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11.9.2007 - Astronomy notes

11.9.2007 - Astronomy notes - r ound st at e is a lyman ser...

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Unformatted text preview: r ound st at e is a lyman ser ies (ult r aviolet ). 11.9.2007 astronomy ed st at e is a balmer ser ies (visible). cit ed st at e is a paschen ser ies (infr ar ed) Br ightness is proportional of luminosity over distance squared B ~ L/D 2 Stellar temperature Stellar colors (crude) Stellar spectra (precise) - Different temperatures, different spectral lines - With hydrogen, you need to be at about 10,000 K, most atoms are in the first excited states, and therefore create a balmer series (visible). - Depending on the lines, you can tell composition and extremely precise temperature readings Stellar classification: - Initial scheme was A P; based on strength of the balmer line - String based on temperature: OBAFGKM (RNS)LT o Our sun is around G5. OBA = hot; KM = cold. o LT = brown dwarfs, failed stars - Subdivisions: 0-9 Stellar size Direct measurement - Adaptive optics - HST Angular diameter = 0.045"; distance = 130pc Diameter = 130 pc * 0.045" = 5.8 pc*arc second = 5.8 AU Indirect measurement 4 Stephan's law: energy flux is proportional to T . - Energy per time per area = flux = luminosity / area - Energy per time = luminosity - L / 4r2 ~ T 4 L ~ R2T 4 L / L sun = (R/R sun) 2 (T/T sun) 4 R = (L/Lsun) 1/2(T/Tsun) -2 * Rsun Classification Giants = 10-100 times size of sun Super giants = 100 1000 t imes size of sun Dwarf: R less than 0.1 Rsun White Dwarf: hot dwarf stars ...
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