Astrophysics
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New submissions for Tue, 16 Sep 08
- [1] arXiv:0809.2283 [ps, pdf, other]
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Title: Environmental Effects on Satellite Galaxies: The Link Between Concentration, Size and Colour ProfileAuthors: Simone M. Weinmann, Guinevere Kauffmann, Frank C. van den Bosch, Anna Pasquali, Daniel H. McIntosh, Houjun Mo, Xiaohu Yang, Yicheng GuoComments: 16 pages, 13 figures, submitted to MNRASSubjects: Astrophysics (astro-ph)
Using the SDSS DR4 group catalogue of Yang et al. (2007), we investigate sizes, concentrations, colour gradients and surface brightness profiles of central and satellite galaxies. We compare central and satellite galaxies at fixed stellar mass, in order to disentangle environmental from stellar mass dependencies. Early and late type galaxies are defined according to concentration. We find that at fixed stellar mass, late type satellite galaxies have smaller radii and larger concentrations than late type central galaxies. No such differences are found for early-type galaxies. We have also constructed surface brightness and colour profiles for the central and satellite galaxies in our sample. We find that late-type satellite galaxies have a lower surface brightness and redder colours than late-type central galaxies. We show that all observed differences between satellite and central galaxies can be explained by a simple fading model, in which the star formation in the disk decreases over timescales of 2-3 Gyr after a galaxy becomes a satellite. Processes that induce strong morphological changes (e.g. harassment) and processes that strip the galaxy of its entire ISM need not to be invoked in order to explain the environmental dependencies we find.
- [2] arXiv:0809.2287 [ps, pdf, other]
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Title: Absolute properties of the spotted eclipsing binary star CV BootisAuthors: Guillermo Torres (CfA), Luiz Paulo R. Vaz (ICEx-UFMG, Brazil), Claud H. Sandberg Lacy (U. of Arkansas)Comments: 17 pages in emulateapj format, including figures and tables. To appear in The Astronomical JournalSubjects: Astrophysics (astro-ph)
We present new V-band differential brightness measurements as well as new radial-velocity measurements of the detached, circular, 0.84-day period, double-lined eclipsing binary system CV Boo. These data along with other observations from the literature are combined to derive improved absolute dimensions of the stars for the purpose of testing various aspects of theoretical modeling. Despite complications from intrinsic variability we detect in the system, and despite the rapid rotation of the components, we are able to determine the absolute masses and radii to better than 1.3% and 2%, respectively. We obtain M(A) = 1.032 +/- 0.013 M(Sun) and R(B) = 1.262 +/- 0.023 R(Sun) for the hotter, larger, and more massive primary (star A), and M(B) = 0.968 +/- 0.012 M(Sun) and R(B) = 1.173 +/- 0.023 R(Sun) for the secondary. The estimated effective temperatures are 5760 +/- 150 K and 5670 +/- 150 K. The intrinsic variability with a period about 1% shorter than the orbital period is interpreted as being due to modulation by spots on one or both components. This implies that the spotted star(s) must be rotating faster than the synchronous rate, which disagrees with predictions from current tidal evolution models according to which both stars should be synchronized. We also find that the radius of the secondary is larger than expected from stellar evolution calculations by about 10%, a discrepancy also seen in other (mostly lower-mass and active) eclipsing binaries. We estimate the age of the system to be approximately 9 Gyr. Both components are near the end of their main-sequence phase, and the primary may have started the shell hydrogen-burning stage.
- [3] arXiv:0809.2290 [ps, pdf, other]
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Title: Fossil Groups in the Millennium Simulation. Evolution of the Brightest GalaxiesAuthors: Eugenia Diaz-Gimenez (1), Hernan Muriel (1), Claudia Mendes de Oliveira (2) ((1) IATE (CONICET-UNC) & OAC (UNC), Cordoba, Argentina. (2) IAG, USP, Sao Paulo, Brazil)Comments: 9 pages, 3 figures, accepted for publication in Astronomy & AstrophysicsSubjects: Astrophysics (astro-ph)
We create a catalogue of simulated fossil groups and study their properties, in particular the merging histories of their first-ranked galaxies. We compare the simulated fossil group properties with those of both simulated non-fossil and observed fossil groups. Using simulations and a mock galaxy catalogue, we searched for massive ($>$ 5 $\times$ 10$^{13} h^{-1} {\cal M}_\odot$) fossil groups in the Millennium Simulation Galaxy Catalogue. In addition, attempted to identify observed fossil groups in the Sloan Digital Sky Survey Data Release 6 using identical selection criteria. Our predictions on the basis of the simulation data are:(a) fossil groups comprise about 5.5% of the total population of groups/clusters with masses larger than 5 x 10$^{13} h^{-1} {\cal M}_\odot$. This fraction is consistent with the fraction of fossil groups identified in the SDSS, after all observational biases have been taken into account; (b) about 88% of the dominant central objects in fossil groups are elliptical galaxies that have a median R-band absolute magnitude of $\sim -23.5-5 log h$, which is typical of the observed fossil groups known in the literature; (c)first-ranked galaxies of systems with $ {\cal M} >$ 5 x 10$^{13} h^{-1} {\cal M}_\odot$, regardless of whether they are either fossil or non-fossil, are mainly formed by gas-poor mergers; (d) although fossil groups, in general, assembled most of their virial masses at higher redshifts in comparison with non-fossil groups, first-ranked galaxies in fossil groups merged later, i.e. at lower redshifts, compared with their non-fossil-group counterparts. We therefore expect to observe a number of luminous galaxies in the centres of fossil groups that show signs of a recent major merger.
- [4] arXiv:0809.2295 [ps, pdf, other]
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Title: Evolution of stellar structure in the Small Magellanic CloudAuthors: M. Gieles (1), N. Bastian (2,3), B. Ercolano (2,4) ((1) ESO/Santiago, (2) IoA Cambridge, (3) UCL, (4) CfA)Comments: Accepted for MNRAS Letters. 5 pages, 4 figures and 1 tableSubjects: Astrophysics (astro-ph)
The projected distribution of stars in the Small Magellanic Cloud (SMC) from the Magellanic Clouds Photometric Survey is analysed. Stars of different ages are selected via criteria based on V magnitude and V-I colour, and the degree of `grouping' as a function of age is studied. We quantify the degree of structure using the two-point correlation function and a method based on the Minimum Spanning Tree and find that the overall structure of the SMC is evolving from a high degree of sub-structure at young ages (~10 Myr) to a smooth radial density profile. This transition is gradual and at ~75 Myr the distribution is statistically indistinguishable from the background SMC distribution. This time-scale corresponds to approximately the dynamical crossing time of stars in the SMC. The spatial positions of the star clusters in the SMC show a similar evolution of spatial distribution with age. Our analysis suggests that stars form with a high degree of (fractal) sub-structure, probably imprinted by the turbulent nature of the gas from which they form, which is erased by random motions in the galactic potential on a time-scale of a galactic crossing time.
- [5] arXiv:0809.2302 [ps, pdf, other]
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Title: A simple toy model of the advective-acoustic instability I. Perturbative approachAuthors: T. FoglizzoComments: 14 pages, 10 figures, submitted to ApJSubjects: Astrophysics (astro-ph)
Some general properties of the advective-acoustic instability are described and understood using a toy model which is simple enough to allow for analytical estimates of the eigenfrequencies. The essential ingredients of this model, in the unperturbed regime, are a stationary shock and a subsonic region of deceleration. For the sake of analytical simplicity, the 2D unperturbed flow is parallel and the deceleration is produced adiabatically by an external potential. The instability mechanism is determined unambiguously as the consequence of a cycle between advected and acoustic perturbations. The purely acoustic cycle, considered alone, is proven to be stable in this flow. Its contribution to the instability can be either constructive or destructive. A frequency cut-off is associated to the advection time through the region of deceleration. This cut-off frequency explains why the instability favours eigenmodes with a low frequency and a large horizontal wavelength. The relation between the instability occurring in this highly simplified toy model and the properties of SASI observed in the numerical simulations of stellar core-collapse is discussed. This simple set up is proposed as a benchmark test to evaluate the accuracy, in the linear regime, of numerical simulations involving this instability. We illustrate such benchmark simulations in a companion paper.
- [6] arXiv:0809.2303 [ps, pdf, other]
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Title: A simple toy model of the advective-acoustic instability. II. Numerical simulationsComments: 8 pages, 9 figures, submitted to ApJSubjects: Astrophysics (astro-ph)
The physical processes involved in the advective-acoustic instability are investigated with 2D numerical simulations. Simple toy models, developped in a companion paper, are used to describe the coupling between acoustic and entropy/vorticity waves, produced either by a stationary shock or by the deceleration of the flow. Using two Eulerian codes based on different second order upwind schemes, we confirm the results of the perturbative analysis. The numerical convergence with respect to the computation mesh size is studied with 1D simulations. We demonstrate that the numerical accuracy of the quantities which depend on the physics of the shock is limited to a linear convergence. We argue that this property is likely to be true for most current numerical schemes dealing with SASI in the core-collapse problem, and could be solved by the use of advanced techniques for the numerical treatment of the shock. We propose a strategy to choose the mesh size for an accurate treatment of the advective-acoustic coupling in future numerical simulations.
- [7] arXiv:0809.2305 [pdf, other]
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Title: Geodynamics and Rate of Volcanism on Massive Earth-like PlanetsSubjects: Astrophysics (astro-ph)
We provide estimates of volcanism versus time for planets with Earth-like composition and masses from 0.25 to 25 times Earth, as a step toward predicting atmospheric mass on extrasolar rocky planets. Volcanism requires melting of the silicate mantle. We use a thermal evolution model, calibrated against Earth, in combination with standard melting models, to explore the dependence of convection-driven decompression mantle melting on planet mass. Here we show that (1) volcanism is likely to proceed on massive planets with plate tectonics over the main-sequence lifetime of the parent star; (2) crustal thickness (and melting rate normalized to planet mass) is weakly dependent on planet mass; (3) stagnant lid planets can have higher rates of melting than their plate tectonic counterparts early in their thermal evolution, but melting shuts down after a few Gyr; (4) plate tectonics may not operate on high mass planets because of the production of buoyant crust which is difficult to subduct; and (5) melting is necessary but insufficient for efficient volcanic degassing - volatiles partition into the earliest, deepest melts, which may be denser than the residue and sink to the base of the mantle on young, massive planets. Magma must also crystallize at or near the surface, and the pressure of overlying volatiles must be fairly low, if volatiles are to reach the surface.
- [8] arXiv:0809.2309 [ps, pdf, other]
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Title: Mapping the QCD Phase Transition with Accreting Compact StarsComments: 8 pages, 3 figures, to appear in Proceedings of the Conference on "A Decade of Accreting Millisecond X-Ray Pulsars, Amsterdam, April 14-18, 2008Subjects: Astrophysics (astro-ph)
We discuss an idea for how accreting millisecond pulsars could contribute to the understanding of the QCD phase transition in the high-density nuclear matter equation of state (EoS). It is based on two ingredients, the first one being a ``phase diagram'' of rapidly rotating compact star configurations in the plane of spin frequency and mass, determined with state-of-the-art hybrid equations of state, allowing for a transition to color superconducting quark matter. The second is the study of spin-up and accretion evolution in this phase diagram. We show that the quark matter phase transition leads to a characteristic line in the Omega-M plane, the phase border between neutron stars and hybrid stars with a quark matter core. Along this line a change in the pulsar's moment of inertia entails a waiting point phenomenon in the accreting millisecond X-ray pulsar (AMXP) evolution: most of these objects should therefore be found along the phase border in the Omega-M plane, which may be viewed as the AMXP analog of the main sequence in the Hertzsprung-Russell diagram for normal stars. In order to prove the existence of a high-density phase transition in the cores of compact stars we need population statistics for AMXP's with sufficiently accurate determination of their masses and spin frequencies.
- [9] arXiv:0809.2330 [pdf, other]
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Title: Hydrodynamics of structure formation in the early UniverseComments: 6 pages 4 figures. Additional information at this http URLSubjects: Astrophysics (astro-ph)
Theory and observations reveal fatal flaws in the standard LambdaCDM model. The cold dark matter hierarchical clustering paradigm predicts a gradual bottom-up growth of gravitational structures assuming linear, collisionless, ideal flows and unrealistic CDM condensations and mergers. Collisional fluid mechanics with viscosity, turbulence, and diffusion predicts a turbulent big bang and top-down viscous-gravitational fragmentation from supercluster to galaxy scales in the plasma epoch, as observed from 0.3 Gpc void sizes, 1.5 Gpc spins and Kolmogorov-fingerprint-turbulence-signatures in the CMB. Turbulence produced at expanding gravitational void boundaries causes a linear morphology of 3 Kpc fragmenting plasma-protogalaxies along vortex lines, as observed in deep HST images. After decoupling, gas-protogalaxies fragment into primordial-density, million-solar-mass clumps of earth-mass planets forming 0.3 Mpc galactic-dark-matter. White-dwarf-heated planet-atmospheres give dimmed SNe Ia events and false gamma-ray-burst luminosity distances, not dark-energy-Lambda. Quasar microlensing observations rule out no-hair black hole models and require galaxy-dark-matter to be planets-in-clumps.
