  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.
