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dc.contributor.authorLee, Eve J.
dc.contributor.authorChiang, Eugene
dc.contributor.authorFerguson, Jason W.
dc.identifier.citationEve J Lee, Eugene Chiang, Jason W Ferguson; Optically thin core accretion: how planets get their gas in nearly gas-free discs, Monthly Notices of the Royal Astronomical Society, Volume 476, Issue 2, 11 May 2018, Pages 2199–2208en_US
dc.descriptionClick on the DOI link to access the article (may not be free).en_US
dc.description.abstractModels of core accretion assume that in the radiative zones of accreting gas envelopes, radiation diffuses. But super-Earths/sub-Neptunes (1-4 R-circle plus, 2-20M(circle plus)) point to formation conditions that are optically thin: their modest gas masses are accreted from short-lived and gas-poor nebulae reminiscent of the transparent cavities of transitional discs. Planetary atmospheres born in such environments can be optically thin to both incident starlight and internally generated thermal radiation. We construct time-dependent models of such atmospheres, showing that super-Earths/sub-Neptunes can accrete their similar to 1 per cent-by-mass gas envelopes, and super-puffs/sub-Saturns their similar to 20 per cent-by-mass envelopes, over a wide range of nebular depletion histories requiring no fine tuning. Although nascent atmospheres can exhibit stratospheric temperature inversions affected by atomic Fe and various oxides that absorb strongly at visible wavelengths, the rate of gas accretion remains controlled by the radiative-convective boundary (rcb) at much greater pressures. For dusty envelopes, the temperature at the rcb T-rcb similar or equal to 2500 K is still set by H-2 dissociation; for dust-depleted envelopes, T-rcb tracks the temperature of the visible or thermal photosphere, whichever is deeper, out to at least similar to 5 au. The rate of envelope growth remains largely unchanged between the old radiative diffusion models and the new optically thin models, reinforcing how robustly super-Earths form as part of the endgame chapter in disc evolution.en_US
dc.description.sponsorshipNSERC of Canada under PGS D3, the Berkeley Fellowship, and the Sherman Fairchild Fellowship at Caltech. EC acknowledges support from the NSF. This research used the Savio computational cluster resource provided by the Berkeley Research Computing programme at the University of California, Berkeley, supported by the UC Berkeley Chancellor, Vice Chancellor for Research, and Chief Information Officer.en_US
dc.publisherOxford University Pressen_US
dc.relation.ispartofseriesMonthly Notices of the Royal Astronomical Society;v.476:no.2
dc.subjectPlanets and satellitesen_US
dc.subjectPhysical evolutionen_US
dc.titleOptically thin core accretion: how planets get their gas in nearly gas-free discsen_US
dc.rights.holder© 2018, Oxford University Pressen_US

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