•T and R vary
smoothly (and together) along the main sequence
•B stars are ~4 times
hotter and ~10 times bigger than sun
•M stars are ~2 times
cooler and ~10 times smaller than sun
•Presence of a line
implies that a single fundamental property
is varying to make some stars B stars
and some stars M stars
•That fundamental
property then controls T, R
•A second property
controls whether we get a giant or dwarfs
•
•Fundamental
properties we could measure
•Location: Doesn’t seem to be of major
importance
•Composition: Outside composition of stars similar (H, He, ...)
•Age: Will be
important – but put off till Chapter 9
•Mass: Turns out to be
the most important parameter