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

Free access article

Issue		A&A Volume 415, Number 1, February III 2004


Page(s)		179 - 187
Section		Interstellar and circumstellar matter
DOI		http://dx.doi.org/10.1051/0004-6361:20034601

A&A 415, 179-187 (2004)
DOI: 10.1051/0004-6361:20034601

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

T. Miyata¹, H. Kataza², Y. K. Okamoto³, T. Onaka⁴, S. Sako^{4, 5}, M. Honda^{4, 5}, T. Yamashita^{5, 4} and K. Murakawa⁵

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

(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 ~ $0.09\arcsec$ , 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 $\mu$ m and 11.2 $\mu$ m are prominently observed. At radii > $1\arcsec$ 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 $\element[][13]{C}$ in polycyclic aromatic hydrocarbons (PAH) like particles. In addition to the UIR emission, a broad feature at 11.27 $\mu$ m 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.

Key words: circumstellar matter -- stars: individual: Red Rectangle -- stars: AGB and post-AGB -- infrared: stars

Offprint request: T. Miyata, miyata@kiso.ioa.s.u-tokyo.ac.jp

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