SN 2022ngb: A faint, slowly evolving Type IIb supernova with a low-mass envelope

¹ South-Western Institute for Astronomy Research, Yunnan Key Laboratory of Survey Science, Yunnan University Kunming 650500 Yunnan, China
² Yunnan Key Laboratory of Survey Science, Yunnan University Kunming 650500 Yunnan, PR China
³ INAF – Osservatorio Astronomico di Padova vicolo dell’Osservatorio 5 I-35122 Padova, Italy
⁴ Yunnan Observatories, Chinese Academy of Sciences (CAS) Kunming 650216, PR China
⁵ International Centre of Supernovae, Yunnan Key Laboratory Kunming 650216, PR China
⁶ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n E-08193 Barcelona, Spain
⁷ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46 23807 Merate (LC), Italy
⁸ School of Astronomy and Space Science, University of Chinese Academy of Sciences Beijing 100049, PR China
⁹ National Astronomical Observatories, Chinese Academy of Sciences Beijing 100101, PR China
¹⁰ INAF – Osservatorio Astronomico d’Abruzzo Via Mentore Maggini Snc 64100 Teramo, Italy
¹¹ School of Physics, O’Brien Centre for Science North, University College Dublin Belfield Dublin 4, Ireland
¹² Fabra Observatory, Royal Academy of Sciences and Arts of Barcelona (RACAB) 08001 Barcelona, Spain
¹³ Institute for Space Studies of Catalonia (IEEC), Campus UPC 08860 Castelldefels (Barcelona), Spain
¹⁴ Department of Physics and Astronomy, University of Turku FI-20014 Turku, Finland
¹⁵ Finnish Centre for Astronomy with ESO (FINCA), Quantum, Vesilinnantie 5, University of Turku FI-20014 Turku, Finland
¹⁶ The Oskar Klein Centre, Department of Astronomy, Stockholm University AlbaNova SE-10691 Stockholm, Sweden
¹⁷ Nordic Optical Telescope, Aarhus Universitet, Rambla José Ana Fernández Pérez 7, local 5, E-38711 San Antonio Breña Baja Santa Cruz de Tenerife, Spain
¹⁸ School of Sciences, European University Cyprus, Diogenes Street Engomi 1516 Nicosia, Cyprus
¹⁹ Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park 146 Brownlow Hill Liverpool L3 5RF, UK
²⁰ Max-Planck-Institut für Astrophysik Karl-Schwarzschild Str. 1 D-85741 Garching, Germany
²¹ School of Physics and Astronomy, University of Leicester University Road Leicester LE1 7RH, UK
²² Universitá degli Studi di Padova, Dipartimento di Fisica e Astronomia Vicolo dell’Osservatorio 2 35122 Padova, Italy
²³ School of Electronic Science and Engineering, Chongqing University of Posts and Telecommunications Chongqing 400065, PR China
²⁴ Tuorla Observatory, Department of Physics and Astronomy, University of Turku FI-20014 Turku, Finland
²⁵ Cosmic Dawn Center (DAWN)
²⁶ Niels Bohr Institute, University of Copenhagen Jagtvej 128 2200 København N, Denmark
²⁷ INAF-Osservatorio Astronomico di Capodimonte Salita Moiariello 16 80131 Napoli, Italy
²⁸ Astrophysics sub-Department, Department of Physics, University of Oxford Keble Road Oxford OX1 3RH, UK
²⁹ Department of Physics and Astronomy, Aarhus University Ny Munkegade 120 DK-8000 Aarhus C, Denmark
³⁰ Technical University of Munich, TUM School of Natural Sciences, Physics Department James-Franck-Str. 1 85741 Garching, Germany
³¹ HUN-REN CSFK Konkoly Observatory, MTA Centre of Excellence, Konkoly Thege M. út 15-17 Budapest 1121, Hungary
³² Department of Experimental Physics, Institute of Physics, University of Szeged Dóm tér 9 Szeged 6720, Hungary
³³ ELTE Eötvös Loránd University, Institute of Physics and Astronomy Pázmány Péter sétány 1A Budapest 1117, Hungary
³⁴ Department of Astronomy, University of Texas at Austin, 2515 Speedway Stop C1400 Austin TX 78712-1205, USA
³⁵ School of Physics and Electrical Engineering, Liupanshui Normal University, Liupanshui Guizhou 553004, PR China
³⁶ Department of Mathematics and Physics, School of Biomedical Engineering, Southern Medical University Guangzhou 510515, PR China

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Received: 9 October 2025
Accepted: 9 December 2025

Abstract

Context. Type IIb supernovae (SNe IIb) are stellar explosions whose spectra reveal transitional features between hydrogen-rich (Type II) and helium-rich (Type Ib) SNe. Their progenitors are massive stars that were mostly stripped of their hydrogen envelope, likely through binary interaction and/or strong stellar winds. This makes such stars key tools in studies of the late stages of the evolution of massive stars.

Aims. We present an extensive photometric and spectroscopic follow-up campaign of the Type IIb SN 2022ngb. Through the detailed modeling of this dataset, we aim to constrain the key physical parameters of the explosion, infer the nature of the progenitor star and its environment, and probe the dynamical properties of the ejecta.

Methods. We analyzed photometric and spectroscopic data of SN 2022ngb. By constructing and modeling the bolometric light curve with semi-analytic models, we were able to estimate the primary explosion parameters. The spectroscopic data were compared with those of well-studied SNe IIb and NLTE models to constrain the properties of the progenitor and the structure of the resulting ejecta.

Results. SN 2022ngb is a low-luminosity SN IIb with a peak bolometric luminosity of L_Bol = 7.76^+1.15_−1.00 × 10⁴¹ erg s⁻¹ and a V-band rising time of 24.32 ± 0.50 days. The light curve modeling indicates an ejecta mass of ∼2.9 − 3.2 M_⊙, an explosion energy of ∼1.4 × 10⁵¹ erg, and a low synthesized ⁵⁶Ni mass of ∼0.045 M_⊙. The nebular phase spectra exhibit asymmetric line profiles, pointing to a nonspherical explosion and an anisotropic distribution of radioactive material. Our analysis reveals a relatively compact stripped-envelope progenitor with a pre-SN mass of approximately 4.7 M_⊙ (corresponding to a 15–16 M_⊙ ZAMS star).

Conclusions. Our analysis suggests that SN 2022ngb originated from the explosion of a moderate-mass relatively compact, stripped-envelope star in a binary system. The asymmetries inferred from the nebular phase spectral line features indicate the occurrence of a nonspherical explosion.