Double Star of the Month - November 2012
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.
STF 162 (01 49 15.54 +47 53 49.0) sits in an obscure corner of Perseus about 6 degrees north and 2 degrees preceding gamma And. It is also about 1.5 degrees south following 51 And. It is a multiple star, four components of which can be seen in 7.5-cm. The closer pair, which consists of components of magnitudes 6.5 and 7.2, was found by Struve in 1828 when the separation was 2".2 and the position angle 227 degrees. At the current epoch these have both decreased to 1".9 and 298 degrees. A third star which remains fixed with respect to A can be found 20" away almost due south, and another at mag 10.1 is 139" distant. The WDS reveals that either A or B is itself an interferometric binary with a separation less than 0".2 and B is also a spectroscopic binary.
Epsilon Sculptoris (01 45 38.65 -25 03 08.8) is a fine pair located in the extreme north-east corner of Sculptor and which can be seen from the UK but which first caught the attention of John Herschel at Feldhausen when he noted 'large * w(hite) small star dull red' an gave the magnitudes as 6 and 10(modern values 5.4 and 8.5). Since then the companion has moved slowly retrograde from the discovery position of 72 degrees to its current value of 20 degrees. In 1969 de Freitas Mourao looked at the observations and decided that they could be fitted by a face-on circular orbit with a separation fixed at 4".65 and a period of almost 1200 years. In recent years, however, the companion has begun to stray ever further from the primary and the separation is now over 5". More observations are needed but the real orbit will not be obvious any time soon, and in fact the apparent motion to date looks more linear than curved. However, epsilon Scl is relatively nearby (92 light years) and the annual proper motion of 0".16 would take it almost 30" from B since discovery if the latter was optical. Hartung called it an easy, bright yellow pair whilst Gould with 175-mm called the primary pale yellow.
Bob Argyle - Double Star Section Director