lect 9 part 1

lect 9 part 1 - Spectral Sequence Brown Dwarfs Most Brown...

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1 Spectral Sequence Brown Dwarfs Most Brown dwarfs are in even cooler spectral classes now called L and T – Unlike true stars, brown dwarfs are too small to sustain thermonuclear fusion Infrared image of a Brown Dwarf Relationship between a star’s luminosity, radius, and surface temperature From Stefan-Boltzmann Law, F = σ T 4 , then L = F x S , where S is the star’s surface ( S=4 π R 2 ) • Stars come in a wide variety of sizes, from - white dwarfs (~ Earth size) - supergiants (1000 R Sun , 10 5 larger than white dwarfs)
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2 Flowchart of Key Stellar Parameters The Hertzsprung-Russell (H-R) Diagram • The H-R diagram is a graph plotting the absolute magnitudes of stars against their spectral types—or, equivalently, their luminosities against surface temperatures The positions on the H-R diagram of most stars are along the main sequence, a band that extends from high luminosity and high surface temperature to low luminosity and low surface temperature On the H-R diagram, giant and supergiant stars lie above the main sequence, while white dwarfs are below the main sequence Stars in the main sequence are like the Sun in that hydrogen fusion is taking place in their cores
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3 By carefully examining a star’s spectral lines, astronomers can determine whether that star is a main-sequence star, giant, supergiant, or white dwarf Full Spectral Typing Spectral Class and Luminosity Class • Luminosity classes (use Roman numerals) –I – Luminous Giant
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This note was uploaded on 02/06/2011 for the course ASTR 113 taught by Professor Geller during the Spring '08 term at George Mason.

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lect 9 part 1 - Spectral Sequence Brown Dwarfs Most Brown...

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