SOUTHERN ASTRONOMICAL DELIGHTS
A Selection of Southern Doubles, Bright Doubles and Variable Stars
RA : 10h to 12h
SOUTHERN DOUBLES :
HJ 4306 ,
RST 3692 ,
J Vel / Rmk 13 ,
OTHER DOUBLES and VARIABLES :
S Car (10094-6133) is a red Mira-type variable star that is likely one of the first variables stars that southern amateurs select, when embarking on observations of variables. It lies 1.1o directly north of IC 2553, and conversely, using S Carinae also finds the planetary nebula. Variations follow a regular pulsation of about 149.49 days, between 4.5 and 9.9 mags. At maximum, the spectra displayed is M4, decreasing to M6 at minimum. Throughout the cycle, emission lines are prominent in the spectra.
HJ 4306 (10191-6440) is a bright and equal 6.5 mag pair that Sir John Herschel discovered and measured in 1836. Visible in 15cm, and easily through 20cm, in a wonderful field. To my eyes both stars are bluish-white. (A0V/ AIV) Burnham incorrectly gives both stars as 7.0 magniude. H.C. Russell on the 24th March 1873 saw both stars as yellow. He described it as Very beautiful, well defined. In the last 162 years, the separation has increased from 2" to 2.5", and the PA of 139o has decreased presently to 134o. From the similar common proper motions, and the closeness of the two stars, it is likely they are physically associated. This pair will be worthwhile watching in the 21st century.
R140 (10191-5601) is another pair in the same field of J Velorum, and 12' W. Discovered and measured by Russell on the 20th June 1881, this moderately bright pair, at 7.8 and 8.3 magnitude, is separated by 2.8" at PA 279o. It is amazing that neither John Herschel, Dunlop nor Rümker saw this obvious pair, and unless the stars were much closer in the 1830's, this is hard to reconcile. Since Russell's measures ρ= 2.88" and θ=277.1o), little has changed in the positions. A 10.5cm can probably separate the duo with care, though it was easy at 127X in the 20cm. This field, including J Vel, has a rough north-south line of stars that divides the field in two.
RST 3692 (10203-6240) is a faint pair that is in the same field some 12'E of NGC 3211. Although it is in a very starry field, RST 3692 is the northern object of two 10th mag. stars, some 80" apart. Discovered by Rossiter in 1936, the pair is a close 0.8" at PA 65o, that incidently points directly to NGC 3211. Both have stated 9.8 and 11.8 mag, respectfully. In a 20cm, I could clearly separate the pair at 310X, and suspect that a well-aligned 15cm could possibly see both stars.
J Velorum / Rmk 13 (10209-5603) is a spectacular triple which lies in a dense stellar field, some 2.6oWSW from x Velorum (or 2.5o WNW from SA2-64). Unlike most system Rumker discovered the AC pair first in 1835, and the AB pair a year later. I suspect he may have missed the brighter AB pair, because of bad seeing and not be carelessness. The main pair is 4.5 and 8.4 mag and separated by 7.2" at PA 102o. I see the colours as blue-white, and could discern no difference. AOST2 describes them as white, and stating ...this is a beautiful object. Spectral types for the two Giant stars are B4 and B9.5. The pair is visible using medium to high power in 10.5cm, and medium power in 20cm. Difficulty in the separation for smaller apertures is more from the Δm=3.9, than the quality of the telescope. Component 'A' has been found to show a variable spectrum, and a suggestion says that this maybe either spectroscopic binary, or that this star has some peculiarities. Some 37" at PA=102oS of the main pair is a 9.8 mag star. (SAO 277958) This wider star is easy in 7.5cm, and I see the colour as yellowish-white. Little has changed in the positions, so it is uncertain if all the stars are physically associated.
R146 (10263-5529) appears as a pleasing pair some 1.84oW, and fractionally north of x Velorum. Russell found it on the same night as R140. The light yellow pair is 8.7 and 9.2 magnitude, though I thought Δm was 0.8 magnitude, either the primary being a main sequence F5-F6 star. In the last 112 years, the pair has significantly increasing in separation. When Russell discovered R146, the separation was 11.6" at PA 99o. In 1998, the separation has doubled to c.20", and the position angle has decreased by 5o. Proper motion shows a large differential in right ascension, so we can say R146 with certainty to be an optical double star.
R 149 (10288-6642) appears as a
moderately faint pair some 2.2oSW of the
Southern Pleiades (IC2602) that is visible as an easy pair
in small 7.5cm apertures. Discovered just before midnight
on the 14th (1874.284), and first measured on the morning
of 7th May 1880 (1880.347), this is fairly easy pair in the
7.5cm to 10.5cm range. He puzzlingly gives the pair
magnitudes as “6½” but it is obvious
this is a gross overestimate. I checked the presented RA
and Dec and the measured positions and concluded this is
the correct pair.
