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WASP-33b is a retrograde hot Jupiter with a period of 1.2 days orbitingaround a rapidly rotating and pulsating A-type star. A previous study foundthat the transit chord of WASP-33b had changed slightly from 2008 to 2014 basedon Doppler tomographic measurements. They attributed the change to orbitalprecession caused by the non-zero oblateness of the host star and themisaligned orbit. We aim to confirm and more precisely model the precessionbehavior using additional Doppler tomographic data of WASP-33b obtained withthe High Dispersion Spectrograph on the 8.2m Subaru telescope in 2011, as wellas the datasets used in the previous study. Using equations of a long-termorbital precession, we constrain the stellar gravitational quadrupole moment$J_{2}=(9.14\pm 0.51)\times 10^{-5}$ and the angle between the stellar spinaxis and the line of sight $i_{\star}=96^{+10}_{-14}$ deg. These values updatethat the host star is more spherical and viewed more equator than the previousstudy. We also estimate that the precession period is $\sim$840 years. We alsofind that the precession amplitude of WASP-33b is $\sim$67 deg and WASP-33btransits in front of the host star for only $\sim$20\% of the whole precessionperiod.

Doppler Tomographic Measurement of the Nodal Precession of WASP-33b