Astro 1050     Wed. Oct. 15, 2003
   Today:  Chapter 8, Properties of Stars

L, T, R, and the H-R diagram
L = 4 p R2 sT4
The main sequence consists very roughly of similar size stars
The giants, supergiants, and white dwarfs are much larger or smaller

Lines of constant R in the H-R diagram

Slide 4

Different “types” of H-R diagrams

Luminosity Classes

Spectra of Different Luminosity Classes

Spectroscopic “Parallax”

What fundamental property of a star
varies along the main sequence?

What fundamental property of a star
varies along the main sequence?

Masses of Binary stars

Masses of Binary stars

Masses of Binary stars

Measuring a and P of binaries
Two types of binary stars
Visual binaries: See separate stars
a large, P long
Can’t directly measure component of a along line of sight
Spectroscopic binaries:  See Doppler shifts in spectra
a small, P short
Can’t directly measure component of a in plane of sky
If star is visual and spectroscopic binary get get full set of information and then get M

Masses and the HR Diagram
Main Sequence position:
M:    0.5 MSun
G:        1 MSun
B:       40 Msun
Luminosity Class
Must be controlled by something else

The Mass-Luminosity Relationship
L = M3.5

Eclipsing Binary Stars
System seen “edge-on”
Stars pass in front of each other
Brightness drops when either is hidden
Used to measure:
size of stars (relative to orbit)
relative “surface brightness”
area hidden is same for both eclipses
drop bigger when hotter star hidden
tells us system is edge on
useful for spectroscopic binaries