February 2020 - Double Star of the Month
Starting at the fine pair 38 Gem (see this column for Feb. 2016) and moving 2 degrees due East, brings the observer on the pair STF 1007 (07 00 37.52 +12 43 24.2) and, a further 20 arc-mins East, upon HJ 3288.
The brighter and wider of the two is STF 1007 which was left out of Lewis' treatise on the Dorpat pairs because it was too wide (the writer found 28 degrees, 67".4 in 2014). In fact, Burnham noted two fainter and closer companions on March 16, 1873 with his 6-inch refractor, neither of which could be seen in the 8-inch Thorrowgood with the micrometer field illumination on. C is 11.4 at 300 degrees, 15" and D is 10.0 at 244 degrees, 22" whilst Burnham called them magnitudes 14 and 12 respectively. The Washington Double Star Catalog (WDS) notes that D was found to be a close lunar occultation double.
HJ 3288 is a pair with magnitudes 7.3 and 8.7 and the writer found 217 degrees, 38" in 2013.
Originally found as a close bright pair by F. G. W. Struve, STF 1104 (07 29 21.91 - 14 49 53.40) turns out to be a physical quintuple system. The AB pair has magnitudes of 6.4 and 7.6 and at discovery was found at 292 degrees, 2".4. At 2017 it was 38 degrees, 1".8 and a preliminary orbit was computed by A. A. Tokovinin in 2014 who found a period of 729 years. This predicts a minimum separation of 1".7 around 2045 so the pair is always within range of 10-cm.
In the 1880s two further stars were noted - an 11.8 at 20" (C) and a 13.2 at 72" (D). Since then D has been rapidly left behind by the considerable proper motion of AB, which is 0".3 per year. C, however, is keeping pace and is clearly physical. Dr. Tokovinin also found that C was a close pair of dwarf stars separated by 0".1 and also noted that a star 1072" away which was noted by Luyten and labelled LP 722-24, is also moving through space with a similar proper motion and distance.
The group is 120 light years from us.
Bob Argyle - Double Star Section Director