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Wikipedia:Featured article candidates/Main sequence

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The following is an archived discussion of a featured article nomination. Please do not modify it. Subsequent comments should be made on the article's talk page or in Wikipedia talk:Featured article candidates. No further edits should be made to this page.

The article was promoted by User:SandyGeorgia 23:07, 13 December 2008 [1].

Main sequence

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Nominator(s): RJH (talk)

I'm nominating this article for featured article because I believe it meets the necessary criteria. The page has undergone a PR and is GA-rated. I've taken it about as far as I can without further input, so please let me know if there are issues that need to be addressed. Thank you.—RJH (talk) 18:02, 26 November 2008 (UTC)[reply]

Image review

  • Image:Dwarf Stars.png - We need a source for the information in this chart (images need to be verifiable, too!).
    • Image removed.
  • Image:PPvsCNO.png - The image needs an English description. Also, did Xenoforme make this image? If so, it should say "selfmade". Finally, we need a source for the information in the graph.
    • I updated the commons page accordingly.
  • Image:Open cluster HR diagram ages.gif - We need a source for the information in this diagram.
    • I added a reference to a journal article showing the color-magnitude diagrams of the two clusters in question. Unfortunately the original image author has retired from Wikipedia, so I can't get a definitive source. If the ref. is inadequate then I guess we'll have to decide if the image is unusable in an FA.
      • As long as all of the information in the diagram can be found in the source, we are fine. Are we fine? Awadewit (talk) 16:35, 29 November 2008 (UTC)[reply]
        • I found a web page that has separate HR diagrams for M67 and NGC 188. (The page is by Dr. Michael W. Richmond: see notes below.) The plots look like a good fit for the data on the wikipedia article, so I've added that as a source to the commons page. I think we're good now.—RJH (talk) 20:15, 29 November 2008 (UTC)[reply]

These issues should be relatively easy to resolve. Awadewit (talk) 22:51, 26 November 2008 (UTC)[reply]

Comments -

Otherwise, sources look okay, links checked out with the link checker tool. Ealdgyth - Talk 13:57, 28 November 2008 (UTC)[reply]
  • Comment. From my perspective as an astrophysics layman, this article doesn't do enough to explain the connection between main sequence and other types of stars. Despite several brief mentions of the connection, I had to read the giant star to understand how main sequence fits into the broader picture of stellar evolution, something that should have been made clear within the lead. One specific bit I found confusing: in the second paragraph of the Lifetime section, it shifts from using the Sun as an example to generalizing about observable stars, and it's not clear enough how the two halves of the paragraph connect.--ragesoss (talk) 01:05, 30 November 2008 (UTC)[reply]
    • Do you mean that the Main_sequence#Evolutionary_tracks section is unclear? The Stellar evolution article covers the topic in detail, so I didn't think it is appropriate to delve into more details of the post-main sequence evolution in this article. I made some changes to the Lifetime section that I hope will address your last concern. Thanks.—RJH (talk) 17:39, 1 December 2008 (UTC)[reply]
      • I think the evolutionary tracks is not detailed enough, particularly in terms of the variability of evolutionary tracks. Do all main sequence stars then become red giants? The text should be more explicit in terms of the way stars of different mass (and composition?) evolve as they leave the main sequence. But the bigger issue is that this section doesn't come until the end (a natural place for it in terms of the life of a star), while understanding how main sequence relates to other regions on the diagram is central to understanding what, in a broad sense, the main sequence is. In particular, this should be addressed more clearly in the lead section.--ragesoss (talk) 17:58, 1 December 2008 (UTC)[reply]

more Comments:

