Stellar and nebular spectra

1
Stellar and nebular spectra

• What we see from different angles.
• For a star, gas is its cooler atmosphere layers
• Whats going on? . (Paint/demo)

2
Hydrogen Spectral Line Formation

• Transitions in Bohr atom model give rise to
  different groups
• Optical Balmer (n2)
• UV Lyman (n1)
• Ionization is transitions to/from infinity.

3
Balmer lines of Hydrogen

• Transitions are to/from n2 level
• 3/2 is smallest change, thus lowest energy, thus
  ?? Color?
• What is the Balmer limit shown?

4
Doppler Effect on spectral lines

• Stationary source as shown at right emits wave
  fronts
• Moving source stretches wavelengths behind and
  shortens ahead

5
Doppler Equation
?? / ?0 v / c Where C speed of light V
radial velocity ?0 rest wavelength ?? change
in wavelength or Doppler shift
Doppler-shifted wavelength ? ?? Shown here ??
is negative (blueshift)
6
Use of Doppler Effect to find Planets

• Discover planets around other stars.
• More than a 200 now known.

7
Use Doppler to make a Radial Velocity Curve
Notes errors