R 149 is presently the separation is 3.7"arcsec along PA 138o. Since 1880, the PA has increased by +4o while the separation has diminished from 4.2" to 3.7" arc seconds. Magnitudes were recently downgraded from 8.83V and 9.80V (1991) to 9.23V and 10.06V (1992). Both stars are likely of B6 spectral class.
Russell also describes the nearby field stars to the pair;
“...Three stars within 12s in R.A. and almost exactly in a line when the wire bisects the first and second; the third is 0.5" south of the line.”
Russell’s “third star” (Star 3) is 11.1
magnitude and has been left behind by the primary’s
rapid northwesterly proper motion of -32 and +33 mas per
decade. “Star 3” now lies 1.7' NNW (PA
338o) (10287-6640) Catalogued as T2 8968:747:1
this star is certainly not associated. The secondary
position has remained relatively fixed.
A fourth 11.7 magnitude star (Star 4) exists 33" NE (PA 34o) from Star 3. Identifying the field, some 19' SSE (PA 155o) from R149, is the bluish-white 6.2 magnitude star HIP 51425 / SAO 250989 /PPM 358033 /HD 91272 (10301-6659.)
The system is likely an optical double.
Δ85 (10288-6235) is found by continuing to move the telescope eastwards of planeatry nebula NGC 3211 from RST 3692 by a further 1o17'E or 77'E, and perhaps fractionally north, is the pair 85. Respective, magnitudes of the two bluish-white stars are 8.8 and 9.2. Since it discovery by measures by Herschel in 1837, little has changed in either the separation of 21.8" or the PA of 220o. Earlier spectra placed the pair as main sequence A0's, but recent observations suggest they are a slightly hotter B6's. Due 3'N is the white 8.3 mag. field star SAO 250977.
Δ87 (10307-6122). Some 1.2oN of Δ85 is another fainter pair Δ87. First found by Dunlop at Parramatta in 1835, this is a charming colour contrasting pair and is a wonderful object even in the smallest of telescopes (and possibly even binoculars). The bright 6.43 and 7.6 magnitudes stars, respectfully. Separation is 82.6" at PA 75o. Colours are red and blue, reflected in the spectral classes; M2 III and B9. Little has changed in the system, and the proper motions of both are almost stationary. It is likely this is an optical pair. Some 2.5'NW of Δ87 is the 7.5 mag blue (B9) star SAO 250491, enhancing the beauty of the object.
HJ 5444 (10318-8155) The pair is bright and wide, and is listed as 7.0 and 9.5 mag, separated by 41.9" at PA 235o. Measures in the last 85 years have shown little change. The last measures in 1983, as quoted in the WDS96 Catalogue, gives a separation of 41.8" with the PA of 223.5o. Later observations have give the spectral class an upgrade in temperature, and the primary is now considered a subgiant B5 III-IV star instead of lust B3. Based on the common proper motions of the two stars it is likely just an optical double star. The pair is visible even in 7.5cm. My observations describe the colours as bluish and yellowish. A neat pair!
x Velorum / Δ95 (AB) and
HJ 4341 (BC) (10393-5536) is third in my Top 5
of favourite double/ multiple stars. I have named it
'Albireo Australis'. (Alpha Centauri is first, Gamma
Velorum is second, Beta Cygni is fourth, Acrux is fifth.)
In 1826, James Dunlop discovered the wide and bright AB
components (4.4 and 6.6 mag) at Parramatta Observatory.
Separation is 51.9" at the position angle of
105o. (See Figure.) Little has
change in the relative positions of the two stars since the
Dunlop's first measures. The ASNSW Double Star Section
during the 'Double Star Colour Estimates Programme' (DSCE)
in 1979-81, saw the star colours as orange-yellow and pale
blue. The thirty-six members of the ASNSW and other
contributing Societies assessed this. H.C.Russell on the
21st March 1873, described the colour as straw yellow and
greenish blue. He comments also that Glimpse
several minute points near this. The colour
difference is magnificent, significantly enhanced by an
optical illusion - reflect by star's spectral classes; G2-3
Ib and B8 V. Δm is 1.2, though the twelve observers
in this part of the programme overall estimated the
difference is closer to 1.8. Closer inspection reveals that
the blue component is again double, and Sir John Herschel
discovered this pair, HJ4341, some eight years later than
Dunlop. Burnham's incorrectly names' it Δ95b, and
saying the primary AB is HJ 4341. Russell also incorrectly
assumes that the HJ 4341 was the AB system, though
Herschel's observation implicitly refers to the BC system.
