Fig'16'17

1
Fig.16.17
Doppler shift is an apparent change in FREQUENCY

• If OBSERVER moves toward light (em wave!)
  source, ze counts more blips in a given time
• ? f rises (blue shift)
• reverse (red shift) for motion away

• If EM SOURCE moves toward hir, ze counts more
  blips in a given time, since emission distance
  keeps shrinking
• ? f rises and reverse for motion away
• this last case is by far most often seen!!!
• The red shift for a source moving away!!

2
Fig.16.18

• if an object is rotating one sees Doppler
  splitting of a spectral line
• figure is highly exaggerated unless surface
  speed is 10 c (!!)

3
Fig.16.19
Herzsprung-Russell Diagram

• Most stars lie on Main Sequence Highest M ??
  Hottest
• Mass .5 2 M
• Giants and Supergiants!!
• Dwarfs!!

4
Fig.16.20
Scatterplot for 21,000 stars
5
The mass-luminosity relationship

• A very cool experimental result
• luminosity is standardized brightness (total
  star power)
• M is now MASS not absolute magnitude
• More Luminous stars are more massive trend is
  very strong

L
M MS L LS 1 1 1.5
4.1 2 11.3
M

• so log L 3.5 log M which will plot to a
  straight line on log-log axes (see next slide)
• Typical star masses range from ? .1 MS to ? 20
  MS
• Brown dwarfs are still less massive (and very
  numerous) Supergiants are still more massive
  (and rare)

6
Fig.16.21
3.5 orders of magnitude
One order of magnitude