Astrophysics

astro-ph new abstracts, Mon, 17 Apr 06 00:00:09 GMT
0604318 -- 0604335 received

astro-ph/0604318 [abs, ps, pdf, other] :: Title: Chandra X-Ray Observations of Nineteen Millisecond Pulsars in the Globular Cluster 47 Tucanae
Authors: Slavko Bogdanov, Jonathan E. Grindlay, Craig O. Heinke, Fernando Camilo, Paulo C. C. Freire, Werner Becker
Comments: 13 pages, 6 figures, accepted for publication in the Astrophysical Journal

We present spectral and long-timescale variability analyses of \textit{Chandra} ACIS-S observations of the 19 millisecond pulsars (MSPs) with precisely known positions in the globular cluster 47 Tucanae. The X-ray emission of the majority of these MSPs is well described by a thermal (blackbody or neutron star hydrogen atmosphere) spectrum with a temperature $T_{\rm eff}\sim(1-3)\times10^6$ K, emission radius $R_{\rm eff}\sim0.1-3$ km, and luminosity $L_{X}\sim10^{30-31}$ ergs s$^{-1}$. For several MSPs, there is indication that a second thermal component is required, similar to what is seen in some nearby field MSPs. The radio-eclipsing binary MSPs 47 Tuc J, O, and W show a significant non-thermal component, with photon index $\Gamma\sim 1-1.5$, which may originate in an shock formed due to interaction between the relativistic pulsar wind and matter from the stellar companion. We re-examine the X-ray--spindown luminosity relation ($L_{X}-\dot{E}$) and find that due to the large uncertainties in both parameters the result is consistent with both the linear $L_{X}-\dot{E}$ relation and the flatter $L_X\propto\dot{E}^{0.5}$ predicted by polar cap heating models. In terms of X-ray properties, we find no clear systematic differences between MSPs in globular clusters and in the field of the Galaxy.
astro-ph/0604319 [abs, ps, pdf, other] :: Title: Pulsational Instabilities in Accreting White Dwarfs
Authors: Phil Arras, Dean M. Townsley, Lars Bildsten
Comments: submitted to ApJL. 3 figures

(Abridged) The Cataclysmic Variable (CV) population harbors a diverse range of donor stars and accreting white dwarfs (WDs). A range of WD masses is expected, from low mass Helium core WDs, to massive WDs which have previously accreted at rates high enough for Hydrogen to burn steadily. Furthermore, a wide range of Helium enrichment is expected in the accreted material depending on the degree to which the donor star is evolved. We investigate the impact of this diversity on the range of effective temperatures ($T_{\rm eff}$) for which g-modes are unstable. The critical $T_{\rm eff}$ below which modes are unstable ("blue edge") depends on both surface gravity, $g$, and He abundance, $Y$. The Hydrogen/first Helium ionization instability strip is more sensitive to $g$ than $Y$. We find that (for solar composition envelopes), relative to a fiducial WD mass $0.6 M_\odot$, the blue edge for a $0.4 M_\odot$ He core WD shifts downward by $\approx 1000 {\rm K}$, while that for a massive $\approx 1.2 M_\odot$ WD shifts upward by $\approx 2000 {\rm K}$. The second Helium ionization instability strip exhibits strong dependences on both $g$ and $Y$. Surprisingly, increasing $Y$ by only 10% relative to solar creates an instability strip near $15,000 {\rm K}$. Hence CV's below the period gap with evolved donor stars of $Y\ga 0.4$ may have an "intermediate" instability strip well outside of the isolated DA and DB variables. This "intermediate" instability strip also occurs for low mass He WD with solar composition envelopes. The lack of pulsations in CV's with $T_{\rm eff}$ in the pure Hydrogen ZZ Ceti instability strip is also easily explained.
astro-ph/0604320 [abs, ps, pdf, other] :: Title: Jet Breaks in Short Gamma-Ray Bursts. II: The Collimated Afterglow of GRB 051221A
Authors: David N. Burrows, Dirk Grupe, Milvia Capalbi, Alin Panaitescu, Sandeep K. Patel, Chryssa Kouveliotou, Bing Zhang, Peter Meszaros, Guido Chincarini, N. Gehrels, Ralph A.M. Wijers
Comments: 10 pages, 4 figures. Submitted to The Astrophysical Journal 13 April 2006

We report the first clear detection of a jet break in a short Gamma-Ray Burst (GRB) afterglow, using Chandra and Swift XRT observations of the X-ray afterglow of GRB 051221A. The combined X-ray light curve, which has three breaks, is similar to those commonly observed in Swift observations of long GRBs. A flat segment of the light curve at ~0.1 days after the burst represents the first clear case of strong energy injection in the external shock of a short GRB afterglow. The last break occurs at ~4 days post-burst and breaks to a power-law decay index of ~2. We interpret this as a jet break, with important implications for models of short GRBs, since it requires collimation of the afterglow into a jet with an initial opening angle ~4-8 degrees and implies a total jet kinetic energy of E_jet ~(1-5) x 10^{49} erg. Combined with the lack of a jet break in GRB 050724, this suggests a wide range in jet collimation in short GRBs, with at least some having collimation similar to that found in long GRBs, though with significantly lower jet energies.
astro-ph/0604321 [abs, ps, pdf, other] :: Title: Star Formation in Satellite Galaxies
Authors: C.M. Gutierrez (1), M.S. Alonso (2), J.G. Funes (3), M.B. Ribeiro (4) ((1)Instituto de Astrofisica de Canarias, Spain, (2) Consejo Nacional de Investigacion Cientificas y Tecnicas, Argentina, (3) Vatican Observatory, Vatican, (4) Universidade Federal do Rio de Janeiro, Brazil)
Comments: 25 pages, 11 figures. Accepted for publication in AJ

We present narrow-band observations of the H$\alpha$ emission in a sample of 31 satellite orbiting isolated giant spiral galaxies. The sample studied spans the range $-19<M_B <-15$ mag. The H$\alpha$ emission was detected in all the spiral and irregular objects with fluxes in the range $1.15-49.80\times 10^{-14}$ erg cm$^{-2}$ s$^{-1}$. The average and maximum values for the current star formation rates are 0.68 and 3.66 M$_\sun$ yr$^{-1}$ respectively. Maps of the spatial distribution of ionized gas are presented. The star-forming regions show a rich structure in which frequently discrete complexes are imposed over more diffuse structures. In general, the current star formation rates are smaller that the mean values in the past obtained from the current stellar content; this probably indicates a declining rhythm with time in the generation of new stars. However, the reserve of gas is enough to continue fueling the current levels of star formation activity for at least another Hubble time. Four of the objects (NGC 2718b, NGC 4541e, NGC 5965a$_1$ and NGC 5965a$_2$) with higher current star formation rates show clear signs of interaction with close companions of comparable brightness at projected distances of 25, 20 and 2 kpc respectively. The only two galaxies in our sample that do not show star formation activity are members of these interacting systems, and it is unclear if this is a consequence of intrinsic properties (both are Hubble early types) or if it is related with possible disruption of the external parts due to the interaction. In the case of the pair NGC 2718a-b there are indications of gas transport between both galaxies.
astro-ph/0604322 [abs, ps, pdf, other] :: Title: Characterizing Charge Diffusion in CCDs with X-rays
Authors: S. A. Rodney, J. L. Tonry
Comments: 12 pages, 8 figures, accepted for publication in PASP

We demonstrate the effectiveness of two techniques for using x-rays to evaluate the amount of charge diffusion in charge coupled devices (CCDs). We quantify the degree of charge diffusion with two parameters: sigma_d, the standard deviation for a Gaussian diffusion model, and Q, a ratio of the point spread function (PSF) peak to its wings. sigma_d and Q are determined by fitting a model to a pixel energy histogram, and by summing the PSF of all x-ray events, respectively. Using seven test devices, we investigate the precision of these two techniques and demonstrate that they produce compatible results. The histogram fitting method is sensitive to the structure of the electric field within these devices, in addition to the inherent charge diffusion properties. The Q ratio is a very simple parameter to measure and provides an easily accessible method for quickly evaluating a CCD's diffusion length.
astro-ph/0604323 [abs, ps, pdf, other] :: Title: Does the Milky Way Produce a Nuclear Galactic Wind?
Authors: Brian A. Keeney (1), Charles W. Danforth (1), John T. Stocke (1), Steven V. Penton (1), J. Michael Shull (1), Kenneth R. Sembach (2) ((1) CASA, Univ. of Colorado, (2) STScI)
Comments: 39 pages, 3 figures, ApJ accepted

We detect high-velocity absorbing gas using Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer medium resolution spectroscopy along two high-latitude AGN sight lines (Mrk 1383 and PKS 2005-489) above and below the Galactic Center (GC). These absorptions are most straightforwardly interpreted as a wind emanating from the GC which does not escape from the Galaxy's gravitational potential. Spectra of four comparison B stars are used to identify and remove foreground velocity components from the absorption-line profiles of O VI, N V, C II, C III, C IV, Si II, Si III, and Si IV. Two high-velocity (HV) absorption components are detected along each AGN sight line, three redshifted and one blueshifted. Assuming that the four HV features trace a large-scale Galactic wind emanating from the GC, the blueshifted absorber is falling toward the GC at a velocity of 250 +/- 20 km/s, which can be explained by "Galactic fountain" material that originated in a bound Galactic wind. The other three absorbers represent outflowing material; the largest derived outflow velocity is +250 +/- 20 km/s, which is only 45% of the velocity necessary for the absorber to escape from its current position in the Galactic gravitational potential. All four HV absorbers are found to reach the same maximum height above the Galactic plane (|z_max| = 12 +/- 1 kpc), implying that they were all ejected from the GC with the same initial velocity. The derived metallicity limits of >10-20% Solar are lower than expected for material recently ejected from the GC unless these absorbers also contain significant amounts of hotter gas in unseen ionization stages.
astro-ph/0604324 [abs, ps, pdf, other] :: Title: Tomography of the Reionization Epoch with Multifrequency CMB Observations
Authors: Carlos Hernandez-Monteagudo (1), Licia Verde (1), Raul Jimenez (1) ((1) University of Pennsylvania)
Comments: 10 pages, 2 figures, submitted to Astrophysical Journal. Comments are welcome

We study the constraints that future multifrequency Cosmic Microwave Background (CMB) experiments will be able to set on the metal enrichment history of the Inter Galactic Medium at the epoch of reionisation. We forecast the signal to noise ratio for the detection of the signal introduced in the CMB by resonant scattering off metals at the end of the Dark Ages. We take into account systematics associated to inter-channel calibration, PSF reconstruction errors and innacurate foreground removal. We develop an algorithm to optimally extract the signal generated by metals during reionisation and to remove accurately the contamination due to the thermal Sunyaev-Zel'dovich effect. Although demanding levels of foreground characterisation and control of systematics are required, they are very distinct from those encountered in HI-21cm studies and CMB polarization, and this fact encourages the study of resonant scattering off metals as an alternative way of conducting tomography of the reionisation epoch. An ACT-like experiment with optimistic assumtions on systematic effects, and looking at clean regions of the sky, can detect changes of 3%-12% (95% c.l.) of the OIII abundance (with respect its solar value) in the redshift range $z\in$ [12,22], for reionization redshift $z_{\rm re}>10$. However, for $z_{\rm re} <10$, it can only set upper limits on NII abundance increments of $\sim$ 60% its solar value in the redshift range $z\in$ [5.5,9], (95% c.l.). These constraints assume that inter-channel calibration is accurate down to one part in $10^{4}$, which constitutes the most critical technical requirement of this method, but still achievable with current technology.
astro-ph/0604325 [abs, ps, pdf, other] :: Title: Delayed X- and Gamma-Ray Line Emission from Solar Flare Radioactivity
Authors: V. Tatischeff, B. Kozlovsky, J. Kiener, R. J. Murphy
Comments: Accepted for publication in ApJS. 29 pages, 12 figures

We have studied the radioactive line emission expected from solar active regions after large flares, following the production of long-lived radioisotopes by nuclear interactions of flare-accelerated ions. This delayed X- and gamma-ray line emission can provide unique information on the accelerated particle composition and energy spectrum, as well as on mixing processes in the solar atmosphere. Total cross sections for the formation of the main radioisotopes by proton, 3-He and alpha-particle reactions are evaluated from available data combined with nuclear reaction theory. Thick-target radioisotope yields are provided in tabular form, which can be used to predict fluxes of all of the major delayed lines at any time after a gamma-ray flare. The brightest delayed line for days after the flare is found to be the 511 keV positron-electron annihilation line resulting from the decay of several beta+ radioisotopes. After ~2 days however, the flux of the 511 keV line can become lower than that of the 846.8 keV line from the decay of 56-Co. Our study has revealed other delayed gamma-ray lines that appear to be promising for detection, e.g. at 1434 keV from the radioactivity of both the isomer and the ground state of 52-Mn, 1332 and 1792 keV from 60-Cu, and 931.1 keV from 55-Co. The strongest delayed X-ray line is found to be the Co Kalpha at 6.92 keV, which is produced from both the decay of the isomer of 58-Co by the conversion of a K-shell electron and the decay of 57-Ni by orbital electron capture. Prospects for observation of these lines with RHESSI or future space instruments are discussed.
astro-ph/0604326 [abs, ps, pdf, other] :: Title: The Swift satellite and redshifts of long gamma-ray bursts
Authors: Z. Bagoly, A. Mészáros, L.G. Balázs, I. Horváth, S. Klose, S. Larsson, P. Mészáros, F. Ryde, G. Tusnády
Comments: 4 pages, accepted as an A&A Research Note

Until 6 October 2005 sixteen redshifts have been measured of long gamma-ray bursts discovered by the Swift satellite. Further 45 redshifts have been measured of the long gamma-ray bursts discovered by other satellites. Here we perform five statistical tests comparing the redshift distributions of these two samples assuming - as the null hypothesis - identical distribution for the two samples. Three tests (Student's $t$-test, Mann-Whitney test, Kolmogorov-Smirnov test) reject the null hypothesis on the significance levels between 97.19 and 98.55%. Two different comparisons of the medians show extreme $(99.78-99.99994)$% significance levels of rejection. This means that the redshifts of the Swift sample and the redshifts of the non-Swift sample are distributed differently - in the Swift sample the redshifts are on average larger. This statistical result suggests that the long GRBs should on average be at the higher redshifts of the Swift sample.
astro-ph/0604327 [abs, ps, pdf, other] :: Title: Top ten accelerating cosmological models
Authors: Marek Szydlowski, Aleksandra Kurek, Adam Krawiec
Comments: RevTeX4, 12 pages, 6 figures

Recent astronomical observations indicate that the Universe is presently almost flat and undergoing a period of accelerated expansion. Basing on Einstein's general relativity all these observations can be explained by the hypothesis of a dark energy component in addition to cold dark matter (CDM). Because the nature of this dark energy is unknown, it was proposed some alternative scenario to explain the current accelerating Universe. The key point of this scenario is to modify the standard FRW equation instead of mysterious dark energy component. The standard approach to constrain model parameters based on the likelihood method gives a best-fit model and confidence ranges for those parameters, we always arbitrary choose the set of parameters which define a model which we compare with observational data. Because in the generic case, the introducing of new parameters improves a fit to the data set, there appears the problem of elimination of model parameters which can play an insufficient role in improving the fit to the data available. The Bayesian information criteria of model selection (the AIC, BIC and Bayes factor) are dedicated to promotion a set of parameters which should be incorporated to the model. We divide class of all accelerating cosmological models into two groups according to the two types of explanation acceleration of the Universe. Then the Bayesian framework of model selection is used to determine the set of parameters which gives preferred fit to the SNIa data. We find a few of flat cosmological models which can be recommend by both the Bayesian factor and distant supernovae data.
astro-ph/0604328 [abs, ps, pdf, other] :: Title: Outflows from the high-mass protostars NGC 7538 IRS1/2 observed with bispectrum speckle interferometry -- Signatures of flow precession
Authors: S. Kraus, Y. Balega, M. Elitzur, K.-H. Hofmann, M. Meyer, Th. Preibisch, A. Rosen, D. Schertl, G. Weigelt, E. T. Young
Comments: 20 pages; 8 figures; Accepted by A&A on April 10, 2006; Image quality reduced due to astro-ph file size limitations

NGC 7538 IRS1 is a high-mass (approx. 30 M_sun) protostar with a CO outflow, an associated UCHII region, and a linear methanol maser structure, which might trace a Keplerian-rotating circumstellar disk. The directions of the various associated axes are misaligned with each other. We investigate the near-infrared morphology of the source to clarify the relations among the various axes. K'-band bispectrum speckle interferometry was performed at two 6-meter-class telescopes -- the BTA 6m telescope and the 6.5m MMT. Complementary IRAC images from the Spitzer Space Telescope Archive were used to relate the structures detected with the outflow at larger scales. High-dynamic range images show fan-shaped outflow structure in which we detect 18 stars and several blobs of diffuse emission. We interpret the misalignment of various outflow axes in the context of a disk precession model, including numerical hydrodynamic simulations of the molecular emission. The precession period is approx. 280 years and its half-opening angle is 40 degrees. A possible triggering mechanism is non-coplanar tidal interaction of an (undiscovered) close companion with the circumbinary protostellar disk. Our observations resolve the nearby massive protostar NGC 7538 IRS2 as a close binary with separation of 195 mas. We find indications for shock interaction between the outflow activities in IRS1 and IRS2. Indications of outflow precession have been discovered to date in a number of massive protostars, all with large precession angles 20--45 degrees. This might explain the difference between the outflow widths in low- and high-mass stars and add support to a common collimation mechanism.
astro-ph/0604329 [abs, ps, pdf, other] :: Title: A close look to quasar-triggered winds: is the black hole-bulge relation self-regulated?
Authors: P. Monaco (DAUT - University of Trieste and INAF-OATs)
Comments: 8 pages, 3 postscript figures, proceedings of the Workshop on "AGN and galaxy evolution", Specola Vaticana, Castel Gandolfo, Italy, 3-6 October 2005

We discuss the role of feedback from AGNs on the formation of spheroidal galaxies. The energy released by an accreting Black Hole (BH) may be injected into the ISM through blast waves arising directly from the central engine, radiation pressure or radiative heating. A scenario is described in which radiative heating perturbs the methabolism of a star-forming spheroid, leading to a critical stage where SNe form a cold expanding shell, pushed out of the galaxy by radiation pressure from the AGN. This mechanism can regulate the BH--bulge relation to the observed value. However, this relation may be simply imprinted by the mechanism responsible for the nearly complete loss of angular momentum of the gas that accretes onto the BH. Using a novel model of galaxy formation that includes AGNs, we show that models without self-regulation have problems in reproducing the correct slope of the AGN luminosity function, while models with winds give a much better fit; however, all these models are almost indistingishable as far as their predicted BH--bulge relation is concerned. Finally, we show that the downsizing of the faint AGNs is most likely due to kinetic feedback in star-forming bulges.
astro-ph/0604330 [abs, ps, pdf, other] :: Title: Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067
Authors: M. Vuckovic (1 and 2), S. D. Kawaler (2), for the WET collaboration ((1)Instituut voor Sterrenkunde, K.U. Leuven, (2) Iowa State University)
Comments: 19 pages, preprint of paper accepted for publication in The Astrophysical Journal

PG 0014+067 is one of the most promising pulsating subdwarf B stars for seismic analysis, as it has a rich pulsation spectrum. The richness of its pulsations, however, poses a fundamental challenge to understanding the pulsations of these stars, as the mode density is too complex to be explained only with radial and nonradial low degree (l < 3) p-modes without rotational splittings. One proposed solution, for the case of PG 0014+067 in particular, assigns some modes with high degree (l=3). On the other hand, theoretical models of sdB stars suggest that they may retain rapidly rotating cores, and so the high mode density may result from the presence of a few rotationally-split triplet (l=1), quintuplet (l=2) modes, along with radial (l=0) p-modes. To examine alternative theoretical models for these stars, we need better frequency resolution and denser longitude coverage. Therefore, we observed this star with the Whole Earth Telescope for two weeks in October 2004. In this paper we report the results of Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067. We find that the frequencies seen in PG 0014+067 do not appear to fit any theoretical model currently available; however, we find a simple empirical relation that is able to match all of the well-determined frequencies in this star.
astro-ph/0604331 [abs, ps, pdf, other] :: Title: Optimal Image Reconstruction in Radio Interferometry
Authors: Edmund C. Sutton, Benjamin D. Wandelt (UIUC)
Comments: 41 pages, 11 figures. High resolution figures 8 and 9 available at this http URL
Journal-ref: Sutton, E. C., and Wandelt, B. D. 2006, ApJS, 162, 401-416

