RA : 12h to 14h
SOUTHERN DOUBLES :
DON 1095 ,
Southern Asterism -
Crux's Diamond ,
RMK 14 ,
BRIGHT STARS : Spica : α Vir ,
OTHER DOUBLES and STARS:
T8989:641:1 / PPM 779298 /
HD 113842 ,
DON 1095 (12047-6703) is a very faint pair first discovered in 1929 by H.F. Donner. Visually, the primary is around 10th magnitude, and lies 14.7'N of NGC 4071. By magnitude, this reddish pair is 10.7 and 13.8, with the separation of 4.5"arc sec along PA 339o. Little is known about this pair, and no one else has bothered to contribute much about it at all. DON 1095 A is listed in the Tycho catalogue as T 8986:2081:1 / GSC 35994:1, with the B-V of 0.988 confirming its reddish colour. Surprisingly, the parallax on the star is large 141.7±47.4 milliarc seconds (mas), corresponding to a close distance of 7.06±1.56pc. (23.0±5.1 ly.) A 20cm easily resolves the pair, though 25cm or larger would certainly improve this.
Southern Asterism (12052-6358) Cruxs Diamond or The Crosss Diamond lies in the SW corner of the constellation of Crux. This involves the stars in south-western Crux and the pairs (ζ1,2) Zeta, (θ) Theta and (η) Eta Crucis, and the star j Centauri. (This is not J Cen, which is a completely different star further to the west.) A diamond lying on its side, it centre is some 2.4oSW of Acrux. These four stars produce an asterism that is trapezium or diamond shaped that can be seen with the naked-eye - even in the city-lights. Each axis is 3.2o and 1.4o It is useful in trying to find several pair in the regions. We already have the Jewel Box in this constellation, so should not we name this Cruxs Diamond or something like the Crosss Diamond.?
W Crucis (12120-5847) is an EB-type eclipsing binary that lies 3oW of the bright star Delta (δ) Crucis and positioned in the middle of three 8th magnitude stars which almost lie in a perfectly straight line. The two either side making good comparison stars. Although this star is relatively faint, the variations in brightness are larger than most eclipsing binaries. The magnitude range is from 8.5v to 9.3v and the UBV light observations show the magnitude range as 9.04B and 10.38B. What is most unusual about W Cru is the long 198.53 days (6.2 months) orbital period. The light-curve parameters determine both stars are separated by 270 million kilometres and that the primary is a supergiant and the secondary a giant. Classed as a giant eclipsing binary, the primary displays the mean diameter of 93 times that of the Sun, while the companion is 116 times. In luminosity, the stars are 10 383 L and 2 884 L while the temperature of the two stars is 4 200K and 3 940K. Total mass of W UMa is 19.85 ΣM, with the individual masses calculated to be 11.67 M and 8.18 M, respectively. Its primary, because of its diameter, is likely in a later state of evolution and certainly has exceeded its Roche Lobe, and consequently the gravitational proximity makes this star appear 'tear-drop' in shape. W Cru's secondary component is believed to be also highly distorted, filling some 85% of the Roche Lobe size criteria. Due to the separation and long orbital period, the effects of the distortion could be considered minimal especially when compared to the effects produced by the total light curve. The combined spectrum reveals the spectral and luminosity class as G2 Iab - indicating supergiant stars. Bright emission lines have characterised this in the observed spectra.
RMK 14 / HIP 59654 (12140-4543) in Centaurus is a surprisingly bright pair in a field of challenging and other faint objects. Lying 2.9oNE (PA 52o) of the faint planetary nebula of Longmore 6. This orange and white pair has 5.60 and 6.76 magnitudes components. Comparing this to the "Delta-m Catalog" in the WDS (2001), the four stated values; being 0.95, 1.17, 1.19 and 1.21, respectively, give a mean μ of 1.13, and close to the 1.16 in the WDS 2001 "Main Pair Catalog." The two stars are separated by 2.7"arcsec along PA 243o (2002). The changes since Rümker discovered this pair find the separation reduced from 4.0" to 2.7" and the PA reducing by 5o. AOST2 describes Rmk 14 as;
Separation and angle of this orange and white pair are slowly lessening; it is an easy object dominating a well-sprinkled star field and common proper motion indicates that the stars are connected.
The spectral class of the primary is K3III (B-V=1.400) while the Tycho gives only the photometric data for both stars as Rmk 14 A ; B-V being 1.501±0.007 and Rmk 14 B; 1.216±0.008. Rmk 14 A is also spectroscopic binary. If the pair is truly connected then Rmk 14's period is certainly long. Evidence from the proper motions suggest attachment but the period might be long of the 5.76±0.83mas parallax from the Hipparcos satellite is to be believed. The distance here being 173pc or 566ly. This lovely pair is great in telescopes larger than 10.5cm.
Epsilon (ε) Muscae
/ HIP59929 / SAO251830 / HD106849 (12176-6758) lies
2.2oNW from α Muscae, along
Musca's western wing. ε Mus mean magnitude is 4.06
and the spectral class of M5 III. Considered as a SRb red
variable, the period varies over about forty days,
fluctuating between about 3.99 and 4.31 mag. Like all SRb
variables, each display unpredictable variations caused by
multiple simultaneous periods. Paradoxically, SRb's can
also remain at constant brightness for long periods, before
again resuming their fluctuations. Little information
exists on this variable, with the period and amplitude
being imprecise. Parallax πis 0.01080±0.0048 and
the high proper motion of pmRA = -231.26 pmDE = -26.37
[Note: Motions are similar to Epsilon (ε) Crucis/ HIP60260/ SAO251862/ HD107442 (12213-6024) some 7.5o due north of ε Mus in both magnitude, π = 0.01430±0.0056; pmRA = -171.06 pmDE=91.82 K3/K4III B-V=1.389.]
