Search Publications
A model for the X-ray spectrum of the symbiotic nova RR Telescopii.
Werner, K.; Jordan, S.; Murset, U.
Pointed ROSAT position sensitive proportional counter (PSPC) observations of the symbiotic nova RR Tel are presented. The PSPC pulse height distribution exhibits a rather soft energy distribution plus few, but significant counts at higher energies. We interprete this as superposition of photospheric flux from the hot component of the symbiotic bin…
Analysis of BD+33 2642: a newly detected planetary nebula in the galactic halo and its central star.
Heber, U.; Napiwotzki, R.; Koeppen, J.
The spectra of the star BD+33 2642 and its surrounding planetary nebula (PN) are analyzed. The stellar parameters are found to be T_eff_=20200K, logg=2.9; the stellar mass is 0.560Msun_. In the stellar atmosphere, He is solar, C, N, O, Mg, Si are depleted by about 1dex, and Fe is depleted by 2dex relative to the sun. This abundance patt…
Spectral analysis of the planetary nebula K 1-27 and its very hot hydrogen-deficient central star.
Rauch, T.; Werner, K.; Koeppen, J.
We present an analysis of the hydrogen-deficient central star of K 1-27 based on NLTE model atmospheres and an analysis of the planetary nebula based on photoionization models. From line profile fits we derive an effective temperature of T_eff_=100+/-15kK and a surface gravity of logg=6.5+/-0.5 for the central star. The atmosphere is dominated by …
X-ray irradiation of white dwarf atmospehres : the soft X-ray spectrum of AM Herculis.
Paerels, Frits; van Teeseling, Andre; Heise, John
We present model atmosphere calculations of white dwarfs irradiated at the surface by hard x-rays. We use a self-consistent treatment of Compton scattering as a noncoherent scattering process. The opacities include the photoionization edges of all individual subshells of the most abundant ions of 15 elements. Because of an 'inverse' blanketing eff…
V348 Sagittarii : analysis of the [WC12] stellar spectrum
Hamann, W. -R.; Leuenhagen, U.
The Wolf-Rayet type spectrum of the highly variable V 348 Sgr, central star of a planetary nebula, is analyzed. An optical spectrum during maximum shows various emission and P-Cygni features, which indicate an expansion of the atmosphere. In order to assess the stellar and atmospheric parameters of this Population II object, a high resolution opti…
The contribution of small particles to the extinction curve.
Boulanger, F.; Gry, C.; Prevot, M. L.
We have searched for a correlation between the strength of the 12 and 25 µm emission measured by IRAS and the UV extinction curve for stars behind the Chamaeleon molecular complex. We find that the mid-IR emission is correlated with the area of the 2200 A bump but bump carriers are not fully depleted in matter with no mid-IR emission. We obs…
Long-term periodic variability in UV absorption lines of the Be star γ Cassiopeiae: on the relation with V/R variations in the Hβ line.
Telting, John H.; Kaper, Lex
We present a quantitative study of the variability in ultraviolet resonance lines of NV, SiIV and CIV of the Be star γ Cas. For this purpose we used IUE spectra obtained over a period of eleven years. Variability occurs in the form of discrete absorption components (DACs), which are formed in the fast-outflowing radiatively driven part of the stel…
Spectral analysis of the hottest known helium-rich white dwarf: KPD0005+5106.
Werner, K.; Heber, U.; Fleming, T.
We present a non-LTE model atmosphere analysis of the helium-rich white dwarf KPD0005+5106. The analysis is based on optical spectra obtained at the Calar Alto 3.5m telescope, ultraviolet observations retrieved from the Hubble Space Telescope data archive, and X-ray data recorded during the ROSAT all-sky survey. From the optical and ultraviolet He…
High time resolution observations of Cygnus X-3 with EXOSAT.
van der Klis, M.; Berger, M.
We have studied the fast timing behaviour of Cygnus X-3 using the entire EXOSAT ME dataset on this source, consisting of 22 observations that cover a total of 320000seconds. This large amount of data allowed us to measure the rapid (>1Hz) X-ray variability of the source to an unprecedented accuracy of 0.2% fractional rms amplitude. Above 256Hz,…
Multiwaveband study of a major X-ray outburst from the Be/X-ray transient system A 1118-616.
Fishman, G. J.; Coe, M. J.; Buckley, D. A. H. +10 more
The Be/X-ray binary system A 1118-616 has been observed to undergo a major outburst in January 1992 by the BATSE all-sky monitor on the Compton Gamma Ray Observatory. Ground-based optical and IR observations, supported by UV observations obtained under an IUE Target of Opportunity programme, have provided us with an excellent multi-wavelength stud…