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Astrophysics

astro-ph new abstracts, Wed, 14 Jun 06 00:00:10 GMT
0606276 -- 0606327 received

astro-ph/0606276 [abs, ps, pdf, other] :

Title: On the First Generation of Stars
Authors: Joseph Silk, Mathieu Langer
Comments: Submitted to MNRAS

We argue that the first stars may have spanned the conventional mass range rather than be identified with the Very Massive Objects (100-1000 solar masses) favoured by numerical simulations. Specifically, we find that magnetic field generation processes acting in the first protostellar systems suffice to produce fields that exceed the threshold for MRI instability to operate and thereby allow the MRI dynamo to generate equipartition-amplitude magnetic fields on protostellar mass scales below 50 solar masses. Such fields allow primordial star formation to occur at essentially any metallicity by regulating angular momentum transfer, fragmentation, accretion and feedback in much the same way as occurs in conventional molecular clouds.

 

astro-ph/0606277 [abs, ps, pdf, other] :

Title: Slow Star Formation in Dense Gas: Evidence and Implications
Authors: Mark R. Krumholz (1), Jonathan C. Tan (2) ((1) Princeton University, (2) University of Florida)
Comments: Submitted to ApJ. 9 pages, 5 figures, emulateapj format

It has been known for more than 30 years that star formation in giant molecular clouds is slow, with only ~1% of the gas forming stars every free-fall time. Here we present evidence that it is equally slow in the much denser gas from which star clusters form. This has important implications for models of star formation, since competing models make differing predictions for the characteristic density at which star formation should transition from slow, with only a few percent of the mass forming stars per free-fall time, to rapid, with order unity of the mass going into stars in a free-fall time. We find that the data are strongly inconsistent with models that explain low star formation rates by appealing to unbound molecular clouds or regulation of star formation solely by galactic-scale gravitational instability, and broadly consistent with models of star formation regulated by either turbulence or magnetic fields in virialized objects. The turbulence-regulated star formation model of Krumholz & McKee quantitatively reproduces the infrared-HCN luminosity correlation recently reported by Gao & Solomon. Slow star formation also implies that the process of star cluster formation cannot be one of global collapse, but must instead proceed over many free-fall times. This suggests that turbulence in star-forming clumps does not decay away in a single crossing time, and that the competitive accretion mechanism does not operate in typical cluster-forming molecular clumps.

 

astro-ph/0606278 [abs, pdf] :

Title: The Robinson Gravitational Wave Background Telescope (BICEP): a bolometric large angular scale CMB polarimeter
Authors: K. W. Yoon, P. A. R. Ade, D. Barkats, J. O. Battle, E. M. Bierman, J. J. Bock, J. A. Brevik, H. C. Chiang, A. Crites, C. D. Dowell, L. Duband, G. S. Griffin, E. F. Hivon, W. L. Holzapfel, V. V. Hristov, B. G. Keating, J. M. Kovac, C. L. Kuo, A. E. Lange, E. M. Leitch, P. V. Mason, H. T. Nguyen, N. Ponthieu, Y. D. Takahashi, T. Renbarger, L. C. Weintraub, D. Woolsey
Comments: 18 pages, 11 figures. To appear in Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III, Proceedings of SPIE, 6275, 2006

The Robinson Telescope (BICEP) is a ground-based millimeter-wave bolometric array designed to study the polarization of the cosmic microwave background radiation (CMB) and galactic foreground emission. Such measurements probe the energy scale of the inflationary epoch, tighten constraints on cosmological parameters, and verify our current understanding of CMB physics. Robinson consists of a 250-mm aperture refractive telescope that provides an instantaneous field-of-view of 17 degrees with angular resolution of 55 and 37 arcminutes at 100 GHz and 150 GHz, respectively. Forty-nine pair of polarization-sensitive bolometers are cooled to 250 mK using a 4He/3He/3He sorption fridge system, and coupled to incoming radiation via corrugated feed horns. The all-refractive optics is cooled to 4 K to minimize polarization systematics and instrument loading. The fully steerable 3-axis mount is capable of continuous boresight rotation or azimuth scanning at speeds up to 5 deg/s. Robinson has begun its first season of observation at the South Pole. Given the measured performance of the instrument along with the excellent observing environment, Robinson will measure the E-mode polarization with high sensitivity, and probe for the B-modes to unprecedented depths. In this paper we discuss aspects of the instrument design and their scientific motivations, scanning and operational strategies, and the results of initial testing and observations.

 

astro-ph/0606279 [abs, ps, pdf, other] :

Title: The First DIRECT Distance Determination to a Detached Eclipsing Binary in M33
Authors: A. Z. Bonanos, K. Z. Stanek, R. P. Kudritzki, L.M. Macri, D. D. Sasselov, J. Kaluzny, P. B. Stetson, D. Bersier, F. Bresolin, T. Matheson, B.J. Mochejska, N. Przybilla, A.H. Szentgyorgyi, J. Tonry, G. Torres
Comments: 36 pages, 12 figures, submitted to ApJ

We present the first direct, i.e. not involving intermediate steps, distance determination to a detached eclipsing binary in M33, which was found by the DIRECT Project. Located in the OB 66 association at coordinates (alpha, delta)=(01:33:46.17,+30:44:39.9) for J2000.0, it was one of the most suitable detached eclipsing binaries found by DIRECT for distance determination, given its apparent magnitude and orbital period. We obtained follow-up BV time series photometry, JHKs photometry and optical spectroscopy from which we determined the parameters of the system. It contains two O7 main sequence stars with masses of 33.4+/-3.5 Mo and 30.0+/-3.3 Mo and radii of 12.3+/-0.4 Ro and 8.8+/-0.3 Ro, respectively. We derive temperatures of 37000+/-1500 K and 35600+/-1500 K. Using BVRJHKs photometry for the flux calibration, we obtain a distance modulus of 24.92+/-0.12 mag (964+/-54 kpc), which is ~0.3 mag longer than the Key Project distance to M33. We discuss the implications of our result and the importance of establishing M33 as an independent rung on the cosmological distance ladder.

 

astro-ph/0606280 [abs, ps, pdf, other] :

Title: Recipes for stellar jets: results of combined optical/infrared diagnostics
Authors: Linda Podio, Francesca Bacciotti, Brunella Nisini, Jochen Eislöffel, Fabrizio Massi, Teresa Giannini, Thomas P. Ray
Comments: 19 pages, 15 figures, accepted by A&A

We examine the conditions of the plasma along a sample of 'classical' Herbig-Haro jets located in the Orion and Vela star forming regions, through combined optical-infrared spectral diagnostics. Our sample includes HH 111, HH 34, HH 83, HH 73, HH 24 C/E, HH 24 J, observed at moderate spatial/spectral resolution. The obtained spectra cover a wide wavelength range from 0.6-2.5 um, including many transitions from regions of different excitation conditions. This allows us to probe the density and temperature stratification which characterises the cooling zones behind the shock fronts along the jet. The derived physical parameters (such as the extinction, the electron density and temperature, the ionisation fraction, and the total density) are used to estimate the depletion onto dust grains of Calcium and Iron with respect to solar abundances. This turns out to be between 70% and 0% for Ca and ~90% for Fe, suggesting that the weak shocks present in the beams are not capable of completely destroying the dust grains. We then derive the mass flux rates (Mdot_jet is on average 5 10^-8 M_solar yr^-1) and the associated linear momentum fluxes. The latter are higher than, or of the same order as, those measured in the coaxial molecular flows, suggesting that the flows are jet driven. Finally, we discuss differences between jets in our sample.

 

astro-ph/0606281 [abs, ps, pdf, other] :

Title: Meta-Cold Dark Matter: Dark Matter Halos with Cores from Hierarchical Structure Formation
Authors: Louis E. Strigari, Manoj Kaplinghat, James S. Bullock
Comments: 5 pages, 1 figure

We show that dark matter emerging from late decays (z < 1000) produces a linear power spectrum identical to that of Cold Dark Matter (CDM) on all observationally relavant scales (> 0.1 Mpc), and simultaneously generates observable constant-density cores in small dark matter halos. We refer to this class of models as meta-Cold Dark Matter (mCDM), because it is born with non-relativistic velocities from the decays of cold thermal relics. The constant-density cores are a result of the low phase-space density of mCDM at birth. Warm dark matter cannot produce similar size phase-space limited cores without saturating the Ly-alpha power spectrum bounds. Dark matter dominated galaxy rotation curves and stellar velocity dispersion profiles may provide the best means to discriminate between mCDM and CDM. mCDM candidates are motivated by the particle spectrum of supersymmetric and extra dimensional extensions to the standard model of particle physics.

