend on the carbon star sample alone to construct a reliable model of the LMC's gravitational potential. We also find red supergiants with peculiar kinematics, but their association with tidal features is unclear, and may instead be interacting with supergiant HI shell SGS4. In addition, although the local velocity dispersion of the red supergiants is small, ~8 km/s, their velocity dispersion about the carbon star rotation solution is 17 km/s, equal to the velocity dispersion of the carbon stars themselves. We thus appear to be witnessing the tidal heating of the LMC's stellar disk.
We present ground-based mid-infrared imaging for 27 M-, S- and C-type Asymptotic Giant Branch (AGB) stars. The data are compared with those of the database available thanks to the IRAS, ISO, MSX and 2MASS catalogues. Our goal is to establish relations between the IR colors, the effective temperature $T_{eff}$, the luminosity $L$ and the mass loss rate $\dot M$, for improving the effectiveness of AGB modelling. Bolometric (absolute) magnitudes are obtained through distance compilations, and by applying previously-derived bolometric corrections; the variability is also studied, using data accumulated since the IRAS epoch. The main results are: i) Values of $L$ and $\dot M$ for C stars fit relations previously established by us, with Miras being on average more evolved and mass losing than Semiregulars. ii) Moderate IR excesses (as compared to evolutionary tracks) are found for S and M stars in our sample: they are confirmed to originate from the dusty circumstellar environment. iii) A larger reddening characterizes C-rich Miras and post-AGBs. In this case, part of the excess is due to AGB models overestimating $T_{eff}$ for C-stars, as a consequence of the lack of suitable molecular opacities. This has a large effect on the colors of C-rich sources and sometimes disentangling the photospheric and circumstellar contributions is difficult; better model atmospheres should be used in stellar evolutionary codes for C stars. iv) The presence of a long-term variability at mid-IR wavelengths seems to be limited to sources with maximum emission in the 8 -- 20 $\mu$m region, usually Mira variables (1/3 of our sample). Most Semiregular and post-AGB stars studied here remained remarkably constant in mid-IR over the last twenty years.
We discuss several results made possible by accurate SDSS astrometric measurements in a large sky area, with emphasis on asteroids and stellar proper motions obtained by comparing POSS and SDSS. SDSS has observed over 200,000 moving objects in five photometric bands, corresponding to about two orders of magnitude increase over previous multi--color surveys. These data were used to extend the measurement of asteroid size distribution to a smaller size limit, to demonstrate that asteroid dynamical families, defined as clusters in orbital parameter space, also strongly segregate in color space, and to discover a correlation between asteroid age and colors. A preliminary analysis of SDSS-POSS proper motions for about 1 million M dwarf stars demonstrates that, in the 0.1-1 kpc distance range, the rotational velocity and its dispersion for disk stars increase with the distance from the Galactic plane.
Quasars signal a unique phase of galaxy evolution -- when massive spheroids are rapidly being assembled, forming stars and growing their central super-massive black holes. Measurements of the metal abundances around quasars provide unique information about these complex evolutionary processes. Here we provide a brief review of the current status and implications of quasar abundance research.
We aim at studying the cluster environment surrounding the UCHII region in IRAS 20293+3952, a region in the first stages of formation of a cluster around a high-mass star. BIMA and VLA were used to observe the 3 mm continuum, N2H+(1-0), NH3(1,1) and (2,2), and CH3OH(2-1) emission of the surroundings of the UCHII region. We studied the kinematics of the region and computed the rotational temperature and column density maps by fitting the hyperfine structure of N2H+ and NH3. The dense gas traced by N2H+ and NH3 shows two different clouds, a main cloud to the east of the UCHII region, of 0.5 pc and 250 Msun, and a western cloud, of 0.15 pc and 30 Msun. The dust emission reveals two strong components in the northern side of the main cloud, associated with Young Stellar Objects (YSOs) driving molecular outflows, and two fainter components in the southern side, with no signs of star forming activity. Regarding the CH3OH, we found strong emission in a fork-like structure associated with outflow B, as well as emission associated with outflow A. The rotational temperature is higher in the northern side of the main cloud, around 22 K, where there are most of the YSOs, than in the southern side, around 16 K. There is strong chemical differentiation in the region, since we determined low values of the NH3/N2H+ ratio, around 50, associated with YSOs in the north of the main cloud, and high values, up to 300, associated with cores with no detected YSOs, in the south of the main cloud. Such a chemical differentiation is likely due to abundance/depletion effects. Finally, interaction between the different sources in the region is important, mainly through their UV radiation and outflows (abridged).
