Talk:Star/Archive 3
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"Atmosphere" correction
At the end of the "Main sequence" subsection, the word "atmospheres" incorrectly points to the term "Atmosphere (unit)" instead of the term "Stellar atmosphere". Please correct and then remove this comment. — Preceding unsigned comment added by 109.100.69.106 (talk) 18:22, 1 October 2012 (UTC)
Largest stellar mass
Sorry if I started this section incorrectly, I'm new at this, so feel free to move/fix/delete as needed.
Anyway, I found this at the end of the section on stellar mass: "However, a star named R136a1 in the RMC 136a star cluster has been measured at 265 solar masses, putting this limit into question."
I was reading somewhere recently that this actually presents a couple of possibilities--first that the Eddington Limit might need to be updated, and second that the star is actually two stars of much lower than Eddington Limit mass. I can't find the reference, so maybe that is not true, but I just thought I'd point it out.
Also, it seems to me that the Eddington Limit tells us that stars above a certain mass will be dominated by the radiation pressure vs the gravity holding them together, and thus will blow apart. Looking at the Wikipedia article on this star, it appears that it is doing exactly as predicted for a star above this limit, it is shedding mass very quickly. Doesn't this mean that the theory is supported, rather than the limit has come into question? I mean, just because a star is above the theoretical limit for the upper mass of stars (which is really just the limit to how big a star can be before radiative pressure starts shedding its mass), that doesn't mean the star can't exist, it just means that above that limit, if a star does exist, it will be very busy blowing its mass into space. Yes? No?
Perhaps a better wording would be to talk about how stars above this mass are rare because of the dominance of radiative pressure (they die very young), and that when a star above this mass is found (such as R136a1, with 265 solar masses) that star should be in the process of blowing itself apart from the moment it is born. Again, I'm not an expert or professional astronomer, and perhaps this is still too new to be considered 'fact,' but I love to point stuff like this out in case I can learn something from it. :) Turboguppy (talk) 18:16, 23 September 2011 (UTC)
- If I recall the issue correctly, I think the concern is not whether a cloud with that much mass can form and start to collapse into a protostar, but how does it become a main sequence star without blowing off the extra mass in the process? I know that one way to do it is to have a star with no metallicity, as is the case with the conjectured population III stars. The ESO article being used as the source suggests another method: the merger of two smaller, but still massive stars. You give the third option yourself: that it is actually a massive binary. As for the wording itself, well I guess that's just a common process in science; exceptions that test the consensus. Regards, RJH (talk) 19:19, 23 September 2011 (UTC)
- Thanks, I think that clears up the confusion for me--it will be interesting to see what comes of it. Thanks! Turboguppy (talk) 03:09, 28 September 2011 (UTC)
Can stars have rings?
Are there any stars that have rings? YouthoNation (talk) 18:15, 30 September 2008 (UTC)
- Yes: Debris disk—RJH
(talk) 19:09, 30 September 2008 (UTC)
- Sort of, but only protostars or possibly brown dwarfs can have anything similar to a planet's ring. Skyintheeye (talk) 21:29, 9 February 2010 (UTC)
- Samples of stars which have ring? Newone (talk) 03:03, 12 October 2010 (UTC)
- Well, one might consider a debris disk a ring, albeit probably not as flat as Saturn's rings. There's also the protoplanetary disk, which is comparable.—RJH (talk) 14:53, 12 October 2010 (UTC)
- Samples of stars which have ring? Newone (talk) 03:03, 12 October 2010 (UTC)
The solar system is made out of the sun, and all of the debri around it. The debri around the star becomes planets and asteroids. So, in essence yes, a young solar system with a star in it has 'rings'. Karicats7 (talk) 21:01, 14 March 2012 (UTC) (talk)
I suggest the asteroid belt in our own solar system is a 'ring'. Jokem (talk) 21:09, 20 July 2012 (UTC)
Definition
"An astronomical object is defined as a star if it emits more heat, light and radiation than it absorbs." Does anyone know where this definition comes from and its vailidity? By this definition Jupiter, apparently, is a star, not a planet. __meco (talk) 10:24, 28 September 2011 (UTC)
- This wording looks to be invalid and has some redundancy; both heat and light are radiation. I have no idea where it comes from. You could perhaps define a star in terms of whether it acquires sufficient mass to perform thermonuclear fusion of protons (not deuterium) to form helium at some point during its lifetime. But there are conjectured to be dark matter stars that could throw that definition out the window. Still, you'd need a definition that excludes deuterium-fusing brown dwarfs. Regards, RJH (talk) 16:16, 28 September 2011 (UTC)
Edit request from 94.66.78.71, 30 September 2011
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Star, derives from a combination of Greek "αστήρ" (endless) with "άστερεον" (non-fixed) and "αστράπτον" (flashy)
94.66.78.71 (talk) 21:52, 30 September 2011 (UTC)
- We'll need a reliable citation for this. It's only partly confirmed here:
- Halsey, Charles Storrs (1882), An etymology of Latin and Greek, p. 80
- The online etymology dictionary shows it as coming from aster, per the first above:
- Harper, Douglas (2010), "star (n.)", Online Etymology Dictionary, retrieved 2011-09-30
- Regards, RJH (talk) 21:54, 30 September 2011 (UTC)
Edit request from , 1 November 2011
{{edit semi-protected}}
Please, change
Chugainov, P. F. (1971). "On the Cause of Periodic Light Variations of Some Red Dwarf Stars". Information Bulletin on Variable Stars 520: 1–3. Bibcode 1977A&A....61..809M to
Chugainov, P. F. (1971). "On the Cause of Periodic Light Variations of Some Red Dwarf Stars". Information Bulletin on Variable Stars 520: 1–3. Bibcode 1971IBVS..520....1C
because the Bibcode is wrong.