 

astro-ph/0606282 [abs, ps, pdf, other] :

Title: The Interplay between Star Formation and the Nuclear Environment of our Galaxy: Deep X-ray Observations of the Galactic Center Arches and Quintuplet Clusters
Authors: Q. Daniel Wang, Hui Dong, Cornelia Lang
Comments: 27 pages, accepted for publication in MNRAS. The full table 1 are available at this http URL

The Galactic center (GC) provides a unique laboratory for a detailed examination of the interplay between massive star formation and the nuclear environment of our Galaxy. Here, we present an 100 ks Chandra ACIS observation of the Arches and Quintuplet star clusters. We also report on a complementary mapping of the dense molecular gas near the Arches cluster made with the Owens Valley Millimeter Array. The number-flux relation of point-like X-ray sources indicates an over-population of relatively bright X-ray sources, which are apparently associated with the clusters. The sources in the core of the Arches and Quintuplet clusters are most likely extreme colliding wind massive star binaries. The diffuse X-ray emission from the core of the Arches cluster has a spectrum showing a 6.7-keV emission line and a surface intensity profile declining steeply with radius, indicating an origin in a cluster wind. In the outer regions near the Arches cluster, the overall diffuse X-ray enhancement demonstrates a bow shock morphology and is prominent in the Fe Kalpha 6.4-keV line emission. Much of this enhancement may result from an ongoing collision between the cluster and the adjacent molecular cloud. The older and less compact Quintuplet cluster contains much weaker X-ray sources and diffuse emission, probably originating from low-mass stellar objects as well as a cluster wind. However, the overall population of these objects, constrained by the observed total diffuse X-ray luminosities, is substantially smaller than expected for both clusters. This deficiency of low-mass objects may be a manifestation of the unique star formation environment of the Galactic center.

 

astro-ph/0606283 [abs, ps, pdf, other] :

Title: Capella Corona Revisited: A Combined View from \textit{XMM-Newton} RGS, \textit{Chandra} HETGS, and LETGS
Authors: M.F. Gu, R. Gupta, J.R. Peterson, M. Sako, S.M. Kahn
Comments: Accepted in ApJ

We present a combined analysis of the X-ray emission of the Capella corona obtained with \textit{XMM-Newton} RGS, \textit{Chandra} HETGS, and LETGS. An improved atomic line database and a new differential emission measure (DEM) deconvolution method are developed for this purpose. Our new atomic database is based on the Astrophysical Plasma Emission Database and incorporates improved calculations of ionization equilibrium and line emissivities for L-shell ions of abundant elements using the Flexible Atomic Code. The new DEM deconvolution method uses a Markov Chain Monte-Carlo (MCMC) technique which differs from existing MCMC or $\chi^2$-fitting based methods. We analyze the advantages and disadvantages of each individual instrument in determining the DEM and elemental abundances. We conclude that results from either RGS or HETGS data alone are not robust enough due to their failure to constrain DEM in some temperature region or the lack of significant continuum emission in the wavelength band of the spectrometers, and that the combination of HETGS and RGS gives more stringent constraints on the DEM and abundance determinations. Using the LETGS data, we show that the recently discovered inconsistencies between the EUV and X-ray lines of Fe XVIII and XIX also exist in more highly charged iron ions, up to Fe XXIII, and that enhanced interstellar absorption due to partially ionized plasma along the Capella line of sight may explain some, but not all, of these discrepancies.

 

astro-ph/0606284 [abs, ps, pdf, other] :

Title: Molecular Line Observations of Infrared Dark Clouds: Seeking the Precursors to Intermediate and Massive Star Formation
Authors: Sarah E. Ragan (1), Edwin A. Bergin (1), Rene Plume (2), David L. Gibson (2), David J. Wilner (3), Shawn O'Brien (4), Erin Hails (5) ((1) University of Michigan (2) University of Calgary (3) Harvard-Smithsonian Center for Astrophysics (4) University of Notre Dame (5) Arizona Radio Observatory)
Comments: Accepted to ApJS, 22 pages, 10 pages of figures. For full-resolution images, see this http URL

We have identified 41 infrared dark clouds from the 8 micron maps of the Midcourse Space Experiment (MSX), selected to be found within one square degree areas centered on known ultracompact HII regions. We have mapped these infrared dark clouds in N2H+(1-0), CS(2-1) and C18O(1-0) emission using the Five College Radio Astronomy Observatory. The maps of the different species often show striking differences in morphologies, indicating differences in evolutionary state and/or the presence of undetected, deeply embedded protostars. We derive an average mass for these clouds using N2H+ column densities of ~2500 solar masses, a value comparable to that found in previous studies of high mass star forming cores using other mass tracers. The linewidths of these clouds are typically ~2.0 - 2.9 km/s. Based on the fact that they are dark at 8 micron, compact, massive, and have large velocity dispersions, we suggest that these clouds may be the precursor sites of intermediate and high mass star formation.

 

astro-ph/0606285 [abs, ps, pdf, other] :

Title: Near-Horizon Solution for DGP Perturbations
Authors: Ignacy Sawicki, Yong-Seon Song, Wayne Hu (KICP, U. Chicago)
Comments: 11 pages, 10 figures, submitted to PRD

We develop a scaling ansatz for the master equation in Dvali, Gabadadze, Porrati cosmologies, which allows us to solve the equations of motion for perturbations off the brane during periods when the on-brane evolution is scale-free. This allows us to understand the behavior of the gravitational potentials outside the horizon at high redshifts and close to the horizon today. We confirm that the results of Koyama and Maartens are valid at scales relevant for observations such as galaxy-ISW correlation. At larger scales, there is an additional suppression of the potential which reduces the growth rate even further and would strengthen the ISW effect.

 

astro-ph/0606286 [abs, ps, pdf, other] :

Title: Large-Scale Tests of the DGP Model
Authors: Yong-Seon Song, Ignacy Sawicki, Wayne Hu (KICP, U. Chicago)
Comments: 8 pages, 5 figures, submitted to PRD

The self-accelerating braneworld model (DGP) can be tested from measurements of the expansion history of the universe and the formation of structure. Current constraints on the expansion history from supernova luminosity distances, the CMB, and the Hubble constant exclude the simplest flat DGP model at about 3sigma. The best-fit open DGP model is, however, only a marginally poorer fit to the data than flat LCDM. Its substantially different expansion history raises structure formation challenges for the model. A dark-energy model with the same expansion history would predict a highly significant discrepancy with the baryon oscillation measurement due the high Hubble constant required and a large enhancement of CMB anisotropies at the lowest multipoles due to the ISW effect. For the DGP model to satisfy these constraints new gravitational phenomena would have to appear at the non-linear and cross-over scales respectively. A prediction of the DGP expansion history in a region where the phenomenology is well understood is that high-redshift galaxies should be substantially correlated with the CMB through the ISW effect. This correlation should provide a sharp test of the DGP model in the future.

 

astro-ph/0606287 [abs, ps, pdf, other] :

Title: Scalar-Tensor Models of Normal and Phantom Dark Energy
Authors: Radouane Gannouji, David Polarski, Andre Ranquet, Alexei A. Starobinsky
Comments: 30 pages, 4 figures

We consider the viability of dark energy (DE) models in the framework of the scalar-tensor theory of gravity, including the possibility to have a phantom DE at small redshifts $z$ as admitted by supernova luminosity-distance data. For small $z$, the generic solution for these models is constructed in the form of a power series in $z$ without any approximation. Necessary constraints for DE to be phantom today and to cross the phantom divide line $p=-\rho$ at small $z$ are presented. Considering the Solar System constraints, we find for the post-Newtonian parameters that $\gamma_{PN}<1$ and $\gamma_{PN,0}\approx 1$ for the model to be viable, and $\beta_{PN,0}>1$ (but very close to 1) if the model has a significantly phantom DE today. However, prospects to establish the phantom behaviour of DE are much better with cosmological data than with Solar System experiments. Earlier obtained results for a $\Lambda$-dominated universe with the vanishing scalar field potential are extended to a more general DE equation of state confirming that the cosmological evolution of these models rule them out. Models of currently fantom DE which are viable for small $z$ can be easily constructed with a constant potential; however, they generically become singular at some higher $z$. With a growing potential, viable models exist up to an arbitrary high redshift.

 

astro-ph/0606288 [abs, ps, pdf, other] :

Title: Speckle nulling for exoplanet detection with space-based coronagraphic telescopes
Authors: Pascal J. Borde, Wesley A. Traub, Brian D. Kern, John T. Trauger, Andreas C. Kuhnert
Comments: 6 pages, 4 figures. This paper will be published in the proceedings of the conference Space Telescopes and Instrumentation I: Optical, Infrared, and Millimeter (SPIE 6265), part of SPIE's Astronomical Telescopes & Instrumentation, 24-31 May 2006, Orlando, FL

To detect Earth-like planets in the visible with a coronagraphic telescope, two major noise sources have to be overcome: the photon noise of the diffracted star light, and the speckle noise due to the star light scattered by instrumental defects. Coronagraphs tackle only the photon noise contribution. In order to decrease the speckle noise below the planet level, an active control of the wave front is required. We have developed analytical methods to measure and correct the speckle noise behind a coronagraph with a deformable mirror. In this paper, we summarize these methods, present numerical simulations, and discuss preliminary experimental results obtained with the High-Contrast Imaging Testbed at NASA's Jet Propulsion Laboratory.

