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New submissions for Tue, 24 Nov 09

[1]  arXiv:0911.4120 [ps, pdf, other]

Title: Open vs closed boundaries in large-scale convective dynamos

Authors: P. J. Käpylä (1,2), M. J. Korpi (1,2), A. Brandenburg (2,3) ((1) University of Helsinki, (2) NORDITA, (3) University of Stockholm)

Comments: 9 pages, 7 figures, submitted to Astron. Astrophys

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Earlier work has suggested that large-scale dynamos can reach and maintain equipartition field strengths on a dynamical time scale only if magnetic helicity of the fluctuating field can be shed from the domain through open boundaries. To test this scenario in convection-driven dynamos by comparing results for open and closed boundary conditions. Three-dimensional numerical simulations of turbulent compressible convection with shear and rotation are used to study the effects of boundary conditions on the excitation and saturation level of large-scale dynamos. Open (vertical field) and closed (perfect conductor) boundary conditions are used for the magnetic field. The contours of shear are vertical, crossing the outer surface, and are thus ideally suited for driving a shear-induced magnetic helicity flux. We find that for given shear and rotation rate, the growth rate of the magnetic field is larger if open boundary conditions are used. The growth rate first increases for small magnetic Reynolds number, Rm, but then levels off at an approximately constant value for intermediate values of Rm. For large enough Rm, a small-scale dynamo is excited and the growth rate in this regime increases proportional to Rm^(1/2). In the nonlinear regime, the saturation level of the energy of the mean magnetic field is independent of Rm when open boundaries are used. In the case of perfect conductor boundaries, the saturation level first increases as a function of Rm, but then decreases proportional to Rm^(-1) for Rm > 30, indicative of catastrophic quenching. These results suggest that the shear-induced magnetic helicity flux is efficient in alleviating catastrophic quenching when open boundaries are used. The horizontally averaged mean field is still weakly decreasing as a function of Rm even for open boundaries.

[2]  arXiv:0911.4121 [ps, pdf, other]

Title: The ACS Nearby Galaxy Survey Treasury IV. The Star Formation History of NGC 2976

Authors: Benjamin F. Williams, Julianne J. Dalcanton, Adrienne Stilp, Karoline M. Gilbert, Rok Roskar, Anil C. Seth, Daniel Weisz, Andrew Dolphin, Stephanie M. Gogarten, Evan Skillman, Jon Holtzman

Comments: 22 pages, 14 figures, 2 tables, accepted for publication by ApJ

Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present resolved stellar photometry of NGC 2976 obtained with the Advanced Camera for Surveys (ACS) as part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. The data cover the radial extent of the major axis of the disk out to 6 kpc, or ~6 scale lengths. The outer disk was imaged to a depth of M_F606W ~ 1, and an inner field was imaged to the crowding limit at a depth of M_F606W ~ -1. Through detailed analysis and modeling of these CMDs we have reconstructed the star formation history of the stellar populations currently residing in these portions of the galaxy, finding similar ancient populations at all radii but significantly different young populations at increasing radii. In particular, outside of the well-measured break in the disk surface brightness profile, the age of the youngest population increases with distance from the galaxy center, suggesting that star formation is shutting down from the outside-in. We use our measured star formation history, along with H I surface density measurements, to reconstruct the surface density profile of the disk during previous epochs. Comparisons between the recovered star formation rates and reconstructed gas densities at previous epochs are consistent with star formation following the Schmidt law during the past 0.5 Gyrs, but with a drop in star formation efficiency at low gas densities, as seen in local galaxies at the present day. The current rate and gas density suggest that rapid star formation in NGC 2976 is currently in the process of ceasing from the outside-in due to gas depletion. This process of outer disk gas depletion and inner disk star formation was likely triggered by an interaction with the core of the M81 group >~1 Gyr ago that stripped the gas from the galaxy halo and/or triggered gas inflow from the outer disk toward the galaxy center.

[3]  arXiv:0911.4125 [pdf, other]

Title: MACSJ1423.8+2404: Gravitational Lensing by a Massive, Relaxed Cluster of Galaxies at z=0.54

Authors: M. Limousin, H. Ebeling, C.-J. Ma, A.M. Swinbank, G.P. Smith, J. Richard, A.C. Edge, M. Jauzac, J.-P. Kneib, P. Marshall, T. Schrabback, I.R. Smail

Comments: Submitted. High resolution available at this http URL

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present results of a gravitational-lensing and optical study of MACS ,J1423.8+2404 (z=0.545, MACS, J1423). Our analysis uses high-resolution images taken with the Hubble Space Telescope in the F555W and F814W passbands, ground based imaging in eight optical and near-infrared filters obtained with Subaru and CFHT, as well as extensive spectroscopic data gathered with the Keck telescopes. At optical wavelengths the cluster exhibits no sign of substructure and is dominated by a cD galaxy that is 2.1 magnitudes (K-band) brighter than the second brightest cluster member, suggesting that MACS, J1423 is close to be fully virialized. Analysis of the redshift distribution of 140 cluster members reveals a Gaussian distribution, mildly disturbed by the presence of a loose galaxy group that may be falling into the cluster along the line of sight. Combining strong-lensing constraints from two spectroscopically confirmed multiple-image systems near the cluster core with a weak-lensing measurement of the gravitational shear on larger scales, we derive a parametric mass model for the mass distribution. All constraints can be satisfied by a uni-modal mass distribution centred on the cD galaxy and exhibiting very little substructure. The derived projected mass of M(<65\arcsec [415 kpc])=(4.3\pm0.6)\times 10^{14} M_sun is about 30% higher than the one derived from X-ray analyses assuming spherical symmetry, suggesting a slightly prolate mass distribution consistent with the optical indication of residual line-of-sight structure. The similarity in shape and excellent alignment of the centroids of the total mass, K-band light, and intra-cluster gas distributions add to the picture of a highly evolved system [ABRIDGED]

[4]  arXiv:0911.4128 [ps, pdf, other]

Title: A new type of scalar field inflation

Authors: Cristiano Germani (LUTH, Observatoire de Paris), Alex Kehagias (NTUA, Athens)

Comments: 5 pages; Proceedings of 'Invisible Universe International Conference', Paris, June 29- July 3, 2009

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

In this short note we discuss the possibility of producing an inflationary background by considering a scalar field whose kinetic term is non-minimally coupled to gravity.

[5]  arXiv:0911.4129 [ps, pdf, other]

Title: Variations on Debris Disks II. Icy Planet Formation as a Function of the Bulk Properties and Initial Sizes of Planetesimals

Authors: Scott J Kenyon (SAO), Benjamin C. Bromley (Physics Dept., Univ. Utah)

Comments: 57 pages, 24 tables, and 34 figures; submitted to ApJS; comments welcome

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We describe comprehensive calculations of the formation of icy planets and debris disks at 30-150 AU around 1-3 solar mass stars. Disks composed of large, strong planetesimals produce more massive planets than disks composed of small, weak planetesimals. The maximum radius of icy planets ranges from roughly 1500 km to 11,500 km. The formation rate of 1000 km objects - `Plutos' - is a useful proxy for the efficiency of icy planet formation. Plutos form more efficiently in massive disks, in disks with small planetesimals, and in disks with a range of planetesimal sizes. Although Plutos form throughout massive disks, Pluto production is usually concentrated in the inner disk. Despite the large number of Plutos produced in many calculations, icy planet formation is inefficient. At the end of the main sequence lifetime of the central star, Plutos contain less than 10% of the initial mass in solid material. This conclusion is independent of the initial mass in the disk or the properties of planetesimals. Debris disk formation coincides with the formation of planetary systems containing Plutos. As Plutos form, they stir leftover planetesimals to large velocities. A cascade of collisions then grinds the leftovers to dust, forming an observable debris disk. In disks with small (< 1-10 km) planetesimals, collisional cascades produce luminous debris disks with maximum luminosity roughly 0.01 times the stellar luminosity. Disks with larger planetesimals produce much less luminous debris disks. Observations of debris disks around A-type and G-type stars strongly favor models with small planetesimals. In these models, our predictions for the time evolution and detection frequency of debris disks agree with published observations. We suggest several critical observations that can test key features of our calculations.

[6]  arXiv:0911.4131 [ps, pdf, other]

Title: On the Brightness and Waiting-time Distributions of a Type III Radio Storm observed by STEREO/WAVES

Authors: J. P. Eastwood, M. S. Wheatland, H. S. Hudson, S. Krucker, S. D. Bale, M. Maksimovic, K. Goetz, J.-L. Bougeret

Comments: 14 pages, 4 figures, 1 table. Accepted for publication in Astrophysical Journal Letters

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Type III solar radio storms, observed at frequencies below approximately 16 MHz by space borne radio experiments, correspond to the quasi-continuous, bursty emission of electron beams onto open field lines above active regions. The mechanisms by which a storm can persist in some cases for more than a solar rotation whilst exhibiting considerable radio activity are poorly understood. To address this issue, the statistical properties of a type III storm observed by the STEREO/WAVES radio experiment are presented, examining both the brightness distribution and (for the first time) the waiting-time distribution. Single power law behavior is observed in the number distribution as a function of brightness; the power law index is approximately 2.1 and is largely independent of frequency. The waiting-time distribution is found to be consistent with a piecewise-constant Poisson process. This indicates that during the storm individual type III bursts occur independently and suggests that the storm dynamics are consistent with avalanche type behavior in the underlying active region.

[7]  arXiv:0911.4134 [ps, pdf, other]

Title: The Comoving Infrared Luminosity Density: Domination of Cold Galaxies across 0<z<1

Authors: N. Seymour (1), M. Symeonidis (1), M.J. Page (1), M. Huynh (2), T. Dwelly (3), I.M. McHardy (3), G. Rieke (4) ((1) Mullard Space Science Laboratory, UCL, (2) Infrared Processing and Analysis Center, (3) University of Southampton, (4) Steward Observatory)

Comments: 5 pages, 3 figures, accepted for publication in MNRAS

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

In this paper we examine the contribution of galaxies with different infrared (IR) spectral energy distributions (SEDs) to the comoving infrared luminosity density, a proxy for the comoving star formation rate (SFR) density. We characterise galaxies as having either a cold or hot IR SED depending upon whether the rest-frame wavelength of their peak IR energy output is above or below 90um. Our work is based on a far-IR selected sample both in the local Universe and at high redshift, the former consisting of IRAS 60um-selected galaxies at z<0.07 and the latter of Spitzer 70um selected galaxies across 0.1<z<1. We find that the total IR luminosity densities for each redshift/luminosity bin agree well with results derived from other deep mid/far-IR surveys. At z<0.07 we observe the previously known results: that moderate luminosity galaxies (L_IR<10^11 Lsun) dominate the total luminosity density and that the fraction of cold galaxies decreases with increasing luminosity, becoming negligible at the highest luminosities. Conversely, above z=0.1 we find that luminous IR galaxies (L_IR>10^11 Lsun), the majority of which are cold, dominate the IR luminosity density. We therefore infer that cold galaxies dominate the IR luminosity density across the whole 0<z<1 range, hence appear to be the main driver behind the increase in SFR density up to z~1 whereas local luminous galaxies are not, on the whole, representative of the high redshift population.

