Search Publications
The radial distribution of galactic gamma rays. III - The distribution of cosmic rays in the Galaxy and the CO-H2 calibration.
Strong, A. W.; Hermsen, W.; Lebrun, F. +7 more
High-energy (>70 MeV) gamma-ray observations are compared to H I and CO surveys over more than half of the Milky Way. The kinematics of both H I and CO are used as a distance indicator to determine, in combination with COS-B gamma-ray data, the galacto-centric distribution of the gamma-ray emissivity (the production rate per H atom) for three g…
In situ gas and ion measurements at comet Halley
Berthelier, J. J.; Eberhardt, P.; Krankowsky, D. +9 more
The neutral mass spectrometer experiment (NMS) carried by the Giotto spacecraft was designed to determine the abundances and the chemical, elemental and isotopic composition of the gases and low-energy ions in the coma of comet Halley. Its first results show the predominance of water vapour (~80% by volume). Preliminary evaluation of the data yiel…
Line Variations in Quasars and Seyfert Galaxies
Gaskell, C. M.; Sparke, L. S.
Quantitative estimates of the sizes of broad-line regions in three well-studied Seyfert I galaxies are presented, and differences between these and previously reported size estimates for NGC 4151 are discussed. Both Lick Observatory and IUE satellite data on NGC 4151 are analyzed, and it is shown that both are consistent with the high-ionization f…
Ion composition and dynamics at comet Halley
Schwenn, R.; Altwegg, K.; Balsiger, H. +16 more
The ion mass spectrometer aboard the Giotto spacecraft measured the composition and velocity distributions of cometary ions at distances of ~7.5×l06 to ~1,300 km from the nucleus of comet Halley. Well outside the bow shock, pick-up cometary H+ ions were found in a diffuse shell-like distribution. Heavier ions (C+, …
The atmosphere of subluminous B stars. II. Analysis of 10 helium poor subdwarfs and the birthrate of sdB stars.
Heber, U.
Ultraviolet and visual spectra of 10 helium-poor hot subluminous subdwarfs are analyzed, and the birthrate of these stars is determined. Effective temperatures range from 25,000 - 75,000 K in the group, which includes three binaries. sdB's occupy a narrow range in gravities and photospheric helium content in contrast to the sdOB ranges of gravitie…
Spectral Energy Distributions of Active Galactic Nuclei between 0.1 and 100 Microns
Malkan, M. A.; Edelson, R. A.
The authors have combined new photometry from IRAS with ground-based optical and near-infrared spectrophotometry and ultraviolet spectrophotometry from IUE to study the spectral energy distributions from 0.1 to 100 µm for 29 active galactic nuclei. After correcting for the effects of starlight and foreground and internal reddening, the autho…
First results from the Giotto magnetometer experiment at comet Halley
Neubauer, F. M.; Glassmeier, K. H.; Pohl, M. +9 more
The Giotto magnetometer experiment at comet Halley has for the first time provided magnetic field measurements in all the important spatial regions characterizing the front-side interaction between the solar-wind magnetoplasma and a cometary atmosphere. Upstream waves of cometary origin have been observed at distances of >2×106 km fr…
First Halley Multicolour Camera imaging results from Giotto
Wilhelm, K.; Keller, H. U.; Barbieri, C. +15 more
The first imaging results from the Halley Multicolour Camera (HMC) during the Giotto fly-by of comet Halley provide images centred on the brightest part of the inner coma which show the silhouette of a large, solid and irregularly shaped cometary nucleus and jet-like dust activity visible in reflected sunlight. A first assessment of the data yield…
An Analysis of the Shapes of Ultraviolet Extinction Curves. I. The 2175 Angstrom Bump
Fitzpatrick, E. L.; Massa, D.
IUE data are used to investigate the properties of the 2175 A interstellar extinction bump toward 45 reddened Milky Way stars. Using analytic fitting functions, parameters are derived which describe the central position, FWHM, and strength of the bump. The bump position is very stable, with an extreme deviation which is still significantly larger …
Radio Emission from Galactic Wolf-Rayet Stars and the Structure of Wolf-Rayet Winds
Churchwell, E.; Abbott, D. C.; Torres, A. V. +1 more
The authors have observed 23 Wolf-Rayet stars with the VLA at 6 cm and reobserved four stars at both 2 and 6 cm. When combined with previous data, these observations form an essentially complete sample of 40 W-R stars within a distance of 3 kpc and north of declination -47°. Available measurements of optical emission lines are used to estimate the…