- [10] arXiv:0809.2334 [ps, pdf, other]
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Title: H.E.S.S. Observations of the Prompt and Afterglow Phases of GRB 060602BComments: 8 pages, 4 figures, 1 table; ApJ in pressSubjects: Astrophysics (astro-ph)
We report on the first completely simultaneous observation of a gamma-ray burst (GRB) using an array of Imaging Atmospheric Cherenkov Telescopes which is sensitive to photons in the very-high-energy (VHE) gamma-ray range (>~100 GeV). On 2006 June 2, the Swift Burst Alert Telescope (BAT) registered an unusually soft gamma-ray burst (GRB 060602B). The burst position was under observation using the High Energy Stereoscopic System (H.E.S.S.) at the time the burst occurred. Data were taken before, during, and after the burst. A total of 5 hours of observations were obtained during the night of 2006 June 2-3, and 5 additional hours were obtained over the next 3 nights. No VHE gamma-ray signal was found during the period covered by the H.E.S.S. observations. The 99% confidence level flux upper limit (>1 TeV) for the prompt phase (9s) of GRB 060602B is 2.9x10^-9 erg cm^-2 s^-1. Due to the very soft BAT spectrum of the burst compared to other Swift GRBs and its proximity to the Galactic center, the burst is likely associated with a Galactic X-ray burster, although the possibility of it being a cosmological GRB cannot be ruled out. We discuss the implications of our flux limits in the context of these two bursting scenarios.
- [11] arXiv:0809.2337 [ps, pdf, other]
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Title: Properties of the molecular gas in a starbursting QSO at z=1.83 in the COSMOS fieldAuthors: Manuel Aravena, Frank Bertoldi, Eva Schinnerer, Axel Weiss, Knud Jahnke, Chris L. Carilli, David T. Frayer, Christian Henkel, Marcella Brusa, Karl M. Menten, Mara Salvato, Vernesa SmolcicComments: Accepted for publication in Astronomy & Astrophysics (A&A)Subjects: Astrophysics (astro-ph)
Using the IRAM 30m telescope, we have detected the CO J=2-1, 4-3, 5-4, and 6-5 emission lines in the millimeter-bright, blank-field selected AGN COSMOS J100038+020822 at redshift z=1.8275. The sub-local thermodynamic equilibrium (LTE) excitation of the J=4 level implies that the gas is less excited than that in typical nearby starburst galaxies such as NGC253, and in the high-redshift quasars studied to date, such as J1148+5251 or BR1202-0725. Large velocity gradient (LVG) modeling of the CO line spectral energy distribution (CO SED; flux density vs. rotational quantum number) yields H2 densities in the range 10^{3.5}--10^{4.0} cm-3, and kinetic temperatures between 50 K and 200 K. The H2 mass of (3.6 - 5.4) x 10^{10} M_sun implied by the line intensities compares well with our estimate of the dynamical mass within the inner 1.5 kpc of the object. Fitting a two-component gray body spectrum, we find a dust mass of 1.2 x 10^{9} M_sun, and cold and hot dust temperatures of 42+/-5 K and 160+/-25 K, respectively. The broad MgII line allows us to estimate the mass of the central black hole as 1.7 x 10^{9} M_sun. Although the optical spectrum and multi-wavelength SED matches those of an average QSO, the molecular gas content and dust properties resemble those of known submillimeter galaxies (SMGs). The optical morphology of this source shows tidal tails that suggest a recent interaction or merger. Since it shares properties of both starburst and AGN, this object appears to be in a transition from a strongly starforming submillimeter galaxy to a QSO.
- [12] arXiv:0809.2355 [ps, pdf, other]
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Title: Young Stars in the Camelopardalis Dust and Molecular Clouds. IV. Spectral Observations of the Suspected YSOsComments: 17 pagesJournal-ref: Baltic Astronomy, vol. 17, 21-37, 2008Subjects: Astrophysics (astro-ph)
In the first three papers of this series, about 200 objects in Camelopardalis and the nearby areas of Cassiopeia, Perseus and Auriga were suspected of being pre-main-sequence stars in different stages of evolution. To confirm the evolutionary status of the 15 brightest objects, their far-red range (600--950 nm) spectra were obtained. Almost all these objects are young stars with emissions in H alpha, OI, CaII and P9 lines. The equivalent widths of emission lines and approximate spectral classes of the objects are determined.
- [13] arXiv:0809.2362 [ps, pdf, other]
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Title: APOGEE: The Apache Point Observatory Galactic Evolution ExperimentAuthors: C. Allende Prieto, S. R. Majewski, R. Schiavon, K. Cunha, P. Frinchaboy, J. Holtzman, K. Johnston, M. Shetrone, M. Skrutskie, V. Smith, J. WilsonComments: 4 pages, 2 figures; proceedings of the conference on Galactic & Stellar Dynamics in Strasbourg 16-20 March 2008Subjects: Astrophysics (astro-ph)
APOGEE is a large-scale, NIR, high-resolution (R~20,000) spectroscopic survey of Galactic stars. It is one of the four experiments in SDSS-III. Because APOGEE will observe in the H band, it will be the first survey to pierce through Galactic dust and provide a vast, uniform database of chemical abundances and radial velocities for stars across all Galactic populations (bulge, disk, and halo). The survey will be conducted with a dedicated, 300-fiber, cryogenic, spectrograph that is being built at the University of Virginia, coupled to the ARC 2.5m telescope at Apache Point Observatory. APOGEE will use a significant fraction of the SDSS-III bright time during a three-year period to observe, at high signal-to-noise ratio (S/N>100), about 100,000 giant stars selected directly from 2MASS down to a typical flux limit of H<13. The main scientific objectives of APOGEE are: (1) measuring unbiased metallicity distributions and abundance patterns for the different Galactic stellar populations, (2) studying the processes of star formation, feedback, and chemical mixing in the Milky Way, (3) surveying the dynamics of the bulge and disk, placing constraints on the nature and influence of the Galactic bar and spiral arms, and (4) using extensive chemodynamical data, particularly in the inner Galaxy, to unravel its formation and evolution.
- [14] arXiv:0809.2364 [ps, pdf, other]
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Title: Chemical Abundances from the ContinuumAuthors: C. Allende Prieto (MSSL, University College London)Comments: 10 pages, 5 figures, to appear in the proceedings of the conference A Stellar Journey, a symposium in celebration of Bengt Gustafsson's 65th birthday, June 23-27, 2008, UppsalaSubjects: Astrophysics (astro-ph)
The calculation of solar absolute fluxes in the near-UV is revisited, discussing in some detail recent updates in theoretical calculations of bound-free opacity from metals. Modest changes in the abundances of elements such as Mg and the iron-peak elements have a significant impact on the atmospheric structure, and therefore self-consistent calculations are necessary. With small adjustments to the solar photospheric composition, we are able to reproduce fairly well the observed solar fluxes between 200 and 270 nm, and between 300 and 420 nm, but find too much absorption in the 270-290 nm window. A comparison between our reference 1D model and a 3D time-dependent hydrodynamical simulation indicates that the continuum flux is only weakly sensitive to 3D effects, with corrections reaching <10% in the near-UV, and <2% in the optical.
- [15] arXiv:0809.2370 [ps, pdf, other]
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Title: Discovery in IC10 of the farthest known symbiotic starAuthors: Denise R. Goncalves (1), Laura Magrini (2), Ulisse Munari (3), Romano L. M. Corradi (4 and 5), Roberto D. D. Costa (6) ((1) UFRJ - Observatorio do Valongo, Brazil; (2) INAF - Osservatorio Astrofisico di Arcetri, Italy; (3) INAF - Osservatorio Astronomico di Padova, Italy; (4) Isaac Newton Group of Telescopes, Spain; (5) Instituto de Astrofisica de Canarias, Spain; (6) IAG - Universidade de Sao Paulo, Brazil)Comments: 5 pages including 3 figures. MNRAS Letters accepted. Also available at this http URLSubjects: Astrophysics (astro-ph)
We report the discovery of the first known symbiotic star in IC10, a starburst galaxy belonging to the Local Group, at a distance of ~750kpc. The symbiotic star was identified during a survey of emission-line objects. It shines at V = 24.62+-0.04, V - R_C = 2.77+-0.05 and R_C - I_C = 2.39+-0.02 and suffers from E(B-V) = 0.85+-0.05 reddening. The spectrum of the cool component well matches that of solar neighborhood M8III giants. The observed emission lines belong to Balmer series, [SII], [NII] and [OIII]. They suggest a low electronic density, negligible optical depth effects and 35,000K < T_eff < 90,000K for the ionizing source. The spectrum of the new symbiotic star in IC10 is an almost perfect copy of that of Hen 2-147, a well known Galactic symbiotic star and Mira.
- [16] arXiv:0809.2389 [ps, pdf, other]
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Title: PAH emission from Herbig AeBe starsAuthors: Luke D. Keller, G.C. Sloan, W.J. Forrest, S. Ayala, P. D'Alessio, S. Shah, N. Calvet, J. Najita, A. Li, L. Hartmann, B. Sargent, D. M. Watson, C. H. ChenComments: 52 pages, 12 figuresJournal-ref: Astrophysical Journal, 2008, 684, 411-429Subjects: Astrophysics (astro-ph)
We present spectra of a sample of Herbig Ae and Be (HAeBe) stars obtained with the Infrared Spectrograph on the Spitzer Space Telescope. All but one of the Herbig stars show emission from polycyclic aromatic hydrocarbons (PAHs) and seven of the spectra show PAH emission, but no silicate emission at 10 microns. The central wavelengths of the 6.2, 7.7--8.2, and 11.3 micron emission features decrease with stellar temperature, indicating that the PAHs are less photo-processed in cooler radiation fields. The apparent low level of photo processing in HAeBe stars, relative to other PAH emission sources, implies that the PAHs are newly exposed to the UV-optical radiation fields from their host stars. HAeBe stars show a variety of PAH emission intensities and ionization fractions, but a narrow range of PAH spectral classifications based on positions of major PAH feature centers. This may indicate that, regardless of their locations relative to the stars, the PAH molecules are altered by the same physical processes in the proto-planetary disks of intermediate-mass stars. Analysis of the mid-IR spectral energy distributions indicates that our sample likely includes both radially flared and more flattened/settled disk systems, but we do not see the expected correlation of overall PAH emission with disk geometry. We suggest that the strength of PAH emission from HAeBe stars may depend not only on the degree of radial flaring, but also on the abundance of PAHs in illuminated regions of the disks and possibly on the vertical structure of the inner disk as well.
- [17] arXiv:0809.2390 [pdf]
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Title: A search for super-large structures in deep galaxy surveysComments: 9 pages, Proceedings of the International conference "Problems of Practical Cosmology", 23-27 June 2008, St.-Petersburg, Russia, see this http URLJournal-ref: in "Practical Cosmology", v.1, pp.69-77, 2008Subjects: Astrophysics (astro-ph)
Recent extensive, multi-color deep surveys of galaxies open a possibility to get observational estimation of sizes for the largest structures in the Universe. Photometric redshift accuracy (about 0.03(1+z)) allows directly study clustering at scales about 1000 Mpc. Thanks to large number of galaxies in each redshift bin one may detect super-large structures if they really exist. Here we show that the observed behavior of the redshift distribution of galaxies in deep surveys such as HUDF and FDF is consistent with existence of super-large structures of luminous matter with scales about 2000 Mpc. We detect a large underdense region in radial galaxy distribution at redshift interval z=1.2 - 2.2 which separate our "Local Hubble Volume" from the neighboring over-density region at z=2.2 - 3.5. This result can also explain the observed deficiency of gamma ray sources at redshift about 2. Observational test on the reality of the supper-large structures may be obtained by organizing sky covering net (cells about 10n x 10n degrees) of very deep narrow angle (1n x 1n arc-minutes) multi-band photometric surveys of galaxies which is achievable for large ground-based telescopes.
