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Abstract Dust associated with various stellar sources in galaxies at all cosmic epochs remains a controversial topic, particularly whether supernovae play an important role in dust production. We report evidence of dust formation in the cold, dense shell behind the ejecta–circumstellar medium (CSM) interaction in the Type Ia-CSM supernova (SN) 2018evt three years after the explosion, characterized by a rise in mid-infrared emission accompanied by an accelerated decline in the optical radiation of the SN. Such a dust-formation picture is also corroborated by the concurrent evolution of the profiles of the Hα emission line. Our model suggests enhanced CSM dust concentration at increasing distances from the SN as compared to what can be expected from the density profile of the mass loss from a steady stellar wind. By the time of the last mid-infrared observations at day +1,041, a total amount of 1.2 ± 0.2 × 10⁻² M_⊙of new dust has been formed by SN 2018evt, making SN 2018evt one of the most prolific dust factories among supernovae with evidence of dust formation. The unprecedented witness of the intense production procedure of dust may shed light on the perceptions of dust formation in cosmic history. 

Photometry shown in Figure Extended Data 4 (a) of Wang, Lingzhi, et al. 2024, Nature Astronomy, https://doi.org/10.1038/s41550-024-02197-9.Phase is days since B-band maximum MJD 58352.BVgri-band photometry from 1-m network at Las Cumbres Observatory.SN2018evt_lcogt_lc.datBVgri-band photometry from 2.4-m LiJiang Telescope (LJT) and 60/90-cm XingLong Schmidt Telescope (XLST)SN2018evt_xlt_ljt_lc.datOptical and NIR spectra data shown in Figures Extended Data 2, 3, and Table Extended Data 2 of Wang, Lingzhi, et al. 2024, Nature Astronomy, NIR spectraSN2018evt_181224_spex.txt SN2018evt_190511_spex.txtSN2018evt_190617_spex.txtSN2018evt_200119_spex.txtSN2018evt_20190101_gnirs.txtSN2018evt_20190108_gnirs.txtSN2018evt_20190516_fire.datSN2018evt_20190712_fire.datOptical spectraOptical spectra observed with 2.4-m LiJiang Telescope (LJT)SN2018evt_190104_LJT_G3.datSN2018evt_190131_LJT_G3.datSN2018evt_190328_LJT_G3.datSN2018evt_190520_LJT_G3.datOptical spectra observed with 2.16-m XingLong Telescope (XLT)SN2018evt_20190208_2458551.3570_bao_bfosc.txtSN2018evt_20190220_2458563.3588_bao-bfosc.txtSN2018evt_20190413_2458587.2169_bao-bfosc.txtOptical spectra observed with 3.6-m ESO New Technology Telescope (NTT)SN2018evt_20180812_NTT_Gr13_Free_slit1.0_58346_1_e.asciSN2018evt_20190425_NTT_Gr13_Free_slit1.0_58599_1_e.asciSN2018evt_20190512_NTT_Gr13_Free_slit1.0_58616_1_e.asciSN2018evt_20190608_NTT_Gr13_Free_slit1.0_58643_1_e.asciSN2018evt_20200218_NTT_Gr13_Free_slit1.0_58899_1_e.asciSN2018evt_20200322_NTT_Gr13_Free_slit1.0_58931_1_e.asciOptical spectrum observed with WiFes mounted on 2.3-m telescope at the Siding Spring Observatory (WiFeS)SN2018evt_20190624_ANU_Wifes.datOptical spectrum observed with 2.0-m Faulkes Telescope North (FTN)/FLOYDSSN2018evt_20191224_FTN-floyds-redblu_145742.306.asciiSN2018evt_20200119_FTN-floyds-redblu_133856.906.asciiSN2018evt_20200203_FTN-floyds-redblu_125905.990.ascii 

ABSTRACT A rare class of supernovae (SNe) is characterized by strong interaction between the ejecta and several solar masses of circumstellar matter (CSM) as evidenced by strong Balmer-line emission. Within the first few weeks after the explosion, they may display spectral features similar to overluminous Type Ia SNe, while at later phase their observation properties exhibit remarkable similarities with some extreme case of Type IIn SNe that show strong Balmer lines years after the explosion. We present polarimetric observations of SN 2018evt obtained by the ESO Very Large Telescope from 172 to 219 d after the estimated time of peak luminosity to study the geometry of the CSM. The non-zero continuum polarization decreases over time, suggesting that the mass-loss of the progenitor star is aspherical. The prominent H α emission can be decomposed into a broad, time-evolving component and an intermediate-width, static component. The former shows polarized signals, and it is likely to arise from a cold dense shell (CDS) within the region between the forward and reverse shocks. The latter is significantly unpolarized, and it is likely to arise from shocked, fragmented gas clouds in the H-rich CSM. We infer that SN 2018evt exploded inside a massive and aspherical circumstellar cloud. The symmetry axes of the CSM and the SN appear to be similar. SN 2018evt shows observational properties common to events that display strong interaction between the ejecta and CSM, implying that they share similar circumstellar configurations. Our preliminary estimate also suggests that the circumstellar environment of SN 2018evt has been significantly enriched at a rate of ∼0.1 M⊙ yr−1 over a period of >100 yr. 

