Complex Spiral Structure in the HD 100546 Transitional Disk as Revealed by GPI and MagAO

Abstract: We present optical and near-infrared high contrast images of the transitional disk HD 100546 taken with the Magellan Adaptive Optics system (MagAO) and the Gemini Planet Imager (GPI). GPI data include both polarized intensity and total intensity imagery, and MagAO data are taken in Simultaneous Differential Imaging mode at H{\alpha}. The new GPI H -band total intensity data represent a significant enhancement in sensitivity and field rotation compared to previous data sets and enable a detailed exploration of substructure in the disk. The data are processed with a variety of differential imaging techniques (polarized, angular, reference, and simultaneous differential imaging) in an attempt to identify the disk structures that are most consistent across wavelengths, processing techniques, and algorithmic parameters. The inner disk cavity at 15 au is clearly resolved in multiple datasets, as are a variety of spiral features. While the cavity and spiral structures are identified at levels significantly distinct from the neighboring regions of the disk under several algorithms and with a range of algorithmic parameters, emission at the location of HD 100546 c varies from point-like under aggressive algorithmic parameters to a smooth continuous structure with conservative parameters, and is consistent with disk emission. Features identified in the HD100546 disk bear qualitative similarity to computational models of a moderately inclined two-armed spiral disk, where projection effects and wrapping of the spiral arms around the star result in a number of truncated spiral features in forward-modeled images.

Overview of Complex Spiral Structure in the HD 100546 Transitional Disk

This paper presents an intricate examination of the HD 100546 transitional disk using data collected with the Magellan Adaptive Optics system (MagAO) and the Gemini Planet Imager (GPI). The authors provide a comprehensive analysis of optical and near-infrared images to unravel the spiral structures and other features of the disk.

Key Discoveries

The high-resolution images acquired from MagAO at the Hα wavelength and GPI at near-infrared bands reveal several crucial facets of the HD 100546 disk:

1. Inner Disk Cavity: The inner cavity is resolved at 15 au and clearly visualized across multiple datasets. This cavity is a defining characteristic of transitional disks, typically indicating ongoing planet formation as one possible mechanism for disk clearing.

2. Spiral Structures: The disk's spiral features, identified consistently across various wavelengths and imaging techniques, suggest a complex morphology. This is indicative of dynamic interactions possibly involving planetary bodies within the disk.

3. Suppressed Emission Variability: Despite an otherwise dynamic environment, emission at the location of the proposed HD 100546 c planet candidate demonstrates variability ranging from point-like to smooth under differing algorithmic parameters.

Implications and Future Work

The presence of prominent spiral features could imply active planet-disk interactions and, accordingly, speak to processes related to planet formation within the disk cavity. This aligns with the notion that spiral structures may be driven by embedded protoplanets, a hypothesis supported by comparative modelling of spiral arm features corresponding to known dynamic principles.

The observations also pose constraints on the detection of any putative planets, specifically at the locations of the HD 100546 b and c candidates. The paper's spectral analysis further indicates that caution must be exercised in interpreting planet signals, especially in such complex structures where aggressive data processing may mask true disk-related features as planetary emissions.

The research offers a solid foundation for using high-contrast imaging to further our understanding of transitional disks. It presents a case for continued developments in adaptive optics and imaging technology, potentially advancing theoretical frameworks that detail planet-disk interaction mechanisms. Future directions might include deeper spectral analyses and planet-driven disk modeling, exploring the parameters that control spiral interactions and their observational signatures.

In conclusion, while the paper refrains from declaring definitive planetary detection, it serves as a cogent reminder of the subtleties inherent in high-contrast astrophysical imaging, underlining the importance of methodical, multi-wavelength approaches in studying circumstellar disks.