Applications of

Radiative Transfer

to stellar and planetary atmospheres
Tenerife, Spain - 13-17 Nov. 2017

Poster abstract details

NLTE chemical abundances in atmospheres of normal BAF type stars
Tatyana Sitnova, Alexeeva Sofya, Tatyana Ryabchikova, Lyudmila Mashonkina


Chemical abundances of BAF-type unevolved stars represent abundances of the galactic matter at modern epoch. We treat accurate methods of abundance determination based on the non-local thermodynamic equilibrium (NLTE) line formation for five chemical elements, namely carbon, oxygen, calcium, titanium, and iron. We apply the comprehensive model atoms for C~I-II, O~I, Ca~I-II, Ti~I-II described in our previous studies. For iron abundance determination a fairly complete model atom for Fe~I-II was used for the first time. Model atom for Fe~I-II by Mashonkina et al. (2011) was updated by including measured and predicted high-excitation ($> 10$ eV) energy levels of Fe~II. NLTE leads to weakened Fe~I lines and to positive NLTE abundance corrections in agreement with Rentzsch-Holm (1996), however, the magnitude of such corrections is smaller compared to the earlier results. Lines of Fe~II are strengthened in NLTE, and the effect grows toward larger line strength. We determine the NLTE abundances of C, O, Ca, Ti, and Fe in ten BAF-type stars with well determined atmospheric parameters using high-resolution and high signal-to-noise ratio spectral observations in wide wavelength range, from UV to IR. It is worth noting, all these elements except O are observed in lines of the two ionisation stages and for each element NLTE leads to consistent abundances from different lines. The C~I and Fe~II emission lines were detected in the near IR spectrum of late B type subgiant star HD160762. Our NLTE methods reproduce these emission lines with classical hydrostatic model atmosphere. Chemical abundances in the investigated stars show regular behaviour, theirs element ratios are close to zero as expected.