Astrophysics

astro-ph new abstracts, Mon, 10 Apr 06 00:00:09 GMT
0604146 -- 0604176 received

astro-ph/0604146 [abs, ps, pdf, other] :: Title: Low T/|W| dynamical instabilities in differentially rotating stars: Diagnosis with canonical angular momentum
Authors: Motoyuki Saijo, Shin'ichirou Yoshida
Comments: 8 pages with 6 eps figures, aipproc.cls. To appear in Proceedings of the Albert Einstein Century International Conference, Paris, France, 2005, edited by Jean-Michel Alimi and Andre Fuzfa (American Institute of Physics)

We study the nature of non-axisymmetric dynamical instabilities in differentially rotating stars with both linear eigenmode analysis and hydrodynamic simulations in Newtonian gravity. We especially investigate the following three types of instability; the one-armed spiral instability, the low T/|W| bar instability, and the high T/|W| bar instability, where T is the rotational kinetic energy and W is the gravitational potential energy. The nature of the dynamical instabilities is clarified by using a canonical angular momentum as a diagnostic. We find that the one-armed spiral and the low T/|W| bar instabilities occur around the corotation radius, and they grow through the inflow of canonical angular momentum around the corotation radius. The result is a clear contrast to that of a classical dynamical bar instability in high T/|W|. We also discuss the feature of gravitational waves generated from these three types of instability.
astro-ph/0604147 [abs, ps, pdf, other] :: Title: Removing the Microlensing Blending-Parallax Degeneracy Using Source Variability
Authors: R.J. Assef, A. Gould (The Ohio State University), the EROS-2, MACHO, OGLE Collaborations
Comments: 15 text pages + 2 tables + 7 figures

Microlensing event MACHO 97-SMC-1 is one of the rare microlensing events for which the source is a variable star, simply because most variable stars are systematically eliminated from microlensing studies. Using observational data for this event, we show that the intrinsic variability of a microlensed star is a powerful tool to constrain the nature of the lens by breaking the degeneracy between the microlens parallax and the blended light. We also present a statistical test for discriminating the location of the lens based on the \chi^2 contours of the vector \Lambda, the inverse of the projected velocity. We find that while SMC self lensing is somewhat favored, neither location can be ruled out with good confidence.
astro-ph/0604148 [abs, ps, pdf, other] :: Title: UV Radiative Feedback on High-Redshift Proto-Galaxies
Authors: Andrei Mesinger, Greg Bryan, Zoltan Haiman
Comments: 18 pages, 18 figures, ApJ submitted

We use three-dimensional hydrodynamic simulations to investigate the effects of a transient photoionizing ultraviolet (UV) flux on the collapse and cooling of pregalactic clouds. These clouds have masses in the range 10^5 -10^7 M_sun, form at high redshifts (z>18), are assumed to lie within the short-lived cosmological HII regions around the first generation of stars. In addition, we study the combined effects of this transient UV flux and a persistent Lyman-Werner (LW) background from distant sources. In the absence of a LW background, we find that a critical specific intensity of J_UV ~ 0.1 x 10^-21 ergs s^-1 cm^-2 Hz^-1 sr^-1 demarcates a transition from net negative to positive feedback for the halo population. A weaker UV flux stimulates subsequent star formation inside the fossil HII regions, by enhancing the H_2 molecule abundance. A stronger UV flux significantly delays star-formation by reducing the gas density, and increasing the cooling time, at the centers of collapsing halos. At a fixed J_UV, the sign of the feedback also depends strongly on the density of the gas at the time of UV illumination. Regardless of the whether the feedback is positive or negative, we find that once the UV flux is turned off, its impact stars to diminish after ~30% of the Hubble time. In the more realistic case when a LW background is present, with J_LW > 0.01 x 10^-21 ergs s^-1 cm^-2 Hz^-1 sr^-1, strong suppression persists down to the lowest redshift (z=18) in our simulations. Finally, we find evidence that heating and photoevaporation by the transient UV flux renders the ~10^6 M_sun halos inside fossil HII regions more vulnerable to subsequent H_2 photo-dissociation by a LW background.
astro-ph/0604149 [abs, ps, pdf, other] :: Title: The End of the Reionization Epoch Probed by Ly-alpha Emitters at z=6.5 in the Subaru Deep Field
Authors: N. Kashikawa, K. Shimasaku, M.A. Malkan, M. Doi, Y. Matsuda, M. Ouchi, Y. Taniguchi, C. Ly, T. Nagao, M. Iye, K. Motohara, T. Murayama, K. Murozono, K. Nariai, K. Ohta, S. Okamura, T. Sasaki, Y. Shioya, M. Umemura
Comments: 17 pages, 13 color figures. Revised version after referee's report. Black&White version is available at this http URL

We report an extensive search for Lyman-alpha emitters (LAEs) at z=6.5 in the Subaru Deep Field. Subsequent spectroscopy with Subaru/Keck identified eight more LAEs, giving us a total of 17 spectroscopically confirmed LAEs at z=6.5. Based on these 17 spectroscopic sample complemented by the 58 photometric sample, we derived a more accurate Ly-alpha luminosity function of LAEs at z=6.5, that reveals an apparent deficit at the bright end, of ~0.75 mag fainter L*, compared with that of z=5.7. The difference of LAE luminosity functions between z=5.7 and z=6.5 has a 3-sigma significance, which is reduced to 2-sigma when taking into account the cosmic variance. This result could be an implication that the reionization of the universe has not been completed at z=6.5. The spatial distribution of LAEs at z=6.5 was found to be homogeneous over the field. We discuss some implications to the reionization of the universe.
astro-ph/0604150 [abs, ps, pdf, other] :: Title: New observational techniques and analysis tools for wide field CCD surveys and high resolution astrometry
Authors: O. Fors
Comments: This is the abstract of my PhD Thesis at University of Barcelona. Abridged and complete summary available from astro-ph. Full thesis (22Mb) in separate chapters and with a summary in Catalan is available from: this http URL

(Abridged) In the first part of this thesis, a general methodology for applying image deconvolution to wide-field CCD imagery. Results show that wavelet-based deconvolution can increase limiting magnitude up to 0.6 mag and improve limiting resolution 1 pixel with respect to original image with no astrometric accuracy degradation.
In the second part, a new observational technique based on CCD fast drift scanning has been proposed for lunar occultations (LO) and speckle interferometry. This enables all kind of professional and high-end amateur observatories to perform such kind of observations.
For LO, 16 new binaries up to 2mas of projected separation were detected and stellar diameters measurements in the 7 mas regime were obtained with that CCD and IR subarray based techniques. A new wavelet-based LO reduction pipeline was implemented.
For speckle, CCD fast drift scanning technique was validated with the observation of four binary systems with well determined orbits. The results of separation, position angle and magnitude difference are in accordance with published measurements. A new approach for calibrating speckle transfer function from the binary power spectrum itself has been introduced. It does not require point source observations, which gives a more effective use of observation time.
astro-ph/0604151 [abs, ps, pdf, other] :: Title: A Simple Two-Parameter Characterization of Gamma-Ray Burst Time Histories
Authors: Jon Hakkila, Timothy W. Giblin (College of Charleston)
Comments: Accepted for publication in The Astrophysical Journal. 29 pages, 10 figures, 1 table

A simple scheme delineates Long GRBs with similar time histories using the Internal Luminosity Function power-law index and the spectral lag. Several generalizations are made about time history morphologies: 1) GRBs with long spectral lags contain fewer pulses that are broader than those found in bursts with short spectral lags, 2) short-lag bursts with small ILF power-law indices have many narrow pulses and are highly variable, while long-lag bursts with small ILF power-law indices are characterized by broad, smooth pulses and have low variability.
GRB time history morphologies primarily identify intrinsic rather than extrinsic characteristics based on correlations with gamma-ray luminosity, afterglow luminosity, and numbers of pulses. These characteristics result because internal relativistic effects due to bulk Lorentz factor are larger than cosmological effects, and because the numbers and shapes of pulses indicate different efficiencies and forms of GRB energy release.
Single-pulsed GRBs are characterized either by large ILF power indices (indicating a range of jet opening angles and Lorentz factors, with a FRED pulse shape), or they have long lags (large jet opening angles with low Lorentz factors, with either a FRED pulse shape or an unpeaked, smooth pulse shape). They also have lower-luminosity afterglows than multi-pulsed GRBs. GRBs with simple time histories are often associated with Type Ibc supernovae. This suggests that some single-pulsed GRBs contain single, beamed blast waves that are similar to and have characteristics that overlap with those of many supernovae. Such a connection may not exist between multi-pulsed GRBs and supernovae.
astro-ph/0604152 [abs, ps, pdf, other] :: Title: A Strong X-Ray Flux Ratio Anomaly in the Quadruply Lensed Quasar PG 1115+080
Authors: David Pooley (UC Berkeley), Jeffrey A. Blackburne, Saul Rappaport, Paul L. Schechter, Wen-fai Fong (MIT)
Comments: submitted to ApJ

PG 1115+080 is a quadruply lensed quasar at z=1.72 whose image positions are well fit by simple models of the lens galaxy (at z=0.31). At optical wavelengths, the bright close pair of images exhibits a modest flux ratio anomaly (factors of ~1.2-1.4 over the past 22 years) with respect to these same models. We show here that as observed in X-rays with Chandra, the flux ratio anomaly is far more extreme, roughly a factor of 6. The contrasting flux ratio anomalies in the optical and X-ray band confirm the microlensing hypothesis and set a lower limit on the size of the optical continuum emission region that is \~10-100 times larger than expected from a thin accretion disk model.
astro-ph/0604153 [abs, ps, pdf, other] :: Title: Are short gamma-ray bursts collimated? GRB050709, a flare but no break
Authors: D. Watson, J. Hjorth, P. Jakobsson, D. Xu, J. P. U. Fynbo, J. Sollerman, C. C. Thöne, K. Pedersen (DARK, Copenhagen)
Comments: 5 pages, 2 figures, submitted to A&A Letters

From the small sample of afterglow lightcurves of short duration gamma-ray bursts (GRBs), the decays are rapid, roughly following a power-law in time. It has been assumed that the afterglow emission in short GRBs is collimated in jets in the same way as in long GRBs. An achromatic break in a short GRB afterglow lightcurve would therefore be strong evidence in favour of collimation in short GRBs. We examine the optical lightcurve of the afterglow of the short GRB050709, the only short GRB where a jet break has been claimed. We show that (1) the decay follows a single power-law from 1.4 to 19 days after the burst and has a decay index alpha = 1.76 (-0.04, +0.11), (2) that an optical flare at ~10 days is required by the data, roughly contemporaneous with a flare in the X-ray data, and (3) that there is no evidence for a break in the lightcurve. This means that so far there is no direct evidence for collimation in the outflows of short GRBs. The available limits on the collimation angles in short GRBs now strongly suggest much wider opening angles than found in long GRBs.
astro-ph/0604154 [abs, ps, pdf, other] :: Title: Ghosts, Instabilities, and Superluminal Propagation in Modified Gravity Models
Authors: Antonio De Felice, Mark Hindmarsh, Mark Trodden
Comments: 17 pages, 1 figure, uses RevTeX

We consider Modified Gravity models involving inverse powers of fourth-order curvature invariants. Using these models' equivalence to the theory of a scalar field coupled to a linear combination of the invariants, we investigate the properties of the propagating modes. Even in the case for which the fourth derivative terms in the field equations vanish, we find that the second derivative terms can give rise to ghosts, instabilities, and superluminal propagation speeds. We establish the conditions which the theories must satisfy in order to avoid these problems in Friedmann backgrounds, and show that the late-time attractor solutions are generically afflicted by superluminally propagating tensor or scalar modes.
astro-ph/0604155 [abs, ps, pdf, other] :: Title: Halo Shapes, Dynamics and Environment
Authors: Manolis Plionis, Cinthia Ragone, Spyros Basilakos
Comments: To be published in "Groups Of Galaxies In The Nearby Universe", held in Chile, December 2005, edited by I.Saviane, V.Ivanov and J.Borissova. Springer-Verlag series "ESO Astrophysics Symposia"

In the hierarchical structure formation model cosmic halos are supposed to form by accretion of smaller units along anisotropic direction, defined by large-scale filamentary structures. After the epoch of primary mass aggregation (which depend on the cosmological model), violent relaxation processes will tend to alter the halo phase-space configuration producing quasi-spherical halos with a relatively smooth density profiles.
Here we attempt to investigate the relation between halos shapes, their environment and their dynamical state. To this end we have run a large ($L=500 h^{-1}$ Mpc, $N_{p}=512^3$ particles) N-body simulation of a flat low-density cold dark matter model with a matter density $\Omega_{\rm m}=1-\Omega_{\Lambda}=0.3$, Hubble constant $H_{\circ}=70$ km s$^{-1}$ Mpc$^{-1}$ and a normalization parameter of $\sigma_{8}=0.9$. The particle mass is $m_{\rm p}\ge 7.7\times 10^{10} h^{-1} M_{\odot}$ comparable to the mass of one single galaxy. The halos are defined using a friends-of-friend algorithm with a linking length given by $l=0.17\bar{\nu}$ where $\bar{\nu}$ is the mean density. This linking length corresponds to an overdensity $\rho/\rho_{\rm mean}\simeq 200$ at the present epoch ($z=0$) and the total number of halos with more than 130 particles ($M>3 \times 10^{13} h^{-1} M_{\odot}$) is 57524.
astro-ph/0604156 [abs, ps, pdf, other] :: Title: The structure and X-ray radiation spectra of illuminated accretion disks in AGN. III. Modeling fractional variability
Authors: R. W. Goosmann (1,3), B. Czerny (2,3), M. Mouchet (3,4), G. Ponti (5,6,7), M. Dovciak (1), V. Karas (1), A. Rozanska (2,3), A.-M. Dumont (3) ((1) Astronomical Institute, Academy of Sciences of the Czech Republic, (2) Copernicus Astronomical Center, Warsaw, Poland, (3) Observatoire de Paris, France, (4) Laboratoire Astroparticules et Cosmologie, Paris, France, (5) Dipartimento di Astronomia, Universita di Bologna, Italy, (6) INAF-IASF Sezione di Bologna, Italy, (7) Institute of Astronomy, Cambridge, UK)
Comments: 15 pages, 12 figures, accepted by Astronomy and Astrophysics

Extending the work of Czerny et al. (2004), we model the fractional variability amplitude due to distributions of hot spots co-orbiting on the accretion disk around a supermassive black hole. From defined radial distributions, our code samples random positions for the hot spots across the disk. The local spot emission is computed as reprocessed radiation coming from a compact primary source above the disk. The structure of the hot spot and the anisotropy of the re-emission are taken into account. We compute the fractional variability spectra expected from such spot ensembles and investigate dependencies on the parameters describing the radial spot distribution. We consider the fractional variability F_var with respect to the spectral mean and also the so-called point-to-point F_pp. Our method includes relativistic corrections for the curved space-time; the black hole angular momentum is a free parameter and subject to the fitting procedure. We confirm that the rms-variability spectra involve intrinsic randomness at a significant level when the number of flares appearing during the total observation time is too small. Furthermore, F_var is not always compatible with F_pp. For MCG -6-30-15, we can reproduce the short-timescale variability and model the suppressed variability in the energy range of the Kalpha line without any need to postulate reprocessing farther away from the center. An increasing rate of energy production by the flares toward the center of the disk, a fast rotation of the central black hole, and considerable suppression of the primary flare emission are required. The modeled line remains consistent with the measured equivalent width of the iron Kalpha line complex.
astro-ph/0604157 [abs, ps, pdf, other] :: Title: The effect of heavy element opacity on pre-main sequence Li depletion
Authors: P. Sestito (INAF/Osservatorio Astronomico .S.Vaiana"di Palermo; INAF/Osservatorio Astrofisico di Arcetri), S. Degl Innocenti (Dipartimento di Fisica Universita'di Pisa; INFN, Sezione di Pisa) P.G. Prada Moroni (Dipartimento di Fisica Universita'di Pisa; INFN, Sezione di Pisa) S. Randich (INAF/Osservatorio Astrofisico di Arcetri)
Comments: A&A accepted, 11 pages, 18 eps figures

Recent 3-D analysis of the solar spectrum data suggests a significant change of the solar chemical composition. This may affect the temporal evolution of the surface abundance of light elements since the extension of the convective envelope is largely affected by the internal opacity value. We analyse the influence of the adopted solar mixture on the opacity in the convective envelope of pre-main sequence (PMS) stars and thus on PMS lithium depletion. The surface Li abundance depends on the relative efficiency of several processes, some of them still not known with the required precision; this paper thus analyses one of the aspects of this ``puzzle''. Focusing on PMS evolution, where the largest amount of Li burning occurs, we computed stellar models for three selected masses (0.8, 1.0 and 1.2 Msun, with Z=0.013, Y=0.27, alpha=1.9) by varying the chemical mixture, that is the internal element distribution in Z. We analysed the contribution of the single elements to the opacity at the temperatures and densities of interest for Li depletion. Several mixtures were obtained by varying the abundance of the most important elements one at a time; we then calculated the corresponding PMS Li abundance evolution. We found that a mixture variation does change the Li abundance: at fixed total metallicity, the Li depletion increases when increasing the fraction of elements heavier than O.
astro-ph/0604158 [abs, ps, pdf, other] :: Title: XRF 050406 late time flattening: appearance of an IC component?
Authors: A. Corsi, L. Piro
Comments: 5 pages, 4 figures, 1 table, submitted to A&A Letters

We investigate on the possible evidence for Inverse Compton (IC) emission in the X-ray afterglow of XRF 050406. In the framework of the standard fireball model, we show how the late time flattening observed in the X-ray light curve between ~10^{4} s and ~10^{6} s can be explained in a synchrotron plus IC scenario, when the IC peak frequency crosses the X-ray band. We thus conclude that the appearance of an IC component above the synchrotron one at late times successfully accounts for the X-ray observations.
astro-ph/0604159 [abs, ps, pdf, other] :: Title: Search for an infrared counterpart of IGR J16358-4756
Authors: Flavio D'Amico (1), Francisco Jablonski (1), Claudia V. Rodrigues (1), Deonisio Cieslinski (1), Gabriel Hickel (2) ((1) INPE/MCT, S. J. dos Campos/Brazil, (2) UNIVAP, S. J. dos Campos/Brazil)
Comments: 5 pages, 2 figures, all styles included; to be published in: "The Transient Milky Way: a perspective for MIRAX", eds. F. D'Amico, J. Braga, and R. E. Rothschild, AIP Conference Proceedings

We report here on near infrared observations of the field around IGR J16358-4756. The source belongs to the new class of highly absorbed X-ray binaries discovered by IBIS/INTEGRAL. Our primary goal was to identify the infrared counterpart of the source, previously suggested to be a LMXB and then further reclassified as a HMXB. We have made use of Chandra observations of the source in order to better constrain the number of possible counterparts. Using the differential photometry technique, in observations spanning a timescale of 1 month, we found no long term variability in our observations. This is compatible, and we suggest here, that the source is a HMXB.
astro-ph/0604160 [abs, ps, pdf, other] :: Title: Bayesian foreground analysis with CMB data
Authors: H. K. Eriksen, C. Dickinson, C. R. Lawrence, C. Baccigalupi, A. J. Banday, K. M. Gorski, F. K. Hansen, E. Pierpaoli, M. D. Seiffert
Comments: 8 pages; for proceedings from CMB workshop at Irvine, March 2006

The quality of CMB observations has improved dramatically in the last few years, and will continue to do so in the coming decade. Over a wide range of angular scales, the uncertainty due to instrumental noise is now small compared to the cosmic variance. One may claim with some justification that we have entered the era of precision CMB cosmology. However, some caution is still warranted: The errors due to residual foreground contamination in the CMB power spectrum and cosmological parameters remain largely unquantified, and the effect of these errors on important cosmological parameters such as the optical depth tau and spectral index n_s is not obvious. A major goal for current CMB analysis efforts must therefore be to develop methods that allows us to propagate such uncertainties from the raw data through to the final products. Here we review a recently proposed method that may be a first step towards that goal.
astro-ph/0604161 [abs, ps, pdf, other] :: Title: Gyrokinetic electron acceleration in the force-free corona with anomalous resistivity
Authors: Kaspar Arzner, Loukas Vlahos

We numerically explore electron acceleration and coronal heating by dissipative electric fields. Electrons are traced in linear force-free magnetic fields extrapolated from SOHO/MDI magnetograms, endowed with anomalous resistivity ($\eta$) in localized dissipation regions where the magnetic twist $\nabla \times \bhat$ exceeds a given threshold. Associated with $\eta > 0$ is a parallel electric field ${\bf E} = \eta {\bf j}$ which can accelerate runaway electrons. In order to gain observational predictions we inject electrons inside the dissipation regions and follow them for several seconds in real time. Precipitating electrons which leave the simulation system at height $z$ = 0 are associated with hard X rays, and electrons which escape at height $z$ $\sim$ 3$\cdot 10^4$ km are associated with normal-drifting type IIIs at the local plasma frequency. A third, trapped, population is related to gyrosynchrotron emission. Time profiles and spectra of all three emissions are calculated, and their dependence on the geometric model parameters and on $\eta$ is explored. It is found that precipitation generally preceeds escape by fractions of a second, and that the electrons perform many visits to the dissipation regions before leaving the simulation system. The electrons impacting $z$ = 0 reach higher energies than the escaping ones, and non-Maxwellian tails are observed at energies above the largest potential drop across a single dissipation region. Impact maps at $z$ = 0 show a tendency of the electrons to arrive at the borders of sunspots of one polarity. Although the magnetograms used here belong to non-flaring times, so that the simulations refer to nanoflares and `quiescent' coronal heating, it is conjectured that the same process, on a larger scale, is responsible for solar flares.
astro-ph/0604162 [abs, ps, pdf, other] :: Title: The History and Future of the Local and Loop I Bubbles
Authors: Dieter Breitschwerdt, Miguel A. de Avillez
Comments: Accepted for publication in Astronomy and Astrophysics Letters. The paper contains 11 figures

The Local and Loop I superbubbles are the closest and best investigated supernova (SN) generated bubbles and serve as test laboratories for observations and theories of the interstellar medium. Since the morphology and dynamical evolution of bubbles depend on the ambient density and pressure distributions, a realistic modelling of the galactic environment is crucial for a detailed comparison with observations. We have performed 3D high resolution (down to 1.25 pc on a kpc-scale grid) hydrodynamic simulations of the Local Bubble (LB) and the neighbouring Loop I (L1) superbubble in a realistically evolving inhomogeneous background ISM, disturbed already by SN explosions at the Galactic rate for 200 Myr before the LB and L1 are generated. The LB is the result of 19 SNe occurring in a moving group, which passed through the present day local HI cavity. We can reproduce (i) the OVI column density in absorption within the LB in agreement with COPERNICUS and recent FUSE observations, giving N(OVI) <2 10^{13} cm^-2 and N(OVI)<7 10^{12} cm^-2, respectively, (ii) the observed sizes of the Local and Loop I superbubbles, (iii) the interaction shell between LB and L1, discovered with ROSAT, (iv) constrain the age of the LB to be 14.5+0.7/-0.4 Myr, (v) predict the merging of the two bubbles in about 3 Myr, when the interaction shell starts to fragment, (vi) the generation of blobs like the Local Cloud as a consequence of a dynamical instability. We find that evolving superbubbles strongly deviate from idealised self-similar solutions due to ambient pressure and density gradients, as well as due to turbulent mixing and mass loading. Hence, at later times the hot interior can break through the surrounding shell, which may also help to explain the puzzling energy "deficit" observed in LMC bubbles.
astro-ph/0604163 [abs, ps, pdf, other] :: Title: Resonant Tidal Excitations of Inertial Modes in Coalescing Neutron Star Binaries
Authors: Dong Lai (Cornell), Yanqin Wu (Toronto)
Comments: 6 pages. Phys. Rev. D. submitted 3/23/06

We study the effect of resonant tidal excitation of inertial modes in neutron stars during binary inspiral. For spin frequencies less than 100 Hz, the phase shift in the gravitational waveform associated with the resonance is small and does not affect the matched filtering scheme for gravitational wave detection. For higher spin frequencies, the phase shift can become significant. Most of the resonances take place at orbital frequencies comparable to the spin frequency, and thus significant phase shift may occur only in the high-frequency band (hundreds of Hertz) of gravitational wave. The exception is a single odd-paity $m=1$ mode, which can be resonantly excited for misaligned spin-orbit inclinations, and may occur in the low-frequency band (tens of Hertz) of gravitational wave and induce significant (>> 1 radian) phase shift.
astro-ph/0604164 [abs, ps, pdf, other] :: Title: Evidence for Shocked Molecular Gas in the Galactic SNR CTB 109 (G109.1-1.0)
Authors: Manami Sasaki (CfA), Roland Kothes (DRAO), Paul P. Plucinsky (CfA), Terrance J. Gaetz (CfA), Christopher M. Brunt (U. of Exeter)
Comments: Accepted for publication in ApJL. 3 figures

We report the detection of molecular clouds around the X-ray bright interior feature in the Galactic supernova remnant (SNR) CTB 109 (G109.1-1.0). This feature, called the Lobe, has been previously suggested to be the result of an interaction of the SNR shock wave with a molecular cloud complex. We present new high resolution X-ray data from the Chandra X-ray Observatory and new high resolution CO data from the Five College Radio Observatory which show the interaction region with the cloud complex in greater detail. The CO data reveal three clouds around the Lobe in the velocity interval -57 < v < -52 km s^-1. The velocity profiles of 12CO at various parts of the east cloud are well fit with a Gaussian; however, at the position where the CO cloud and the Lobe overlap, the velocity profile has an additional component towards higher negative velocities. The molecular hydrogen density in this part of the cloud is relatively high (N_H2 = 1.9 x 10^20 cm^-2), whereas the foreground absorption in X-rays (N_H = 4.5 x 10^21 cm^-2), obtained from Chandra data, is lower than in other parts of the cloud and in the north and south cloud. These results indicate that this cloud has been hit by the SNR blast wave on the western side, forming the bright X-ray Lobe.
astro-ph/0604165 [abs, ps, pdf, other] :: Title: On the Distance to the Bright Nonthermal Radio Sources in the Direction of an Extraordinarily Massive Cluster of Red Giants
Authors: Alfonso Trejo, Luis F. Rodriguez
Comments: 6 pages, 3 figures

An extraordinarily massive cluster of red supergiants has been recently reported in the direction of the galactic coordinates $l = 25\rlap.^\circ3$; $b = -0\rlap.^\circ2$. This cluster is associated with an X-ray source, a very high-energy $\gamma$-ray source, and three bright non-thermal radio sources. The \sl a priori \rm probability of these associations being only line-of-sight coincidences is very small. However, we have analyzed VLA archive data taken toward these three radio sources and find from their HI absorption spectra that they are extragalactic and thus not directly associated with the galactic cluster.
astro-ph/0604166 [abs, ps, pdf, other] :: Title: Age distribution of young clusters and field stars in the SMC
Authors: E. Chiosi, A. Vallenari, E. V. Held, L. Rizzi, A. Moretti
Comments: 15 pages, 24 figures, A&A accepted

