how to solve it?
How about trying to write an equation for stellar evolution. One has a 1M (solar mass if I read the symbol correctly) leaving the main sequence at 20 L. What's the significance of that?
We ask students to provide some work and effort when asking for assistance.
thanks a lot. But what is the equation of evolution? if you can provide me a little more info on that, I think I can make it further.
Here are some useful notes on stellar lifetimes. I haven't gone through the details, but there appears to be some variation. It would be worthwhile to do a comparison.
THE MAIN SEQUENCE
Star main sequence lifetime = [star's mass / star's luminosity] × 1010 years.
Star main sequence lifetime = 1010 / (star's mass)(p - 1), where p = 3 for stars more massive than 30 solar masses and p = 4 for stars less massive than 10 solar masses.
http://astronomy.swin.edu.au/cosmos/M/Main+Sequence+Lifetime (this page seems pretty good)
Notes on Stars
Separate names with a comma.