The goal of this study is to measure parameters of the integrated HI emission for twenty-two dwarf galaxies with oxygen abundance 12+log(O/H) in the range of 7.42 to 7.65, which are representatives of the eXtremely Metal-Deficient (XMD) galaxy group. Some of them are expected to be similar to the well-known candidates for local young galaxies, IZw18 and SBS 0335-052 that have most of their baryon mass in the form of neutral gas. Therefore, the HI 21-cm line observations are crucial to understanding their group and individual properties. The Nancay Radio Telescope (NRT) with the upgraded focal receiver was used for observations of the 21-cm HI-line. This permitted the detection of the faintest sources with rms of ~1 mJy per 10.5 km/s resolution element. For eighteen detected galaxies we present the parameters of their integrated HI line emission and describe the data on individual objects in more detail. For four undetected XMD galaxies, we give upper limits on their M$(HI). For 70% of the twenty studied non low surface brightness XMD galaxies, we find evidence (both from HI and optical data) for their interaction with neighboring objects. In the brief discussion of the group HI properties of the observed subsample (the total O/H range is of 0.23 dex, or a factor of 1.7), we underline the broad distributions of the HI mass (range is of 2 orders of magnitude), of the ratio M(HI)/L_B (of 1 order of magnitude), and of the blue luminosity (range is of 2 orders of magnitude). We also obtained HI parameters of six galaxies that do not belong to the XMD sample. These data increase the number of XMD galaxies with known integrated HI parameters (or upper limits) by a factor of two. This allows us to address statistical properties of this group, which will be presented in a forthcoming paper. (Abridged).
(Abridged) The Large Synoptic Survey Telescope (LSST) is currently by far the most ambitious proposed ground-based optical survey. Solar System mapping is one of the four key scientific design drivers, with emphasis on efficient Near-Earth Object (NEO) and Potentially Hazardous Asteroid (PHA) detection, orbit determination, and characterization. In a continuous observing campaign of pairs of 15 second exposures of its 3,200 megapixel camera, LSST will cover the entire available sky every three nights in two photometric bands to a depth of V=25 per visit (two exposures), with exquisitely accurate astrometry and photometry. Over the proposed survey lifetime of 10 years, each sky location would be visited about 1000 times. The baseline design satisfies strong constraints on the cadence of observations mandated by PHAs such as closely spaced pairs of observations to link different detections and short exposures to avoid trailing losses. Equally important, due to frequent repeat visits LSST will effectively provide its own follow-up to derive orbits for detected moving objects. Detailed modeling of LSST operations, incorporating real historical weather and seeing data from LSST site at Cerro Pachon, shows that LSST using its baseline design cadence could find 90% of the PHAs with diameters larger than 250 m, and 75% of those greater than 140 m within ten years. However, by optimizing sky coverage, the ongoing simulations suggest that the LSST system, with its first light in 2013, can reach the Congressional mandate of cataloging 90% of PHAs larger than 140m by 2020.
(Abridged) The Large Synoptic Survey Telescope (LSST) is currently by far the most ambitious proposed ground-based optical survey. The main science themes that drive the LSST system design are Dark Energy and Matter, the Solar System Inventory, Transient Optical Sky and the Milky Way Mapping. The LSST system, with its 8.4m telescope and 3,200 Megapixel camera, will be sited at Cerro Pachon in northern Chile, with the first light scheduled for 2013. In a continuous observing campaign, LSST will cover the entire available sky every three nights in two photometric bands to a depth of V=25 per visit (two 15 second exposures), with exquisitely accurate astrometry and photometry. Over the proposed survey lifetime of 10 years, each sky location would be observed about 1000 times, with the total exposure time of 8 hours distributed over six broad photometric bandpasses (ugrizY). This campaign will open a movie-like window on objects that change brightness, or move, on timescales ranging from 10 seconds to 10 years. The survey will have a data rate of about 30 TB/night, and will collect over 60 PB of data over its lifetime, resulting in an incredibly rich and extensive public archive that will be a treasure trove for breakthroughs in many areas of astronomy. I describe how this archive will impact the AGB star research and speculate how the system could be further optimized by utilizing narrow-band TiO and CN filters.
We compare Stetson's photometric standards with measurements listed in a standard star catalog constructed using repeated SDSS imaging observations. The SDSS catalog includes over 700,000 candidate standard stars from the equatorial stripe 82 (|Dec|<1.266 deg) in the RA range 20h 34' to 4h 00', and with the $r$ band magnitudes in the range 14--21. The distributions of measurements for individual sources demonstrate that the SDSS photometric pipeline correctly estimates random photometric errors, which are below 0.01 mag for stars brighter than (19.5, 20.5, 20.5, 20, 18.5) in ugriz, respectively (about twice as good as for individual SDSS runs). We derive mean photometric transformations between the SDSS gri and the BVRI system using 1165 Stetson stars found in the equatorial stripe 82, and then study the spatial variation of the difference in zeropoints between the two catalogs. Using third order polynomials to describe the color terms, we find that photometric measurements for main-sequence stars can be transformed between the two systems with systematic errors smaller than a few millimagnitudes. The spatial variation of photometric zeropoints in the two catalogs typically does not exceed 0.01 magnitude. Consequently, the SDSS Standard Star Catalog for Stripe 82 can be used to calibrate new data in both the SDSS ugriz and the BVRI systems with a similar accuracy.
In addition to optical photometry of unprecedented quality, the Sloan Digital Sky Survey (SDSS) is also producing a massive spectroscopic database. We discuss determination of stellar parameters, such as effective temperature, gravity and metallicity from SDSS spectra, describe correlations between kinematics and metallicity, and study their variation as a function of the position in the Galaxy. We show that stellar parameter estimates by Beers et al. show a good correlation with the position of a star in the g-r vs. u-g color-color diagram, thereby demonstrating their robustness as well as a potential for photometric parameter estimation methods. Using Beers et al. parameters, we find that the metallicity distribution of the Milky Way stars at a few kpc from the galactic plane is bimodal with a local minimum at [Z/Zo]~ -1.3. The median metallicity for the low-metallicity [Z/Zo]<-1.3 subsample is nearly independent of Galactic cylindrical coordinates R and z, while it decreases with z for the high-metallicity [Z/Zo]> -1.3 sample. We also find that the low-metallicity sample has ~2.5 times larger velocity dispersion and that it does not rotate (at the ~10 km/s level), while the rotational velocity of the high-metallicity sample decreases smoothly with the height above the galactic plane.
