Astrophysics
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New submissions for Thu, 19 Nov 09
- [1] arXiv:0911.3391 [ps, pdf, other]
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Title: The distance to the Andromeda Galaxy from eclipsing binariesComments: 7 pages, 3 figures, accepted for publication in A&A (Nov 6, 2009)Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Solar and Stellar Astrophysics (astro-ph.SR)
The cosmic distance scale largely depends on distance determinations to Local Group galaxies. In this sense, the Andromeda Galaxy (M31) is a key rung to better constrain the cosmic distance ladder. A project was started in 1999 to firmly establish a direct and accurate distance to M31 using eclipsing binaries (EBs). After the determination of the first direct distance to M31 from EBs, the second direct distance to an EB system is presented: M31V_J00443610+4129194. Light and radial velocity curves were obtained and fitted to derive the masses and radii of the components. The acquired spectra were combined and disentangled to determine the temperature of the components. The analysis of the studied EB resulted in a distance determination to M31 of (m-M)o = 24.30 +/- 0.11 mag. This result, when combined with the previous distance determination to M31, results in a distance modulus of (m-M)o = 24.36 +/- 0.08 mag (744 +/- 33 kpc), fully compatible with other distance determinations to M31. With an error of only 4%, the obtained value firmly establishes the distance to this important galaxy and represents the fulfillment of the main goal of our project.
- [2] arXiv:0911.3392 [ps, pdf, other]
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Title: The initial mass function of early-type galaxiesAuthors: T.Treu (1), M.W.Auger (1), L.V.E.Koopmans (2), R.Gavazzi (3), P.J.Marshall (1), A.S.Bolton (4) ((1) UCSB; (2) Kapteyn; (3) IAP; (4) Utah)Comments: 10 pages 4 figures. Resubmitted to ApJ taking into account referee's commentsSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We determine an absolute calibration of the initial mass function (IMF) of early-type galaxies, by studying a sample of 56 gravitational lenses identified by the SLACS Survey. Under the assumption of standard Navarro, Frenk & White dark matter halos, a combination of lensing, dynamical, and stellar population synthesis models is used to disentangle the stellar and dark matter contribution for each lens. We define an "IMF mismatch" parameter \alpha=M*(L+D)/M*(SPS) as the ratio of stellar mass inferred by a joint lensing and dynamical models (M*(L+D)) to the current stellar mass inferred from stellar populations synthesis models (M*(SPS)). We find that a Salpeter IMF provides stellar masses in agreement with those inferred by lensing and dynamical models (<\log \alpha>=0.00+-0.03+-0.02), while a Chabrier IMF underestimates them (<\log \alpha>=0.25+-0.03+-0.02). A tentative trend is found, in the sense that \alpha appears to increase with galaxy velocity dispersion. Taken at face value, this result would imply a non universal IMF, perhaps dependent on metallicity, age, or abundance ratios of the stellar populations. Alternatively, the observed trend may imply non-universal dark matter halos with inner density slope increasing with velocity dispersion. While the degeneracy between the two interpretations cannot be broken without additional information, the data imply that massive early-type galaxies cannot have both a universal IMF and universal dark matter halos.
- [3] arXiv:0911.3394 [ps, pdf, other]
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Title: Tidal disruption, global mass function and structural parameters evolution in star clustersAuthors: Michele Trenti (1), Enrico Vesperini (2), Mario Pasquato (3) ((1) Colorado, (2) Drexel, (3) Pisa)Comments: 33 pages, 11 figures, ApJ acceptedSubjects: Galaxy Astrophysics (astro-ph.GA)
[abridged] We present a unified picture for the evolution of star clusters on the two-body relaxation timescale. We use direct N-body simulations of star clusters in a galactic tidal field starting from different multi-mass King models, up to 10% of primordial binaries and up to Ntot=65536 particles. An additional run also includes a central Intermediate Mass Black Hole. We find that for the broad range of initial conditions we have studied the stellar mass function of these systems presents a universal evolution which depends only on the fractional mass loss. The structure of the system, as measured by the core to half mass radius ratio, also evolves toward a universal state, which is set by the efficiency of heating on the visible population of stars induced by dynamical interactions in the core of the system. Interactions with dark remnants are dominant over the heating induced by a moderate population of primordial binaries (3-5%), especially under the assumption that most of the neutron stars and black holes are retained in the system. All our models without primordial binaries undergo a deep gravothermal collapse in the radial mass profile. However their projected light distribution can be well fitted by medium concentration King models (with parameter W0 ~ 8), even though there tends to be an excess over the best fit for the innermost points of the surface brightness. This excess is consistent with a shallow cusp in the surface brightness (mu(R) ~ R^{-v} with v ~ 0.4-0.7), like it has been observed for many globular clusters from high-resolution HST imaging. Classification of core-collapsed globular clusters based on their surface brightness profile is likely to fail in systems that have already bounced back to lower concentrations.
- [4] arXiv:0911.3396 [ps, pdf, other]
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Title: Universal properties of Dark Matter halosComments: 4 pages, 1 figure, revtexSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We discuss the universal relation between density and size of Dark Matter halos.This relation was recently shown to hold on a wide range of scales, from dwarf galaxies to galaxy clusters, both in astronomical observations and numerical simulations of structure formation in the Universe. The nature of this relation has not been previously understood. We demonstrate that this relation can be derived analytically in a "secondary infall" model of structure formation. Qualitative understanding given by this model provides a new tool to observationally constrain the properties of DM and large scale modifications of gravity.
- [5] arXiv:0911.3397 [pdf, other]
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Title: Surprising phenomena in a rich new class of inflationary modelsComments: 11 pages, 10 figures, 1 tableSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We report on a new class of fast-roll inflationary models. In a huge part of its parameter space, inflationary perturbations exhibit quite unusual phenomena such as scalar and tensor modes freezing out at widely different times, as well as scalar modes reentering the horizon during inflation. In another, narrower range of parameters, this class of models agrees with observations. One specific point in parameter space is characterized by extraordinary behavior of the scalar perturbations. Freeze-out of scalar perturbations as well as particle production at horizon crossing are absent. Also the behavior of the perturbations around this quasi-de Sitter background is dual to a quantum field theory in flat space-time. Finally, the form of the primordial power spectrum is determined by the interaction between different modes of scalar perturbations.
- [6] arXiv:0911.3400 [ps, pdf, other]
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Title: The association between gas and galaxies III: The Cross-correlation of Galaxies and Ly-alpha Absorbers at z ~ 1Comments: 22 pages, 18 figures. Accepted for publication in MNRASSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
We have measured the 2D 2-point correlation function, Xi_AG, between low column density Ly-alpha absorbers and galaxies at a redshift z ~ 1. We measured Ly-alpha absorbers between redshifts z=0.68 to 1.51 over a total redshift path length of Delta z=1.08 from HST STIS E230M absorption spectra towards the quasars HE 1122-1648 (z=2.4) and PKS 1127-145 (z=1.187). The column density of the Ly-alpha absorbers ranged from 13.2< log(N_HI (cm^-2))<17.4, with a median column density of log(N_HI)=14.0 . A total of 193 galaxy redshifts within the surrounding 6.8' x 5.7' field of view of both quasars were identified in a R magnitude limited survey (21.5<R_Vega<24.5) using the FORS2 spectrograph at the VLT, of which 95 were higher than the minimum redshift z=0.68 to be used in the correlation function. A 3 sigma upper-limit of Xi_AG=2.8 was found when 145 Ly-alpha absorber-galaxy pairs were binned in redshift space, in a bin of size Delta sigma=1.0, Delta pi=2.0 h^-1 Mpc along the projected separation and line of sight distances respectively. The upper-limit in the cross-correlation was found to be 5.4 sigma lower than the central peak in the galaxy auto-correlation within the same redshift range, Xi_GG, which was in our data equal to 10.7+/-1.4. Thus we have shown for the first time that the clustering between low column density absorbers and galaxies at a redshift of 1 is weaker than that between galaxies at the same redshift.
