The Position of the Sun in the HR Diagram

Abstract

Since the absolute magnitude of the Sun is known accurately and the solar spectrum defines spectral type G2 V, it would appear that the position of the Sun in the HR diagram is well established. However, the color of the Sun and its metallicity relative to other stars remains controversial. It is known from theory that stellar groups of differing composition will have different main sequences.

The observed difference in the strength of the metallic lines in Coma stars relative to Hyades stars is caused by a systematic difference in [Fe/H] of less than 0.2 dex or 50%. Photographs and quantitative measures of the systematic differences between the Hyades and Coma spectra are presented. Visual comparison and quantitative analysis of the solar spectrum relative to Hyades and Coma spectra reveal that the Sun is metal rich similar to the Hyades stars rather than of normal disk metallicity as represented by Coma stars. Evidence is presented showing that the color and spectral line strengths of the Sun are more similar to stars classified G3 and G4 in the literature than G2. If the Hyades modulus is y = 3^m.25, the (B-V) color of the Sun must be 0^m.65 or redder for the Sun to be on or above the Hyades main sequence.