our analysis, we combined high-quality deep near-IR observations with images and catalogs from the Spitzer Cygnus-X Legacy Survey [@Hora:2009aa hereafter CXLS]. We also made use of archival data from the Chandra X-Ray Observatory. By combining these datasets we prepared a multi-wavelength photometry catalog for the stellar population in DR15, which we use to reconstruct the history of star formation in the region.

Near Infrared Observations {#obs:nir}
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Near-infrared images of the Cygnus-X DR15 region were obtained with the OMEGA 2000 camera at the 3.5m telescope of the Calar Alto Observatory, atop Sierra de los Filabres in Almería, Spain, during the nights of February 2nd and March 3rd, 2010, with excellent weather conditions. The dataset consists of 900 second co-added exposures in the $J$, $H$ and $K$ bands (1.209, 1.648 and 2.208 $\mu$m, respectively). The seeing values –measured directly from the average FWHM of stars in the final reduced mosaics– were 1.17, 1.13 and 0.98$\arcsec$ in $J$, $H$ and $K$, respectively.

The reduction of the images and the extraction of Point Spread Function (PSF) photometry lists for all bands were performed with custom `IRAF` pipelines, and the `SExtractor` algorithm [@Bertin:1996aa], following a methodology equivalent to the one described in @Roman:2010aa.

We 