Talk:Carbon star

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Carbon star cleanup plan[edit]

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. written

A provisional text is emerging in When better than the text in the article, it will replace the current article. Rursus 12:58, 6 January 2007 (UTC)

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. Rursus 15:03, 8 January 2007 (UTC)

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.

Rursus 13:05, 8 January 2007 (UTC)

The article speax advanced tecchish – before going on, I'm going to compare and make it more similar to other articles handling astroobjectcategories. Rursus 13:25, 10 January 2007 (UTC)


Must fix Carbon Star#The Revised Morgan-Keenan system table - it's not consistent with the rest of the text. I made the table, I'll do it if none else happen to be faster: then be welcome! Rursus 13:15, 20 January 2007 (UTC)

R/N, C x,y and C-H, C-J, C-N and more[edit]

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? Rursus 12:46, 23 October 2006 (UTC)

Try reading Carlos Abia's review (2003, PASA 20,314).
Says who? And where's that review? Rursus 10:35, 4 January 2007 (UTC)
This discussion obsoleted by now - the article text explains all of this. Rursus 13:26, 20 January 2007 (UTC)


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. Rursus 12:42, 23 October 2006 (UTC) ... (more below)

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. Rursus 12:42, 23 October 2006 (UTC) (...)
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. Rursus 15:18, 4 January 2007 (UTC)
No, TiO Rursus 15:20, 4 January 2007 (UTC)

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. Rursus 12:42, 23 October 2006 (UTC) (...)

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.

Agree. Rursus 12:42, 23 October 2006 (UTC)

Binary scenario[edit]

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.

BSVulturis 17:33, 13 December 2006 (UTC)

This was far time ago, so now both the R CrB stars and the variable type RCB have their own articles. Said: Rursus () 13:43, 26 October 2008 (UTC)

High Temp. needed to make carbon (more luminous, perhaps, or hi pressure)[edit]

"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? 00:20, 11 June 2007 (UTC)David

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. Timb66 11:43, 12 June 2007 (UTC)

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. BSVulturis 22:24, 3 August 2007 (UTC)

Carbon-rich giants are red giants[edit]

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? Timb66 06:05, 13 June 2007 (UTC)

I'm. I think your reflection is related to the fact that
  1. Barium stars and non-classic carbon stars seem to be related,
  2. that C-J and RCrB may have a similar mechanism,
  3. that classic C-stars are related to AGB stars (Carbon shell burners),
  4. 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)
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;
!!! Since when did any diagram have any scientific say? The definition weights bubkes! Said: Rursus 10:47, 11 August 2007 (UTC)
But the rest of the article is pretty OK. I improved the definition. Said: Rursus 11:15, 11 August 2007 (UTC)

CEMP is missing[edit]

This page needs updates in mentioning the CEMP types. Carbon-Enhanced Metal-Poor star.

  • CEMP
    • CEMP-α
    • CEMP-r
    • CEMP-r-II
    • CEMP-s
    • CEMP-r/s
    • CEMP-no
    • CEMP-no/s
  • NEMP, Nitrogen-Enhanced Metal-Poor star (theoretical)

Thanks, Marasama (talk) 18:13, 3 June 2009 (UTC)

CEMP star. I'll make some investigation whether they are carbon stars really. Rursus dixit. (mbork3!) 19:10, 18 April 2017 (UTC)
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)
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)
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)


"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)

Beryllium (specifically 7
. 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)
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)
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)
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)

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