Properties of oscillatory motions in a facular region

¹ Main Astronomical Observatory, NAS, 03680 Kyiv, Ukraine
e-mail: kostik@mao.kiev.ua
² Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain

Received: 25 July 2013
Accepted: 30 September 2013

Abstract

Aims. We study the properties of waves in a facular region of moderate strength in the photosphere and chromosphere. Our aim is to statistically analyse the wave periods, power, and phase relations as a function of the magnetic field strength and inclination.

Methods. 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 Ba ii 4554 Å line to measure velocity and intensity variations through the photosphere and, simultaneously, the Tenerife Infrared Polarimeter (TIP-II), in the Fe i 1.56 μm lines to measure the Stokes parameters and magnetic field strength in the lower photosphere. Additionally, we use the simultaneous broad-band filtergrams in the Ca ii  H line to obtain information about intensity oscillations in the chromosphere.

Results. 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° is detected in the facula. (iii) The most powerful chromospheric Ca ii  H 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 low phase speeds, and temperature–velocity phase shifts between 0° and 90°. (iv) The power of the photospheric velocity oscillations from the Ba ii line increases linearly with decreasing magnetic field inclination, reaching its maximum at strong field locations.