Age Spreads and Systematics in {\lambda} Orionis with Gaia DR2 and the
  SPOTS tracks
  In this paper we investigate the robustness of age measurements, age spreads,
and stellar models in young pre-main sequence stars. For this effort, we study
a young cluster, $\lambda$ Orionis, within the Orion star-forming complex. We
use Gaia data to derive a sample of 357 targets with spectroscopic temperatures
from spectral types or from the automated spectroscopic pipeline in APOGEE Net.
After accounting for systematic offsets between the spectral type and APOGEE
temperature systems, the derived properties of stars on both systems are
consistent. The complex ISM, with variable local extinction, motivates a
star-by-star dereddening approach. We use a spectral energy distribution (SED)
fitting method calibrated on open clusters for the Class III stars. For the
Class II population, we use a Gaia G-RP dereddening method, minimizing
systematics from disks, accretion, and other physics associated with youth. The
cluster age is systematically different in models incorporating the structural
impact of starspots or magnetic fields than in nonmagnetic models. Our mean
ages range from 2-3 Myr (nonmagnetic models) to 3.9$\pm$0.2 Myr in the SPOTS
model (f=0.34). We find star-by-star dereddening methods distinguishing between
pre-MS classes provide a smaller age spread than techniques using a uniform
extinction, and infer a minimum age spread of 0.19 dex and a typical age spread
of 0.35 dex after modelling age distributions convolved with observed errors.
This suggests that the $\lambda$ Ori cluster may have a long star formation
timescale and that spotted stellar models significantly change age estimates
for young clusters.