We introduce a method for analyzing radio interferometry data which produces maps which are optimal in the Bayesian sense of maximum posterior probability density, given certain prior assumptions. It is similar to maximum entropy techniques, but with an exact accounting of the multiplicity instead of the usual approximation involving Stirling's formula. It also incorporates an Occam factor, automatically limiting the effective amount of detail in the map to that justified by the data. We use Gibbs sampling to determine, to any desired degree of accuracy, the multi-dimensional posterior density distribution. From this we can construct a mean posterior map and other measures of the posterior density, including confidence limits on any well-defined function of the posterior map.
astro-ph/0604332 [abs, ps, pdf, other] :: Title: Detection of a 63 Degree Cold Stellar Stream in the Sloan Digital Sky Survey
Authors: Carl J. Grillmair, Odysseas Dionatos
Comments: 12 pages, 2 figures, accepted for publication in the Astrophysical Journal Letters

We report on the detection in Sloan Digital Sky Survey data of a 63 degree-long tidal stream of stars, extending from Ursa Major to Cancer. The stream has no obvious association with the orbit of any known cluster or galaxy. The contrast of the detected stream is greatest when using a star count filter which is matched to the color-magnitude distribution of stars in M 13, suggesting that the stars making up the stream are old and metal poor. The visible portion of the stream is very narrow and about 8.5 kpc above the Galactic disk, suggesting that the progenitor is or was a globular cluster. While the surface density of the stream varies considerably along its length, its path on the sky is very smooth and uniform, showing no evidence of perturbations by large mass concentrations in the nearby halo. While definitive constraints cannot be established without radial velocity information, the combination of the stream's projected path and estimates of its distance suggest that we are observing the stream near the perigalacticon of its orbit.
astro-ph/0604333 [abs, ps, pdf, other] :: Title: The secrets of the nearest starburst cluster: II. The present-day mass function in NGC 3603
Authors: Andrea Stolte, Wolfgang Brandner, Bernhard Brandl, Hans Zinnecker
Comments: accepted for publication in AJ A high-resolution version of the preprint can be found at this http URL

Based on deep VLT/ISAAC JHK photometry, we have derived the present-day mass function of the central starburst cluster NGC 3603 YC (Young Cluster) in the giant HII region NGC 3603. The effects of field contamination, individual reddening, and a possible binary contribution are investigated. The MF slopes resulting from the different methods are compared, and lead to a surprisingly consistent cluster MF with a slope of Gamma = -0.9 +/- 0.15. Analyzing different radial annuli around the cluster core, no significant change in the slope of the MF is observed. However, mass segregation in the cluster is evidenced by the increasing depletion of the high-mass tail of the stellar mass distribution with increasing radius. We discuss the indications of mass segregation with respect to the changes observed in the binned and cumulative stellar mass functions, and argue that the cumulative function as well as the fraction of high- to low-mass stars provide better indicators for mass segregation than the MF slope alone. (abridged)
astro-ph/0604334 [abs, ps, pdf, other] :: Title: The UCSD Radio-Selected Quasar Survey for Damped Lyman alpha System
Authors: Regina A. Jorgenson, Arthur M. Wolfe, Jason X. Prochaska, Limin Lu, J. Christopher Howk, Jeff Cooke, Eric Gawiser, Dawn M. Gelino
Comments: 12 pages, 9 Figures. Accepted to ApJ April 11, 2006

As large optical quasar surveys for damped Lya become a reality and the study of star forming gas in the early Universe achieves statistical robustness, it is now vital to identify and quantify the sources of systematic error. Because the nature of optically-selected quasar surveys makes them vulnerable to dust obscuration, we have undertaken a radio-selected quasar survey for damped Lya systems to address this bias. We present the definition and results of this survey. We then combine our sample with the CORALS dataset to investigate the HI column density distribution function f(N) of damped Lya systems toward radio-selected quasars. We find that f(N) is well fit by a power-law f(N) = k_1 N^alpha_1, with log k_1 = 22.90 and alpha_1 = -2.18. This power-law is in excellent agreement with that of optically-selected samples at low N(HI), an important yet expected result given that obscuration should have negligible effect at these gas columns. However, because of the relatively small size of the radio-selected sample, 26 damped Lya systems in 119 quasars, f(N) is not well constrained at large N(HI) and the first moment of the HI distribution function, Omega_g, is, strictly speaking, a lower limit. The power-law is steep enough, however, that extrapolating it to higher column densities implies only a modest, logarithmic increase in Omega_g. The radio-selected value of Omega_g = 1.15 x 10^-3, agrees well with the results of optically-selected surveys. While our results indicate that dust obscuration is likely not a major issue for surveys of damped Lya systems, we estimate that a radio-selected sample of approximately 100 damped Lya systems will be required to obtain the precision necessary to absolutely confirm an absence of dust bias.
astro-ph/0604335 [abs, ps, pdf, other] :: Title: Cosmological parameters from combining the Lyman-alpha forest with CMB, galaxy clustering and SN constraints
Authors: Uros Seljak, Anze Slosar, Patrick McDonald
Comments: 11 pages, 4 figures

We combine the Ly-alpha forest power spectrum (LYA) from the Sloan Digital Sky Survey (SDSS) and high resolution spectra with the cosmic microwave background (CMB) including 3-year WMAP, supernovae (SN) and galaxy clustering constraints to derive new constraints on cosmological parameters. The existing LYA power spectrum analysis is supplemented by constraints on the mean flux decrement derived using a principal component analysis for quasar continua, which improves the LYA constraints on the linear power. The joint analysis reduces the errors on all parameters and prefers the simplest 6 parameter cosmological model. We find some tension between the WMAP3 and LYA power spectrum amplitudes, at the ~2 sigma level, which is partially alleviated by the inclusion of other observations: we find sigma_8=0.85+-0.02 compared to sigma_8=0.80+-0.03 without LYA. For the slope we find n_s=0.965+-0.012. We find no evidence for running of the spectral index, dn/dln k=-0.020+-0.012, in agreement with inflation. The limits on the sum of neutrino masses are significantly improved: sum(m_nu)<0.17 eV at 95% (<0.32 eV at 99.9%). This result, when combined with atmospheric and solar neutrino mixing constraints, requires that the neutrino masses cannot be degenerate, m_3/m_1>1.3 (95%). Assuming a thermalized fourth neutrino we find m_s<0.14 eV at 95% c.l. and such neutrino cannot be an explanation for the LSND results. The fit is poor even in the limit of massless sterile neutrino since the constraint on the number of relativistic neutrino species is N_nu=3.19+0.19-0.15 and N_nu>4 is excluded at 99.76%. The constraint on the dark energy equation of state is w=-1.04+-0.06. The constraint on curvature is Omega_k=-0.003+-0.006. Cosmic strings limits are G mu<2.3 10^-7 at 95% c.l.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Tue, 18 Apr 06 00:00:08 GMT
0604336 -- 0604357 received

astro-ph/0604336 [abs, ps, pdf, other] :: Title: Resolving the Dusty Circumstellar Structure of the Enigmatic Symbiotic Star CH Cygni with the MMT Adaptive Optics System
Authors: Beth A. Biller, Laird M. Close, Aigen Li, Massimo Marengo, John H. Bieging, Phil M. Hinz, William F. Hoffmann, Guido Brusa, Doug Miller
Comments: 18 pages, 7 figures, accepted by the Astrophysical Journal

We imaged the symbiotic star CH Cyg and two PSF calibration stars using the unique 6.5m MMT deformable secondary adaptive optics system. Our high-resolution (FWHM=0.3"), very high Strehl (98%+-2%) mid-infrared (9.8 and 11.7 um) images of CH Cyg allow us to probe finer length scales than ever before for this object. CH Cyg is significantly extended compared to our unresolved PSF calibration stars (Mu UMa and Alpha Her) at 9.8 and 11.7 um. We estimated the size of the extension by convolving a number of simple Gaussian models with the Mu UMa PSF and determining which model provided the best fit to the data. Adopting the Hipparcos distance for this object of 270 pc, we found a nearly Gaussian extension with a FWHM at 9.8 um of ~40.5+-2.7 AU (0.15+-0.01") and a FWHM at 11.7 um of 45.9+-2.7 AU (0.17+-0.01"). After subtracting out the Gaussian component of the emission (convolved with our PSF), we found a faint \~0.7" asymmetric extension which peaks in flux ~0.5" north of the stars. This extension is roughly coincident with the northern knotlike feature seen in HST WFPC2 images obtained in 1999.
astro-ph/0604337 [abs, ps, pdf, other] :: Title: Periodic Modulations in an X-ray Flare from Sagittarius A*
Authors: Guillaume Belanger (CEA/Dapnia/Sap, Apc), Okkie De Jager, Andrea Goldwurm (CEA/Dapnia/Sap, Apc), Fulvio Melia, Regis Terrier (CEA/Dapnia/Sap, Apc)
Comments: 4 pages, 6 figures, submitted to ApJL

We present the highly significant detection of a quasi-periodic flux modulation with a period of 22.2 min seen in the X-ray data of the Sgr A* flare of 2004 August 31. This flaring event, which lasted a total of about three hours, was detected simultaneously by EPIC on XMM-Newton and the NICMOS near-infrared camera on the HST. Given the inherent difficulty in, and the lack of readily available methods for quantifying the probability of a periodic signal detected over only several cycles in a data set where red noise can be important, we developed a general method for quantifying the likelihood that such a modulation is indeed intrinsic to the source and does not arise from background fluctuations. We here describe this Monte Carlo based method, and discuss the results obtained by its application to a other XMM-Newton data sets. Under the simplest hypothesis that we witnessed a transient event that evolved, peaked and decayed near the marginally stable orbit of the supermassive black hole, this result implies that for a mass of 3.5 x 10^{6} Msun, the central object must have an angular momentum corresponding to a spin parameter of a=0.22.
astro-ph/0604338 [abs, ps, pdf, other] :: Title: A Flare of AE Aquarii Observed with XMM-Newton
Authors: Chul-Sung Choi (KASI), Tadayasu Dotani (ISAS/JAXA)
Comments: 15 pages, 3 tables, 9 figures, accepted for publication in ApJ

We present the results of analyzing the XMM-Newton data obtained in 2001 November 7 - 8. A flare is observed simultaneously in X-ray and UV together with a quiescence. We find that during the flare event X-ray flux varies with UV with no significant time lag, indicating a close correlation of flux variation for X-ray and UV flares. An upper limit of the lag is estimated to be \~1 min. From a timing analysis for X-ray data, we find that both pulsed and unpulsed flux increase clearly as the flare advances in the entire energy band 0.15 - 10 keV. The net increase of pulsed flux to the quiescence is, however, small and corresponds to about 3 - 4% of the increase in unpulsed flux, confirming that a flux variation of flare in AE Aqr is dominated by unpulsed X-rays. A spectral analysis reveals that the energy spectrum is similar to that of the quiescence at the beginning of the flare, but the spectrum becomes harder as the flare advances. Based on these results, we discuss the current issues that need to be clarified, e.g., the possible flaring site and the mass accretion problem of the white dwarf. We also discuss the flare properties obtained in this study.
astro-ph/0604339 [abs, pdf] :: Title: Telescope Spectrophotometric and Absolute Flux Calibration, and National Security Applications, Using a Tunable Laser on a Satellite
Authors: Justin Albert, William Burgett, Jason Rhodes
Comments: 11 pages, 4 figures

We propose a tunable laser-based satellite-mounted spectrophotometric and absolute flux calibration system, to be utilized by ground- and space-based telescopes. As uncertainties on the photometry, due to imperfect knowledge of both telescope optics and the atmosphere, will in the near future begin to dominate the uncertainties on fundamental cosmological parameters such as Omega_Lambda and w in measurements from SNIa, weak gravitational lensing, and baryon oscillations, a method for reducing such uncertainties is needed. We propose to improve spectrophotometric calibration, currently obtained using standard stars, by placing a tunable laser and a wide-angle light source on a satellite by early next decade (perhaps included in the upgrade to the GPS satellite network) to improve absolute flux calibration to 0.1% and relative spectrophotometric calibration to better than 0.001% across the visible and near-infrared spectrum. As well as fundamental astrophysical applications, the system proposed here potentially has broad utility for defense and national security applications such as ground target illumination and space communication.
astro-ph/0604340 [abs, ps, pdf, other] :: Title: Dissipative transformation of non-nucleated dwarf galaxies into nucleated systems
Authors: Kenji Bekki, Warrick J. Couch, Yasuhiro Shioya
Comments: 13 pages, 4 figures (1 color), ApJL in press

Recent photometric observations by the {\it Hubble Space Telescope (HST)} have revealed the physical properties of stellar galactic nuclei in nucleated dwarf galaxies in the Virgo cluster of galaxies. In order to elucidate the formation processes of nucleated dwarfs, we numerically investigate gas dynamics, star formation, and chemical evolution within the central 1 kpc of gas disks embedded within the galactic stellar components of non-nucleated dwarfs. We find that high density, compact stellar systems can be formed in the central regions of dwarfs as a result of dissipative, repeated merging of massive stellar and gaseous clumps developed from nuclear gaseous spiral arms as a result of local gravitational instability. The central stellar components are found to have stellar masses which are typically $~$5% of their host dwarfs and show very flattened shapes, rotational kinematics, and central velocity dispersions significantly smaller than those of their host dwarfs. We also find that more massive dwarfs can develop more massive, more metal-rich, and higher density stellar systems in their central regions, because star formation and chemical enrichment proceed more efficiently owing to the less dramatic suppression of star formation by supernovae feedback effects in more massive dwarfs. Based on these results, we suggest that gas-rich, non-nucleated dwarfs can be transformed into nucleated ones as a result of dissipative gas dynamics in their central regions. We discuss the origin of the observed correlations between physical properties of stellar galactic nuclei and those of their host galaxies.
astro-ph/0604341 [abs, ps, pdf, other] :: Title: Low- and Medium-Dispersion Spectropolarimetry of Nova V475 Sct (Nova Scuti 2003): Discovery of an Asymmetric High-Velocity Wind in a Moderately Fast Nova
Authors: Koji S. Kawabata, Youichi Ohyama, Noboru Ebizuka, Tadafumi Takata, Michitoshi Yoshida, Mizuki Isogai, Yuji Norimoto, Akira Okazaki, Masashi S. Saitou
Comments: 27 pages, 7 figures, accepted for publication in AJ

We present low-resolution ($R\sim 90$) and medium-resolution ($R\sim 2500$) spectropolarimetry of Nova V475 Sct with the HBS instrument, mounted on the 0.91-m telescope at the Okayama Astrophysical Observatory, and with FOCAS, mounted on the 8.2-m Subaru telescope. We estimated the interstellar polarization toward the nova from the steady continuum polarization components and H$\alpha$ line emission components. After subtracting the interstellar polarization component from the observations, we found that the H$\alpha$ emission seen on 2003 October 7 was clearly polarized. In the polarized flux spectrum, the H$\alpha$ emission had a distinct red wing extending to $\sim +4900$ km s$^{-1}$ and a shoulder around $+3500$ km s$^{-1}$, showing a constant position angle of linear polarization $\theta_{\rm *}\simeq 155\arcdeg\pm 15\arcdeg$. This suggests that the nova had an asymmetric outflow with a velocity of $v_{\rm wind}\simeq 3500$ km s$^{-1}$ or more, which is six times higher than the expansion velocity of the ionized shell at the same epoch. Such a high-velocity component has not previously been reported for a nova in the `moderately fast' speed class. Our observations suggest the occurrence of violent mass-loss activity in the nova binary system even during the common-envelope phase. The position angle of the polarization in the H$\alpha$ wing is in good agreement with that of the continuum polarization found on 2003 September 26 ($p_{\rm *}\simeq 0.4$--0.6 %), which disappeared within the following 2 d. The uniformity of the PA between the continuum polarization and the wing polarization on October 7 suggests that the axis of the circumstellar asymmetry remained nearly constant during the period of our observations.
astro-ph/0604342 [abs, ps, pdf, other] :: Title: Evidence for a Cosmological Phase Transition From the Dark Energy Scale
Authors: James Lindesay
Comments: 42 pages, 9 figures

A finite vacuum energy density implies the existence of a UV scale for gravitational modes. This gives a phenomenological scale to the dynamical equations governing the cosmological expansion that must satisfy constraints consistent with quantum measurability and spatial flatness. Examination of these constraints for the observed dark energy density establishes a time interval from the transition to the present, suggesting major modifications from the thermal equations of state far from Planck density scales. The assumption that a phase transition initiates the radiation dominated epoch is shown under several scenarios to produce fluctuations to the CMB of the order observed. Quantum measurability constraints (eg. uncertainly relations) define cosmological scales bounded by luminal expansion rates. It is shown that the dark energy can consistently be interpreted as being due to the vacuum energy of collective gravitational modes which manifest as the zero-point motions of coherent Planck scale mass units prior to the UV scale onset of gravitational quantum de-coherence for the cosmology.
astro-ph/0604343 [abs, ps, pdf, other] :: Title: The nature of the DLS fast transients
Authors: S. R. Kulkarni, A. Rau (Caltech)
Comments: 4 pages, 2 figures, ApJL submitted

The discovery and study of highly transient sources, especially those which rise to high brightness and then fade to obscurity, has been a major part of modern astrophysics. Well known examples include supernovae and novae. A byproduct of the Deep Lens Survey (DLS) was the discovery of three transients which varied on a timescale of less than an hour. All three had faint and red counterparts, the brightest of which was identified with an M star. However, the remaining two showed hints of an extra-galactic origin (spatially extended counterpart and projected on the outskirts of a bright elliptical galaxy in a cluster). Such an origin implies an entirely new class of exotic explosive transients. We undertook spectroscopic observations with the Keck telescope and find the remaining two counterparts are also late type Galactic dwarfs. Flares from M dwarfs constitute a dense foreground fog and dominate over any conceivable class of extragalactic fast transients by at least two orders of magnitude. Overcoming this fog will likely require dedicated surveys with careful optimization of target field location, filter(s) and cadence, pre-search imaging to filter out late type dwarfs and a well planned rapid followup plan.
astro-ph/0604344 [abs, ps, pdf, other] :: Title: A photon breeding mechanism for the high-energy emission of relativistic jets
Authors: Boris E. Stern, Juri Poutanen
Comments: 11 pages, 10 figures, submitted to MNRAS

We propose a straightforward and efficient mechanism for the high-energy emission of relativistic astrophysical jets associated with an exchange of interacting high-energy photons between the jet and external environment. Physical processes playing the main role in this mechanism are electron-positron pair production by photons and the inverse Compton scattering. This scenario has been studied analytically as well as with numerical simulations demonstrating that a relativistic jet moving through the sufficiently dense soft radiation field inevitably undergoes transformation into a luminous state. The process has a supercritical character: the high-energy photons breed exponentially being fed directly by the bulk kinetic energy of the jet. Eventually particles feed back on the fluid dynamics and the jet partially decelerates. As a result, a significant fraction (at least 10--20 per cent) of the jet kinetic energy is converted into radiation mainly in the MeV -- GeV energy range. The mechanism maybe responsible for the bulk of the emission of relativistic jets in active galactic nuclei, microquasars and gamma-ray bursts.
astro-ph/0604345 [abs, ps, pdf, other] :: Title: Accretion-powered Millisecond Pulsar Outbursts
Authors: Duncan K. Galloway
Comments: 5 pages, 2 figures, to be published in: "The Transient Milky Way: a perspective for MIRAX", eds. F. D'Amico, J. Braga & R. Rothschild, AIP Conf. Proc