- [7] arXiv:0911.3408 [ps, pdf, other]
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Title: Type IIB Supernovae with Compact and Extended ProgenitorsComments: 12 pages, ApJL, submittedSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
The classic example of a Type IIb supernova is SN 1993J, which had a cool extended progenitor surrounded by a dense wind. There is evidence for another category of Type IIb supernova which has a more compact progenitor with a lower density, probably fast, wind. Distinguishing features of the compact category are: weak optical emission from the shock heated envelope at early times; nonexistent or very weak H emission in the late nebular phase; rapidly evolving radio emission; rapid expansion of the radio shell; and expected nonthermal as opposed to thermal X-ray emission. Type IIb supernovae that have one or more of these features include SNe 1996cb, 2001ig, 2003bg, 2008ax, and 2008bo. All of these with sufficient radio data (the last four) show evidence for presupernova wind variability. We estimate a progenitor envelope radius ~1e11 cm for SN 2008ax, a value consistent with a compact Wolf-Rayet progenitor. Supernovae in the SN 1993J extended category include SN 2001gd and probably the Cas A supernova. We suggest that the compact Type IIb events be designated Type cIIb and the extended ones Type eIIb.
- [8] arXiv:0911.3409 [ps, pdf, other]
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Title: Properties of active galactic star-forming regions probed by imaging spectroscopy with the Fourier transform spectrometer (FTS) onboard AKARIAuthors: Yoko Okada (1 and 2), Mitsunobu Kawada (3), Noriko Murakami (3 and 4), Takafumi Ootsubo (2), Hidenori Takahashi (5), Akiko Yasuda (2 and 3), Daisuke Ishihara (6 and 3), Hidehiro Kaneda (3), Hirokazu Kataza (2), Takao Nakagawa (2), Takashi Onaka (6) ((1) Universität zu Köln, (2) ISAS/JAXA, (3) Nagoya University, (4) Bisei Astronomical Observatory, (5) Gunma Astronomical Observatory, (6) University of Tokyo)Comments: 14 pages with 15 figures, accepted for publication in Astronomy and AstrophysicsSubjects: Galaxy Astrophysics (astro-ph.GA)
We investigate the structure of the interstellar medium (ISM) and identify the location of possible embedded excitation sources from far-infrared (FIR) line and mid-infrared continuum emission maps. We carried out imaging spectroscopic observations of four giant Galactic star-forming regions with the Fourier Transform Spectrometer (FTS) onboard AKARI. We obtained [OIII] 88 micron and [CII] 158 micron line intensity maps of all the regions: G3.270-0.101, G333.6-0.2, NGC3603, and M17. For G3.270-0.101, we obtained high-spatial-resolution [OIII] 88 micron line-emission maps and a FIR continuum map for the first time, which imply that [OIII] 88 micron emission identifies the excitation sources more clearly than the radio continuum emission. In G333.6-0.2, we found a local [OIII] 88 micron emission peak, which is indicative of an excitation source. This is supported by the 18 micron continuum emission, which is considered to trace the hot dust distribution. For all regions, the [CII] 158 micron emission is distributed widely as suggested by previous observations of star-forming regions. We conclude that [OIII] 88 micron emission traces the excitation sources more accurately than the radio continuum emission, especially where there is a high density and/or column density gradient. The FIR spectroscopy provides a promising means of understanding the nature of star-forming regions.
- [9] arXiv:0911.3410 [ps, pdf, other]
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Title: A Second-Order Unsplit Godunov Scheme for Cell-Centered MHD: the CTU-GLM schemeComments: 31 Pages, 16 Figures Accepted for publication in Journal of Computational PhysicsSubjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE); Computational Physics (physics.comp-ph)
We assess the validity of a single step Godunov scheme for the solution of the magneto-hydrodynamics equations in more than one dimension. The scheme is second-order accurate and the temporal discretization is based on the dimensionally unsplit Corner Transport Upwind (CTU) method of Colella. The proposed scheme employs a cell-centered representation of the primary fluid variables (including magnetic field) and conserves mass, momentum, magnetic induction and energy. A variant of the scheme, which breaks momentum and energy conservation, is also considered. Divergence errors are transported out of the domain and damped using the mixed hyperbolic/parabolic divergence cleaning technique by Dedner et al. (J. Comput. Phys., 175, 2002). The strength and accuracy of the scheme are verified by a direct comparison with the eight-wave formulation (also employing a cell-centered representation) and with the popular constrained transport method, where magnetic field components retain a staggered collocation inside the computational cell. Results obtained from two- and three-dimensional test problems indicate that the newly proposed scheme is robust, accurate and competitive with recent implementations of the constrained transport method while being considerably easier to implement in existing hydro codes.
- [10] arXiv:0911.3417 [ps, pdf, other]
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Title: Triggering Collapse of the Presolar Dense Cloud Core and Injecting Short-Lived Radioisotopes with a Shock Wave. I. Varied Shock SpeedsComments: 39 pages, 14 figures. in press, ApJSubjects: Earth and Planetary Astrophysics (astro-ph.EP)
The discovery of decay products of a short-lived radioisotope (SLRI) in the Allende meteorite led to the hypothesis that a supernova shock wave transported freshly synthesized SLRI to the presolar dense cloud core, triggered its self-gravitational collapse, and injected the SLRI into the core. Previous multidimensional numerical calculations of the shock-cloud collision process showed that this hypothesis is plausible when the shock wave and dense cloud core are assumed to remain isothermal at ~10 K, but not when compressional heating to ~1000 K is assumed. Our two-dimensional models (Boss et al. 2008) with the FLASH2.5 adaptive mesh refinement (AMR) hydrodynamics code have shown that a 20 km/sec shock front can simultaneously trigger collapse of a 1 solar mass core and inject shock wave material, provided that cooling by molecular species such as H2O, CO, and H2 is included. Here we present the results for similar calculations with shock speeds ranging from 1 km/sec to 100 km/sec. We find that shock speeds in the range from 5 km/sec to 70 km/sec are able to trigger the collapse of a 2.2 solar mass cloud while simultaneously injecting shock wave material: lower speed shocks do not achieve injection, while higher speed shocks do not trigger sustained collapse. The calculations continue to support the shock-wave trigger hypothesis for the formation of the solar system, though the injection efficiencies in the present models are lower than desired.
- [11] arXiv:0911.3419 [ps, pdf, other]
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Title: Constraints on Secondary Eclipse Probabilities of Long-Period Exoplanets from Orbital ElementsAuthors: Kaspar von Braun, Stephen R. Kane (NASA Exoplanet Science Institute / California Institute of Technology)Comments: 3 pages, 1 figure, 1 table; to appear in ASP Conf. Proceedings: "Pathways Towards Habitable Planets" 2009, Barcelona, Spain (eds.: D. Gelino, V. Coude du Foresto, I. Ribas)Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Long-period transiting exoplanets provide an opportunity to study the mass-radius relation and internal structure of extrasolar planets. Their studies grant insights into planetary evolution akin to the Solar System planets, which, in contrast to hot Jupiters, are not constantly exposed to the intense radiation of their parent stars. Observations of secondary eclipses allow investigations of exoplanet temperatures and large-scale exo-atmospheric properties. In this short paper, we elaborate on, and calculate, probabilities of secondary eclipses for given orbital parameters, both in the presence and absence of detected primary transits, and tabulate these values for the forty planets with the highest primary transit probabilities.
- [12] arXiv:0911.3426 [ps, pdf, other]
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Title: Target selection for the SUNS and DEBRIS surveys for debris discs in the solar neighbourhoodAuthors: N. M. Phillips, J. S. Greaves, W. R. F. Dent, B. C. Matthews, W. S. Holland, M. C. Wyatt, B. SibthorpeComments: 67 pages with full tables, 7 figures, accepted to MNRASSubjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Debris discs - analogous to the Asteroid and Kuiper-Edgeworth belts in the Solar system - have so far mostly been identified and studied in thermal emission shortward of 100 um. The Herschel space observatory and the SCUBA-2 camera on the James Clerk Maxwell Telescope will allow efficient photometric surveying at 70 to 850 um, which allow for the detection of cooler discs not yet discovered, and the measurement of disc masses and temperatures when combined with shorter wavelength photometry. The SCUBA-2 Unbiased Nearby Stars (SUNS) survey and the DEBRIS Herschel Open Time Key Project are complimentary legacy surveys observing samples of ~500 nearby stellar systems. To maximise the legacy value of these surveys, great care has gone into the target selection process. This paper describes the target selection process and presents the target lists of these two surveys.
