(spectroscopic parallax) < < prev next > > (Chapter 16)

To measure the mass of a star, we use Kepler's law and the momentum equation (or center of mass equation) for binary stars. When we graph the luminosity vs. mass of main sequence stars, we get something like the graph shown below.

This graph is called a log-log graph because the axis divisions are powers of 10. The slope of the line shown in this graph is 4. This means that the luminosity is proportional to mass to the 4th power. This is called the mass-luminosity relation and is expressed mathematically as

If you double the mass of a star, by what factor does its luminosity increase?

Therefore, the mass-luminosity relation gives us the following method for calculating the mass of a main sequence star. (1) Determine the luminosity of a star and (2) calculate the mass of the star.

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Semester: Fall Spring Summer

Year: 2015

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