Theoretical Study of the Solar Lyman-Alpha Proffle.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Theoretical Study of the Solar Lyman-Alpha Proffle. Widing, K. G. ; Morton, D. C. Abstract An attempt is made to find a theoretical profile of the solar Lyman-alpha line to account for the one observed with a rocket-borne spectrograph by J. D. Purcell and R. Tousey on July 21, 1959. The emission line and the shallow central reversal are assumed to be formed in the chromosphere, while the deep central absorption is supposed to be formed outside the sun. The analysis is based on the chromospheric theories of Jeffries and Thomas which combine solutions of the statistical equilibrium equation and the transfer equation, without requiring thermodynamic equilibrium. It is assumed that the absorption coefficient has a Doppler profile and that the line is formed by completely noncoherent scattering. As a first approximation, the region of line formation is taken to be isothermal. The depth of the central reversal and the width between the maxima are reproduced by an electron temperature of 1.3X 101~K and a total number of ground-state hydrogen atoms of 3X 10i4 cm~1. However the predicted wings drop much more steeply than the observed ones. For an electron density of 1080 cm~3 the predicted central intensity is 4.4X 10-8 erg sec~i cm~1 sr~1 cps-1 which agrees with the value of 3X 10-8 deduced from the observed profile and measurements of the total Lyman-alpha intensity made during the flight. For a second approximation we represent the Planck function by Bp(T~ =Si(1+Ae-cro), where ro is the optical depth at the center of the line. We neglect the radiative-excitation term relative to the collisional-excitation term. A profile with a central reversal similar to the observed one is obtained for a c of 0.15 and any A between 10~ and 1010. The profile differs little from the one given by the isothermal model, and again the predicted wings drop far too steeply. The central intensity, for an electron density of 1010 cm~18 is 2.1 X 10-~ erg sec-i cm~1 sr~1 cps-i, too large by an order of magnitude. Lowering the electron density to 100 cm~1 will give agreement with the observations. Publication: The Astronomical Journal Pub Date: 1960 DOI: 10.1086/108145 Bibcode: 1960AJ.....65S..58W full text sources ADS |