Thermal Starless Ammonia Core Surrounded by CCS in the Orion A Cloud
  We imaged two starless molecular cloud cores, TUKH083 and TUKH122, in the
Orion A giant molecular cloud in the CCS and ammonia (NH$_3$) emission with the
Very Large Array. TUKH122 contains one NH$_3$ core "TUKH122-n," which is
elongated and has a smooth oval boundary. Where observed, the CCS emission
surrounds the NH$_3$ core. This configuration resembles that of the N$_2$H$^+$
and CCS distribution in the Taurus starless core L1544, a well-studied example
of a dense prestellar core exhibiting infall motions. The linewidth of
TUKH122-n is narrow (0.20 km s$^{-1}$) in the NH$_3$ emission line and
therefore dominated by thermal motions. The smooth oval shape of the core
boundary and narrow linewidth in NH$_3$ seem to imply that TUKH122-n is
dynamically relaxed and quiescent. TUKH122-n is similar to L1544 in the kinetic
temperature (10 K), linear size (0.03 pc), and virial mass ($\sim$ 2
$M_{\odot}$). Our results strongly suggest that TUKH122-n is on the verge of
star formation. TUKH122-n is embedded in the 0.2 pc massive (virial mass $\sim$
30 $M_{\odot}$) turbulent parent core, while the L1544 NH$_3$ core is embedded
in the 0.2 pc less-massive (virial mass $\sim$ 10 $M_{\odot}$) thermal parent
core. TUKH083 shows complicated distribution in NH$_3$, but was not detected in
CCS. The CCS emission toward TUKH083 appears to be extended, and is resolved
out in our interferometric observations.
