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astro-ph new abstracts, Mon, 1 May 06 00:00:12 GMT
0604581 -- 0604619 received

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astro-ph/0604581 [abs, ps, pdf, other] :

Title: Environment and the cosmic evolution of star formation
Authors: Ravi K. Sheth (Penn), Raul Jimenez (Penn, OCIW), Ben Panter (MPA), Alan Heavens (IfA, Edinburgh)
Comments: 4 pages, 4 figures, submitted to ApJL

We present a mark correlation analysis of the galaxies in the Sloan Digital Sky Survey using weights provided by MOPED. The large size of the sample permits statistically significant statements about how galaxies with different metallicities and star formation histories are spatially correlated. Massive objects formed a larger fraction of their stars at higher redshifts and over shorter timescales than did less massive objects (sometimes called down-sizing). We find that those galaxies which dominated the cosmic star formation at z~3 are predominantly in clusters today, whereas galaxies which dominate the star formation at z~0 inhabit substantially lower mass objects in less dense regions today. Hence, our results indicate that star formation and chemical enrichment occured first in the denser regions of the Universe, and moved to less dense regions at later times.

 

astro-ph/0604582 [abs, ps, pdf, other] :

Title: Neutral atom transport from the termination shock to 1 AU
Authors: Maciej Bzowski, Slawomir Tarnopolski
Comments: submitted to Proceedings of the 5-th IGPP Astrophysics Conference, Honolulu HI, March 2006; 6 pages

Dynamics of H, D, and heavy Energetic Neutral Atoms (ENA) between the termination shock and 1 AU is discussed in the context of the forthcoming NASA SMEX mission IBEX. In particular, effects of the velocity-dependent radiation pressure on atomic trajectories are considered and ionization losses between TS and 1 AU are studied. It is shown, among others, that most of the dynamical effects and ionization losses are induced within a few AU from the Sun, which translates to the time domain into $\sim 1 - 3$ solar rotations before detection. This loosens considerably time requirements for tracking the ionization and radiation pressure history to just prior 3 months. ENA seem excellent tracers of the processes within the heliospheric interface, with the transport effects between the termination shock and detector relatively mild and easy to account for.

 

astro-ph/0604583 [abs, ps, pdf, other] :

Title: Filaments, Bubbles, and Weak Shocks in the Gaseous Atmosphere of M87
Authors: W. Forman, E.Churazov, C. Jones, M. Markevitch, P. Nulsen, A. Vikhlinin, M. Begelman, H. Bohringer, J. Eilek, S. Heinz, R. Kraft, F. Owen
Comments: 8 pages, 6 figures

We present the first results from a 500 ksec Chandra ACIS-I observation of M87. At soft energies (0.5-1.0 keV), we detect a complex filamentary structure associated with the eastern and southwestern arms. Many filaments are spatially resolved and have widths of ~300 pc. This filamentary structure is particularly striking in the eastern arm where we suggest the filaments are outer edges of a series of buoyant bubbles filled with relativistic plasma, produced by the central supermassive black hole, in a succession of small outbursts occurring every ~6 x 10^6 years. The X-ray structures may be influenced by magnetic filamentation. At hard energies (3.5-7.5 keV), we detect a nearly circular shell of outer radius 2.8' (13 kpc). This ring of hard X-ray emission provides an unambiguous signature of a weak shock, driven by an outburst from the SMBH, traversing the M87 atmosphere. The observed spectral hardening corresponds to a temperature rise from 2.0 to 2.4 keV, which translates to a Mach number M~1.2 for monoatomic gas with gamma=5/3. In addition, we detect two additional surface brightness edges (at radii of ~0.6' and ~1.2'). The ~0.6' feature may be the gas just outside the ``piston'' driving the 2.8' shock, while the ~1.2' feature is probably produced by a secondary outburst.

 

astro-ph/0604584 [abs, ps, pdf, other] :

Title: The star formation rate at redshift one: H-alpha spectroscopy with CIRPASS
Authors: Michelle Doherty, Andrew Bunker, Robert Sharp, Gavin Dalton, Ian Parry, Ian Lewis
Comments: Accepted for publication in MNRAS. 13 pages including 9 figures

We have conducted an H-alpha survey of 38 0.77<z<1 galaxies over ~100 arcmin^2 of the Hubble Deep Field North and Flanking Fields, to determine star formation rates (SFRs), with the near-infrared multi-object spectrograph CIRPASS on the WHT. This represents the first successful application of this technique to observing high redshift galaxies. Stacking the spectra in the rest-frame to infer a total SFR for the field, we find a lower limit (uncorrected for dust reddening) on the star formation rate density at redshift z = 1 of 0.04Msol/yr/Mpc^3. This implies rapid evolution in the star formation rate density from z = 0 to z = 1 which is proportional to (1+z)^{3.1}.

 

astro-ph/0604585 [abs, ps, pdf, other] :

Title: AGN Jet Mass Loading and Truncation by Stellar Winds
Authors: Alexander Hubbard, Eric G. Blackman
Comments: 13 pages, 2 figures

Active Galactic Nuclei can produce extremely powerful jets. While tightly collimated, the scale of these jets and the stellar density at galactic centers implies that there will be many jet/star interactions, which can mass-load the jet through stellar winds. Previous work employed modest wind mass outflow rates, but this does not apply when mass loading is provided by a small number of high mass-loss stars. We construct a framework for jet mass-loading by stellar winds for a broader spectrum of wind mass-loss rates than has been previously considered. Given the observed stellar mass distributions in galactic centers, we find that even highly efficient (0.1 Eddington luminosity) jets from supermassive black holes of masses $M_{BH} \la 10^4M_{\odot}$ are rapidly mass loaded and quenched by stellar winds. For $10^4 M_{\odot}<M_{BH}<10^8 M_{\odot}$, the quenching length of highly efficient jets is independent of the jet's mechanical luminosity. Stellar wind mass-loading is unable to quench efficient jets from more massive engines, but can account for the observed truncation of the inefficient M87 jet, and implies a baryon dominated composition on scales $\ga 2$ kpc therein even if the jet is initially pair plasma dominated.

 

astro-ph/0604586 [abs, ps, pdf, other] :

Title: Planetary nebulae as probes for galactic chemical evolution
Authors: Roberto D.D. Costa, Walter J. Maciel
Comments: 8 pages, 6 figures, LaTeX, To be published in the Proceedings of the IAU Symposium 234: Planetary Nebulae in Our Galaxy and Beyond

The role of planetary nebulae as probes for the galactic chemical evolution is reviewed. Their abundances throughout the Galaxy are discussed for key elements, in particular oxygen and other alpha elements. The abundance distribution derived from planetary nebulae leads to the establishment of radial abundance gradients in the galactic disk that are important constraints to model the chemical evolution of the Galaxy. The radial gradient, well determined for the solar neighborhood, is examined for distinct regions. For the galactic anticenter in particular, the observational data confirm results from galactic evolution models that point to a decreasing in the gradient slope at large galactocentric distances. The possible time evolution of the radial gradient is also examined comparing samples of planetary nebulae of different ages, and the results indicate that a flattening in the gradient occurred, which is confirmed by some galactic evolution models. The galactic bulge is another important region whose modeling can be constrained by observational results obtained from planetary nebulae. Results derived in the last few years indicate that bulge nebulae have an abundance distribution similar to that of disk objects, however with a larger dispersion.

