2025A&A...703A.244T

Context. Streamers are newly identified channels that transport mass from large, molecular-cloud scales down to small, protoplanetary-disk scales. To better understand their impact on planet formation, it is essential to study their physical and chemical properties.
Aims. In this framework, we aim to characterize the longest streamer identified in carbon chain emission within the Class I system L1489 IRS, connecting the nearby prestellar core L1489 to the young stellar object (YSO).
Methods. We observed multiple transitions of C₂H, ortho-c-C₃H₂ and HC₃N in L1489 IRS with NOEMA and IRAM-30m at 3 and 2 mm. Using a variety of radiative transfer methods, including a hyperfine structure (HFS) fitting, rotational diagrams, and proposing a new self-consistent Markov chain Monte Carlo approach combined with the non-LTE RADEX code, we derived the column densities and abundances of those molecules, as well as the H₂ number density along the streamer. This enabled us to estimate its mass, infall rate, and its impact on the * system's mass.
Results. We found lower limits on the streamer mass of ≥(4.67-18.3) × 10^–3M_⊙ (i.e., ≥0.65-2.57 times the current disk mass) and an infallrate of ≥(1.94-7.57) × 10^–7M_⊙ yr^–1, where the ranges correspond to the different molecular tracers. These values are consistent with those derived in similar Class I objects. This suggests that the disk could be fully replenished by streamer material. Given its mass, the streamer is likely at the origin of the external warped disk seen in this system, as predicted by numerical simulations. Moreover, the first investigations based on the C₂H/c-C₃H₂ and HC₃N/c-C₃H₂ abundance ratios suggest that the streamer chemistry may be inherited from the core. These results suggest, for the first time, that the chemical composition of a Class I object is affected by a streamer connecting a Class I YSO to its natal environment.
Conclusions. We demonstrate that the streamer in L1489 IRS has a significant impact on its disk. To better constrain how the streamer influences the disk's chemistry and determine whether its composition is inherited from the nearby core, further molecular surveys will be necessary toward the prestellar core, the streamer, and the YSO. Our findings reinforce the importance of characterizing the natal environment of protoplanetary disks both physically (e.g., structure formation) and chemically (e.g., material enrichment) to fully understand their evolution.