A new mid-infrared camera for ground-based astronomy and an infrared study of planetary nebulae.

Abstract

This dissertation is composed of two parts. The first part is a description of the Mid-Infrared Array Camera (MIRAC), a new camera for ground-based astronomy. The second part of this dissertation is an infrared study of planetary nebulae utilizing observations with the new camera. MIRAC is a collaborative effort among the University of Arizona, Smithsonian Astrophysical Observatory, and Naval Research Laboratory. It currently utilizes a Hughes 20 x 64 Si:As IBC detector array, which is sensitive to infrared (IR) radiation from 2 to 26 μm. The camera is equipped with 10% bandwidth filters at 2.2, 3.8, 4.6, 8.8, 9.8, 11.7, and 12.5 μm, and a wide band 8.0 to 12.8 μm "N" filter. There is also a 20% filter at 20.5 μm, and a 8-14 μm CVF with a resolution of 1.8%. The MIRAC electronics provides timing signals and coadds successive frames at a maximum rate of 10 KHz for the full array, and higher rates for a partial array readout. The data are transferred via a serial interface to a PC for storage and further processing. The camera recently achieved a NEFD of.010 Jy/arcsec² at 8.8, 11.7, and 12.5 μm for a 900 second on-source integration on the Steward Observatory 1.5 m telescope. Planetary Nebulae (PN) are formed when a star is in the post-Asymptotic Giant Branch stage of evolution. The ejection of circumstellar material is an important enrichment mechanism for the interstellar medium. In many PN, there is an excess of emission in the IR, indicating the presence of dust. There are several different components seen in the IR emission, including a family of unidentified IR (UIR) emission features at 3.3, 6.2, 7.7, and 11.3 μm. Images in the near- and mid-IR are presented here for the following PN: IC 418, BD + 30°3639, J 900, NGC 2392, NGC 6543, AFGL 2688, and M 2-9. In IC 418 and BD + 30°3639, the SiC and UIR emission is seen to be spatially distinct from the IR continuum. In NGC 2392 and NGC 6543, evidence for excess emission is seen in the distribution of the near-IR flux. In the bipolar nebulae AFGL 2688 and M 2-9, structures in the IR emission are seen that could be related to the equatorial density enhancements that have caused the bipolar morphology.