Fomalhaut b: Independent Analysis of the Hubble Space Telescope Public Archive Data

TL;DR

This paper reanalyzes Hubble data on Fomalhaut b, confirming its presence but challenging previous flux variability claims and suggesting it may be a circumplanetary disk or collision remnant rather than a planet.

Contribution

It provides an independent analysis of HST data, confirming Fomalhaut b's detection, and proposes new models for its spectral energy distribution.

Findings

Fomalhaut b detected at 0.43 microns for the first time.

No flux variability observed at 0.6 microns over two years.

SED suggests a circumplanetary disk or collision remnant, not a massive planet.

Abstract

The nature and even the existence of a putative planet-mass companion ("Fomalhaut b") to Fomalhaut has been debated since 2008. In the present paper we reanalyze the multi-epoch ACS/STIS/WFC3 Hubble Space Telescope (HST) optical/near infrared images on which the discovery and some other claims were based. We confirm that the HST images do reveal an object in orbit around Fomalhaut but the detailed results from our analysis differ in some ways from previous discussions. In particular, we do not confirm flux variability over a two-year interval at 0.6 microns wavelength and we detect Fomalhaut b for the first time at the short wavelength of 0.43 microns. We find that the HST image of Fomalhaut b at $0.8\,\mu$m may be extended beyond the PSF. We cannot determine from our astrometry if Fomalhaut b will cross or not the dust ring. The optical through mid-infrared spectral energy distribution (SED) of Fomalhaut b cannot be explained as due to direct or scattered radiation from a massive planet. We consider two models to explain the SED: (1) a large circumplanetary disk around an unseen planet and (2) the aftermath of a collision during the past 50-150 years of two Kuiper Belt-like objects of radii 50 km.