UMBRAL DYNAMICS IN THE NEAR-INFRARED CONTINUUM

We detected peaks of oscillatory power at 3 and ∼6.5 minutes in the umbra of the central sunspot of the active region NOAA AR 10707 in data obtained in the near-infrared (NIR) continuum at 1565.7 nm. The NIR data set captured umbral dynamics around 50 km below the τ500 = 1 level. The umbra does not oscillate as a whole, but rather in distinct parts that are distributed over the umbral surface. The most powerful oscillations, close to a period of ∼6.5, do not propagate upward. We noted a plethora of large umbral dots (UDs) that persisted for ≥30 minutes and stayed in the same locations. The peaks of oscillatory power above the detected UDs are located at 3 and 5 minute oscillations, but are very weak in comparison with the oscillations of ∼6.5 minutes.