Complex Organic Molecules Towards Embedded Low-Mass Protostars
  Complex organic molecules (COMs) have been observed towards several low-mass
young stellar objects (LYSOs). Small and heterogeneous samples have so far
precluded conclusions on typical COM abundances, as well as the origin(s) of
abundance variations between sources. We present observations towards 16 deeply
embedded (Class 0/I) low-mass protostars using the IRAM 30m telescope. We
detect CH$_2$CO, CH$_3$CHO, CH$_3$OCH$_3$, CH$_3$OCHO, CH$_3$CN, HNCO, and
HC$_3$N towards 67%, 37%, 13%, 13%, 44%, 81%, and 75% of sources respectively.
Median column densities derived using survival analysis range between
6.0x10$^{10}$ cm$^{-2}$ (CH$_3$CN) and 2.4x10$^{12}$ cm$^{-2}$ (CH$_3$OCH$_3$)
and median abundances range between 0.48% (CH$_3$CN) and 16% (HNCO) with
respect to CH$_3$OH. Column densities for each molecule vary by about one order
of magnitude across the sample. Abundances with respect to CH$_3$OH are more
narrowly distributed, especially for oxygen-bearing species. We compare
observed median abundances with a chemical model for low-mass protostars and
find fair agreement, although some modeling work remains to bring abundances
higher with respect to CH$_3$OH. Median abundances with respect to CH$_3$OH in
LYSOs are also found to be generally comparable to observed abundances in hot
cores, hot corinos, and massive young stellar objects. Compared with comets,
our sample is comparable for all molecules except HC$_3$N and CH$_2$CO, which
likely become depleted at later evolutionary stages.
