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Astrophysics

astro-ph new abstracts, Fri, 27 Jan 06 01:00:09 GMT
0601579 -- 0601617 received

astro-ph/0601579 [abs, ps, pdf, other] :

Title: An efficient technique for pre-selecting low redshift damped Lyman alpha systems
Authors: Sara L. Ellison
Comments: MNRAS accepted

The number of z ~ 1 damped Lyman alpha systems (DLAs, log N(HI) >= 20.3) per unit redshift is approximately 0.1, making them relatively rare objects. Large, blind QSO surveys for low redshift DLAs are therefore an expensive prospect for space-borne UV telescopes. Increasing the efficiency of these surveys by pre-selecting DLA candidates based on the equivalent widths of metal absorption lines has previously been a successful strategy. However, the success rate of DLA identification is still only ~ 35% when simple equivalent width cut-offs are applied, the majority of systems having 19.0 < log N(HI)<20.3. Here we propose a new way to pre-select DLA candidates. Our technique requires high-to-moderate resolution spectroscopy of the MgII 2796 transition, which is easily accessible from the ground for 0.2 < z < 2.4. We define the D-index, the ratio of the line's equivalent width to velocity spread and measure this quantity for 19 DLAs and 8 sub-DLAs in archival spectra obtained with echelle spectrographs. For the majority of absorbers, there is a clear distinction between the D-index of DLAs compared with sub-DLAs (Kolmogorov-Smirnov probability = 0.8%). Based on this pilot data sample, we find that the D-index can select DLAs with a success rate of up to 90%, an increase in selection efficiency by a factor of 2.5 compared with a simple equivalent width cut. We test the applicability of the D-index at lower resolution and find that it remains a good discriminant of DLAs for FWHM < 1.5 A. However, the recommended D-index cut-off between DLAs and sub-DLAs decreases with poorer resolution and we tabulate the appropriate D-index values that should be used with spectra of different resolutions.

 

astro-ph/0601580 [abs, ps, pdf, other] :

Title: A Successful Targeted Search for Hypervelocity Stars
Authors: Warren R. Brown, Margaret J. Geller, Scott J.Kenyon, Michael J. Kurtz (Smithsonian Astrophysical Observatory)
Comments: 5 pages, submitted to ApJ Letters

Hypervelocity stars (HVSs) travel with velocities so extreme that dynamical ejection from a massive black hole is their only suggested origin. Following our discovery of the first HVS, we have undertaken a dedicated survey for more HVSs in the Galactic halo and present here the resulting discovery of two new HVSs: SDSS J091301.0+305120 and SDSS J091759.5+672238, traveling with Galactic rest-frame velocities at least +558+-12 and +638+-12 km/s, respectively. Assuming the HVSs are B8 main sequence stars, they are at distances ~75 and ~55 kpc, respectively, and have travel times from the Galactic Center consistent with their lifetimes. The existence of two B8 HVSs in our 1900 deg^2 survey, combined with the Yu & Tremaine HVS rate estimates, is consistent with HVSs drawn from a standard initial mass function but inconsistent with HVS drawn from a truncated mass function like the one in the top-heavy Arches cluster. The travel times of the five currently known HVSs provide no evidence for a burst of HVSs from a major in-fall event at the Galactic Center in the last \~160 Myr.

 

astro-ph/0601581 [abs, ps, pdf, other] :

Title: Globular Clusters as a Test for Gravity in the Weak Acceleration Regime
Authors: Riccardo Scarpa, Gianni Marconi, Roberto Gilmozzi
Comments: Comments: To Appear in the proceeding of the "First crisis in cosmology" conference, published in the American Institute of Physiscs' proceedings series, Vol. 822. (includes 3 pages and 1 fig)

Non-baryonic Dark Matter (DM) appears in galaxies and other cosmic structures when and only when the acceleration of gravity, as computed considering only baryons, goes below a well defined value a0=1.2e-8 cm/s/s. This might indicate a breakdown of Newton's law of gravity (or inertia) below a0, an acceleration smaller than the smallest probed in the solar system. It is therefore important to verify whether Newton's law of gravity holds in this regime of accelerations. In order to do this, one has to study the dynamics of objects that do not contain significant amounts of DM and therefore should follow Newton's prediction for whatever small accelerations. Globular clusters are believed, even by strong supporters of DM, to contain negligible amounts of DM and therefore are ideal for testing Newtonian dynamics in the low acceleration limit. Here, we discuss the status of an ongoing program aimed to do this test. Compared to other studies of globular clsuters, the novelty is that we trace the velocity dispersion profile of globular clusters far enough from the center to probe gravitational accelerations well below a0. In all three clusters studied so far the velocity dispersion is found to remain constant at large radii rather than follow the Keplerian falloff. On average, the flattening occurs at the radius where the cluster internal acceleration of gravity is 1.8+-0.4 x 10^{-8} cm/s/s, fully consistent with MOND predictions.

 

astro-ph/0601582 [abs, ps, pdf, other] :

Title: The Bolocam 1.1 mm Lockman Hole Galaxy Survey: SHARC II 350 micron Photometry and Implications for Spectral Models, Dust Temperatures, and Redshift Estimation
Authors: G. T. Laurent (U. Colorado), J. Glenn (U. Colorado), E. Egami (U. of Arizona), G. H. Rieke (U. Arizona), R. J. Ivison (UK Astronomy Technology Centre), M. S. Yun (U. Massachusetts), J. E. Aguirre (NRAO, U. Colorado), P. R. Maloney (U. Colorado)
Comments: In Press (to appear in Astrophysical Journal, ApJ 20 May 2006 v643 1) 47 pages, 10 figures, 4 tables

We present 350 micron photometry of all 17 galaxy candidates in the Lockman Hole detected in a 1.1 mm Bolocam survey. Several of the galaxies were previously detected at 850 microns, at 1.2 mm, in the infrared by Spitzer, and in the radio. Nine of the Bolocam galaxy candidates were detected at 350 microns and two new candidates were serendipitously detected at 350 microns (bringing the total in the literature detected in this way to three). Five of the galaxies have published spectroscopic redshifts, enabling investigation of the implied temperature ranges and a comparison of photometric redshift techniques.
Lambda = 350 microns lies near the spectral energy distribution peak for z = 2.5 thermally emitting galaxies. Thus, luminosities can be measured without extrapolating to the peak from detection wavelengths of lambda > 850 microns. Characteristically, the galaxy luminosities lie in the range 1.0 - 1.2 x 10^13 L_solar, with dust temperatures in the range of 40 K to 70 K, depending on the choice of spectral index and wavelength of unit optical depth. The implied dust masses are 3 - 5 x 10^8 M_solar. We find that the far-infrared to radio relation for star-forming ULIRGs systematically overpredicts the radio luminosities and overestimates redshifts on the order of Delta z ~ 1, whereas redshifts based on either on submillimeter data alone or the 1.6 micron stellar bump and PAH features are more accurate.

