June 2014 - Double Star of the Month
STF1883 (14 48 53.22 +05 57 15.9) is in Virgo near the northern border with Bootes. In `Celestial Objects' however it appears in Bootes. In Thomas Lewis' work on the Struve stars he gives the magnitudes of both stars as 7.0. The WDS however lists 7.02 and 8.95. The current value for B must be somewhere between these limits as the writer has resolved this pair with the 8-inch Cooke at Cambridge which would have been much more difficult if B was near magnitude 9. The WDS notes than one star is variable - this is presumably B and the amplitude must be considerable if the stars were deemed to be equally bright a century ago. The star has only the designation SV ZI1089 and does not appear to be a fully-fledged IBVS variable star. STF1883 is a binary star of period 216 years which has a highly inclined and eccentric orbit. Near 1".2 at discovery in 1830, it closed to around 0".25 in the early 1930's before widening to 1" where it is today. This value will not increase very much before the stars begin to close again in about 30 years time.
HJ 4788 is d Lupi (15 35 53.25 -44 57 30.0) which can be found as one of triangle of naked-eye stars some three degrees following epsilon Lupi. This pretty pair consists of pale and deep yellow components in a well-occupied field (according to E. J. Hartung). The stars are mags 4.60 and 6.51 and the separation has slowly decreased from 3".1 in 1836 to 1".9 in 2013 whilst the position angle has increased from 349° to 13° over the same time interval. The primary is an early B-type dwarf which is 428 light years away and the WDS notes it is a spectroscopic binary.
Bob Argyle - Double Star Section Director