Photometric and spectroscopic data for two Low Luminosity Type IIP Supernovae (LL SNe IIP) 2020cxd and 2021aai are presented. SN 2020cxd was discovered two days after explosion at an absolute magnitude of Mr = –14.02 ± 0.21 mag, subsequently settling on a plateau which lasts for ∼120 days. Through the luminosity of the late light curve tail, we infer a synthesized 56Ni mass of (1.8±0.5) × 10−3 M⊙. During the early evolutionary phases, optical spectra show a blue continuum (T > 8000 K) with broad Balmer lines displaying a P Cygni profile, while at later phases Ca II, Fe II, Sc II and Ba II lines dominate the spectra. Hydrodynamical modelling of the observables yields R ≃ 575 R⊙ for the progenitor star, with Mej = 7.5 M⊙ and E ≃ 0.097 foe emitted during the explosion. This low–energy event originating from a low–mass progenitor star is compatible with both the explosion of a red supergiant (RSG) star and with an Electron Capture Supernova arising from a super asymptotic giant branch star. SN 2021aai reaches a maximum luminosity of Mr = –16.57 ± 0.23 mag (correcting for AV=1.92 mag), at the end of its remarkably long plateau (∼140 days). The estimated 56Ni mass is (1.4±0.5) × 10−2 M⊙. The expansion velocities are compatible with those of other LL SNe IIP (few 103 km s−1). The physical parameters obtained through hydrodynamical modelling are R ≃ 575 R⊙, Mej = 15.5 M⊙ and E = 0.4 foe. SN 2021aai is therefore interpreted as the explosion of a RSG, with properties that bridge the class of LL SNe IIP with standard SN IIP events.
We report on the first polarimetric study of (3200) Phaethon, the target of JAXA’s DESTINY+ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric albedo. We conducted observations at low phase angles (Sun-target-observer angle, α = 8.8–32.4○) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree Pmin = −1.3 ± 0.1 per cent, a polarimetric slope h = 0.22 ± 0.02 per cent deg−1, and an inversion angle α0 = 19.9 ± 0.3○. The derived geometric albedo is pV = 0.11 (in the range of 0.08–0.13). These polarimetric properties are consistent with anhydrous chondrites, and contradict hydrous chondrites and typical cometary nuclei.
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