Morphology and Energetics of the Molecular Gas within a Core and a Diffuse Region in the Filamentary Dark Cloud GF 9

July 2000 • 2000AJ....120..393C

Authors • Ciardi, David R. • Woodward, Charles E. • Clemens, Dan P. • Harker, David E. • Rudy, Richard J.

Abstract • We have performed a CO, ¹³CO, and CS survey of a dense core region (GF 9-Core) and a diffuse filamentary region (GF 9-Fila) within the dark cloud GF 9 (LDN 1082). Spectra in each line were obtained toward 120 positions within each region covering areas of 8^'×10^'. GF 9-Core is associated with the Class 0 protostar IRAS PSC 20503+6006, while GF 9-Fila has no associated IRAS point sources. The median CO excitation temperature of the core region is 7.2+/-0.5 K; for the filament region, the median temperature is 7.8+/-0.5 K. The mass derived from the LTE isothermal analysis of ¹³CO is 53+/-8 and 40+/-6 M_solar for GF 9-Core and GF 9-Fila, respectively. Using near-infrared extinction data to trace the H₂ column density, the isothermal LTE assumptions for ¹³CO appear to break down at A_V>~3 mag. The near-infrared extinction data are used to correct the derived ¹³CO column densities, yielding mass estimates that are ~20% larger than the LTE-derived masses. The average H₂ volume densities for GF 9-Core and GF 9-Fila are ~5000+/-700 and ~1700+/-200 cm^-3. Each region contains a 15+/-3 M_solar centrally condensed CS core, which is approximately 3 times more dense than the ambient ¹³CO regions. In GF 9-Core, the high-density gas core appears to be physically associated with the IRAS point source. Both high-density cores appear to be in virial equilibrium; however, the CS line widths in GF 9-Core are almost twice as large as those measured in GF 9-Fila. Because GF 9-Core is associated with the Class 0 protostar PSC 20503+6006, the CS line widths may be enhanced by outflow or infall motion. The additional nonturbulent line-broadening component caused by outflow/infall motion required to explain the line width implies a supersonic velocity of at least 0.3 km s^-1 (Mach 1.5).

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David Ciardi

Senior Scientist