January 2016 - Double Star of the Month
STT 147 (06 34 19.37 +38 04 33.6) is located in Auriga and is about 35 arc minutes south preceding the very red star UU Aur which is visual magnitude 5.3 and has an exceptional B-V colour index of +2.6. The field can also be found from the bright binary theta Aurigae by moving about 9 degrees due east. Burnham describes it as an almost equilateral triangle with the sides being about 40" long and the stars A, B and C being respectively 6.8, 8.7 and 9.9. Sissy Haas notes that A is
bright orange and indeed the spectral type of this star is K0.
When the pair was first observed by Otto Struve at Pulkovo he also noted that C was a very close and difficult pair. The WDS gives the magnitudes as 10.6 and 11.0 with PA 109 and separation 0".5. There seems to be little motion in this system. Burnham notes that it was 'difficult' in the 18.5-inch Dearborn refractor and no measures have been made since 1957.
So here is a challenge for the larger aperture user and a real test of the seeing and transparency. Another neat pair (STF 928) can be found 27' north following, mags 7.9 and 8.6 at 131 degs and 3".5. These stars have common proper motion and appear to form a binary pair. An unconnected mag 12.4 can be found at 124 degs and 131" to B.
HJ 3857 is in Columba (06 24 01.02 -36 42 28.4) about 2.5 degrees south following the 4.4 magnitude kappa. This is also an easy triple although star B did not appear to Dunlop when he recorded this pair as number 28 in his catalogue, but was swept up a few years later by John Herschel at Feldhausen.
The WDS catalogue values for the magnitudes are 5.7 (A), 9.8 (B) and 6.9 for C. The Dunlop component would appear to be a field star and has moved 6" closer to the closer pair over the last 2 centuries or so. Gould, using 175-mm, notes that the primary is orange and the wider companion is bluish.
Bob Argyle - Double Star Section Director