- [18] arXiv:0809.2400 [ps, pdf, other]
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Title: Modeling pulse profiles of accreting millisecond pulsarsAuthors: Juri Poutanen (University of Oulu)Comments: Invited review, to appear in the proceedings of the workshop 'A Decade of Accreting Millisecond X-ray Pulsars' (Amsterdam, April 2008)Subjects: Astrophysics (astro-ph)
I review the basic observational properties of accreting millisecond pulsars that are important for understanding the physics involved in formation of their pulse profiles. I then discuss main effects responsible for shaping these profiles. Some analytical results that help to understand the results of simulations are presented. Constraints on the pulsar geometry and the neutron star equation of state obtained from the analysis of the pulse profiles are discussed.
- [19] arXiv:0809.2403 [ps, pdf, other]
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Title: A cosmic abundance standard: chemical homogeneity of the solar neighbourhood & the ISM dust-phase compositionAuthors: Norbert Przybilla (1), M. Fernanda Nieva (1,2), Keith Butler (3) ((1) Dr. Remeis-Observatory Bamberg, (2) MPI for Astrophysics Garching, (3) University Observatory Munich)Comments: 4 pages, 2 figures. Resubmitted to ApJ Letters after referee's commentsSubjects: Astrophysics (astro-ph)
A representative sample of unevolved early B-type stars in nearby OB associations and the field is analysed to high precision using NLTE techniques. The resulting chemical composition is found to be more metal-rich and much more homogeneous than indicated by previous work. A rms scatter of ~10% in abundances is found for the sample, the same as reported for ISM gas-phase abundances. A cosmic abundance standard for the present-day solar neighbourhood is proposed, implying mass fractions for hydrogen, helium and metals of X=0.715, Y=0.271 and Z=0.014. Good agreement with solar photospheric abundances as reported from recent 3D radiative-hydrodynamical simulations of the solar atmosphere is obtained. As a first application we use the cosmic abundance standard as a proxy for the determination of the local ISM dust-phase composition, putting tight observational constraints on dust models.
- [20] arXiv:0809.2404 [pdf, other]
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Title: Accretion onto Seed Black Holes in the First GalaxiesComments: 9 pages, 1 figureSubjects: Astrophysics (astro-ph)
The validity of the hypothesis that the massive black holes in high redshift quasars grew from stellar-sized "seeds" is contingent on a seed's ability to double its mass every few ten million years. This requires that the seed accrete at approximately the Eddington-limited rate. In the specific case of radiatively efficient quasiradial accretion in a metal-poor protogalactic medium, for which the Bondi accretion rate is often prescribed in cosmological simulations of massive black hole formation, we examine the effects of the radiation emitted near the black hole's event horizon on the structure of the surrounding gas flow. We find that the radiation pressure from photoionization significantly reduces the steady-state accretion rate and renders the quasiradial accretion flow unsteady and inefficient. The time-averaged accretion rates are a small fraction of the Eddington-limited accretion rate for Thomson scattering. The pressure of Ly-alpha photons trapped near the HII region surrounding the black hole may further attenuate the inflow. These results suggest that an alternative to quasiradial, radiatively efficient Bondi-like accretion should be sought to explain the rapid growth of quasar-progenitor seed black holes.
- [21] arXiv:0809.2405 [ps, pdf, other]
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Title: Stellar Velocity Distribution in Galactic DisksComments: 8 pages, 3 figures, to appear in the Proceedings of "Chaos in Astronomy", Athens, G. Contopoulos & P.A. Patsis (eds.)Subjects: Astrophysics (astro-ph)
We present numerical studies of the properties of the stellar velocity distribution in galactic disks which have developed a saturated, two-armed spiral structure. In previous papers we used the Boltzmann moment equations (BME) up to second order for our studies of the velocity structure in self-gravitating stellar disks. A key assumption of our BME approach is the zero-heat flux approximation, i.e. the neglection of third order velocity terms. We tested this assumption by performing test particle simulations for stars in a disk galaxy subject to a rotating spiral perturbation. As a result we corroborated qualitatively the complex velocity structure found in the BME approach. It turned out that an equilibrium configuration in velocity space is only slowly established on a typical timescale of 5 Gyrs or more. Since many dynamical processes in galaxies (like the growth of spirals or bars)act on shorter timescales, pure equilibrium models might not be fully appropriate for a detailed comparison with observations like the local Galactic velocity distribution. Third order velocity moments were typically small and uncorrelated over almost all of the disk with the exception of the 4:1 resonance region (UHR). Near the UHR (normalized) fourth and fifth order velocity moments are still of the same order as the second and third order terms. Thus, at the UHR higher order terms are not negligible.
- [22] arXiv:0809.2411 [ps, pdf, other]
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Title: Structures of the magnetoionic media around the FR I radio galaxies 3C 31 and Hydra AAuthors: R. A. Laing (1), A. H. Bridle (2), P. Parma (3), M. Murgia (3 and 4) ((1) ESO, (2) Nrao, (3) Inaf-Ira, (4) Inaf-Cagliari)Comments: 33 pages, 25 figures, accepted for publication in MNRASSubjects: Astrophysics (astro-ph)
We use high-quality VLA images of the Fanaroff & Riley Class I radio galaxy 3C 31 at six frequencies in the range 1365 to 8440MHz to explore the spatial scale and origin of the rotation measure (RM) fluctuations on the line of sight to the radio source. We analyse the distribution of the degree of polarization to show that the large depolarization asymmetry between the North and South sides of the source seen in earlier work largely disappears as the resolution is increased. We show that the depolarization seen at low resolution results primarily from unresolved gradients in a Faraday screen in front of the synchrotron-emitting plasma. We establish that the residual degree of polarization in the short-wavelength limit should follow a Burn law and we fit such a law to our data to estimate the residual depolarization at high resolution. We show that the observed RM variations over selected areas of 3C 31 are consistent with a power spectrum of magnetic fluctuations in front of 3C 31 whose power-law slope changes significantly on the scales sampled by our data. The power spectrum can only have the form expected for Kolmogorov turbulence on scales <5 kpc. On larger scales we find a flatter slope. We also compare the global variations of RM across 3C 31 with the results of three-dimensional simulations of the magnetic-field fluctuations in the surrounding magnetoionic medium. We show that our data are consistent with a field distribution that favours the plane perpendicular to the jet axis - probably because the radio source has evacuated a large cavity in the surrounding medium. We also apply our analysis techniques to the case of Hydra A, where the shape and the size of the cavities produced by the source in the surrounding medium are known from X-ray data. (Abridged)
- [23] arXiv:0809.2416 [ps, pdf, other]
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Title: When efficient star formation drives cluster formationAuthors: G. Parmentier (1,2), U. Fritze (3) ((1) AIfA, Bonn, Germany; (2) IAGL, Liege, Belgium; (3) CAR, Hertfordshire, UK)Comments: 8 pages, accepted in ApJSubjects: Astrophysics (astro-ph)
We investigate the impact of the star formation efficiency in cluster forming cores on the evolution of the mass in star clusters over the age range 1-100Myr, when star clusters undergo their infant weight-loss/mortality phase. Assuming a constant formation rate of gas-embedded clusters and a weak tidal field, we show that the ratio between the total mass in stars bound to the clusters over that age range and the total mass in stars initially formed in gas-embedded clusters is a strongly increasing function of the averaged local SFE, with little influence from any assumed core mass-radius relation. Our results suggest that, for young starbursts with estimated tidal field strength and known recent star formation history, observed cluster-to-star mass ratios, once corrected for the undetected clusters, constitute promising probes of the local SFE, without the need of resorting to gas mass estimates. Similarly, the mass ratio of stars which remain in bound clusters at the end of the infant mortality/weight-loss phase depends sensitively on the mean local SFE, although the impacts of the width of the SFE distribution function and of the core mass-radius relation require more careful assessment in this case. Following the recent finding by Bastian (2008) that galaxies form, on the average, 8% of their stars in bound clusters regardless of their star formation rate, we raise the hypothesis that star formation in the present-day Universe is characterized by a near-universal distribution for the local SFE. A related potential application of our model consists in tracing the evolution of the local SFE over cosmological lookback times by comparing the age distribution of the total mass in star clusters to that in field stars. We describe model aspects which are still to be worked out before achieving this goal.
- [24] arXiv:0809.2417 [ps, pdf, other]
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Title: Effects of dark matter annihilation on the first starsComments: Proceedings of the IAU Symposium 255, "Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies"; L.K. Hunt, S. Madden and R. Schneider edsSubjects: Astrophysics (astro-ph)
We study the evolution of the first stars in the universe (Population III) from the early pre-Main Sequence until the end of helium burning in the presence of WIMP dark matter annihilation inside the stellar structure. The two different mechanisms that can provide this energy source are the contemporary contraction of baryons and dark matter, and the capture of WIMPs by scattering off the gas with subsequent accumulation inside the star. We find that the first mechanism can generate an equilibrium phase, previously known as a "dark star", which is transient and present in the very early stages of pre-MS evolution. The mechanism of scattering and capture acts later, and can support the star virtually forever, depending on environmental characteristic of the dark matter halo and on the specific WIMP model.
- [25] arXiv:0809.2418 [ps, pdf, other]
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Title: Enlightening the structure and dynamics of Abell 1942Authors: H.V. Capelato (1), D. Proust (2), G.B. LIma Neto (3), W.A. Santos (3), L. Sodre Jr. (3) ((1) INPE/MCT, (2) Observatoire de Paris-Meudon, (3) IAG/USP)Comments: Accepted for publication in Astronomy & Astrophysics, 15 pages, 15 figures, table w/ positions, photometric data and redshiftsSubjects: Astrophysics (astro-ph)
We present a dynamical analysis of the galaxy cluster Abell 1942 based on a set of 128 velocities obtained at the European Southern Observatory. Data on individual galaxies are presented and the accuracy of the determined velocities is discussed as well as some properties of the cluster. We have also made use of publicly available Chandra X-ray data. We obtained an improved mean redshift value z = 0.22513 \pm 0.0008 and velocity dispersion sigma = 908^{+147}_{-139} km/s. Our analysis indicates that inside a radius of ~1.5 h_{70}^{-1} Mpc (~7 arcmin) the cluster is well relaxed, without any remarkable feature and the X-ray emission traces fairly well the galaxy distribution. Two possible optical substructures are seen at ~5 arcmin from the centre towards the Northwest and the Southwest direction, but are not confirmed by the velocity field. These clumps are however, kinematically bound to the main structure of Abell 1942. X-ray spectroscopic analysis of Chandra data resulted in a temperature kT = 5.5 \pm 0.5 keV and metal abundance Z = 0.33 \pm 0.15 Z_odot. The velocity dispersion corresponding to this temperature using the T_X-sigma scaling relation is in good agreement with the measured galaxies velocities. Our photometric redshift analysis suggests that the weak lensing signal observed at the south of the cluster and previously attributed to a "dark clump", is produced by background sources, possibly distributed as a filamentary structure.
- [26] arXiv:0809.2423 [ps, pdf, other]
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Title: The fully connected N-dimensional skeleton: probing the evolution of the cosmic webComments: Submitted to MNRASSubjects: Astrophysics (astro-ph)
A method to compute the full hierarchy of the critical subsets of a density field is presented. It is based on a watershed technique and uses a probability propagation scheme to improve the quality of the segmentation by circumventing the discreteness of the sampling. It can be applied within spaces of arbitrary dimensions and geometry. This recursive segmentation of space yields, for a $d$-dimensional space, a $d-1$ succession of $n$-dimensional subspaces that fully characterize the topology of the density field. The final 1D manifold of the hierarchy is the fully connected network of the primary critical lines of the field : the skeleton. It corresponds to the subset of lines linking maxima to saddle points, and provides a definition of the filaments that compose the cosmic web as a precise physical object, which makes it possible to compute any of its properties such as its length, curvature, connectivity etc... When the skeleton extraction is applied to initial conditions of cosmological N-body simulations and their present day non linear counterparts, it is shown that the time evolution of the cosmic web, as traced by the skeleton, is well accounted for by the Zel'dovich approximation. Comparing this skeleton to the initial skeleton undergoing the Zel'dovich mapping shows that two effects are competing during the formation of the cosmic web: a general dilation of the larger filaments that is captured by a simple deformation of the skeleton of the initial conditions on the one hand, and the shrinking, fusion and disappearance of the more numerous smaller filaments on the other hand. Other applications of the N dimensional skeleton and its peak patch hierarchy are discussed.
