  Accurate age and mass determinations for young pre-main sequence stars are
made challenging by the presence of large-scale starspots. We present results
from a near-infrared spectroscopic survey of ten T-Tauri Stars in Taurus-Auriga
that characterize spot filling factors and temperatures, the resulting effects
on temperature and luminosity determinations, and the consequences for inferred
stellar masses and ages. We constructed composite models of spotted stars by
combining BTSettl-CIFIST synthetic spectra of atmospheres to represent the
spots and the photosphere along with continuum emission from a warm inner disk.
Using a Markov-Chain Monte-Carlo algorithm, we find the best-fit spot and
photospheric temperatures, spot filling factors, as well as disk filling
factors. This methodology allowed us to reproduce the 0.75-2.40 micron stellar
spectra and molecular feature strengths for all of our targets, disentangling
the complicated multi-component emission. For a subset of stars with
multi-epoch observations spanning an entire stellar rotation, we correlate the
spectral variability and changes in the filling factors with rotational periods
observed in K2 and AAVSO photometry. Combining spot-corrected effective
temperatures and Gaia distances, we calculate luminosities and use the Stellar
Parameters of Tracks with Starspots (SPOTS) models to infer spot-corrected
masses and ages for our sample of stars. Our method of accounting for spots
results in an average increase of 60% in mass and a doubling in age with
respect to traditional methods using optical spectra that do not account for
the effect of spots.
