Exoplanets and
Brown Dwarfs

Questions and Objectives

• How do planets form? Are there multiple mechanisms of formation? In what circumstances do they operate?
• What is the frequency of planets as a function of planet mass, primary mass, separation, age, metallicity, and star-forming environment? What does this frequency tell us about the process of planet formation?
• How often do planetary systems have architectures similar to the Solar System? Is the Solar System's configuration of giant planets at and beyond 5 AU and terrestrial planets within 5 AU the norm, rare, or practically unique?
• Can we find systems that are definitely the result of disk migration, planet-planet scattering, or other forms of dynamical evolution?
• How common are rocky planets? How often are they habitable?
• What is the smallest mass of brown dwarfs? How do brown dwarfs form?
• How should we define giant planetary companions and brown dwarf companions, and how do we distinguish between them observationally?
• Do planets form around brown dwarfs? How does planet formation compare between stars and brown dwarfs?
• Can we use the coolest brown dwarfs to test models of planetary atmospheres?

Discoveries and Milestones

• Alex Wolszczan discovered the first known planet outside the solar system.
• Steinn Sigurdsson used the Hubble Space Telescope to detect a white dwarf orbiting a pulsar, which demonstrated that the timing anomalies from the pulsar were caused by a planetary companion.
• Kevin Luhman has discovered some of the least massive known brown dwarfs (~5 M_Jup).
• Using the Keck, Lick, and Hobby-Eberly telescopes, Jason Wright and his collaborators have discovered a substantial number of all known multiplanet systems.
• Kevin Luhman discovered a candidate for the coolest body directly observed outside the solar system, with a temperature similar to that of Earth.
• Suvrath Mahadevan has conducted successful on-site tests of an infrared laser frequency comb at the Hobby-Eberly Telescope with the Pathfinder spectrograph.

Current Projects

• Sara Gettel and Alex Wolszczan are using the radial velocity measurements from the Hobby-Eberly Telescope to search for planets around K giants.
• Matthew Route and Alex Wolszczan are using Arecibo to search for radio emission from free-floating brown dwarfs and giant planetary companions.
• Suvrath Mahadevan and Larry Ramsey are developing and testing the Pathfinder spectrograph, which will be used to search for planets around low-mass stars using infrared radial velocity measurements.
• John Bochanski, Kevin Luhman, and Sonali Shukla are using images from the Hubble Space Telescope to search for young brown dwarfs down to ~3 M_Jup, providing a better constraint on the minimum mass at which free-floating bodies can form.
• Suvrath Mahadevan is participating in the MARVELS exoplanet survey and the APOGEE H-band radial velocity survey within SDSS-III. He is also participating in the TERMS survey for transiting planets.
• Jason Wright is using the Hobby-Eberly Telescope to track long-period planets around the nearest stars, and to improve its ability to detect very low mass planets.
• Rebekah Dawson, Andrew Shannon, Jonathan Jackson, Mariah MacDonald, and Matthias He are studying the formation, dynamics, and stability of planetary systems.
• Arpita Roy and Suvrath Mahadevan are involved with the commissioning of the PARAS instrument in India and developing data analysis pipeline for first light.
• Genady Pilyavsky and Suvrath Mahadevan are developing a high precision photometric pipeline for the TERMS survey to search for bright transiting exoplanets.
• Kevin Luhman is continuing to search for substellar companions to stars in the solar neighborhood using infrared images from the Spitzer Space Telescope.

Student Highlights

• Stephen Redman helped to develop the Pathfinder spectrograph for searching for planetary companions to low-mass stars via radial velocity measurements at infrared wavelengths. He also has produced a new atlas of calibrations of hollow cathode lamps for use in infrared spectroscopy.
• Kamen Todorov discovered a planetary-mass companion to a young brown dwarf using high-resolution images from the Hubble Space Telescope.
• Amanda Morrow used spectra from the Spitzer Space Telescope to show that grain growth in disks -- one of first steps in planet formation -- may occur faster for brown dwarfs than for stars.
• Jacob Luhn, working with Jason Wright and Fabienne Bastien, discovered several new planets and hints of several more orbiting evolved stars a bit more massive than the sun.

Participants

Faculty

Rebekah Dawson
James Kasting (Geosciences)
Kevin Luhman
Suvrath Mahadevan
Larry Ramsey
Steinn Sigurdsson
Alex Wolszczan
Jason Wright

Students

Mathias He
Jonathan Jackson
Mariah MacDonald
Jackson Norris
Arpita Roy

Links

Center for Exoplanets and Habitable Worlds
exoplanets.org
Penn State Astrobiology Research Center
SDSS-III
A detailed description of Mercedes Richards' work related to exoplanets and brown dwarfs