Astrophysics

astro-ph new abstracts, Wed, 21 Jun 06 00:00:13 GMT
0606459 -- 0606492 received

astro-ph/0606459 [abs, ps, pdf, other] :: Title: Constraining the Spatial and Time Variation of the Higgs Vacuum Expectation Value by the Primordial $^4He$ Abundance
Authors: Josef M. Gassner, Harald Lesch

We constrain the possible spatial and time variation of the Higgs vacuum expectation value (v) by recent results on the primordial $^4He$ abundance (Y_P). For that, we derive an analytic expression for Y_P and approximate the key-parameters (the mean lifetime of the free neutron and the binding energy of the deuteron) by terms of v/v_0 (where v_0 denotes the present theoretical estimate). The most stringent limit that we derive is given by: -5.4 x 10^{-4} < (v-v_0)/v_0 < 4.4 x 10^{-4}.
astro-ph/0606460 [abs, ps, pdf, other] :: Title: The Connection Between Barstrength and Circumnuclear Dust Structure
Authors: Molly Peeples, Paul Martini (Ohio State)
Comments: Submitted to ApJ. High resolution version available at this http URL Individual high resolution figures available at this http URL

We present a comparison of barstrength Qb and circumnuclear dust morphology for 75 galaxies in order to investigate how bars affect the centers of galaxies. We trace the circumnuclear dust morphology and amount of dust structure with structure maps generated from visible-wavelength HST data, finding that tightly wound nuclear dust spirals are primarily found in weakly barred galaxies. While strongly barred galaxies sometimes exhibit grand design structure within the central 10 percent of D25, this structure rarely extends to within ~10 pc of the galaxy nucleus. In some galaxies, these spiral arms terminate at a circumnuclear starburst ring. Galaxies with circumnuclear rings are generally more strongly barred than galaxies lacking rings. Within these rings, the dust structure is fairly smooth and usually in the form of a loosely wound spiral. These data demonstrate that multiple nuclear morphologies are possible in the most strongly barred galaxies: chaotic central dust structure inconsistent with a coherent nuclear spiral, a grand design spiral that loses coherence before reaching the nucleus, or a grand design spiral that ends in a circumnuclear ring. These observations may indicate that not all strong bars are equally efficient at fueling material to the centers of their host galaxies. Finally, we investigate the longstanding hypothesis that SB(s) galaxies have weak bars and SB(r) galaxies have strong bars, finding the opposite to be the case: namely, SB(r) galaxies are less strongly barred and have less dust structure than SB(s) galaxies. In general, more strongly barred galaxies tend to have higher nuclear dust contrast.
astro-ph/0606461 [abs, ps, pdf, other] :: Title: Chandra Observations of Candidate "True" Seyfert 2 Nuclei
Authors: Himel Ghosh (1), Richard W. Pogge (1), Smita Mathur (1), Paul Martini (1), Joseph C. Shields (2) ((1) OSU, (2) Ohio Univ)
Comments: 26 pages, 12 figures, submitted to ApJ

The Unification Model for active galactic nuclei posits that Seyfert 2s are intrinsically like Seyfert 1s, but that their broad-line regions (BLRs) are hidden from our view. A Seyfert 2 nucleus that truly lacked a BLR, instead of simply having it hidden, would be a so-called "true" Seyfert 2. No object has as yet been conclusively proven to be one. We present a detailed analysis of four of the best "true" Seyfert 2 candidates discovered to date: IC 3639, NGC 3982, NGC 5283, and NGC 5427. None of the four has a broad H-alpha emission line, either in direct or polarized light. All four have rich, high-excitation spectra, blue continua, and Hubble Space Telescope (HST) images showing them to be unresolved sources with no host-galaxy obscuration. To check for possible obscuration on scales smaller than that resolvable by HST, we obtained X-ray observations using the Chandra X-ray Observatory. All four objects show evidence of obscuration and therefore could have hidden BLRs. The picture that emerges is of moderate to high, but not necessarily Compton-thick, obscuration of the nucleus, with extra-nuclear soft emission extended on the hundreds-of-parsecs scale that may originate in the narrow-line region. Since the extended soft emission compensates, in part, for the nuclear soft emission lost to absorption, both absorption and luminosity are likely to be severely underestimated unless the X-ray spectrum is of sufficient quality to distinguish the two components. This is of special concern where the source is too faint to produce a large number of counts, or where the source is too far away to resolve the extended soft X-ray emitting region.
astro-ph/0606462 [abs, ps, pdf, other] :: Title: Temporal Variation in Excited Fe^+ Near a GRB Afterglow
Authors: Miroslava Dessauges-Zavadsky (1), Hsiao-Wen Chen (2), Jason X. Prochaska (3), Joshua S. Bloom (4), Aaron J. Barth (5) ((1) Observatoire de Geneve, (2) U Chicago, (3) UCO/Lick Observatory, (4) UC Berkeley, (5) UC Irvine)
Comments: 10 pages, 3 figures. Submitted to ApJL

Excited Si^+ and Fe^+ species are routinely observed in the host environment of gamma-ray burst (GRB) afterglows, but are not commonly seen in other extragalactic locations. Their presence signals unusual properties in the gaseous environment of these GRB hosts that arise either as a result of the intense ionizing radiation of the afterglow or through collision excitation in a dense cloud. In particular, the photon pumping scenario has explicit expectations for temporal variation in the strength of the excited lines, owing to the decline in the ionizing flux of the GRB afterglow. We analyze afterglow spectra of GRB 020813 obtained in two epochs of ~16 hours apart, and examine transitions from the first excited state of Fe^+ at J=7/2 in these two sets of data. We report a significant decline by at least a factor of five in the equivalent width of the FeII 2396 transition, the strongest from the J=7/2 state. We perform a Monte-Carlo analysis and determine that this temporal variation is present at more than 3sigma level of significance. This observation represents the first detection in the temporal variation of the excited Fe+ states in the GRB host ISM, a direct influence of the burst itself on its environment. We further estimate that the Fe^+ gas resides in 50-100 pc from the afterglow, based on the afterglow lightcurve and the presence and absence of the excited FeII 2396 in the two-epoch observations.
astro-ph/0606463 [abs, ps, pdf, other] :: Title: Gaseous Tidal Debris found in the NGC 3783 Group
Authors: Virginia A. Kilborn, Duncan A. Forbes, Baerbel S. Koribalski, Sarah Brough, Katie Kern
Comments: 12 pages, MNRAS accepted: full resolution paper available at this http URL

We have conducted wide-field HI mapping of a ~5.5 x 5.5 degree region surrounding the NGC 3783 galaxy group, to an HI mass limit of ~4 x 10^8 Msun. The observations were made using the multibeam system on the Parkes 64-m radiotelescope, as part of the Galaxy Evolution Multiwavelength Study (GEMS). We find twelve HI detections in our Parkes data, four more than catalogued in HIPASS. We find two new group members, and discover an isolated region of HI gas with an HI mass of ~4 x 10^8 Msun, without a visible corresponding optical counterpart. We discuss the likelihood of this HI region being a low surface brightness galaxy, primordial gas, or a remnant of tidal debris. For the NGC 3783 group we derive a mean recession velocity of 2903 km/s, and a velocity dispersion of 190 km/s. The galaxy NGC 3783 is the nearest galaxy to the luminosity weighted centre of the group, and is at the group mean velocity.
From the X-ray and dynamical state of this galaxy group, this group appears to be in the early stages of its evolution.
astro-ph/0606464 [abs, pdf] :: Title: pMatlab Parallel Matlab Library
Authors: Nadya Bliss, Jeremy Kepner
Comments: 31 Pages, 17 Figures

MATLAB has emerged as one of the languages most commonly used by scientists and engineers for technical computing, with ~1,000,000 users worldwide. The compute intensive nature of technical computing means that many MATLAB users have codes that can significantly benefit from the increased performance offered by parallel computing. pMatlab (www.ll.mit.edu/pMatlab) provides this capability by implementing Parallel Global Array Semantics (PGAS) using standard operator overloading techniques. The core data structure in pMatlab is a distributed numerical array whose distribution onto multiple processors is specified with a map construct. Communication operations between distributed arrays are abstracted away from the user and pMatlab transparently supports redistribution between any block-cyclic-overlapped distributions up to four dimensions. pMatlab is built on top of the MatlabMPI communication library (www.ll.mit.edu/MatlabMPI) and runs on any combination of heterogeneous systems that support MATLAB, which includes Windows, Linux, MacOSX, and SunOS. Performance is validated by implementing the HPC Challenge benchmark suite and comparing pMatlab performance with the equivalent C+MPI codes. These results indicate that pMatlab can often achieve comparable performance to C+MPI at usually 1/10th the code size. Finally, we present implementation data collected from a sample of 10 real pMatlab applications drawn from the ~100 users at MIT Lincoln Laboratory. These data indicate that users are typically able to go from a serial code to a well performing pMatlab code in about 3 hours while changing less than 1% of their code.
astro-ph/0606465 [abs, ps, pdf, other] :: Title: Discovery of two pulsars towards the Galactic Centre
Authors: Simon Johnston, M. Kramer, D. R. Lorimer, A. G. Lyne, M. McLaughlin, B. Klein, R. N. Manchester
Comments: Submitted to MNRAS Letters

We report the discovery of two highly dispersed pulsars in the direction of the Galactic Centre made during a survey at 3.1 GHz with the Parkes radio telescope. Both PSRs J1745-2912 and J1746-2856 have an angular separation from the Galactic Centre of less than 0.3 degrees and dispersion measures in excess of 1100 cm-3pc, placing them in the top 10 pulsars when ranked on this value. The frequency dependence of the scatter-broadening in PSR J1746-2856 is much shallower than expected from simple theory. We believe it likely that the pulsars are located between 150 and 500 pc from the Galactic Centre on the near side, and are part of an excess population of neutron stars associated with the Centre itself. A second survey made at 8.4 GHz did not detect any pulsars. This implies either that there are not many bright, long-period pulsars at the Galactic Centre or that the scattering is more severe at high frequencies than current models would suggest.
astro-ph/0606466 [abs, ps, pdf, other] :: Title: A Search for EUV Emission from Comets with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
Authors: T. P. Sasseen, M. Hurwitz, C.M. Lisse, V. Kharchenko, D. Christian, S. J. Wolk, M. M. Sirk, A. Dalgarno
Comments: 28 pages total, 4 tables, 7 figures. Accepted by The Astrophysical Journal

We have obtained EUV spectra between 90 and 255 \AA of the cometsC/2002 T7 (LINEAR), C/2001 Q4 (NEAT), and C/2004 Q2 (Machholz) near their perihelion passages in 2004 with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS). We obtained contemporaneous data on Comet NEAT Q4 with the $Chandra$ X-ray Observatory ACIS instrument, marking the first simultaneous EUV and X-ray spectral observations of a comet. The total CHIPS/EUV observing times were 337 ks for Q4, 234 ks for T7, and 483 ks for Machholz and for both CHIPS and $Chandra$ we calculate we have captured all the comet flux in the instrument field of view. We set upper limits on solar wind charge exchange emission lines of O, C, N, Ne and Fe occurring in the spectral bandpass of CHIPS. The spectrum of Q4 obtained with $Chandra$ can be reproduced by modeling emission lines of C, N O, Mg, Fe, Si, S, and Ne solar wind ions. The measured X-ray emission line intensities are consistent with our predictions from a solar wind charge exchange model. The model predictions for the EUV emission line intensities are determined from the intensity ratios of the cascading X-ray and EUV photons arising in the charge exchange processes. They are compatible with the measured limits on the intensities of the EUV lines. For comet Q4, we measured a total X-ray flux of 3.7$\times 10^{-12}$ ergs cm$^{-2}$ s$^{-1}$, and derive from model predictions a total EUV flux of 1.5$\times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$. The CHIPS observations occurred predominantly while the satellite was on the dayside of Earth. For much of the observing time, CHIPS performed observations at smaller solar angles than it was designed for and EUV emission from the Sun scattered into the instrument limited the sensitivity of the EUV measurements.
astro-ph/0606467 [abs, ps, pdf, other] :: Title: Violent Stellar Merger Model for Transient Events
Authors: Noam Soker (Technion, Israel), Romuald Tylenda (N.Copernicus Ast. Center, Poland)
Comments: Submitted to MNRAS

We derive the constraints on the mass ratio for a binary system to merge in a violent process. We find that the secondary to primary stellar mass ratio should be ~0.003 < (M_2/M_1) < ~0.15. A more massive secondary star will keep the primary stellar envelope in synchronized rotation with the orbital motion until merger occurs. This implies a very small relative velocity between the secondary star and the primary stellar envelope at the moment of merger, and therefore very weak shock waves, and low flash luminosity. A too low mass secondary will release small amount of energy, and will expel small amount of mass, which is unable to form an inflated envelope. It can however produce a quite luminous but short flash when colliding with a low mass main sequence star.
Violent and luminous mergers, which we term mergebursts, can be observed as V838 Monocerotis type events, where a star undergoes a fast brightening lasting days to months, with a peak luminosity of up to ~10^6 Lo followed by a slow decline at very low effective temperatures.
astro-ph/0606468 [abs, pdf] :: Title: Terrestrial planetary dynamics: a view from U, Th geochemistry
Authors: Xuezhao Bao
Comments: 32 pages, 4 figures, 2 tables

The migration of U and Th inside a planet is controlled by its oxidation state imposed by the volatile composition. In the deep interior of a planet, an absence of oxidative volatiles will cause U and Th to stay in a state of metal or low valance compounds with a big density. Consequently, they migrate to the bottom of its mantle first, and then are gradually sequestered to its metal core. Earth is rich in oxidative volatiles including water, therefore, U and Th in the core can be moved up by an internal circulation system consisting of the outer core, hot super plumes, asthenosphere and subduction zone (or cold super plumes). This internal circulation system is the key for the formation of plate tectonics, the geodynamo and the consequent geomagnetic field. Moreover, plentiful oxidative volatiles and water within Earth is the precondition to form such a circulation system. In the early stage (> 4 Ga), Mars developed an Earth-like internal circulation system due to relatively large amount of oxidative volatile compositions coming from its building material. This would have produced a dynamo and correspondingly an Earth-like magnetic field. However, this internal circulation system was destroyed by one or several giant impact events in the early stage, which drove off these volatile compositions. These events also shaped the striking hemispheric dichotomy structure on the Martian surface. The other result is that its dynamo and geomagnetic field have also disappeared. Since then, Mars has been the same as Mercury and Venus in that the heat release from the U and Th in their cores can not be moved by an internal circulation system gently, but by sporadically catastrophic resurfacing events (Venus), or super plumes (Mars) or gradual heat conduction (Mercury).
astro-ph/0606469 [abs, ps, pdf, other] :: Title: A search for distant radio galaxies from SUMSS and NVSS: III. radio spectral energy distributions and the z-alpha correlation
Authors: I.J. Klamer, R.D. Ekers, J.J. Bryant, R.W. Hunstead, E.M. Sadler, C. De Breuck
Comments: MNRAS in press

This is the third in a series of papers that present observations and results for a sample of 76 ultra-steep-spectrum radio sources designed to find galaxies at high redshift. Here we present multi-frequency radio observations, from the Australia Telescope Compact Array, for a subset of 37 galaxies from the sample. Matched resolution observations at 2.3, 4.8 and 6.2GHz are presented for all galaxies, with the z<2 galaxies additionally observed at 8.6 and 18GHz. New angular size constraints are reported for 19 sources based on high resolution 4.8 and 6.2GHz observations. Functional forms for the rest-frame spectral energy distributions are derived: 89% of the sample is well characterised by a single power law, whilst the remaining 11% show some flattening toward higher frequencies: not one source shows any evidence for high frequency steepening. We discuss the implications of this result in light of the empirical correlation between redshift and spectral index seen in flux limited samples of radio galaxies. Finally, a new physical mechanism to explain the redshift -- spectral index correlation is posited: extremely steep spectrum radio galaxies in the local universe usually reside at the centres of rich galaxy clusters. We argue that if a higher fraction of radio galaxies, as a function of redshift, are located in environments with densities similar to nearby rich clusters, then this could be a natural interpretation for the correlation. We briefly outline our plans to pursue this line of investigation.
astro-ph/0606470 [abs, ps, pdf, other] :: Title: INTEGRAL and XMM-Newton observations towards the unidentified MeV source GRO J1411-64
Authors: Diego F. Torres, Shu Zhang, Olaf Reimer, Xavier Barcons, Amalia Corral, Valenti Bosch-Ramon, Josep M. Paredes, Gustavo E. Romero, Jin Lu Qu, Werner Collmar, V. Schonfelder, Yousaf Butt

The COMPTEL unidentified source GRO J1411-64 was observed by INTEGRAL, and its central part, also by XMM-Newton. The data analysis shows no hint for new detections at hard X-rays. The upper limits in flux herein presented constrain the energy spectrum of whatever was producing GRO J1411-64, imposing, in the framework of earlier COMPTEL observations, the existence of a peak in power output located somewhere between 300-700 keV for the so-called low state. The Circinus Galaxy is the only source detected within the 4$\sigma$ location error of GRO J1411-64, but can be safely excluded as the possible counterpart: the extrapolation of the energy spectrum is well below the one for GRO J1411-64 at MeV energies. 22 significant sources (likelihood $> 10$) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6-635932, is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the COMPTEL source position uncertainty make an association hard to quantify and thus risky. The unique peak of the power output at high energies (hard X-rays and gamma-rays) resembles that found in the SED seen in blazars or microquasars. However, an analysis using a microquasar model consisting on a magnetized conical jet filled with relativistic electrons which radiate through synchrotron and inverse Compton scattering with star, disk, corona and synchrotron photons shows that it is hard to comply with all observational constrains. This and the non-detection at hard X-rays introduce an a-posteriori question mark upon the physical reality of this source, which is discussed in some detail.
astro-ph/0606471 [abs, ps, pdf, other] :: Title: Low-mass star formation in Lynds 1333
Authors: M. Kun, S. Nikolic, L.E.B. Johansson, Z. Balog, A. Gaspar
Comments: 7 pages, 4 figures, accepted by MNRAS

