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Astrophysics

astro-ph new abstracts, Thu, 8 Jun 06 00:00:08 GMT
0606126 -- 0606168 received

astro-ph/0606126 [abs, ps, pdf, other] :

Title: Search for Diffuse Astrophysical Neutrino Flux Using Ultra-High Energy Upward-Going Muons in Super-Kamiokande I
Authors: The Super-Kamiokande Collaboration: M.E.C. Swanson, et al
Comments: 10 pages, 6 figures, submitted to ApJ

Many astrophysical models predict a diffuse flux of high energy neutrinos from active galactic nuclei and other extra-galactic sources. At muon energies above a TeV, the upward-going muon flux induced by neutrinos from active galactic nuclei is expected to exceed the flux due to atmospheric neutrinos. We have performed a search for this astrophysical neutrino flux by looking for upward-going muons in the highest energy data sample from the Super-Kamiokande detector using 1679.6 live days of data. We found 1 extremely high energy upward-going muon event, compared with an expected atmospheric neutrino background of 0.46 plus or minus 0.23 events. Using this result, we set an upper limit on the diffuse flux of upward-going muons due to neutrinos from astrophysical sources in the muon energy range 3.16-100 TeV.

 

astro-ph/0606127 [abs, ps, pdf, other] :

Title: Testing the Disk Regulation Paradigm with Spitzer Observations. I. Rotation Periods of Pre-main Sequence Stars in the IC 348 Cluster
Authors: Lucas Cieza, Nairn Baliber
Comments: 40 pages, 11 figures. Accepted for publication in ApJ

We present 74 new stellar rotation periods in the young cluster IC348. Stars estimated to be less massive than 0.25 Mo show a unimodal distribution with a peak at P ~1-2 d) and a tail of slower rotators, while stars estimated to be more massive than 0.2 Mo show a bimodal distribution with peaks at ~2 and ~8 d. We combine all published rotation periods in IC348 with Spitzer/IRAC photometry in order to test the disk-braking paradigm. We find no evidence that the tail of slow rotators in low-mass stars or the long period peak in high-mass stars are preferentially populated by objects with disks as might be expected based on the current disk-braking model. Also, we find no significant correlation between period and the magnitude of the IR-excess, regardless of the mass range considered. Our results do not support a strong correlation in this cluster between rotation period and the presence of a disk as predicted by disk-braking theory. Rather, they are consistent with the suggestion that the correlation between period and the amplitude of the (I-K) excess reported in the past is a secondary manifestation of the correlation between the amplitude of near-IR excess and mass. Finally, we find some indication that the disk fraction decreases significantly for stars with very short periods (P < 1.5 d). This is the only feature of our sample that could potentially be interpreted as evidence for disk braking. It has been proposed that the observational signatures of disk braking might be significantly masked by the intrinsic breadth of the initial period distribution. We argue that more rigorous modeling of angular momentum evolution and a quantitative analysis of the observational data are required before the disk-braking model can be regarded as inconsistent with observations.

 

astro-ph/0606128 [abs, pdf] :

Title: Discrete Self-Similarity Of RR Lyrae Stars II. Period Spectrum For A Very Large Sample
Authors: R. L. Oldershaw
Comments: 8 Pages, 1 Figure, 2 Tables, comments/criticism welcome

A recent paper demonstrated a considerable degree of self-similarity between RR Lyrae stars and their atomic scale analogues: excited helium atoms undergoing single-level transition between n = 7 and n = 10. Discrete self-similarity between these fractal analogues was indentified in terms of their masses, radii, oscillation periods, basic morphologies and kinematics. In this second paper on the subject, an extremely large and carefully analyzed sample of RR Lyrae oscillation periods provides further evidence for a unique match between the predicted set of discrete periods, based exclusively on the known helium spectrum and the discrete scaling equations of a fractal cosmological paradigm, and the observed period spectra of RR Lyrae stars.

 

astro-ph/0606129 [abs, ps, pdf, other] :

Title: Thermal Infrared Constraint to a Planetary Companion of Vega with the MMT Adaptive Optics System
Authors: Philip M. Hinz, A. N. Heinze, Suresh Sivanandam, Douglas L. Miller, Matthew A. Kenworthy, Guido Brusa, Melanie Freed, J.R.P. Angel
Comments: accepted to ApJ June 6, 2006

Vega may have a massive companion in a wide orbit, as evidenced by structure in its cold dust debris. We have tested this hypothesis by direct imaging with adaptive optics in the M band. The observations were made with a newly commissioned thermal infrared camera, Clio, on the 6.5 MMT AO system with low-background deformable secondary. The observations constrain a planet to be less than 7 M$_J$ at the approximate position angle expected from the dust structure and at a radius $>$ 20AU (2.5 arcsec) . This result is more stringent than similar previous near-infrared observations of Vega, that achieve limits of 20 and 10 M$_J$ at separations of 7 arcsec. The higher sensitivity is due both to the more favorable contrast of gas giant planets at M band and to the higher Strehl and more stable point spread function at longer wavelengths. Future L' or M band observations could provide a powerful approach for wide separation planet detection, especially for cooler, and thus older or less massive planets. The natural best targets are nearby stars where planets in the range of 5-15 M$_J$ and as old as several Gyr are expected to be detectable with this technique.

 

astro-ph/0606130 [abs, ps, pdf, other] :

Title: Revealing the Dark TeV Sky: The Atmospheric Cherenkov Imaging Technique for Very High Energy Gamma-ray Astronomy
Authors: Trevor C. Weekes
Comments: To be published in the Proceedings of the International Workshop on "Energy Budget in the High Energy Universe", Kashiwa, Japan, February 22-24, 2006

The Atmospheric Cherenkov Imaging Technique has opened up the gamma-ray spectrum from 100 GeV to 50 TeV to astrophysical exploration. The development of the technique (with emphasis on the early days) is described as are the basic principles underlying its application to gamma-ray astronomy. The current generation of arrays of telescopes, in particular, VERITAS is briefly described.

 

astro-ph/0606131 [abs, ps, pdf, other] :

Title: Clio: a 3-5 micron AO planet-finding camera
Authors: S. Sivanandam, P. M. Hinz, A. N. Heinze, M. Freed, A. H. Breuninger
Comments: 10 pages, 4 figures, SPIE Astronomical Telescopes and Instrumentation 2006 Conference Proceedings, in press

Clio is an adaptive-optics camera mounted on the 6.5 meter MMT optimized for diffraction-limited L' and M-band imaging over a ~15'' field. The instrument was designed from the ground up with a large well-depth, fast readout thermal infrared (~3-5 micron) 320 by 256 pixel InSb detector, cooled optics, and associated focal plane and pupil masks (with the option for a coronograph) to minimize the thermal background and maximize throughput. When coupled with the MMT's adaptive secondary AO (two warm reflections) system's low thermal background, this instrument is in a unique position to image nearby warm planets, which are the brightest in the L' and M-band atmospheric windows. We present the current status of this recently commissioned instrument that performed exceptionally during first light. Our instrument sensitivities are impressive and are sky background limited: for an hour of integration, we obtain an L'-band 5 sigma detection limit of of 17.0 magnitudes (Strehl ~80%) and an M-band limit of 14.5 (Strehl ~90%). Our M-band sensitivity is lower due to the increase in thermal sky background. These sensitivities translate to finding relatively young planets five times Jupiter mass at 10 pc within a few AU of a star. Presently, a large Clio survey of nearby stellar systems is underway including a search for planets around solar-type stars, M dwarfs, and white dwarfs. Even with a null result, we can place strong constraints on planet distribution models.

