J/AJ/158/88 Oscillations in KOI-976's Kepler photometry (Ahlers+, 2019)
Dealing with δ-Scuti variables: transit light curve analysis of planets
orbiting rapidly rotating, seismically active A/F stars.
Ahlers J.P., Barnes J.W., Myers S.A.
<Astron. J., 158, 88-88 (2019)>
=2019AJ....158...88A 2019AJ....158...88A (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, eclipsing ; Stars, variable ; Photometry ; Models
Keywords: planets and satellites: detection -
planets and satellites: fundamental parameters -
stars: variables: delta Scuti
Abstract:
We measure the bulk system parameters of the seismically active,
rapidly rotating δ-Scuti KOI-976 and constrain the orbit geometry
of its transiting binary companion using a combined approach of
asteroseismology and gravity-darkening light curve analysis. KOI-976
is a 1.62±0.2 M☉ star with a measured v sin(i) of 120±2 km/s
and seismically induced variable signal that varies by ∼0.6% of the star's
total photometric brightness. We take advantage of the star's oblate shape
and seismic activity to perform three measurements of its obliquity angle
relative to the plane of the sky. We first apply a rotational splitting
theory to the star's variable signal observed in short-cadence Kepler
photometry to constrain KOI-976's obliquity angle, and then subtract off
variability from that data set using the linear algorithm for significance
reduction software LASR. We perform gravity-darkened fits to Kepler
variability-subtracted short-cadence photometry and to Kepler's
phase-folded long-cadence photometry to obtain two more measurements of
the star's obliquity. We find that the binary system transits in a grazing
configuration with measured obliquity values of 36°±17°,
46°±16°, and 43°±20°, respectively, for the three
measurements. We perform these analyses as a way to demonstrate overcoming
the challenges high-mass stars can present to transit light curve fitting
and to prepare for the large number of exoplanets that the Transiting
Exoplanet Survey Satellite will discover orbiting A/F stars.
Description:
In this work, we choose the δ-Scuti KOI-976 - KIC 3441784 - as
our target system for analysis. The Exoplanet Follow-up Observing Program
(ExoFOP) lists this system as an eclipsing binary consisting of an F0 star
and an M-dwarf companion. The F0 star (hereafter called the primary star)
is rotating rapidly with an ExoFOP-reported v sin(i) of 120 km/s and
seismically induced amplitude variations of ∼3.0 mmag.
This work includes a four-stage analysis of KOI-976, observed by Kepler.
We first measure the primary star's obliquity angle and rotation rate
by applying asteroseismic theory to KOI-976's seismically active
out-of-transit photometry. We then subtract out stellar variability
from KOI-976's short-cadence transit event to prepare the data set for
further analysis. Finally, we perform a joint analysis of both the
long-cadence and short-cadence Kepler transit light curves using a
gravity-darkened model to measure bulk parameters of the system and to
test the validity of variability subtraction as a path for cleaning
transit light curves.
Objects:
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RA (ICRS) DE Designation(s)
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19 23 46.65 +38 32 19.9 KOI-976 = BD+38 3569
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 103 204 The best-fit frequencies, amplitudes, and phases
of 204 statistically significant oscillations
in KOI-976's short-cadence Kepler photometry
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See also:
J/AJ/142/160 : Kepler Mission. II. Eclipsing binaries in DR2
(Slawson+, 2011)
J/ApJS/197/2 : Transit timing observations from Kepler. I. (Ford+, 2011)
J/MNRAS/474/4322 : Orbital parameters of 341 new binaries (Murphy+, 2018)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Num [1/204] Oscillation number (1)
5- 12 F8.4 uHz Freq [0.23/500.264] Frequency
14- 19 F6.4 uHz e_Freq [0.0002/0.14] Uncertainty in Freq
21- 25 F5.3 10-3ppm Amp [0.022/2.778] Amplitude
27- 31 F5.3 10-3ppm e_Amp [0.004/0.03] Uncertainty in Amp
33- 38 F6.3 --- Phase [0/40] Phase
40- 44 F5.3 --- e_Phase [0.003/0.4] Uncertainty in Phase
46-103 A58 --- Comb Combination frequency
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Note (1): We subtract each oscillation using the Linear Algorithm for
Significance Reduction (LASR) and calculate uncertainties following
Ahlers et al. (2018A&A...615A.128A 2018A&A...615A.128A). We also identify possible combination
frequencies of the six highest amplitude frequencies and the rotation
frequency. We find that 160 out of 204 total oscillations match combination
values of KOI-976's dominant modes of oscillation and identified rotation
frequency. All predicted combinations are within 1σ of their observed
values, with the average uncertainty of all combinations below 0.5σ.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 09-Oct-2019