2,224 research outputs found
Chemical Variation in Molecular Cloud Cores in the Orion A Cloud
We have observed molecular cloud cores in the Orion A giant molecular cloud
(GMC) in CCS, HC3N, DNC, and HN13C to study their chemical characteristics. We
have detected CCS in the Orion A GMC for the first time. CCS was detected in
about a third of the observed cores. The cores detected in CCS are not
localized but are widely distributed over the Orion A GMC. The CCS peak
intensity of the core tends to be high in the southern region of the Orion A
GMC. The HC3N peak intensity of the core also tends to be high in the southern
region, while there are HC3N intense cores near Orion KL, which is not seen in
CCS. The core associated with Orion KL shows broad HC3N line profile, and star
formation activity near Orion KL seems to enhance the HC3N emission. The column
density ratio of NH3 to CCS is lower near the middle of the filament, and is
higher toward the northern and southern regions along the Orion A GMC filament.
This ratio is known to trace the chemical evolution in nearby dark cloud cores,
but seems to be affected by core gas temperature in the Orion A GMC: cores with
low NH3 to CCS column density ratios tend to have warmer gas temperature. The
value of the column density ratio of DNC to HN13C is generally similar to that
in dark cloud cores, but becomes lower around Orion KL due to higher gas
temperature.Comment: 26 pages, 18 figures, to be published in Publications of the
Astronomical Society of Japa
Search for High-Mass Protostellar Objects in Cold IRAS Sources
We present the results of CS J=2-1 mapping observations towards 39 massive
star-forming regions selected from the previous CO line survey of cold IRAS
sources with high-velocity CO flows along the Galactic plane (Yang et al.
2002). All sources are detected in CS J=2-1 showing the existence of CS clumps
around the IRAS sources. However, one-third of the sources are not deeply
embedded in the dense clumps by comparison of the central powering IRAS sources
and the morphologies of CS clumps. Physical parameters of the dense molecular
clumps are presented. We have identified 12 high-mass protostellar object
(HMPO) candidates by checking the association between the dense cores and the
IRAS sources, the detection of water maser, and the radio properties towards
the IRAS sources. We find that the HMPO sources are characterized by low FIR
luminosity to virial mass ratios since they are in very early evolutionary
stages when the massive protostars have not reached their full luminosities,
which are typical for zero-age main sequence stars. Large turbulent motion in
the HMPO sources may be largely due to the large kinetic energy ejected by the
central protostars formed in the dense clumps. However, alternative means or
undetected outflows may also be responsible for the turbulence in the clumps.Comment: 20 pages, 4 figures, accepted for publication in A
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