Keck AO observations of Io in and out of eclipse
We present adaptive optics (AO) observations of Io taken with the W.M. Keck II telescope on 18 December 2001 (UT) before the satellite went into eclipse, and while it was in Jupiter's shadow. Making these kind of Io-in-eclipse observations, as well as the associated data reduction and analysis...
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| Published in: | Icarus (New York, N.Y. 1962) N.Y. 1962), 2004-05, Vol.169 (1), p.250-263 |
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| Main Authors: | , , , , , , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | We present adaptive optics (AO) observations of Io taken with the W.M. Keck II telescope on 18 December 2001 (UT) before the satellite went into eclipse, and while it was in Jupiter's shadow. Making these kind of Io-in-eclipse observations, as well as the associated data reduction and analysis are challenging; hence one focus of the paper is to explain the methods and tools used for these data sets. For the sunlit images Io itself was used as the wavefront reference source, while nearby Ganymede was used as reference ‘star’ when Io was in eclipse. Observations were obtained in K′-, L′-, and M-bands. The sunlit images have been deconvolved using
MISTRAL. The Io-in-eclipse data were deconvolved with
IDAC and
MISTRAL. The former gives better results, both in absolute photometry and in matching the original images. We determined the flux densities of the hot spots from the original Io-in-eclipse data with StarFinder, as well as from the deconvolved images by integrating the intensity over the relevant areas. We determined the highly anisoplanatic PSF via a FFT method from the original data, and used this in StarFinder and as a starting PSF for
IDAC and
MISTRAL. We derived temperatures and areal coverage of all 19 spots detected in both K′- and L′-band images of Io-in-eclipse. We also determined temperatures and areal coverage of the hot spots visible on the L′- and M-band images of sunlit Io. Most volcanoes contain a compact hot ‘core’ (≲10 km
2 at 600–800 K) within a larger area at lower temperatures (e.g., ∼10
2–10
4 km
2 at 300–500 K). The total heat flow contributed by these active volcanoes is 0.2 W
m
−2, ∼8% of the average global heat flow measured at 5–20 μm by Veeder et al. [J. Geophys. Res. 99 (1994) 17095]. |
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| ISSN: | 0019-1035 1090-2643 |