First images of phosphorus molecules towards a proto-Solar analog
  The chemistry of phosphorus in star- and planet-forming regions is poorly
understood, despite the central role of phosphorus in terrestrial biochemistry.
We present ALMA Band 3 and 4 observations of PO and PN towards the Class I
protostar B1-a, representing the first spatially resolved observations of
phosphorus carriers towards a Solar-type star forming region. The phosphorus
molecules emit from two distinct clumps, which coincide with regions where the
protostellar outflow (traced by SiO) interacts with a filament of dense gas
(traced by CCS). Thus, the gas-phase phosphorus seems to originate from the
shocking of dense interstellar clumps. Based on the observed emission patterns,
PO and PN appear to be daughter products of a solid phosphorus carrier with an
intermediate volatility between ices and silicate grains. Interstellar shocks
may therefore play an important role in converting semi-refractory phosphorus
to a more volatile form prior to incorporation into cometary ices. Indeed, the
(PO+PN)/CH3OH ratio is similar in B1-a and comet 67P, implying a comparable
reservoir of volatile phosphorus. The PO/PN ratio ranges from ~1-8 across B1-a.
The northern emission clump exhibits a lower PO/PN ratio and weaker 13CH3OH
emission than southern clump, indicating distinct shock physics and chemistry
at the two positions. Resolved observations of P carriers towards additional
sources are needed to better understand what regulates such variations in the
PO/PN ratio in protostellar environments.
