Frequency of planets orbiting M dwarfs in the Solar neighbourhood (1906.04644v2)

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.

• The paper presents a detailed statistical analysis of 426 M dwarfs using extensive radial velocity data to estimate planet occurrence rates.
• The study identifies 118 candidate planets, highlighting a notable abundance of cool mini-Neptunes and Neptunes around low-mass M dwarfs.
• The findings have significant implications for exoplanet detection, guiding the design of future surveys to explore habitable environments around M dwarfs.

Frequency of Planets Orbiting M Dwarfs in the Solar Neighborhood

The paper, "Frequency of planets orbiting M dwarfs in the Solar neighbourhood" by Tuomi et al., presents a comprehensive analysis of the occurrence of planetary systems around M dwarfs, which are the most common type of stars in the Galaxy. Leveraging multiple surveys conducted using instruments like HIRES, PFS, HARPS, and UVES, the authors compile a detailed radial velocity dataset for 426 nearby M dwarfs, enabling a statistical investigation into the frequency and characteristics of planets orbiting these stars.

Key findings from the paper reveal a notable abundance of low-mass planets orbiting M dwarfs, with an identified total of 118 candidate planets. Notably, the average occurrence rate is estimated to be at least 2.39 planets per star, accounting for selection biases and detection thresholds. When sensitivities across different methods are factored in, the occurrence rate potentially increases to upwards of three planets per star.

The research identifies a significant presence of cool mini-Neptunes and Neptunes, found to be more frequent by a factor of ten around the least massive M dwarfs in the sample. This suggests a correlation between stellar and planetary system properties, providing insights into planetary formation and distribution theories around low-mass stars.

Implications of these findings are substantial, particularly for missions and studies focused on the search for exoplanets in habitable zones. M dwarfs, given their ubiquity and the frequency of planet occurrence, offer fertile ground for discovering Earth-like planets and assessing habitable zone characteristics. The evidence for a large number of low-mass planets enhances the potential for finding planets with suitable conditions for life as we know it.

The paper also paves the way for future developments in exoplanetary science, emphasizing the need for improved detection techniques to better distinguish between planetary signals and stellar activity. Insights from this paper are expected to guide the design of future radial velocity surveys and missions aimed at dissecting further the planetary systems around M dwarfs. The work reinforces the idea that M dwarfs are a keystone in the broader understanding of planet formation and the potential for habitable environments in our Galaxy.