 

astro-ph/0606132 [abs, ps, pdf, other] :

Title: Massive-Star Supernovae as Major Dust Factories
Authors: Ben E. K. Sugerman, Barbara Ercolano, M. J. Barlow, A. G. G. M. Tielens, Geoffrey C. Clayton, Albert A. Zijlstra, Margaret Meixner, Angela Speck, Tim M. Gledhill, Nino Panagia, Martin Cohen, Karl D. Gordon, Martin Meyer, Joanna Fabbri, J. E. Bowey, Douglas L. Welch, Michael W. Regan, Robert C. Kennicutt, Jr
Comments: 11 pages, 1 figure. Accepted 2006 May 30 for publication in Science; Published in 2006 May 8 edition of ScienceExpress

We present late-time optical and mid-infrared observations of the Type-II supernova 2003gd in NGC 628. Mid-infrared excesses consistent with cooling dust in the ejecta are observed 499-678 days after outburst, and are accompanied by increasing optical extinction and growing asymmetries in the emission-line profiles. Radiative-transfer models show that up to 0.02 solar masses of dust has formed within the ejecta, beginning as early as 250 days after outburst. These observations show that dust formation in supernova ejecta can be efficient and that massive-star supernovae can be major dust producers throughout the history of the Universe.

 

astro-ph/0606133 [abs, ps, pdf, other] :

Title: A Lower Limit to the Scale of an Effective Theory of Gravitation
Authors: R. R. Caldwell, Daniel Grin
Comments: 4 pages, 1 figure

We consider a linearized, effective quantum theory of gravitation which is cut off at a low energy scale in order to accommodate the smallness of the cosmological constant. This theory predicts departures from the static Newtonian inverse-square force law on distances below ~0.05 mm. However, we show that such a cutoff also leads to changes in the long-range behavior of gravity, and is inconsistent with observed gravitational lenses.

 

astro-ph/0606134 [abs, ps, pdf, other] :

Title: Constraining the population of 6 < z < 10 star-forming galaxies with deep near-IR images of lensing clusters
Authors: Johan Richard (OMP, Caltech), Roser Pello (OMP), Daniel Schaerer (Obs Geneva, OMP), Jean-Francois Le Borgne (OMP), Jean-Paul Kneib (LAM, Caltech)
Comments: 35 pages, 19 figures; Accepted for publication in A&A; Full version with high resolution figures available at this http URL

(abridged) We present the first results of our deep survey of lensing clusters aimed at constraining the abundance of star-forming galaxies at z~6-10. Deep near-IR photometry of two lensing clusters (A1835 and AC114) was obtained with ISAAC/VLT. These images, combined with existing data in the optical bands, including HST images, were used to select very high redshift candidates at z>~6 among the optical-dropouts. We have identified 18(8) first and second-category optical dropouts in A1835 (AC114), detected in more than one filter up to H(Vega)~23.8 (AB~25.2,uncorrected for lensing). Among them, 8(5) exhibit homogeneous SEDs compatible with star-forming galaxies at z>~6, and 5(1) are more likely intermediate-redshift EROs based on luminosity considerations. We have also identified a number of fainter sources in these fields fulfilling our photometric selection and located around the critical lines. We use all these data to make a first attempt at constraining the density of star-forming galaxies present at 6<z<10 using lensing clusters. Taken at face value, it appears that the number of candidates found seems to be higher than the one achieved in blank fields with similar photometric depth in the near-IR. The luminosity function derived for z>6 candidates appears compatible with that of LBGs at z~3. The turnover observed by Bouwens et al. (2005) towards the bright end relative to the z~3 LF is not observed in this sample. Also the upper limit for the UV SFR density at z~6-10 is compatible with the usual values derived at z~5-6, but higher than the estimates obtained in the NICMOS Ultra Deep Field (UDF). Increasing the number of blank and lensing fields with ultra-deep near-IR photometry is essential to get more accurate constraints on the abundance of z>6 galaxies.

 

astro-ph/0606135 [abs, ps, pdf, other] :

Title: Mapping the ZZ Ceti Instability Strip: Discovery of 6 New Pulsators
Authors: A. Gianninas, P. Bergeron, G. Fontaine
Comments: 5 pages, 5 figures, 4 tables, accepted for publication in the Astronomical Journal

As part of an ongoing program to map better the empirical instability strip of pulsating ZZ Ceti white dwarfs, we present a brief progress report based on our last observing season. We discuss here high-speed photometric measurements for 6 new pulsators. These stars were selected on the basis of preliminary measurements of their effective temperature and surface gravity that placed them inside or near the known ZZ Ceti instability strip. We also report detection limits for a number of DA white dwarfs that showed no sign of variability. Finally, we revisit the ZZ Ceti star G232-38 for which we obtained improved high-speed photometry.

 

astro-ph/0606136 [abs, ps, pdf, other] :

Title: Astrometry and Photometry with Coronagraphs
Authors: Anand Sivaramakrishnan, Ben R. Oppenheimer
Comments: To appear in ApJ August 2006, 27 preprint style pages 4 figures

We propose a solution to the problem of astrometric and photometric calibration of coronagraphic images with a simple optical device which, in theory, is easy to use. Our design uses the Fraunhofer approximation of Fourier optics. Placing a periodic grid of wires (we use a square grid) with known width and spacing in a pupil plane in front of the occulting coronagraphic focal plane mask produces fiducial images of the obscured star at known locations relative to the star. We also derive the intensity of these fiducial images in the coronagraphic image. These calibrator images can be used for precise relative astrometry, to establish companionship of other objects in the field of view through measurement of common proper motion or common parallax, to determine orbits, and to observe disk structure around the star quantitatively. The calibrator spots also have known brightness, selectable by the coronagraph designer, permitting accurate relative photometry in the coronagraphic image. This technique, which enables precision exoplanetary science, is relevant to future coronagraphic instruments, and is particularly useful for `extreme' adaptive optics and space-based coronagraphy.

