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Astrophysics

astro-ph new abstracts, Tue, 28 Mar 06 01:00:12 GMT
0603687 -- 0603740 received

astro-ph/0603687 [abs, ps, pdf, other] :

Title: Persistent Patterns in Accretion Disks
Authors: Mustafa A. Amin, Andrei V. Frolov
Comments: 4 pages, 5 figures; MNLaTeX 2.2

We present a set of new characteristic frequencies associated with accretion disks around compact objects. These frequencies arise from persistent rotating patterns in the disk that are finite in radial extent and driven purely by the gravity of the central body. Their existence depends on general relativistic corrections to orbital motion and, if observed, could be used to probe the strong gravity region around a black hole. We also discuss a possible connection to the puzzle of quasi-periodic oscillations.

 

astro-ph/0603688 [abs, ps, pdf, other] :

Title: The NOAO Fundamental Plane Survey - III. Variations in the stellar populations of red-sequence galaxies from the cluster core to the virial radius
Authors: Russell J. Smith (Waterloo, Durham), Michael J. Hudson (Waterloo), John R. Lucey (Durham), Jenica E. Nelan (Dartmouth, Yale), Gary A. Wegner (Dartmouth)
Comments: Twenty pages, thirteen figures; revised version as returned to MNRAS following minor comments from the referee

We analyse absorption line-strength indices for ~3000 red-sequence galaxies in 94 nearby clusters, to investigate systematic variations of their stellar content with location in the host cluster. The data are drawn from the NOAO Fundamental Plane Survey. Our adopted method is a generalization of that introduced by Nelan et al. to determine the global age-mass and metallicity-mass relations from the same survey. We find strong evidence for a change in galaxy properties, at fixed mass, over a range from the cluster centre to the virial radius, R_200. For example, red-sequence galaxies further out in the clusters have weaker Mgb5177 (at ~8 sigma significance) and stronger Hbeta and Hgamma absorption (~3 sigma, ~4 sigma) than galaxies of the same velocity dispersion in the cluster cores. The Fe5270 and Fe5335 indices show only very weak trends with radius. Using a total of twelve indices, the pattern of cluster-centric gradients is considered in light of their different dependences on stellar age and chemical composition. The measured gradients for all twelve indices can be reproduced by a model in which red-sequence galaxies at ~1 R_200 have on average younger ages (by 15+/-4%) and lower alpha-element abundance ratios (by 10+/-2%), than galaxies of the same velocity dispersion but located near the cluster centre. For the total metallicity, Z/H, no significant gradient is found (2+/-3% larger at R_200 than in the core). The cluster-centric age and alpha/Fe gradients are in the sense expected if galaxies in the cluster core were accreted at an earlier epoch than those at larger radii, and if this earlier accretion contributed to an earlier cessation of star formation. The size of the observed age trend is comparable to predictions from semi-analytic models of hierarchical galaxy formation.

 

astro-ph/0603689 [abs, ps, pdf, other] :

Title: HST and Spitzer Observations of the Host Galaxy of GRB 050904: A Metal-Enriched, Dusty Starburst at z=6.295
Authors: E. Berger, R. Chary, L. L. Cowie, P. A. Price, B. P. Schmidt, D. B. Fox, S. B. Cenko, S. G. Djorgovski, A. M. Soderberg, S. R. Kulkarni, P. J. McCarthy, M. D. Gladders, B. A. Peterson, A. J. Barger
Comments: Submitted to ApJ; 11 pages, 5 figures; A high-resolution version of figure 1 can be found at this http URL

We present deep Hubble Space Telescope and Spitzer Space Telescope observations of the host galaxy of GRB 050904 at z=6.295. The host is detected in the H-band and marginally at 3.6 micron. From these detections, and limits in the z'-band and 4.5 micron, we infer an extinction-corrected absolute magnitude, M(UV)=-20.7 mag, or ~L*, a substantial star formation rate of 15 solar masses per year, and a stellar mass of a few 10^9 solar masses. A comparison to the published sample of spectroscopically-confirmed galaxies at z>5.5 reveals that the host of GRB 050904 would evade detection and/or confirmation in any of the current surveys due to the lack of detectable Ly-alpha emission, which is likely the result of dust extinction (A[1200]~1.5 mag). This suggests that not all luminous starburst galaxies at z~6 are currently being accounted for. Most importantly, using the metallicity of Z~0.05 solar inferred from the afterglow absorption spectrum, our observations indicate for the first time that the observed evolution in the mass- and luminosity-metallicity relations from z=0 to z~2 continues on to z>6. The ease of measuring redshifts and metallicities from the afterglow emission suggests that in tandem with the next generation ground- and space-based telescopes, a GRB mission with dedicated near-IR follow-up can provide unique information on the evolution of stars and galaxies through the epoch of re-ionization.

 

astro-ph/0603690 [abs, ps, pdf, other] :

Title: Cross-correlation of WMAP 3rd year and the SDSS DR4 galaxy survey: new evidence for Dark Energy
Authors: A.Cabre, E.Gaztanaga, M.Manera, P.Fosalba, F.Castander (IEEC/CSIC)
Comments: 5 pages, 5 figures, submitted to MNRAS Letter

We cross-correlate the third-year WMAP data with galaxy samples extracted from the SDSS DR4 covering 13% of the sky, increasing by a factor of 3.7 the volume sampled in previous analyses. The new measurements confirm a positive cross-correlation with higher significance (total signal-to-noise of about 4.7). The correlation as a function of angular scale is well fitted by the integrated Sachs-Wolfe (ISW) effect for LCDM flat FRW models with a cosmological constant (w=-1). The combined analysis of different samples gives Omega_L=0.75-0.80 (68% Confidence Level, CL) or 0.70-0.82 (95% CL). We find that the best fit Omega_L decreases from 0.82 to 0.75 (95% CL) when we increase the median redshift of the galaxy sample from z~0.3 to z~0.5. The quick drop of the measured signal with z is too fast for the LCDM cosmology. The data can be better reconciled with a model with an effective dark energy equation of state w<-1.5. Such phantom cosmology reduces by up to ~20% the amplitude of the lower multipoles of the CMB temperature anisotropies with respect the w=-1 prediction, which also brings the models closer to the observations.

 

astro-ph/0603691 [abs, ps, pdf, other] :

Title: Improved 3D Fabry-Perot Data Reduction Techniques
Authors: O. Daigle, C. Carignan, O. Hernandez, L. Chemin, P. Amram
Comments: 10 pages, 9 figures, accepted for publication in MNRAS

Improved data reduction techniques for 3D data cubes obtained from Fabry-Perot integral field spectroscopy are presented. They provide accurate sky emission subtraction and adaptive spatial binning and smoothing. They help avoiding the effect analogous to the beam smearing, seen in HI radio data, when strong smoothing is applied to 3D data in order to get the most extended signal coverage. The data reduction techniques presented in this paper allow one to get the best of both worlds: high spatial resolution in high signal-to-noise regions and large spatial coverage in low signal-to-noise regions.

 

astro-ph/0603692 [abs, ps, pdf, other] :

Title: Structures in the Great Attractor Region
Authors: D. J. Radburn-Smith (1), J. R. Lucey (1), P. A. Woudt (2), R. C. Kraan-Korteweg (2), F. G. Watson (3) ((1) University of Durham, (2) University of Cape Town, (3) Anglo-Australian Observatory)
Comments: 13 pages, 8 figures. Accepted for publication in MNRAS. High resolution versions of Fig. 4, 7 & 8 are available in the refereed publication

To further our understanding of the Great Attractor (GA), we have undertaken a redshift survey using the 2dF on the AAT. Clusters and filaments in the GA region were targeted with 25 separate pointings resulting in approximately 2600 new redshifts. Targets included poorly studied X-ray clusters from the CIZA catalogue as well as the Cen-Crux and PKS 1343-601 clusters, both of which lie close to the classic GA centre. For nine clusters in the region, we report velocity distributions as well as virial and projected mass estimates. The virial mass of CIZA J1324.7-5736, now identified as a separate structure from the Cen-Crux cluster, is found to be ~3x10^14 M_sun, in good agreement with the X-ray inferred mass. In the PKS 1343-601 field, five redshifts are measured of which four are new. An analysis of redshifts from this survey, in combination with those from the literature, reveals the dominant structure in the GA region to be a large filament, which appears to extend from Abell S0639 (l=281\deg, b=+11\deg) to (l~5\deg, b~-50\deg), encompassing the Cen-Crux, CIZA J1324.7-5736, Norma and Pavo II clusters. Behind the Norma Cluster at cz~15000 km/s, the masses of four rich clusters are calculated. These clusters (Triangulum-Australis, Ara, CIZA J1514.6-4558 and CIZA J1410.4-4246) may contribute to a continued large-scale flow beyond the GA. The results of these observations will be incorporated into a subsequent analysis of the GA flow.