 

astro-ph/0604587 [abs, ps, pdf, other] :

Title: Dark matter halo response to the disk growth
Authors: Jun-Hwan Choi, Yu Lu, H. J. Mo, Martin D. Weinberg
Comments: 6 pages, 6 figures, submitted to MNRAS

We consider the sensitivity of the circular-orbit adiabatic contraction approximation \citep{bw84, blumenthal86} to the timing of baryon condensation and the orbital structure of dark matter halos in the $\Lambda$CDM paradigm. Using one-dimensional hydrodynamic simulations including the dark matter halo mass accretion history and gas cooling, we demonstrate that the adiabatic approximation is approximately valid even though halos and disks may assemble simultaneously. We further demonstrate the validity of the simple approximation for $\Lambda$CDM halos \citep[e.g.][hereafter NFW]{NFW97} with isotropic velocity distributions using three-dimensional N-body simulations. This result is easily understood: an isotropic velocity distribution in a cuspy halo requires more circular orbits than radial orbits. Conversely, the approximation considerably differs in the extreme case of a radial orbit halo. The approximation overestimates the response a core dark matter halo, where radial orbit fraction is larger. Because no astronomically relevant models are dominated by low-angular momentum orbits in the vicinity of the disk and the growth time scale is never shorter than a dynamical time, we conclude that the adiabatic contraction approximation is generally acceptable in the CDM cosmology.

 

astro-ph/0604588 [abs, ps, pdf, other] :

Title: Integral Field Unit Observations of NGC 891: Kinematics of the Diffuse Ionized Gas Halo
Authors: George H. Heald (UNM), Richard J. Rand (UNM), Robert A. Benjamin (UW-Whitewater), Matthew A. Bershady (UW-Madison)
Comments: 31 pages, 10 figures. Accepted for publication in the Astrophysical Journal

We present high and moderate spectral resolution spectroscopy of diffuse ionized gas (DIG) emission in the halo of NGC 891. The data were obtained with the SparsePak integral field unit at the WIYN Observatory. The wavelength coverage includes the [NII]6548,6583, Halpha, and [SII]6716,6731 emission lines. Position-velocity (PV) diagrams, constructed using spectra extracted from four SparsePak pointings in the halo, are used to examine the kinematics of the DIG. Using two independent methods, a vertical gradient in azimuthal velocity is found to be present in the northeast quadrant of the halo, with magnitude approximately 15-18 km/s/kpc, in agreement with results from HI observations. The kinematics of the DIG suggest that this gradient begins at approximately 1 kpc above the midplane. In another part of the halo, the southeast quadrant, the kinematics are markedly different, and suggest rotation at about 175 km/s, much slower than the disk but with no vertical gradient. We utilize an entirely ballistic model of disk-halo flow in an attempt to reproduce the kinematics observed in the northeast quadrant. Analysis shows that the velocity gradient predicted by the ballistic model is far too shallow. Based on intensity cuts made parallel to the major axis in the ballistic model and an Halpha image of NGC 891 from the literature, we conclude that the DIG halo is much more centrally concentrated than the model, suggesting that hydrodynamics dominate over ballistic motion in shaping the density structure of the halo. Velocity dispersion measurements along the minor axis of NGC 891 seem to indicate a lack of radial motions in the halo, but the uncertainties do not allow us to set firm limits.

 

astro-ph/0604589 [abs, ps, pdf, other] :

Title: The X-ray properties of the dwarf Magellanic-type galaxy NGC 55
Authors: A-M. Stobbart, T. P. Roberts, R. S. Warwick (University of Leicester, UK)
Comments: 17 pages, 8 figures, accepted for publication in MNRAS

We present an analysis of the X-ray properties of the Magellanic-type galaxy NGC 55 based on two contiguous XMM-Newton observations. We detect a total of 137 X-ray sources in the field of view, 42 of which are located within the optical confines of the galaxy. On the basis of X-ray colour classification and after correcting for background objects, we conclude that our source sample includes ~ 20 X-ray binaries, 5 supernova remnants and 7 very soft sources (including 2 good candidate supersoft sources) associated with NGC 55. Detailed spectral and timing analysis was carried out on 4 of the brightest X-ray sources. One of these objects is identified with a Galactic foreground star and is a possible new RS CVn system. The other three are consistent with accreting X-ray binaries, though further evidence of short term variability is required to confirm this. We also find evidence of an underlying component, which is concentrated on the bar region but has an extent of at least 6' (3 kpc) in the plane of the galaxy and +/- 1' (+/- 500 pc) perpendicular to it. This emission is best fitted by a thermal plasma plus power-law model but with high intrinsic absorption consistent with its location in the central disc of the galaxy. We interpret the soft component as diffuse thermal emission linked to regions of current star formation, whilst the hard power-law component may originate in unresolved X-ray binary sources. The intrinsic luminosity of this residual disc emission may exceed Lx ~ 6e38 ergs/s (0.3-6 keV). A comparison with other Magellanic systems confirms that, in terms of both its discrete X-ray source population and its extended emission, NGC 55 has X-ray properties which are typical of its class.

 

astro-ph/0604590 [abs, ps, pdf, other] :

Title: An Empirical UBVRIJHK Color-Temperature Calibration for Stars
Authors: G. Worthey, H.-c. Lee
Comments: 13 figures, 4 in color. Uses emulateapj and revtex4. 8 or 9 pages. Submitted to the Astrophysical Journal Supplement Series

A collection of Johnson/Cousins photometry for stars with known [Fe/H] is used to generate color-color relations that include the abundance dependence. Literature temperature and bolometric correction dependences are attached to the color relations. The main result of this work is the tabulation of seven colors and the V-band bolometric correction as a function of Teff, log g, and [Fe/H] for -1.06 < V-K < 10.2 and an accompanying interpolation program. Improvements to the present calibration would involve filling photometry gaps, obtaining more accurate and on-system photometry, knowing better log g and [Fe/H] values, improving the statistics for data-impoverished groups of stars such as K dwarfs, applying small tweaks in the processing pipeline, and obtaining better empirical temperature and bolometric correction relations, especially for supergiants and M stars. A way to estimate dust extinction from M dwarf colors is pointed out.

