Talk:Main sequence

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[edit] Temperatures in table

What part of the star do the temperatures in this table refer to? Surface? Core? Could someone with the appropriate knowledge alter this for clarity? QmunkE 15:47, 10 March 2006 (UTC)

All the temperatures refer to surface temp. Any text-book with the Hertzprung-Russel diagram will tell you that!

[edit] Dwarf?

Could someone explain the reason why stars on this sequence are called "dwarf stars"? The article doesn't explain the origin of the term at all. --LostLeviathan 05:01, 20 March 2006 (UTC)

These stars are hot, dim, and tiny compared to the Sun. They are actually remnants of stars. They are called dwarfs simply because they are very small. There is no real "origin" of the term.

I disagree with the above (unsigned) argument. I think LostLeviathan was asking about Main Sequence stars being described as dwarfs, and not about White Dwarfs which are hot, dim, tiny, stellar remnants but are not on the main sequence.
Stars appear to be described as "dwarf" or "giant" with no "normal" size between the two. I think the most likely explanation (and feel free to correct me on this point if you think I'm wrong here), is that at the time the phrase was first coined around 1910, these were the smallest, dimmest stars of their colour that had been observed. Since then we have discovered white dwarfs, metal-poor sub-dwarfs and other types of small, dim stars.
Astronaut 16:54, 28 July 2006 (UTC)


I was going to ask the same thing. Why are main sequence stars also called dwarf stars? This definately needs to be explained in the article. Especially since the table at the end of the article seems to describe stars in their main sequence, yet includes a star or 16 solar radii and over 100 solar masses! I am generally quite knowledgable about astronomical topics, but if this has me confused it's safe to say the vast majority of readers will be as well.
So someone in the know: why are main sequence stars also called dwarf stars, and just how big a range does this classification have? ie, how big can a star be while still being called a dwarf? Harley peters 19:45, 8 October 2006 (UTC)

[edit] Bet you find this Interesting?

I had a thought the other day. And tried to find this answer to this on Wikipedia and other sources. But as a complete layman became very confused, parsecs/light years ect. This is my thought, we (the human race) have been sending out RF signals of a reasonable strength since 1922, please correct me on this if I have this wrong. Based on this knowledge, I wondered how far and how many star like suns (G class stars) have these RF signals reached by this year, 2007 ? You know where I'm going with this thought, and yes maybe life is not restricted to G class stars, or maybe it is, or maybe only to G2V, and we all known G2V's are capable! Then there's the age of these stars, and then the metallic make up as well. I wish someone with the right knowledge would draw up a list of theses stars. And using the above knowledge. We could then break the list up into the most lightly to the most unlikely places that intelligent life may exist. And that have also received RF signals from us. I believe this list would be helpful to SETI, to reduce their listing down to size, so they can focus on a more broader range of RF signals. As I also believe the RF's they are searching are far too narrow, and I feel a lot of time and money is going to waist at SETI. If anyone can help me with this please do, maybe I've got this wrong as I'm just a layman. But in any case, post me something, its bugging me!

The brief answer... According to [1], there are 133 sun-like stars withing 50 light years. Astronaut 01:20, 15 July 2007 (UTC)
The longer (POV) answer... It's my opinion that planets are possible round most stars, and with over 100 billion stars in the milky way galaxy alone that makes a hell of a lot of planets. Probably most are not capable of supporting "life as we know it" because they are too cold, too hot, too young, or in weird orbits round multiple stars, etc; but if even a tiny proportion of 1% of billions of planets were capable of life, there are still many places to look. For Earth's radio/TV transmissions to have reached an extraterrestial civilization and for them to have recognised it and replied to us, they would have to be no more than about 50 light years away for us to be detecting their reply now. Even so, restricting the search to such possible replies, leaves perhaps hundreds of potential targets for SETI.
But, if you also consider that if, say, an extraterrestial civilization started experimenting with radio 500 years ago, their signals would now be detectable from 500 light years away, then SETI needs to consider this possibility as well.
I think SETI have deliberately set out their search to cover most if not all nearby stars, and a select list of more distant stars.
Astronaut 01:53, 15 July 2007 (UTC)

[edit] Source of Main Sequence Data?

What is the source of the "Main Sequence Data" table that contains the stellar class, radius, luminosity, and temperature? I've never seen a table like that, and it's very useful for figuring out what specific stars are like. Does it come from the Encyclopedia of Astronomy and Astrophysics?

Raddick 17:50, 25 July 2007 (UTC)

[edit] Major revision

Hi Bob. The article on the main sequence is in need of fixing up. You have done such a great job on other astronomy pages, do you have time for that one? I can't spend much time on it, but am happy to pitch in or offer advice if needed. Timb66 10:21, 1 December 2007 (UTC)

Hi. Thank you for the suggestion. Yes I can try to expand it. — RJH (talk) 17:48, 2 December 2007 (UTC)
Okay I have expanded it. There's still some references needed and I'll work on that. When you have a moment, could you look through it and see what needs expanding, clarifying or even removing? I'm sure there may be some corrections needed and a bit of fine tuning. Thank you. — RJH (talk) 18:46, 6 December 2007 (UTC)

Hi Bob. Many thanks for a great and thorough job. I haven't had time to read carefully yet, but my first impression is that some of this might be better in the main article on the Hertzsprung-Russell_diagram. What do you think? Timb66 (talk) 05:34, 7 December 2007 (UTC)

Yes it may be that the two articles could be merged. What parts did you have in mind?
In some places I included content I thought necessary for explanation of information related to the main sequence. These, of course, discussed topics related to the HR diagram as a whole. There are probably a few areas that could be pruned, such as mention of the triple alpha process. But if it is to remain a separate article, I thought it needs to at least briefly explain both pre- and post-main sequence. — RJH (talk) 16:36, 7 December 2007 (UTC)

[edit] GA review—on hold

The article basicly satisfies GA criteria. However there are some errors that should be fixed.