Zeta Muscae / ζ 1,2 Mus / HDO 215 / HIP 60320/ SAO251866/ HD107566 (12221-6731) is a 5.15 magnitude star 35'NE (PA 46o) of ε Mus or 1.7oE and 14'S of the planetary nebula, NGC 4071. Again, this is a bright star with a faint companion, separated by 32.4" at PA 130o. In an attractive background of stars, this white/ yellowish pair can easily be seen in 7.5cm. Magnitudes are 5.2 and 10.7.
α Cru / Δ122 &
Δ123 / α 1,2 Cru /
Alpha Crucis / Acrux / α
2 Cru - TOK 7 Ca, Cb, Cd
(12266-6306) is likely in the Top 3 of all southern doubles
and multiples and certainly in the Top 5 of the
entire sky and is often the first or second targets for
newcomers to amateur astronomy. Alpha Crucis is one of the
brightest and most prominent of the southern binaries,
whose magnificent 1st magnitude sapphire blue pair of 1.1
and 1.5 mag. and is presently separated now about 4 arcsec.
There is some evidence that the two are showing a seemingly
reducing separation over time. This is "must see" double for
southern observers shares its prominence with
Spica / α Virginis being both
spectrally, chemically and approximately by mass.
In my own opinion Acrux is the second best double in the sky and only just falling behind only Alpha Centauri. (Any northern observer might have either Mizar or Alberio in these two places, but Acrux is actually much brighter.) In regards of the constellation of Crux, it is either the best or second best object, whose place is strongly contended with NGC 4755 - The Jewel Box - but I leave that debate to you!) The C component is some 90" away, and is about 4.8 magnitude, and is easily seen in 7x50 binoculars with care. (Saw this a moment ago looking out my back door, however, because of the smoke from the bushfires, both appear orange - more like p Eridani in fact!) An additional 12.5 mag α Cru D??? field star lies about midway and slightly east of the wide pair, making an obvious right- angle triangle. Acrux's field is also sprinkled with many stars.
Another interesting problem is just about to be corrected with the WDS, and this is the case of Alpha Crucis (Acrux) is the 14th brightest star in the sky.
According to R.H. Allen "Star Lore: Their Name and Meaning", and stated by Robert Burnham in his Celestial Handbook, that Acruxs duplicity was discovered by;
...some Jesuit missionaries sent by King Louis XIV to Siam in 1685.
There is significant debate on whether they saw the main AB
pair or the more distant 'C' star some 90 arc sec away -
neither of which is often mentioned in many common astronomical
sources. The "Binary Stars" by Robert Aitken says that it was
Father Fontenay discovered the pair from the Cape of Good Hope
in 1685, though I have never found out the source of this
statement. This incidentally place Acrux as the FIRST
far southern double star to be discovered and even before Alpha
Centauri in 1689!
However as to the discovery of the duplicity of Acrux, it is likely that Robert Aitken is correct about this. Since Burnham made the statement in the first place, the discoverer has remained as the statement above. (I have seen no statements since the Burnham's Handbook was published in any text that gives Father Fontenay as the discoverer - the it is uncertain if he saw the AB pair or the AC pair). The discovery of the main α Cru AB was truly identified by James Dunlop in 1826, and the WDS has recognised this as such - a point I will get to in a moment.
Acrux is actually a complex multiple, perhaps with at least
five (5) components, whose structure and association is still
open to some debate. The 'A' component
α1 Cru A is actually the
spectroscopic binary α Cru Aa whose period is some
seventy-nine (79) days long. The first estimations of this
period were made by Neubauer, F.J.; Lick. Obs. Bull.,
15, 190 (1932) gave both 'A' and 'B' as spectroscopic
binaries both with the period was about a day. In 1934,
Luyten, W.J ; PASP., 47, 196 (1935) found that
the periods could be matched to the data as having 59.31 and
56 days, respectively! [Some difference
perhaps!] Luyten had also produced the orbital
elements for both stars. Thackeray, A.D. and Hill, G. ;
The System of Alpha Crucis.; MNRAS.,
268, 55-59 (1974) said that the period was more like
75.769 days. They also found that they could not explain
the spectroscopic α Cru B data, and from their
additional observations, they concluded;
There is no evidence from the material [Neubauer or Thackeray/ Hill] that star α Cru B is a binary, and in particular no evidence for variations in a period of near twenty-four (24) hours.Much disinformation appears in the literature, many sources having a combination of data extracted from various papers or common amateur astronomical texts.
