In NSP4, we discussed at length the Triangulum Australe bright planetaries’ NGC 5844 and NGC 5979.In this part, we move to the eastern and opposite side of Triangulum Australe to encounter three moderately difficult planetaries, one that once took me, on a very cold evening, nearly two hours to find! The area contains one Mira variable an interesting double and a variable. After this, we move to my ‘other’ all-time favourite, NGC 3195 in Chamaeleon, that is the most southern of all the bright planetaries.

Three Moderately Difficult Planetaries in TrA.

SA2-157 (He2-182/ WRAY 16-238/ PK325-12.1) TrA (16546-6415) lies 15'min.arc. of the eastern border of Triangulum Australe and Ara. It can be found by setting the telescope on Iota ( ) TrA, then moving East by 3.7^O to the starry field of the planetary. Using a medium magnification, three 9th magnitude stars are seen in a straight line, with an 8.6 magnitude star directly east (I used a 26mm. Plossel with a C8 at 78X which yields a field some 38'min.arc. in diameter.) The planetary is marked by a faint pair at magnitude 11.9 and 13.2, respectfully, separated by 16.8"sec.arc at PA 285^O. The brighter star is the planetary, being ‘Neptunian-sized’ at a mere 3.0"sec.arc that is clearly visible is a 20cm and possibly even with a 15cm. At a photographic magnitude of 12.0, the object is fairly bright, yet I estimated the visual magnitude to be more like 12.4. An O-III filter is required to find it, by simply switching the O-III filter across the field. The colour appears to me to be a bluish-grey circular disk with no apparent surface detail. The central star is listed as magnitude 13.4 and is readily seen using high magnification. Spectral type of the PNN is type ‘O’ with a Zanstra surface temperature of 36 000^OK. Little is known about this planetary, including its distance and type.

SA2-162 (He2-185/ WRAY 16-244/ PK 321-16.1) TrA (17013-7006) lies a mere 6'min.arc. from the border of Triangulum Australe and Apus, and near the orange K2 1.9 magnitude star Alpha ( ) TrA (Atria) (SAO 253700) (16487-6902) by some 1.9^O SE (or 12.2'min.arc. East then 1.1^O South.) This planetary is a little larger than SA2-157, being some 5.0"sec.arc., however the magnitude is about half a magnitude fainter at 12.3. Again an O-III filter is really required to find it. In the hydrogen beta filter the nebulosity appears slightly brighter than the O III. The planetary is perfectly circular and I could see no colour nor surface detail. Little is known about this object.

He2-138 (WRAY 15-137(7)/ PK 320-9.1) (15560-6609) TrA is located in the middle of the ‘Triangle’ of TrA, some 1.9^O East of the 4.4 magnitude Epsilon ( ) TrA. At visual magnitude 13.2, this is a tough object for telescopes below 25cm. The nebulosity is particularly faint, subtending an angle of some 7.0"sec.arc., however, the PNN is at a bright magnitude of 10.9 and is obvious even in a 10cm. telescope - if you can find it! [It took me two hours to identify this object conclusively!] The nebulosity is particularly faint and if glimpsed with averted vision appear annular. A 30cm. or larger is really required to see it clearly. Astronomers have noted that the nebulosity is much brighter and larger in hydrogen-alpha. (17"sec.arc.) In this case an O-III filter or a Hydrogen-Beta emission filter there appears little difference between the visual appearance of the planetary and its nucleus. Observers with both O-III and H-Beta filters may like to comment if they can observe any difference between the two filter types. This has is one of the brightest PNN/ nebulosity ratio of all planetaries, giving astronomers a unique opportunity to investigate a planetary nucleus. The white dwarf in the central star is one of the coolest known among the planetaries. It has a spectral class of O1a, and is rated temperature between 23 000^O to 27 000^OK. This information was gained by ultraviolet spectra via the IAU satellite in 1982, and later by Mendez. et.al. in 1988. Because of the low temperature, it is often referred as a rare ‘low excitation planetary.’

