[AG Abs.15 P58]

ORFEUS II echelle spectra: 
H_2 towards the northern Galactic pole


We examine the distribution of molecular hydrogen in the local interstellar 
medium towards the northern galactic pole at latitudes b>45°. High resolution 
UV echelle spectra of the nearby sdO stars BD +37 1977 (l=187.1, b=+45.6) and 
HD 128220 (l=19.9, b=+64.9) observed during the ORFEUS II mission are analysed.
Distances for these stars are calculated to be 1030 pc and 440 pc, respectively,
with an error of about 30%.

We determine column densities for H_2 rotational excitation states up to J=7. 
For BD +37 1977 we find a low total H_2 column density of 
2.1(+0.4/-0.2)x10^15 1/cm^2. Probably, the molecular gas is excited by UV 
pumping to an equivalent excitation temperature of T=395(+/-11) K. For HD 128220
the total H_2 column density is 6.5(+3.3/-4.1)x10^17 1/cm^2 in two unresolved 
absorption components. The Boltzmann excitation temperature has a value of 
T=77(+/-10) K. The equivalent temperature of the stages normally excited by UV 
pumping (J=4 to 7), which are only observed in one of the components, is 
T<1500 K.

We further obtain column densities for H I from Lyman profile fitting and for S
and Si. Only 10% or less of the H I seen in absorption is found in H I 21 cm 
spectra. This indicates either gas concentrated in a few (or only one) dense, 
possibly circumstellar clumps, or extended flocculent molecular gas in the 
northern polar disk region of our Galaxy. Assuming pressure equilibrium, a 
layer of flocculent molecular gas at a height z = 80 pc could be possible. For 
that, an analysis of further lines of sight is neccessary.