Tie Liu

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.

Evolution of the Dust/Gas Environment around Herbig Ae/Be Stars

Using the KOSMA 3 m telescope, 54 Herbig Ae/Be (HAe/Be) stars were surveyed in CO and 13CO emission lines. The properties of the stars and their circumstellar environments were studied by fitting spectral energy distributions (SEDs). The mean line width of 13CO (2–1) lines of this sample is 1.87 km s–1. The average column density of H2 is found to be 4.9 × 1021 cm–2 for stars younger than 106 yr, while this drops to 2.5 × 1021 cm–2 for those older than 106 yr. No significant difference is found among the SEDs of HAe and HBe stars of the same age. Infrared excess decreases with age, envelope masses and envelope accretion rates decease with age after 105 yr, the average disk mass of the sample is 3.3 × 10–2 M ☉, the disk accretion rate decreases more slowly than the envelope accretion rate, and a strong correlation between the CO line intensity and the envelope mass is found.

GASEOUS CO ABUNDANCE—AN EVOLUTIONARY TRACER FOR MOLECULAR CLOUDS

Planck cold clumps are among the most promising objects to investigate the initial conditions of the evolution of molecular clouds. In this work, by combing the dust emission data from the survey of the Planck satellite with the molecular data of 12 CO/ 13 CO/C 18 O (1–0) lines from observations with the Purple Mountain Observatory 13.7 m telescope, we investigate the CO abundance, CO depletion, and CO-to-H2 conversion factor of 674 clumps in the early cold cores sample. The median and mean values of the CO abundance are 0.89 × 10 −4 and 1.28 × 10 −4 , respectively. The mean and median of CO depletion factor are 1.7 and 0.9, respectively. The median value of XCO-to-H2 for the whole sample is 2.8 × 10 20 cm −2 K −1 km −1 s. The CO abundance, CO depletion factor, and CO-to-H2 conversion factor are strongly (anti-)correlated to other physical parameters (e.g., dust temperature, dust emissivity spectral index, column density, volume density, and luminosity-to-mass ratio). To conclude, the gaseous CO abundance can be used as an evolutionary tracer for molecular clouds.

Interactions of the Infrared bubble N4 with ITS surroundings

The physical mechanisms that induce the transformation of a certain mass of gas in new stars are far from being well understood. Infrared bubbles associated with H II regions have been considered to be good samples for investigating triggered star formation. In this paper we report on the investigation of the dust properties of the infrared bubble N4 around the H II. region G11.898+0.747, analyzing its interaction with its surroundings and star formation histories therein, with the aim of determining the possibility of star formation triggered by the expansion of the bubble. Using Herschel PACS and SPIRE images with a wide wavelength coverage, we reveal the dust properties over the entire bubble. Meanwhile, we are able to identify six dust clumps surrounding the bubble, with a mean size of 0.50 pc, temperature of about 22 K, mean column density of 1.7 x 10(22) cm(-2), mean volume density of about 4.4 x 10(4) cm(-3), and a mean mass of 320M(circle dot). In addition, from PAH emission seen at 8 mu m, free-free emission detected at 20 cm, and a probability density function in special regions, we could identify clear signatures of the influence of the H II region on the surroundings. There are hints of star formation, though further investigation is required to demonstrate that N4 is the triggering source.

Properties and Gravitational Collapse of the Core in G19.61 - 0.23

We present the results of an observational study toward the core in G19.61 – 0.23 with the Submillimeter Array. The continuum at 900 μm revealed that the core has a mass of 15 M ☉. The rotational temperature and the column density of CH3CN are 552 K and 3.4 × 1016 cm–2, respectively. No UC H II region or infrared source was found at the peak position of the core. Inverse P Cygni profiles were clearly exhibited in the 13CO J = 3-2 and CN N = 3-2 lines, strongly indicating that material infall is taking place in this compact hot core. The mass-infall rate estimated from the 13CO J = 3-2 line is 6.1 × 10–3 M ☉ yr–1, which agrees with the value calculated from a free-fall model. The mass-infall rate, together with the difference of the infall velocities estimated from the 13CO J = 3-2 and CN J = 3-2 lines as well as the spatial distribution of their absorption show that the inflow motion originates from gravitational potential and is consistent with the inside-out model. The prior maser observations indicated outflow activities in this core. The signatures of both inflow and outflow activities suggest that there may be an embedded early high-mass star forming via gas accretion. After comparing the emissions of CO and its isotopes with the other widely used inflow motion tracers, we find that the CO lines may also be useful to trace inflow motion in a small scale when the continuum background is bright enough.

A study of dynamical processes in the Orion KL region using ALMA—probing molecular outflow and inflow

This work reports a high spatial resolution observations toward Orion KL region with high critical density lines of CH

INFALL AND OUTFLOW MOTIONS IN THE HIGH-MASS STAR-FORMING COMPLEX G9.62+0.19

_{3}

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

CN (12

HIGH-RESOLUTION CO OBSERVATION OF THE CARBON STAR CIT 6 REVEALING THE SPIRAL STRUCTURE AND A NASCENT BIPOLAR OUTFLOW

_{4}

Competitive accretion in the protocluster G10.6-0.4?

-11