J/MNRAS/498/2456 Spectroscopic study of Kepler A-type variables (Sikora+, 2020)
A spectroscopic test of the rotational modulation origin of periodic Kepler
photometric variability of A-type stars.
Sikora J., Wade G.A., Rowe J.
<Mon. Not. R. Astron. Soc., 498, 2456-2471 (2020)>
=2020MNRAS.498.2456S 2020MNRAS.498.2456S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, early-type ; Stars, variable ; Milky Way ;
Effective temperatures ; Rotational velocities ;
Stars, diameters ; Stars, masses ; Radial velocities ;
Photometry ; Spectroscopy ; Optical
Keywords: stars: early-type - stars: magnetic - stars: rotation
Abstract:
High-precision space-based photometry obtained by the Kepler and TESS
missions has revealed evidence of rotational modulation associated
with main-sequence (MS) A- and late B-type stars. Generally, such
variability in these objects is attributed to inhomogeneous surface
structures (e.g. chemical spots), which are typically linked to strong
magnetic fields (B≳100G) visible at the surface. It has been reported
that ∼44 per cent of all A-type stars observed during the Kepler
mission exhibit rotationally modulated light curves. This is
surprising considering that =<10 per cent of all MS A-type stars are
known to be strongly magnetic (i.e. they are Ap/Bp stars). We present
a spectroscopic monitoring survey of 44 A- and late B-type stars
reported to exhibit rotational modulation in their Kepler light
curves. The primary goal of this survey is to test the hypothesis that
the variability is rotational modulation by comparing each star's
rotational broadening (vsini) with the equatorial velocities (veq)
inferred from the photometric periods. We searched for chemical
peculiarities and binary companions in order to provide insight into
the origin of the apparent rotational modulation. We find that 14
stars in our sample have vsini>veq and/or have low-mass companions
that may contribute to or be responsible for the observed variability.
Our results suggest that more than 10 per cent of all MS A- and late
B-type stars may exhibit inhomogeneous surface structures; however,
the incidence rate is likely =<30 per cent.
Description:
The photometric variability associated with the 44 stars in our sample
was first reported by Balona (2013MNRAS.431.2240B 2013MNRAS.431.2240B, Cat.
J/MNRAS/431/2240) based on light curves obtained with the Kepler
spacecraft (Borucki et al. 2010Sci...327..977B 2010Sci...327..977B).
All of the Kepler observations used for the 44 stars in this study
were obtained from the Mikulski Archive for Space Telescopes (MAST)
(https://archive.stsci.edu/kepler/) following data release 25. We used
all of the available long cadence light curves (i.e.
Δt=30min), which were taken over a time period of 4yr from
2009 May 2 to 2013 May 11.
The Stokes I spectroscopic measurements presented in this study were
obtained using the ESPaDOnS Echelle spectrograph installed at the 3.6m
CFHT. This instrument has a high spectral resolving power (R∼65000)
and is optimized for a wavelength range of approximately
3600-10000Å. All of the measurements were reduced using the Upena
pipeline feeding the libre-esprit reduction code described by Donati
et al. (1997MNRAS.291..658D 1997MNRAS.291..658D). A total of 319 Stokes I observations
were obtained over a time period spanning ∼11months from 2018 January
31 to 2018 December 21; each of the 44 stars in our sample was
observed between six and nine times.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
spparam.dat 63 44 Various parameters derived from the
spectroscopic observations of the 44 stars in
our sample
hrdparam.dat 95 43 Various fundamental parameters associated with
43 of the 44 stars in our sample with known
distances
rv1.dat 37 282 Radial velocities for those targets with one
stellar component that was identified in the
LSD profiles
rv2.dat 42 16 Radial velocities for those targets with two
