Search Publications
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 …
Astrometry using the hubble space telescope fine guidance sensors
Benedict, G. F.; Hemenway, P. D.; Jefferys, W. H. +2 more
The U. S. National Aeronautics and Space Administration in a cooperative effort with the European Space Agency has developed a large optical telescope with an aperture of 2.4 meters and a length of 8.8 meters. This instrument, the Hubble Space Telescope was launched by the space shuttle (STS-31) on the morning of 24 April 1990 and was placed in ea…
Ultraviolet observations of cataclysmic variables
Verbunt, Frank
The ultraviolet spectra of cataclysmic variables provide us with information on the mass transfer in these systems, and on the variations therein on different time scales. The combined ultraviolet and optical spectra cannot be fitted with simple model spectra, and accordingly, our interpretations of the observed spectra are subject to uncertainty.…
Scientific requirements for very accurate astrometry
Turon, C.; Kovalevsky, J.
Two types of accurate astrometric data are considered:
1) Survey astrometry providing absolute parallaxes and annual proper motions with an accuracy of 2 milli-arcsec, to a few tenth of a milli-arcsec. Parallax determinations will advance our basic knowledge of the Universe by giving the necessary strong foundations for the first steps of the…The EXOSAT GSPC Iron Line Catalogue
White, N. E.; Gottwald, M.
X-Ray Observations of the Seyfert 1 Galaxy Markarian 464
Piro, L.; Frontera, F.; Costa, E. +3 more
In this paper we present results of EXOSAT (0.05-10 keV) and hard X- ray (25-45 keV) balloon observations (XG-8 1) of the Seyfert 1 galaxy Mrk 464. The spectrum observed with EXOSAT is well fitted by a power law with a photon spectral index 1.70+/-0.15, in agreement with a previous measurement by HEAO 1 A-2. The absorption column density is found …
Doublet 2800 Mg II in close binary systems
Perez, M.; Gurzadian, G. A.
It is shown that the emission ultraviolet doublet 2800 MgII in radio stars, actually in close binary systems, do not have chromospheric origin, but is generated in the space between the components of the system, filled by clouds or streams of two types — emission (A) and absorption (B). It is shown also that the strongly deformed or distorted form…
Ultraviolet light curves of V535 Arae
Eaton, Joel A.
Observations of V535 Ara obtained with IUE define the light curve of this long-period W UMa binary in the ultraviolet and let us estimate its gravity darkening. This star was chosen as a contact binary near the high-Teff limit for convection. The ultraviolet colours and spectral type correspond to (B‑V)0=0.24, or A8V, and imp…
UBVRI photometry of G, K, M HIPPARCOS stars. II.
Jordi, C.; Figueras, F.; Torra, J. +2 more
As indicated by Grenon (1989), the data of the present series of reports on the UBVRI photometry of late-type stars in the Hipparcos Input Catalog are to be employed in computations of Hipparcos observing time, as well as in evaluating the observability of faint stars by the satellite. Attention is here given to late type stars in the V = 8-12 ran…
Hipparcos calibration
Schrijver, Hans
The methods and results of various Hipparcos in-flight calibrations are described. The geometrical calibrations allow the determination of the instrument distortions in the main field of view to better than a milli-arcsecond. A systematic decrease of the basic angle at a rate of two milli-arcseconds per month has been measured during the first 7 m…