Seventy-two grids of stellar evolutionary tracks, along with the capability to generate isochrones and luminosity/color functions from them, are presented in this investigation. Sixty of them extend (and encompass) the sets of models reported by VandenBerg et al. (2000, ApJ, 532, 430) for 17 [Fe/H] values from -2.31 to -0.30 and alpha-element abundances corresponding to [alpha/Fe] = 0.0, 0.3, and 0.6 (at each iron abundance) to the solar metallicity and to sufficiently high masses (up to ~2.2 solar masses) that isochrones may be computed for ages as low as 1 Gyr. The remaining grids contain tracks for masses from 0.4 to 4.0 solar masses and 12 [Fe/H] values between -0.60 and +0.49 (assuming solar metal-to-hydrogen number abundance ratios): in this case, isochrones may be calculated down to ~0.2 Gyr. The extent of convective core overshooting has been modelled using a parameterized version of the Roxburgh (1989, A&A, 211, 361) criterion, in which the value of the free parameter at a given mass and its dependence on mass have been determined from analyses of binary star data and observed color-magnitude diagrams for several open clusters. Because the calculations reported herein satisfy many empirical constraints, they should provide useful probes into the properties of both simple and complex stellar populations. [All of the model grids may be obtained from the Canadian Astronomy Data Center (this http URL ).]
I use HST spectrophotometry to analyze the calibration of 3 optical photometry systems: Tycho-2 B_T V_T, Str\"omgren u v b y, and Johnson U B V. For Tycho-2, I revisit the analysis of Ma\'iz Apell\'aniz (2005) to include the new recalibration of grating/aperture corrections, vignetting, and charge transfer inefficiency effects produced by the STIS group and to consider the consequences of both random and systematic uncertainties. The new results reaffirm the good quality of both the Tycho-2 photometry and the HST spectrophotometry, but yield a slightly different value for ZP_B_T-V_T. For the Str\"omgren v, b, and y and the Johnson B and V filters I find that the published sensitivity curves are consistent with the available photometry and spectrophotometry and I derive new values for the associated ZP_b-y, ZP_m_1, and ZP_B-V. The situation is different for the Str\"omgren u and the Johnson U filters. There I find that the published sensitivity curves yield results that are inconsistent with the available photometry and spectrophotometry, likely caused by an incorrect treatment of atmospheric effects in the short-wavelength end. I reanalyze the data to produce new average sensitivity curves for those two filters and new values for ZP_c_1 and ZP_U-B. The new computation of synthetic U-B and B-V colors uses a single B sensitivity curve, which eliminates the previous unphysical existence of two different definitions. Finally, I find that if one uses values from the literature where uncertainties are not given, reasonable estimates for these are 1-2% for Str\"omgren b-y, m_1, and c_1 and 2-3% for Johnson B-V and U-B. The use of the results in this article should lead to a significant reduction of systematic errors when comparing synthetic photometry models with real colors and indices.
We use high resolution Eulerian hydrodynamics simulations to study kinematic
properties of the low ionization species in damped Ly$\alpha$ systems at
redshift $z=3$. Our adaptive mesh refinement simulations include most key
ingredients relevant for modeling neutral gas in high-column density absorbers:
hydrodynamics, gravitational collapse, continuum radiative transfer and gas
chemistry, but no star formation. We model high-resolution Keck spectra with
unsaturated low ion transitions in two Si II lines (1526 and $1808\AA$), and
compare simulated line profiles to the data from the SDSS DLA survey.
We find that with increasing grid resolution the models show a trend in
convergence towards the observed distributions of both the column densities and
the velocity widths. While in our highest resolution model we recover the
cumulative number of DLAs per unit absorption distance, at this stage we cannot
match precisely the observed absorption width distribution. At $z=3$ a
non-negligible fraction of DLAs with column densities below $10^{21}\cm^{-2}$
is caused by tidal tails due to galaxy-galaxy interactions in more massive halo
environments. Lower column density absorbers with $N_{\rm HI} <
10^{21.4}\cm^{-2}$ are sensitive to changes in the UV background resulting in a
10% reduction of the cumulative number of DLAs for twice the quasar background
relative to the fiducial value. We find that the mass cut-off below which a
large fraction of dwarf galaxies cannot retain gas after reionization is $\sim
7\times 10^7\msun$, lower than the previous estimates. Finally, we show that
models with self-shielding commonly used in the literature produce
significantly lower DLA velocity widths than the full radiative transfer runs.
Although Sgr A* is known to be variable in radio, millimeter, near-IR and X-rays, the correlation of the variability across its spectrum has not been fully studied. Here we describe highlights of the results of two observing campaigns in 2004 to investigate the correlation of flare activity in different wavelength regimes, using a total of nine ground and space-based telescopes. We report the detection of several new near-IR flares during the campaign based on {\it HST} observations. The level of near-IR flare activity based on {\it HST} data can be as low as $\sim0.15$ mJy at 1.6 $\mu$m and continuous up to $\sim$40% of the total observing time, thus placing better limits than ground-based near-IR observations. We also show the detection of a simultaneous bright X-ray and near-IR flare in which we observe for the first time correlated substructures as well as a submillimeter and near-IR flare using the NICMOS instrument on the {\it HST}, the {\it XMM-Newton} and {\it Caltech Submillimeter} observatories. X-ray emission as arising from the population of near-IR-synchrotron-emitting relativistic particles, which scatter submillimeter seed photons within the inner 10 Schwarzschild radii (R$_{sch}$) of Sgr A* up to X-ray energies. In addition, using the inverse Compton scattering picture, we explain the high energy 20-120 keV emission from the direction toward Sgr A*, and the lack of one-to-one X-ray counterparts to near-IR flares, by the variation of the magnetic field and the spectral index distributions of this population of nonthermal particles. In this picture, the evidence for the variability of submillimeter emission during a near-IR flare is accounted for by the low-energy component of the population of particles emitting synchrotron near-IR emission.
We present ground-based optical and Spitzer infrared imaging observations of the interacting galaxy UGC 10214, the "Tadpole Galaxy" (z = 0.0310), focusing on the star formation activity in the nuclear, disk, spiral arms and tidal tail regions. The major findings of this study are that the Tadpole is actively forming stars in the main disk outside of the nucleus and in the tidal plume, with an estimated mean star formation rate of ~2 to 4 M_sun/yr. The most prominent sites of mid-infrared emission define a "ring" morphology that, combined with the overall morphology of the system, suggest the interaction may belong to the rare class of off-center collisional ring systems that form both shock-induced rings of star formation and tidal plumes. The nuclear emission is solely powered by older stars, with little evidence for ongoing star formation at the center of the Tadpole. Extra-nuclear star formation accounts for >50% of the total star formation in the disk and spiral arms, featuring infrared-bright 'hot spots' that exhibit strong PAH emission, whose band strength is comparable to that of late-type star-forming disk galaxies. The tidal tail, which extends 2 arcmin (~75 kpc) into the intergalactic medium, is populated by super massive star clusters likely triggered by the galaxy-galaxy interaction that has distorted UGC 10214 into its current "tadpole" shape.
The temperatures and colors of stellar models are much less secure than predicted luminosities; consequently, it is important to ensure that the models which are used to interpret data for stellar populations satisfy existing observational constraints on these properties. At the present time, the available Teff constraints do not appear to pose a problem for evolutionary calculations. However, the evidence seems compelling that adjustments of the color transformations from model atmospheres are needed to achieve consistency with observations of cool stars. Stellar models that are normalized to the Sun and transformed to the observed plane using recent semi-empirical color-Teff relations are able to provide superb fits to the M67 and Hyades color-magnitude diagrams. As highlighted in the following examination of Population II subdwarfs and several well-observed globular clusters (M3, M5, M68, M92, and 47 Tuc), it is much harder to constrain the Teff and color scales at low metallicities than at [Fe/H] near 0.0. It is not clear that significant improvements to current semi-empirical color-Teff relations for metal-deficient stars will be possible until much tigher observational constraints become available. Brief comparisons of the evolutionary tracks computed by different workers are also included in this investigation.
We report high resolution (R~37,000) integral field spectroscopy of the central region (r<14arcsec) of the Red Rectangle nebula surrounding HD44179. The observations focus on the 5800A emission feature, the bluest of the yellow/red emission bands in the Red Rectangle. We propose that the emission feature, widely believed to be a molecular emission band, is not a molecular rotation contour, but a vibrational contour caused by overlapping sequence bands from a molecule with an extended chromophore. We model the feature as arising in a Polycyclic Aromatic Hydrocarbon (PAH) with 45-100 carbon atoms.
Observational evidence indicating that the expansion of the universe is accelerating has surprised cosmologists in recent years. Cosmological models have sought to explain this acceleration by incorporating `dark energy', of which the traditional cosmological constant is just one possible candidate. Several cosmological models involving an evolving equation of state of the dark energy have been proposed, as well as possible energy exchange to other components, such as dark matter. This paper summarises the forms of the most prominent models and discusses their implications for cosmology and astrophysics. Finally, this paper examines the current and future observational constraints on the nature of dark energy.
The X-ray emission from the circumstellar interaction in Type II supernovae with a dense circumstellar medium is calculated. In Type IIL and Type IIn supernovae mass loss rates are generally high enough for the region behind the reverse shock to be radiative, producing strong radiation, particularly in X-rays. We present a model for the emission from the cooling region in the case of a radiative reverse shock. Under the assumption of a stationary flow, a hydrodynamic model is combined with time dependent ionization balance and multilevel calculations. The applicability of the steady state approximation is discussed for various values of the ejecta density gradient and different sets of chemical composition. We show how the emerging spectrum depends strongly on the reverse shock velocity and the composition of the shocked gas. We discuss differences between a spectrum produced by this model and a single-temperature spectrum. Large differences for especially the line emission are found, which seriously can affect abundance estimates. We also illustrate the effects of absorption in the cool shocked ejecta. The applicability of our model for various types of supernovae is discussed.
Notwithstanding the big efforts devoted to the investigation of the mechanisms responsible for the high-energy (E>100 MeV) gamma-ray emission in active galactic nuclei (AGN), the definite answer is still missing. The X-ray energy band (0.4-10 keV) is crucial for this type of study, since both synchrotron and inverse Compton emission can contribute to the formation of the continuum. Within an ongoing project aimed at the investigation of the gamma-ray emission mechanism acting in the AGN detected by the EGRET telescope onboard CGRO, we firstly focused on the sources for which X-ray and optical/UV data are available in the XMM-Newton public archive. The preliminary results are outlined here.
Using NACO on the VLT in the imaging mode we have detected an object at a distance of only 0.7 arcsec from GQ Lup. The object turns out to be co-moving. We have taken two K-band spectra with a resolution of lambda /Delta lambda=700. In here, we analyze the spectra in detail. We show that the shape of spectrum is not spoiled by differences in the Strehl ratio in the blue and in the red part, as well as differential refraction. We reanalyze the spectra and derive the spectral type of the companion using classical methods. We find that the object has a spectral type between M9V and L4V, which corresponds to a Teff between 1600 and 2500 K. Using GAIA-dusty models, we find that the spectral type derivation is robust against different log(g)-values. The Teff derived from the models is again in the range between 1800 and 2400 K. While the models reproduce nicely the general shape of the spectrum, the 12CO-lines in the spectrum have about half the depth as those in the model. We speculate that this difference might be caused by veiling, like in other objects of similar age, and spectral class. We also find that the absolute brightness of the companion matches that of other low-mass free-floating objects of similar age and spectral type. A comparison with the objects in USco observed by Mohanty et al. (2004) shows that the companion of GQ Lup has a lower mass than any of these, as it is of later spectral type, and younger. The same is as true, for the companion of AB Pic. To have a first estimate of the mass of the object we compare the derived Teff and luminosity with those calculated from evolutionary tracks. We also point out that future instruments, like NAHUAL, will finally allow us to derive the masses of such objects more precisely.
We present the analysis of 200 high-resolution and 150 low-resolution spectra of the pulsating subdwarf close binary KPD 1930+2752 obtained with the Keck and the Calar Alto 2.2 m telescopes. Using metal-rich, line blanketed LTE model atmospheres the atmospheric parameters T_{eff} = 35500 +/- 500 K, log g = 5.56 +/- 0.05 and log n(He)/n(H) = -1.48 +/- 0.02 were derived. The radial velocity curve was measured and combined with all available published and unpublished radial velocity data in order to get results of high accuracy (K = 341 +/- 1 km/s, P = 0.0950933 +/- 0.0000015 d). For the first time we measured the projected rotational velocity. The preliminary result is v_{rot}sin{i} = 97 +/- 9 km/s. Since the rotation of the sdB star is very likely tidally locked to the orbit, we can constrain the inclination of the system. Assuming the companion to be a white dwarf, the mass of the sdB is limited from 0.44M_{sun} to 0.63M_{sun} and the total mass range of the system is 1.3 M_{sun} to 2.0 M_{sun}. It is very likely that the total mass exceeds the Chandrasekhar limit. Hence KPD 1930+2752 is a candidate for a progenitor of a Type Ia supernova. According to the derived limits for the inclination angle, eclipses are likely to occur.
We observed the nearby early-type spiral galaxy NGC 4594 (M 104, Sombrero galaxy) with the Very Large Array at 4.86 GHz, with the Effelsberg 100-m telescope at 8.35 GHz as well as with the Heinrich Hertz Telescope at 345 GHz in radio continuum. The 4.86 and 8.35 GHz data contain polarization information and hence information about the magnetic fields: we detected a large-scale magnetic field which is to our knowledge the first detection of a large-scale magnetic field in an Sa galaxy in the radio range. The magnetic field orientation in M104 is predominantly parallel to the disk but has also vertical components at larger z-distances from the disk. This field configuration is typical for normal edge-on spiral galaxies. The 345 GHz data pertain to the cold dust content of the galaxy. Despite the optical appearance of the object with the huge dust lane, its dust content is smaller than that of more late-type spirals.
The angular-diameter distance D_A of a galaxy cluster can be measuread by combining its X-ray emission with the cosmic microwave background fluctution due to the Sunyaev-Zeldovich effect. The application of this distance indicator usually assumes that the cluster is spherically symmetric, the gas is distributed according to the isothermal beta-model, and the X-ray temperature is an unbiased measure of the electron temperature. We test these assumptions with galaxy clusters extracted from an extended set of cosmological N-body/hydrodynamical simulations of a LCDM concordance cosmology, which include the effect of radiative cooling, star formation and energy feedback from supernovae. We find that, due to the steep temperature gradients which are present in the central regions of simulated clusters, the assumption of isothermal gas leads to a significant underestimate of D_A. This bias is efficiently corrected by using the polytropic version of the beta-model to account for the presence of temperature gradients. In this case, once irregular clusters are removed, the correct value of D_A is recovered with a ~ 5 per cent accuracy on average, with a ~ 20 per cent intrinsic scatter due to cluster asphericity. This result is valid when using either the electron temperature or a spectroscopic-like temperature. When using instead the emission-weighted definition for the temperature of the simulated clusters, D_A is biased low by \~ 20 per cent. We discuss the implications of our results for an accurate determination of the Hubble constant H_0 and of the density parameter Omega_m. We find that H_0 can be potentially recovered with exquisite precision, while the resulting estimate of Omega_m, which is unbiased, has typical errors Delta(Omega_m) ~ 0.05.
We use the evolutionary turbulent model of Jupiter's subnebula described by Alibert et al. (2005a) to constrain the composition of ices incorporated in its regular icy satellites. We consider CO2, CO, CH4, N2, NH3, H2S, Ar, Kr, and Xe as the major volatile species existing in the gas-phase of the solar nebula. All these volatile species, except CO2 which crystallized as a pure condensate, are assumed to be trapped by H2O to form hydrates or clathrate hydrates in the solar nebula. Once condensed, these ices were incorporated into the growing planetesimals produced in the feeding zone of proto-Jupiter. Some of these solids then flowed from the solar nebula to the subnebula, and may have been accreted by the forming Jovian regular satellites. We show that ices embedded in solids entering at early epochs into the Jovian subdisk were all vaporized. This leads us to consider two different scenarios of regular icy satellites formation in order to estimate the composition of the ices they contain. In the first scenario, icy satellites were accreted from planetesimals that have been produced in Jupiter's feeding zone without further vaporization, whereas, in the second scenario, icy satellites were accreted from planetesimals produced in the Jovian subnebula. In this latter case, we study the evolution of carbon and nitrogen gas-phase chemistries in the Jovian subnebula and we show that the conversions of N2 to NH3, of CO to CO2, and of CO to CH4 were all inhibited in the major part of the subdisk. Finally, we assess the mass abundances of the major volatile species with respect to H2O in the interiors of the Jovian regular icy satellites. Our results are then compatible with the detection of CO2 on the surfaces of Callisto and Ganymede and with the presence of NH3 envisaged in subsurface oceans within Ganymede and Callisto.
An evaluation of the background due to atmospheric muons in the ANTARES high energy neutrino telescope is presented. Two different codes for atmospheric shower simulation have been used. Results from comparisons between these codes at sea level and detector level are presented. The first results on the capability of ANTARES to reject this class of background are given.
Emission-line regions in active galactic nuclei and other photoionized nebulae should become larger in size when the ionizing luminosity increases. This 'breathing' effect is observed for the Hbeta emission in NGC 5548 by using Hbeta and optical continuum lightcurves from the 13-year 1989-2001 AGN Watch monitoring campaign. To model the breathing, we use two methods to fit the observed lightcurves in detail: (i) parameterized models and, (ii) the MEMECHO reverberation mapping code. Our models assume that optical continuum variations track the ionizing radiation, and that the Hbeta variations respond with time delays due to light travel time. By fitting the data using a delay map that is allowed to change with continuum flux, we find that the strength of the Hbeta response decreases and the time delay increases with ionizing luminosity. The parameterized breathing models allow the time delay and the Hbeta flux to depend on the continuum flux so that, the time delay is proportional to the continuum flux to the power beta, and the Hbeta flux is proportional to the continuum flux to the power alpha. Our fits give 0.1 < beta < 0.46 and 0.57 < alpha < 0.66. alpha is consistent with previous work by Gilbert and Peterson (2003) and Goad, Korista and Knigge (2004). Although we find beta to be flatter than previously determined by Peterson et al. (2002) using cross-correlation methods, it is closer to the predicted values from recent theoretical work by Korista and Goad (2004).
We present a discovery of a giant stellar halo in NGC 6822, a dwarf irregular galaxy in the Local Group. This halo is mostly made of old red giants, showing striking features: 1) it is several times larger than the main body of the galaxy seen in the optical images, and 2) it is elongated in the direction almost perpendicular to the HI disk of NGC 6822. The structure of this stellar halo looks similar to the shape of dwarf elliptical galaxies, indicating that the halos of dwarf irregular galaxies share the same origin with those of the dwarf elliptical galaxies.
We report the discovery of three new star clusters in the halo of the Local Group dwarf irregular galaxy NGC 6822. These clusters were found in the deep images taken with the MegaPrime at the CFHT, covering a total field of 2 deg x 2 deg. The most remote cluster is found to be located as far as 79 arcmin away from the center of NGC 6822. This distance is several times larger than the size of the region in NGC 6822 where star clusters were previously found. Morphological structures of the clusters and color-magnitude diagrams of the resolved stars in the clusters show that at least two of these clusters are proabably old globular clusters.
An extended Godel universe which incorporates expansion along with rotation is compared to data from type 1a supernovas. The model does not conflict with any known cosmological observations. We obtain bounds on an anisotropic redshift versus magnitude relationship, and accompanying parameters of the Godel-Obukhov metric.
The warps in many spiral galaxies are now known to asymmetric. Recent sensitive observations have revealed that asymmetry of warps may be the norm rather than exception. However there exists no generic mechanism to generate these asymmetries in warps. We have derived the dispersion relation in a compact form for the S-shaped warps(described by the m=1 mode) and the bowl-shaped distribution(described by the m=0 mode) in galactic disk embedded in a dark matter halo. We then performed the numerical modal analysis and used the linear and time-dependent superposition principle to generate asymmetric warps in the disk. On doing the modal analysis we find the frequency of the $m=0$ mode is much larger than that of the $m=1$ mode. The linear and time-dependent superposition of these modes with their unmodulated amplitudes(that is, the coefficients of superposition being unity) results in an asymmetry in warps of ~ 20 - 40 %, whereas a smaller coefficient for the m=0 mode results in a smaller asymmetry. The resulting values agree well with the recent observations. We study the dependence of the asymmetry index on the dark matter halo parameters. This approach can also naturally produce U-shaped warps and L-shaped warps. We show that a rich variety of possible asymmetries in the z-distribution of the spiral galaxies can naturally arise due to a dynamical wave interference between the first two bending modes(i.e. m=0 and m=1) in the disk. This is a simple but general method for generating asymmetric warps that is independent of how the individual modes arise in the disk.
The epoch of the end of reionization and the Thomson optical depth to the cosmic microwave background depend on the power spectrum amplitude on small scales and on the ionizing photon emissivity per unit mass in collapsed halos. In this paper is investigated the role of the radiative feedback effects for the temporal evolution of the ionizing emissivity. It is shown that the observational constrains on hydrogen photo-ionization rate based on Ly-$\alpha$, Ly-$\beta$ and Ly-$\gamma$ Gunn-Peterson troughs and an electron optical depth consistent with the latest CMB measurements requires an emissivity of $\sim$10 ionizing photons per baryon and Hubble time at $z=6$. Through E-mode CMB polarization power spectrum measurements, it is expected that Planck experiment will have the sensitivity to distinguish between different histories of stellar evolution.
There is strong observational evidence of shocks and clumping in radiation-driven stellar winds from hot, luminous stars. The resulting non monotonic velocity law allows for radiative coupling between distant locations, which is so far not accounted for in hydrodynamic wind simulations. In the present paper, we determine the Sobolev source function and radiative line force in the presence of radiative coupling in spherically symmetric flows, extending the geometry-free formalism of Rybicki and Hummer (1978) to the case of three-point coupling, which can result from, e.g., corotating interaction regions, wind shocks, or mass overloading. For a simple model of an overloaded wind, we find that, surprisingly, the flow decelerates at all radii above a certain height when nonlocal radiative coupling is accounted for. We discuss whether radiation-driven winds might in general not be able to re-accelerate after a non monotonicity has occurred in the velocity law.
