V Bootis is a bright semiregular of the northern skies. Earlier in the 20th century, V Boo had a larger amplitude and much more regular light curve than it did during this 5000-day span of data from the mid-1980's to mid-1990's. V Boo is what we call a multimode pulsator. When a star undergoes pulsation, the motions of the star's surface and interior are described by the pulsation mode, a mathematical means of describing the radial and angular components of the pulsations. You may hear of stars undergoing "radial mode pulsations" which mean that the star pulsates radially inward and outward with perfect spherical symmetry; "nonradial pulsations" describe pulsations where some parts of the star's surface are moving inwards when other parts are moving outwards. The light curve can become very complex when more than one mode is pulsating in a single star at the same time, and that is what is happening in V Boo. There are likely two modes pulsating in this star at the same time, one with a period around 258 days, and another with a period around 134 days; both are probably radial modes with different radial orders. These two modes interfere or "beat", sometimes constructively and sometimes destructively. The result is that the light can vary strongly at some times, but only weakly at others.
Prepared By: Matthew Templeton