[8]  arXiv:0911.4154 [ps, pdf, other]

Title: Dynamics, Origin, and Activation of Main Belt Comets

Authors: Nader Haghighipour

Comments: 9 pages, 4 figures, to appear in the proceedings of IAU Symposium 263: Icy Bodies of the Solar System (Eds. D. Lazzaro, D. Prialnik, o. Schulz and J.A. Fernandez), Cambridge Univ. Press

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The discovery of Main Belt Comets (MBCs) has raised many questions regarding the origin and activation mechanism of these objects. Results of a study of the dynamics of these bodies suggest that MBCs were formed in-situ as the remnants of the break-up of large icy asteroids. Simulations show that similar to the asteroids in the main belt, MBCs with orbital eccentricities smaller than 0.2 and inclinations lower than 25 degrees have stable orbits implying that many MBCs with initially larger eccentricities and inclinations might have been scattered to other regions of the asteroid belt. Among scattered MBCs, approximately 20 percent reach the region of terrestrial planets where they might have contributed to the accumulation of water on Earth. Simulations also show that collisions among MBCs and small objects could have played an important role in triggering the cometary activity of these bodies. Such collisions might have exposed sub-surface water ice which sublimated and created thin atmospheres and tails around MBCs. This paper discusses the results of numerical studies of the dynamics of MBCs and their implications for the origin of these objects. The results of a large numerical modeling of the collisions of m-sized bodies with km-sized asteroids in the outer part of the asteroid belt are also presented and the viability of the collision-triggering activation scenario is discussed.

[9]  arXiv:0911.4176 [ps, pdf, other]

Title: UHECR besides CenA: hints of galactic sources

Authors: Daniele Fargion

Comments: 3 pages, 6 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Ultra High Energy Cosmic Rays, UHECR, maybe protons, as most still believe and claim, or nuclei; in particular lightest nuclei as we advocated recently. The first (Auger Collaboration) nucleon proposal (2007)[2] foresaw to trace clearly the UHECR GZK Universe reaching far (up to 100 Mpc) Super-Galactic-Plane, with little angular dispersion. On the contrary Lightest Nuclei model (2008)[3], inspired by observed composition and by nearest CenA clustering (almost a quarter of the AUGER events) explains a modest and narrow (few Mpc) Universe view, as well as the puzzling Virgo absence: lightest nuclei offer a fragile (and therefore very nearby) blurred Astronomy. Here we address to a part of the remaining scattered events in the new up-dated Auger map (March 2009-ICRC09). We found within rarest clustering the surprising imprint of a few galactic sources, a partial component of UHECR sources. In particular we recognize a first trace of Vela, brightest gamma and radio galactic source, and smeared sources along Galactic Plane and Center. The clustering may imply additional tails of fragments (by nuclei photo-dissociation) at half energies. The UHECR light-nuclei fragility and opacity may also reflect into a train of secondaries as gamma and neutrinos UHE events at tens-hundred PeVs. These UHE neutrinos might be detectable in a coming future within nearest AUGER and Array Fluorescence Telescope views,(few km distances) by fast fluorescence flashing of horizontal up-going tau Air-showers.

[10]  arXiv:0911.4188 [ps, pdf, other]

Title: Very long-term X-ray variations in LMXBs: solar cycle-like variations in the donor?

Authors: M.M.Kotze, P.A.Charles

Comments: 5 pages, 3 tables, 3 figures. Accepted for publication in MNRAS

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

Long-term monitoring of Low Mass X-ray Binaries (LMXBs) by the All Sky Monitor on board the Rossi X-ray Timing Explorer now covers ~13 yrs and shows that certain LMXB types display very long-term (~several to tens of years) quasi-periodic modulations. These timescales are much longer than any "super-orbital" periods reported hitherto and likely have a different origin. We suggest here that they are due to long-term variations in the mass-transfer rate from the donor, which are a consequence of solar-like magnetic cycles that lead to orbital period changes (as proposed by Richman, Applegate & Patterson 1994 for similar long-term variations in CVs). Atoll sources display much larger amplitude modulations than Z sources over these timescales, presumably because Z sources are Eddington limited and hence unable to respond as readily as Atoll sources to fluctuations in the mass-transfer rate from the donor.

[11]  arXiv:0911.4189 [ps, pdf, other]

Title: Klein-Nishina effects on the high-energy afterglow emission of gamma-ray bursts

Authors: Xiang-Yu Wang (NJU), Hao-Ning He (NJU), Zhuo Li (PKU), Xue-Feng Wu (PSU, PMO), Zi-Gao Dai (NJU)

Comments: 8 page (emulateapj style), 8 figures, submitted to ApJ

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Extended high-energy(>100MeV) gamma-ray emission that lasts much longer than the prompt sub-MeV emission has been detected from quite a few gamma-ray bursts (GRBs) by Fermi Large Area Telescope (LAT) recently. A plausible scenario is that this emission is the afterglow synchrotron emission produced by electrons accelerated in the forward shocks. In this scenario, the electrons that produce synchrotron high-energy emission also undergo inverse-Compton (IC) loss and the IC scattering with the synchrotron photons should be in the Klein-Nishina regime. Here we study effects of the Klein-Nishina scattering on the high-energy synchrotron afterglow emission. We find that, at early times the Klein-Nishina suppression effect on those electrons that produce the high-energy emission is usually strong and therefore their inverse-Compton loss is small with a Compton parameter Y < a few for a wide range of parameter space. This leads to a relatively bright synchrotron afterglow at high energies that can be detected by Fermi LAT. As the Klein-Nishina suppression effect weakens with time, the inverse-Compton loss increases and could dominate over the synchrotron loss in some parameter space. This will lead to a faster temporal decay of the high-energy synchrotron emission than what is predicted by the standard synchrotron model, which may explain the observed rapid decay of the early high-energy gamma-ray emission in GRB090510 and GRB090902B.

[12]  arXiv:0911.4195 [ps, pdf, other]

Title: Are Newly Discovered HI High Velocity Clouds Minihalos in the Local Group?

Authors: Riccardo Giovanelli (1), Martha P. Haynes (1), Brian R. Kent (2), Elizabeth K. Adams (1) (1 Cornell University, 2 National Radio Astronomy Observatory)

Comments: 4 pages, 3 figures, 1 table; to appear Ap.J. Letters

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

A set of HI sources extracted from the north Galactic polar region by the ongoing ALFALFA survey has properties that are consistent with the interpretation that they are associated with isolated minihalos in the outskirts of the Local Group (LG). Unlike objects detected by previous surveys, such as the Compact High Velocity Clouds of Braun & Burton (1999), the HI clouds found by ALFALFA do not violate any structural requirements or halo scaling laws of the LambdaCDM structure paradigm, nor would they have been detected by extant HI surveys of nearby galaxy groups other than the LG. At a distance of d Mpc, their HI masses range between $5 x 10^4 d^2 and 10^6 d^2 solar and their HI radii between <0.4d and 1.6 d kpc. If they are parts of gravitationally bound halos, the total masses would be on order of 10^8--10^9 solar, their baryonic content would be signifcantly smaller than the cosmic fraction of 0.16 and present in a ionized gas phase of mass well exceeding that of the neutral phase. This study does not however prove that the minihalo interpretation is unique. Among possible alternatives would be that the clouds are shreds of the Leading Arm of the Magellanic Stream.

[13]  arXiv:0911.4198 [pdf]

Title: Enhanced lithium depletion in Sun-like stars with orbiting planets

Authors: Garik Israelian, Elisa Delgado Mena, Nuno Santos, Sergio Sousa, Michel Mayor, Stephane Udry, Carolina Dominguez Cerdeña, Rafael Rebolo, Sofia Randich

Comments: 13 pages, 2 figures

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The surface abundance of lithium on the Sun is 140 times less than protosolar, yet the temperature at the base of the surface convective zone is not hot enough to burn Li. A large range of Li abundances in solar type stars of the same age, mass and metallicity is observed, but theoretically difficult to understand. An earlier suggestion that Li is more depleted in stars with planets was weakened by the lack of a proper comparison sample of stars without detected planets. Here we report Li abundances for an unbiased sample of solar-analogue stars with and without detected planets. We find that the planet-bearing stars have less than 1 per cent of the primordial Li abundance, while about 50 per cent of the solar analogues without detected planets have on average 10 times more Li. The presence of planets may increase the amount of mixing and deepen the convective zone to such an extent that the Li can be burned.

[14]  arXiv:0911.4217 [ps, pdf, other]

Title: High-energy gamma-ray afterglows from low-luminosity gamma-ray bursts

Authors: Hao-Ning He (NJU), Xiang-Yu Wang (NJU), Yun-Wei Yu (NJU, HNU), Peter Meszaros (PSU)

Comments: Published in ApJ, 29 pages (aastex style), 6 figures

Journal-ref: The Astrophysical Journal, 706:1152-1162, 2009

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The observations of gamma-ray bursts (GRBs) such as 980425, 031203 and 060218, with luminosities much lower than those of other classic bursts, lead to the definition of a new class of GRBs -- low-luminosity GRBs. The nature of the outflow responsible for them is not clear yet. Two scenarios have been suggested: one is the conventional relativistic outflow with initial Lorentz factor of order of $\Gamma_0\ga 10$ and the other is a trans-relativistic outflow with $\Gamma_0\simeq 1-2$. Here we compare the high energy gamma-ray afterglow emission from these two different models, taking into account both synchrotron self inverse-Compton scattering (SSC) and the external inverse-Compton scattering due to photons from the cooling supernova or hypernova envelope (SNIC). We find that the conventional relativistic outflow model predicts a relatively high gamma-ray flux from SSC at early times ($<10^4 {\rm s}$ for typical parameters) with a rapidly decaying light curve, while in the trans-relativistic outflow model, one would expect a much flatter light curve of high-energy gamma-ray emission at early times, which could be dominated by both the SSC emission and SNIC emission, depending on the properties of the underlying supernova and the shock parameter $\epsilon_e$ and $\epsilon_B$. The Fermi Gamma-ray Space Telescope should be able to distinguish between the two models in the future.

[15]  arXiv:0911.4220 [ps, pdf, other]

Title: Comparing Hbeta Line Profiles in the 4D Eigenvector 1 Context

Authors: J. W. Sulentic (1), P. Marziani (2), S. Zamfir (3) ((1) Instituto de Astrofisica de Andalucia, Granada, Spain; (2) INAF, Osservatorio Astronomico di Padova, Italy; (3) University of Alabama, Tuscaloosa)

Comments: 11 pages, 4 figures

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We describe a 4D Eigenvector 1 (4DE1) space that serves as a surrogate H-R diagram for quasars. It provides a context for describing and unifying differences between all broad line AGN. Quasar spectra can be averaged in a non-random way using 4DE1 just as stellar spectra can be averaged non-randomly within the OBAFGKM classification sequence. We find that quasars with FWHM H_beta less than (Population A) and greater than (Population B) 4000 km/s show many significant differences that may point to an actual dichotomy. Broad line profile measures and fits reenforce the idea of a dichotomy because they are fundamentally different: Pop.A - Lorentzian-like and Pop.B - double Gaussian. The differences have implications both for BH mass estimation and for inferences about source structure and kinematics.

