M type stars show typically intense and broad TiO molecular absorption bands. These stars are thus very rewarding targets for low resolution spectroscopy using the Star Analyser. The band spectrum of TiO falls into the category of molecular spectrum known as vibronic. The structural features of this spectrum result from transitions involving vibrational substates of electronic states. These structural features can be, indeed, resolved using a SA-200 grism. However, the assignments of the structural features to distinct electronic and vibrational states can be quite cumbersome because the classical books in spectroscopy for amateur astronomers do not contain the relevant information (e.g. Walker's Spectroscopic Altas or Gray's and Corbally's Stellar Spectral Classification). A search in the primary literature is necessary and this task was very welcome to me in times of Corona lock-downs and cloudy nights:
The star for this purpose was U Ceti, which is a Mira variable star. It's spectrum was captured 01/10/21. Differential photometry using the green channel of my DSLR yielded an apparent brightness of 8.4 and shows that U Ceti is close to its maximum when compared with AAVSO data:
H gamma and H delta lines are clearly in emission due to shock waves:
The transitions between the electronic energy states could be assigned to the corresponding bands on the basis of this paper: http://adsabs.harvar...ApJS...26..313P
The resolution of the SA-200 was high enough to resolve the vibrational structure of most of the bands and allowed an assignment on the basis of this paper: https://iopscience.i...owBJzibF1DHah3E
There are still some unassigned TiO bands in the near infrared part of the spectrum around 8500 A and hints for other publications on this topic would be very welcome.
Edited by mwr, 13 January 2021 - 10:10 AM.