Unlocking CO Depletion in Protoplanetary Disks. II. Primordial C/H Predictions inside the CO Snowline

doi:10.3847/1538-4357/ab1c5e

	Unlocking CO Depletion in Protoplanetary Disks. II. Primordial C/H Predictions inside the CO Snowline
	Schwarz, Kamber R.1; Bergin, Edwin A.2; Cleeves, L. Ilsedore 3; Zhang, Ke 4; Oberg, Karin, I 5; Blake, Geoffrey A.6; Anderson, Dana E.7
	2019-06-01
发表期刊	ASTROPHYSICAL JOURNAL
ISSN	0004-637X
EISSN	1538-4357
卷号	877 期号:2
摘要	CO is thought to be the main reservoir of volatile carbon in protoplanetary disks, and thus the primary initial source of carbon in the atmospheres of forming giant planets. However, recent observations of protoplanetary disks point toward low volatile carbon abundances in many systems, including at radii interior to the CO snowline. One potential explanation is that gas phase carbon is chemically reprocessed into less volatile species, which are frozen on dust grain surfaces as ice. This mechanism has the potential to change the primordial C/H ratio in the gas. However, current observations primarily probe the upper layers of the disk. It is not clear if the low volatile carbon abundances extend to the midplane, where planets form. We have run a grid of 198 chemical models, exploring how the chemical reprocessing of CO depends on disk mass, dust grain size distribution, temperature, cosmic-ray and X-ray ionization rate, and initial water abundance. Building on our previous work focusing on the warm molecular layer, here we analyze the results for our grid of models in the disk midplane at 12 au. We find that either an ISM level cosmic-ray ionization rate or the presence of UV photons due to a low dust surface density are needed to chemically reduce the midplane CO gas abundance by at least an order of magnitude within 1 Myr. In the majority of our models CO does not undergo substantial reprocessing by in situ chemistry and there is little change in the gas phase C/H and C/O ratios over the lifetime of the typical disk. However, in the small subset of disks where the disk midplane is subject to a source of ionization or photolysis, the gas phase C/O ratio increases by up to nearly 9 orders of magnitude due to conversion of CO into volatile hydrocarbons.
关键词	astrochemistry circumstellar matter ISM: abundances ISM: molecules protoplanetary disks
DOI	10.3847/1538-4357/ab1c5e
收录类别	SCI
语种	英语
WOS关键词	Astronomy & Astrophysics
WOS研究方向	Science & Technology
WOS类目	Astronomy & Astrophysics
WOS记录号	WOS:000470741900004
出版者	IOP PUBLISHING LTD
引用统计
文献类型	期刊论文
专题	任务一_子任务一循证社会科学证据集成任务一
作者单位	1.Univ Michigan, Dept Astron, 1085 South Univ Ave, Ann Arbor, MI 48109 USA 2.Univ Arizona, Lunar & Planetary Lab, 1629 E Univ Blvd, Tucson, AZ 85721 USA 3.Univ Michigan, Dept Astron, 1085 South Univ Ave, Ann Arbor, MI 48109 USA 4.Univ Virginia, Dept Astron, 530 McCormick Rd, Charlottesville, VA 22904 USA 5.Univ Michigan, Dept Astron, 1085 South Univ Ave, Ann Arbor, MI 48109 USA 6.Harvard Smithsonian Ctr Astrophys, 60 Garden St, Cambridge, MA 02138 USA 7.CALTECH, Div Geol & Planetary Sci, MC 150-21,1200 E Calif Blvd, Pasadena, CA 91125 USA
推荐引用方式 GB/T 7714	Schwarz, Kamber R.,Bergin, Edwin A.,Cleeves, L. Ilsedore,et al. Unlocking CO Depletion in Protoplanetary Disks. II. Primordial C/H Predictions inside the CO Snowline[J]. ASTROPHYSICAL JOURNAL,2019,877(2).
APA	Schwarz, Kamber R..,Bergin, Edwin A..,Cleeves, L. Ilsedore.,Zhang, Ke.,Oberg, Karin, I.,...&Anderson, Dana E..(2019).Unlocking CO Depletion in Protoplanetary Disks. II. Primordial C/H Predictions inside the CO Snowline.ASTROPHYSICAL JOURNAL,877(2).
MLA	Schwarz, Kamber R.,et al."Unlocking CO Depletion in Protoplanetary Disks. II. Primordial C/H Predictions inside the CO Snowline".ASTROPHYSICAL JOURNAL 877.2(2019).