Showing papers by "William F. Hoffmann published in 1997"

Infrared observations of dust emission from comet hale-bopp

Abstract: We present infrared imaging and photometry of the bright, giant comet C/1995 O1 (Hale-Bopp) The comet was observed in an extended infrared and optical observing campaign in 1996–1997 The infrared morphology of the comet was observed to change from the 6 to 8 jet “porcupine” structure in 1996 to the “pinwheel” structure seen in 1997; this has implications for the position of the rotational angular momentum vector Long term light curves taken at 113 μm indicate a dust production rate that varies with heliocentric distance as ∶ r−14 Short term light curves taken at perihelion indicate a rotational periodicity of 113 hours and a projected dust outflow speed of ∶ 04 km s−1 The spectral energy distribution of the dust on October 31, 1996 is well modeled by a mixture of 70% silicaceous and 30% carbonaceous non-porous grains, with a small particle dominated size distribution like that seen for comet P/Halley (McDonnell et al, 1991), an overall dust production rate of 2 × 105 kg s−1, a dust-to-gas ratio of ∶5, and an albedo of 39%

Enhancing CRFP panels with silicon monoxide to improve as-replicated figure accuracy

Abstract: We have been able to utilize silicon monoxide (SiO) as a refractory coating to improve on the replicated figure of composite optics made from carbon fiber reinforced plastic (CFRP) sandwich panels. We apply an evaporative coating of SiO to the surface of the mirror and polish that coating to obtain the desired figure for the complete mirror. We have developed this technique to allow the use of CFRP optics which are both stable and have a low areal density. This represents a novel use of thin film vacuum coating to produce an optical substrate rather than a simple reflective or protective overcoating and represents an advance in producing thick SiO coatings (10 - 40 micrometers) over large areas (25 - 60 cm).© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Mid-Infrared Imaging of Dust Shells around Young Planetary and Proto-Planetary Nebulae

Abstract: The results presented here are from an ongoing mid-infrared imaging study of PPNe and PNe, using MIRAC2 the UA/SAO mid-IR camera. Our 8–21 μm observations have a spatial resolution of about 0.7″ to 1.5″, and a pixel scale of 0.25″/pixel (at UKIRT) or 0.34″/pixel (at IRTF). The high S/N and good spatial sampling in our images of IRAS 22272+5435 and IRAS 07134+1005 allow us to construct temperature and optical depth maps. Using our 11.7μm and 20.6μm images we also construct maps which isolate the 11.3μm (UIR) and 21μm emission features (Justannont et al. 1995). As a second part of this project, we are modelling the dust emission from PPNe and young PNe, using a axisymmetrical radiative transfer code.