A Selection of Southern Doubles, Bright Doubles and Variable Stars

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RA :  00h to 03h
Dec: -30° to -90°

Scl, For, Phe, Eri,
Tuc, Hor, Hyd, Oct

Best Observed: Jun - Oct

(Text Ordered by RA)

Δ1 / β12 Tuc , LCL 119 AC Tuc , B 7 AB / Aa Tuc , I 260 CD Tuc , B8 / β3 Tuc , LDS 6092 , RST 10 ,
COO 03 , Δ2 / λ1 Tuc , ζ Phe / RMK 2 AC / RST 1205 AB , κ Tuc / HJ 3423 , Δ4 , Δ5: p Eri , Chi(χ) Eri ,
Δ6 / Phi (φ) Eri , Δ7 / I 386 BC , HDS 354 , HJ 3534 , Gamma (γ1) For / HJ2161 AC- BU877 AB ,
I 268 AB , HJ 3541 , Δ8 / S423 AB-C / ADS 2242 + B 741 AB + HDS 379 CD , Δ9: Theta (θ) Eri :




Δ1 / β1, β2 Tuc /LCL 119 (00315-6258) is a wide optical double star. It was first recognised as such by N. de Lacaillé but was rediscovered, or more precisely re-catalogued, by James Dunlop at in 1826. β1, β2 Tuc features as the first double star in his 256-pair double star catalogue as the pairs are ordered in right ascension. Another whitish star is β3Tucanae some 9.1'SW of the main pair. All three of these stars are visible in binoculars. Closer inspection find these stars are again doubles with similar proper motions and it is likely we are looking at a multiple star system with at least six or seven components in the system.

β1 and β2 Tucanae

LCL 119 AC (00315-6258) was measured by Dunlop using a homemade micrometer with both stars finding the separation as 24.86" along PA 84o 05'np corresponding to the PA of 354.1o. Dunlop has confused β1 and β2 Tuc here suggesting β2 is the brighter component. The stars are the reverse of this, so Dunlop's PA should actually read 174.1o for 1826. John Herschel measures are taken in the WDS01 as the first value, finding the PA as 172o in 1835. The AC main pair is significantly wide - though the true aspects of the all the stars in the system were not recognised by Lacaillé, Dunlop or John Herschel. In the WDS01 this is given as the wide 4.53v magnitude "C" companion making the visual pair LCL 119 AC that lies presently some 27.0"arcsec away at PA 168o - with the PA continuing to slowly diminish.
The primary "A" is a blue B9 V star of 4.36v with the "C" companion being 4.53v magnitude. Both these stars seem to be associated as they have similar proper motions. If we assume the mean parallax as 21.45±1.75mass, then the system lies 46.62±3.82pc or 152.1±12.5 ly away. Based on the observed separation, both are separated by 1 260AU. I see the respective colours as bluish-white, white matching both the given B9V and A2V main sequence stars of Mv of +1.09 and +1.19.

β1 Tucanae

B 7 AB / Aa (00315-6258) is the main β1 AB system was found by van den Bos in 1926. The primary "A" is 4.4 magnitude with the difficult to see "B" companion being the faint 13.5 magnitude star separated by 2.6"arcsec along PA 153o, which seems to remained relatively fixed. "A" itself is also a suspected spectroscopic binary "Aa", but it doesn't appear in Batten's "8th Spectroscopic Orbital Catalogue" (1992) because of the lack of suitable observations. Hipparcos find the parallax of β1 Tucanae as 23.35±0.52mas, suggesting the distance is 42.82±0.95pc or 139.7±3.11 ly. If these stars are attached, then the true separation between the two stars is 105AU. This is a tough pair to split and I have only read one amateur description that splits the duo - and that was in 40cm. I suspect 30cm could see it if the observing conditions were just right.

β2 Tucanae

I 260 CD / HIP 2487 / HD 2885 (00316-6258) is the visual binary with the short period of 44.43 years. Discovered by R.T.A. Innes in 1895, this duo's 4.8v and 6.0v magnitude makes it a very tough pair for amateur apertures. It is likely only to be seen when the stars are at their maximum distance apart which is in the order of about 0.58"arcsec along the PA around 280o. Presently (2002), the retrograde orbit is diminishing and has become impossible to see for amateur eyes until about 2030 A.D, with the next periastron occurring in May 2012 (2012.36). (Last being December 1967 (1967.93)). Several orbits have been produced for this star with the latest being the first of two possible orbital solutions as determined by Eggen in 1965. The main sequence spectral types are given as A2 and A7 corresponding to the respective temperatures of 8 870K and 7 810K. Innes described the "D" star as "...decidedly yellow, although the spectrum is A."

