Title: 

What is (are) the total D/H ratio(s) within 1 kpc of the Sun?



Jeffrey Linsky
JILA/University of Colorado
Boulder, CO

Abstract:

      Analyses of spectra obtained with FUSE, together with previous
Copernicus and IMAPS spectrometer observations, reveal a very wide range
in the deuterium/hydrogen (D/H) ratios for interstellar gas in the
Galactic disk within 1 kpc of the Sun. This result is very difficult to
explain only on the basis of nuclear processes in stars that convert
deuterium to 3He and 4He and the infall of deuterium rich gas from the
Galactic halo and the intergalactic medium, because the D/H ratio
differs greatly on very short spatial scales. We argue instead that
spatial variations in the depletion of deuterium onto dust grains can
explain these local variations in the gas phase D/H ratios. The D/H
measurements appear to fall into three regimes depending on the line of
sight hydrogen column density. Our dynamic deuterium depletion model
naturally explains the constant D/H measurements for the local Bubble
(log N(HI) < 19.2), the wide range of gas phase D/H ratios found in the
intermediate regime (log N(HI) = 19.2-20.5), and the low gas phase D/H
ratios at larger hydrogen column densities. We argue that the most
representative value for the total (gas plus dust) D/H ratio within 1
kpc of the Sun is 23 +/- 4 ppm (parts per million), which constrains
Galactic chemical evolution models to have small deuterium astration
rates.