Quantifying the C/O ratio in the planet-forming environments around very low-mass stars

Quantifying the C/O ratio in the planet-forming environments around very low-mass stars Javiera K. Díaz-Berríos ([email protected]), Catherine Walsh Ewine F. van Dishoeck ESO Workshop — Towards new frontiers, ESO Garching Credits background: NASA/JPL-Caltech Díaz-Berríos, J. K., Walsh, C., and van Dishoeck, E. F. (submiBed to ApJ, under review) Protoplanetary disks CHEMISTRY IN PLANET-FORMING REGIONS r [au] 0.1 1 10 100 scattered light dust thermal emission Adapted from Miotello+2023 2 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Context Credits background: NASA/JPL-Caltech Tabone+2023, van Dishoeck+2023 3 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Context Disks around Very low-mass stars THE CASE OF J160532’ JWST OBSERVATIONS Tabone+2023, van Dishoeck+2023 3 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Context Disks around Very low-mass stars THE CASE OF J160532’ JWST OBSERVATIONS ISO-CHAI 147 Arabhavi+2024 C2H2+13CCH2 Total model C6H6 HCN HC3N CO2+13CO2 C2H6 C3H4 C4H2 CH3 SZ28 Kanwar+2024 Tabone+2023, van Dishoeck+2023 3 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Context Disks around Very low-mass stars THE CASE OF J160532’ JWST OBSERVATIONS ISO-CHAI 147 Arabhavi+2024 C2H2+13CCH2 Total model C6H6 HCN HC3N CO2+13CO2 C2H6 C3H4 C4H2 CH3 SZ28 Kanwar+2024 JWST has revealed hydrocarbon rich inner disks of now three sources What are the implications for planet formation? What could be responsible for such high abundances? 4 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Chemical model What mechanisms could be occurring in the disk to affect the C/O ratio? Hydrocarbon chemistry is sensitive to C/O ratios van Dishoeck+2023, Tabone+2023, Díaz-Berríos, J. K., Walsh, C., and van Dishoeck, E. F. (submiBed to ApJ, under review) Credits background: NASA/JPL-Caltech How to explain the high abundances? C-rich grains Silicate grains CO2-ice mantle 10 AU1 AU0.1 AU H2O-ice mantle H2OCO2 Soot line 4 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Chemical model Hydrocarbon chemistry is sensitive to C/O ratios What mechanisms could be occurring in the disk to affect the C/O ratio? Credits background: NASA/JPL-Caltech How to explain the high abundances? Carbon grain destruction releasing carbon into the gas phase van Dishoeck+2023, Tabone+2023, Díaz-Berríos, J. K., Walsh, C., and van Dishoeck, E. F. (submiBed to ApJ, under review) C-rich grains Silicate grains CO2-ice mantle 10 AU1 AU0.1 AU H2O-ice mantle H2OCO2 Gap Soot line 4 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Chemical model Hydrocarbon chemistry is sensitive to C/O ratios What mechanisms could be occurring in the disk to affect the C/O ratio? Credits background: NASA/JPL-Caltech How to explain the high abundances? Carbon grain destruction releasing carbon into the gas phase Oxygen depletion due to icy pebble trapping in the outer disk van Dishoeck+2023, Tabone+2023, Díaz-Berríos, J. K., Walsh, C., and van Dishoeck, E. F. (submiBed to ApJ, under review) Carbon grain destruction releasing carbon into the gas phase Oxygen depletion due to icy pebble trapping in the outer disk Hydrocarbon chemistry is sensitive to C/O ratios C-rich grains Silicate grains CO2-ice mantle 10 AU1 AU0.1 AU H2O-ice mantle H2OCO2 Gap Soot line 4 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Chemical model What mechanisms could be occurring in the disk to affect the C/O ratio? Credits background: NASA/JPL-Caltech How to explain the high abundances? Goal of this work What degree of carbon enrichment and/or oxygen depletion reproduce the trend in observations? van Dishoeck+2023, Tabone+2023, Díaz-Berríos, J. K., Walsh, C., and van Dishoeck, E. F. (submiBed to