 

astro-ph/0603693 [abs, ps, pdf, other] :

Title: Long-Term X-Ray and TeV variability of Mrk 501
Authors: M. Gliozzi (GMU), R. Sambruna (NASA-GSFC), I. Jung, H. Krawczynski (S. Louis), D. Horan (CfA), F. Tavecchio (INAF Brera)
Comments: 20 pages, 11 figures, accepted for publication in ApJ

We present X-ray observations of the blazar Mrk501 obtained with RXTE during 1997, 1998, 1999, 2000, and 2004. The goal of this study is twofold: 1) characterize the long-term X-ray flux and spectral variability of the source with a model-independent analysis, and 2) investigate the X-ray and TeV correlation on long timescales. The spectral and temporal variability properties appear to be markedly different compared to those of non-jet-dominated radio-loud and radio-quiet AGN monitored with RXTE. To investigate the X-ray/TeV correlation on long timescales we compared RXTE data with HEGRA and Whipple historical light curves. We confirm the presence of a direct correlation, which appears to be stronger when the source is brighter. The analysis of individual flares shows that the X-ray\TeV correlated activity is heterogeneous. However, more sensitive TeV observations are necessary to confirm these findings, and to put tighter constraints on jet models (abridged).

 

astro-ph/0603694 [abs, ps, pdf, other] :

Title: On Kinematic Substructure in the Sextans Dwarf Spheroidal Galaxy
Authors: Matthew G. Walker, Mario Mateo, Edward W. Olszewski, Jayanta Kumar Pal, Bodhisattva Sen, Michael Woodroofe
Comments: accepted for publication in ApJ Letters; 4 figures (2 color)

We present multifiber echelle radial velocity results for 551 stars in the Sextans dwarf spheroidal galaxy and identify 294 stars as probable Sextans members. The projected velocity dispersion profile of the binned data remains flat to a maximum angular radius of $30^{\prime}$. We introduce a nonparametric technique for estimating the projected velocity dispersion surface, and use this to search for kinematic substructure. Our data do not confirm previous reports of a kinematically distinct stellar population at the Sextans center. Instead we detect a region near the Sextans core radius that is kinematically colder than the overall Sextans sample with 95% confidence.

 

astro-ph/0603695 [abs, ps, pdf, other] :

Title: High resolution OH maser survey in star forming regions
Authors: A. E. Ruiz-Velasco (1), V. Migenes (1), V. Slysh (2), I. E. Val'tts (2) ((1) Depto. de Astronomia, Univ. Guanajuato, Mexico, (2) Astro Space Center of the Lebedev Physical Center of RAS, Russia)
Comments: 2 pages, 1 figure., To appear in the Proceedings of the "11th Latin American IAU Regional Meeting of Astronomy" LARIM2005, December 12-16 2005, Pucon, Chile; RevMexAst Conf Series

We present results of a high resolution survey of OH masers in Galactic Star Forming Regions in order to study the maser emission and establish a list of suitable candidates for higher resolution instruments follow up. We used the Very Long Baseline Array (VLBA) to observe the 1665, 1667, 1612 and 1720 MHz OH maser transitions within 41 regions. These are the first high resolution observations for most of the sources. For all the transitions 30 sites of maser emission were detected, 4 of the sources have new detections, and approximately 40% of the sources in the sample exhibit highly compact structure. Finally we consider that the spectrum observed in W75N shows the early stage of a long period OH maser flare in the 1665 MHz line, the first of its kind.

 

astro-ph/0603696 [abs, ps, pdf, other] :

Title: Redshift and Shear Calibration: Impact on Cosmic Shear Studies and Survey Design
Authors: Van Waerbeke, L., White, M., Hoekstra, H., Heymans, C
Comments: 22 pages, submitted to Astroparticle Physics

The cosmological interpretation of weak lensing by large-scale structures requires knowledge of the redshift distribution of the source galaxies. Current lensing surveys are often calibrated using external redshift samples which span a significantly smaller sky area in comparison to the lensing survey, and are thus subject to sample variance. Some future lensing surveys are expected to be calibrated in the same way, in particular the fainter galaxy populations where the entire color coverage, and hence photometric redshift estimate, could be challenging to obtain. Using N-body simulations, we study the impact of this sample variance on cosmic shear analysis and show that, to first approximation, it behaves like a shear calibration error 1+/-epsilon. Using the Hubble Deep Field as a redshift calibration survey could therefore be a problem for current lensing surveys. We discuss the impact of the redshift distribution sampling error and a shear calibration error on the design of future lensing surveys, and find that a lensing survey of area Theta square degrees and limiting magnitude m_lim}, has a minimum shear and redshift calibration accuracy requirements given by epsilon = epsilon_0 10^{beta(m_lim-24.5)} / sqrt(Theta/ 200). Above that limit, lensing surveys would not reach their full potential. Using the galaxy number counts from the Hubble Ultra-Deep Field, we find (epsilon_0,beta)=(0.015,-0.18) and (epsilon_0,beta)=(0.011,-0.23) for ground and space based surveys respectively. Lensing surveys with no or limited redshift information and/or poor shear calibration accuracy will loose their potential to analyse the cosmic shear signal in the sub-degree angular scales, and therefore complete photometric redshift coverage should be a top priority for future lensing surveys.

 

astro-ph/0603697 [abs, ps, pdf, other] :

Title: The low-luminosity galaxy population in the NGC 5044 Group (Conference proceeding)
Authors: Sergio A. Cellone (Facultad de Ciencias Astronomicas y Geofisicas, UNLP, Argentina), Alberto Buzzoni (INAF - Osservatorio Astronomico di Bologna, Italy)
Comments: 5 pages. To appear in ESO Astrophysics Symposia: "Groups of Galaxies in the Nearby Universe"

Detailed surface photometry for 79 (mostly dwarf) galaxies in the NGC 5044 Group area is analysed, revealing the existence of different morphologies among objects originally classified as early-type dwarfs. Particularly, a significant fraction of bright dwarf "ellipticals" show a distinct bulge+disc structure; we thus re-classify these objects as dwarf lenticulars (dS0). Our finding points at a possible scenario where these systems are the remnants of "harassed" disc galaxies. This is emphasized by the discovery of a few objects with hints for very low-surface brightness spiral-like structure. The colours, structure, and spatial distribution of the different galaxy types suggest that our classification may indeed be separating objects with different origins and/or evolutionary paths.

 

astro-ph/0603698 [abs, ps, pdf, other] :

Title: M 33 X-7: ChASeM33 reveals the first eclipsing black hole X-ray binary
Authors: W. Pietsch, F. Haberl, M. Sasaki, T.J. Gaetz, P.P. Plucinsky, P. Ghavamian, K.S. Long, T.G. Pannuti
Comments: 14 pages, 5 figures, ApJ accepted

The first observations conducted as part of the Chandra ACIS survey of M 33 (ChASeM33) sampled the eclipsing X-ray binary M 33 X-7 over a large part of the 3.45 d orbital period and have resolved eclipse ingress and egress for the first time. The occurrence of the X-ray eclipse allows us to determine an improved ephemeris of mid-eclipse and binary period as HJD (2453639.119+-0.005) +- N x (3.453014+-0.000020) and constrain the eclipse half angle to (26.5+-1.1) degree. There are indications for a shortening of the orbital period. The X-ray spectrum is best described by a disk blackbody spectrum typical for black hole X-ray binaries in the Galaxy. We find a flat power density spectrum and no significant regular pulsations were found in the frequency range of 10^{-4} to 0.15 Hz. HST WFPC2 images resolve the optical counterpart, which can be identified as an O6III star with the help of extinction and colour corrections derived from the X-ray absorption. Based on the optical light curve, the mass of the compact object in the system most likely exceeds 9 M_sun. This mass, the shape of the X-ray spectrum and the short term X-ray time variability identify M 33 X-7 as the first eclipsing black hole high mass X-ray binary.

 

astro-ph/0603699 [abs, ps, pdf, other] :

Title: Spectral Statistics and Local Luminosity Function of a Hard X-ray Complete Sample of Brightest AGNs
Authors: K. Shinozaki, T. Miyaji, Y. Ishisaki, Y. Ueda, Y. Ogasaka
Comments: 43 pages(one column), 10 figures(5 electronic only figures have been included in the preprint source (tar.gz file)), accepted by The Astronomical Journal, 9. Mar 2006

We have measured the X-ray spectral properties of a complete flux-limited sample of bright AGNs from HEAO-1 all-sky catalogs to investigate their statistics and provide greater constraints on the bright-end of the hard X-ray luminosity function (HXLF) of AGNs and the AGN population synthesis model of the X-ray background. Spectral studies using data from ASCA, XMM-Newton and/or Beppo-SAX observations have been made for almost all AGNs in this sample.
The spectral measurements enable us to construct the neutral absorbing column density (Log nH) distribution and separate HXLFs for absorbed (Log nH[cm-2]> 21.5) and unabsorbed AGNs in the local universe. Our results show evidence for a difference in the shapes of HXLFs of absorbed and unabsorbed AGNs in that absorbed AGN HXLF drops more rapidly at higher luminosities than that of unabsorbed AGNs, which is similar to that previously reported. In the Lx - nH plot, we found no AGN in the high-luminosity high-intrinsic absorption regime (Log Lx[erg/s]> 44.5, Log nH[cm-2]> 21.5) in our sample, where we expect about 5 AGNs if we assume that absorbed and unabsorbed having identical AGN HXLF shapes. We also find that the observed flux with ASCA or XMM-Newton is smaller than that with HEAO-1 by a factor of 0.29 on average, which is expected for re-observation of sources with a factor 2.5 variability amplitude scale.

