A metallicity study of F, G, K and M dwarfs in the Coma Berenices open cluster from the APOGEE survey

Abstract

We present a study of metallicities in a sample of main sequence stars with spectral types M, K, G and F ($T_{\mathrm{eff}}$ $\sim$ 3200 -- 6500K and log $g$ $\sim$ 4.3 -- 5.0 dex) belonging to the solar neighborhood young open cluster Coma Berenices. Metallicities were determined using the high-resolution (R=$\hat{I}»$/$\hat{I}”$ $\hat{I}»$ $\sim$ 22,500) NIR spectra ($\hat{I}»$1.51 -- $\hat{I}»$1.69 $\hat{I}¼$m) of the SDSS-IV APOGEE survey. Membership to the cluster was confirmed using previous studies in the literature along with APOGEE radial velocities and Gaia DR2. An LTE analysis using plane-parallel MARCS model atmospheres and the APOGEE DR16 line list was adopted to compute synthetic spectra and derive atmospheric parameters ($T_{\mathrm{eff}}$ and log $g$) for the M dwarfs and metallicities for the sample. The derived metallicities are near solar and are homogeneous at the level of the expected uncertainties, in particular when considering stars from a given stellar class. The mean metallicity computed for the sample of G, K, and M dwarfs is $⟨$[Fe/H]$⟩$ = +0.04 $\pm$ 0.02 dex; however, the metallicities of the F-type stars are slightly lower, by about 0.04 dex, when compared to cooler and less massive members. Models of atomic diffusion can explain this modest abundance dip for the F dwarfs, indicating that atomic diffusion operates in Coma Berenices stars. The [Fe/H] dip occurs in nearly the same effective temperature range as that found in previous analyses of the lithium and beryllium abundances in Coma Berenices.

Accepted to ApJ