Chemical evolution during the formation of a protoplanetary disk

Abstract

Context. The chemical composition of protoplanetary disks is expected to impact the composition of the forming planets. Characterizing the diversity of chemical composition in disks and the physicochemical factors that lead to this diversity is consequently of high interest. Aims. The aim of this study is to investigate the chemical evolution from the prestellar phase to the formation of the disk, and to determine the impact that the chemical composition of the cold and dense core has on the final composition of the disk. Methods. We performed 3D nonideal magneto-hydrodynamic (MHD) simulations of a dense core collapse using the adaptive-meshrefinement RAMSES code. For each particle ending in the young rotationally supported disk, we ran chemical simulations with the three-phase gas-grain chemistry code Nautilus. Two different sets of initial abundances, which are characteristic of cold cores, were considered. The final distributions of the abundances of common species were compared to each other, as well as with the initial abundances of the cold core. Results. We find that the spatial distributions of molecules reflect their sensitivity to the temperature distribution. The main carriers of the chemical elements in the disk are usually the same as the ones in the cold core, except for the S-bearing species, where HS is replaced by H 2 S 3 , and the P-bearing species, where atomic P leads to the formation of PO, PN, HCP, and CP. However, the abundances of less abundant species change over time. This is especially the case for "large" complex organic molecules (COMs) such as CH 3 CHO, CH 3 NH 2 , CH 3 OCH 3 , and HCOOCH 3 which see their abundances significantly increase during the collapse. These COMs often present similar abundances in the disk despite significantly different abundances in the cold core. In contrast, the abundances of many radicals decrease with time. A significant number of species still show the same abundances in the cold core and the disk, which indicates efficient formation of these molecules in the cold core. This includes H 2 O, H 2 CO, HNCO, and "small" COMs such as CH 3 OH, CH 3 CN, and NH 2 CHO. We computed the MHD resistivities within the disk for the full gas-grain chemical evolution and find results in qualitative agreement with the literature assuming simpler chemical networks. Conclusions. In conclusion, the chemical content of prestellar cores is expected to affect the chemical composition of disks. The impact is more or less important depending on the type of species. Users of stand-alone chemical models of disks should pay special attention to the initial abundances they choose.

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): A Hot Corino Survey toward Protostellar Cores in the Orion Cloud

“…See Table C1 for the references. Simulations have suggested that methanol mainly forms during the prestellar phase (Drozdovskaya et al 2015;Coutens et al 2020). If the fractional abundance of methanol is comparable among the hot corinos, one would also expect that the total number of gas-phase methanol is positively correlated with the bolometric luminosity based on the correlation between the extent of methanol and the bolometric luminosity.…”

The young protostellar disk in IRAS16293-2422 B is hot and shows signatures of gravitational instability

“…This shift of the peak from the center can arise by considering highly asymmetric spiral arms, unlike those shown by our RHD model. For instance, recent non-ideal MHD simulations presented by Coutens et al (2020) showed a spiral arm pattern, produced by considering the collapse of a non-rotating 1 M core initialized with turbulence. Such an asymmetric structure, likely produced by the effect of the initial turbulent velocity field and magnetic field could explain the shift of the peak observed toward source B.…”

X-ray induced chemistry of water and related molecules in low-mass protostellar envelopes

“…In many studies of chemical modeling in disks (e.g., Walsh et al 2015;Bosman et al 2018b), initial chemical abundances were assumed to be inherited from dark clouds, pre-stellar cores, and protostellar envelopes, and they are water-rich, on the basis of previous observations (e.g., Visser et al 2009Visser et al , 2011Boogert et al 2015). However, whether the disk chemical evolution is started from initial abundance conditions of the chemical reset (by e.g., irradiation, accretion shocks) or the inheritance from the dark clouds and protostellar envelopes is an important question (e.g., Yoneda et al 2016;Coutens et al 2020;Jørgensen et al 2020;van't Hoff et al 2020;Öberg & Bergin 2021). Eistrup et al (2016Eistrup et al ( , 2018 and Notsu et al (2020) discussed that the chemical abundances in Class II disks are strongly affected by ionisation rates in disks and the adopted initial molecular abundances (inheritance or reset).…”