In this paper we discuss the cluster and field star formation in the central part of the Small Magellanic Cloud.
The main goal is to study the correlation between young objects and their interstellar environment.
The ages of about 164 associations and 311 clusters younger than 1 Gyr are determined using isochrone fitting. The spatial distribution of the clusters is compared with the HI maps, with the HI velocity dispersion field, with the location of the CO clouds and with the distribution of young field stars. The cluster age distribution supports the idea that clusters formed in the last 1 Gyr of the SMC history in a roughly continuous way with periods of enhancements. The two super-shells 37A and 304A detected in the HI distribution are clearly visible in the age distribution of the clusters: an enhancement in the cluster formation rate has taken place from the epoch of the shell formation. A tight correlation between young clusters and the HI intensity is found. The degree of correlation is decreasing with the age of the clusters. Clusters older than 300 Myr are located away from the HI peaks. Clusters and associations younger than 10 Myr are related to the CO clouds in the SW region of the SMC disk.
A positive correlation between the location of the young clusters and the velocity dispersion field of the atomic gas is derived only for the shell 304A, suggesting that the cloud-cloud collision is probably not the most important mechanism of cluster formation. Evidence of gravitational triggered episode due to the most recent close interaction between SMC and LMC is found both in the cluster and field star distribution.
astro-ph/0604167 [abs, ps, pdf, other] :: Title: Laboratory Testing of a Lyot Coronagraph Equipped with an Eighth-Order Notch Filter Image Mask
Authors: Justin R. Crepp, Jian Ge, Andrew D. Vanden Heuvel, Shane P. Miller, Marc J. Kuchner
Comments: Accepted to ApJ. 16 pages, 7 figures, Contact jcrepp@astro.ufl.edu for high resolution images

We have built a series of notch filter image masks that make the Lyot coronagraph less susceptible to low-spatial-frequency optical aberrations. In this paper, we present experimental results of their performance in the lab using monochromatic light. Our tests show that these ``eighth-order'' masks are resistant to tilt and focus alignment errors, and can generate contrast levels of 2 x 10^-6 at 3 lambda/D and 6 x 10^-7 at 10 lambda/D without the use of corrective optics such as deformable mirrors. This work supports recent theoretical studies suggesting that eighth-order masks can provide the Terrestrial Planet Finder Coronagraph with a large search area, high off-axis throughput, and a practical requisite pointing accuracy.
astro-ph/0604168 [abs, ps, pdf, other] :: Title: Relaxation paths for single modes of vibrations in isolated molecules
Authors: Renaud Papoular
Comments: 25 pages, 15 figures; accepted by J. Atom. Phys. B

A numerical simulation of vibrational excitation of molecules was devised, and used to excite computational models of common molecules into a prescribed, pure, normal vibration mode in the ground electronic state, with varying, controlable energy content. The redistribution of this energy (either non-chaotic or irreversible IVR) within the isolated, free molecule is then followed in time with a view to determining the coupling strength between modes. This work was triggered by the need to predict the general characters of the infrared spectra to be expected from molecules in interstellar space, after being excited by photon absorption or reaction with a radical. It is found that IVR from a pure normal mode is very "restricted" indeed at energy contents of one mode quantum or so. However, as this is increased, or when the excitation is localized, our approach allows us to isolate, describe and quantify a number of interesting phenomena, known to chemists and in non-linear mechanics, but difficult to demonstrate experimentally: frequency dragging, mode locking or quenching or, still, instability near a potential surface crossing, the first step to generalized chaos as the energy content per mode is increased.
astro-ph/0604169 [abs, ps, pdf, other] :: Title: Basic considerations about experimental approaches to the B-mode of the CMB Polarization
Authors: S. Cortiglioni (INAF-IASF Bologna), E. Carretti (INAF-IRA)
Comments: 20 pages, 7 figures. Article for Review Book "Cosmic Polarization", ed. Roberto Fabbri, Publisher: Research Signpost

The B-mode detection of Cosmic Microwave Background polarization will require new technological developments, able to get sensitivities at least 2 orders of magnitude better than for the E-mode. This really ambitious goal cannot be reached simply by either improving the present technology or by adding more detectors to current design, at least in the frame of having a new space mission operating within a decade. Thus, the scientific community have to take important decisions about the most suitable technologies on which converge the needed effort. Basically, at present two receiver families do exist: bolometric and radiometric. Both of them are continuoulsly improving their basic performances, but the optimal approach to B-modes may require some decisions have to be taken in short time scale. In any case, radiometric and bolometric receivers have to deal with some common sources of systematics as well as they both require some cryogenics. Thus, we should expect that systematics and cryogenics may play as watershed line in designing future experiments aimed at measuring the B-mode of Cosmic Microwave Background.
astro-ph/0604170 [abs, ps, pdf, other] :: Title: New mechanism of generation of large-scale magnetic fields in merging protogalactic and protostellar clouds
Authors: I. Rogachevskii, N. Kleeorin, A.D. Chernin, E. Liverts
Comments: 4 pages, 2 figures, Astron. Nachr., in press

A new mechanism of generation of large-scale magnetic fields in colliding protogalactic clouds and merging protostellar clouds is discussed. Interaction of the colliding clouds produces large-scale shear motions which are superimposed on small-scale turbulence. Generation of the large-scale magnetic field is due to a ''shear-current" effect (or "vorticity-current" effect), and the mean vorticity is caused by the large-scale shear motions of colliding clouds. This effect causes the generation of the mean magnetic field even in a nonrotating and nonhelical homogeneous turbulence. There is no quenching of the nonlinear shear-current effect contrary to the quenching of the nonlinear alpha effect, the nonlinear turbulent magnetic diffusion, etc. During the nonlinear growth of the mean magnetic field, the shear-current effect only changes its sign at some value of the mean magnetic field which determines the level of the saturated mean magnetic field. Numerical study shows that the saturated level of the mean magnetic field is of the order of the equipartition field determined by the turbulent kinetic energy. The estimated large-scale magnetic field for merging protogalactic clouds is about several microgauss, and for merging protostellar clouds is of the order of several tenth of microgauss.
astro-ph/0604171 [abs, ps, pdf, other] :: Title: Detection Limits from the McDonald Observatory Planet Search Program
Authors: Robert A. Wittenmyer, Michael Endl, William D. Cochran, Artie P. Hatzes, G.A.H. Walker, S.L.S. Yang, Diane B. Paulson
Comments: 21 pages, 15 figures, accepted for publication in AJ

Based on the long-term radial-velocity surveys carried out with the McDonald Observatory 2.7m Harlan J. Smith Telescope from 1988 to the present, we derive upper limits to long-period giant planet companions for 31 nearby stars. Data from three phases of the McDonald Observatory 2.7m planet-search program have been merged together and for 17 objects, data from the pioneering Canada-France-Hawaii Telescope (CFHT) radial-velocity program have also been included in the companion-limits determination. For those 17 objects, the baseline of observations is in excess of 23 years, enabling the detection or exclusion of giant planets in orbits beyond 8 AU. We also consider the possibility of eccentric orbits in our computations. At an orbital separation of 5.2 AU, we can exclude on average planets of M sin i > 2.0+/-1.1 Mjup (e=0) and M sin i > 4.0+/-2.8 Mjup (e=0.6) for 25 of the 31 stars in this survey. However, we are not yet able to rule out "true Jupiters," i.e. planets of M sin i ~ 1 Mjup in 5.2 AU orbits. These limits are of interest for the Space Interferometry Mission (SIM), Terrestrial Planet Finder (TPF), and Darwin missions which will search for terrestrial planets orbiting nearby stars, many of which are included in this work.
astro-ph/0604172 [abs, ps, pdf, other] :: Title: Binary post-AGB stars and their Keplerian discs
Authors: Hans Van Winckel, Tom Lloyd Evans, Maarten Reyniers, Pieter Deroo, Clio Gielen
Comments: to be included in the conference proceedings of the 8th Torino Workshop held in Granada

In this contribution we give a progress report on our systematic study of a large sample of post-AGB stars. The sample stars were selected on the basis of their infrared colours and the selection criteria were tuned to discover objects with hot dust in the system. We started a very extensive, multi-wavelength programme which includes the analysis of our radial velocity monitoring; our optical high-resolution spectra; our groundbased N-band spectral data as well as the Spitzer full spectral scans; the broad-band SED and the high spatial-resolution interferometric experiments with the VLTI. In this contribution we highlight the main results obtained so far and argue that all systems in our sample are indeed binaries, which are surrounded by dusty Keplerian circumbinary discs. The discs play a lead role in the evolution of the systems.
astro-ph/0604173 [abs, ps, pdf, other] :: Title: Mapping Large-Scale Gaseous Outflows in Ultraluminous Infrared Galaxies with Keck II ESI Spectra: Spatial Extent of the Outflow
Authors: Crystal L. Martin (UCSB)
Comments: Accepted to ApJ. Text and figures available as a single document at this http URL

The kinematics of neutral gas and warm ionized gas have been mapped in one-dimension across ultraluminous starburst galaxies using interstellar absorption and emission lines, in Keck II ESI spectra. Blue-shifted absorption is found along more of the slit than anticipated, exceeding scales of 15 kpc across several systems. The large velocity gradient measured across some of these outflows is inconsistent with a flow diverging from the central starburst -- angular momentum conservation reduces the rotational velocity of an outflow as it expands. More widespread star formation, likely triggered by the merger, probably drives these outflows, although some models suggest the collision itself could generate a wind by shock heating interstellar gas throughout the disk. Young mergers with separated nuclei present the highest outflow masses, due mainly to the larger area over which the cool gas can be detected. In a typical ULIG, the mass carried by the cool phase of the outflow is around 10^8Msun, or a few percent of the total dynamical mass. Assuming the starburst activity has proceeded at the observed rate for the past 10 Myr, the kinetic energy of the cool outflows is a few percent of the supernova energy, consistent with starbursts powering the outflows. The cool wind is expected to be accelerated by momentum deposition, possibly from radiation pressure as well as supernovae. Such models imply turn-around radii for the cool outflows of at least 30 to 90 kpc. This cross-section presents a significant NaI absorption cross section. If most L > 0.1L* galaxies pass through a luminous starburst phase, then relics of cool outflows will create a significant redshift-path density. Galaxy formation models should include this cool phase of the outflow in addition to a hot wind in feedback models.
astro-ph/0604174 [abs, ps, pdf, other] :: Title: Primordial Black Hole Minimum Mass
Authors: James R. Chisholm
Comments: 6 pages, no figures, to be submitted to Phys. Rev. D

Primordial black holes (PBHs) are not created exactly at the horizon mass, but rather at some fraction of it. Numerical results show that this fraction is a power law of the overdensity above threshold, which can imply an arbitrarily small mass for the PBH. We show that from entropy considerations, this cannot be true, and that there is a minimum PBH mass.
astro-ph/0604175 [abs, ps, pdf, other] :: Title: X-Ray Emission from the Warm Hot Intergalactic Medium
Authors: E. Ursino M. Galeazzi
Comments: 19 pages, 6 figures

The number of detected baryons in the Universe at z<0.5 is much smaller than predicted by standard big bang nucleosynthesis and by the detailed observation of the Lyman alpha forest at red-shift z=2. Hydrodynamical simulations indicate that a large fraction of the baryons today is expected to be in a ``warm-hot'' (10^5-10^7K) filamentary gas, distributed in the intergalactic medium. This gas, if it exists, should be observable only in the soft X-ray and UV bands. Using the predictions of a particular hydrodynamic model, we simulated the expected X-ray flux as a function of energy in the 0.1-2 keV band due to the Warm-Hot Intergalactic Medium (WHIM), and compared it with the flux from local and high red-shift diffuse components. Our results show that as much as 20% of the total diffuse X-ray background (DXB) in the energy range 0.37-0.925keV could be due to X-ray flux from the WHIM, 70% of which comes from filaments at redshift z between 0.1 and 0.6. Simulations done using a FOV of 3', comparable with that of Suzaku and Constellation-X, show that in more than 20% of the observations we expect the WHIM flux to contribute to more than 20% of the DXB. These simulations also show that in about 10% of all the observations a single bright filament in the FOV accounts, alone, for more than 20% of the DXB flux. Red-shifted oxygen lines should be clearly visible in these observations.
astro-ph/0604176 [abs, ps, pdf, other] :: Title: Improved Calculation of the Primordial Gravitational Wave Spectrum in the Standard Model
Authors: Yuki Watanabe, Eiichiro Komatsu (Univ. of Texas at Austin)
Comments: 25 papes, 11 figures, submitted to PRD

We show that the energy density spectrum of the primordial gravitational waves has characteristic features due to the successive changes in the relativistic degrees of freedom during the radiation era. These changes make the evolution of radiation energy density deviate from the conventional adiabatic evolution, \rho_r~ a^{-4}, and thus cause the expansion rate of the universe to change suddenly at each transition which, in turn, modifies the spectrum of primordial gravitational waves. We take into account all the particles in the Standard Model of elementary particles. In addition, free-streaming of neutrinos damps the amplitude of gravitational waves, leaving characteristic features in the energy density spectrum. Our calculations are solely based on the standard model of cosmology and particle physics, and therefore these features must exist. Our calculations significantly improve the previous ones which ignored these effects and predicted a smooth, featureless spectrum.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Tue, 11 Apr 06 00:00:10 GMT
0604177 -- 0604214 received

astro-ph/0604177 [abs, ps, pdf, other] :: Title: Simulations and Analytic Calculations of Bubble Growth During Hydrogen Reionization
Authors: Oliver Zahn, Adam Lidz, Matthew McQuinn, Suvendra Dutta, Lars Hernquist, Matias Zaldarriaga, Steven R. Furlanetto
Comments: 15 pages, 11 figures, submitted to ApJ

We present results from a large volume simulation of Hydrogen reionization. We combine 3d radiative transfer calculations and an N-body simulation, describing structure formation in the IGM, to detail the growth of HII regions around high redshift galaxies. Our simulation tracks 1024^3 dark matter particles, in a box of side length 65.6 Mpc/h. This large volume allows us to accurately characterize the size distribution of HII regions throughout most of the reionization process. At the same time, our simulation resolves many of the small galaxies likely responsible for reionization. It confirms a picture anticipated by analytic models: HII regions grow collectively around highly-clustered sources, and have a well-defined characteristic size, evolving from a sub-Mpc scale at the beginning of reionization to R>10 Mpc towards the end. We present a detailed statistical description of our results, and compare them with a numerical hybrid scheme based on the analytic model by Furlanetto, Zaldarriaga, and Hernquist. We find that the analytic calculation reproduces the size distribution of HII regions, and the 21 cm power spectrum of the radiative transfer simulation remarkably well. The ionization field from the simulation, however, has more small scale structure than the analytic calculation, owing to Poisson scatter in the simulated abundance of galaxies on small scales. We validate a simple scheme to incorporate this scatter into our calculations. Our results suggest that analytic calculations are sufficiently accurate to aid in predicting and interpreting the results of future 21 cm surveys. In particular, our fast numerical scheme is useful for forecasting constraints from future 21 cm surveys, and in constructing mock surveys to test data analysis procedures.
astro-ph/0604178 [abs, ps, pdf, other] :: Title: Magnetic draping of merging cores and radio bubbles in clusters of galaxies
Authors: Maxim Lyutikov (UBC)
Comments: 16 pages, 2 figures

Sharp fronts observed by Chandra satellite between dense cool cluster cores moving with near-sonic velocity through the hotter intergalactic gas, require strong suppression of thermal conductivity across the boundary. This may be due to magnetic fields tangential to the contact surface separating two plasma components. We point out that a super-Alfvenic motion of a plasma cloud (a core of a merging galaxy) through a weakly magnetized intercluster medium leads to "magnetic draping", formation of a thin, strongly magnetized boundary layer with a tangential magnetic field. For supersonic cloud motion, M_s > 1, magnetic field inside the layer reaches near-equipartition values with thermal pressure. Typical thickness of the layer is L /M_A^2 << L, where L is the size of the obstacle (plasma cloud) moving with Alfven Mach number M_A >> 1. To a various degree, magnetic draping occurs both for sub- and supersonic flows, random and ordered magnetic fields and it does not require plasma compressibility. The strongly magnetized layer will thermally isolate the two media and may contribute to the Kelvin-Helmholtz stability of the interface. Similar effects occur for radio bubbles, quasi-spherical expanding cavities blown up by AGN jets; in this case the thickness of the external magnetized layer is smaller, L /M_A^3 << L.
astro-ph/0604179 [abs, ps, pdf, other] :: Title: Weak Lensing of the Cosmic Microwave Background by Foreground Gravitational Waves
Authors: Chao Li (Caltech), Asantha Cooray (UC Irvine)
Comments: 11 pages, 4 figures, comments are welcome

Weak lensing distortion of the background cosmic microwave background (CMB) temperature and polarization patterns by the foreground density fluctuations is well studied in the literature. We discuss the gravitational lensing modification to CMB anisotropies and polarization by a stochastic background of primordial gravitational waves between us and the last scattering surface. While density fluctuations perturb CMB photons via gradient-type deflections only, foreground gravitational waves distort CMB anisotropies via both gradient- and curl-type displacements. The latter is a rotation of background images, while the former is related to the lensing convergence. For a primordial background of inflationary gravitational waves, with an amplitude corresponding to a tensor-to-scalar ratio below the current upper limit of $\sim$ 0.3, the resulting modifications to the angular power spectra of CMB temperature anisotropy and polarization are below the cosmic variance limit. This suggests that lensing by foreground gravitational waves can be ignored when interpreting high sensitivity CMB observations.
astro-ph/0604180 [abs, ps, pdf, other] :: Title: Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars
Authors: Inese I. Ivans, Jennifer Simmerer, Christopher Sneden, James E. Lawler, John J. Cowan, Roberto Gallino, Sara Bisterzo
Comments: 22 pages, 12 figures (10 colour), 6 tables, accepted by ApJ

Employing high resolution spectra obtained with the near-UV sensitive detector on the Keck I HIRES, supplemented by data obtained with the McDonald Observatory 2-d coude, we have performed a comprehensive chemical composition analysis of the bright r-process-rich metal-poor red giant star HD221170. Analysis of 57 individual neutral and ionized species yielded abundances for a total of 46 elements and significant upper limits for an additional five. Model stellar atmosphere parameters were derived with the aid of ~200 Fe-peak transitions. From more than 350 transitions of 35 neutron-capture (Z > 30) species, abundances for 30 neutron-capture elements and upper limits for three others were derived. Utilizing 36 transitions of La, 16 of Eu, and seven of Th, we derive ratios of log epsilon(Th/La) = -0.73 (sigma = 0.06) and log epsilon(Th/Eu) = -0.60 (sigma = 0.05), values in excellent agreement with those previously derived for other r-process-rich metal-poor stars such as CS22892-052, BD+17 3248, and HD115444. Based upon the Th/Eu chronometer, the inferred age is 11.7 +/- 2.8 Gyr. The abundance distribution of the heavier neutron-capture elements (Z >= 56) is fit well by the predicted scaled solar system r-process abundances, as also seen in other r-process-rich stars. Unlike other r-process-rich stars, however, we find that the abundances of the lighter neutron-capture elements (37 < Z < 56) in HD221170 are also statistically in better agreement with the abundances predicted for the scaled solar r-process pattern.
astro-ph/0604181 [abs, ps, pdf, other] :: Title: The early X-ray afterglows of optically bright and dark Gamma-Ray Bursts
Authors: Yi-Qing Lin
Comments: 10 pages, 3 figures, 1 table; accepted by ChJAA

A systematical study on the early X-ray afterglows of both optically bright and dark gamma-ray bursts (B-GRBs and D-GRBs) observed by Swift has been presented. Our sample includes 25 GRBs. Among them 13 are B-GRBs and 12 are D-GRBs. Our results show that the distributions of the X-ray afterglow fluxes ($F_{X}$), the gamma-ray fluxes ($S_{\gamma}$), and the ratio ($R_{\gamma, X}$) for both the D-GRBs and B-GRBs are similar. The differences of these distributions for the two kinds of GRBs should be statistical fluctuation. These results indicate that the progenitors of the two kinds of GRBs are the same population. Their total energy explosions are comparable. The suppression of the optical emissions from D-GRBs should results from circumburst but not their central engine.
astro-ph/0604182 [abs, ps, pdf, other] :: Title: Synthesis Imaging of Dense Molecular Gas in the N113 HII Region of the Large Magellanic Cloud
Authors: Tony Wong (1 and 2), John B. Whiteoak (1), Juergen Ott (1), Yi-nan Chin (3), Maria R. Cunningham (2) ((1) CSIRO ATNF, (2) UNSW, Australia, (3) Tamkang University, Taiwan))
Comments: 10 pages, 6 figures, to appear in ApJ

We present aperture synthesis imaging of dense molecular gas in the Large Magellanic Cloud, taken with the prototype millimeter receivers of the Australia Telescope Compact Array (ATCA). Our observations of the N113 HII region reveal a condensation with a size of ~6" (1.5 pc) FWHM, detected strongly in the 1-0 lines of HCO+, HCN and HNC, and weakly in C_2H. Comparison of the ATCA observations with single-dish maps from the Mopra Telescope and sensitive spectra from the Swedish-ESO Submillimetre Telescope indicates that the condensation is a massive clump of ~10^4 solar masses within a larger ~10^5 solar mass molecular cloud. The clump is centered adjacent to a compact, obscured HII region which is part of a linear structure of radio continuum sources extending across the molecular cloud. We suggest that the clump represents a possible site for triggered star formation. Examining the integrated line intensities as a function of interferometer baseline length, we find evidence for decreasing HCO+/HCN and HCN/HNC ratios on longer baselines. These trends are consistent with a significant component of the HCO+ emission arising in an extended clump envelope and a lower HCN/HNC abundance ratio in dense cores.
astro-ph/0604183 [abs, ps, pdf, other] :: Title: First Detection of Near-Infrared Intraday Variations in the Seyfert 1 Nucleus NGC4395
Authors: T. Minezaki, Y. Yoshii, Y. Kobayashi, K. Enya, M. Suganuma, H. Tomita, S. Koshida, M. Yamauchi, T. Aoki
Comments: 4 pages including figures, accepted for publication in ApJL

We carried out a one-night optical V and near-infrared JHK monitoring observation of the least luminous Seyfert 1 galaxy, NGC4395, on 2004 May 1, and detected for the first time the intraday flux variations in the J and H bands, while such variation was not clearly seen for the K band. The detected J and H variations are synchronized with the flux variation in the V band, which indicates that the intraday-variable component of near-infrared continuum emission of the NGC4395 nucleus is an extension of power-law continuum emission to the near-infrared and originates in an outer region of the central accretion disk. On the other hand, from our regular program of long-term optical BVI and near-infrared JHK monitoring observation of NGC4395 from 2004 February 12 until 2005 January 22, we found large flux variations in all the bands on time scales of days to months. The optical BVI variations are almost synchronized with each other, but not completely with the near-infrared JHK variations. The color temperature of the near-infrared variable component is estimated to be T=1320-1710 K, in agreement with thermal emission from hot dust tori in active galactic nuclei (AGNs). We therefore conclude that the near-infrared variation consists of two components having different time scales, so that a small K-flux variation on a time scale of a few hours would possibly be veiled by large variation of thermal dust emission on a time scale of days.
astro-ph/0604184 [abs, ps, pdf, other] :: Title: 4C 39.29 - Extended emission around a powerful Type 2 quasar
Authors: P. Gandhi (IoA Cambridge; ESO Chile), A.C. Fabian, C.S. Crawford (IoA)
Comments: MNRAS accepted. PDF version with higher resolution figures at this http URL

We present new X-ray and optical spectroscopy of a Type 2 quasar candidate selected from a follow-up program of hard, optically-dim, serendipitous Chandra sources. The source is confirmed to be a Type 2 quasar at z=0.536 with an intrinsic 2-10 keV luminosity L_{2-10}=5x10^{44} h_{0.7}^{-2} erg/s, an absorbing column density N_H=8x10^{23} cm^{-2} and a neutral Fe K alpha line detected by XMM-Newton EPIC-MOS1 as well as Chandra ACIS-S. An extended optical forbidden emission line cloud is detected at the same redshift, and at about 15 kpc in projected separation. This cloud lies in close proximity to the peak of the compact steep spectrum radio source 4C+39.29, which has previously been identified with a foreground galaxy in the cluster Abell 963. We present evidence to show that 4C+39.29 is associated with the background X-ray Type 2 quasar. The radio luminosity is dominated by lobes with complex structure and the radio core is weak in comparison to narrow-line radio galaxies at the same X-ray luminosity. The morphology and emission line properties of the extended region are consistent with an on-going jet-cloud interaction. 4C+39.29 possesses a combination of high power and high absorbing column density compared with other X-ray Type 2 quasars in the literature. These observations highlight the efficacy of using X-rays to identify the primary energy source of complex radio sources and distant obscured AGN.
astro-ph/0604185 [abs, ps, pdf, other] :: Title: Magnetorotational Instability in Electrically Driven Flow of Liquid Metal: Spectral Analysis
Authors: I. V. Khalzov (1, 2), A. I. Smolyakov (1, 2), V. I. Ilgisonis (1) ((1) Russian Research Center "Kurchatov Institute", (2) University of Saskatchewan, Canada)
Comments: 20 pages, 15 figures (eps-format)

The spectral stability of liquid metal differentially rotating in transverse magnetic field is studied numerically by solving the eigenvalue problem with rigid-wall boundary conditions. The equilibrium velocity profile used in calculations corresponds to the electrically driven flow in circular channel with the rotation law \Omega(r)~1/r^2. This type of flow profile is planned to be used in new experimental device to test the magnetorotational instability (MRI) in laboratory. Our analysis includes calculations of the eigen-frequency spectra for both axisymmetric and non-axisymmetric modes. It is found that for chosen device parameters the flow is always spectrally unstable due to MRI with the fastest growth rate corresponding to the axisymmetric mode.
astro-ph/0604186 [abs, ps, pdf, other] :: Title: A "Missing" Supernova Remnant revealed by the 21-cm Line of Atomic Hydrogen
Authors: B-C Koo, J-h Kang, C.J. Salter
Comments: 12 pages, 3 figures, To appear in The Astrophysical Journal Letters

Although some 20--30,000 supernova remnants (SNRs) are expected to exist in the Milky Way, only about 230 are presently known. This implies that most SNRs are ``missing''. Recently, we proposed that small ($\simlt 1^\circ$), faint, high-velocity features seen in large-scale 21-cm line surveys of atomic hydrogen ({\sc Hi}) in the Galactic plane could be examples of such {\it missing} old SNRs. Here we report on high-resolution \schi observations of one such candidate, FVW 190.2+1.1, which is revealed to be a rapidly expanding ($\sim 80$ \kms) shell. The parameters of this shell seem only consistent with FVW 190.2+1.1 being the remnant of a SN explosion that occurred in the outermost fringes of the Galaxy some $\sim 3\times 10^5$ yr ago. This shell is not seen in any other wave band suggesting that it represents the oldest type of SNR, that which is essentially invisible except via its \schi line emission. FVW 190.2+1.1 is one of a hundred "forbidden-velocity wings" (FVWs) recently identified in the Galactic plane, and our discovery suggests that many of these are likely to be among the oldest SNRs. We discuss the possible link between FVWs and fast-moving atomic clouds in the Galaxy.
astro-ph/0604187 [abs, ps, pdf, other] :: Title: Supernova remnant energetics and magnetars: no evidence in favour of millisecond proto-neutron stars
Authors: Jacco Vink (1), Lucien Kuiper (2) ((1) Utrecht University, The Netherlands, (2) SRON Netherlands Institute for Space Research, Utrecht, The Netherlands)
Comments: Accepted for publication in MNRAS Letters. 5 pages, one color figure

