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

Data on molecular CO in absorbing gas towards X Per, from the International Ultraviolet Explorer (IUE) and the echelle mode of the Goddard High Resolu tion 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) x 10(16) cm(-2)] is determined by the approximation of observed GHRS high-resolution spectra. The result is repeated using equival ent widths of CO bands (the IUE and GHRS data). The cloud pressure (Pk appr oximate to 2500 +/- 500 K cm(-3)) and full width at half-maximum (FWHM) of the line profile of the cloud (Delta V = 1.6 +/- 0.2 km s(-1)) are obtained by approximation of GHRS spectra. Synthetic spectra are created and compar ed with GHRS spectra. The data show that the cloud has more complex structu re, and at least a two-component approximation should be used to obtain mor e accurate results.