- [13] arXiv:0911.3445 [ps, pdf, other]
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Title: Panchromatic observations and modeling of the HV Tau C edge-on diskAuthors: G. Duchene, C. McCabe, C. Pinte, K. R. Stapelfeldt, F. Menard, G. Duvert, A. M. Ghez, H. L. Maness, H. Bouy, D. Barrado y Navascues, M. Morales-Calderon, S. Wolf, D. L. Padgett, T. Y. Brooke, A. Noriega-CrespoComments: 26 pages, 11 figures, editorially accepted for publication in ApJSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8 and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images reveal an unusually slow orbital motion within the tight HV Tau AB pair that suggests a highly eccentric orbit and/or a large deprojected physical separation. Scattered light images of the HV Tau C edge-on protoplanetary disk suggest that the anisotropy of the dust scattering phase function is almost independent of wavelength from 0.8 to 5 micron, whereas the dust opacity decreases significantly over the same range. The images further reveal a marked lateral asymmetry in the disk that does not vary over a timescale of 2 years. We further detect a radial velocity gradient in the disk in our 12CO map that lies along the same position angle as the elongation of the continuum emission, which is consistent with Keplerian rotation around an 0.5-1 Msun central star, suggesting that it could be the most massive component in the triple system. We use a powerful radiative transfer model to compute synthetic disk observations and use a Bayesian inference method to extract constraints on the disk properties. Each individual image, as well as the spectral energy distribution, of HV Tau C can be well reproduced by our models with fully mixed dust provided grain growth has already produced larger-than-interstellar dust grains. However, no single model can satisfactorily simultaneously account for all observations. We suggest that future attempts to model this source include more complex dust properties and possibly vertical stratification. (Abridged)
- [14] arXiv:0911.3448 [ps, pdf, other]
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Title: Weak lensing forecasts for dark energy, neutrinos and initial conditionsComments: 4 pages, proceedings for Grassmannian Conference in Fundamental Cosmology 09Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Weak gravitational lensing provides a sensitive probe of cosmological parameters by measuring the mass distribution and the geometry of the low redshift universe. We show how an all-sky weak lensing tomographic survey can jointly constrain different sets of cosmological parameters describing dark energy, massive neutrinos, and the primordial power spectrum. Using the Fisher matrix formalism with and without CMB priors, we examine how the constraints vary as the parameter set is enlarged. We find that weak lensing with CMB priors provides robust constraints on dark energy parameters and can simultaneously provide strong constraints on all three parameter sets. We also find that the dark energy sector is largely insensitive to the inclusion of the other cosmological sectors.
- [15] arXiv:0911.3485 [ps, pdf, other]
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Title: Radio-Loud Narrow-Line Seyfert 1 as a New Class of Gamma-Ray AGNComments: 16 pages, 1 figure. Accepted for publication on ApJ Letters. Corresponding author: Luigi FoschiniSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We report the discovery with Fermi/LAT of gamma-ray emission from three radio-loud narrow-line Seyfert 1 galaxies: PKS 1502+036 (z=0.409), 1H 0323+342 (z=0.061) and PKS 2004-447 (z=0.24). In addition to PMN J0948+0022 (z=0.585), the first source of this type to be detected in gamma rays, they may form an emerging new class of gamma-ray active galactic nuclei (AGN). These findings can have strong implications on our knowledge about relativistic jets and the unified model of AGN.
- [16] arXiv:0911.3486 [ps, pdf, other]
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Title: Do WMAP5 data favor neutrino mass and a coupling between Cold Dark Matter and Dark Energy?Comments: Proceedings of 'Invisible Universe International Conference', Paris, June 29- July 3, 2009Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We fit WMAP5 and related data by allowing for a CDM--DE coupling and non--zero neutrino masses, simultaneously. We find a significant correlation between these parameters, so that simultaneous higher coupling and \nu--masses are allowed. Furthermore, models with a significant coupling and \nu--mass are statistically favoured in respect to a cosmology with no coupling and negligible neutrino mass (our best fits are: C ~ 1/2m_p, m_\nu ~ 0.12eV per flavor). We use a standard Monte Carlo Markov Chain approach, by assuming DE to be a scalar field self--interacting through Ratra--Peebles or SUGRA potentials.
- [17] arXiv:0911.3500 [ps, pdf, other]
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Title: Meaurement of Cosmic Ray elemental composition from the CAKE balloon experimentComments: 5 pages, 8 figuresSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)
CAKE (Cosmic Abundances below Knee Energies) was a prototype balloon experiment for the determination of the charge spectra and of abundances of the primary cosmic-rays (CR) with Z$>$10. It was a passive instrument made of layers of CR39 and Lexan nuclear track detectors; it had a geometric acceptance of $\sim$0.7 m$^2$sr for Fe nuclei. Here, the scanning and analysis strategies, the algorithms used for the off-line filtering and for the tracking in automated mode of the primary cosmic rays are presented, together with the resulting CR charge distribution and their abundances.
- [18] arXiv:0911.3506 [ps, pdf, other]
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Title: Multi-strand coronal loop model and filter-ratio analysisSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
We model a coronal loop as a bundle of seven separate strands or filaments. Each of the loop strands used in this model can independently be heated (near their left footpoints) by Alfv\'en/ion-cyclotron waves via wave-particle interactions. The Alfv\'en waves are assumed to penetrate the strands from their footpoints, at which we consider different wave energy inputs. As a result, the loop strands can have different heating profiles, and the differential heating can lead to a varying cross-field temperature in the total coronal loop. The simulation of TRACE observations by means of this loop model implies two uniform temperatures along the loop length, one inferred from the 171:195 filter ratio and the other from the 171:284 ratio. The reproduced flat temperature profiles are consistent with those inferred from the observed EUV coronal loops. According to our model, the flat temperature profile is a consequence of the coronal loop consisting of filaments, which have different temperatures but almost similar emission measures in the cross-field direction. Furthermore, when we assume certain errors in the simulated loop emissions (e.g., due to photometric uncertainties in the TRACE filters) and use the triple-filter analysis, our simulated loop conditions become consistent with those of an isothermal plasma. This implies that the use of TRACE/EIT triple filters for observation of a warm coronal loop may not help in determining whether the cross-field isothermal assumption is satisfied or not.
- [19] arXiv:0911.3507 [pdf, other]
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Title: Correlation between technetium and lithium in a sample of oxygen-rich AGB variablesAuthors: Stefan Uttenthaler (Instituut voor Sterrenkunde, K. U. Leuven, Belgium), Thomas Lebzelter (Department of Astronomy, University of Vienna, Austria)Comments: 12 pages, 7 figures, accepted for publication in A&ASubjects: Solar and Stellar Astrophysics (astro-ph.SR)
The aims of this paper are: 1) to revisit the Tc content of a sample of oxygen-rich asymptotic giant branch (AGB) variables and 2) to increase the number of such stars for which the Li abundance has been measured to provide constraints on theoretical models of extra-mixing processes. To this end, we analysed high-resolution spectra of 18 sample stars for the presence of absorption lines of Tc and Li. The abundance of the latter was determined by comparing the observed spectra to hydrostatic MARCS model spectra. Bolometric magnitudes were established from near-IR photometry and pulsation periods. We reclassify the star V441 Cyg as Tc-rich, and the unusual Mira star R Hya, as well as W Eri, as Tc-poor. The abundance of Li, or an upper limit to it, was determined for all of the sample stars. In all stars with Tc we also detected Li. Most of them have a Li content slightly below the solar photospheric value, except for V441 Cyg, which has ~1000 times the solar abundance. We also found that, similar to Tc, a lower luminosity limit seems to exist for the presence of Li. We conclude that the higher Li abundance found in the cooler and higher luminosity objects could stem from a Li production mechanism operating on the AGB. The stellar mass might have a crucial influence on this (extra-mixing) production mechanism. It was speculated that the declining pulsation period of R Hya is caused by a recent thermal pulse (TP). While not detecting Tc does not rule out a TP, it indicates that the TPs are not strong enough to drive dredge-up in R Hya. V441 Cyg, on the other hand, could either be a low-mass, intrinsic S-star that produced its large amount of Li by extra-mixing processes, or an intermediate-mass star (M>=M_sun) undergoing Li production due to hot bottom burning.
