February 2026 - Double Star of the Month
About 10 degrees east of beta Aurigae lies a coarse cluster of mostly naked eye stars all bearing the label ψ (psi). The Cambridge Double Star Atlas (2nd edition) shows that ψ2, ψ5 and ψ7 are all double but they do not appear in the catalogue, presumably because they are all too wide. Nevertheless, 56 Aur = ψ5 Aur (06 46 44.34 +44 34 37.3), is worth looking at because it has a fine colour contrast.
It was found by William Herschel in 1782 when the position angle (PA) and separation were 17 degrees and 53". and he noted colours of white and pale red. By 2022 the values of PA and separation were 44 degrees and 28" due mostly to a proper motion, largely in declination, of the A star. In 1970 I found the colours to be yellow-orange and blue with a 21-cm mirror.
Pi Puppis (07 17 08.56 -37 05 51.0) is a wide, unequal double star found by James Dunlop at Parramatta in New South Wales. It is about 8 degrees south of the blue supergiant eta CMa (V = 2.5). The primary is a very bright (V = 2.9) K4 giant whilst there is a V = 7.9 companion at 213 degrees and 69" with this separation slowly decreasing with time.
Gaia DR3 gives distances of 560 and 970 light-years respectively for A and B but the parallax measured for has a 20% error and this is because the Hipparcos mission in the early 1990s found that A itself was a double star with a V = 6.9 companion 0".7 distant. Since discovery this star has moved just 3 degrees but it does not appear in DR3.
Pi Puppis lies in a cluster called Collinder 135 which has six members brighter than magnitude 6. It might have had a common origin with a nearby cluster UBC 7. The centres of the clusters are currently 24 pc apart but the stellar motions indicate they would have been closer in the past.
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.