Medium-resolution optical spectroscopy of the candidate YSOs associated with the small, nearby molecular cloud Lynds~1333 revealed four previously unknown classical T Tauri stars, two of which are components of a visual double, and a Class I source, IRAS 02086+7600. The spectroscopic data, together with new V,R_ C,I_C photometric and 2MASS J, H, and K_s data allowed us to estimate the masses and ages of the new T Tauri stars. We touch on the possible scenario of star formation in the region. L1333 is one of the smallest and nearest known star forming clouds, therefore it may be a suitable target for studying in detail the small scale structure of a star forming environment.
astro-ph/0606472 [abs, ps, pdf, other] :: Title: HH135/HH136 - a luminous H$_2$ outflow towards a high-mass protostar
Authors: Roland Gredel

Near-infrared observations towards the luminous IRAS source IRAS11101-5928 and the associated Herbig-Haro objects HH135/HH136 are presented. The observations reveal the presence of a well-collimated, parsec-sized H$_2$ outflow with a total H$_2$ luminosity of about $2L_\odot$. The bulk of the molecular gas is characterized by a ro-vibrational excitation temperature of $2000\pm200$ K. A small fraction (0.3%) of the molecular gas is very hot, with excitation temperatures around 5500 K. The molecular emission is associated with strong [FeII] emission. The H$_2$ and [FeII] emission characteristics indicate the presence of fast, dissociative J-shocks at speeds of $v_\mathrm{s} \approx$ 100 km s$^{-1}$. Electron densities of $n_\mathrm{e}$ = 3500-4000 cm$^{-3}$ are inferred from the [FeII] line ratios. The large H$_2$ luminosity combined with the very large source luminosity suggests that the high-mass protostar that powers the HH135/HH136 flow forms via accretion, but with a significantly increased accretion rate compared to that of low-mass protostars.
astro-ph/0606473 [abs, ps, pdf, other] :: Title: Experimental evidence for magnetorotational instability in a helical magnetic field
Authors: Frank Stefani, Thomas Gundrum, Gunter Gerbeth, Günther Rüdiger, Manfred Schultz, Jacek Szklarski, Rainer Hollerbach
Comments: 4 pages, 4 figures

A recent paper [R. Hollerbach and G. Rudiger, Phys. Rev. Lett. 95, 124501 (2005)] has shown that the threshold for the onset of the magnetorotational instability (MRI) in a Taylor-Couette flow is dramatically reduced if both axial and azimuthal magnetic fields are imposed. In agreement with this prediction, we present results of a Taylor-Couette experiment with the liquid metal alloy GaInSn, showing evidence for the existence of the MRI at Reynolds numbers of order 1000 and Hartmann numbers of order 10.
astro-ph/0606474 [abs, ps, pdf, other] :: Title: Transplanckian signatures in WMAP3?
Authors: Ulf H. Danielsson
Comments: 8 pages

In this note we investigate how a possible signal in the WMAP3 data of rapid oscillations in the primordial spectrum can be accomodated into an effective model of transplanckian physics including back reaction. The results, if due to a real effect, would indicate the presence of a low fundamental scale -- possibly the string scale -- around $2.2\cdot10^{-5}M_{pl}$.
astro-ph/0606475 [abs, ps, pdf, other] :: Title: Integrated Sachs-Wolfe effect from the cross-correlation of WMAP 3 year and NVSS: new results and constraints on dark energy
Authors: Davide Pietrobon, Amedeo Balbi, Domenico Marinucci
Comments: 8 pages, 6 figures. Submitted to PRD

We cross-correlate the new 3 year Wilkinson Microwave Anistropy Probe (WMAP) cosmic microwave background (CMB) data with the NRAO VLA Sky Survey (NVSS) radio galaxy data, and find further evidence of late integrated Sachs-Wolfe (ISW) effect taking place at late times in cosmic history. Our detection makes use of a novel statistical method based on a new construction of spherical wavelets, called needlets. The null hypothesis (no ISW) is excluded at more than 99.7% confidence. When we compare the measured cross-correlation with the theoretical predictions of standard, flat cosmological models with a generalized dark energy component parameterized by its density, $\omde$, equation of state $w$ and speed of sound $\cs2$, we find $0.3\leq\omde\leq0.8$ at 95% c.l., independently of $\cs2$ and $w$. If dark energy is assumed to be a cosmological constant ($w=-1$), the bound on density shrinks to $0.41\leq\omde\leq 0.79$. Models without dark energy are excluded at more than $4\sigma$. The bounds on $w$ depend rather strongly on the assumed value of $\cs2$. We find that models with more negative equation of state (such as phantom models) are a worse fit to the data in the case $\cs2=1$ than in the case $\cs2=0$.
astro-ph/0606476 [abs, ps, pdf, other] :: Title: Multicolour Optical Surface Brightness Profiles Decomposition of the Seyfert Galaxies III Zw 2, Mrk 506 and Mrk 509
Authors: L. Slavcheva-Mihova, B. Mihov, G. Petrov, V. Kopchev
Comments: a poster presented at the 5th Bulgarian-Serbian Conference "Astronomy and Space Science"

We present the results of the UBVRcIc surface brightness profiles decomposition of the Seyfert galaxies III Zw 2, Mrk 506 and Mrk 509. The profiles were modelled as a sum of a Gaussian, a Sersic law and an exponent. A Ferrers bar and a Gaussian ring were added to the model profiles of III Zw 2 and Mrk 506, respectively. The parameters and the total magnitudes of the structural components were derived.
astro-ph/0606477 [abs, ps, pdf, other] :: Title: Rotation of Cosmic Voids and Void-Spin Statistics
Authors: Jounghun Lee, Daeseong Park (Seoul Nat'l Univ.)
Comments: submitted to ApJ, 15 pages, 5 figures

We present a theoretical study of void spins and their correlation properties. Both the analytical and numerical approaches are used for our study. Analytically, we adopt the linear tidal torque model to evaluate the void spin-spin and spin-density correlations, assuming that a void forms in the initial region where the inertia momentum and the tidal shear tensors are maximally uncorrelated with each other. Numerically, we use the Millennium run galaxy catalog to find voids and calculate their spin statistics. The numerical results turn out to be in excellent agreement with the analytic predictions, both of which consistently shows that there are strong spatial alignments between the spin axes of voids and strong anti-alignments between the spin axes of voids and the directions to the nearest voids. We expect that our work will provide a deeper insight into the origin and properties of voids and the large scale structure.
astro-ph/0606478 [abs, ps, pdf, other] :: Title: Statistical Analysis of Point-like Sources in Chandra Galactic Center Survey
Authors: J. F. Wu, S. N. Zhang, F. J. Lu, Y. K. Jin
Comments: 14 pages, 8 figures, accepted by Chinese Journal of Astronomy & Astrophysics

{\it Chandra} Galactic Center Survey detected $\sim 800$ X-ray point-like sources in the $2^{\circ} \times 0.8^{\circ}$ sky region around the Galactic Center. In this paper, we study the spatial and luminosity distributions of these sources according to their spectral properties. Fourteen bright sources detected are used to fit jointly an absorbed power-law model, from which the power-law photon index is determined to be $\sim$2.5. Assuming that all other sources have the same power-law form, the relation between hardness ratio and HI column density $N_H$ is used to estimate the $N_H$ values for all sources. Monte Carlo simulations show that these sources are more likely concentrated in the Galactic center region, rather than distributed throughout the Galactic disk. We also find that the luminosities of the sources are positively correlated with their HI column densities, i.e. a more luminous source has a higher HI column density. From this relation, we suggest that the X-ray luminosity comes from the interaction between an isolated old neutron star and interstellar medium (mainly dense molecular clouds). Using the standard Bondi accretion theory and the statistical information of molecular clouds in the Galactic center, we confirm this positive correlation and calculate the luminosity range in this scenario, which is consistent with the observation ($10^{32}\sim 10^{35}$ ergs s$^{-1}$).
astro-ph/0606479 [abs, ps, pdf, other] :: Title: The Excitation of N$_2$H$^+$ in Interstellar Molecular Clouds. I - Models
Authors: F. Daniel, J. Cernicharo, M.-L. Dubernet
Comments: 13 pages, 12 figures

We present LVG and non-local radiative transfer calculations involving the rotational and hyperfine structure of the spectrum of N$_2$H$^+$ with collisional rate coefficients recently derived by us. The goal of this study is to check the validity of the assumptions made to treat the hyperfine structure and to study the physical mechanisms leading to the observed hyperfine anomalies.
We find that the usual hypothesis of identical excitation temperatures for all hyperfine components of the $J$=1-0 transition is not correct within the range of densities existing in cold dense cores, i.e., a few 10$^4$ $\textless$ n(H$_2$) $\textless$ a few 10$^6$ cm$^{-3}$. This is due to different radiative trapping effects in the hyperfine components. Moreover, within this range of densities and considering the typical abundance of N$_2$H$^+$, the total opacity of rotational lines has to be derived taking into account the hyperfine structure. The error made when only considering the rotational energy structure can be as large as 100%. Using non-local models we find that, due to saturation, hyperfine anomalies appear as soon as the total opacity of the $J$=1-0 transition becomes larger than $\simeq$ 20. Radiative scattering in less dense regions enhance these anomalies, and particularly, induce a differential increase of the excitation temperatures of the hyperfine components. This process is more effective for the transitions with the highest opacities for which emerging intensities are also reduced by self-absorption effects. These effects are not as critical as in HCO$^+$ or HCN, but should be taken into account when interpreting the spatial extent of the N$_2$H$^+$ emission in dark clouds.
astro-ph/0606480 [abs, ps, pdf, other] :: Title: Thermal and non-thermal components of the interstellar medium at sub-kiloparsec scales in galaxies
Authors: R. Paladino, M. Murgia, T.T. Helfer, T. Wong, R. Ekers, L. Blitz, L. Gregorini, L. Moscadelli
Comments: 27 pages, 9 figures (low resolution), accepted for publication in A&A. High resolution version of the paper is available at: this http URL

Aims: We present new radio continuum observations of ten BIMA SONG galaxies, taken at 1.4 GHz with the Very Large Array. These observations allow us to extend the study of the relationships between the radio continuum (RC) and CO emission to 22 CO luminous galaxies for which single dish CO images have been added to interferometric data. New Spitzer infrared (IR) images of six of these galaxies have been released. The analysis of these high resolution images allowed us to probe the RC-IR-CO correlations down to linear scales of a few hundred pc. Results: for the 22 galaxies analysed, the RC-CO correlation on scales from $\sim10$ kpc down to $\sim100$ pc is nearly linear and has a scatter of a factor of two, i.e. comparable to that of the global correlations. There is no evidence for any severe degradation of the scatter below the kpc scale. This also applies to the six galaxies for which high-resolution mid-IR data are available. In the case of NGC 5194, we find that the non-thermal radio spectral index is correlated with the RC/FIR ratio. Conclusions: The scatter of the point-by-point correlations does not increase significantly with spatial resolution. We thus conclude that we have not yet probed the physical scales at which the correlations break down. However, we observe local deviations from the correlations in regions with a high star formation rate, such as the spiral arms, where we observe a flat radio spectrum and a low RC/FIR ratio. In the intra-arm regions and in the peripheral regions of the disk, the RC/FIR is generally higher and it is characterized by a steepening of the radio spectrum.
astro-ph/0606481 [abs, ps, pdf, other] :: Title: X-ray temperature spectroscopy of simulated cooling clusters
Authors: R. Valdarnini
Comments: 46 pages, 10 figures, 3 tables, accepted for publication in NewA

Results from a large sample of hydrodynamical/N-body simulations of galaxy clusters in a LCDM cosmology are used to simulate cluster X-ray observations as expected from Chandra observations. The physical modeling of the gas includes radiative cooling, star formation, energy feedback and metal enrichment. The biasing of spectral temperatures with respect to mass-weighted temperatures is found to be influenced by two independent processes. The first scale dependency is absent in adiabatic runs and is due to cooling, whose efficiency to transform cold gas into stars is higher for cool clusters and this in turn implies a strong dependency of the spectral versus mass-weighted temperature relation on the cluster mass. The second dependency is due to photon emission because of cool gas which is accreted during merging events and biases the spectral fits. These events have been quantified according to the power ratio method and a robust correlation is found to exist between the spectral bias and the amount of cluster substructure. The shape of the simulated temperature profiles is not universal and it is steeper at the cluster center for cool clusters than for the massive ones. The profiles are in good agreement with data in the radial range between $\sim 0.1 r_{vir}$ and $\sim 0.4 r_{vir}$; at small radii ($r< 0.1 r_{vir}$) the cooling runs fail to reproduce the shape of the observed profiles. The fit is improved if one considers a hierarchical merging scenario in which cluster cores can accrete cooler gas through merging with cluster subclumps, though the shape of the temperature profiles is modified in a significant way only in the regime where the mass of the substructure is a large fraction of the cluster mass.
astro-ph/0606482 [abs, ps, pdf, other] :: Title: Intergalactic medium heating by dark matter
Authors: E. Ripamonti (1), M. Mapelli (2), A. Ferrara (2) ((1) Kapteyn Astronomical Institute, University of Groningen, (2) SISSA, Trieste)
Comments: 11 pages, 7 figures, submitted to MNRAS

We derive the evolution of the energy deposition in the intergalactic medium (IGM) by dark matter (DM) decays/annihilations for both sterile neutrinos and light dark matter (LDM) particles. At z > 200 sterile neutrinos transfer a fraction f_abs~0.5 of their rest mass energy into the IGM; at lower redshifts this fraction becomes <~ 0.3 depending on the particle mass. The LDM particles can decay or annihilate. In both cases f_abs~0.4-0.9 at high (> 300) redshift, dropping to ~0.1 below z=100. These results indicate that the impact of DM decays/annihilations on the IGM thermal and ionization history is less important than previously thought. We find that sterile neutrinos (LDM) decays are able to increase the IGM temperature by z=5 at most up to 10K (100K), about 20-50 times less than predicted by estimates based on the assumption of complete energy transfer to the gas.
astro-ph/0606483 [abs, ps, pdf, other] :: Title: The impact of dark matter decays and annihilations on the formation of the first structures
Authors: E. Ripamonti (1), M. Mapelli (2), A. Ferrara (2) ((1) Kapteyn Astronomical Institute, University of Groningen, (2) SISSA, Trieste)
Comments: 8 pages, 7 figures, submitted to MNRAS

We derive the effects of DM decays and annihilations on structure formation. We consider moderately massive DM particles (sterile neutrinos and LDM), as they are expected to give the maximum contribution to heating and reionization. The energy injection from DM decays and annihilations produces both an enhancement in the abundance of coolants (H_2 and HD) and an increase of gas temperature. We find that for all the considered DM models (sterile neutrino decays, LDM decays and annihilations) the critical halo mass for collapse, m_crit, is higher than in the unperturbed case. However, the variation of m_crit is small. In the most extreme case, i.e. considering LDM decays and halos virializing at redshift z_vir~10, m_crit increases by a factor 2. The variations of m_crit are also sensitive to the assumed concentration of the DM halo. Furthermore, we note that the fraction of gas which is retained inside the halo is substantially reduced (to ~40 per cent of the cosmic value), especially in the smallest halos, as a consequence of the energy injection by DM decays and annihilations.
astro-ph/0606484 [abs, ps, pdf, other] :: Title: First astrophysical results from AMBER/VLTI
Authors: Fabien Malbet (LAOG), Romain G. Petrov (LUAN), Gerd Weigelt (MPIFR), Philippe Stee, Eric Tatulli (OAA), Armando Domiciano De Souza (LUAN), Florentin Millour (LAOG, LUAN), the AMBER consortium Collaboration
Comments: SPIE 6268 proceedings
Journal-ref: Advances in Stellar Interferometry, \'{E}tats-Unis d'Am\'{e}rique (2006)

The AMBER instrument installed at the Very Large Telescope (VLT) combines three beams from as many telescopes to produce spectrally dispersed fringes from milli-arcsecond angular scale in the near infrared. Two years after installation, first scientific observations have been carried out during the Science Demonstration Time and the Guaranteed Time mostly on bright sources due to some VLTI limitations. In this paper, we review these first astrophysical results and we show which types of completely new information is brought by AMBER. The first astrophysical results have been mainly focusing on stellar wind structure, kinematics, and its interaction with dust usually concentrated in a disk. Because AMBER has dramatically increased the number of measures per baseline, this instrument brings strong constraints on morphology and models despite a relatively poor (u, v) coverage for each object.
astro-ph/0606485 [abs, ps, pdf, other] :: Title: A Quantitative Analysis of the Available Multicolor Photometry for Rapidly Pulsating Hot B Subdwarfs
Authors: P.-E. Tremblay, G. Fontaine, P. Brassard, P. Bergeron, S.K. Randall
Comments: 59 pages, 18 figures, accepted for publication in the Astrophysical Journal Supplement Series

