Searching for the HR 8799 Debris Disk with HST/STIS

TL;DR

This paper introduces a new high contrast imaging algorithm for space telescopes and applies it to HR 8799 data, finding that observed over-luminosity is likely due to telescope breathing and spectral differences, leading to upper limits on dust belt mass.

Contribution

The paper presents OSFi, a novel normalization algorithm for high contrast imaging, and demonstrates its application to HR 8799 data, addressing false positives in debris disk detection.

Findings

Over-luminosity likely caused by telescope breathing and spectral differences.

Upper limits on HR 8799 dust belt mass derived from non-detection.

Flux of micron-sized dust grains is consistent with other debris disks.

Abstract

We present a new algorithm for space telescope high contrast imaging of close-to-face-on planetary disks called Optimized Spatially Filtered (OSFi) normalization. This algorithm is used on HR 8799 Hubble Space Telescope (HST) coronagraphic archival data, showing an over-luminosity after reference star point spread function (PSF) subtraction that may be from the inner disk and/or planetesimal belt components of this system. The PSF-subtracted radial profiles in two separate epochs from 2011 and 2012 are consistent with one another, and self-subtraction shows no residual in both epochs. We explore a number of possible false-positive scenarios that could explain this residual flux, including telescope breathing, spectral differences between HR 8799 and the reference star, imaging of the known warm inner disk component, OSFi algorithm throughput and consistency with the standard spider normalization HST PSF subtraction technique, and coronagraph misalignment from pointing accuracy. In comparison to another similar STIS dataset, we find that the over-luminosity is likely a result of telescope breathing and spectral difference between HR 8799 and the reference star. Thus, assuming a non-detection, we derive upper limits on the HR 8799 dust belt mass in small grains. In this scenario, we find that the flux of these micron-sized dust grains leaving the system due to radiation pressure is small enough to be consistent with measurements of other debris disk halos.