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Spectroscopic binary orbits from ultraviolet radial velocities. Paper 15: LY Aurigae (HD 35921)

Stickland, D. J.; Pachoulakis, I.; Koch, R. H. +1 more

Optical and Ultraviolet Observations of 3C 279 During Outburst

McCollum, B.; Shrader, C. R.; Smith, A. G. +6 more

An ongoing program of photometric monitoring of selected active galactic nuclei has revealed a significant outburst in the optically violently variable QSO 3C 279. The event occurred during May and June of 1992, and was characterized by a peak amplitude of 2.3 mag in the R band. We obtained nearly simultaneous optical and ultraviolet spectroscopy …

A Search for Chromospheric Emission in A-Type Stars Using the Goddard High-Resolution Spectrograph

Gilliland, Ronald L.; Simon, Theodore; Landsman, Wayne B.

We have used the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) to search for chromospheric emission in the ultraviolet C II 1335 A lines of eight A-type stars. The B-V colors of these stars range from 0.12 to 0.22. We have detected emission in the spectrum of the A7 V star Altair, but in no other star. We present …

On the cross-field diffusion of ions in one- and two-dimensional hybrid simulations of collisionless shocks

Giacalone, Joe

It can be demonstrated analytically that under certain geometries used in numerical simulations of collisionless shocks in which there is at least one ignorable spatial coordinate, the transport of particles across the magnetic field is essentially zero. This notion is tested using one- and two-dimensional hybrid simulations (kinetic ions/ fluid e…

Extragalactic symbiotic systems I. IUE observations of LMC 1, N 67, SMC 3, and S 154

Vogel, M.; Morgan, D. H.

We present UV spectra of 4 symbiotic systems in the Magellanic Clouds obtained with IUE. Relative CNO abundances of the nebular material are given, and it is shown that the nature of the cool companion giant is reflected in the nebular chemistry. Estimates for the temperature and luminosity of the hot radiation source are given. Because the distan…

Low resolution IUE spectra of Wolf-Rayet stars.

Niedzielski, A.; Rochowicz, K.

We present uniformly reduced and measured equivalent widths, FWHM and observed line fluxes for 94 "single" WR stars (34 galactic WN, 22 galactic WC, 31 LMC WN and 7 LMC WC) based on the archive IUE spectra of WR stars gathered from different observational runs and from different epochs. The spectra are used for spectral classification in the ultra…

Extreme-ultraviolet spectrophotometry of HD 15638 and HR 8210 (IK Peg).

Barstow, M. A.; Koester, D.; Holberg, J. B.

The main-sequence stars HR 8210 (1K Peg) and HD 15638 have both been found to have DA white dwarf companions by observations with the lUE satellite, following their discovery as bright EUV sources by the ROSA T Wide Field Camera. Accurate estimates of the temperature and surface gravity of each white dwarf, based on the lUE data, were oniy possibl…

A new hot DA white dwarf in a region of exceptionally low HI density.

Kepler, S. O.; Fontaine, G.; Barstow, M. A. +11 more

We report the discovery of the hot DA white dwarf RE 0457-281 which has the lowest line-of-sight neutral hydrogen column density yet measured. The star was found independently by the ROSAT EUV, Montreal-Cambridge-Tololo and Edinburgh-Cape surveys. With an effective temperature of 60700 K and very soft EUV spectrum, this white dwarf resembles the w…

The Nature of the Source of CO in Comet P/Halley

Samarasinha, Nalin H.; Belton, Michael J. S.

We show by numerical simulations that the CO distribution in the coma of Comet P/Halley as measured by neutral gas mass spectrometer aboard Giotto spacecraft (P. Eberhardt et al., 1987, Astron, Astrophys, 187, 481-484) can be explained by an extended jet source originating from vent 1 in the rotational model of M. J. S. Belton et al. (1991, Icarus…

Ultraviolet stellar spectral classification using a multilevel tree neural network

Gupta, R.; Gulati, R. K.; Gothoskar, P. +1 more

Here we present a pattern classification technique based on an Artificial Neural Network (ANN) in a multi-level tree configuration to classify ultraviolet stellar spectra from the IUE Low-Dispersion Spectra Reference Atlas. Preliminary results of this technique show that 94% of the spectra have been classified correctly with an accuracy of one sub…