RA : 14h to 16h
SOUTHERN DOUBLES :
β Cen / Hadar / Agena ,
Δ159 Cen ,
Δ161 Cen ,
Δ162 Lup ,
Δ163 Lup ,
Δ164 / η Cen ,
α Cen / Rigel Kentaurus
/ Δ165 ,
BRIGHT STARS :
OTHER DOUBLES :
Beta (β) Centauri /
Hadar / Agena / VOU 31 / HIP 68702 / SAO 252582 / PPM
360515 / HD122451 (14038-6022) is the 11th brightest
naked-eye star in the sky. Its position marks one of the
so-called Southern Pointers. It remains
the bright star on the Australian National Flag, and lies
between Alpha Centauri and bright star of the Southern
Cross. In earlier times, these stars were also associated
with Argo Navis - likely because of heir proximity to the
horizon. The southern declination meant that two thousand
years ago, Hadar appeared some 5o
above the horizon from the Egyptian city of Cairo. Chinese
observers once called this star the "horse's belly". The
star today has two common names in use - Hadar or Agena.
Equal usage of these names has existed for the last hundred
years or so in the literature, though lately, Hadar is more
common. Hadar in Arabic means Ground, as used like a mortar
and pestle to break grain husks into flour. (Arabic
observers also give Alpha Centauri name as Wazn, the tool
known as the or Weight.) It was the American Elijah H.
Burritt who named this star Agena that appears to come into
use about 1880. According to Richard Allen the meaning of
the name is unknown.
Beta Centauri is a noted double star, whose duplicity was first discovered by J.G.Voute in 1935. Listed as VOU 31, 1.3"arc sec. separates Hadar, showing respective magnitudes of 0.9 and 4.1. (Later, some sources like the Washington Double Star Catalogue (WDS96) say the magnitudes are 0.7 and 3.7. I could not find this later source.) The separation has remained fix since discovery, though the position angle has decreased from 259o to 247o in the last sixty-five odd years, suggesting physical connection. If this is true, the period is likely lengthy, but this pair will remain interesting to watch in the 21st Century.
From the observed data, the brighter component contributes most of the light. Currently, Hadar "A" has a temperature of 25 800K, whose diameter of 14R or 19.5 million kilometres across and with an absolute magnitude being -5.1. Overall this is about 9 500 times brighter than the Sun, making the blue β Centauri a B1III giant, placed at the very top of the Main Sequence of stars. Photometric observations show Beta Centauri is the brightest example as a short-period variable known as a Beta Cephei (BCEP). The mean magnitude is 0.61 varies by 0.045 mag over 0.157 days (3h 46m). Little is known about the companion.
VOU 31 remains challenging for moderate apertures. Hartung claims to have seen this with 20cm aperture using a neutral density filter - but I personally find this hard to believe. I assume that Hartung used an aperture stop - a most useful device for amateurs who would like to know the extinction of pair separations or limiting magnitudes. Using several cardboard circular diameter holes can simply make this corresponding to various common telescope apertures, and is based on the variable star extinction aperture, which functions like a gigantic camera iris. This is a simple device, quite useful to have on hand, especially if you are writing observational text, as it can determine the minimum aperture to see a particular object.
I have tried separating the pair, even under perfect seeing conditions, more than a dozen times with 30cm, and still couldn't resolve it. I did glimpse this pair at the ASNSW's observing site at Bowen Mountain way back in April 1981 using 30cm It was really tough though! The only time I can say I really saw it cleanly separated was by using the 40cm Cassegrain at the now closed Black Birch Observatory in the South Island of New Zealand, and that was during the well deserved coffee break being taken by the other observers! Another 10.5 magnitude star appears 2.5'E, which is just visible in 15cm.