 

astro-ph/0606289 [abs, ps, pdf, other] :

Title: Determinations of temperature and density for solar-like Stars using Si XI soft X-ray emission lines
Authors: G. Y. Liang, G. Zhao
Comments: 21 pages, 6 figures, Accepted in AJ

We study temperature and density sensitivities of ratios of Si XI soft X-ray emission lines, in the wavelength range of 43--54\AA . The typical temperature of the formation of the analyzed lines is around 1.6~MK, which makes this analysis complementary to the analysis of He-like triplets being sensitive to hotter plasma. We present theoretical calculations and compare them with ratios obtained from high-resolution X-ray spectra of five solar-like stars: Procyon, $\alpha$ Cen A$&$B, $\epsilon$ Eri, and Capella. We find that our results are in good agreement with results obtained by other authors through different diagnostics, namely the analysis of density- and temperature-sensitive He-like triplet lines. We further estimate the coronal pressure and filling factors from Si~XI lines in this study.

 

astro-ph/0606290 [abs, pdf] :

Title: Instruments without optics: an integrated photonic spectrograph
Authors: J. Bland-Hawthorn, A. Horton (Anglo-Australian Observatory)
Comments: 14 pages, 7 figures, to be published in Proc. SPIE 6269 Ground-based and Airborne Instrumentation for Astronomy

In recent years, a great deal of emphasis has been placed on achieving the diffraction limit with large aperture telescopes. For a well matched focal-plane instrument, the diffraction limit provides the highest possible angular resolution and sensitivity per pixel. But it offers another key advantage as we now show. Conventionally, as the telescope aperture D grows, the instrument size grows in proportion to D, and cost increases as D^2 or faster. However, an instrument that operates at the diffraction limit can break the trend of spiralling costs. In traditional instruments, the light must pass through a succession of large lenses, mirrors and gratings, making it difficult to conserve the integrity of such as small psf. An alternative approach, as we now show, is to couple the diffraction limited beam directly into an integrated photonic spectrograph operating in low-order modes.

 

astro-ph/0606291 [abs, ps, pdf, other] :

Title: Coupling light into optical fibres near the diffraction limit
Authors: Anthony J. Horton, Joss Bland-Hawthorn (Anglo-Australian Observatory)
Comments: 11 pages, 5 figures, to be published in Proc. SPIE 6269 Ground-based and Airborne Instrumentation for Astronomy

The burgeoning field of astrophotonics explores the interface between astronomy and photonics. Important applications include photonic OH suppression at near-infrared wavelengths, and integrated photonic spectroscopy. These new photonic mechanisms are not well matched to conventional multi-mode fibres and are best fed with single or few-mode fibres. We envisage the largest gains in astrophotonics will come from instruments that operate with single or few-mode fibres in the diffraction limited or near diffraction limited regimes. While astronomical instruments have largely solved the problem of coupling light into multi-mode fibres this is largely unexplored territory for few-mode and single-mode fibres. Here we describe a project to explore this topic in detail, and present initial results on coupling light into single and few-mode fibres at the diffraction limit. We find that fibres with as few as ~5 guided modes have qualitatively different behaviour to single-mode fibres and share a number of the beneficial characteristics of multi-mode fibres.

 

astro-ph/0606292 [abs, ps, pdf, other] :

Title: Proto-clusters in the Lambda CDM Universe
Authors: Tamon Suwa, Asao Habe, Kohji Yoshikawa
Comments: 4 pages, 5 figures, Accepted for publication in ApJ Letters

We compare the highly clustered populations of very high redshift galaxies with proto-clusters identified numerically in a standard $\Lambda$CDM universe ($\Omega_0=0.3, \lambda_0=0.7$) simulation. We evolve 256^3 dark matter particles in a comoving box of side 150h^{-1}Mpc. By the present day there are 63 cluster sized objects of mass in excess of 10^{14}h^{-1}Mo in this box. We trace these clusters back to higher redshift finding that their progenitors at z=4--5 are extended regions of typically 20--40 Mpc (comoving) in size, with dark halos of mass in excess of 10^{12}h^{-1}Mo and are overdense by typically 1.3--13 times the cosmological mean density. Comparison with the observation of Lyman alpha emitting (LAEs) galaxies at z=4.86 and at z=4.1 indicates that the observed excess clustering is consistent with that expected for a proto-cluster region if LAEs typically correspond to massive dark halos of more than 10^{12}h^{-1}Mo. We give a brief discussion on the relation between high redshift concentration of massive dark halos and present day rich clusters of galaxies.

 

astro-ph/0606293 [abs, ps, pdf, other] :

Title: Unconstrained Astrometric Orbits for Hipparcos Stars with Stochastic Solutions
Authors: Alexey Goldin, Valeri Makarov

A considerable number of astrometric binaries whose positions on the sky do not obey the standard model of mean position, parallax and linear proper motion, were observed by the Hipparcos satellite. Some of them remain non-discovered, and their observational data have not been properly processed with the more adequate astrometric model that includes nonlinear orbital motion. We develop an automated algorithm based on "genetic optimization", to solve the orbital fitting problem with no prior information about the orbital elements is available (from, e.g., spectroscopic data or radial velocity monitoring). We test this method on Hipparcos stars with known orbital solutions in the catalog, and further apply it to stars with stochastic solutions, which may be unresolved binaries. At a confidence level of 99%, orbital fits are obtained for 65 stars, most of which have not been known as binary. A few of the new probable binaries with A-type primaries with periods 444-2015 d are chemically peculiar stars, including Ap and \lambda Boo type. The anomalous spectra of these stars are explained as admixture of the light from the unresolved, sufficiently bright and massive companions. We estimate the apparent orbits of four stars which have been identified as members of the 300 Myr-old UMa kinematic group. Another four new nearby binaries may include low-mass M-type or brown dwarf companions. Similar astrometric models and algorithms can be used for binary stars and planet hosts observed by SIM PlanetQuest and Gaia.

 

astro-ph/0606294 [abs, ps, pdf, other] :

Title: On the investigations of galaxy redshift periodicity
Authors: K. Bajan, P. Flin, W. Godlowski, V.P. Pervushin
Comments: 10 pages, 4 figures, to be published in Part. and Nucl. Lett. 2006

In this article we present a historical review of study of the redshift periodicity of galaxies, starting from the first works performed in the seventies of the twentieth century until the present day. We discuss the observational data and methods used, showing in which cases the discretization of redshifts was observed. We conclude that galaxy redshift periodisation is an effect which can really exist. We also discussed the redshift discretization in two different structures: the Local Group of galaxies and the Hercules Supercluster. Contrary to the previous studies we consider all galaxies which can be regarded as a structure member disregarding the accuracy of velocity measurements. We applied the power spectrum analysis using the Hann function for weighting, together with the jackknife error estimator. In both the structures we found weak effects of redshift periodisation.

 

astro-ph/0606295 [abs, pdf] :

Title: Advances in infrared and imaging fibres for astronomical instrumentation
Authors: Roger Haynes (1), Pam McNamara (2), Jackie Marcel (1), Nemanja Jovanovic (3) ((1) Anglo-Australian Observatory, (2) Optical Fibre Technology Centre, (3) Centre for Ultrahigh-bandwidth Devices for Optical Systems)
Comments: 11 pages, 7 figures, to be published in Proc. SPIE 6273 Optomechanical Technologies for Astronomy

Optical fibres have already played a huge part in ground based astronomical instrumentation, however, with the revolution in photonics currently taking place new fibre technologies and integrated optical devices are likely to have a profound impact on the way we manipulate light in the future. The Anglo-Australian Observatory, along with partners at the Optical Fibre Technology Centre of the University of Sydney, is investigating some of the developing technologies as part of our Astrophotonics programme. In this paper we discuss the advances that have been made with infrared transmitting fibre, both conventional and microstructured, in particular those based on flouride glasses. Flouride glasses have a particularly wide transparent region from the UV through to around 7um, whereas silica fibres, commonly used in astronomy, only transmit out to about 2um. We discuss the impact of advances in fibre manufacture that have greatly improved the optical, chemical resistance and physical properties of the flouride fibres. We also present some encouraging initial test results for a modern imaging fibre bundle and imaging fibre taper.