- [27] arXiv:0809.2428 [ps, pdf, other]
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Title: Detection and extraction of signals from the epoch of reionization using higher order one-point statisticsAuthors: Geraint J. A. Harker (1), Saleem Zaroubi (1), Rajat M. Thomas (1), Vibor Jelic (1), Panagiotis Labropoulos (1), Garrelt Mellema (2), Ilian T. Iliev (3), Gianni Bernardi (1), Michiel A. Brentjens (4), A. G. de Bruyn (1 and 4), Benedetta Ciardi (5), Leon V. E. Koopmans (1), V. N. Pandey (1), Andreas H. Pawlik (6), Joop Schaye (6), Sarod Yatawatta (1) ((1) Kapteyn Institute, (2) Stockholm Observatory, (3) Institute for Theoretical Physics, Zurich, (4) ASTRON, (5) MPA, Garching, (6) Leiden Observatory)Comments: 10 pages, 9 figures; submitted to MNRASSubjects: Astrophysics (astro-ph)
Detecting redshifted 21cm emission from neutral hydrogen in the early Universe promises to give direct constraints on the epoch of reionization (EoR). It will, though, be very challenging to extract the cosmological signal from foregrounds and noise which are orders of magnitude larger. Fortunately, the signal has some characteristics which differentiate it from the foregrounds and noise, and we suggest that using the correct statistics may tease out signatures of reionization. We generate mock datacubes simulating the output of the LOFAR EoR experiment. These cubes combine realistic models for Galactic and extragalactic foregrounds and the noise with three different simulations of the cosmological signal. We fit out the foregrounds, which are smooth in the frequency direction, to produce residual images in each frequency band. We denoise these images and study the skewness of the one-point distribution in the images as a function of frequency. We find that, under sufficiently optimistic assumptions, we can recover the main features of the redshift evolution of the skewness in the 21cm signal. We argue that some of these features - such as a dip at the onset of reionization, followed by a rise towards its later stages - may be generic, and give us a promising route to a statistical detection of reionization.
- [28] arXiv:0809.2432 [ps, pdf, other]
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Title: Inverse Compton gamma-ray models for remnants of Galactic type Ia supernovae?Authors: H.J. Voelk (1), L.T. Ksenofontov (2), E.G. Berezhko (2) ((1) Max-Planck Institut fuer Kernphysik, Heidelberg, Germany, (2) Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia)Comments: 6 pages, 1 figure, accepted for publication in Astronomy and AstrophysicsSubjects: Astrophysics (astro-ph)
We theoretically and phenomenologically investigate the question whether the gamma-ray emission from the remnants of the type Ia supernovae SN 1006, Tycho's SN and Kepler's SN can be the result of electron acceleration alone. The observed synchrotron spectra of the three remnants are used to determine the average momentum distribution of nonthermal electrons as a function of the assumed magnetic field strength. Then the inverse Compton emission spectrum in the Cosmic Microwave Background photon field is calculated and compared with the existing upper limits for the very high energy gamma-ray flux from these sources. It is shown that the expected interstellar magnetic fields substantially overpredict even these gamma-ray upper limits. Only rather strongly amplified magnetic fields could be compatible with such low gamma-ray fluxes. However this would require a strong component of accelerated nuclear particles whose energy density substantially exceeds that of the synchrotron electrons, compatible with existing theoretical acceleration models for nuclear particles and electrons. Even though the quantitative arguments are simplistic, they appear to eliminate simplistic phenomenological claims in favor of a inverse Compton gamma-ray scenario for these sources.
- [29] arXiv:0809.2438 [ps, pdf, other]
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Title: Profile and polarization characteristics of energetic pulsarsComments: 26 pages, 11 figures, accepted for publication in MNRAS. Astro-ph version is missing 528 figures due to file size restrictions. Please download complete paper from this http URLSubjects: Astrophysics (astro-ph)
In this paper we compare the characteristics of pulsars with a high spin-down energy loss rate (Edot) against those with a low Edot. We show that the differences in the total intensity pulse morphology between the two classes are in general rather subtle. A much more significant difference is the fractional polarization which is very high for high Edot pulsars and low for low Edot pulsars. The Edot at the transition is very similar to the death line predicted for curvature radiation. This suggests a possible link between high energy and radio emission in pulsars and could imply that gamma-ray efficiency is correlated with the degree of linear polarization in the radio band. The degree of circular polarization is in general higher in the second component of doubles, which is possibly caused by the effect of co-rotation on the curvature of the field lines in the inertial observer frame.
The most direct link between the high energy emission and the radio emission could be the sub-group of pulsars which we call the energetic wide beam pulsars. These young pulsars have very wide profiles with steep edges and are likely to be emitted from a single magnetic pole. The similarities with the high energy profiles suggest that both types of emission are produced at the same extended height range in the magnetosphere. Alternatively, the beams of the energetic wide beam pulsars could be magnified by propagation effects in the magnetosphere. This would naturally lead to decoupling of the wave modes, which could explain the high degree of linear polarization. As part of this study, we have discovered three previous unknown interpulse pulsars (and we detected one for the first time at 20 cm). We also obtained rotation measures for 18 pulsars whose values had not previously been measured. - [30] arXiv:0809.2442 [pdf]
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Title: Event-horizon-scale structure in the supermassive black hole candidate at the Galactic CentreAuthors: Sheperd Doeleman (1), Jonathan Weintroub (2), Alan E.E. Rogers (1), Richard Plambeck (3), Robert Freund (4), Remo P.J. Tilanus (5 and 6), Per Friberg (5), Lucy M. Ziurys (4), James M. Moran (2), Brian Corey (1), Ken H. Young (2), Daniel L. Smythe (1), Michael Titus (1), Daniel P. Marrone (7 and 8), Roger J. Cappallo (1), Douglas C.J. Bock (9), Geoffrey C. Bower (3), Richard Chamberlin (10), Gary R. Davis (5), Thomas P. Krichbaum (11), James Lamb (12), Holly Maness (3), Arthur E. Niell (1), Alan Roy (11), Peter Strittmatter (4), Daniel Werthimer (13), Alan R. Whitney (1), David Woody (12) ((1) MIT Haystack Observatory, (2) Harvard-Smithsonian Center for Astrophysics, (3) UC Berkeley, (4) University of Arizona - Arizona Radio Observatory, (5) James Clerk Maxwell Telescope, (6) Netherlands Organization for Scientific Research, (7) National Radio Astronomy Observatory, (8) Kavli Institute for Cosmological Physics, (9) Combined Array for Research in Millimeter-wave Astronomy, (10) Caltech Submillimeter Observatory, (11) Max-Planck-Institut fur Radioastronomie, (12) Owens Valley Radio Observatory, (13) UC Berkeley Space Sciences Laboratory)Comments: 12 pages including 2 figuresJournal-ref: Nature, vol 455, p 78, 2008Subjects: Astrophysics (astro-ph)
The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation (ref 1). Sagittarius A*, the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4 million times that of the Sun (refs. 2,3). A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A* where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering (refs. 4-7). Here we report observations at a wavelength of 1.3 mm that set a size of 37 (+16, -10; 3-sigma) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of SgrA* emission may not be not centred on the black hole, but arises in the surrounding accretion flow.
- [31] arXiv:0809.2448 [ps, pdf, other]
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Title: Hard X-Ray Spectrum from West Lobe of Radio Galaxy Fornax A Observed with SuzakuComments: 8 pages, 6 figures; accepted for publication in PASJ (Publications of the Astronomical Society of Japan) Suzaku 3rd special issueSubjects: Astrophysics (astro-ph)
An observation of the West lobe of radio galaxy Fornax A (NGC 1316) with Suzaku is reported. Since Feigelson et al. (1995) and Kaneda et al. (1995) discovered the cosmic microwave background boosted inverse-Comptonized (IC) X-rays from the radio lobe, the magnetic field and electron energy density in the lobes have been estimated under the assumption that a single component of the relativistic electrons generates both the IC X-rays and the synchrotron radio emission. However, electrons generating the observed IC X-rays in the 1 -- 10 keV band do not possess sufficient energy to radiate the observed synchrotron radio emission under the estimated magnetic field of a few micro-G. On the basis of observations made with Suzaku, we show in the present paper that a 0.7 -- 20 keV spectrum is well described by a single power-law model with an energy index of 0.68 and a flux density of 0.12+/-0.01 nJy at 1 keV from the West lobe. The derived multiwavelength spectrum strongly suggests that a single electron energy distribution over a Lorentz factor gamma = 300 - 90000 is responsible for generating both the X-ray and radio emissions. The derived physical quantities are not only consistent with those reported for the West lobe, but are also in very good agreement with those reported for the East lobe.
- [32] arXiv:0809.2463 [ps, pdf, other]
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Title: High-frequency VLBI observations of SgrA* during a multi-frequency campaign in May 2007Authors: R.-S. Lu, T. P. Krichbaum, A. Eckart, S. König, D. Kunneriath, G. Witzel, A. Witzel, J. A. ZensusComments: 6 pages, 5 figures;necessary style files included; contribution for the conference "The Universe under the Microscope" (AHAR 2008), held in Bad Honnef (Germany) in April 2008, to be published in Journal of Physics: Conference Series by Institute of Physics Publishing, R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.)Subjects: Astrophysics (astro-ph)
In May 2007 the compact radio source Sgr A* was observed in a global multi-frequency monitoring campaign, from radio to X-ray bands. Here we present and discuss first and preliminary results from polarization sensitive VLBA observations, which took place during May 14-25, 2007. Here, Sgr A* was observed in dual polarization on 10 consecutive days at 22, 43, and 86 GHz. We describe the VLBI experiments, our data analysis, monitoring program and show preliminary images obtained at the various frequencies. We discuss the data with special regard also to the short term variability.
- [33] arXiv:0809.2464 [ps, pdf, other]
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Title: The Correlation between X-ray and UV Properties of BAL QSOsComments: 29 pages,6 figures,4 tables, accepted for publication in ApJSubjects: Astrophysics (astro-ph)
We compile a large sample of broad absorption lines (BAL) quasars with X-ray observations from the \xmm archive data and Sloan Digital Sky Survey Data Release 5. The sample consists of 41 BAL QSOs. Among 26 BAL quasars detected in X-ray, spectral analysis is possible for twelve objects. X-ray absorption is detected in all of them. Complementary to that of \citet{gall06} (thereafter G06), our sample spans wide ranges of both BALnicity Index (BI) and maximum outflow velocity (\vmax). Combining our sample with G06's, we find very significant correlations between the intrinsic X-ray weakness with both BALnicity Index (BI) and the maximum velocity of absorption trough. We do not confirm the previous claimed correlation between absorption column density and broad absorption line parameters. We tentatively interpret this as that X-ray absorption is necessary to the production of the BAL outflow, but the properties of the outflow are largely determined by intrinsic SED of the quasars.
- [34] arXiv:0809.2465 [pdf, other]
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Title: The Hubble Legacy Archive NICMOS Grism DataAuthors: Wolfram Freudling, Martin Kümmel, Jonas Haase, Richard Hook, Harald Kuntschner, Marco Lombardi, Alberto Micol, Felix Stoehr, Jeremy WalshComments: 18 pages, 21 figures, accepted for publication in Astronomy & AstrophysicsSubjects: Astrophysics (astro-ph)
The Hubble Legacy Archive (HLA) aims to create calibrated science data from the Hubble Space Telescope archive and make them accessible via user-friendly and Virtual Observatory (VO) compatible interfaces. It is a collaboration between the Space Telescope Science Institute (STScI), the Canadian Astronomy Data Centre (CADC) and the Space Telescope - European Coordinating Facility (ST-ECF). Data produced by the Hubble Space Telescope (HST) instruments with slitless spectroscopy modes are among the most difficult to extract and exploit. As part of the HLA project, the ST-ECF aims to provide calibrated spectra for objects observed with these HST slitless modes. In this paper, we present the HLA NICMOS G141 grism spectra. We describe in detail the calibration, data reduction and spectrum extraction methods used to produce the extracted spectra. The quality of the extracted spectra and associated direct images is demonstrated through comparison with near-IR imaging catalogues and existing near-IR spectroscopy. The output data products and their associated metadata are publicly available through a web form at this http URL and via VO interfaces. In total, 2470 spectra of 1923 unique targets are included in the current release.
