An Infrared/X-ray Survey for New Members of the Taurus Star-Forming
  Region
  We present the results of a search for new members of the Taurus star-forming
region using data from the Spitzer Space Telescope and the XMM-Newton
Observatory. We have obtained optical and near-infrared spectra of 44 sources
that exhibit red Spitzer colors that are indicative of stars with circumstellar
disks and 51 candidate young stars that were identified by Scelsi and coworkers
using XMM-Newton. We also performed spectroscopy on four possible companions to
members of Taurus that were reported by Kraus and Hillenbrand. Through these
spectra, we have demonstrated the youth and membership of 41 sources, 10 of
which were independently confirmed as young stars by Scelsi and coworkers. Five
of the new Taurus members are likely to be brown dwarfs based on their late
spectral types (>M6). One of the brown dwarfs has a spectral type of L0, making
it the first known L-type member of Taurus and the least massive known member
of the region (M=4-7 M_Jup). Another brown dwarf exhibits a flat infrared
spectral energy distribution, which indicates that it could be in the
protostellar class I stage (star+disk+envelope). Upon inspection of archival
images from various observatories, we find that one of the new young stars has
a large edge-on disk (r=2.5=350 AU). The scattered light from this disk has
undergone significant variability on a time scale of days in optical images
from the Canada-France-Hawaii Telescope. Using the updated census of Taurus, we
have measured the initial mass function for the fields observed by XMM-Newton.
The resulting mass function is similar to previous ones that we have reported
for Taurus, showing a surplus of stars at spectral types of K7-M1 (0.6-0.8
M_sun) relative to other nearby star-forming regions like IC 348, Chamaeleon I,
and the Orion Nebula Cluster.