 

astro-ph/0604591 [abs, ps, pdf, other] :

Title: SHARC-2 350 Micron Observations of Distant Submillimeter Selected Galaxies
Authors: A. Kovacs, S. C. Chapman, C. D. Dowell, A. W. Blain, R. J. Ivison, I. Smail, T. G. Phillips
Comments: 12 pages, 9 figures, accepted for publication in ApJ

We present 350um observations of 15 Chapman et al. (2005) submillimeter galaxies (SMGs) with radio counterparts and optical redshifts. We detect 12 and obtain sensitive upper limits for 3, providing direct, precise measurements of their far-infrared luminosities and characteristic dust temperatures. With these, we verify the linear radio--far-infrared correlation at redshifts of z ~ 1-3 and luminosities of 10^11-10^13 L_sun, with a power-law index of 1.02+-0.12, and rms scatter of 0.12 dex. However, either the the correlation constant 'q' or the dust emissivity 'beta' is lower than measured locally. The best fitting q ~ 2.14 is consistent with SMGs being predominantly starbust galaxies, without significant AGN contribution, at far-infrared wavelengths. Gas-to-dust mass ratios are estimated at 54+-13 kappa(850um)/0.15 m^2 kg^-1], depending on the absoption efficiency 'kappa', with intrinsic dispersion ~ 40% around the mean value. Dust temperatures consistent with 34.6+-3K [beta/1.5]^-0.71, at z ~ 1.5-3.5, suggest that far-infrared photometric redshifts may be viable, and perhaps accurate to 10% <~ dz/(1+z), for up to 80% of the SMG population in this range, if the above temperature characterizes the full range of SMGs. However, observed temperature evolution of T_d ~ (1+z) is also plausible, and could result from selection effects. From the observed luminosity--temperature (L-T) relation, L ~ T_obs^(2.82+-0.29), we derive scaling relations for dust mass vs. dust temperature, and identify expressions to inter-relate the observed quantities. These suggest that measurements at a single wavelength, in the far-infrared, submillimeter or radio wavebands, might constrain dust temperatures and far-infrared luminosities for most SMGs with redshifts at z ~ 0.5-4.

 

astro-ph/0604592 [abs, ps, pdf, other] :

Title: Manganese Abundances in Cluster and Field Stars
Authors: J.S. Sobeck, I.I. Ivans, J. A. Simmerer, C. Sneden, P. Hoeflich, J.P. Fulbright, R. P. Kraft
Comments: 43 Pages, 7 Figures

We have derived Mn abundances for more than 200 stars in 19 globular clusters. In addition, Mn abundance determinations have been made for a comparable number of halo field and disk stars possessing an overlapping range of metallicities and stellar parameters. Our primary data set was comprised of high resolution spectra previously acquired at the McDonald, Lick and Keck Observatories. To enlarge our data pool, we acquired globular and open cluster spectra from several other investigators. Data were analyzed using synthetic spectra of the 6000 \AA Mn I triplet. Hyperfine structure parameters were included in the synthetic spectra computations. Our analysis shows that for the metallicity range $-0.7>$[Fe/H]$>$$-$2.7 stars of 19 globular clusters have a a mean relative abundance of $<$[Mn/Fe]$>$= $-0.37\pm0.01$ ($\sigma$ = 0.10), a value in agreement with that of the field stars: $<$[Mn/Fe]$>$= $-0.36\pm0.01$ ($\sigma$ = 0.08). Despite the 2 orders of magnitude span in metallicity, the $<$[Mn/Fe]$>$ ratio remains constant in both stellar populations. Our Mn abundance data indicate that there is no appreciable variation in the relative nucleosynthetic contribution from massive stars that undergo core-collapse supernovae and thus, no significant change of the associated initial mass function in the specified metallicity range.

 

astro-ph/0604593 [abs, ps, pdf, other] :

Title: Japanese Virtual Observatory (JVO) as an advanced astronomical research enviroment
Authors: Y.Shirasaki, M.Tanaka, S.Kawanomoto, S.Honda, M.Ohishi, Y.Mizumoto, N.Yasuda, Y.Masunaga, Y.Ishihara, J.Tsutsumi, H.Nakamoto, Y.Kobayashi, M.Sakamoto
Comments: 13 pages, 6 figures, submitted to SPIE Astronomical Telescopes & Instrumentation, the Advanced Software and Control for Astronomy conference in Orlando

We present the design and implementation of the Japanese Virtual Observatory (JVO) system. JVO is a portal site to various kinds of astronomical resources distributed all over the world. We have developed five components for constructing the portal: (1) registry, (2) data service, (3) workflow system, (4) data analysis service (5) portal GUI. Registry services are used for publishing and searching data services in the VO, and they are constructed using an OAI-PMH metadata harvesting protocol and a SOAP web service protocol so that VO standard architecture is applied. Data services are developed based on the Astronomical Data Query Language (ADQL) which is an international VO standard and an extension of the standard SQL. The toolkit for building the ADQL-based service is released to the public on the JVO web site. The toolkit also provides the protocol translation from a Simple Image Access Protocol (SIAP) to ADQL protocol, so that both the VO standard service can be constructed using our toolkit. In order to federate the distributed databases and analysis services, we have designed a workflow language which is described in XML and developed execution system of the workflow. We have succeeded to connect to a hundred of data resources of the world as of April 2006. We have applied this system to the study of QSO environment by federating a QSO database, a Subaru Suprim-Cam database, and some analysis services such a SExtractor and HyperZ web services. These experiences are described is this paper.

 

astro-ph/0604594 [abs, ps, pdf, other] :

Title: Outflows driven by Giant Protoplanets
Authors: Masahiro N. Machida Shu-ichiro Inutsuka Tomoaki Matsumoto
Comments: 12 pages, 3 figures, Submitted to ApJL, For high resolution figures see this http URL

We investigate outflows driven by a giant protoplanet using three-dimensional MHD nested grid simulations. We consider a local region around the protoplanet in the protoplanetary disk, and calculate three models: (a) unmagnetized disk model, (b) magnetized disk model having magnetic field azimuthally parallel to the disk, and (c) magnetic field perpendicular to the disk. Outflows with velocities, at least, 10 km/s are driven by the protoplanets in both magnetized disk models, while outflow does not appear in unmagnetized disk model. Tube-like outflows along the azimuthal direction of the protoplanetary disk appear in model with magnetic field being parallel to the disk. In this model, the magnetically dominated regions (i.e., density gap) are clearly contrasted from other regions and spiral waves appear near the protoplanet. On the other hand, in model with magnetic field being perpendicular to the disk, outflows are driven by a protoplanet with cone-like structure just as seen in the outflow driven by a protostar. Magnetic field lines are strongly twisted near the protoplanet and the outflows have well-collimated structures in this model.These outflows can be landmarks for searching exo-protoplanets in their formation stages. Our results indicate that the accretion rate onto the protoplanet tend to have a larger value than that expected from previous hydrodynamical calculations, since a fraction of the angular momentum of circum-planetary disk is removed by outflows, enhanced non-axisymmetric patterns caused by magnetic field, and magnetic braking. Possible implications for observation are also briefly discussed.

