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Astrophysics

astro-ph new abstracts, Tue, 7 Feb 06 01:00:14 GMT
0602088 -- 0602132 received

astro-ph/0602088 [abs, ps, pdf, other] :

Title: The Evolution of Galaxy Mergers and Morphology at z<1.2 in the Extended Groth Strip
Authors: J.M. Lotz, M. Davis, S.M. Faber, P. Guhathakurta, S. Gwyn, J. Huang, D.C. Koo, E. Le Floc'h, L. Lin, J. Newman, K. Noeske, C. Papovich, C.N.A. Willmer, A. Coil, C.J. Conselice, M. Cooper, A.M. Hopkins, A. Metevier, J. Primack, G. Rieke, B. J. Weiner
Comments: 33 pages, including 2 tables and 10 figures, submitted to the Astrophysical Journal

We present the quantitative morphological evolution and galaxy merger fraction at 0.2 < z < 1.2 for a large sample of galaxies observed by the HST Advanced Camera for Surveys, the DEEP2 Galaxy Redshift Survey, and the Canada-France-Hawaii Telescope Legacy Survey over ~ 710 arcmin^2 in the Extended Groth Strip (EGS). We identify mergers and classify galaxy morphology for a volume-limited sample of 1475 galaxies brighter than M_B = -20.5 and a pure luminosity evolution sample of 2368 galaxies brighter than 0.4 L_B^*. We find that the merger fraction for both samples remains roughly constant at 7 \pm 2% for 0.2 < z < 1.2. For the luminosity evolution sample, the fraction of E|S0|Sa increases from 14^{+3}_{-2}% at z ~ 1.1 to 33^{+7}_{-6}% at z ~ 0.3, while the fraction of Sc|d|Ir decreases from 57^{+7}_{-6}% at z ~ 1.1 to 46^{+9}_{-7}% at z ~ 0.3. The majority of z < 1.2 24 micron sources with L(IR) > 10^11 L_sun are Sc|d|Irs, and only ~ 10% are major merger candidates. The morphological make-up of the red galaxy population changes with redshift. Disk galaxies dominate the number density of the red sequence at z ~ 1.1, while E|S0|Sa make up 84^{+11}_{-22}% of the red sequence at z ~ 0.3. Approximately 5% of red galaxies at 0.2 < z < 1.2 are red mergers. We conclude (1) the merger rate does not evolve strongly at 0.2 < z < 1.2; (2) the decrease in the volume-averaged star-formation rate since z ~ 1 is a result of decreased star-formation in late-type disks rather than a disappearing population of major mergers; (3) the number density of E|S0|Sa increases by a factor of ~ 2.5 from z ~ 1.1 to z ~ 0.3, hence the build-up of the red sequence at z < 1 found by other studies can be explained by the dramatic increase in the number of spheroidals.

 

astro-ph/0602089 [abs, ps, pdf, other] :

Title: The Large and Small Scale Structures of Dust in the Star-Forming Perseus Molecular Cloud
Authors: Helen Kirk, Doug Johnstone, James Di Francesco
Comments: 38 pages, 12 figures, accepted by Astrophysical Journal

We present an analysis of ~3.5 square degrees of submillimetre continuum and extinction data of the Perseus molecular cloud. We identify 49 clumps in the submillimetre map and we identify 39 structures (`cores') and 11 associations of structures (`super cores') in the extinction map. The cumulative mass distributions of the submillimetre clumps and extinction cores have steep slopes (alpha ~ 2 and 1.5 - 2 respectively), steeper than the Salpeter IMF (alpha = 1.35), while the distribution of extinction super cores has a shallow slope (alpha ~ 1). Most of the submillimetre clumps are well fit by stable Bonnor-Ebert spheres with 10K < T < 19K and 5.5 < log(P_ext/k) < 6.0. The clumps are found only in the highest column density regions (AV > 5 - 7 mag), although Bonnor-Ebert models suggest that we should have been able to detect them at lower column densities if they exist. These observations provide a stronger case for an extinction threshold than that found in analysis of less sensitive observations of the Ophiuchus molecular cloud. The relationship between submillimetre clumps and their parent extinction core has been analyzed.The submillimetre clumps tend to lie offset from the larger extinction peaks, suggesting the clumps formed via an external triggering event, consistent with previous observations.

 

astro-ph/0602090 [abs, ps, pdf, other] :

Title: Evolutive Unification in Composite Active Galactic Nuclei
Authors: Sebastian Lipari, Roberto Terlevich
Comments: 14 pages, 6 figures (submitted MNRAS)

In this paper we explore an evolutionary Unified scenario involving super massive black hole and starburst with outflow, that seems capable of explaining most of the observational properties of at least part of AGNs. Our suggestion is explored inside the expectations of the Starburst model close associated with the AGN where the NLR, BLR and BAL region are produced in part by the outflow process with shells and in compact supernova remnants. The outflow process in BAL QSOs with extreme IR and Fe II emission is studied. In addition, the Fe II poblem regarding the BLR of AGN is analysed. Neither the correlations between the BAL, IR emission, FeII intensity and the intrinsic properties of the AGN are clearly understood. We suggest here that the behaviour of the BAL, IR and FeII emission in AGNs can be understood inside an evolutionary and composite model for AGNs. In our model, strong BAL systems and Fe II emission are present (and intense) in young IR objects. Orientation/ obscuration effects take the role of a second parameter providing the segregation between Sy1/Sy2 and BLRG/NLRG.

 

astro-ph/0602091 [abs, ps, pdf, other] :

Title: Comprehensive Analysis of RXTE Data from Cyg X-1: Spectral Index-Quasi-Periodic Oscillation Frequency-Luminosity Correlations
Authors: Nickolai Shaposhnikov (USRA/GSFC), Lev Titarchuk (GMU/NRL/GSFC)
Comments: 28 pages, 15 figures and two tables. Accepted for publication in the ApJ

We present timing and spectral analysis of ~ 2.2 Ms of RXTE archival data from Cyg X-1. Using a generic Comptonization model we reveal that the spectrum of Cyg X-1 consists of three components: a thermal seed photon spectrum, a Comptonized part of the seed photon spectrum and the iron line. We find a strong correlation between the 0.1-20 Hz frequencies of quasiperiodic oscillations (QPOs) and the spectral index. Presence of two spectral phases (states) are clearly seen in the data when the spectral indices saturate at low and high values of QPO frequencies. This saturation effect was discovered earlier in a number of black hole candidate (BHC) sources and now we strongly confirm this phenomenon in Cyg X-1. In the soft state this index-QPO frequency correlation shows a saturation of the photon index Gamma ~ 2.1 at high values of the low frequency \nu_{L}. The saturation level of Gamma~ 2.1 is the lowest value found yet in BHCs. The bolometric luminosity does not show clear correlation with the index. We also show that Fe K_{\alpha} emission line strength (equivalent width, EW) correlates with the QPO frequency. The EW increases from 200 eV in the low/hard state to 1.5 keV in the high/soft state. The observational correlations revealed compel us to propose a scenario for the spectral transition and iron line formation which occur in BHC sources. We also present the spectral state (power-law index) evolution for eight years of Cyg X-1 observations by RXTE.

