Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Z09: Stars, White Dwarfs, & Thermonuclear SupernovaeLive
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Sponsoring Units: DAP Chair: Hyun Lim, Los Alamos National Laboratory |
Tuesday, April 20, 2021 3:45PM - 3:57PM Live |
Z09.00001: Conformally Flat Polytropes for Anisotropic Fluid in f(R) Gravity Zoha Tariq, Muhammnad Zaeem-Ul-Haq Bhatti This paper provides a detailed analysis of conformally flat spherically symmetric fluid distributions governed by a polytropic equation of state utilizing the metric f (R) gravity, R being the Ricci scalar. The Lane-Emden equation is formulated using Bianchi identity and couple of polytropic equation of states. We discussed two families of relativistic polytropes and the constraints are evaluated for their necessary physical applications. The physical practicability of polytropes is scrutinized via energy conditions. An explicit relation of the Weyl tensor with material variables is explored. The condition of vanishing Weyl tensor is imposed on the Lane-Emden equation in the background of particular f (R) model in both cases to explore physical constraints on polytropes. [Preview Abstract] |
Tuesday, April 20, 2021 3:57PM - 4:09PM Live |
Z09.00002: Neon Cluster Formation and Phase Separation during White Dwarf Cooling Matt Caplan, Chuck Horowitz, Andrew Cumming Recent observations of Galactic white dwarfs (WDs) with Gaia suggest there is a population of massive crystallizing WDs exhibiting anomalous cooling— the Q branch. While single-particle $^{22}$Ne sedimentation has long been considered a possible heat source, recent work suggests that $^{22}$Ne must separate into clusters, enhancing diffusion, in order for sedimentation to provide heating on the observed timescale. We show definitively that $^{22}$Ne cannot separate to form clusters in C/O WDs using molecular dynamics simulations, and we further present a general C/O/Ne phase diagram showing that strong $^{22}$Ne enrichment is not achievable for $^{22}$Ne abundance $>30$\%. We conclude that the anomalous heating cannot be due to $^{22}$Ne cluster sedimentation and that Q branch WDs may have an unusual composition, possibly rich with heavier elements. [Preview Abstract] |
Tuesday, April 20, 2021 4:09PM - 4:21PM Live |
Z09.00003: Diffusion Coefficients for White Dwarf Astrophysics Ian Freeman, Matt Caplan Recent advances in observation and theory motivate us to revisit the diffusion coefficients of Coulomb plasmas for white dwarf astrophysics. We use molecular dynamics simulations to determine the diffusion coefficients for pure compositions of $0.40 \leq Z/A \leq 0.50$ nuclei with a range of screening factors typical for white dwarf interiors between $2 < \Gamma < 200$. We propose an empirical law which is valid in across coupling regimes, building on of earlier extensions of Chapman-Spitzer. This law is intended for easy implementation in stellar evolution codes and should be accurate to the percent level which should be sufficient to remove any modeling uncertainty due to the diffusion coefficients. [Preview Abstract] |
Tuesday, April 20, 2021 4:21PM - 4:33PM Live |
Z09.00004: Stellar Solutions for the Cosmological Lithium Problem Charles Marrder, Grant Mathews, Luca Boccioli, In-Saeng Suh The cosmological lithium problem is a shortcoming in the successful theory of Big Bang nucleosynthesis (BBN). While BBN accurately predicts the primordial abundance of light elements such as H and He, BBN over-predicts primordial $^7$Li by about a factor of 3. Possible explanations of this deficit include stellar diffusion, convection, and magnetic fields by which $^7$Li could be gradually depleted. Among other things, we are exploring convective overshoot and micro-turbulence in the evolution of metal-poor halo stars as possible means of explaining a uniform depletion by a factor of 3 in primordial $^7$Li abundance. [Preview Abstract] |
Tuesday, April 20, 2021 4:33PM - 4:45PM Live |
Z09.00005: Studying Type Ia Supernovae Progenitor Parameters via Light Curve Analysis Sudeshna Chakraborty We analyze Light Curve data sets from Carnegie Supernova Project I (CSPI) and II to study intrinsic primary parameter variations and effects of secondary parameters as main sequence mass and central density of the progenitor of SNe Ia via monochromatic differential Light Curve analysis. A V band LC template is used to determine stretch in a restricted temporal range. Generic progenitor parameters are determined by solving an overdetermined system, and mapped into physical space using priors of physical parameter ranges. Starting with a small data set of CSPI SNe Ia, methods have been developed to handle large less homogeneous data sets for transients like in CSPII and future LSST to study SN/host correlations. Comparing CSPI and II, we find that overall trend in secondary parameter distributions are similar. At low redshift sample distribution main sequence mass of progenitors peak at 5 to 7 solar masses, so SNe Ia can be expected to be related with star formation and present at high redshift. Central density extends to values lower than possible for Hydrogen accretors, which indicates He/C accretion from He-stars and tidally disrupted WD companions. Our method can be used to find outliers apart from normal SNe Ia by just using LC, which is useful where spectra are unavailable. [Preview Abstract] |
Tuesday, April 20, 2021 4:45PM - 4:57PM Live |
Z09.00006: Hard X-ray emitting symbiotics: candidates for type Ia supernova progenitors Ashkbiz Danehkar Hard X-ray emitting symbiotics are a subclass of symbiotic binary stars, consisting of an accreting white dwarf (WD) and a red-giant star, which show hard X-ray emission in addition to common soft X-ray. It was thought that their hard X-ray emission is associated with massive WD, so they could be progenitors of type Ia supernovae (SN). In our recent study (MNRAS.500:4801-4817,2021), we investigated X-ray features of the hard X-ray emitting symbiotic star RT Cru using Chandra observations. Our study revealed the presence of soft and hard thermal plasma components in this object, which make this object similar to other hard X-ray emitting symbiotics containing two thermal components. The soft thermal component detected in hard X-ray emitting symbiotics could originate from either a jet or a colliding wind. Recent Suzaku and NuStar +Swift observations of RT Cru also yielded a WD mass of at least 1.25 solar mass, so this symbiotic system could explode as a type Ia SN when its compact core reaches the Chandrasekhar limit. Further X-ray studies of other hard X-ray emitting symbiotics will lead to other candidates for type Ia SN progenitors, which also have some implications for gravitational wave research. [Preview Abstract] |
Tuesday, April 20, 2021 4:57PM - 5:09PM Live |
Z09.00007: SN Ia DDT Explosions Powered by the Zel'dovich Reactivity Gradient Mechanism Ezra Brooker, Tomasz Plewa, Daniel Fenn The deflagration-to-detonation transition (DDT) mechanism remains one of the major unsolved problems of combustion physics. Astrophysicists have suspected for almost 40 years that it is also directly responsible for a subclass of white dwarf (WD) explosions powering Type Ia supernovae (SN Ia). Much of the research on DDT in SN Ia has focused on the interactions of deflagration fronts with turbulence generated by the flame itself. Other work has focused on turbulence in the WD existing prior to ignition and the influence that turbulent properties, such as the compressibility and turbulent intensity, have on the detonability of the plasma. In our work, we construct and analyze weakly compressible turbulence combustion models for carbon/oxygen plasma at a density expected for DDT to occur. We observe formation of carbon deflagrations and transient carbon detonations at early times. As turbulence becomes increasingly inhomogeneous, sustained carbon detonations are initiated by the Zel'dovich reactivity gradient mechanism. The fuel is suitably preconditioned by the action of compressive turbulent modes with wavelength comparable to the size of resolved turbulent eddies. Oxygen detonations are initiated either by aid of reactivity gradients or by collisions of carbon detonations. [Preview Abstract] |
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