A new upper limit to the abundance ratio of atomic deuterium to hydrogen in the direction of the galactic centre

Abstract

We report a new upper halt for the strength of the 327 MHz absorption line of deuterium In the direction of the galactic centre. Our observations do not confirm the possible detection of this line reported by Cesarsky et al (1973) and Pasachoff and (1974). We obtain an upper limit of 5.8 × I0^-5 for the atomic D/H ratio by correlating the observed spectrum with the HI absorption spectrum of Sgr A. This limit is comparable to that of Weinreb (1962) of 8 × 10^-5 for the direction of Cas A, and with the direct measurement of the D/H ratio in nearby interstellar clouds from UV observations by the Copernicus satellIte.