- [35] arXiv:0809.2467 [ps, pdf, other]
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Title: Intrinsic absorption in 3C 279 at GeV-TeV energies and consequences for estimates of the EBLComments: 5 pages, 4 figures, submitted to MNRASSubjects: Astrophysics (astro-ph)
We revisit the limits of the level of the extragalactic background light (EBL) recently reported by the MAGIC collaboration based on the observed gamma-ray spectrum of the quasar 3C279, considering the impact of absorption of high-energy gamma-ray photons inside the broad line region (BLR) of the quasar. We use the photoionization code CLOUDY to calculate the expected optical-UV radiation field inside the BLR and the optical depth to gamma-rays for a relatively extended set of the parameters. We found that the absorption of gamma-ray photons, though important for the estimate of the true radiative output of the source, does not produce an important hardening of the spectrum of 3C279 in the energy band accessible by MAGIC, supporting the method used to infer the upper limits to the level of the EBL.
- [36] arXiv:0809.2470 [ps, pdf, other]
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Title: On the spin distributions of $\Lambda$CDM haloesAuthors: N. HiotelisComments: 10 pages, 8 figuresJournal-ref: Astrophys Space Sci (2008) 315:191-200Subjects: Astrophysics (astro-ph)
We used merger trees realizations, predicted by the extended Press-Schechter theory, in order to study the growth of angular momentum of dark matter haloes. Our results showed that: 1) The spin parameter $\lambda'$ resulting from the above method, is an increasing function of the present day mass of the halo. The mean value of $\lambda'$ varies from 0.0343 to 0.0484 for haloes with present day masses in the range of $ 10^9\mathrm{h}^{-1}M_{\odot}$ to $10^{14}\mathrm{h}^{-1}M_{\odot}$. 2)The distribution of $\lambda'$ is close to a log-normal, but, as it is already found in the results of N-body simulations, the match is not satisfactory at the tails of the distribution. A new analytical formula that approximates the results much more satisfactorily is presented. 3) The distribution of the values of $\lambda'$ depends only weakly on the redshift. 4) The spin parameter of an halo depends on the number of recent major mergers. Specifically the spin parameter is an increasing function of this number.
- [37] arXiv:0809.2478 [ps, pdf, other]
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Title: Dynamical Simulations of NGC 2523 and NGC 4245Comments: 29 pages, 3 tables, 13 figures. Accepted for publication in The Astronomical JournalSubjects: Astrophysics (astro-ph)
We present dynamical simulations of NGC 2523 and NGC 4245, two barred galaxies (types SB(r)b and SB(r)0/a, respectively) with prominent inner rings. Our goal is to estimate the bar pattern speeds in these galaxies by matching a sticky-particle simulation to the $B$-band morphology, using near-infrared $K_s$-band images to define the gravitational potentials. We compare the pattern speeds derived by this method with those derived in our previous paper using the well-known Tremaine-Weinberg continuity equation method. The inner rings in these galaxies, which are likely to be resonance features, help to constrain the dynamical models. We find that both methods give the same pattern speeds within the errors.
- [38] arXiv:0809.2481 [ps, pdf, other]
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Title: Pulsating B and Be stars in the Magellanic CloudsComments: Contribution to the Proceedings of the Wroclaw HELAS Workshop, 2008Subjects: Astrophysics (astro-ph)
Stellar pulsations in main-sequence B-type stars are driven by the $\kappa$-mechanism due to the Fe-group opacity bump. The current models do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the Magellanic Clouds has been measured to be around $Z=0.002$ for the SMC and $Z=0.007$ for the LMC, they constitute a very suitable objects to test these predictions.
- [39] arXiv:0809.2484 [ps, pdf, other]
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Title: Two distinct phases of hard x-ray emissions in a solar eruptive flareAuthors: Bhuwan Joshi, Astrid Veronig, K. -S. Cho, S. -C. Bong, Y. -J. Moon, Jeongwoo Lee, B. V. Somov, P. K. Manoharan, Y. -H. KimComments: Submitted to ApJ (under review)Subjects: Astrophysics (astro-ph)
We present a detailed analysis of the evolution of an M7.6 flare that occurred near the south-east limb on October 24, 2003 utilizing a multi-wavelength data set. Preflare images at TRACE 195 A show that the bright and complex system of coronal loops already existed at the flaring site. The X-ray light curves clearly reveal two phases of flare evolution. The emission during the first phase is seen in GOES and RHESSI measurements at energies below 25 keV, while the second phase is evident in all the X-ray energies as high as 300 keV. The first phase is gradual whereas the second phase shows impulsive emission with several individual hard X-ray bursts. The first phase starts with the appearance of an X-ray loop-top (LT) source in RHESSI images below 25 keV. About 5 minute later, the TRACE 195 A images show an intense emission that is cospatial with RHESSI LT source. This hot and diffuse TRACE emission is attributed to the existence of 15-20 MK plasma, heated directly from the primary energy source. Both X-ray and TRACE LT sources exhibit an altitude decrease for ~11 minute. The first phase seems to be mostly dominated by hot thermal emission from flaring loops with temperatures T >25 MK. The second phase is found to be dominantly non-thermal in nature, with distinct emission from hard X-ray footpoints and the spectra at high energies follow hard power laws (\gamma = 2.6-2.8$). The observations of the second phase are mostly consistent with the standard flare model while the results of the first phase contains evidence for the collapsing trap effect in solar flare.
- [40] arXiv:0809.2486 [ps, pdf, other]
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Title: The Metallicity Distribution of Distant F and G type stars in the CFHT Legacy Survey Deep FieldComments: 6 pages, 6 figures, accepted for publication in the Publications of the Astronomical Society of AustraliaSubjects: Astrophysics (astro-ph)
We study the metal abundances of F and G type stars in the Galactic disk and halo using.
- [41] arXiv:0809.2487 [ps, pdf, other]
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Title: Morphology of galaxies in the Coma cluster region down to M_B=-14.25. I. A catalog of 473 membersComments: A&A, in press. Tables are available at CDS and at this http URL (Table1), this http URL (Table 2)Subjects: Astrophysics (astro-ph)
This paper presents morphological type, membership, and U-V color for a sample of galaxies in the Coma cluster direction, complete down to M_B=-15.00 mag and extending down to M_B=-14.25 mag. We have examined 1155 objects from the GMP 1983 catalog on B and V images of the CFH12K camera, and obtained the Hubble type in most cases. Coma cluster membership for 473 galaxies was derived using morphology, apparent size, and surface brightness, and, afterward, redshift. The comparison among morphology- and redshift- memberships and among luminosity functions derived from this morphologically-selected sample, or by using statistical members or spectroscopic members, all show that the morphological membership provided here can be trusted. For the first time, the morphological classification of Coma galaxies reaches magnitudes that are faint enough to observe the whole magnitude range of the giant types, E, S0, and spiral stages. The data presented in this paper makes our sample the richest environment where membership and morphology for complete samples down to faint magnitudes M_B~-15 mag are available, thereby enlarging the baseline of environmental studies.
- [42] arXiv:0809.2491 [ps, pdf, other]
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Title: On the 511 keV emission line of positron annihilation in the Milky WayAuthors: N. PrantzosComments: 7 pages, 2 figures, paper presented in "Astronomy with Radioactivities" (Ringberg, Germany, january 2008), to appear in New Astronomy ReviewsSubjects: Astrophysics (astro-ph)
I review our current understanding of positron sources in the Galaxy, on the basis of the reported properties of the observed 511 keV annihilation line. It is argued here that most of the disk positrons propagate away from the disk and the resulting low surface brightness annihilation emission is currently undetectable by SPI/INTEGRAL. It is also argued that a large fraction of the disk positrons may be transported via the regular magnetic field of the Galaxy into the bulge and annihilate there. These ideas may alleviate current difficulties in interepreting INTEGRAL results in a "conventional" framework.
- [43] arXiv:0809.2492 [ps, pdf, other]
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Title: The old Galactic open clusters FSR1716 and Czernik23Comments: 15 pages and 13 figures. Accepted by A&ASubjects: Astrophysics (astro-ph)
Open clusters older than $\sim4$ Gyr are rare in the Galaxy. Affected by a series of mass-decreasing processes, the stellar content of most open clusters dissolves into the field in a time-scale shorter than $\sim1$ Gyr. In this sense, improving the statistics of old objects may provide constraints for a better understanding of the dynamical dissolution of open clusters. Isochrone fits indicate that FSR 1716 is more probably an old ($\sim7$ Gyr) and absorbed ($\aV=6.3\pm0.2$) open cluster, located $\approx0.6$ kpc inside the Solar circle in a contaminated central field. However, we cannot rule out the possibility of a low-mass, loose globular cluster. Czernik 23 is shown to be an almost absorption-free open cluster, $\sim5$ Gyr old, located about 2.5 kpc towards the anti-centre. In both cases, Solar and sub-Solar ($[Fe/H]\sim-0.5$) metallicity isochrones represent equally well the stellar sequences. Both star clusters have a low mass content ($\la200 \ms$) presently stored in stars. Their relatively small core and cluster radii are comparable to those of other open clusters of similar age. These structural parameters are probably consequence of the several Gyrs of mass loss due to stellar evolution, tidal interactions with the disk (and bulge in the case of FSR 1716), and possibly giant molecular clouds. Czernik 23, and especially FSR 1716, are rare examples of extreme dynamical survivors. The identification of both as such represents an increase of $\approx10%$ to the known population of open clusters older than $\sim4$ Gyr in the Galaxy.
- [44] arXiv:0809.2500 [ps, pdf, other]
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Title: The Magellanic system X-ray sourcesAuthors: Andrew J. Gosling (1), Sean A. Farrell (2), Natalie A. Webb (2), Jari J. E. Kajava (1) ((1) University of Oulu, Oulu, Finland, (2) C.E.S.R., Touluouse, France)Comments: 4 pages, 2 figures. Poster to appear in proceedings of IAU Symposium 256, The Magellanic System: Stars, Gas, and Galaxies. Keele Univeristy, UKSubjects: Astrophysics (astro-ph)
Using archival X-ray data from the second XMM-Newton serendipitous source catalogue, we present comparative analysis of the overall population of X-ray sources in the Large and Small Magellanic Clouds. We see a difference between the characteristics of the brighter sources in the two populations in the X-ray band. Utilising flux measurements in different energy bands we are able to sort the X-ray sources based on similarities to other previously identified and classified objects. In this manner we are able to identify the probable nature of some of the unknown objects, identifying a number of possible X-ray binaries and Super Soft Sources.
- [45] arXiv:0809.2504 [ps, pdf, other]
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Title: A cosmic-ray precursor model for a Balmer-dominated shock in Tycho's supernova remnantComments: 13 pages, 5 figures, to be published in ApJSubjects: Astrophysics (astro-ph)
We present a time-dependent cosmic-ray modified shock model for which the calculated H-alpha emissivity profile agrees well with the H-alpha flux increase ahead of the Balmer-dominated shock at knot g in Tycho's supernova remnant, observed by Lee et al (2007). The backreaction of the cosmic ray component on the thermal component is treated in the two-fluid approximation, and we include thermal particle injection and energy transfer due to the acoustic instability in the precursor. The transient state of our model that describes the current state of the shock at knot g, occurs during the evolution from a thermal gas dominated shock to a smooth cosmic-ray dominated shock. Assuming a distance of 2.3 kpc to Tycho's remnant we obtain values for the cosmic ray diffusion coefficient, the injection parameter, and the time scale for the energy transfer of 10^{24} cm^{2} s^{-1}, 4.2x10^{-3}, and 426 y, respectively. We have also studied the parameter space for fast (300 km s^{-1} - 3000 km s^{-1}), time-asymptotically steady shocks and have identified a branch of solutions, for which the temperature in the cosmic ray precursor typically reaches 2-6x10^{4} K and the bulk acceleration of the flow through the precursor is less than 10 km s^{-1}. These solutions fall into the low cosmic ray acceleration efficiency regime and are relatively insensitive to shock parameters. This low cosmic ray acceleration efficiency branch of solutions may provide a natural explanation for the line broadening of the H-alpha narrow component observed in non-radiative shocks in many supernova remnants.
- [46] arXiv:0809.2505 [ps, pdf, other]
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Title: SPITZER survey of dust grain processing in stable discs around binary post-AGB starsComments: 22pages, 50 figures (in appendix), accepted for A&ASubjects: Astrophysics (astro-ph)
Aims: We investigate the mineralogy and dust processing in the circumbinary discs of binary post-AGB stars using high-resolution TIMMI2 and SPITZER infrared spectra. Methods: We perform a full spectral fitting to the infrared spectra using the most recent opacities of amorphous and crystalline dust species. This allows for the identification of the carriers of the different emission bands. Our fits also constrain the physical properties of different dust species and grain sizes responsible for the observed emission features. Results: In all stars the dust is oxygen-rich: amorphous and crystalline silicate dust species prevail and no features of a carbon-rich component can be found, the exception being EPLyr, where a mixed chemistry of both oxygen- and carbon-rich species is found. Our full spectral fitting indicates a high degree of dust grain processing. The mineralogy of our sample stars shows that the dust is constituted of irregularly shaped and relatively large grains, with typical grain sizes larger than 2 micron. The spectra of nearly all stars show a high degree of crystallinity, where magnesium-rich end members of olivine and pyroxene silicates dominate. Other dust features of e.g. silica or alumina are not present at detectable levels. Temperature estimates from our fitting routine show that a significant fraction of grains must be cool, significantly cooler than the glass temperature. This shows that radial mixing is very efficient is these discs and/or indicates different thermal conditions at grain formation. Our results show that strong grain processing is not limited to young stellar objects and that the physical processes occurring in the discs are very similar to those in protoplanetary discs.