 

astro-ph/0602092 [abs, ps, pdf, other] :

Title: Do extragalactic cosmic rays induce cycles in fossil diversity?
Authors: Mikhail V. Medvedev, Adrian L. Melott (University of Kansas)
Comments: 13 pages, 3 figures, submitted to Nature

The idea of cycles in fossil diversity has recently been put on a firm statistical footing, revealing a 62{plus-minnus}3-million-year cycle in the number of marine genera. The strong signal requires a periodic process extending back at least 540 My, which is difficult to explain by any terrestrial process. While astro- and geophysical phenomena may be periodic for such a long time, no plausible mechanism has been found. The fact that the period of the diversity cycle is close to the 64 My period of the vertical oscillation of the Solar system relative to the galactic disk is suggestive. However, any model involving cosmogenic processes modulated by the Sun's midplane crossing or its maximal vertical distance from the galactic plane predicts a half-period cycle, i.e. about 32 My. Here we propose that the diversity cycle is caused by the anisotropy of cosmic ray (CR) production in the galactic halo/wind/termination shock and the shielding effect of the galactic magnetic fields. CRs influence cloud formation, can affect climate and harm live organisms directly via increase of radiation dose. The CR anisotropy is caused by the galactic north-south asymmetry of the termination shock due to the interaction with the ``warm-hot intergalactic medium'' as our galaxy falls toward the Virgo cluster (nearly in the direction of the galactic north pole) with a velocity of order 200 km/s. Here we revisit the mechanism of CR propagation in the galactic magnetic fields and show that the shielding effect is strongly position-dependent. It varies by a factor of a hundred and reaches a minimum at the maximum northward displacement of the Sun. Very good phase agreement between maximum excursions of the Sun toward galactic north and minima of the fossil diversity cycle further supports our model.

 

astro-ph/0602093 [abs, ps, pdf, other] :

Title: Comptonisation of Cosmic Microwave Background Photons in Dwarf Spheroidal Galaxies
Authors: Thomas L. Culverhouse (Cambridge), N. Wyn Evans (Cambridge), S. Colafrancesco (Rome)
Comments: 10 pages, 5 figures, MNRAS, in press

We present theoretical modelling of the electron distribution produced by annihilating neutralino dark matter in dwarf spheroidal galaxies (dSphs). In particular, we follow up the idea of Colafrancesco (2004) and find that such electrons distort the cosmic microwave background (CMB) by the Sunyaev-Zeldovich effect. For an assumed neutralino mass of 10 GeV and beam size of 1'', the SZ temperature decrement is of the order of nano-Kelvin for dSph models with a soft core. By contrast, it is of the order of micro-Kelvin for the strongly cusped dSph models favoured by some cosmological simulations. Although this is out of reach of current instruments, it may well be detectable by future mm telescopes, such as ALMA. We also show that the upscattered CMB photons have energies within reach of upcoming X-ray observatories, but that the flux of such photons is too small to be detectable soon. Nonetheless, we conclude that searching for the dark matter induced Sunyaev-Zeldovich effect is a promising way of constraining the dark distribution in dSphs, especially if the particles are light.

 

astro-ph/0602094 [abs, ps, pdf, other] :

Title: FUV and X-ray Observations of the Reverse Shock in the SMC SNR 1E 0102.2-7219
Authors: Manami Sasaki (CfA), Terrance J. Gaetz (CfA), William B. Blair (JHU), Richard J. Edgar (CfA), Jon A. Morse (ASU), Paul P. Plucinsky (CfA), Randall K. Smith (JHU/NASA GSFC)
Comments: 28 pages, 5 figues, Fig. 1 as JPEG. To be published in ApJ (01 May 2006, v. 642, 1 issue)

We present FUSE and XMM-Newton data for the reverse shock of the O-rich SNR 1E0102.2-7219 in the SMC. The FUSE observations cover three regions with significantly different optical [O III] intensities, all associated with the relatively bright part of the X-ray ring. Emission lines of O VI 1032, 1038 are clearly detected in the FUSE spectra. By combining this O VI doublet emission with the O VII triplet and O VIII Lyalpha fluxes from the XMM-Newton spectra and assuming a non-equilibrium ionization model with a single ionization timescale for the spectra, we are able to find a narrow range of temperatures and ionization timescales that are consistent with the respective line ratios. However, if we assume a plane-parallel shock model with a distribution of ionization timescales, the O VI emission appears to be inconsistent with O VII and O VIII in X-rays. We also analyze the total XMM-Newton EPIC-MOS 1/2 spectra for the three regions. The X-ray spectra are dominated by strong emission lines of O, Ne, and Mg, however, we detect an emission component that accounts for 14 - 25% of the flux and can be attributed to shocked ISM. We find that there is no consistent set of values for the temperature and ionization timescale which can explain the observed line ratios for O, Ne, and Mg. This would be consistent with a structured distribution of the ejecta as the O, Ne, Mg would have interacted with the reverse shock at different times.

 

astro-ph/0602095 [abs, ps, pdf, other] :

Title: Strange stars at finite temperature
Authors: Subharthi Ray, Manjari Bagchi, Jishnu Dey, Mira Dey
Comments: To be published in the proceedings of The Third 21COE Symposium, held at Department of Physics, Waseda University, Tokyo, Japan, September 1-3, 2005

We calculate strange star properties, using large N_c approximation with built-in chiral symmetry restoration (CSM). We used a relativistic Hartree Fock mean field approximation method, using a modified Richardson potential with two scale parameters \Lambda and \Lambda^\prime, to find a new set of equation of states for strange quark matter. We take the effect of temperature (T) on gluon mass, in addition to the usual density dependence, and find that the transition T from hadronic matter to strange matter is 80 MeV. Therefore formation of strange stars may be the only signal for formation of QGP with asymptotic freedom and CSM.

 

astro-ph/0602096 [abs, ps, pdf, other] :

Title: The Sky in Dust -- Methods and Prospects of Dust Astronomy
Authors: M. Landgraf (1), E. Grün (2 and 3), R. Srama (3), S. Helfert (3), S. Kempf (3), G. Morgas-Klostermeyer (3), M. Rachev (3), A. Srowig (3), S. Auer (4), M. Horànyi (5), Z. Sternovsky (5), D. Harris (2) ((1) ESA/ESOC, Robert-Bosch-Str. 5, Darmstadt, Germany, (2) HIGP Honolulu, HI, USA, (3) MPI-K Heidelberg, Germany, (4) A & M Assoc., Basye, USA, (5) LASP Boulder, CO, USA)
Comments: 2 pages, 3 figures, XXXVIIth Lunar and Planetary Science Conference, check this http URL

Information about the make-up of the galaxy arrives in the Solar system in many forms: photons of different energies, classically collected by ground- and space-based telescopes, neutral and charged atomic particles, and solid macroscopic particles: cosmic dust particles. Dust particles, like photons, carry information from remote sites in space and time. This information can be analysed in order to understand the processes and mechanisms that are involved in the formation and evolution of solid matter in the galaxy. This approach is called ``Dust Astronomy'' which is carried out by means of a dust telescope on a dust observatory in space. The analysis of cosmic grains collected in the high atmosphere of the Earth has shown that each dust grain is a small world with various sub-grains featuring different galactic origin and evolution, which is identified on the basis of elementary and isotopic analysis. Independent information about the origin and evolution of the grains coming from the kinematic properties of the arrival trajectory would be invaluable for linking the isotopic signature of the formation of heavy elements in old stars and supernovae to distinctive regions in our galaxy, e.g. known star-forming regions. Here we present a skymap of potential dust sources together with a report on already existing lab hardware of a trajectory sensor and a large-area mass spectrometre.

 

astro-ph/0602097 [abs, pdf] :

Title: A restoration in the time-symmetric theory and associated new results
Authors: Evangelos Chaliasos
Comments: 10 pages with 2 figures

The concept of absorption of a photon moving backwards in time is reexamined, and it is found that its interpretation as absorption is wrong, its original interpretation rather as an emission being restored. The result is that the anticosmos is invisible rather than indistinguishable from the cosmos, and as such it is qualitatevely a candidate for constituting the dark matter. Newton&#180;s law of gravitation is then generalized to refer either to matter (of the cosmos) and/or antimatter (of the anticosmos), and quantitatevely is found for the anticosmos to constitute the dark matter, as being (absolutely) equal in ammount of antimatter to the ammount of matter in the cosmos.Finally, a mechanism of gravitational repulsion from antimatter is proposed to explain the observed deceleration of Pioneer 10 and Pioneer 11, and an analytical way is exposed to calculate the position, as well as its (anti-)mass, of the responsible anti-body.

