supernova remnant versus planetary nebula

[arecibo]

Hi. My name is Miguel, and I started learning Astrophotography (by doing) about one year ago.

With a 750/150 SkyWatcher newtonian, several Canon EOS cameras, and miscellaneous accessories, in a heavily urban light polluted site, and a highly turbulent place (meaning, that I have very poor seeing, almost at all times).

So I've tried every "easy" Deep Sky Object in sight (mi field of view covers from about 10º South to 60º North of Declination).

The case is that I've noticed that, mostly (considering the circumstances), supernova remnants tend to have O-III emission in the outer shell, and H-alfa in the inner. While planetary nebulae tend to reverse the distribution.

And I was wondering if that's a known (and explained) Astrophysics fact, or just chance (due to my less than complete experience).

Cheers.

[ZeroID]

Hi Miguel, :welcome: to IIS.
An intriguing question indeed. Hopefully someone will be able to give you an answer to this as I certainly don't know. Have you searched for the answer on Google or elsewhere ?

[arecibo]

Thank you, Brent.

No, I have not. But it's not a bad idea ... perhaps a bit difficult to apply because of the overflow of answers :)

PS: I just tried; to no avail, the terms are too general to find anything meaningful (404000 results in google).

[bojan]

Go to Wikipedia, stellar evolution (http://en.wikipedia.org/wiki/Stellar_evolution) and start from there...

[madbadgalaxyman]

I am not sure that I can answer your question, Miguel, as I am not an astrophysicist, but here are some pertinent facts. I hope some of our resident "physics heavies" will contribute to this thread.

Much to my chagrin, though I have spent considerable time studying the Interstellar Medium, I am still somewhat in the dark about the physical conditions in Supernova Remnants (SNRs)! Supernovae have enormous effects on the interstellar medium in a galaxy, and the consequent energy injection can either enhance or suppress star formation, depending upon the circumstances. Further, supernovae and SNRs pump lots of heavy elements into space, providing the raw materials for the formation of planets.

Lawrence H.Aller, in his classic , extremely detailed, but very clear & cogent, semi-popular-level book about stars and the interstellar medium, “Atoms, Stars and Nebulae”(3rd edn)(1991)(Cambridge University Press), writes that strong shock waves in the Interstellar Medium produce spectral lines of highly ionized atoms. In the optical regime, this implies the production of [OI], [OII], [OIII], and [SII] spectral lines. (also, plenty of UV lines are produced)

In a supernova remnant, a compressed shell or sheet of gas travels into a rarified gas with a speed exceeding that of sound in that medium, and this produces a shock wave. To quote Aller: The atoms in the advancing shock front are all moving parallel to one another, but the collision causes kinetic energy to be converted to heat”. Aller compares the collision between the surrounding diffuse interstellar medium and the gas expelled from a supernova or planetary nebula , to a bullet hitting a target and melting due to the conversion of kinetic energy into heat. There has to be a sudden rise in gas temperature and density where the shock wave hits the surrounding low-density gaseous medium.

The shell structures of young SNRs are known to expand at very high velocity, of the order 6000 km/s. According to the book ‘An Introduction to Radio Astronomy” by Bernard Burke and Francis Graham-Smith (a valuable and clear book that explains much about emission mechanisms in the interstellar medium), the shapes of the “shell-like” SNRs such as IC 443 and Gum Nebula and the Cygnus Loop are largely determined by the collision of the remnant with interstellar clouds.

Typical sizes of SNRs: The Crab Nebula is about 4 parsecs across, as is Cassiopeia A. The remnant of Tycho’s Supernova (1572) is about 9 parsecs across. The Cygnus Loop, a much older supernova remnant, is over 40 parsecs across. It is obvious, from the variety of sizes, that the physical conditions can vary very greatly between various Supernova Remnants, so it is going to be hard to say something that applies to the spectra of all SNRs.

