Search Publications
A link between X-ray variability and ultraviolet emission in Seyfert 1 type AGN.
Walter, R.; Courvoisier, T. J. -L.
We analyse the behaviour of X-ray spectral variations in Seyfert 1 type active galactic nuclei observed many times in the 2-10 keV energy band. The selected sources are compatible with a separation into two groups distinguished by different kinds of X-ray variability and by different ratios of ultraviolet to X-ray fluxes. In the first group of obj…
Comparison of the first results from the HIPPARCOS star mappers with the HIPPARCOS Input Catalogue
Evans, D. W.; Arenou, F.; van Leeuwen, F. +1 more
Preliminary positions and magnitudes derived from the analysis of 12 weeks of observations from the Hipparcos star mappers are systematically compared with the various sources of ground-based data used in the Hipparcos Input Catalogue. These comparisons allow us to cross-check the accuracies claimed by the various sources of ground-based data and …
X-ray spectrum of NGC 3783 : detection of soft excess and an emission line.
Ghosh, K. K.; Soundararajaperumal, S.; Sivarani, T. +1 more
Results of the X-ray (0.1-10 keV) spectral analysis of the Seyfert I galaxy, NGC 3783, which was observed with EXOSAT on three epochs between 1983 and 1985, are presented here. No low energy absorption, intrinsic to the source, was found in this galaxy and the spectral index of the power law fit did not vary during the EXOSAT observations. Soft ex…
AI II as an electron density diagnostic for the upper chromosphere/lower transition region in late-type stars.
Doyle, J. G.; Keenan, F. P.; Harra, L. K. +2 more
The ratio of the Al II resonance line 3s2 1S-3sp 1P1 at 1670 A to the inter-system line 3s2 1S-3s3p 3P1 at 2669 A is a useful electron density diagnostic for N(e) greater than 10 exp 10/cu cm. However, it is also sensitive to the adopted electron temperature, and, in fact, should be a useful electron temperature diagnostic when Ne is not greater t…
Imaging Observations of Jupiter's Sodium Magneto-Nebula During the Ulysses Encounter
Mendillo, Michael; Flynn, Brian; Baumgardner, Jeffrey
Jupiter's great sodium nebula represents the largest visible structure traversed by the Ulysses spacecraft during its encounter with the planet in February 1992. Ground-based imaging conducted on Mount Haleakala, Hawaii, revealed a nebula that extended to at least ±300 Jovian radii (spanning ~50 million kilometers); it was somewhat smaller in scal…
Bartkevicius A., Sperauskas J., Rastorguev A.S., Tokovinin
Rastorguev, A. S.; Bartkevicius, A.; Sperauskas, J. +1 more
Radial velocity measurements are presented for 81 Population II stars. The sample comprises components of metal-poor binary stars, spectroscopic binary candidates, high latitude supergiants, metal-deficient stars with spectroscopic determinations of Fe/H, HIPPARCOS program stars, and some other stars of metal-poor population. The radial velocity m…
The continuum radiation of the symbiotic star AG Draconis in quiescence and during outbursts.
Leibowitz, E. M.; Formiggini, L.
Results of spectroscopic measurements of the continuum radiation of the symbiotic star AG Dra in the UV and optical regions are presented. The observations extend over a period of eight years and cover the quiescent state of the star as well as three outbursts which occurred during those years. The results suggest that outbursts of AG Dra are trig…
The Ionization Conditions in the Milky Way Halo: Infalling Gas toward the North Galactic Pole
Danly, Laura
The observations of gas in the Milky Way are reviewed with an eye toward the theoretical predictions of the Galactic Fountain model for the production of halo gas. Data are shown which indicate significant variations in the ionization conditions in infalling halo gas in the northern galactic hemisphere. Besides being interesting in its own right, …
EXOSAT Observations of the Broad-Line Radio Galaxy 3C 382
Ghosh, K. K.; Soundararajaperumal, S.
X-ray observations of the broad-line radio galaxy 3C 382 were carried out with EXOSAT on many occasions (>20) between 1983 and 1985. Low and Medium Energy (LE and ME) spectra of this source were obtained from the EXOSAT data base. The hard-X-ray luminosity light curve of 3C 382 which was constituted from Ariel V, HEAO 1, Einstein, EXOSAT, and G…
Absorption-Line Profiles in a Companion Spectrum of a Mass-losing Cool Supergiant
Boehm-Vitense, Erika; Rodrigues, Liliya L.
Cool star winds can best be observed in resonance absorption lines seen in the spectrum of a hot companion, due to the wind passing in front of the blue star. We calculated absorption line profiles that would be seen in the ultraviolet part of the blue companion spectrum. Line profiles are derived for different radial dependences of the cool star …