The Classification of the Red Carbon Stars.

Abstract

The subdivisions of spectral classes R and N do not appear to represent a consistent progression in temperature. In order to set up a more definite temperature sequence, a new classification is suggested on the basis of four criteria: (i) atomic line ratios which are sensitive to temperature changes; (2) inten- sity gradient of the continuous spectrum in the yellow and red regions; (3) strength of the D-lines of so- dium; and (~) intensity gradient within the X 5635-bafld group of the molecule C2. In the new classification the double maximum shown by the C2 bands in the R-N system disappears and is replaced by a single broad maximum. The "lithium" star, WZ Cassiopeiae, whose spectral type in the R-N system is Nip is reclassii5ed at the low-temperature end of the carbon sequence; it appears to be the coolest carbon star known, and the great strength of Li may possibly be explained. A group of five carbon stars has been found which is characterized by extreme weakness of the atomic lines in the photographic region. The bands of CH occur with great strength in their spectra; in addition, all five stars have very high radial velocities. The intensities of the carbon bands vary greatly among stars of the same subclass; this is probably to be considered as evidence of different abundances of carbon in the atmospheres of different stars