lect 9 - Spectral Sequence Brown Dwarfs Most Brown dwarfs...

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Spectral Sequence
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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
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Relationship between a star’s luminosity, radius, and surface temperature Stars come in a wide variety of sizes, from - white dwarfs (~ Earth size) - supergiants (1000 R Sun , 10 5 larger than white dwarfs) From Stefan-Boltzmann Law, F = σT 4 , then L = F x S , where S is the star’s surface ( S=4πR 2 )
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Flowchart of Key Stellar Parameters
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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
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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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By carefully examining a star’s spectral lines, astronomers can determine whether that star is a main-sequence star, giant, supergiant, or white dwarf
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Full Spectral Typing Spectral Class and Luminosity Class • Luminosity classes
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lect 9 - Spectral Sequence Brown Dwarfs Most Brown dwarfs...

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