Southern Doubles, Stars and Variables
SOUTHERN ASTRONOMICAL DELIGHTS : Presented by Andrew James
|PAGE DS 013
10 Mar 2009
|RA : 13h
Dec : -30° to -90°
Constellations : Hya, Cen,
Mus, Cir, Aps, Cha, Oct.
Best Observed : Mar - Aug (Text Ordered by RA)
|RA : 13h
Dec : -30° to -90°
SELECTED SOUTHERN DOUBLES and VARIABLES
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
If we assume the epoch is 2429393.686 then the minimum of
primary eclipse (or Minima-I) should occur roughly one month apart
and gain just a few days. An ephemerides would be roughly be
between 2002 and 2005.
All results given in the Table (=>) are in three period lengths of 100.4613 days. To estimate the primary minima between the dates add either 33.4871 days or 66.9742 days, which is better approximated by adding 33 days 12 hours or 66 days 00 hours to the date in the Table.
I.e. 24 Jan 2002 at 08h has the next minima on 26 Feb 2002 at 20hours. The second (or next) minima is on 19 Sep 2003 at 06 hours; etc.
Those brave enough to attempt finding the time of the 1.41 day 0.2 magnitude secondary minima (Minima-II) (like impossible to see visually) should add an additional 17.4133 days (17 days 10 hours) to the dates above or too those that have been calculated.
NOTE: The exact time of primary minima is likely to be in error and will suffer accumulated errors over time. However, this eclipsing binary’s period is fairly long, so visual observations should still be able to see the changes in magnitude at the specified date.
TABLE : Maxima for FU Mus 28th Apr 2003 | 13th Nov 2003 30th May 2004 | 15th Dec 2004 02nd Jul 2005 | 17th Jan 2006
FU Mus (13017-6749) is merely 3'N of I 363. Sky Catalogue and Atlas 2000.0 nor Uranometria 2000.0 both don’t mention this pair, nor the variable. Little is known about this star, except its period is 199.5 days, starting from the maxima on the 21st June 1963. Table 1 gives the expected maximums of FU Muscae. Although most Mira type variables changing brightness like clockwork, variations can be out by as much as one month. FU Mus minimum magnitude is thought to be below 16.1, but longer-term observations might find the minima one or two magnitudes lower. No finder chart or comparison stars exist for FU Mus, so it is best too roughly make estimates using the brightness of the pair. See if you can visually find any variability for a month or so around the predicted maxima. Approximate dates of each maximum is calculated as in the attached Table.
HJ 4564 (13028-5541) in Centaurus is another attractive pair that was surprisingly missed by Dunlop. Roughly similar in magnitude (8.2 and 10.2) to Δ127, both stars appear either deep yellow or perhaps even orangery-red - matching the K1III spectral class quite well. It lies 29'ENE (PA 61°) of Δ127. It was discovered by John Herschel in 1834 who found the separation as 18.0"arcsec aligned at PA 220°. The WDS96 oddly gives the first measure as 1894 (Sep. 22.0" at PA 219°), and this to me looks like a very poor measure compared to the other five we know. Stated magnitudes are also quite strangely different, as the visual observations give the companion as 9.5v instead of the currently used one in the WDS of 10.16v magnitude. The presented Hipparcos magnitude measure of 10.43V, this is nearly a whole magnitude different than the earlier visual estimates! When I observed it, I thought the 9.5v value was much closer to the truth. Confusingly, the Tycho data (that should be used instead, incidentally) gives a value half-way between the two at 9.97V. No "modern" Δm photometric data has been obtained since 1991 and it will be interesting to see what values another survey would produce.
Latest observations of the positions using the 1991 Hipparcos data suggesting the PA of 214° and an increasing separation to 19.7 arcsec. Looking at the various obtained proper motions this is certainly seems to be an optical pair. This is a charming wide pair that is worth searching for in small telescopes.
HJ 4564 Pair 1 (13036-5550) is in the same field is an unlisted pair some 12'SE of HJ 4564. At 10.3 and 12.2 magnitude, the duo is separated by 18.7 arcsec along PA 292° (WNW) It can be identified easily as there is another 10.5 magnitude star 2'E of the pair. Both colours are very slightly yellowish. Easy in 20cm, possible even in 10cm or 12cm.
X Mus (13030-6514) is 23'NW of Y Musca. Like Z Mus below, little is known about this star, other than the spectral type is M7, and the variations from 13.20B, which falling by at least four mags. The only paper published in the last twenty years was in the ‘Variable Star Bulletin’ (1998), reporting that X Mus is suspected variable star in the IRAS source catalogue. Like most of these faint southern variables any observations of this star would be appreciated. The FK5 (2000.0) exact position is 13h 02m 59.6s, -65° 14' 49″.
