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Измоденов Владислав Валерьевич

Базовая кафедра физики космоса Института космических исследований РАН

Профиль на hse.ru ↗ тел.: 15250
Публикаций
42
Языков
1
Наград
3
Конференций
0
Профиль Публикации (42) Курсы (4)

Профессиональные интересы

космическая газовая динамикаФизика плазмымагнитная гидродинамикагелиосферамежзвездная средаастросферыкинетическая теория газов

Должности

  • Профессор — Базовая кафедра физики космоса Института космических исследований РАН

Био

  • · Начал работать в НИУ ВШЭ в 2017 году.
  • · Научно-педагогический стаж: 31 год.

Образование

  • 2008 · Доктор физико-математических наук
  • 1993 · Специалитет: Московский государственный университет им. М.В. Ломоносова, специальность «Механика, прикладная математика», квалификация «Механик»

Опыт работы

  • · 1997 г.: С июля работает на механико-математическом факультете МГУ в должности младшего научного сотрудника, ассистента (с
  • · 1998 г: ), доцента (с
  • · 2002 г.: по
  • · 2010 г: ), профессора (с
  • · 2011 г.: по наст. время)
  • · 2005 г.: С по настоящее время работает в Институте космических исследований РАН заведующим лабораторией (по совмест.) «Межпланетной среды» отдела физики планет и малых тел солнечной системы

Награды и поощрения

  • · Благодарность факультета физики НИУ ВШЭ (ноябрь 2022)
  • · Надбавка за публикацию в журнале из Списка А (и приравненном к нему научном издании) (2025–2026, 2024–2025, 2023–2024)
  • · Надбавка за публикацию в международном рецензируемом научном издании (2022–2023, 2021–2022, 2019–2021, 2018–2019)

Гранты и проекты

  • — · на соискание учёной степени кандидата наук

Идентификаторы исследователя

Публикации (42)

Heliospheric energetic neutral atoms: Non-stationary modelling and comparison with IBEX-Hi data

2020 · ARTICLE · en

The interstellar boundary explorer (IBEX) has been measuring fluxes of the energetic neutral atoms (ENAs) using the IBEX-Hi (0.3–6 keV) instrument since 2008. We have developed a numerical time-depended code to calculate globally distributed flux (GDF) of hydrogen ENAs employing both (1) 3D kinetic-MHD model of the global heliosphere and (2) reconstruction of atom trajectories from 1 au, where they are observed by IBEX, to the point of their origin in the inner heliosheath (IHS). The key factor in the simulation is a detailed kinetic consideration of the pickup ions (PUIs), the supra-thermal component of protons in the heliosphere, which is ‘parental’ to the ENAs and originates in the region of the supersonic solar wind being picked by the heliospheric magnetic field. As a result of our study, we have concluded that (1) the developed model is able to reproduce the geometry of the multilobe structure seen in the IBEX-Hi GDF maps, (2) the GDF is extremely sensitive to the form of the velocity distribution function of PUIs in the IHS, and the accounting for the existence of an additional energetic population of PUIs is essential to explain the data, (3) despite a relatively good agreement, there are some quantitative differences between the model calculations and IBEX-Hi data. Possible reasons for these differences are discussed.

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Lagrangian fluid approach for the modelling of peculiarities of the interstellar dust distribution in the astrospheres/heliosphere

2020 · ARTICLE · en

Interstellar dust (ISD) penetrates into the heliosphere/astrosphere due to relative motion of the Sun and the local interstellar medium (LISM). Inside the heliosphere/astrosphere and at the heliospheric boundaries, where the solar/stellar wind interacts with LISM, distribution of the ISD is modified due to an action of electromagnetic forces, the solar gravitation, and radiation pressure. In this paper, we show that the distribution of the ISD particles in the heliosphere has peculiarities of high-density layers. In order to understand the nature of the peculiarities Osiptsov’s Lagrangian method has been employed and developed for the case when the force acting on the particles has discontinuity as it is for the electromagnetic force at the helioshperic current sheet (HCS). In the result of the modelling, we demonstrate existence of multiple layers of high density of the ISD located at 0.03–10 au north and south with respect to the HCS.

