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IP Pegasi

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Here's a light curve that just looks cool -- the eclipsing dwarf nova IP Pegasi, where the eclipses were tracked during a recent outburst.  Dwarf novae consist of a pair of stars, one a normal dwarf star, and the other a degenerate white dwarf.  The stars orbit close enough to one another that the white dwarf can pull matter off of the normal star, and the accretion disk of this material around the white dwarf is the source of dwarf nova outbursts.  IP Peg happens to be a binary system that's inclined closely enough to our line of sight that the disk is eclipsed during the orbit, resulting in very prominent eclipses during the outburst cycle.  Such eclipses not only produce striking light curves, they also allow you to investigate the structure of the accretion disk via spectroscopy; material in the disk moves at different line of sight velocities relative to us, and as different parts of the disk are eclipsed, you can see the shape of the spectra change.

Prepared By: Matthew Templeton
AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484