A Selection of Southern Doubles, Bright Doubles and Variable Stars

T Hor (03008-5038) this moderately bright Mira variable that lies 54' (PA 319^o) from Δ10. *(See Below) Magnitude range averages between 7.2 and 13.7 magnitude for this richly coloured red star over some 217.6 days (JDE 2441957). The rise in brightness is almost sinusoidal, with the change in brightness roughly 48% of the period. An entire cycle can be seen in dark skies with 20cm. Spectral class is M5IIIe. A precise position is RA : 03h 00m 51.9s Dec. : -50^o 38' 30".

Δ10 (03046-5119) is a yellow and orange pair that lives in Horologium. This moderately wide pair has a one magnitude difference for the 7.6 and 8.6 magnitude pair. Dunlop discovered it in 1828 and the separation has continued to increased from 30.0" to 38.3"arcsec while the PA has decreased from 75^o to 70^o. From the available proper motions, this is likely a real pair that is presently widening, If so, the period must be very long. This is a quite nice pair for apertures as low as 5cm.

Δ11 (03075-5823) is described by Dunlop as “A triangle of stars. The following a double star.” Precessed position is 03h 07m 30s -58^o 23' (2000), but nothing from the clues appears here, and observations confirm no such pair exists in this place. It is obvious that Dunlop has likely given an incorrect position. Possibilities for this pair are still uncertain.

RZ For / SAO168619 (03325-2530) in Fornax is a deep red SRa regular variable in the same field as the plantary NGC 1360. Directions to find this variable are likely obvious - but it does lie 18'NE. SRa's are fairly stable in their light curves with regular amplitudes. Another SRA example of the class is Antares. RZ For has the spectrum as late M5, while the magnitude variations are about 0.8 magnitude. This changes between 8.5 and 9.4 magnitude (9.2p to 10.0p), over the period of 64.6 days (Julian Date for the period is stated in the General Variable Star Catalogue (Version 4) and Sky Catalogue 2000.0 as JD 2428075, as long ago as the 30 August 1935!)

Δ13 / Dun 13 (03377-4005) is listed by Dunlop as the Bode star 172 Eridani. Seeing Δ13 as triple, he describes the appearence as; “A triangle of stars. Large star fine yellow.” No one has listed it in any of the more modern double star catalogues. The stellar position in 1827 Epoch is 03h 31m 34s -40^o 41', however, Dunlop gives no positions or angles for the components except the magnitudes being 5th, 8th and 9th - making identification today a bit difficult.
Dunlop's precessed coordinates are 03h 37m 47s -40^o 06' (2000) and no actual star marks these coordinates, however, the star he is certainly referring to is 4.57 magnitude y Eridani / HIP 16870 / PPM 307805 / SAO 216405 (03371-4017) some 13.4'SW (PA 219^o) away. This star has the spectral type of K0III and has the B-V of 1.017. Distance is 67pc or 220ly. If this is the correct star, then the only one that would match it is orange 9.4 magnitude PPM 307794 some 8.6'E and the white 10.0 magnitude PPM 307813 some 9.0'NNE of HIP 16870. These seem a little too wide for atypical Dunlop pairs, especially as few Dunlop pairs exceeded 1' or 2' separation. Yet there is no other 5th magnitude star within 5^o.
Another suspect grouping for these stars is about 2.5^oN from yellowish e Eridani, and is placed some 1^oE of the galaxy NGC 1291, however, these are also too wide apart. Nothing else exists within several degrees that matches this grouping of stars. Another Dunlop mystery. Nearby is Δ15 merely 33'W (PA 99^o)

Note: Do not confuse the "y Eridani" with Gamma (γ) Eridani. (See γ Below)

Δ14 / DUN 14 (03382-5947) is a wide yellow pair in Reticulum with the separation of 58.2" arcsec along PA 270^o. Magnitudes are given as 7.1 and 8.9 and both appear in an average starry field, which Dunlop originally listed as 7.8 and 8. He also gave the separation as 45" angled at 10^onp or equal to the PA of 280^o, the value presently listed in the WDS 01. It seems the separation has increased almost by 25% since this time, while the position angle has reduced nearly 10^o. Common proper motion (c.p.m.) suggests the stars are associated, and the period is perhaps several hundreds of years. Both are main sequence class F3V and F5V. Δ14 is easy in even 5.0cm.

