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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)

On the minimum of line width of the backscattered solar Ly-α profile measured by SOHO/SWAN

2026 в печати · ARTICLE · en

Solar Ly-alpha photons are scattered by interstellar hydrogen (H) atoms that penetrate into the heliosphere through the region of the solar wind interaction with the local interstellar medium. The spectra of scattered Ly-alpha reflect the properties of the velocity distribution of the interstellar H atoms. The spectra of backscattered Ly-alpha have been reconstructed in anti-sunward directions by Quemerais et al. (Quémerais et al., 1999, Quémerais et al., 2006a). One of the spectacular results of this reconstruction was the discovery of the minimum of the width of the backscattered spectra in the direction (nearly) perpendicular to the interstellar flow direction. Originally, the minimum was interpreted as a proof of the secondary interstellar atom presence inside the heliosphere. However, later Katushkina and Izmodenov (2011), using a two-population kinetic model of the interstellar H atoms in the heliosphere, demonstrated that the minimum cannot be produced in their quite complete model. In this paper, we performed numerical calculations of solar backscattered Ly-alpha spectra with the same model as in Katushkina and Izmodenov (2011). A key novel aspect of the presented analyses is the procedure of the obtaining the width values. Specifically, we obtain the widths following the same approach as in the analysis of SOHO/SWAN data: the numerically computed spectra are truncated at velocities of +-30 km/s and subsequently fitted with symmetric Gaussian functions. Our results show that the minimum arises as a direct consequence of applying this procedure to spectra generated by a two-population model. When the same analysis is performed on a single-population model, no such minimum appears. Thus, the longstanding issue of providing a theoretical explanation for the observed minimum is resolved.

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Effects of angular scattering and H+p, H+H collisions on the properties of interstellar atoms in the heliosphere

2025 · ARTICLE · en

Interstellar hydrogen atoms (H atoms) penetrate into the heliosphere through the region of the solar wind interaction with the interstellar plasma due to their large mean free path. Resonant charge exchange of H atoms with protons has been considered as the main interaction process between the components. In the majority of models, other processes like elastic H-H and H-p collisions are not included. Moreover, it has been assumed that the velocities of the colliding particles remain unchanged during charge exchange. This corresponds to the scattering on the angle of π in the centre mass rest frame. The goal of this paper is to explore effects of the elastic H-H and H-p collisions as well as the angular scattering during charge exchange on the distribution of the interstellar atoms in the heliosphere and at its boundary. We present results of simple (and therefore, easily repeatable) kinetic model of the interstellar atom penetration through the region of the solar and interstellar winds interaction into the heliosphere. As a result of the model we compute the distribution function of the interstellar atoms at different heliospheric distances. Further, this distribution function is used to compute its moments and potentially observable features such as absorption and backscattered spectra in the Lyman-alpha line. Results show that there are differences in the behavior of the distribution function when considering elastic collisions and the changes in the moments of the distribution achieve 10%. Therefore, in cases where precise calculation of H atom parameters is essential, such as in the modeling of backscattered Lyman-α emission, elastic collisions must be considered.

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Understanding the IBEX ribbon using the kinetic model of pickup proton transport in a scatter-free limit

2025 · ARTICLE · en

One of the most remarkable discoveries by the Interstellar Boundary Explorer (IBEX) is the ribbon – a narrow band of enhanced energetic neutral atom (ENA) fluxes observed in the sky. The prevailing explanation attributes the IBEX ribbon to the secondary ENA mechanism. In this process, “primary” hydrogen ENAs, produced via charge exchange between solar wind protons and interstellar hydrogen atoms within the heliosphere, travel beyond the heliopause and undergo further charge exchange with protons of the local interstellar medium (LISM), generating pickup protons. Some of these pickup protons subsequently experience charge exchange with interstellar hydrogen atoms, forming “secondary” ENAs, some of which travel back toward the Sun and are detected by the IBEX. This paper presents a kinetic model developed to simulate secondary ENA fluxes. Ribbon simulations are performed using global distributions of plasma and hydrogen atoms in the heliosphere derived from a kinetic-magnetohydrodynamic model of the solar wind interaction with the LISM. The model accounts for all relevant primary ENA populations, including neutralized thermal solar wind protons, neutralized pickup protons, and ENAs originating in the inner heliosheath. The transport of pickup protons beyond the heliopause is described by the focused transport equation for a gyrotropic velocity distribution in the scatter-free limit, assuming no pitch-angle scattering or energy diffusion. Our simulations qualitatively reproduce IBEX-Hi (0.5–6 keV) ribbon observations and exhibit good quantitative agreement at low heliolatitudes. However, the model underestimates fluxes at high heliolatitudes, likely due to the omission of non-stationary solar wind behavior in the stationary framework used in this work. The study highlights the importance of ENAs from the inner heliosheath, a population considered for the ribbon production in the frame of the kinetic model of pickup proton transport in the heliosphere for the first time, for accurately reproducing ribbon fluxes observed by IBEX-Hi at the highest energy steps.