We present a quantitative and homogeneous analysis of the broadband multicolor photometric data sets gathered so far on rapidly pulsating hot B subdwarf stars. This concerns seven distinct data sets related to six different stars. Our analysis is carried out within the theoretical framework developed by Randall et al., which includes full nonadiabatic effects. The goal of this analysis is partial mode identification, i.e., the determination of the degree index l of each of the observed pulsation modes. We assume possible values of l from 0 to 5 in our calculations. For each target star, we compute a specific model atmosphere and a specific pulsation model using estimates of the atmospheric parameters coming from time-averaged optical spectroscopy. For every assumed value of l, we use a formal chi-squared approach to model the observed amplitude-wavelength distribution of each mode, and we compute a quality-of-fit Q probability to quantify the derived fit and to discriminate objectively between the various solutions. We find that no completely convincing and unambiguous l identification is possible on the basis of the available data, although partial mode discrimination has been reached for 25 out of the 41 modes studied. A brief statistical study of these results suggests that a majority of the modes must have l values of 0, 1, and 2, but also that modes with l = 4 could very well be present while modes with l = 3 appear to be rarer. This is in line with recent results showing that l = 4 modes in rapidly pulsating B subdwarfs have a higher visibility in the optical domain than modes with l = 3. Although somewhat disappointing in terms of mode discrimination, our results still suggest that the full potential of multicolor photometry for l identification in pulsating subdwarfs is within reach.
astro-ph/0606486 [abs, ps, pdf, other] :: Title: Very High Energy Gamma-Ray Observations with H.E.S.S
Authors: Christopher van Eldik (Max-Planck-Institute for Nuclear Physics)
Comments: 8 pages, 4 figures, to appear in the proceedings of the 41st Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Aosta Valley, Italy, 11-18 March 2006

The H.E.S.S. Imaging Atmospheric Cherenkov Telescope Array is currently the most sensitive instrument for Very High Energy (VHE) gamma-ray observations in the energy range of about 0.1-10 TeV. During more than two years of operation with the complete 4-telescope array, many galactic and extragalactic VHE gamma-ray sources have been discovered. With its superior sensitivity and its large field-of-view camera, H.E.S.S. is particularly suited for surveys and detailed studies of extended sources. A selection of recent H.E.S.S. results is presented in this proceeding.
astro-ph/0606487 [abs, ps, pdf, other] :: Title: Statistical analysis of BATSE gamma-ray bursts: Self-similarity and the Amati-relation
Authors: L. Borgonovo, C.-I. Bjornsson (Stockholm Observatory)
Comments: 13 pages, 6 figures, submitted for publication to ApJ

The statistical properties of a complete, flux limited sample of 197 long gamma--ray bursts (GRBs) detected by BATSE are studied. In order to bring forth their main characteristics, care was taken to define a representative set of ten parameters. A multivariate analysis gives that ~70% of the total variation in parameter values is driven by only three principal components. The variation of the temporal parameters is clearly distinct from that of the spectral ones. A close correlation is found between the half-width of the autocorrelation function (tau) and the emission time (Tem); most importantly, this correlation is self-similar in the sense that the mean values and dispersions of both tau and Tem scale with the duration of the burst (T90). It is shown that the Amati-relation can be derived from the sample and that the scatter around this relation is correlated with the value of tau. Hence, tau has a role similar to that of the break in the afterglow light curve (Tb) in the Ghirlanda-relation. In the standard GRB-scenario, the close relation between a global parameter (Tb) and a local one (tau) indicates that some of the jet-properties do not vary much for different lines of sight. Finally, it is argued that the basic temporal and spectral properties are associated with individual pulses, while the overall properties of a burst is determined mainly by the number of pulses.
astro-ph/0606488 [abs, ps, pdf, other] :: Title: INTEGRAL observations of AGN obscured by the Galactic Plane
Authors: M. Molina, A. Malizia, L. Bassani, A.J. Bird, A.J. Dean, R. Landi, A. De Rosa, R. Walter, E.J. Barlow, D.J. Clark, A.B. Hill, V. Sguera

In this paper we present INTEGRAL observations of 7 AGNs: two newly discovered type 1 Seyferts, IGR J18027-1455 and IGR J21247+5058, and five well known Seyferts, NGC 6814 (type 1.5), Cyg A (Type 2), MCG-05-23-16 (type 2), ESO 103-G035 (type2) and GRS1734-292. For IGR J18027-1455 and IGR J21247+5058 only INTEGRAL/IBIS data were available, while broadband spectra are presented and discussed for the remaining 5 sources for which either BeppoSAX or ASCA data were used in conjunction with INTEGRAL measurements. In the cases of NGC 6814 and GRS 1734-292, data taken in different periods indicate variability in the flux: in the case of NGC 6814 by a factor of 16 over a period of about 10 years. Although limited in size, our sample can be used to investigate the parameter space of both the photon index and cut-off energy. The mean photon index is 1.8, while the cut-off energy ranges from 30-50 keV to greater than 200 keV; in the particular case of MCG-05-23-16, ESO 103-G035 and GRS 1734-292 the cut-off energy is well constrained at or below 100 keV. We have also tested an enlarged sample, which includes INTEGRAL data of 3 more AGNs, against the correlation found by a number of authors between the photon index and the cut-off energy but have found no evidence for a relation between these two parameters. Our analysis indicates that there is a diversity in cut-off energies in the primary continuum of Seyfert galaxies.
astro-ph/0606489 [abs, ps, pdf, other] :: Title: Galactic Nuclei and Jets in Wave Gravity
Authors: Kris Krogh
Comments: 14 pages, LaTeX2e, no figures

"Wave gravity" refers to a quantum-mechanical gravity theory introduced in two previous papers [1,2]. Although based on the optics of de Broglie waves instead of curved space-time, it agrees with the standard tests of general relativity. As in that theory, galactic nuclei are dark objects where gravity prevents the escape of most radiation. In this case, collapse is counteracted by rising internal pressure and black hole singularities don't occur. Unlike black holes, these nuclei can have internal magnetic fields, and high-energy plasma can escape along magnetic field lines closely aligned with the gravitational field direction. This allows a different model of jets from active galactic nuclei, where jets can arise without direct fueling by accretion disks.
astro-ph/0606490 [abs, ps, pdf, other] :: Title: The Star Formation History and Evolution of the Circumnuclear Region of M100
Authors: Emma L. Allard, Johan H. Knapen, Reynier F. Peletier, Marc Sarzi
Comments: 21 pages, soon for publication in MNRAS, referee's suggestions included

Star-forming nuclear rings in barred galaxies are common in nearby spirals, and their detailed study can lead to important insights into the evolution of galaxies, their bars, and their central regions. We present integral field spectroscopic observations obtained with SAURON of the bar and circumnuclear region of the barred spiral galaxy M100, complemented by new {\it Spitzer Space Telescope} imaging of the region. We use these data to enhance our understanding of the formation, evolution, and current properties of the bar and ring. We derive the kinematics of the gas and the stars and quantify circular and non-circular motions using kinemetry. We analyse this in conjunction with the optical and infrared morphology, and our previously published dynamical modelling. By comparing line indices to simple stellar population models we estimate the ages and metallicities of the stellar populations present within the region, especially in and around the ring. Our kinematic and morphological results all confirm the picture in which the nuclear ring in M100, considered typical, is fed by gas flowing in from the disc under the action of the bar, is slowed down near a pair of resonances, and forms significant amounts of massive stars. Detailed stellar population modelling shows how the underlying bulge and disc were put in place a number of Gyr ago, and that the nuclear ring has been forming stars since about 500~Myr ago in a stable succession of bursts. This confirms that nuclear rings of this kind can form under the influence of a resonant structure set up by a bar, and proves that they are stable features of a galaxy rather than one-off starburst events.
astro-ph/0606491 [abs, ps, pdf, other] :: Title: Infrared observations of V838 Mon
Authors: M. T. Rushton, T. R. Geballe, A. Evans, J. Th. van Loon, B. Smalley, S. P. S. Eyres
Comments: 7 pages, 7 figures, to appear in ASP Conf. Ser., The Nature of V838 Mon and Its Light Echo, eds. R.L.M. Corradi and U. Munari

We describe the results of fitting simple spherically symmetric models to the first overtone CO and AlO A-X (2-0) bands in V838 Mon. We find that the temperature and column of both CO and AlO systematically decline over the period 2002 October - 2005 February and that an additional, hotter and denser, component is present from 2005 January. We also describe the results of an observation of the star and its light echo at 850micron. We do not detect the `infrared' echo at these wavelength, and place an upper limit of 3x10^7 cm^-2 on the column of grains.
astro-ph/0606492 [abs, ps, pdf, other] :: Title: Diffuse, Non-Thermal X-ray Emission from the Galactic Star Cluster Westerlund 1
Authors: Michael P. Muno, Casey Law, J. Simon Clark, Sean M. Dougherty, Richard de Grijs, Simon Portegies Zwart, Farhad Yusef-Zadeh
Comments: 10 pages, 3 figures (one color), and 3 tables. Accepted to ApJ

We present the diffuse X-ray emission identified in Chandra observations of the young, massive Galactic star cluster Westerlund 1. After removing point-like X-ray sources down to a completeness limit of 2e31 erg/s, we identify 3e34 erg/s (2--8 keV) of diffuse emission. The spatial distribution of the emission can be described as a slightly-elliptical Lorentzian core with a half-width half-maximum along the major axis of 25+/-1", similar to the distribution of point sources in the cluster, plus a 5' halo of extended emission. The spectrum of the diffuse emission is dominated by a hard continuum component that can be described as a kT>3 keV thermal plasma that has a low iron abundance (<0.3 solar), or as non-thermal emission that could be stellar light that is inverse-Compton scattered by MeV electrons. Only 5% of the flux is produced by a kT=0.7 keV plasma. The low luminosity of the thermal emission and the lack of a 6.7 keV iron line suggests that <40,000 unresolved stars with masses between 0.3 and 2 Msun are present in the cluster. Moreover, the flux in the diffuse emission is a factor of two lower than would be expected from a supersonically-expanding cluster wind, and there is no evidence for thermal remnants produced by supernovae. Less than 1e-5 of the mechanical luminosity of the cluster is dissipated as 2--8 keV X-rays, leaving a large amount of energy that either is radiated at other wavelengths, is dissipated beyond the bounds of our image, or escapes into the intergalactic medium.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Thu, 22 Jun 06 00:00:10 GMT
0606493 -- 0606532 received

astro-ph/0606493 [abs, ps, pdf, other] :: Title: Discovery of a new high redshift QSO at z=5.96 with the Subaru telescope
Authors: Tomotsugu Goto (ISAS/JAXA)
Comments: accepted for publication in MNRAS

We report a discovery of a new high redshift quasar at $z=5.96$, observed with the FOCAS long-slit spectrograph on board the Subaru telescope. The spectrum shows strong and broad Ly$\alpha$+NV emission lines with a sharp discontinuity to the blue side. A Ly$\beta$+OVI emission line is also detected, providing a consistent redshift measurement with the Ly$\alpha$+NV emission. The QSO has an absolute magnitude of $M_{AB,1450}=-26.9$ ($H_{0}=50$km s$^{-1}$ Mpc$^{-1}$, $q_0=0.5$).
The spectrum shows significant flux in the region 8000-8300 $\AA$ and thus does not show a complete Gunn-Peterson trough in the redshift range 5.58 to 5.82, along the line of sight to this $z=5.96$
QSO. Therefore the Universe was already highly ionized at $z=5.82$
astro-ph/0606494 [abs, ps, pdf, other] :: Title: Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. III. Optical Variability and X-ray/UV/Optical Correlations
Authors: Louis-Benoit Desroches (1), Alexei V. Filippenko (1), Shai Kaspi (2,3), Ari Laor (2), Dan Maoz (3), Mohan Ganeshalingam (1), Weidong Li (1), Edward C. Moran (4), Brandon Swift (1), Misty C. Bentz (5), Luis C. Ho (6), Kirpal Nandra (7), Paul M. O'Neill (7), Bradley M. Peterson (5) ((1) UC Berkeley, (2) Technion, Israel, (3) Wise Observatory, (4) Wesleyan University, (5) Ohio State University, (6) Carnegie Observatories, (7) Imperial College London)
Comments: 29 pages, 16 figures, emulateapj, accepted for publication in ApJ

We present optical observations of the low-luminosity Seyfert 1 nucleus of NGC 4395, as part of a multiwavelength reverberation-mapping program. Observations were carried out over two nights in 2004 April at Lick, Wise, and Kitt Peak Observatories. We obtained V-band and B-band photometry, and spectra over the range 3500-6800 Angstroms. Simultaneous Hubble Space Telescope UV and Chandra X-ray observations are presented in companion papers. Even though NGC 4395 was in an extremely low state of activity, we detect significant continuum variability of 2-10%, increasing toward shorter wavelengths. The continuum light curves, both spectroscopic and photometric, are qualitatively similar to the simultaneous UV and X-ray light curves. Inter-band cross-correlations suggest that the optical continuum emission lags behind the UV continuum emission by 24 +7/-9 min, and that the optical continuum emission lags behind the X-ray continuum emission by 44 +/- 13 min, consistent with a reprocessing model for active galactic nucleus emission. There are also hints of Balmer emission lines lagging behind the optical continuum by an amount slightly larger than the emission-line lag detected in the UV. These results are all similar to those of other Seyfert 1 nuclei. The emission-line lag yields a mass measurement of the central black hole, which although not very significant, is consistent with the value derived from the simultaneous UV data.
astro-ph/0606495 [abs, ps, pdf, other] :: Title: Search for Lambda-Doubling Transitions of SiH in Orion KL
Authors: Vincent L. Fish (NRAO)
Comments: 4 pages, color, to appear in ApJL

A recent submillimeter line survey of Orion KL claimed detection of SiH. This paper reports on GBT observations of the 5.7 GHz Lambda-doubling transitions of SiH in Orion. Many recombination lines, including C164-delta, are seen, but SiH is not detected. The nondetection corresponds to an upper limit of 1.5 x 10^15 cm^-2 (4 sigma) for the beam-averaged column density of SiH. This suggests that the fractional abundance of SiH in the extended ridge is no more than twice that in the hot core.
astro-ph/0606496 [abs, ps, pdf, other] :: Title: Low Mach Number Modeling of Type Ia Supernovae. II. Energy Evolution
Authors: A. S. Almgren, J. B. Bell, C. A. Rendleman, M. Zingale
Comments: 30 pages; accepted to the Astrophysical Journal

The convective period leading up to a Type Ia supernova (SN Ia) explosion is characterized by very low Mach number flows, requiring hydrodynamical methods well-suited to long-time integration. We continue the development of the low Mach number equation set for stellar scale flows by incorporating the effects of heat release due to external sources. Low Mach number hydrodynamics equations with a time-dependent background state are derived, and a numerical method based on the approximate projection formalism is presented. We demonstrate through validation with a fully compressible hydrodynamics code that this low Mach number model accurately captures the expansion of the stellar atmosphere as well as the local dynamics due to external heat sources. This algorithm provides the basis for an efficient simulation tool for studying the ignition of SNe Ia.
astro-ph/0606497 [abs, ps, pdf, other] :: Title: The Planets-Capture Model of V838 Monocerotis
Authors: Alon Retter (Penn State University), Bing Zhang (University of Nevada, Las Vegas), Lionel Siess (Universite Libre de Bruxelles), Amir Levinson (Tel Aviv University), Ariel Marom (Rafael Institute)
Comments: 9 pages, uses asp2004.sty, an invited talk in the conference on V838 Mon, La Palma, Spain, May 2006, to appear in ASP Conf. Ser., The Nature of V838 Mon and Its Light Echo, eds. R.L.M. Corradi and U. Munari

The planets capture model for the eruption of V838 Mon is discussed. We used three methods to estimate the location where the planets were consumed. There is a nice consistency for the results of the three different methods, and we find that the typical stopping / slowing radius for the planets is about 1Ro. The three peaks in the optical light curve of V838 Mon are either explained by the swallowing of three planets at different radii or by three steps in the slowing down process of a single planet. We discuss the other models offered for the outburst of V838 Mon, and conclude that the binary merger model and the planet/s scenario seem to be the most promising. These two models have several similarities, and the main differences are the stellar evolutionary stage, and the mass of the accreted material. We show that the energy emitted in the V838 Mon event is consistent with the planets scenario. We suggest a few explanations for the trigger for the outburst and for the double structure of the optical peaks in the light curve of V838 Mon.
astro-ph/0606498 [abs, ps, pdf, other] :: Title: Detection of additional Wolf-Rayet stars in the starburst cluster Westerlund 1 with SOAR
Authors: J. H. Groh (1,2), A. Damineli (1), M. Teodoro (1), C. L. Barbosa (3) ((1) IAG/USP, (2) University of Pittsburgh, (3) IP&D-Univap)
Comments: 5 pages, 4 figures, submitted to A&A

We report the detection of 3 additional Wolf-Rayet stars in the young cluster Westerlund 1. They were selected as emission-line star candidates based on 1 micron narrow-band imaging of the cluster carried out at OPD/LNA (Brazil), and then confirmed as Wolf-Rayet stars by K-band spectroscopy performed at the 4.1 m SOAR telescope (Chile). Together with previous works, this increases the population of Wolf-Rayet stars detected in the cluster to 22 members. Moreover, it is presented for the first time a K-band spectrum of the luminous blue variable W243, which apparently implies in a higher temperature than that derived from optical spectra taken in 2003. The WC9 star WR-F was also observed, showing clear evidence of dust emission in the K-band.
astro-ph/0606499 [abs, ps, pdf, other] :: Title: Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope
Authors: The Nearby Supernova Factory Collaboration: G. Aldering, P. Antilogus, S. Bailey, C. Baltay, A. Bauer, N. Blanc, S. Bongard, Y. Copin, E. Gangler, S. Gilles, R. Kessler, D. Kocevski, B. C. Lee, S. Loken, P. Nugent, R. Pain, E. Pecontal, R. Pereira, S. Perlmutter, D. Rabinowitz, G. Rigaudier, R. Scalzo, G. Smadja, R. C. Thomas, L. Wang, B. A. Weaver
Comments: 50 pages, 12 figures; accepted to ApJ. Note: online abstract is abbreviated