In distance, some references still quote values as low as 123pc (400ly), but the Hipparcos satellite data firmly places its distance as 161±13pc or 525±43ly, which is based on the parallax of 6.21±0.56mas.yr<<small>sup>-1<</sup>/small>)
R Centauri / HIP 69754 / SAO 241580/ HD 124601 / PPM 3424701 (14166-5954) is one of the first variables that a southern observer undertakes in a variable star observing programme. Its position is easy to find, as R Cen is roughly just slightly north of the imaginary line between α and β Centauri, but more implicitly is closer to β Centauri - some 1.6o to the NEE (PA 74o). R Cen is contained in a quite starry field. The deep blood red colour of this star is remarkable, reminding me of X TrA or even EsB 365 near β Crucis. Throughout the near predictable 550-odd day period, the star changes colour with magnitude, and this is reflected in the M4e to M8 IIIe emission spectra. AOST2 says that the star;
...near maximum is a fine red star... while near minimum looks crimson. I playfully experimented with an O-III filter, and found the star had simply disappear from view. The prism image, under steady conditions, shows many dark lines with one or two brighter ones - at either side of the observed spectrum.
According to the 4th edition of the General Variable Star
Catalogue (GVSC4), R Cen is a Mira variable with a visual
magnitude varies between 5.3 and 11.8 magnitude in a period
between successive minima of 546.2 days. Earlier references
often quote the earlier period of 531.0 days, and this was
found almost fifty years ago. The observed light curve is
quite different from many other Mira's, as it also shows
another less deep light curve some 160 days from the deep
minima. After this 0.4 drop in brightness, the light again
increases by another 1.4 mag in c.100 days. Speculation by
the theorists thinks this behaviour is similar another
variable star class - the RV Tauri's. These appear as
"semi-regular Cepheids", having the characteristics of a
consistent period with irregularly bright maxims and
minims. The cause of these two periods is uncertain.
Russian theorist Tsesevitch in 1955, proposed that these
dual pulsations are caused by shock waves emanating from
the star which appears to speed up and slow down as the
wave moves through the extended outer thin atmosphere of
the outer layers. In turn, this pressure varies the
emission spectral lines, that are seen to change over
For distance, some references still quote values as low as 123pc. (400ly.), but the Hipparcos satellite data places it at 161±13pc. or 525±43ly. (π is 6.21±0.56m.arc.yr-1) away from us. During the collection of the Hipparcos observations, the magnitude found was 7.18 with the inaccurate measured parallax of 1.56"m.sec.arc., giving the distance of 640pc. or 2100 ly.
An example of S Car light curve on this star either at or . Although the latter reference is in Spanish, the text can be translated easily, and the general guist can be worked out with a little patience. (Similar informtion can be found other southern variables like R Car and L2 Puppis. R Cen or 1409-59. When I looked up the observations of R Cen the page told me that some 209 observers had contributed the total of 5983 observations! If you wish to see the power of visual observations - just look at some of the curves. 5.2 to 11.5 on the particular curves between JD 2440000 and 2453000. In this time, the amplitude of the light curve shows a gradual decrease over time, where the range is more like 6.0 to 9.5. In the beginning of the light-curve there are deep minima followed by a shallow one and next one again deep. The mechanism seems to be regularly switching on and off that is no doubt something to do with the interal workings inside the star.
(14226-5827) is a bright easy double star 3oNE
of Beta Centauri (PA 54o), and forming the apex
of a naked-eye equilateral triangle with Alpha and Beta
Centauri. To me this pair looks like a fainter version of
Alpha Centauri, with similar colours and spectral classes.
AOST2 says the colours are yellow and white, though I see
them as yellow and deep yellow - similar to the G8 III and
F5 spectral class. For me, this was the third double star I
ever observed, behind Alpha Centauri and Alpha Crucis, with
more than twenty different observations in the 1980's
alone! The Washington Double Star Catalogue gives the
respective magnitudes as 4.9 and 7.0. Since discovered by
James Dunlop in 1826, the separation has changed from 9.5"
to 9.2" while the position angle has similarly reduced from
159o. To me
the separation seems less than 9.2". The field is marked by
another 7.6 mag star (HIP 70228/ HD125545/ SAO 241669) in
the field, seen using medium power 11' nf.
