Search Publications
Temperature and luminosity of hot components in symbiotic stars.
Vogel, M.; Nussbaumer, H.; Schmid, H. M. +1 more
Typical radiation temperatures and luminosities are derived for the hot component of a representative sample of symbiotic systems by adapting the Zanstra method to the special requirements of symbiotic stars. Temperatures are derived by comparing the He II 1640 nebular recombination line with the underlying continuum. Particle-bounded and radiatio…
Non-LTE analysis of four PG1159 stars.
Werner, K.; Heber, U.; Hunger, K.
A spectral analysis of four members of the PG1159 class is performed. These stars are believed to be very hot pre-White Dwarf stars. It is shown that the photospheres of PG1159 stars are dominated by helium and carbon and that a significant amount of oxygen is present. It is also found that the nonradial pulsations observed in some PG1159 stars ar…
Magnetic structure in cool stars. XVII. Minimum radiative losses from theouter atmosphere.
Rutten, R. G. M.; Schrijver, C. J.; Zwaan, C. +1 more
The emissions in several chromospheric and transition region lines and in coronal soft X-rays are analyzed for a sample of cool stars. The nature of the lower-limit flux densities is explored, and evidence is given for the possibility of a basal, nonmagnetic heating mechanism being responsible for these emission fluxes up to, and perhaps including…
New insights from a statistical analysis of IUE spectra of dwarf novae and nova-like stars. I. Inclination effects in lines and continua.
La Dous, Constanze
IUE observations of dwarf novae at maximum at quiescence and novalike objects at the high brightness state are analyzed for effects of the inclination angle on the emitted continuum and line radiation. A clear pattern in the continuum flux distribution is exhibited only by dwarf novae at maximum where some 80 percent of the non-double-eclipsing sy…
Spectral energy distribution of compact planetary nebulae.
Kwok, S.; Zhang, C. Y.
The spectral energy distributions between 0.1 and 100 microns of 66 compact planetary nebulae are presented. The observed energy distributions are fitted with a model consisting of the stellar, nebular, and dust components. It is found that on the average, 38 +/-21, 25 +/-16, and 37 +/-14 percent of the emergent fluxes in the above wavelength rang…
Empirical velocity laws for cool giants. I. The symbiotic binary EG Andromedae.
Vogel, M.
An empirical velocity law is presented for the wind of a cool giant. The analysis is performed for the symbiotic binary EG And. The system consists of an M2.4 III giant and a hot subdwarf. The UV radiation of the compact hot component is Rayleigh-scattered in the wind of the cool giant. The column density for Rayleigh scattering varies with the or…
Variability of the post-AGB star HR 4049 : dust obscuration in a binary system.
Waters, L. B. F. M.; Ferlet, R.; Vidal-Madjar, A. +5 more
Results obtained from a large number of coordinated photometric and spectroscopic observations lead to the conclusion that HR 4049 is a binary with an orbital period near 434 days and a companion of similar mass which either is a white dwarf or a main-sequence star, more likely the second. The H-alpha line is in emission with either a P Cygni prof…
NLTE analysis of the unique pre-white dwarf H 1504+65.
Werner, K.
High S/N optical spectra and line profile fits with line-blanketed non-LTE model atmospheres show that H 1504 + 65 is the hottest star ever analyzed by model atmosphere methods. It is also noted that the atmospheric composition of this prewhite dwarf is almost entirely carbon and oxygen by equal parts, and that it is virtually devoid of H and He. …
Interpretation of the ion mass spectra in the mass per charge range 25-35 amu/e obtained in the inner coma of Halley's comet by the HIS-sensor of the Giotto IMS experiment
Altwegg, K.; Balsiger, H.; Geiss, J. +6 more
The IMS-HIS double-focusing mass spectrometer that flew on the Giotto spacecraft covered the mass per charge range from 12 to 56 (amu/e). By comparing flight data, calibration data and results of model calculations of the ion population in the inner coma, the absolute mass scale is established, and ions in the mass range 25 to 35 are identified. I…
On the evolutionary link between white dwarfs and central stars of planetary nebulae : NLTE analysis of PG 1144+005.
Werner, K.; Heber, U.
Line-blanketed non-LTE (NLTE) model atmospheres are used to study the optical spectra of the hydrogen-deficient prewhite dwarf PG 1144 + 005 by means of a spectral analysis. The star is compared to a prototype PG 1159 star for the analysis, and the stellar parameters of the PG 1144 dwarf show that the N/O ratio is indicative of very strong nitroge…