November 2019 - Double Star of the Month

STF 79 (01 00 03.56 +44 42 47.7) This is a beautiful, easy pair in Andromeda about 4.5 degrees north-east of M31. It was missed by William Herschel on his first two surveys for new double stars but swept up eventually in 1786 and is catalogued as H N 45.

Sissy Haas notes that the stars are pearly white and pale blue-violet. When I last observed it in 1968 I recorded it as 'bluish-white and bluish(?)' in a 21-cm reflector at x96. Strangely it has not been measured with the Cambridge telescope at all, although an easy object and with the stars of magnitudes 6.0 and 6.8, and the current position is 195 degrees and 7".9.

An image of the pair appears on the Asociacion Astronomica de Hubble website. The observer JCS noted that the stars appeared to be a delicate shade of sky-blue and there did not appear to be any contrast between them.

Both stars are spectroscopic binaries and probably form a quadruple system. DR2 places them 494 light years away.

H 2 58 (01 59 00.72 -22 55 11.2) is in Cetus, about 0.5 degree south-east of 56 Cet. It is one of William Herschel's discoveries. He noted that the stars were considerably unequal but the WDS gives 7.3 and 7.6 and Gaia gives a magnitude difference in the G band of just 0.17. Herschel also gave both colours as dusky white and the spectral types are A7 and G0 according to the WDS.

Found at 315 degrees and 5".0 in 1782, the stars had widened to 8".3 in 2015 with the PA decreasing to 302 degrees. More recently, the primary was found to be a W UMa ellipsoidal eclipsing binary system which is now known as AA Cet. The period of variation is 0.536 days and the magnitude range is 6.2 to 6.7. Both stars are given as F2 in the Catalogue of Eclipsing Variables by Avvakumova (2013).

Bob Argyle - Double Star Section Director