Note: some weak lines may be hard to measure in some stars, especially
given that we're working with low-resolution spectra.  Also note,
these are real stars and lines may be redshifted or blueshifted by
a few angstroms -- use Halpha or some other identifiable line to check.
Be careful about line blends (e.g., H-epsilon at 3970 and the Ca II H
line at 3969).  These are the only lines/elements you should worry 
about for this homework -- the stellar spectra we have aren't really
good enough for the weaker features, and some of these lines may be
tough.  At a minimum, concern yourself with H, Ca II, Mg I, and TiO.


HI: 6563, 4861, 4340, 4102, 3970, 3889, etc.
Ca I: 4227
Ca II: 3934, 3969
He I: 4471
He II: 4686
Mg I: 5170, 5183
Na I: 5890 
TiO (broad bands around): 6230, 6830, 7170, etc.