Search Publications
Missions
Journals
Publication Years
A different view of plasma flow inside P/Halley
Balsiger, H.; Neubauer, F. M.; Ip, W. -H. +4 more
The Giotto spacecraft carried two different instruments - the JPA and the IMS - for the observation of hot ions in the coma of P/Halley. Although there are many similarities in the time and distance profiles of the plasma flow parameters (bulk velocity, number density, and temperature) computed from the two data sets, there are also some significa…
X-ray variability in a sample of Seyfert 1 type AGN.
Walter, R.; Courvoisier, T. J. -L.
X-ray observations of several Seyfert 1 type AGN observed many times with EXOSAT are presented and analysed. The spectral parameters are extracted independently in the medium and soft X-ray spectral ranges. The variations observed in the two spectral bands and their relation are discussed and compared to the spectral variations observed in other w…
Solar system objects observed by HIPPARCOS
Bec-Borsenberger, A.
While the vast majority of objects contained in the Hipparcos observing program are stars, 48 minor planets and two satellites of the major planets are also observable and included within the observing program. These observations have very particular scientific values, and the inclusion of the objects in the Input Catalogue have posed very specifi…
Jovian Bremsstrahlung X rays: A Ulysses prediction
Stern, S. A.; Hurley, K. C.; Sommer, M. +2 more
The Jovian aurora is the most powerful planetary aurora in the solar system; to date, however, it has not been possible to establish conclusively which mechanisms are involved in the excitation of the auroral emissions that have been observed at ultraviolet, infrared, and soft X ray wavelengths. Precipitation of Iogenic heavy sulfur and oxygen ion…
Intrinsic chromospheric emission from dzeta Aurigae binaries.
Eaton, Joel A.
The question of whether the eclipses of Zeta Aur binaries reveal information about the chromospheres of single stars is addressed. It is concluded that Al II 2669 A, and the fluorescent iron lines, as well as CI II 2325 A are formed by the intrinsic thermal processes of the chromospheres of the K supergiant components of the Zeta Aur binaries. Tha…
AL II Emission-Line Strengths in Low-Density Astrophysical Plasmas
Feibelman, W. A.; Keenan, F. P.; Harra, L. K. +1 more
Theoretical values of the emission-line ratio R are derived for the transitions 3s2 1S-3s3p 3P2 and 3s2 1S-3s3p 3P1 in Al II, at 2660 and 2669 A, respectively. These ratios are compared with IUE observations of the planetary nebula NGC 7027 and the symbiotic star RR Tel, to illustrate the usefulness of the R as an electron density diagnostics. A v…
HIPPARCOS photometry - NDAC reductions
van Leeuwen, Floor; Hog, E.; Penston, Margaret J. +2 more
The Hipparcos mission will provide astrometry for about 120,000 stars. It will also give very accurate photometry for these stars. The resulting data base will by far surpass any existing photometric catalog, both in accuracy and number of stars measured. This paper describes the calibrations and initial reductions of the photometry carried out by…
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…