High-Dispersion Classification of K2-M6 Giants of High and Low Velocity
Abstract
The classification of early M-type giants by the usual criteria of TiO band strengths has been tested by estimating ratios of weak atomic lines on coudé spectrograms of scale 9-10 A mm1. No systematic dif- ferences are found between the types given by the two methods for Population I stars and for high- velocity stars of intermediate Population II. Published V - I and U - I colors also give sequences in agreement with the spectral types. Although there is thus no evidence that TiO bands differ in strength between giants of the two popula- tions studied, in several of the M stars of high velocity a slight weakening of the stronger atomic lines ap- pears to be present. In several stars representing both populations, the absorption lines at Hy and Ho show intensity changes on a time scale of weeks or months; but other absorption lines and bands appear not to vary
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1969
- DOI:
- 10.1086/149951
- Bibcode:
- 1969ApJ...156..107D