In S star spectra ZrO almost entirely replaces the TiO absorption. The chemistry behind this phenomenon is quite interesting and well explained in Richard Walker's excellent chapter on "Spectral Class S on the AGB" in his "Spectroscopic Atlas" Version 3.0 (2012). In this chapter he gives some valuable hints for the observation of S-class stars but he states at the same time that "the dissapointment is great for beginners, when in low resolution spectra, if at all, only weak signs of zirconium can be seen". I have chosen TV Aur (Class S 7.5 Zr 5) to test wether signs of Zr can be detected with my low resolution SA-100 setup (20 frames at 200 sec. each were stacked).
Several band heads of ZrO were indeed detectable. To distinguish these ZrO bands from TiO bands, I have compared this spectrum with a spectrum of Mira (o cet; M-class), which shows intense TiO bands:
Some ZrO bands of TV Aur are separated from the TiO bands of Mira and do not overlap. M- and S-class can thus clearly be distinguished.
To check for artefacts, I have compared my spectrum with a ProAm spectrum of TV Aur (ALPY 600) from J Foster https://britastro.or...ment=&plot=Plot
Finally, I have determined the magnitude (v-T) of TV Aur and compared it with recently available AAVSO data:
So my spectrum has apparently been recorded around the minimum of TV Aur.
Again, it would be interesting to see other SA-100 spectra of S-class stars (perhaps of the SX(e) class; the showcase object R Cyg is obstructed by the roof of my neighbour's house).
I have just ordered the SA-200, so this is probably the last post of my beginner SA-100 era.
Edited by mwr, 01 December 2019 - 11:43 AM.