Latitudinal properties of the Lyman alpha and O VI profiles in the extended solar corona

We have analysed the latitudinal properties of the profiles of the H I Lyma n a line at 1215.6 Angstrom and of the O VI doublet at 1031.9 Angstrom and 1037.6 Angstrom in the extended solar corona, between 1.5 R. and 2.0 R.. Ob servations have been performed with the Ultra Violet Coronagraph Spectromet er (UVCS) on board the ESA-NASA solar satellite SOHO (SOlar and Heliospheri c Observatory). The results show that these lines have quite a different be haviour with latitude: the Ly ct line has larger full width at half maximum (FWHM) values in the streamer region and narrower ones towards polar latit udes, while the O VI lines have a minimum FWHM at the center of the streame r, which almost steadily increases towards polar regions. The observations have been analysed looking also for an interpretation in terms of selective heating mechanisms. The implications of our results for coronal heating th eories are also examined. In particular we discuss the possibility for the presence of the ion-cyclotron coronal heating mechanism. Moreover, we point out an interesting correlation between the intensity of the coronal lines and their widths, which may be relevant to the open question of the differe nt morphological features visible in the Ly alpha and O VI lines.