Starlight conclusion Apply Wiens law and Kirchoffs Laws

Starlight (conclusion) Apply Wien’s law and Kirchoff’s Laws to deduce Properties of stars

Kirchoff’s First Law + Wien’s Law • Hot, opaque objects produce continuous spectrum • The hotter the object, the bluer it is • Wien’s Law lmax = 2. 9 E-03/T • The hotter an object, the brighter it is Demo

Kirchoff’s First Law + Wien’s Law

Kirchoff’s 2 nd Law: Emission Line Spectra Wavelengths of emission lines unique “fingerprint” of element

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 (Figure 16. 11)…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 O 5 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 Hipparchos spacecraft

The Hertzsprung-Russell Diagram and the Types of Stars • • • See Figure 16. 19 Types of stars, important terms Main Sequence Giants Supergiants White dwarfs What does it all mean?

The Hertzsprung-Russell Diagram

Understanding the Main Sequence (stars like the Sun) • A statistical argument (no physics) • Physical argument 1: what holds stars up? • Physical argument 2: what powers the stars (where do they get their energy supply? )

The nature of the Main Sequence #1: the MS as a Cambus Stop Many more people seen on the sidewalk near a Cambus stop than a random point

The Main Sequence is a long-lived phase of stellar evolution. Stars spend a much longer time here than in other parts of the HR diagram