2009 Science/AAAS PhD Dance Entry: Prof. Adam Burgasser

My thesis work was on the search for and discovery of a class of brown dwarfs called T dwarfs. Brown dwarfs are objects that share the properties of low-mass stars (e.g., they are mostly isolated, form from the gravitational collapse of giant molecular clouds, and are present throughout the Galaxy) and the properties of giant planets (small, very low mass, and can't fuse hydrogen so they get colder and fainter over time). Brown dwarfs can therefore be considered either "failed stars" or "super-Jupiters" depending on your point of view (or source of funding). T dwarfs are the coldest and faintest known brown dwarfs, and have remarkable atmospheres that resemble those of giant planets: methane, water and ammonia gases and even clouds (of dirt). The dance traces out the development of my thesis work, starting just after the first brown dwarf was identified, a T dwarf named Gliese 229B. As a young grad student with no idea of what to do for my thesis, I first try to study Gliese 229B and figure out what she is, but I'm not very productive. Several other astronomers are searching for other brown dwarfs like Gliese 229B, and I try to jump in but again I don't really know what to do. Then I learn to use the 2MASS catalog, a near-infrared survey of the sky that was taking place while I was a graduate student. With this new perspective I see lots of interesting objects, but so many that I can't tell which are T dwarfs. However, when I start to look for stars that have the same characteristics as Gliese 229B (in this case, the same dance moves), I find several of them. Having assembled my sample, I measure their spectra and come up with a way to arrange them in a particular order - my definition of the T spectral class. With that work, I am bestowed my PhD, ready to join the rank and file of astronomy. The T dwarfs are distinguished by a particular dance, which was designed to represent their special characteristics. The arm motions - up, sidewise, down - represent the letter T for the spectral class. The crossing of the arms at the end of each cycle indicates that these objects are cold. The twisting motion reflects their rapid spinning.