July 2023 - Double Star of the Month
STF 2367 (18 41 16.36 +30 17 40.9) is a challenge to the observer with 30-cm available. It is always a difficult object throughout its 92 year orbital cycle, partly because the apparent orbit is inclined and very eccentric and so at times the separation of the stars dips below 0".02 and the angular motion amounts to 1 degree every 6 days. At apastron the stars reach a maximum separation of 0".45 which is where they are now, (actually apastron is reached in 2027), so this is a very good opportunity to resolve this difficult pair.
The stars have magnitudes of 7.7 and 8.0 but another star of magnitude 8.8 is 14" distant and there are three much fainter components at 22" (mag. 12), 42" (15.1) and 152" (11). The system lies in Lyra in a region to the south-west of beta and gamma Lyrae but with no obvious pointers to aid location. There is a curve of stars nearby which can be found from gamma Lyrae.
H 6 50 (18 49 40.96 -05 54 46.2) lies in Scutum close to the Wild Duck Cluster (M11) which is just 25 arc minutes to the south-east. The Cambridge Double Star Atlas (2nd ed.) also shows the pair STF 2391 (18 48 39.49 -06 00 15.5) nestling just 15 arc minutes to the west-south-west.
H 6 50 is a very wide and somewhat unequal pair. The magnitudes are 6.2 and 8.2 and the stars are 112" apart in 2016 at PA 171 degress. A much fainter star, magnitude 12.5 was added by Burnham in 1879. It is due north and 25 arc seconds distant. A rather puzzling note in the Washington Double Star catalog (WDS) Notes identifies H 6 50 AB with STF 2391 but it is difficult to see how this can be. STF 2391 has, according to the WDS, magnitudes of 6.5 and 9.6 at 332 degrees and 38".
Bob Argyle - Double Star Section Director