WDS Information: The WDS 2001 on the three amin stars gives the following information;
|Δ252 AB||1826 to 1994||5.4" to 4.0"||114o to 114o||A=1.25 B=1.15 mag.||B1V||pmRA: -0.36 pmDec: -012|
|Δ252 AC||1826 to 1991||87.2" to 90.0"||200o to 202o||A=1.25 B=4.80 mag.||B4IV||pmRA: -042 pmDec: -012|
|Δ252 BC||1859 to 1947||89.8" to 90.6"||205o to 205o||A=2.3 B=6.0 mag.?||B1V||pm RA -0.36 pm Dec -012|
Δ252 AB and AC have similar proper motions and are certainly related. However in 1907 Token found a further three nearby stars or possible components were found by speckle interferometry. These are now catalogued as TOK 7 Ca, TOK 7 Cb and TOK 7 Cc, whose designations were added by the United States Naval Observatory (U.S.N.O.) on the 1st November 2001. It is uncertain if these star could eer be seen visually as the main star are overwhelmed these components brightness. There 1997 positions were made as follows;
|12266-6306||TOK 7 Ca||52o||2.2"arcsec|
|12266-6306||TOK 7 Cb||214o||4.9"arcsec|
|12266-6306||TOK 7 Cc||119o||6.7"arcsec|
The "WDS 2001 Notes" gives;
DUN 252 /α1 is a spectroscopic binary and shares common proper motion with HR 4729 and 4731. It is cureently thought there are at least five (5) components in the system. Both the coordinates and proper motions are similar being obtained from ACRS, PPM, IRS, FK5 catalogs.
Acrux is catalogued in the WDS (and elsewhere) as Dunlop
252 (Δ252), and this appears in Megastar and many
other sources. However, this is perplexingly wrong.
James Dunlop in his double star catalog (Dunlop, J.;
XVII. Approximate Places of Double Stars in
the Southern Hemisphere, observed at Parramatta in
New South Wales.; Memoirs. Astronomical
Society of London, 3, 257; (1829)) is;
Δ122 and Δ123 (12266-6306) are given for Alpha (α) Crucis - with DUN 122 for the AB pair and DUN 123 for the AB-C pair. At first I was fooled by this in Megastar Versions 3.0, and 4.0.31 and 5.0.5, as if you type either Δ252, Δ122 or Δ123 you still get Alpha Crucis. But if you look at the data box you still get Δ252. It turns out the Megastar cannot identify the pair in question, it finds the last star listed in that catalog you are looking up. Hence Δ122 and Δ123 dont actually exist! DUN 252 is also used in Sky Catalog 2000.0. Amazingly, Astronomical Objects for Southern Telescopes (AOST2) fail to mention the catalog number as Δ252 for Alpha Crucis. (Note : This is object No.522 in AOST2 - coincidently this is 252 if you switch the first two numbers!)
Furthermore, Dunlop's pairs appear in Right Ascension order. Hence, Δ124 is &gamnma; Cru (Gacrux) and Δ125 is Beta Crucis (Mimosa and NEVER Becrux!). Here is an example. According to James Dunlop from the same source given above, DUN 252 is actually the Bode star 29 Tucanae, whose 1827 position is 23h 34m 00s -65o 22' ( 23h 43m 37s -64o 24'). Dunlop says this is an orange sf 6 and 8 magnitude stars a position angle of 27.4o and the separation of 3.4' - a wide double indeed! 29 Tuc is located 2oNW of 4.5 magnitude Epsilon (epsilon;) Tucanae. This particular pair also doesnt appear in the WDS for obvious reasons. I also checked in Dunlop's 629 deep-sky object to look for DUN 255, and find it is an elliptical nebula no where near Acrux.
The source of this error is likely the Index of Double Stars (IDS) of 1963, and is the first reference I could find with this problem. Worst the usage has now become quite universal and the error appears in many many sources and has stayed so for many decades.
Again this highlights many problems with southern stars that have been perpetuated over the years.
Gamma (γ) Crucis /
Δ124 / Gacrux (12312-5707) at 1.67
magnitude is the 23rd brightest star in the sky, An
orange-red colour, Gamma Crucis in the northern part of the
Cross and is left with the unfortunate proper name of
Gacrux. This both ugly and inelegant name still makes me
wince, and was first given it by Elijah H. Burritt in the
1840's. When viewed with binoculars or a small telescope,
the bluish-white 6.39 mag companion (Hartung in AOST1 says
white) makes the pair Δ124 AB, and this contrasts
nicely with orange-red primary. For some reason, the WSD
2001 gives it a slightly lower 6.45 magnitude, though much
of the earlier data present the view that the magnitude was
6.71v. The component is presently a very easy 125.4" away
(1991), and it seems that this distance over time continues
to increase by an amazing about 39.2"arcsec per century.
From this we can estimate that in 2002, the separation is
about 129.7"arcsec, and 130.1 in 2003. Also the PA since
Dunlop discovered the pair in PA has also decreased by
17o or about 0.8o per
decade. Today's PA is about 26o
The brightest star in this multiple is Δ124 A is catalogued as HIP 61084 / PPM 341058 / SAO 240019 / HD 108903. This star displays a significant proper motion of -264.33±0.47mas in Dec and 27.94±0.54, so it is heading almost due south from its position and roughly towards Acrux. It parallax is given as 37.09±0.67mas, which gives Gacrux a distance of 26.96±0.49pc. or 87.93±1.60ly. Spectrally the primary is M3.5 III, and the B-V is 1.516, meaning it is a cool giant star. Gamma Crucis A itself is a variable star that has been designated 34G Cru or as NSV 5672, which varies irregularly between 1.60V and 1.67V magnitude. The prism image is noticeable revealing several prominent dark lines that have also been discussed by Hartung in ASOT1 (1968). This the first star I ever looked at with a spectroscope, and I could see the main lines Hartung was talking about immediately - two in the red and orange, two in the yellow and green, a strong green band, and (several lines in the violet. This is a great example of the spectra of stars, and worthy to someone who hasn't seen this before.
