Poster Presentation
Molecular Gas Conditions in the Cores Before and After Onset of Star Formation
Presenter: Tsung-Han Chuang (Tamkang University/ASIAA)
We present the Atacama Compact Array (ACA) 7m array observations of the N2H+ 4-3, ortho-H2D+ 1 (1,0)-1(1,1), and DCO+ 5-4 line emission from one prestellar core and one protostellar core in the Orion molecular complex. The prestellar core, G209.29-19.65-S1 (G209-S1) is considered to be an evolved prestellar core with high density (> 10^7 cm^-3), and the protostellar core, G204.4-11.3A2-NE (G204-NE) harboring a very low luminosity source of 0.027 L_sun is considered to be in the very early stage of the protostellar evolution. The angular resolution of the ACA 7-meter array is 4.2" which corresponds to 1680 au. In G209-S1, the N2H+ and H2D+ show centrally peaked distributions that correlate well with the 360 GHz continuum emission, while DCO+ shows its peak near the edge of the continuum. The N2D+/N2H+ ratio of this source derived using the archival N2D+ 3-2 data is around 0.4, which corresponds to the highest value in the prestellar cores with N2D+/N2H+ ratio measurements. The CO depletion factor derived from the archival C18O 2-1 data is ~25 in this source. In contrast, H2D+ emission was not detected in G204NE. In this source, the DCO+ and N2H+ show a good correlation with the continuum. The N2D+/N2H+ ratio and the CO depletion factor in G204-NE are around 0.1 and 6.3, respectively. These results suggest that H2D+ disappears quickly once the protostar is formed and that the N2D+/N2H+ ratio also decreases significantly.
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