Double Star of the Month - January 2008
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.
The two binary stars being highlighted this month have in common long orbital periods but differ in other respects. Whilst 14 Ori has a relatively circular, face-on orbit, the orbit of HJ 3683 is both highly inclined and highly eccentric.
14 Ori = STT98 (05 07 52.87 +08 29 54.9) This is one of Otto Struve's discoveries with the 15-inch refractor at Pulkova. The stars are magnitude 5.76 and 6.67 and both appear white to the writer but Hartung saw them as pale and deep yellow. The primary is of spectral type Am. The orbital period of 198 years sees the stars range in separation from 0.7 to 1.1 arc seconds so they can be seen with small to moderate apertures on most occasions, although the quoted magnitude difference of 0.9 always seems a little optimistic and good seeing is essential to see them well from the latitude of the UK. The writer found the pair at 305°.9, 0".90 in late 2006. Hartung points out that the fainter pair STF643 some 6 arc minutes south has the same proper motion.
HJ 3683 (04 40 17.72 -58 56 39.6) was picked up by John Herschel in sweep 518 with his 20-foot reflector and he noted the pair as `very fine' and noted them as equally bright on two occasions whilst the WDS gives the magnitudes as 7.33 and 7.45. At the time of discovery the separation was about 3.5 arc seconds but the pair began to close and when Innes observed it in 1922, the star was single. At the last measurement recorded in the WDS for 2002 the pair appeared close to its discovery position. This is a system very similar to gamma Virginis but with an even more eccentric orbit (e = 0.95) and longer period (326 years). At periastron in 1918 the angular separation was 0.03 arc seconds and the angular velocity 1 degree per day. This pair of G dwarfs is 31.2 parsecs distant according to the revised parallax calculated by Floor van Leeuwen in his book `Hipparcos, the New Reduction of the Raw Data' issued by Springer (2007).
Bob Argyle - Double Star Section Director