lecture15_ch11b - Apply what you know: Surveying the Stars...

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Unformatted text preview: Apply what you know: Surveying the Stars • Why is the sky blue? • Why are sunsets red? • Why is the Sun look yellow if its surface temperature makes it look white in space? (Reading questions) Why is a star’s mass its most important property? Each starʼs properties depend mostly on mass and age Stellar Properties Review Luminosity: from brightness and distance Core pressure of a higher-mass star needs to be larger in order to balance gravity; temperature is somewhat larger. (0.08 MSun) 10-4 LSun - 106 LSun (100 M Sun) Temperature: from color and spectral type Higher core temperature boosts fusion rate A LOT, leading to larger luminosity (0.08 MSun) 3,000 K - 50,000 K (100 M Sun) Mass: from period (p) and average separation (a) of binary-star orbit 0.08 M Sun - 100 MSun Hydrostatic Equilibrium 1 Mass & Lifetime Sunʼs life expectancy: 10 billion years Summary of Stellar Properties Until core hydrogen (10% of total) is used up “Officially Bill Always Felt Guilty Kissing Monica” (Hottest) Life expectancy of 10 MSun star: OBAFGKM (Coolest) Blue Small Luminosity Short Lives Life expectancy of 0.1 M Sun star: Low Mass Huge luminosity 10 million years ~ 10 billion years x 10 / 104 Red High mass 10 times as much fuel, uses it 104 times as fast Long Lives 0.1 times as much fuel, uses it 0.01 times as fast 100 billion years ~ 10 billion years x 0.1 / 0.01 Luminosity What is a HertzsprungRussell Diagram? An H-R diagram plots the luminosity and temperature of stars Generate_hr_diagram Temperature High-Mass Stars Normal hydrogenburning stars reside on the main sequence of the H-R diagram SUPERGIANTS GIANTS Stars with low temperature and high luminosity must have large radii Low-Mass Stars 2 SUPERGIANTS Temperature Color Luminosity GIANTS H-R diagram depicts: Stars with high temperature and low luminosity must have small radii Spectral Type Luminosity Radius WHITE DWARFS Mass Lifespan Age Determine_stellar_sizes Temperature Stars in a Star Cluster How can we know this if stars live millions or billions of years? 1) Born at the same time 2) All about the same distance 3) Same chemical composition Star clusters are extremely useful for testing models of stellar evolution!! What are the two types of star clusters? Open cluster: A few thousand loosely packed stars 3 Globular cluster: Up to a million or more stars in a dense ball How do we measure the age of a star cluster? Stars in a globular cluster are so densely packed that they occasionally collide and merge Massive blue stars die first, followed by white, yellow, orange, and red stars Stellar cluster evolving Pleiades now has no stars with life expectancy less than around 100 million years Main-sequence turnoff Turnoff point progresses down the main sequence as cluster grows older, from upper left to lower right. HR Diagram and Age of cluster 4 Main-sequence turnoff point of a cluster tells us its age Detailed modeling of the oldest globular clusters reveals that they are about 13 billion years old 5 ...
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This note was uploaded on 11/13/2011 for the course ISP 205 taught by Professor Donahue during the Fall '08 term at Michigan State University.

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