Such a discrepancy is difficult to explain satisfactorily,
as the AB pair is too obvious. The third 11th mag yellowish
star is found opposite to the 'A' component, at PA
176o. We measure separation of
20.2" as one third the distance between A and B. This can
glimpse this in 7.5cm, though a 10.5cm will prove better in
seeing the component from the bright glare of the 'B'
All three stars have the same common proper motion, so it is still possible that this might be a physical system. However, if it is, the periods are likely to be very long time. The general field is dense with stars, and contains another 8.2 mag star some 6' at PA 120o. This colourful triple is one of the most attractive objects in the south - even for the smallest of telescopes.
Double and Multiple Stars in the Inner Eta Carinae Nebula
NGC 3372 / Eta (η) Carinae Nebula
(10440-5930) is the brightest of the emission nebulae in
the southern skies, whose diameter extends more than more
than 3-degrees of sky. Is very centre is found near the
open star cluster Tr14 (See Below) This region
abounds with bright and dark nebulosity and the edges
contain many bays and complex structures. In small
telescopes it is extraordinary in the space it occupied,
covering at least eight times the area of the Great Orion
Nebula, and which all southern observers know pales the
Orion Nebula to second grade. Eta Carinae and the star that
gives the name to the brightest, and I dare say also the
best nebulae in the sky.
Eta Carinae and the environs it appears to contain many astronomical objects including many pairs and open star clusters. In most cases nearly all are easily visible to the amateur. The region contains enough objects and structures worthy of several nights observing.
η Car with its associated star clusters and the great diffuse gaseous nebula enveloping it form one of the finest telescopic objects; on a clear dark night the region is beautiful beyond description, even for small apertures.This nebula lies at a distance between 1 800 to 2 500 pc. (6 000 to 8 000 ly.) from us and within the Carinae arm of out Milky Way galaxy. In size the true nebulosity is estimated to be some 400 ly. across, some ten to twelve times the area of the Orion Nebula. If it was at the same distance as the Orion Nebula, it would cover the entire area of Orion's "Pot" or "Venus's Mirror", being an incredibly bright -2.4 magnitude!
See 123 (10440-5932) is the faint pair of 9.6 and 12.2 magnitude pair separated by about 7.0" along PA 330o. Which I estimated in 1997. The last measures were made in 1934, when the positions were 4.5" and 311o . It lies merely 1' from the cluster's centre and both appear bluish or bluish white and a lovely sight against the backdrop of nebulosity. Easy in 7.5 cm.
HJ 4353 (10437-5935) is a solitary faint pair of 10.8 and 10.5 "B" magnitude, and I estimated about the same for the visual ones. This pair is not among the "stun-wahs" in the many pairs that I have observed, yet it does lie within the same field of Trumpler 14, even though it might not be a true cluster member. Since discovery by Herschel in 1837, it has shown clear tendencies of increasing in separation, but the PA of 180o (due south) has not changed at all. The WDS01 shows that the last measure was in 1959 with the given separation of 4.9"arcsec. In my eyes the separation is today (1994) beyond 6"arcsec. I saw both these star without colour (white perhaps) and easy in the 20cm. Smaller apertures as low as 10.5cm should be able to see this duo - perhaps even 7.5cm with care. This star is also not mentioned in AOST2.- Nothing really to write home about though!
HJ 4356 (10440-5933) lies in
the very heart of Tr 14, making it its brightest star. John
Herschel discovered this pair in 1836 and little has
changed in the positions at all. These two stars are a
little closer together than the rest whose 9.0 and 10.4
components are separated by 2.8" with the PA being in a SE
direction at 149o. Any 7.5cm
telescope should be able to see both white stars which make
up the "AB" system. There are another two companion stars
HJ 4356 AC is 13.0 magnitude and is about 5.0"arc seconds PA of 270o (West). I glimpsed this once in the 20cm C8 under very good seeing, though 25cm or 30cm might make this easier. My notes says that I looked at this pair with 30cm in 1986 and that I could not see it - I didn't write much on the conditions so I'm unsure why I did not see it. Yet another companion- the "AD" system. The 'D' star is an even fainter 13.5 magnitude star along PA 187o with the separation of 3.0"arc seconds. This star was a little tougher because of the delta-m of 4.5 magnitude. In the same evening using the 20cm it appeared elongated with the A component even using high 333x magnification and I thought I glimpsed it once in a period of about five minutes. This is not an easy pair to see as it is almost in-line with the 'C' component. This did not seem much better in 30cm, for the same reasons above, but this time A, D and B had merged into a small line of haze - something I've never seen before. I also suspect this star was harder to see than I suspected and it might actually be closer than what the WDS is saying. I would love to see this in 40cm or 50cm Dobsonian. The A and B star are mentioned in AOST1, but the other two are not, even though they should be visible in 20cm to 30cm telescopes. What is also mentioned in this same reference is the primary 'A' component which is quite rightly brought to the attention of the observer. This star is SAO238396 / HD 93129A / PPM 339375 and is given as spectral class B - even though the measured B-V is 0.206, suggesting a late A spectral class star, However, there is much obscuration from the surround nebulosity meaning that the star light has been reddened somewhat. All these stars here seemed white to my eyes.
