Absolute magnitudes of stars from widths of chromospheric CaII emission lines.

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Abstract

Absolute magnitudes of about 700 late-type subgiants, giants, and supergiants are derived from measures of the widths of the chromospheric emission components of the Ca ii K line. They are tabulated along with other pertinent information. The data are essentially complete for all suitable stars down to m = 5.0 and declination 250. The moduli derived from the Mv(K) are plotted against the trigonometric parallaxes for all stars for which the latter have weights >20. It is found that there is a systematic difference in the fit to the m - M = -s - 5 log curve for stars with b < 250 compared to those with b > 250. Since the numbers of stars in these two groups are equal, the difference is believed to originate with the parallaxes. Estimates against nearby Fe i lines have been made for the strength of Sr ii A4077, which is a luminosity criterion for these stars. When the logarithms of the A4077 intensities are plotted against the Mv(K), the bulk of the stars in the diagram fall approximately along a linear relationship. However, there is a group of stars between Mv(K) = +1.5 and -3 for which the estimated A4077 intensities are too strong, compared to the average for the other stars, by amounts well in excess of the errors of estimation. Further investigation indicates that the G-K stars in this group are probably barium stars, but M-type stars also participate in the Sr ii anomaly. The color-magnitude diagram constructed from the Mv(K) has several interesting features which are discussed in the text. In particular, the C-M diagram of NGC 188 by Sandage forms an excellent lower boundary to the assemblage of field stars. Subject headings: Ca ii emission - stars: late-type - stars: luminosities

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