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| Titel |
Probing the vertical cloud structure of Uranus and Neptune with ground-based near-infrared observations at UKIRT, IRTF and Gemini-North |
| VerfasserIn |
Patrick G. J. Irwin, Nicholas N. Teanby, Gary R. Davis, Glenn Orton, Leigh Fletcher, Dane Tice, Jane Hurley |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035439
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| Zusammenfassung |
| In 2006, 2007 and 2008 observations of the near-infrared spectrum of Uranus were made with
the UIST instrument of the UK Infrared Telescope, covering the period of Uranus’ Northern
Spring Equinox in 2008. A significant change in the visible appearance of Uranus occurred
during this time with the southern polar zone at 45-S fading, while a corresponding zone at
45-N began to form. In addition, the visibility of the equatorial zone and darker mid-latitude
belts increased. The observed spectra were fitted (Irwin et al., Icarus 203, 287 – 302,
2009), using the NEMESIS optimal estimation retrieval model to determine the
variation in the latitudinal and vertical cloud structure during this time. However, since
publication, a new set of methane absorption data has become available (Karkoschka
and Tomasko, 2009, Icarus, submitted), which appears to be more reliable at the
cold temperatures and high pressures of Uranus’ deep atmosphere. We have fitted
k-coefficients to these new methane absorption data and we find that although the
inter-annual changes reported by Irwin et al. (2009) stand, the new k-data place the main
cloud deck at lower pressures (2-3 bars) than derived previously in the H-band
of ~ 3-4 bars and ~ 6 bars in the J-band. In addition, we find that using the new
methane coefficients it is much easier to fit simultaneously the 1.6, 1.3 and 1.1 μm
peaks.
During the Uranus observations in 2007, corresponding observations were also made of
Neptune’s near-infrared spectrum, albeit with substantially poorer spatial resolution. The
spectra were nevertheless sufficient to retrieve the gross variation in Neptune’s
latitudinal-vertical cloud structure and, like previous studies, we find the main cloud deck to
exist at similar pressure levels to the main Uranus cloud deck, but with considerably thicker
overlying stratospheric haze. The retrieved vertical-latitudinal cloud structure on
Uranus and Neptune, observed with identical instrument setups, will be presented and
discussed.
Observations of both Uranus and Neptune were also made in 2009 with the SpeX
instrument (0.8 to 2.4 μm) on the NASA Infrared Telescope Facility and also with the NIFS
and NIRI instruments on the Gemini North telescope. The IRTF measurements were made
with seeing conditions of approximately 0.5 arcsec, while the Gemini observations were
made with Adaptive Optics and thus have considerably better spatial resolution. We intend to
use the NIFS observations to study the limb-darkening curves from 1.45 to 1.75
μm, which should provide better constraints in the vertical cloud structure and we
intend to use the IRTF measurements to extend our analysis to shorter wavelengths
and also provide better radiometric calibration between the different reflectance
peaks.
These new observations will be presented and compared with the previous UKIRT
observations. |
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