scholarly journals PORTAL: Three-dimensional polarized (sub)millimeter line radiative transfer

2020 ◽  
Vol 636 ◽  
pp. A14 ◽  
Author(s):  
Boy Lankhaar ◽  
Wouter Vlemmings
Keyword(s):  
Magnetic Field ◽  
Radiative Transfer ◽  
Three Dimensional ◽  
Line Emission ◽  
Local Anisotropy ◽  
Alignment Mechanism ◽  
Dimensional Simulation ◽  
Regular Line ◽  
Atomic States ◽  
Radiative Transfer Modeling

Context. Magnetic fields are important to the dynamics of many astrophysical processes and can typically be studied through polarization observations. Polarimetric interferometry capabilities of modern (sub)millimeter telescope facilities have made it possible to obtain detailed velocity resolved maps of molecular line polarization. To properly analyze these for the information they carry regarding the magnetic field, the development of adaptive three-dimensional polarized line radiative transfer models is necessary. Aims. We aim to develop an easy-to-use program to simulate the polarization maps of molecular and atomic (sub)millimeter lines in magnetized astrophysical regions, such as protostellar disks, circumstellar envelopes, or molecular clouds. Methods. By considering the local anisotropy of the radiation field as the only alignment mechanism, we can model the alignment of molecular or atomic species inside a regular line radiative transfer simulation by only making use of the converged output of this simulation. Calculations of the aligned molecular or atomic states can subsequently be used to ray trace the polarized maps of the three-dimensional simulation. Results. We present a three-dimensional radiative transfer code, POlarized Radiative Transfer Adapted to Lines (PORTAL), that can simulate the emergence of polarization in line emission through a magnetic field of arbitrary morphology. Our model can be used in stand-alone mode, assuming LTE excitation, but it is best used when processing the output of regular three-dimensional (nonpolarized) line radiative transfer modeling codes. We present the spectral polarization map of test cases of a collapsing sphere and protoplanetary disk for multiple three-dimensional magnetic field morphologies.

scholarly journals Radiative-transfer modeling of nebular-phase type II supernovae

2020 ◽  
Vol 642 ◽  
pp. A33
Author(s):  
Luc Dessart ◽  
D. John Hillier
Keyword(s):  
Radiative Transfer ◽  
Massive Star ◽  
Line Emission ◽  
Doppler Width ◽  
Large Set ◽  
Type Ii ◽  
Non Local ◽  
Radiative Transfer Modeling ◽  
Chemical Mixing ◽  
Phase Spectra

Nebular phase spectra of core-collapse supernovae (SNe) provide critical and unique information on the progenitor massive star and its explosion. We present a set of one-dimensional steady-state non-local thermodynamic equilibrium radiative transfer calculations of type II SNe at 300 d after explosion. Guided by the results obtained from a large set of stellar evolution simulations, we craft ejecta models for type II SNe from the explosion of a 12, 15, 20, and 25 M⊙ star. The ejecta density structure and kinetic energy, the 56Ni mass, and the level of chemical mixing are parametrized. Our model spectra are sensitive to the adopted line Doppler width, a phenomenon we associate with the overlap of Fe II and O I lines with Ly α and Ly β. Our spectra show a strong sensitivity to 56Ni mixing since it determines where decay power is absorbed. Even at 300 d after explosion, the H-rich layers reprocess the radiation from the inner metal rich layers. In a given progenitor model, variations in 56Ni mass and distribution impact the ejecta ionization, which can modulate the strength of all lines. Such ionization shifts can quench Ca II line emission. In our set of models, the [O I] λλ 6300, 6364 doublet strength is the most robust signature of progenitor mass. However, we emphasize that convective shell merging in the progenitor massive star interior can pollute the O-rich shell with Ca, which would weaken the O I doublet flux in the resulting nebular SN II spectrum. This process may occur in nature, with a greater occurrence in higher mass progenitors, and this may explain in part the preponderance of progenitor masses below 17 M⊙ that are inferred from nebular spectra.

scholarly journals Combining magnetohydrostatic constraints with Stokes profiles inversions

2019 ◽  
Vol 632 ◽  
pp. A111 ◽  
Author(s):  
J. M. Borrero ◽  
A. Pastor Yabar ◽  
M. Rempel ◽  
B. Ruiz Cobo
Keyword(s):  
Magnetic Field ◽  
Radiative Transfer ◽  
Boundary Conditions ◽  
Optical Depth ◽  
Transfer Equation ◽  
Radiative Transfer Equation ◽  
Three Dimensional ◽  
Gas Pressure ◽  
Order Of Magnitude

