On the Road to Imaging Extrasolar Planets: Null Results, other Discoveries along the Way, and Signposts for the Future

Abstract

I present my experiences designing, conducting, and analyzing the results from direct imaging surveys for extrasolar giant planets. Using the young, low mass star AB Dor C, I show that models for low-mass stars and brown dwarfs at young ages are good representations of reality. I discuss the design of the Simultaneous Differential Imaging survey, and how Monte Carlo simulations of giant planet populations allow for the design of imaging surveys, including the choice of target list, that maximizes the expected yield of extrasolar planets. With the conclusion of the SDI survey, I examine how its null result for planets sets constraints on the allowable populations of long-period exoplanets, finding that fewer than 8% of sun-like stars can have planets more massive than 4 Jupiter masses between 20 and 100 AU, at 68% confidence. When I include null results from other direct imaging surveys, these constraints are further strengthened: at 68% confidence, fewer than 20% of sun-like stars can have planets more massive than 4 Jupiter masses, at orbital semi-major axes between 8.1 and 911 AU. Even when applying the mass scaling of Johnson et al. (2007), and the "cold start" planet luminosity models of Fortney et al. (2008), the results remain consistent: giant planets are rare at large separations around sun-like stars. I explain how these constraints and planet simulations were used to design the Gemini South NICI Planet-Finding Campaign survey and target list, in order to maximize the chance of NICI detecting a planet, and so giving the campaign the greatest ability to strongly constrain populations of extrasolar giant planets, even in the case of a null result. Finally, I discuss future directions for direct imaging planet searches, and the steps needed tomove fromexisting surveys to a truly unified distribution of extrasolar planet populations.