The companion Δ124 B is of spectral class A3V, displaying a B-V of 0.167. Listed as T8654:3421:1 and not in the Hipparcos catalogue, the measures however, are still as telling. All three parameters - pm RA, pmDec and Parallax are well outside the primary's data. Ie. pmRA; 10.20±2.80mas, pmDec; -15.90±2.10, while the parallax is 4.20±2.80 - suggesting distance of 238pc or 776ly. There is also significant agreement in the PPM star catalogue, so both these stars are certainly unrelated.
Another star is classed in the pair, and this is Δ124 C. Dunlop discovered this deep yellow star in 1825, but it was not measured until H.C. Russell did so twice in 1879 - and it hasn't been measured since! At 9.5 magnitude it lies (according to the WDS01 at 155.1"arcsec from the primary along PA 82o. Looking at the Tycho position of some ten years ago (1992), the only catalogue available with this star, the position is now more like ~234o along PA 78o. The Tycho data also gives a significantly different proper motion and parallax; being pmRA; 103.30±13.5, pmDec 23.70±14.5 and the parallax of 19.40±14.00. Although these errors are quite large, they are in different directions, suggesting this star is unrelated to either Δ124 A or Δ124 B. Although the star hasn't had a spectrum obtained as yet, the B-V of 0.66 tells us it must be either a late G-type star or early K-type star.
So although all three stars are not physically connected, the AB pair has a wonderful colour contrast, that is especially attractive with smaller instruments, with the third star adding to the star-spangled field. This is a wide and easy double, easily seen in apertures as low as 5cm, and still colourful in larger apertures.
Beta (β) Musca / "Bemusca" /
R 207 / Syd 1-207 / HIP 62322 / SAO252019 (12463-6806)
rates somewhere in the Top 10 of southern pairs, and is a
"must see" for all southern amateurs. Culminating on the
12th May at 9pm and 27th March at midnight, Beta Musca is
the most northerly star of the main trapezium-shaped body
of the "Southern Fly", and appears
1.3oN along PA
40o, from Alpha Musca
(12372-6908). A renown binary system, R 207 was first seen
by H.C. Russell at Sydney Observatory mid-evening on the
15th April 1878. In 1882, Russell claimed in "New Double
Stars found while measuring Herschel's Cape Stars in 1882",
that β Musca was, ...this is one of the
closest doubles I know. Measures made during the
1880's on this star were prolific - twice by Russell
himself, and eight times by J.A.Pollock. As mentioned in
AOST2, the first measures, and subsequent ones at Sydney
Observatory. Russell was well aware of the significance of
this pair, and had the fortune to find R207 having its
fastest orbital motion in the orbit during its closest
approach (periastron) sometime in the early 1870's - later
determined from the observed orbital motion as 1872.290 -
10th April 1872. As Herschel had missed this obvious but
difficult pair, it was natural to assume that the star had
begun to significantly widened since Herschel's
Magnitudes are 3.6 and 3.9, with the combined magnitude being 3.04, but the "Sixth Orbit Catalog" gives 3.04 and 3.52. PA is presently about 45o (2002), with the separation is c.1.3"arc seconds. Presently both stars can be easily seen in 20cm, but remains difficult in anything less than 15cm.
...the stars reached a separation of 1.4" in about 1950 and now seem to be gradually closing again; 12.5cm will separate the stars on a night of good seeing. This is a long-period binary, and a fine object in a starry field.
The Washington Double Star Catalogue 1996 (WDS96) states in the notes that the period is 383.12 yr., a=1.74"arc sec, while the motion is direct. Component 'A' has also been observed to have a variable radial velocity, so it might be also binary itself. The "6th Catalog of Binary Stars" (2002)) gives the orbital elements as;
|Elements :||P = 383.120 yr||T = 1872.29||a = 1.735||e = 0.526||i = 61.30o||ω = 98.32o||
The most reliable data to date was first published by F.
Mourao (1963) and appeared in (Bul.Astr.Obs. R.Bel.,
5,143 (1964)). All the orbital elements remain
uncertain, as only a quarter of orbit has been observed,
and this is all just after periastron - the most critical
position for determining orbital elements. I have used the
latest data to draw the apparent orbit. Closest approach
was sometime in the beginning of 1872. The pair then
widened until its first maxima were reached in the mid
1960s. Presently the pair is slowly decreasing in
separation, and this will continue until 2 029AD, where the
separation reaches 1.25"arcsec - the second minima in the
orbit. Again the orbit increases in separation, reaching
the greatest apparent separation of 1.715"arc sec in 2
165AD. About the same time, observations of Beta Musca will
increase in precision, and the true period, etc. of the
system will be properly known. Over the next hundred years
or so, after about 2 165AD, the separation and position
angle changes more rapidly. By 2 258AD, the separation
again reaches the minimum separation of 0.38"arcsec, making
it difficult pair in most amateur telescopes below 30cm,
and even larger if the seeing is poor.