 

astro-ph/0601583 [abs, ps, pdf, other] :

Title: Far-ultraviolet Observations of the North Ecliptic Pole with SPEAR
Authors: Eric J. Korpela (1), Jerry Edelstein (1), Julia Kregenow (1), Kaori Nishikida (1), Kyoung-Wook Min (2), Dae-Hee Lee (2,3), Kwangsun Ryu (2), Wonyong Han (3) Uk-Won Nam (3), Jang-Hyun Park (3) ((1) Space Sciences Laboratory, University of California, Berkeley, (2) Korea Advanced Institute of Science and Technology, Daejeon, Korea, (3) Korea Astronomy and Space Science Institute, Daejeon, Korea)
Comments: 5 pages, 3 figures, Accepted for publication in ApJ Letters

We present SPEAR/FIMS far-ultraviolet observations near the North Ecliptic Pole. This area, at b~30 degrees and with intermediate HI column, seems to be a fairly typical line of sight that is representative of general processes in the diffuse ISM. We detect a surprising number of emission lines of many elements at various ionization states representing gas phases from the warm neutral medium (WNM) to the hot ionized medium (HIM). We also detect fluorescence bands of H2, which may be due to the ubiquitous diffuse H2 previously observed in absorption.

 

astro-ph/0601584 [abs, ps, pdf, other] :

Title: Far-UV Observations of a Thermal Interface in the Orion-Eridanus Superbubble
Authors: J. Kregenow, J. Edelstein, E. Korpela, B. Welsh, C. Heiles, K. Ryu, K. Min, Y. Lim, I. Yuk, H. Jin, K. Seon
Comments: 4 pages, 4 figures Accepted to ApJLetters

Diffuse far-UV emission arising from the edge of the Orion-Eridanus superbubble was observed with the SPEAR imaging spectrometer, revealing numerous emission lines arising from both atomic species and H2. Spatial variations in line intensities of CIV, SiII, and OVI, in comparison with soft X-ray, H-alpha and dust data, indicate that these ions are associated with processes at the interface between hot gas inside the bubble and the cooler ambient medium. Thus our observations probe physical conditions of an evolved thermal interface in the ISM.

 

astro-ph/0601585 [abs, ps, pdf, other] :

Title: Morpho-kinematic modeling of gaseous nebulae with SHAPE
Authors: Wolfgang Steffen, Jose Alberto Lopez
Comments: 7 pages, 5 figures, accepted for publication in RevMexAA, some figures are low resolution for packing adequate for the arXive (see this http URL for highres version.)

We present a powerful new tool to analyse and disentangle the 3-D geometry and kinematic structure of gaseous nebulae. The method consists in combining commercially available digital animation software to simulate the 3-D structure and expansion pattern of the nebula with a dedicated, purpose built rendering software that produces the final images and long slit spectra which are compared to the real data. We show results for the complex planetary nebulae NGC 6369 and Abell 30 based on long slit spectra obtained at the San Pedro Martir observatory.

 

astro-ph/0601586 [abs, ps, pdf, other] :

Title: Far Ultraviolet Spectral Images of the Vela Supernova Remnant
Authors: K. Nishikida, J. Edelstein, E. J. Korpela, R. Sankrit, W. M. Feuerstein, K. W. Min, J-H. Shinn, D-H. Lee, I-S. Yuk, H. Jin, K-I. Seon
Comments: Accepted by ApJL

We present far-ultraviolet (FUV) spectral-imaging observations of the Vela supernova remnant (SNR), obtained with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR) instrument, also known as FIMS. The Vela SNR extends 8 degrees in the FUV and its global spectra are dominated by shock-induced emission lines. We find that the global FUV line luminosities can exceed the 0.1-2.5 keV soft X-ray luminosity by an order of magnitude. The global O VI:C III ratio shows that the Vela SNR has a relatively large fraction of slower shocks compared with the Cygnus Loop.

 

astro-ph/0601587 [abs, ps, pdf, other] :

Title: The Spectroscopy of Plasma Evolution from Astrophysical Radiation Mission
Authors: J. Edelstein, K. W. Min, W. Han, E. J. Korpela, K. Nishikida, B.Y. Welsh, C. Heiles, J. Adolfo, M. Bowen, W.M. Feuerstein, K. McKee, J.-T. Lim, K. Ryu, J.-H. Shinn, U.-W. Nam, J.-H. Park, I.-S. Yuk, H. Jin, K.I Seon, D.H. Lee, E. Sim

The Spectroscopy of Plasma Evolution from Astrophysical Radiation (or the Far-ultraviolet Imaging Spectrograph) instruments, flown aboard the STSAT-1 satellite mission, have provided the first large-area spectral mapping of the cosmic far ultraviolet (FUV, lambda 900-1750 Ang) background. We observe diffuse radiation from hot (10^4 to 10^6 K) and ionized plasmas, molecular hydrogen, and dust scattered starlight. These data provide for the unprecedented detection and discovery of spectral emission from a variety of interstellar environments, including the general medium, molecular clouds, supernova remnants, and super-bubbles. We describe the mission and its data, present an overview of the diffuse FUV sky's appearance and spectrum, and introduce the scientific findings detailed later in this volume.

 

astro-ph/0601588 [abs, ps, pdf, other] :

Title: The SPEAR Instrument and On-Orbit Performance
Authors: Jerry Edelstein, Eric Korpela, Joe Adolfo, Mark Bowen, Michael Feuerstein, Jeffrey Hull, Sharon Jelinsky, Kaori Nishikida, Ken McKee, Peter Berg, Ray Chung, Jorg Fischer, Kyoung-Wook Min, Seung-Han Oh, Jin-Guen Rhee, Kwangsun Ryu, Jong-Ho Shinn, Wonyong Han, Ho Jin, Dae-Hee Lee, Uk-Won Nam, Jang-Hyun Park, Kwang-Il Seon, In-Soo Yuk

The SPEAR (or 'FIMS') instrumentation has been used to conduct the first large-scale spectral mapping of diffuse cosmic far ultraviolet (FUV, 900-1750 AA) emission, including important diagnostics of interstellar hot (10^4 K - 10^6 K) and photoionized plasmas, H_2, and dust scattered starlight. The instrumentation's performance has allowed for the unprecedented detection of astrophysical diffuse far UV emission lines. A spectral resolution of 550 and an imaging resolution of 5' is achieved on-orbit in the Short (900 - 1175 AA) and Long (1335 - 1750 AA) bandpass channels within their respective 7.4 deg x 4.3' and 4.0 deg x 4.6' fields of view. We describe the SPEAR imaging spectrographs, their performance, and the nature and handling of their data.