 

astro-ph/0602098 [abs, pdf] :

Title: The role of nonextensivity in the equilibrium of a star
Authors: Du Jiulin
Comments: 9 pages,14 references

Stellar nonextensivity is introduced by the equation of state of the gas based on the nonextensive kinetic theory and is understood with relation to the nonisothermal characteristic of the system under the long-range interactions of gravitational potential. In this work, we have revisited the condition for the stable existence of stars (S.Chandrasekhar, MNRAS, 96(1936)644) when the nonextensivity is taken into consideration. We find that to the extent the nonextensivity does affect the base of the equilibrium of actual stars in the Maxwellian sense; the maximum radiation pressure allowed at the center of a star of a given mass is dependent on the nonextensive parameter q that may be generally different from unity.

 

astro-ph/0602099 [abs, ps, pdf, other] :

Title: Angular Trispectrum of CMB Temperature Anisotropy from Primordial Non-Gaussianity with the Full Radiation Transfer Function
Authors: Noriyuki Kogo, Eiichiro Komatsu
Comments: 6 pages, 2 figures, submitted to PRD

We calculate the CMB angular trispectrum, spherical harmonic transform of the four-point correlation function, from primordial non-Gaussianity in primordial curvature perturbations characterized by a constant non-linear coupling parameter, $f_{\rm NL}$. We fully take into account the effect of the radiation transfer function, and thus provide the most accurate estimate of the signal-to-noise ratio of the angular trispectrum of CMB temperature anisotropy. We find that the predicted signal-to-noise ratio of the trispectrum summed up to a given $l$ is approximately a power-law, $(S/N)(<l)\sim 2.2\times 10^{-9}f^2_{\rm NL}l^2$, up to the maximum multipole that we have reached in our numerical calculation, $l=1200$, assuming that the error is dominated by cosmic variance. Our results indicate that the signal-to-noise ratio of the temperature trispectrum exceeds that of the bispectrum at the critical multipole, $l_c \sim 1500~(50/|f_{\rm NL}|)$. Therefore, the trispectrum of the Planck data is more sensitive to primordial non-Gaussianity than the bispectrum for $|f_{\rm NL}|\gtrsim 50$. We also report the predicted constraints on the amplitude of trispectrum, which may be useful for other non-Gaussian models such as curvaton models.

 

astro-ph/0602100 [abs, ps, pdf, other] :

Title: Spurs and feathering in spiral galaxies
Authors: C. L. Dobbs, I. A. Bonnell
Comments: 6 pages, 6 figures, accepted for publication in MNRAS

We present Smoothed Particle Hydrodynamics (SPH) simulations of the response of gas discs to a spiral potential. These simulations show that the commonly observed spurs and feathering in spiral galaxies can be understood as being due to structures present in the spiral arms that are sheared by the divergent orbits in a spiral potential. Thus, dense molecular cloud-like structures generate the perpendicular spurs as they leave the spiral arms. Subsequent feathering occurs as spurs are further sheared into weaker parallel structures as they approach the next spiral passage. Self-gravity of the gas is not included in these simulations, stressing that these features are purely due to the hydrodynamics in spiral shocks. Instead, a necessary condition for this mechanism to work is that the gas need be relatively cold (1000 K or less) in order that the shock is sufficient to generate structure in the spiral arms, and such structure is not subsequently smoothed by the gas pressure.

 

astro-ph/0602101 [abs, ps, pdf, other] :

Title: The Cosmic Stellar Birth and Death Rates
Authors: John F. Beacom (Ohio State University)
Comments: Accepted for publication in New Astronomy Reviews (invited talk at "Astronomy with Radioactivities V", Clemson Univ., Sept. 2005). 9 pages, 5 figures

The cosmic stellar birth rate can be measured by standard astronomical techniques. It can also be probed via the cosmic stellar death rate, though until recently, this was much less precise. However, recent results based on measured supernova rates, and importantly, also on the attendant diffuse fluxes of neutrinos and gamma rays, have become competitive, and a concordant history of stellar birth and death is emerging. The neutrino flux from all past core-collapse supernovae, while faint, is realistically within reach of detection in Super-Kamiokande, and a useful limit has already been set. I will discuss predictions for this flux, the prospects for neutrino detection, the implications for understanding core-collapse supernovae, and a new limit on the contribution of type-Ia supernovae to the diffuse gamma-ray background.

 

astro-ph/0602102 [abs, pdf] :

Title: Hubble's law and Superluminity Recession Velocities
Authors: Leonid S. Sitnikov
Comments: 7 pages, 3 figures

The extending the so-called "empty" (with zero combined density of all components of cosmic surroundings) universe and cosmological redshift in it are considered in this paper. Its space-time can be submitted not only as manifold with Friedman-Robertson-Walker metrics (FRW) of the general theory of relativity (GR) but also as space-time with usual Minkowski metrics (M-metrics) of the special theory of relativity (SR); the transfer of metrics can be done by suitable transformation of reference frame. Both below-mentioned statements are equally fair for such the universe. First: the distant galaxies can have superluminity recession velocities in FRW-space of GR; we have no right to use here the formula of relativistic Doppler effect. Secondly: the SR theory is fair in the M-space and, accordingly, recession velocities of the same galaxies here can aspire to the speed of light only.
In this article it is shown that, despite opposite pictures in FRW- and M- spaces, in the careful account of all details both approaches yield results agreed among themselves. Thus, actually there are no contradictions between the interpretations of cosmological redshift, based on SR and GR.

 

astro-ph/0602103 [abs, ps, pdf, other] :

Title: The formation of molecular clouds in spiral galaxies
Authors: C. L. Dobbs, I. A. Bonnell, J. E. Pringle
Comments: 13 pages, 17 figures, submitted to MNRAS

We present Smoothed Particle Hydrodynamics (SPH) simulations of molecular cloud formation in spiral galaxies. These simulations model the response of a non-self-gravitating gaseous disk to a galactic potential. The formation of molecular gas occurs when cold ($T \le 100$ K) gas is compressed during the passage of a spiral arm. The spiral arms display considerable structure and the molecular gas accumulates into dense clouds. We identify the formation of these structures as due to the dynamics of clumpy shocks, which perturb the orbits of particles passing through the spiral arm. In addition, the spiral shocks induce a large velocity dispersion in the spiral arms, comparable with the magnitude of the velocity dispersion observed in molecular clouds. The molecular clouds are largely confined to the spiral arms, since most molecular gas is photodissociated to atomic hydrogen upon leaving the arms. However a low photodissociation rate increases the amount of interarm molecular gas, and the possibility of molecular gas passing from one arm to another.

 

astro-ph/0602104 [abs, ps, pdf, other] :

Title: Nuclear Astrophysics of Worlds in the String Landscape
Authors: Craig J. Hogan
Comments: 27 pages, Latex, 2 figures

Motivated by landscape models in string theory, the cosmic behavior of matter is analyzed allowing the Standard Model Higgs expectation value $w$ to take values different from that in our world ($w\equiv 1$), while holding the Yukawa couplings fixed. Astrophysical consequences are described, and thresholds in $w$ are estimated, associated with changes in nuclear stability and reactions. A new lower limit on $w$ is derived, corresponding to the threshold where the neutron and not the proton becomes the ground state of an isolated baryon, in terms of the mass difference of the up and down quarks in our world. The effect of a stable neutron on nuclear evolution in the Big Bang and stars is shown to lead to radical differences from our world, such as a predominance of heavy r-process and s-process nuclei and a lack of normal stars and planets, which justify using the threshold as a possible anthropic constraint. Estimates are made of upper limits on $w$ deriving from thresholds for pp and pep reactions, the stability of deuterons, helium, and heavier nuclei, and changes in carbon and oxygen production during stellar nucleosynthesis. Although the thresholds and the astrophysical consequences are not evaluated rigorously, estimates suggest that significant changes in behavior occur with changes in $w$ of order ten percent. It is shown that $w$ is more finely tuned for some effects near the upper end of the currently allowed range for the down quark mass than it is at the lower end, which may allow some landscape models to make testable predictions for the real-world quark masses.

