New Constraint on the Atmosphere of (50000) Quaoar from a Stellar Occultation

We report observations of a stellar occultation by the classical Kuiper Belt object (50000) Quaoar that occurred on 2019 June 28. A single-chord high-cadence (2 Hz) photometry data set was obtained with the Tomo-e Gozen CMOS camera mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The obtained ingress and egress data do not show any indication of atmospheric refraction and allow new 1? and 3? upper limits of 6 and 16 nbar, respectively, to be set for the surface pressure of a pure methane atmosphere. These upper limits are lower than the saturation vapor pressure of methane at Quaoar?s expected mean surface temperature (T?44 K) and imply the absence of a ?10 nbar-level global atmosphere formed by methane ice on Quaoar?s surface.