Search Publications
Complex Mg II Absorption in the Outer Disk of M61
Bowen, David V.; Pettini, Max; Blades, J. Chris
The increasing availability of high-quality spectra of QSO absorption-line systems at resolutions of only a few kilometers per second is expected to facilitate the translation of the kinematics of components comprising the lines into the spatial distribution of gas around an absorbing galaxy. In this Letter we present Hubble Space Telescope (HST) …
Non-LTE model chromospheres of zeta Aurigae stars
Marshall, K. P.
Plane-parallel, one-component, non-local thermodynamic equilibrium (LTE), semi-empirical model chromospheres have been constructed for the primary stars in the zeta Aurigae systems HR 6902 and 22 Vul. This has been accomplished by means of radiative transfer calculations undertaken with a non-LTE multilevel radiative transfer code, MULTI, and curv…
Mg Emission from Hybrid-Chromosphere Stars: 1.5 Decades of Chromospheric Variability Monitoring
Ayres, Thomas R.; Bennett, Philip D.; Brown, Alexander +2 more
We present an analysis of the available long-wavelength, high-dispersion spectra of seven hybrid-chromosphere stars obtained with the International Ultraviolet Explorer between 1978 and 1993. Our investigation of the variability of the Mg II h and k resonance doublet demonstrates that the emission- line fluxes are not rotationally modulated with t…
Revised chemical models of ζ Oph based on HST data
Williams, D. A.; Wagenblast, R.
Hubble Space Telescope observations by Savage, Cardelli and Sofia (1992) and Cardelliet al. (1993) have led to improved gas phase abundances for many elements in the diffuse cloud towards the star ζ Oph. Most remarkably, it was found that oxygen is much more strongly depleted than previousCopernicus observations indicated. As a consequence, chemic…
Cometary ion pressure anisotropies at comets Halley and Grigg-Skjellerup
Coates, A. J.; Neubauer, F. M.; Johnstone, A. D.
Cometary water group ions are the dominant population controlling the interaction of comets with the solar wind. The distribution function of this population has important effects on the overall structure and boundaries in the comet-solar wind interaction and on the plasma wave activity produced. In this paper we present new results on the behavio…
Gamma-Ray Bursts and Very High Energy Gamma-Ray Astronomy
Hurley, K.
The current status of gamma-ray burst astronomy is reviewed briefly, with emphasis on experiments which might determine the burster distance scale. Recent observations by the EGRET experiment aboard the Compton Observatory, indicating the presence of delayed, high energy emission, are summarized. It is shown that searches for TeV emission from bur…
The IUE Spectrum of the Unusual Wolf-Rayet PG 1159--Type Star Sanduleak 3
Feibelman, Walter A.
Archival and new lUE spectra are resented for the very hot WC 0 vi star Sand 3 (= WR 72), covering the wavelength range 1170-3200 Å. Emission-line fluxes were measured and terminal wind velocities were determined from the P Cyg N V and C iv doublets. Sand 3 is known to show some of the highest excitation stellar lines in the optical region, and th…
ISOPHOT observations of R CrB: a star caught smoking.
Walker, H. J.; Richards, P. J.; Klaas, U. +2 more
R CrB is a very unusual star, being extremely hydrogen deficient and undergoing irregular deep minima in its visible light. R CrB started to undergo a fading episode in October 1995. The Infrared Space Observatory (ISO) observed the star after it had faded by 7 magnitudes. The inner, warm dust shell has been observed by ISOPHOT, using the long wav…
The CO Abundance on Neptune from HST Observations
Strobel, Darrell; Gautier, Daniel; Courtin, Régis
We have marginally detected two CO absorption bands in the UV reflection spectrum of Neptune measured by the HST Faint Object Spectrograph (FOS). They are the (1, 0) and (0, 0) Cameron bands at 1992 and 2063 Å. The interpretation of these features with a radiative transfer model-including Rayleigh, Raman, and particulate scattering processes-impli…
Low energy charged particles in the high latitude heliosphere.
Lanzerotti, L. J.; Armstrong, T. P.; Gold, R. E. +3 more
Low energy ion and electron measurements made over the south and north polar regions of the sun by the HI-SCALE instrument on the Ulysses spacecraft during its solar minimum polar passages are summarized. The polar flux levels were considerably reduced in comparison to fluxes in the vicinity of the heliospheric current sheet. Flux variations with …