December 2025 - Double Star of the Month
During the course of his long observing life, Thomas William Webb happened upon a number of wide double stars which were not included in the catalogues of the time. The Washington Double Star catalog (WDS) contains 10 pairs with the discoverer number WEB. One of these (WEB 2) lies in Camelopardalis at 03 42 42.73 +59 58 09.8.
The primary star, which is a K4 giant, was catalogued by Piazzi in 1814 and is called P III 97. In fact, Piazzi did note the fainter companion to the north but did not measure it. Webb noted the companion star B on Mar 2, 1854. It is V = 8.5 whilst the primary is just above naked-eye visibility at V = 5.7. Both stars should be visible in a good pair of binoculars but a small telescope should show the distinct orange tinge of the primary and the bluish tinge of the secondary. Thomas Espin added three fainter companions. The components are currently at 36 degrees and 55". Both stars are 1790 light-years away.
Many of the bright pairs in the Dunlop catalogues are rather wide and any relative motion is in general very small. However a small number of pairs do show significant orbital motion including p Eri (Dun 5) and Dun 23 in Puppis. The latter binary can be found at 06 04 46.76 -48 27 30.2.
Since Dunlop found the pair in 1826 the companion has moved 160 degrees. A recent orbit gives a period of 553 years and the predicted position for the time of writing is 132 degrees and 2".5. With the star magnitudes of 7.3 and 7.7 this is a pair which should be well seen in 10-cm.
Radial velocity observations using the 2.5 metre reflector at CTIO in Chile by Andrei Tokovinin showed that A is a spectroscopic binary with a period of 2.51 days and the WDS notes that B may be a very close pair although the radial velocity showed very little variation. This system is 100 light-years distant.
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.
