Double Star of the Month in Carina

• March 2017 - Double Star of the Month

  STF 1282 in Lynx (08 50 44.28 +35 04 15.4) is a neat pair which can be found 7 degrees north of iota Cnc and a little east. The components are magnitude 7.6 and 7.8 and in 2015 I found the relative position to be 282 degrees and 3".41.

  There has been little motion between the two stars since the pair was found by F. G. W. Struve. Also called S 582. Burnham records yellowish white and very white.

  A faint and distant star, mag 12.4 at 49", has a common proper motion with AB and is therefore likely to be a physical member of the system. It was found by the French observer G. Soulie. It, in turn, has a companion of magnitude 14.6 some 19" away which was found by Robo-AO, the first robotic adaptive optics system which is mounted a 60-inch telescope on Palomar Mountain.

  upsilon Carinae (09 47 06.12 -65 04 19.2) is a 3rd magnitude (actually V = 2.97) star which is brilliant white and is accompanied by a mag 6.0 companion which is also white.

  The separation between the two has barely changed since the early 19th century when the pairing was first noted by Rumker in Australia. It is almost certain that this is a binary system and both stars are massive, luminous and hot.

  The primary is an A8Ib supergiant with an absolute magnitude of -5 giving it a luminosity of about 9000 suns whilst the companion is somewhat earlier in spectral type (B3 or B4) and is about 600 times brighter than the Sun.

  Not surprisingly Sissy Haas includes it as a showcase pair and small telescopes should suffice in dividing the stars although the significant brightness difference might militate against using too small an aperture - the separation is currently 5".

  A paper written in 1986 speculates that the period of the pair might be close to 19,500 years, and gives the distance as 400 pc. In 2007 the Hipparcos satellite found 440 pc but with a formal error of 54 pc. E. J. Hartung notes the pair HJ 4252 (9.3, 9.5, 303 degrees, 12") about 5 arc mins south following.

  Bob Argyle - Double Star Section Director

• 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