TABLE : Maxima for V495 Cen
 
      JDE       Date  Year  Hour
                            (UT)
 2452700.7076  02 Mar 2003   05 
 2452801.1689  10 Jun 2003   15 
 2452901.6302  19 Sep 2003   03 
 2453002.0915  28 Dec 2003   14 
 2453102.5528  07 Apr 2004   01 
 2453203.0141  16 Jul 2004   12 
 2453303.4754  24 Oct 2004   23 
 2453403.9367  02 Feb 2005   10 

 TABLE : Maxima for FU Mus
28th Apr 2003 |  13th Nov 2003
30th May 2004 |  15th Dec 2004
02nd Jul 2005 |  17th Jan 2006

Wolf-Rayet Stars in the Field and Planetary Nuclei Although Wolf-Rayets are quite rare, they can be distinguished by two distinct groups. These are as follows; 1) PNe Wolf-Rayets Abbreviated as WR PNe Wolf Rayets stars are the demonstration of the early exposed core of the star some between the transition of the Asymptotic Giant Branch (AGB) and the formation of the PNe shell itself. The main criteria of the all WR-stars is their extreme temperatures, which exceed roughly 60 000K to 110 000K, so it is reasonable to assume that the AGB-PNe shell phase occurs about the same time as when the cooling temperature of the stellar core from tens of million degrees to the typical stellar surface temperatures of several thousands or tens of thousands of degrees. The majority of these stars have “WC” spectral types, indicating Carbon in the spectra. 2) Field Wolf Rayets Abbreviated as [WR] These are stars, unlike the PNe Wolf-Rayet stars, are born massive ultra-hot stars and are considered to be greater than 10M⊙ and up to about 30M⊙ Solar Masses. So hot are these WR-star surface temperatures that the outer atmosphere has been literally torn from the surface and spewed into the surrounding interstellar space. It has been known for sometime that evidence of dust gas and dust shells surrounding these WR-stars. Structurally, most of the observed shells closely mimic the PNe gaseous nebula, however, they have two distinct differences, they are not caused by old stars, and they are chemically quite different. Most astrophysicists consider the Field Wolf-Rayet stars are prime Supernovae Type II candidates. A majority of these stars have “WN” spectral types, indicating Nitrogen in their spectra. The example of Theta Muscae own WR, is obviously classed as Field Binary even though its spectral class is WC.

θ Musca’s Wolf-Rayet component is catalogued as HIP 64094 / PPM 359890 / SAO 252162 / HD 113904, but it is also listed as He3-862. Its WC6 spectral class is unusual, as they are more often featured as PNe central stars. Other binary systems do contain WR’s, but ones like the ‘Aa’ system of θ Mus are fairly rare, making some 12.5% [20 of 159] of a population of known systems. In addition, 10% are WR+O-type stars. Only 2.5% (including Theta Muscae) have unseen companions.

Although W.W. Campbell was the first to discover the peculiar spectra of Theta Muscae (as WWC 17) in his published catalogue of 1894, it was Williamina Fleming in 1912 (as star WPF 48) who realise it was an usually hot star. At the time, Theta Musca’s Wolf-Rayet status was rejected, and the star ended being classified as “O-type” spectral type, and it was again rejected, when the spectroscopic binary system was discovered in 1930’s. Its resurrection in the literature as a Wolf-Rayet type star likely sometime in 1962, whose more modern and refined WC6 classification for the primary star was only confirmed as recently as 1971, by C.B. Stephenson and N. Sanduleak.

The obtained spectrum has also revealed much about the system. For example, the system’s radial velocity is 28.4kms^-1 towards us, while the primary WC9 star likely has a fast rotational velocity (v.sin i) of 106kms^-1. θ Mus has been observed in several different wavelength, I.e. As a moderately strong UV source being observed twenty-one different times by the IUE satellite in 1996. The star was also found to be an X-ray source as seen by the HEAO / Einstein Satellite in 1994. This multiple system was even investigated during December 1990 by Astro-1 orbital laboratory from the Space Shuttle. Observations here were made in UV-light and with optical polarimetry of the various emission spectral lines. The information yielded much on the effects of interstellar absorption and the effects of the winds being generated by the central star. Over the last twenty years, over 150 references have appeared in the literature.