I 260 CD Orbital Elements (Eggen (2) 1965 ; Grade 4 and Ephemrides

T P a e i Ω ω
1923.50 44.43 0.385 0.80 142 40.3 282.1
Year PA Sep
2002 271 0.47
2003 268 0.45
2004 267 0.44
2005 266 0.43

β3 Tucanae

B8 / β3 Tucanae (00327-6302) is another whitish 5.14v magnitude star is β3 Tucanae, lies some 9.1'SW at PA 118o. It also shares similar proper motion with the main and wide "AC" pair. Known as B 8, its duplicity was found by van den Bos in 1926. It remains "unsplitable" in all amateur telescopes as the separation is merely 0.1"arcsec, which has remained the almost the same despite some twenty-four observations being made since 1964. Some evidence exists that the PA has reduced from 173o to 171o but this is likely reflects more random errors than any real motion for such a close system. Few observations since this date have been achieved. The spectral class is A0V. No doubt this is a binary system.

Summary of the Beta Tucanae System

A Aa B C D A B β1,2 - β3
Related Component β1/ B7 β1 β1 β2 β2 β3/ B8 β3 β1
Magnitude 4.36   13.5 4.53 6 5.8 6 5.07
Spectral Class B9V   G? A2V A7 A0 A5? A0V
Separation ("arcsec) ---   2.6 27 0.58 --- 0.1 546
Postion Angle (deg) ---   151 169 280 --- 171 117
Parallax (mas) 23.35   --- 20.20 --- 21.52 --- ---
Distance (pc) 42.82   --- 49.51 --- 46.46 --- ---
True Sep (AU) ---   150 --- 1260   4.7 25400
Mv 1.09   10.3 --- 1.19 2.5 2.7 ---

LDS 6092 (00323-6302) is a very faint pair that was discovered by Luyten as recently as 1985 and appears in his proper motion catalogue. Much interest has been with this pair as the proximity to Beta Tucanae suggested association. The parallax of 38.85±1.1 gives the distance of 25.74±0.73pc or about 84ly. Furthermore, the motion is 539.7'arc sec (or 9.00'arcmin) per millennia and moving along the northeastern PA of 101o
Presently the separation is 1.1"arc sec along PA 131o, but the 11.2 and 14.5 magnitude companion makes it a faint pair possibly seen in 20cm to 25cm. Based on this data, the projected separation is 28 AU, roughly the distance between the Sun and Neptune. It is likely, if the two are associated, that the period of this pair is around 100-odd years Observation is the first half of this century may prove this prediction true.
I haven't observed this pair because of its relative "newness" and my lack of aperture, but I estimate it is a perhaps a little easier to see. Else, little is known of the pair but the future interest in this pair will be drawn by the proximity.

RST 10 (00310-6237) is another faint pair some 16'N of β Tucanae itself. Since measured in 1928 the PA shows indications of minor changes in the position angle, which is only 2o. At present the separation is 1.6"arcsec aligned along PA 97o. The magnitude of the component is a faint 11.3 and 11.4. RST 10 can be separated in 20cm, though I have no really suggestion of what aperture could separate this faint pair. Those with 10.5cm in good skies might like to try this pair for themselves. Little is known about this pair.

COO 03 (00445-6230), in Tucana, was discovered at the Cordoba Observatory in 1894. Suprizingly missed, especially or such a bright star, by Herschel, Dunlop and Russell, COO 03 is placed some 1.6oENE of β Tucanae with the yellowish and yellow pair having its companion 2.3"arcsec away at PA 66o. The magnitudes are 6.31 and 8.01, but the three recent photometric observations give the Δm as 1.78. Since 1894 the PA has change by some 24o while the separation has decreased by 1.3"arcsec. The combined spectra is F5III-IV and it is likely the two are connected. Distance from the 11.89±0.67 parallax is 84.31±4.80pc.
COO03 has a significant proper motion of 103.35" 100yr-1, and is moving almost eastward (PA 86.5o) from its current position. However, it is only about a quarter that of LDS 6092. A 10.5cm will clearly separate the two with a reasonable seeing night. Overall, an uncommonly beautiful pair.

