S320p.20 — Flares in A-type stars?

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Aug 10th at 6:00 PM until 7:30 PM

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Author(s): Victoria Antoci1, May Gade Pedersen1

Institution(s): 1. Stellar Astrophysics Centre, Aarhus University

Recent studies show evidence of flare-like features in 32 Kepler A-type stars which were interpreted to be intrinsic, contradicting theory. Flares in late type stars are generated through the reconnection of magnetic field lines in stellar atmospheres. For magnetic fields to be sufficiently strong to emerge at the surface and form flares a dynamo is required, which is operated by a convective envelope. A-type stars only possess shallow convective envelopes of the order of 1-3% of the total stellar radius and therefore are not expected to support flaring. On the other hand X-ray flares have been observed in early B-type stars. They are produced by stellar wind activity which vanish for late B-type stars.
We re-investigated the light curves of 26 flaring A-type stars setting specific criteria in order to identify these features. Our preliminary results reveal significantly fewer flare candidates than those previously detected even including more data. However, the positively detected flares follow the expected correlation between flare intensity and duration. We investigated the variations in the light curves of one of the stars in detail and found that these variations could be due to spots based on the observed vsini. Currently we are following up on those results and investigating RV data for 3-4 different epochs for the 10 brightest flaring A-type stars. The actual pixel data of the entire sample of flaring A-type stars is likewise being analyzed.