  We investigate the feasibility of detecting quiescent black hole X-ray
binaries using optical photometric techniques. To test this we employ a
combination of r-band and Halpha filters currently available at the Roque de
los Muchachos Observatory. Photometric observations of four dynamical black
holes (GRO J0422+320, A 0620-00, XTE J1118+480 and XTE J1859+226) at
SNR>~35-50, supplemented with near simultaneous spectroscopic data, demonstrate
that it is possible to recover the FWHM of the Halpha emission line to better
than 10% for targets with a wide range of line EWs and down to magnitude r~22.
We further explore the potential of our photometric system to disentangle other
populations of compact stars and Halpha emitters. In particular, we show that
HAWKs, a survey designed to unveil quiescent black holes, will also provide a
detailed census of other Galactic populations, most notably short period
(eclipsing) cataclysmic variables, neutron star X-ray binaries and
ultra-compact binaries.
