Search Publications
Multiwavelength observations of the quasar Q 1821+643 during the ROSAT All Sky Survey.
Malkan, M. A.; Ulrich, M. -H.; Heidt, J. +4 more
Temporal variations of the flux in the optical, UV, soft X-ray and medium X-ray ranges occur in most AGN studied, but no general correlation has emerged between the variations in these different energy ranges. Because of its high ecliptic latitude the radio-quiet quasar Q 1821 + 643 was surveyed for 37 days by ROSAT during the ROSAT All Sky Survey…
Solar particle composition: Measurements in the March 1991 event at 2.5AU
Forsyth, R.; Tappin, S. J.; Lanzerotti, L. J. +3 more
The time evolution of the very large solar particle event occurring on days 82-90 (March 23-31), 1991, as measured at 2.5 AU by the instrumentation on the Ulysses spacecraft was quite complex. Measurements by the HI-SCALE instrument of the nuclear composition (emphasizing Z≥6) of the interplanetary particles at a time resolution of two hours provi…
Detection of a White Dwarf in a Visual Binary System
Boehm-Vitense, Erika
The F6 giant HD 160365 was detected to have a white dwarf companion about 8 arcsec south of the star. The UV energy distribution observed with IUE shows that the white dwarf has an effective temperature of 23,000 +/- 2000 K. If log g = 8 the Lya profile indicates an effective temperature around 24,500 K. Using the theoretical models by Wesemael et…
Delta CAP - the secondary revealed.
Bromage, G. E.; Kellett, B. J.; Lloyd, C. +5 more
The recent detection of the eclipsing metallic-lined binary Delta Cap in the EUV as part of the Wide-Field Camera All-Sky Survey has prompted a reexamination of the available data in order to attempt to locate the source of the emission. It can be shown that a white dwarf is unable to account for the emission, and the possibility of coronal emissi…
Pluto's extended atmosphere: An escape model and initial observations
Stern, S. A.; Clarke, John T.; Trafton, Laurence M.
We have calculated the rates of production and hydrodynamic outflow of atomic hydrogen resulting from the photodissociation of methane in the upper atmosphere of Pluto. Under the present near-perihelion conditions this yields an extended cloud of H around Pluto which is likely to be the most easily observable signature of Pluto's extended atmosphe…
Mesures de vitesses radiales. VI. Accompagnement AU sol du programme d'observation du satellite Hipparcos.
Burnage, R.; Fehrenbach, Ch.; Figuiere, J.
A list of radial velocities of 2601 stars obtained with the Fehrenbach objective prism associated with the Schmidt telescope of the Haute Provence Observatory is presented. These stars belong to specially chosen fields containing several Hipparcos input catalog star members. A total of 440 probable radial-velocity variable was observed. Sixty-nine…
Modelling the torques affecting the HIPPARCOS satellite
Perryman, M. A. C.; van Leeuwen, Floor; Penston, Margaret J. +2 more
A description of the models used to derive a model of the torques working on the Hipparcos satellite and results based on 12 weeks of data spread over 14 months are presented. Most of the prelaunch estimates of the satellite's solar radiation torques is confirmed qualitatively. A reconstruction of the torques near apogee to a level of a few microa…
Deconvolution and photometry of Faint Object Camera images with point sources.
Mackay, C. D.; Schade, D. J.; Thomson, R. C. +2 more
The peculiar characteristics of images obtained with the Hubble Space Telescope have raised important questions concerning the proper method for processing data in which the point spread function is seriously distorted. In particular, there is considerable confusion over whether or not it is useful to deconvolve the images, and to what extent the …
TYCHO background determination and monitoring
Wicenec, A.; Baessgen, G.
Attention is given to the method of background determination in the Tycho photon counts. A part of the data from the first eight months is used to study the periodical and aperiodical behavior of the background and provide statistics on the usability of Tycho data. The scientific value of the Tycho mission is directly correlated to the amount of l…
The X-ray spectrum of the superluminal quasar 1928+73.
Ghosh, K. K.; Soundararajaperumal, S.
EXOSAT observations (0.1-10 keV) of the radio-loud quasar 1928+73, which displays superluminal motion, were made at four epochs between 1983/283 and 1984/009, and we obtained spectra of this source from the EXOSAT database. The X-ray spectrum (0.1-10 keV) can be explained by a power law and uniform absorption model. No significant low-energy absor…