Z TrA is a Mira variable 1.5^O directly south (16547-6512) The magnitude range is between 9.8, and as low as 12.8 (JD 2429710) the period is 150.55 days, and the spectrum changes between M3e and M5 IIe. An aperture of 10cm. will show the deep red colour of the star, and under good conditions observers could see the entire 3.0 magnitude variation in brightness. Having a 150-day period, the entire cycle can be seen during a single year. As the entire constellation is circumpolar, the star can be monitored over the entire year if you have a clear southern horizon. The period of observation is worst between November and March, as it is close to the horizon. The field is devoid of bright stars.

Iota ( ) TrA/ 201 TrA (16280-6404) (SAO 253555) is an interesting pair of unequal brightness, at 5.3 and 10.3, respectfully. The object was discovered by Dunlop in 1826 and later measured by Sir John Herschel in late August 1836. On the 13th July 1871, H.C.Russell saw the colour as light yellow and bluish but the primary to me is a distinct yellow colour, reflected by the F3-F4 IV spectral type. In the last 160 years the separation has gradually decreased from 24.6"sec.arc. to a mere 10.2"sec.arc, while the position angle has decreased from 25^O to about 12^O. (Last measure in May 1997.) There is some uncertainty on whether the pair is actually physically connected. Some consider that the proper motions favour that the stars are in chance alignment. If it is a binary, the period is likely to be very long, which is unlikely to be found out even in the next century!

The ‘A’ component is a known spectroscopic binary that has small component velocities around ~6 kms^-1. In the 1920's, the period was determined to be 39.8880 days, first published by Jones in 1928. Orbital information has deduced an average separation of about 20 million kilometres. Little data about the Aa system has been made since Jones’s observations.

X TrA or EsB 422 (SAO253062) (15146-7004) lays 1.4^O SSW of the third magnitude star Gamma ( ) TrA, and 24'min.arc. 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 west by 9^O 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 ESB365 next to Beta 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 5.0 and 6.2 in visual magnitude or 8.1 to 9.1 as a photographic 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 one of the largest B-V magnitudes in the sky at a large 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 2 500^OK. Interestingly, Webb states that the magnitude is 6.2, however, visual estimations of red stars are notorious for being unreliable. This magnitude 6.2 ‘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.)

NGC 3195 Cha (He2-44/ SA2-57/ PK 296-20.1) (10093-8051) lies 2^O from the southern border of Chameleon (Megastar Finder Chart)and Octans, and can be found exactly halfway between the 5th magnitude stars Delta 1 and Delta 2 ( ₁, ₂) Cha and Theta ( ) Cha. The field contains few bright stars, however, aperture does not reveal many more. Discovered by John Herschel in 1835, the planetary is fairly bright and large. AOST1 and 2 both state that is "easily seen in a 10.5cm., but the prism image in 15cm." The visual magnitude is given as 11.6, while the photographic magnitude is stated as 11.5. In size the diameter has been stated as between 42" to 44"sec.arc. Burham’s Celestial Handbook states 40"x30"sec.arc. AOST2 states little difference in all respects except in the diameter of 30"sec.arc. According to my visual estimates, the apparent diameter is closer to the 40"sec.arc. mark. The shape is ovoid along the axis PA 170^O/350^O. I like this planetary because it is so bright. An O-III filter definitely enhances this object, and with high magnification the disk also appears mottled. Visually, the overall surface brightness across the disk is even that shows little structure, reflected in the Vorontov-Velyaminov classification of Type III. Along the southern outer boundary, the planetary has a slightly ‘wavy’ appearance seen in apertures above 20cm.

Spectroscopy has revealed (AJ 334, pg.842 (1992)) that the planetary is approaching us at a radial velocity of +17±3 kms^-1, with the nebulosity expanding at about 40 kms^-1. Total mass of the nebulosity is estimated to be about 8.6% that of the Sun. The PNN is magnitude 15.3, but is obscured by the nebulosity in all amateur telescopes.

Distance is estimated to lie between 1.6 and 1.8 kpc., though the more recent estimates are 1.67 kpc.

I you haven’t looked at this object - I am sure you will not be disappointed.