Context. Inversion codes for the polarized radiative transfer equation, when applied to spectropolarimetric observations (i.e., Stokes vector) in spectral lines, can be used to infer the temperature T, line-of-sight velocity vlos, and magnetic field B as a function of the continuum optical-depth τc. However, they do not directly provide the gas pressure Pg or density ρ. In order to obtain these latter parameters, inversion codes rely instead on the assumption of hydrostatic equilibrium (HE) in addition to the equation of state (EOS). Unfortunately, the assumption of HE is rather unrealistic across magnetic field lines, causing estimations of Pg and ρ to be unreliable. This is because the role of the Lorentz force, among other factors, is neglected. Unreliable gas pressure and density also translate into an inaccurate conversion from optical depth τc to geometrical height z. Aims. We aim at improving the determination of the gas pressure and density via the application of magnetohydrostatic (MHS) equilibrium instead of HE. Methods. We develop a method to solve the momentum equation under MHS equilibrium (i.e., taking the Lorentz force into account) in three dimensions. The method is based on the iterative solution of a Poisson-like equation. Considering the gas pressure Pg and density ρ from three-dimensional magnetohydrodynamic (MHD) simulations of sunspots as a benchmark, we compare the results from the application of HE and MHS equilibrium using boundary conditions with different degrees of realism. Employing boundary conditions that can be applied to actual observations, we find that HE retrieves the gas pressure and density with an error smaller than one order of magnitude (compared to the MHD values) in only about 47% of the grid points in the three-dimensional domain. Moreover, the inferred values are within a factor of two of the MHD values in only about 23% of the domain. This translates into an error of about 160 − 200 km in the determination of the z − τc conversion (i.e., Wilson depression). On the other hand, the application of MHS equilibrium with similar boundary conditions allows determination of Pg and ρ with an error smaller than an order of magnitude in 84% of the domain. The inferred values are within a factor of two in more than 55% of the domain. In this latter case, the z − τc conversion is obtained with an accuracy of 30 − 70 km. Inaccuracies are due in equal part to deviations from MHS equilibrium and to inaccuracies in the boundary conditions. Results. Compared to HE, our new method, based on MHS equilibrium, significantly improves the reliability in the determination of the density, gas pressure, and conversion between geometrical height z and continuum optical depth τc. This method could be used in conjunction with the inversion of the radiative transfer equation for polarized light in order to determine the thermodynamic, kinematic, and magnetic parameters of the solar atmosphere.

scholarly journals Radiative-transfer modeling of supernovae in the nebular-phase

2020 ◽  
Vol 643 ◽  
pp. L13
Author(s):  
L. Dessart ◽  
D. John Hillier
Keyword(s):  
Radiative Transfer ◽  
Line Emission ◽  
Core Collapse ◽  
Rapid Variation ◽  
Simple Method ◽  
Formidable Challenge ◽  
Fluid Instabilities ◽  
The Origin Of Life ◽  
Radiative Transfer Modeling ◽  
The Universe

Supernova (SN) explosions play a pivotal role in the chemical evolution of the Universe and the origin of life through the metals they release. Nebular phase spectroscopy constrains such metal yields, for example through forbidden line emission associated with O I, Ca II, Fe II, or Fe III. Fluid instabilities during the explosion produce a complex 3D ejecta structure, with considerable macroscopic, but no microscopic, mixing of elements. This structure sets a formidable challenge for detailed nonlocal thermodynamic equilibrium radiative transfer modeling, which is generally limited to 1D in grid-based codes. Here, we present a novel and simple method that allows for macroscopic mixing without any microscopic mixing, thereby capturing the essence of mixing in SN explosions. With this new technique, the macroscopically mixed ejecta are built by shuffling the shells from the unmixed coasting ejecta in mass space, or equivalently in velocity space. The method requires no change to the radiative transfer, but it necessitates high spatial resolution to resolve the rapid variation in composition with depth inherent to this shuffled-shell structure. We show the results for a few radiative-transfer simulations for a Type II SN explosion from a 15 M⊙ progenitor star. Our simulations capture the strong variations in temperature or ionization between the various shells that are rich in H, He, O, or Si. Because of nonlocal energy deposition, γ rays permeate through an extended region of the ejecta, making the details of the shell arrangement unimportant. The greater physical consistency of the method delivers spectral properties at nebular times that are more reliable, in particular in terms of individual emission line strengths, which may serve to constrain the SN yields as well as the progenitor mass for core collapse SNe. The method works for all SN types.

