Altair's inclination from line profile analysis

Abstract

We present a detailed spectroscopic study of line broadening in the A7IV-V star Altair. In a wavelength region covering 690 Å we reconstruct the overall broadening profile taking into account more than 650 spectral lines. From the broadening profile we determine the projected rotational velocity v sin i, derive an upper limit for the equatorial velocity v from the shape of the profile and search for signatures of differential rotation. Our redetermined value of v sin i is (227 ± 11 ) kms-1 Measuring the first two zeros of the Fourier transformed broadening profile yields no signatures of differential rotation. We derive that Altair is seen under an inclination angle higher than i = 68° and it rotates at v < 245 kms-1 or slower than 53% of breakup velocity on a 1σ level.