The halo plays a crucial role in the evolution of barred galaxies. Its near-resonant material absorbs angular momentum emitted from some of the disc particles and helps the bar become stronger. As a result, a bar (oval) forms in the inner parts of the halo of strongly barred disc galaxies. It is thinner in the inner parts (but still considerably fatter than the disc bar) and tends to spherical at larger radii. Its length increases with time, while always staying shorter than the disc bar. It is roughly aligned with the disc bar, which it trails only slightly, and it turns with roughly the same pattern speed. The bi-symmetric component of the halo density continues well outside the halo bar, where it clearly trails behind the disc bar. The length and strength of the disc and halo bars correlate; the former being always much stronger than the latter. If the halo is composed of weakly interacting massive particles, then the formation of the halo bar, by redistributing the matter in the halo and changing its shape, could influence the expected annihilation signal. This is indeed found to be the case if the halo has a core, but not if it has a steep cusp. The formation and evolution of the bar strongly affect the halo orbits. A fraction of them becomes near-resonant, similar to the disc near-resonant orbits at the same resonance, while another fraction becomes chaotic. Finally, a massive and responsive halo makes it harder for a central mass concentration to destroy the disc bar.
From this vast subject, I will pick out and review three specific topics, namely the formation and evolution of bars, the formation of bulges, and the evolution during multiple major mergers. Bars form naturally in galactic discs. Their evolution is driven by the exchange of angular momentum within the galaxy. This is emitted mainly by near-resonant material in the inner disc (bar), and is absorbed by near-resonant material in the outer disc and in the halo. As a result of this, the bar becomes stronger and rotates slower. Bulges are not a homogeneous class of objects. Based on their formation history, one can distinguish three types. Classical bulges are mainly formed before the actual disc component, from collapses or mergers and the corresponding dissipative processes. Boxy/peanut bulges are parts of bars seen edge-on. Finally, disc-like bulges are formed by the inflow of material to the center due to bar torques. Major mergers bring strong and fast evolution and can turn discs into ellipticals. I present results from simulations of multiple mergers in groups of disc or of elliptical galaxies and discuss the orbital anisotropy in the merger remnant.
As a short introduction to the astronomy session, the response of the community to the Call for Themes issued by ESA and the specific themes selected by the Astronomy Working Group are briefly presented in connection with the four grand themes finally selected for the ESA Science Programme. They are placed in the context of the main discoveries of the past decade and the astronomy projects currently in their development or definition phase. Finally, possible strategies for their implementation are summarised.
Lateral distributions for electrons and muons in extensive air showers measured with the array of the KASCADE experiment are compared to results of simulations based on the high-energy hadronic interaction models QGSJet and SIBYLL. It is shown, that the muon distributions are well described by both models. Deviations are found for the electromagnetic component, where both models predict a steeper lateral shape than observed in the data. For both models the observed lateral shapes of the electron component indicate a transition from a light to a more heavy composition of the cosmic ray spectrum above the knee.
First-order Fermi acceleration processes at ultrarelativistic shocks are studied with Monte Carlo simulations. The accelerated particle spectra are derived by integrating the exact particle trajectories in a turbulent magnetic field near the shock. ''Realistic'' features of the field structure are included. We show that the main acceleration process at superluminal shocks is the particle compression at the shock. Formation of energetic spectral tails is possible in a limited energy range only for highly perturbed magnetic fields, with cutoffs occuring at low energies within the resonance energy range considered. These spectral features result from the anisotropic character of particle transport in the downstream magnetic field, where field compression produces effectively 2D perturbations. Because of the downstream field compression, the acceleration process is inefficient in parallel shocks for larger turbulence amplitudes, and features observed in oblique shocks are recovered. For small-amplitude turbulence, wide-energy range particle spectra are formed and modifications of the process due to the existence of long-wave perturbations are observed. In both sub- and superluminal shocks, an increase of \gamma leads to steeper spectra with lower cut-off energies. The spectra obtained for the ``realistic'' background conditions assumed here do not converge to the ``universal'' spectral index claimed in the literature. Thus the role of the first-order Fermi process in astrophysical sources hosting relativistic shocks requires serious reanalysis.
We study the neutral hydrogen distribution and kinematics in the Local Group
dwarf irregular galaxy IC 1613 and compare them with the ionized gas
distribution and stellar content of the galaxy. We discuss several mechanisms
which may be responsible for the origin of the observed complicated HI
morphology and compare parameters of the most prominent kpc-scale HI structure
with the multiple SNe scenario.
The observations were performed with the Vary Large Array of NRAO with a
linear resolution ~23 pc at the adopted distance of 725 kpc and the spectral
channel width of 2.57 km/s. The numerical calculations have been provided with
our 2.5D Lagrangian scheme based on the thin layer approximation.
We found that the ISM of the galaxy is highly inhomogeneous and identified a
number of intermediate-scale (200 pc - 300 pc in diameter) HI arcs and shells
having expansion velocities of 10 to 20 km/s. Besides these shells, several
giant holes and arc-shaped structures have been revealed, whose radii exceed
several hundred parsecs. We found that parameters of the most prominent (M_HI =
2.8 x 10^7 Msol) kpc-scale structure and the level of the detected star
formation activity are inconsistent with the multiple SNe hypothesis.
We present spectroscopic observations of ESO 184-G82, the host galaxy of GRB980425/SN1998bw, and six galaxies in its field. A host redshift of z=0.0087+/-0.0006 is derived, consistent with that measured by Tinney et al. (1998). Redshifts are obtained for the six surrounding galaxies observed. Three of these galaxies lie within 11 Mpc of each other, confirming the suggestion that some of these galaxies form a group. However, all of the field galaxies observed lie at significantly greater distances than ESO 184-G82 and are therefore not associated with it. The host galaxy of GRB980425/SN1998bw thus appears to be an isolated dwarf galaxy and interactions with other galaxies do not seem to be responsible for its star formation.
We use numerical hydrodynamical simulations of early structure formation in a LCDM universe to investigate the spin temperature and 21cm brightness of the diffuse intergalactic medium (IGM) prior to the epoch of cosmic reionization, at z<20. In the absence of any radiative heating, collisions between neutral hydrogen atoms can efficiently decouple the spin temperature from the CMB only in dense minihalos and filaments. Shock heated gas shines in emission, surrounded by cooler gas visible in absorption. In the case of a warm, mostly neutral IGM, produced here by X-ray emission from an early miniquasar, the 21cm signal is strongly enhanced. Even slightly overdense filaments now shine in emission against the CMB, possibly allowing future radio arrays to probe the distribution of neutral hydrogen before reionization.
It is shown that there are at least 21 QSOs within 1 degree of the nearby active spiral galaxy NGC3079. Many of them are bright (mag<18) so that the surface density of those closer than 15 arc minutes to the galaxy centre is close to 100 times the average in the field. The probability that this is an accidental configuration is shown to be less or equal to one in a million. Discovery selection effects and microlensing fail by a large factor to explain the phenomenon, suggesting that the QSOs may lie in the same physical space as NGC3079. However, two of them make up the apparently lensed pair 0957+561A, B whose lensing galaxy lies at z=0.355. This problem is discussed in the concluding section.
We investigate the effect of foreground residuals in the WMAP data (Bennet et al. 2004) by adding foreground contamination to Gaussian ensembles of CMB signal and noise maps. We evaluate a set of non-Gaussian estimators on the contaminated ensembles to determine with what accuracy any residual in the data can be constrained using higher order statistics. We apply the estimators to the raw and cleaned Q, V, and W band first year maps. The foreground subtraction method applied to clean the data in Bennet et al. (2004a) appears to have induced a correlation between the power spectra and normalized bispectra of the maps which is absent in Gaussian simulations. It also appears to increase the correlation between the dl=1 inter-l bispectrum of the cleaned maps and the foreground templates. In a number of cases the significance of the effect is above the 98% confidence level.
We present a systematic study of the low mass X-ray binary (LMXB) populations of 6 elliptical galaxies. We utilize Chandra archival data to identify 665 X-ray point sources and HST archival data supplemented by ground observations to identify 6173 GCs. We associate 209 LMXBs with red GC (RGC) and 76 LMXBs with blue GCs (BGC), while we find no optical GC counterpart for 258 LMXBs. This is the largest GC-LMXB sample studied so far. We confirm previous reports suggesting that the fraction of GCs associated with LMXBs is 3 times larger in RGCs than in BGCs, indicating that metallicity is a primary factor in the GC-LMXB formation. While as already known, the brighter (and bigger) GCs have a higher probability to host LMXBs, we find that this optical luminosity (or mass) dependency is stronger in RGCs than in BGCs. We also find that GCs located near the galaxy center have a higher probability to harbor LMXBs compared to those in the outskirts. The radial distributions of GC-LMXBs (for both RGC and BGC) are steeper than those of the whole optical GC sample, but consistent with those of the optical halo light, suggesting that there must be another parameter (in addition to metallicity) governing LMXB formation in GCs. This second parameter must depend on the galacto-centric distance. We find no statistically significant difference in the X-ray properties among RGC-LMXBs, BGC-LMXBs and field-LMXBs. The similarity of the X-ray spectra of BGC-LMXBs and RGC-LMXBs is inconsistent with the irradiation-induced stellar wind model prediction. The similarity of the X-ray luminosity functions (XLFs) of GC-LMXBs and field-LMXBs indicates that there is no significant difference in the fraction of BH binaries present in these two populations, in contrast to Galactic LMXBs where BH binaries are not found in GCs.
We investigate the nature of the continuum emission and stellar populations in the inner 1-3 kiloparsecs of a complete sample of twenty-four southern radio galaxies, and compare the results with a control sample of eighteen non-active early-type galaxies. Twelve of the radio galaxies are classified as Fanaroff-Riley type I (FRI), eight as FRII and four as intermediate or undefined type (FRx). Optical long-slit spectra are used to perform spectral synthesis as a function of distance from the nucleus at an average sampling of 0.5-1.0kpc and quantify the relative contributions of a blue featureless continuum and stellar population components of different ages. Our main finding is a systematic difference between the stellar populations of the radio and control sample galaxies: the former have a larger contribution from an intermediate age (1Gyr) component, suggesting a connection between the present radio activity and a starburst which occurred about 1Gyr ago. In addition, we find a correlation between the contribution of the 1Gyr component and the radio power, suggesting that more massive starbursts have led to more powerful radio emission. A similar relation is found between the radio power and the mean age of the stellar population, in the sense that stronger nuclear activity is found in younger galaxies.
Cosmological simulations of galaxy formation predict a universal form for the mass profile of dark matter (DM) halos from cluster to galaxy scales. Remarkably few interesting constraints exist, however, on DM halos in early-type galaxies. Using Chandra we present the temperature, density and mass profiles of a small sample of early-type galaxies, revealing significant DM in each case. When a component is included to account for stellar mass and the DM halo is allowed to respond adiabatically to the baryonic condensation into stars, the mass profiles are well-fitted by the universal profile, with Virial masses and concentrations in agreement with simulations. However, only ~half, or less, of the mass within R_e seems attributable to the stars, implying stellar M_*/L_B ~1-5.
A sample of white dwarfs is selected from SDSS DR3 imaging data using their reduced proper motions, based on improved proper motions from SDSS plus USNO-B combined data. Numerous SDSS and followup spectra (Kilic et al. 2005) are used to quantify completeness and contamination of the sample; kinematic models are used to understand and correct for velocity-dependent selection biases. A luminosity function is constructed covering the range 7 < M_bol < 16, and its sensitivity to various assumptions and selection limits is discussed. The white dwarf luminosity function based on 6000 stars is remarkably smooth, and rises nearly monotonically to M_bol = 15.3. It then drops abruptly, although the small number of low-luminosity stars in the sample and their unknown atmospheric composition prevent quantitative conclusions about this decline. Stars are identified that may have high tangential velocities, and a preliminary luminosity function is constructed for them.
The formation of tidal dwarf galaxies (TDG) inside tidal arms of interacting disk galaxies has been studied with N-body and N-body/SPH simulations at different resolutions. In pure N-body simulations no bound objects are formed at high resolution. At low resolution bound objects can form in tidal tails in agreement with previous work. We conclude that these previous findings were numerical artefacts. Tidal dwarf galaxies are not likely to form by pure collisionless collapse in tidal tails. However, the presence of a sufficiently massive and extended gas component in the progenitor disk can trigger the formation of bound stellar objects in the tidal arms. Our results clearly favor a dissipation supported scenario in which the formation of TDGs is induced by the local collapse of gas which then triggers the collapse of the stellar component. We present a detailed kinematical and photometric analysis for our most massive TDG candidate.
We summarize the results of a multiwavelength observing campaign on the massive eclipsing binary CPD-41deg7742, another remarkable object in the young open cluster NGC 6231. Our campaign relies on high resolution echelle spectroscopy, narrow-band optical photometry, and XMM-Newton X-ray observations. Combined with the spectroscopic analysis, the light curve analysis provides a direct measurement of the masses and sizes of the system components. However, the most outstanding results come from the XMM-Newton observations. Our 180 ks campaign towards NGC 6231, and CPD-41deg7742, provides an unprecedented phase coverage of such a close early-type binary. The EPIC-MOS light curves almost fully cover the 2.4 day period of the system and the brightness of the object is sufficient to yield a time resolution as tight as 1 ks. The X-ray flux presents clear variations along the orbit, that we interpret as the signature of an unusual wind interaction. We indeed expect that, in this O+B system, the dominant primary wind crashes into the secondary surface, leading to a wind-photosphere interaction. As a strong support to our interpretation, we provide a geometrical model that associates an extra X-ray emission to the secondary inner surface. Though quite simple, the present model matches the main features of the X-ray light curve.
The dynamical evolution of barred galaxies depends crucially on the fraction and their spacial distribution of chaotic orbits in them. In order to distinguish between the two kinds of orbits, we use the Smaller Alignment Index (SALI) method, a very powerful method which can be applied to problems of galactic dynamics. Using model potentials, and taking into account the full 3D distribution of matter, we discuss how the distribution of chaotic orbits depends on the main model parameters, like the mass of the various components and the bar axial ratio.
A very important issue in the area of galactic dynamics is the detection of chaotic and ordered motion inside galaxies. In order to achieve this target, we use the Smaller ALignment Index (SALI) method, which is a very suitable tool for this kind of problems. Here, we apply this index to 3D barred galaxy potentials and we present some results on the chaotic behavior of the model when its main parameters vary.
The gravitational field produced by a domain wall acts as a medium with spacetime-dependent permittivity \epsilon. Therefore, the fine structure constant \alpha = e^2/4 \pi \epsilon will be a time-dependent function at fixed position. The most stringent constraint on the time-variation of \alpha comes from the natural reactor Oklo and gives |\dot{\alpha}/\alpha| < few 10^{-17} yr^{-1}. This limit constrains the tension of a cosmic domain wall to be less than \sigma \lesssim 10^{-2} MeV^3, and then represents the most severe limit on the energy density of a cosmic wall stretching our Universe.
We present the data acquisition strategy and characterization procedures for
the Canada-France Ecliptic Plane Survey (CFEPS), a sub-component of the
Canada-France-Hawaii Telescope Legacy Survey. The survey began in early 2003
and as of summer 2005 has covered 430 square degrees of sky within a few
degrees of the ecliptic. Moving objects beyond the orbit of Uranus are detected
to a magnitude limit of $m_R$=23 -- 24 (depending on the image quality). To
track as large a sample as possible and avoid introducing followup bias, we
have developed a multi-epoch observing strategy that is spread over several
years. We present the evolution of the uncertainties in ephemeris position and
orbital elements as the objects progress through the epochs. We then present a
small 10-object sample that was tracked in this manner as part of a preliminary
survey starting a year before the main CFEPS project.
We describe the CFEPS survey simulator, to be released in 2006, which allows
theoretical models of the Kuiper Belt to be compared with the survey
discoveries since CFEPS has a well-documented pointing history with
characterized detection efficiencies as a function of magnitude and rate of
motion on the sky. Using the pre-survey objects we illustrate the usage of the
simulator in modeling the classical Kuiper Belt.
We report on Spitzer IRAC observations of the spectroscopically confirmed z=6.56 lensed Ly-alpha emitting source HCM 6A which was found behind the cluster Abell 370. Detection of the source at 3.6 and 4.5 microns, corresponding to rest-frame optical emission, allows us to study the stellar population of this primeval galaxy. The broadband flux density at 4.5 microns is enhanced compared to the continuum at other wavelengths, likely due to the presence of strong H-alpha in emission. The derived H-alpha line flux corresponds to a star-formation rate of around 140 M_{sun}/yr, more than an order of magnitude larger than estimates from the ultraviolet continuum and Ly-alpha emission line. The dust extinction required to explain the discrepancy is A_V of about 1 mag. The inference of dust at such high redshifts is surprising and implies that the first epoch of star-formation in this galaxy occurred at z~20.
The GOODS-North field centered around the historical Hubble Deep Field-North provides one of the richest multiwavelength datasets compiled, spanning radio to X-ray frequencies, for studying the formation and evolution of galaxies at high redshift. In particular, the unprecedented sensitivity of the Spitzer/GOODS 24 micron observations allows an unbiased measure of dust-enshrouded star-formation and AGN activity in typical L* galaxies rather than the extreme, hyperluminous galaxies which far-infrared surveys detect. We consider a spectroscopically selected sample of 226 galaxies at z$>$1.5 of which 135 are in the redshift range 1.5$<z<3$. Less than 1/4 of galaxies considered here are detected at 24 microns. They primarily have red UV slopes but consitute about only 20 percent of the red galaxies in this sample indicating that the red UV colors of the majority of objects is due to an evolved stellar population. Although 24 micron sources are sparse in number, their combined energy output in the 1.5$<z<3$ range exceeds the combined UV luminosity of the sample by a factor of about 30. We also find that AGN, identified by their X-ray to infrared luminosity ratios, account for less than 10 percent of the sources considered and contribute less than 30 percent of the total budget in this redshift range. The infrared luminous galaxies which are increasingly being found at high-z appear to dominate the global energetics of the Universe out to z~3 as has previously been predicted.
We report the updated UV luminosity function (LF) of Lyman break galaxies (LBGs) at z~5. Combining with lower redshift data, we found that the evolution of UV LF is differential depending on the UV luminosity; i.e., the number density of luminous LBGs does not change significantly from z=5 to 3, while the number density of faint (L<L*) galaxies increases by a factor of five. We also found the signs of differential evolution within other observational results for LBGs at z~5. UV-luminous objects show strong clustering, and they have weak or no Lyman-alpha emissions while showing prominent metal absorption lines. There is also a clear deficiency of objects with blue UV-optical colors for those bright in rest-frame optical bands (from the Spitzer/IRAC data obtained by the GOODS project). By the SED fitting using rest-frame optical to near-infrared photometry data it is suggested that most luminous objects at z~5 have already accumulated stellar mass more than 10^10 Msun. We discuss that this differential evolution might be understood as a consequence of the biased galaxy evolution.
We report results of deep optical spectroscopy with Subaru/FOCAS for Lyman Break Galaxy (LBG) candidates at z~5. So far, we made spectroscopic observations for 24 LBG candidates among ~200 bright (z'<25.0) LBG sample and confirmed 9 objects to be LBGs at z~5. Intriguingly, these bright LBGs show no or a weak Ly-alpha emission and relatively strong low ionization interstellar metal absorption lines. We also identified 2 faint (z'>25.0) objects to be at z~5 with their strong (EW_rest>20AA) Ly-alpha emission. Combining our results with other spectroscopic observations of galaxies at the similar redshift range, we found a clear luminosity dependence of EW_rest of Ly-alpha emission, i.e., the lack of strong Ly-alpha emission in bright LBGs. If the absence of Ly-alpha emission is due to dust absorption, these results suggest that bright LBGs at z~5 are in dusty and more chemically evolved environment than faint ones. This interpretation implies that bright LBGs started star formation earlier than faint ones, suggesting biased star formation.
[Context.] The hot subdwarf B star HS0702+6043 is known as a large-amplitude,
short-period p-mode pulsator of the EC14026 type. Its atmospheric parameters
place it at the common boundary between the empirical instability regions of
the EC14026 variables and the typically cooler long-period g-mode pulsators of
the PG1716 kind.
[Aims.] We analyse and interpret the photometric variability of HS0702+6043
in order to explore its asteroseismological potential.
[Methods.] We report on rapid wide band CCD photometric observations to
follow up on and confirm the serendipitous discovery of multiperiodic
long-period luminosity variations with typical time scales of ~1h in
HS0702+6043, in addition to the two previously known pulsations at 363s and
383s. In particular, we isolate a relatively low-amplitude (~4 mmag),
long-period (3538+-130s) light variation.
[Results.] We argue that the most likely origin for this luminosity variation
is the presence of an excited g-mode pulsation. If confirmed, HS0702+6043 would
constitute a rare addition to the very select class of pulsating stars showing
simultaneously parts of their pressure and gravity mode pulsation spectra. The
asteroseismological potential of such stars is immense, and HS0702+6043 thus
becomes a target of choice for future investigations. While our discovery
appears consistent with the location of HS0702+6043 at the common boundary
between the two families of pulsating sdB stars, it does challenge theory's
current description of stability and driving mechanisms in pulsating B
subdwarfs.
The discovery of a long-period g-mode oscillation in the previously known short-period p-mode sdB pulsator HS0702+6043 makes this star an extraordinary object, unique as a member of the family of sdB pulsators, and one of the very few known pulsating stars overall exhibiting excited modes along both the acoustic and gravity branches of the nonradial pulsation spectrum. Because p-modes and g-modes probe different regions of a pulsating star, HS0702+6043 holds a tremendous potential for asteroseismological investigations. We present preliminary results from the first extended campaign on this object.
