48 AUSTRALIAN SKY & TELESCOPE May | June 2018
DOUBLE STARS by Ross GouldReturn to the Wolf’s den
Sink your teeth into the double stars of Lupus.
I
t’s been eight years since this column
last visited Lupus, the Wolf, and — as
always — the doubles I mention here
are a short selection from many in the
region. If you have a mid-size scope,
there are a lot more within your reach.
Near the Lupus/Centaurus border,
HJ 4672 is 3 degrees west-southwest
from 2nd-magnitude Eta Centauri. Little
changed since John Herschel’s discovery
in 1837, this is a bright yellow star with
small companion when seen at 100×
with 18 cm; an attractive pairing in a
sparse field. Hartung saw it with 7.5 cm.
Some 5½ degrees south-southeast
of HJ 4672 is R 244, discovered in 1881
by H.C. Russell, director of Sydney
Observatory. There has been no definite
change since, and 18 cm at 100×
showed a bright white star with a tiny
companion southeast in a rich field.
Northwest 1½ degrees from Alpha
Lupi, HJ 4690 is one of two bright
orange stars dominating the field.
It’s wide and easy, with contrasting
brightness and colours, orange and blue-
white. More than 100 years after John
Herschel’s discovery, in 1951 W.S. Finsen
in South Africa with a 26.5-inch (69-cm)
refractor found that the primary starconsists of near-equal 6th-magnitude
stars. These are very close at all times, in
an orbit currently estimated at 140 years.
The 1950s measures were around 0.14”;
the most recent, 2014, is 0.19”.
HJ 4706 is found 1½ degrees east
of 2nd-magnitude Alpha Lupi, an easy
7” separation though not a bright
pair. My 18-cm scope at 100× showed
a dull, deep yellow primary, the lesser
companion making a nice combination,
in a field with a little arc of three
magnitude 10 stars some 8’ southwest.
It’s a nice double for middle apertures,
though visible with 80 mm.
HJ 4715 is 1 degree southeast from
HJ 4706, and is a much brighter pair of
slightly unequal white stars, in a faint
star field. It has closed somewhat since
the 1830s, but 80 mm will show it.
Kappa Lupi, DUN 177, is wide and
bright. It appears to be a gravitationally
bound pair of long period. The unequally
bright stars look pale yellow to me, as
they did to Hartung, who remarked on
this “fine object for small apertures”.
Distant about 180 light-years, the orbit is
huge, some 1400-plus a.u.
COO 179 was discovered in the 1870s
at Cordoba Observatory, an easy but notbright white pair that was nicely seen
with 18 cm at 100×. The field is middling
starry; altogether a good effect.
Nearly midway between Beta and
Epsilon Lupi is I 228, a discovery by
Robert Innes with a 7-inch refractor.
Not bright, and fairly close, I found it
showed well with 18 cm at 180×, an
equal, pale yellow, close pair in a quite
starry (though mostly faint) field.
Half a degree or so northeast of I 228
is DUN 179, another easy unequal white
pair in a starry field; 80 mm will show
it, and it’s attractive with 18 cm.
I discussed Gamma Lupi on these
pages in 2010 and it’s worth re-visiting.
My first observation of Gamma in 1996
with an 18-cm refractor showed two
discs in contact at 330×, bright and
equal. In 2016, with my 21-cm Dall-
Kirkham, 300× showed bare separation.
A very fine double for those with
not-too-small scopes; the separation
currently is just over 0.8”.
Gamma Lupi’s orbital period was a
puzzle for many years, but now seems
well established at around 190 years.
The only controversy these days is
about photometry. All the earlier visual
observers gave the brightness difference
of the stars as 0.3 magnitude or less.
Hipparcos in 1991 gave a ~0.1 magnitude
difference with three different filters.
This matches my own observations. Only
Tycho gives the brightness difference
of 1.5 magnitudes that is listed in the
WDS. This appears to be another Tycho
aberration. The Tycho magnitude for star
A is similar to the combined brightness
of the two stars as measured by others,
which may suggest where the error
originated. I have used the Hipparcos
magnitudes in the accompanying table.■ ROSS GOULD observes the sky from
the nation’s capital. He can be reached
at [email protected]DoublestarsofLupus
Star Name R. A. Dec. Mag. Sep. Position angle measureDate of Spectrum
HJ 4672 14 h 20.2m -43° 04 ́ 5.8, 7.9 3.5 ̋ 301° 2016 G8III
R 244 14 h 22.6m -48° 19 ́ 6.1, 9.5 4.0 ̋ 121° 2010 B1III
HJ 4690 14 h 37.3m -46° 08 ́ AB 5.6, 7.7 19.6 ̋ 024° 2016 G8III+A1V
HJ 4706 14 h 51.3m -47° 24 ́ 7.7, 9. 0 7. 0 ̋ 220° 2016 K2III+K
HJ 4715 14 h 56.5m -47° 15 ́ 6.0, 6.8 2.1 ̋ 281° 2016 B9V
Kappa (DUN 177) 15 h 11.9m -48° 44 ́ 3.8, 5.5 26.5 ̋ 143° 2010 B9.5V+A5V
COO 179 15 h 13.0m -37° 15 ́ 8.0, 8.1 6.3 ̋ 227° 2010 A3/4V
I 228 15 h 14.0m -43° 48 ́ 8.0, 8.2 1.2 ̋ 013° 2016 A4/5IV/V
DUN 179 15 h 14.5m -43° 23 ́ 7.3, 8.5 10.5 ̋ 045° 2016 A1V
Gamma (HJ 4786) 15 h 35.1m -41° 10 ́ 3.4, 3.5 0.83 ̋ 276° 2014 B2IV
Data from the Washington Double Star Catalog, with additions.