ASTR101 s07 AstronomyFinalReview

ASTR101 s07 AstronomyFinalReview - 1 Astronomy Final Review...

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1 Astronomy Final Review Models of the Solar Interior o Ideal Gas For a fixed volume, a hotter gas exerts a higher pressure Relation between temperature, pressure, and volume o Hydrostatic Equilibrium Aids the sun in not collapsing rapidly Gravity balances internal pressure (pressure  gravity) True at all layers of the sun o Continuity of mass Smooth distribution throughout the star o Continuity of energy Amount entering the bottom layer is equal to the amount leaving the top o Energy Transport How energy is moved from the core to the surface Stellar Groupings o One must study groups of stars since individual stars take a long time to evolve, be careful to avoid bias and eliminate variables An example would be one which is apparently the brightest and one that is the nearest Nearby stars are cooler, bright stars are hotter o A way to avoid bias is to study groups of stars that are bound by gravity The distance across the group of stars is small so they are about the same distance from us, so, the ratios of apparent brightness and intrinsic luminosity are about the same The groups are loosely bound so they must have formed together, so they all have the same chemical composition Star Clusters o If a star is in a star cluster you can tell how old it is, all the stars in the same cluster have the same age and composition o Can be classified based upon how “tight” they are o Open clusters are less compact, and have a small number of stars, a few hundred, small and irregular o Globular clusters are more compact, and have a large number of stars (a few thousand), spherical o You can plot the apparent brightness instead of the intrinsic luminosity on the temperature luminosity The physical size of a cluster is only a few dozen light years All of the cluster stars have the same distance from us to an accuracy of a few percent No pattern in apparent magnitude vs. color since each star is at a different distance There is a pattern of luminosity since it is a physical characteristic The sequences occupied by cluster stars changes from cluster to cluster This is related to the life cycle of stars Life Cycle of Stars o Mass-Luminosity Relation The luminosity of a star is related to its mass: L ~ M p where p is almost 4 The luminosity of a star represents the amount of energy emitted per second There must be a source of this energy and it can’t last forever The amount of “fuel” a star has is proportional to its initial mass The length of time that the fuel can be spent is equal to the amount of fuel divided by its consumption rate o Age mass/luminosity = mass/(mass)^4=1/(mass)3 ̃ Age – time on the main sequence Mass – initial mass o Mass-Age Relation
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2 More massive stars die much more quickly than less massive stars o Star Clusters The sequences occupied by cluster stars changes from cluster to cluster On the main sequence O and B stars (the bluest ones) are the most massive. Their lifetimes are relatively
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This note was uploaded on 02/15/2008 for the course ASTR 101 taught by Professor Orosz during the Spring '05 term at UCSD.

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ASTR101 s07 AstronomyFinalReview - 1 Astronomy Final Review...

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