Poster Open Access

The Lines are Not Fine: Measuring Vanadium Abundances in M dwarfs from Hyperfine-Split Lines

Shan, Yutong; Reiners, Ansgar; Fabbian, Damian; Marfil, Emilio; Montes, David; Tabernero, Hugo M; Ribas, Ignasi; Caballero, Jose A.; Quirrenbach, Andreas; Amado, Pedro J.; Aceituno, J.; Bejar, Victor J. S.; Cortes-Contreras, Miriam; Dreizler, Stefan; Hatzes, Artie P.; Henning, Thomas; Jeffers, Sandra V.; Kaminski, Adrian; Kürster, Martin; Lafarga, Marina; Morales, Juan Carlos; Nagel, Evangelos; Rodriguez-Lopez, Cristina; Passegger, Vera M.; Schweitzer, Andreas; Zechmeister, Mathias

Wolk, Scott

Cool star atmospheres present challenges to chemical abundance studies. To date, only a handful of elements have been quantified for a handful of M dwarfs. In high-resolution spectra from the CARMENES survey, we identify a series of dramatically hyperfine-split vanadium features between 800 and 910 nm, which have strong and clean profiles throughout the early M-dwarf range. These ‘bucket-shaped’ line regions can be well-modeled with standard model atmospheres combined with the latest atomic data from VALD. From these line regions, we measure vanadium abundances for 140 nearby early M dwarfs in the CARMENES GTO sample and confirm that they follow the same trend with metallicity as the FG-type stars in the solar neighborhood, i.e., significantly above predictions from galactic chemical evolution models. Exhibiting a tight correlation with iron, vanadium abundances show promise as a potential metallicity indicator for M dwarfs. We also present evidence that several well-known chemical studies of K dwarfs have systematically overestimated their vanadium abundances largely as a result of neglecting to model hyperfine structure, a bias that worsens with decreasing temperature. Our work highlights opportunities for robust chemical analysis of cool stars afforded by high-quality spectra redward of visible. 

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