The chemistry of protoplanetary fragments formed via gravitational instabilities
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In this paper, we model the chemical evolution of a 0.25 M⊙ protoplanetary disc surrounding a 1 M⊙ star that undergoes fragmentation due to self-gravity. We use smoothed particle hydrodynamics including a radiative transfer scheme, along with a time-dependent chemical evolution code to follow the composition of the disc and resulting fragments over approximately 4000 yr. Initially, four quasi-stable fragments are formed, of which two are eventually disrupted by tidal torques in the disc. From the results of our chemical modelling, we identify species that are abundant in the fragments (e.g. H2O, H2S, HNO, N2, NH3, OCS, SO), species that are abundant in the spiral shocks within the disc (e.g. CO, CH4, CN, CS, H2CO) and species that are abundant in the circumfragmentary material (e.g. HCO+). Our models suggest that in some fragments it is plausible for grains to sediment to the core before releasing their volatiles into the planetary envelope, leading to changes in, e.g., the C/O ratio of the gas and ice components. We would therefore predict that the atmospheric composition of planets generated by gravitational instability should not necessarily follow the bulk chemical composition of the local disc material.
Ilee , J D , Forgan , D H , Evans , M G , Hall , C , Booth , R , Clarke , C J , Rice , W K M , Boley , A C , Caselli , P , Hartquist , T W & Rawlings , J M C 2017 , ' The chemistry of protoplanetary fragments formed via gravitational instabilities ' Monthly Notices of the Royal Astronomical Society , vol 472 , no. 1 , pp. 189-204 . DOI: 10.1093/mnras/stx1966
Monthly Notices of the Royal Astronomical Society
© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.1093/mnras/stx1966
JDI, RB and CJC gratefully acknowledge support from the DISCSIM project, grant agreement 341137, funded by the European Research Council under ERC-2013-ADG. DHF gratefully acknowledges support from the ECOGAL project, grant agreement 291227, funded by the European Research Council under ERC-2011-ADG. DHF and WKMR also acknowledge support from STFC grant ST/J001422/1. MGE acknowledges a studentship funded by, and PC, TWH and AB acknowledge financial support from, the European Research Council (project PALs 320620). CH gratefully acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 681601).
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