466 research outputs found
Depletion of CCS in a Candidate Warm-Carbon-Chain-Chemistry Source L483
We have carried out an observation of the CCS (=21) line
with the Very Large Array in its D-configuration toward a protostellar core
L483 (IRAS~181400440). This is a candidate source of the newly found
carbon-chain rich environment called "Warm-Carbon-Chain-Chemistry (WCCC)",
according to the previous observations of carbon-chain molecules. The CCS
distribution in L483 is found to consist of two clumps aligned in the
northwest-southeast direction, well tracing the CCS ridge observed with the
single-dish radio telescope. The most remarkable feature is that CCS is
depleted at the core center. Such a CCS distribution with the central hole is
consistent with those of previously observed prestellar and protostellar cores,
but it is rather unexpected for L483. This is because the distribution of CS,
which is usually similar to that of CCS, is centrally peaked. Our results imply
that the CCS (=21) line would selectively trace the outer
cold envelope in the chemically less evolved phase that is seriously resolved
out with the interferometric observation. Thus, it is most likely that the high
abundance of CCS in L483 relative to the other WCCC sources is not due to the
activity of the protostar, although it would be related to its younger chemical
evolutionary stage, or a short timescale of the prestellar phase.Comment: 10 pages, 3 figures, accepted for publication in ApJ Part
L1521E: A Starless Core in the Early Evolutionary Stage ?
We have studied the physical and chemical properties of a quiescent starless
core L1521E with various molecular lines. It is found that there exists a
compact dense core traced by the H^13CO^+, HN^13C, CCS, and HC_3N lines; their
distributions have a single peak at the same position. The core radius is as
small as 0.031 pc, whereas the H_2 density at the peak position is as high as
(1.3-5.6)times10^5 cm^-3. Although the density is high enough to excite the
inversion transitions of NH_3, these lines are found to be very faint in
L1521E. The distributions of NH_3 and CCS seem to be different from those of
well-studied starless cores, L1498 and L1544, where the distribution of CCS
shows a shell-like structure while that of NH_3 is concentrated at the center
of the core. Abundances of carbon-chain molecules are higher in L1521E than the
other dark cloud cores, and especially those of sulfur-bearing molecules C_nS
are comparable to the cyanopolyyne peak of TMC-1. Our results suggest that
L1521E would be in a very early stage of physical and chemical evolution.Comment: 10 pages, 3 EPS figures, uses aaspp4.sty and epsf.sty, AAS LaTeX
macros v4.0, The Astrophysical Journal, in pres
H2O maser motions and the distance of the star forming region G192.16-3.84
We present the results of astrometic observations of H2O masers associated
with the star forming region G192.16-3.84 with the VLBI Exploration of Radio
Astrometry (VERA). The H2O masers seem to be associated with two young stellar
objects (YSOs) separated by \sim1200 AU as reported in previous observations.
In the present observations, we successfully detected an annual parallax of
0.66 \pm 0.04 mas for the H2 O masers, which corresponds to a distance to
G192.16-3.84 of D = 1.52 \pm 0.08 kpc from the Sun. The determined distance is
shorter than the estimated kinematic distance. Using the annual parallax
distance and the estimated parameters of the millimeter continuum emission, we
estimate the mass of the disk plus circumstellar cloud in the southern young
stellar object to be 10.0+4.3M\cdot. We also estimate the galactocentric
distance and the peculiar motion -3.6 of G192.16-3.84, relative to a circular
Galactic rotation: R\star = 9.99 \pm 0.08 kpc, Z\star = -0.10 \pm 0.01 kpc, and
(U\star,V\star,W\star)=(-2.8\pm1.0,-10.5\pm0.3,4.9\pm2.7)[kms-1]respectively.
