arXiv subjects

Julio David Melon Fuksman

Publications and source records attributed to Julio David Melon Fuksman.

13 recordsLinked to original sources

arXiv2025

Monte Carlo post-processing for radiation hydro simulations of accreting planets in protoplanetary disks

This paper is part of a series investigating the observational appearance of planets accreting from their nascent protoplanetary disk (PPD). We evaluate the differences between gas temperature distributions determined in our radiation hydrodynamical (RHD) simulations and those recalculated via post-processing with a Monte Carlo (MC) radiative transport (RT) scheme. Our MCRT simulations were performed for global PPD models, each composed of a local 3D high-resolution RHD model embedded in an axisymmetric global disk simulation. We report the level of agreement between the two approaches and point out several caveats that prevent a perfect match between the temperature distributions with our respective methods of choice. Overall, the level of agreement is high, with a typical discrepancy between the RHD and MCRT temperatures of the high-resolution region of only about 10 percent. The largest differences were found close to the disk photosphere, at the transition layer between optically dense and thin regions, as well as in the far-out regions of the PPD, occasionally exceeding values of 40 percent. We identify several reasons for these discrepancies, which are mostly related to general features of typical radiative transfer solvers used in hydrodynamical simulations (angle- and frequency-averaging and ignored scattering) and MCRT methods (ignored internal energy advection and compression and expansion work). This provides a clear pathway to reduce systematic temperature inaccuracies in future works. Based on MCRT simulations, we finally determined the expected error in flux estimates, both for the entire PPD and for planets accreting gas from their ambient disk, independently of the amount of gas piling up in the Hill sphere and the used model resolution.

astro-ph.EP↗

arXiv2024

Can gap-edge illumination excite spirals in protoplanetary disks? Three-temperature radiation hydrodynamics and NIR image modelling

The advent of high-resolution, near-infrared instruments such as VLT/SPHERE and Gemini/GPI has helped uncover a wealth of substructure in planet-forming disks, including large, prominent spiral arms in MWC 758, SAO 206462, and V1247 Ori among others. In the classical theory of disk-planet interaction, these arms are consistent with Lindblad-resonance driving by multi-Jupiter-mass companions. Despite improving detection limits, evidence for such massive bodies in connection with spiral substructure has been inconclusive. In search of an alternative explanation, we use the PLUTO code to run 3D hydrodynamical simulations with two comparatively low planet masses (Saturn-mass, Jupiter-mass) and two thermodynamic prescriptions (three-temperature radiation hydrodynamics, and the more traditional $β$-cooling) in a low-mass disk. In the radiative cases, an $m = 2$ mode, potentially attributable to the interaction of stellar radiation with gap-edge asymmetries, creates an azimuthal pressure gradient, which in turn gives rise to prominent spiral arms in the upper layers of the disk. Monte Carlo radiative transfer (MCRT) post-processing with RADMC3D reveals that in near-infrared scattered light, these gap-edge spirals are significantly more prominent than the traditional Lindblad spirals for planets in the mass range tested. Our results demonstrate that even intermediate-mass protoplanets -- less detectable, but more ubiquitous, than super-Jupiters -- are capable of indirectly inducing large-scale spiral disk features, and underscore the importance of including radiation physics in efforts to reproduce observations.

astro-ph.EP↗

arXiv2024

Three-temperature radiation hydrodynamics with PLUTO: Thermal and kinematic signatures of accreting protoplanets

