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The HIPPARCOS Catalogue

Grewing, M.; Arenou, F.; Lindegren, L. +17 more

The principal observational characteristics of the Hipparcos Catalogue, and a summary of its main astrometric and photometric properties, are presented. Median astrometric standard errors (in position, parallax, and annual proper motion) are in the range 0.7-0.9 milliarcsec (mas) for stars brighter than 9 mag at the catalogue epoch (J1991.25). The…

Measurements of the Cosmological Parameters Ω and Λ from the First Seven Supernovae at z >= 0.35

Filippenko, A. V.; Goldhaber, G.; Goobar, A. +21 more

We have developed a technique to systematically discover and study high-redshift supernovae that can be used to measure the cosmological parameters. We report here results based on the initial seven of more than 28 supernovae discovered to date in the high-redshift supernova search of the Supernova Cosmology Project. We find an observational dispe…

Evolution since z = 0.5 of the Morphology-Density Relation for Clusters of Galaxies

Smail, Ian; Ellis, Richard S.; Dressler, Alan +6 more

Using traditional morphological classifications of galaxies in 10 intermediate-redshift (z ~ 0.5) clusters observed with WFPC2 on the Hubble Space Telescope, we derive relations between morphology and local galaxy density similar to that found by Dressler for low-redshift clusters. Taken collectively, the ``morphology-density'' relationship, T - Σ…

The Centers of Early-Type Galaxies with HST. IV. Central Parameter Relations.

Gebhardt, Karl; Richstone, Douglas; Kormendy, John +7 more

We analyze Hubble Space Telescope surface-brightness profiles of 61 elliptical galaxies and spiral bulges (hereafter "hot" galaxies). The profiles are parameterized by break radius r_βand break surface brightness 1_β These are combined with central velocity dispersions, total luminosities, rotation velocities, and isophote shap…

Notes on the convection in the ATLAS9 model atmospheres.

Castelli, F.; Gratton, R. G.; Kurucz, R. L.

The mixing-length theory for the convection, as it is used in the ATLAS9 code (Kurucz, 1993a), is summarized and discussed. We investigated the effect of the modification called ``approximate overshooting'' on the model structure of the Sun and of stars with T_eff_ included between 4000K and 8500K, logg included between 2.5 and 4.5, and metallicit…

Measurements of Flow Speeds in the Corona Between 2 and 30 R_⊙

Llebaria, A.; St. Cyr, O. C.; Michels, D. J. +16 more

Time-lapse sequences of white-light images, obtained during sunspot minimum conditions in 1996 by the Large Angle Spectrometric Coronagraph on the Solar and Heliospheric Observatory, give the impression of a continuous outflow of material in the streamer belt, as if we were observing Thomson scattering from inhomogeneities in the solar wind. Pursu…

A Composite HST Spectrum of Quasars

Kriss, Gerard A.; Zheng, Wei; Davidsen, Arthur F. +2 more

We construct a composite quasar spectrum from 284 HST FOS spectra of 101 quasars with redshifts z > 0.33. The spectrum covers the wavelengths between 350 and 3000 Å in the rest frame, with a peak S/N level of ~130 per Å at ~1200 Å. Since ~90% of the sample quasars have redshift z < 1.5, the spectrum is suitable for studying the wavelength re…

Hubble Space Telescope Images of a Sample of 20 Nearby Luminous Quasars

Schneider, Donald P.; Bahcall, John N.; Kirhakos, Sofia +1 more

Observations with the Wide-Field Camera of the Hubble Space Telescope (HST) are presented for a representative sample of 20 intrinsically luminous quasars with redshifts smaller than 0.30. These observations show that luminous quasars occur in diverse environments that include ellipticals as bright as the brightest cluster galaxies (two), apparent…

The spectrum of comet Hale-Bopp (C/1995 O1) observed with the infrared space observatory at 2.9 astronomical units from the sun.

Altieri, B.; Keller, H. U.; Lellouch, E. +5 more

Eta Carinae and Its Environment

Humphreys, Roberta M.; Davidson, Kris

Eta Carinae (Eta) is one of the most remarkable of all well-studied stars and perhaps the most poorly understood. Observations with the Hubble Space Telescope and other modern instruments have solved a few of the mysteries concerning this object while opening a comparable number of new ones. In this review we first recount some essential backgroun…