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Title: INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE

Abstract

This paper presents a three-dimensional analytical solution, in the limit of very low plasma beta-ratio, for the distortion of the interstellar magnetic field surrounding the heliopause. The solution is obtained using a line dipole method that is the integration of point dipole along a semi-infinite line; it represents the magnetic field caused by the presence of the heliopause. The solution allows the variation of the undisturbed magnetic field at any inclination angle. The heliosphere is considered as having blunt-nosed geometry on the upwind side and it asymptotically approaches a cylindrical geometry having an open exit for the continuous outflow of the solar wind on the downwind side. The heliopause is treated as a magnetohydrodynamic tangential discontinuity; the interstellar magnetic field lines at the boundary are tangential to the heliopause. The interstellar magnetic field is substantially distorted due to the presence of the heliopause. The solution shows the draping of the field lines around the heliopause. The magnetic field strength varies substantially near the surface of the heliopause. The effect on the magnetic field due to the presence of the heliopause penetrates very deep into the interstellar space; the depth of penetration is of the same order of magnitude as themore » scale length of the heliosphere.« less

Authors:
 [1]
  1. Catholic University of America, Washington, DC 20064 (United States)
Publication Date:
OSTI Identifier:
21394465
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 710; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/710/2/936
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANALYTICAL SOLUTION; DIPOLES; GEOMETRY; HELIOSPHERE; INCLINATION; INTERSTELLAR MAGNETIC FIELDS; INTERSTELLAR SPACE; SOLAR WIND; ATMOSPHERES; MAGNETIC FIELDS; MATHEMATICAL SOLUTIONS; MATHEMATICS; MULTIPOLES; SOLAR ACTIVITY; SOLAR ATMOSPHERE; SPACE; STELLAR ACTIVITY; STELLAR ATMOSPHERES; STELLAR WINDS

