Fanyi Meng

Gas Emissions in Planck Cold Dust Clumps?A Survey of the J = 1-0 Transitions of 12CO, 13CO, and C18O

A survey toward 674 Planck cold clumps of the Early Cold Core Catalogue (ECC) in the J?= 1-0 transitions of 12CO, 13CO, and C18O has been carried out using the Purple Mountain Observatory 13.7?m telescope. Six hundred seventy-three clumps were detected with 12CO and 13CO emission, and 68% of the sample has C18O emission. Additional velocity components were also identified. A close consistency of the three line peak velocities was revealed for the first time. Kinematic distances are given for all the velocity components, and half of the clumps are located within 0.5 and 1.5?kpc. Excitation temperatures range from 4 to 27?K, slightly larger than those of Td . Line width analysis shows that the majority of ECC clumps are low-mass clumps. Column densities span from 1020 to 4.5 ? 1022?cm?2 with an average value of (4.4 ? 3.6) ? 1021?cm?2. cumulative fraction distribution deviates from the lognormal distribution, which is attributed to optical depth. The average abundance ratio of the 13CO to C18O in these clumps is 7.0 ? 3.8, higher than the terrestrial value. Dust and gas are well coupled in 95% of the clumps. Blue profile asymmetry, red profile asymmetry, and total line asymmetry were found in less than 10% of the clumps, generally indicating that star formation is not yet developed. Ten clumps were mapped. Twelve velocity components and 22 cores were obtained. Their morphologies include extended diffuse, dense, isolated, cometary, and filament, of which the last is the majority. Twenty cores are starless, and only seven cores seem to be in a gravitationally bound state. Planck cold clumps are the most quiescent among the samples of weak red IRAS, infrared dark clouds, UC H II candidates, extended green objects, and methanol maser sources, suggesting that Planck cold clumps have expanded the horizon of cold astronomy.

Mapping Study of 71 Planck Cold Clumps in the Taurus, Perseus, and California Complexes

A mapping study of 71 Planck cold clumps was made with 12CO(1-0), 13CO(1-0), and C18O(1-0) lines at the 13.7 m telescope of Purple Mountain Observatory. For all the clumps, 12CO(1-0) and 13CO(1-0) emissions were detected, while for 55 of them, C18O(1-0) emissions were detected. Of the 71 Clumps, 34 are in the Taurus Complex, 24 in the California Complex, and 13 are in the Perseus Complex. In the 76 velocity components, 38 cores are found in 27 clumps; 19 of these cores are in the Taurus Complex, 16 in the California Complex, and 3 in the Perseus Complex. We acquired V lsr, TA and FWHM of lines. Physical parameters including T ex, , σTherm, σNT, and σ3D were calculated. Generally, the cores are of T ex = 2-16 K, cm–2, and σ3D = 0.2-1.0 km s–1. In the Taurus Complex, the cores are less dense on average and have smaller σTherm than the cores in the Perseus and California Complexes. Two of the three cores in the Perseus Complex are revealed to have larger T ex, , and σ3D than the mean values in the other two regions. Most of the cores have σNT larger than σTherm, suggesting a dominance of turbulence in our cores. The majority of the cores have M vir/M LTE 1, which indicates these cores are not bound and will disperse. By comparing our results with the dust properties revealed by the Planck Early Release Cold Cores Catalog, we investigated the coupling of gas and dust components. We found that most of the cores have dust temperatures higher than their gas temperatures. The stellar objects associated with our sources were checked and 90% of the cores were found to be starless.

Planck Cold Clumps in the λ Orionis Complex. I : Discovery of an Extremely Young Class 0 Protostellar Object and a Proto-brown Dwarf Candidate in the Bright-rimmed Clump PGCC G192.32-11.88

We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the lambda Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32-11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound brightrimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32-11.88 is externally heated and compressed. G192N probably has the lowest bolometric luminosity (similar to 0.8 L-circle dot) and accretion rate (6.3 x 10(-7) M-circle dot yr(-1)) when compared with other young Class 0 sources (e.g., PACS Bright Red Sources) in the Orion complex. It has slightly larger internal luminosity (0.21 +/- 0.01 L-circle dot) and outflow velocity (similar to 14 km s(-1)) than the predictions of first hydrostatic cores (FHSCs). G192N might be among the youngest Class 0 sources, which are slightly more evolved than an FHSC. Considering its low internal luminosity (0.08 +/- 0.01 L-circle dot) and accretion rate (2.8 x 10(-8) M-circle dot yr(-1)), G192S is an ideal proto-brown dwarf candidate. The star formation efficiency (similar to 0.3%-0.4%) and core formation efficiency (similar to 1%) in PGCC G192.32-11.88 are significantly smaller than in other giant molecular clouds or filaments, indicating that the star formation therein is greatly suppressed owing to stellar feedback.

