April 2026 - Double Star of the Month
STF 1527 (11 18 59.91 +14 16 06.9) is a fine binary star located about 1.5 degrees south-east of theta Leo, and also just over a degree north of the galaxies M65 and M66.
In 1822 it was found at 10 degrees and 3".7 but it was closing, and by the end of 1990s it was well below 1 arc-second. I was able to measure it in 1998 with the Cambridge 8-inch at 0".9 and I have not managed to resolve it since. The stars approached to one-third of an arc-second in 2010 and at present are opening again with the 415 year orbit of Tokovinin predicting 325 degrees and 0".76 for mid-2026, making it once more a target for the Cooke refractor.
The stars have magnitudes 7.0 and 8.0 and are almost exactly 100 light-years away according to an earlier Gaia catalogue. When Gaia DR4 comes out at the end of this year we should get much more certainty in the value of the distance to each component.
Another fine sight is DUN 159 in Centaurus (14 22 37.52 -58 27 33.0). It can be found 3 degrees north of the midpoint of the line joining alpha and beta Centauri.
Ross Gould, observing from Australia with a 175-mm refractor finds that the colours are bright yellow and dull yellow and notes that the field contains some faint pairs and star groups. I measured both AB and a nearby magnitude 10.7 star (D) with the Johannesburg refractor in 2016. The bright pair has magnitudes of 5.0 and 7.6 and the PA was 157 degrees and 9".1, down from 161 degrees and 12".8 found by Dunlop in 1826. Star D is at 9 degrees and 43".6.
A has no data in Gaia DR3 presumably because it is a known spectroscopic binary but the B component lies at a distance of 250 light-years. The The Washington Double Star Catalog gives an additional component C also magnitude 10.7 at 254 degrees and 17".5 but this was not seen and neither this star nor C appear to be in the Gaia catalogue.
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.
