Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum

DÍAZ, G.; GONZALEZ, J. F.; LEVATO, H.; GROSSO, M.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2011 p. 143 - 153

0004-6361

Aims. We propose a method for measuring the projected rotational velocity v sin i with high precision even in spectra with blendedlines. Though not automatic, our method is designed to be applied systematically to large numbers of objects without excessive com-putational requirement.Methods. We calculated the cross correlation function (CCF) of the object spectrum against a zero-rotation template and used theFourier transform (FT) of the CCF central maximum to measure the parameter v sin i taking the limb darkening effect and its wave-length dependence into account. The procedure also improves the definition of the CCF base line, resulting in errors related to thecontinuum position under 1% even for v sin i = 280 km s−1 . Tests with high-resolution spectra of F-type stars indicate that an accuracywell below 1% can be attained even for spectra where most lines are blended.Results. We have applied the method to measuring v sin i in 251 A-type stars. For stars with v sin i over 30 km s−1 (2–3 times ourspectra resolution), our measurement errors are below 2.5% with a typical value of 1%. We compare our results with Royer et al.(2002a) using 155 stars in common, finding systematic differences of about 5% for rapidly rotating stars.