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November 2014 - Double Star of the Month
10 Arietis (=STF 208, 02 03 39.26 +25 56 07.6) is a marginally naked-eye star at the preceding end of a string of similar stars some 2.5 degrees north of alpha Arietis. Found by F G W Struve in 1821, when the separation was 2", the motion of the companion over the next 80 years appeared more or less linear but it became progressively more curved as the pair closed to 1". The companion then made a closest approach at 0".3 in 1920 or so and since then has widened and can be found at 347 degs, 1".49 in 2014.8. The currently accepted period is 325 years but this could well be an underestimate as nothing is known about the motion at apastron. The pair should be divided in 15-cm but a good night is needed because the magnitudes of the stars are 5.8 and 7.8. A 13.5 mag. can be glimpsed 95" distant in PA 150 degs.
kappa Tucanae (01 25 45.50 -68 52 34.5) is located about 5 degrees north following the Small Magellanic Cloud and Burnham's Handbook spends a lot of time on the latter but only notes in passing the former which is a splendid object for both binoculars and telescope. For the binocular user there is a mag 7.8 star which is 319" from the mag 5.00 primary. John Herschel found A to be a fine pair (HJ 3423, mags 5.0 and 7.7) - 'very beautiful' was his verdict. E J Hartung gives the colours as yellow and orange. Two measures at Feldhausen yielded separations of 2" and 2.5" and a mean position angle of 11.7 degrees. Recent measures in 2009 show that the separation has doubled to 4".8 and the position angle is now 319 degs. This is a binary system with a period of about 850 years.
In 1895 Robert Innes found that the distant 7.8 mag star was also double but much more equal in brightness (7.8 and 8.4) and also a binary of fairly short period. He was using a reflecting telescope owned by Mr. F. Dixon Edmonds, an early member of the BAA, and in presenting his list of 16 new pairs Innes said that the telescope had enabled the 'discovery of more new double stars than all the rest of the silver-on-glass reflectors ever made'. I 27 CD revolves every 85.2 years in a circular orbit only slightly tilted to the line of sight so the separation ranges between 0".9 an 1".1 and the angular motion is a fairly constant 4 degrees or so. Innes also noted that both AB and CD have similar proper motions so this is likely a quadruple system.
Bob Argyle - Double Star Section Director
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Double Star of the Month - November 2013
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.
Three degrees north of alpha Ari is a line of four stars of marginal naked-eye visibility. The most westerly of these stars is 10 Arietis, a close visual binary. The third star is 14 Ari - a coarse triple. 10 Ari (02 03 39.26 +35 56 07.6) was found by Wilhelm Struve at Dorpat and during the remainder of the nineteenth century the star closed slowly, leading Burnham to comment (in 1906) 'Probably orbital motion, although the measures are well represented on the hypothesis of rectilinear motion'. From a distance of 1".98 in 1833, the companion passed by the primary around 1920 at a distance of about 0".3 and has been widening since. The current catalogue period is 325 years and gives a position of for 2014.0 of 346° and 1".48. It is a nice pair in the Cambridge 8-inch but needs a night of good seeing to see the companion of magnitude 7.9 close against the mag 5.8 primary.
omega Fornacis (02 33 50.71 -28 13 56.4) was swept up by John Herschel at Feldhausen in 1834 and is catalogued as HJ 3506. He noted that it was a 'very fine star but ill-defined'. The stars are magnitudes 5.0 and 7.5 and there has been little motion since discovery, the latest position in the WDS gives 10".8 and 245°. Sissy Haas calls this a 'showcase pair' and gives colours of goldish-white and smoke-grey whilst Magda Streicher with a larger aperture notes yellow-white and light grey-blue. Hartung does not pronounce on colours but notes a similar pair about 2' west. It seems likely that the two stars are physically connected. Hipparcos gives a distance of 484 light years and the primary is a subgiant of spectral type B9.5.
Bob Argyle - Double Star Section Director
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Deep-Sky Objects and Observations