 

astro-ph/0606296 [abs, ps, pdf, other] :

Title: Spitzer observations of acetylene bands in carbon-rich AGB stars in the Large Magellanic Cloud
Authors: M. Matsuura, P.R. Wood, G.C. Sloan, A.A. Zijlstra, J.Th. van Loon, M.A.T. Groenewegen, J.A.D.L. Blommaert, M.-R.L. Cioni, M.W. Feast, H.J. Habing, S. Hony, E. Lagadec, C. Loup, J.W. Menzies, L.B.F.M. Waters, P.A. Whitelock
Comments: 7 pages, accepted by MNRAS

We investigate the molecular bands in carbon-rich AGB stars in the Large Magellanic Cloud (LMC), using the InfraRed Spectrograph (IRS) on board the Spitzer Space Telescope (SST) over the 5--38 micron range. All 26 low-resolution spectra show acetylene (C2H2) bands at 7 and 14 micron. The hydrogen cyanide (HCN) bands at these wavelengths are very weak or absent. This is consistent with low nitrogen abundances in the LMC. The observed 14 micron C2H2 band is reasonably reproduced by an excitation temperature of 500 K. There is no clear dilution of the 14 micron band by circumstellar dust emission. This 14 micron band originates from molecular gas in the circumstellar envelope in these high mass-loss rate stars, in agreement with previous findings for Galactic stars. The C2H2,column density, derived from the 13.7 micron band, shows a gas mass-loss rate in the range 3x10^-6 to 5x10^{-5} Msun yr-1. This is comparable with the total mass-loss rate of these stars estimated from the spectral energy distribution. Additionally, we compare the line strengths of the 13.7 micron C2H2 band of our LMC sample with those of a Galactic sample. Despite the low metallicity of the LMC, there is no clear difference in the C2H2 abundance among LMC and Galactic stars. This reflects the effect of the 3rd dredge-up bringing self-produced carbon to the surface, leading to high C/O ratios at low metallicity.

 

astro-ph/0606297 [abs, ps, pdf, other] :

Title: On the radio properties of the highest redshift quasars
Authors: M. Cirasuolo, M. Magliocchetti, G. Gentile, A. Celotti, S. Cristiani, L. Danese
Comments: Accepted for publication in MNRAS, 8 pages, 6 figures

We present deep radio observations of the most distant complete quasar sample drawn from the Sloan Digital Sky Survey. Combining our new data with those from literature we obtain a sample which is ~100 per cent complete down to S_1.4GHz = 60 \mu Jy over the redshift range 3.8 < z < 5. The fraction of radio detections is relatively high (~43 per cent), similar to what observed locally in bright optical surveys. Even though the combined radio and optical properties of quasars remain overall unchanged from z ~ 5 to the local Universe, there is some evidence for a slight over-abundance of radio-loud sources at the highest redshifts when compared with the lower-z regime.
Exploiting the deep radio VLA observations we present the first attempt to directly derive the radio luminosity function of bright quasars at z ~ 4. The unique depth -- both in radio and optical -- allows us to thoroughly explore the population of optically bright FR~II quasars up to z ~ 5 and opens a window on the behaviour of the brightest FR~I sources. A close investigation of the space density of radio loud quasars also suggests a differential evolution, with the more luminous sources showing a less pronounced cut-off at high z when compared with the less luminous ones.

 

astro-ph/0606298 [abs, ps, pdf, other] :

Title: Large-scale structure of Lyman break galaxies around a radio galaxy protocluster at z~4
Authors: H. T. Intema (1), B. P. Venemans (1), J. D. Kurk (1 and 2), M. Ouchi (3), T. Kodama (4 and 5), H. J. A. Rottgering (1), G. K. Miley (1), R. A. Overzier (1) ((1) Sterrewacht Leiden, (2) INAF, (3) STSCI, (4) NOAJ, (5) ESO)
Comments: 5 pages, 4 figures. Accepted for publication in A&A. Full resolution version available at this http URL

We present broad-band imaging with the Subaru Telescope of a 25'x25' field surrounding the radio galaxy TN J1338-1942 at redshift z=4.1. The field contains excesses of Lyman-alpha emitters (LAEs) and Lyman break galaxies (LBGs) identified with a protocluster surrounding the radio galaxy. Our new wide-field images provide information about the boundary of the protocluster and its surroundings. There are 874 candidate LBGs within our field, having redshifts in the range z=3.5-4.5. An examination of the brightest of these (with i'< 25.0) shows that the most prominent concentration coincides with the previously discovered protocluster. The diameter of this galaxy overdensity corresponds to ~2 Mpc at z=4, consistent with the previous estimation using LAEs. Several other concentrations of LBGs are observed in the field, some of which may well be physically connected with the z=4.1 protocluster. The observed structure in the smoothed LBG distribution can be explained as the projection of large-scale structure, within the redshift range z=3.5-4.5, comprising compact overdensities and prominent larger voids. If the 5-8 observed compact overdensities are associated with protoclusters, the observed protocluster volume density is ~5x10^-6 Mpc^-3, similar to the volume density of rich clusters in the local Universe.

 

astro-ph/0606299 [abs, ps, pdf, other] :

Title: Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
Authors: L. Decin, S. Hony, A. de Koter, K. Justtanont, A.G.G.M. Tielens, L.B.F.M. Waters
Comments: 18 pages, 10 figures, accepted for publication in "Astronomy & Astrophysics"

Context: Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). The gas and dust ejected during this phase are a major source in the mass budget of the interstellar medium. Recent studies have pointed towards the importance of variations in the mass-loss history of such objects. Aims: By modelling the full line profile of low excitation CO lines emitted in the circumstellar envelope, we can study the mass-loss history of AGB stars. Methods: We have developed a non-LTE radiative transfer code, which calculates the velocity structure and gas kinetic temperature of the envelope in a self-consistent way. The resulting structure of the envelope provides the input for the molecular line radiative calculations which are evaluated in the comoving frame. The code allows for the implementation of modulations in the mass-loss rate. This code has been benchmarked against other radiative transfer codes and is shown to perform well and efficiently. Results: We illustrate the effects of varying mass-loss rates in case of a superwind phase. The model is applied to the well-studied case of VY CMa. We show that both the observed integrated line strengths as the spectral structure present in the observed line profiles, unambiguously demonstrate that this source underwent a phase of high mass loss (~ 3.2E-4 Msun/yr) some 1000 yr ago. This phase took place for some 100 yr, and was preceded by a low mass-loss phase (~ 1E-6 Msun/yr) taking some 800 yr. The current mass-loss rate is estimated to be in the order of 8E-5 Msun/yr. Conclusions: In this paper, we demonstrate that both the relative strength of the CO rotational line profiles and the (non)-occurrence of spectral structure in the profile offer strong diagnostics to pinpoint the mass-loss history.

 

astro-ph/0606300 [abs, ps, pdf, other] :

Title: Methanol Maser Polarization in W3(OH)
Authors: W.H.T. Vlemmings (1), L. Harvey-Smith (2), R.J. Cohen (1) ((1) Jodrell Bank (2) JIVE)
Comments: 5 pages, 2 figures, accepted for publication in MNRAS

We present the first 6.7 GHz methanol maser linear polarization map of the extended filamentary maser structure around the compact HII region W3(OH). The methanol masers show linear polarization up to 8 per cent and the polarization angles indicate a magnetic field direction along the North-South maser structure. The polarization angles are consistent with those measured for the OH masers, taking into account external Faraday rotation toward W3(OH), and confirm that the OH and methanol masers are found in similar physical conditions. Additionally we discuss the Zeeman splitting of the 6.7 GHz methanol transition and present an upper limit of ~22 mG for the magnetic field strength in the maser region. The upper limit is fully consistent with the field strengths derived from OH maser Zeeman splitting.

 

astro-ph/0606301 [abs, ps, pdf, other] :

Title: The density profiles of hot galactic halo gas
Authors: Steen H. Hansen, Jesper Sommer-Larsen
Comments: 5 pages, 2 figures

Extended gas haloes around galaxies are a ubiquitous prediction of galaxy formation scenarios. However, the density profiles of this hot halo gas is virtually unknown, although various profiles have been suggested on theoretical grounds. In order to quantitatively address the gas profile, we compare galaxies from direct cosmological simulations with analytical solutions of the underlying gas equations. We find remarkable agreement between simulations and theoretical predictions. We present an expression for this gas profile with a non-trivial dependence on the total mass profile. This expression is useful when setting up equilibrium galaxy models for numerical experiments.

