Rotational velocities of A-type stars I. Measurement of vsini in the southern hemisphere

TL;DR

This study measures the projected rotational velocities (vsini) of 525 southern hemisphere A-type stars using Fourier transform techniques, revealing systematic differences from previous standard values due to binarity and model atmospheres.

Contribution

It provides a large, homogeneous set of vsini measurements for A-type stars in the southern hemisphere using Fourier analysis, improving upon previous underestimated values.

Findings

Measured vsini for 525 stars with ~6% error

Identified systematic shift from previous standard values

Attribution of discrepancies to binarity and model atmospheres

Abstract

Within the scope of a Key Programme determining fundamental parameters of stars observed by HIPPARCOS, spectra of 525 B8 to F2-type stars brighter than V=8 have been collected at ESO. Fourier transforms of several line profiles in the range 4200-4500 A are used to derive vsini from the frequency of the first zero. Statistical analysis of the sample indicates that measurement error is a function of vsini and this relative error of the rotational velocity is found to be about 6% on average. The results obtained are compared with data from the literature. There is a systematic shift from standard values from Slettebak et al. (1975), which are 10 to 12% lower than our findings. Comparisons with other independent vsini values tend to prove that those from Slettebak et al. are underestimated. This effect is attributed to the presence of binaries in the standard sample of Slettebak et al., and to the model atmosphere they used.