Andrew Skumanich connected stellar age to this phenomenon, lithium depletion, and calcium emission. For 10 points each:
[10h] Name this phenomenon whose correlation with observed stellar X-ray activity was first quantified by Pallavicini (“PAH-lah-vee-CHEE-nee”) et. al in 1981 when they showed that X-ray luminosity scales as “v sine i” to the power of 1.9.
ANSWER: stellar rotation [accept descriptions of a star rotating or revolving about its axis; reject “orbiting” or “rotating/revolving around another star/object”]
[10m] Stars undergo this kind of rotation in which the rate of rotation varies across the star, usually with the equatorial region rotating more quickly. This kind of rotation occurs in the convective zone, but not the radiative zone.
ANSWER: differential rotation
[10e] Stellar rotation rates can be estimated by observing these surface features. The approximately 11-year solar cycle is tied to the change in the number and the distribution of these features.
ANSWER: sunspots [or starspots]
<Other Science>