Exotic Star Binaries
Not all stars shine with a constant light– some stars can double in brightness in a few seconds, and increase in brightness by a factor of a hundred within a few hours. These stars are accreting binary systems, where a compact object such as a white dwarf, neutron star, or black hole is in a close orbit with an ordinary star. The two stars are almost touching, and the orbital periods can be as little as 11 minutes. The gravitational field of the compact object pulls gas off the surface of the ordinary star, and this gas spirals around the compact object to form an accretion disk, and then slams onto its surface. Rather than flowing in an even stream, the gas comes off the surface of the donor star in irregular chunks. As each chunk hits the disk of gas spiraling in to the compact object, the collision heats the gas and causes a burst of X-rays and light. Blobs of gas from the inner edge of the accretion disk similarly slam on to the surface of the compact object and cause a flash of X-rays and light.
In a collaboration with Dr. Keith Horne that began several years ago when we were freshmen in college, I designed and built detectors and data systems to study rapidly varying light from stars. Some of the systems I built were:
- a millisecond photometer for use on small telescopes
- a millisecond photometer for use on the 60″ and 100″ telescopes at Mount Wilson, the 60″ at Palomar, and the 100″ at Las Campanas
- a data link between Steve Shectman’s Shectograph on the 100″ at Mt. Wilson and the 60″ at Mt. Wilson, allowing us to do exact simultaneous spectroscopy and photometry with the two telescopes.
- a high speed datasystem for Steve Shectman’s 2D-Fruitti spectrometer. This allowed us to do continuous millisecond spectroscopy of the black hole binary A0260-00 with the 200″ at Palomar, and similar work with the 100″ at Las Campanas.
- a datasystem for the LRIS spectrograph at the 10 meter Keck telescope on Mauna Kea, allowing us to take 14 spectra per second continuously, with coordinated observations using the Rossi XTE X-ray satellite.
With these data systems, we found a wealth of unexpected phenomena. For instance, in AE Aquarii, we found that the rapidly rotating magnetic field from the spinning white dwarf acts a propeller, spraying gas out of the system.