 

astro-ph/0602105 [abs, ps, pdf, other] :

Title: First Results from the CHARA Array. IV. The Interferometric Radii of Low-Mass Stars
Authors: D. H. Berger, D. R. Gies, H. A. McAlister, T. A. ten Brummelaar, T. J. Henry, J. Sturmann, L. Sturmann, N. H. Turner, S. T. Ridgway, J. P. Aufdenberg, A. Merand
Comments: 24 pages, 5 figures, accepted for publication in the ApJ

We have measured the angular diameters of six M dwarfs with the CHARA Array, a long-baseline optical interferometer located at Mount Wilson Observatory. Spectral types range from M1.0 V to M3.0 V and linear radii from 0.38 to 0.69 Rsun. These results are consistent with the seven other M-dwarf radii measurements from optical interferometry and with those for sixteen stars in eclipsing binary systems. We compare all directly measured M dwarf radii to model predictions and find that current models underestimate the true stellar radii by up to 15-20%. The differences are small among the metal-poor stars but become significantly larger with increasing metallicity. This suggests that theoretical models for low mass stars may be missing some opacity source that alters the computed stellar radii.

 

astro-ph/0602106 [abs, ps, pdf, other] :

Title: The Large Peculiar Velocity of the cD Galaxy in Abell 3653
Authors: Kevin A. Pimbblet, Isaac G. Roseboom, Marianne T. Doyle
Comments: 16 pages, including 7 figures and a long table. Accepted for publication in MNRAS

We present a catalogue of galaxies in Abell 3653 from observations made with the 2dF spectrograph at the Anglo-Australian Telescope. Of the 391 objects observed, we find 111 are bone-fide members of Abell 3653. We show that the cluster has a velocity of cz = 32214 +/- 83 km/s (z=0.10738 +/- 0.00027), with a velocity dispersion typical of rich, massive clusters of sigma_{cz} = 880^{+66}_{-54}. We find that the cD galaxy has a peculiar velocity of 683 +/- 96 km/s in the cluster restframe - some 7sigma away from the mean cluster velocity, making it one of the largest and most significant peculiar velocities found for a cD galaxy to date. We investigate the cluster for signs of substructure, but do not find any significant groupings on any length scale. We consider the implications of our findings on cD formation theories.

 

astro-ph/0602107 [abs, ps, pdf, other] :

Title: Neutron-capture elements in the very metal-poor star HD122563
Authors: S. Honda, W. Aoki, Y. Ishimaru, S. Wanajo, S. G. Ryan
Comments: 29 pages, 7 figures, Accepted for publication in ApJ

We obtained high resolution, high S/N spectroscopy for the very metal-poor star HD122563 with the Subaru Telescope High Dispersion Spectrograph. Previous studies have shown that this object has excesses of light neutron-capture elements, while its abundances of heavy ones are very low. In our spectrum covering 3070 - 4780 A of this object, 19 neutron-capture elements have been detected, including seven for the first time in this star (Nb, Mo, Ru, Pd, Ag, Pr, and Sm). Upper limits are given for five other elements including Th. The abundance pattern shows a gradually decreasing trend, as a function of atomic number, from Sr to Yb, which is quite different from those in stars with excesses of r-process elements. This abundance pattern of neutron-capture elements provides new strong constraints on the models of nucleosynthesis responsible for the very metal-poor stars with excesses of light neutron-capture elements but without enhancement of heavy ones.

 

astro-ph/0602108 [abs, ps, pdf, other] :

Title: Study of a detector array for Upward Tau Air-Showers
Authors: M. Iori, A. Sergi, D. Fargion, M.Gallinaro, M. Kaya
Comments: 18 pages, 16 figures

The cosmic ray spectrum extends to energies above 10^20 eV. In direct production or acceleration models, as well as by photo-pion interaction high energy cosmic ray flux must contain neutrinos and photons. The latter are absorbed by cosmic radiations while neutrinos are not. The need of a Neutrino Astronomy is compelling. In this paper a study of a detector array designed to measure horizontal tau air-showers emerging from the ground, produced by nu_tau interactions with the Earth's crust, is presented. Each array unit is composed of a pair of scintillator tiles mounted on a frame with a front field of view of about 0.1 sr, optimized to distinguish between up-going and down-going crossing particles by their time of flight. The detector array sensitivity, the size of the array and the tau shower identification are discussed. Because of the almost complete mixing of nu_mu to nu_tau the ultrahigh energy neutrino tau and its minimal consequent tau-airshower rate is estimated; assuming that the neutrino energy spectrum follows a Fermi-like power law E^-2, the sensitivity with 3 years of observation is estimated to be about 60 eV cm^-2s^-1sr^-1 in the energy range 10^{17-20} eV. This value would provide competitive upper limit with present and future experiments. We found also that, in the same time, this system can observe about one GZK neutrino event per km^2.

 

astro-ph/0602109 [abs, ps, pdf, other] :

Title: Systematic errors in the determination of Hubble constant due to the asphericity and non-isothermality of clusters of galaxies
Authors: Y.-G. Wang, Z.-H. Fan
Comments: 33 pages, 14 figures. Accepted for publication in ApJ

Joint analyses on X-ray and Sunyaev-Zel'dovich (SZ) effect of a cluster of galaxies can give rise to an estimate on the angular diameter distance to the cluster. With the redshift information of the cluster, the Hubble constant $H_0$ can then be derived. Furthermore, such measurements on a sample of clusters with a range of redshift can potentially be used to discriminate different cosmological models. In this paper, we present statistical studies on the systematic errors in the determination of $H_0$ due to the triaxiality and non-isothermality of clusters of galaxies. Different from many other studies that assume artificially a specific distribution for the intracluster gas, we start from the triaxial model of dark matter halos obtained from numerical simulations. The distribution of the intracluster gas is then derived under the assumption of the hydrodynamic equilibrium. For the equation of state of the intracluster gas, both the isothermal and the polytropic cases are investigated. We run Monte Carlo simulations to generate samples of clusters according to the distributions of their masses, axial ratios, concentration parameters, as well as line-of-sight directions. To mimic observations, the estimation of the Hubble constant is done by fitting X-ray and SZ profiles of a triaxial cluster with the isothermal and spherical $\beta$-model. We find that for a sample of clusters with $M=10^{14}h^{-1}\hbox{M}_{\odot}$ and $z=0.1$, the value of the estimated $H_0$ is positively biased with $H_0^{peak}(estimated)\approx 1.05H_0(true)$ and $H_0^{ave}(estimated)\approx 1.05H_0(true)$ for the isothermal case. For the polytropic case with $\gamma=1.15$, the bias is rather large with $H_0^{peak}(estimated)\approx 1.35H_0(true)$ and $H_0^{ave}(estimated)\approx 3H_0(true)$. (abridged)

 

astro-ph/0602110 [abs, ps, pdf, other] :

Title: Star Cluster Analyses from Multi-Band Photometry: the Key Advantage of SALT's U-band Sensitivity
Authors: Uta Fritze - v. Alvensleben (1), Polychronis Papaderos (1), Peter Anders (1), Thomas Lilly (1), Barbara Cunow (2), Jay Gallagher (3) ((1) Univ. Goettingen, Germany, (2) Unisa, Pretoria, SA, (3) Univ. of Wisconsin, Madison, US)
Comments: Contributed Talk, 7 pages, to appear in IAU Symp. 232, ``The Scientific Requirements for Extremely Large Telescopes'', eds. P. Whitelock, B. Leibundgut, M. Dennefeld, Cambridge Univ. Press

