On the rotational velocity of Sirius A. (arXiv:2009.07143v1 [astro-ph.SR])

On the rotational velocity of Sirius A. (arXiv:2009.07143v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Takeda_Y/0/1/0/all/0/1">Yoichi Takeda</a>

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 1st-zero frequencies (q_1) 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 q_1 values for many Fe I and Fe II lines: (1) The projected rotational
velocity (vsini) for Sirius A is fairly well established at 16.3 (+/-0.1) km/s
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, which corresponds to 25 < i(deg) < 90.
Accordingly, Sirius A is an intrinsically slow rotator for an A-type star,
being consistent with its surface chemical peculiarity.

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 1st-zero frequencies (q_1) 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 q_1 values for many Fe I and Fe II lines: (1) The projected rotational
velocity (vsini) for Sirius A is fairly well established at 16.3 (+/-0.1) km/s
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, which corresponds to 25 < i(deg) < 90.
Accordingly, Sirius A is an intrinsically slow rotator for an A-type star,
being consistent with its surface chemical peculiarity.

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