The first cosmological results from the ESSENCE supernova survey (Wood-Vasey
et al. 2007) are extended to a wider range of cosmological models including
dynamical dark energy and non-standard cosmological models. We fold in a
greater number of external data sets such as the recent Higher-z release of
high-redshift supernovae (Riess et al. 2007) as well as several complementary
cosmological probes. Model comparison statistics such as the Bayesian and
Akaike information criteria are applied to gauge the worth of models. These
statistics favor models that give a good fit with fewer parameters.
Based on this analysis, the preferred cosmological model is the flat
cosmological constant model, where the expansion history of the universe can be
adequately described with only one free parameter describing the energy content
of the universe. Amongst the more exotic models that provide good fits to the
data, we note a preference for models whose best-fit parameters reduce them to
the cosmological constant model.
VLBA and Global VLBI observations of M87 at 43 GHz, some new and some
previously published, are used to study the structural evolution of the jet
with a spatial resolution of under 100 Schwarzschild radii. The images, taken
between 1999 and 2004, have an angular resolution of 0.00043" x 0.00021". An
edge-brightened jet structure and an indication of a large opening angle at the
jet base are seen in all five epochs. In addition, a probable counter-jet is
seen in the latter three epochs. A 22 GHz VLBA image also confirms many of the
structures seen at the higher frequency, including the counter-jet. A
comparison of the counter-jet flux density at 22 and 43 GHz reveals that it is
not free-free absorbed at these frequencies.
Attempts to obtain speeds from the proper motions of jet and counter-jet
components indicate that these observations are undersampled. The closest pair
of images gives apparent speeds of 0.25 to 0.40c for the jet and 0.17c for the
counter-jet. These speeds should be treated as lower limits because of possible
errors in associating components between epochs. If they are real, they
indicate that the jet is oriented 30-45 degrees from the line-of-sight and that
the component speeds along the jet are 0.3-0.5c. Using the jet orientation
derived from proper motions, the spectral index of the the counter-jet, and a
jet-to-counter-jet brightness ratio of 14.4, the inferred bulk flow is
0.6-0.7c, which, given the considerable uncertainties in how to measure the
brightness ratio, is not significantly larger than the component speed.
Supermassive black holes are nowadays believed to reside in most local galaxies. Observations have revealed us vast information on the population of local and distant black holes, but the detailed physical properties of these dark massive objects are still to be proven. Accretion of gas and black hole mergers play a fundamental role in determining the two parameters defining a black hole: mass and spin. We briefly review here the basic properties of the population of supermassive black holes, focusing on the still mysterious formation of the first massive black holes, and their evolution from early times to now.
There are many indications that anthropogenic global warming poses a serious threat to our civilization and its ecological support systems. Ideally this problem will be overcome by reducing greenhouse gas emissions. Various space-based methods, including large-scale solar shades, diffusers or atmospheric pollutants, have been considered to reduce the solar constant (input flux) and the warming in case emissions reductions are not achieved in a timely way. Here it is pointed out that proposed technologies for near-Earth orbiting comet deflection, suggest a different kind of space-based solar shade. This shade would be made up of micron-sized dust particles derived from comet fragments or lunar mining, and positioned in orbits near the triangular Lagrange points of the Earth-Moon system. Solar radiation pressure can render such orbits unstable, but a class of nearly resonant, and long-lived orbits is shown to exist, though the phase space volume of such orbits depends on dust grain size. Advantages and disadvantages of this scheme relative to others are considered.
We discuss images of the central ~10 kpc (in projection) of the galaxy merger NGC 6240 at H and K' bands, taken with the NIRC2 narrow camera on Keck II using natural guide star adaptive optics. We detect 28 star clusters in the NIRC2 images, of which only 7 can be seen in the similar-spatial-resolution, archival WFPC2 Planetary Camera data at either B or I bands. Combining the NIRC2 narrow camera pointings with wider NICMOS NIC2 images taken with the F110W, F160W, and F222M filters, we identify a total of 32 clusters that are detected in at least one of these 5 infrared (lambda > 1 micron) bandpasses. By comparing to instantaneous burst, stellar population synthesis models (Bruzual & Charlot 2003), we estimate that most of the clusters are consistent with being ~15 Myr old and have photometric masses ranging from 7E5 M_sun to 4E7 M_sun. The total contribution to the star formation rate (SFR) from these clusters is approximately 10 M_sun/year, or ~10% of the total SFR in the nuclear region. We use these newly discovered clusters to estimate the extinction toward NGC 6240's double nuclei, and find values of A_V as high as 14 magnitudes along some sightlines, with an average extinction of A_V~7 mag toward sightlines within ~3 arcsec of the double nuclei.