We report Nearby Supernova Factory observations of SN 2005gj, the second confirmed case of a "hybrid" Type Ia/IIn supernova. Our early-phase photometry of SN 2005gj shows that the interaction is much stronger than for the prototype, SN 2002ic. Our first spectrum shows a hot continuum with broad and narrow H-alpha emission. Later spectra, spanning over 4 months from outburst, show clear Type Ia features combined with broad and narrow H-gamma, H-beta, H-alpha and HeI 5876,7065 in emission. At higher resolution, P Cygni profiles are apparent. Surprisingly, we also observe an inverted P Cygni profile for [OIII] 5007. We find that the lightcurve and measured velocity of the unshocked circumstellar material imply mass loss as recently as 8 years ago. The early lightcurve is well-described by a flat radial density profile for the circumstellar material. However, our decomposition of the spectra into Type Ia and shock emission components allows for little obscuration of the supernova, suggesting an aspherical or clumpy distribution for the circumstellar material. We suggest that the emission line velocity profiles arise from electron scattering rather than the kinematics of the shock. This is supported by the inferred high densities, and the lack of evidence for evolution in the line widths. Ground- and space-based photometry, and Keck spectroscopy, of the host galaxy are used to ascertain that the host galaxy has low metallicity Z/Zsun < 0.3; (95% confidence) and that this galaxy is undergoing a significant star formation event that began roughly 200+/-70 Myr ago. We discuss the implications of these observations for progenitor models and cosmology using Type Ia supernovae.
astro-ph/0606500 [abs, ps, pdf, other] :: Title: On the Perils of Curve-of-Growth Analysis: Systematic Abundance Underestimates for the Gas in Gamma-Ray Burst Host Galaxies
Authors: Jason X. Prochaska (UCO/Lick Observatory)
Comments: 9 pages, 9 figures. Accepted to ApJ

We examine the practice of deriving interstellar medium (ISM) abundances from low-resolution spectroscopy of GRB afterglows. We argue that the multi-ion single-component curve-of-growth analysis technique systematically underestimates the column densities of the metal-line profiles commonly observed for GRB. This systematic underestimate is accentuated by the fact that many GRB line-profiles (e.g. GRB 050730, GRB 050820, GRB 051111) are comprised of `clouds' with a bi-modal distribution of column density. Such line-profiles may be characteristic of a sightline which penetrates both a high density star-forming region and more distant, ambient ISM material. Our analysis suggests that the majority of abundances reported in the literature are systematically underestimates and that the reported errors are frequently over-optimistic. Further, we demonstrate that one cannot even report precise relative abundances with confidence. The implications are profound for our current understanding on the metallicity, dust-to-gas ratio, and chemical abundances of the ISM in GRB host galaxies. For example, we argue that all but a few sightlines allow for the gas to have at least solar metallicity. Finally, we suggests new approaches for constraining the abundances.
astro-ph/0606501 [abs, ps, pdf, other] :: Title: The Recurrent Eclipse of an Unusual Pre--Main-Sequence Star in IC 348
Authors: S. Nordhagen, W. Herbst, E. C. Williams, E. Semkov
Comments: Accepted for publication in ApJ (Letters)

The recurrence of a previously documented eclipse of a solar-like pre--main-sequence star in the young cluster IC 348 has been observed. The recurrence interval is 4.7 $\pm 0.1$ yr and portions of 4 cycles have now been seen. The duration of each eclipse is at least 3.5 years, or $\sim 75$% of a cycle, verifying that this is not an eclipse by a stellar companion. The light curve is generally symmetric and approximately flat-bottomed. Brightness at maximum and minimum have been rather stable over the years but the light curve is not perfectly repetitive or smooth and small variations exist at all phases. We confirm that the star is redder when fainter. Models are discussed and it is proposed that this could be a system similar to KH 15D in NGC 2264. Specifically, it may be an eccentric binary in which a portion of the orbit of one member is currently occulted during some binary phases by a circumbinary disk. The star deserves sustained observational attention for what it may reveal about the circumstellar environment of low-mass stars of planet-forming age.
astro-ph/0606502 [abs, ps, pdf, other] :: Title: Integral Field Spectroscopy of the Extended Emission-Line Region of 3C 249.1
Authors: Hai Fu, Alan Stockton (IfA Hawaii)
Comments: submitted to ApJ. 7 pages including 7 figures

We present Gemini Multiobject Spectrograph (GMOS) integral field spectroscopy of the extended emission-line region associated with quasar 3C 249.1. The complex global kinematics revealed by the velocity field of the [O III] 5007 line cannot be explained by a simple dynamical model, but the local velocity fields of some distinct emission clouds appear to be consistent with simple rotating disks. The temperatures of the ionized gas appear uniform (varying from ~12000 to 15000 K), while the densities vary from a few tens to a few hundreds cm^{-3}. The emission mechanism of all of the emission clouds, as indicated by the line-ratio diagnostics, is consistent both with ``shock + precursor" and pure photoionization models. The total mass of the ionized gas is on the order of 10^9 M_Sun. We estimate the total kinetic energy and momentum of 2.5*10^{57} M_9 v_{500}^2 ergs and 10^{50} M_9 v_{500} dyne s, respectively. By comparing the injection rates of kinetic energy and momentum of different galactic wind models with the observation, we argue that the emission-line regions are most likely a direct result from the feedback of the quasar. We also discuss the nature of the extended X-ray emission surrounding the quasar.
astro-ph/0606503 [abs, ps, pdf, other] :: Title: The new HiVIS spectropolarimeter and spectropolarimetric calibration of the AEOS telescope
Authors: D.M. Harrington, J.R. Kuhn, K. Whitman
Comments: PASP 118, June 2006

We designed, built, and calibrated a new spectropolarimeter for the HiVIS spectrograph (R 12000-49000) on the AEOS telescope. We also did a polarization calibration of the telescope and instrument. We will introduce the design and use of the spectropolarimeter as well as a new data reduction package we have developed, then discuss the polarization calibration of the spectropolarimeter and the AEOS telescope. We used observations of unpolarized standard stars at many pointings to measure the telescope induced polarization and compare it with a Zemax model. The telescope induces polarization of 1-6% with a strong variation with wavelength and pointing, consistent with the altitude and azimuth variation expected. We then used scattered sunlight as a linearly polarized source to measure the telescopes spectropolarimetric response to linearly polarized light. We then made an all-sky map of the telescope's polarization response to calibrate future spectropolarimetry.
astro-ph/0606504 [abs, ps, pdf, other] :: Title: Standing Accretion Shocks in the Supernova Core: Effects of Convection and Realistic EOS
Authors: Tatsuya Yamasaki, Shoichi Yamada
Comments: accepted by ApJ, 20 pages, 8 figures

We investigated the structure of the spherically symmetric accretion flows through the standing shock wave onto the proto-neutron star in the post-bounce phase of the collapse-driven supernova. We assume that the accretion flow is in a steady state controlled by the neutrino luminosity and mass accretion rate that are kept constant. We obtain solutions of the steady Euler equations for a wide range of neutrino luminosity and mass accretion rate. We employ a realistic EOS and neutrino-heating rates. More importantly, we take into account the effect of convection phenomenologically. For each mass accretion rate, we find the critical neutrino luminosity, above which there exists no steady solution. These critical points are supposed to mark the onset of the shock revival. As the neutrino luminosity increases for a given mass accretion rate, there appears a convectively unstable region at some point before the critical value is reached. We introduce a phenomenological energy flux by convection so that the negative entropy gradient should be canceled out. We find that the convection lowers the critical neutrino luminosity substantially. We also consider the effect of the self-gravity. It is found that the self-gravity is important only when the neutrino luminosity is high. The critical luminosity, however, is little affected if the energy transport by convection is taken into account.
astro-ph/0606505 [abs, ps, pdf, other] :: Title: Transients from Initial Conditions in Cosmological Simulations
Authors: M. Crocce, S. Pueblas, R. Scoccimarro
Comments: 14 pages, 14 figures, code to generate 2LPT initial conditions available at this http URL

We study the impact of setting initial conditions in numerical simulations using the standard procedure based on the Zel'dovich approximation (ZA). As it is well known from perturbation theory, ZA initial conditions have incorrect second and higher-order growth and therefore excite long-lived transients in the evolution of the statistical properties of density and velocity fields. We also study the improvement brought by using more accurate initial conditions based on second-order Lagrangian perturbation theory (2LPT). We show that 2LPT initial conditions reduce transients significantly and thus are much more appropriate for numerical simulations devoted to precision cosmology. Using controlled numerical experiments with ZA and 2LPT initial conditions we show that simulations started at redshift z_i=49 using the ZA underestimate the power spectrum in the nonlinear regime by about 2,4,8 % at z=0,1,3 respectively, whereas the mass function of dark matter halos is underestimated by 5% at m=10^15 M_sun/h (z=0) and 10% at m=2x10^14M_sun/h (z=1). The clustering of halos is also affected to the few percent level at z=0. These systematics effects are typically larger than statistical uncertainties in recent mass function and power spectrum fitting formulae extracted from numerical simulations. At large scales, the measured transients in higher-order correlations can be understood from first principle calculations based on perturbation theory.
astro-ph/0606506 [abs, ps, pdf, other] :: Title: Strong gravitational lens probability in TeVeS
Authors: Da-Ming Chen, HongSheng Zhao
Comments: 5 pages, 4 figures, submitted to ApJL

We calculate the strong lensing probability with the image-separation greater than a given value $\Delta\theta$ and the image flux ratio $q_r$ less than 10 in a TeVeS (tensor-vector-scalar) cosmology, which is a relativistic version of the MOND (modified Newtonian dynamics). The lensing galaxy is modeled by the Hernquist profile. We assume a flat cosmology with $\Omega_b=0.04$ and the simplest interpolating function $\mu(x)$ with $\mu(x)=x$ for $x<1$ and $\mu(x)=1$ for $x>1$. Our calculations show that MOND exhibits a very high lengsing efficiency compared with the CDM paradigm. In order to match the well defined sample of the combined radio Cosmic Lens All-Sky Survey (CLASS) and Jodrell Bank/Very Large Array Astrometric Survey (JVAS), the upper limit of the mass of galaxies should be $1.7\times 10^{11} M_\sun$. The galaxies produce much more large image-separation lenses in MOND regime than that in CDM regime, while at small image-separation both regimes match the observational data well.
astro-ph/0606507 [abs, ps, pdf, other] :: Title: Simulation for KM3NeT using ANTARES-Software
Authors: S. Kuch (Erlangen - Nuremberg U.)
Comments: Presented at VLVnT2 Workshop, Catania, Siciliy, Italy, 8-11 Nov 2005

The KM3NeT project is a common European effort for the design of a km3-scale deep-sea neutrino telescope in the Mediterranean. For the upcoming Design Study simulations have been done using modified ANTARES software. Several concepts and ideas have been tested for their merits and feasibility.
astro-ph/0606508 [abs, ps, pdf, other] :: Title: On the Nature of Part Time Radio Pulsars
Authors: Xiang-Dong Li
Comments: 9 pages, accepted to ApJL

The recent discovery of rotating radio transients and the quasi-periodicity of pulsar activity in the radio pulsar PSR B1931$+$24 has challenged the conventional theory of radio pulsar emission. Here we suggest that these phenomena could be due to the interaction between the neutron star magnetosphere and the surrounding debris disk. The pattern of pulsar emission depends on whether the disk can penetrate the light cylinder and efficiently quench the processes of particle production and acceleration inside the magnetospheric gap. A precessing disk may naturally account for the switch-on/off behavior in PSR B1931$+$24.
astro-ph/0606509 [abs, ps, pdf, other] :: Title: On the dependence of the spectral parameters on the observational conditions in homogeneous time dependent models of the TeV blazars
Authors: Ludovic Sauge, Gilles Henri
Comments: Letter to Editor, accepted for publication in A&A

Most of current models of TeV blazars emission assume a Synchrotron Self-Compton mechanism where relativistic particles emit both synchrotron radiation and Inverse Compton photons. For sake of simplicity, these models usually consider only steady state emission. The spectral features are thus only related to the shape of the particle distribution, and do not depend on the timing of observations. In this letter, we study the effect of, firstly, the lag between the beginning of the injection of the fresh particles and the trigger of the observation, and secondly, of a finite injection duration. We illustrate these effects considering an analytical time-dependent model of the synchrotron emission by a monoenergetic distribution of leptons. We point out that the spectral shape can be in fact very dependent on observational conditions if the particle injection term is time-dependent, particularly taking into account the effect of the time averaging procedure on the final shape of the SED. Consequences on the acceleration process are also discussed.
astro-ph/0606510 [abs, ps, pdf, other] :: Title: Linear Stability of Ring Systems
Authors: Robert J. Vanderbei
Comments: 8 pages, associated website is this http URL

Consider the planar (n+1)-body problem consisting of a large central body of mass M surrounded by a large number, n, of smaller bodies each having a common mass $m$ distributed uniformly in a circle of radius r and in circular orbit about the central body. By analyzing the situation where one of the smaller bodies is perturbed from this ideal configuration, a linear stability analysis shows that the system is linearly stable if m <= 0.982 M/n^3 . Numerical simulation indicates that this stability threshold is correct to within a factor of about 2.
astro-ph/0606511 [abs, ps, pdf, other] :: Title: The CMB polarization: status and prospects
Authors: Amedeo Balbi, Paolo Natoli, Nicola Vittorio
Comments: 20 pages, 5 figures. Invited review article, to appear in the volume "Cosmic Polarization", ed. R. Fabbri (RSP)

The study of cosmic microwave background (CMB) polarization is still in a pioneering stage, but promises to bring a huge advancement in cosmology in the near future, just as high-accuracy observations of the anisotropies in the total intensity of the CMB revolutionized our understanding of the universe in the past few years. In this contribution, we outline the scientific case for observing CMB polarization, and review the current observational status and future experimental prospects in the field.
astro-ph/0606512 [abs, ps, pdf, other] :: Title: Cosmological quests in the CMB sky
Authors: Tarun Souradeep (IUCAA)
Comments: Plenary talk at the International Conference on Einstein's Legacy in the New Millennium, December 15 - 22, 2005, Puri, India; to appear in the Proceedings to be published in IJMPD; 18 pages, 7 figures

Observational Cosmology has indeed made very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation Measurements of CMB anisotropy and, more recently, polarization have played a very important role. Besides precise determination of various parameters of the `standard' cosmological model, observations have also established some important basic tenets that underlie models of cosmology and structure formation in the universe -- `acausally' correlated initial perturbations in a flat, statistically isotropic universe, adiabatic nature of primordial density perturbations. These are consistent with the expectation of the paradigm of inflation and the generic prediction of the simplest realization of inflationary scenario in the early universe. Further, gravitational instability is the established mechanism for structure formation from these initial perturbations. In the next decade, future experiments promise to strengthen these deductions and uncover the remaining crucial signature of inflation -- the primordial gravitational wave background.
astro-ph/0606513 [abs, ps, pdf, other] :: Title: A new method for the spectroscopic identification of stellar non-radial pulsation modes. I. The method and numerical tests
Authors: W. Zima
Comments: 12 pages, 14 figures

We present the Fourier parameter fit method, a new method for spectroscopically identifying stellar radial and non-radial pulsation modes based on the high-resolution time-series spectroscopy of absorption-line profiles. In contrast to previous methods this one permits a quantification of the statistical significance of the computed solutions. The application of genetic algorithms in seeking solutions makes it possible to search through a large parameter space. The mode identification is carried out by minimizing chi-square, using the observed amplitude and phase across the line profile and their modeled counterparts. Computations of the theoretical line profiles are based on a stellar displacement field, which is described as superposition of spherical harmonics and that includes the first order effects of the Coriolis force. We made numerical tests of the method on a grid of different mono- and multi-mode models for 0 <= l <= 4 in order to explore its capabilities and limitations. Our results show that whereas the azimuthal order m can be unambiguously identified for low-order modes, the error of l is in the range of pm 1. The value of m can be determined with higher precision than with other spectroscopic mode identification methods. Improved values for the inclination can be obtained from the analysis of non-axisymmetric pulsation modes. The new method is ideally suited to intermediatley rotating Delta Scuti and Beta Cephei stars.
astro-ph/0606514 [abs, ps, pdf, other] :: Title: Elevation angle dependence of the SMA antenna focus position
Authors: Satoki Matsushita (1,3), Masao Saito (2,3), Kazushi Sakamoto (2,3), Todd R. Hunter (3), Nimesh A. Patel (3), Tirupati K. Sridharan (3), Robert W. Wilson (3) ((1) ASIAA, (2) NAOJ, (3) CfA)
Comments: 10 pages, 6 figures; to appear in the Proceedings of SPIE Vol. 6275 "Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III"

We report the measurement results and compensation of the antenna elevation angle dependences of the Sub-millimeter Array (SMA) antenna characteristics. Without optimizing the subreflector (focus) positions as a function of the antenna elevation angle, antenna beam patterns show lopsided sidelobes, and antenna efficiencies show degradations. The sidelobe level increases and the antenna efficiencies decrease about 1% and a few %, respectively, for every 10 degrees change in the elevation angle at the measured frequency of 237 GHz. We therefore obtained the optimized subreflector positions for X (azimuth), Y (elevation), and Z (radio optics) focus axes at various elevation angles for all the eight SMA antennas. The X axis position does not depend on the elevation angle. The Y and Z axes positions depend on the elevation angles, and are well fitted with a simple function for each axis with including a gravity term (cosine and sine of elevation, respectively). In the optimized subreflector positions, the antenna beam patterns show low level symmetric sidelobe of at most a few %, and the antenna efficiencies stay constant at any antenna elevation angles. Using one set of fitted functions for all antennas, the SMA is now operating with real-time focusing, and showing constant antenna characteristics at any given elevation angle.
astro-ph/0606515 [abs, ps, pdf, other] :: Title: A new method for the spectroscopic identification of stellar non-radial pulsation modes. II. Mode identification of the Delta Scuti star FG Virginis
Authors: W. Zima, D. Wright, J. Bentley, P.L. Cottrell, U. Heiter, P. Mathias, E. Poretti, H. Lehmann, T.J. Montemayor, M. Breger
Comments: 14 pages, 26 figures