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Self-oscillations of the two-jet collimated astrosphere: new type of instability

2025 · ARTICLE · en

Recently, there have been discussions about the shape of the heliopause. Some scientists question the classical form, which is close to a paraboloid. They suggest that the heliopause may have a two-jet collimated shape. While we disagree with this view of the heliopause shape, it seems likely that for stars with stronger stellar magnetic fields and those that are at rest or moving slowly through the interstellar medium, the astropause will have a two-jet collimated shape. This paper raises the question of the stability of the two-jet collimated astrosphere. Recent studies have noted the emergence of instability in the heliosheath near the axis of the heliospheric jets, linking this to the action of neutral hydrogen atoms. We note in this paper that astrospheric jets can become unstable in the presence of strong magnetic fields, even without the influence of atoms, which is unexpected. Furthermore, due to a feedback mechanism, astrospheric jets undergo self-oscillation. We investigated the development of this instability, the nature of the feedback mechanism, and the period of self-oscillation for different system parameters. Our findings provide valuable insights into the behaviour of these unique plasma structures, and they are another step towards studying the stability of two-jet collimated astrospheres.

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Mathematical Modeling of Kelvin–Helmholtz Instability at Tangential Discontinuities in Partially Ionized Plasma: Application to Heliopause Dynamics

2025 · ARTICLE · en

The stability of the heliopause, the tangential discontinuity separating the solar wind from the interstellar medium, is influenced by various processes, including the Kelvin–Helmholtz instability. This study investigates the role of charge exchange collisions between protons and hydrogen (H) atoms in reduction of the Kelvin–Helmholtz growth rate at the heliopause. Using a two-dimensional gasdynamic model with the inclusion of H atoms, we perform numerical simulations of the plasma flow near the heliopause flanks. We conduct a parametric study by varying the Knudsen number. Our results indicate that charge exchange collisions play a crucial role in suppressing the Kelvin–Helmholtz instability. As the Knudsen number decreases, the flow transitions from an unstable regime to a smoother state.

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Manifestation of the stellar wind cycle in infrared images: Example of the heliosphere

2025 · ARTICLE · en

Aims. The regions in which stellar winds interact with the interstellar medium, also known as astrospheres, can be observed in detail through the thermal emission of the interstellar dust particles, resided in plasma. Interstellar dust is also directly observed in the vicinity of the Sun with dust detectors onboard spacecraft, and it is known to be affected by the interplanetary magnetic field. The main goal of this work is to show how the change in the interplanetary magnetic field with the solar cycle affects the infrared picture of the heliosphere. Methods. To compose a synthetic intensity map of the interstellar dust thermal emission, we used the Monte Carlo method to calculate the distribution of the dust particles inside the heliosphere. We considered the effects of the heliosphere boundaries and the non-stationary current sheet. Results. The change in the Parker magnetic field caused by the solar activity cycle leads distinguishable features in the mid-infrared emission maps of the heliosphere. The distribution of the interstellar dust in the vicinity of the Sun we calculated suggests that small particles linger outside of the heliosphere, and medium-size particles are mostly affected by the changing interplanetary magnetic field, which leads to number density waves in the tail region of the heliosphere. Finally, large particles form a bulge behind the Sun.

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The global structure of astrospheres: Effect of Knudsen number

