Philip C. Keenan

REVISED MK SPECTRAL CLASSIFICATION OF THE RED CARBON STARS

The spectral classification of the red carbon stars has been brought into the Revised MK system by combining some of the features of the old R, N, and C classifications, as modified by Yamashita, and adding numerical abundance indices. The new types are intended to: (1) Define the population to which the star belongs. (2) Allow quick interpolation between the detailed atmospheric analyses of individual stars. (3) Indicate the differences between carbon stars in different parts of our galaxy, and in other galaxies. It is the flexibility of the notation, allowing the incorporation of improved criteria, that should make the new system useful.

Spectral types and their uses

The principles involved in setting up any viable system of spectral classification are discussed. Their application is illustrated by reviewing the essential features of the original MK system of two dimensions and its extension to additional dimensions, particular attention being paid to the Revised MK System as applied to stars of types G0 through M8. The domain of wavelengths within which stars at a given temperature can be classified on a consistent system is defined. The application of spectral types to the preparation of observing programs, to statistical studies of the distribution of selected groups of stars, and to the direct estimation of physical properties of stars is discussed briefly.

Recognition and classification of strong-CN giants

Fifty of the stars designated as super-metal-rich by Spinrad and Taylor (1969) are classified here on the Revised MK System. Positive CN indices are assigned in recognition of the characteristic excesses of carbon and nitrogen in their atmospheres, as compared to normal Population I stars. For only a few of the stars, an abnormal strength of the iron lines or of Ca 4226 A is so noticeable that they need to be distinguished by positive indices for these metals.

IS THE SPECTRAL TYPE OF THE SUN CONSTANT

The spectral type of the whole sun was monitored from August 25, 1988 through October 2, 1990. No changes as large as half a spectral subdivison were detected. The spectral type remained at G2 V.

PROBLEMS IN THE TEMPERATURE CLASSIFICATION OF THE RED GIANT STARS

Effective temperatures determined by Tsuji (1981) by the infrared-flux method were shown by him to remain nearly constant in the range M0 to M2. It is easily shown that this is not due to any luminosity effect in the spectral types. Rather, revised MK types based primarily on TiO band strengths in this range are shown to be more sensitive to temperature changes than are the commonly used color indices.

Spectral Classification and the Relations Between Peculiar Giants

Spectral classification may make a modest contribution to our understanding of the stars with anomalous atmospheric abundances. For one thing, the more spectra we examine the more evident it becomes that the groups that we are talking about here are practically never discrete and clearly bounded. There always seem to be marginal stars that blur the distinctions between the so-called groups.

VARIABLE CALCIUM CHLORIDE ABSORPTION BANDS IN WZ CASSIPEIAE.

The orange and red bands of CaCl were very strong in a 1958 Lick spectrogram of WZ Cas, but not noticeable in a 1974 Perkins spectrogram. This is the first reported case of such variation in a semiregular variable.