2014 programme

It takes Two to Tango: the Intertwined Lives of Close Binary Stars

Tom Richards

Variable Stars South

It's well known that eclipsing binaries provide the only direct way of measuring absolute stellar masses, radii, sizes, luminosities and distances – all together. That alone provides powerful tests for theories of stellar structure and evolution, as well as extending those properties to other stars of all classes. Moreover as one star eclipses another, we can detect and measure starspots, limb darkening and other photospheric and atmospheric phenomena.

But more than that: binaries close enough to eclipse can also affect each other by tidally changing their shapes and rotation periods, irradiating each other, and exchanging mass. This leads to quite different and often startling evolutionary behaviour for the half or more of all stars in close binary orbits. All of that provides more complex and demanding tests for the theories of stellar structure and evolution than do isolated stars.

Unfortunately acquiring the photometric and spectroscopic data that underpins all this is very demanding of telescope time so not popular professionally. But since thousands of eclipsing binaries are bright enough for study with very small telescopes – under half a metre – the amateur armed with a tracking telescope and a camera and a computer can fill the gap and make significant contributions to astrophysics.