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Numerical modeling of the convective Kelvin-Helmholtz instabilities of astropauses

2020 · ARTICLE · en

In this paper we present the numerical modeling results of the problem of the hypersonic stellar wind interaction with fully ionized interstellar medium that moves with respect to the star with supersonic speed. This is the classical problem that has been firstly studied in 1970 by Baranov et al. [1] under the thin layer approximation.In this paper we present results of numerical solutions obtained with high spatial resolution of the numerical grid. The computations were performed by using GPU processors with high-performance parallel programming technology CUDA from NVIDIA. It is shown that the stationary solution depends only on two dimensionless parameters - Mach number in the interstellar medium, M∞, and adiabatic index, γ. The stationary solutions were obtained for different values of M∞ for low and medium resolution of the numerical grids. For the numerical grids of high spatial resolution the Kelvin-Helmholtz instability appears at the tangential discontinuities (both primary and secondary) in the tail part of interaction region. The instability is convective as it should be according to the linear analyses by Ruderman et al. [6]. We explore the instability evolution with increasing resolution of the numerical grid. Effects of the numerical scheme are also studied.

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SWAN/SOHO Lyman-α mapping: the Hydrogen Geocorona Extends Well Beyond The Moon

2019 · ARTICLE · ru

The Earth’s hydrogen exosphere Lyman-α radiation was mapped with the SWAN/SOHO instrument in January 1996, 1997 and 1998 (low solar activity). The use of a hydrogen absorption cell allowed to disentangle the interplanetary emission from the geocoronal one and to assign the absorbed signal almost entirely to the geocorona. The geocorona was found to extend at least up to 100 Earth Radii (R E ) with an intensity of 5 Rayleigh, an unprecedented distance well exceeding the recent results of LAICA imager (∼50 R E ), and encompassing the orbit of the Moon (∼60 R E ). We developed a numerical kinetic model of the hydrogen atoms distribution in the exosphere which includes the solar Lyman-α radiation pressure and the ionization. The radiation pressure compresses the H exosphere on the day side, producing a bulge of H density between 3 and 20 R E which fits observed intensities very well. The SWAN Lyman-α distribution of intensity was compared both to LAICA (2015) and to OGO-5 (1968) measurements. Integrated H densities of SWAN at a tangent distance of 7 R E are larger than LAICA/OGO-5 by factors 1.1-2.5, while we should expect a stronger effect of the radiation pressure at solar max. We discuss the possible role of H atoms in satellite orbits to explain this apparent contradiction. An onion-peeling technique is used to retrieve hydrogen number density in the exosphere for the three SWAN observations. They show an excess of density versus models at large distances, which is likely due to non-thermal atoms (not in the model).

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An astrosphere around the blue supergiant kappa Cas: possible explanation of its filamentary structure

2018 · ARTICLE · en

High-resolution mid-infrared observations carried out by the Spitzer Space Telescope allowed one to resolve the fine structure of many astrospheres. In particular, they showed that the astrosphere around the B0.7 Ia star κ Cas (HD 2905) has a clear-cut arc structure with numerous cirrus-like filaments beyond it. Previously, we suggested a physical mechanism for the formation of such filamentary structures. Namely, we showed theoretically that they might represent the non-monotonic spatial distribution of the interstellar dust in astrospheres (viewed as filaments) caused by interaction of the dust grains with the interstellar magnetic field disturbed in the astrosphere due to colliding of the stellar and interstellar winds. In this paper, we invoke this mechanism to explain the structure of the astrosphere around κ Cas. We performed 3D magnetohydrodynamic modelling of the astrosphere for realistic parameters of the stellar wind and space velocity. The dust dynamics and the density distribution in the astrosphere were calculated in the framework of a kinetic model. It is found that the model results with the classical MRN (Mathis, Rumpl & Nordsieck 1977) size distribution of dust in the interstellar medium do not match the observations, and that the observed filamentary structure of the astrosphere can be reproduced only if the dust is composed mainly of big (μm-sized) grains. Comparison of the model results with observations allowed us to estimate parameters (number density and magnetic field strength) of the surrounding interstellar medium.

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Secondary Interstellar Oxygen in the Heliosphere: Numerical Modeling and Comparison with IBEX-Lo Data

2017 · ARTICLE · en

Quantitative analysis of the interstellar heavy (oxygen and neon) atom fluxes obtained by the Interstellar Boundary Explorer (IBEX) suggests the existence of the secondary interstellar oxygen component. This component is formed near the heliopause due to charge exchange of interstellar oxygen ions with hydrogen atoms, as was predicted theoretically. A detailed quantitative analysis of the fluxes of interstellar heavy atoms is only possible with a model that takes into account both the filtration of primary and the production of secondary interstellar oxygen in the boundary region of the heliosphere as well as a detailed simulation of the motion of interstellar atoms inside the heliosphere. This simulation must take into account photoionization, charge exchange with the protons of the solar wind and solar gravitational attraction. This paper presents the results of modeling interstellar oxygen and neon atoms through the heliospheric interface and inside the heliosphere based on a three-dimensional kinetic-MHD model of the solar wind interaction with the local interstellar medium and a comparison of these results with the data obtained on the IBEX spacecraft.

