On the internal structure of starless cores II. A molecular survey of L1498 and L1517B

By M. Tafalla, J. Santiago, P. Myers, P. Caselli, C. Walmsley, A. Crapsi. 2006

164 citations recorded by the source corpus.

Context. Low mass starless cores present an inhomogeneous chemical composition. Species like CO and CS deplete at their dense interiors, while N 2 H + and NH 3 survive in the gas phase. As molecular line observations are used to determine the physical conditions and kinematics of the core gas, chemical inhomogeneities can introduce a serious bias. Aims. We have carried out a molecular survey towards two starless cores, L1498 and L1517B. These cores have been selected for their relative isolation and close-to-round shape. They have been observed in a number of lines of 13 molecular species in order to determine a self-consistent set of abundance profiles. Methods. In a previous paper we modeled the physical structure of L1498 and L1517B. Here we use this work together with a spherically-symmetric Monte Carlo radiative transfer code to determine the radial profile of abundance for each species in the survey. Our model aims to fit simultaneously the radial profile of integrated intensity and the emerging spectrum from the core center. Results. L1498 and L1517B present similar abundance patterns, with most species suffering a significant drop toward the core center. This occurs for CO, CS, CH 3 OH, SO, C 3 H 2 , HC 3 N, C 2 S, HCN, H 2 CO, HCO + , and DCO + , which we fit with profiles having a sharp central hole. The size of this hole varies with molecule: DCO + , HCN, and HC 3 N have the smallest holes, while SO, C 2 S and CO have the largest holes. Only N 2 H + and NH 3 seem present in the gas phase at the core centers. Conclusions. From the different behavior of molecules, we select SO, C 2 S, and CH 3 OH as the most sensitive tracers of molecular depletion. Comparing our abundance determinations with the predictions from current chemical models we find order of magnitude discrepancies. Finally, we show how the "contribution function" can be used to study the formation of line profiles from the different regions of a core.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/b2220a8bfc8701f5a63d3cc8e569268b9d7f0461

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Citations in the corpus

The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere? (2012, background): “The ICF, discussed in Tafalla et al. (2006) and Pavlyuchenkov et al. (2008), shows the relative contribution to the line emission along a ray.”
Cold Dark Clouds: The Initial Conditions for Star Formation (2007, background): “A clear point is that evolutionary timescales at densities near ∼ 104 cm−3 cannot be much longer than ∼ 0.5− 1 Myr as significant CO freeze-out would be produced at densities below where it is observed (Flower et al. 2005; Tafalla et al. 2006).”
Cores, filaments, and bundles: hierarchical core formation in the L1495/B213 Taurus region (2013, background): “Its abundance, however, is especially sensitive to the evolutionary state of the material, and is higher during the earliest phases of gas contraction (Tafalla et al. 2006; Hacar & Tafalla 2011).”
Physical Processes in the Interstellar Medium (2014, background): “Subsonic turbulence contributes less to the energy budget of the cloud than thermal pressure and so cannot provide sufficient support against gravitational collapse (Myers 1983; Goodman et al. 1998; Tafalla et al. 2006).”
Our astrochemical heritage (2012, unknown): “Others show expanding motions (Tafalla et al. 2004).”
On The Internal Structure Of Starless Cores. Physical and Chemical Properties of L1498 and L1517B (2004, unknown): “2 mm point sources (Tafalla et al. 2002), and can therefore be considered starless. Over the last decade, L1498 has been the subject of a number of detailed studies: Lemme et al. (1995) mapped its C18O and CS emission, Kuiper et al. (1996) first identified it as a chemically differentiated system, a”
Chemical modeling of L183 (= L134N) : an estimate of the ortho/para H2 ratio (2008, background): “Nitrogen–bearing species like CN, NH3 and N2H+ appear to subsist longer before freezing-out onto the dust grains (Tafalla et al. 2006, Pagani et al. 2007, Hily-Blant et al. 2008).”
Dense core formation by fragmentation of velocity-coherent filaments in L1517 (2011, background): “The brightest 1.2 mm emission corresponds to core B, whose structure and chemical composition has been studied in detail by Tafalla et al. (2004, 2006).”
The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers (2015, methodology): “More sophisticated tools such as the Contribution Function (Tafalla et al. 2006) may be used to determine the various contributions to the observed line profile along the line of sight (see Pavlyuchenkov et al. 2008 for a detailed analysis of these techniques).”