THETA MUSCAE NEBULA SHELL(S)

As AOST2 mentions in its descriptive text, Theta Musca’s nebula was discovered in 1982 at the Anglo-Australian Observatory (AAO). Images of the nebulosity were obtained discovered using deep photographic imaging some 0.5°S of the star which appearss as faint amorphous concave arc, shaped almost like a telescope mirror. Closer examination showed the arc finds it extended almost at almost parallel straight lines some 1° long.

More recent discoveries, revealed much more refined details than when the shells were first found. These later images were made at two wavelengths - namely [O-III] and H . De Castro & Niemela (1998) showing compelling evidence of complete sets of multiple rings surrounding the star. They also found evidence of abundant “stratification” across and within the optical rings, including filamentary structure - similar to what is seen in supernova remnants (SNR’s) and PNe’s structures, like NGC 5189. Evidence was found that the composition of the nebula cannot be all attributed mass-loss, but from swept-up galactic material from the Milky Way itself or possibly even the remnant of the original nebula (pre-stellar matter) from the star’s initial formation.

DISTANCE OF THETA MUSCAE

Theta Musca is thought to be joined to the Cen OB1 Association, surrounding NGC 4755 / The Jewel Box (12536-6022). Exacting the distance to θ Mus remains uncertain, but because of its apparent brightness and spectral type, it is likely to be a similar distance to Kappa Crucis which is about 2kpc.

References

1. Marchenko, S,V. et al.,"Wolf-Rayet stars and O-star runaways with HIPPARCOS. II. Photometry"; Astron.& Astroph., 331, p.1022-1036 (1998))
2. Moffat, A.F.,("The Wolf-Rayet Binary Theta Muscae.";Astron.& Astroph., 54, 607 (1977))

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V592 Cen (13085-5923) is the other SR semi-regular red variable that varies between 11.6p and 12.8p over the period of about 40 days. Clearly visible in 7.5cm and the colour clearly in 10cm, this red-orange coloured variable can be found some 30' NNE (PA 16°) from R 213. Little is known about this variable.

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WW Cen (13094-6015) is a fairly bright SRB semi-regular located  28'SE (PA 147°) from R 213 and some 2.5°E of Beat Crucis. It is also in the same field as NZO 38. This deep-red variable varies between 8.8V and 11.6V in the  period of about 304 days. Spectral class changes between M5 and M7 during this period. The visual colour I thought was orangery-red.

What was more startling the first time I saw it was the bright 7.8 magnitude field star T8989:641:1 /PPM 779298 /HD 113842 (13075-6016) some 14'WSW (PA 246°). Deep-red in colour, this star is even darker than WW Cen itself and this star. It is possible that this star could be used to compare the variable’s colour throughout its cycle, though thinking about it, it might be a bit too bright. T8989:641:1 is not known to be variable and has the B-V of +2.060. The earlier PPM catalogue gave the spectral class as M0III but this surely must be nearer to about M5 as it is redder than the variable - especially with the PPM's B-V of 3.6. PPM also says the distance is about 20pc which disagrees with the Tycho’s poorer estimate. WW Cen, T 8989:641:1 and NZO 38 adds up to an interesting field.

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NZO 38 (13097-6026) is a faint pair in the same field as WW Cen being 1.1'S (PA 170°). Discovered in 1929 at the national observatory of New Zealand, at the Carter Observatory in Wellington, this 11.2 and 11.3 magnitude pair is separated by 4.6 arcsec along PA 20°. I saw no colour in this faint pair in 20cm, and separated the two in moderate magnification.

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COO 152 AB / HDS 1850  Aa (13129-5949) is a moderately wide yellow and orange pair with some moderate difference in magnitude. Located 41'W (PA 87°) of nearby R 213 the main pair is quite easy in 7.5cm being certainly suitable for small apertures. Discovered in 1892, this 6.2 and 8.8 (6.7V and 9.42V) magnitude but Wallenquist in 1948 found the Δm of 3.17 that oddly does not agree with the two quote values today.  At the moment COO 152 AB is separated by 25.1 arcsec along position angle 146°. Little has change in the relative positions and the separation has merely reduced by some -1.1 arcsec.

