Abstract
The surface gravity of Arcturus is estimated from the strength of the MgH features (the Mg abundance being derived from MgI lines), from strong metal lines and from the FeI/FeII ionization equilibrium. The MgH lines give log g = 1.7 (cgs units) and 4375 K for the effective temperature. This value of log g is consistent with the gravity derived from the sample of strong pressure-broadened lines from FeI, CaI and NaI which gives log g = 1.6, and what we obtain from the ionization equilibrium of Fe, log g = 1.4. The corresponding estimates of the maximum error are 0.3, 0.2 and 0.5 dex, respectively. The mass of Arcturus is found to be in the interval 0.6–1.0 solar masses. It is concluded that the MgH features offer good possibilities for determining gravities of late-type stars, when good estimates of effective temperatures are available.
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