arXiv.org > astro-ph

Astrophysics

astro-ph new abstracts, Fri, 20 Jan 06 01:00:08 GMT
0601400 -- 0601453 received

astro-ph/0601400 [abs, ps, pdf, other] :

Title: Red Mergers and the Assembly of Massive Elliptical Galaxies: the Fundamental Plane and its Projections
Authors: Michael Boylan-Kolchin, Chung-Pei Ma, Eliot Quataert (UC Berkeley)
Comments: 9 pages, 4 figures; submitted to MNRAS

Several recent observations suggest that gas-poor (dissipationless) mergers of elliptical galaxies build up the massive end of the red sequence. We perform a series of major merger simulations to investigate the spatial and velocity structure of the remnants of such mergers. Regardless of orbital energy or angular momentum, we find that the stellar remnants lie on the fundamental plane defined by their progenitors, a result of virial equilibrium with a small tilt due to an increasing central dark matter fraction. However, the locations of merger remnants in the projections of the fundamental plane -- the Faber-Jackson and R_e-M_* relations -- depend strongly on the merger orbit, and the relations steepen significantly from the canonical scalings (L~sigma^4 and R_e~M_*^0.6) for mergers on radial orbits. Our results imply that the projections of the fundamental plane -- but not necessarily the plane itself -- provide a powerful way of investigating the assembly history of massive elliptical galaxies, including the brightest cluster galaxies at or near the centers of galaxy clusters. We argue that most massive ellipticals are formed by anisotropic merging during cluster formation and that their fundamental plane projections should thus differ noticeably from those of lower mass ellipticals even though they should lie on the same fundamental plane. Current observations are consistent with this conclusion. The steepening in the L-sigma relation for luminous ellipticals may also be reflected in a corresponding steepening in the M_BH-sigma relation for massive black holes.

 

astro-ph/0601401 [abs, ps, pdf, other] :

Title: Fossils of Reionization in the Local Group
Authors: Nickolay Y. Gnedin (1,2), Andrey V. Kravtsov (2,3) (1 - Fermilab, 2 - U.Chicago, 3 - KICP)
Comments: 8 pages, 9 figures; submitted to ApJ

We use a combination of high-resolution gasdynamics simulations of high-redshift dwarf galaxies and dissipationless simulations of a Milky Way sized halo to estimate the expected abundance and spatial distribution of the dwarf satellite galaxies that formed most of their stars around z~8 and evolved only little since then. Such galaxies can be considered as fossils of the reionization era, and studying their properties could provide a direct window into the early, pre-reionization stages of galaxy formation. We show that 5-15% of the objects existing at z~8 do indeed survive until the present in the MW like environment without significant evolution. This implies that it is plausible that the fossil dwarf galaxies do exist in the Local Group. Because such galaxies form their stellar systems early during the period of active merging and accretion, they should have spheroidal morphology regardless of their current distance from the host galaxy. We show that both the expected luminosity function and spatial distribution of dark matter halos which are likely to host fossil galaxies agree reasonably well with the observed distributions of the luminous (L_V>10^6 Lsun) Local Group fossil candidates near the host galaxy (d<200 kpc). However, the predicted abundance is substantially larger (by a factor of 2-3) for fainter galaxies (L_V<10^6 Lsun) at larger distances (d>300 kpc). We discuss several possible explanations for this discrepancy.

 

astro-ph/0601402 [abs, ps, pdf, other] :

Title: On the baryon mass function for galaxy clusters
Authors: S. E. Nuza (IAFE), A. Blanchard (LATT)
Comments: 5 pages, A&A accepted

The evolution of the cluster abundance with redshift is known to be a powerful cosmological constrain when applied to X-ray clusters. Recently, the use of the evolution of the baryon mass function has been proposed as a new variant that is free of the uncertainties present in the Temperature-Mass relation. A flat model with Omega_matter ~ 0.3 was shown to be preferred in the case of a standard cold dark matter scenario. We have compared the high redshift predictions of the baryon mass in clusters for a more general class of spectra having a varying shape factor Gamma in models normalized to reproduce the local baryon mass function. We have found that models with Omega_matter ~ 1 and Gamma ~ 0.12 reproduce high redshift cluster data equally well as the concordance model and we conclude that the baryon mass function evolution on its own is not an efficiently discriminant among the more general family of flat cosmological models with non-standard power spectra.

 

astro-ph/0601403 [abs, ps, pdf, other] :

Title: The Fundamental Plane for z=0.8-0.9 cluster galaxies
Authors: Inger Jorgensen (1), Kristin Chiboucas (1), Kathleen Flint (1 and 2), Marcel Bergmann (1), Jordi Barr (3), Roger Davies (3) ((1) Gemini Observatory, (2) University of Oxford UK, (3) State University of New York at Stony Brook)
Comments: 4 pages, 2 color figures, emulateapj. Accepted for publication in Astrophysical Journal Letters

We present the Fundamental Plane (FP) for 38 early-type galaxies in the two rich galaxy clusters RXJ0152.7-1357 (z=0.83) and RXJ1226.9+3332 (z=0.89), reaching a limiting magnitude of M_B =-19.8 mag in the rest frame of the clusters. While the zero point offset of the FP for these high redshift clusters relative to our low redshift sample is consistent with passive evolution with a formation redshift of z_form ~ 3.2, the FP for the high redshift clusters is not only shifted as expected for a mass-independent z_form, but rotated relative to the low redshift sample. Expressed as a relation between the galaxy masses and the mass-to-light ratios the FP is significantly steeper for the high redshift clusters than found at low redshift. We interpret this as a mass dependency of the star formation history, as has been suggested by other recent studies. The low mass galaxies (10^10.3 M_sun) have experienced star formation as recently as z ~ 1.35 (1.5 Gyr prior to their look back time), while galaxies with masses larger than 10^11.3 M_sun had their last major star formation episode at z > 4.5.

 

astro-ph/0601404 [abs, ps, pdf, other] :

Title: Does the Fornax dwarf spheroidal have a central cusp or core?
Authors: Tobias Goerdt (1), Ben Moore (1), J. I. Read (1), Joachim Stadel (1), Marcel Zemp (1,2), ((1) University of Zürich, (2) ETH Zürich)
Comments: 6 pages, 5 figures, submitted to MNRAS

The dark matter dominated Fornax dwarf spheroidal has five globular clusters orbiting at several hundred parsecs from its centre. In a cuspy CDM halo the globulars would sink to the centre from their current positions within half a billion years. We show that this timing problem is even more severe when interactions between the globular clusters are taken into account. Even when two globulars start at initially very similar radii (within ~100pc of each other), but quite different orientations, the globulars arrive at one certain radius at very different times (separated by ~1Gyr). We show that a solution to these timing problems is to adopt a cored dark matter halo. We use numerical simulations and analytic calculations to show that, under these conditions, the sinking time becomes many Hubble times; the globulars effectively stall at the dark matter core radius. We conclude that the Fornax dwarf spheroidal has a shallow inner density profile with a core radius defined by the observed positions of its globular clusters. If the phase space density of the core is primordial then it implies a warm dark matter particle with mass ~0.5keV, consistent with that required to significantly alleviate the substructure problem.

 

astro-ph/0601405 [abs, ps, pdf, other] :

Title: Chandra Study of the Cepheus B Star Forming Region: Stellar Populations and the Initial Mass Function
Authors: Konstantin V. Getman, Eric D. Feigelson, Leisa Townsley, Patrick Broos, Gordon Garmire, Masahiro Tsujimoto
Comments: 72 pages, 31 figures, 8 tables. Accepted for publication in ApJ

Cepheus B (Cep B) molecular cloud and a portion of the nearby Cep OB3b OB association, one of the most active regions of star formation within 1 kpc, has been observed with the ACIS detector on board the Chandra X-ray Observatory. We detect 431 X-ray sources, of which 89% are confidently identified as clustered pre-main sequence stars. Two main results are obtained. First, we provide the best census to date for the stellar population of the region. We identify many members of two rich stellar clusters: the lightly obscured Cep OB3b association, and the deeply embedded cluster in Cep B whose existence was previously traced only by a handful of radio sources and T Tauri stars. Second, we find a discrepancy between the X-ray Luminosity Functions of the Cep OB3b and the Orion Nebula Cluster. This may be due to different Initial Mass Functions of two regions (excess of ~0.3 solar mass stars), or different age distributions. Several other results are obtained. A diffuse X-ray component seen in the field is attributed to the integrated emission of unresolved low mass PMS stars. The X-ray emission from HD 217086 (O7n), the principle ionizing source of the region, follows the standard model involving many small shocks in an unmagnetized radiatively accelerated wind. The X-ray source #294 joins a number of similar superflare PMS stars where long magnetic structures may connect the protoplanetary disk to the stellar surface.