Δ15 / DUN 15 (03398-4022) is a moderately faint pair in the same wide field 0.5^oE of y Eridani (which is possibly Δ13) and 3.4^oSW of f Eridani / Δ16 as mentioned below. The magnitudes of the white pair are 6.55v and 7.45v, respectively, with the north-south PA of 327^o and the separation of about 7.9"arc sec. The pair has continued to increase in separation (by 2.9"arcsec) and decreased in PA (by 8^o) since 1826. The spectral class of the primary is a white main sequence A3V and the secondary is likely mid-"A"V. Looking at the Tycho data - the only catalogue to show data on the two stars finds attachment of the two seems unlikely. To add to the thirty-six measures to date shows linearity instead of typical orbital curvature. Distance is c.130pc, and if attached, this suggests a rough separation of 1000AU and a rough estimated orbital period of 15 000yr. Enjoyable pair in apertures of 7.5cm or above.
Note: Tycho gives this 6.91 mag star the parallax as 6.30±4.60mas and the cpm as RA 15.50±6.4 Dec 4.60±5.00. The secondary is presented as 7.79 magnitude with the parallax of 9.30±5.70. Cpm is RA 27.20±7.60 and Dec 20.60±6.30

HJ 3589 (03441-4040) lies a further 0.8^oE of Δ15. 5.2"arc sec separates this duo along PA 349^o. Little has changed in the stars since discovery by John Herschel in 1837. I saw both stars as rich orange in colour, with the secondary even showing a hint of red. The component magnitudes are 6.6 and 9.2, and should be visible in 7.5cm. This pair was good in 20cm. Little is known of the pair.

Δ16 / f Eri (03486-3737) is a moderately close pair in mid-southern Eridanus and is placed in a faintish triangle of stars with h and g Eri. The prominence of the double is that it is 3^oSE of the centre of the well-known Fornax cluster of galaxies, and that southern deep-sky observers have used both the triangle and f Eridani to find this rich galaxy cluster. At 4.30 and 4.90 magnitude, this marvellous pair sees both stars as blue and white that is visible even in smallest of telescopes. Visible easily in 7.5cm, both components have slowly widened since discovery while the PA has increased by nearly +15^o in the last 180 years to 217^o (2002). Proper motions suggest this is likely a binary with a long period. One component is suspected to be a Beta Lyrae eclipsing binary because the overall light-curve suggests periodic behaviour - but this needs much more observation to confirm this is the case. Spectral classes are given as B9V and A1V approximating the colour of the stars seen in the telescope. This is a great pair.

Gamma (γ) Eridani / 34 Eri / HJ 3608 (03580-1330) is a long irregular period giant of spectral type M0 III whose spectrum also shows lines of both Calcium and Chromium. Varying in brightness over 64 days, the magnitude difference is merely 0.08 mag between 2.88-2.96V. Gamma Eri is also a double star whose primary is 3.2 magnitude, while the companion is 12.7. First measured in 1877, the separation is a wide 52.8", while the PA is 242^o. Even 7.5cm should have little trouble separating this red and yellow pair.

Δ17 / I 269BC (04010-5424) is a uneventful pair contain four stars in northern Reticulum some 4.9^oW of Alpha Doradus. Dunlop saw the stars as a triple, with the separations of 63 and 41"arcsec, with the main pair aligned at the angle of 49^o 23' sf equivalent to PA 139.4^o. 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 magnitudes as 7, 8 and 8, describing it as; "A triangle of stars".
Today, this brightish wide pair of Δ17 AB is still attractive in small telescopes, and separated by 64.2"arcsec along PA 142^o. Magnitudes are given as 7.70 and 8.17, and I saw both a white. Since discovery in 1826, both stars have slightly widened by 1.3 to 1.5"arcsec while the PA has increased by merely +2^o. Looking at the proper motions of the two it is likely that of Δ7 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^o - some 10^o 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^o. 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 these components' position since found by Innes in 1900, and the positions seem right, although few measures have been obtained. The alignment is along PA 196^o, and it is unknown if this star is attached BC or even the A star. These latter components are both white.
A wide telescope field also shares this double with the moderately bright and elongated spiral galaxy NGC 1515 / NGC 1515A (04041-5406) 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.
A better challenge is the companion galaxy NGC 1515A , which is 1.8'WSW (PA 243^o) of NGC 1515A. 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" at PA 45^o. 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" at PA 104^o. Again, little has changed in the pair since the discovery by S.G. Barton.

