The Short-Period Cepheid SU Cassiopeiae: Spectroscopic Diagnosis of its Rotation and Atmospheric Turbulence

A detailed non-LTE profile analysis of OI 7771–5 and KI 7699 based on the classical line-broadening model (i.e., rigid rotation, microturbulence, and radial-tangential macroturbulence) was carried out for the short-period Cepheid SU Cas at the phase of near-maximum radius, in order to establish its rotational velocity by separating the effect of atmospheric turbulence, which was motivated by the suspicion that its appreciably large radius, empirically derived by using the radial-velocity information (e.g., Wesselink method), might be nothing but due to an apparent rotational effect, shifting the position of the line-peak significantly. It turned out, however, that the best-fit was accomplished at ve sin i ≃ 0 km s⁻¹ for both cases of the line-profiles. This evidently indicates that the rotation is practically of negligible importance, and can not be the key to the “radius problem” of SU Cas, for which some other different explanation must be invoked.