Southern Doubles, Stars and Variables
SOUTHERN ASTRONOMICAL DELIGHTS : Presented by Andrew James
|PAGE DS 010
10 Mar 2009
|RA : 10h
Dec : -30° to -90°
Constellations : Ant, Vel, Car, Oct.
Best Observed : Jan - Jun (Text Ordered by RA)
|RA : 10h
Dec : -30° to -90°
SELECTED SOUTHERN DOUBLES and VARIABLES
Magnitudes : 6.24V / 12.11V : Spectral Class : B8V n=3
All three stars have the same common proper motion, so it is still possible that this might be a physical system. However, if it is, the periods are likely to be very long time. The general field is dense with stars, and contains another 8.2 mag star some 6' at PA 120°. This colourful triple is one of the most attractive objects in the south - even for the smallest of telescopes.
μ Vel / R 155 / Mu Velorum (10468-4925) is a bright 2.6 magnitude star that lies some 10°N of the Eta Carina Nebula or 6.7°N of the colourful x Velorum. Deep yellow in colour, Mu Vel appears as written text in Burnham’s Celestial Handbook Vol.3. p.2038.
“Mu Velorum is a rather difficult binary, first measured by H.C.Russell in 1880 when the separation was 2.8 arcsec in PA 55°; it has since closed down to about 0.7" in PA 90° (1942) and, according to a note in the Lick Index Catalogue of Visual Double Stars in 1961, has not been seen with certainty since. The computed distance of the star is about 110 light years, and the total luminosity about 75 times that of the Sun. The star shows an annual proper motion of 0.08"; the radial velocity is 4 miles per second in recession.”
NGC 3372 / Eta (η) Carinae Nebula (10440-5930) is the brightest of the emission nebulae in the southern skies, whose diameter extends more than more than 3° of sky. Is very centre is found near the open star cluster Tr14. (See Below.) This region abounds with bright and dark nebulosity and the edges contain many bays and complex structures. In small telescopes it is extraordinary in the space it occupied, covering at least eight times the area of the Great Orion Nebula, and which all southern observers know pales the Orion Nebula to second grade. Eta Carinae and the star that gives the name to the brightest, and I dare say also the best nebulae in the sky.
Eta Carinae and the environs it appears to contain many astronomical objects including many pairs and open star clusters. In most cases nearly all are easily visible to the amateur. The region contains enough objects and structures worthy of several nights observing.
In Webb’s “Celestial Objects for Common Telescopes”, the southern addendum Appendix II, quotes;
“Great diffused branching milky nebulae with interior dark around η Argús.”
In “Astronomical Objects for Southern Telescopes”, E.J. Hartung describes;
“η Car with its associated star clusters and the great diffuse gaseous nebula enveloping it form one of the finest telescopic objects; on a clear dark night the region is beautiful beyond description, even for small apertures.”
Distance of the nebulosity from us is between 1 800 to 2 500 pc. (6 000 to 8 000 ly.) being within the Carinae arm of our Milky Way galaxy. In size the true nebulosity is perhaps some 400 ly. across, some ten to twelve times the area of the Orion Nebula. If it were at the same distance as the Great Orion Nebula M42, it would cover the entire area of Orion’s “Pot” or “Venus’s Mirrors” and be an shine incredibly bright at -2.4 magnitude!
See 123 (10440-5932) is the faint pair of 9.6 and 12.2 magnitude pair separated by about 7.0 arcsec along PA 330°, which I roughly estimated in 1997. Last measures were made in 1934, when the positions were 4.5 arcsec and 311°. This bluish or bluish white pair lies merely 1' from the cluster's centre and both appear as a lovely sight against the backdrop of nebulosity. Easy enough for 10cm.
HJ 4353 (10437-5935) is a solitary faint pair of 10.8 and 10.5B magnitude, and I estimated about the same for the visual ones. This pair is not among the “stun-wahs” in the many pairs that I have observed, yet it does lie within the same field of Trumpler 14 - even though it might not be a true cluster member. Since discovery by Herschel in 1837, it has shown clear tendencies of increasing in separation, but the PA of 180° (due south) has not changed at all. The WDS01 shows that the last measure was in 1959 with the given separation of 4.9 arcsec. In my eyes the separation was in 1994 beyond 6 arcsec. I saw both these star without colour (white perhaps) and easy in the 20cm.
Smaller apertures as low as 10.5cm should be able to see this duo - perhaps even 7.5cm with care. This star is also not mentioned in AOST2.- Nothing really to write home about though!
HJ 4356 (10440-5933) lies in the very heart of Tr 14, making it its brightest star. John Herschel discovered this pair in 1836 and little has changed in the positions at all. These two stars are a little closer together than the rest whose 9.0 and 10.4 components are separated by 2.8 arcsec with the PA being in a SE direction at 149°. Any 7.5cm telescope should be able to see both white stars which make up the “AB” system. There are another two visual companion stars nearby.