We present results based on the first INTEGRAL AGN catalogue. The catalogue includes 42 AGN, of which 10 are Seyfert 1, 17 are Seyfert 2, and 9 are intermediate Seyfert 1.5. The fraction of blazars is rather small with 5 detected objects, and only one galaxy cluster and no star-burst galaxies have been detected so far. The sample consists of bright (fx > 5e-12 erg/cm**2/s), low luminosity (L = 2e43 erg/s), local (z = 0.020) AGN. Although the sample is not flux limited, we find a ratio of obscured to unobscured AGN of 1.5 - 2.0, consistent with luminosity dependent unified models for AGN. Only four Compton-thick AGN are found in the sample. This implies that the missing Compton-thick AGN needed to explain the cosmic hard X-ray background would have to have lower fluxes than discovered by INTEGRAL so far.
We suggest a plausible interpretation for the twin kiloHertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries. We identify the upper kHz QPO frequencies to be the rotational frequency and the lower kHz QPOs the standing kink modes of loop oscillations at the inner edge of the accretion disk, respectively. Taking into account the interaction between the neutron star magnetic field and the disk, this model naturally relates the twin QPO frequencies with the star's spin frequencies. We have applied the model to four X-ray sources with kHz QPOs detected simultaneously and known spin frequencies.
We use low-dispersion spectra obtained at the Magellan Observatory to study the broad H-alpha emission from the reverse shock of the infant supernova remnant SNR1987A. These spectra demonstrate that the spatio-kinematic structure of the reverse shock can be distinguished from that of the circumstellar ring and hotspots, even at ground-based spatial resolution. We measure a total dereddened H-alpha flux of 1.99(pm0.22)e-13 ergs/s/cm2 at an epoch 18.00 years after outburst. At 50 kpc, the total reverse shock luminosity in H-alpha is roughly 15 Lsun, which implies a total flux of neutral hydrogen atoms across the reverse shock of 8.9e46/s, or roughly 2.3e-3 Msun/yr. This represents an increase by a factor ~4 since 1997. Lyman continuum radiation from gas shocked by the forward blast wave can ionize neutral hydrogen atoms in the supernova debris before they reach the reverse shock. If the inward flux of ionizing photons exceeds the flux of hydrogen atoms approaching the reverse shock, this pre-ionization will shut off the broad Ly-alpha and H-alpha emission. The observed X-ray emission of SNR1987A implies that the ratio of ionizing flux to hydrogen atom flux across the reverse shock is presently at least 0.04. The X-ray emission is increasing much faster than the flux of atoms, and if these trends continue, we estimate that the broad Ly-alpha and H-alpha emission will vanish within about 7 years.
We present moderate and high-dispersion 1-2.5 micron spectra of the 10 arcsec nebula around P Cygni, dominated by bright emission lines of [Fe II]. Observed [Fe II] line ratios disagree with theoretical transition rates in the literature, so we use the spectrum of P Cygni's nebula to constrain the atomic data for low-lying levels of [Fe II]. Of particular interest is the ratio [Fe II] 12567/16435, often used as a reddening indicator, for which we empirically derive an intrinsic value of 1.49, which is 10--40 per cent higher than previous estimates. High-dispersion spectra of [Fe II] 16435 constrain the geometry, detailed structure, and kinematics of P Cygni's nebula, which is the major product of P Cygni's outburst in 1600 A.D. We use the [N II]/[N I] line ratio to conclude that the nebula is mostly ionized with a total mass of ~0.1 Msun; more than the mass lost by the stellar wind since the eruption. For this mass, we would expect a larger infrared excess than observed. We propose that the dust which obscured the star after the outburst has since been largely destroyed, releasing Fe into the gas phase to produce the bright [Fe II] emission. The kinetic energy of this shell is ~2e46 ergs, far less than the kinetic energy released during the giant eruption of eta Car in the 1840s. The mass and kinetic energy in the nebulae of eta Car and P Cygni give insight to the range of parameters expected for extragalactic eta Car-like eruptions.
We present an empirical model for single pulses of radio emission from pulsars based on gaussian probability distributions for relevant variables. The radiation at a specific pulse phase is represented as the superposition of radiation in two (approximately) orthogonally polarized modes (OPMs) from one or more subsources in the emission region of the pulsar. For each subsource, the polarization states are drawn randomly from statistical distributions, with the mean and the variance on the Poincar\'e sphere as free parameters. The intensity of one OPM is chosen from a log-normal distribution, and the intensity of the other OPM is assumed to be partially correlated, with the degree of correlation also chosen from a gaussian distribution. The model is used to construct simulated data described in the same format as real data: distributions of the polarization of pulses on the Poincar\'e sphere and histograms of the intensity and other parameters. We concentrate on the interpretation of data for specific phases of PSR B0329+54 for which the OPMs are not orthogonal, with one well defined and the other spread out around an annulus on the Poincar\'e sphere at some phases. The results support the assumption that the radiation emerges in two OPMs with closely correlated intensities, and that in a statistical fraction of pulses one OPM is invisible.
We have obtained Gemini/GMOS spectra for 22 GCs associated with NGC 3379. We
derive ages, metallicities and alpha-element abundance ratios from simple
stellar population models using the multi-index chi^2 minimisation method of
Proctor & Sansom (2002). All of these GCs are found to be consistent with old
ages, i.e. >10 Gyr, with a wide range of metallicities. A trend of decreasing
alpha-element abundance ratio with increasing metallicity is indicated.
The projected velocity dispersion of the GC system is consistent with being
constant with radius. Non-parametric, isotropic models require a significant
increase in the mass-to-light ratio at large radii. This result is in contrast
to that of Romanowsky et al. (2003) who find a decrease in the velocity
dispersion profile as determined from planetary nebulae. Our constant
dispersion requires a normal sized dark halo, although without anisotropic
models we cannot rigorously determine the dark halo mass.
A two-sided chi^2 test over all radii, gives a 2 sigma difference between the
mass profile derived from our GCs compared to the PN-derived mass model of
Romanowsky et al. (2003). However, if we restrict our analysis to radii beyond
one effective radius and test if the GC velocity dispersion is consistently
higher, we determine a >3 sigma difference between the mass models, and hence
favor the conclusion that NGC 3379 does indeed have dark matter at large radii
in its halo. (abridged)
We discuss an overlooked factor in dark matter studies. Namely, if massless particles are captured into a local structure and stop free streaming in the universe, they no longer lose energy by cosmological red-shift, and no longer smear out density fluctuations beyond their ``confinement'' scale. If this occurred at the stage when radiation dominated over baryonic matter in energy density, then these captured massless particles would comprise the major part of dark matter in today's universe, leaving no room for other dark matter scenarios. The most probable such particles are gravitons with non-linear self-interaction.
We study the nonlinear dynamics of a warped or twisted accretion disc, in which the viscosity coefficients are assumed to be locally proportional to the rotational velocity (beta- prescription). Using asymptotic methods for thin discs, dynamical equations of the disc are obtained in a warped spherical polar coordinates. These equations are solved by the method of the separation of the variables. This analysis constitutes an analogous study of the nonlinear theory of an alpha model warped disc which has been studied by Ogilvie (1999). We have compared our results with Ogilvie's analysis. The dynamical behaviors of these models have also been discussed. Our results show that different viscosity prescriptions and magnitudes (alpha and beta prescriptions) affect dynamics of a warped accretion disc. Therefore it can be important in determining the viscosity law even for a warped disc.
We explore the impact of spatial fluctuations in the intergalactic medium (IGM) temperature on the Lyman-alpha forest flux power spectrum near z ~ 3. We develop a semi-analytic model to examine temperature fluctuations resulting from inhomogeneous HI and incomplete HeII reionizations. Detection of these fluctuations might provide insight into the reionization histories of hydrogen and helium. Furthermore, these fluctuations, neglected in previous analyses, could bias constraints on cosmological parameters from the Lyman-alpha forest. We find that the temperature fluctuations resulting from inhomogeneous HI reionization are likely to be very small, with an r.m.s. amplitude of < 5%, $\sigma_{T_0}/<T_0> \la 0.05$. More important are the temperature fluctuations that arise from incomplete HeII reionization, which might plausibly be as large as 50%, $\sigma_{T_0}/<T_0> ~ 0.5$. In practice, however, these temperature fluctuations have only a small effect on flux power spectrum predictions. The smallness of the effect is possibly due to density fluctuations dominating over temperature fluctuations on the scales probed by current measurements. On the largest scales currently probed, k ~ 0.001 s/km (~ 0.1 h/Mpc), the effect on the flux power spectrum may be as large as ~ 10% in extreme models. The effect is larger on small scales, up to ~ 20% at k = 0.1 s/km, due to thermal broadening. Our results suggest that the omission of temperature fluctuations effects from previous analyses does not significantly bias constraints on cosmological parameters. (Abridged)
Torsional Alfven waves are likely excited with bursts in rotating magnetars. These waves are probably propagated through corotating atmospheres toward a vacuum exterior. We have studied the physical effects of the azimuthal wave number and the characteristic height of the plasma medium on wave transmission. In this work, explicit calculations were carried out based on the three-layered cylindrical model. We found that the coupling strength between the internal shear and the external Alfven modes is drastically enhanced, when resonance occurs in the corotating plasma cavity. The spatial structure of the electromagnetic fields in the resonance cavity is also investigated when Alfven waves exhibit resonance.
We have discovered a sample of 17 metal-poor, yet luminous, star-forming galaxies at redshifts z~0.7. They were selected from the initial phase of the DEEP2 survey of 3900 galaxies and the Team Keck Redshift Survey (TKRS) of 1536 galaxies as those showing the temperature-sensitive [OIII]l4363 auroral line. These rare galaxies have blue luminosities close to L*, high star formation rates of 5 to 12 solar masses per year, and oxygen abundances of 1/3 to 1/10 solar. They thus lie significantly off the luminosity-metallicity relation found previously for field galaxies with strong emission lines at redshifts z~0.7. The prior surveys relied on indirect, empirical calibrations of the R23 diagnostic and the assumption that luminous galaxies are not metal-poor. Our discovery suggests that this assumption is sometimes invalid. As a class, these newly-discovered galaxies are: (1) more metal-poor than common classes of bright emission-line galaxies at z~0.7 or at the present epoch; (2) comparable in metallicity to z~3 Lyman Break Galaxies but less luminous; and (3) comparable in metallicity to local metal-poor eXtreme Blue Compact Galaxies (XBCGs), but more luminous. Together, the three samples suggest that the most-luminous, metal-poor, compact galaxies become fainter over time.
There is a growing need for massive computational resources for the analysis of new astronomical datasets. To tackle this problem, we present here our first steps towards marrying two new and emerging technologies; the Virtual Observatory (e.g, AstroGrid) and the computational grid (e.g. TeraGrid, COSMOS etc.). We discuss the construction of VOTechBroker, which is a modular software tool designed to abstract the tasks of submission and management of a large number of computational jobs to a distributed computer system. The broker will also interact with the AstroGrid workflow and MySpace environments. We discuss our planned usages of the VOTechBroker in computing a huge number of n-point correlation functions from the SDSS data and massive model-fitting of millions of CMBfast models to WMAP data. We also discuss other applications including the determination of the XMM Cluster Survey selection function and the construction of new WMAP maps.
We discuss here the main goals and some interesting results of the "XMM-Newton Bright Serendipitous Survey", a research program conducted by the XMM-Newton Survey Science Center in two complementary energy bands (0.5-4.5 keV and 4.5-7.5 keV) in the bright (>~7E-14) flux regime. The very high identification rate (96%) for the X-ray source sample selected in the 4.5-7.5 keV band is used here to have, in this energy range, an "unbiased" view of the extragalactic hard X-ray sky at bright fluxes.
Ground-based photometric surveys have led to the discovery of six transiting exoplanets, five of which were detected by the OGLE survey. The FLAMES multi-object spectrograph on the VLT has permitted a very efficient follow-up of the OGLE transit candidates, characterising not only the 5 planets but also more than 50 systems producing similar photometric signatures -- mainly eclipsing binaires. The presence of these ubiquitous "impostors" is a challenge for transit surveys. Another difficulty is the presence of red noise in the photometry, which implies a much lower sensitivity to transiting planets than usually assumed. We outline a method to estimate how the red noise will affect the expected yield of photometric transit searches.
The mysteriously low CMB power on the largest scales might point to a Universe which consists of a multi-connected space. In addition to a suppression of large-scale power, a multi-connected space can be revealed by its circles-in-the-sky signature. In this paper, a detailed search for this signature is carried out for those three homogeneous multi-connected spherical space forms that lead to the smallest large-scale power. A simultaneous search for all occurring paired circles is made using filtered CMB sky maps which enhance the ordinary Sachs-Wolfe contribution. A marginal hint is found for the right-handed Poincare dodecahedron at Omega_tot = 1.015 and for the right-handed binary tetrahedral space at Omega_tot = 1.068. However, due to the complicated noise and foreground structure of the available microwave sky maps, we cannot draw firm conclusions from our findings.
We present results of our intermediate-band optical imaging survey for high-$z$ Ly$\alpha$ emitters (LAEs) using the prime focus camera, Suprime-Cam, on the 8.2m Subaru Telescope. In our survey, we use eleven filters; four broad-band filters ($B$, $R_{\rm c}$, $i^\prime$, and $z^\prime$) and seven intermediate-band filters covering from 500 nm to 720 nm; we call this imaging program as the Mahoroba-11. The seven intermediate-band filters are selected from the IA filter series that is the Suprime-Cam intermediate-band filter system whose spectral resolution is $R = 23$. Our survey has been made in a $34^\prime \times 27^\prime$ sky area in the Subaru XMM Newton Deep Survey field. We have found 409 IA-excess objects that provide us a large photometric sample of strong emission-line objects. Applying the photometric redshift method to this sample, we obtained a new sample of 198 LAE candidates at $3 < z < 5$. We found that there is no evidence for evolution of the number density and the star formation rate density for LAEs with $\log L({\rm Ly}\alpha) ({\rm erg s^{-1}}) > 42.67$ between $z \sim 3$ and 5.
We discuss the possibilities of the simultaneous determination of the neutrino masses and the evolution of dark energy from future cosmological observations such as cosmic microwave background (CMB), large scale structure (LSS) and the cross correlation between them. Recently it has been discussed that there is a degeneracy between the neutrino masses and the equation of state for dark energy. It is also known that there are some degeneracies among the parameters describing the dark energy evolutions. We discuss the implications of these on the cross correlation of CMB with LSS in some details. Then we consider to what extent we can determine the neutrino masses and the dark energy evolution using the expected data from CMB, LSS and their cross correlation.
The capabilities of the Global mm-VLBI Array are summarized and demonstrated through actual images from our monitoring of extragalactic radio jets. This sensitive 3mm-VLBI interferometer is able to provide images of up to 50 microarcseconds resolution. For the near future, ALMA, the GBT, the LMT, CARMA, SRT, Yebes, Nobeyama and Noto are some of the most sensitive stations suitable to participate in mm-VLBI. This future array, together with the present Global mm-VLBI Array, would achieve 10 times better sensitivities than nowadays. Image fidelity would also largely increased. T he addition of ALMA would improve the (u,v)-coverage for sources with low declination (<20 deg.) and facilitate the VLBI imaging of the Galactic Centre source SgrA*.
We report the discovery of water maser emission in eight active galactic nuclei (AGN) with the 70-m NASA Deep Space Network (DSN) antennas at Tidbinbilla, Australia and Robledo, Spain. The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 sigma (0.3 arcsec radio and 1.3 arcsec optical) and most likely mark the locations of the embedded central engines. The spectra of two sources, NGC 3393 and NGC 5495, display the characteristic spectral signature of emission from an edge-on accretion disk, with orbital velocities of ~600 and ~400 km s^-1, respectively. In a survey with DSN facilities of 630 AGN selected from the NASA Extragalactic Database, we have discovered a total of 15 water maser sources. The resulting incidence rate of maser emission among nearby (v_sys < 7000 km s^-1) Seyfert 1.8-2.0 and LINER systems is ~10 percent for a typical rms noise level of ~14 mJy over 1.3 km s^-1 spectral channels. As a result of this work, the number of nearby AGN (v_sys < 7000 km s^-1) observed with <20 mJy rms noise has increased from 130 to 449.
We present the spectral and temporal analysis of the X-ray flash XRF 011030 observed with BeppoSAX. This event is characterized by a very long X-ray bursting activity that lasts about 1500 s, the longest ever observed by BeppoSAX. In particular a precursor and a late flare are present in the light curve. We connect the late X-ray flare observed at about 1300 s to the afterglow emission observed by Chandra and associate it with the onset of the afterglow emission in the framework of external shock by a long duration engine activity. We find that the late X-ray flare and the broad-band afterglow data, including optical and radio measurements, are consistent either with a fireball expanding in a wind environment or with a jetted fireball in a ISM.
We present the new HST near-infrared polarimetry, broad and narrow-band
imaging, and MERLIN 4.5GHz Multi-Frequency Synthesis radio imaging of 3C 293, a
unique radio galaxy whose host is an obvious merger remnant, in an
exceptionally under-dense region of space. We have discovered near-infrared,
optical, and ultra-violet synchrotron emission from the jet. In the optical,
the jet is mostly obscured by a dust lane, but three knots are clear in our HST
NICMOS images at 1.6 and 2.0 microns, clearly aligning with features in the
radio. The outer jet knot is highly polarized (~15%) at 2 microns, confirming
the synchrotron emission mechanism. The radio-IR spectral index steepens
significantly with distance from the nucleus, as in 3C 273 and in contrast to M
87. The inner knot is visible (with hindsight) on the WFPC2 and STIS images
obtained for the earlier 3CR HST snapshot surveys. There is no [Fe II] emission
seen associated with the jet, constraining the role of shock-induced ionisation
by the jet. Overall there is a strong implication that the NIR jet emission is
indeed synchrotron.
From our NIR images, the core of the galaxy is clearly identifiable with the
main feature in the western extension of the radio ``jet'' image, although no
unresolved AGN component is identifiable even at K-band, consistent with an
FRII-like nucleus obscured by an optically thick torus. The galaxy appears to
have a single nucleus, with any multiple nuclei falling within the central
</~100 pc.
The solar magnetism is no more considered as a purely superficial phenomenon. The SoHO community has shown that the length of the solar cycle depends on the transition region between radiation and convection. Nevertheless, the internal solar (stellar) magnetism stays poorly known. Starting in 2008, the American instrument HMI/SDO and the European microsatellite PICARD will enrich our view of the Sun-Earth relationship. Thus obtaining a complete MHD solar picture is a clear objective for the next decades and it requires complementary observations of the dynamics of the radiative zone. For that ambitious goal, space prototypes are being developed to improve gravity mode detection. The Sun is unique to progress on the topology of deep internal magnetic fields and to understand the complex mechanisms which provoke photospheric and coronal magnetic changes and possible longer cycles important for human life. We propose the following roadmap in Europe to contribute to this "impressive" revolution in Astronomy and in our Sun-Earth relationship: SoHO (1995-2007), PICARD (2008-2010), DynaMICS (2009-2017) in parallel to SDO (2008-2017) then a world-class mission located at the L1 orbit or above the solar poles.
We have studied the generation of magnetic fields by the Biermann mechanism in the pair-instability supernovae explosions of the first stars. The Biermann mechanism produces magnetic fields in the shocked region between the bubble and interstellar medium (ISM), even if magnetic fields are absent initially. We have performed a series of two-dimensional magnetohydrodynamic simulations with the Biermann term and estimate the amplitude and total energy of the produced magnetic fields. We find that magnetic fields with amplitude $10^{-14}-10^{-17}$ G are generated inside the bubble, though the amount of magnetic fields generated depend on specific values of initial conditions. This corresponds to magnetic fields of $10^{28}-10^{31}$ ergs per each supernova remnant, which is strong enough to be the seed magnetic field for a galactic and/or interstellar dynamo.
We present a {\em Spitzer}-based mid-infrared study of a large sample of Blue Compact Dwarf galaxies (BCD) using the Infrared Spectrograph (IRS), including the first mid-IR spectrum of IZw18, the archetype for the BCD class and among the most metal poor galaxies known. We show the spectra of Polycyclic Aromatic Hydrocarbon (PAH) emission in low-metallicity environment. We find that the equivalent widths (EW) of PAHs at 6.2, 7.7, 8.6 and 11.2 $\mu$m are generally weaker in BCDs than in typical starburst galaxies and that the fine structure line ratio, [NeIII]/[NeII], has a weak anti-correlation with the PAH EW. A much stronger anti-correlation is shown between the PAH EW and the product of the [NeIII]/[NeII] ratio and the UV luminosity density divided by the metallicity. We conclude that PAH EW in metal-poor high-excitation environments is determined by a combination of PAH formation and destruction effects.
We present a method for selecting high-redshift type Ia supernovae (SNe Ia) located via rolling SN searches. The technique, using both color and magnitude information of events from only 2-3 epochs of multi-band real-time photometry, is able to discriminate between SNe Ia and core collapse SNe. Furthermore, for the SNe Ia, the method accurately predicts the redshift, phase and light-curve parameterization of these events based only on pre-maximum-light data. We demonstrate the effectiveness of the technique on a simulated survey of SNe Ia and core-collapse SNe, where the selection method effectively rejects most core-collapse SNe while retaining SNe Ia. We also apply the selection code to real-time data acquired as part of the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). During the period May 2004 to January 2005 in the SNLS, 440 SN candidates were discovered of which 70 were confirmed spectroscopically as SNe Ia and 15 as core-collapse events. For this test dataset, the selection technique correctly identifies 100% of the identified SNe II as non-SNe Ia with only a 1-2% false rejection rate. The predicted parameterization of the SNe Ia has a precision of |delta_z|/(1+z_spec)<0.09 in redshift, and +/- 2-3 rest-frame days in phase, providing invaluable information for planning spectroscopic follow-up observations. We also investigate any bias introduced by this selection method on the ability of surveys such as SNLS to measure cosmological parameters (e.g., w and omega matter), and find any effect to be negligible.
