Hi Tony,
That is the broad Raman scattered O VI line at 6825A. See http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1989A%26A…211L..31S&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf
It was a mystery for a long time until Schmid published his paper. It’s a trademark of symbiotic stars with high excitation nebulae.
David