HJ 4356 AC is 13.0 magnitude and is about 5.0 arcsec following PA of 270° (West). I glimpsed this once in the 20cm C8 under very good seeing, though 25cm or 30cm might make this easier. My notes says that I looked at this pair with 30cm in 1986 and that I could not see it - I didn’t write much on the conditions so I’m unsure why I did not see it. Yet another companion- the ‘AD’ system. The ‘D’ star is an even fainter 13.5 magnitude star along PA 187° with the separation of 3.0 arcsec. This star was a little tougher because of the δm of 4.5 magnitude. In the same evening using the 20cm it appeared elongated with the A component even using high 333× magnification and I thought I glimpsed it once in a period of about five minutes. This is not an easy pair to see as it is almost in-line with the ‘C’ component. This did not seem much better in 30cm, for the same reasons above, but this time A, D and B had merged into a small line of haze - something I’ve never seen before. I also suspect this star was harder to see than I suspected and it might actually be closer than what the WDS is saying. I would love to see this in 40cm or 50cm Dobsonian. The ‘A’ and ‘B’ star are mentioned in AOST1, but the other two are not, even though they should be visible in 20cm to 30cm telescopes. What is also mentioned in this same reference is the primary ‘A’ component which is quite rightly brought to the attention of astronomers.
This star is HD 93129A / SAO238396 / PPM 339375 and has a given spectral class of “O2 If*” - with a measured B-V of -0.206, it suggesting a late B spectral class star. However the difference here is suspected only because there is much obscuration from the surrounding nebulosity meaning that the star light has been reddened somewhat. All these stars here seemed white to my eyes.
HJ 4356 A / HD 93129A appears in
several professional papers being described as
one of the most luminous stars known, and ranks
in some ways, like Eta Carinae itself. This star
shines very brightly in the ultra-violet and has
the unusual spectral lines of highly ionized N
IV, C IV and N V, that are more characteristic
of the central stars of planetary nebulae.
According to Simon, K.P. et.al, A&A., 125, 345 (1983), by mass all the stars within HJ 4356 total some 60M⊚, each having; HD 93128 HD 93129A HDE 303308 the respective radii of 11±1R⊚, 21±2R⊚, 13±2R⊚ and having the luminosities log 5.7L⊚, 6.2L⊚ and 5.8L⊚ Teff 48 000±3 000K, 45 000±2 000 and 45 000±3000K Like most high temperature stars they are rapidly losing mass from their surfaces at a prodigious rate - something in the order of 10-4 to 10-6 M⊚ per year! According to Benaglia, P.; Koribalski, B. “Radio Observations of HD93129A : The earliest O star with the highest mass loss”.;A&A., 416, 171-178 (2004) the measured mass loss was 5.1x10-5 M⊚ per year. They also found a distance of 2.8kpc. From the observed spectra, the gas outflows from HD 93129A are can change anywhere between 2 000 and 3 000 kms-1.
According to Brian Skiff (2004) HD 93129A was recently resolved as an astrometric binary using the Fine Guidance Sensor of the Hubble Space Telescope. If this is so, then HD 93129A may not be as massive as once thought.
In all, HJ 4356 is an interesting quadruple system, and if they are all truly associated, the periods may be very long. We know little of the distance to these stars as the parallaxes are far too small, though some work has been done on the galactic cluster Tr14 and the nebula itself, giving the distance around 3.2 to 3.3 kpc.
Zeta Puppis / HIP 39429
/ SAO 198752 / Noas (08037-4000) is
suspected by astronomers to possibly outshine HD
93129A. This really monstrous O5Iaf star by some
estimates could range in mass anywhere between
50M⊚ and 70M⊚. Others
suspect it could be even heavier. At the
magnitude of 2.2v, this supergiant star has an
absolute magnitude (Mv) of -7.4 and lies at the
very top left-hand corner of the HR Diagram.
Surface temperature of Noas has been estimated
to be in the order of 38 000K to 41 000K. Its
spectra also shows bright emission lines of He
II and N III. Strong variable stellar winds have
been observed to average around 2 300
kms-1. Mass loss is estimated by
Schaerer et.al ApJ.Let., 484,
153-156 (1997) as 2.7x10-6 M.yr-1 and
by Lammers and Cassinelli "introduction to
Stellar Winds" Cambridge Uni Press (1999) as
2.4x10-6 M.yr-1. Distance is about
735pc. or 2 400ly.
Telescopically, Noas to me appears ultra-blue, though other amateurs like Les Dalrymple of the Sutherland Astronomical Society, see it more as a powdery blue colour.
γ1 Vel / Gamma (1) Velorum (08095-4721) is another example of another rival star is the 4.25 magnitude which has a similar temperature, distance and absolute magnitude to Noas. A small spectroscope or direct-vision prism on either of these stars show bright lines of oxygen, nitrogen and helium. There is very little doubt that these stars will sometime in the future end their lives as Supernovae Type II’s - with the catastrophic explosion rivalling the brightness of the Moon for the peoples of the Earth.
|MULTIPLE SYSTEM : Δ65|
|NAME||Δ85 AB||Δ85 AC||Δ85 AD||Δ85 BC||Δ85 CD||I 1175 DE||Δ85 Aa|
|Mags.||1.8 / 4.3||2.2 / 8.5||2.2 / 9.4||6.0 / 8.0||9.0 / 11.0||9.4 / 12.8||1.79|
NOTE: Both Zeta Puppis and Gamma Velorum lie within the enormous Gum Nebula - a supernova remnant. γ2 is not a member of the foreground open cluster Cr 173, and there continues to be some debate on whether it is attached to the Vel OB2 association. However, γ2 Vel is one of the main ionising sources of the Gum Nebula. ζ puppis lies at the back of the Gum Nebula and lies at a disance of 429±120pc.
