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THE<i>SPITZER</i>c2d SURVEY OF NEARBY DENSE CORES. VII. CHEMISTRY AND DYNAMICS IN L43
Chen, Jo-Hsin,Evans, Neal J.,Lee, Jeong-Eun,Bourke, Tyler L. IOP Publishing 2009 The Astrophysical journal Vol.705 No.2
<P>We present results from the Spitzer Space Telescope and molecular line observations of nine species toward the dark cloud L43. The Spitzer images and molecular line maps suggest that it has a starless core and a Class I protostar evolving in the same environment. CO depletion is seen in both sources, and DCO+ lines are stronger toward the starless core. With a goal of testing the chemical characteristics from pre- to protostellar stages, we adopt an evolutionary chemical model to calculate the molecular abundances and compare with our observations. Among the different model parameters we tested, the best-fit model suggests a longer total timescale at the pre-protostellar stage, but with faster evolution at the later steps with higher densities.</P>
Lee, Jeong-Eun,Lee, Ho-Gyu,Shinn, Jong-Ho,Dunham, Michael M.,Kim, Il-Suk,Kim, Chang Hee,Bourke, Tyler L.,Evans, Neal J.,Choi, Yunhee IOP Publishing 2010 ASTROPHYSICAL JOURNAL LETTERS - Vol.709 No.1
<P>A long infrared jet has been discovered by the Spitzer c2d Legacy Program in core A of L1251. It is associated with a very embedded Class 0 object with an accretion luminosity of about 0.9 L(circle dot) derived by radiative transfer model fitting to the observed spectral energy distribution. Comparing the observed Infrared Array Camera colors along the infrared jet with those calculated from a model of an admixture of gas with a power-law temperature distribution indicates that the jet is possibly created by a paraboloidal bow shock propagating into the ambient medium of n(H(2)) = 10(5) cm(-3). In addition, the variation of the power-law index along the jet suggests that the portion of hot gas decreases with distance from the jet engine. The molecular outflow in this region has been mapped for the first time using CO data. From the calculated outflow momentum flux, a very strong lower limit to the average accretion luminosity is 3.6 sin i/cos(3) i L(circle dot), indicative of a decrease in the accretion rate with time.</P>
Kim, Hyo Jeong,Evans II, Neal J.,Dunham, Michael M.,Chen, Jo-Hsin,Lee, Jeong-Eun,Bourke, Tyler L.,Huard, Tracy L.,Shirley, Yancy L.,De Vries, Christopher IOP Publishing 2011 The Astrophysical journal Vol.729 No.2
<P>We present new observations of the CB130 region composed of three separate cores. Using the Spitzer Space Telescope, we detected a Class 0 and a Class II object in one of these, CB130-1. The observed photometric data from Spitzer and ground-based telescopes are used to establish the physical parameters of the Class 0 object. Spectral energy distribution fitting with a radiative transfer model shows that the luminosity of the Class 0 object is 0.14-0.16 L-circle dot, which is low for a protostellar object. In order to constrain the chemical characteristics of the core having the low-luminosity object, we compare our molecular line observations to models of lines including abundance variations. We tested both ad hoc step function abundance models and a series of self-consistent chemical evolution models. In the chemical evolution models, we consider a continuous accretion model and an episodic accretion model to explore how variable luminosity affects the chemistry. The step function abundance models can match observed lines reasonably well. The best-fitting chemical evolution model requires episodic accretion and the formation of CO2 ice from CO ice during the low-luminosity periods. This process removes C from the gas phase, providing a much improved fit to the observed gas-phase molecular lines and the CO2 ice absorption feature. Based on the chemical model result, the low luminosity of CB130-1 is explained better as a quiescent stage between episodic accretion bursts rather than being at the first hydrostatic core stage.</P>
Choi, Yunhee,Lee, Jeong-Eun,Bourke, Tyler L.,II, Neal J. Evans American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.2
<P>We present observations and analyses of the low-mass star-forming region, Taurus Molecular Cloud-1 (TMC-1). CS (J = 2-1)/N2H+ (J = 1-0) and (CO)-O-17 (J = 2-1)/(CO)-O-18 (J = 2-1) were observed with the. Five College Radio Astronomy Observatory and the. Seoul Radio Astronomy Observatory, respectively. In addition, Spitzer infrared data and 1.2 mm continuum data observed with Max-Planck Millimetre Bolometer are used. We also perform chemical modeling to investigate the relative molecular distributions of the TMC-1 filament. Based on Spitzer observations, there is no young stellar object along the TMC-1 filament, while five Class II and one Class I young stellar objects are identified outside the filament. The comparison between column densities calculated from dust continuum and (CO)-O-17 2-1 line emission shows that CO is depleted much more significantly in the ammonia peak than in the cyanopolyyne peak, while the column densities calculated from the dust continuum are similar at the two peaks. N2H+ is not depleted much in either peak. According to our chemical calculation, the differential chemical distribution in the two peaks can be explained by different timescales required to reach the same density, i.e., by different dynamical processes.</P>