Citation Formats

Whang, Y. C., E-mail: whang@cua.ed. INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE. United States: N. p., 2010. Web. doi:10.1088/0004-637X/710/2/936.
Whang, Y. C., E-mail: whang@cua.ed. INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE. United States. doi:10.1088/0004-637X/710/2/936.
Whang, Y. C., E-mail: whang@cua.ed. 2010. "INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE". United States. doi:10.1088/0004-637X/710/2/936.
@article{osti_21394465,
title = {INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE},
author = {Whang, Y. C., E-mail: whang@cua.ed},
abstractNote = {This paper presents a three-dimensional analytical solution, in the limit of very low plasma beta-ratio, for the distortion of the interstellar magnetic field surrounding the heliopause. The solution is obtained using a line dipole method that is the integration of point dipole along a semi-infinite line; it represents the magnetic field caused by the presence of the heliopause. The solution allows the variation of the undisturbed magnetic field at any inclination angle. The heliosphere is considered as having blunt-nosed geometry on the upwind side and it asymptotically approaches a cylindrical geometry having an open exit for the continuous outflow of the solar wind on the downwind side. The heliopause is treated as a magnetohydrodynamic tangential discontinuity; the interstellar magnetic field lines at the boundary are tangential to the heliopause. The interstellar magnetic field is substantially distorted due to the presence of the heliopause. The solution shows the draping of the field lines around the heliopause. The magnetic field strength varies substantially near the surface of the heliopause. The effect on the magnetic field due to the presence of the heliopause penetrates very deep into the interstellar space; the depth of penetration is of the same order of magnitude as the scale length of the heliosphere.},
doi = {10.1088/0004-637X/710/2/936},
journal = {Astrophysical Journal},
number = 2,
volume = 710,
place = {United States},
year = 2010,
month = 2
}
  • As the local interstellar plasma flows past our heliosphere, it is slowed and deflected around the magnetic obstacle of the heliopause. The interstellar magnetic field, frozen into this plasma, then becomes draped around the heliopause in a characteristic manner. We derive the analytical solution for this draped magnetic field in the limit of weak field intensity, assuming an ideal potential flow around the heliopause, which we model as a Rankine half-body. We compare the structure of the model magnetic field with observed properties of the Interstellar Boundary Explorer (IBEX) ribbon and with in situ observations at the Voyager 1 spacecraft. Wemore » find reasonable qualitative agreement, given the idealizations of the model. This agreement lends support to the secondary ENA model of the IBEX ribbon and to the interpretation that Voyager 1 has crossed the heliopause. We also predict that the magnetic field measured by Voyager 2 after it crosses the heliopause will not be significantly rotated away from the direction of the undisturbed interstellar field.« less
  • The combination of the Interstellar Boundary Explorer (IBEX) all-sky maps of the energetic neutral atom (ENA) fluxes with the Voyager in situ measurements provides a unique opportunity to learn about the physics governing the solar wind interaction with the local interstellar medium. The first IBEX results revealed a sky-spanning 'ribbon' of unexpectedly intense emissions of ENAs that had not been predicted previously by any physical model. A number of explanations were proposed to explain the IBEX ribbon, some of them associated with the distribution of the interstellar magnetic field (ISMF) coupled with the interplanetary magnetic field at the heliopause. Themore » position of the ribbon in the sky correlates with the line-of-sight directions perpendicular to the modeled ISMF. In this paper, we analyze such distributions for a variety of ISMF strengths and directions in order to reveal the topology of the surface that may potentially contain the ENA sources creating the ribbon. We also analyze the distributions of total pressure exerted on the heliopause as a result of its draping by the ISMF. The effects of solar cycle variations on the ribbon topology are discussed.« less
  • Voyager 1 (V1) was beyond the heliopause between 2013.00 and 2014.41, where it was making in situ observations of the interstellar magnetic field (ISMF). The average azimuthal angle and elevation angle of the magnetic field B were (λ) = 292.°5 ± 1.°4 and (δ) = 22.°1 ± 1.°2, respectively. The angles λ and δ varied linearly at (1.°4 ± 0.°1) yr{sup –1} and (–1.°1 ± 0.°1) yr{sup –1}, respectively, suggesting that V1 was measuring the draped ISMF around the heliopause. The distributions of hourly averages of λ and δ were Gaussian distributions, with most probable values 292.°5 and 22.°1, andmore » standard deviations (SDs) 1.°3 and 1.°1, respectively. The small SD indicates little or no turbulence transverse to B . An abrupt decrease in B from 0.50 nT on 2013/129.9 to 0.46 nT on 2013/130.6 was observed, possibly associated with a weak reverse shock or magnetoacoustic pressure wave following a burst of electron plasma oscillations. Between 2013/130.6 and 2013/365.3, (B) = 0.464 ± 0.009 nT, (λ) = 292.°6 ± 0.°8, and (δ) = 22.°1 ± 1.°1. The corresponding distribution of hourly averages of B was Gaussian with the most probable value 0.464 nT and σ = 0.009 nT. Since the uncertainty σ corresponds to the instrument and digitization noise, these observations provided an upper limit to the turbulence in the ISMF. The distributions of the hourly increments of B were Gaussian distributions with σ = 0.05 nT, 0.°4, and 0.°4, respectively, indicating that the V1 did not detect evidence of ''intermittent bursts'' of interstellar turbulence.« less
  • Based on the difference between the orientation of the interstellar and the solar magnetic fields, there was an expectation by the community that the magnetic field direction will rotate dramatically across the heliopause (HP). Recently, the Voyager team concluded that Voyager 1 (V1) crossed into interstellar space last year. The question is then why there was no significant rotation in the direction of the magnetic field across the HP. Here we present simulations that reveal that strong rotations in the direction of the magnetic field at the HP at the location of V1 (and Voyager 2) are not expected. The solar magneticmore » field strongly affects the drapping of the interstellar magnetic field (B {sub ISM}) around the HP. B {sub ISM} twists as it approaches the HP and acquires a strong T component (East-West). The strong increase in the T component occurs where the interstellar flow stagnates in front of the HP. At this same location the N component B{sub N} is significantly reduced. Above and below, the neighboring B {sub ISM} lines also twist into the T direction. This behavior occurs for a wide range of orientations of B {sub ISM}. The angle δ = asin (B{sub N} /B) is small (around 10°-20°), as seen in the observations. Only after some significant distance outside the HP is the direction of the interstellar field distinguishably different from that of the Parker spiral.« less
  • The solar wind carves a cavity in the interstellar plasma bounded by a surface, called the heliopause (HP), that separates the plasma and magnetic field of solar origin from those of interstellar origin. It is now generally accepted that in 2012 August Voyager 1 (V1) crossed that boundary. Unexpectedly, the magnetic fields on both sides of the HP, although theoretically independent of each other, were found to be similar in direction. This delayed the identification of the boundary as the HP and led to many alternative explanations. Here, we show that the Voyager 1 observations can be readily explained and,more » after the Interstellar Boundary Explorer (IBEX) discovery of the ribbon, could even have been predicted. Our explanation relies on the fact that the Voyager 1 and undisturbed interstellar field directions (which we assume to be given by the IBEX ribbon center (RC)) share the same heliolatitude (∼34.°5) and are not far separated in longitude (difference ∼27°). Our result confirms that Voyager 1 has indeed crossed the HP and offers the first independent confirmation that the IBEX RC is in fact the direction of the undisturbed interstellar magnetic field. For Voyager 2, we predict that the difference between the inner and outer magnetic field directions at the HP will be significantly larger than that observed by Voyager 1 (∼30° instead of ∼20°), and that the outer field direction will be close to the RC.« less