The population of accretion-powered millisecond pulsars has grown rapidly over the last four years, with the discovery of six new examples to bring the total sample to seven. While the first six discovered are transients active for a few weeks every two or more years, the most recently-discovered source HETE J1900.1-2455, has been active for more than 8 months. We summarise the transient behaviour of the population to estimate long-term time-averaged fluxes, and equate these fluxes to the expected mass transfer rate driven by gravitational radiation in order to constrain the distances. We also estimate an upper limit of 6 kpc to the distance of IGR J00291+5934 based on the non-detection of bursts from this source.
astro-ph/0604346 [abs, ps, pdf, other] :: Title: Alignment Tests for low CMB multipoles
Authors: L. Raul Abramo, Armando Bernui, Ivan S. Ferreira, T. Villela, C. Alexandre Wuensche
Comments: 12 Pages, 6 Figures. Results for additional maps, the normalized frequencies for the tests and a Mathematica Notebook that computes the tests can be found on this http URL

We investigate the large scale anomalies in the angular distribution of the cosmic microwave background radiation as measured by WMAP using several tests. These tests, based on the multipole vector expansion, measure correlations between the phases of the multipoles as expressed by the directions of the multipole vectors and their associated normal planes. We have computed the probability distribution functions for 46 such tests, for the multipoles $\ell=2-5$. We confirm earlier findings that point to a high level of alignment between $\ell=2$ (quadrupole) and $\ell=3$ (octopole), but with our tests we do not find significant planarity in the octopole. In addition, we have found other possible anomalies in the alignment between the octopole and the $\ell=4$ (hexadecupole) components, as well as in the planarities of $\ell=4$ and $\ell=5$. We introduce the notion of a total likelihood to estimate the relevance of the low-multipoles tests of non-gaussianity. We show that, as a result of these tests, the CMB maps which are most widely used for cosmological analysis lie within the $\sim$ 10% of randomly generated maps with lowest likelihoods.
astro-ph/0604347 [abs, ps, pdf, other] :: Title: Spitzer Observations of High Redshift QSOs
Authors: D. C. Hines (1), O. Krause (2), G. H. Rieke (2), X. Fan (2), M. Blaylock (2), G. Neugebauer (2) ((1) Space Science Institute, (2) The University of Arizona)
Comments: 1 eps figure
Journal-ref: Hines, D.C. et al. 2006, ApJ, 641, L85

We have observed 13 z >= 4.5 QSOs using the Multiband Imaging Photometer for Spitzer, nine of which were also observed with the Infrared Array Camera. The observations probe rest wavelengths ~ 0.6-4.3 micron, bracketing the local minimum in QSO spectral energy distributions (SEDs) between strong optical emission associated directly with accretion processes and thermal emission from hot dust heated by the central engine. The new Spitzer photometry combined with existing measurements at other wavelengths shows that the SEDs of high redshift QSOs (z >= 4.5) do not differ significantly from typical QSOs of similar luminosity at lower redshifts (z <~ 2). This behavior supports other indications that all the emission components and physical structures that characterize QSO activity can be established by z = 6.4. The similarity also suggests that some QSOs at high redshift will be very difficult to identify because they are viewed along dust-obscured sight lines.
astro-ph/0604348 [abs, ps, pdf, other] :: Title: The N2K Consortium VI: Doppler Shifts Without Templates and Three New Short-Period Planets
Authors: John Asher Johnson, Geoffrey W. Marcy, Debra A. Fischer, Gregory Laughlin, R. Paul Butler, Gregory W. Henry, Jeff A. Valenti, Eric B. Ford, Steven S. Vogt, Jason T. Wright
Comments: 39 pages, 12 figures, 8 tables (ApJ Accepted)

We present a modification to the iodine cell Doppler technique that eliminates the need for an observed stellar template spectrum. For a given target star, we iterate toward a synthetic template spectrum beginning with an existing spectrum of a similar star. We then perturb the shape of this first-guess template to match the program observation of the target star taken through an iodine cell. The elimination of a separate template observation saves valuable telescope time, a feature that is ideally suited for the quick-look strategy employed by the ``Next 2000 Stars'' (N2K) planet search program. Tests using Keck/HIRES spectra indicate that synthetic templates yield a short-term precision of 3 m/s and a long-term, run-to-run precision of 5 m/s. We used this new Doppler technique to discover three new planets: a 1.5 Mjup planet in a 2.1375 d orbit around HD 86081; a 0.71 Mjup planet in circular, 26.73 d orbit around HD 224693; and a Saturn-mass planet in an 18.179 d orbit around HD 33283. The remarkably short period of HD 86081b bridges the gap between the extremely short-period planets detected in the OGLE survey and the 16 Doppler-detected hot jupiters (P < 15 d), which have an orbital period distribution that piles up at about three days. We have acquired photometric observations of two of the planetary host stars with the automated photometric telescopes at Fairborn Observatory. HD 86081 and HD 224693 both lack detectable brightness variability on their radial velocity periods, supporting planetary-reflex motion as the cause of the radial velocity variability. HD 86081 shows no evidence of planetary transits in spite of a 17.6% transit probability.
astro-ph/0604349 [abs, ps, pdf, other] :: Title: Revisiting the characteristics of the spectral lags in short gamma-ray bursts
Authors: Zhibin Zhang, J. G. Deng, L. Z. Lv
Comments: 16 pages, 7 figures, 1 table

In this paper, we restudy the spectral lag features of short bright gamma-ray bursts (T90 < 2.6s) with a BATSE time-tagged event (TTE) sample including 65 single pulse bursts. We draw the conclusions as follows: 1) Spectral lags of short GRBs are normally distributed and concentrated on around the value of 0.014 with 40 percent of them having negative lags. With K-S test, we find the lag distribution is identical with a normal one caused by white noises, which indicates the lags of the vast majority of short bursts are so small that they are negligible as Norris et al. have suggested; 2) We assume spectral lag tau is proportional to Gamma^(-w) with w > 2. It is shown that high lorentz factors together with large w could lead to a smaller lag; 3) RSL distribution is gaussian too and has an expectation value of 0.082 with standard deviation 0:42; 4) Spectral lags and RSLs across energy channels 1 and 3 is respectively correlated with those across channels 2 and 3, and besides, they are strongly associated with each other; and 5) Peak fuxes of short bursts with positive lags exhibit a tendency of anti-correlation with the RSLs. On the contrary, there are no correlation between them for bursts with minus lags. We argue that the short bursts with positive lags as long ones could be used as a redshift estimator. It suggests that the classification of GRBs based on positive and negative lags might be equally reasonable, because the fundamental emission mechanisms of them could be largely different.
astro-ph/0604350 [abs, ps, pdf, other] :: Title: A New Galactic 6cm Formaldehyde Maser
Authors: E. Araya (1), P. Hofner (1,2), W. M. Goss (2), S. Kurtz (3), H. Linz (4), L. Olmi (5,6) ((1) New Mexico Institute of Mining and Technology, Socorro, USA, (2) National Radio Astronomy Observatory, Socorro, USA, (3) Centro de Radioastronomia y Astrofisica, UNAM, Morelia, Mexico, (4) Max-Planck-Institut fur Astronomie, Heidelberg, Germany, (5) Istituto di Radioastronomia, CNR, Florence, Italy, (6) University of Puerto Rico, San Juan, Puerto Rico)
Comments: Accepted for publication in The Astrophysical Journal Letters

We report the detection of a new H2CO maser in the massive star forming region G23.71-0.20 (IRAS 18324-0820), i.e., the fifth region in the Galaxy where H2CO maser emission has been found. The new H2CO maser is located toward a compact HII region, and is coincident in velocity and position with 6.7 GHz methanol masers and with an IR source as revealed by Spitzer/IRAC GLIMPSE data. The coincidence with an IR source and 6.7 GHz methanol masers suggests that the maser is in close proximity to an embedded massive protostar. Thus, the detection of H2CO maser emission toward G23.71-0.20 supports the trend that H2CO 6cm masers trace molecular material very near young massive stellar objects.
astro-ph/0604351 [abs, ps, pdf, other] :: Title: Detailed Study of the Ursa Major Supercluster of Galaxies Using the 2MASS and SDSS Catalogs
Authors: Flera Kopylova, Alexander Kopylov
Comments: 16 pages, 5 figures
Journal-ref: Astron. Letters 32 (2006) 84-90; Pis'ma v Astron. Zhur. 32 (2006) 95-101

We study the infrared (K_s band) properties of clusters of galaxies in the Ursa Major supercluster using data from 2MASS (Two-Micron All-Sky Survey) and SDSS (Sloan Digital Sky Survey). We identified three large filaments with mean redshifts of z = 0.051, 0.060, and 0.071. All clusters of the supercluster are located in these filaments. We determined the total K_s-band luminosities and masses for 11 clusters of galaxies within comparable physical regions (within a radius R_200 close to the virial radius) using a homogeneous method. We constructed a combined luminosity function for the supercluster in this region, which can be described by the Schechter function with the following parameters: M*_K = -24^m.50 and \alpha = -0.98. The infrared luminosities of the clusters of galaxies correlate with their masses; the M/L_K ratios of the systems increase with their masses (luminosities), with most of the Ursa Major clusters of galaxies (particularly the richer ones) closely following the relations derived previously for a large sample of clusters and groups of galaxies. The total mass-to-infrared-luminosity ratio is 52 M_{\odot}/L_{\odot} for six Abell clusters and 49 M_{\odot}/L_{\odot} for all of the clusters, except Anon2.
astro-ph/0604352 [abs, ps, pdf, other] :: Title: A synoptic comparison of the MHD and the OPAL equations of state
Authors: R. Trampedach, W. Dappen, V. A. Baturin
Comments: 33 pages, 26 figures

A detailed comparison is carried out between two popular equations of state (EOS), the Mihalas-Hummer-Dappen (MHD) and the OPAL equations of state, which have found widespread use in solar and stellar modeling during the past two decades. They are parts of two independent efforts to recalculate stellar opacities; the international Opacity Project (OP) and the Livermore-based OPAL project. We examine the difference between the two equations of state in a broad sense, over the whole applicable rho-T range, and for three different chemical mixtures. Such a global comparison highlights both their differences and their similarities.
We find that omitting a questionable hard-sphere correction, tau, to the Coulomb interaction in the MHD formulation, greatly improves the agreement between the MHD and OPAL EOS. We also find signs of differences that could stem from quantum effects not yet included in the MHD EOS, and differences in the ionization zones that are probably caused by differences in the mechanisms for pressure ionization. Our analysis do not only give a clearer perception of the limitations of each equation of state for astrophysical applications, but also serve as guidance for future work on the physical issues behind the differences. The outcome should be an improvement of both equations of state.
astro-ph/0604353 [abs, ps, pdf, other] :: Title: Fe K Emission and Absorption in the XMM-EPIC Spectrum of the Seyfert Galaxy IC 4329a
Authors: A. Markowitz (1 and 2), J. Reeves (1 and 3), V. Braito (1 and 3) ((1) NASA/GSFC, (2) NASA Post-doc Research Associate, (3) Johns Hopkins University)
Comments: Accepted for publication in The Astrophysical Journal; 25 pages; 11 figures

We present a detailed analysis of the XMM-Newton long-look of the Seyfert galaxy IC 4329a. The Fe K bandpass is dominated by two resolved peaks at 6.4 keV and 7.0 keV, consistent with neutral or near-neutral Fe K alpha and K beta emission. There is a prominent redward asymmetry in the 6.4 keV line, which could indicate emission from a Compton shoulder. Alternatively, models using dual relativistic disklines are found to describe the emission profile well. A low-inclination, moderately-relativistic dual-diskline model is possible if the contribution from narrow components, due to distant material, is small or absent. A high-inclination, moderately relativistic profile for each peak is possible if there are roughly equal contributions from both the broad and narrow components. Combining the XMM-Newton data with RXTE monitoring data, we explore the time-resolved spectral behavior on time scales from hours to 2 years. We find no strong evidence for variability of the Fe K line flux on any time scale, likely due to the minimal level of continuum variability. We detect, at high significance, a narrow absorption line at 7.68 keV. This feature is most likely due to Fe XXVI K alpha absorption blueshifted to about 0.1c relative to the systemic velocity, suggesting a high-velocity, highly-ionized outflow component. As is often the case with similar outflows seen in high-luminosity quasars, the power associated with the outflow represents a substantial portion of the total energy budget of the AGN. The outflow could arise from a radiatively-driven disk wind, or it may be in the form of a discrete, transient blob of ejected material.
astro-ph/0604354 [abs, ps, pdf, other] :: Title: A New Milky Way Dwarf Satellite in Canes Venatici
Authors: D. B. Zucker (1), V. Belokurov (1), N. W. Evans (1), M. I. Wilkinson (1), M. J. Irwin (1), T. Sivarani (2), S. Hodgkin (1), D. M. Bramich (1), J. M. Irwin (1), G. Gilmore (1), B. Willman (3), S. Vidrih (1), M. Fellhauer (1), P. C. Hewett (1), T. C. Beers (2), E. F. Bell (4), E. K. Grebel (5), D. P. Schneider (6), H. J. Newberg (7), R. F. G. Wyse (8), C. M. Rockosi (9), B. Yanny (10), R. Lupton (11), J. A. Smith (12), J. C. Barentine (13), H. Brewington (13), J. Brinkmann (13), M. Harvanek (13), S. J.Kleinman (13), J. Krzesinski (13,14), D. Long (13), A. Nitta (13), S. A. Snedden (13) ((1) Cambridge University, (2) Michigan State University, (3) New York University, (4) MPIA, Heidelberg, (5) University of Basel, (6) Pennsylvania State University, (7) Rensselaer Polytechnic Institute, (8) JHU, (9) Lick Observatory/UCSC, (10) FNAL, (11) Princeton University, (12) LANL, (13) Apache Point Observatory, (14) Cracow Pedagogical University)
Comments: 4 pages, 4 figures; submitted to ApJ Letters

In this Letter, we announce the discovery of a new dwarf satellite of the Milky Way, located in the constellation Canes Venatici. It was found as a stellar overdensity in the North Galactic Cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The satellite's color-magnitude diagram shows a well-defined red giant branch, as well as a horizontal branch. As judged from the tip of the red giant branch, it lies at a distance of ~220 kpc. Based on the SDSS data, we estimate an absolute magnitude of Mv ~ -7.9, a central surface brightness of mu_0,V ~ 28 mag arcsecond^-2, and a half-light radius of \~ 8.5' (~ 550 pc at the measured distance). The outer regions of Canes Venatici appear extended and distorted. The discovery of such a faint galaxy in proximity to the Milky Way strongly suggests that more such objects remain to be found.
astro-ph/0604355 [abs, ps, pdf, other] :: Title: A Faint New Milky Way Satellite in Bootes
Authors: V. Belokurov (1), D. B. Zucker (1), N. W. Evans (1), M. I. Wilkinson (1), M. J. Irwin (1), S. Hodgkin (1), D. M. Bramich (1), J. M. Irwin (1), G. Gilmore (1), B. Willman (2), S. Vidrih (1), H. J. Newberg (3), R. F. G. Wyse (4), M. Fellhauer (1), P. C. Hewett (1), N. Cole (3), E. F. Bell (5), T. C. Beers (6), C. M. Rockosi (7), B. Yanny (8), E. K. Grebel (9), D. P. Schneider (10), R. Lupton (11), J. C. Barentine (12), H. Brewington (12), J. Brinkmann (12), M. Harvanek (12), S. J.Kleinman (12), J. Krzesinski (12,13), D. Long (12), A. Nitta (12), J. A. Smith (14), S. A. Snedden (12) ((1) Cambridge University, (2) New York University, (3) Rensselaer Polytechnical Institute, (4) JHU, (5) MPIA, Heidelberg, (6) Michigan State University, (7) Lick Observatory, UCSC, (8) FNAL, (9) University of Basel, (10) Pennsylvania State University, (11) Princeton University, (12) Apache Point Observatory, (13) Cracow Pedagogical University, (14) LANL)
Comments: Submitted to ApJ (Letters)

In this Letter, we announce the discovery of a new satellite of the Milky Way in the constellation of Bootes at a distance of 60 kpc. It was found in a systematic search for stellar overdensities in the North Galactic Cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The color-magnitude diagram shows a well-defined turn-off, red giant branch, and extended horizontal branch. Its absolute magnitude is -5.7, which makes it fainter than the faintest galaxy known. The half-light radius is 220 pc. The isodensity contours are elongated and have an irregular shape.
astro-ph/0604356 [abs, ps, pdf, other] :: Title: Scalar quantities as detectors of non-Gaussianity on CMB maps
Authors: C. Monteserin, R.B. Barreiro, E. Martinez-Gonzalez, J.L. Sanz
Comments: Submitted to MNRAS. 13 pages, 3 figures

We study the power of several scalar quantities constructed on the sphere (presented in Monteserin et al. 2005) to detect non-Gaussianity on the temperature distribution of the cosmic microwave background (CMB). The test has been performed using non-Gaussian CMB simulations with injected skewness or kurtosis generated through the Edgeworth expansion. We have also taken into account in the analysis the effect of anisotropic noise and the presence of a Galactic mask. We find that the best scalars to detect an excess of skewness in the simulations are the derivative of the gradient, the fractional isotropy, the Laplacian and the shape index. For the kurtosis case, the fractional anisotropy, the Laplacian and the determinant are the quantities that perform better.
astro-ph/0604357 [abs, ps, pdf, other] :: Title: The AGN Outflow in the HDFS Target QSO J2233-606 from a High-Resolution VLT/UVES Spectrum
Authors: Jack R. Gabel, Nahum Arav, Tae-Sun Kim
Comments: 12 pages, 10 figures, emulateapj, accepted for publication in ApJ

We present a detailed analysis of the intrinsic UV absorption in the central HDFS target QSO J2233-606, based on a high-resolution, high S/N (~25 -- 50) spectrum obtained with VLT/UVES. This spectrum samples the cluster of intrinsic absorption systems outflowing from the AGN at radial velocities v ~ -5000 -- -3800 km/s in the key far-UV diagnostic lines - the lithium-like CNO doublets and H I Lyman series. We fit the absorption troughs using a global model of all detected lines to solve for the independent velocity-dependent covering factors of the continuum and emission-line sources and ionic column densities. This reveals increasing covering factors in components with greater outflow velocity. Narrow substructure is revealed in the optical depth profiles, suggesting the relatively broad absorption is comprised of a series of multiple components. We perform velocity-dependent photoionization modeling, which allows a full solution to the C, N, and O abundances, as well as the velocity resolved ionization parameter and total column density. The absorbers are found to have supersolar abundances, with [C/H] and [O/H] ~0.5 -- 0.9, and [N/H] ~ 1.1 -- 1.3, consistent with enhanced nitrogen production expected from secondary nucleosynthesis processes. Independent fits to each kinematic component give consistent results for the abundances. The lowest-ionization material in each of the strong absorbers is modeled with similar ionization parameters. Components of higher-ionization (indicated by stronger O VI relative to C IV and N V) are present at velocities just redward of each low-ionization absorber. We explore the implications of these results for the kinematic-geometric-ionization structure of the outflow.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Wed, 19 Apr 06 00:00:10 GMT
0604358 -- 0604387 received

astro-ph/0604358 [abs, ps, pdf, other] :: Title: Galaxy surveys, inhomogeneous reionization, and dark energy
Authors: Jonathan R. Pritchard (1), Steven R. Furlanetto (2), Marc Kamionkowski (1) ((1) Caltech, (2) Yale)
Comments: 9 pages, 8 figures, submitted to MNRAS

We examine the effect of inhomogeneous reionization on the galaxy power spectrum and the consequences for probing dark energy. To model feedback during reionization, we apply an ansatz setting the galaxy overdensity proportional to the underlying ionization field. Thus, inhomogeneous reionization may leave an imprint in the galaxy power spectrum. We evolve this imprint to low redshift and use the Fisher-matrix formalism to assess the effect on parameter estimation. We show that a combination of low- (z=0.3) and high- (z=3) redshift galaxy surveys can constrain the size of cosmological HII regions during reionization. This imprint can also cause confusion when using baryon oscillations or other features of the galaxy power spectrum to probe the dark energy. We show that when bubbles are large, and hence detectable, our ability to constrain w can be degraded by up to 50%. When bubbles are small, the imprint has little or no effect on measuring dark-energy parameters.
astro-ph/0604359 [abs, ps, pdf, other] :: Title: The QUEST RR Lyrae Survey II: The Halo Overdensities in the First Catalog
Authors: A. Katherina Vivas (CIDA, Venezuela), Robert Zinn (Yale University, USA)
Comments: Accepted for publication in the Astronomical Journal