Abstract We present high-cadence ultraviolet through near-infrared observations of the Type Ia supernova (SN Ia) 2023bee atD= 32 ± 3 Mpc, finding excess flux in the first days after explosion, particularly in our 10 minutes cadence TESS light curve and Swift UV data. Compared to a few other normal SNe Ia with early excess flux, the excess flux in SN 2023bee is redder in the UV and less luminous. We present optical spectra of SN 2023bee, including two spectra during the period where the flux excess is dominant. At this time, the spectra are similar to those of other SNe Ia but with weaker Siii, Cii,and Caiiabsorption lines, perhaps because the excess flux creates a stronger continuum. We compare the data to several theoretical models on the origin of early excess flux in SNe Ia. Interaction with either the companion star or close-in circumstellar material is expected to produce a faster evolution than observed. Radioactive material in the outer layers of the ejecta, either from double detonation explosion or from a⁵⁶Ni clump near the surface, cannot fully reproduce the evolution either, likely due to the sensitivity of early UV observable to the treatment of the outer part of ejecta in simulation. We conclude that no current model can adequately explain the full set of observations. We find that a relatively large fraction of nearby, bright SNe Ia with high-cadence observations have some amount of excess flux within a few days of explosion. Considering potential asymmetric emission, the physical cause of this excess flux may be ubiquitous in normal SNe Ia. 

The type Ia supernova (SN) 2012fr displayed an unusual combination of its Si II λλ5972, 6355 features. This includes the ratio of their pseudo-equivalent widths, placing it at the border of the shallow silicon (SS) and core normal (CN) spectral subtype in the Branch diagram, while the Si II λ6355 expansion velocities place it as a high-velocity (HV) object in the Wang et al. spectral type that most interestingly evolves slowly, placing it in the low-velocity gradient (LVG) typing of Benetti et al. Only 5% of SNe Ia are HV and located in the SS+CN portion of the Branch diagram, and fewer than 10% of SNe Ia are both HV and LVG. These features point toward SN 2012fr being quite unusual, similar in many ways to the peculiar SN 2000cx. We modeled the spectral evolution of SN 2012fr to see if we could gain some insight into its evolutionary behavior. We use the parameterized radiative transfer code SYNOW to probe the abundance stratification of SN 2012fr at pre-maximum, maximum, and post-maximum light epochs. We also use a grid of W7 models in the radiative transfer code PHOENIX to probe the effect of different density structures on the formation of the Si II λ6355 absorption feature at post-maximum epochs. We find that the unusual features observed in SN 2012fr are likely due to a shell-like density enhancement in the outer ejecta. We comment on possible reasons for atypical Ca II absorption features, and suggest that they are related to the Si II features. This paper includes data gathered with the 6.5 m Magellan Baade Telescope, located at Las Campanas Observatory, Chile. 

Abstract We present high-cadence optical, ultraviolet (UV), and near-infrared data of the nearby ( D ≈ 23 Mpc) Type II supernova (SN) 2021yja. Many Type II SNe show signs of interaction with circumstellar material (CSM) during the first few days after explosion, implying that their red supergiant (RSG) progenitors experience episodic or eruptive mass loss. However, because it is difficult to discover SNe early, the diversity of CSM configurations in RSGs has not been fully mapped. SN 2021yja, first detected within ≈ 5.4 hours of explosion, shows some signatures of CSM interaction (high UV luminosity and radio and x-ray emission) but without the narrow emission lines or early light-curve peak that can accompany CSM. Here we analyze the densely sampled early light curve and spectral series of this nearby SN to infer the properties of its progenitor and CSM. We find that the most likely progenitor was an RSG with an extended envelope, encompassed by low-density CSM. We also present archival Hubble Space Telescope imaging of the host galaxy of SN 2021yja, which allows us to place a stringent upper limit of ≲ 9 M ☉ on the progenitor mass. However, this is in tension with some aspects of the SN evolution, which point to a more massive progenitor. Our analysis highlights the need to consider progenitor structure when making inferences about CSM properties, and that a comprehensive view of CSM tracers should be made to give a fuller view of the last years of RSG evolution.