 

astro-ph/0601589 [abs, ps, pdf, other] :

Title: Internal Kinematics of Galaxies: 3D Spectroscopy on Russian 6m Telescope
Authors: A.V. Moiseev (Special Astrophysical Observatory, Russia)
Comments: 5 pages, 3 figures, to appear in "Science Perspectives for 3D Spectroscopy", eds. M. Kissler-Patig, M. M. Roth and J. R. Walsh, ESO Astrophysics Symposia

We have considered some results concerning gas and stars kinematics of nearby galaxies recently obtained on the SAO RAS 6m telescope using the panoramic spectroscopy methods. The circumnuclear regions of the galaxies were observed with integral-field spectrograph MPFS. The large-scale ionized gas kinematics was studied with the scanning Fabry-Perot interferometer (FPI) in the multi-mode focal reducer SCORPIO. The main attention is given for kinematically decoupled regions in the galaxies: bars, spirals, polar disks and rings.

 

astro-ph/0601590 [abs, ps, pdf, other] :

Title: Molecular Hydrogen Fluorescence in the Eridanus Superbubble
Authors: K. Ryu, K. W. Min, J. W. Park, D. H. Lee, W. Han, U. W. Nam, J. H. Park, J. Edelstein, E. J. Korpela, K. Nishikida, E. F. van Dishoeck
Comments: 10 pages, 3 figures, apjl accepted

The first FUV (lambda lambda 1350-1750 A) spectral imaging observations of the Eridanus superbubble, obtained with the SPEAR/FIMS mission, have revealed distinct fluorescent emission from molecular hydrogen. In this study, the observed emission features were compared with those from a photo-dissociation region model with assumed illuminating stellar fields. The result showed rather high line ratios of I_{1580}/I_{1610}, which may imply the existence of high-temperature molecular clouds in the region. The H_2 fluorescence intensity showed a proportional correlation with H-alpha emission, indicating that the fluorescence and the recombination emission have similar physical origins.

 

astro-ph/0601591 [abs, ps, pdf, other] :

Title: Soft X-ray emission lines of Fe XV in solar flare observations and the Chandra spectrum of Capella
Authors: F. P. Keenan, J. J. Drake, S. Chung, N. S. Brickhouse, K. M. Aggarwal, A. Z. Msezane, R. S. I. Ryans, D. S. Bloomfield
Comments: 27 pages, 10 figures, Astrophysical Journal, in press

Recent calculations of atomic data for Fe XV have been used to generate theoretical line ratios involving n = 3-4 transitions in the soft X-ray spectral region (52-83 A), for a wide range of electron temperatures and densities applicable to solar and stellar coronal plasmas. A comparison of these with solar flare observations from a rocket-borne spectrograph (XSST) reveals generally good agreement between theory and experiment. In particular, the 82.76 A emission line in the XSST spectrum is identified, for the first time to our knowledge in an astrophysical source. Most of the Fe XV transitions which are blended have had the species responsible clearly identified, although there remain a few instances where this has not been possible. The line ratio calculations are also compared with a co-added spectrum of Capella obtained with the Chandra satellite, which is probably the highest signal-to-noise observation achieved for a stellar source in the 25-175 A soft X-ray region. Good agreement is found between theory and experiment, indicating that the Fe XV lines are reliably detected in Chandra spectra, and hence may be employed as diagnostics to determine the temperature and/or density of the emitting plasma. However the line blending in the Chandra data is such that individual emission lines are difficult to measure accurately, and fluxes may only be reliably determined via detailed profile fitting of the observations. The co-added Capella spectrum is made available to hopefully encourage further exploration of the soft X-ray region in astronomical sources.

 

astro-ph/0601592 [abs, ps, pdf, other] :

Title: The UKIRT Infrared Deep Sky Survey ZYJHK Photometric System: Passbands and Synthetic Colours
Authors: Paul C. Hewett (1), Stephen J. Warren (2), Sandy K. Leggett (3), Simon T. Hodgkin (1) ((1) Institute of Astronomy, Cambridge, (2) Imperial College, London, (3) JAC, Hawaii)
Comments: Monthly Notices, in press. Paper and file containing ASCII-format tables for download available at this http URL

The UKIRT Infrared Deep Sky Survey is a set of five surveys of complementary combinations of area, depth, and Galactic latitude, which began in 2005 May. The surveys use the UKIRT Wide Field Camera (WFCAM), which has a solid angle of 0.21deg^2. Here we introduce and characterise the ZYJHK photometric system of the camera, which covers the wavelength range 0.83-2.37 microns. We synthesise response functions for the five passbands, and compute colours in the WFCAM, SDSS and 2MASS bands, for brown dwarfs, stars, galaxies and quasars of different types. We provide a recipe for others to compute colours from their own spectra. Calculations are presented in the Vega system, and the computed offsets to the AB system are provided, as well as colour equations between WFCAM filters and the SDSS and 2MASS passbands. We highlight the opportunities presented by the new Y filter at 0.97-1.07 microns for surveys for hypothetical Y dwarfs (brown dwarfs cooler than T), and for quasars of very--high redshift, z>6.4.

 

astro-ph/0601593 [abs, ps, pdf, other] :

Title: On the CMB large-scales angular correlations
Authors: Armando Bernui, Thyrso Villela, Carlos A. Wuensche, Rodrigo Leonardi, Ivan Ferreira
Comments: 7 pages, 11 color figures, accepted for publication in A&A

We study the large-scale angular correlation signatures of the Cosmic Microwave Background (CMB) temperature fluctuations from WMAP data in several spherical cap regions of the celestial sphere, outside the Kp0 or Kp2 cut-sky masks. We applied a recently proposed method to CMB temperature maps, which permits an accurate analysis of their angular correlations in the celestial sphere through the use of normalized histograms of the number of pairs of such objects with a given angular separation versus their angular separation. The method allows for a better comparison of the results from observational data with the expected CMB angular correlations of a statistically isotropic Universe, computed from Monte Carlo maps according to the WMAP best-fit Lambda CDM model. We found that the, already known, anomalous lack of large-scale power in full-sky CMB maps are mainly due to missing angular correlations of quadrupole-like signature. This result is robust with respect to frequency CMB maps and cut-sky masks. Moreover, we also confirm previous results regarding the unevenly distribution in the sky of the large-scale power of WMAP data. In a bin-to-bin correlations analyses, measured by the full covariance matrix chi^2 statistic, we found that the angular correlations signatures in opposite Galactic hemispheres are anomalous at the 98%-99% confidence level.

