Origins of complex organic molecules in L1551 IRS 5
Year: 2026
Type: article
Abstract: Context . Complex organic molecules (COMs) are typically observed in the warm inner envelopes of Class 0 protostars (hot corinos). In evolved Class I sources, detecting COMs is challenging, as the emission becomes confined to the compact inner disk and obscured by high dust opacity. However, the FU Orionis-type binary L1551 IRS 5 offers a valuable opportunity to probe disk chemistry, as its outburst luminosity thermally sublimates ices out to large radii. Aims . We sought to spatially resolve the origins of COMs in this system in order to distinguish between central radiative heating and shock-induced chemistry driven by heterogeneous accretion pathways. Methods . We analyzed high-angular-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) Science Archive, focusing on COMs (e.g., CH 3 OH, CH 3 OCHO) and the shock tracer SO. By comparing their spatial morphologies and kinematics, we diagnosed the excitation conditions associated with different accretion flows. Results . We find that the COM emission in L1551 IRS 5 arises from both radiative heating and localized accretion shocks. In the northern source, the widespread low-excitation COM emission is primarily consistent with thermal heating by the recent outburst, while the source also exhibits dual-mode accretion with distinct chemical signatures: COMs along the spiral arm tracing steady equatorial circumbinary disk-to-circumstellar disk accretion and high-excitation COMs with bright SO along the eastern disk surface tracing a vertical envelope-to-disk streamer impact. In the southern source, methanol is confined to the southeastern streamer impact site, whereas SO forms a ring-like structure at the tidal truncation radius. We attribute this difference to differential chemical survival timescales. Conclusions . Our study demonstrates that COM emission in this evolved protostellar binary arises from a complex interplay of thermal heating and shocks driven by multiple accretion and interaction pathways. L1551 IRS 5 thus serves as an ideal laboratory to investigate how shock chemistry and binary-regulated accretion shape the chemical structure of protostellar disks, warranting further high-resolution studies.
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Science Foundation, National Radio Astronomy Observatory, National Research Foundation, Korea Astronomy and Space Science Institute, National Research Foundation of Korea, National Astronomical Observatory of Japan, Ministry of Science and ICT, South Korea, Japan Society for the Promotion of Science, National Institutes of Natural Sciences
OpenAlex ID: W7203749567