Double Star of the Month - October 2008
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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. |
This month's pairs ar
both bright, well-observed binaries and well seen in small to medium apertures.
36 And (00 54 58.02 +23 37 42.4) is a beautiful pair following the Square of
Pegasus, some 3 degrees south following zeta Andromedae. The two stars are
strong yellow (Webb) or golden (Smyth) and form a binary system whose period is
167.7 years so it has passed the position it occupied when discovered by F G W
Struve in 1827. The current PA and separation are 322 degrees and 1".1 making it
a fine sight in a 15-cm telescope. It is strangely absent from Hartung's book,
which includes more northerly objects of less distinction such as AC 1. This
system is almost 38 pc distant and the primary is a K1 subgiant. The star itself
is just visible to the naked-eye with the components being
magnitudes 6.1 and 6.5.
p Eri (01 39 47.24 -56 11 47.2) is one of Dunlop's discoveries (Dun 5) and is
probably the nearest equivalent to 61 Cygni in the southern hemisphere. It is
close (5.3 parsecs according to Hipparcos), it contains two K dwarfs (in this
case K0 and K5) which have visual magnitudes 5.8 and 5.9 respectively, has a
similarly long period (483 years) and is also well-separated - reaching a
maximum distance of 11.8 arc seconds in 2040. The Chambers edition of Smyth's
Celestial Objects which contains a southern extension, also identifies the star
as 6 Eri but does not mention colours, neither does John Herschel in his Cape
observations. Hartung records both as deep yellow.
Bob Argyle