A SPHERE survey of self-shadowed planet-forming disks

TL;DR

This study investigates faint, self-shadowed planet-forming disks using VLT/SPHERE imaging, revealing their limited scattered light detection and the role of inner disk rims in shadowing the outer disk regions.

Contribution

It provides new insights into the demography of faint, self-shadowed disks and highlights the importance of inner disk rims in their illumination patterns, expanding understanding beyond bright disk observations.

Findings

Self-shadowed disks show limited scattered light detection.

Inner disk rims intercept starlight, causing outer disk shadowing.

Disk brightness distribution is similar across spectral types.

Abstract

To date, nearly two hundred planet-forming disks have been imaged with high resolution. Our propensity to study bright and extended objects is however biasing our view of the disk demography. In this work, we contribute to alleviate this bias by analyzing fifteen disks targeted with VLT/SPHERE that look faint in scattered light. Sources were selected based on a low far-IR excess from the spectral energy distribution. The comparison with the ALMA images available for a few sources shows that the scattered light surveyed by these datasets is only detected from a small portion of the disk extent. The mild anti-correlation between the disk brightness and the near-IR excess demonstrates that these disks are self-shadowed: the inner disk rim intercepts much starlight and leaves the outer disk in penumbra. Based on the uniform distribution of the disk brightness in scattered light across all spectral types, self-shadowing would act similarly for inner rims at a different distance from the star. We discuss how the illumination pattern of the outer disk may evolve with time. Some objects in the sample are proposed to be at an intermediate stage toward bright disks from the literature with either no shadow or with sign of azimuthally confined shadows.