Liu Zongli, C. Sterken, J.-P. De Cuyper
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I.N. Cummings
abstract
A.M van Genderen
abstract
A photometric atlas of Comet Halley images
We present a catalogue of over one hundred digitised photographic images of comet Halley obtained during the 1985--1986 apparition. The data were taken using telescopes at Xinglong Station of Beijing Observatory, China, and at Mt. John Observatory, New Zealand. Many activities of the plasma tail, such as jets, kinks, helices, rays, condensations and disconnections were recorded. All photographic images have been digitised using the PDS 2020GM microdensitometer at the Astronomical Institute of the University of Muenster, Germany. We present the catalogue of density and intensity images, and give the transformation formulae for calculating the relative intensities. A similar number of standard-star density frames are included, as well as about 400 spot-sensitometer calibration frames.
High precision radial-velocity measurements of
late-type evolved stars (Ph.D. Thesis)
Late-type evolved stars include the variable red giants, like Mira and semi-regular variables, and the pulsating supergiant RV Tauri stars. Despite this, K-type giants in the past were generally believed to be constant in photometry and radial velocity, but in the last decade it has been discovered that this is not necessarily the case. This was the motivation for spectroscopic observations of 44 late-type evolved stars to be carried out over three years, in the hope of helping to determine how common K giants variable in radial velocity are and whether the variations are related to those seen for other late-type evolved stars.
The observations were obtained at Mount John University Observatory and used with digital cross-correlation to achieve relative radial velocities of 50 m/s precision. At this precision all but eight of the observed stars were found to be variable in radial velocity. Thirteen stars also had broad-band photometry taken, because any one of orbital motion, rotation with starspots, pulsation and the motion of large convective cells could cause apparent radial-velocity variations. Knowledge of the relationship between light and radial-velocity variations can help distinguish between these different mechanisms.
The timescales for these different mechanisms were also estimated to help determine which was responsible for the variations observed. Generally the observed K-giant radial-velocity timescales were of the order of a few hundred days, which indicates they are due to one of binary motion, rotational modulation or non-acoustic non-radial pulsation. However, for M giants and supergiants the situation was very different with both short-term and long-term radial-velocity timescales being found in most stars. In most cases the short-term timescale is due to acoustic pulsation, while the long-term timescale could be due to any one of binary motion, surface features (including the motion of large convective cells) or non-acoustic non-radial pulsation.
(Book Review) C. Sterken and C. Jaschek
1996, Cambridge University Press, ISBN 052190168
Since about the early seventies no proper book on variable stars has been written. The probable reason is the explosive growth of the field of variable-star research during the 25 years since. It was not only the amount of observational data which grew so fast, but also the number of new types of variable stars and the knowledge of the causes of their variability. Variable stars also became of fastly growing importance for distance determinations, for the physics of stellar interiors and for stellar evolution. The two editors, together with seven other experts on variable stars have now found a perfect recipe to write a conveniently-sized book on variable stars. The time was ripe. They compiled a pictorial atlas of at least 200 typical light curves of tens of different kinds of variable stars. The book also gives a clear introduction to the historical background, the photometric systems, the nomenclature and the classifications. Each chapter provides a detailed account of each subclass and gives a concise description of the physical processes responsible for the variations. All specific variables discussed in the text can easily be located with the aid of object-name and subject indexes. The reference list contains about 600 entries, a guarantee that one can access a particular subject quickly and in debt. The quality of the figures and the tables is very good. Very useful is the inclusion of three lists, 'Journal abbreviations', 'Acronyms and abbreviations' and 'Addresses of interest', and of three tables concerning constellation names, Julian dates, and specialized newsletters on variable stars. This unique guide will be absolutely invaluable to students taking courses in variable-star research, as well as for professional and amateur astronomers.