The first catalog of the RR Lyrae stars (RRLS) in the Galactic halo by the QUEST Survey has been searched for significant overdensities that may be debris from disrupted dwarf galaxies or globular clusters. Away from the major overdensities, the distribution of these stars is adequately fit by a smooth halo model, in which the flattening of the halo decreases with increasing galactocentric distance (Preston et al 1991). This model was used to estimate the ``background'' of RRLS on which the halo overdensities are overlaid. A procedure was developed for recognizing groups of stars that constitute significant overdensities with respect to this background. To test this procedure, a Monte Carlo routine was used to make artificial RRLS surveys that follow the smooth halo model, but with Poisson distributed noise in the numbers of RRLS and, within limits, random variations in the positions and magnitudes of the artificial stars. The artificial surveys created by this routine were examined for significant groups in exactly the same way as the QUEST survey. These calculations provided estimates of the frequencies with which random fluctuations produce significant groups. In the QUEST survey, there are six significant overdensities that contain six or more stars and several smaller ones. The small ones and possibly one or two of the larger ones may be artifacts of statistical fluctuations, and they need to be confirmed by measurements of radial velocity and/or proper motion. The most prominent groups are the northern stream from the Sagittarius dwarf spheroidal galaxy and a large group in Virgo. Two other groups lie in the direction of the Monoceros stream and at approximately the right distance for membership. Another group is related to the globular cluster Palomar 5.
astro-ph/0604360 [abs, ps, pdf, other] :: Title: Smooth Particle Lensing
Authors: Dominique Aubert (SAp, CEA Saclay), Adam Amara (SAp, CEA Saclay), R. Benton Metcalf (MPA Garching)
Comments: 11 pages, 11 figures, submitted to MNRAS

We present a numerical technique to compute the gravitational lensing induced by simulated haloes. It relies on a 2D-Tree domain decomposition in the lens plane combined with a description of N-Body particles as extended clouds with a non-singular density. This technique is made fully adaptive by the use of a density-dependent smoothing which allows one to probe the lensing properties of haloes from the densest regions in the center or in substructures to the low-density regions in the outskirts. 'Smooth Particle Lensing' has some promising features. First, the deflection potential, the deflection angles, the convergence and the shear are direct and separate end-products of the SPL calculation and can be computed at an arbitrary distribution of points on the lens plane. Second, this flexibility avoids the use of interpolation or a finite differentiation procedure on a grid, does not require padding the region with zeros and focuses the computing power on relevant regions. The SPL algorithm is tested by populating isothermal spheres and ellipsoids with particles and then comparing the lensing calculations to the classical FFT-based technique and analytic solutions. We assess issues related to the resolution of the lensing code and the limitations set by the simulations themselves. We conclude by discussing how SPL can be used to predict the impact of substructures on strong lensing and how it can be generalized to weak lensing and cosmic shear simulations.
astro-ph/0604361 [abs, ps, pdf, other] :: Title: On the Robustness of the Acoustic Scale in the Low-Redshift Clustering of Matter
Authors: Daniel J. Eisenstein, Hee-jong Seo (Arizona), Martin White (UC Berkeley)
Comments: 27 pages, LaTeX. Submitted to the Astrophysical Journal

We discuss the effects of non-linear structure formation on the signature of acoustic oscillations in the late-time galaxy distribution. We argue that the dominant non-linear effect is the differential motion of pairs of tracers separated by 150 Mpc. These motions are driven by bulk flows and cluster formation and are much smaller than the acoustic scale itself. We present a model for the non-linear evolution based on the distribution of pairwise Lagrangian displacements that provides a quantitative model for the degradation of the acoustic signature, even for biased tracers in redshift space. The Lagrangian displacement distribution can be calibrated with a significantly smaller set of simulations than would be needed to construct a precise power spectrum. By connecting the acoustic signature in the Fourier basis with that in the configuration basis, we show that the acoustic signature is more robust than the usual Fourier-space intuition would suggest because the beat frequency between the peaks and troughs of the acoustic oscillations is a very small wavenumber that is well inside the linear regime. We argue that any possible shift of the acoustic scale is related to infall on 150 Mpc scale, which is O(0.5%) fractionally at first-order even at z=0. For the matter, there is a first-order cancellation such that the mean shift is O(10^{-4}). However, galaxy bias can circumvent this cancellation and produce a sub-percent systematic bias.
astro-ph/0604362 [abs, ps, pdf, other] :: Title: Improving Cosmological Distance Measurements by Reconstruction of the Baryon Acoustic Peak
Authors: Daniel J. Eisenstein, Hee-jong Seo (Arizona), Edwin Sirko, David Spergel (Princeton)
Comments: 5 pages, LaTeX. Submitted to the Astrophysical Journal

The baryon acoustic oscillations are a promising route to the precision measure of the cosmological distance scale and hence the measurement of the time evolution of dark energy. We show that the non-linear degradation of the acoustic signature in the correlations of low-redshift galaxies is a correctable process. By suitable reconstruction of the linear density field, one can sharpen the acoustic peak in the correlation function or, equivalently, restore the higher harmonics of the oscillations in the power spectrum. With this, one can achieve better measurements of the acoustic scale for a given survey volume. Reconstruction is particularly effective at low redshift, where the non-linearities are worse but where the dark energy density is highest. At z=0.3, we find that one can reduce the sample variance error bar on the acoustic scale by at least a factor of 2 and in principle by nearly a factor of 4. We discuss the significant implications our results have for the design of galaxy surveys aimed at measuring the distance scale through the acoustic peak.
astro-ph/0604363 [abs, ps, pdf, other] :: Title: Collisional Ionization Equilibrium for Optically Thin Plasmas. I. Updated Recombination Rate Coefficients for Bare though Sodium-like Ions
Authors: P. Bryans, N. R. Badnell, T. W. Gorczyca, J. M. Laming, W. Mitthumsiri, D. W. Savin
Comments: 83 pages, 38 figures, 41 tables

Reliably interpreting spectra from electron-ionized cosmic plasmas requires accurate ionization balance calculations for the plasma in question. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and are often highly suspect. This translates directly into the reliability of the collisional ionization equilibrium (CIE) calculations. We make use of state-of-the-art calculations of dielectronic recombination (DR) rate coefficients for the hydrogenic through Na-like ions of all elements from He up to and including Zn. We also make use of state-of-the-art radiative recombination (RR) rate coefficient calculations for the bare through Na-like ions of all elements from H through to Zn. Here we present improved CIE calculations for temperatures from $10^4$ to $10^9$ K using our data and the recommended electron impact ionization data of \citet{Mazz98a} for elements up to and including Ni and Mazzotta (private communication) for Cu and Zn. DR and RR data for ionization stages that have not been updated are also taken from these two additional sources. We compare our calculated fractional ionic abundances using these data with those presented by Mazzotta et al. for all elements from H to Ni. The differences in peak fractional abundance are up to 60%. We also compare with the fractional ionic abundances for Mg, Si, S, Ar, Ca, Fe, and Ni derived from the modern DR calculations of \citet{Gu03a,Gu04a} for the H-like through Na-like ions, and the RR calculations of \citet{Gu03b} for the bare through F-like ions. These results are in better agreement with our work, with differences in peak fractional abundance of less than 10%.
astro-ph/0604364 [abs, ps, pdf, other] :: Title: Force-Free Electrodynamics of Pulsars
Authors: Andrei Gruzinov (CCPP, NYU)
Comments: 9 pages, 5 figures

We show that FFE (Force-Free Electrodynamics) describes pulsar magnetospheres -- even when radiation and particle wind power are comparable to the spin-down power. At the same time, we show that FFE is insufficient for calculating pulsar magnetospheres. This is because FFE admits a large family of stationary solutions with different currents flowing in the closed line region. To choose the actual solution one needs a model of current generation which goes beyond pure FFE.
We calculate several FFE magnetospheres for the aligned rotator. The Poynting power of these solutions fills the range $c^{-3}\mu ^2\Omega^4~< ~L~ <~ 0.67 c^{-3}\mu ^2\Omega^4(c/\Omega R_s)^2$, for angular velocity $\Omega$ and magnetic field which is a pure dipole $\mu$ on the surface of the star of radius $R_s$.
Anomalous braking indices of young pulsars might be explained by currents flowing in the closed-line region.
astro-ph/0604365 [abs, ps, pdf, other] :: Title: Design and Performance of the Soft Gamma-ray Detector for the NeXT mission
Authors: H. Tajima (1), T. Kamae (1), G. Madejski (1), T. Mitani (2 and 3), K. Nakazawa (2), T. Tanaka (2 and 3), T. Takahashi (2 and 3), S. Watanabe (2), Y. Fukazawa (4), T. Ikagawa (5), J. Kataoka (5), M. Kokubun (3), K. Makishima (3), Y. Terada (6), M. Nomachi (7), M. Tashiro (8) ((1) Stanford Linear Accelerator Center, (2) Institute of Space and Astronautical Science, (3) University of Tokyo. (4) Hiroshima University, (5) Tokyo Institute of Technology, (6) RIKEN, (7) Osaka University, (8) Saitama University)
Comments: 9 pages, 17 figures, Contributed to IEEE Nuclear Science Symposium, Roma, Italia, October 16-October 22, 2004
Journal-ref: IEEE Transactions on Nuclear Science, 52, 2749-2757 (2005)

The Soft Gamma-ray Detector (SGD) on board the NeXT (Japanese future high energy astrophysics mission) is a Compton telescope with narrow field of view (FOV), which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor gamma-ray detector which consists of silicon and CdTe (cadmium telluride) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 x 10^-7 counts/cm^2/s; the silicon layers are required to improve the performance at a lower energy band (<0.3 MeV). Excellent energy resolution is the key feature of the SGD, allowing it to achieve both high angular resolution and good background rejection capability. An additional capability of the SGD, its ability to measure gamma-ray polarization, opens up a new window to study properties of astronomical objects. We will present the development of key technologies to realize the SGD: high quality CdTe, low noise front-end ASIC and bump bonding technology. Energy resolutions of 1.7 keV (FWHM) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of Monte Carlo simulation used to evaluate the performance of the SGD.
astro-ph/0604366 [abs, ps, pdf, other] :: Title: Analysis of White Dwarfs with Strange-Matter Cores
Authors: G. J. Mathews, I.-S. Suh, B. O'Gorman, N. Q. Lan, W. Zech, K. Otsuki, F. Weber
Comments: 11 pages, 6 figures, accepted for publication in J. Phys. G: Nucl. Part. Phys

We summarize masses and radii for a number of white dwarfs as deduced from a combination of proper motion studies, Hipparcos parallax distances, effective temperatures, and binary or spectroscopic masses. A puzzling feature of these data is that some stars appear to have radii which are significantly smaller than that expected for a standard electron-degenerate white-dwarf equations of state. We construct a projection of white-dwarf radii for fixed effective mass and conclude that there is at least marginal evidence for bimodality in the radius distribution forwhite dwarfs. We argue that if such compact white dwarfs exist it is unlikely that they contain an iron core. We propose an alternative of strange-quark matter within the white-dwarf core. We also discuss the impact of the so-called color-flavor locked (CFL) state in strange-matter core associated with color superconductivity. We show that the data exhibit several features consistent with the expected mass-radius relation of strange dwarfs. We identify eight nearby white dwarfs which are possible candidates for strange matter cores and suggest observational tests of this hypothesis.
astro-ph/0604367 [abs, ps, pdf, other] :: Title: Two populations of metal-free stars in the early Universe
Authors: Thomas H. Greif, Volker Bromm
Comments: 11 pages, 5 figures, submitted to MNRAS

We construct star formation histories at redshifts z > 5 for two physically distinct populations of primordial, metal-free stars, motivated by theoretical and observational arguments that have hinted towards the existence of an intermediate stellar generation between Population III and Population I/II. Taking into account the cosmological parameters as recently revised by WMAP after three years of operation, we determine self-consistent reionization histories and discuss the resulting chemical enrichment from these early stellar generations. We find that the bulk of ionizing photons and heavy elements produced at high redshifts must have originated in Population II.5 stars, which formed out of primordial gas in haloes with virial temperatures >= 10^4 K, and had typical masses >= 10 M_sun. Classical Population III stars, formed in minihaloes and having masses >= 100 M_sun, on the other hand, had only a minor impact on reionization and early metal enrichment. Specifically, we find that only 5 - 10 per cent by mass went into Population III star formation.
astro-ph/0604368 [abs, ps, pdf, other] :: Title: What is special about HBRPs
Authors: N. Vranesevic, D. B. Melrose, R. N. Manchester
Comments: 6 pages, 5 figures, in press ChJAA

The Parkes Multibeam Survey led to the identification ofa number of long-period radio pulsars with magnetic field well above the quantum critical field of 4.4 times 10 to 13 G (defined as high magnetic field radio pulsars - HBRPs). Traditional pulsar emission theories postulate that radio emission is suppressed above this critical field. The aim of thisproject is to understand emission properties of HBRPs.
astro-ph/0604369 [abs, ps, pdf, other] :: Title: Unusual PAH Emission in Elliptical Galaxies
Authors: J.D. Bregman, J.N. Bregman, P. Temi
Comments: To appear in proceedings of "The Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution", held in Pasadena, November 2005

In a sample of thirty normal elliptical galaxies observed with the Spitzer IRS, one galaxy, NGC4697, shows strong PAH emission, but with an apparently weak 7.7 micron feature. We find that the PAH emission is confined to the central regions of the galaxy and that once a quiescent elliptical galaxy spectrum is subtracted, the PAH feature ratios are normal. We show that the PAH spectrum resembles the diffuse ISM of our galaxy rather than an HII region, and is not indicative of a starburst galaxy. We suggest that the PAHs in NGC4697 are consistent with a recent but now past burst of star formation.
astro-ph/0604370 [abs, ps, pdf, other] :: Title: Neutrino-Dominated Accretion Models for Gamma-Ray Bursts: Effects of General Relativity and Neutrino Opacity
Authors: Wei-Min Gu, Tong Liu, Ju-Fu Lu
Comments: 11 pages, 3 figures, accepted by ApJ Letters

We first refine the fixed concept in the literature that the usage of the Newtonian potential in studies of black hole accretion is invalid and the general relativistic effect must be considered. As our main results, we then show that the energy released by neutrino annihilation in neutrino-dominated accretion flows is sufficient for gamma-ray bursts when the contribution from the optically thick region of the flow is included, and that in the optically thick region advection does not necessarily dominate over neutrino cooling because the advection factor is relevant to the geometrical depth rather than the optical depth of the flow.
astro-ph/0604371 [abs, ps, pdf, other] :: Title: A Time-Symmetric Block Time-Step Algorithm for N-Body Simulations
Authors: Junichiro Makino, Piet Hut, Murat Kaplan, Hasan Saygin

The method of choice for integrating the equations of motion of the general N-body problem has been to use an individual time step scheme. For the sake of efficiency, block time steps have been the most popular, where all time step sizes are smaller than a maximum time step size by an integer power of two. We present the first successful attempt to construct a time-symmetric integration scheme, based on block time steps. We demonstrate how our scheme shows a vastly better long-time behavior of energy errors, in the form of a random walk rather than a linear drift. Increasing the number of particles makes the improvement even more pronounced.
astro-ph/0604372 [abs, ps, pdf, other] :: Title: Bright OB stars in the Galaxy - III. Constraints on the radial stratification of the clumping factor in hot star winds from a combined Halpha, IR and radio analysis
Authors: J. Puls, N. Markova, S. Scuderi, C. Stanghellini, O.G. Taranova, A.W. Burnley, I.D. Howarth
Comments: 40 pages, 17 figures, accepted by A&A

Recent results strongly challenge the canonical picture of massive star winds: various evidence indicates that currently accepted mass-loss rates, Mdot, may need to be revised downwards significantly. This is because the most commonly used mass-loss diagnostics are affected by ``clumping'' (small-scale density inhomogeneities), influencing our interpretation of observed spectra and fluxes. Such downward revisions would have dramatic consequences for the evolution of, and feedback from, massive stars, and thus robust determinations of the clumping properties and mass-loss rates are urgently needed. Here, we present a first attempt to constrain the radial stratification of the so-called clumping factor. To this end, we have analyzed a sample of 19 Galactic O-type supergiants/giants, by combining data for Halpha, IR, mm and radio fluxes, and using appropriate analysis methods. Clumping has been included into our analysis in the ``conventional'' way, by assuming the inter-clump matter to be void. Because (almost) all our diagnostics depends on the square of density, we cannot derive absolute clumping factors, but only factors normalized to a certain minimum. This minimum was usually found to be located in the outermost, radio-emitting region, i.e., the radio mass-loss rates are the lowest ones, compared to Mdot derived from Halpha and the IR. The radio rates agree well with those predicted by theory, but are only upper limits, due to unknown clumping in the outer wind. Our most important result concerns a (physical) difference between denser and thinner winds: for denser winds, the innermost region is more strongly clumped than the outermost one (with a normalized clumping factor of 4.1+/-1.4), whereas thinner winds have similar clumping properties in the inner and outer regions.
astro-ph/0604373 [abs, ps, pdf, other] :: Title: The z=3 QSO Luminosity Function with SWIRE
Authors: B. Siana, M. Polletta, H. E. Smith, C. J. Lonsdale, E. Gonzalez-Solares, D. Farrah, T. S. R. Babbedge, M. Rowan-Robinson, J. Surace, D. Shupe, F. Fang
Comments: 4 pages, 2 color figures. To appear in the proceedings for the Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution, Ed. R. Chary. November, 2005, Pasadena

We use a simple optical/infrared photometric selection of high redshift QSOs which identifies a Lyman Break in the optical and requires a red IRAC color to distinguish QSOs from common interlopers. We find 100 U-dropout (z=3) QSO candidates with r'<22 within 11.2 deg^2 in the ELAIS-N1 & ELAIS-N2 fields in the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Legacy Survey. Spectroscopy of 10 candidates shows that they are all QSOs with 2.83<z<3.44. We use detailed simulations which incorporate variations in QSO SEDs, IGM transmission and imaging depth to derive a completeness of 85-90% between 3.0<z<3.4. The resulting luminosity function is two magnitudes fainter than SDSS and, when combined with those data, gives a faint end slop \beta = 1.62 \pm 0.18, consistent with measurements at z<2 and steeper than initial measurements at the same redshift.
astro-ph/0604374 [abs, ps, pdf, other] :: Title: From AMANDA to IceCube
Authors: Per Olof Hulth, for the IceCube Collaboration
Comments: 12 pages, 6 figures, 1 table. Invited talk at the NO-VE 2006, Neutrino Oscillations in Venice, Italy, February 7-10, 2006

The success of the AMANDA neutrino telescope has shown that the ice sheet at the geographical South Pole is a suitable medium for optical Cherenkov detection of high energy neutrino interactions. Several thousands of atmospheric neutrinos have been recorded by AMANDA and the sensitivity for cosmic neutrinos has continuously improved. So far no cosmic neutrino signals have been detected. The deployment of the much larger and more sensitive IceCube neutrino observatory has started and nine out of 80 strings have been installed. This paper summarizes some of the results obtained by the AMANDA telescope and presents the status of the IceCube project.
astro-ph/0604375 [abs, ps, pdf, other] :: Title: Do mean-field dynamos in nonrotating turbulent shear-flows exist?
Authors: G. Ruediger, L. L. Kitchatinov
Comments: 6 pages, 2 figures, toappear in Astron. Nachr

A plane-shear flow in a fluid with forced turbulence is considered. If the fluid is electrically-conducting then a mean electromotive force (EMF) results even without basic rotation and the magnetic diffusivity becomes a highly anisotropic tensor. It is checked whether in this case self-excitation of a large-scale magnetic field is possible (so-called WxJ-dynamo) and the answer is NO. The calculations reveal the cross-stream components of the EMF perpendicular to the mean current having the wrong signs, at least for small magnetic Prandtl numbers. After our results numerical simulations with magnetic Prandtl number of about unity have only a restricted meaning as the Prandtl number dependence of the diffusivity tensor is rather strong. If, on the other hand, the turbulence field is stratified in the vertical direction then a dynamo active alpha-effect is produced. The critical magnetic Reynolds number for such a self-excitation in a simple shear flow is slightly above 10 like for the other - but much more complicated - flow patterns used in existing dynamo experiments with liquid sodium or gallium.
astro-ph/0604376 [abs, ps, pdf, other] :: Title: The Mexican Hat Wavelet Family. Application to point source detection in CMB maps
Authors: J. Gonzalez-Nuevo, F. Argueso, M. Lopez-Caniego, L. Toffolatti, J. L. Sanz, P. Vielva, D. Herranz
Comments: 14 pages and 4 figures. Accepted for publication on MNRAS

