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Homework 1 Solutions

# it is a hot star but has a very small radius so this

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Unformatted text preview: e, assuming the brighter component is a Sun ­ like star. Component A will have absolute magnitude 4.83, so Equal brightness: 5 log (d/10pc) = 7.97 ­4.83 = 3.14 => d = 10x10(3.14/5) = 42 pc Half ­brightness: 5 log (d/10pc) = 7.66 ­4.83 = 2.83 => d = 10x10(2.83/5) = 37 pc (5) Properties of a Hot Star [25 pts] The star PG 1159 ­035 is located 440 pc away from the Sun, has a surface temperature of 136,000 K and a luminosity of 200 L. (a) [2.5 pts] What is its radius (in units of solar radii)? In solar units, L/L¤ = (R/R¤)2(T/T¤)4 => R = [200/(136000/5800)4]1/2 = 0.03 R¤ (b) [2.5 pts] What is its absolute bolometric magnitude? Sun’s Mbol = 4.74 => Mbol (PG 1159) = Mbol (Sun)  ­ 2.5 log (L/L) = 4.74 – 2.5 log 200 =  ­1.01 (c) [5 pts] At what wavelength is this star brightest? What part of the electromagnetic...
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