Southern Doubles, Stars and Variables
SOUTHERN ASTRONOMICAL DELIGHTS : Presented by Andrew James
|PAGE DS 005
10 Mar 2009
|RA : 05h
Dec : -30° to -90°
Constellations : Cae, Col, Pic, Dor, Men, Oct.
Best Observed : Nov - Mar (Text Ordered by RA)
|RA : 05h
Dec : -30° to -90°
SELECTED SOUTHERN DOUBLES and VARIABLES
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.
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 410 A.U. or 61.5 billion km. Hipparcos has produced the parallax for both these stars of 3.62±0.88 arcsec, giving the distance of c.276±54 pc. or 890±165 ly. This value is give further credence from the derived dynamical parallax of 4.0 mas discovered in 1952.
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.
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.)
Figure 2- “The Eclipsing Binary η Ori Aab”
Later observations place the upper limit of the combined mass (ΣM⊚) of 24.89 M⊚, giving the 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.
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 arcsec NE of Eta Ori ‘AB’ itself at PA of 53°. (At the exact position RA 05h 34m 34.4s -02° 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 / I 345 AB-C / θ Pic / Theta Pictoris (05248-5219) is a triple with in a fairly poor star field that can be found some 9.9°W of Canopus. This wide bright yellowish visual pair was discovered and first measured by Dunlop in 1826.
AR 5h 20m; Decl. 55° 28′S
5.6 and 6.7m : L. yellow; S bluish white
Pos.14° 14′ np.; 4 obs; Diff.= 4°,96
AR = 04S,19; 5 obs; Diff.= 0S,25
Decl.= 09″,055; 11 obs; Diff.= 1″,50
Dist.= 38″,516; 5 obs; Diff.= 0″,95
Dunlop found the separation as 38.52 arcsec along position angle 14° 04'np, equivalent to the PA of 284.1°. His individual observations were presented in the Mem. Astr. Soc. London; 3, p.257-275 (1829) p.265 were as follows;
Dunlop’s position translates this as to 38.516 arcsec along PA 360-14.23° or 345.77° (345.8°) John Herschel some ten years later also found similar results.
Listed today as 20 AC, and lovely in the smallest of telescopes, this near equal 6.9v and 7.2v ("AB" 6.26 and "C" 6.90V) magnitude pair is worth searching in your observation program. Giving the present relative positions as 288° and 38.1 arcsec, little has changed except fora small +4° increase in PA and the reduction of separation by about 0.4 arcsec. Spectral types are A0V and A2V, but like β² Tuc’s companion, both stars visually appear more yellow than their given types suggest.
Similar proper motions of A: pmRA -6 and pmDec. -30 and B: pmRA: -007 and pmDec. -29 (in mas.yr.-1) suggest these two are very likely associated. Based on the Hipparcos distance of 155±13.2pc. or 507.2±42.9 ly. from the mean parallax of 6.43±0.54 mas gives the true separation as c.5 400 A.U. Absolute magnitudes (Mv) are 0.94 and 1.24, respectively, calculating a sum mass (ΣM⊚) of 5.0 and individual masses of AB of 2.6 M⊚ and ‘C’ of 2.4 M⊚.
I 345 AB-C is the very close inner AB pair which was discovered by Innes in 1900. This is a difficult pair to split and no doubt part of this entire system. Of AB=6.3v (A=6.9v / B=7.2v) and C=6.8v magnitude, the two stars are presently separated by 0.1 arcsec along PA c.30° (2002) and remains presently invisible to all amateur telescopes. Motion of I 345 is retrograde with the position angle decreasing from 197° to 24° (PA of -173°) (WDS03) in the last hundred-odd years (2004).
Hartung says he saw the duo in 1960 with 30cm suggesting the companion was south preceding (sp) -180°-270°, but surely if the orbit is truly retrograde, this should have been south-following (sf). In AOST1, Hartung says the two stars had widening, but in the latter half of the last century, the stars have significantly reduced. Using the data in the IDS (1976) the 1960 measure was 0.2 arcsec and 152°. Based on this, 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 Hartung is saying. Could it be possible he is observing 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 arcsec at PA 56°, and the position angle today is certainly smaller than this. Extrapolating the available data (2003), the PA might even now be in the 4th quadrant (>360°) and about the same separation as in 1990.
Spectral class of the companion is likely “early-A”. Using the mean distance calculated for 20 for I 34AB, the minimum period from Innes 0.5 arcsec is about 309 years from a true separation of 77AU. Individual masses for AB of 2.6 M⊚ breakdown to 1.4⊚ and 1.2 M⊚, which incidentally acts as a point source to the far more distant “C” component.
No doubt this entire system will be an interesting system to watch in the coming decades. This is a truly classical triple. [Version 2 : 21/10/03]
Δ21 AD / HJ 3767 A-BC / RST 136 BC (05302-4705) is an extremely wide pair in a multiple system in a faint but charming field in mid-northern Pictor, and the system can be found 4.8°NW (PA 320°) from 3.9 magnitude Beta (β) Pictoris. Dunlop lists this star as 25 Pictoris. Δ21 AD is easily visible and divided in binoculars, whose 5.5 and 6.6 magnitude components are separated by 197.2 arcsec (3.5') along an east-west PA of 271°. These yellow and light-yellow stars really fall outside the criteria of a visual double star and would normally be dropped from any double star catalogue. Δ21 is certainly an optical pair as the proper motion in declination is seventeen (17) times larger.
