Solar flux atlases

The significantly smaller activity levels measured in the MA atlas, compared to the other atlases, relative to the QS atlas, underscores the dominance of instrumental effects over solar activity in their impact on spectral lines, which cannot be corrected through simple line convolution to match resolutions of other atlases. Additionally, our investigation unexpectedly revealed a substantial intensity shift in the CaII H & K lines of other atlases compared to our HARPS-N atlases, likely resulting from the assumptions made when applying normalisation techniques for the early Kitt Peak atlases.

With an average spot number of zero, our QS atlas is well suited to serve as an absolute benchmark atlas representative of solar minimum for the visible spectrum, which other atlases can be compared against. Our recommendations going forward include: 1) the publication of a detailed log along with the observations to include exact dates and indications of solar activity; and 2) given the dominance of instrumental effects over variations caused by activity, quiet Sun reference atlases must be constructed with the same instruments to ensure high precision.