We present a mode identification based on new high-resolution time-series spectra of the non-radially pulsating Delta Scuti star FG~Vir (HD 106384, V = 6.57, A5V). From 2002 February to June a global Delta Scuti Network (DSN) campaign, utilizing high-resolution spectroscopy and simultaneous photometry has been conducted for FG~Vir in order to provide a theoretical pulsation model. In this campaign we have acquired 969 Echelle spectra covering 147 hours at six observatories. The mode identification was carried out by analyzing line profile variations by means of the Fourier parameter fit method, where the observational Fourier parameters across the line are fitted with theoretical values. This method is especially well suited for determining the azimuthal order m of non-radial pulsation modes and thus complementary with the method of Daszynska-Daszkiewicz (2002) which does best at identifying the degree l. 15 frequencies between 9.2 and 33.5 c/d were detected spectroscopically. We determined the azimuthal order m of 12 modes and constrained their harmonic degree l. Only modes of low degree (l <= 4) were detected, most of them having axisymmetric character mainly due to the relatively low projected rotational velocity of FG Vir. The detected non-axisymmetric modes have azimuthal orders between -2 and 1. We derived an inclination of 19 degrees, which implies an equatorial rotational rate of 66 km/s.
astro-ph/0606516 [abs, ps, pdf, other] :: Title: The Minimum Description Length Principle and Model Selection in Spectropolarimetry
Authors: A. Asensio Ramos (IAC)
Comments: Accepted for publication in the Astrophysical Journal

It is shown that the two-part Minimum Description Length Principle can be used to discriminate among different models that can explain a given observed dataset. The description length is chosen to be the sum of the lengths of the message needed to encode the model plus the message needed to encode the data when the model is applied to the dataset. It is verified that the proposed principle can efficiently distinguish the model that correctly fits the observations while avoiding over-fitting. The capabilities of this criterion are shown in two simple problems for the analysis of observed spectropolarimetric signals. The first is the de-noising of observations with the aid of the PCA technique. The second is the selection of the optimal number of parameters in LTE inversions. We propose this criterion as a quantitative approach for distinguising the most plausible model among a set of proposed models. This quantity is very easy to implement as an additional output on the existing inversion codes.
astro-ph/0606517 [abs, ps, pdf, other] :: Title: Confirmation of the Planet Hypothesis for the Long-period Radial Velocity Variations of Beta Geminorum
Authors: A.P. Hatzes, W.D. Cochran, M. Endl E.W. Guenther, S.H. Saar, G.A.H. Walker, S. Yang, M. Hartmann, M. Esposito, D.B. Paulson
Comments: 10 pages, 9 figures, Astronomy and Astrophysics, in press

We present precise stellar radial velocity measurements for the K giant star Beta Gem spanning over 25 years. These data show that the long period low amplitude radial velocity variations found by Hatzes & Cochran (1993) are long-lived and coherent. An examination of the Ca II K emission, spectral line shapes from high resolution data (R = 210,000), and Hipparcos photometry show no significant variations of these quantities with the RV period. These data confirm the planetary companion hypothesis suggested by Hatzes & Cochran (1993). An orbital solution assuming a stellar mass of 1.7 M_sun yields a period, P = 589.6 days, a minimum mass of 2.3 M_Jupiter, and a semi-major axis, and a = 1.6 AU. The orbit is nearly circular (e = 0.02). Beta Gem is the seventh intermediate mass star shown to host a sub-stellar companion and suggests that planet-formation around stars much more massive than the sun may common.
astro-ph/0606518 [abs, ps, pdf, other] :: Title: Radial Velocity Studies of Southern Close Binary Stars.I
Authors: Slavek M. Rucinski, Hilmar Duerbeck
Comments: to appear in AJ October 2006; 3 figures

Radial-velocity measurements and sine-curve fits to the orbital velocity variations are presented for nine contact binaries, V1464 Aql, V759 Cen, DE Oct, MW Pav, BQ Phe, EL Aqr, SX Crv, VZ Lib, GR Vir; for the first five among these, our observations are the first available radial velocity data. Among three remaining radial velocity variables, CE Hyi is a known visual binary, while CL Cet and V1084 Sco are suspected to be multiple systems where the contact binary is spectrally dominated by its companion (which itself is a binary in V1084 Sco). Five additional variables, V872 Ara, BD Cap, HIP 69300, BX Ind, V388 Pav, are of unknown type, but most are pulsating stars; we give their mean radial velocities and Vsini.
astro-ph/0606519 [abs, ps, pdf, other] :: Title: The hierarchical formation of the brightest cluster galaxies
Authors: Gabriella De Lucia, Jeremy Blaizot
Comments: 13 pages, 17 figures, submitted to MNRAS

We use semi-analytic techniques to study the formation and evolution of brightest cluster galaxies (BCGs). We show the extreme hierarchical nature of these objects and discuss the limits of simple ways to capture their evolution. In a model where cooling flows are suppressed at late times by AGN activity, the stars of BCGs are formed very early (50 per cent at z~5, 80 per cent at z~3) and in many small galaxies. The high star formation rates in these high-z progenitors are fuelled by rapid cooling, not by merger-triggered starbursts. We find that model BCGs assemble surprisingly late: half their final mass is typically locked-up in a single galaxy after z~0.5. Because most of the galaxies accreted onto BCGs have little gas content and red colours, late mergers do not change the apparent age of BCGs. It is this accumulation of a large number of old stellar populations -- driven mainly by the merging history of the dark matter halo itself -- that yields the observed homogeneity of BCG properties. In the second part of the paper, we discuss the evolution of BCGs to high redshifts, from both observational and theoretical viewpoints. We show that our model BCGs are in qualitative agreement with high-z observations. We discuss the hierarchical link between high-z BCGs and their local counter-parts. We show that high-z BCGs belong to the same population as the massive end of local BCG progenitors, although they are not in general the same galaxies. Similarly, high-z BCGs end-up as massive galaxies in the local Universe, although only a fraction of them are actually BCGs of massive clusters.
astro-ph/0606520 [abs, ps, pdf, other] :: Title: Interacting models of soft coincidence
Authors: Sergio del Campo, Ramon Herrera, German Olivares, Diego Pavon
Comments: 18 pages, 9 figures; to be published in the Physical Review, section D

The coincidence problem of late cosmic acceleration is a serious riddle in connection with our understanding of the evolution of the Universe. In this paper we show that an interaction between the dark energy component (either phantom or quintessence) and dark matter can alleviate it. In this scenario the baryon component is independently conserved. This generalizes a previous study [S. del Campo, R. Herrera, and D. Pavon, Phys. Rev. D 71, 123529 (2005)] in which neither baryons nor phantom energy were considered.
astro-ph/0606521 [abs, ps, pdf, other] :: Title: The Different Environmental Dependencies of Star-formation for Giant and Dwarf Galaxies
Authors: C. P. Haines, F. La Barbera, A. Mercurio, P. Merluzzi, G. Busarello (INAF-OAC, Naples)
Comments: 4 pages, 4 figures, accepted for publication in ApJL

We examine the origins of the bimodality observed in the global properties of galaxies around a stellar mass of 3x10^10 M_sun by comparing the environmental dependencies of star-formation for the giant and dwarf galaxy populations. The Sloan Digital Sky Survey DR4 spectroscopic dataset is used to produce a sample of galaxies in the vicinity of the supercluster centered on the cluster A2199 at z=0.03 that is ~90% complete to a magnitude limit of M*+3.3. From these we measure global trends with environment for both giant (M_r<-20 mag) and dwarf (-19<M_r<-17.8 mag) subsamples using the luminosity-weighted mean stellar age and H_alpha emission as independent measures of star-formation history. The fraction of giant galaxies classed as old (t>7 Gyr) or passive (EW[H_alpha]<4 A) falls gradually from ~80% in the cluster cores to ~40% in field regions beyond 3-4 R_virial, as found in previous studies. In contrast, we find that the dwarf galaxy population shows a sharp transition at ~1 R_virial, from being predominantly old/passive within the cluster, to outside where virtually all galaxies are forming stars and old/passive galaxies are only found as satellites to more massive galaxies. These results imply fundamental differences in the evolution of giant and dwarf galaxies: whereas the star-formation histories of giant galaxies are determined primarily by their merger history, star-formation in dwarf galaxies is much more resilient to the effects of major mergers. Instead dwarf galaxies become passive only once they become satellites within a more massive halo, by losing their halo gas reservoir to the host halo, or through other environment-related processes such as galaxy harassment and/or ram-pressure stripping.
astro-ph/0606522 [abs, ps, pdf, other] :: Title: Meteorologic parameters analysis above Dome C made with ECMWF data
Authors: K. Geissler (1,3), E. Masciadri (2,3) ((1) ESO, Santiago del Chile, Chile (2) INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy (3) Max-Planck Institut fur Astronomie, Heidelberg, Germany)
Comments: 28 pages, 14 figures, pdf file, to be published on July 2006 - PASP, see also this http URL

In this paper we present the characterization of all the principal meteorological parameters (wind speed and direction, pressure, absolute and potential temperature) extended over 25 km from the ground and over two years (2003 and 2004) above the Antarctic site of Dome C. The data set is composed by 'analyses' provided by the General Circulation Model (GCM) of the European Center for Medium Weather Forecasts (ECMWF) and they are part of the catalog MARS. A monthly and seasonal (summer and winter time) statistical analysis of the results is presented. The Richardson number is calculated for each month of the year over 25 km to study the stability/instability of the atmosphere. This permits us to trace a map indicating where and when the optical turbulence has the highest probability to be triggered on the whole troposphere, tropopause and stratosphere. We finally try to predict the best expected isoplanatic angle and wavefront coherence time employing the Richardson number maps, the wind speed profiles and simple analytical models of CN2 vertical profiles.
astro-ph/0606523 [abs, ps, pdf, other] :: Title: The conversion of Neutron star to Strange star : A two step process
Authors: Abhijit Bhattacharyya, Sanjay K. Ghosh, Partha S. Joardar, Ritam Mallick, Sibaji Raha
Comments: 18 pages including 9 figures

The conversion of neutron matter to strange matter in a neutron star have been studied as a two step process. In the first step, the nuclear matter gets converted to two flavour quark matter. The conversion of two flavour to three flavour strange matter takes place in the second step. The first process is analysed with the help of equations of state and hydrodynamical equations, whereas, in the second process, non-leptonic weak interaction plays the main role. Velocities and the time of travel through the star of these two conversion fronts have been analysed and compared.
astro-ph/0606524 [abs, ps, pdf, other] :: Title: Quark matter and the masses and radii of compact stars
Authors: Mark Alford, David Blaschke, Alessandro Drago, Thomas Klahn, Giuseppe Pagliara, Juergen Schaffner-Bielich
Comments: 3 pages, LaTeX

Ozel, in a recent reanalysis of EXO 0748-676 observational data (astro-ph/0605106), concluded that quark matter probably does not exist in the center of compact stars. We show that the data is actually consistent with the presence of quark matter in compact stars.
astro-ph/0606525 [abs, ps, pdf, other] :: Title: The Role of Evolutionary Age and Metallicity in the Formation of Classical Be Circumstellar Disks I. New Candidate Be Stars in the LMC, SMC, and Milky Way
Authors: John P. Wisniewski (1), Karen S. Bjorkman (2); ((1) USRA/NASA GSFC, (2) University of Toledo)
Comments: 42 pages (4 figures, 9 tables), accepted in ApJ; online-only figures and table available at this http URL

We present B, V, R, and H alpha photometry of 8 clusters in the Small Magellanic Cloud, 5 in the Large Magellanic Cloud, and 3 Galactic clusters, and use 2 color diagrams (2-CDs) to identify candidate Be star populations in these clusters. We find evidence that the Be phenomenon is enhanced in low metallicity environments, based on the observed fractional early-type candidate Be star content of clusters of age 10-25 Myr. Numerous candidate Be stars of spectral types B0 to B5 were identified in clusters of age 5-8 Myr, challenging the suggestion of Fabregat & Torrejon (2000) that classical Be stars should only be found in clusters at least 10 Myr old. These results suggest that a significant number of B-type stars must emerge onto the zero-age-main-sequence as rapid rotators. We also detect an enhancement in the fractional content of early-type candidate Be stars in clusters of age 10-25 Myr, suggesting that the Be phenomenon does become more prevalent with evolutionary age. We briefly discuss the mechanisms which might contribute to such an evolutionary effect. A discussion of the limitations of utilizing the 2-CD technique to investigate the role evolutionary age and/or metallicity play in the development of the Be phenomenon is offered, and we provide evidence that other B-type objects of very different nature, such as candidate Herbig Ae/Be stars may contaminate the claimed detections of ``Be stars'' via 2-CDs.
astro-ph/0606526 [abs, ps, pdf, other] :: Title: The slope of the GRB Variability/Peak Luminosity Correlation
Authors: C. Guidorzi (1,2), F. Frontera (2,3), E. Montanari (2,4), F. Rossi (2), L. Amati (3), A. Gomboc (5), C.G. Mundell (1) ((1) Liverpool John Moores University, UK, (2) Physics Dept. University of Ferrara, Italy, (3) Istituto di Astrofisica Spaziale e Fisica Cosmica, Bologna/INAF, Italy, (4) ITA "Calvi", Finale Emilia (MO) Italy, (5) Faculty of Mathematics and Physics, University of Ljubljana, Slovenia)
Comments: 9 pages, 10 figures, accepted by MNRAS

From a sample of 32 GRBs with known redshift (Guidorzi et al. 2005) and then a sample of 551 BATSE GRBs with derived pseudo-redshift (Guidorzi 2005), the time variability/peak luminosity correlation (V vs. L) found by Reichart et al. (2001) was tested. For both samples the correlation is still found but less relevant due to a much higher spread of the data. Assuming a straight line in the logL-logV plane (logL = m logV + b), as done by Reichart et al., the slope was found lower than that derived by Reichart et al.: m = 1.3_{-0.4}^{+0.8} (Guidorzi et al. 2005), m = 0.85 +- 0.02 (Guidorzi 2005), to be compared with m = 3.3^{+1.1}_{-0.9} (Reichart et al. 2001). Reichart & Nysewander (2005) attribute the different slope to the fact we do not take into account in the fit the variance of the sample, and demonstrate that, using the method by Reichart (2001), the data set of Guidorzi et al. (2005) in logL-logV plane is still well described with slope m = 3.4^{+0.9}_{-0.6}. Here we compare the results of two methods accounting for the variance of the sample, that implemented by Reichart (2001) and that by D'Agostini (2005). We demonstrate that the method by Reichart (2001) provides an inconsistent estimate of the slope when the sample variance is comparable with the interval of values covered by the variability. We also show that, using the D'Agostini method, the slope is consistent with that derived by us earlier and inconsistent with that derived by Reichart & Nysewander (2005). Finally we discuss the implications on the interpretations and show that our results are in agreement with the peak energy/variability correlation found by Lloyd-Ronning & Ramirez-Ruiz (2002) and the peak energy/peak luminosity correlation (Yonetoku et al. 2004; Ghirlanda et al. 2005) [abridged].
astro-ph/0606527 [abs, ps, pdf, other] :: Title: Lyman Break Galaxies Under a Microscope: The Small Scale Dynamics and Mass of an Arc in the Cluster 1E0657-56
Authors: N.P.H. Nesvadba, M.D. Lehnert, F. Eisenhauer, R. Genzel, S. Seitz, R.I. Davies, R.P. Saglia, D. Lutz, L. Tacconi, R. Bender, R. Abuter
Comments: Accepted for publication in the Astrophysical Journal

Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we have studied the spatially-resolved dynamics in the z=3.2 strongly lensed galaxy 1E0657-56 ``arc+core''. The lensing configuration suggests that the high surface brightness ``core'' is the M=20 magnified central 1 kpc of the galaxy (seen at a spatial resolution of about 200 pc in the source plane), whereas the fainter ``arc'' is a more strongly magnified peripheral region of the same galaxy at about a half-light radius, which otherwise appears to be a typical z=3 Lyman break galaxy.
The overall shape of the position-velocity diagram resembles the ``rotation curves'' of the inner few kpcs of nearby L* spiral galaxies. The projected velocities rise rapidly to 75 km/s within the core. This implies a dynamical mass of M_dyn = 10^9.3 M_sun within the central kpc, and suggests that in this system the equivalent of the mass of a present-day L* bulge at the same radius was already in place by z>=3. Approximating the circular velocity of the halo by the measured asymptotic velocity of the rotation curve, we estimate a dark matter halo mass of M_halo = 10^11.7 +/- 0.3, in good agreement with large-scale clustering studies of Lyman break galaxies. The baryonic collapse fraction is low compared to actively star-forming ``BX'' and low-redshift galaxies around z=2, perhaps implying comparatively less gas infall to small radii or efficient feedback. Even more speculatively, the high central mass density might indicate highly dissipative gas collapse in very early stages of galaxy evolution, in approximate agreement with what is expected for ``inside-out'' galaxy formation models.
astro-ph/0606528 [abs, ps, pdf, other] :: Title: Contour binning: a new technique for spatially-resolved X-ray spectroscopy applied to Cassiopeia A
Authors: J.S. Sanders (IoA, Cambridge)
Comments: Accepted by MNRAS, 14 pages, colour, high quality and B&W versions available at this http URL