 

astro-ph/0601594 [abs, ps, pdf, other] :

Title: Weak Gravitational Lensing of the CMB
Authors: Antony Lewis, Anthony Challinor
Comments: Invited review for Physics Reports, comments welcome; 87 pages, PDF fully hyperlinked

Weak gravitational lensing has several important effects on the cosmic microwave background (CMB): it changes the CMB power spectra, induces non-Gaussianities, and generates a B-mode polarization signal that is an important source of confusion for the signal from primordial gravitational waves. The lensing signal can also be used to help constrain cosmological parameters and lensing mass distributions. We review the origin and calculation of these effects. Topics include: lensing in General Relativity, the lensing potential, lensed temperature and polarization power spectra, implications for constraining inflation, non-Gaussian structure, reconstruction of the lensing potential, delensing, sky curvature corrections, simulations, cosmological parameter estimation, cluster mass reconstruction, and moving lenses/dipole lensing.

 

astro-ph/0601595 [abs, ps, pdf, other] :

Title: Faint emission lines in the Galactic H II regions M16, M20 and NGC 3603
Authors: J. Garcia-Rojas, C. Esteban, M. Peimbert, M.T. Costado, M. Rodriguez, A. Peimbert, M.T. Ruiz
Comments: 22 pages, 13 Tables, 7 Figures. Accepted for publication by MNRAS

We present deep echelle spectrophotometry of the Galactic {\hii} regions M16, M20 and NGC 3603. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100 to 10400 \AA range. We have detected more than 200 emission lines in each region. Physical conditions have been derived using different continuum and line intensity ratios. We have derived He$^{+}$, C$^{++}$ and O$^{++}$ abundances from pure recombination lines as well as abundances from collisionally excited lines for a large number of ions of different elements. We have obtained consistent estimations of the temperature fluctuation parameter, {\ts}, using different methods. We also report the detection of deuterium Balmer lines up to D$\delta$ (M16) and to D$\gamma$ (M20) in the blue wings of the hydrogen lines, which excitation mechanism seems to be continuum fluorescence. The temperature fluctuations paradigm agree with the results obtained from optical CELs and the more uncertain ones from far IR fine structure CELs in NGC 3603, although, more observations covering the same volume of the nebula are necessary to obtain solid conclusions.

 

astro-ph/0601596 [abs, ps, pdf, other] :

Title: Energy balance in two phase models for temperature fluctuations in HII regions
Authors: C. Giammanco, J.E. Beckman
Comments: To be submitted to A&A, 5 pag

We use a two phase model to explore scenarios which can give rise to the temperature fluctuations in HII regions observed via their emission lines, and not predicted by standard photoionization models. The case where they result from warm cloud emission in a hot tenuous substrate is rejected since the temperature required for the latter is shown to be an order of magnitude greater than either model predictions or observations. A model in which ~50% of a medium of uniform density is heated to a temperature within 2000K of the mean (~10000K) can yield observed fluctuation amplitudes with plausible heating requirements: the excess energy is of the same order as the underlying photoionization input. Using the reconnection of turbulent magnetic fields as a mechanism requires field strengths of order 10 muG, using the Orion nebula as our example. The model predicts observable local temperature variability on timescales of days.

 

astro-ph/0601597 [abs, ps, pdf, other] :

Title: Small scale contributions to CMB: A coherent analysis
Authors: Marian Douspis (IAS, LATT), Nabila Aghanim (IAS), Mathieu Langer (IAS)
Comments: 9 pages

We reanalyse Cosmic Microwave Background data from experiments probing both large and small scales. We assume that measured anisotropies are due not only to primary fluctuations but also, especially at small scales, to secondary effects (namely the Sunyaev-Zel'dovich effect) and possible point source contaminations. We first consider primary and secondary anisotropies only. For the first time in such analyses, the cosmological dependence of secondary fluctuations is fully taken into account. We show in that case that a higher value of the normalisation $\sigma\_8$ is preferred, as found by previous studies, but also higher values of the optical depth $\tau$ and power spectrum index $n\_s$ are needed. In the second part of our analysis, we further include possible contaminations from unresolved and unremoved point sources. Under these considerations, we discuss the effects on the cosmological parameters. We further obtain the best combination of relative contributions of the three kinds of sources to the measured microwave power on small scales at each frequency. Our method allows us to simultaneously obtain cosmological parameters and explain the so-called small scale power excess in a consistent way.

 

astro-ph/0601598 [abs, ps, pdf, other] :

Title: Holographic dark energy with a constant vacuum energy density
Authors: B. Guberina, R. Horvat, H. Nikolic
Comments: 12 pages, 2 figures

We present a holographic dark-energy model in which the Newton constant $G_{N}$ scales in such a way as to render the vacuum energy density a true constant. Nevertheless, the model acts as a dynamical dark-energy model since the scaling of $G_{N}$ goes at the expense of deviation of concentration of dark-matter particles from its canonical form and/or of promotion of their mass to a time-dependent quantity, thereby making the effective equation of state (EOS) variable and different from -1 at the present epoch. Thus the model has a potential to naturally underpin Dirac's suggestion for explaining the large-number hypothesis, which demands a dynamical $G_{N}$ along with the creation of matter in the universe. We show that with the aid of observational bounds on the variation of the gravitational coupling, the effective-field theory IR cutoff can be strongly restricted, being always closer to the future event horizon than to the Hubble distance. As for the observational side, the effective EOS restricted by observation can be made arbitrary close to -1, and therefore the present model can be considered as a ``minimal'' dynamical dark-energy scenario. In addition, for nonzero but small curvature $(|\Omega_{k0}| \lsim 0.003)$, the model easily accommodates a transition across the phantom line for redshifts $z \lsim 0.2 $, as mildly favored by the data. A thermodynamic aspect of the scenario is also discussed.

