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The peculiar UV and optical spectrum of the LMC supergiant HD 269216.
Prinja, R. K.; Schild, H.
Low resolution IUE UV and optical observations are presented of HD 269216, the visually brightest member of the LH 39 association in the LMC. Although the UV and optical line spectra are broadly consistent with a B 8 Ia spectral type for HD 269216, the classification is complicated by several discrepancies. The observed UV continuum flux distribut…
Leptonic origin of diffuse galactic high-energy gamma rays - Indications for a varying cosmic ray proton-to-electron ratio
Schlickeiser, R.; Pohl, M.
The flux of high-energy (more than 300 MeV) gamma rays - caused by nonthermal bremsstrahlung and inverse Compton scattering - and the synchrotron flux at 408 MHz are calculated with the same power-law spectrum of relativistic electrons. Both are compared with the values observed at higher latitudes in the anticenter direction by employing the COS-…
Pollution of P Cygni profiles by Fe IV and FeV photospheric absorption inthe ultraviolet spectrum of O-type stars.
Surdej, J.; Nemry, F.; Hernaiz, A.
It is reported that the main pollution in the spectral ranges 1270-1500 and 1500-1860 A is caused by photospheric absorption lines of FeV and FeIV, respectively. Making use of the first order moment W1 of a P Cygni line profile, it is shown that the effect of this photospheric pollution may lead to systematic errors, exceeding typically 50 percent…
Quiscent and flaring X-rays from both Gliese 867A and Gliese 867B.
Tagliaferri, G.; Pallavicini, R.; Pollock, A. M. T.
X-ray observations of the flare-star binary system Gliese 867AB obtained with the Low Energy instrument on the Exosat Observatory were analyzed. By applying a likelihood method, it is shown that both components of the system were contributing to the observed X-ray emission with an intensity ratio A:B of about 3:1. It is also shown that X-ray flare…
Chromospheric activity in δ Scuti stars: the suspected variable τ Cygni.
Fracassini, M.; Pastori, L.; Pasinetti Fracassini, L. E. +2 more
High-resolution IUE spectra of the suspected variable τ Cyg were obtained to search for a possible variability of the Mg II h, k double-peaked emission. The observations, spanning an interval of about 6.3 h, have shown flux excursions within or just near 15%, value suggested by some authors as limit to detect actual variations with IUE spectra. A …
The "noisy" pulsar in HER X-1.
Belloni, T.; Kahabka, P.; Hasinger, G.
The results of a comparative analysis of coherent and noncoherent variations in the X-ray emission of Hercules X-1 are presented, based on Exosat archive data. In the broad band power spectrum of the source a strong noise component, variable with the 35-days cycle, is present. These changes, and the relation between the noise rms and the pulsed rm…
X-ray spectrum of the radio-loud quasar PKS 1217+023.
Ghosh, K. K.; Soundararajaperumal, S.
A study of the X-ray (0.1-10 keV) spectrum from the radio-loud quasar, PKS 1217+023 is presented. This quasar was observed with EXOSAT on two epochs in 1984 January 29 and May 14. The data were obtained from the EXOSAT archives. The soft (0.1-2 keV) and hard (2-10 keV) X-ray fluxes have displayed significant changes between the two observations. T…
EXOSAT observations of the quasar PKS 2135-147
Singh, K. P.; Rao, A. R.; Vahia, M. N.
A study of X-ray emission from the low polarization quasar, PKS 2135-147 (PHL 1657), is presented based on the EXOSAT observations carried out on two occasions separated by a week in 1984. There is little evidence for any variations in the X-ray intensity on hourly time scales during either of the two observations. About 30% change in the soft X-r…
The discovery of a hot companion to the K-type supergiant HD 4817.
Cassatella, A.; Smolinski, J.
The discovery, through observations with the International Ultraviolet Explorer, of a B5 main sequence companion to the cool supergiant star HD 4817 (K2Ib-II) is reported. The object might be a new member of the Zeta Aur class. The UV observations indicate that HD 4817 is quite heavily reddened (E/B - V/ = 0.52) and that its distance is 1030 +/-80…
The soft X-ray variability of NGC 5548.
Kaastra, J. S.
The soft X-ray variability of NGC 5548 is studied using EXOSAT's low energy telescope in conjunction with the channel multiplyer array (CMA). For the first time, the pulse height distribution of the CMA data is used to infer information on the spectral variability. The spectrum of NGC 5548 consists of a hard power law and a soft component. During …