Individual Tycho parallaxes of these two stars are significant, though the companion is showing twice the motion. I.e. 26.90±0.25 and 46.22±15.90, respectively, giving a distance of 37.9±0.35pc. and 28.6±8.44pc., respectfully. Furthermore, the Tycho proper motions are very similar.  I.e. Star A : pmRA of 7.40±1.80 / pmDec of -105.70±1.80 and Star 2 : pmRA of -15.70±14.70 / pmDec of -105.00±11.90. I would suspect that these stars must be associated but the proof is lacking from the secondary's trigometric parallax.

Note: Hipparcos gives information only for the primary star HIP 64478 as the more precise parallax of 25.12±0.72 pmRA 8.23±0.25 and pmDec of -107.89±0.50 - agreeing well with the Tycho catalogue.

COO 152A was also found to be a double in 1991 using speckle interferometry. This primary would be impossible to resolve in any amateur telescope as it is 6.3 and 9.4 magnitude and with the separation of a tiny 0.2 arcsec  with it true measurement was 0.187±0.048 arcsec. For the record, the position angle is 96° and it is suspected that in time HDS 1850 will prove to be a spectroscopic binary. This would properly match the presumption of the given current ‘Aa' designation.

Comment : The three doubles, two variables are associated with this Centaurus pair are; COO 147, R 213, V592 Cen, WW Cen, Red star T8989:641:1 and NZO 38.

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I 923 (13216-6630) this near equal magnitude yellow pair was discovered by Innes in 1911. The WDS96 gives 9.4 and 9.9. The PA (132°)has changed little since this time, though the separation has increased from 1.3 to 2.7 arcsec. Looking at the proper motions, it is likely this pair is an optical one and that the angle will continue to widen. Seen with care in 7.5cm, it should be easily visible in apertures above 10.5cm.

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Δ133 / J Cen / / Δ133 AB-C / V790 Cen / HIP 65271 (13227-6059) is a distinctly bright blue double star/ triple that was discovered by Dunlop in 1836. Magnitudes are 4.5v and 6.2v, with J Cen A being SAO 252284/ HD 116087 and J Cen B / SAO 252283/ HD116072. This wide pair is separated by 61.7 arcsec along PA 343°. (Latest data gives c.60.0±0.3 arcsec and 345.5°) In 1879, Russell made the last serious measure of the pair, when it became obvious that this is just a pair of chance alignment. Little has changed in the positions since then and looking at the proper motions of the components, only confirms today's view that this is just another pretty optical duo. The two individual spectra are B3 and B2.5V/ B3.

Within a dense starry field, this stunningly blue duo is simple wonderful - even in the smallest of telescopes. I though it was very similar in many respects to Δ131 / η Mus which is near the planetary nebula IC 4191 in central northern Musca that I observed on the same night.

The secondary component is again double. Known as FIN 208AB, this was revealed by Finsen in 1930. This is certainly a binary, and both stars are equally 5.2 magnitude. However, this is not an easy pair, and it is unlikely that amateur telescopes could see them, as the separation is a small 0.2 arcsec, and this may have increased between 1930 and 1990, but this is hard to tell with only six measures to date. Also the position angle certainly has decreased from c.168° to 137°. The Washington Double Star Catalogue (WDS96) states in the Notes; “Too close, measures uncertain”. As yet no interferometry observations have been made.

One of these components is suspected to be an example of a Beta Cepheid type variable star. The star is known as V790 Cen, whose visual light variations change roughly between 6.16 and 6.27 magnitude in an unknown period. Estimates for the visible AB system range between 6.2 and 6.4, so it could possible that variability is lower than 6.27. Which component is the actual variable is not known, but the combined spectral class of this star is typically B2.5 VN - B3V.

