February 2016 - Double Star of the Month

38 Gem (06 54 38,63 +13 10 40.1) can easily be swept up since it directly follows the 3.4 mag xi Gem by a little over 2 degrees.

The current orbital period, 1898 years, as determined by Brian Mason in 2014, is clearly very uncertain but the position for 2016.0 is 143° and 7".31 in close agreement with measures by the writer late last year. The stars are of visual magnitude 4.8 and 7.8 so the quadrant in which B lies is certainly the second whilst Sissy Haas puts it in the 4th.

Admiral Smyth gives light yellow and purple, but E. J. Hartung sees yellowish and pale-orange, whilst to Sissy Haas the colours appear lemon-white and greyish.

A third, much fainter star C of mag. 11.3 can be seen at a distance of 119" whilst Andrei Tokovinin noticed a 15.0 mag dot at 151". The primary, a dwarf star of spectral class F0 is 96 light years away.

STF1121 (07 36 35.71 -14 29 00.3) is not a double or multiple star - rather it forms the bright core of the open cluster M47 in Puppis.

This cluster was discovered by the Italian astronomer Giovanni Hodierna sometime before 1654. As well as finding a dozen or so deep-sky objects before Messier catalogued them, Hodierna also compiled a small list of double stars.

The WDS contains 26 entries to cover this system and its large array of comites, but the small telescope user will easily be able to see AB (6.9, 7.3 at 300° and 6".5), whilst amongst the more obvious comites D is mag 9.5 at 72" (distance increasing), E is 9.9 at 70" (distance decreasing) and G is 7.7 at 82".

It is perhaps best seen with a pair of large binoculars. A report on the Cloudy Nights website for 2004 notes that the AB pair can be split easily with Celestron 25 x 100s. M47 and nearby M46 can be swept up in a wide-field telescope by moving 20 degrees due south of Procyon.

Bob Argyle - Double Star Section Director