Fig. 2.

image

Fit to the light curve χ2 map as a function of the distance of closest approach of Haleakala Observatory to Pluto’s shadow center, ρ, and the pressure at a radius of 1215 km, p1215, which has been referred to be a reference radius by previous studies (Yelle & Elliot 1997; Sicardy et al. 2016; Meza et al. 2019). Darker zones correspond to lower χ2 values. The white circular point is the best-fit value corresponding to the minimum χ2 value of with 73 degrees of freedom. The inner and outer closed curves correspond to 1σ (provided by ), 2σ (), and 3σ () levels, respectively. The solid horizontal line shows p1215 value obtained in 2016 (p1215 = 6.61 ± 0.22 μbar, Meza et al. 2019), and the upper and lower dashed lines correspond to its 1σ upper and lower limits, respectively.

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