6 Conclusions

Our determination for the cluster distance and reddening confirm earlier studies. From the small dispersion around the cluster main sequence in Fig. 3 we may conclude that most of the stars in Fig. 1 and Table 2 are physical members of NGC 6604. From the spatial concentration of early spectral types in Table 3, the diameter of NGC 6604 is of the order of $\sim$10 arcmin. The $E_{B-V}= 1.02\pm0.01$ reddening follows the standard R_V = 3.1 reddening law, with no evidence for a marked differential reddening over this cluster. The cluster age is estimated as 5 10⁶ years. Our observations do not go faint enough to address the reality of the pre-ZAMS objects suspected by FD. Extrapolating from the turn-on tracks by Stauffer et al. (2000), pre-ZAMS objects in NGC 6604 should have $V\geq$ 16, corresponding to a ZAMS spectral type somewhat later than A0. Thus, star #14 (which is $\sim$2 mag off the ZAMS) looks too bright both for a pre-ZAMS object and for an equal-mass binary, and therefore it should be a field star.