Revisiting the solid HDO/H2O abundances

Abstract

We revisit the reported detection and upper limits on HDO in ice mantles present in the molecular cloud environments of the massive young protostars G1 2136 and W33 A, using independent VLT-ISAAC and UKIRT-CGS4 spectroscopic observations. We also present VLT and UKIRT spectra of RAFGL 7009 near the HDO absorption wavelength and reanalyze the ISO-SWS spectral data for NGC 7538 IRS9, Orion-BN and S140. We demonstrate that the previously reported detections of HDO in W33 A and NGC 7538 IRS9 are incorrect. We present an in-depth analysis that shows that, besides the sensitivity limits, detection of low levels of HDO is difficult in amorphous ice mantles when features from solid methanol, a common grain mantle constituent, are present. We discuss the specific problems arising in the ISO data in this wavelength range for NGC 7538 IRS9. Using VLT-ISAAC observations, we also investigate the HDO/H2O ratio toward the intermediate mass stars IRAS 05329-0728 and IRAS 08448-4343. Our derived upper limits for the D/H ratio in water ice range from HDO/H2O < 1% to 0.2% in the different sources, and we discuss these limits in comparison with values derived in other environments.