January 2017 - Double Star of the Month

The two pairs selected for this month are ostensibly relatively, bright and wide pairs; easy for the small aperture, or even binoculars. In fact, both are more complex.

The northern object is S 503 in Orion (05 56 03.43 +13 55 29.7). The brightest stars are mags 6.7 and 8.4 and they are currently 76" apart in position angle 322 degrees. The WDS however lists 6 companions, most are field stars but at least one is travelling through space with S 503.

Component C (mag 11.6 at 310° and 55".3) and D (mag 8.2 at 334° and 299") both also found by South are optical and should be visible in 10-cm aperture. Willem Luyten found a 13 magnitude star at 205° and 47" (E) which has the same space motion as A and which the WDS notes is a white dwarf.

In late 2015, Marcel Fay, who has been publishing his CCD astrometry with a 283mm reflector in El Observador de Estrellas Dobles found two further stars of around magnitude 13 (F and G) at distances of 32" and 9" from A. The status of these is as yet unclear but further measures will show whether they are co-moving with A.

In 2011 Shaya and Olling published a list of widely separated pairs of stars with common proper motions. This list includes pairs such as Capella and 50 Per, and gamma and tau Persei which have almost 100% probability of being physically related.

Number 185 on this list is a wide pair of apparently unrelated stars in Columba: SHY 185 (06 36 54.07 -36 05 18.4). Star A is a G1 dwarf of visual mag 6.4. Some 288" away in PA 129 is a mag 7.3 star (B) of spectral type G0V. Both stars are close binaries of short period.

A is RST 4816 which has a period of 14 years and is currently at 99° and 0".1 according to the orbit, whilst B was found by W. S. Finsen (FIN 19) and is predicted to be 339° and 0".3 at present. The Hipparcos parallaxes for A and B agree well within the quoted errors and the proper motions are similar.

There are two other double stars to be found close by. One is UC 1454 (7.2 and 12, 181°, 33"), on the southern edge of SHY 185 and about 40 arc minutes south of the group is the fine pair BU 755 whose stars of mags 5.9 and 6.9 are now 1".5 apart and a faint third component which is mag 11.5 can be see 21" away (HJ 3875).

Bob Argyle - Double Star Section Director