The occultation of SAO 78505 by Jupiter

On 13 December 1989, Jupiter occulted a star with visual magnitude 8.7 and an estimated K magnitude of 7. We observed the event from Kitt Peak, Arizona, using a 64 x 64 infrared camera at a wavelength of 2.16 microns. The resulting data on refractive defocusing of the stellar signal give information on the temperature of the jovian atmosphere at pressures approximately 2 to 10 microbar, at near-equatorial latitudes. These are the first new stellar-occulation data for the high jovian atmosphere since the widely observed occulation of beta Sco A and C in 1971. Because of improvements in instrumental capability, our data are comparable to the best beta Sco A data though the star is six magnitudes fainter. We derive a mean atmospheric temperature of 176 +/- 12 K on a level surface corresponding to an equatorial radius of 71,880 km and a pressure of 1.8 microbar at a jovi- centric latitude of 8 deg. This result complements the beta Sco results by providing improved precision at low jovicentric latitudes where the fainter star beta Sco C was used in 1971.