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^oN 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^o, which has continued to reduce from 234^o 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!>

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^oSWW of Theta Pictoris /Δ20 (See Below) Since discovery the pair has changed from PA only 2^o to today's 60^o, 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" 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.

Eta (η¹) Pic / RST 120 (05028-4909) is a bright yellow star some 33'NW (PA 320^o) from η² Pic (05050-4934). This star has a faint component of 5.1 and 13.0 magnitude that is separated by 10.6"arc sec along PA 198^o. Since discovery in 1928 the PA has reduced by some 8^o and the separation has slowly broadened. This is a difficult pair in small apertures because the brighter component literally swamps the light of its companion. The companion is visible in 30cm using the hexagonal diaphragm though it still requires good seeing. As time passes the pair is getting easier to see. Another star is found some 2.6'NE (PA 303^o) and appears as a 10.6 magnitude yellow or yellowish star. This, however, should not be confused with RST 120. Few measures have been made of these two stars and their association is still uncertain. Using the Hipparcos data, the parallax is 38.19±0.51mas giving the distance as 26.18±0.35pc or 85.42±1.14 ly (±1.3%). Proper motions are pmRA -43.96±.49"arcsec per century and pmDec +27.18±0.52"arc per century. Spectral class is F2V- hotter than the Sun but still a "run-of-the-mill" main sequence star.

Eta (η²) Pic (05050-4934) is one of my “own” pair that missed the Dunlop's “wide-pair catch net”. The field here is just wonderful which is more appealing, as the galaxy NGC 1803 (05054-4934) is just 4.5'E (PA 85^o) of the main star. The "primary" is HIP 23649 / SAO 217164 / PPM 309337, and appears as a rich orange K5 star, and seems coloured much more strongly than nearby η1 Pic. The B-V is 1.484, and the later catalogues than the PPM gives the spectral class of M2 III. It is also is the suspected variable NSV1827 / HR 1663, whose variations are 5.0V to 5.1V magnitude in an unknown period. Hipparcos gives the parallax as 6.88±0.50mas, giving the distance of 145±11pc or xx 474±35ly. Proper motion is 68.74"arcsec per century in RA and -3.03"arcsec per century.
An 8.4 magnitude white A5 "companion" star is 5.7' away (WSW - PA 256^o) making a startling contrast. This is SAO 217159/ PPM 309230. A third 9.8 magnitude yellow star lies another 3.5'S. This is PPM 309319. Another faint 13th magnitude "D" star appears between "B" and "C", roughly 1.5'S (90") of "B". It seems that the "A" star is not associated with the "B" and "C" stars. "B" and "C" show similar motions through space.
Note: NGC 1803 (05054-4934) is the 13.4B magnitude barred spiral galaxy appears as a small and slightly elongated 0.5' smudge. It is catalogued in the RC3 as 1.2'x0.7' of class .SBS4* inclined at PA 62^o. The radial velocity is +4 127kms^-1, giving the distance as about 63.5Mpc. Another 2.2'SE is the 14.0p magnitude companion galaxy, which is likely associated with NGC 1803, has the radial velocity is + 4 389kms^-1, giving the distance as 67.5Mpc. This is ESO 203-19 / Fair 302 (05056-4936) being visible in 20cm or 25cm under dark skies. This is a bit more difficult to see because of the nearby 5th magnitude η² Pic. Using the occultation bar in the 20cm improves its appearance. ESO 203-19 is classed as an LXR+ type galaxy in the RC3.

Eta Pictoris Pair "2" / PPM309302 and T8081:1425:1 (05033-4930) lies 17.4'W (PA 268.6^o) is another orange and yellowish wide pair some 1.4' apart at PA 210^o. Magnitudes are 7.2 and 10.7, and this pair forms a flat triangle, equidistant from η¹ and η² Pic. This pair forms the top of a gaggle of ten 8th to 12th magnitude stars some 13' long in a north-south direction. Some 3.3'NE is a tiny near edge-on galaxy that can be seen in 25cm with care. At 15.0 magnitude is the spiral galaxy is ESO 203-17 which is catalogued as 0.9'x0.3', that I estimated was more like 0.5'x0.1' or 30"x6"arcsec.
Note: To see all these objects around the Eta Pictoris stars field use the centre coordinates as (05039-4923) in an 0.65^o eyepiece field.

