Has rapid solar core rotation been observed?

Abstract

Internal rotation and gravitational quadropole moment of the Sun are of interest to solar physics, the study of stellar structure and to investigations related to the test of gravitational theories. High precision measurements of fluctuations in the limb darkening function and in the spectral line shifts have raised the possibility that the interior of the Sun may be studied more directly than had previously been possible. Recently, Claverie et al.¹ argued that their detection of a 13.1±0.2 day velocity signal give further experimental evidence that the solar core is rotating more rapidly than the observable surface. We show here that the phase as well as the magnitude of the observed signal amplitude may be predicted without any rapid core rotation by taking into account the presence of sunspots and their contribution to the spectral line profile as integrated over the disk of the Sun. Hence, we conclude that the existence of a 13.1–day apparently periodic velocity signal with amplitude 6.5 m s⁻¹ during the 88 days observing period cannot be taken as evidence for a rapidly rotating solar core.