Low-mass star formation and the initial mass function in IC 348

We have performed deep infrared and optical spectroscopy of virtually the entire stellar population within the 5′ × 5′ core of IC 348, measuring K (2.2 μm) band and optical spectral types that are in good agreement. We have also identified several sources that may be substellar depending on the choice of temperature scales and evolutionary tracks, with three particularly late-type objects (M7.5-M8) that are likely bonafide brown dwarfs. In conjunction with the theoretical evolutionary tracks of D'Antona & Mazzitelli, the H-R diagram indicates a spread in ages from 0.5 to 10 Myr, with most of the core star formation occurring in the last 3 Myr. Using K-band imaging to provide a completeness correction to the spectroscopic sample, we arrive at an initial mass function (IMF) that matches that of Miller & Scalo from 0.25 to 3 M_⊙. The IMF appears to fall slowly from 0.25 M_⊙ to the hydrogen burning limit, slightly below the IMF of Miller & Scalo, which is flat in logarithmic units (as compared to slopes of ∼1.35 and -2.6 for Salpeter and Scalo). Correction for unresolved binary systems could steepen the slope of the low-mass IMF by about 0.5, which implies a single-star IMF that is roughly flat below 0.25 M_⊙. The low-mass IMF in IC 348 is similar to that derived in studies of most other young clusters, implying that the IMF does not vary dramatically among clusters of differing environments; however, the derived IMF is dependent on the evolutionary tracks and the detailed shape of the IMF should be viewed with caution until these models are tested against observations, particularly at low masses (<0.3 M_⊙) and young ages (<10 Myr). Hα and Brγ emission strengths are consistent with predictions of magnetospheric accretion models of Muzerolle, Calvet, & Hartmann for accretion rates of 10^-9-10^-8 M_⊙ yr^-1. Combining our data with the Hα measurements of Herbig, we find that ∼25% of stars within the core of IC 348 and younger than 3 Myr exhibit signatures of disks in the form of strong Hα (>10 Å) or Brγ (>1 Å) emission or X-band continuum veiling (r_K ≥ 0.5). Since no sources older than 3 Myr show evidence for massive disks, disk lifetimes in the core of IC 348 appear to be shorter than those observed in Taurus or in the outer regions of IC 348.