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