SPECTROSCOPY OF MIRA VARIABLES AT DIFFERENT PHASES

Spectroscopic measurements of Mira variable stars, as a function of ph ase, probe the stellar atmospheres and underlying pulsation mechanisms , Modeling the atmospheres is difficult due to the hydrodynamic nature of the gas as deduced from the large light variations and velocity me asurements of various spectral lines. Many questions still need to be resolved concerning the atmospheres of these stars. Are the depths of formation of the molecular species such as TiO, VO, and ZrO produced i n an extended region above the layers where Balmer line emission occur s or below this shocked region? What is the explanation for the Balmer -line increment, where the strongest Balmer line at phase zero is H de lta and not H alpha? Furthermore, why is the H epsilon line virtually absent in the spectra of Miras when the other Balmer lines are strong? A new program of low resolution (1.08 Angstrom/pixel) spectroscopy fr om about 6000 Angstrom to 8750 Angstrom is presented in this paper. Th e spectra are taken in a region which includes H alpha, TiO, VO, ZrO, and the Ca II infrared (IR) triplet. Spectra of nine Mira variables ar e presented. Seven Mira variable stars (o Cet [Mira], U Ori, R Leo, V CVn, R CVn, V Boo, and chi Cyg) were observed at more than one phase. Two other Mira variables (R Tri and R Gem) were observed at a single p hase, but both show strong H alpha emission, In this paper, we investi gate the final question listed above by noting variations in the Ca II IR tripler in relationship with H alpha variations as a function of p hase. These preliminary observations suggest that H epsilon's observat ional characteristics result from an interaction of H epsilon photons with the Ca II H line. (C) 1997 American Astronomical Society.