 

astro-ph/0604595 [abs, ps, pdf, other] :

Title: Mid-IR selected Quasars in the First Look Survey
Authors: A.Petric, M. Lacy, L.J. Storrie-Lombardi, A. Sajina, L. Armus, G. Canalizo, S. Ridgway
Comments: Comments: 4 pages, 4 figures. To appear in the proceedings for the Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution, Ed. R. Chary. November, 2005, Pasadena

We present a preliminary investigation of the spectral energy distributions (SEDs), and star-formation properties of a sample of Mid-IR selected Quasars. The mid-infrared SEDs of our objects are consistent with that expected from clumpy torus models. At longer wavelengths, the radio to infrared ratios of several objects are consistent with those of star-forming galaxies.

 

astro-ph/0604596 [abs, ps, pdf, other] :

Title: Bigradient Phase Referencing
Authors: Akihiro Doi
Comments: 10 pages, 4 figures, accepted for publication in PASJ

We propose bigradient phase referencing (BPR), a new radio-observation technique, and report its performance using the Japanese very-long-baseline-interferometry network (JVN). In this method, a weak source is detected by phase-referencing using a primary calibrator, in order to play a role as a secondary calibrator for phase-referencing to a weak target. We will be given the opportunity to select a calibrator from lots of milli-Jansky sources, one of which may be located at the position closer to the target. With such a smaller separation, high-quality phase-referencing can be achieved. Furthermore, a subsequent more-sophisticated calibration can relocate array's focus to a hypothetical point much closer to the target; a higher quality of phase referencing is available. Our demonstrative observations with strong radio sources have proved the capabilities of BPR in terms of image dynamic ranges and astrometric reproducibility. The image dynamic range on a target has been improved with a factor of about six compared to that of normal phase-referencing; the resultant position difference of target's emission between two epochs was only 62+-50 micro-arcsecond, even with less than 2300-km baselines at 8.4 GHz and fast-switching of a target-calibrator pair of a 2.1-degree separation.

 

astro-ph/0604597 [abs, ps, pdf, other] :

Title: Optical spectroscopy of (candidate) ultra-compact X-ray binaries: constraints on the composition of the donor stars
Authors: G. Nelemans, P.G. Jonker, D. Steeghs
Comments: Accepted for publication in MNRAS

We present optical spectroscopy of several (candidate) ultra-compact X-ray binaries (UCXBs) obtained with the ESO VLT and Gemini-North telescopes. In only one of five observed UCXB candidates did we find evidence for H in its spectrum (4U 1556-60). For XB 1905+00 the optical counterpart is not detected. For the known UCXBs 4U 1626-67 and XB 1916-05 we find spectra consistent with a C/O and a He/N accretion disc respectively, the latter is the first optical spectrum of a He-rich donor in an UCXB. Interestingly, the C/O spectrum of 4U 1626-67 shows both similarities as well as marked differences from the optical C/O spectrum of 4U 0614+09. We obtained phase resolved spectroscopy of 4U 0614+09 and the 44 min transient XTE J0929-314. In neither object were we able to detect clear orbital periodicities, highlighting the difficulties of period determinations in UCXBs. We reanalysed the spectra of XTE J0929-314 that were taken close to the peak of its 2003 X-ray outburst and do not confirm the detection of Halpha emission as was claimed in the literature. The peak spectra do show strong C or N emission around 4640A, as has also been detected in other UCXBs. We discuss the implications of our findings for our understanding of the formation of UCXBs and the Galactic population of UCXBs. At the moment all studied systems are consistent with having white dwarf donors, the majority being C/O rich.

 

astro-ph/0604598 [abs, ps, pdf, other] :

Title: Gravitational Clustering in Redshift Space: Non-Gaussian Tail of the Cosmological Density Distribution Function
Authors: J. S. Bagla, Suryadeep Ray
Comments: 10 pages, 5 figures, MNRAS format. comments welcome

We study the non-Gaussian tail of the probability distribution function of density in cosmological N-Body simulations for a variety of initial conditions. We compare the behaviour of the non-Gaussian tail in the real space with that in the redshift space. The form of the PDF in redshift space is of great significance as galaxy surveys probe this and not the real space analogue predicted using theoretical models. We model the non-Gaussian tail using the halo model. In the weakly non-linear regime the moments of counts in cells in the redshift space approach the values expected from perturbation theory for moments in real space. We show that redshift space distortions in the non-linear regime dominate over signatures of initial conditions or the cosmological background. We illustrate this using Skewness and higher moments of counts in cells, as well as using the form of the non-Gaussian tail of the distribution function. We find that at scales smaller than the scale of non-linearity the differences in Skewness, etc. for different models are very small compared to the corresponding differences in real space. We show that bias also leads to smaller values of higher moments, but the redshift space distortions are typically the dominant effect.

 

astro-ph/0604599 [abs, ps, pdf, other] :

Title: Internal dynamics of the massive cluster Abell 697: a multiwavelength analysis
Authors: M. Girardi, W. Boschin, R. Barrena
Comments: 17 pages, 11 eps figures, A&A accepted

We conduct an intensive study of the rich, X-ray luminous, and hot galaxy cluster Abell 697 (at z=0.282), likely containing a diffuse radio emission, to determine its dynamical status. Our analysis is based on new spectroscopic data obtained at the TNG telescope for 93 galaxies and on new photometric data obtained at the INT telescope. We combine galaxy velocity and position information to select 68 cluster members, determine global dynamical properties, and detect possible substructures. The investigation of the dynamical status is also performed by using X-ray data stored in the Chandra archive. We compute the line-of-sight (LOS) velocity dispersion of galaxies, sigma_v=1334 km s^-1, in agreement with the high average X-ray temperature T_X=10.2 keV recovered from Chandra data. Assuming that the cluster is in dynamical equilibrium and mass follows the galaxy distribution, we find that A697 is a very massive cluster obtaining M(<R_max=0.75 Mpc h^-1)=9.5x10^14 solar masses h^-1 and M(<R_vir=3.85 Mpc h^-1)=4.5x10^15 solar masses h^-1 for the region well sampled by the spectroscopic data and for the entire virialized region, respectively. Further investigations find that A697 is not fully relaxed, as shown by the non Gaussianity of the velocity distribution, the elongation of the X-ray emission, and the presence of small-size substructures in the central region. Our results suggest that we are looking at a cluster undergone to a complex cluster merger occurring roughly mainly along the LOS, with a transverse component in the SSE-NNW direction. Our study supports the hypothesis of a relation between extended radio emission and merging phenomena.