Conventionally, CMD analyses of nearby star clusters are based on observations in 2 passbands. They are plagued by considerable degeneracies between age, metallicity, distance (and extinction) that can largely be resolved by including additional passbands with U being most appropriate for young SCs and I or a NIR band for old globular clusters. For star clusters that cannot be resolved, integrated photometry in suitably selected passbands was shown to be as accurate as spectroscopy in independently revealing ages, metallicities, internal extinction, and photometric masses and their respective 1 sigma uncertainties, when analysed with a dedicated analysis tool for their Spectral Energy Distributions (SEDs) (cf. Anders et al. 2004a, b, de Grijs et al. 2003b). For external galaxies, rich star cluster populations can thus be efficiently analysed using deep exposures in 4 suitable filters. Again, the inclusion of the U-band significantly reduces the uncertainties in the cluster parameters. The age and metallicity distributions of star cluster systems yield valuable information about the formation history of their parent galaxies (Fritze - v. A. 2004). Here, we present our GALEV evolutionary synthesis models for star clusters of various metallicities (Anders, Fritze - v. A. 2003), recently extended to include the time evolution of CMDs, the dedicated SED Analysis Tool AnalySED we developed, show results on the basis of HST data, and present first data for a young star cluster system in the ongoing spiral-spiral merger NGC 1487 obtained with SALT during the SALTICAM Performance Verification Phase.

 

astro-ph/0602111 [abs, ps, pdf, other] :

Title: Magnetoconvection and dynamo coefficients III: alpha-effect and magnetic pumping in the rapid rotation regime
Authors: P. J. Käpylä (Oulu & KIS), M. J. Korpi (Helsinki), M. Ossendrijver (KIS), M. Stix (KIS)
Comments: 13 pages, 11 figures, submitted to Astronomy & Astrophysics

Aims. The convective alpha- and gamma-effects, which are responsible for the generation and turbulent pumping of large scale magnetic fields, respectively, are determined in the rapid rotation regime corresponding to the deep layers of the solar convection zone.
Methods. A 3D rectangular local model is used for solving the full set of MHD equations in order to compute the electromotive force (emf), E = <u x b>, generated by the interaction of imposed weak gradient-free magnetic fields and turbulent convection with varying rotational influence and latitude. By expanding the emf in terms of the mean magnetic field, E_i = a_ij <B_j>, all nine components of a_ij are computed. The diagonal elements of a_ij describe the alpha-effect, whereas the off-diagonals represent magnetic pumping. The latter is essentially the advection of magnetic fields by means other than the underlying large-scale velocity field. Comparisons are made to analytical expressions of the coefficients derived under the first-order smoothing approximation (FOSA).
Results. In the rapid rotation regime the latitudinal dependence of the alpha-components responsible for the generation of the azimuthal and radial fields does not exhibit a peak at the poles, as is the case for slow rotation, but at a latitude of about 30 degrees. The magnetic pumping is predominantly radially down- and latitudinally equatorward as in earlier studies. The numerical results compare surprisingly well with analytical expressions derived under first-order smoothing, although the present calculations are expected to lie near the limits of the validity range of FOSA.

 

astro-ph/0602112 [abs, ps, pdf, other] :

Title: Zeeman tomography of magnetic white dwarfs III. The 70-80 Megagauss magnetic field of PG 1015+014
Authors: F. Euchner (1), S. Jordan (2), K. Beuermann (1), K. Reinsch (1), B.T. Gaensicke (3) ((1) Inst. für Astrophysik, Univ. Göttingen, Germany (2) Astron. Rechen-Institut am ZAH, Heidelberg, Germany (3) Dept. of Physics, Univ. of Warwick, Coventry, UK)
Comments: 12 LaTeX pages, 9 EPS figures, accepted for publication in Astronomy & Astrophysics. Full-resolution colour figues can be found at this http URL

<b>Aims:</b> We analyse the magnetic field geometry of the magnetic DA white dwarf PG 1015+014 with our Zeeman tomography method.<br> <b>Methods:</b> This study is based on rotation-phase resolved optical flux and circular polarization spectra of PG 1015+014 obtained with FORS1 at the ESO VLT. Our tomographic code makes use of an extensive database of pre-computed Zeeman spectra. The general approach has been described in Papers I and II of this series.<br> <b>Results:</b> The surface field strength distributions for all rotational phases of PG 1015+014 are characterised by a strong peak at 70 MG. A separate peak at 80 MG is seen for about one third of the rotation cycle. Significant contributions to the Zeeman features arise from regions with field strengths between 50 and 90 MG. We obtain equally good simultaneous fits to the observations, collected in five phase bins, for two different field parametrizations: (i) a superposition of individually tilted and off-centred zonal multipole components; and (ii) a truncated multipole expansion up to degree l = 4 including all zonal and tesseral components. The magnetic fields generated by both parametrizations exhibit a similar global structure of the absolute surface field values, but differ considerably in the topology of the field lines. An effective photospheric temperature of T_eff = 10000 &plusmn; 1000 K was found.<br> <b>Conclusions:</b> Remaining discrepancies between the observations and our best-fit models suggest that additional small-scale structure of the magnetic field exists which our field models are unable to cover due to the restricted number of free parameters.<br>

 

astro-ph/0602113 [abs, ps, pdf, other] :

Title: Study of the cyclotron feature in MXB 0656-072
Authors: V.A. McBride (1), J. Wilms (2), M.J. Coe (1), I. Kreykenbohm (3,4), R.E. Rothschild (5), W. Coburn (6), J.L. Galache (1), P. Kretschmar (7), W.R.T. Edge (1), R. Staubert (3) ((1) Southampton, (2) Warwick, (3) IAA Tuebingen, (4) ISDC, (5) CASS-UCSD, (6) SSL-UCB, (7) ESAC Madrid)
Comments: 7 pages, 6 figures, accepted for publication in A&A

We have monitored a Type II outburst of the Be/X-ray binary MXB 0656-072 in a series of pointed RXTE observations during October through December 2003. The source spectrum shows a cyclotron resonance scattering feature at 32.8 +/- 0.5 keV, corresponding to a magnetic field strength of (3.67 +/- 0.06) x 10^12 G and is stable through the outburst and over the pulsar spin phase. The pulsar, with an average pulse period of 160.4 +/- 0.4 s, shows a spin-up of 0.45 s over the duration of the outburst. From optical data, the source distance is estimated to be 3.9 +/- 0.1 kpc and this is used to estimate the X-ray luminosity and a theoretical prediction of the pulsar spin-up during the outburst.

 

astro-ph/0602114 [abs, ps, pdf, other] :

Title: Water destruction by X-rays in young stellar objects
Authors: P. Stauber, J.K. Jorgensen, E.F. van Dishoeck, S.D. Doty, A.O. Benz
Comments: 12 pages, 14 figures, Accepted for publication in A&A

We study the H2O chemistry in star-forming environments under the influence of a central X-ray source and a central far ultraviolet (FUV) radiation field. The gas-phase water chemistry is modeled as a function of time, hydrogen density and X-ray flux. To cover a wide range of physical environments, densities between n_H = 10^4-10^9 cm^-3 and temperatures between T = 10-1000 K are studied. Three different regimes are found: For T < 100 K, the water abundance is of order 10^-7-10^-6 and can be somewhat enhanced or reduced due to X-rays, depending on time and density. For 100 K < T < 250 K, H2O is reduced from initial x(H2O) ~ 10^-4 following ice evaporation to x(H2O) ~ 10^-6 for F_X > 10^-3 ergs s-1 cm^-2 (t = 10^4 yrs) and for F_X > 10^-4 ergs s^-1 cm^-2 (t = 10^5 yrs). At higher temperatures (T > 250 K) and hydrogen densities, water can persist with x(H2O) ~ 10^-4 even for high X-ray fluxes. The X-ray and FUV models are applied to envelopes around low-mass Class 0 and I young stellar objects (YSOs). Water is destroyed in both Class 0 and I envelopes on relatively short timescales (t ~ 5000 yrs) for realistic X-ray fluxes, although the effect is less prominent in Class 0 envelopes due to the higher X-ray absorbing densities there. FUV photons from the central source are not effective in destroying water. The average water abundance in Class I sources for L_X > 10^27 ergs s^-1 is predicted to be x(H2O) < 10^-6.

