[AG Abs.15 P57]

ORFEUS II Echelle Spectra: 
Interstellar Deuterium and Molecular Hydrogen towards BD +39 3226


The FUV echelle spectrum obtained during the ORFEUS II mission in Nov./Dec. 1996
is used to derive H I, D I, H_2, and metal column densities on the line of sight
towards BD +39 3226. This sdO star is located at l=65.00, b=+28.77 in a distance
of about 270 pc. It has a pure helium line spectrum in the optical and some 
additional lines of highly ionized metals in the UV, which are well separated
from the interstellar lines because of the stellar radial velocity of 
v=-273 km/s. A theoretical fit to the Ly alpha line taking into account the
stellar He II line ca. 1.57 A bluewards gives a H I column density of 
1.12(+0.29/-0.23)x10^20 1/cm^2. This value is consistent with a curve-of-growth
analysis of the D and H Lyman series, including Ly delta, epsilon, zeta, and 
kappa, which leads to N(H I)=1.6(+0.9/-0.6)x10^20 1/cm^2 and 
N(D I)=1.45(+0.50/-0.38)x10^15 1/cm^2. Averaging the N(H I) results we derive 
D/H=1.2(+0.5/-0.4)x10^(-5).

We also investigated metal lines in ORFEUS and IUE spectra. Their column 
densities indicate only moderate depletion (<=1.7 dex), in agreement with the
small E(B-V)=0.05 and the low abundance of H_2 
(N(H_2)=4.8(+2.0/-1.6)x10^15 1/cm^2). H_2 is examined for absorption by 
rotational exitation states up to J=7. The column densities of these exitation 
states reveal a H_2 ortho-to-para ratio of 2.5, a Boltzmann excitation
temperature of 130 K and UV-pumping with an equivalent temperature of <1800 K.