Scattered light shadows in warped protoplanetary discs

Abstract

3D hydrodynamic numerical simulations have demonstrated that the structure of a protoplanetary disc may be strongly affected by a planet orbiting in a plane that is misaligned to the disc. When the planet is able to open a gap, the disc is separated into an inner, precessing disc and an outer disc with a warp. In this work, we compute infrared scattered light images to investigate the observational consequences of such an arrangement. We find that an inner disc misaligned by less than a degree to the outer disc is indeed able to cast a shadow at larger radii. In our simulations, a planet of {≳ }6 M_J inclined by ≳2° is enough to warp the disc and cast a shadow with a depth of {≳ } 10{{ per cent}} of the average flux at that radius. We also demonstrate that the warp in the outer disc can cause a variation in the azimuthal brightness profile at large radii. Importantly, this latter effect is a function of the distance from the star and is most prominent in the outer disc. We apply our model to the TW Hya system, where a misaligned, precessing inner disc has been invoked to explain a recently observed shadow in the outer disc. Consideration of the observational constraints suggests that an inner disc precessing due to a misaligned planet is an unlikely explanation for the features found in TW Hya.