[16]  arXiv:0911.4233 [ps, pdf, other]

Title: Beginning of the Super-Soft Phase of the Classical Nova V2491 Cygni

Authors: D. Takei, J.-U. Ness

Comments: Accepted for publication in Astronomische Nachrichten (4 pages, 2 figures)

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present the results of soft X-ray studies of the classical nova V2491 Cygni using the Suzaku observatory. On day 29 after outburst, a soft X-ray component with a peak at $\sim$0.5 keV has appeared, which is tantalising evidence for the beginning of the super-soft X-ray emission phase. We show that an absorbed blackbody model can describe the observed spectra, yielding a temperature of 57 eV, neutral hydrogen column density of 2$\times10^{21}$ cm$^{-2}$, and a bolometric luminosity of $\sim10^{36}$ erg s$^{-1}$. However, at the same time, we also found a good fit with an absorbed thin-thermal plasma model, yielding a temperature of 0.1 keV, neutral hydrogen column density of 4$\times10^{21}$ cm$^{-2}$, and a volume emission measure of $\sim10^{58}$ cm$^{-3}$. Owing to low spectral resolution and low signal-to-noise ratio below 0.6 keV, the statistical parameter uncertainties are large, but the ambiguity of the two very different models demonstrates that the systematic errors are the main point of concern. The thin-thermal plasma model implies that the soft emission originates from optically thin ejecta, while the blackbody model suggests that we are seeing optically thick emission from the white dwarf.

[17]  arXiv:0911.4246 [ps, pdf, other]

Title: The WiggleZ Dark Energy Survey: Survey Design and First Data Release

Authors: Michael J. Drinkwater, Russell J. Jurek, Chris Blake, David Woods, Kevin A. Pimbblet, Karl Glazebrook, Rob Sharp, Michael B. Pracy, Sarah Brough, Matthew Colless, Warrick J. Couch, Scott M. Croom, Tamara M. Davis, Duncan Forbes, Karl Forster, David G. Gilbank, Michael Gladders, Ben Jelliffe, Nick Jones, I-hui Li, Barry Madore, D. Christopher Martin, Gregory B. Poole, Todd Small, Emily Wisnioski, Ted Wyder, H.K.C. Yee

Comments: Accepted by MNRAS; this has some figures in low resolution format. Full resolution PDF version (7MB) available at this http URL

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

The WiggleZ Dark Energy Survey is a survey of 240,000 emission line galaxies in the distant universe, measured with the AAOmega spectrograph on the 3.9-m Anglo-Australian Telescope (AAT). The target galaxies are selected using ultraviolet photometry from the GALEX satellite, with a flux limit of NUV<22.8 mag. The redshift range containing 90% of the galaxies is 0.2<z<1.0. The primary aim of the survey is to precisely measure the scale of baryon acoustic oscillations (BAO) imprinted on the spatial distribution of these galaxies at look-back times of 4-8 Gyrs. Detailed forecasts indicate the survey will measure the BAO scale to better than 2% and the tangential and radial acoustic wave scales to approximately 3% and 5%, respectively.
This paper provides a detailed description of the survey and its design, as well as the spectroscopic observations, data reduction, and redshift measurement techniques employed. It also presents an analysis of the properties of the target galaxies, including emission line diagnostics which show that they are mostly extreme starburst galaxies, and Hubble Space Telescope images, which show they contain a high fraction of interacting or distorted systems. In conjunction with this paper, we make a public data release of data for the first 100,000 galaxies measured for the project.

[18]  arXiv:0911.4248 [ps, pdf, other]

Title: Solar abundances and 3D model atmospheres

Authors: H.-G. Ludwig, E. Caffau, M. Steffen, P. Bonifacio, B. Freytag, R. Cayrel

Comments: Contributed paper, to be published in the proceedings of IAU Symposium 265, eds. K. Cunha, M. Spite, and B. Barbuy, Cambridge University Press (CUP). 2 figures, 4 pages

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present solar photospheric abundances for 12 elements from optical and near-infrared spectroscopy. The abundance analysis was conducted employing 3D hydrodynamical (CO5BOLD) as well as standard 1D hydrostatic model atmospheres. We compare our results to others with emphasis on discrepancies and still lingering problems, in particular exemplified by the pivotal abundance of oxygen. We argue that the thermal structure of the lower solar photosphere is very well represented by our 3D model. We obtain an excellent match of the observed center-to-limb variation of the line-blanketed continuum intensity, also at wavelengths shortward of the Balmer jump.

[19]  arXiv:0911.4251 [ps, pdf, other]

Title: Accuracy of spectroscopy-based radioactive dating of stars

Authors: H.-G. Ludwig, E. Caffau, M. Steffen, P. Bonifacio, L. Sbordone

Comments: Accepted for publication in A&amp;A

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Combined spectroscopic abundance analyses of stable and radioactive elements can be applied for deriving stellar ages. The achievable precision depends on factors related to spectroscopy, nucleosynthesis, and chemical evolution. We quantify the uncertainties arising from the spectroscopic analysis, and compare these to the other error sources. We derive formulae for the age uncertainties arising from the spectroscopic abundance analysis, and apply them to spectroscopic and nucleosynthetic data compiled from the literature for the Sun and metal-poor stars. We obtained ready-to-use analytic formulae of the age uncertainty for the cases of stable+unstable and unstable+unstable chronometer pairs, and discuss the optimal relation between to-be-measured age and mean lifetime of a radioactive species. Application to the literature data indicates that, for a single star, the achievable spectroscopic accuracy is limited to about +/- 20% for the foreseeable future. At present, theoretical uncertainties in nucleosynthesis and chemical evolution models form the precision bottleneck. For stellar clusters, isochrone fitting provides a higher accuracy than radioactive dating, but radioactive dating becomes competitive when applied to many cluster members simultaneously, reducing the statistical errors by a factor sqrt(N). Spectroscopy-based radioactive stellar dating would benefit from improvements in the theoretical understanding of nucleosynthesis and chemical evolution. Its application to clusters can provide strong constraints for nucleosynthetic models.

[20]  arXiv:0911.4252 [ps, pdf, other]

Title: Fermi Observations of the Very Hard Gamma-ray Blazar PG 1553+113

Authors: The Fermi-LAT Collaboration

Comments: Accepted for publication in the Astrophysical Journal (28 pages, 5 figures)

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report the observations of PG 1553+113 during the first ~200 days of Fermi Gamma-ray Space Telescope science operations, from 4 August 2008 to 22 February 2009 (MJD 54682.7-54884.2). This is the first detailed study of PG 1553+113 in the GeV gamma-ray regime and it allows us to fill a gap of three decades in energy in its spectral energy distribution. We find PG 1553+113 to be a steady source with a hard spectrum that is best fit by a simple power-law in the Fermi energy band. We combine the Fermi data with archival radio, optical, X-ray and very high energy (VHE) gamma-ray data to model its broadband spectral energy distribution and find that a simple, one-zone synchrotron self-Compton model provides a reasonable fit. PG 1553+113 has the softest VHE spectrum of all sources detected in that regime and, out of those with significant detections across the Fermi energy bandpass so far, the hardest spectrum in that energy regime. Thus, it has the largest spectral break of any gamma-ray source studied to date, which could be due to the absorption of the intrinsic gamma-ray spectrum by the extragalactic background light (EBL). Assuming this to be the case, we selected a model with a low level of EBL and used it to absorb the power-law spectrum from PG 1553+113 measured with Fermi (200 MeV - 157 GeV) to find the redshift which gave the best fit to the measured VHE data (90 GeV - 1.1 TeV) for this parameterisation of the EBL. We show that this redshift can be considered an upper limit on the distance to PG 1553+113.

[21]  arXiv:0911.4255 [pdf, other]

Title: Benchmark ultra-cool dwarfs in widely separated binary systems

Authors: Z.H. Zhang, D. J. Pinfield, A. C. Day-Jones, B. Burningham, H. R. A. Jones

Comments: 4 pages, 3 figures, conference, "New Technologies for Probing the Diversity of Brown Dwarfs and Exoplanets"

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)

Ultra-cool dwarfs as wide companions to subgiants, giants, white dwarfs and main sequence stars can be very good benchmark objects, for which we can infer physical properties with minimal reference to theoretical models, through association with the primary stars. We have searched for benchmark ultra-cool dwarfs in widely separated binary systems using SDSS, UKIDSS, and 2MASS. We then estimate spectral types using SDSS spectroscopy and multi-band colors, place constraints on distance, and perform proper motions calculations for all candidates which have sufficient epoch baseline coverage. Analysis of the proper motion and distance constraints show that eight of our ultra-cool dwarfs are members of widely separated binary systems. Another L3.5 dwarf, SDSS 0832, is shown to be a companion to the bright K3 giant Eta Cancri. Such primaries can provide age and metallicity constraints for any companion objects, yielding excellent benchmark objects. This is the first wide ultra-cool dwarf + giant binary system identified.

[22]  arXiv:0911.4273 [ps, pdf, other]

Title: Redundant failures of the dip model of the extragalactic cosmic radiation

Authors: Antonio Codino

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The proton flux and the chemical composition of the cosmic radiation measured, respectively, by the Kascade and Auger experiments entail radical changes in Cosmic Ray Physics. A large discrepancy emerges by comparing the proton flux predicted by the dip model and that measured by Kascade in the critical energy interval 5 x 10 ** 16 - 10 ** 17 eV. It is mentioned and substantiated that the proton flux measurements of the Kascade experiment are consistent with other pertinent empirical observations. It is shown that the chemical composition measured by Auger by two independent procedures, using the mean depth reached by cosmic nuclei in giant air cascades, is incompatible with that predicted by the dip model. A notable consequence suggested here based on the failures of the dip model is that the spectral index softening of the primary cosmic radiation above 6 x 10 ** 19 eV observed by HiRes and Auger experiments, is not due to the extragalactic cosmological protons suffering energy losses in the intergalactic space via the reactions, p gamma -> pi0 p, pi+ n, but to some physical phenomena occurring in the cosmic vicinity.

[23]  arXiv:0911.4276 [ps, pdf, other]

Title: The first year of the Fermi Large Area Telescope: a new light on the high-energy Universe

Authors: Luigi Tibaldo, for the Fermi/LAT collaboration

Comments: Contribution to the 2009 Europhysics Conference on High Energy Physics (Krakow, Poland); 6 pages, 4 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

For almost one year the Large Area Telescope on board the Fermi observatory has been surveying high-energy phenomena in our Universe. We will present an overview of the status of the mission and of some results from the first year of observations, focusing on the topics of particular interest for the high-energy Physics community: detection of high-energy gamma-ray bursts, the discovery of new populations of gamma-ray sources, non-confirmation of the excess of diffuse GeV gamma-ray emission seen by EGRET and, in greater detail, the recent measurement of the cosmic-ray electron spectrum from 20 GeV to 1 TeV.