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Non-monotonic distribution of the interstellar dust in astrospheres: finite gyroradius effect

2017 · ARTICLE · en

High-resolution mid-infrared observations of astrospheres show that many of them have filamentary (cirrus-like) structure. Using numerical models of dust dynamics in astrospheres, we suggest that their filamentary structure might be related to specific spatial distribution of the interstellar dust around the stars, caused by a gyrorotation of charged dust grains in the interstellar magnetic filed. Our numerical model describes the dust dynamics in astrospheres under an influence of the Lorentz force and assumption of a constant dust charge. Calculations are performed for the dust grains with different sizes separately. It is shown that non-monotonic spatial dust distribution (viewed as filaments) appears for dust grains with the period of gyromotion comparable with the characteristic time scale of the dust motion in the astrosphere. Numerical modelling demonstrates that number of filaments depends on charge-to-mass ratio of dust.

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Two-jet astrosphere model: Effect of azimuthal magnetic field

2017 · ARTICLE · en

Opher et al., Drake, Swisdak and Opher have shown that the heliospheric magnetic field results in formation of two-jet structure of the solar wind flow in the inner heliosheath, i.e. in the subsonic region between the heliospheric termination shock (TS) and the heliopause. In this scenario, the heliopause has a tube-like topology as compared with a sheet-like topology in the most models of the global heliosphere. In this paper, we explore the two-jet scenario for a simplified astrosphere in which (1) the star is at rest with respect to the circumstellar medium, (2) radial magnetic field is neglected as compared with azimuthal component and (3) the stellar wind outflow is assumed to be hypersonic (both the Mach number and the Alfvénic Mach number are much greater than unity at the inflow boundary). We have shown that the problem can be formulated in dimensionless form, in which the solution depends only on one dimensionless parameter ε that is reciprocal of the Alfvénic Mach number at the inflow boundary. This parameter is proportional to stellar magnetic field. We present the numerical solution of the problem for various values of ε. Three first integrals of the governing ideal magnetohydrodynamic equations are presented, and we make use of them in order to get the plasma distribution in the jets. Simple relations between distances to the TS, astropause and the size of the jet are established. These relations allow us to determine the stellar magnetic field from the geometrical pattern of the jet-like astrosphere.

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Voyager 1/UVS Lyman alpha Measurements at the Distant Heliosphere (90–130 AU): Unknown Source of Additional Emission

2017 · ARTICLE · en

In this work, we present for the first time the Lyman α intensities measured by Voyager 1/UVS in 2003–2014 (at 90–130 AU from the Sun). During this period Voyager 1 measured the Lyman α emission in the outer heliosphere at an almost fixed direction close to the upwind (i.e.“ toward the interstellar flow). The data show an unexpected behavior in 2003–2009: the ratio of observed intensity to the solar Lyman α flux is almost constant. Numerical modeling of these data is performed in the frame of a state-of-the-art self-consistent kinetic-MHD model of the heliospheric interface. The model results, for various interstellar parameters, predict a monotonic decrease of intensity not seen in the data. We propose two possible scenarios that explain the data qualitatively. The first is the formation of a dense layer of hydrogen atoms near the heliopause. Such a layer would provide an additional backscattered Doppler-shifted Lyman α emission, which is not absorbed inside the heliosphere and may be observed by Voyager. About 35 R of intensity from the layer is needed. The second scenario is an external nonheliospheric Lyman α component, which could be galactic or extragalactic. Our parametric study shows that ∼25 R of additional emission leads to a good qualitative agreement between the Voyager 1 data and the model results.

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Acceleration of interstellar pickup protons at the heliospheric termination shock: Voyager 1/2 energetic proton fluxes in the inner heliosheath

2016 · ARTICLE · en

Fluxes of energetic protons in the range from 30 keV up to several MeV measured at the Voyager 1/2spacecraft downstream of the heliospheric termination shock can be explained by shock-drift acceleration theory, which includes variations of the magnetic field direction in a vicinity of the shock. The variations can be connected with the sector structure of the interplanetary magnetic field near the solar equatorial plane. Theoretical fluxes of accelerated protons are calculated numerically in the framework of a 3D kinetic-magnetohydrodynamic model of the interaction of the solar wind and local interstellar medium.

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Курсы (4)