Using the results of recent optical surveys we conclude that the {\it non}-detection of quasars down to faint magnitudes implies a significant flattening of the high redshift (z~6) optical active galactic nuclei (AGN) luminosity function for M_{1450}>-26.7. We find that all the data are consistent with a faint-end slope for the optical AGN luminosity function of \beta=-2.2 and \beta=-2.8, at the 90% and 99% confidence level respectively, flatter than the bright-end slope of \beta'~ -3.2. We also show that X-ray deep surveys have probed even fainter magnitudes than the optical ones yielding more significant constraints on the shallow faint-end slope of the optical luminosity function. The inclusion of Type II AGN candidates, detected in the Chandra deep fields, hints towards an higher normalization for the total AGN luminosity function, if these sources lie at 5<z <6.5. We then discuss simple theoretical models of AGN formation and evolution in the context of cold dark matter cosmology. The comparison with the total AGN luminosity function favors a redshift-dependent relation between black hole and dark matter halo masses of the type M_BH~M_ halo^\alpha, with 1.3< \alpha< 1.7, compatible with independent studies from statistical analysis and rotation curve measurements. Finally we compute the quasar contribution to reionization to be <9% at z~6, up to ~30% when integrated within 5.5< z<6.5, significantly smaller than that from galaxies.
The mass-loss rates of hot, massive, luminous stars are considered a decisive parameter in shaping the evolutionary tracks of such stars and influencing the interstellar medium on galactic scales. The small-scale structures (clumps) omnipresent in such winds may reduce empirical estimates of mass-loss rates by an evolutionarily significant factor of >=3. So far, there has been no direct observational evidence that wind-clumping may persist at the same level in environments with a low ambient metallicity, where the wind-driving opacity is reduced. Here we report the results of time-resolved spectroscopy of three presumably single Population I Wolf-Rayet stars in the Small Magellanic Cloud, where the ambient metallicity is ~1/5 Z_Sun.We detect numerous small-scale emission peaks moving outwards in the accelerating parts of the stellar winds.The general properties of the moving features, such as their velocity dispersions,emissivities and average accelerations, closely match the corresponding characteristics of small-scale inhomogeneities in the winds of Galactic Wolf-Rayet stars.
We survey the theory and experimental tests for the propagation of cosmic rays in the Galaxy up to energies of 10^15 eV. A guide to the previous reviews and essential literature is given, followed by an exposition of basic principles. The basic ideas of cosmic-ray propagation are described, and the physical origin of its processes are explained. The various techniques for computing the observational consequences of the theory are described and contrasted. These include analytical and numerical techniques. We present the comparison of models with data including direct and indirect - especially gamma-ray - observations, and indicate what we can learn about cosmic-ray propagation. Some particular important topics including electrons and antiparticles are chosen for discussion.
The luminosity of the Tip of the Red Giant Branch (TRGB) provides an excellent measure of galaxy distances and is easily determined in the resolved images of nearby galaxies observed with Hubble Space Telescope. There is now a large amount of archival data relevant to the TRGB methodology and which offers comparisons with other distance estimators. Zero-point issues related to the TRGB distance scale are reviewed in this paper. Consideration is given to the metallicity dependence of the TRGB, the transformations between HST flight systems and Johnson-Cousins photometry, the absolute magnitude scale based on Horizontal Branch measurements, and the effects of reddening. The zero-point of the TRGB is established with a statistical accuracy of 1%, modulo the uncertainty in the magnitude of the Horizontal Branch, with a typical rms uncertainty of 3% in individual galaxy distances at high Galactic latitude. The zero-point is consistent with the Cepheids period-luminosity relation scale but invites reconsideration of the claimed metallicity dependence with that method. The maser distance to NGC 4258 is consistent with TRGB but presently has lower accuracy.
In this paper, three kinds of simple parameterized deceleration parameters are reconstructed from the latest released observations of Sne Ia and Hubble data. It is found out that the transition redshift from decelerated expansion to accelerated expansion is about $z_T\sim 0.36-0.39$ in these three kinds of parameterizations by only using Gold Sne Ia datasets. By adding the Hubble parameter data, the $z_T$ becomes in the range of $0.37-0.77$ and the errors become bigger than that in the cases of only Sne Ia datasets cases. It is also pointed out that the differences of the best fit values of transition time from decelerated expansion to accelerated expansion are due to the concrete parameterized forms. But, in $1\sigma$ range, they are consistent with each other. At last, in this way some equation of state of dark energy and some dark energy models will be rule out, but this much rely on the errors at the transition redshift.
Since the successful launch of NASA's dedicated gamma-ray burst (GRB) mission, Swift, the study of cosmological GRBs has entered a new era. Here I review the rapid observational and theoretical progress in this dynamical research field during the first two-year of the Swift mission, focusing on how observational breakthroughs have revolutionized our understanding of the physical origins of GRBs. Besides summarizing how Swift helps to solve some pre-Swift mysteries, I also list some outstanding problems raised by the Swift observations. An outlook of GRB science in the future, especially in the GLAST era, is briefly discussed.
A new, unique mechanism accounting for the knee and the ankle in the energy spectrum of the cosmic radiation is presented. The interplay of the form and strength of the galactic magnetic field, the rising trend of the nuclear cross sections with energy, the position of the solar cavity within the Galaxy and disc size generates knees and ankles of individual ions. The influence of these observational data on the cosmic-ray intensity at Earth is determined by the appropriate simulation of the cosmic-ray trajectories in the galactic volume. The solid and extensive accord between the computed and measured energy spectra of individual ions and of all ions is discussed and emphasized.