[24]  arXiv:0911.4287 [ps, pdf, other]

Title: Spectral analysis of YSOs and other emission-line stars in the North America and Pelican nebulae region

Authors: C. J. Corbally, V. Straizys, V. Laugalys

Comments: 29 pages, 6 figures

Journal-ref: Baltic Astronomy, Vol.18, No.2, pages 111-139, 2009

Subjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

Far red spectra for 34 stars with V magnitudes between 15 and 18 in the direction of the North America and Pelican nebulae (NAP) star-forming region are obtained. Some of these stars were known earlier as emission-line objects, others were suspected as pre-main-sequence stars from photometry in the J, H, Ks and Vilnius systems. We confirm the presence of the H alpha line emission in the spectra of 19 stars, some of them exhibit also emission in the O I and Ca II lines. In some of the stars the H alpha absorption line is filled with emission. To estimate their evolutionary status, the spectral energy distributions, based on Vilnius, 2MASS, MSX and Spitzer photometry, are applied. Only eight emission-line stars are found to be located at a distance of the NAP complex. Others are either chromospherically active stars in front of the complex or distant luminous stars with H alpha absorption and emission components. For five stars with faint emission the data are not sufficient to estimate their distance. One star is found to be a heavily reddened K-supergiant located in the Outer arm. The stars, for which we failed to confirm the emission in H alpha, are mostly red dwarfs located in front of the NAP complex, two of them could be binaries with L-type components. Taking into account the stars suspected to be YSOs by their 2MASS colors we conclude that the NAP complex can possess a considerable population of young stars hidden behind the dust cloud.

[25]  arXiv:0911.4295 [ps, pdf, other]

Title: Travel Time Shifts due to Amplitude Modulation in Time-Distance Helioseismology

Authors: R. Nigam, A. G. Kosovichev

Comments: 17 pages, 1 figure, accepted for publication in ApJ

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Correct interpretation of acoustic travel times measured by time-distance helioseismology is essential to get an accurate understanding of the solar properties that are inferred from them. It has long been observed that sunspots suppress p-mode amplitude, but its implications on travel times has not been fully investigated so far. It has been found in test measurements using a 'masking' procedure, in which the solar Doppler signal in a localized quiet region of the Sun is artificially suppressed by a spatial function, and using numerical simulations that the amplitude modulations in combination with the phase-speed filtering may cause systematic shifts of acoustic travel times. To understand the properties of this procedure, we derive an analytical expression for the cross-covariance of a signal that has been modulated locally by a spatial function that has azimuthal symmetry, and then filtered by a phase speed filter typically used in time-distance helioseismology. Comparing this expression to the Gabor wavelet fitting formula without this effect, we find that there is a shift in the travel times, that is introduced by the amplitude modulation. The analytical model presented in this paper can be useful also for interpretation of travel time measurements for non-uniform distribution of oscillation amplitude due to observational effects.

[26]  arXiv:0911.4297 [ps, pdf, other]

Title: Environment of MAMBO galaxies in the COSMOS field

Authors: Manuel Aravena, Frank Bertoldi, Chris L. Carilli, Eva Schinnerer, Henry J. McCracken, Mara Salvato, Dominik Riechers, Kartik Sheth, Vernesa Smolcic, Peter Capak, Anton Koekemoer, Karl M. Menten

Comments: Accepted for publication in ApJ Letters

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Submillimeter galaxies (SMG) represent a dust-obscured high-redshift population undergoing massive star formation activity. Their properties and space density have suggested that they may evolve into spheroidal galaxies residing in galaxy clusters. In this paper, we report the discovery of compact (~10"-20") galaxy overdensities centered at the position of three SMGs detected with the Max-Planck Millimeter Bolometer camera (MAMBO) in the COSMOS field. These associations are statistically significant. The photometric redshifts of galaxies in these structures are consistent with their associated SMGs; all of them are between z=1.4-2.5, implying projected physical sizes of ~170 kpc for the overdensities. Our results suggest that about 30% of the radio-identified bright SMGs in that redshift range form in galaxy density peaks in the crucial epoch when most stars formed.

[27]  arXiv:0911.4319 [ps, pdf, other]

Title: GALEX Ultraviolet Imaging of Dwarf Galaxies and Star Formation

Authors: Deidre A. Hunter (1), Bruce G. Elmegreen (2), Bonnie C. Ludka (1,3) ((1) Lowell Observatory (2) IBM T. J. Watson Research Center, (3) Scripps Institution of Oceanography)

Comments: 28 pages, 22 figures, 7 tables, to be published in Astronomical Journal

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

We present ultraviolet integrated and azimuthally-averaged surface photometric properties of a sample of 44 dIm, BCD, and Sm galaxies measured from archival NUV and FUV images obtained with GALEX. We compare the UV to Halpha and V-band properties and convert FUV, Halpha, and V-band luminosities into star formation rates (SFRs). We also model the star formation history from colors and compare the integrated SFRs and SFR profiles with radius for these methods. In most galaxies, the UV photometry extends beyond Halpha in radius, providing a better measure of the star formation activity in the outer disks. The Halpha appears to be lacking in the outer disk because of faintness in low density gas. The FUV and V-band profiles are continuous with radius, although they sometimes have a kink from a double exponential disk. There is no obvious difference in star formation properties between the inner and outer disks. No disk edges have been observed, even to stellar surface densities as low as 0.1 Msun/pc2 and star formation rates as low as 10^{-4} Msun/yr/kpc2. Galaxies with low HI to luminosity ratios have relatively low FUV compared to V-band emission in the outer parts, suggesting a cessation of star formation there. Galaxies with relatively high HI apparently have fluctuating star formation with a Gyr timescale.

[28]  arXiv:0911.4333 [ps, pdf, other]

Title: A search for VHE counterparts of Galactic Fermi bright sources and GeV to TeV spectral characterization

Authors: P.H. Thomas Tam, Stefan Wagner, Omar Tibolla, Ryan Chaves

Comments: 18 pages, 12 figures, 5 tables

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

Very high-energy (VHE; E>100 GeV) gamma-rays have been detected from a wide range of astronomical objects, such as SNRs, pulsars and pulsar wind nebulae, active galactic nuclei, gamma-ray binaries, molecular clouds, and possibly star-forming regions as well. At lower energies, sources detected using the Large Area Telescope (LAT) aboard Fermi provide a rich set of data which can be used to study the behaviour of cosmic accelerators in the GeV to TeV energy bands. In particular, the improved angular resolution in both bands compared to previous instruments significantly reduces source confusion and facilitates the identification of associated counterparts at lower energies. In this paper, a comprehensive search for VHE gamma-ray sources which are spatially coincident with Galactic Fermi/LAT bright sources is performed, and the available GeV to TeV spectra of coincident sources are compared. It is found that bright LAT GeV sources are correlated to TeV sources, in contrast to previous studies using EGRET data. Moreover, a single spectral component seems unable to describe the MeV to TeV spectra of some coincident GeV/TeV sources. It is suggested that gamma-ray pulsars are accompanied by VHE gamma-ray emitting nebulae, a notion that can be tested by VHE observations of these pulsars.

[29]  arXiv:0911.4339 [ps, pdf, other]

Title: A delta Scuti star in the post-MS contraction phase: 44 Tauri

Authors: P. Lenz, A. A. Pamyatnykh, T. Zdravkov, M. Breger

Comments: 8 pages, 7 figures, 3 tables, accepted for publication in A&amp;A

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The evolutionary stage of the delta Scuti star 44 Tau has been unclear. Recent asteroseismic studies have claimed models on the main sequence, as well as in the expansion phase of the post-main sequence evolution. However, these models could not reproduce all of the observed frequencies, the mode instability range, and the fundamental stellar parameters simultaneously. A recent photometric study has increased the number of detected independent modes in 44 Tau to 15, and a newly found gravity mode at 5.30 c/d extends the observed frequency range.
Aims. One of the possible evolutionary stages of 44 Tau has not yet been considered: the overall contraction phase after the main sequence. We computed asteroseismic models to examine whether models in this evolutionary stage provide a better fit of the observed frequency spectrum.
Methods. We used Dziembowski's pulsation code to compute nonadiabatic frequencies of radial and nonradial modes. Observation of two radial modes and an avoided crossing of dipole modes put strong constraints on the models. A two-parametric overshooting routine is utilized to determine the efficiency of element mixing in the overshoot layer above the convective core.
Results. We find that pulsation models in the post-MS contraction phase successfully reproduce the observed frequency range, as well as the frequency values of all individual radial and nonradial modes. The theoretical frequencies of the mixed modes at 7.79 c/d and 9.58 c/d are in better agreement with the observations if efficient element mixing in a small overshoot layer is assumed.

[30]  arXiv:0911.4345 [ps, pdf, other]

Title: Turbulence in a 3D deflagration model for type Ia SNe: II. Intermittency and the deflagration-to-detonation transition probability

Authors: W. Schmidt, F. Ciaraldi-Schoolmann, J. C. Niemeyer, F. K. Roepke, W. Hillebrandt

Comments: 33 pages, 10 figures, submitted to ApJ

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

The delayed detonation model describes the observational properties of the majority of type Ia supernovae very well. Using numerical data from a three-dimensional deflagration model for type Ia supernovae, the intermittency of the turbulent velocity field and its implications on the probability of a deflagration-to-detonation (DDT) transition are investigated. From structure functions of the turbulent velocity fluctuations, we determine intermittency parameters based on the log-normal and the log-Poisson models. On the other hand, the analysis of the turbulent velocity fluctuations in the vicinity of the flame front by Roepke suggests a much higher probability of large velocity fluctuations on the grid scale in comparison to the log-normal intermittency model. Following Pan et al., we computed probability density functions for a DDT for the different distributions. Assuming that a DDT can occur in the stirred flame regime, as proposed by Woosley et al., the log-normal model would imply a delayed detonation between 0.7 and 0.8 seconds after the beginning of the deflagration phase for the multi-spot ignition scenario used in the simulation. However, the probability drops to virtually zero if a DDT is further constrained by the requirement that the turbulent velocity fluctuations reach about 500 km/s. Under this condition, delayed detonations are only possible if the distribution of the velocity fluctuations is not log-normal.
From our calculations follows that the distribution obtained by Roepke allow for multiple DDTs around 0.8 seconds after ignition at a transition density close to 1x10^7 g/cm^3.

