The abundance signature of M dwarf stars with planets
Planetary systems are found around a wide variety of stellar hosts from brown dwarfs and low-mass stars, to red giants, pulsars and even white dwarfs. However, our understanding of which stellar properties influence planet formation is still largely biased towards main-sequence, solar-type stars.
The study of chemical abundances of stars with planetary companions proved fundamental for our understanding of the formation and evolution of planetary systems finding that the frequency of gas-giant planets is a strong function of the host star metallicity while low-mass planets do not seem to be preferentially around metal-rich stars. At the same time the planetary architecture (orbital periods and eccentricities) depends on the presence of heavy elements in the stellar host.
To the best of our understanding, detailed chemical studies of large samples of low-mass stars (M dwarfs) with planets are still missing. This is because the accurate determination of the stellar parameters and abundances of M dwarfs is a difficult task as these stars are faint at optical wavelengths and their optical spectra are largely covered by molecular bands that blend or hid most of the atomic lines.
To overcome this difficulty we developed for the first time a methodology to determine stellar abundances of elements others than iron for M dwarf stars from high-resolution, optical spectra. Our methodology is based on the use of principal component analysis and sparse Bayesian’s methods. We made use of a set of M dwarfs orbiting around an FGK primary with known abundances to train our methods.
We applied our methods to derive stellar metallicities and abundances of a large sample of M dwarfs observed within the framework of current radial velocity surveys.
Our results confirm that gas-giant planet hosts show a planet-metallicity correlation as well as a dependence with the stellar mass. On the other hand, the frequency of low-mass planets is not a function of the stellar metallicity or mass. For other elements besides iron, we show for the first time that there seems to be no differences in the abundance distributions of stars with and without planets.
These results are in line with what is known from the chemical analysis of solar-type stars and can be explained within the framework of core-accretion models.
Full details of our technique and our results can be found in Maldonado et al. (2020, accepted by A&A), https://arxiv.org/abs/2010.14867
Our codes are available at https://github.com/jesusmaldonadoprado/mdwarfs_abundances