1997A&A...327..125M

The fourteen brightest OB stars of the Trumpler 37 Cluster have been observed in the V,R,I,J,H,K photometric bands. These have been used to derive accurate measurements of the quantity R_V=A_V/E(B-V). Different from previous studies it is found that <R_V> in Trumpler 37 is close to the mean interstellar value of 3.1. Most of the reddening towards Trumpler 37 is found to be of foreground origin. This is consistent with the lack of variations, observed by us, of R_V with the projected distance from the center of the cluster. In two highly reddened stars of the cluster, whose reddening is certainly mostly local, the observed R_V is lower than the mean interstellar value of 3.1. This is to be compared with the behaviour of the Trapezium stars in Orion, whose R_V is quite above such value whereas the age of the cluster is similar to the one of Trumpler 37.