  • The relationship between the final paragraph of the introduction and the topic of 'main sequence', as well as the 'Structure' section, isn't made clear. It's implicit that the description of star structure applies to main sequence stars as opposed to other kinds, but that should be made explicit.
    • I modified the paragraph to tighten up the description and add some details relevant to main sequence stars.—RJH (talk)
  • It seems that equilibrium is a central aspect of what defines main sequence stars; this should probably be discussed within the introduction.
    • I added a couple of sentences to the lead. It applies to other stars as well, so I'd rather avoid characterizing this as a core aspect of the main sequence.
  • It would be helpful if one of the H-R diagrams pointed out the dividing line between upper and lower main sequence.
    • I put some wording in the text about what spectral classes are typically upper and lower main sequence.
  • It would be helpful if there was a bit more info about the transition, along the main sequence, from lower to upper. It says that 1.5 solar masses is the point where both processes are equally efficient. First, does this mean that the processes are actually contributing 50% of the energy each? (Are there other significant minor reactions that contribute nontrivially as well?) Second, how fast does the transition occur? Is there a significant amount of both reactions in a 1 or a 2 solar mass star? The answers to these questions are in the PP vs. CNO graph, but they should be addressed in the text as well; the graph alone could be misleading for readers who aren't used to dealing with log graphs. The graph caption is also a bit confusing: "relative energy output (log ε)" could be read to mean that "log ε" is a shorthand for "relative energy output", instead of what it actually is, a log graph of ε (energy output) for different reactions, which is plotted in relative (i.e., dimensionless) terms.
  • A graph might be helpful for the luminosity-color section, highlighting the places across the main sequence a single star might go through. This would make more clear what the "broadening" of the main sequences means, since (because it is plotted as a mostly diagonal band) readers might get confused by assuming stars move along the main sequence rather than perpendicular (?) to it.
    • I am unclear about this. Stars moving along the main sequence wouldn't broaden it. Doesn't broaden mean to widen or thicken? I added a note.
      • But broad and wide can be, on the one hand, the opposite of thin or long, but on the other had, can be the converse of tall. That is, broaden and widen are often associated with horizontal extension (i.e., stretching along the x-axis). I think it will be clear to most people, I was just pointing out that the potential for confusion is there.--ragesoss (talk) 20:33, 4 December 2008 (UTC)[reply]
  • Just a thought: the "Lifetime" section might make more sense immediately after the "Energy generation" section.
    • My thinking was to move spacially from the interior outward, thus: energy generation, structure and luminosity-color variation of the photosphere. This is followed by the chronological details: lifetime and evolutionary tracks.
      • It seems to me that "Lifetime" is basically a function of energy generation and the interior composition (i.e., how much hydrogen is available), so I think it would still make sense within your organizational scheme.--ragesoss (talk) 20:33, 4 December 2008 (UTC)[reply]
        • There's points to both viewpoints; Lifetime also belongs with the Evolutionary Tracks, and I think that shoving both in there would break apart the flow. Sorry but I'd prefer to stick with the current arrangement unless there's a wider consensus.—RJH (talk)
  • In the "Lifetime" section, it wouldn't hurt to have a citation for: "For massive stars, however, this mass-luminosity relationship poorly matches the estimated lifetime. A more accurate representation gives a different function for various ranges of mass." The next two paragraphs do follow up on that, with citations, but it's not immediately clear that that's what is going on.
    • I couldn't find the original source for this so I removed it. As you pointed out, the following text covers the same topic so I think it's unecessary.

Overall, I think it's a solid article that will be Feature-worthy with some straightforward fixes.--ragesoss (talk) 21:03, 3 December 2008 (UTC)[reply]

Thanks. I think I've addressed most of your concerns.—RJH (talk) 20:36, 4 December 2008 (UTC)[reply]

Image:PPvsCNO.png (Note: They don't want us displaying graphics in here.)

Comment.