Some complications exist in the catalogues, and I spent sometimes trying to sort out the mess in the magnitudes and positions. The Guide Star Catalogue (GSC) lists 159 as 5.0 mag, while the Tycho catalogue (T8690:3220:1) inexplicably states the magnitude is 6.91. The Hipparchos Catalogue gives Δ159 as a separate star - HIP 70264, which correspond well with the star SAO241673/ HD 125628/ PPM 342793 (14h 22m 37.120s -58o 27' 33.00") HIP 70264 is stated to have has a visual magnitude of 4.76, B-V of 0.795±0.003, while the distance is 86pc. or 280 ly. (π=11.56±3.09"mas.) and an usual combined spectra of " G8/K1 +F/G". A second "stellar" measure is given with the parallax of 0.70"mas and the B-V being 0.455. I can only assume this refers to the companion star. Megastar 4.0 also shows a whole collection of 15th to 16th magnitude stars surrounding Δ59 to about 2.5'. These are obviously artifacts from the measuring machine during the production of the GSC Catalogue.
TDS 9199 (14258-5449). While writing this text, I found that the latest WDS03 gives a new TDS (Tycho Double Star) pair in Lupus. Magnitudes are given as 11.39V and 12.28V and this roughly matches the previous combined magnitude of 11.4v. In 1991, the star’s positions were 2.2"arcsec along PA 224o. I have not seen this star but have identified it using the accurate position of 14h 25m 46.0s -54o 48' 39". It is the next star some 58" SW (PA 233o) from HJ 4675. The stars here might be difficult to see in 20cm because of the brightness of the stars - especially as fainter pairs are sometimes notoriously difficult to split. I suspect 20cm should see this duo but a 30cm might be better.
HJ 4675 (14259-5448). What lured me to NGC 5593 in Lupus was that the brightest component is the double HJ 4675 near the centre of the cluster, whose components measure 10.0 and 11.0 magnitude. Although the pair was discovered by John Herschel, his measures were omitted for a number of years because his positions of 5.0" and PA being did not seem to reconcile with later data from Russell and Innes data. In the WDS01 the measures of Russell and Innes are given as the first and last positions within the period of (23) twenty-three years. Last measures were produced in 1915 and were given as 8.2" and 338o. To me these positions look similar today (2003). The Hipparcos/ Tycho results somehow did not resolve the stars. The pair was easy to resolve in 20cm, and suspect 7.5cm could see it with care.
NGC 5593 (14259-5447) (U430)
is an open cluster in Lupus 1.8oW from
Δ163. This cluster is a bit odd because it looks just
like a small collection of eleven (11) 10th-11th magnitude
stars in a line some 7'arcsec in length. Throughout the
cluster there seems about six, maybe seven, 14th magnitude
stars. There seems no grading of magnitudes in the cluster
itself. In 20cm I had much trouble identifying the field.
Catalogues class NGC 5593 as “ III 2 p” and lists about twenty stars. Except for the nearby presence of the pair, this is a merger example of an open cluster.
V745 Cen (14272-6204) is
an eclipsing binary lying 45'N and 10'W of the nearest
star to the Sun Proxima Centauri. This 8.1 magnitude star
is some 4'S of the variable's position identify
it easily, with the field containing a few much fainter
stars. V 745 Cen varies in the period of 3.0251 days and
the light-curve changes between 9.3 and 10.3v magnitude.
Readers should also note that Burnham's Celestial Handbook
Vol. 1 pg.544 gives the older visual magnitude range as
9.8v to 10.8v. Both stars are separated by 12.2 million
kilometres, while the mass primary star is 3 M - the companion being 2.6
M. In luminosity,
both are 424 L and 54
L, while the
temperatures of the two stars are 15 210K and 9 720K. Total
mass of the system is 7.89 M, with the individual masses calculated as
4.75 M and 3.14 M. Spectral classes are
given between B3 and B8 and both have been determined to be
Note: V735 Cen is plotted on in the top 'Proxima inset' in Sky Atlas 2000.0 Map 25. V745 is located right in the middle of the figure!
Δ161 (14286-5439) No pair is located in this position in Centaurus and no likely matches with 8,8. Dunlop’s pair is nf in Quadrant 1 whose only clue is the positions differences are ΔRA 2.86" and ΔDec 40.36"arcsec, producing the PA of 85o and the separation of 41.5"arcsec. The general positions are likely wrong and Δ161 remains presently unidentified.
