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Lecture 19: We use binary stars
to measure stellar masses
Measure V and r and you get M (plus
details, details)
The masses of stars (and their
luminosities)
Main
Sequence
stars
The more massive a MS star is, the
more luminous it is (Big Time)
L/Ls = (M/Ms)3.5
Example: 8 solar mass star
L/Ls = 83.5 = 1448 !
Put 2 and 2 together: the
rudiments of stellar evolution
• The fuel of a main sequence star is its own mass
• More massive stars have more fuel than less
massive stars.
• But they are using their fuel up at a fast rate, much
faster than proportional to their mass.
• So, massive stars run out of fuel sooner. The more
massive, the shorter their Main Sequence lifetime
An analogy with cars
• Car A has a ten gallon gas tank, and gets
40mpg
• Car B has a twenty gallon gas tank, and gets
10 mpg (uses fuel at a faster rate)
• So Car A travels further (400 miles versus
200) even through it has less fuel.
• The same is true with Main Sequence stars,
only more pronounced
The Main Sequence Lifetime = time it takes a
MS star to fuse the hydrogen in its core to
helium (10 Gyr for Sun)
The question of stellar evolution:
What happens after the MS, and what
before?
Big hints in the sky: star clusters
(open and globular)