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Re: [Phys-l] the sun



On 11/12/2008 01:44 PM, Folkerts, Timothy J wrote:

With all due respect, this link is of almost no value in answering the
question!

First of all, the HR diagram says nothing directly about mass -- only
temperature and luminosity.

With all due respect, sometimes "almost no value" is 100%
of the available value.

For simplicity, let us restrict attention to "main sequence"
stars.

Unless you get lucky (e.g. some binary systems) the HR diagram
tells you almost everything you are going to know about the mass
of the star.
*) High mass --> hot and bright
*) Low mass --> cool and faint


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.

In fact there is some scatter, i.e. some "thickness" to the
main sequence, so we know there are other contributions,
notably some dependence on chemical composition ... but they
can be considered second-order correction terms.