On the derivation of empirical limits on the helium abundance in coronal holes below 1.5 solar radius

Abstract

view Abstract Citations (13) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Derivation of Empirical Limits on the Helium Abundance in Coronal Holes below 1.5 R sub sun Habbal, Shadia Rifai ; Esser, Ruth Abstract We present a simple technique describing how limits on the helium abundance, alpha, defined as the ratio of helium to proton number density, can be inferred from measurements of the electron density and temperature below 1.5 solar radius. As an illustration, we apply this technique to two different data sets: emission-line intensities in the extreme ultraviolet (EUV) and white-light observations, both measured in polar coronal holes. For the EUV data, the temperature gradient is derived from line intensity ratios, and the density gradient is replaced by the gradient of the line intensity. The lower limit on alpha derived from these data is 0.2-0.3 at 1 solar radius and drops very sharply to interplanetary values of a few percent below 1.06 solar radius. The white-light observations yield density gradients in the inner corona beyond 1.25 solar radius but do not have corresponding temperature gradients. In this case we consider an isothermal atmosphere, and derive an upper limit of 0.2 for alpha. These examples are used to illustrate how this technique could be applicable to the more extensive data to be obtained with the upcoming SOHO mission. Although only ranges on alpha can be derived, the application of the technique to data currently available merely points to the fact that alpha can be significantly large in the inner corona. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/187187 Bibcode: 1994ApJ...421L..59H Keywords: Coronal Holes; Helium Ions; Magnetohydrodynamic Waves; Solar Corona; Solar Wind; Theoretical Physics; Electron Density (Concentration); Instruments; Soho Mission; Solar Orbits; Astrophysics; SUN: SOLAR WIND; SUN: ABUNDANCES; SUN: CORONA full text sources ADS |