By Andrew
James, Astronomical Society of New South Wales, Inc.
(This is a special series appearing on
Doug Snyder's Planetary
Nebulae Observer's Home Page)
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Neat Southern Planetaries XVII
Surrounding Field of He2-111.
(cont.)Alpha Centauri/ Rigel Kentaurus/ Imperatorius Astrum/ HIP71683/ SAO252838 (14398-6050) Mag=-0.29 (13.5' PA=127O) is one of the most impressive of the stellar ornaments, remaining a major highlight for the amateur astro. 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,
a 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 "Astronomical Objects for Southern Telescopes" using one word - "brilliant". As the third brightest star in the sky, lying two hours in Right Ascension east of the Cross is
a 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, a Centauri (AB) and a 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.)Alpha Centauri lies midway within a bright part of the Milky Way - so the telescopic field contains many many background stars.
In 1999-2000, 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
a Cen just after 2010, and between the years 2023 and 2031. The minimum aperture to separate the pair when 10"sec.arc. apart will be a 11.5cm telescope.As separations reduce below 5"sec.arc., 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 (Beta 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"sec.arc. on the eastern or preceding side. (PA=112o) Changes in Position Angle for five or six months reaches 5O degrees 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"-15"/A (cm.).
At minimum separation, H.C.Russell did measured the pair on the 18th February 1878; 1.66"sec.arc., but he was using a sizeable refractor! A 25cm may be able to glimpse the duplicity, and a 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'min.arc. or 1380"sec.arc. This is the best stellar conjunction for 1st magnitude stars for the next 400 000 years.
The Orbit of Alpha Centauri.
Alpha Centauri takes 79.92 years to complete a single orbit, whose the apparent orbit is
inclined at 79.3o to the true orbital plane. The maximum separation for this
system is c.22.1"sec.arc. (January 1984), the closest is 1.7"sec.arc. May 2038.
Alpha Centauri's eccentricity has been found as 0.519, close in shape of a cricket oval.
Between the years about 1968 and 1996, the main pair remained near their greatest separation, and little changed in the observed positions. In the true orbit, the separations vary between 11.9AU and 34.9AU. The combined mass of
a Cen (AB) is currently measured as 1.92 <<SOLAR MASS SIGN>>, while individually, "Cen A" and "Cen B" have respective solar masses of 1.07 <<SOLAR MASS SIGN>> and 0.85 <<SOLAR MASS SIGN>>,and include Proxima Centauri, the total mass of the system is closer to 2.13 <<SOLAR MASS SIGN>>.Brightness of Alpha Centauri
Past observations by the astronomers such as Lacillae, John Herschel and even H.C.Russell
have suggested that the difference in magnitude was about three to four magnitudes, with
the average of all WDS(96) observations being 2.49. The "average" magnitudes of
the two components in the last 300 years has alleged risen in brightness, with relatively
small changes in the difference in magnitude. Today, it is clearly only about 1.5. My own
thirty-one observations of estimating the difference in magnitude, between the years 1981
and 1990, range between 1.1 and 1.8, producing an average of 1.4. Hipparcos (1996)
measured this difference as 1.36, so this is about right. Why this difference is so large
by these early and notable observers remain still a mystery. This problem with magnitudes
is also briefly stated in Burnham's Celestial Handbook Vol.1. Another issue, not
mentioned by Burnham, is the way magnitudes were reported through most of the 19th
Century. Unlike the modern magnitude system first set of by the variable, early observers
tended to use "personal" magnitude scale, which could vary a much as six or
seven magnitudes among visual astronomers. These variations were analysed in 1856 by
Norman Pogson - the founder of the logarithmic magnitude scale that we use today. Here he
found that the John Herschel (and to some extent William Smyth) underestimated the
brightness of the first magnitude stars. (Hearnshaw., John, B."Origins of the
Stellar Magnitude Stars"; S&T, 84, 5, pg.494-499 Nov. (1992))
It is quite possible that the companion star has brightened in the last 100 to 200 years, though such changes would be, in many aspects, contrary to our current understanding of stellar evolution. The 'A' components' variability could also have an small influence on the estimates, but it should be average out instead of being consistently out by such a large amount.