 

astro-ph/0606302 [abs, ps, pdf, other] :

Title: Searching for Gas-Rich Disks around T Tauri Stars in Lupus
Authors: T.A. van Kempen, E.F. van Dishoeck, C. Brinch, M.R. Hogerheijde (Leiden Observatory)
Comments: 8 pages, with online section, accepted by A&A

AIMS : To characterize the molecular environment of classical T Tauri stars in Lupus observed with the Spitzer Space Telescope and to search for gas-rich disks toward these sources.
METHODS : Submillimeter observations of 12CO, 13CO and C18O in the J=3-2 and 2-1 lines were obtained with the James Clerk Maxwell Telescope toward a sample of 21 T Tauri stars with disks in the Lupus molecular clouds. Pointings at the sources and at selected off-positions are presented in order to disentangle material associated with disks from ambient cloud material.
RESULTS : One source, IM Lup (Sz 82), has been found with double-peaked 12CO and 13CO profiles characteristic of a large rotating gas disk. The inclination of the disk is found to be ~20 degrees, with an outer radius of 400-700 AU. For most other sources, including GQ Lup with its substellar companion, the single-dish 12CO lines are dominated by extended cloud emission with a complex velocity structure. No evidence for molecular outflows is found. Compact C18O emission due to dense circumstellar material has been detected toward only two sources. Future searches for gas-rich disks in Lupus should either use interferometers or perform very deep single-dish integrations in dense gas tracers to separate the cloud and disk emission.

 

astro-ph/0606303 [abs, ps, pdf, other] :

Title: Timescales of merger, starburst and AGN activity in radio galaxy B2 0648+27
Authors: B.H.C. Emonts (1), R. Morganti (1,2), C.N. Tadhunter (3), J. Holt (3), T.A. Oosterloo (1,2), J.M. van der Hulst (1), K.A. Wills (3) ((1) Kapteyn Astronomical Institute, Groningen, (2) Netherlands Foundation for Research in Astronomy, (3) Dep. of Physics and Astronomy, Univ. Sheffield)
Comments: 13 pages, 11 figures. Accepted for publication in A&A. A version with full resolution figures is available at this http URL

In this paper we use neutral hydrogen HI and optical spectroscopic observations to compare the timescales of a merger event, starburst episode and radio-AGN activity in the radio galaxy B2 0648+27. We detect a large ring-like structure of HI in emission around the early-type host galaxy of B2 0648+27 (M_HI = 8.5 x 10^9 Msun, diameter = 190 kpc). We interpret this as the result of a major merger that occurred > 1.5 Gyr ago. From modelling optical long-slit spectra we find that a young stellar population of 0.3 Gyr, indicative of a past starburst event, dominates the stellar light throughout the galaxy. The off-set in time between the merger event and the starburst activity in B2 0648+27 suggests that the starburst was triggered in an advanced stage of the merger, which can be explained if the gas-rich progenitor galaxies contained a bulge. Although the exact age of the radio source remains uncertain, there appears to be a significant time-delay between the merger/starburst event and the current episode of radio-AGN activity. We also observe an outflow of emission-line gas in this system, which is likely related to superwinds driven by the stars that formed during the starburst event. We argue that the radio galaxy B2 0648+27 is a link in the evolutionary sequence between Ultra-Luminous Infrared Galaxies (ULIRGs) and genuine early-type galaxies.

 

astro-ph/0606304 [abs, ps, pdf, other] :

Title: The co-evolution of the obscured quasar PKS1549-79 and its host galaxy: evidence for a high accretion rate and warm outflow
Authors: J. Holt (1), C. N. Tadhunter (1), R. Morganti (2,3), M. Bellamy (1), R.M. Gonzalez Delgado (4), A. Tzioumis (5), K.J. Inskip (1) ((1) Sheffield, UK; (2) ASTRON, NL; (3) Kapteyn Institute, University of Groningen, NL; (4) Instituto de Astrofisica de Andalucia, Granada, Spain; (5) ATNF-CSIRO, Australia)
Comments: 21 pages, 12 figures, accepted for publication in MNRAS

ABRIDGED: We use deep optical, IR and radio observations to explore the symbiosis between the nuclear activity and galaxy evolution in the southern compact radio source PKS1549-79 (z=0.1523). The optical imaging observations reveal the presence of tidal tail features which provide strong evidence that the host galaxy has undergone a major merger in the recent past. This is further supported by the detection of a young stellar population which was formed 50-250Myr ago and makes up 1-30% of the total stellar mass. Despite the core-jet structure of the radio source we detect HI absorption associated with both the core and the jet. The luminous, quasar-like AGN (M_V < -23.5) is highly extinguished (A_v > 4.9) at optical wavelengths and shows many properties in common with narrow line Seyfert 1 galaxies (NLS1), including relatively narrow permitted lines (FWHM ~ 1940 km/s), highly blueshifted [OIII] lines (~680 km/s), and evidence that the putative supermassive black hole is accreting at a high Eddington ratio. This suggests that accretion at high Eddington ratio does not prevent the formation of powerful jets. Our observations lend strong support to the predictions of some recent numerical simulations of galaxy mergers in which the black hole grows rapidly through merger-induced accretion following the coalescence of the nuclei of two merging galaxies; the major growth phase largely hidden by the natal gas and dust. Although the models predict that AGN-driven outflows will eventually remove the gas from the bulge of the host galaxy, the visible warm outflow in PKS1549-79 is not currently capable of doing so. ABRIDGED

 

astro-ph/0606305 [abs, ps, pdf, other] :

Title: Integral field spectroscopy of H-alpha emission in cooling flow cluster cores: disturbing the molecular gas reservoir
Authors: R. J. Wilman, A. C. Edge, A. M. Swinbank (Durham University)
Comments: 15 pages, 16 figures (7 with essential colour), accepted by MNRAS

We present optical integral field spectroscopy of the H-alpha-luminous (>1E42 erg/s) central cluster galaxies in the cores of the cooling flows A1664, A1835, A2204 and Zw8193. From the [NII]+H-alpha complex we derive 2-D views of the distribution and kinematics of the emission line gas, and further diagnostics from the [SII] and [OI] lines. The H-alpha emission shows a variety of disturbed morphologies with velocity gradients and splittings of several hundred km/s on scales of 20 kpc or more. Despite the small sample size, there are some generic features. The most disturbed H-alpha emission appears to be associated with secondary galaxies within 10-20 kpc (projected) of the central galaxy and close in velocity to the H-alpha. The global H-alpha kinematics match those of CO(1-0) emission in single-dish data. The [NII]/H-alpha, [SII]/H-alpha and [OI]/H-alpha ratios vary little with position, local H-alpha surface brightness or between clusters. We propose that the H-alpha and CO emission arise in molecular clouds heated by a starburst which has been triggered by interaction with a secondary galaxy. Such CO emission is known to trace massive (>1E10 M_sun) compact (<20 kpc) reservoirs of cool molecular gas, which an infalling galaxy may disturb, distorting the H-alpha morphology and initiating widespread star formation. We suggest that cloud-cloud collisions in the undisturbed molecular gas reservoir might be an important excitation source for the emission line gas in the cores of lower H-alpha luminosity cluster cores with less intense star formation (abridged).

 

astro-ph/0606306 [abs, ps, pdf, other] :

Title: The SUGRA Quintessence Model Coupled to the MSSM
Authors: Philippe Brax, Jerome Martin
Comments: 33 pages, 7 figures

We study the cosmological evolution of the universe when quintessence is modeled within supergravity, supersymmetry is broken in a hidden sector, and we also include observable matter in a third independent sector. We find that the presence of hidden sector supersymmetry breaking leads to modifications of the quintessence potential. We focus on the coupling of the SUGRA quintessence model to the MSSM and investigate two possibilities. First one can preserve the form of the SUGRA potential provided the hidden sector dynamics is tuned. The currently available limits on the violations of the equivalence principle imply a universal bound on the vacuum expectation value of the quintessence field now, \kappa ^{1/2}Q\ll 1. On the other hand, the hidden sector fields may be stabilised leading to a minimum of the quintessence potential where the quintessence field acquires a mass of the order of the gravitino mass, large enough to circumvent possible gravitational problems. However, the cosmological evolution of the quintessence field is affected by the presence of the minimum of the potential. The quintessence field settles down at the bottom of the potential very early in the history of the universe. Both at the background and the perturbation levels, the subsequent effect of the quintessence field is undistinguishable from a pure cosmological constant

 

astro-ph/0606307 [abs, ps, pdf, other] :

Title: Unveiling the nature of the highly absorbed X-ray source SAXJ1748.2-2808 with XMM-Newton
Authors: L. Sidoli (1), S. Mereghetti (1), F. Favata (2), T. Oosterbroek (2), A.N. Parmar (2) ((1)-INAF/IASF Milano, Italy; (2) ESA/ESTEC Noordwijk, The Netherlands)
Comments: accepted for publication in A&A

We report on the results of an EPIC XMM-Newton observation of the faint source SAXJ1748.2-2808 and the surrounding field. This source was discovered during the BeppoSAX Galactic center survey performed in 1997-1998. A spatial analysis resulted in the detection of 31 sources within the EPIC field of view. SAXJ1748.2-2808 is clearly resolved into 2 sources in EPIC images with the brighter contributing almost 80% of the 2-10keV flux. Spectral fits to this main source are consistent with an absorbed power-law with a photon index of 1.4+/-0.5 and absorption equivalent to 14E22cm-2 together with an iron line at 6.6+/-0.2 keV with an equivalent width of ~780eV. The significantly better statistics of the XMM-Newton observation, compared with BeppoSAX,allows to exclude a thermal nature for the X-ray emission. A comparison with other observations of SAXJ1748.2-2808 does not reveal any evidence for spectral or intensity long-term variability. Based on these properties we propose that the source is a low-luminosity high-mass X-ray binary located in the Galactic center region.

