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...
arXiv commentAccepted in A&A, 23 pages, 18 figures
References in corpus (60)
- Revisiting the Sunspot Number
- State of the Field: Extreme Precision Radial Velocities
- Recent variability of the solar spectral irradiance and its impact on climate modelling
- The new Sunspot Number: assembling all corrections
- Using the Sun to estimate Earth-like planets detection capabilities II. Impact of plages
- Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program I. Comparison of activity indices
- The Sun as a planet-host star: Proxies from SDO images for HARPS radial-velocity variations
- A public HARPS radial velocity database corrected for systematic errors
- PEPSI: The high-resolution echelle spectrograph and polarimeter for the Large Binocular Telescope
- POLLUX : a database of synthetic stellar spectra
- STiC -- A multi-atom non-LTE PRD inversion code for full-Stokes solar observations
- 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
- Planetary detection limits taking into account stellar noise. II. Effect of stellar spot groups on radial-velocities
- HARPS-N observes the Sun as a star
- Measuring precise radial velocities on individual spectral lines : II. Dependance of stellar activity signal on line depth
- The IAG solar flux atlas: Accurate wavelengths and absolute convective blueshift in standard solar spectra
- How realistic are solar model atmospheres?
- Halpha line profile asymmetries and the chromospheric flare velocity field
- The solar chromosphere at high resolution with IBIS. IV. Dual-line evidence of heating in chromospheric network
- PEPSI deep spectra. I. The Sun-as-a-star
- On the Formation Height of the SDO/HMI Fe 6173 Doppler Signal
- SSTRED: Data- and metadata-processing pipeline for CHROMIS and CRISP
- Reconstructing the solar integrated radial velocity using MDI/SOHO
- Three-dimensional modeling of the Ca II H&K lines in the solar atmosphere
- 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
- A Frequency Comb calibrated Solar Atlas
- RASSINE: Interactive tool for normalising stellar spectra I. Description and performance of the code
- Fe I line shifts in the optical spectrum of the Sun
- Long-term radial-velocity variations of the Sun as a star: The HARPS view
- Astrophysical Insights into Radial Velocity Jitter from an Analysis of 600 Planet-search Stars
- Convective Nature of Sunspot Penumbral Filaments: Discovery of Downflows in the Deep Photosphere
- Blue wing enhancement of the chromospheric Mg II h and k lines in a solar flare
- Stray-light contamination and spatial deconvolution of slit-spectrograph observations
- 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
- New wavelength calibration of the HARPS spectrograph
- 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
- The IAG spectral atlas of the spatially resolved Sun: Centre-to-limb observations
- Hα spectroscopy and multiwavelength imaging of a solar flare caused by filament eruption
- Center-to-limb variation of spectral lines and continua observed with SST/CRISP and SST/CHROMIS
- SUPPNet: Neural network for stellar spectrum normalisation
- How different are the Liège and Hamburg atlases of the solar spectrum?
- The spectral impact of magnetic activity on disk-integrated HARPS-N solar observations: exploring new activity indicators
- Characterization of the ESPRESSO Line-Spread Function and Improvement of the Wavelength Calibration Accuracy
- The New 2018 Version of the Meudon Spectroheliograph
- H and H emission in a C3.3 solar flare: comparison between observations and simulations
- 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
- Shapes of stellar activity cycles
- Convective characteristics of Fe I lines across the solar disc
- The wings of Ca II H and K as photospheric diagnostics and the reliability of one-dimensional photosphere modeling
- Convective Line Shifts in the Spectra of Solar-Type Stars
- An Atlas of Spectroheliograms from 3641 to 6600 Å