are in turn based in the IRAC color criteria of @Gutermuth:2008uc. Then, using the Chandra CSC catalogs we identified Class III sources as X-ray sources with infrared counterparts and no excess associated to circumstellar material. Finally, we identified additional Class I and Class II sources as X-ray CSC sources with infrared excess, by applying criteria that combine near-infrared and IRAC colors [see appendix of  @Gutermuth:2008uc].

Figure \[fig:hardness\] shows a $H-K$ vs. $K-[4.5]$ color-color diagram for all infrared sources that coincide in position with X-ray CSC sources. The colors of the symbols are indicative of the Hardness ratio, calculated from the hard and soft X-ray fluxes, $H$ and $S$, estimated from aperture photometry measurements, as $(H-S)/(H+S)$. It is clear that most of the sources have large hardness ratios, which indicates that in most cases X-ray sources are obscured by large amounts of dust which reduces the soft X-ray emission.

![$H-K$ vs. $K-[4.5]$ color-color diagram for CSC X-ray sources coinciding with an source in our infrared master catalog. Open diamond symbols are sources without an infrared excess indicative of a disk. Open square symbols indicate sources classified as Class I. Open triangle symbols indicate sources classified as Class II. The colors of 