3 Rotational velocities

Different methods can be found in the literature to calculate rotational velocities. In this work we have used the technique based on the Fourier transform proposed by Gray (1992) which has shown to give superior results than those based on the convolution of a non-rotating standard star of similar spectral type with a rotational function or on the identification of a particular parameter of the spectral lines (e.g. FWHM). Whereas these two latter methods require one to build up a calibration of rotational velocities, Gray's method provides a direct and independent measurement of $v \sin i$. In short, the method relies on the relation between $v \sin i$  and the frequencies where the Fourier transform of the rotational profile reaches a relative minimum. Instrumental broadening may add relative minima in the Fourier transform but at higher frequencies than those used to calculate the rotational velocity. Projected rotational velocities for our sample of stars are given in Table 2.