 

astro-ph/0601599 [abs, ps, pdf, other] :

Title: Andromeda X, A New Dwarf Spheroidal Satellite of M31: Photometry
Authors: Daniel B. Zucker, Alexei Y. Kniazev, David Martinez-Delgado, Eric F. Bell, Hans-Walter Rix, Eva K. Grebel, Jon A. Holtzman, Rene A. M. Walterbos, Constance M. Rockosi, Donald G. York, J. C. Barentine, Howard Brewington, J. Brinkmann, Michael Harvanek, S. J. Kleinman, Jurek Krzesinski, Dan Long, Eric H. Neilsen, Jr., Atsuko Nitta, Stephanie A. Snedden
Comments: 4 pages, 4 figures; submitted to Astrophysical Journal Letters

We report the discovery of Andromeda X, a new dwarf spheroidal satellite of M31, based on stellar photometry from the Sloan Digital Sky Survey (SDSS). Using follow-up imaging data we have estimated its distance and other physical properties. We find that Andromeda X has a dereddened central surface brightness of mu_V,0 ~ 26.7 mag arcsec^-2 and a total apparent magnitude of V_tot ~ 16.1, which at the derived distance modulus, (m - M)_0 ~ 24.12 - 24.34, yields an absolute magnitude of M_V ~ -8.1 +/- 0.5; these values are quite comparable to those of Andromeda IX, a previously-discovered low luminosity M31 satellite. The discoveries of Andromeda IX and Andromeda X suggest that such extremely faint satellites may be plentiful in the Local Group.

 

astro-ph/0601600 [abs, ps, pdf, other] :

Title: Statistical Mechanics of the Self-Gravitating Gas: Thermodynamic Limit, Unstabilities and Phase Diagrams
Authors: H. J. de Vega, N. G. Sanchez
Comments: 12 pages, Invited lecture at `Statistical Mechanics of Non-Extensive Systems', Observatoire de Paris, October 2005, to be published in a Special issue of `Les Comptes rendus de l'Acade'mie des sciences', Elsevier

We show that the self-gravitating gas at thermal equilibrium has an infinite volume limit in the three ensembles (GCE, CE, MCE) when (N, V) -> infty, keeping N/V^{1/3} fixed, that is, with eta = G m^2 N/[ V^{1/3} T] fixed. We develop MonteCarlo simulations, analytic mean field methods (MF) and low density expansions. We compute the equation of state and find it to be locally p(r) = T rho_V(r), that is a local ideal gas equation of state. The system is in a gaseous phase for eta < eta_T = 1.51024...and collapses into a very dense object for eta > eta_T in the CE with the pressure becoming large and negative. The isothermal compressibility diverges at eta = eta_T. We compute the fluctuations around mean field for the three ensembles. We show that the particle distribution can be described by a Haussdorf dimension 1 < D < 3.

 

astro-ph/0601601 [abs, ps, pdf, other] :

Title: Self-Gravitating Phase Transitions: Point Particles, Black Holes and Strings
Authors: Norma G. Sanchez, Observatoire de Paris, LERMA, CNRS
Comments: Invited lecture at `Statistical Mechanics of Non-Extensive Systems', Observatoire de Paris, 24-25 October 2005, to be published in a Special issue of `Les Comptes rendus de l'Academie des sciences', Elsevier

We compute the quantum string entropy S_s(m,j) of the microscopic string states of mass m and spin j in two physically relevant backgrounds: Kerr (rotating) black holes and de Sitter (dS) space-time. We find a new formula for the quantum gravitational entropy S_{sem} (M, J), as a function of the usual Bekenstein-Hawking entropy S_{sem}^(0)(M, J). We compute the quantum string emission by a black hole in de Sitter space-time (bhdS). In all these cases: (i) strings with the highest spin, and (ii) in dS space-time, (iii) quantum rotating black holes, (iv) quantum dS regime, (v) late bhdS evaporation, we find a new gravitational phase transition with a common distinctive universal feature: A square root branch point singularity in any space-time dimensions. This is the same behavior as for the thermal self-gravitating gas of point particles (de Vega-Sanchez transition), thus describing a new universality class.

 

astro-ph/0601602 [abs, ps, pdf, other] :

Title: Production of antimatter in the galaxy
Authors: Pierre Salati
Comments: Invited talk at the TAUP 2005 Conference in Zaragoza (Spain)

The astronomical dark matter could be made of weakly interacting massive species whose mutual annihilations should produce antimatter particles and distortions in the corresponding energy spectra. The propagation of cosmic rays inside the Milky Way plays a crucial role and is briefly presented. The uncertainties in its description lead to considerable variations in the predicted primary fluxes. This point is illustrated with antiprotons. Finally, the various forthcoming projects are rapidly reviewed with their potential reach.

 

astro-ph/0601603 [abs, ps, pdf, other] :

Title: Multi-Dimensional Simulations of the Accretion-Induced Collapse of White Dwarfs to Neutron Stars
Authors: Luc Dessart, Adam Burrows, Christian Ott, Eli Livne, Sung-Chul Yoon, Norbert Langer
Comments: 25 pages, 19 figures, submitted to ApJ, high resolution of the paper available at this http URL

We present 2.5D radiation-hydrodynamics simulations of the accretion-induced collapse (AIC) of white dwarfs, starting from 2D rotational equilibrium configurations. Electron capture leads to the collapse to nuclear densities of these cores within a few tens of milliseconds. The shock generated at bounce moves slowly, but steadily, outwards. Within 50-100ms, the stalled shock breaks out of the white dwarf along the poles. The blast is followed by a neutrino-driven wind that develops within the white dwarf, in a cone of ~40deg opening angle about the poles, with a Mdot of 5-8 x 10^{-3} Msun/s. The ejecta have an entropy on the order of 20-50 k_B/baryon, and an electron fraction distribution that is bimodal. By the end of the simulations, at >600ms after bounce, the explosion energy has reached 3-4 x 10^49 erg and the outflowing mass has reached a few times 0.001Msun. We estimate the asymptotic explosion energies to be lower than 10^50 ergs, significantly lower than those inferred in the core collapse of massive progenitors. AIC of WDs thus represents one instance where a neutrino mechanism leads undoubtedly to a successful, albeit weak, explosion. We document in detail the numerous effects of the fast rotation of the progenitors: the neutron stars are aspherical; the ``\nu_{\mu}'' and \bar{\nu}_e luminosities are reduced compared to the \nu_e luminosity; the deleptonized region has a butterfly shape; the neutrino flux and electron fraction depend strongly upon latitude (a la von Zeipel); and a quasi-Keplerian 0.1-0.5Msun accretion disk is formed [abridged].

