The WFC3 Galactic Bulge Treasury Program: Metallicity Estimates for the
  Stellar Population and Exoplanet Hosts
  We present new UV-to-IR stellar photometry of four low-extinction windows in
the Galactic bulge, obtained with the Wide Field Camera 3 on the Hubble Space
Telescope (HST). Using our five bandpasses, we have defined reddening-free
photometric indices sensitive to stellar effective temperature and metallicity.
We find that the bulge populations resemble those formed via classical
dissipative collapse: each field is dominated by an old (~10 Gyr) population
exhibiting a wide metallicity range (-1.5 < [Fe/H] < 0.5). We detect a
metallicity gradient in the bulge population, with the fraction of stars at
super-solar metallicities dropping from 41% to 35% over distances from the
Galactic center ranging from 0.3 to 1.2 kpc. One field includes candidate
exoplanet hosts discovered in the SWEEPS HST transit survey. Our measurements
for 11 of these hosts demonstrate that exoplanets in the distinct bulge
environment are preferentially found around high-metallicity stars, as in the
solar neighborhood, supporting the view that planets form more readily in
metal-rich environments.