It is expected that specific globular clusters can contain up to a hundred of millisecond pulsars. These pulsars can accelerate leptons at the shock waves originated in collisions of the pulsar winds and/or inside the pulsar magnetospheres. Energetic leptons diffuse gradually through the globular cluster comptonizing stellar and microwave background radiation. We calculate the GeV-TeV $\gamma$-ray spectra for different models of injection of leptons and parameters of the globular clusters assuming reasonable, of the order of 1%, efficiency of energy conversion from the pulsar winds into the relativistic leptons. It is concluded that leptons accelerated in the globular cluster cores should produce well localized $\gamma$-ray sources which are concentric with these globular clusters. The results are shown for four specific globular clusters (47 Tuc, Ter 5, M13, and M15), in which significant population of millisecond pulsars have been already discovered. We argue that the best candidates, which might be potentially detected by the present Cherenkov telescopes and the planned satellite telescopes (AGILE, GLAST), are 47 Tuc on the southern hemisphere, and M13 on the northern hemisphere. We conclude that detection (or non-detection) of GeV-TeV $\gamma$-ray emission from GCs by these instruments put important constraints on the models of acceleration of leptons by millisecond pulsars.
We present the main scientific goals and characteristics of the ESA Planck satellite mission, as well as the main features of the survey strategy and simulated performance in terms of measuring the temperature and polarization of the Cosmic Microwave Background fluctuations.
We describe an algorithm that computes the linear dispersion relation of waves and instabilities in relativistic plasmas within a Vlasov-Maxwell description. The method used is fully relativistic and involves explicit integration of particle orbits along the unperturbed equilibrium trajectories. We check the algorithm against the dispersion curves for a single component magnetised plasma and for an unmagnetised plasma with counter-streaming components in the non-relativistic case. New results on the growth rate of the Weibel or two-stream instability in a hot unmagnetised pair plasma consisting of two counter-streaming relativistic Maxwellians are presented. These are relevant to the physics of the relativistic plasmas found in gamma-ray bursts, relativistic jets and pulsar winds.
The formation of low-mass protostars and especially of brown dwarfs currently are ``hot topics'' in cool star research. The talks contributed to this splinter session discussed how low in mass and how low in luminosity objects might exist, if these substellar objects show evidence for circum(sub)stellar disks, and how the bottom of the mass function in young clusters after the formation process looks like. In a lively open discussion, a vast majority of the speakers and the audience expressed why, given the available data, a stellar-like formation mechanism down to the lowest masses should be preferred.
Observations have revealed a large variety of structures (global asymmetries, warps, belts, rings) and dynamical phenomena ("falling-evaporating bodies" or FEBs, the "Beta Pic dust stream") in the disc of Beta Pictoris, most of which may indicate the presence of one or more planets orbiting the star. Because planets of Beta Pic have not been detected by observations yet, we use dynamical simulations to find "numerical evidence" for a planetary system. We show that already one planet at 12 AU with a mass of 2 to 5 Mjup and an eccentricity smaller or equal 0.1 can probably account for three major features (main warp, two inner belts, FEBs) observed in the Beta Pic disc. The existence of at least two additional planets at about 25 AU and 45 AU from the star seems likely. We find rather strong upper limits of 0.6 Mjup and 0.2 Mjup on the masses of those planets. The same planets could, in principle, also account for the outer rings observed at 500 - 800 AU.
Whether the upcoming cycle 24 of solar activity will be strong or not is being hotly debated. The solar cycle is produced by a complex dynamo mechanism. We model the last few solar cycles by `feeding' observational data of the Sun's polar magnetic field into our solar dynamo model. Our results fit the observed sunspot numbers of cycles 21-23 extremely well and predict that cycle~24 will be about 35% weaker than cycle~23.
We construct a speculative scenario for rotation-induced extra helium mixing to the envelope of horizontal branch (HB) stars. This scenario differs from previous ones in that the mixing occurs after the star has left the red giant branch (RGB). We follow the evolution of a low metallicity star from the RGB to the HB, and examine the density profile and radius in the core-envelope boundary region. In the transition from the RGB to the HB the envelope shrinks by two orders of magnitude in size and the core swells, such that any non-negligible rotation on the RGB will result in a strong rotational shear at the core-envelope boundary. For a non-negligible rotation to exist on the RGB the star has to be spun up by a companion spiraling inside its envelope (a common envelope evolution). We speculate that shear instabilities on the HB might mix helium-rich core material to the envelope. The shallow density profile on the HB is less likely to prevent mixing. As previously shown, extra helium mixing can account for the overluminous blue HB stars found in some globular clusters. Although being speculative, this study supports the idea that the presence of low mass companions, from planets to low mass main sequence stars, influence the evolution of stars, and can explain some properties of the color-magnitude (Herzsprung-Russel) diagram of globular clusters. Namely, low mass companions can be an ingredient in the so called `second parameter' of globular clusters.
