Extra-solar Planet Studies

Penn State has a very active extra-solar planet study program! Exciting research is being carried out in a number of fields, including:

Surveys for extra-solar planets using Doppler radial velocity technique. Prof. Ge and his research group have developed a new kind of radial velocity technique, called dispersed fixed-delay interferometry, for high precision Doppler radial velocity measurements. The Doppler measurements are conducted through monitoring the stellar fringe phase shifts of the interferometer instead of absorption line centroid shifts as in state-of-the-art echelle spectroscopy. A prototype interferometric instrument has successfully detected radial velocity curves of 51 Peg and Upsilon Andromedae using the Kitt Peak National Observatory 2.1 meter telescope, confirming previous detection with a totally independent radial velocity method. Initial observation results demonstrate photon noise limited short term radial velocity precision, ~ 3 m/s with eta Cas, a radial velocity stable star. It is very likely that this instrument will reach sub m/s logn term Doppler precision for planet detection as well as asteroseismology study since this instrument has very simple and stable response, unlike the echelle instruments. A survey instrument is being developed and will be commissioned at the KPNO 2.1m in the summer 2003 for a long term radial velocity survey for planets. A multiple object radial velocity interferometric instrument is being planned for the WIYN wide field telescope to allow simultaneously monitor ~ 100 stars for planets.


High contrast imaging of extra-solar planets and brown dwarfs. Prof. Ge's group and his collaborators, at Princeton University, Harvard-Smithsonian Center for Astrophysics and Ball Aerospace Technology Inc. are developing new coronagraph techniques for the NASA Terrestrial Planet Finder mission, to be launched in 2015. They have successfully demonstrated the feasibility of a shaped pupil coronagraph for high contrast imaging in the lab, as well as, at the astronomical telescope. In the lab, they have reached ~ 10-6 contrast at ~ 5 times diffraction-limited Airy disk size. At the Mt. Wilson 100inch telescope with a high order adaptive optics system, they have reached ~ 10-4 at the ~ 10 times diffraction-limited Airy disk size. They have successfully detected faint companions around nearby stars using this new high contrast imaging technique. They are working on developing new techniques for further improvement in image contrast. Their goal is to reach ~ 10-10 contrast to allow TPF to detect Earth-like planets in space in next decade. Prof. Ge's group is also taking advantage of the new high contrast imaging techniques to search for brown dwarfs and giant planets around nearby stars. To date, they have detected two transition objects, and a brown dwarf candidates.

Studies of protoplanets and young stellar objects . Prof. Ge and his research group are working on detecting protoplanets using silicon immersion gratings they developed at Penn State nanofabrication facility. Detection of dynamic gas gaps formed by protoplanets in planetary disks is perhaps the most feasible way for detecting planet formation. However, it requires a spectral resolution of at least R = 100,000 at 4.6 micron. The silicon immersion gratings, due to their more than 3x dispersing power than conventional gratings, make this high resolution IR spectroscopy possible at large ground-based telescopes. A silicon immersion grating with a resolving power of R ~ 120,000 at 4.6 micron is being manufactured and will be available for observing in 2003. In demonstration observations with a prototype silicon grism, they detected a rotating disk with a FWHM of 550 km/s around a Be star, BD +65 1638 (a possible progenitor of a fast rotating Be star), for the first time.
Emission lines from the CO 4.6 micron band and other molecular bands formed in the dynamic gaps among all ~ 300 T Tauri stars out to the distance of Taurus (d = 140 pc) will be searched. This will form a sufficient statistical sample for comparison with results from precision Doppler velocity surveys. Since both the Doppler and silicon immersion grating techniques probe similar orbital regions around stars, the results from these surveys will be used to investigate if orbital migration and dynamical scattering play a significant role in planet formation and evolution.

Venus transit experiments. The upcoming Venus transits across the solar disk are rare events, occurring in pairs less than once per century. Prof. Ge's group and his collaborators, Dr. Sara Seager and her group at the Carnegie Institute of Washington, are working on preparing a 3-D imaging spectrograph for capturing transit spectra. This data will be used for testing the feasibility of detection of terrestrial planet transmission spectra within the signal of a non-spatially resolved star for future space missions. The eventual detection and characterization of extra-solar terrestrial planets, especially those with signs of atmospheric modification by life, will have a huge impact on science and society.

Extra-solar planets around pulsars . Prof. Alex Wolszczan and his research group are leading this effort. Penn State's Pulsar group was the first in detecting extra-solar planets.




Extra-solar planets around white dwarfs . Prof. Steinn Sigurdsson and his research group have developed a theoretical model for planet formation and evolution around white dwarfs.





Web page by Jian Ge (jian@astro.psu.edu), Last update: 2002, December 17