On the observability of individual Population III stars and their
  stellar-mass black hole accretion disks through cluster caustic transits
  Recent near-IR power-spectra and panchromatic Extragalactic Background Light
measurements provide upper limits on the near-IR surface brightness (SB>31
mag/arcsec^2) that may come from Pop III stars and accretion disks around
resulting stellar-mass black holes (BHs) in the epoch of First Light (z=7-17).
Physical parameters for zero metallicity Pop III stars at z>7 can be estimated
from MESA stellar evolution models through helium-depletion, and for BH
accretion disks from quasar microlensing results and multicolor accretion
models. Second-generation stars can form at higher multiplicity, so that BH
accretion disks may be fed by Roche-lobe overflow from lower-mass companions in
their AGB stage. The near-IR SB constraints can be used to calculate the number
of caustic transits behind lensing clusters that JWST and the 25~39 m
ground-based telescopes may detect for both Pop III stars and stellar mass BH
accretion disks. Because Pop III stars and stellar mass BH accretion disks have
sizes of a few x 10^-11 arcsec at z>7, typical caustic magnifications can be
mu=10^4~10^5, with rise times of hours and decline times of < 1 year for
cluster transverse velocities of v<1000 km/s. Microlensing by intracluster
medium objects can modify transit magnifications, and lengthen visibility
times. Depending on BH masses, accretion-disk radii and feeding efficiencies,
stellar-mass BH accretion-disk caustic transits could outnumber those from Pop
III stars. To observe Pop III caustic transits directly may require monitoring
3~30 lensing clusters to AB< 29 mag over a decade or more. Such a program must
be started with JWST in Cycle 1, and -- depending on the role of microlensing
in the Intra Cluster Light -- should be continued for decades with the GMT and
TMT, where JWST and the ground-based telescopes each will play a unique and
strongly complementary role.
