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Table 3
Summary of evolution of chemical tracers.
| Component | Class 0 | Class I |
|---|---|---|
| Envelope | Cold, dense envelope results in cold tracers (DCO+, N2H+, N2D+) | Envelope dissipates, extent of cold tracers is much smaller |
| Jet | O-bearing molecules (CO, SiO, SO, H2CO) are present in high-velocity bullets | Molecular jet disappears, seen only in atomic and ionised gas |
| Outflow | Ice sputtering (CH3OH, HNCO) and grain destruction (SO, SiO) tracers are present | Decreased outflow mass and less dense envelope result in no tracers of sputtering and grain destruction, only faint CO remains |
| Cavity walls | Prominent signs of UV-irradiated cavity walls (CN, C2H, c-C3H2) | No prominent signs of hydrocarbons in cavity walls, CN still present |
| Hot core | COMs and simple tracers of ice sublimation and high-temperature chemistry (H2S, OCS) | Small extent plus disk shadowing results in less complexity, except for outbursting sources |
| Disk | Warm disk with COMs, dust obscuration | Colder disk molecules, Keplerian rotation seen in H2CO, C18O, CN in the disk surface. |
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