SELECTED SOUTHERN DOUBLES and VARIABLES
R.A. 04 Hours
Δ17 /
I269BC-BD (04010-5424) is a
uneventful system containing four stars that
lies in northern Reticulum some
4.9°W of Alpha Doradus. James Dunlop
saw only a triple, with the respective
separations of 63 and 41 arcsec, with the
main pair aligned at the angle of
49° 23'sf equivalent to PA
139.4°. No position angle is given
for the third star, but it is identified as I
269 BD in present catalogues. (Should this be
really designated ‘Δ17 D’ ?)
He gave all as “7, 8 and 8”
magnitude describing it as; “A triangle
of stars.”
Today, Δ17 AB is a brightish equally
white pair being quite attractive in small
telescopes, being currently separated by
64.2 arcsec along PA 142° with
magnitudes of 7.7 and 8.2. Since discovery in
1826, both stars have slightly widened by 1.3
to 1.5 arcsec while the PA has increased by
merely +2°. Looking at the proper
motions of the two it is likely that of
Δ17 is an optical pair.
Closer inspection finds that there are another
two components. The ‘B’ star is
again double, showing the companion as a 11.57
magnitude star some 3.5 arcsec along an
extrapolated PA of 77° - some
10° less than when discovered in
1898. This is the pair I 269BC, and it
is likely that the two are gravitationally
bound. I saw both as white in 20cm. Another
star, about one magnitude fainter at magnitude
than the ‘C’ star lies some
27.7 arcsec away at PA 196°. This
is I 269 BD and this pair is visible in
20cm, and even possibly 15cm with care and
good optics. Little has changed in the
components positions since found by Innes in
1900, and the positions seem right, although
few measures have been obtained. The alignment
is along PA 196°, and it is unknown
if this star is attached BC or even the A
star. These latter components are both white.
NGC 1515 / NGC
1515A (04041-5406) also shares
Δ17 in a wide telescope field with the
moderately bright and elongated spiral galaxy
which both appear in nearby Dorado. Lying
32'NE of Δ17 finds NGC 1515 which
is listed as a SXS4 type aligned as an
elongated gossamer almost in a north-south
direction. It covers about 5.2'x1.1' of sky
and is about half of this in 20cm. At 11.03v
or 12.6B magnitude and surface brightness of
12.6 this galaxy is easily visible in 10.5cm
in dark skies.
NGC 1515A is a better challenge is the
companion galaxy which is 1.8' WSW (PA
243°) of NGC 1515. Just visible in
20cm, and better in 25cm, it appears about
40"x30"arcsec in size as a tiny smudge without
any visible details. The RC3 says this is a
spiral of type SBR3. It is almost certain that
this galaxy is not attached to the much larger
galaxy as the radial velocity is +13
265kms-1 thus giving D as 204Mpc
and ten times the distance of NGC 1515.
Not mentioned in AOST2 for some reason, it is
still worth seeking out. Sky Atlas 2000.0
gives the RV as 884kms-1 while the
RC3 gives +1 216kms-1. If we take
the latter value, then D is 19Mpc.
GAL 364
(04140-1222) is a dainty pair located in a
starry field in Eridanus some 21'N of NGC
1535. Discovered in 1871 by J.Gallo, the pair
is near equal brightness at magnitudes 8.9 and
9.0. Separation between the AB components is
21.1 arcsec at PA 45°. No change has been
observed since the first measures in 1901.
BRT 2634
(04160-1244) is a very faint white pair in
Eridanus that is so easy to find that I had to
include it. BRT 2634 lies 22' due east of NGC
1535. Set the telescope using medium
magnification then glide the telescope by the
one or two star fields. Both stars are both
12.0 mag. Separation of the two stars is 3.1 arcsec
at PA 104°. Again, little has
changed in the pair since the discovery by
S.G. Barton.
R Dor / HJ 3679 AB / HJ
3679 AC (04368-6205) is a semi-regular
(SR) variable star that varies between 4.8 and
6.6 magnitude in a rough period of 338 days. R
Dor is position merely 2.2' inside the Dorado
border with Reticulum. It is best to use the
orangery-red M2III 4.6 magnitude star δ
Ret / Delta Reticuli (03587-6124) and move the
telescope 4.5°ESE (PA
102°) or alternatively move
2.6°E (PA 86°) of 3.3
magnitude α Ret / Alpha Reticuli
/ HIP 19780 / SAO 248969 (04144-6228).
R Dor has a rich red almost vermillion
colouration and was classed as both EsB 94 and
EsB 95 in the Espin-Birmingham’s
“Stars With Remarkable Spectra”
Catalogue. The error seems to have been a
simple duplication being identified with HR
1492. In the GVCS classification for the
variable is designated as "R Dor 0435-62" in
1900 co-ordinates and appears on RASNZ Series
3. Chart No. 78. Spectrum is M8 IIIq:e
Hartung in AOST1&2 describes the field and
variable of R Dor as;
“This orange-crimson star ornaments a
field sown with less bright stars, some quite
close to it. The star is an irregular
Mira-type variable of period averaging 338
days and has a fine spectrum crossed by many
dark and bright lines and bands. 10.5cm will
show some of these near the star’s
maximum.”