 

astro-ph/0604600 [abs, ps, pdf, other] :

Title: Simultaneous X-ray and optical observations of S5~0716+714 after the outburst of March 2004
Authors: L. Foschini, G. Tagliaferri, E. Pian, G. Ghisellini, A. Treves, L. Maraschi, F. Tavecchio, G. Di Cocco, S.R. Rosen
Comments: 8 pages, 6 figures. Accepted for publication on A&A Main Journal

At the end of March 2004, the blazar S5 0716+714 underwent an optical outburst, that prompted for quasi-simultaneous Target-of-Opportunity observations with the INTEGRAL and XMM-Newton satellites. In this paper, we report the results of the XMM-Newton and INTEGRAL OMC data analysis. The X-ray spectrum is well represented by a concave broken power law model, with the break at about 2 keV. In the framework of the synchrotron self-Compton model, the softer part of the spectrum, that is described by a power law of index alpha ~ 1.8 (f_nu propto nu^-alpha), is probably due to synchrotron emission, while the harder part of the spectrum, that has $\alpha \simeq 1$, is due to inverse Compton emission. The blazar shows long and short term variability, typical of Low-Frequency Peaked BL Lac (LBL): the former is manifested by a gradual decrease of the optical flux from the peak observed by ground telescopes at the end of March 2004, while the latter is characterized by soft X-ray and optical flares on time scales from a few thousand seconds to few hours. We can follow spectral variations on sub-hour time scales and study their correlation with the flux variability. We find evidence that the peak energy of the time-resolved spectra is increasing with flux. The modeling of the spectral energy distribution compared with archival observations suggests that the long term variability (from outburst to quiescence or viceversa) could be due to a change in the injected power, while the short term variability (flares) could be explained with changes in the slope of the distribution of the electrons.

 

astro-ph/0604601 [abs, ps, pdf, other] :

Title: Gaussian Decomposition of HI Surveys - II. Separation of Problematic Gaussians
Authors: U. Haud (Tartu Observatory, Estonia), P. M. W. Kalberla (Radioastronomisches Institut der Universität Bonn, Germany)
Comments: 22 pages, 14 figures. Accepted for publication in Baltic Astronomy. High-resolution version available at this http URL 4.38 MBaits)

We have analyzed the Gaussian decomposition of the Leiden/Dwingeloo Survey (LDS) of galactic neutral hydrogen for the presence of Gaussians probably not directly related to galactic HI emission. It is demonstrated that at least three classes of such components can be distinguished. The narrowest Gaussians mostly represent stronger random noise peaks in profiles and some still uncorrected radio-interferences. Many of slightly wider weak Gaussians are caused by increased uncertainties near the profile edges and with the still increasing width the baseline problems become dominating among weak components. Statistical criteria are given for separation of the parameter space regions, most likely populated with the problematic components from those where the Gaussians are with higher probability describing the actual Milky Way HI emission. The same analysis is applied to the Leiden/Argentina/Bonn survey (LAB). It is demonstrated that the selection criteria for dividing the parameter space are to a great extent independent of the particular survey in use. The presence of the baseline problems in the LDS is indicated by the peculiarities of the distribution of the widest Gaussians in the sky. A similar plot for the northern part of the LAB demonstrates considerably lower numbers of spurious components, but there are still problems with the southern part of the LAB. The strange characteristics of the observational noise in the southern part of the LAB are pointed out.

 

astro-ph/0604602 [abs, ps, pdf, other] :

Title: Coupled Quintessence and CMB
Authors: Seokcheon Lee
Comments: 10 pages, 3 figures, the ICGA7 conference proceedings published by World Scientific

We revise the stability of the tracking solutions and briefly review the potentials of quintessence models. We discuss the evolution of linear perturbations for $V(\phi) = V_{0} \exp(\lambda \phi^2/2)$ potential in which the scalar field is non-minimally coupled to cold dark matter. We consider the effects of this coupling on both cosmic microwave background temperature anisotropies and matter perturbations. We find that the phenomenology of this model is consistent with current observations up to the coupling power $n_{c} \leq 0.01$ while adopting the current parameters measured by WMAP, $\Omega_{\phi}^{(0)}=0.76$, $\Omega_{cdm}^{(0)}=0.191$, $\Omega_{b}^{(0)}=0.049$, and $h=0.70$. Upcoming cosmic microwave background observations continuing to focus on resolving the higher peaks may put strong constraints on the strength of the coupling.

 

astro-ph/0604603 [abs, ps, pdf, other] :

Title: A detailed modelling of the chemically rich clumps along the CB3 outflow
Authors: Milena Benedettini (1,2), Jeremy A. Yates (2), Serena Viti (2), Claudio Codella (3) ((1)INAF-IFSI Italy, (2) UCL UK, (3) INAF-IRA Italy)
Comments: 11 pages, 9 figures, accepted by MNRAS

In order to investigate the origin and the structure of the low velocity, chemically rich clumps observed along the lobes of low- and intermediate-mass outflows, we construct a detailed model of the S1 clump along the CB3 outflow. We use a time-dependent chemical model coupled with a radiative transfer model to reproduce the observed line profile for a direct comparison with previous observations of this clump. We find that the simultaneous fitting of multiple species and transitions is a powerful tool in constraining the physical parameters of the gas. Different scenarios for the clump formation have been investigated. The models that better reproduce all the observed lines are those where the clump is formed, at least partially, before the advent of the outflow; with the advent of the outflow the clump undergoes a short period of non-dissociative shock and the consequent release of the icy mantle together with the high temperature chemistry leads to the observed chemical enrichment. Our results also suggest the presence of substructure within the clump: a more extended component traced by CS, SO and the lower energy transitions (3_k-2_k and 2_k-1_k) of CH_3OH, and a more compact component traced by H_2CO, SO_2 and the higher energy transitions (5_k-4_k) of CH_3OH.

 

astro-ph/0604604 [abs, ps, pdf, other] :

Title: Warm Dust and Spatially Variable PAH Emission in the Dwarf Starburst Galaxy NGC 1705
Authors: John M. Cannon, John-David T. Smith, Fabian Walter, George J. Bendo, Daniela Calzetti, Daniel A. Dale, Bruce T. Draine, Charles W. Engelbracht, Karl D. Gordon, George Helou, Robert C. Kennicutt, Jr., Claus Leitherer, Lee Armus, Brent A. Buckalew, David J. Hollenbach, Thomas H. Jarrett, Aigen Li, Martin J. Meyer, Eric J. Murphy, Michael W. Regan, George H. Rieke, Marcia J. Rieke, Helene Roussel, Kartik Sheth, Michele D. Thornley
Comments: ApJ, in press; please retrieve full-resolution version from this http URL

We present Spitzer observations of the dwarf starburst galaxy NGC 1705 obtained as part of SINGS. The galaxy morphology is very different shortward and longward of ~5 microns: short-wavelength imaging shows an underlying red stellar population, with the central super star cluster (SSC) dominating the luminosity; longer-wavelength data reveals warm dust emission arising from two off-nuclear regions offset by ~250 pc from the SSC. These regions show little extinction at optical wavelengths. The galaxy has a relatively low global dust mass (~2E5 solar masses, implying a global dust-to-gas mass ratio ~2--4 times lower than the Milky Way average). The off-nuclear dust emission appears to be powered by photons from the same stellar population responsible for the excitation of the observed H Alpha emission; these photons are unassociated with the SSC (though a contribution from embedded sources to the IR luminosity of the off-nuclear regions cannot be ruled out). Low-resolution IRS spectroscopy shows moderate-strength PAH emission in the 11.3 micron band in the eastern peak; no PAH emission is detected in the SSC or the western dust emission complex. There is significant diffuse 8 micron emission after scaling and subtracting shorter wavelength data; the spatially variable PAH emission strengths revealed by the IRS data suggest caution in the interpretation of diffuse 8 micron emission as arising from PAH carriers alone. The metallicity of NGC 1705 falls at the transition level of 35% solar found by Engelbracht and collaborators; the fact that a system at this metallicity shows spatially variable PAH emission demonstrates the complexity of interpreting diffuse 8 micron emission. A radio continuum non-detection, NGC 1705 deviates significantly from the canonical far-IR vs. radio correlation. (Abridged)

