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.

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

References in corpus (5)

• The Gaia mission
• Reconstruction of total and spectral solar irradiance from 1974 to 2013 based on KPVT, SoHO/MDI and SDO/HMI observations
• Magnitudes and Timescales of Total Solar Irradiance Variability
• A new SATIRE-S spectral solar irradiance reconstruction for solar cycles 21--23 and its implications for stratospheric ozone
• Effect of metallicity on the detectability of rotational periods in solar-like stars

Cited by in corpus (8)

• 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
• Measuring periods in aperiodic light curves -- Applying the GPS method to infer rotation periods of solar-like stars
• Forward modelling of brightness variations in Sun-like stars -- II. Light curves and variability
• 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