We propose a new detection technique in the plane based on an isotropic wavelet family. This family is naturally constructed as an extension of the Gaussian-Mexican Hat Wavelet pair and for that reason we call it the Mexican Hat Wavelet Family (MHWF). We show the performance of these wavelets when dealing with the detection of extragalactic point sources in cosmic microwave background (CMB) maps: a very important issue within the most general problem of the component separation of the microwave sky. Specifically, flat two-dimensional simulations of the microwave sky comprising all astrophysical components plus instrumental noise have been analyzed for the channels at 30, 44 and 70 GHz of the forthcoming ESA's Planck mission Low Frequency Instrument (LFI). We adopt up-to-date cosmological evolution models of extragalactic sources able to fit well the new data on high-frequency radio surveys and we discuss our current results on point source detection by comparing them with those obtained using the Mexican Hat Wavelet (MHW) technique, which has been already proven a suitable tool for detecting point sources. By assuming a 5% reliability level, the first new members of the MHWF, at their ``optimal scale'', provide three point source catalogues on half of the sky (at galactic latitude |b|> 30) at 30, 44 and 70 GHz of 639, 387 and 340 extragalactic sources, respectively. The corresponding flux detection limits are 0.38, 0.45 and 0.47 Jy . By using the same simulated sky patches and at the same frequencies as before, the MHW at its optimal scale provides 543, 322 and 311 sources with flux detection limits of 0.44, 0.51 and 0.50 Jy, respectively (5% reliability level). These results show a clear improvement when we use the new members of the MHWF and, in particular, the MHW2 with respect to the MHW.
astro-ph/0604377 [abs, ps, pdf, other] :: Title: The origin of the hot metal-poor gas in NGC1291: Testing the hypothesis of gas dynamics as the cause of the gas heating
Authors: I. Perez, K. Freeman
Comments: 6 pages, 6 figures. A&A accepted

In this paper we test the idea that the low-metallicity hot gas in the centre of NGC 1291 is heated via a dynamical process. In this scenario, the gas from the outer gas-rich ring loses energy through bar-driven shocks and falls to the centre. Heating of the gas to X-ray temperatures comes from the high velocity that it reaches ($\approx$ 700 \kms) as it falls to the bottom of the potential well. This would explain why the stellar metallicity in the bulge region is around solar while the hot gas metallicity is around 0.1 solar. We carried out an observational test to check this hypothesis by measuring the metallicity of HII regions in the outer ring to check whether they matched the hot gas metallicity. For this purpose we obtained medium resolution long slit spectroscopy with FORS1 on the ESO VLT at Paranal and obtained the metallicities using emission line ratio diagnostics. The obtained metallicities are compatible with the bulge stellar metallicities but very different from the hot-gas metallicity. However, when comparing the different time-scales, the gas in the ring had time enough to get enriched through stellar processes, therefore we cannot rule out the dynamical mechanism as the heating process of the gas. However, the blue colours of the outer ring and the dust structures in the bar region could suggest that the origin of the X-ray hot gas is due to the infall of material from further out.
astro-ph/0604378 [abs, ps, pdf, other] :: Title: Strange magnification pattern in the large separation lens SDSS J1004+4112 from optical to X-rays
Authors: G. Lamer, A. Schwope, L. Wisotzki, L. Christensen
Comments: 11 pages, 10 figures, accepted for publication in Astronomy & Astrophysics

We present simultaneous XMM-Newton UV and X-ray observations of the quadruply lensed quasar SDSS J1004+4112 (RBS 825). Simultaneously with the XMM-Newton observations we also performed integral field spectroscopy on the two closest lens images A and B using the Calar Alto PMAS spectrograph. In X-rays the widely spaced components C and D are clearly resolved, while the closer pair of images A and B is marginally resolved in the XMM-EPIC images. The integrated X-ray flux of the system has decreased by a factor of 6 since it was observed in the ROSAT All Sky Survey in 1990, while the X-ray spectrum became much harder with the power law index evolving from Gamma=-2.3 to -1.86. By deblending the X-ray images of the lensed QSO we find that the X-ray flux ratios between the lens images A and B are significantly different from the simultaneously obtained UV ratios and previously measured optical flux ratios. Our optical spectrum of lens image A shows an enhancement in the blue emission line wings, which has been observed in previous epochs as a transient feature. We propose a scenario where intrinsic UV and X-ray variability gives rise to line variations which are selectively magnified in image A by microlensing. The extended emission of the lensing cluster of galaxies is clearly detected in the EPIC images, we measure a 0.5-2.0 keV luminosity of 1.4 E44 erg/s. Based on the cluster X-ray properties, we estimate a mass of 2-6 E14 solar masses.
astro-ph/0604379 [abs, ps, pdf, other] :: Title: Flux predictions of high-energy neutrinos from pulsars
Authors: Bennett Link (Montana State University, Bozeman, USA), Fiorella Burgio (INFN Sezione di Catania, Italy)
Comments: 6 pages, 3 figures

Young, rapidly rotating neutron stars could accelerate ions from their surface to energies of $\sim 1$ PeV. If protons reach such energies, they will produce pions (with low probability) through resonant scattering with x-rays from the stellar surface. The pions subsequently decay to produce muon neutrinos. Here we calculate the energy spectrum of muon neutrinos, and estimate the event rates at Earth. The spectrum consists of a sharp rise at $\sim 50$ TeV, corresponding to the onset of the resonance, above which the flux drops with neutrino energy as $\epsilon_\nu^{-2}$ up to an upper-energy cut-off that is determined by either kinematics or by the maximum energy to which protons are accelerated. We estimate event rates as high as 10-100 km^${-2}$ yr$^{-1}$ from some candidates, a flux that would be easily detected by IceCube. Lack of detection would allow constraints on the energetics of the poorly-understood pulsar magnetosphere.
astro-ph/0604380 [abs, ps, pdf, other] :: Title: Scaling Law for the Magnetic Field of the Planets Based on a Thermodynamic Model
Authors: F. X. Alvarez

A thermodynamic model for the generation of magnetic fields in the planets is proposed, considering crossed effects between gravitational and electric forces. The magnetic field of the Earth is estimated and found to be in agreement with the actual field. The ratio between the field of several planets and that of the Earth is calculated in the model and compared with the same ratio for the measured fields. These comparisons are found to be qualitatively consistent. Once the value of the magnetic field is calculated, the model is used to obtain the tilt of the magnetic dipole with respect to the rotation axis. This model can explain why Uranus and Neptune magnetic fields have higher quadrupole moment than the other magnetic fields of the Solar System and why Saturn, that has a highly axysymmetric field, has lower quadrupolar component. The model also explains the double peak of the magnetic field observed by Voyager 2 while recording the field of Neptune. The Earth paleomagnetic data are analysed and found to be consistent with the model, that predicts higher quadrupole components for the more tilted dipoles. A field is predicted for all the planets and satellites of the Solar System with enough mass. Objections are made to the theories that predict that this effect could not generate a field agreeing with the measured one.
astro-ph/0604381 [abs, ps, pdf, other] :: Title: Quiet Sun magnetic fields from simultaneous inversions of visible and infrared spectropolarimetric observations
Authors: Itahiza Dominguez Cerdena (1), Jorge Sanchez Almeida (1), Franz Kneer (2) ((1) Instituto de Astrofisica de Canarias, La Laguna, Spain, (2) Institut fuer Astrophysik, Goettingen, Germany)
Comments: 16 pages and 14 figures

We study the quiet Sun magnetic fields using spectropolarimetric observations of the infrared and visible Fe I lines at 6301.5, 6302.5, 15648 and 15653 A. Magnetic field strengths and filling factors are inferred by the simultaneous fit of the observed Stokes profiles under the MISMA hypothesis. The observations cover an intra-network region at the solar disk center. We analyze 2280 Stokes profiles whose polarization signals are above noise in the two spectral ranges, which correspond to 40% of the field of view. Most of these profiles can be reproduced only with a model atmosphere including 3 magnetic components with very different field strengths, which indicates the co-existence of kG and sub-kG fields in our 1.5" resolution elements. We measure an unsigned magnetic flux density of 9.6 G considering the full field of view. Half of the pixels present magnetic fields with mixed polarities in the resolution element. The fraction of mixed polarities increases as the polarization weakens. We compute the probability density function of finding each magnetic field strength. It has a significant contribution of kG field strengths, which concentrates most of the observed magnetic flux and energy. This kG contribution has a preferred magnetic polarity, while the polarity of the weak fields is balanced.
astro-ph/0604382 [abs, ps, pdf, other] :: Title: A population of high-redshift type-2 quasars-I. Selection Criteria and Optical Spectra
Authors: Alejo Martinez-Sansigre, Steve Rawlings, Mark Lacy, Dario Fadda, Matt J. Jarvis, Francine R. Marleau, Chris Simpson, Chris J. Willott
Comments: 22 Pages, 12 Figures

We discuss the relative merits of mid-infrared and X-ray selection of type-2 quasars. We describe the mid-infrared, near-infrared and radio selection criteria used to find a population of redshift z~2 type-2 quasars which we previously argued suggests that most supermassive black hole growth in the Universe is obscured (Martinez-Sansigre et al., 2005). We present the optical spectra obtained from the William Herschel Telescope, and we compare the narrow emission line luminosity, radio luminosity and maximum size of jets to those of objects from radio-selected samples. This analysis suggests that these are genuine radio-quiet type-2 quasars, albeit the radio-bright end of this population. We also discuss the possibility of two different types of quasar obscuration, which could explain how the ~3:1 ratio of type-2 to type-1 quasars preferred by modelling our population can be reconciled with the ~1:1 ratio predicted by unified schemes.
astro-ph/0604383 [abs, ps, pdf, other] :: Title: Deep GMOS Spectroscopy of Extremely Red Galaxies in GOODS-South: Ellipticals, Mergers and Red Spirals at 1<z<2
Authors: Nathan Roche, James Dunlop, Karina Caputi, Ross McLure, Chris Willott, David Crampton
Comments: 19 pages, 9 figures

We have performed a deep spectroscopic survey of extremely red galaxies on the GOODS-South field, using GMOS on Gemini South. We present here spectra and redshifts for 16 ERGs at 0.87<z<2.02, to a limit K=20.2. The ERHs are a mixture of spheroidals, mergers and spirals, with one AGN. For at least 10 of these galaxies we observe [OII] emission lines. We perform an age-dating analysis by fitting the spectra and 9-band photometry of the ERGs with models of passively evolving stellar populations combined with a younger star-forming component. The best-fitting ages for the old stellar components range from 0.6 to 4.5 Gyr, with a mean 2.1 Gyr. Masses range from 3 to 20 times 10^10 solar masses. The star-forming component typically forms a few per cent of the total mass, with dust reddening averaging E(B-V)=0.35. Its timescale tends to be short for mergers (<50 Myr) and longer (200-800 Myr) for spiral ERGs.
astro-ph/0604384 [abs, pdf] :: Title: Star Formation in the Era of the Three Great Observatories
Authors: Scott J. Wolk, Norbert Schulz, John Stauffer, Nancy Evans, Leisa Townsley, Tom Megeath, Dave Huenemoerder, Claus Leitherer, Ray Jayawardana
Comments: Conference Summary "White Paper", Accepted by PASP, 9 pages including 3 figures

This paper summarizes contributions and suggestions as presented at the Chandra Workshop Star Formation in the Era of Three Great Observatories conducted in July 2005. One of the declared goals of the workshop was to raise recognition within the star formation research community about the sensible future utilization of the space observatories Spitzer, Hubble, and Chandra in their remaining years of operation to tackle imminent questions of our understanding of stellar formation and the early evolution of stars. A white paper was generated to support the continuous and simultaneous usage of observatory time for star formation research. The contents of this paper have been presented and discussed at several other meetings during the course of 2005 and January 2006.
astro-ph/0604385 [abs, ps, pdf, other] :: Title: Automated derivation of stellar atmospheric parameters and chemical abundances: the MATISSE algorithm
Authors: A. Recio-Blanco, A. Bijaoui, P. de Laverny

We present an automated procedure for the derivation of atmospheric parameters (Teff, log g, [M/H]) and individual chemical abundances from stellar spectra. The MATrix Inversion for Spectral SythEsis (MATISSE) algorithm determines a basis, B_\theta(\lambda), allowing to derive a particular stellar parameter \theta by projection of an observed spectrum. The B_\theta(\lambda) function is determined from an optimal linear combination of theoretical spectra and it relates, in a quantitative way, the variations in the spectrum flux with variations in \theta. An application of this method to the GAIA/RVS spectral range is described, together with its performances for different types of stars of various metallicities. Blind tests with synthetic spectra of randomly selected parameters and observed input spectra are also presented. The method gives rapid, accurate and stable results and it can be efficiently applied to the study of stellar populations through the analysis of large spectral data sets, including moderate to low signal to noise spectra.
astro-ph/0604386 [abs, ps, pdf, other] :: Title: Magnetars' Giant Flares: the case of SGR 1806-20
Authors: Nanda Rea (SRON - Netherlands Institute for Space Research), et al
Comments: 6 pages, 2 figures; accepted for publication in the Chinese Journal for Astronomy and Astrophysics (Vulcano conference - 2005)

We first review on the peculiar characteristics of the bursting and flaring activity of the Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars. We then report on the properties of the SGR 1806-20's Giant Flare occurred on 2004 December 27th, with particular interest on the pre and post flare intensity/hardness correlated variability. We show that these findings are consistent with the picture of a twisted internal magnetic field which stresses the star solid crust that finally cracks causing the giant flare (and the observed torsional oscillations). This crustal fracturing is accompanied by a simplification of the external magnetic field with a (partial) untwisting of the magnetosphere.
astro-ph/0604387 [abs, ps, pdf, other] :: Title: A numerical study of non-gaussianity in the curvaton scenario
Authors: Karim A. Malik, David H. Lyth
Comments: 14 pages, 9 figures, some in colour

We study the curvaton scenario using gauge-invariant second order perturbation theory and solving the governing equations numerically. Focusing on large scales we calculate the non-linearity parameter f_nl in the two-fluid curvaton model and compare our results with previous analytical studies employing the sudden decay approximation. We find good agreement of the two approaches for large curvaton energy densities at curvaton decay, Omega_dec, but significant differences of up to 10 percent for small Omega_dec.

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Thu, 20 Apr 06 00:00:09 GMT
0604388 -- 0604413 received

astro-ph/0604388 [abs, ps, pdf, other] :: Title: H-alpha Observations of a Large Sample of Galaxies at z~2: Implications for Star Formation in High Redshift Galaxies
Authors: Dawn K. Erb (CfA), Charles C. Steidel (Caltech), Alice E. Shapley (Princeton), Max Pettini (IoA), Naveen A. Reddy (Caltech), Kurt L. Adelberger (McKinsey)
Comments: 14 pages, 7 figures, 1 table. Accepted for publication in ApJ

Using H-alpha spectra of 114 rest-frame UV-selected galaxies at z~2, we compare inferred star formation rates (SFRs) with those determined from the UV continuum luminosity. After correcting for extinction using standard techniques based on the UV continuum slope, we find excellent agreement between the indicators, with <SFR_Ha> = 31 Msun/yr and <SFR_UV> = 29 Msun/yr. The agreement between the indicators suggests that the UV luminosity is attenuated by an typical factor of ~4.5 (with a range from no attenuation to a factor of ~100 for the most obscured object in the sample), in good agreement with estimates of obscuration from X-ray, radio and mid-IR data. The H-alpha luminosity is attenuated by a factor of ~1.7 on average, and the maximum H-alpha attenuation is a factor of ~5. In agreement with X-ray and mid-IR studies, we find that the SFR increases with increasing stellar mass and at brighter K magnitudes, to <SFR_Ha> ~ 60 Msun/yr for galaxies with K<20; the correlation between K magnitude and SFR is much stronger than the correlation between stellar mass and SFR. All galaxies in the sample have SFRs per unit area Sigma_SFR in the range observed in local starbursts. We compare the instantaneous SFRs and the past average SFRs as inferred from the ages and stellar masses, finding that for most of the sample, the current SFR is an adequate representation of the past average. There is some evidence that the most massive galaxies (M_star >10^11 Msun) have had higher SFRs in the past.
astro-ph/0604389 [abs, ps, pdf, other] :: Title: Relativistic ejecta from XRF 060218 and the complete census of cosmic explosions
Authors: A. M. Soderberg, S. R. Kulkarni, E. Nakar, E. Berger, D. B. Fox, D. A. Frail, A. Gal-Yam, R. Sari, S. B. Cenko, M. Kasliwal, P. B. Cameron, R. A. Chevalier, T. Piran, P. A. Price, B. P. Schmidt, G. Pooley, D.-S. Moon, B. E. Penprase, N. Gehrels, J. A. Nousek, D. N. Burrows, S. E. Perrson, P. J. McCarthy
Comments: Submitted to Nature (13 pages, 3 figures)

Over the last decade, long-duration gamma-ray bursts (GRBs) and X-ray flashes (XRFs) have been revealed to be a rare variety of Type Ibc supernova (SN). While all these events result from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary Type Ibc SNe by many orders of magnitude. The essential physical process that causes a dying star to produce a GRB or XRF, and not just an SN, remains the crucial open question. Here we present radio and X-ray observations of XRF 060218 (associated with SN 2006aj), the second nearest GRB identified to-date, which allow us to measure its total energy and place it in the larger context of cosmic explosions. We show that this event is 100 times less energetic but ten times more common than cosmological GRBs. Moreover, it is distinguished from ordinary Type Ibc SNe by the presence of 10^48 erg of mildly-relativistic ejecta, along with a central engine which produces X-rays for weeks after the explosion. This suggests that the presence of relativistic ejecta is the key physical distinction between GRBs/XRFs and ordinary SNe, while the nature of the central engine (black hole or magnetar) may distinguish cosmological GRBs from the low-luminosity and spherical events like XRF 060218.
astro-ph/0604390 [abs, ps, pdf, other] :: Title: The Formation Epoch of Early-Type Galaxies in the z~0.9 CL1604 Supercluster
Authors: N.L. Homeier (JHU), S. Mei (JHU), J.P. Blakeslee (WSU), M. Postman (STScI), B. Holden (UCSC), H.C. Ford (JHU), L.D. Bradley (JHU), R. Demarco (JHU), M. Franx (Leiden), G.D. Illingworth (UCSC), M.J. Jee (JHU), F. Menanteau (JHU), P. Rosati (ESO-Garching), A. van der Wel (JHU), A. Zirm (JHU)
Comments: ApJ accepted

We analyse the cluster color-magnitude relation (CMR) for early-type galaxies in two of the richer clusters in the z~0.9 supercluster system to derive average ages and formation redshifts for the early-type galaxy population. Both clusters were observed with the Advanced Camera for Surveys aboard the {\it Hubble Space Telescope} through the F606W and F814W filters, which brackets the rest-frame 4000~\AA~break at the cluster redshifts of z\sim 0.9. We fit the zeropoint and slope of the red cluster sequence, and model the scatter about this relation to estimate average galaxy ages and formation redshifts. We find intrinsic scatters of $0.038-0.053$ mag in ($V_{606}-I_{814}$) for the E and E+S0 populations, corresponding to average ages of 3.5-3.7 Gyr and formation redshifts z_{f}=2.4-2.6. We find at least one significant difference between the Cl1604+4304 and Cl1604+4321 early-type CMRs. Cl1604+4321, the less X-ray luminous and massive of the two, lacks bright L^* ellipticals. We combine the galaxy samples to fit a composite CMR down to 0.15L^*, and find that the slope of the combined cluster CMR is significantly steeper than for RX~J0152.7-1357 but consistent with MS 1054-03, both at similar redshift. The slope of the Cl1604 CMR at the bright end (L > 0.5L^*) is flatter and consistent with the CMR slopes found for other high redshift clusters. We find evidence for increasing scatter with increasing magnitude along the early-type CMR, consistent with a 'downsizing' scenario, indicating younger mean ages with decreasing galaxy mass.
astro-ph/0604391 [abs, ps, pdf, other] :: Title: Comparing Dynamical and Stellar Population Mass-to-Light Ratio Estimates
Authors: Roelof S. de Jong (STScI), Eric Bell (MPIA)
Comments: 9 pages, 3 figures. To appear in the conference proceedings of Island Universes, Structure and Evolution of Disk Galaxies, ed. R.S. de Jong (Springer, Dordrecht)

