| A new brown dwarf and increasing number of inhabitants of the brown dwarf desert |
| Csizmadia Szilárd |
| Deutsches Zentrum für Luft-und Raumfahrt, PF-EPA, Berlin |
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It was found in the 1960s, 1970s, when the minimum possible mass of a star was determined that is able to maintain hydrogen fusion in its core,
that there is no strict limit between gaseous giant planets without nuclear fusion and stars with fusion. After some hesitation, the objects in
the transition regime between stars and planets were named `brown dwarfs'. These objects fuse deuterium (sometimes lithium) for about
50,000-100,000 years and they cool down slowly.
The first brown dwarf was discovered in 1995, exactly 20 years ago. While about 1500 single brown dwarfs were found, there are only a handful
in binary sytems and the close-in brown dwarfs are rarities. The regime of close-in brown dwarfs (orbital separation is less than a few
astronomical units) is called 'brown dwarf desert' where no brown dwarfs were known before 2008.
One part of the talk will be about CoRoT-33b (orbital period is 5.8 days), a transiting object in the brown dwarfd esert with 3:2 commensurability with its host star: while the brown dwarf orbits its star three times, the host star rotates twice. It will be shortly explained how the tidal forces and magnetic braking of the star can set this strange commensurability. Other part of the talk will discuss the increasing number of inhabitants of the brown dwarf desert. The cause of no or small number of objects in the close (a<2-4 AU) vicinity of the host stars is usually explained by how planetary systems are formed. However, more and more systems are found in this regime by space-observatories (CoRoT, Kepler) and by ground-based surveys (radial velocity, gravitational microlensing) in the last few years. This is certainly related to the planetary formation theories and it gives clues and constraints for it. |