Chemical signatures of a warped protoplanetary disc

TL;DR

This study models how a misaligned embedded planet in a protoplanetary disc causes azimuthal variations in chemical abundances and line emissions, aiding the detection of unseen companions.

Contribution

It introduces a chemical modelling approach showing azimuthal abundance variations due to small disc-planet misalignments, highlighting their observational signatures.

Findings

Azimuthal chemical abundance variations occur even with small misalignments.

Line emission variations can indicate hidden embedded companions.

Nonaxisymmetric chemistry affects interpretation of molecular line maps.

Abstract

Circumstellar discs may become warped or broken into distinct planes if there is a stellar or planetary companion with an orbit that is misaligned with respect to the disc. There is mounting observational evidence for protoplanetary discs with misaligned inner discs and warps that may be caused by such interactions with a previously undetected companion, giving us a tantalising indication of possible planets forming there. Hydrodynamical and radiative transfer models indicate that the temperature varies azimuthally in warped discs due to the variable angle at which the disc surface faces the star and this impacts the disc chemistry. We perform chemical modelling based on a hydrodynamical model of a protoplanetary disc with an embedded planet orbiting at a 12$^{\circ}$ inclination to the disc. Even for this small misalignment, abundances of species including CO and HCO$^+$ vary azimuthally and this results in detectable azimuthal variations in submillimetre line emission. Azimuthal variations in line emission may therefore indicate the presence of an unseen embedded companion. Nonaxisymmetric chemical abundances should be considered when interpreting molecular line maps of warped or shadowed protoplanetary discs.