Astrochemistry

The First JWST View of a 30-Myr-old Protoplanetary Disk Reveals a Late-stage Carbon-rich Phase

By Keith Cowing

Status Report

astro-ph.EP

December 17, 2024

Filed under astro-ph.EP, astrobiology, astrochemistry, biochemistry, biosignature, imaging, J0446B, JWST, organic chemistry, primordial disk, proto-planetary disk, Spectroscopy, WISE J044634.16−262756.1B

The First JWST View of a 30-Myr-old Protoplanetary Disk Reveals a Late-stage Carbon-rich Phase — The spectral energy distribution of J0446B including the JWST MIRI/MRS spectrum in blue (the noisy longwavelength range is marked with lighter color). The grey curve shows a stellar photospheric model with Teff = 3100 K (Allard et al. 2012). The four WISE band photometry encompassed both stellar components in the binary system of J0446; the triangles represent the contribution of J0446B to W1 and W2 bands assuming the same flux ratio as the Ks band. The insert panel highlights the 10 µm silicate features, where the orange curve marks the identified continuum, two dashed lines represent emissivity curves of amorphous silicates (olivine) for a single grain size of 0.1 and 2.5 µm (Jaeger et al. 1994), and the dotted line represents that for crystalline silicate of forsterite (Koike et al. 2003). — astro-ph.EP

We present a JWST MIRI/MRS spectrum of the inner disk of WISE J044634.16−262756.1B (hereafter J0446B), an old (∼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 (H₂, CH₃, CH4, C₂H₂, ¹³CCH₂, C₂H₄, C₂H₆, C₃H₄, C₄H₂, C₆H₆, HCN, HC₃N, CO₂ and ¹³CO₂) 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 H2 and Ne gas strongly supports that J0446B hosts a long-lived primordial disk, rather than a debris disk.

The marginal H₂O detection and the high C₂H₂/CO₂ column density ratio indicate that the inner disk of J0446B has a very carbon-rich chemistry, with a gas-phase C/O ratio ≳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 ≲10⁻⁴.

This study represents the first detailed characterization of disk gas at ∼30 Myr, strongly motivating further studies into the final stages of disk evolution.

Feng Long, Ilaria Pascucci, Adrien Houge, Andrea Banzatti, Klaus M. Pontoppidan, Joan Najita, Sebastiaan Krijt, Chengyan Xie, Joe Williams, Gregory J. Herczeg, Sean M. Andrews, Edwin Bergin, Geoffrey A. Blake, María José Colmenares, Daniel Harsono, Carlos E. Romero-Mirza, Rixin Li, Cicero X. Lu, Paola Pinilla, David J. Wilner, Miguel Vioque, Ke Zhang, the JDISCS collaboration

Comments: Accepted by ApJL. 8 figures in the main text
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2412.05535 [astro-ph.EP] (or arXiv:2412.05535v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2412.05535
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Submission history
From: Feng Long
[v1] Sat, 7 Dec 2024 04:37:16 UTC (3,380 KB)
https://arxiv.org/abs/2412.05535
Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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