We report results from the XMM-Newton observation of the radio-loud quasar PG 1425+267 (z=0.366). The EPIC-pn data above 2 keV exhibit a double-peaked emission feature in the Fe K band. The higher energy peak is found at 6.4 keV and is consistent with being narrow, while the lower energy one is detected at 5.3 keV and is much broader than the detector resolution. We confirm the significance of the detection of the broad red part of the line via Montecarlo simulations. We explore two possible origins of the line profile i.e. a single relativistic iron line from the accretion disc, and the superposition of a narrow 6.4 keV line from distant material and a relativistic one. We find that a contribution from a distant reflector is not required by the data. We also perform a time-resolved analysis searching for short-timescale variability of the emission line. Results tentatively suggest that the line is indeed variable on short timescales and better quality data are needed to confirm it on more firm statistical grounds. We also detect clear signatures of a warm absorber in the soft X-ray energy band.
We present results from a multi-wavelength campaign to monitor the 2005 outburst of the low-mass young star V1118 Ori. Although our campaign covers the X-ray, optical, infrared, and radio regimes, we focus in this Letter on the properties of the X-ray emission in V1118 Ori during the first few months after the optical outburst. Chandra and XMM-Newton detected V1118 Ori at three epochs in early 2005. The X-ray flux and luminosity stayed similar within a factor of two, and at the same level as in a pre-outburst observation in 2002. The hydrogen column density showed no evidence for variation from its modest pre-outburst value of $N_\mathrm{H} \sim 3 \times 10^{21}$ cm$^{-2}$. However, a spectral change occurred from a dominant hot plasma ($\sim 25$ MK) in 2002 and in January 2005 to a cooler plasma ($\sim 8$ MK) in February 2005 and in March 2005. We hypothesize that the hot magnetic loops high in the corona were disrupted by the closing in of the accretion disk due to the increased accretion rate during the outburst, whereas the lower cooler loops were probably less affected and became the dominant coronal component.
The structure of strange dwarfs and that of hybrid stars with same baryonic number is compared. There is a critical mass (M~0.24M_sun) in the strange dwarf branch, below which configurations with the same baryonic number in the hybrid star branch are more stable. If a transition occurs between both branches, the collapse releases an energy of about of 3x10^{50} erg, mostly under the form of neutrinos resulting from the conversion of hadronic matter onto strange quark matter. Only a fraction (~4%) is required to expel the outer neutron-rich layers. These events may contribute significantly to the chemical yield of nuclides with A>80 in the Galaxy, if their frequency is of about one per 1500 years.
This article investigates the physics that is responsible for creating the outgoing Poynting flux emanating from the ergosphere of a rotating black hole in the limit that the magnetic energy density greatly exceeds the plasma rest mass density (magnetically dominated limit). The underlying physics is derived from published 3-D simulations that obey the general relativistic equations of perfect magnetohydrodynamics (MHD). It is found that the majority of the outgoing radial Poynting flux emitted from the magnetically dominated regions of the ergosphere is injected into the magnetosphere by a source outside of the event horizon. It is concluded that the primary source of the Poynting flux is associated with inertial forces in the magnetically dominated region proper or in the lateral boundaries of the region. However, the existing numerical data does not rule out the possibility that large computational errors are actually the primary source of the Poynting flux.
Since it was first announced at ADASS 2 the Smithsonian/NASA Astrophysics
System Abstract Service (ADS) has played a central role in the information
seeking behavior of astronomers. Central to the ability of the ADS to act as a
search and discovery tool is its role as metadata agregator. Over the past 13
years the ADS has introduced many new techniques to facilitate information
retrieval, broadly defined. We discuss some of these developments; with
particular attention to how the ADS might inta754-1.pseract with the virtual
observatory, and to the new myADS-arXiv customized open access virtual journal.
The ADS is at this http URL
We explore the halo structure of four gravitational lenses with well-observed, thin Einstein rings. We find that the gravitational potentials are well described by ellipsoidal density distributions in the sense that the best-fit nonellipsoidal models have parameters consistent with their ellipsoidal counterparts. We find upper limits on the standard parameters for the deviation from an ellipse of |a_3/a_0|<0.023, 0.019, 0.037, and 0.035, and |a_4/a_0|<0.034, 0.041, 0.051, and 0.064 for SDSS J0924+0219, HE0435-1223, B1938+666, and PG1115+080, respectively. We find that the lens galaxies are at the centers of their dark matter halos, and obtain upper limits for the offset of each center of mass from the center of light of |Delta x|<0.004, 0.005, 0.009, and 0.005 arcsec, corresponding to 22, 29, 70, and 23 pc. These limits also exclude the possibility of any significant lopsidednessof the dark matter halos and set an upper limit of f_sat<sqrt(N)% on the mass fraction of massive substructures inside the Einstein ring if they are divided over N satellites. We also explore the properties of galaxies as substructures in groups for the lens PG1115+080, finding evidence for dark matter halos associated with the galaxies but no evidence for a clear distinction between satellite and central galaxies.
In order to explain disk galaxy formation within the hierarchical structure formation, it seems that gas rich mergers must play an important role. We review here our previous studies which have shown the importance of mergers at high redshift being gas rich, in the formation of both the stellar halo and thick disk components of disk galaxies. Regulation of star formation in the building blocks of our galaxy is required to form a low mass low metallicity stellar halo. This regulation results in high redshift, gas rich mergers during which the thick disk forms. In these proceedings, we categorise stars from our simulated disk galaxy into thin and thick disk components by using the Toomre diagram.
An explanation is given of the low value of $R_\lambda \equiv A_\lambda/E(B-V) $, the ratio of absolute to selective extinction deduced from Type Ia supernova observations. The idea involves scattering by dust clouds located in the circumstellar environment, or at the highest velocity shells of the supernova ejecta. The scattered light tends to reduce the effective $R_\lambda$ in the optical, but has an opposite effect in the ultraviolet. The presence of circumstellar dust can be tested by ultraviolet to near infrared observations and by multi-epoch spectropolarimetry of SNe Ia.
(Abridged) The projected structures and integrated properties of the Andromeda I, II, III, V, VI, VII and Cetus dwarf spheroidal galaxies are analysed based upon resolved counts of red giant branch stars. For each object, we have derived isopleth maps, surface brightness profiles, absolute magnitudes, central surface brightnesses, and a large number of other morphological parameters. Our analysis probes to larger radius and fainter surface brightnesses than most previous studies and as a result we find that the galaxies are generally larger and brighter than has previously been recognised. In particular, the luminosity of Andromeda V is found to be consistent with the higher metallicity value which has been derived for it. Andromeda I shows strong evidence of tidal disruption and S-shaped tidal tails are clearly visible. On the other hand, Cetus does not show any evidence of tidal truncation, let alone disruption. Andromeda II shows compelling evidence of a large excess of stars at small radius and suggests that this galaxy consists of a secondary core component. Comparing the M31 dwarf spheroidal population with the Galactic population, we find that the scale radii of the M31 population are larger than those for the Galactic population by at least a factor of two, for all absolute magnitudes. We also find that the two populations are offset from one another in the central surface brightness - luminosity relation. Finally, we find that the M31 dwarf spheroidals show the same correlation with distance-from-host as shown by the Galactic population, such that dwarf spheroidals with a higher central surface brightness are found further from their host. This again suggests that environment plays a significant role in dwarf galaxy evolution.
We used fully cosmological, high resolution N-body + SPH simulations to follow the formation of disk galaxies with a rotational velocity between 140 and 280 Km/sec in a Lambda CDM universe. The simulations include gas cooling, star formation, the effects of a uniform UV background and a physically motivated description of feedback from supernovae. The host dark matter halos have a spin and last major merger redshift typical of galaxy sized halos as measured in recent large scale N-Body simulations. Galaxies formed rotationally supported disks with realistic exponential scale lengths and fall on the I-band and baryonic Tully Fisher relations. The combination of UV background and SN feedback drastically reduced the number of visible satellites orbiting inside a Milky Way sized halo, bringing it fair agreement with observations. Feedback delays SF in small galaxies and more massive ones contain older stellar populations. The current star formation rates as a function of galaxy stellar mass are in good agreement with those measured by the SDSS.
(abridged) We investigate how the properties of the corona and solar wind in the open coronal holes depend on the properties of the magnetic fields and their footpoint motions at the surface, by perfoming 1D MHD simulations from the photosphere to 0.3 or 0.1AU. We impose low-frequency (<0.05Hz) transverse fluctuations of the field lines at the photosphere with various amplitude, spectrum, and polarization in the open flux tubes with different photospheric field strength, B, and super-radial expansion of the cross section, f_max. We find that a transonic solar wind is the universal consequence. The atmosphere is also stably heated up to >10^6K by the dissipation of the Alfven waves through compressive-wave generation and wave reflection in the case of the sufficient wave input with photospheric amplitude, <dv> > 0.7km/s. The density, and accordingly the mass flux, of solar winds show a quite sensitive dependence on <dv> because of an unstable aspect of the heating by the nonlinear Alfven waves. A case with <dv>=0.4km/s gives ~50 times smaller mass flux than the fiducial case for the fast wind with <dv>=0.7km/s; solar wind almost disappears only if <dv> becomes half. We also find that the solar wind speed has a positive correlation with B/f_max, which is consistent with recent observations. We finally show that both fast and slow solar winds can be explained by the single process, the dissipation of the low-frequency Alfven waves, with different sets of <dv> and B/f_max. Our simulations naturally explain the observed (i) anticorrelation of the solar wind speed and the coronal temperature and (ii) larger amplitude of the Alfvenic fluctuations in the fast winds. In Appendix, we also explain our implementation of the outgoing boundary condition of the MHD waves with some numerical tests.
Two fundamental questions regarding our description of the Universe concern the geometry and topology of its 3-dimensional space. While geometry is a local characteristic that gives the intrinsic curvature, topology is a global feature that characterizes the shape and size of the 3-space. The geometry constrains, but does not dictate the the spatial topology. We show that, besides determining the spatial geometry, the knowledge of the spatial topology allows to place tight constraints on the density parameters associated with dark matter ($\Omega_m$) and dark energy ($\Omega_{\Lambda}$). By using the Poincar\'e dodecahedral space as the observable spatial topology, we reanalyze the current type Ia supenovae (SNe Ia) constraints on the density parametric space $\Omega_{m} - \Omega_{\Lambda}$. From this SNe Ia plus cosmic topology analysis, we found best fit values for the density parameters, which are in agreement with a number of independent cosmological observations.
The solar interior has been scrutinized by two different and independent probes during the last twenty years with important revisions of the solar model, including a recent heavy element abundance revision. Today, we get a quantitatively coherent picture (even incomplete) of the solar (stellar) radiative zones. In this review, we recall the clues for solar gravitational settling definitively established by the seismic determination of the photospheric helium content. We comment also on the need for mixing in the transition region between radiation and convection in the case of the Sun and of population II stars. We finally list the open questions and the importance to continue more precise investigations of the solar (stellar) radiative zone in detecting gravity modes with the project DynaMICS.
We present high-resolution imaging of a sample of 10 SCUBA submillimetre galaxies, obtained using the ACS camera on the Hubble Space Telescope. We find that the majority show compact, disturbed morphologies. Using quantitative morphological classification, we find that at least 6 are classified as major mergers. Simulations suggest that the morphological parameters are unlike local spirals and ellipticals, but similar to those of local ULIRGs. Compared to Lyman-break galaxies, the submillimetre-selected galaxies are on average more asymmetric, but also significantly more concentrated in their light distributions. This is consistent with a higher fraction of the stellar mass being contained within a central spheroid component. Despite their different morphologies, we find that submm galaxies are similar in size to luminous (>~L*) Lyman-break galaxies, with half-light radii in the range 2.8 - 4.6kpc.
We describe the serendipitous discovery in the spectroscopic data of the Sloan Digital Sky Survey of a star-like object, SDSSJ103913.70+533029.7, at a heliocentric radial velocity of +1012 km/s. Its proximity in position and velocity to the spiral galaxy NGC 3310 suggests an association with the galaxy. At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star cluster and a projected distance of 17 kpc from NGC 3310. Its spectroscopic and photometric properties imply a mass of > 10^6 solar masses and an age close to that of the tidal shells seen around NGC 3310, suggesting that it formed in the event which formed the shells.
This is a theoretical investigation on the formation of the linearly polarized line spectrum of ionized cerium in the sun. We calculate the scattering line polarization pattern emergent from a plane-parallel layer of Ce {\sc ii} atoms illuminated from below by the photospheric radiation field, taking into account the differential pumping induced in the various magnetic sublevels by the anisotropic radiation field. We find that the line polarization pattern calculated with this simple model is in good qualitative agreement with reported observations. Interestingly, the agreement improves when some amount of atomic level depolarization is considered. We find that the best fit to the observations corresponds to the situation where the ground and metastable levels are depolarized to about one fifth of the corresponding value obtained in the absence of any depolarizing mechanism. One possibility to have this situation is that the depolarizing rate value of elastic collisions is exactly $D=10^6{\rm s}^{-1}$, which is rather unlikely. Therefore, we interpret that fact as} due to the presence of a turbulent magnetic field in the limit of saturated Hanle effect for the lower-levels. For this turbulent magnetic field we obtain a lower limit of 0.8 gauss and an upper limit of 200-300 gauss.
We compare the peculiar velocity field within 65 $h^{-1}$ Mpc predicted from 2MASS photometry and public redshift data to three independent peculiar velocity surveys based on type Ia supernovae, surface brightness fluctuations in ellipticals, and Tully-Fisher distances to spirals. The three peculiar velocity samples are each in good agreement with the predicted velocities and produce consistent results for $\beta_{K}=\Omega\sbr{m}^{0.6}/b_{K}$. Taken together the best fit $\beta_{K} = 0.49 \pm 0.04$. We explore the effects of morphology on the determination of $\beta$ by splitting the 2MASS sample into E+S0 and S+Irr density fields and find both samples are equally good tracers of the underlying dark matter distribution, but that early-types are more clustered by a relative factor $b\sbr{E}/b\sbr{S} \sim 1.6$. The density fluctuations of 2MASS galaxies in $8 h^{-1}$ Mpc spheres in the local volume is found to be $\sigma\sbr{8,K} = 0.9$. From this result and our value of $\beta_{K}$, we find $\sigma_8 (\Omega\sbr{m}/0.3)^{0.6} = 0.91\pm0.12$. This is in excellent agreement with results from the IRAS redshift surveys, as well as other cosmological probes. Combining the 2MASS and IRAS peculiar velocity results yields $\sigma_8 (\Omega\sbr{m}^/0.3)^{0.6} = 0.85\pm0.05$.
This paper investigates Magnetic Reynolds number dependence of the ``self-similar evolution model'' (Nitta et al. 2001) of fast magnetic reconnection. I focused my attention on the flow structure inside and around the reconnection outflow, which is essential to determine the entire reconnection system (Nitta et al. 2002). The outflow is consist of several regions divided by discontinuities, e.g., shocks, and it can be treated by a shock-tube approximation (Nitta 2004). By solving the junction conditions (e.g., Rankine-Hugoniot condition), the structure of the reconnection outflow is obtained. Magnetic reconnection in most astrophysical problems is characterized by a huge dynamic range of its expansion ($sim 10^7$ for typical solar flares) in a free space which is free from any influence of external circumstances. Such evolution results in a spontaneous self-similar expansion which is controlled by two intrinsic parameters: the plasma-$beta$ and the magnetic Reynolds number. The plasma-$beta$ dependence had been investigated in our previous paper. This paper newly clarifies the relation between the reconnection rate and the inflow structure just outside the Petschek-like slow shock: As the magnetic Reynolds number increases, strongly converging inflow toward the Petschek-like slow shock forms, and it significantly reduces the reconnection rate.
We report the first detection of an extragalactic millimeter wavelength H2O maser at 183 GHz towards NGC 3079 using the Submillimeter Array (SMA), and a tentative submillimeter wave detection of the 439 GHz maser towards the same source using the James Clerk Maxwell Telescope (JCMT). These H2O transitions are known to exhibit maser emission in star-forming regions and evolved stars. NGC 3079 is a well-studied nuclear H2O maser source at 22 GHz with a time-variable peak flux density in the range 3 -- 12 Jy. The 183 GHz H2O maser emission, with peak flux density $\sim$0.5 Jy (7$\sigma$ detection), also originates from the nuclear region of NGC 3079 and is spatially coincident with the dust continuum peak at 193 GHz (53 mJy integrated). Peak emission at both 183 and 439 GHz occurs in the same range of velocity as that covered by the 22 GHz spectrum. We estimate the gas to dust ratio of the nucleus of NGC 3079 to be $\approx$150, comparable to the Galactic value of 160. Discovery of maser emission in an active galactic nucleus beyond the long-known 22 GHz transition opens the possibility of future position-resolved radiative transfer modeling of accretion disks and outflows $<1$ pc from massive black holes.
We present the results of a Keck spectroscopic study of globular clusters associated with the Virgo Cluster dwarf elliptical VCC 1386. We analyze blue spectroscopic absorption lines from 3500-5500 A for 13 globular cluster candidates and confirm that five are associated with VCC 1386. By comparing metal and Balmer line indices of these globular clusters with alpha-enhanced single stellar population models we find that these systems are metal poor with [Fe/H] < -1.35 and old, with ages > 5 Gyr at 3 sigma confidence, placing their formation at z >1. This is one of the first spectroscopic studies of globular clusters surrounding dwarfs in a cluster, revealing that some low mass galaxies in rich environments form at least part of their stellar mass early in the history of the universe. We further find that the luminosity weighted stellar population of VCC 1386 itself is younger, and more metal rich than its globular clusters, consistent with (V-I)_0 colors from Hubble Space Telescope imaging. This implies that VCC 1386, like Local Group dEs, has had multiple episodes of star formation. Globular clusters associated with low luminosity systems however appear to be roughly as old as those associated with giant galaxies, contrary to the `downsizing' formation of their bulk stellar populations.
The effect of smooth cloud boundaries on the interaction of steady planar shock waves with interstellar clouds is studied using a high-resolution local AMR technique with a second-order accurate axisymmetric Godunov hydrodynamic scheme. A 3D calculation is also done to confirm the results of the 2D ones. We consider an initially spherical cloud whose density distribution is flat near the cloud center and has a power-law profile in the cloud envelope. When an incident shock is transmitted into a smooth cloud, velocity gradients in the cloud envelope steepen the smooth density profile at the upstream side, resulting in a sharp density jump having an arc-like shape. Such a ``slip surface'' forms immediately when a shock strikes a cloud with a sharp boundary. For smoother boundaries, the formation of slip surface and therefore the onset of hydrodynamic instabilities are delayed. Since the slip surface is subject to the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, the shocked cloud is eventually destroyed in $\sim 3-10$ cloud crushing times. After complete cloud destruction, small blobs formed by fragmentation due to hydrodynamic instabilities have significant velocity dispersions of the order of 0.1 $v_b$, where $v_b$ is the shock velocity in the ambient medium. This suggests that turbulent motions generated by shock-cloud interaction are directly associated with cloud destruction. The interaction of a shock with a cold HI cloud should lead to the production of a spray of small HI shreds, which could be related to the small cold clouds recently observed by Stanimirovic & Heiles (2005). The linewidth-size relation obtained from our 3D simulation is found to be time-dependent. A possibility for gravitational instability triggered by shock compression is also discussed.
To use type Ia supernovae as standard candles for cosmology we need accurate broadband magnitudes. In practice the observed magnitude may differ from the ideal magnitude-redshift relationship either through intrinsic inhomogeneities in the type Ia supernova population or through observational error. Here we investigate how we can choose filter bandpasses to reduce the error caused by both these effects. We find that bandpasses with large integral fluxes and sloping wings are best able to minimise several sources of observational error, and are also least sensitive to intrinsic differences in type Ia supernovae. The most important feature of a complete filter set for type Ia supernova cosmology is that each bandpass be a redshifted copy of the first. We design practical sets of redshifted bandpasses that are matched to typical high resistivity CCD and HgCdTe infra-red detector sensitivities. These are designed to minimise systematic error in well observed supernovae, final designs for specific missions should also consider signal-to-noise requirements and observing strategy. In addition we calculate how accurately filters need to be calibrated in order to achieve the required photometric accuracy of future supernova cosmology experiments such as the SuperNova-Acceleration-Probe (SNAP), which is one possible realisation of the Joint Dark-Energy mission (JDEM). We consider the effect of possible periodic miscalibrations that may arise from the construction of an interference filter.
Modelling the flow in a thin accretion disc like a dynamical system, we analyse the nature of the critical points of the steady solutions of the flow. For the simple inviscid disc there are two critical points, with the outer one being a saddle point and the inner one a centre type point. For the weakly viscous disc, there are four possible critical points, of which the outermost is a saddle point, while the next inner one is a spiral. Coupling the nature of the critical points with the outer boundary condition of the flow, gives us a complete understanding of all the important physical features of the flow solutions in the subsonic regions of the disc. In the inviscid disc, the physical realisability of the transonic solution passing through the saddle point is addressed by considering a temporal evolution of the flow, which is a very likely non-perturbative mechanism for selecting the transonic inflow solution from among a host of other possible stable solutions. For the weakly viscous disc, while a linearised time-dependent perturbation imposed on the steady mass inflow rate causes instability, the same perturbative analysis reveals that for the inviscid disc, there is a very close correspondence between the equation for the propagation of the perturbation and the metric of an acoustic black hole. Compatible with the transport of angular momentum to the outer regions of the disc, a viscosity-limited length scale is defined for the spatial extent of the inward rotational drift of matter.