 

astro-ph/0601406 [abs, ps, pdf, other] :

Title: Radiation Transport Around Kerr Black Holes
Authors: Jeremy D. Schnittman
Comments: PhD thesis in astrophysics from MIT; submitted on the occasion of the first anniversary of my defense. 212 pp, 53 figs, 8 tables, uses mitthesis.cls. For full-resolution version, see this http URL

This Thesis describes the basic framework and applications of a relativistic ray-tracing code for analyzing accretion processes around Kerr black holes. We begin in Chapter 1 with a brief historical summary of the major advances in black hole astrophysics over the past few decades. In Chapter 2 we present a detailed description of the ray-tracing code, which is used to calculate the transfer function between the accretion disk and the detector. In Chapter 3, we employ a simple ``hot spot'' model to explain the frequencies and amplitudes of quasi-periodic oscillations (QPOs). In Chapter 4, we introduce additional features to the hot spot model to explain the broadening of the QPO peaks as well as the damping of higher-frequency harmonics in the power spectrum. In Chapter 5 we present a description of the structure of a relativistic alpha-disk around a Kerr black hole, and the observed spectrum from such a disk. The features of this modified thermal spectrum may be used to infer the physical properties of the accretion disk and the central black hole. In Chapter 6 we develop a Monte Carlo code to calculate the detailed propagation of photons from a hot spot emitter scattering through a corona surrounding the black hole. The coronal scattering has two major observable effects: the inverse-Compton process alters the photon spectrum by adding a high energy power-law tail, and the random scattering of each photon effectively damps out the highest frequency modulations in the X-ray light curve.

 

astro-ph/0601407 [abs, ps, pdf, other] :

Title: The environmental dependence of galaxy clustering in the Sloan Digital Sky Survey
Authors: Ummi Abbas (1), Ravi K. Sheth (2) ((1) U. Pittsburgh, (2) U. Pennsylvania)
Comments: 6 pages, 3 figures, MNRAS submitted

A generic prediction of hierarchical clustering models is that the mass function of dark haloes in dense regions in the Universe should be top-heavy. We provide a novel test of this prediction using a sample of galaxies drawn from the Sloan Digital Sky Survey. To perform the test, we compare measurements of galaxy clustering in dense and underdense regions. We find that galaxies in dense regions cluster significantly more strongly than those in less dense regions. This is true over the entire 0.1--30 Mpc pair separation range for which we can make accurate measurements. We make similar measurements in realistic mock catalogs in which the only environmental effects are those which arise from the predicted correlation between halo mass and environment. We also provide an analytic halo-model based calculation of the effect. Both the mock catalogs and the analytic calculation provide rather good descriptions of the SDSS measurements. Thus, our results provide strong support for hierarchical models. They suggest that, unless care is taken to study galaxies at fixed mass, correlations between galaxy properties and the surrounding environment are almost entirely due to more fundamental correlations between galaxy properties and host halo mass, and between halo mass and environment.

 

astro-ph/0601408 [abs, ps, pdf, other] :

Title: A Spitzer View of Massive Galaxies at z~1-3
Authors: Casey Papovich (1), GOODS, MIPS GTO teams ((1) Steward Observatory)
Comments: To appear in the Proceedings of the 2005 Lijiang Conference "Extreme Starbursts: Near and Far", editors: Yu Gao & D. B. Sanders, to be published in a special issue of Pub. of PMO. 8 pgs, some color figures. Uses ppmo.cls (included)

I discuss constraints on star--formation and AGN activity in massive galaxies at z~1-3 using observations from the Spitzer Space Telescope. In particular I focus on a sample of distant red galaxies (DRGs) with J-K>2.3 in GOODS-S. Based on their ACS, ISAAC, and IRAC photometry, the DRGs have typical stellar masses >10^11 Msol. Interestingly, the majority (>50%) of these objects have 24 micron detections. If attributed to star formation, this implies SFRs of ~100-1000 Msol/yr. Thus, massive galaxies at z~1.5-3 have specific SFRs equal to or exceeding the global average value at that epoch. In contrast, galaxies with >10^11 Msol at z~0.3-0.75 have specific SFRs less than the global average, and more than an order of magnitude lower than that at z~1.5-3. Thus, the bulk of assembly of massive galaxies is largely complete by z~1.5. At the same time, based on the X-ray luminosities and near-IR colors, as many as 25% of the massive galaxies at z>1.5 host AGN, implying that the growth of supermassive black holes coincides with massive-galaxy assembly. The analysis of high-redshift galaxies depends on bolometric corrections between the observed 24 micron data and total IR luminosity. I review some of the sources of the (significant) uncertainties on these corrections, and discuss improvements for the future.

 

astro-ph/0601409 [abs, ps, pdf, other] :

Title: The Inclination Angle of and Mass of the Black Hole in XTE J1118+480
Authors: Dawn M. Gelino (MSC/Caltech), Solen Balman, Umit Kizilouglu, Arda Yilmaz (Middle East Technical University), Emrah Kalemci (Sabanci University), John A. Tomsick (CASS/UCSD)
Comments: 6 pages, 3 figures, To appear in ApJ 01 May 2006 issue

We have obtained optical and infrared photometry of the quiescent soft X-ray transient XTE J1118+480. In addition to optical and J-band variations, we present the first observed H- and K_s-band ellipsoidal variations for this system. We model the variations in all bands simultaneously with the WD98 light curve modeling code. The infrared colors of the secondary star in this system are consistent with a K7V, while there is evidence for light from the accretion disk in the optical. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 68 +/- 2 deg. This inclination angle corresponds to a primary black hole mass of 8.53 +/- 0.60 M_sun. Based on the derived physical parameters and infrared colors of the system, we determine a distance of 1.72 +/- 0.10 kpc to XTE J1118+480.

 

astro-ph/0601410 [abs, ps, pdf, other] :

Title: General Relativistic Force-Free Electrodynamics: A New Code and Applications to Black Hole Magnetospheres
Authors: Jonathan C. McKinney (Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics)
Comments: 14 pages, 4 figures, accepted for publication in MNRAS Main Journal

The force-free limit of magnetohydrodynamics (MHD) is often a reasonable approximation to model black hole and neutron star magnetospheres. We describe a general relativistic force-free (GRFFE) formulation that allows general relativistic magnetohydrodynamic (GRMHD) codes to directly evolve the GRFFE equations of motion. Established, accurate, and well-tested conservative GRMHD codes can simply add a new inversion piece of code to their existing code, while continuing to use all the already-developed facilities present in their GRMHD code. We show how to enforce the $\mathbf{E}\cdot\mathbf{B}=0$ constraint and energy conservation, and we introduce a simplified general model of the dissipation of the electric field to enforce the $B^2-E^2>0$ constraint. We also introduce a simplified yet general method to resolve current sheets, without much reconnection, over many dynamical times. This formulation is incorporated into an existing GRMHD code (HARM), which is demonstrated to give accurate and robust GRFFE results for Minkowski and black hole space-times.

 

astro-ph/0601411 [abs, ps, pdf, other] :

Title: Relativistic Force-Free Electrodynamic Simulations of Neutron Star Magnetospheres
Authors: Jonathan C. McKinney (Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics)
Comments: 5 pages, 5 figures, accepted for publication in MNRAS LETTERS

The luminosity and structure of neutron star magnetospheres are crucial to our understanding of pulsar and plerion emission. A solution found using the force-free approximation would be an interesting standard with which any model with more physics could be compared. Prior quasi-analytic force-free solutions may not be stable, while prior time-dependent magnetohydrodynamic models used unphysical model parameters. We use a time-dependent relativistic force-free electrodynamics code with no free parameters to find a unique stationary solution for the axisymmetric rotating pulsar magnetosphere in a Minkowski space-time in the case of no surface currents on the star. The solution is similar to the force-free quasi-analytic solution of \citet{cont99} and the numerical magnetohydrodynamic solution of \citet{kom05}. The magnetosphere structure and the usefulness of the classical y-point in the general dissipative regime are discussed. The pulsar luminosity is found to be $L \approx 0.99\pm 0.01 \mu^2\Omega_\star^4/c^3$ for a dipole moment $\mu$ and stellar angular frequency $\Omega_\star$.

