Light Curves of Mira Variables at 1.04 Microns

Near-infrared light curves have been compiled for twenty-five Mira variables of types M and S from photoelectric measurements of the radiation contained in a narrow bandpass near 1.04 An average of twenty-seven observations per star was collected over a S-year interval. The 1(104) magnitudes are almost completely free from molecular blanketing; the amplitudes at this wavelength are typically only 1.0 mag and never exceed 2.5 mag. Observations at the same phase in different cycles usually agree to within 0.1 mag, hut differences as large as 0.5 mag have been recorded. Maximum light in 1(104) occurs approximately 0.1 period after visual maximum. Light curves at different infrared wavelengths with varying degrees of blanketing all have the same general character as the visual light curve of each star, although the amplitude depends upon the amount of blanketing. Spectral types have been derived from measurements of TiO and VO hands made simultaneously with the measurements of 1(104). We give 595 spectral types for the twenty-two M and mild S stars and a judgment as to each star's most representative type at minimum light. Pronounced humps on the rising branch, near phase 0.7, were observed in many stars; several stars have shown humps in some cycles but not in others. They cannot be attributed to changes in blanketing, since they are as evident in 1(104) as at other wavelengths and since the spectral type actually stays constant at its latest value during the rapid rise from minimum to secondary maximum. The rise from minimum seems to be associated with an increase in photospheric temperature, while the delay in the resulting dissociation of TiO and VO emphasizes the extreme stratification of these atmospheres.