Southern Doubles, Stars and Variables
10 Mar 2009
RA : 02h
Dec : -30° to -90°
Constellations : For, Eri, Phe, Hyi, Hor, Oct.
Best Observed : Sep - Feb (Text Ordered by RA)
RA : 02h
Dec : -30° to -90°
DS 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 10h 11h
NEW 12h 13h 14h 15h 16h 17h 18h 19h 20h 21h 22h 23h

Δ6 / Phi (φ) Eri
Δ7 / I 386 BC
HDS 354
HJ 3534
γ1 For/ HJ 2161AC/ BU 877AB
I 268 AB
HJ 3541
Δ8 / S423 AB-C +
B 741 AB / HDS 379 CD

Δ9: / θ Eri
None Listed
None Listed

None Listed

Positions given as;
I.e. (13583-6018), are;
13h 58.3m
-60° 15'
This follows the current
WDS Conventions.

or arcsec
In arc seconds or
or arcmin
In arc minutes or
mas - milli arc seconds

( ° ) Angle in degrees.
Measured from
North through East

v - visual (naked-eye)
p - photographic
V - Photometric Visual
B - Photometric Blue
MV - Absolute @ 10pc.

pc. - parsecs
ly. - light-years
AU - Astronomical Unit


T: Periastron (yr.)
P: Period (yr.)
a: Semi-Major Axis (arc sec.)
e: Eccentricity
i: Inclination
Ω: Orbital Node (°)
ω: Angle True Orbit (°)

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 stars 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. Russells 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.

DUNLOP 8 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 Dunlops 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.

Dunlops 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 todays 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 Souths 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 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)
10 Mar 2009