Search Publications
Rest-frame variability of quasars and Seyfert galaxies in the ultraviolet: constraints on the discrete-event models.
Paltani, S.; Courvoisier, T. J. -L.
A study of the ultraviolet continuum variability (Paltani & Courvoisier, 1994A&A...291...74P) has shown that the relative variability of quasars and Seyfert galaxies decreases when the luminosity increases. The spectral information included in the IUE spectra allows us to study this dependence in the rest frame of the objects. The trend is…
Low-mass stars and star clusters in the dark Galactic halo
Kerins, E. J.
In a previous study it was proposed that the Galactic dark matter being detected by gravitational microlensing experiments such as MACHO may reside in a population of dim halo globular clusters comprising mostly or entirely low-mass stars just above the hydrogen-burning limit. It was shown that, for the case of a standard isothermal halo, the scen…
HST confirmation of the lensed quasar J03.13.
Surdej, J.; Claeskens, J. -F.; Remy, M. +4 more
In order to definitely prove the claim by Claeskens et al. (1996A&A...305L...9C) that J03.13 is a doubly imaged quasar, WFPC2 direct imaging and FOS spectroscopy of this compact system have been obtained with HST. These textbook case observations clearly show that J03.13 consists of two point-like images separated by 0.849"+/-0.001" with a mag…
Mass and radius of the white dwarf in the binary V471 Tau from ORFEUS and HIPPARCOS observations.
Rauch, T.; Werner, K.
We present a model atmosphere analysis of the white dwarf component in the K2V/DA eclipsing binary system V471 Tau, based upon FUV spectra obtained by the ORFEUS satellite. This system is regarded as the prototype of a post-common envelope WD+MS binary and, hence, is of considerable importance for our understanding of close binary evolution. From …
Spectroscopic study of the planetary nebulae with Wolf-Rayet nuclei in the Magellanic Clouds.
Pena, M.; Torres-Peimbert, S.; Ruiz, M. T.
UV and optical spectrophotometric data of planetary nebulae with WR nuclei in the Magellanic Clouds are presented. Analysis of the nebular characteristics shows that the ionized gas, in all the objects, is extremely C-rich, probably due to contamination with freshly-made C from stellar nucleosynthesis. Very high electron densities are found (N_e_&…
Blue stars in the center of the S0 galaxy NGC 5102.
Crane, P.; Disney, M. J.; Jedrzejewski, R. +2 more
The S0 galaxy NGC 5102 has been observed with the Faint Object Camera on-board the Hubble Space Telescope. Individual blue stars have been resolved in the central region and measured photometrically through the F175W and F342w filters. The limits of detection and completeness are not uniform over the field observed because the unresolved galaxy li…
HST polarization observations of the jet of M87.
Macchetto, F. D.; Capetti, A.; Sparks, W. B. +1 more
We present the results of pre-refurbishment HST polarization observations of the jet of M 87 taken with the Faint Object Camera in the ultraviolet and with the WF/PC-I in the visual. From these observations we produce polarization maps of unprecedentedly high resolution. The structure of the projected magnetic field is extremely complex and change…
UV to X-ray spectra of radio-quiet quasars. Comparison with accretion disk models.
Brunner, H.; Staubert, R.; Mueller, C. +3 more
We present UV to soft X-ray spectra of 31 radio-quiet quasars, comprising data from the IUE ULDA database and the ROSAT pointed observation phase. 90 % of the sample members show a soft X-ray excess above an underlying hard X-ray power law spectrum. Particularly for the steep X-ray spectrum (α_energy_>1.5), low redshift subsample (17 objects) t…
The ultraviolet to X-ray spectrum of the Seyfert 1 galaxy E 1615+061: accretion disk and reflection models.
Piro, L.; Perola, G. C.; Fiore, F. +4 more
The Seyfert 1 galaxy E 1615+061 is a candidate for the strongest variability in soft X-rays, changing from a very steep high state ({GAMMA}=~4), as implied by HEAO1 observations performed in 1977, to a two orders of magnitude dimmer state with a flatter spectrum ({GAMMA}=~2), as observed by EXOSAT in 1985. In this paper we present the results of a…
The mass-loss history of the symbiotic nova RR Telescopii.
Nussbaumer, H.; Dumm, T.
Mass loss in symbiotic novae is of interest to the theory of nova-like events as well as to the question whether symbiotic novae could be precursors of type Ia supernovae. RR Tel began its outburst in 1944. It spent five years in an extended state with no mass-loss before slowly shrinking and increasing its effective temperature. This transition w…