Carbon Isotope Chemistry In Protoplanetary Disks: Effects Of C/O Ratios

Carbon isotope fractionation of CO has been reported in the disk around TW Hya, where elemental carbon is more abundant than elemental oxygen ([C/O]elem> 1).

We investigated the effects of the [C/O]elem ratio on carbon fractionation using astrochemical models that incorporate isotope-selective photodissociation and isotope-exchange reactions.

The ¹²CO/¹³CO ratio could be lower than the elemental carbon isotope ratio due to isotope exchange reactions when the [C/O]elem ratio exceeds unity. The observed ¹²CO/¹³CO and H¹²CN/H¹³CN ratios around TW Hya could be reproduced when the [C/O]elem ratio is 2~5.

In the vicinity of the lower boundary of the warm molecular layer, the formation of ices leads to the gas phase [C/O]elem ratio approaching unity, irrespective of the total (gas + ice) [C/O]elem ratio. This phenomenon reduces the variation in the ¹²CO/¹³CO ratio across different [C/O]elem ratios.

Seokho Lee, Hideko Nomura, Kenji Furuya

Comments: Accepted in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2404.01635 [astro-ph.GA] (or arXiv:2404.01635v1 [astro-ph.GA] for this version)
Submission history
From: Seokho Lee
[v1] Tue, 2 Apr 2024 04:49:15 UTC (1,553 KB)
https://arxiv.org/abs/2404.01635
Astrobiology, Astrochemistry,