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We present radio-interferometric observations of HCN J=1-0 line emission fromthe carbon star R Scl, obtained with the interim 3-mm receivers of theAustralia Telescope Compact Array. The emission is resolved into a centralsource with a Gaussian FWHM of ~1 arcsec, which we identify as the present massloss envelope. Using a simple photodissociation model and constraints fromsingle-dish HCN spectra, we argue that the present mass-loss rate is low, ~2 x10^{-7} Msol/yr, supporting the idea that R Scl had to experience a briefepisode of intense mass loss in order to produce the detached CO shell at ~10arcsec radius inferred from single-dish observations. Detailed radiativetransfer modelling yields an abundance of HCN relative to H_2, of ~10^{-5} inthe present-day wind. There appears to be a discrepancy between model resultsobtained with higher transition single-dish data included and those from theJ=1-0 interferometer data alone, in that the interferometer data suggest asmaller envelope size and larger HCN abundance than the single-dish data. Thelack of HCN in the detached shell is consistent with the rapidphotodissociation of HCN into CN as it expands away from the star.Comment: 9 pages, 8 figures, accepted by A&

Australia Telescope Compact Array imaging of circumstellar HCN line emission from R Scl