2005/09/10 by Simon C. Schuler, Jeremy R. King, D. M. Terndrup +4 · 1 citation
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/497952
published as Astrophys.J.636:432-444,2005 · 40 pages, 7 figures; Accepted for publication in ApJ
arxiv created 2005/09/10 · openalex publication_date 2005/12/21 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Oxygen abundances have been derived from the near-IR, high-excitation O I λ7774 triplet in high-resolution, high signal-to-noise ratio spectra of 45 Hyades dwarfs using standard one-dimensional, plane-parallel LTE models. Effective temperatures of the stellar sample range from 4319 to 6301 K, and the derived relative O abundances as a function of T eff evince a trichotomous morphology. At T eff > 6100 K, there is evidence of an increase in the O abundances with increasing T eff , consistent with non-LTE (NLTE) predictions. At intermediate T eff (5450 K ≤ T eff ≤ 6100 K), the O abundances are flat, and star-to-star values are in good agreement, having a mean value of [O/H] = +0.25 ± 0.02; however, systematic errors at the ≲0.10 dex level might exist. The O abundances for stars with T eff ≤ 5450 K show a striking increase with decreasing T eff , in stark contrast to expectations and canonical NLTE calculations. The cool Hyades triplet results are compared to those recently reported for dwarfs in the Pleiades cluster and the UMa moving group; qualitative differences between the trends observed in these stellar aggregates point to a possible age-related diminution of triplet abundance trends in cool open cluster dwarfs. Correlations with age-related phenomena, i.e., chromospheric activity and photospheric spots, faculae, and/or plages, are investigated. No correlation with Ca II H+K chromospheric activity indicators is observed. Multicomponent LTE "toy" models have been constructed in order to simulate photospheric temperature inhomogeneities that could arise from the presence of starspots, and we demonstrate that photospheric spots are a plausible source of the triplet trends among the cool dwarfs.