Orientation of the true orbit is placed as along the dotted lines in Figure xx. This is inclined 8.3o to the east-west line, with "P" and "A" being the date of the respective periastron and apastron of the orbit.
Hipparcos found the distance as 95.41±5.56pc (311.2±18.1 ly) from the Sun, using the measured parallax of 10.48±0.65mas. The results here seem questionable. For example, the parallax measured in the Tycho catalogue gives the distance as 39±4pc (25.60±6.10mas), more the two-and-a-half times larger than Hipparcos. Using the dynamical parallax, the theoretical distance of the system derived from the magnitudes and orbital data, finds the distance of 50.6pc (164.9 ly.) I again calculated this using the "full" Baize-Romani method (first determined in 1945) and obtained 51pc. Such divergence in the values makes the mass and size of the orbit as doubtful. From the available data, I think that the Hipparcos distance is likely too large, and it is certainly much closer than the quoted error. It is possible that the proximity of the two stars might be causing an incorrect measurement. The Hipparcos satellite had significant problems, due to the configuration of the optical system, in measuring pairs between about 1.5 and 0.2 arc seconds. β Musca, because of the stars brightness, lies on the boundary of this region. Overall, I think the 51pc distance is likely closest to the truth. Compared to the Solar System, Beta Muscae's true orbital dimensions are huge. If the Hipparcos distance of 95.41pc is correct, then the dimensions of the true, then at the time of periastron passage the two stars are some 42.4AU apart, this increases to the furthest apastron distance of nearly 200AU - five times the orbit of Pluto! If the correct distance is closer at 50.6pc, then the proportion of the orbital size is smaller, dimensioning periastron at 22.3AU and apastron as 104AU. Proper motions suggests the motion of travel is moving further south each century by some -40.40" in RA and -10.32" in declination, with Beta Musca is moving way from us at about +42kms-1. Spectral class of both main sequence stars is B2V and B2.5V, implying effective surface temperatures of 24 400K and 20 950K, respectively. The measured B-V for both star's combined light is -0.178, reflecting its visual blue colour. Absolute magnitudes (Mabs) are -1.3 and -1.0, respectively, making the two stars 275 L and 208 L times the luminosity of the Sun. Using this data, and applying the results from the dynamical parallax, produces the minimum value for the total combined solar mass of 4.6 M, and individual masses of 2.33 M and 2.28 M, respectively. Furthermore, the minimum radii of each star are about 3.0 R and 2.6 R, roughly four million kilometres across. Limitations on mass, radius and absolute magnitude using evolution theory place possible value about 30% to 40% higher than the ones quoted above.
In all, this is an interesting system and challenging for those with moderate apertures. Due to the brightness of the two stars, cleanly separating the two is highly dependant on the seeing. Using 20cm (C8) at 225X and 333X, I have observed the pair on more than three or four dozen times, seeing the two Airy disks clearly separated perhaps only 40% of the time. (Incidentally, I have tried without success to observe this pair using the 30cm (11.75") Refractor at Sydney Observatory in 1977 and 1978. This was mainly limited by the seeing, however!)
Beta (β) Crucis /
Δ125 / I 362AB / Mimosa (12477-5941) is a
blue supergiant star and is the 20th naked-eye star in the
sky having the diameter some thirteen times larger than the
Sun. Beta Crucis "A" is a Beta Cepheid-type variable star,
some of which appear also in the nearby Jewel Box / NGC
4755 which is about 1oSE of
Mimosa. Observation of Beta Cepheids are often found
to vary in periods anywhere between 0.1 to 0.7 days,
displaying only small changes in luminosity by between 0.1
and 0.3 magnitudes. Spectral classes are often found
between B0 to B3, and this applies across all the seven
main categories of luminosity classes. β Crucis is of
B0.5III-IV spectral type. Common bright examples of field
Beta Cepheids included nearby to the Jewel Box - δ
Crucis λ Crucis and β Centauri (See NSP 16 at
β Canis Majoris.
Beta Crucis varies between 1.28V and 1.31V magnitude (0.034V in recent estimates) over 0.2365072 days. It also shows seven different harmonic periods combining to producing the main "P0" period. These other periods are;
|Period No.||Period (days)||Magnitude Range|
β Crucis has a nearby companion that is also known as
Δ125 AC, is about 2.5'SW or 361.7"arcsec (2002 AD)
away along PA 23o. It appears as
a deep ruby red of about 8.6 magnitude star EsB-365.
Easily seen even in 7.5 cm telescopes, and admired by Sir
John Herschel, it truly came to prominence within the Espin
Birmingham 1900's catalogue because of its remarkable
spectra. The displayed colour is a testament to both its
grandfather-like age and remarkably cool temperature.
EsB-365 is technically known as a carbon star, mainly as
the spectral lines of Carbon and Nitrogen are quite
prominent, while the other common lines are either faint or
are not seen at all. The positions have decreased by
12.4"arcsec in 124 years since last measured, while the PA
has remanded fixed at 23o. This
10.0"arcsec per century suggest that in the sky both stars
will join together in the year 4 550 AD. About the year 4
050 AD and 5 050AD, this will become one of the best colour
contrasting pairs in the entire sky. It is still almost
certain that these two stars are not associated.
