A Spectroscopic Analysis of the Hyades Cool Giants

Abstract

Abstract High-resolution spectroscopic observations of the four cool giants in the Hyades cluster, taken at the Elginfield Observatory, are analyzed. The velocity of γ Tau between 2002 and 2009 is constant to a few m s−1; small variations, compatible with the planetary orbit, are seen for ε Tau. The primary-to-secondary mass ratio of θ 1 Tau is found to be 2.33 ± 0.07. Absolute radial velocities are determined for three of the giants from third-signature plots that correct for granulation blueshifts: 38,615 ± 50, 38,760 ± 100, and 38,570 ± 50 m s−1 for γ Tau, δ Tau, and ε Tau respectively. Line–depth ratios show that γ Tau is 33 ± 5 K, δ Tau is 53 ± 10 K, and θ 1 Tau is 30 ± 6 K hotter than ε Tau. Although the λ6253 line bisectors are similar for all four giants, there are significant differences in the line profiles. Fourier analysis of the profile shapes yields projected rotation rates of 2.1, 2.4, 2.8, and 2.8 km s−1 for γ Tau, δ Tau, ε Tau, and θ 1 Tau respectively, with an uncertainty of ±0.3 km s−1. The corresponding radial–tangential macroturbulence dispersions are 5.07, 5.66, 5.55, and 4.65 km s−1, with a uncertainty of ±0.10 km s−1. Scale factors for third-signature plots are close to unity, ±10%, implying that the granulation velocity gradient through their photospheres is similar to the Sun's. Bisector mapping returns flux differences between granules and lanes, with average granule-to-lane temperature differences ∼125 K.