Reguitti, A.Pastorello, A.Pignata, G.Fraser, M.Stritzinger, M.D.Brennan, S.J.Cai, Y.-Z.Elias-Rosa, N.Fugazza, D.Gutierrez, C.P.Kankare, E.Kotak, R.Lundqvist, P.Mazzali, P.A.Moran, S.Salmaso, I.Tomasella, L.Valerin, G.Kuncarayakti, H.2024-04-252024-04-252022-06-01Astronomy and Astrophysics, Volume 662, 1 June 2022, Article number L100004-6361https://repositorio.unab.cl/handle/ria/56416Indexación: Scopus.We present photometric and spectroscopic data of the unusual interacting supernova (SN) 2021foa. It rose to an absolute magnitude peak of Mr= 18 mag in 20 days. The initial light curve decline shows some luminosity fluctuations before a long-lasting flattening. A faint source (Mr∼ 14 mag) was detected in the weeks preceding the main event, showing a slowly rising luminosity trend. The r-band absolute light curve is very similar to those of SN 2009ip-like events, with a faint and shorter duration brightening ('Event A') followed by a much brighter peak ('Event B'). The early spectra of SN 2021foa show a blue continuum with narrow (∼400 km s1) H emission lines that, two weeks later, reveal a complex profile, with a narrow P Cygni on top of an intermediate-width (∼2700 km s1) component. At +12 days, metal lines in emission appear and Hea lines become very strong, with Hea λ5876 reaching half of the Hα luminosity, much higher than in previous SN 2009ip-like objects. We propose that SN 2021foa is a transitional event between the H-rich SN 2009ip-like SNe and the He-rich Type Ibn SNe. © A. Reguitti et al. 2022.enSupernovae: generalSupernovae: individual: SN 2021foaLuminanceLight curvesLong lastingMain eventPhotometric dataShort durationsSpectroscopic dataSupernovae: individual: sn 1987aTransitional eventsArtículoCC BY 4.0 DEED Attribution 4.0 International10.1051/0004-6361/202243340