SELECTED SOUTHERN DOUBLES and VARIABLES
R.A. 02 Hours
φ
Eri / Δ6 / Phi Eridani (02165-5131)
appears in Eridanus some 3.2°W of Chi
(χ) Eridani that makes an
interesting pair in small apertures. The primary is given
as 3.52 magnitude and its companion as 9.32. Since
discovered in 1826, the PA has increased by 4° to lie
at PA 220°. Although the separation has decreased from
90.0 to 88.6 arcsec., this blue and yellowish pair has an
attractive colour contrast that makes it quite appealing.
Based on the proper motions this is certainly an optical
pair. Nice in 5cm. binoculars or 7.5cm. telescopes.
Δ7 / DUN 7 A-BC /
I 386 BC (02397-5934) is a wide and easy double for
apertures as small as 5cm and is placed in the faint
southern constellation of Horologium. The field can be
easily found 3.0°E of the pale yellow 5.0 magnitude
star Mu (μ) Horologii. Dunlop
in 1826 lists this pair as “Anonym.”, giving
the position as 02h 34m 57s -60° 21′, and
according to the original reference is placed at PA
20°np and separated by 35 arcsec. Magnitudes are given
by Dunlop as both 8th, which visually is now given as 7.2v
and 7.5v and photometrically 7.62V and 7.68V. Colours of
Δ7 are yellowish white and the companion a moderately
deep-yellow. Position angle of the two stars is given as
97°, with the earliest measure being 290°. Values
here are likely not an indication of significant change in
angle but an interpretational problem between the
identification of the A and B components. Based on the
seemingly increasing separation of 35.0 (1901) to 36.5
arcsec (1993) it is certain the PA of 97° is correct.
If this is true, then the PA has only decreased by
13°. Looking at the Hipparcos data, both stars (HIP
12401/ HIP 12405) seem to have similar proper motions and
parallaxes, but drawing any conclusion from this seems at
this time uncertain. A mean distance from the parallaxes of
4.70±0.71mas and 3.95±1.09mas is
232±50pc.
I 386 BC, the pair
resolved for the Δ7 ‘B’ star, was found
by R.T.A. Innes in 1901. Although impossible to see in
amateur telescopes, little has changed between the BC
components, whose separation is presently 0.4 arcsec along
PA 320°. Since discovery the pair has perhaps widened
by 0.1 arcsec but any real movement from the nine measures
up till 1991 remain still inconclusive. Given spectra
classes of the respective three stellar components by
decreasing magnitude is G0, A9IV and K0III. B-V values
are; A=0.274, B=0.506 C=0.571.
Magnitudes break down according to the WDS
Nov02 as 7.68V and 8.39V — but this seems wrong as
the same value for ‘B’ for Δ7. If this is
the case, the combined magnitude of the stars would be
7.23V (7.68 and 8.39) Using Megastar 5.0 is more confusing,
as the Tycho catalogue gives the Primary ‘A’
7.68V, ‘B’ 10.15V and ‘C’ 10.34V.
If this were the case the combined magnitude would be
9.52V. In all there seems to be some problem with the given
magnitudes, and unless one of the star’s is variable
it is hard to reconcile these differences.
HDS 354
(02421-6004) is a faint orange star located 48′ (PA
299°) from Δ7, and can be identified as a yellow
9.5 magnitude star lies 6'NW. With care this star proves to
be a lose pair which is difficult to see through amateur
telescopes below 15cm. The 8.7 and 11.7 magnitude stars are
separated by 1.3 arcsec along it near north-south
orientation of 187°. No notable changes have been
observed in this star, but it is useful placed to identify
the galaxy NGC 1096 and its associated sextuplet of
the field galaxy group.
HJ 3534 / HJ 3534 AB-C
(02469-6009) is a wide but faint yellowish pair that lies
1.1° (PA 124°) from Δ7 or 35& (PA 99°)
from HDS 354 above. Discovered by John Herschel in 1836,
the separation is presently 21.3 arcsec along PA 215°,
whose magnitudes are 8.8v and 10.8v. This was an easy pair
in dark skies through 10.5cm, but the 20cm was required to
detect the faint colour. It is unlike this wide pair is
actually attached, and since discovery has decreased by
-3.7 arcsec (from 25.0 arcsec) in 167 years (2003).
