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Not much seems to happen, so I'll deal with it then. Cleanup plan:
topic name
why doubt??
status
red giant stuff
carbon stars are red giants, really?? The
red giant article says red giants are K to M type, carbon stars are analogous to late G to M type, but never have G, K or M spectral types.
rewritten to be like red giants
CO stuff
MrX (below) and me doubting CO to be maincharacteristix, i believe C2 and CN spectral band presence
some small reformulation
Duplicity stuff
MrX doubting most carbon stars being doubles
rewritten
Visibity stuff
MrX and me questioning hard-to-observe statement
rewritten
Ablation stuff
MrX and me questioning ablation and invisibility of carbon stars
missing – BSVulturis rewrote!
C spectra
C:s are C-N, C-R, C-H, C-Hd, C-J, and a few CS:es.
Na, it won't – it would be much harder to read... I've changed my mind, I'll cut-n-paste extras from my article to the current.
Rursus15:03, 8 January 2007 (UTC)reply
Now, I'm preparing the
Carbon star (original) article for merger – it's explanation and text is OK (better than what I use to produce), some incorrect details removed:
only non-classical carbon stars are believed to be all binaries,
classical carbon stars are AGB:s,
the carbon stars are easily visible, not invisible (probable confusion with L and T stars, or with
Purkinje effect,
no "intrinsic carbon star type", just classical carbon star type,
classicals may be miras, beside irregular and semiregular variables.
The article speax advanced tecchish – before going on, I'm going to compare and make it more similar to other articles handling astroobjectcategories.
Rursus13:25, 10 January 2007 (UTC)reply
I can remember 3 kinds of spectral classifications of carbon stars:
the R/N kind, the C x,y kind, f.ex. C8,2 and the C-α-x kind, f.ex. C-H3, something. Somebody who knows more about this?
Rursus12:46, 23 October 2006 (UTC)reply
Try reading Carlos Abia's review (2003, PASA 20,314).
I am skeptical about some of the information in this article.
Hi, Mr X!! How's Ms Y doing? I'll comment some on this, because I initially wanted to sketch some future improvements of this page.
Rursus12:42, 23 October 2006 (UTC) ... (more below)reply
carbon star is a red giant (or occasionally red dwarf) star whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide and other carbon compounds.
My recollection is that the spectrum of these stars is dominated by the Swan bands of dicarbon (C2) with a lesser contribution from CH. Carbon monoxide isn't really important because the oxygen content is so low relative to carbon.
I remember the ordinarily distinguishing features as C2-, CN- and CH- absorption in the blue, so: agreed!. Besides, carbon stars aren't what we precisely call red giants, since red giants IMHO are M type stars, but there's ambiguities of meaning there.
Rursus12:42, 23 October 2006 (UTC) (...)reply
I object against Red Giant = M Giant. I'm not sure of any spectral characteristic – rather they are late-type (G to M) and has some C2-, CN- and CH- bands.
Rursus15:18, 4 January 2007 (UTC)reply
Many carbon stars are really binary stars, where one star is a giant star and the other a white dwarf. The giant star accretes carbon onto the surface of the white dwarf, thus the spectrum of the star shows that it's carbon enhanced.
The last sentence is a bit garbled, but almost certainly wrong. It is all but unheard of for a giant star to accrete from a white dwarf companion. (The opposite process, where a white dwarf accretes from a giant companion, is very common.)
Although very large, carbon stars are visibly dim and hard to spot without specialized equipment; the stars are a distinctly deep red or brown colour described as "smoky".
I don't believe that they are particularly hard to spot. The brightest, R Corona Borealis, is visible to the unaided eye and is strikingly red in a small telescope. The spectrum is highly distinctive due to the Swan bands, which really stand out, particularly at high resolution.
The original author got it very wrong - carbon stars are red which makes their magnitude very hard to estimate by the eye, due to the
Purkinje effect. Other means of observation recommended.
Rursus12:42, 23 October 2006 (UTC) (...)reply
The ablated material surrounding a carbon star may blanket it to the extent that the dust absorbs all visible light.
I don't think "ablated" is the right word to describe the expelled material. Ablation usually refers to a process of vaporizing or otherwise eroding material off the surface of a cold body.
I've overhauled the description of the binary carbon star scenario to make it clear that the carbon came from the star that is now the white dwarf -- but it came when that star was not a white dwarf. Included is a reference and link to Bob McClure's paper describing these carbon stars and other related objects. I think this should alleviate the "disputed" nature of the material, though I've left the tag in there for now.
The R CrB stars (there's a number of them) mentioned above on this page are a wierd bunch of beasties, being hydrogen-deficient as well as carbon-rich; they seem to be single. I left them unmentioned in the main article. If anything, they deserve a stub article on their own. They are carbon stars in the sense that there's more carbon than oxygen in the atmosphere, but they are almost certainly distinct from the other carbon stars, and are now referred to as "hydrogen-deficient carbon stars" in the discipline to make their difference clear. Last I heard they were suggested to come from WC-type Wolf-Rayet stars, but that remains (as far as I know) unresolved and not fully accepted.
I deleted the word "ablated" ... that's entirely the wrong concept for the shells around carbon stars.
High Temp. needed to make carbon (more luminous, perhaps, or hi pressure)
"Many of these extrinsic carbon stars are not luminous or cool enough to have made their own carbon, which was a puzzle until their binary nature was discovered."
I don't understand. Extrinsic carbon stars are not luminous enough or are too cool....
Doesn't the core carbon formation need high temperature or pressure?
