A Survey of Near Infrared Emission in Visual Reflection Nebulae

Abstract

We present a survey for extended 2.2 $μ$m emission in 20 new visual reflection nebulae, illuminated by stars with temperatures of 3,600 --- 33,000 K. We detect extended 2.2 $μ$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 $K-L'$, as well as obtaining surface brightness measurements at the wavelength of the 3.3 $μ$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 $μ$m feature in emission with similar feature-to-continuum ratios. The 3.3 $μ$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 $μ$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 $μ$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 $μ$m to 100 $μ$m surface brightnesses in reflection nebulae illuminated by stars with temperatures of 5,000--33,000 K.

38 pages (87 kB), AASTex format. Also 7 Postscript figures (80 kB), tarred, compressed and uuencoded, added with 'figure' command. Postscript file or hardcopy available upon request to sellgren@payne.mps.ohio-state.edu. ** Sep. 13, 1995: revised Fig. 1. Compressed postscript text+figs now available at ftp://bessel.mps.ohio-state.edu/pub/sellgren/survey.ps.Z ** Accepted, ApJS (Feb. 1996)