Starlight continued How study of stellar spectra reveals the nature of the stars

Spectra (plural of spectrum) The solar spectrum A fundamental measurement to extract more information from starlight Spread out light according to wavelength See Section 16.5

Kirchoff’s Laws of Radiation Demo of Kirchoff’s 3rd Law

Kirchoff’s First Law + Wien’s Law Hot, opaque objects produce continuous spectrum The hotter the object, the bluer it is Wien’s Law wmax = 2.9E-03/T The hotter an object, the brighter it is demo

Why does Wien’s Law look like that? A physicist is bothered when he or she sees an equation like: The form which emerges from fundamental equations of physics is:

What is the little “h” that appears in the correct form of Wien’s Law? The speed of light The scale height of the Sun’s atmosphere The Universal Gas constant Planck’s constant The electrical charge of the electron

Kirchoff’s First Law + Wien’s Law

Important point: a hotter blackbody is brighter at all wavelengths than a cooler blackbody of the same size

Kirchoff’s Third Law: Absorption Spectra See Figure 16.6

Starlight…application of spectroscopy to stars Continuous spectrum gives surface temperature (Wien’s Law) Spectral lines give chemical composition, temperature (also), speed of rotation (How?) and other properties Examples of stellar spectra…what can we say?

Spectral classes of stars: O,B,A,F,G,K,M What can you say about the temperatures of these stars?

Examples of stellar spectra Question: apply Wien’s Law to the O5 star. What Can you say about its Temperature (relative to the Sun?)

With information provided by spectroscopy, we can search for correlations between stellar properties

What the data show: the Hertzsprung-Russell Diagram Highest quality data from the Hipparchus spacecraft

The Sun is generically related to most other stars. How? Why? The Sun is here The Sun is generically related to most other stars. How? Why?

Filling out the Hertzsprung-Russell diagram

The Hertzsprung-Russell Diagram and the Types of Stars See Figure 16.20 Types of stars, important terms Main Sequence (luminosity class V) Giants (luminosity class III) Supergiants (luminosity class I) White dwarfs What does it all mean?

The Hertzsprung-Russell Diagram

The scientific classification scheme for the Sun The Sun is a class G2V star…the Galaxy probably has a billion of them

The Hertzsprung-Russell diagram is a plotting board for the nature and evolution of stars