It is generally accepted that Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) are magnetars, i.e. neutron stars with extremely high surface magnetic fields (B > 10^{14} G). The origin of these high magnetic fields is uncertain, but a popular hypothesis is that magnetars are born with an initial spin period close to the break-up limit (~1 ms), which results in a powerful dynamo action, amplifying the seed magnetic field to > 10^{15} G. A neutron star spinning at such a rate has a rotational energy in excess of 10^{52} erg, and part of that energy will power the supernova through rapid magnetic braking. It is therefore expected that if magnetars are born with periods < 3 ms their supernova remnants should be an order of magnitude more energetic than ordinary supernova remnants. However, we list here evidence that the explosion energies of these supernova remnants associated with AXPs and SGRs -- Kes 73 (AXP 1E 1841-045), CTB 109 (AXP 1E2259+586) and N49 (SGR 0526-66) -- are close to the canonical supernova explosion energy of 10^{51} erg.
We therefore do not find evidence that magnetars are formed from rapidly rotating proto-neutron stars, allowing for the possibility that they descend from stellar progenitor with high magnetic field cores, and discuss the merits of both formation scenarios.
In an appendix we describe the analysis of XMM-Newton observations of Kes 73 and N49 used to derive the explosion energies for these remnants.
astro-ph/0604188 [abs, ps, pdf, other] :: Title: Coronal density diagnostics with Si X: CHANDRA/LETGS observations of Procyon, $\alpha$ Cen A$&$B, Capella and $\epsilon$ Eri
Authors: G. Y. Liang, G. Zhao, J. R. Shi
Comments: 24 pages. The Astronomical Journal Accepted

Electron density diagnostics based on a line intensity ratio of Si X are applied to the X-ray spectra of Procyon, $\alpha$ Cen A$&$B, Capella and $\epsilon$ Eri measured with the Low Energy Transmission Grating Spectrometer (LETGS) combined with High-resolution Camera (HRC) on board the {\it Chandra X-ray Observatory}. The ratio $R_1$ of the intensities of the Si X lines at 50.524 \AA and 50.691 \AA is adopted. A certain of the temperature effect in $R_1$ appears near the low-density limit region, which is due to the contamination of Si X line at 50.703 \AA . Using the emission measure distribution (EMD) model derived by Audard et al. (2001) for Capella and emissivities calculated with APEC model by Smith et al. (2001), we successfully estimate contributions of Fe XVI lines at 50.367 \AA and 50.576 \AA (73% and 62%, respectively). A comparison between observed ratios and theoretical predictions constrains the electron densities (in logarithmic) for Procyon to be 8.61$^{+0.24}_{-0.20}$ cm$^{-3}$, while for $\alpha$ Cen A$&$B, Capella and $\epsilon$ Eri to be 8.81$^{+0.27}_{-0.23}$ cm$^{-3}$, 8.60$^{+0.39}_{0.32}$ cm$^{-3}$, 9.30$_{-0.48}$ cm$^{-3}$ and 9.11$^{+1.40}_{-0.38}$ cm$^{-3}$, respectively. The comparison of our results with those constrained by the triplet of He-like carbon shows a good agreement. For normal stars, our results display a narrow uncertainty, while for active stars, a relatively larger uncertainty, due to the contamination from Fe XVI lines, is found. Another possible reason may be that the determination of the continuum level, since the emission lines of Si X become weak for the active stars. For $\epsilon$ Eri, an electron density in the C V forming region was estimated firstly through Si X emissions.
astro-ph/0604189 [abs, ps, pdf, other] :: Title: Mapping and Mass Measurement of the Cold Dust in NGC 205 with Spitzer
Authors: F. R. Marleau (1), A. Noriega-Crespo (1), K.A. Misselt (2), K.D. Gordon (2), C.W. Engelbracht (2), G.H. Rieke (2), P. Barmby (3), S.P. Willner (3), J. Mould (4), R.D. Gehrz (5), C.E. Woodward (5) ((1) SPITZER Science Center, (2) Steward Observatory, (3) Harvard-Smithsonian Center for Astrophysics, (4) NOAO, (5) University of Minnesota)
Comments: PDF, 10 pages, simulated ApJ, accepted for publication

We present observations at 3.6, 4.5, 5.8, 8, 24, 70 & 160um of NGC 205, the dwarf elliptical companion of M31, obtained with the Spitzer Space Telescope. The point sources subtracted images at 8 and 24um display a complex and fragmented infrared emission coming from both very small dust particles and larger grains. The extended dust emission is spatially concentrated in three main emission regions, seen at all wavelengths from 8 to 160um. These regions lie approximately along NGC 205's semi-major axis and range from ~100 to 300 pc in size. Based on our mid-to-far infrared flux density measurements alone, we derive a total dust mass estimate of the order of 3.2e4 solar masses, mainly at a temperature of ~20K. The gas mass associated with this component matches the predicted mass returned by the dying stars from the last burst of star formation in NGC 205 (~0.5 Gyr ago). Analysis of the Spitzer data combined with previous 1.1mm observations over a small central region or "Core'' (18" diameter), suggest the presence of very cold (~12K) dust and a dust mass about sixteen times higher than is estimated from the Spitzer measurements alone. Assuming a gas to dust mass ratio of 100, these two datasets, i.e.with and without the millimeter observations, suggest a total gas mass range of 3.2e6 to 5e7 solar masses.
astro-ph/0604190 [abs, ps, pdf, other] :: Title: Microlensing in phase space II: Correlations analysis
Authors: Artem V. Tuntsov, Geraint F. Lewis (Sydney Uni)
Comments: 17 pages, 8 figure. Accepted for publication in MNRAS. Part I is currently with the referee

Applications of the phase space approach to the calculation of the microlensing autocorrelation function are presented. The continuous propagation equation for a random star field with a Gaussian velocity distribution is solved in the leading non-trivial approximation using the perturbation technique. It is shown that microlensing modulations can be important in the interpretation of optical and shorter-wavelength light curves of pulsars, power spectra of active galactic nuclei and coherence estimates for quasi-periodic oscillations of dwarf novae and low-mass X-ray binaries. Extra scatter in the brightness of type Ia supernovae due to gravitational microlensing is shown to be of order up to 0.2 stellar magnitudes depending on the extent of the light curves.
astro-ph/0604191 [abs, ps, pdf, other] :: Title: Common Correlations between 60, 100 and 140 um Intensities in the Galactic Plane and Magellanic Clouds
Authors: Yasunori Hibi, Hiroshi Shibai, Mitsunobu Kawada, Takafumi OOtsubo, Hiroyuki Hirashita
Comments: Accepted for publication in The Publications of the Astronomical Society of Japan. 11 pages, 9 figures

We investigate the far-infrared SED of the Galaxy and the Magellanic Clouds by using the COBE (COsmic Background Explorer) / DIRBE (Diffuse InfraRed Background Experiment) ZSMA (Zodi - Subtracted Mission Average) maps at wavelengths of 60 um, 100 um and 140 um. We analyze three regions: the Galactic plane region with the Galactic latitude |b|<5 degree, the Large Magellanic Cloud (LMC) region, and the Small Magellanic Cloud (SMC) region. Because the dust optical depth is much smaller in the far-infrared than in the visible, we may observe cumulative far-infrared radiation from regions with various interstellar radiation field (IRSF) in a line of sight. As consequence of considering such an effect, we find a common far-infrared color correlation between the 140 - 100 um and 60 - 100 um intensity ratios in all the three galaxies. Although this color correlation cannot be explained by any existing model, it fits very well the far-infrared color of nearby star forming galaxies.
astro-ph/0604192 [abs, ps, pdf, other] :: Title: Stochastic Acceleration in Turbulent Electric Fields Generated by 3-D Reconnection
Authors: Marco Onofri, Heinz Isliker, Loukas Vlahos
Comments: accepted for publication in Physical Review Letters

Electron and proton acceleration in three-dimensional electric and magnetic fields is studied through test particle simulations. The fields are obtained by a three-dimensional magnetohydrodynamic simulation of magnetic reconnection in slab geometry. The nonlinear evolution of the system is characterized by the growth of many unstable modes and the initial current sheet is fragmented with formation of small scale structures. We inject at random points inside the evolving current sheet a Maxwellian distribution of particles. In relatively short time (less than a millisecond) the particles develop a power law tail. The acceleration is extremely efficient and the electrons absorb a large percentage of the available energy in a small fraction of the characteristic time of the MHD simulation, suggesting that resistive MHD codes, used extensively in the current literature, are unable to represent the full extent of particle acceleration in 3D reconnection.
astro-ph/0604193 [abs, ps, pdf, other] :: Title: XMM-Newton observation of the Be/neutron star system RX J0146.9+6121: a soft X-ray excess in a low luminosity accreting pulsar
Authors: Nicola La Palombara, Sandro Mereghetti (INAF/IASF Milano (I))
Comments: 8 pages, 7 figures, 4 tables. Accepted for publication by Astronomy & Astrophysics

We report on the XMM-Newton observation of the Be/neutron star X-ray binary system RX J0146.9+6121, a long period (~ 23 m) pulsar in the NGC 663 open cluster. The X-ray luminosity decreased by a factor two compared to the last observation carried out in 1998, reaching a level of ~ 10^34 erg/s, the lowest ever observed in this source. The spectral analysis reveals the presence of a significant excess at low energies over the main power-law spectral component. The soft excess can be described by a black-body spectrum with a temperature of about 1 keV and an emitting region with a radius of ~ 140 m. Although the current data do not permit to ascertain whether the soft excess is pulsed or not, its properties are consistent with emission from the neutron star polar cap. This is the third detection of a soft excess in a low luminosity (~ 10^34 erg/s) pulsar, the other being X Per and 3A 0535+262, suggesting that such spectral component, observed up to date in higher luminosity systems, is a rather common feature of accreting X-ray pulsars. The results on these three sources indicate that, in low luminosity systems, the soft excess tends to have a higher temperature and a smaller surface area than in the high luminosity ones.
astro-ph/0604194 [abs, ps, pdf, other] :: Title: On the Mass of Dense Star Clusters in Starburst Galaxies from Spectro-Photometry
Authors: J.-J. Fleck, C. M. Boily, A. Lançon, S. Deiters
Comments: 20 pages, 16 figures, accepted for publication in MNRAS

The mass of unresolved young star clusters derived from spectro-photometric data may well be off by a factor of 2 or more once the migration of massive stars driven by mass segregation is accounted for. We quantify this effect for a large set of cluster parameters, including variations in the stellar IMF, the intrinsic cluster mass, and mean mass density. Gas-dynamical models coupled with the Cambridge stellar evolution tracks allow us to derive a scheme to recover the real cluster mass given measured half-light radius, one-dimensional velocity dispersion and age. We monitor the evolution with time of the ratio of real to apparent mass through the parameter eta. When we compute eta for rich star clusters, we find non-monotonic evolution in time when the IMF stretches beyond a critical cutoff mass of 25.5 solar mass. We also monitor the rise of color gradients between the inner and outer volume of clusters: we find trends in time of the stellar IMF power indices overlapping well with those derived for the LMC cluster NGC 1818 at an age of 30 Myr. We argue that the core region of massive Antennae clusters should have suffered from much segregation despite their low ages. We apply these results to a cluster mass function, and find that the peak of the mass distribution would appear to observers shifted to lower masses by as much as 0.2 dex. The star formation rate (SFR) derived for the cluster population is then underestimated by from 20 to 50 per cent.
astro-ph/0604195 [abs, ps, pdf, other] :: Title: Noncommutative chaotic inflation and WMAP three year results
Authors: Xin Zhang, Feng-Quan Wu
Comments: 8 pages, 3 figures

Noncommutative inflation is based upon the consideration of some effects of the space-time uncertainty principle motivated by ideas from string/M theory. The CMB anisotropies may carry a signature of this very early Universe correction from the space-time uncertainty principle and can be used to place constraints on the parameters of the noncommutative inflation model. In this paper we analyze the noncommutative chaotic inflation model by means of the WMAP three year results. We show that the noncommutative chaotic inflation model can produce a large negative running of spectral index within a reasonable range of $e$-folding number $N$, provided that the value of $p$ in the potential $V(\phi)\propto \phi^p$ is enhanced roughly to $p\sim 12-18$. Applying a likelihood analysis to the WMAP results, we find the best-fit values of parameters for the noncommutative chaotic inflation model. In addition, this model predicts a rather big gravitational wave which may be tested by the upcoming experiments.
astro-ph/0604196 [abs, ps, pdf, other] :: Title: The $\dot{M} - M$ relationship in pre-main sequence stars
Authors: C.J.Clarke, J.E.Pringle
Comments: accepted for publication in MNRAS

We examine the recent data and analysis of Natta et al. concerning the accretion rate on to young stars as a function of stellar mass, and conclude that the apparently steep dependence of accretion rate on mass is strongly driven by selection/detection thresholds. We argue that a convincing demonstration of a physical relationship between accretion and stellar mass requires further studies which, as is the case for Natta et al., include information on upper limits, and which quantify the possible incompleteness of the sample, at both low and high accretion rates. We point out that the distribution of detections in the ($M, \dot{M}$)-plane is consistent with conventional accretion disc models, and that higher sensitivity observations might be able to test the hypothesis of accelerated disc clearing at late times.
astro-ph/0604197 [abs, ps, pdf, other] :: Title: Observation of VHE Gamma Radiation from HESS J1834-087/W41 with the MAGIC Telescope
Authors: J. Albert et al. (MAGIC collaboration)
Comments: Accepted by ApJ Letters

Recently, the HESS array has reported the detection of gamma-ray emission above a few hundred GeV from eight new sources located close to the Galactic Plane. The source HESS J1834-087 is spatially coincident with SNR G23.3-0.3 (W41). Here we present MAGIC observations of this source, resulting in the detection of a differential gamma-ray flux consistent with a power law, described as dN/(dA dt dE) = (3.7 +/- 0.6)*10^(-12) (E/TeV)^(-2.5 +/- 0.2) \ cm^(-2)s^(-1)TeV^(-1). We confirm the extended character of this flux. We briefly discuss the observational technique used, the procedure implemented for the data analysis, and put this detection in the perspective of the molecular environment found in the region of W41. We present 13CO and 12CO emission maps showing the existence of a massive molecular cloud in spatial superposition with the MAGIC detection.
astro-ph/0604198 [abs, ps, pdf, other] :: Title: Barium even-to-odd isotope abundance ratios in thick disk and thin disk stars
Authors: L. Mashonkina, G. Zhao
Comments: 10 pages, 7 figures, accepted for publication in Astronomy and Astrophysics

We present the Ba even-to-odd isotope abundance ratios in 25 cool dwarf stars with the metallicity [Fe/H] ranged between 0.25 and --1.35. Our method takes advantage of the hyperfine structure (HFS) affecting the \ion{Ba}{ii} resonance line of the odd isotopes. The fractional abundance of the odd isotopes of Ba is derived from a requirement that Ba abundances from the resonance line $\lambda 4554$ and subordinate lines $\lambda 5853$ and $\lambda 6496$ must be equal. The results are based on NLTE line formation and analysis of high resolution (R $\sim60000$) high signal-to-noise (S/N $\ge 200$) observed spectra. We find that the fraction of the odd isotopes of Ba grows toward the lower Ba abundance (or metallicity) and the mean value in the thick disk stars equals 33 $\pm$ 4%. This indicates the higher contribution of the $r-$process to barium in the thick disk stars compared to the solar system matter. The obtained fraction increases with the [Eu/Ba] abundance ratio growth in agreement with expectations. A significant fraction of the \emph{even} isotopes of Ba found in old Galactic stars (the thick disk stars), $\sim67$%, is in contrast to the prediction of the "classical" model of the $s-$process and favors the value predicted by the "stellar" models of Arlandini et al. (1999) and Travaglio et al. (1999).
astro-ph/0604199 [abs, ps, pdf, other] :: Title: Satellite Detection of Radio Pulses from Ultrahigh Energy Neutrinos Interacting with the Moon
Authors: O. Stål, J. Bergman, B. Thidé, L. K. S. Daldorff, G. Ingelman
Comments: 4 pages, 3 figures, uses RevTeX 4

The Moon provides a huge effective detector volume for ultrahigh energy cosmic neutrinos, which generate coherent radio pulses in the lunar surface layer due to the Askaryan effect. We report systematic Monte Carlo simulations which show that radio instruments on board a Moon-orbiting satellite can detect Askaryan pulses from neutrinos with energies above 10^{19} eV, i.e. near and above the interesting GZK limit, at the very low fluxes predicted in different scenarios.
astro-ph/0604200 [abs, ps, pdf, other] :: Title: Models of inflation with primordial non-Gaussianities
Authors: Francis Bernardeau, Tristan Brunier, Jean-Philippe Uzan
Comments: 8 pages with 3 eps figures. To appear in Proceedings of the Albert Einstein Century International Conference, UNESCO, Paris, France, 18-22 July 2005

We present a class of models in which the primordial metric fluctuations do not necessarily obey Gaussian statistics. These models are realizations of mechanisms in which non-Gaussianity is first generated by a light scalar field and then transferred into curvature fluctuations during or at the end of inflation. For this class of models we present generic results for the probability distribution functions of the metric perturbation at the end of inflation. It is stressed that finite volume effects can induce non trivial effects that we sketch.
astro-ph/0604201 [abs, ps, pdf, other] :: Title: Evolutionary Status of SNR 1987A at the Age of Eighteen
Authors: Sangwook Park (Penn State), Svetozar A. Zhekov (Colorado, SRI), David N. Burrows, Gordon P. Garmire, Judith L. Racusin (Penn State), Richard McCray (Colorado)
Comments: 21 pages including 9 figures, Accepted by ApJ

$\sim$18 yr after the supernova explosion, the blast wave of SNR 1987A is entering the main body of the equatorial circumstellar material, which is causing a dramatic brightening of the remnant. We recently reported the observational evidence for this event from our {\it Chandra} data (Park et al. 2005b; P05 hereafter). We present here the temporal evolution of the X-ray emitting shock parameters and the detailed description of the spectral and image analysis of SNR 1987A, on which P05 was based. While the remnant becomes brighter, the softening of the overall X-ray spectrum continues and is enhanced on around day $\sim$6200 (since the explosion). The two-component shock model indicates that the electron temperatures have been changing for the last $\sim$6 yr. The X-ray spectrum is now described by $kT$ $\sim$ 0.3 keV and 2.3 keV thermal plasmas which are believed to characteristically represent the shock-heated density gradient along the boundary between the H{\small II} region and the dense inner ring. As the blast wave sweeps through the inner circumstellar ring shining in X-rays, we expect that the shock parameters continue to change, revealing the density and abundance structure of the inner ring. Follow-up {\it Chandra} observations will thus uncover the past history of the progenitor's stellar evolution. The origin of the relatively faint hard X-ray emission ($E$ $>$ 3 keV) from SNR 1987A is still unclear (thermal vs. nonthermal). Considering the continuous brightening of the hard band intensity, as well as the soft band flux, follow-up monitoring observations will also be essential to reveal the origin of the hard X-ray emission of SNR 1987A.
astro-ph/0604202 [abs, ps, pdf, other] :: Title: Halos and voids in a multifractal model of cosmic structure
Authors: Jose Gaite
Comments: 14 pages, 9 PS figure files

On the one hand, the large scale structure of matter is arguably scale invariant, and, on the other hand, halos and voids are recognized as prominent features of that structure. To unify both approaches, we propose to model the dark matter distribution as a set of fractal distributions of halos of different kinds. This model relies on the concept of multifractal as the most general scaling distribution and on a plausible notion of halo as a singular mass concentration in a multifractal. Voids arise as complementary to halos, namely, as formed by regular mass depletions. To provide halos with definite size and masses, we coarse-grain the dark matter distribution, using the length given by the lower cutoff to scaling. This allows us to relate the halo mass function to the multifractal spectrum. Hence, we find that a log-normal model of the mass distribution nicely fits in this picture and, moreover, the Press-Schechter mass function can be recovered as a bifractal limit.
To support our model of fractal distributions of halos, we perform a numerical study of the distribution produced in cosmological N-body simulations. In the Virgo L-CDM GIF2 simulation, we indeed find fractal distributions of halos with various dimensions and a halo mass function of bifractal type. However, this mass function is not of Press-Schechter's type, and we interprete it instead as caused by the undersampling of the distribution at the scale of halos, due to discretization.
astro-ph/0604203 [abs, ps, pdf, other] :: Title: Core Structure of Intracluster Gas: Effects of Radiative Cooling on Core Sizes
Authors: Takuya Akahori, Kuniaki Masai
Comments: 7 pages, 11 figures; To be published in PASJ vol 58, No. 3(June 2006)

We investigate the core structure of radiatively cooling intracluster gas, using a hydrodynamics code. We calculate evolution of model clusters of the initial core radii 160--300 kpc until the initial central cooling time, and analyze the resultant clusters using the double beta-model as done by observational studies. It is found that the core-size distribution thus obtained shows two peaks \sim 30--100 kpc and \sim 100--300 kpc and marginally can reproduce the observed distribution which exhibits two distinct peaks around \sim 50 kpc and \sim 200 kpc. This result may suggest radiative-cooling origin for small cores, while cooling is yet insignificant in the clusters of large cores. It should be noted that the small core peak is reproduced by clusters that are still keeping quasi-hydrostatic balance before the initial central cooling time has elapsed.
astro-ph/0604204 [abs, ps, pdf, other] :: Title: The CMB Initial Data and Fundamental Operator Quantization of General Relativity
Authors: Victor N. Pervushin
Comments: 10 pages, submitted to XXXIII International Conference On High Energy Physics, Particle astrophysics & cosmology (ICHEP'06 Moscow, 26.07-02.08, 2006; this http URL)

The observational data on CMB radiation revealed that our Universe can be an ordinary physical object moving with respect to the Earth observer with the occasional initial data. The simplest fit of the observational CMB data is given in the framework of the fundamental operator quantization of GR and SM that includes occasional gauge-invariant and frame-covariant initial data and their units of measurement.
astro-ph/0604205 [abs, ps, pdf, other] :: Title: The dynamical state of massive galaxy clusters
Authors: E. S. Cypriano, L. Sodre Jr., J.-P. Kneib, L. E. Campusano
Comments: 2 pages, 2 figures. Contributed talk, XIth IAU Latin-American Regional Meeting (Dec. 2005, Pucon, Chile), to appear in RMxAA

We study the mass distribution of a sample of 24 X-ray bright Abell clusters through weak gravitational lensing. This method is independent of the dynamical state of the galaxy cluster. Hence, by comparing dynamical and lensing mass estimators, we can access the dynamical state of these clusters. We have found that clusters with ICM temperatures above 8 keV show strong deviations from the relaxation, as well as the presence of prominent sub-structures. For the remaining clusters (the majority of the sample) we have found agreement among the several mass estimators, which indicates that most of the clusters are in or close to a state of dynamical equilibrium.
astro-ph/0604206 [abs, ps, pdf, other] :: Title: Power-law Parameterized Quintessence Model
Authors: Sohrab Rahvar, M. Sadegh Movahed
Comments: 11 pages, 16 figures, submitted to JCAP

We introduce a power-law parameterized quintessence model for the dark energy. An exponential potential of scalar field is reconstructed in terms of present fraction of dark energy and parameters of equation of state for this model. We use Supernova Type Ia (SNIa) Gold sample data, size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), the position of the acoustic peak from the CMB observations and structure formation from the 2dFGRS survey to constrain the parameters of the quintessence model. The best fit parameters indicates that the equation of state of this model at the present time is less than one $(w_0<-1)$ and violates the energy condition in General Relativity. Finally we compare the age of old objects with age of universe in this model.
astro-ph/0604207 [abs, ps, pdf, other] :: Title: The science of PAMELA space mission
Authors: P.Picozza, A.Morselli
Comments: 8 pages, 7 figures, To be published in "12th Lomonosov Conference on Elementary Particle Physics" Moscow, August, 2005, World Scientific Publishing Co

Many different mechanisms can contribute to antiprotons and positrons production, ranging from conventional reactions up to exotic processes like neutralino annihilation. The open problems are so fundamental (i.e.: is the universe symmetric in matter and antimatter ?) that experiments in this field will probably be of the greatest interest in the next years. Here we will summarize the present situation, showing the different hypothesis and models and the experimental measurements needed to lead to a more established scenario.
astro-ph/0604208 [abs, ps, pdf, other] :: Title: A SCUBA imaging survey of ultracompact HII regions: The environments of massive star formation
Authors: M.A. Thompson, J. Hatchell, A.J. Walsh, G.H. Macdonald, T.J. Millar
Comments: Accepted by A&A. Note that due to size constraints the Online Supplement cannot be reproduced here and that several of the figures are low-resolution versions. A complete preprint (in PDF format) with full resolution images is available at this http URL

We present a SCUBA submillimetre (450 & 850 micron) survey of the environment of 105 IRAS point sources, selected from the Wood & Churchwell (1989a) and Kurtz, Churchwell & Wood (1994) radio ultracompact (UC) HII region surveys. We detected a total of 155 sub-mm clumps associated with the IRAS point sources and identified three distinct types of object: ultracompact cm-wave sources that are not associated with any sub-mm emission (sub-mm quiet objects), sub-mm clumps that are associated with ultracompact cm-wave sources (radio-loud clumps); and sub-mm clumps that are not associated with any known ultracompact cm-wave sources (radio-quiet clumps). 90% of the sample of IRAS point sources were found to be associated with strong sub-mm emission. We consider the sub-mm colours, morphologies and distance-scaled fluxes of the sample of sub-mm clumps and show that the sub-mm quiet objects are unlikely to represent embedded UC HII regions unless they are located at large heliocentric distances. Many of the 2.5 arcmin SCUBA fields contain more than one sub-mm clump, with an average number of companions (the companion clump fraction) of 0.90. The clumps are more strongly clustered than other candidate HMPOs and the mean clump surface density exhibits a broken power-law distribution with a break at 3 pc. We demonstrate that the sub-mm and cm-wave fluxes of the majority of radio-loud clumps are in excellent agreement with the standard model of ultracompact HII regions. We speculate on the nature of the radio-quiet sub-mm clumps and, whilst we do not yet have sufficient data to conclude that they are in a pre-UC HII region phase, we argue that their characteristics are suggestive of such a stage.
astro-ph/0604209 [abs, ps, pdf, other] :: Title: Non-Gaussian Inflationary Perturbations from the dS/CFT Correspondence
Authors: David Seery, James E. Lidsey
Comments: 23 pages, uses iopart.cls. Submitted to JCAP

We calculate for the first time the holographically renormalized three-point correlation function for a deformed Euclidean CFT that is dual to single-field, slow-roll inflation under Maldacena's version of the dS/CFT correspondence. This correlator can be related to the three-point function of the curvature perturbation generated during single-field inflation, and we find exact agreement with previous bulk QFT calculations. This provides a consistency check on previous derivations of the non-Gaussianity from single-field inflation and also yields insight into the nature of the dS/CFT correspondence. As a result of our calculation, we obtain the properly renormalized dS/CFT one-point function, including boundary contributions where derivative interactions are present in the bulk. In principle, our method may be employed to derive the n-point correlators of the inflationary curvature perturbation within the context of (n-1)th-order perturbation theory, rather than nth-order theory as in conventional approaches.
astro-ph/0604210 [abs, pdf] :: Title: Determining the H+ Region/PDR Equation of State in Star Forming Regions
Authors: N. P. Abel, G. J. Ferland
Comments: 21 pages, 7 figures, accepted for publication in ApJ

The emission line regions of starburst galaxies and active nuclei reveal a wealth of spectroscopic information. A unified picture of the relationship between ionized, atomic, and molecular gas makes it possible to better understand these observations. We performed a series of calculations designed to determine the equation of state, the relationship between density, temperature, and pressure, through emission-line diagnostic ratios that form in the H+ region and PDR. We consider a wide range of physical conditions in the H+ region. We connect the H+ region to the PDR by considering two constant pressure cases, one with no magnetic field and one where the magnetic field overwhelms the thermal pressure. We show that diagnostic ratios can yield the equation of state for single H+ regions adjacent to single PDRs, with the results being more ambiguous when considering observations of entire galaxies. As a test, we apply our calculations to the Orion H+/PDR region behind the Trapezium. We find the ratio of thermal to magnetic pressure in the PDR to be \~1.2. If magnetic and turbulent energy are in equipartition, our results mean the magnetic field is not the cause of the unexplained broadening in M 42, but may significantly affect line broadening in the PDR. Since Orion is often used to understand physical processes in extragalactic environments, our calculations suggest magnetic pressure should be considered in modeling such regions.
astro-ph/0604211 [abs, ps, pdf, other] :: Title: The Millennium Galaxy Catalogue: a census of local compact galaxies
Authors: J. Liske (ESO), S.P. Driver (RSAA, St Andrews), P.D. Allen (RSAA), N.J.G. Cross (IfA, Edinburgh), R. De Propris (CTIO)
Comments: Accepted for publication in MNRAS, 19 pages, 15 figures. Table 3 available at the MGC WWW site at this http URL

