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Giotto IMS measurements of the production rate of hydrogen cyanide in the coma of comet Halley.
Schwenn, R.; Balsiger, H.; Geiss, J. +7 more
The ion composition measurements in the ionosphere of comet Halley by the ion mass spectrometer (IMS) experiment on the Giotto spacecraft are used to estimate the relative abundance of HCN. From a comparison of the normalized number density of ions with mass-to-charge (M/q) ratio of 28 AMU/e with steady-state photochemical models, it can be determ…
A New Powerful Test for Periodic Pulsed Emission of High-Energy Photons
Swanepoel, J. W. H.; de Beer, C. F.
A novel stastistical test devised for detecting periodic pulsations in a series of photon arrival times is found to perform powerfully in the detection of multiple, narrow peaked light curve shapes against a uniform background, especially if the light curve has multiple peaks. The statistical test has been applied to observations of the first 1350…
The UV spectrum of the WC 11 star CPD -56 8032.
Nandy, K.; Kameswara Rao, N.; Giridhar, S.
UV observations of the WC 11 central star of the compact planetary nebula CPD -56 deg 8032 show that the continuum flux is variable. This variability appears to be caused by a change in the circumstellar extinction properties. The UV energy distribution can be fitted with helium star models with T(eff) about 25000 K, after correcting for two types…
Hot Degenerates in the MCT Survey. I. MCT 0130-1937, a New, Color-selected PG 1159 Object
Kepler, S. O.; Fontaine, G.; Wesemael, F. +4 more
In the course of a survey for high-latitude, UV excess objects in the Southern Hemisphere, a new white dwarf star belonging to the PG 1159 spectroscopic class was discovered. A variety of spectroscopic observations show this object to be similar to the prototype PG 1159 - 035 in exhibiting He II, C IV, and O VI features in its optical spectrum, as…
X-ray spectra of three BL Lac objects.
Maccagni, D.; Garilli, B.
We present the results of the analysis of twin EXOSAT observations of three BL Lac objects, namely PKS 0521-365, PKS 0548-322, and I Zw 186. The energy spectra between 0.02 and ~ 7 keV can generally be described by power laws with a low energy cut off due to absorption by hydrogen in our galaxy. However, while PKS 0521-365 has a spectrum with an e…
The IUE spectrum of the Wolf-Rayet system HD 193077.
Koenigsberger, G.
The results of a detailed line-identification study of the IUE(1100-1900 A) spectrum of the Wolf-Rayet star HD 193077 (WR 138) is presented. The emission line spectrum is shown to be dominated by Fe V+Fe VI lines below 1500 A. The interstellar-line spectrum contains a large variety of atomic and ionic species, ranging from C I to Si IV and C IV, a…
VLBI and Optical Astrometry of Southern Extragalactic Radio Sources and Radio Stars
White, Graeme L.; Jauncey, David L.; Lestrade, Jean-Francois +3 more
Mark III very long baseline interferometry (VLBI) has been used to determine the positions of ten compact extragalactic radio sources in the southern hemisphere. These positions are relative to the Jet Propulsion Laboratory VLBI celestial reference frame and are accurate at the 0.01" level, more than an order of magnitude improvement compared to t…
Spectroscopic binary orbits from ultraviolet radial velocities. Paper 6: Gamma 2 Velorum
Stickland, D. J.; Lloyd, C.
Off-nucleus IUE observations of NGC 1275.
Norgaard-Nielsen, H. U.; Jorgensen, H. E.; Hansen, L.
We have mapped the brightest parts of the two velocity systems of ionized gas in NGC 1275 with IUE. We have detected extended Lyα and an UV continuum at several positions. The Lyα emission originates from the low velocity system and, we argue, probably also the UV continuum. The UV continuum is consistent with star bursts with ages <= 2 10^7^ y…
Hydrogenated Amorphous Carbon Grains in Comet Halley?
Colangeli, L.; Fonti, S.; Bussoletti, E. +3 more
Recent IR observations of Comets Halley, Wilson, and Bradfield have shown the existence of an emission feature falling at around 3.4 microns. In this paper, it is shown that a good fit of both the IR continuum and the band can be obtained by assuming a simple thermal emission model based upon the optical properties of hydrogenated amorphous carbon…