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Astron. Astrophys. 321, L13-L16 (1997)

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1. Introduction

The spectrum of Saturn is characterized by a solar reflected component and a thermal component, corresponding to the internal heat source and to the absorbed part of the solar energy. At [FORMULA] [FORMULA] 4 µm, thermal radiation prevails, with some contribution from the reflected component up to about 7 µm. In the thermal range, spectral signatures strongly depend upon the thermal profile, which shows a temperature inversion at the tropopause, at a pressure level of about 0.1 bar. Depending upon the region where they are formed, below or above the tropopause (troposphere or stratosphere), molecular signatures appear in absorption or in emission respectively.

Previous spectra of Saturn have been recorded in the 4.5-5.2 µm window, from the ground (Noll and Larson, 1990) and from the KAO (Larson et al., 1980). The IRIS-Voyager infrared spectrometer recorded the spectrum of Saturn between 5 and 50 µm (Hanel et al., 1981). The Voyager observations were limited to a spectral resolution of 4.3 cm-1 (resolving power ranging from 50 to 500) and a sensitivity of about 1000 Jy per spectrum. The ISO SWS spectrum offers for the first time a continuous spectral coverage from 2.3 to 45 µm, a resolving power of 1500 and a sensitivity limit better than 1 Jy. We report here on the observed spectrum between 4.5 µm and 16.0 µm.

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998