Search Publications
First Polymer in Space Identified in Comet Halley
Huebner, W. F.
The heavy-ion mass spectrum obtained in the inner coma of comet Halley with the PICCA instrument on the Giotto spacecraft has been examined. Short polymer chains of polyoxymethylene and their decay products are identified as the source for the spectrum with six mass peaks between about 45 and 120 atomic mass units. The properties of polyoxymethyle…
The relationship of active comets, ``extinct'' comets, and dark asteroids
Cruikshank, D. P.; Tholen, D. J.; Hartmann, W. K.
Spectrophotometric data on groups of asteroids in different types of orbits reveal different distributions of spectral properties, depending on whether the orbits are cometary or noncometary. In a list of 10 asteroids frequently suggested on purely dynamical grounds to be extinct or dormant comets, all have properties suggestive of spectral classe…
Evidence for methane and ammonia in the coma of comet P/Halley
Ip, W. -H.; Allen, M.; Yung, Y. +2 more
Methane and ammonia abundances in the coma of Halley are derived from Giotto IMS data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto HIS ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio (m/q) = 19/18 as a function of distance from the nucleus is not reproduced…
Magnetic structure in cool stars. XII - Chromospheric activity and rotation of giants and dwarfs
Rutten, R. G. M.
The relation between the Ca II H and K line-core flux density and rotation rate is studied for 313 F- to M-type stars ranging in luminosity class from II-III to V. The activity-rotation relation for Ca II is compared with similar relations for Mg II and soft X-rays. Dwarfs and the majority of the giants studied follow the same color-dependent rela…
The Planetary Nebula NGC 3918
Harrington, J. P.; Walsh, J. R.; Barlow, M. J. +1 more
A detailed study of the planetary nebula NGC 3918, based on UV, optical, and radio observations, is presented. The central star has a predicted V magnitude of 14.6 and a luminosity of 6000 solar luminosities for a distance of 1.5 kpc. A contour map of the nebula in H-beta light is given. Velocity profiles of forbidden O II optical lines show that …
X-Ray Spectra of PG Quasars. II. The X-Ray--Ultraviolet Excess of PG 1211+143
Elvis, Martin; Green, Richard F.; Bechtold, Jill +2 more
Observations of the quasar PG 1211 + 143 are presented and its continuum is modelled in terms of an accretion disk and an underlying power law. The X-ray spectrum in the Einstein imaging proportional counter band is well described by a power law with the very steep spectral index 2.2 + or - 0.4. The overall continuum spectral energy distribution c…
On the Evolution and Activity of Cometary Nuclei
Bar-Nun, A.; Prialnik, D.
The thermal evolution of a spherical cometary nucleus (initial radius of 2.5 km), composed initially of very cold amorphous ice and moving in comet Halley's orbit, is simulated numerically for 280 revolutions. It is found that the phase transition from amorphous to crystalline ice constitutes a major internal heat source. This transition does not …
The progenitor of SN1987A
Panagia, N.; Talavera, A.; Clavel, J. +6 more
One of the reasons why the bright supernova SN1987A is of such importance is the fact that its proximity would allow for the first time, the identification of a supernova progenitor star. Attempts to establish which star was the progenitor have led to uncertainties, however. Here we use spatial and spectroscopic information from International Ultr…
Rotational modulation and flares on RS CVn and BY DRA stars. III. IUEobserations of V711 Tau = (HR 1099), II Peg and AR Lac.
Doyle, J. G.; Linsky, J. L.; Simon, T. +8 more
The authors present observations of three RS CVn stars, which were obtained over the stellar rotation cycles with the IUE satellite. Emission lines from high-temperature transition regions and chromospheres analogous to those observed in the solar spectrum were observed. However, the stellar line surface fluxes are hundreds of times the solar valu…
IUE Observations of Comet p/ Halley - Evolution of the Ultraviolet Spectrum Between 1985SEP and 1986JUL
Feldman, P. D.; A'Hearn, M. F.; Schleicher, D. G. +13 more
The ultraviolet spectrum of comet P/Halley (1982 i) was monitored with the International Ultraviolet Explorer (IUE) satellite observatory between 1985 September 12 and 1986 July 8 (r < 2.6 AU pre- and post-perihelion) at regular time intervals except for a two-month period around the time of perihelion. A complete characterization of the UV spe…