spectro-aras.com

Long Period Variable stars are classified as Mira, Semiregular or Irregular types.
https://www.aavso.org/media/jaavso/2840.pdf
Often the arbitrary classes do not reflect physical differences (between RGB or AGB stars, fundamental or overtone pulsators, carbon rich or oxygen rich, for example).
Photometry on thousands of stars! in the LMC has shown that brightness increases with the period length. Mira variables often have the longest periods and greatest luminosities (by definition) but often their position in the period/luminosity plane overlap with other variable types. Mira variables pulsate in the fundamental mode. Other types may pulsate in the fundamental mode and/or first overtone mode.
http://iopscience.iop.org/article/10.10 ... /2/167/pdf
Red Giant Branch stars may also pulsate in the fundamental mode with long periods similar to Mira variables
https://arxiv.org/pdf/1706.09166.pdf

I'm not sure that all the details are worked out, but I think that cool stars with a sufficient hydrogen ionization zone can pulsate in the fundamental mode via the kappa mechanism.
https://en.wikipedia.org/wiki/Kappa_mechanism
One result of this pulsation are shock waves that generate Balmer emission lines that change with the pulsation phase.
Note this survey of Mira variables that suggests that a Balmer increment (H-delta>H-gamma) is found for stars M4 and later.
https://arxiv.org/pdf/1708.04703.pdf

My intent is to observe some of these variable stars with my Alpy 600. Any comments or criticisms are welcome.
I have found the AAVSO to be a great place to find targets
https://www.aavso.org/sites/default/fil ... in2018.pdf

First up is R Leonis (for all but the first spectra I used Eta Leo as the reference)
Mira, period 309.95 days.
It looks like my observation coincided with a relatively brighter maximum Here is recent AAVSO data

Two weeks later, here is the standard Eta Leo (reference in blue is A0I) 03/17/2018 Here is R Leo

A week later 03/24/2018
Eta Leo reference and R Leo

on 03/26/2018
Eta Leo reference and R Leo

On 03/31/2018
Eta Leo reference R Leo

04/07/2018 was a little after maximum, when Balmer emission is likely at maximum, but the results were a little surprising, so any opinions are welcome.
Here is the reference, Eta Leo, 20 images of 12 s, the same as all the others It looks very similar to me. In ISIS the rms for the calibration was often between 0.15 and 0.2.
Here is R Leo Not only have the Balmer intensities increased and higher order Balmer lines are visible, the blue continuum seems to have increase.
Here is an overlay with the spectrum of 03/17/2018 and here is a zoom on the Balmer emissions Notice also the blue shift in the Balmer emissions on 04/07/2018 (black) compared to 03/17/20 (blue).
I could rationalize this as the earlier redshifted Balmer emission as being material falling back towards the star, away from us, that is ionized by the precursor (ahead of the shock front). When the shock passes, the material is then moving towards us and is blueshifted. Does that explanation sound reasonable? Is it possible that I can see that with the Alpy 600?

Is the enhanced blue continuum real or an artifact?

Thanks for any opinions.

Two days later...
Eta Leo reference and R Leo The increase in the UV part of the continuum seems much less.

5 days later, slowly decreasing
Eta Leo R Leo A week after this.
Eta Leo and R Leo

And finally, last night under a bright moon.
Eta Leo and R Leo, slowly dimishing

Great!
It will be interesting to see the graph EW = f(JD)
All the best,
François