- [20] arXiv:0911.3535 [pdf, other]
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Title: Tidal deformability of neutron stars with realistic equations of state and their gravitational wave signatures in binary inspiralComments: 12 pages, submitted to PRDSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
The early part of the gravitational wave signal of binary neutron star inspirals can potentially yield robust information on the nuclear equation of state. The influence of a star's internal structure on the waveform is characterized by a single parameter: the tidal deformability lambda, which measures the star's quadrupole deformation in response to the companion's perturbing tidal field. We calculate lambda for a wide range of equations of state and find that the value of lambda spans an order of magnitude for the range of equation of state models considered.
An analysis of the feasibility of discriminating between neutron star equations of state with gravitational wave observations of the early part of the inspiral reveals that the measurement error in lambda increases steeply with the total mass of the binary. Comparing the errors with the expected range of lambda, we find that Advanced LIGO observations of binaries at a distance of 100 Mpc will probe only unusually stiff equations of state, while the proposed Einstein Telescope is likely to see a clean tidal signature. - [21] arXiv:0911.3536 [ps, pdf, other]
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Title: The kinematic component of the cosmological redshiftAuthors: Michał Chodorowski (Copernicus Center)Comments: 7 pages, 1 figureSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
It is widely believed that the cosmological redshift is not a Doppler shift. However, Bunn & Hogg have recently pointed out that to settle properly this problem, one has to transport parallelly the velocity four-vector of a distant galaxy to the observer's position. Performing such a transport along the null geodesic of photons arriving from the galaxy, they found that the cosmological redshift is purely kinematic. Here we argue that one should rather transport the velocity four-vector along the geodesic connecting the points of intersection of the world-lines of the galaxy and the observer with the hypersurface of constant COSMIC TIME. We find that the resulting relation between the transported velocity and the redshift of arriving photons is NOT given by a relativistic Doppler formula. Instead, for small redshifts it coincides with the well known non-relativistic decomposition of the redshift into a Doppler (kinematic) component and a gravitational component. We perform such a decomposition for arbitrary large redshifts and derive a formula for the kinematic component of the cosmological redshift, valid for any FLRW cosmology. In particular, in a universe with Omega_m = 0.24 and Omega_Lambda = 0.76, a quasar at a redshift 6, at the time of emission of photons reaching us today had the recession velocity v = 0.997c. This can be contrasted with v = 0.96c, had the redshift been entirely kinematic. Thus, for recession velocities of such high-redshift sources, the effect of deceleration of the early Universe clearly prevails over the effect of its relatively recent acceleration.
- [22] arXiv:0911.3540 [ps, pdf, other]
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Title: Thermonuclear explosions of rapidly rotating white dwarfs - I. DeflagrationsComments: 13 pages, 10 figures, accepted for publication by A&ASubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
Context: Turbulent deflagrations of Chandrasekhar mass White Dwarfs are commonly used to model Type Ia Supernova explosions. In this context, rapid rotation of the progenitor star is plausible but has so far been neglected. Aims: The aim of this work is to explore the influence of rapid rotation on the deflagration scenario. Methods: We use three dimensional hydrodynamical simulations to model turbulent deflagrations ignited within a variety of rapidly rotating CO WDs obeying rotation laws suggested by accretion studies. Results: We find that rotation has a significant impact on the explosion. The flame develops a strong anisotropy with a preferred direction towards the stellar poles, leaving great amounts of unburnt matter along the equatorial plane. Conclusions: The large amount of unburnt matter is contrary to observed spectral features of SNe Ia. Thus, rapid rotation of the progenitor star and the deflagration scenario are incompatible in order to explain SNe Ia.
- [23] arXiv:0911.3545 [ps, pdf, other]
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Title: Thermonuclear explosions of rapidly rotating white dwarfs - II. DetonationsComments: 7 pages, 5 figures, accepted for publication by A&ASubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
Context: Superluminous type Ia supernovae (SNe Ia) may be explained by super-Chandrasekhar-mass explosions of rapidly rotating white dwarfs (WDs). In a preceding paper, we showed that the deflagration scenario applied to rapidly rotating WDs generates explosions that cannot explain the majority of SNe Ia. Aims: Rotation of the progenitor star allows super-Chandrasekhar-mass WDs to form that have a shallower density stratification. We use simple estimates of the production of intermediate and iron group elements in pure detonations of rapidly rotating WDs to assess their viability in explaining rare SNe Ia. Methods: We numerically construct WDs in hydrostatic equilibrium that rotate according to a variety of rotation laws. The explosion products are estimated by considering the density stratification and by evaluating the result of hydrodynamics simulations. Results: We show that a significant amount of intermediate mass elements is produced for theoretically motivated rotation laws, even for prompt detonations of WDs. Conclusions: Rapidly rotating WDs that detonate may provide an explanation of rare superluminous SNe Ia in terms of both burning species and explosion kinematics.
- [24] arXiv:0911.3546 [ps, pdf, other]
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Title: Soft X-ray emission from the inner disk of M33Comments: 13 pages, 4 figures, 5 tables. Accepted for publication in MNRASSubjects: Galaxy Astrophysics (astro-ph.GA)
We present a study, based on archival XMM-Newton observations, of the extended X-ray emission associated with the inner disk of M33. After the exclusion of point sources with L_X > 2 x 10^{35} erg/s (0.3-6 keV), we investigate the morphology and spectrum of the residual X-ray emission. This residual emission has a soft X-ray spectrum which can be fitted with a two-temperature thermal model, with kT = 0.2 keV and 0.6 keV. The soft X-ray surface brightness distribution shows a strong correlation with FUV emission, indicative of a close connection between recent star-formation activity and the production of soft X-rays. Within 3.5 kpc of the nucleus of M33, the soft X-ray and FUV surface brightness distributions exhibit similar radial profiles. This implies that the ratio of the soft X-ray luminosity (0.3-2.0 keV) to the star formation rate (SFR) per unit disk area remains fairly constant within this inner disk region. We derive a value for this ratio of 1-1.5 x 10^{39} (erg/s)/(M_sun/yr), consistent with previous studies. In the same region, the ratio of soft X-ray luminosity to stellar mass (derived from K-band photometry) is 4 x 10^{28} erg/s/M_sun, a factor of 5-10 higher than is typical of dwarf elliptical galaxies, suggesting that 10-20% of the unresolved emission seen in M33 may originate in its old stellar population. The remainder of the soft X-ray emission is equally split between two spatial components, one which closely traces the spiral arms of the galaxy and the other more smoothly distributed across the inner disk of M33. The former must represent a highly clumped low-filling factor component linked to sites of recent or ongoing star formation, whereas the distribution of the latter gives few clues as to its exact origin.
- [25] arXiv:0911.3550 [ps, pdf, other]
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Title: Non-Gaussianity constrains hybrid inflationComments: 26pp, 2 figsSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
In hybrid inflationary models, inflation ends by a sudden instability associated with a steep ridge in the potential. Here we argue that this feature can generate a large contribution to the curvature perturbation on observable scales. This contribution is almost scale-invariant but highly non-Gaussian. The degree of non-Gaussianity can exceed current observational bounds, unless the inflationary scale is extremely low or the hybrid potential contains very large coupling constants. Non-linear effects on small scales may quench the non-Gaussian signal, and while we find no compelling evidence that this occurs, full lattice simulations are required to definitively address this issue.
- [26] arXiv:0911.3552 [ps, pdf, other]
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Title: Projected Constraints on Modified Gravity Cosmologies from 21cm Intensity MappingComments: 9 pages, 5 figures, 1 table. To be submitted to Phys. Rev. DSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We present projected constraints on modified gravity models from the observational technique known as 21cm intensity mapping, where cosmic structure is detected without resolving individual galaxies. The resulting map is sensitive to both BAO and weak lensing, two of the most powerful cosmological probes. It is found that a 200m x 200m cylindrical telescope, sensitive out to z=2.5, would be able to distinguish DGP from most dark energy models, and constrain the Hu & Sawicki f(R) model to |f_{R0}| < 9x10^(-6) at 95% confidence. The latter constraint makes extensive use of the lensing spectrum in the nonlinear regime. These results show that 21cm intensity mapping is not only sensitive to modifications of the standard model's expansion history, but also to structure growth. This makes intensity mapping a powerful and economical technique, achievable on much shorter time scales than optical experiments that would probe the same era.
