arXiv subjects

Vladislav V. Izmodenov

Publications and source records attributed to Vladislav V. Izmodenov.

8 recordsLinked to original sources

arXiv2026

New possible way to determine stellar wind terminal velocity from analysis of Lyman-$α$ absorption spectra

Stellar winds interact with the partially ionized interstellar medium (ISM), forming astrospheres. A key feature of this interaction is the hydrogen wall - secondary interstellar atoms produced via charge exchange near the tangential discontinuity separating the stellar wind from the ionized ISM component. This secondary component is decelerated and heated compared to primary interstellar hydrogen, making the hydrogen wall detectable through Lyman-$α$ absorption spectra toward nearby stars. Such structures have been observed by the Hubble Space Telescope around the Sun and other stars. In this paper, we propose that another feature of the stellar wind/partially ionized ISM interaction may also be detectable in Lyman-$α$ spectra: the neutral stellar wind. It forms via charge exchange between supersonic stellar wind protons and interstellar atoms penetrating deep into the astrosphere due to their long mean free paths. We present a parametric numerical analysis of astrospheric structures and their synthetic Lyman-$α$ absorption spectra. Using a 2D kinetic-hydrodynamic model, we vary the terminal wind velocity while maintaining constant dynamic pressure to keep the astrosphere size consistent. For winds slower than the solar wind (terminal velocities $V_0 \lesssim 200$ km/s), charge exchange efficiency in the supersonic region increases dramatically, producing a distinct and observable absorption feature from the neutral wind. This signature is negligible for solar-like winds ($V_0 \approx 400$ km/s) but emerges as a direct spectroscopic diagnostic for winds up to $\sim 200$ km/s. Detecting this neutral wind absorption offers a novel method to directly constrain stellar wind velocities.

astro-ph.SR↗

arXiv2020

Magnitude and direction of the local interstellar magnetic field inferred from Voyager 1 and 2 interstellar data and global heliospheric model

In this Letter, we provide constraints on the direction and magnitude of the pristine (i.e., unperturbed by the interaction with the Sun) local interstellar magnetic field. The constraints are based on analysis of the interstellar magnetic field components at the heliopause measured by magnetometer instruments on board Voyager 1 and 2 spacecraft. The analysis was performed with the help of our kinetic-magnetohydrodynamical (MHD) model of the global heliosphere. The model shows that the solar-induced disturbances of the interstellar magnetic field are extended relatively far from the Sun up to 400-500 AU. The field is draped around the heliopause and compressed. By comparison of the model results with Voyager data we found that the model provides results comparable with the data for the interstellar magnetic field of $B_{LISM}$ = 3.7-3.8 $μ$G in magnitude and directed towards $\approx$125$^\circ$ in longitude, and $\approx$37$^\circ$ in latitude in the heliographic inertial (HGI) coordinate system.

physics.space-ph↗

arXiv2014

Neutral interstellar helium parameters based on Ulysses/GAS and IBEX-Lo observations: what are the reasons for the differences?

Recent analysis of the interstellar helium fluxes measured in 2009-2010 at Earth orbit by the Interstellar Boundary Explorer (IBEX) has suggested that the interstellar velocity (both direction and magnitude) is inconsistent with that derived previously from Ulysses/GAS observations made in the period from 1990 to 2002 at 1.5-5.5 AU from the Sun. Both results are model-dependent and models that were used in the analyses are different. In this paper, we perform an analysis of the Uysses/GAS and IBEX-Lo data using our state-of-the-art 3D time-dependent kinetic model of interstellar atoms in the heliosphere. For the first time we analyze Ulysses/GAS data from year 2007, the closest available Ulysses/GAS observations in time to the IBEX observations. We show that the interstellar velocity derived from the Ulysses 2007 data is consistent with previous Ulysses results and does not agree with the velocity derived from IBEX. This conclusion is very robust since, as is shown in the paper, it does not depend on the ionization rates adopted in theoretical models. We conclude that Ulysses data are not consistent with the new LISM velocity vector from IBEX. In contrast, IBEX data, in principle, could be explained with the LISM velocity vector derived from the Ulysses data. This is possible for the models with the interstellar temperature increased from 6300 K to 9000 K. There is a need to perform further study of possible reasons for the broadening of the helium signal core measured by IBEX. This could be an instrumental effect or due to unconsidered physical processes.

astro-ph.SR↗

arXiv2011

Spectral properties of backscattered solar Ly-alpha radiation in the heliosphere: a theoretical search of the heliospheric boundaries effects

