The solar hydrogen Lyman-alpha observation by the TAIYO satellite

The absolute intensity of hydrogen Lyman-alpha (H Ly-α: 1216 A) from the total solar disk is currently monitored by an ion chamber as a part of the satellite mission TAIYO. The apparatus consists of an ion chamber with a special mask and associated electronics. The ion chamber with an MgF2 window and filled with NO gas is sensitive to a narrow spectral band including the H Ly-α line. The special mask serves to keep the angular response of the detector constant at the elevation angle of the sun relative to the plane perpendicular to the spinning axis of the satellite within an error of the order of 1%, when the angle is within +-300. From the currently observed data, the absolute intensity of the solar H Ly-α was estimated as 3.2 x 1011 photons/cm2 sec at 1A.U. and constant within +-4.2% during the period from 24 February to 30 September, 1975. No remarkable correlations with other indices such as F sub(10.7) and Calcium plage indices were observed. The density distribution of hydrogen atoms in the altitude range from about 800 km to 3000 km was obtained. The observed absorption profiles by oxygen molecules agreed with the simulation curves calculated by referring to the CIRA '72 Mean Atmosphere. (author)