Stars Star field taken with Hubble Space Telescope

Hertzsprung–Russell diagram

Pleiades

Star Massive, luminous ball of plasmaplasma Held together by gravity Shines due to thermonuclear fusion of hydrogen in its corethermonuclear fusion

Betelgeuse

Spectra of stars Allow astronomers to determine a star’s: Composition Luminosity Velocity Mass

Spectrum of the Sun

3 types of spectra

1.Continuous- produced by a glowing body 2. Absorption line (dark line)- produced when a cooler gas lies between observer and glowing body – this is the type used to ID stars 3.Emission line (bright line)- emission from a glowing gas, used to study nebulae

Star classification Stars are all made of the same material Spectral differences are due to temperature

Coolest stars are red, hottest stars are blue

Classification system O B A F G K M O hottest M coolest

H R (Hertzsprung Russell) Diagrams Stars plotted according to: 1.Luminosity (absolute magnitude) – brightest stars at the top 2.Temperature (spectral class) – hotter stars to the left

H R Diagram (cont.) 1.Main sequence – Band from hot (blue) to cool (red) – 90% of stars – e.g. the Sun 2.Giants – Luminous and cool – x size of the Sun – e.g. Aldebaran in Taurus

3.Super Giants – 1000x larger than the Sun – e.g. Betelguese in Orion Antares in Scorpius

4.White Dwarfs – Very hot, but low luminosity due to small size – e.g. Sirius B – NO fusion in core, glow due to contraction? Gravitational forces

Binary star state.edu/~pogge/TeachRes/Movies162/#spbin state.edu/~pogge/TeachRes/Movies162/#spbin

Albireo (the Cal star)

Stellar Evolution

Fusion

Carbon-carbon fusion

supernova

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Stellar Evolution Stars do not live forever Eventually nuclear fuel runs out and star dies

Stages of Stellar Evolution 1.Pre-main sequence – Stars form in a dense, cool cloud of dust and gas – Gravitational attraction causes it to start to glow – NO fusion yet  Protostar

Once fusion starts the star enters the main sequence