 

astro-ph/0606308 [abs, ps, pdf, other] :

Title: Neutron star masses: dwarfs, giants and neighbors
Authors: S.B. Popov (1), D. Blaschke (2,3), H. Grigorian (2,4), M.E. Prokhorov (1) (1- Sternberg Astronomical Institute; 2- University of Rostock; 3 - JINR Dubna; 4 - Yerevan State University)
Comments: 4 pages, 1 figure, Ap&SS style, to be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface"

We discuss three topics related to the neutron star (NS) mass spectrum. At first we discuss the possibility to form low-mass ($ M \stackrel{<}{\sim} 1 M_{\odot}$) and suggest this is possible only due to fragmentation of rapidly rotating proto-NSs. Such low-mass NSs should have very high spatial velocities which could allow identification. A critical assessment of this scenario is given. Secondly, we discuss mass growth due to accretion for NSs in close binary systems. With the help of numerical population synthesis calculations we derive the mass spectrum of massive ($M > 1.8 M_{\odot}$) NSs. Finally, we discuss the role of the mass spectrum in population studies of young cooling NSs. We formulate a kind of {\it mass constraint} which can be helpful, in our opinion, in discussing different competive models of the thermal evolution of NSs.

 

astro-ph/0606309 [abs, ps, pdf, other] :

Title: VLT/ISAAC Spectra of the H-beta Region in Intermediate-Redshift Quasars II. Black Hole Mass and Eddington Ratio
Authors: J. W. Sulentic, P. Repetto, G. M. Stirpe, P. Marziani, D. Dultzin-Hacyan, M. Calvani
Comments: Accepted for publication in Astronomy & Astrophysics

We derive black hole masses for a sample of about 300 AGNs in the redshift range 0 < z < 2.5. We use the same virial velocity measure (FWHM Hbeta broad component) for all sources which represents a significant improvement over previous studies. We review methods and caveats for determining AGN black hole masses via the virial assumption for motions in the gas producing low ionization broad emission lines. We derive a corrected FWHM measure for the broad component of H-beta that better estimates the virialized line emitting component by comparing our FWHM measures with a sample of reverberated sources with H-beta radial velocity dispersion measures. We also consider the FWHM of the FeII 4570 blend as a potential alternative velocity estimator. We find a range of black hole mass between log M ~ 6 - 10, where the black hole mass M is in solar masses. Estimates using corrected FWHM, as well as FWHM(Fe II) measures, reduce the number of sources with log M > 9.5 and suggest that extremely large M values (log M >~ 10) may not be realistic. Derived Eddington ratio values values show no evidence for a significant population of super-Eddington radiators especially after correction is made for sources with extreme orientation to our line of sight. Sources with FWHM(Hbeta broad component) <~ 4000 km/s show systematically higher Eddington ratio and lower M values than broader lined AGNs (including almost all radio-loud sources).

 

astro-ph/0606310 [abs, ps, pdf, other] :

Title: Seismic signatures of strange stars with crust
Authors: A.I. Chugunov
Comments: 15 pages, 3 figures, Accepted for publication in MNRAS

We study acoustic oscillations (eigenfrequencies, velocity distributions, damping times) of normal crusts of strange stars. These oscillations are very specific because of huge density jump at the interface between the normal crust and the strange matter core. The oscillation problem is shown to be self-similar. For a low (but non-zero) multipolarity l the fundamental mode (without radial nodes) has a frequency ~300 Hz and mostly horizontal oscillation velocity; other pressure modes have frequencies >=20 kHz and almost radial oscillation velocities. The latter modes are similar to radial oscillations (have approximately the same frequencies and radial velocity profiles). The oscillation spectrum of strange stars with crust differs from the spectrum of neutron stars. If detected, acoustic oscillations would allow one to discriminate between strange stars with crust and neutron stars and constrain the mass and radius of the star.

 

astro-ph/0606311 [abs, ps, pdf, other] :

Title: Discovery of the two wings of the Kookaburra complex in VHE gamma -rays with H.E.S.S
Authors: The H.E.S.S. Collaboration: F.A. Aharonian, et al
Comments: 9 pages, 4 figures, accepted for publication in A&A

Aims. Search for Very High Energy gamma-ray emission in the Kookaburra complex through observations with the H.E.S.S. array. Methods. Stereoscopic imaging of Cherenkov light emission of the gamma-ray showers in the atmosphere is used for the reconstruction and selection of the events to search for gamma-ray signals. Their spectrum is derived by a forward-folding maximum likelihood fit. Results. Two extended gamma-ray sources with an angular (68%) radius of 3.3-3.4' are discovered at high (>13sigma) statistical significance: HESS J1420-607 and HESS J1418-609. They exhibit a flux above 1 TeV of (2.97+/-0.18stat +/-0.60sys)x10-12 and (2.17+/-0.17stat +/-0.43sys)x10-12 cm-2 s-1, respectively, and similar hard photon indices ~2.2. Multi-wavelength comparisons show spatial coincidence with the wings of the Kookaburra. Two pulsar wind nebulae candidates, K3/PSR J1420-6048 and the Rabbit, lie on the edge of the H.E.S.S. sources. Conclusions. The two new sources confirm the non-thermal nature of at least parts of the two radio wings which overlap with the gamma-ray emission and establish their connection with the two X-ray pulsar wind nebulae candidates. Given the large point spread function of EGRET, the unidentified source(s) 3EG J1420-6038/GeV J1417-6100 could possibly be related to either or both H.E.S.S. sources. The most likely explanation for the Very High Energy gamma-rays discovered by H.E.S.S. is inverse Compton emission of accelerated electrons on the Cosmic Microwave Background near the two candidate pulsar wind nebulae, K3/PSR J1420-6048 and the Rabbit. Two scenarios which could lead to the observed large (~10 pc) offset-nebula type morphologies are briefly discussed.

 

astro-ph/0606312 [abs, ps, pdf, other] :

Title: Comptonization model for Prompt optical and infrared emission of GRB 041219A
Authors: Zheng Zheng (1,2), Ye Lu (1,3), Yong-Heng Zhao (1) ((1) NAOC, (2) GUCAS, (3) Univ. of Hong Kong)
Comments: Accepted for publication in ApJL

Prompt optical emission from the $\gamma$-ray burst of GRB 041219A has been reported by \citet{ves05}. The facts that the fast rise of optical emission simultaneous with the dominant $\gamma$-ray pulse, and a tight correlation with the prompt $\gamma$-ray emission have been displayed. These indicate that the prompt optical emission and $\gamma$-ray emission would naturally have a common origin. We then propose that this optical component could be modelled by considering the $Comptonization$ of $\gamma$-ray photons by an electron cloud. As a result of this mechanism, the arrival time of the optical photons is delayed comparing with that of the $\gamma$-rays. We restrict that the lagging time is shorter than 10 s, within which the prompt optical emission is considered as varying simultaneously with the prompt $\gamma$-ray emission. Taking into account of the observations of GRB 041219A, we derive the number density of the surrounding electron cloud required by $Comptonization$. The red-shift of GRB 041219A is predicted as $z\lesssim 0.073$ as well.

 

astro-ph/0606313 [abs, ps, pdf, other] :

Title: XMM-Newton observations of the supernova remnant IC443: I. soft X-ray emission from shocked interstellar medium
Authors: E. Troja, F. Bocchino, F. Reale
Comments: 10 pages, 10 figures, accepted for publication in ApJ (20 September 2006, v649). For hi-res figures, see this http URL

The shocked interstellar medium around IC443 produces strong X-ray emission in the soft energy band (E<1.5 keV). We present an analysis of such emission as observed with the EPIC MOS cameras on board the XMM-Newotn observatory, with the purpose to find clear signatures of the interactions with the interstellar medium (ISM) in the X-ray band, which may complement results obtained in other wavelenghts. We found that the giant molecular cloud mapped in CO emission is located in the foreground and gives an evident signature in the absorption of X-rays. This cloud may have a torus shape and the part of torus interacting with the IC443 shock gives rise to 2MASS-K emission in the southeast. The measured density of emitting X-ray shocked plasma increases toward the northeastern limb, where the remnant is interacting with an atomic cloud. We found an excellent correlation between emission in the 0.3-0.5 keV band and bright optical/radio filament on large spatial scales. The partial shell structure seen in this band therefore traces the encounter with the atomic cloud.