HJ 4356 A appears in several professional papers it is described as one of the most luminous stars known, and ranks in some ways like Eta Carina itself. Some even suspect it may even be outshining the really monstrous ultra-blue O5 Iaf for Zeta Puppis / HIP 39429 / SAO 198752 / Noas (08037-4000) which is 2.2 magnitude. This supergiant star has an absolute magnitude (MV) of -7.4 and whose distance is about 735 pc. or 2 400ly. Another example of another rival star is the 4.25 magnitude γ1 Vel / Gamma (1) Velorum (08095-4721) which has a similar temperature, distance and absolute magnitude. A small spectroscope or direct-vision prism, on either of these stars show bright lines of oxygen, nitrogen and helium. There is very little doubt that these star will some day end their lives as supernovae - with the explosion rivalling the brightness of the moon for the peoples of the Earth sometime in the future.
This is an interesting quadruple system, and if they are truly associated, the periods may be very long. We know little of the distance to these stars as the parallaxes are too small, though some work has been done on the galactic cluster Tr14 and the nebula itself, giving the distance around 3.2 to 3.3 kpc.
HJ 4360 (10441-5935) is likely
the prettiest pair of the four pairs we are discussed here,
but it is as just as interesting as HJ 4356 mentioned about
because it is another multiple with five stars this time.
HJ 4360 lies in the same field as the other three pairs so
far mentioned, and lies some 2.2'SE (PA
140o) from HJ 4365.
HJ 4360 AB is the main pair is a near equal 8.59 and 8.64 magnitude, though AOST2 for some reason gives the bright values of 7.8 and 7.8 - and I could not find its original source. Both stars are separated by 2.1"arcsec along PA 117o. The two are easily seen in good conditions in 7.5cm telescope. Like HJ 4365, the primary 'A' is another O6 spectral class star. Little has change in these two except for perhaps a minute decrease in apparent distance.
HJ 4360 AC is another internal pair that is little easier to see, as it is 12.5"arcsec apart along PA 289o (WNW). Easily seen in 7.5cm, and possibly even 5cm with due care, these 8.59 and 7.89 duo appear to me white and yellowish-white. Over time it seems that the PA is increased by about 1o per fifty years or so, while the separation has reduced by 1.1"arcsec since discovered in 1835 by J. Herschel. All three of these stars are very attractive for the observer with small instruments. All these main stars remind me of a miniature Alpha Crucis except that all the stars are either white or yellowish - again reddened by interstellar absorption of starlight.
HJ 4360 AE is the fourth companion of the system. This is another bright star that is aligned nearly parallel the close AB pair. Users of Megastar 4.0 should note that HJ 4360 AE is wrongly identified as the principal AB pair in this system, and this might have discouraged a few southern observers not to view this multiple at all. This time the 'E' component is 9.0 magnitude add lies along the easterly PA of 97o and is separated by 7.7"arcsec. These stars are also easy to spot in 7.5cm, though it was certainly more impressive in 20cm. I saw 'E' as white as well.
FIN 412 CD can be seen if you look carefully at the 'C' component the star splits in two with apertures around 20cm or more. Discovered by Finsen in 1934 it makes the 'D' component of the system. This time the alignment roughly matches the AC system where the separation is some 2.4"arc sec along PA 305o, which I estimated in mid-1984. It seems these stars are showing the most movement of all the components, where the PA (my estimation) has increased by 11o in fifty years since 1934. This is the only star to show significant motion of these components in all these pairs we have so far discussed. This star has the best chance of being the true binary, however the proper motions and parallax are essentially zero. It may take some time to prove it has physical connection as a binary. I would be interested to hear if the PA has continued in its motion or not, and if so, it would be encouraging to see some new measures of this duo. Looking in January 2002 the distance seemed just a little wider. The distance is likely to be the same as the stars in the open cluster Tr 14 and the other pairs mentioned above. All in all this is a nice easy system for small to moderate apertures. But even in larger telescopes and applying moderate magnification this pair is further enhanced, as the nebulosity nearby is bright and adds much to this truly majestical and regal field.