In circumstellar disks around young stars, the gravitational influence of nascent planets produces telltale patterns in density, temperature, and kinematics. To better understand these signatures, we first performed 3D hydrodynamical simulations of a 0.012 $M_{\odot}$ disk, with a Saturn-mass planet orbiting circularly in-plane at 40 au. We tested four different disk thermodynamic prescriptions (in increasing order of complexity, local isothermality, $β$-cooling, two-temperature radiation hydrodynamics, and three-temperature radiation hydrodynamics), finding that $β$-cooling offers a reasonable approximation for the three-temperature approach when the planet is not massive or luminous enough to substantially alter the background temperature and density structure. Thereafter, using the three-temperature scheme, we relaxed this assumption, simulating a range of different planet masses (Neptune-mass, Saturn-mass, Jupiter-mass) and accretion luminosities (0, $10^{-3} L_{\odot}$) in the same disk. Our investigation revealed that signatures of disk-planet interaction strengthen with increasing planet mass, with circumplanetary flows becoming prominent in the high-planet-mass regime. Accretion luminosity, which adds pressure support around the planet, was found to weaken the midplane Doppler-flip, potentially visible in optically thin tracers like C$^{18}$O, while strengthening the spiral signature, particularly in upper disk layers sensitive to thicker lines, like those of $^{12}$CO.

astro-ph.EP↗

arXiv2023

Vertical shear instability in two-moment radiation-hydrodynamical simulations of irradiated protoplanetary disks I. Angular momentum transport and turbulent heating

We studied the linear and nonlinear evolution of the Vertical Shear Instability (VSI) in axisymmetric models of protoplanetary disks, focusing on the transport of angular momentum, the produced temperature perturbations, and the applicability of local stability conditions. We modeled the gas-dust mixture via high-resolution two-moment (M1) radiation-hydrodynamical simulations including stellar irradiation with frequency-dependent opacities. We found that, given sufficient depletion of small grains (with a dust-to-gas mass ratio of $10\%$ of our nominal value of $10^{-3}$ for $<0.25$ $μ$m grains), the VSI can operate in surface disk layers while being inactive close to the midplane, resulting in a suppression of the VSI body modes. The VSI reduces the initial vertical shear in bands of approximately uniform specific angular momentum, whose formation is likely favored by the enforced axisymmetry. Similarities with Reynolds stresses and angular momentum distributions in 3D simulations suggest that the VSI-induced angular momentum mixing in the radial direction may be predominantly axisymmetric. The stability regions in our models are well explained by local stability criteria, while the employment of global criteria is still justifiable up to a few scale heights above the midplane, at least as long as VSI modes are radially optically thin. Turbulent heating produces only marginal temperature increases of at most $0.1\%$ and $0.01\%$ in the nominal and dust-depleted models, respectively, peaking at a few (approximately three) scale heights above the midplane. We conclude that it is unlikely that the VSI can, in general, lead to any significant temperature increase since that would either require it to efficiently operate in largely optically thick disk regions or to produce larger levels of turbulence than predicted by models of passive irradiated disks.

astro-ph.EP↗

arXiv2023

Vertical shear instability in two-moment radiation-hydrodynamical simulations of irradiated protoplanetary disks II. Secondary instabilities and stability regions

The vertical shear instability (VSI) is a hydrodynamical instability likely to produce turbulence in the dead zones of protoplanetary disks. Various aspects of this instability remain to be understood, including the disk regions where it can operate and the physical phenomena leading to its saturation. In this work, we studied the growth and evolution of secondary instabilities parasitic to the VSI, examining their relation with its saturation in axisymmetric radiation-hydrodynamical simulations of protoplanetary disks. We also constructed stability maps for our disk models, considering temperature stratifications enforced by stellar irradiation and radiative cooling and incorporating the effects of dust-gas collisions and molecular line emission. We found that the flow pattern produced by the interplay of the axisymmetric VSI modes and the baroclinic torque forms bands of nearly uniform specific angular momentum. In the high-shear regions in between these bands, the Kelvin-Helmholtz instability (KHI) is triggered. The significant transfer of kinetic energy to small-scale eddies produced by the KHI and possibly even the baroclinic acceleration of eddies limit the maximum energy of the VSI modes, likely leading to the saturation of the VSI. A third instability mechanism, consisting of an amplification of eddies by baroclinic torques, forms meridional vortices with Mach numbers up to $\sim 0.4$. Our stability analysis suggests that protoplanetary disks can be VSI-unstable in surface layers up to tens of au for reasonably high gas emissivities, even in regions where the midplane is stable. This picture is consistent with current observations of disks showing thin midplane millimeter-sized dust layers while appearing vertically extended in optical and near-infrared wavelengths.

