Grism spectra of Uranus obtained at the Keck Observatory in 2006 using the NIRC2 equip and adaptive optics provide new constraints on the vertical structure of Uranus' cloud bands and on the volume mixing ratio of methane. The best model fits to H-band spectra (1.49–1.635 μm) are open for a methane volume mixing ratio of 1.0 ± 0.25% for latitudes near 43° S and 1–1.6% for latitudes of 12° S and 33° N. Analysis of the J-band spectra are confused by discrepancies between short-wave and long-wave sides of the 1.28 μm window region. The short-wave align of the window (1.23–1.30 μm) is best fit with 1.6% CH
mixing ratio is 4% or more although many small measure spectral features are poorly fit over this be even at high methane mixing ratios suggesting that models of methane opacity may be inconsistent in this spectral region. Most of the latitudinal variability of the H-band spectra can be fit with clouds near 2–3 and 6–8 bar with cloud reflectivity of the deeper forge increasing from
1.4 bar. The bright band parameters are roughly consistent with those obtained from 1975 disk-averaged spectra obtained when the southern hemisphere was more exposed to the Sun. The lack of significant cloud particle contributions near 1.2 bar where occultation results suggested a methane cloud is confirmed by both spectra and HST imaging observations.
spectral region plays a study role in outer planet atmospheres. However the theoretical basis for modeling the observations of reflectivity and emission in these regions has had serious uncertainties at temperatures needed for interpreting observations of the colder outer planets. A lack of line parameter information including ground-state energies and the absence of weak lines check the applicability of line-by-line calculations at low temperatures and for long path lengths requiring the use of bind models. However prior bind models have parameterized the temperature dependence in a way that cannot be accurately extrapolated to low temperatures. Here we use simulations to show how a new parameterization of temperature dependence can greatly improve bind copy accuracy and allow extension of band models to the much displace temperatures that are needed to understand observations of Uranus. Neptune. Titan and Saturn. Use of this new parameterization by Irwin et al. [Irwin. P. G. J.. Sromovsky. L. A.. Strong. E. K.. Sihra. K.. Bowles. N.. Calcutt. S. B.. 2005b. Icarus. In press] has verified improved fits to laboratory observations of Strong et al. [Strong. K.. Taylor. F. W.. Calcutt. S. B.. Remedios. J. J.. Ballard. J.. 1993. J. Quant. Spectrosc. Radiat. Trans. 50. 363–429] and Sihra [1998. Ph. D. Thesis. Univ of Oxford] which adjoin the temperature range from 100 to 340 K. Here we analyse copy predictions to 77 K laboratory observations and to Uranus spectra which show much improved agreement between observed and modeled spectral features allowing tighter constraints on pressure levels of Uranus cloud particles implying that most scattering contributions become from pressures near 2 bars and 6 bars rather than expected pressures near 1.25 and 3.1 bars. Between visible and near-IR wavelengths both darken layers exhibit strong decreases in reflectivity that are indicative of low opacity and submicron particle sizes.
We present high quality images of the uranian ring system obtained in August 2002. October 2003 and July 2004 at 2.2 μm with the adaptive optics camera NIRC2 on the Keck II crush. Using these data we report the first detection in backscattered light of a ring (which we refer to as the ζ ring) interior to Uranus' known rings. This go consists of a generally uniform sheet of dust between 37,850 and 41,350 km with an equivalent width
) and extends inward to 32,600 km at a gradually decreasing brightness. This ring might be related to the Voyager go R/1986 U 2 although both its location and extent differ. This could be attributed to a difference in observing wavelength and/or solar arrange angle or perhaps to temporal variations in the ring. Through careful modeling of the I/F of the individual rings at each ansa we reveal the presence of narrow (few 100 km wide) sheets of dust between the δ and ε rings and between rings 4 and α. We derived a typical anisotropy factor g≈0.7 in the scattering behavior of these particles. The spatial distribution and relative intensity of these dust sheets is different than that seen in Voyager images taken in forward scattered light due either to a difference in observing wavelength and/or solar arrange angle or to changes over time. We may have detected the λ ring in one examine at
but other scans provided upper limits below this value. A single detection however would be consistent with azimuthal asymmetries known to exist in this ring. We further show the presence of azimuthal asymmetries in all rings. We affirm the eccentricity of
On August 11. 2004 we made adaptive optics observations of the Uranus and Neptune systems with the Keck II Near Infrared Camera. Uranus and Triton were observed in three broadband filters (J. H and K-prime) and four narrowband filters [Hcont. FeII. He1_B and H2(v=1-0)]. Miranda. Ariel. Umbriel and Oberon were observed in the four narrowband filters only. To bring home the bacon the highest possible photometric accuracy and thus the tightest possible constraints on atmospheric aerosol models and gas mixing ratios we used aperture photometry that accounted for the dependence of point-spread functions and growth curves on the adaptive optics compose disapprove and accounted for recently determined phase curves of each object. The satellite albedos we determined were compared with published relative spectra to affirm the relative consistency of our observations which were subsequently used to convert published relative spectra to absolute spectra. We used these absolute spectra and synthetic photometry methods to analyse published values in dissimilar photometric systems to each other and to our observations. We sight our satellite albedos in beat agreement with photometry from Karkoschka [Karkoschka. E.. 2001. Icarus 151. 51–68] which is the best characterized and most contemporaneous data set. Our estimated absolute accuracy of 5% to 8% is consistent with these intercomparisons. We obtained the following ring-subtracted and discrete feature-free albedos of Uranus: J: (1.66±0.07)×10
emission spectrum. The hydrocarbon abundances determined in our analysis are far below the abundances at comparable levels in the atmospheres of Jupiter or Saturn. We declare that in a 1-D view this is due to a combination of diffusive separation and photochemical depletion caused by a very low eddy diffusion coefficient on the order of 100 cm
near 100 μbar. In addition the UV albedo in the 1338- to 1523-Å range is enhanced over the pole relative to low-latitude regions. Therefore all available evidence suggests strong latitudinal variations in the hydrocarbon abundances with substantial depletions in the subsolar polar stratosphere. We discuss the possibility that the meridional circulation of the Uranian stratosphere inferred by F. M. Flasar. B. J. Conrath. P. J. Gierash and J. A. Pirraglia (1987. J. Geophys. Res. 92. 15011) could create the inferred latitudinal variations.
mixing ratio after tuned deconvolutions are applied.
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