Spectra taken two nights ago (9/18) of X Oph show strong emission with inverse P Cygni profiles of the IR CaII triplet (849.8, 854.2, 866.2 nm), strong emission at H alpha, and noticable emission at H beta. The H alpha emission is blue shifted, but the underlying molecular band makes it difficult to tell whether there's a red side absorption component. H beta is probably also inverse P Cygni profile, but much weaker. X Oph is currently on the descending side of the light curve, slightly past maximum. None of the 13 current spectra in the AAVSO database show emission at either H line, although none are on the descending side or include the IR triplet, so it may be interesting to follow the development of the emission lines as the star dims.
These three spectra have been submitted to the database. These spectra were obtained with C-11, LHiRes with 1800 g/mm grating (R 12000 @ H alpha & orange 2nd order blocking filter for Ca II). The Ca II emission lines are the clearest but require the order blocking filter and aren't available with the 2400 g/mm grating. X Oph is currently about mag 7 visually & fading. I plan to continue monitoring it, as long as it's accessible, probably with lower resolution gratings, until early Nov. here in southern Arizona.
Interesting catch! Thank you for submitting these spectra to AVSpec. All three have been published:
I wonder what's causing the inverse P Cyg profile on the Ca II triplet. Do you frequently see such profiles in Miras?
Inverse P Cyg profiles are usually interpreted as in-flow onto the star. That could possibly be a result of the decreasing size of the star after maximum. I could also imagine blue shifted emission from a large flare that rises towards us, although that would have to be pretty bright. I only have a few LPV spectra that include any of the IR Ca Triplet lines, but (without having actually checked) I don't remember any showing strong emission or absorption lines of Ca II. So my answers are basically I don't know. I've started looking for information though.
As I understand it the blue shifted emission seen at certain phases in Miras is caused by shocks eg
https://iopscience.iop.org/article/10.1086/317131/pdf (Mg II in the UV)
It was also seen at H alpha in my spectra during the recent dimming of RW Cep
A shock in the…
A shock in the atmosphere sounds like a good explanation, caused by the reversal of flow at pulsation extremes. The shock emission would be shifted, but the underlying absorption line isn't. The H alpha profiles in the Gillet etal paper are consistent with what I see in X Oph, blue shifted emission (but indeterminate red profile). They don't show any absorption component, as seen in H beta & strongly at Ca II triplet, but that could be due to the Balmer decrement & the significantly lower excitation potential of the Ca II lines. The prediction would be then that the emission should strengthen as the star fades before weakening & disappearing. It will be interesting to see how the behavior of the Ca lines compares to H.
Also, I was mistaken in my earlier comment about the Ca lines. Of the few spectra I have of Miras that include the Ca IR triplet, they all show absorption lines, but no emission. I haven't looked up the phases of those spectra yet, however.