High CO/H2 ratio supports an exocometary origin for a CO-rich debris disc

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Table D.1

CO to H₂ ratios and age for discs.

Name	$\frac{CO}{H_{2}}$ $Mathematical equation: $\frac{\text{CO}}{\text{H}_2}$$ Ratio	Age (Myr)	CO Method	H₂ Method	Age Method	Type	References
ISM	−4.00	—	—	—	—	ISM	—
HL Tau	$- {4.17}_{- 0.03}^{+ 0.04}$ $Mathematical equation: $-4.17^{+0.04}_{-0.03}$$	${0.8}_{- 0.25}^{+ 0.25}$ $Mathematical equation: $0.8^{+0.25}_{-0.25}$$	¹³CO	Dust	SED	PPD	[1,2]
DG Tau	$- {4.34}_{- 0.04}^{+ 0.04}$ $Mathematical equation: $-4.34^{+0.04}_{-0.04}$$	${0.9}_{- 0.25}^{+ 0.25}$ $Mathematical equation: $0.9^{+0.25}_{-0.25}$$	¹³CO	Dust	SED	PPD	[1,2]
TMC1A	$- {3.68}_{- 0.04}^{+ 0.02}$ $Mathematical equation: $-3.68^{+0.02}_{-0.04}$$	${0.5}_{- 0.1}^{+ 0.1}$ $Mathematical equation: $0.5^{+0.1}_{-0.1}$$	¹³CO	Dust	SED	PPD	[1,2]
Oph-IRS67	$- {3.68}_{- 0.30}^{+ 0.30}$ $Mathematical equation: $-3.68^{+0.30}_{-0.30}$$	${0.45}_{- 0.1}^{+ 0.1}$ $Mathematical equation: $0.45^{+0.1}_{-0.1}$$	C¹⁷O	Dust	SED	PPD	[3,2]
DM Tau	$- {4.24}_{- 0.21}^{+ 0.15}$ $Mathematical equation: $-4.24^{+0.15}_{-0.21}$$	${1.5}_{- 0.25}^{+ 0.8}$ $Mathematical equation: $1.5^{+0.8}_{-0.25}$$	¹³CO, C¹⁸O	N₂H⁺	SED	PPD	[2,4,30]
TW Hya	$- {5.84}_{- 0.30}^{+ 0.00}$ $Mathematical equation: $-5.84^{+0.00}_{-0.30}$$	$8_{- 1}^{+ 1}$ $Mathematical equation: $8^{+1}_{-1}$$	¹³CO, C¹⁸O	Dust	TW Hydra	PPD	[4,28]
HD 163296	$- {4.28}_{- 0.21}^{+ 0.17}$ $Mathematical equation: $-4.28^{+0.17}_{-0.21}$$	${6.03}_{- 0.27}^{+ 0.28}$ $Mathematical equation: $6.03^{+0.28}_{-0.27}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[4,5,30]
IM Lup	$- {4.45}_{- 0.20}^{+ 0.21}$ $Mathematical equation: $-4.45^{+0.21}_{-0.20}$$	${1.2}_{- 0.25}^{+ 0.8}$ $Mathematical equation: $1.2^{+0.8}_{-0.25}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[4,29,30]
J1609 J1608	<-6.00	$8_{- 3}^{+ 3}$ $Mathematical equation: $8^{+3}_{-3}$$	C¹⁸O	N₂H⁺	Upper Sco	PPD	[6,30]
HD 100546	$- {4.70}_{- 0.30}^{+ 0.30}$ $Mathematical equation: $-4.70^{+0.30}_{-0.30}$$	${4.8}_{- 1.1}^{+ 2}$ $Mathematical equation: $4.8^{+2}_{-1.1}$$	¹²CO, ¹³CO, C¹⁸O	HD	Isochrones	PPD	[7,8,9,31]
PDS 66	$- {5.53}_{- 0.29}^{+ 0.28}$ $Mathematical equation: $-5.53^{+0.28}_{-0.29}$$	${3.1}_{- 0.9}^{+ 0.9}$ $Mathematical equation: $3.1^{+0.9}_{-0.9}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[10,30,32]
AA Tau	$- {4.60}_{- 0.22}^{+ 0.24}$ $Mathematical equation: $-4.60^{+0.24}_{-0.22}$$	7	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[11,30,32]
AS 209	$- {4.68}_{- 0.26}^{+ 0.25}$ $Mathematical equation: $-4.68^{+0.25}_{-0.26}$$	${0.75}_{- 0.25}^{+ 0.25}$ $Mathematical equation: $0.75^{+0.25}_{-0.25}$$	¹³CO, C¹⁸O	N₂H⁺	ρ Ophiuchi	PPD	[12,30, 33]
CQ Tau	$- {4.50}_{- 0.08}^{+ 0.30}$ $Mathematical equation: $-4.50^{+0.30}_{-0.08}$$	10.0	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[13,30]
Elias 2-27	$- {4.20}_{- 0.19}^{+ 0.14}$ $Mathematical equation: $-4.20^{+0.14}_{-0.19}$$	0.8	¹³CO, C¹⁸O	N₂H⁺	ρ Orph	PPD	[14,30,34]
GM Aur	$- {4.38}_{- 0.23}^{+ 0.21}$ $Mathematical equation: $-4.38^{+0.21}_{-0.23}$$	${6.5}_{- 3.5}^{+ 3.5}$ $Mathematical equation: $6.5^{+3.5}_{-3.5}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[15,30,35]
HD 135344B	$- {4.13}_{- 0.17}^{+ 0.10}$ $Mathematical equation: $-4.13^{+0.10}_{-0.17}$$	${9.0}_{- 2.0}^{+ 2.0}$ $Mathematical equation: $9.0^{+2.0}_{-2.0}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[16,30]
HD 143006	$- {5.11}_{- 0.23}^{+ 0.25}$ $Mathematical equation: $-5.11^{+0.25}_{-0.23}$$	${8.0}_{- 4.0}^{+ 4.0}$ $Mathematical equation: $8.0^{+4.0}_{-4.0}$$	¹³CO, C¹⁸O	N₂H⁺	Upper Sco	PPD	[17,30]
HD 34282	$- {4.11}_{- 0.12}^{+ 0.07}$ $Mathematical equation: $-4.11^{+0.07}_{-0.12}$$	${6.4}_{- 0.5}^{+ 0.5}$ $Mathematical equation: $6.4^{+0.5}_{-0.5}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[18,30]
LkCa 15	$- {4.46}_{- 0.21}^{+ 0.20}$ $Mathematical equation: $-4.46^{+0.20}_{-0.21}$$	${2.0}_{- 1.0}^{+ 2.0}$ $Mathematical equation: $2.0^{+2.0}_{-1.0}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[19,30]
HD 31648	$- {4.22}_{- 0.21}^{+ 0.15}$ $Mathematical equation: $-4.22^{+0.15}_{-0.21}$$	${6.55}_{- 0.55}^{+ 0.55}$ $Mathematical equation: $6.55^{+0.55}_{-0.55}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[20,30]
HD 36112	$- {4.25}_{- 0.21}^{+ 0.15}$ $Mathematical equation: $-4.25^{+0.15}_{-0.21}$$	${8.5}_{- 0.5}^{+ 0.4}$ $Mathematical equation: $8.5^{+0.4}_{-0.5}$$	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[21,30]
RXJ 1615.3-3255	$- {4.12}_{- 0.12}^{+ 0.08}$ $Mathematical equation: $-4.12^{+0.08}_{-0.12}$$	1.0	¹³CO, C¹⁸O	N₂H⁺	Lupus	PPD	[22,30]
RXJ 1842.9-3532	$- {4.60}_{- 0.22}^{+ 0.21}$ $Mathematical equation: $-4.60^{+0.21}_{-0.22}$$	10.0	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[23,30]
V4046 Sgr	$- {4.60}_{- 0.21}^{+ 0.20}$ $Mathematical equation: $-4.60^{+0.20}_{-0.21}$$	12.0	¹³CO, C¹⁸O	N₂H⁺	Isochrones	PPD	[24,30]
HD 131488	>-4.66	$16_{- 2}^{+ 2}$ $Mathematical equation: $16^{+2}_{-2}$$	¹²CO	H₂	Upper Centaurus Lupus	Debris Disc	[25,26]
HD 110058	>-2.45	$17_{- 3}^{+ 3}$ $Mathematical equation: $17^{+3}_{-3}$$	¹²CO	H₂	Lower Centaurus Crux	Debris Disc	[25,27]
Beta Pictoris	>-3.19	$23_{- 8}^{+ 8}$ $Mathematical equation: $23^{+8}_{-8}$$	¹²CO	H₂	β Pictoris	Debris Disc	[36,37]

