From scattered-light to millimeter emission: A comprehensive view of the Gyr-old system of HD 202628 and its eccentric debris ring

TL;DR

This study combines multi-wavelength observations to analyze the eccentric debris ring around HD 202628, revealing its structure, eccentricity, grain size distribution, and potential planetary influences, providing new insights into its formation and dynamics.

Contribution

It offers a comprehensive multi-wavelength analysis of HD 202628's debris ring, including new ALMA, Herschel, and HST data, and constrains the properties of potential planetary perturbers.

Findings

Ring inner and outer edges at 143.1 and 165.5 AU

Eccentricity of the ring is approximately 0.09

Detection of point-like sources possibly indicating a planet or circumplanetary material

Abstract

We present here new observations of the eccentric debris ring surrounding the Gyr-old solar-type star HD 202628: at millimeter wavelengths with ALMA, at far-infrared wavelengths with \textit{Herschel}, and in scattered light with \textit{HST}. The ring inner edge is found to be consistent between ALMA and \textit{HST} data. As radiation pressure affects small grains seen in scattered-light, the ring appears broader at optical than at millimeter wavelengths. The best fit to the ring seen with ALMA has inner and outer edges at $143.1 \pm 1.7$ AU and $165.5 \pm 1.4$, respectively, and an inclination of $57.4^\circ \pm 0.4$ from face-on. The offset of the ring centre of symmetry from the star allows us to quantify its eccentricity to be $e=0.09_{-0.01}^{+0.02}$. This eccentric feature is also detected in low resolution \textit{Herschel}/PACS observations, under the form of a pericenter-glow. Combining the infrared and millimeter photometry, we retrieve a disk grain size distribution index of $\sim -3.4$, and therefore exclude in-situ formation of the inferred belt-shaping perturber, for which we provide new dynamical constraints. Finally, ALMA images show four point-like sources that exceed 100$\,\mu$Jy, one of them being just interior to the ring. Although the presence of a background object cannot be excluded, we cannot exclude either that this source is circumplanetary material surrounding the belt-shaper, in which case degeneracies between its mass and orbital parameters could be lifted, allowing us to fully characterize such a distant planet in this mass and age regime for the very first time.