We explore the observational characteristics of jet-driven supernovae (SNe) by simulating bipolar-jet-driven explosions in a red supergiant (RSG) progenitor. We present results of four models in ...which we hold the injected kinetic energy at a constant 1051 erg across all jet models but vary the specific characteristics of the jets to explore the influence of the nature of jets on the structure of the SN ejecta. We evolve the explosions past shock-breakout and into quasi-homologous expansion of the SN envelope into a RSG wind. The simulations have sufficient numerical resolution to study the stability of the flow. Our simulations show the development of fluid instabilities that produce pristine helium clumps in the hydrogen envelope. The oppositely directed, nickel-rich jets give a large-scale asymmetry that may account for the nonspherical excitation and substructure of spectral lines such as Ha and He I 10830 A. Jets with a large fraction of kinetic to thermal energy punch through the progenitor envelope and give rise to explosions that would be observed to be asymmetric from the earliest epochs, inconsistent with spectropolarimetric measurements of Type II SNe. Jets with higher thermal energy fractions result in explosions that are roughly spherical at large radii but are significantly elongated at smaller radii, deep inside the ejecta, in agreement with the polarimetric observations. We present shock-breakout light curves that indicate that strongly aspherical shock breakouts are incompatible with recent Galaxy Evolution Explorer observations of shock breakout from RSG stars. Comparison with observations indicates that jets must deposit their kinetic energy efficiently throughout the ejecta while in the hydrogen envelope. Thermal-energy-dominated jets satisfy this criterion and yield many of the observational characteristics of Type II SNe.
We study the effects of rotation on the dynamics, energetics, and super(56)Ni production of pair instability supernova (PISN) explosions by performing rotating two-dimensional ("2.5D") hydrodynamics ...simulations. We calculate the evolution of eight low-metallicity (Z = 10 super(-3), 10 super(-4) Z sub(middot in circle)) massive (135-245 M sub(middot in circle)) PISN progenitors with initial surface rotational velocities of 50% of the critical Keplerian value using the stellar evolution code MESA. We allow for both the inclusion and the omission of the effects of magnetic fields in the angular momentum transport and in chemical mixing, resulting in slowly rotating and rapidly rotating final carbon-oxygen cores, respectively. Increased rotation for carbon-oxygen cores of the same mass and chemical stratification leads to less energetic PISN explosions that produce smaller amounts of super(56)Ni due to the effect of the angular momentum barrier that develops and slows the dynamical collapse. We find a non-monotonic dependence of super(56)Ni production on rotational velocity in situations when smoother composition gradients form at the outer edge of the rotating cores. In these cases, the PISN energetics are determined by the competition of two factors: the extent of chemical mixing in the outer layers of the core due to the effects of rotation in the progenitor evolution and the development of angular momentum support against collapse. Our 2.5D PISN simulations with rotation are the first presented in the literature. They reveal hydrodynamic instabilities in several regions of the exploding star and increased explosion asymmetries with higher core rotational velocity.
ABSTRACT Most viable models of Type Ia supernovae (SNe Ia) require the thermonuclear explosion of a carbon/oxygen white dwarf that has evolved in a binary system. Rotation could be an important ...aspect of any model for SNe Ia, whether single or double degenerate, with the white dwarf mass at, below, or above the Chandrasekhar limit. Differential rotation is specifically invoked in attempts to account for the apparent excess mass in the super-Chandrasekhar events. Some earlier work has suggested that only uniform rotation is consistent with the expected mechanisms of angular momentum transport in white dwarfs, while others have found pronounced differential rotation. We show that if the baroclinic instability is active in degenerate matter and the effects of magnetic fields are neglected, both nearly uniform rotation and strongly differential rotation are possible. We classify rotation regimes in terms of the Richardson number, Ri. At small values of Ri 0.1, we find both the low-viscosity Zahn regime with a nonmonotonic angular velocity profile and a new differential rotation regime for which the viscosity is high and scales linearly with the shear, . Employment of Kelvin-Helmholtz viscosity alone yields differential rotation. Large values of Ri > 1 produce a regime of nearly uniform rotation for which the baroclinic viscosity is of intermediate value and scales as . We discuss the gap in understanding of the behavior at intermediate values of Ri and how observations may constrain the rotation regimes attained by nature.
The early phases of the Type Iax supernova SN 2011ay Szalai, Tamás; Vinkó, József; Sárneczky, Krisztián ...
Monthly notices of the Royal Astronomical Society,
10/2015, Letnik:
453, Številka:
2
Journal Article
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We present a detailed study of the early phases of the peculiar supernova (SN) 2011ay based on BVRI photometry obtained at Konkoly Observatory, Hungary, and optical spectra taken with the ...Hobby–Eberly Telescope at McDonald Observatory, Texas. The spectral analysis carried out with syn++ and synapps confirms that SN 2011ay belongs to the recently defined class of SNe Iax, which is also supported by the properties of its light and colour curves. The estimated photospheric temperature around maximum light, T
phot ∼ 8000 K, is lower than in most SNe Ia, which results in the appearance of strong Fe ii features in the spectra of SN 2011ay, even during the early phases. We also show that strong blending with metal features (those of Ti ii, Fe ii, Co ii) makes the direct analysis of the broad spectral features very difficult, and this may be true for all SNe Iax. We find two alternative spectrum models that both describe the observed spectra adequately, but their photospheric velocities differ by at least ∼3000 km s−1. The quasi-bolometric light curve of SN 2011ay has been assembled by integrating the ultraviolet–optical spectral energy distributions. Fitting a modified Arnett model to L
bol(t), the moment of explosion and other physical parameters, i.e. the rise time to maximum, the 56Ni mass and the total ejecta mass are estimated as t
rise ∼ 14 ± 1 d, M
Ni ∼ 0.22 ± 0.01 M⊙ and M
ej ∼ 0.8 M⊙, respectively.