ApJ, under review) J160532 ISO-ChaI 147 Díaz-Berríos+submiBed C2H2/CO2 How do the models compare with observations? SOME TRENDS: COLUMN DENSITY RATIOS C/O 1 carbon! rich oxygen rich 10 100 6 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Sz28 Atmosphere + Midplane component! up to 0.1 au J160532 ISO-ChaI 147 Díaz-Berríos+submiBed C2H2/CO2 How do the models compare with observations? SOME TRENDS: COLUMN DENSITY RATIOS C/O 1 carbon! rich oxygen rich 10 100 6 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Sz28 Despite Sz28 and ISO-ChaI 147 appearing significantly more hydrocarbon rich than J160532 through the number of species detected, the ratio between C2H2/CO2 suggests that these sources are globally less carbon-rich than J160532. 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Where is the carbon going? MAIN CARBON CARRIERS IN THE DISK Atmosphere component C/O~8.8! ↑C⨉2! ↓Ox10 Fiducial! C/O~0.44! (Walsh+2015) 0.04 au 1 au 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Where is the carbon going? MAIN CARBON CARRIERS IN THE DISK Atmosphere component C/O~8.8! ↑C⨉2! ↓Ox10 Fiducial! C/O~0.44! (Walsh+2015) 0.04 au HCN! 8% Other CO! 19% LCC! 61% C2H2! 6% 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Where is the carbon going? MAIN CARBON CARRIERS IN THE DISK Atmosphere component C/O~8.8! ↑C⨉2! ↓Ox10 Fiducial! C/O~0.44! (Walsh+2015) 0.04 au HCN! 8% Other CO! 19% LCC! 61% C2H2! 6% 1 au Other LCC! 3% CO! 86% CO2! 5% 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Where is the carbon going? MAIN CARBON CARRIERS IN THE DISK Atmosphere component C/O~8.8! ↑C⨉2! ↓Ox10 Fiducial! C/O~0.44! (Walsh+2015) 0.04 au HCN! 8% Other CO! 19% LCC! 61% C2H2! 6% 1 au Other LCC! 3% CO! 86% CO2! 5% HCN! 7% CO! 6% LCC! 78% Other 0.04 au LCC! 92% Other 1 au 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Where is the carbon going? MAIN CARBON CARRIERS IN THE DISK Atmosphere component C/O~8.8! ↑C⨉2! ↓Ox10 Fiducial! C/O~0.44! (Walsh+2015) 0.04 au HCN! 8% Other CO! 19% LCC! 61% C2H2! 6% 1 au Other LCC! 3% CO! 86% CO2! 5% HCN! 7% CO! 6% LCC! 78% Other 0.04 au LCC! 92% Other 1 au Long carbon chains dominate the carbon budget at 0.04 au in the disk atmosphere when C/O=0.44, showing that carbon enrichment is not always necessary for the efficient synthesis of hydrocarbons. key points and conclusions WHAT DID WE LEARN FROM THE MODELS? 8 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Conclusions Credits background: NASA/JPL-Caltech Which physical mechanisms lead to that particular C/O ratio is still an open question. The systems observed so far show a range of C/O, suggesting that the magnitude of the mechanisms that set the inner-disk composition is not necessarily equal for the sources even if they all show a hydrocarbon-rich inner disk. key points and conclusions WHAT DID WE LEARN FROM THE MODELS? 8 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Conclusions Credits background: NASA/JPL-Caltech Our results suggest that carbon enrichment is not necessarily required to reach the column densities of observed hydrocarbon species provided that the midplane is exposed. Do we always need a C/O>1 to obtain the high abundances of hydrocarbons? Which physical mechanisms lead to that particular C/O ratio is still an open question. The systems observed so far show a range of C/O, suggesting that the magnitude of the mechanisms that set the inner-disk composition is not necessarily equal for the sources even if they all show a hydrocarbon-rich inner disk. What are the implications for planet formation? On the other hand, terrestrial planets could be accreting carbon-poor material. If gas giant planets are actively forming in these disks they could be accreting carbon-rich gas. key points and conclusions WHAT DID WE LEARN FROM THE MODELS? 