HJ 3767 A-BC : This pair was somehow completely missed by Dunlop. Herschel discovered this 11.0 magnitude fainter and moderately wide component separated by 26.4 arcsec in 1835. Today little has changed in separation of 25.9 arcsec though the position angle has changed from 223° to 256° as measured in 1933. It seems that Herschel's PA position is wrong, as visually the position was close to the 256° PA. Both of these components are visible in 10.5cm.
RST 136 BC : Closer inspection of the B component find it is again double that was discovered by R.A. Rossiter in 1930. These two quite faint 11.7 and 12.7 magnitudes stars are presently 0.8 arcsec along PA 85°, and I thought that these were certainly wider than this in 1993 and perhaps as wide as 1.0 arcsec. This was fairly easy in the 20cm at 333x though the faintness of the components made this more complicated in the moderate seeing. It is quite likely RST 136 is physically attached.
Note: The southern and western fields from Δ21 contains seven galaxy clusters and a dozen very faint galaxies. Those with large apertures (>40 cm) may like to inspect the field to see if they can see any of the these.
ESO 253-9 / PGC 17377 (05309-4657) lies 11'NE from Δ21. This 15.7 magnitude galaxy was not seen in the 20cm. I suspect 30cm could see this 0.8'x0.6' spiral galaxy as a faint oval smudge in the field.
I 62 (05305-4712) lies some 8.5' (PA 155°) from Δ21. This near equal pair of 8.3 and 8.9 magnitude is separated by a close 0.8 arcsec along PA 178°. I had some trouble separating the two stars in moderate seeing using 20cm but could detect only some elongation in the Airy disks using 200x. At 333x, in moments of good seeing, I could clearly see the two components. The most recent version of the WDS03 gives the magnitudes as 8.79V and 9.30V, which in my opinion does not match the visual appearance of 8.3v and 8.9v at all. The difference here does appear a little two large and almost half a magnitude fainter for both components. The primary is a nice light yellow but I could not see any in the secondary. Little has changed in the positions since R.T.A. Innes discovered the pair in 1896 except for a slight decrease from 1.0 to 0.8 arcsec in separation. True attached of these two stars is presently uncertain but they both do have similar proper motions of -21 and +25 arcsec per century. To the east by 1.5' are two stars of 12th and 14th magnitude separated by about 22 arcsec in an SSE direction. This properly identifies the field.
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° of sky with only fainter than 6th magnitude stars. Also nearby is the rather unexciting globular cluster NGC 1841, some 1.3°E of TZ Mus’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!
Δ22 (05312-4219) is a nice pair found in southern Columba and lies 35′N from the Pictor border. The general wide field contains about ten stars of 9th, 10th and 11th magnitude stars within a circlet of stars some 20' across. Δ22 is the brightest and eastern most star of this stellar circlet. Dunlop gives this star as Δ26 Pictoris, but in his times the boundaries between the constellations were not properly organised by right ascension and declination but were often by the selection of the observer themselves. This is an easy white and yellowish pair even in 7.5cm though identifying the general field might be a bit tough from the lack of any bright stars. It is best to use the 3.9 mag. orange star Eta (η) Col and move the telescope 5.2° due west. Δ22 is listed as 6.7 and 7.5 magnitude with the two stars are separated by 7.4 arcsec along PA 169°. Proper motions suggest this pair is an optical one.
The general star field also contains the 9.7 mag reddish-orange star, HIP 25775 / PPM 309772, some 26' (PA 204°) of spectrum M0V. HIP 25775 has the parallax 51.56±3.73 and shows significant proper motion. Distance is 19.39±1.41pc. (63.3±4.6 ly.)
Four faint galaxies appear in the same field as the pair. Both ESO 306-4 (05292-4213) and ESO 306-9 (05317-4210) can be seen in dark skies with 20cm, while the fainter companions require at least 30cm and possibly even 40cm. ESO 306-9 is 10' PA33° from Δ22.
hh mm ss.s
o mm ss
|ESO 306-4||VV 599||PGC 17343||05 29 13.4||-42 12 37||14.7p||1.3'x 0.6'||018||E+4 pec|
|ESO 306-9||Fair 1135||PGC 17396||05 31 41.0||-42 09 51||14.0p||1.3'x 1.1'||145||(R')SA(r)ab pec.|
|MAC 0529-4209||-||-||05 29 09.8||-42 09 45||16||0.4'x 0.2'||068||?|
|MAC 0531-4206||-||-||05 31 22.2||-42 06 32||15||0.4'x 0.3'||054||?|
β Pic / Beta Pictoris (05473-5104) is a single star which was the first star to show the direct evidence of the possibility of other solar systems outside our own. It was revealed using both CCD-imaging and infra-red observations as first found by astronomers in 1986 from the Las Campanas Observatory in Chile. This proved that the star was surround, like the 1st-magnitude star Vega (Alpha Lyrae), by a cool disk of grainy material some 25 arcsec either side of β Pic that corresponds to some 800 to 1000 AU across. This is about sixteen to twenty times the size of our own planetary system of Sol.
β Pic itself lies 6°SWW of Canopus in a fairly uninteresting field. Listed as HIP 27321 / SAO 234134 / PPM 334622 / HD 39060 at the position of RA: 05h 47m 17.1s and Dec: -51° 04⁐ 00″ this 3.85V magnitude star is an slightly under-luminous A3V spectral class star displaying a colour index (B-V) of +0.171. Using the parallax from Hipparcos of 51.87±0.51gives the distance as 19.28±0.20 pc. or 62.9±0.64 ly. Beta Pictoris is moving at 82mas per year along PA 19°. Radial velocity is +28kms-1 away from us. Spectral class is A5V dwarf and it is a known shell star.
|“Southern Astronomical Delights”
10 Mar 2009