 

astro-ph/0602115 [abs, ps, pdf, other] :

Title: A 0535+26: Back in business
Authors: M J Coe (Southampton), P Reig (Crete), V A McBride (Southampton), J L Galache (Southampton), J Fabregat (Valencia)
Comments: Accepted for publication in MNRAS

In May/June 2005, after 10 years of inactivity, the Be/X-ray binary system A 0535+26 underwent a major X-ray outburst. In this paper data are presented from 10 years of optical, IR and X-ray monitoring showing the behaviour of the system during the quiescent epoch and the lead up to the new outburst. The results show the system going through a period when the Be star in the system had a minimal circumstellar disk and then a dramatic disk recovery leading, presumably, to the latest flare up of X-ray emission. The data are interpreted in terms of the state of the disk and its interaction with the neutron star companion.

 

astro-ph/0602116 [abs, ps, pdf, other] :

Title: Cosmic Evolution with Early and Late Acceleration Inspired by Dual Nature of the Ricci Scalar Curvature
Authors: S.K.Srivastava
Comments: 24 pages

It is found that dark energy emerges spontaneously from the higher-derivative gravity. According to cosmological scenario, obtained here, the universe inflates for $\sim 10^{-37}$ sec. in the beginning and late universe accelerates after 8.58 Gyrs. During the long intermediate period, it decelerates driven by radiation and subsequently by matter. Emerged gravitational dark energy mimics quintessence and its density falls by 115 orders from its initial value $2.58\times 10^{68} {\rm GeV}^4$ to its current value $2.19\times 10^{-47} {\rm GeV}^4$ .

 

astro-ph/0602117 [abs, ps, pdf, other] :

Title: Advanced Topics in Cosmology: A Pedagogical Introduction
Authors: T. Padmanabhan
Comments: 40 pages; 6 figures; RevTex4; Extended version of Lecture Courses given at several places including X Special Courses at Observatorio Nacional, Rio de Janeiro, Brazil during 26-30 Sept, 2005. To appear in the Proceedings

These lecture notes provide a concise, rapid and pedagogical introduction to several advanced topics in contemporary cosmology. The discussion of thermal history of the universe, linear perturbation theory, theory of CMBR temperature anisotropies and the inflationary generation of perturbation are presented in a manner accessible to someone who has done a first course in cosmology. The discussion of dark energy is more research oriented and reflects the personal bias of the author. Contents: (I) The cosmological paradigm and Friedmann model (II) Thermal history of the universe (III) Structure formation and linear perturbation theories (IV) Perturbations in dark matter and radiation (V) Transfer function for matter perturbations (VI) Temperature anisotropies of CMBR (VII) Generation of initial perturbations from inflation (VIII) The dark energy.

 

astro-ph/0602118 [abs, ps, pdf, other] :

Title: Dissipative or Conservative cosmology with dark energy ?
Authors: Marek Szydlowski, Orest Hrycyna
Comments: RevTeX4, 23 pages, 12 figures

All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analysed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property -- acceleration -- is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in 1D potential which is parametrised by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We characterise the class of dark energy models that admit late time de Sitter attractor solution in terms of the potential function of corresponding conservative system. We argue that inclusion of dissipation effects makes the model more realistic because of its structural stability. We also confront viscous models with SNIa observations. The best fitted models are obtained by minimising the $\chi^{2}$ function which is illustrated by residuals and $\chi^{2}$ levels in the space of model independent parameters.
The general conclusion is that SNIa data supports the viscous model without the cosmological constant. The obtained values of $\chi^{2}$ statistic are comparable for both the viscous model and $\Lambda$CDM model. The Bayesian information criteria are used to compare the models with different power law parametrisation of viscous effects. Our result of this analysis shows that SNIa data supports viscous cosmology more than $\Lambda$CDM if the coefficient in viscosity parametrisation is fixed.

 

astro-ph/0602119 [abs, ps, pdf, other] :

Title: The First Direct Spectroscopic Detection of a White Dwarf Primary in an AM CVn System
Authors: E.M. Sion, J.E. Solheim, P. Szkody, B. T. Gaensicke, S.B. Howell
Comments: 13 pages, 3 figures
Journal-ref: ApJ letters, January 2006

We report the results of a synthetic spectral analysis of Hubble STIS spectra of the AM CVn-type cataclysmic variable CP Eri obtained when the system was in quiescence. The FUV spectrum is best fitted by a helium-dominated, hybrid composition (DBAZ) white dwarf with Teff=17,000K +/- 1000K, log g=8, He abundance ~1000 times solar, H abundance ~0.1 times solar, metallicity Z ~ 0.05 times solar, V sin i = 400 km/s. This is the first directly detected primary white dwarf in any AM CVn and the surface abundance and rotation rate for the white dwarf primary are the first to be reported for AM CVn systems. The model-predicted distance is ~ 1000 pc. The spectral fits using pure He photospheres or He-rich accretion disks were significantly less successful. Based upon the analysis of our FUV spectra, CP Eri appears to contain a hybrid composition DBAZ white dwarf with a metallicity which sets it apart from the other two AM Cvn stars which have been observed in quiescence and are metal-poor. The implications of this analysis for evolutionary channels leading to AM CVn systems are discussed.

 

astro-ph/0602120 [abs, ps, pdf, other] :

Title: A Far Ultraviolet Study of the Hot White Dwarf in the Dwarf Nova WW Ceti
Authors: P. Godon, L. Seward, E.M. Sion, P. Szkody
Comments: 25 pages, 3 tables, 8 figures (including 2 color ones), final version
Journal-ref: AJ, May 2006 issue. vi

We present a synthetic spectral analysis of IUE archival and FUSE FUV spectra of the peculiar dwarf nova WW Ceti. During the quiescence of WW Ceti, a white dwarf with Twd=26,000K can account for the FUV flux and yields the proper distance. However, the best agreement with the observations is provided by a two-temperature white dwarf model with a cooler white dwarf at Twd=25,000K providing 75% of the FUV flux and a hotter region (accretion belt or optically thick disk ring) with T=40,000K contributing 25% of the flux for the proper distance. We find from the FUSE spectrum that the white dwarf is rotating with a projected rotational velocity V sin{i} = 600 km/s. Our temperature results provide an additional data point in the distribution of Twd versus orbital period above the CV period gap where few Twds are available.

 

astro-ph/0602121 [abs, ps, pdf, other] :

Title: The most metal-poor damped Ly alpha system at z<3: constraints on early nucleosynthesis
Authors: P. Erni, P. Richter, C. Ledoux, P. Petitjean
Comments: 9 pages, 4 figures, accepted for publication in Astronomy and Astrophysics

To constrain the conditions for very early nucleosynthesis in the Universe we compare the chemical enrichment pattern of an extremely metal-poor damped Lyman alpha (DLA) absorber with predictions from recent explosive nucleosynthesis model calculations. For this, we have analyzed chemical abundances in the DLA system at z_abs=2.6183 toward the quasar Q0913+072 (z_em=2.785) using public UVES/VLT high spectral resolution data. The total neutral hydrogen column density in this absorber is logN(HI)=20.36. Accurate column densities are derived for CII, NI, OI, AlII, SiII, and FeII. Upper limits are given for FeIII and NiII. With [C/H]=-2.83, [N/H]=-3.84, and [O/H]=-2.47, this system represents one of the most metal-poor DLA systems investigated so far. It offers the unique opportunity to measure accurate CNO abundances in a protogalactic structure at high redshift. Given the very low overall abundance level and the observed abundance pattern, the data suggest that the chemical evolution of this DLA system is dominated by one or at most a few stellar generations. With reference to numerical model calculations, the chemical abundances in the DLA system are consistent with an enrichment from a single starburst of a zero-metallicity population of massive stars (10-50 M_sun) exploding as core-collapse Supernovae (SNe), i.e., the classical Type II Supernovae (SNeII), and possibly as hyper-energetic (E>10^51erg) core-collapse Supernovae, so-called Hypernovae (HNe), as well. In contrast, models using non-zero metallicity progenitors or other explosion mechanisms, such as pair-instability Supernovae (PISNe) or Type Ia Supernovae (SNeIa), do not match the observed abundance pattern.