Δ162 (14339-4628) Dunlop identifies as 295 Centauri but the star is in Lupus. At 7.5 and 10.5 magnitude, the present alignment is PA 241o and is separated by 72.2"arccsec. Spectrum is G6/8 III.
η Cen / Δ164 Eta Centauri (14355-4210) is an optical pair that is very suitable for small binoculars or telescopes. Eta Cen lies 21'N of the more southern Lupus border. Colours are blue and white for the 2.3 and 9.0 magnitude stars, and both of these are separated by 2.1' and aligned towards the southeast. The blue primary is Eta Centauri / HIP 71352 / PPM 319680 / SAO 225044 / HD 127972 with the precise position of 14h 35m 30.5s -42o 09' 27.9". This star has a B-V of -0.157 and the spectrum of combined spectrum of B1Vn + A. The companion is only listed as T 7814:3668:1 with the V magnitude of 9.04. The general field is stacked with stars including a number of other bright field stars. Understandably not listed in the WDS.
R249 (14371-6230)is a faint pair
(PA189o) of α Centauri and
is contained in the most profusely populate fields that I
have seen. The field stars are all oriented along a
wide 'line' approximately the NW to SE, averaging
magnitudes between 9.5 and 13.5. (This cannot be seen
clearly in Sky Atlas 2000 nor Uranometria 2000.0, but is
visible in the Millennium Star Atlas.)
Some problem exists on the discovery date by H.C.Russell. This pair could have been seen by Russell as early as the 11th June 1871, as it is close to the 11th magnitude pairs; R245 (2") and R246 (15") As no evidence is written on this earlier observation, then the stated discovery date must remain ten years later on the 9th August 1881.
R 249 is an orange pair (KO III) with magnitudes of 8.2 and 9.8, who Russell positions at (1428-6203 (1880)) with a separation of 2.77" at PA 33.633o (8 and 10 mag.)
Other than Russell's positions, little has changed in the 3.0" separation along PA 24o, which was last measured in 1960. I have used this double in the past for finding 11.3 mag Proxima Centauri / V645 Cen (14302-6242), which is 49'WSW (@PA 260o) from R 249. Listed as HIP 1475 / PPM360885 / SAO252821, the combined magnitude is measured at 7.5±0.4, but was unresolvable using the Hipparchos instruments. The parallax is measured as 4.77±1.58"mas, giving 209±69pc. (680±225lty.) As the distance. Using this distance to estimate the separation, the two stars are some 94 billion kilometres (630AU) apart. If this is a true binary, then period is around 15 000 years. Little wonder we have seen little motion over in the last 120-odd years!
Δ163 (14380-5431) is in
located in Lupus near the southern boundary of the
constellation. This pair can be found 6.3o due
north of Alpha Centauri (Δ165) and the field is only
57'NW from to one of the very best southern double - the
much neglected Δ168. It also mimics another bright
Dunlop pair Δ169 in northern-western Circinus, which
is some 1.5oSE (PA 137o) from our
Δ163. *(See both pairs below). Δ163 is also
approximately halfway between the open clusters NGC 5749 /
Cr 287 (14489-5430) and NGC 5593 (14259-5447), which are
1.6oE and 1.8oW, respectively.
Δ163 of 8.0 and 8.4 magnitude, which Dunlop called “8,8”, is an attractive object in binoculars or small telescopes. Present separation is about 65"arcsec along the near easterly PA of 102o. What is most attractive is the very neat equal bright colour contrast of the yellow and blue stars. What I find interesting is that the wide spacing between the components means that any colour contrast effects are nullified. If this were a close pair, this might be a bit more spectacular. Telescopically it might be best to look the pair at very low magnification to make the proximity more spectacular. I experimented 1with binocular and my small 50cm solar eclipse refractor, and thought that thee stars looked far more attractive in these than the 20cm !
