May 2024 - Double Star of the Month

STF 1834 (14 20 17,6 +48 30 25.1) sits in the north of Boötes, about half way between theta and lambda Boo and 2.5 degrees north north-east of the latter.

Finder chart for the double star STF 1834 in Boötes
A finder chart for the double star STF 1834 in Boötes created with Cartes du Ciel.

It is a well-known binary and the Washington Double Star catalog (WDS) notes than 250 direct measurements have been since discovery by Struve at Pulkova. From about 1830 to 1900 the two stars, magnitudes 8.1 and 8.3, closed steadily from 1".7 but then in just a few years the companion swung around its partner at which point it was out of range of even the large refractors of the time and began heading out towards the discovery position.

The period of the pair is 413 years and at the present time the position angle and separation are 204 degrees and 1".7. The relative faintness of the stars would suggest that an aperture of 15-cm would be better to view them.

About 1 degree south-east is STF 1843, a pair of stars of magnitude 7.7 and 9.2 currently at 186 degrees and 19".8. The stars lie at a similar distance and have common proper motion.

Near the border of Libra with Lupus, HJ 4774 (15 28 58.69 -28 52 00.5) was discovered by John Herschel from Feldhausen during his stay at the Cape of Good Hope. The brightest star is magnitude 7.0 and has a 9.6 magnitude companion almost 10 arc-seconds distance in PA 11 degrees.

Finder chart for the double star HJ 4774 in Libra
A finder chart for the double star HJ 4774 in Libra created with Cartes du Ciel.

In 1889 the eagle-eyed S. W. Burnham found that the primary star was double again with a 7.7 magnitude star at a distance of 0".7. Since then the separation of the close pair has closed to 0".1. A recent orbit by Dr. Andrei Tokovinin indicates that the orbit is only 0.6 degrees from being edge-on and in 2027 when periastron occurs the two stars will be only 8 milliarcseconds apart.

Bob Argyle - Double Star Section Director