 

astro-ph/0601412 [abs, ps, pdf, other] :

Title: Sersic Properties of Disc Galaxy Mergers
Authors: H. Aceves, H. Velazquez, F. Cruz
Comments: 10 pages, 10 figures, submitted to MNRAS

Sersic parameters characterising the density profiles of remnants formed in collision-less disc galaxy mergers are obtained; no bulge is included in our simulations. For the luminous component we find that the Sersic index is n ~ (1.5,5.3) with <n> ~ 3 +/- 1 and an effective radius of R_e ~ (1.6,12.9) kpc with <R_e> ~ 5 +/- 3 kpc. A strong correlation of n with the central projected density I_0 is found [n ~ I_0^(-0.14)] which is consistent with observations. No positive linear correlation between the size (R_e) and structure (n) of our remnants is found; we do not advocate the existence of this. The photometric plane (PHP) of the luminous component [n ~ R_e^(0.05) I_0^(0.15)] agrees well, within the uncertainties and the assumption of a constant mass-to-light ratio, with those observationally determined for ellipticals. We found that the surface defined by Sersic parameters (n, R_e, mu_0) in log-space is not a true plane, but a pseudo-plane with a small curvature at low values of n owed to intrinsic properties of the Sersic model. The dark haloes of the remnants have a 3-dimensional Sersic index of <n> ~ 4 +/- 0.5 that are smaller than the ones obtained for dark haloes in LCDM cosmologies <n> ~ 6 +/- 1. A tight dark Sersic ``plane'' (DSP) is also defined by the parameters of the remnants haloes with n \~ r_e^(0.07) rho_0^(0.10). We conclude that collision-less merger remnants of pure disc galaxies have Sersic properties and correlations consistent with those of observed in early-type galaxies and local remnants. It seems that a ``primordial'' bulge in spirals is not a necessary condition to form bona fide ellipticals on grounds of the Sersic properties of remnants.

 

astro-ph/0601413 [abs, ps, pdf, other] :

Title: Spitzer Observations of Centaurus A: Synchrotron Emission in the Infrared
Authors: M. H. Brookes, C. R. Lawrence, D. Stern, V. Gorijan, M. Werner, V. Charmandaris
Comments: 5 pages, submitted to ApJL

We present measurements obtained with the Spitzer Space Telescope in five bands from 3.6-24microns of the northern inner radio lobe of Centaurus A, the nearest powerful radio galaxy. We show that this emission is synchrotron in origin. Comparison with ultraviolet observations from GALEX shows that diffuse ultraviolet emission exists in a smaller region than the infrared but also coinciding with the radio jet. It is plausible that synchrotron emission extends to ultraviolet wavelengths without a break, however further data are required to confirm this.

 

astro-ph/0601414 [abs, ps, pdf, other] :

Title: Exploring the surface properties of Transneptunian Objects and Centaurs with polarimetric FORS1/VLT observations
Authors: S. Bagnulo, H. Boehnhardt, K. Muinonen, L. Kolokolova, I. Belskaya, M.A. Barucci
Comments: 11 pages, 7 postscript figures, accepted by A&A

Polarization is a powerful remote-sensing method to investigate solar system bodies. It is an especially sensitive diagnostic tool to reveal physical properties of the bodies whose observational characteristics are governed by small scatterers (dust, regolith surfaces). For these objects, at small phase angles, a negative polarization is observed, i.e., the electric vector E oscillates predominantly in the scattering plane, contrary to what is typical for rather smooth homogeneous surfaces. The behavior of negative polarization with phase angle depends on the size, composition and packing of the scatterers. These characteristics can be unveiled by modelling the light scattering by the dust or regolith in terms of the coherent backscattering mechanism.

 

astro-ph/0601415 [abs, ps, pdf, other] :

Title: Light Element Production in the Circumstellar Matter of Energetic Type Ic Supernovae
Authors: Ko Nakamura, Susumu Inoue, Shinya Wanajo, Toshikazu Shigeyama
Comments: 11 pages, 2figures, ApJ submitted

We investigate energetic type Ic supernovae as production sites for $^6$Li and Be in the early stages of the Milky Way. Recent observations have revealed that some very metal-poor stars with [Fe/H]$<-2.5$ possess unexpectedly high abundances of $^6$Li, and a couple of them also exhibit enhanced abundances of Be as well as N. From a theoretical point of view, recent studies of the evolution of metal-poor massive stars show that rotation-induced mixing can enrich the outer H and He layers with C, N, and O (CNO) elements, particularly N, and at the same time cause intense mass loss of these layers. Here we consider energetic supernova explosions occurring after the progeniter star has lost all but a small fraction of the He layer. The fastest portion of the supernova ejecta can interact directly with the circumstellar matter (CSM), both composed of He and CNO, and induce light element production through spallation and He-He fusion reactions. We calculate the resulting $^6$Li/O and $^9$Be/O ratios in the ejecta$+$CSM material out of which the very metal-poor stars may form, and find that they are consistent with the observed values if the mass of the He layer remaining on the pre-explosion core is $\sim 0.01-0.1 \Msun$, and the mass fraction of N mixed in the He layer is $\sim 0.01$. Further observations of $^6$Li, Be and N at low metallicity should provide critical tests of this production scenario.

 

astro-ph/0601416 [abs, ps, pdf, other] :

Title: Rotating compact star with superconducting quark matter
Authors: P. K. Panda, H. S. Nataraj
Comments: 11 pages, 5 figures

A compact star with superconducting quark core, the hadron crust and the mixed phase between the two is considered. The quark meson coupling model for hadron matter and the color flavor locked quark model for quark matter is used in order to construct the equation of state for the compact star. The effect of pairing of quarks in the color flavor locked phase and the mixed phase on the mass, radius, and period of the rotating star is studied.

 

astro-ph/0601417 [abs, ps, pdf, other] :

Title: SINFONI's take on Star Formation, Molecular Gas, and Black Hole Masses in AGN
Authors: R. Davies, R. Genzel, L. Tacconi, F. Muller Sanchez, J. Thomas, S. Friedrich
Comments: 5 pages, 2 figures. To appear in Science Perspectives for 3D Spectroscopy. ESO Astrophysics Symposia. Ed by M. Kissler-Patig, M. Roth and J. Walsh

We present some preliminary (half-way) results on our adaptive optics spectroscopic survey of AGN at spatial scales down to 0.085arcsec. Most of the data were obtained with SINFONI which provides integral field capability at a spectral resolution of R~4000. The themes on which we focus in this contribution are: star formation around the AGN, the properties of the molecular gas and its relation to the torus, and the mass of the black hole.

 

astro-ph/0601418 [abs, ps, pdf, other] :

Title: Analysis of the circumstellar environment of the B[e] star HD 45677 (FS CMa)
Authors: Gérard Muratorio (LAM), Corinne Rossi (DF), Michael Friedjung (IAP)
Comments: 14 pages, submitted to Astronomy and Astrophysics

We studied the circumstellar environment of the B[e] star HD 45677 through the analysis of the emission lines from ionized metals. We used the statistical approach of the self absorption curve method (SAC) to derive physical parameters of the line emitting region. The Fe II and Cr II double-peaked emission line structure is explained by the presence of a thin absorption component red shifted by ~3 km/s. This absorption component can be interpreted geometricaly as being due to infalling material perpendicularly to the disk seen nearly pole-on, as indicated by the emission line structure. The Cr II and Fe II emission lines have a complex structure with two (narrow and broad) components, of 45 and 180 km/s FWHM for the permitted lines and 25 and 100 km/s FWHM for the forbidden ones, respectively. We argue that the narrow components are principaly emitted by an optically thin disk seen nearly pole-on, in a region whose minimum radius is estimated to be 4 10^12 cm, while the broad ones are formed in a disk-linked wind.

 

astro-ph/0601419 [abs, ps, pdf, other] :

Title: Discovery of two new methanol masers in NGC 7538
Authors: M. Pestalozzi, V. Minier, F. Motte, J. Conway
Comments: Accepted for publication in A&A. Figure 1 is available at this http URL (eps file, 3.6MB)

Context: NGC7538 is known to host a 6.7 and 12.2GHz methanol maser cospatial with a Ultra Compact (UC) HII region, IRS1.
Aims: We report on the serendipitous discovery of two additional 6.7GHz methanol masers in the same region, not associated with IRS1.
Methods: Interferometry maser positions are compared with recent single-dish and interferometry continuum observations.
Results: The positions of the masers agree to high accuracy with the 1.2mm continuum peak emission in NGC7538 IRS9 and NGC7538 S. This clear association is also confirmed by the positional agreement of the masers with existing high resolution continuum observations at cm and/or mm wavelengths.
Conclusions: Making use of the established strong relation between methanol masers and high-mass star formation, we claim that we have accurately positioned the high-mass protostars within the regions where they are detected. The variety of objects hosting a 6.7GHz methanol maser in NGC7538 shows that this emission probably traces different evolutionary stages within the protostellar phase.

