Showing papers by "Joseph L. Hora published in 1993"
TL;DR: In this paper, the authors presented new NIR images in the I, J, H, and K bandpasses of a bipolar nebula surrounding a post-asymptotic giant branch star and is in transition toward becoming a planetary nebula.
Abstract: The object AFGL 2688 is a bipolar nebula surrounding a post-asymptotic giant branch star and is in transition toward becoming a planetary nebula. We present new NIR images in the I, J, H, and K bandpasses. These images reveal a wealth of structure in the nebula not previously seen. We find that the northern lobe is not smooth, but clumpy. There is evidence in the I-band image for periodic variations in mass-loss rate. In addition, we present narrowband images centered on the V = 1 - 0 S(1) line of molecular hydrogen and nearby continuum. The narrowband images reveal that broadband flux found in the equatorial region is dominated by line emission from vibrationally excited molecular hydrogen. H2 emission is also present in the lobes. Our K-band images show the equatorial emission to be in the form of a ring or torus extending around the object at a distance R about 7 x 10 exp 16 (D/1 kpc) cm. Mechanisms for exciting the equatorial H2 emission are discussed; we conclude that shocks are the only plausible source. We have analyzed the broadband images using models which assume single scattering of photons from the central star. We find that the bipolar axis is inclined to the plane of the sky by i about 5 deg. The images are best reproduced by models in which the density of scattering dust decreases fairly rapidly with increasing stellar latitude, with little or no dust near the poles. Furthermore, the optical depth is found to have very little wavelength dependence, which implies that the dust in AFGL 2688 is different from that in the interstellar medium.
32 citations
TL;DR: MIRAC2 was built for ground-based astronomy at Steward Observatory, University of Arizona and Harvard-Smithsonian Center for Astrophysics and utilizes a Rockwell HF-16 128x128 arsenic-doped silicon blocked-impurity-band (BIB) hybrid array with a wavelength range of 2 to 28 μm operating in a liquid helium-cooled cryostat at 5 K as discussed by the authors.
Abstract: MIRAC2 was built for ground-based astronomy at Steward Observatory, University of Arizona and Harvard-Smithsonian Center for Astrophysics. It utilizes a Rockwell HF-16 128x128 arsenic-doped silicon blocked-impurity-band (BIB) hybrid array with a wavelength range of 2 to 28 μm operating in a liquid helium-cooled cryostat at 5 K. Reflective optics, and externally actuated detector and pupil slides provide a variety of magnification and focal ratio settings without opening the cryostat. Nominal settings at the NASA IRTF and UKIRT give diffraction-limited imaging with .34 and .27 arcsec/pixel, respectively. The sensitivity on the IRTF at 11.7 μm, 10% bandwidth filter, chop-nod, source in one beam, 1 sigma, one minute total time is 25 mJy/arcsec surface brightness and 43 mJy point source.
29 citations
TL;DR: In this paper, the authors presented near and mid-IR images of the planetary nebulae BD +30 deg 3639 and IC 418, with a unique combination of high spatial and spectral resolution.
Abstract: We present near- and mid-IR images of the planetary nebulae BD +30 deg 3639 and IC 418, with a unique combination of high spatial and spectral resolution. The mid-IR images were obtained with MIRAC, a new IR array camera. For BD +30 deg 3639, the mid-IR images at 10.0, 11.2, 12.4, 12.8, and 13.2 microns have allowed us to separate the various spectral emission components such as the broad UIR features, the 12.8-micron forbidden Ne II emission feature, and continuum emission, to determine the distribution of these components in the nebula. For IC 418, we have obtained high-resolution images in both the near- and mid-IR. The images in the near-IR at J, H, and K are important for determining the source of the IR excess; one component of the excess is located near the central star. We have also imaged the halo emission at H and K, which has been detected in earlier studies, and have determined its spatial extent. The mid-IR images at 9.8 and 11.7 microns show continuum emission coincident with the ionized zone and suggest that SiC emission originates from the region near the central star.
18 citations
01 Jan 1993
TL;DR: In this article, the carbon-rich PPN M 2-9 and IRAS 21282+5050 are known to exhibit UIR feature emission at 7.7, 8.6, and 11.22 µm.
Abstract: The carbon-rich PPN M 2–9 and IRAS 21282+5050 are known to exhibit UIR feature emission at 7.7, 8.6, and 11.22 µm. The two nebulae have been imaged in the mid-IR with the UA/SAO/NRL Mid-Infrared Array Camera (MIRAC) in bandpasses which include UIR feature emission (8.8 and 11.22 µm). Near-infrared images of the nebulae have also been taken with the NICMOS 3 Hg:Cd:Te array camera at J, H, and K for M 2–9 and at K for IRAS 21282+5050.