R Dor also has two fainter companions. HJ
3679 AC is of 11.0 magnitude that lies
24.5 arcsec along PA 124°. HJ
3679 AB is of 11.9 magnitude that lies
38.4 arcsec along PA 13°.
A distance from the Hipparcos parallax of
16.02±0.69 mas gives
62.42±2.69pc. or 203.6±8.78 ly.
Proper motions show that R Hor is moving
towards the southwest at the rate of pmRA;
-68.46±0.73 pmDec; -72.22±0.78,
calculating a common proper motion of 99.51mas
per year along PA 226.5°.
[NOTE: HIP 21479 / PPM 354226 / SAO
249066 / GSC 8880:1071 Mag(v) is 5.59 and the
B-V of +1.500 Spect: M8e]
HJ 3686
(04417-6113) lies 1.0°NNE from R
Dor (PA 30°) or by moving the
telescope 5.1° due east (PA
91°) from the red 4.6 magnitude
δ Ret / Delta Reticuli
(03587-6124). The component magnitudes are a
near equal 7.7 and 7.8 (8.37V and 8.45V) for
the whitish pair each separated by 7.2 arcsec
along PA 221°. Dissimilar proper
motions mean that this is likely an optical
double. Little change has been seen with HJ
3686. Spectral classes are described as
A1/2V+A. This is a nice pair in a starkly bare
place of stellar objects.
COR 23 / CorO 23
(04419-4750) is a bright pair discovered at
the Cordoba Observatory in 1896, and
considering its brightness, it is unlucky that
neither Dunlop, Rümker, J. Herschel, or
Russell missed it. It appears 2°N
of Lambda Pictoris in a small square of sky in
western Pictor that was added too just to
accommodate the variable R Pictoris (See
Below) The respective magnitudes are 7.4 and
9.9, and the duo is separated by 3.6 arcsec
and has remained without any change since
first found. The PA is presently
219°, which has continued to reduce
from 234° some 106 years ago
(2002). I saw the primary as yellow and the
companion as white. I have not seen this pair
discussed anywhere in the literature - a
question that I cannot figure-out why. I have
seen much poorer pairs than this being
discussed and venerated and this one outstrips
many of the Struve pairs that I have seen.
This is one of the unrecognised southern
astronomical delights. A must see!
R Pic (04462-4915)
is an semi-regular SR variable whose average
variations change between 6.4 and 10.1 in the
period of 170.9 days. This orangery-red star
has an observed spectral class also varies
during the cycle between M1IIe-M4II.e. R Pic
can be found 2.7°W of 5.4 magnitude
η1 Pic / Eta (1) Pictoris or
alternatively 1.3°NNE (PA
24°) from orange 5.3 magnitude
Lambda Pictoris. The RASNZ Variable Chart
number is 9 and R Pic is designated in the
variable star scheme as R Pic 0443-49.
Δ18 / Iota
(ι) Pic (04509-5328) is a
wonderful bright light yellow pair with about
a magnitude difference between the components,
and unlikely most Dunlop pairs, the separation
is reasonably close. I think Δ18 could
be considered a paler mimic of the bright p
Eridani (Δ5), however, Russell described
this pair as "Both straw yellow." The duo can
be found some 5.4°SWW of Theta
Pictoris /Δ20 (See Below) Since
discovery the pair has changed from PA only
2° to today’s 60°,
while the separation is the same distance of
12.5 arcsec.
The spectral class of the stars are F0IV and
F4V. Some evidence suggests that the primary
shows an unusual variable radial velocity.
This suggesting the star maybe a spectroscopic
binary or that there is some turbulence in the
stellar atmosphere. Yet the spectral class is
a little to cool to understand changes in
current stellar evolution theory. Also, no
true variability in brightness has been found.
Both stars might be slightly younger than the
Sun. Distance is about 37pc. Looking at the
significant largish proper motions the stars
seem connected, but if this is so, then the
period is likely to be very long. A great pair
for small telescopes.
Omega (ω)
Aurigae / Σ616 (04593+3753) is a
brilliant pair to observe, whose name just
seems to just roll of the tounge! Magnitudes
of the duo are 5.1 and 8.1, being separated by
4.6 arcsec and perfectly aligned north-south.
Discovered by F.G.W.Struve in 1822, and is
catalogued as STF 616 or Σ616. With care
any 7.5cm should just resolve this stunning
pair in a faint, in a very starry field. A
10.5cm telescope however, shoould have no
problems at all.
I saw the colours of the two stars as having
quite different shades of yellow, but thought
the primary star was strongly influencing the
perceived colour of the secondary; and
applying some imagination, saw the stars as
white and gold. This pair has slowly been
reducing in separation in the last 180-odd
years, and is likely a binary of a long but
undetermined period.
“Southern Astronomical Delights”
© (2009) |
LAST UPDATED
10 Mar 2009 |
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