Evolutionary view through the starless cores in Taurus: deuteration in TMC 1-C and TMC 1-CP

Navarro-Almaida, D.; Fuente, A.; Majumdar, L.; Wakelam, V.; Caselli, P.; Rivière-Marichalar, P.; Treviño-Morales, S. P.; Cazaux, S.; Jiménez-Serra, I.; Kramer, C.; Chacón-Tanarro, A.; Kirk, J. M.; Ward-Thompson, D.; Tafalla, M.

doi:10.48550/arxiv.2107.00423

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“…We also present observations towards the pre-stellar core TMC1-C (Schnee et al 2007(Schnee et al , 2010. Several observational evidences suggest that this core is a later evolutionary stage than TMC1 (CP), presenting higher deuteration fractions, more similar to those in L1544 (Crapsi et al 2005;Navarro-Almaida et al 2021). The spectra of the 2 1,2 -1 1,1 (E 2 ) transition of methanol overlaid with the 1-0 transition of C 18 O towards TMC-1C, TMC-1 CP and TMC-1 NH 3 are shown in Figures A.1-A.3.…”

Section: Tmc-1 Cloudmentioning

confidence: 71%

Gas phase Elemental abundances in Molecular cloudS (GEMS) V. Methanol in Taurus

Spezzano,

Fuente,

Caselli

et al. 2021

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Context. Methanol, one of the simplest complex organic molecules in the Interstellar Medium (ISM), has been shown to be present and extended in cold environments such as starless cores. Studying the physical conditions at which CH3OH starts its efficient formation is important to understand the development of molecular complexity in star-forming regions. Aims. We aim at studying methanol emission across several starless cores and investigate the physical conditions at which methanol starts to be efficiently formed, as well as how the physical structure of the cores and their surrounding environment affect its distribution. Methods. Methanol and C 18 O emission lines at 3 mm have been observed with the IRAM 30m telescope within the large program "Gas phase Elemental abundances in Molecular CloudS" (GEMS) towards 66 positions across 12 starless cores in the Taurus Molecular Cloud. A non-LTE radiative transfer code was used to compute the column densities in all positions. We then used state-of-the-art chemical models to reproduce our observations. Results. We have computed N(CH3OH)/N(C 18 O) column density ratios for all the observed offsets, and two different behaviours can be recognised: the cores where the ratio peaks at the dust peak, and the cores where the ratio peaks with a slight offset with respect to the dust peak (∼10000 AU). We suggest that the cause of this behaviour is the irradiation on the cores due to protostars nearby which accelerate energetic particles along their outflows. The chemical models, which do not take into account irradiation variations, can reproduce fairly well the overall observed column density of methanol, but cannot reproduce the two different radial profiles observed. Conclusions. We confirm the substantial effect of the environment onto the distribution of methanol in starless cores. We suggest that the clumpy medium generated by protostellar outflows might cause a more efficient penetration of the interstellar radiation field in the molecular cloud and have an impact on the distribution of methanol in starless cores. Additional experimental and theoretical work is needed to reproduce the distribution of methanol across starless cores.

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