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HIPPARCOS parallaxes and the nature of δ Scuti stars.
Hog, E.; Petersen, J. O.
Hipparcos parallaxes give new tests of the nature of δ Sct variables. For many individual stars accurate distances are now available, i.e. directly determined luminosities and radii can be used to test theoretical models. Of particular interest are the at present very unclear relations between high-amplitude δ Sct stars and the much more abundant …
Lyα-induced Fluorescence of H2 and Co in Hubble Space Telescope Spectra of a Comet Shoemaker-Levy 9 Impact Site on Jupiter
Wolven, Brian C.; Feldman, Paul D.; Strobel, Darrell F. +1 more
Far-ultraviolet spectra of Jupiter obtained on 1994 July 20 in the region of the Shoemaker-Levy 9 G-fragment impact site contain features that differ markedly from the typical Jovian dayglow spectrum. These features are identified as fluorescence of H2 due to pumping by solar Lyα photons, which requires the presence of a substantial pop…
Correlated X-ray spectral and fast-timing behaviour of 4U 1636-53.
van der Klis, M.; Prins, S.
We present a study of the persistent X-ray emission from the low-mass X-ray binary 4U 1636-53 based on the entire archival EXOSAT ME data set. We performed a homogeneous analysis of all five EXOSAT observations in terms of the correlated rapid X-ray variability and X-ray spectral properties by means of power spectra, and colour-colour and hardness…
Infrared Observations Of Volatile Molecules In Comet Hale-Bopp
Crovisier, J.
Infrared observations of comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp) benefited from the high spectral resolution and sensitivity of échelle spectrometers now equipping ground-based telescopes and from the availability of the Infrared Space Observatory (ISO). From the ground, several hydrocarbons were unambiguously detected for the first…
Temperatures and Altitudes of Jupiter's Ultraviolet Aurora Inferred from GHRS Observations with the Hubble Space Telescope
Fox, J. L.; Caldwell, John J.; Kim, Y. H.
We observed the jovian UV auroral regions with the Goddard high resolution spectrograph (GHRS) on board the Hubble Space Telescope (HST) on Apr. 29, May 2, and June 10, 1995. Observations of target areas were made in pairs in the two wavelength ranges 1257-1293 Å and 1587-1621 Å. Spectra in the long wavelength range are dominated by emissions of t…
On the Nature of the Strong Emission-Line Galaxies in Cluster CL 0024+1654: Are Some the Progenitors of Low-Mass Spheroidals?
Koo, David C.; Gallego, Jesús; Wirth, Gregory D. +1 more
We present new size, line ratio, and velocity width measurements for six strong emission-line galaxies in the galaxy cluster, Cl 0024+1654, at redshift z ~ 0.4. The velocity widths from Keck spectra are all narrow (30 <~ σ <~ 120 km s-1), with three profiles showing double peaks. Four galaxies have low masses (M <~ 1010
Ultraviolet Imaging Observations of the cD Galaxy in Abell 1795: Further Evidence for Massive Star Formation in a Cooling Flow
O'Connell, Robert W.; Bohlin, Ralph C.; Smith, Andrew M. +5 more
We present images from the Ultraviolet Imaging Telescope (UIT) of the Abell 1795 cluster of galaxies. We compare the cD galaxy morphology and photometry of these data with those from existing archival and published data. The addition of a far-UV color helps us to construct and test star formation model scenarios for the sources of UV emission. Mod…
The Absence of Diffuse Gas around the Dwarf Spheroidal Galaxy Leo I
Bowen, David V.; Ferrara, Andrea; Blades, J. Chris +2 more
We have obtained spectra of three QSO/AGNs with the GHRS aboard the Hubble Space Telescope to search for absorption from low column density gas in the halo of the dwarf spheroidal (dSph) galaxy Leo I. The probe sight lines pass 2.1, 3.7, and 8.1 kpc from the center of the galaxy, but no C IV, Si II, or Si IV absorption is found at the velocity of …
Quasar Variability and Gravitational Microlensing
Taylor, A. N.; Hawkins, M. R. S.
In this Letter we examine the claim by Baganoff & Malkan that the timescale of brightness variations of quasars increases with decreasing optical wavelength, and that this effect can offset a time dilation effect at high redshift. They base their case on a thin accretion disk model that implies that timescales become shorter as the observed pa…
Boron Abundances of B Stars of the Orion Association
Gies, Douglas R.; Cunha, Katia; Lambert, David L. +2 more
The boron abundance of four B-type stars from the Orion association has been determined from Goddard High Resolution Spectrograph (GHRS)/Hubble Space Telescope (HST) spectra covering the B II 1362 Å resonance line. After correction for large non-LTE effects, the mean boron abundance is similar to the meteoritic abundance, but a factor of 4 (0.6 de…