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.
