  Episodic accretion in protostars leads to luminosity outbursts that end up
heating their surroundings. This rise in temperature pushes the snow lines
back, enabling the desorption of chemical species from dust grain surfaces,
which may significantly alter the chemical history of the accreting envelope.
However, a limited number of extensive chemical surveys of eruptive young stars
have been performed thus far. In the present study, we carry out a large
spectral survey of the binary Class I protostar L1551 IRS 5, known to be a
FUor-like object, in the 3mm and 2mm bands with the IRAM-30m telescope. As a
result, we detected more than 400 molecular lines. The source displays a great
chemical richness with the detection of 75 species, including isotopologues.
Among these species, there are 13 hydrocarbons, 25 N-bearing species, 30
O-bearing species, 15 S-bearing species, 12 deuterated molecules, and a total
of 10 complex organic molecules (l-C4H2, CH3CCH, CH2DCCH, CH3CHO, CH3CN,
CH3OCH3, CH3OCHO, CH3OH, CH2DOH, and HC5N). With the help of local
thermodynamic equilibrium (LTE) and non-LTE models, we determined the column
densities of most molecules as well as excitation and kinetic temperatures.
While most of those molecules trace the cold envelope (< 20 K), the OCS and
CH3OH emission arise from the warm (> 100 K) innermost (< 2'' ) regions. We
compared the chemical inventory of L1551 IRS 5 and its column density ratios,
including isotopic ratios, with other protostellar sources. A broad chemical
diversity is seen among Class I objects. More observations with both
single-dish telescopes and interferometers are needed to characterize the
diversity in a larger sample of protostars, while more astrochemical models
would help explain this diversity, in addition to the impact of luminosity
outbursts on the chemistry of protostellar envelopes.