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HJ 4586 (13234-6457) is a bright white pair that has been well known as an attractive for small telescopes. It can be found 1.2°ESE (PA 244°) from the PNe Sa2-96. Discovered by John Herschel in 1837, the 7.3 and 9.1 magnitude pair has slowly been decreasing. In 1837, the separation was 3.7 arcsec, while the latest position in 1983 (WDS96) was 2.8 arcsec. I looked at this pair in 1994, and the separation did seem slightly smaller than this. Position angle has also decreased by about 10° (PA 150° to 140°) in the last 165 years (2002). This pair will be interesting to watch, as the narrowing separation will make it difficult to separate in modest apertures. If the separation continues to decrease at this rate, it will become an impossible target for apertures less than 30cm in about 2090 A.D. Looking at the proper motions, it is likely this is a true binary, though it will take many centuries to tie down the orbital parameters adequately for predicting it future positions. A worthy southern pair.

HJ 4586 / HIP 65719 / SAO252318 / HD116865 / PPM360125 (13284-6752) is some 2°S and fractionally east of NGC 5189 in Musca. It is also lies merely 8.7' from the Musca-Circinus border. How James Dunlop missed this beautiful bluish and yellowish pair is hard to understand as a 7.5cm using medium to high power and moderate seeing should be able to separate the diffraction patterns of the two stars will care, but apertures greater than 10cm should have little problems. Since John Herschel discovered and measured this duo in 1837, the pair has slowly diminished, by about 10° in PA, and 1.0 arcsec separation (2000). The last measures were made in 1991, with each co-ordinate being 2.9 arcsec and 141°, respectively. If the pair continues to close, it will become difficult to resolve. HJ 4586’s continued motion throughout the 21st Century certainly will be interesting.

Hipparcos measured the combined spectral class is A5III/IV, with the single combined magnitude of 7.06, with the B-V being 0.500. Its parallax of 6.544±0.98mas is dubious, especially if the stars are not really associated. Why this statement is true is because the Hipparcos satellite had an unavoidable flaw in measuring pairs using the adopted interferometric design. Unfortunately, HJ 4586 falls closely inside this ‘trap’. Assuming the pair is associated, then the adopted distance of 152±21pc (496±681y) is similar to nearby Alpha Crucis. Using simple trigonometry, the two stars are separated by some 450 A.U. Roughly, based on the amount of motion already seen, the period is more thanabout 4 000 years.

If you are a true double star afficionado - don’t miss this one, or even Theta Muscae in the next object paragraphs!

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α Vir / Alpha Virginus / Spica / 67 Vir / HIP 65474 / SAO 157923 / PPM 227262 / HD 11665 (13252-1110) is the brightest star in the zodiacal constellation of Virgo and the 17th brightest in the entire sky. Culminating at 9pm on the 28th May (or 12am on the 12th April), rising after sunset to arrival of autumn in the southern hemisphere) or spring in the northern hemisphere. This first–magnitude star of 0.98 magnitude is an astoundingly gorgeous sapphire blue, and to me appears as the most vivid of the blue coloured stars. The combined spectral type is B1V and the B–V magnitude is -0.236±0.008.

Spica was one of the very first spectroscopic binaries to be found, and was discovered by Vogel in 1890. to have an orbital period of 4.014604 days (JDE 2440284.78). For sometime it was the closest known pair to be observed using intensity interferometry. These orbital parameters and distance of these two near-equal stars were discovered by Australian astronomer R.R. Shobbrook MNRAS, 156, 165 (1972)) to be separated is about 0.0015 arcsec averaging to about 0.13 A.U. or 19.5 million kilometres apart. The orbit is also highly eccentric (e=0.18).

Masses have been calculated to be 10.9⊚ and 6.8⊚, respectively. Spica also shines with an absolute magnitude of -3.55 and has the overall luminosity some 2250 times brighter than our Sun.