Δ2 / Lambda (λ1) Tucanae (00524-6930) lies in southern Tucana some 3oN and just above the Small Magellanic Cloud. Alternatively it is placed 1.6oNNW of the globular cluster NGC 362. The field contains three stars, λ1 A and λ1 B (Δ2) and λ2. All three stars appear yellow, with λ2 perhaps being deeper in colour. Not recognised as a pair, both λ1 and λ2 Tuc are separated by 13.5'E (PA 96o). λ1 is about 1.2 magnitudes brighter than the Δ2 pair. It seems that all three stars maybe associated as the cpm is about the same order an in similar directions.
Δ2 itself is a moderately wide 6.67 and 7.56 magnitude yellow pair separated by some 20.4"arcsec along PA 82o, and should not be confused with the wider λ1, λ2 Tuc. Since discovery by Dunlop in 1826 and the first measure by Herschel in 1834, the PA has increased by some 5o and the separation has reduced by some 2.1"arcsec. The primary is a gorgeous deep yellow which reminded me very much of the companion to p Eridani. It is odd that Dunlop describes by micrometric measurements for the separation as 6.62"arcsec., but the distance is certainly three times this value. This field contains few other stars and does look magnificent in binoculars or small telescopes. A magnificent visual treat.

UPDATE on Zeta Phe : 7th September 2003

Zeta (ζ) Phoenicis / RMK 2 & RST 1205 / HIP 5348 / SAO232306 / HD 6882 / (01084-5455) is an interesting bright quadruple system. Shining at 3.9 magnitude, it is very easy to find as it lies some 4.5oW from the first magnitude star Achernar in Eridanus. The wider ABxC pair is RMK 2, was discovered by Charles Rümker at Parramatta Observatory in 1835. How Dunlop missed it is a mystery. Both stars are 4.0 and 7.0 magnitude, separated by 6.4"arcsec and the PA of 242o. Since discovery, the last thirty-four measures (2000) has shown a +2.8"arcsec increase in Sep with the PA increasing by 3o.

John Herschel once described this visual system as “a very beautiful system, in a starry field”, and it is difficult not to disagree with him. AOST2 describes;

This beautiful white pair ornaments [in] a field with a few stars.”

An Identification Error of RMK 2 by H.C. Russell

H.C. Russell made a significant error in the position of this star. In his “Double Star Results, Measures 1871-1881.”, he says he observed the pair on 20th November 1878, describes the pair (His catalogue #21) “After h.3416” and the colours as “greenish yellow and copper red”. He further remarks, “Position doubtful. H[erschel] says nothing about colour.
Three clues says he is really observing RMK 2.

1) His approximate RA and Dec is 01h 03m -55o 56' (1880) is nearly the same as the current position. (Ie. 01h 08m - 55o 18')
2) The two measures give PA is 239.47 and the Separation is 6.25"arcsec. - matching this pair almost exactly.
3) The magnitudes are given as "3 and 7" with no other pairs this bright nearby.
Yet the final clue is that HJ 3416 (01076-2601) is placed in the constellation of Sculptor (Near the globular NGC 288), and which are a 10.4 and 11.1 magnitude and were measured in 1919 (By Innes?) As 11.5" along PA327o. The only true mystery is the strange colours he describes.

