Oscillations in a sunspot with light bridges

Journal Article · Mon Sep 01 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/792/1/41· OSTI ID:22365204

Yuan, Ding; Su, Jiangtao; Yan, Yihua; Tan, Baolin ^[1]; Nakariakov, Valery M. ^[2]; Huang, Zhenghua; Li, Bo ^[3]

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1. Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)
2. Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)
3. School of Space Science and Physics, Shandong University, Weihai 246209 (China)

The Solar Optical Telescope on board Hinode observed a sunspot (AR 11836) with two light bridges (LBs) on 2013 August 31. We analyzed a two-hour Ca II H emission intensity data set and detected strong five-minute oscillation power on both LBs and in the inner penumbra. The time-distance plot reveals that the five-minute oscillation phase does not vary significantly along the thin bridge, indicating that the oscillations are likely to originate from underneath it. The slit taken along the central axis of the wide LB exhibits a standing wave feature. However, at the center of the wide bridge, the five-minute oscillation power is found to be stronger than at its sides. Moreover, the time-distance plot across the wide bridge exhibits a herringbone pattern that indicates a counter-stream of two running waves, which originated at the bridge's sides. Thus, the five-minute oscillations on the wide bridge also resemble the properties of running penumbral waves. The five-minute oscillations are suppressed in the umbra, while the three-minute oscillations occupy all three cores of the sunspot's umbra, separated by the LBs. The three-minute oscillations were found to be in phase at both sides of the LBs. This may indicate that either LBs do not affect umbral oscillations, or that umbral oscillations at different umbral cores share the same source. It also indicates that LBs are rather shallow objects situated in the upper part of the umbra. We found that umbral flashes (UFs) follow the life cycles of umbral oscillations with much larger amplitudes. They cannot propagate across LBs. UFs dominate the three-minute oscillation power within each core; however, they do not disrupt the phase of umbral oscillation.

• OSTI ID: 22365204
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 792; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AMPLITUDES
CHROMOSPHERE
DISTANCE
EMISSION
LIFE CYCLE
MAGNETOHYDRODYNAMICS
OSCILLATIONS
STANDING WAVES
STREAMS
SUN
SUNSPOTS
TELESCOPES
VISIBLE RADIATION