 

astro-ph/0604605 [abs, ps, pdf, other] :

Title: A periodically active pulsar giving insight into magnetospheric physics
Authors: M. Kramer, A.G. Lyne, J.T. O'Brien, C.A. Jordan, D.R. Lorimer (Jodrell Bank Observatory, University of Manchester, Macclesfield, SK11 9DL, UK)
Comments: 12 pages, 2 figures
Journal-ref: Published in Science, 2006, Vol. 312, 549-551

PSR B1931+24 (J1933+2421) behaves as an ordinary isolated radio pulsar during active phases that are 5-10 days long. However, the radio emission switches off in less than 10 seconds and remains undetectable for the next 25-35 days, then it switches on again. This pattern repeats quasi-periodically. The origin of this behaviour is unclear. Even more remarkably, the pulsar rotation slows down 50% faster when it is on than when it is off. This indicates a massive increase in magnetospheric currents when the pulsar switches on, proving that pulsar wind plays a substantial role in pulsar spin-down. This allows us, for the first time, to estimate the currents in a pulsar magnetospheric during the occurrence of radio emission.

 

astro-ph/0604606 [abs, ps, pdf, other] :

Title: Global properties of the HI high velocity sky, a statistical investigation based on the LAB survey
Authors: Peter M.W. Kalberla, Urmas Haud
Comments: Accepted for publication in A&A

We study the properties of all major HVC complexes from a sample compiled 1991 by Wakker & van Woerden (WvW). We use the Leiden/Argentine/Bonn all sky 21-cm line survey and decompose the profiles into Gaussian components. We find a well defined multi-component structure for most of the HVC complexes. The cold HVC phase has lines with typical velocity dispersions of sigma = 3 km/s and exists only within more extended broad line regions, typically with sigma = 12 km/s. The motions of the cores relative to the envelopes are characterized by Mach numbers M = 1.5. The center velocities of the cores within a HVC complex have typical dispersions of 20 km/s. Remarkable is the well defined two-component structure for some prominent HVC complexes in the outskirts of the Milky Way: Complex H, the Magellanic Stream and the Leading Arm. There might be some indications for an interaction between HVCs and disk gas at intermediate velocities. This is possible for complex H, M, C, WB, WD, WE, WC, R, G, GCP, and OA, but not for complex A, MS, ACVHV, EN, WA, and P. Conclusions: The line widths, determined by us, imply that estimates of HVC masses, as far as derived from the WvW database, need to be scaled up by a factor 1.4. Correspondingly, guesses for the external pressure of a confining coronal gas need to be revised upward by a factor of 2. The HVC multi-phase structure implies in general that currently the halo pressure is significantly underestimated. In consequence, the HVC multi-phase structure may indicate that most of the complexes are circum-galactic. HVCs have turbulent energy densities which are an order of magnitude larger than that of comparable clumps in the Galactic disk.

 

astro-ph/0604607 [abs, ps, pdf, other] :

Title: Measurement of extragalactic magnetic fields by TeV gamma ray telescopes
Authors: A.Neronov, D.V.Semikoz
Comments: 4 pages, 1 figure

We propose a method of measurement of extragalactic magnetic fields in observations of TeV gamma-rays from distant blazars. Multi-TeV gamma-rays are emitted by these sources in narrow jet with opening angle of few degrees. These primary gamma-rays interact with the infrared photon background producing secondary electrons and positrons, which can be just slightly deflected by extragalactic magnetic fields before they emit secondary gamma-rays via inverse Compton scattering of cosmic microwave background photons. Secondary gamma-rays emitted toward an observer on the Earth can be detected as extended emission around initially point source. Energy dependent angular size of extended emission is related to the value of extragalactic magnetic field along the line of sight. Small magnetic fields B < 10^{-12} G in the voids of the large scale structure can be measured in this way. This allows, in principle, to detect the primordial magnetic fields.

 

astro-ph/0604608 [abs, ps, pdf, other] :

Title: An IR study of pure and ion irradiated frozen formamide
Authors: John R. Brucato, Giuseppa A. Baratta, Giovanni Strazzulla
Comments: 6 pages, 3 figures. Accepted for publication in A&A

Context. The chemical evolution of formamide (HCONH2), a molecule of astrobiological interest that has been tentatively identified in interstellar ices and in cometary coma, has been studied in laboratory under simulated astrophysical conditions such as ion irradiation at low temperature.
Aims. To evaluate the abundances of formamide observed in space or in laboratory, the integrated absorbances for all the principal IR features of frozen amorphous pure formamide deposited at 20 K were measured. Further evidence that energetic processing of ices occurring in space is extremely relevant both to astrochemistry and to astrobiology has been found, showing that new molecular species are synthesized by ion irradiation at a low temperature.
Methods. Pure formamide were deposited at 20 K and IR transmission spectra measured for different ice thicknesses. The ice thickness was derived by looking at the interference pattern (intensity versus time) of a He-Ne laser beam reflected at an angle of 45 deg by the vacuum-film and film-substrate interfaces. Samples of formamide ice were irradiated with 200 keV H+ ions and IR spectra recorded at different ion fluences.
Results. New molecules were synthesized among which are CO, CO2, N2O, isocyanic acid (HNCO), and ammonium cyanate (NH4+OCN-). Some of these species remain stable after warming up to room temperature.

 

astro-ph/0604609 [abs, pdf] :

Title: Solar ions in the heliosheath: a possible new source of heavy neutral atoms
Authors: S. Grzedzielski, M. Wachowicz, M. Bzowski, V. Izmodenov
Comments: Submitted for IGGP Astrophysics Conference, March 2006; 6 pages

We show that multiply ionized coronal C, N, O, Mg, Si, S ions carried by the solar wind and neutralized by consecutive electron captures from neutral interstellar atoms constitute an important new source of neutral atoms in the inner heliosheath, with energies up to ~ 1 keV/n. In the model we developed, the heavy ions are treated as test particles carried by hydrodynamic plasma flow (with a Monte-Carlo description of interstellar neutrals) and undergoing all relevant atomic processes determining the evolution of all charge-states of considered species (radiative and dielectronic recombination, charge exchange, photo-, and electron impact ionization). The total strength of the source is from ~10^6 g/s for S to ~10^8 g/s for O, deposited as neutrals below the heliopause. These atoms should provide, as they drift to supersonic wind region, important sources of PUIs and eventually ACRs, especially for species that are excluded from entering the heliosphere because of their ionization in the LISM. The expected corresponding ENA fluxes at 1 AU are in the range 10^-4 - 10^0 at./(cm^2 s sr), depending on the species and direction (Table 1).