 

astro-ph/0603700 [abs, ps, pdf, other] :

Title: The internal dynamics of the Local Group dwarf elliptical galaxies NGC147, NGC185, and NGC205
Authors: S. De Rijcke, P. Prugniel, F. Simien, H. Dejonghe
Comments: Accepted for publication in MNRAS, 14 pages, 13 figures

We present three-integral dynamical models for the three Local Group dwarf elliptical galaxies: NGC147, NGC185, and NGC205. It is the first time models are constructed for the Local Group dEs that allow for the presence of dark matter at large radii and that are constrained by kinematics out to at least one half-light radius. The B-band mass-to-light ratios of all three galaxies are rather similar, (M/L)_B = 3-4. Within the inner two half-light radii, about 40-50% of the mass is in the form of dark matter, so dEs contain about as much dark matter as bright ellipticals.
NGC205 and NGC147 have a relatively isotropic velocity dispersion tensor within the region where the internal dynamics are strongly constrained by the data. Our estimated inclination for NGC185 is i ~ 50 degrees because in that case the model has an intrinsic flattening close to the peak of the intrinsic shape distribution of dEs and it, like the best fitting models for NGC147 and NGC205, is nearly isotropic. We also show that the dynamical properties of the bright nucleus of NGC205 are not unlike those of a massive globular cluster.

 

astro-ph/0603701 [abs, ps, pdf, other] :

Title: Deep seawater inherent optical properties in the Southern Ionian Sea
Authors: G. Riccobene, A.Capone, the NEMO collaboration
Comments: 15 page, figures included, submitted to Astroparticle Physics

The NEMO (NEutrino Mediterranean Observatory) Collaboration has been carrying out since 1998 an evaluation programme of deep sea sites suitable for the construction of the future Mediterranean km3 Cerenkov neutrino telescope. We investigated the seawater optical and oceanographic properties of several deep sea marine areas close to the Italian Coast. Inherent optical properties (light absorption and attenuation coefficients) have been measured as a function of depth using an experimental apparatus equipped with standard oceanographic probes and the commercial transmissometer AC9 manufactured by WETLabs. This paper reports on the visible light absorption and attenuation coefficients measured in deep seawater of a marine region located in the Southern Ionian Sea, 60-100 km SE of Capo Passero (Sicily). Data show that blue light absorption coefficient is about 0.015 1/m (corresponding to an absorption length of 67 m) close to the one of optically pure water and it doe not show seasonal variation.

 

astro-ph/0603702 [abs, ps, pdf, other] :

Title: Millimetric observation of the SZ effect in the Corona Borealis supercluster
Authors: E.S.Battistelli, M.De Petris, L.Lamagna, R.A.Watson, R.Rebolo, F.Melchiorri, R.Génova-Santos, G.Luzzi, S. De Gregori, J.A. Rubiño-Martin, R.D.Davies, R.J.Davis, K. Grainge, M.P. Hobson, R.D.E.Saunders, P.F.Scott
Comments: 27 pages, 6 figures, accepted ApJ

We have observed the Corona Borealis Supercluster with the Millimeter and Infrared Testa grigia Observatory (MITO), located in the Italian Alps, at 143, 214, 272, and 353 GHz. We present a description of the measurements, data analysis, and results of the observations together with a comparison with observations performed at 33 GHz with the Very Small Array (VSA) interferometer situated at the Teide Observatory (Tenerife-Spain). Observations have been made in the direction of the supercluster towards one Cosmic Microwave Background (CMB) cold spot previously detected in a VSA temperature map. Observational strategy and data analysis are described in detail, explaining the procedures used to disentangle primary and secondary anisotropies in the resulting maps.
From a first level of data analysis we find evidence in MITO data of primary anisotropy, however still with room for the presence of secondary anisotropy, especially when VSA results are included. With a second level of data analysis using map-making and the maximum entropy method we claim a weak detection of a faint signal compatible with a SZ effect characterized at most by a Comptonization parameter $y=(7.8^{+5.3}_{-4.4})\times10^{-6}$ 68% CL. The low level of confidence in the presence of a SZ signal invite us to study this sky region with higher sensitivity and angular resolution experiments like the already planned upgraded versions of VSA and MITO.

 

astro-ph/0603703 [abs, ps, pdf, other] :

Title: Are f(R) dark energy models cosmologically viable ?
Authors: Luca Amendola (INAF/OAR Italy), David Polarski (LPTA France), Shinji Tsujikawa (Gunma Nat. Coll. Techn. Japan)
Comments: 4 pages

We show that all f(R) modified gravity theories are conformally identical to models of quintessence in which matter is coupled to dark energy with a large coupling. This strong coupling induces a cosmological evolution radically different from standard cosmology. We find that in all f(R) theories that behave as a power of R at large or small R (which include all those proposed so far in the literature) the scale factor during the matter phase grows as t^{1/2} instead of the standard law t^{2/3}. This behaviour is grossly inconsistent with cosmological observations (e.g. WMAP), thereby ruling out these models even if they pass the supernovae test and can escape the local gravity constraints.

 

astro-ph/0603704 [abs, ps, pdf, other] :

Title: Dark Matter Velocity Distribution in the Context of Eddington's Theory
Authors: J.D. Vergados (University of Ioannina, Ioannina, Greece), D. Owen (Department of Physics, Ben Gurion University, Israel)
Comments: 19 LaTex pages, 26 figures

Exotic dark matter together with the vacuum energy (associated with the cosmological constant) seem to dominate the Universe. Thus its direct detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). One essential ingredient in obtaining the direct detection rates is the density and the velocity distribution of the LSP in our vicinity. In the present paper we study simultaneously density profiles and velocity distributions in the context of the Eddington's theory. In such a theory, unlike the commonly assumed Maxwell-Boltzmann (M-B) distribution, the upper bound of the velocity arises naturally from the potential.

 

astro-ph/0603705 [abs, ps, pdf, other] :

Title: Infrared Spectra and Visibilities as Probes of the Outer Atmospheres of Red Supergiant Stars
Authors: Takashi Tsuji
Comments: 47 pages, 14 Postscript figures, to be published in the Astrophysical Journal

In the light of the recent results of the stellar interferometry, we examine the nature of the extra molecular layer outside the photosphere of red super- giant stars, so far studied mostly with the use of the infrared spectra. Although the visibility data are more direct probes of the spatial structure of the outer atmosphere, it is essential that they are analyzed in combination with the spectral data of a wide spectral coverage. In the case of the M2 supergiant mu Cephei, several sets of data, both spectra and visibilities, strongly suggested the presence of an extra-molecular layer, and its basic parameters are estimated to be: excitation temperature T_ex = 1600 K, column densities of CO and H2O N_col = 3.0d+20/cm2, and inner radius R_in = 2.0R*. The result shows reasonable agreement with the one based on the infrared spectra alone, and this may be because the infrared spectra already include some information on the spatial structure of the outer atmosphere. It is important, however, that the model inferred from the spectra is now fully supported with the recent visibility data. In the case of the M2 supergiant alpha Orionis, the infrared spectra and visibilities show a consistent picture in that its molecular layer is closer to the photosphere (R_in = 1.3R*) with higher gas temperature (T_ex = 2250 K) and lower gas column density (N_col = 1.0d+20/cm2), compared with that of mu Cephei. Some controversy on the interpretation of the mid infrared data of alpha Orionis can be reconciled.

 

astro-ph/0603706 [abs, ps, pdf, other] :

Title: Planetary Nebula Velocities in the Disk and Bulge of M31
Authors: C. Halliday, D. Carter, T.J. Bridges, Z.C. Jackson, M.I. Wilkinson, D.P. Quinn, N.W. Evans, N.G. Douglas, H.R. Merrett, M.R. Merrifield, A.J. Romanowsky, K. Kuijken, M.J. Irwin
Comments: 27 pages, accepted for publication in MNRAS

We present radial velocities for a sample of 723 planetary nebulae (PNe) in the disk and bulge of M31, measured using the WYFFOS fibre spectrograph on the William Herschel telescope. Velocities are determined using the [OIII] 5007 Angstrom emission line. Rotation and velocity dispersion are measured to a radius of 50 arcminutes (11.5 kpc), the first stellar rotation curve and velocity dispersion profile for M31 to such a radius. Our kinematics are consistent with rotational support at radii well beyond the bulge effective radius of 1.4kpc, although our data beyond a radius of 5kpc are limited. We present tentative evidence for kinematic substructure in the bulge of M31 to be studied fully in a later work. This paper is part of an ongoing project to constrain the total mass, mass distribution and velocity anisotropy of the disk, bulge and halo of M31.

 

astro-ph/0603707 [abs, ps, pdf, other] :

Title: Interactions, Mergers and the Fundamental Mass Relations of Galaxies
Authors: Patricia B. Tissera, Analia Smith Castelli, Cecilia Scannapieco
Comments: 11 pages, 7 figures, accepted for publication in A&A

We present a study of the effects of mergers and interactions on the mass distribution of galactic systems in hierarchical clustering scenarios using the disc-bulge structural parameters and their dynamical properties to quantify them. We focus on the analysis of the Fundamental Mass Plane relation, finding that secular evolution phases contribute significantly to the determination of a plane with a slope in agreement to that of the observed luminosity relation. In these simulations, secular phases are responsible for the formation of compact stellar bulges with the correct structural parameter combination. We also test that the relations among these parameters agree with observations. Taking into account these results, the hierarchical growth of the structure predicts a bulge formation scenario for typical field spiral galaxies where secular evolution during dissipate mergers plays a fundamental role. Conversely, subsequent mergers can help to enlarge the bulges but do not seem to strongly modify their fundamental mass relations. Systems get to the local mass relations at different stages of evolution (i.e. different redshifts) so that their formation histories introduce a natural scatter in the relations. Our results suggest that the formation mechanisms of the bulge and disc components, satisfying their corresponding fundamental mass relations, might be coupled and that secular evolution could be the possible connecting process.