We investigate the mass-to-light ratios of stellar populations as predicted by stellar population synthesis codes and compare those to dynamical/gravitational measurements. In Bell & de Jong (2001) we showed that population synthesis models predict a tight relation between the color and mass-to-light ratio of a stellar population. The normalization of this relation depends critically on the shape of the stellar IMF at the low-mass end. These faint stars contribute significantly to the mass, but insignificantly to the luminosity and color of a stellar system. In Bell & de Jong (2001) we used rotation curves to normalize the relation, but rotation curves provide only an upper limit to the stellar masses in a system. Here we compare stellar and dynamical masses for a range of stellar systems in order to constrain the mass normalization of stellar population models. We find that the normalization of Bell & de Jong (2001) should be lowered by about 0.05-0.1 dex in M/L. This is consistent with a Kroupa (2001), Chabrier (2003) or a Kennicutt (1983) IMF, but does not leave much room for other unseen components.
astro-ph/0604392 [abs, ps, pdf, other] :: Title: Arecibo and the ALFA Pulsar Survey
Authors: J. van Leeuwen, J. M. Cordes, D. R. Lorimer, P. C. C. Freire, F. Camilo, I. H. Stairs, D. J. Nice, D. J. Champion, R. Ramachandran, A. J. Faulkner, A. G. Lyne, S. M. Ransom, Z. Arzoumanian, R. N. Manchester, M. A. McLaughlin, J. W. T. Hessels, W. Vlemmings, A. A. Deshpande, N. D. R. Bhat, S. Chatterjee, J. L. Han, B. M. Gaensler, L. Kasian, J. S. Deneva, B. Reid, T. J. W. Lazio, V. M. Kaspi, F. Crawford, A. N. Lommen, D. C. Backer, M. Kramer, B. W. Stappers, G. B. Hobbs, A. Possenti, N. D'Amico, C.-A. Faucher-Giguère, M. Burgay
Comments: 8 pages, invited review for the Hanas Pulsar Symposium, ChJAA in press

The recently started Arecibo L-band Feed Array (ALFA) pulsar survey aims to find ~1000 new pulsars. Due to its high time and frequency resolution the survey is especially sensitive to millisecond pulsars, which have the potential to test gravitational theories, detect gravitational waves and probe the neutron-star equation of state. Here we report the results of our preliminary analysis: in the first months we have discovered 21 new pulsars. One of these, PSR J1906+0746, is a young 144-ms pulsar in a highly relativistic 3.98-hr low-eccentricity orbit. The 2.61 +- 0.02 solar-mass system is expected to coalesce in ~300 Myr and contributes significantly to the computed cosmic inspiral rate of compact binary systems.
astro-ph/0604393 [abs, ps, pdf, other] :: Title: Baryon Dynamics, Dark Matter Substructure, and Galaxies
Authors: David H. Weinberg, Stephane Colombi, Romeel Davé, Neal Katz
Comments: 32 pages including 16 figs. Submitted to ApJ. PDF file with higher quality versions of Figs 2 and 3 available at this http URL

By comparing a collisionless cosmological N-body simulation (DM) to an SPH simulation with the same initial conditions, we investigate the correspondence between the dark matter subhalos produced by collisionless dynamics and the galaxies produced by dissipative gas dynamics in a dark matter background. When galaxies in the SPH simulation become satellites in larger groups, they retain local dark matter concentrations (SPH subhalos) whose mass is typically five times their baryonic mass. The more massive subhalos of the SPH simulation have corresponding subhalos of similar mass and position in the DM simulation; at lower masses, there is fairly good correspondence, but some DM subhalos are in different spatial positions and some suffer tidal stripping or disruption. The halo occupation statistics of DM subhalos -- the mean number of subhalos, pairs, and triples as a function of host halo mass -- are very similar to those of SPH subhalos and SPH galaxies. Gravity of the dissipative baryon component amplifies the density contrast of subhalos in the SPH simulation, making them more resistant to tidal disruption. Relative to SPH galaxies and SPH subhalos, the DM subhalo population is depleted in the densest regions of the most massive halos. The good agreement of halo occupation statistics between the DM subhalo and SPH galaxy populations leads to good agreement of their two-point correlation functions and higher order moments on large scales. The depletion of DM subhalos in dense regions depresses their clustering at R<1 Mpc/h. In these simulations, the "conversation" between dark matter and baryons is mostly one-way, with dark matter dynamics telling galaxies where to form and how to cluster, but the "back talk" of the baryons influences small scale clustering by enhancing the survival of substructure in the densest environments.
astro-ph/0604394 [abs, ps, pdf, other] :: Title: NICMOS Status
Authors: Roelof S. de Jong, Santiago Arribas, Elizabeth Barker, Louis E. Bergeron, Ralph C. Bohlin, Daniela Calzetti, Ilana Dashevsky, Mark Dickinson, Anton M. Koekemoer, Sangeeta Malhotra, Bahram Mobasher, Keith S. Noll, Adam G. Riess, Alfred B. Schultz, Megan L. Sosey, Thomas Wheeler, Tommy Wiklind, Chun Xu
Comments: 12 pages, 10 figures. More information on the newly discovered NICMOS count-rate dependent non-linearity and how to correct for it can be found at this http URL
Journal-ref: Conference proceedings of The 2005 HST Calibration Workshop, eds. A. Koekemoer, P. Goudfrooij, L. Dressel, p. 121

We provide an overview of the most important calibration aspects of the NICMOS instrument on board of HST. We describe the performance of the instrument after the installation of the NICMOS Cooling System, and show that the behavior of the instrument has become very stable and predictable. We detail the improvements made to the NICMOS pipeline and outline plans for future developments. The derivation of the absolute photometric zero-point calibration is described in detail. Finally, we describe and quantify a newly discovered count-rate dependent non-linearity in the NICMOS cameras. This new non-linearity is distinctly different from the total count dependent non-linearity that is well known for near-infrared detectors. We show that the non-linearity has a power law behavior, with pixels with high system, or vice versa, pixels with low count rate detecting slightly less than expected. The effect has a wavelength dependence with observations at the shortest wavelengths being the most affected (~0.05-0.1 mag per dex flux change at ~1 micron, 0.03 mag per dex at 1.6 micron).
astro-ph/0604395 [abs, ps, pdf, other] :: Title: Mass Distribution of Spiral Galaxies in a Thin Disk Model with Velocity Curve Extrapolation
Authors: Valentin Kostov

We model a spiral galaxy by a thin axially symmetric disk that includes both visible and dark matter. The surface mass density of the disk is calculated directly from the rotational velocity curve without extra assumptions. We simplify the standard application of the model. Since most velocity curves are known out to some radius, r_{max}, we extrapolate them by attaching a Keplerian tail. The numerical procedure and the extrapolation are tested with a known toy mass density and shown to reconstruct it with a good precision if r_{max} includes a sufficient part of the velocity curve. Mass density curves are calculated for Milky Way and NGC 3198. We vary the extent of the flat part of the velocity curves from 30 kpc to 200 kpc and show that does not affect appreciably the calculated mass density inside r_{max}=30 kpc. The reconstructed masses for Milky Way are 15 x 10^10 solar masses inside the visible disk and 23 x 10^10 solar masses inside 30 kpc. For NGC 3198, the reconstructed mass inside the visible disk is 6.5 x 10^10 solar masses and 11 x 10^10 solar masses inside 30 kpc. The total galactic masses are roughly proportional to the extent of the flat part of the velocity curves which is currently unknown. The high light-to-mass ratios obtained for the visible disks of the galaxies - 11 solar units for Milky way and 9.3 for NGC 3198 - suggest presence of dark matter. The method is also applied to NGC 3031 - a spiral galaxy with a declining velocity curve in which case it is able to reconstruct both the mass density curve and the total mass (14 x 10^10 solar masses).
astro-ph/0604396 [abs, ps, pdf, other] :: Title: Optical spectroscopy of the dwarf nova U Geminorum
Authors: Unda-Sanzana, E. Marsh, T. R. Morales-Rueda, L

U Gem is unique in having a direct measurement of K1 = 107 +- 2 km/s, Long et al. 1999). We present high-resolution optical spectra of the dwarf nova U Gem in quiescence taken to test the accuracy to which the HST value can be recovered from optical data. We find that, even with data of very high S/N we cannot recover Long et al.'s value to better than about 20% by any method. Contamination by neighbouring emission lines seems a likely culprit. Our data reveal a number of new features: Doppler tomograms show emission at low velocity, close to the centre of mass, and a transient, narrow absorption feature is seen in the Balmer lines near the line centres at the time of eclipse. We suggest that stellar prominences, as previously invoked for the dwarf novae IP Peg and SS Cyg in outburst, may explain both of these features. The He II 4686.75 A line emission is dominated by the gas stream/disc impact region. Two distinct spots are seen in Doppler maps, the first being very narrow and showing a velocity close to that of the accretion disc in the impact region, and the second much broader and located between the velocities of the (ballistic) stream and the (Keplerian) disc. We present tentative evidence of weak spiral structure. We find no evidence of stream-disc overflow in the system. Our data suggests an inclination angle > 70 degrees, adding to the evidence of a puzzle in the mass of U Gem's white dwarf. The mass donor is clearly seen in the Doppler maps, with emission concentrated towards its poles, and mainly on the side facing the white dwarf. This suggests irradiation with shielding by the disc from which we estimate an H/R ratio between 0.15 and 0.25.
astro-ph/0604397 [abs, ps, pdf] :: Title: Compton Spectrum from Poynting Flux Accelerated e+e- Plasma
Authors: Shinya Sugiyama, Edison Liang, Koichi Noguchi, Hideaki Takabe
Comments: 4 pages, 4 figures, submitted to Swift GRB Workshop Proceedings 2006 (in press)

We report the Compton scattering emission from the Poynting flux acceleration of electron- positron plasma simulated by the 2-1/2 dimensional particle-in-cell(PIC) code. We show these and other remarkable properties of Poynting flux acceleration and Compton spectral output, and discuss the agreement with the observed spectra of GRBs and XRFs.
astro-ph/0604398 [abs, pdf] :: Title: Particle Acceleration by Electromagnetic-Dominated Outflows
Authors: Edison Liang, Koichi Noguchi
Comments: 12 pages, 15 figures
Journal-ref: RevMex A A (Serie de Conferencias) 23, 43 (2005)

We review recent developments in particle acceleration by Poynting flux using plasma kinetic simulations, and discuss their potential applications to gamma-ray burst phenomenology
astro-ph/0604399 [abs, ps, pdf, other] :: Title: The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions
Authors: Joel N. Bregman, Pasquale Temi, Jesse D. Bregman
Comments: Accepted for publication in ApJ

The mean ages of early-type galaxies obtained from the analysis of optical spectra, give a mean age of 8 Gyr at z = 0, with 40% being younger than 6 Gyr. Independent age determinations are possible by using infrared spectra (5-21 microns), which we have obtained with the Infrared Spectrograph on the Spitzer Observatory. This age indicator is based on the collective mass loss rate of stars, where mass loss from AGB stars produces a silicate emission feature at 9-12 microns. This feature decreases more rapidly than the shorter wavelength continuum as a stellar population ages, providing an age indicator. From observations of 30 nearby early-type galaxies, 29 show a spectral energy distribution dominated by stars and one has significant emission from the ISM and is excluded. The infrared age indicators for the 29 galaxies show them all to be old, with a mean age of about 10 Gyr and a standard deviation of only a few Gyr. This is consistent with the ages inferred from the values of M/L_B, but is inconsistent with the ages derived from the optical line indices, which can be much younger. All of these age indicators are luminosity-weighted and should be correlated, even if multiple-age components are considered. The inconsistency indicates that there is a significant problem with either the infrared and the M/L_B ages, which agree, or with the ages inferred from the optical absorption lines.
astro-ph/0604400 [abs, ps, pdf, other] :: Title: Variability of the NGC 1333 IRAS 4A Outflow: Molecular Hydrogen and Silicon Monoxide Images
Authors: Minho Choi, Klaus W. Hodapp, Masahiko Hayashi, Kentaro Motohara, Soojong Pak, Tae-Soo Pyo

The NGC 1333 region was observed in the H2 1-0 S(1) line. The H2 images cover a 5' x 7' region around IRAS 4. Numerous H2 emission features were detected. The northeast-southwest bipolar outflow driven by IRAS 4A was studied by combining the H2 images with SiO maps published previously. The SiO-H2 outflows are continuous on the southwestern side but show a gap on the northeastern side. The southwestern outflow lobe curves smoothly, and the position angle increases with the distance from the driving source. The base and the outer tip of the northeastern outflow lobe are located at positions opposite to the corresponding parts of the southwestern lobe. This point-symmetry suggests that the outflow axis may be drifting or precessing clockwise in the plane of the sky and that the cause of the axis drift may be intrinsic to the outflow engine. The axis drift model is supported by the asymmetric lateral intensity profile of the SiO outflow. The axis drift rate is about 0.011 deg yr-1. The middle part of the northeastern outflow does not exactly follow the point symmetry because of the superposition of two different kinds of directional variability: the axis drift of the driving source and the deflection by a dense core. The axis drift model provides a good explanation for the large deflection angle of the northeastern outflow. Other H2 emission features around the IRAS 4 region are discussed briefly. Some of them are newly found outflows, and some are associated with outflows already known before.
astro-ph/0604401 [abs, ps, pdf, other] :: Title: Talk about Pivots
Authors: Damien Martin, Andreas Albrecht
Comments: 3 pages; brief comment

We consider two different methods of parameterizing the dark energy equation of state in order to assess possible ``figures of merit'' for evaluating dark energy experiments. The two models are $w(a) = w_0 + (1-a)w_a$ and $w(a) = w_p + (a_p - a)w_a$. This brief note shows that the size of the error contours cannot change under such a reparameterization. This makes the figures of merit associated with these parameterizations mathematically identical. This also means that any ``bias'' exhibited by one model is equally present in the other.
astro-ph/0604402 [abs, ps, pdf, other] :: Title: The Great Attractor and the Shapley Concentration
Authors: Krzysztof Bolejko, Charles Hellaby
Comments: MN2e LaTex, 9 pages, 14 figures

We develop a non-linear relativistic model of the Shapley Concentration (SC) and its environs, including the Great Attractor (GA) and the Local Group (LG). We take the Shapley concentration as a major attractive centre, and we use the Lemaitre-Tolman model. We constrain our model with present day observations, plus the requirement that it have a physically reasonable evolution from small perturbations at last scattering. We investigate possible mass and velocity distributions, and we find that the peculiar velocity maximum near the SC is \~800 km/s inwards, the density between GA and SC must be about ~0.9 times background, the mass of the GA is probably 4 - 6 x 10^15 M_sun, the SC's contribution to the LG motion is negligible, and the value of the cosmological constant is not significant on this scale.
astro-ph/0604403 [abs, ps, pdf, other] :: Title: Primordial gas cooling behind shock waves in merging halos
Authors: E.O. Vasiliev, Yu.A. Shchekinov
Comments: 17 pages, 5 fugures, submitted in New Astronomy

We investigate thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos. We find a fraction of the shocked gas cooled by radiation of HD molecules down to the temperature of the cosmic microwave background (CMB): this fraction increases sharply from about $f_{\rm c}\sim 10^{-3}$ for dark halos of $M=5\times 10^7\msun$ to $\sim 0.1$ for halos with $M=10^8\msun$ at $z=10$. We show, however, that further increase of the mass does not lead to a significant growth of $f_{\rm c}$ -- the assymptotic value for $M\gg 10^8\msun$ is of 0.2. We estimate star formation rate associated with such shock waves, and show that it can be a small but not negligible fraction of the star formation connected with cooling by HI and H$_2$. We argue that extremely metal-poor low-mass stars in the Milky Way may have been formed from primordial gas behind such shocks.
astro-ph/0604404 [abs, ps, pdf, other] :: Title: High frequency observations of southern pulsars
Authors: {Simon Johnston, Aris Karastergiou, Kyle Willett
Comments: Accepted by MNRAS. 13 pages. 6 figures

We present polarization data for 32 mainly southern pulsars at 8.4 GHz. The observations show that the polarization fraction is low in most pulsars at this frequency except for the young, energetic pulsars which continue to show polarization fractions in excess of 60 per cent. All the pulsars in the sample show evidence for conal emission with only one third also showing core emission. Many profiles are asymmetric, with either the leading or the trailing part of cone not detectable. Somewhat surprisingly, the asymmetric profiles tend to be more polarized than the symmetrical profiles. Little or no pulse narrowing is seen between 1 and 8.4 GHz. The spectral behaviour of the orthogonal polarization modes and radius to frequency mapping can likely account for much of the observational phenomenology. Highly polarized components may orginate from higher in the magnetosphere than unpolarized components.
astro-ph/0604405 [abs, ps, pdf, other] :: Title: The stellar masses of 25000 galaxies at 0.2<z<1.0 estimated by the COMBO-17 survey
Authors: Andrea Borch, Klaus Meisenheimer, Eric F. Bell, Hans-Walter Rix, Christian Wolf, Simon Dye, Martina Kleinheinrich, Zoltan Kovacs, Lutz Wisotzki
Comments: Astronomy and Astrophysics in press. 15 pages, 12 figures

We present an analysis of stellar mass estimates for a sample of 25000 galaxies from the COMBO-17 survey over the interval 0.2<z<1.0. We have developed, implemented, and tested a new method of estimating stellar mass-to-light ratios, which relies on redshift and spectral energy distribution (SED) classification from 5 broadband and 12 medium band filters. We find that the majority (>60%) of massive galaxies with M_* > 10^{11} solar masses at all z<1 are non-star-forming; blue star-forming galaxies dominate at lower masses. We have used these mass estimates to explore the evolution of the stellar mass function since z=1. We find that the total stellar mass density of the universe has roughly doubled since z~1. Our measurements are consistent with other measurements of the growth of stellar mass with cosmic time and with estimates of the time evolution of the cosmic star formation rate. Intriguingly, the integrated stellar mass of blue galaxies with young stars has not significantly changed since z~1, even though these galaxies host the majority of the star formation: instead, the growth of the total stellar mass density is dominated by the growth of the total mass in the largely passive galaxies on the red sequence.
astro-ph/0604406 [abs, ps, pdf, other] :: Title: Chandra Observations of Nuclear Outflows in the Elliptical Galaxy NGC4552 in the Virgo Cluster
Authors: M. Machacek, P.E.J. Nulsen, C. Jones, W.R. Forman (CfA)
Comments: second part (sec. 4) of astroph/0508588v1 with expanded intro and discussion; 16 pages, 8 figs., ApJ, submitted

We use a 54.4 ks Chandra observation to study nuclear outflow activity in NGC4552 (M89), an elliptical galaxy in the Virgo Cluster. Chandra images in the 0.5-2 keV band show two ring-like features ~1.7 kpc in diameter in the core of NGC4552, as reported previously by Filho et al. We use spherically symmetric point explosion shock models to argue that the shape of the surface brightness profile across the rims of the rings and the temperature of hot gas in the rings are consistent with a Mach 1.7 shock carrying mean mechanical power L_shock ~ 3 x 10^{41} ergs/s produced by a ~1.4 x 10^{55} ergs nuclear outburst \~1 - 2 Myr ago. We find the gas temperature in the central ~100 pc of the galaxy to be 1.0 +/- 0.2 keV, hotter than elsewhere in the galaxy, suggesting that we may be observing directly the reheating of the galaxy ISM by the outburst.
astro-ph/0604407 [abs, ps, pdf, other] :: Title: Eight billion years of disk galaxy evolution: no galaxy is an island
Authors: Eric F. Bell, Marco Barden, Xianzhong Zheng, Casey Papovich, Emeric Le Floc'h, George Rieke, Christian Wolf, the GEMS, MIPS Instrument, COMBO-17 teams
Comments: 6 pages, To appear in the proceedings of the "Island Universes: Structure and Evolution of Disk Galaxies" conference held in Terschelling, Netherlands, July 2005, ed. R. de Jong (Springer: Dordrecht)