Beta (β) Orionis / Rigel / SAO 131907 / 19 Orionis / Σ668AB / STF668AB / ADS3823 (05145-0812) appears opposite to the Orion's red giant Betelgeuse in the sky and whose name is translated from the Arabic as literally Orion's "Left Foot". Its vivid blue, with the B-V =-0.03 a B8 Iae: spectral class, suggests a blue supergiant with the surface temperature around 10 700K and the diameter of some 116 million kilometres. From evolution theory rather than using the stellar parallax, distance has been estimated to be about 250pc. or 860ly. Hipparcos found the parallax of 4.22±0.81mas equal to 237±40pc or 773±130ly - giving just a marginal improvement to this value. The determined absolute magnitude (M_v) is around -7.0±0.2 - some sixty thousand times more luminous than the Sun. If Rigel were placed at 32.6 light years from us, its brightness would easily rival either the four or five-day old Moon at (-7 magnitude), but would still appear as just a tiny stellar point. In the overall ranking, this puts Rigel near the top of all the stars in our Galaxy.
F.G.W. Struve discovered in 1822 as a visual double. The brightness is +0.12 and 10.4 magnitude companion whose present separation is 9.5"arcsec along PA 204^o (2002). The separation has not really changed in the years that have followed, however, the PA has increase marginally by some 5^o.
In the 1880's using the 36" Refractor at Lick Observatory, both Burnham and Sadler suspected that the companion sometimes appeared elongated, stating that; “ ...perhaps a very rapid binary, that is never wider than 0.2"arcsec ” (This shows the amazing visual acuity of these 19th Century observers, as 0.2"arcsec is far below the resolution limit due to atmospheric seeing.)
Later in 1908, J.S. Plaskett (AJ., 28, 266 (1909)) found the companion (Bb) to be a spectroscopic binary, making Rigel a triple star. Yet the data was so poor that details of the orbital data were rejected for some time because no one could verify its spectroscopic nature - likely because the secondary's light was swamped by the intense brightness of Rigel itself. (Refer "Burnham's Celestial Handbook" Vol.2 pg.1300) In late-1939, using more detailed observations of the fluctuating spectral lines, the period was finally tied down to 9.86 days during the beginning of 1940. The separation between the pair varies between 3.4 million and 4.3 million kilometres in its orbit, though the minimum masses of 0.11 and 0.08 seem far too small for their spectral type, unless there has been significant mass loss from the system in the past. By mass the star weighs about 8.4% of its primary. If Rigel B is about 1.5 then the companion is a tiny 0.13
Rigel A is also thought to be the new suspected variable - NSV 1882 or ZI 362, changing between 0.03 and 0.30 magnitude over an unknown period. The type of variable is also unknown.

