March 2026 - Double Star of the Month
Sir William Herschel decribed 12 Lyncis (06 46 14.15 +59 26 30.1) when he observed it in 1780, and called it a curious treble star
. He recorded colours of white
and white inclining to rose colour
for the two closest components, whilst the more distant 3rd star appeared to him to be pale red. In 1831 F. G. W. Struve catalogued 12 Lyn as STF 948 and measured separations of 1".5 between stars A and B and 8".7 between A and C.
Since then the close pair has moved through more than 80 degrees of position angle with only a slight increase in separation. During the same interval star C moved through 7 degrees of position angle. AB are at postion angle (PA) 64 degrees and 1".9 for the current date. This is a physical triple system with the period of AB given as 733 years in an orbit calculated by Izmailov in 2019. Measurements with the Cambridge 8-inch Cooke showed that the PA decreased by 8 degrees between 1995 and 2017.
A drawing by Jeremy Perez shows colours of yellow for A and C with B being bluish. These can be compared to the estimates by Reverend Webb who on three occasions between 1832 and 1852 noted the hues as white, ruddy and bluish, but in 1854 noted C to be ruddy. Sissy Haas record colours of yellow, yellow and bluish silver in her book Double Stars For Small Telescopes, and labels it a showcase
system which no-one would argue with.
Five-and-a-half degrees south of Beta (β) Carinae (V = 1.7) lies HJ 4206 (09 17 25.21 -74 53 39.8). It was found by John Herschel during sweep 547 with the 20-foot reflector at Feldhausen on Feb. 22, 1835. He decribed the system as delicate and beautiful
and noted that the primary was accompanied by a magnitude 13 at 5" and a magnitude 11 at 40".
The Washington Double Star Catalog gives the magnitudes of B and C as 9.6 and 10.3, so not only considerably brighter but also reversing the order of brightness. The corresponding positions are 344 degrees and 7".1, and 354 degrees and 46".
In late 1894, Robert Innes, using a 6.25-inch Cooke refractor borrowed from Walter Gale, noted that the primary was a very close pair (I 12). In fact, he registered only an elongation on the first occasion he looked at it, and then the star was single in good seeing a month or so later. Recent measures put the stars 0".3 apart with little apparent motion. The magnitudes are 5.3 and 6.6.
Bob Argyle - Double Star Section Director
If you'd like to try out the Clear Skies Observing Guides (CSOG), you can download observing guide for the current Double Stars of the Month without the need to register. CSOG are not associated with the Webb Deep-Sky Society but the work of Victor van Wulfen.
