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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…
The chemical composition of the lambda Bootis stars.
Baschek, B.; Slettebak, A.
Measurements of the equivalent widhts of 24 UV lines from IUE spectra of 10 λ Bootis or suspected λ Bootis stars and 19 normal standard stars of spectral types B8-A7 are compared with line strengths calculated from model atmospheres. The light elements (C, N, and O) in the λ Boo stars are in the range slightly overabundant relative to the standard…
Co-ordinated VLA and EXOSAT observations of the flrae stars UV Ceti, EQ Pegasi, YZ Canis Minoris and AD Leonis.
Pallavicini, R.; Kundu, M. R.; White, S. M. +1 more
The authors have observed four flare stars (UV Cet, EQ Peg, YZ CMi and AD Leo) simultaneously with the VLA and the EXOSAT satellite over continuous periods of 7 - 10 h. This is the first time that flare stars were observed simultaneously in X-rays and at microwave frequencies with high sensitivity instrumentation. All stars were detected both at t…
Time variability in the X-ray emission of dM stars observed by EXOSAT.
Schmitt, J. H. M. M.; Pasquini, L.; Collura, A.
The authors studied the variability in the X-ray emission of 13 dMe stars observed with the LE+CMA onboard EXOSAT. The basic aim of this paper is to search for frequently occurring impulsive events with small energy releases in an effort to find out whether the "quiescent" X-ray emission from dM stars is really quiescent. The authors do not find, …
Rotational modulation and flares on RS CVn and BY DRA stars. IX. IUE spectroscopy and photometry of II Peg and V711 Tau during February 1983.
Linsky, J. L.; Catalano, S.; Rodono, M. +11 more
Evidence is presented for spots, plages, and flares on the noneclipsing RS CVn system II Peg and V 711 Tau. The large spot originally found on II Peg in 1981.8 could still be identified in 1983. Two spectroscopic flares of II Peg were detected. For the larger flare the fluxes in the strongest transition-region lines reached about six times their q…
IUE low resolution observations of the symbiotic star CH Cygni in 1979-1986.
Hack, M.; Mikolajewska, J.; Selvelli, P. L.
Data from IUE observations of the semiregular variable CH Cyg are presented compiled in extensive tables and graphs and analyzed with reference to theoretical models. The UV/optical continuum emission is accounted for by combining a Kurucz (1979) low-gravity A-type model atmosphere at Te = 8500-9000 K with hydrogen bound-free + free-free emission …
A correlation between Balmer and soft X-ray emission from stellar andsolar flares.
Foing, B. H.; Rodono, M.; Butler, C. J.
Simultaneous optical spectroscopy and X-ray monitoring of stellar and solar flares shows that a well-defined linear correlation exists between the integrated Hγ and soft X-ray flux that extends over four orders of magnitude. The existence of this relationship implies a direct proportionality between the emission from the cooler and denser regions …