SN 2024abfo: A partially stripped type II supernova from a yellow supergiant

¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate, (LC), Italy
² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
³ Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
⁴ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
⁵ Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
⁶ Graduate Institute of Astronomy, National Central University, 300 Jhongda Road, 32001 Jhongli, Taiwan
⁷ School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
⁸ Astrophysics Research Institute, Liverpool John Moores University, ic2, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁹ CENTRA, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
¹⁰ INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80121 Naples, Italy
¹¹ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago, Chile
¹² Millennium Institute of Astrophysics MAS, Nuncio Monseñor Sótero Sanz 100, Off. 104, Providencia, Santiago, Chile
¹³ Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
¹⁴ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
¹⁵ Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC, 08860 Castelldefels, (Barcelona), Spain
¹⁶ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, E-08193 Barcelona, Spain
¹⁷ Department of Physics and Astronomy, University of Turku, Vesilinnantie 5 FI-20500, Finland
¹⁸ Cardiff Hub for Astrophysics Research and Technology, School of Physics & Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
¹⁹ Finnish Centre for Astronomy with ESO, (FINCA), University of Turku, 20014 Turku, Finland
²⁰ School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
²¹ Instituto de Ciencias Exactas y Naturales (ICEN), Universidad Arturo Prat, Iquique, Tarapacá, Chile
²² The Oskar Klein Centre, Department of Astronomy, Stockholm University, Albanova University Center, SE 106 91 Stockholm, Sweden
²³ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, I-35122 Padova, Italy

^⋆ Corresponding author: andrea.reguitti@inaf.it

Received: 5 March 2025
Accepted: 24 April 2025

Abstract

We present photometric and spectroscopic data of the type IIb supernova (SN) 2024abfo in NGC 1493 (at 11 Mpc). The steroid Terrestrial-impact Last Alert System (ATLAS) survey discovered the object just a few hours after the explosion and observed a fast rise on the first day. Signs of the sharp shock breakout peak and the subsequent cooling phase are observed in the ultraviolet and the bluest optical bands in the first couple of days, while no peak is visible in the reddest filters. Subsequently, in analogy with normal SNe IIb, the light curve of SN 2024abfo rises again in all bands to the broad peak, with the maximum light reached around 1 month after the explosion. Its absolute magnitude at peak is M_r = −16.5 ± 0.1 mag, making it a faint SN IIb. The early spectra are dominated by Balmer lines with broad P Cygni profiles, indicating ejecta velocity of 22 500 km s⁻¹. One month after the explosion, the spectra display a transition towards being He-dominated, though the H lines do not completely disappear, supporting the classification of SN 2024abfo as a relatively H-rich SN IIb. We identify the progenitor of SN 2024abfo in archival images of the Hubble Space Telescope, the Dark Energy Survey, and the XMM-Newton space telescope, in multiple optical filters. From its spectral energy distribution, the progenitor is consistent with being a yellow supergiant, having an initial mass of 15 M_⊙. This detection supports an emerging trend of SN IIb progenitors being more luminous and hotter than SN II ones, and being primaries of massive binaries. Within the SN IIb class, fainter events such as SN 2024abfo tend to have cooler and more expanded progenitors than luminous SNe IIb.