Near-Infrared Observations of Barnard's Merope Nebula (IC 349)

We report results of \it JHK^' and narrowband near-infrared photometry of the reflection nebula IC 349 in the Pleiades. The data fail to show evidence for shock- or fluorescence-induced emission from the v=1-0 S(1) and v=2-1 S(1) transitions of H₂ and the 2-0 band head of ¹²CO expected of species illuminated by soft-UV photons from the nearby star 23 Tauri. The lack of significant gas content supports the conclusion that there is no protostellar object within the nebula's dusty envelope; a new observational determination of the upper limit on the luminosity of a hypothetical protostar gives -3.73 ≤ log ((L)/(L_{⊙ )}) ≤ -3.58. Small-particle scattering in the nebular medium becomes negligible by K^' (λ ₀ = 2.114 μ m), suggesting that dust grain sizes are compatible with cold molecular cloud composition. Total mass estimates, based on both diffusion of assumed primordial gas in the nebula and integration of the observed dust column, range between 3×10^-7 M_⊙ ≤ M ≤ 8×10^-1 M_⊙ . These results point toward an origin for IC 349 as a substellar-mass cloudlet escaped from a larger cloud complex, whose original gas content has been lost likely due to thermal diffusion.

We acknowledge the Astrophysical Research Consortium (ARC) and Planetary Science Institute (PSI) for support of this work.