SKYSURF-11: A New Zodiacal Light Model Optimized for Optical Wavelengths

TL;DR

This paper introduces ZodiSURF, an improved zodiacal light model optimized for optical wavelengths, utilizing HST data to enhance accuracy over previous infrared-based models.

Contribution

The paper develops a new zodiacal light model, ZodiSURF, with wavelength-dependent scattering and albedo, improving predictions in optical wavelengths based on extensive HST measurements.

Findings

ZodiSURF reduces prediction uncertainty to ~4.5%.

HST sky measurements show an excess diffuse light not explained by the model.

A toy model suggests a possible dim spherical dust cloud component.

Abstract

We present an improved zodiacal light model, optimized for optical wavelengths, using archival Hubble Space Telescope (HST) imaging from the SKYSURF program. The Kelsall et al. 1998 model used infrared imaging from the Diffuse Infrared Background Experiment (DIRBE) on board the Cosmic Background Explorer to create a 3D structure of the interplanetary dust cloud. However, this model cannot accurately represent zodiacal light emission outside of DIRBE's nominal wavelength bandpasses, the bluest of which is 1.25 micron. We present a revision to this model (called ZodiSURF) that incorporates analytical forms of both the scattering phase function and albedo as a function of wavelength, which are empirically determined across optical wavelengths (0.3-1.6 micron) from over 5,000 HST sky surface brightness (sky-SB) measurements. This refined model results in significantly improved predictions of zodiacal light emission at these wavelengths and for Sun angles greater than 80 deg. Fits to HST data show an uncertainty in the model of ~4.5%. Remarkably, the HST sky-SB measurements show an excess of residual diffuse light (HST Sky - ZodiSURF - Diffuse Galactic Light) of 0.013 +/- 0.006 MJy/sr. We suggest that a very dim spherical dust cloud may need to be included in the zodiacal light model, which we present here as a toy model.