Examinando por Autor "Itagaki, K."
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Ítem Forbidden hugs in pandemic times: I. Luminous red nova at 2019zhd, a new merger in M 31(EDP Sciences, 2021-02-01) Pastorello, A.; Fraser, M.; Valerin, G.; Reguitti, A.; Itagaki, K.; Ochner, P.; Williams, S.C.; Jones, D.; Munday, J.; Smartt, S.J.; Smith, K.W.; Srivastav S., S.; Elias-Rosa, N.; Kankare, E.; Karamehmetoglu, E.; Lundqvist, P.; Mazzali, P. A.; Munari, U.; Stritzinger, M. D.; Tomasella, L.; Anderson, J. P.; Chambers, K. C.; Rest, A.We present the follow-up campaign of the luminous red nova (LRN) AT 2019zhd, the third event of this class observed in M 31. The object was followed by several sky surveys for about five months before the outburst, during which it showed a slow luminosity rise. In this phase, the absolute magnitude ranged from Mr =-2.8 ± 0.2 mag to Mr =-5.6 ± 0.1 mag. Then, over a four to five day period, AT 2019zhd experienced a major brightening, reaching a peak of Mr =-9.61 ± 0.08 mag and an optical luminosity of 1.4 × 1039 erg s-1. After a fast decline, the light curve settled onto a short-duration plateau in the red bands. Although less pronounced, this feature is reminiscent of the second red maximum observed in other LRNe. This phase was followed by a rapid linear decline in all bands. At maximum, the spectra show a blue continuum with prominent Balmer emission lines. The post-maximum spectra show a much redder continuum, resembling that of an intermediate-type star. In this phase, Hα becomes very weak, Hβ is no longer detectable, and a forest of narrow absorption metal lines now dominate the spectrum. The latest spectra, obtained during the post-plateau decline, show a very red continuum (Teff ≈ 3000 K) with broad molecular bands of TiO, similar to those of M-type stars. The long-lasting, slow photometric rise observed before the peak resembles that of LRN V1309 Sco, which was interpreted as the signature of the common-envelope ejection. The subsequent outburst is likely due to the gas outflow following a stellar merging event. The inspection of archival HST images taken 22 years before the LRN discovery reveals a faint red source (MF555W = 0.21 ± 0.14 mag, with F555W-F814W = 2.96 ± 0.12 mag) at the position of AT 2019zhd, which is the most likely quiescent precursor. The source is consistent with expectations for a binary system including a predominant M5-type star.Ítem Intermediate-luminosity red transients: Spectrophotometric properties and connection to electron-capture supernova explosions(EDP Sciences, 2021-10-01) Cai, Y.-Z.; Pastorello, A.; Fraser, M.; Botticella, M. T.; Elias-Rosa, N.; Wang, L.-Z.; Kotak, R.; Benetti, S.; Cappellaro, E.; Turatto, M.; Reguitti, A.; Mattila, S.; Smartt, S. J.; Ashall, C.; Benitez, S.; Chen, T.-W.; Harutyunyan, A.; Kankare, E.; Lundqvist, P.; Mazzali, P. A.; Morales-Garoffolo, A.; Ochner, P.; Pignata, G.; Prentice, S. J.; Reynolds, T. M.; Shu, X.-W.; Stritzinger, M. D.; Tartaglia, L.; Terreran, G.; Tomasella, L.; Valenti, S.; Valerin, G.; Wang, G.-J.; Wang, X.-F.; Borsato, L.; Callis, E.; Cannizzaro, G.; Chen, S.; Congiu, E.; Ergon, M.; Galbany, L.; Gal-Yam, A.; Gao, X.; Gromadzki, M.; Holmbo, S.; Huang, F.; Inserra, C.; Itagaki, K.; Kostrzewa-Rutkowska, Z.; Maguire, K.; Margheim, S.; Moran, S.; Onori, F.; Sagués Carracedo, A.; Smith, K. W.; Sollerman, J.; Somero, A.; Wang, B.; Young, D. R.We present the spectroscopic and photometric study of five intermediate-luminosity red transients (ILRTs), namely AT 2010dn, AT 2012jc, AT 2013la, AT 2013lb, and AT 2018aes. They share common observational properties and belong to a family of objects similar to the prototypical ILRT SN 2008S. These events have a rise time that is less than 15 days and absolute peak magnitudes of between-11.5 and-14.5 mag. Their pseudo-bolometric light curves peak in the range 0.5-9.0 × 1040 erg s-1 and their total radiated energies are on the order of (0.3-3) × 1047 erg. After maximum brightness, the light curves show a monotonic decline or a plateau, resembling those of faint supernovae IIL or IIP, respectively. At late phases, the light curves flatten, roughly following the slope of the 56Co decay. If the late-time power source is indeed radioactive decay, these transients produce 56Ni masses on the order of 10-4 to 10-3 M⊙. The spectral energy distribution of our ILRT sample, extending from the optical to the mid-infrared (MIR) domain, reveals a clear IR excess soon after explosion and non-negligible MIR emission at very late phases. The spectra show prominent H lines in emission with a typical velocity of a few hundred km s-1, along with Ca II features. In particular, the [Ca II] λ7291,7324 doublet is visible at all times, which is a characteristic feature for this family of transients. The identified progenitor of SN 2008S, which is luminous in archival Spitzer MIR images, suggests an intermediate-mass precursor star embedded in a dusty cocoon. We propose the explosion of a super-asymptotic giant branch star forming an electron-capture supernova as a plausible explanation for these events.Ítem Observations of the very young Type Ia Supernova 2019np with early-excess emission(Oxford University Press, 2022-08-01) Sai, Hanna; Wang, Xiaofeng; Elias Rosa, Nancy; Yang, Yi; Zhang, Jujia; Lin, Weili; Mo, Jun; Piro, Anthony L; Zeng, Xiangyun; Andrea, Reguitti; Brown, Peter; Burns, Christopher R; Cai, Yongzhi; Fiore, Achille; Hsiao, Eric Y; Isern, Jordi; Itagaki, K.; Li, Wenxiong; Li, Zhitong; Pessi, Priscila J; Phillips, M.M.; Schuldt, Stefan; Shahbandeh, Melissa; Stritzinger, Maximilian D; Tomasella, Lina; Vogl, Christian; Wang, Bo; Wang, Lingzhi; Wu, Chengyuan; Yang, Sheng; Zhang, Jicheng; Zhang, Tianmeng; Zhang, XinghanEarly-time radiative signals from Type Ia supernovae (SNe Ia) can provide important constraints on the explosion mechanism and the progenitor system. We present observations and analysis of SN 2019np, a nearby SN Ia discovered within 1-2 days after the explosion. Follow-up observations were conducted in optical, ultraviolet, and near-infrared bands, covering the phases from ∼-16.7 d to ∼+ 367.8 d relative to its B-band peak luminosity. The photometric and spectral evolutions of SN 2019np resemble the average behaviour of normal SNe Ia. The absolute B-band peak magnitude and the post-peak decline rate are Mmax(B) =-19.52 ± 0.47 mag and Δm15(B) = 1.04 ± 0.04 mag, respectively. No Hydrogen line has been detected in the nebular-phase spectra of SN 2019np. Assuming that the 56Ni powering the light curve is centrally located, we find that the bolometric light curve of SN 2019np shows a flux excess up to 5.0 per cent in the early phase compared to the radiative diffusion model. Such an extra radiation perhaps suggests the presence of an additional energy source beyond the radioactive decay of central nickel. Comparing the observed colour evolution with that predicted by different models, such as interactions of SN ejecta with circumstellar matter (CSM)/companion star, a double-detonation explosion from a sub-Chandrasekhar mass white dwarf (WD) and surface 56Ni mixing, we propose that the nickel mixing is more favoured for SN 2019np. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.