Double Star of the Month - February 2009
In this series of short articles, a double star in both the northern and southern hemispheres will be highlighted for observation with small telescopes, with new objects being selected for each month.
STF1338 (09 20 59.4 +38 11 17.9) is a beautiful binary about 1.5 degrees north of the 4th magnitude star 38 Lyncis which is also a pretty pair. Its almost equal components are given as mags 6.72 and 7.08 in the WDS which also notes a third faint star (mag 11.4) some 144" away in PA 166 degs. Hartung finds the colours both bright yellow whilst Smyth and Chambers in the Cycle of Celestial Objects second edition of 1881 give both stars to be white. The WDS perhaps favours the latter colours listing the spectral types as F2V and F4V. Orbital motion is slow and from the discovery position of 121 degrees, 1".76 the pair has advanced to 303 degrees, 1".01 in 2009 according to the 303 year period given in the USNO 6th Orbit Catalogue. This pair is 42 parsecs distant according to Hipparcos and is an easy object in a small telescope at all times. It reached a maximum distance of 1".65 in 1865 and closest approach will be about 0".96 in 2044.
Gamma Volantis (or Piscis Volantis) (07 08 44.82 -70 29 57.1) is a showcase pair according to Sissy Haas in her book and an observation by Ross Gould with 35-cm records the colours as deep yellow and dull yellow. With magnitudes 3.86 and 5.43 this is clearly one of the sky's most spectacular pairs but Smyth and Chambers merely note: 'A double star'. Hartung gives bright golden and pale yellow for the stars whose spectral types are KOIII and F2V. The discoverer was Dunlop and it is number 42 in his catalogue. Since 1826 there has been little motion in either PA or separation - possibly a slight closing but at 14".4 this is a pair for the small telescope or stabilized binoculars. The bright star is some 53 parsecs away.
Bob Argyle - Double Star Section Director