A STUDY OF STELLAR POPULATION IN THE ORION CLUSTER - NGC-1999 VICINITY

UBYRI' photometric data for 167 stars of 5,7-15,m7V, projected on the L 1642 dark cloud in the zone -6 05--7-degrees-00' are presented. The photometric catalogue was made using the Mt. Maidanak 60-cm reflector with pulse-counting photometer in 1978-1990. The far away background objects are utterly excluded due to star selection. 83 cluster members were selected from neighbouring stars. The selection method is described. The H-R diagram supplies the arguments for the existence of the main-sequence dwards branch as for 15,(m)OV detected recently by Shevchenko. Most B3-B9 stars lie on the pre-main sequence. The stars with enhanced luminosity are mainly K0-K7, the great number being variable and emission objects. It is noted that 5 Ae/Be Herbig stars, i. e. almost the whole totality of the Orion cluster objects, are concentrated in the region studied. That no relation is found between the stars peculiarities (IR, UV-excess, variability, line emission) and spectral type, suggests as a possible explanation that any <<evolutionary succession>> is absent in the cluster. 7 new objects are suspected in variability, including the Ae-Herbig star P2649. The luminosity function in discussed. Authors assume that the enhanced luminosity and nonstability of the cluster members are caused by the accretion from the circumstellar discs and accompanying phenomena. The appreciable numder os stars which are kernels of accretion formations seem to lie on the main sequence.