C.R. Kitchin, in his book “Stars, Nebulae and The Interstellar Medium”(1987)(a useful simplification of astrophysics for non-physicists such as myself!), gives the following phases in the evolution of a SNR:
(1) Initial phase, where the density of the hot gases exploding outwards at about 10,000 km/s is very much higher than that of the surrounding interstellar medium, so that the expansion is essentially into a vacuum.
(2) When the SNR reaches about one parsec in size, the interstellar gas swept up by the expanding remnant reaches densities at which it starts to impede the expansion. This leads to the formation of a turbulent and strong shock wave, with strong synchrotron emission.
(3) The expansion velocity slowly decreases, and there is increasing emission of optical lines from heavier elements.
(4) The remnant will eventually merge with the interstellar medium, after a few hundred thousand years.

Best Regards,
mad galaxy man

TO BE CONTINUED, in another post!!!

[arecibo]

Thank you, Robert.

Somehow, you confirm (or add evidence to) my growing suspicion that I was jumping to conclusions with limited data. Not a very scientific attitude :lol:

(and waiting for the continuation)

[madbadgalaxyman]

Miguel, it was an interesting observation that you made.
The good thing is that amateur astronomers can now make these sorts of observations with affordable equipment.

It may be that, after making further observations of various Supernova Remnants and Planetary Nebulae, you might (or might not) modify your conclusions;
but the question of the spatial distribution of [OIII] emission vs. H-alpha emission is certainly worth thinking about......so perhaps you can find some more observational support for your interesting hypothesis. A scientific hypothesis can be either 'strong' or 'weak', depending upon the amount of observational support, so an informed conjecture or idea, even if later proved to be partly wrong, is still worthwhile. [ After all, Galileo claimed that Venus showed phases, somewhat before he was able to see the phases clearly in his telescope; and he later proved that the planet does show phases!! ]

I will shortly contribute some more info regarding the spectral lines emitted by SNRs in the optical regime, and their mechanisms of causation. I have some experience with stellar spectra, but much less with nebular spectra, however I will do my best!

[Dave2042]

Not a physics heavy at all, but once got a mediocre degree with honours in astrophysics, so I'll put in my two cents' worth.

As Bojan correctly points out, this is an aspect of stellar evolution. My understanding is that this is a field where the basics are quite well understood (gravitational collapse forming a star, progressive fusion from H through the various metals, finally leading to various things like supernova, white dwarf, black hole etc).

On the other hand, the finer details are much less understood. What you are talking about is definitely a finer detail.

Based on my limited understanding and a quick trawl of the web, I don't think what you suggest is 'known'. On the face of it, I can't see why it would be the case, however that's certainly not a reason to believe it isn't. So don't assume there is anything wrong with posing the question.

As Robert suggests, a sensible and worthwhile thing to do is make more observations. Maybe it will turn out there is no effect generally, and you just saw something random. That alone is something worthwhile. On the other hand, you might find there is a real and general difference. That would be very interesting.

I'd love to hear about progress if you pursue this.

[arecibo]

Thank you, Dave. You summarize quite accurately what I'm thinking about the issue right now.

As Homer Simpson would say "mental note: pursue the thing" (I haven't seen the series in English, so I'm not sure what he says in the original). However, I hope I'll be more consistent than the character :)

[madbadgalaxyman]

I have found a general description of spectral line formation (for those lines found at optical and UV wavelengths) within SNRs in one of my “old standby” Reference Books that provide detailed explanations of diverse phenomena (see the last paragraph for its name and details). There follows a very general description, without any specifics about the detailed modeling and existing observations of the space distribution of the emission of various optical spectral lines in Supernova Remnants.

Here is an abstract of part of an encyclopedia entry entitled “SUPERNOVA REMNANTS, OBSERVED PROPERTIES” :

Visible & Ultraviolet wavelengths Emission from supernova remnants is largely from gas that has been excited and compressed by the expanding blast wave and by thermal instabilities. The optically visible gas, usually visible as filamentary structures, is at near to 10,000 degrees Kelvin and a density of a few hundred atoms per cubic cm.

