Sejong open cluster survey (SOS) - III. The young open cluster NGC 1893 in the H II region W8

We present a UBVI and Hα photometric study of the young open cluster NGC 1893 in the HII region W8 (IC 410 or Sh 2-236). A total of 65 early-type members are selected from photometric diagrams. A mean reddening of the stars is <E(B - V)> = 0.563 ± 0.083 mag. The published photometric data in the near- and mid-infrared passbands are used to test the reddening law towards the cluster, and we confirm that the reddening law is normal (RV = 3.1). Zero-age main-sequence fitting gives a distance modulus of V0 - MV = 12.7 ± 0.2mag, equivalent to 3.5 ± 0.3 kpc. From Hα photometry, 125 Hα emission stars and candidates are identified as pre-main-sequence (PMS). The lists of young stellar objects and X-ray sources published by previous studies allow us to select a large number of PMS members down to 1M⊙. Isochrone fitting in the Hertzsprung-Russell diagram gives a turn-off age of 1.5Myr and the median age of 1.9Myr from the PMS members with a spread of ~5Myr. We derive the initial mass function (IMF) for stars with mass larger than 1M⊙. The slope of the IMF (> =-1.3 ± 0.1) is well consistent with the Salpeter/Kroupa IMF. A total mass of the cluster appears to be in excess of 1300 M⊙. Finally, we estimate the mass accretion rate of 82 PMS members in the mass range of 0.6-5M⊙.