J/MNRAS/431/2240 Activity in A-type stars from Kepler (Balona, 2013)
Activity in A-type stars.
Balona L.A.
<Mon. Not. R. Astron. Soc., 431, 2240-2252 (2013)>
=2013MNRAS.431.2240B 2013MNRAS.431.2240B
ADC_Keywords: Stars, A-type ; Stars, variable
Keywords: stars: activity - stars: oscillations - stars: rotation - starspots -
stars: variables: general
Abstract:
Two years of Kepler data are used to investigate low-frequency
variations in A-type stars. In about 875 (40%) A-type stars, the
periodogram shows a simple peak and its harmonic. If we assume that
the photometric period is the period of rotation, we can derive the
equatorial rotational velocity from a suitable radius estimate. It
turns out that the distribution of equatorial velocities derived in
this way is similar to the distribution of equatorial velocities of
A-type main-sequence stars in the general field derived from
spectroscopic line broadening, verifying our initial assumption. We
suggest that the light variation is due to rotational modulation
caused by starspots or some other corotating structure. In many stars
the rotation peak in the periodogram has a characteristic shape which
is not understood. The light amplitudes are highly variable. We deduce
from the amplitude distribution that the sizes of starspots in A-type
stars are similar to the largest sunspots. From the widths of the
peaks in the periodogram we deduce that differential rotation in these
stars is similar to that in the Sun. We find that the period-colour
relationship used for gyrochronology in late-type stars extends to
early F-type and probably late A-type stars as well. Flares in A-type
stars have been recently detected. We add 13 additional A-type flare
stars to this sample, which means that about 1.5% of A-type stars in
the Kepler field show flares. We conclude that A-type stars are active
and, like cooler stars, have starspots and flares.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 47 287 List of A-type δ Sct stars with possible
rotation frequencies
tablea2.dat 47 9 List of A-type γ Dor stars with possible
rotation frequencies
tablea3.dat 47 579 List of A-type rotational variables with possible
rotation frequencies
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
Byte-by-byte Description of file: tablea1.dat tablea2.dat tablea3.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- KIC KIC number (Cat. V/133)
9 A1 --- n_KIC [p] "p" for stars having the characteristic
periodogram described in the main article
11- 16 F6.3 d-1 f0 Rotation frequency
18- 23 F6.3 mmag A0 Amplitude of the frequency
25- 29 F5.1 --- S/N0 Local signal-to-noise (ratio of the amplitude to
mean local background noise in the periodogram)
31- 36 F6.3 mmag A1 Amplitude of first harmonic
38- 42 F5.1 --- S/N1 First harmonic signal-to-noise
44- 47 F4.2 --- sA/A [0/1.5]? Fractional amplitude variation between
quarters (1)
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Note (1): To calculate this, we fitted a truncated Fourier series with
frequencies f0 and its harmonic to individual Kepler quarters. The standard
deviation, sA, of the amplitudes of the fundamental f0 component from
quarter to quarter was calculated, from which sA/A was determined. Missing
values indicate that only data from one or two quarters are available.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 16-Jun-2014