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Understanding the Physics of thermonuclear explosions of a White Dwarf star (WD), so called Type Ia Supernovae (SNe Ia), provide a playground for modern physics, computational methods, and are a key to modern cosmology. We identify new and investigate a variety of observational signatures of underlying physical processes related to the thermonuclear runaway, the flame propagation and the environment. Being intrinsically multi-dimensional phenomena, probing the physics requires multi-dimensional radiation-hydrodynamics and MHD simulations. For this task, we developed and employed methods for photon transport for the X-, gamma- and of low energy and of positrons under non-LTE conditions. We identify signatures in the light curves and spectra, in particular, line profiles and polarization spectra. Consistent treatment of high energy processes is critical. Therefore, our framework and results can be used directly a variety of scenarios for SNe Ia including merging WDs and explosions of sub-Chandrasekhar mass WDs. Current simulations have limitations but, nevertheless, when combined with recent JWST and VLT observations solutions emerge to many of decade old problems on the ignition process, flame physics and thermonuclear explosion.

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. By day 1,041 after explosion, SN Ia-CSM 2018evt had produced an estimated 0.01 solar masses of dust in the cold, dense shell behind the supernova ejecta–circumstellar medium interaction, ranking it as one of the most prolific dust-producing supernovae ever recorded.

We present an analysis of high precision V light curves (LC) for 18 local Type Ia supernovae (SNe Ia) as obtained with the same telescope and setup at the Las Campanas Observatory (LCO). This homogeneity provides an intrinsic accuracy of a few hundredths of a magnitude with respect to individual LCs and between different objects. Based on the single degenerate (SD) scenario, we identify patterns which have been predicted by model calculations as signatures of the progenitor and accretion rate which change the explosion energy and the amount of electron capture, respectively. Using these templates as principle components and the overdetermined system of SNe pairs, we reconstruct the properties of progenitors and progenitor systems. All LCO SNe Ia follow the brightness decline relation except 2001ay. After subtraction of the two components, the remaining scatter is reduced to ≈0.01m−0.03m. SNe Ia seem to originate from progenitors with main-sequence masses MMS > 3 M⊙ with the exception of two subluminous SNe Ia with MMS < 2 M⊙. The component analysis indicates a wide range of accretion rates in the progenitor systems closing the gap to accretion induced collapses (AIC). SN1991t-like objects show differences in decline rate (dm15) but no tracers of our secondary parameters. This may point to a different origin such as the double degenerate or pulsating delayed detonation scenarios. SN2001ay does not follow the decline relation. It can be understood in the framework of C-rich white dwarfs (WDs), and this group may produce an anti-Phillips relation. We suggest that this may be a result of a common envelope phase and mixing during central He burning as in SN1987A.

We report evidence of dust formation in the cold, dense shell behind the ejecta-circumstellar medium (CSM) interaction in the Type Ia (SNIa) SN2018evt three years after the explosion, characterized by a rise in the mid-infrared (MIR) flux accompanied by an accelerated decline in the optical. Such a dust-formation picture is also corroborated by the concurrent evolution of the profiles of the Ha emission lines. Our models suggest enhanced 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. This may indicate an enhanced dust presence at larger distances from the progenitor star. The dust distribution can be modeled in terms of a double-shell which assumes a sudden change of the density profile of the dust or a single-shell model with a flatter radial profile. The inferred mass-loss history of SN2018evt is consistent with a progenitor's mass loss in a binary system containing a C/O white dwarf and a massive asymptotic giant branch star. The grand rebrightening in the MIR after day +310 is attributed to the formation of new dust within the CDS region behind the forward shock. The mass of the newly-formed dust increases rapidly with time and follows a power law with an index of 4. By the time of the last MIR observations at day +1041, a total amount of 1.2+-0.2 x 10^{-2} Msun of dust has been produced, making SN 2018evt one of the most prolific dust factory among SNe with evidence of dust formations.

We present a study of the influence of magnetic field strength and morphology in Type Ia Supernovae and their late-time light curves and spectra. In order to both capture self-consistent magnetic field topologies as well evolve our models to late times, a two stage approach is taken. We study the early deflagration phase (1s) using a variety of magnetic field strengths, and find that the topology of the field is set by the burning, independent of the initial strength. We study late time (~1000 days) light curves and spectra with a variety of magnetic field topologies, and infer magnetic field strengths from observed supernovae. Lower limits are found to be 106G. This is determined by the escape, or lack thereof, of positrons that are tied to the magnetic field. The first stage employs 3d MHD and a local burning approximation, and uses the code Enzo. The second stage employs a hybrid approach, with 3D radiation and positron transport, and spherical hydrodynamics. The second stage uses the code HYDRA. In our models, magnetic field amplification remains small during the early deflagration phase. Late-time spectra bear the imprint of both magnetic field strength and morphology. Implications for alternative explosion scenarios are discussed.