We use the Millennium Galaxy Catalogue (MGC) to study the effect of compact galaxies on the local field galaxy luminosity function. Here we observationally define as `compact' galaxies that are too small to be reliably distinguished from stars using a standard star-galaxy separation technique. In particular, we estimate the fraction of galaxies that are misclassified as stars due to their compactness. We have spectroscopically identified all objects to B_MGC = 20 mag in a 1.14 deg^2 sub-region of the MGC, regardless of morphology. From these data we develop a model of the high surface brightness incompleteness and estimate that ~1 per cent of galaxies with B_MGC < 20 mag are misclassified as stars, with an upper limit of 2.3 per cent at 95 per cent confidence. However, since the missing galaxies are preferentially sub-L* their effect on the faint end of the luminosity function is substantially amplified: we find that they contribute ~6 per cent to the total luminosity function in the range -17 < M_B < -14 mag, which raises the faint end slope alpha by 0.03^{+0.02}_{-0.01}. Their contribution to the total B-band luminosity density is ~2 per cent. Roughly half of the missing galaxies have already been recovered through spectroscopy of morphologically stellar targets selected mainly by colour. We find that the missing galaxies mostly consist of intrinsically small, blue, star-forming, sub-L* objects. In combination with the recent results of Driver et al. (2005) we have now demonstrated that the MGC is free from both high and low surface brightness selection bias for giant galaxies (M_B <~ -17 mag). Dwarf galaxies, on the other hand, are significantly affected by these selection effects. To gain a complete view of the dwarf population will require both deeper and higher resolution surveys.
astro-ph/0604212 [abs, pdf] :: Title: The H+ Region Contribution to [C II] 158 Micron Emission
Authors: N. P. Abel
Comments: 18 pages, 7 figures, accepted for publication in the MNRAS

The [C II] 158 micron line is an important emission line diagnostic in Photodissociation Regions (PDRs), but this emission line can also emerge from ionized gas. This work calculates the contribution of [C II] emission from ionized gas over a wide range of parameter space by considering the simplified case of an H+ region and PDR in pressure equilibrium. Additionally, these calculations also predict the strong correlation observed between [N II] 205 micron emission and [C II] discussed by previous authors. Overall, the results of these calculations have wide-ranging applications to the interpretation of [C II] emission in astrophysical environments.
astro-ph/0604213 [abs, ps, pdf, other] :: Title: SiO in C-rich circumstellar envelopes of AGB stars: effects of non-LTE chemistry and grain adsorption
Authors: F. L. Schoeier, H. Olofsson, A. A. Lundgren
Comments: Accepted for publication in A&A, 11 pages, 7 figures

New SiO multi-transition millimetre line observations of a sample of carbon stars, including J=8-7 observations with the APEX telescope, are used to probe the role of non-equilibrium chemistry and the influence of grains in circumstellar envelopes of carbon stars. A detailed radiative transfer modelling, including the effect of dust emission in the excitation analysis, of the observed SiO line emission is performed. A combination of low- and high-energy lines are important in constraining the abundance distribution. It is found that the fractional abundance of SiO in these C-rich environments can be several orders of magnitude higher than predicted by equilibrium stellar atmosphere chemistry. In fact, the SiO abundance distribution of carbon stars closely mimic that of M-type (O-rich) AGB stars. A possible explanation for this behaviour is a shock-induced chemistry, but also the influence of dust grains, both as a source for depletion as well as production of SiO, needs to be further investigated. As observed for M-type AGB stars, a clear trend that the SiO fractional abundance decreases as the mass-loss rate of the star increases is found for the carbon stars. This indicates that SiO is accreted onto dust grains in the circumstellar envelopes.
astro-ph/0604214 [abs, ps, pdf, other] :: Title: Implications of a Running Spectral Index for Slow Roll Inflation
Authors: Richard Easther (Yale), Hiranya Peiris (KICP/EFI, U. Chicago)
Comments: 4 pages

We analyze the weak (2 sigma) evidence for a running spectral index seen in the three-year WMAP dataset and its implications for single field, slow roll inflation. We assume that the running is comparable to the central value found from the WMAP data analysis, and use the Hubble Slow Roll formalism to follow the evolution of the slow roll parameters. For all parameter choices consistent with a large, negative running, single field, slow roll inflation lasts less than 30 efolds after CMB scales leave the horizon. Thus, a definitive observation of a large negative running would imply that any inflationary phase requires multiple fields or the breakdown of slow roll. Alternatively, if single field, slow roll inflation is sources the primordial fluctuations, we can expect the observed running to move much closer to zero as the CMB is measured more accurately at small angular scales.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Wed, 12 Apr 06 00:00:10 GMT
0604215 -- 0604248 received

astro-ph/0604215 [abs, ps, pdf, other] :: Title: Neutrino Coannihilation on Dark-Matter Relics?
Authors: Gabriela Barenboim, Olga Mena Requejo, Chris Quigg
Comments: 5 pages, 3 figures, uses RevTeX 4

High-energy neutrinos may resonate with relic background neutralinos to form short-lived sneutrinos. In some circumstances, the decay chain that leads back to the lightest supersymmetric particle would yield few-GeV gamma rays or charged-particle signals. Although resonant coannihilation would occur at an appreciable rate in our galaxy, the signal in any foreseeable detector is unobservably small.
astro-ph/0604216 [abs, ps, pdf, other] :: Title: Studies of Virgo cluster early-type dwarf galaxies with the SDSS: I. On the possible disk nature of bright early-type dwarfs
Authors: Thorsten Lisker, Eva K. Grebel, Bruno Binggeli (University of Basel)
Comments: 25 pages, 20 figures. Accepted for publication by AJ. Full resolution version available at this http URL

We present a systematic search for disks in 476 Virgo cluster early-type dwarf (dE) galaxies. Disk features (spiral arms, edge-on disks, or bars) were identified by applying unsharp masks to a combined image from three bands (g, r, i), as well as by subtracting the axisymmetric light distribution of each galaxy from that image. 14 objects are unambiguous identifications of disks, 10 objects show 'probable disk' features, and 17 objects show 'possible disk' features. The number fraction of these galaxies, for which we introduce the term dEdi, reaches more than 50% at the bright end of the dE population, and decreases to less than 5% for magnitudes B>16. The luminosity function of our full dE sample can be explained by a superposition of dEdis and ordinary dEs, strongly suggesting that dEdis are a distinct type of galaxy. This is supported by the projected spatial distribution: dEdis show basically no clustering and roughly follow the spatial distribution of spirals and irregulars, whereas ordinary dEs are distributed similarly to the strongly clustered E/S0 galaxies. While the flattening distribution of ordinary dEs is typical for spheroidal objects, the distribution of dEdis is significantly different and agrees with their being flat oblate objects. We therefore conclude that the dEdis are not spheroidal galaxies that just have an embedded disk component, but are instead a population of genuine disk galaxies. Several dEdis display well-defined spiral arms with grand design features that clearly differ from the flocculent, open arms typical for late-type spirals that have frequently been proposed as progenitors of early-type dwarfs. This raises the question of what process is able to create such spiral arms - with pitch angles like those of Sab/Sb galaxies - in bulgeless dwarf galaxies. (Abridged)
astro-ph/0604217 [abs, ps, pdf, other] :: Title: Redshift-Space Distortions with the Halo Occupation Distribution II: Analytic Model
Authors: Jeremy L. Tinker (KICP, UChicago)
Comments: 21 pages, submitted to MNRAS

We present an analytic model for the galaxy two-point correlation function in redshift space. The model is constructed within the framework of the Halo Occupation Distribution (HOD), which quantifies galaxy bias on linear and non- linear scales. We model one-halo pairwise velocities by assuming that satellite galaxy velocities follow a Gaussian distribution with dispersion proportional to the virial dispersion of the host halo. Two-halo velocity statistics are a combination of virial motions and host halo motions. The velocity distribution function (DF) of halo pairs is a complex function with skewness and kurtosis that vary substantially with scale. Using a series of collisionless N-body simulations, we demonstrate that the shape of this DF is determined primarily by the distribution of local densities around a halo pair, and at fixed density the velocity DF is close to Gaussian and nearly independent of halo mass. We calibrate a model for the conditional probability function of densities around halo pairs on these simulations. With this model, the full shape of the halo velocity DF can be accurately calculated as a function of halo mass, radial separation, angle, and cosmology. The HOD approach to redshift-space distortions utilizes clustering data from linear to non-linear scales to break the standard degeneracies inherent in previous models of redshift-space clustering. The parameters of the occupation function are well constrained by real-space clustering alone, separating constraints on bias and cosmology. We demonstrate the ability of the model to separately constrain Omega_m, sigma_8, and galaxy velocity bias in models that are constructed to have the same value of beta at large scales as well as the same finger-of-god distortions at small scales. [Abridged]
astro-ph/0604218 [abs, ps, pdf, other] :: Title: Feedback from Clustered Sources During Reionization
Authors: Roban Hultman Kramer, Zoltan Haiman (Columbia), S. Peng Oh (UCSB)
Comments: submitted to ApJ, 9 emulateapj pages with 7 figures

The reionization history of the intergalactic medium (IGM) at high redshift (z > 6) was likely strongly shaped by several global feedback processes. Because the earliest ionizing sources formed at the locations of the rare density peaks, their spatial distribution was strongly clustered. Here we demonstrate that this clustering significantly boosts the impact of feedback processes operating at high redshift. We build a semi-analytical model to include feedback and clustering simultaneously, and apply this model to the suppression of star-formation in minihalos due to photoionization. The model is built on the excursion-set-based formalism of Furlanetto, Zaldarriaga and Hernquist (2004), which incorporates the clustering of ionizing sources, and which we here extend to include suppression of star formation in minihalos. We find that clustering increases the mean HII bubble size by a factor of several, and it dramatically increases the fraction of minihalos that are suppressed, by a factor of up to 60 relative to a randomly distributed population. This enhanced suppression can significantly reduce the electron scattering optical depth, as required by the three-year data from the Wilkinson Microwave Anisotropy Probe (WMAP). We argue that source clustering is likely to similarly boost the importance of a variety of other feedback mechanisms.
astro-ph/0604219 [abs, pdf] :: Title: A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei
Authors: J. F. Gallimore, D. J. Axon, C. P. O'Dea, S. A. Baum, A. Pedlar
Comments: to appear in the Astronomical Journal, Vol 132 (projected)

Seyfert galaxies commonly host compact jets spanning 10-100 pc scales, but larger structures (KSRs) are resolved out in long baseline, aperture synthesis surveys. We report a new, short baseline Very Large Array (VLA) survey of a complete sample of Seyfert and LINER galaxies. Out of all of the surveyed radio-quiet sources, we find that 44% (19 / 43) show extended radio structures at least 1 kpc in total extent that do not match the morphology of the disk or its associated star-forming regions. The KSR Seyferts stand out by deviating significantly from the far-infrared - radio correlation for star-forming galaxies, and they are more likely to have a relatively luminous, compact radio source in the nucleus; these results argue that KSRs are powered by the AGN rather than starburst. KSRs probably originate from jet plasma that has been decelerated by interaction with the nuclear ISM. We demonstrate the jet loses virtually all of its power to the ISM within the inner kiloparsec to form the slow KSRs.
astro-ph/0604220 [abs, ps, pdf, other] :: Title: The Nearby Damped Lyman-alpha Absorber SBS 1543+593: A Large HI Envelope in a Gas-Rich Galaxy Group
Authors: J. L. Rosenberg, D. V. Bowen, T. M. Tripp, E. Brinks
Comments: 11 pages, AJ accepted

We present a Very Large Array (VLA) HI 21cm map and optical observations of the region around one of the nearest damped Lyman-alpha absorbers beyond the local group, SBS 1543+593. Two previously uncataloged galaxies have been discovered and a redshift has been determined for a third. All three of these galaxies are at the redshift of SBS 1543+593 and are ~185 kpc from the damped Lyman-alpha absorber. We discuss the HI and optical properties of SBS 1543+593 and its newly identified neighbors. Both SBS 1543+593 and Dwarf 1 have baryonic components that are dominated by neutral gas -- unusual for damped Lyman-alpha absorbers for which only ~5% of the HI cross-section originates in such strongly gas-dominated systems. What remains unknown is whether low mass gas-rich groups are common surrounding gas-rich galaxies in the local universe and whether the low star-formation rate in these systems is indicative of a young system or a stable, slowly evolving system. We discuss these evolutionary scenarios and future prospects for answering these questions.
astro-ph/0604221 [abs, ps, pdf, other] :: Title: Laboratory Plasma Dynamos, Astrophysical Dynamos, and Magnetic Helicity Evolution
Authors: Eric G. Blackman, Hantao Ji
Comments: accepted by MNRAS

The term ``dynamo'' means different things to the laboratory fusion plasma and astrophysical plasma communities. To alleviate the resulting confusion and to facilitate interdisciplinary progress, we pinpoint conceptual differences and similarities between laboratory plasma dynamos and astrophysical dynamos. We can divide dynamos into three types: 1. magnetically dominated helical dynamos which sustain a large scale magnetic field against resistive decay and drive the magnetic geometry toward the lowest energy state, 2. flow-driven helical dynamos which amplify or sustain large scale magnetic fields in an otherwise turbulent flow, and 3. flow-driven nonhelical dynamos which amplify fields on scales at or below the driving turbulence. We discuss how all three types occur in astrophysics whereas plasma confinement device dynamos are of the first type. Type 3 dynamos requires no magnetic or kinetic helicity of any kind. Focusing on type 1 and 2 dynamos, we show how different limits of a unified set of equations for magnetic helicity evolution reveal both types. We explicitly describe a steady-state example of a type 1 dynamo, and three examples of type 2 dynamos: (i) closed volume and time dependent; (ii) steady-state with open boundaries; (iii) time dependent with open boundaries.
astro-ph/0604222 [abs, ps, pdf, other] :: Title: Spitzer IRS spectra of a large sample of Seyfert galaxies: a variety of infrared SEDs in the local AGN population
Authors: Catherine L. Buchanan (1), Jack F. Gallimore (2), Christopher P. O'Dea (1), Stefi A. Baum (3), David J. Axon (1), Andrew Robinson (1), Moshe Elitzur (4), Martin Elvis (5) ((1) Dept of Physics, Rochester Institute of Technology; (2) Bucknell University; (3) Center for Imaging Science, Rochester Institute of Technology; (4) University of Kentucky; (5) Harvard-Smithsonian Center for Astrophysics)
Comments: 39 pages, 17 figures, accepted to AJ, version with high-resolution figures available at this http URL

We are conducting a large observing program with the Spitzer Space Telescope to determine the mid-to-far infrared spectral energy distributions of a well-defined sample of 87 nearby, 12 micron-selected Seyfert galaxies. In this paper we present the results of IRS low-resolution spectroscopy of a statistically representative subsample of 51 of the galaxies (59%), with an analysis of the continuum shapes and a comparison of the Seyfert types. We find that the spectra clearly divide into groups based on their continuum shapes and spectral features. Some spectral features are clearly related to a starburst contribution to the IR spectrum, while the mechanisms producing observed power-law continuum shapes, attributed to an AGN component, may be dust or non-thermal emission. The infrared spectral types appear to be related to the Seyfert types. Principal component analysis results suggest that the relative contribution of starburst emission may be the dominant cause of variance in the observed spectra. We find that Sy 1's have higher ratios of IR/radio emission than Sy 2's, as predicted by the unified model if the torus is optically thick in the mid-IR. However, smooth-density torus models predict a much larger difference between type 1's and 2's than observed in our sample. Our observations may be consistent with clumpy torus models containing a steep radial distribution of optically thick dense clumps. (Abridged)
astro-ph/0604223 [abs, ps, pdf, other] :: Title: The 21 Centimeter Forest
Authors: Steven Furlanetto (Yale)
Comments: 9 pages, 5 figures, submitted to MNRAS

We examine the prospects for studying the pre-reionization intergalactic medium (IGM) through the so-called 21 cm forest in spectra of bright high-redshift radio sources. We first compute the evolution of the mean optical depth for models that include X-ray heating of the IGM gas, Wouthuysen-Field coupling, and reionization. Under most circumstances, the spin temperature T_S grows large well before reionization begins in earnest. As a result, the optical depth is less than 0.001 throughout most of reionization, and background sources must sit well beyond the reionization surface in order to experience measurable absorption. HII regions produce relatively large "transmission gaps" and may therefore still be observable during the early stages of reionization. Absorption from sheets and filaments in the cosmic web fades once T_S becomes large and should be rare during reionization. Minihalos can produce strong (albeit narrow) absorption features. Measuring their abundance would yield useful limits on the strength of feedback processes in the IGM as well as their effect on reionization.
astro-ph/0604224 [abs, ps, pdf, other] :: Title: A sample of low-redshift BL Lacertae objects. II. EVN and MERLIN data and multi-wavelength analysis
Authors: M. Giroletti (1 and 2), G. Giovannini (1 and 2), G. B. Taylor (3 and 4), R. Falomo (5) ((1) INAF Institute of Radioastronomy, (2) Univ. of Bologna, (3) Univ. of New Mexico, (4) NRAO Socorro, (5) INAF Observatory of Padua)
Comments: Accepted by ApJ. 17 pages

We present new radio observations of 9 members of a sample of 29 nearby (z < 0.2) BL Lac objects. The new data have been obtained with the European VLBI Network and/or the MERLIN at 1.6 and 5 GHz and complement previous observations. For one object, the TeV source Mrk 421, we also present deep multi-epoch VLBA and Global VLBI data, which reveal a resolved diffuse jet, with clear signatures of limb brightening. We use the new and old data to estimate physical parameters of the jets of the sample from which the subset with new radio data is drawn. We derive Doppler factors in the parsec scale radio jet in the range ~2 < delta < ~9. Using HST data, we separate the contribution of the host galaxy from that of the active core. From the measured and de-beamed observables, we find a weak correlation between radio power and black hole mass, and a tight correlation between radio and optical core luminosities. We interpret this result in terms of a common synchrotron origin, with little contribution from a radiatively efficient accretion disk. The BL Lacs in our sample have de-beamed properties similar to low power radio galaxies, including the fundamental plane of black hole activity.
astro-ph/0604225 [abs, ps, pdf, other] :: Title: Non-existence of self-similar solutions containing a black hole in a universe with a stiff fluid or scalar field or quintessence
Authors: Tomohiro Harada, Hideki Maeda, B. J. Carr
Comments: 17 pages, 6 figures, submitted to Phys. Rev. D

We consider the possible existence of self-similar solutions containing black holes in a Friedmann background with a stiff fluid or a scalar field. We carefully study the relationship between the self-similar equations in these two cases and emphasize the crucial role of the similarity horizon. We show that there is no self-similar black hole solution surrounded by an exact or asymptotically flat Friedmann background containing a massless scalar field. This applies even if there is a scalar potential, as in the quintessence scenario. This extends the result previously found in the stiff fluid case and strongly suggests that accretion onto primordial black holes is ineffective even during scalar field domination. It also contradicts recent claims that such black holes can grow appreciably by accreting quintessence. Appreciable growth might be possible with very special matter fields but this requires {\it ad hoc} and probably unphysical conditions.
astro-ph/0604226 [abs, ps, pdf, other] :: Title: Spitzer Observations of High Redshift Radio Galaxies
Authors: N. Seymour (1), D. Stern (2 and 1), C. De Breuck (3) for the SHiZRaG collaboration ((1) SSC, (2) JPL, (3) ESO)
Comments: 6 pages, 5 figures, to appear in the proceedings of "The Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution", held in Pasadena, November 2005

We present the results of a comprehensive Spitzer survey of 70 radio galaxies across 1<z<5.2. Using IRAC, IRS and MIPS imaging we determine the rest-frame AGN contribution to the stellar emission peak at 1.6um. The stellar luminosities are found to be consistent with that of a giant elliptical with a stellar mass of 10^11-12Msun. The mean stellar mass remains constant at \~10^11.5Msun up to z=3 indicating that the upper end of the mass function is already in place by this redshift. The mid-IR luminosities imply bolometric IR luminosities that would classify all sources as ULIRGs. The mid-IR to radio luminosity generally correlate implying a common origin for these emissions. The ratio is higher than that found for lower redshift, ie z<1, radio galaxies.
astro-ph/0604227 [abs, ps, pdf, other] :: Title: Colour Dependence of the Distribution of IRAS Galaxies revealed by Multifractal Measures
Authors: Jun Pan (Nottingham, UK; PMO, China)
Comments: submitted to AA, 8 pages, 7 figures

Multifractal measures are applied to three IRAS galaxy subsamples selected by colour from the PSCz catalogue. As shown by generalised dimension spectrum, hot IRAS galaxies are found less clustered than cold galaxies, but the difference is very weak. An alternative tool, the conditional multifractal dimension spectrum reveals apparent peculiarity of the distribution of hot galaxies, especially at high orders. The conditional multifractal measure is basically measuring the environment of selected galaxies. A detailed analysis of the distribution of galaxies with their number of neighbours turns out that cold galaxies are more likely living in over dense regions than hot galaxies. Further studies suggest that, since the colour of IRAS galaxies is a good trace of star formation rate, it is possible that we have statistical evidence here for enhanced star formation rate due to galaxy interactions
astro-ph/0604228 [abs, ps, pdf, other] :: Title: Note on Redshift Distortion in Fourier Space
Authors: Yan-Chuan Cai, Jun Pan (PMO, China; NAOC, China)
Comments: 14 pages, 8 figures. In ChJAA format

We explore features of redshift distortion in Fourier analysis of N-body simulations. The peculiar motion along the line of sight shifts the phases of Fourier modes in a non-trivia way. On very large scales phases hardly changes as predicted by linear perturbation theory of redshift distortion, while in general the phase shifts induced by redshift distortion is stochastic and the PDF is symmetric to the peak at zero shift. Analysis of the phase shifts opens the possibility of constructing appropriate phenomenological models for the monopoles of bispectrum in redshift space. Comparison with simulations indeed shows our toy models successful in modeling bispectrum of equilaterals and isosceles at large scales. To test the plane parallel approximation, we compare the monopoles of the power spectrum and bispectrum in the radial and plane parallel distortion. Difference of power spectrum is at the level of 10%, and in the reduced bispectrum such difference is as small as a few percents. However, on the plane k_z=0 perpendicular to the line of sight, the difference in power spectrum between the radial and plane parallel approximation can be more than ~10%, and even worse on very small scales. Such difference is also prominent for bispectrum, especially for those configurations of tilted triangles. The non-Gaussian signals under radial distortion on small scales are systematically biased downside than that in plane parallel approximation, while amplitudes of such differences depends on the opening angle of the sample to the observer. The observation gives warning to the practice of using the power spectrum and bispectrum on the k_z=0 plane as estimation of the real space statistics.
astro-ph/0604229 [abs, ps, pdf, other] :: Title: New Observations and Models of the Kinematics of the Zodiacal Dust Cloud
Authors: G.J. Madsen (AAO), R.J. Reynolds (U. Wisc.), S.I. Ipatov (U. Maryland), A.S. Kutyrev, J.C. Mather, S.H. Moseley (NASA - GSFC)
Comments: 4 pages, 3 figures, to appear in refereed proceedings of 'Dust in Planetary Systems' (ESA), ed. H. Kruger & A. Graps, Sept. 2005

We report on new observations of the motion of zodiacal dust using optical absorption line spectroscopy of zodiacal light. We have measured the change in the profile shape of the scattered solar Mg I 5184 line toward several lines of sight in the ecliptic plane as well as the ecliptic pole. The variation in line centroid and line width as a function of helio-ecliptic longitude show a clear prograde signature and suggest that significant fraction of the dust follows non-circular orbits that are not confined to the ecliptic plane. When combined with dynamical models, the data suggest that the zodiacal dust is largely cometary, rather than asteroidal, in origin.
astro-ph/0604230 [abs, ps, pdf, other] :: Title: The first year of SN 2004dj in NGC 2403
Authors: J.Vinko, K.Takats, K.Sarneczky, Gy.M.Szabo, Sz.Meszaros, R.Csorvasi, T.Szalai, A.Gaspar, A.Pal, Sz.Csizmadia, A.Kospal, M.Racz, M.Kun, B.Csak, G.Furesz, H.DeBond, J.Grunhut, J.Thomson, S.Mochnacki, T.Koktay
Comments: 19 pages, accepted in MNRAS

New BVRI photometry and optical spectroscopy of the Type IIp supernova 2004dj in NGC 2403, obtained during the first year since discovery, are presented. The progenitor cluster, Sandage 96, is also detected on pre-explosion frames. The light curve indicates that the explosion occured about 30 days before discovery, and the plateau phase lasted about +110 \pm 20 days after that. The plateau-phase spectra have been modelled with the SYNOW spectral synthesis code using H, NaI, TiII, ScII, FeII and BaII lines. The SN distance is inferred from the Expanding Photosphere Method and the Standard Candle Method applicable for SNe IIp. They resulted in distances that are consistent with each other as well as earlier Cepheid- and Tully-Fisher distances. The average distance, D = 3.47 \pm 0.29 Mpc is proposed for SN 2004dj and NGC 2403. The nickel mass produced by the explosion is estimated as 0.02 \pm 0.01 M_o. The SED of the progenitor cluster is reanalysed by fitting population synthesis models to our observed BVRI data supplemented by U and JKH magnitudes from the literature. The chi^2-minimization revealed a possible "young" solution with cluster age T_{cl} = 8 Myr, and an "old" solution with T_{cl} = 20 - 30 Myr. The "young" solution would imply a progenitor mass M > 20 M_o, which is higher than the previously detected progenitor masses for Type II SNe.
astro-ph/0604231 [abs, ps, pdf, other] :: Title: Particle decay in the early universe: predictions for 21 cm
Authors: Yu. A. Shchekinov, E. O. Vasiliev
Comments: 5 pages, 4 figures, submitted in MNRAS

The influence of ultra-high energy cosmic rays (UHECRs) and decaying dark matter particles on the emission and absorption characteristics of neutral hydrogen in 21 cm at redshifts $z = 10-50$ is considered. In presence of UHECRs 21 cm can be seen in absorption with the brightness temperature $T_b=-(5\div 10)$ mK in the range $z=10-30$. Decayng particles can stimulate a 21 cm signal in emission with $T_b\sim 50-60$~mK at $z =50$, and $T_b \simeq 10$~mK at $z \sim 20$. Observational possibilities to detect manifestations of UHECRs and/or decaying particles in 21 cm with the future radio telescopes (LOFAR, PAST and SKA), and to distinguish contributions from them are briefly discussed.
astro-ph/0604232 [abs, ps, pdf, other] :: Title: The role of the LIRG and ULIRG phases in the evolution of Ks-selected galaxies
Authors: K.I. Caputi, H. Dole, G. Lagache, R.J. McLure, J.S. Dunlop, J.-L. Puget, E. Le Floc'h, P.G. Perez-Gonzalez
Comments: Accepted for publication in A&A. 9 pages, 6 figures

