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ay45c4-page27 - Here the right hand sides are completely...

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Unformatted text preview: Here the right hand sides are completely known, so we infer the lefthand sides. These data only give masses if we know the inclination of the orbit, i. But, in general, we will not know this, so our data only measure a combination of masses and i. For one special group of stars, we do get M1 and M2 directly | from \eclipsing" binaries, where the light curve shows an eclipse (see gure). light flux, F/(F1 +F2 ) 1.2 τ 1 secondary eclipse .8 .6 primary eclipse .4 .2 0 0 .5 1 time, t /τ 1.5 Here, the stars are eclipsing one another . This scenario is only possible if i  90 (provided that the stellar radii  separation, which we can check in the above equations; if this is not true, the stars are so distorted that we cannot use this method anyway). Thus, sin i  1. Errors in i have little e ect on the masses derived, because sin i changes slowly at i  90. In fact, the best data on masses of stars comes from eclipsing spectroscopic double-lined binaries, even though these are hard to nd. An alternative approach is to measure many noneclipsing binaries, assume i to be selected at random, and use statistics to derive the distribution of masses, M1 and M2. 86 ...
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