interpretable, unsupervised models for spectroscopy?

Gaby Contardo (Flatiron) and I got in some research time at the end of the day today, visualizing data from SDSS-IV APOGEE data on stars on the upper red-giant branch. The question we are trying to ask is: Are there spectral differences between the stars that are going up the red-giant branch and stars that are going down? The problem we face is that we don't have a good training set. Is there some way we can find this, but unsupervised? I have an intuition that we can. Right now we are visualizing the data in photometric space, spectroscopic-parameter space, and PCA-amplitude space (where the PCA was performed on the spectral data).