  We present a new method to model a HST/COS spectrum, aimed to analyze
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 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 fit the COS spectrum. Three intrinsic absorbers outflowing with
velocities ~500 km/s 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 Lyman alpha. Their outflow velocities,
ionization states and column densities are consistent with the lowest and
moderately ionization warm absorbers (WAs) in the X-ray domain found by Chandra
observations, suggesting an one-to-one correspondence between the absorbing gas
in the UV and X-ray bands. The small turbulent velocities of the WAs
(v_turb~<100 km/s) 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 ~65% 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 modeling of the broad line emission suggests a higher
covering fraction of clouds when they are very closer to the black hole.