It is commonly adopted that X-rays from O stars are produced deep inside the stellar wind, and transported outwards through the bulk of the expanding matter which attenuates the radiation and affects the shape of emission line profiles. The ability of Chandra and XMM-Newton to resolve these lines spectroscopically provided a stringent test for the theory of X-ray production. It turned out that none of the existing models was able to reproduce the observations consistently. The major caveat of these models was the underlying assumption of a smooth stellar wind. Motivated by the various observational evidence that the stellar winds are in fact structured, we present a 2-D model of a stochastic, inhomogeneous wind. The X-ray radiative transfer is derived for such media. It is shown that profiles from a clumped wind differ drastically from those predicted by conventional homogeneous models. We review the up-to-date observations of X-ray line profiles from stellar winds and present line fits obtained from the inhomogeneous wind model. The necessity to account for inhomogeneities in calculating the X-ray transport in massive star winds, including for HMXB is highlighted.
We describe a long term project aimed at deriving information on the chemical evolution of the Galactic disk from a large sample of open clusters. The main property of this project is that all clusters are analyzed in a homogeneous way, to guarantee the robustness of the ranking in age, distance and metallicity. Special emphasis is devoted to the evolution of the earliest phases of the Galactic disk evolution, where clusters have superior reliability with respect to other types of evolution indicators. The project is twofold: on the one hand we derive age, distance and reddening (and indicative metallicity) interpreting deep and accurate photometric data with stellar evolution models, and, on the other hand, we derive the chemical abundances from high-resolution spectroscopy. Here we describe our overall goals and approaches, and report on the mid-term project status of the photometric part, with 16 clusters already studied, covering an age interval from 0.1 to 6 Gyr and Galactocentric distances from 6.6 to 21 kpc. The importance of quantifying the theoretical uncertainties by deriving the cluster parameters with various sets of stellar models is emphasized. Stellar evolution models assuming overshooting from convective regions appear to better reproduce the photometric properties of the cluster stars. The examined clusters show a clear metallicity dependence on the Galactocentric distance and no dependence on age. The tight relation between cluster age and magnitude difference between the main sequence turn off and the red clump is confirmed.
We present the preliminary analysis of a deep (100ks) XMM-Newton observation of M82. The spatial distribution of the abundances of chemical elements (Fe, O, Ne, Mg, Si, S) is investigated through narrow-band imaging analisys and spatially-resolved spectroscopy. We find that the abundances of alpha-elements follow a bipolar distribution, these elements being more abundant in the gaseous outflow than in the galaxy centre. This behaviour is found to be more marked for lighter elements (O, Ne) than for heavier elements.
XMM-Newton EPIC observations reveal the population of X-ray sources of the bright Local Group spiral galaxy M 31, a low-star-formation-rate galaxy like the Milky Way, down to a 0.2-4.5 keV luminosity of 4.4E34 erg/s. With the help of X-ray hardness ratios and optical and radio information different source classes can be distinguished. The survey detected 856 sources in an area of 1.24 square degrees. Sources within M 31 are 44 supernova remnants (SNR) and candidates, 18 super-soft sources (SSS), 16 X-ray binaries (XRBs) and candidates, as well as 37 globular cluster sources (GlC) and candidates, i.e. most likely low mass XRBs within the GlC. 567 hard sources may either be XRBs or Crab-like SNRs in M 31 or background AGN. 22 sources are new SNR candidates in M 31 based on X-ray selection criteria. Time variability information can be used to improve the source classification. Two GlC sources show type I X-ray bursts as known from Galactic neutron star low mass XRBs. Many of the M 31 SSS detected with XMM-Newton, Chandra and ROSAT, could be identified with optical novae. Soft X-ray light curves can be determined in M 31 center observations for several novae at a time opening a new area of nova research.
White-light observations of the solar corona show that there are two characteristic types of Coronal Mass Ejections (CMEs) in terms of speed-height profiles: so-called fast CMEs that attain high speeds low in the corona and slow CMEs that gradually accelerate from low initial speeds. Low and Zhang (2002) have recently proposed that fast and slow CMEs result from initial states with magnetic configurations characterized by normal prominences (NPs) and inverse prominences (IPs), respectively. To test their theory, we employed a two-dimensional, time-dependent, resistive magnetohydrodynamic code to simulate the expulsion of CMEs in these two different prominence environments. Our numerical simulations demonstrate that (i) a CME-like expulsion is more readily produced in an NP than in an IP environment, and, (ii) a CME originating from an NP environment tends to have a higher speed early in the event than one originating from an IP environment. Magnetic reconnection plays distinct roles in the two different field topologies of these two environments to produce their characteristic CME speed-height profiles. Our numerical simulations support the proposal of Low and Zhang (2002) although the reconnection development for the NP associated CME is different from the one sketched in their theory. Observational implications of our simulations are discussed.
We studied the period-K magnitude (P-K) relations of nearby Mira and Mira-like variables with relatively good Hipparcos parallaxes. They form at least two prominent sequences on the P-K plane, corresponding to the sequences C (Mira variables pulsating in the fundamental mode) and C'(Mira variables pulsating in the 1st overtone mode), that were found in the LMC. As a part of an ongoing study to see the differences between the Mira variables pulsating in the fundamental and the 1st overtone mode, we searched for SiO masers in the nearby variables on the sequences C' and C using the Nobeyama 45m radio telescope. We observed 28 selected nearby Mira and Mira-like variables without previous maser observations, and found 3 new emitters. The observational result shows that there is few or no SiO maser emitters pulsating in the 1st overtone mode.
An excess of sight-lines close to Lyman-break galaxies (LBGs) with little or no absorption in QSO absorption spectra has been reported and has been interpreted as the effect of galactic winds on the Intergalactic Medium. We use here numerical simulations to investigate the flux probability function close to plausible sites of LBGs. We show that the flux distribution near our LBGs in the simulation depends strongly on redshift, and is very sensitive to the averaging procedure. We show that a model without galactic winds and a model with a wind bubble size of 0.5Mpc/h (comoving) are equally consistent with the new determination of the conditional flux distribution by Adelberger et al. (2005). Models with the larger bubble sizes suggested by the previous observations of Adelberger et al. (2003) based on a much smaller sample at higher redshift are not consistent with the new data. We therefore argue that the volume filling factor of galactic winds driven by LBGs may be much smaller than previously thought, and that most of the metals responsible for the metal absorption associated with the low column density Lya forest are unlikely to have been ejected by LBGs.
Aims: We measure the redshift of the lensing galaxy in seven gravitationally
lensed quasars in view of determining the Hubble parameter from the time delay
method.
Methods: Deep VLT/FORS1 spectra of lensed quasars are spatially deconvolved
in order to separate the spectrum of the lensing galaxies from the glare of the
much brighter quasar images. A new observing strategy is devised. It involves
observations in Multi-Object-Spectroscopy (MOS) which allows the simultaneous
observation of the target and of several PSF and flux calibration stars. The
advantage of this method over traditional long-slit observations is a much more
reliable extraction and flux calibration of the spectra.
Results: For the first time we measure the redshift of the lensing galaxy in
three multiply-imaged quasars: SDSS J1138+0314 (z=0.445), SDSS J1226-0006
(z=0.517), SDSS J1335+0118 (z=0.440), and we give a tentative estimate of the
redshift of the lensing galaxy in Q 1355-2257 (z=0.701). We confirm three
previously measured redshifts: HE 0230-2130 (z=0.523), HE 0435-1223 (z=0.454)
and WFI J2033-4723 (z=0.661). In addition, we determine the redshift of the
second lensing galaxy in HE 0230-2130 (z=0.526). The spectra of all lens
galaxies are typical for early-type galaxies, except for the second lensing
galaxy in HE 0230-2130 which displays prominent O II emission.
QuantEYE is designed to be the highest time-resolution instrument on ESO:s planned Overwhelmingly Large Telescope, devised to explore astrophysical variability on microsecond and nanosecond scales, down to the quantum-optical limit. Expected phenomena include instabilities of photon-gas bubbles in accretion flows, p-mode oscillations in neutron stars, and quantum-optical photon bunching in time. Precise timescales are both variable and unknown, and studies must be of photon-stream statistics, e.g., their power spectra or autocorrelations. Such functions increase with the square of the intensity, implying an enormously increased sensitivity at the largest telescopes. QuantEYE covers the optical, and its design involves an array of photon-counting avalanche-diode detectors, each viewing one segment of the OWL entrance pupil. QuantEYE will work already with a partially filled OWL main mirror, and also without [full] adaptive optics.
We investigate the effect of galactic winds on the Lyalpha forest in cosmological simulations of structure and galaxy formation. We combine high resolution N-body simulations for the evolution of the dark matter with a semi-analytic model for the formation and evolution of galaxies which includes detailed prescriptions for the long-term evolution of galactic winds. We find that the main statistical properties of the Lyalpha forest, namely the power spectrum P(k) and the flux probability distribution function (PDF), are not significantly affected by winds and do not give a unique answer when trying to rule out or constrain wind models. Winds expanding around galaxies do, however, produce detectable signatures in the forest, in the form of increased flux transmissivity inside hot bubbles and narrow, saturated absorption lines corresponding to dense cooled shells. We find that the Lyalpha flux transmissivity is highly enhanced in proximity of wind-blowing galaxies, which represent up to half the galaxies in our sample, in agreement with the results of Adelberger et al. (2005). We finally propose a new method to test for the presence of absorption lines due to wind shells in the Lyalpha forest: we calculate the number distribution of saturated regions in spectra as a function of their width and we find that the number of saturated regions with widths smaller than about 1 Angstrom at z=3 and 0.6 Angstrom at z=2 may be more than doubled. This effect should be clearly detectable in real spectra.
By combining the first year data from the Supernova Legacy Survey (SN LS) and the recent detection of the baryon acoustic peak in the Sloan Digital Sky Survey data, we are able to place strong constraints on models where the cosmic acceleration is due to the leakage of gravity from the brane into the bulk on large scales. In particular, we are able to show that the DGP model is not compatible with a spatially flat universe. We generalize our analysis to phenomenological toy models where the curvature of the brane enters into the Friedmann equations in different ways.
We investigate the accretion disc structure in the strongly Comptonised spectra seen at high luminosities from galactic black holes (variously termed the very high or steep power law dominant state). We use simultaneous ASCA-RXTE data on two such spectra from the black hole transient XTE J1550-564 to constrain the disc and Comptonized luminosity. The broad bandpass of the data gives robust estimates of the disc temperature and luminosity despite the strong Comptonisation distorting the spectrum. The disc temperature is much lower than that seen from the same source at the same luminosity in its disc dominated spectra. This implies that the disc emissivity or/and the disc area has changed between the two states. We build a spectral model of a Comptonising corona over an inner disc to show explicitally that a standard disc emissivity requires a large increase in inner disc radius for the very high state spectra. While such models can describe the spectra, it seems more probable that the disc emissivity changes in the presence of the corona. We model a coupled inner disc-corona, in which some fraction f of the accretion power is dissipated in the corona leaving only a fraction 1-f to be dissipated in the optically thick disc (Svensson & Zdziarski 1994). We show that this can explain very high state disc emission with only a small increase in radius of the disc. While the inferred disc truncation is probably not significant given the model uncertainties, it is consistent with the low frequency QPO and gives continuity of properties with the low/hard state spectra. Irrespective of such details, there is clear evidence in the very high state spectra that the growth of the corona affects the disc, strongly favouring models in which the corona is part of the same accretion flow structure as gives rise to the disc.
We present new elemental abundance studies of seven damped Lyman-alpha systems (DLAs). Together with the four DLAs analyzed in Dessauges-Zavadsky et al. (2004), we have a sample of eleven DLA galaxies with uniquely comprehensive and homogeneous abundance measurements. These observations allow one to study the abundance patterns of 22 elements and the chemical variations in the interstellar medium of galaxies outside the Local Group. Comparing the gas-phase abundance ratios of these high redshift galaxies, we found that they show low RMS dispersions, reaching only up 2-3 times the statistical errors for the majority of elements. This uniformity is remarkable given that the quasar sightlines cross gaseous regions with HI column densities spanning over one order of magnitude and metallicities ranging from 1/55 to 1/5 solar. The gas-phase abundance patterns of interstellar medium clouds within the DLA galaxies detected along the velocity profiles show, on the other hand, a high dispersion in several abundance ratios, indicating that chemical variations seem to be more confined to individual clouds within the DLA galaxies than to integrated profiles. The analysis of the cloud-to-cloud chemical variations within seven individual DLAs reveals that five of them show statistically significant variations, higher than 0.2 dex at more than 3 sigma. The sources of these variations are both the differential dust depletion and/or ionization effects; however, no evidence for variations due to different star formation histories could be highlighted. These observations place large constraints on the mixing timescales of protogalaxies and on scenarios of galaxy formation within the CDM hierarchical theory. Finally, we provide an astrophysical determination of the oscillator strength of the NiII 1317 transition.
The 2-m Liverpool Telescope (LT), owned by Liverpool John Moores University, is located in La Palma (Canary Islands) and operates in fully robotic mode. In 2005, the LT began conducting an automatic GRB follow-up program. On receiving an automatic GRB alert from a Gamma-Ray Observatory (Swift, INTEGRAL, HETE-II, IPN) the LT initiates a special override mode that conducts follow-up observations within 2-3 min of the GRB onset. This follow-up procedure begins with an initial sequence of short (10-s) exposures acquired through an r' band filter. These images are reduced, analyzed and interpreted automatically using pipeline software developed by our team called "LT-TRAP" (Liverpool Telescope Transient Rapid Analysis Pipeline); the automatic detection and successful identification of an unknown and potentially fading optical transient triggers a subsequent multi-color imaging sequence. In the case of a candidate brighter than r'=15, either a polarimetric (from 2006) or a spectroscopic observation (from 2007) will be triggered on the LT. If no candidate is identified, the telescope continues to obtain z', r' and i' band imaging with increasingly longer exposure times. Here we present a detailed description of the LT-TRAP and briefly discuss the illustrative case of the afterglow of GRB 050502a, whose automatic identification by the LT just 3 min after the GRB, led to the acquisition of the first early-time (< 1 hr) multi-color light curve of a GRB afterglow.
We present high-dispersion spectra of two extremely massive star clusters in galactic merger remnants. One cluster, W30, is located in the ~500 Myr old merger remnant NGC 7252 and has a velocity dispersion and effective radius of sigma=27.5+-2.5 km/s and R_eff=9.3+-1.7 pc, respectively. The other cluster, G114, located in the ~3 Gyr old merger remnant NGC 1316, is much more compact, R_eff=4.08+-0.55 pc, and has a velocity dispersion of sigma=42.1+-2.8 km/s. These measurements allow an estimate of the virial mass of the two clusters, yielding M_dyn(W30)=1.59(+-0.26) * 10^7 Msun and M_dyn(G114)=1.64(+-0.13) *10^7 Msun. Both clusters are extremely massive, being more than three times heavier than the most massive globular clusters in the Galaxy. For both clusters we measure light-to-mass ratios, which when compared to simple stellar population (SSP) models of the appropriate age, are consistent with a Kroupa-type stellar mass function. Using measurements from the literature we find a strong age dependence on how well SSP models (with underlying Kroupa or Salpeter-type stellar mass functions) fit the light-to-mass ratio of clusters. Based on this result we suggest that the large scatter in the light-to-mass ratio of the youngest clusters is not due to variations in the underlying stellar mass function, but instead to the rapidly changing internal dynamics of young clusters. Finally, based on the positions of old globular clusters, young massive clusters (YMCs), ultra-compact dwarf galaxies (UCDs) and dwarf-globular transition objects (DGTOs) in kappa-space we conclude that 1) UCDs and DGTOs are consistent with the high mass end of star clusters and 2) YMCs occupy a much larger parameter space than old globular clusters, consistent with the idea of preferential disruption of star clusters. (abridged)
Recent observations of young galaxies at redshifts z ~ 3 have revealed simultaneous AGN and starburst activity, as well as galaxy-wide superwinds. I show that there is probably a close connection between these phenomena by extending an earlier treatment of the M_BH - sigma relation (King, 2003). As the black hole grows, an outflow drives a shell into the surrounding gas. This stalls after a dynamical time at a size determined by the hole's current mass and thereafter grows on the Salpeter timescale. The gas trapped inside this bubble cools and forms stars and is recycled as accretion and outflow. The consequent high metallicity agrees with that commonly observed in AGN accretion. Once the hole reaches a critical mass this region attains a size such that the gas can no longer cool efficiently. The resulting energy-driven flow expels the remaining gas as a superwind, fixing both the M_BH - sigma relation and the total stellar bulge mass at values in good agreement with observation. Black hole growth thus produces starbursts and ultimately a superwind.
We present numerical radiation-hydrodynamic simulations of cometary HII regions for a number of champagne flow and bowshock models. For the champagne flow models we study smooth density distributions with both steep and shallow gradients. We also consider cases where the ionizing star has a strong stellar wind, and cases in which the star additionally has a proper motion within the ambient density gradient. We present simulated emission-measure maps and long-slit spectra of our results. Our numerical models are not tailored to any particular object but comparison with observations from the literature shows that, in particular, the models combining density gradients and stellar winds are able to account for both the morphology and radial velocity behavior of several observed cometary HII regions, such as the well-studied object G29.96-0.02.
MIRI, the Mid-InfraRed Instrument, is one of four instruments being built for the James Webb Space Telescope. It is being developed jointly between an European Consortium (21 institutes from 10 countries, under the auspices of ESA), and the US. MIRI consists of an imager, a coronograph, a low-resolution spectrograph, and an Integral Field Unit (IFU) Medium Resolution Spectrometer (MIRI-MRS). The latter will be the first mid-infrared IFU spectrograph, and one of the first IFUs to be used in a space mission. To give the MIRI community a preview of the properties of the MIRI-MRS data products before the telescope is operational, the Specsim tool has been developed to model, in software, the operation of the spectrometer. Specsim generates synthetic data frames approximating those which will be taken by the instrument in orbit. The program models astronomical sources and transforms them into detector frames using the predicted optical properties of the telescope and MIRI. These frames can then be used to illustrate and inform a range of operational activities, including data calibration strategies and the development and testing of the data reduction software for the MIRI-MRS. Specsim will serve as a means of communication between the many consortium members by providing a way to easily illustrate the performance of the spectrometer under different circumstances, tolerances of components and design scenarios.
We consider a differentially rotating, 2D stellar disk perturbed by two steady state spiral density waves moving at different patterns speeds. Our investigation is based on direct numerical integration of initially circular test-particle orbits. We examine a range of spiral strengths and spiral speeds and show that stars in this time dependent gravitational field can be heated (their random motions increased).This is particularly noticeable in the simultaneous propagation of a 2-armed spiral density wave near the corotation resonance (CR), and a weak 4-armed one near the inner and outer 4:1 Lindblad resonances. In simulations with 2 spiral waves moving at different pattern speeds we find: (1) the variance of the radial velocity, sigma_R^2, exceeds the sum of the variances measured from simulations with each individual pattern; (2) sigma_R^2 can grow with time throughout the entire simulation; (3) sigma_R^2 is increased over a wider range of radii compared to that seen with one spiral pattern; (4) particles diffuse radially in real space whereas they don't when only one spiral density wave is present. Near the CR with the stronger, 2-armed pattern, test particles are observed to migrate radially. These effects take place at or near resonances of both spirals so we interpret them as the result of stochastic motions. This provides a possible new mechanism for increasing the stellar velocity dispersion in galactic disks. If multiple spiral patterns are present in the Galaxy we predict that there should be large variations in the stellar velocity dispersion as a function of radius.
In previous attempts to perform seismic modelling of pulsating subdwarf-B stars, various mode identification techniques are used with uncertain results. We investigated a method so far neglected in sdB stars, but very successful for Main Sequence pulsators, that is, mode identification from the line-profile variations caused by stellar pulsation. We report the calculation of time-resolved synthetic spectra for sdB stars pulsating with various combinations of pulsation modes; these calculations were carried out over appropriate ranges of effective temperature, surface gravity and helium abundances. Preliminary tests using these synthetic line-profile variations demonstrated their potential for mode identification by comparison with observation.
The Swift XRT has been observing GRB afterglows since December 23, 2004. Three-quarters of these observations begin within 300 s of the burst onset, providing an unprecendented look at the behavior of X-ray emission from GRB afterglows in the first few hours after the burst. While most of the early afterglows have smoothly declining lightcurves, a substantial fraction has large X-ray flares on short time-scales. We suggest that these flares provide support for models with extended central engine activity producing late-time internal shocks.
We have performed a comparative analysis of three recent and reliable SnIa datasets available in the literature: the Full Gold (FG) dataset (157 data points $0<z<1.75$), a Truncated Gold (TG) dataset (140 data points $0<z<1$) and the most recent Supernova Legacy Survey (SNLS) dataset (115 data points $0<z<1$). We have analyzed and compared the likelihood of cosmological constant and dynamical dark energy parametrizations allowing for crossing of the phantom divide line (PDL). We find that even though the constraints obtained using the three datasets are consistent with each other at the 95% confidence level, the latest (SNLS) dataset shows distinct trends which are not shared by the Gold datasets. We find that the best fit dynamical $w(z)$ obtained from the SNLS dataset does not cross the PDL $w=-1$ and remains above and close to the $w=-1$ line for the whole redshift range $0<z<1$ showing no evidence for phantom behavior. The LCDM parameter values ($w_0=-1$, $w_1=0$) almost coincide with the best fit parameters of the dynamical $w(z)$ parametrizations. In contrast, the best fit dynamical $w(z)$ obtained from the Gold datasets (FG and TG) clearly crosses the PDL and departs significantly from the PDL $w=-1$ line while the LCDM parameter values are about $2\sigma$ away from the best fit $w(z)$. In addition, the $(\Omega_{0m},\Omega_\Lambda)$ parameters in a LCDM parametrization without a flat prior, fit by the SNLS dataset, favor the minimal flat LCDM concordance model. The corresponding fit with the Gold datasets mildly favors a closed universe and the flat LCDM parameter values are $1\sigma - 2\sigma$ away from the best fit $(\Omega_{0m},\Omega_\Lambda)$.
We provide the first quantitative calculation of the dominant contribution to the bispectrum for general multiple-field inflation models that give large non-Gaussianity. Our bispectrum expression captures the nonlinear superhorizon influence of the isocurvature modes on the adiabatic mode during inflation. It involves only background quantities and linear perturbation quantities at horizon crossing. We also derive a simple analytic estimate and demonstrate that it is possible to get large non-Gaussianity even with the simplest quadratic two-field potential.
