Relationship between giant planet frequency and stellar metallicity

Abstract

We describe results from two independent analyses of the [Fe/H] abundance of stars in two separate planet search programs. For the Keck, AAT and Lick (KAL) planet search program, we determined stellar parameters spectroscopically. Results for the CORALIE and KAL both show a similar steep increase in the fraction of stars with known planets as stellar [Fe/H] increases. This planet metallicity correlation is a key observational constraint on the formation and evolution of giant planets. We rule out changes in velocity precision as the cause of the correlation. By comparing stars with different convection zone depths (along and off the main sequence), we rule out chemical enrichment by accretion as the origin of the correlation. Most known planets have migrated inwards since formation. The end point of migration does not depend on stellar [Fe/H], but it is still possible that migration occurs only above some metallicity threshold. The planet–metallicity correlation is consistent with core-accretion scenarios of giant planet formation and inconsistent with gravitational instability models (unless migration occurs preferentially in metal-rich disks).