- [47] arXiv:0809.2507 [ps, pdf, other]
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Title: On the chemical evolution of the Milky WayAuthors: N. Prantzos (Institut d'Astrophysique de Paris)Comments: 12 pages, 13 figures, Invited talk at IAU Symposium No. 254 "The Galaxy Disk in Cosmological Context", Eds. J. Andersen et al., in pressSubjects: Astrophysics (astro-ph)
I discuss three different topics concerning the chemical evolution of the Milky Way (MW). 1) The metallicity distribution of the MW halo; it is shown that this distribution can be analytically derived in the framework of the hierarchical merging scenario for galaxy formation, assuming that the component sub-haloes had chemical properties similar to those of the progenitors of satellite galaxies of the MW. 2) The age-metallicity relationship (AMR) in the solar neighborhood; I argue for caution in deriving from data with important uncertainties (such as the age uncertainties in the Geneva-Kopenhaguen survey) a relationship between average metallicity and age: derived relationships are shown to be systematically flatter than the true ones and should not be directly compared to models. 3) The radial mixing of stars in the disk, which may have important effects on various observables (scatter in AMR, extension of the tails of the metallicity distribution, flatenning of disk abundance profiles). Recent SPH + N-body simulations find considerable radial mixing, but only comparison to observations will ultimately determine the extent of that mixing.
- [48] arXiv:0809.2513 [ps, pdf, other]
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Title: High redshift quasars in the COSMOS survey: the space density of z>3 X-ray selected QSOsAuthors: M. Brusa (1), A. Comastri (2), R. Gilli (2), G. Hasinger (1), K. Iwasawa (2,1), V. Mainieri (3), M. Mignoli (2), M. Salvato (4), G. Zamorani (2), A. Bongiorno (1), N. Cappelluti (1), F. Civano (5), F. Fiore (6), A. Merloni (1,7), J. Silverman (8), J. Trump (9), C. Vignali (10), P. Capak (4), M. Elvis (5), O. Ilbert (11), C. Impey (9), S. Lilly (8) (1 - MPE, 2 - INAF-OaBo, 3 - ESO, 4 - Caltech, 5 - CfA, 6 - INAF-OaRoma, 7 -Excellence Cluster, 8 - ETH, 9 - Steward Observatory, 10 - UniBo, 11 - Univ. of Hawaii)Comments: 36 pages, 9 figures, 4 tables. To appear on ApJ, version revised according to referee commentsSubjects: Astrophysics (astro-ph)
We present a new measurement of the space density of high redshift (3.0<z<4.5), X-ray selected QSOs obtained by exploiting the deep and uniform multiwavelength coverage of the COSMOS survey. We have assembled a statistically large (40 objects), X-ray selected (F_{0.5-2 keV} >10^{-15} cgs), homogeneous sample of z>3 QSOs for which spectroscopic (22) or photometric (18) redshifts are available. We present the optical (color-color diagrams) and X-ray properties, the number counts and space densities of the z>3 X-ray selected quasars population and compare our findings with previous works and model predictions. We find that the optical properties of X-ray selected quasars are not significantly different from those of optically selected samples. There is evidence for substantial X-ray absorption (logN_H>23 cm^{-2}) in about 20% of the sources in the sample. The comoving space density of luminous (L_X >10^{44} erg s^-1) QSOs declines exponentially (by an e--folding per unit redshift) in the z=3.0-4.5 range, with a behavior similar to that observed for optically bright unobscured QSOs selected in large area optical surveys. Prospects for future, large and deep X-ray surveys are also discussed.
- [49] arXiv:0809.2518 [ps, pdf, other]
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Title: Extragalactic Constraints on the Initial Mass FunctionComments: 6 pages, 5 figures, accepted to MNRASSubjects: Astrophysics (astro-ph)
The local stellar mass density is observed to be significantly lower than the value obtained from integrating the cosmic star formation history (SFH), assuming that all the stars formed with a Salpeter initial mass function (IMF). Even other favoured IMFs, more successful in reconciling the observed $z=0$ stellar mass density with that inferred from the SFH, have difficulties in reproducing the stellar mass density observed at higher redshift. In this study we investigate to what extent this discrepancy can be alleviated for any universal power-law IMF. We find that an IMF with a high-mass slope shallower (2.15) than the Salpeter slope (2.35) reconciles the observed stellar mass density with the cosmic star formation history, but only at low redshifts. At higher redshifts $z>0.5$ we find that observed stellar mass densities are systematically lower than predicted from the cosmic star formation history, for any universal power-law IMF.
- [50] arXiv:0809.2534 [ps, pdf, other]
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Title: Shock heating in the group atmosphere of the radio galaxy B2 0838+32AComments: 11 pages, 7 figures, Figure 3 in colour. Accepted, MNRASSubjects: Astrophysics (astro-ph)
We present Chandra and radio observations, and analysis of Sloan Digital Sky Survey data, of the radio galaxy B2 0838+32A (4C 32.26) and its environment. The radio galaxy is at the centre of a nearby group that has often been identified with the cluster Abell 695, but we argue that the original Abell cluster is likely to be an unrelated and considerably more distant system. The radio source is a restarting radio galaxy and, using our Chandra data, we argue that the currently active lobes are expanding supersonically, driving a shock with Mach number $2.4^{+1.0}_{-0.5}$ into the inter-stellar medium. This would be only the third strong shock round a young radio source to be discovered, after Centaurus A and NGC 3801. However, in contrast to both these systems, the host galaxy of B2 0838+32A shows no evidence for a recent merger, while the AGN spectrum shows no evidence for the dusty torus that would imply a large reservoir of cold gas close to the central black hole. On the contrary, the AGN spectrum is of a type that has been associated with the presence of a radiativelyinefficient accretion flow that could be controlled by AGN heating and subsequent cooling of the hot, X-ray emitting gas. If correct, this means that B2 0838+32A is the first source in which we can directly see entropy-increasing processes (shocks) driven by accretion from the hot phase of the interstellar medium.
- [51] arXiv:0809.2539 [ps, pdf, other]
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Title: Accelerated recombination and primordial baryonic clouds: the recent CMB and SDSS data constraint, and the constraint forecast for the PLANCK surveyorComments: submitted to JCAPSubjects: Astrophysics (astro-ph)
We have constrained the extended (delayed and accelerated) models of hydrogen recombination, by investigating associated changes of the position and the width of the last scattering surface. Using the recent CMB and SDSS data, we find that the recent data constraints favor the accelerated recombination model, though the other models (standard, delayed recombination) are not ruled out at 1-$\sigma$ confidence level. If the accelerated recombination had actually occurred in our early Universe, baryonic clustering on small-scales is likely to be the cause of it. By comparing the ionization history of baryonic cloud models with that of the best-fit accelerated recombination model, we find that some portion of our early Universe has baryonic underdensity. We have made the forecast on the PLANCK data constraint, which shows that we will be able to rule out the standard or delayed recombination models, if the recombination in our early Universe had proceeded with $\epsilon_\alpha\sim-0.01$ or lower, and residual foregrounds and systematic effects are negligible.
- [52] arXiv:0809.2540 [ps, pdf, other]
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Title: Cosmological perturbations from multi-field inflationAuthors: David LangloisComments: Invited plenary talk at ICGC-07 (International Conference on Gravitation and Cosmology), 17-21 December 2007, IUCAA, Pune, India; 10 pages, no figureSubjects: Astrophysics (astro-ph)
We briefly review the standard derivation of the spectra of cosmological perturbations in the simplest models of inflation. We then consider models with several scalar fields, described by Lagrangians with an arbitrary dependence on the kinetic terms. We illustrate our general formalism with the case of multi-field DBI inflation.
- [53] arXiv:0809.2556 [ps, pdf, other]
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Title: The 15--43-GHz Parsec-scale Circular Polarization of 41 Active Galactic NucleiComments: Accepted for publication in Monthly Notices of the Royal Astronomical SocietySubjects: Astrophysics (astro-ph)
We present the results of parsec-scale circular polarization (CP) measurements based on VLBA data for a number of radio-bright, core-dominated AGN obtained simultaneously at 15, 22 and 43 GHz. The degrees of CP $m_c$ for the VLBI core region at 15 GHz are similar to values reported earlier at this wavelength, with typical values of a few tenths of a percent.We find that $m_c$ as often rises as falls with increasing frequency between 15 and 22 GHz, while $m_c$ at 43 GHz is in all cases higher than at 22 and 15 GHz. This behaviour seems contrary to expectations, since the degree of CP from both synchrotron radiation and Faraday conversion of linear to circular polarization should {\em decrease} towards higher frequencies if the source is homogeneous. The increase in $m_c$ at 43 GHz may be due to the presence of regions of both positive and negative CP with different frequency dependences on small scales within the core region; alternatively, it may be associated with the intrinsic inhomogeneity of a Blandford-K\"onigl-like jet. In several objects, the detected CO appears to be near, but not coincident with the core, although further observations are needed to confirm this. We find several cases of changes in sign with frequency, most often between 22 and 43 GHz. We find tentative evidence for transverse structure in the CP of 1055+018 and 1334$-$127 that is consistent with their being generated by either the synchrotron mechanism or Faraday conversion in a helical magnetic field. Our results confirm the earlier finding that the sign of the CP at a given observing frequency is generally consistent across epochs separated by several years or more, suggesting stability of the magnetic field orientation in the innermost jets.
- [54] arXiv:0809.2557 [ps, pdf, other]
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Title: A linear filter to reconstruct the ISW effect from CMB and LSS observationsComments: 8 pages, 6 figures, accepted for publication in the IEEE Journal of Selected Topics in Signal ProcessingSubjects: Astrophysics (astro-ph)
The extraction of a signal from some observational data sets that contain different contaminant emissions, often at a greater level than the signal itself, is a common problem in Astrophysics and Cosmology. The signal can be recovered, for instance, using a simple Wiener filter. However, in certain cases, additional information may also be available, such as a second observation which correlates to a certain level with the sought signal. In order to improve the quality of the reconstruction, it would be useful to include as well this additional information. Under these circumstances, we have constructed a linear filter, the linear covariance-based filter, that extracts the signal from the data but takes also into account the correlation with the second observation. To illustrate the performance of the method, we present a simple application to reconstruct the so-called Integrated Sachs-Wolfe effect from simulated observations of the Cosmic Microwave Background and of catalogues of galaxies.
- [55] arXiv:0809.2559 [ps, pdf, other]
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Title: Tombaugh 2: The First Open Cluster with a Significant Abundance Spread or Embedded in a Cold Stellar Stream?Authors: P. M. Frinchaboy (U.Wisc), A. F. Marino (Padova), S. Villanova (Concepcion), G. Carraro (ESO), S. R. Majewski (UVa), D. Geisler (Concepcion)Comments: 15 pages, 7 figure, MNRAS in pressSubjects: Astrophysics (astro-ph)
We present new abundances and radial velocities for stars in the field of the open cluster Tombaugh 2, which has been suggested to be associated with the Galactic Anticenter Stellar Structure (also known as the Monoceros stream). Using VLT/FLAMES with the UVES and GIRAFFE spectrographs, we find a radial velocity (RV) of <V_{r}> = 121 \pm 0.4 km/s using eighteen Tombaugh 2 cluster stars. Our abundance analysis of RV-selected members finds that Tombaugh 2 is more metal-rich than previous studies have found; moreover, unlike the previous work, our larger sample also reveals that stars with the velocity of the cluster show a relatively large spread in chemical properties (e.g., Delta[Fe/H] > 0.2). This is the first time a possible abundance spread has been observed in an open cluster, though this is one of several possible explanations for our observations. While there is an apparent trend of [alpha/Fe] with [Fe/H], the distribution of abundances of these "RV cluster members" also may hint at a possible division into two primary groups with different mean chemical characteristics -- namely (<[Fe/H]>,<[Ti/Fe]>) ~ (-0.06, +0.02) and (-0.28, +0.36). Based on position and kinematics Tombaugh 2 is a likely member of the GASS/Monoceros stream, which makes Tombaugh 2 the second star cluster within the originally proposed GASS/Monoceros family. However, we explore other possible explanations for the observed spread in abundances and two possible sub-populations, with the most likely explanation being that the metal-poor ([Fe/H] = -0.28), more centrally-concentrated population being the true Tombaugh 2 clusters stars and the metal-rich ([Fe/H] = -0.06) population being an overlapping, and kinematically associated, but "cold" (sigma_V < 2 km/s) stellar stream at R_{gc} >= 15 kpc.