Alpha (α) Aurigae / Capella / 13 Aur / ST 3 (05167+4600) is the sign of the beginning of the southern summer and the Christian festive season of Christmas, which is marked by the early-evening appearance of the bright first-magnitude deep yellow star Capella. This is the brightest star of the northern constellation of Auriga the Charioteer, whose name is though to be Assyrian in origin. Some consider have considered it is was likely known as this from even earlier times. One of the ancient Greeks myths say Auriga is the mythological son of Vulcan, Erechthonis. Legend holds that Erechthonis was born with physical deformities, and because of the likely disapproval of the Gods, his mother Athene hid the boy away from their eyes. Eventually he was adopted and raised by Amalthea. (A name usually associated with the fifth moon of Jupiter.) Although disabled, his mind proved to be both inventive and clever, a trait he inherited from his famous father. On his coming of age, and cured from his affliction by a drop of blood from the dreadful Medusa, he became the King of all Attica whose throne was held in Athens. One of his main inventions was creating the four horse chariot and showing the inhabitants how to forge and use metallic silver. Zeus was so impressed with this practical invention, he placed Erechthonis among the stars. [This story comes from the poem written in Hyginus' "Poetic Astronomy" (ii.13.)] Capella's name is thought to come from Roman times, meaning "The Little She-Goat" - literally the Nanny Goat. Throughout many cultures this star has held several dozen names - but has always been related to goats or chariots.
Capella is the most northern of the first magnitude stars (0.09 mag.) whose rank among the distant stars is sixth brightest. Observers from Southern and Central New South Wales see this star culminating at midnight on the 8th December, and at 9pm on the 23rd January. From Sydney's latitude, the star rises a mere 20^o, on any given night will remain 3 hours and 9 minutes above the horizon.(Assumes a perfectly flat site!) As Capella is close to the horizon, it is more prone to suffer from the effects of seeing, and often with the resultant very poor conditions, can be seen to spectrally dance in a rapidly changing in multitude of colours. Be grateful you don't live in Tasmania or Southern New Zealand, as this star rises merely 5^o from the horizon.
The true distance of the star is estimated to be 45 light years away from us, thought the latest Hipparcos data suggest it is a bit closer at 42.2 light-years. Capella is known to be moving away from us at about 30kms^-1 - equivalent to 946 million kilometres each year.
Investigations have shown this is a yellow spectral G6 type star is a spectroscopic binary. Binaries of this type are only different from the so-called telescopic visual binaries, in that they generally cannot be resolved by naked eye - and only revealed by the duplication of their spectral lines. Almost exactly ninety nine years ago, W.W. Campbell and H.F. Newall in October and November 1899, independently discovered the duplicity. Examining the spectral lines quickly found the periods of the two stars was 104 days 29 minutes, which is inclined to the line of sight at 27^o to the equatorial plane. In terms of velocity, both stars change their speeds by about ±26kms^-1, close to the observed orbital velocity of the planet Venus around the Sun. Capella A and B were the first stars resolved by the observational technique known as interferometry by J. Anderson in 1920, who found near perfect circular orbits. Combining these results from the orbital elements obtained by spectroscopy, allowed astronomers to determine the physical natures of the component stars. Both stars are giants, having masses of 4.2 Mand 3.3 Msuns, respectfully, and are separate in real terms by some 126 million kilometres - and in Solar System terms, about half way between the orbits of Earth and Venus. The apparent magnitude of the components is c.0.7 and 1.2, combining to the 0.06 magnitude as stated earlier. In solar diameters, both are about three times bigger than our own Sun.
Orbiting the bright Capella is the faint red dwarf pair ST 3 (0517.7+4551), which was discovered in 1935 by C. Stearns. This 10.5 and 13.0 magnitude pair is located some 13.5'SE of Capella, and since discovery, the separation has increased from 1.8" to about 4.1"arcsec, and the current motion is prograde, with a current PA of c.172^o. In real terms, these stars are 0.02 ly (1 100 AU or 165 billion kilometres) from Capella AB. This double is difficult because of the overwhelming brightness of Capella. The pair is best made using an occultation bar to block out Capella, but 20cm or 25cm is required to see them.

Δ19 / Kappa (κ) Col (05178-3326) is not listed as a pair in most double star catalogues. Dunlop gives the positions as RA (1827) : 05h 10m 17s DEC: -33^o 44', which precesses to 05h 16m 38s -33^o 33'. The only details we are give is that this pairs angular alignment is 48^o 12' sp - equivalent to PA 270 - 40.2 or 229.8^o, and that the duo is “7,7”. Unfortunately, Kappa Col appears at position (06165-3508) and is significantly different from Dunlop's position. If we assume Dunlop got the coordinate as 06h 10m 17s -33^o 44', we get the precessed coordinates as (06165-3347) for Kappa Columba - still 1.5^o too far north. Secondly the 7th and 7th magnitudes do not match the total 4.4 magnitude for Kappa Columba.
I think Dunlop used Kappa Col to find the position of his pair and has wrongly given the name of the pair as Kappa Col - and for us he disappointingly gives us no further clues. Nearest to the coordinates is yellow 6.95 magnitude HIP 24577 / PPM195705 / SAO195705 (05164-3332), which is some 3.0'W of this position. No other star of this brightness is near here, but there is a wide pair some 20.5'ENE (PA 73^o) from this place. These are Δ19? / PPM 281284 and PPM 281292 (05178-3326) - separated by 4.6' at PA 277^o and listed as 8.1v and 8.6v (PPM) - 7.87V and 8.61V magnitude (Tycho). Both these stars I saw as blue and white with about 0.5 magnitude difference.
Which stars are now the double remains uncertain, though there is an outside chance that the wide pair mentioned above might be the culprit as there are no other possibilities with 2^o. However, if they are attached, the separation of the two, assuming the Tycho's catalogue parallax is 6.61±5.5mas, giving the distance as 158pc or 517ly, then the rough true separation is 0.2pc, 0.7ly or 44 000AU. Chandrasekar, S. (AJ, 99, 54, (1944)) calculated that the gravitational stable limit of pairs to be less than about 40 000AU, so these two stars are near the very limits of any possible binary star. If we examine the catalogue limits where the maximum separation is "A" and "mv" is the mean visual magnitude. Then the largest acceptable distance apart is;

A = 10 ^{( 2.8 - 0.2 x mv )}

In this case, the limit of interest for the pair stops at separations larger than about 14.5"arcsec. Consequently these stars remain astronomically uninteresting. Overall, this is a mysteriously missing pair that is certainly not the claimed Kappa (κ) Columbae !