 

astro-ph/0601604 [abs, ps, pdf, other] :

Title: OH maser disc and outflow in the Orion-BN/KL region
Authors: R. J. Cohen, N. Gasipron, J. Meaburn, M. F. Graham
Comments: 23 pages, 10 figures. Accepted for publication in MNRAS

MERLIN measurements of 1.6-GHz OH masers associated with Orion-BN/KL are presented, and the data are compared with data on other masers, molecular lines, compact radio continuum sources and infrared sources in the region. OH masers are detected over an area 30 arcsec in diameter, with the majority lying along an approximately E-W structure that extends for approx. 18~arcsec, encompassing the infrared sources IRc2, IRc6 and IRc7. Radial velocities range from -13 to +42 km/s. The system of OH masers shows a velocity gradient together with non-circular motions. The kinematics are modelled in terms of an expanding and rotating disc or torus. The rotation axis is found to be in the same direction as the molecular outflow. There is an inner cavity of radius approx 1300 au with no OH masers. The inner cavity, like the water `shell' masers and SiO masers, is centred on radio source I. Some of the OH masers occur in velocity-coherent strings or arcs that are longer than 5~arcsec (2250 au). One such feature, Stream A, is a linear structure at position angle approx 45 degree, lying between IRc2 and BN. We suggest that these masers trace shock fronts, and have appeared, like a vapour trail, 200 yr after the passage of the runaway star BN. The radio proper motions of BN, source I and source n project back to a region near the base of Stream A that is largely devoid of OH masers. The 1612-MHz masers are kinematically distinct from the other OH masers. They are also more widely distributed and appear to be associated with the outflow as traced by water masers and by the 2.12-micron emission from shocked H2 The magnetic field traced by the OH masers ranges from 1.8 to 16.3 mG, with a possible reversal. No OH masers were found associated with even the most prominent proplyds within 10 arcsec of Theta1 Ori C.

 

astro-ph/0601605 [abs, ps, pdf, other] :

Title: Velocity field and star formation in the Horsehead nebula
Authors: Pierre Hily-Blant (IRAM), David Teyssier (SRON), Sabin Philipp (MPIFR), Rolf Gusten (MPIFR)
Comments: 11 pages, 9 figures, A&A

Using large scale maps in C18O(2-1) and in the continuum at 1.2mm obtained at the IRAM-30m antenna with the Heterodyne Receiver Array (HERA) and MAMBO2, we investigated the morphology and the velocity field probed in the inner layers of the Horsehead nebula. The data reveal a non--self-gravitating (m/mvir = 0.3) filament of dust and gas (the "neck", diameter = 0.15-0.30 pc) connecting the Horsehead western ridge, a Photon-Dominated Region illuminated by sigmaOri, to its parental cloud L1630. Several dense cores are embedded in the ridge and the neck. One of these cores appears particularly peaked in the 1.2 mm continuum map and corresponds to a feature seen in absorption on ISO maps around 7 micr. Its \cdo emission drops at the continuum peak, suggestive of molecular depletion onto cold grains. The channel maps of the Horsehead exhibit an overall north-east velocity gradient whose orientation swivels east-west, showing a somewhat more complex structure than was recently reported by \cite{pound03} using BIMA CO(1-0) mapping. In both the neck and the western ridge, the material is rotating around an axis extending from the PDR to L1630 (angular velocity=1.5-4.0 km/s). Moreover, velocity gradients along the filament appear to change sign regularly (3 km/s/pc, period=0.30 pc) at the locations of embedded integrated intensity peaks. The nodes of this oscillation are at the same velocity. Similar transverse cuts across the filament show a sharp variation of the angular velocity in the area of the main dense core. The data also suggest that differential rotation is occurring in parts of the filament. We present a new scenario for the formation and evolution of the nebula and discuss dense core formation inside the filament.

 

astro-ph/0601606 [abs, ps, pdf, other] :

Title: The photometric evolution of dissolving star clusters I: First predictions
Authors: Henny J.G.L.M. Lamers (1,2), Peter Anders (3), Richard de Grijs (4) ((1) Astronomical Institute, Utrecht University, (2) SRON Laboratory for Space Research, Utrecht, (3) Institut fuer Astrophysik, University Goettingen, (4) Department of Physics & Astronomy, University of Sheffield)
Comments: accepted for publication in A&A

We calculated the broad-band photometric evolution of unresolved star clusters, including the preferential loss of low-mass stars due to mass segregation. The stellar mass function of a cluster evolves due to three effects: (a) the evolution of massive stars; (b) early tidal effects reduce the mass function independently of the stellar mass; (c) after mass segregation has completed, tidal effects preferentially remove the lowest-mass stars from the cluster. Results: (1) During the first ~40% of the lifetime of a cluster the cluster simply gets fainter due to the loss of stars by tidal effects. (2) Between ~40 and ~80% of its lifetime the cluster gets bluer due to the loss of low-mass stars. This will result in an underestimate of the age of clusters if standard cluster evolution models are used (0.15 -- 0.5 dex). (3) After ~80% of the total lifetime of a cluster it will rapidly get redder. This is because stars at the low-mass end of the main sequence, which are preferentially lost, are bluer than the AGB stars that dominate the light at long wavelengths, resulting in an age overestimate. (4) Clusters with mass segregation and the preferential loss of low-mass stars evolve along almost the same tracks in colour-colour diagrams as clusters without mass segregation. Therefore it will be difficult to distinguish this effect from that due to the cluster age for unresolved clusters, unless the total lifetime of the clusters can be estimated. (5) The changes in the colour evolution of unresolved clusters due to the preferential loss of low-mass stars will affect the determination of the SFHs. (6) The preferential loss of low-mass stars might explain the presence of old (~13 Gyr) clusters in NGC 4365 which are photometrically disguised as intermediate-age clusters (2 - 5 Gyr). [Abridged]

 

astro-ph/0601607 [abs, ps, pdf, other] :

Title: Dissipative structures of diffuse molecular gas: I - Broad HCO$^+$(1-0) emission
Authors: E. Falgarone (LERMA), G. Pineau Des Forêts (IAS), P. Hily-Blant (LAM/IRAM), P. Schilke (MPIFR)
Comments: 14 pages

Results: We report the detection of broad HCO+(1-0) lines (10 mK < T < 0.5 K). The interpretation of 10 of the HCO+ velocity components is conducted in conjunction with that of the associated optically thin 13CO emission. The derived HCO+ column densities span a broad range, $10^{11}< N(HCO+)/\Delta v <4 \times 10^{12} \rm cm^2/(km/s^{-1}$, and the inferred HCO+ abundances, $2 \times 10^{-10}<X(HCO+) < 10^{-8}$, are more than one order of magnitude above those produced by steady-state chemistry in gas weakly shielded from UV photons, even at large densities. We compare our results with the predictions of non-equilibrium chemistry, swiftly triggered in bursts of turbulence dissipation and followed by a slow thermal and chemical relaxation phase, assumed isobaric. The set of values derived from the observations, i.e. large HCO+ abundances, temperatures in the range of 100--200 K and densities in the range 100--1000 cm3, unambiguously belongs to the relaxation phase. The kinematic properties of the gas suggest in turn that the observed HCO+ line emission results from a space-time average in the beam of the whole cycle followed by the gas and that the chemical enrichment is made at the expense of the non-thermal energy. Last, we show that the "warm chemistry" signature (i.e large abundances of HCO+, CH+, H20 and OH) acquired by the gas within a few hundred years, the duration of the impulsive chemical enrichment, is kept over more than thousand years. During the relaxation phase, the \wat/OH abundance ratio stays close to the value measured in diffuse gas by the SWAS satellite, while the OH/HCO+ ratio increases by more than one order of magnitude.

