The occultation of HIP 107302 by Jupiter^⋆

¹ Armagh Observatory, College Hill, Armagh, BT61 9DG UK
e-mail: aac@arm.ac.uk
² International Occultation Timing Association – European Section  
³ Institut de Ciències de l’ Espai (IEEC – CSIC), Spain
⁴ Agrupació Astronòmica de Sabadell, 08200 Barcelona, Spain
⁵ Instituto de Astrofísica de Canarias, 38205 La Laguna ( Tenerife), Spain
⁶ Universidade Federal do Rio de Janeiro, Observatorio do Valongo, Ladeira Pedro Antonio 43, 20080-090 Rio de Janeiro, Brazil
⁷ IMCCE/Observatorie de Paris, 77 Avenue Denfert Rochereau, 75014 Paris, France
⁸ Observatorio Nacional/MCT, R. General Jose Cristino 77, 20921-400 Rio de Janeiro, Brazil
⁹ Observatoire de Paris/LESIA, bâtiment 10, 92195 Meudon Cedex, France
¹⁰ IAS Observatory, 9000 Hakos, Namibia
¹¹ Astronomical Union of Sparta, 23100 Sparta, Greece
¹² Ellinogermaniki Agogi Observatory, Dimitrios Panegeas Str., 153 51 Pallini, Greece
¹³ Department of Astrophysics, Astronomy and Mechanics, University of Athens, Panepistimiopolis, 157 84 Zografos, Athens, Greece

Received: 1 May 2013
Accepted: 21 June 2013

Abstract

Aims. 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.

Methods. The event was observed at multiple sites in Europe, Africa and South America and with instruments ranging in aperture from 0.4 m to 2.2 m. All observations, except one, were carried out in methane absorption bands centred at 0.89 μm and 2.2 μm 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.

Results. 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 20−30 km with an inverse-variance weighted mean of 23.6 ± 0.4 km, in good agreement with previous works. A comparison between half-light times at ingress and at egress implies an astrometric offset of 10−15 mas 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 3−10 μbar. The inferred temperature of 165 ± 5 K 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.