We investigate the role of the luminous infrared galaxy (LIRG) and ultra-luminous infrared galaxy (ULIRG) phases in the evolution of Ks-selected galaxies and, in particular, Extremely Red Galaxies (ERGs). With this aim, we compare the properties of a sample of 2905 Ks<21.5 (Vega mag) galaxies in the GOODS/CDFS with the sub-sample of those 696 sources which are detected at 24 microns. We find that LIRGs constitute 30% of the galaxies with stellar mass M>1x10^{11} Msun assembled at redshift z=0.5. A minimum of 65% of the galaxies with M>2.5x10^{11} Msun at z~2-3 are ULIRGs at those redshifts. 60% of the ULIRGs in our sample have the characteristic colours of ERGs. Conversely, 40% of the ERGs with stellar mass M>1.3x10^{11} Msun at 1.5<z<2.0 and a minimum of 52% of those with the same mass cut at 2.0<z<3.0 are ULIRGs. The average optical/near-IR properties of the massive ERGs at similar redshifts that are identified with ULIRGs and that are not have basically no difference, suggesting that both populations contain the same kind of objects in different phases of their lives.
LIRGs and ULIRGs have an important role in galaxy evolution and mass assembly, and, although they are only able to trace a fraction of the massive (M>1x10^{11} Msun) galaxies present in the Universe at a given time, this fraction becomes very significant (>50%) at redshifts z>~2.
astro-ph/0604233 [abs, ps, pdf, other] :: Title: X-ray number counts of normal galaxies
Authors: A. Georgakakis (1), I. Georgantopoulos (2), A. Akylas (2), A. Zezas (3), P. Tzanavaris (2) ((1) Imperial College, (2) Athens Observatory, (3) CfA)
Comments: to appear in ApJL

We use the number counts of X-ray selected normal galaxies to explore their evolution by combining the most recent wide-angle shallow and pencil-beam deep samples available. The differential X-ray number counts, dN/dS, for early and late-type normal galaxies are constructed separately and then compared with the predictions of the local X-ray luminosity function under different evolution scenarios. The dN/dS of early type galaxies is consistent with no evolution out to z~0.5. For late-type galaxies our analysis suggests that it is the sources with X-ray--to--optical flux ratio logfx/fopt>-2 that are evolving the fastest. Including these systems in the late-type galaxy sample yields evolution of the form ~(1+z)^{2.7} out to z~0.4. On the contrary late-type sources with logfx/fopt<-2 are consistent with no evolution. This suggests that the logfx/fopt>-2 population comprises the most powerful and fast evolving starbursts at moderate and high-z. We argue that although residual low-luminosity AGN contamination may bias our results toward stronger evolution, this is unlikely to modify our main conclusions.
astro-ph/0604234 [abs, ps, pdf, other] :: Title: Two extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey
Authors: Y. I. Izotov (1), P. Papaderos (2), N. G. Guseva (1), K. J. Fricke (2), T. X. Thuan (3) ((1) Main Astronomical Observatory, Kyiv, Ukraine, (2) Institute for Astrophysics, Goettingen, Germany, (3) University of Virginia, Charlottesville, USA)
Comments: 5 pages, 3 figures. Accepted for publication in Astronomy and Astrophysics

We present spectroscopic observations with the 3.6m ESO telescope of two emission-line galaxies, J2104-0035 and J0113+0052, selected from the Data Release 4 (DR4) of the Sloan Digital Sky Survey (SDSS). From our data we determine the oxygen abundance of these systems to be respectively 12+logO/H = 7.26+/-0.03 and 7.17+/-0.09, making them the two most metal-deficient galaxies found thus far in the SDSS and placing them among the five most metal-deficient emission-line galaxies ever discovered. Their oxygen abundances are close to those of the two most metal-deficient emission-line galaxies known, SBS0335-052W with 12+logO/H = 7.12+/-0.03 and I Zw 18 with 12+logO/H = 7.17+/-0.01.
astro-ph/0604235 [abs, ps, pdf, other] :: Title: Stochastic wake field particle acceleration in Gamma-Ray Bursts
Authors: G. Barbiellini (1), F. Longo (1), N. Omodei (2), A. Celotti (3), M. Tavani (4) ((1) University and INFN of Trieste, (2) INFN of Pisa, (3) SISSA, (4) INAF-IASF and University of Tor Vergata Roma)
Comments: 5 pages, 1 figure, submitted to MNRAS

Gamma-Ray Burst (GRB) prompt emission can, for specific conditions, be so powerful and short-pulsed to strongly influence any surrounding plasma. In this paper, we briefly discuss the possibility that a very intense initial burst of radiation produced by GRBs satisfy the intensity and temporal conditions to cause stochastic wake-field particle acceleration in a surrounding plasma of moderate density. Recent laboratory experiments clearly indicate that powerful laser beam pulses of tens of femtosecond duration hitting on target plasmas cause efficient particle acceleration and betatron radiation up to tens of MeV. We consider a simple but realistic GRB model for which particle wake-field acceleration can first be excited by a very strong low-energy precursor, and then be effective in producing the observed prompt X-ray and gamma-ray GRB emission. We also briefly discuss some of the consequences of this novel GRB emission mechanism.
astro-ph/0604236 [abs, ps, pdf, other] :: Title: Spitzer/MIPS 24 micron galaxies: the link to near-IR galaxies and the cosmic IR background
Authors: K.I. Caputi, H. Dole, G. Lagache, J.-L. Puget
Comments: To appear in the proceedings of "The Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution", Pasadena, November 2005. 8 pages, 5 figures

We present the results of our most recent works on Spitzer/MIPS 24 micron galaxies. Through a multiwavelength analysis, we study different properties (redshifts, luminosities, stellar masses) characterising the sources which produce the bulk of the mid-IR background. From a comparative study with the total population of Ks-selected galaxies, we determine that 24 micron sources account for an important fraction of the most massive galaxies present at different redshifts. On the other hand, we determine that 24 micron galaxies also produce most of the energy contained in the far-IR cosmic background at 70 and 160 microns. Furthermore, we are able to set tight constraints on the Cosmic Infrared Background (CIB) spectral energy distribution (SED). Our results help to clarify the links between these presumably different IR galaxy populations.
astro-ph/0604237 [abs, ps, pdf, other] :: Title: Comment on "187Re(gamma,n) cross section close to and above the neutron threshold"
Authors: T. Rauscher (Univ. Basel)
Comments: 2 pages; accepted for publication in Phys. Rev. C

The work of M\"uller et al. [Phys. Rev. C 73, 025804 (2006); astro-ph/0512603] provides interesting experimental data on neutron emission by photodisintegration of 187Re. However, the comparison to theory and the discussed implications for the Re/Os clock require considerable amendment.
astro-ph/0604238 [abs, ps, pdf, other] :: Title: Spitzer/IRAC and ISOCAM/CVF insights on the origin of the Near to Mid-IR Galactic diffuse emission
Authors: N. Flagey (1), F. Boulanger (1), L. Verstraete (1), M.A. Miville Deschenes (1), A. Noriega Crespo (2), W.T. Reach (2) ((1) Institut d'Astrophysique Spatiale, France, (2) Spitzer Science Center, California Institute of Technology, Pasadena, CA)
Comments: 11 pages, 11 figures accepted by A&A

We measure IRAC colors of extended emission in several fields covering a range of Galactic latitudes and longitudes outside of star forming regions. We determine the nature of the Galactic diffuse emission in Spitzer/IRAC images by combining them with spectroscopic data. We show that PAH features make the emission in the IRAC 5.8 and 8.0 $\mu$m channels, whereas the 3.3 $\mu$m feature represents only 20 to 50% of the IRAC 3.6 $\mu$m channel. A NIR continuum is necessary to account for IRAC 4.5 $\mu$m emission and the remaining fraction of the IRAC 3.6 $\mu$m emission. This continuum cannot be accounted by scattered light. It represents 9% of the total power absorbed by PAHs and 120% of the interstellar UV photon flux. The 3.3 $\mu$m feature is observed to vary from field-to-field with respect to the IRAC 8.0 $\mu$m channel. The continuum and 3.3 $\mu$m feature intensities are not correlated. We present model calculations which relate our measurements of the PAHs spectral energy distribution to the particles size and ionization state. Cation and neutral PAHs emission properties are inferred empirically from \object{NGC7023} observations. PAHs caracteristics are best constrained in a line of sight towards the inner Galaxy, dominated by the Cold Neutral Medium phase : we find that the PAH cation fraction is about 50% and that their mean size is about 60 carbon atoms. A significant field-to-field dispersion in the PAH mean size, from 40 to 80 carbon atoms, is necessary to account for the observed variations in the 3.3 $\mu$m feature intensity relative to the IRAC 8.0 $\mu$m flux. However, one cannot be secure about the feature interpretation as long as the continuum origin remains unclear.
astro-ph/0604239 [abs, ps, pdf, other] :: Title: Galactic Warp in the overdensity of the Canis Major Region
Authors: M. Lopez-Corredoira
Comments: 6 pages, 3 figures, accepted to be published in MNRAS

Bellazzini et al. (2006b) claim that Lopez-Corredoira et al.'s (2002) warp model is totally unable to reproduce the Canis Major structure in the red clump stars. However, slight variations in the azimuth of the Lopez-Corredoira et al. (2002) warp model, justified by the uncertainties in the parameter as well as the local irregularities with respect to the average model, derive a result much closer to the observations of the overdensity south/north. The bump of red clump stars with m_K=13-13.5 around l=241 deg., b=-8.5 deg. and the depth of the Canis Major structure are also explainable in terms of the warp with an appropriate extrapolation of constant height between galactocentric radii of 13 and 16 kpc, as observed roughly in the southern warp, instead of a monotonically increasing height like the northern warp; and the observed velocity distribution of stars cannot exclude the warp possibility. A warp model is therefore still a possible explanation of the Canis Major overdensity, and the hypothesis of the existence of a dwarf galaxy is unnecessary, although still a possibility too.
astro-ph/0604240 [abs, ps, pdf, other] :: Title: Extinction techniques and impact on dust property determination
Authors: Dirk Froebrich (1), Carlos del Burgo (1,2) ((1) Dublin Institute for Advanced Studies, (2) Dunsink Observatory)
Comments: 10 pages, 9 figures, 1 table, accepted for publication in MNRAS

The near infrared extinction powerlaw index ($\beta$) and its uncertainty is derived from three different techniques based on star counts, colour excess and a combination of them. We have applied these methods to 2MASS data to determine maps of $\beta$ and near infrared extinction of the small cloud IC 1396 W. The combination of star counts and colour excess results in the most reliable method to determine $\beta$. It is found that the use of the correct $\beta$-map to transform colour excess values into extinction is fundamental for column density profile analysis of clouds. We describe how artificial photometric data, based on the model of stellar population synthesis of the Galaxy (Robin et al. 2003), can be used to estimate uncertainties and derive systematic effects of the extinction methods presented here. We find that all colour excess based extinction determination methods are subject to small but systematic offsets, which do not affect the star counting technique. These offsets occur since stars seen through a cloud do not represent the same population as stars in an extinction free control field.
astro-ph/0604241 [abs, ps, pdf, other] :: Title: Bisectors of the cross-correlation function applied to stellar spectra. Discriminating stellar activity, oscillations and planets
Authors: T. H. Dall (1), N. C. Santos (2 and 3), T. Arentoft (4), T. R. Bedding (5), H. Kjeldsen (4) ((1) ESO, (2) Observatorio Astronomico de Lisboa, (3) Observatoire de Geneve, (4) University of Aarhus, (5) University of Sydney)
Comments: 10 pages, 13 figures. Accepted for publication in A&A

Aims: We investigate whether bisectors derived from cross-correlation functions (CCF) of single-exposure spectra can be used to provide information on stellar atmospheres, and whether they can be used to discriminate between radial velocity changes caused by planets, magnetic activity and oscillations.
Methods: Using a sample of bright stars observed with the HARPS spectrograph, we examine the shapes of the bisectors of individual strong spectral lines in summed spectra, comparing with similar studies in the literature. Moreover, we examine four different quantitative CCF bisector measures for correlations with radial velocity and stellar parameters.
Results: We show that CCF bisector measures can be used for quantitative analysis, employing both the absolute values and the variations. From absolute values, log g and absolute magnitude can be approximated, and from the correlations with radial velocity one can distinguish between magnetic activity, oscillations and orbiting planets as the probable cause of radial velocity variations. We confirm that different isolated spectral lines show different bisector shapes, even between lines of the same element, calling for caution in trying to derive global stellar properties from the bisector of a CCF. For the active star HR 1362 we suggest from the bisector shape an extra photospheric heating caused by the chromosphere of several hundred degrees. We confirm the fill-in of spectral lines of the Sun taken on the daylight sky caused by Rayleigh-Brillouin and aerosol scattering, and we show for the first time that the fill-in has an asymmetric component.
astro-ph/0604242 [abs, ps, pdf, other] :: Title: An Observational Test for the Anthropic Origin of the Cosmological Constant
Authors: Abraham Loeb (Harvard)
Comments: 5 pages, submitted to JCAP

The existence of multiple regions of space beyond the observable Universe (within the so-called "multiverse") where the vacuum energy density takes different values, has been postulated as an explanation for the low non-zero value observed for it in our Universe. It is often argued that our existence pre-selects regions where the cosmological constant is sufficiently small to allow galaxies like the Milky Way to form and intelligent life to emerge. Here we propose a simple empirical test for this anthropic argument within the boundaries of the observable Universe. We make use of the fact that dwarf galaxies formed in our Universe at redshifts as high as z~10 when the mean matter density was larger by a factor of ~10^3 than today. Existing technology enables to check whether planets form in nearby dwarf galaxies and globular clusters by searching for microlensing or transit events of background stars. The oldest of these nearby systems may have formed at z~10. If planets are as common per stellar mass in these descendents as they are in the Milky Way galaxy, then the anthropic argument would be weakened considerably since planets could have formed in our Universe even if the cosmological constant was three orders of magnitude larger than observed. For a flat probability distribution, this would imply that the probability for us to reside in a region where the cosmological constant obtains its observed value is lower than \~10^{-3}. A precise version of the anthropic argument could then be ruled-out at a confidence level of ~99.9%, which constitutes a satisfactory measure of a good experimental test.
astro-ph/0604243 [abs, ps, pdf, other] :: Title: ACIS-I observations of NGC2264. Membership and X-ray properties of PMS stars
Authors: E. Flaccomio, G. Micela, S. Sciortino
Comments: 23 pages, 22 figures (one in color), accepted by A&A. (a .pdf file with full resolution versions of figures 1, 2 and 13 is available at this http URL)

We analyze a deep, 100 ksec long, Chandra ACIS observation of NGC2264. We detect 420 sources, 85% of which are associated with known optical and NIR counterparts. More than 90% of these counterparts are NGC2264 members, thus significantly increasing the known low mass cluster population by about 100 objects. Among the sources without counterpart, ~50% are likely members, several of which we expect to be previously unknown protostellar objects. We confirm several previous findings on the X-ray activity of low mass PMS stars: X-ray luminosity is related to stellar mass, although with a large scatter; L_X/L_bol is close to but almost invariably below the saturation level, 1e-3. A comparison between CTTS and WTTS shows several differences: CTTS are on average less active than WTTS; their emission may also be more time variable and is on average slightly harder. However, we find evidence in some CTTS of extremely cool, ~0.1-0.2 keV, plasma which we speculate is heated by accretion shocks. We conclude that activity in low mass PMS stars, while generally similar to that of saturated MS stars, may be affected by mass accretion in several ways: accretion is likely responsible for very soft X-ray emission directly produced in the accretion shock; it may reduce the average energy output of solar-like coronae, at the same time making them hotter and more dynamic.
astro-ph/0604244 [abs, ps, pdf, other] :: Title: Can the thermal instability drive turbulence?
Authors: Axel Brandenburg (Nordita), Maarit J. Korpi (Helsinki), Antony J. Mee (Newcastle)
Comments: 9 pages, 13 figures

The thermal instability with a piecewise power law cooling function is investigated using one- and three-dimensional simulations with periodic and shearing-periodic boundary conditions. The flow behavior depends on the average density, <rho>. When <rho> is in the range 1-5 x 10^{-24} g cm^{-3} the system is unstable and segregates into cool and warm phases with temperatures of roughly 100 K and 10^4 K, respectively. However, in all cases the resulting average pressure <p> is independent of <rho> and just a little above the minimum value. For a constant heating rate of 0.015 erg g^{-1} s^{-1}, the mean pressure is around 24 x 10^{-14} dyn (corresponding to p/k_B ~ K cm^{-3}). Cool patches tend to conglomerate into bigger ones. In all cases investigated there is no sustained turbulence. Simulations where turbulence is driven by a body force show that when root-mean-square velocities of between 10 and 30 km/s are obtained, the resulting dissipation rates rates are comparable to the thermal energy input rate. The resulting mean pressures are then about 30 x 10^{-14} dyn, corresponding to p/k_B ~ 2170 K cm^{-3}. This is comparable to the value expected for the Galaxy. Differential rotation tends to make the flow two-dimensional, i.e. uniform in the streamwise direction, but this does not lead to instability.
astro-ph/0604245 [abs, ps, pdf, other] :: Title: Direct measurement of the size of 2003 UB313 from the Hubble Space Telescope
Authors: M.E. Brown, E.L. Schaller, H.G. Roe, D.L. Rabinowitz, C.A. Trujillo

We have used the Hubble Space Telescope to directly measure the angular size of the large Kuiper belt object 2003 UB313. By carefully calibrating the point spread function of a nearby field star, we measure the size of 2003 UB313 to be 34.3$\pm$1.4 milliarcseconds, corresponding to a diameter of 2400$\pm$100 km or a size $\sim5$% larger than Pluto. The V band geometric albedo of 2003 UB313 is $86\pm7$%. The extremely high albedo is consistent with the frosty methane spectrum, the lack of red coloring, and the lack of observed photometric variation on the surface of 2003 UB313. Methane photolysis should quickly darken the surface of 2003 UB313, but continuous evaporation and redeposition of surface ices appears capable of maintaining the extreme alebdo of this body.
astro-ph/0604246 [abs, ps, pdf, other] :: Title: Can Ejecta-Dominated Supernova Remnants be Typed from their X-ray Spectra? The Case of G337.2-0.7
Authors: Cara E. Rakowski, Carles Badenes, B. M. Gaensler, Joseph D. Gelfand, John P. Hughes, Patrick O. Slane
Comments: 21 pages emulateapj including 9 figures, 5 tables, accepted for publication in the Astrophysical Journal

In this paper we use recent X-ray and radio observations of the ejecta-rich Galactic supernova remnant (SNR) G337.2-0.7 to determine properties of the supernova (SN) explosion that formed this source. H I absorption measurements from the Australia Telescope Compact Array (ATCA) constrain the distance to G337.2-0.7 to lie between 2.0 +/- 0.5 and 9.3 +/- 0.3 kpc. Combined with a clear radio image of the outer blast-wave, this distance allows us to estimate the dynamical age (between 750 and 3500 years) from the global X-ray spectrum obtained with the XMM-Newton and Chandra observatories. The presence of ejecta is confirmed by the pattern of fitted relative abundances, which show Mg, Ar and Fe to be less enriched (compared to solar) than Si, S or Ca, and the ratio of Ca to Si to be 3.4 +/- 0.8 times the solar value (under the assumption of a single electron temperature and single ionization timescale). With the addition of a solar abundance component for emission from the blast-wave, these abundances (with the exception of Fe) resemble the ejecta of a Type Ia, rather than core-collapse, SN. Comparing directly to models of the ejecta and blast-wave X-ray emission calculated by evolving realistic SN Ia explosions to the remnant stage allows us to deduce that one-dimensional delayed detonation and pulsed delayed detonation models can indeed reproduce the major features of the global spectrum. In particular, stratification of the ejecta, with the Fe shocked most recently, is required to explain the lack of prominent Fe-K emission.
astro-ph/0604247 [abs, ps, pdf, other] :: Title: The B-Supergiant Components of the Double-Lined Binary HD1383
Authors: T. S. Boyajian, D. R. Gies, M. E. Helsel, A. B. Kaye, M. V. McSwain, R. L. Riddle, D. W. Wingert
Comments: Accepted for publication in ApJ: 20 pages, 5 figures

We present new results from a study of high quality, red spectra of the massive binary star system HD 1383 (B0.5 Ib + B0.5 Ib). We determined radial velocities and revised orbital elements (P = 20.28184 +/- 0.0002 d) and made Doppler tomographic reconstructions of the component spectra. A comparison of these with model spectra from non-LTE, line blanketed atmospheres indicates that both stars have almost identical masses (M_2/M_1 = 1.020 +/- 0.014), temperatures (T_eff = 28000 +/- 1000 K), gravities (log g = 3.25 +/- 0.25), and projected rotational velocities (V sin i < 30 km/s). We investigate a number of constraints on the radii and masses of the stars based upon the absence of eclipses, surface gravity, stellar wind terminal velocity, and probable location in the Perseus spiral arm of the Galaxy, and these indicate a range in probable radius and mass of R/R_sun = 14 - 20 and M/M_sun = 16 - 35, respectively. These values are consistent with model evolutionary masses for single stars of this temperature and gravity. Both stars are much smaller than their respective Roche radii, so the system is probably in a pre-contact stage of evolution. A fit of the system's spectral energy distribution yields a reddening of E(B-V)=0.55 +/- 0.05 and a ratio of total-to-selective extinction of R=2.97 +/- 0.15. We find no evidence of H-alpha emission from colliding stellar winds, which is probably the consequence of the low gas densities in the colliding winds zone.
astro-ph/0604248 [abs, ps, pdf, other] :: Title: Scalar Perturbations in Two-Temperature Cosmological Plasmas
Authors: Joachim Moortgat, Mattias Marklund
Comments: 9 pages. Accepted for publication in MNRAS, 5 April 2006 (submitted 20 Januari 2006)

We study the properties of density perturbations of a two-component plasma with a temperature difference on a homogeneous and isotropic background. For this purpose we extend the general relativistic gauge invariant covariant (GIC) perturbation theory to include a multi-fluid with a particular equations of state (ideal gas) and imperfect fluid terms due to the relative energy flux between the two species. We derive closed sets of GIC vector and subsequently scalar evolution equations. We then investigate solutions in different regimes of interest. In particular, we study long wavelength and arbitrary wavelength Langmuir and ion-acoustic perturbations. The harmonic oscillations are superposed on a Jeans type instability. We find a generalised Jeans criterion for collapse in a two-temperature plasma, which states that the species with the largest sound velocity determines the Jeans wavelength. Furthermore, we find that within the limit for gravitational collapse, initial perturbations in either the total density or charge density lead to a growth in the initial temperature difference. These results are relevant for the basic understanding of the evolution of inhomogeneities in cosmological models.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Thu, 13 Apr 06 00:00:08 GMT
0604249 -- 0604278 received

astro-ph/0604249 [abs, ps, pdf, other] :: Title: Numerical simulation of small perturbation on an accretion disk due to the collision of a star with the disk near the black hole
Authors: Orhan Donmez
Comments: 20pages, 8 figures, accepted for publication in Astrophysics and Space Science

In this paper, perturbations of an accretion disk by a star orbiting around a black hole are studied. We report on a numerical experiment, which has been carried out by using a parallel-machine code originally developed by D\"{o}nmez (2004). An initially steady state accretion disk near a non-rotating (Schwarzschild) black hole interacts with a "star", modeled as an initially circular region of increased density. Part of the disk is affected by the interaction. In some cases, a gap develops and shock wave propagates through the disk. We follow the evolution for order of one dynamical period and we show how the non-axisymetric density perturbation further evolves and moves downwards where the material of the disk and the star become eventually accreted onto the central body.
When the star perturbs the steady state accretion disk, the disk around the black hole is destroyed by the effect of perturbation. The perturbed accretion disk creates a shock wave during the evolution and it loses angular momentum when the gas hits on the shock waves. Colliding gas with the shock wave is the one of the basic mechanism of emitting the $X-$rays in the accretion disk. The series of supernovae occurring in the inner disk could entirely destroy the disk in that region which leaves a more massive black hole behind, at the center of galaxies.
astro-ph/0604250 [abs, ps, pdf, other] :: Title: A New Measurement of the Stellar Mass Density at z~5: Implications for the Sources of Cosmic Reionization
Authors: D.P. Stark (Caltech), A.J. Bunker (Exeter), R.S. Ellis (Caltech), L.P. Eyles (Exeter), M. Lacy (SSC)
Comments: Submitted to ApJ, 31 pages

We present a new measurement of the integrated stellar mass per comoving volume at redshift 5 determined via spectral energy fitting drawn from a sample of 214 photometrically-selected galaxies with z'<26.5 in the southern GOODS field. We estimate stellar masses for various sub-samples for which reliable and unconfused Spitzer IRAC detections are available. A spectroscopic sample of 14 of the most luminous sources with <z>=4.92 provides a firm lower limit of 2e6 Msun/Mpc^3. We then consider a larger sample whose photometric redshifts in the publicly-available GOODS-MUSIC catalog lie in the range 4.4<z<5.6. After excising probable stellar contaminants and using the z'-J color to exclude any remaining foreground red galaxies, we conclude that 153 sources are likely to be at z~5. The implied mass density from the unconfused IRAC fraction of this sample, scaled to the total available, is 7e6 Msun/Mpc^3. We discuss the likelihood that we have underestimated the true mass density. Including fainter and quiescent sources the total integrated density could be as high as 2e7 Msun/Mpc^3. Such a high mass density only 1.2 Gyr after the Big Bang has interesting consequences for the implied past average star formation during the period when cosmic reionization is now thought to have taken place. Using the currently available (but highly uncertain) rate of decline in the star formation history over 5<z<10, it is only possible to account for the assembled mass at z~5 by appealing to significant dust extinction at early times or extending the luminosity function to very faint limits. As mass density estimates improve at z~5-6, our method is likely to provide one of the tightest constraints on the question of whether star forming sources were responsible for reionizing the Universe. [abridged]
astro-ph/0604251 [abs, ps, pdf, other] :: Title: Surface Brightness Profiles of Galactic Globular Clusters from Hubble Space Telescope Images
Authors: E. Noyola, K. Gebhardt (University of Texas at Austin)
Comments: 23 pages, 14 figures, AJ accepted

Hubble Space Telescope allows us to study the central surface brightness profiles for globular clusters at unprecedented detail. We have mined the HST archives to obtain 38 WFPC2 images of galactic globular clusters with adequate exposure times and filters, which we use to measure their central structure. We outline a reliable method to obtain surface brightness profiles from integrated light that we test on an extensive set of simulated images. Most clusters have central surface brightness about 0.5 mag brighter than previous measurements made from ground-based data, with the largest differences around 2 magnitudes. Including the uncertainties in the slope estimates, the surface brightness slope distribution is consistent with half of the sample having flat cores and the remaining half showing a gradual decline from 0 to -0.8 (dlog(Sigma)/dlogr). We deproject the surface brightness profiles in a non-parametric way to obtain luminosity density profiles. The distribution of luminosity density logarithmic slopes show similar features with half of the sample between -0.4 and -1.8. These results are in contrast to our theoretical bias that the central regions of globular clusters are either isothermal (i.e. flat central profiles) or very steep (i.e. luminosity density slope ~-1.6) for core-collapse clusters. With only 50% of our sample having central profiles consistent with isothermal cores, King models appear to poorly represent most globular clusters in their cores.
astro-ph/0604252 [abs, ps, pdf, other] :: Title: Spitzer Observations of Red Galaxies at High Redshifts
Authors: Casey Papovich (1), GOODS, MIPS GTO teams ((1) Steward Obs.)
Comments: Contributed talk to appear in proceedings for the Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution, Ed. R. Chary. 6 pages, 3 color figures, uses asp2004.sty (included)

