Solar Flux Atlases: The new HARPS-N Quiet Sun Benchmark and Ca II H & K Lines Continuum Normalisation
arXiv:2508.07912 · doi:10.1051/0004-6361/202451874
Abstract
Context. 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, and are utilized as reference material for a wide range of solar applications such as stellar chemical abundances, atmospheric physics, stellar activity, and radial velocity signals. Aims. We provide a detailed comparison of solar activity 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 that are published, for the first time, in this work. Methods. Ten of the widely used individual spectral lines from each flux atlas were selected to compare solar activity using three methods: 1) Equivalent Widths 2) Activity number, a novel activity measure which we introduce in this work. 3) Bisectors and radial velocity. Results. The significantly smaller activity 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 Ca ii H & K lines of other atlases compared to our HARPS-N atlases, likely caused by assumptions in normalisation techniques used in the early Kitt Peak atlases. Conclusions. 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 that other atlases can be compared against. Our recommendations are 1) publication of a detailed log along with the observations, to include exact dates and indications of solar activity...
Accepted in A&A, 23 pages, 18 figures
References in corpus (31)
- A public HARPS radial velocity database corrected for systematic errors
- PEPSI: The high-resolution echelle spectrograph and polarimeter for the Large Binocular Telescope
- Three years of Sun-as-a-star radial-velocity observations on the approach to solar minimum
- Sun-as-a-Star Spectrum Variations 1974-2006
- Three Years of HARPS-N High-Resolution Spectroscopy and Precise Radial Velocity Data for the Sun
- Measuring precise radial velocities on individual spectral lines : II. Dependance of stellar activity signal on line depth
- YARARA: Significant improvement of RV precision through post-processing of spectral time-series
- 'Ultimate' Information Content in Solar and Stellar Spectra: Photospheric line asymmetries and wavelength shifts
- RASSINE: Interactive tool for normalising stellar spectra I. Description and performance of the code
- Astrophysical Insights into Radial Velocity Jitter from an Analysis of 600 Planet-search Stars
- The Changing Face of Centauri B: Probing plage and stellar activity in K-dwarfs
- YARARA V2: Reaching sub m/s precision over a decade using PCA on line-by-line RVs
- A new wavelength calibration for echelle spectrographs using Fabry-Perot etalons
- Temporal evolution and correlations of optical activity indicators measured in Sun-as-a-star observations
- Inference of the chromospheric magnetic field configuration of solar plage using the Ca II 8542 Å line
- The Lightweaver Framework for NLTE Radiative Transfer in Python
- A comparative study of two X2.2 and X9.3 solar flares observed with HARPS-N: Reconciling Sun-as-a-star spectroscopy and high-spatial resolution solar observations in the context of the solar-stellar connection
- Hα spectroscopy and multiwavelength imaging of a solar flare caused by filament eruption
- The IAG spectral atlas of the spatially resolved Sun: Centre-to-limb observations
- Center-to-limb variation of spectral lines and continua observed with SST/CRISP and SST/CHROMIS
- SUPPNet: Neural network for stellar spectrum normalisation
- Characterization of the ESPRESSO Line-Spread Function and Improvement of the Wavelength Calibration Accuracy
- The spectral impact of magnetic activity on disk-integrated HARPS-N solar observations: exploring new activity indicators
- H and H emission in a C3.3 solar flare: comparison between observations and simulations
- The New 2018 Version of the Meudon Spectroheliograph
- Characterization of chromospheric activity based on Sun-as-a-star spectral and disk-resolved activity indices
- Numerical non-LTE 3D radiative transfer using a multigrid method
- Convective characteristics of Fe I lines across the solar disc
- Shapes of stellar activity cycles
- Convective Line Shifts in the Spectra of Solar-Type Stars
- An Atlas of Spectroheliograms from 3641 to 6600 Å