ORFEUS II echelle spectra: deuterium and molecular hydrogen in the ISM towards BD +39 3226

Abstract

In ORFEUS II spectra of the sdO star BD +39 3226 interstellar hydrogen and deuterium is detected. >From Ly alpha profile fitting and a curve of growth analysis of the Lyman series of H I and D I we derive the column densities N_H = 1.20^{+0.28}_-0.22}{*10{20} cm^-2 and N_D = 1.45^{+0.50}_-0.38}{*10{15} cm^-2. >From the analysis of metal absorption lines in ORFEUS and IUE spectra we obtain column densities for 11 elements. In addition, we examine absorption lines of H_2 for rotational excitation states up to J=7. We find an H_2 ortho-to-para ratio of 2.5, the fractional abundance of molecular hydrogen has a low value of log f=-4.08 for a total amount of N(H_2)=4.8^{+2.0}_-1.6}{*10{15}cm^{- 2}. The column densities of the excitation states reveal a moderate Boltzmann excitation temperature of 130 K and an equivalent excitation temperature for the excited upper states due to UV pumping of <1800 K. Based on data obtained under the DARA ORFEUS guest observer programme