T Col / HIP 24824 (05193-3342) is a variable star 1.2^oN of 4.8 magnitude Omicron (ο) Columbae or alternatively 35'ESE of my suspected pair for Δ19? / PPM 281284 and PPM 281292 (05178-3326) T Col is a red variable that Dunlop also does not note in his observations of Δ19, although it makes a good marker as an identifier for this pair. T Col itself has a magnitude range of 6.6p to 12.7p magnitude over the period of 225.84 days. The shape of the light-curve is almost sinusoidal and is positively a Mira-type variable. The spectrum has been also observed to change between M3e and M6e - the latter being at the time of minima. Hipparcos gives the parallax as 0.52 mas suggesting the distance is too uncertain to predict. This is a common fault with all red variables double enhanced with uncertain luminosities. To me, T Col seems orange-red than the familiar red to deep red colour.

ARTICLE : The Multiple System of Eta Orionis

Eta (η) Ori / 28 Ori / DA5 AaB - MCA 18 Aa - H 67 AaC / HIP 25281 (05245-0224) is the main visual "AaB" pair that was discovered by W.R.Dawes in 1848. Now labelled as DA 5, this pair is one of my favourite double stars, the AB pair can be easily found as it lies on the lip of the popular southern asterism known as the “Saucepan”, appearing to opposite to Orion's sword. Rev T.W.Webb in the classic book “Celestial Objects for Common Telescopes” said this was an “Excellent test” for 14 cm refractor he was using when the seapation was 1.2"arcsec. This 3.56 and 4.87 magnitude pair today is visible under high power (and good seeing) in 10.5cm but is much easier in 20cm. Since the first measures were made, the separation has slowly increased from 0.9" to 1.7"arcsec, while the PA has decreased by some 10^o (87^o to 78^o)(2002). I saw the colours as bluish and bluish on 30th December 1979 and then bluish and bluish-grey on the 7th February 1983 - reflect nicely the B1V+B2e spectral type.
Four stars, possibly five, are associated with this system, making a good “classical” archetypal example of a hierarchical multiple. Eta Orionis stands out from others multiples, because each component makes a visual binary, a spectroscopic binary and one eclipsing binary. All the stars and have very similar in spectral class, ranging between B1 and B3, and masses between 1.0 and 1.3 M.
Some eighty multiple systems are known to contain eclipsing binaries, but only a handful has this type of hierarchical configuration. With multiples, the property of the “hierarchy” is based on the orbital arrangements of the individual gravitational “pairs”. First theorised by Evans in 1968, these arrangements can be likened to a child's mobile, where each of the varying masses throughout the entire system can be balanced. Each level of an existing pair is measured downwards, so the widest binary is Level 1, a second sub-binary is Level 2, etc.

Figure 1 - “Mobile Diagram of Eta Orionis”; shows the configuration of likely Eta Orionis - so this system is classed as a Level 3 multiple. To paint the mental picture of the separation within each levels; if the eclipsing binary on Level 3 was 1cm apart, then the spectroscopic component on Level 2 would orbit 42cm from the combined masses. Moving up to the visual pair on Level 1, the three sub-components would be separated by about 100cm.

η Ori AB

Telescopically, and using the meagre data available, the AB pair’s period is about 1470 years, though the more recent analysis by Chambliss (PASP, 184, 663-677 (1992)) gives 2300 years. A rough computation, using the combined masses of the trio “A” component, finds 23.05 M, with the inaccurate 'B' mass of 9 M, computed by the magnitude difference. Photometric observation shows variations between 3.14 and 3.35 magnitudes, which is likely caused by the fluctuating light of the eclipsing binary. According to this data, the AB system has a separation axis of 1.65"arcsec, suggesting that the pair is near its greatest true separation - its apastron. Calculations suggest the mean true separation of about 410AU or 61.5 billion km. (6.5x10^-3 ly.) Hipparcos has produced the high quality parallax for both these stars of 0.00362"±0.00088"arc sec, giving the distance of c.276±54 pc or 890±165 ly. This value is give further credence from the derived dynamical parallax of 0.004" discovered in 1952.

