Double Star of the Month - March 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.

6 Leo (09 31 57.58 +09 42 56.8) can be found about 2 degrees preceding omicron Leo, and is in the same low power field as omega Leo - a splendid binary (see the column for March 2008). Not unsurprisingly it was first catalogued by Sir William Herschel on 1781 Feb 21 when he noted that the `Large' star was red and the `Small' star `dusky'. It then seems to have appeared in everyone else's catalogue (SHJ 107, STTA 101).The primary is a K giant star and has visual magnitude 5.22. It is accompanied at 75° and 37".5 by a magnitude 9.3 star whose relative position has changed little over 200 years. T. W. Webb noted colours of deep orange and green with his 3.7-inch Tulley refractor and again, in 1882, presumably with the 9.3-inch where he notes pale orange and blue. Hipparcos places the primary star at just over 500 light years away.

J Velorum (10 20 54.81 -56 02 35.6) is near the southern border of Vela with Carina and is located almost on the galactic equator. It is 2 degrees north of the Smile nebula (NGC 3199), a cloud of gas some 75 light years in diameter and 12000 light years distant formed by the interaction of a hot Wolf-Rayet stellar wind and the surrounding interstellar medium. On sweep 435 with his 18-inch reflector at Feldhausen, Herschel described it as `A very large and very remarkable nebula, which is brighter to the S.f. part, and dies off to the N.p., having a curved form and forked tail. In the head of it is a double star. The nebula is pretty bright, very large, figure irregular, 8' long 4' broad'. The double star mentioned is HJ 4302 (10.9, 12.1, 116°, 22".7). Whilst J Velorum was first observed as a double by Rumker (it is RMK13) he missed the brighter but closer B component and recorded only A and C. It was John Herschel who noted the star as triple and referred to it as T Velorum. AB has mags of 4.5 and 7.2 which are currently at 102° and 7".1. C, which is V= 9.2, is 36" away in PA 191° and the distance is slowly widening. Andrew James calls it a spectacular triple. The colours are blue, white and yellow.

Bob Argyle - Double Star Section Director