Double Star of the Month - August 2008

In this series of short articles, a double star in both the northern and southern hemispheres will be highlighted for observation with small telescopes, with new objects being selected for each month.

95 Herculis (18 01 30.40 +21 35 44.5) is a double star much beloved of the Victorian observers, due to the suspicion that the colours of the components changed over a period of years. Hartung records pale and deep yellow, a conclusion agreed with by Frew and Malin in their revision of his book. Chambers, in his revised version of Smyth's `Celestial Cycle' notes that a friend of Smyth, a Mr. Higgens of Bedford, claimed that the intensity of the green and red colours of A and B varied from time to time and that the green star recovered its hue first. `On this statement being submitted to Sir G. B. Airy he did not view it with favour'.

It seems likely that this pair is binary - the significant proper motion in dec of A (0.039 arc seconds per year) would have carried it 9 arc seconds away from B over 230 years, whilst the separation has reduced from 9".0 in 1777 to 6".3 in 2007 with a small decrease in position angle. The revised Hipparcos parallax puts the A5 giant primary at 123 parsecs. This is one of the finest pairs in the northern sky for small telescopes.

The Australian amateur Walter Gale has his name on three stars in the WDS catalogue. Gle 3 was described in August 2007 notes and Gle 2 is xi Pavonis, (18 23 13.62 -61 29 38.1) a bright yellow giant K4 star. The revised Hipparcos parallax puts the star at 143 parsecs and the relative position of the companion has changed from 140°, 4".0 in 1894 to 156°, 3".4 in 1988. Hartung gives the colour of the companion, some 3.7 magnitudes fainter than the V=4.4 primary, as white.

Bob Argyle - Double Star Section Director