The First JWST View of a 30-Myr-old Protoplanetary Disk Reveals a Late-stage Carbon-rich Phase
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2024
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| author | Long, Feng Pascucci, Ilaria Houge, Adrien Banzatti, Andrea Pontoppidan, Klaus M. Najita, Joan Krijt, Sebastiaan Xie, Chengyan Williams, Joe Herczeg, Gregory J. Andrews, Sean M. Bergin, Edwin Blake, Geoffrey A. Colmenares, María José Harsono, Daniel Romero-Mirza, Carlos E. Li, Rixin Lu, Cicero X. Pinilla, Paola Wilner, David J. Vioque, Miguel Zhang, Ke collaboration, the JDISCS |
| author_facet | Long, Feng Pascucci, Ilaria Houge, Adrien Banzatti, Andrea Pontoppidan, Klaus M. Najita, Joan Krijt, Sebastiaan Xie, Chengyan Williams, Joe Herczeg, Gregory J. Andrews, Sean M. Bergin, Edwin Blake, Geoffrey A. Colmenares, María José Harsono, Daniel Romero-Mirza, Carlos E. Li, Rixin Lu, Cicero X. Pinilla, Paola Wilner, David J. Vioque, Miguel Zhang, Ke collaboration, the JDISCS |
| contents | We present a JWST MIRI/MRS spectrum of the inner disk of WISE J044634.16$-$262756.1B (hereafter J0446B), an old ($\sim$34 Myr) M4.5 star but with hints of ongoing accretion. The spectrum is molecule-rich and dominated by hydrocarbons. We detect 14 molecular species (H$_2$, CH$_3$, CH$_4$, C$_2$H$_2$, $^{13}$CCH$_2$, C$_2$H$_4$, C$_2$H$_6$, C$_3$H$_4$, C$_4$H$_2$, C$_6$H$_6$, HCN, HC$_3$N, CO$_2$ and $^{13}$CO$_2$) and 2 atomic lines ([Ne II] and [Ar II]), all observed for the first time in a disk at this age. The detection of spatially unresolved H$_2$ and Ne gas strongly supports that J0446B hosts a long-lived primordial disk, rather than a debris disk. The marginal H$_2$O detection and the high C$_2$H$_2$/CO$_2$ column density ratio indicate that the inner disk of J0446B has a very carbon-rich chemistry, with a gas-phase C/O ratio $\gtrsim$2, consistent with what have been found in most primordial disks around similarly low-mass stars. In the absence of significant outer disk dust substructures, inner disks are expected to first become water-rich due to the rapid inward drift of icy pebbles, and evolve into carbon-rich as outer disk gas flows inward on longer timescales. The faint millimeter emission in such low-mass star disks implies that they may have depleted their outer icy pebble reservoir early and already passed the water-rich phase. Models with pebble drift and volatile transport suggest that maintaining a carbon-rich chemistry for tens of Myr likely requires a slowly evolving disk with $α-$viscosity $\lesssim10^{-4}$. This study represents the first detailed characterization of disk gas at $\sim$30 Myr, strongly motivating further studies into the final stages of disk evolution. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2412_05535 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The First JWST View of a 30-Myr-old Protoplanetary Disk Reveals a Late-stage Carbon-rich Phase Long, Feng Pascucci, Ilaria Houge, Adrien Banzatti, Andrea Pontoppidan, Klaus M. Najita, Joan Krijt, Sebastiaan Xie, Chengyan Williams, Joe Herczeg, Gregory J. Andrews, Sean M. Bergin, Edwin Blake, Geoffrey A. Colmenares, María José Harsono, Daniel Romero-Mirza, Carlos E. Li, Rixin Lu, Cicero X. Pinilla, Paola Wilner, David J. Vioque, Miguel Zhang, Ke collaboration, the JDISCS Earth and Planetary Astrophysics Astrophysics of Galaxies Solar and Stellar Astrophysics We present a JWST MIRI/MRS spectrum of the inner disk of WISE J044634.16$-$262756.1B (hereafter J0446B), an old ($\sim$34 Myr) M4.5 star but with hints of ongoing accretion. The spectrum is molecule-rich and dominated by hydrocarbons. We detect 14 molecular species (H$_2$, CH$_3$, CH$_4$, C$_2$H$_2$, $^{13}$CCH$_2$, C$_2$H$_4$, C$_2$H$_6$, C$_3$H$_4$, C$_4$H$_2$, C$_6$H$_6$, HCN, HC$_3$N, CO$_2$ and $^{13}$CO$_2$) and 2 atomic lines ([Ne II] and [Ar II]), all observed for the first time in a disk at this age. The detection of spatially unresolved H$_2$ and Ne gas strongly supports that J0446B hosts a long-lived primordial disk, rather than a debris disk. The marginal H$_2$O detection and the high C$_2$H$_2$/CO$_2$ column density ratio indicate that the inner disk of J0446B has a very carbon-rich chemistry, with a gas-phase C/O ratio $\gtrsim$2, consistent with what have been found in most primordial disks around similarly low-mass stars. In the absence of significant outer disk dust substructures, inner disks are expected to first become water-rich due to the rapid inward drift of icy pebbles, and evolve into carbon-rich as outer disk gas flows inward on longer timescales. The faint millimeter emission in such low-mass star disks implies that they may have depleted their outer icy pebble reservoir early and already passed the water-rich phase. Models with pebble drift and volatile transport suggest that maintaining a carbon-rich chemistry for tens of Myr likely requires a slowly evolving disk with $α-$viscosity $\lesssim10^{-4}$. This study represents the first detailed characterization of disk gas at $\sim$30 Myr, strongly motivating further studies into the final stages of disk evolution. |
| title | The First JWST View of a 30-Myr-old Protoplanetary Disk Reveals a Late-stage Carbon-rich Phase |
| topic | Earth and Planetary Astrophysics Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2412.05535 |