J/A+A/702/A97 Solar flux atlases (Hanassi-Savari+, 2025)
Solar flux atlases. The new HARPS-N quiet Sun benchmark and continuum
normalisation of the Ca II H & K lines.
Hanassi-Savari F., Pietrow A.G.M., Druett M.K., Cretignier M., Ellwarth M.
<Astron. Astrophys. 702, A97 (2025)>
=2025A&A...702A..97H 2025A&A...702A..97H (SIMBAD/NED BibCode)
ADC_Keywords: Sun ; Spectroscopy
Keywords: line: profiles - methods: data analysis - Sun: activity
Abstract:
Solar flux atlases observe the spatially integrated light from the
Sun, treating it as a star. They are fundamental tools for gaining
insight into the composition of the Sun and other stars. They are
utilised as reference material for a wide range of solar applications
such as stellar chemical abundances, atmospheric physics, stellar
activity, and radial velocity signals.
We provide a detailed comparison of solar activity reported in some of
the well-known solar atlases against the new High Accuracy Radial
velocity Planet Searcher for the Northern hemisphere (HARPS-N) Quiet
Sun (QS) and Measured Activity (MA) atlases published, for the first
time, in this work.
Ten of the widely used individual spectral lines from each flux atlas
were selected to compare solar activity based on three methods: 1)
equivalent widths; 2) a novel activity measure introduced in this work
and referred to as the activity number; and 3) bisectors and radial
velocity.
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.
Description:
Three solar flux atlases: Quiet Sun (QS) and Measure Activity (MA)
atlases form HARPS-N, and spatially resolved modified version of the
IAG quiet Sun CLV atlas (Ellwarth et al. (2023b)), IAG23, which
included tellurics. QS and MA atlases covers the wavelength range from
3900Å to 6834Å, IAG23 covers 4200Å to 8000Å. All atlases
include normalized flux.
For each atlas, the following columns are provided:
WAVELENGTH: Wavelength in Angstroms (Å
FLUX: Normalised flux intensities
The QS atlas corresponds to periods of minimum solar activity and has
an average spot number of zero. MA spot number = 67. The IAG23 atlas
uniquely quiet because the observations that make up each µ-bin
were taken in areas of the Sun where the Sun was quiet.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 104 3 List of individual spectra
fits/* . 3 Individual spectra
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See also:
J/A+A/673/A19 : Spatially resolved solar spectra (Ellwarth+, 2023)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- Nx Number of pixels along X-axis
9- 13 I5 Kibyte size Size of FITS file
15- 33 A19 --- FileName Name of FITS file, in subdirectory fits
35-104 A70 --- Title Title of the FITS file
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Acknowledgements:
Foad Hanassi-Saavri, fhanassi-savari1(at)sheffield.ac.uk
(End) Patricia Vannier [CDS] 29-Aug-2025