# The Observational Evidence for the Internal Excitation of Sunspot Oscillations Inferred from the Fe I 5435 A Line

## TL;DR

This study provides observational evidence that magnetoconvection within sunspot umbrae, particularly around umbral dots, can internally excite 3-minute oscillations, challenging the view that external p-modes are the primary source.

## Contribution

The paper presents direct observational evidence linking internal magnetoconvection in sunspots to the excitation of umbral oscillations, a connection rarely investigated before.

## Key findings

- Identified 4 coherent oscillation patterns of about 2000 km size.
- Oscillations lasted approximately 7.9 minutes with amplitudes around 0.093 km/s.
- Oscillation power concentrated in the 3-minute band above umbral dots.

## Abstract

The umbral oscillations of velocity are commonly observed in the chromosphere of a sunspot. Their sources are considered to be either the external p-mode driving or the internal excitation by magnetoconvection. Even though the possibility of the p-mode driving has been often considered, the internal excitation has been rarely investigated. We report the identification of the oscillation patterns that may be closely related to the events of internal excitation from the observations of velocity oscillations in the temperature minimum region of two sunspots. The velocities were determined from the spectral data of the Fe I 5435 A line, a magnetically insensitive line, taken with the Fast Imaging Solar Spectrograph of the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. As a result, we identified 4 oscillation patterns of 2.0 * 10^3 km coherent size that were clearly identified for about 7.9 minutes with oscillation amplitude of 9.3 * 10^-2 km/s. The power of the oscillations in these centers was concentrated in the 3 minute band. All the oscillation centers were located above the umbral dots undergoing noticeable morphological and dynamical changes that may be regarded as an observable signature of small-scale magnetoconvection inside the umbrae. Our results support the notion that magnetoconvection associated with umbral dots inside sunspots can drive the 3 minute umbral oscillations.