 

astro-ph/0601420 [abs, ps, pdf, other] :

Title: Motion toward the Great Attractor from an ether-drift experiment
Authors: M. Consoli, E. Costanzo, V. Palmisano
Comments: 12 pages, plain Latex

Since the end of 80's, the region of sky of galactic coordinates (l\sim 309^o, b\sim 18^o), corresponding to a declination \gamma\sim -44^o and right ascension \alpha\sim 202^o, usually denoted as the "Great Attractor", is known to control the overall galaxy flow in our local Universe. In this sense, this direction might represent a natural candidate to characterize a hypothetical Earth's "absolute motion". Our analysis of the extensive ether-drift observations recently reported by an experimental group in Berlin provides values of \alpha and \gamma that coincide almost exactly with those of the Great Attractor and not with the values \gamma\sim -6^o and \alpha\sim 168^o obtained from a dipole fit to the anisotropy of the CMB. This supports in a new fashion the existence of a discrepancy between the observed motion of the Local Group and the direction obtained from the CMB dipole.

 

astro-ph/0601421 [abs, ps, pdf, other] :

Title: The infrared jet in Centaurus A: multiwavelength constraints on emission mechanisms and particle acceleration
Authors: M. J. Hardcastle, R. P. Kraft, D. M. Worrall
Comments: Accepted by MN letters. 5 pages, 4 colour figures. Some figures reduced in quality

We report on Spitzer and Gemini observations of the jet of Centaurus A in the infrared, which we combine with radio, ultraviolet and X-ray data. Spitzer detects jet emission from about 2 arcmin from the nucleus, becoming particularly bright after the jet flare point at ~3.4 arcmin. Where X-ray and infrared emission are seen together the broad-band data strongly support a synchrotron origin for the X-rays. The jet flare point is marked by a broad, diffuse region of X-rays which may be associated with a shock: we discuss possible physical mechanisms for this. The infrared jet persists after the flare point region although X-ray emission is absent; it is plausible that here we are seeing the effects of particle acceleration followed by downstream advection with synchrotron losses. Gemini data probe the inner regions of the jet, putting limits on the mid-infrared flux of jet knots.

 

astro-ph/0601422 [abs, ps, pdf, other] :

Title: Upper limits on density of dark matter in Solar system
Authors: I.B. Khriplovich, E.V. Pitjeva
Comments: 4 pages

The analysis of the observational data for the secular perihelion precession of Mercury, Earth, and Mars, based on the EPM2004 ephemerides, results in new upper limits on density of dark matter in the Solar system.

 

astro-ph/0601423 [abs, ps, pdf, other] :

Title: Two-dimensional spectroscopy of a sunspot. III Thermal and kinematic structure of the penumbra at 0.5"
Authors: L. R. Bellot Rubio, R. Schlichenmaier, A. Tritschler
Comments: 15 pages with 18 Postscript figures. Submitted to Astronomy and Astrophysics (December 2005)

We investigate the thermal and kinematic configuration of a sunspot penumbra using very high spectral and spatial resolution intensity profiles of the non-magnetic Fe I 557.6 nm line. The dataset was acquired with the 2D solar spectrometer TESOS. The profiles are inverted using a one-component model atmosphere with gradients of the physical quantities. From this inversion we obtain the stratification with depth of temperature, line-of-sight velocity, and microturbulence across the penumbra. Our results suggest that the physical mechanism(s) responsible for the penumbral filaments operate preferentially in the lower photosphere. We confirm the existence of a thermal asymmetry between the center and limb-side penumbra, the former being hotter by 100-150 K on average. We also investigate the nature of the bright ring that appears in the inner penumbra when sunspots are observed in the wing of spectral lines. The line-of-sight velocities retrieved from the inversion are used to determine the flow speed and flow angle at different heights in the photosphere. Both the flow speed and flow angle increase with optical depth and radial distance. Downflows are detected in the mid and outer penumbra, but only in deep layers (log tau_{500} < -1.4). We demonstrate that the velocity stratifications retrieved from the inversion are consistent with the idea of penumbral flux tubes channeling the Evershed flow. Finally, we show that larger Evershed flows are associated with brighter continuum intensities in the inner center-side penumbra. Dark structures, however, are also associated with significant Evershed flows. This leads us to suggest that the bright and dark filaments seen at 0.5" resolution are not individual flow channels, but a collection of them.

 

astro-ph/0601424 [abs, ps, pdf, other] :

Title: The Contribution of the Intergalactic Medium to Cosmic Microwave Background Anisotropies
Authors: F. Atrio-Barandela, J.P. Muecket
Comments: 22 pages, 7 figures, accepted for publication in the Astrophysical Journal

We compute the power spectrum of the Cosmic Microwave Background temperature anisotropies generated by the Intergalactic Medium. To estimate the electron pressure along the line of sight and its contribution to the Sunyaev-Zeldovich component of the CMB anisotropies, we assume the non-linear baryonic density contrast is well described by a log-normal distribution. For model parameters in agreement with observations and for an experiment operating in the Rayleigh-Jeans regime, the largest IGM contribution is expected at scales corresponding to multipole numbers of about 2000. The amplitude is rather uncertain and could be as large as 100-200 [mikroK]^2, comparable to the contribution of galaxy clusters. The actual value is strongly dependent on the gas polytropic index and the amplitude of the matter power spectrum sigma_8. At all redshifts, the largest contribution comes from scales very close to the comoving baryon Jeans length. This scale is not yet resolved in numerical simulations that follow the evolution of gas on cosmological scales. The anisotropy generated by the Intergalactic Medium could make compatible the excess of power measured by Cosmic Background Imager (CBI) on scales of l > 2000 with sigma_8=0.9. Taking the CBI result as an upper limit, the polytropic index can be constrained to < 1.5 at 2-sigma level at redshifts z ~ 0.1-0.4. With its large frequency coverage, the PLANCK satellite will be able to measure the secondary anisotropies coming from hot gas. Cluster and Intergalactic Medium contributions could be separated by cross correlating galaxy/cluster catalogs with CMB maps. This measurement will determine the state of the gas at low and intermediate redshifts.

 

astro-ph/0601425 [abs, ps, pdf, other] :

Title: On the Origin of the High Helium Sequence in $\omega$ Centauri
Authors: André Maeder, Georges Meynet
Comments: 5 pages, 3 figures, accepted for publication in A&A

The blue Main Sequence (bMS) of $\omega$ Cen implies a ratio of helium to metal enrichment $\Delta Y/\Delta Z \approx 70$, which is a major enigma.
We show that rotating models of low metallicity stars, which account for the anomalous abundance ratios of extremely metal poor stars, are also useful for understanding the very high $\Delta Y/\Delta Z$ ratio in $\omega$ Cen. Models of massive stars with moderate initial rotation velocities produce stellar winds with large He-- and N--excesses, but without the large C-- (and O--) excesses made by very fast rotation, in agreement with the observed chemical abundance ratios in $\omega$ Cen. It is still uncertain whether the abundance peculiarities of $\omega$ Cen result from the fact that the high velocity contributions of supernovae escaped the globular cluster, usually considered as a tidally stripped core of a dwarf galaxy. Another possibility is a general dominance of wind ejecta at very low $Z$, due to the formation of black holes. Some abundance and isotopic ratios like $Mg/Al$, $Na/Mg$, $Ne/N$, $^{12}C/^{13}C$, $^{16}O/^{18}O$ and $^{17}O/^{18}O$ may allow us to further discriminate between these scenarios and between the AGB and massive star contributions.

 

astro-ph/0601426 [abs, ps, pdf, other] :

Title: Comment on "PIC simulations of circularly polarised Alfv\'en wave phase mixing: A new mechanism for electron acceleration in collisionless plasmas" by Tsiklauri et al
Authors: Fabrice Mottez (LUTH), Vincent Génot (CESR), Philippe Louarn (CESR)
Comments: 2 pages. Accepted at "Astronomy and Astrophysics"

Tsiklauri et al. recently published a theoretical model of electron acceleration by Alfv\'en waves in a nonuniform collisionless plasmas. We compare their work with a series of results published earlier by an another team, of which Tsiklauri et al. were probably unaware. We show that these two series of works, apparently conducted independently, lead to the same conclusions. This reinforces the theoretical consistency of the model.