We present a brief discussion of the evolution of disk galaxy stellar masses, sizes, rotation velocities, and star formation rates over the last eight billion years. Recent observations have failed to detect significant evolution in the stellar mass Tully-Fisher relation, stellar mass-size relation, and the stellar mass function of disk galaxies. Yet, most z<1 star formation is in disks, and this star formation would be expected to drive a rapid growth of the total stellar mass (and therefore mass function) of disks in the last eight billion years. Such a build-up is not seen; instead, a rapid build-up in the total stellar mass in non-star-forming spheroid-dominated galaxies is observed. Large numbers of disk-dominated galaxies are systematically shutting off their star formation and building up a spheroid (or losing a disk) in the epoch 0<z<1.
astro-ph/0604408 [abs, ps, pdf, other] :: Title: An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
Authors: W. Van Dyke Dixon (1), Ravi Sankrit (1), Birgit Otte (2) ((1) Johns Hopkins University, (2) University of Michigan)
Comments: 27 pages, 16 figures, accepted by ApJ

We present a survey of diffuse O VI emission in the interstellar medium obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Spanning 5.5 years of FUSE observations, from launch through 2004 December, our data set consists of 2925 exposures along 183 sight lines, including all of those with previously-published O VI detections. The data were processed using an implementation of CalFUSE v3.1 modified to optimize the signal-to-noise ratio and velocity scale of spectra from an aperture-filling source. Of our 183 sight lines, 73 show O VI 1032 emission, 29 at > 3-sigma significance. Six of the 3-sigma features have velocities |v_LSR| > 120 km/s, while the others have |v_LSR| < 50 km/s. Measured intensities range from 1800 to 9100 LU, with a median of 3300 LU. Combining our results with published O VI absorption data, we find that an O VI-bearing interface in the local ISM yields an electron density n_e = 0.2--0.3 cm^-3^ and a path length of 0.1 pc, while O VI-emitting regions associated with high-velocity clouds in the Galactic halo have densities an order of magnitude lower and path lengths two orders of magnitude longer. Though the O VI intensities along these sight lines are similar, the emission is produced by gas with very different properties.
astro-ph/0604409 [abs, ps, pdf, other] :: Title: Confronting quintessence models with recent high-redshift supernovae data
Authors: G. Barro Calvo, A. L. Maroto
Comments: 8 pages, 12 figures

We confront the predictions of different quintessence models with recent measurements of the luminosity distance from two sets of supernovae type Ia. In particular, we consider the 157 SNe Ia in the Gold dataset with z<1.7, and the more recent data containing 71 supernovae obtained by the Supernova Legacy Survey (SNLS) with z<1. We numerically solve the evolution equations for the Ratra-Peebles inverse power law model, the double exponential and the hyperbolic cosine quintessence models. We obtain confidence regions from the two datasets in the \Omega_M-\alpha and \Omega_M-w_\phi planes for the different models and compare their predictions with dark energy models with constant equation of state.
astro-ph/0604410 [abs, ps, pdf, other] :: Title: Occam's razor meets WMAP
Authors: Joao Magueijo, Rafael D. Sorkin

Using a variety of quantitative implementations of Occam's razor we examine the low quadrupole, the ``axis of evil'' effect and other detections recently made appealing to the excellent WMAP data. We find that some razors {\it fully} demolish the much lauded claims for departures from scale-invariance. They all reduce to pathetic levels the evidence for a low quadrupole (or any other low $\ell$ cut-off), both in the first and third year WMAP releases. The ``axis of evil'' effect is the only anomaly examined here that survives the humiliations of Occam's razor, and even then in the category of ``strong'' rather than ``decisive'' evidence. Statistical considerations aside, differences between the various renditions of the datasets remain worrying.
astro-ph/0604411 [abs, ps, pdf, other] :: Title: Precision Measurement of Optical Pulsation using a Cherenkov Telescope
Authors: J. A. Hinton, G. Hermann, P. Kroetz, S. Funk
Comments: Accepted for publication in Astroparticle Physics, 14 pages, 7 figures

During 2003, a camera designed to measure the optical pulsations of pulsars was installed on a telescope of the H.E.S.S. array. The array is designed for gamma-ray astronomy in the ~100 GeV - 100 TeV energy regime. The aims of this exercise were two-fold: to prove the pulsar timing capabilities of H.E.S.S. on all relevant time-scales, and to explore the possibility of performing sensitive optical pulsar measurements using the ~100 m^2 mirror of a Cherenkov telescope. Measurements of the Crab pulsar with this instrument demonstrate an order of magnitude sensitivity improvement over previous attempts using Cherenkov telescopes. Here we describe the design and performance of the system and discuss design considerations for future instruments of this type.
astro-ph/0604412 [abs, pdf] :: Title: The Carbon-Rich Gas in the Beta Pictoris Circumstellar Disk
Authors: Aki Roberge, Paul D. Feldman, Alycia J. Weinberger, Magali Deleuil, Jean-Claude Bouret
Comments: Accepted for publication in Nature. The paper is under press embargo until publication. PDF document, 12 pages. Supplementary information may be found at this http URL

The edge-on disk surrounding the nearby young star Beta Pictoris is the archetype of the "debris disks", which are composed of dust and gas produced by collisions and evaporation of planetesimals, analogues of Solar System comets and asteroids. These disks provide a window on the formation and early evolution of terrestrial planets. Previous observations of Beta Pic concluded that the disk gas has roughly solar abundances of elements [1], but this poses a problem because such gas should be rapidly blown away from the star, contrary to observations of a stable gas disk in Keplerian rotation [1, 2]. Here we report the detection of singly and doubly ionized carbon (CII, CIII) and neutral atomic oxygen (OI) gas in the Beta Pic disk; measurement of these abundant volatile species permits a much more complete gas inventory. Carbon is extremely overabundant relative to every other measured element. This appears to solve the problem of the stable gas disk, since the carbon overabundance should keep the gas disk in Keplerian rotation [3]. New questions arise, however, since the overabundance may indicate the gas is produced from material more carbon-rich than the expected Solar System analogues.
astro-ph/0604413 [abs, ps, pdf, other] :: Title: The potential for tidally heated icy and temperate moons around exoplanets
Authors: Caleb A. Scharf
Comments: 28 pages, 8 Figures, AASTex, Accepted for publication in the Astrophysical Journal

Moons of giant planets may represent an alternative to the classical picture of habitable worlds. They may exist within the circumstellar habitable zone of a parent star, and through tidal energy dissipation they may also offer alternative habitable zones, where stellar insolation plays a secondary, or complementary, role. We investigate the potential extent of stable satellite orbits around a set of 74 known extrasolar giant planets located beyond 0.6 AU from their parent stars - where moons should be long-lived with respect to removal by stellar tides. Approximately 60\% of these giant planets can sustain satellites or moons in bands up to $\sim 0.04$ AU in width. For comparison, the Galiean satellites extend to $\sim 0.013$ AU. We investigate the stellar insolation that moons would experience for these exoplanet systems, and the implications for sublimation loss of volatiles. We find that between 15 and 27\% of {\em all} known exoplanets may be capable of harboring small, icy, moons. In addition, some 22-28\% of all known exoplanets could harbor moons within a ``sublimation zone'', with insolation temperatures between 273 K and 170 K. A simplified energy balance model is applied to the situation of temperate moons, maintained by a combination of stellar insolation and tidal heat flow. We demonstrate that large moons ($>0.1 $M$_{\oplus}$), at orbital radii commensurate with those of the Galilean satellites, could maintain temperate, or habitable, surface conditions during episodes of tidal heat dissipation of the order 1-100 times that currently seen on Io. (Abridged).

Astrophysics authors/titles "new"

Astrophysics

astro-ph new abstracts, Fri, 21 Apr 06 00:00:09 GMT
0604414 -- 0604440 received

astro-ph/0604414 [abs, ps, pdf, other] :: Title: Substructure in lensing clusters and simulations
Authors: Priyamvada Natarajan (Yale), Gabriella De Lucia (MPA), Volker Springel (MPA)
Comments: 16 pages, 9 figures, submitted to MNRAS

We present high-resolution mass reconstructions for five massive cluster-lenses spanning a redshift range from $z = 0.18$--0.57 utilising archival {\it Hubble Space Telescope} ({\it HST}) data and applying galaxy-galaxy lensing techniques. These detailed mass models were obtained from the observations by combining constraints from the strong and weak lensing regimes. We ascribe local weak distortions in the shear maps to perturbations induced by the presence of galaxy haloes around individual bright early-type cluster member galaxies. This technique constrains the mass enclosed within an aperture for these subhaloes. We are sensitive to a specific mass range for these subhaloes, $10^{11}$ -- $10^{12.5} \msun$, which we associate with galaxy-scale subhaloes. Adopting a parametric model for the subhaloes, we also derive their velocity dispersion function and the aperture radius function. The mass spectrum of substructure in the inner regions of the observed clusters is directly compared with that in simulated clusters extracted from the {\it Millennium Simulation}. The massfunction, aperture radii and velocity dispersion function are compared in detail. Overall, we find good agreement between the distribution of substructure properties retrieved using the lensing analysis and those obtained from the simulation (truncated abstract).
astro-ph/0604415 [abs, ps, pdf, other] :: Title: The O VI Absorbers Toward PG0953+415: High Metallicity, Cosmic-Web Gas Far From Luminous Galaxies
Authors: Todd M. Tripp (1), Bastien Aracil (1), David V. Bowen (2), Edward B. Jenkins (2) ((1) Univ. Massachusetts, (2) Princeton Univ.)
Comments: Submitted for publication in the Astrophysical Journal Letters. Figs. 1 and 2 compressed for astro-ph. High-resolution version available at this http URL

The spectrum of the low-redshift QSO PG0953+415 shows two strong, intervening O VI absorption systems. To study the nature of these absorbers, we have used the Gemini Multiobject Spectrograph to conduct a deep spectroscopic galaxy redshift survey in the 5' x 5' field centered on the QSO. This survey is fully complete for r' < 19.7 and is 73% complete for r' < 21.0. We find three galaxies at the redshift of the higher-z O VI system (z = 0.14232) including a galaxy at projected distance rho = 155 kpc. We find no galaxies in the Gemini field at the redshift of the lower-z O VI absorber (z = 0.06807), which indicates that the nearest galaxy is more than 195 kpc away or has L < 0.04 L*. Previous shallower surveys covering a larger field have shown that the z = 0.06807 O VI absorber is affiliated with a group/filament of galaxies, but the nearest known galaxy has rho = 736 kpc. The z = 0.06807 absorber is notable for several reasons. The absorption profiles reveal simple kinematics indicative of quiescent material. The H I line widths and good alignment of the H I and metal lines favor photoionization and, moreover, the column density ratios imply a high metallicity: [M/H] = -0.3 +/- 0.12. The z = 0.14232 O VI system is more complex and less constrained but also indicates a relatively high metallicity. Using galaxy redshifts from SDSS, we show that both of the PG0953+415 O VI absorbers are located in large-scale filaments of the cosmic web. Evidently, some regions of the web filaments are highly metal enriched. We discuss the origin of the high-metallicity gas and suggest that the enrichment might have occurred long ago (at high z).
astro-ph/0604416 [abs, ps, pdf, other] :: Title: CMB Anisotropies at Second Order I
Authors: N. Bartolo (ICTP, Trieste), S. Matarrese (Univ. of Padova), A. Riotto (CERN)
Comments: 26 pages, LaTeX file

We present the computation of the full system of Boltzmann equations at second-order describing the evolution of the photon, baryon and cold dark matter fluids. These equations allow to follow the time evolution of the Cosmic Microwave Background (CMB) anisotropies at second-order at all angular scales from the early epoch, when the cosmological perturbations were generated, to the present through the recombination era. This paper sets the stage for the computation of the full second-order radiation transfer function at all scales and for a a generic set of initial conditions specifying the level of primordial non-Gaussianity. In a companion paper, we will present the computation of the three-point correlation function at recombination which is so relevant for the issue of non-Gaussianity in the CMB anisotropies.
astro-ph/0604417 [abs, ps, pdf, other] :: Title: Proposing a Experimental Astronomical Test to the Existence of the Quantum Strings
Authors: Paulo da Costa Moreira
Comments: 12 pages, no figures, LATEX of PCTEX 3.2

It is proposed a model of Kaluza Klein that does make the quantification of the electric charges without magnetic monopoles. This model of Kaluza Klein allows to calculate de radius of compactation proposed for Klein. The model is of Kaluza Klein, but it has consequences in the theory of the quantum strings, and it is possible to indicate a manner of to test the existence of the quantum strings.The model indicates that: if the quantum strings exist really, the cosmological variation of the fine structure constant would do quantum jumps. If this variation is continuous, the quantum strings does not exist.It is possible to the astronomers to decide this.
astro-ph/0604418 [abs, ps, pdf, other] :: Title: On Universal Halos and the Radial Orbit Instability
Authors: Joseph D. MacMillan, Lawrence M. Widrow, Richard N. Henriksen
Comments: 31 pages, 11 figures, submitted to the Astrophysical Journal

The radial orbit instability drives dark matter halos toward a universal structure. This conclusion, first noted by Huss, Jain, and Steinmetz, is explored in detail through a series of numerical experiments involving the collapse of an isolated halo into the non-linear regime. The role played by the radial orbit instability in generating the density profile, shape, and orbit structure is carefully analyzed and, in all cases, the instability leads to universality independent of initial conditions. New insights into the underlying physics of the radial orbit instability are presented.
astro-ph/0604419 [abs, ps, pdf, other] :: Title: A Hot DQ White Dwarf in the Open Star Cluster M35
Authors: Kurtis A. Williams (1), James Liebert (1), Michael Bolte (2), Robert B. Hanson (2) ((1) Steward Observatory, (2) UCO/Lick Observatory)
Comments: 9 pages with 2 figures, uses LaTeX/AASTeX 5.2. Accepted for publications in ApJ Letters

We report the discovery of a hot DQ white dwarf, NGC 2168:LAWDS 28, that is a likely member of the 150-Myr old cluster NGC 2168 (Messier 35). The spectrum of the white dwarf is dominated by CII features. The effective temperature is difficult to estimate but likely > 20,000 K based on the temperatures of hot DQs with similar spectra. NGC2168:LAWDS 28 provides further evidence that hot DQs may be the ``missing'' high-mass helium-atmosphere white dwarfs. Based on published studies, we find that the DBA WD LP 475-242 is likely a member of the Hyades open cluster, as often assumed. These two white dwarfs are the entire sample of known He-atmosphere white dwarfs in open clusters with turnoff masses >2 solar masses. Based on the number of known cluster DA white dwarfs and a redetermination of the H-atmosphere:He-atmosphere ratio, commonly known as the DA:DB ratio, we re-examine the hypothesis that the H- to He-atmosphere ratio in open clusters is the same as the ratio in the field. Under this hypothesis, we calculate that five He-atmosphere WDs are expected to have been discovered, with a probability of finding fewer than three He-atmosphere white dwarfs of 0.08, or at the ~ 2-sigma level.
astro-ph/0604420 [abs, ps, pdf, other] :: Title: Vegetation signature in the observed globally-integrated spectrum of Earth: Modeling the red edge strength using simultaneous cloud data and application for extrasolar planets
Authors: Pilar Montanes-Rodriguez, E. Palle, P.R. Goode
Comments: 13 pages, 9 figures, submitted to ApJ

The vegetation's ``red edge'', an intensity bump in the Earth's spectrum near 700 $nm$ when sunlight is reflected from greenery, is often suggested as a tool in the search for life in terrestrial-like extrasolar planets. Here, through ground-based observations of the Earth's spectrum, satellite observations of clouds, and an advanced atmospheric radiative transfer code, we determine the temporal evolution of the vegetation signature of Earth. The excellent agreement between models and observations motivated us to probe more deeply into the red edge detectability using real cloud observations at longer time scales. Overall, we find the evolution of the red edge signal in the globally-averaged spectra to be weak, and only attributable to vegetation changes when the real land and cloud distributions for the day are known. However, it becomes prominent under certain Sun-Earth-Moon orbital geometries, which are applicable to the search for life in extrasolar planets. Our results indicate that vegetation detection in Earth-like planets will require a considerable level of instrumental precision and will be a difficult task, but not as difficult as the normally weak earthshine signal might seem to suggest.
astro-ph/0604421 [abs, ps, pdf, other] :: Title: Discovery of 14 radio pulsars in a survey of the Magellanic Clouds
Authors: R N Manchester, G Fan, A G Lyne, V M Kaspi
Comments: In press, ApJ

A systematic survey of the Large and Small Magellanic Clouds for radio pulsars using the Parkes radio telescope and the 20-cm multibeam receiver has resulted in the discovery of 14 pulsars and the redetection of five of the eight previously known spin-powered pulsars believed to lie in the Magellanic Clouds. Of the 14 new discoveries, 12 are believed to lie within Clouds, three in the Small Cloud and nine in the Large Cloud, bringing the total number of known spin-powered pulsars in the Clouds to 20. Averaged over all positions within the survey area, the survey had a limiting flux density of about 0.12 mJy. Observed dispersion measures suggest that the mean free electron density in the Magellanic Clouds is similar to that in the disk of our Galaxy. The observed radio luminosities have little or no dependence on pulsar period or characteristic age and the differential luminosity function is consistent with a power-law slope of -1 as is observed for Galactic pulsars.
astro-ph/0604422 [abs, ps, pdf, other] :: Title: Strangeness in Neutron Stars
Authors: Fridolin Weber, Alexander Ho, Rodrigo P. Negreiros, Philip Rosenfield (San Diego State University)
Comments: 16 pages, 5 figures, 3 tables; Accepted for publication in the Proceedings of the International Workshop on Astronomy and Relativistic Astrophysics (IWARA) 2005, Int. J. Mod. Phys. D

It is generally agreed on that the tremendous densities reached in the centers of neutron stars provide a high-pressure environment in which several intriguing particles processes may compete with each other. These range from the generation of hyperons to quark deconfinement to the formation of kaon condensates and H-matter. There are theoretical suggestions of even more exotic processes inside neutron stars, such as the formation of absolutely stable strange quark matter. In the latter event, neutron stars would be largely composed of strange quark matter possibly enveloped in a thin nuclear crust. This paper gives a brief overview of these striking physical possibilities with an emphasis on the role played by strangeness in neutron star matter, which constitutes compressed baryonic matter at ultra-high baryon number density but low temperature which is no accessible to relativistic heavy ion collision experiments.
astro-ph/0604423 [abs, ps, pdf, other] :: Title: Secondary Star Formation in a Population III Object
Authors: Hajime Susa, Masayuki Umemura
Comments: 4pages, 2 figures, submitted to ApJ

We explore the possibility of subsequent star formation after a first star forms in a Pop III object, by focusing on the radiation hydrodynamic (RHD) feedback brought by ionizing photons as well as H2 dissociating photons. For the purpose, we perform three-dimensional RHD simulations, where the radiative transfer of ionizing photons and H2 dissociating photons from a first star is self-consistently coupled with hydrodynamics based on a smoothed particle hydrodynamics method. As a result, it is shown that density peaks above a threshold density can keep collapsing owing to the shielding of H2 dissociating radiation by an H2 shell formed ahead of a D-type ionization front. But, below the threshold density, an M-type ionization front accompanied by a shock propagates, and density peaks are radiation hydrodynamically evaporated by the shock. The threshold density is dependent on the distance from a source star, which is $\approx 10^2 cm^{-3}$ for the source distance of 30pc. Taking into consideration that the extent of a Pop III object is $\approx 100$pc and density peaks within it have the density of $10^{2-4}$cm$^{-3}$, it is concluded that the secondary star formation is allowed in the broad regions in a Pop III object.
astro-ph/0604424 [abs, ps, pdf, other] :: Title: Magnetic Jets from Swirling Disks
Authors: D. Lynden-Bell
Comments: 23 pages, 7 figures. To be published in MNRAS