 

astro-ph/0603708 [abs, ps, pdf, other] :

Title: XMM-Newton Discovery of the X-ray Transient XMMU J181227.8-181234 in the Galactic Plane
Authors: Edward M. Cackett (St Andrews), Rudy Wijnands (Amsterdam), Ron Remillard (MIT)
Comments: 7 pages, 6 figures, 1 table, submitted to MNRAS

We report the discovery of an X-ray transient, observed in outburst with XMM-Newton on March 20, 2003, and with position 18h12m27.8s, -18 12 34 (J2000, approximate positional error 2"). No known source is present at this position and the source was not detected during published ROSAT or ASCA observations of that region. However, the source may be associated with 1H1812-182 detected by HEAO 1, although the error bars on the HEAO 1 position are very large and the two sources could also be unrelated. Therefore, we name the source XMMU J181227.8-181234. Initially, the source was not detected using the All-Sky Monitor (ASM) on-board the Rossi X-ray Timing Explorer, however, reprocessing of the ASM data shows that the source was in fact detected and it was active for about 50 days. The X-ray spectrum of this transient is fitted equally well by an absorbed power-law (with a spectral index of 2.5) or multi-colour disk blackbody model (with kT ~ 2 keV), where we find that the source is highly absorbed. We detect an unabsorbed 0.5-10 keV flux in the range (2-5)E-9 ergs cm^{-2} s^{-1}, which at a distance of 8 kpc corresponds to a 0.5-10 keV luminosity of (1-4)E37 ergs s^{-1}. No pulsations were detected by timing analysis. A colour-colour diagram from ASM data of different accreting objects suggests that the transient is a high-mass X-ray binary, as is also suggested by the high absorption compared to the average interstellar value in the direction of the source. However, the power-law spectral index is far more typical of a low-mass X-ray binary. Thus, we are unable to conclusively identify the nature of the transient. We also report on three sources first detected by the ASCA Galactic Plane Survey that are close to this transient.

 

astro-ph/0603709 [abs, ps, pdf, other] :

Title: The Limits of Bound Structures in the Accelerating Universe
Authors: Rolando Dünner, Pablo A. Araya, Andrés Meza, Andreas Reisenegger
Comments: 10 pages, 11 figures
Journal-ref: MNRAS 366, 803-811 (2006)

According to the latest evidence, the Universe is entering an era of exponential expansion, where gravitationally bound structures will get disconnected from each other, forming isolated `island universes'. In this scenario, we present a theoretical criterion to determine the boundaries of gravitationally bound structures and a physically motivated definition of superclusters as the largest bound structures in the Universe. We use the spherical collapse model self-consistently to obtain an analytical condition for the mean density enclosed by the last bound shell of the structure (2.36 times the critical density in the present Universe, assumed to be flat, with 30 per cent matter and 70 per cent cosmological constant, in agreement with the previous, numerical result of Chiueh and He). $N$-body simulations extended to the future show that this criterion, applied at the present cosmological epoch, defines a sphere that encloses $\approx 99.7$ per cent of the particles that will remain bound to the structure at least until the scale parameter of the Universe is 100 times its present value. On the other hand, $(28\pm 13)$ per cent of the enclosed particles are in fact not bound, so the enclosed mass overestimates the bound mass, in contrast with the previous, less rigorous criterion of, e.~g., Busha and collaborators, which gave a more precise mass estimate. We also verify that the spherical collapse model estimate for the radial infall velocity of a shell enclosing a given mean density gives an accurate prediction for the velocity profile of infalling particles, down to very near the centre of the virialized core.

 

astro-ph/0603710 [abs, ps, pdf, other] :

Title: Relative spectral lag: an new redshift indicator to measure the cosmos with gamma-ray bursts
Authors: Zhi-Bin Zhang, Jia-Gan Deng, Rui-Jing Lu, Hai-Feng Gao
Comments: 16 pages, 5 figures

Using 64 ms count data for long gamma-ray bursts ($T_{90}>$2.6s), we analyze the quantity, relative spectral lag (RSL), which is defined as $\tau_{31}/FWHM_{(1)}$, where $\tau_{31}$ is the spectral lag between energy bands 1 and 3, and $FWHM_{(1)}$ denotes full width at half maximum of the pulse in energy channel 1. To get insights into features of the RSLs, we investigate in detail all the correlations between them and other parameters with a sub-sample including nine long bursts. The general cross-correlation technique is adopted to measure the lags between two different energy bands. We can derive the below conclusions. Firstly, the distribution of RSLs is normal and oncentrates on around the value of 0.1. Secondly, the RSLs are weakly correlated with $FWHM$, asymmetry, peak flux ($F_{p}$), peak energy ($E_{p}$) and spectral indexes ($\alpha$ and $\beta$), while they are uncorrelated with $\tau_{31}$, hardness-ratio ($HR_{31}$) and peak time ($t_m$). The final but important discovery is that redshift ($z$) and peak luminosity ($L_{p}$) are strongly correlated with the RSLs which can be measured easily and directly. We find that the RSL is a good redshift and peak luminosity estimator.

 

astro-ph/0603711 [abs, ps, pdf, other] :

Title: Current Advances in the Methodology and Computational Simulation of the Formation of Low-Mass Stars
Authors: Richard I. Klein, Shu-ichiro Inutsuka, Paolo Padoan, Kohji Tomisaka
Comments: Protostars and Planets Chapter

Developing a theory of low-mass star formation ($\sim 0.1$ to 3~M$_{\odot}$) remains one of the most elusive and important goals of theoretical astrophysics. The star-formation process is the outcome of the complex dynamics of interstellar gas involving non-linear interactions of turbulence, gravity, magnetic field and radiation. The evolution of protostellar condensations, from the moment they are assembled by turbulent flows to the time they reach stellar densities, spans an enormous range of scales, resulting in a major computational challenge for simulations. Since the previous Protostars and Planets conference, dramatic advances in the development of new numerical algorithmic techniques have been successfully implemented on large scale parallel supercomputers. Among such techniques, Adaptive Mesh Refinement and Smooth Particle Hydrodynamics have provided frameworks to simulate the process of low-mass star formation with a very large dynamic range. It is now feasible to explore the turbulent fragmentation of molecular clouds and the gravitational collapse of cores into stars self-consistently within the same calculation. The increased sophistication of these powerful methods comes with substantial caveats associated with the use of the techniques and the interpretation of the numerical results. In this review, we examine what has been accomplished in the field and present a critique of both numerical methods and scientific results. We stress that computational simulations should obey the available observational constraints and demonstrate numerical convergence. Failing this, results of numerical simulations do not advance our understanding of low-mass star formation.

 

astro-ph/0603712 [abs, ps, pdf, other] :

Title: The Correlation of Narrow Line Emission and X-ray Luminosity in Active Galactic Nuclei
Authors: Hagai Netzer, V. Mainier, P. Rosati, Benny Trakhtenbrot
Comments: 10 pages, 3 diagrams, accepted by A&A

We combine emission line and X-ray luminosities for 45 sources from the Chandra Deep Field South (CDF-S), and seven HELLAS sources, to obtain a new sample of 52 X-ray selected type-II active galactic nuclei (AGNs). Eighteen of our sources are very luminous with a typical, absorption-corrected 2-10 keV luminosity of few 10^{44} erg/sec (type-II QSOs). We compare the emission line properties of the new sources with emission line and X-ray luminosities of known low redshift, mostly lower luminosity AGNs by using a composite spectrum. We find that ${\rm L_{[OIII]}}$/${\rm L_{2-10}}$ and ${\rm L_{[OII]}}$/${\rm L_{2-10}}$ decrease with L(2-10 keV) such that ${\rm L_{[OIII]}}/{\rm L_{2-10}} \propto {\rm L_{2-10}}^{-0.42}$. The trend was already evident, yet neglected in past low redshift samples. This lead to erroneous calibration of the line-to-X-ray luminosity in earlier AGN samples. The analysis of several type-I samples shows the same trend with a similar slope but a median ${\rm L_{[OIII]}}$/${\rm L_{2-10}}$ which is larger by a factor of about two compared with optically selected type-II samples. We interpret this shift as due to additional reddening in type-II sources and comment in general on the very large extinction in many type-II objects and the significantly smaller average reddening of the SDSS type-II AGNs. The decrease of ${\rm L_{[OIII]}}$/${\rm L_{2-10}}$ with L(2--10 keV) is large enough to suggest that a significant fraction of high luminosity high redshift type-II AGNs have very weak emission lines that may have escaped detection in large samples. A related decrease of EW([OIII]) with optical continuum luminosity is demonstrated by an analysis of 12,000 type-I SDSS AGNs.