 

astro-ph/0606314 [abs, ps, pdf, other] :

Title: Small Magellanic Cloud Be stars: colour-magnitude relations and mass-loss
Authors: W.J. de Wit, H.J.G.L.M. Lamers, J.B. Marquette, J.P. Beaulieu
Comments: 2 pages - Conference proceedings to 'Mass Loss from stars and the evolution of stellar clusters' - Lunteren, The Netherlands, May 29 - June 1, 2006. A. de Koter, L. Smith & R. Waters

We present an analysis of optical lightcurves of Small Magellanic Cloud Be-type stars. Observations show that (1) optical excess flux is correlated with near-IR excess flux indicating a similar mechanism and (2) the lightcurves can trace out ``loops'' in a colour-magnitude diagram. A simple model for the time dependent bound-free and free-free emission produced by an outflowing circumstellar disk gives reasonable fits to the observations.

 

astro-ph/0606315 [abs, ps, pdf, other] :

Title: Antisymmetric Metric Field as Dark Matter
Authors: Tomislav Prokopec, Wessel Valkenburg (Utrecht University)
Comments: 22 pages, 5 eps figures

We consider the generation and evolution of quantum fluctuations of a massive nonsymmetric gravitational field (B-field) from inflationary epoch to matter era in the simplest variant of the nonsymmetric theory of gravitation (NGT), which consists of a gauge kinetic term and a mass term.
We observe that quite generically a nonsymmetric metric field with mass, m_B ~ 0.03(H_I/10^(13) GeV)^4 eV, is a good dark matter candidate, where H_I denotes the inflationary scale. The most prominent feature of this dark matter is a peak in power at a comoving momentum, k ~ sqrt(m_B H_0)/(1+z_eq)^(1/4), where z_eq is the redshift at equality. This scale corresponds roughly to the Earth-Sun distance.

 

astro-ph/0606316 [abs, ps, pdf, other] :

Title: Probing Neutrino Dark Energy with Extremely High-Energy Cosmic Neutrinos
Authors: Andreas Ringwald (DESY), Lily Schrempp (DESY)
Comments: 38 pages, 19 figures

Recently, a new non-Standard Model neutrino interaction mediated by a light scalar field was proposed, which renders the big-bang relic neutrinos of the cosmic neutrino background a natural dark energy candidate, the so-called Neutrino Dark Energy. As a further consequence of this interaction, the neutrino masses become functions of the neutrino energy densities and are thus promoted to dynamical, time/redshift dependent quantities. Such a possible neutrino mass variation introduces a redshift dependence into the resonance energies associated with the annihilation of extremely high-energy cosmic neutrinos on relic anti-neutrinos and vice versa into Z-bosons. In general, this annihilation process is expected to lead to sizeable absorption dips in the spectra to be observed on earth by neutrino observatories operating in the relevant energy region above 10^13 GeV. In our analysis, we contrast the characteristic absorption features produced by constant and varying neutrino masses, including all thermal background effects caused by the relic neutrino motion. We firstly consider neutrinos from astrophysical sources and secondly neutrinos originating from the decomposition of topological defects using the appropriate fragmentation functions. On the one hand, independent of the nature of neutrino masses, our results illustrate the discovery potential for the cosmic neutrino background by means of relic neutrino absorption spectroscopy. On the other hand, they allow to estimate the prospects for testing its possible interpretation as source of Neutrino Dark Energy within the next decade by the neutrino observatories ANITA and LOFAR.

 

astro-ph/0606317 [abs, ps, pdf, other] :

Title: COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses V. The time delay in SDSS J1650+4251 from two seasons of monitoring
Authors: C. Vuissoz (1), F. Courbin (1), D. Sluse (1), G. Meylan (1), M. Ibrahimov (2), I. Asfandiyarov (2), E. Stoops (1,3), A. Eigenbrod (1), L. Le Guillou (4), H. van Winckel (4), P. Magain (3) ((1) EPFL, Lausanne, Switzerland, (2) Academy of Sciences, Tashkent, Uzbekistan,(3) Univ. Liege, Belgium, (4) Kath. Univ. Leuven, Belgium)
Comments: 9 pages, 12 figures, submitted to A&A

Aims: To measure the time delay between the two gravitationally lensed images of the z = 1.547 quasar SDSS J1650+4251, in order to estimate the Hubble constant H_0.
Methods: Our measurement is based on R-band light curves with 57 epochs obtained at Maidanak Observatory, in Uzbekistan, from May 2004 to September 2005. The photometry is performed using simultaneous deconvolution of the data, which provides the individual light curves of the otherwise blended quasar images. The time delay is determined from the light curves using two very different numerical techniques, i.e., polynomial fitting and direct cross-correlation. The time delay is converted into H_0 following analytical modeling of the potential well.
Results: Our best estimate of the time delay is Dt = 49.5 +/- 1.9 days, i.e., we reach a 3.8% accuracy. The R-band flux ratio between the quasar images, corrected for the time delay and for slow microlensing, is F_A /F_B = 6.2.
Conclusions: The accuracy reached on the time delay allows to discriminate well between families of lens models. As for most other multiply imaged quasars, only models of the lensing galaxy that have a constant mass-to-light ratio give a Hubble constant compatible with the current most popular value (H_0 = 72 +/- 8 km s-1 Mpc-1). Using a de Vaucouleurs mass profile and external shear, we find H_0 = 80.8 +7.0 -3.0 km s-1 Mpc-1. A more realistic Singular Isothermal Sphere model plus external shear gives H_0 = 51.7 +4.0 -3.0 km s-1 Mpc-1.

 

astro-ph/0606318 [abs, ps, pdf, other] :

Title: Systematic quantum corrections to screening in thermonuclear fusion
Authors: Shirish M. Chitanvis

We develop a series expansion of the plasma screening length away from the classical limit in powers of $\hbar^{2}$. It is shown that the leading order quantum correction increases the screening length in solar conditions by approximately 2% while it decreases the fusion rate by approximately $ 0.34%$. We also calculate the next higher order quantum correction which turns out to be approximately 0.05%.

 

astro-ph/0606319 [abs, ps, pdf, other] :

Title: Swift and infra-red observations of the blazar 3C~454.3 during the giant X-ray flare of May 2005
Authors: P. Giommi, A.J. Blustin, M. Capalbi, S. Colafrancesco, A. Cucchiara, L. Fuhrmann, H.A. Krimm, N. Marchili, E. Massaro, M. Perri, G. Tagliaferri, G. Tosti, A. Tramacere, D.N. Burrows, G. Chincarini, A. Falcone, N. Gehrels, J. Kennea, R. Sambruna
Comments: 7 pages, 4 figures, accepted for publication in A&A

We present the results of a series of Swift and quasi simultaneous ground-based infra-red observations of the blazar 3C 454.3 carried out in April-May 2005 when the source was 10 to 30 times brighter than previously observed. We found 3C 454.3 to be very bright and variable at all frequencies covered by our instrumentation. The broad-band Spectral Energy Distribution (SED) shows the usual two-bump shape (in nu-nu f(nu) space) with the Infra-red, optical and UV data sampling the declining part of the synchrotron emission that, even during this extremely large outburst, had its maximum in the far-infrared. The X-ray spectral data from the XRT and BAT instruments are flat and due to inverse Compton emission. The remarkable SED observed implies that at the time of the Swift pointings 3C 454.3 was one of the brightest objects in the extragalactic sky with a gamma-ray emission similar or brighter than that of 3C 279 when observed in a high state by EGRET. Time variability in the optical-UV flux is very different from that in the X-ray data: while the first component varied by about a factor two within a single exposure, but remained approximately constant between different observations, the inverse Compton component did not vary on short time-scales but changed by more than a factor of 3 between observations separated by a few days. This different dynamical behaviour illustrates the need to collect simultaneous multi-frequency data over a wide range of time-scales to fully constrain physical parameters in blazars.

 

astro-ph/0606320 [abs, ps, pdf, other] :

Title: Rapid X-ray Declines in Swift Gamma Ray Burst Lightcurves Explained by A Highly Radiative Blast Wave Phase
Authors: Charles D. Dermer (NRL)
Comments: 19 pages, 4 figs, presented at Venice Swift GRB workshop, June 8, 2006, submitted to ApJ

X-ray lightcurves of GRBs show rapid declines some hundreds of seconds after the burst trigger in ~ 30% of GRBs in the Swift sample. Treating the standard blast model in a uniform circumburst medium, we show that if GRBs accelerate ultra-high energy cosmic rays through a Fermi mechanism, then the hadronic component can be rapidly depleted by means of photopion processes on time scales ~10^2 -- 10^4 s after the GRB explosion. While discharging the hadronic energy in the form of ultra-high energy cosmic ray neutrons and escaping cosmic ray ions, the blast wave will go through a strongly radiative phase that drives the mean blast wave Lorentz factor to a radiative asymptote. This process is argued to cause the steep declines observed with Swift in the X-ray light curves of GRBs, implying that GRB sources showing rapid X-ray declines take place in rather dense media, with n >~ 100 cm^{-3} out to >~ 10^{17} cm.

