INFRARED-SPECTROSCOPY AND IMAGING POLARIMETRY OF THE DISK AROUND THE T-TAURI STAR RNO-91

We present 3-5 mum spectra and a 2.2 mum polarimetric image of the T Tauri star RNO 91. We report the detection of three absorption bands centered at 3250 cm-1 (3.08 mum), 2139 cm-1 (4.68 mum), and 2165 cm-1 (4.62 pm) in spectra of RNO 91. These features are due to frozen H2O, CO, and possibly XCN along the line of sight toward RNO 91. Our 2187-2107 cm-1 spectrum of RNO 90, the only other T Tauri star in the dark cloud L43, does not show the CO or XCN absorption bands. By comparing our observed polarimetric image with modeled images of scattered light from bipolar nebulae or circumstellar disks as well as with known morphology of the RNO 91 bipolar outflow, we demonstrate that the reflection nebulosity seen in the near-infrared is most likely a circumstellar disklike structure with a radius of approximately 1700 AU. The location of both RNO 90 and RNO 91 in front of or near the front of L43 suggests that the intracloud optical depths toward both stars are small and, therefore, that the frozen H2O, CO, and XCN molecules are located on grains in circumstellar material around RNO 91 at distances from the central star of perhaps 10-1700 AU. This frozen material may represent precometary grains orbiting RNO 91.