In contrast, the “not optically visible Gas” surrounding the filaments is at a million degrees Kelvin or more and has a density of less than one atom per cubic centimeter; so this diffuse Very Hot gas emits in the X-ray regime, by the thermal bremsstrahlung mechanism. This Very Hot gas is heated by the passage of shock waves through supernova ejecta and through the surrounding interstellar gas.
[ denser regions of the SNR will tend to cool faster (by radiation?), and thereby become more compressed, in order to maintain pressure balance with the surrounding diffuse super-hot gas ]

The temperature and density of the optical filaments can be modeled and calculated by starting with the observed ratios of the intensities of various observed spectral lines. For instance, the observed ratio of the intensities of the two [SII] lines (photons coming from singly ionized sulfur, at 671.7 nm and 673.1 nm) depends on the number of collisions between atoms, which depends on the density of the gas. Thus, the [SII] line ratio can be used to calculate gas density.

The H-alpha line (656.3 nanometers) is produced brightly in SNRs
(but this reference gives no comparison with H-alpha line formation in other types of nebulae, for instance Planetary nebulae and HII regions). (I am not sure how or if H-alpha line formation differs between various types of objects!)

In Supernova Remnants, the [OIII] line at 500.7 nanometers, from doubly ionized oxygen, is used as a diagnostic of shock waves, because shock waves provide the energy to remove the two electrons from the atom. The [OIII] line is very prominent in SNRs due to this ionization resulting from a strong shock wave.

In addition, emission from Supernova Remnants can be observed at visual and ultraviolet wavelengths; emanating from very highly ionized and excited gas, such as nine-times-ionized iron.

Much of the gas that is detected at visible wavelengths in SNRs is not actually gas that originated in the supernova explosion itself (!), because most supernova remnants have swept up a large quantity of the surrounding interstellar gas. This fact makes it extremely difficult to use the observed optical spectrum of a SNR to figure out the quantity of heavy elements that the progenitor supernova is adding to the interstellar medium.

Most of the optically visible Supernova Remnants have radiated away only a negligible fraction of their energy, so the gradual slowing down of their expansion with the passage of time is thought to be due to the accumulation of mass from the surrounding interstellar gas.
___________________________

In this post, I have abstracted information from:
“The Astronomy and Astrophysics Encyclopedia”(editor: Stephen P. Maran)(Published 1992)(ISBN: 0521417449)
This book is one of the essential references for people aspiring to obtain really detailed “physical” knowledge about the full range of astronomical phenomena, processes, and objects. The readership level is at the extreme upper end of “semi-popular”, so those mid-level amateur astronomers who are not used to a “densely technical” style will find this book to be heavy going. However, the long and very detailed entries avoid mathematics, except where absolutely necessary.
See my review of this book at www.amazon.com (http://www.amazon.com/), where I am called R.A. Lang
__________________________

[arecibo]

Hi, Robert. Thanks for the effort.

Very informative and interesting. I'm going to ask my Department to buy me the Encyclopedia :D

[madbadgalaxyman]

It is an excellent single-volume reference for 'finding out what is really going on, in detail" without excessive jargon and technicalities and unnecessary complexity.
There are plenty of cheap copies available on the internet.

There was a very similar (but this time Multi-volume) encyclopedia, published in 2001 and edited by Paul Murdin, which is more expensive. I have just decided to buy the Murdin encyclopedia as well!

I am currently trying to achieve a more detailed understanding of the physical conditions and evolution of a SNR!
[ It really helps that I already own about a dozen books about the interstellar medium.]
Then I will do a literature search for scientific papers about the spectral lines detected from supernova remnants and about the spatial distribution of the emission from the various lines.

I am pretty sure that the various spectral lines in the optical and UV regimes, and their characteristic distributions in space, have already been characterized in the professional literature ;
this is the sort of work that some of the less-talented professional astronomers like to do, as it merely requires some observations and their presentation in a paper, without too much analysis and without firm conclusions......they get to publish a paper, merely by presenting observations.
(not much harder than the work that the top amateur astronomers do!)

[arecibo]

Hi, Robert. I'll order the Encyclopaedia anyways because I'm generally interested in Astrophysics (and bored of Math literature, ailing of the same defects -or worse- that you point out on AP scientific papers). And of course, because of my question in this thread.

