Non-LTE calculations for neutral Na in late-type stars using improved atomic data

By K. Lind, Martin Asplund, Paul Barklem, A. K. Belyaev. 2011

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Neutral sodium is a minority species in the atmospheres of late-type stars, and line formation in local thermodynamic equilibrium (LTE) is often a poor assumption, in particular for strong li nes. We present an extensive grid of non-LTE calculations for several Na I lines in cool stellar atmospheres, including metal-ric h and metal-poor dwarfs and giants. For the first time, we cons tructed a Na model atom that incorporates accurate quantum mechanical calculations for collisional excitation and ionisation b y electrons as well as collisional excitation and charge exchange reactions with neutral hydrogen. Similar to Li I, the new rates for hydrogen impact excitation do not affect the statistical equilibrium calculations, while charg e exchange reactions have a small but non-negligible influence. The presented LTE and non-LTE curves-of-growth c an be interpolated to obtain non-LTE abundances and abundance corrections for arbitrary stellar parameter combinations and line strengths. The typical corrections for weak lines a re−0: 1::: − 0: 2 dex, whereas saturated lines may overestimate the abundance in LTE by more than 0.5 dex. The non-LTE Na abundances appear very robust with respect to uncertainties in the input collision al data.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/c4d99d7cb5428434610849298679b7fe93a810e0

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Citations in the corpus

Exploring the Milky Way stellar disk - A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood (2013, methodology): “For sodium we applied the NLTE corrections from Lind et al. (2011), using an IDL script that was kindly provided by Karin Lind.”
High-precision abundances of elements in solar twin stars - Trends with stellar age and elemental condensation temperature (2015, background): “7, the calculations of Lind et al. (2011), indicate similar numerical corrections as in the case of Fei lines, but withopposite sign.”
SPECTRAL PROPERTIES OF COOL STARS: EXTENDED ABUNDANCE ANALYSIS OF 1,617 PLANET-SEARCH STARS (2016, methodology): “We obtained corrections for lines in common with our line list of oxygen (Amarsi et al. 2015), sodium (Lind et al. 2011), magnesium (Osorio et al. 2015), titanium (Bergemann 2011), and iron (Bergemann et al. 2012; Lind et al. 2012).”
The elemental composition of the Sun - I. The intermediate mass elements Na to Ca (2014, methodology): “NLTE calculations have been performed by Lind et al. (2011), using realistic quantum mechanical calculations by Barklem et al. (2010) for inelastic collisions with hydrogen, instead of the dubious classical Drawin (1968) formula almost always adopted in NLTE studies.”
The GALAH Survey: Second Data Release (2018, methodology): “For DR2 We incorporate non-LTE line formation for several key elements, including Li (Lind et al. 2009), O (Amarsi et al. 2016a), Na (Lind et al. 2011), Mg (Osorio et al. 2015), Al (Nordlander & Lind 2017), Si (Amarsi & Asplund 2017), and Fe (Amarsi et al. 2016b), mostly with additional dedicated…”
THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, methodology): “Non-LTE Na Abundances For Na, Lind et al. (2011) computed non-LTE abundance corrections for a number of lines, including the resonance lines used in our analysis.”
A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS (2014, methodology): “We adopt corrections to our LTE abundances using the grid presented by Lind et al. (2011).”
The two metallicity groups of the globular cluster M 22: a chemical perspective (2011, methodology): “We applied NLTE corrections from Lind et al. (2011b) to the Na abundances.”