Institute of Astronomy

Giants and Dwarfs: Do M Dwarfs Really Host Fewer Giant Planets?

SpeakerTalk DateTalk Series
Eric Gaidos29 July 2014Across HR 2014 Talks


Stellar mass may be an important parameter in giant planet formation: If more massive stars are born with more massive disks, the prevailing ""core-first"" scenario of giant planet formation predicts a higher (lower) occurrence of giant planets around more (less) massive stars. Johnson et al. (2010) found that giant planet occurrence in Doppler surveys is proportional to stellar mass and that M dwarf stars have about half as many giant planets as solar-mass stars. However, the occurrence of giant planets is also a rapidly increasing function of host star metallicity such that a difference of only 0.1-0.2 dex in mean [Fe/H] between samples equates to a factor of two in occurrence (Neves et al. 2013). Until recently, the metallicities of M dwarfs have not been determined to this precision. We have developed a precise (+/- 0.07 dex) method of measuring the metallicities of M dwarfs using features in their infrared spectra (Mann et al. 2012). We present the metallicity distribution of nearly all of the ~150 M dwarfs used by the analysis of Johnson et al. We rigorously compare these to the SPOCS catalog of solar-mass Doppler target stars (Valenti & Fischer 2005), control for metallicity, and constrain the dependence of giant planet occurrence on stellar mass, a potential test of the giant planet formation scenarios. Finally, we predict the number of giant planets we expect to detect in our ongoing MERMAIDS Doppler survey of metal-rich M dwarfs.