Rotation and differential rotation in rapidly rotating field stars

TL;DR

This study investigates stellar latitudinal differential rotation in approximately 180 rapidly rotating stars, identifying ten with significant differential rotation and confirming the rarity of such features among fast rotators.

Contribution

It extends previous research by analyzing a larger sample of stars, using Fourier transform methods to detect differential rotation signatures in spectral line profiles.

Findings

Ten stars with 10-54% differential rotation identified

More than 40 stars show line shapes consistent with rigid rotation

Differential rotation is rare among rapid rotators

Abstract

We continue our studies on stellar latitudinal differential rotation. The presented work is a sequel of the work of Reiners et al. who studied the spectral line broadening profile of hundreds of stars of spectral types A through G at high rotational speed (vsini > 12 km/s). While most stars were found to be rigid rotators, only a few tens show the signatures of differential rotation. The present work comprises the rotational study of some 180 additional stars. The overall broadening profile is derived according to Reiners et al. from hundreds of spectral lines by least-squares deconvolution, reducing spectral noise to a minimum. Projected rotational velocities vsini are measured for about 120 of the sample stars. Differential rotation produces a cuspy line shape which is best measured in inverse wavelength space by the first two zeros of its Fourier transform. Rigid and differential rotation can be distinguished for more than 50 rapid rotators (vsini > 12 km/s) among the sample stars from the available spectra. Ten stars with significant differential rotation rates of 10-54 % are identified, which add to the few known rapid differential rotators. Differential rotation measurements of 6 % and less for four of our targets are probably spurious and below the detection limit. Including these objects, the line shapes of more than 40 stars are consistent with rigid rotation.