28 Years of Sun-as-a-star Extreme Ultraviolet Light Curves from SOHO EIT

Abstract

The Solar and Heliospheric Observatory (SOHO) Extreme-ultraviolet Imaging Telescope (EIT) has been taking images of the Solar disk and corona in four narrow EUV bandpasses (171Å, 195Å, 284Å, and 304Å) at a minimum cadence of once per day since early 1996. The time series of fully-calibrated EIT images now spans approximately 28 years, from early 1996 to early 2024, covering solar cycles 23, 24, and the beginning of cycle 25. We convert this extensive EIT image archive into a time series of `Sun-as-a-star' light curves in EIT's four bandpasses, providing a long-term record of solar EUV variability. These Sun-as-a-star light curves, available for download from https://doi.org/10.5281/zenodo.15474179, trace the Sun as if it were a distant point source, viewed from a fixed perspective. We find that our EUV light curves trace the $\sim$ 11-year solar activity cycle and the $\sim$ 27-day rotation period much better than comparable optical observations. In particular, we can accurately recover the solar rotation period from our 284Ålight curve for 26 out of 28 calendar years of EIT observations (93% of the time), compared to only 3 out of 29 calendar years (10% of the time) of the VIRGO total solar irradiance time series, which is dominated by optical light. Our EIT light curves, in conjunction with Sun-as-a-star light curves at optical wavelengths, will be valuable to those interested in inferring the EUV/UV character of stars with long optical light curves but no intensive UV observations, as well as to those interested in long-term records of solar and space weather.

arXiv comment19 pages, 14 figures. Accepted for publication in A&A. Abstract abridged

References in corpus (29)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• dynesty: A Dynamic Nested Sampling Package for Estimating Bayesian Posteriors and Evidences
• Fast and scalable Gaussian process modeling with applications to astronomical time series
• Evolution of the Solar Activity over Time and Effects on Planetary Atmospheres: I. High-energy Irradiances (1-1700 A)
• The MUSCLES Treasury Survey I: Motivation and Overview
• A simple method to estimate radial velocity variations due to stellar activity using photometry
• Using the Sun to estimate Earth-like planets detection capabilities II. Impact of plages
• Inferring probabilistic stellar rotation periods using Gaussian processes
• The UV and X-ray activity of the M dwarfs within 10pc of the Sun
• JHelioviewer - Time-dependent 3D visualisation of solar and heliospheric data
• Three years of Sun-as-a-star radial-velocity observations on the approach to solar minimum
• An observational correlation between stellar brightness variations and surface gravity
• The stellar wind cycles and planetary radio emission of the Tau Boo system
• Searching for Young M Dwarfs with GALEX
• Characterising stellar micro-variability for planetary transit searches
• The MUSCLES Treasury Survey IV: Scaling Relations for Ultraviolet, Ca II K, and Energetic Particle Fluxes from M Dwarfs
• The HARPS search for southern extra-solar planets. XXX. Planetary systems around stars with solar-like magnetic cycles and short-term activity variation
• The solar magnetic field since 1700: I. Characteristics of sunspot group emergence and reconstruction of the butterfly diagram
• Stellar Activity in the Broad-Band Ultraviolet
• Do stellar magnetic cycles influence the measurement of precise radial velocities?
• Estimating Stellar Radial Velocity Variability from Kepler and GALEX: Implications for the Radial Velocity Confirmation of Exoplanets
• Solar cycle variation of ${\nu }_{\max }$ in helioseismic data and its implications for asteroseismology
• Detectability of Solar Rotation Period Across Various Wavelengths

Cited by in corpus (1)

• Initial radiometric calibration of the High-Resolution EUV Imager (${\text{HRI}}_{\text{EUV}}$) of the Extreme Ultraviolet Imager (EUI) instrument onboard Solar Orbiter