- [27] arXiv:0911.3566 [ps, pdf, other]
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Title: Variable precession of the neutron star in Her X-1Comments: 2 pages, 1 figureSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
We present evidence for an identical behavior of the precession of the accretion disk and that of the neutron star (NS) in Her X-1, based on investigating the well established 35 day modulation in Her X-1 in two different ways: 1) following the turn-ons, thought to be due to the precession of the accretion disk, and 2) following the re-appearance of the shape of the pulse profiles, which we assume to be due to precession of the NS. The turn-on evolution and the evolution of the phase-zero values of the precessing NS (as determined from the pulse profiles) track each other very closely. Since the turn-on evolution is strongly correlated with the pulse period evolution, this means that there is also a strong correlation between the spin and the precession of the NS. There is a very strong physical coupling between the NS and the accretion disk, we suggest through physical feedback in the binary system. The apparent long-term stability of the 35 d clock may be due to the interior of the NS, the coupling of which to the observable surface effects is of general importance for the physics of super-dense, highly magnetized material.
- [28] arXiv:0911.3576 [ps, pdf, other]
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Title: Ground Layer Adaptive Optics: PSF effects on ELT scalesComments: 5 pages, 5 figures, proceeding of "Instrumentation for Extremely Large Telescopes", a Workshop held at Ringberg Castle, Bavaria 25-29 July 2005Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
On certain extent the behavior of the Adaptive Optics correction for Extremely Large Telescope scales with diameter size. But in Ground Layer Adaptive Optics the combined effect of a Large Field of View and the large overlap of Guide Stars pupil footprints at high atmospheric altitude introduces severe changes in the behavior of the correction returning a very different distribution of the energy going from known 8-10meter to 100m diameters. In this paper we identify the reasons and the ways of these different behaviors.
- [29] arXiv:0911.3585 [ps, pdf, other]
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Title: Transit timing analysis of CoRoT-1bAuthors: Sz. Csizmadia, S. Renner, P. Barge, E. Agol, S. Aigrain, R. Alonso, J. M. Almenara, A. S. Bonomo, P. Borde, F. Bouchy, J. Cabrera, H. J. Deeg, R. De la Reza, M. Deleuil, R. Dvorak, A. Erikson, E. W. Guenther, M. Fridlund, P. Gondoin, T. Guillot, A. Hatzes, L. Jorda, H. Lammer, C. Lázaro, A. Leger, A. Llebaria, P. Magain, C. Moutou, M. Ollivier, M. Paetzold, D. Queloz, H. Rauer, D. Rouan, J. Schneider, G. Wuchterl, D. GandolfiComments: 6 pages, accepted at A&ASubjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
CoRoT, the pioneer space-based transit search, steadily provides thousands of high-precision light curves with continuous time sampling over periods of up to 5 months. The transits of a planet perturbed by an additional object are not strictly periodic. By studying the transit timing variations (TTVs), additional objects can be detected in the system.
A transit timing analysis of CoRoT-1b is carried out to constrain the existence of additional planets in the system.
We used data obtained by an improved version of the CoRoT data pipeline (version 2.0). Individual transits were fitted to determine the mid-transit times, and we analyzed the derived $O-C$ diagram. N-body integrations were used to place limits on secondary planets.
No periodic timing variations with a period shorter than the observational window (55 days) are found. The presence of an Earth-mass Trojan is not likely. A planet of mass greater than $\sim 1$ Earth mass can be ruled out by the present data if the object is in a 2:1 (exterior) mean motion resonance with CoRoT-1b. Considering initially circular orbits: (i) super-Earths (less than 10 Earth-masses) are excluded for periods less than about 3.5 days, (ii) Saturn-like planets can be ruled out for periods less than about 5 days, (iii) Jupiter-like planets should have a minimum orbital period of about 6.5 days. - [30] arXiv:0911.3587 [ps, pdf, other]
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Title: A Photometric Transit Search for Planets around Cool Stars from the Italian Alps: Results from a Feasibility StudyAuthors: M. Damasso, P. Calcidese, A. Bernagozzi, E. Bertolini, P. Giacobbe, M.G. Lattanzi, R. Smart, A. SozzettiComments: Two-page contribution to the International Conference "Pathways towards habitable planets" (included 2 eps figures, asp2006.sty, psfig.sty)Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
A feasibility study was carried out at the Astronomical Observatory of the Autonomous Region of the Aosta Valley demonstrating that it is a well-poised site to conduct an upcoming observing campaign aimed at detecting small-size (R<R_Neptune) transiting planets around nearby cool M dwarf stars. Three known transiting planet systems were monitored from May to August 2009 with a 25 cm f/3.8 Maksutov telescope. We reached seeing-independent, best-case photometric RMS less than 0.003 mag for stars with V<, with a median RMS of 0.006 mag for the whole observing period.
- [31] arXiv:0911.3588 [ps, pdf, other]
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Title: Rotation of young stars in Cepheus OB3bComments: accepted for publication in MNRASSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
We present a photometric study of I-band variability in the young association Cepheus OB3b. The study is sensitive to periodic variability on timescales of less than a day, to more than 20 days. After rejection of contaminating objects using V, I, R and narrowband H-alpha photometry, we find 475 objects with measured rotation periods, which are very likely pre-main-sequence members of the Cep OB3b star forming region.
We revise the distance and age to Cep OB3b, putting it on the self-consistent age and distance ladder of Mayne & Naylor (2008). This yields a distance modulus of 8.8 +/- 0.2 mags, corresponding to a distance of 580 +/- 60 pc, and an age of 4-5Myrs.
The rotation period distribution confirms the general picture of rotational evolution in young stars, exhibiting both the correlation between accretion (determined in this case through narrowband H-alpha photometry) and rotation expected from disc locking, and the dependence of rotation upon mass that is seen in other star forming regions. However, this mass dependence is much weaker in our data than found in other studies. Comparison to the similarly aged NGC 2362 shows that the low-mass stars in Cep OB3b are rotating much more slowly. This points to a possible link between star forming environment and rotation properties. Such a link would call into question models of stellar angular momentum evolution, which assume that the rotational period distributions of young clusters and associations can be assembled into an evolutionary sequence, thus ignoring environmental effects. - [32] arXiv:0911.3590 [pdf, other]
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Title: Kelvin-Helmholtz Instability of the Magnetopause of Disc-Accreting StarsComments: 8 pages, 7 figuresSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
This work investigates the short wavelength stability of the magnetopause between a rapidly-rotating, supersonic, dense accretion disc and a slowly-rotating low-density magnetosphere of a magnetized star. The magnetopause is a strong shear layer with rapid changes in the azimuthal velocity, the density, and the magnetic field over a short radial distance and thus the Kelvin-Helmholtz (KH) instability may be important. The plasma dynamics is treated using non-relativistic, compressible (isentropic) magnetohydrodynamics. It is necessary to include the displacement current in order that plasma wave velocities remain less than the speed of light. We focus mainly on the case of a star with an aligned dipole magnetic field so that the magnetic field is axial in the disc midplane and perpendicular to the disc flow velocity. However, we also give results for cases where the magnetic field is at an arbitrary angle to the flow velocity. For the aligned dipole case the magnetopause is most unstable for KH waves propagating in the azimuthal direction perpendicular to the magnetic field which tends to stabilize waves propagating parallel to it. The wave phase velocity is that of the disc matter. A quasi-linear theory of the saturation of the instability leads to a wavenumber ($k$) power spectrum $\propto k^{-1}$ of the density and temperature fluctuations of the magnetopause, and it gives the mass accretion and angular momentum inflow rates across the magnetopause. For self-consistent conditions this mass accretion rate will be equal to the disc accretion rate at large distances from the magnetopause.