We present a new technique for choosing spatial regions for X-ray spectroscopy, called "contour binning". The method chooses regions by following contours on a smoothed image of the object. In addition we re-explore a simple method for adaptively smoothing X-ray images according to the local count rate, we term "accumulative smoothing", which is a generalisation of the method used by FADAPT. The algorithms are tested by applying them to a simulated cluster data set. We illustrate the techniques by using them on a 50 ks Chandra observation of the Cassiopeia A supernova remnant. Generated maps of the object showing abundances in eight different elements, absorbing column density, temperature, ionisation timescale and velocity are presented. Tests show that contour binning reproduces surface brightness considerably better than other methods. It is particularly suited to objects with detailed spatial structure such as supernova remnants and the cores of galaxy clusters, producing aesthetically pleasing results.
astro-ph/0606529 [abs, ps, pdf, other] :: Title: New "Bigs" in cosmology
Authors: Artyom V. Yurov, Prado Martin Moruno, Pedro F. Gonzalez-Diaz
Comments: 7 figures, 13 pages, RevTeX

This paper contains a detailed discussion on new cosmic solutions describing the early and late evolution of a universe that is filled with a kind of dark energy that may or may not satisfy the energy conditions. The main distinctive property of the resulting space-times is that they make to appear twice the single singular events predicted by the corresponding quintessential (phantom) models in a manner which can be made symmetric with respect to the origin of cosmic time. Thus, big bang and big rip singularity are shown to take place twice, one on the positive branch of time and the other on the negative one. We have also considered dark energy and phantom energy accretion onto black holes and wormholes in the context of these new cosmic solutions. It is seen that the space-times of these holes would then undergo swelling processes leading to big trip and big hole events taking place on distinct epochs along the evolution of the universe. In this way, the possibility is considered that the past and future be connected in a non-paradoxical manner in the universes described by means of the new symmetric solutions.
astro-ph/0606530 [abs, ps, pdf, other] :: Title: Extreme gas kinematics in the z=2.2 powerful radio galaxy MRC1138-262: Evidence for efficient AGN feedback in the early Universe?
Authors: N.P.H.Nesvadba, M.D.Lehnert, F.Eisenhauer, A.Gilbert, M.Tecza, R.Abuter
Comments: Accepted for publication in the Astrophysical Journal

To explain the properties of the most massive low-redshift galaxies and the shape of their mass function, recent models of galaxy evolution include strong AGN feedback to complement starburst-driven feedback in massive galaxies. Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we searched for direct evidence for such a feedback in the optical emission line gas around the z=2.16 powerful radio galaxy MRC1138-262, likely a massive galaxy in formation. The kpc-scale kinematics, with FWHMs and relative velocities <= 2400 km/s and nearly spherical spatial distribution, do not resemble large-scale gravitational motion or starburst-driven winds. Order-of-magnitude timescale and energy arguments favor the AGN as the only plausible candidate to accelerate the gas, with a total energy injection of a few x 10^60 ergs or more, necessary to power the outflow, and relatively efficient coupling between radio jet and ISM. Observed outflow properties are in gross agreement with the models, and suggest that AGN winds might have a similar, or perhaps larger, cosmological significance than starburst-driven winds, if MRC1138-262 is indeed archetypal. Moreover, the outflow has the potential to remove significant gas fractions (<= 50%) from a >L* galaxy within a few 10 to 100 Myrs, fast enough to preserve the observed [alpha/Fe] overabundance in massive galaxies at low redshift. Using simple arguments, it appears that feedback like that observed in MRC1138-262 may have sufficient energy to inhibit material from infalling into the dark matter halo and thus regulate galaxy growth as required in some recent models of hierarchical structure formation.
astro-ph/0606531 [abs, ps, pdf, other] :: Title: The Tully-Fisher relation and its evolution with redshift in cosmological simulations of disc galaxy formation
Authors: L. Portinari, J. Sommer-Larsen
Comments: 13 pages, 6 figures, submitted to MNRAS

We present predictions on the evolution of the Tully-Fisher (TF) relation with redshift, based on cosmological N-body/hydrodynamical simulations of disc galaxy formation and evolution. The simulations invoke star formation and stellar feedback, chemical evolution with non-instantaneous recycling, metallicity dependent radiative cooling and effects of a meta-galactic UV field, including simplified radiative transfer.
At z=0, the simulated and empirical TF relations are offset by about 0.4 magnitudes (1 sigma) in the B and I bands. The origin of these offsets is somewhat unclear, but it may not necessarily be a problem of the simulations only.
As to evolution, we find a brightening of the TF relation between z=0 and z=1 of about 0.85 mag in rest-frame B band, with a non-evolving slope. The brightening we predict is intermediate between the (still quite discrepant) observational estimates. This evolution is primarily a luminosity effect, while the stellar mass TF relation shows negligible evolution. The individual galaxies do gain stellar mass between z=1 and z=0, by a 50-100%; but they also correspondingly increase their characteristic circular speed. As a consequence, individually they mainly evolve ALONG the stellar mass TF relation, while the relation as such does not show any significant evolution.
astro-ph/0606532 [abs, ps, pdf, other] :: Title: Spitzer/MIPS Imaging of NGC 650: Probing the History of Mass Loss on the Asymptotic Giant Branch
Authors: Toshiya Ueta
Comments: 9 pages in the emulated ApJ format with 6 figures, to appear in ApJ

We present the far-infrared (IR) maps of a bipolar planetary nebula (PN), NGC 650, at 24, 70, and 160 micron taken with the Multiband Imaging Photometer for Spitzer (MIPS) on-board the Spitzer Space Telescope. While the two-peak emission structure seen in all MIPS bands suggests the presence of a near edge-on dusty torus, the distinct emission structure between the 24 micron map and the 70/160 micron maps indicates the presence of two distinct emission components in the central torus. Based on the spatial correlation of these two far-IR emission components with respect to various optical line emission, we conclude that the 24 micron emission is largely due to the [O IV] line at 25.9 micron arising from highly ionized regions behind the ionization front, whereas the 70 and 160 micron emission is due to dust continuum arising from low-temperature dust in the remnant asymptotic giant branch (AGB) wind shell. The far-IR nebula structure also suggests that the enhancement of mass loss at the end of the AGB phase has occurred isotropically, but has ensued only in the equatorial directions while ceasing in the polar directions. The present data also show evidence for the prolate spheroidal distribution of matter in this bipolar PN. The AGB mass loss history reconstructed in this PN is thus consistent with what has been previously proposed based on the past optical and mid-IR imaging surveys of the post-AGB shells.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Fri, 23 Jun 06 00:00:11 GMT
0606533 -- 0606567 received

astro-ph/0606533 [abs, ps, pdf, other] :: Title: Can A Galaxy Redshift Survey Measure Dark Energy Clustering?
Authors: Masahiro Takada (Tohoku Univ., Japan)
Comments: 14 pages, 7 figures

(abridged) A wide-field galaxy redshift survey allows one to probe galaxy clustering at largest spatial scales, which carries an invaluable information on horizon-scale physics complementarily to the cosmic microwave background (CMB). Assuming the planned survey consisting of z~1 and z~3 surveys with areas of 2000 and 300 square degrees, respectively, we study the prospects for probing dark energy clustering from the measured galaxy power spectrum, assuming the dynamical properties of dark energy are specified in terms of the equation of state and the effective sound speed c_e in the context of an adiabatic cold dark matter (CDM) model. The dark energy clustering adds a power to the galaxy power spectrum amplitude at spatial scales greater than the sound horizon, and the enhancement is sensitive to redshift evolution of the net dark energy density, i.e. the equation of state. We find that the galaxy survey, when combined with Planck, can distinguish dark energy clustering from a smooth dark energy model such as the quintessence model (c_e=1), when c_e<0.04 (0.02) in the case of the constant equation of state w_0=-0.9 (-0.95). An ultimate full-sky survey of z~1 galaxies allows the detection when c_e<0.08 (0.04) for w_0=0.9 (-0.95). We also investigate a degeneracy between the dark energy clustering and the non-relativistic neutrinos implied from the neutrino oscillation experiments, because the two effects both induce a scale-dependent modification in the galaxy power spectrum shape at largest spatial scales accessible from the galaxy survey. It is shown that a wider redshift coverage can efficiently separate the two effects by utilizing the different redshift dependences, where dark energy clustering is apparent only at low redshifts z<1.
astro-ph/0606534 [abs, ps, pdf, other] :: Title: N-flationary magnetic fields
Authors: Mohamed M. Anber, Lorenzo Sorbo
Comments: 12pages

There is increasing interest in the role played by pseudo Nambu-Goldstone bosons (pNGBs) in the construction of string-inspired models of inflation. In these models the inflaton is expected to be coupled to gauge fields, and will lead to the generation of magnetic fields that can be of cosmological interest. We study the production of such fields mainly focusing on the model of N-flation, where the collective effect of several pNGBs drives inflation. Because the produced fields are maximally helical, inverse cascade processes in the primordial plasma increase significantly their coherence length. We discuss under what conditions inflation driven by pNGBs can account for the observed cosmological magnetic fields. A constraint on the parameters of this class of inflationary scenarios is also derived by requiring that the magnetic field does not backreact on the inflating background.
astro-ph/0606535 [abs, ps, pdf, other] :: Title: Averaging Spherically Symmetric Spacetimes in General Relativity
Authors: A. A. Coley, N. Pelavas
Comments: 6 pages

We discuss the averaging problem in general relativity, using the form of the macroscopic gravity equations in the case of spherical symmetry in volume preserving coordinates. In particular, we calculate the form of the correlation tensor under some reasonable assumptions on the form for the inhomogeneous gravitational field and matter distribution. On cosmological scales, the correlation tensor in a Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) background is found to be of the form of a spatial curvature. On astrophysical scales the correlation tensor can be interpreted as the sum of a spatial curvature and an anisotropic fluid. We briefly discuss the physical implications of these results.
astro-ph/0606536 [abs, ps, pdf, other] :: Title: Measuring the Average Evolution of Luminous Galaxies at z<3: The Rest-frame Optical Luminosity Density, Spectral Energy Distribution, and Stellar Mass Density
Authors: Gregory Rudnick, Ivo Labbe, Natascha M. Foerster Schreiber, Stijn Wuyts, Marijn Franx, Kristian Finlator, Mariska Kriek, Alan Moorwood, Hans-Walter Rix, Huub Roettgering, Ignacio Trujillo, Arjen van der Wel, Paul van der Werf, Pieter G. van Dokkum
Comments: Accepted for publication in the Astrophysical Journal, 24 pages, 16 figures

(Abridged) We present the evolution of the volume averaged properties of the rest-frame optically luminous galaxy population to z~3, determined from four disjoint deep fields with optical to near-infrared wavelength coverage. We select galaxies above a rest-frame V-band luminosity of 3x10^10 Lsol and characterize their rest-frame UV through optical properties via the mean spectral energy distribution (SED). To measure evolution we apply the same selection criteria to a sample of galaxies from the Sloan Digital Sky Survey and COMBO-17. The mean rest-frame 2200Ang through V-band SED becomes steadily bluer with increasing redshift but at z<3 the mean SED falls within the range defined by ``normal'' galaxies in the nearby Universe. We measure stellar mass-to-light ratios (Mstar/L) by fitting models to the rest-frame UV-optical SEDs and derive the stellar mass density. The stellar mass density in luminous galaxies has increased by a factor of 3.5-7.9 from z=3 to z=0.1, including field-to-field variance uncertainties. After correcting to total, the measured mass densities at z<2 lie below the integral of the star formation rate (SFR) density as a function of redshift as derived from UV selected samples. This may indicate a systematic error in the mass densities or SFR(z) estimates. We find large discrepancies between recent model predictions for the evolution of the mass density and our results, even when our observational selection is applied to the models. Finally we determine that Distant Red Galaxies (selected to have J_s - K_s>2.3) in our LV selected samples contribute 30% and 64% of the stellar mass budget at z~2 and z~ 2.8 respectively. These galaxies are largely absent from UV surveys and this result highlights the need for mass selection of high redshift galaxies.
astro-ph/0606537 [abs, ps, pdf, other] :: Title: GALEX and Optical Light Curves of EF Eridanus During a Low State: the Puzzling Source of UV Light
Authors: Paula Szkody (1), Thomas E. Harrison (2), Richard M. Plotkin (1), Steve B. Howell (3), Mark Seibert (4), Luciana Bianchi (5) ((1) U of Washington, (2) NMSU, (3) NOAO, (4) Cal Tech, (5) JHU)
Comments: 10 pages, 4 figures to be published in ApJ Letters

Low state optical photometry of EF Eri during an extended low accretion state combined with GALEX near and far UV time-resolved photometry reveals a source of UV flux that is much larger than the underlying 9500K white dwarf, and that is highly modulated on the orbital period. The near UV and optical light curves can be modeled with a 20,000K spot but no spot model can explain both the large amplitude FUV variations and the SED. The limitations of limb darkening, cyclotron and magnetic white dwarf models in explaining the observations are discussed.
astro-ph/0606538 [abs, ps, pdf, other] :: Title: Point source power in three-year Wilkinson Microwave Anisotropy Probe data
Authors: K. M. Huffenberger, H. K. Eriksen, F. K. Hansen
Comments: 4 pages, 4 figures, 1 table

Using a set of multifrequency cross-spectra computed from the three year WMAP sky maps, we fit for the unresolved point source contribution. For a white noise power spectrum, we find a Q-band amplitude of A = 0.011 +/- 0.001 muK^2 sr (antenna temperature), significantly smaller than the value of 0.017 +/- 0.002 muK^2 sr used to correct the spectra in the WMAP release. Modifying the point source correction in this way largely resolves the discrepancy Eriksen et al. (2006) found between the WMAP V- and W-band power spectra. Correcting the co-added WMAP spectrum for both the low-l power excess due to residual foregrounds and the high-l power deficit due to over-subtracted point sources, we find that the net effect in terms of cosmological parameters is a ~ 0.7 sigma shift in n_s to larger values: For the combination of WMAP, BOOMERanG and Acbar data, we find n_s = 0.969 +/- 0.016, lowering the significance of n_s not equal to 1 from ~ 2.7 sigma to ~ 2.0 sigma.
astro-ph/0606539 [abs, ps, pdf, other] :: Title: Magnetohydronamic Evolution of HII Regions in Molecular Clouds: Simulation Methodology, Tests, and Uniform Media
Authors: Mark R. Krumholz, James M. Stone, Thomas A. Gardiner (Princeton University)
Comments: Submitted to ApJ. 17 pages, 18 figures, emulateapj format. Full resolution figures and movies of simulations available are at this http URL

We present a method for simulating the evolution of HII regions driven by point sources of ionizing radiation in magnetohydrodynamic media, implemented in the three-dimensional Athena MHD code. We compare simulations using our algorithm to analytic solutions and show that the method passes rigorous tests of accuracy and convergence. The tests reveal several conditions that an ionizing radiation-hydrodynamic code must satisfy to reproduce analytic solutions. As a demonstration of our new method, we present the first three-dimensional, global simulation of an HII region expanding into a magnetized gas. The simulation shows that magnetic fields suppress sweeping up of gas perpendicular to magnetic field lines, leading to small density contrasts and extremely weak shocks at the leading edge of the HII region's expanding shell. They also generate an instability at the ionization front that causes gas to collect into clumps and pilars along field lines. We discuss possible implications of these results for the evolution of HII regions and triggered star formation.
astro-ph/0606540 [abs, ps, pdf, other] :: Title: The radio structure of radio-quiet quasars
Authors: Christian Leipski (1), Heino Falcke (2,3), Nicola Bennert (1,4), Susanne Huettemeister (1); ((1) AIRUB Univ. Bochum, (2) ASTRON Dwingeloo, (3) Radboud University Nijmegen, (4) IGPP UC Riverside)
Comments: 14 pages, 15 figures, accepted for publication in A&A

We investigate the radio emitting structures of radio-quiet active galactic nuclei with an emphasis on radio-quiet quasars to study their connection to Seyfert galaxies. We present and analyse high-sensitivity VLA radio continuum images of 14 radio-quiet quasars and six Seyfert galaxies. Many of the low redshift radio-quiet quasars show radio structures that can be interpreted as jet-like outflows. However, the detection rate of extended radio structures on arcsecond scales among our sample decreases with increasing redshift and luminosity, most likely due to a lack of resolution. The morphologies of the detected radio emission indicate strong interactions of the jets with the surrounding medium. We also compare the radio data of seven quasars with corresponding HST images of the [OIII] emitting narrow-line region (NLR). We find that the scenario of interaction between the radio jet and the NLR gas is confirmed in two sources by structures in the NLR gas distribution as previously known for Seyfert galaxies. The extended radio structures of radio-quiet quasars at sub-arcsecond resolution are by no means different from that of Seyferts. Among the luminosities studied here, the morphological features found are similar in both types of objects while the overall size of the radio structures increases with luminosity. This supports the picture where radio-quiet quasars are the scaled-up versions of Seyfert galaxies. In addition to known luminosity relations we find a correlation of the NLR size and the radio size shared by quasars and Seyferts.
astro-ph/0606541 [abs, ps, pdf, other] :: Title: Robust Machine Learning Applied to Astronomical Datasets I: Star-Galaxy Classification of the SDSS DR3 Using Decision Trees
Authors: Nicholas M. Ball (1 and 2), Robert J. Brunner (1 and 2), Adam D. Myers (1 and 2), David Tcheng (2) ((1) University of Illinois at Urbana-Champaign, (2) National Center for Supercomputing Applications)
Comments: 27 pages, 12 figures, to be published in ApJ, uses emulateapj.cls

