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Double Star of the Month - November 2012
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.
STF 162 (01 49 15.54 +47 53 49.0) sits in an obscure corner of Perseus about 6 degrees north and 2 degrees preceding gamma And. It is also about 1.5 degrees south following 51 And. It is a multiple star, four components of which can be seen in 7.5-cm. The closer pair, which consists of components of magnitudes 6.5 and 7.2, was found by Struve in 1828 when the separation was 2".2 and the position angle 227 degrees. At the current epoch these have both decreased to 1".9 and 298 degrees. A third star which remains fixed with respect to A can be found 20" away almost due south, and another at mag 10.1 is 139" distant. The WDS reveals that either A or B is itself an interferometric binary with a separation less than 0".2 and B is also a spectroscopic binary.
Epsilon Sculptoris (01 45 38.65 -25 03 08.8) is a fine pair located in the extreme north-east corner of Sculptor and which can be seen from the UK but which first caught the attention of John Herschel at Feldhausen when he noted 'large * w(hite) small star dull red' an gave the magnitudes as 6 and 10(modern values 5.4 and 8.5). Since then the companion has moved slowly retrograde from the discovery position of 72 degrees to its current value of 20 degrees. In 1969 de Freitas Mourao looked at the observations and decided that they could be fitted by a face-on circular orbit with a separation fixed at 4".65 and a period of almost 1200 years. In recent years, however, the companion has begun to stray ever further from the primary and the separation is now over 5". More observations are needed but the real orbit will not be obvious any time soon, and in fact the apparent motion to date looks more linear than curved. However, epsilon Scl is relatively nearby (92 light years) and the annual proper motion of 0".16 would take it almost 30" from B since discovery if the latter was optical. Hartung called it an easy, bright yellow pair whilst Gould with 175-mm called the primary pale yellow.
Bob Argyle - Double Star Section Director
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Double Star of the Month - April 2012
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.
2 CVn = STF1622 (12 16 07.55 +40 39 36.6) is a beautiful pair with components of contrasting hues which sits near the western border of Canes Venatici with Ursa Major and about 5 degrees following beta CVn. The primary star, an early M giant is accompanied by a late F dwarf and many writers have commented upon the colours to be seen here: - Webb called them very gold and blue, Dembowski thought them yellow and azure, Franks made them orange and blue and more recently Sissy Haas recalled brick red and silvery sapphire. The stars are magnitudes 5.9 and 8.7 and are currently separated by about 11".4 which makes them an easy target even for the small telescope.
mu Crucis (12 54 35.66 -57 10 40.4) is simply one of the most beautiful doubles in the sky. A pair whose components of visual magnitude 3.9 and 5.0 share common proper motion and distance, this system belongs with the Scorpio OB2 association of young hot stars, and Hipparcos places both stars about 412 light years away. Shatsky and Tokovinin used the ADONIS near infrared adaptive optics system on the ESO 3.6-metre reflector to search for faint, close companions and they found two objects within 5" of component B. No magnitudes or proper motions are available so it is too early to say if these are physically connected but the two bright stars certainly form a very long period binary. Mu Crucis was found by Dunlop in 1826. The spectral types are both B and Hartung record them as both white whereas Richard Jaworski sees a tinge of yellow in the fainter star. The current separation of 35" and the brightness of the stars almost makes this a southern equivalent of Albireo but without the colours.
Bob Argyle - Double Star Section Director
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Deep-Sky Objects and Observations
