Journal
ASTRONOMY & ASTROPHYSICS
Volume 649, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/202140429
Keywords
Sun: atmosphere; Sun: magnetic fields; Sun: photosphere; Sun: oscillations
Categories
Funding
- Research Council of Norway [262622]
- Royal Society [Hooke18b/SCTM, IES/R1/191114, IE/170301]
- Invest NI
- Randox Laboratories Ltd. [059RDEN-1]
- UK Science and Technology Facilities Council (STFC) [ST/T00021X/1]
- Science and Technology Facilities Council (STFC) [ST/V000977/1]
- European Research Council under the European Union [682462]
- Northern Ireland Department for the Economy
- STFC [ST/S000240/1]
- National Science Foundation [1829258]
- Deanship of Scientific Research (DSR), King Faisal University, Al-Hassa, KSA [186354]
- European Union [82135, 814335, 739500]
- MINECO/AEI/FEDER, UE [AYA2017-85465-P]
- European Research Council (ERC) [682462] Funding Source: European Research Council (ERC)
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The study explores an unusual oscillation phenomenon in pores of sunspots, where a dominant frequency of 5 mHz is observed instead of the expected 3 mHz. By analyzing Doppler velocities and spectropolarimetry, researchers have identified distinct ridges in the B-omega diagram that are clear signatures of resonant magneto-hydrodynamic (MHD) oscillations confined within the pore umbra. This novel finding opens up a new avenue for identifying MHD wave modes in the umbral regions of both pores and sunspots.
The umbral regions of sunspots and pores in the solar photosphere are generally dominated by 3 mHz oscillations, which are due to p-modes penetrating the magnetic region. In these locations, wave power is also significantly reduced with respect to the quiet Sun. However, here we study a pore where not only is the power of the oscillations in the umbra comparable to, or even larger than, that of the quiet Sun, but the main dominant frequency is not 3 mHz as expected, but instead 5 mHz. By combining Doppler velocities and spectropolarimetry and analysing the relationship between magnetic field strength and frequency, the resultant B-omega diagram reveals distinct ridges that are remarkably clear signatures of resonant magneto-hydrodynamic (MHD) oscillations confined within the pore umbra. We demonstrate that these modes, in addition to velocity oscillations, are also accompanied by magnetic oscillations, as predicted from MHD theory. The novel technique of B-omega analysis proposed in this article opens up an exciting new avenue for identifying MHD wave modes in the umbral regions of both pores and sunspots.
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