Selection and characterisation of the M dwarf targets in the PLATO Input Catalogue

Context. The aim of the European Space Agency’s PLAnetary Transits and Oscillations of Stars (PLATO) mission is to detect planets orbiting around dwarfs and subgiant stars with spectral type F5 or later, including M dwarfs. The PLATO Input Catalogue (PIC) contains all PLATO targets available for observation by the PLATO nominal science. The latest version, PIC2.1.0.1, focuses on the Southern PLATO field, named LOPS2, selected as the first long observation field, and includes the P4 sample, one of the four target samples outlined in the Science Requirement Document. P4 includes the M dwarfs with magnitudes brighter than V = 16 located within LOPS2. Aims. A characterisation of the M dwarfs in the PIC is essential for assessing their potentiality to host exoplanets, and eventually for estimating the hosted planet(s) properties. The purpose of this paper is to describe how we selected the P4 M dwarf targets, and obtained their fundamental parameters and properties. Methods. Measuring stellar parameters is a challenging task. Interferometry provides direct estimates of radii, whereas alternative approaches relying on theoretical assumptions are still affected by significant uncertainties. In this work, we introduce the P4 sample and detail the methodologies, all based on photometric criteria, adopted for the measurement of their stellar parameters. Results. Based on a statistical analysis of the P4 sample, we assess both the photometric and volume completeness, and classify the stellar populations according to their Galactic spatial-velocity components. The adopted stellar parameters are validated by comparison with independent methods from the literature used to estimate stellar radii. Conclusions. We conclude that the P4 sample is compliant with the PLATO science requirements. Being magnitude limited, its volume completeness decreases going towards distances larger than 30 pc, where late-type targets are progressively less covered. The observed large spread in the colour-magnitude diagram is likely due to the combination of several effects such as metallicity, age, binarity, and activity. The strategy we adopted for deriving stellar parameters provides results consistent with those obtained in the literature with different and independent methods.