Photoelectric multiband photometry of M giants and supergiants in the blue-visual spectral region

Photoelectric photometry of M stars has been carried out in nine narrow bands in the range from 4050 to 5500 A, and various classification indices based on these observations are discussed. It is shown that six bands define two parameters which clearly separate the spectral type and the luminosity and determine these quantities with an accuracy of about 0.1 subclass and 0.5 mag., respectively. For giants, the value of the color index R--I can be calculated with an accuracy corresponding to that of direct determinations and with practically no effect from interstellar reddening. The spectral type parameter is in good agreement with the TiO index measured by Wing, and the luminosity parameter agrees well with M/sub V/(K) determined by the Wilson--Bappu method. A three-dimensional classification of M stars may be possible by means of the present blue-visual quantities in combination with the infrared TiO and CN absorption indices determined by Wing