| 1. |
- Pandhi, A., et al.
(författare)
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Alignment of dense molecular core morphology and velocity gradients with ambient magnetic fields
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 525:1, s. 364-392
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Tidskriftsartikel (refereegranskat)abstract
- Studies of dense core morphologies and their orientations with respect to gas flows and the local magnetic field have been limited to only a small sample of cores with spectroscopic data. Leveraging the Green Bank Ammonia Survey alongside existing sub-millimeter continuum observations and Planck dust polarization, we produce a cross-matched catalogue of 399 dense cores with estimates of core morphology, size, mass, specific angular momentum, and magnetic field orientation. Of the 399 cores, 329 exhibit 2D v(LSR) maps that are well fit with a linear gradient, consistent with rotation projected on the sky. We find a best-fit specific angular momentum and core size relationship of J/M & PROP; R-1.82 & PLUSMN; 0.10, suggesting that core velocity gradients originate from a combination of solid body rotation and turbulent motions. Most cores have no preferred orientation between the axis of core elongation, velocity gradient direction, and the ambient magnetic field orientation, favouring a triaxial and weakly magnetized origin. We find, however, strong evidence for a preferred anti-alignment between the core elongation axis and magnetic field for protostellar cores, revealing a change in orientation from starless and prestellar populations that may result from gravitational contraction in a magnetically-regulated (but not dominant) environment. We also find marginal evidence for anti-alignment between the core velocity gradient and magnetic field orientation in the L1228 and L1251 regions of Cepheus, suggesting a preferred orientation with respect to magnetic fields may be more prevalent in regions with locally ordered fields.
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| 2. |
- Petrashkevich,, et al.
(författare)
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Deuterium fractionation in cold dense cores in the low-mass star-forming region L1688
- 2024
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 528:2, s. 1327-1353
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we study deuterium fractionation in four starless cores in the low-mass star-forming region L1688 in the Ophiuchus molecular cloud. We study how the deuterium fraction (R-D) changes with environment, compare deuteration of ions and neutrals, core centre and its envelope, and attempt to reproduce the observed results with a gas-grain chemical model. We chose high and low gas density tracers to study both core centre and the envelope. With the IRAM 30 m antenna, we mapped N2H+(1-0), N2D+(1-0), (HCO+)-C-13 (1-0) and (2-1), DCO+(2-1), and p-NH2D(1(11)-1(01)) towards the chosen cores. The missing p-NH3 and N2H+(1-0) data were taken from the literature. To measure the molecular hydrogen column density, dust and gas temperature within the cores, we used the Herschel/SPIRE dust continuum emission data, the Green Bank Ammonia Survey data (NH3), and the COMPLETE survey data to estimate the upper limit on CO depletion. We present the deuterium fraction maps for three species towards four starless cores. Deuterium fraction of the core envelopes traced by DCO+/(HCO+)-C-13 is one order of magnitude lower (similar to 0.08) than that of the core central parts traced by the nitrogen-bearing species (similar to 0.5). Deuterium fraction increases with the gas density as indicated by high deuterium fraction of high gas density tracers and low deuterium fraction of lower gas density tracers and by the decrease of R-D with core radii, consistent with the predictions of the chemical model. Our model results show a good agreement with observations for R-D(N2D+/N2H+) and R-D(DCO+/HCO+) and underestimate the R-D(NH2D/NH3).
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