Stellar Oddities: MOOG Derived M-Star Parameters and Abundances

M-stars provide an exciting avenue for both chemical evolution studies and the exploration of host star-planet connections. In M-giants, the formation of complex molecules in the infrared enables chemical evolution surveys of odd-Z elements and measurements of isotopic ratios. M-dwarfs provide the best opportunities to study the composition and characteristics of a large sample of rocky planet hosts, using stellar Mg, Si, and Fe as a proxy for the main planetary building-blocks. However, the cool, complex atmosphere of M-stars makes precise chemical analysis difficult. To overcome these challenges, we have used the radiative transfer code MOOG, with up-to-date molecular linelists, to conduct the first chemical evolution study of Cl in M-giants and abundance analysis of planet-hosting M-dwarfs.

We have performed the first chemical evolution study of Cl and using IR L-band spectra of M-giants. We have demonstrated that this element is likely made in a mix of Type Ia and core-collapse SN. Isotopic ratios of Cl are complex and seem to vary significantly in stars, similar to what is observed in the ISM.

We have also analyzed high-resolution, infrared IGRINS spectra of dozens of planet hosting M-dwarfs. We have derived the Teff using water and OH features and the iron abundance from FeH lines. The spectroscopic effective temperatures differ from photometry-derived Teff to within an average of -13 ± 113 K. We also have a preliminary detection of MgO in TRAPPIST-1, which is a potential way to measure Mg in extremely cool stars.