 

astro-ph/0602122 [abs, ps, pdf, other] :

Title: Not Alone: Tracing the Origins of Very Low Mass Stars and Brown Dwarfs Through Multiplicity Studies
Authors: Adam J. Burgasser (MIT), I. Neill Reid (STScI), Nick Siegler (UA Steward), Laird Close (UA Steward), Peter Allen (Penn State), Patrick Lowrance (SSC), John Gizis (U Delaware)
Comments: 16 pages, 7 figures, contributed chapter for Planets and Protostars V meeting (October 2005); full table of VLM binaries can be obtained at this http URL

The properties of multiple stellar systems have long provided important empirical constraints for star formation theories, enabling (along with several other lines of evidence) a concrete, qualitative picture of the birth and early evolution of normal stars. At very low masses (VLM; M <~ 0.1 M_sun), down to and below the hydrogen burning minimum mass, our understanding of formation processes is not as clear, with several competing theories now under consideration. One means of testing these theories is through the empirical characterization of VLM multiple systems. Here, we review the results of various VLM multiplicity studies to date. These systems can be generally characterized as closely separated (93% have projected separations Delta < 20 AU) and near equal-mass (77% have M_2/M_1 >= 0.8) occurring infrequently (perhaps 10-30%). Both the frequency and maximum separation of stellar and brown dwarf binaries steadily decrease for lower system masses, suggesting that VLM binary formation and/or evolution may be a mass-dependent process. There is evidence for a fairly rapid decline in the number of loosely-bound systems below ~0.3 M_sun, corresponding to a factor of 10-20 increase in the minimum binding energy of VLM binaries as compared to more massive stellar binaries. This wide-separation ``desert'' is present among both field (~1-5 Gyr) and older (> 100 Myr) cluster systems, while the youngest (<~10 Myr) VLM binaries, particularly those in nearby, low-density star forming regions, appear to have somewhat different systemic properties. We compare these empirical trends to predictions laid out by current formation theories, and outline future observational studies needed to probe the full parameter space of the lowest mass multiple systems.

 

astro-ph/0602123 [abs, ps, pdf, other] :

Title: Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leo
Authors: I. Crespo-Chacon (1), D. Montes (1), D. Garcia-Alvarez (2,3), M.J. Fernandez-Figueroa (1), J. Lopez-Santiago (1,4), B.H. Foing (5), ((1) Dept. Astrofisica, UCM, Universidad Complutense de Madrid, (2) Harvard-Smithsonian Center for Astrophysics, (3) Armagh Observatory, (4) INAF - Osservatorio Astronomico di Palermo, (5) Research Division, ESA Space Science Dept., ESTEC/SCI-R)
Comments: Latex file with 17 pages, 11 figures. Available at this http URL Accepted for publication in: Astronomy & Astrophysics (A&A)

We report the results of a high temporal resolution spectroscopic monitoring of the flare star AD Leo. During 4 nights, more than 600 spectra were taken in the optical range using the Isaac Newton Telescope (INT) and the Intermediate Dispersion Spectrograph (IDS). We have observed a large number of short and weak flares occurring very frequently (flare activity > 0.71 hours-1). This is in favour of the very important role that flares can play in stellar coronal heating. The detected flares are non white-light flares and, though most of solar flares belong to this kind, very few such events had been previously observed on stars. The behaviour of different chromospheric lines (Balmer series from H_alpha to H_11, Ca II H & K, Na I D_1 & D_2, He I 4026 AA and He I D_3) has been studied in detail for a total of 14 flares. We have also estimated the physical parameters of the flaring plasma by using a procedure which assumes a simplified slab model of flares. All the obtained physical parameters are consistent with previously derived values for stellar flares, and the areas - less than 2.3% of the stellar surface - are comparable with the size inferred for other solar and stellar flares. Finally, we have studied the relationships between the physical parameters and the area, duration, maximum flux and energy released during the detected flares.

 

astro-ph/0602124 [abs, ps, pdf, other] :

Title: Voigt Profile Fitting to Quasar Absorption Lines: A Simple Approximation to the Voigt-Hjerting Function
Authors: Thorsten Tepper García
Comments: 9 pages, 7 figures, submitted to MNRAS

The Voigt-Hjerting function is fundamental in order to correctly model the profiles of absorption lines imprinted in the spectra of bright background sources (e.g quasars) by intervening neutral hydrogen. In this work we present a simple analytical approximation to this function in the context of intergalactic neutral hydrogen absorption-line profiles. Using basic calculus tools, we derive an expression that contains only fourth order polynomial and Gaussian functions, and that approximates this function with an accuracy better than $10^{-3}$ per cent. In connection with the absorption coefficient of intergalactic neutral hydrogen, $\tau_{\mathrm{H I}}(\lambda)$, this approximation is valid for an arbitrary wavelength baseline, for column densities up to $\nhi = 10^{22} \mathrm{cm}^{-2}$, and for damping parameters $a \leq 10^{-4}$, i.e. the entire range of parameters characteristic for intergalactic neutral hydrogen in a variety of absorbers. We hence derive an approximation to the Voigt-Hjerting function that is both accurate enough and easy to handle, and with which Voigt profiles can be calculated in a reliable and very simple manner.

 

astro-ph/0602125 [abs, ps, pdf, other] :

Title: Dynamics of compact objects: A post-Newtonian study
Authors: Gabor Kupi, Pau Amaro-Seoane, Rainer Spurzem
Comments: 5 pages, needs mn2e.bst and mn2e.cls (included in the tar.gz file) submitted to MNRAS

Compact object clusters are likely to exist in the centre of some galaxies because of mass segregation. The high densities and velocities reached in them deserves a better understanding. The formation of binaries and their subsequent merging by gravitational radiation emission is important to the evolution of such clusters. We address the evolution of such a system in a relativistic regime. The recurrent mergers at high velocities create an object with a mass much larger than the average. For this aim we modified the direct Nbody6++ code to include post-Newtonian effects to the force during two-body encounters. We adjusted the equations of motion to include for the first time the effects of both periastron shift and energy loss by emission of gravitational waves and so to study the eventual decay and merger of radiating binaries. The method employed allows us to give here an accurate post-Newtonian description of the formation of a run-away compact object by successive mergers with surrounding particles, as well as the distribution of characteristic eccentricities in the events. This study should be envisaged as a first step towards a detailed, accurate study of possible gravitational waves sources thanks to the combination of the direct Nbody numerical tool with the implementation of post-Newtonian terms on it.

