Double Star of the Month - May 2008
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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