And glad to know about any thing you find on the subject. We say that four eyes can see more than two.

[madbadgalaxyman]

The one-volume encylopedia edited by Maran. is a good way to start on the journey towards really detailed understanding of astronomy.

As for me.....
I am going to have to bury my head in some Astrophysics books regarding line formation in nebulae!
It is a long time since I thought about exactly how this emission takes place; I do know the basics, such as how emission lines and absorption lines are formed, and a little about some of the electronic transitions that cause emission and absorption at specific wavelengths, but I don't really have any detailed knowledge of atomic astrophysics.

I am considering buying a copy of "Atomic Astrophysics & Spectroscopy" by Pradhan and Nahar, (2011), Cambridge University Press, ISBN: 0521825369
(this book is heavy going; it requires that the reader have a good few units of physics at the university level, or the equivalent background obtained from personal study of physics and astronomy)

There are a number of good introductory astrophysics textbooks :
for instance "An Introduction to Modern Astrophysics"(2nd edition) by Carroll & Ostlie, and "Astrophysical Concepts"(4th edition) by Martin Harwit, but even basic astrophysics books are hard!!
Unfortunately, these general astrophysics books tend to give only a small amount of detail about the processes going on in HII regions and planetary nebulae and SNRs ; they provide only a broad overview of nebular processes.

Looks like we are going to have to figure out what lines are formed, and where they are formed, and why, at different points within planetary nebulae and SNRS......I don't think any physics heavies are going to answer!

[arecibo]

Hi, Robert.

The issue is taking off, it seems. Good to see that it's interesting enough. In any case, it appears to be a "take it easy, don't hurry" theme.

I've started a list of pertaining DSO objects. It's more complicated than I thought; Up to now, I only have objects that I've tried to image:

Supernova remnants
match; imaged; Common name; Id; Const
√; √; Veils (Gygnus Loop); Sh 103; Cygnus
√; √; Crescent; NGC6888; Cygnus
√; √; Jellyfish; IC443; Gemini
?; √; Crab; M1; Taurus

Planetary nebulae
match; imaged; Common name; Id; Const
√; √; Ring; M57; Lyra
√; √; Dumbell; M27; Vulpecula
√; √; Little Dumbell; M76; Perseus
√; √; no common name; NGC6781; Aquila
√; √; no common name; NGC7048; Cygnus
√; √; Owl; M97; Ursa Major
?; √; Medusa; Abell 21; Gemini


In that list (sorry for the format), I'm not sure if M1 matches my, say, "hypothesis" (I have not enough susbs yet). I'd say the same about Abell 21, though the current "image in the making" seems to match too.

However, surfing the web, I've learned that planetary nebulae are (at least) of two kinds: bipolar, and non bipolar.

A paradigmatic bipolar example could be the Twin Jet Nebula (just in my southern imaging border -a bit small for my scope and site-), Minkowski 2-9 (in Ophiuchus), and it's interesting because the distribution of the shells might match other PN in my list.

I've found a scientific paper on that PN: http://iopscience.iop.org/0004-637X/552/2/685/pdf/0004-637X_552_2_685.pdf

But (in a quick fast reading -if one can do that with a scientific paper-) it does not describe the emission lines dominant in the shells.

Keep searching ...

The case of SNR it's tougher. Most google results point to multiwavelenght images, without enough details.

Keep searching ...

[madbadgalaxyman]

I am currently "having a really fun time" doing personal study of line formation in HII regions, planetary nebulae, and SN remnants; so I may make a detailed comment about your very interesting and exciting project, when I can find the time.

The Crab Nebula is very different from older Supernova Remnants, in that much of the radiant energy from the Crab nebula is actually energized by the central spinning neutron star (the central pulsar).

For older SN remnants, the radiated electromagnetic radiation comes from:

(1) Shock Heating: X-rays are emitted via the thermal bremsstrahlung mechanism : compression of the gas, by shock wave, raises its temperature to 10E6 -10E7 (1 million to 10 million) degrees celsius.

