2013A&A...556A.118C

Occultations of bright stars by planets provide information on the state of their atmospheres. An occultation of the bright star 45 Capricornii (HIP 107302) by Jupiter occurred on the night of 3/4 August 2009. The event was observed at multiple sites in Europe, Africa and South America and with instruments ranging in aperture from 0.4m to 2.2m. All observations, except one, were carried out in methane absorption bands centred at 0.89µm and 2.2µm to minimise the planetary contribution to the measured stellar flux. Following the application of special post-processing techniques, differential photometry was performed. Nearby bright satellites were used as reference sources. Fifteen lightcurves were obtained. The photometric time series for fourteen of these were fitted to a model atmosphere of constant scale height (H). Estimates of H for most lightcurves lie within the range 20-30km with an inverse-variance weighted mean of 23.6±0.4km, in good agreement with previous works. A comparison between half-light times at ingress and at egress implies an astrometric offset of 10-15mas in Jupiter's position relative to the star. Five lightcurves - two for ingress and three for egress - were numerically inverted into profiles of pressure versus temperature. Isothermal, mutually consistent behaviour is observed within the pressure range 3-10µbar. The inferred temperature of 165±5K is consistent with, but slightly higher than, that measured by the Galileo Probe at 5° S latitude in 1995 at the same pressure level. Subtraction of isothermal models for nine cases show the presence of at least one, and possibly two, non-isothermal layers a few tens of km below the half-light datum. Their altitudes are similar to those of features previously reported during the occultation of HIP 9369 in 1999. Our temperature estimates are consistent with the expected small magnitude of the perturbation of the atmosphere following the impact event on Jupiter in July 2009.