Spica is also known as an E-II eclipsing binary whose primary Aa is also a Beta Cepheid variable, which Burnham wrongly describes as Beta Canis Majoris-type. The eclipsing binary undergoes only partial eclipses which match the orbital period of the two stars and contributes most of the light variation whch amounts to 0.1 magnitudes. The variability of the Beta Cepheid component is less certain which is especially difficult to determine because of the problems with the combined light. However, the individual spectral types are known as B1 III+B2 V. Hipparcos found the parallax of 12.44±0.86mas corresponding to the distance of 80.4±5.6 pc or 262±18 ly, and this agrees well with the 84 pc (274 ly) distance derived from the Narrabri intensity interferometry observations in 1968. The proper motions are moderate; RA -42.50±0.79 and in Dec -31.73±0.52.

Spica is also catalogued as the wide pair BUP 150 in 1879, whose separation of the 10.5 magnitude is a distant 360 arcsec (6′NE), but this is surely an optical double.

Although not much can be made observation-wise by amateurs, this star makes an interesting story in its history.

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LDS 444 / HD117007 and LDS 444B / CPD-65 2344 (13292-6605) is the dainty yellow pair discovered by J.J Luyten in his Bruce Proper Motion Survey, and appears in his subsequent catalogue made between 1939 and 1963. LDS 444 is located in the next field, almost due west, and perhaps slightly south following, some 28′ away from NGC 5189. It is just visible in 7.5cm, though 10cm would be much better. The current measured separation in the WDS01 is 26.9 arcsec along PA 131°, and I could resolve the pair cleanly in the C8 at 60X magnification at Bowen Mountain, some 80km northwest of Sydney, and it looked best using 150X. Both stars are nearly equal in magnitude, namely 8.6 and 8.9, though I estimate the difference as about 0.2mag. Latest photometric estimates give 8.62 and 9.23, giving the m as 0.51 magnitudes. Visually this does not seem right. The combined magnitude is 9.1 (9.6B), while spectral class is F7/8V and G as first determined in 1975. Little has changed in position angle, however, the separation has increased by 0.3 arcsec. Proper motions, as mention in the Notes in the Washington Double Star Catalogue-2003(WDS 2003), finds that both stars have similar motions in space, so the pair could be physically associated, with the period being very long.

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Y Cir (13392-6502) is classed as a suspected semi-detached ‘SD’ eclipsing binary, whose magnitude variations change between 10.8p and 11.8p every 3.17 days, whose epoch dates back to the 23rd March 1928. Listed as GSC8999:1445, the variable is merely 2.6' from Musca’s eastern border and some 37'SE from T Cir (13434-6528) (See Above). The spectral type is estimated to be Ap.

Interestingly, nothing had been written in the literature since the 3rd General Variable Star Catalogue (GVSC3). I suspect that this star might not be variable, though I could find nothing to confirm or deny this. Deep-sky observers once they look at this section’s PNe, might like to identify this variable from time to time to see if they could see any variations. If sure Any amateur who can identify its periodicity, preferably with CCD or photographic evidence, could become fairly popular among the variable star community.

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I 1073 (13409-5916) is another Innes pair that lies 24'E of Δ142 or 3.3'SW of the 7.7 magnitude HIP 66772 as mentioned in the text of I 519. Discovered in 1894, the magnitude of the two stars is 9.1 and 11.1 with the separation and position angle presently (2000) being 2.8 arcsec and 26°, and this pair continues to very slightly decrease in these quantities. I found this faintly yellowish pair easy in 20cm, and would estimate that 7.5cm could just see the duo under high magnification but would be much easier in 10.5cm. Little is known about these stars except for the odd spectral type of F8/G2 A/F.

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Δ141 / Q Cen / 195 Centauri (13417-5434) is a bright and moderate close bluish pair in a starry field containing a few different coloured stars. The pair is easily and quickly located some 2.7°NW of β Cen / Beta Centauri or 1.1°SSE from ε Cen / Epsilon Centauri - the same stars used for the naked-eye to find the brightest globular Omega Centauri, with Q Centauri being visible to the naked-eye. Magnitudes are given as 5.0v and 6.4v (4.98V and 6.37V). Some change has been observed with the system, whose present distance is 5.5 arcsec and with the position angle of 163°. Dunlop measures estimate the initial separation as “3 or 4” arc seconds but his quoted “Angle of Position” 78° 24' sp does match the initial 168° position angle later observed by John Herschel.