With best regards, Andras Holl (IBVS technical editor)
Andrasholl (talk) 10:22, 1 November 2011 (UTC)
- Changed, thank you. Materialscientist (talk) 10:29, 1 November 2011 (UTC)
Dead links
So many wrong links! Newone (talk) 05:02, 11 April 2012 (UTC)
- Fixed. This is quite "normal" for a large article which has not been overhauled for deadlinks for some time. Materialscientist (talk) 05:22, 11 April 2012 (UTC)
Red giant mass Discrepancy
Solar mass required for a star to become a Red giant according to various articles:
- Red Giant - 0.35
- Star - 0.4
- Stellar Evolution - 0.5
The same discrepancies can be found a mass limit for a star to fuse helium in various articles.
- Horizontal branch - 0.26 (presumably a mass for a star to become red giant)
- Star - 0.4 (not directly said)
- Helium flash - "about 0.5"
- Stellar Evolution - 0.5
--Artman40 (talk) 01:23, 17 June 2012 (UTC)
They should all probably be based on the lower bound for fusing helium, so around 0.5.(D'oh... I was mistaken. The lower bound would probably be a hydrogen-burning shell stage with an inert helium core, rather than helium fusing.) We need to find a definitive reference that will serve on all of the articles. Also, I'm not sure if there is significant variation caused by metallicity. Regards, RJH (talk) 22:42, 21 June 2012 (UTC)
If it is of any help, the following source estimates the lower limit at around 0.25, with stars needing 0.5 to reach the tip of the RGB:
- Laughlin, Gregory; Bodenheimer, Peter; Adams, Fred C. (1997), "The End of the Main Sequence", Astrophysical Journal, 482: 420, Bibcode:1997ApJ...482..420L, doi:10.1086/304125.
{{citation}}: Unknown parameter|month=ignored (help)
I'm not sure if there is a more definitive source available, but this seems pretty decent. Shrug. Regards, RJH (talk) 03:41, 22 June 2012 (UTC)
- Thanks for the ref. There's a conference proceeding version that's a little easier to read: 2004RMxAC..22...46A. My summary for this purpose is that the maximum luminosity of stars increases for stars in the 0.16 to 0.25 solar mass range; there doesn't seem to be a sharp transition. All that said, there are no observable tests of this aspect of the model. I'll try to incorporate this into an article where appropriate, if someone doesn't beat me to it.
- Re what determines the lower bound: it's the fully convective interior. Fully convective interior means no red giant phase (because convection mixes mass from through the star, so the star can fuse nearly all of the hydrogen in the star, not just the hydrogen in the core); radiative interior means red giant. I haven't (yet) looked at the articles to see if this is said well; if it isn't, it should be. —Alex (ASHill | talk | contribs) 10:01, 22 June 2012 (UTC)
- Adams, F. C.; Graves, G. J. M.; Laughlin, G. (2004), García-Segura, G.; Tenorio-Tagle, G.; Franco, J.; Yorke, H. W. (eds.), "Gravitational Collapse: From Massive Stars to Planets. / First Astrophysics meeting of the Observatorio Astronomico Nacional. / A meeting to celebrate Peter Bodenheimer for his outstanding contributions to Astrophysics", Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias), 22: 46–49, Bibcode:2004RMxAC..22...46A.
{{citation}}:|contribution=ignored (help); Unknown parameter|month=ignored (help)
- Adams, F. C.; Graves, G. J. M.; Laughlin, G. (2004), García-Segura, G.; Tenorio-Tagle, G.; Franco, J.; Yorke, H. W. (eds.), "Gravitational Collapse: From Massive Stars to Planets. / First Astrophysics meeting of the Observatorio Astronomico Nacional. / A meeting to celebrate Peter Bodenheimer for his outstanding contributions to Astrophysics", Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias), 22: 46–49, Bibcode:2004RMxAC..22...46A.
- Perhaps I'm mistaken, but I got the impression from the first article that stars with 0.25 solar masses may develop radiative core regions later in their lives, even though they are normally fully convective. (Perhaps from the higher abundance of helium?) Interesting if true. Regards, RJH (talk) 14:44, 22 June 2012 (UTC)

