Properties of oscillatory motions in a facular region

Abstract

We study the properties of waves in a facular region of moderate strength in the photosphere and chromosphere. Our aim is to analyse statistically the wave periods, power and phase relations as a function of the magnetic field strength and inclination. Our work is based on observations obtained at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife) using two different instruments: the Triple Etalon SOlar Spectrometer (TESOS), in the BaII 4554 A line to measure velocity and intensity variations through the photosphere; and, simultaneously, the Tenerife Infrared Polarimeter (TIP-II), in the FeI 1.56 mm lines to the measure the Stokes parameters and magnetic field strength in the lower photosphere. Additionally, we use the simultaneous broad-band filtergrams in the CaIIH line to obtain information about intensity oscillations in the chromosphere. We find several clear trends in the oscillation behaviour: (i) the period of oscillation increases by 15-20 % with the magnetic field increasing from 500 to 1500 G; (ii) the temperature-velocity phase shifts show a strikingly different distribution in the facular region compared to the quiet region, a significant number of cases in the range from -180 to 180 degrees is detected in the facula. (iii) the most powerful chromospheric CaIIH intensity oscillations are observed at locations with strong magnetic fields (1.3-1.5 kG) inclined by 10-12 degrees, as a result of upward propagating waves with rather small phase speeds, and temperature-velocity phase shifts between 0 and 90 degrees; (iv) the power of the photospheric velocity oscillations from the \BaII\ line increases linearly with decreasing magnetic field inclination, reaching its maximum at strong field locations.