We provide classifications for all 143 million non-repeat photometric objects in the Third Data Release of the Sloan Digital Sky Survey (SDSS) using decision trees trained on 477,068 objects with SDSS spectroscopic data. We demonstrate that these star/galaxy classifications are expected to be reliable for approximately 22 million objects with r < ~20. The general machine learning environment Data-to-Knowledge and supercomputing resources enabled extensive investigation of the decision tree parameter space. This work presents the first public release of objects classified in this way for an entire SDSS data release. The objects are classified as either galaxy, star or nsng (neither star nor galaxy), with an associated probability for each class. To demonstrate how to effectively make use of these classifications, we perform several important tests. First, we detail selection criteria within the probability space defined by the three classes to extract samples of stars and galaxies to a given completeness and efficiency. Second, we investigate the efficacy of the classifications and the effect of extrapolating from the spectroscopic regime by performing blind tests on objects in the SDSS, 2dF Galaxy Redshift and 2dF QSO Redshift (2QZ) surveys. Given the photometric limits of our spectroscopic training data, we effectively begin to extrapolate past our star-galaxy training set at r ~ 18. By comparing the number counts of our training sample with the classified sources, however, we find that our efficiencies appear to remain robust to r ~ 20. As a result, we expect our classifications to be accurate for 900,000 galaxies and 6.7 million stars, and remain robust via extrapolation for a total of 8.0 million galaxies and 13.9 million stars. [Abridged]
astro-ph/0606542 [abs, ps, pdf, other] :: Title: All physical transforms from RW coordinates require the same variable physical photon velocity
Authors: Robert C. Fletcher
Comments: 21 pages, 1 figure, 2 files

I have investigated what coordinate systems, other than the Robertson-Walker (RW) system, there might be to describe a homogeneous and isotropic universe that are physical close to the origin, i.e., covariant transforms from RW that use physical clocks and rulers and have a photon velocity that is invariant under reflection. I show that there are an infinte number of such systems. Amazingly, all of these systems require the same variable photon velocity close to their origin, which is consistent with the RW system also having the same variable photon velocity. Implausible though it may seem, if the criteria for physicality are valid, it seems inescapable that this must represnt the physical photon velocity. The assumption of homogeneity makes it applicable to physical processes throughout the universe. I find that the analytic expression for it is c(t) = aH, the cosmic scale factor times the Hubble ratio in appropriate units. The existence of variabliity derives from the phsicality criteria being applied to the transformed coordinates expanded from the origin out to the lowest order of the RW radial coordinate, and not to gravitational enegy density, which determines only its magnitude. The Lorentz transform and the field equation can be generalized by using a generalized time for which the differential is c(t)dt.
astro-ph/0606543 [abs, ps, pdf, other] :: Title: An XMM-Newton Observation of the Massive Edge-on Sb Galaxy NGC 2613
Authors: Zhiyuan Li, Q. Daniel Wang, Judith A. Irwin, Tara Chaves
Comments: 17 pages, accepted by MNRAS

We present an XMM-Newton observation of the massive edge-on Sb galaxy NGC 2613. We discover that this galaxy contains a deeply embedded active nucleus with a 0.3-10 keV luminosity of 3.3x10^40 erg/s and a line-of-sight absorption column of 1.2x10^23 cm^-2. Within the 25 mag/arcsec^2 optical B-band isophote of the galaxy, we detect an additional 4 sources with an accumulated luminosity of 4.3x10^39 erg/s. The bulk of the unresolved X-ray emission spatially follows the near-infrared (NIR) K-band surface brightness distribution; the luminosity ratio L_X/L_K ~ 8x10^-4 is consistent with that inferred from galactic discrete sources. This X-ray-NIR association and the compatibility of the X-ray spectral fit with the expected spectrum of a population of discrete sources suggest that low-mass X-ray binaries (LMXBs) are the most likely emitters of the unresolved emission in the disk region. The remaining unresolved emission is primarily due to extraplanar hot gas. The luminosity of this gas is at least a factor of 10 less than that predicted by recent simulations of intergalactic gas accretion by such a massive galaxy with a circular rotation speed V_c ~ 304 km/s^2 (Toft et al. 2002). Instead, we find that the extraplanar hot gas most likely represents discrete extensions away from the disk, including two ``bubble-like'' features on either side of the nucleus. These extensions appear to correlate with radio continuum emission and, energetically, can be easily explained by outflows from the galactic disk.
astro-ph/0606544 [abs, ps, pdf, other] :: Title: Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: II. Control of the \HII Region Parameters
Authors: Michael A. Dopita, Joerg Fischera, Ralph S. Sutherland, Lisa J. Kewley, , Richard J. Tuffs, Cristina C. Popescu, Wil van Breugel, Brent A. Groves, Claus Leitherer
Comments: 36 pages, 8 figures. To be published in Astrophysical Journal, August 2006

We examine, from a theoretical viewpoint, how the physical parameters of HII regions are controlled in both normal galaxies and in starburst environments. These parameters are the HII region luminosity function, the time-dependent size, the covering fraction of molecular clouds, the pressure in the ionized gas and the ionization parameter. The factors which control them are the initial mass function of the exciting stars, the cluster mass function, the metallicity and the mean pressure in the surrounding interstellar medium. We investigate the sensitivity of the H$\alpha$ luminosity to the IMF, and find that this can translate to more than a factor two variation in derived star formation rates. The molecular cloud dissipation timescale is estimated from a case study of M17 to be $\sim1$ Myr for this object. Based upon HII luminosity function fitting for nearby galaxies, we suggest that the \HII region cluster mass function is fitted by a log-normal form peaking at $\sim 100 M_{\odot}$. The cluster mass function continues the stellar IMF to higher mass. The pressure in the HII regions is controlled by the mechanical luminosity flux from the central cluster. Since this is closely related to the ionizing photon flux, we show that the ionization parameter is not a free variable, and that the diffuse ionized medium may be composed of many large, faint and old HII regions. Finally, we derive theoretical probability distributions for the ionization parameter as a function of metallicity and compare these to those derived for SDSS galaxies.
astro-ph/0606545 [abs, ps, pdf, other] :: Title: The Virial Mass Function of Nearby SDSS Galaxy Clusters
Authors: Kenneth Rines (Yale/YCAA), Antonaldo Diaferio (Torino), Priyamvada Natarajan (Yale/YCAA)
Comments: 22 pages, 11 figures, submitted to ApJ

We present a new determination of the cluster mass function and velocity dispersion function in a volume $\sim10^7 h^3$Mpc$^{-3}$ using the Fourth Data Release of the Sloan Digital Sky Survey (SDSS). We use the caustic technique to remove foreground and background galaxies. The cluster virial mass function agrees very well with recent estimates from both X-ray observations and cluster richnesses. The mass function lies between those predicted by the First-Year and Three-Year WMAP data. We constrain the cosmological parameters $\Omega_m$ and $\sigma_8$ and find good agreement with WMAP and constraints from other techniques. With the CIRS mass function alone, we estimate $\Omega_m=0.23^{+0.14}_{-0.09}$ and $\sigma_8=0.91^{+0.17}_{-0.19}$, or $\sigma_8=0.81\pm$0.03 when holding $\Omega_m=0.3$ fixed. We also use the WMAP parameters as priors and constrain velocity segregation in clusters. Using the First and Third-Year results, we infer velocity segregation of $\sigma_{gxy}/\sigma_{DM}\approx0.91\pm$0.04 or 1.30$\pm$0.05 respectively. We compare the velocity dispersion function of clusters to that of early-type galaxies and conclude that clusters comprise the high-velocity end of the velocity dispersion function of dark matter haloes. The evolution of cluster abundances provides constraints on dark energy models; the mass function presented here offers an important low redshift calibration benchmark.
astro-ph/0606546 [abs, ps, pdf, other] :: Title: Stellar halos and elliptical galaxy formation: Origin of dynamical properties of the planetary nebular systems
Authors: Kenji Bekki, Eric Peng
Comments: 17 pages, 22 figures (including color figures), accepted by MNRAS

Recent spectroscopic observations of planetary nebulae (PNe) in several elliptical galaxies have revealed structural and kinematical properties of the outer stellar halo regions. In order to elucidate the origin of the properties of these planetary nebula systems (PNSs), we consider the merger scenario in which an elliptical galaxy is formed by merging of spiral galaxies. Using numerical simulations, we particularly investigate radial profiles of projected PNe number densities, rotational velocities, and velocity dispersions of PNSs extending to the outer halo regions of elliptical galaxies formed from major and unequal-mass merging. We find that the radial profiles of the project number densities can be fitted to the power-law and the mean number density in the outer halos of the ellipticals can be more than an order of magnitude higher than that of the original spiral's halo. The PNSs are found to show a significant amount of rotation (V/sigma >0.5) in the outer halo regions ($R$ $>$ $5R_{\rm e}$) of the ellipticals. Two-dimensional velocity fields of PNSs are derived from the simulations and their dependences on model parameters of galaxy merging are discussed in detail. We compare the simulated kinematics of PNSs with that of the PNS observed in NGC 5128 and thereby discuss advantages and disadvantages of the merger model in explaining the observed kinematics of the PNS. We also find that the kinematics of PNSs in elliptical galaxies are quite diverse depending on the orbital configurations of galaxy merging, the mass ratio of merger progenitor spirals, and the viewing angle of the galaxies. This variation translates directly into possible biases by a factor of more than two in observational mass estimation (abridged). ~ ~
astro-ph/0606547 [abs, ps, pdf, other] :: Title: HCN and HNC mapping of the protostellar core Cha-MMS1
Authors: P.P. Tennekes, J.Harju, M. Juvela, L.V. Toth
Comments: 9 pages, 8 figures, accepted for publication in Astronomy & Astrophysics

Aims. The purpose of this study is to investigate the distributions of the isomeric molecules HCN and HNC and estimate their abundance ratio in the protostellar core Cha-MMS1 located in Chamaeleon {\sc i}.
Methods. The core was mapped in the J=1-0 rotational lines of HCN, HNC, and HN13C. The column densities of H13CN, HN13C, H15NC and NH3 were estimated towards the centre of the core.
Results. The core is well delineated in all three maps. The kinetic temperature in the core, derived from the NH3 (1,1) and (2,2) inversion lines, is 12.1+/-0.1 K. The HN13C/H13CN column density ratio is between 3 and 4, i.e. similar to values found in several other cold cores. The HN13C/H15NC column density ratio is about 7. In case no 15N fractionation occurs in HNC (as suggested by recent modelling results), the HNC/HN13C abundance ratio is in the range 30-40, which indicates a high degree of 13C fractionation in HNC. Assuming no differential 13C fractionation the HCN and HNC abundances are estimated to be about 7E-10 and about 2E-9, respectively, the former being nearly two orders of magnitude smaller than that of NH3. Using also previously determined column densities in Cha-MMS1, we can put the most commonly observed nitrogenous molecules in the following order according to their fractional abundances: X(NH3) > X(HC3N) > X(HNC) > X(HCN) > X(N2H+).
Conclusions. The relationships between molecular abundances suggest that Cha-MMS1 represents an evolved chemical stage, experiencing at present the 'late-time' cyanopolyyne peak. The possibility that the relatively high HNC/HCN ratio derived here is only valid for the $^{13}$C isotopic substitutes cannot be excluded on the basis of the present and other available data.
astro-ph/0606548 [abs, ps, pdf, other] :: Title: Constraining fundamental physics with the cosmic microwave background
Authors: Anthony Challinor
Comments: 21 pages. Invited review at the Workshop on Cosmology and Gravitational Physics, 15-16 December 2005, Thessaloniki, Greece

The temperature anisotropies and polarization of the cosmic microwave background (CMB) radiation provide a window back to the physics of the early universe. They encode the nature of the initial fluctuations and so can reveal much about the physical mechanism that led to their generation. In this contribution we review what we have learnt so far about early-universe physics from CMB observations, and what we hope to learn with a new generation of high-sensitivity, polarization-capable instruments.
astro-ph/0606549 [abs, ps, pdf, other] :: Title: The Upper Limit of Magnetic Field Strength in Dense Stellar Hadronic Matter
Authors: Somenath Chakrabarty
Comments: 6 pages Revtex, 2 .eps figures, fig.(1) is not included

It is shown that in strongly magnetized neutron stars, there exist upper limits of magnetic field strength, beyond which the self energies for both neutron and proton components of neutron star matter become complex in nature. As a consequence they decay within the strong interaction time scale. However, in the ultra-strong magnetic field case, when the zeroth Landau level is only occupied by protons, the system again becomes stable against strong decay.
astro-ph/0606550 [abs, ps, pdf, other] :: Title: Monte Carlo radiative transfer in protoplanetary disks
Authors: Christophe Pinte, Francois Menard, Gaspard Duchene, Pierre Bastien
Comments: 10 pages, 5 figures, accepted for publication in A&A

We present a new continuum 3D radiative transfer code, MCFOST, based on a Monte-Carlo method. MCFOST can be used to calculate (i) monochromatic images in scattered light and/or thermal emission, (ii) polarisation maps, (iii) interferometric visibilities, (iv) spectral energy distributions and (v) dust temperature distributions of protoplanetary disks. Several improvements to the standard Monte Carlo method are implemented in MCFOST to increase efficiency and reduce convergence time, including wavelength distribution adjustments, mean intensity calculations and an adaptive sampling of the radiation field. The reliability and efficiency of the code are tested against a previously defined benchmark, using a 2D disk configuration. No significant difference (no more than 10%, and generally much less) is found between the temperatures and SEDs calculated by MCFOST and by other codes included in the benchmark. A study of the lowest disk mass detectable by Spitzer, around young stars, is presented and the colours of ``representative'' parametric disks are compared to recent IRAC and MIPS Spitzer colours of solar-like young stars located in nearby star forming regions.
astro-ph/0606551 [abs, ps, pdf, other] :: Title: Eclipsing binaries observed with the WIRE satellite I. Discovery and photometric analysis of the new bright A0IV eclipsing binary Psi Centauri
Authors: H. Bruntt, J. Southworth, G. Torres, A.J. Penny, J.V. Clausen, D.L. Buzasi
Comments: 9 pages, 4 figures, accepted for publication in A&A. Photometric data will be made available at the CDS once the final version appears. The resolution in Fig. 1 has been reduced

Determinations of stellar mass and radius with realistic uncertainties at the level of 1% provide important constraints on models of stellar structure and evolution. We present a high-precision light curve of the A0IV star Psi Centauri, from the star tracker on board the WIRE satellite and the Solar Mass Ejection Imager camera on the Coriolis spacecraft. The data show that Psi Cen is an eccentric eclipsing binary system with a relatively long orbital period. The WIRE light curve extends over 28.7 nights and contains 41334 observations with 2 mmag point-to-point scatter. The eclipse depths are 0.28 and 0.16 mag, and show that the two eclipsing components of Psi Cen have very different radii. As a consequence, the secondary eclipse is total. We find the eccentricity to be e=0.55 with an orbital period of 38.8 days from combining the WIRE light curve with data taken over two years from the Solar Mass Ejection Imager camera. We have fitted the light curve with EBOP and have assessed the uncertainties of the resulting parameters using Monte Carlo simulations. The fractional radii of the stars and the inclination of the orbit have random errors of only 0.1% and 0.01 degrees, respectively, but the systematic uncertainty in these quantities may be somewhat larger. We have used photometric calibrations to estimate the effective temperatures of the components of Psi Cen to be 10450+-300 and 8800+-300 K, indicating masses of about 3.1 and 2.0 Msun. There is evidence in the WIRE light curve for g-mode pulsations in the primary star.
astro-ph/0606552 [abs, ps, pdf, other] :: Title: The Cosmic Microwave Background and the Ionization History of the Universe
Authors: Antony Lewis, Jochen Weller, Richard Battye

Details of how the primordial plasma recombined and how the universe later reionized are currently somewhat uncertain. This uncertainty can restrict the accuracy of cosmological parameter measurements from the Cosmic Microwave Background (CMB). More positively, future CMB data can be used to constrain the ionization history using observations. We first discuss how current uncertainties in the recombination history impact parameter constraints, and show how suitable parameterizations can be used to obtain unbiased parameter estimates from future data. Some parameters can be constrained robustly, however there is clear motivation to model recombination more accurately with quantified errors. We then discuss constraints on the ionization fraction binned in redshift during reionization. Perfect CMB polarization data could in principle distinguish different histories that have the same optical depth. We discuss how well the Planck satellite may be able to constrain the ionization history, and show the currently very weak constraints from WMAP three-year data.
astro-ph/0606553 [abs, pdf] :: Title: Observing with a space-borne gamma-ray telescope: selected results from INTEGRAL
Authors: S. Schanne
Comments: Invited talk at the NPDC19 Conference of the European Physical Society, Pavia, September 2005. Published in the IoP J. Phys. (2006) Conf. Ser. 41 46-60
Journal-ref: J. Phys. (2006) Conf. Ser. 41 46-60

The International Gamma-Ray Astrophysics Laboratory, i.e. the INTEGRAL satellite of ESA, in orbit since about 3 years, performs gamma-ray observations of the sky in the 15 keV to 8 MeV energy range. Thanks to its imager IBIS, and in particular the ISGRI detection plane based on 16384 CdTe pixels, it achieves an excellent angular resolution (12 arcmin) for point source studies with good continuum spectrum sensitivity. Thanks to its spectrometer SPI, based on 19 germanium detectors maintained at 85 K by a cryogenic system, located inside an active BGO veto shield, it achieves excellent spectral resolution of about 2 keV for 1 MeV photons, which permits astrophysical gamma-ray line studies with good narrow-line sensitivity. In this paper we review some goals of gamma-ray astronomy from space and present the INTEGRAL satellite, in particular its instruments ISGRI and SPI. Ground and in-flight calibration results from SPI are presented, before presenting some selected astrophysical results from INTEGRAL. In particular results on point source searches are presented, followed by results on nuclear astrophysics, exemplified by the study of the 1809 keV gamma-ray line from radioactive 26Al nuclei produced by the ongoing stellar nucleosynthesis in the Galaxy. Finally a review on the study of the positron-electron annihilation in the Galactic center region, producing 511 keV gamma-rays, is presented.
astro-ph/0606554 [abs, ps, pdf, other] :: Title: CO emission from candidate photo-dissociation regions in M81
Authors: J.H. Knapen (1), R.J. Allen (2), H.I Heaton (3), N. Kuno (4,5), N. Nakai (6) ((1) Univ. of Hertfordshire, (2) STScI, (3) JHU APL, (4) Nobeyama, (5) Graduate Univ. for Advanced Studies Tokyo, (6) Univ. of Tsukuba)
Comments: 8 pages latex, 4 figures, Accepted for publication as a Research Note in Astronomy & Astrophysics