stellar components that were identified in the
LSD profiles
rv3.dat 55 21 Radial velocities for those targets with three
stellar components that were identified in the
LSD profiles
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See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
Byte-by-byte Description of file: spparam.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- KIC KIC identifier
10- 14 I5 K Teff Effective temperature
16- 19 I4 K e_Teff Error on Teff
21- 22 A2 --- l_logg [=< ] Limit flag on logg
24- 26 F3.1 [cm/s2] logg Surface gravity
28- 30 F3.1 [cm/s2] e_logg ? Error on logg
32- 33 A2 --- l_[M/H] [=<> ] Limit flag on [M/H]
35- 39 F5.2 [-] [M/H] Metallicity
41- 44 F4.2 [-] e_[M/H] ? Error on [M/H]
46- 48 I3 km/s vsini Projected rotational broadening
50- 52 I3 km/s e_vsini Error on vsini
54- 55 A2 --- l_xi [=< ] Limit flag on vt
57- 59 F3.1 km/s xi ? Microturbulence broadening
61- 63 F3.1 km/s e_xi ? Error on xi
--------------------------------------------------------------------------------
Byte-by-byte Description of file: hrdparam.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- KIC KIC identifier
10- 14 F5.3 mag E(B-V) Reddening
16- 19 F4.2 [K] logTeff Logarithm of the effective temperature
21- 24 F4.2 [K] e_logTeff Error on logTeff
26- 29 F4.2 [Lsun] logL Logarithm of the star luminosity
31- 34 F4.2 [Lsun] e_logL Error on logg
36- 39 F4.2 Rsun R Star radius
41- 44 F4.2 Rsun e_R Error on R
46- 49 F4.2 Msun Mass Star mass
51- 54 F4.2 Msun e_Mass Lower error on Mass
56- 59 F4.2 Msun E_Mass Error on Mass
61- 64 F4.2 [Gyr] logt Logarithm of the absolute age
66- 69 F4.2 [Gyr] e_logt Lower error on logt
71- 74 F4.2 [Gyr] E_logt Upper error on logt
76- 81 F6.4 --- tau Fractional main sequence age
83- 88 F6.4 --- e_tau Lower error on tau
90- 95 F6.4 --- E_tau Upper error on tau
--------------------------------------------------------------------------------
Byte-by-byte Description of file: rv1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- KIC KIC identifier
10- 16 F7.3 d HJD Heliocentric Julian Date (HJD-2458000)
18- 22 F5.1 km/s RVA Radial velocity of the primary component
derived from the spectral fits
24- 27 F4.1 km/s e_RVA Error on RVA
29- 33 F5.1 km/s RVALSD ? Radial velocity of the primary component
derived from the LSD profiles
35- 37 F3.1 km/s e_RVALSD ? Error on RVALSD
--------------------------------------------------------------------------------
Byte-by-byte Description of file: rv2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- KIC KIC identifier
10- 16 F7.3 d HJD Heliocentric Julian Date (HJD-2458000)
18- 20 I3 km/s RVA Radial velocity of the primary component
derived from the spectral fits
22 I1 km/s e_RVA Error on RVA
24- 28 F5.1 km/s RVALSD ? Radial velocity of the primary component
derived from the LSD profiles
30- 32 F3.1 km/s e_RVALSD ? Error on RVALSD
34- 38 F5.1 km/s RVBLSD Radial velocity of the secondary component
derived from the LSD profiles
40- 42 F3.1 km/s e_RVBLSD Error on RVBLSD
--------------------------------------------------------------------------------
Byte-by-byte Description of file: rv3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 I7 --- KIC KIC identifier
9- 15 F7.3 d HJD Heliocentric Julian Date (HJD-2458000)
17- 21 F5.1 km/s RVA Radial velocity of the primary component
derived from the spectral fits
23- 25 F3.1 km/s e_RVA Error on RVA
27- 31 F5.1 km/s RVALSD ? Radial velocity of the primary component
derived from the LSD profiles
33- 35 F3.1 km/s e_RVALSD ? Error on RVALSD
37- 41 F5.1 km/s RVBLSD ? Radial velocity of the secondary component
derived from the LSD profiles
43- 45 F3.1 km/s e_RVBLSD ? Error on RVBLSD
47- 51 F5.1 km/s RVCLSD ? Radial velocity of the tertiary component
derived from the LSD profiles
53- 55 F3.1 km/s e_RVCLSD ? Error on RVCLSD
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 03-Aug-2023