Spectro-imaging observations of Jupiter's 2-μm auroral emission. I. H3 distribution and temperature

We report on spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope. The use of narrow-band filters at 2.09 and 2.12 μm, combined with high spectral resolution (0.2 cm⁻¹), allowed us to map emission from the H₂S₁(1) quadrupole line and from several H₃⁺ lines. The H₂ and H₃⁺ emission appears to be morphologically different, especially in the north, where the latter notably exhibits a “hot spot” near 150°-170° System III longitude. This hot spot coincides in position with the region of increased and variable hydrocarbon, FUV and X-ray emission, but is not seen in the more uniform H₂S₁(1) emission. We also present the first images of the H₂ emission in the southern polar region. The spectra include a total of 14 H₃⁺ lines, including two hot lines from the 3ν₂-ν₂ band, detected on Jupiter for the first time. They can be used to determine H₃⁺ column densities, rotational (T_rot) and vibrational (T_vib) temperatures. We find the mean T_vib of the v₂=3 state to be lower (960±50 K) than the mean T_rot in v₂=2 (1170±75 K), indicating an underpopulation of the v₂=3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from ν₂ observations. This is a likely consequence of a large positive temperature gradient in the sub-microbar auroral atmosphere. While the signal-to-noise is not sufficient to take full advantage of the 2-D capabilities of the observations, the search for correlations between line intensities, T_vib and column densities, indicates that variations in line intensities are mostly due to correlated variations in the H₃⁺ column densities. The thermostatic role played by H₃⁺ at ionospheric levels may provide an explanation. The exception is the northern “hot spot,” which exhibits a T_vib about 250 K higher than other regions. A partial explanation might invoke a homopause elevation in this region, but a fully consistent scenario is not yet available. The different distributions of the H₂ and H₃⁺ emission are equally difficult to explain.     

Speckle imaging of Titan at 2 microns: surface albedo, haze optical depth, and tropospheric clouds 1996-1998

We present results from 14 nights of observations of Titan in 1996-1998 using near-infrared (centered at 2.1 microns) speckle imaging at the 10-meter W.M. Keck Telescope. The observations have a spatial resolution of 0.06 arcseconds. We detect bright clouds on three days in October 1998, with a brightness about 0.5% of the brightness of Titan. Using a 16-stream radiative transfer model (DISORT) to model the central equatorial longitude of each image, we construct a suite of surface albedo models parameterized by the optical depth of Titan's hydrocarbon haze layer. From this we conclude that Titan's equatorial surface albedo has plausible values in the range of 0-0.20. Titan's minimum haze optical depth cannot be constrained from this modeling, but an upper limit of 0.3 at this wavelength range is found. More accurate determination of Titan's surface albedo and haze optical depth, especially at higher latitudes, will require a model that fully considers the 3-dimensional nature of Titan's atmosphere.     

Keck near-infrared observations of Saturn's E and G rings during Earth's ring plane crossing in August 1995

We present near-infrared (1.24-2.26 μm) images of Saturn's E and G rings which were taken with the W.M. Keck telescope in 1995 August 9-11, during the period that Earth crossed Saturn's ring plane. Our data confirm that the E ring is very blue. Its radial and vertical structure are found to be remarkably similar to that apparent in the HST ringplane crossing data at visible wavelengths, reinforcing models of the ring's peculiar narrow or very steep particle size distribution. Our data show unambiguously that the satellite Tethys is a secondary source of material for the E ring. The G ring is found to be distinctly red, similar in color to Jupiter's main ring, indicative of a (more typical) broad particle size distribution.     

VLBI相位校正信号提取的软件实现方法

从VLBI相关处理结果中提取的延迟值包括了天线、终端等设备的时延,必须对其加以修正,最终结果才能达到精度要求。提取相位校正信号,可以消除这些设备引入的时延,从而校正同一波前信号到达基线两端的几何时延。该文介绍了提取相位校正信号的原理、算法及软件实现方法。软件采用多线程和SSE技术,具备4台站多通道全部相位校正信号提取能力。     

Measurements of winds on Mars with Hubble Space Telescope images in 2003 opposition

The winds of Mars at the water cloud level are measured by tracking cloud features in sequential high-resolution Hubble Space Telescope UV images for 5 days during the perihelion season in 2003. Global circulation model (GCM) predictions are in general agreement with the observations for the zonal wind component, but reveal significant differences for the meridional component.