December 2024 - Double Star of the Month
STF 430 Tauri (03 40 28.04 +05 07 33.2) is a coarse and unequal triple star found 1.5° WSW of 29 Tauri. The AB consist of stars of visual magnitude 6.8 and 9.8 separated by 26" at a PA of 57 degrees.
The primary is a K2III and appears distinctly orange in the eyepiece. An observation made with a 10-inch mirror at x48 showed that B is blue as is the further companion, C, which is 34" away and is somewhat fainter than B.
Although A and B have similar parallaxes they are not the same within the errors quoted in the Gaia DR3 catalogue, and actually the faintest star is much closer to us than the other stars.
In southern Eridanus near the border with Caelum lies 41 Eridani (04 17 53.62 -33 47 54).
This is a star which has an unusual chemical composition which contains significant amounts of mercury and manganese. Such stars are found to be common in spectroscopic binary systems and in 2012 a team using the VLTI in Chile resolved 41 Eri into two with a period of 5 days and a separation of a few milli-seconds of arc.
A century before, however, Robert Innes, using a 7-inch refractor from the Cape of Good Hope, found the star to be a close double bright (I 270) with magnitudes of 3.6 and 4.
The pair began to close in and were last seen in 1933 when the distance was 0".1. Later attempts to resolve the stars have failed - between 2017 and 2019, Dr. Andrei Tokovinin was unable to see the companion using a 4-metre telescope and it is now supposed that this is not a visual double star.
In 1836 John Herschel found a faint companion (HJ 3636 AC) about 60" distant and gave the magnitudes as 3 and 14. Today the WDS gives magnitudes of 3.9 and 11.8 with PA and separation of 8 degrees and 49".
Whilst in the area check out another HJ pair, no. 3642 just a few arc-minutes SSE - 6.6, 8.7, 157 degrees, 5".2.
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.