astro-ph.EP↗

arXiv2023

Three-temperature radiation hydrodynamics with PLUTO: Tests and applications to protoplanetary disks

In circumstellar disks around T Tauri stars, visible and near-infrared stellar irradiation is intercepted by dust at the disk's optical surface and reprocessed into thermal infrared; this subsequently undergoes radiative diffusion through the optically thick bulk of the disk. The gas component -- overwhelmingly dominant by mass, but contributing little to the opacity -- is heated primarily by gas-grain collisions. In hydrodynamical simulations, however, typical models for this heating process (local isothermality, $β$-cooling, two-temperature radiation hydrodynamics) incorporate simplifying assumptions that limit their ranges of validity. To build on these methods, we develop a ``three-temperature" numerical scheme, which self-consistently models energy exchange between gas, dust, and radiation, as a part of the PLUTO radiation-hydrodynamics code. With a range of test problems in 0D, 1D, 2D, and 3D, we demonstrate the efficacy of our method, and make the case for its applicability to a wide range of problems in disk physics, including hydrodynamic instabilities and disk-planet interaction.

astro-ph.IM↗

arXiv2023

Thermal instabilities in accretion disks II: Numerical Experiments for the Goldreich-Schubert-Fricke Instability and the Convective Overstability in disks around young stars

The linear stability analysis of a stratified rotating fluid (see paper I) showed that disks with a baroclinic stratification under the influence of thermal relaxation will become unstable to thermal instabilities. One instability is the Goldreich-Schubert-Fricke instability (GSF), which is the local version of the Vertical Shear Instability (VSI) and the other is a thermal overstability, the Convective Overstability (COS). In the present paper we reproduce the analytic predicted growth rates for both instabilities in numerical experiments of small axisymmetric sections of vertically isothermal disks with a radial temperature gradient, especially for cooling times longer than the critical cooling time for VSI. In this cooling time regime our simulations reveal the simultaneous and independent growth of both modes: COS and GSF. We consistently observe that GSF modes exhibit a faster growth rate compared to COS modes. Near the midplane, GSF modes eventually stop growing, while COS modes continue to grow and ultimately dominate the flow pattern. Away from the midplane, we find GSF modes to saturate, when bands of constant angular momentum have formed. In these bands we observe the formation and growth of eddies driven by the baroclinic term, further enhancing the velocity perturbations. In geophysics this effect is known as horizontal convection or sea-breeze instability. Three-dimensional simulations will have to show whether similar effects will occur when axisymmetry is not enforced. Our local simulations help to reveal the numerical resolution requirements to observe thermal instabilities in global simulations of disks around young stars.

