Color magnitude diagram of stars searched in a region centered in S169. Black dots are young spectral type stars with different reddening values (see text in Sect. 5). Magenta, green, and yellow crosses represent the O9V, B1V, and B2V (or later) stars, all of them ionizing candidate stars displayed with the same colors in Fig. 10. Green and black curves represent the MS shifted according to the distance modulus adopted with and without reddening, respectively. Red line indicates the normal reddening path (R_v = 3.1).