Analysing the available data finds the Hipparcos (HIP
12973) with the parallax of 8.95±1.81mas making the
distance of 112±24pc. Like HJ 3541, some southerly
proper motion is seen. Using this, the true separation of
the two stars would be as wide as 2 380AU. The combined
spectra is F7/8V.
I 268AB, the A star
is a close pair itself, whose near equal magnitudes of 8.6v
and 8.9v are separated by 0.5 arcsec along PA 253°.
Since discovery by Innes in 1900, the separation has almost
halved since discovery (2000), making it challenging to near
an impossible object to split. It is possible that these
two are associated, however, if it is, the orbit maybe
almost edge-wise to our line of sight.
γ1
For / HJ2161 AC- BU877
AB / Gamma Fornicis (02498-2434) is a
triple star about 1.7°WNW of Δ8. This is an
interesting orange (K1 III) and yellowish pair
that is visible in small to moderate apertures
and easy using 20cm, and even possibly under
good conditions with 7.5cm. The widest and
easiest components are for HJ 2161 AC,
whose 6.1 and 10.7 magnitude components are
presently given the 1954 measures of 40.9 arcsec
along PA 143°. When I
observed this in 1994, I thought the
separation was smaller than this - perhaps a
low as 35 arcsec, but at least the PA did seem about
correct. Measures so far indicate the distance
between the two stars is decreasing over time,
while the PA has decreased from
157° to 143°.
BU 877 AB is the close Burnham pair of
γ For, but this is not so easy for
amateur observers. Visual magnitudes are 6.1
and 12.7, whose components are separated by
12.1 arcsec along 145°. In 20cm at
333x magnification, I saw the ‘B’
component that is conveniently aligned in the
same direction as the ‘C’
component but some one third the distance
between them. The ‘C’ component
certainly made its visibility far more
difficult. A 25cm should make it more easy to
see but a larger aperture would be an
advantage. BU 877 has increased slightly in
separation but the PA has remained virtually
fixed. No colour was seen in the faint
component.
Whether all the stars are really attach is yet
to be ascertained. If so, both periods would
likely be long. True separation of the wide
pair (AB-C) is about 4 500 A.U. and for the AB
system 1 400 A.U. Distance using the Hiparchos
data gives the distance as 111pc. (364ly.)
HJ 3541
(02525-5955) lies another 44′ (PA
73°) from HJ 3584. This is a far
more interesting pair than HJ 3534 as the 8.3v
and 9.4v (8.67V and 9.89V) magnitude stars are
a moderately close 2.5 arcsec apart along PA
165°. The pair was noted by John
Herschel in 1836 with the positions of
151° and 1.5 arcsec. HJ 3541 was
not again measured until H.C. Russell’s
observation in 1883. I saw the colours as
yellow and orange-yellow.
Hipparcos found that this both stars have a
moderately high southerly proper motion in
declination (-144 mas.yr.-1). At
the distance of 95.1±10.3pc. derived
from the parallax of 10.51±1.13.
Assuming this distance, the separation of the
two main stars is 237AU
(3.6×1010km.) which is well within
a acceptable range, giving a period of about 3
600 years. This further makes the absolute
magnitude of the late main-sequence G-type
(G8) stars as +3.4 and +4.3 with the projected
combined mass of 1.1 Σ⊚. It is almost certain
that these two stars are associated, though a
useful orbit might take a whole millennia.
Δ8 / S423 AB-C
/ DUN 8 / ADS 2242 (02572-2459) is a multiple
star in a fairly unremarkable field that lies
some 37'NEE (PA 301°) of Zeta
(ζ) Fornacis. James South in 1824 first
discovered the main S 423 AB-C wide pair and
it was then found again independently by
Dunlop in 1828. In Dunlop’s favour, he
had no real means of knowing that it had
already been previously found, and he lists
the pair as 41 Applied Chemici - in the now
defunct southern constellation of the Applied
Chemical Furnace.