astro-ph.EP↗

arXiv2023

MeV, GeV and TeV neutrinos from binary-driven hypernovae

We analyze neutrino ($ν$) emission channels in energetic ($\gtrsim 10^{52}$ erg) long gamma-ray bursts within the binary-driven hypernova model. The binary-driven hypernova progenitor is a binary system composed of a carbon-oxygen star and a neutron star (NS) companion. The gravitational collapse leads to a type Ic supernova (SN) explosion and triggers an accretion process onto the NS. For orbital periods of a few minutes, the NS reaches the critical mass and forms a black hole (BH). Two physical situations produce MeV $ν$s. First, during the accretion, the NS surface emits $ν$-$\barν$ pairs by thermal production. We calculate the properties and the flavor evolution of such a $ν$ emission. Second, if the angular momentum of the SN ejecta is high enough, an accretion disk might form around the BH. The disk's high density and temperature are ideal for MeV-$ν$ production. We estimate the flavor evolution and find that $ν$ oscillation inside the disk leads to flavor equipartition. This effect reduces (compared to assuming frozen flavor content) the energy deposition rate of $ν$-$\barν$ annihilation into electron-positron ($e^+e^-$) pairs in the BH vicinity. We then analyze the production of GeV-TeV $ν$s around the BH. The magnetic field surrounding the BH interacts with the BH gravitomagnetic field producing an electric field that leads to spontaneous $e^+e^-$ pairs by vacuum breakdown. The pairs plasma self-accelerates due to its internal pressure and engulfs protons during the expansion. The hadronic interaction of the protons in the expanding plasma with the ambient protons leads to $ν$ emission via the decay chain of $π$ and $μ$, around and far from the BH, along different directions. These $ν$s have GeV-TeV energies, and we calculate their spectrum and luminosity. We also outline the detection probability by some current and future $ν$ detectors.

astro-ph.HE↗

arXiv2022

No self-shadowing instability in 2D radiation-hydrodynamical models of irradiated protoplanetary disks

Theoretical models of protoplanetary disks including stellar irradiation often show a spontaneous amplification of scale height perturbations, produced by the enhanced absorption of starlight in enlarged regions. In turn, such regions cast shadows on adjacent zones that consequently cool down and shrink, eventually leading to an alternating pattern of overheated and shadowed regions. Previous investigations have proposed this to be a real self-sustained process, the so-called self-shadowing or thermal wave instability, which could naturally form frequently observed disk structures such as rings and gaps, and even potentially enhance the formation of planetesimals. All of these, however, have assumed in one way or another vertical hydrostatic equilibrium and instantaneous radiative diffusion throughout the disk. In this work we present the first study of the stability of accretion disks to self-shadowing that relaxes these assumptions, relying instead on radiation-hydrodynamical simulations. We first construct hydrostatic disk configurations by means of an iterative procedure and show that the formation of a pattern of enlarged and shadowed regions is a direct consequence of assuming instantaneous radiative diffusion. We then let these solutions evolve in time, which leads to a fast damping of the initial shadowing features in layers close to the disk surface. These thermally relaxed layers grow towards the midplane until all temperature extrema in the radial direction are erased in the entire disk. Our results suggest that radiative cooling and gas advection at the disk surface prevent a self-shadowing instability from forming, by damping temperature perturbations before these reach lower, optically thick regions.

astro-ph.EP↗

arXiv2022

Protostellar disks subject to infall: a one-dimensional inviscid model and comparison with ALMA observations

A new one-dimensional, inviscid, and vertically integrated disk model with prescribed infall is presented. The flow is computed using a second-order shock-capturing scheme. Included are vertical infall, radial infall at the outer radial boundary, radiative cooling, stellar irradiation, and heat addition at the disk-surface shock. Simulation parameters are chosen to target the L1527 IRS disk which has been observed using ALMA (Atacama Large Millimeter Array). The results give an outer envelope of radial infall and $u_ϕ\propto 1/r$ which encounters a radial shock at $r_\mathrm{shock} \sim 1.5\ \times$ the centrifugal radius ($r_\mathrm{c}$) across which the radial velocity is greatly reduced and the gas temperature rises from a pre-shock value of $\approx 25$ K to $\approx 180$ K over a spatially thin region calculated using a separate shock structure code. At $r_\mathrm{c}$, the azimuthal velocity $u_ϕ$ transitions from being $\propto 1/r$ to being nearly Keplerian. These results qualitatively agree with recent ALMA observations which indicate a radial shock where SO is sublimated as well as a transition from a $u_ϕ\sim 1/r$ region to a Keplerian inner disk. However, in one set of observations, the position-velocity map of cyclic-C$_3$H$_2$, together with a certain ballistic maximum velocity relation, has suggested that the radial shock coincides with a ballistic centrifugal barrier, which places the shock at $r_\mathrm{shock} = 0.5 r_\mathrm{c}$, i.e, inward of $r_\mathrm{c}$, rather than outward as given by our simulations. It is argued that radial velocity plots from previous magnetic rotating-collapse simulations also indicate that the radial shock is located outward of $r_\mathrm{c}$. The discrepancy with observations is analyzed and discussed, but remains unresolved.

