Chemical Variation in Molecular Cloud Cores in the Orion A Cloud. II
  We have mapped six molecular cloud cores in the Orion A giant molecular cloud
(GMC), whose kinetic temperatures range from 10 to 30 K, in CCS and N2H+ with
Nobeyama 45 m radio telescope to study their chemical characteristics. We
identified 31 intensity peaks in the CCS and N2H+ emission in these molecular
cloud cores. It is found for cores with temperatures lower than ~ 25 K that the
column density ratio of N(N2H+)/N(CCS) is low toward starless core regions
while it is high toward star-forming core regions, in case that we detected
both of the CCS and N2H+ emission. This is very similar to the tendency found
in dark clouds (kinetic temperature ~ 10 K). The criterion found in the Orion A
GMC is N(N2H+)/N(CCS) ~ 2-3. In some cases, the CCS emission is detected toward
protostars as well as the N2H+ emission. Secondary late-stage CCS peak in the
chemical evolution caused by CO depletion may be a possible explanation for
this. We found that the chemical variation of CCS and N2H+ can also be used as
a tracer of evolution in warm (10-25 K) GMC cores. On the other hand, some
protostars do not accompany N2H+ intensity peaks but are associated with dust
continuum emitting regions, suggesting that the N2H+ abundance might be
decreased due to CO evaporation in warmer star-forming sites.
