D/H-Ratio: Observations with ORFEUS II

Abstract

During the second flight of the ORFEUS-SPAS satellite (Nov./Dec. 96) high resolution (^ = 10,000) Echelle-spectra of BD+28° 4211 in the wavelength regime 912-1400 A have been taken. Deuterium can be clearly identified in the ORFEUSII Echelle-spectra of this star. For the first time it was possible to take spectra of faint, not redshifted objects in the far ultraviolet with a sufficient spectral resolution to study the deuterium column density in the whole spectral range of the Lyman-series down to the Lyman-limit. We obtained a value of log(N D ) = 14.7 (±0.3) towards BD+28° 4211. The hydrogen column density has been determined using ORFEUS Echelle-and /fZE-spectra of Ly-a (log(Nn) = 19.8 (±0.2)). Thus a value of 8 x 10~6 can be obtained for the D/H-ratio on the line-of-sight towards BD+28° 4211.