MID-INFRARED SPECTRO-IMAGING OBSERVATIONS OF COMET HALE–BOPP


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Abstract

Comet C/1995 O1 (Hale–Bopp)) was observed with camiras, the Saclay mid-infrared camera, mounted on the Nordic Optical Telescope (Roque de los Muchachos, La Palma)), from April 14th to April 25th, 1997. This observing run was part of the European campaign devoted to Hale–Bopp observations from the Canary Islands (PI R. West)). camiras spectro-imaging capabilities, achieved with a Circular Variable Filter (of spectral resolution R ≈ 50)), were used to obtain spectra of the comet in the N atmospheric window (8–13 μm)) over a large field of view (52‘‘ × 78‘‘)), at a spatial resolution of ∼1 arcsec. Data were also collected at shorter wavelengths (in the L and M bands)). The silicate dust feature around 10 μm is clearly apparent in the data. The shape of the feature varies continuously according to the position in the field. A dust model developed at Saclay in the framework of β-Pictoris dust disk studies was used to interpret the observations. The presence of both olivine and pyroxene with a high degree of crystallinity is needed to account for the observations. A change in the size distribution of the grains allows to reproduce the spatial change of the silicate feature according to the position in the field.

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