The peculiar motion of G192.16-3.84 is within that typically found in recent
VLBI astrometric results. The angular distribution and three-dimensional
velocity field of H2O maser features associated with the northern YSO indicate
the existence of a bipolar outflow with a major axis along the
northeast-southwest direction.Comment: 9 pages, 2 figures and 4 tables. Accepted for publication on PAS
A Methodology of Estimation on Air Pollution and Its Health Effects in Large Japanese Cities
The correlation between air pollution and health effects in large Japanese cities presents a great challenge owing to the limited availability of data on the exposure to pollution, health effects and the uncertainty of mixed causes. A methodology for quantitative relationships (between the emission volume and air quality, and the air quality and health effects) is analysed with a statistical method in this article; the correlation of air pollution reduction policy in Japan from 1974 to 2007.
This chapter discusses a step-by-step methodology of determining the direct correlation between emission volumes, air quality, and health effects.
The relationship between total emissions (NOx, PM) (from both stationary and mobile sources) and air quality (NO2, TSP) was found to be significant. The correlation analysis of emission volume, and air quality suggests that NOx and PM levels worsen according to increases in NO2.
When the correlation between the air pollutant and the type of health effect (certified, mortality, recovery, and newly registered) was examined according to the certified area, an inverse relationship was observed. The relationship between air quality (NO2) and health effect was found to be significant. When NO2 worsens, certified patients, mortality rates and newly certified patients increase, according to the data from 1989 to 2007 with dummy variable analysis
Molecular Line Observations of Carbon-Chain-Producing Regions L1495B and L1521B
We present the first comprehensive study on physical and chemical properties
of quiescent starless cores L1495B and L1521B, which are known to be rich in
carbon-chain molecules like the cyanopolyyne peak of TMC-1 and L1521E. We have
detected radio spectral lines of various carbon-chain molecules such as CCS,
CS, CH, HCN, and HCN. On the other hand, the NH
lines are weak and the NH lines are not detected. According to our
mapping observations of the HCN, CCS, and CS lines, the dense cores
in L1495B and L1521B are compact with the radius of 0.063 and 0.044 pc,
respectively, and have a simple elliptical structure. The distributions of CCS
seem to be different from those of well-studied starless cores, L1498 and
L1544, where the distribution of CCS shows a shell-like structure. Since the
HCO, HNC, and CS lines are detected in L1495B and
L1521B, the densities of these cores are high enough to excite the NH and
NH lines. Therefore, the abundances of NH and NH
relative to carbon-chain molecules are apparently deficient, as observed in
L1521E. We found that longer carbon-chain molecules such as HCN and
CH are more abundant in TMC-1 than L1495B and L1521B, while those of
sulfur-bearing molecules such as CS, CCS, and CS are comparable.
Both distributions and abundances of the observed molecules of L1495B and
L1521B are quite similar to those of L1521E, strongly suggesting that L1495B
and L1521B is in a very early stage of physical and chemical evolution.Comment: 19 pages, 6 figures, accepted to The Astrophysical Journa
DNC/HNC Ratio of Massive Clumps in Early Evolutionary Stages of High-Mass Star Formation
We have observed the HN13C J=1-0 and DNC J=1-0 lines toward 18 massive
clumps, including infrared dark clouds (IRDCs) and high-mass protostellar
objects (HMPOs), by using the Nobeyama Radio Observatory 45 m telescope. We
have found that the HN13C emission is stronger than the DNC emission toward all
the observed sources. The averaged DNC/HNC ratio is indeed lower toward the
observed high-mass sources (0.009\pm0.005) than toward the low-mass starless
and star-forming cores (0.06). The kinetic temperature derived from the NH3 (J,
K) = (1, 1) and (2, 2) line intensities is higher toward the observed high-mass
sources than toward the low-mass cores. However the DNC/HNC ratio of some IRDCs
involving the Spitzer 24 {\mu}m sources is found to be lower than that of
HMPOs, although the kinetic temperature of the IRDCs is lower than that of the
HMPOs. This implies that the DNC/HNC ratio does not depend only on the current
kinetic temperature. With the aid of chemical model simulations, we discuss how
the DNC/HNC ratio decreases after the birth of protostars. We suggest that the
DNC/HNC ratio in star-forming cores depends on the physical conditions and
history in their starless-core phase, such as its duration time and the gas
kinetic temperature.Comment: 27 pages, 4 figures, accepted to Ap
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