Non-LTE abundances of Mg and K in extremely metal-poor stars and the evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the Milky Way

Abstract

Aims. LTE abundances of light elements in extremely metal-poor (EMP) stars have been previously derived from high quality spectra. New derivations, free from the NLTE effects, will better constrain the models of the Galactic chemical evolution and the yields of the very first supernovae. Methods. The NLTE profiles of the magnesium and potassium lines have been computed in a sample of 53 extremely metal-poor stars with a modified version of the program MULTI and adjusted to the observed lines in order to derive the abundances of these elements. Results. The NLTE corrections for magnesium and potassium are in good agreement with the works found in the literature. The abundances are slightly changed, reaching a better precision: the scatter around the mean of the abundance ratios has decreased. Magnesium may be used with confidence as reference element. Together with previously determined NLTE abundances of sodium and aluminum, the new ratios are displayed, for comparison, along the theoretical trends proposed by some models of the chemical evolution of the Galaxy, using different models of supernovae.

SYSTEMATIC NON-LTE STUDY OF THE −2.6 ≤ [Fe/H] ≤ 0.2 F AND G DWARFS IN THE SOLAR NEIGHBORHOOD. II. ABUNDANCE PATTERNS FROM Li TO Eu*

“…For two stars their spectra were obtained with CFHT/ESPaDOnS, as described in Paper I. The high-quality observed spectrum of HD140283 was taken from the ESO UVESPOP survey (Bagnulo et al 2003). For some stars our observational material was complemented with the data from our earlier projects, namely, VLT2/UVES, 67.D-0086A (HD 74000, BD −04°3208), and 2.2 m/FOCES (HD 59374, HD 59984, HD 103095, HD 134169).…”

“…principles of non-LTE (NLTE) line formation and codes capable of such calculations have been around for a long time but have only been explored in a more systematic fashion for a wide range of stellar parameters over the past decade or so (e.g., Zhao et al 1998;Zhao & Gehren 2000;Mashonkina & Gehren 2001;Takeda et al 2002;Gehren et al 2004;Fabbian et al 2006;Mashonkina & Zhao 2006;Zhang et al 2006b;Mashonkina et al 2007aMashonkina et al , 2008Bergemann & Gehren 2008;Zhang et al 2008;Lind et al 2009;Shi et al 2009;Andrievsky et al 2010;Bergemann & Cescutti 2010;Spite et al 2011Spite et al , 2012Yan et al 2015). Before the observations are used to give constraints to the GCE models, we need to take into account the analysis errors of the stellar abundances, such as the departures from LTE and uncertainties in the atmospheric parameters.…”

Tracing the evolution of NGC 6397 through the chemical composition of its stellar populations

“…Upper limits are treated as detections for the second generation averages for Al (two stars) and O (one star) when computing the mean and standard deviation. The literature data for halo field stars are assembled as follows; bullets represent Gehren et al (2006), star symbols represent Andrievsky et al (2007Andrievsky et al ( , 2008Andrievsky et al ( , 2010, open triangles Cayrel et al (2004), and open diamonds Nissen et al (2002).…”

Chemical composition of semi-regular variable giants. II.

“…For all investigated chemical elements, except for carbon, oxygen, sodium, magnesium, aluminum, sulfur, potassium, and barium, the elemental abundances were derived with the help of Kurucz's LTE WIDTH9 code. Abundances of the elements listed above were found using the NLTE spectrum synthesis based on the modified version of the MULTI code (see Carlsson 1986 for the MULTI description; and Korotin et al 1999a,b;Korotin & Mishenina 1999;Andrievsky et al 2001Andrievsky et al , 2007bAndrievsky et al , 2008Andrievsky et al , 2009Andrievsky et al , 2010 references therein, for the description of the code modification and applied atomic models).…”