scholarly journals Three-Dimensional Simulation Study of the Interactions of Three Successive CMEs during 4–5 November 1998

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 431
Author(s):  
Yufen Zhou ◽  
Xueshang Feng
Keyword(s):  
Magnetic Field ◽  
Interplanetary Space ◽  
Ambient Medium ◽  
Three Dimensional ◽  
The Third ◽  
Halo Cmes ◽  
Dimensional Simulation ◽  
The Individual ◽  
Basic Features ◽  
The Magnetic Field

In this paper, using a 3D magnetohydrodynamics (MHD) numerical simulation, we investigate the propagation and interaction of the three halo CMEs originating from the same active region during 4–5 November 1998 from the Sun to Earth. Firstly, we try to reproduce the observed basic features near Earth by a simple spherical plasmoid model. We find that the first component of the compound stream at 1 AU is associated to the first CME of the three halo CMEs. During the propagation in the interplanetary space, the third CME overtakes the second one. The two CMEs merge to a new, larger entity with complex internal structure. The magnetic field of the first CME in the three successive CMEs event is compressed by the following complex ejecta. The interaction between the second and third CME results in the deceleration of the third CME and the enhancement of the density, total magnetic field and south component of the magnetic field. In addition we study the contribution of a single CME to the final simulation results, as well as the effect of the CME–CME interactions on the propagation of an isolated CME and multiple CMEs. This is achieved by analysing a single CME with or without the presence of the preceding CMEs. Our results show that the CME moves faster in a less dense, faster medium generated by the interaction of the preceding CME with the ambient medium. In addition, we show that the CME–CME interactions can greatly alter the kinematics and magnetic structures of the individual events.

scholarly journals The ALMA-PILS survey: 3D modeling of the envelope, disks and dust filament of IRAS 16293–2422

2018 ◽  
Vol 612 ◽  
pp. A72 ◽  
Author(s):  
S. K. Jacobsen ◽  
J. K. Jørgensen ◽  
M. H. D. van der Wiel ◽  
H. Calcutt ◽  
T. L. Bourke ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
3D Model ◽  
Line Emission ◽  
Protoplanetary Disk ◽  
Scale Height ◽  
High Angular Resolution ◽  
High Scale ◽  
Disk Model ◽  
Complex Morphology ◽  
Radiative Transfer Modeling

Context. The Class 0 protostellar binary IRAS 16293–2422 is an interesting target for (sub)millimeter observations due to, both, the rich chemistry toward the two main components of the binary and its complex morphology. Its proximity to Earth allows the study of its physical and chemical structure on solar system scales using high angular resolution observations. Such data reveal a complex morphology that cannot be accounted for in traditional, spherical 1D models of the envelope. Aims. The purpose of this paper is to study the environment of the two components of the binary through 3D radiative transfer modeling and to compare with data from the Atacama Large Millimeter/submillimeter Array. Such comparisons can be used to constrain the protoplanetary disk structures, the luminosities of the two components of the binary and the chemistry of simple species. Methods. We present 13CO, C17O and C18O J = 3–2 observations from the ALMA Protostellar Interferometric Line Survey (PILS), together with a qualitative study of the dust and gas density distribution of IRAS 16293–2422. A 3D dust and gas model including disks and a dust filament between the two protostars is constructed which qualitatively reproduces the dust continuum and gas line emission. Results. Radiative transfer modeling in our sampled parameter space suggests that, while the disk around source A could not be constrained, the disk around source B has to be vertically extended. This puffed-up structure can be obtained with both a protoplanetary disk model with an unexpectedly high scale-height and with the density solution from an infalling, rotating collapse. Combined constraints on our 3D model, from observed dust continuum and CO isotopologue emission between the sources, corroborate that source A should be at least six times more luminous than source B. We also demonstrate that the volume of high-temperature regions where complex organic molecules arise is sensitive to whether or not the total luminosity is in a single radiation source or distributed into two sources, affecting the interpretation of earlier chemical modeling efforts of the IRAS 16293–2422 hot corino which used a single-source approximation. Conclusions. Radiative transfer modeling of source A and B, with the density solution of an infalling, rotating collapse or a protoplanetary disk model, can match the constraints for the disk-like emission around source A and B from the observed dust continuum and CO isotopologue gas emission. If a protoplanetary disk model is used around source B, it has to have an unusually high scale-height in order to reach the dust continuum peak emission value, while fulfilling the other observational constraints. Our 3D model requires source A to be much more luminous than source B; LA ~ 18 L⊙ and LB ~ 3 L⊙.

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