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The Evolution of the Effective Equation of State of the Intergalactic Medium
Shull, J. Michael; Ricotti, Massimo; Gnedin, Nickolay Y.
We develop a method to extract the ``effective equation of state'' of the intergalactic medium from the Doppler (b) parameter distribution of the low-density Lyα forest. We test the method on numerical simulations and then apply it to published observations of the Lyα forest at redshifts z~=0-4. We find that the effective equation of state is clos…
An ISOCAM absorption survey of the structure of pre-stellar cloud cores
Abergel, A.; Puget, J. -L.; Bontemps, S. +3 more
We present the results of a mid-infrared (lambda =~ 7 mu m) imaging survey of a sample of 24 starless dense cores carried out at an angular resolution of 6arcsec with the ISOCAM camera aboard the Infrared Space Observatory (ISO). The targeted cores are believed to be pre-stellar in nature and to represent the initial conditions of low-mass, isolat…
A Search for Environmental Effects on Type IA Supernovae
Phillips, M. M.; Suntzeff, Nicholas B.; Hamuy, Mario +4 more
We use integrated colors and B and V absolute magnitudes of Type Ia supernova (SN) host galaxies in order to search for environmental effects on the SN optical properties. With the new sample of 44 SNe we confirm the conclusion by Hamuy et al. that bright events occur preferentially in young stellar environments. We find also that the brightest SN…
The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXIV. The Calibration of Tully-Fisher Relations and the Value of the Hubble Constant
Kelson, Daniel D.; Illingworth, Garth D.; Huchra, John P. +15 more
This paper presents the calibration of BVRIH-0.5 Tully-Fisher relations based on Cepheid distances to 21 galaxies within 25 Mpc and 23 clusters within 10,000 km s-1. These relations have been applied to several distant cluster surveys in order to derive a value for the Hubble constant, H0, mainly concentrating on a…
Optical Imaging of Nova Shells and the Maximum Magnitude-Rate of Decline Relationship
Downes, Ronald A.; Duerbeck, Hilmar W.
An optical imaging study of 30 recent novae has been undertaken using both ground-based and space-based observations. Resolved shells have been detected around nine objects in the ground-based data, while another four objects have shells detected by Hubble Space Telescope observations; for RW UMi, we fail to detect a shell that was observed 5 year…
Disk Accretion in the 10 MYR Old T Tauri Stars TW Hydrae and Hen 3-600A
Briceño, C.; Calvet, N.; Muzerolle, J. +2 more
We have found that two members of the TW Hydrae association, TW Hydrae and Hen 3-600A, are still actively accreting, based on the ballistic infall signature of their broad Hα emission profiles. We present the first quantitative analysis of accretion in these objects and conclude that the same accretion mechanisms which operate in the well-studied …
The Nature of the lithium rich giants. Mixing episodes on the RGB and early-AGB
Charbonnel, C.; Balachandran, S. C.
We present a critical analysis of the nature of the so-called Li-rich RGB stars. For a majority of the stars, we have used Hipparcos parallaxes to determine masses and evolutionary states by comparing their position on the Hertzsprung-Russell diagram with theoretical evolutionary tracks. Among the twenty Li-rich giants whose location on the HR dia…
Construction and verification of the Tycho-2 Catalogue
Makarov, V. V.; Bastian, U.; Fabricius, C. +6 more
The construction of the Tycho-2 Catalogue is described. The catalogue contains astrometric positions and proper motions as well as two-colour photometric data for 2.5 million stars. The Tycho-2 positions and magnitudes are based on precisely the same observations as the original Tycho Catalogue (hereafter Tycho-1) collected by the sky mapper of th…
A Hubble Space Telescope Snapshot Survey of Proto-Planetary Nebula Candidates: Two Types of Axisymmetric Reflection Nebulosities
Ueta, Toshiya; Meixner, Margaret; Bobrowsky, Matthew
We report the results from an optical imaging survey of proto-planetary nebula candidates using the Hubble Space Telescope (HST). The goals of the survey were to image low surface brightness optical reflection nebulosities around proto-planetary nebulae and to investigate the distribution of the circumstellar dust, which scatters the star light fr…
Chandra Discovery of a 100 kiloparsec X-Ray Jet in PKS 0637-752
Elvis, M.; Birkinshaw, M.; Worrall, D. M. +18 more
The quasar PKS 0637-752, the first celestial X-ray target of the Chandra X-Ray Observatory, has revealed asymmetric X-ray structure extending from 3" to 12" west of the quasar, coincident with the inner portion of the jet previously detected in a 4.8 GHz radio image (Tingay et al. 1998). At a redshift of z=0.651, the jet is the largest (>~100 k…