Search Publications
The reflection nebula around HD 26676.
Centurion, M.; Vladilo, G.
The gaseous component of the reflection nebula surrounding HD 26676 is investigated by comparing the UV spectrum of the star with that of the foreground star HD 26793. The physical properties of the cloud are constrained under the assumption of Mg photoionization and H ionization by cosmic rays and taking into account the effect of the stellar rad…
An upper limit on the high-energy gamma-ray emission of VELA X-1.
Kanbach, G.; Oegelman, H.; Mattox, J. R.
The possibility of high-energy gamma-ray emission from the X-ray binary Vela X-1 was investigated by analyzing the COS-B satellite observations, using the COS-B X-ray detector for a phase coherent analysis in the search of rotational periodicity. The rotational upper limit is compared to the X-ray, TeV, and PeV fluxes reported by Chodil et al. (19…
Perturbations of Test Mass Motion in the Schwarzschild Spacetime Using the Method of Hamilton and Jacobi.
Friedjung, M.; Andrade, A. A.
This thesis develops and applies Hamilton-Jacobi perturbation theory to describe relativistic test mass motion in the Schwarzschild spacetime. The form of Hamiltonian used is rigorously derived from the relativistic Lagrangian. A justification for other choices of Hamiltonians is also given. The results of all the intermediate calculations needed …
HD 145206 : the first semibarium star with a main-sequence close companion ?
Jorissen, A.; Boffin, H. M. J.
A 12 A/mm photographic spectrum of the binary red giant HD 145206 revealed slightly enhanced s-process lines with respect to standard stars of the same temperature and luminosity. The spectrum closely resembles that of a Ba0.5 semibarium star (following the classification of Keenan and Pitts, 1980) used for comparison. The mass transfer scenario g…
The radial distribution of galactic gamma rays. IV. The whole galaxy.
Strong, A. W.; Grenier, I. A.; Hermsen, W. +6 more
The correlation between diffuse galactic γ-rays and gas tracers is studied using the final COS-B database and H I and CO surveys covering the entire galactic plane. A good quantitative fit to the γ-rays is obtained, with a small gradient in the γ-ray emissivity per hydrogen atom. The average ratio of H2 column density to integrated CO t…
The beta Pictoris circumstellar disk. VI. Evidence for material falling on to the star.
Ferlet, R.; Vidal-Madjar, A.; Lagrange-Henri, A. M.
New archive observations with International Ultraviolet Explorer are used to study the temporal variations of the circumstellar absorption towards β Pictoris. The authors first show that strong variations occur in the redshifted part of the resonance lines of Al III, Mg II, and Fe II, and also of metastable lines of Fe II. These variations are the…
Relative C, N, O abundances in red giants, planetary nebulae, novae and symbiotic stars.
Vogel, M.; Nussbaumer, H.; Schild, H. +1 more
C/N and O/N abundance ratios deduced from UV data are presented for 24 symbiotic stars. There is little scatter in these ratios, indicating that the symbiotic phenomenon only occurs in a well defined evolutionary stage. Comparison with related objects such as red giants, novae, and planetary nebulae reveals that symbiotic objects best fit the CNO …
Rotational modulation and flares on RS CVn and BY DRA systems. VII. simultaneous X-ray, radio and optical data for the dMe star YZ CMi on 4/5 March 1985.
Doyle, J. G.; Butler, C. J.; van den Oord, G. H. J. +1 more
Broad-band photometric observations of YZ CMi show a 1.2mag U-band flare at 19:55 UT on 4 March 1985, however, simultaneous X-ray observations from EXOSAT show no detectable increase. Two possible explanations for the lack of an X-ray flare may be i) a flare occurring low in the chromosphere, where the chromosphere may not have been coupled to the…
A non-LTE stellar atmosphere study of nitrogen-rich early-type stars.
Butler, K.; Kudritzki, R. P.; Herrero, A. +4 more
Spectrograms of a sample of nitrogen-rich early type stars (OBN stars) are analyzed differentially to normal stars of similar spectral types by means of NLTE methods. Effective temperatures, gravities and atmospheric helium contents are derived by fitting theoretical profiles of hydrogen and helium lines to the observations. The abundance analysis…
An EXOSAT observation of an X-ray flare and quiescent emission from the RS CVn binary sigma2 CrB.
Mewe, R.; Brinkman, A. C.; van den Oord, G. H. J.
The RS CVn binary sigma2 Coronae Borealis was observed with medium-energy and low-energy detectors and the transmission grating spectrometer aboard EXOSAT, and a strong X-ray flare rising within about five minutes and lasting more than two hours was detected. The temperature rises steeply within three minutes from 19 MK to a value well above 70 MK…