Distant halo giants using PS1 (incl. proper motions)

Can we use PS1 & (who else?) WISE colors to identify distant halo giants,
using PS1 to weed-out proper motions?
We want tip-of-the-RGB stars that are bright enough for good follow-up, i.e. m_r<19.5,
which should also provide good PM constraints.
What are the candidate source densities?

Things to be checked:
   -- to what distance do we reach with such constraints
   -- what IR photometry coverage do we have and how useful are these colors
   -- what PM do we expect?
   -- probably use either galaxy or Besancon models to explore