Search Publications
Circinus X-1 revisited: fast-timing properties in relation to spectral state.
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +2 more
We have studied the X-ray spectral and fast-timing variations of Cir X-1 by performing a homogenous analysis of all EXOSAT ME data on this source using X-ray hardness-intensity diagrams (HIDs), colour-colour diagrams (CDs), and power spectra. Cir X-1 exhibits a wide range of power spectral shapes and a large variety in X-ray spectral shapes. At di…
Preliminary link of the HIPPARCOS and VLBI reference frames
Lindegren, L.; Mignard, F.; Lestrade, J. -F. +12 more
We present a comparison of VLBI and Hipparcos astrometric parameters of several optically bright radio-emitting stars. The systematic discrepancies found in these preliminary data can be removed by performing a single global rotation between the extragalactic and Hipparcos reference frames. Two estimates of this rotation and its time derivative ha…
The electron temperature in the inner coma of comet P/Halley.
Eberhardt, P.; Krankowsky, D.
From the CH_3_OH_2_^+^/H_3_O^+^ and H_3_O^+^/H_2_O^+^ ratios measured by the Giotto Neutral Mass Spectrometer in the inner coma (distance <20000km) of comet P/Halley we derive two independent electron temperature profiles. They agree very well and the electron temperature T_e_ increases gradually from =~100K at 2000km to =~900K at 8500km follow…
Low-mass stars in globular clusters. III. The mass function of 47 Tucanae.
Paresce, F.; de Marchi, G.
We have used the WFPC2 on board HST to investigate the stellar population in a field located 4'6 E of the center of the globular cluster 47 Tuc (NGC 104), close to the half-mass radius, through wide band imaging at 606 and 812nm. A total of ~3000 stars are accurately classified by two-color photometry to form a color-magnitude diagram extending do…
The sensitivity of the size distribution to the grain dynamics: simulation of the dust flux measured by GIOTTO at P/Halley.
Fulle, M.; Mennella, V.; Colangeli, L. +2 more
A cometary dust emission model, based on rigorous keplerian dynamics, is developed and, for the first time, the dependence of fluence on the probability distribution of the dust ejection velocity vector is demonstrated. The results are compared with the fluences measured by the DIDSY experiment on board the GIOTTO spacecraft during the Halley's fl…
Proof of a fast wind in the symbiotic nova AG Pegasi.
Schmutz, W.; Vogel, M.; Nussbaumer, H.
Hubble Space Telescope observations of the symbiotic nova AG Peg reveal a P Cygni profile in N V λl240. This proves that the hot compact object in the binary system loses material through a fast wind. High resolution spectra allow to discern three different emission regions: the wind from the hot compact star, a nebular emission region of relative…
Fading and variations in the spectrum of the central star of the very young planetary nebula SAO 244567 (Hen 1357).
Pottasch, S. R.; de Martino, D.; Parthasarathy, M. +6 more
The optical spectrum of SAO 244567 obtained in 1971 shows that it was a post-AGB B1 or B2 supergiant at that time. It has turned into a planetary nebula (PN ) within the last 20 years. The IUE ultraviolet spectra obtained during the last seven years show that the central star is rapidly evolving. It is found that the central star of this young PN …
Ultra-high excitation features in hot white dwarfs: A DAO and three DO stars discovered by the Hamburg-Schmidt survey.
Dreizler, S.; Heber, U.; Napiwotzki, R. +1 more
We report on the discovery of four hot white dwarfs, one DAO (HS2115+1148) and three DO (HS0158+2335, HS 0727+6003 and HS 2027+0651). The spectra of these stars exhibit shallow metal absorption lines from ultrahighly excited ionization stages (C V, C VI/N VI, N VII/O VII, O VIII, Ne IX, Ne X) with ionization energies ranging from 392eV to 1362eV. …
Comparative study of the asteroidal motion in the 3:2 and 2:1 resonances with Jupiter. I. Planar model.
Ferraz-Mello, S.; Michtchenko, T. A.
The long-period behavior of the asteroids in the 3:2 and 2:1 resonances with Jupiter is investigated by integrating numerically the equations of motion of the planar three-body system. The results of the numerical integration procedure were submitted to a low-pass filtering and the decimation parameter was chosen in accordance with the filter. The…
Metal abundances in subdwarf O stars.
Husfeld, D.; Bauer, F.
We describe a non-LTE analysis of seven subdwarf O stars and four central stars of planetary nebulae. The analysis yields metal abundances (or upper limits to these) of C, N, O, Mg, Al, and Si for most of these stars. Also effective temperature, surface gravity and helium abundance were determined for those programme stars for which no reliable es…