Stellar spectroscopy in NGC 6611: Binary frequency and new spectral types of several early type stars

We present a study of radial velocities of the ten earliest type stars in t he young open cluster NGC 6611. With the radial velocity measurements we ha ve examined the possible existence of spectroscopic binaries. Among the stu died stars, one is definitely a short period single-lined binary, and two o ther stars are longer period double-lined binaries. Three other stars may a lso be multiple. The mean radial velocity of the cluster stars is found to be similar to the value determined from the recombination lines of the inte rstellar gas in the related HII region. Additionally, we have also determin ed spectral types for fainter stars in the region of NGC 6611, finding seve ral B type stars to be possible cluster members.