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Register a new userThe TMRT K Band Observations towards 26 Infrared Dark Clouds: NH$_{3}$, CCS, and HC$_{3}$N
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We present one of the first Shanghai Tian Ma Radio Telescope (TMRT) K Band observations towards a sample of 26 infrared dark clouds (IRDCs). We observed the (1,1), (2,2), (3,3), and (4,4) transitions of NH$_{3}$ together with CCS (2$_{1}$-1$_{0}$) and HC$_{3}$N $J,$=2-1, simultaneously. The survey dramatically increases the existing CCS-detected IRDC sample from 8 to 23, enabling a better statistical study of the ratios of carbon-chain molecules (CCM) to N-bearing molecules in IRDCs. With the newly developed hyperfine group ratio (HFGR) method of fitting NH$_{3}$ inversion lines, we found the gas temperature to be between 10 and 18 K. The column density ratios of CCS to NH$_{3}$ for most of the IRDCs are less than 10$^{-2}$, distinguishing IRDCs from low-mass star-forming regions. We carried out chemical evolution simulations based on a three-phase chemical model NAUTILUS. Our measurements of the column density ratios between CCM and NH$_{3}$ are consistent with chemical evolutionary ages of $lesssim$10$^{5}$ yr in the models. Comparisons of the data and chemical models suggest that CCS, HC$_{3}$N, and NH$_{3}$ are sensitive to the chemical evolutionary stages of the sources.
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Integrated pulse profiles at 8.6~GHz obtained with the Shanghai Tian Ma Radio Telescope (TMRT) are presented for a sample of 26 pulsars. Mean flux densities and pulse width parameters of these pulsars are estimated. For eleven pulsars these are the first high-frequency observations and for a further four, our observations have a better signal-to-noise ratio than previous observations. For one (PSR J0742-2822) the 8.6~GHz profiles differs from previously observed profiles. A comparison of 19 profiles with those at other frequencies shows that in nine cases the separation between the outmost leading and trailing components decreases with frequency, roughly in agreement with radius-to-frequency mapping, whereas in the other ten the separation is nearly constant. Different spectral indices of profile components lead to the variation of integrated pulse profile shapes with frequency. In seven pulsars with multi-component profiles, the spectral indices of the central components are steeper than those of the outer components. For the 12 pulsars with multi-component profiles in the high-frequency sample, we estimate the core width using gaussian fitting and discuss the width-period relationship.
The dominant mechanism leading to the formation of brown dwarfs (BDs) remains uncertain. The most direct keys to formation, which are obtained from younger objects (pre-BD cores and proto-BDs), are limited by the very low number statistics available. We aim to identify and characterize a set of pre- and proto-BDs as well as Class II BDs in the Lupus 1 and 3 molecular clouds to test their formation mechanism. We performed ALMA band 6 (1.3 mm) continuum observations of a selection of 64 cores previously identified from AzTEC/ASTE data (1.1 mm), along with previously known Class II BDs in the Lupus 1 and 3 molecular clouds. Surveyed archival data in the optical were used to complement these observations. We expect these ALMA observations prove efficient in detecting the youngest sources in these regions, since they probe the frequency domain at which these sources emit most of their radiation. We detected 19 sources from 15 ALMA fields. Considering all the pointings in our observing setup, the ALMA detection rate was $sim$23% and the derived masses of the detected sources were between $sim$0.18 and 124 $mathrm{M_{Jup}}$. We classified these sources according to their spectral energy distribution as 5 Class II sources, 2 new Class I/0 candidats, and 12 new possible pre-BD or deeply embedded protostellar candidates. We detected a promising candidate for a Class 0/I proto-BD source and inferred the disk dust mass of a bona fide Class II BD. The pre-BD cores might be the byproduct of an ongoing process of large-scale collapse. The Class II BD disks follow the correlation between disk mass and the mass of the central object that is observed at the low-mass stellar regime. We conclude that it is highly probable that the sources in the sample are formed as a scaled-down version of low-mass star formation, although disk fragmentation may be responsible for a considerable fraction of BDs.
