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Re: [Phys-l] the sun



Yes, I do indeed know that there are very strong correlations between
1) luminosity and temperature
2) luminosity and mass
And hence there is a strong correlation between
3) temperature and mass (for main sequence stars)

So, yes, in the end, an HR diagram does tell you a lot about the mass as
well.


Think about the physics: To a first approximation, mass _must_
determine what's going on. For any given mass, there is one solution
to the equation of state. Otherwise, if there were (say)
two solutions, there would be two main sequences, not the observed one.

My (first) point was that it is a bit much to expect someone who is
asking a basic question about stellar populations to
1) know the important parameters of stars (mass, composition, luminosity
...)
2) know the relevant physics in detail (hydrostatics, hydrodynamics,
nuclear fusion ...)
2) solve the equations of state of a star, and then
3) infer the mass distribution from an HR diagram.


(1) Yes, the comment from Tim Folkerts to John Denker that the
HR diagram doesn't tell us anything about the mass is incorrect.

That isn't quite what I said. I said "the HR diagram says nothing
*DIRECTLY* about mass". And I stand by that that. It DIRECTLY tells us
about temperature and luminosity.

I fully agree INDIRECTLY the HR diagram relates to mass. But to derive
such relationships (as JD was implying) is PhD level work for a team of
people and a powerful computer.

Sure, it's great to recognize how such things are possible. Sure it is
great to start with first principles and figure out the consequences.
But it is also nice sometimes to get a simple answer (like Michael's
distribution and rough analysis). :-)


Tim F