# The HARPS search for southern extra-solar planets. X. A m sin i = 11 Mearth planet around the nearby spotted M dwarf GJ 674

## TL;DR

This paper reports the discovery of an 11 Earth-mass planet around the nearby M dwarf GJ 674 using radial velocity measurements, highlighting the prevalence of Neptune-mass planets around low-mass stars and analyzing stellar activity effects.

## Contribution

First detection of a Neptune-mass planet around an M dwarf using precise radial velocity data, and analysis of stellar activity's impact on signal interpretation.

## Key findings

- The 4.69-day signal is caused by a planet, GJ 674b.
- The 35-day signal is due to stellar rotation and magnetic activity.
- Low probability that planet-hosting and non-hosting M dwarfs share the same metallicity distribution.

## Abstract

Context: How planet properties depend on stellar mass is a key diagnostic of planetary formation mechanisms. Aims: This motivates planet searches around stars which are significantly more massive or less massive than the Sun, and in particular our radial velocity search for planets around very-low mass stars. Methods: As part of that program, we obtained measurements of GJ 674, an M2.5 dwarf at d=4.5 pc, which have a dispersion much in excess of their internal errors. An intensive observing campaign demonstrates that the excess dispersion is due to two superimposed coherent signals, with periods of 4.69 and 35 days. Results: These data are well described by a 2-planet Keplerian model where each planet has a ~11 Mearth minimum mass. A careful analysis of the (low level) magnetic activity of GJ 674 however demonstrates that the 35-day period coincides with the stellar rotation period. This signal therefore originates in a spot inhomogeneity modulated by stellar rotation. The 4.69-day signal on the other hand is caused by a bona-fide planet, GJ 674b. Conclusion: Its detection adds to the growing number of Neptune-mass planets around M-dwarfs, and reinforces the emerging conclusion that this mass domain is much more populated than the jovian mass range. We discuss the metallicity distributions of M dwarf with and without planets and find a low 11% probability that they are drawn from the same parent distribution. Moreover, we find tentative evidence that the host star metallicity correlates with the total mass of their planetary system.