 

astro-ph/0602126 [abs, ps, pdf, other] :

Title: The Dwarf Novae During Quiescence
Authors: Joel A. Urban, Edward M. Sion
Comments: 36 pages, 3 tables, 8 figures, final accepted version of manuscript
Journal-ref: ApJ, 2006, May 10 issue

We present a synthetic spectral analysis of nearly the entire FUV IUE archive of spectra of DNe in or near quiescence. We have examined all of the systems for which S/N permitted an analysis. The study includes 53 systems of all DN subtypes both above and below the period gap. The spectra were uniformly analyzed using synthetic spectral codes for optically thick accretion disks and stellar photospheres along with the best-available distance measurements or estimates. We present newly determined approximate WD temperatures or upper limits and estimated accretion rates. The average temperature of WDs in DNe below the period gap is ~18,000K. For WDs in DNe above the period gap, the average WD temperature is ~26,000K. There is a flux component, in addition to a WD photosphere, which contributes >60% of the flux in the FUV in 53% of the quiescent DNe in this study. We find that for 41% of the DNe in our sample, a WD photosphere provides >60% of the FUV flux. Accretion rates estimated from the FUV alone for the sample of DNe during quiescence ranged from 10^-12 Msun/yr to 10^-10 Msun/yr.The additional flux component is almost certainly not an optically thick accretion disk since, according to the disk instability model, the disk should be optically thin and too cool during DN quiescence to be a significant FUV continuum emitter. Among the candidates for the second component of FUV light are the quiescent inner disk, a hot equatorial accretion belt, and a hot rotating ring. The implications of our study for disk accretion physics and CV evolution are discussed.

 

astro-ph/0602127 [abs, ps, pdf, other] :

Title: X-ray spectral properties of AGN in the Chandra Deep Field South
Authors: P. Tozzi (INAF, OAT), R. Gilli, V. Mainieri, C. Norman, G. Risaliti, P. Rosati, J. Bergeron, S. Borgani, R. Giacconi, G. Hasinger, M. Nonino, A. Streblyanska, G. Szokoly, J.X. Wang, W. Zheng
Comments: 86 pages, A&A accepted, full version available at this http URL

We present a detailed X-ray spectral analysis of the sources in the 1Ms catalog of the Chandra Deep Field South (CDFS) taking advantage of optical spectroscopy and photometric redshifts for 321 sources. As a default spectral model, we adopt a power law with slope Gamma with an intrinsic redshifted absorption N_H, a fixed Galactic absorption and an unresolved Fe emission line. For 82 X-ray bright sources, we perform the X-ray spectral analysis leaving both Gamma and N_H free. The weighted mean value is <Gamma>~ 1.75+-0.02, with an intrinsic dispersion of sigma~0.30. We do not find hints of a correlation between Gamma and the N_H. We detect the presence of a scattered component at soft energies in 8 sources, and a pure reflection spectrum, typical of Compton-thick AGN, in 14 sources (Compton-thick AGN candidates). The intrinsic N_H distribution shows a lognormal shape, peaking around log(N_H)~23.1 and with sigma~1.1. We find that the fraction of absorbed sources (with N_H>10^{22} cm^{-2}) in the sample is constant (at the level of about 75%) or moderately increasing with redshift. Finally, we compare the optical classification to the X-ray spectral properties, confirming that the correspondence of unabsorbed (absorbed) X-ray sources to optical Type I (Type II) AGN is accurate for at least 80% of the sources with spectral identification (1/3 of the total X-ray sample).

 

astro-ph/0602128 [abs, ps, pdf, other] :

Title: A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
Authors: Philip Massey, K. A. G. Olsen, Paul W. Hodge, Shay B. Strong, George H. Jacoby, Wayne Schlingman, R. C. Smith
Comments: Accepted by the Astronomical Journal. A version with higher resolution figures can be found at: this http URL

We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the KPNO 4-m telescope. The survey covers 2.2 sq degrees of M31, and 0.8 sq degrees of M33, chosen so as to include all of the regions currently active in forming massive stars. The catalog contains 371,781 and 146,622 stars in M31 and M33, respectively, where every star has a counterpart (at least) in B, V, and R. We compare our photometry to previous studies. We provide cross references to the stars confirmed as members by spectroscopy, and compare the location of these to the complete set in color-magnitude diagrams. While follow-up spectroscopy is needed for many projects, we demonstrate the success of our photometry in being able to distinguish M31/M33 members from foreground Galactic stars. We also present the results of newly obtained spectroscopy, which identifies 34 newly confirmed members, including B-A supergiants, the earliest O star known in M31, and two new Luminous Blue Variable candidates whose spectra are similar to that of P Cygni.

 

astro-ph/0602129 [abs, ps, pdf, other] :

Title: The uncombed penumbra
Authors: J.M. Borrero, M. Rempel, S.K. Solanki
Comments: 6 pages, 2 figures. to appear in the proceedings of the Solar Polarization Workshop IV

The uncombed penumbral model explains the structure of the sunspot penumbra in terms of thick magnetic fibrils embedded in a magnetic surrounding atmosphere. This model has been successfully applied to explain the polarization signals emerging from the sunspot penumbra. Thick penumbral fibrils face some physical problems, however. In this contribution we will offer possible solutions to these shortcomings.

 

astro-ph/0602130 [abs, ps, pdf, other] :

Title: Magnetic field vector retrieval with HMI
Authors: J.M. Borrero, S. Tomczyk, A. Norton, T. Darnell, J. Schou, P. Scherrer, R. Bush, Y. Lui
Comments: 4 pages, 2 figures. to appear in the proceedings of the Solar Polarizaton Workshop IV

The Helioseismic and Magnetic Imager (HMI), on board the Solar Dynamics Observatory (SDO), will begin data acquisition in 2008. It will provide the first full disk, high temporal cadence observations of the full Stokes vector with a 0.5 arc sec pixel size. This will allow for a continuous monitoring of the Solar magnetic field vector. HMI data will advance our understanding of the small and large-scale magnetic field evolution, its relation to the solar and global dynamic processes, coronal field extrapolations, flux emergence, magnetic helicity and the nature of the polar magnetic fields. We summarize HMI's expected operation modes, focusing on the polarization cross-talk induced by the solar oscillations and how this affects the magnetic field vector determinations.

 

astro-ph/0602131 [abs, ps, pdf, other] :

Title: An ultradeep submillimetre map: beneath the SCUBA confusion limit with lensing and robust source extraction
Authors: K.K. Knudsen, V.E. Barnard, P.P. van der Werf, P. Vielva, J.-P. Kneib, A.W. Blain, R.B. Barreiro, R.J. Ivison, I. Smail, J.A. Peacock
Comments: 11 pages, 6 figures. Accepted for publication in MNRAS. Figures 2 and 4 (lower panel) available in higher resolution this http URL

Extracting sources with low signal-to-noise from maps with structured background is a non-trivial task which has become important in studying the faint end of the submillimetre number counts. In this article we study source extraction from submillimetre jiggle-maps from the Submillimetre Common-User Bolometer Array (SCUBA) using the Mexican Hat Wavelet (MHW), an isotropic wavelet technique. As a case study we use a large (11.8 arcmin^2) jiggle-map of the galaxy cluster Abell 2218, with a 850um 1sigma r.m.s. sensitivity of 0.6-1mJy. We show via simulations that MHW is a powerful tool for reliable extraction of low signal-to-noise sources from SCUBA jiggle-maps and nine sources are detected in the A2218 850um image. Three of these sources are identified as images of a single background source with an unlensed flux of 0.8mJy. Further, two single-imaged sources also have unlensed fluxes <2mJy, below the blank-field confusion limit. In this ultradeep map, the individual sources detected resolve nearly all of the extragalactic background light at 850um, and the deep data allow to put an upper limit of 44 sources per arcmin^2 to 0.2mJy at 850um.

 

astro-ph/0602132 [abs, ps, pdf, other] :

Title: Astroparticle Physics with High Energy Neutrinos: from AMANDA to IceCube
Authors: Francis Halzen
Comments: 37 pages, 16 postsript figures, review article submited to EPJC

Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of $10^{20}$\,eV and $10^{13}$\,eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the science reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos. The outline of this review is as follows:
Introduction
Why Kilometer-Scale Detectors?
Cosmic Neutrinos Associated with the Highest Energy Cosmic Rays
High Energy Neutrino Telescopes: Methodologies of Neutrino Detection
High Energy Neutrino Telescopes: Status