I discuss constraints on star formation and AGN in massive, red galaxies at z~1-3 using Spitzer observations at 3-24 micron. In particular I focus on a sample of distant red galaxies (DRGs) with J - K > 2.3 in the southern Great Observatories Origins Deep Survey (GOODS-S) field. The DRGs have typical stellar masses >10^11 solar masses. Interestingly, the majority (>50%) of these objects have 24 micron flux densities >50 micro-Jy. At these redshifts massive galaxies undergo intense (and possibly frequent) IR-active phases, which is in constrast to lower-redshift massive galaxies. If the 24 micron emission in these z~1-3 galaxies is attributed to star formation, then it implies star formation rates (SFRs) in excess of ~100 solar masses per year. These galaxies have specific SFRs equal to or exceeding the global average value at that epoch. Thus, this is an active period in their assembly. Based on their X-ray luminosities and near-IR colors, as many as 25% of the massive galaxies at z>1.5 host AGN, suggesting that the growth of supermassive black holes coincides with massive-galaxy assembly.
astro-ph/0604253 [abs, ps, pdf, other] :: Title: Bringing VY Canis Majoris Down to Size: An Improved Determination of Its Effective Tempeature
Authors: Philip Massey, Emily M. Levesque, Bertrand Plez
Comments: Accepted by the Astrophysical Journal

The star VY CMa is a late-type M supergiant with many peculiarities, mostly related to the intense circumstellar environment due to the star's high mass-loss rate. Claims have been made that would suggest this star is considerably more luminous (L = 5 x 10^5 Lo) and larger (R=2800 Ro) than other Galactic red supergiants (RSGs). Indeed, such a location in the H-R diagram would be well in the "Hayashi forbidden zone" where stars cannot be in hydrostatic equilibrium. These extraordinary properties, however, rest upon an assumed effective temperature of 2800-3000 K, far cooler than recent work have shown RSGs to be. To obtain a better estimate, we fit newly obtained spectrophotometry in the optical and NIR with the same MARCS models used for our recent determination of the physical properties of other RSGs; we also use $V-K$ and $V-J$ from the literature to derive an effective temperatures. We find that the star likely has a temperature of 3650 K, a luminosity L = 6 x 10^4 Lo, and a radius of 600Ro. These values are consistent with VY CMa being an ordinary evolved 15 Mo RSG, and agree well with the Geneva evolutionary tracks. We find that the circumstellar dust region has a temperature of 760 K, and an effective radius of approximately 130 AU, if spherical geometry is assumed for the latter. What causes this star to have such a high mass-loss, and large variations in brightness (but with little change in color), remains a mystery at present, although we speculate that perhaps this star (and NML Cyg) are simply normal RSGs caught during an unusually unstable time.
astro-ph/0604254 [abs, ps, pdf, other] :: Title: Signals of Inflation in a Friendly String Landscape
Authors: John March-Russell, Francesco Riva
Comments: 20 pages, 11 figures

Following Freivogel {\it et al} we consider inflation in a predictive (or `friendly') region of the landscape of string vacua, as modeled by Arkani-Hamed, Dimopoulos and Kachru. In such a region the dimensionful coefficients of super-renormalizable operators unprotected by symmetries, such as the vacuum energy and scalar mass-squareds are freely scanned over, and the objects of study are anthropically or `environmentally' conditioned probability distributions for observables. In this context we study the statistical predictions of (inverted) hybrid inflation models, where the properties of the inflaton are probabilistically distributed. We derive the resulting distributions of observables, including the deviation from flatness $|1-\Omega|$, the spectral index of scalar cosmological perturbations $n_s$ (and its scale dependence $dn_s/d\log k$), and the ratio of tensor to scalar perturbations $r$. The environmental bound on the curvature implies a solution to the $\eta$-problem of inflation with the predicted distribution of $(1-n_s)$ indicating values close to current observations. We find a relatively low probability ($<3%$) of `just-so' inflation with measurable deviations from flatness. Intermediate scales of inflation are preferred in these models.
astro-ph/0604255 [abs, ps, pdf, other] :: Title: From Radio to X-ray: The Quiescent Atmosphere of the dMe Flare Star EV Lacertae
Authors: R. A. Osten, S. L. Hawley, J. Allred, C. M. Johns-Krull, A. Brown, G. M. Harper
Comments: accepted, Astrophysical Journal

We report on multi-wavelength observations spanning radio to X-ray wavelengths of the M dwarf flare star, EV Lacertae, probing the characteristics of the outer atmospheric plasma from the upper chromosphere to the corona. We detect the star at a wavelength of 2 cm (15 GHz) for the first time. UV and FUV line profiles show evidence of nonthermal broadening, and the velocity width appear to peak at lower temperatures than in the Sun; this trend is confirmed in another active M dwarf flare star. Electron density measurements indicate nearly constant electron pressures between $\log T=$5.2 and 6.4. At higher coronal temperatures, there is a sharp increase of two orders of magnitude in density (n$_{e}\sim10^{13}$ cm$^{-3}$ at $\log T=$6.9). X-ray, EUV, FUV and NUV spectra constrain the DEM from the upper chromosphere through the corona. The coronal pressures are inconsistent with the assumption of hydrostatic equilibrium, either through EM modeling or application of scaling laws, and imply large conductive loss rates and a large energy input at the highest temperatures. The timescales for radiative and conductive losses in EV Lac's upper atmosphere imply that significant continued heating must occur for the corona to maintain its quiescent properties. The high frequency radio detection requires the high temperature X-ray-emitting coronal plasma to be spatially distinct from the radio emission source. Length scales in the low-temperature corona are markedly larger than those in the high-temperature corona, further suggestions of an inhomogeneous mixture of thermal and nonthermal coronal plasma.
astro-ph/0604256 [abs, ps, pdf, other] :: Title: Accurate Astrometry and Photometry of Saturated and Coronagraphic Point Spread Functions
Authors: C. Marois, D. Lafreniere, B. Macintosh, R. Doyon
Comments: 25 pages, 6 figures, accepted for publication in ApJ

Accurate astrometry and photometry of saturated and coronagraphic point spread functions (PSFs) are fundamental to both ground- and space-based high contrast imaging projects. For ground-based adaptive optics imaging, differential atmospheric refraction and flexure introduce a small drift of the PSF with time, and seeing and sky transmission variations modify the PSF flux distribution. For space-based imaging, vibrations, thermal fluctuations and pointing jitters can modify the PSF core position and flux. These effects need to be corrected to properly combine the images and obtain optimal signal-to-noise ratios, accurate relative astrometry and photometry of detected objects as well as precise detection limits. Usually, one can easily correct for these effects by using the PSF core, but this is impossible when high dynamic range observing techniques are used, like coronagrahy with a non-transmissive occulting mask, or if the stellar PSF core is saturated. We present a new technique that can solve these issues by using off-axis satellite PSFs produced by a periodic amplitude or phase mask conjugated to a pupil plane. It will be shown that these satellite PSFs track precisely the PSF position, its Strehl ratio and its intensity and can thus be used to register and to flux normalize the PSF. A laboratory experiment is also presented to validate the theory. This approach can be easily implemented in existing adaptive optics instruments and should be considered for future extreme adaptive optics coronagraph instruments and in high-contrast imaging space observatories.
astro-ph/0604257 [abs, ps, pdf, other] :: Title: Mid-Infrared Source Multiplicity within Hot Molecular Cores traced by Methanol Masers
Authors: S. N. Longmore (1 and 2), M. G. Burton (1), V. Minier (3), A.J.Walsh (1) ((1) University of New South Wales, Sydney, Australia (2) Australia Telescope National Facility, CSIRO, Sydney, Australia (3) Service d'Astrophysique, DAPNIA/DSM/CEA Saclay, France)
Comments: 6 pages, 1 figure

We present high resolution, mid-infrared images toward three hot molecular cores signposted by methanol maser emission; G173.49+2.42 (S231, S233IR), G188.95+0.89 (S252, AFGL-5180) and G192.60-0.05 (S255IR). Each of the cores was targeted with Michelle on Gemini North using 5 filters from 7.9 to 18.5 microns. We find each contains both large regions of extended emission and multiple, luminous point sources which, from their extremely red colours (F[18.5]/F[7.9] >= 3), appear to be embedded young stellar objects. The closest angular separations of the point sources in the three regions are 0.79, 1.00 and 3.33 arcseconds corresponding to linear separations of 1,700, 1,800 and 6,000AU respectively. The methanol maser emission is found closest to the brightest MIR point source (within the assumed 1 arcsecond pointing accuracy). Mass and luminosity estimates for the sources range from 3-22 Msol and 50-40,000 Lsol. Assuming the MIR sources are embedded objects and the observed gas mass provides the bulk of the reservoir from which the stars formed, it is difficult to generate the observed distributions for the most massive cluster members from the gas in the cores using a standard form of the IMF.
astro-ph/0604258 [abs, ps, pdf, other] :: Title: A WENO Algorithm for the Radiative Transfer and Ionized Sphere at Reionization
Authors: Jing-Mei Qiu (1), Chi-Wang Shu (1), Long-Long Feng (2), Li-Zhi Fang (3) ((1) Division of Applied Mathematics, Brown University (2) Purple Mountain Observatory (3) Department of Physics, University of Arizona)
Comments: Elsart Latex file, 20 pages, 8 figures included, accepted for publication in New Astronomy

We show that the algorithm based on the weighted essentially nonoscillatory (WENO) scheme with anti-diffusive flux corrections can be used as a solver of the radiative transfer equations. This algorithm is highly stable and robust for solving problems with both discontinuities and smooth solution structures. We test this code with the ionized sphere around point sources. It shows that the WENO scheme can reveal the discontinuity of the radiative or ionizing fronts as well as the evolution of photon frequency spectrum with high accuracy on coarse meshes and for a very wide parameter space. This method would be useful to study the details of the ionized patch given by individual source in the epoch of reionization. We demonstrate this method by calculating the evolution of the ionized sphere around point sources in physical and frequency spaces. It shows that the profile of the fraction of neutral hydrogen and the ionized radius are sensitively dependent on the intensity of the source.
astro-ph/0604259 [abs, ps, pdf, other] :: Title: A Survey for Spectroscopic Binaries Among Very Low-Mass Stars
Authors: Gibor Basri, Ansgar Reiners
Comments: 36 pages, accepted for publication in AJ, abstract shortened for arXiv.org

We report on the results of a survey for radial velocity variability in a heterogeneous sample of very low-mass stars and brown dwarfs. One distinguishing characteristic of the survey is its timespan, which allows an overlap between spectroscopic binaries and those which can be found by high angular-resolution imaging. We are able to place a new constraint on the total binary fraction in these objects, which suggests that they are more likely the result of extending the same processes at work at higher masses into this mass range, rather than a distinct mode of formation. Our basic result is that there are $6 \pm 2$ out of 53, or $11^{+0.07}_{-0.04}$% spectroscopic binaries in the separation range 0-6 AU, nearly as many as resolved binaries. This leads to an estimate of an upper limit of $26 \pm 10$% for the binary fraction of VLM objects (it is an upper limit because of the possible overlap between the spectroscopic and resolved populations). A reasonable estimate for the very low-mass binary fraction is $20 - 25$%. We consider several possible separation and frequency distributions, including the same one as found for GK stars, a compressed version of that, a version of the compressed distribution truncated at 15 AU, and a theoretical distribution which considers the evaporation of small-N clusters. We conclude that the latter two bracket the observations, which may mean that these systems form with intrinsically smaller separations due to their smaller mass, and then are truncated due to their smaller binding energy. We do not find support for the ``ejection hypothesis'' as their dominant mode of formation, particularly in view of the similarity in the total binary fraction compared with slightly more massive stars, and the difficulty this mechanism has in producing numerous binary systems.
astro-ph/0604260 [abs, ps, pdf, other] :: Title: Circumstellar material in the Vega inner system revealed by CHARA/FLUOR
Authors: O. Absil, E. di Folco, A. Merand, J.-C. Augereau, V. Coude du Foresto, J. P. Aufdenberg, P. Kervella, S. T. Ridgway, D. H. Berger, T. A. ten Brummelaar, J. Sturmann, L. Sturmann, N. H. Turner, H. A. McAlister
Comments: A&A, accepted -- Press release available at this http URL

Only a handful of debris disks have been imaged up to now. Due to the need for high dynamic range and high angular resolution, very little is known about the inner planetary region, where small amounts of warm dust are expected to be found. We investigate the close neighbourhood of Vega with the help of infrared stellar interferometry and estimate the integrated K-band flux originating from the central 8 AU of the debris disk. We performed precise visibility measurements at both short (~30 m) and long (~150 m) baselines with the FLUOR beam-combiner installed at the CHARA Array (Mt Wilson, California) in order to separately resolve the emissions from the extended debris disk (short baselines) and from the stellar photosphere (long baselines). After revising Vega's K-band angular diameter (3.202+/-0.005 mas), we show that a significant deficit in squared visibility (1.88+/-0.34%) is detected at short baselines with respect to the best-fit uniform disk stellar model. This deficit can be either attributed to the presence of a low-mass stellar companion around Vega, or as the signature of the thermal and scattered emissions from the debris disk. We show that the presence of a close companion is highly unlikely, as well as other possible perturbations (stellar morphology, calibration), and deduce that we have most probably detected the presence of dust in the close neighbourhood of Vega. The resulting flux ratio between the stellar photosphere and the debris disk amounts to 1.29+/-0.19% within the FLUOR field-of-view (~7.8 AU). Finally, we complement our K-band study with archival photometric and interferometric data in order to evaluate the main physical properties of the inner dust disk. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations.
astro-ph/0604261 [abs, ps, pdf, other] :: Title: Envelope Expansion with Core Collapse. III. Similarity Isothermal Shocks in a Magnetofluid
Authors: Cong Yu, Yu-Qing Lou, Fu-Yan Bian, Yan Wu
Comments: 21 pages, 33 figures, accepted by MNRAS

We explore MHD solutions for envelope expansions with core collapse (EECC) with isothermal MHD shocks in a quasi-spherical symmetry and outline potential astrophysical applications of such magnetized shock flows. MHD shock solutions are classified into three classes according to the downstream characteristics near the core. Class I solutions are those characterized by free-fall collapses towards the core downstream of an MHD shock, while Class II solutions are those characterized by Larson-Penston (LP) type near the core downstream of an MHD shock. Class III solutions are novel, sharing both features of Class I and II solutions with the presence of a sufficiently strong magnetic field as a prerequisite. Various MHD processes may occur within the regime of these isothermal MHD shock similarity solutions, such as sub-magnetosonic oscillations, free-fall core collapses, radial contractions and expansions. We can also construct families of twin MHD shock solutions as well as an `isothermal MHD shock' separating two magnetofluid regions of two different yet constant temperatures. The versatile behaviours of such MHD shock solutions may be utilized to model a wide range of astrophysical problems, including star formation in magnetized molecular clouds, MHD link between the asymptotic giant branch phase to the proto-planetary nebula phase with a hot central magnetized white dwarf, relativistic MHD pulsar winds in supernova remnants, radio afterglows of soft gamma-ray repeaters and so forth.
astro-ph/0604262 [abs, ps, pdf, other] :: Title: Lyman-alpha emission galaxies at a redshift of z = 5.7 in the FORS Deep Field
Authors: C. Tapken, I. Appenzeller, A. Gabasch, J. Heidt, U. Hopp, R. Bender, D. Mehlert, S. Noll, S. Seitz, W. Seifert
Comments: 9 pages, 17 figures. Accepted by A&A. PDF version with higher resolution figures here: this http URL

We present the results of a search for Lyman-alpha emission galaxies at z~ 5.7 in the FORS Deep Field. The objective of this study is to improve the faint end of the luminosity function of high-redshift Lyman-alpha emitting galaxies and to derive properties of intrinsically faint Lyman-alpha emission galaxies in the young universe. Using FORS2 at the ESO VLT and a set of special interference filters, we identified candidates for high-redshift Lyman-alpha galaxies. We then used FORS2 in spectroscopic mode to verify the identifications and to study their spectral properties. The narrow-band photometry resulted in the detection of 15 likely Lyman-alpha emission galaxies. Spectra with an adequate exposure time could be obtained for eight galaxies. In all these cases the presence of Lyman-alpha emission at z = 5.7 was confirmed spectroscopically. The line fluxes of the 15 candidates range between 3 and 16 * 10^-21 Wm^-2, which corresponds to star-formation rates not corrected for dust between 1 and 5 Msun/yr. The luminosity function derived for our photometrically identified objects extends the published luminosity functions of intrinsically brighter Lyman-alpha galaxies. With this technique the study of high-redshift Lyman-alpha emission galaxies can be extended to low intrinsic luminosities.
astro-ph/0604263 [abs, ps, pdf, other] :: Title: Relaxation of a 1-D gravitational system
Authors: Patrick Valageas
Comments: 15 pages, submitted

We study the relaxation towards thermodynamical equilibrium of a 1-D gravitational system. This OSC model shows a series of critical energies $E_{cn}$ where new equilibria appear and we focus on the homogeneous ($n=0$), one-peak ($n=\pm 1$) and two-peak ($n=2$) states. Using numerical simulations we investigate the relaxation to the stable equilibrium $n=\pm 1$ of this $N-$body system starting from initial conditions defined by equilibria $n=0$ and $n=2$. We find that in a fashion similar to other long-range systems the relaxation involves a fast violent relaxation phase followed by a slow collisional phase as the system goes through a series of quasi-stationary states. Moreover, in cases where this slow second stage leads to a dynamically unstable configuration (two peaks with a high mass ratio) it is followed by a new sequence ``violent relaxation/slow collisional relaxation''. We obtain an analytical estimate of the relaxation time $t_{2\to \pm 1}$ through the mean escape time of a particle from its potential well in a bistable system. We find that the diffusion and dissipation coefficients satisfy Einstein's relation and that the relaxation time scales as $N e^{1/T}$ at low temperature, in agreement with numerical simulations.
astro-ph/0604264 [abs, ps, pdf, other] :: Title: Comment on "Heavy element production in inhomogeneous big bang nucleosynthesis"
Authors: T. Rauscher (Univ. Basel)
Comments: 2 pages, submitted to Phys. Rev. D on Feb 23, 2006

The work of Matsuura et al. [Phys. Rev. D 72, 123505 (2005); astro-ph/0507439] claims that heavy nuclei could have been produced in a combined p- and r-process in very high baryon density regions of an inhomogeneous big bang. However, they do not account for observational constraints and previous studies which show that such high baryon density regions did not significantly contribute to big bang abundances.
astro-ph/0604265 [abs, ps, pdf, other] :: Title: Casimir Effect confronts Cosmological Constant
Authors: Gaurang Mahajan, Sudipta Sarkar, T. Padmanabhan
Comments: revtex4; four pages; 5 figs

It has been speculated that the zero-point energy of the vacuum, regularized due to the existence of a suitable ultraviolet cut-off scale, could be the source of the non-vanishing cosmological constant that is driving the present acceleration of the universe. We show that the presence of such a cut-off can significantly alter the results for the Casimir force between parallel conducting plates and even lead to repulsive Casimir force when the plate separation is smaller than the cut-off scale length. Using the current experimental data we rule out the possibility that the observed cosmological constant arises from the zero-point energy which is made finite by a suitable cut-off. Any such cut-off which is consistent with the observed Casimir effect will lead to an energy density which is about 10^{12} times larger than the observed one, if gravity couples to these modes. The implications are discussed.
astro-ph/0604266 [abs, ps, pdf, other] :: Title: Photometric survey of marginally investigated open clusters: I. Basel 11b, King 14, Czernik 43
Authors: M. Netopil, H. M. Maitzen, E. Paunzen, A. Claret
Comments: A&A accepted, 7 pages, 5 figures

To progress in galactic studies based on open clusters, e.g. cluster formation rate or kinematical properties, one needs to improve the number of open clusters observed. However, only half of the 1700 known galactic open clusters have been properly observed so far, making any statistical investigation insignificant, especially at larger distances from the Sun. We study marginally investigated or neglected open clusters with Bessell CCD BVR photometry, whose data were used to fit isochrones to the individual color-magnitude diagrams. We examined the galactic clusters Basel 11b, King 14 and Czernik 43, the last being observed for the first time to this extent. As well as a careful comparison to available photometry, their parameters such as age, interstellar reddening, distance and apparent diameter were determined. The obtained cluster properties were verified by near infrared 2MASS data. The three investigated intermediate age clusters are all located in the galactic disk with distances between 1.8 and 3.0kpc from the Sun.
astro-ph/0604267 [abs, ps, pdf, other] :: Title: The opaque nascent starburst in NGC 1377: Spitzer SINGS observations
Authors: H. Roussel (1 and 2), G. Helou (1), J.D. Smith (3), B.T. Draine (4), D.J. Hollenbach (5), J. Moustakas (3), H.W. Spoon (6), R.C. Kennicutt (7 and 3), G.H. Rieke (3), F. Walter (2), L. Armus (1), D.A. Dale (8), K. Sheth (1), G.J. Bendo (9), C.W. Engelbracht (3), K.D. Gordon (3), M.J. Meyer (10), M.W. Regan (10), E.J. Murphy (11) ((1) Caltech, (2) MPIA, (3) Steward Observatory, (4) Princeton University, (5) NASA Ames, (6) Cornell University, (7) IoA, Cambridge, (8) University of Wyoming, (9) Imperial College, London, (10) STScI, Baltimore, (11) Yale University)
Comments: accepted for publication in ApJ ; 28 pages of text + 2 tables + 14 figures

We analyze extensive data on NGC1377 from the Spitzer Infrared Nearby Galaxies Survey (SINGS). Within the category of nascent starbursts, that we previously selected by their infrared to radio continuum ratios in large excess of the average and their hot dust, NGC1377 has the largest infrared excess yet measured. Optical imaging reveals a morphological distortion suggestive of a recent accretion event. Infrared spectroscopy reveals a compact and opaque source dominated by a hot, self-absorbed continuum (tau ~ 20 in the 10 micron silicate band). We provide physical evidence against non-stellar activity being the heating source. HII regions are detected through the single [NeII] line, probing <1% of the ionizing radiation. Not only is the optical depth very high, but >85% of ionizing photons are suppressed by dust. The only other detected emission features are molecular hydrogen lines, arguably excited mainly by shocks, besides photodissociation regions, and weak aromatic bands. The new observations support our interpretation in terms of an extremely young starburst (<1 Myr). More generally, galaxies deficient in radio synchrotron are likely observed within a few Myr of the onset of a starburst and after a long quiescence, prior to the replenishment of the ISM with cosmic rays. The similar infrared-radio properties of NGC1377 and some infrared-luminous galaxies suggest that NGC1377 constitutes an archetype to better understand starburst evolution. Although rare locally because observed in a brief evolutionary stage, nascent starbursts may represent a non-negligible fraction of merger-induced starbursts dominating deep infrared counts. Since they differ dramatically from usual starburst templates, they bear important consequences for the interpretation of deep surveys.
astro-ph/0604268 [abs, ps, pdf, other] :: Title: A Chemical Abundance Study of three RHB and two RGB stars in NGC6637 (M69)
Authors: Jae-Woo Lee, Mercedes Lopez-Morales
Comments: to appear in the Proceedings of the 7th Pacific Rim Conference on Stellar Astrophysics, November 1--5, 2005, Sejong University, Seoul, Korea, ASP Conference Series, 2006

We present a detailed chemical abundance study of three red horizontal branch and two red giant branch stars in the metal-rich globular cluster NGC 6637 (M69). The value of [Fe/H] derived from LTE calculations is $-$0.77 $\pm$ 0.02 dex. We also discuss the anticorrelation between oxygen and sodium abundances in the program stars and compare the [Si/Ti] ratio of NGC 6637 with those of other globular clusters.
astro-ph/0604269 [abs, ps, pdf, other] :: Title: Quasar acceleration by a one-side jet and asymmetric radiation
Authors: A.I. Tsygan
Comments: 3 pages

A quasar (as well as an active galactic nucleus) which emits a one-side jet (or which is an anisotropic emitter of particles and quanta) can be accelerated and leave its host galaxy.
astro-ph/0604270 [abs, ps, pdf, other] :: Title: Oxygen abundance variations in the system of the two blue compact dwarf galaxies SBS 0335-052E and SBS 0335-052W
Authors: P. Papaderos (1), Y.I. Izotov (2), N.G. Guseva (2), T.X. Thuan (3), K.J. Fricke (1) ((1) Institute for Astrophysics, University of Goettingen, Germany, (2) Main Astronomical Observatory, Kyiv, Ukraine, (3) University of Virginia, Charlottesville, USA)
Comments: 6 pages, 5 figures, uses psfig.sty, Accepted for publication in Astronomy and Astrophysics

We present 3.6m ESO telescope spectroscopic observations of the system of the two blue compact dwarf galaxies SBS 0335-052W and SBS 0335-052E. The oxygen abundance in SBS 0335-052W is 12 + log O/H = 7.13 +/- 0.08, confirming that this galaxy is the most metal-deficient emission-line galaxy known. We find that the oxygen abundance in SBS 0335-052E varies from region to region in the range from 7.20 to 7.31, suggesting the presence of an abundance gradient over a spatial scale of 1 kpc. Signatures of early carbon-type Wolf-Rayet stars are detected in cluster 3 of SBS 0335-052E, corresponding to the emission of three to eighteen WC4 stars, depending on the adopted luminosity of a single WC4 star in the CIV 4658 emission line.
astro-ph/0604271 [abs, pdf] :: Title: TNG publications 1989-2005
Authors: W. Boschin
Comments: 72 pages

This document lists a set of (refereed and unrefereed) scientific publications based on data taken with the instruments of the Italian Telescopio Nazionale Galileo (TNG, mainly from the year 2000 onward) and the technical papers describing the development of the TNG project from the "phase A" (late '80s) until the end of year 2005. The collection is compiled by searching for publications on the internet. In particular, the search engines of the NASA Astrophysics Data System and Google Scholar are used. This work represents the first attempt to probe the scientific production of the TNG and will be updated regularly from year to year. Comments and suggestions are welcome.
astro-ph/0604272 [abs, ps, pdf, other] :: Title: Confronting Dark Energy Models with Astrophysical Data
Authors: John Ellis, N.E. Mavromatos, V.A. Mitsou, D.V. Nanopoulos
Comments: 25 pages latex, 6 eps figures

We discuss fits of cosmological dark energy models to the available data on high-redshift supernovae and baryon oscillations. We consider a conventional model with Cold Dark Matter and a cosmological constant (LambdaCDM), a model invoking super-horizon perturbations (SHDM) and models based on Liouville strings in which dark energy is provided by a rolling dilaton field (Q-cosmology). The two main high-redshift supernova data sets give compatible constraints on these models. We find that LambdaCDM fits very well the combined supernova data sets. These are also compatible with the data on baryon acoustic oscillations, yielding together a determination of the matter density in the LambdaCDM (assuming a flat Universe) which is comparable with that provided by the three-year WMAP data. The supernova data are also fit quite well by the super-horizon model. A naive version of the Q-cosmology model does not fit the supernova data, but a simple parametrization of the full version of the model that includes off-shell effects fits the data very well. A detailed discussion of the model-dependent off-shell corrections to the Q-cosmology model is given in the Appendix.
astro-ph/0604273 [abs, ps, pdf, other] :: Title: Radio emission of highly inclined cosmic ray air showers measured with LOPES
Authors: J. Petrovic, LOPES collaboration
Journal-ref: 29th ICRC proc., 6, 337 (2005)

LOPES (LOFAR Prototype Station) is an array of dipole antennas used for detection of radio emission from air showers. It is co-located and triggered by the KASCADE (Karlsruhe Shower Core and Array Detector) experiment, which also provides informations about air shower properties. Even though neither LOPES nor KASCADE are completely optimized for the detection of highly inclined events, a significant number of showers with zenith angle larger than 50$^o$ have been detected in the radio domain, and many with very high field strengths. Investigation of inclined showers can give deeper insight into the nature of primary particles that initiate showers and also into the possibility that some of detected showers are triggered by neutrinos. In this paper, we show the example of such an event and present some of the characteristics of highly inclined showers detected by LOPES.
astro-ph/0604274 [abs, ps, pdf, other] :: Title: Accretion column structure of magnetic cataclysmic variables from X-ray spectroscopy
Authors: R. Hoogerwerf, N.S. Brickhouse, C.W. Mauche
Comments: 12 pages, 3 figures, accepted for publication in the ApJ Letters

