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Paper: A Grid of MARCS Model Atmospheres for S Stars
Volume: 445, Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants
Page: 71
Authors: Van Eck, S.; Neyskens, P.; Plez, B.; Jorissen, A.; Edvardsson, B.; Eriksson, K.; Gustafsson, B.; Jørgensen, U. G.; Nordlund, Å.
Abstract: S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing AGB. A large grid of S-star model atmospheres has been computed covering the range 2700 ≤ Teff(K) ≤ 4000 with 0.5 ≤ C/O ≤ 0.99. ZrO and TiO band strength indices as well as VJHKL photometry are needed to disentangle Teff, C/O and [s/Fe]. A “best-model finding tool” has been developed using a set of well-chosen indices and checked against photometry as well as low- and high-resolution spectroscopy. It is found that applying M-star model atmospheres (i.e., with a solar C/O ratio) to S stars can lead to errors in Teff up to 400 K. We constrain the parameter space occupied by the S stars of the vast Henize sample in terms of Teff, [C/O] and [s/Fe].
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