•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 most stars similar (H, He, ...)
•Age: Will be
important – but put off till Chapter 9
•Mass: Turns out to be
the most important parameter