- [56] arXiv:0809.2562 [ps, pdf, other]
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Title: SCP06F6: A carbon-rich extragalactic transient at redshift z~0.14Comments: submitted to ApJ LettersSubjects: Astrophysics (astro-ph)
We show that the spectrum of the unusual transient SCP06F6 is consistent with emission from a cool, carbon-rich atmosphere at a redshift of z~0.14. The extragalactic nature of the transient rules out novae, shell flashes, and V838 Mon-like events as cause of the observed brightening. The distance to SCP 06F6 implies a peak magnitude of M_I~-18, in the regime of supernovae. The morphology of the light curve of SCP 06F6 around the peak in brightness resembles the slowly evolving TypeII supernovae SN 1994Y and SN 2006 gy. We further report the detection of an X-ray source co-incident with SCP 06F6 in a target of opportunity XMM-Newton observation made during the declining phase of the transient. The X-ray luminosity of L_X~(5+-1)x10^42 erg/s is two orders of magnitude higher than observed to date from supernovae. If related to a supernova event, SCP 06F6 would define a new class. An alternative, though less likely, scenario is the tidal disruption of a carbon-rich star.
- [57] arXiv:0809.2580 [ps, pdf, other]
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Title: A 600 minute near-infrared lightcurve of Sagittarius A*Comments: 12 pages, 3 figures; accepted by ApJ Letters for publicationSubjects: Astrophysics (astro-ph)
We present the longest, by a factor of two, near-infrared lightcurve from Sgr A* - the supermassive black hole in the Galactic center. Achieved by combining Keck and VLT data from one common night, which fortuitously had simultaneous Chandra and SMA data, this lightcurve is used to address two outstanding problems. First, a putative quasi-periodicity of ~20 min reported by groups using ESO's VLT is not confirmed by Keck observations. Second, while the infrared and mm-regimes are thought to be related based on reported time lags between lightcurves from the two wavelength domains, the reported time lag of 20 min inferred using the Keck data of this common VLT/Keck night only is at odds with the lag of ~100 min reported earlier. With our long lightcurve, we find that (i) the simultaneous 1.3 millimeter observations are in fact consistent with a ~100 min time lag, (ii) the different methods of NIR photometry used by the VLT and Keck groups lead to consistent results, (iii) the Lomb-Scargle periodogram of the whole NIR lightcurve is featureless and follows a power-law with slope -1.6, and (iv) scanning the lightcurve with a sliding window to look for a transient QPO phenomenon reveals for a certain part of the lightcurve a 25 min peak in the periodogram. Using Monte Carlo simulations and taking the number of trials into account, we find it to be insignificant.
- [58] arXiv:0809.2583 [ps, pdf, other]
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Title: High-resolution radio observations of X-ray binariesAuthors: James Miller-Jones (NRAO)Comments: 10 pages. To appear in proceedings of "The Universe under the Microscope - Astrophysics at High Angular Resolution" (Bad Honnef, Germany, April 2008), eds. R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros, published in Journal of Physics: Conference Series by Institute of Physics PublishingSubjects: Astrophysics (astro-ph)
I present an overview of important results obtained using high-resolution very long baseline interferometry (VLBI) observations of X-ray binary systems. These results derive from both astrometric observations and resolved imaging of sources, from black holes to neutron star and even white dwarf systems. I outline a number of upcoming developments in instrumentation, both new facilities and ongoing upgrades to existing VLBI instruments, and I conclude by identifying a number of important areas of investigation where VLBI will be crucial in advancing our understanding of X-ray binaries.
- [59] arXiv:0809.2591 [ps, pdf, other]
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Title: Do the photometric colors of Type II-P Supernovae allow accurate determination of host galaxy extinction?Authors: Kevin Krisciunas, Mario Hamuy, Nicholas B. Suntzeff, Juan Espinoza, David Gonzalez, Luis Gonzalez, Sergio Gonzalez, Kathleen Koviak, Wojtek Krzeminski, Nidia Morrell, Mark M. Phillips, Miguel Roth, Joanna Thomas-OsipComments: 24 pages, 6 figuresSubjects: Astrophysics (astro-ph)
We present infrared photometry of SN 1999em, plus optical photometry, infrared photometry, and optical spectroscopy of SN 2003hn. Both objects were Type II-P supernovae. The V-[RIJHK] color curves of these supernovae evolved in a very similar fashion until the end of plateau phase. This allows us to determine how much more extinction the light of SN 2003hn suffered compared to SN 1999em. Since we have an estimate of the total extinction suffered by SN 1999em from model fits of ground-based and space-based spectra as well as photometry of SN 1999em, we can estimate the total extinction and absolute magnitudes of SN 2003hn with reasonable accuracy. Since the host galaxy of SN 2003hn also produced the Type Ia SN 2001el, we can directly compare the absolute magnitudes of these two SNe of different types.
- [60] arXiv:0809.2592 [ps, pdf, other]
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Title: On the frequency, intensity and duration of starburst episodes triggered by galaxy interactions and mergersComments: 22 pages, 28 figures, A&A accepted. High resolution version available at this http URLSubjects: Astrophysics (astro-ph)
We investigate the intensity enhancement and the duration of starburst episodes, triggered by major galaxy interactions and mergers. To this aim, we analyze two large statistical datasets of numerical simulations. These have been obtained using two independent and different numerical techniques to model baryonic and dark matter evolution, that are extensively compared for the first time. One is a Tree-SPH code, the other one is a grid-based N-body sticky-particles code. We show that, at low redshift, galaxy interactions and mergers in general trigger only moderate star formation enhancements. Strong starbursts where the star formation rate is increased by a factor larger than 5 are rare and found only in about 15% of major galaxy interactions and mergers. Merger-driven starbursts are also rather short-lived, with a typical duration of the activity of a few 10^8 yr. These conclusions are found to be robust, independent from the numerical techniques and star formation models. At higher redshifts where galaxies contain more gas, gas inflow-induced starbursts are neither stronger neither longer than their local counterparts. In turn, the formation of massive gas clumps, results of local Jeans instability that can occur spontaneously in gas-rich disks or be indirectly favored by galaxy interactions, could play a more important role in determining the duration and intensity of star formation episodes.
- [61] arXiv:0809.2595 [ps, pdf, other]
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Title: NoSOCS in SDSS. I. Sample Definition and Comparison of Mass EstimatesComments: 21 pages, 17 figures, 5 tables, Accepted to MNRASSubjects: Astrophysics (astro-ph)
We use Sloan Digital Sky Survey (SDSS) data to investigate galaxy cluster properties of systems first detected within DPOSS. With the high quality photometry of SDSS we derived new photometric redshifts and estimated richness and optical luminosity. For a subset of low redshift ($z \le 0.1$) clusters, we have used SDSS spectroscopic data to identify groups in redshift space in the region of each cluster, complemented with massive systems from the literature to assure the continuous mass sampling. A method to remove interlopers is applied, and a virial analysis is performed resulting in estimates of velocity dispersion, mass, and a physical radius for each low-$z$ system. We discuss the choice of maximum radius and luminosity range in the dynamical analysis, showing that a spectroscopic survey must be complete to at least M$^*+1$ if one wishes to obtain accurate and unbiased estimates of velocity dispersion and mass. We have measured X-ray luminosity for all clusters using archival data from RASS. For a smaller subset (twenty-one clusters) we selected temperature measures from the literature and estimated mass from the M-T$_X$ relation, finding that they show good agreement with the virial estimate. However, these two mass estimates tend to disagree with the caustic results. We measured the presence of substructure in all clusters of the sample and found that clusters with substructure have virial masses higher than those derived from T$_X$. This trend is not seen when comparing the caustic and X-ray masses. That happens because the caustic mass is estimated directly from the mass profile, so it is less affected by substructure.
- [62] arXiv:0809.2597 [ps, pdf, other]
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Title: Can the Copernican principle be tested by cosmic neutrino background?Comments: Revtex4,5 pages,3 figuresSubjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)
The Copernican principle, stating that we do not occupy any special place in our universe, is usually taken for granted in modern cosmology. However recent observational data of supernova indicate that we may live in the under-dense center of our universe, which makes the Copernican principle challenged. It thus becomes urgent and important to test the Copernican principle via cosmological observations. Taking into account that unlike the cosmic photons, the cosmic neutrinos of different energies come from the different places to us along the different worldlines, we here propose cosmic neutrino background as a test of the Copernican principle. It is shown that from the theoretical perspective cosmic neutrino background can allow one to determine whether the Copernican principle is valid or not, but to implement such an observation the larger neutrino detectors are called for.
- [63] arXiv:0809.2598 [ps, pdf, other]
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Title: Sharpening the Tip of the Red Giant BranchComments: 9 pages, 6 figures; to be published in the Astrophysical JournalSubjects: Astrophysics (astro-ph)
We introduce a modified detection method for measuring the luminosity of the tip of the red giant branch (TRGB) by introducing the composite magnitude T = I - beta [(V-I)_o - 1.50], where beta is the slope of the tip magnitude as a function of color (or metallicity). The method is specifically designed to account for known systematics due to metallicity. In doing so, this simple transformation does away with arbitrary color selections in measuring the tip, and thereby significantly boosts the population of resolved stars that go into defining the TRGB distance. Moreover this method coincidentally reduces the impact of reddening on the true modulus as well as its final uncertainty.
Cross-lists for Tue, 16 Sep 08
- [64] arXiv:0705.0800 (cross-list from physics.atom-ph) [ps, pdf, other]
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Title: Non-uniform convergence of two-photon decay rates for excited atomic statesAuthors: Ulrich D. JentschuraComments: 3 pages; LaTeXJournal-ref: J.Phys.A 40 (2007) F223-F227Subjects: Atomic Physics (physics.atom-ph); Astrophysics (astro-ph)
Two-photon decay rates in simple atoms such as hydrogenlike systems represent rather interesting fundamental problems in atomic physics. The sum of the energies of the two emitted photons has to fulfill an energy conservation condition, the decay takes place via intermediate virtual states, and the total decay rate is obtained after an integration over the energy of one of the emitted photons. Here, we investigate cases with a virtual state having an energy intermediate between the initial and the final state of the decay process, and we show that due to non-uniform convergence, only a careful treatment of the singularities infinitesimally displaced from the photon integration contour leads to consistent and convergent results.
- [65] arXiv:0806.4434 (cross-list from gr-qc) [ps, pdf, other]
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Title: Nonminimal coupling of perfect fluids to curvatureComments: 6 pages. V2: minor changes and references addedJournal-ref: Phys.Rev. D78 (2008) 064036Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); High Energy Physics - Theory (hep-th)
In this work, we consider different forms of relativistic perfect fluid Lagrangian densities, that yield the same gravitational field equations in General Relativity. A particularly intriguing example is the case with couplings of the form $[1+f_2(R)]{\cal L}_m$, where $R$ is the scalar curvature, which induces an extra force that depends on the form of the Lagrangian density. It has been found that, considering the Lagrangian density ${\cal L}_m = p$, where $p$ is the pressure, the extra-force vanishes. We argue that this is not the unique choice for the matter Lagrangian density, and that more natural forms for ${\cal L}_m$ do not imply the vanishing of the extra-force. Particular attention is paid to the impact on the classical equivalence between different Lagrangian descriptions of a perfect fluid.
- [66] arXiv:0807.0648 (cross-list from physics.atom-ph) [ps, pdf, other]
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Title: Two-Photon Decays Reexamined: Cascade Contributions and Gauge InvarianceAuthors: Ulrich D. JentschuraComments: 10 pages, LaTeXJournal-ref: J.Phys.A 41 (2008) 155307Subjects: Atomic Physics (physics.atom-ph); Astrophysics (astro-ph)
The purpose of this paper is to calculate the two-photon decay rate corresponding to the two-photon transitions nS->1S and nD->1S in hydrogenlike ions with a low nuclear charge number Z (for principal quantum numbers n = 2,...,8. Numerical results are obtained within a nonrelativistic framework, and the results are found to scale approximately as (Z alpha)^6/n^3, where alpha is the fine-structure constant. We also attempt to clarify a number of subtle issues regarding the treatment of the coherent, quasi-simultaneous emission of the two photons as opposed to one-photon cascades. In particular, the gauge invariance of the decay rate is shown explicitly.