The Inner Pair RST 1205

Zeta’s inner main “AB” pair is RST 1205 and was discovered by R.A. Rossiter in 1931. At 0.6"arcsec apart and with respective magnitudes of 4.1 and 7.0, (4.13 and 6.29 in the WDS01) Now it is becoming very much easier for telescopes around 30 cm apertures to see, though it still requires good optics and brilliant seeing. I've never been able to see this inner pair, though I once suspected the disk to be elongated in 30cm (1987). I'm certainly 40cm with spilt the two.
More significant is the change in PA, which changed from 22o to 79o in 1987. The last time looked in 1994. Most odd is the value quoted in the WDS 1996 for the separation which stated 0.9" - suggesting there has been an increased separation of 0.3" since discovery. According to the latest version of the WDS01 the PA has returned to 0.6" arc sec again! Even AOST2 says the separation is now 0.94"arcsec - but it is certainly less now. Worst is the fact that in the PA in this case has only increased from 79o (1987) to 95o (1999) The results are indicating that some significant changes have occurred in the orbit - though it seems it will be a long time before any orbital elements are produced - simply on so few observations.
Although there have been twelve measures to date, it would certainly pay for someone to re-measure these components!
The primary is the pair Zeta Phe "Aa" is listed as only Zeta Phe in the GVSC4 - with out the normal designations usually given to variable stars. It is the brighter A component in this pair that is the eclipsing variable / spectroscopic binary.
Observations for this detached (EA / DM) eclipsing binary are difficult to make because of the proximity to the 'B' star. Magnitudes vary between 3.92 V and 4.42 V, over the period of 1.6697671 days equal to 01 day 16 hours 04.5 min (JDE 2441643.689). It rises in brightness in 0.20037 days - almost exactly four hours. Both are main sequence star with the given spectral classifications of B6V and B9V.
Little is known about eclipsing binary and the system’s physical data is a little scant. Hartung's AOST2 states that the eclipsing binary has the total mass of about 9Msolar mass, which is close to the most recent calculations placed on the total mass. Individual masses are respectively, 6Msolar mass and 3Msolar mass suns.
Distance has been previously estimated to be about 67pc or 218 ly from the Sun. Hipparcos gives the parallax as 11.66±0.77mas implying a distance of 85.76±5.81pc or 279.8±19.0ly. The system is receding from us at +18kms-1.
The wider pair, of the pair RMK 2 (AB- C system) in the multiple is likely physically associated. All the visual stars appear bluish, white and white.

κ Tuc / Kappa Tucanae / HJ 3423 (01158-6853) is a lovely colour contrasting pair some 4oN of the Small Magellanic Cloud and 2oENE of Lambda Tuc (See Δ2) Innes says the stars are “yellow, purple or bluish”, yet if you read both AOST1 and 2, the pair’s colours are described as “yellow and orange.” I very much fooled for some time with these colours and I could not figure out who was describing what. Hartung in AOST is referring to the wide pair Ie. HJ 3423AB and the companion pair I 27CD than just HJ 3432AB alone. The text in both of these editions is slightly ambiguous. Innes is comparing the colour of HJ 3432AB - the pair Kappa itself. AOST says the main pair is “...beautiful in a moonlit field” I tried this and have no disagreement! It is certainly very attractive.

Δ3 / R Scl / R Sculptoris (01270-3233) is a remarkable object that was discovered by Benjamin Apthorp Gould in 1878 and which Innes later knew of the variability of this star. Although not even really a optical double star and therefore is not listed in the WDS 01. Dunlop says in (Ref.1) of this star;

"A very singular star of the 7th magnitude, of an uncommon red purple colour, very dusky and ill-defined; 3 obs(ervations) on this star; a small star preceding, and another following."
Dunlop's position when precession is taken into account find the co-ordinates as 01h 27m 41s -32o 37'. This is certainly the "star" Dunlop was referring too with today's position merely 10.2'N (PA347.6o).
Dunlop's paper refers to a "small star preceding" (west) and this is 9.4 magnitude HIP6719/ SAO193317/ HD8833/ PPM277033 (01265-3233) that lies some 6.4' away at PA 263o. The spectral class of this yellow star is F8. Another star following is obvious deep yellow 10.2 magnitude PPM277055/ T7002:1474:1 (01277-3232). The Tycho-2 data gives the parallax as 65.70±24.90mas. An unconfirmed double star of R Scl, and near 3's position, is LDS 2199 in Sculptor, which would not have been seen by Dunlop. Although this star is separated in 1955 by 10"arcsec along PA 234, this 8.0 and 19.0 magnitude pair is of little interest to the amateur.
R Scl is presently the 14th brightest SRB type variable star known which varies between 9.1p to 12.9p in some 370 days. (363.1days in some texts) The spectra of the Carbon star is C6,5 EA(NP). Burnham's describes it in the older type of as N3p. R Scl also appears in the RASNZ's variable star map No.70. A suitable chart on the net is also available at http://www.trilobytes.com.au/astronomy/bvstars/bvchart1.gif.
R Scl is also listed by Brian Skiff. "A Revised Catalogue of the Espin-Birmingham Red Stars." (1998) as EB 26, with the following details.