(( Note: The gas in SN remnants is not all from the supernova itself: The emitting gas is a mixture of:
- ejecta from the SN itself
- a part of the surrounding ambient interstellar medium, which has been swept up by the shock wave
- circumstellar gas which was already there before the supernova explosion, as it was emitted by the supernova progenitor in its red giant phase of evolution.
))

(2) Synchrotron emission: caused by relativistic (near light speed) electrons spiralling through a magnetic field: SNR emission from the synchrotron process occurs at a very broad range of wavelengths, but it is especially prominent in the radio regime (most SN remnants are too obscured at visual wavelengths to make it worthwile to survey for them using ordinary telescopes; use a radio telescope for SN Remnant surveys!). The gas surrounding the supernova has some magnetic field lines locked into it, and this magnetic field is boosted, because it is squeezed and stretched by the compression process of the expanding shock wave. Relativistic electrons spiral through the enhanced magnetic field, causing Strong synchrotron emission.

(3) Collisional excitation: Free electrons (and protons) collide with atoms of heavy elements (e.g. Oxygen), bumping them into a higher energy state. The blast wave of a SNR leads to a high rate of collisions between the atoms in the gas, and this leads to an enhanced rate of collisional excitations.
This type of excitation leads to the radiation of several prominent emission lines in the optical and UV regimes.
A good example of collisional excitation in SNRs is the [O III] doublet which is emitted in two different lines at wavelengths of 4959 and 5007 Angstroms. The Oxygen atoms are floating around (as a relatively small impurity in the gas!), and an oxygen atom can be hit by one of the many free electrons that exist in the ionized gas, in which case the atom picks up some of the kinetic energy of the electron. The excited Oxygen ion can decay radiatively to two (out of its three existing) lowest energy levels, thereby releasing an emission-line photon.

The symbol OIII actually refers (somewhat confusingly) to an Oxygen atom which is an ion that has lost two electrons, and which therefore has two units of positive charge. A much clearer and better Symbol to represent this ion is to use the letter O with a superscript of 2+ , because this symbol clearly shows that two negative charges have been lost by the atom. These two distinct [O III] spectral lines are emitted by the transition of one of these Oxygen ions from an excited energy level to its fine-split ground level (as can be appreciated by drawing a diagram of a simple Bohr Model of an Oxygen atom nucleus and its surrounding electrons that are able to move between different energy levels)

(Another emission line that is emitted by the OIII ion is at 4363 angstroms, This comes from a different transition between electronic energy levels.)
______________________

It gets a lot more complicated than this, as a popular model for SN remnants has two shock waves;
the (as expected) expanding shock wave, but also another shock wave caused by the ejecta's impact with the surrounding gas.....and this second shock wave is an inward travelling shock wave!!
It seems counterintuitive to have two shock waves travelling in the opposite direction to each other, within a single object, but if you know anything about abstruse physical theory, you are moved to repeat the words of Obi Wan Kenobe :

"These are the truths that we must cling to, Luke"

[sjastro]

Interesting discussion. Sorry for the following diversion.

OIII emissions are examples of "forbidden transitions". According to the selection rules for quantum mechanics electrons can carry off single units of orbital angular momentum when going from a ground to excited state and vice versa. The probability of an electron carrying anything other than a single unit of orbital angular momentum is very low.
In fact OIII emissions have never been observed in the laboratory. Excited O atoms in the laboratory lose energy through collisions making forbidden transitions extremely unlikely.
Not so in outer space. The density of your emission nebula, planetary nebula or SNR remnant is so low compared to a "laboratory sample" that the O atoms do not lose energy through collisions. Excited O atoms can exist in a an extended excited transition state, and the probability of a transition to a lower energy or ground state via a forbidden transition is greatly increased.

Before the advent of quantum mechanics the observation of forbidden lines in the spectra of emission nebulae led to the "discovery" of a new element, the appropriately named Nebulium.
Unfortunately Nebulium caused havoc amongst scientists of the time. It effectively threw the Periodic Table classification of elements out the window as Nebulium did not sit anywhere in the table.
Through quantum mechanics the problem was solved, Nebulium was nothing more than excited Oxygen.

