1. Physics of Astronomy week 2 Thus. 13 April 2006 Astronomy: Universe Ch.6: Optics & Scopes Astrophysics: CO 8: Classification of Stellar Spectra

2. Astronomy: Optics & Scopes Workshop: Make a real image Make a telescope Investigate

3. Astrophysics: C&O Ch.8 Classification of Stellar Spectra Spectra and O B A F G K M Temperatures and Maxwell-Boltzmann dist. Ionization and excitation states Hertzsprung-Russell diagram Line shifting and broadening

4. Spectra and O B A F G K M http://www.gothard.hu/astronomy/astroteaching/anloos/specclass.html

5. Temperatures and Maxwell-Boltzmann The number of gas particles per unit volume with speed between v and dv is: HW: Do 8.1-4

6. Ionization and excitation states Boltzmann equation = ratio of EXCITATION states (8.4) p.231 higher T → higher v, BUT higher T → fewer particles Saha equation = ratio of IONIZATION states (8.6) p.234 higher T → more excited e -, BUT higher T → more IONIZED atoms (lost their e - )

7. Ionization and excitation states Fig.8.7: N 2 /N total for Hydrogen (p.236) excitationionization (Boltzmann)(Saha)

8. Hertzsprung-Russell diagram Recall that flux =  T 4 = L/area: solve for R Same T→ brighter is bigger. HW: Do 8.15-16

9. Line shifting and broadening (Figs. 9,14) Spectral lines can be shifted by: motions: Doppler shift magnetic fields: Zeeman splitting Spectral lines can be broadened by: temperatures: jiggling of gas particles collisions (increasing with density) Spectral lines can be distorted by companions, e.g. binaries or planets.

10. Homework and hints: 8.1-4 (Maxwell-Boltzmann distribution) 8.15 White dwarf 8.16: apparent visual magnitude V = m = 1.19 Mv = absolute visual magnitude = ___ (from H-R) d ~ 10 (m-M+5)/5