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Lecture05 - The Hertzsprung Russell Diagram The fundamental...

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The Hertzsprung Russell Diagram The fundamental tool for understanding stars! First used in ~1913, independently by Hertzsprung and Russell. Also known as the Color – Magnitude diagram What are the easiest stellar observations? apparent magnitude c o l o r
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The H-R Diagram (continued) When field stars are plotted, get a scatter diagram (nonsense) Why? color is an intrinsic property of the star (measures temperature) apparent brightness is related not only to the star’s properties – the distance effect randomizes it
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The H-R Diagram Use absolute magnitude, or luminosity Well-defined structures main sequence giants white dwarfs One problem: need distances to convert apparent magnitudes to luminosities use star clusters, where all stars at same distance
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Stellar Size from the H-R Diagram At a given color, there can be two (or more) groups of stars on an H-R diagram Wein’s law: color determines temperature So why different brightness groups?
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