Connecting measurements of solar and stellar brightness variations

Abstract

Comparing solar and stellar brightness variations is hampered by the difference in spectral passbands used in observations as well as by the possible difference in the inclination of their rotation axes from the line of sight. We calculate the rotational variability of the Sun as it would be measured in passbands used for stellar observations. In particular, we consider the filter systems used by the CoRoT, $Kepler$, TESS, and $Gaia$ space missions. We also quantify the effect of the inclination of the rotation axis on the solar rotational variability. We employ the Spectral And Total Irradiance REconstructions (SATIRE) model to calculate solar brightness variations in different filter systems as observed from the ecliptic plane. We then combine the simulations of the surface distribution of the magnetic features at different inclinations using a surface flux transport model (SFTM) with the SATIRE calculations to compute the dependence of the variability on the inclination. For an ecliptic-bound observer, the amplitude of the solar rotational variability, as observed in the total solar irradiance (TSI) is 0.68 mmag (averaged over solar cycles 21-24). We obtained corresponding amplitudes in the $Kepler$ (0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), $Gaia$ (0.74 mmag), $Gaia{G}_{RP}$ (0.62 mmag), and ), $Gaia{G}_{BP}$ (0.86 mmag) passbands. Decreasing the inclination of the rotation axis decreases the rotational variability. For a sample of randomly inclined stars, the variability is on average 15% lower in all filter systems considered in this work. This almost compensates for the difference in the amplitudes of the variability in TSI and $Kepler$ passbands, making the amplitudes derived from the TSI records an ideal representation of the solar rotational variability for comparison to $Kepler$ stars with unknown inclinations.

arXiv comment9 pages, 9 figures, accepted for publication in Astronomy & Astrophysics

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Cited by in corpus (12)

• Amplification of brightness variability by active-region nesting in solar-like stars
• Forward modelling of Kepler-band variability due to faculae and spots
• Modeling stellar Ca II H & K emission variations. I. Effect of inclination on the S-index
• Spatially resolved spectroscopy across stellar surfaces. V. Observational prospects: Toward Earth-like exoplanet detection
• Predictions of astrometric jitter for Sun-like stars. I. The model and its application to the Sun as seen from the ecliptic
• Solar Photospheric Spectrum Microvariability I. Theoretical searches for proxies of radial-velocity jittering
• Forward modelling of brightness variations in Sun-like stars -- II. Light curves and variability
• Measuring periods in aperiodic light curves -- Applying the GPS method to infer rotation periods of solar-like stars
• Blackbody temperature of 200+ stellar flares observed with the CoRoT satellite
• The relationship between bipolar magnetic regions and their sunspots
• Detectability of Solar Rotation Period Across Various Wavelengths
• Reconstruction of total solar irradiance variability as simultaneously apparent from Solar Orbiter and Solar Dynamics Observatory