We have carried out survey observations of molecular emission lines from HC$_{3}$N, N$_{2}$H$^{+}$, CCS, and cyclic-C$_{3}$H$_{2}$ in the 81$-$94 GHz band toward 17 high-mass starless cores (HMSCs) and 28 high-mass protostellar objects (HMPOs) with the Nobeyama 45-m radio telescope. We have detected N$_{2}$H$^{+}$ in all of the target sources except one and HC$_{3}$N in 14 HMSCs and in 26 HMPOs. We investigate the $N$(N$_{2}$H$^{+}$)/$N$(HC$_{3}$N) column density ratio as a chemical evolutionary indicator of massive cores. Using the Kolmogorov-Smirnov (K-S) test and Welchs t test, we confirm that the $N$(N$_{2}$H$^{+}$)/$N$(HC$_{3}$N) ratio decreases from HMSCs to HMPOs. This tendency in high-mass star-forming regions is opposite to that in low-mass star-forming regions. Furthermore, we found that the detection rates of carbon-chain species (HC$_{3}$N, HC$_{5}$N, and CCS) in HMPOs are different from those in low-mass protostars. The detection rates of cyanopolyynes (HC$_{3}$N and HC$_{5}$N) are higher and that of CCS is lower in high-mass protostars, compared to low-mass protostars. We discuss a possible interpretation for these differences.
We have selected 43 southern massive star-forming regions to study the spatial distribution of HNCO 4$_{04}$-3$_{03}$, SiO 2-1 and HC$_{3}$N 10-9 line emission and to investigate their spatial association with the dust emission. The morphology of HNCO 4$_{04}$-3$_{03}$ and HC$_{3}$N 10-9 agrees well with the dust emission. HC$_{3}$N 10-9 tends to originate from more compact regions than HNCO 4$_{04}$-3$_{03}$ and SiO 2-1. We divided our sources into three groups: those in the Central Molecular Zone (CMZ), those associated with bubbles (Bubble), and the remaining sources, which are termed normal star forming regions (NMSFR). These three groups, subdivided into three different categories with respect to line widths, integrated intensities, and column densities, hint at the presence of different physical and chemical processes. We find that the dust temperature $T_{rm d}$, and the abundance ratios of $N_{rm HNCO}/N_{rm SiO}$ and $N_{rm HNCO}/N_{rm HC3N}$ show a decreasing trend towards the central dense regions of CMZ sources, while $N_{rm HC3N}/N_{rm SiO}$ moves into the opposite direction. Moreover, a better agreement is found between $T_{rm d}$ and $N_{rm HC3N}/N_{rm SiO}$ in Bubble and NMSFR category sources. Both outflow and inflow activities have been found in eight of the sixteen bubble and NMSFR sources. The low outflow detection rate indicates that in these sources the SiO 2-1 line wing emission is either below our sensitivity limit or that the bulk of the SiO emission may be produced by the expansion of an H{sc,ii} region or supernova remnant, which has pushed molecular gas away forming a shock and yielding SiO.
Context. Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet they play a crucial role in breeding newly-formed stars. Aims. With the aim of further understanding the dynamics, chemistry, and evolution of IRDCs, we carried out multi-wavelength observations on a small sample. Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m telescopes, with tracers ${rm HCO^+}$, HCN, ${rm N_2H^+}$, ${rm C^{18}O}$, DCO$^+$, SiO, and DCN toward six IRDCs G031.97+00.07, G033.69-00.01, G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05. Results. We investigated 44 cores including 37 cores reported in previous work and seven newly-identified cores. Toward the dense cores, we detected 6 DCO$^+$, and 5 DCN lines. Using pixel-by-pixel spectral energy distribution (SED) fits of the $textit{Herschel}$ 70 to 500 $mu$m, we obtained dust temperature and column density distributions of the IRDCs. We found that ${rm N_2H^+}$ emission has a strong correlation with the dust temperature and column density distributions, while ${rm C^{18}O}$ showed the weakest correlation. It is suggested that ${rm N_2H^+}$ is indeed a good tracer in very dense conditions, but ${rm C^{18}O}$ is an unreliable one, as it has a relatively low critical density and is vulnerable to freezing-out onto the surface of cold dust grains. The dynamics within IRDCs are active, with infall, outflow, and collapse; the spectra are abundant especially in deuterium species. Conclusions. We observe many blueshifted and redshifted profiles, respectively, with ${rm HCO^+}$ and ${rm C^{18}O}$ toward the same core. This case can be well explained by model envelope expansion with core collapse (EECC).
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