 

astro-ph/0606137 [abs, ps, pdf, other] :

Title: Performance of AAOmega: the AAT multi-purpose fibre-fed spectrograph
Authors: R. Sharp, W. Saunder, G. Smith, V. Churilov, D. Correll, J. Dawson, T. Farrel, G. Frost, R. Haynes, R. Heald, A. Lankshear, D. Mayfield, L. Waller, D. Whittard
Comments: 13 pages, 4 figures; presented at SPIE, Astronomical Telescopes and Instrumentation, 24 - 31 May 2006, Orlando, Florida USA

AAOmega is the new spectrograph for the 2dF fibre-positioning system on the Anglo-Australian Telescope. It is a bench-mounted, double-beamed design, using volume phase holographic (VPH) gratings and articulating cameras. It is fed by 392 fibres from either of the two 2dF field plates, or by the 512 fibre SPIRAL integral field unit (IFU) at Cassegrain focus. Wavelength coverage is 370 to 950nm and spectral resolution 1,000-8,000 in multi-Object mode, or 1,500-10,000 in IFU mode. Multi-object mode was commissioned in January 2006 and the IFU system will be commissioned in June 2006.
The spectrograph is located off the telescope in a thermally isolated room and the 2dF fibres have been replaced by new 38m broadband fibres. Despite the increased fibre length, we have achieved a large increase in throughput by use of VPH gratings, more efficient coatings and new detectors - amounting to a factor of at least 2 in the red. The number of spectral resolution elements and the maximum resolution are both more than doubled, and the stability is an order of magnitude better.
The spectrograph comprises: an f/3.15 Schmidt collimator, incorporating a dichroic beam-splitter; interchangeable VPH gratings; and articulating red and blue f/1.3 Schmidt cameras. Pupil size is 190mm, determined by the competing demands of cost, obstruction losses, and maximum resolution. A full suite of VPH gratings has been provided to cover resolutions 1,000 to 7,500, and up to 10,000 at particular wavelengths.

 

astro-ph/0606138 [abs, ps, pdf, other] :

Title: First results from SAPAC: towards a 3D-picture of the Fornax cluster core
Authors: Laura P. Dunn, Helmut Jerjen
Comments: 33 pages, 7 figures, accepted to The Astronomical Journal

A sophisticated SBF analysis package has been developed, designed to measure distances of early-type galaxies by means of surface brightness fluctuations of unresolved stars. This suite of programs called SAPAC is made readily available to the astronomical community for extensive testing with the long-term goal to provide the necessary tools for systematic distance surveys of early-type galaxies using modern optical/NIR telescopes equipped with wide-field cameras. We discuss the technical and scientific concepts of SAPAC and demonstrate its capabilities by analysing deep B and R-band CCD images of 10 dwarf elliptical (dE) galaxy candidates in the Fornax cluster obtained with FORS1 at the VLT. All candidates are confirmed as cluster members. We then turn our attention to the innermost region of the Fornax cluster. A total of 29 early-type galaxies closer than three cluster core radii (2 degrees) from the central galaxy NGC1399 have radial velocities and SBF distances. Their Hubble diagram exhibits a pronounced S-shaped infall pattern suggesting a picture that Fornax is still in the process of formation during the present epoch through a general collapse and possible accretion of distinct groups of galaxies. The associated collapse time is 2.9(+1.6, -0.9)Gyr. After cleansing our galaxy sample from a few kinematical outliers the true distance of the Fornax cluster core is determined at 20.13+-0.40 Mpc [(m-M)_0=31.51+-0.04mag]. Applying a bootstrap resampling technique on the distance distribution with individual distance errors taken into account further reveals a small intrinsic cluster depth of sigma_int=0.74(+0.52,-0.74)Mpc in best agreement with the cluster's linear extension in the sky: sigma_R.A=sigma_DEC~=0.5Mpc. (Abridged)

 

astro-ph/0606139 [abs, ps, pdf, other] :

Title: The Deep Chandra Survey of the Groth Strip - II. optical identification of the X-ray sources
Authors: A. Georgakakis (1), K . Nandra (1), E. S. Laird (2), S. Gwyn (3), C. C. Steidel (4), V. L. Sarajedini (5), P. Barmby (6), S. M. Faber (2), A. L. Coil (7), M. C. Cooper (8), M. Davis (8), J. A. Newman (8) ((1) Imperial College, (2) UCO/Lick, (3) Victoria, (4) Caltech, (5) Florida, (6) CfA, (7) Steward Observatory, (8) Berkeley)
Comments: MNRAS in press

We discuss the optical and X-ray spectral properties of the sources detected in a single 200ks Chandra pointing in the Groth-Westphal Strip region. Optical identifications and spectroscopic redshifts are primarily from the DEEP2 survey. This is complemented with deeper (r~26mag) multi-waveband data (ugriz) from the Canada France Hawaii Legacy Survey to estimate photometric redshifts and to optically identify sources fainter than the DEEP2 magnitude limit (R(AB)~24.5mag). We focus our study on the 2-10keV selected sample comprising 97 sources to the limit ~8e-16erg/s/cm2, this being the most complete in terms of optical identification rate (86%) and redshift determination fraction (63%; both spectroscopic and photometric). We first construct the redshift distribution of the sample which shows a peak at z~1. This is in broad agreement with models where less luminous AGNs evolve out to z~1 with powerful QSOs peaking at higher redshift, z~2. Evolution similar to that of broad-line QSOs applied to the entire AGN population (both type-I and II) does not fit the data. We also explore the observed N_H distribution of the sample and estimate a fraction of obscured AGN (N_H>1e22) of ~48%. This is found to be consistent with both a luminosity dependent intrinsic N_H distribution, where less luminous systems comprise a higher fraction of type-II AGNs, and models with a fixed ratio 2:1 between type-I and II AGNs. We further compare our results with those obtained in deeper and shallower surveys. We argue that a luminosity dependent parametrisation of the intrinsic N_H distribution is required to account for the fraction of obscured AGN observed in different samples over a wide range of fluxes.

 

astro-ph/0606140 [abs, ps, pdf, other] :

Title: Effects of a Supermassive Black Hole Binary on a Nuclear Gas Disk
Authors: Hidenori Matsui, Asao Habe, Takayuki R. Saitoh
Comments: 19 pages, 11 figures, accepted to ApJ

We study influence of a galactic central supermassive black hole (SMBH) binary on gas dynamics and star formation activity in a nuclear gas disk by making three-dimensional Tree+SPH simulations. Due to orbital motions of SMBHs, there are various resonances between gas motion and the SMBH binary motion. We have shown that these resonances create some characteristic structures of gas in the nuclear gas disk, for examples, gas elongated or filament structures, formation of gaseous spiral arms, and small gas disks around SMBHs. In these gaseous dense regions, active star formations are induced. As the result, many star burst regions are formed in the nuclear region.

 

astro-ph/0606141 [abs, ps, pdf, other] :

Title: Self-consistent computation of gamma-ray spectra due to proton-proton interactions in black hole systems
Authors: S. Bhattacharyya (BARC), N. Bhatt (BARC), R. Misra (IUCAA)
Comments: Accepted for publication in MNRAS

In the inner regions of an accretion disk around a black hole, relativistic protons can interact with ambient matter to produce electrons, positrons and $\gamma$-rays. The resultant steady state electron and positron particle distributions are self-consistently computed taking into account Coulomb and Compton cooling, $e^-e^+$ pair production (due to $\gamma-\gamma$ annihilation) and pair annihilation. While earlier works used the diffusion approximation to obtain the particle distributions, here we solve a more general integro-differential equation that correctly takes into account the large change in particle energy that occur when the leptons Compton scatter off hard X-rays. Thus this formalism can also be applied to the hard state of black hole systems, where the dominant ambient photons are hard X-rays. The corresponding photon energy spectrum is calculated and compared with broadband data of black hole binaries in different spectral states. The results indicate that the $\gamma$-ray spectra ($E > 0.8$ MeV) of both the soft and hard spectral states and the entire hard X-ray/$\gamma$-ray spectrum of the ultra-soft state, could be due to $p-p$ interactions. These results are consistent with the hypothesis that there always exists in these systems a $\gamma$-ray spectral component due to $p-p$ interactions which can contribute between 0.5 to 10% of the total bolometric luminosty. The model predicts that {\it GLAST} would be able to detect black hole binaries and provide evidence for the presence of non-thermal protons which in turn would give insight into the energy dissipation process and jet formation in these systems.