A second companion is I 362 AB. which is another white star of 11.4 magnitude and extends about 44.3 arcseconds along PA 322o from the primary.The positions of the primary and this star have not moved since Innes discovery in 1901.
PLEASE NOTE: The name for MIMOSA lately has the name BECRUX now used in modern star atlases and software, including Astronomy 1999. This was introduced in 1993 by American observers. In no circumstances should this name be used nor promoted!
Comment: Nearby is the Jewel Box / NGC 4755. This magnificent open star cluster, the was discovered by James Dunlop (Δ301) that John Herschel named the Jewel Box NGC 4755, which is both east, and slightly south of β Crucis. NGC 4755 is a small A shaped asterism and is different than most open cluster because of its 6' size and numerous bright stars. This is a nice cluster in a starry field whose distance is some 2.4 kpc. (See NGC 4755 Text on this Homepage.)
Mu (μ) Crucis / Δ126 (12546-5711) is located 2.7oN, and a little east, of β Crucis. This broad, bright bluish pair has no common name. (Mucrux might be a suitable name.) Discovered by Dunlop in 1826, and listed as Δ126 in his catalogue, this beautiful blue duo is located in a star-studded field. It is certainly easy to resolve in small telescopes. The magnitudes are 4.03 and 5.10, while the separation is a wide 34.7"arc sec at PA 17o. The spectral class are B2IIV-V and B5Vne, respectively. Looking at the Hipparcos data some credence adds that this pair is likely attached, as the proper motions and distances are quite similar. Ie. Distances are μ1 = 116±7pc (or 361±24ly.) and μ2=111±7pc (or 361±24ly.), Common proper motions; π1=RA:-30.45±0.37"arc sec and Dec:-13.55±0.41"arc sec. And μ1=RA:-32.45±0.37" and Dec:-10.93±0.40". This gives the mean distance to Mu Crucis as 113.5pc or 370ly. If this is so, then the two stars in space are separated by some 0.0192pc or 0.063ly suggesting the period maybe as long 30 000 years. The second star, μ2 Crucis, is Gamma Cassiopeia-type (GCAS) variable, changing by 0.19 mag in an unknown period. Little has changed positions since discovery, and the twelve other observations have shown little additional data. This pair is a good test for 7x50's binoculars that can just separate the duo, but likely during poor seeing, this might be a bit more difficult.
Δ127 (12598-5555) is one
of the nicest pairs I have seen and I have taken great
delight in observing this pair numerous times in the last
thirty odd years of double star observing. Puzzlingly
missed in both the AOST's and most other noted deep-sky
descriptions, like because it is overshadowed by the
brighter gems in nearby Crux and entaurus. This pair cqan
be found in mid-southern Centaurus and the north-eastern
corner of Crux. It is easily located some
61o) of the magnificent Mu Crucis
(Δ125). Dunlop discovered the pair sometime in 1825,
although his first measure appears as 1826 in the WDS01.
Δ127 appears as two distinct blue stars of 8.27v and
8.98v magnitude and is presently aligned along PA
126o. Easily seen in 7.5cm, the
separation has slowly widened from 13.0"arcsec to its
present 16.8"arcsec (2002). Dunlop listed the pair as
"Anonym" and gave the 1827 position as RA: 12h 49m 00s Dec:
-54o 57', precessed to 12h 59.2m
-55o 53' (2000), and identifying
the 7th and 8th magnitude star about 5'W of the positions
given for Δ127; in the WDS01. Although Dunlop's
separation is given as 10"arcsec, it is likely that this is
an error by him, as the measures since then make it
impossible for it to have been this close. The WDS01 seems
to be sligning itself to use the Herschel measures that the
observation was made in 1835 for the separation and using
Dunlop's 1826 PA of 51osf
(129o). Is this really an error
in the WDS01?
Looking at the general observational data, DUN 127 A is HIP 63422/ PPM 341501/ SAO 240455, which Hipparcos gives as the 8.27 magnitude stated above. Also the parallax is 13.54±3.02, the spectral class is B7IV/V and the B-V=0.040. DUN 127 B is HIP 63424 / PPM 341502 / SAO 240457 and gives the fainter magnitude of 8.98. Parallax is stated as 14.15±7.02mas, suggesting the mean distance of 70.7pc. Dun 127 B's spectral class of B9 matches near to the B-V of 0.110.
Also from these data, both the parallaxes and proper motions seem very similar, and we can conclude that these two stars have a very high probability of being gravitationally attached. The Tycho data matches the Hipparcos data quite well except for the cpm which are significantly different. Tycho gives the magnitudes as 8.21 and 8.90, while the PPM says 8.5 and 9.1. Overall the Δm;'s are 0.71, 0.69 and 0.6, and although not listed in the WDS02's Deltam catalogue, the mean of the Hipparcos-Tycho value of 0.70 seems about right. The Guide Star Catalogue lists the primary twice as GSC 8652:1908 and GSC 8652:192. It is likely the measuring machine has read the individual stars once as the "A" component and again as the combined "AB" component.
Overall, Δ127 is contained in a field of many 10th and 11th magnitude stars, which I thought seem to be winding NE to SW across the field. This is a lovely wide pair.
