Qiliang Fang

We investigate the multiband photometric properties of seven supernovae (SNe) showing double-peaked light-curve evolution and prominent shock-cooling emission, observed by the Wide Field Survey Telescope during its first year of operation. By jointly employing an analytic early shock-cooling model and the Arnett radioactive-diffusion model, we fit the bolometric light curves and infer ejecta masses in the range 1.1–2.6 M _⊙ , consistent with a transitional population between ultrastripped SNe and normal stripped-envelope SNe. The envelope masses are estimated to be M _env = 0.1–0.4 M _⊙ , while the progenitors are constrained to be yellow or blue supergiants with radii of R = 120–300 R _⊙ . Using empirical relations, we estimate progenitor luminosities of L = 10 ^4.6 –10 ^4.9 L _⊙ , corresponding to zero-age main-sequence masses of 8–20 M _⊙ . Theoretical models suggest that such progenitors are more naturally produced through binary evolution channels, as single-star evolutionary pathways are unable to yield ejecta masses this low.

We present optical photometric and spectroscopic observations of the Type IIb supernova (SN) 2017ati. It reached maximum light about 27 d after explosion, and the light curve shows a broad, luminous peak with an absolute r -band magnitude of M _r = −18.48 ± 0.16 mag. At about 50 d after maximum light, SN 2017ati exhibited a decline rate close to that expected from the ⁵⁶ Co → ⁵⁶ Fe radioactive decay, at 0.98 mag per 100 days, as is usually observed in SNe IIb. However, it remains systematically brighter at late times by about 1–2 mag, exceeding the usual upper luminosity range of this class. As a result, modelling the light curve of SN 2017ati with a standard ⁵⁶ Ni decay scenario requires a large nickel mass of up to ∼0.37 M _⊙ and still fails to reproduce the early-time light curve adequately. In contrast, incorporating additional energy input from a magnetar yields a significantly improved fit to the light curve of SN 2017ati, which would reduce the nickel mass to ∼0.21 M _⊙ , which is still close to the upper end of the range typically inferred for SNe IIb. Comparing the fitted results of SN 2017ati with the known sample of SNe IIb indicates that its luminosity evolution is best explained by a combination of neutron star spin-down energy and radioactive nickel deposition. From late-time nebular spectra of SN 2017ati, the luminosity of the [O I ] λλ 6300, 6364 doublet implies an oxygen mass of ∼1.82 − 3.34 M _⊙ , and the combination of a [Ca II ]/[O I ] flux ratio of ∼0.5 with nebular spectral model comparisons favours a progenitor zero-age main-sequence mass of ≥17 M _⊙ .

We present a photometric and spectroscopic analyses of the Type Ibn supernova (SN) 2024acyl. It rises to an absolute magnitude peak of M _o = −17.58 ± 0.15 mag in 10.6 days, and displays a rapid linear post-peak light-curve decline in all bands (e.g. γ _0 − 60 ( V ) = 0.097 ± 0.002 mag day ⁻¹ ), similar to most SNe Ibn. The optical pseudobolometric light curve peaks at (3.5 ± 0.8)×10 ⁴² erg s ⁻¹ , with a total radiated energy of (5.0 ± 0.4)×10 ⁴⁸ erg. The spectra are dominated by a blue continuum at early stages, with narrow P-Cygni He I lines and flash-ionisation emission lines of C III , N III , and He II . The P-Cygni He I features gradually evolve and become emission-dominated in late-time spectra. The H α line is detected throughout the entire spectral evolution, which indicates that the circumstellar material (CSM) is helium-rich with some residual amount of hydrogen. Our multi-band light-curve modelling yields estimates of the ejecta mass of M _ej = 0.49 ^+0.11 _−0.09 M _⊙ with a kinetic energy of E _k = 0.06 ^+0.01 _−0.01 × 10 ⁵¹ erg, and a ⁵⁶ Ni mass of M _Ni = 0.018 M _⊙ . The inferred CSM properties are characterised by a mass of M _CSM = 0.51 ^+0.05 _−0.04 M _⊙ , an inner radius of R ₀ =17.8 ^+3.6 _−3.0 AU, and a density of ρ _CSM = (8.3 ^+2.7 _−1.2 ) × 10 ⁻¹² g cn ⁻³ . The multi-epoch spectra are well reproduced by the CMFGEN/ he4p0 model, corresponding to a He-ZAMS mass of 4 M _⊙ (H-ZAMS mass 18.11 M _⊙ , pre-SN mass 3.16 M _⊙ ). These findings are consistent with a scenario of an SN powered by ejecta-CSM interaction originating from a low-mass helium star that evolved within an interacting binary system where the CSM with some residual hydrogen may originate from the mass-transfer process. We also discuss an extreme scenario involving the possible merger of a helium white dwarf. In addition, a channel of core-collapse explosion of a late-type Wolf-Rayet (WR) star with hydrogen, or a transitional star between an Of and a WR type (e.g. an Ofpe/WN9 star) with fallback accretion cannot be entirely ruled out.