We discuss the current status of our hydrodynamical radiation (HYDRA) code for rapidly expanding, low-density envelopes commonly found in core collapse and thermonuclear supernovae. In supernovae, one of the main issues is the coupling between a radiation field and properties of the matter. Due to the low densities, nonthermal excitation by high-energy photons from radioactive decays and the time dependence of the problem, significant departures from local thermodynamical equilibrium (LTE) are common throughout the envelope even at large optical depths. This effect must be taken into account to simulate the evolution of spectra and light curves which are the basic tools to link between explosion physics and observations.The large velocity fields and the non-LTE problem result in a coupling of spatial, frequency space and the level population. This physical system can be described by a large system of coupled integro-differential equations for which the spatial and energy discretization (and its errors) are coupled. For the numerical solution, we use variable separation, analytic solutions and approximations, and iterative schemes. The need for adaptive mesh refinement (AMR) is demonstrated. As example, we show detailed spectra and light curves for the thermonuclear Supernova SN99by.

Type Ia supernovae (SNe Ia) are important cosmological probes and contributors to galactic nucleosynthesis, particularly of the iron group elements. To improve both their reliability as cosmological probes and to understand galactic chemical evolution, it is vital to understand the binary progenitor system and explosion mechanism. The classification of SNe Ia into Branch groups has led to some understanding of the similarities and differences among the varieties of observed SNe Ia. However, partly due to small sample size, little work has been done on the broad-line or 02bo group. We perform direct spectral analysis on the pre-maximum spectra of the broad-line SN 2019ein and compare and contrast it to the core-normal SN~2011fe. Both SN 2019ein and SN 2011fe were first observed spectroscopically within two days of discovery, allowing us to follow the spectroscopic evolution of both supernovae in detail. We find that the optical depths of the primary features of both the CN and BL supernovae are very similar, except that there is a velocity shift between them. We further examine the SN 2002bo-like subclass and show that for nine objects with pre-maximum spectra in the range -6 -- -2 days with respect to B-maximum all the emission peaks of the Si II {\\lambda}6355 line of BL are blueshifted pre-maximum, making this a simple classification criterion.

We present theoretical semi-analytic models for the interaction of stellar winds with the interstellar medium (ISM) or prior mass loss implemented in our code SPICE (Supernovae Progenitor Interaction Calculator for parameterized Environments, available on request), assuming spherical symmetry and power-law ambient density profiles and using the Pi-theorem. This allows us to test a wide variety of configurations, their functional dependencies, and to find classes of solutions for given observations. Here, we study Type Ia (SN~Ia) surroundings of single and double degenerate systems, and their observational signatures. Winds may originate from the progenitor prior to the white dwarf (WD) stage, the WD, a donor star, or an accretion disk (AD). For M_Ch explosions,the AD wind dominates and produces a low-density void several light years across surrounded by a dense shell. The bubble explains the lack of observed interaction in late time SN light curves for, at least, several years. The shell produces narrow ISM lines Doppler shifted by 10-100 km/s, and equivalent widths of approximately 100 mA and 1 mA in case of ambient environments with constant density and produced by prior mass loss, respectively. For SN 2014J, both mergers and M_Ch mass explosions have been suggested based on radio and narrow lines. As a consistent and most likely solution, we find an AD wind running into an environment produced by the RG wind of the progenitor during the pre-WD stage, and a short delay, 0.013 to 1.4 Myr, between the WD formation and the explosion. Our framework may be applied more generally to stellar winds and star-formation feedback in large scale galactic evolution simulations.

We present multicolor Hubble Space Telescope ( HST) WFPC2 broadband observations of the Type Ic SN 1994I obtained similar to 280 d after maximum light. We measure the brightness of the SN and, relying on the detailed spectroscopic database of SN 1994I, we transform the ground-based photometry obtained at early times to the HST photometric system, deriving light curves for the WFPC2 F439W, F555W, F675W, and F814W passbands that extend from 7 days before to 280 days after maximum. We use the multicolor photometry to build a quasi-bolometric light curve of SN 1994I, and compare it with similarly constructed light curves of other supernovae. In doing so, we propose and test a scaling in energy and time that allows for a more meaningful comparison of the exponential tails of different events. Through comparison with models, we find that the late-time light curve of SN 1994I is consistent with that of spherically symmetric ejecta in homologous expansion, for which the ability to trap the gamma-rays produced by the radioactive decay of Co-56 diminishes roughly as the inverse of time squared. We also find that by the time of the HST photometry, the light curve was significantly energized by the annihilation of positrons.

We present multicolor Hubble Space Telescope (HST) WFPC2 broadband observations of the Type Ic SN 1994I obtained [image]280 d after maximum light. We measure the brightness of the SN and, relying on the detailed spectroscopic database of SN 1994I, we transform the ground-based photometry obtained at early times to the HST photometric system, deriving light curves for the WFPC2 F439W, F555W, F675W, and F814W passbands that extend from 7 days before to 280 days after maximum. We use the multicolor photometry to build a quasi-bolometric light curve of SN 1994I, and compare it with similarly constructed light curves of other supernovae. In doing so, we propose and test a scaling in energy and time that allows for a more meaningful comparison of the exponential tails of different events. Through comparison with models, we find that the late-time light curve of SN 1994I is consistent with that of spherically symmetric ejecta in homologous expansion, for which the ability to trap the -rays produced by the radioactive decay of super(56)Co diminishes roughly as the inverse of time squared. We also find that by the time of the HST photometry, the light curve was significantly energized by the annihilation of positrons.