One of the most puzzling aspects of Dunlop’s catalogue description is that the magnitude he sees is “6 and 9”. This is odd only because he is seeing this same pair as fainter than the nearby pairs Δ142, Δ143 and Δ144. At first I thought the position of the pair might have been wrong, and even though Dunlop’s position of 13h 30m 56″ -53° 41' (1825) when precessed for 2000 co-ordinates is 27'NNE, no other pair like this describing a 6th and 9th stars.

This is one of the brighter and closer separated pairs of Dunlop that is very easy to find and quite attractive for apertures above 7.5cm. Little information is available to ascertain possible attachment. Stun-wah!

AOST1&2 describes Δ141 as;

“In a well-sprinkled star field this beautiful white pair is a fine object for small apertures. It was first measured by John Herschel in 1835 and there has been no change since. If a binary system, the period must be very long.”

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HDS 1926 (13420-5435) lies some 3'ESE and in the same field as Δ141. This is a faint 9.2 and 12.2 magnitude pair which is separated by 11.2 arcsec along PA 60°. Little has changed in the relative positions.

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I 519 (13420-5911) lies 15.5'W (280°) from Δ142. I 519 can be identified easily as there is another star of similar magnitude 1.1' almost due north. There is also two other 7.7 (HIP 66772 ; bluish) and 9th magnitude stars 6'W separated by a similar margin. This pair is a moderately faint pair of 9.2 and 10.5 magnitude which is separated by 1.6 arcsec along position angle 287°. Little has changed in these stars since discovered in 1912. Spectral type of the primary is A4III:

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T Cir (13434-6528) lies 1.1° along PA 65° from the PNe, NGC 5189. One of the most prominent of the southern eclipsing binaries, and this is mainly because of the significant 1.5 magnitude drop in brightness during primary eclipse. Known as an evolved Algol semi-detached eclipsing binary, at maximum brightness is 9.3v magnitude, which can fall to 10.6 mag. Beginning at mid-primary eclipse on the 15th August 1938 (JDE=2429095.586), the fairly exacting period is 03h 07m 09m 44.35s (3.2984345days). [Note: Any slight error in the period’s precision means that the time of minima changes slightly. For T Cir, the times of future eclipse are likely to be slightly different than what is observed in a telescope.]

Time spent during eclipses is 13% of the period, 0.428797 days or 10h 17m 28.01s, with the primary eclipse lasting half this time - 5hr 08m 44s, dropping the whole 1.5 magnitudes in 1hr 28m. If the star was observed to begin falling in brightness at the time of sunset, then the minima could be seen to bottom out just prior to sunrise. The entire stellar total eclipse lasts about 3hr 40m. Secondary minima is a small 0.1 magnitudes.

As the stars are so close, gravitational forces have distorted the stars into ‘teardrop’ shapes. As the surfaces are non-circular, the observed light curve appears a bit more smoothed instead of being ‘jagged’. Separated in true terms by 17.84R⊙ or 6.2 million kilometres, and each star has respective radii of 4.46R⊙ and 6.25R⊙ with the relative solar luminosities of 179 L*/L⊙ and 110 L*/L⊙.

Spectra further reveals a B9 and F6 III system with respective temperatures of 10 060K and 7 500K. By mass, the orbital parameters give the combined mass of 7.0⊙, found by alternative means, give individual masses of 4.67 and 2.33⊙. According to the analysis of data in the catalogue “Classical (Evolved) Algol-Type Binary Candidates” by Ed Budding (BICDS., 27, 91B (1984)), the observed light curve has several unexplained errors, claiming this could be possibly solved by a slightly larger combined mass, so further observations are thus required.

