Double Star of the Month - June 2010
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.
To the small telescope user STF1964 (15 38 12.96 +36 14 48.3) is a pair of 7.9 and mag 8.0 white stars separated by about 14". Readers of Celestial Objects for Common Telescopes will note that the stars are given as mags 6.8 and 7.3, a considerable difference to the quoted WDS magnitudes above. STF1964 lies about half a degree south preceding zeta CrB, a much brighter and somewhat closer pair. STF1964 is, however, not without its attractions. Each of the two stars is a visual double - the fainter component actually known as C was found by Struve and the writer managed to measure this 1".4 pair last year. The brighter star A (=HU 1167) is somewhat closer but the companion (B) is fainter and this system is a challenge to those with 25 to 30-cm of aperture. In 1970, professional observer Richard Walker of USNO reported that star A had another closer companion at a distance of 0".1 but there has not yet been confirmation of this star.
HN 28 (14 57 27.99 -21 24 55.8) is also known as Hh457 in Webb. Star A is number 570 in the Gliese Catalogue of Nearby Stars. It is 19.1 light years distant and with both stars moving through space at more than 2" per year, it is a physical system. In 1806 Piazzi measured both stars and at that time the position was 251 degs and 9".4. In 2009, the writer found 306 degrees and 25".3. The stars are 5.8 and 8.2 and offer a fine colour contrast. Star A is spectral type K5V and orange in colour whilst B is type M2V and red, the colours being noted by Hartung. Sissy Haas calls it 33 Lib and notes that Smyth made it ``straw coloured and orpiment yellow". The USNO 6th orbit catalogue includes it with a period of 2130 years. In 1990 B was found to be a close binary with a period of 308 days and a separation of 0".2. To the small telescope user there are a number of fainter companions ranging from mag 9.5 to 13 or so all of which are being left behind by the principal stars.
Bob Argyle - Double Star Section Director