Is the Sun an oblique magnetic rotator?

Abstract

The recent observation¹ of rotational splitting of the non-radial p modes of l = 1 and l = 2 (with it n∼20) of the 5-min global oscillation of the Sun was interpreted in terms of rotational splitting associated with a rapid rotation of the solar interior. The precise value deduced for the angular velocity Ω of the interior depends on the assumed variation of Ω with depth and on the weighting function. Thus with a weighting function² of the form

&Ω̄=∫Ω(r)/V(r) dr ∫dr/V(r) (1)

where V(r) is the local velocity of sound at radius r, one obtains values of Ω_core/Ω_surface ranging from 2 to 9 as the radius at which Ω, assumed to be constant for smaller r, ranges from 0.6 to 0.15 of the solar radius. Such a weighting function proportional to the time the wave spends at any particular radius seems very plausible for the effect of any parameter, be it angular velocity or magnetic field, on the propagation of nearly plane waves as they bounce between the centre and the surface. Here I attempt to correlate the size of the observed rotational splitting with the enigmatic 12.2-day variation in the measurement of solar oblateness discovered by Dicke³ previously⁴ and to interpret the observed near equality of the amplitudes of the m- components of the l = 1 and l = 2 rotationally split modes. This leads to the first empirical evidence that an asymmetric magnetic rotator with megagauss magnetic fields exists in the interior of the Sun. It also suggests that the magnetic energy of young stars is a sizeable fraction of their gravitational energy.