Looking at the radii and mass of the two stars we can see the so-called Algol Paradox at play - where the lesser mass star seems to be the most evolved, seemingly acting ‘against the face’ of stellar evolution theory. In fact is was the primary which first to evolve, swelling into a red giant until it reached its critical volume and fills its so-called Roche Lobe. The hot surface gas has nowhere to go but to transfer mass to the secondary. In time, the secondary ages, hastened by the additional added mass, and so begins to become a red giant. Again the critical Roche Lobe is exceeded, and the surface material of the secondary is recycled back into the primary’s mass. Here we reach the current status of T Cir, where a large percentage of the mass has now flowed from the secondary back into its companion.

All eclipsing binaries transferring mass show some effects of their true celestial marriage. So intertwined have they become, that it becomes difficult to tell by looking at the spectra the chemical evolution of each star. Eventually both stars completely fill their Roche Lobes, causing material along the critical surface of both stars to begin being discarded into interstellar space. One star eventually became a white dwarf and its companion a red giant.

The future of these Algol-binaries eclipsing binaries is most likely a binary white dwarf. But for the closest of systems their demise is little less certain. In some scenarios it is possible that they could become either dwarf novae, novae, FK Coma Berenices variables (merging white dwarfs) or even R Corona Borealis variables - those anti-novae variables that suddenly drop by up to ten magnitudes in a several days. For those close binary stars having the combined masses exceeding 1.44⊚, the so-called Chandrasekar Limit, and have the real possibility of merging together to meet their demise ‘ultra-violently’ by ending as the hugely catastrophic explosions of the Type I supernovae.

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Δ142 (13440-5914) is located in a moderately starry field some 2.7°NW of β Cen / Beta Centauri and some 25′E from the faint and uninteresting open star cluster NGC 5284. Δ142 is a widely separated bluish pair divided by some 33.2 arcsec along the due east position angle of 90°. Some change has been observed sine discovery, with the position angle decreasing by 5° and the separation increasing by only 0.8 arcsec. This nice bright pair (6.5 and 7.8 magnitude) appears blue and bluish to my eyes and similar to the four other occasions that I have seen it. Δ142 is likely that this pair is attached as the proper motions and parallaxes are somewhat similar. If the Hipparcos is correct, then the distance is about 212pc. and the star having a true separation of about 7 000 A.U. A pair worth seeking out. Dunlop comments on the pair as having “With two stars of the 14th magnitude between them.” In both 20cm and 30cm these stars are not there. It is likely that proper motion has taken its toll on these foreground stars. As the proper motion of the stars is larger in RA, the two ‘14th’ stars should appear further east of the pair. Indeed there are two 13.5 mag. star separated by 25 arcsec some 1.5′ further to the east. I suspect it is the first two that Dunlop is talking about. Another possibility is an 11.9 mag. star to the 1.1′SW, but its placement seem wrong.

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Δ140 (13458-7159) is a Musca pair near the border with Apus. Located in a field of several faintish stars, locating it is a difficult to find pair for the lack of bright reference stars. I found it best to use Delta Musca, and move the telescope 3.4° further east and 0.2° south. This is one of the of the fainter Dunlop pairs, being listed as 8.7 and 9.7 magnitude. Separation is presently about 9.8 arcsec along PA 75° and has widened by about 1 arcsec while the PA has changed by about 4°. (The WDS Nov02 actually states the PA as 0°, but this is only because it was not initially measured by Dunlop.) Colours were seen as both as white.

It is likely that these two stars are attached, as the proper motions are similar and it will be an interesting pair to observe in the future for change in relative motion.

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M Centauri / HDO 225 / SAO 241157 (13467-5126) is some 4.5′SE of the Centaurus globular NGC 5207. This bright yellow 4.7 mag star was discovered as a double star by Holden. This pair is tough, though it can be seen easily in a 20cm using high power. Magnitudes are 4.7 and 11.0, separated by c.4.0 arcsec along PA 54°. Colours of both stars I saw as yellow and white.

The primary is the spectroscopic binary, Boss 3547, having the period of 437.0 days, first discovered in 1922. Orbital parameters were first determined by Jones in 1927 and published in 1928. The analysis found the cyclic variation with the velocity of ±5kms^-1 - a likely candidate for future interferometry measures. True separation between the stars is 73 million kilometres, some half the distance between the Sun and the Earth. Little observational data has been achieved in the last six decades.

