The Spectra and Rotational Velocities of the Bright Stars of Draper Types A3-G0.

Abstract

Rotational velocities (v sin i's) have been determined by spectroscopic means for the bright stars of Draper types , plus a few standards of spectral type later than GO. The total number of stars considered was 215. Spectral types and luminosity classes on the MK system were estimated for all stars not already MK standards. The principal results of this and a previous investigation for 159 stars which were judged to be normal main-sequence and intermediate-luminosity stars in the range A3-G0 are as follows: 1. As has been generally known, axial rotation decreases along the main sequence from the middle A-type stars to the late F-type and early G-type stars. Main-sequence stars later than about F5 have very little axial rotation. 2. Anial rotation also decreases from the middle A-type to the late F- and early G-type stars of intermediate luminosity but persists to later spectral types than for the main-sequence stars. 3. The stars of intermediate luminosity have generally greater axial rotation than the corresponding main-sequence stars in the range F(kGO. Among the middle A-type stars, the two groups probably have about the same axial rotation. Axial rotation is also discussed for a number of groups of stars not included in the afore-mentioned discussion, including the luminous giant and supergiant stars, the metallic4ine stars, the peculiar A stars, and the stars with composite spectra. The variation of axial rotation across the H-R diagram as determined from the present investigation and two previous investigations by the writer is summarized.