  The MYStIX project (Massive Young Star-Forming Complex Study in Infrared and
X-rays) provides a comparative study of 20 Galactic massive star-forming
complexes (d = 0.4 to 3.6 kpc). Probable stellar members in each target complex
are identified using X-ray and/or infrared data via two pathways: (1) X-ray
detections of young/massive stars with coronal activity/strong winds; or (2)
infrared excess (IRE) selection of young stellar objects (YSOs) with
circumstellar disks and/or protostellar envelopes. We present the methodology
for the second pathway, using Spitzer/IRAC, 2MASS, and UKIRT imaging and
photometry. Although IRE selection of YSOs is welltrodden territory, MYStIX
presents unique challenges. We combine IR spectral energy distribution (SED)
fitting with IR color cuts and spatial clustering analysis to identify IRE
sources and isolate probable YSO members in each MYStIX target field from the
myriad types of contaminating sources that can resemble YSOs: extragalactic
sources, evolved stars, nebular knots, and even unassociated
foreground/background YSOs. Applying our methodology consistently across 18 of
the target complexes, we produce the MYStIX IRE Source (MIRES) Catalog
comprising 20,719 sources, including 8686 probable stellar members of the
MYStIX target complexes. We also classify the SEDs of 9365 IR counterparts to
MYStIX X-ray sources to assist the first pathway, the identification of X-ray
detected stellar members. The MIRES catalog provides a foundation for follow-up
studies of diverse phenomena related to massive star cluster formation,
including protostellar outflows, circumstellar disks, and sequential star
formation triggered by massive star feedback processes.
