Search Publications
A comprehensive study of intense star formation bursts in irregular and compact galaxies
Mas-Hesse, J. Miguel; Kunth, Daniel
We have analyzed the properties of the star formation episodes taking place in a sample of blue compact and irregular galaxies by comparing their multiwavelength observational properties with the predictions of evolutionary population synthesis models. This method has allowed us to constrain the age, star formation regime (instantaneous or extende…
The ISO spectrum of the young star HD 142527
Waters, L. B. F. M.; de Koter, A.; Waelkens, C. +2 more
We present a detailed analysis of SWS (2.35-45 mu m) and LWS (43-200 mu m) spectra obtained with the Infrared Space Observatory (ISO) (Kessler et al. 1996) of the dusty circumstellar disk surrounding the isolated young Fe star HD 142527. Two dust populations can be clearly discriminated: a warm component which is dominated by very strong silicate …
Long- and short-term variability in O-star winds. II. Quantitative analysis of DAC behaviour
Kaper, L.; Henrichs, H. F.; Nichols, J. S. +1 more
A quantitative analysis of time series of ultraviolet spectra from a sample of 10 bright O-type stars (cf. Kaper et al. \cite{KH96}, Paper I) is presented. Migrating discrete absorption components (DACs), responsible for the observed variability in the UV resonance doublets, are modeled. To isolate the DACs from the underlying P Cygni lines, a met…
TT Arietis: the low state revisited
Gänsicke, B. T.; Beuermann, K.; Sion, E. M. +3 more
We present optical and ultraviolet spectroscopy of TT Ari obtained during the 1982-85 low state. In November/December 1983, accretion had almost completely ceased, unveiling both the white dwarf and the secondary star. The IUE spectrum obtained during that occasion contains absorption lines of Lyalpha , \Si IV, \C IV, and \He II. We derive a photo…
ORFEUS spectroscopy of the O BT VI lines in symbiotic stars and the Raman scattering process
Schmutz, W.; Grewing, M.; Schild, H. +16 more
We present orfeus spectra of the O vi lambda lambda 1032,1038 emission lines in the symbiotic stars AG Dra, V1016 Cyg, RR Tel, CD-43(deg) 14304, AG Peg and Z And. The O vi emission lines can convert into broad and highly polarized emission lines at lambda 6825 and lambda 7082 in a Raman scattering process by neutral hydrogen. From a comparison of …
Analysis of ultraviolet and extreme-ultraviolet spectra of the DA white dwarf G 191-B2B using self-consistent diffusion models
Dreizler, S.; Wolff, B.
We present a multi-wavelength spectral analysis of the DA white dwarf G 191-B2B. The employed atmospheric models account for gravitational settling and radiative levitation, which are, for the first time, calculated self-consistently with the atmospheric structure. The resulting spectra can reproduce the complete EUVE spectrum and the ultraviolet …
Wolf-Rayet nebulae as tracers of stellar ionizing fluxes. I. M1-67
Schmutz, W.; Hillier, D. J.; de Koter, A. +3 more
We use WR124 (WN8h) and its associated nebula M1-67, to test theoretical non-LTE models for Wolf-Rayet (WR) stars. Lyman continuum ionizing flux distributions derived from a stellar analysis of WR124, are compared with nebular properties via photo-ionization modelling. Our study demonstrates the significant role that line blanketing plays in affec…
Transient supersoft X-ray emission from V 751 Cygni during the optical low-state
Greiner, J.; González-Riestra, R.; Di Stefano, R. +4 more
We have observed V 751 Cyg with the ROSAT HRI in a target-of-opportunity mode during its recent optical low state and clearly detect it at a count rate of 0.015 cts s(-1) . The X-ray intensity is a factor of 7-19 (depending on the exact X-ray spectral shape) higher than the upper limit obtained with the ROSAT PSPC during the optical high state, th…
Activity cycle and surface differential rotation of the single Pleiades star HD 82443 (DX Leo)
Lanza, A. F.; Messina, S.; Guinan, E. F. +1 more
The results of a long-term photometric monitoring of the young Pleiades moving group member HD 82443 are presented. A sequence of fifteen optical light curves obtained from 1989 to 1998 confirms the presence of a rotational modulation with a mean period of 5.377 days attributable to cool photospheric spots. The Maximum Entropy and the Tikhonov reg…
Strong optical line variability in MKN 110
Kollatschny, W.; Bischoff, K.
We present results of a long-term variability campaign on the Seyfert 1 galaxy Markarian 110. Mkn 110 is a narrow-line Seyfert 1 object hosted in a morphological peculiar galaxy. We monitored the optical continuum and the line intensities as well as their profiles over a time interval of nearly ten years. The continuum and the Balmer lines varied …