An Analysis of the Infrared Reflection Nebula and Circumstellar Environment of GL 2136

Abstract

The star formation region GL 2136 has been imaged using narrowband filters at 2.2, 3.08, and 3.45 μm. Water ice absorption at 3.08 μm is commonly seen in molecular clouds toward embedded objects such as GL 2136. By constructing and analyzing a water ice absorption map and a M2.2 - M3.45 color map, we are able to set constraints upon the location, size, and scattering properties of grains in the GL 2136 region. Through detailed modeling of the composition and size distribution of the grains in the reflection nebula, we calculate a dust photospheric temperature of 660 K for IRS 1. Our analysis indicates that absorption is occurring within a circumstellar disk in addition to absorption in the molecular cloud. For the density of water ice in the molecular cloud, we find an upper limit of 7 H2O molecules cm-3 and a water ice abundance of 1.2 × 10-5 by number with respect to hydrogen. The south and east lobes of the reflection nebula have small values of M2.2 - M3.45 and τice compared to those of IRS 1, and appear to line a conical cavity created by the blueshifted molecular outflow. From the apparent positions of the reflection lobes, the estimated opening angle of the outflow is 45°. We also present a schematic diagram of the geometry of the region as determined by the results of this study.