I spent most of the day reading and summarizing published work on tidal streams as possible measuring devices for massive substructure in the Galaxy halo. So far I have found no analytic calculations, and no investigations of individual features in individual streams.
In conversation with Tsalmantza, I worked out a fully empirical methodology for constructing a set of spectral archetypes that fully
represents all of the galaxy spectra in the SDSS. Before today, the only methodology I had involved theoretical spectral fitting. But the work we have been doing on constructing a reliable and useful PCA subspace may actually pay off (despite my dislike of PCA).