October 2014 - Double Star of the Month
About 2 degrees north of iota Cephei can be found the pair STF2947 (22 49 00.68 +68 34 12.2). This neat 4".6 pair can be well seen in 15-cm and the magnitudes are 6.9 and 7.2. Sissy Haas notes that iota is golden colour and STF2947 is a pair of yellowish-peach stars. Hipparcos does not appear to have observed this pair but it does appear in the 1952 Yale Catalogue of Parallax where the distance is given as 120 light years but with an uncertainty of 20%. A third star of magnitude 12.5 can be found at 208 degrees and 121" but it does not share the space motion of the close pair. About two degrees south is STF2948 (7.3, 8.6, 4 degs, 2".6))
Theta Gruis (23 06 52.77 -43 31 17.2) is the brighter component of the very wide pair SHY 366. The nomenclature refers to Shaya and Olling who in 2010 made a study of wide pairs in the Hipparcos catalogue for which the proper motions were very similar. In the case of Theta Gruis they concluded that the likelihood that A and C (mags 4.5 and 7.8, 292 degs, 159") were physical was 100%. The distances to A and C are respectively 131.9 and 130.4 light years. Jacob then discovered that A itself was a close pair with star B of magnitude 6.6, being found at 114 degrees and 1".5 in 2009. William Stephen Jacob was an Army engineer with a deep interest in astronomy an during secondment on duty in India in the 1840s managed to make some observations of double stars. He used the 6.3-inch Lerebours refractor at Madras to make some micrometric measurements and also discovered a number of new pairs. The WDS contains 24 pairs bearing his discovery number which also includes the binary JC 8 and the Antares lookalike-pair 21 Sgr = JC 6 (see the column for Sep 2008).
Bob Argyle - Double Star Section Director