- [33] arXiv:0911.3592 [ps, pdf, other]
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Title: Early Universe cosmology with mirror dark matterAuthors: Paolo CiarcellutiComments: 10 pages, 2 figures; contributed to "Invisible Universe International Conference", Paris, June 29 - July 3 2009; to be published in AIP proceedingsSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
Mirror matter is a stable self-collisional dark matter candidate. If exact mirror parity is a conserved symmetry of nature, there could exist a parallel hidden (mirror) sector of the Universe which has the same kind of particles and the same physical laws of our (visible) sector. The two sectors interact each other predominantly via gravity, therefore mirror matter is naturally "dark". Here I briefly review the cosmological signatures of mirror dark matter, as Big Bang nucleosynthesis, primordial structure formation and evolution, cosmic microwave background and large scale structure power spectra, together with its compatibility with the interpretation of the DAMA annual modulation signal in terms of photon--mirror-photon kinetic mixing. Summarizing the present status of research and comparing theoretical results with observations/experiments, it emerges that mirror matter is not just a viable, but a promising dark matter candidate.
- [34] arXiv:0911.3593 [ps, pdf, other]
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Title: The Submillimetre Properties of Ultraluminous Infrared GalaxiesComments: Accepted for publication in MNRASSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
We present the results of SCUBA observations of a complete sample of local ULIRGs. Twenty of the initial sample of 23 sources are detected at 850 um and nearly half of the objects are also detected at 450 um. This data is combined with existing observations of a further seven ULIRGs to produce the largest sample of submm observations of ULIRGs currently available. We use similar techniques to the SLUGS survey to fit dust spectral energy distributions (SEDs) to their far-IR emission. We find that ULIRGs have a higher dust temperature than lower luminosity objects (42K compared to 35K) and a steeper emissivity index. For those objects where 450 um fluxes are available we also attempt a two component dust SED fit, with warm and cool dust and a dust emissivity index of beta=2. Such a model has been found to be a good fit to lower luminosity systems. We find that it also works well for ULIRGs, but that ULIRGs have a smaller cold dust component. Comparison of the dust mass derived for ULIRGs and more normal spiral galaxies suggests that the dust content of a ULIRG is simply the combined dust content of the two galaxies whose merger has triggered the ULIRG activity. We examine the high end of the 850 um luminosity function and find results consistent with those of the earlier SLUGS survey. We also find that ULIRGs make up only about 50% of the high end of the 850 um luminosity function, with LIRGs containing a large mass of cool dust likely to be responsible for the rest.
- [35] arXiv:0911.3594 [ps, pdf, other]
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Title: A double radio halo in the close pair of galaxy clusters Abell 399 and Abell 401Comments: 6 pages, 4 figures, accepted for publication in A&ASubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Radio halos are faint radio sources usually located at the center of merging clusters of galaxies. These diffuse radio sources are rare, having so far been found only in about 30 clusters of galaxies, suggesting that particular conditions are needed to form and maintain them. It is interesting to investigate the presence of radio halos in close pairs of interacting clusters in order to possibly clarify their origin in relation to the evolutionary state of the merger. In this work, we study the case of the close pair of galaxy clusters A399 and A401. A401 is already known to contain a faint radio halo, while a hint of diffuse emission in A399 has been suggested based on the NVSS. To confirm this possibility, we analyzed deeper Very Large Array observations at 1.4 GHz of this cluster. We find that the central region of A399 is permeated by a diffuse low-surface brightness radio emission that we classify as a radio halo with a linear size of about 570 kpc and a central brightness of 0.3 micro-Jy/arcsec^2. Indeed, given their comparatively small projected distance of about 3 Mpc, the pair of galaxy clusters A401 and A399 can be considered as the first example of double radio halo system. The discovery of this double halo is extraordinary given the rarity of these radio sources in general and given that current X-ray data seem to suggest that the two clusters are still in a pre-merger state. Therefore, the origin of the double radio halo is likely to be attributed to the individual merging histories of each cluster separately, rather than to the result of a close encounter between the two systems.
- [36] arXiv:0911.3598 [ps, pdf, other]
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Title: The Stellar Population of the Thin DiskAuthors: Carlos Allende PrietoComments: 9 pages, 2 figures, to appear in the proceedings of the IAU Symp. 265 Chemical Abundances in the Universe: Connecting First Stars to Planet, K. Cunha, M. Spite and B. Barbuy, edsSubjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
We discuss recent observations of stars located close to the symmetry plane of the Milky Way, and examine them in the context of theories of Galaxy formation and evolution. The kinematics, ages, and compositions of thin disk stars in the solar neighborhood display complex patterns, and interesting correlations. The Galactic disk does not seem to pose any unsurmountable obstacles to hierarchical galaxy formation theories, but a model of the Milky Way able to reproduce the complexity found in the data will likely require a meticulous study of a significant fraction of the stars in the Galaxy. Making such an observational effort seems necessary in order to make a physics laboratory out of our own galaxy, and ultimately ensure that the most relevant processes are properly understood.
- [37] arXiv:0911.3642 [ps, pdf, other]
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Title: Suzaku broadband spectroscopy of Swift J1753.5-0127 in the Low-Hard StateComments: 12 pages, 7 figures, formatted using emulateapj.cls. Accepted for publication in ApJSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
We present Suzaku observations of the Galactic black hole candidate Swift J1753.5-0127 in the low-hard state. The broadband coverage of Suzaku enables us to detect the source over the energy range 0.6 -- 250 keV. The broadband spectrum (2 -- 250 keV) is found to be consistent with a simple power-law (gamma \sim 1.63). In agreement with previous observations of this system, a significant excess of soft X-ray flux is detected consistent with the presence of a cool accretion disc. Estimates of the disc inner radius infer a value consistent with the ISCO (R_{in} \lesssim 6 R_g, for certain values of, e.g. N_H, i), although we cannot conclusively rule out the presence of an accretion disc truncated at larger radii (R_{in} \sim 10 - 50 R_g). A weak, relativistically-broadened iron line is also detected, in addition to disc reflection at higher energy. However, the iron-K line profile favours an inner radius larger than the ISCO (R _{in} \sim 10 - 20 R_g). The implications of these observations for models of the accretion flow in the low-hard state are discussed.
Cross-lists for Thu, 19 Nov 09
- [38] arXiv:0710.0317 (cross-list from physics.comp-ph) [ps, pdf, other]
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Title: A General Strategy for Physics-Based Model Validation Illustrated with Earthquake Phenomenology, Atmospheric Radiative Transfer, and Computational Fluid DynamicsComments: 50 pages, 5 figures, be published in the Lecture Notes in Computational Science and Engineering, Vol. TBD), Proceedings of in Computational Methods in Transport, Granlibakken 2006, F. Graziani and D. Swesty (Eds.), Springer-Verlag, New York (NY), 2007Subjects: Computational Physics (physics.comp-ph); Earth and Planetary Astrophysics (astro-ph.EP); Materials Science (cond-mat.mtrl-sci); Atmospheric and Oceanic Physics (physics.ao-ph); Data Analysis, Statistics and Probability (physics.data-an); Fluid Dynamics (physics.flu-dyn); Geophysics (physics.geo-ph); Quantum Physics (quant-ph)
Validation is often defined as the process of determining the degree to which a model is an accurate representation of the real world from the perspective of its intended uses. Validation is crucial as industries and governments depend increasingly on predictions by computer models to justify their decisions. In this article, we survey the model validation literature and propose to formulate validation as an iterative construction process that mimics the process occurring implicitly in the minds of scientists. We thus offer a formal representation of the progressive build-up of trust in the model, and thereby replace incapacitating claims on the impossibility of validating a given model by an adaptive process of constructive approximation. This approach is better adapted to the fuzzy, coarse-grained nature of validation. Our procedure factors in the degree of redundancy versus novelty of the experiments used for validation as well as the degree to which the model predicts the observations. We illustrate the new methodology first with the maturation of Quantum Mechanics as the arguably best established physics theory and then with several concrete examples drawn from some of our primary scientific interests: a cellular automaton model for earthquakes, an anomalous diffusion model for solar radiation transport in the cloudy atmosphere, and a computational fluid dynamics code for the Richtmyer-Meshkov instability. This article is an augmented version of Sornette et al. [2007] that appeared in Proceedings of the National Academy of Sciences in 2007 (doi: 10.1073/pnas.0611677104), with an electronic supplement at URL this http URL Sornette et al. [2007] is also available in preprint form at physics/0511219.