The actual colour of this star may have also changed from a deep yellow to a light-yellow/ yellow, as reported by both Herschel and Russell.
Minor variations in brightness for
a Cen was reported in S&T, 76, 6, pg.509 Dec. 1984 in the "News Notes", first reported in the French professional Journal "Comptes Rendus" in 7th June 1984 by the collaboration of several French astronomers. Lead by Eric Fossat, working in the European Southern Observatory in Chile discovered these small periodic variations over a six day observing window. Although the primary has the same spectral class as the Sun, being a G2 star, however, the star oscillates slightly in brightness every twenty minutes by c.0.65 magnitudes. Such oscillations are not uncommon in G-type stars, and such brightness fluctuations have been detected in the Sun, which varies in periods around five minutes. Since discovered in the Sun in 1965, the variations have been found in several stars using high-speed photometry centred on the narrow double-yellow Sodium lines in the combined spectrum. In the Sun, this is achieved using a bolometer - a very small telescope attached to a photometer, and is very useful in measuring small changes in temperatures and energy fluxes. It seems that the "A" component is the culprit, whose data was subtracted from the combined light. The origins of these brightness fluctuations is unknown, but several projects in the field known as helioseismology, are slowly revealing the inner workings of the Sun and the how energy and material is transferred from the solar furnace in the core to the surface.(Interestingly, it is the same page as the announcement and image of the disk surrounding Beta Pictoris and the likely formation of a planetary system discovered IRAS satellite in January 1984.)
Distance of Alpha Centauri
Presently the Hipparcos data give the adopted distance as 1.3478±0.0026pc. or
4.3955±0.0082lty. from the most accurate parallax known to date of
0.74212"±0.00140". This distance is universal adopted, but in reality decreases
measurably from year to year.
Statistical Data on Alpha Centauri.
| Alpha Cen A Component/ HIP71683/ SAO252838A |
Alpha Cen B Component/ HIP71681/ SAO252838B |
Proxima/ 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" |
| Solar Mass | 1.07 | 0.87 | 0.4 |
| Spectra | G2 V | K1 Vd | M5 VII E |
| Total Magnitude | -0.04 | --- | 12.1 - 13.12 B.Mag |
| App. Magnitude | -0.29 | 1.35 | 11.01(var) |
| Abs. Magnitude | 4.38 | 5.74 | 15.4 |
| B-V Mag. | 0.71 | 0.9 | 1.807 |
| Solar Luminosity | 1.5 | 0.4 | 0.00001 |
| Solar Radii | 1.22 | 0.92 | 0.35 |
| Separation (AU) | 35 (Max) | 55 (Min) | 13 000 |
| Radial Velocity (Rv) | -26Km.sec-1 | -18 | -16 |
| Proper Motion (RA) "sec/century |
-3.678.19±1.510"dyr-1-3 | 600.35±26.10"dyr-1 | -3775.64±1.52"dyr-1 |
| Proper Motion (Dec) | +481.84±1.24"dyr-1 | +952.11±19.75dyr-1 | +768.16±1.82"dyr-1 |
| Distance (parsecs) | 1.3478±0.002 5pc | 1.3478±0.002 7pc | 1.295 |
| Distance (ltys.) | 4.3964 | 4.3964 | 4.223 |
| Period (Years) | 79.92 | 79.92 | 100 000 |
| Parallax("sec.arc) | 0.74212±0.00140 | 0.74212±0.00141 | 0.77233±0.00242 |
Note 1: Distances here
are quoted from calculations made by Jahreiss and Morrison in 1993 using |
|||
Note 2: Proper Motion expressed in "sec.arc. per Century or "sec.arc. in decayears (10 years) ("d.yr-1) |
|||
Note 3: Orbital Elements
of Main AxB System. |
|||
** Note: This is the abridged version of the four part article on Alpha Centauri entitled
"The Imperial Star" that is soon to be published in ASNSW's "UNIVERSE"
in mid 1999.
