Search Publications
Constraints for the shape of the UV background at z=2.
Reimers, D.; Vogel, S.
Spectroscopic UV observations with the Hubble Space Telescope of the QSO HS 1700+6416 (z = 2.72) (Reimers et al. 1992,1993) offer for the first time the possibility to measure column densities of C, N and O simultaneously in several ionization stages (O III to O VI, C III and C IV, N II to N V). Photoionization models have been computed and fitted…
The discovery and properties of the ultra-soft X-ray transient EXO 1846-031.
Parmar, A. N.; White, N. E.; Angelini, L. +1 more
We report the discovery of a previously uncataloged ultra-soft X-ray transient EXO 1846-031 which was in outburst during 1985 April to September. The X-ray spectrum consists of an ultra-soft component and a high-energy power-law tail that extends to at least 25 keV. The ultra-soft component may be modeled by either a cutoff power-law or a multicol…
Ultraviolet spectroscopic variability of the WN5 star HD 50896 : timescales and linear physical dimensions of the perturbations.
Howarth, I. D.; Willis, A. J.; Smith, L. J. +4 more
We present the results of an analysis of a sequence of 130 high resolution SWP IUE spectra of the WN 5 star HD 50896 obtained over a period of 6 consecutive days in December 1988. Substantial variability has been found in the absorption and emission components of the major P Cygni profiles of N V 1250 A, C IV 1550 A, He II 1640 A, and N IV 1718 A …
Hubble Space Telescope Astrometric Observations of Pre-Main Sequence Stars from the HIPPARCOS Program
Badiali, M.; Cardini, D.; Emanuele, A. +6 more
We report on the first set of high angular resolution observations with Fine Guidance Sensor (FGS) #3 aboard the Hubble Space Telescope of a sample of T-Tauri and Herbig Ae/Be pre-main sequence stars, which have also been observed with the HIPPARCOS satellite. Among the 5 Ae/Be stars observed so far of particular interest is the new double HIPPARC…
The X-ray time variability and spectrum of gamma Cassiopeiae (X 0053+604).
Stella, L.; Parmar, A. N.; White, N. E. +1 more
A 30 h duration EXOSAT observation made in 1985 December is used to examine the X-ray time variability and spectrum of the Be star γ Cassiopeiae (X 0053+604). We find that the X-ray lightcurve is dominated by irregular energy-independent flaring on time-scales ≳ 100 s. This flaring markedly decreases the sensitivity to any periodic signals. We fin…
HS 0209+0832 : a DAB white dawrf with a temperature fittinginto the DB gap.
Heber, U.; Jordan, S.; Koester, D. +1 more
The white dwarf H50209+0832 (B ≈13m.9), belonging to the sparse class of spectral type DAB, was discovered by follow-up spectroscopy of candidates selected from objective- prism plates of the Hamburg Schmidt sky survey. An analysis of the optical spectrum, clearly showing the He I λ4471 line besides the Balmer lines, yields a He/H ratio…
Cool stars : spectral energy distributions and model atmosphere fluxes.
Morossi, C.; Malagnini, M. L.; Kurucz, R. L. +2 more
The main results of a program of systematic comparison between observed and computed spectral energy distributions of late G and K type solar chemical composition stars are illustrated. We built the observed energy distributions of eleven representative stars, from the ultraviolet to the infrared, starting from lUE archive data, supplemented by ou…
The accreting circumstellar gas envelope of HD 176386 a young star inthe R Coronae Austrinae star formation region.
Grady, C. A.; Perez, M. R.; The, P. S.
We report recent and archival IUE observations of the Herbig Be star HD 176386. We find accreting gas toward the star with velocities up to +300 km s-1 in C IV and Si IV. Detection of these species in a B9.5 star is consistent with collisional ionization of the accreting gas to temperatures in excess of the stellar Teff. The …
R 40 : the first luminous blue variable in the Small Magellanic Cloud.
Stahl, O.; Bouchet, P.; Zickgraf, F. -J. +3 more
During the past decade R 40 in the SMC has brightened in the visual range by about 0.5 magnitudes. Correlated with the brightening the spectral type has changed from B8Ia to A3Ia-O. This behaviour shows R 40 to be an LBV, the first one discovered in the SMC. During the past eight years we obtained extensive Stromgren photometry. R 40 was also obse…
Compact subarcsec structures of the double nucleus of NGC 6240 revealed with HST.
Boksenberg, A.; Barbieri, C.; Weigelt, G. +18 more
We have used the Faint Object Camera on board of the Hubble Space Telescope to obtain a high spatial resolution ultraviolet image of the central region of NGC 6240. This image resolves the well known double nucleus of the galaxy into several compact knots with sizes 0.1"-0.2" (about 45-90 pc for H_0_ = 75 km s^-1^Mpc^-1^) and extended low surface …