Dunlop’s position is RA : 02h 58m 13s
Dec : -24° 58′ 09″ 1825) converts
to 02h 58h 18m -24° 57′ in the
present 2000 epoch, and some 14.5'E of
today’s real position. Although wide,
the 1954 position for this pair has increased
from 27.7 to 28.6 arcsec while the PA has increased
from 219° to 224°.
Visual magnitudes of 7.3 and 7.8 were closely
estimated by Dunlop as “7,7”, but
he never achieved any initial micrometric
measures with this duo. Dunlop also estimated
the position angle as 49° 06′ sp,
that translates to the PA of 220.2°
— corresponding well with South’s
219°. Since then the PA has increased frm 219° to
226° (1991). No separation measure
or estimate was given by Dunlop.
Closer inspection finds that the brighter
component is again double. This is B 741
AB, which was discovered by the truly
prolific double star observer Burnham in 1878.
Near equal brightness, this 7.3v and 7.4v
magnitude pair has slowly widened from 0.6 to
around 1.0 arcsec. (Hipparcos giving
0.914 arcsec along PA 333°.) B
741 is a near impossible object in apertures
below 10.5cm and in fact would be much easier
in 15cm. I could clearly divide the duo on the
two attempts and have seen it using 20cm under
moderate to good seeing - but this would
surely be easier in 30cm.
Later the C component was also found double.
Now the pair HDS 379 CD, it is
presently separated by 5.1 arcsec along
PA 172° (1991) (Note: Hiparchos
(HIP 13769) gives 5.086±0.064 arcsec.)
HDS 379 is more difficult pair in
amateur scopes because of the proximity of the
other stars and the difference in magnitude.
Just visible in 15cm to 20cm, the separation
is presently 5.1 arcsec along position angle 172°.
Magnitudes are 7.8v and 11.7v (7.84V and 11.73V).
When observed all the stars appeared to me as
yellowish-orange in colour which matches well
with the K1 to K2 spectral classes. They are
later spectral classes than the sun. All stars
have similar common proper motions (cpm) both
in magnitude and size (AC : pmRA=15.44±1.47 mas,
pmDec=-320.54 mas and CD : pmRA=30.21±2.39 mas,
pmDec=-36.90±1.01 mas ), strongly suggesting
that all four are actually physically
connected, while the Hiparchos data gives
similar parallaxes, being 38.87±1.50mas
and 44.49±2.55mas, respectively. Using
the avarage value of 41.68mas gives the
distance of 24.0pc (78.3ly.)
Derived parameters for this multiple system are as
follows;
For S423 AB-C, the true minimum separation is presently
about 690 A.U. (if associated), with B 741 AB about 24 A.U.
and HDS 379 CD about 122 A.U. Periods calculate to about
5,000 years (AB-CD), 200 years (AB), 1,300 years (CD).
Estimated masses using the mass-luminosity relationship
ind A = 1.7 M⊚, B = 1.1 M⊚, C = 1.0 M⊚
and D = 0.2 M⊚, with the respective absolute
magnitudes (Mv) of 5.4, 5.5, 5.9 and 9.8. No doubt this
will be an interesting pair to watch in the future.
θ
Eri / Δ9 / Theta Eridani / Acarma /
Pz2 / (02583-4018) is wonderful for telescopic observers
who are looking for a really decent southern double star.
Theta Eridani or Acarma was first discovered by G. Piazzi,
and is now listed as Pz2, this bright bluish-white/
blue-white double star has respective 3.4 and 4.5
magnitudes, separated by 8.4 arcsec along an east-west line
at PA 92°. Even 7.5cm can easily split this duo. I can
truly recommend this magnificent pair. If it is not in your
Top 10 of all time pairs - it soon will be!
Ross Gould in “Constellation of the
Month - Eridanus, Southern Half”;
Southern Cross - Dec. 1998
“ Theta Eridani...is a showpiece
pair, a fine slightly unequal double that is a fine object
even in 6cm refractor. Both stars are white, a brilliant
couple in medium telescopes. There has been little change
over time, with only a slow increase in angle. Magnitudes
are 3.4v and 4.5v... The field has only a few faint
stars.”
“Southern Astronomical Delights”
© (2009) |
LAST UPDATED
10 Mar 2009 |
|