NGC 3149 (10037-8025) is a galaxy that lies near the same field of NGC 3195. It can see in the same field if the planetary is placed at the bottom SE edge of the eyepiece, with the galaxy being near the edge in the NW. At magnitude 13.1 it is clearly visible in a 20cm., subtending a circular size some 2'x1.9' min.arc. I could see no detail in the faint ‘smudge’, in what I describe as another typically unexciting galaxy. This object is not listed in Sky Catalogue 2000.0 or Sky Atlas 2000.0. Both the NGC and RNGC description is F,S,LE, VLBM,*15INV ‘Faint, small, little extended, very little brighter in middle, 15 stars involved.’

HJ 5444 (10318-8155) The pair is bright and wide, and is listed as magnitude 7.0 and 9.5, separated by 41.9"sec.arc. at position angle 235^O. Measures in the last 80 years have shown little change. The last measures in 1983, as quoted in the WDS96, gives a separation of 41.8"sec.arc. with a position angle 223.5^O. Later observations have give the spectral class an upgrade in temperature, and the primary is now considered a B5 subgiant star of luminosity class III-IV, instead of B3. Based on the common proper motions of the two stars it is likely just an optical double star. The pair is visible even in a 7.5cm. My own observations describe the colours as bluish and yellowish. A neat pair!

R133 (09432-8120) has magnitudes 9.5 and 9.5 was first discovered by H.C.Russel from Sydney Observatory on the 26th May 1880. His observation is given as 3.5"sec.arc PA 44^O. In 1983, the separation was measured at 3.65"sec.arc. while the position angle is given as 46^O, indicating little change. This is a delightful even pair, with yellowish components. As both have similar common proper motions, it is likely that these stars maybe associated. If it is a true binary, the period is probably very long.

Postscript: Letter Regarding Planetary Nebula and Evolution Theory.

On 11th July 1997, Dr.Jessica Chapman of the AAO addressed the Society on ‘The Life and Death of Stars’. Within this talk, she discussed the Asymptotic Giant Branch Phase (AGB) and the Formation of Planetary Nebulae. Unfortunately due to time constrictions in the old venue, Dr. Chapman did not have enough time to discuss some ideas within her talk. As we have been talking about planetaries in this series, some important points were raised in a personal communication about some glaring discrepancies with information often published in popular books and magazines. I thought that the following could be of some interest to members of the Society. If you attended my own lecture to the Society (Sept.1996) on ‘Planetary Nebulae’, some of the statements made during this lecture have had to be updated.

A major question that was bugging me for more than three years - Will the Sun form a Planetary? Most common books and articles, (including my presentation and text), as recent as August 1997 still state this incorrectly - the Sun will form a planetary.

The Letter to Dr.Chapman was as follows;

Thank you for your address at the Astronomical Society of NSW last Friday night. It was certainly an enjoyable lecture, and also obtained a good general response. I am sorry that the circumstances of occupying the hall made everything so rushed, and had little time to talk to you.

In summary:- I have been an adult education teacher for the last ten years, and am interested in the general topic of stellar evolution. I have found that most topics within this subject are usually easily to explain. This is made using the H-R Diagrams and a series of slides - from the birth of stars to their deaths as either SN's, neutron stars and white dwarfs. ( N.B. The level that I am teaching is similar to many portions of your lecture.)

In regards, planetaries I have been explaining (with suitable given text) that the progenitors generally are between 4.0 and 8.0 solar masses, producing WD's 0.7 to 1.3 solar masses. This data is based primarily (and elsewhere) on Iben, I. Jr. article in the QJRAS Vol.26, entitled "Life and Times of an Intermediate Mass Stars- in Isolation/in a Close Binary." This I was recommended by other sources.

In the literature I have searched (till Jan 1997), this range of the original progenitors is as low as 1.5 solar masses, with the upper limit around 10. The only general text I know about that discusses mass ranges in any detail is Ken Croswell 'The Alchemy of the Heavens' (1996).

These following questions, and her replies were;

1. What is the mass range of the progenitors of planetaries in current theory prior to the AGB (Asymptotic Giant Branch) stage?