He2-102/ SA2-101/ PK311+2.1/ WRAY 16-142 (13582-5855) is a brighter planetary than He2-103, that is both tiny and takes sometime to identify with certainty. He2-102 is found in Centaurus, some 1.6O northwest of the first magnitude star Beta Centauri. Travelling from Beta Centauri towards the cluster, there is a sudden drop-off in the number of stars. The cut-off magnitude is about 12.5 in a 20cm. to some 0.6O away from Centauri, not because of the scope's magnitude limit, but because of the bluish diamond-like brilliance of Agena/ Hadar kills some of your precious dark adaption! If you do use Agena to find the planetary, it might be a good idea to wait a minute or two to give time for the eyes to adapt to the surrounding dark skies. (Note this also applies to the planetary He2-111 (NSP 16) and the nearby Alpha Centauri mentioned above.)
He2-102 is listed as magnitude 13.5p and give no visual magnitude, but I suspect it is a little brighter than 13.5. The centred position of the 11.8 magnitude "star" in the Guide Star Catalogue (GSC) 13h 58m13.86s -58O 54' 31.5"), which is fractionally further south of the planetary's actual position. Visually, I did not see this star, so I have to conclude that the GSC has actually imaged the actual PNe. To see He2-102 requires at least a 20cm. Size is given as 9.0"sec.arc., yet I saw about a half this diameter. This diameter did not change with an O-III, which made the image of the object a little brighter. The PNN is listed as magnitude 17.2, is quite invisible to all amateur telescopes. The literature is very scant on any information about this object, and the distance is uncertain.
Surrounding Field of He2-102.
Beta 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"sec.arc 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 800OK, a diameter of 14 R or 19.5 million kilometres with the absolute magnitude being -5.1. Overall this is about 9 500 times brighter than the Sun, making
b Centauri a blue B1 III 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, varying by 0.045 mag in 0.157 days (3h 46m). Little is known about the companion.VOU 31 remains a fair challenge for moderate apertures. Hartung claims to have seen this with a 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 a 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 a 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 a well deserved coffee break being taken by the other observers! Another 10.5 magnitude star appears 2.5' to the east, which is just visible in a 15cm.
In distance, some references still quote values as low as 123pc. (400lty), but the Hipparchos satellite data firmly places its distance as 161pc.±13pc. or 525±43 ltys (Based on the parallax 6.21±0.56m.arc.yr-1)
QQ Centauri (13588-5852), is in the same field as He2-102, and is known as a SR variable star that varies between magnitude 14.3ph to 16.7ph. QQ Cen lies 5.3'min.arc. to the northeast (PA 62O) of He2-102. The period is estimated to be about 323 days, first determined with mid-minima on 10th March 1929. This is visual challenge is to find this red M4e variable in the eyepiece, as the magnitude varies between the magnitude limit of a 25cm. to 30cm. to below visibility. Little is known about this variable.
Another faint variable in the field of He2-102 is the faint semi-detatached eclipsing binary PV Centauri/ PV Cen (13566-5847) Situated 14.6' NEE (PA300O), this variable changes between 11.4 and 12.5 over a period of 1.91733 days whose primary eclipse begins on the14th March 1929. Like most faint variables, little is also known about this system.
NGC 5381 (14007-5933) is an open cluster, a field or two southwards (42') and slightly east (10') of QQ Cen. Listed as 13' in diameter and classified by the Trumpler System as "2 2 m -", some fifty stars are said to be associated with NGC 5381. Although it's "nothing to write home to your grandmother about", this faint cluster has an attractive layout. The cluster averages about 12.5 magnitude and is marked by a roughly pentagonal asterism, which is on the clusters southern boundary, and to the north, there is a small 60"sec.arc. "box" of four 12th magnitude stars. Brightest field star is a bluish-white 9.6 magnitude star (HIP68422/ SAO241364) while another obviously yellow 10th magnitude star lies to the northwest. Visually, I saw a total of some thirty-odd stars in a 20cm, and all seemed slightly reddish in colour - likely because of the strong interstellar absorption in the region.
A further 5' South of this pentagon is an obvious 11th magnitude reddish star, which I mention because it lies a close 16pc. (60ltys.) away (Parallax= 0.051"sec.arc.)
Surrounding NGC 5381, is a circle of open star clusters, all of which appear difficult to ascertain without a suitable finder chart. The field south and east of NGC 5381 is literally littered with faint stars.
Under city skies this entire region is rather uninteresting, but viewed at a deep-sky site, it's worthy of a wee look.