[31]  arXiv:0911.4355 [ps, pdf, other]

Title: [The Impact of Nuclear Star Formation on Gas Inflow to AGN

Authors: R.I. Davies, E. Hicks, M. Schartmann, R. Genzel, L.J. Tacconi, H. Engel, A. Burkert, M. Krause, A. Sternberg, F. Mueller Sanchez, W. Maciejewski

Comments: to appear in: Co-Evolution of Central Black Holes and Galaxies; 7 pages

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Our adaptive optics observations of nearby AGN at spatial resolutions as small as 0.085arcsec show strong evidence for recent, but no longer active, nuclear star formation. We begin by describing observations that highlight two contrasting methods by which gas can flow into the central tens of parsecs. Gas accumulation in this region will inevitably lead to a starburst, and we discuss the evidence for such events. We then turn to the impact of stellar evolution on the further inflow of gas by combining a phenomenological approach with analytical modelling and hydrodynamic simulations. These complementary perspectives paint a picture in which all the processes are ultimately regulated by the mass accretion rate into the central hundred parsecs, and the ensuing starburst that occurs there. The resulting supernovae delay accretion by generating a starburst wind, which leaves behind a clumpy interstellar medium. This provides an ideal environment for slower stellar outflows to accrete inwards and form a dense turbulent disk on scales of a few parsecs. Such a scenario may resolve the discrepancy between the larger scale structure seen with adaptive optics and the small scale structure seen with VLTI.

[32]  arXiv:0911.4360 [ps, pdf, other]

Title: PAH destruction and survival in the disks of T Tauri stars

Authors: Ralf Siebenmorgen, Endrik Krügel (European Southern Observatory, Max-Planck-Institut f"ur Radioastronomie)

Comments: 17 pages, 8 figures, to be acc. by A&amp;A

Subjects: Galaxy Astrophysics (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP)

In Spitzer observations of Tauri stars and their disks, PAH features are detected in less than 10% of the objects, although the stellar photosphere is sufficiently hot to excite PAHs. To explain the deficiency, we discuss PAH destruction by photons assuming that the star has beside its photospheric emission also a FUV, an EUV and an X-ray component with fractional luminosity of 1%, 0.1% and 0.025%, respectively. As PAH destruction process we consider unimolecular dissociation and present a simplified scheme to estimate the location from the star where the molecules become photo-stable. We find that soft photons with energies below ~20eV dissociate PAHs only up to short distances from the star (r < 1AU); whereas dissociation by hard photons (EUV and X-ray) is so efficient that it would destroy all PAHs (from regions in the disk where they could be excited). As a possible path for PAH survival we suggest turbulent motions in the disk. They can replenish PAHs or remove them from the reach of hard photons. For standard disk models, where the surface density changes like 1/r and the mid plane temperature like 1/r^{0.5}, the critical vertical velocity for PAH survival is proportional to r^{-3/4} and equals ~5m/s at 10AU which is in the range of expected velocities in the surface layer. The uncertainty in the parameters is large enough to explain both detection and non-detection of PAHs. Our approximate treatment also takes into account the presence of gas which, at the top of the disk, is ionized and at lower levels neutral.

[33]  arXiv:0911.4363 [ps, pdf, other]

Title: Strong near-infrared emission in the sub-AU disk of the Herbig Ae star HD163296: evidence for refractory dust?

Authors: M. Benisty, A. Natta, A. Isella, J-P. Berger, F. Massi, J-B. LeBouquin, A. Merand, G. Duvert, S. Kraus, F. Malbet, J. Olofsson, S. Robbe-Dubois, L. Testi, M. Vannier, G. Weigelt

Comments: 14 pages; 12 figures; accepted by A&amp;A

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present new long-baseline spectro-interferometric observations of the HerbigAe star HD163296 obtained in the H and K bands with the AMBER instrument at VLTI. The observations cover a range of spatial resolutions between 3 and 12 milli-arcseconds, with a spectral resolution of ~30. With a total of 1481 visibilities and 432 closure phases, they result in the best (u,v) coverage achieved on a young star so far. The circumstellar material is resolved at the sub-AU spatial scale and closure phase measurements indicate a small but significant deviation from point-symmetry. We discuss the results assuming that the near-infrared excess in HD163296 is dominated by the emission of a circumstellar disk. A successful fit to the spectral energy distribution, near-infrared visibilities and closure phases is found with a model where a dominant contribution to the H and K band emissions arises from an optically thin, smooth and point-symmetric region extending from about 0.1 to 0.45 AU. At the latter distance from the star, silicates condense, the disk becomes optically thick and develops a puffed-up rim, whose skewed emission can account for the non-zero closure phases. We discuss the nature of the inner disk emission and tentatively rule out dense molecular gas as well as optically thin atomic or ionized gas as its possible origin. We propose instead that the inner emission traces the presence of very refractory grains in a partially cleared region, extending at least to 0.5 AU. If so, we may be observing the disk of HD163296 just before it reaches the transition disk phase. However, we note that the nature of the refractory grains or even the possibility for any grain to survive at the very high temperatures we require (~2100-2300 K at 0.1 AU from the star) is unclear and should be investigated further.

[34]  arXiv:0911.4364 [ps, pdf, other]

Title: A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: VI. s-Process and Titanium Abundance Variations Along the Sagittarius Stream

Authors: Mei-Yin Chou, Katia Cunha, Steven R. Majewski, Verne V. Smith, Richard J. Patterson, David Martinez-Delgado, Doug Geisler

Comments: Accepted for publication in ApJ

Subjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We present high-resolution spectroscopic measurements of the abundances of titanium (Ti), yttrium (Y) and lanthanum (La) for M giant candidates of the Sagittarius (Sgr) dwarf spheroidal (dSph) + tidal tail system pre-selected on the basis of position and radial velocity. The majority of these stars show peculiar abundance patterns compared to those of nominal Milky Way (MW) stars. The overall [Ti/Fe], [Y/Fe], [La/Fe] and [La/Y] patterns with [Fe/H] of the Sgr stream plus Sgr core do resemble those seen in the Large Magellanic Cloud (LMC) and other dSphs, only shifted [Fe/H] by ~+0.4 from the LMC and by ~+1 dex from the other dSphs; these relative shifts reflect the faster and/or more efficient chemical evolution of Sgr compared to the other satellites, and show that Sgr has had an enrichment history more like the LMC than the other dSphs. By tracking the evolution of the abundance patterns along the Sgr stream we can follow the time variation of the chemical make-up of dSph stars donated to the MW halo by Sgr. This evolution demonstrates that while the bulk of the stars currently in the Sgr dSph are quite unlike those of the MW halo, an increasing number of stars farther along the Sgr stream have abundances like MW halo stars, a trend that shows clearly how the MW halo could have been contributed by present day satellite galaxies even if the present chemistry of those satellites is now different from typical halo field stars. Finally, we analyze the chemical abundances of a moving group of M giants among the Sgr leading arm stars at the North Galactic Cap, but having radial velocities unlike the infalling Sgr leading arm debris there. Through use of "chemical fingerprinting", we conclude that these northern hemisphere M giants also are Sgr stars, likely trailing arm debris overlapping the leading arm in the north.

[35]  arXiv:0911.4376 [ps, pdf, other]

Title: The low wind expansion velocity of metal-poor carbon stars in the Halo and the Sagittarius stream

Authors: Eric Lagadec, Albert Zijlstra, Nicolas Mauron, Gary Fuller, Eric Josselin, G.C. Sloan, A.J.E. Riggs

Comments: 10 pages, 7 figures, accepted for publication in MNRAS

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We report the detection, from observations using the James Clerk Maxwell Telescope, of CO J $=$ 3$\to$ 2 transition lines in six carbon stars, selected as members of the Galactic Halo and having similar infrared colors. Just one Halo star had been detected in CO before this work. Infrared observations show that these stars are red (J-K $>$3), due to the presence of large dusty circumstellar envelopes. Radiative transfer models indicates that these stars are losing mass with rather large dust mass-loss rates in the range 1--3.3 $\times$$10^{-8}$M$_{\odot}$yr$^{-1}$, similar to what can be observed in the Galactic disc. We show that two of these stars are effectively in the Halo, one is likely linked to the stream of the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph), and the other three stars certainly belong to the thick disc. The wind expansion velocities of the observed stars are low compared to carbon stars in the thin disc and are lower for the stars in the Halo and the Sgr dSph stream than in the thick disc. We discuss the possibility that the low expansion velocities result from the low metallicity of the Halo carbon stars. This implies that metal-poor carbon stars lose mass at a rate similar to metal-rich carbon stars, but with lower expansion velocities, as predicted by recent theoretical models. This result implies that the current estimates of mass-loss rates from carbon stars in Local Group galaxies will have to be reconsidered.

[36]  arXiv:0911.4381 [pdf]

Title: Jupiter - friend or foe? III: the Oort cloud comets

Authors: J Horner, B W Jones, J Chambers

Comments: 21 pages, 4 Figures. Accepted for publication in the International Journal of Astrobiology

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

It has long been assumed that the planet Jupiter acts as a giant shield, significantly lowering the impact rate of small bodies on the Earth. However, until recently, very little work had been carried out examining the role played by Jupiter in determining the frequency of such collisions. In this work, the third of a series of papers, we examine the degree to which the impact rate on Earth resulting from the Oort cloud comets is enhanced or lessened by the presence of a giant planet in a Jupiter-like orbit, in an attempt to more fully understand the impact regime under which life on Earth has developed. Our results show that the presence of a giant planet in a Jupiter-like orbit significantly alters the impact rate of Oort cloud comets on the Earth, decreasing the rate as the mass of the giant increases. The greatest bombardment flus is observed when no giant planet is present.

[37]  arXiv:0911.4382 [ps, pdf, other]

Title: The Progeny of Stellar Dynamics and Stellar Evolution within an N-body model of NGC 188

Authors: A. M. Geller, J. R. Hurley, R. D. Mathieu

Comments: Contributed talk at IAUS 266 'Star clusters: basic galactic building blocks', R. de Grijs and J.R.D. Lepine, eds. 6 pages, 4 figures

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present a direct N-body simulation modeling the evolution of the old (7 Gyr) open cluster NGC 188. This is the first N-body open cluster simulation whose initial binary population is directly defined by observations of a specific open cluster: M35 (150 Myr). We compare the simulated color-magnitude diagram at 7 Gyr to that of NGC 188, and discuss the blue stragglers produced in the simulation. We compare the solar-type main sequence binary period and eccentricity distributions of the simulation to detailed observations of similar binaries in NGC 188. These results demonstrate the importance of detailed observations in guiding N-body open cluster simulations. Finally, we discuss the implications of a few discrepancies between the NGC 188 model and observations and suggest a few methods for bringing N-body open cluster simulations into better agreement with observations.

