Is there really a debris disc around $\zeta^2\,\mathrm{Reticuli}$ ?

TL;DR

High-resolution ALMA observations show no evidence of a debris disc around ζ² Reticuli, contradicting earlier infrared detections and highlighting the importance of follow-up imaging to confirm debris disc presence.

Contribution

This study provides the first unambiguous ALMA/ACA imaging that refutes previous debris disc claims around ζ² Reticuli, emphasizing the role of high-resolution observations in debris disc confirmation.

Findings

No flux detected around ζ² Reticuli at 1.3 mm and 870 microns.

Surface brightness upper limits set at 5.7 μJy/arcsec² and 26 μJy/arcsec².

Background confusion can mimic debris disc features in infrared observations.

Abstract

The presence of a debris disc around the Gyr-old solar-type star $\zeta^2\,\mathrm{Reticuli}$ was suggested by the $\mathit{Spitzer}$ infrared excess detection. Follow-up observations with $\mathit{Herschel}$/PACS revealed a double-lobed feature, that displayed asymmetries both in brightness and position. Therefore, the disc was thought to be edge-on and significantly eccentric. Here we present ALMA/ACA observations in Band 6 and 7 which unambiguously reveal that these lobes show no common proper motion with $\zeta^2\,\mathrm{Reticuli}$. In these observations, no flux has been detected around $\zeta^2\,\mathrm{Reticuli}$ that exceeds the $3\sigma$ levels. We conclude that surface brightness upper limits of a debris disc around $\zeta^2\,\mathrm{Reticuli}$ are $5.7\,\mathrm{\mu Jy/arcsec^2}$ at 1.3 mm, and $26\,\mathrm{\mu Jy/arcsec^2}$ at 870 microns. Our results overall demonstrate the capability of the ALMA/ACA to follow-up $\mathit{Herschel}$ observations of debris discs and clarify the effects of background confusion.