Spectral classes of the two are; ‘A’ F0 III and ‘B’ B8 III, whose colour as roughly similar to Beta Cygni ‘A’ is a K1 star). Looking at the proper motions, both are travelling in the same way, but the primary’s velocity is about four times bigger. Furthermore, the primary has the Hipparcos parallax.
This is certainly an optical pair that is wonderful for in binoculars or small telescopes.
Alpha (α) Centauri /
Δ165/ Rigel Kentaurus/ Imperatorius
Astrum/ HIP71683/ SAO252838 (14398-6050) is a bright
-0.29 magnitude and) is one of the most impressive of the
stellar ornaments, remaining a major highlight for the
amateur astro. It lies merely 13.5'ESE (PA
127o) from the planetary He2-111
(NSP16). Every amateur in the southern hemisphere has seen
it - and likely most of our fellow northerners have at
least heard about it. Ranked the third brightest star in
the sky, only behind Sirius and southern Canopus, α
Centauri holds particular reverence over all the stars as
our closest galactic neighbour. (Australians, however, seem
to have forgotten this reverence, as it is the only star of
the "Cross and the Pointers" left off the Australian Flag!)
For me it remains imperatorius astrum - the Imperial Star.
Hartung must have been a modest man judging by his
'elegant' literary style, as he describes Alpha Centauri in
AOST2 using one word - "brilliant". As the third brightest
star in the sky, lying two hours in Right Ascension east of
the Cross is α Cen. For some reason some northern
authors often place Rigel Kent behind the first magnitude
star Arcturus - and this is seemingly often slyly done by
listing the two stars individually. Either way, α
Centauri (AB) and α Centauri "A" is brighter.
Navigators amazingly did not name it Rigel Kent until the
early days of aviation, who often used it as a stellar
beacon for global positioning.) α Centauri lies
midway within a bright part of the Milky Way - so the
telescopic field contains many many background stars.
In 2002, this binary is easily separated - even in a small telescope. A 5cm telescope can probably resolve it 50% of the time, though combination of the brightness of the pair and poor seeing, sometimes make this difficult. I have seen it with a pair of 7x50 binoculars, but it had to be firmly fixed to a tripod. The minimum aperture for resolution is presently (1999) between 4cm and 4.5cm On good nights, my small 5cm refractor has little trouble with powers greater than about 25x magnification. In the city, some six stars occupy a 0.25o field, increasing to about ten in darker country skies. Both stars can easily be found during daylight and separated cleanly in apertures above 7.5cm In daylight the colours lose their yellowness, appearing like brilliant white "diamonds" against the blue sky. Due to the overwhelming sky, I had some trouble separating the pair with the 5cm refractor. This is reverse to my understanding of optical and double star theory as this should become easier as the images cannot 'blur' together so easily. Three attempts by me have been made - none successful. (Maybe I was just unlucky!) To find Alpha Centauri in daylight, an equatorial telescope is a distinct advantage, as the position can be simply dialled up using the setting circles.
In the decades to come the decreasing separation will make resolution far more difficult. Observers may tend to make calculations on telescopic resolution using Dawes Limit where visual separation is stated as 11.58"/ Aperture (cm) or 4.54"/ A (inch) Frankly applying this is useless, as the brightness of the two stars overwhelms true separation. Problems with this will apply to α Centauri just after 2010, and between the years 2023 and 2031. The minimum aperture to separate the pair when 10"arcsec. apart will be 11.5cm telescope.
As separations reduce below 5"arcsec, this will become even more difficult, due to the problems with the seeing and so-called proximity. A good comparative test of this particular problem is the other "pointer" - Hadar/ Agena (β Centauri). (See below) The value in the Dawes's equation this instance should be set to about 13.5"/ A(cm). Around 2013 to 2017, and the years 2035 and 2039, the minimum size telescope required will be a 20cm but a 25cm will have no difficulties. A neutral density filter may have to be used to cleanly separate the two stars during periods of poor seeing. November 2037 is the closest approach in the orbit where separation decreases to a meagre 1.71"arc sec on the eastern or preceding side. (PA of 12o) Changes in Position Angle for five or six months reaches 5o each month. For a few years, depending on the seeing conditions, the pair will be very hard to resolve. It is best to use a hexagonal diaphragm - a hexagonal shaped cover placed over the mirror or lens, or by using a neutral density filter. Estimating the constant used in the Dawes equation will likely be between 14"/A (cm). and 15"/A (cm).
