Year: 2026
Type: article
Abstract: Luminous red novae (LRNe) are potential signatures of common envelope evolution (CEE), a critical yet poorly understood phase in compact-binary formation. AT2025abao, an LRN in the Andromeda galaxy, originated from an asymptotic giant branch (AGB) progenitor and exhibited a prolonged pre-outburst transient. Lacking direct constraints on the companion, however, the system’s evolutionary fate remains unclear. Here, we unravel the binary nature of AT2025abao by modeling its complete evolution, from precursor to final outcome. We show that the 8 yr infrared precursor arises from a ~ 1 . 4 − 0.3 + 0.2 M ⊙ main-sequence companion inspiralling through the wind of a ∼6.9 M ⊙ AGB star. As CEE commences, the companion plunges into the envelope and launches a shock. Radiation hydrodynamic modeling of this outburst constrains the total ejecta mass to ∼0.92 M ⊙ and energy to ∼1.25 × 10 47 erg, revealing that only ∼0.57 M ⊙ becomes unbound. Subsequent radiative transfer simulations successfully reproduce the evolving spectral energy distribution. Crucially, our models indicate the main-sequence companion and AGB core survive in an eccentric orbit without merging at least 400 days after CEE onset. AT2025abao may therefore be the first observed CEE event caught forming a close compact binary, bridging a long-standing observational gap in compact-binary formation.
Institutions: Tsinghua University, Chinese Academy of Sciences, Osservatorio Astronomico di Padova, National Institute for Astrophysics, University of Chinese Academy of Sciences, University of Science and Technology of China, Guizhou University, Deep Space Exploration Laboratory, National Institutes of Natural Sciences
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Awards: G3002654571, G306243560, G3746203731
OpenAlex ID: W7223415276