Presented at the AAVSO
Session on Mira Stars (part of the 85th Annual Meeting), November 1, 1996
The spectra of Mira
variables are extremely complex, with atomic lines in absorption and emission
and strong molecular bands, all varying with phase. Magnitudes measured by eye
or with wide-band photometry represent averages over so much information that
they are hard to interpret. Here narrow-band photometry can help, since filters
can be chosen both to avoid absorption bands and to measure some of the
strongest ones. Some surprising results that have been obtained for Miras by
this method are discussed. A simple three-color system measuring two
near-infrared continuum points and a TiO (titanium oxide) band can be use to
obtain a magnitude, a color index, and a spectral type for normal M-type Miras.
The light curves obtained with such a system can be interpreted in terms of
variations in luminosity, temperature, and diameter.