MULTIPLE SYSTEM : HJ 4360
|HJ 4360 AB||117||2.1||8.59||8.64|
|HJ 4360 AC||288||12.5||8.59||7.89|
|HJ 4360 AE||097||07.7||8.59||9.0|
|FIN 412 CD||299||2.9||8.4||12.5|
Tr 14 / Trumpler 14 / Cr230 (10439-5933) contains some twenty (20) brightish star all within an area of 5' and is something akin to the area seen with the Jewel Box (NGC 4755) Tr 14 contains the pair See 123, and possibly the pairs of HJ 4353, HJ 4356 and HJ 4360. All of these are visible in 10.5cm with care.
Tr 16/ Trumpler 16 / Cr233 (10452-5943). Tr 16 is estimated to have an average O5 spectral type star and contains about fourteen (14) others. Covering about 10', the total integrated magnitude is 5.0 magnitude. In age, this cluster is about ten million years old.
HJ 4432 (11212-6441)
is a particularly bright double star in the very
far western corner of Musca being some 1.6'S of the
Crux and 18.4'E of the Carina borders. It can also
be found some 1.3oNW from the planetary
Discovered by John Herschel in 1836 snd somehow missed by John Dunlop, these 5.7 and 6.8 mag. stars are separated by 2.4" along PA 310o. I first examined this pair in 10.5cm refractor in early 1981 and easily separated the duo at medium magnification. I would think that any aperture above 7.5cm should be able to split the two. I thought the primary was bluish and the secondary white, though on a second occasion in March 1985 I saw them as both white. Peter Williams comments on this pair in Telescopic Targets (Universe, 32, 7, July 1985) saying;
Moving from IC 2948 [in Centaurus], almost 2.5o sp. is an attractive multiple star just within the bordering constellation of Musca. This pair, HJ 4432, is a close and uneven pair lying in a field of fain and scattered stars. A magnification of 100X sows this is a close but clearly separated pair in which the companion lies a little north of preceding. Both stars are white in colour.
Of the twenty-six measures so far the 2.4" has not changed, but the P.A. has increased from 288o to 310o. The primary is listed as HIP 55596/ T8967:1170(2)/ SAO 251383/ PPM 358676, and the Hipparcos Catalogue gives the distance of 145pc or 470ly. from the parallax of π=6.87±0.59mas. At this distance the true separation is about 4.8 billion kilometres - approximately the distance between the Sun and Neptune. It is likely this pair is associated and by calculating using simple Keplerian motion, suggests the period is over 180 years. This pair will make an interesting object to observe during the 21st Century.
NZO 23 (11327-6552) is a reasonably bright pair requiring 15cm under steady conditions and high power, and is easily to resolve in 20cm. NZO 23 is a close 8.3'NE (PA 42.1o) of the planetary nebulae He2-68, and was discovered in 1914 at New Zealands National Observatory in Wellington. Presently the stated magnitudes of the blue and white pair in the WDS96 (Washington Double Star Catalogue) are 8.8 and 9.2, respectively. Visually, I though this to be about right. Separation is about 1"arc sec along PA 239o that was last measured in 1983. From the three measures so far acheived, the apperance has changed very little. NZO 23 lies in an interesting find. Within 2' is small circular telescopic asterism of eight or nine 14th magnitude stars that appears to the 1.5' NW. This little asterism is quite obvious on dark nights in 20cm and above.
HJ 4460 (11392-5744)
is another pair, 1.7oSEE
of the planetary nebula NGC 3198. It is
brightish pair of 7.7 and 8.9 (7.2V and 8.2V) mags.
separated by 8.6" at PA 177o. Little has
changed in the positions since the first measures
by H.C.Russell on the 9th June 1874 using the 7.25"
Refractor at Sydney Observatory. So far the only
spurious observation of the eleven known measures
was made by Hargrave who measured 8.0" arcsec on
the very same telescope on the 6th June 1879.
Russell described both stars as white, but I see them as bluish. Proper motion are likely too large a difference for this to be a real double, however, HJ 4460 lies in an elegant starry field and is worthy to glance. (Updated 08/09/03)
I 890 (11449-5528) lies in Centaurus and in the next field some 36'W of COO129 with I 891 some 2.6' NNE (PA 20o). I 890 is a 7.6 and 10.4 mag. pair separated by 2.1" along 301o. Since discovery the PA has decreased 9o and if this pair is associated, as the proper motions seem to show, then the orbit is likely to be prograde and about a thousand years long. This white A1V pair is easily split in 10.5cm.
I 891 (11450-5525) lies in some 36'W of COO129 along with another second fainter pair I 890 some 2.6' SSE (PA 200o). This 10.5 and 11.0 (11.25V and 12.43V) mag. pair is separated by 2.8" along 28o. Since discovery the PA has cahnged little but the separation has increased by +0.3" (1991) This pair is almost certainly associated. It is likely visible 10.5cm or 15cm with care, but did appeared quite faint in 20cm. This is an attractive field along with the second pair I 890.