FIN 64 (13032-5607) is a very close pair some 26'S of HJ 4564 position that was discovered by W.S. Finsen in 1928. (Union Obs. Circ., 6, 104 (1951)). At 8.3 magnitude, it is the brightest star among five 10th to 11th magnitude stars that surround it. Within 4' are four near-equal c.18 arcsec pairs between 10th and 13th magnitude, but the FIN 64 pair in question cannot be misidentified as it is much closer. Of the eight observations to date, this 8.5 and 9.1 magnitude pair are separated by 0.5 arcsec along PA 263° and thus require at least 30cm to 40cm to split the duo. Since found this twosome has slowly widened from 0.3 to 0.5 arcsec (1995). Using the photometric data from the Tycho data (Hipparcos satellite) Fabricius and Makarov (A&A, 356, 141 (2000)) found the accurate Δm’s as 1.10V and 0.94V magnitudes (Mean of 1.0V, which is slightly larger than the observed Δm of 0.6 given by subsequent observers.
I have never split this star, though I observed the single star colour as pale blue. Hipparcos gives the parallax of 2.55mas suggesting the distance of 392pc (1 279ly). If this is true, then this is a luminous sub-giant B9 system, whose overall absolute magnitude must be +0.5 and +1.5 or 55 and 50 times more luminous than our Sun. Diameters would be twice that of the Sun. Projected true separation would be about 200AU and a period around 1000 years. However, from the scant positional data, it is still uncertain if this is a true binary system or just chance alignment. Recommended, but certainly not for the faint hearted! An interesting system to watch in this coming centuries.
COO 147 (13033-5936) is placed directly 2°W of Beta Crucis or alternatively 24'W of the open cluster NGC 4852. Discovered in 1902 at the South American Cordoba Observatory, this equally bright light yellow or yellowish double is a faintish qual magnitude 9.4 and 9.4 (9.52V and 9.55V). This is an easy moderately close pair that is separated by 3.5 arcsec along the nearly perfectly northerly position angle of 358°. This is easily visible in 10cm and with care in 7.5cm. COO 147 has shown some significant motion in the last 100-odd years with the separation decreasing from 4.6" to 3.5"arc second while the position angle has moved from 344° to 358°. In the next few centuries these stars will be harder to divide into two in the telescope.Â Proper motions are seemingly identical and no doubt this is a long period binary star. Spectral classes are for the primary F5IV/V and either as A or F for the secondary. Easy and nice.
Z Mus (13057-6518) is a suspected S-spectral type variable 14.7p-(17.0p in the same field (14.6'W at PA 272°) from Theta Muscae. Photographic brightness changes are between 14.7p, and certainly below 17.0p, but little else is known about this very deep-red M9 variable. I spent sometime searching the literature and came up with very little. Details of the star first appeared in the GVSC3 published in 1971. Any observation, or even sighting of this variable, including simply just SEEING the variable, would be appreciated by the RASNZ. All interested observers can get a copy of the same chart used for Y Mus, and this is useful for comparison magnitudes. The FK5 exact position is 13h 05m 48s -65° 17.8'.
Y Mus / HIP 63911 / T8997:2223:1 (13058-6531) is 20.8'SW of Theta Musca and appears as a 10.4 mag star. Y Muscae is of suspected spectral class ‘Fp’, and is both a rare cool hydrogen-deficient star and an R CrB variable. In the telescope, the star does appear distinctly yellow or yellow-orange, and with the B-V of 1.015, this is expected. The Hipparcos magnitude is 10.26v, while the exact measured position is 13h 05m 48.2s-65° 30' 47″. The still slightly uncertain parallax is 8.02mas, giving the distance as 125pc. (400 ly), and it is more likely that the distance must be much further than this. Magnitude ranges are between 10.5p and 12.1p, as listed in the GCVS4, but drops in brightness below 14th have been seen.
R 213 (13074-5952) is a close pair that was discovered and measured by H. C. Russell on the 9th April 1874 at around 10pm. He saw the stars as “8,8” magnitude and “both orange”, measuring the separation as a narrow 0.32 arcsec along the mean position angle of 27.08°. When discovered this would have been a difficult pair for nearly all observers, though it is possible that Russell probably over-measured R 213, as it would have certainly pushed the very limits of the Sydney Observatory’s 7.25-inch Merz refractor. Unless the seeing was absolutely perfect, I really doubt this telescope could have resolved it. It is possible that the measure is about twice what he gives as about 0.5 to 0.6 arcsec.
R213 is easy to find, being directly 2.5°E of β Cru and crossing from eastern Crux into western Centaurus. Magnitudes obtained by Russell are a little too large, with the 6.7 and 6.9 magnitude and the WDS03 gives 6.59 and 7.04V. Several Δm observations gives and average of 0.31 for this double.
E.J. Hartung in AOST1 and 2 (Object No. 506) says;
“Since the measures of Russell in 1878 there has been little change in this close deep yellow pair except perhaps some increase in separation. In 1961 the stars were just clear of one another with 20cm; the proper motion seems to be shared, denoting a binary system and the colour looks too deep for the given spectral type.”
Note: In the introductory table in AOST1 gives the wrong separation 0.9 arcsec and I know of no measure that has been this wide.
Spectral classes were once given as a composite for many years but recent observations show it as B9IV and F8-G2. The literature seems to suggest that there is a continuing debate on the colour and spectral classes with the pair I saw the pair in 1994 as white and yellowish-white for a just clearly split this duo.
