A Survey of Near Infrared Emission in Visual Reflection Nebulae

We present a survey for extended 2.2 $\mu$m emission in 20 new visual reflection nebulae, illuminated by stars with temperatures of 3,600 — 33,000 K. We detect extended 2.2 $\mu$m emission in 13 new nebulae, illuminated by stars with temperatures of 6,800 – 33,000 K. For most of these 13 nebulae we have measured $J-K$, $H-K$, and $K-L^{\mathrm{\prime }}$, as well as obtaining surface brightness measurements at the wavelength of the 3.3 $\mu$m emission feature. All of the reflection nebulae with extended near infrared emission in excess over scattered starlight have very similar near infrared colors and show the 3.3 $\mu$m feature in emission with similar feature-to-continuum ratios. The 3.3 $\mu$m feature-to-continuum ratio ranges from $\sim$3 to $\sim$9, both within individual nebulae and from nebula to nebula, which suggests that the 3.3 $\mu$m 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 $\mu$m feature-to-continuum ratio, over a factor of two in stellar temperature. This is similar to our previous IRAS results, in which we found no dependence of the ratio of 12 $\mu$m to 100 $\mu$m surface brightnesses in reflection nebulae illuminated by stars with temperatures of 5,000–33,000 K.