Near infrared spectroscopy of highly reddened stars in the galactic plane

Near Infrared spectroscopic observations of highly reddened stars in the Galactic Plane compiled by Stephenson [AJ, 103,263 (1992)] an presented. We observed nine highly reddened stars and detected the 3.4 mu m absorption feature in the spectra of five stars. The 3.4 mu m absorption depth and the visual extinction show a positive correlation. The observed strength of this feature is tau(3.4)/A(V) similar to 0.003, similar to previous results by Pendleton er al. [ApJ, 437, 683 (1994)] for lines of sight other than the Galactic Center. One star shows the 3.1 mu m absorption feature which is probably of molecular cloud origin, but no 3.4 mu m absorption feature. This is consistent with Brooke er al. [ApJ, 359, 209 (1996)] who find that the spectra of objects embedded in or located behind molecular cloud material consistently show a 3.1 mu m ice band, but never show a 3.4 mu m band which resembles the diffuse interstellar medium band. These results support the hypothesis that the 3.4 mu m absorption feature is caused by organic materials ubiquitously distributed in the diffuse interstellar medium. Although these stars were originally selected from an I band objective prism survey for the absence of molecular features in their spectra, we detected the CO absorption feature near 2.3 mu m in all nine stars we observed. Consequently, these stars are likely to be moderately to highly reddened stars of late spectral type. (C) 1996 American Astronomical Society.