Interstellar CO towards X Persei (HD 24534) — I. One-component model

Abstract

Data on molecular CO in absorbing gas towards X Per, from the International Ultraviolet Explorer (IUE) and the echelle mode of the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope, are reported. A statistical equilibrium model is used to recreate equivalent widths of CO bands and reproduce high-resolution GHRS spectra. The CO column density N(CO)=(1.0±0.2)×1016 cm−2] is determined by the approximation of observed GHRS high-resolution spectra. The result is repeated using equivalent widths of CO bands (the IUE and GHRS data). The cloud pressure (Pk≈2500±500 K cm−3) and full width at half-maximum (FWHM) of the line profile of the cloud (ΔV=1.6±0.2 km s−1) are obtained by approximation of GHRS spectra. Synthetic spectra are created and compared with GHRS spectra. The data show that the cloud has more complex structure, and at least a two-component approximation should be used to obtain more accurate results.