Photometry and Spectrophotometry of Long-Period Variables.

Photoelectric (UB V) and low-dispersion spectroscopic observations of twenty-nine Mira-type stars, twelve semiregular M-type variables, and several non-variable and irregularly variable M giants are reported. The B and V magnitudes, and consequently the B - V and U - B color indices of all M giants are strongly affected by the absorption in the TiO bands. The U - B colors of Mira-type variables are also correlated with the intensity of the Balmer emission lines. The effect of TiO on the magnitudes and colors of M giants (in the UB V system) is determined from the observational U - B versus S and B - V versus S relations where S is spectral t e) combined with theoretical, black body, U - B versus and B - V versus T relations. Rediscussion of radiometric data by Pettit and Nicholson (1933) together with the present UB V data shows that the amplitudes of the light-curves of Mira-type stars at different wavelengths can be explained by the variations of temperatures and rad of these stars together with the effects of TiO absorption. Mean absolute bolometric magnitudes of Mira-type stars are determined from recent data on their absolute visual magnitudes (Osvalds and Risley 1961), by allowance for the effect of the TiO absorption and for bolometric corrections. Variables of later spectral types and longer periods, which were known to be fainter in Mv, appear to be brighter in than variables of earlier spectra and shorter periods. The mean absolute bolometric magnitudes (at maximum) range from about = -4 for (S) = M1.9 and (P) = 131 days to about M = -6.6 for (S) = M6.5 and (P) 500 days.