At minimum separation, H.C.Russell did measured the pair on the 18th February 1878; 1.66"arc sec., but he was using a sizeable refractor! A 25cm may be able to glimpse the duplicity, and 30cm and above will have no real problems! It is fortunate for the observer that within two years this difficult period of observation will soon pass.
Alpha Centauri's also has a rapid common proper motion producing a close approach or stellar conjunction with Centauri in 6200AD. The minimum distance reaches 23'arcmin or 1380"arc sec This is the best stellar conjunction for 1st magnitude stars for the next 400 000 years, and becoming truely the best double star in the sky!
Alpha Cen A
Alpha Cen B
V645 Type: UV Ceti/ HIP70890
|R.A. (2000)||14h 39' 40.90"||14h 39' 39.39"||14h 29' 47.750"|
|Dec. (2000)||-60° 50' 00.65"||-60° 50' 22.10"||-60° 42' 52.90"|
|Spectra||G2 V||K1 Vd||M5 VII E|
|Total Magnitude||-0.04||-0.04||12.1 - 13.12 B.Mag|
|Separation (AU)||35 (Max)||55 (Min)||13 000|
|Radial Velocity (Rv)||-26 kms-1||-18||-16|
Proper Motion (RA)
|Proper Motion (Dec)||+481.84±1.24"dyr-1||+952.11±19.75dyr-1||+768.16±1.82"dyr-1|
|Distance (pc.)||1.3478±0.002 5pc||1.3478±0.002 7pc||1.295|
|Period (Years)||79.92||79.92||100 000|
Note 1: Distances here are quoted from
calculations made by Jahreiss and Morrison (1993)
Note 2: Proper Motion expressed in "arcsec. per Century or "arcsec in decayears (10 years) ("d.yr-1)
Note 3: Orbital Elements of Main AxB System.
P=79.906yr.; T=1955.607; e=0.519; a=17.537"; i=79.327; Ω=205.023o;ω=231.897o (RA=14.328 Dec.=-60.250)
RST 3894 (14427-6457) lies inside the larger dark nebula in Circinus B 145E and there are few interesting stars except for the pair. This star is easily found by drifting 0.8oE of α Cir. The magnitude of the two stars is 10.5 and 11.0, and separated by 2.2"arcsec at PA 160o. This pair is easily visible in 7.5cm and little has changed in the positions since Rossiter first measured the pair in 1936.*
Alpha (α) Circini / Δ166 (14424-6458) is a bright 3.4 mag star which is a wide binary with a beautiful colour contrast. The primary appears distinctly yellow while the companion is reddish. Discovered by Dunlop in 1828 and first measured by John Herschel in 1837, little change has occurred in the last 160 years except for a decrease in position angle by some 18o, showing a retrograde orbit. As of 1994, the current separation is 15.7" and the PA is 246o. Once in the Third Catalogue of Visual Binaries this system was quoted as having a thousand-year long orbit, only to be rejected in the latest 4th Catalogue. If it is a true binary, the period must be a few millennia. Recently, the 'A' component was thought by double star observers to be a variable. (Ie. WDS96) As yet it is not listed in the NSV. The pair is easily visible in 7.5cm. In larger apertures, it is absolutely beautiful in a star-studded field. Between the Golden Horseshoe and α Circini is a dark nebula. Typically dark nebulae are boring. However, this one is interesting because of a major drop in the number of stars both east and south of Α Circini, and this is visually obvious some 1oE of Α Circini.
NGC 5749 (14489-5430) (U431)
is a cluster 1.6oE of Δ168. This cluster
looks like a small gaggle of stars shaped in like a
‘A’. In 15cm there are about eleven (11) stars
from 9th to 12th magnitude, and in the 20cm I saw about
twenty-five (25) stars. Larger apertures may well begin to
see some of the fainter stars that total about thirty-odd.
