The galactic environment of the Sun

The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun and constrains the physical characteristics of the interplanetary medium. This paper compares interstellar dust grain properties observed within the solar system with dust properties inferred from observations of the cloud surrounding the solar system. Properties of diffuse clouds in the solar vicinity are discussed to gain insight into the properties of the diffuse cloud complex flowing past the Sun. Evidence is presented for changes in the galactic environment of the Sun within the next 10$^4$--10$^6$ years. The combined history of changes in the interstellar environment of the Sun, and solar activity cycles, will be recorded in the variability of the ratio of large- to medium-sized interstellar dust grains deposited onto geologically inert surfaces. Combining data from lunar core samples in the inner and outer solar system will assist in disentangling these two effects.Comment: 30 pages, 2 figures, JGR-Space Physics, in pres

The Heliosphere---Blowing in the Interstellar Wind

Measurements of the velocity of interstellar HeI inside of the heliosphere have been conducted over the past forty years. These historical data suggest that the ecliptic longitude of the direction of the interstellar flow has increased at an average rate of about 0.19 degrees per year over time. Possible astronomical explanations for these short-term variations in the interstellar gas entering the heliosphere are presented.Comment: Accepted for the proceedings of Solar Wind 1

The Solar Galactic Environment

Combined heliosphere-astronomical data and models enrich our understanding both of effects the solar galactic environment might have on the inner heliosphere, and of interstellar clouds. Present data suggest that FeII/DI increases toward the upwind direction of the cluster of interstellar clouds (CLIC) flowing past the Sun. Cloud kinematics and abundances suggest an origin related to a supershell around the Scorpius-Centaurus Association. The solar space trajectory indicates the Sun entered the CLIC gas relatively recently.Comment: 3rd Annual IGPP-UCR Astrophysics Conference: Physics of the Outer Heliosphere [AIP

Tentative Identification of Interstellar Dust in the Nose of the Heliosphere

Observations of the weak polarization of light from nearby stars, reported by Tinbergen (1982), are consistent with polarization by small, radius <0.14 microm, interstellar dust grains entrained in the magnetic wall of the heliosphere. The direction of maximum polarization is offset by ~35 deg from the heliosphere nose, and extends to low ecliptic latitudes. An offset is found between the direction of the best aligned dust grains, and the upwind direction of the undeflected large interstellar grains seen by Ulysses and Galileo. In the aligned-grain region, the strength of polarization anti-correlates with ecliptic latitude, indicating that the magnetic wall is predominantly at negative ecliptic latitudes, which is consistent with predictions of Linde (1998). These data are consistent with an interstellar magnetic field tilt of 60 deg with respect to the ecliptic plane, and parallel to the galactic plane. Interstellar dust grains captured in the heliosheath may also introduce a weak, but important, large scale contaminant for the cosmic microwave background signal with a symmetry consistent with the relative tilts of \Bis and the ecliptic.Comment: Submitted to Astrophysical Journal Letter

Boundary Conditions of the Heliosphere

Radiative transfer equilibrium models of nearby interstellar matter (ISM) yield the boundary conditions of the heliosphere when constrained with observations of ISM inside and outside of the heliosphere. Filtration factors for interstellar neutrals crossing the heliosheath region, from charge exchange with interstellar plasma, are given for H, He, N, O, Ar, and Ne. The best models predict n(HI)~0.2 /cc, n(e)~0.1 /cc, however if the isotropic 2 kHz emission observed by Voyager (Kurth & Gurnett 2003) is formed in the surrounding ISM, an alternate model with lower electron densities is indicated. Observations of nearby ISM, the radiative transfer models, and historical 10Be records provide information on past variations in the galactic environment of the Sun