EB 26*/ HD 8879 / R Scl RA: 01h 26m 58.0s Dec: -32o 32' 36" / 5.8 / 3.9 / C6,5
EB 26 / HR 423. Spec also C5,4 and C6,4. photom also V = 6.4 / B-V = 4.8 (ApJ, 167,521).
1. The astronomer Benjamin Apthorp Gould (1824-1896) has an interesting history. Gould was the first American to receive a PhD in astronomy and the founder of The Astronomical Journal, which printed its first edition in 1849.

Δ4 / DUN 4 (01388-5327) lies in Eridanus is some 3.8o due north of the first magnitude star Achernar or 2.8o N due north of 5. Dunlop's position when precessed finds good agreement with the coordinates being 01h 38s 54.5m -53o 25' (2000) This light yellow pair is a slightly fainter version of p Eridani / DUN 5 system and is oddly not given a mentioned in either AOST1 or 2. Visual magnitudes are 7.1 and 8.6 (7.11V and 8.64V) is an interesting moderate bright pair whose combined spectral classes are given as F5IV-V that agrees well with the colours of my own visual observations. Δ4 has shown a moderate decline in separation (15.8"arcsec to 10.1"arcsec.) and position angle (107o to 104o), which will likely in the future will gain more interest towards the end of the 21st Century. This is really good and interesting pair for 7.5cm small telescopes and easily visible in 10.5cm. No doubt this is likely a binary with a substantial period. A pretty pair which is quite attractive for amateur eyes and remains among my favourites.

Δ5 / p Eridani / 6 Eri / h.3453 (01398-5612) ranks as one of the best southern double strs. Even though it is far from the Milky Way, Δ5 is easy to find as it is some 1.1oN (PA 16o) from Achernar / Alpha Eridani at the end of the river. The stars to the naked-eye appear as 5.3 mag star; and telescopically both 5.8 and 5.9 magnitudes, respectively.

Dunlop described the pair p Eridani as; “Very nearly equal. Pretty d.(ouble)star

Furthermore, he says of the pair; (Ref 1. pg.259)

A beautiful double star; both stars white; the preceding a little dusky. I cannot say which of the stars is large; perhaps following, if there be any difference. The distance is about equal to one diameter of the following star, which I estimate at about 2½ seconds.

Since discovery in December 1825, this pair has slowly widened from 2.5"arc sec at PA 343.1o, to 11.5" at PA is 190.4o (2001). By the time of John Herschel's mean observations in 1835.144, the separation was 3.68" and the PA has changed by some 40o to 301.7o. Next in the measures were by Jacobs in 1846 (276.3o at 4.21")and 1856 (259.6o at 4.61"). By the time of the H.C. Russell's three main observations 1870 (253.4o and 5.46"), 1878 (236.8o and 6.09") and 1880 (234.7o and 6.30") the pair continued to widen in a straight line. Russell said in the paper "New Double Stars, and Measures of some of those found by Sir John Herschel" Royal Society of NSW (7th September 1881) about p Eri's orbit, that;

...as I endeavoured to show you last year, in reference to p Eridani, in the supposed orbit of which , as the observations accumulated, the ellipse had gradually to be increased, until in the end the most probable curve, if I may so express myself, were shown to be a straight line, or, in other words, the motion which was supposed to prove it a binary is found to be probably due to proper and not orbital motion.

Russell was certain that the orbit was in fact due to proper motion, and he published in the "Sydney Morning Herald"that he has determined that the two stars were merely close together in the sky and not associated as a binary. Another article appeared in Nature p.589 on 19th April 1883.

THE BINARY STAR p ERIDANI - In Communication to the Royal Society of New South Wales in June, 1980, Mr. Russell, the director of the Observatory at Sydney, suggested, from the measures made since 1856, including his own up to 1880, that this object might not be a binary star at all, but merely afforded an instance of one star passing before another by reason of its proper motion. This opinion is repeated in the volume of double-star results obtained at Sydney, published last year. "In fact," observes Mr. Russell, "a straight line accords better with the observations made subsequent to Herschel's than an ellipse, and it would appear that the changes are due to simply to proper motion ; of this I think there cannot be any doubt...." The question has just been very fully and carefully considered by Mr. Downing, of the Royal Observatory, Greenwich, who arrives at an opposite conclusion to that of Mr. Russell, and considers "there is not sufficient evidence to justify us in asserting that p Eridani is other than a binary star." We entirely agree with Mr. Downing in his opinions. If we only compare the measures made by Jacob in 1845.46, with those of Russell and Tebbutt, 1878.80, we get the following expressions :-

