Sejong open cluster survey (SOS) - II. IC 1848 cluster in the H II region W5 west

Abstract

IC 1848 is one of the young open clusters in the giant star-formingCas OB6association. Several interesting aspects relating to star formation processes in giant star-forming regions attracted us to study the initial mass function (IMF), star formation mode and properties of pre-mainsequence (PMS) stars. A UBVI and Hα photometric study of the young open cluster IC 1848 was conducted as part of the 'Sejong Open Cluster Surve'y. We have selected 105 earlytype members from photometric diagrams. Their mean reddening is (E(B-V))=0.660±0.054 mag. Using the published photometric data with near-and mid-infrared archival data we confirmed the normal reddening law (RV = 3.1) towards the cluster (IC 1848). A careful zero-age main-sequence fitting gives a distance modulus of V0-MV = 11.7±0.2mag, equivalent to 2.2± 0.2 kpc. Hα photometry and the list of young stellar objects identified by Koenig et al. permitted us to select a large number of PMS stars comprising 196 Hα emission stars, 35 Hα emission candidates, 5 Class I, 368 Class II and 24 transition disc candidates. From the Hertzsprung-Russell diagram using stellar evolution models, we estimate an age of 5 Myr from several evolved stars and 3 Myr from the PMS stars. The IMF was derived from stars with mass larger than 3⊙, and the slope is slightly steeper (Γ = -1.6±0.2) than the Salpeter/Kroupa IMF. Finally, we estimated the mass accretion rate of PMS stars with an ultraviolet excess. The mean mass accretion rate is about 1.4×10-8M⊙yr-1 in the mass range of 0.5-2M⊙ whereas intermediate-mass stars (≥=2.5M⊙) exhibit a much higher accretion rate of M>10-6M⊙yr-1.