NGC 6383 - I. The central core

NGC 6383 is a young open cluster with a strong central core and a possible extended halo. From photoelectric UBV photometry and MK spectroscopy of stars in the core, we find the following; reddening, $$E_{B-V}=0.33\pm0.02\enspace \text {(sd)}$$, apparent distance modulus $$V-M_V=11.9\pm0.25$$, distance d = 1.5 ± 0.2 kpc, radius R = 1.25 arcmin (which corresponds to 0.54 pc at the derived distance), and an age of 1.7 ± 0.4 Myr. In the core, we find 21 probable cluster members brighter than B = 14.7, compared with 18 ± 4 expected from star counts. Eight stars in the core appear to be pre-main sequence stars. The central star, HD 159176 (a spectroscopic binary consisting of two 07 V stars, each of mass 35 ± 5 M_⊙, radius 15 ± 2 R_⊙, and age 2.8 ± 0.5 Myr) is probably older than the rest of the cluster core and might have initiated star formation in the core and beyond.