Shadowing in the Protoplanetary Disk of ZZ Tau IRS with HST

Abstract

An inner component misaligned from an outer component in a protoplanetary disk can result in the former casting shadows on the latter. We present a new instance of shadowing on the outer disk around a very-low-mass star, ZZ Tau IRS. Through the analysis of near-infrared (NIR) archival data at λ = 1.6 μ m acquired with the Wide Field Camera 3 on the Hubble Space Telescope, we identified brightness asymmetries in the top and bottom halves of the highly inclined outer disk, separated by a dark lane. The brighter sides in the top and bottom halves are on the opposite sides, which we attributed to shadows cast by a misaligned inner disk. Radiative transfer modeling of the system with a misaligned angle of 15 deg between the inner and outer disks well reproduced the observations. Additionally, we found an elevated brightness temperature of ^12 CO (3–2) at r ∼ 30 au on the brighter side in NIR wavelengths in the top half disk, which can be explained by the shadowing effect too. While the origin of the misaligned inner disk remains unclear, future monitoring observations to search for temporal variations in brightness asymmetries will likely provide useful clues.

Keywords

• Protoplanetary disks
• Planetary-disk interactions
• Exoplanet formation
• M stars
• Near infrared astronomy