Modelling warm absorption in HST/COS spectrum of Mrk 290 with xstar

We present a new method to model an HST/COS (Hubble Space Telescope/Cosmic Origins Spectrograph) spectrum, aimed to analyse intrinsic UV absorption from the outflow of Mrk 290, a Seyfert I galaxy. We use newly updated XSTAR to generate photoionization models for the intrinsic absorption from the active galactic nuclei (AGN) outflow, the line emission from the AGN broad-and narrow-line regions, and the local absorption from high-velocity clouds and Galactic interstellar medium. The combination of these physical models accurately fits the COS spectrum. Three intrinsic absorbers outflowing with velocities similar to 500 km s(-1) are identified, two of which are found directly from two velocity components of the N V and C IV doublets, while the third is required by the extra absorption in the Ly alpha. Their outflow velocities, ionization states and column densities are consistent with the lowest and moderate ionization warm absorbers (WAs) in the X-ray domain found by Chandra observations, suggesting a one-to-one correspondence between the absorbing gas in the UV and X-ray bands. The small turbulent velocities of the WAs (v(turb) less than or similar to 100 km s(-1)) support our previous argument from the X-ray study that the absorbers originate from the inner side of the torus due to thermal evaporation. Given the covering fractions of similar to 65 per cent for the three WAs, we deduce that the lengths and the thicknesses of the WAs are comparable, which indicates that the geometry of WAs are more likely clouds rather than flat and thin layers. In addition, the modelling of the broad-line emission suggests a higher covering fraction of clouds when they are very closer to the black hole.