Observations of CO on Saturn and Uranus at millimeter wavelengths: New upper limit determinations - Archive ouverte HAL Access content directly
Journal Articles Astronomy and Astrophysics - A&A Year : 2008

Observations of CO on Saturn and Uranus at millimeter wavelengths: New upper limit determinations

Abstract

We tried to detect CO lines at millimeter wavelength on Saturn and Uranus in order to better constrain the origin of this compound in the atmospheres of these planets. CO sources can be either of internal or of external origin. Methods. We recorded broad multi-band spectra of Saturn and Uranus at the frequencies of the J=1"0 and J=2"1 CO lines, at the IRAM 30m-telescope, Spain, using Lellouch et al. (2005) and Hesman et al. (2007) observing technique. Results. As we do not detect any CO line in the spectra, we derive new upper limits of the abundance of CO in the atmospheres of Saturn and Uranus. The value we obtain for Saturn (6.3×10−8, restricted to the stratosphere) is larger than the value of the CO mixing ratio in the external origin model of Noll & Larson (1991). New observations with better sensitivity and/or more observing time should enable us to state on the CO external source strength. The upper limit we derive on Uranus is slightly lower (2.7 × 10−8, restricted to the stratosphere) than the value derived from the first observation of CO on Uranus, at infrared wavelength, by Encrenaz et al. (2004). As their fluorescence model did not take scattering effects into account, we suggest that their value could be overestimated.
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Dates and versions

hal-00261897 , version 1 (10-03-2008)

Identifiers

Cite

T. Cavalié, F. Billebaud, T. Fouchet, E. Lellouch, J. Brillet, et al.. Observations of CO on Saturn and Uranus at millimeter wavelengths: New upper limit determinations. Astronomy and Astrophysics - A&A, 2008, 484, pp.555-561. ⟨10.1051/0004-6361:20079170⟩. ⟨hal-00261897⟩
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