To the east of the 8'arc minute cluster there are four
pairs each about 1' apart that are arranged in a straight
line. In the very centre is a 10th magnitude orange-red or
red star. The stars within the cluster are an odd random
mixture of spectral types, which might appear better in
dark skies. Identifying the cluster is the 9.6
orange-yellow star, HIP 72519 - appearing 6' or 7' east
from the open star cluster’s heart.
Data on the cluster says the total magnitude is about 8.8, which to me seem to suggest this is an eye-catching open cluster, but when I looked at it I was a bit disappointed. It is classed in the Trumpler System (1930) as III 2 p with the number of stars being about thirty (30).
In summary, NGC 5749 is an unspectacular cluster.
Golden Horseshoe (1451-6612) is another brighter
asterism that lies between α Circini and γ
Triangulum Australis, and some two-thirds the bisected
distance in a straight line between these stars. To the
naked eye the brightest star in the asterism is the 6.2 mag
bluish ζ Circini (SAO 252951). The Golden Horseshoe
has a diameter c.0.8o and
contains some twenty-five stars - three of 6th magnitude,
six are 7th, eleven of 8th and five of 9th. It also
contains a number of double stars.
In the finder, this asterism is obvious, though the larger telescopes may have serious trouble in getting the object within the telescopic field. A small telescope, say 7.5cm or 10cm using low power will have no trouble placing it into one field.
Another 'mini-asterism' lies in the northern part of the 'horseshoe', which I call the 'Golden Snake'. This is an 'S' shaped line of stars that extends NNE from the 7.6 mag star SAO 252951 (GSC9019:467) by some 12' in length towards α Circini. Twisted like a snake, the line of twelve 11th and 12th mag stars end in a 'forked tongue'. A 7.5cm should see these easily in dark skies, a 10cm if you are in a sky-lit suburb.
I 369 (14487-6635) is the bottom star of the straight line of five stars in the southeastern part of the field of the horseshoe. This is the Innes triple, whose magnitudes of the wide AB pair are 5.90 and 9.0, separated by 30.0" at PA 80o (WDS01). Visually, 30"sec.arc. is closer to the truth. Checking the observational data, Geoffrey Douglass of the US Navel Observatory confirmed this is correct. The spectral types of the AB system are B2.5Ve and B7/8V. All proper motions are also similar, suggesting that the three stars are really associated. However, little has changed in the positions since Innes observations in 1902.
HJ 4707 (14544-6625) is the
John Herschel pair on the opposite end of the horseshoe is
the John Herschel. This nearly equal yellow and white pair,
has quoted magnitudes of 7.5 and 7.9. Since the first
observation in 1837 the separation had slowly decreased,
until sometime is the early 1960's. Ie. 1.5" to a minimum
of 0.54". Since then the separation has began to increase
and according to the calculated ephemerides of the 4th
Catalogue of Visual Binaries, the current separation is
0.84" at PA 294o. Then if this is
correct, an aperture of 20cm could just resolve the pair
under good seeing conditions and medium-high magnification.
Visually, I can just see it in 30cm, suggesting a
separation of ~0.65-0.7 arcsec and the PA may also be out
by +10o or so. It is possible
that the binary star ephemeris is incorrect.
To my eyes, the pair appears strongly yellow in colour. It is no doubt, from the forty-one measures made to date, it is likely a long period binary. In 1948 Woolley and Mason calculated the retrograde orbit has a period of 288 years. Another known problem is the observed magnitude difference. Herschel's observations state a Δm of 0.4 - and this figure is given in the IDS. The most recent observations suggest no difference at all Ie. Both 7.00 magnitude, respectively. My own observation suggests that the difference is nearer Herschel's. Could this be a suspected variable?
