  The high abundances of Complex Organic Molecules (COMs) with respect to
methanol, the most abundant COM, detected towards low-mass protostars, tend to
be underpredicted by astrochemical models. This discrepancy might come from the
large beam of the single-dish telescopes, encompassing several components of
the studied protostar, commonly used to detect COMs. To address this issue, we
have carried out multi-line observations of methanol and several COMs towards
the two low-mass protostars NGC1333-IRAS2A and -IRAS4A with the Plateau de Bure
interferometer at an angular resolution of 2 arcsec, resulting in the first
multi-line detection of the O-bearing species glycolaldehyde and ethanol and of
the N-bearing species ethyl cyanide towards low-mass protostars other than IRAS
16293. The high number of detected transitions from COMs (more than 40 methanol
transitions for instance) allowed us to accurately derive the source size of
their emission and the COMs column densities. The COMs abundances with respect
to methanol derived towards IRAS2A and IRAS4A are slightly, but not
substantitally, lower than those derived from previous single-dish
observations. The COMs abundance ratios do not vary significantly with the
protostellar luminosity, over five orders of magnitude, implying that low-mass
hot corinos are quite chemically rich as high-mass hot cores. Astrochemical
models still underpredict the abundances of key COMs, such as methyl formate or
di-methyl ether, suggesting that our understanding of their formation remains
incomplete.