I have identified four faint pairs in the field using the 20cm where the limiting magnitude was about 13.8. These pairs are not listed as pairs, as such, but they can be seen in the 18'x18' STScI image surrounding Δ127. (See Attached Image)
Δ127 Pair 1 (12599-5548) is a north-south 11th and 12th magnitude pair (PA of 6o) and 18"arcsec apart. Both have the respective magnitudes of 11.3 and 12.6 in the GSC matching fairly well with my estimates. Pair 1's position can be identified easily because it is in the same field about 7.4'N of Δ127.
Δ127 Pair 2 (12594-5550) appears 6.0'NW (PA 325o) of Δ127. I estimated the magnitudes as 11th and 13th and the separation of around 15"arcsec. Using the GSC star data, the magnitude of the primary is GSC 8652:263 at 12.4 magnitude while the secondary star GSC 8652:1538 is 13.3 magnitude. Positional differences is about 17.7" along PA 80o. It can be identified as the pair is the most eastern of a brood of nine 10th to 12th magnitude stars and also being closest to my Pair 1. I saw both stars displaying just a hint yellowish and slightly dingy-red.
Δ127 Pair 3 (12596-5558) is the second brightest in my listing and lies 4.0'SSW of Δ127. The primary is 11th (GSC says 11.2) magnitude and the companion is 12th (GSC says 12.8, though I estimate it is slightly brighter than this. Pair 3 is 19.6"arcsec apart along PA 246o (WSW). The bright star is GSC 8652:581 and I thought it a tad bluish. I saw no colour in its companion.
Δ127 Pair 4 (13007-5603) lies some 11'SE (PA 137o) from Δ127 and is the brightest in my listing. Pair 4 A is GSC 8652:116 and is given as a 9.9 magnitude star - the most northerly star of a 2' triangle of c.9th magnitude stars. The Pair 4 B companion is listed as a 12.6 magnitude "Non-Star" even though it appears on the STScI image. I thought it was slightly brighter than this, and certainly brighter than seen in the image. I calculated the distance apart as 15.7" along PA 314o (NW). This seems about right.
Δ127 Pair 5 (13009-5550) is another pair I first noticed on the STScI image. The GSC gives this as an 11.0 magnitude "Non-Star" though it is clearly visible. I estimate the companion must be at least 13.5 magnitude and the separation must be about 5" to 6"arcsec aligned toward PA 260o. I haven't tried to observe this star, but it should be visible in 20cm, and definitely in 25cm or 30cm.
Several other pairs are in this field, though they are of little interest as they are a little too wide. In the 26mm Plössel with 20cm appears at the SW edge of the field (some 18' away from Δ127) is a obvious wide unlisted 9.7 and 11.1 magnitude pair separated by about 36"arcsec around PA 45o. The primary is deep-yellow in colour and its companion seems white.
NGC 4852 / Mel 116 / Cr 266 (13001-5937) is a moderately bright open cluster in Centaurus some 1.6oE (PA 89o) of Beta Crucis / Mimosa and lies to the NW of the Jewel Box NGC 4755. NGC 4852 has a total of magnitude of 8.9, the cluster is surprisingly obvious, especially as it is not a very familiar cluster to amateurs even though it is quite near a bright star. There are some sixty stars associated in an approximate diameter of 11'arcmin. It is classed in the Trumpler classification as 1 3 r -.
I 363 (13016-6751) was discovered by R.T.A Innes from South Africa in 1902, and can be found 43'W of the tiny planetary nebula, IC4191. Although the field is liberally sprinkled stars, I 363 is easily identified, as it is the only bright star in a medium magnification eyepiece. Confirmation of the pair is easily made as there appears the 12th mag Mira variable FU Muscae. (Mentioned below) The white A2V pair of I 363 is listed as 8.7 and 10.2 mag, separated by 2.7"arc seconds along PA 193o Little has changed in the star's relative positions, and if these stars are truly associated, the period must certainly be long. A 15cm is required to easily resolve the pair, but it is worthy while trying this in 10cm.
FU Muscae (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 for;
V495 Cen (13016-5605) was
discovered in 1938 and can be found by moving 18'SE of
& Delta;127. Its light-curve was first ascertained from
Sydney's Riverview Observatory by Father D. O'Connell in
1953 (Ric. Astr., 3, N2 (1954)). Appearing in
the same field the pair is an eclipsing binary that appears
in the middle of two other 11th magnitude stars some 2'
either side of it. Using the latest GSCV4 (2001) contends
the magnitude ranges between is 10.4p and 11.9p in the
period of 33.4871 days. Magnitudes during primary eclipse
may drop, according to this same source, by takes some 9%
of the period - a time of almost exactly three days (3.01
days). Any observer looking successive nights during the
time of the main eclipse could easily confirm the drop by
looking three nights in a row. Here the brightness would be
at normal brightness, drops towards the minimum brightness,
and on the third day rises back to its original magnitude.
This an easy experiment to do, especially if you have never
before seen an eclipsing binary in action "so-to-speak".
You would need at least 10.5cm to achieve this successfully
- 25cm or 30cm if observing from suburban skies. Less
eventful is the secondary minimum takes some 4.2% of the
period dropping by about 0.2 magnitudes (10.6) in 1.41
days. Overall, between both minimums are 52% (17.4133 days)
of the whole cycle. V 495 is classed as a "EB/DS" -
Eclipsing binary as a Detached system, where the primary is
a subgiant star that has not evolved enough to fill it
particular roche lobe.
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 2004 ;
All results above are in three period length intervals 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.
