We present ALMA Band 6 observations ( 1.3 mm/233 GHz ) of Fomalhaut and its debris disc .
The observations achieve a sensitivity of 17 \mu Jy and a resolution of 0.28 arcsec ( 2.1 au at a distance of 7.66 pc ) , which are the highest resolution observations to date of the millimetre grains in Fomalhaut ’ s main debris ring .
The ring is tightly constrained to 139 ^ { +2 } _ { -3 } au with a FWHM of 13 \pm 3 au , following a Gaussian profile .
The millimetre spectral index is constrained to \alpha _ { mm } = -2.73 \pm 0.13 .
We explore fitting debris disc models in the image plane , as well as fitting models using visibility data directly .
The results are compared and the potential advantages/disadvantages of each approach are discussed .

The detected central emission is indistinguishable from a point source , with a most probable flux of 0.90 \pm 0.12 mJy ( including calibration uncertainties ) .
This implies that any inner debris structure , as was inferred from far-Infrared observations , must contribute little to the total central emission .
Moreover , the stellar flux is less than 70 % of that predicted by extrapolating a black body from the constrained stellar photosphere temperature .
This result emphasizes that unresolved inner debris components can not be fully characterized until the behaviour of the host star ’ s intrinsic stellar emission at millimetre wavelengths is properly understood .