Search Publications
Low frequency magnetic signals associated with Langmuir waves
Balogh, A.; Goetz, K.; Forsyth, R. J. +4 more
With the URAP experiment on Ulysses, we have observed low frequency signals with a magnetic component in close time correlation with electrostatic Langmuir waves at the plasma frequency. In most, if not all, of these cases, the Langmuir waves are part of a Type III solar burst. We investigate this effect and show that the low frequency waves are i…
Non-LTE line formation for iron group elements.
Butler, K.; Becker, S. R.
A non-LTE line formation calculation for Fe v is introduced. The data for radiative bound-bound transitions which have been derived as part of this work are described and their accuracy is evaluated. The theoretical non-LTE spectrum of Fe v is compared to the HST spectrum of the sdO star BD + 75 deg 325 resulting in a determination of the iron abu…
The Coolest DA White Dwarfs Detected at Soft X-Ray Wavelengths
Barstow, M. A.; Wesemael, F.; Holberg, J. B. +2 more
New soft X-ray/EUV photometric observations of the DA white dwarfs KPD 0631 + 1043 = WD 0631 + 107 and PG 1113 + 413 = WD 1113 + 413 are analyzed. Previously reported soft X-ray detections of three other DAs and the failure to detect a fourth DA in deep Exosat observations are investigated. New ground-based spectra are presented for all of the obj…
Ultraviolet and Optical Spectral Morphology of Melnick 42 and Radcliffe 136a in 30 Doradus
Walborn, Nolan R.; Ebbets, Dennis C.; Parker, Joel Wm. +2 more
HST/GHRS ultraviolet spectrograms of the individual O3 If */WN6-A object Mk 42 in 30 Dor and the adjacent, central multiple system R136a are compared with each other and with an appropriate sequence of O3 If* and WN6-A standards from the IUE archive. The analogous spectral montages covering the blue-violet region, based on new, homogeneous, digita…
Ulysses plasma observations of coronal mass ejections near 2.5 AU
Balogh, A.; McComas, D. J.; Forsyth, R. J. +5 more
The Ulysses solar wind plasma experiment observed a series of interplanetary shocks and coronal mass ejections (CMEs), the latter evidenced by counterstreaming electrons and a variety of ion signatures, during March and April 1991. A striking sequence was observed near 2.5 AU from March 23 through April 2, with the second of two counterstreaming e…
Stratification of chemical elements in the atmosphere of the AP star 53 Camelopardalis.
Babel, J.; Lanz, T.
A detailed abundance analysis of Cr, Fe, Mn, Ca, and Ti in the Ap star 53 Cam from IUE high-resolution spectra has been performed. It is found that UV lines give significantly lower abundance than visible lines for Cr and Fe. Theoretical spectra of Cr II line calculated with the stratified chromium abundance distributions predicted a priori by the…
The outer atmospheres of the 'hybrid' bright giants : the chromospheres of alpha TrA (K4 II), IOTA AUR (K3 II), gamma AQL (K3 II) , and theta HER (K1 II).
Harper, Graham M.
Detailed models of the chromospheres of several 'hybrid' bright giants are presented. The models extend from the base of the chromosphere and into the transition area. These chromospheric models are based on radiative transfer calculations for a range of atoms and emission lines. The presence of steep turbulent velocity gradients leads to profiles…
Far-Ultraviolet Observations of the Crab Nebula Using the Hopkins Ultraviolet Telescope
Blair, William P.; Kriss, Gerard A.; Davidsen, Arthur F. +5 more
Observations of the FUV spectrum of the central portion of the Crab Nebula SNR using the Hopkins Ultraviolet Telescope (HUT) aboard the Astro-1 space shuttle mission in December 1990 are reported. The C IV 1549-A emission line shows two resolved components representing the front and back sides of the shell expanding at roughly +/- 1100 km/s. The H…
R Aquarii : an attempt at a unified model.
Burgarella, D.; Vogel, M.; Paresce, F.
Consideration is given to a new model of R Aqr in which the binary system is composed of an M7 Mira with a mass of about 1.5 solar mass, a temperature of about 2800 K, a bolometric magnitude of about -4.56, and a radius of about 300 solar radii, plus a hot stellar source in an intermediate phase between a subdwarf and a white dwarf with a radiatio…
Time dependence of the UV resonance lines in the cataclyspic variables YZCnc, IR GEM and V 3885 Sgr.
Verbunt, F.; Collier Cameron, A.; Woods, J. A. +2 more
Orbital variations are observed in the UV resonance lines of YZ Cnc, IR Gem and V3885 Sgr. Optical spectroscopic observations of YZ Cnc show that the maximum absorption in the UV lines occurs about 0.7-0.8 orbits after the transition from red to blue of the optical emission lines. IR Gem shows orbital variations in the UV lines that are as strong …