A Survey of Near-Infrared Emission in Visual Reflection Nebulae

Abstract

We present a survey for extended 2.2 μm emission in 20 new visual reflection nebulae, illuminated by stars with temperatures of 3600-33,000 K. We detect extended 2.2 μm emission in 13 new nebulae, illuminated by stars with temperatures of 6800-33,000 K. For most of these 13 nebulae we have measured J - K, H - K, and K - L' and obtained surface brightness measurements at the wavelength of the 3.3 m emission feature. All the reflection nebulae with extended near-infrared emission in excess over scattered starlight have very similar near-infrared colors and show the 3.3 μm feature in emission with similar feature-to-continuum ratios. The 3.3 μm feature-to-continuum ratio ranges from ∼3 to ∼9, both within individual nebulae and from nebula to nebula, which suggests that the 3.3 μm feature and its underlying continuum arise from different materials, or from different ranges of sizes within a size distribution of particles. No dependence on the temperature of the illuminating star is seen in the near-infrared colors or 3.3 m feature-to-continuum ratio, over a factor of 2 in stellar temperature. This is similar to our previous IRAS results, in which we found no dependence of the ratio of 12 μm to 100 μm surface brightnesses in reflection nebulae illuminated by stars with temperatures of 5000-33,000 K.