“ABUNDÂNCIAS QUÍMICAS DE ESTRELAS ANÃS M COM PLANETAS OBSERVADAS PELO APOGEE”

Abstract

M dwarf stars are the most numerous in the Galaxy and stand out for being particularly favorable to the detection of Earth-like planets. The analysis of the chemical abundances of these stars is essential to understand both the chemical evolution of the Milky Way and the correlations between stellar composition and planetary system formation. This work investigated the chemical abundances of 49 M dwarf stars with effective temperatures ranging from 3260 to 3989 K, surface gravities between 4.62 and 5.05, and metallicities ([Fe/H]) varying from -0.92 to +0.25. Among them, 39 have confirmed planets and 10 have no detected planets but are part of binary systems with FGK stars. Using high-resolution spectra (R~22,500) in the near-infrared (1.50–1.70 μm) from the APOGEE survey, the abundances of thirteen chemical elements (C, O, Na, Mg, Al, Si, Ca, K, Ti, V, Mn, Cr, and Fe) were determined through spectral synthesis, employing 1D LTE MARCS atmospheric models, the APOGEE DR17 line list, and the radiative transfer code Turbospectrum. The methodology was validated by comparing the abundances of the M dwarfs with those of their FGK companions, showing an average agreement within 0.10 dex for most elements, except for aluminum, where the largest discrepancy is associated with the star having the lowest effective temperature in the sample. The results indicate that the abundances determined here are systematically higher than those automatically derived by the APOGEE ASPCAP pipeline, suggesting possible systematic uncertainties in this method for M dwarfs. The analyzed M dwarfs follow chemical abundance patterns similar to FGK field stars, although differences in aluminum and titanium compared to red giants require further investigation. Statistical tests show that M dwarfs without detected planets exhibit abundance distributions similar to those hosting planets, indicating that undetected planets may be present. Additionally, no clear correlation was found between most elemental abundances and planetary radius, except for some iron-peak elements, which suggest weak to moderate correlations. The elemental ratios C/O and Mg/Si, related to planetary mineralogy, indicate that most planets orbiting the M dwarfs in the sample likely have internal compositions similar to Earth.