2024 · ARTICLE · en

The interaction between stellar winds and the partially ionized local interstellar medium (LISM) is quite common in astrophysics. However, the main difficulty in describing the neutral components lies in the fact that the mean free path of an interstellar atom, l, can be comparable to the characteristic size of an astrosphere, L (i.e. the Knudsen number, which is equal to l/L, is approximately equal to 1, as in the case of the heliosphere). In such cases, a single-fluid approximation becomes invalid, and a kinetic description must be used for the neutral component. In this study, we consider a general astrosphere and use a kinetic-gas dynamics model to investigate how the global structure of the astrosphere depends on the Knudsen number. We present numerical results covering an extremely wide range of Knudsen numbers (from 0.0001 to 100). Additionally, we explore the applicability of single-fluid approaches for modelling astrospheres of various sizes. We have excluded the influence of interstellar and stellar magnetic fields in our model to make parametric study of the kinetic effects feasible. The main conclusion of this work is that, for large astrospheres (with a distance to the bow shock greater than 600 AU) a heated rarefied plasma layer forms in the outer shock layer near the astropause. The formation of this layer is linked to localized heating of the plasma by atoms (specifically, ENAs) that undergo charge exchange again behind the astropause. This process significantly alters the flow structure in the outer shock layer and the location of the bow shock, and it cannot be described by a single-fluid model. Additionally, this paper discusses how atoms weaken the bow shocks at near-heliospheric conditions.

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The unexpected role of heliospheric boundaries in facilitating interstellar dust penetration at 1–5 AU

2024 · ARTICLE · en

Aims. Interstellar dust (ISD) particles penetrate the heliosphere because of the relative motion of the local interstellar cloud and the Sun. The penetrated particles pass through the heliospheric interface, that is, the region in which solar wind and interstellar plasma interact. As a result, the ISD flow is modified after the passage through this region under the influence of electromagnetic force. The main goal of this work is to show how the heliospheric interface affects the distribution of ISD particles near the Sun. Methods. We have developed a Monte Carlo model of the ISD distribution in the heliosphere. It first takes the effects of the heliospheric interface and the rotating heliospheric current sheet into account. The effects of the heliospheric interface were probed using a global heliospheric model. Results. The computation results show that the heliospheric interface strongly influences the distribution of relatively small (radius a = 150 − 250 nm) astronomical silicates. The unexpected finding is that the heliospheric interface facilitates the penetration of a = 150 nm particles at small heliocentric distances and, particularly, to the Ulysses orbit (1 − 5 AU). We demonstrate that the deflection of ISD particles in the outer heliosheath is the principal mechanism that causes the effects of the heliospheric interface on the distribution near the Sun. The computations with different heliospheric models show that the distribution near the Sun is sensitive to the plasma parameters in the pristine local interstellar medium. Thus, we demonstrated that being measured near the Sun, the ISD may serve as a new independent diagnostics of the local interstellar medium and the heliospheric boundaries.

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Effects of charge exchange on plasma flow in the heliosheath and astrosheathes

2024 · ARTICLE · en

Shock boundary layers are regions bounded by a shock wave on the one side and tangential discontinuity on the other side. These boundary layers are commonly observed in astrophysics. For example, they exist in the regions of the interaction of the stellar winds with the surrounding interstellar medium. Additionally, the shock layers are often penetrated by the flows of interstellar atoms, as, for instance, in the astrospheres of the stars embedded by the partially ionized interstellar clouds. This paper presents a simple toy model of a shock layer that aims to qualitatively describe the influence of charge exchange with interstellar hydrogen atoms on the plasma flow in astrospheric shock layers. To clearly explore this effect, magnetic fields are neglected, and the geometry is kept as simple as possible. The model explains why the cooling of plasma due to charge exchange in the inner heliosheath leads to an increase in plasma density in front of the heliopause. It also demonstrates that the source of momentum causes changes in the pressure profile within the shock layer. The paper also discusses the decrease in plasma density near the astropause in the outer shock layer in the case of layer heating, which is particularly relevant in light of the Voyager measurements in the heliospheric shock layer.

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The Influence of H–p, H–H Elastic Collisions, and Charge Transfer with Angular Scattering on the H Atom Velocity Distribution Function in a Plasma Layer

2024 · ARTICLE · en

In this study, we examine the influence of hydrogen–proton (H–p) and hydrogen–hydrogen (H–H) elastic collisions, along with charge transfer with angular scattering, on the velocity redistribution of hydrogen atoms within a plasma layer. To achieve this, we developed a kinetic model to explore H atom behavior in a homogeneous plasma region, assessing how these effects influence the maxwellization of the H atom distribution function relative to the case where only charge exchange is considered. The homogeneous layer results provide a simplified but valuable demonstration of how elastic collisions impact H atom behavior, creating a foundation for future studies in more complex, spatially varying plasma environments. Calculations of the distribution functions at various distances reveal that combined H–p and H–H collisions lead to faster maxwellization and blur the distinction between hydrogen atoms that have undergone charge exchange and those that have not interacted with protons.

DOI ↗ PDF ↗

Курсы (4)