January 2023 - Double Star of the Month

STF 845 lies in Auriga (06 11 36.59 +48 42 39.6) and is also known as 41 Aurigae and it is also H 3 82, observed by William Herschel in November 1782 and recorded by him as a pretty double star. It is a beautiful pair for the small telescope. The writer first saw it in 1969 using the 12-inch reflector of a friend. At x208 the colours were noted as yellow and lilac. The Washington Double Star (WDS) catalogue gives the spectral types as A1V and A6V.

Image of a finder chart for the double star STF 845 in Auriga
A finder chart for the double star STF 845 in Auriga created with Cartes du Ciel.

James Dunlop found the 30th entry in his catalogue in 1826. It is located in Pictor at 06 29 40.03 -50 14 20.7 some 2.5 degrees NNE of Canopus. It offers a fine sight to the small telescope user.

The stars are magnitudes 6.0 and 8.0 and at present they are separated by 11".5, being 14" apart when observed by Dunlop. The position angle has hardly changed between these two epochs and is currently 312 degrees.

Image of a finder chart for the double star DUN 30 in Pictor
A finder chart for the double star DUN 30 in Pictor created with Cartes du Ciel.

In 1871, Russell, observing with an 11-inch refractor at Sydney Observatory, found the primary star to be a close double. R 65 has a period of 111 years according to Docobo and Ling in 2021. The stars are almost equally bright but according to the orbit, which is extremely eccentric, the separation never exceeds 0".7 and, at times, drops to 0".012 which was the case in mid-2021. By 2027 the stars will be at least 0".4 apart.

In the 1890s Harvard Observatory was site testing in the Peruvian Andes and was using a 13-inch refractor. This telescope discovered several hundred new double stars amongst which was the fainter companion of DUN 30. This has also turned out to be a binary pair of period 101 years, giving a predicted position of 224 degrees, 0".44 in early 2023. The stars have visual magnitudes 8.0 and 8.7.

Bob Argyle - Double Star Section Director