November 2024 - Double Star of the Month
George Knott was a Victorian amateur astronomer with an interest in double stars. Using a 7.3-inch Clark refractor which once belonged to W. R. Dawes at his observatory in Cuckfield, West Sussex, he made a number of discoveries, five of which can be found in the current Washington Double Star catalog.
The primary star of KNT 1 (01 02 18.34 +81 52 32.1) is the variable star U Cephei. It is an eclipsing binary with a period of 2.5 days and in mid-eclipse the star drops by almost three magnitudes. At maximum, it is V = 6.7 and has a faint companion of magnitude 11.8 some 14" distant in PA 63 degrees.
Rather surprisingly both stars lie at the same distance (632 light-years) and have very similar proper motions. A slighter fainter, and definitely unconnected, third star can be found at PA 315 degrees (increasing) and 24" (decreasing).
Another pair of stars with a variable primary is HJ 3476 (02 00 26.77 -08 31 25.8). This is AR Cet which is probably a semi-regular variable. John Herschel swept them up from Feldhausen and noted Large star very yellow
. The primary is an M3 giant and its catalogue magnitude is given as 5.7 with the companion 61" away in PA 202 degrees. Herschel noted magnitudes 6 and 10.
The position angle has reduced 20 degrees since discovery but this is due to the proper motion of the primary star which is 536 light-years away whilst its faint companion lies 2160 light-years distant.
HJ 3476 lies about 3 degrees NE of zeta Cet which is also known as Baten Kaitos. This, too, is a very unequal and wide double with the components of 3.8 and 10.5 being divided by 106".
Bob Argyle - Double Star Section Director