Since discovery the pair has continued to widen and there is little doubt that this is likely a true binary, but as yet enough points can be used to ascertain any definitive orbit. If R213 is truly binary then the orbit appears it might be almost edge-on. This will be an interesting pair to observe in the next couple of decades. In all, a good observational challenge for moderately sized telescopes.
Separation is presently 0.7 arcsec (1997) and I suspect this could just be seen in 15cm on really steady and clear nights and certainly visible in 20cm under the same conditions. Position angle is presently a northerly 22° from the 27.1° since 1874.
NOTE : The three doubles, two variables are associated with this Centaurus pair are; COO 147, V592 Cen, WW Cen, Red star T8989:641:1, NZO 38 and COO 152 AB.
R 212 (13076-6144) is a faint and lonely yellow pair of 9.2 and 10.0 (9.59V and 10.28V) magnitude within the northwestern edge of the Coal Sack and being the obvious addition to the star field. R 212 lies along the fixed position angle of 109° whilst the separation has reduced from 5.5 arcsec to its present 5.1 arcsec (1991).
Discovered by Russell on the 16th June 1874, his measures have left some uncertainty about his own find. Although his measures are given as 5.80 arcsec along PA 169.4°, his given location is in reality some 1.2°W (PA 270°) being now within the neighbouring constellation Crux. Â As there are too few candidates of pairs of 10th magnitude, it is hard to understand if this is some wrongly located double. Three things don't match here, the separation is too large (though probably correct), the position angle is 164° (possible) and his only clues says the star colours are white (which they are not.) The given positions in the WDS are actually the first ones of Innes and not Russell’s, which have been previously deleted as wrong. As the R.A. and Dec.Â positions in the sky are exactly due west, it is assumed that this must be a position error by Russell himself.
Proper motions of the two stars suggest that they may not be associated. Spectral class is F8V. This is a faint but dainty pair but there is not very much around here to get excited about.
NOTE: In the WDS03 Notes it says that there is a comment on the R 212. For some reason this has been omitted or deleted from the current WDS notes.
θ Mus / RMK 16 / Theta Musca (13081-6518) is simply one of the most brilliant southern gems, and remains in my Top 10 of pairs. This is a multiple triple system with the wide pair is known as RMK 16 AB. The field is star-studded, and the addition of this blue and white pair makes it simply “stun wah”. Combined magnitude of the visual pair is 5.4, with the individual magnitudes being 5.7 and 7.8. Of the nineteen observations so far obtained, the last in 1991, according to the WDS 2003, finds the two stars remaining relatively fixed at 5.3 arcsec separation along PA 187°. AOST2 lists it as Object #574, and is one of the longest descriptions of all doubles listed within its pages. Spectral class of the primary is often given as the combined B0, or more recently O9.5, while the fainter companion is B3 II as first found by H.J. Smith in 1955. (Most references get this wrong as they are often referring to the close binary.)
The inner Aa system is usually given as either spectral type B0 Ia+WC6 or O9.5 Ia+WC6. No doubt this is a particular heavyweight system and joins the ranks of the very few known massive stars and is both spectroscopic and an eclipsing binary, however, the monster companion itself remains merged to all amateur telescopes. In 1996, this binary was resolved by speckle interferometry, which the WDS 2000 now includes as the pair CHR 247. The companion of the “Aa” star is also listed in Batten et al. “Sixth Catalogue of Spectroscopic Binaries” (1985) as Object #751, whose period is about 18.34 days orientated at the inclination of about 100°. Its eclipsing binary status is listed in the GCVS4 as WR48, with the slightly more accurate period of 18.341, centred on epoch 15th March 1970 (JD 2440661.4).
Magnitudes vary only fractionally, somewhere between 5.50v and 5.52v. Furthermore, observations by the Hipparcos satellite shows long-term light variations of several weeks, speculating that the WR-star has other unexplained instabilities.
Moffat (1977) was first to analyse the orbit of this system, finding the two stars orbit almost along the line of sight (1.51°), with the orbit being highly elliptical. Batten et al. (1985), gives the change in separation between 1.51 to 1.10 million kilometres. Overall, the combined mass is determined to be 11M⊚, subdividing approximately into the respective masses of 6.9M⊚ and 4.1M⊚. However, the gross uncertainty with the spectroscopic orbit, means the orbit can only be considered as an educated guess. It is more likely the masses are much higher than this. Also finding that the system is: Spectroscopic, eclipsing (photometric), and now an interferometric binary systems, should mean that determining the orbital parameters, is possible. The only problem seems to be the lack of data. Certainly sometime in the 21st century, enough data will be obtained to refine these parameters.
Wolf-Rayet Stars in the Field
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.
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.
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.
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))
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.
WW Cen (13094-6015) is a fairly bright SRB semi-regular located Â 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 Â 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.
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.
COO 152 AB / HDS 1850 Â 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. Â 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. Â 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 Â 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.
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.
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.
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!
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.
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.
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.
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.
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.”
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.
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:
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.
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.
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.
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.
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
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!
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]
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.
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.
|“Southern Astronomical Delights”
10 Mar 2009