The Pulsation Mode of the Cepheid Polaris

Abstract

A previously derived photometric parallax of 10.10 ± 0.20 mas, d = 99 ± 2 pc, is confirmed for Polaris by a spectroscopic parallax derived using line ratios in high dispersion spectra for the Cepheid. The resulting estimates for the mean luminosity of langM_V rang = -3.07 ± 0.01 s.e., average effective temperature of langT _effrang = 6025 ± 1 K s.e., and intrinsic color of (langBrang - langVrang)₀ = +0.56 ± 0.01 s.e., which match values obtained previously from the photometric parallax for a space reddening of E _{B - V} = 0.02 ± 0.01, are consistent with fundamental mode pulsation for Polaris and a first crossing of the instability strip, as also argued by its rapid rate of period increase. The systematically smaller Hipparcos parallax for Polaris appears discrepant by comparison.