We present optical photometric and spectroscopic observations of the rapidly declining Type IIL supernova (SN) 2016iog. SN 2016iog reached its peak ∼14 days after explosion, with an absolute magnitude in the V band of −18.64 ± 0.15 mag, followed by a steep decline of 8.85 ± 0.15 mag (100 d) ⁻¹ post-peak. Such a high decline rate makes SN 2016iog one of the fastest-declining Type IIL SNe observed to date. The rapid rise in the light curve, combined with the nearly featureless continuum observed in the spectrum at +9.3 days, suggests the presence of interaction. In the recombination phase, we observed broad H α lines that persist at all epochs. In addition, the prominent double-peaked H α feature observed in the late-time spectrum (+190.8 days) is likely attributable either to significant dust formation within a cool dense shell or to asymmetric circumstellar material. These features suggest the presence of a sustained interaction around SN 2016iog. We propose that the observed characteristics of SN 2016iog can be qualitatively explained by assuming a low-mass H-rich envelope surrounding a red supergiant progenitor star with low-density circumstellar material.

We present a comprehensive analysis of 32 type II supernovae (SNe II) with plateau phase photometry and late phase (nebular) spectroscopy available, aiming to bridge the gap between the surface and core of their red supergiant (RSG) progenitors. Using MESA+STELLA, we compute an extensive grid of SN II light-curve models originating from RSG with effective temperatures T _eff around 3650 K and hydrogen-rich envelopes artificially stripped to varying degrees. These models are then used to derive the hydrogen-rich envelope masses M _Henv for SNe II from their plateau phase light curves. Nebular spectroscopy further constrains the progenitor RSG’s luminosity log L _prog and is employed to remove the degeneracies in light-curve modeling. The comparison between log L _prog–M _Henv reveals that M _Henv spans a broad range at the same log L _prog, and almost all SNe II have lower M _Henv than the prediction of the default stellar wind models. We explore alternative wind prescriptions, binary evolution models, and the possibility of more compact RSG progenitors. Although binary interaction offers a compelling explanation for the nonmonotonicity and large scatter in the log L _prog–M _Henv relation, the high occurrence rate of partially stripped RSGs cannot be accounted for by stable binary mass transfer alone without fine-tuned orbital parameters. This highlights that, despite being the most commonly observed class of core-collapse SNe, SNe II likely originate from a variety of mass-loss histories and evolutionary pathways that are more diverse and complex than typically assumed in standard stellar evolution models.

SN 2023ixf is one of the most well-observed core-collapse supernovae in recent decades, yet there is inconsistency in the inferred zero-age main-sequence (ZAMS) mass M _ZAMS of its progenitor. Direct observations of the pre-supernova (SN) red supergiant (RSG) estimate M _ZAMS spanning widely from 11 to 18 M _⊙. Additional constraints, including the host environment and the pulsation of its progenitor RSG, suggest a massive progenitor with M _ZAMS > 17 M _⊙. However, the analysis of the SN properties, from light-curve modeling to late-phase spectroscopy, favors a relatively low-mass scenario (M _ZAMS < 15 M _⊙). In this work, we conduct a systematic analysis of SN 2023ixf, from the RSG progenitor, plateau phase light curve to late-phase spectroscopy. Using MESA+STELLA to simulate the RSG progenitor and their explosions, we find that a range of the RSG models having M _ZAMS that vary from 12 to 17.5 M _⊙ can reproduce its multiband light curves if the hydrogen-rich envelope mass and the explosion energy are allowed to vary. Using late-phase spectroscopy as an independent measurement, the oxygen line [O i] indicates an intermediate-massive progenitor (M _ZAMS ∼ 16.0 M _⊙). By incorporating the velocity structure derived from the light-curve modeling into an axisymmetric model, we generated [O i] line profiles that are consistent with the [O i] line observed in late-phase spectroscopy of SN 2023ixf. Bringing these analyses together, we conclude that SN 2023ixf is the aspherical explosion of an intermediate-massive star (M _ZAMS = 15–16 M _⊙), with the hydrogen envelope being stripped to 4–5 M _⊙ prior to its explosion.

We present a systematic study of Type II supernovae (SNe II) originating from progenitors with effective temperatures (T _eff) and luminosities closely resembling red supergiants (RSGs) observed in pre-supernova (SN) images and in the Galaxy. Using Modules for Experiments in Stellar Astrophysics, we compute a large grid of massive stars with T _eff ranging from 3200 to 3800 K at their RSG phases, with hydrogen envelopes artificially stripped to varying extents (3–10 M _⊙). The light curves of SNe IIP resulting from the explosions of these Galactic-RSG–like progenitors are modeled using STELLA. Our survey of the light curves reveals that partial stripping of the hydrogen envelope creates diversity in the magnitude and duration of SNe IIP light curves, without affecting the position of the RSG progenitor on the Hertzsprung–Russell diagram. For these Galactic-RSG-like progenitor models, we establish an indicator based on the light-curve properties to estimate the hydrogen envelope mass. Additionally, we discuss the effects of material mixing and ⁵⁶Ni heating. Applying our model grid to a large sample of approximately 100 observed SNe IIP reveals a considerably broader range of hydrogen-rich envelope masses than predicted by standard stellar wind models. This finding suggests that if SNe IIP are explosions of Galactic-like RSGs to explain the diversity in the observed light curves, a significant fraction of them must have experienced substantial mass loss beyond the standard mass-loss prescription prior to their explosions. This finding highlights the uncertainties involved in massive star evolution and the pre-SN mass-loss mechanism.