A vertical motion map of the Galactic disk with TGAS (Gaia DR1)

In a separate post, I have sketched out what "Gaia DR1 (TGAS)" contains in astrophysical terms,
here is a zoom-in on a possible Gaia-day1 project:

Idea: can we make a map of the vertical motions of the Galactic disk, using only
proper motions and parallaxes; no spectroscopic information, to get spectrophotometric distances.

1) no spectroscopy --> take low-latitude stars (|b|<5deg),
    where all the vertical motion is in the plane of the sky.

2) we need stars with good photometric distance:
       these could be
      a) RC stars (can we pick them photometrically; I think we can?);
          there should be 60.000 RC stars at |b|<5deg in TGAS, with <D>~800pc
      b) MS stars (can we pick MS stars)? the plot below shows that we can eliminate non-MS stars by their parallax measurements (of we have a parallax accuracy of ~0.5mas

 

Note:  there are only 100 G-MS stars at |b|<5deg in TGAS, with <D>~100pc; that pins down the solar velocity?

3) that would lead to the following spatial distribution of the two tracers

which should be good enough to make a vertical disk corrugation map (by simple binning of the vertical proper motions).