Sky and Telescope - June 2018 - 55
Early Summer Doubles
ν1 and ν2 CrB
μ Her A, BC
μ Her BC
ξ Sco AB
ξ Sco AC
ν Sco AB
ν Sco AC
ν Sco CD
Angular sizes and separations are from recent catalogs. Visually, an object's size is often smaller than
the cataloged value and varies according to the aperture and magnification of the viewing instrument.
Right ascension and declination are for equinox 2000.0.
double, that is to say, a chance alignment of unrelated stars.
Also in Hercules, Mu (μ) Her can
be seen as a triplet when the timing is
right. In the 130-mm scope at 37×, the
bright, yellow primary is mated to a
much dimmer, orange spark west-southwest. The companion is a close pair (BC)
with an orbital period of only 43 years.
This June the 10.7-magnitude C component is an excruciatingly close 0.6″
north of the 10.2-magnitude B component. My 14.5-inch scope at 245× offers
a kissing duo, each glimmering orange.
Five years from now they'll have widened to 1.2″, presenting a much easier
target. Is your seeing (image steadiness)
good enough to wrest them apart?
Strolling down to the Scorpion we
ﬁnd another twofer in the guise of Xi
(ξ) Scorpii and Struve 1999 (Σ1999 or
STF 1999). I most recently dropped in
on these stars with my 105-mm refractor. At 36× Xi AC is a close, unequal
pair with a yellow companion huddled
northeast of its yellow-white primary.
East-southeastward in the same ﬁeld
of view, the components of Σ1999 are
more widely separated. Here the primary is deep yellow, while the companion to its east sparkles yellow-orange.
Xi Scorpii's primary has another
companion (B) visible to backyard
scopes, perhaps with some difﬁculty.
Together they form a visual binary with
a period of only 46 years, and B currently dwells a mere 1.1″ north and a
bit east of the A component. Although
I've split similar doubles at 203× with
the little refractor, this pair only yields
a shape that looks like a snowman -
probably because it's fairly low in my
sky where the image steadiness isn't
as good. At 381× I get a hairline split
during spells of good seeing. Unlike the
custom for most doubles, the B designation belongs to the brighter of the two
stars, but they look pretty equal to me.
Nu (ν) Sco is an 8.3° drop southsoutheast from Xi Sco and a lovely
quadruple star through a telescope. In
the 130-mm scope at 63×, three of the
components are visible. The 4.4-magnitude primary has two companions 41.6″
to the north-northwest and 2.5″ apart.
sk yandtelescope.com * J U N E 2 018