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19 April 2024 |
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Oxygen from the Lambda 7774 High-Excitation Triplet in Open Cluster Dwarfs: Hyades | | Simon C. Schuler
; Jeremy R. King
; Donald M. Terndrup
; Marc H. Pinsonneault
; Norman Murray
; L.M. Hobbs
; | | Date: |
10 Sep 2005 | | Subject: | astro-ph | | Affiliation: | Clemson Univ.), Jeremy R. King (Clemson Univ.), Donald M. Terndrup (Ohio St. Univ.), Marc H. Pinsonneault (Ohio St. Univ.), Norman Murray (Univ. of Toronto), and L.M. Hobbs (Univ. of Chicago/Yerkes Obs. | | Abstract: | Oxygen abundances have been derived from the near-IR, high-excitation Lambda 7774 O I triplet in high-resolution, high signal-to-noise spectra of 45 Hyades dwarfs using standard one dimensional, plane-parallel LTE models. Effective temperatures of the stellar sample range from 4319-6301 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 < 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. Multi-component 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. | | Source: | arXiv, astro-ph/0509271 | | Services: | Forum | Review | PDF | Favorites | |
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