  Context. While Class II stars have already accreted most of their mass, the
continued inflow of fresh material via Bondi-Hoyle accretion acts as an
additional mass reservoir for their circumstellar disks. This may explain the
observed accretion rates of pre-main- sequence (PMS) stars, as well as
observational inconsistencies in the mass and angular momentum balance of their
disks. Aims. Using a new simulation that reproduces the stellar IMF, we want to
quantify the role of Bondi-Hoyle accretion in the formation of Class II disks,
as well address the prospect of its observational detection with the James Webb
Space Telescope (JWST). Methods. We study the mass and angular momentum of the
accreting gas using passively-advected tracer particles in the simulation, and
we carry out radiative transfer calculations of near-infrared scattering to
generate synthetic JWST observations of Bondi-Hoyle trails of PMS stars.
Results. Gas accreting on Class II PMS stars approximately 1 Myr after their
formation has enough mass and angular momentum to strongly affect the evolution
of the preexisting disks. The accreted angular momentum is large enough to also
explain the observed size of Class II disks. The orientation of the angular
momentum vector can differ significantly from that of the previously accreted
gas, which may result in a significant disk warping or misalignment. We also
predict that JWST observations of Class II stars will be able to detect
Bondi-Hoyle trails with a 90% success rate with only 2 min exposure time, if
stars with accretion rates \dot{M} > 5e-10 Msol/yr and luminosity of L > 0.5
Lsol are selected.