We analyze a series of full-Sun observations, which was performed with the SoHO/SUMER instrument between March and October 1996. Some parameters (radiance, shift and width) of the S VI 93.3 nm, S VI 94.4 nm, and Lyman Epsilon line profiles were computed on board. Radiances and line-of-sight velocities in a large central region of the Sun are studied statistically: distributions of solar structures, field Fourier spectra and structure functions are obtained. The structures have distributions with power-law tails, the Fourier spectra of the radiance fields also display power laws, and the normalized structure functions of the radiance and velocity fields increase at small scales. These results support the idea of the existence of small scales, created by turbulence, and of intermittency of the observed fields. These properties may provide insight into the processes needed for heating the transition region, or, if confirmed in the corona, the corona itself. The difficulties encountered in this analysis, especially for the velocity data, underline the needs for sensitive ultraviolet imaging spectrometers.
Recent breakthroughs in cosmology reveal that a quarter of the Universe is composed of dark matter, but the microscopic identity of dark matter remains a deep mystery. I review recent progress in resolving this puzzle, focusing on two well-motivated classes of dark matter candidates: WIMPs and superWIMPs. These possibilities have similar motivations: they exist in the same well-motivated particle physics models, the observed dark matter relic density emerges naturally, and dark matter particles have mass around 100 GeV, the energy scale identified as interesting over 70 years ago by Fermi. At the same time, they have widely varying implications for direct and indirect dark matter searches, particle colliders, Big Bang nucleosynthesis, the cosmic microwave background, and halo profiles and structure formation. If WIMPs or superWIMPs are a significant component of dark matter, we will soon be entering a golden era in which dark matter will be studied through diverse probes at the interface of particle physics, astroparticle physics, and cosmology. I outline a program of dark matter studies for each of these scenarios, and discuss the prospects for identifying dark matter in the coming years.
We present spatially-resolved analysis of the temperature and gas density profiles in 6 relaxed galaxy clusters at z = 0.4-0.54 using long-exposure Chandra observations. We derived the total cluster masses within the radius r_500 assuming hydrostatic equilibrium but without assuming isothermality of the intracluster gas. Together with a similar study based on the XMM-Newton observations (Kotov & Vikhlinin), we obtained the mass and temperature measurements for 13 galaxy clusters at 0.4<z<0.7 spanning a temperature interval of 3keV<T<14keV. The observed evolution of the M-T relation, relative to the low-redshift references from the Chandra sample of Vikhlinin et al., follows M_500/T^{3/2} ~ E(z)^alpha, where we measure alpha=1.02\pm0.20 and alpha=1.33\pm0.20 for the spectroscopic and gas mass-weighted temperatures, respectively. Both values are in agreement with the expected self-similar evolution, alpha=1. Assuming that the cluster mass for given temperature indeed evolves self-similarly, the derived slopes, $\gamma$, of the high-redshift M-T relation, E(z)M_500 ~ T^gamma, are gamma=1.55\pm0.14 for T_spec and gamma=1.65\pm0.15 for T_mg. Our results show that both the shape and evolution of the cluster M-T relation at z~0.5 is close to predictions of the self-similar theory.
We present the first detailed spectroscopic and photometric analysis of an eclipsing binary in the Andromeda Galaxy (M31). This is a 19.3-mag semi-detached system with components of late-O and early-B spectral types. From the light and radial velocity curves we have carried out an accurate determination of the masses and radii of the components. Their effective temperatures have been estimated from the modeling of the absorption line spectra. The analysis yields an essentially complete picture of the properties of the system, and hence an accurate distance determination to M31. The result is d=772+/-44 kpc ((m-M)_0=24.44+/-0.12 mag). The study of additional systems, currently in progress, should reduce the uncertainty in the M31 distance to better than 5%.
We obtain models for a triaxial Milky Way spheroid based on data by Newberg and Yanny. The best fits to the data occur for a spheroid center that is shifted by 3kpc from the Galactic Center. We investigate effects of the triaxiality on the microlensing optical depth to the Large Magellanic Cloud (LMC). The optical depth can be used to ascertain the number of Massive Compact Halo Objects (MACHOs); a larger spheroid contribution would imply fewer Halo MACHOs. On the one hand, the triaxiality gives rise to more spheroid mass along the line of sight between us and the LMC and thus a larger optical depth. However, shifting the spheroid center leads to an effect that goes in the other direction: the best fit to the spheroid center is_away_ from the line of sight to the LMC. As a consequence, these two effects tend to cancel so that the change in optical depth due to the Yanny/Newberg triaxial halo is at most 50%. After subtracting the spheroid contribution in the four models we consider, the MACHO contribution (central value) to the mass of the Galactic Halo varies from \~(8-20)% if all excess lensing events observed by the MACHO collaboration are assumed to be due to MACHOs. Here the maximum is due to the original MACHO collaboration results and the minimum is consistent with 0% at the 1 sigma error level in the data.
We introduce a new technique for constructing three-dimensional (3D) models
of incompressible Riemann S-type ellipsoids and compressible triaxial
configurations that share the same velocity field as that of
Riemann S-type ellipsoids. Our incompressible models are exact steady-state
configurations; our compressible models represent approximate steady-state
equilibrium configurations. Models built from this method can be used to study
a variety of relevant astrophysical and geophysical problems.
The amount of mass loss is of fundamental importance to the lives and deaths of very massive stars, the input of chemical elements and momentum into the interstellar and intergalactic media, as well as the emitted ionizing radiation. I review mass-loss predictions for hot massive stars as a function of metal content for groups of OB stars, Luminous Blue Variables, and Wolf-Rayet stars. Although it is found that the predicted mass-loss rates drop steeply with decreasing metal content (Mdot ~ Z^{0.7-0.85}), I highlight two pieces of physics that are often overlooked: (i) mass-loss predictions for massive stars approaching the Eddington limit, and for (ii) stars that have enriched their own atmospheres with primary elements such as carbon. Both of these effects may significantly boost the mass-loss rates of the first stars - relevant for the reionization of the Universe, and a potential pre-enrichment of the intergalactic medium - prior to the first supernova explosions.
The early X-ray afterglow for a significant number of gamma-ray bursts detected by the Swift satellite is observed to have a phase of very slow flux decline with time ($F_\nu \propto t^{-\alpha}$ with $0.2 \lesssim \alpha \lesssim 0.8$) for $10^{2.5} s \lesssim t \lesssim 10^4$ s, while the subsequent decline is the usual $1 \lesssim \alpha_3 \lesssim 1.5$ behavior, that was seen in the pre-Swift era. We show that this behavior is a natural consequence of a small spread in the Lorentz factor of the ejecta, by a factor of $\sim 2-4$, where the slower ejecta gradually catch-up with the shocked external medium, thus increasing the energy of forward shock and delaying its deceleration. The end of the ``shallow'' flux decay stage marks the beginning of the Blandford-McKee self similar external shock evolution. This suggests that most of the energy in the relativistic outflow is in material with a Lorentz factor of $\sim 30-50$.
The Pisces-Cetus supercluster (redshift z~0.06) is one of the richest nearby (z<0.1) superclusters of galaxies, and emerges as a remarkable filament of galaxies at the edges of the two-degree-field galaxy redshift survey and the ongoing Sloan Digital Sky Survey. We explore the extent of the supercluster on the sky and in redshift space, and map the distribution of its constituent clusters and groups. We find evidence of enhanced star formation in galaxies belonging to groups in the supercluster compared to those in the field. This effect appears to be higher among the poorer groups than in the richer ones. In contrast, star formation is suppressed in the galaxies in rich clusters, which is consistent with previous studies. We identify two major filaments in this supercluster, consisting of 11 and 5 Abell clusters, including Abell 133 and Abell 85 respectively, and estimate the virial masses of the clusters from their velocity dispersions and optical surface brightness profiles. The lower limit to the masses of these filaments, amounting to the total virial mass of the constituent clusters, turns out to be 5.2 x10^15, h_70^-1, M_sun and 6.0x10^15, h_70^-1, M_sun over volumes of almost 6750, h_70^-3 Mpc^3 and 19600, h_70^-3 Mpc^3 respectively. This corresponds to mass overdensities of Omega/Omega_crit=delta_M>4.7 and delta_M>1.3 for the two filaments making up the supercluster.
The sample of known exoplanets is strongly biased to masses larger than the ones of the giant gaseous planets of the solar system. Recently, the discovery of two extrasolar planets of considerably lower masses around the nearby stars GJ 436 and $\rho$ Cancri was reported. They are like our outermost icy giants, Uranus and Neptune, but in contrast, these new planets are orbiting at only some hundredth of the Earth-Sun distance from their host stars, raising several new questions about their origin and constitution. Here we report numerical simulations of planetary accretion that show, for the first time through N-body integrations that the formation of compact systems of Neptune-like planets close to the hosts stars could be a common by-product of planetary formation. We found a regime of planetary accretion, in which orbital migration accumulates protoplanets in a narrow region around the inner edge of the nebula, where they collide each other giving rise to Neptune-like planets. Our results suggest that, if a protoplanetary solar environment is common in the galaxy, the discovery of a vast population of this sort of 'hot cores' should be expected in the near future.
In the two parts of this contribution we describe two related XMM-Newton programs. The first part summarizes our study of the X-ray spectral properties and variability of z>4 quasars (Shemmer et al. 2005). The second part presents preliminary results from our ongoing XMM-Newton program to investigate the X-ray spectral properties and variability of luminous, high accretion-rate quasars at z~2--3. We find that the X-ray photon index does not depend on luminosity or redshift, and there is suggestive evidence that it may depend on the accretion rate. None of our quasars is significantly absorbed, and none shows signatures of reflection. By jointly fitting high-quality spectra of eight radio-quiet z>4 quasars, including three from our XMM-Newton observations, we place tight constraints on the mean X-ray spectral properties of such sources. Most of our quasars are significantly X-ray variable on timescales of months--years, but none shows rapid (~1 hr timescale) variations.
(ABRIDGED) We examine the fundamental scaling relations of elliptical
galaxies formed through mergers. Using hundreds of simulations to judge the
impact of progenitor galaxy properties on merger remnants, we find that gas
dissipation provides an important contribution to tilt in the Fundamental Plane
relation. Dissipationless mergers of disks produce remnants that occupy the
virial plane. As the gas content of disk galaxies is increased, the tilt of the
Fundamental Plane relation increases and the slope of the Re-M_* relation
steepens. For gas fractions fgas > 30%, the simulated Fundamental Plane
scalings approach those observed in the K-band. In our simulations, feedback
from supermassive black hole growth has only a minor influence on the
stellar-mass scaling relations of spheroidal galaxies, but may play a role in
maintaining the observed Fundamental Plane tilt at optical wavelengths by
suppressing residual star formation in merger remnants.
We estimate that \approx 40-100% of the Fundamental Plane tilt induced by
structural properties owes to trends in the central total-to-stellar mass ratio
M_total/M_* produced by dissipation. Lower mass systems obtain greater phase-
space densities than higher mass systems, producing a galaxy mass-dependent
central M_total/M_* and a corresponding tilt in the Fundamental Plane.
The cross-correlation between cosmic microwave background (CMB) temperature anisotropies and the large scale structure (LSS) traced by the galaxy distribution, or sources at different wavelengths, is now well known. This correlation results from the integrated Sachs-Wolfe (ISW) effect in CMB anisotropies generated at late times due to the dark energy component of the Universe. In a reionized universe, the ISW quadrupole rescatters and contributes to the large-scale polarization signal. Thus, in principle, the large-scale polarization bump in the E-mode should also be correlated with the galaxy distribution. Unlike CMB temperature-LSS correlation that peaks for tracers at low redshifts this correlation peaks mostly at redshifts between 1 and 3. Under certain conditions, mostly involving a low optical depth to reionization, if the Universe reionized at a redshift around 6, the cross polarization-source signal is marginally detectable, though challenging as it requires all-sky maps of the large scale structure at redshifts between 1 and 3. If the Universe reionized at a redshift higher than 10, it is unlikely that this correlation will be detectable even with no instrumental noise all-sky maps. While our estimates do not guarantee a detection unknown physics related to the dark energy as well as still uncertain issues related to the large angular scale CMB and polarization anisotropies may motivate attempts to measure this correlation using upcoming CMB polarization E-mode maps.
We revisit the dynamics of Prometheus and Pandora, two small moons flanking Saturn's F ring. Departures of their orbits from freely precessing ellipses result from mutual interactions via their 121:118 mean motion resonance. Motions are chaotic because the resonance is split into four overlapping components. Orbital longitudes were observed to drift away from Voyager predictions, and a sudden jump in mean motions took place close to the time at which the orbits' apses were antialigned in 2000. Numerical integrations reproduce both the longitude drifts and the jumps. The latter have been attributed to the greater strength of interactions near apse antialignment (every 6.2 years), and it has been assumed that this drift-jump behavior will continue indefinitely. We re-examine the dynamics by analogy with that of a nearly adiabatic, parametric pendulum. In terms of this analogy, the current value of the action of the satellite system is close to its maximum in the chaotic zone. Consequently, at present, the two separatrix crossings per precessional cycle occur close to apse antialignment. In this state libration only occurs when the potential's amplitude is nearly maximal, and the 'jumps' in mean motion arise during the short intervals of libration that separate long stretches of circulation. Because chaotic systems explore the entire region of phase space available to them, we expect that at other times the system would be found in states of medium or low action. In a low action state it would spend most of the time in libration, and separatrix crossings would occur near apse alignment. We predict that transitions between these different states can happen in as little as a decade. Therefore, it is incorrect to assume that sudden changes in the orbits only happen near apse antialignment.
We have discovered a correlation between the X-ray absorbing column densities within Seyfert galaxies and the relative alignment between the central engines and their host galactic disks. This correlation carries several implications for Seyfert unification models. (1) In addition to small-scale circumnuclear absorbers, there are absorbing systems associated with the host galactic plane that are capable of obscuring the broad line region emission. (2) The misalignment between the central engine axis and that of the host galaxy arises on intermediate scales between these absorbers. (3) The small-scale absorbers have systematically higher column densities and may be universally Compton-thick.
The Extended Chandra Deep Field-South (E-CDF-S) survey consists of 4 Chandra ACIS-I pointings and covers ~1100 square arcminutes (~0.3 deg^2) centered on the original CDF-S field to a depth of approximately 228 ks (PI: Niel Brandt; Lehmer et al, 2005). This is the largest Chandra survey ever conducted at such depth. In our analysis (Virani et al, 2005), we detect 651 unique sources -- 587 using a conservative source detection limit and 64 using a lower source detection limit. Of these 651 sources, 561 are detected in the full 0.5--8.0 keV band, 529 in the soft 0.5--2.0 keV band, and 335 in the hard 2.0--8.0 keV band. For point sources near the aim point, the limiting fluxes are approximately $1.7 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ and $3.9 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ in the 0.5--2.0 keV and 2.0--8.0 keV bands, respectively. We present the optical properties of these X-ray sources, specifically the R-band magnitude distribution and a preliminary spectroscopic redshift distribution. One exciting result is the discovery of 7 new Extreme X-ray-to-Optical flux ratio objects (EXOs) found in the E-CDF-S field.
In this note I describe an inexpensive and simple laser-based method to measure the flatness of the LSST focal plane assembly (FPA) in situ, i.e. while the FPA is inside its cryostat, at -100 C and under vacuum. The method may also allow measurement of the distance of the FPA to lens L3, and may be sensitive enough to measure gravity- and pressure-induced deformations of L3 as well. The accuracy of the method shows promise to be better than 1 micron.
HH 212 is a highly collimated jet discovered in H2 powered by a young Class 0 source, IRAS 05413-0104, in the L1630 cloud of Orion. We have mapped around it in 1.33 mm continuum, 12CO ($J=2-1$), 13CO ($J=2-1$), C18O ($J=2-1$), and SO ($J_K = 6_5-5_4$) emission at $\sim$ \arcs{2.5} resolution with the Submillimeter Array. A dust core is seen in the continuum around the source. A flattened envelope is seen in C18O around the source in the equator perpendicular to the jet axis, with its inner part seen in 13CO. The structure and kinematics of the envelope can be roughly reproduced by a simple edge-on disk model with both infall and rotation. In this model, the density of the disk is assumed to have a power-law index of $p=-1.5$ or -2, as found in other low-mass envelopes. The envelope seems dynamically infalling toward the source with slow rotation because the kinematics is found to be roughly consistent with a free fall toward the source plus a rotation of a constant specific angular momentum. A 12CO outflow is seen surrounding the H2 jet, with a narrow waist around the source. Jetlike structures are also seen in 12CO near the source aligned with the H2 jet at high velocities. The morphological relationship between the H2 jet and the 12CO outflow, and the kinematics of the 12CO outflow along the jet axis are both consistent with those seen in a jet-driven bow shock model. SO emission is seen around the source and the H2 knotty shocks in the south, tracing shocked emission around them.
Upcoming observatories will be able to detect the kinetic Sunyaev-Zel'dovitch (kSZ) effect with unprecendented signal-to-noise, and cross-correlations with foreground signals such as galaxy counts are a promising way to extract additional cosmological information. We consider how well a tomographic galaxy-count cross-correlation experiment, using data from WMAP, ACT and SALT, can significantly constrain the properties of dark energy. We include the need to model a wide range of effects, including those associated with complicated baryonic physics, in our analysis. We demonstrate how much of the cosmological information contained in the kSZ comes from larger scales than that in the galaxy power spectrum, and thus how use of the kSZ can help avoid difficult systematics associated with non-linear and scale-dependent bias at k>1h Mpc^{-1}.
In the context of a cosmological study of the bulk flows in the Universe, we present a detailed study of the statistical properties of the kinematic Sunyaev-Zel'dovich (kSZ) effect. We first compute analytically the correlation function and the power spectrum of the projected peculiar velocities of galaxy clusters. By taking into account the spatial clustering properties of these sources, we perform a line-of-sight computation of the {\em all-sky} kSZ power spectrum and find that at large angular scales ($l<10$), the local bulk flow should leave a visible signature above the Poisson-like fluctuations dominant at smaller scales, while the coupling of density and velocity fluctuations should give much smaller contribution. We conduct an analysis of the prospects of future high resolution CMB experiments (such as ACT and SPT) to detect the kSZ signal and to extract cosmological information and dark energy constraints from it. We present two complementary methods, one suitable for ``deep and narrow'' surveys such as ACT and one suitable for ``wide and shallow'' surveys such as SPT. Both methods can constraint the equation of state of dark energy $w$ to about 5-10% when applied to forthcoming and future surveys, and probe $w$ in complementary redshift ranges, which could shed some light on its time evolution. These determinations of $w$ do not rely on the knowledge of cluster masses, although they make minimal assumptions on cluster physics.
The main performance bottleneck of gravitational N-body codes is the force
calculation between two particles. We have succeeded in speeding up this
pair-wise force calculation by factors between two and ten, depending on the
code and the processor on which the code is run. These speedups were obtained
by writing highly fine-tuned code for x86_64 microprocessors. Any existing
N-body code, running on these chips, can easily incorporate our assembly code
programs.
In the current paper, we present an outline of our overall approach, which we
illustrate with one specific example: the use of a Hermite scheme for a direct
N^2 type integration on a single 2.0 GHz Athlon 64 processor, for which we
obtain an effective performance of 4.05 Gflops, for double precision accuracy.
In subsequent papers, we will discuss other variations, including the
combinations of N log N codes, single precision implementations, and
performance on other microprocessors.
We have made a high-resolution VLBI observation of the gamma-ray loud quasar PKS 1622-297 with the HALCA spacecraft and ground radio telescopes at 5 GHz in 1998 February, almost three years after the source exhibited a spectacular GeV gamma-ray flare. The source shows an elongated structure toward the west on the parsec scale. The visibility data are well modeled by three distinct components; a bright core and two weaker jet components. Comparison with previous observations confirms that the jet components have an apparent superluminal motion up to 12.1 h^{-1}c, with the inner jet components having lower superluminal speeds. We apply the inverse Compton catastrophe model and derive a Doppler factor, \delta, of 2.45, which is somewhat lower than that of other gamma-ray loud active galactic nuclei (AGNs), suggesting the source was in a more quiescent phase at the epoch of our observation. As an alternative probe of the sub-parsec scale structure, we also present the results from multi-epoch ATCA total flux monitoring, which indicate the presence of persistent intraday variability consistent with refractive interstellar scintillation. We examine the gamma-ray emission mechanism in the light of these observations.
The ionization fraction is an important factor in determining the chemical
and physical evolution of star forming regions. In the dense, dark starless
cores of such objects, the ionization rate is dominated by cosmic rays; it is
therefore possible to use simple analytic estimators, based on the relative
abundances of different molecular tracers, to determine the cosmic ray
ionization rate.
This paper uses a simple model to investigate the accuracy of two well-known
estimators in dynamically evolving molecular clouds. It is found that, although
the analytical formulae based on the abundances of H3+,H2,CO,O,H2O and HCO+
give a reasonably accurate measure of the cosmic ray ionization rate in static,
quiescent clouds, significant discrepancies occur in rapidly evolving
(collapsing) clouds. As recent evidence suggests that molecular clouds may
consist of complex, dynamically evolving sub-structure, we conclude that simple
abundance ratios do not provide reliable estimates of the cosmic ray ionization
rate in dynamically active regions.
Korean VLBI Network (KVN) is the first dedicated mm-wavelength VLBI Network in East Asia and will be available from the middle of 2008. KVN consists of three stations and has the maximum observation frequency of 129 GHz with the maximum baseline length of 480 km. KVN has unique characteristics in the multifrequency, simultaneous observing system. By taking advantage of this we are considering various science topics, including not only maser emitting regions and young stellar objects in our galaxy, but also extragalactic objects. Construction of the first site is in progress. We are concurrently developing components, including receivers, data acquisition systems, and a correlator, and also arranging the international collaboration.
