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lecture17

# lecture17 - Calculating Stellar Masses watch out for units...

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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

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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 object’s orbit, we  know the mass of the object it’s 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.

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Binary Stars If we can distinguish the two stars visually,  it’s 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

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Spectroscopic binary Sometimes we can’t 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 - Calculating Stellar Masses watch out for units...

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