 

astro-ph/0606142 [abs, ps, pdf, other] :

Title: Imaging Across the Spectrum: Synergies Between SKA and Other Future Telescopes
Authors: Andrei P. Lobanov (Max-Planck-Institut for Radioastronomy, Bonn, Germany)
Comments: 2 pages, 1 figure; "Exploring the Cosmic Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical Symposia Series

The Square Kilometer Array will be operating at the same time with several new large optical, X-ray and Gamma-ray facilities currently under construction or planned. Fostering synergies in astrophysical research made across different spectral bands presents a compelling argument for designing the SKA such that it would offer imaging capabilities similar to those of other future telescopes. Imaging capabilities of the SKA are compared here with those of the major future astrophysical facilities.

 

astro-ph/0606143 [abs, ps, pdf, other] :

Title: Active Galactic Nuclei at the Crossroads of Astrophysics
Authors: Andrei P. Lobanov, J. Anton Zensus (Max-Planck-Institut for Radioastronomy, Bonn, Germany)
Comments: 16 pages, 5 figures; review contribution; "Exploring the Cosmic Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical Symposia Series

Over the last five decades, AGN studies have produced a number of spectacular examples of synergies and multifaceted approaches in astrophysics. The field of AGN research now spans the entire spectral range and covers more than twelve orders of magnitude in the spatial and temporal domains. The next generation of astrophysical facilities will open up new possibilities for AGN studies, especially in the areas of high-resolution and high-fidelity imaging and spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These studies will address in detail a number of critical issues in AGN research such as processes in the immediate vicinity of supermassive black holes, physical conditions of broad-line and narrow-line regions, formation and evolution of accretion disks and relativistic outflows, and the connection between nuclear activity and galaxy evolution.

 

astro-ph/0606144 [abs, ps, pdf, other] :

Title: 2-Dimensional Kinematics of Simulated Disc Merger Remnants
Authors: Roland Jesseit, Thorsten Naab, Reynier Peletier, Andreas Burkert
Comments: submitted

We present a two-dimensional kinematic analysis for a sample of simulated binary disc merger remnants with mass ratios 1:1 and 3:1. For the progenitor discs we used pure stellar models as well as models with 10% of their mass in gas. A multitude of phenomena also observed in real galaxies are found in the simulations. These include misaligned rotation, embedded discs, gas rings, counter-rotating cores and kinematic misaligned discs. Using the 2D maps we illustrate projection effects and the change in properties of a merger remnant when gas is included in the merger. We find that kinematic peculiar subsystems are preferably formed in equal mass mergers. Equal-mass collisionless remnants can show almost no rotation, regular rotation or strong kinematic misalignment. The inclusion of gas makes the remnants appear more round(1:1) and axisymmetric(3:1). Counter-Rotating Cores (CRCs) are almost exclusively formed in equal-mass mergers with a dissipational component. 3:1 remnants show a much more regular structure. We quantify these properties by applying the kinemetric methods recently developed by Krajnovi\'c et al. This work will help to understand observations of elliptical galaxies with 2D field spectrographs, like SAURON and Sinfoni.

 

astro-ph/0606145 [abs, ps, pdf, other] :

Title: Design and manufacture of micro-optical arrays using 3D diamond machining techniques
Authors: Juergen Schmoll, David J. Robertson, David A. Ryder
Comments: 8 pages, 11 figures. Copyright 2006 Society of Photo-Optical Engineers. This paper will be published in SPIE Conf. Series 6273 and is made available as an electronic preprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or commercial purposes, or modification of the content of the paper are prohibited

We describe our work towards the manufacture of micro-optical arrays using freeform diamond machining techniques. Simulations have been done to show the feasibility of manufacturing micro-lens arrays using the slow-tool servo method. Using this technique, master shapes can be produced for replication of micro-lens arrays of either epoxy-on-glass or monolthic glass types. A machine tool path programme has been developed on the machine software platform DIFFSYS, allowing the production of spherical, aspherical and toric arrays. In addition, in theory spatially varying lenslets, sparse arrays and dithered lenslet arrays (for high contrast applications) are possible to produce. In practice, due to the diamond tool limitations not all formats are feasible. Investigations into solving this problem have been carried out and a solution is presented here.

 

astro-ph/0606146 [abs, ps, pdf, other] :

Title: Absolute timing of the Crab Pulsar at optical wavelengths with STJs
Authors: T. Oosterbroek, J.H.J. de Bruijne, D. Martin, P. Verhoeve, M.A.C. Perryman, C. Erd, R. Schulz
Comments: 5 pages, 2 figures, accepted for publication in Astronomy & Astrophysics

We have observed the Crab Pulsar in the optical with S-Cam, an instrument based on Superconducting Tunneling Junctions (STJs) with $\mu$s time resolution. Our aim was to study the delay between the radio and optical pulse. The Crab Pulsar was observed three times over a time span of almost 7 years, on two different locations, using three different versions of the instrument, and using two different GPS units. We consistently find that the optical peak leads the radio peak by 49$\pm$90, 254$\pm$170, and 291$\pm$100 $\mu$s. On assumption of a constant optical lead, the weighted-average value is $\sim$170 $\mu$s, or when rejecting (based on a perhaps questionable radio ephemeris) the first measurement, 273$\pm$100 $\mu$s.

 

astro-ph/0606147 [abs, ps, pdf, other] :

Title: Effects of alpha particles on the angular momentum loss from the Sun
Authors: Bo Li, Xing Li
Comments: 12 pages, 4 figures, accepted for publication in A&A

The classic Weber-Davis model of the solar wind is reconsidered by incorporating alpha particles and by allowing the solar wind to flow out of the equatorial plane in an axisymmetrical configuration. In the ion momentum equations of the solar wind, the ion gyro-frequency is many orders of magnitude higher than any other frequency. This requires that the difference between proton and alpha velocity vectors be aligned with the background magnetic field. With the aid of this alignment condition, the governing equations of the multi-fluid solar wind are derived from the standard transport equations. The governing equations are numerically solved along a prescribed meridional magnetic field line located at colatitude $70^\circ$ at 1AU and a steady state fast solar wind solution is found. A general analysis concludes, in agreement with the Weber-Davis model, that the magnetic field helps the coronal plasma to achieve an effective corotation out to the Alfv\'enic radius, where the poloidal Alfv\'enic Mach number $M_T$ equals unity ($M_T$ is defined by equation (\ref{eq:mach})). The model computations show that, magnetic stresses predominate the angular momentum loss of the Sun. For the fast wind considered, the proton contribution to the angular momentum loss, which can be larger than the magnetic one, is almost completely canceled by the alpha particles that develop an azimuthal speed in the direction opposite to the solar rotation. The Poynting flux associated with the azimuthal components is negligible in the energy budget. However, the solar rotation can play some role in reducing the relative speed between alpha particles and protons for low latitude fast solar wind streams in interplanetary space.