COO 129 (11455-5530)
appears in the eyepiece field some 14'NW from the
open cluster NGC 3960 I saw the components
colours as white and perhaps yellowish in 1981,
for this 9.0 and 9.9 mag. pair whose separation is
2.4" along PA 79o. Both are listed
as a single 8.3 mag. star in the SAO Catalogue
Spectral type is A3m and the B-V colour index is
COO 129 was discovered at the Cordoba Observatory in Peru in 1913 and little has changed. The WDS 2001 notes an increase of 1o and a decrease of 0.1", but such changes are insufficiently accurate to offer any conclusions. If these stars are truly attached then the period must be certainly long. (Updated 08/09/03)
λ Mus /
Lambda Muscae/ HJ 4471/ HIP 57363/ SAO251575/
HD102249 (11457-6644) is bright 3.63 mag star that
is also a wide pair 3.3oNWW (PA
288o) of Epsilon Muscae or
5.3o NWW of Alpha Muscae. Alternatively,
HJ 4471 can be also found 1.9OESE of NGC
4071 along PA 285.9o. This pair is 3.6
and 12.8 mag. and is separated by 40.6" along PA
275o. I could easily see the companion
in 20cm and estimated that perhaps 10.5cm should
have no problems - though any 7.5cm might have
problems with the Δm is 8.8.
Looking at the Hipparcos 1991 data, the distance of the bright star is 39.29±3.84pc. or 128.1±12.6ly. Parallax (π) of 2.545±0.540"mas. Furthermore the proper motion of the star is quite high in RA. (pmRA=-100.42"arc seconds per century and pmDE=33.21" per century.) Interesingly this motion is roughly shared with both ε Mus and ε Cru. This maybe no coincidence! HJ 4471 is very likely a chance alignment, although this white pair has changed very little since discovery.
R179 (11460-5805) lies
213o) of NGC 3918. Appearing in a
moderately starry field, it shares its position with the
triple HU 1485 and the pair JSP 499. (See Below) R177 was
discovered by H.C. Russell from Sydney Observatory using
18cm (7.25") Merz refractor (at 159x) on the 1871.369
Russell describes the equal 9th magnitude pair as "yellow",
he measured the separation as 5.07"arc sec along PA
355.2o Of the nine separate
occasions that the pair has since been measure little has
changed in the separation, which remains as 5.1"arcsec. The
current position angle is given as
176o, which is
180o from Russell's designated
value. Usually the discoverer's designation dictates the
nomenclature, but in this case it has been ignored. The
1937 discovery of the small Δm of only 0.1
magnitudes, which forced the PA to be changed by
180o. Stated magnitudes in the
WDS2001 are 9.24 and 9.38, respectively.
My own observations in 1981 found both these stars as bluish-white, which matches well with the B2/3Vn spectral class. This is an interesting pair and worth searching for even in small apertures.
HU 1485 (11465-5802) is a
triple star merely 4.5'NE (PA
44o) from R179. HU 1485 AC was
discovered by Hussey in 1895, while HU 1485AB was later
found by Hussey in 1913 when he reinspected the field. It
is surprising how Russell missed this system - especially
during the time he was looking for faint triples in the
1880's. The likely explanation is that Russell never
returned to R179, and the 18cm (7.25") Merz Refractor was
too small to see HU 1485's components. The AC system is the
easiest to see, and can be view in 15cm, and possibly even
10.5cm. From the primary, the companion is located some
7.9"arc sec. along PA 276o.
Colours observed sees the primary as bluish with the
fainter wide companion as white. Measures suggest that the
two stars are widening, changing between 7.0 and 7.8 since
discovery some 110 years ago. (2001).
The AB system, which was discovered later by Hussey, is separated by 2.9"arc sec along PA 320o. This close pair, with a significant Δm of 4.25 magnitudes, as a challenge for observers below 20cm apertures, though easily seen in 30cm. Its position is about third-way in between the 'A' and 'C' stars, whose angle is slightly offset. I saw the primary as blue and the 'B' companion as whitish. Since discovery, little has changed in these two stars relative positions.
Observationally, this HU 1485 system is one of the only triples I know that appears like a thin line instead of three pinpoints under low magnification! It would be worthwhile trying to find the threshold where all three components can be seen.
