Synthesizing Exoplanet Demographics from Radial Velocity and Microlensing Surveys, II: The Frequency of Planets Orbiting M Dwarfs

TL;DR

This study combines microlensing and radial velocity data to estimate the frequency of giant planets around M dwarfs, revealing lower occurrence rates compared to FGK stars but confirming the presence of such planets.

Contribution

It develops a methodology to predict radial velocity survey sensitivities based on microlensing results and combines both methods to estimate planet frequencies around M dwarfs.

Findings

Jupiter and super-Jupiter planet frequency around M dwarfs is about 2.9%.

All giant planets with periods up to 10,000 days occur at a rate of 15%.

The overall planet occurrence rate around M dwarfs is approximately 1.9%.

Abstract

In contrast to radial velocity surveys, results from microlensing surveys indicate that giant planets with masses greater than the critical mass for core accretion ($\sim 0.1~M_{\rm Jup}$) are relatively common around low-mass stars. Using the methodology developed in the first paper, we predict the sensitivity of M-dwarf radial velocity (RV) surveys to analogs of the population of planets inferred by microlensing. We find that RV surveys should detect a handful of super-Jovian ($>M_{\rm Jup}$) planets at the longest periods being probed. These planets are indeed found by RV surveys, implying that the demographic constraints inferred from these two methods are consistent. We combine the results from both methods to estimate planet frequencies spanning wide regions of parameter space. We find that the frequency of Jupiters and super-Jupiters ($1\lesssim m_p\sin{i}/M_{\rm Jup}\lesssim 13$) with periods $1\leq P/{\rm days}\leq 10^4$ is $f_{\rm J}=0.029^{+0.013}_{-0.015}$, a median factor of 4.3 ($1.5-14$ at 95% confidence) smaller than the inferred frequency of such planets around FGK stars of $0.11\pm 0.02$. However, we find the frequency of all giant planets with $30\lesssim m_p\sin{i}/M_{\oplus}\lesssim 10^4$ and $1\leq P/{\rm days}\leq 10^4$ to be $f_{\rm G}=0.15^{+0.06}_{-0.07}$, only a median factor of 2.2 ($0.73-5.9$ at 95% confidence) smaller than the inferred frequency of such planets orbiting FGK stars of $0.31\pm 0.07$. For a more conservative definition of giant planets ($50\lesssim m_p\sin{i}/M_{\oplus}\lesssim 10^4$), we find $f_{\rm G'}=0.11\pm 0.05$, a median factor of 2.2 ($0.73-6.7$ at 95% confidence) smaller than that inferred for FGK stars of $0.25\pm 0.05$. Finally, we find the frequency of all planets with $1\leq m_p\sin{i}/M_{\oplus}\leq 10^4$ and $1\leq P/{\rm days}\leq10^4$ to be $f_p=1.9\pm 0.5$.