- [39] arXiv:0911.1814 (cross-list from hep-th) [ps, pdf, other]
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Title: Stellar center is dynamical in Horava-Lifshitz gravityComments: 9 pagesSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
In Horava-Lifshitz gravity, regularity of a solution requires smoothness of not only the spacetime geometry but also the foliation. As a result, the regularity condition at the center of a star is more restrictive than in general relativity. Assuming that the energy density is a piecewise-continuous, non-negative function of the pressure and that the pressure at the center is positive, we prove that the momentum conservation law is incompatible with the regularity at the center for any spherically-symmetric, static configurations. The proof is totally insensitive to the structure of higher spatial curvature terms and, thus, holds for any values of the dynamical critical exponent $z$. Therefore, we conclude that a spherically-symmetric star should include a time-dependent region near the center. We also comment on the condition under which linear instability of the scalar graviton does not show up.
- [40] arXiv:0911.2727 (cross-list from hep-th) [ps, pdf, other]
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Title: Astrophysical implications of the Asymptotic Safety Scenario in Quantum GravityAuthors: Alfio BonannoComments: 28 pages, 6 figures. Invited talk at Workshop on Continuum and Lattice Approaches to Quantum Gravity. Sept. 2008, Brighton UK. To appear in the ProceedingsSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
In recent years it has emerged that the high energy behavior of gravity could be governed by an ultraviolet non-Gaussian fixed point of the (dimensionless) Newton's constant, whose behavior at high energy is thus {\it antiscreened}. This phenomenon has several astrophysical implications. In particular in this article recent works on renormalization group improved cosmologies based upon a renormalization group trajectory of Quantum Einstein Gravity with realistic parameter values will be reviewed. It will be argued that quantum effects can account for the entire entropy of the present Universe in the massless sector and give rise to a phase of inflationary expansion. Moreover the prediction for the final state of the black hole evaporation is a Planck size remnant which is formed in an infinite time.
- [41] arXiv:0911.2786 (cross-list from hep-th) [ps, pdf, other]
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Title: Enhancing non-Gaussianities by breaking local Lorentz invarianceAuthors: Hael CollinsComments: 10 pages, 1 figure; a talk presented at the Invisible Universe International Conference at the Palais de l'UNESCO, ParisSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
This talk briefly explains how the breaking of a Lorentz-invariant description of nature at tiny space-time intervals might affect the non-Gaussian character of the primordial fluctuations left by inflation. For example, a model that contains irrelevant operators that only preserve the spatial symmetries along constant-time surfaces can generate a larger non-Gaussian component in the pattern of primordial fluctuations than is ordinarily predicted by inflation. This property can be useful for constraining models that allow some Lorentz violation at short distances, beyond the constraints possible from the power spectrum alone.
- [42] arXiv:0911.3126 (cross-list from hep-th) [ps, pdf, other]
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Title: Relativistic diffusive transportAuthors: Z.HabaComments: 24 pagesSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)
We discuss transport equations resulting from relativistic diffusions in the proper time. We show that a solution of the transport equation can be obtained from the solution of the diffusion equation by means of an integration over the proper time. We study the stochastic processes solving the relativistic diffusion equation and the relativistic transport equation. We show that the relativistic transport equation for massive particles in the light cone coordinates and for massless particles in spatial momentum coordinates are related to the (generalized) Bessel diffusion which has an analytic solution. The solution describes a particle moving in a fixed direction whose frequency distribution is the Bessel process. An approach to an equilibrium in a moving frame is discussed. We formulate the equilibrating diffusion and transport processes in a Lorentz covariant way.
- [43] arXiv:0911.3165 (cross-list from hep-th) [ps, pdf, other]
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Title: Asymptotically Safe InflationAuthors: Steven WeinbergComments: 13 pagesSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
Inflation is studied in the context of asymptotically safe theories of gravitation. It is found to be possible under several circumstances to have a long period of nearly exponential expansion that eventually comes to an end.
- [44] arXiv:0911.3196 (cross-list from hep-th) [ps, pdf, other]
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Title: Fluctuations in a Hořava-Lifshitz Bouncing CosmologyComments: 19 pagesSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
Ho\v{r}ava-Lifshitz gravity is a potentially UV complete theory with important implications for the very early universe. In particular, in the presence of spatial curvature it is possible to obtain a non-singular bouncing cosmology. The bounce is realized as a consequence of higher order spatial curvature terms in the gravitational action. Here, we extend the study of linear cosmological perturbations in Ho\v{r}ava-Lifshitz gravity coupled to matter in the case when spatial curvature is present. As in the case without spatial curvature, we find that there is no extra dynamical degree of freedom for scalar metric perturbations. We study the evolution of fluctuations through the bounce and show that the solutions remain non-singular throughout. If we start with quantum vacuum fluctuations on sub-Hubble scales in the contracting phase, and if the contracting phase is dominated by pressure-less matter, then for $\lambda = 1$ and in the infrared limit the perturbations at late times are scale invariant. Thus, Ho\v{r}ava-Lifshitz gravity can provide a realization of the ``matter bounce'' scenario of structure formation.
- [45] arXiv:0911.3235 (cross-list from hep-ph) [ps, pdf, other]
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Title: Decaying Dark Matter in Supersymmetric SU(5) ModelsComments: 18 pages, 6 figures, LatexSubjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE)
Motivated by recent observations from Pamela, Fermi and H.E.S.S., we consider dark matter decays in the framework of supersymmetric SU(5) grand unification theories. An SU(5) singlet S is assumed to be the main component of dark matters, which decays into visible particles through dimension six operators suppressed by the grand unification scale. Under certain conditions, S decays dominantly into a pair of sleptons with universal coupling for all generations. Subsequently, electrons and positrons are produced from cascade decays of these sleptons. These cascade decay chains smooth the electron/positron spectrum, which permit naturally a good fit to the Fermi LAT data. The observed positron fraction upturn by PAMELA can be reproduced simultaneously. We have also calculated diffuse gamma-ray spectra due to the electron/positron excesses and compared them with the preliminary Fermi LAT data from 0.1 GeV to 10 GeV in the region 0<l <360, 10<|b|<20. The photon spectrum of energy above 100 GeV, mainly from final state radiations, may be checked in the near future.
- [46] arXiv:0911.3286 (cross-list from hep-th) [ps, pdf, other]
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Title: Holographic Cosmology from the First Law of Thermodynamics and the Generalized Uncertainty PrincipleAuthors: James E. LidseyComments: 4 pagesSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
The cosmological Friedmann equation sourced by the trace anomaly of a conformal field theory that is dual to the five-dimensional Schwarzschild-AdS geometry can be derived from the first law of thermodynamics if the apparent horizon of the boundary spacetime acquires a logarithmically-corrected Bekenstein-Hawking entropy. It is shown that such a correction to the entropy can arise when the generalized uncertainty principle (GUP) is invoked. The necessary condition for such a thermodynamic derivation directly relates the GUP parameter to the conformal anomaly. It is consistent with the existence of a gravitational cutoff for a theory containing $n$ light species. The absolute minimum in position uncertainty can be identified with the scale at which gravity becomes effectively five-dimensional.
- [47] arXiv:0911.3338 (cross-list from hep-ph) [ps, pdf, other]
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Title: Detecting light long-lived particle produced by cosmic rayComments: 7pages, 5figuresSubjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE)
We investigate the possibility of detecting light long-lived particle (LLP) produced by high energy cosmic ray colliding with atmosphere. The LLP may penetrate the atmosphere and decay into a pair of muons near/in the neutrino telescope. Such muons can be treated as the detectable signal for neutrino telescope. This study is motivated by recent cosmic electron/positron observations which suggest the existence of $O(TeV)$ dark matter and new light $O(GeV)$ particle. It indicates that dark sector may be complicated, and there may exist more than one light particles, for example the dark gauge boson $A'$ and associated dark Higgs boson $h'$. In this work, we discuss the scenario with $A'$ heavier than $h'$ and $h'$ is treated as LLP. Based on our numerical estimation, we find that the large volume neutrino telescope IceCube has the capacity to observe several tens of di-muon events for favorable parameters if the decay length of LLP can be comparable with the depth of atmosphere. The challenge here is how to suppress the muon backgrounds induced by cosmic rays and atmospheric neutrinos.