Magnitudes of the stars are; 'A' is 7.72 (7.7), 'B' is 11.97 (12.0) and 'C' is 10.57 (10.6). It is interesting to note that the WDS1996 and WDS2001 show that all of these stars are brighter than earlier estimates. Differences between these two values are extraordinarily large, +0.28, +0.53 and +0.93 magnitude, respectively. Furthermore, the ‘B' component is 1.4 magnitudes fainter than the ‘C' star - questioning Hussey's designation. It is possible that either the 'B' or 'C' star is variable, though no one (including the WDS) has suggested this possibility. Observers might like to look at this system from time to time to see if they can detect any differences between the three stars. Gravitation connection to all three stars is still uncertain and it will be perhaps a century from now when we find the nature of this system.
JSP 499 (11469-5807) is the
third pair alongside R179 and HU 1485. This close pair lies
some 7.3'ESE (PA 110o) from R179
or alternatively 6.8'SE (PA 148o)
from HU 1485. It placed is marked by two stars of 9.6 and
11.6 magnitude separated by 19.2"arc sec, with the 9.6
magnitude star being the pair JSP 499. Separated by merely
0.9"arc sec, this slightly unequal bright pair is roughly
aligned north-south along PA
170o. This is hard to split being
impossible to see in 20cm and only just in 30cm. I saw the
pair as both yellow, though this was by no means certain
regarding the companion star.
When discovered, the magnitudes were given as 10.1 and 10.8, but later photometric observations gave the more precise values of 10.19 and 10.66, reducing the Δm from 0.7 to 0.47. Since discovery by M.K. Jessep in 1929, little has changed in the position. If this is truly a binary star, we may have to wait sometime for some indication of motion.
TX Mus (11471-6524) is a type "AB" RR Lyrae variable, some 7.5'SW further from B2730. This 12.4 magnitude star is positioned 3'N of the 9th mag star PPM 778644 / HD 102466 (11472-6527). Varying between 12.4 and 12.8 magnitude in 0.473226 days or 11h 21m 26.7s, whose 0.4 rise in brightness occurs in about 13.6 minutes. The most recent epoch is 19th April 1925 at 18h 30m UT (2424260.264), so predicting when it falls in brightness is almost anybody's guess. Visual observation could confirm a more up-to-date epoch, but this still requires observations. We know little else about this variable star.
BC Mus / GSC8981:2285
(11475-6443) is merely 1.6'N from the Centaurus / Musca
border. This 12.1 mag semi-detached eclipsing binary can be
seen is a moderate field, with the PNe He2-73 due south and
at the bottom of the field. IC2966 is on the eastern edge
of the same field with BC Mus on the NW edge. (Actually
20'NE of IC2966 or 26'NNW (PA
345o)) Alternatively, use the
bluish 7.0 magnitude HIP 57451/ SAO 251582/ HD 102370/ BD
-64 564/ PPM 358966 (11466-6446) some 6.8'NE (PA
70o) The target star is marked by
the roughly 1.4' equilateral triangle of stars, whose apex
points due south, with the blue-coloured star to the east
being the variable.
BC Mus varies between 12.2p and 14.5:p over 3.511171 days, based at maxima on the 11th March 1927 (JDE 2424951.363), the ratio of the primary eclipse to the period is 12% - some 0.42134052 days. Seeing a deep 2.3 magnitude fall in brightness for an eclipsing binary is unusual, and to catch the magnitude drop of the eclipse the field would have to be inspected several times. Incidentally, northeast, by 10' to 15' from this triangle, is a small void almost empty of stars, while the encompassing fields are scattered with many stars below about 10th magnitude.
B 2730 (11478-6519) is the second but fainter pair placed in the same field and some 12.6'SSE of He2-73. Easily visible in dark skies using 7.5cm apertures, B2730 is a "new" double star that was first discovered by W.H. van den Bos but only measured as recently as 1987, presumable while they were measuring nearby COO 130. Separation was measured, also in 1987, as 6.4"arc seconds along PA 104o, being 9.5 and 11.5 magnitude. I saw this pair coloured as bluish and colourless.
Mu (μ) Muscae / HIP 58581/ SAO251597/ HD102584 / HR 4530 / EsB 334 (11482-6649) lies some 16'ESE of the pair of l Musca. (See Below) Although this star does not have a common name, it should be perhaps be called "Mumus", like the name given to the Crux stars north of it. This orange 4.74 magnitude K4 III star shows a remarkable colour and spectra, which is confirmed with the B-V value of 1.522. Mu Musca's position is exactly 1.6oS of the planetary He2-73 - leaving yet another method to finding the PNe's position. Appearing in the 19th Century "Epsin-Birmingham Catalogue of Red Stars" as ESB 344, and also appears in the updated catalogue produced by Brian Skiff "A Revised Catalogue of the Espin-Birmingham Red Stars" (1998). Hipparcos measured the parallax of 7.55±0.52mas suggesting the distance is some 132pc or 432ly. This star has a moderate proper motion, being in the order of +30.77±0.45 in RA and -16.25±0.48 in Declination. These motions are quite larger than the PPM Star Catalogue - certainly an unusual discrepancy. Mu Muscae is travelling the same direction as the last proper motion star L145-141.
