October 2025 - Double Star of the Month

34 Piscium (00 10 02.18 +11 08 44.9) lies near the border between Pisces and Pegasus. It is 4.5 degrees south of, and slightly preceding gamma Pegasi (V = 2.8). It was found by F. G. W. Struve and included as number 5 in his Dorpat Catalogue. This is a fine, but very unequal pair, and 15-cm should give a good view of the stars.

Finder chart for the double star 34 Piscium in Pisces
A finder chart for the double star 34 Piscium in Pisces created with Cartes du Ciel.

The Washington Double Star catalog gives magnitudes of 5.5 and 9.4 making them a rather tricky prospect for a small aperture and classifies the primary as B9V. The stars have remained fixed in separation since discovery and are currently 7".5 apart in position angle 159 degrees.

Gaia DR3 gives parallaxes for the stars but the error on the primary star is almost five times that of the secondary and even allowing for the combined errors the parallaxes are different, although the proper motions are similar. Hopefully DR4 which is due out at the end of 2026 will throw more light on the situation.

HJ 3375 (00 44 43.80 -35 00 07.3) is 2.5 degrees SSE of eta Sculptoris and about 5.5 degrees west and slightly south of the Sculptor Dwarf Galaxy. It was found by John Herschel at the Cape. Over the past 190 years there has been little angular motion and in 2015 the companion was found in position angle 171 degrees at a separation of 4".4.

Finder chart for the double star HJ 3375 in Sculptor
A finder chart for the double star HJ 3375 in Sculptor created with Cartes du Ciel.

This is a relatively nearby binary system - the distance is 110.7 light-years and both components are moving across the sky at more than 0.5 arc-seconds per year.

Four degrees SE of HJ 3375 is the wide pair lambda 1,2 Scl. The easterly component (lam 1) is a K giant (V = 7.1) whilst 20 arc-minutes to the west is lam 2 (B9.5V). This is a visual binary which is now slowly separating and is currently near 0".8. The components have magnitudes 6.6 and 7.0.

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.