# An Optical/near-infrared investigation of HD 100546 b with the Gemini Planet Imager and MagAO

## TL;DR

This study uses optical and near-infrared observations to analyze the protoplanet HD 100546b, revealing that its detected emission is likely a disk feature rather than a planet or accreting object, with implications for understanding planet formation.

## Contribution

It provides new spectroscopic and photometric data showing the emission is consistent with scattered light, challenging previous interpretations of HD 100546b as an accreting protoplanet.

## Key findings

- H band emission is likely scattered light, not a planet.
- Emission appears stationary over 4.6 years, inconsistent with orbit.
- Upper limits on accretion rate suggest no active accretion at detection level.

## Abstract

We present H band spectroscopic and Halpha photometric observations of HD 100546 obtained with GPI and MagAO. We detect H band emission at the location of the protoplanet HD 100546b, but show that choice of data processing parameters strongly affects the morphology of this source. It appears point-like in some aggressive reductions, but rejoins an extended disk structure in the majority of the others. Furthermore, we demonstrate that this emission appears stationary on a timescale of 4.6 yrs, inconsistent at the 2sigma level with a Keplerian clockwise orbit at 59 au in the disk plane. The H band spectrum of the emission is inconsistent with any type of low effective temperature object or accreting protoplanetary disk. It strongly suggests a scattered light origin, as it is consistent with the spectrum of the star and the spectra extracted at other locations in the disk. A non detection at the 5sigma level of HD 100546b in differential Halpha imaging places an upper limit, assuming the protoplanet lies in a gap free of extinction, on the accretion luminosity and accretion rate of 1.7E-4 Lsun and MMdot<6.4E-7Mjup^2/yr for 1Rjup. These limits are comparable to the accretion luminosity and rate of TTauri-stars or LkCa 15b. Taken together, these lines of evidence suggest that the H band source at the location of HD 100546b is not emitted by a planetary photosphere or an accreting circumplanetary disk but is a disk feature enhanced by the PSF subtraction process. This non-detection is consistent with the non-detection in the K band reported in an earlier study but does not exclude the possibility that HD 100546b is deeply embedded.