The differential rotation of epsilon Eri from MOST data

Abstract

From high-precision MOST photometry spanning 35 days the existence of two spots rotating with slightly differing periods is confirmed. From the marginal probability distribution of the derived differential rotation parameter k its expectation value as well as confidence limits are computed directly from the data. The result depends on the assumed range in inclination i, not on the shape of the prior distributions. Two cases have been considered: (a) The priors for angles, inclination i of the star and spot latitudes beta_1,2, are assumed to be constant over i, beta_1, and beta_2. (b) The priors are assumed to be constant over cosi, sin beta_1, and sin beta_2. In both cases the full range of inclination is considered: 0^o< = i< = 90^o. Scale-free parameters, i.e. periods and spot areas (in case of small spots) are taken logarithmically. Irrespective of the shape of the prior, k is restricted to 0.03 < = k < = 0.10 (one-sigma limits). The inclination i of the star is photometrically ill-defined.