 

astro-ph/0603713 [abs, ps, pdf, other] :

Title: 4U 1344-60: a bright intermediate Seyfert galaxy at z=0.012 with a relativistic Fe Kalpha emission line
Authors: E. Piconcelli (1,2), M. Sanchez-Portal, M. Guainazzi, A. Martocchia, C. Motch, A. C. Schroeder, S. Bianchi, E. Jimenez-Bailon, G. Matt ((1) Osservatorio Astronomico di Roma, (2) European Space Astronomy Center (ESA))
Comments: Accepted for publication in Astronomy & Astrophysics

We present analysis of the optical and X-ray spectra of the low Galactic latitude bright (F(2-10) = 3.6 10^{-11} erg/cm2/s) source 4U 1344-60. On the basis of the optical data we propose to classify 4U 1344-60 as an intermediate type Seyfert galaxy and we measure a value of z=0.012+/-0.001 for its redshift.
From the XMM-Newton observation we find that the overall X-ray spectral shape of 4U 1344-60 is complex and can be described by a power-law continuum (Gamma ~ 1.55) obscured by two neutral absorption components (Nh(f) ~ 10^{22} cm^{-2} and Nh(p) ~ 4 10^{22} cm^{-2}), the latter covering only the ~50% of the primary X-ray source. The X-ray data therefore lend support to our classification of 4U 1344-60. It exhibits a broad and skewed Fe Kalpha line at 6.4 keV, which suggests the existence of an accretion disk that is able to reprocess the primary continuum down to a few gravitational radii. Such a line represents one of the clearest examples of a relativistic line observed by XMM-Newton so far. Our analysis has also revealed the marginal presence of two narrow line-like emission features at ~4.9 and ~5.2 keV.

 

astro-ph/0603714 [abs, ps, pdf, other] :

Title: The star formation history of early-type galaxies as a function of mass and environment
Authors: M.S. Clemens, A. Bressan, B. Nikolic, P. Alexander, F. Annibali, R. Rampazzo
Comments: 19 pages, 15 figures. Submitted to MNRAS

Using the third data release of the Sloan Digital Sky Survey (SDSS) we have rigorously defined a volume limited sample of early-type galaxies in the redshift range z < 0.1. We have defined the density of the local environment for each galaxy using a method which takes account of the redshift bias introduced by survey boundaries if traditional methods are used. At luminosities greater than our absolute r-band magnitude cutoff of -20.45 the mean density of environment shows no trend with redshift. We calculate the Lick indices for the entire sample and correct for aperture effects and velocity dispersion in a model independent way. Although we find no dependence of redshift or luminosity with environment we do find that the mean velocity dispersion, sigma, of early-type galaxies in dense environments tends to be higher than in low density environments. Taking account of this effect we find that several indices show small but very significant trends with environment that are not the result of the correlation between indices and velocity dispersion. The statistical significance of the data is sufficiently high to reveal that models accounting only for alpha-enhancement struggle to produce a consistent picture of age and metallicity of the sample galaxies, whereas a model that also includes carbon enhancement fares much better. We find that early-type galaxies in the field are younger than those in environments typical of clusters but that neither metallicity, alpha-enhancement nor carbon enhancement are influenced by the environment. The youngest early-type galaxies in both field and cluster environments are those with the lowest sigma. However, there is some evidence that the objects with the largest sigma are slightly younger, especially in denser environments.

 

astro-ph/0603715 [abs, ps, pdf, other] :

Title: XSS J00564+4548 and IGR J00234+6141 -- new cataclysmic variables from RXTE and INTEGRAL all sky surveys
Authors: I. F. Bikmaev (1,2), M. G. Revnivtsev (3,4), R. A. Burenin (3), R. A. Sunyaev (3,4) ((1) KSU, Kazan, Russia, (2) Academy of Sciences of Tatarstan, Kazan, Russia, (3) IKI, Moscow, Russia, (4) MPA, Garching, Germany)
Comments: 5 pages, 8 figures, accepted for publication in Astronomy Letters

We present the results of optical identification of two X-ray sources from RXTE and INTEGRAL all sky surveys: XSS J00564+4548 and IGR J00234+6141. Using the optical data from Russian-Turkish 1.5-m Telescope (RTT150) and SWIFT X-ray observations, we show that these sources most probably are intermediate polars, i.e. binary systems with accreting white dwarfs with not very strong magnetic field (<~10 MG). Periodical oscillations of optical emission with periods 480 s and 570 s were found. We argue that these periods most probably correspond to the rotating periods of the white dwarfs in these systems. Further optical observations scheduled at RTT150 will allow to study the parameters of these systems in more detail.

 

astro-ph/0603716 [abs, ps, pdf, other] :

Title: Photometric observations of Supernovae 2000E, 2001B, 2001V, and 2001X
Authors: D. Yu. Tsvetkov
Comments: 12 pages, 8 figures, 6 tables
Journal-ref: Variable Stars (Peremennye Zvezdy) Vol. 26, No. 3, 2006, http://www.astronet.ru/db/varstars/msg/1212583

CCD BVRI photometry is presented for two type Ia supernovae 2000E and 2001V, for SN Ib 2001B and SN II-P 2001X. The parameters of light curves and absolute magnitudes at maximum light are estimated. It is shown that all four supernovae are typical for their classes considering the shape of their light curves and maximum luminosity.

 

astro-ph/0603717 [abs, ps, pdf, other] :

Title: Cygnus A: A Long Wavelength Resolution of the Hot Spots
Authors: T. J. W. Lazio (1), A. S. Cohen (1), N. E. Kassim (1), R. A. Perley (2), W. C. Erickson (3), C. L. Carilli (2), P. C. Crane (1) ((1) NRL; (2) NRAO; (3) Bruny Island Radio Spectrometer and U. Tasmania)
Comments: 7 pages, AASTeX, 3 figures; accepted in ApJL

This paper presents observations of Cygnus A at 74 and 327 MHz at angular resolutions of approximately 10" and 3", respectively. These observations are among the highest angular resolutions obtained below 1000 MHz for this object. While the angular resolution at 74 MHz is not sufficient to separate clearly the hot spots from the lobes, guided by 151 and 327 MHz images, we have estimated the 74 MHz emission from the hot spots. We confirm that the emission from both the western and eastern hot spots flattens at low frequencies and that there is a spectral asymmetry between the two. For the eastern hot spot, a low-energy cutoff in the electron energy spectrum appears to explain the flattening, which implies a cutoff Lorentz factor \gamma_min ~ 300, though we cannot exclude the possibility that there might be a moderate level of free-free absorption. For the western hot spot, the current observations are not sufficient to distinguish between a free-free absorped power-law spectrum and a synchrotron self-absorbed spectrum.

 

astro-ph/0603718 [abs, ps, pdf, other] :

Title: Structure of the hot object in the symbiotic prototype Z And during its 2000-03 active phase
Authors: A. Skopal, A. Vittone, L. Errico, M. Otsuka, S. Tamura, M. Wolf, V. Elkin
Comments: 18 pages (printed format), 9 figures, 4 tables, 2 appendices; accepted for publication in A&A (02/03/2006)

Aims: To investigate structure of the hot object in the symbiotic prototype Z And during its major 2000-03 active phase. Methods: Analysis of the far ultraviolet, optical low- and high-resolution spectroscopy and UBVR photometry. Reconstruction of the spectral energy distribution (SED) during the outburst. The Raman scattering process. Results: At the initial stages of the outburst the hot object was characterized by the two-temperature spectrum (a warm stellar radiation and a strong nebular emission) with signatures of a mass-outflow at moderate (100-200 km/s) and very high (1000-2000 km/s) velocities. The corresponding structure of the hot object consists of an optically thick, slowly-expanding disk-like material encompassing the accretor at the orbital plane and a fast optically thin wind over the remainder of the star. A striking similarity of [FeVII]6087 and Raman 6825 profiles at/after the dilution of the disk suggested their origin within the interaction zone where the winds from the binary components collide.

 

astro-ph/0603719 [abs, ps, pdf, other] :

Title: GeV photons from up-scattering of supernova shock breakout X-rays by an outside GRB jet
Authors: Xiang-Yu Wang, Peter Meszaros
Comments: 10 pages, no figures, submitted to ApJL

Shock breakout X-ray emission has been reported for the first time from a supernova connected with a gamma-ray burst, namely GRB060218/SN2006aj. The gamma-ray emission and the power-law decaying X-ray afterglow are ascribed to a highly relativistic jet, while the thermal soft X-rays are thought to be produced when the radiation-dominated shock breaks from the optically thick stellar wind. We study the inverse Compton emission of the breakout thermal soft X-rays scattered by relativistic electrons in the jet forward shock, which is is expected to be at larger radii than the breakout shock. This IC emission produces sub-GeV to GeV photons, which may be detectable by GLAST. The detection of such GeV photons simultaneously with the supernova shock breakout emission would give evidence for the presence of a GRB jet ahead of the shock while the shock is breaking out. The anisotropic scattering between the X-rays and relativistic electrons may lead to large angle emission outside of the jet opening angle. This has implications for the detection of GeV photons from burstless type Ib/c hypernova shock breakout, which due to its more isotropic emission might be observed with wide-field X-ray cameras such as LOBSTER.