  • Returning the PP vs. CNO graph, I think the graph itself is a problem. The energy curves for PP and CNO are continuous over the big gap in x-axis magnitude (which jumps from 20 to 100); that can't be accurate. It's an important (essential, I would say) graph, but I think it needs to be redone.--ragesoss (talk) 20:47, 4 December 2008 (UTC)[reply]
  • One thing that might be worth mentioning to make more clear the suddenness of the PP to CNO transition (which is not obvious in the log graph) is this fact I found in the CNO cycle article: "The sun has a temperature of around ~15.7×106 K and only 1.7% of 4He nuclei being produced in the Sun are born in the CNO cycle." That it goes from 1.7% at 1 solar mass to 50% at 1.5 solar masses (to what, >>99% at 2 solar masses?) gives perhaps a better sense of the division between upper and lower main sequence than the log graph based on core temperature (a property that is not given less attention in the article than mass, and might be confused with spectral temperature)--ragesoss (talk) 21:03, 4 December 2008 (UTC)[reply]
    • A graph of mass versus the proportion of P-P vs. CNO energy generation might be informative. I'm not sure whether such exists, but I'll take a look around.—RJH (talk)
      • I had no luck finding specifics. This details are probably more appropriate to Stellar nucleosynthesis anyway. I'm going to take a pass. Sorry.—RJH (talk) 17:55, 5 December 2008 (UTC)[reply]
        • This is intimately tied to stellar structure & evolution ... a higher temperature sensitivity of the dominant energy-generation reaction means convective energy transport is more important than radiative transport in the star. That manifests itself in the evolutionary tracks. For example, look at [2] and there's such a diagram about halfway down that page. Whenever there's a "jerk" in an evolutionary track back to the left (warmer temperature) at the end of the main sequence, that means the stellar core is convective (i.e., CNO is more important than P-P). In that linked figure, that happens for all the tracks with masses more than 1 solar mass. There are some webtools out there now for rolling your own color-magnitude diagrams and evolutionary tracks which might provide you with the raw data needed to construct the diagram you think you want, but it'll be annoying and may violate the OR guidelines to do so. I certainly don't recall seeing a diagram of the kind you're thinking of. BSVulturis (talk) 23:23, 5 December 2008 (UTC)[reply]
  • Support. All my major concerns have been addressed. The articles seems clear, complete and well-referenced to me. I still think the energy production section could be expanded a small amount, with more explanation within the main text that unpacks the relevant features of the new and improved diagram, including a mention of the triple-helix process, which (if I understand correctly) is important for very high mass main sequence stars. But I'll leave that to your judgment, RJH.--ragesoss (talk) 04:27, 6 December 2008 (UTC)[reply]
    • Thank you. I did some modification of the paragraph to try and make it clearer. However, I couldn't find any reference to a stellar "triple-helix" process, even under google scholar. It's not listed in the stellar nucleosynthesis article. Does it go by another name, perhaps?—RJH (talk) 17:41, 7 December 2008 (UTC)[reply]
      • Sorry, I meant triple-alpha, and I got my physics mixed up with my biochemistry (alpha helix).--ragesoss (talk) 20:55, 7 December 2008 (UTC)[reply]
        • Okay. Perhaps you are thinking of shell burning stages for evolved massive stars? I think this only kicks in after core hydrogen burning has ceased, but I may be mistaken. (I'm not sure about first generation stars.)—RJH (talk) 23:56, 9 December 2008 (UTC)[reply]
          • You're probably correct; I think I got that impression from some of the less developed articles along with the diagram. Since the triple alpha process is on the diagram, it should probably be mentioned in the text, if only to restate what you said here, that it becomes important during the transition to red giant stage but not during the hydrogen-burning period.--ragesoss (talk) 02:26, 10 December 2008 (UTC)[reply]
  • SupportComments
    1) In the lead I read Hydrostatic equilibrium is maintained by a balance between the thermal radiation within the star and the pressure from the overlying mass. This balance occurs because the rate of energy generation at the core depends on the temperature and pressure. I suggest instead All main sequence stars are in hydrostatic equilibrium, where pressure in the hot core is balanced by the pressure from the overlying mass. The strong dependence of the rate of energy generation in the core on the temperature and pressure helps to sustain it.
    I adopted your wording, with minor modifications.
    2) The first paragraph in 'Properties' section is unreferenced and redundant, in my my opinion.
    Deleted.
    3) The last paragraph in 'Luminosity-color variation' section should mention that unstable main-sequence stars, which result from the intersection of the instability strip with the main sequence, are called Delta Scuti variable stars. There are other classes of unstable main sequence stars like beta Cephei variable stars, which are unrelated to the instability strip.
    Okay.
    4) In the 'Lifetime' section I found As the energy output of the helium fusion process per unit mass is only about a tenth the energy output of the hydrogen process, this stage will only last for about 10% of a star's total active lifetime. Thus, about 90% of the observed stars above 0.5 solar masses will be on the main sequence. I doubt the accuracy of this estimate. In the case of the Sun helium-burning stage will last only for about 60 mya, which is only 0.5% of its lifetime. The difference is luminosities should be taken into account.
    I'll need to double-check this because it has shown up in several sources.
    You can see Formation and evolution of the Solar System article and ref 86 in it (Schroder). Ruslik (talk) 07:51, 9 December 2008 (UTC)[reply]
    I'm getting a lot of mixed messages from the various references about this. It seems to vary quite a bit by mass (especially for low mass stars) and the quotes values vary from 1% up to 25% of the MS lifetime. I think I'm just going to remove the 10% value and use a general statement instead. Sorry.—RJH (talk) 23:51, 9 December 2008 (UTC)[reply]
    5) In the last section Stars with at least four solar masses can also fuse elements with higher atomic numbers. I actually read that this limit is 7-8 Solar masses.
    The carbon burning article lists 4 solar masses, but that is also unreferenced. Section 10.3.1 of this page lists a model with 5 solar masses where carbon burning takes place (step G). I need a better ref.
    See this: 7.5-9.25 Solar masses for SAGB stars. Ruslik (talk) 07:51, 9 December 2008 (UTC)[reply]
    I had just inserted this reference, which listed just over 5 solar masses. At this point I'm not sure what to do.—RJH (talk)
    I think the higher mass is more accurate, because Poelarend et.al. used more accurate simulations. The onset of carbon burning depends on the helium core mass, which is significantly reduced during the second dredge-up of the convective envelope. The influence of the latter is difficult to calculate—treatment of the convection requires an enormous computational power. However you can simply state that this mass lies somewhere between 5-7.5 Solar masses. Ruslik (talk) 20:05, 9 December 2008 (UTC)[reply]
    Okay, I put in the range and used both references. I'm sure it'll get further refined later. Thanks.—RJH (talk) 23:03, 9 December 2008 (UTC)[reply]
    6) The use of word cataclysmic for SNII type explosions should be avoided, because it can confuses readers. They may think that they related to cataclysmic variables.
    Okay, I removed the word.
I hope my comments will be helpfull. Ruslik (talk) 11:45, 8 December 2008 (UTC)[reply]
Yes, they are helpful. Thank you.—RJH (talk) 23:02, 8 December 2008 (UTC)[reply]
The above discussion is preserved as an archive. Please do not modify it. No further edits should be made to this page.
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