Starspot patterns on the M dwarfs HK Aqr and RE 1816+541

We present the first Doppler images of two M dwarfs in the solar neighbourh ood. Late-type dwarfs are generally too faint to enable spectra with suffic ient signal-to-noise (SIN) ratios for Doppler imaging to be obtained in sho rt enough exposure times. Using the large number of photospheric absorption lines in each spectrum, we apply least-squares deconvolution to derive com posite line profiles with S/N ratios of 100-500. The surface images of HK A qr reveal a moderately spotted surface, with the majority of starspots appe aring at low latitudes, whereas RE 1816 +541 exhibits spots at all latitude s. Neither star shows significant evidence for the oft-observed polar spot. Despite the boost in S/N ratio achieved with the least-squares deconvoluti on technique, the images are not consistent enough to determine reliably th e magnitude of differential rotation. Nevertheless, the images are consiste nt enough to place upper limits on the rate of surface shear.