Superhumping

By Michael on July 11, 2008 at 11:26 am | In Astrophysics, Blog Posts |

You’ve maybe heard of cataclysmic variable stars. They are binary systems where one of the stars is stealing material from the other star due to their close proximity. This material forms a pancake around the star called an accretion disk. We’ve never imaged one of these systems but we have a very, very good theoretical model of how they work.

Every once in a while that accretion disk gets unstable and essentially blows up in what we call an outburst. Sometimes these outbursts are extra bright and carry a signature in their light curve called “superhumps”. These are large oscillations in the light curve at a period very near, but not exactly equal to, the orbital period of the system.

On 6/30/08 one of these systems, VY Aqr, went into a superoutburst. This is a fairly infrequent event for this star. The outbursts themselves happen every few years and the superoutbursts less often than that.

I was heading out to my observatory when the word came in so I slewed my fancy 0.212m telescope (doesn’t that sound more impressive than 8.3″?) and got some data. So did a few other people and I downloaded all of their data from the AAVSO. If you click the image above a light curve will open in a new window. Let me explain it to you.

This is a phase plot using the superhump period of this star (P_sh = 92.7 minutes). So anything that happens 92.7 minutes after something else is plotted at the same phase. So the X axis is the phase of the superhump period and the Y axis is the brightness of the star. Because the star is getting dimmer, each day’s data is lower on the graph than the previous day. So each night is folded upon itself but each subsequent night is below the previous night.

You can see there are some interesting things going on! The superhump amplitude and phase change over time as the systems fades.

The latest papers on this object included Doppler tomography, new parallax measurements and spectroscopy from the Hubble Space Telescope. There is a lot of interesting physics in these systems and they are the subject of on-going study by astronomers. Including me!