The mass range is not well determined but the minimum mass is below one solar mass while the upper mass is currently thought to be between 6 and 8 solar masses. The lower and upper limits are difficult to pin down precisely as the evolutionary models depend critically on things like the stellar metallicies and on the rate and duration of mass-loss in the AGB phase.

2. As the mass increases within this range, is their any known correlation between the structures observed in the PN to the amount of gas ejected in the AGB phase as seen in the illuminated circumstellar envelope?

Good question - I wish I knew the answer to this. About half of planetary nebulae show non-spherical shapes. I don't think there is a known correlation though between shape and progenitor mass. In some cases the asymmetries (especially bipolarity) may be caused by binary companions. In other cases its thought to be related to an enhancement of a small density variation in the AGB phase which gets `amplified' in the post-AGB phase. The stellar magnetic fields may also play a role - though no-one has yet proved this.

3. What is the minimum mass suggested for the mass of the PNN - that does not have enough UV energy to illuminate the circumstellar envelope?

As above - I'm not sure exactly but well below 1 solar mass.

4. In current theory, does Sun produce a (proto-) planetary nebula?

YES DEFINITELY!

5. Could you also suggest other authors that may assist in this subject (Other than Iben. )

Here's a list of some related research papers. Most of these are heavy going but have useful tables or diagrams.

Referred References:

1. Chapman J.M. & Cohen R.J., ‘The Circumstellar Envelope of VX Sgr.’ MNRAS 220, 513 (1986)
- A detailed radio maser study of mine

2. Bedijn P.J.; ‘Pulsation, Mass-Loss and Evolution of AGB Stars’ Astron.& Astrophy. 205, 105 (1988)
- Bedijn's work produced many of the current ideas on AGB evolution

3. Vassiliadas and Wood, ‘Evolution of Low and Intermediate Mass Stars to the End of the AGB.’ AJ. 413, 641 (1993) - Probably best current paper on this topic

4. Vassiliadas and Wood; ‘Post-AGB Evolution of Low and Intermediate Mass Stars.’, AJ. Supplement Series 92, 125 (1994) - On evolution from AGB to PN and white dwarfs.

5. Habing H.J. ‘Circumstellar Envelopes and AGB Stars.’ Astron.& Astrophy. Review, 7, 97 (1996)
- Good review paper with hundreds of references

Second Letter Regarding Planetary Nebula and Evolution Theory.

It is interesting to note that the text published in so many general sources are wrong in their presentation on the formation and evolution on PN's. If I may suggest, this information should be directly available for educational purposes. One of the most important aspects in teaching in evolution theory in astronomy is the relationship of the Sun to the other stars. Most of the text that I am aware of never actually state that the Sun will produce a planetary nebula, and if it does, the detail explaining this is often minor.

At present, a popularized article is well in order. An article in a magazine like Sky and Telescope maybe a suitable place for an overview. If you know of someone in the AAO staff who could right such an article, this maybe a good idea to publish - besides, it would make good publicity for the AAO!

If I should be so bold, a final suggestion for your 'popular' presentations of your Research is the relationship to the discards of the AGB phase of stars to the formation of elements essential to life and planetary formation. (Carl Sagan's 'Star Stuff'.) In education, this gives a 'personal' relationship to the evolution of stars. More importantly, if the Sun does produce a planetary nebula - this gives a visual and understandable relationship to the spectacular images of PN's, like those of David Malin.

Again, thank you for you very much for your time, and best wishes for the Research projects that you follow in the future.

Regards, Andrew James

Dr.Chapman Replies;

I should perhaps have told you that I did in fact write up a popular article on just this topic - for the Australian Sky and Space magazine. I think the issue was December 95. I've also seen other good popular articles on stellar evolution in the American Sky and Telescope magazine.

The whole field of mass-loss from stars is very recent. The importance of mass-loss has only been recognised within the last 20 years and many of the details (i.e. structures/mass-ranges) are not yet properly understood. It is irritating that most of the popular text books present very out of date ideas on this topic but it does take time for front-line research to become properly known in the popular literature. Personally I try to give occasional popular talks on my own research as do many of my colleagues. Probably the best source for more recent information is the magazines, especially Scientific American and I think you can send them enquiries for past issues on selected topics.