We present a statistical study of a very large sample of HII galaxies taken from the literature. We focus on the differences in several properties between galaxies that show the auroral line [OIII]l4363 and those that do not present this feature in their spectra. It turns out that objects without this auroral line are more luminous, more metal-rich and present a lower ionization degree. The underlying population is found to be much more important for objects without the [OIII]l 4363 line, and the effective temperature of the ionizing star clusters of galaxies not showing the auroral line is probably lower. We also study the subsample of HII galaxies whose properties most closely resemble the properties of the intermediate-redshift population of Luminous Compact Blue Galaxies (LCBGs). The objects from this subsample are more similar to the objects not showing the [OIII]l 4363 line. It might therefore be expected that the intermediate-redshift population of LCBGs is powered by very massive, yet somewhat aged star clusters. The oxygen abundance of LCBGs would be greater than the average oxygen abundance of local HII galaxies.
The low mass X-ray binary (LMXB) associated with the M31 globular cluster Bo 158 is known to exhibit intensity dips on a ~2.78 hr period. This is due to obscuration of the X-ray source on the orbital period by material on the outer edge of the accretion disc. However, the depth of dipping varied from <10% to \~83% in three archival XMM-Newton observations of Bo 158. Previous work suggested that the dip depth was anticorrelated with the X-ray luminosity. However, we present results from three new XMM-Newton observations that suggest that the evolution of dipping is instead due to precession of the accretion disc. Such precession is expected in neutron star LMXBs with mass ratios <0.3 (i.e. with orbital periods <4 hr), such as the Galactic dipping LMXB 4U 1916-053. We simulated the accretion disc of Bo 158 using cutting-edge 3D smoothed particle hydrodynamics (SPH), and using the observed parameters. Our results show disc variability on two time-scales. The disc precesses in a prograde direction on a period of 81+/-3 hr. Also, a radiatively-driven disc warp is present in the inner disc, which undergoes retrograde precesson on a \~31 hr period. From the system geometry, we conclude that the dipping evolution is driven by the disc precession. Hence we predict that the dipping behaviour repeats on a ~81 hr cycle.
There is growing evidence that two classes of high-energy sources, the Soft Gamma Repeaters and the Anomalous X-ray Pulsars contain slowly spinning ``magnetars'', i.e. neutron stars whose emission is powered by the release of energy from their extremely strong magnetic fields (>10^15 G. We show here that the enormous energy liberated in the 2004 December 27 giant flare from SGR1806-20 (~5 10^46 erg), together with the likely recurrence time of such events, requires an internal field strength of > 10^16 G. Toroidal magnetic fields of this strength are within an order of magnitude of the maximum fields that can be generated in the core of differentially-rotating neutron stars immediately after their formation, if their initial spin period is of a few milliseconds. A substantial deformation of the neutron star is induced by these magnetic fields and, provided the deformation axis is offset from the spin axis, a newborn fast-spinning magnetar would radiate for a few weeks a strong gravitational wave signal the frequency of which (0.5-2 kHz range) decreases in time. The signal from a newborn magnetar with internal field > 10^16.5 G could be detected with Advanced LIGO-class detectors up to the distance of the Virgo cluster (characteristic amplitude h_c about 10^-21). Magnetars are expected to form in Virgo at a rate approx. 1/yr. If a fraction of these have sufficiently high internal magnetic field, then newborn magnetars constitute a promising new class of gravitational wave emitters.
The lifetime of the structure in grand design spiral galaxies is observationally ill-determined, but is essentially set by how accurately the pattern's rotation can be characterized by a single angular pattern speed. This paper derives a generalized version of the Tremaine-Weinberg method for observationally determining pattern speeds, in which the pattern speed is allowed to vary arbitrarily with radius. The departures of the derived pattern speed from a constant then provides a simple metric of the lifetime of the spiral structure. Application of this method to CO observations of NGC 1068 reveal that the pattern speed of the spiral structure in this galaxy varies rapidly with radius, and that the lifetime of the spiral structure is correspondingly very short. If this result turns out to be common in grand-design spiral galaxies, then these features will have to be viewed as highly transient phenomena.
This paper reports the results of a survey of Doppler shift oscillations measured during solar flares in emission lines of S XV and Ca XIX with the Bragg Crystal Spectrometer (BCS) on Yohkoh. Data from 20 flares that show oscillatory behavior in the measured Doppler shifts have been fitted to determine the properties of the oscillations. Results from both BCS channels show average oscillation periods of 5.5 +/- 2.7 minutes, decay times of 5.0 +/-2.5 minutes, amplitudes of 17.1 +/- 17.0 km/s, and inferred displacements of 1070 +/- 1710 km, where the listed errors are the standard deviations of the sample means. For some of the flares, intensity fluctuations are also observed. These lag the Doppler shift oscillations by 1/4 period, strongly suggesting that the oscillations are standing slow mode waves. The relationship between the oscillation period and the decay time is consistent with conductive damping of the oscillations.
We consider the physics of neutrinos in a fireball, i.e. a tightly coupled plasma of photons, positrons and electrons. Such a fireball is believed to form in the first stages of a gamma-ray burst. We assume the fireball is radiation-dominated and spherically symmetric. Energy considerations limit the allowed baryon density, from which it follows that the neutrino physics is dominated by leptonic processes. We find that, for quite general initial conditions, neutrinos start out in thermodynamic equilibrium with the fireball and follow the usual hydrodynamical evolution. As the fireball cools, the plasma becomes transparent to neutrinos which subsequently decouple from the plasma. Although a sizable fraction of the total energy is carried away, the detection possibility of these neutrino bursts is limited due to the isotropic outflow and the relatively low mean energy of approximately 60 MeV.
We report on a simultaneous Chandra and RossiXTE observation of the low-mass X-ray binary atoll bursting source MXB 1728-34 performed on 2002 March 3-5. We fit the 1.2-35 keV continuum spectrum with a blackbody plus a Comptonized component. Large residuals at 6-10 keV can be fitted by a broad (FWHM ~ 2 keV) Gaussian emission line or, alternatively, by two absorption edges associated with lowly ionized iron and Fe XXV/XXVI at ~7.1 keV and ~9 keV, respectively. In this interpretation, we find no evidence of broad, or narrow, emission lines between 6 and 7 keV. We test our alternative modelling of the iron K shell region by reanalysing a previous BeppoSAX observation of MXB 1728-34, finding a general agreement with our new spectral model.
In this brief WEB note we comment on recent papers related to our paper "On Acceleration Without Dark Energy".
Rotating massive stars at $Z=10^{-8}$ and $10^{-5}$ lose a great part of their initial mass through stellar winds. The chemical composition of the rotationally enhanced winds of very low $Z$ stars is very peculiar. The winds show large CNO enhancements by factors of $10^3$ to $10^7$, together with large excesses of $^{13}$C and $^{17}$O and moderate amounts of Na and Al. The excesses of primary N are particularly striking. When these ejecta from the rotationally enhanced winds are diluted with the supernova ejecta from the corresponding CO cores, we find [C/Fe], [N/Fe],[O/Fe] abundance ratios very similar to those observed in the C--rich extremely metal poor stars (CEMP). We show that rotating AGB stars and rotating massive stars have about the same effects on the CNO enhancements. Abundances of s-process elements and the $^{12}$C/$^{13}$C ratio could help us to distinguish between contributions from AGB and massive stars. On the whole, we emphasize the dominant effects of rotation for the chemical yields of extremely metal poor stars.
The high gradient of magnification across the source during both small impact parameter events and caustic crossings offers a unique opportunity for determining the surface brightness profile of the source. Furthermore, models indicate that these events can also provide an appreciable polarisation signal -- arising from differential magnification across the otherwise symmetric source. In a previous paper, polarimetric variations from point lensing of a circumstellar envelope were considered, as would be suitable for an extended envelope around a red giant. In this work we examine the polarisation in the context of caustic crossing events, the scenario which represents the most easily accessible situation for actually observing a polarisation signal in Galactic microlensing.
The QSO 3C 48 and its host galaxy constitute a nearby template object of the proposed merger-driven evolutionary sequence from ULIRGs to QSOs. In this contribution multi-wavelength observations and N-body simulations studying the structural and compositional properties of this late-stage major merger will be presented. Key questions addressed will be the nature of the apparent second nucleus 3C 48A and absence of a counter tidal tail. The results will be used to review the role of 3C 48 in the ULIRG-QSO evolutionary scenario.
The controversy over whether ultraluminous X-ray sources (ULXs) contain a new intermediate-mass class of black holes (IMBHs) remains unresolved. We present new analyses of the deepest XMM-Newton observations of ULXs that address their underlying nature. We examine both empirical and physical modelling of the X-ray spectra of a sample of thirteen of the highest quality ULX datasets, and find that there are anomalies in modelling ULXs as accreting IMBHs with properties simply scaled-up from Galactic black holes. Most notably, spectral curvature above 2 keV in several sources implies the presence of an optically-thick, cool corona. We also present a new analysis of a 100 ks observation of Holmberg II X-1, in which a rigorous analysis of the temporal data limits the mass of its black hole to no more than 100 solar masses. We argue that a combination of these results points towards many (though not necessarily all) ULXs containing black holes that are at most a few 10s of solar mass in size.
OTELO (OSIRIS Tunable Emission Line Object Survey) will be carried out with the OSIRIS instrument at the 10 m GTC telescope at La Palma, and is aimed to be the deepest and richest survey of emission line objects to date. The deep narrow-band optical data from OSIRIS will be complemented by means of additional observations that include: (i) an exploratory broad-band survey that is already being carried out in the optical domain, (ii) FIR and sub-mm observations to be carried with the Herschel space telescope and the GTM, and (iii) deep X-Ray observations from XMM-Newton and Chandra.Here we present a preliminary analysis of public EPIC data of one of the OTELO targets,the Groth-Westphal strip, gathered from the XMM-Newton Science Archive (XSA). EPIC images are combined with optical BVRI data from our broadband survey carried out with the 4.2m WHT at La Palma. Distance-independent diagnostics (involving X/O ratio, hardness ratios, B/T ratio) are tested.
We use 8.3 um mid-infrared images acquired with the Midcourse Space Experiment satellite to identify and catalog Infrared Dark Clouds (IRDCs) in the first and fourth quadrants of the Galactic plane. Because IRDCs are seen as dark extinction features against the diffuse Galactic infrared background, we identify them by first determining a model background from the 8.3 um images and then searching for regions of high decremental contrast with respect to this background. IRDC candidates in our catalog are defined by contiguous regions bounded by closed contours of a 2 sigma decremental contrast threshold. Although most of the identified IRDCs are actual cold, dark clouds, some as yet unknown fraction may be spurious identifications. For large, high contrast clouds, we estimate the reliability to be 82%. Low contrast clouds should have lower reliabilities. Verification of the reality of individual clouds will require additional data. We identify 10,931 candidate infrared dark clouds. For each IRDC, we also catalog cores. These cores, defined as localized regions with at least 40% higher extinction than the cloud's average extinction, are found by iteratively fitting 2-dimensional elliptical Gaussians to the contrast peaks. We identify 12,774 cores. The catalog contains the position, angular size, orientation, area, peak contrast, peak contrast signal-to-noise, and integrated contrast of the candidate IRDCs and their cores. The distribution of IRDCs closely follows the Galactic diffuse mid-infrared background and peaks toward prominent star forming regions, spiral arm tangents, and the so-called 5 kpc Galactic molecular ring.
The effects of rotation on low-metallicity stellar models are twofold: first, the models reach break-up during main sequence and may lose mass by mechanical process; second, strong internal mixing brings freshly synthesized elements towards the surface and raises the effective metallicity to higher values, so that the initially very low radiative winds are enhanced. Those two effects are also found in Z=0 models, but to a lesser degree because of structural differences. This weak mass loss becomes interesting though in the case of the black hole-doomed stars (25-140 M_\sun and > 260 M_\sun) because it allows these stars to contribute to the enrichment of the medium by stellar winds.
We present a detailed study of the peculiar HI-deficient Virgo cluster spiral galaxies NGC 4064 and NGC 4424, using $^{12}$CO 1-0 interferometry, optical imaging and integral-field spectroscopic observations, in order to learn what type of environmental interactions have afected these galaxies. Optical imaging reveals that NGC 4424 has a strongly disturbed stellar disk, with banana-shaped isophotes and shells. NGC 4064, which lies in the cluster outskirts, possesses a relatively undisturbed outer stellar disk and a central bar. In both galaxies H-alpha emission is confined to the central kiloparsec. CO observations reveal bilobal molecular gas morphologies, with H-alpha emission peaking inside the CO lobes, implying a time sequence in the star formation process.Gas kinematics reveals strong bar-like non-circular motions in the molecular gas in both galaxies, suggesting that the material is radially infalling. In NGC 4064 the stellar kinematics reveal strong bar-like non-circular motions in the central 1 kpc. On the other hand, NGC 4424 has extremely modest stellar rotation velocities (Vmax ~ 30 km s-1), and stars are supported by random motions as far out as we can measure it. The observations suggest that the peculiarities of NGC 4424 are the result of an intermediate-mass merger plus ram pressure stripping. In the case of NGC 4064, the evidence suggests an already stripped "truncated/normal" galaxy that recently suffered a minor merger or tidal interaction with another galaxy. We propose that galaxies with "truncated/compact" H-alpha morphologies such as these are the result of the independent effects of ram pressure stripping, which removes gas from the outer disk, and gravitational interactions such as mergers, which heat stellar disks, drive gas to the central kpc and increase the central mass concentrations.
Although it is well known that a massive planet opens a gap in a proto-planetary gaseous disk, there is no analytic description of the surface density profile in and near the gap. The simplest approach, which is based upon the balance between the torques due to the viscosity and the gravity of the planet and assumes local damping, leads to gaps with overestimated width, especially at low viscosity. Here, we take into account the fraction of the gravity torque that is evacuated by pressure supported waves. With a novel approach, which consists of following the fluid elements along their trajectories, we show that the flux of angular momentum carried by the waves corresponds to a pressure torque. The equilibrium profile of the disk is then set by the balance between gravity, viscous and pressure torques. We check that this balance is satisfied in numerical simulations, with a planet on a fixed circular orbit. We then use a reference numerical simulation to get an ansatz for the pressure torque, that yields gap profiles for any value of the disk viscosity, pressure scale height and planet to primary mass ratio. Those are in good agreement with profiles obtained in numerical simulations over a wide range of parameters. Finally, we provide a gap opening criterion that simultaneously involves the planet mass, the disk viscosity and the aspect ratio.
(abridged) Thus far our impressions regarding the evolutionary time scales
for young circumstellar disks have been based on small number statistics. Over
the past decade, however, in addition to precision study of individual
star/disk systems, substantial observational effort has been invested in
obtaining less detailed data on large numbers of objects in young star
clusters. This has resulted in a plethora of information now enabling
statistical studies of disk evolutionary diagnostics. Along an ordinate one can
measure disk presence or strength through indicators such as ultraviolet/blue
excess or spectroscopic emission lines tracing accretion, infrared excess
tracing dust, or millimeter flux measuring mass. Along an abscissa one can
track stellar age.
While bulk trends in disk indicators versus age are evident, observational
errors affecting both axes, combined with systematic errors in our
understanding of stellar ages, both cloud and bias any such trends Thus
detailed understanding of the physical processes involved in disk dissipation
and of the relevant time scales remains elusive. Nevertheless, a clear effect
in current data that is unlikely to be altered by data analysis improvements is
the dispersion in disk lifetimes. The age at which evidence for inner accretion
disks ceases to be apparent for the vast majority (90%) of stars is in the
range 3-8 Myr. More distant, terrestrial zone dust is traced by mid-infrared
emission where sufficient sensitivity and uniform data collection are only now
being realized with data return from the Spitzer Space Telescope.
We present a phase-connected timing solution for the nearby isolated neutron star RX J1308.6+2127 (RBS 1223). From dedicated Chandra observations as well as archival Chandra and XMM-Newton data spanning a period of five years, we demonstrate that the 10.31-sec pulsations are slowing down steadily at a rate of Pdot=1.120(3)e-13 s/s. Under the assumption that this is due to magnetic dipole torques, we infer a characteristic age of 1.5 Myr and a magnetic field strength of 3.4e13 G. As with RX J0720.4-3125, the only other radio-quiet thermally emitting isolated neutron star for which a timing solution has been derived, the field strength is consistent with what was inferred earlier from the presence of a strong absorption feature in its X-ray spectrum. Furthermore, both sources share that the characteristic age is in excess of the cooling age inferred from standard cooling models. The sources differ, however, in their timing noise: while RX J0720.4-3125 showed considerable timing noise, RX J1308.6+2127 appears relatively stable.
The lens candidate CSL-1 has been interpreted as evidence for a cosmic string. Here we test the hypothesis that the lensing comes from a tidally disrupted dark matter halo. We calculate the mass-density relationship that one would expect from structure formation theory and come to the conclusion that in order to explain the lensing using dark matter, the halo would have to have a mass greater than the Milky Way. There is apparently no such object seen in the data. If the follow up observations confirm that the two objects are indeed images of the same galaxy, then it seems difficult to explain the lens using dark matter.
Type Ia Supernovae are standard candles so their mean apparent magnitude has been exploited to learn about the redshift-distance relationship. Besides intrinsic scatter in this standard candle, additional source of scatter is caused by gravitational magnification by large scale structure. Here we probe the dependence of this dispersion on cosmological parameters and show that information about the amplitude of clustering, \sigma_8, is contained in the scatter. In principle, it will be possible to constrain \sigma_8 to within 5% with observations of 2000 Type Ia Supernovae. However, extracting this information requires subtlety as the distribution of magnifications is far from Gaussian. If one incorrectly assumes a Gaussian distribution, the estimate of the clustering amplitude will be biased three-\sigma away from the true value.
The Carina dwarf spheroidal (dSph) galaxy is the only galaxy of this type that shows clearly episodic star formation separated by long pauses. Here we present metallicities for 437 radial velocity members of this Galactic satellite. We obtained medium-resolution spectroscopy with the multi-object spectrograph FLAMES at the ESO VLT. Our target red giants cover the entire projected surface area of Carina. Our spectra are centered at the near-infrared Ca triplet, which is a well-established metallicity indicator for old and intermediate-age red giants. The resulting data sample provides the largest collection of spectroscopically derived metallicities for a Local Group dSph to date. Four of our likely radial velocity members of Carina lie outside of this galaxy's nominal tidal radius, supporting earlier claims of the possible existence of such stars beyond the main body of Carina. We find a mean metallicity of [Fe/H]=-1.7 dex. The formal full width at half maximum of the metallicity distribution is 0.92 dex, while the full range of metallicities spans ~-3.0<[Fe/H]<0.0 dex. The metallicity distribution might be indicative of several subpopulations. There appears to be a mild radial gradient such that more metal-rich populations are more centrally concentrated, matching a similar trend for an increasing fraction of intermediate-age stars. This as well as the photometric colors of the more metal-rich red giants suggest that Carina exhibits an age-metallicity relation. Indeed the age-metallicity degeneracy seems to conspire to form a narrow red giant branch despite the considerable spread in metallicity and wide range of ages. The metallicity distribution is not well-matched by a simple closed-box model of chemical evolution, but requires models that take into account also infall and outflows. (Abridged)
INTEGRAL monitoring of the Galactic Plane is revealing a growing number of recurrent X-ray transients, characterised by short outbursts with very fast rise times (~ tens of minutes) and typical durations of a few hours. Here we show that several of these transients are associated with OB supergiants and hence define a new class of massive X-ray binaries which we call Supergiant Fast X-ray Transients (SFXTs). Many other transient X-ray sources display similar X-ray characteristics, suggesting that they belong to the same class. Since they are difficult to detect and their number is growing fast and steadily, they could represent a major class of X-ray binaries.
We present the first measurements of the weak gravitational lensing signal induced by the large scale mass distribution from data obtained as part of the ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data used in this analysis are from the Wide Synoptic Survey, which aims to image ~170 square degree in five filters. We have analysed ~22 deg2 (31 pointings) of i' data spread over two of the three survey fields. These data are of excellent quality and the results bode well for the remainder of the survey: we do not detect a significant `B'-mode, suggesting that residual systematics are negligible at the current level of accuracy. Assuming a Cold Dark Matter model and marginalising over the Hubble parameter h=[0.6,0.8], the source redshift distribution and systematics, we constrain sigma_8, the amplitude of the matter power spectrum. At a fiducial matter density Omega_m=0.3 we find sigma_8=0.85+-0.06. This estimate is in excellent agreement with previous studies. Combination of our results with those from the Deep component of the CFHTLS enables us to place a constraint on a constant equation of state for the dark energy, based on cosmic shear data alone. We find that w_0<-0.8 at 68% confidence.
We present the first cosmic shear measurements obtained from the T0001 release of the Canada-France-Hawaii Telescope Legacy Survey. The data set covers three uncorrelated patches (D1, D3 and D4) of one square degree each observed in u*, g', r', i' and z' bands, out to i'=25.5. The depth and the multicolored observations done in deep fields enable several data quality controls. The lensing signal is detected in both r' and i' bands and shows similar amplitude and slope in both filters. B-modes are found to be statistically zero at all scales. Using multi-color information, we derived a photometric redshift for each galaxy and separate the sample into medium and high-z galaxies. A stronger shear signal is detected from the high-z subsample than from the low-z subsample, as expected from weak lensing tomography. While further work is needed to model the effects of errors in the photometric redshifts, this results suggests that it will be possible to obtain constraints on the growth of dark matter fluctuations with lensing wide field surveys. The various quality tests and analysis discussed in this work demonstrate that MegaPrime/Megacam instrument produces excellent quality data. The combined Deep and Wide surveys give sigma_8= 0.88 pm 0.07 assuming the Peacock & Dodds non-linear scheme and sigma_8=0.85 pm 0.07 for the halo fitting model and Omega_m=0.3. We assumed a Cold Dark Matter model with flat geometry. Systematics, Hubble constant and redshift uncertainties have been marginalized over. Using only data from the Deep survey, the 1 sigma upper bound for w_0, the constant equation of state parameter is w_0 < -0.32.
