J/MNRAS/467/1830 Starspots on A stars (Balona, 2017)
Starspots on A stars.
Balona L.A.
<Mon. Not. R. Astron. Soc., 467, 1830-1837 (2017)>
=2017MNRAS.467.1830B 2017MNRAS.467.1830B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, A-type ; Stars, variable
Keywords: stars: rotation - starspots
Abstract:
Rotation modulation of Kepler light curves in mid-A to late-B stars is
shown to be present. This is demonstrated by the high correlation of
projected rotational velocities with photometric frequencies in 30
stars. The time-frequency diagrams show stochastic variations in all
respects similar to those in spotted cool stars. This disposes of any
explanation in terms of binary proximity effects. More than half of
the sample of stars with effective temperatures in the range of
8300-12000K show rotational modulation, indicating that starspots
are the rule rather than the exception among A stars. The periodograms
of a subset of these stars show a characteristic pattern in which a
broad peak is flanked by a sharp peak at a slightly higher frequency.
It is demonstrated that the sharp peak has the same width as the
spectral window, indicating a stable period over the duration of the
4-yr Kepler observations. It is speculated that this might be a
signature of a reflection effect in a non-transiting planet. These
observations suggest that the presence of localized magnetic fields in
A and B stars and that current views of radiative stellar envelopes
need to be revised.
Description:
Visual inspection of the light curves and periodograms of Kepler stars
is used to classify the variability type of stars in the original
Kepler field. Stars with Kepler magnitude Kp<13 and with effective
temperatures in the range 8300-12000K observed in long-cadence mode
during Quarters 0-17 were selected. There are 639 stars observed in
this temperature range. Pre-search data conditioning (PDC) data were
used to construct the periodogram. For stars classified as possible
rotational variables, visual inspection of the time - frequency
diagram was used to estimate the spread in rotational frequency, which
is assumed to be the result of differential rotation. In this table,
the variability type of the stars and the stellar parameters from the
Kepler Input Catalogue (Brown et al., 2011AJ....142..112B 2011AJ....142..112B, Cat.
J/AJ/142/112) are listed. For stars classified as possible rotational
variables, the rotation frequency, estimated frequency spread and
light amplitude is listed. It should be noted that for the great
majority of the rotational variables the frequencies and amplitudes
are variable. The frequency spread may be taken as a general
indication of the frequency variation. For the same reason, the
amplitude listed here is only a general indication of the typical
light amplitude and corresponds to the peak amplitude in the
periodogram at the given frequency. The typical nominal standard
deviation in frequency is approximately 1.0e-4c/d and the nominal
standard deviation in amplitude is about 3 ppm.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 56 639 Results described above
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- KIC Kepler number
10- 17 A8 --- VType Variability type (1)
19- 24 F6.3 mag Kp Kepler magnitude (2)
26- 30 I5 K Teff Effective Temperature (2)
32- 36 F5.3 [cm/s2] logg ? Surface gravity (2)
38- 43 F6.4 d-1 Freq ? Rotational frequency (3)
46- 50 F5.3 d-1 DelFreq ? Frequency spread (3)
52- 56 I5 ppm Amp ? Amplitude (3)
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Note (1): Type of variability as follows:
- = Not variable.
DSCT = Delta Scuti.
ECL = Eclipsing
ELL = Ellipsoidal
GDOR = Gamma Doradus
MAIA = Maia variable
ROT = Rotational variable
ROTD = Peculiar rotational variable
SPB = Slowly pulsating variable
Note (2): These values are from the Kepler Input Catalogue
(Brown et al., 2011AJ....142..112B 2011AJ....142..112B)
Note (3): The rotational frequency, frequency spread and amplitude are only
valid for rotational variables.
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History:
From electronic version of the journal
(End) L. A. Balona [SAA], Patricia Vannier [CDS] 18-Nov-2019