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

Abstract

The presence of a debris disc around the Gyr-old solar-type star ${\zeta }^2\mathrm{Reticuli}$ was suggested by the $Spitzer$ infrared excess detection. Follow-up observations with $Herschel$/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 $5.7\mu Jy/arcse{\mathrm{c}}^2$ at 1.3 mm, and $26\mu Jy/arcse{\mathrm{c}}^2$ at 870 microns. Our results overall demonstrate the capability of the ALMA/ACA to follow-up $Herschel$ observations of debris discs and clarify the effects of background confusion.

6 pages, 2 figures, 2 tables