 

astro-ph/0606148 [abs, ps, pdf, other] :

Title: An alternative to grids and glasses: Quaquaversal pre-initial conditions for N-body simulations
Authors: Steen H. Hansen, Oscar Agertz, Michael Joyce, Joachim Stadel, Ben Moore, Doug Potter
Comments: 7 pages, 3 figures

N-body simulations sample their initial conditions on an initial particle distribution, which for cosmological simulations is usually a glass or grid, whilst a Poisson distribution is used for galaxy models, spherical collapse etc. These pre-initial conditions have inherent correlations, noise due to discreteness and preferential alignments, whilst the glass distribution is poorly defined and computationally expensive to construct. We present a novel particle distribution which can be useful as a pre-initial condition for N-body simulations, using a simple construction based on a ``quaquaversal'' tiling of space. This distribution has no preferred orientation (i.e. is statistically isotropic), has a rapidly vanishing large scale power-spectrum (P(k) ~ k^{4}), and is trivial to create. This should be particularly useful for warm dark matter and cold collapse simulations.

 

astro-ph/0606149 [abs, ps, pdf, other] :

Title: Spectroscopic analysis of southern B and Be stars
Authors: R. S. Levenhagen, N. V. Leister
Comments: 10 pages, 6 figures

Spectroscopic monitoring of 141 southern &#64257;eld B type stars, 114 of them known to exhibit the Be phenomenon, allowed the estimation of their projected rotational velocities, effective temperatures and super&#64257;cial gravities from both line and equivalent width &#64257;tting procedures. Stellar ages, masses and bolometric luminosities were derived from internal structure models. Without taking into account for the effects of gravity darkening, we notice the occurrence of the Be phenomenon in later stages of main sequence phase.

 

astro-ph/0606150 [abs, ps, pdf, other] :

Title: A method for detection of structure
Authors: M. Gustafsson, J.L. Lemaire, D. Field
Comments: Astronomy and Astrophysics, in press

Context. In order to understand the evolution of molecular clouds it is important to identify the departures from self-similarity associated with the scales of self-gravity and the driving of turbulence.
Aims. A method is described based on structure functions for determining whether a region of gas, such as a molecular cloud, is fractal or contains structure with characteristic scale sizes.
Methods. Using artificial data containing structure it is shown that derivatives of higher order structure functions provide a powerful way to detect the presence of characteristic scales should any be present and to estimate the size of such structures. The method is applied to observations of hot H2 in the Kleinman-Low nebula, north of the Trapezium stars in the Orion Molecular Cloud, including both brightness and velocity data. The method is compared with other techniques such as Fourier transform and histogram techniques.
Results. It is found that the density structure, represented by H2 emission brightness in the K-band (2-2.5micron), exhibits mean characteristic sizes of 110, 550, 1700 and 2700AU. The velocity data show the presence of structure at 140, 1500 and 3500AU. Compared with other techniques such as Fourier transform or histogram, the method appears both more sensitive to characteristic scales and easier to interpret.

 

astro-ph/0606151 [abs, ps, pdf, other] :

Title: Superhumps in Binary Systems and Their Connection to Precessional Spiral Density Waves
Authors: P.V. Kaygorodov (1), D.V. Bisikalo (1), O.A. Kuznetsov (1,2), A. A. Boyarchuk (1) ((1)Institute of Astronomy of the Russian Acad. of Sci., Moscow, Russia; (2) Keldysh Institute of Applied Mathematics, Moscow, Russia)
Comments: LaTeX, 12 pages, 6 figures; figure 3 was improved
Journal-ref: Astronomy Reports, 2006, Vol. 50, No 7, pp. 537-543

We consider a mechanism for the formation of superhumps in the TV Col system, based on the possible existence of a precessional spiral wave in the accretion disk of the system. This mechanism can act in binaries with arbitrary component-mass ratios, and our precessional spiral wave model can be applied to explain observed superhumps of all types.

 

astro-ph/0606152 [abs, ps, pdf, other] :

Title: Shapley Optical Survey II: The effect of environment on the colour-magnitude relation and galaxy colours
Authors: C. P. Haines, P. Merluzzi, A. Mercurio, A. Gargiulo, N. Krusanova, G. Busarello, F. La Barbera, M. Capaccioli
Comments: 13 pages, 8 figures, accepted for publication in MNRAS

We present an analysis of the effects of environment on the photometric properties of galaxies in the core of the Shapley Supercluster at z=0.05, one of the most massive structures in the local universe. The Shapley Optical Survey (SOS) comprises archive WFI optical imaging of a 2.0 deg^2 region containing the rich clusters A3556, A3558 and A3562 which demonstrate a highly complex dynamical situation including ongoing cluster mergers. The B-R/R colour-magnitude relation has an intrinsic dispersion of 0.045 mag and is 0.015\pm0.005 mag redder in the highest-density regions, indicative of the red sequence galaxy population being 500 Myr older in the cluster cores than towards the virial radius. The B-R colours of galaxies are dependent on their environment, whereas their luminosities are independent of the local density, except for the very brightest galaxies (M_R<-22). The global colours of faint (>M*+2) galaxies change from the cluster cores where ~90% of galaxies lie along the cluster red sequence to the virial radius, where the fraction has dropped to just ~20%. This suggests that processes related to the supercluster environment are responsible for transforming faint galaxies, rather than galaxy merging, which should be infrequent in any of the regions studied here. The largest concentrations of faint blue galaxies are found between the clusters, coincident with regions containing high fractions of ~L* galaxies with radio emission indicating starbursts. Their location suggests star-formation triggered by cluster mergers, in particular the merger of A3562 and the poor cluster SC1329-313, although they may also represent recent arrivals in the supercluster core complex. (abstract truncated)

 

astro-ph/0606153 [abs, ps, pdf, other] :

Title: Solar Carbon Monoxide, Thermal Profiling, and the Abundances of C, O, and their Isotopes
Authors: Thomas R. Ayres, Claude Plymate, Christoph U. Keller
Comments: 90 pages, 19 figures (some with parts "a", "b", etc.); to be published in the Astrophysical Journal Supplements

A solar photospheric "thermal profiling" analysis is presented, exploiting the infrared rovibrational bands of carbon monoxide (CO) as observed with the McMath-Pierce Fourier transform spectrometer (FTS) at Kitt Peak, and from above the Earth's atmosphere by the Shuttle-borne ATMOS experiment. Visible continuum intensities and center-limb behavior constrained the temperature profile of the deep photosphere, while CO center-limb behavior defined the thermal structure at higher altitudes. The oxygen abundance was self consistently determined from weak CO absorptions. Our analysis was meant to complement recent studies based on 3-D convection models which, among other things, have revised the historical solar oxygen (and carbon) abundance downward by a factor of nearly two; although in fact our conclusions do not support such a revision. Based on various considerations, an oxygen abundance of 700+/-100 ppm (parts per million relative to hydrogen) is recommended; the large uncertainty reflects the model sensitivity of CO. New solar isotopic ratios also are reported for 13C, 17O, and 18O.