- [67] arXiv:0809.1888 (cross-list from gr-qc) [pdf]
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Title: Special relativity may account for the spacecraft flyby anomaliesAuthors: Jean Paul MbelekComments: 3 pages, no figure, error corrected and approximation improved in section 2Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)
Recently, J. D. Anderson et al. [1] have proposed an empirical formula that accurately reproduces all the Earth flyby anomalies observed yet. Here, we show that special relativity (SR) transverse Doppler shift together with the addition of velocities may reproduce that formula.
- [68] arXiv:0809.2104 (cross-list from hep-ph) [ps, pdf, other]
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Title: Inflation scenario via the Standard Model Higgs boson and LHCComments: 13 pages, LaTeXSubjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)
We consider a quantum corrected inflation scenario driven by a generic GUT or Standard Model type particle model whose scalar field playing the role of an inflaton has a strong non-minimal coupling to gravity. We show that currently widely accepted bounds on the Higgs mass falsify the suggestion of the paper arXiv:0710.3755 (where the role of radiative corrections was underestimated) that the Standard Model Higgs boson can serve as the inflaton. However, if the Higgs mass could be raised to $\sim 230$ GeV, then the Standard Model could generate an inflationary scenario with the spectral index of the primordial perturbation spectrum $n_s\simeq 0.935$ (barely matching present observational data) and the very low tensor-to-scalar perturbation ratio $r\simeq 0.0006$.
- [69] arXiv:0809.2123 (cross-list from gr-qc) [ps, pdf, other]
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Title: Statefinder parameters for quantum effective Yang-Mills condensate dark energy modelComments: 11 pages, 5 figures, accepted for publication in Int. J. Mod. Phys. DSubjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)
The quantum effective Yang-Mills condensate (YMC) dark energy model has some distinguished features that it naturally solves the coincidence problem and, at the same time, is able to give an equation of state $w$ crossing -1. In this work we further employ the Statefinder pair $(r,s)$ introduced by Sahni et al to diagnose the YMC model for three cases: the non-coupling, the YMC decaying into matter only, and the YMC decaying into both matter and radiation. The trajectories $(r,s)$ and $(r,q)$, and the evolutions $r(z)$, $s(z)$ are explicitly presented. It is found that, the YMC model in all three cases has $r\simeq 1$ for $ z < 10$ and $s\simeq 0$ for $z<5$ with only small deviations $\simeq 0.02$, quite close to the cosmological constant model (LCDM), but is obviously differentiated from other dark energy models, such as quiesence, kinessence etc.
- [70] arXiv:0809.2242 (cross-list from hep-ph) [ps, pdf, other]
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Title: Non-Gaussianity from Baryon AsymmetryComments: 25 pages, 7 figuresSubjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph)
We study a scenario that large non-Gaussianity arises from the baryon asymmetry of the Universe. There are baryogenesis scenarios containing a light scalar field, which may result in baryonic isocurvature perturbations with some amount of non-Gaussianity. As an explicit example we consider the Affleck-Dine mechanism and show that a flat direction of the supersymmeteric standard model can generate large non-Gaussianity in the curvature perturbations, satisfying the observational constraints on the baryonic isocurvature perturbations. The sign of a non-linearity parameter, f_{NL}, is negative, if the Affleck-Dine mechanism accounts for the observed baryon asymmetry; otherwise it can be either positive or negative.
- [71] arXiv:0809.2263 (cross-list from hep-th) [ps, pdf, other]
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Title: Cusps on cosmic superstrings with junctionsComments: 22 pages, 5 figuresSubjects: High Energy Physics - Theory (hep-th); Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
The existence of cusps on non-periodic strings ending on D-branes is demonstrated and the conditions, for which such cusps are generic, are derived. The dynamics of F-, D-string and FD-string junctions are investigated. It is shown that pairs of FD-string junctions, such as would form after intercommutations of F- and D-strings, generically contain cusps. This new feature of cosmic superstrings opens up the possibility of extra channels of energy loss from a string network. The phenomenology of cusps on such cosmic superstring networks is compared to that of cusps formed on networks of their field theory analogues, the standard cosmic strings.
Replacements for Tue, 16 Sep 08
- [72] arXiv:0710.3169 (replaced) [ps, pdf, other]
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Title: New Gamma-Ray Contributions to Supersymmetric Dark Matter AnnihilationComments: Replaced Fig. 2c which by mistake displayed the same spectrum as Fig. 2d; the radiative corrections reported here are now implemented in DarkSUSY which is available at this http URLJournal-ref: JHEP 01 (2008) 049Subjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph)
- [73] arXiv:0801.0221 (replaced) [ps, pdf, other]
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Title: Double-peaked Oxygen Lines Are not Rare in Nebular Spectra of Core-Collapse SupernovaeAuthors: Maryam Modjaz (1,2), R. P. Kirshner (2), S. Blondin (2), P. Challis (2), T. Matheson (3) ((1) UC Berkeley, (2) Harvard-Smithsonian CfA, (3) NOAO)Comments: 5 pages, 3 figures, emulateapj, v2: accepted ApJ Letters versionSubjects: Astrophysics (astro-ph)
- [74] arXiv:0802.1074 (replaced) [ps, pdf, other]
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Title: Giant AGN Flares and Cosmic Ray BurstsComments: Obtained a more constraining prediction for photon counterparts of the predicted AGN flares, elaborated the discussion of AGN luminosity associated with UHECR acceleration, and corrected minor typosSubjects: Astrophysics (astro-ph)
- [75] arXiv:0802.3396 (replaced) [ps, pdf, other]
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Title: Generalized Tests for Selection Effects in GRB High-Energy CorrelationsComments: 8 pages, 3 figures, submitted to ApJ, Revised and ExpandedSubjects: Astrophysics (astro-ph)
- [76] arXiv:0803.3842 (replaced) [ps, pdf, other]
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Title: The Complex Structure of the Cl 1604 Supercluster at z~0.9Comments: Final version, appearing in ApJJournal-ref: 2008ApJ...684..933GSubjects: Astrophysics (astro-ph)
- [77] arXiv:0804.4318 (replaced) [ps, pdf, other]
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Title: The population of pulsars with interpulses and the implications for beam evolutionComments: 7 pages, 2 figures, published in MNRAS. Corrected typoSubjects: Astrophysics (astro-ph)
- [78] arXiv:0806.0007 (replaced) [ps, pdf, other]
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Title: Baryon acoustic signature in the clustering of density maximaAuthors: Vincent DesjacquesComments: Revised version. 19 pages, 8 figures. Corrected an error in the linear mean streaming of peak pairs. Nonlinear local nature of the peak biasing emphasised. Presentation improvedSubjects: Astrophysics (astro-ph)
- [79] arXiv:0806.0862 (replaced) [ps, pdf, other]
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Title: Quasars Probing Quasars III: New Clues to Feedback, Quenching, and the Physics of Massive Galaxy FormationComments: Accepted to ApJ. 38 pages, 11 figuresSubjects: Astrophysics (astro-ph)
- [80] arXiv:0806.2545 (replaced) [ps, pdf, other]
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Title: Measuring parameters of AGN central engines with very high energy gamma-ray flaresComments: 11 pages, 3 figure, accepted to MNRASSubjects: Astrophysics (astro-ph)
- [81] arXiv:0806.3074 (replaced) [ps, pdf, other]
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Title: Marginal distributions for cosmic variance limited CMB polarization dataComments: 8 pages, 3 figures; minor adjustment, accepted for publication in ApJSSubjects: Astrophysics (astro-ph)
- [82] arXiv:0807.1020 (replaced) [ps, pdf, other]
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Title: How the Scalar Field of Unified Dark Matter Models Can ClusterAuthors: Daniele Bertacca (1,2,3), Nicola Bartolo (4,5), Antonaldo Diaferio (1,3), Sabino Matarrese (4,5) ((1) Dip. di Fisica Generale (U. di Torino) (2) Dip. di Fisica Teorica (U. di Torino) (3) INFN (Torino) (4) Dip. di Fisica (U. di Padova) (5) INFN (Padova))Comments: 26 pages, 1 figure, JCAP, in pressSubjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
- [83] arXiv:0807.2242 (replaced) [ps, pdf, other]
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Title: Bayesian analysis of sparse anisotropic universe models and application to the 5-yr WMAP dataComments: 13 pages, 10 figures, accepted by ApJSubjects: Astrophysics (astro-ph)
- [84] arXiv:0807.3044 (replaced) [ps, pdf, other]
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Title: The Rotating Nuclear Star Cluster in NGC 4244Authors: Anil C. Seth, Robert D. Blum, Nate Bastian, Nelson Caldwell, Victor P. Debattista, Thomas H. PuziaComments: Accepted by ApJ. 7 page 5 figuresSubjects: Astrophysics (astro-ph)
- [85] arXiv:0807.3747 (replaced) [ps, pdf, other]
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Title: The Stellar Populations of Stripped Spiral Galaxies in the Virgo ClusterComments: 17 pages, 19 figures, accepted for publication in AJ. Replaced submission corrects Table names and matches figure style of Journal articleJournal-ref: The Astronomical Journal 136 (2008) 1623-1644Subjects: Astrophysics (astro-ph)
- [86] arXiv:0808.2469 (replaced) [ps, pdf, other]
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Title: MMT Hypervelocity Star SurveyAuthors: Warren R. Brown, Margaret J. Geller, Scott J. Kenyon (Smithsonian Astrophysical Observatory)Comments: 10 pages, accepted to ApJ with minor revisionsSubjects: Astrophysics (astro-ph)
- [87] arXiv:0809.0242 (replaced) [pdf]
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Title: Using SPICA Space Telescope to characterize ExoplanetsAuthors: J.R. Goicoechea, B. Swinyard, G. Tinetti, T. Nakagawa, K. Enya, M.Tamura, M. Ferlet, K.G. Isaak, M. Wyatt, A.D. Aylward, M. Barlow, J.P. Beaulieu, A. Boccaletti, J. Cernicharo, J. Cho, R. Claudi, H. Jones, H. Lammer, A. Leger, J. Martín-Pintado, S. Miller, F. Najarro, D. Pinfield, J. Schneider, F. Selsis, D.M. Stam, J. Tennyson, S. Viti, G. WhiteComments: A White Paper for ESA's Exo-Planet Roadmap Advisory Team, submitted on 2008 July 29Subjects: Astrophysics (astro-ph)
- [88] arXiv:0809.0595 (replaced) [ps, pdf, other]
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Title: Probability for chance coincidence of a gamma-ray burst with a galaxy on the skyComments: 8 pages, 5 figures. Accepted by MNRASSubjects: Astrophysics (astro-ph)
- [89] arXiv:0809.0852 (replaced) [ps, pdf, other]
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Title: The Properties of Early-type Stars in the Magellanic CloudsAuthors: Christopher J. Evans (UKATC, Edinburgh)Comments: 12 pages, invited review at IAU Symposium 256, van Loon J.Th. & Oliviera J.M., eds., Cambridge Univ. Press, v2: minor correctionsSubjects: Astrophysics (astro-ph)
- [90] arXiv:0809.0987 (replaced) [pdf, other]
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Title: Coupling from the photosphere to the chromosphere and the coronaComments: 33 pages, 16 figures; to appear in the Space Science Series of ISSI by Springer and in Space Science Reviews (accepted)Subjects: Astrophysics (astro-ph)
- [91] arXiv:0809.1976 (replaced) [ps, pdf, other]
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Title: Dark Matter Gravitational Clustering With a Long-Range Scalar InteractionComments: 13 pages, 10 figures, submitted to Phys. Rev. D, minor typos fixed, replaced Fig. 5Subjects: Astrophysics (astro-ph)
- [92] arXiv:0809.2266 (replaced) [pdf, other]
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Title: A Scalable Correlator Architecture Based on Modular FPGA Hardware, Reuseable Gateware, and Data PacketizationAuthors: Aaron Parsons, Donald Backer, Henry Chen, Pierre Droz, Terry Filiba, Jason Manley, David MacMahon, Peter McMahon, Arash Parsa, Andrew Siemion, Dan Werthimer, Melvyn WrightComments: Accepted to Publications of the Astronomy Society of the Pacific. 31 pages. Revision: corrected typoSubjects: Astrophysics (astro-ph)
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