 

astro-ph/0601427 [abs, ps, pdf, other] :

Title: The non-Gaussian Cold Spot in WMAP: significance, morphology and foreground contribution
Authors: M. Cruz, M. Tucci, E. Martinez-Gonzalez, P. Vielva
Comments: 11 pages, 8 figures, submitted to MNRAS

The non--Gaussian cold spot in the 1-year WMAP data, described in Vielva et al. and Cruz et al., is analysed in detail in the present paper. First of all, we perform a more rigorous calculation of the significance of the non-zero kurtosis detected in WMAP maps by Vielva et al. in wavelet space, mainly generated by the Spot. We confirm the robustness of that detection, since the probability of obtaining this deviation by chance is 0.69%. Afterwards, the morphology of the Spot is studied by applying Spherical Mexican Hat Wavelets with different ellipticities. The shape of the Spot is found to be almost circular. Finally, we discuss if the observed non-Gaussianity in wavelet space can arise from bad subtracted foreground residues in the WMAP maps. We show that the flat frequency dependence of the Spot cannot be explained by a thermal Sunyaev-Zeldovich effect. Based on our present knowledge of Galactic foreground emissions, we conclude that the significance of our detection is not affected by Galactic residues in the region of the Spot. Considering different Galactic foreground estimates, we always obtain an upper tail probability below 1% for the size of the Spot compared to the simulations.

 

astro-ph/0601428 [abs, ps, pdf, other] :

Title: Deuterium at High Redshifts: Recent Advances and Open Issues
Authors: Max Pettini (Institute of Astronomy, University of Cambridge)
Comments: 12 pages, to appear in `Astrophysics in the Far Ultraviolet', eds. G. Sonneborn, H. W. Moos, and B-G Andersson, ASP Conf. Series No.348

Among the light elements created in the Big Bang, deuterium is one of the most difficult to detect but is also the one whose abundance depends most sensitively on the density of baryons. Thus, although we still have only a few positive identifications of D at high redshifts--when the D/H ratio was close to its primordial value--they give us the most reliable determination of the baryon density, in excellent agreement with measures obtained from entirely different probes, such as the anisotropy of the cosmic microwave background temperature and the average absorption of the UV light of quasars by the intergalactic medium. In this review, I relate observations of D/H in distant gas clouds to the large body of data on the local abundance of D obtained in the last few years with the FUSE satellite. I also discuss some of the outstanding problems in light element abundances and consider future prospects for advances in this area.

 

astro-ph/0601429 [abs, ps, pdf, other] :

Title: The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse
Authors: D.R.Flower, G.Pineau des Forets, C.M.Walmsley
Comments: 10 pages, 7 figures

We have studied the evolution of molecular gas during the early stages of protostellar collapse. In addition to allowing for the freeze out of `heavy' species on to grains, we have computed the variation of population densities of the different nuclear spin states of ``tracer'' molecular ions such as H2D+ and D2H+. Processes which determine the relative populations of the nuclear spin states of molecules and molecular ions have received much less attention in the literature than those involved in their deuteration; but in fact the former processes are as significant as the latter and often involve the same reactants. We find that the ortho:para ratio of some species, e.g. H2D+, vary considerably as the density increases. Because the dynamical timescale is much shorter than some of the chemical timescales, there can be large departures of the predictions of the free--fall model from the steady state solution at the same density and temperature. In the case of H2, it seems unlikely that the steady state value of the ortho:para ratio is attained before protostellar collapse from the progenitor molecular cloud commences. Values of the ortho:para H2 ratio much higher than in steady state, which would prevail in ``young'' molecular clouds, are found to be inconsistent with high levels of deuteration of the gas. The internal energy of ortho--H2 acts as a reservoir of chemical energy which inhibits the deuteration of H3+ and hence of other species, such as N2H+ and NH3. In essence, the deuteration of molecular ions and molecules is sensitive to the ortho:para H2 ratio and hence to the chemical and thermal history of the parent molecular cloud.

 

astro-ph/0601430 [abs, ps, pdf, other] :

Title: Extreme superstarclusters
Authors: Paul P. van der Werf, Leonie Snijders
Comments: invited talk, to appear in proceedings of the workshop "Extreme starbursts - near and far" in Lijiang, China, 2005; 5 pages; version with full resolution figures can be found at this http URL

The presence of superstarclusters is a characteristic feature of starburst galaxies. We examine the properties of star forming regions and young star clusters in various environments, ranging from common to extreme. We then discuss new high spatial resolution mid-infrared imaging and spectroscopy of extreme superstarclusters in the obscured region of the Antennae (NGC4038-4039). We find that the PAH emission in this region is not dominated by the superstarclusters but is mostly diffuse. Emission line ratios found in our high spatial resolution data differ significantly from those in larger apertures, strongly affecting the derived results.

 

astro-ph/0601431 [abs, ps, pdf, other] :

Title: Modified gravity without dark matter
Authors: R.H. Sanders
Comments: 28 pages, 10 figures, lecture given at Third Aegean Summer School, The Invisible Universe: Dark Matter and Dark Energy

On an empirical level, the most successful alternative to dark matter in bound gravitational systems is the modified Newtonian dynamics, or MOND, proposed by Milgrom. Here I discuss the attempts to formulate MOND as a modification of General Relativity. I begin with a summary of the phenomenological successes of MOND and then discuss the various covariant theories that have been proposed as a basis for the idea. I show why these proposals have led inevitably to a multi-field theory. I describe in some detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and discuss its successes and shortcomings. This lecture is primarily pedagogical and directed to those with some, but not a deep, background in General Relativity

 

astro-ph/0601432 [abs, ps, pdf, other] :

Title: A Catalogue of RR Lyrae Stars from the Northern Sky Variability Survey
Authors: Patrick Wils, Chris Lloyd, Klaus Bernhard
Comments: Submitted to MNRAS

A search for RR Lyrae stars has been conducted in the publicly available data of the Northern Sky Variability Survey (NSVS). Candidates have been selected by the statistical properties of their variation; the standard deviation, skewness and kurtosis with appropriate limits determined from a sample 314 known RRab and RRc stars listed in the GCVS. From the period analysis and light curve shape of over 3000 candidates 785 RR Lyrae have been identified of which 188 are previously unknown. The light curves were examined for the Blazhko effect and several new stars showing this were found. Seven double-mode RR Lyrae stars were also found of which three are new discoveries. Some previously known variables have been reclassified as RR Lyrae stars and similarly some RR Lyrae stars have been found to be other types of variable, or not variable at all.

 

astro-ph/0601433 [abs, ps, pdf, other] :

Title: Constraining Cosmic Topology with CMB Polarization
Authors: Alain Riazuelo, Samuel Caillerie, Marc Lachièze-Rey, Roland Lehoucq, Jean-Pierre Luminet
Comments: 10 pages, submitted to PRD

Multiply connected space sections of the universe on a scale smaller than the horizon size can leave an imprint on cosmic microwave background polarization maps, in such a way that the so-called ``circles-in-the-sky'' method can be used to detect or constrain the topology. We investigate some specific cases, namely toroidal and sixth-turn spaces, in order to show the influence of topology on CMB polarization. The correlation between matched points happens to be always positive and higher than 75% regardless of the angular scale and of the cosmological parameters, except for reionization. This figure is better than what occurs in temperature maps, but is achieved only in the absence of noise. It is only slightly reduced by the filtering scheme.

 

astro-ph/0601434 [abs, ps, pdf, other] :

Title: The SDSS Quasar Survey: Quasar Luminosity Function from Data Release Three
Authors: Gordon T. Richards, Michael A. Strauss, Xiaohui Fan, Patrick B. Hall, Sebastian Jester, Donald P. Schneider, Daniel E. Vanden Berk, Chris Stoughton, Scott F. Anderson, Robert J. Brunner, Jim Gray, James E. Gunn, Zeljko Ivezic, Margaret E. Kirkland, G.R. Knapp, Jon Loveday, Avery Meiksin, Adrian Pope, Alexander S. Szalay, Anirudda R. Thakar, Brian Yanny, Donald G. York, et al., for the SDSS Collaboration
Comments: 57 pages, 21 figures (9 color), 7 tables; AJ submitted; higher resolution version available at this ftp URL

We determine the number counts and z=0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform statistical sample possible, consisting of 15,343 quasars within an effective area of 1622 deg^2 that was derived from a parent sample of 46,420 spectroscopically confirmed broad-line quasars in the 5282 deg^2 of imaging data from SDSS Data Release Three. The sample extends from i=15 to i=19.1 at z<3 and to i=20.2 for z>3. The number counts and luminosity function agree well with the results of the 2dF QSO Survey, but the SDSS data probe to much higher redshifts than does the 2dF sample. The number density of luminous quasars peaks between redshifts 2 and 3, although uncertainties in the selection function in this range do not allow us to determine the peak redshift more precisely. Our best fit model has a flatter bright end slope at high redshift than at low redshift. For z<2.4 the data are best fit by a redshift-independent slope of beta = -3.1 (Phi(L) propto L^beta). Above z=2.4 the slope flattens with redshift to beta=-2.37 at z=5. This slope change, which is significant at a >5-sigma level, must be accounted for in models of the evolution of accretion onto supermassive black holes.