 

astro-ph/0606321 [abs, ps, pdf, other] :

Title: Spitzer Space Telescope Infrared Imaging and Spectroscopy of the Crab Nebula
Authors: Tea Temim (1), Robert D. Gehrz (1), Charles E. Woodward (1), Thomas L. Roellig (2), Nathan Smith (3 and 6), Lawrence R. Rudnick (1), Elisha F. Polomski (1), Kris Davidson (1), Lunming Yuen (4), Takashi Onaka (5) ((1) Department of Astronomy, University of Minnesota, (2) NASA Ames Research Center, Moffett Field, CA, (3) Center for Astrophysics and Space Astronomy, University of Colorado, (4) Technosciences Corp., Moffett Field, CA, (5) University of Tokyo, Tokyo, Japan, (6) Visiting Astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (NOAO))
Comments: 21 pages, 4 tables, 16 figures

We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- and High-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-based image made in the light of [Fe II]1.644 micron. The 8.0 micron image, made with a bandpass that includes [Ar II]7.0 micron, resembles the general morphology of visible H-alpha and near-IR [Fe II] line emission, while the 3.6 and 4.5 micron images are dominated by continuum synchrotron emission. The 24 micron and 70 micron images show enhanced emission that may be due to line emission or the presence of a small amount of warm dust in the nebula on the order of less than 1% of a solar mass. The ratio of the 3.6 and 4.5 micron images reveals a spatial variation in the synchrotron power law index ranging from approximately 0.3 to 0.8 across the nebula. Combining this information with optical and X-ray synchrotron images, we derive a broadband spectrum that reflects the superposition of the flatter spectrum jet and torus with the steeper diffuse nebula, and suggestions of the expected pileup of relativistic electrons just before the exponential cutoff in the X-ray. The pulsar, and the associated equatorial toroid and polar jet structures seen in Chandra and HST images (Hester et al. 2002) can be identified in all of the IRAC images. We present the IR photometry of the pulsar. The forbidden lines identified in the high resolution IR spectra are all double due to Doppler shifts from the front and back of the expanding nebula and give an expansion velocity of approximately 1264 km/s.

 

astro-ph/0606322 [abs, ps, pdf, other] :

Title: Rotochemical Heating of Neutron Stars: Rigorous Formalism with Electrostatic Potential Perturbations
Authors: Andreas Reisenegger, Paula Jofre, Rodrigo Fernandez, Elena Kantor
Comments: 14 pages, including 4 eps figures. Accepted for publication in The Astrophysical Journal

The electrostatic potential that keeps approximate charge neutrality in neutron star matter is self-consistently introduced into the formalism for rotochemical heating presented in a previous paper by Fernandez and Reisenegger. Although the new formalism is more rigorous, we show that its observable consequences are indistinguishable from those of the previous one, leaving the conclusions of the previous paper unchanged.

 

astro-ph/0606323 [abs, ps, pdf, other] :

Title: The DRaGONS Survey: A Search for High Redshift Radio Galaxies And Heavily Obscured AGNs
Authors: S. J. Schmidt, A. J. Connolly (University of Pittsburgh), A. M. Hopkins (University of Sydney)
Comments: Accepted for pulication in the Astrophysical Journal, 19 pages, 16 figures, 6 tables. A version with full resolution figures is available at this http URL

We present the first results from the Distant Radio Galaxies Optically Non-detected in the SDSS (DRaGONS) Survey. Using a novel selection technique for identifying high redshift radio galaxy (HzRG) candidates, a large sample of bright (S_{1.4GHz} > 100mJy) radio sources from the FIRST survey having no optical counterpart in the SDSS is compiled. K-band imaging with the FLAMINGOS instrument on the 4-meter telescope at Kitt Peak for 96 such candidates allows preliminary identification of HzRG candidates through the well-known K-z relation. Of the initial candidates, we identify 70 with magnitudes brighter than K \approx 19.5, and compute limiting magnitudes for the remainder. Assigning redshifts based on the K-z Hubble diagram gives a mean redshift for our sample of z=2.5 and a median redshift of z=2.0. This selection is also sensitive to a previously unseen population of anomalously red radio galaxies (r-K > 6.5-7), which may indicate significant obscuration at moderate redshifts. These obscured objects can be used to test the completeness of QSO surveys to the effects of reddenning. More than ten percent of our sample falls into this category, which may represent a sizable radio loud population missing from current optically selected AGN samples. We additionally identify 479 bright Extremely Red Objects (EROs) in the fields surrounding our HzRG candidates, to a magnitude of K=17.5, within a non-contiguous area of 2.38 square degrees. This constitutes a small overdensity of EROs surrounding the radio galaxy candidates over random fields, and we see possible evidence for a physical association of the EROs with the radio galaxies. However, examining the clustering of all K < 19.0 galaxies around the radio targets reveals no evidence of a global galaxy excess.

 

astro-ph/0606324 [abs, ps, pdf, other] :

Title: Global Asymmetry of the Heliosphere
Authors: Merav Opher, Edward C. Stone, Paulett C. Liewer, Tamas Gombosi
Comments: 6 pages, 5 figures, AIP Proceedings of the 5th IGPP "The Physics of the Inner Heliosheath: Voyager Observations, Theory and Future Prospects"

Opher et al. 2006 showed that an interstellar magnetic field parallel to the plane defined by the deflection of interstellar hydrogen atoms can produce a north/south asymmetry in the distortion of the solar wind termination shock. This distortion is consistent with Voyager 1 and Voyager 2 observations of the direction of field-aligned streaming of the termination shock particles upstream the shock. The model also indicates that such a distortion will result in a significant north/south asymmetry in the distance to the shock and the thickness of heliosheath. The two Voyager spacecraft should reveal the nature and degree of the asymmetry in the termination shock and heliosheath.

 

astro-ph/0606325 [abs, pdf] :

Title: Fossil Biodiversity: Red Noise Plus Signal
Authors: Adrian L. Melott, Bruce S. Lieberman (University of Kansas)
Comments: 3 page comment including one figure

We have examined the Fourier power spectrum as well as the Hurst exponent of extinction, origination, and total biodiversity in the marine fossil record, using a recently improved geologic timescale. We find all of them strongly inconsistent with past claims of self-similarity as well as inconsistent with random walk behavior. Instead, they are dominated by low-frequency power, with approximate f^-2 power over one decade in frequency. The spectrum turns over at about 10^5 y, lending plausibility to connections with galactic dynamics. Even in the background of this low-frequency dominance, a previously noted 62 My biodiversity cycle stands out with better than 99% confidence above the noise level, accounting for about 35% of the total variance in the fossil biodiversity record.

 

astro-ph/0606326 [abs, pdf] :

Title: A History and Informal Assessment of the Slacker Astronomy Podcast
Authors: A. Price, P. Gay, T. Searle, G. Brissenden
Comments: 14 pages
Journal-ref: The Astronomy Education Review, Issue 1, Volume 5, 2006

Slacker Astronomy is a weekly podcast that covers a recent astronomical news event or discovery. The show has a unique style consisting of irreverent, over-the-top humor combined with a healthy dose of hard science. According to our demographic analysis, the combination of this style and the unique podcasting distribution mechanism allows the show to reach audiences younger and busier than those reached via traditional channels. We report on the successes and challenges of the first year of the show, and provide an informal assessment of its role as a source for astronomical news and concepts for its approximately 15,500 weekly listeners.

 

astro-ph/0606327 [abs, ps, pdf, other] :

Title: Kinematics of the ultra-compact helium accretor AM Canum Venaticorum
Authors: G.H.A. Roelofs, P.J. Groot, G. Nelemans (Nijmegen), T.R. Marsh (Warwick), D. Steeghs (CfA)
Comments: 13 pages, 14 figures, to appear in MNRAS

We report on the results from a five-night campaign of high-speed spectroscopy of the 17-minute binary AM Canum Venaticorum, obtained with the 4.2-m William Herschel Telescope on La Palma.
We derive a mass ratio q=0.18+/-0.01 for AM CVn, which is significantly higher than the value found in previous, less direct measurements. We discuss the implications for AM CVn's evolutionary history and show that a helium star progenitor scenario is strongly favoured. We further discuss the implications for the interpretation of AM CVn's superhump behaviour, and for the detectability of its gravitational-wave signal with LISA.
We further test the predictions of an eccentric, precessing disc that are based on AM CVn's observed superhump behaviour. We limit the effective eccentricity in the outermost part of the disc, where the resonances that drive the eccentricity are thought to occur, to e=0.04+/-0.01, which is smaller than previous models indicated.