The Non-Sphericity of Triton's Atmosphere as Evidenced by Stellar Occultations

Abstract In an attempt to reconcile and understand recent measurements of the non-sphericity inTriton's atmosphere, the Tr148 occultation data set was reanalyzed. Recent new data from theHubble Space Telescope Fine Guidance System allowed the separation and position angle of theTr148 double star to be independently incorporated into the occultation analysis rather than beingfreely fit during the occultation reduction. The separation of 0.3855 ± 0.0004 arcsec and positionangle of 67.17 ± 0.05 deg determined here differ from the values determined solely from theoccultation timings of 0.3874 ± 0.0011 arcsec and 65.16 ± 0.14 deg. This resulted in a change inthe calculated ellipticity and position angle of Triton's half-light ellipse from their originally fittedvalues of 0.029 ± 0.016 and 70.3 ± 10.1 deg to improved values of 0.033 ± 0.013 and 65.1 ± 8.8deg. By fixing the separation parameters to independently determined values instead of freelyfitting for them, the confidence in the new ellipticity fit (as measure by the reduced chi-squaredresults) is significantly increased. This work ends with a discussion of these new values and theirimplications for Triton's atmosphere.