R225 (13500-5925) is a double star 1.1O SW from He2-102, or 1.9O SW (along PA 242O) from Beta ( ) Centauri. H.C.Russell discovered this 10th/11th magnitude pair on the 27th June 1881, who positioned this star at (13h 42m -58O56'), and measured the position on the same night as 9.12"sec.arc. along position angle 341.3O.
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 magnitude stars will always be difficult.
The last measure in the WDS(96) is given as 10.5"sec.arc 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"sec.arc, 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.
R Centauri / HIP69754/ SAO241580/ 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 Alpha and Beta Centauri, but more implicitly is closer to Beta 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 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 the 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 (GVSC), 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 magnitudes in about 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 time.
For distance, some references still quote values as low as 123pc. (400lty), but the Hipparchos satellite data places its distance as 161pc.±13pc. or 525±43 ltys. (Plx=6.21±0.56m.arc.yr-1)
During the collection of the Hipparchos observations, the magnitude was 7.18 with the inaccurate measured parallax of 1.56"m.sec.arc., giving a distance of 640 parsecs or 2100 light years.
D159 (14226-5827) is a bright easy double star 3O NE 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 20 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 161O to 159O. To me the separation seems less than 9.2"arc.sec. The field is marked by another 7.6 magnitude 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
D159 as mag.5.0, while the Tycho catalogue (T8690:3220:1) inexplicably states the magnitude is 6.91. The Hipparchos Catalogue gives D159 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=0.795±0.003, while the distance is 86pc. or 280 lty. (Plx=11.56±3.09 m."sec.arc.) and an usual combined spectra of "G8/K1 +F/G". A second "stellar" measure is given with a parallax is 0.70"m.arc.sec. and a B-V = 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 159 to about 2.5'min.arc. These are obviously artifacts from the measuring machine during the production of the GSC Catalogue.
RR Centauri / HIP 69779/ PPM 342705/ SAO 241587/ HD 124689 (14170-5752) is a W Ursa Majoris type eclipsing binary, 1O NW from 159, where it remains the brightest white star in the next field of a wide-field eyepiece. Its alternative position can be found very quickly. It is exactly 2O due north of R Centauri.
Like all W UMa stars, this star shows a continuous variation of brightness between 7.27 and 7.68 mag, over a period of 14h 32m 11.64s (0.60569029 days) whose primary maxima starts on the 21st March 1925. [JDE 2424231.0981] Although W UMa is the archetypal of the class, both S Aps and RR Cen are brighter and have period length twice that of W UMa itself. Interestingly, like W UMa itself, RR Cen shows slow unpredictable (discontinuous) variations in the period. It is assumed that the changes are due to mass transfer and material losses due to a strong stellar wind depleting the net mass. Also different of most variables of this type, observations of the light curve to find a true period is unreliable because of the "teardrop" shapes of the stars, and this has to be found by analysing all the observations to find "a best fit".
Analysis of the light curve has found details of some of the parameters of the close binary. Separation between each star is 7.6 million kilometres, whose stars have respective diameters of 7.2 and 1.6 million kilometres. The primary shows that it has filled its Roche Lobe, suggesting that material is flowing from the primary to the secondary at ~10-7
per year. By luminosity the system is about a hundred times more than the Sun, while the
total mass is about 2.0 which subdivides into 1.65 and
0.35 Solar Masses, respectfully.
Both stars have a spectra of A9+F0V, which has be confirmed independently from the
temperatures of 9 950K and 7 000K.
Hipparchos suggests a parallax of 9.76±0.85"m.arc.arc., giving a relatively close distance of 102pc. or 334lty. This is also confirmed by the yearly proper motions of -0.05269"arc.sec in RA and -0.02237"arc.sec in Dec.
Observation by professionals continue to be of some importance because of its unusual proximity to the Sun.
Loden 289 (14146-5751) is the 70'min.arc open star cluster on the western edge of the same field of RR Cen. This a poorly rated cluster, classed as "4 3 r -" , which containing 100 stars. The field to me seemed scattered, and I thought I could just see the cluster from the numerous field stars.
Next : The difficult and challenging planetary He2-90 and the open cluster "Gemma Australis Magnifica"!
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Douglas Snyder, June. 1999