Using narrowband photometry to detect young brown dwarfs in IC 348

We report the discovery of a population of young brown dwarf candidates in the open star cluster IC 348 and the development of a new spectroscopic classification technique using narrowband photometry. Observations were made using FLITECAM, the First Light Camera for SOFIA, at the 3 m Shane telescope at Lick Observatory. FLITECAM is a new 1-5 μm camera with an 8′ field of view. Custom narrowband filters were developed to detect absorption features of water vapor (at 1.495 μm) and methane (at 1.66 μ) characteristic of brown dwarfs. These filters enable spectral classification of stars and brown dwarfs without spectroscopy. FLITECAM's narrow- and broadband photometry was verified by examining the color-color and color-magnitude characteristics of stars whose spectral type and reddening was known from previous surveys. Using our narrowband filter photometry method, it was possible to identify an object measured with a signal-to-noise ratio of 20 or better to within ±3 spectral class subtypes for late-type stars. With this technique, very deep images of the central region of IC 348 (H ∼ 20.0) have identified 18 sources as possible L or T dwarf candidates. Out of these 18, we expect that between 3 and 6 of these objects are statistically likely to be background stars, the remainder being true low-mass members of the cluster. If confirmed as cluster members, then these are very low mass objects (∼5M _Jup). We also describe how two additional narrowband filters can improve the contrast between M, L, and T dwarfs as well as provide a means to determine the reddening of an individual object.