 

astro-ph/0606154 [abs, ps, pdf, other] :

Title: Cosmic Calibration
Authors: Katrin Heitmann, David Higdon, Charles Nakhleh, Salman Habib
Comments: 4 pages, 4 figures, accepted for publication in ApJL

The complexity and accuracy of current and future precision cosmology observational campaigns has made it essential to develop an efficient technique for directly combining simulation and observational datasets to determine cosmological and model parameters; a procedure we term calibration. Once a satisfactory calibration of the underlying cosmological model is achieved, independent predictions for new observations become possible. For this procedure to be effective, robust characterization of the uncertainty in the calibration process is highly desirable. In this Letter, we describe a statistical methodology which can achieve both of these goals. An application example based around dark matter structure formation simulations and a synthetic mass power spectrum dataset is used to demonstrate the approach.

 

astro-ph/0606155 [abs, ps, pdf, other] :

Title: Molecular excitation in the Eagle nebula's fingers
Authors: F. Schuller (1), S. Leurini (1), C. Hieret (1), K. M. Menten (1), S. D. Philipp (1), R. Guesten (1), P. Schilke (1), L.-A. Nyman (2) ((1) Max Planck Institut fuer Radioastronomie, (2) European Southern Observatory)
Comments: 4 pages, APEX A&A special issue, accepted

Context: The M16 nebula is a relatively nearby Hii region, powered by O stars from the open cluster NGC 6611, which borders to a Giant Molecular Cloud. Radiation from these hot stars has sculpted columns of dense obscuring material on a few arcmin scales. The interface between these pillars and the hot ionised medium provides a textbook example of a Photodissociation Region (PDR).
Aims: To constrain the physical conditions of the atomic and molecular material with submillimeter spectroscopic observations.
Methods: We used the APEX submillimeter telescope to map a ~3'x3' region in the CO J=3-2, 4-3 and 7-6 rotational lines, and a subregion in atomic carbon lines. We also observed C18O(3-2) and CO(7-6) with longer integrations on five peaks found in the CO(3-2) map. The large scale structure of the pillars is derived from the molecular lines' emission distribution. We estimate the magnitude of the velocity gradient at the tips of the pillars and use LVG modelling to constrain their densities and temperatures. Excitation temperatures and carbon column densities are derived from the atomic carbon lines.
Results: The atomic carbon lines are optically thin and excitation temperatures are of order 60 K to 100 K, well consistent with observations of other Hii region-molecular cloud interfaces. We derive somewhat lower temperatures from the CO line ratios, of order 40 K. The Ci/CO ratio is around 0.1 at the fingers tips.

 

astro-ph/0606156 [abs, ps, pdf, other] :

Title: The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
Authors: JF Donati, ID Howarth, MM Jardine, P Petit, C Catala, JD Landstreet, JC Bouret, E Alecian, JR Barnes, T Forveille, F Paletou, N Manset
Comments: Accepted for publication in the 'Monthly Notices of the Royal Astronomical Society'

We report the discovery of a medium-strength (~0.5kG) magnetic field on the young, massive star tauSco (B0.2V), which becomes the third-hottest magnetic star known. Circularly polarized Zeeman signatures are clearly detected in observations collected mostly with the ESPaDOnS spectropolarimeter, recently installed on the 3.6-m Canada-France-Hawaii Telescope; temporal variability is also clearly established in the polarimetry, and can be unambiguously attributed to rotational modulation with a period close to 41d. Archival UV spectra confirm that this modulation repeats over timescales of decades.
By reconstructing the large-scale structure of its magnetic topology, we find that the magnetic structure is unusually complex for a hot star. The surface topology is dominated by a potential field, although a moderate toroidal component is probably present. We fail to detect intrinsic temporal variability of the magnetic structure over the 1.5-yr period of our spectropolarimetric observations (in agreement with the stable temporal variations of the UV spectra), and infer that any differential surface rotation must be very small.
The topology of the extended magnetic field that we derive from the photospheric magnetic maps is also more complex than a global dipole, and features in particular a significantly warped torus of closed magnetic loops encircling the star (tilted at about 90deg to the rotation axis), with additional, smaller, networks of closed field lines. This topology appears to be consistent with the exceptional Xray properties of tauSco and also provides a natural explanation of the variability observed in wind-formed UV lines. We conclude that its magnetic field is most probably a fossil remnant from the star-formation stage.

 

astro-ph/0606157 [abs, ps, pdf, other] :

Title: Rapid Star Formation in the Presence of Active Galactic Nuclei
Authors: Chris Lintott, Serena Viti (University College London)
Comments: 4 pages, 1 figure. Accepted by the Astrophysical Journal Letters

Recent observations reveal galaxies in the early Universe (2<z<6.4) with large reservoirs of molecular gas and extreme star formation rates. For a very large range of sources, a tight relationship exists between star formation rate and the luminosity of the HCN J=1-0 spectral line, but sources at redshifts of z~2 and beyond do not follow this trend. The deficit in HCN is conventionally explained by an excess of infrared (IR) radiation due to active galactic nuclei (AGN). We show in this letter not only that the presence of AGN cannot account for the excess of IR over molecular luminosity, but also that the observed abundance of HCN is in fact consistent with a population of stars forming from near-primordial gas.

 

astro-ph/0606158 [abs, ps, pdf, other] :

Title: Spitzer Quasar and ULIRG evolution study (QUEST): I. The origin of the far infrared continuum of QSOs
Authors: M. Schweitzer, D. Lutz, E. Sturm, A. Contursi, L.J. Tacconi, M.D. Lehnert, K. Dasyra, R. Genzel, S. Veilleux, D. Rupke, D.-C. Kim, A.J. Baker, H. Netzer, A. Sternberg, J. Mazzarella, S. Lord
Comments: 39 pages, 8 figures, accepted for publication in ApJ

This paper addresses the origin of the far-infrared (FIR) continuum of QSOs, based on the Quasar and ULIRG Evolution Study (QUEST) of nearby QSOs and ULIRGs using observations with the Spitzer Space Telescope. For 27 Palomar-Green QSOs at z <~ 0.3, we derive luminosities of diagnostic lines ([NeII]12.8um, [NeV]14.3um, [OIV]25.9um) and emission features (PAH7.7um emission which is related to star formation), as well as continuum luminosities over a range of mid- to far-infrared wavelengths between 6 and 60um. We detect star-formation related PAH emission in 11/26 QSOs and fine-structure line emission in all of them, often in multiple lines. The detection of PAHs in the average spectrum of sources which lack individual PAH detections provides further evidence for the widespread presence of PAHs in QSOs. Similar PAH/FIR and [NeII]/FIR ratios are found in QSOs and in starburst-dominated ULIRGs and lower luminosity starbursts. We conclude that the typical QSO in our sample has at least 30% but likely most of the far-infrared luminosity (~ 10^(10...12)Lsun) arising from star formation, with a tendency for larger star formation contribution at the largest FIR luminosities. In the QSO sample, we find correlations between most of the quantities studied including combinations of AGN tracers and starburst tracers. The common scaling of AGN and starburst luminosities (and fluxes) is evidence for a starburst-AGN connection in luminous AGN. Strong correlations of far-infrared continuum and starburst related quantities (PAH, low excitation [NeII]) offer additional support for the starburst origin of far-infrared emission.

