Sub-arcsecond imaging and spectroscopic observations of the Red Rectangle in the N-band

We carried out imaging and long-slit spectroscopic observations of the Red Rectangle in the N-band using the 8.2-m SUBARU telescope. The resulting images reveal a central bright core and an extended nebula. The central core is slightly extended in the N-band. The core radius is estimated to be similar to0.09", which corresponds to 60 AU. The core spectrum is well modeled by blackbody emission with a temperature of 358 K. The estimated size and temperature are in good agreement with the predictions of recent dusty torus models. In the north / south nebula, unidentified infrared (UIR) emission features at 8.6 mum and 11.2 mum are prominently observed. At radii > 1" they completely dominate the N-band spectra, suggesting that the nebula seen at N-band wavelengths is primarily brightened by the UIR-band emission, not by scattered light. We also detected shifts in the UIR-feature peaks with increasing distance from the center. These may be attributed to isotopic shifts due to the presence of C-13 in polycyclic aromatic hydrocarbons (PAH) like particles. In addition to the UIR emission, a broad feature at 11.27 mum is seen at a distance of 0.3" on all sides of the nebula. We attribute this to crystalline silicate olivine grains around the central torus.