astro-ph.EP↗

arXiv2021

A two-moment radiation hydrodynamics scheme applicable to simulations of planet formation in circumstellar disks

We present a numerical code for radiation hydrodynamics designed as a module for the freely available PLUTO code. We adopt a gray approximation and include radiative transfer following a two-moment approach by imposing the M1 closure to the radiation fields. This closure allows for a description of radiative transport in both the diffusion and free-streaming limits, and is able to describe highly anisotropic radiation transport as can be expected in the vicinity of an accreting planet in a protoplanetary disk. To reduce the computational cost caused by the timescale disparity between radiation and matter fields, we integrate their evolution equations separately in an operator-split way, using substepping to evolve the radiation equations. We further increase the code's efficiency by adopting the reduced speed of light approximation (RSLA). Our integration scheme for the evolution equations of radiation fields relies on implicit-explicit schemes, in which radiation-matter interaction terms are integrated implicitly while fluxes are integrated via Godunov-type solvers. The module is suitable for general astrophysical computations in 1, 2, and 3 dimensions in Cartesian, spherical and cylindrical coordinates, and can be implemented on rotating frames. We demonstrate the algorithm performance on different numerical benchmarks, paying particular attention to the applicability of the RSLA for computations of physical processes in protoplanetary disks. We show 2D simulations of vertical convection in disks and 3D simulations of gas accretion by planetary cores, which are the first of their kind to be solved with a two-moment approach.

astro-ph.EP↗

arXiv2019

A radiative transfer module for relativistic magnetohydrodynamics in the PLUTO code

We present a numerical implementation for the solution of the relativistic radiation hydrodynamics and magnetohydrodynamics equations, designed as an independent module within the freely available code PLUTO. The radiation transfer equations are solved under the grey approximation and imposing the M1 closure, which allows the radiation transport to be handled in both the free-streaming and diffusion limits. Equations are integrated following an implicit-explicit scheme, where radiation-matter interaction terms are integrated implicitly, whereas transport and all of the remaining source terms are solved explicitly by means of the same Godunov-type solvers included in PLUTO. Among these, we introduce a new Harten-van Leer-contact (HLLC) solver for optically thin radiation transport. The code is suitable for multidimensional computations in Cartesian, spherical and cylindrical coordinates, using either a single processor or parallel architectures. Adaptive grid computations are also made possible, by means of the CHOMBO library. The algorithm performance is demonstrated through a series of numerical benchmarks by investigating various different configurations with a particular emphasis on the behavior of the solutions in the free-streaming and diffusion limits.

astro-ph.IM↗

arXiv2017

On the Casimir interaction between two smoothly deformed cylindrical surfaces

We generalize the derivative expansion (DE) approach to the interaction between almost-flat smooth surfaces, to the case of surfaces which are optimally described in cylindrical coordinates. As in the original form of the DE, the obtained method does not depend on the nature of the interaction. We apply our results to the study of the static, zero-temperature Casimir effect between two cylindrical surfaces, obtaining approximate expressions which are reliable under the assumption that the distance between those surfaces is always much smaller than their local curvature radii. To obtain the zero-point energy, we apply known results about the thermal Casimir effect for a planar geometry. To that effect, we relate the time coordinate in the latter to the angular variable in the cylindrical case, as well as the temperature to the radius of the cylinders. We study the dependence of the applicability of the DE on the kind of interaction, considering the particular cases where Dirichlet or Neumann conditions are applied to a scalar field.

hep-th↗