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

¹ Kiso Observatory, Institute of Astronomy, School of Science, University of Tokyo, Kiso, Nagano, Japan e-mail: miyata@kiso.ioa.s.u-tokyo.ac.jp
² Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, Japan
³ Institute of Physics, Center for Natural Science, Kitasato University, Sagamihara, Kanagawa, Japan
⁴ Department of Astronomy, School of Science, University of Tokyo, Hongo, Tokyo, Japan
⁵ Subaru Telescope, National Astronomical Observatory of Japan, Hilo, USA

Corresponding author: T. Miyata, miyata@kiso.ioa.s.u-tokyo.ac.jp

Received: 9 July 2003
Accepted: 13 October 2003

Abstract

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 ~, 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 μm and 11.2 μm are prominently observed. At radii > 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  in polycyclic aromatic hydrocarbons (PAH) like particles. In addition to the UIR emission, a broad feature at 11.27 μm 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.