A broad swathe of astrophysical phenomena, ranging from tubular planetary nebulae through Herbig-Haro objects, radio-galaxy and quasar emissions to gamma-ray bursts and perhaps high-energy cosmic rays, may be driven by magnetically-dominated jets emanating from accretion disks. We give a self-contained account of the analytic theory of non-relativistic magnetically dominated jets wound up by a swirling disk and making a magnetic cavity in a background medium of any prescribed pressure, p(z). We solve the time-dependent problem for any specified distribution of magnetic flux P(R,0) emerging from the disk at z=0, with any specified disk angular velocity Omega_d(R). The physics required to do this involves only the freezing of the lines of force to the conducting medium and the principle of minimum energy.
astro-ph/0604425 [abs, ps, pdf, other] :: Title: GRB 990413: Insight into the thermal phase evolution
Authors: Z. Bosnjak (1,2), A. Celotti (1), G. Ghirlanda (2) ((1) S.I.S.S.A, Trieste, (2)INAF-Osservatorio Astronomico di Brera)
Comments: 6 pages, 5 figures, 2 tables. Accepted for publication in MNRAS Letter

GRB 990413 shows a very hard spectrum (with a low energy spectral component F(E) \propto E^{2.49}) which is well represented by a black body model with characteristic temperature ~70 keV. It thus belongs to the subset of GRBs which might be revealing a thermal phase. We find that the temperature/luminosity evolution is consistent with that found in the other ``thermal'' GRBs. The time resolved spectral analysis indicates the presence of a second non--thermal component contributing (for about 1 s) up to 30 per cent of the total flux. Differently from the other thermal GRBs, GRB 990413 shows significantly high level of variability and the evolution of the thermal/non--thermal spectral components is strongly correlated with the flux variations. This GRB thus offers the unique opportunity to test the standard fireball photospheric and internal shock phases and their reciprocal influence. GRB 990413 was not selected on the basis of its spectrum and thus hints to the possibility that this early behavior might be more common than currently known.
astro-ph/0604426 [abs, ps, pdf, other] :: Title: The UKIRT Infrared Deep Sky Survey (UKIDSS)
Authors: A. Lawrence, S. J. Warren, O. Almaini, A. C. Edge, N. C. Hambly, R. F. Jameson, P. Lucas, M. Casali, A. Adamson, S. Dye, J. P. Emerson, S. Foucaud, P. Hewett, P. Hirst, S. T. Hodgkin, M. J. Irwin, N. Lodieu, R. G. McMahon, C. Simpson, I. Smail, D. Mortlock, M. Folger
Comments: Seventeen pages, three tables, thirteen figures. Submitted to MNRAS April 7th 2006

We describe the goals, design, and implementation of the UKIRT Infrared Deep Sky Survey (UKIDSS), a seven year sky survey which began in May 2005. It is a portfolio of five survey components covering various combinations of the filter set ZYJHK and H_2. The Large Area Survey, the Galactic Cluster Survey, and the Galactic Plane Survey cover approximately 7000 square degrees to a depth of K~18; the Deep Extragalactic Survey covers 35 square degrees to K~21, and the Ultra Deep Survey covers 0.77 square degrees to K~23. The prime aim of UKIDSS is to provide a long term astronomical legacy database; the design is however driven by a series of specific goals -- for example to find the nearest and faintest sub-stellar objects; to break the z=7 quasar barrier; to determine the epoch of re-ionisation; to determine the substellar mass function; to discover Population II brown dwarfs, if they exist; to measure the growth of structure from z=3 to the present day; to determine the epoch of spheroid formation; and to map the Milky Way through the dust, to several kpc. The data are being made available in a series of staged releases, the first of which (the "Early Data Release (EDR)") is described in Dye et al (2006). The data are immediately public to astronomers in all ESO member states, and available to the world after eighteen months. Before the formal survey began, UKIRT and the UKIDSS consortium collaborated in obtaining and analysing a series of small science verification (SV) projects to complete the commissioning of the camera. We show some results from these SV projects in order to demonstrate the likely power of the eventual complete survey.
astro-ph/0604427 [abs, ps, pdf, other] :: Title: Modelling the Galactic Interstellar Extinction Distribution in Three Dimensions
Authors: D.J. Marshall, A.C. Robin, C. Reyle, M. Schultheis, S. Picaud
Comments: 20 pages, 15 figures, accepted for publication in A&A. Online data will shortly be available at the CDS

The Two Micron All Sky Survey, along with the Stellar Population Synthesis Model of the Galaxy, developed in Besancon, is used to calculate the extinction distribution along different lines of sight. By combining many lines of sight, the large scale distribution of interstellar material can be deduced. The Galaxy model is used to provide the intrinsic colour of stars and their probable distances, so that the near infrared colour excess, and hence the extinction, may be calculated and its distance evaluated. Such a technique is dependent on the model used, however we are able to show that moderate changes in the model parameters result in insignificant changes in the predicted extinction. This technique has now been applied to over 64000 lines of sight, each separated by 15 arcmin, in the inner Galaxy (|l|<=100 deg, |b|<=10 deg). Using our extinction map, we have derived the main characteristics of the large scale structure of the dust distribution: scale height and warp of the ISM disc as well as the angle of the dust in the Galactic Bar. This resulting extinction map will be useful for studies of the inner Galaxy and its stellar populations.
astro-ph/0604428 [abs, ps, pdf, other] :: Title: Hamilton's Eccentricity Vector Generalised to Newton Wonders
Authors: D. Lynden-Bell
Comments: 8 pages, no figures. To be published in Observatory

The vectorial velocity is given as a function of the position of a particle in orbit when a Newtonian central force is supplemented by an inverse cubic force as in Newton's theorem on revolving orbits. Such expressions are useful in fitting orbits to radial velocities of orbital streams. The Hamilton-Laplace-Runge-Lenz eccentricity vector is generalised to give a constant of the motion for these systems and an approximate constant for orbits in general central potentials. A related vector is found for Hooke's centred ellipse.
astro-ph/0604429 [abs, ps, pdf, other] :: Title: Parametric modelling of the 3.6um to 8um colour distributions of galaxies in the SWIRE Survey
Authors: Payam Davoodi, Seb Oliver, Maria del Carmen Polletta, Michael Rowan-Robinson, Richard S. Savage, Ian Waddington, Duncan Farrah, Tom Babbedge, Carol Lonsdale, Tracey Evans, Fan Fang, Eduardo Gonzalez-Solares, Tom Jarrett, David L. Shupe, Brian Siana, Harding E. Smith, Jason Surace, C. Kevin Xu
Comments: 44 pages, 10 figures, 6 tables. Accepted for publication in the Astronomical Journal

We fit a parametric model comprising a mixture of multi-dimensional Gaussian functions to the 3.6 to 8um colour and optical photo-z distribution of galaxy populations in the ELAIS-N1 and Lockman Fields of SWIRE. For 16,698 sources in ELAIS-N1 we find our data are best modelled (in the sense of the Bayesian Information Criterion) by the sum of four Gaussian distributions or modes (C_a, C_b, C_c and C_d). We compare the fit of our empirical model with predictions from existing semi-analytic and phenomological models. We infer that our empirical model provides a better description of the mid-infrared colour distribution of the SWIRE survey than these existing models. This colour distribution test is thus a powerful model discriminator and complementary to comparisons of number counts. We use our model to provide a galaxy classification scheme and explore the nature of the galaxies in the different modes of the model. C_a consists of dusty star-forming systems such as ULIRG's. Low redshift late-type spirals are found in C_b, where PAH emission dominates at 8um. C_c consists of dusty starburst systems at intermediate redshifts. Low redshift early-type spirals and ellipticals dominate C_d. We thus find a greater variety of galaxy types than one can with optical photometry alone. Finally we develop a new technique to identify unusual objects, and find a selection of outliers with very red IRAC colours. These objects are not detected in the optical, but have very strong detections in the mid-infrared. These sources are modelled as dust-enshrouded, strongly obscured AGN, where the high mid-infrared emission may either be attributed to dust heated by the AGN or substantial star-formation. These sources have z_ph ~ 2-4, making them incredibly infrared luminous, with a L_IR ~ 10^(12.6-14.1) L_sun.
astro-ph/0604430 [abs, ps, pdf, other] :: Title: Neutrino Astronomy and Cosmic Rays Spectroscopy at Horizons
Authors: D.Fargion
Comments: 24 pages, 24 figures, Conference NO-VE, Venice, 09-02-2006

A new air-showering physics may rise in next years at horizon, offering at different angles and altitudes a fine tuned filtered Cosmic Rays astrophysics and an upward Neutrino induced air-showering astronomy. Most of this opportunity arises because of neutrino masses, their mixing and the consequent replenishment of rarest tau flavor during its flight in Space. Horizontal air atmosphere act as a filter for High energy Cosmic Rays (CR) and as a beam dump for Ultra High Energy (UHE) neutrinos and a powerfull amplifier for its tau decay in air by its wide showering areas. Earth sharp shadows plays the role of a huge detector volume for UHE neutrino and a noise-free screen for upcoming EeVs tau air-showers (as well PeVs anti-neutrino electron air interactions). Projects for Tau Airshowers are growing at the top of a mountains or at the edge of a cliff. ASHRA in Hawaii and CRNTN in Utah are tracking fluorescence lights, while other novel projects on Crown array detectors on mountains, on balloons and satellites are elaborated for Cherenkov lights. AUGER, facing the Ande edges, ARGO located within a deep valley are testing inclined showers; MILAGRO (and MILAGRITO) may be triggered by horizontal up-going muon bundles from the Earth edges; HIRES and AUGER UHECR detectors, linking twin array telescopes along their axis may test horizontal Cerenkov blazing photons. MAGIC (Hess, Veritas) and Shalon Telescopes may act already like a detector for few PeVs and Glashow resonance neutrino events; MAGIC pointing downward to terrestrial ground acts as a massive tens of km^3 detector, making it the most sensitive dedicated neutrino telescope. MAGIC facing the sea edges must reveal mirrored downward UHECR Air-showers Cherenkov flashes. Magic-crown systems may lead to tens km^3, neutrino detectors.
astro-ph/0604431 [abs, ps, pdf, other] :: Title: Cosmological viability of f(R)-gravity as an ideal fluid and its compatibility with a matter dominated phase
Authors: S. Capozziello, S. Nojiri, S.D. Odintsov, A. Troisi
Comments: 9 pages, 1 figure

We show that f(R)-gravity can, in general, give rise to cosmological viable models compatible with a matter-dominated epoch evolving into a late accelerated phase. We discuss the various representations of f(R)-gravity as an ideal fluid or a scalar-tensor gravity theory, taking into account conformal transformations. We point out that mathematical equivalence does not correspond, in several cases, to the physical equivalence of Jordan frame and Einstein frame. Finally, we show that wide classes of f(R)-gravity models, including matter and accelerated phases, can be phenomenologically reconstructed by means of observational data. In principle, any popular quintessence models could be "reframed" as an f(R)-gravity model.
astro-ph/0604432 [abs, ps, pdf, other] :: Title: The Environments around Long-Duration Gamma-Ray Burst Progenitors
Authors: Chris L. Fryer, Gabriel Rockefeller, Patrick A. Young
Comments: 44 pages including 11 figures

Gamma-ray burst (GRB) afterglow observations have allowed us to significantly constrain the engines producing these energetic explosions. Te redshift and position information provided by these afterglows have already allowed us to limit the progenitors of GRBs to only a few models. The afterglows may also provide another observation that can place further constraints on the GRB progenitor: measurements telling us about the environments surrounding GRBs. Current analyses of GRB afterglows suggest that roughly half of long-duration gamma-ray bursts occur in surroundings with density profiles that are uniform. We study the constraints placed by this observation on both the classic ``collapsar'' massive star progenitor and its relative, the ``helium-merger'' progenitor. We study several aspects of wind mass-loss and find that our modifications to the standard Wolf-Rayet mass-loss paradigm are not sufficient to produce constant density profiles. Although this does not rule out the standard ``collapsar'' progenitor, it does suggest a deficiency with this model. We then focus on the He-merger models and find that such progenitors can fit this particular constraint well. We show how detailed observations can not only determine the correct progenitor for GRBs, but also allow us to study binary evolution physics.
astro-ph/0604433 [abs, ps, pdf, other] :: Title: GRB030406 an extremely hard burst outside of the INTEGRAL field of view
Authors: R. Marcinkowski, M. Denis, T. Bulik, P. Goldoni, Ph. Laurent, A. Rau
Comments: Astronomy and Astrophysics in press

Using the IBIS Compton mode, the INTEGRAL satellite is able to detect and localize bright and hard GRBs, which happen outside of the nominal INTEGRAL telescopes field of view. We have developed a method of analyzing such INTEGRAL data to obtain the burst location and spectra. We present the results for the case of GRB030406. The burst is localized with the Compton events, and the location is consistent with the previous Interplanetary Network position. A spectral analysis is possible with the detailed modeling of the detector response for such a far off-axis source with the offset of 36.9 $^\circ$. The average spectrum of the burst is extremely hard: the photon index above 400 \kev is -1.7, with no evidence of a break up to 1.1 \mev at 90% confidence level.
astro-ph/0604434 [abs, ps, pdf, other] :: Title: The origin and fate of short-period low-mass black-hole binaries
Authors: L. R. Yungelson, J.-P. Lasota, G. Nelemans, G. Dubus, E. P. J. van den Heuvel, J. Dewi, S. Portegies Zwart
Comments: 13 pages, 6 figures, accepted for publication in A&A

We present results of a population synthesis study for semidetached short orbital period binaries which contain low-mass(<1.5 Msun) donors and black hole (>4 Msun) accretors. Evolution of these binaries is determined by nuclear evolution of the donors and/or orbital angular momentum loss due to magnetic braking by the stellar wind of the donors and gravitational wave radiation. According to our model, the estimated total number of this type of black-hole binaries in the Galaxy is about 10000. If the magnetic braking is described by the Verbunt & Zwaan formula, the model predicts around 3000 transient systems with periods >2 hours and around 300 luminous stable systems with periods between 3 and 8 hours. Several dozens of these bright systems should be above the RXTE ASM sensitivity limit. The absence of such systems implies that angular momentum losses are reduced by a factor more than 2 with respect to the Verbunt & Zwaan prescription. We show that it is unlikely that the transient behaviour of black-hole short-period X-ray binaries is explained by the evolved nature of the stellar companion. A substantial fraction of black-hole binaries with periods >3 hours could be faint with truncated, stable cold accretion discs as proposed by Menou et al. Most of the semidetached black-hole binaries are expected to have periods shorter than ~2 hours. Properties of such, still to be observed, very small mass-ratio (q<0.02) binaries are different from those of their longer period cousins.
astro-ph/0604435 [abs, ps, pdf, other] :: Title: Gravitational lensing in fourth order gravity
Authors: S. Capozziello, V.F. Cardone, A. Troisi
Comments: 10 pages, 3 figures, accepted for publication on Physical Review D

Gravitational lensing is investigated in the weak field limit of fourth order gravity in which the Lagrangian of the gravitational field is modified by replacing the Ricci scalar curvature R with an analytical expression $f(R)$. Considering the case of a pointlike lens, we study the behaviour of the deflection angle in the case of power law Lagrangians, i.e. with f(R) = f_0 R^n. In order to investigate possible detectable signatures, the position of the Einstein ring and the solutions of the lens equation are evaluated considering the change with respect to the standard case. Effects on the amplification of the images and the Paczynski curve in microlensing experiments are also estimated.
astro-ph/0604436 [abs, ps, pdf, other] :: Title: Measuring proton energies and fluxes using EIT (SOHO) CCD areas outside the solar disk images
Authors: L.V. Didkovsky, D.L. Judge, A.R. Jones, E.J. Rhodes, Jr., J.B. Gurman
Comments: 7 pages, 6 figures
Journal-ref: Astron. Nachr. / AN 327, No. 4, 314-320 (2006)

An indirect proton flux measuring tool based on discrimination of the energy deposited by protons in 128 x 128 pixel EIT CCD areas outside the solar disk images is presented. Single pixel intensity events are converted into proton incident energy flux using modeled energy deposition curves for angles of incidence 60 deg in four EIT spatial areas with different proton stopping power. The extracted proton flux is corrected for both the loss of one-pixel events in the range of angles of incidence as well as for the contribution to the single pixel events resulting from scattered middle-energy protons (low-energy or high-energy particles are stopped by the EIT components or pass through them, accordingly). A simple geometrical approach was found and applied to correct for a non-unique relation between the proton-associated CCD output signal and the incident proton energy. With this geometrical approximation four unique proton incident energy ranges were determined as 45--49, 145--154, 297--335, and 390--440 MeV. The indirect proton flux measuring tool has been tested by comparing Solar Energetic Particles (SEP) flux temporal profiles extracted from the EIT CCD frames and downloaded from the GOES database for the Bastille Day (BD) of 2000 July 14 and the more recent 2005 January 20 events. The SEP flux temporal profiles and proton spectra extracted from the EIT in the relatively narrow energy ranges between 45 and 440 MeV reported here are consistent with the related GOES profiles. The four additional EIT extracted ranges provide higher energy resolution of the SEP data.
astro-ph/0604437 [abs, ps, pdf, other] :: Title: High Energy Neutrino Flash from Far-UV/X-ray Flares of Gamma-Ray Bursts
Authors: Kohta Murase, Shigehiro Nagataki
Comments: 5 pages, 4 figures

The recent observations of bright optical and X-ray flares by the Swift satellite suggest these are produced by the late activities of the central engine. We study the neutrino emission from far-UV/X-ray flares under the late internal shock model. Since the efficiency of pion production in the highest energy is higher than that of the prompt bursts, such neutrino flashes from flares can give comparable or larger contributions to a diffuse very high energy neutrino background if the total energy input into flares is comparable to the radiated energy of the prompt bursts. These signals are very important because they have possibility to probe the nature of flares (baryonic or magnetic, the photon field, the magnetic field, and so on).
astro-ph/0604438 [abs, ps, pdf, other] :: Title: Nova V4743 Sagittarii 2002: An Intermediate Polar Candidate
Authors: Tae W. Kang, Alon Retter, Alex Liu, Mercedes Richards
Comments: 7 pages, 6 figures, AJ accepted

We present the results of 11 nights of CCD unfiltered photometry of V4743 Sgr (Nova Sgr 2002 # 3) from 2003 and 2005. We find two periods of 0.2799 d ~ 6.7 h and 0.01642 d ~ 24 min in the 2005 data. The long period is also present in the 2003 data, but only weak evidence of the shorter period is found in this year. The 24-min period is somewhat longer than the 22-min period, which was detected from X-ray observations. We suggest that the 6.7-h periodicity represents the orbital period of the underlying binary system and that the 24-min period is the beat periodicity between the orbital period and the X-ray period, which is presumably the spin period of the white dwarf. Thus, V4743 Sgr should be classified as an intermediate polar (DQ Her star). About six months after the nova outburst, the optical light curve of V4743 Sgr seemed to show quasi-periodic oscillations, which are typical of the transient phase in classical nova. Therefore, our results support the previous suggestion that the trans ition phase in novae may be related to intermediate polars.
astro-ph/0604439 [abs, ps, pdf, other] :: Title: Antimatter from Microscopic Black Holes
Authors: R. G. Daghigh, J. I. Kapusta
Comments: 7 pages, 3 figures

The spectrum of positrons and antiprotons produced by the outflow of high temperature matter surrounding microscopic black holes is calculated for energies between five GeV and the Planck energy. The results may be applicable for the last few hours and minutes of a microscopic black hole's lifetime.
astro-ph/0604440 [abs, pdf] :: Title: Comment on: Protecting Life in the Milky Way: Metals Keep the GRBs Away by Stanek et al
Authors: Adrian L. Melott (University of Kansas)

Stanek et al. (astro-ph/0604113) have noted that the four low-redshift long-duration gamma-ray bursts (LSB) observed to date all occurred in faint, metal-poor galaxies. Given this selection, they argue that it is improbable that there has been a substantial population of Milky Way galaxy bursts sufficiently recently to affect life on Earth. This argument ignores the heterogeneity of stellar populations in the Milky Way, with evidence for continuing mergers with low-metallicity dwarf galaxies; observational analysis that points to LSBs being hosted by such galaxies undergoing interaction; and the existence of a likely recent GRB remnant in our galaxy.

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0604336 -- 0604357 received

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0604358 -- 0604387 received

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0604388 -- 0604413 received

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0604414 -- 0604440 received