The Interstellar Magnetic Field Close to the Sun. Ii.

Abstract

The magnetic field in the local interstellar medium (ISM) provides a key indicator of the galactic environment of the Sun and influences the shape of the heliosphere. We have studied the interstellar magnetic field (ISMF) in the solar vicinity using polarized starlight for stars within 40 pc of the Sun and 90 • of the heliosphere nose. In Frisch et al. (Paper I), we developed a method for determining the local ISMF direction by finding the best match to a group of interstellar polarization position angles obtained toward nearby stars, based on the assumption that the polarization is parallel to the ISMF. In this paper, we extend the analysis by utilizing weighted fits to the position angles and by including new observations acquired for this study. We find that the local ISMF is pointed toward the • 25 pc −1 . This conclusion is conditioned on the small sample of stars available for defining this rotation. Variations from the ordered component suggest a turbulent component of ∼23 • . The ordered component and standard relations between polarization, color excess, and H o column density predict a reasonable increase of N(H) with distance in the local ISM. The similarity of the ISMF directions traced by the polarizations, the IBEX Ribbon, and pulsars inside the Local Bubble in the third galactic quadrant suggest that the ISMF is relatively uniform over spatial scales of 8-200 pc and is more similar to interarm than spiral-arm magnetic fields. The ISMF direction from the polarization data is also consistent with small-scale spatial asymmetries detected in GeV-TeV cosmic rays with a galactic origin. The peculiar geometrical relation found earlier between the cosmic microwave background dipole moment, the heliosphere nose, and the ISMF direction is supported by this study. The interstellar radiation field at ∼975 Å does not appear to play a role in grain alignment for the low-density ISM studied here.

CIRCULARITY OF THEINTERSTELLAR BOUNDARY EXPLORERRIBBON OF ENHANCED ENERGETIC NEUTRAL ATOM (ENA) FLUX

“…The center of the ribbon, which appears to be the fundamental direction that governs the overall structure responsible for the ribbon, lies in the vicinity of the average magnetic field direction between the Sun and nearby stars (Frisch et al 2012). The first three years of IBEX observations have also shown a temporal decrease in the observed ribbon flux (McComas et al 2012c) as well as a heliotail structure through which the ribbon might pass .…”

Cosmic-Ray Small-Scale Anisotropies and Local Turbulent Magnetic Fields

“…Since the MHD simulation can be scaled to an arbitrary injection scale, in this study, two physical scenarios are investigated: an injection scale of L inj =10 pc, which is approximately the magnitude typical of the Milky Way spiral arms, and L inj =100 pc, which is characteristic of the interarm regions (see Section 2). Although the ISM surrounding the solar system seems to have interarm properties (Frisch et al 2012;Frisch 2015), both cases are taken into consideration. Assuming a particle gyroradius of five grid-points (corresponding to the smallest spatial scale in the MHD simulation), the injection scale sets the particle energy scale.…”

The interstellar cloud surrounding the Sun: a new perspective

“…9) the Mg II and Fe II abundances against Galactic longitude, taken as a very approximate indicator for the strength of their 975 Å radiation field, according to Fig. 12 of Frisch et al (2012) that shows that the field increases smoothly from l = 100 • , where it is minimum, to l = 280 • , where it is maximum. With this definition for the field strength (based simply on Δl, not an angular distance from any point on the sky), we still find no correlation.…”