On the rotational velocity of Sirius A
Abstract
With an aim of getting information on the equatorial rotation velocity (ve) 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 ve 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 ve 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 (vesin-=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 ve and i is difficult, ve is concluded to be in the range of $16 \le v_{\rm e} \lesssim$ 30-40 km s-1, which corresponds to $25^{\circ } \lesssim i \le 90^{\circ }$ . Accordingly, Sirius A is an intrinsically slow rotator for an A-type star, being consistent with its surface chemical peculiarity.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 2020
- DOI:
- 10.1093/mnras/staa2869
- arXiv:
- arXiv:2009.07143
- Bibcode:
- 2020MNRAS.499.1126T
- Keywords:
-
- stars: atmospheres;
- stars: chemically peculiar;
- stars: early-type;
- stars: individual: Sirius;
- stars: rotation;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 17 pages, 11 figures, with online supplementary data