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An Investigation of the Formation and Line Properties of MgH in 3D Hydrodynamical Model Stellar Atmospheres

Thygesen, Anders O. and Kirby, Evan N. and Gallagher, Andrew J. and Ludwig, Hans-G. and Caffau, Elisabetta and Bonifacio, Piercarlo and Sbordone, Luca (2017) An Investigation of the Formation and Line Properties of MgH in 3D Hydrodynamical Model Stellar Atmospheres. Astrophysical Journal, 843 (2). Art. No. 144. ISSN 1538-4357. doi:10.3847/1538-4357/aa79a0.

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Studies of the isotopic composition of magnesium in cool stars have so far relied upon the use of 1D model atmospheres. Since the isotopic ratios derived are based on asymmetries of optical MgH lines, it is important to test the impact from other effects affecting line asymmetries, like stellar convection. Here, we present a theoretical investigation of the effects of including self-consistent modeling of convection. Using spectral syntheses based on 3D hydrodynamical CO^5BOLD models of dwarfs (4000 K ≾ T_(eff) ≾ 5160 K, 4.0 ≤ log g ≤ 4.5, -3.0 ⩽ [Fe/H] ⩽ -1.0) and giants (T_(eff) ~ 4000 K, log g = 1.5, -3.0 ⩽ [Fe/H] ⩽ -1.0), we perform a detailed analysis comparing 3D and 1D syntheses. We describe the impact on the formation and behavior of MgH lines from using 3D models, and perform a qualitative assessment of the systematics introduced by the use of 1D syntheses. Using 3D model atmospheres significantly affect the strength of the MgH lines, especially in dwarfs, with 1D syntheses requiring an abundance correction of up to +0.69 dex, with the largest for our 5000 K models. The corrections are correlated with T_(eff) and are also affected by the metallicity. The shape of the strong ^(24) MgH component in the 3D syntheses is poorly reproduced in 1D. This results in 1D syntheses underestimating ^(25)Mg by up to ~5 percentage points and overestimating ^(24)Mg by a similar amount for dwarfs. This discrepancy increases with decreasing metallicity. ^(26)Mg is recovered relatively well, with the largest difference being ~2 percentage points. The use of 3D for giants has less impact, due to smaller differences in the atmospheric structure and a better reproduction of the line shape in 1D.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Thygesen, Anders O.0000-0002-4912-1183
Kirby, Evan N.0000-0001-6196-5162
Gallagher, Andrew J.0000-0003-3014-8981
Additional Information:© 2017 The American Astronomical Society. Received 2017 May 9; revised 2017 June 9; accepted 2017 June 12; published 2017 July 14. H.G.L. acknowledges financial support by the Sonderforschungsbereich SFB 881 "The Milky Way System" (subproject A4) of the German Research Foundation (DFG). A.J.G. acknowledges the support of the FONDATION MERAC, the matching fund granted by the Scientific Council of Observatoire de Paris, and the Collaborative Research Centre SFB 881 (Heidelberg University) of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). Software: CO^5BOLD (Freytag et al. 2012), Linfor3D (Steffen et al. 2015), Matplotlib (Hunter 2007), Fitprofile (Thygesen et al. 2016).
Group:Astronomy Department
Funding AgencyGrant Number
Deutsche Forschungsgemeinschaft (DFG)SFB 881
Scientific Council of Observatoire de ParisUNSPECIFIED
Subject Keywords:hydrodynamics – line: formation – line: profiles – molecular processes – stars: atmospheres – techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20170714-160235113
Persistent URL:
Official Citation:Anders O. Thygesen et al 2017 ApJ 843 144
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79116
Deposited By: Tony Diaz
Deposited On:14 Jul 2017 23:27
Last Modified:15 Nov 2021 17:45

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