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Oscillations in stellar superflares

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Balona, L. A., Broomhall, Anne-Marie, Kosovichev, A., Nakariakov, V. M., Pugh, Chloe E. and Van Doorsselaere, Tom (2015) Oscillations in stellar superflares. Monthly Notices of the Royal Astronomical Society, 450 (1). pp. 956-966. doi:10.1093/mnras/stv661 ISSN 0035-8711.

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Official URL: http://dx.doi.org/10.1093/mnras/stv661

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Abstract

Two different mechanisms may act to induce quasi-periodic pulsations (QPP) in whole-disc observations of stellar flares. One mechanism may be magnetohydromagnetic forces and other processes acting on flare loops as seen in the Sun. The other mechanism may be forced local acoustic oscillations due to the high-energy particle impulse generated by the flare (known as ‘sunquakes’ in the Sun). We analyse short-cadence Kepler data of 257 flares in 75 stars to search for QPP in the flare decay branch or post-flare oscillations which may be attributed to either of these two mechanisms. About 18 per cent of stellar flares show a distinct bump in the flare decay branch of unknown origin. The bump does not seem to be a highly damped global oscillation because the periods of the bumps derived from wavelet analysis do not correlate with any stellar parameter. We detected damped oscillations covering several cycles (QPP), in seven flares on five stars. The periods of these oscillations also do not correlate with any stellar parameter, suggesting that these may be a due to flare loop oscillations. We searched for forced global oscillations which might result after a strong flare. To this end, we investigated the behaviour of the amplitudes of solar-like oscillations in eight stars before and after a flare. However, no clear amplitude change could be detected. We also analysed the amplitudes of the self-excited pulsations in two δ Scuti stars and one γ Doradus star before and after a flare. Again, no clear amplitude changes were found. Our conclusions are that a new process needs to be found to explain the high incidence of bumps in stellar flare light curves, that flare loop oscillations may have been detected in a few stars and that no conclusive evidence exists as yet for flare induced global acoustic oscillations (starquakes).

Item Type: Journal Article
Subjects: Q Science > QB Astronomy
Divisions: Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH): Flare stars
Journal or Publication Title: Monthly Notices of the Royal Astronomical Society
Publisher: Oxford University Press
ISSN: 0035-8711
Official Date: 11 June 2015
Dates:
DateEvent
11 June 2015Published
24 March 2015Accepted
24 March 2015Submitted
Volume: 450
Number: 1
Number of Pages: 11
Page Range: pp. 956-966
DOI: 10.1093/mnras/stv661
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Restricted or Subscription Access
Date of first compliant deposit: 25 April 2016
Date of first compliant Open Access: 25 April 2016
Funder: United States. National Aeronautics and Space Administration (NASA), National Research Foundation (South Africa) (NRF), European Research Council (ERC), Science and Technology Facilities Council (Great Britain) (STFC), University of Warwick. Institute of Advanced Study (IAS)
Grant number: NAS5- 26555 (NASA), NNX09AF08G (NASA), 321141 (ERC), ST/L000733/1 (STFC), NNX14AB68G (NASA)

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