Deep Search for a scattered light dust halo around Vega with the Hubble Space Telescope

TL;DR

This study reports a tentative detection of a scattered light dust halo around Vega using deep Hubble Space Telescope coronagraphy, revealing an extended halo of small dust grains from 10.5 to 30 arcseconds, with implications for debris disk structure.

Contribution

First deep HST coronagraphic imaging of Vega's debris disk revealing an extended dust halo, enhancing understanding of debris disk morphology and dust distribution.

Findings

Detected a dust halo extending from 10.5" to 30" around Vega.

Halo likely composed of small dust grains.

No clear separation between planetesimal belt and dust halo.

Abstract

We present a provisory scattered light detection of the Vega debris disk using deep Hubble Space Telescope coronagraphy (PID 16666). At only 7.7 parsecs, Vega is immensely important in debris disk studies both for its prominence and also because it allows the highest physical resolution among all debris systems relative to temperature zones around the star. We employ the STIS coronagraph's widest wedge position and classical Reference Differential Imaging to achieve among the lowest surface brightness sensitivities to date ($\sim 4\,\mu Jy/arcsec^{2}$) at wide separations using 32 orbits in Cycle 29. We detect a halo extending from the inner edge of our effective inner working angle at $10^{\prime\prime}.5$ out to the photon noise floor at $30^{\prime\prime}$ (80 - 230 au). The face-on orientation of the system and the lack of a perfectly color-matched PSF star have provided significant challenges to the reductions, particularly regarding artifacts from the imperfect color matching. However, we find that a halo of small dust grains provides the best explanation for the observed signal. Unlike Fomalhaut (a close twin to Vega in luminosity, distance, and age), there is no clear distinction in scattered light between the parent planetesimal belt observed with ALMA and the extended dust halo. These HST observations complement JWST GTO Cycle 1 observations of the system with NIRCam and MIRI.