We explore imprints of the solar wind interaction with the local interstellar medium on spectral properties of the backscattered solar Ly-alpha radiation. We employ newly developed effective model for the interstellar H atom velocity distribution function in the heliosphere (Katushkina and Izmodenov 2010, 2011). This model takes into account both global effects of H atom perturbations at the heliospheric boundaries and local (i.e. within 10-20 AU from the Sun) effects of the solar ionization, charge exchange, solar gravitation and radiation pressure. Backscattered solar Ly-alpha profiles and their zero, first and second moments were computed at 1 AU for the anti-solar directions of line-of-sight. Then the moments are compared with the moments calculated by using more simplified one-component and two-component hot models. The comparison shows that the Ly-alpha intensities calculated in the frame of new model are somewhat smaller than those calculated by means of the simplified models. Small differences in the first moment (i.e. line-shift) are also observed in the downwind direction. The largest difference between new model and hot models is seen in the second moment of the backscattered Ly-alpha profile. This moment is also called as line-of-sight temperature or line-width of the backscattered spectra. The spectral width depends on the width of the H atom velocity distribution function within few AU from the Sun. We show that the line-widths calculated on the basis of the our model is qualitatively different from those of simplified models.

astro-ph.SR↗

arXiv2007

Dependence of Heliospheric Lyman-alpha Absorption on the Interstellar Magnetic Field

We use newly developed 3D kinetic MHD models of the heliosphere to predict heliospheric H I Lyman-alpha absorption for various lines of sight. These predictions are compared with actual Lyman-alpha spectra from the Hubble Space Telescope, many of which have yielded previous detections of heliospheric absorption. We find that the absorption predicted by the models is weakly affected by both the magnitude and orientation of the assumed ISM magnetic field. Models with B=1.25-2.5 micro-Gauss and an angle of alpha=15-45 deg with respect to the upwind direction of the ISM flow generally provide the best fits to the data, but the sensitivity of the Lyman-alpha absorption to many model input parameters makes it difficult to fully characterize the region of parameter space allowed by the data. We also use the models to assess the degree to which heliospheric asymmetries induced by the ISM field should be apparent in Lyman-alpha absorption. An ISM field that is skewed with respect to the ISM flow vector results in substantial azimuthal asymmetries in both the hydrogen wall and heliosheath, but only the heliosheath asymmetries yield potentially detectable asymmetries in Lyman-alpha absorption; and then only in downwind directions, where comparison with the data is complicated by few actual absorption detections and an insufficient model grid extent.

astro-ph↗

arXiv2006

Lyman-alpha Absorption from Heliosheath Neutrals

We assess what information HST observations of stellar Ly-alpha lines can provide on the heliosheath, the region of the heliosphere between the termination shock and heliopause. To search for evidence of heliosheath absorption, we conduct a systematic inspection of stellar Ly-alpha lines reconstructed after correcting for ISM absorption (and heliospheric/astrospheric absorption, if present). Most of the stellar lines are well centered on the stellar radial velocity, as expected, but the three lines of sight with the most downwind orientations relative to the ISM flow (Chi1 Ori, HD 28205, and HD 28568) have significantly blueshifted Ly-alpha lines. Since it is in downwind directions where heliosheath absorption should be strongest, the blueshifts are almost certainly caused by previously undetected heliosheath absorption. We make an initial comparison between the heliosheath absorption and the predictions of a pair of heliospheric models. A model with a complex multi-component treatment of plasma within the heliosphere predicts less absorption than a model with a simple single-fluid treatment, which leads to better agreement with the data. Finally, we find that nonplanetary energetic neutral atom (ENA) fluxes measured by the ASPERA-3 instrument on board Mars Express, which have been interpreted as being from the heliosheath, are probably too high to be consistent with the relative lack of heliosheath absorption seen by HST. This would argue for a local interplanetary source for these ENAs instead of a heliosheath source.

astro-ph↗

arXiv2003

Model of the tail region of the heliospheric interface

Physical processes in the tail of the solar wind interaction region with the partially ionized local interstellar medium are investigated in a framework of the self-consistent kinetic-gas dynamic model. It is shown that the charge exchange process of the hydrogen atoms with the plasma protons results in suppression of the gas dynamic instabilities and disappearance the contact discontinuity at sufficiently (~3000 AU) large distances from the Sun. The solar wind plasma temperature decreases and, ultimately, the parameters of the plasma and hydrogen atoms approach to the corresponding parameters of the unperturbed interstellar medium at large heliocentric distances.

astro-ph↗

arXiv2002

Models of the Solar Wind Interaction with Local Interstellar Cloud

This paper reviews the theoretical approaches and existing models of the solar wind interaction with the Local Interstellar Cloud (LIC). Models discussed take into account the multi-component nature of the solar wind and local interstellar medium. Basic results of the modeling and their possible applications to interpretation of space experiments are summarized. Open questions of global modeling of the solar wind/LIC interaction and future perspectives are discussed.

astro-ph↗