 

astro-ph/0601435 [abs, ps, pdf, other] :

Title: Dusty Sources at the Galactic Center: The N- and Q-band view with VISIR
Authors: T. Viehmann, A. Eckart, R. Schoedel, J.-U. Pott, J. Moultaka
Comments: 18 pages, 4 figures, 1 table, accepted for publication in the Astrophysical Journal

We present mid-infrared N- and Q-band photometry of the Galactic Center from images obtained with the mid-infrared camera VISIR at the ESO VLT in May 2004. The high resolution and sensitivity possible with VISIR enables us to investigate a total of over 60 point-like sources, an unprecedented number for the Galactic Center at these wavelengths. Combining these data with previous results at shorter wavelengths (Viehmann et al. 2005) enables us to construct SEDs covering the H- to Q-band regions of the spectrum, i.e. 1.6 to 19.5 $\mu$m. We find that the SEDs of certain types of Galactic Center sources show characteristic features. We can clearly distinguish between luminous Northern Arm bow-shock sources, lower luminosity bow-shock sources, hot stars, and cool stars. This characterization may help clarify the status of presently unclassified sources.

 

astro-ph/0601436 [abs, ps, pdf, other] :

Title: Burst Detector Sensitivity: Past, Present & Future
Authors: David L. Band (GSFC & Jca/Umbc)
Comments: To appear in the proceedings of the 16th Annual October Astrophysics Conference in Maryland, "Gamma Ray Bursts in the Swift Era", Washington DC., November 29-December 2, 2005, 4 pages, 3 figures

I compare the burst detection sensitivity of CGRO's BATSE, Swift's BAT, the GLAST Burst Monitor (GBM) and EXIST as a function of a burst's spectrum and duration. A detector's overall burst sensitivity depends on its energy sensitivity and set of accumulations times Delta t; these two factors shape the detected burst population. For example, relative to BATSE, the BAT's softer energy band decreases the detection rate of short, hard bursts, while the BAT's longer accumulation times increase the detection rate of long, soft bursts. Consequently, Swift is detecting long, low fluence bursts (2-3x fainter than BATSE).

 

astro-ph/0601437 [abs, ps, pdf, other] :

Title: Colliding Clouds: The Star Formation Trigger of the Stellar Cluster Around BD+40 4124
Authors: L.W. Looney (UIUC), S. Wang (UIUC), M. Hamidouche (UIUC), P.N. Safier (UMd), R. Klein (MPE)
Comments: ApJ Accepted. 24 pages

We present BIMA and SCUBA observations of the young cluster associated with BD +40 4124 in the dense molecular gas tracer CS J=2-1 and the continuum dust continuum at 3.1 mm and 850 micron. The dense gas and dust in the system is aligned into a long ridge morphology extending ~0.4 pc with 16 gas clumps of estimated masses ranging from 0.14 - 1.8 Solar masses. A north-south variation in the CS center line velocity can be explained with a two cloud model. We posit that the BD +40 4124 stellar cluster formed from a cloud-cloud collision. The largest linewidths occur near V1318 Cyg-S, a massive star affecting its natal environment. In contrast, the dense gas near the other, more evolved, massive stars displays no evidence for disruption; the material must either be processed into the star, dissipate, or relax, fairly quickly. The more evolved low-mass protostars are more likely to be found near the massive stars. If the majority of low-mass stars are coeval, the seemingly evolved low-mass protostars are not older: the massive stars have eroded their structures. Finally, at the highest resolution, the 3.1 mm dust emission is resolved into a flattened structure 3100 by 1500 AU with an estimated mass of 3.4 Solar masses. The continuum and CS emission are offset by 1.1 arcsec from the southern binary source. A simple estimate of the extinction due to the continuum emission structure is AV = 700 mag. From the offset and as the southern source is detected in the optical, the continuum emission is from a previously unknown very young, intermediate-mass, embedded stellar object. (see high resolution figures at this http URL).

 

astro-ph/0601438 [abs, ps, pdf, other] :

Title: Large dust grains in the inner region of circumstellar disks
Authors: Andrea Isella (1,2), Leonardo Testi (1), Antonella Natta (1) ((1) INAF-Osservatorio Astrofisico di Arcetri, (2) Dipartimento di Fisica - Universita' di Milano)
Comments: Accepted for publication in A&A. 11 pages, 8 figures

CONTEXT: Simple geometrical ring models account well for near-infrared interferometric observations of dusty disks surrounding pre-main sequence stars of intermediate mass. Such models demonstrate that the dust distribution in these disks has an inner hole and puffed-up inner edge consistent with theoretical expectations. AIMS: In this paper, we reanalyze the available interferometric observations of six intermediate mass pre-main sequence stars (CQ Tau, VV Ser, MWC 480, MWC 758, V1295 Aql and AB Aur) in the framework of a more detailed physical model of the inner region of the dusty disk. Our aim is to verify whether the model will allow us to constrain the disk and dust properties. METHODS: Observed visibilities from the literature are compared with theoretical visibilities from our model. With the assumption that silicates are the most refractory dust species, our model computes self-consistently the shape and emission of the inner edge of the dusty disk (and hence its visibilities for given interferometer con gurations). The only free parameters in our model are the inner disk orientation and the size of the dust grains. RESULTS: In all objects with the exception of AB Aur, our self-consistent models reproduce both the interferometric results and the near-infrared spectral energy distribution. In four cases, grains larger than 1.2 micron, and possibly much larger are either required by or consistent with the observations. The inclination of the inner disk is found to be always larger than 30 deg, and in at least two objects much larger.

 

astro-ph/0601439 [abs, ps, pdf, other] :

Title: Planetary nebulae with emission-line central stars
Authors: K. Gesicki, A. A. Zijlstra, A. Acker, S. K. Gorny, K. Gozdziewski, J. R. Walsh
Comments: 14 pages, 9 figures, accepted to A&A

The kinematic structure of a sample of planetary nebulae, consisting of 23 [WR] central stars, 21 weak emission line stars (wels) and 57 non-emission line central stars, is studied. The [WR] stars are shown to be surrounded by turbulent nebulae, a characteristic shared by some wels but almost completely absent from the non-emission line stars. The fraction of objects showing turbulence for non-emission-line stars, wels and [WR] stars is 7%, 24% and 91%, respectively. The [WR] stars show a distinct IRAS 12-micron excess, indicative of small dust grains, which is not found for wels. The [WR]-star nebulae are on average more centrally condensed than those of other stars. On the age-temperature diagram, the wels are located on tracks of both high and low stellar mass, while [WR] stars trace a narrow range of intermediate masses. Emission-line stars are not found on the cooling track. One group of wels may form a sequence wels--[WO] stars with increasing temperature. For the other groups both the wels and the [WR] stars appear to represent several, independent evolutionary tracks. We find a discontinuity in the [WR] stellar temperature distribution and suggest different evolutionary sequences above and below the temperature gap. One group of cool [WR] stars has no counterpart among any other group of PNe and may represent binary evolution. A prime factor distinguishing wels and [WR] stars appears to be stellar luminosity. We find no evidence for an increase of nebular expansion velocity with time.

 

astro-ph/0601440 [abs, ps, pdf, other] :

Title: Discovery of the Closest Brown Dwarf to the Sun? A Methane Rich Brown Dwarf around the Nearby M8.5 Star SCR 1845
Authors: B.A. Biller, M. Kasper, L.M. Close, W. Brandner, S. Kellner
Comments: 5 pages, 3 figures. Submitted to the Astrophysical Journal. Some figures are currently omitted and will be supplied with the final, accepted version

We present VLT/NACO SDI images of the very nearby star SCR 1845-6357 (hereafter SCR 1845). SCR 1845 is a recently discovered (Hambly et al. 2004) M8.5 star just 3.5 pc from the sun (Deacon et al. 2005). Using the capabilities of the unique SDI device, we discovered a substellar companion to SCR 1845 at a separation of 4 AU (1.170"+-0.003'' on the sky, PA=170.20 degrees +- 0.13 degrees) and a Delta F1(1.575 um) of 3.57+-0.057 mag. This substellar companion has an H magnitude of 13.3{+0.24}{-0.21}, and an absolute H magnitude of 15.5{+0.30}{-0.20}. The unique Simultaneous Differential Imager (SDI) consists of 3 narrowband filters placed around the 1.6 um methane absorption feature characteristic of T-dwarfs (Teff < 1200 K). The flux of the substellar companion drops by a factor of 2.7+-0.1 between the SDI F1(1.575 um) filter and the SDI F3(1.625 um) filter, consistent with strong methane absorption in a substellar companion. We estimate a spectral type of T6+-1 for the companion based on the strength of the break. The chances that this object is a background T dwarf are vanishing small -- and there is no isolated background T-dwarf anywhere near these coordinates in the field according to 2MASS. Thus, it is a bound companion, hereafter SCR 1845-6357B. For an age range of 100 Myr - 10 Gyr and spectral type range of T5-T7, we find a mass range of 8.5 - 60 MJup for SCR 1845B from the Baraffe et al. (2003) COND models. This is likely the closest brown dwarf to the Sun (in the 16th closest stellar system to the sun.

