The Pulsation Mode of the Cepheid Polaris

TL;DR

This study confirms Polaris's distance and fundamental pulsation mode using spectroscopic data, aligning with previous photometric estimates and suggesting it is crossing the instability strip for the first time.

Contribution

The paper provides spectroscopic confirmation of Polaris's distance and pulsation mode, supporting its classification as a first-crossing Cepheid and clarifying previous parallax discrepancies.

Findings

Spectroscopic parallax confirms Polaris's distance at 99 pc.

Polaris's luminosity and temperature match fundamental mode pulsation.

Hipparcos parallax appears inconsistent with spectroscopic and photometric data.

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 <Mv>=-3.07+-0.01 s.e., average effective temperature of <Teff>=6025+-1 K s.e., and intrinsic color of (<B>-<V>)o=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.