2014ApJ...796...88G

A nine-season spectroscopic study of the photosphere of β Gem (K0 III) shows this low-luminosity giant to be stable, with no effective temperature variations above ∼2 K, and no secular temperature variations over the 2002-2010 time span above 0.2 K per year. The radial-velocity variations are consistent with an orbital variation of ∼40 m/s. The projected rotation rate is found to be 1.70±0.20 km/s with a macroturbulence dispersion of 4.53±0.10 km/s. The third-signature plot is also invariant and shows a granulation velocity gradient 20% smaller than the solar gradient. The absolute shift of the third-signature plot gives a blueshift-corrected radial velocity of 3385±70 m/s. Bisector mapping of the Fe I λ6253 line yields a flux deficit of 12%±1% in area, somewhat smaller than for other giants, but the shape and the position of the peak at 4.8 km/s is consistent with other giants. All of the investigated photospheric parameters are consistent with β Gem being a low-luminosity giant in agreement with its absolute magnitude.