The Pan-STARRS1 Proper-motion Survey for Young Brown Dwarfs in Nearby
  Star-forming Regions. I. Taurus Discoveries and a Reddening-free
  Classification Method for Ultracool Dwarfs
  We are conducting a proper-motion survey for young brown dwarfs in the
Taurus-Auriga molecular cloud based on the Pan-STARRS1 3$\pi$ Survey. Our
search uses multi-band photometry and astrometry to select candidates, and is
wider (370 deg$^{2}$) and deeper (down to $\approx$3 M$_{\rm Jup}$) than
previous searches. We present here our search methods and spectroscopic
follow-up of our high-priority candidates. Since extinction complicates
spectral classification, we have developed a new approach using low-resolution
($R \approx 100$) near-infrared spectra to quantify reddening-free spectral
types, extinctions, and gravity classifications for mid-M to late-L ultracool
dwarfs ($\approx 100-3$ M$_{\rm Jup}$ in Taurus). We have discovered 25
low-gravity (VL-G) and the first 11 intermediate-gravity (INT-G) substellar
(M6-L1) members of Taurus, constituting the largest single increase of Taurus
brown dwarfs to date. We have also discovered 1 new Pleiades member and 13 new
members of the Perseus OB2 association, including a candidate very wide
separation (58 kAU) binary. We homogeneously reclassify the spectral types and
extinctions of all previously known Taurus brown dwarfs. Altogether our
discoveries have thus far increased the substellar census in Taurus by $\approx
40\%$ and added three more L-type members ($\approx 5-10$ M$_{\rm Jup}$). Most
notably, our discoveries reveal an older ($>$10 Myr) low-mass population in
Taurus, in accord with recent studies of the higher-mass stellar members. The
mass function appears to differ between the younger and older Taurus
populations, possibly due to incompleteness of the older stellar members or
different star formation processes.
