Circumstellar Disk Lifetimes In Numerous Galactic Young Stellar Clusters
  Photometric detections of dust circumstellar disks around pre-main sequence
(PMS) stars, coupled with estimates of stellar ages, provide constraints on the
time available for planet formation. Most previous studies on disk longevity,
starting with Haisch, Lada & Lada (2001), use star samples from PMS clusters
but do not consider datasets with homogeneous photometric sensitivities and/or
ages placed on a uniform timescale. Here we conduct the largest study to date
of the longevity of inner dust disks using X-ray and 1--8 micrometre infrared
photometry from the MYStIX and SFiNCs projects for 69 young clusters in 32
nearby star-forming regions with ages t<=5 Myr. Cluster ages are derived by
combining the empirical AgeJX method with PMS evolutionary models, which treat
dynamo-generated magnetic fields in different ways. Leveraging X-ray data to
identify disk-free objects, we impose similar stellar mass sensitivity limits
for disk-bearing and disk-free YSOs while extending the analysis to stellar
masses as low as M~0.1 Mo. We find that the disk longevity estimates are
strongly affected by the choice of PMS evolutionary model. Assuming a disk
fraction of 100% at zero age, the inferred disk half-life changes
significantly, from t1/2 ~ 1.3--2 Myr to t1/2 ~ 3.5 Myr when switching from
non-magnetic to magnetic PMS models. In addition, we find no statistically
significant evidence that disk fraction varies with stellar mass within the
first few Myr of life for stars with masses <2 Mo, but our samples may not be
complete for more massive stars. The effects of initial disk fraction and
star-forming environment are also explored.
