Chemical survey of Class I protostars with the IRAM-30m.

Class I protostars are a bridge between Class 0 protostars, and Class II protoplanetary disks. Recent studies show gaps and rings in the dust distribution of disks younger than 1 Myr, suggesting that planet formation may start already at the Class I stage. To understand what chemistry planets will inherit, it is crucial to characterize the chemistry of Class I sources and to investigate how chemical complexity evolves from Class 0 protostars to protoplanetary disks. The goal is twofold: to obtain a census of the molecular complexity in a sample of four Class I protostars, and to compare it with the chemical compositions of earlier and later phases of the Sun-like star formation process. We performed IRAM-30m observations towards Class I objects (L1489-IRS, B5-IRS1, L1455-IRS1, and L1551-IRS5). The column densities of the detected species are derived assuming LTE or LVG. We detected 27 species: C-chains, N-bearing, S-bearing, Si-bearing species, deuterated molecules, and iCOMs. Different spectral profiles are observed: narrow lines towards all the sources, broader lines towards L1551-IRS5, and line wings due to outflows. Narrow c-C3H2 emission originates from the envelope. The iCOMs in L1551-IRS5 reveal the occurrence of hot corino chemistry, with CH3OH and CH3CN lines originating from a compact and warm region. Finally, OCS and H2S seem to probe the circumbinary disks in the L1455-IRS1 and L1551-IRS5 binary systems. The deuteration in terms of elemental D/H in the molecular envelopes and hot corino are derived. In addition, B5 IRS1, L1455-IRS1 and L1551-IRS5 show a low excitation methanol line, suggesting an origin from an extended structure, plausibly UV illuminated. The abundance ratios of iCOMs with respect CH3OH measured towards the L1551-IRS5 hot corino and the deuteration in our sample are comparable to that estimated at earlier stages, as well as to that found in comets.