lect 13 part 1

lect 13 part 1 - Stellar Evolution The Deaths of Stars...

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3/17/2010 1 Stellar Evolution: The Deaths of Stars Chapter 20 part I: Low-mass Stars Pathways of Stellar Evolution Low-mass stars go through two distinct red-giant stages •A low-mass star becomes –a red giant when shell hydrogen fusion begins a horizonta branch – a horizontal-branch star when core helium fusion begins – an asymptotic giant branch (AGB) star when the helium in the core is exhausted and shell helium fusion begins
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3/17/2010 2
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3/17/2010 3 Bringing the products of nuclear fusion to a giant star’s surface •A s a low-mass star ages, convection occurs over a larger portion of its volume • This takes heavy elements formed in the star’s interior and distributes them throughout the star A Carbon Star is a AGB star that has undergone a 3 rd dredge-up Carbon is transported to the surface by convection, and there are strong absorption bands of carbon-rich elements Stellar winds eject carbon-rich outer layers into space Low-mass stars die by gently ejecting their outer layers, creating planetary nebulae • Helium shell flashes in an old, low-mass star produce thermal pulses during which
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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 13 part 1 - Stellar Evolution The Deaths of Stars...

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