Using Chandra HETG data we present light curves for individual spectral lines of Mg XI and Mg XII for EX Hydrae, an intermediate-polar type cataclysmic variable. The Mg XI light curve, folded on the white dwarf spin period, shows two spikes that are not seen in the Mg XII or broad-band light curves. Occultation of the accretion column by the body of the white dwarf would produce such spikes for an angle between the rotation axis and the accretion columns of alpha = 18 degrees and a height of the Mg XI emission above the white dwarf surface of < 0.0004 white dwarf radii or < 4 km. The absence of spikes in the Mg XII and broad-band light curves could then be explained if the bulk of its emission forms at much larger height, > 0.004 white dwarf radii or > 40 km, above the white dwarf surface, although this is not consistent with the predictions of the standard Aizu model of the accretion column.
astro-ph/0604275 [abs, ps, pdf, other] :: Title: AD Mensae: a dwarf nova in the period gap
Authors: L. Schmidtobreick, C. Tappert
Comments: 5 pages, 6 figures, accepted by A&A

AD Men was classified as a probable long-period dwarf nova based on its long-term variability. Recent spectroscopic data instead suggested a short-period system. With the here presented observations we aim at clarifying its nature. Time--resolved photometry and spectroscopy has been used to get information on the orbital period of this system. The light curve shows the typical flickering and a clear hump--like periodic modulation with an average amplitude of 0.3mag and a period of P=2.20(02)h. The radial velocity measurements of the Halpha emission line confirm this value as the orbital period. AD Men is thus located at the lower end of, but clearly inside, the gap of the period distribution of cataclysmic variables, making it one of only 11 dwarf novae in this important period range.
astro-ph/0604276 [abs, ps, pdf, other] :: Title: Mapping Global Star Formation in the Interacting Galaxy Pair ARP 32
Authors: I. Damjanov, D. Fadda, F. Marleau, P. Appleton, P. Choi, M. Lacy, L. Storrie-Lombardi, L. Yan (Spitzer Science Center, CalTech)
Comments: 4 pages, 3 figures, to be published in the Proceedings of the Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution (14-16 November 2005, Pasadena, CA)

A multi-wavelength set of photometric data including UV (GALEX), optical, near-IR, infrared (Spitzer) and radio (VLA 20cm) images and spectroscopic observations are used to map the dust-obscured and unobscured star formation in the galaxy pair ARP 32. The system consists of an actively star-forming galaxy and another one with depressed star formation. The most active galaxy has disrupted morphology and different sites of star formation. Spectroscopic data show hints of nuclear activity in its core, intense star formation in limited regions of the galaxy as well as an underlying population of stars witnessing a past episode of star formation. Current star formation rates are estimated from UV and bolometric IR luminosities.
astro-ph/0604277 [abs, ps, pdf, other] :: Title: A Comprehensive Search for Gamma-Ray Lines in the First Year of Data from the INTEGRAL Spectrometer
Authors: B. J. Teegarden, K. Watanabe
Comments: Accepted for publication in ApJ

We have carried out an extensive search for gamma-ray lines in the first year of public data from the Spectrometer (SPI) on the INTEGRAL mission. INTEGRAL has spent a large fraction of its observing time in the Galactic Plane with particular concentration in the Galactic Center (GC) region (~ 3 Msec in the first year). Hence the most sensitive search regions are in the Galactic Plane and Center. The phase space of the search spans the energy range 20-8000 keV and line widths from 0-1000 keV (FWHM). It includes both diffuse and point-like emission. We have searched for variable emission on time scales down to ~ 1000 sec. Diffuse emission has been searched for on a range of different spatial scales from ~ 20 deg (the approximate field-of-view of the spectrometer) up to the entire Galactic Plane. Our search procedures were verified by the recovery of the known gamma-ray lines at 511 keV and 1809 keV at the appropriate intensities and significances. We find no evidence for any previously unknown gamma-ray lines. The upper limits range from a few x 10^-5 cm^-2 s^-1 to a few x 10^-2 cm^-2 s^-1 depending on line width, energy and exposure; regions of strong instrumental background lines were excluded from the search. Comparison is made between our results and various prior predictions of astrophysical lines.
astro-ph/0604278 [abs, pdf] :: Title: Gravitational Microlensing
Authors: Joachim Wambsganss
Comments: 93 pages, 51 figures; to appear (April 2006) in: Kochanek, C.S., Schneider, P., Wambsganss, J.: "Gravitational Lensing: Strong, Weak & Micro", Proceedings of the 33rd Saas-Fee Advanced Course; G. Meylan, P. Jetzer, P. North, eds. (Springer-Verlag, Heidelberg); pp. 457

This review forms the microlensing part of the 33rd Saas-Fee Advanced Course "Gravitational Lensing: Strong, Weak & Micro'', which was held in April 2003 in Les Diablerets. It contains an introduction to the lensing effects of single and binary stars and it summarizes the state-of-the-art of microlensing observations and prospects at the time of the meeting. Stellar microlensing as well as quasar microlensing are covered.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Fri, 14 Apr 06 00:00:16 GMT
0604279 -- 0604317 received

astro-ph/0604279 [abs, ps, pdf, other] :: Title: Unveiling Hidden Patterns in CMB Anisotropy Maps
Authors: Tuhin Ghosh, Amir Hajian, Tarun Souradeep
Comments: 55 pages, 9 figures

Bianchi VII_h models have been recently proposed to explain potential anomalies in the CMB anisotropy as observed by WMAP. We investigate the statistical isotropy of embedded Bianchi VII_h templates in the CMB anisotropy maps to determine whether the existence of a hidden Bianchi template in the WMAP data is consistent with the previous null detection of the bipolar power spectrum in the WMAP first year maps. We compute the bipolar power spectrum for low density Bianchi VII_h models embedded in the background CMB anisotropy maps with the power spectrum that best fits the first year WMAP data. By examining statistical isotropy of these maps, we put a limit of (sigma/H)_0>2.55e-10 (99.9% CL) on the shear parameter in Bianchi VII_h models which is (marginally) consistent with Jaffe et al. (2005) but not with the enhanced Bianchi templates of Cayon et al. (2006). In this paper we also present a detailed review of Bianchi models and their properties.
astro-ph/0604280 [abs, ps, pdf, other] :: Title: Biased Cosmology: Pivots, Parameters, and Figures of Merit
Authors: Eric V. Linder
Comments: 9 pages, 6 figures

In the quest for precision cosmology, one must ensure that the cosmology is accurate as well. We discuss figures of merit for determining from observations whether the dark energy is a cosmological constant or dynamical, with special attention to the best determined equation of state value, at the ``pivot'' or decorrelation redshift. We show this is not necessarily the best lever on testing consistency with the cosmological constant, and moreover is subject to bias. The standard parametrization of w(a)=w_0+w_a(1-a) by contrast is quite robust, as tested by extensions to higher order parametrizations and modified gravity. Combination of complementary probes gives strong immunization against inaccurate, but precise, cosmology.
astro-ph/0604281 [abs, ps, pdf, other] :: Title: Supermassive Black Hole Merger Rates: Uncertainties from Halo Merger Theory
Authors: Adrienne L. Erickcek (1), Marc Kamionkowski (1), Andrew J. Benson (2) ((1) California Institute of Technology, (2) University of Oxford)
Comments: 13 pages, 14 figures, submitted to MNRAS

The merger of two supermassive black holes is expected to produce a gravitational-wave signal detectable by the satellite LISA. The rate of supermassive-black-hole mergers is intimately connected to the halo merger rate, and the extended Press-Schechter formalism is often employed when calculating the rate at which these events will be observed by LISA. This merger theory is flawed and provides two rates for the merging of the same pair of haloes. We show that the two predictions for the LISA supermassive-black-hole-merger event rate from extended Press-Schechter merger theory are nearly equal because mergers between haloes of similar masses dominate the event rate. An alternative merger rate may be obtained by inverting the Smoluchowski coagulation equation to find the merger rate that preserves the Press-Schechter halo abundance, but these rates are only available for power-law power spectra. We compare the LISA event rates derived from the extended Press-Schechter merger formalism to those derived from the merger rates obtained from the coagulation equation and find that the extended Press-Schechter LISA event rates are thirty percent higher for a power spectrum spectral index that approximates the full Lambda-CDM result of the extended Press-Schechter theory.
astro-ph/0604282 [abs, ps, pdf, other] :: Title: The cosmological information content of the halo-model dark-matter power spectrum
Authors: Mark C. Neyrinck, István Szapudi (IfA, Hawaii), Christopher D. Rimes (JILA, Colorado)
Comments: 5 pages, 4 figures, submitted to MNRAS letters

Using the halo model, we investigate the cosmological Fisher information in the non-linear dark-matter power spectrum about the initial amplitude of linear power (i.e. sigma_8). We find that there is little information on `translinear' scales (where the one- and two-halo terms are both significant) beyond what is on linear scales, but that additional information is present on small scales, where the one-halo term dominates. This behavior agrees with the surprising results that Rimes & Hamilton (2005, 2006) found using N-body simulations. We argue that the translinear plateau in cumulative information arises largely from fluctuations in the numbers of large haloes in a finite volume. This implies that more information could be extracted on non-linear scales if the masses of the largest haloes in a survey are known.
astro-ph/0604283 [abs, ps, pdf, other] :: Title: Discovery of magnetic fields in the beta Cephei star xi^1 CMa and in several Slowly Pulsating B stars
Authors: S. Hubrig, M. Briquet, M. Schoeller, P. De Cat, G. Mathys, C. Aerts
Comments: 5 pages, 2 figures, 2 tables, accepted as a letter to MNRAS

We present the results of a magnetic survey of a sample of eight beta Cephei stars and 26 Slowly Pulsating B stars with FORS1 at the VLT. A weak mean longitudinal magnetic field of the order of a few hundred Gauss is detected in the beta Cephei star xi^1 CMa and in 13 SPB stars. The star xi^1 CMa becomes the third magnetic star among the beta Cephei stars. Before our study, the star zeta Cas was the only known magnetic SPB star. All magnetic SPB stars for which we gathered several magnetic field measurements show a field that varies in time. We do not find a relation between the evolution of the magnetic field with stellar age in our small sample. Our observations imply that beta Cephei stars and SPBs can no longer be considered as classes of non-magnetic pulsators, but the effect of the fields on the oscillation properties remains to be studied.
astro-ph/0604284 [abs, ps, pdf, other] :: Title: Millimagnitude Optical Photometry for the Transiting Planetary Candidate OGLE-TR-109
Authors: Jose Miguel Fernandez, Dante Minniti, Grzegorz Pietrzynski, Wolfgang Gieren, Maria Teresa Ruiz, Manuela Zoccali, Andrzej Udalski, Thomas Szeifert

We present precise V-band photometry for the low-amplitude transit candidate star OGLE-TR-109. This is an extreme case among the transiting candidates found by the OGLE group because of the early spectral type of the star (F0V), of the low transit amplitude (A_I=0.008 mag), and of the very short period (P=0.58909 days) of the orbiting companion. Using difference image photometry, we are able to achieve millimagnitude errors in the individual data points. One transit of this star is well defined in our light curve. This confirms the OGLE detection and rules out the possibility of a false positive. The measurement of this transit allows to refine the transit amplitude (A_V=0.006 +/- 0.001 mag), and the ephemerides for this interesting system, as well as the radius of the possible orbiting companion (R_P=0.90 +/- 0.09 ~R_J), and the inclination of the orbit (i=77 +/- 5 deg). Two other transits observed at lower S/N confirm the period of this system measured by OGLE. There is no evidence for a blend of the F-type main sequence star with a redder eclipsing binary, or for secondary transits in the present observations. The absence of ellipsoidal modulation in the light curve of the primary rules out a low mass star companion or brown dwarf with M>14 +/- 8 M_J. The remaining possibilities for OGLE-TR-109 are a blend between the F-type star and a binary with a bluer primary star, or a new transiting extrasolar planet.
astro-ph/0604285 [abs, ps, pdf, other] :: Title: Toward 1% Photometry: End-to-end Calibration of Astronomical Telescopes and Detectors
Authors: Christopher W. Stubbs, John L. Tonry
Comments: 25 pages, no figures. To be published in ApJ

We review the systematic uncertainties that have plagued attempts to obtain high precision and high accuracy from ground-based photometric measurements using CCDs. We identify two main challenges in breaking through the 1% precision barrier: 1) fully characterizing atmospheric transmission, along the instrument's line of sight, and 2) properly identifying, measuring and removing instrumental artifacts. We discuss approximations and limitations inherent in the present methodology, and we estimate their contributions to systematic photometric uncertainties. We propose an alternative conceptual scheme for the relative calibration of astronomical apparatus: the availability of calibrated detectors whose relative spectral sensitivity is known to better than one part in $10^3$ opens up the possibility of in situ relative throughput measurements, normalized to a precision calibrated detector, using a stable but uncalibrated narrowband light source. An implementation scheme is outlined, which exploits the availability of tunable lasers to map out the relative wavelength response of an imaging system, using a flatfield screen and a calibrated reference photodiode. The merits and limitations of this scheme are discussed. In tandem with careful measurements of atmospheric transmission, this approach could potentially lead to reliable ground-based photometry with fractional uncertainties below the percent level.
astro-ph/0604286 [abs, ps, pdf, other] :: Title: Dynamical Masses in Luminous Infrared Galaxies
Authors: Joannah L. Hinz, George H. Rieke (University of Arizona)
Comments: 14 pages, 2 figures, accepted to ApJ

We have studied the dynamics and masses of a sample of ten nearby luminous and ultraluminous infrared galaxies (LIRGS and ULIRGs), using 2.3 micron CO absorption line spectroscopy and near-infrared H- and Ks-band imaging. By combining velocity dispersions derived from the spectroscopy, disk scale-lengths obtained from the imaging, and a set of likely model density profiles, we calculate dynamical masses for each LIRG. For the majority of the sample, it is difficult to reconcile our mass estimates with the large amounts of gas derived from millimeter observations and from a standard conversion between CO emission and H_2 mass. Our results imply that LIRGs do not have huge amounts of molecular gas (10^10-10^11 Msolar) at their centers, and support previous indications that the standard conversion of CO to H_2 probably overestimates the gas masses and cannot be used in these environments. This in turn suggests much more modest levels of extinction in the near-infrared for LIRGs than previously predicted (A_V~10-20 versus A_V~100-1000). The lower gas mass estimates indicated by our observations imply that the star formation efficiency in these systems is very high and is triggered by cloud-cloud collisions, shocks, and winds rather than by gravitational instabilities in circumnuclear gas disks.
astro-ph/0604287 [abs, ps, pdf, other] :: Title: Breaking the scale invariance of the primordial spectrum or not: the new WMAP data
Authors: Davor Palle
Comments: 7 pages, 2 figures, 16 references

It seems that new WMAP data requires a fit with a primordial spectrum containig small negative tilt index in addition to the featureless Harrison-Zeldovich- Peebles spectrum thus implying a broken scale invariance. We show that the data could be otherwise interpreted by a scale invariant primordial spectrum with the scale non-invariant evolution of density contrast using the Press-Schechter formalism. The estimate of the acceleration parameter, as a source of the inhomogeneity of spacetime, is made by searching for the minima of the deviation measure defined by the Press-Schechter mass functions for this interpretation compared to the assumptions implicit in the WMAP fit.
astro-ph/0604288 [abs, ps, pdf, other] :: Title: The Parkes Pulsar Timing Array
Authors: R N Manchester
Comments: 10 pages, in press ChJAA

Given sufficient sensitivity, pulsar timing observations can make a direct detection of gravitational waves passing over the Earth. Pulsar timing is most sensitive to gravitational waves with frequencies in the nanoHertz region, with the most likely astronomical sources being binary super-massive black holes in galaxy cores. The Parkes Pulsar Timing Array project uses the Parkes 64-m radio telescope to make precision timing observations of a sample of about 20 millisecond pulsars with a principal goal of making a direct detection of gravitational waves. Observations commenced about one year ago and so far sub-microsecond timing residuals have been achieved for more than half of these pulsars. New receiver and software systems are being developed with the aim of reducing these residuals to the level believed necessary for a positive detection of gravitational waves.
astro-ph/0604289 [abs, ps, pdf, other] :: Title: Clusters of Galaxies at 1 < z < 2 : The Spitzer Adaptation of the Red-Sequence Cluster Survey
Authors: Gillian Wilson (1), Adam Muzzin (2), Mark Lacy (1), Howard Yee (2), Jason Surace (1), Carol Lonsdale (3), Henk Hoekstra (4), Subhabrata Majumdar (2), David Gilbank (2), Mike Gladders (5) ((1) Spitzer Science Center, (2) U.Toronto, (3) IPAC, (4) U.Vic (5) Carnegie Obs.)
Comments: 6 pages, 4 figures, uses asp2004 style file. To appear in the proceedings of "The Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution", held in Pasadena, November 2005

As the densest galaxy environments in the universe, clusters are vital to our understanding of the role that environment plays in galaxy formation and evolution. Unfortunately, the evolution of high-redshift cluster galaxies is poorly understood because of the ``cluster desert'' that exists at 1 < z < 2. The SpARCS collaboration is currently carrying out a 1-passband (z') imaging survey which, when combined with the pre-existing 50 square degree 3.6 micron Spitzer SWIRE Legacy Survey data, will efficiently detect hundreds of clusters in the cluster desert using an infrared application of the well-proven cluster red-sequence technique. We have already tested this 1-color (z' - [3.6]) approach using a 6 square degree ``pilot patch'' and shown it to be extremely successful at detecting clusters at 1 < z < 2. The clusters discovered in this project will be the first large sample of ``nascent'' galaxy clusters which connect the star-forming proto-cluster regions at z > 2 to the quiescent population at z < 1. The existing seven-passband Spitzer data (3.6, 4.5, 5.8, 8.0, 24, 70, 160 micron) will allow us to make the first measurements of the evolution of the cluster red-sequence, IR luminosity function, and the mid-IR dust-obscured star-formation rate for 1 < z < 2 clusters.
astro-ph/0604290 [abs, ps, pdf, other] :: Title: The blue stragglers formed via mass transfer in old open clusters
Authors: B. Tian, L. Deng, Z. Han, X.B. Zhang
Comments: 12 pages, 6 figures, A&A accepted

In this paper, we present the simulations for the primordial blue stragglers in the old open cluster M67 based on detailed modelling of the evolutionary processes. The principal aim is to discuss the contribution to the blue straggler population in M67 from mass transfer between the components of close binaries. Firstly, we follow the evolution of a binary of 1.4M$_\odot$+0.9M$_\odot$. The synthetic evolutionary track of the binary system reveals that a primordial blue straggler can stay at the observed blue straggler region in Color-Magnitude diagram with a long lifetime to secure observable probability. Secondly, a grid of models of close binary systems experiencing mass exchanging are computed from 1Gyr to 6Gyr in order to account for primordial blue straggler formation in a time sequence. Based on such a grid, Monte-Carlo simulations are applied for the old open cluster M67. Adopting appropriate orbital parameters, 4 primordial blue stragglers are predicted by our simulations. This is consistent with the observational fact that only a few blue stragglers in M67 are binaries with short orbital periods. An upper boundary of the primordial blue stragglers in the Color-Magnitude diagram is defined and can be used to distinguish blue stragglers that are not formed via mass exchange. Using the grid of binary models, the orbital periods of the primordial BSs can be predicted. Compared with the observations, the predicted blue stragglers via mass exchange from the simulations is insufficient to fit the blue stragglers population in M67. There should be several processes to form the observed blue stragglers in M67.
astro-ph/0604291 [abs, ps, pdf, other] :: Title: Host Galaxies of Hard X-ray Selected Type-2 Active Galactic Nuclei at Intermediate Redshifts
Authors: Gaku Kiuchi, Kouji Ohta, Masayuki Akiyama, Kentaro Aoki, Yoshihiro Ueda
Comments: 21 pages, 8 figures, ApJ accepted

We study properties of the host galaxies of 15 hard X-ray selected type-2 active galactic nuclei (AGNs) at intermediate redshifts (0.05$<z<$0.6) detected in $ASCA$ surveys. The absorption corrected hard X-ray luminosities $L_{\rm 2-10 keV}$ range from 10$^{42}$ erg s$^{-1}$ to $10^{45}$ erg s$^{-1}$. We took the $R$-band image of these AGNs with the University of Hawaii 2.2m telescope. Thanks to the intrinsic obscuration of nuclear light, we can decompose the galaxies with a spheroid component and a disk component. The resulting spheroid luminosities correlate with $L_{\rm 2-10 keV}$; higher (lower) X-ray luminosity AGNs tend to reside in luminous (less luminous) spheroids. It is also found that the hosts of luminous AGNs show a large spheroid-to-disk luminosity ratio ($\sim$1), while those of less luminous AGNs spread between 0 and 1. The correlation between $L_{\rm 2-10keV}$ and spheroid luminosity indicates that the relation between mass of a supermassive black hole (SMBH) and spheroid luminosity (BS-relation) agrees with that in the local universe if the Eddington ratio of 0.24 is adopted, which is a mean value determined from our $ASCA$ type-1 AGN sample at similar redshifts through the broad-line width and continuum luminosity. The present study demonstrates the effectiveness of using type- 2 AGNs at high redshifts to study their host properties.
astro-ph/0604292 [abs, ps, pdf, other] :: Title: Quantum noise and a low cosmic microwave background quadrupole
Authors: Chun-Hsien Wu, Kin-Wang Ng, Wolung Lee, Da-Shin Lee, Yeo-Yie Charng
Comments: 4 pages, 2 figures

We propose a new scenario that cosmological density perturbation may originate from passive fluctuations of the inflaton during inflation. These fluctuations are driven dynamically by a colored quantum noise which is generated from the coupling of the inflaton to the quantum environment. They grow with time after the beginning of the inflation and become nearly scale-invariant at small scales. However, the larger-scale modes cross out the horizon earlier and do not have enough time to grow, thus resulting in a suppression of the density perturbation on large scales. This may explain the observed low quadrupole in the WMAP cosmic microwave background anisotropy data and potentially unveil the initial time of inflation.
astro-ph/0604293 [abs, ps, pdf, other] :: Title: The properties of the "standard" type Ic supernova 1994I from spectral models
Authors: D. N. Sauer (1,9), P. A. Mazzali (2,1,4,7,9), J. Deng (3,4,9), S. Valenti (5,6), K. Nomoto (4,7,9), A. V. Filippenko (8) ((1) INAF, Oss. Astron. d. Trieste, Italy, (2) MPA, Garching, Germany, (3) Nat. Astron. Observatories, Chinese Academy of Sciences, Beijing, China, (4) Department of Astronomy, School of Science, Univ. of Tokyo, Japan, (5) ESO, Garching, Germany, (6) Physics Department, Univ. of Ferrara, Ferrara, Italy, (7) Research Center for the Early Universe, School of Science, Univ. of Tokyo, Tokyo, Japan, (8) Department of Astronomy, Univ. of California, Berkeley, USA, (9) KITP, Univ.of California, Santa Barbara, USA)
Comments: 11 pages, 8 figures. Acccepted for publication in MNRAS

The properties of the type Ic supernova SN 1994I are re-investigated. This object is often referred to as a "standard SN Ic" although it exhibited an extremely fast light curve and unusually blue early-time spectra. In addition, the observations were affected by significant dust extinction. A series of spectral models are computed based on the explosion model CO21 (Iwamoto et al. 1994) using a Monte Carlo transport spectral synthesis code. Overall the density structure and abundances of the explosion model are able to reproduce the photospheric spectra well. Reddening is estimated to be E(B-V)=0.30 mag, a lower value than previously proposed. A model of the nebular spectrum of SN 1994I points toward a slightly larger ejecta mass than that of CO21. The photospheric spectra show a large abundance of iron-group elements at early epochs, indicating that mixing within the ejecta must have been significant. We present an improved light curve model which also requires the presence of 56Ni in the outer layers of the ejecta.
astro-ph/0604294 [abs, ps, pdf, other] :: Title: McScatter: a Simple Three-Body Scattering Package with Stellar Evolution
Authors: Douglas C. Heggie (Edinburgh), Simon Portegies Zwart (Amsterdam), Jarrod Hurley (Monash)
Comments: 16 pages, Accepted for publication in New Astronomy. Source codes available at: this http URL and this http URL

We describe a simple computer package which illustrates a method of combining stellar dynamics with stellar evolution. Though the method is intended for elaborate applications (especially the dynamical evolution of rich star clusters) it is illustrated here in the context of three-body scattering, i.e. interactions between a binary star and a field of single stars. We describe the interface between the dynamics and the two independent packages which describe the internal evolution of single stars and binaries. We also give an example application, and introduce a stand alone utility for the visual presentation of simulation results.
astro-ph/0604295 [abs, ps, pdf, other] :: Title: SPH Simulations with Reconfigurable Hardware Accelerator
Authors: N.Nakasato (RIKEN), T.Hamada (RIKEN), T.Fukushige (University of Tokyo)
Comments: 27 pages, 13 figures, submitted to PASJ

We present a novel approach to accelerate astrophysical hydrodynamical simulations. In astrophysical many-body simulations, GRAPE (GRAvity piPE) system has been widely used by many researchers. However, in the GRAPE systems, its function is completely fixed because specially developed LSI is used as a computing engine. Instead of using such LSI, we are developing a special purpose computing system using Field Programmable Gate Array (FPGA) chips as the computing engine. Together with our developed programming system, we have implemented computing pipelines for the Smoothed Particle Hydrodynamics (SPH) method on our PROGRAPE-3 system. The SPH pipelines running on PROGRAPE-3 system have the peak speed of 85 GFLOPS and in a realistic setup, the SPH calculation using one PROGRAPE-3 board is 5-10 times faster than the calculation on the host computer. Our results clearly shows for the first time that we can accelerate the speed of the SPH simulations of a simple astrophysical phenomena using considerable computing power offered by the hardware.
astro-ph/0604296 [abs, ps, pdf, other] :: Title: Extinction and metal column density of HI regions up to redshift z~2
Authors: G.Vladilo, M.Centurion, S.A.Levshakov, C.Peroux, P. Khare, V.P. Kulkarni, D.G. York
Comments: Accepted for publication on Astronomy & Astrophysics, 18 pages, 5 figures

We used the photometric database of the Sloan Digital Sky Survey (SDSS) to estimate the reddening of 13 SDSS quasars selected on the basis of the presence of zinc absorption lines in an intervening Damped Ly alpha (DLA) system. In 5 of these quasars the reddening is detected at ~2 sigma confidence level in two independent color indices of the SDSS ugriz photometric system. A detailed analysis of the data supports an origin of the reddening in the intervening absorbers. We used these rare measurements of extinction in DLA systems to probe the relation between extinction and metal column density in the interval of absorption redshift 0.7 </~ z </~ 2.0. We find that the mean extinction in the V band per atom of iron in the dust is remarkably similar to that found in interstellar clouds of the Milky Way. This result lends support to previous estimates of the dust obscuration effect in DLA systems based on a Milky Way extinction/metal column density relation. We propose a simple mechanism, based on dust grain destruction/accretion properties, which may explain the approximate constancy of the extinction per atom of iron in the dust.
astro-ph/0604297 [abs, ps, pdf, other] :: Title: The nucleosynthesis of Al26 and Fe60 in solar metallicity stars extending in mass from 11 to 120 Msun: the hydrostatic and explosive contributions
Authors: Marco Limongi (INAF-OAR), Alessandro Chieffi (INAF-IASF)
Comments: 63 pages, 17 figures, 5 tables, ApJ accepted