128.195.84.18800:20, 11 June 2007 (UTC)Davidreply
I agree this is confusing. The temperature referred to here is presumably the surface temperature (or, most precisely, the [effective temperature]]. For the star to be classified as a carbon star, this must be low enough for molecules to form in its atmosphere (such as CO, CN and C2). But that doesn't helkp us to understand the sentence in question since that is talking about the formation of carbon. Perhaps it means they are not sufficiently evolved to have formed (and then dredged up) their own carbon.
Timb6611:43, 12 June 2007 (UTC)reply
Correct: the "not luminous or cool enough" refers to the surface temperature. The creation of the carbon takes triple-alpha process fusion, and then the subsequent deep convection to get that synthesized carbon to the surface layers requires a yet higher core temperature (and hence higher luminosity and cooler surface temperature). Therein was the puzzle: extrinsic carbon stars are unlikely to be evolved enough, that is, to have ever reached the stage at which carbon synthesis and dredge-up happened in them. The mass transfer idea gets around that problem. So, I need to find the time to whip the language into better shape.
BSVulturis22:24, 3 August 2007 (UTC)reply
Carbon-rich giants are red giants
Carbon-rich giants are less common than oxygen-rich (M-type) giants, but both are considered to be red giants by astronomers. This article and the one on
red giants need to be corrected to reflect this, but I don't have time at the moment. Any volunteers?
Timb6606:05, 13 June 2007 (UTC)reply
I'm. I think your reflection is related to the fact that
Barium stars and non-classic carbon stars seem to be related,
that C-J and RCrB may have a similar mechanism,
that classic C-stars are related to AGB stars (Carbon shell burners),
that C-J stars may have some relation to RGB stars (Carbon core burners).
But it is also notable that there are dwarf carbon stars, so that it is not as simple as just regarding C-stars as red giants, but the connections are to be improved. Said:
Rursus☻10:35, 11 August 2007 (UTC)reply
Eehm!
Red giants definitely in need to be improved! It says the horrible:
According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M;
CEMP stars and Carbon stars are two different things. No harm in mentioning this in the article though, to reduce the possibility of confusion.
Lithopsian (
talk)
19:20, 18 April 2017 (UTC)reply
It seems so, but one must distinguish between observational types and physical kinds. Carbon stars is the older observational type defined by Swan bands and heavy lines of carbons, it not a coherent physical kind. CEMP is the newer observational type, it is defined by low metallicity (diverse MP:s) with primarily CH added. CEMP were discovered in a specific search for the oldest stars, while carbon stars were just discovered without expectations, when the classifying of star spectra was in its infancy. Whether there is an observational criteria overlap or not, I don't know yet. It seems CEMP-no is a natural kind, but I don't know yet, regarding the other CEMP:s.
Rursus dixit. (
mbork3!)
07:36, 19 April 2017 (UTC)reply
It appears that there is some connection between CH stars and CEMP stars, there might be a common underlying mechanism ("physical kind") shared by CH stars and some kinds of CEMP stars. And CEMP-no might not be a physical kind.
Rursus dixit. (
mbork3!)
15:02, 20 April 2017 (UTC)reply
Barium?
"Other elements formed through helium fusion and the s-process are also "dredged up" in this way, including lithium and barium." Barium can't be right; it's far too big an atom. Should that be beryllium or boron?
RTBoyce (
talk)
12:01, 8 October 2016 (UTC)reply
Beryllium (specifically 7 Be . Its half-life is only 59 days, but it's still listed in the significant products of hydrogen burning - Astrophysical Formulae, table 42 (page 422 in the 2nd edition).
Tarl N. (
discuss)
23:20, 8 October 2016 (UTC)reply
The article mentions both the products of helium fusion and of s-process neutron capture. Barium is one of the most common s-process elements found in AGB atmospheres after a third dredge-up.
Lithopsian (
talk)
12:58, 9 October 2016 (UTC)reply
Thanks - If I'd spent more than the 60 seconds I did thinking about it, I would have realized that a 59-day half-life is way insufficient for nuclei to make it from the core to the surface. Do you have a cite we can use on this, so some other enthusiastic amateur doesn't make the same mistake? Barium (All the way down at element 56) is certainly not what I'd guess would be a common element associated with Lithium in being dredged up from the S-process.
Tarl N. (
discuss)
01:00, 12 October 2016 (UTC)reply
Of course Ba can be dredged up. It is not a diffusion process, it is a convective movement that mixes the envelope with the core. Even though Ba ions (neutral atoms aren't likely) are heavy, they might be "swept up in the wind".
Rursus dixit. (
mbork3!)
10:07, 20 April 2017 (UTC)reply
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Is an Extreme Carbon Star something that is distinct? Is it too specific? Should there be a redirect from Extreme Carbon Star to this article?
RJFJR (
talk)
01:48, 18 January 2019 (UTC)reply
As best I can tell from the articles which refer to extreme carbon stars, they are referring to appearance (particularly sooty), rather than necessarily any extreme composition.
Tarl N. (
discuss)
07:02, 18 January 2019 (UTC)reply
Extreme carbon stars are not really distinct objects. Extreme is an adjective to indicate that such stars are carbon stars with particularly strong characteristics of the class: high C/O ratio; low temperature; highly self-obscured to the point of optical invisibility. There could be a redirect to here, or the extreme can be ignored and the carbon star bit linked as is. A section in
carbon star might be nice, maybe a separate article one day if someone really went to town on the subject.
Lithopsian (
talk)
14:48, 18 January 2019 (UTC)reply
It is probably misleading to refer to these stars as main sequence. Carbon stars less luminous than giants or even subgiants are known, but researchers are careful to call them dwarfs star rather than main sequence. A group called carbon-enhanced metal-poor stars also includes some that may have luminosities similar to main sequence stars. Here's a couple of papers to read, although there are no clearcut answers to what these stars are: