Examinando por Autor "Mehner, Andrea"

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    Exploring the final stages of massive stars through type iin supernova precursors and LBV variability
    (Universidad Andrés Bello, 2023) Reguitti, Andrea; Pignata, Giuliano; Pastorello, Andrea; Mehner, Andrea; Moriya, Takashi; Facultad de Ciencias Exactas
    Current panoramic astronomical surveys are discovering events that challenge the existing stellar evolutionary models. Among them, Type IIn supernovae (SNe) are a class of transients that show evidence of interaction between the SN ejecta and pre-existing H-rich circumstellar medium. Massive stars are known to lose large amount of mass, and a prolonged phase of mass loss is needed to explain the observables of interacting transients. In an increasing number of cases, bright non-terminal events, dubbed SN impostors, are observed a few years before the explosion of some SNe IIn. Luminous Blue Variable (LBV) are massive, evolved H-rich stars that lose mass through eruptive episodes of variability known as LBV giant eruptions, which may explain the SN impostors phenomena. Therefore, LBVs are often proposed to be the progenitors of SNe IIn. However, other evidences point to multiple explosion channels for SNe IIn. Hence it is debated whether LBVs are indeed good candidates as their progenitors. In this thesis, we want to test this hypothesis via two approaches: by studying the variability of known LBVs and the properties of pre-explosion variability observed prior to SNe IIn. To do this, we analyse a sample of 20 LBVs in nearby galaxies by reconstructing their light curves over a very long (>100 years) time. Then, we search in the archives of major astronomical observatories and surveys for images of the fields of 27 close-by (within 60 Mpc) SNe IIn taken years before the explosion, with the goal of detecting progenitor’s precursor variability. We find pre-SN variability for 7 out of the 27 SNe IIn. We study the properties of the SN precursors, estimate their frequency (which we find to be in line with previous estimations) and compare them to the variability of LBVs to verify if they are similar. While we note that the pre-SN events are generally brighter and shorter than the eruptions from LBVs, it is possible that we are only detecting the brightest peaks of the progenitor variability. Instead, they are more similar to the short but luminous LBV outbursts. We cannot confirm that LBVs are indeed the progenitors of SNe IIn, although there are some similarities between SN impostors and LBV eruptions, for instance their red colours. Within the context of massive stars which experienced former activity before the final explosion, we study the interacting transient SN 2021foa, a Type IIn/Ibn SN which matches the criteria with which we constructed the sample of 27 SNe, and indeed we observe a luminous outburst before the explosion. Its light curve and spectra are similar to those of SN 2009ip-like events, though with stronger He I lines. Based on the velocity of the wind and the strength of the He I lines, we suggest an LBV star transitioning towards a Wolf-Rayet as the progenitor, providing a clue in support of the LBV-SNe IIn connection. The structure of the thesis is as follows: in Chapter 1, we introduce the concept and the classification scheme of SNe, including interacting SNe, the Luminous Blue Variables, the SN precursor and impostor events. The datasets and data reduction techniques are described in Chapter 2. Chapter 3 is dedicated to the study of the photometric variability of LBV stars, while Chapter 4 is focused on the search and characterisation of precursor events prior to the explosion of SNe IIn. In Chapter 5, we report our research on the interacting transient SN 2021foa. Finally, we present our discussion and conclusive remarks in Chapter 6.