NIR Spectroscopy of the HAeBe Star HD 100546: III. Further Evidence of an Orbiting Companion?

TL;DR

This study uses high-resolution NIR spectroscopy to find indirect evidence of a potential orbiting companion near HD 100546, consistent with giant planet formation signatures, through analysis of CO and OH emission lines.

Contribution

It provides new observational evidence supporting the presence of a companion near the disk wall, using spectroscopic diagnostics that resemble theoretical predictions.

Findings

CO and OH emission lines suggest a companion near 13 au.

Spectroastrometric variability indicates an orbiting source of CO emission.

Emission characteristics are consistent with a circumplanetary disk hypothesis.

Abstract

We report high resolution NIR spectroscopy of CO and OH emission from the Herbig Be star HD100546. We discuss how our results bear striking resemblance to several theoretically predicted signposts of giant planet formation. The properties of the CO and OH emission lines are consistent with our earlier interpretation that these diagnostics provide indirect evidence for a companion that orbits the star close to the disk wall (at ~13au). The asymmetry of the OH spectral line profiles and their lack of time variability are consistent with emission from gas in an eccentric orbit at the disk wall that is approximately stationary in the inertial frame. The time variable spectroastrometric properties of the CO v=1-0 emission line point to an orbiting source of CO emission with an emitting area similar to that expected for a circumplanetary disk (~0.1au^2) assuming the CO emission is optically thick. We also consider a counterhypothesis to this interpretation, namely that the variable CO emission arises from a bright spot on the disk wall. We conclude with a brief suggestion of further work that can distinguish between these scenarios.