Research ProjectsOur observational research is mainly divided among two areas. We use transit observations to carry out detailed characterization of exoplanets, and we use radial velocity observations to detect new planets.
When planets eclipse (transit) their host stars, we can measure their masses and radii, and probe their atmospheres as well. This unique opportunity makes transiting planets an important laboratory for learning about the detailed characteristics of exoplanets. Our work in this area is focussed on atmospheric studies using spectroscopic techniques, so-called "transit spectroscopy." We aim to reveal the composition and physical conditions of exoplanet atmospheres. The use of ground-based observatories is a major part of our research in this area. We use many of the largest telescopes in the world for transit spectroscopy observations, including the Magellan,
Transmission spectrum of the super-Earth GJ1214b obtained with the FORS instrument on the VLT and presented in Bean et al. (2010c). The lack of strong features in this spectrum suggests that heavy molecules like water vapor make up a significant fraction of the planet's atmosphere.
Radial velocity measurements are one of the best ways to reveal planet frequency statistics. Our research using radial velocity observations is currently focused on two poorly studied stellar populations: solar twins and very low-mass M dwarfs.
The very low-mass M dwarfs are the most numerous stars in the Galaxy and offer important advantages for characterizing potentially habitable planets. However, they have been neglected in planet searches to date because of their extreme intrinsic faintness at optical wavelengths. We are carrying out radial velocity searches for planets around these kinds of stars with the VLT and Subaru telescopes in the near-infrared region using our new ammonia cell calibration approach (Bean et al. 2010b).
Very accurate chemical abundance determinations are possible for strictly defined solar twins (Teff within 100 K, log g within 0.1 dex, and [M/H] within 0.1 dex of the solar values; Melendez et al. 2009). This opens up the possibility of studying the connection between stellar abundances and planet occurrence in more detail. We are carrying out a planet search targeting a large sample of solar twins using the HARPS instrument on the ESO 3.6m telescope. This project is in collaboration with Jorge Melendez, Martin Asplund, and Ivan Ramirez.