Lyman Alpha intensities in a polar coronal hole from a 2-D model

We simulate the coronal H I Lyman alpha intensity for heliocentric distances between 1.5 and 2.5 R&unknown;, and latitudes between 90o (North pole) and 30o, making use of a 2D semiempirical coronal hole model. Observations are made with the UltraViolet Coronagraph Spectrometer (UVCS) on board the ESA-NASA solar satellite SOHO (SOlar and Heliospheric Observatory). Model electron densities are derived from the collisional part of the O VI lambda1037.6 Å line and the proton outflow speed is calculated from mass flux conservation along the magnetic field lines. The expansion factor and the direction of the magnetic flux tubes have been derived by adopting a simple analytical magnetic field configuration. The intensities of the Ly alpha line predicted by the model are compared with the observed intensities.