References. (1) Zhang et al. (2020); (2) Robitaille et al. (2007); (3) Artur de la Villarmois et al. (2018); (4) Zhang et al. (2019); (5) Wichittanakom et al. (2020); (6) Anderson et al. (2019); (7) Kama et al. (2016); (8) Bruderer et al. (2012); (9) Pineda et al. (2019); (10) Asensio-Torres et al. (2021); (11) Schneider et al. (2018); (12) Natta et al. (2006); (13) Mannings & Sargent (2000); (14) Andrews et al. (2009); (15) Macías et al. (2018); (16) Müller et al. (2011); (17) Pecaut et al. (2012); (18) Merín et al. (2004); (19) Kraus & Hillenbrand (2009); (20) Simon et al. (2000); (21) Vioque et al. (2018); (22) Makarov (2007); (23) Neuhäuser et al. (2000); (24) Torres et al. (2008); (25) This work; (26) Pecaut et al. (2012); (27) Pecaut et al. (2012);(28) Rhee et al. (2007); (29) Mawet et al. (2012); (30) Trapman et al. (2025); (31) Bergin & Williams (2017); (32) Siess et al. (2000); (33) D’Antona & Mazzitelli (1997); (34) Luhman & Rieke (1999), (35) Zaire et al. (2024) (36) Lee et al. (2024); (37) Lecavelier des Etangs et al. (2001)

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