 

astro-ph/0604610 [abs, ps, pdf, other] :

Title: The FSVS Cluster Catalogue: Galaxy Clusters and Groups in the Faint Sky Variability Survey
Authors: Ilona K. Soechting (Oxford University), Mark E. Huber (Lawrence Livermore National Laboratory), Roger G. Clowes (University of Central Lancashire), Steve B. Howell (WIYN Observatory and National Optical Astronomy Observatory)
Comments: 19 pages and 17 figures, MNRAS accepted

We describe a large sample of 598 galaxy clusters and rich groups discovered in the data of the Faint Sky Variability Survey. The clusters have been identified using a fully automated, semi-parametric technique based on a maximum likelihood approach applied to Voronoi tessellation, and enhanced by colour discrimination. The sample covers a wide range of richness, has a density of ~28 clusters per sqdeg, and spans a range of estimated redshifts of 0.05 < z < 0.9 with mean <z> = 0.345. Assuming the presence of a cluster red sequence, the uncertainty of the estimated cluster redshifts is assessed to be \~0.03. Containing over 100 clusters with z > 0.6, the catalogue contributes substantially to the current total of optically-selected, intermediate-redshift clusters, and complements the existing, usually X-ray selected, samples. The FSVS fields are accessible for observation throughout the whole year, making them particularly suited for large follow-up programmes. The construction of this FSVS Cluster Catalogue completes a fundamental component of our continuing programmes to investigate the environments of quasars and the chemical evolution of galaxies. We publish here the list of all clusters with their basic parameters, and discuss some illustrative examples in more detail. The full FSVS Cluster Catalogue, together with images and lists of member galaxies etc., will be issued as part of the ``NOAO data products'', and accessible at this http URL We describe the format of these data and access to them.

 

astro-ph/0604611 [abs, ps, pdf, other] :

Title: Non-gaussianity for a Two Component Hybrid Model of Inflation
Authors: Laila Alabidi

We consider a quadratic potential, in which two fields drive inflation. Our results suggest that ${3/5}f_{NL}\ll{}1$ within the limits allowed by the recent WMAP year 3 data.

 

astro-ph/0604612 [abs, ps, pdf, other] :

Title: Near-IR spectroscopy of OH/IR stars in the Galactic Centre
Authors: E. Vanhollebeke, J.A.D.L. Blommaert, M. Schultheis, B. Aringer, A. Lancon
Comments: 20 pages, 21 figures, accepted for publication in A&A on 18/04/2006

Context. Galactic Centre (GC) OH/IR stars can be, based on the expansion velocities of their circumstellar shells, divided into two groups which are kinematically different and therefore are believed to have evolved from different stellar populations. Aims. To study the metallicity distribution of the OH/IR stars population in the GC on basis of a theoretical relation between EW(Na), EW(Ca) and EW(CO) and the metallicity. Methods. For 70 OH/IR stars in the GC, we obtained near-IR spectra. The equivalent line widths of NaI, CaI, 12CO(2,0) and the curvature of the spectrum around 1.6 micron due to water absorption are determined. Results. The near-IR spectrum of OH/IR stars is influenced by several physical processes. OH/IR stars are variable stars suffering high mass-loss rates. The dust that is formed around the stars strongly influences the near-IR spectra and reduces the equivalent line widths of NaI, CaI. A similar effect is caused by the water content in the outer atmosphere of the OH/IR star. Because of these effects, it is not possible with our low resolution near-infrared spectroscopy to determine the metallicities of these stars.

 

astro-ph/0604613 [abs, ps, pdf, other] :

Title: Interaction of a Moreton/EIT wave and a coronal hole
Authors: Astrid M. Veronig, Manuela Temmer, Bojan Vrsnak, Julia Thalmann
Comments: 14 pages, 6 figures, accepted for publication in the ApJ

We report high-cadence H-alpha observations of a distinct Moreton wave observed at Kanzelhoehe Solar Observatory associated with the 3B/X3.8 flare and CME event of 2005 January 17. The Moreton wave can be identified in about 40 H-alpha frames over a period of 7 min. The EIT wave is observed in only one frame but the derived propagation distance is close to that of the simultaneously measured Moreton wave fronts indicating that they are closely associated phenomena. The large angular extent of the Moreton wave allows us to study the wave kinematics in different propagation directions with respect to the location of a polar coronal hole (CH). In particular we find that the wave segment whose propagation direction is perpendicular to the CH boundary (``frontal encounter'') is stopped by the CH which is in accordance with observations reported from EIT waves (Thompson et al. 1998). However, we also find that at a tongue-shaped edge of the coronal hole, where the front orientation is perpendicular to the CH boundary (the wave ``slides along'' the boundary), the wave signatures can be found up to 100 Mm inside the CH. These findings are briefly discussed in the frame of recent modeling results.

 

astro-ph/0604614 [abs, ps, pdf, other] :

Title: Polarimetric survey of asteroids with the Asiago telescope
Authors: S. Fornasier, I.N. Belskaya, Yu.G. Shkuratov, C. Pernechele, C. Barbieri, E. Giro, H. Navasardyan
Comments: 8 pages, paper accepted for pubblication on A&A

We present the first results of an asteroid photo--polarimetry program started at Asiago--Cima Ekar Observatory. The aim of our survey is to estimate diversity in polarimetric properties of asteroids belonging to different taxonomic and dynamical classes. The data were obtained with the polarization analyser placed inside the Faint Object Spectrographic Camera (AFOSC) of the 1.8m telescope. This instrument allows simultaneous measurements of the two first Stokes parameters without any lambda/2 retarding plate. Our survey began in 2002, and up to now we have obtained data on a sample of 36 asteroids; most of them are being investigated with the polarimetric technique for the first time. Combining our data with those already available in literature, we present an estimate of the inversion angle for 7 asteroids in this paper. Furthermore, we present the polarimetric measurements of the rare asteroid classes belonging to the A and D types and a detailed VRI observations at extremely small phase angles of the low albedo asteroid 1021 Flammario

 

astro-ph/0604615 [abs, ps, pdf, other] :

Title: Star formation through gravitational collapse and competitive accretion
Authors: Ian A. Bonnell (St Andrews), Matthew R. Bate (Exeter)
Comments: 7 pages, 1 figure, MNRAS, in press

Competitive accretion, a process to explain the origin of the IMF, occurs when stars in a common gravitational potential accrete from a distributed gaseous component. We show that concerns recently raised on the efficiency of competitive accretion are incorrect as they use globally averaged properties which are inappropriate for the detailed physics of a forming stellar cluster. A full treatment requires a realistic treatment of the cluster potential, the distribution of turbulent velocities and gas densities. Accreting gas does not travel at the global virial velocity of the system due to the velocity-sizescale relation inherent in turbulent gas and due to the lower velocity dispersion of small-N clusters in which much of the accretion occurs. Stars located in the gas-rich centres of such systems initially accrete from low relative velocity gas attaining larger masses before needing to accrete the higher velocity gas. Stars not in the centres of such potentials, or that enter the cluster later when the velocity dispersion is higher, do not accrete significantly and thus retain their low-masses. In competitive accretion, most stars do not continue to accrete significantly such that their masses are set from the fragmentation process. It is the few stars which continue to accrete that become higher-mass stars. Competitive accretion is therefore likely to be responsible for the formation of higher-mass stars and can explain the mass distribution, mass segregation and binary frequency of these stars. Global kinematics of competitive accretion models include large-scale mass infall, with mean inflow velocities of order 0.5 km/s at scales of 0.5 pc, but infall signatures are likely to be confused by the large tangential velocities and the velocity dispersion present.