Regards

Steven

[madbadgalaxyman]

An interesting and strongly-physical perspective, Steven.
Sounds like it comes from someone who has had intensive physics training, unlike me (my approach, all my life, has been to learn only the physics & maths that is absolutely necessary for me to understand the astronomy I happen to be studying, but no more than that)

Q. All the astrophysics books talk about 'collisional excitation' (which sounds like a very exciting type of excitation!) of the OIII ion, but they never mention if there are any transitions of this atom that can be set off by energy that is provided to the atom by photons (that is, by electromagnetic radiation).
Can OIII be excited by a photon?

I am buying a copy of the aforementioned book "Atomic Astrophysics and Spectroscopy", because I find that most astrophysics textbooks only give a sketch of physical processes in ionized gas regions.

One book that I do use is "Physics of the Interstellar and Intergalactic Medium", (2011), by Bruce T. Draine, (Princeton University Press)(ISBN: 9780691122144).
I find this solidly graduate-level text to be heavy going, for the most part, and I have to keep referring back to physics textbooks when I use it, because I only have a unit or three of tertiary-level physics.
[ A more famous book is Osterbrock & Ferland (2005) "Astrophysics of Gaseous Nebulae and Active Galactic Nuclei."]
I find that while I do own lots of easier books about the ISM, I am still forced to tiptoe through graduate level texts, as the interstellar medium is so remarkable in its complexity!

There seem to be a lot of high-level ISM books coming out, of late (by: A.G.G.M Tielens, Sun Kwok, the Draine book that I mentioned, etc). I wonder if anyone is reading them?

[sjastro]

While Quantum mechanics (QM) is taught at an undergraduate level in Physics and at a more introductory level in Chemistry, it is fact a branch of Applied Mathematics. When taught as an Applied Maths subject one goes far deeper into the theory due to the mathematical nature of QM.



Most definitely. In fact the primary mechanism for the observation of OIII lines in the spectra of emission nebulae is the absorption of electromagnetic energy from stars into the surrounding gas.
Photons are absorbed by oxygen resulting in ionization.
Electrons are recaptured by the ionized oxygen. When oxygen returns to its ground state photons are re-emitted at energies corresponding to the OIII frequencies at 495.9 and 500.7 nm.



I need to brush upon my astrophysics, I'll keep an eye out on these publications.

Regards

Steven

[madbadgalaxyman]

Here is a useful overview paper, by Sun Kwok, about planetary nebulae, and here are some lecture notes about Planetaries by Jacob Arnold:

132505

132506

You will note that the article by Sun Kwok is from an entire IAU Symposium (S283) in 2011, which was devoted to the latest research on planetary nebulae.

If you go to the website:
http://journals.cambridge.org (http://journals.cambridge.org/)
and find the "Proceedings of The International Astronomical Union", you will find that you can view and/or download a lot of the "single topic" astronomical symposiums from about 2010 and backwards, in pdf files.
The access policy is remarkably liberal, which is just as well, as the paper volumes of these symposium proceedings cost " a king's ransom"

This is a good way to find out about the current research on "most everything" in astronomy. It is undeniably one of the best resources for bringing you up to speed on the "now" of astronomical research.

[arecibo]

Thank you Robert & Steven.

I've been too involved with academic hassle (as every first half of any week) to return to this issue.

It's very gratifying to read how, many scrap knowledge I had on the subject, is put together by your contribution.

I've done little progress meanwhile. My first setback was discovering that the Encyclopaedia is out of print :(

I was reluctant to resort to the Astrophysics Department in my University, but I'm reconsidering it. And, of course, I should raid the Library, just in case.

Anyways, please, keep contributing as you are doing.

PS: I'm starting to read Jacob's paper; it seems to answer half of my question: the distribution of the visible emission lines in PN. As I'm prone to jumping to conclusions (it's builtin, I can't avoid it, lol), please take it with as many grains of salt as convenient.

