2020MNRAS.499.1126T

With an aim of getting information on the equatorial rotation velocity (v_e) of Sirius A separated from the inclination effect (sin i), a detailed profile analysis based on the Fourier transform technique was carried out for a large number of spectral lines, while explicitly taking into account the line-by-line differences in the centre-limb behaviours and the gravity darkening effect (which depend on the physical properties of each line) based on model calculations. The simulations showed that how the first-zero frequencies (q₁) of Fourier transform amplitudes depends on v_e is essentially determined by the temperature-sensitivity parameter (K) differing from line to line, and that Fe I lines (especially those of very weak ones) are more sensitive to v_e than Fe II lines. The following conclusions were drawn by comparing the theoretical and observed q₁ values for many Fe I and Fe II lines: (1) The projected rotational velocity (v_esin i) for Sirius A is fairly well established at 16.3(±0.1) km s^–1 by requiring that both Fe I and Fe II lines yield consistent results. (2) Although precise separation of v_e and i is difficult, v_e is concluded to be in the range of 16 ≤v_ e_ ≲30-40 km s^–1, which corresponds to 25^○^ ≲i ≤90^○^. Accordingly, Sirius A is an intrinsically slow rotator for an A-type star, being consistent with its surface chemical peculiarity.