 

astro-ph/0603720 [abs, ps, pdf, other] :

Title: Imaging the Dust Trail and Neckline of 67P/Churyumov-Gerasimenko
Authors: J. Agarwal (1), H. Boehnhardt (2), E. Gruen (1 and 3) ((1) MPI-K Heidelberg, (2) MPS Katlenburg-Lindau, (3) HIGP Honolulu)
Comments: 4 pages, 3 figures, to be published in the proceedings book of the conference "Dust in Planetary Systems 2005"

We report on the results of nearly 10 hours of integration of the dust trail and neckline of comet 67P/Churyumov-Gerasimenko (67P henceforth) using the Wide Field Imager at the ESO/MPG 2.2m telescope in La Silla. The data was obtained in April 2004 when the comet was at a heliocentric distance of 4.7 AU outbound. 67P is the target of the Rosetta spacecraft of the European Space Agency. Studying the trail and neckline can contribute to the quantification of mm-sized dust grains released by the comet. We describe the data reduction and derive lower limits for the surface brightness. In the processed image, the angular separation of trail and neckline is resolved. We do not detect a coma of small, recently emitted grains.

 

astro-ph/0603721 [abs, ps, pdf, other] :

Title: A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an alpha-enhanced metal distribution
Authors: A. Pietrinferni (INAF-OA Teramo), S. Cassisi (INAF-OA Teramo), M. Salaris (J. Moores Univ, Liverpool), F. Castelli, (INAF-OA Trieste)
Comments: 46 pages, 20 figures, ApJ in press, the whole database presented in this paper can be foud at this http URL

[Abridged] We present a large, new set of stellar evolution models and isochrones for an alpha-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our stellar model library for a distribution already presented in Pietrinferni et al.(2004). The effect of the alpha-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state and, for the first time, the bolometric corrections, and color transformations. This allows us to avoid the inconsistent use - common to all alpha-enhanced model libraries currently available - of scaled-solar bolometric corrections and color transformations for alpha-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U,B portion of stellar spectra for T_{eff}<=6500K, are significantly affected by the metal mixture, especially at the higher metallicities. We also provide complete sets of evolutionary models for low-mass, He-burning stellar structures covering the whole metallicity range, to enable synthetic horizontal branch simulations. We compare our database with several widely used stellar model libraries from different authors, as well as with various observed color magnitude and color-color diagrams (Johnson-Cousins BVI and near infrared magnitudes, Stromgren colors) of Galactic field stars and globular clusters. We also test our isochrones comparing integrated optical colors and Surface Brightness Fluctuation magnitudes with selected globular cluster data. We find a general satisfactory agreement with the empirical constraints.

 

astro-ph/0603722 [abs, ps, pdf, other] :

Title: Characterizing stellar populations in spiral disks
Authors: M. Molla, S. Cantin, C. Robert, A. Pellerin, E. Hardy
Comments: 5 pages, to be published in "Science Perspectives for 3D Spectroscopy", Eds. M. Kissler-Patig, M.M. Roth and J.R. Walsh (Springer-Verlag, ESO astrophysics symposia series)

It is now possible to measure detailed spectral indices for stellar populations in spiral disks. We propose to interpret these data using evolutionary synthesis models computed from the Star Formation Histories obtained from chemical evolutionary models. We find that this technique is a powerful tool to discriminate between old and young stellar populations. We show an example of the power of Integral Field spectroscopy in unveiling the spatial distribution of populations in a barred galaxy.

 

astro-ph/0603723 [abs, ps, pdf, other] :

Title: Observational constraints on energetic particle diffusion in young SNRs: amplified magnetic field and maximum energy
Authors: E. Parizot, A. Marcowith, J. Ballet, Y. A. Gallant
Comments: 11 pages, 3 figures, accepted for publication in A&A

Constraints on the diffusion and acceleration parameters in five young supernova remnants (SNRs) are derived from the observed thickness of their X-ray rims, as limited by the synchrotron losses of the highest energy electrons, assuming uniform and isotropic turbulence. It is shown that the magnetic field must be amplified up to values between 250 and 500 microGauss in the case of Cas A, Kepler, and Tycho, or ~ 100 microGauss in the case of SN 1006 and G347.3-0.5. The diffusion coefficient at the highest electron energy can also be derived from the data, by relating the X-ray energy cutoff to the acceleration timescale. Values typically between 1 and 10 times the Bohm diffusion coefficient are found to be required. We also find interesting constraints on the energy dependence of the diffusion coefficient. This favours diffusion regimes between the Kraichnan and the Bohm regime, and rejects turbulence spectrum indices larger than ~ 3/2. Finally, the maximum energy of the accelerated particles is found to lay between 10^13 and 5 10^13 eV for electrons, and around Z \times 8 10^14 eV at most for nuclei (or ~ 2.5 times less if a Bohm diffusion regime is assumed), roughly independently of the compression ratio assumed at the shock. Even by taking advantage of the uncertainties on the measured parameters, it appears very difficult for the considered SNRs in their current stage of evolution to produce protons up to the knee of the cosmic-ray spectrum, at ~ 3 10^15 eV, and essentially impossible to accelerate Fe nuclei up to either the ankle at ~ 3 10^18 eV or the second knee at ~ 5 10^17 eV.

 

astro-ph/0603724 [abs, ps, pdf, other] :

Title: Evidence for precession of the isolated neutron star RX J0720.4-3125
Authors: F. Haberl (MPE), R. Turolla (Univ. Padova), C.P. De Vries (SRON), S. Zane (MSSL), J. Vink (Univ. Utrecht), M. Mendez (SRON), F. Verbunt (Univ. Utrecht)
Comments: Accepted for publication in A&A Letters, 5 pages, 5 figures

The XMM-Newton spectra of the isolated neutron star RX J0720.4-3125 obtained over 4.5 years can be described by sinusoidal variations in the inferred blackbody temperature, the size of the emitting area and the depth of the absorption line with a period of 7.1 +/- 0.5 years, which we suggest to be the precession period of the neutron star. Precession of a neutron star with two hot spots of different temperature and size, probably not located exactly in antipodal positions, may account for the variations in the X-ray spectra, changes in the pulsed fraction, shape of the light curve and the phase-lag between soft and hard energy bands observed from RX J0720.4-3125. An independent sinusoidal fit to published and new pulse timing residuals from a coherent analysis covering ~12 years yields a consistent period of 7.7 +/- 0.6 years supporting the precession model.

 

astro-ph/0603725 [abs, ps, pdf, other] :

Title: Study of time lags in HETE-2 Gamma-Ray Bursts with redshift: search for astrophysical effects and Quantum Gravity signature
Authors: J.Bolmont, J.-L.Atteia, A.Jacholkowska, F.Piron, G.Pizzichini
Comments: 12 pages, 12 figures

We present an analysis of 12 Gamma-Ray Bursts with measured redshift, detected by the HETE-2 mission in view of measurement of time lags related to astrophysical effects, and search for Quantum Gravity signature in the frame of an extra-dimension string model. The study of time lags between spikes in the light curves in different energy bands as a function of redshift may lead to the detection of effects due to Quantum Gravity. The wavelet transform procedures are used both for de-noising the light curves and for sharp transition detection. Various energy ranges are considered and systematic effects due to selections and cuts are evaluated. No significant Quantum Gravity effect is detected from the study of the maxima of the spikes and a lower limit at 95% CL on the Quantum Gravity scale parameter of 2x10^15 GeV is set. The analysis of the minima in the light curves leads to a more significant result on the Quantum Gravity scale, to be further investigated with higher statistics.

 

astro-ph/0603726 [abs, ps, pdf, other] :

Title: Analisys of the Luminosity-Stellar Mass-Metallicity Relation in cosmological simulations
Authors: Maria Emilia De Rossi (1), Patricia Beatriz Tissera (1), Cecilia Scannapieco (1) ((1) Institute for Astronomy and Space Physics, Ciudad de Buenos Aires, Argentina)
Comments: To appear in the proceedings of the 11th Latin-American Regional IAU Meeting, (Dec 2005) Pucon, Chile

We study the Luminosity-Metallicity Relation and the Stellar Mass-Metallicity Relation by performing chemo-dynamical simulations in a cosmological scenario. Our results predict a tight linear correlation between oxygen chemical abundance and luminosity for galactic systems up to z=3. The Luminosity-Metallicity Relation evolves with redshift in such a way that systems at a given oxygen abundance were ~3 dex brighter at z=3 compared to local ones, in good agreement with observations. We determin also a characteristic stellar mass M_c~10^(10.2) M_sun/h above which the Stellar Mass-Metallicity Relation starts to flatten. We encounter that this mass arises as a consequence of the hierarchical aggregation of structure in a LCDM universe and segregates two galactic populations with different astophysical properties.

 

astro-ph/0603727 [abs, ps, pdf, other] :

Title: Bulk Motion of Ultrarelativistic Conical Blazar Jets
Authors: Gopal-Krishna, Paul J. Wiita, Samir Dhurde
Comments: 7 pages, 3 figures; accepted for publication in MNRAS

Allowing for the conical shape of ultrarelativistic blazar jets with opening angles of a few degrees on parsec-scales we show that their bulk Lorentz factors and viewing angles can be much larger than the values usually inferred by combining their flux variability and proper motion measurements. This is in accord with our earlier finding that such ultrarelativistic (Lorentz factor, Gamma > 30) conical jets can reconcile the relatively slow apparent motions of VLBI knots in TeV blazars with the extremely fast flows implied by their rapid gamma-ray variability. This jet geometry also implies that de-projected jet opening angles will typically be significantly underestimated from VLBI measurements. In addition, de-projected jet lengths will be considerably overestimated if high Lorentz factors and significant opening angles are not taken into account.

