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We use the Subaru Hyper Suprime-Cam (HSC) data to study structural parametersand systemic proper motion of the Sextans dwarf spheroidal galaxy at theheliocentric distance of 86 kpc, which is one of the most important targets forstudies of dark matter nature and galaxy formation physics. Thanks to thesuperb image quality and wide area coverage of the Sextans field, the HSC dataenables a secure selection of member star candidates based on thecolour-magnitude cut, yielding about 10,000 member candidates at magnitudesdown to $i\sim 24$. We use a likelihood analysis of the two-dimensionaldistribution of stars to estimate the structural parameters of Sextans takinginto account the contamination of foreground halo stars in the Milky Way, andfind that the member star distribution is well-fitted by an elliptical Kingprofile with ellipticity $\epsilon \simeq 0.25$ and the core and tidal radii of$R_c=(368.4\pm 8.5)$ pc and $R_t=(2.54\pm 0.046)$ kpc, respectively. Then usingthe two HSC datasets of 2.66 years time baseline on average, we find thesystemic proper motions of Sextans to be $(\mu_\alpha,\mu_\delta)=(-0.448\pm{0.075},0.083\pm{0.078})$ $\mathrm{mas}\\mathrm{yr}^{-1}$, which is consistent with some of the previous works usingthe $Gaia$ data of relatively bright member stars in Sextans. Thus, our resultsgive a demonstration that a ground-based, large-aperture telescope data whichcovers a wide solid angle of the sky and has a long time baseline, such as theupcoming LSST data, can be used to study systemic proper motions of dwarfgalaxies.

Study of structural parameters and systemic proper motion of Sextans dwarf spheroidal galaxy with Subaru Hyper Suprime-Cam data