d . sin p = -4361 - [8.3894](t-1850.0)

d . cos p = +0122 - [9.1017] (t-1850.0)

showing differences from Herschel's mean measures, epoch 1834.996, of -51 in position, and +082 in distance, which is too large to be tolerated. This star has been occasionally miscalled 6 Eridani, which would imply that it was one of Flamsteed's stars. Flamsteed, it is true, has a star which he calls 6 Eridani, and which is B.A.C. 926 ; the binary is B.A.C. 521. The letter p was attached to a star by Lacaillé in the catalogue at the end of his Cælum Australe Stelliferum. The number 6 is merely borrowed from Bode.

Russell main thrust in his argument which assumes that both Dunlop's and Herschel's observations were both under-measured - mainly due to their relatively poor equipment, of poor quality, and so, were simply reject. His support for this was based on the re-measures of all John Herschel pairs south of -34o declination, in which he summarises;

In very many cases considerable differences between h.'s (John Herschel) observations with the reflector and mine have been found; but a complete list of them has not been made, because the reflector observations so often differ from those of h. made with his equatorial that it did not appear worthwhile.

In 1880 only seven southern binaries were known (twenty-seven in the entire sky), and that p Eridani's rejection reduced this number to six. Eventually, after the observations and orbit analysis by R.T.A. Innes in 1911 from the Union Observatory, Johannesburg, South Africa reinstated p Eridani binary star status. From the four observations, the mean PA was 216.9o at 8.3". Gore was the first to publish the first orbit in 1912, stating that it was a binary's orbital period was 302 years - predicting that apastron would occur during 1975 and that the rate of change would be 2o every three years. Innes also says of p Eridani;

Assuming that the mass of this system is equal to that of the sun, its parallax would be 0.16" (20 light years); or if it is assumed that its luminosity is equal to the sun's, it parallax would be 0.09" (36 light years.)

Several orbital elements were published as more observations were added, but the next analyses gave significantly shorter periods. For example, B. Dawson in 1919 found a short period of about 219 years. Next was W.J. Luyten and E.G. Ebbinghausen in 1934, who found a period of 251 years and an orbital eccentricity of 0.80. This was followed by the more modern T.S. van Albada's (1957), whose elements were much used in the 1960's and 1970's, and gave a much longer period of 483.66 years and an eccentricity of 0.554.
Presently, the orbital period of this retrograde pair is estimated to be 484 years, whose semi-major axis is 7.8". Periastron for the system in 1813 and just after Dunlop's observations. Then the positions were fairly close but they have continue to widen. Furthest separation is presently expected to be sometime during 2048, if you use the properly round period values of 483.7 years. If the full 483.66 value is used, the van Albada's elements, this is more likely closer to 2055. At this time, the separation will be about 11.82" arc sec.
If the present elements are adopted, periastron was in 1826, and will again occur in 2310 AD. Closest approach is 3.40"arcsec. Incidentally, the companion passed through the descending node of the orbit in 1989.
This is one of the nicest binary systems in the sky.

χ Eridani / Chi Eri / HJ 3473 (01560-5137) is a close pair with a significant difference in magnitude. It lies some 3.2oE of Phi Eri, and since discovery, the pair's separation has slowly diminished from 12.0" arcsec in 1899 to 4.9"arcsec (1956) while the PA has increased from 196o to 204o. Projecting the values suggests the separation should now be widening on the opposite side of the primary, and should be about 0.8"arcsec and about PA 40o (2002). The magnitude of the stars is 3.7 and 10.7. The pair is said to be yellow and white. As time moves on this pair has become more difficult. According to Hartung in 1968, 25cm is needed to see the companion, and this is when the projected separation was 3.4"arcsec. If we consider these changes, possibly 30cm is now required to see it. With the hexagonal diaphragm it might be now possible to see them in as little as 20cm. However, doing all this in 1994 with 20cm C-8, I failed to resolve this pair. To again meet the conditions that Hartung observed under the 3.4"arcsec separation will occur in about 2020 AD. This is likely a bound system and will be interesting to watch in the coming years. If attached, the period is certainly fairly long.

