From: chrono.surfer@verizon.net   
      
   Can anybody tell me or point me to a source for formulas for the main   
   sequence lifetime and luminosity change with age given a star's mass?   
      
   The usually-quoted and easily found main sequence lifetime equation   
   t=1/M^2.5 is horribly inaccurate according to all of the tables I have found   
   listing Mass vs. Lifetime. I strongly suspect that this is because in the   
   equation t=fMc^2/L, f (the fraction of the stars mass converted into energy   
   during its lifetime) is not the same for all stars, as it would have to be   
   in order to simply replace it with proportionality constant as is done to   
   get t=1/M^2.5. Unfortunately, I have had no luck in finding an equation that   
   will give me the fraction of mass converted to energy as a function of the   
   star's initial mass. Another major problem is probably that the   
   usually-quoted equation for average luminosity over the star's lifetime,   
   L=M^3.5, isn't all that accurate either, since the exponent should change   
   based on the structure of radiation and convection zones in the star's   
   interior, which is also a function of mass. BTW, having said that, I'd be   
   most grateful if someone could point me to the correct exponents for the   
   mass ranges <.7 solar masses, .8-4 solar masses, and 4< solar masses to   
   replace the catch-all 3.5.   
      
   -l.   
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