 

astro-ph/0601441 [abs, ps, pdf, other] :

Title: Discovery of the Closest Brown Dwarf to the Sun? A Methane Rich Brown Dwarf around the Nearby M8.5 Star SCR 1845-6357
Authors: B.A. Biller, M. Kasper, L.M. Close, W. Brandner, S. Kellner
Comments: 5 pages, 3 figures. Submitted to the Astrophysical Journal. Some figures are currently omitted and will be supplied with the final, accepted version

We present VLT/NACO SDI images of the very nearby star SCR 1845-6357 (hereafter SCR 1845). SCR 1845 is a recently discovered (Hambly et al. 2004) M8.5 star just 3.5 pc from the sun (Deacon et al. 2005). Using the capabilities of the unique SDI device, we discovered a substellar companion to SCR 1845 at a separation of 4 AU (1.170"+-0.003'' on the sky, PA=170.20 degrees +- 0.13 degrees) and a Delta F1(1.575 um) of 3.57+-0.057 mag. This substellar companion has an H magnitude of 13.3{+0.24}{-0.21}, and an absolute H magnitude of 15.5{+0.30}{-0.20}. The unique Simultaneous Differential Imager (SDI) consists of 3 narrowband filters placed around the 1.6 um methane absorption feature characteristic of T-dwarfs (Teff < 1200 K). The flux of the substellar companion drops by a factor of 2.7+-0.1 between the SDI F1(1.575 um) filter and the SDI F3(1.625 um) filter, consistent with strong methane absorption in a substellar companion. We estimate a spectral type of T6+-1 for the companion based on the strength of the break. The chances that this object is a background T dwarf are vanishing small -- and there is no isolated background T-dwarf anywhere near these coordinates in the field according to 2MASS. Thus, it is a bound companion, hereafter SCR 1845-6357B. For an age range of 100 Myr - 10 Gyr and spectral type range of T5-T7, we find a mass range of 8.5 - 60 MJup for SCR 1845B from the Baraffe et al. (2003) COND models. This is likely the closest brown dwarf to the Sun (in the 16th closest stellar system to the sun.

 

astro-ph/0601442 [abs, ps, pdf, other] :

Title: Smear fitting: a new deconvolution method for interferometric data
Authors: Robert I. Reid
Comments: 16 pages, 38 figures (some have been lossily compressed for astro-ph). Uses the hyperref LaTeX package. Accepted for publication by the Monthly Notices of the Royal Astronomical Society

A new technique is presented for producing images from interferometric data. The method, ``smear fitting'', makes the constraints necessary for interferometric imaging double as a model, with uncertainties, of the sky brightness distribution. It does this by modelling the sky with a set of functions and then convolving each component with its own elliptical gaussian to account for the uncertainty in its shape and location that arises from noise. This yields much sharper resolution than CLEAN for significantly detected features, without sacrificing any sensitivity. Using appropriate functional forms for the components provides both a scientifically interesting model and imaging constraints that tend to be better than those used by traditional deconvolution methods. This allows it to avoid the most serious problems that limit the imaging quality of those methods. Comparisons of smear fitting to CLEAN and maximum entropy are given, using both real and simulated observations. It is also shown that the famous Rayleigh criterion (resolution = wavelength / baseline) is inappropriate for interferometers as it does not consider the reliability of the measurements.

 

astro-ph/0601443 [abs, ps, pdf, other] :

Title: The C-flash and the ignition conditions of type Ia supernovae
Authors: P. Lesaffre, Z. Han, C. A. Tout, Ph. Podsiadlowski, R. G. Martin
Comments: 10 pages, 14 figures, MNRAS accepted

Thanks to a stellar evolution code able to compute through the
C-flash we link the binary population synthesis of single degenerate progenitors of type Ia supernovae (SNe Ia) to their physical condition at the time of ignition. We show that there is a large range of possible ignition densities and we detail how their probability distribution depends on the accretion properties. The low density peak of this distribution qualitatively reminds of the clustering of the luminosities of Branch-normal SNe Ia. We tighten the possible range of initial physical conditions for explosion models: they form a one-parameter family, independent of the metallicity. We discuss how these results may be modified if we were to relax our hypothesis of a permanent Hachisu wind or if we were to include electron captures.

 

astro-ph/0601444 [abs, ps, pdf, other] :

Title: The OGLE-II event sc5_2859 : a Classical Nova outburst?
Authors: C.Afonso, J.F.Glicenstein, A.Gould, M.C.Smith, R.M.Wagner, the EROS Collaboration
Comments: Accepted for publication in Astronomy and Astrophysics

The OGLE-II event sc5_2859 was previously identified as the third longest microlensing event ever observed. Additional photometric observations from the EROS (Experience de Recherche d'Objets Sombres) survey and spectroscopic observations of the candidate star are used to test the microlensing hypothesis.The combined OGLE and EROS data provide a high quality coverage of the light curve. The colour of the sc5_2859 event is seen to change with time. A spectrum taken in 2003 exhibits a strong Halpha emission line. The additionnal data show that the OGLE-II sc5_2859 event is actually a classical nova outburst.

 

astro-ph/0601445 [abs, ps, pdf, other] :

Title: Microwave sky and the local Rees-Sciama effect
Authors: Aleksandar Rakic, Syksy Rasanen, Dominik J. Schwarz
Comments: 5 pages, 2 figures, 2 tables

The microwave sky shows unexpected features at the largest angular scales, among them the alignments of the dipole, quadrupole and octopole. Motivated by recent X-ray cluster studies, we investigate the possibility that local structures at the 100 h^-1 Mpc scale could be responsible for such correlations. These structures give rise to a local Rees-Sciama contribution to the microwave sky that may amount to \Delta T/T \sim 10^-5 at the largest angular scales. We model local structures by a spherical overdensity (Lemaitre-Tolman-Bondi model) and assume that the Local Group is falling toward the centre. We superimpose the local Rees-Sciama effect on a statistically isotropic, gaussian sky. As expected we find alignments among low multipoles, but a closer look reveals that they do not agree with the type of correlations revealed by the data.

 

astro-ph/0601446 [abs, ps, pdf, other] :

Title: Period-color and amplitude-color relations in classical Cepheid variables III: The Large Magellanic Cloud Cepheid models
Authors: Shashi Kanbur (SUNY-Oswego), Chow-Choong Ngeow (UIUC)
Comments: 18 pages, 6 tables and 16 figures, MNRAS submitted

Period-colour (PC) and amplitude-colour (AC) relations are studied for the Large Magellanic Cloud (LMC) Cepheids under the theoretical framework of the hydrogen ionization front (HIF) - photosphere interaction. LMC models are constructed with pulsation codes that include turbulent convection, and the properties of these models are studied at maximum, mean and minimum light. As with Galactic models, at maximum light the photosphere is located next to the HIF for the LMC models. However very different behavior is found at minimum light. The long period (P>10days) LMC models imply that the photosphere is disengaged from the HIF at minimum light, similar to the Galactic models, but there are some indications that the photosphere is located near the HIF for the short period (P<10 days) LMC models. We also use the updated LMC data to derive empirical PC and AC relations at these phases. Our numerical models are broadly consistent with our theory and the observed data, though we discuss some caveats in the paper. We apply the idea of the HIF-photosphere interaction to explain recent suggestions that the LMC period-luminosity (PL) and PC relations are non-linear with a break at a period close to 10 days. Our empirical PC and PL relations are also found to be non-linear with the F-test. Our explanation relies on the properties of the Saha ionization equation, the HIF-photosphere interaction and the way this interaction changes with the phase of pulsation and metallicity to produce the observed changes in the Cepheid PC and PL relations.

