Sunday 1 January 2012

Third body in the AV Canis Minoris system.

AV Canis Minoris is a binary star system in the constellation of Canis Minor; the name implies the 74th variable star in Canis Minor, the star appearing variable as each of the component stars passes in front of the other in our line of sight. It was discovered in 1968 by the German astrophysicist Cuno Hoffmeister, working at the Sonneberg Observatory, and has been largely ignored ever since.

This study revealed that the two primary bodies of the system are an F2-type yellow-white dwarf star (hotter and slightly more massive than our sun) and a G5-type yellow dwarf star (similar to our sun) orbiting one-another every 2.28 days. They also found a smaller third component in the system, which transited the stars every 12 hours; each transit taking 3.3 hours and causing a 2.6% drop in the luminosity of the system. They concluded that this body must be a large Hot Jupiter type planet (a gas giant close to its parent star) or a small brown dwarf (an object large enough to emit more heat than it receives, but to small to fuse hydrogen). They were not able to establish which of the other bodies in the system this object orbited, as the stars are similar in nature and close together, and the orbit of the third body appeared to be highly irregular.

This month Liakos and Niarchis published a new study, along with Dimitris Mislis of the Institute of Astronomy at the University of Cambridge in a paper on the arXiv database, that will also be published in From Interacting Binaries to Exoplanets: Essential Modeling Tools. Proceedings of the IAU Symposium No. 282, 2011. This study used additional observations of the system, combined with improved modeling techniques, and came to the following conclusion.

The object is a Brown Dwarf. It actually emits 2% of the light emitted by the AV Canis Minoris system, although since it is dimmer than the other two objects in the system it does cause a net dimming when it passes between us and them. The object orbits the larger of the two other stars, and probably has a radius 6.4 times that of Jupiter, which would give it a volume of 1098 times that of Jupiter, far to large to be a planet.

The most likely resolution of the AV Canis Minoris system. The Brown Dwarf obits the larger of the two stars, the two stars orbiting their mutual centre of gravity.