37 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
A collimated jet and an infalling-rotating disk in G192.16-3.84 traced by H2O maser emission
We report H2O masers associated with the massive-star forming region
G192.16-3.84 observed with the new Japan VLBI network at three epochs spanned
for two months, which have revealed the three-dimensional kinematical structure
of the whole \h2o maser region in G192.16-3.84, containing two young stellar
objects separated by ~1200 AU. The maser spatio-kinematical structure has well
persisted since previous observations, in which the masers are expected to be
associated with a highly-collimated bipolar jet and an infalling-rotating disk
in the northern and southern clusters of H2O maser features, respectively. We
estimated a jet expansion speed of ~100 km/s and re-estimated a dynamical age
of the whole jet to be 5.6x10^4 yrs. We have investigated the spatial
distribution of Doppler velocities during the previous and present observations
and relative proper motions of H2O maser features in the southern cluster, and
a relative bulk motion between the two maser clusters. They are well explained
by a model of an infalling-rotating disk with a radius of ~1000 AU and a
central stellar mass of 5-10 M_sun, rather than by a model of a bipolar jet
perpendicular to the observed CO outflow. Based on the derived H2O maser
spatio-kinematical parameters, we discuss the formation mechanism of the
massive young stellar objects and the outflow development in G192.16-3.84.Comment: 30 pages, 3 figures, 3 tables, to be published in the Publication of
the Astronomical Society of Japan issued on 2006 October 2
N2H+ Observations of Molecular Cloud Cores in Taurus
N2H+ observations of molecular cloud cores in Taurus with the Nobeyama 45 m
radio telescope are reported. We compare ``cores with young stars'' with
``cores without young stars''. The differences in core radius, linewidth, and
core mass are small. Linewidth is dominated by thermal motions in both cases.
N2H+ maps show that the intensity distribution does not differ much between
cores without stars and those with stars. This is in contrast to the result
previously obtained in H13CO+ toward Taurus molecular cloud cores. Larger
degree of depletion of H13CO+ in starless cores will be one possible
explanation for this difference. We studied the physical state of molecular
cloud cores in terms of ``critical pressure'' for the surface (external)
pressure. There is no systematic difference between starless cores and cores
with stars in this analysis. Both are not far from the critical state for
pressure equilibrium. We suggest that molecular cloud cores in which thermal
support is dominated evolve toward star formation by keeping close to the
critical state. This result is in contrast with that obtained in the
intermediate-mass star forming region OMC-2/3, where molecular cloud cores
evolve by decreasing the critical pressure appreciably. We investigate the
radial distribution of the integrated intensity. Cores with stars are found to
have shallow (-1.8 to -1.6) power-law density profiles.Comment: 19 pages, 5 figure
SiO Emission in the Multi-Lobe Outflow associated with IRAS 16293-2422
We have mapped the thermal emission line of SiO (v = 0; J = 2-1) associated
with the quadrupolar molecular outflow driven by the very cold far-infrared
source IRAS 16293-2422. The SiO emission is significantly enhanced in the
northeastern red lobe and at the position ~50" east of the IRAS source. Strong
SiO emission observed at ~50" east of the IRAS source presents evidence for a
dynamical interaction between a part of the eastern blue lobe and the dense
ambient gas condensation, however, such an interaction is unlikely to be
responsible for producing the quadrupolar morphology. The SiO emission in the
northeastern red lobe shows the spatial and velocity structure similar to those
of the CO outflow, suggesting that the SiO emission comes from the molecular
outflow in the northeastern red lobe itself. The observed velocity structure is
reproduced by a simple spatio-kinematic model of bow shock with a shock
velocity of 19-24 km/s inclined by 30-45 deg from the plane of the sky. This
implies that the northeastern red lobe is independent of the eastern blue lobe
and that the quadrupolar structure is due to two separate bipolar outflows.
The SiO emission observed in the western red lobe has a broad pedestal shape
with low intensity. Unlike the SiO emission in the northeastern red lobe, the
spatial extent of the SiO emission in the western red lobe is restricted to its
central region. The spatial and velocity structures and the line profiles
suggest that three different types of the SiO emission are observed in this
outflow; the SiO emission arises from the interface between the outflowing gas
and the dense ambient gas clump, the SiO emission coming from the outflow lobe
itself, and the broad SiO emission with low intensity observed at the central
region of the outflow lobe.Comment: 14 pages, 6 figures (figures 1 and 4 are color), gzipped tar file, To
appear in the Ap