Relative Occurrence Rate between Hot and Cold Jupiters as an Indicator to Probe Planet Migration

Abstract

We propose a second-order statistic parameter ε, the relative occurrence rate between hot Jupiters (HJs) and cold Jupiters (CJs) (ε = η HJ/η CJ), to probe the migration of gas giants. Since the planet occurrence rate is the combined outcome of the formation and migration processes, a joint analysis of HJ and CJ frequency may shed light on the dynamical evolution of giant planet systems. We first investigate the behavior of ε as the stellar mass changes observationally. Based on the occurrence rate measurements of HJs (η HJ) from the Transiting Exoplanet Survey Satellite survey and CJs (η CJ) from the California Legacy Survey, we find a tentative trend (97% confidence) that ε drops when the stellar mass rises from 0.8 to 1.4 M ⊙, which can be explained by different giant planet growth and disk migration timescales around different stars. We carry out planetesimal and pebble accretion simulations, both of which can reproduce the results of η HJ, η CJ, and ε. Our findings indicate that the classical core accretion + disk migration model can explain the observed decreasing trend of ε. We propose two ways to increase the significance of the trend and verify the anticorrelation. Future works are required to better constrain ε, especially for M dwarfs and for more massive stars.