JSP 500 (11486-5807) was a pair I looked for after observing the previous pair JSP 499. This pair can be easily found as it is directly 13.2'E of it, but about one magnitude fainter. JSP 500 can be placed in the same field as the three pairs listed above, if JSP499 is placed about 5'W. This pair is easier to split than JSP 499 as the 10.5 and 11.4 components are separated by 1.6"arc sec along PA 188o. Although easily seen to be double under high power in 20cm, the 30cm certainly made it appear more attractive, with the colours in both apertures seen as white. Other than the small PA increased change of 2o, little has been seen to change, so any true association remains unknown.
HU 1487 (11509-5553) is another pair that lies in the eyepiece field of NGC 3960. Lying 13'S (PA 169o), the two near equal components are 9.5 and 9.9 magnitude, respectively, being separated by 0.9"arc sec along PA 238o. Visible in 20cm, and 15cm on good seeing nights, this yellow pair contrasts nicely against nearby COO 129. Since discovery by W.J. Hussey in 1913, the two stars have decreased by 0.4"arc sec(1991) in the last ninety-odd years, and it is likely these stars are gravitationally connected.
TZ Mus (11509-6508) is fainter than UU Muscae. Discovered before UU Mus, it lies 6.9'NW at PA 306o and varies between 11.16 and 12.12 in the period of 4.944885 days. Epoch 2424259.37. This yellow-orange star can be checked, because of the wide Pair 1 (11515-6504) to the NE of TZ Mus is a mere 5.3' away. This white 10.0 magnitude star is PPM 778689, and I estimated the magnitudes as 10 and 11.5, separated by c.30"arc.sec at PA 20o. No one has listed this faint pair in any of the double star catalogues.
COO 130 / HIP57851 / SAO 251617
/ HD103079 (11518-6512) lies in the same field as the PNe
and appears as the single 4.89 magnitude star, and is plced
useful for finding nearby planetary nebula He2-73. S.I.
Bailey discovered this pair at the Cordova Observatory in
1894, during the required observations to produce the CD
Star Catalogue beginning in the 1890's. It is really
surprising that both John Herschel and H.C. Russell missed
it in their double star surveys. However, it is possible
that the star did appear single between 1835 and 1880.
Else, the accounting for this discrepancy is hard. COO 130
is almost 20.4'E (PA 99o) of
He2-73, and any low powered field marks three stars in a
bent line towards the southeastern edge. These stars have
respective magnitudes from south to north, of 7.5, 7.5 and
9.5, forming an odd-shaped triangle figure.
COO 130 pair is 5.2 and 7.4 magnitude, with the separation of 1.8"arcsec and PA of 159o as last measured in 1940. Resolution is possible in 15cm telescopes but this becomes much easier in 20cm. AOST2 claims this is ...just possible... in 7.5cm, but my four different observations between 1978 and 1981 using the 7.5cm f/10 reflector and 10.8cm Refractor, clearly could not resolve the pair - even under good seeing. I saw the colours as bluish and white, or perhaps blue and white, which is about right when compared with the primary's B4V spectra. This is another classic example of bright prominent double stars that we often neglected likely just because it is not either one of the prominent Russell, Herschel or Dunlop pair. Also featured in AOST2 as #483, COO 130's connection is stated as;
... the angle is slowly increasing but separation has not changed...Physical connection between the stars seems likely.
HLD 114 (11551-5605) is 1.2oNE from NGC 3918, and is the "top star" of the three to find the PNe. These two yellow 7th mag stars (7.3/7.7) are separated by 3.8" at PA 169o Since the discovery by E.S. Holden in 1887, the pair has slowly widened, while the PA has decreased by some 40o. As yet it is uncertain that this pair is physically associated, but if so, it is likely a very long period.
I 892 (11552-5659) lays 22'NE of from the planetary nebula NGC 3918, being the closest star to the PNe of the three recommended earlier to find the target planetary. Discovered by Innes in 1911, the 5.7 and 11.0 stars are widely separated by 57", these primary 11th mag star is again double, separated by a smaller 5.2". Known as I 892b, it forms a direct line at PA 122o with the distant third component. Burnham's states that the PA has slightly decrease since discovery, but the WDS 2001 suggests it has increased. The primary appears white in colour, while the others are too faint to tell. Since discovery, the I 892a pair has slowly increased at the rate of 1.1"/decade while the PA has changed very little. It is likely this is an optical triple.
Southern Astronomical Delights © Andrew James 2002 Sydney, Australia