Photometric and spectroscopic study of the young open cluster NGC 1893

Abstract

We present uvby-beta CCD photometry of the field of the open cluster NGC 1893. Our photometry is deep enough to cover the complete main sequence B spectral type. We identify ~50 very likely members of the cluster down to spectral type B9-A0, some of which have much higher reddenings than the average. We derive a color excess E(b-y) = 0.33+-0.03 and a dereddened distance modulus V_0 - M_V = 13.9+-0.2. From the beta index, we identify several candidates as emission-line stars, for which we have obtained spectroscopy. Three of them display spectra corresponding to spectral type F, but showing H-alpha in emission. Photometric measurements in this and previous studies indicate strong variability. These characteristics show them to be pre-main-sequence stars of spectral type F. We also identify two likely Herbig Be stars. These results hint at the existence of a sizable pre-main-sequence population in NGC 1893.