Ie. 24 Jan 2002 @ 08h has the next minima on 26 Feb 2002 @
The second (or next) minima is on 19 Sep 2003 @ 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 (17days 10hours) to the dates above or too those that have been calculated.
Note: The exact time of primary minima is likely to 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.
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
61o) of Δ127. It was
discovered by John Herschel in 1834 who found the
separation as 18.0"arcsec aligned at PA
220o. The WDS96 oddly gives the
first measure as 1894 (Sep. of 22.0" at
PA219o), 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 214o 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.
COO 147 (13033-5936) is placed directly 2oW 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 nortlyh position angle of 358o. 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 344o to 358o. In the next few centuries these stars will be harder to divide into two in the telescope. 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.
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 292o (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.
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
263o 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.
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" along the mean
position angle of 27.08o. 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 Observatorys 7.25" 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
R213 is easy to find, being directly 2.5oE of Beta Crucis 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 - but the WDS03 gives 6.59 and 7.04V. Several Δm observations gives and average of 0.31 for this double.
E.J. Hartung in AOST1and 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.
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 22o from the 27.1o since 1874.
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.
Comment : 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
109o whilst the separation has
reduced from 5.5"arcsec to its present 5.1"arcsec
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 169.4o, his given location is in reality some 1.2oW (PA 270o) being now within the neighbouring constellation Crux. 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 164o (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 Russells, which have been previously deleted as wrong. As the R.A. and Dec. 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.
Theta (θ) Musca /
RMK 16 (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 Rmk16AB. The field is star-studded, and the
addition of 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 2000, finds the two stars remaining relatively
fixed at 5.3" separation along PA 187o . 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 particular "heavyweight" system joins the ranks of very few known massive stars. Classed as a spectroscopic and a eclipsing binary, however, the "monster" companion remains invisible to all amateur telescopes. In 1996, this binary was resolved by interferometry, which the WDS 2000 now includes as the pair CHR 247. The companion "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 inclination c.100o. 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 this system, finding the two stars orbit almost along the line of sight (c. 1.51o), with the orbit being highly elliptical. Batten et.al (1985), gives the change in separation between 1 510 000 to 11 000 000 kilometres. Overall, the combined mass is determined to be 11, subdividing approximately into the respective masses of 6.9 and 4.1. 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 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 likely be obtained to refine this.
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 16o) from R 213. (*See Below) Little is known about this variable.
WW Cen (13094-6015) is a fairly
bright SRB semi-regular located 28'SE (PA 147o)
from R 213 and some 2.5oE 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 246o). 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 variables 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 Tychos 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 170o). 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"arc seconds along PA 20o. I saw no colour in this faint pair in 20cm, and separated the two in moderate magnification.
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 87o) 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"arc
seconds along position angle 146o. 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. Ie. 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. Ie. 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 96o 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 (132o)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.
J Centauri / Δ133 /
Δ133 AB-C / V790 Cen / HIP 65271
(13227-6059) is a distinctly blue double star/ triple 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 343o.
(Latest data gives c.60.0±0.3" and
345.5o) 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 Eta Muscae / Δ131 (NSP 19) (near planetary nebula IC 4191 in central northern Musca) which 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"arc sec, 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.168o to 137o. 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 variations change roughly between 6.16 and 6.27 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 known as an attractive for small telescopes. It can be found 1.2oESE (PA 244o ) from 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"arc seconds, while the latest position in 1983 (WDS96) was 2.8". I looked at this pair in 1994, and the separation did seem slightly smaller than this. Position angle has also decreased by about 10o (PA 150o to 140o) 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 AD. 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, worthy of a "look-see".
Alpha (α) Vir /
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.
Alpha Virginis 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"arc sec averaging to about 0.13 AU 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" (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"arc sec along PA 131o, 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"arcseconds. 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.
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 54o. 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.
R225 (13500-5925) is a double
star 1.1oSW from the planetary
nebula He2-102, or 1.9oSW
(along PA 242o) from β
Centauri. H.C.Russell discovered this 10th / 11th mag pair
on the 27th June 1881 and positioned this star at (13h 42m
-58o56'), and measured the
position on the same night as 9.12" along PA
More modern observations give the magnitudes as 10.1 and 10.5. (GSC 8672:480 states 9.2 for the primary, but it is certainly fainter than this.) I saw the primary in the C8 as very slightly yellowish and colourless. Either way, in moderate apertures, colours of 10th mag stars will always be difficult.
The last measure in the WDS(96) is given as 10.5"arcsec at 341.3o in 1965, though visually in 1990, I thought it appeared a bit wider than this. Since discovery, the pair has continued to widen by at least by an additional 1.9"arcsec in the last 118 years. Based on the small parallax stated in the Tycho Catalogue for the star T8676:480:1 (0.0098") and the direction and velocity of the observed motion, it is likely just an optical pair.
Δ145 (13546-6654), which Dunlop found in 1837, is located 23'S from except a small 2o decrease in PA. The 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!
Δ150 AB / HJ 4633
BC (13575-5743) is positioned
343o) 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"arc seconds
which has significantly reduced from Herschel's measure in
1834 as 70"arcsec, while the PA has changed little from the
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 magnitudeand appeared bluish to me. Spectral class is given as B7 III, which I assume is combined spectral of 'B' 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 © Andrew James 2003 Sydney, Australia