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

Original · EN

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)*10²0 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 H₂ for rotational excitation states up to J=7. We find an H₂ 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(H₂)=4.8(+2.0/-1.6)*10¹5 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.