 

astro-ph/0603728 [abs, ps, pdf, other] :

Title: Active Galactic Nuclei: Unification, Blazar Variability and the Radio Galaxy/Cosmology Interface
Authors: Paul J. Wiita (Georgia State U.)
Comments: 10 pages, 0 figures; to appear in J. Korean Physical Society; summary of lectures presented at the 2006 Winter School on Black Hole Astrophysics, Pohang, Korea

We first review some basic properties of the most important classes of active galactic nuclei (AGN), including quasars, blazars, Seyfert galaxies and radio galaxies. The most commonly accepted type of scheme designed to individually unify the radio-loud and radio-quiet categories of AGN is based upon three parameters: black hole mass, accretion rate, and our orientation to the accretion flow. Some recent evidence from optical microvariability of several classes of AGN points in favor of a strong unification scheme that unites both radio-loud and radio-quiet categories. An important question concerning the nature of blazars and other AGN whose jet emission appears to dominate their spectral energy distributions involves the velocities of those flows. A variety of apparently contradictory observations can be reconciled if such flows are ultrarelativistic but have an opening angle of a few degrees. Radio galaxies (RGs) were much more numerous at redshifts ~2 than they are today. Combining this fact with the realization that older RGs at such redshifts are very difficult to detect, and with cosmological simulations of the growth of structure in the universe has led us to propose that RG lobes have impacted a significant fraction of the cosmic web of baryons. These impacts may have triggered extensive star formation and perhaps even engendered new galaxies; they also probably played important roles in the spreading of magnetic fields and heavier elements into the intergalactic medium.

 

astro-ph/0603729 [abs, ps, pdf, other] :

Title: Nearby debris disk systems with high fractional luminosity reconsidered
Authors: A. Moor, P. Abraham, A. Derekas, Cs. Kiss, L.L. Kiss, D. Apai, C. Grady, Th. Henning
Comments: 47 pages, 6 figures, AASTeX preprint. Accepted for publication in the Astrophysical Journal

By searching the IRAS and ISO databases we compiled a list of 60 debris disks which exhibit the highest fractional luminosity values (fd>10^-4) in the vicinity of the Sun (d<120pc). Eleven out of these 60 systems are new discoveries. Special care was taken to exclude bogus disks from the sample. We computed the fractional luminosity values using available IRAS, ISO, and Spitzer data, and analysed the galactic space velocities of the objects. The results revealed that stars with disks of high fractional luminosity often belong to young stellar kinematic groups, providing an opportunity to obtain improved age estimates for these systems. We found that practically all disks with fd>5x10^-4 are younger than 100Myr. The distribution of the disks in the fractional luminosity versus age diagram indicates that (1) the number of old systems with high fd is lower than was claimed before; (2) there exist many relatively young disks of moderate fractional luminosity; and (3) comparing the observations with a current theoretical model of debris disk evolution a general good agreement could be found.

 

astro-ph/0603730 [abs, ps, pdf, other] :

Title: The multiwavelength afterglow of GRB 050721: a puzzling rebrightening seen in the optical but not in the X-ray
Authors: L.A. Antonelli, V. Testa, P. Romano, D. Guetta, K. Torii, V. D Elia, D. Malesani, G. Chincarini, S. Covino, P. D Avanzo, M. Della Valle, F. Fiore, D. Fugazza, A. Moretti, L. Stella, G. Tagliaferri, S. Barthelmy, D. Burrows, S. Campana, M. Capalbi, G. Cusumano, N. Gehrels, P. Giommi, D. Lazzati, V. La Parola, V. Mangano, T. Mineo, J. Nousek, P. T. OBrien, M. Perri
Comments: 8 pages, 7 figures, submitted to Astronomy & Astrophysics

Context. GRB050721 was detected by Swift and promptly followed-up, in the X-ray by Swift itself and, in the optical band, by the VLT operated, for the first time, in rapid response mode. A multiwavelength monitoring campaign was performed in order to study its afterglow behavior. Aims. We present the analysis of the early and late afterglow emission in both the X-ray and optical bands, as observed by Swift, a robotic telescope, and the VLT. We compare early observations with late afterglow observations obtained with Swift and the VLT in different bands in order to constrain the density of the medium in which the fireball is expanding. Methods. We have analyzed both the X-ray and the optical light curves and compared the spectral energy distribution of the afterglow at two different epochs. Results. We observed an intense rebrightening in the optical band at about one day after the burst which was not seen in the X-ray band. This is the first observation of a GRB afterglow in which a rebrightening is observed in the optical but not in the X-ray band. The lack of detection in X-ray of such a strong rebrightening at lower energies can be described with a variable external density profile. In such a scenario, the combined X-ray and optical observations allow us to derive the matter density at 10^15 cm from the burst. This is about a factor of 10 higher than in the inner region.

 

astro-ph/0603731 [abs, ps, pdf, other] :

Title: Jet-dominated advective systems: radio and X-ray luminosity dependence on the accretion rate
Authors: Elmar Koerding (Southampton), Rob Fender (Southampton), Simone Migliari (UCSD)
Comments: Accepted for publication in MNRAS

We present a novel method to measure the accretion rate of radio emitting X-ray binaries (XRBs) and active galactic nuclei (AGN) independently of the X-ray luminosity. The radio emission of the jet is used as a tracer for the accretion rate and is normalised using sources of known accretion rates: island state neutron stars and efficiently radiating black holes close to a state transition. We show that the radio power in black holes and neutron stars is comparable for a given mass accretion rate and verify empirically the assumed analytic scaling of the radio luminosity with accretion rate. As our accretion measure is independent of the X-ray luminosities, we can search for radiatively inefficient accretion in black holes by comparing the X-ray luminosities with the accretion rate in XRBs and AGN. While the X-ray luminosity of efficiently radiating objects scales linearly with accretion rate, the scaling of hard state black holes is quadratical, in agreement with theoretical models. We show that the turnover from the inefficient quadratic scaling to the linear scaling has to occur at accretion rates of 1-10 % Eddington both in XRBs and AGN. The comparison of both accretion states supports the idea that in a black hole in the hard state some accretion power is advected into the black hole while the jet power exceeds the X-ray luminosity: these are therefore jet-dominated advective systems.

 

astro-ph/0603732 [abs, ps, pdf, other] :

Title: Velocity dispersion, mass and the luminosity function of the fossil cluster RX J1416.4+2315
Authors: Eduardo S. Cypriano, Claudia L. Mendes de Oliveira, Laerte Sodré Jr
Comments: Submitted to AJ - 14 pages, 6 figures

We study the properties of the fossil cluster RX J1416.4+2315 through g' and i'-band imaging and spectroscopy of 25 member galaxies. The system is at a mean redshift of 0.137 and has a velocity dispersion of 584 km s^-1. Superimposed onto one quadrant of the cluster field there is a group of five galaxies at a mean redshift of 0.131, which, if included as part of the cluster, increases the velocity dispersion to 846 km/s. The central object of RX J1416.4+2315 is a normal elliptical galaxy, with no cD envelope. The luminosity function of the system, estimated by the number counts, and statistical background correction, in the range -22.6< M_g'< -16.6, is well fitted by a Schechter function with M_g'^* = -21.2 +/- 0.8 and alpha = -1.2 +/- 0.2 (H_0 = 70 km s^-1 Mpc^-1, Omega_M=0.3, Omega_Lambda=0.7). The luminosity function obtained from the spectroscopically confirmed members in both g' and i' bands agrees with the photometric results. The mass of the system, M ~ 0.9 \times 10^14 h^-1_70 M_sun, its M/L of 445 h_70 M_sun/L_B_sun and L_X of 11 10^43 h^-2_70 ergs s^-1 (bolometric) suggest that this system is the second example of known fossil cluster, after RX~J1552.2+2013, confirmed in the literature.

 

astro-ph/0603733 [abs, ps, pdf, other] :

Title: FH Leonis, the first dwarf nova member of a multiple star system?
Authors: N. Vogt
Comments: 3 pages, accepted for publication in Astronomy & Astrophysics

Sudden brightenings of HD 96273 or BD+07 2411B were observed with the HIPPARCOS satellite in 1992,which still require a convincing explanation. A new analysis of all known data of these two stars is given, including additional information on the Balmer line equivalent widths. The brightenings can be explained as SU UMa type dwarf nova outbursts, superimposed on the combined light of two normal F and G type main sequence stars. Since the hypothetical dwarf nova turns out to be located at the same distance as HD 96273 and BD+07 2411B, we possibly see here the first case of a cataclysmic variable as a member of a multiple star system. Questions on history and evolution, as well as possible ways to confirm this interpretation, are briefly outlined.

 

astro-ph/0603734 [abs, ps, pdf, other] :

Title: New DQ white dwarfs in the Sloan Digital Sky Survey DR4: confirmation of two sequences
Authors: D. Koester, S. Knist
Comments: submitted to Astronomy and Astrophysics

Using photometric selection criteria, and in a final step visual inspection of spectra, we find 65 DQ white dwarfs in the Data Release 4 of the Sloan Digital Sky Survey. 37 of these are new identifications, three more are reclassified DQ from DC, the other 25 have been described as DQ before in the literature. We derive effective temperatures and carbon abundances for 60 of these stars. The results confirm the main conclusions of Dufour et al.(2005). The majority of stars defines a clear sequence in the C abundance vs. Teff diagram, with high abundances found at high Teff and vice versa. We also confirm with high significance a second sequence with an abundance about 1 dex higher at the same Teff, and discuss the nature and possible origin of the high-C sequence.