HJ 4360 (10441-5935) is likely the prettiest pair of the four pairs we are discussed here, but it is as just as interesting as HJ 4356 mentioned about because it is another multiple with five stars this time. HJ 4360 lies in the same field as the other three pairs so far mentioned, and lies some 2.2'SE (PA 140°) from HJ 4365.
HJ 4360 AB is the main pair is a near
equal 8.59 and 8.64 magnitude, though AOST2
for some reason gives the bright values of 7.8
and 7.8 - and I could not find its original
source. Both stars are separated by 2.1 arcsec
along PA 117°. The two are easily
seen in good conditions in 7.5cm telescope.
Like HJ 4365, the primary 'A' is another O6
spectral class star. Little has change in
these two except for perhaps a minute decrease
in apparent distance.
HJ 4360 AC is another internal pair that is little easier to see, as it is 12.5 arcsec apart along PA 289° (WNW). Easily seen in 7.5cm, and possibly even 5cm with due care, these 8.59 and 7.89 duo appear to me white and yellowish-white. Over time it seems that the PA is increased by about 1° per fifty years or so, while the separation has reduced by 1.1 arcsec since discovered in 1835 by J. Herschel. All three of these stars are very attractive for the observer with small instruments. All these main stars remind me of a miniature Alpha Crucis except that all the stars are either white or yellowish - again reddened by interstellar absorption of starlight.
HJ 4360 AE is the fourth companion of the system. This is another bright star that is aligned nearly parallel the close AB pair. Users of Megastar 4.0 & 5.0 should note that HJ 4360 AE is wrongly identified as the principal AB pair in this system, and this might have discouraged a few southern observers not to view this multiple at all. This time the 'E' component is 9.0 magnitude add lies along the easterly PA of 97° and is separated by 7.7 arcsec. These stars are also easy to spot in 7.5cm, though it was certainly more impressive in 20cm. I saw 'E' as white as well.
FIN 412 CD can be seen if you look carefully at the ‘C’ component the star splits in two with apertures around 20cm or more. Discovered by Finsen in 1934 it makes the ‘D’ component of the system. This time the alignment roughly matches the AC system where the separation is some 2.4 arcsec along PA 305°, which I estimated in mid-1984. It seems these stars are showing the most movement of all the components, where the PA (my estimation) has increased by 11° in fifty years since 1934. This is the only star to show significant motion of these components in all these pairs we have so far discussed. This star has the best chance of being the true binary, however the proper motions and parallax are essentially zero. It may take some time to prove it has physical connection as a binary. I would be interested to hear if the PA has continued in its motion or not, and if so, it would be encouraging to see some new measures of this duo. Looking in January 2002 the distance seemed just a little wider. The distance is likely to be the same as the stars in the open cluster Tr 14 and the other pairs mentioned above. All in all this is a nice easy system for small to moderate apertures. But even in larger telescopes and applying moderate magnification this pair is further enhanced, as the nebulosity nearby is bright and adds much to this truly majestical and regal field.
|MULTIPLE SYSTEM : HJ 4360|
|HJ 4360 AB||117||2.1||8.59||8.64|
|HJ 4360 AC||288||12.5||8.59||7.89|
|HJ 4360 AE||097||7.7||8.59||9.0|
|FIN 412 CD||299||2.9||8.4||12.5|
Tr 14 / Trumpler 14 / Cr230 (10439-5933) within the Eta Carina Nebula contains some twenty (20) brightish stars all within an area of 5' and is something akin to the area seen with the Jewel Box (NGC 4755) Tr 14 contains the pair See 123, and possibly the other pairs of HJ 4353, HJ 4356 and HJ 4360. All of these are visible in 10.5cm with care.
Tr 16/ Trumpler 16 / Cr233 (10452-5943) is within the η Car Nebula. Tr 16 is estimated to has an average O5 spectral type star and contains about fourteen (14) others. Covering about 10', the total integrated magnitude is 5.0 magnitude. In age of this cluster is about ten million years old.
Δ98 / DUN 98 Aa-H (10451-5941) was discovered by Dunlop in 1826. This is the wide pair that includes the magnificent star η Car and the nearby bright star ‘H’. The wide 8.14 magnitude companion star that lies 60.7 arcsec along the P.A. angle 17° (1991). Observations have shown a very slow increase in separation by 0.5 arcsec and the PA increasing from 11° to 17°. As the proper motions are small and we assume that the two stars are at a distance of the nebulosity, it is almost certain that this is just an optical pair.
|“Southern Astronomical Delights”
10 Mar 2009