A spectroscopic analysis of the K0 III binary ∈ Cygni.
Abstract (from CDS):
Spectroscopic observations of ∈ Cyg (K0 III) taken over 12 seasons from 1999 to 2010 with a resolving power ∼100,000 are analyzed for radial velocities, granulation properties, and projected rotation rate. The new radial velocities, which are on an absolute velocity scale with convective blueshifts removed, contribute to the determination of the 55-year orbit parameters, but are insufficient to be definitive. Line-depth ratios show photospheric temperature variations amounting to ∼4 K, likely arising from a magnetic cycle. A small velocity variation, ∼100 m/s, may mimic the temperature variations. Fourier analysis of the line broadening yields the projected rotation rate v sin i = 1.0±0.2 and macroturbulence dispersion ζRT = 4.45±0.05 km/s. A possible rotation modulation in velocity with a period of ∼1.5 years is noted. The third signature of granulation, i.e., greater blueshifts for weaker lines, is measured and indicates a photospheric velocity gradient in ∈ Cyg that is 1.1±0.1 times the Sun's, which is consistent with previously measured K giants. Mapping the line bisector of the Fe i λ6253 line on to the third-signature plot results in a flux deficit with a maximum 4.9 km/s redward of the line core and an amplitude of 16.5%±0.5% of the core depth, values typical of K giants. A 145 K disk-averaged temperature difference between granules and lanes is implied.