Δ6 / Phi (φ) Eridani / DUN 6 (02165-5131) appears in Eridanus some 3.2oW 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 4o to lie at PA 220o. 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 5 cm 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. This pair’s field can be easily found 3.0oE of the pale yellow 5.0 magnitude star Mu (μ) Horologii. Dunlop in 1826 lists this pair as “Anonym.”, giving the position as 2h 34m 57s -60o 21', and according to the original reference is placed at position angle 20onp 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. The position angle of the two stars is given as 97o, with the earliest measure being 290o. 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 97o is correct. If this is true, then the PA has only decreased by 13o. Looking at the Hipparchos 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 of4.70+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 320o. 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. The given spectra class of the respective three stellar components by decreasing magnitude is G0, A9IV and K0III. The 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 299o) 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 187o. 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 1.1o (PA 124o) from Δ7 or 35' (PA 99o) from HDS 354 above. Discovered by John Herschel in 1836, the separation is presently 21.3"arcsec along PA 215o, whose magnitudes are 8.8 and 10.8. 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 Hipparchos (HIP 12973) with a parallax of 8.95+1.81mas - giving a distance of 112+24pc. Like HJ 3541, some southerly proper motion is seen. Using this, the true separation of the two stars would be a wide 2 380AU. The combined spectra is F7/8V.
I 268AB, the A star is a close pair itself, whose near equal magnitudes of 8.6 and 8.9 are separated by 0.5"arcsec along PA 253o. Since discovery by Innes in 1900, the separation has almost halved since discovery (2000), making it a challenging to a near 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 / Gamma (1) Fornacis / HJ2161 AC- BU877 AB (02498-2434) is a triple star about 1.7oWNW of Δ8 / S423- AB-C. (See Below) 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"arc seconds along PA 143o. When I observed this in 1994, I thought the separation was smaller than this - perhaps a low as 35"arc seconds, 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 157o to 143o.
Close inspection sees that the bright pair is again double, being the Burnham pair BU 877 AB - but this is not as easy. Visual magnitudes are given as 6.1 and 12.7, whose components are separated by 12.1"arcsec along 145o. In 20cm at 333x magnification, I saw the ‘B' component that is conveniently aligned in the same direction as the ‘C' component but some 1/3rd 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 4500AU and for the AB system 1400AU. Distance using the Hiparchos data gives the distance as 111pc. (364ly.)

HJ 3541 (02525-5955) lies another 44' (PA 73o) 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 165o. The pair was noted by John Herschel in 1836 with the positions of 151o 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.
Hipparchos found that this both stars have a moderately high southerly proper motion in declination (-144"arc per century). 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 (3.6x1010km.) 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 a projected combined mass of 1.1⊙. 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 301o) 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 constellation of the Applied Chemical Furnace. Dunlop's position is RA : 02h 58m 13s Dec : -24o 58' 9 (1825) converts to 02h 58h 18m -24o 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" while the PA has increased from 219o to 224o. 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 49o 06' sp, that translates to a PA of 220.2o - corresponding well with South's 219o. Since this time the PA has increased 219o to 226o (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 7.3 and 7.4 magnitude pair has slowly widened from 0.6" to around 1.0"arc seconds. (Hiparchos giving 0.914"arc seconds along PA 333o.) 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"arc seconds along PA 172o (1991) (Note: Hiparchos (HIP 13769) gives 5.086±0.064"arc seconds.) 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"arc seconds along position angle 172o. The magnitude of the duo is 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", pmDec=-320.54 and CD : pmRA=30.21±2.39, pmDec=-36.90±1.01), 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 separation is presently about 690AU (if associated), with B 741 AB about 24AU and HDS 379 CD about 122AU. Periods calculate to about 5 000 years (AB-CD), 200 years (AB), 1 300 years (CD). Estimated solar masses using the mass-luminosity relationship find A=1.7 Msolar mass , B=1.1 Msolar mass , C=1.0 Msolar mass and D=0.2 Msolar mass , 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.

Theta (θ) Eridani / Acarma / Pz2 / Δ9 (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 listed as Pz2, this bright bluish-white/ blue-white double star has respective 3.4 and 4.5 magnitudes, separated by 8.4" along an east-west line at PA 92o. 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!

Positions are given as ; Ie. (02583-4018). This is Right Ascension 02h 58.3m and Declination -40o 18',following the WDS Conventions.

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Last Update : 07 September 2003

Southern Astronomical Delights”   © Andrew James (2002)          Sydney, Australia

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