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The radial distribution of galactic gamma rays. IV. The whole galaxy.
Strong, A. W.; Grenier, I. A.; Hermsen, W. +6 more
The correlation between diffuse galactic γ-rays and gas tracers is studied using the final COS-B database and H I and CO surveys covering the entire galactic plane. A good quantitative fit to the γ-rays is obtained, with a small gradient in the γ-ray emissivity per hydrogen atom. The average ratio of H2 column density to integrated CO t…
The beta Pictoris circumstellar disk. VI. Evidence for material falling on to the star.
Ferlet, R.; Vidal-Madjar, A.; Lagrange-Henri, A. M.
New archive observations with International Ultraviolet Explorer are used to study the temporal variations of the circumstellar absorption towards β Pictoris. The authors first show that strong variations occur in the redshifted part of the resonance lines of Al III, Mg II, and Fe II, and also of metastable lines of Fe II. These variations are the…
Relative C, N, O abundances in red giants, planetary nebulae, novae and symbiotic stars.
Vogel, M.; Nussbaumer, H.; Schild, H. +1 more
C/N and O/N abundance ratios deduced from UV data are presented for 24 symbiotic stars. There is little scatter in these ratios, indicating that the symbiotic phenomenon only occurs in a well defined evolutionary stage. Comparison with related objects such as red giants, novae, and planetary nebulae reveals that symbiotic objects best fit the CNO …
Rotational modulation and flares on RS CVn and BY DRA systems. VII. simultaneous X-ray, radio and optical data for the dMe star YZ CMi on 4/5 March 1985.
Doyle, J. G.; Butler, C. J.; van den Oord, G. H. J. +1 more
Broad-band photometric observations of YZ CMi show a 1.2mag U-band flare at 19:55 UT on 4 March 1985, however, simultaneous X-ray observations from EXOSAT show no detectable increase. Two possible explanations for the lack of an X-ray flare may be i) a flare occurring low in the chromosphere, where the chromosphere may not have been coupled to the…
A non-LTE stellar atmosphere study of nitrogen-rich early-type stars.
Butler, K.; Kudritzki, R. P.; Herrero, A. +4 more
Spectrograms of a sample of nitrogen-rich early type stars (OBN stars) are analyzed differentially to normal stars of similar spectral types by means of NLTE methods. Effective temperatures, gravities and atmospheric helium contents are derived by fitting theoretical profiles of hydrogen and helium lines to the observations. The abundance analysis…
An EXOSAT observation of an X-ray flare and quiescent emission from the RS CVn binary sigma2 CrB.
Mewe, R.; Brinkman, A. C.; van den Oord, G. H. J.
The RS CVn binary sigma2 Coronae Borealis was observed with medium-energy and low-energy detectors and the transmission grating spectrometer aboard EXOSAT, and a strong X-ray flare rising within about five minutes and lasting more than two hours was detected. The temperature rises steeply within three minutes from 19 MK to a value well above 70 MK…
Stellar coronae with EXOSAT : broad band spectroscopy of nearby coronal sources.
Schmitt, J. H. M. M.; Monsignori-Fossi, B. C.; Landini, M. +1 more
Broad-band observations of stellar coronae obtained with the Low Energy experiment on board the Exosat satellite are presented, together with a technique for the analysis of Exosat low-energy data. The limitations of filter spectroscopy with Exosat are discussed. Specific relationships are provided for extracting physical quantities (temperature, …
High energy gamma rays from the VELA pulsar : long-term variability and energy distribution.
Grenier, I. A.; Hermsen, W.; Clear, J.
New results on the temporal and spectral characteristics of the high energy (50 MeV to 5 GeV) gamma ray emission from the Vela pulsar are presented. A new sensitive analysis method using maximum likelihood techniques has been applied to the final COS-B dataset. The whole pulsed flux is found to exhibit long term variability. The energy spectrum of…
Ultraviolet observations of AM Her.
Heise, J.; Verbunt, F.
Observations of AM Her at different flux levels obtained with IUE are presented. From the observations obtained at the lowest flux level, an upper limit to the white dwarf temperature of about 20,000 K, is derived, confirming an earlier temperature determination by Schmidt et al. (1981) from optical spectrophotometry. The increased flux levels at …
Optical polarimetry of P/Halley - Synthesis of the measurements in the continuum
Le Borgne, J. -F.; Bastien, P.; Levasseur-Regourd, A. C. +2 more
Ground-based observations of the linear polarization of P/Halley in the continuum by several independent groups of observers are analysed in common to produce synthetic polarization data. Curves of polarization as a function of phase angle are derived for the bright envelope around the nucleus, for the dust grains after they emerge from this envel…