B831 (15085-6438) in TrA is 17.0'W of B832 by and 3.0'N of the planetary nebula NGC 5844. The magnitudes are 8.7 and 10.9 respectively, separated by 2.6" towards PA 108o. Little has also changed with this pair in the last seventy years since its discovery. I see both stars as yellowish-white. Located 13'NEE (PA ~55o), and centred on position 15h 12m 23s Dec. -64o 32' 29" is a lovely asterism of eight stars and finding it is easy. This object has no common name, and is not listed as a multiple star. The two brightest and closest stars (GSC9029:374 and GSC9029:167) are 7.4 and 7.8 mag. All the other stars are between 9.8 and 13.8 mag in an area of about 4.0'. It would take 20cm in dark skies to see them all, that is best viewed using medium magnifications. (c.200X)
B832 (15109-6439) in Triangulum Australe is 4.0' from he planetary nebula NGC 5844 Both stars are 9.4 and 11.4 mag, respectfully, appear as yellow and orange. Since the first measure in 1927, little has changed with these stars that are separated by some 4.8" at PA 79o.
Δ194 / SLR 11
(15549-6045) is a stunningly brilliant multiple star,
1.0oNE of NGC 5979. The primary
pair, SLR 11 (AB) has the components as 6.5 and 8.8
magnitudes, being separated by 1.3" at the due east PA of
93o. To me the primary is
yellowish, and the secondary is blue in colour. Spectrally
this star is given as B9 II, but there is some doubt, ie.
the WDS Notes, that suggests it maybe more like a 'K-type
star. A 20cm telescope, using medium to high magnification
and good seeing will just easily separate the pair. 25cm or
30cm will perhaps separate the pair more easily. Since the
first measures by Sellors in 1891, the separation has
slowly increased by 0.4"arcsec - with the last reliable
measure made in 1962. The 'A' component is an unknown type
suspected variable NSV 7310, displaying a small magnitude
range of 6.11v to 6.15v. It is also a spectroscopic binary
of uncertain period - making this a likely triple.
Two fainter yellowish companions are associated with the main pair that was discovered by Dunlop at Parramatta Observatory in 1832. The brightest lies north followed by the principle pair. Δ194 (AC) has the additional C component at 9.1 mag, some 45.0" apart at PA 48o. Since the first measures by H.C.Russell in 1883, the separation has increased by 1.5"arc sec while the PA diminished by merely 3o. The second star is Δ194 (AD) lies south preceding. At 8.7 mag, it is separated by 48.1" at PA 225.7o. Since 1883, the separation has diminished by 1.2". Due to the small motion of these stars, little is known of the true connect of these outlying stars. The 'C' and 'D' components display opposite common proper motions. They maybe orbiting in a very long period - but it is more likely they are mere field stars.
In all this multiple makes an attractive set of stars in a prolifically starry field.
X TrA / EsB 422 / SAO253062 / (15146-7004) lays 1.4o SSW of the third magnitude star Gamma (γ) TrA, and 24' from the Triangulum Australe and Octans border. Positioned on the western corner of TrA, it can be easily found by moving an equatorial mounted telescope directly 9oW from the planetary Sa2-162. I came across the deep red star while journeying in the southern part of the constellation. Its redness is obvious when once seen. It is similar to the garnet star EsB 365 next to β Crucis. The variable star classification of X Tra was made during the turn of the century, and was classed as a Lb type irregular variable - so it tends to exhibit slow changes in brightness. In X TrA case, the brightness variations seem to be between 5.0v and 6.2v magnitude or 8.1p to 9.1p magnitude. One reference to this star is found in Webb's Celestial Objects for Common Telescopes'; Vol 2. under Stars with Remarkable Spectra. The EsB is the Epsin-Bimingham 'Red Star Catalogue' produced photographical and visual observations in 1897, yet EsB 422 was by discovered by Fleming in 1895. It also has a large B-V magnitudes of 2.7. Spectrally it is classed as Nb, which was later upgraded to a carbon star of spectral type C5,5, corresponding to a surface temperature around 2 500K. Interestingly, Webb states 6.2 mag, however, visual estimations of red stars are notorious for being unreliable. This 6.2 mag 'minima' are still quoted in the magnitude range, though it has never been this faint since this time. (Note: Espin Updated Addition of the Handbook was made in 1917. The observation by Epsin was actually made by Innes.)
Last Update : 06 September 2003
Southern Astronomical Delights © Andrew James 2002 Sydney, Australia