The complex organic molecular content in the L1498 starless core
  Observations carried out toward starless and pre-stellar cores have revealed
that complex organic molecules are prevalent in these objects, but it is
unclear what chemical processes are involved in their formation. Recently, it
has been shown that complex organics are preferentially produced at an
intermediate-density shell within the L1544 pre-stellar core at radial
distances of ~4000 au with respect to the core center. However, the spatial
distribution of complex organics has only been inferred toward this core and it
remains unknown whether these species present a similar behaviour in other
cores. We report high-sensitivity observations carried out toward two positions
in the L1498 pre-stellar core, the dust peak and a position located at a
distance of ~11000 au from the center of the core where the emission of
CH$_3$OH peaks. Similarly to L1544, our observations reveal that small
O-bearing molecules and N-bearing species are enhanced by factors ~4-14 toward
the outer shell of L1498. However, unlike L1544, large O-bearing organics such
as CH3CHO, CH3OCH3 or CH3OCHO are not detected within our sensitivity limits.
For N-bearing organics, these species are more abundant toward the outer shell
of the L1498 pre-stellar core than toward the one in L1544. We propose that the
differences observed between O-bearing and N-bearing species in L1498 and L1544
are due to the different physical structure of these cores, which in turn is a
consequence of their evolutionary stage, with L1498 being younger than L1544.
