Measurement of the Cosmological Deuterium to Hydrogen Abundance Ratio (cycle 4, High)

Details Measurement of the Cosmological Deuterium to Hydrogen Abundance Ratio (cycle 4, High) Measurement of the Cosmological Deuterium to Hydrogen Abundance Ratio (cycle 4, High)

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.5488t&link_type=abstract

HST Proposal ID #5488

Mathematics

Logic

Hst Proposal Id #5488 Quasars &Amp, Agn Quasar Absorption

Scientific paper

We propose to directly measure the primordial Deuterium/Hydrogen (D/H) abundance ratio in one QSO absorption system by observing the Lyman Alpha line with the GHRS (G270M). The D/H ratio is in principle the best measure of the cosmological baryon to photon ratio (ETA), which leads to the baryon mass density, a critical parameter which tests the Big Bang model. Solar system and local interstellar measurements of D/H are highly uncertain (factor of 10) because of chemical fractionation, line blending and destruction of D in stars. Selected QSO absorption systems should be free of all these uncertainties, giving a direct, high precision measurement. During the past decade we have been searching for suitable systems, which must have high HI column density N(HI) and extraordinarily low velocity dispersion (b). The one absorption system which we propose to observe is the only one that we know of. It is a Lyman-Alpha forest cloud (primordial gas) with log N(HI)=17.17 +/- 5% towards Q1718+481. If primordial D/H=10(-4), the best guess, our error on D/H would be 30% (+/- 15% on ETA). If D is not detected, our 95% confidence upper limit would be 1.9x10(-5) (barely consistent with corrected local measurements).

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