The observations of W UMa type stars show a well-defined short-period limit
of 0.22 d, which is equivalent to a lower mass limit of approximately 1 solar
mass for the total binary mass. It is currently believed that cool contact
binaries are formed from detached binaries losing angular momentum (AM) via a
magnetized wind. Orbital evolution of detached binaries with various component
masses was followed until the primary component reached the critical Roche
surface and the Roche lobe overflow (RLOF) began. It was assumed that the
minimum initial, i.e. ZAMS, orbital period of such binaries is equal to 2 d and
that the components lose AM just as single stars. According to the
mass-dependent formula for AM loss rate of single stars, derived in this paper,
the AM loss time scale increases substantially with decreasing stellar mass.
The formula was applied to binaries with the initial primary component masses
between 1.0 and 0.6 solar mass and two values of mass ratio q=1 and 0.5.
Detailed calculations show that the time needed to reach RLOF by a 1 solar
mass primary is of the order of 7.5 Gyr, but it increases to more than 13 Gyr
for a binary with an initial primary mass of 0.7 solar mass. Binaries with less
massive primaries have not yet had time to reach RLOF even within the age of
the Universe. This sets a lower mass limit for the presently existing contact
binaries
The halo of the Miky Way might contain numerous and dense substructures inside which the putative weakly interacting massive particles (suggested as the main constituent of the astronomical dark matter) would produce a stronger annihilation signal than in the smooth regions. The closer the nearest clump, the larger the positron and antiproton cosmic ray fluxes at the Earth. But the actual distribution of these substructures is not known. The predictions on the antimatter yields at the Earth are therefore affected by a kind of cosmic variance whose analysis is the subject of this contribution. The statistical tools to achieve that goal are presented and Monte Carlo simulations are compared to analytic results.
Using reliable trigonometric measurements, we find that the absolute magnitude of cataclysmic variables depends on the orbital period and de-reddened $(J-H)_{0}$ and $(H-K_{s})_{0}$ colours of {\em 2MASS} (Two Micron All Sky Survey) photometric system. The calibration equation covers the ranges $0.032^{d} < P_{orb} \leq 0.454^{d}$, $-0.08 < (J-H)_{0} \leq 1.54$, $-0.03 <(H-K_{s})_{0} \leq 0.56$ and $2.0 < M_{J} < 11.7$; It is based on trigonometric parallaxes with relative errors of $(\sigma_{\pi}/\pi) \leq 0.4$. By using the period-luminosity-colours (PLCs) relation, we estimated the distances of cataclysmic variables with orbital periods and {\em 2MASS} observations and compared them with distances found from other methods. We suggest that the PLCs relation can be a useful statistical tool to estimate the distances of cataclysmic variables.
The effects of magnetic coupling (MC) process on the inner edge of the disc are discussed in detail. It is shown that the inner edge can deviate from the innermost stable circular orbit (ISCO) due to the magnetic transfer of energy and angular momentum between a Kerr black hole (BH) and its surrounding accretion disc. It turns out that the inner edge could move inward and outward for the BH spin $a_{*}$ being greater and less than 0.3594, respectively. The MC effects on disc radiation are discussed based on the displaced inner edge. A very steep emissivity can be provided by the MC process, which is consistent with the observation of MCG-6-30-15. In addition, the BH spins of GRO J1655-40 and GRS 1915+105 are detected by X-ray continuum fitting based on this model.
Extended and updated grids of TP-AGB tracks have been implemented in the TRILEGAL population synthesis code, which generates mock stellar catalogues for a galaxy given its mass, distance, star formation history and age-metallicity relation, including also the Milky Way foreground population. Among the stellar parameters that are simulated, we now include the surface chemistry, mass-loss rates, pulsation modes and periods of LPVs. This allows us to perform a series of consistency checks between AGB model predictions and observations, that we are just starting to explore. We present a few examples of model--data comparisons, mostly regarding the near-infrared and variability data for AGB stars in the Magellanic Clouds.
Observations of the Spitzer extragalactic First Look Survey field taken at 610 MHz with the Giant Metrewave Radio Telescope are presented. Seven individual pointings were observed, covering an area of 4 square degrees with a resolution of 5.8'' x 4.7'', PA 60 deg. The r.m.s. noise at the centre of the pointings is between 27 and 30 microJy before correction for the GMRT primary beam. The techniques used for data reduction and production of a mosaicked image of the region are described, and the final mosaic, along with a catalogue of 3944 sources detected above 5 sigma, are presented. The survey complements existing radio and infrared data available for this region.
Using two-dimensional velocity maps and I-band photometry, we have created mass models of 40 spiral galaxies using the Milgrom relation (the basis of modified Newtonian dynamics, or MOND) to complement previous work. A Bayesian technique is employed to compare several different dark matter halo models to Milgrom and Newtonian models. Pseudo-isothermal dark matter halos provide the best statistical fits to the data in a majority of cases, while the Milgrom relation generally provides good fits as well. We also find that Milgrom models give mass-to-light ratios that roughly correlate with galaxy color, as predicted by stellar population models. A subsample of galaxies in the Hydra cluster follow a tight relation between mass-to-light and color, but one that is significantly different from relations found in previous studies. Ruling out the Milgrom relation with rotational kinematics is difficult due to systematic uncertainties in the observations as well as underlying model assumptions. We discuss in detail two galaxies for which the Milgrom relation appears to fail and find that relaxing the assumption of constant stellar mass-to-light ratio can maintain Milgrom models' viability.