[38]  arXiv:0911.4386 [ps, pdf, other]

Title: The nature of the Sloan Digital Sky Survey galaxies in various classes based on morphology, colour and spectral features - III. Environments

Authors: Joon Hyeop Lee (1,2), Myung Gyoon Lee (2), Changbom Park (3), Yun-Young Choi (4) ((1) Korea Astronomy and Space Science Institute, Daejeon, Korea; (2) Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul, Korea; (3) Korea Institute for Advanced Study, Seoul, Korea; (4) Astrophysical Research Center for the Structure and Evolution of the Cosmos, Sejong University, Seoul, Korea)

Comments: 21 pages, 19 figures, accepted for publication in MNRAS

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present a study on the environments of the SDSS galaxies divided into fine classes based on their morphology, colour and spectral features. The SDSS galaxies are classified into early-type and late-type; red and blue; passive, HII, Seyfert and LINER, which returns a total of 16 fine classes of galaxies. We estimate the local number density, target-excluded local luminosity density, local colour, close pair fraction and the luminosity and colour of the brightest neighbour, which are compared between the fine classes comprehensively. The morphology-colour class of galaxies strongly depends on the local density, with the approximate order of high-density preference: red early-type galaxies (REGs) -- red late-type galaxies (RLGs) -- blue early-type galaxies (BLGs) -- blue late-type galaxies (BLGs). We find that high-density environments (like cluster environments) seem to suppress AGN activity. The pair fraction of HII REGs does not show statistically significant difference from that of passive REGs, while the pair fraction of HII BLGs is smaller than that of non-HII BLGs. HII BLGs show obvious double (red + blue) peaks in the distribution of the brightest neighbour colour, while red galaxies show a single red peak. The brightest neighbours of Seyfert BLGs tend to be blue, while those of LINER BLGs tend to be red, which implies that the difference between Seyfert and LINER may be related to the pair interaction. Other various environments of the fine classes are investigated, and their implication on galaxy evolution is discussed.

[39]  arXiv:0911.4392 [ps, pdf, other]

Title: Orientation of the galaxy groups in the Local Supercluster

Authors: Piotr Flin, Wlodzimierz Godlowski

Comments: Contribution in: XXXIemes Rencontres de Blois, Windows on the Universe 21 June 2009 - Monday, 27 July 2009, Chateau de Blois, Blois, France

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The paper discusses the problem of the orientation of galaxies in groups in the Local Supercluster (LSC). The existence of the preferred orientation of galaxy group is shown. We found that the orientation of galaxy groups in the Local Supercluster in the scale till about 20 Mpc is strongly correlated with the distribution of neighbouring groups. The line joining the two brightest galaxies is in alignment with both the group major axes and the direction toward the centre of the LSC, i.e. Virgo cluster. These correlations suggest that two brightest galaxies were formed in filaments of matter directed towards the protosupercluster centre. Afterwards, the hierarchical clustering leads to aggregation of galaxies around these two galaxies. Our results are in agreement with the predictions of numerical simulations.

[40]  arXiv:0911.4396 [ps, pdf, other]

Title: Evolution of the solar magnetic flux on time scales of years to millenia

Authors: L.E.A. Vieira, S. Solanki

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We improve the description of the evolution of the Sun's open and total magnetic flux on time scales of years to millenia. In the model employed here the evolution of the solar total and open magnetic flux is computed from the flux emerging at the solar surface in the form of bipolar magnetic features, which is related to the sunspot number cycle parameters and can be estimated from historical records. Compared to earlier versions of the model in addition to the long-lived open flux, now also a more rapidly decaying component of the open flux is considered. The model parameters are constrained by comparing its output with observations of the total surface magnetic flux and with a reconstruction of the open magnetic flux based on the geomagnetic indexes. A method to compute the Sun's total magnetic flux and the sunspot number during the Holocene, starting from the open flux obtained from cosmogenic isotopes records, is also presented. By considering separately a rapdly evolving and a slowly evolving component of the open flux the model reproduces the Sun's open flux, as reconstructed based on the aa-index, much better and a reasonable description of the radial component of interplanetary magnetic field data are obtained. The greatest improvement is in the reproduction of the cyclic variation of the open flux, including the amplitudes of individual cycles. Furthermore, we found that approximately 25% of the modeled open flux values since the end of the Maunder Minimum are lower than the averaged value during the current low minimum. The same proportion is observed in reconstructions of the open flux during the Holocene based on cosmogenic isotopes, which suggests that the present solar minimum conditions are below average, but not exceptional in terms of the magnetic flux.

[41]  arXiv:0911.4399 [ps, pdf, other]

Title: Supersonic Line Broadening within Young and Massive Super Star Clusters

Authors: G. Tenorio-Tagle, R. Wunsch, S. Silich, C. Munoz-Tunon, J. Palous

Comments: 17 pages, 3 figures, accepted by ApJ

Subjects: Galaxy Astrophysics (astro-ph.GA)

The origin of supersonic infrared and radio recombination nebular lines often detected in young and massive superstar clusters are discussed. We suggest that these arise from a collection of repressurizing shocks (RSs), acting effectively to re-establish pressure balance within the cluster volume and from the cluster wind which leads to an even broader although much weaker component. The supersonic lines are here shown to occur in clusters that undergo a bimodal hydrodynamic solution (Tenorio-Tagle et al. 2007), that is within clusters that are above the threshold line in the mechanical luminosity or cluster mass vs the size of the cluster (Silich et al. 2004). The plethora of repressurizing shocks is due to frequent and recurrent thermal instabilities that take place within the matter reinserted by stellar winds and supernovae. We show that the maximum speed of the RSs and of the cluster wind, are both functions of the temperature reached at the stagnation radius. This temperature depends only on the cluster heating efficiency ($\eta$). Based on our two dimensional simulations (Wunsch et al. 2008) we calculate the line profiles that result from several models and confirm our analytical predictions. From a comparison between the predicted and observed values of the half-width zero intensity of the two line components we conclude that the thermalization efficiency in SSC's above the threshold line must be lower than 20%.

[42]  arXiv:0911.4405 [ps, pdf, other]

Title: Analysis of a global Moreton wave observed on October 28, 2003

Authors: N. Muhr, B. Vrsnak, M. Temmer, A. M. Veronig, J. Magdalenic

Comments: accepted to ApJ

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We study the well pronounced Moreton wave that occurred in as- sociation with the X17.2 are/CME event of October 28, 2003. This Moreton wave is striking for its global propagation and two separate wave centers, which implies that two waves were launched simultane- ously. The mean velocity of the Moreton wave, tracked within different sectors of propagation direction, lies in the range of v ~ 900-1100 km/s with two sectors showing wave deceleration. The perturbation profile analysis of the wave indicates amplitude growth followed by amplitude weakening and broadening of the perturbation profile, which is con- sistent with a disturbance first driven and then evolving into a freely propagating wave. The EIT wavefront is found to lie on the same kinematical curve as the Moreton wavefronts indicating that both are different signatures of the same physical process. Bipolar coronal dim- mings are observed on the same opposite East-West edges of the active region as the Moreton wave ignition centers. The radio type II source, which is co-spatially located with the first wave front, indicates that the wave was launched from an extended source region (& 60 Mm). These findings suggest that the Moreton wave is initiated by the CME expanding flanks.

[43]  arXiv:0911.4411 [ps, pdf, other]

Title: Constraints on neutrino -- dark matter interactions from cosmic microwave background and large scale structure data

Authors: P. Serra, F. Zalamea, A. Cooray, G. Mangano, A. Melchiorri

Comments: 4 pages, 4 figures

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We update a previous investigation of cosmological effects of a non-standard interaction between neutrinos and dark matter. Parameterizing the elastic-scattering cross section between the two species as a function of the temperature of the universe, the resulting neutrino-dark matter fluid has a non-zero pressure, which determines diffusion-damped oscillations in the matter power spectrum similar to the acoustic oscillations generated by the photon-baryon fluid. Using cosmic microwave background data in combination with large scale structure experiment results, we then put constraints on the fraction of the interacting dark matter component as well as on the corresponding opacity.

[44]  arXiv:0911.4421 [ps, pdf, other]

Title: Density Profiles in Molecular Cloud Cores Associated with High-Mass Star-Forming Regions

Authors: Lev E. Pirogov

Comments: 12 pages, 3 figures, 4 tables

Journal-ref: Astronomy Reports 2009, vol. 53, pp. 1127-1135

Subjects: Galaxy Astrophysics (astro-ph.GA)

Radial density profiles for the sample of dense cores associated with high-mass star-forming regions from southern hemisphere have been derived using the data of observations in continuum at 250 GHz. Radial density profiles for the inner regions of 16 cores (at distances $\la 0.2-0.8$ pc from the center) are close on average to the $\rho\propto r^{-\alpha}$ dependence, where $\alpha=1.6\pm 0.3$. In the outer regions density drops steeper. An analysis with various hydrostatic models showed that the modified Bonnor-Ebert model, which describes turbulent sphere confined by external pressure, is preferable compared with the logotrope and polytrope models practically in all cases. With a help of the Bonnor-Ebert model, estimates of central density in a core, non-thermal velocity dispersion and core size are obtained. The comparison of central densities with the densities derived earlier from the CS modeling reveals differences in several cases. The reasons of such differences are probably connected with the presence of density inhomogenities on the scales smaller than the telescope beam. In most cases non-thermal velocity dispersions are in agreement with the values obtained from molecular line observations.

[45]  arXiv:0911.4422 [ps, pdf, other]

Title: VLTI/AMBER spectro-interferometric imaging of VX Sgr's inhomogenous outer atmosphere

Authors: A. Chiavassa, S. Lacour, F. Millour, T. Driebe, M. Wittkowski, B. Plez, E. Thiebeaut, E. Josselin, B. Freytag, M. Scholz, X. Haubois

Comments: 9 Pages, Accepted for publication on Astronomy &amp; Astrophysics

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Aims. We aim to explore the photosphere of the very cool late-type star VX Sgr and in particular the existence and characterization of molecular layers above the continuum forming photosphere. Methods. We obtained interferometric observations with the VLTI/AMBER interferometer using the fringe tracker FINITO in the spectral domain 1.45-2.50 micron with a spectral resolution of about 35 and baselines ranging from 15 to 88 meters.We perform independent image reconstruction for different wavelength bins and fit the interferometric data with a geometrical toy model.We also compare the data to 1D dynamical models of Miras atmosphere and to 3D hydrodynamical simulations of red supergiant (RSG) and asymptotic giant branch (AGB) stars. Results. Reconstructed images and visibilities show a strong wavelength dependence. The H-band images display two bright spots whose positions are confirmed by the geometrical toy model. The inhomogeneities are qualitatively predicted by 3D simulations. At about 2:00 micron and in the region 2:35 - 2:50 micron, the photosphere appears extended and the radius is larger than in the H band. In this spectral region, the geometrical toy model locates a third bright spot outside the photosphere that can be a feature of the molecular layers. The wavelength dependence of the visibility can be qualitatively explained by 1D dynamical models of Mira atmospheres. The best-fitting photospheric models show a good match with the observed visibilities and give a photospheric diameter of theta = 8:82+-0:50 mas. The H2O molecule seems to be the dominant absorber in the molecular layers. Conclusions. We show that the atmosphere of VX Sgr rather resembles Mira/AGB star model atmospheres than RSG model atmospheres. In particular, we see molecular (water) layers that are typical for Mira stars.

