The impact of the oblateness of Regulus on the motion of its companion

TL;DR

This paper examines how the oblateness of the rapidly spinning star Regulus affects the orbit of its close companion, aiming to detect measurable deviations from Kepler's law caused by the star's quadrupole moment.

Contribution

It provides a detailed analysis of the influence of Regulus's quadrupole moment on the orbital period of its companion, offering potential observational constraints.

Findings

Potential measurable deviations from Kepler's law due to Regulus's oblateness.

Constraints on the mass ratio of the system based on orbital deviations.

Assessment of current measurement accuracy for detecting quadrupole effects.

Abstract

The fast spinning B-star Regulus has recently been found to be orbited by a fainter companion in a close circular path with orbital period P_b = 40.11(2) d. Being its equatorial radius R_e 32% larger than the polar one R_p, Regulus possesses a remarkable quadrupole mass moment Q. We investigate the effects of Q on the orbital period P_b of its companion in order to see if they are measurable, given the present-day level of accuracy in measuring P_b. Conversely, we will look for deviations from the third Kepler law, attributed to the quadrupole mass moment Q of Regulus, to constrain the ratio \gamma=m/M of the system's masses.