Double Star of the Month - June 2013

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.

Situated in the north of Bootes, STT 298 (15 36 02.59 +39 48 08.7) is one of the more rapid binary systems found by Otto Struve at Pulkovo and it now embarking on its fourth orbit since discovery. Look for the naked-eye pair nu1 and nu2 Bootis some 6° following beta Bootis and STT 298 can be found just south preceding phi Bootis. The star is nearby (the distance is 73 light years) so the orbit is relatively large in angular terms. The stars are almost near peristron and at 182°, 1".18 in mid-2013 they offer a good opportunity to see a pair with a period of only 55.6 years. The system moves across the sky at almost 0".5 per year and is accompanied at a distance of 121" by star C which is mag 7.8 and also a K dwarf. For the telescopic observer there are two fainter but unrelated stars of mags 12.1 and 13.9.

DUN 178 (15 11 34.82 -45 16 39.0) is an orange KOIII giant star of mag 6.3 accompanied at a distance of 30".6 by a mag 7.3 white star according to Richard Jaworski using a 100-mm aperture in Australia. Both these stars appear in the Hipparcos catalogue but do not appear to be connected in any way. A is 510 light years away whilst B is 400 light years distant. At discovery in 1826 the pair were separated by 40" so the change is purely due to different proper motions. This pair is located in the heart of Lupus, a constellation rich in visual double stars, and can be found in the same low-power field as lambda Lupi. In 1929 Willem van den Bos, using the 26.5-inch refractor in Johannesburg, found a companion of mag 9.6 some 1".1 distant from A. There has been little change in the position of this star in the intervening 80 years and it offers a challenge to a 30-cm telescope in a good location.

Bob Argyle - Double Star Section Director