Double Star of the Month - December 2009

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.

80 Tau (4 30 08.60 +15 38 16.2) is a an unequally bright (5.70, 8.12) binary star with a highly inclined orbit in the cluster of bright stars close to Aldebaran, more specifically about half a degree south following the bright binocular pair theta1,2 Tauri. Found by Struve in 1831, the companion headed towards the primary until by 1878, the great Italian observer Dembowski, in one of his last observations, failed to see B in his 7-inch Merz dialyte and by the 1890s the companion was invisible in the largest apertures. The companion passed close to A in the following years and since then has been continuing to widen, reaching maximum separation (1".75) in around 1987. By 2010.0 the star is at 16 degs, 1".64 and should be visible for several decades in 20-cm but choose a good night because the large difference in magnitude makes this a far from easy pair. A itself is a spectroscopic binary and the distance to this system is 150 light years.

Iota Pic (04 50 55.31 -53 27 41.5) is, according to Hartung, "an excellent object for small telescopes" and recorded the colours as yellow. The stars are magnitudes 5.61 and 6.24 and of spectral class F0IV and F4. Each component appears in the Hipparcos catalogue as a separate entry and the parallaxes, whilst each possessed of rather a large error, indicate that the stars are at the same distance from us i.e. about 130 light years and the similar proper motions confirm that this is a true binary system. The WDS catalogue notes that the PA of 59 degs and separation of 12".6 for 2002 is virtually unchanged since the pair was discovered by Dunlop in 1826. The star can be found in western Pictor, about 3 degrees north following alpha Doradus.

Bob Argyle - Double Star Section Director