We present the \nuk{Al}{26} and \nuk{Fe}{60} yields produced by a generation of solar metallicity stars ranging in mass between 11 and 120\msun. We discuss the production sites of these $\gamma$ ray emitters and quantify the relative contributions of the various components. More specifically we provide the separate contribution of the wind, the C convective shell and the explosive Ne/C burning to the total \nuk{Al}{26} yield per each stellar model in our grid. We provide the contributions of the He convective shell, the C convective shell and the explosive Ne/C burning to the \nuk{Fe}{60} yield as well. From these computations we conclude that, at variance with current beliefs, \nuk{Al}{26} is mainly produced by the explosive C/Ne burning over most of the mass interval presently analyzed while \nuk{Fe}{60} is mainly produced by the C convective shell and the He convective shell.
astro-ph/0604298 [abs, ps, pdf, other] :: Title: The Non-Gaussianity of Racetrack Inflation Models
Authors: Cheng-Yi Sun, De-Hai Zhang
Comments: 8 pages, no figures

In this paper, we use the result in [7] to calculate the non-Gaussianity of the racetrack models in [3, 5]. Our results show that the non-Gaussianity in [3] is reasonable, while the non-Gaussianity in [5] is beyond the observational limits.
astro-ph/0604299 [abs, ps, pdf, other] :: Title: Interaction of massive black hole binaries with their stellar environment: I. Ejection of hypervelocity stars
Authors: A. Sesana (1), F. Haardt (1), P. Madau (2) ((1)Universita' dell'Insubria, Como, Italy,(2)University of California, Santa Cruz CA, USA)
Comments: 9 pages, 12 figures, submitted to ApJ

We use full three-body scattering experiments to study the ejection of hypervelocity stars (HVSs) by massive black hole binaries (MBHBs) at the center of galaxies. Ambient stars drawn from a Maxwellian distribution unbound to the binary are expelled by the gravitational slingshot. Accurate measurements of thermally averaged hardening, mass ejection, and eccentricity growth rates (H, J, and K) for MBHBs in a fixed stellar background are obtained by numerical orbit integration from initial conditions determined by Monte Carlo techniques. Three-body interactions create a subpopulation of HVSs on nearly radial, corotating orbits, with a spatial distribution that is initially highly flattened in the inspiral plane of the MBHB, but becomes more isotropic with decreasing binary separation. The degree of anisotropy is smaller for unequal mass binaries and larger for stars with higher kick velocities. Eccentric MBHBs produce a more prominent tail of high-velocity stars and break planar symmetry, ejecting HVSs along a broad jet perpendicular to the semimajor axis. The jet two-sidedness decreases with increasing binary mass ratio, while the jet opening-angle increases with decreasing kick velocity and orbital separation. The detection of a numerous population of HVSs in the halo of the Milky Way by the next generation of large astrometric surveys like GAIA may provide a unique signature of the history, nature, and environment of the MBH at the Galactic center.
astro-ph/0604300 [abs, ps, pdf, other] :: Title: Earth matter effects in supernova neutrinos: Optimal detector locations
Authors: A. Mirizzi (Univ. of Bari & INFN, Bari), G.G. Raffelt, P.D. Serpico (Max Planck Inst., Munich)
Comments: 17 pages, 6 eps figures. Online tool to calculate the Earth shadowing probabilities available at this http URL . High-resolution color version of fig_2a and fig_2b available at this http URL

A model-independent experimental signature for flavor oscillations in the neutrino signal from the next Galactic supernova (SN) would be the observation of Earth matter effects. We calculate the probability for observing a Galactic SN shadowed by the Earth as a function of the detector's geographic latitude. This probability depends only mildly on details of the Galactic SN distribution. A location at the North Pole would be optimal with a shadowing probability of about 60%, but a far-northern location such as Pyhasalmi in Finland, the proposed site for a large-volume scintillator detector, is almost equivalent (58%). We also consider several pairs of detector locations and calculate the probability that only one of them is shadowed, allowing a comparison between a shadowed and a direct signal. For the South Pole combined with Kamioka this probability is almost 75%, for the South Pole combined with Pyhasalmi it is almost 90%. One particular scenario consists of a large-volume scintillator detector located in Pyhasalmi to measure the geo-neutrino flux in a continental location and another such detector in Hawaii to measure it in an oceanic location. The probability that only one of them is shadowed exceeds 50% whereas the probability that at least one is shadowed is about 80%.
astro-ph/0604301 [abs, ps, pdf, other] :: Title: The flow field in the sunspot canopy
Authors: Reza Rezaei, R. Schlichenmaier, C.A.R. Beck, L.R. Bellot Rubio
Comments: 10 pages, accepted to A&A

We investigate the flow field in the sunspot canopy using simultaneous Stokes vector spectropolarimetry of three sunspots ($\theta$ = 27, 50, 75 deg) and their surroundings in visible (630.15 and 630.25 nm) and near infrared (1564.8 and 1565.2 nm) neutral iron lines.} {To calibrate the Doppler shifts, we compare an absolute velocity calibration using the telluric $O_2$-line at 630.20 nm and a relative velocity calibration using the Doppler shift of Stokes V profiles in the umbra under the assumption that the umbra is at rest. Both methods yield the same result within the calibration uncertainties (~150 m/s). We study the radial dependence of Stokes V profiles in the directions of disk center and limb side. Maps of Stokes V profile shifts, polarity, amplitude asymmetry, field strength and magnetic field azimuth provide strong evidence for the presence of a magnetic canopy and for the existence of a radial outflow in the canopy. Our findings indicate that the Evershed flow does not cease abruptly at the white-light spot boundary, but that at least a part of the penumbral Evershed flow continues into the magnetic canopy.
astro-ph/0604302 [abs, ps, pdf, other] :: Title: Microlensing in phase space I: Continuous propagation of variability moments
Authors: Artem V. Tuntsov, Geraint F. Lewis (Sydney Uni)
Comments: Accepted for publication in MNRAS. 15 pages, 4 figures. The second part of this little series is available at this http URL

A method to calculate the statistical properties of microlensing light curves is developed. The approach follows works by Deguchi & Watson, Seitz & Schneider and Neindorf, attempting to clarify the ideas involved and techniques used in the calculations. The method is then modified to include scattering by multiple lensing planes along the line of sight and transition to a continuous limit of this treatment for average quantities is performed leading to a Fokker-Planck type equation. The equation is solved for a particular model of the random star field and microlensing effect on the flux temporal variability is extracted. Applications in astrophysically relevant situations are discussed.
astro-ph/0604303 [abs, ps, pdf, other] :: Title: Investigating halo substructures with annual modulation signature
Authors: R. Bernabei (1), P. Belli (1), F. Montecchia (1), F. Nozzoli (1), F. Cappella (2), A. Incicchitti (2), D. Prosperi (2), R. Cerulli (3), C.J. Dai (4), H.L. He (4), H.H. Kuang (4), J.M. Ma (4), X.D. Sheng (4), Z.P. Ye (4), M. Martinez (5), G. Giuffrida (6) ((1) Univ. and INFN Roma Tor Vergata, (2) Univ. and INFN Roma, (3) INFN LNGS, (4) IHEP Beijing, (5) Univ. Zaragoza, (6) Univ. Roma Tor Vergata and INAF)
Comments: 17 pages, 10 figures, to appear in Eur. Phys. J. C

Galaxy hierarchical formation theories, numerical simulations, the discovery of the Sagittarius Dwarf Elliptical Galaxy (SagDEG) in 1994 and more recent investigations suggest that the dark halo of the Milky Way can have a rich phenomenology containing non thermalized substructures. In the present preliminary study, we investigate the case of the SagDEG (the best known satellite galaxy in the Milky Way crossing the solar neighbourhood) analyzing the consequences of its dark matter stream contribution to the galactic halo on the basis of the DAMA/NaI annual modulation data. The present analysis is restricted to some WIMP candidates and to some of the astrophysical, nuclear and particle Physics scenarios. Other candidates such as e.g. the light bosonic ones, we discussed elsewhere, and other non thermalized substructures are not yet addressed here.
astro-ph/0604304 [abs, ps, pdf, other] :: Title: Black Holes: from Speculations to Observations
Authors: Thomas W. Baumgarte
Comments: 15 pages, 6 Figures; to appear in the Proceedings of the Albert Einstein Century International Conference, Paris, France, 2005

This paper provides a brief review of the history of our understanding and knowledge of black holes. Starting with early speculations on ``dark stars'' I discuss the Schwarzschild "black hole" solution to Einstein's field equations and the development of its interpretation from "physically meaningless" to describing the perhaps most exotic and yet "most perfect" macroscopic object in the universe. I describe different astrophysical black hole populations and discuss some of their observational evidence. Finally I close by speculating about future observations of black holes with the new generation of gravitational wave detectors.
astro-ph/0604305 [abs, ps, pdf, other] :: Title: A high-significance detection of non-Gaussianity in the WMAP 3-year data using directional spherical wavelets
Authors: J. D. McEwen, M. P. Hobson, A. N. Lasenby, D. J. Mortlock
Comments: 5 pages, 5 figures, submitted to MNRAS

We repeat the directional spherical real Morlet wavelet analysis used to detect non-Gaussianity in the WMAP 1-year data (McEwen et al. 2005a), on the WMAP 3-year data. The non-Gaussian signal previously detected is indeed present in the 3-year data, although the significance of the detection is reduced. Using our most conservative method for constructing significance measures, we find the significance of the detection of non-Gaussianity drops from 98.3+/-0.4% to 94.9+/-0.7%; the significance drops from 99.3+/-0.3% to 97.2+/-0.5% using a method based on the $\chi^2$ statistic. The wavelet analysis allows us to localise most likely sources of non-Gaussianity on the sky. We detect very similar localised regions in the WMAP 1-year and 3-year data, although the regions extracted appear more pronounced in the 3-year data. When all localised regions are excluded from the analysis the 3-year data is consistent with Gaussianity.
astro-ph/0604306 [abs, ps, pdf, other] :: Title: Optical polarimetry and infrared photometry of two AM Her binaries: 1RXS J161008.0+035222 and 1RXS J231603.9-052713
Authors: C. V. Rodrigues (1), F. J. Jablonski (1), F. D'Amico (1), D. Cieslinski (1), J. E. Steiner (2), M. P. Diaz (2), G. R. Hickel (3) ((1) INPE/Brazil, (2) IAG/USP, (3) IP&D/UNIVAP)
Comments: MNRAS accepted

We present the first optical circular and linear polarization measurements of two polar candidates from ROSAT: 1RXS J161008.0+035222 and 1RXS J231603.9-052713. We also present H band near-infrared photometry of the last object. The presence of strong circular polarization confirms them as AM Her systems. 1RXS J231603.9-052713 was observed in two different brightness states. The orbital phase dependence of the flux and polarization of 1RXS J161008.0+035222 is reasonably fitted with a simple model in which the binary is observed at a small inclination and the magnetic field axis is almost parallel to the white-dwarf rotation axis resulting in the accretion column axis being seen from top during the whole orbital revolution. The magnetic field is probably in the 10 to 20 MG range. The circular polarization of 1RXS J231603.9-052713 is complex and highly variable. The light-curves of that object have been fitted using a model which includes the white-dwarf, a heated secondary and a point-like accretion region. The secondary emission contributes significantly even in optical wavelengths. This model also reproduces the main features of the optical polarization of 1RXS J231603.9-052713. We estimate the main parameters of the binary, of the accretion region and the distance to the system. However, a more precise interpretation of this system should take in account an extended and inhomogeneous accreting region as well as non-radial accretion.
astro-ph/0604307 [abs, pdf] :: Title: Thermonuclear Ignition of Dark Galaxies
Authors: J. Marvin Herndon

Dark matter is thought to be at least an order of magnitude more abundant than luminous matter in the Universe, but there has yet to be an unambiguous identification of a wholly dark, galactic-scale structure. There is, however, increasing evidence that VIRGOHI 21 may be a dark galaxy. If VIRGOHI 21 turns out to be composed of dark stars, having approximately the same mass of stars found in luminous galaxies, it will pose an enigma within the framework of current astrophysical models, but will provide strong support for my concept, published in 1994 in the Proceedings of the Royal Society of London, of the thermonuclear ignition of stars by nuclear fission, and the corollary, non-ignition of stars. The possibility of galactic thermonuclear ignition is discussed from that framework and leads to my suggestion that the distribution of luminous stars in a galaxy may simply be a reflection of the galactic distribution of the heavy elements.
astro-ph/0604308 [abs, ps, pdf, other] :: Title: AGN Outflows and the Matter Power Spectrum
Authors: Robyn Levine, Nickolay Y. Gnedin
Comments: submitted to ApJL

We have investigated the effects of AGN outflows on the amplitude of the matter power spectrum in a simple model of spherically symmetric outflows around realistically clustered AGN population. We find that two competing effects influence the matter power spectrum in two opposite directions. First, AGN outflows move baryons from high to low density regions, decreasing the amplitude of the matter power spectrum by up to 20%. Second, high clustering of the AGN transfers the power from small to larger scales. The exact balance between these two effects depends on the details of outflows on small scales, and quantitative estimates will require much more sophisticated modeling than presented here.
astro-ph/0604309 [abs, ps, pdf, other] :: Title: Dynamics of the NGC 4636 Globular Cluster System - An extremely dark matter dominated galaxy?
Authors: Y. Schuberth (1,2), T. Richtler (2), B. Dirsch (2), M. Hilker (1), S. S. Larsen (3), M. Kissler-Patig (3), U. Mebold (1) ((1) Universität Bonn, (2) Universidad de Concepcíon, Chile, (3) ESO, Garching)
Comments: 19 pages, 18 figures. Accepted for publication in A&A. Appendix A (velocity tables) will be published in the online version of the journal

We present the first dynamical study of the globular cluster system of NGC 4636. This giant elliptical galaxy is claimed to be extremely dark matter dominated, according to X-ray observations. Using the VLT with FORS2/MXU, we obtained velocities for 174 globular clusters. The clusters have projected galactocentric distances in the range 4 to 70 kpc, the overwhelming majority lie within 30 kpc. We find some indication for a rotation of the red (metal-rich) clusters about the minor axis. Out to a radius of 30 kpc, we find a roughly constant projected velocity dispersion for the blue clusters of ~200 km/s. The red clusters exhibit a distinctly different behavior: at a radius of about 13 kpc, the velocity dispersion drops by ~50 km/s to about 170 km/s which then remains constant out to a radius of 30 kpc.
Using only the blue clusters as dynamical tracers, we perform Jeans-analyses for different assumptions of the orbital anisotropy. Depending on the anisotropy and the adopted M/L-values, we find that the dark matter fraction within one effective radius can vary between 20% and 50% with most a probable range between 20% and 30%. A main source of uncertainty is the ambiguity of the velocity dispersion in the outermost bin.
Although the dark halo mass still cannot be strongly constrained, NGC 4636 does not seem to be extremely dark matter dominated. The derived circular velocities are also consistent with Modified Newtonian Dynamics.
astro-ph/0604310 [abs, ps, pdf, other] :: Title: The Lyman-alpha forest and WMAP year three
Authors: Matteo Viel, Martin G. Haehnelt, Antony Lewis
Comments: 5 pages, 4 figs, 2 tables

A combined analysis of Cosmic Microwave Background (CMB) and Lyman-a forest data allows to constrain the matter power spectrum from small scales of about 1 Mpc/h all the way to the horizon scale. The long lever arm and complementarity provided by such an analysis has previously led to a significant tightening of the constraints on the shape and the amplitude of the power spectrum of primordial density fluctuations. We present here a combined analysis of the WMAP three year results with Lyman-a forest data. The amplitude of the matter power spectrum sigma_8 and the spectral index ns inferred from the joint analysis with high resolution Lyman-a forest data and low resolution Lyman-a forest data as analyzed by Viel & Haehnelt (2006) are consistent with the new WMAP results to within 1 sigma. The joint analysis with the low resolution data as analysed by McDonald et al. (2005) suggest a value of sigma_8 which is ~ 2 sigma higher than that inferred from the WMAP three year data alone. The joint analysis of the three year WMAP and the Lyman-a forest data also does not favour a running of the spectral index. The best fit values for a combined analysis of the three year WMAP data, other CMB data, 2dF and the \lya forest data are (sigma_8, ns) = (0.78\pm 0.03,0.96 \pm 0.01).
astro-ph/0604311 [abs, ps, pdf, other] :: Title: On the status of superheavy dark matter
Authors: R. Aloisio, V. Berezinsky, M. Kachelriess
Comments: 7 pages, 4 eps figures

Superheavy particles are a natural candidate for the dark matter in the universe and our galaxy, because they are produced generically during inflation in cosmologically interesting amounts. The most attractive model for the origin of superheavy dark matter (SHDM) is gravitational production at the end of inflation. The observed cosmological density of dark matter determines the mass of the SHDM particle as $m_X=$(a few)$\:\times 10^{13}$ GeV, promoting it to a natural candidate for the source of the observed ultra-high energy cosmic rays (UHECR). After a review of the theoretical aspects of SHDM, we up-date its predictions for UHECR observations: no GZK cutoff, flat energy spectrum with $dN/dE\approx 1/E^{1.9}$, photon dominance and galactic anisotropy. We analyze the existing data and conclude that SDHM as explanation for the observed UHECRs is at present disfavored but not yet excluded. We calculate the anisotropy relevant for future Auger observations that should be the conclusive test for this model. Finally, we emphasize that negative results of searches for SHDM in UHECR do not disfavor SHDM as a dark matter candidate. Therefore, UHECRs produced by SHDM decays and with the signatures as described should be searched for in the future as subdominant effect.
astro-ph/0604312 [abs, ps, pdf, other] :: Title: Acoustic oscillations in rapidly rotating polytropic stars I. Effects of the centrifugal distortion
Authors: F. Lignieres, M. Rieutord, D. Reese
Comments: accepted for publication in A&A

A new non-perturbative method to compute accurate oscillation modes in rapidly rotating stars is presented. In this paper, the effect of the centrifugal force is fully taken into account while the Coriolis force is neglected. This assumption is valid when the time scale of the oscillation is much shorter than the inverse of the rotation rate and is expected to be suitable for high radial order p-modes of $\delta$ Scuti stars. Axisymmetric p-modes have been computed in uniformly rotating polytropic models of stars. In the frequency and rotation range considered, we found that as rotation increases (i) the asymptotic structure of the non-rotating frequency spectrum is first destroyed then replaced by a new form of organization (ii) the mode amplitude tends to concentrate near the equator (iii) differences with perturbative methods become significant as soon as the rotation rate exceeds about fifteen percent of the Keplerian limit. The implications for the seismology of rapidly rotating stars are then discussed.
astro-ph/0604313 [abs, ps, pdf, other] :: Title: On the AU Mic debris disk: density profiles, grain properties and dust dynamics
Authors: J. C. Augereau (1 and 2), H. Beust (1) ((1) Grenoble Observatory, (2) Leiden Observatory)
Comments: 17 pages, 11 figures. To appear in A&A

We present the first comprehensive analysis of the AU Mic debris disk properties since the system was discovered by Kalas et al. (2004), and we explore whether the dynamical model, successful to reproduce the Beta Pic brightness profile could apply to AU Mic. We calculate the surface density profile of the AU Mic disk by performing the inversion of the near-IR and visible scattered light brightness profiles measured by Liu (2004a) and Krist et al. (2005), respectively. We discuss the grain properties by analysing the blue color of the disk in the visible (Krist et al. 2005) and by fitting the disk spectral energy distribution. We show that irrespective of the mean scattering asymmetry factor of the grains, most of the emission arises from an asymmetric, collisionally-dominated region that peaks close to the surface brightness break around 35 AU. The elementary scatterers at visible wavelengths are found to be sub-micronic, but the inferred size distribution underestimates the amount of large grains, resulting in too low sub-millimeter emissions compared to the observations. From our inversion procedure, we find that the V- to H-band scattering cross sections ratio increases outside 40 AU, in line with the observed color gradient of the disk. We show that a standard, solar-like stellar wind generates a pressure force onto the dust particles that behaves much like a radiation pressure force. With an assumed Mdot ~ 300 Mdot_sun, the wind pressure overcomes the radiation pressure and this effect is enhanced by the stellar flares. This explains the similarity between the Beta Pic and AU Mic brightness profiles. In both cases, the color gradient beyond 120 AU for Beta Pic and 35 AU for AU Mic, is believed to be a direct consequence of the dust dynamics.
astro-ph/0604314 [abs, ps, pdf, other] :: Title: The White Dwarf in AE Aqr Brakes Harder
Authors: Christopher W. Mauche (Lawrence Livermore Nat'l Lab.)
Comments: 5 pages including 2 tables and 3 encapsulated postscript figures; LaTeX format, uses mn2e.cls; accepted on 2006 April 13 for publication in Monthly Notices of the Royal Astronomical Society

Taking advantage of the very precise de Jager et al. optical white dwarf orbit and spin ephemerides; ASCA, XMMN, and Chandra X-ray observations spread over 10 yrs; and a cumulative 27 yr baseline, we have found that in recent years the white dwarf in AE Aqr is spinning down at a rate that is slightly faster than predicted by the de Jager et al. spin ephemeris. At the present time, the observed period evolution is consistent with either a cubic term in the spin ephemeris with Pdouble_dot = 3.46(56)E-19 per d, which is inconsistent in sign and magnitude with magnetic-dipole radiation losses, or an additional quadratic term with Pdot = 2.0(1.0)E-15 d/d, which is consistent with a modest increase in the accretion torques spinning down the white dwarf. Regular monitoring, in the optical, ultraviolet, and/or X-rays, is required to track the evolution of the spin period of the white dwarf in AE Aqr.
astro-ph/0604315 [abs, ps, pdf, other] :: Title: Low Mass Stars and Brown Dwarfs in NGC 2024: Constraints on the Substellar Mass Function
Authors: J. L. Levine, A. Steinhauer, R. J. Elston, E. A. Lada
Comments: 22 pages, 9 figures, accepted by ApJ

We present results from a near-infrared spectroscopic study of candidate brown dwarfs and low mass stars in the young cluster NGC 2024. Using FLAMINGOS on the KPNO 2.1m and 4m telescopes, we have obtained spectra of ~70 new members of the cluster and classified them via the prominent J and H band water absorption features. Derived spectral types range from ~M1 to later than M8 with typical classification errors of 0.5-1 subclasses. By combining these spectral types with JHK photometry, we place these objects on the H-R diagram and use pre-main sequence evolutionary models to infer masses and ages. The mean age for this low mass population of NGC 2024 is 0.5 Myr and derived masses range from ~0.7-0.02 solar masses with 23 objects falling below the hydrogen-burning limit. The logarithmic mass function rises to a peak at ~0.2 solar masses before turning over and declining into the substellar regime. There is a possible secondary peak at ~0.035 solar masses however the errors are also consistent with a flat IMF in this region. The ratio of brown dwarfs to stars is similar to that found in the Trapezium but roughly twice the ratio found in IC 348, leading us to conclude that the substellar IMF in young clusters may be dependent on the local star forming environment.
astro-ph/0604316 [abs, ps, pdf, other] :: Title: Optical, Infrared, and Ultraviolet Observations of the X-Ray Flash GRB 050416A
Authors: S. T. Holland (1,2), P. T. Boyd (3), J. Gorosabel (4), J. Hjorth (5), P. Schady (6,7), B. Thomsen (8), T. Augusteijn (9), A. J. Blustin (6), A. Breeveld (6), M. De Pasquale (6), J. P. U. Fynbo (5), N. Gehrels (3), C. Gronwall (7), S. Hunsberger (7), M. Ivanushkina (7,10), W. Landsman (3,11), P. Laursen (5), K. McGowan (6,12), V. Mangano (13), C. B. Markwardt (3), F. Marshall (3), K. O. Mason (6,14), A. Moretti (15), M. J. Page (6), T. Poole (6), P. Roming (7), S. Rosen (6), M. Still (2,3,16) ((1) NASA's GSFC, (2) USRA, (3) NASA's GSFC, (4) CSIC, (5) DARK, (6) MSSL, (7) Penn State, (8) Aarhus, (9) NOT, (10) Brigham Young, (11) SSAI, (12) Southampton, (13) INAF Palermo, (14) PPARC, (15) INAF Brera (16) SAAO)
Comments: 13 pages, 5 figures, LaTeX, AASTeX 5.2

We present ultraviolet, optical, and infrared photometry of the afterglow of the X-ray flash GRB 050416A taken between approximately 100 seconds and 36 days after the burst. We find an intrinsic spectral slope between 1930 Angstrom and 22,200 Angstrom of -1.14 +/- 0.20 and a decay rate of -0.86 +/- 0.15. There is no evidence for a change in the decay rate between approximately 0.7 and 4.7 days after the burst. Our data implies that there is no spectral break between the optical and X-ray bands between 0.7 and 4.7 days after the burst, and is consistent with the cooling break being redward of the K_s band (22,200 Angstrom) at 0.7 days. The combined ultraviolet/optical/infrared spectral energy distribution shows no evidence for a significant amount of extinction in the host galaxy along the line of sight to GRB 050416A. Our data suggest that the extragalactic extinction along the line of sight to the burst is only approximately A_V = 0.2 mag, which is significantly less than the extinction expected from the hydrogen column density inferred from $X$-ray observations of GRB 050416A assuming a dust-to-gas ratio similar to what is found for the Milky Way. The observed extinction, however, is consistent with the dust-to-gas ratio seen in the Small Magellanic Cloud. We postulate that GRB 050416A may have a two-component jet similar to what has been proposed for GRB 030329. If this is the case the lack of an observed jet break between 0.7 and 42 days is an illusion due to emission from the wide jet dominating the afterglow after approximately 1.5 days.
astro-ph/0604317 [abs, ps, pdf, other] :: Title: SINFONI adaptive optics integral field spectroscopy of the Circinus Galaxy
Authors: F. Mueller Sanchez, R.I. Davies, F. Eisenhauer, L.J. Tacconi, R. Genzel, A. Sternberg
Comments: 15 pages, 10 figures, Accepted for publication in A&A

Aims. To investigate the star formation activity and the gas and stellar dynamics on scales of a few parsecs in the nucleus of the Circinus Galaxy. Methods.Using the adaptive optics near infrared integral field spectrometer SINFONI on the VLT, we have obtained observations of the Circinus galaxy on scales of a few parsecs and at a spectral resolution of 70 km s^{-1} FWHM. The physical properties of the nucleus are analyzed by means of line and velocity maps extracted from the SINFONI datacube. Starburst models are constrained using the Br-gamma flux, stellar continuum (as traced via the CO absorption bandheads longward of 2.3um), and radio continuum. Results. The similarity of the morphologies of the H_2 (1-0)S(1) 2.12um and Br-gamma 2.17um lines to the stellar continuum and also their kinematics, suggest a common origin in star formation. Within 8 pc of the AGN we find there has been a recent starburst in the last 100 Myr, which currently accounts for 1.4% of the galaxy's bolometric luminosity. The similarity of the spatial scales over which the stars and gas exist indicates that this star formation is occuring within the torus; and comparison of the gas column density through the torus to the maximum possible optical depth to the stars implies the torus is a clumpy medium. The coronal lines show asymmetric profiles with a spatially compact narrow component and a spatially extended blue wing. These characteristics are consistent with some of the emission arising in clouds gravitationally bound to the AGN, and some outflowing in cloudlets which have been eroded away from the bound clouds.

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0604146 -- 0604176 received

astro-ph new abstracts, Tue, 11 Apr 06 00:00:10 GMT
0604177 -- 0604214 received

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0604215 -- 0604248 received

astro-ph new abstracts, Thu, 13 Apr 06 00:00:08 GMT
0604249 -- 0604278 received

astro-ph new abstracts, Fri, 14 Apr 06 00:00:16 GMT
0604279 -- 0604317 received