Search

M dwarfs are the prominent targets of planet search projects, while the complexity of their spectra has limited the understanding of their individual elemental abundances. We have been developing a method to determine the abundances of Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Sr from the near-infrared high-resolution spectra of M dwarfs. This was previously applied to the targets of the IRD planet survey (Subaru Telescope) to show that the abundance distributions were consistent with the Galactocentric space velocities calculated with Gaia astrometry (Ishikawa et al. 2022). The method was verified by Ishikawa et al. (2020) using the CARMENES archive data of five M dwarfs that have G- or K-type binary companions with known composition. However, verification at a lower temperature range has been required. We have observed eight M dwarfs including those with effective temperature (Teff) down to 3000 K in binary systems with hotter primary stars with the CARMENES or the IRD. We present that the results of the most abundances agree with those of primaries. We also investigated the sensitivity of the FeH lines to Teff and estimated the Teff of M dwarfs using them as the Teff indicators. The Teff values derived from the FeH line share a common trend among the IRD planet-survey targets with the literature values, such as the Teff estimated from the Gaia color, and have smaller statistical errors., {"references":["Ishikawa, H. T. et al. (2020), PASJ, 72, 102","Ishikawa, H. T. et al. (2022), AJ, 163, 72","Kawahara, H. et al. (2022), ApJS, 258, 31","Montes, D. et al. (2018), MNRAS, 479, 1332","Stassun, K. et al. (2019), AJ, 158, 138"]}

Recent studies have been detecting many planets around M dwarfs. Determining the detailed chemical compositions of M dwarfs is crucial for revealing the formation processes of the planetary systems and constraining the internal structures of the terrestrial planets around them. However, their intrinsic faintness and dominant molecular absorption hinder the well-established measurements of accurate chemical composition with high-resolution optical spectra. The problems are mitigated in near-infrared wavelength. The high-resolution near-infrared spectroscopy is now promising because of the increasing development of new spectrometers enabling it. IRD is such a new instrument for the Subaru Telescope constructed for a planet search around nearby M dwarfs. IRD is the first instrument for 8m-class telescopes to cover the Y, J, and H bands simultaneously with a maximum spectral resolution of 70,000. The large diameter and broadband coverage have made it possible to observe more atomic lines than ever before in near-IR spectra of faint M dwarfs. We verified that the quality of IRD spectra is comparable to the existing ones such as CRIRES spectra in terms of wavelength assignment and resolution. We report the interpretation of IRD spectra of Barnard’s Star. We identified the absorption lines throughout the Y, J, and H bands. We detected more than 100 FeH lines, which are dominant in Y band, and examined their behavior. We also determined the elemental abundances for Fe, Ti, Cr, Na, Mg, Al, Si, K, Ca, V, and Mn, based on the equivalent width of the corresponding atomic lines. The result, where the metallicity is lower than the Sun and the abundances of alpha elements (Mg, Al, Si, Ti) are higher than that of Fe, is consistent with the prediction from kinematics and rotation period that the Barnard’s Star is an old star belonging to the thick disk in our galaxy. Besides, we observed LHS 1140 with a similar temperature to the Barnard’s Star and found that it is metal-richer and alpha-poorer than Barnard’s Star., {"references":["Gustafsson, B et al. (2008)","Kupka, F e al. (1999)","Önehag, A et al. (2012)"]}