Rocket Observation of Interstellar Molecular Hydrogen

Abstract

The Lyman resonance-absorption bands of interstellar molecular hydrogen have been observed in the far-ultraviolet spectrum of the star Persei. The column density of H2 is estimated to be about 1.3x10^20 cm^-2. The column density of interstellar atomic hydrogen, determined from the Lalfa absorption line in the same spectrum, is about 4.2x10^20 cm^-2. Hence, in this line of sight, where visual total extinction by dust is about 1 mag, nearly half of the total hydrogen may be in molecular form. This is in agreemnt with theoretical predictions.