Search Publications
EXOSAT measurements of the pulse period of VELA X-1.
Raubenheimer, B. C.; Oegelman, H.
Seven new pulse period determinations of Vela X-1 have been made using the existing Exosat data. The measurements span one year and partly fill in the 3.2 yr gap between Tenma and Ginga measurements. The new results show that one pulse period of Vela X-1 continued with an epoch or near-constant period starting in 1981 and lasting up to at least Ma…
First observations of a corona of a cool bright giant with height resolution.
Reimers, D.; Baade, R.; Schroeder, K. -P. +1 more
Two time series of observations of the corona of HR 6902, as seen in the CIV and SiIV absorption lines during the 1988 and 1989 eclipses, are used to examine the density distribution of the expanding corona as a function of height. It is shown that the scaling laws for thermally driven winds predict coronal densities and mass-loss rates too low by…
The UV spectrum of the WC 11 star CPD -56 8032.
Nandy, K.; Kameswara Rao, N.; Giridhar, S.
UV observations of the WC 11 central star of the compact planetary nebula CPD -56 deg 8032 show that the continuum flux is variable. This variability appears to be caused by a change in the circumstellar extinction properties. The UV energy distribution can be fitted with helium star models with T(eff) about 25000 K, after correcting for two types…
X-ray spectra of three BL Lac objects.
Maccagni, D.; Garilli, B.
We present the results of the analysis of twin EXOSAT observations of three BL Lac objects, namely PKS 0521-365, PKS 0548-322, and I Zw 186. The energy spectra between 0.02 and ~ 7 keV can generally be described by power laws with a low energy cut off due to absorption by hydrogen in our galaxy. However, while PKS 0521-365 has a spectrum with an e…
Off-nucleus IUE observations of NGC 1275.
Norgaard-Nielsen, H. U.; Jorgensen, H. E.; Hansen, L.
We have mapped the brightest parts of the two velocity systems of ionized gas in NGC 1275 with IUE. We have detected extended Lyα and an UV continuum at several positions. The Lyα emission originates from the low velocity system and, we argue, probably also the UV continuum. The UV continuum is consistent with star bursts with ages <= 2 10^7^ y…
Extinction-independent determination of temperatures for central stars of planetary nebulae.
Grewing, M.; Neri, R.
A method to determine temperatures for central stars of planetary nebulae from ultraviolet color indices which are essentially extinction-independent is described and applied. Using a standard extinction law (Seaton, 1979) and assuming that the continuum emission from the nuclei of planetary nebulae can be approximated by black-body distributions,…
Activity in late-type stars. V. Rotational modulation and flaring in UV lines on the most rapidly rotating dMe star, GL 890 (BD -16 6218).
Byrne, P. B.; McKay, D.
A series of UV spectra of GI 890 taken at two epochs separated by more than two years (on October 11-13, 1984 and on December 26, 1986) where obtained by the IUE satellite and using both the spectrograph's short-wavelength and long-wavelength cameras. Based on these data, the energy balance in the star's magnetically heated chromosphere and the tr…
Activity in late-type stars. VII. Chromospheric and transition region line fluxes in 2 dM and dM(e) stars.
Doyle, J. G.; Byrne, P. B.
Ultraviolet spectra of the two dM stars Gl380 and Gl411 and the dM(e) Gl900 are presented. The dM stars show mean surface fluxes in a variety of emission lines arising throughout the chromosphere and the lower transition region which are very similar to those of the quiet sun. In the one star in which it could be determined the electron density at…
EXOSAT observation toward S 147 and A 0535+26.
Ballet, J.; Rothenflug, R.; Sauvageot, J. L.
Observations have been made in the direction of the old SNR S 147 with the X-ray satellite Exosat. No emission was detected with the low-energy experiment, constraining the SNR parameters (energy and ambient density) for a Sedov model or a radiative one. A weak source was detected with the medium-energy experiment which could be associated with th…
Similarities in the wind characteristics of hot stars.
Prinja, R. K.
The direct observational similarities in the characteristics of winds in a wide selection of hot stars are considered. Data are presented which demonstrate that discrete absorption components are observed in the UV resonance line profiles of WR stars, WR + O type binaries, B supergiants, B emission-line stars, subdwarf O stars, and the central sta…