Context At least a fraction of the atomic hydrogen in spiral galaxies is suspected to be the result of molecular hydrogen which has been dissociated by radiation from massive stars.
Aims In this paper, we extend our earlier set of data from a small region of the Western spiral arm of M81 with CO observations in order to study the interplay between the radiation field and the molecular and atomic hydrogen.
Methods We report CO(1-0) observations with the Nobeyama 45 m dish and the Owens Valley interferometer array of selected regions in the Western spiral arm of M81.
Results From our Nobeyama data, we detect CO(1-0) emission at several locations, coinciding spatially with HI features near a far-UV source. The levels and widths of the detected CO profiles are consistent with the CO(1-0) emission that can be expected from several large photo-dissociation regions with typical sizes of some 50x150 pc located within our telescope beam. We do not detect emission at other pointings, even though several of those are near far-UV sources and accompanied by bright HI. This non-detection is likely a consequence of the marginal area filling factor of photo-dissociation regions in our observations. We detect no emission in our Owens Valley data, consistent with the low intensity of the CO emission detected in that field by the Nobeyama dish.
Conclusions We explain the lack of CO(1-0) emission at positions farther from far-UV sources as a consequence of insufficient heating and excitation of the molecular gas at these positions, rather than as an absence of molecular hydrogen.
astro-ph/0606555 [abs, ps, pdf, other] :: Title: Spatial curvature and holographic dark energy
Authors: Winfried Zimdahl, Diego Pavon
Comments: 17 pages, no figures, key words: cosmology, dark energy, holography, curvature

We show that a non-zero spatial curvature in Friedmann--Lema\^{\i}tre--Robertson--Walker universes originates an interesting dynamics in holographic dark energy models whose infrared cutoff scale is set by the Hubble length. A generic interaction between this holographic dark energy and pressureless dark matter induces a transition from decelerated to accelerated expansion and significantly alleviates the coincidence problem.
astro-ph/0606556 [abs, ps, pdf, other] :: Title: High Accuracy Matching of Planetary Images
Authors: Giuseppe Vacanti, Ernst-Jan Buis
Comments: 6 pages, 8 figures, to appear in the proceedings of the First International Conference on Impact Cratering in the Solar System (40th ESLAB Symposium), held in Noordwijk, the Netherlands, May 8-12, 2006

We address the question of to what accuracy remote sensing images of the surface of planets can be matched, so that the possible displacement of features on the surface can be accurately measured. This is relevant in the context of the libration experiment aboard the European Space Agency's BepiColombo mission to Mercury. We focus here only on the algorithmic aspects of the problem, and disregard all other sources of error (spacecraft position, calibration uncertainties, etc.) that would have to be taken into account. We conclude that for a wide range of illumination conditions, translations between images can be recovered to about one tenth of a pixel r.m.s.
astro-ph/0606557 [abs, pdf] :: Title: LIINUS/SERPIL: a design study for interferometric imaging spectroscopy at the LBT
Authors: Csaba Gal, Francisco Mueller-Sanchez
Comments: 12 pages, SPIE conference proceeding, Orlando, 2006

LIINUS/SERPIL is a design study to augment LBTs interferometric beam combiner camera LINC-NIRVANA with imaging spectroscopy. The FWHM of the interferometric main beam at 1.5 micron will be about 10 mas, offering unique imaging and spectroscopic capabilities well beyond the angular resolution of current 8-10m telescopes. At 10 mas angular scale, e.g., one resolution element at the distance of the Galactic Center corresponds to the average diameter of the Pluto orbit (79 AU), hence the size of the solar system. Taking advantage of the LBT interferometric beam with an equivalent maximum diameter of 23 m, LIINUS/SERPIL is an ideal precursor instrument for (imaging) spectrographs at extremely large full aperture telescopes. LIINUS/SERPIL will be built upon the LINC-NIRVANA hardware and LIINUS/SERPIL could potentially be developed on a rather short timescale. The study investigates several concepts for the optical as well as for the mechanical design. We present the scientific promises of such an instrument together with the current status of the design study.
astro-ph/0606558 [abs, ps, pdf, other] :: Title: Water masers in the Local Group of galaxies
Authors: A. Brunthaler (1,2), C. Henkel (1), W.J.G. de Blok (3), M.J. Reid (4), L.J. Greenhill (3), H. Falcke (5,6) ((1) Max-Planck-Institut fuer Radioastronomie, (2) Joint Institute for VLBI in Europe (JIVE), (3) Mount Stromlo Observatory, (4) Harvard-Smithsonian Center for Astrophysics, (5) ASTRON, (6) Universiteit Nijmegen)
Comments: Astronomy & Astrophysics, accepted, 9 pages, 9 figures, also available at this http URL

We compare the number of detected 22 GHz H2O masers in the Local Group galaxies M31, M33, NGC6822, IC10, IC1613, DDO187, GR8, NGC185, and the Magellanic Clouds with the water maser population of the Milky Way. To accomplish this we searched for water maser emission in the two Local Group galaxies M33 and NGC6822 using the Very Large Array (VLA) and incorporated results from previous studies. We observed 62 HII regions in M33 and 36 regions with H-alpha emission in NGC6822. Detection limits are 0.0015 and 0.0008 Lsun for M33 and NGC6822, respectively (corresponding to 47 and 50 mJy in three channels with 0.7 km/s width). M33 hosts three water masers above our detection limit, while in NGC6822 no maser source was detected. We find that the water maser detection rates in the Local Group galaxies M31, M33, NGC6822, IC1613, DDO187, GR8, NGC185, and the Magellanic Clouds are consistent with expectations from the Galactic water masers if one considers the different star formation rates of the galaxies. However, the galaxy IC10 exhibits an overabundance of masers, which may result from a compact central starburst.
astro-ph/0606559 [abs, ps, pdf, other] :: Title: Homotopy symmetry in the multiply connected twin paradox of special relativity
Authors: Boudewijn F. Roukema (1), Stanislaw Bajtlik (2) ((1) Torun Centre for Astronomy, (2) CAMK)
Comments: 10 pages, 8 figures, submitted to Astronomy & Astrophysics

In multiply connected space, the two twins of the special relativity twin paradox move with constant relative speed and meet each other a second time without requiring any acceleration. The new paradox is the apparent symmetry of the twins' situations despite the time dilation effect implied by their relative speed. Here, the suggestion that the apparent symmetry is broken by homotopy classes of the twins' worldlines is reexamined using space-time diagrams. (i) It is found that each twin finds her own spatial path to have zero winding index and that of the other twin to have unity winding index, i.e. the twins' worldlines' relative homotopy classes are symmetrical. (ii) However, an asymmetrical property of the global space-time, unrelated to the twins' worldlines' homotopy classes, is also found, generalising from Peters' (1983) earlier results: For a non-favoured twin (a twin who identifies spatial fundamental domain boundaries non-simultaneously), there exist pairs of distinct events which are both spacelike and timelike separated in the covering space-time. Although the twins' apparent symmetry is broken by the need for the non-favoured twin to non-simultaneously identify spatial domain boundaries, and by the non-favoured twin's problems in clock synchronisation, the non-favoured twin cannot detect her disfavoured state by measuring the homotopy class of the two twins' projected worldlines: homotopy classes (numbers of windings) do not distinguish the two twins of the twin paradox, contrary to what was previously suggested.
astro-ph/0606560 [abs, ps, pdf, other] :: Title: First observations with CONDOR, a 1.5 THz heterodyne receiver
Authors: M. C. Wiedner, G. Wieching, F. Bielau, M. Emprechtinger, K. Rettenbacher, N. H. Volgenau, U. U. Graf, C. E. Honingh, K. Jacobs, B. Vowinkel, K. M. Menten, K. M., L. Nyman, R. Güsten, S. Philipp, D. Rabanus, J. Stutzki, F. Wyrowski
Comments: 4 pages + list of objects, 3 figures, to be published in A&A special APEX issue

The THz atmospheric windows centered at roughly 1.3 and 1.5~THz, contain numerous spectral lines of astronomical importance, including three high-J CO lines, the N+ line at 205 microns, and the ground transition of para-H2D+. The CO lines are tracers of hot (several 100K), dense gas; N+ is a cooling line of diffuse, ionized gas; the H2D+ line is a non-depleting tracer of cold (~20K), dense gas. As the THz lines benefit the study of diverse phenomena (from high-mass star-forming regions to the WIM to cold prestellar cores), we have built the CO N+ Deuterium Observations Receiver (CONDOR) to further explore the THz windows by ground-based observations. CONDOR was designed to be used at the Atacama Pathfinder EXperiment (APEX) and Stratospheric Observatory For Infrared Astronomy (SOFIA). CONDOR was installed at the APEX telescope and test observations were made to characterize the instrument. The combination of CONDOR on APEX successfully detected THz radiation from astronomical sources. CONDOR operated with typical Trec=1600K and spectral Allan variance times of 30s. CONDOR's first light observations of CO 13-12 emission from the hot core Orion FIR4 (= OMC1 South) revealed a narrow line with T(MB) = 210K and delta(V)=5.4km/s. A search for N+ emission from the ionization front of the Orion Bar resulted in a non-detection. The successful deployment of CONDOR at APEX demonstrates the potential for making observations at THz frequencies from ground-based facilities.
astro-ph/0606561 [abs, ps, pdf, other] :: Title: Chaotic motion and spiral structure in self-consistent models of rotating galaxies
Authors: N. Voglis (1), I. Stavropoulos (1 and 2), C. Kalapotharakos (1) ((1) Academy of Athens, Research Center for Astronomy, (2) University of Athens, Department of Physics, Section of Astrophysics)
Comments: 30 pages, 17 figures, submitted to MNRAS

Dissipationless N-body models of rotating galaxies, iso-energetic to a non-rotating model, are examined as regards the mass in regular and in chaotic motion. The values of their spin parameters $\lambda$ are near the value $\lambda=0.22$ of our Galaxy.
We obtain the distinction between the sets of particles moving in regular and in chaotic orbits and we show that the spatial distribution of these two sets of particles is much different. The rotating models are characterized by larger fractions of mass in chaotic motion ($\thickapprox 65%$) compared with the fraction of mass in chaotic motion in the non-rotating iso-energetic model ($\thickapprox 32%$). Furthermore, the Lyapunov numbers of the chaotic orbits in the rotating models become by about one order of magnitude larger than in the non-rotating model. Chaotic orbits are concentrated preferably in values of the Jacobi integral around the value of the effective potential at the corotation radius.
We find that density waves form a central rotating bar embedded in a thin and a thick disc with exponential surface density profile. A surprising new result is that long living spiral arms are exited on the disc, composed almost completely by chaotic orbits.
The bar excites an $m=2$ mode of spiral waves on the surface density of the disc, emanating from the corotation radius. These spiral waves are deformed, fade, or disappear temporarily, but they grow again re-forming a well developed spiral pattern. Spiral arms are discernible up to 20 or 30 rotations of the bar (lasting for about a Hubble time).
astro-ph/0606562 [abs, ps, pdf, other] :: Title: Modelling the spectral energy distribution of galaxies. IV Correcting apparent disk scalelengths and central surface brightnesses for the effect of dust at optical and near-infrared wavelengths
Authors: C. Möllenhoff (Landessternwarte, Heidelebrg), C. C. Popescu (MPIK, Heidelberg), R. J. Tuffs (MPIK, Heidelberg)
Comments: 16 pages, 13 figures and 5 tables; accepted for publication in Astronomy & Astrophysics

We present corrections for the change in the apparent scalelengths, central surface brightnesses and axis ratios due to the presence of dust in pure disk galaxies, as a function of inclination, central face-on opacity in the B-band (tau^f_B) and wavelength. The correction factors were derived from simulated images of disk galaxies created using geometries for stars and dust which can reproduce the entire spectral energy distribution from the ultraviolet (UV) to the Far-infrared (FIR)/submillimeter (submm) and can also account for the observed surface-brightness distributions in both the optical/Near-infrared and FIR/submm. We found that dust can significantly affect both the scalelength and central surface brightness, inducing variations in the apparent to intrinsic quantities of up to 50 percent in scalelength and up to 1.5 magnitudes in central surface brightness. We also identified some astrophysical effects for which, although the absolute effect of dust is non-negligible, the predicted variation over a likely range in opacity is relatively small, such that an exact knowledge of opacity is not needed. Thus, for a galaxy at a typical inclination of 37 degrees and having any tau^f_B>2, the effect of dust is to increase the scalelength in B relative to that in I by a factor of 1.12 +- 0.02 and to change the B-I central colour by 0.36 +- 0.05 magnitudes. Finally we use the model to analyse the observed scalelength ratios between B and I for a sample of disk-dominated spiral galaxies, finding that the tendency for apparent scalelength to increase with decreasing wavelength is primarily due to the effects of dust.
astro-ph/0606563 [abs, pdf] :: Title: First Fruits of the Spitzer Space Telescope: Galactic and Solar System Studies
Authors: M.Werner, G.Fazio, G.Rieke, T.Roellig, D.Watson
Comments: Review article to appear in slightly different format in Vol.44 of Annual Reviews of Astronomy and Astrophysics, 2006

This article provides a brief overview of the Spitzer Space Telescope and discusses its initial scientific results on galactic and solar system science.
astro-ph/0606564 [abs, ps, pdf, other] :: Title: One-dimensional Hybrid Approach to Extensive Air Shower Simulation
Authors: T. Bergmann, R. Engel, D. Heck, N. N. Kalmykov, S. Ostapchenko, T. Pierog, T. Thouw, K. Werner

An efficient scheme for one-dimensional extensive air shower simulation and its implementation in the program CONEX are presented. Explicit Monte Carlo simulation of the high-energy part of hadronic and electromagnetic cascades in the atmosphere is combined with a numeric solution of cascade equations for smaller energy sub-showers to obtain accurate shower predictions. The developed scheme allows us to calculate not only observables related to the number of particles (shower size) but also ionization energy deposit profiles which are needed for the interpretation of data of experiments employing the fluorescence light technique. We discuss in detail the basic algorithms developed and illustrate the power of the method. It is shown that Monte Carlo, numerical, and hybrid air shower calculations give consistent results which agree very well with those obtained within the CORSIKA program.
astro-ph/0606565 [abs, ps, pdf, other] :: Title: Thermal Emission from a Hot Cocoon Surrounding the Jet of XRF 060218
Authors: Enwei Liang, Bing Zhang, Bin-Bin Zhang, Z. G. Dai
Comments: 11 pages, 4 figures

It is long speculated that long duration gamma-ray bursts (GRBs) originate froma relativistic jet emerging from a collapsing massive star progenitor. Although associations of core-collapsing supernovae with long GRB afterglows have been identified in a number of systems, including the latest X-ray flash (XRF) 060218/SN 2006aj connection detected by Swift, direct evidence of a relativistic jet emerging from a collapsing star is still lacking. Here we report the detection of a thermal emission component (high-T component) accompanying the prompt X-ray emission of XRF 060218, with temperature kT_H=1.21+0.22/-0.24 keV and effective blackbody radius R_H~ 5\times 10^{9} cm. This high-T component co-exists with another low-T thermal component as reported by Campana et al. 2006 for at least 2700 seconds, but evolves independently with respect to the low-T component by tracing the lightcurve of the non-thermal component. We identify this high-T thermal component as the emission of a hot cocoon surrounding the relativistic jet, as expected from the theoretical models.
astro-ph/0606566 [abs, ps, pdf, other] :: Title: Galilean Equivalence for Galactic Dark Matter
Authors: Michael Kesden, Marc Kamionkowski
Comments: 4 pages, 3 figures, submitted to PRL

Satellite galaxies of the Milky Way experience a tidal disruption as they orbit in the Milky Way's dark halo. While the bound core of the satellite remains dominated by dark matter, the tidally disrupted stars behave like purely baryonic tracers of the Milky Way's potential well. If dark matter experiences a stronger self attraction than visible matter, stars will preferentially gain rather than lose energy during tidal disruption. This leads to a relative enhancement in the trailing as compared to the leading tidal stream. We show that the absence of a strong asymmetry in the surface brightness of the leading and trailing tidal streams already constrains the equivalence of acceleration of dark matter and baryons in a gravitational field to less than ten percent--thus ruling out a recently proposed mechanism to clear dwarf galaxies from voids. Future observations should be sensitive at the percent level to departures from the equivalence of dark matter and baryons.
astro-ph/0606567 [abs, ps, pdf, other] :: Title: The prompt optical/near-infrared flare of GRB 050904: the most luminous transient ever detected
Authors: D. A. Kann, N. Masetti, S. Klose
Comments: Submitted to the Astrophysical Journal; 7 pages, 2 figures

With a redshift of z=6.295, GRB 050904 is the most distant gamma-ray burst ever discovered. It was an energetic event at all wavelengths and the afterglow was observed in detail in the near-infrared bands. We gathered all available optical and NIR afterglow photometry of this GRB to construct a composite NIR light curve spanning several decades in time and flux density. Transforming the NIR light curve into the optical, we find that the afterglow of GRB 050904 was more luminous at early times than any other GRB afterglow in the pre-\emph{Swift} era, making it at these wavelengths the most luminous transient ever detected. Given the intrinsic properties of GRB 050904 and its afterglow, we discuss if this burst is markedly different from other GRBs at lower redshifts.

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