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The exciting star of the small bubble N 120A in the Large Magellanic Cloud
Gry, C.; Rosado, M.; Marcelin, M. +2 more
UV characteristics of the star BI 141 show that it is the exciting star of the nebula N 120A of the LMC. We determine its UV spectral classification as O_9.5_I and we derive the terminal velocity and mass-loss rate of its stellar wind, in agreement with the usual values found for galactic supergiants of the same spectral type. The energetic balanc…
Variation of QSO color indices with redshift
Fan, Xiao-hui; Chen, Jian-sheng
In this paper we discuss the effect of features in the spectrum of QSOs on their color indices and the consequent variation of the latter with the redshift. As the redshift increases, the various absorption features shortwards of the Lyα emission line enter into the visible region and alter the way in which the color indices vary with the redshift…
On Mass Loss from HD46300 - a Supergiant of Luminosity Class 1B
Oganesyan, D. B.
Using archival IUE data we give the results of an analysis of the profile of the Mg II k and h lines for HD46300, an AO1b-supergiant. Evidence of mass loss by the star was detected; its most probable nature is the ejection of matter in a cloud. Estimates are made for certain parameters of this cloud.
Comparative analysis of the data of Saturn's photometry from ground-based observations and from the Hubble Space Telescope measurements.
Tejfel, V. G.
The results of a detailed photometry of Saturn from HST obtained in June 1991 were compared with photographic observations of Saturn in July 1991 made with 1-meter telescope at good image quality. The latitudinal variations of Minnaert's limb darkening coefficients derived from these observations are in very good agreement as well as the relations…
Monitoring the Winds of Hot Stars with HST/GHRS
Heap, Sara R.
We present observations obtained with the Goddard High Resolution Spectrograph (GHRS) of three O-type stars:ξ per (O7 III),λ Cep (O6 Iaf) and 10 Lac (O9 V). These observations show evidence of instabilities in the winds of all three stars, although not necessarily those expected from current models of structured winds.
A morphological study of the circumstellar dust shell of Herbig Ae/Be stars
Wang, Jun-jie; Hu, Jing-yao
In this paper the Kurucz stellar atmosphere model is fitted to the observed IUE, IRAS, ground-based optical and near-infrared data of 22 Herbig Ae/Be stars. A statistical analysis is made based on energy balance between the central star and the circumstellar shell. It is concluded that the shells are disk-shaped.
How tracer objects can improve competitive learning algorithms in astronomy
Murtagh, F.; Hernandez-Pajares, M.; Floris, J.
The main objective of this paper is to discuss how the use of tracer objects in competitive learning can improve results in stellar classification. To do this, we work with a Kohonen network applied to a reduced sample of the Hipparcos Input Catalogue, which contains missing values. The use of synthetic stars as tracer objects allows us to determi…
Nonthermal Pair Models, Reflection, and X-Ray Spectral Variability of Active Galaxies
Done, C.; Grandi, P.; Urry, C. M.
Standard nonthermal electron-positron pair cascades, including the effects of reflection from an accretion disk, can explain reasonably well the mean spectra of low-luminosity, Seyfert-type active galaxies. We test this model using the spectral variability observed by EXOSAT between 0.05 and 10 keV in five active galaxies: NGC 5548, 3C 120, 3C 273…
The Effect of Double Stars on the Guiding System of the Hubble Space Telescope
Hershey, John L.; Bely, Pierre Y.
The interferometric system used for guidance of HST is sensitive to close binaries. Before the launch of HST it was believed that up to 25% of all guide star pairs would lead to guidance failure due to duplicity. After more than 3 years of operation the actual failure rate ascribable to duplicity is estimated to be just below 1%. A computer simula…
Optical and Ultraviolet Spectroscopy of VW Hydri
Saygac, A. Talat
Spectra of the SU UMa type dwarf nova VW Hydri obtained in the visual (lambda-lambda 3400-7200A) and ultraviolet (lambda-lambda 1150-3200A) spectral regions are presented. During the quiescent phase, visual spectra of VW Hydri present strong double-peaked Balmer emission lines. In addition, He I lambda 5876, Fe II lambda-lambda 4233, 5196 He I lam…