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Table 3

Diffusion data: fractional mass in the convection zone, diffusion timescales τ for C and Si, and diffusion fluxes.

Object log  (ΔMcvz/M) log  (ΔM(1) /M) τ(C) [yrs] τ(Si) [yrs] fdiff(C) [g/s] C/Si

WDJ1929+4447 −12.661 > −10.962 31.05 11.91 < 4.67 × 105
WD1654+160 −12.466 > −10.721 36.23 15.14 < 4.27 × 105
EC20058-5234 −11.656 −10.178 114.89 55.77 5.90 × 106 137.5
EC04207-4748 −11.592 −10.045 179.67 85.29 6.81 × 106 512.0
PG1115+158 −11.373 > −9.822 204.64 103.40 5.52 × 105 0.11

WD0100-068 −8.419 > −6.062 1.82 × 104 1.40 × 104 1.26 × 106 0.52
WD0435+410 −6.676 > −3.627 2.43 × 105 2.05 × 105 < 9.36 × 104 < 0.005
WD0840+262 −7.263 > −4.437 8.49 × 104 6.81 × 104 < 4.69 × 105 < 1.72
WD1557+192 −8.184 > −5.681 2.36 × 104 1.90 × 104 < 5.63 × 105 < 0.68
WD1822+410 −6.130 > −3.644 7.42 × 105 6.64 × 105 7.16 × 106 0.61
WD1940+374 −6.393 > −3.499 4.57 × 105 4.01 × 105 < 3.35 × 105
WD2144-079 −6.482 > −3.686 3.28 × 105 2.81 × 105 < 4.17 × 105 <0.07

Sun 3.56
Bulk Earth 0.00990.0228
CI 0.325

Notes. ΔM(1) /M is the fractional mass above the layer with [C/He] = 1. In the last column the mass ratio C/Si of the accreted matter is given (with the assumption that the metal pollution is caused by accretion). The last three rows in this column give the mass ratio C/Si for the Sun (Asplund et al. 2009), bulk Earth (Allègre et al. 2001), and CI chondrites (Lodders et al. 2009).

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