 

astro-ph/0601608 [abs, ps, pdf, other] :

Title: First detection of Lyman continuum photon escape from a local starburst galaxy
Authors: Nils Bergvall, Erik Zackrisson, B-G Andersson, Daniel Arnberg, Josefa Masegosa, Goran Ostlin

The dominating reionization source in the young universe has yet to be identified. Possible candidates include metal poor starburst dwarf galaxies of which the Blue Compact Galaxy Haro 11 may represent a local counterpart. Using the Far Ultraviolet Spectroscopic Explorer (FUSE) we obtained spectra of Haro 11 to search for leaking ionizing radiation. A weak signal shortwards of the Lyman break is identified as Lyman continuum (LyC) emission escaping from the ongoing starburst. From profile fitting to weak metal lines we derive column densities of the low ionization species. Adopting a metallicity typical of the H II regions of Haro 11, the corresponding H I column density is optically thick in the LyC. Therefore most of the LyC photons must escape through transparent holes in the interstellar medium. Using spectral evolutionary models we constrain the escape fraction of the produced LyC photons to between 4 and 10%, assuming a normal Salpeter IMF. We argue that in a hierarchical galaxy formation scenario, this allows for a substantial contribution to cosmic reionization by starburst dwarf galaxies at high redshifts.

 

astro-ph/0601609 [abs, ps, pdf, other] :

Title: Planets and Asteroids in the gamma Cephei System
Authors: P.E. Verrier (Cambridge), N.W. Evans (Cambridge)
Comments: 10 pages, 14 figures, MNRAS, submitted

The binary star system gamma Cephei is unusual in that it harbours a stable giant planet around the larger star at a distance only about a tenth of that of the stellar separation. Numerical simulations are carried out into the stability of test particles in the system. This provides possible locations for additional planets and asteroids. To this end, the region interior to the planet is investigated in detail and found to permit structured belts of particles. The region between the planet and the secondary star however shows almost no stability. The existence of an Edgeworth-Kuiper belt analogue is found to be a possibility beyond 65 au from the barycentre of the system, although it shows almost no structural features. Finally, the region around the secondary star is studied for the first time. Here, a zone of stability is seen out to 1.5 au for a range of inclinations. In addition, a ten Jupiter-mass planet is shown to remain stable about this smaller star, with the habitability and observational properties of such an object being discussed.

 

astro-ph/0601610 [abs, ps, pdf, other] :

Title: Contact Binaries with Additional Components.I. The Extant Data
Authors: Theodor Pribulla, Slavek M. Rucinski
Comments: Submitted to AJ. 10 figures

We have attempted to establish an observational evidence for presence of distant companions which may have acquired and/or absorbed the angular momentum during evolution of multiple systems thus facilitating or enabling formation of contact binaries. In this preliminary investigation we use several techniques (some of them distance-independent) and mostly disregard detection biases of individual techniques in an attempt to establish a lower limit to the frequency of triple systems. While the whole sample of 151 contact binary stars brighter than V_max = 10 mag. gives a firm lower limit of 42%+/-5%, the corresponding number for the much better observed Northern-sky sub-sample is 59%+/-8%. These estimates indicate that most contact binary stars exist in multiple systems.

 

astro-ph/0601611 [abs, ps, pdf, other] :

Title: The effect of uncertainties on chemical models of dark clouds
Authors: Valentine Wakelam, Eric Herbst, Franck Selsis (CRAL)
Comments: Accepted for publication in A&A. Astronomy and Astrophysics in press (2006) in press

The gas-phase chemistry of dark clouds has been studied with a treatment of uncertainties caused both by errors in individual rate coefficients and uncertainties in physical conditions. Moreover, a sensitivity analysis has been employed to attempt to determine which reactions are most important in the chemistry of individual species. The degree of overlap between calculated errors in abundances and estimated observational errors has been used as an initial criterion for the goodness of the model and the determination of a best 'chemical' age of the source. For the well-studied sources L134N and TMC-1CP, best agreement is achieved at so-called "early times" ~10$^{5}$ yr, in agreement with previous calculations but here put on a firmer statistical foundation. A more detailed criterion for agreement, which takes into account the degree of disagreement, is also proposed. Poorly understood but critical classes of reactions are delineated, especially reactions between ions and polar neutrals. Such reactions will have to be understood better before the chemistry can be made more secure. Nevertheless, the level of agreement is low enough to indicate that a static picture of physical conditions without consideration of interactions with grain surfaces is inappropriate for a complete understanding of the chemistry.

 

astro-ph/0601612 [abs, ps, pdf, other] :

Title: Two-body problem with the cosmological constant and observational constraints
Authors: Ph. Jetzer (Uni. Zurich) M. Sereno (Uni. Zurich)
Comments: 8 pages, accepted for publication in Phys. Rev. D

We discuss the influence of the cosmological constant on the gravitational equations of motion of bodies with arbitrary masses and eventually solve the two-body problem. Observational constraints are derived from measurements of the periastron advance in stellar systems, in particular binary pulsars and the solar system. Up to now, Earth and Mars data give the best constraint, Lambda < 10^{-36} km^{-2}; bounds from binary pulsars are potentially competitive with limits from interplanetary measurements. If properly accounting for the gravito-magnetic effect, this upper limit on $\Lambda$ could greatly improve in the near future thanks to new data from planned or already operating space-missions.

 

astro-ph/0601613 [abs, ps, pdf, other] :

Title: Formation of a partially-screened inner acceleration region in radio pulsars: drifting subpulses and thermal X-ray emission from polar cap surface
Authors: Janusz Gil, George Melikidze, Bing Zhang

Formation of a partially-screened inner acceleration region in 102 pulsars with drifting subpulses is considered. This is motivated by that spark discharges leading to drifting subpulses cannot be produced in a steady polar cap flow and thus the inner accelerator should be intermittent in nature, that the traditional pure vacuum gap model predicts too fast a sub-pulse drifting rate, and that recent X-ray observations as well as the radio drifting data are both consistent with the inner gap being partially screened. By means of the condition $T_{\rm c}/T_{\rm s}>1$ (where $T_{\rm c}$ is the critical temperature above which the surface delivers a thermal flow to adequately supply the corotation charge density, and $T_{\rm s}$ is the actual surface temperature), it is found that a partially-screened acceleration region can be formed given that the near surface magnetic fields are very strong and curved. We consider both curvature radiation (CR) and resonant inverse Compton scattering (ICS) to produce seed photons for pair production. It is found that the ICS mechanism is unlikely to develop a partially screened gap, while the CR mechanism can naturally drive the sparking discharge of such a gap. Observational signatures of thermal radiation from the spark-heated polar caps are consistent with the model that invokes a partially screened gap formed in strong nondipolar surface magnetic fields.

