Charting the interstellar magnetic field causing the interstellar boundary explorer (IBEX) ribbon of energetic neutral atoms

Journal Article · Tue Dec 01 04:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/814/2/112· OSTI ID:22882367

Frisch, P. C. ^[1]; Berdyugin, A.; Piirola, V. ^[2]; Magalhaes, A. M.; Seriacopi, D. B. ^[3]; Wiktorowicz, S. J. ^[4]; Andersson, B-G ^[5]; Funsten, H. O. ^[6]; McComas, D. J. ^[7]; Schwadron, N. A. ^[8]; Slavin, J. D. ^[9]; Hanson, A. J. ^[10]; Fu, C. -W. ^[11]

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1. Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States)
2. Finnish Centre for Astronomy with ESO, University of Turku (Finland)
3. Inst. de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo (Brazil)
4. Department of Astronomy, University of California at Santa Cruz, Santa Cruz, CA (United States)
5. SOFIA Science Center, USRA, Moffett Field, CA (United States)
6. Los Alamos National Laboratory, Los Alamos, NM (United States)
7. Southwest Research Institute, San Antonio, TX (United States)
8. Space Science Center, University of New Hampshire (United States)
9. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
10. School of Informatics and Computing, Indiana University, Bloomington, IN (United States)
11. School of Computer Engineering, Nanyang Technological University (Singapore)

The interstellar magnetic field (ISMF) near the heliosphere is a fundamental component of the solar galactic environment that can only be studied using polarized starlight. The results of an ongoing survey of the linear polarizations of local stars are analyzed with the goal of linking the ISMF that shapes the heliosphere to the nearby field in interstellar space. We present new results on the direction of the magnetic field within 40 pc obtained from analyzing polarization data using a merit function that determines the field direction that provides the best fit to the polarization data. Multiple magnetic components are identified, including a dominant interstellar field, B{sub POL}, that is aligned with the direction ℓ, b = 36.°2, 49.°0 (±16.°0). Stars tracing B{sub POL} have the same mean distance as stars that do not trace B{sub POL}, but show weaker average polarizations consistent with a smaller column density of polarizing material. B{sub POL} is aligned with the ISMF traced by the IBEX Ribbon to within 7.6{sub −7.6}{sup +14.9} degrees. The variations in the polarization position angle directions derived from the data that best match B{sub POL} indicate a low level of magnetic turbulence, ∼9° ± 1°. The direction of B{sub POL} is obtained after excluding polarization data tracing a separate magnetic structure that appears to be associated with interstellar dust deflected around the heliosphere. The velocities of local interstellar clouds relative to the Local Standard of Rest (LSR) increase with the angles between the LSR velocities and B{sub POL}, indicating that the kinematics of local interstellar material is ordered by the ISMF. The Loop I superbubble that extends close to the Sun contains dust that reddens starlight and whose distance is determined by the color excess E(B − V) of starlight. Polarizations caused by grains aligned with respect to B{sub POL} are consistent with the location of the Sun in the rim of the Loop I superbubble. An angle of 76.8{sub −27.6}{sup +23.5} between B{sub POL} and the bulk LSR velocity the local interstellar material indicates a geometry that is consistent with an expanding superbubble. The efficiency of grain alignment in the local interstellar medium has been assessed using stars where both polarization data and hydrogen column density data are available. Nearby stars appear to have larger polarizations than expected based on reddened sightlines, which is consistent with previous results, but uncertainties are large. Optical polarization and color excess E(B − V) data indicate the presence of nearby interstellar dust in the BICEP2 field. Color excess E(B − V) indicates an optical extinction of A{sub V} > 0.6 in the BICEP2 field, while the polarization data indicate that A{sub V} > 0.09 mag. The IBEX Ribbon ISMF extends to the boundaries of the BICEP2 region.

• OSTI ID: 22882367
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 814; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ATOMS
COSMIC DUST
DISTANCE
HELIOSPHERE
HYDROGEN
INTERSTELLAR MAGNETIC FIELDS
INTERSTELLAR SPACE
POLARIZATION
TURBULENCE
VELOCITY