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 in Triton's atmosphere, the Tr148 occultation data set was reanalyzed. Recent new data from the Hubble Space Telescope Fine Guidance System allowed the separation and position angle of the Tr148 double star to be independently incorporated into the occultation analysis rather than being freely fit during the occultation reduction. The separation of 0.3855 ± 0.0004 arcsec and position angle of 67.17 ± 0.05 deg determined here differ from the values determined solely from the occultation timings of 0.3874 ± 0.0011 arcsec and 65.16 ± 0.14 deg. This resulted in a change in the calculated ellipticity and position angle of Triton's half-light ellipse from their originally fitted values of 0.029 ± 0.016 and 70.3 ± 10.1 deg to improved values of 0.033 ± 0.013 and 65.1 ± 8.8 deg. By fixing the separation parameters to independently determined values instead of freely fitting for them, the confidence in the new ellipticity fit (as measure by the reduced chi-squared results) is significantly increased. This work ends with a discussion of these new values and their implications for Triton's atmosphere.