Letter to the Editor

FAUST

XXX. Dust enhancement in the young binary L1551 IRS 5

¹ Univ. Grenoble Alpes, CNRS, IPAG 38000 Grenoble, France
² INAF, Osservatorio Astrofisico di Arcetri Largo E. Fermi 5 I-50125 Firenze, Italy
³ Excellence Cluster ORIGINS Boltzmannstraße 2 D-85748 Garching bei München, Germany
⁴ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, A.P. 3-72 (Xangari) 8701 Morelia, Mexico
⁵ Max-Planck-Institut für extraterrestrische Physik (MPE) Gießenbachstr. 1 D-85741 Garching, Germany
⁶ National Radio Astronomy Observatory PO Box O Socorro NM 87801, USA
⁷ RIKEN Cluster for Pioneering Research, 2-1, Hirosawa, Wako-shi Saitama 351-0198, Japan
⁸ ESO Karl Schwarzchild Srt. 2 85478 Garching bei München, Germany
⁹ NRC Herzberg Astronomy and Astrophysics 5071 West Saanich Road Victoria BC V9E 2E7, Canada
¹⁰ Department of Physics and Astronomy, University of Victoria Victoria BC V8P 5C2, Canada
¹¹ Center for Frontier Science, Chiba University, 1-33 Yayoi-cho Inage-ku Chiba 263-8522, Japan
¹² Centro de Astrobiología (CSIC/INTA), Ctra. de Torrejón a Ajalvir km 4 28806 Torrejón de Ardoz, Spain
¹³ SOKENDAI, Shonan Village, Hayama Kanagawa 240-0193, Japan

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 8 February 2025
Accepted: 10 December 2025

Abstract

Young binary stars with discs provide unique laboratories for studying the earliest stages of planet formation in star-forming environments. The detection of substructure in discs around Class I protostars challenges current models of disc evolution, and suggests that planets may form earlier than previously expected (< 1 Myr). In the context of the FAUST Large Program, we present observations of the circumbinary disc (CBD) around the young binary system L1551 IRS 5. The CBD exhibits two prominent over-densities in the continuum emission at the edge of the cavity, with the northern over-density being about 20% brighter than the southern one. By analysing the disc morphology and kinematics of L1551 IRS 5, we delineate dynamical constraints on the binary’s orbital parameters. Additionally, we present 3D hydrodynamical models of the CBD to predict both the dust and the gas surface densities. Then, we compare the resulting synthetic observations with ALMA observations of the continuum emission at 1.3 mm and the C¹⁸O line emission. Our analysis suggests that the density enhancements observed with ALMA in L1551 IRS 5 can be caused by interactions between the binary stars and the CBD, leading to dust concentration within the disc. We conclude that the observed over-density corresponds to a location where solids could potentially grow in size under favourable conditions.