Double Star of the Month Archive 2024

In this series of short articles, a double star in both the northern and southern hemispheres will be highlighted for observation with small telescopes, with new objects being selected for each month.

February 2024 - Double Star of the Month

S 548 (07 27 40.54 +22 08 29.3) was noted by William Herschel in 1782 and catalogued by him as H V 66. He noted that the stars were very unequal and the larger one was pale red and the smaller one was dusky. The distance was noted as 34" 39'". Little has changed in the relative positions since then with the Washington Double Star catalog (WDS) giving 277 degrees and 35".3 for 2019.

Image of a finder chart for the double star S 548 in Gemini
A finder chart for the double star S 548 in Gemini created with Cartes du Ciel.

The pair can be found two degrees following delta Gem (see this column for Feb 13). The catalogue magnitudes are 7.0 and 8.9. In 1892 Thomas Espin added a faint companion of magnitude 12.4 at 24 degrees and 11".9. The three stars are unrelated. A lies 1800 light-years away, B is 940 and C is 8350 light-years distant.

In southern Puppis right on the border with Vela is HJ 4093 (08 26 17.74 -39 03 32.3). This is a fine pair for the small aperture, it is triple in apertures of 40-cm or more, whilst the spectrograph reveals that component A is an Algol system called NO Pup.

Image of a finder chart for the double star HJ 4093 in Puppis
A finder chart for the double star HJ 4093 in Puppis created with Cartes du Ciel.

Stars A and B (magnitudes 6.5 and 7.1) are currently at PA 122 degrees and 15".0 having almost doubled their separation since discovery by John Herschel. Using the 26.5-inch refractor at Johannesburg, Willem van den Bos found that B is a close double (Ba,Bb), with stars of magnitude 7.9 and 8.1, currently 0".2 apart and a binary with a period of 103 years. In addition the WDS notes that Andrei Tokovinin finds a close component (D) only 5".4 from A but with a K magnitude of 17.3, but this star does not appear in the Multiple Star Catalogue.

Examining Gaia DR3 with a field of radius 100" shows two stars of magnitudes 12.2 and 13.1 respectively 64" and 66" from A which share the same parallax, so perhaps this is a small cluster. There is, however, no data for the B component and the significant change in the AB distance since discovery may indicate that B is unrelated.

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.

January 2024 - Double Star of the Month

Admiral Smyth's Bedford Catalogue contains an entry for 124 Tauri, and from his description of it as a coarse quadruple star of which components B and C are 6".2 apart in PA 318 degrees this appears to agree with Struve's catalogue entry of STF 755 (05 39 09.17 +23 17 17.7).

Image of a finder chart for the double star STF 755 in Taurus
A finder chart for the double star STF 755 in Taurus created with Cartes du Ciel.

According to the Washington Double Star catalog (WDS) A is magnitude 7.8 at 31 degrees and 149". This is HD 37387, a K2 giant star which appears close to the reflection nebula GN 05.36.2.The fourth star, D, is 50 degrees and 95" from A and has V = 11.1.

There is no label for 124 Tauri in the the Cambridge Double Star Atlas (2nd edition) but the star appears about 30' W of a small right-angled triangle of 6th magnitude stars which in turn sits 2 degrees NNE of zeta Tauri. Smyth happened upon it in 1835 whilst looking for Comet Halley. He gives the colours as garnet (A), pale blue-white (B,C) and bluish (D).

Some 3.5 degrees WSW of epsilon CMa is a triangle of 5th and 6th magnitude stars, the brightest of which is 10 CMa. In the same field, north following is HJ 3891 (06 45 31.20, -30 56 56.3), a double star discovered by John Herschel from the Cape of Good Hope.

Image of a finder chart for the double star HJ 3891 in Canis Major
A finder chart for the double star HJ 3891 in Canis Major created with Cartes du Ciel.

The primary is a B2III star of V = 5.7, and is accompanied by a 8.2 magnitude star at 223 degrees and 5".0. There has been little change since 1838. The stars have similar parallaxes and the mean distance to the system is 1968 light-years. The primary star is also called HP CMa.

Just 90 arc-minutes to the SE is a wide pair swept up by the elder Herschel in 1782. H V 108 has stars of similar brightness (5.8 and 7.7) but they are separated by 43" in PA 66 degrees. The A component has a particularly close and faint companion just 0".6 away which was discovered from Robert Rossiter in South Africa, whilst the WDS notes that the B star has a variable radial velocity. Andrei Tokovinin regards this as a physical quadruple - the brighter stars appear in Gaia DR3 with respective distances of 634 and 623 light-years.

Bob Argyle - Double Star Section Director