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

We have analysed the latitudinal properties of the profiles of the H I Lyman α line at 1215.6 ˚ A and of the O VI doublet at 1031.9 ˚ A and 1037.6 ˚ A in the extended solar corona, between 1.5 R and 2.0 R. Observations have been performed with the UltraViolet Coronagraph Spectrometer (UVCS) on board the ESA-NASA solar satellite SOHO (SOlar and He-liospheric Observatory). The results show that these lines have quite a different behaviour with latitude: the Ly α line has larger full width at half maximum (FWHM) values in the streamer region and narrower ones towards polar latitudes, while the O VI lines have a minimum FWHM at the center of the streamer, 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 theories 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 different morphological features visible in the Ly α and O VI lines.