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Δ143 (13492-6206) bright and relatively fixed moderately wide pair in a very starry field. It lies some 2.5°SW of Beta Centauri and merely 38′ at PA248° from the open cluster NGC 5316. The distinctly blue and orange pair definitely makes a nice contrast, and it is certainly a most attractive of the southern gems. It seems surprising omission to me that it ‘missed the cut’ in Hartung’s AOST1&2. Magnitudes are 7.6v and 8.0v (7.55V and 8.01V). Since discovered in 1826, the position angle has increased from 11.2 to 13.0 arcsec while the position angle has increased by 7° to its present 37°. It is unlikely that the two stars are attached as the proper motion in declination is in the opposite direction even though the right ascension proper motion is small. Spectral classes are given as B2(II) and K2/3 II/III

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Δ145 (13546-6654), which Dunlop found in 1837, is located 23'S from NGC 5316. Liile has changed in the relative positions except perhaps for a small 2° decrease in PA. Magnitudes are stated as 8.2 and 9.2, though I thought the difference (Δm) was more like 0.7. According to my observing book, and using a 32mm Erfle, I could fit both objects within “...the very starry field.” Finding this bluish-white/ white pair (B9/A0) alone is more than worthwhile!

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R 225 (13505-5925) is faint pair discovered by H.C. Russell at 11pm 26 June 1881 at around 11pm. R 225 lies some 51′ESE (102°) of Δ142 or alternatively, is 1.1°SW from the PNe He2-102. It is also 1.9°SW from β Centauri. R 225’s field is identified by a 8.4 magnitude bluish star some 2.9′ due north.

Russell’s initial observation found the mean separation of 9.12 arcsec along PA 341.325° for the two 10th and 11th magnitude stars. Since found the separation has increased to 10.7 arc sec and the PA has remained fixed at 340°. The primary is listed as a dubious suspected variable NSV 6459 of 9.0V magnitude. I saw the pair having a difference of about one magnitude without any discernable colouration. Certainly there is nothing spectacular about this pair. [Version 2 12/11/03]

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PK 311+2.2 / PNG 311.0+2.4 (13557-5923) is an impossibly faint and largish PNe in Centaurus which is 40′ due east of R225 - finding this pair while looking for this PNe. A 7.84V blue star, HIP 68034 / SAO 241302 / PPM 342398, is merely 1.4' E of PK321+2.2 which masks the faint light of the planetary. I looked a the field and nothing was discernable in 30cm, except the faint 12.2 central star. Little is known about the object except that its size is given as 65.0 arcsec.

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Δ150 AB / HJ 4633 BC (13575-5743) is positioned 2.8°N (PA 343°) of Beta Centauri. Three main stars are in the field - one wide pair and one moderately closer one. The wide pair is the Dunlop pair Δ150 AB and makes a nice colour contrast - red and white. Separation was observed in 1991 58.8 arcsec which has significantly reduced from Hersche’s measure in 1834 as 70 arcsec, while the PA has changed little from the present 266°.

The ‘A’ star in Δ150 is the red LB type variable V412 Cen, which varies between 7.1B and 9.6B magnitudes in an uncertain period. The spectral type of this star is interesting, as it varies between spectral classes M3Iab/b and M7. The observed parallax is small 0.74±0.93mas.

HJ 4633 BC is the third component in the system. Since discovered by John Herschel in 1834, the separation has continued to narrow while the PA has slowly increased. The ‘C’ star is 11.0 magnitude and appeared bluish to me. Spectral class is given as B7 III, which I assume is combined spectral of ‘A’ and ‘C’ components.

As the proper motions are similar, this is likely a real triple system. To me it is one of the most unusual in the sky, as one of the components is variable and quite evolved while the others are still main sequence stars. This is an easy to find pair and is quite attractive even in small apertures. Δ150 AB being visible in binoculars.

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“Southern Astronomical Delights” © (2009)

LAST UPDATED 10 Mar 2009