Search Publications
A Deconvolution Technique for Hubble Space Telescope FGS Fringe Analysis
Hershey, John L.
A technique has been developed for directly transforming interferometer fringe visibility functions (``S-curves") from the HST Fine Guidance Sensors (FGSs) into intensity profiles of the program object. In a process analogous to Fourier transform image deconvolution, an S-curve from a double star yields a pair of narrow profiles containing informa…
The HIPPARCOS Input Catalogue. II. Astrometric Data.
Le Poole, R. S.; Jahreiß, H.; Argue, A. N. +12 more
A positional accuracy of 1.5 arcsec rms at the epoch of observation was required for the stars proposed for observation by the Hipparcos satellite. How this was achieved by collecting and investigating already available positions and proper motions in a special compilation catalog, carrying out new ground-based measurements, and a detailed analysi…
The Luminosity of the Classical Cepheid T VUL
Evans, Nancy R.
The classical Cepheid T Vul has been discovered to have a hot companion on International Ultraviolet Explorer satellite spectra. The companion has a spectral type of A0.8 V. The absolute magnitude of the Cepheid determined from the companion is Mv = -3.43 mag. Because the companion is significantly fainter and less massive than the Ceph…
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…