245 research outputs found

    Chemical Variation in Molecular Cloud Cores in the Orion A Cloud

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    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

    Depletion of CCS in a Candidate Warm-Carbon-Chain-Chemistry Source L483

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    We have carried out an observation of the CCS (JNJ_{N}=21_{1}-10_{0}) line with the Very Large Array in its D-configuration toward a protostellar core L483 (IRAS~18140-0440). 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 (JNJ_{N}=21_{1}-10_{0}) 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

    A collimated jet and an infalling-rotating disk in G192.16-3.84 traced by H2O maser emission

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    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

    L1521E: A Starless Core in the Early Evolutionary Stage ?

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    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