Analysis of spectra obtained with the gamma-ray spectrometer SPI onboard INTEGRAL of the GOES X17-class flare on October 28, 2003 is presented. In the energy range 600 keV - 8 MeV three prominent narrow lines at 2.223, 4.4 and 6.1 MeV, resulting from nuclear interactions of accelerated ions within the solar atmosphere could be observed. Time profiles of the three lines and the underlying continuum indicate distinct phases with several emission peaks and varying continuum-to-line ratio for several minutes before a smoother decay phase sets in. Due to the high-resolution Ge detectors of SPI and the exceptional intensity of the flare, detailed studies of the 4.4 and 6.1 MeV line shapes was possible for the first time. Comparison with calculated line shapes using a thick target interaction model and several energetic particle angular distributions indicates that the nuclear interactions were induced by downward-directed particle beams with alpha-to-proton ratios of the order of 0.1. There are also indications that the 4.4 MeV to 6.1 MeV line fluence ratio changed between the beginning and the decay phase of the flare, possibly due to a temporal evolution of the energetic particle alpha-to-proton ratio.
Infrared ~5--35 um spectra for 40 solar-mass T Tauri stars and 7 intermediate-mass Herbig Ae stars with circumstellar disks were obtained using the Spitzer Space Telescope as part of the c2d IRS survey. This work complements prior spectroscopic studies of silicate infrared emission from disks, which were focused on intermediate-mass stars, with observations of solar-mass stars limited primarily to the 10 um region. The observed 10 and 20 um silicate feature strengths/shapes are consistent with source-to-source variations in grain size. A large fraction of the features are weak and flat, consistent with um-sized grains indicating fast grain growth (from 0.1--1.0 um in radius). In addition, approximately half of the T Tauri star spectra show crystalline silicate features near 28 and 33 um indicating significant processing when compared to interstellar grains. A few sources show large 10-to-20 um ratios and require even larger grains emitting at 20 um than at 10 um. This size difference may arise from the difference in the depth into the disk probed by the two silicate emission bands in disks where dust settling has occurred. The 10 um feature strength vs. shape trend is not correlated with age or Halpha equivalent width, suggesting that some amount of turbulent mixing and regeneration of small grains is occurring. The strength vs. shape trend is related to spectral type, however, with M stars showing significantly flatter 10 um features (larger grain sizes) than A/B stars. The connection between spectral type and grain size is interpreted in terms of the variation in the silicate emission radius as a function of stellar luminosity, but could also be indicative of other spectral-type dependent factors (e.g, X-rays, UV radiation, stellar/disk winds, etc.).
We have performed a 1 square degree 1.2mm dust continuum survey in the rho Oph molecular cloud. We detect a number of previously unknown sources, ranging from extended cores over compact, starless cores to envelopes surrounding young stellar objects of Class 0, Class I, and Class II type. We analyse the mass distribution, spatial distribution and the potential equilibrium of the cores. For the inner regions, the survey results are consistent with the findings of previous narrower surveys. The core mass function resembles the stellar initial mass function, with the core mass function shifted by a factor of two to higher masses (for the chosen opacity and temperature). In addition, we find no statistical variation in the core mass function between the crowded inner regions and those in more isolated fields except for the absence of the most massive cores in the extended cloud. The inner region contains compacter cores. This is interpreted as due to a medium of higher mean pressure although strong pressure variations are evident in each region. The cores display a hierarchical spatial distribution with no preferred separation scale length. However, the frequency distribution of nearest neighbours displays two peaks, one of which at 5000AU can be the result of core fragmentation. The orientations of the major axes of cores are consistent with an isotropic distribution. In contrast, the relative orientations of core pairs are preferentially in the NW-SE direction on all separation scales. These results are consistent with core production and evolution in a turbulent environment. We report a new low-mass Class 0 object and its CO outflow.
We examine 14 hot white dwarfs for signs of infrared excess using the Spitzer Space Telescope. Twelve of the objects are massive white dwarfs which have been suggested to be the result of binary mergers. The remaining two objects are undermassive white dwarfs which again may be the result of mergers or the inspiral of a substellar companion. In no case do we find any evidence for significant infrared excesses out to wavelengths of 8 microns. This places strong constraints on the presence of orbiting dust and weaker constraints on the presence of close substellar companions.
Class 0 objects, which are thought to be the youngest protostars, are identified in terms of NIR or radio emission and/or the presence of molecular outflows. We present combined hydrodynamic and radiative transfer simulations of the collapse of a star-forming molecular core, which suggest two criteria for identifying dense cores with deeply embedded very young protostars that may not be observable in the NIR or radio with current telescopes. We find that cores with protostars are relatively warm (T>15K) with their SEDs peaking at wavelengths <170 micron, and they tend to appear circular.
The X-ray Telescope (XRT), on board the {\it Swift} satellite, provides: automated source detection and position with few arcsecond accuracy within few seconds from target acquisition; CCD spectroscopy and imaging capability (0.2-10 keV), with the capability of detecting a milliCrab source in about 10 seconds; automatic adjusting of the CCD readout mode to optimize the science return as the source fades. Swift main scientific goal is the study of gamma-ray burst (GRBs). XRT can observe GRB afterglows over several orders of magnitude in flux. The first results obtained during the first ten months of operation confirm that XRT is fully compliant with the requirements and is providing excellent results. In particular it is detecting a very steep decay in the early X-ray light curve of many afterglows. Often there are also strong flares superimposed to the X-ray light curve, probably related to the continued internal engine activity. XRT is also localising for the first time the X-ray counterparts to short bursts.
We select the Luminous Infrared Galaxies by cross-correlating the Faint Source Catalogue (FSC) and Point Source Catalogue (PSC) of the IRAS Survey with the Second Data Release of the SDSS for studying their infrared and optical properties. The total number of our sample is 1267 for FSC and 427 for PSC by using 2$\sigma$ significance level cross-section. The "likelihood ratio" method is used to estimate the sample's reliability and for a more reliable subsample (908 for FSC and 356 for PSC) selection. Then a Catalog with both the infrared, optical and radio informations is presented and will be used in further works. Some statistical results show that the Luminous Infrared Galaxies are quite different from the Ultra-Luminous Infrared Galaxies. The AGN fractions of galaxies with different infrared luminosities and the radio to infrared correlations are consist with previous studies.
The excellent sensitivity and high resolution capability of wide FoV ground-based imaging atmospheric Cerenkov telescopes allow us for the first time to resolve the morphological structures of pulsar wind nebulae (PWN) which are older and more extended than the Crab Nebula. VHE gamma-ray observations of such extended nebulae (with field strengths below ~ 20 micro Gauss) probe the electron component corresponding to the unseen extreme ultraviolet (EUV) synchrotron component, which measures electron injection from earlier evolutionary epochs. VHE observations of PWN therefore introduce a new window on PWN research. This review paper also identifies conditions for maximal VHE visbility of PWN. Regarding pulsar pulsed emission, it is becoming clear that the threshold energies of current telescopes are not sufficient to probe the pulsed gamma-ray component from canonical pulsars. Theoretical estimates of pulsed gamma-ray emission from millisecond pulsars seem to converge and it becomes clear that such detections with current 3rd generation telescopes will not be possible, unless the geometry is favourable.
One of the main goals of the COROT mission is to get precise photometric observations of selected bright stars in order to allow the modelling of their interior through asteroseismology. However, in order to interpret the asteroseismological data, the effective temperature, surface gravity, and chemical composition of the stars must be known with sufficient accuracy. To carry out this task, we have developed a spectroscopic method called APASS (Atmospheric Parameters and Abundances from Synthetic Spectra) which allows precise analysis of stars with a moderate to high rotational velocity, which is the case for most primary COROT targets. Our method is based on synthetic spectra and works differentially with respect to the Sun. Using high signal-to-noise spectra and the APASS method, we determined the atmospheric parameters and chemical abundances of 13 primary COROT targets. Our results agree well with those obtained by Bruntt using his software VWA and with those obtained with the software TEMPLOGG. However, in both cases, our error bars are significantly smaller than those of other methods. Our effective temperatures are also in excellent agreement with those obtained with the IR photometry method. For five stars with relatively low rotational velocity, we also performed an analysis with a classical equivalent-width method to test agreement with APASS results. We show that equivalent-width measurements by Gaussian or Voigt profile-fitting are sensitive to the rotational broadening, leading to systematic errors whenever the projected rotation velocity is non-negligible. The APASS method appears superior in all cases and should thus be preferred.
We have obtained FUSE and HST/STIS time-resolved spectroscopy of the polar AM Herculis during a deep low state. The spectra are entirely dominated by the emission of the white dwarf. Both the far-ultraviolet (FUV) flux as well as the spectral shape vary substantially over the orbital period, with maximum flux occurring at the same phase as during the high state. The variations are due to the presence of a hot spot on the white dwarf, which we model quantitatively. The white dwarf parameters can be determined from a spectral fit to the faint phase data, when the hot spot is self-eclipsed. Adopting the distance of 79+8-6pc determined by Thorstensen, we find an effective temperature of 19800+-700K and a mass of Mwd=0.78+0.12-0.17Msun. The hot spot has a lower temperature than during the high state, ~34000-40000K, but covers a similar area, ~10% of the white dwarf surface. Low state FUSE and STIS spectra taken during four different epochs in 2002/3 show no variation of the FUV flux level or spectral shape, implying that the white dwarf temperature and the hot spot temperature, size, and location do not depend on the amount of time the system has spent in the low state. Possible explanations are ongoing accretion at a low level, or deep heating, both alternatives have some weaknesses that we discuss. No photospheric metal absorption lines are detected in the FUSE and STIS spectra, suggesting that the average metal abundances in the white dwarf atmosphere are lower than 1e-3 times their solar values.
We report the results of a deep Chandra survey of the Sculptor dwarf spheroidal galaxy. We find five X-ray sources with L_X of at least 6*10^33 ergs/sec with optical counterparts establishing them as members of Sculptor. These X-ray luminosities indicate that these sources are X-ray binaries, as no other known class of Galactic point sources can reach 0.5-8 keV luminosities this high. Finding these systems proves definitively that such objects can exist in an old stellar population without stellar collisions. Three of these objects have highly evolved optical counterparts (giants or horizontal branch stars), as do three other sources whose X-ray luminosities are in the range which includes both quiescent low mass X-ray binaries and the brightest magnetic cataclysmic variables. Large area surveys should also turn up large numbers of quiescent X-ray binaries. (Modified)
We created a sample of nearby QSOs selected from the Hamburg/ESO survey and the Veron-Cetty & Veron catalog, with a limiting redshift of z<0.06, which consists of 63 objects. In this contribution, we present the results of our ISAAC Ks-band spectroscopic and H and Ks-band photometric observations of 9 sources of this sample. In seven sources we find hydrogen recombination lines Paalpha and Brgamma of which five galaxies show a broad component. In three sources, extended molecular hydrogen emission is detected in the 1-0S(1) line. The stellar CO-absorption feature is only detectable in 5 objects, those sources with J-H and H-K colors closest to those of ordinary galaxies.
X-ray emission from the eastern radio lobe of the FRII Radio Galaxy Pictor A was serendipitously discovered by a short observation of XMM-Newton in 2001. The X-ray spectrum, accumulated on a region covering about half of the entire radio lobe, was well described by both a thermal model and a power law, making non-univocal the physical interpretation. A new XMM-Newton observation performed in 2005 has allowed the detection of the X-ray emission from both radio lobes and unambiguously revealed its non-thermal origin. The X-ray emission is due to Inverse Compton (IC) of the cosmic microwave background photons by relativistic electrons in the lobe. We confirm the discrepancy between the magnetic field, as deduced from the comparison of the IC X-ray and radio fluxes, and the equipartition value.
We determine the instantaneous aperture and integrated exposure of the surface detector of the Pierre Auger Observatory, taking into account the trigger efficiency as a function of the energy, arrival direction (with zenith angle lower than 60 degrees) and nature of the primary cosmic-ray. We make use of the so-called Lateral Trigger Probability function (or LTP) associated with an extensive air shower, which summarizes all the relevant information about the physics of the shower, the water tank Cherenkov detector, and the triggers.
The deepest space and ground-based observations find metal-enriched galaxies at cosmic times when the Universe was <1 Gyr old. These stellar populations had to be preceded by the metal-free first stars, Population III. Recent cosmic microwave background polarization measurements indicate that stars started forming early when the Universe was $\lsim200$ Myr old. Theoretically it is now thought that Population III stars were significantly more massive than the present metal-rich stellar populations. While such sources will not be individually detectable by existing or planned telescopes, they would have produced significant cosmic infrared background radiation in the near- infrared, whose fluctuations reflect the conditions in the primordial density field. Here we report a measurement of diffuse flux fluctuations after removing foreground stars and galaxies. The anisotropies exceed the instrument noise and the more local foregrounds and can be attributed to emission from massive Population III stars, providing observational evidence of an era dominated by these objects.
It appears that there is a genuine shortage of radio pulsars with surface magnetic fields significantly smaller than $\sim 10^8$ Gauss. We propose that the pulsars with very low magnetic fields are actually strange stars locked in a state of minimum free energy and therefore at a limiting value of the magnetic field which can not be lowered by the system spontaneously.
Following a brief introduction we show that the observations obtained so far with the Swift satellite begin to shed light over a variety of problems that were left open following the excellent performance and related discoveries of the Italian - Dutch Beppo SAX satellite. The XRT light curves show common characteristics that are reasonably understood within the framework of the fireball model. Unforeseen flares are however detected in a large fraction of the GRB observed and the energy emitted by the brightest ones may be as much as 85% of the total soft X ray emission measured by XRT. These characteristics seems to be common to long and short bursts.
In the introduction we give the main characteristics of the Swift mission outlining how the design was driven by the science goals and by the heritage we got from the Italian - Dutch satellite Beppo SAX. We show some of the new characteristics of the X - ray light curves that became evident soon after we obtained the first set of data. In addition to the early phase steep slope afterglow discovered by Swift, we discuss the frequently observed GRB flares and the first localization of a short burst.
Planetary nebulae (PNe) are known to possess a variety of small-scale structures that are usually in a lower ionization state than the main body of the nebulae. The morphological and kinematic properties of these low-ionization structures (LISs) vary from type to type in the sense that LISs can appear in the form of pairs of knots, filaments, jets, and isolated features moving with velocities that either do not differ substantially from that of the ambient nebula, or instead move supersonically through the environment. The high-velocity jets and pairs of knots, also known as FLIERs, are likely to be shock-excited. So far, most of the FLIERs analyzed with ground-based small and medium telescopes, as well as with the HST, do not show the expected shock-excited features --either the bow-shock geometry or the shock excited emission lines. In this talk we discuss the crucial problem of the excitation mechanisms of FLIERs --through the comparison of jets and knots of NGC 7009 and K 4-47-- and what might be the contribution of large telescopes.
We have discovered new diffuse radio sources likely associated with groups of galaxies at low redshift (0.01-0.04) and without apparent AGN by using the WENSS and WISH catalogs to perform an unbiased survey. These sources resemble the radio halos, mini-halos, and 'relics' of rich clusters, which are thought to be powered by shocks and turbulence from infall into their deep potential wells. Our detection of similar sources within the shallow potential wells of groups of galaxies challenges this model. Their radio luminosities are approximately two orders of magnitude higher than expected from the extrapolation of the apparent rich cluster radio/X-ray luminosity relation. Even if these sources are misidentified distant clusters, they would lie above the apparent rich cluster radio/X-ray luminosity relation in the literature, suggesting that detections of radio halos and relics thus far may be more biased than previously thought.
How well do we know the physical/chemical properties of PNe? 1D (CLOUDY) and
3D (MOCASSIN) photoionisation codes are used in this contribution to model the
PNe K 4-47 and NGC 7009 as an attempt to question whether or not the high Te
(higher than 21,000K) of the K 4-47's core and the N overabundance of the outer
knots in NGC 7009 are real.
These are very basic parameters, obtained for Galactic PNe, e.g. nearby
objects, even though with large uncertainties. Based on the comparison of the
modelling with, mainly, optical images and long-slit spectroscopic data, it is
suggested here that K 4-47 high Te can be explained if its core is composed of
a very dense and small inner region --that matches the radio measurements-- and
a lower density outer core --matching the optical observations. This approach
can account for the strong auroral emission lines [OIII]4363A and [NII]5755A
observed, and so for the high temperatures. This teaches us that the assumption
of a homogeneous distribution of the gas is completely wrong for the core of
such PN.
In the case of NGC 7009 a simple 3D model that reproduces the observed
geometry of this nebula is constructed. The aim of this modelling was to
explore the possibility that the enhanced [NII] emission observed in the outer
knots may be due to ionisation effects instead to a local N overabundance. Here
it is discussed the model that can best reproduce the observations employing a
homogeneous set of abundances throughout the nebula, not only for nitrogen but
also for all the other elements considered.
ASCA X-ray spectra of many ULXs were described in terms of optically thick emission from hot (kT ~1-2keV) accretion disks, while recent XMM-Newton and Chandra observations have revealed a cool (kT ~0.2keV), soft X-ray excess emission from a number of them. Here we utilize improved calibration and high signal-to-noise XMM-Newton spectra of NGC1313 X-1 to present evidence for a cool (~0.2keV) soft excess and a curved or a cutoff power-law (Gamma ~1-1.5, E_cutoff ~3-8keV). The high energy curvature may also be described by a hot (~1-2.5keV) multicolor disk blackbody. The soft excess emission is unlikely to arise from a cool disk as its blackbody temperature is similar in three XMM-Newton observations, despite a change in the observed flux by a factor of about two. Thus, previous estimates of the black hole mass of 1000Msun for NGC1313 X-1 based on the temperature of the soft excess emission is unlikely to be correct. The power-law cutoff energy is found to decrease from ~8keV to \~3keV when the ULX brightened by a factor of about two. The unusual spectral properties of NGC1313 X-1 are difficult to understand in the framework of the disk/corona models generally adopted for the black hole binaries or active galactic nuclei and may require to invoke super-critical accretion rates.
We present an overview of unbiased studies of diffuse extragalactic radio sources. We use a previously developed filtering technique to remove compact sources from large surveys such as WENSS, WISH, and NVSS and examine the residual diffuse emission. A search of these residuals, unbiased by optical or X-ray selection, has uncovered a wide variety of diffuse sources, including those associated with groups of galaxies, "blank" fields, and previously unrecognized diffuse radio galaxy emission, as well as halos and relics of rich clusters. A second, targeted survey of the brightest X-ray clusters results in a number of new sources, and illuminates some important selection effects. When the well-established relationship between X-ray and radio halo luminosities is extrapolated to lower levels, the apparent correlation holds quite well for any type of diffuse source, even background noise. The observed correlations must therefore be scrutinized for possible selection effects before physical interpretations are made. We briefly mention a wide-field mapping project to search for large-scale structures, and goals for the next generation of studies in magnetic field - angular size parameter space.
We have constructed a 3D photoionisation model of a planetary nebula (PN) similar in structure to NGC 7009 with its outer pair of knots (also known as FLIERs --fast, low-ionization emission regions). The work is motivated by the fact that the strong [N II]6583A line emission from FLIERs in many planetary nebulae has been attributed to a significant local overabundance of nitrogen. We explore the possibility that the apparent enhanced nitrogen abundance previously reported in the FLIERs may be due to ionization effects. Our model is indeed able to reproduce the main spectroscopic and imaging characteristics of NGC 7009's bright inner rim and its outer pairs of knots, assuming homogeneous elemental abundances throughout the nebula, for nitrogen as well as all the other elements included in the model. Because of the fact that the (N+/N)/(O+/O) ratio predicted by our models are 0.60 for the rim and 0.72 for the knots, so clearly in disagreement with the N+/N=O+/O assumption of the ionization correction factors method (icf), the icfs will be underestimated by the empirical scheme, in both components, rim and knots, but more so in the knots. This effect is partly responsible for the apparent inhomogeneous N abundance empirically derived. The differences in the above ratio in these two components of the nebula may be due to a number of effects including charge exchange --as pointed out previously by other authors-- and the difference in the ionization potentials of the relevant species --which makes this ratio extremely sensitive to the shape of the local radiation field. Because of the latter, a realistic density distribution is essential to the modelling of a non-spherical object, if useful information is to be extracted from spatially resolved observations, as in the case of NGC 7009.
The discovery of the X-ray source IGR J17252-3616 by INTEGRAL was reported on
9 February 2004. Regular monitoring by INTEGRAL shows that IGR J17252-3616 is a
persistent hard X-ray source with an average count rate of 0.96 counts/s (~6.4
mCrab) in the 20-60 keV energy band. A follow-up observation with XMM-Newton,
which was performed on 21 March 21 2004, showed that the source is located at
R.A.(2000.0)=17h25m11.4 and Dec.=-36degr16'58.6" with an uncertainty of 4". The
only infra-red counterpart to be found within the XMM-Newton error circle was
2MASS J17251139-3616575, which has a Ks-band magnitude of 10.7 and is located
1" away from the XMM-Newton position.
The analysis of the combined INTEGRAL and XMM-Newton observations shows that
the source is a binary X-ray pulsar with a spin period of 413.7 s and an
orbital period of 9.72 days. The spectrum can be fitted with a flat power law
plus an energy cut off (Gamma~0.02,Ecut~8.2 keV) or a Comptonized model
(kTe~5.5 keV, tau~7.8). The spectrum also indicates a large hydrogen column
density of Nh~15x1e22 atoms/cm-2 suggesting an intrinsic absorption. The Fe
Kalpha line at 6.4 keV is clearly detected. Phase-resolved spectroscopy does
not show any variation in the continuum except the total emitted flux. The
absorption is constant along the pulse phase. This source can be associated
with EXO 1722-363 as both systems show common timing and spectral features. The
observations suggest that the source is a wind-fed accreting pulsar accompanied
by a supergiant star.