 

astro-ph/0601614 [abs, ps, pdf, other] :

Title: Low Carbon Abundance in Type Ia Supernovae
Authors: G. H. Marion, P. Hoeflich, J.C. Wheeler, E. L. Robinson (1), C. L. Gerardy (1 and 2), W. D. Vacca (3) ((1) University of Texas at Austin, (2) Astrophysics Group, Imperial College London, (3) SOFIA-USRA, NASA Ames Research Center)
Comments: accepted for publication in ApJ

We investigate the quantity and composition of unburned material in the outer layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr and 20 04bw. Pristine matter from a white dwarf progenitor is expected to be a mixture of oxygen and carbon in approximately equal abundance. Using near-infrared (NIR, 0.7-2.5 microns) spectra, we find that oxygen is abundant while carbon is severely depleted with low upper limits in the outer third of the ejected mass. Strong features from the OI line at rest wavelength = 0.7773 microns are observed through a wide range of expansion velocities approx. 9,000 - 18,000 km/s. This large velocity domain corresponds to a physical region of the supernova with a large radial depth. We show that the ionization of C and O will be substantially the same in this region. CI lines in the NIR are expected to be 7-50 times stronger than those from OI but there is only marginal evidence of CI in the spectra and none of CII. We deduce that for these three normal SNe Ia, oxygen is more abundant than carbon by factors of 100 - 1,000. MgII is also detected in a velocity range similar to that of OI. The presence of O and Mg combined with the absence of C indicates that for these SNe Ia, nuclear burning has reached all but the extreme outer layers; any unburned material must have expansion velocities greater than 18,000 km/s. This result favors deflagration to detonation transition (DD) models over pure deflagration models for SNe Ia.

 

astro-ph/0601615 [abs, ps, pdf, other] :

Title: SPEAR Far Ultraviolet Spectral Images of the Cygnus Loop
Authors: Kwang-Il Seon, Wonyong Han, Uk-Won Nam, Jang-Hyun Park, Jerry Edelstein, Eric J. Korpela, Ravi Sankrit, Kyoung-Wook Min, Kwangsun Ryu, Il-Joong Kim
Comments: 13 pages, 3 figures, 1 table, accepted for publication in ApJL

We present far-ultraviolet (FUV) spectral images, measured at C IV 1550, He II 1640, Si IV+O IV] 1400, and O III] 1664, of the entire Cygnus Loop, observed with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR) instrument, also known as FIMS. The spatial distribution of FUV emission generally corresponds with a limb-brightened shell, and is similar to optical, radio and X-ray images. The features found in the present work include a ``carrot'', diffuse interior, and breakout features, which have not been seen in previous FUV studies. Shock velocities of 140-160 km/s is found from a line ratio of O IV] to O III], which is insensitive not only to resonance scattering but also to elemental abundance. The estimated velocity indicates that the fast shocks are widespread across the remnant. By comparing various line ratios with steady-state shock models, it is also shown that the resonance scattering is widespread.

 

astro-ph/0601616 [abs, ps, pdf, other] :

Title: A search for magnetic fields in the variable HgMn star $\alpha$ Andromedae
Authors: G.A. Wade, M. Auriere, S. Bagnulo, J.-F. Donati, N. Johnson, J.D. Landstreet, F. Lignieres, P. Petit, N. Toque, E. Alecian, C. Folsom

With this work, we have conducted an extensive search for magnetic fields in the photosphere of $\alpha$~And. We have acquired new circular polarisation spectra with the MuSiCoS and ESPaDOnS sp ectropolarimeters. We have also obtained FORS1 circular polarisation spectra fro m the ESO Archive, and considered all previously published magnetic data. This e xtensive dataset has been used to systematically test for the presence of magnet ic fields in the photosphere of $\alpha$~And. We have also examined the high-res olution spectra for line profile variability. The polarimetric and magnetic data provide no convincing evidence for photospheric magnetic fields. The highest-S/N phase- and velocity-resolved Stokes $V$ profiles, obtained with ESPaDOnS, allow us to place a $3\sigma$ upper limit of abou t 100~G on the possible presence of any undetected pure dipolar, quadrupolar or octupolar surface magnet ic fields (and just 50~G for fields with significant obliquity). We also conside r and dismiss the possible existence of more complex fossil and dynamo-generated fields, and discuss the implications of these results for explaining the non-un iform surface distribution of Hg. The very high-quality ESPaDOnS spectra have al lowed us to confidently detect variability of Hg~{\sc ii} $\lambda 6149$, $\lamb da 5425$ and $\lambda 5677$. The profile variability of the Hg~{\sc ii} lines is strong, and similar to that of the Hg~{\sc ii} $\lambda 3984$ line. On the ot her hand, variability of other lines (e.g. Mn, Fe) is much weaker, and appears to be attributable to orbital modulation, continuum normalisation differences and weak, variable fringing.

 

astro-ph/0601617 [abs, ps, pdf, other] :

Title: Stochastic Gravitational Wave Production After Inflation
Authors: Richard Easther, Eugene A. Lim (Yale)
Comments: 11 pages

In many models of inflation, the period of accelerated expansion ends with preheating, a highly non-thermal phase of evolution during which the inflaton pumps energy into a specific set of momentum modes of field(s) to which it is coupled. This necessarily induces large, transient density inhomogeneities which can source a significant spectrum of gravitational waves. In this paper, we consider the generic properties of gravitational waves produced during preheating, perform detailed calculations of the spectrum for several specific inflationary models, and identify problems that require further study. In particular, we argue that if these gravitational waves exist they will necessarily fall within the frequency range that is feasible for direct detection experiments -- from laboratory through to solar system scales. We extract the gravitational wave spectrum from numerical simulations of preheating after $\lambda \phi^4$ and $m_{\phi}^2 \phi^2$ inflation, and find that they lead to a gravitational wave amplitude of around $\Omega_{gw}h^2\sim 10^{-10}$. This is considerably higher than the amplitude of the primordial gravitational waves produced during inflation. However, the typical wavelength of these gravitational waves is considerably shorter than LIGO scales, although in extreme cases they may be visible at scales accessible to the proposed BBO mission. We survey possible experimental approaches to detecting any gravitational wave background generated during preheating.