Helium and minor ions in the corona and solar wind: Dynamics and charge states

Abstract

A theoretical model of the acceleration region of the solar wind with major species (p, c~, e) and minor ions (e.g., 3He, C, O, Mg, Si) is presented. Observed ne-profiles and the equations of continuity and momentum are used to calculate profiles of T, n, and u for all species, as well as charge states of minor ions. The disagreement of the results of a pure p-e model with observations is discussed in some detail, and it is shown that a model consistent with observations both in the corona and at 1 AU requires a finite abundance of He § +. This model predicts a strong enhancement of He/H in the lower corona. The results for the frozen-in charge states in the p-~-e model are in agreement with measurements in the low speed solar wind, especially for the well determined pair 06+/07+. Finally, a model for a coronal hole is investigated and it is found that wave pressure is necessary to model successfully the observed solar wind speeds and abundances.Although various simplifying assumptions had to be introduced, care was taken to ensure that the model remains physically consistent, i.e., that the same physics is used for the major species as well as the minor ions.

Polar coronal holes during the past solar cycle: Ulysses observations

“…Figure 4 also includes a line of equal temperatures (i.e., T O = T C ), which shows that the freezing-in of C and O does not occur at the same location. Both, C and O charge states are known to freeze in very close to the Sun [Bürgi and Geiss, 1986;Geiss et al, 1995], but C has a shorter recombination time, causing freeze-in to occur at a higher density and therefore closer to the Sun as compared to O. This ordering remains the same for each of the time periods as both T O and T C move to progressively smaller values.…”

“…[11] The distribution of ionic charge states of a given element is determined by collisions with hot electrons in the inner corona where most of the energy deposition and heating of the open corona occurs [Hundhausen et al, 1968;Bürgi and Geiss, 1986]. Upon expansion into the solar wind these ionic charge states are first in equilibrium with the electrons, but then freeze in individually when their total collision timescale with the electrons approximately equals the expansion timescale of the wind.…”

“…Besides its high speed and unique dynamic signatures [Bame et al, 1977], PCHassociated solar winds also exhibit compositional signatures in their heavy-ion components, which distinguish them from other, generally slower and more variable solar wind streams that are associated with streamers and tend to dominate the space environment near the ecliptic plane [Geiss et al, 1995;Zurbuchen, 2007]. The ionization charge states of heavy elements indicate a substantially lower temperature of the solar wind source region, especially for C and O, whose ionization state is defined within the first 1.5 R s above the photosphere [Bürgi and Geiss, 1986]; the elemental composition of heavy ions is nearly photospheric, in contrast to streamer-associated wind, which is enriched in elements with a first ionization potential (FIP) <10 eV [von Steiger et al, 1997].…”

Analysis of Interplanetary Coronal Mass Ejection Parameters as a Function of Energetics, Source Location, and Magnetic Structure

“…Ionic, or charge state, composition is directly related to the electron temperature at the source region, with hotter source material resulting in higher in situ charge states (Hundhausen et al 1968;Buergi & Geiss 1986). Unusually high solar wind charge states (e.g., O +7 /O +6 and Q Fe ) are often associated with ICMEs ( Bame et al 1979;Henke et al 1998Henke et al , 2001Richardson & Cane 2004), indicating that a strong, possibly flare related, heating mechanism (Bame et al 1979;Lepri & Zurbuchen 2004;Reinard 2005a), operates during the CME initiation process.…”

Diffusion Models for Magnetic Ap Stars

“…Is it a cold or hot wind? Is there some analogies with the solar wind and while some elements are trapped in the transition region others are dragged by the wind (Burgi & Geiss 1986) ? Detailed abundance analysis of rare earths could give very precious informations about the wind structure of magnetic stars.…”