finding emission lines (and other oddities) in hot stars

I showed my robust spectral decomposition (dimensionality reduction) and residuals to the MPIA Binaries group today. There was much useful feedback (including that my H-gamma was actually H-delta; embarassing!). One comment was that the model isn't truly a causal separation between star and lines, so there will be some mean lines in the star model; lines aren't entirely outliers. That's true! The group suggested that I iterate to remove stars with lines from the training set.

After the meeting, I implemented some of that, but problems like this have a pathology: If you carefully remove stars with high residuals at some wavelength, then the training data will be deficient, or low, at that wavelength. And then the model will go lower, and then more stars will have excess at that wavelength and: Disaster. So when I implemented, I required a 2-sigma deviation, and I removed both high and low outliers. I don't know if this will work, but I am testing now.