The I-V phase difference with Magneto-Optical Filters

The phase dierence between the intensity and velocity signals is a powerful diagnostic for the dynamics of the solar atmosphere. The phases are used to quantify the nonadiabatic degree of the acoustic modes and, recently, to infer the characteristics of the source of the solar oscillations. For this reason, the error attributed to the phase obtained from the observations plays an important role in distinguishing between dierent phenomena. In this paper we discuss the results obtained with the systems using a Magneto-Optical Filter. A model to correct for the contamination induced by the velocity in the intensity signal is described and the phases in the sodium D lines presented. We also discuss the dierence between the results obtained when the phase values are computed with a local analysis or when the elle - nu diagram is obtained.