Measurements of solar irradiance and effective temperature as a probe of solar interior magnetic fields

Abstract

We argue that a variety of solar data suggest that the activity-cycle timescale variability of the total irradiance, is produced by structural adjustments of the solar interior. Assuming these adjustments are induced by variations of internal magnetic fields, we use measurements of the total irradiance and effective temperature over the period from 1978 to 1992, to infer the magnitude and location of the magnetic field. Using an updated stellar evolution model, which includes magnetic fields, we find that the observations can be explained by fields whose peak values range from 120k to 2.3k gauss, located in the convection zone between $0.959R_{\sun}$ and $0.997R_{\sun}$, respectively. The corresponding maximal radius changes, are 17 km when the magnetic field is located at $0.959R_{\sun}$ and 3 km when it is located at $0.997R_{\sun}$. At these depths, the $W$ parameter(defined by $Δ\ln R / Δ\ln L$, where $R$ and $L$ are the radius and luminosity) ranges from 0.02 to 0.006. All these predictions are consistent with helioseismology and recent measurements carried out by the MDI experiment on SOHO.