The Classification of Stellar Spectra. The Formation of Spectral Lines The Hertzsprung-Russell Diagram. Midterm Exam. Midterm Thursday February 21 (chapters 1-6) A review session will be held during the regularly scheduled lecture time on Tuesday February 19. Stellar Spectra.
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Midterm Thursday February 21 (chapters 1-6)
A review session will be held during the regularly scheduled lecture time on Tuesday February 19.
The spectra of stars contain much information about the properties of stars….What can be learned? First need to observe…Then classify/categorize
What is the source of the underlying order???
Need to understand…
First excited state occupancy for hydrogen atom from Boltzmann Equation
Boltzmann Energy Distribution
Saha Ionization Equation
The root-mean-squared is the square root of the average value of v2
Example 8.1.1 Determine the fraction of hydrogen atoms in a gas at T=10,000 K with speeds between v1 and v2
The probability distribution of a system occupying a given energy state may be described by the Boltzmann Factor…
T=85,000K n2=n1….for Hydrogen atom
But what about Ionization?
Example 8.1.3 At what temperature does N2=N1 for hydrogen ???
Degeneracy of levels
But… Balmer lines reach maximum intensity at T~9520K!!
Line Strength for each element (and ionization level) depends upon temperature as shown above….
The Hertzsprung-Russell Diagram