Double Star of the Month - May 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.

Both binaries in this months notes had orbits calculated for them about 20 years ago by Wulff Heintz, a great visual observer who died on June 10, 2006 after more than 50 years of observational activity. The orbits remain in the catalogue.

Located in the western part of Bootes, STF1785 (13 49 0.28 +26 58 48.5) is a rather faint (mags 7.4 and 8.1) but attractive pair of orange K-type dwarf stars, discovered by Sir James South in 1823. The system is located fairly near the Sun at a distance of about 45 light years. The predicted position for mid-2008 is 179o.9, 3".13 but recent measures by the writer seem to indicate that the position angle is about 3 degrees smaller than this possibly suggesting that the 155.75 year period is a little short.

Lupus is a bright constellation located halfway between the head of Scorpio and alpha and beta Centauri and it contains some beautiful pairs for telescopes of all apertures. Gamma Lupi, (15 35 08.46 -41 10 00.1) a brilliant white binary whose primary is a distant B subgiant has a highly inclined orbit of 190 years period and at times of closest approach the two

components are only 0.07 arc seconds apart as happened in 1930. The stars of apparent magnitude 2.95 and 4.45 are currently almost at maximum separation (0".83 in 2013) so see them whilst you can. Fortunately this pair was near widest separation when found by John Herschel from the Cape in 1835.

Bob Argyle - Double Star Section Director