Frequency of planets orbiting M dwarfs in the Solar neighbourhood

TL;DR

This study combines multiple surveys to estimate that M dwarfs host at least 3 planets on average, revealing a high occurrence of small, cool planets, especially around the least massive M dwarfs.

Contribution

It provides a comprehensive analysis of planet occurrence rates around M dwarfs using combined radial velocity data and accounts for observational biases.

Findings

At least 2.39$^{+4.58}_{-1.36}$ planets per M dwarf

At least 3.0 planets per star when considering survey sensitivities

Higher frequency of mini-Neptunes around less massive M dwarfs

Abstract

The most abundant stars in the Galaxy, M dwarfs, are very commonly hosts to diverse systems of low-mass planets. Their abundancy implies that the general occurrence rate of planets is dominated by their occurrence rate around such M dwarfs. In this article, we combine the M dwarf surveys conducted with the HIRES/Keck, PFS/Magellan, HARPS/ESO, and UVES/VLT instruments supported with data from several other instruments. We analyse the radial velocities of an approximately volume- and brightness-limited sample of 426 nearby M dwarfs in order to search for Doppler signals of cadidate planets. In addition, we analyse spectroscopic activity indicators and ASAS photometry to rule out radial velocity signals corresponding to stellar activity as Doppler signals of planets. We calculate estimates for the occurrence rate of planets around the sample stars and study the properties of this occurrence rate as a function of stellar properties. Our analyses reveal a total of 118 candidate planets orbiting nearby M dwarfs. Based on our results accounting for selection effects and sample detection threshold, we estimate that M dwarfs have on average at least 2.39$^{+4.58}_{-1.36}$ planets per star orbiting them. Accounting for the different sensitivities of radial velocity surveys and Kepler transit photometry implies that there are at least 3.0 planets per star orbiting M dwarfs. We also present evidence for a population of cool mini-Neptunes and Neptunes with indications that they are found an order of magnitude more frequently orbiting the least massive M dwarfs in our sample.