Follow-Up Observations Toward Planck Cold Clumps with Ground-Based Radio Telescopes

The physical and chemical properties of prestellar cores, especially massive ones, are still far from being well understood due to the lack of a large sample. The low dust temperature ( ows, indicating that not all PCCs are in a prestellar phase. We have identified hundreds of starless dense clumps from a mapping survey with the Purple Mountain Observatory (PMO) 13.7-m telescope. Follow-up observations suggest that these dense clumps are ideal targets to search for prestellar objects.

DENSE GAS IN MOLECULAR CORES ASSOCIATED WITH PLANCK GALACTIC COLD CLUMPS

We present the first survey of dense gas towards Planck Galactic Cold Clumps (PGCCs). Observations in the J=1-0 transitions of HCO+ and HCN towards 621 molecular cores associated with PGCCs were performed using the Purple Mountain Observatory 13.7-m telescope. Among them, 250 sources have detection, including 230 cores detected in HCO+ and 158 in HCN. Spectra of the J=1-0 transitions from CO, 13CO, and C18O at the centers of the 250 cores were extracted from previous mapping observations to construct a multi-line data set. The significantly low detection rate of asymmetric double-peaked profiles, together with the well consistence among central velocities of CO, HCO+, and HCN spectra, suggests that the CO-selected Planck cores are more quiescent compared to classical star-forming regions. The small difference between line widths of C18O and HCN indicates that the inner regions of CO-selected Planck cores are not more turbulent than the exterior. The velocity-integrated intensities and abundances of HCO+ are positively correlated with those of HCN, suggesting these two species are well coupled and chemically connected. The detected abundances of both HCO+ and HCN are significantly lower than values in other low- to high-mass star-forming regions. The low abundances may be due to beam dilution. On the basis of the inspection of the parameters given in the PGCC catalog, we suggest that there may be about 1 000 PGCC objects having sufficient reservoir of dense gas to form stars.

GAS EMISSIONS IN PLANCK COLD DUST CLUMPS-A SURVEY OF THE J=1-0 TRANSITIONS OF (CO)-C-12, (CO)-C-13, AND (CO)-O-18

A survey toward 674 Planck cold clumps of the Early Cold Core Catalogue (ECC) in the J?= 1-0 transitions of 12CO, 13CO, and C18O has been carried out using the Purple Mountain Observatory 13.7?m telescope. Six hundred seventy-three clumps were detected with 12CO and 13CO emission, and 68% of the sample has C18O emission. Additional velocity components were also identified. A close consistency of the three line peak velocities was revealed for the first time. Kinematic distances are given for all the velocity components, and half of the clumps are located within 0.5 and 1.5?kpc. Excitation temperatures range from 4 to 27?K, slightly larger than those of Td . Line width analysis shows that the majority of ECC clumps are low-mass clumps. Column densities span from 1020 to 4.5 ? 1022?cm?2 with an average value of (4.4 ? 3.6) ? 1021?cm?2. cumulative fraction distribution deviates from the lognormal distribution, which is attributed to optical depth. The average abundance ratio of the 13CO to C18O in these clumps is 7.0 ? 3.8, higher than the terrestrial value. Dust and gas are well coupled in 95% of the clumps. Blue profile asymmetry, red profile asymmetry, and total line asymmetry were found in less than 10% of the clumps, generally indicating that star formation is not yet developed. Ten clumps were mapped. Twelve velocity components and 22 cores were obtained. Their morphologies include extended diffuse, dense, isolated, cometary, and filament, of which the last is the majority. Twenty cores are starless, and only seven cores seem to be in a gravitationally bound state. Planck cold clumps are the most quiescent among the samples of weak red IRAS, infrared dark clouds, UC H II candidates, extended green objects, and methanol maser sources, suggesting that Planck cold clumps have expanded the horizon of cold astronomy.