η Ori Aa

Unlike most systems, the "A" is again another single line spectroscopic binary with an estimated period of 9.22 years, while the WDS01 states in 9.51 years. In 1981, speckle interferometry first resolved these stars, finding separations ranging between c.0.16" and 0.05"arcsec. From the orbital data, deduced by McAlister (1976), the total mass subdivides into 21.8 solar masses for "Ab" and a minimum mass of 1.25 M for the "Ac" components. This apparent orbit is highly elliptical, with a mean orbital velocity of 19.5kms^-1. Speckle interferometry observations in November 1985 revealed the true orientation of the orbits, but unlike most spectroscopic binaries, here the orbital data is deemed fairly accurate. Mean separation of this binary pair is 1.88 billion kilometres, but due to the eccentricity of the orbit, this may vary between 2.7 and 1.0 billion kilometres - roughly the size of Uranus's orbit down too just a tad larger of Jupiter's one.

η Ori Aab

Another level down shows the "A" component splitting again into another eclipsing / spectroscopic binary that is listed as the "Aab" system. Details of the comparatively minuscular orbit were first obtained by Adams and Stanford in 1903, but later revised by the same team in 1928. This eclipsing binary during the primary eclipse is 3.31 and 3.60. From the orbital elements, the period is 7 days 23h 44.5m (7.989268 days) (11th Jan 1902), though later data suggest the period is 7 minutes less (7.9841 days). Using the orbital data from the "8th Catalogue of Spectroscopic Binaries." (A.H.Batten et.al. (1989)), the component's masses are 11.2 M and 10.6 M, respectively. Throughout the near circular orbit, the true separation is about 0.218 AU or 32.7±2.0 million kilometres, though earlier values gave a separation of 28 million kilometres or 49.1 R. Both stars move with an orbital velocity of 34.6kms^-1. (See Eta Ori : Figure 2.)

Later observations place the upper limit of the combined mass (ΣM) of 24.89 M, giving upper individual masses of 12.76 M and 12.13 M. Kaukarkin (1974) was first to state that this is a detached Beta Lyrae type eclipsing binary.

Compared to another nearby eclipsing binary, Delta (δ) Orionis, both stars are intermediately massive and luminous, with the respective diameters of the two stars being 15.68 R and 20.52 R, respectively. Both throughout the orbit range between 20.6 and 27.1 million kilometres, while the measured relative solar luminosities are 6853 L and 5826 L (Roche Lobes are presently filled to 42% and 52%.) Temperatures are 18 870K and 15 860K, reflected by the given B0.5VEA+B3V spectral types. The stellar sizes and the light curve is shown in Eta Ori Aab : Figure 2.

Glancing at the properties of this system, you might notice that the most massive star happens to be the smallest, seemingly "thumbing its nose" in complete defiance of modern stellar evolution theory. Algol's Paradox seems to be needed to be apply here, suggesting that some mass transfer has occurred in the past between the eclipsing binary's components - but additional observations are required to confirm this. However if this were so, then how these stars now appear in this configuration is a bit of a mystery! The secondary ("Ab") of the eclipsing binary also shows evidence of being a Beta Cephei variable of an uncertain period - as found by examining the eclipsing binary's secondary light curve. (Beta Centauri and Beta Orionis are other examples of Beta Cepheids - all brighter, incidentally, than its namesake Beta Cepheid!) Waelkens and Lampens (1988) suspect that this data is in error, and that the more distant Eta Ori B is the star producing the slight variations.

η Ori AB-C

A remote fifth component star, component "C" was discovered by William Herschel who catalogue the "AC" pair H VI 67, but it was not properly measured until 1904. The physical association of this star to η Ori was first suspected by the double star observer Robert Aitken in the 1928. Known as BD-02135C, this 9.4 magnitude star lies 116.8"arc sec NE of Eta Ori "AB" itself at PA of 53^o. (At the exact position RA 05h 34m 34.4s -02^o 22' 34") and I thought the brightness of this star to be about one magnitude fainter than this. Little is known about this star because of its proximity to the brighter pair. It can easily be seen in 7.5cm., but if you want see "C" in a star atlas, it doesn't appear on any of them, including Uranometria 2000.0, the Millennium Star Atlas, or even Megastar 4.0. Both the modern Hipparcos and Tycho catalogues don’t list it, nor does it appear in the PPM Catalogue. Looking at the near nonexistent proper motion data of this star, it is likely just a optical foreground or background star.

