Photometry of CN15/16/17. Black dots are stars identified in J, H and K_S bands, gray dots (upper-right: only) are stars identified only in H and K_S. YSOs are shown in red (class I), green (class II) and yellow (reddened class II). Among the YSOs, the circles are sources with JHK_S photometry, the squares are objects with only HK_S detections, the diamonds are objects with only K_S and the crosses are objects detected neither in J, H or K_S. The black arrows in the near-infrared diagrams are the reddening vectors for A_KS = 0.5 mag, according to the Rieke & Lebofsky (1985) reddening law (suitable for these wavelengths). Upper left: K_S vs. J − K_S diagram. Upper right: K_S vs. H − K_S diagram. Lower left: J − H vs. H − K_S diagram. Lower right: IRAC [3.6]–[4.5] vs. [5.8]–[8.0] color–color diagram. The cyan box indicates the locus of class II objects according to Allen et al. (2004). The two black lines are parallel to the reddening vector derived by the Mathis (1990) extinction law (suited for mid infrared wavelengths) and enclose the region of reddened class II objects according to Megeath et al. (2004).