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Griffin R.F.,The Observatories | Filiz Ak N.,Erciyes University | Filiz Ak N.,Pennsylvania State University
Astrophysics and Space Science | Year: 2010

We present spectroscopic orbits for the active stars HD 82159 (GS Leo), HD 89959, BD +39° 2587 (a visual companion to HD 112733), HD 138157 (OX Ser), HD 143705, and HD 160934. This paper is a sequel to one published in this journal in 2006, with similar avowed intention, by Gálvez et al. They showed only graphs, and gave no data, and no orbital elements apart from the periods (only two of which were correct) and in some cases the eccentricities. Here we provide full information and reliable orbital elements for all the stars apart from HD 160934, which has not completed a cycle since it was first observed for radial velocity. © 2010 Springer Science+Business Media B.V.

Griffin R.F.,The Observatories
Journal of Astrophysics and Astronomy | Year: 2012

The 'Redman K stars' project, described more particularly in the paper immediately following this one, involved the repeated measurement on a quasi-annual basis of the radial velocities of a group of 86 seventh-magnitude late-type stars over an interval of 45 years. Certain of the stars proved to vary in velocity and were then transferred to a different observing programme, in which they were measured more frequently with a view to determining their orbits. Orbits have already been published for 18 of the stars. Presented here (and summarized in Table 9) are the results on six more; all are single-lined. One of them (HD 191046, a star which has a literature coverage about ten times as rich as that of any of the others, probably on account of its high space velocity which includes a γ-velocity of nearly -100 km s -1) has a good orbit with a period of about 8000 days (22 years). Five others (HD 3345, 15728, 20509, 188058 and 191084) have orbits that are perfectly secure in principle, but their periods range between 40 and perhaps 70 years, and (particularly in some cases) their radial velocities have not been observed well enough for long enough to establish either the periods or the orbits very accurately. One star, HD 9354, has exhibited a monotonic variation of velocity throughout the duration of the observing programme; it is possible to draw a Keplerian velocity curve that does justice to the measurements, but it cannot be expected to have much predictive power. © 2012 Indian Academy of Sciences.

Griffin R.F.,The Observatories
AIP Conference Proceedings | Year: 2011

This contribution is about the application of spectroscopic techniques to the study of binary stars. Some examples analyzed by the author are shown. © 2011 American Institute of Physics.

Griffin R.F.,The Observatories | Fuhrmann K.,Ruhr University Bochum | Fuhrmann K.,Isaac Newton Group of Telescopes
Monthly Notices of the Royal Astronomical Society | Year: 2013

HD 75767 is a nearby solar-type star. It has an unseen companion with which it is in an orbit that is very slightly off-circular and has a period of about 10 d. In addition, it has a faint visual companion. Wraight et al., in a recent paper, have built a considerable edifice on the idea that the orbital period has shown a perceptible change within the last 100 yr. We point out that the phase shift that constitutes their evidence for such a change arises only from their use of their own, relatively inaccurate, value for the period. Rotational-velocity measurements for HD 75767, published independently by each of the authors and by others, have all been smaller than would correspond to the equatorial velocity if the star's rotation were synchronized to the orbital revolution. Each of the present authors has accordingly proposed (explicitly on the assumption of synchronism) an inclination corresponding to his favoured value of v sin i. There is, therefore, implicit surprise at the discovery by Wraight et al. that the system exhibits eclipses and therefore the orbital inclination must be close to 90° The logical conclusion must be that the star is rotating more slowly than would correspond to synchronism with the orbit.2013 The Authors.

Griffin R.F.,The Observatories | Stroe A.,The Observatories
Journal of Astrophysics and Astronomy | Year: 2012

The 'Redman K stars' are a group of 80-odd seventh-magnitude late-type stars, nearly all giants, distributed along the Galactic equator between approximate longitudes 50° and 150° (roughly Sagitta to Cassiopeia). Their radial velocities have been measured systematically once per season in 30 of the 45 seasons from 1966 to 2010/11. At least 26 of them (30%) have proved to vary in velocity. Orbits have been derived for all but one of the 26, many of them having longer periods than have normally been associated with spectroscopic binaries; several are comparable with, or longer than, the present duration of the observing campaign. Also reported here are radial-velocity measurements made casually of stars seen in the fields of some of the Redman stars. Two of the companions have proved to vary in velocity on long time-scales, and (somewhat preliminary) orbits are given for them. © 2012 Indian Academy of Sciences.

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