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P. M. Fry (University of Wisonsin - Madison), L. A. Sromovsky (University of Wisconsin - Madison)
We observed Neptune with the Keck 2 telescope using NIRC2 and Adaptive Optics on 15-16 August 2003 and 11-12 July and 11-12 August 2004. Crude cloud height discrimination was obtained using J, H, K' filters. Image resolution reached 0.06 arcseconds. Numerous small cloud features were observed, but many retained consistent morphology for only brief periods. Our preliminary cloud tracking netted 74 wind vectors, but 35 could not be tracked for more than 2 hours. The largest number of features was observed in the 20-60 S region (42). Our preliminary data set contains 6 vectors with better than 20 m/s accuracy, 12 between 20 m/s and 30 m/s, and 7 between 30 m/s and 40 m/s. The most accurate wind measurements generally agreed with the Voyager fit (Sromovsky et al., Icarus \bf 105, 110-141, 1993). A significant disagreement is found for a complex of features extending from 5N to 35N that seemed to move as a group. We observed south polar features in 2003 and during both 2004 runs, providing improved measurements of the south polar jet. Latitudes from 20N to the northern limb and from 20-60 S were densely populated with mainly streaky cloud features. Improved determination of wind structure at latitudes between 30 and 45 N, needed to better understand dark spot motion, will probably need to use averaging of large numbers of very noisy observations of features evolving over short time intervals. Few cloud features were seen near the equator. Many of the clouds near 30-45 N and 25-35 S were relatively more prominent in K' than in J or H, indicating high altitude but not high optical depths.
We thank the W. M. Keck Observatory, Keck Foundation, and NASA, for making these observations possible. This research was supported by Planetary Astronomy Grant NAG5-12206.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.