- [48] arXiv:0911.3363 (cross-list from gr-qc) [ps, pdf, other]
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Title: Spinning Black Holes as Particle AcceleratorsComments: 3 pagesSubjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
It has recently been pointed out that particles falling freely from rest at infinity outside a Kerr black hole can in principle collide with arbitrarily high center of mass energy in the limiting case of maximal black hole spin. Here we aim to elucidate the mechanism for this fascinating result, and to point out its practical limitations, which imply that ultra-energetic collisions cannot occur near black holes in nature.
Replacements for Thu, 19 Nov 09
- [49] arXiv:0902.4278 (replaced) [ps, pdf, other]
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Title: Sterile neutrinos produced near the EW scale I: mixing angles, MSW resonances and production ratesComments: 31 pagesSubjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [50] arXiv:0904.4725 (replaced) [ps, pdf, other]
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Title: Wavelength Accuracy of the Keck HIRES Spectrograph and Measuring Changes in the Fine Structure ConstantAuthors: Kim Griest, Jonathan B. Whitmore, Arthur M. Wolfe, J. Xavier Prochaska, J. Christopher Howk, Geoffrey W. MarcyComments: 19 pages, 10 figures, to appear in ApJ, Dec 2009 Many corrections and changes made, some new figuresSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)
- [51] arXiv:0905.1162 (replaced) [ps, pdf, other]
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Title: A new interpretation of the gamma-ray observations of active galactic nucleiComments: 11 pages, 2 figuresSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [52] arXiv:0906.3435 (replaced) [pdf, other]
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Title: From gas to satellitesimals: disk formation and evolutionComments: 23 pages, 6 figures, accepted for publication, to appear on Space Science Reviews and on Europlanet vol. on Icy SatellitesSubjects: Earth and Planetary Astrophysics (astro-ph.EP)
- [53] arXiv:0907.5199 (replaced) [ps, pdf, other]
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Title: Massive Galaxies in COSMOS: Evolution of Black hole versus bulge mass but not versus total stellar mass over the last 9 Gyrs?Authors: Knud Jahnke, Angela Bongiorno, Marcella Brusa, Peter Capak, Nico Cappelluti, Mauricio Cisternas, Francesca Civano, James Colbert, Andrea Comastri, Martin Elvis, Günther Hasinger, Chris Impey, Katherine Inskip, Anton M. Koekemoer, Simon Lilly, Christian Maier, Andrea Merloni, Dominik Riechers, Mara Salvato, Eva Schinnerer, Nick Z. Scoville, John Silverman, Yoshi Taniguchi, Jonathan R. Trump, Lin YanComments: Published in ApJL; 7 pages, 2 figures; updated to accepted version (methods changed, results unchanged)Journal-ref: Jahnke et al., 2009, ApJ, 706, L205Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [54] arXiv:0908.2400 (replaced) [ps, pdf, other]
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Title: Dynamics and Depletion in Thermally Supercritical Starless CoresComments: accepted for publication in MNRASSubjects: Galaxy Astrophysics (astro-ph.GA)
- [55] arXiv:0908.4123 (replaced) [ps, pdf, other]
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Title: Can ghost condensate decrease entropy?Authors: Shinji MukohyamaComments: 16 pages, paper invited to the open astronomy journal hot topic "Gravitational Alternative for Dark Energy and Inflation"; (v2) typo corrected, reference addedSubjects: High Energy Physics - Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
- [56] arXiv:0909.0486 (replaced) [pdf, other]
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Title: The massive star binary fraction in young open clusters - II. NGC 6611 (Eagle Nebula)Comments: Accepted by MNRAS; 15 pages, 17 figSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
- [57] arXiv:0909.0942 (replaced) [ps, pdf, other]
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Title: Practical tools for third order cosmological perturbationsComments: 17 pages, revtex4; v2: corresponds to version published in JCAPJournal-ref: JCAP 11 (2009) 012Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [58] arXiv:0909.1093 (replaced) [ps, pdf, other]
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Title: Bayesian reconstruction of gravitational wave burst signals from simulations of rotating stellar core collapse and bounceAuthors: Christian Röver, Marie-Anne Bizouard, Nelson Christensen, Harald Dimmelmeier, Ik Siong Heng, Renate MeyerComments: 17 pages, 9 figuresJournal-ref: Physical Review D, 80(10):102004, 2009Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)
- [59] arXiv:0909.3843 (replaced) [ps, pdf, other]
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Title: The discovery of a pulsar wind nebula around the magnetar candidate AXP 1E1547.0-5408Comments: Accepted by Astrophysical Journal Letters (4 pages, 3 figures, 2 tables). This new version has a longer introductory section and an improved discussion on dust scatteringSubjects: High Energy Astrophysical Phenomena (astro-ph.HE)
- [60] arXiv:0909.4302 (replaced) [ps, pdf, other]
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Title: Assembly bias and the dynamical structure of dark matter halosComments: 5 pages, 2 figures, accepted for publication in ApJSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [61] arXiv:0910.0687 (replaced) [ps, pdf, other]
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Title: High Energy Photons From Gamma Ray BurstsComments: Added material, references and 2 new figures. Submitted to ApJSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [62] arXiv:0910.1384 (replaced) [ps, pdf, other]
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Title: The Power Spectrum of Turbulence in NGC 1333: Outflows or Large-Scale Driving?Comments: Submitted to APJ Letters on September 22, 2009 - Accepted on November 18, 2009Subjects: Galaxy Astrophysics (astro-ph.GA)
- [63] arXiv:0910.1774 (replaced) [ps, pdf, other]
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Title: The mass ratio and formation mechanisms of Herbig Ae/Be star binary systemsComments: Accepted for publication in MNRAS, minor changes made in proof stageSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
- [64] arXiv:0910.4027 (replaced) [ps, pdf, other]
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Title: The CoRoT target HD 49933: 1- Role of the metal abundanceComments: corrected title & author list ; 8 pages, 4 figures, accepted for publication in Astronomy & Astrophysics. Updated references. Language improvementsSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
- [65] arXiv:0910.4037 (replaced) [ps, pdf, other]
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Title: The CoRoT target HD 49933: 2- Comparison of theoretical mode amplitudes with observationsAuthors: R. Samadi, H.-G. Ludwig, K. Belkacem, M.J. Goupil, O. Benomar, B. Mosser, M.-A. Dupret, F. Baudin, T. Appourchaux, E. MichelComments: 8 pages, 3 figures (B-W and color), accepted for publication in Astronomy & Astrophysics. Corrected typo in Eq. (4). Updated references. Language improvementsSubjects: Solar and Stellar Astrophysics (astro-ph.SR)
- [66] arXiv:0911.2927 (replaced) [ps, pdf, other]
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Title: Testing homogeneity with galaxy number counts : general low-redshift expansion for a central observer in a matter dominated isotropic universe without cosmological constantAuthors: Antonio Enea RomanoComments: 13 pagesSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
- [67] arXiv:0911.3247 (replaced) [pdf, other]
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Title: The formation of disks in massive spiral galaxiesComments: AIP Proceedings of a review given at the "Invisible Universe International Conference" held in Paris, June 2009. 16 pages, 9 FiguresSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
- [68] arXiv:0911.3320 (replaced) [ps, pdf, other]
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Title: Timescale of Mass Accretion in Pre-Main-Sequence StarsAuthors: D. Fedele (MPIA), M. E. van den Ancker (ESO), Th. Henning (MPIA), R. Jayawardhana (University of Toronto), J. M. Oliveira (Keele University)Comments: Accepted for publicationSubjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
- [69] arXiv:0911.3327 (replaced) [ps, pdf, other]
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Title: Simulating magnetic fields in the Antennae galaxiesComments: 13 pages, 10 figuresSubjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
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