 

astro-ph/0606159 [abs, ps, pdf, other] :

Title: Supermassive black hole formation during the assembly of pre-galactic discs
Authors: Giuseppe Lodato (1), Priya Natarajan (2,3) ((1) Institute of Astronomy, Cambridge, UK, (2) Department of Astronomy, Yale University, New Haven, USA, (3) Department of Physics, Yale University, New Haven, USA)
Comments: 12 pages, 8 figures, submitted to MNRAS

In this paper we discuss the evolution of gravitationally unstable pre-galactic discs that result from the collapse of haloes at high redshift $z \approx 10$ or so, which have not yet been enriched by metals. In cases where molecular hydrogen formation is suppressed the discs are maintained at a temperature of a few thousand degrees Kelvin. However, when molecular hydrogen is present cooling can proceed down to a few hundred degrees Kelvin. Analogous to the case of the larger scale proto-galactic discs, we assume that the evolution of these discs is mainly driven by angular momentum redistribution induced by the development of gravitational instabilities in the disc. We also properly take into account the possibility of disc fragmentation. We thus show that this simple model naturally predicts the formation of supermassive black holes in the nuclei of such discs and provides a robust determination of their mass distribution as a function of halo properties. We estimate that roughly 5% of discs resulting from the collapse of haloes with $M\approx 10^7 M_{\odot}$ should host a massive black hole with a mass $M_{\rm BH}\approx 10^5 M_{\odot}$. We confirm our arguments with time-dependent calculations of the evolution of the surface density and of the accretion rate in these primordial discs. This mechanism offers an efficient way to form seed black holes at high redshift. The predicted masses for our black hole seeds enable the comfortable assembly of $10^9 M_{\odot}$ black holes powering the luminous quasars detected by the Sloan Digital Sky Survey at $z = 6$ for a concordance cosmology. (abridged)

 

astro-ph/0606160 [abs, ps, pdf, other] :

Title: 3D photoionisation and dust RT modelling with MOCASSIN: geometry effects on the emission line spectra of star-forming regions
Authors: Barbara Ercolano, Nate Bastian (Department of Physics and Astronomy University College London)
Comments: 2 pages, 1 figure - Conference proceedings to 'Mass Loss from stars and the evolution of stellar clusters' - Lunteren, The Netherlands, May 29 - June 1, 2006. A. de Koter, L. Smith & R. Waters

Emission line spectra from HII regions are often used to study properties of the gas in star-forming regions, as well as temperatures and luminosities of the ionising sources. Empirical diagnostics for the interpretation of observational data must often be calibrated with the aid of photoionisation models. Most studies so far have been carried out by assuming spherical or plane-parallel geometries, with major limitations on allowed gas and dust density distributions and with the spatial distribution of multiple, non-centrally-located ionising sources not being accounted for. We present the first results of our theoretical study of geometric effects, via the construction of a number of 3D photoionisation models using the MOCASSIN code for a variety of spatial configurations and ionisation sources. We compare integrated emission line spectra from such configurations and show evidence of systematic errors caused by the simplifying assumption of a single, central location for all ionising sources.

 

astro-ph/0606161 [abs, ps, pdf, other] :

Title: Detection of VHE radiation from the BL Lac PG 1553+113 with the MAGIC telescope
Authors: J. Albert et al. (MAGIC collaboration)
Comments: Submitted to ApJ Letters, 12 pages, 4 figures

The MAGIC telescope has observed very high energy gamma-ray emission from the distant BL Lac object PG 1553+113 in 2005 and 2006. The overall significance is 8.8 sigma in 18.8h. The light curve shows no significant flux variations on a daily time-scale, the flux level during 2005 was, however, significantly higher compared to 2006. The differential energy spectrum between ~90 GeV and 500 GeV is well described by a power law with spectral index 4.2 +- 0.3. The combined 2005 and 2006 energy spectrum allowed to pose an upper limit of z=0.78 on the redshift of the object.

 

astro-ph/0606162 [abs, ps, pdf, other] :

Title: XMM-Newton Detection of the Rare FR II BAL Quasar FIRST J101614.3+520916
Authors: Justin J. Schaefer, Michael S. Brotherton, Zhaohui Shang, Michael D. Gregg, Robert H. Becker, Sally A. Laurent-Muehleisen, Mark Lacy, Robert L. White
Comments: 5 pages, 2 figures. Accepted in AJ

We have detected FIRST J101614.3+520916 with the XMM-Newton X-ray Observatory. FIRST J101614.3+520916, one of the most extreme radio-loud, broad absorption line (BAL) quasars so far discovered, is also a Fanaroff-Riley type II (FR II) radio source. We find that, compared to its estimated intrinsic X-ray flux, the observed X-rays are likely suppressed, and that the observed hardness ratio indicates significant soft X-ray photons. This is inconsistent with the simplest model, a normal quasar spectrum absorbed by a large neutral HI column density, which would primarily absorb the softer photons. More complex models, involving partial covering, an ionized absorber, ionized mirror reflection, or jet contributions need to be invoked to explain this source. The suppressed but soft X-ray emission in this radio-loud BAL quasar is consistent with the behavior displayed by other BAL quasars, both radio-loud and radio-quiet.

 

astro-ph/0606163 [abs, ps, pdf, other] :

Title: The distribution of ND2H in LDN1689N
Authors: Maryvonne Gerin (LERMA), Dariuscz C. Lis (CALTECH), Sabine Philipp (MPIFR), Rolf Güsten (MPIFR), Evelyne Roueff (LUTH), Vincent Reveret (ESO)
Comments: 4 pages Accepted by Astronomy and Astrophysics, special APEX edition

Finding tracers of the innermost regions of prestellar cores is important for understanding their chemical and dynamical evolution before the onset of gravitational collapse. While classical molecular tracers, such as CO and CS, have been shown to be strongly depleted in cold, dense gas by condensation on grain mantles, it has been a subject of discussion to what extent nitrogen-bearing species, such as ammonia, are affected by this process. As deuterium fractionation is efficient in cold, dense gas, deuterated species are excellent tracers of prestellar cores. A comparison of the spatial distribution of neutral and ionized deuterated species with the dust continuum emission can thus provide important insights into the physical and chemical structure of such regions. We study the spatial distribution of the ground-state 335.5 GHz line of ND2H in LDN1689N, using APEX, and compare it with the distribution of the DCO+(3--2) line, as well as the 350 micron dust continuum emission observed with the SHARC~II bolometer camera at CSO. While the distribution of the ND2H emission in LDN1689N is generally similar to that of the 350 microns dust continuum emission, the peak of the ND2H emission is offset by ~10'' to the East from the dust continuum and DCO+ emission peak. ND2H and ND3 share the same spatial distribution. The observed offset between the ND2H and DCO+ emission is consistent with the hypothesis that the deuterium peak in LDN1689N is an interaction region between the outflow shock from IRAS16293--2422 and the dense ambient gas. We detect the J = 4 - 3 line of H13CO+ at 346.998 GHz in the image side band serendipitously. This line shows the same spatial distribution as DCO+(3--2), and peaks close to the 350 mic emission maximum which provides further support for the shock interaction scenario.

