# High-Resolution Near Infrared Spectroscopy of HD~100546: IV. Orbiting Companion Disappears on Schedule

## TL;DR

This study tracks a suspected orbiting companion in the disk of HD~100546 through high-resolution near-infrared spectroscopy, confirming its disappearance as predicted and providing insights into planet-disk interactions.

## Contribution

It provides observational evidence of an orbiting companion within the disk's inner hole and confirms its disappearance on schedule, supporting the circumplanetary disk hypothesis.

## Key findings

- Orbiting source of excess CO emission disappeared in 2017
- Spectroastrometric signals confirmed the companion's orbit
- Remaining CO lines unchanged suggest localized emission

## Abstract

HD~100546 is a Herbig Ae/Be star surrounded by a disk with a large central region that is cleared of gas and dust (i.e., an inner hole). High-resolution near-infrared spectroscopy reveals a rich emission spectrum of fundamental ro-vibrational CO emission lines whose time variable properties point to the presence of an orbiting companion within the hole. The Doppler shift and spectroastrometric signal of the CO v=1-0 P26 line, observed from 2003 to 2013, are consistent with a source of excess CO emission that orbits the star near the inner rim of the disk. The properties of the excess emission are consistent with those of a circumplanetary disk. In this paper, we report follow up observations that confirm our earlier prediction that the orbiting source of excess emission would disappear behind the near side of the inner rim of the outer disk in 2017. We find that while the hotband CO lines remained unchanged in 2017, the v=1-0 P26 line and its spectroastrometric signal returned to the profile observed in 2003. With these new observations, we further constrain the origin of the emission and discuss possible ways of confirming the presence of an orbiting planetary companion in the inner disk.