Formation Timescales for High-Mass X-ray Binaries in M33
  We have identified 55 candidate high-mass X-ray binaries (HMXBs) in M33 using
available archival {\it HST} and {\it Chandra} imaging to find blue stars
associated with X-ray positions. We use the {\it HST} photometric data to model
the color-magnitude diagrams in the vicinity of each candidate HMXB to measure
a resolved recent star formation history (SFH), and thus a formation timescale,
or age for the source. Taken together, the SFHs for all candidate HMXBs in M33
yield an age distribution that suggests preferred formation timescales for
HMXBs in M33 of $<$ 5 Myr and $\sim$ 40 Myr after the initial star formation
episode. The population at 40 Myr is seen in other Local Group galaxies, and
can be attributed to a peak in formation efficiency of HMXBs with neutron stars
as compact objects and B star secondary companions. This timescale is preferred
as neutron stars should form in abundance from $\sim$ 8 M$_{\odot}$
core-collapse progenitors on these timescales, and B stars are shown
observationally to be most actively losing mass around this time. The young
population at $<$ 5 Myr has not be observed in other Local Group HMXB
population studies, but may be attributed to a population of very massive
progenitors forming black holes very early on. We discuss these results in the
context of massive binary evolution, and the implications for compact object
binaries and gravitational wave sources.