8 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Conclusions Which physical mechanisms lead to that particular C/O ratio is still an open question. Credits background: NASA/JPL-Caltech Our results suggest that carbon enrichment is not necessarily required to reach the column densities of observed hydrocarbon species provided that the midplane is exposed. Do we always need a C/O>1 to obtain the high abundances of hydrocarbons? The systems observed so far show a range of C/O, suggesting that the magnitude of the mechanisms that set the inner-disk composition is not necessarily equal for the sources even if they all show a hydrocarbon-rich inner disk. 5 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Backup How do the models compare with observations? COLUMN DENSITIES AND RATIOS Quantifying the C/O ratio in the planet-forming environments around very low-mass stars 19 ! ! ! ! ! ! ! ! ! J160532 (Tabone+2024) ISO-ChaI 147 (Arabhavi+2024) (Kaeufer+2024) Sz28 Sz28 (Kanwar+2024b) Disk-averaged column density up to 10.0 au (atmosphere) Disk-averaged column density up to 1.0 au (atmosphere) Disk-averaged column density up to 0.1 au (atmosphere) Figure 12. Left: Column densities of C2H2,H 2O, CO2,C 6H6,C 4H2,CH 4,HCN,C 2H4,andC 3H4. The values estimated here are the disk-averaged column density up to 0.1, 1, and 10 au (each row), integrating vertically down to the ⌧= 1 surface at 14 µm. Middle and right: Column density ratios of C2H2/H2O, C2H/CO2,andCO 2/H2O. The orange, green, and purple crosses represent the results from Tabone et al. (2023), Arabhavi et al. (2024), Kanwar et al. (2024b)andKaeufer et al. (2024) for the J160532, ISO-ChaI 147, and Sz28 disks, respectively. The shaded blue bars in the left-hand and middle panels represent the results from our chemical models with di↵erent C/O ratios. The right-hand panel shows the discrete values for the di↵erent models. 6 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Backup How do the models compare with observations? COLUMN DENSITIES AND RATIOS Quantifying the C/O ratio in the planet-forming environments around very low-mass stars 19 ! ! ! ! ! ! ! ! ! J160532 (Tabone+2024) ISO-ChaI 147 (Arabhavi+2024) (Kaeufer+2024) Sz28 Sz28 (Kanwar+2024b) Disk-averaged column density up to 10.0 au (atmosphere) Disk-averaged column density up to 1.0 au (atmosphere) Disk-averaged column density up to 0.1 au (atmosphere) Figure 12. Left: Column densities of C2H2,H 2O, CO2,C 6H6,C 4H2,CH 4,HCN,C 2H4,andC 3H4. The values estimated here are the disk-averaged column density up to 0.1, 1, and 10 au (each row), integrating vertically down to the ⌧= 1 surface at 14 µm. Middle and right: Column density ratios of C2H2/H2O, C2H/CO2,andCO 2/H2O. The orange, green, and purple crosses represent the results from Tabone et al. (2023), Arabhavi et al. (2024), Kanwar et al. (2024b)andKaeufer et al. (2024) for the J160532, ISO-ChaI 147, and Sz28 disks, respectively. The shaded blue bars in the left-hand and middle panels represent the results from our chemical models with di↵erent C/O ratios. The right-hand panel shows the discrete values for the di↵erent models. 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Backup How do the models compare with observations? COLUMN DENSITIES AND RATIOS Quantifying the C/O ratio in the planet-forming environments around very low-mass stars 19 ! ! ! ! ! ! ! ! ! J160532 (Tabone+2024) ISO-ChaI 147 (Arabhavi+2024) (Kaeufer+2024) Sz28 Sz28 (Kanwar+2024b) Disk-averaged column density up to 10.0 au (atmosphere) Disk-averaged column density up to 1.0 au (atmosphere) Disk-averaged column density up to 0.1 au (atmosphere) Figure 12. Left: Column densities of C2H2,H 2O, CO2,C 6H6,C 4H2,CH 4,HCN,C 2H4,andC 3H4. The values estimated here are the disk-averaged