1) In the fourth paragraphs in 'History' there is a sentence "Russell proposed that the giant stars must have a lower density or higher surface-brightness than dwarfs". What does "higher surface brighteness" means. The brightnees is determened by the temperature, is not it? And the temperature is similar for both red dwarfs and red giants.

The source article from Russell states that the "giant stars must have low density or great surface-brightness, and the reverse is true of dwarf stars". I'll use a quotation.

2) The last paragraph in the 'History' and the last paragraph in 'Characteristics' duplicate each other and should be merged. In addition the paragraph in 'Characteristics' lacks any citations.

Merged the common content.

3) Please, change bold font to the normal. I mean "zero age main sequence", or ZAMS in 'Formation' and main sequence in the caption of the last figure.

Fixed.

4) 'Cross-section of a Sun-like star, showing the different regions.'— there should be no period at the end of this caption.

Fixed.

5) In the 'Evolutionary tracks' there is a sentence "For intermediate-mass stars of more than 2 solar masses, the core can reach a temperature where it becomes hot enough to burn helium into carbon via the triple alpha process.". This implies that the Sun will never burn helium, which is wrong. The lower limit for the stars to burn helium is around 0.65 solar masses, which is enough to form a helium core of 0.45 solar masses.

Fixed w/ references.

6) The second paragraph from the end in 'Lifetime' is unreferenced.

References added.

7) The Vega may be a bad example of A0 star (in the table). It looks hot only because we look at its pole. It real mass is 2.1 solar masses, which is similar to β Pictoris. Its average spectral class is probably A3-A4 and luminosity is 37 solar (remember Vega article).

I changed the example.

Ruslik (talk) 19:31, 7 January 2008 (UTC)

Thanks.—RJH (talk) 17:04, 8 January 2008 (UTC)

I will promote the article, but 0.5 solar masses value is an underestimate. They seem to forget about large mass loss during RGB phase. I think this point deserves further research. Ruslik (talk) 17:54, 8 January 2008 (UTC)

The various sources I checked seem to be all over the map with regards to the minimum solar masses for triple-alpha fusion:
The article http://arxiv.org/abs/astro-ph/9509062 does give a value of 0.6 for stars to subsequently follow the AGB. Thanks.—RJH (talk) 21:02, 8 January 2008 (UTC)

[edit] Contradictory information

The Main sequence and the Luminosity articles give contradictory information about luminosity being proportional to a power of stelar mass. The Main Sequence article mentions M^3.5 while the luminosity article mentions M^3.9. Could someone correct this? -Paul- (talk) 01:28, 9 February 2008 (UTC)

[edit] Va vs. Vb

This is a new one to me. Can someone explain the difference between a main-sequence 'a' and main-sequence 'b' star? The classification system gets finer and finer! Is the Sun a G2Va or G2Vb star? 68Kustom (talk) 10:21, 10 February 2008 (UTC)

Supergiants can be Ia or Ib. Perhaps that is what you mean? I haven't seen a stellar classification Va or Vb. Do you have an example?—RJH (talk) 22:18, 12 February 2008 (UTC)
Found 'em: http://en.wikipedia.org/wiki/85_Pegasi Lists 85 as a G5Vb. http://en.wikipedia.org/wiki/51_Pegasi. The clincher: http://en.wikipedia.org/wiki/Stellar_classification (scroll to the Yerkes classification info). 68Kustom (talk) 02:31, 17 February 2008 (UTC)
Ah, okay. I think the suffix may be from Spectral class#Spectral peculiarities (although that table doesn't look complete). The "b" would be for a spectroscopic binary, but I'm not sure about the "a". SIMBAD gives a classification of G2V+ for 51 Peg.[2] As for the stellar classification page, the Va and Vb don't seem to be mentioned on the Morgan & Keenan paper cited,[3] so I'm a little skeptical about that table.
I'm not sure that it would be beneficial for this article to get in to the messy details of peculiar spectra. We've already got a peculiar star page. Thanks.—RJH (talk) 17:53, 17 February 2008 (UTC)
I thought too that somebody might have been a bit too organized in assigning 'a' and 'b' to main sequence stars. Perhaps the mixup is over something like Alpha Cen A and B? In terms of supergiants, though, what's the difference between Ia and Ib? 68Kustom (talk) 23:29, 17 February 2008 (UTC)
The Ia-0/Ia/Iab/Ib sub-categories just seem to be a difference in supergiant luminosity.—RJH (talk) 19:57, 28 February 2008 (UTC)

[edit] Power Laws

What do people feel about a new section discussing the approximate power law relationships on the Main Sequence, and how they are derived? Luminosity-temp, Temp-Mass, Luminosity-Mass, and Stellar lifetime-Mass relationships could all be included for low, medium, and high mass main sequence stars. Density, radius, and other variables may also be included in their own scalings if wanted.... I'm not an expert so I wouldn't feel comfortable writing it up accurately, although if someone has the requisite background, I think it could be very useful.... —Preceding unsigned comment added by Firth m (talk • contribs) 17:23, 28 February 2008 (UTC)

Would it be of interest to the readership? If it tells a reader something more than just a set of derived empirical relationships then it could be useful. But it would need to be properly referenced.—RJH (talk) 19:51, 28 February 2008 (UTC)