Abstract
We explore the possible nature of high-velocity features in Type Ia supernovae by presenting synthetic spectra generated from hydrodynamic models of interaction between the supernova and a ...compact circumstellar shell. We use tardis to compute the spectra and compare model spectra to data from SN 2011fe at 2, 5, and 9 d after the explosion. We apply abundance models to the shells that consist of a hydrogen, helium, or carbon–oxygen substrate with overall solar abundance of metals and depletion or enhancement of calcium abundance. We vary the calcium abundances in the shell and the ejecta to study the effect on the photospheric and high-velocity components of the calcium near-infrared triplet. The substrate leaves no imprint upon the spectra, but helium substrates are discouraged by demanding excessive calcium abundances. We find that we can approximately reproduce the blended high-velocity and photospheric velocity features at 2 and 5 d. The 9 d spectrum shows a distinct high-velocity component of the line. We are unable to reproduce this specific feature with the current models. We also explore helium-shell double detonation models, finding they tend to give no high-velocity features or excessively strong features. A very carefully chosen helium-shell mass might give a reasonable reproduction of the observed calcium features. We discuss the implications of our models for the nature of high-velocity features and their significance to the evolution and explosion of SN Ia.
We present optical and ultraviolet observations of nearby Type Ic supernova (SN Ic) SN 2017ein, as well as a detailed analysis of its progenitor properties from both the early-time observations and ...the prediscovery Hubble Space Telescope (HST) images. The optical light curves started from within 1 day to ∼275 days after explosion, and optical spectra range from ∼2 days to ∼90 days after explosion. Compared to other normal SNe Ic like SN 2007gr and SN 2013ge, SN 2017ein seems to have more prominent C ii absorption and higher expansion velocities in early phases, suggestive of relatively lower ejecta mass. The earliest photometry obtained for SN 2017ein shows indications of shock cooling. The best fit obtained by including a shock-cooling component gives an estimate of the envelope mass as ∼0.02 M and stellar radius as 8 4 R . Examining the pre-explosion images taken with the HST WFPC2, we find that the SN position coincides with a luminous and blue point-like source, with an extinction-corrected absolute magnitude of MV ∼ −8.2 mag and MI ∼ −7.7 mag. Comparisons of the observations to the theoretical models indicate that the counterpart source was either a single W-R star or a binary whose members had high initial masses, or a young compact star cluster. To further distinguish between different scenarios requires revisiting the site of the progenitor with HST after the SN fades away.
ABSTRACT We present multiple-epoch measurements of the size and surface brightness of the light echoes from supernova (SN) 2014J in the nearby starburst galaxy M82. Hubble Space Telescope (HST) ...ACS/WFC images were taken ∼277 and ∼416 days after B-band maximum in the filters F475W, F606W, and F775W. Observations with HST WFC3/UVIS images at epochs ∼216 and ∼365 days are included for a more complete analysis. The images reveal the temporal evolution of at least two major light-echo components. The first one exhibits a filled ring structure with position-angle-dependent intensity. This radially extended, diffuse echo indicates the presence of an inhomogeneous interstellar dust cloud ranging from ∼100 to ∼500 pc in the foreground of the SN. The second echo component appears as an unresolved luminous quarter-circle arc centered on the SN. The wavelength dependence of scattering measured in different dust components suggests that the dust producing the luminous arc favors smaller grain sizes, while that causing the diffuse light echo may have sizes similar to those of the Milky Way dust. Smaller grains can produce an optical depth consistent with that along the supernova-Earth line of sight measured by previous studies around maximum light. Therefore, it is possible that the dust slab from which the luminous arc arises is also responsible for most of the extinction toward SN 2014J. The optical depths determined from the Milky Way-like dust in the scattering matters are lower than the optical depth produced by the dust slab.
Abstract
Herein we analyse late-time (post-plateau; 103 < t < 1229 d) optical spectra of low-redshift (z < 0.016), hydrogen-rich Type IIP supernovae (SNe IIP). Our newly constructed sample contains ...91 nebular spectra of 38 SNe IIP, which is the largest data set of its kind ever analysed in one study, and many of the objects have complementary photometric data. The strongest and most robust result we find is that the luminosities of all spectral features (except those of helium) tend to be higher in objects with steeper late-time V-band decline rates. A steep late-time V-band slope likely arises from less efficient trapping of γ-rays and positrons, which could be caused by multidimensional effects such as clumping of the ejecta or asphericity of the explosion itself. Furthermore, if γ-rays and positrons can escape more easily, then so can photons via the observed emission lines, leading to more luminous spectral features. It is also shown that SNe IIP with larger progenitor stars have ejecta with a more physically extended oxygen layer that is well-mixed with the hydrogen layer. In addition, we find a subset of objects with evidence for asymmetric 56Ni ejection, likely bipolar in shape. We also compare our observations to theoretical late-time spectral models of SNe IIP from two separate groups and find moderate-to-good agreement with both sets of models. Our SNe IIP spectra are consistent with models of 12–15 M⊙ progenitor stars having relatively low metallicity (Z ≤ 0.01).
Betelgeuse: a review Wheeler, J Craig; Chatzopoulos, Emmanouil
Astronomy & geophysics : the journal of the Royal Astronomical Society,
06/2023, Letnik:
64, Številka:
3
Journal Article
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Abstract
Was Betelgeuse once in a binary star system? What causes it to vary over a vast range of timescales? Why did it dim dramatically in 2020? When and how will it explode? J. Craig Wheeler and ...Manos Chatzopoulos present a host of challenges to both observers and theorists.
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