October 2019 - Double Star of the Month
STTA 1 in Cepheus (00 14 02.61 +76 01 37.2) can be found 2.5 degrees south-east of gamma Cephei. It is the first entry in the appendix catalogue of 256 pairs with separations between 32" and 2' which Otto Struve compiled when he surveyed the heavens for new close pairs with the large refractor at Poulkova.
Gaia DR2 confirms that the difference in the stars' distances is more than 300 light-years. The primary is an M4 giant whilst the secondary is spectral type G5.
Just over one degree north is the binary STF 13.
In late 2019 the stars can be found at 48 degrees and 1". The writer always found it somewhat difficult to see clearly due to the difference in the magnitudes, but the Washington Double Star Catalog (WDS) gives 7.0 and 7.1, whilst in the G-band, similar to V, DR2 gives a deltaM of about 0.4.
About 4.5 degrees north and east of the first magnitude star Fomalhaut is epsilon PsA, a star of magnitude 4.2. Head due south by about 1.5 degrees and you will alight on the wide pair H VI 119, (22 39 44.12 -28 19 32.0) an object found by the elder Herschel in 1783.
The current position is 159 degrees and 86" and the magnitudes are 6.4 and 7.5. Even with small apertures, however, it should be apparent that B itself is a double star, a fact that Herschel discovered when he revisited the system around 1800 and called it H N 117. The close pair was rediscovered by John Herschel in 1834, giving it the number HJ 5356, but this has now been discontinued.
Ross Gould, who has observed it with 175-mm, notes that the primary is deep yellow whilst both stars in the close double companion are pale yellow. The 7.5 and 8.6 magnitude stars are separated by 3" in PA 70 degrees with both these values increasing slowly since discovery. This is a physical triple - DR2 shows almost identical parallaxes and proper motions.
Bob Argyle - Double Star Section Director