[46]  arXiv:0911.4424 [pdf]

Title: Mapping the Probability of Microlensing Detection of Extra-Solar Planets

Authors: Karan Molaverdikhani, Maryam Tabeshian

Comments: 11 pages, 25 figures Presented in 59th International Astronautical Congress(IAC), 37th Symposium on the Search for Extraterrestrial Intelligence (SETI)

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Galaxy Astrophysics (astro-ph.GA)

The growing rate of increase in the number of the discovered extra-solar planets which has consequently raised the enthusiasm to explore the universe in hope of finding earth-like planets has resulted in the wide use of Gravitational Microlensing as a planet detection method. However, until November 2009, only 9 out of the overall 405 discovered exoplanets have been detected through Microlensing, a fact which shows that this method is relatively new in the detection of extra-solar planets. Therefore, preparing a map of the sky which pinpoints the regions with higher probability of planet detection by this method and is drawn based on the available equipments and other regional factors would, indeed, help speed up the discovery of exoplanets. This paper provides calculations and reasoning to suggest looking toward two distinct regions in constellations Centaurus and Sagittarius in addition to the customary Galactic Bulge in the search for other habitable worlds.

[47]  arXiv:0911.4441 [pdf, other]

Title: Identifying birth places of young isolated neutron stars

Authors: Nina Tetzlaff, Ralph Neuhaeuser, Markus M. Hohle, Gracjan Maciejewski

Comments: 14 figures, 13 tables

Subjects: Galaxy Astrophysics (astro-ph.GA)

Young isolated radio-quiet neutron stars are still hot enough to be detectable at X-ray and optical wavelengths due to their thermal emission and can hence probe cooling curves. An identification of their birth sites can constrain their age. For that reason we try to identify the parent associations for four of the so-called Magnificent Seven neutron stars for which proper motion and distance estimates are available. We are tracing back in time each neutron star and possible birth association centre to find close encounters. The associated time of the encounter expresses the kinematic age of the neutron star which can be compared to its characteristic spin-down age. Owing to observational uncertainties in the input data, we use Monte-Carlo simulations and evaluate the outcome of our calculations statistically. RX J1856.5-3754 most probably originated from the Upper Scorpius association about 0.3 Myr ago. RX 0720.4-3125 was either born in the young local association TWA about 0.4 Myr ago or in Tr 10 0.5 Myr in the past. Also RX J1605.3+3249 and RBS 1223 seem to come from a nearby young association such as the Sco-Cen complex or the extended Corona-Australis association. For RBS 1223 also a birth in Sct OB2 is possible. We also give constraints on the observables as well as on the radial velocity of the neutron star. Given the birth association, its age and the flight time of the neutron star, we estimate the mass of the progenitor star. Some of the potential supernovae were located very nearby (<100pc) and thus should have contributed to the 10Be and 60Fe material found in the Earth's crust. In addition we reinvestigate the previously suggested neutron star/ runaway pair PSR B1929+10/ zeta Ophiuchi and conclude that it is very likely that both objects were ejected during the same supernova event.

[48]  arXiv:0911.4448 [pdf, other]

Title: Tuning of Kilopixel Transition Edge Sensor Bolometer Arrays with a Digital Frequency Multiplexed Readout System

Authors: K. MacDermid, P. Hyland, F. Aubin, E. Bissonnette, M. Dobbs, J. Hubmayr, G. Smecher, S. Warraich

Comments: 5 pages, 4 figures

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

A digital frequency multiplexing (DfMUX) system has been developed and used to tune large arrays of transition edge sensor (TES) bolometers read out with SQUID arrays for mm-wavelength cosmology telescopes. The DfMUX system multiplexes the input bias voltages and output currents for several bolometers on a single set of cryogenic wires. Multiplexing reduces the heat load on the camera's sub-Kelvin cryogenic detector stage. In this paper we describe the algorithms and software used to set up and optimize the operation of the bolometric camera. The algorithms are implemented on soft processors embedded within FPGA devices operating on each backend readout board. The result is a fully parallelized implementation for which the setup time is independent of the array size.

[49]  arXiv:0911.4453 [ps, pdf, other]

Title: High energy emission components in the short GRB 090510

Authors: Alessandra Corsi, Dafne Guetta, Luigi Piro

Comments: 15 pages, 2 color figures, submitted to the Astrophysical Journal

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We investigate the origin of the prompt and delayed emission observed in the short GRB 090510. We first attempt to explain the soft-to-hard spectral evolution associated to the delayed onset of a GeV tail, in the hypothesis that the prompt burst and the high energy tail both originate from a single process, namely synchrotron emission from internal shocks. Considerations on the compactness of the source imply that the high energy tail should be produced in a lately emitted shell, characterized by a Lorentz factor greater than the one generating the prompt burst. However, in this hypothesis, the evolution of the synchrotron peak frequency does not agree with the observed soft-to-hard one, unless a substantial change in the micro-physics of the shocks developing in the two shells does happen. Given the difficulties of a single mechanism hypothesis, we test two alternative double-component scenarios. In the first, the prompt burst is explained as synchrotron radiation from internal shocks, while the high energy emission (up to about 1 s since the trigger) as internal shock synchrotron-self-Compton. In the second scenario, in view of its long duration (\sim 100 s), the high energy tail is decoupled from the prompt burst and has an external shock origin. In this case, we show that a reasonable choice of parameters does indeed exist to accommodate the optical-to-GeV data, provided the Lorentz factor of the shocked shell is sufficiently high. We finally attempt to model the chromatic break observed around \sim 10^3 s under the hypothesis of a structured jet model, finding that this might be a viable explanation, which lowers the high value of the burst energy derived assuming isotropy (\sim 1e53 ergs), down to \sim 1e49 ergs, more compatible with the energetics from a binary merger progenitor.

[50]  arXiv:0911.4457 [ps, pdf, other]

Title: On the shape of the spectrum of cosmic-rays accelerated inside superbubbles

Authors: Gilles Ferrand (SAp), Alexandre Marcowith (LPTA)

Comments: accepted for publication in A&amp;A (language might still be edited)

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Supernova remnants are believed to be a major source of cosmic-rays in the Galaxy. As their progenitors are commonly found clustered in OB associations, one has to consider the possibility of collective effects in the acceleration process. In this work we investigate the shape of the spectrum of protons accelerated inside the superbubbles blown around clusters of massive stars. To do so we embed semi-analytical models of particle acceleration and transport inside Monte-Carlo simulations of OB associations timelines. We consider regular acceleration at the shock front of supernova remnants, as well as stochastic re-acceleration and escape occurring between the shocks. We observe that particle spectra, although strongly intermittent, get a distinctive shape resulting from a competition between acceleration and escape: they are harder at the lowest energies and softer at the highest energies. The momentum at which this spectral break occurs depends on a single dimensionless parameter, which we evaluate for a selection of objects. The behaviour of a superbubble regarding acceleration depends on the magnetic turbulence: if B is low the superbubble is simply the host of a collection of individual supernovae shocks, but if B is high enough it acts as a global accelerator, producing distinctive spectra ? which has important implications on the high-energy emission from these objects.

[51]  arXiv:0911.4479 [ps, pdf, other]

Title: Physical characterisation of southern massive star-forming regions using Parkes NH$_3$ observations

Authors: T. Hill, S. N. Longmore, C. Pinte, M. R. Cunningham, M. G. Burton, V. Minier

Comments: 20 pages, 9 Figures, 1 appendix (to appear in full online only, a sample appendix in the paper); 7 tables. Accepted by MNRAS

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)

We have undertaken a Parkes ammonia spectral line study, in the lowest two inversion transitions, of southern massive star formation regions, including young massive candidate protostars, with the aim of characterising the earliest stages of massive star formation. 138 sources from the submillimetre continuum emission studies of Hill et al., were found to have robust (1,1) detections, including two sources with two velocity components, and 102 in the (2,2) transition.
We determine the ammonia line properties of the sources: linewidth, flux density, kinetic temperature, NH$_3$ column density and opacity, and revisit our SED modelling procedure to derive the mass for 52 of the sources. By combining the continuum emission information with ammonia observations we substantially constrain the physical properties of the high-mass clumps. There is clear complementarity between ammonia and continuum observations for derivations of physical parameters.
The MM-only class, identified in the continuum studies of Hill et al., display smaller sizes, mass and velocity dispersion and/or turbulence than star-forming clumps, suggesting a quiescent prestellar stage and/or the formation of less massive stars.

Cross-lists for Tue, 24 Nov 09

[52]  arXiv:0911.1187 (cross-list from gr-qc) [ps, pdf, other]

Title: Static spherically symmetric solutions in the IR limit of nonrelativistic quantum gravity

Authors: Tomohiro Harada, Umpei Miyamoto, Naoki Tsukamoto

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

We investigate static spherically symmetric vacuum solutions in the IR limit of projectable nonrelativistic quantum gravity, including the renormalisable quantum gravity recently proposed by Ho\v{r}ava. It is found that the projectability condition plays an important role. Without the cosmological constant, the spacetime is uniquely given by the Schwarzschild solution. With the cosmological constant, the spacetime is uniquely given by the Kottler (Schwarzschild-(anti) de Sitter) solution for the entirely vacuum spacetime. However, the ``ultra-static'' metric of spherical and hyperbolic spaces can be also admissible for the locally empty region, for the positive and negative cosmological constants, respectively, if its nonvanishing contribution to the global Hamiltonian constraint can be compensated by that from the nonempty or nonstatic region. This implies that static spherically symmetric entirely vacuum solutions would not admit the freedom to reproduce the observed flat rotation curves of galaxies. On the other hand, the result for locally empty regions implies that the IR limit of nonrelativistic quantum gravity theories does not simply recover general relativity but includes it.

[53]  arXiv:0911.1267 (cross-list from hep-ph) [ps, pdf, other]

Title: Higgs production as a probe of dark energy interactions

Authors: Philippe Brax, Clare Burrage, Anne-Christine Davis, David Seery, Amanda Weltman

Comments: 22 pages, 5 figures. Uses iopart.cls and feynmf.sty

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

We study Higgs production under the influence of a light, scalar dark energy field with chameleon-like couplings to matter. Our analysis is relevant for hadron colliders, such as the Large Hadron Collider, which are expected to manufacture Higgs particles through weak boson fusion, or associated production with a Z or W. We show that the corrections arising in these models are too small to be observed. This result can be attributed to the gauge invariance of the low energy Lagrangian. As a by-product of our analysis, we provide the first microphysical realization of a dark energy model coupled to the electromagnetic field strength. In models where dark energy couples to all matter species in a uniform manner we are able to give a new, stringent bound on its coupling strength.

