NESSY: NLTE spectral synthesis code for solar and stellar atmospheres

Abstract

Context. Physics-based models of solar and stellar magnetically-driven variability are based on the calculation of synthetic spectra for various surface magnetic features as well as quiet regions, which are a function of their position on the solar or stellar disc. Such calculations are performed with radiative transfer codes tailored for modeling broad spectral intervals. Aims. We aim to present the NLTE Spectral SYnthesis code (NESSY), which can be used for modeling of the entire (UV-visible-IR and radio) spectra of solar and stellar magnetic features and quiet regions. Methods. NESSY is a further development of the COde for Solar Irradiance (COSI), in which we have implemented an accelerated Λ-iteration (ALI) scheme for co-moving frame (CMF) line radiation transfer based on a new estimate of the local approximate Λ-operator. Results. We show that the new version of the code performs substantially faster than the previous one and yields a reliable calculation of the entire solar spectrum. This calculation is in a good agreement with the available observations.

Readdressing the UV solar variability with SATIRE-S: non-LTE effects

“…-Calculation of LTE populations of the levels specified in the atomic model described above; -ODF synthesis in the 100 nm -1000 nm spectral range using the LTE populations; -Solution of the SBEs, i.e., calculation of non-LTE populations of the levels in the atomic model taking into account the ODF; -Spectral synthesis using the non-LTE populations. For the spectral region considered in this paper (100 nm -1100 nm) this ODF procedure gives the same results as the procedure described by Haberreiter et al (2008) and Tagirov et al (2017). The described atomic model, the pseudo non-LTE approach and the ODF procedure for taking the effects of line-blanketing on SBEs have been shown to be adequate for representation of the solar spectrum (Shapiro et al 2010;Tagirov et al 2017).…”

“…For the spectral region considered in this paper (100 nm -1100 nm) this ODF procedure gives the same results as the procedure described by Haberreiter et al (2008) and Tagirov et al (2017). The described atomic model, the pseudo non-LTE approach and the ODF procedure for taking the effects of line-blanketing on SBEs have been shown to be adequate for representation of the solar spectrum (Shapiro et al 2010;Tagirov et al 2017). Figure 2 compares the quiet Sun and active component spectra calculated with NESSY to the spectra calculated with ATLAS9 and to observations.…”

“…The gray area is the 1σ uncertainty range of the observations. The calculated spectra were convolved with the SIRS WHI spectral window (the procedure is the same as in Tagirov et al 2017).…”

“…To remove the need for such a correction, we have constructed the non-LTE version of SATIRE-S. In this version the ATLAS9 (Kurucz 1992;Castelli & Kurucz 1994) LTE spectra of quiet Sun and active components have been replaced with the non-LTE spectra synthesized with the NESSY code (Tagirov et al 2017). Additionally, for the quiet Sun and facular contrast terms of Eq.…”

“…In this paper we use the non-LTE Spectral Synthesis (NESSY) code (Tagirov et al 2017) to compute the emergent spectra of the various atmospheric components used in SATIRE-S and to model SSI variability over cycle 24 without the need for any empirical corrections. We emphasize that the aim of this paper is not to update the SATIRE-S model, but rather to compare LTE and non-LTE active region contrasts and to verify the model in the UV part of the solar spectrum.…”