How different are the Liège and Hamburg atlases of the solar spectrum?

Abstract

Context. The high-fidelity solar spectral atlas prepared by Delbouille et al. (Liège atlas, 1973) and the atlas by Neckel (Hamburg atlas, 1999, Sol. Phys., 184, 421) are widely recognised as the most important collection of reference spectra of the Sun at disc centre in the visible wavelength range. The two datasets serve as fundamental resources for many researchers, in particular for chemical abundance analyses. But despite their similar published specifications (spectral resolution and noise level), the shapes of the spectral lines in the two atlases differ significantly and systematically. Aims. Knowledge of any instrumental degradations is imperative to fully exploit the information content of spectroscopic data. We seek to investigate the magnitude of these differences and explain the possible sources. We provide the wavelength-dependent correction parameters that need to be taken into account when the spectra are to be compared with synthetic data, for instance. Methods. A parametrically degraded version of the Hamburg spectrum was fitted to the Liège spectrum. The parameters of the model (wavelength shift, broadening, intensity scaling, and intensity offset) represent the different characteristics of the respective instruments, observational strategies, and data processing. Results. The wavelength scales of the Liège and Hamburg atlases differ on average by 0.5 mÅ with a standard deviation of ±2 mÅ, except for a peculiar region around 5500 Å. The continuum levels are offset by up to 18% below 5000 Å, but remain stably at a 0.8% difference towards the red. We find no evidence for spectral stray light in the Liège spectrum. Its resolving power is almost independent of wavelength but limited to about 216 000, which is between two to six times lower than specified. When accounting for the degradations determined in this work, the spectra of the two atlases agree to within a few parts in 10 3 .

PEPSI deep spectra

“…At this point, we note again that the PEPSI solar spectra in this paper did not reach the full 2-pixel resolution at all wavelengths but about 80% of it on average. For comparison, lower than predicted resolution was also found for the Liége disk-center atlas by Doerr et al (2016), but with even two to six times lesser resolution than specified.…”

“…Besides the Li problem, a multitude of other science cases has led in the past to the creation of high-fidelity solar spectral atlases either disk centered or disk averaged. Among the first was the Utrecht atlas by Minnaert et al (1940) and several followed, most notably the Sacramento Peak atlas (Beckers et al 1976), the Liège atlas (Delbouille et al 1973) and the Hamburg atlas (Neckel & Labs 1984) (see the recent comparison of the latter two by Doerr et al 2016). Subsequent solar atlases were also used to identify blended transitions in stellar spectra that otherwise do not reach comparable spectral resolutions.…”

Accurate Short-Characteristics Radiative Transfer in A Numerical Tool for Astrophysical RESearch (ANTARES)

“…We prefer the FTS solar atlas to the "Photometric Atlas of The Solar Spectrum from λ3000 to λ10000" published by the University of Liège (Delbouille, Roland, and Neven, 1973) because of the higher spectral resolution of λ/ λ ≈ 500,000. As was shown by Doerr, Vitas, and Fabbian (2016), where the authors carry out a detailed comparison of FTS and Liège atlases, the spectral resolution of the Liège atlas is between two and Figure 12 Comparison of the λ = 5584.76 Å spectral line from MPS-ATLAS and SPECTR-3D synthesis and in the Hamburg solar atlas at the solar disk center (Neckel, 1999). six times lower.…”

MPS-ATLAS: A fast all-in-one code for synthesising stellar spectra

“…Then, using these models, we calculated the intensity at disc-centre on a high-resolution wavelength grid with resolving power R=500 000 for each of the two line lists. Figure 8 shows both intensities in the range between 5340 Å-5360 Å together with the Hamburg atlases of the solar spectrum 4 (Neckel 1999;Doerr et al 2016). For this comparison, we degraded the resolving power of the calculated flux using a Gaussian kernel.…”