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

TL;DR

PLATO's exoplanet program requires well-characterized M-dwarf targets, so this study defines and characterizes the P4 M-dwarf sample within the PIC 2.1.0.1 for the LOPS2 field. It develops a photometric calibration to derive $T_{\rm eff}$, radii, and masses from Gaia DR3 and 2MASS data, and uses CAMD boundaries together with $V \le 16$ to select 15140 P4 targets (plus 17 additional M-dwarfs) for a total of 15157. Completeness is assessed with the $\langle V/V_{\max} \rangle$ test, showing near-total completeness for $V<16$ and a completeness limit around $37$ pc, with the sample remaining complete to $208$ pc only for the earliest M-dwarfs; the P4 radii agree with literature (e.g., Mann15) but show systematic offsets from Gaia DR3 radii. The CAMD spread is attributed to metallicity and magnetic activity, supported by kinematic population analysis and comparisons with isochrones; these results support PLATO's target strategy and quantify the exoplanet-hosting potential of nearby low-mass stars.

Abstract

The ESA's PLAnetary Transits and Oscillations of Stars (PLATO) mission aims 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 targets available for observation by the 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 V < 16 located within LOPS2. A characterisation of the M-dwarfs in the PIC is essential for assessing their potentiality to host exoplanets, and eventually estimate 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. In this work, we introduce the P4 sample and detail the methodologies adopted for the measurement of their stellar parameters. 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. 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.

Figures (15)

• Figure 1: Top panel: synthetic two-colour diagram of $(G - V)_0$ versus $(G_{\rm BP} - G_{\rm RP})_0$ for dwarf star models taken from the stellar libraries indicated in the legend. The solid line represents the best-fit polynomial to the synthetic colours. Bottom panel: residuals between the synthetic $(G - V)_0$ values and the best-fit relation, plotted as a function of the synthetic $(G_{\rm BP} - G_{\rm RP})_0$ colour.
• Figure 2: colour-absolute magnitude diagram of the P4 sample targets. The colour map indicates the distance of the targets. The black and red lines represent the adopted limits indicated by the first two relations given in the Eq. \ref{['eq:p4sel']}. The histogram of the $(G_{\rm BP}-G_{\rm RP})_0$ colours is also shown in the top panel.
• Figure 3: Distribution of apparent $G$ and $V$ magnitudes for the P4 sample.
• Figure 4: Near-infrared (J–H vs. H–Ks) colour–colour diagram of the P4 sample targets. Enlarged grey circles highlight the outliers in this diagram. The solid red line shows the mean colours of dwarfs from peca13. The cyan line indicates the subset of stars from M0V to M6V. An inset provides a zoomed-in view of the high-density core of the distribution, allowing better visualisation of the main-sequence locus. The typical errors in the colours are indicated in the bottom-right corner.
• Figure 5: Boxplots of the $J-H$, $H-Ks$, and $J-Ks$ colour distributions for the selected P4 sample. Each box represents the IQR (25th to 75th percentile), with the central red line indicating the median. The whiskers extend to the most extreme data points that are not considered outliers. Individual points beyond the whiskers represent outliers, i.e., values that deviate significantly from the main distribution.