[54]  arXiv:0911.4073 (cross-list from nucl-th) [ps, pdf, other]

Title: Statistical Model for a Complete Supernova Equation of State

Authors: Matthias Hempel, Jürgen Schaffner-Bielich

Comments: 33 pages, 22 pages

Subjects: Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)

A statistical model for the equation of state (EOS) and the composition of supernova matter is presented with focus on the liquid-gas phase transition of nuclear matter. It consists of an ensemble of nuclei and interacting nucleons in nuclear statistical equilibrium. A relativistic mean field model is applied for the nucleons. The masses of the nuclei are taken from nuclear structure calculations which are based on the same nuclear Lagrangian. For known nuclei experimental data is used directly. Excluded volume effects are implemented in a thermodynamic consistent way so that the transition to uniform nuclear matter at large densities can be described. Thus the model can be applied at all densities relevant for supernova simulations, i.e. rho=10^5 - 10^15 g/cm^3, and it is possible to calculate a complete supernova EOS table. The model allows to investigate the role of shell effects, which lead to narrow-peaked distributions around the neutron magic numbers for low temperatures. At larger temperatures the distributions become broad. The significance of the statistical treatment and the nuclear distributions for the composition is shown. We find that the contribution of light clusters is very important and is only poorly represented by alpha-particles alone. The results for the EOS are systematically compared to two commonly used models for supernova matter which are based on the single nucleus approximation. Apart from the composition, in general only small differences of the different EOSs are found. The differences are most pronounced around the (low-density) liquid-gas phase transition line where the distribution of light and intermediate clusters has an important effect. Possible extensions and improvements of the model are discussed.

Replacements for Tue, 24 Nov 09

[55]  arXiv:0811.0560 (replaced) [ps, pdf, other]

Title: Galaxy evolution from strong lensing statistics: the differential evolution of the velocity dispersion function in concord with the LambdaCDM paradigm

Authors: Kyu-Hyun Chae

Comments: MNRAS, accepted (20 pages, 12 figures), parts of section 6 of v2 moved to a following work

Subjects: Astrophysics (astro-ph)

[56]  arXiv:0812.2470 (replaced) [ps, pdf, other]

Title: On The Origin Of The Highest Redshift Gamma-Ray Bursts

Authors: Krzysztof Belczynski, Daniel E. Holz, Chris L. Fryer, Edo Berger, Dieter H. Hartmann, Brian O'Shea

Comments: 16 pages, ApJ accepted (2010)

Subjects: Astrophysics (astro-ph)

[57]  arXiv:0901.2119 (replaced) [ps, pdf, other]

Title: X-ray and Radio Timing of the Pulsar in 3C 58

Authors: Margaret A. Livingstone, Scott Ransom, Fernando Camilo, Victoria M. Kaspi, Andrew Lyne, Michael Kramer, Ingrid H. Stairs

Comments: 19 pages, 12 figures. Published in the Astrophysical Journal. Includes additional data analysis and two new figures

Journal-ref: Astrophys.J.706:1163-1173,2009

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

[58]  arXiv:0901.4229 (replaced) [ps, pdf, other]

Title: Slow pressure modes in thin accretion discs

Authors: Tarun Deep Saini, Mamta Gulati, S. Sridhar

Comments: 9 pages, 7 figures, 1 table, accepted in MNRAS for pulication

Subjects: Galaxy Astrophysics (astro-ph.GA)

[59]  arXiv:0902.1754 (replaced) [ps, pdf, other]

Title: Formation of Isolated Dwarf Galaxies with Feedback

Authors: Till Sawala, Cecilia Scannapieco, Umberto Maio, Simon D.M. White (Max-Planck Institute for Astrophysics Garching)

Comments: 17 pages, 14 figures. MNRAS accepted

Subjects: Galaxy Astrophysics (astro-ph.GA)

[60]  arXiv:0902.3802 (replaced) [ps, pdf, other]

Title: The MiniBooNE anomaly and heavy neutrino decay

Authors: S.N. Gninenko

Comments: version accepted for publication in Phys. Rev. Lett

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Experiment (hep-ex)

[61]  arXiv:0904.0002 (replaced) [ps, pdf, other]

Title: The propagation of uncertainties in stellar population synthesis modeling II: The challenge of comparing galaxy evolution models to observations

Authors: Charlie Conroy, Martin White, James E. Gunn

Comments: 14 pages, 7 figures. ApJ accepted

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

[62]  arXiv:0904.0660 (replaced) [ps, pdf, other]

Title: Model of two-fluid reconnection

Authors: Leonid M. Malyshkin

Comments: 4 pages, 1 figure, accepted to Physical Review Letters

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

[63]  arXiv:0904.2513 (replaced) [ps, pdf, other]

Title: Significant foreground unrelated non-acoustic anisotropy on the one degree scale in WMAP 5-year observations

Authors: Bi-Zhu Jiang, Richard Lieu, Shuang-Nan Zhang, Bart Wakker

Comments: Final version to appear in ApJ

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

[64]  arXiv:0904.3943 (replaced) [ps, pdf, other]

Title: Studies of Millimeter-Wave Atmospheric Noise Above Mauna Kea

Authors: J. Sayers, S. R. Golwala, P. A. R. Ade, J. E. Aguirre, J. J. Bock, S. F. Edgington, J. Glenn, A. Goldin, D. Haig, A. E. Lange, G. T. Laurent, P. D. Mauskopf, H. T. Nguyen, P. Rossinot, J. Schlaerth

Comments: 48 pages, 16 figures, accepted for publication in ApJ

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

[65]  arXiv:0905.3439 (replaced) [ps, pdf, other]

Title: Strange stars with different quark mass scalings

Authors: Ang Li, Ren-Xin Xu, Ju-Fu Lu

Comments: 5 pages, 6 figures, 1 table. accepted by MN

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

[66]  arXiv:0906.4115 (replaced) [ps, pdf, other]

Title: Two phase galaxy formation: The Gas Content of Normal Galaxies

Authors: M. Cook, C. Evoli, E. Barausse, G.L. Granato, A. Lapi

Comments: 16 pages, 12 figures, 1 table. Moderate revision to match version accepted for publication in MNRAS

Subjects: Galaxy Astrophysics (astro-ph.GA)

[67]  arXiv:0907.2433 (replaced) [ps, pdf, other]

Title: Propagation of ultrahigh energy nuclei in clusters of galaxies: resulting composition and secondary emissions

Authors: K. Kotera, D. Allard, K. Murase, J. Aoi, Y. Dubois, T. Pierog, S. Nagataki

Comments: 19 pages, 15 figures, version to appear in ApJ (minor changes)

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

[68]  arXiv:0907.4232 (replaced) [pdf, other]

Title: The Largest Gravitational Lens: MACS J0717.5+3745 (z=0.546)

Authors: Adi Zitrin, Tom Broadhurst, Yoel Rephaeli, Sharon Sadeh

Comments: 5 pages, 5 figures, accepted to the ApJ Letters; title modified; minor changes

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

[69]  arXiv:0907.4990 (replaced) [ps, pdf, other]

Title: On the Apparent Lack of Be X-ray Binaries with Black Holes

Authors: Krzysztof Belczynski, Janusz Ziolkowski

Comments: 13 pages, ApJ 2009 (accepted)

Subjects: Galaxy Astrophysics (astro-ph.GA)

[70]  arXiv:0908.0765 (replaced) [ps, pdf, other]

Title: A New Solution for the Dispersive Element in Astronomical Spectrographs

Authors: Harland W. Epps, Judith G. Cohen, J. Christopher Clemens

Comments: Revised version submitted to PASP, contains efficiency calculations

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

[71]  arXiv:0908.1005 (replaced) [ps, pdf, other]

Title: Large scale evolution of the curvature perturbation in Horava-Lifshitz cosmology

Authors: Tsutomu Kobayashi, Yuko Urakawa, Masahide Yamaguchi

Comments: 6 pages; v2: published version

Journal-ref: JCAP 0911:015,2009

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

[72]  arXiv:0908.1359 (replaced) [ps, pdf, other]

Title: The nature of pulsar radio emission

Authors: J. Dyks, B. Rudak, P. Demorest

Comments: 16 pages, 18 figures, accepted by MNRAS after minor revision

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

[73]  arXiv:0908.2773 (replaced) [ps, pdf, other]

Title: Contamination of short GRBs by giant magnetar flares: Significance of downward revision in distance to SGR 1806-20

Authors: Paul A Crowther (Sheffield), Joanne L Bibby (Sheffield), James P Furness (Sheffield), J Simon Clark (Open University)

Comments: 5 pages, 4 figures, contributed talk from `Neutron Stars and Gamma Ray Bursts' to appear in dedicated volume of Advances in Space Research

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

[74]  arXiv:0909.1262 (replaced) [src]

Title: Search for cosmic neutrino point sources with the 5-line ANTARES telescope

Authors: Antares Collaboration

Comments: This paper has been withdrawn due a problem with the estimation of background

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

[75]  arXiv:0910.0839 (replaced) [ps, pdf, other]

Title: A Dialogue on the Nature of Gravity

Authors: T. Padmanabhan

Comments: Based on lectures given in several conferences (including VR lecture of IAGRG); results have been updated and format has been changed to one involving a dialogue; version 2: discussion significantly extended; references added; 3 figures; 37 pages

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

[76]  arXiv:0910.2232 (replaced) [ps, pdf, other]

Title: The evolution of Black Hole scaling relations in galaxy mergers

Authors: Peter H. Johansson, Andreas Burkert, Thorsten Naab

Comments: 6 pages, 4 figures, accepted to ApJL (minor revisions to match accepted version)

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

[77]  arXiv:0910.3910 (replaced) [ps, pdf, other]

Title: Two phase galaxy formation: The Evolutionary Properties of Galaxies

Authors: M Cook, E Barausse, C Evoli, A Lapi, GL Granato

Comments: 15 pages, 11 figures. Version polished for publication in MNRAS

Subjects: Galaxy Astrophysics (astro-ph.GA)

[78]  arXiv:0910.3998 (replaced) [ps, pdf, other]

Title: On the detectability of HI 21-cm in MgII absorption system

Authors: S. J. Curran

Comments: 9 pages, accepted by MNRAS

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

[79]  arXiv:0910.4532 (replaced) [ps, pdf, other]

Title: Black hole gas in the early universe

Authors: Monica Borunda, Manuel Masip

Comments: 16 pages. Substantial changes. We have redefined the TeV gravity model to make it consistent with bounds from Cosmology

Subjects: 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)

[80]  arXiv:0911.1806 (replaced) [ps, pdf, other]

Title: HST's hunt for intermediate-mass black holes in star clusters

Authors: Julio Chanamé (1), Justice Bruursema (2), Rupali Chandar (3), Jay Anderson (4), Roeland van der Marel (4), Holland Ford (2) ((1) Carnegie DTM, (2) Johns Hopkins University, (3) University of Toledo, (4) Space Telescope Science Institute)

Comments: 7 pages; Invited talk at IAU Symposium 266 "Star clusters: basic galactic building blocks" (Rio de Janeiro, 10-14 August 2009), R. de Grijs and R.D. Lepine, eds; v2 reflects a better citation of some references and corrected typos

Subjects: Galaxy Astrophysics (astro-ph.GA)

• New submissions
• Cross-lists
• Replacements