HADES RV programme with HARPS-N at TNG

Abstract

Context. Most of our current knowledge on planet formation is still based on the analysis of main sequence, solar-type stars. Conversely, detailed chemical studies of large samples of M dwarfs hosting planets are still missing. Aims. Correlations exist between the presence of different types of planets around FGK stars and metallicity, individual chemical abundance, and stellar mass. We aim to test whether or not these correlations still hold for the less-massive M dwarf stars. Methods to determine stellar abundances of M dwarfs from high-resolution optical spectra in a consistent way are still missing. The present work is a first attempt to fill this gap. Methods. We analyse a large sample of M dwarfs with and without known planetary companions in a coherent and homogeneous way. We develop for the first time a methodology to determine stellar abundances of elements other than iron for M dwarf stars from high-resolution optical spectra. Our methodology is based on the use of a principal component analysis and sparse Bayesian 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 metalliticies and abundances of a large sample of M dwarfs observed within the framework of current radial-velocity surveys. We then used a sample of nearby FGK stars to cross-validate our technique by comparing the derived abundance trends in the M dwarf sample with those found on the FGK stars. Results. The metallicity distribution of the different subsamples reveals a correlation between the metallicities of M dwarfs and their probability of hosting giant planets. We also find a correlation between this latter probability and stellar mass. M dwarfs hosting low-mass planets do not seem to follow the so-called planet–metallicity correlation. We also find that the frequency of low-mass planets does not depend on the mass of the stellar host. These results appear to be in agreement with those of previous works. However, we note that for giant-planet hosts our metallicities predict a weaker planet–host metallicity correlation but a stronger mass-dependency than corresponding values derived from photometric results. We show for the first time that there seems to be no differences between M dwarfs with and without known planets in terms of their abundance distributions of elements different from iron. Conclusions. Our data show that low-mass stars with planets follow the same metallicity, mass, and abundance trends as their FGK counterparts, which are usually explained within the framework of core-accretion models.

The CARMENES search for exoplanets around M dwarfs. Stellar atmospheric parameters of target stars with SteParSyn

“…Regarding log g, our values appear to be higher (between 0.02 and 0.17 dex on average with respect to the literature), except for Rajpurohit et al (2018b), although even in that case the discrepancies are compatible with zero. As to metallicity, our [Fe/H] scale seems to agree best with the results by Rojas-Ayala et al ( 2012), Mann et al (2015), and Maldonado et al (2015Maldonado et al ( , 2020. In contrast, large discrepancies in metallicity can be seen when comparing our results with Passegger et al (2018, 2019.…”

“…The approaches to the computation of stellar parameters in the Mdwarf regime are manifold and generally dependent on the covered wavelength region ∆λ, the spectral resolution R, and the S/N of the spectra. For instance, T eff can be derived from the H 2 O-K2 index (Rojas-Ayala et al 2012), the pseudo-EW of spectral features (Maldonado et al 2015(Maldonado et al , 2020, and spectral fitting to a variety of synthetic grids, including PHOENIX-ACES (Passegger et al 2018;Schweitzer et al 2019), PHOENIX-SESAM (Passegger et al 2019), and grids based on BT-Settl models Mann et al 2015;Rajpurohit et al 2018b). As for log g, in some studies it is left as a free parameter in the fitting procedure (Rajpurohit et al 2018b), while in others log g is kept fixed instead based on evolutionary models to break the observed degeneracy in the M-dwarf parameter space (Rojas-Ayala et al 2012;Passegger et al 2018Passegger et al , 2019.…”

“…In the context of exoplanet research, a thorough account of the general properties of host stars directly affects the determination of the position of the habitable zone (Selsis et al 2007;Kopparapu et al 2013), the radius and mass of detected exoplanets, and their composition (Maldonado et al 2020;Ishikawa et al 2020). In addition, planet formation theories attempt to explain the observed occurrence rate of exoplanets (Johnson et al 2010;Howard et al 2012;Buchhave et al 2012;Sabotta et al 2021) and selection effects (Winn & Fabrycky 2015) in terms of the stellar parameters.…”

“…Passegger et al 2018Passegger et al , 2019Rajpurohit et al 2018b;Souto et al 2020;Hejazi et al 2020), pseudo-EWs (e.g. Mann et al 2013aMann et al , 2014Neves et al 2014;Maldonado et al 2015Maldonado et al , 2020, and spectral indices (e.g. Rojas-Ayala et al 2012;Khata et al 2020), all of which can be further investigated following a machine-learning approach (e.g.…”

Warm terrestrial planet with half the mass of Venus transiting a nearby star

“…5.3). However, deriving individual abundances of M dwarfs from visible spectra is a very difficult task (e.g., Maldonado et al 2020). We estimated the abundances of Mg and Si following the procedure described in Adibekyan et al (2017).…”