 

astro-ph/0604616 [abs, ps, pdf, other] :

Title: Extending the WMAP Bound on the Size of the Universe
Authors: Joey Shapiro Key, Neil J. Cornish, David N. Spergel, Glenn D. Starkman
Comments: 9 pages, 16 figures

Clues to the shape of our Universe can be found by searching the CMB for matching circles of temperature patterns. A full sky search of the CMB, mapped extremely accurately by NASA's WMAP satellite, returned no detection of such matching circles and placed a lower bound on the size of the Universe at 24 Gpc. This lower bound can be extended by optimally filtering the WMAP power spectrum. More stringent bounds can be placed on specific candidate topologies by using a a combination statistic. We use optimal filtering and the combination statistic to rule out the infamous "soccer ball universe'' model.

 

astro-ph/0604617 [abs, ps, pdf, other] :

Title: Elemental Abundance Measurements in Low-redshift Damped Lyman Alpha Absorbers
Authors: Joseph Meiring, Varsha Kulkarni, Pushpa Khare, Jill Bechtold, Donald G. York, Jun Cui, James T. Lauroesch, Arlin P.S. Crotts, Osamu Nakamura
Comments: 20 pages, 16 figures

We present elemental abundance measurements for 9 damped Ly-alpha systems
(DLAs) and 1 sub-DLA at 0.1 < z < 1.5 from recent observations with the Multiple Mirror Telescope. Most of these absorbers are found to be metal-poor, while 2 are found to have ~ 30-50 solar metallicities. Combining our data with other data from the literature, we find that the systems with higher [Zn/H] also have stronger depletion as measured by [Cr/Zn] and [Fe/Zn]. The relationship between the metallicity and H I column density is also investigated. Together with our previous MMT survey (Khare et al. 2004) we have discovered 2 of the 4 known absorbers at z < 1.5 that lie above (although near) the "obscuration threshold". This appears to be a result of selecting absorbers with strong metal lines in our sample. It would be interesting to find other similar systems by observing a larger sample and study how much such systems contribute to the cosmic budget of metals. Finally, an analysis of the N(H I)-weighted mean metallicity vs. redshift for our sample combined with data from the literature supports previous conclusions that the N(H I)-weighted mean global DLA metallicity rises slowly at best and falls short of solar levels by a factor of > 4 even at z=0.

 

astro-ph/0604618 [abs, ps, pdf, other] :

Title: Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: I. Early X-ray emission from the shocked ejecta and red giant wind
Authors: M.F. Bode, T.J. O'Brien, J.P. Osborne, K.L. Page, F. Senziani, G.K. Skinner, S. Starrfield, J-U. Ness, J.J. Drake, G. Schwarz, A.P. Beardmore, M.J. Darnley, S.P.S. Eyres, A. Evans, N. Gehrels, M.R. Goad, P. Jean, J. Krautter, G. Novara
Comments: 20 pages, 4 figures, submitted to ApJ

RS Oph is a recurrent nova which began its latest outburst on 2006 Feb 12. Previous outbursts have shown that high velocity ejecta interact with a pre-existing red giant wind (RGW), setting up shock systems analogous to those seen in SN Remnants. However, in the previous outburst in 1985, X-ray observations with EXOSAT did not commence until 55d after the initial explosion. Here we report on Swift observations covering the first month of the 2006 outburst with both the Burst Alert (BAT) and X-ray Telescope (XRT) instruments. With the BAT it was possible to trace the evolution of the hard X-ray flux from the earliest phases, with a clear detection in a band 14-25keV from t=0d to t~6d, and a less strong detection at 25-50keV during the first few days. It was also observed with XRT from 0.3-10keV, starting 3.17d after outburst. The XRT spectra clearly show the presence of both line and continuum emission. These rapidly evolving spectra can be fitted by thermal emission from hot gas whose characteristic temperature, overlying absorbing column and resulting unabsorbed total flux decline monotonically after the first few days. Shock velocities from the fitted plasma temperatures are in good agreement with those from observations at other wavelengths. Similarly, the circumstellar column density is in accord with that expected from the RGW ahead of the forward shock. These observations confirm the basic models of the 1985 outburst and lead us to conclude that Phase I of remnant evolution (ejecta supply energy to the shocked ambient medium) terminated by t~10d and the remnant then rapidly evolved to display behaviour characteristic of Phase III (well cooled shocked material). Around t=26d however, a new, luminous, highly variable, soft X-ray source appeared in the spectra whose origin will be explored subsequently.

 

astro-ph/0604619 [abs, ps, pdf, other] :

Title: Mass segregation in rich LMC clusters from modelling of deep HST colour-magnitude diagrams
Authors: L. O. Kerber (1,2), B. X. Santiago (1) ((1) Instituto de Fisica, UFRGS, Porto Alegre, Brazil; (2) IAG, USP, Sao Paulo, Brazil)
Comments: 11 pages, 11 Postscript figures, Astronomy & Astrophysics, accepted 10 January 2006

We used the deep colour-magnitude diagrams (CMDs) of five rich LMC clusters (NGC1805, 1818, 1831, 1868, and Hodge14) observed with HST/WFPC2 to derive their present day mass function (PDMF) and its variation with position within the cluster. The PDMF was parameterized as a power law in the available main-sequence mass range of each cluster, typically 0.9 <~ m/M_sun <~ 2.5; its slope was determined at different positions spanning from the very centre out to several core radii. The CMDs in the central regions of the clusters were carefully studied earlier, resulting in accurate age, metallicity, distance modulus, and reddening values. The slope alpha (where Salpeter is 2.35) was determined in annuli by following two distinct methods: 1) a power law fit to the PDMF obtained from the systemic luminosity function (LF); 2) a statistical comparison between observed and model CMDs. In all clusters, significant mass segregation is found from the positional dependence of the PDMF slope: alpha <~ 1.8 for R <= 1.0 R_core and alpha ~ Salpeter inside R=2~3 R_core (except for Hodge 14, where alpha ~ Salpeter for R ~ 4 R_core). The results are robust in the sense that they hold true for both methods used. The CMD method reveals that unresolved binaries flatten the PDMF obtained form the systemic LF, but this effect is smaller than the uncertainties in the alpha determination. For each cluster we estimated dynamical ages inside the core and for the entire system. In both cases we found a trend in the sense that older clusters have flatter PDMF, consistent with a dynamical mass segregation and stellar evaporation.

 

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