 

astro-ph/0603735 [abs, ps, pdf, other] :

Title: Asteroseismic inferences on GW Vir variable stars in the frame of new PG 1159 evolutionary models
Authors: A. H. Córsico, L. G. Althaus
Comments: 24 pages, 6 tables and 11 figures. Accepted for publication in Astronomy and Astrophysics

An adiabatic, nonradial pulsation study of GW Vir stars is presented. The pulsation calculations are based on PG1159 evolutionary sequences with different stellar massess artificially derived from a full evolutionary sequence of 0.5895 Mo that has been computed taking into account the evolutionary history of the progenitor star. The artificial sequences were constructed by appropriately scaling the stellar mass of the 0.5895 Mo sequence well before the models reach the low-luminosity, high-gravity stage of the GW Vir domain. We compute g-mode pulsation periods appropriate to GW Vir variable stars. The implications for the mode-trapping properties of our PG 1159 models are discussed at length. We found that the mode-trapping features characterizing our PG 1159 models are mostly fixed by the stepped shape of the core chemical profile left by prior convective overshooting. This is particularly true at least for the range of periods observed in GW Vir stars. In addition, we make asteroseismic inferences about the internal structure of the GW Vir stars PG 1159-035, PG 2131+066, PG 1707+427 and PG 0122+200.

 

astro-ph/0603736 [abs, ps, pdf, other] :

Title: Asteroseismic inferences on GW Vir variable stars in the frame of new PG 1159 evolutionary models
Authors: A. H. Córsico, L. G. Althaus
Comments: 24 pages, 6 tables and 11 figures. Accepted for publication in Astronomy and Astrophysics

An adiabatic, nonradial pulsation study of GW Vir stars is presented. The pulsation calculations are based on PG1159 evolutionary sequences with different stellar masses artificially derived from a full evolutionary sequence of 0.5895 Mo that has been computed taking into account the evolutionary history of the progenitor star. The artificial sequences were constructed by appropriately scaling the stellar mass of the 0.5895 Mo sequence well before the models reach the low-luminosity, high-gravity stage of the GW Vir domain. We compute g-mode pulsation periods appropriate to GW Vir variable stars. The implications for the mode-trapping properties of our PG 1159 models are discussed at length. We found that the mode-trapping features characterizing our PG 1159 models are mostly fixed by the stepped shape of the core chemical profile left by prior convective overshooting. This is particularly true at least for the range of periods observed in GW Vir stars. In addition, we make asteroseismic inferences about the internal structure of the GW Vir stars PG 1159-035, PG 2131+066, PG 1707+427 and PG 0122+200.

 

astro-ph/0603737 [abs, ps, pdf, other] :

Title: Understanding Infrared Galaxy Populations: the SWIRE Legacy Survey
Authors: Michael Rowan-Robinson, Carol Lonsdale, Gene Smith, Jason Surace, Dave Shupe, Maria Polletta, Brian Siana, Tom Babbedge, Seb Oliver, Ismael Perez-Fournon, Alberto Franceschini, Alejandro Afonso Luis, David Clements, Payam Davoodi, Donovan Domingue, Andreas Efstathiou, Fan Fang, Duncan Farrah, Dave Frayer, Evanthia Hatziminaoglou, Eduardo Gonzalez-Solares, Kevin Xu, Deborah Padgett, Mattia Vaccari
Comments: 8 pages, 14 figures, to appear in proceedings of 'Spitzer IR Diagnostics Conference, Nov 14-16, 2005'

We discuss spectral energy distributions, photometric redshifts, redshift distributions, luminosity functions, source-counts and the far infrared to optical luminosity ratio for sources in the SWIRE Legacy Survey. The spectral energy distributions of selected SWIRE sources are modelled in terms of a simple set of galaxy and quasar templates in the optical and near infrared, and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and AGN dust torus) in the mid infrared. The optical data, together with the IRAC 3.6 and 4.5 mu data, have been used to determine photometric redshifts. For galaxies with known spectroscopic redshifts there is a notable improvement in the photometric redshift when the IRAC data are used, with a reduction in the rms scatter from 10% in (1+z) to 5%. While further spectroscopic data are needed to confirm this result, the prospect of determining good photometric redshifts for the 2 million extragalactic objects in SWIRE is excellent. The distribution of the different infrared sed types in the L{ir}/L{opt} versus L{ir} plane, where L{ir} and L{opt} are the infrared and optical bolometric luminosities, is discussed. Source-counts at 24, 70 and 160 mu are discussed, and luminosity functions at 3.6 and 24 mu are presented.

 

astro-ph/0603738 [abs, ps, pdf, other] :

Title: Swift XRT Observations of the Afterglow of XRF 050416A
Authors: Vanessa Mangano, Valentina La Parola, Giancarlo Cusumano, Teresa Mineo, Daniele Malesani, Jaroslaw Dyks, Sergio Campana, Milvia Capalbi, Guido Chincarini, Paolo Giommi, Alberto Moretti, Matteo Perri, Patrizia Romano, Gianpiero Tagliaferri, David N. Burrows, Olivier Godet, Stephen T. Holland, Jamie A. Kennea, Kim L. Page, Judith L. Racusin, Peter W. A. Roming, Bing Zhang
Comments: 28 pages, 3 tables, 6 figures. Shortened abstract for posting to astro-ph. Submitted to ApJ

Swift discovered XRF 050416A with the BAT and began observing it with its narrow field instruments only 64.5 s after the burst onset. Its very soft spectrum classifies this event as an X-ray flash. The afterglow X-ray emission was monitored up to 74 days after the burst. The X-ray light curve initially decays very fast, subsequently flattens and eventually steepens again, similar to many X-ray afterglows. The first and second phases end about 172 and 1450 s after the burst onset, respectively. We find evidence of spectral evolution from a softer emission with photon index $\Gamma \sim 3.0$ during the initial steep decay, to a harder emission with $\Gamma \sim 2.0$. The spectra show intrinsic absorption in the host galaxy. The consistency of the initial photon index with the high energy BAT photon index suggests that the initial phase of the X-ray afterglow may be the low-energy tail of the prompt emission. This also requires that the spectral peak energy of the burst decreased from the time of the BAT to the time of the XRT observation, becoming as low as $\simlt 1$ keV. Hardness ratio evolution during the prompt emission also supports this interpretation. The lack of jet break signatures in the X-ray afterglow light curve is not consistent with the Ghirlanda and Liang relations. The standard uniform jet model can give a possible description of the XRF 050416A X-ray afterglow for an opening angle larger than a few tens degrees, although numerical simulations show that the late time decay is slightly flatter than expected from on-axis viewing of a uniform jet. A structured Gaussian-type jet model with uniform Lorentz factor distribution and viewing angle outside the Gaussian core is another possibility although a full agreement with data is not achieved with the numerical models explored.

 

astro-ph/0603739 [abs, ps, pdf, other] :

Title: Spitzer 4.5 micron Luminosity-Metallicity and Mass-Metallicity Relations for Nearby Dwarf Irregular Galaxies
Authors: Henry Lee (1), E. D. Skillman (1), J. M. Cannon (2), D. C. Jackson (1), R. D. Gehrz (1), E. Polomski (1), C. E. Woodward (1) ((1) University of Minnesota, (2) MPIA Germany)
Comments: 5 pages, 3 figures. To appear in the proceedings of ESO Astrophysics Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V. Ivanov, & J. Borissova (Springer)

For a sample of 25 dwarf irregular galaxies with distances D < 5 Mpc and measured oxygen abundances, we present results derived from stellar masses and galaxy luminosities from near-infrared imaging with IRAC on the Spitzer Space Telescope. We have constructed the appropriate luminosity-metallicity (L-Z) and mass-metallicity (M-Z) relations, and compared these relations with their corresponding relations from the Sloan Digital Sky Survey (SDSS). We obtain the following results. 1. The dispersion in the near-infrared L-Z relation is reduced with respect to the dispersion in the optical L-Z relation, which agrees with expectations for reduced variations of stellar mass-to-light ratios at longer wavelengths compared to optical wavelengths. 2. The dispersion in the optical L-Z relation is similar over approximately 11 mag in optical luminosity. 3. With our constructed M-Z relation, we have extended the SDSS M-Z relation to lower masses by about 2.5 dex in stellar mass. 4. The dispersion in the M-Z relation appears to be comparable over a range of 5.5 dex in stellar mass.

 

astro-ph/0603740 [abs, ps, pdf, other] :

Title: Newtonian and Pseudo-Newtonian Hill Problem
Authors: A.F. Steklain, P.S. Letelier
Comments: 12 pages, 4 figures, 1 table
Journal-ref: Physics Letters A, 352, 398-403 (2006)

A pseudo-Newtonian Hill problem based on the Paczynski-Wiita pseudo-Newtonian potential that reproduces general relativistic effects is presented and compared with the usual Newtonian Hill problem. Poincare maps, Lyapunov exponents and fractal escape techniques are employed to study bounded and unbounded orbits. In particular we consider the systems composed by Sun, Earth and Moon and composed by the Milky Way, the M2 cluster and a star. We find that some pseudo-Newtonian systems - including the M2 system - are more stable than their Newtonian equivalent.