[madbadgalaxyman]

Hello Miguel,

Yes, the Maran encyclopedia is out of print, but there are still plenty of secondhand copies of it, available for purchase on the internet.
Try one of the "book price comparison engines", and put in the ISBN of the encyclopedia into the search box:
www.abebooks.com
www.bookfinder.com
www.bookfinder4u.com
www.fetchbook.info
- also, can try the secondhand network of amazon.com

I agree, Jacob does address the issue of the distribution of emission lines in a planetary nebula. But, the situation within a SNR must be a lot more complex than in a planetary nebula, due to the existence of multiple shockwaves within the object.
(I seem to recall that planetary nebulae expand at a relatively low velocity of about 20-50 km/s)

cheers, Mad Galaxy Man

[Merlin66]

You should also have a look at Gaposchkin's "The Galactic Novae"
Chapter 10: "Comparative study of Spectral Development" gives a good insight into the subject.

Also James Kaler's "Stars and their Spectra" discusses both SN and Planetary spectra, with example spectra.

[madbadgalaxyman]

Kaler's book is excellent.

"Stars and Their Spectra" by James Kaler is one of the clearest and most cogent "popular-level" introductions to stellar evolution, stellar spectra, the OBAFGKM sequence, and the Hertzprung-Russell Diagram(= color-magnitude diagram). The second edition was published in 2011.

It is quite remarkable how Kaler manages to effortlessly convey a detailed understanding of stellar evolution and stellar spectra, without muddy explanations and without unnecessary complexities and complications.

He takes the relatively easy approach of explaining and linking together the observables such as stellar spectra, stellar luminosity, stellar color, and stellar spectral type, instead of "getting really heavy" with a detailed discussion of the internal constitution of the stars.

I note that one of the reviewers at amazon.com says that the spectra are very poorly reproduced in the second edition. (I have the very nicely produced First Edition). One of the most important features of the book is the spectra, so this would be a major flaw.
____________________

Ken, is that Payne-Gaposchkin's book written in the early 1960s?
She was a very very good writer of astronomy books, but the date of publication would indicate that some caution is in order;
humankind's knowledge of planetary nebulae was only in its infancy in the 1960s.
Because much of the basic information about planetaries was obtained between 1960 and 1980, I would be a little cautious about the book's conclusions as to what is going on in these nebulae.
_______________________

[Merlin66]

Robert,
I have both the 1st and the 2nd Editions in hardcover and the printing of the spectra is 100% OK.
I did have a paperback copy of the 1st edition where the reproduction of the spectra (and illustrations in general) was very poor.

[arecibo]

Hi, all.

Good to see that my rather naïve question gave birth to a brain storm of far from naïve contributions.

I'm interested in almost everything Astrophysical, so you've given me enough food for thought for month or years to come.

I would like to summarize what I've learned in this thread: My question (I realize now) was one about morphology (and the underlying Physics, of course). Or, rather, two questions about morphology, with a third implicit.

When you see images of nebulae, you notice three kind of shapes:

Highly regular, in many planetary nebulae.

Highly irregular, like in M42, M78, IC1318, IC5146, NGC7000, The Cone Nebula region, M8, M20, etc (I mention ones that I've imaged or seen at a telescope).

And mildly regular, in supernova remnants (I've seen less of these).

So it was an easy jump (not really well founded) to associate shape with physical origin. I know that (bright) irregular nebulae are of two kinds (emission and/or reflection), and that some ENe and RNe can be rather regular in shape (The Rosette Nebula, for example).

Ok. So, the shape of PNe is more or less explained to (my) satisfaction. The "less" part is to account for new developments (and variations on the nebula formation process and "final" shape, not because I'm not satisfied). The general shape of emission and reflection nebulae does not need a general explanation.

And my observations of SN was too limited for allowing a general conclussion about their shapes.

Let's say that my quest is fulfilled. However, I'll read "con gusto" more contributions to the theme.

