Search Publications
Non-LTE spectral analyses of Wolf-Rayer stars : the nitrogen spectrum of the WN6 prototype HD 192163 (WR 136).
Hamann, W. -R.; Koesterke, L.; Wessolowski, U.
Non-Local Thermodynamic Equilibrium (LTE) model calculations for Wolf-Rayet spectra of the nitrogen sequence (WN) are presented, accounting for a complex nitrogen model atom. A detailed fit to the observed spectrum of WR 136 alias HD 192163 (subtype WN6) is performed, providing an observational test of the 'standard model' which implies the ideali…
An analysis of whistler waves at interplanetary shocks
Forsyth, R.; Balogh, A.; Farrell, W. M. +2 more
We present an analysis of whistler wave magnetic and electric field amplitude ratios from which we compute wave propagation angles and energies of electrons in resonance with the waves. To do this analysis, we compute the theoretical dependence of ratios of wave components on the whistler wave propagation angle Theta for various combinations of or…
Hot Degenerates in the Montreal-Cambridge-Tololo Survey. II. Two New Hybrid White Dwarfs, MCT 0128-3846 and MCT 0453-2933, and the Nature of the DAB Stars
Kepler, S. O.; Fontaine, G.; Bergeron, P. +7 more
We report the discovery, in the course of a survey for high-latitude, ultraviolet-excess objects in the southern hemisphere, of two new hybrid DAB stars. Both objects exhibit a weak He I 4471 A line superposed onto the usual Balmer line spectrum. Analysis of the Balmer series with both homogeneous and stratified models show these stars to have spe…
Imaging the shell of nova Cygni 1992 with HST.
Paresce, Francesco
The Faint Object Camera (FOC) on the Hubble Space Telescope (HST) observed Nova Cyg 1992 on May 31, 1993 in the UV. The images reveal a bright, well defined, circular, inhomogeneous ring of emission of 0.13 sec radius centered on the star. The data indicate that the ring is most likely due to a thin, limb-brightened shell of emitting material of r…
X-Ray Continuum and Iron K Emission Line from the Radio Galaxy 3C 390.3
Elvis, M.; Fabbiano, G.; Hayashida, K. +8 more
X-ray properties of the radio galaxy 3C 390.3 were investigated using the EXOSAT and Ginga satellites. Long-term, large-amplitude X-ray intensity changes were detected over a period extending from 1984 through 1991, and high-quality X-ray spectra were obtained especially with Ginga. The X-ray continuum spectra were described with power-law model w…
On the modulated light in the intermediate polar FO Aquarii/H 2215-086.
Mukai, K.; de Martino, D.; Buckley, D. A. H. +1 more
The modulated light in the intermediate polar FO Aqr at the three periods Pspin = 20.9 min, Porb = 4.85 h and Pbeat = 22.5 min is studied in different spectral ranges to derive information on their nature. In this system the accretion geometry, with or without an accretion disc, is still a matter of debate (Hellier…
Follow-Up Observations of the Remarkable Double-Degenerate Binary LB 11146
Glenn, Jason; Liebert, James; Schmidt, Gary D.
LB 11146 is a double-degenerate binary system consisting of two white dwarfs of very similar mass and surface temperature, but widely different magnetic field strengths. In an attempt to contrain the possible evolutionary tracks of the object, time-series H-alpha spectroscopy and the DA component was obtained with a time resolution as high as 11.5…
First Hubble Space Telescope Observations of the Brightest Stars in the Virgo Galaxy M100 = NGC 4321
Casertano, Stefano; Ballester, Gilda E.; Kennicutt, Robert C. +24 more
As part of both the Early Release Observations from the Hubble Space Telescope and the Key Project on the Extragalactic Distance Scale, we have obtained multiwavelength BVR WFPC2 images for the face-on Virgo cluster spiral galaxy M100 = NGC 4321. We report here preliminary results from those observations, in the form of a color-magnitude diagram f…
Ultraviolet Spectra of HZ Herculis/Hercules X-1 from HST: Hot Gas during Total Eclipse of the Neutron Star
Anderson, Scott F.; Blair, William P.; Halpern, Jules P. +3 more
The Faint Object Spectrograph (FOS) aboard Hubble Space Telescope (HST) has been used in the UV to observe the prototypical X-ray pulsar Her X-1 and its companion HZ Her. Optical spectra were also obtained contemporaneously at the Kitt Peak National Observatory (KPNO) 2.1 m. The FOS spectra encompass the 1150-3300 A range near binary orbital phase…
The induced magnetosphere of comet Halley: Interplanetary magnetic field during Giotto encounter
Neubauer, F. M.; Israelevich, P. L.; Ershkovich, A. I.
Direction of the interplanetary magnetic field (IMF) which governs the orientation of the Halley's magnetosphere was restored by using Giotto magnetic field data. The Giotto trajectory was a twisted curve in the coordinate system rotating with IMF vector and covered rather uniformly the transverse cross section of the comet. Magnetic field vectors…