That's a nice solution.  However, I'm not sure I fully agree.  The functions temp_em() and goes_chianti_tem() are very likely going to be used off the command line and not just written in scripts.  In which case typing out the fully word "photospheric" or "coronal" every time will be an annoying.  Although we want people to write good readable code, what's the trade-off for easy usage?  This is a philosophical issue which perhaps has been discussed in sunpy.  If so, what did you decide?