[Weltevreden SA]

We shouldn't overlook (pardon the pun) the role of magnetohydrodynamics (MHD) in PN and SN remnant formation. Filaments and threads are magnetic sheets that we can see, and MHD turbulence plays a major role in stellar evolution, from coalescing molecular clouds to final dispersion into the intergalactic medium. Without magnetic forces our sun would be a hot but very boring object. There are so many papers on how MHD affects both PN shapes and SN remnant dispersion that one can get a bit addlepated trying to keep up with it all. Google Scholar lists the following references for MHD in PNs:

http://scholar.google.co.za/scholar?hl=en&q=Magnetohydrodynamics+in+planetary +nebula&btnG=&as_sdt=1%2C5&as_sdtp=

amid which this paper is a good starter kit:

http://www.annualreviews.org/doi/abs/10.1146/annurev.astro.40.060401.093849?jour nalCode=astro

For MHD in SNrs:

http://scholar.google.co.za/scholar?hl=en&q=Magnetohydrodynamics+and+supernov as&btnG=&as_sdt=1%2C5&as_sdtp=

arXiv weighs in as well, though less voluminously:

http://arxiv.org/find/all/1/all:+AND+nebulae+AND+magnetohydrody namics+planetary/0/1/0/all/0/1

http://arxiv.org/find/all/1/all:+AND+magnetohydrodynamics+super nova/0/1/0/all/0/1

Most of this stuff is a lot chewier than the books Robert recommends. The turgid prose of professional papers is redeemed by their up-to-the-minute data, but they sure are a handful to read.

[Weltevreden SA]

Hardly had I sent off my earlier message than I came across this brand-new paper (http://arxiv.org/abs/1302.5663) (6 days old, publ. 22 Feb 13) on arXiv that lucidly explains all the basic terms and ideas in galactic MHD. The lead author is Rainer Beck, a familiar name on enthusiast forums. For a startling visual analog to a late-stage SNr only on a grand scale, check out the polarization map of the MW on p.13.

[madbadgalaxyman]

Very interesting comment, Dana. You are quite obviously someone who loves astrophysics.

I hope that I am going to have the time to read the papers you mention!

I have read some of Beck's papers on the magnetic fields within galaxies, and I have managed to understand some current ideas about the effects of magnetic fields in the formation of protostars and stars.
On the whole, I do look at things from the "galaxies" point of view:
I mainly read papers on the morphology and classification of galaxies, the kinematics/dynamics of galaxies and their constituents, on AGNs, plus the necessary papers on Star Formation and the ISM and Supernovae (for the purpose of enhancing my understanding of galaxies. )

I do wish that I knew more astrophysics so as to better interpret astronomical data, as I am more of the practical astronomer, with a love of good data and observations, such as: mass & luminosity functions of various objects, galaxy magnitudes, spectral line emission, photometric systems, distance measurement techniques, the space distribution & the peculiar velocity field of galaxies, etc.
However, as the career of Fritz Zwicky conclusively proved , you can discover an awful lot of things in astronomy without knowing every part of the physics; he had great physical insight, and an enormously creative ability to come up with new and physically plausible ideas, plus he was so extremely arrogant that he didn't at all care if everybody else thought that one of his ideas was very wrong. )

cheers, Robert

[Weltevreden SA]

Thanks to you, too, Robert. I didn’t know anything about the GALEX discoveries of hot gas cloud formation in galactic exurbs till I read your info in the SN 2013aa / NGC 5643 thread. Interestingly, the XMM-Newton time allocators haven’t ventured into intergalactic gas properties the way the GALEX team has.

The Carnegie-Irvine Galaxy Survey image of 5643 and other images you ferreted out were very informative, and likewise news to me. The same goes for the Lauberts and Valentijn Catalog (ESO-LV). I’ve been relying on WikiSky and RC3, neither of which give the depth of motion and spectral data that ESO and NED provides. I looked at Project Pluto at your behest. At present I’m been using AstroPlanner. I must decide whether Pluto’s data fits my needs better.

Interesting that you mentioned Fritz Zwicky. Before PhD programs were formalized in their current form, everyone was self-taught. E E Barnard was self-taught and made immense contributions to our understanding. I haven’t the time to look into self-trained astronomers of contemporary times, but the world of geology has, if anything, even more home-brew geniuses than astronomy. To say nothing of Linneus the botanist.

I really look forward to your comments in these and future topics. Learning something new every day is as good for mental health as an apple a day is for body health.