column density up to 0.1, 1, and 10 au (each row), integrating vertically down to the ⌧= 1 surface at 14 µm. Middle and right: Column density ratios of C2H2/H2O, C2H/CO2,andCO 2/H2O. The orange, green, and purple crosses represent the results from Tabone et al. (2023), Arabhavi et al. (2024), Kanwar et al. (2024b)andKaeufer et al. (2024) for the J160532, ISO-ChaI 147, and Sz28 disks, respectively. The shaded blue bars in the left-hand and middle panels represent the results from our chemical models with di↵erent C/O ratios. The right-hand panel shows the discrete values for the di↵erent models. 8 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Backup How do the models compare with observations? COLUMN DENSITIES AND RATIOS Quantifying the C/O ratio in the planet-forming environments around very low-mass stars 21 ! ! ! ! ! ! ! ! ! J160532 (Tabone+2024) ISO-ChaI 147 (Arabhavi+2024) (Kaeufer+2024) Sz28 Sz28 (Kanwar+2024b) Disk-averaged column density up to 10.0 au (midplane) Disk-averaged column density up to 1.0 au (midplane) Disk-averaged column density up to 0.1 au (midplane) Figure 13. Same as Fig. 12 for integration down to the midplane. 9 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Backup How do the models compare with observations? COLUMN DENSITIES AND RATIOS Quantifying the C/O ratio in the planet-forming environments around very low-mass stars 21 ! ! ! ! ! ! ! ! ! J160532 (Tabone+2024) ISO-ChaI 147 (Arabhavi+2024) (Kaeufer+2024) Sz28 Sz28 (Kanwar+2024b) Disk-averaged column density up to 10.0 au (midplane) Disk-averaged column density up to 1.0 au (midplane) Disk-averaged column density up to 0.1 au (midplane) Figure 13. Same as Fig. 12 for integration down to the midplane. 10 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Backup How do the models compare with observations? COLUMN DENSITIES AND RATIOS Quantifying the C/O ratio in the planet-forming environments around very low-mass stars 21 ! ! ! ! ! ! ! ! ! J160532 (Tabone+2024) ISO-ChaI 147 (Arabhavi+2024) (Kaeufer+2024) Sz28 Sz28 (Kanwar+2024b) Disk-averaged column density up to 10.0 au (midplane) Disk-averaged column density up to 1.0 au (midplane) Disk-averaged column density up to 0.1 au (midplane) Figure 13. Same as Fig. 12 for integration down to the midplane. 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Where is the carbon going? MAIN CARBON CARRIERS IN THE DISK C/O~8.8! ↑C⨉2! ↓Ox10 Atmosphere component Atmosphere + Midplane component 0.04 au 1 au 0.04 au 1 au Fiducial! C/O~0.44! (Walsh+2015) 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Where is the carbon going? MAIN CARBON CARRIERS IN THE DISK 0.04 au 1 au C/O~8.8! ↑C⨉2! ↓Ox10 HCN! 8% Other CO! 19% LCC! 61% HCN! 7% CO! 6% LCC! 78% Other Atmosphere component Other LCC! 3% CO! 86% LCC! 92% Other CH4! 28% HCN! 10% LCC! 12% CO! 48% Other HCN! 8% LCC! 58% Other Other CO! 68% LCC! 87% Other 0.04 au 1 au 0.04 au 1 au 0.04 au 1 au Atmosphere + Midplane component Fiducial! C/O~0.44! (Walsh+2015) C2H2! 6% CO2! 5% CO2! 17% CO! 7% CH4! 27% LCC! 5% 7 QuanNfying the C/O raNo in planet-forming environments around very low-mass stars — Discussion Where is the carbon going? MAIN CARBON CARRIERS IN THE DISK 0.04 au 1 au C/O~8.8! ↑C⨉2! ↓Ox10 HCN! 8% Other CO! 19% LCC! 61% HCN! 7% CO! 6% LCC! 78% Other Atmosphere component Other LCC! 3% CO! 86% LCC! 92% Other CH4! 28% HCN! 10% LCC! 12% CO! 48% Other HCN! 8% LCC! 58% Other Other CO! 68% LCC! 87% Other 0.04 au 1 au 0.04 au 1 au 0.04 au 1 au Atmosphere + Midplane component Fiducial! C/O~0.44! (Walsh+2015) C2H2! 6% CO2! 5% CO2! 17% CO! 7% CH4! 27% LCC! 5% Long carbon chains dominate the carbon budget at 0.04 au in the disk atmosphere when C/O=0.44, showing that carbon enrichment is not always necessary for the efficient synthesis of hydrocarbons.