Search Publications
Constraints from the UV delay in dwarf nova outbursts.
Meyer, F.; Meyer-Hofmeister, E.
Observations of outbursts of the dwarf nova system VW Hydri show a delay of the rise of the UV flux with respect to that of the optical flux. The difficulties in modeling this feature in the context of the accretion disk instability are discussed and a modified limit cycle based on the same value of the frictional parameter alpha for the cool disk…
X-Ray Timing and Spectral Measurements of X Persei
Robba, N. R.; Warwick, R. S.
The results of an X-ray timing and spectral study of the Be star X-ray binary system X Per are reported, based on two series of Exosat observations. The timing measurements indicate that the neutron star in the X Per system was in a net spin-down mode during the 1984-1986 period and that this trend may have been in progress since 1978. The phase-a…
IUE observations of variability in the WN6 star HD 192163.
Willis, A. J.; Smith, L. J.; Conti, P. S. +3 more
Results are presented of a study of 77 high-resolution IUE spectra of the WN6 star HD 192163, for which new IUE observations obtained over 48 hrs in 1987 were combined with data drawn from the IUE archive, covering various epochs over the 1978-1987 period. The 1987 series of 48 spectra were found to exhibit significant variability over a period of…
The X-ray spectrum of QSO 1821+643.
Barstow, M. A.; Warwick, R. S.; Yaqoob, T.
Pravdo & Marshall have reported an unusually soft X-ray spectrum for the high-luminosity QSO 1821 + 643, based on measurements from the A2 experiment on HEAO-1. However, in a series of EXOSAT observations of this object we have found the medium-energy X-ray spectrum to be consistent with the canonical form observed in low-luminosity active gal…
Activity in late-type dwarfs. III. Chromospheric and transition region line fluxes for two dM stars.
Doyle, J. G.; Byrne, P. B.
Weak upper-chromospheric and transition-region emission from two dM stars (Gl 784 and Gl 825) has been observed using deep UV spectroscopy. Ly-alpha fluxes for the two stars were also determined for the first time. Using these results it is shown that the transition from weakly active dM to active dMe star is probably due to increasing surface cov…
On the Nature of Newly Formed Dust around the Hydrogen-deficient Star V348 Sagittarii
Drilling, J. S.; Schoenberner, D.
IUE spectra of V348 Sgr have been used to determine the extinction law from 1250 to 3080 A for circumstellar material recently ejected from it. This law differs from the standard extinction law in showing a bump at 2500 A rather than 2200 A, and in showing much lower extinction values for lambda less than 2000 A. These differences are attributed t…
A correlation between shape and (UV-V) color for early-type galaxies.
Bender, R.; Longo, G.; Capaccioli, M. +1 more
We present a correlation between the isophotal-shape parameter α_4_/α (Bender et al. 1989a) and the ultraviolet (UV) color index (1330 A-V) (Longo et al. 1989): boxy galaxies are found to be UV brighter than disky galaxies. The interpretation of the correlation between Mg_2_ and the UV color suggested by Burstein et al. (1988; hereafter BBBFL) is …
Revisited mass-loss rates for a sample of central stars of planetary nebulae.
Surdej, J.; Hutsemekers, D.
Using improved relations for the first order moment of a P Cygni line profile, mass-loss rates have been rederived for a sample of seventeen central stars of planetary nebulae observed with IUE in the low resolution mode. The average value of the mass-loss rates lies between 10 to the -7th and 10 to the -8th solar masses/yr. It is confirmed that t…
Energetic Ion Fluxes in the Inner Coma of Comet P/Halley
Balsiger, H.; Young, D. T.; Goldstein, R. +3 more
The particle phenomenon observed inside the magnetic field-free cavity near the nucleus of Comet P/Halley by the Giotto Ion Mass Spectrometer High-Energy Range Spectrometer sensor is studied. The question of access to the cavity of particles ionized farther out in the coma is addressed. A quantitative model of a mechanism for creating the observed…
Non--Equilibrium Ionization Effects in the Supernova Remnant RCW 86
Kaastra, J. S.; Smith, A.; Peacock, A. +2 more
X-ray images show that the SNR RCW 86 consists of two emission regions. The electron temperature of both two regions is 3.4 keV. The low-energy flux (0.2-2 keV) is strongly enhanced compared to a simple thermal bremsstrahlung spectrum with Te = 3.4 keV fitted to the 2-10 keV data. This enhancement is most likely caused by nonequilibrium ionization…