Double Star of the Month - February 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.
15 Lyn (06 57 16.60 +58 25 23.0) is on the western edge of a coarse cluster of double stars which also includes the close binaries 4 and 14 Lyn. Discovered at Pulkova by Otto Struve at a distance of about 0".5 the two stars slowly widened reaching around 0".9 at the turn of the last century before the companion made a close (0".1) approach to the primary and is now slowly widening again. This is a good opportunity to see this pair which needs 20-cm on a good night because there is also a substantial difference in brightness of about a magnitude. Andreas Alzner's orbit from 2000 gives the ephemeris position of 232° 0".67 for 2012.0. It is missing from Sissy Haas' book which is a little odd given that 4 Lyn is included and is similarly difficult to resolve. A good night may also show the faint companion discovered by Burnham. This 12.5 mag star can be seen at 346° and 29" whilst a more distant 9.5 is some 187" away and the distance to AB is decreasing due to proper motion of the bright pair.
Dun 39 (07 03 15.12 -59 10 41.1) is in Carina, lying about 3 degrees north preceding alpha Pictoris and forms a beautiful white pair which is easily resolvable in a small aperture. When discovered by Dunlop from Australia in 1826 the stars were separated by 2".8. The revised version of Hartung (1995) by Malin and Frew repeats the note in the original edition that it can just be seen with 7.5-cm aperture, but the two stars are closing and the last measure in 1997 put the separation at 1".4. In 2006 Graeme Jenkinson and Tin Napier-Nunn of the Astronomical Association of Queensland noted that x320 was needed on a 15-cm f/8 OG to see it clearly so it will be interesting to see if it is still accessible to 7.5-cm now. The pair is clearly binary and lies almost 500 light years away.
Bob Argyle - Double Star Section Director