I will briefly review the state of the art of evolutionary population synthesis (EPS) models that include the contribution from AGB stars.
The discovery of a gravitational lens candidate is reported. The quasars SDSS J111611.73+411821.5 and SDSS J111610.68+411814.4 are recognized as two images of the same object, being strongly lensed by the closer galaxy SDSS J111611.03+411820.9. The source is located at a redshift of z~3, while the redshift of the lens galaxy is z~0.25. The separation of the images is large,~13 arcsec. Commonly used models of the mass distribution for the lens galaxy with values of the parameters in the expected range describe the positions and fluxes of the images.
Faraday rotation measurements of the solar corona made with the Very Large Array (VLA) at frequencies of 1465 and 1665 MHz are reported. The measurements were made along 20 lines of sight to 19 extragalactic radio sources in March and April, 2005. The closest heliocentric distances of the lines of sight ranged from 9.7 to 5.6 $R_{\odot}$. Measured rotation measures range from -25 to +61 rad/m$^2$. The purpose of these observations is to probe the three dimensional structure of the coronal plasma in the heliocentric distance range $5-10 R_{\odot}$, and particularly the strength and structure of the coronal magnetic field. The measured rotation measures are compared with models for the coronal plasma structure. For the majority of the lines of sight, the observed rotation measures are reasonably well represented by the predictions from the models. However, 4 of the 20 lines of sight have large observed-model residuals, which do not seem associated with coronal mass ejections. The magnitude of the field necessary to reproduce the majority of the observations is in the range 46-120 milliGauss at $5 R_{\odot}$, with a smaller, preferred range of 46-52 mG at $5 R_{\odot}$.
The well-known quasar 3C48 is the most powerful compact steep-spectrum radio-loud QSO at low redshifts. It also has two unusual optical features within the radius of the radio jet (~1"): (1) an anomalous, high-velocity narrow-line component, having several times as much flux as does the narrow-line component coinciding with the broad-line redshift; and (2) a bright continuum peak (3C48A) ~1" northeast of the quasar. Both of these optical features have been conjectured to be related to the radio jet. Here we explore these suggestions. We have obtained Gemini North GMOS integral-field-unit (IFU) spectroscopy of the central region around 3C48. We use the unique features of the IFU data to remove unresolved emission at the position of the quasar. The resolved emission at the wavelength of the high-velocity component is peaked <~0.25" north of the quasar, at virtually the same position angle as the base of the radio jet. These observations appear to confirm that this high-velocity gas is connected with the radio jet. However, most of the emission comes from a region where the jet is still well collimated, rather than from the regions where the radio maps indicate strong interaction with an external medium. We also present the results of HST STIS spectroscopy of 3C48A. We show that 3C48A is dominated by stars with a luminosity-weighted age of ~1.4 X 10^8 years, substantially older than any reasonable estimate for the age of the radio source. Our IFU data indicate a similar age. Thus, 3C48A almost certainly cannot be attributed to jet-induced star formation. The host galaxy of 3C48 is clearly the result of a merger, and 3C48A seems much more likely to be the distorted nucleus of the merging partner, in which star formation was induced during the previous close passage.
In this paper, we used the database of the university of Michigan Radio Astronomy Observatory (UMRAO) at three (4.8 GHz, 8.0 GHZ, and 14.5 GHz) radio frequency to analyze the radio light curves by the power spectral analysis method in search of possible periodicity. The analysis results showed that the radio sources display astrophysically meaningful periodicity ranging from 2.2 to 20.8 years in their light curves at the three frequencies. We also calculated the variability parameters and investigated the correlations between the variability parameter and the flux density. For the variability parameters, we found that the parameters at higher frequency are higher than those in the lower frequency. In addition, the variability parameters of BL Lacertae objects are larger than those of flat-spectrum radio quasars. suggesting that they are more variable than flat spectrum radio quasars.
We perform collisionless N-body simulations of 1:1 galaxy mergers, using models which include a galaxy halo, disc and bulge, focusing on the behaviour of the halo component. The galaxy models are constructed without recourse to a Maxwellian approximation. We investigate the effect of varying the galaxies' orientation, their mutual orbit, and the initial velocity anisotropy or cusp strength of the haloes upon the remnant halo density profiles and shape, as well as on the kinematics. We observe that the halo density profile (determined as a spherical average, an approximation we find appropriate) is exceptionally robust in mergers, and that the velocity anisotropy of our remnant haloes is nearly independent of the orbits or initial anisotropy of the haloes. The remnants follow the halo anisotropy - local density slope (\beta-\gamma) relation suggested by Hansen & Moore (2006} in the inner parts of the halo, but \beta is systematically lower than this relation predicts in the outer parts. Remnant halo axis ratios are strongly dependent on the initial parameters of the haloes and on their orbits. We also find that the remnant haloes are significantly less spherical than those described in studies of simulations which include gas cooling.
High precision planet orbital data extracted from direct observation, spacecraft explorations and laser ranging techniques enable to put a strong constraint on the maximal dark matter density of a spherical halo centered around the Sun. The maximal density at Earth's location is of the order $10^5$ ${\rm GeV/cm^3}$ and shows only a mild dependence on the slope of the halo profile, taken between 0 and -2. This bound is somewhat better than that obtained from the perihelion precession limits.
