Kinematics and binaries in young stellar aggregates I. The trapezium system BD+00 degrees 1617 in Bochum 2

Internal kinematics, spectroscopic binaries and sal galactic motion are inv estigated for the trapezium system BD+00 degrees 1617 (which lies at the he art of the young open cluster Bochum 2) by means of 73 high resolution Eche lle+CCD spectra secured over the period 1994-98. Two of the three O-type me mber stars are found to be binaries on close and highly eccentric orbits of 6.8 and 11.0 day period. The spectra of the two binaries show large variat ions in the half-intensity and equivalent widths of the HeI absorption line s, which are intrinsic to the primaries and are not correlated to the orbit al phase. Astrometric and radial velocities exclude that one of the compone nt is leaving as a runaway star, but upper limits are still. compatible wit h the trapezium evaporating at very low relative velocities. The projected rotational velocities of the three-constituent O-type stars are low. This c onforms to expectations from the high frequency of binaries. The observed r adial velocity of Bochum 2 agrees with Hron (1987) expression for the Galax y rotation inside the:latter's quoted errors.