Are M dwarfs good targets for planet searches and do we care?

Angelle Tanner (JPL)

Joint SSP/OIR seminar

Here I illustrate the advantages and disadvantages of focusing different types of planet searches on M dwarfs. Ideally, these stars are good targets for both radial velocity (RV) and astrometric searches since their reduced mass results in larger signals, however, they have not been the focus of the original long term RV programs due to their being faint and associated with large photospheric variability. Since observing techniques have matured, there are now both radial velocity and astrometric programs devoted to searching for planets, with three RV planetary systems discovered to date and the first astrometrically detected planet around an M dwarf soon to come. Those planets around M dwarfs have some of the lowest masses discovered to date (< 20 M_J / sin i). Ironically, the fact that M dwarfs are faint makes them ideal targets for both transit and direct imaging programs due to improved contrast levels between the star and planet. Larger telescopes and improvements in high contrast and imaging capabilities are making M dwarfs more viable targets for direct imaging and transit surveys. It is believed that a dedicated transit M dwarf survey could result in the detection of superEarths. In addition to the observational arguments, I will address the theoretical expectations for the population of planets around M dwarfs given current planet formation models. The observed frequency of planets around M dwarfs can distinguish core accretion or disk instability as the dominant planet formation mechanism around low mass stars. Finally, I will discuss the potential for detecting terrestrial mass planets around the nearest M dwarfs with SIM PlanetQuest.