Disentangling disc and atmospheric signatures of young brown dwarfs with JWST/NIRSpec

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Volume 703 (November 2025)

A&A, 703 (2025) A65

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Table 1

Isotope ratios derived from JWST/NIRSpec observations.

Target	TWA 27A	TWA 28
¹²CO/¹³CO	$53_{- 3}^{+ 3}$ $\[53_{-3}^{+3}\]$	$75_{- 2}^{+ 2}$ $\[75_{-2}^{+2}\]$
¹²CO/¹³CO (calibrated)	$79_{- 11}^{+ 14}$ $\[79_{-11}^{+14}\]$	−
¹²CO/C¹⁸O	$428_{- 37}^{+ 42}$ $\[428_{-37}^{+42}\]$	$685_{- 46}^{+ 49}$ $\[685_{-46}^{+49}\]$
$H_{2}^{16} O / H_{2}^{18} O$ $\[\mathrm{H}_2^{16} \mathrm{O} / \mathrm{H}_2^{18} \mathrm{O}\]$	$645_{- 70}^{+ 80}$ $\[645_{-70}^{+80}\]$	$681_{- 50}^{+ 53}$ $\[681_{-50}^{+53}\]$

Notes. The uncertainties represent the 16th and 84th percentiles of the posterior distributions. The calibrated ¹²CO/¹³CO ratios account for oxygen isotope homogeneity using the gamma factor $γ = (H_{2}^{16} O / H_{2}^{18} O) \times {(^{12} C O / C^{18} O)}^{- 1}$ $\[\gamma= \left(\mathrm{H}_{2}^{16} \mathrm{O} / \mathrm{H}_{2}^{18} \mathrm{O}\right) \times\left(^{12} \mathrm{CO} / \mathrm{C}^{18} \mathrm{O}\right)^{-1}\]$ to ensure consistent oxygen isotope ratios between CO and H₂O molecules. For TWA 28, γ ≈ 1 within uncertainties, so no calibration is applied.

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