 

astro-ph/0606164 [abs, ps, pdf, other] :

Title: Evidence for Differential Rotation on a T Tauri Star
Authors: W. Herbst, S. Dhital, A. Francis, L. Lin, N. Tresser, E. Williams
Comments: Acepted for publication in PASP

Five years of photometric monitoring of the T Tauri star HBC 338 in NGC 1333 has revealed that it is a periodic variable, but the period has changed significantly with time. From 2000-2003, a period near 5.6 days was observed, while in the last two seasons, the dominant period is near 4.6 days. No other T Tauri star has been seen to change its period by such a large percentage. We propose a model in which a differentially rotating star is seen nearly equator-on and a high latitude spot has gradually been replaced by a low latitude spot. We show that this model provides an excellent fit to the observed shapes of the light curves at each epoch. The amplitude and sense of the inferred differential rotation is similar to what is seen on the Sun. This may be surprising given the likely high degree of magnetic surface activity on the star relative to the Sun but we note that HBC 338 is clearly an exceptional T Tauri star.

 

astro-ph/0606165 [abs, ps, pdf, other] :

Title: The Dwarf Galaxy Population in Nearby Groups. The data
Authors: Eleazar R. Carrasco (Gemini Observatory/Southern Operations Center), Claudia M. de Oliveira (IAG-USP/Brazil), Leopoldo Infante (PUC/Chile)
Comments: 23 pages, 13 figures, 6 inserted tables using emulateapj.cls style; revision of previously submitted AJ paper

We used V and I CCD photometry to search for low-surface brightness dwarf galaxies (LSBD) in the central (<0.5 h^-1 Mpc) region of the groups NGC 6868, NGC 5846, HCG 42 and the poor cluster IC 4765. Using the parameters given by the exponential profile fit, we identified 80 LSBD candidates with magnitudes 17 < V < 22 mag and with colors V-I < 1.5 mag at the limiting isophote of 25.8 V mag/arcsec^2. The galaxies have mu0 > 22.5 V mag/arcsec^2, h > 1.5 arcsec, and diameters larger than 1.2 h^-1 kpc. Twenty of the eighty galaxies are extended LSB galaxies that were detected only on smoothed images, after masking all high surface brightness objects. The completeness in the detection is ~80% for galaxies with V<=20 and 22.5<mu0<24.5 V mag/arcsec^2, and below 50% at fainter magnitudes and central surface brightnesses. In this last bin, the completeness increases to ~80% when we search for galaxies in smoothed images instead. The detected LSBD galaxies are highly concentrated towards the center of the four groups in the inner 250 h^-1 kpc. The best fit power-law slope of the surface density distribution is, on average, beta ~ -1.5 (R < 250 h^-1 kpc), in agreement with the values found for satellites dwarfs around isolated E/S0 galaxies and in X-ray groups. The LSBD galaxies in the Mv-mu0 plane does not show a clear correlation, suggesting that the correlation noted by other studies could be produced by selection effects. The LSBD dwarf galaxies follow a well defined color-magnitude relation, extending for more than ten magnitudes (from bright ellipticals to faint dwarfs). A similar well defined color-magnitude relation from giants to dwarfs is known to be valid for galaxy clusters but it is the first time that it is demonstrated in the sparse environments of groups. (Abridge)

 

astro-ph/0606166 [abs, ps, pdf, other] :

Title: Probing long-period companions to planetary hosts. VLT and CFHT near infrared coronographic imaging survey
Authors: G. Chauvin, A.-M. Lagrange, S. Udry, T. Fusco, F. Galland, D. Naef, J.-L. Beuzit, M. Mayor
Comments: 16 pages and 56 figures, accepted in A&A

We present the results of a deep imaging survey of stars surrounded by planets detected through the radial velocity technique. The purpose is to search for and to characterize long-period stellar and substellar companions. The sample contains a total of 26 stars, among which 6 exhibit additional radial velocity drifts. We used NACO, at the ESO Very Large Telescope, and PUEO-KIR, at the Candian French Hawaiian Telescope, in order to conduct a near-infrared coronographic survey with adaptive optics of the faint circumstellar environment of the planetary hosts. The domain investigated ranges between typically 0.1 to 15" (i.e. about 3 to 500 AU, according to the mean distance of the sample). The survey is sensitive to companions within the stellar and the substellar domains, depending on the distance to the central stars and on the stars properties. The images of 14 stars do not reveal any companions once the field objects are removed. 8 stars have close potential companions that need to be re-observed within 1-2 years to check for physical companionship. 4 stars are surrounded by faint objects which are confirmed or very probable companions. The companion to HD 13445 (Gl 86) is already known. The HD 196885 star is a new close visual binary system with a high probability for being bound. Finally, the 2 newly discovered companions, HD 1237 B and HD 27442 B, share common proper motions with the central stars. Orbital motion is, in addition, detected for HD 1237 B. HD 1237 B is likely a low-mass M star, located at 70 AU (projected distance) from the primary. Surprisingly, HD 27442 B is most probably a white dwarf companion located at about 240 AU (projected distance).

 

astro-ph/0606167 [abs, ps, pdf, other] :

Title: New constrains on Gliese 86 B
Authors: A.-M. Lagrange, H. Beust, S. Udry, G. Chauvin, M. Mayor
Comments: 10 pages, 18 figures, accepted in A&A

We present the results of multi epochs imaging observations of the companion to the planetary host Gliese 86. Associated to radial velocity measurements, this study aimed at characterizing dynamically the orbital properties and the mass of this companion (here after Gliese 86 B), but also at investigating the possible history of this particular system. We used the adaptive optics instrument NACO at the ESO Very Large Telescope to obtain deep coronographic imaging in order to determine new photometric and astrometric measurements of Gliese 86 B. Part of the orbit is resolved. The photometry of Gliese B indicates colors compatible with a ~70 Jupiter mass brown dwarf or a white dwarf. Both types of objects allow to fit the available, still limited astrometric data. Besides, if we attribute the long term radial velocity residual drift observed for Gliese A to B, then the mass of the latter object is ~0.5 Msun. We analyse both astrometric and radial velocity data to propose first orbital parameters for Gliese B. Assuming Gliese B is a ~0.5 Msun white dwarf, we explore the constraints induced by this hypothesis and refine the parameters of the system.

 

astro-ph/0606168 [abs, ps, pdf, other] :

Title: Near Scale Invariance with Modified Dispersion Relations
Authors: C. Armendariz-Picon
Comments: 7 pages and no figures. Uses RevTeX4

We describe a novel mechanism to seed a nearly scale invariant spectrum of adiabatic perturbations during a non-inflationary stage. It relies on a modified dispersion relation that contains higher powers of the spatial momentum of matter perturbations. We implement this idea in the context of a massless scalar field in an otherwise perfectly homogeneous universe. The couplings of the field to background scalars and tensors give rise to the required modification of its dispersion relation, and the couplings of the scalar to matter result in an adiabatic primordial spectrum. This work is meant to explicitly illustrate that it is possible to seed nearly scale invariant primordial spectra without inflation, within a conventional expansion history.