Search Publications
He I absorption lines in high-redshift Lyman limit systems of the QSO HS 1700+6416.
Reimers, D.; Vogel, S.
We report the detection of He I resonance lines in four high- redshift Lyman limit systems of the QSO HS 1700+6416 (z = 2.72) observed with the Faint Object Spectrograph on board the Hubble Space Telescope. We find neutral hydrogen to neutral helium column density ratios N_HI_/N_HeI_ ~ 30 (possible range 20 to 70). Ionization calculations using CL…
Observations of stellar winds in high-mass X-ray binaries : evidence for a non-monotonic velocity structure.
van Loon, J. Th.; Hammerschlag-Hensberge, G.; Kaper, L.
We report variations with orbital phase in UV resonance lines of HD77581 (B0.5 Iab), the optical counterpart of the high-mass X-ray binary system Vela X-1 (4U0900-40), occurring at low and intermediate negative velocities. We argue that these variations are caused by ionization effects in the stellar wind by the X-ray source, just like the well-kn…
H-alpha interferometric, optical and near IR photometric studies of star forming regions. I. The Cepheus B/Sh2-155/Cepheus OB3 association complex.
Wagner, S.; Moreno-Corral, M. A.; C., Chavarria-K. +1 more
Here we report the results of a near IR photo- metric study of about 40 stars of the Cepheus OB3 association (subpopulations a and b), of an attempt to detect near IR counterparts of the discrete radio continuum sources reported by Felli et al. (1978), and of the nature of the IR source AFGL 3000. We also give the results of a Hα interferometric, …
Proof for a wind from the hot component in the symbiotic system EG Andromedae.
Vogel, M.
One of the most debated issue in symbiotic research concerns the nature of the hot component. In this Letter we give observational evidence that in the symbiotic binary EG And the hot compact star loses mass through a stellar wind. The wind velocity is ≈ 500 km s -1, and the mass loss rate is Mṡ ≈ 5 × 10-9 Msu…
Spectral analysis of extremely helium rich subdwarfs O-stars.
Dreizler, S.
The NLTE analyses of four extremely helium rich sdO stars based on high resolution, high S/N CASPEC spectra are presented. Effective temperatures, gravities and the abundances of H, He, C, N, O, Ne, Mg, and Si have been deter- mined. It is found that LSIV+1O°9, LSS 1274, and UV 0832-01 have very similar parameters: Teff = 445…
The beta Pictoris circumstellar disk. XV. Highly ionized species near beta Pictoris.
Deleuil, M.; Feldman, P. D.; Moos, H. W. +7 more
Temporal variations of the Fe II, Mg II, and Al III circumstellar lines towards Beta Pictoris have been detected and monitored since 1985. However, the unusual presence of Al III ions is still puzzling, since the UV stellar flux from an A5V star such as Beta Pic is insufficient to produce such an ion. In order to better define the origin of such a…
A far UV investigation of luminous hot stars in the SMC cluster NGC 330.
Caloi, V.; Castellani, V.; Cassatella, A. +1 more
IUE observations of luminous blue stars in the SMC young cluster NGC 330 have been used to determine the reddening and the effective temperatures of the program objects. The reddening is estimated to be E(B - V) = 0.09 +/- 0.02, intermediate between old (~0.02) and recent (~0.12) evaluations. Stars with no recognized atmospheric anomaly show a goo…
NLTE analysis of sublimous O stars : the hot subdwarf in the binary system HD 128220.
Rauch, T.
We present a precise NLTE analysis of the hot subdwarf in the double-lined spectroscopic-binary system HD128220 (BD+19°2824, SAO 101094), based on 38 high- resolution IUE spectra. Very detailed NLTE models were constructed using the Accelerated Lambda Iteration technique. Model atoms for H I, He I/He II, C III/C IV, N III/N IV and O IV/O V are car…
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…