2020ApJ...898..131L

There is mounting evidence that the composition and structure of planetary systems are intimately linked to their birth environments. During the past decade, several spectral surveys probed the chemistry of the earliest stages of star formation and late planet-forming disks. However, very little is known about the chemistry of intermediate protostellar stages, i.e., class I young stellar objects (YSOs), where planet formation may have already begun. We present here the first results of a 3 mm spectral survey performed with the IRAM 30 m telescope to investigate the chemistry of a sample of seven class I YSOs located in the Taurus star-forming region. These sources were selected to embrace the wide diversity identified for low-mass protostellar envelope and disk systems. We present detections and upper limits of 13 small (N_atoms <= 3) C, N, O, and S carriers-namely, CO, HCO⁺, HCN, HNC, CN, N₂H⁺, C₂H, CS, SO, HCS⁺, C₂S, SO₂, and OCS-and some of their D, ¹³C, ¹⁵N, ¹⁸O, ¹⁷O, and ³⁴S isotopologues. Together, these species provide constraints on gas-phase C/N/O ratios, D and ¹⁵N fractionation, source temperature, and UV exposure, as well as the overall S chemistry. We find substantial evidence of chemical differentiation among our source sample, some of which can be traced back to class I physical parameters, such as the disk-to-envelope mass ratio (proxy for class I evolutionary stage), source luminosity, and UV field strength. Overall, these first results allow us to start investigating the astrochemistry of class I objects; however, interferometric observations are needed to differentiate envelope versus disk chemistry.