Note : A main description of Eta Orionis also appears in “Burnham's Celestial Handbook” Vol.2, p.1306) - but this description is so out of data, that most of the information can now be veiwed as historical.

Δ20 / Theta (θ) Pic / I 345 AB (05248-5219) is a triple that can be found some 9.9^oW of Canopus. Dunlop in 1826 discovered and measured this wide bright yellowish pair, who found the separation as 38.52"arcsec along position 14^o 04'np, equal to PA 284.1^o. John Herschel found similar results some ten years later. Listed today as Δ20 AC, and lovely in the smallest of telescopes, this near equal 6.26 and 6.90 magnitude pair is worth searching in your observation programme. Little has changed in the position except for +5^o increase in PA and the reduction of separation by 0.4 to 0.5"arcsec, giving the present relative positions as 289^o and 38.0"arcsec. Spectral types are A0V and A2V, but like Beta (2) Tuc's companion, both stars appear more yellow than their types suggest.
Innes in 1900 discovered the inner AB pair, I 345. This is a difficult pair that is no doubt a binary system. Of 6.26 and 6.90 magnitude, the two stars are presently separated by 0.1"arcsec along PA c.30^o, and is invisible to all amateur telescopes at present (2002). Motion of the two is retrograde, and the position angle has decrease from 197^o to 30^o (167^o) in the last hundred years. Hartung says he saw the duo in 1960 with 30cm suggesting the companion was south preceding (sp) -180^o-270^o, but surely if the orbit is truly retrograde, this should have been south-following (sf). In AOST1, Hartung says the two stars were widening, but in the latter half of the last century, the stars have significantly reduced. David Frew in AOST2 says;

“...but the separation was only 0.2" at the time, so Hartung could not have resolved them with his telescope.”

Based on this evidence it is hard to understand what being said here. It is possible he observed the wrong star. This error is very unusual for E.J. Hartung because the accuracy of his descriptions is almost unquestionable - hence the extraordinary value of the “Astronomical Objects for Southern Telescopes” Handbook for observers.
AOST2 described the observations made in 1989.9 of 0.13" at PA 56^o, and the position angle today is much smaller than this. Extrapolating the available data (2002), the PA might even now be in the 4th quadrant (Less than 360^o) and about the same separation as in 1990. The spectral class of the companion is likely "early-A". No doubt this will be an interesting system to watch in the next few coming decades.

TZ Men (05302-8447) is an eclipsing binary EA system. This far southern system is located right on the mutual border of the constellaions of Mensa and Octans. TZ Men has a is rather solitary star field, and it shares an area within about 5^o of sky with only fainter than 6th magnitude stars. Also nearby is the rather unexciting globular cluster NGC 1841, some 1.3^oE of TZ Muscae's position.
Magnitude variations are between 6.23v and 6.9v over a 8.569 days period. Very little observationally work has been done with this star in recent years and this is probably because of its far southern declination. Times predicting for primary eclipse is certainly with significant errors.
Total mass of this system totals 6.5 ΣM, with the primary at 3.6 M and the secondary at 2.9 M. Relative luminosities are equally about fifty times that of the Sun. Both stars are separated by 22 million kilometres, each with respective diameters of about 3.6 and 2.7 million kilometres. Spectrally, the first surveys listed this star as B9.5 IV-V, as stated in Sky Catalogue 2000.0 but the more recent data indicates the spectral classes of A1 III and B9 V. The computed temperatures are 9 370K and 10 850K, unusual as the primary is cooler, but this is not too unique among eclipsing binaries.

Note: NGC 1841 appears as a nebulous ’glow’ of 12.2 magnitude that is unresolvable in telescopes below 30cm. They do not list NGC 1841 as mentioned above in Sky Catalogue 2000.0, but is listed in the companion Sky Atlas. Also note that the other GSC in Mensa, projected on to the Large Magellanic Cloud (LMC) is NGC 2121. This is the reverse problem of NGC 1841. They list it in the Catalogue, but not on the Sky Atlas!

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

Last Update : 28 August 2003

“Southern Astronomical Delights” © Andrew James 2003          Sydney, Australia