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lecture17 - 5/9/08 Calculating Stellar Masses watch out for...

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Unformatted text preview: 5/9/08 Calculating Stellar Masses watch out for units and equations Mass-Luminosity Relation Colors and Temperatures of Stars Main Sequence Sizes of Stars DEMO Two light bulbs have same luminosity Their flux (apparent brightness) changes depending on their distance to you. Measuring Stellar Masses The mass of an object is a key detail. If we can measure an objects orbit, we know the mass of the object its orbiting. we did this all over the solar system, with moons around planets! Lucky for astronomers, stars are often in binary systems Binary stars: a pair of stars that are orbiting around their common center of mass. Binary Stars If we can distinguish the two stars visually, its a visual binary. We can determine the two masses: M 1 and M 2 : masses of stars in solar masses a: semimajor axis, in AU P: period of orbit, in years M 1 + M 2 = a 3 P 2 Visual Binary Spectroscopic binary Sometimes we cant visually distinguish the two stars But then we look at the spectrum and we see velocities of two objects! Since their velocities change (with respect to us) as they orbit each other, the locations of the spectral lines changes Masses and Luminosities Now we have measured the masses and luminosities of a wide range of stars....
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lecture17 - 5/9/08 Calculating Stellar Masses watch out for...

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