Abstract
For flares to be generated, stars have to have a sufficiently deep outer
convection zone (F5 and later), strong large-scale magnetic fields
(Ap/Bp-type stars) or strong, radiatively driven winds (B5 and earlier).
Normal A-type stars possess none of these and therefore should not
flare. Nevertheless, flares have previously been detected in the Kepler
light curves of 33 A-type stars and interpreted to be intrinsic to the
stars. Here, we present new and detailed analyses of these 33 stars,
imposing very strict criteria for the flare detection. We confirm the
presence of flare-like features in 27 of the 33 A-type stars. A study of
the pixel data and the surrounding field of view reveals that 14 of
these 27 flaring objects have overlapping neighbouring stars and five
stars show clear contamination in the pixel data. We have obtained
high-resolution spectra for 2/3 of the entire sample and confirm that
our targets are indeed A-type stars. Detailed analyses revealed that 11
out of 19 stars with multiple epochs of observations are spectroscopic
binaries. Furthermore, and contrary to previous studies, we find that
the flares can originate from a cooler, unresolved companion. We note
the presence of Hα emission in eight stars. Whether this emission
is circumstellar or magnetic in origin is unknown. In summary, we find
possible alternative explanations for the observed flares for at least
19 of the 33 A-type stars, but find no truly convincing target to
support the hypothesis of flaring A-type stars.
Original language | English |
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Pages (from-to) | 3060-3076 |
Number of pages | 17 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 466 |
Issue number | 3 |
DOIs | |
Publication status | Published - Apr 2017 |
MoE publication type | A1 Journal article-refereed |
Keywords
- stars: activity
- binaries: spectroscopic
- circumstellar matter
- stars: flare
- stars: magnetic field