 

astro-ph/0601447 [abs, ps, pdf, other] :

Title: Period-colour and amplitude-colour relations in classical Cepheid variables IV: The multi-phase relations
Authors: Chow-Choong Ngeow (UIUC), Shashi Kanbur (SUNY-Oswego)
Comments: 11 pages, 1 table and 12 figures, MNRAS submitted

The superb phase resolution and quality of the OGLE data on LMC and SMC Cepheids, together with existing data on Galactic Cepheids, are combined to study the period-colour (PC) and amplitude-colour (AC) relations as a function of pulsation phase. Our results confirm earlier work that the LMC PC relation (at mean light) is more consistent with two lines of differing slopes, separated at a period of 10 days. However, our multi-phase PC relations reveal much new structure which can potentially increase our understanding of Cepheid variables. These multi-phase PC relations provide insight into why the Galactic PC relation is linear but the LMC PC relation is non-linear. This is because the LMC PC relation is shallower for short (log P < 1) and steeper for long (log P > 1) period Cepheids than the corresponding Galactic PC relation. Both of the short and long period Cepheids in all three galaxies exhibit the steepest and shallowest slopes at phases around 0.75-0.85, respectively. A consequence is that the PC relation at phase ~0.8 is highly non-linear, at least for the Galactic and LMC Cepheids. Further, the Galactic and LMC Cepheids with log P > 1 display a flat slope in the PC plane at phases close to the maximum light. When the LMC period-luminosity (PL) relation is studied as a function of phase, we confirm that it changes with the PC relation. The LMC PL relation in $V$- and $I$-band near the phase of 0.8 provides compelling evidence that this relation is also consistent with two lines of differing slopes joined at a period close to 10 days.

 

astro-ph/0601448 [abs, pdf] :

Title: Discovery and application of Frequency Ratio Method to the new multiperiodic gamma Dor star HD 218427
Authors: E. Rodriguez, P.J. Amado, J.C. Suarez, A. Moya, M.A. Dupret, E. Poretti, A. Grigahcene, V. Costa, M.J. Lopez-Gonzalez
Comments: 10 pages, 3 figures. Accepted by A&A

gamma Dor-type oscillations have been discovered in the star HD218427 through simultaneous uvby photometric observations carried out in the year 2003. A few Hbeta-Crawford measurements were also collected for calibration purposes which place this star well-located inside the gamma Dor instability region. Deficiency in metal content, similar to other well-defined gamma Dor stars, is found in HD218427 and the possibility of a lambda Boo nature is discussed. Frequency analysis was carried out for different filters, the combined "vby" filter was also used and five frequencies were found as significant with periods ranging between 0.3 and 0.8 days. The recently developed Frequency Ratio Method is used in order to perform an identification of the excited modes. The results are consistent with an l=2 identification for all the modes and high radial quantum numbers (n~40) for the three main observed periodicities. The possibility of multiplet structures is also discussed. However, no consistency is found when the Time-Dependent Convection treatment is used for modes discrimination. The disagreement can be due to the large rotation velocity taking place in HD218427 and, consequently, the significant coupling between the modes.

 

astro-ph/0601449 [abs, ps, pdf, other] :

Title: Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data
Authors: G.I. Rubtsov, L.G. Dedenko, G.F. Fedorova, E.Yu. Fedunin, A.V. Glushkov, D.S. Gorbunov, I.T. Makarov, M.I. Pravdin, T.M. Roganova, I.E. Sleptsov, S.V. Troitsky
Comments: revtex, 8 pages, 4 figures

We present the interpretation of the muon and scintillation signals of ultra-high-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest energy events with known muon content and conclude that at the 95% confidence level (C.L.) none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at 95% C.L. on the fraction of primary photons in the cosmic-ray flux above 10^20 eV. This result disfavors the Z-burst and superheavy dark-matter solutions to the GZK-cutoff problem.

 

astro-ph/0601450 [abs, ps, pdf, other] :

Title: Upper limits on the central black hole masses of 47Tuc and NGC6397
Authors: S. De Rijcke, P. Buyle, H. Dejonghe
Comments: 4 pages, 1 figure, accepted for publication by MNRAS

We present upper-limits on the masses of the putative central intermediate-mass black holes in two nearby Galactic globular clusters: 47Tuc (NGC104), the second brightest Galactic globular cluster, and NGC6397, a core-collapse globular cluster and, with a distance of 2.7 kpc, quite possibly the nearest globular cluster, using a technique suggested by T. Maccarone. These mass estimates have been derived from 3sigma upper limits on the radio continuum flux at 1.4 GHz, assuming that the putative central black hole accretes the surrounding matter at a rate between 0.1% and 1% of the Bondi accretion rate. For 47Tuc, we find a 3sigma upper limit of 2060 - 670 solar masses, depending on the actual accretion rate of the black hole and the distance to 47Tuc. For NGC6397, which is closer to us, we derive a 3sigma upper limit of 1290 - 390 solar masses. While estimating mass upper-limits based on radio continuum observations requires making assumptions about the gas density and the accretion rate of the black hole, their derivation does not require complex and time consuming dynamical modeling. Thus, this method offers an independent way of estimating black hole masses in nearby globular clusters. If, generally, central black holes in stellar systems accrete matter faster than 0.1% of the Bondi accretion rate, then these results indicate the absence of black holes in these globular clusters with masses as predicted by the extrapolated M-sigma relation.

 

astro-ph/0601451 [abs, ps, pdf, other] :

Title: Discovery of 35 New Supernova Remnants in the Inner Galaxy
Authors: C. L. Brogan, J. D. Gelfand, B. M. Gaensler, N. E. Kassim, T. J. Lazio
Comments: 5 pages; Accepted to ApJL, high resolution figures available from this http URL

We report the discovery of up to 35 new supernova remnants (SNRs) from a 42 arcsec resolution 90cm multi-configuration Very Large Array survey of the Galactic plane covering 4.5 deg< l <22.0 deg and |b| < 1.25 deg. Archival 20cm, 11cm, and 8 micron data have also been used to identify the SNRs and constrain their properties. The 90cm image is sensitive to SNRs with diameters 2.5 arcmin to 50 arcmin and down to a surface brightness limit of about 10^{-21} W m^{-2} Hz^{-1} sr^{-1}. This survey has nearly tripled the number of SNRs known in this part of the Galaxy, and represents an overall 15% increase in the total number of Galactic SNRs. These results suggest that further deep low frequency surveys of the inner Galaxy will solve the discrepancy between the expected number of Galactic SNRs and the significantly smaller number of currently known SNRs.

 

astro-ph/0601452 [abs, ps, pdf, other] :

Title: AGN and Galaxy evolution from Deep X-ray surveys
Authors: P. Tozzi, R. Gilli, the CDFS Team
Comments: 8 pages, 10 Figures, to be published in Mem SAIt, Proceedings of the Workshop on "AGN and Galaxy Evolution", held in the Specola Vaticana, Castel Gandolfo, Italy - October 2005

Deep X-ray surveys are providing crucial information on the evolution of AGN and galaxies. We review some of the latest results based on the X-ray spectral analysis of the sources detected in the Chandra Deep Field South, namely: i) constraints on obscured accretion; ii) constraints on the missing fraction of the X-ray background; iii) the redshift distribution of Compton-thick sources and TypeII QSO; iv) the detection of star formation activity in high-z galaxies through stacking techniques; v) the detection of large scale structure in the AGN distribution and its effect on nuclear activity. Such observational findings are consistent with a scenario where nuclear activity and star formation processes develop together in an anti-hierarchical fashion.

 

astro-ph/0601453 [abs, ps, pdf, other] :

Title: Observational constraints on the acceleration of the Universe
Authors: Yungui Gong, Anzhong Wang
Comments: 9 figures, revtex

We first parameterize the deceleration parameter to discuss its behavior. The advantage of this parametrization is that we do not need to assume any underlying theory of gravity. By fitting the model to the 157 gold sample supernova Ia data, we find strong evidence that the Universe is currently accelerating and it accelerated in the past. By fitting the model to the 115 nearby and Supernova Legacy Survey supernova Ia data, the evidence that the Universe is currently accelerating is weak and there is strong evidence that the Universe once accelerated in the past. We then use a dark energy parametrization to discuss the problem again. If we fit the model to the supernova Ia data alone, we find weak evidence that the Universe is accelerating and the current matter density is higher than that measured from other experiments. Therefore we add the Sloan Digital Sky Survey data to constrain the dark energy model. The behavior of the deceleration parameter is almost the same as that obtained from parameterizing the deceleration parameter.