We discuss the power of time-evolving photoionization as a diagnostic tool to measure the electron density of photoionized gas. We apply this technique to a XMM-Newton observation of the ionized absorber in the Seyfert 1 galaxy NGC 4051, and present the first measurements of the its volume density, its distance from the central ionizing source, and so its mass outflow rate. By extrapolating these measurements to high-luminosity, large black hole mass, quasars, we speculate that AGN winds can play important roles both in the AGN-host-galaxy and AGN-IGM feedback processes.
Chiang et al. 2006, hereafter C06 have recently proposed that the observed structure of the Kuiper belt could be the result of a dynamical instability of a system of ~5 primordial ice giant planets in the outer Solar System. According to this scenario, before the instability occurred, these giants were growing in a highly collisionally damped environment according to the arguments in Goldreich et al. (2004a,b, hereafter G04). Here we test this hypothesis with a series of numerical simulations using a new code designed to incorporate the dynamical effects of collisions. We find that we cannot reproduce the observed Solar System. In particular, G04 and C06 argue that during the instability, all but two of the ice giants would be ejected from the Solar System by Jupiter and Saturn, leaving Uranus and Neptune behind. We find that ejections are actually rare and that instead the systems spread outward. This always leads to a configuration with too many planets that are too far from the Sun. Thus, we conclude that both G04's scheme for the formation of Uranus and Neptune and C06's Kuiper belt formation scenario are not viable in their current forms.
Clusters of galaxies and the large scale filaments that connect neighboring clusters are expected to be sites of acceleration of charged particles and sources of non-thermal radiation from radio frequencies to gamma rays. Gamma rays are particularly interesting targets of investigation, since they may provide precious information on the nature and efficiency of the processes of acceleration and magnetic confinement of hadrons within clusters of galaxies. Here we review the status of viable scenarios that lead to the production of gamma rays from large scale structures and are compatible with the multifrequency observations that are already available. We also discuss the possibility of detection of gamma rays with space-borne telescopes such as GLAST and ground based Cherenkov telescopes, and the physical information that may be gathered from such observations.
We present the results of the correlation between the nuclear 2-10 keV X-ray and radio (at 2cm, 6cm and 20cm) luminosities for a well defined sample of local Seyfert galaxies. We use a sample of low luminosity radio galaxies (LLRGs) for comparison. In both Seyfert and LLRGs samples, X-ray and radio luminosities are significantly correlated over 8 orders of magnitude, indicating that the X-ray and radio emission sources are strongly coupled. Moreover, both samples show a similar regression slope, L(X)$\propto$ L(R)^(0.97), but Seyfert galaxies are three orders of magnitude less luminous in the radio band than LLRGs. This suggests that either similar physical mechanisms are responsible for the observed emission or a combination of different mechanisms ends up producing a similar correlation slope. Indeed, the common belief for LLRG is that both the X-ray and radio emission are likely dominated by a relativistic jet component, while in Seyfert galaxies the X-ray emission probably arises from a disk-corona system and the radio emission is attributed to a jet/outflow component. We investigate the radio loudness issue in the two samples and find that the Seyfert galaxies and the LLRGs show a different distribution of the radio loudness parameters. No correlation is found between the luminosity and the radio loudness, however the latter is related to the black hole mass and anti-correlated with the Eddington ratio. The dichotomy in the radio loudness between Seyfert and LLRG observed down to low Eddington ratios, L(2-10)/L(Edd) $\sim$ 10^(-8), does not support the idea that the origin of the radio loudness is due to a switch in the accretion mode.
We combine optical (HST) and UV (GALEX) imaging of two intermediate redshift galaxy clusters with spectroscopy of member galaxies, to study the relation between the formation history of cluster galaxies and the assembly history of the cluster structure itself. We identify key differences in the large-scale structure and intracluster medium properties of each cluster. In order to assess the importance of cluster substructure and the ICM in the evolution of cluster galaxies, we examine several key indicators of the recent star-formation and assembly history of cluster galaxies. We find that galaxies in cluster MS0451 (z=0.54) exhibit a markedly lower incidence of recent star formation activity than galaxies in cluster Cl0024 (z=0.39), likely the result of starvation by the ICM. In addition, Cl0024 members show evidence for kinematic disturbances that can be linked to the assembly of substructure.
Long duration Gamma-Ray Bursts (GRBs) have eight luminosity relations where observable burst properties can yield the burst luminosity and hence distance. This turns GRBs into useful tools of cosmology. Recently, two tests have been proposed (by Nakar & Piran and by Li) for which one of the eight relations is claimed to have significant problems. In this paper, we generalize these tests and apply them to all eight GRB luminosity relations. (a) All eight relations pass the Nakar & Piran test after accounting for the uncertainties on the data and the dispersions of the correlations. (b) All eight relations are good when the GRB redshifts are known, for example for calibration of the relations and for GRB Hubble diagram purposes. (c) We confirm the earlier results that the E_gamma,iso - E_peak Amati relation must produce very large error bars whenever an unknown redshift being sought is >1.4. (d) The E_gamma - E_peak relation of Ghirlanda et al. must produce very large error bars whenever an unknown redshift being sought is >3.4. (e) The other six relations have no problem at all from the ambiguity test of Li.