J/MNRAS/431/3240 Ji photometry of WTS 19g-4-02069 (Nefs+, 2013)
A highly unequal-mass eclipsing M-dwarf binary in the WFCAM Transit Survey.
Nefs S.V., Birkby J.L., Snellen I.A.G., Hodgkin S.T., Sipocz B.M.,
Kovacs G., Mislis D., Pinfield D.J., Martin E.L.
<Mon. Not. R. Astron. Soc., 431, 3240-3257 (2013)>
=2013MNRAS.431.3240N 2013MNRAS.431.3240N
ADC_Keywords: Binaries, eclipsing ; Photometry
Keywords: binaries: eclipsing - stars: low-mass - stars: starspots
Abstract:
Star formation theory predicts that short-period M-dwarf binaries
with highly unequal-mass components are rare. First, the mass ratio
of close binary systems is driven to unity due to the secondary
preferentially accreting gas with high angular momentum. Secondly,
both dynamical decay of multiple systems and interactions with
tertiary stars that tighten the binary orbit will eject the lowest
mass member. Generally, only the two most massive stars are paired
after such interactions, and the frequency of tight unequal-mass
binaries is expected to decrease steeply with primary mass. In this
paper, we present the discovery of a highly unequal-mass eclipsing
M-dwarf binary, providing a unique constraint on binary star formation
theory and on evolutionary models for low-mass binary stars. The
binary is discovered using high-precision infrared light curves from
the United Kingdom Infrared Telescope (UKIRT) Wide Field Camera
(WFCAM) Transit Survey and has an orbital period of 2.44d. We find
stellar masses of M1=0.53(±0.02)M☉ and
M2=0.143(±0.006)M☉ (mass ratio 0.27), and radii of
R1=0.51(±0.01)R☉ and R2=0.174(±0.006)R☉. This puts
the companion in a very sparsely sampled and important late M-dwarf
mass regime. Since both stars will share the same age and metallicity
and straddle the theoretical boundary between fully and partially
convective stellar interiors, a comparison can be made to model
predictions over a large range of M-dwarf masses using the same model
isochrone. Both stars appear to have a slightly inflated radius
compared to 1Gyr` model predictions for their masses, but future work
is needed to properly account for the effects of star spots on the
light-curve solution. A significant, subsynchronous, ∼2.56d signal
with ∼2% peak-to-peak amplitude is detected in the WFCAM light
curve, which we attribute to rotational modulation of cool star spots.
We propose that the subsynchronous rotation is either due to a stable
star-spot complex at high latitude on the (magnetically active)
primary (i.e. differential rotation), or additional magnetic braking,
or interaction of the binary with a third body or circumbinary disc
during its pre-main-sequence phase.
Description:
The WFCAM Transit Survey (WTS), in operation since 2007 August on the
UKIRT Wide Field Camera (WFCAM), is awarded 200 nights of observing
time on UKIRT.
We obtain follow-up photometric observations in the Sloan i band on
the 2.5m Isaac Newton Telescope (INT) on La Palma, using the Wide
Field Camera (WFC), to refine our best-fitting light-curve solution
from the WFCAM J-band survey data. The observations are part of a
wider WTS follow-up campaign to confirm planetary transit candidates,
between 2010 July 18 and August 01, leaving a few windows to observe
binary eclipses.
Objects:
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RA (2000) DE Designation(s)
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19 35 03.55 +36 31 16.4 WTS 19g-4-02069 = SDSS J193503.55+363116.4
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2a.dat 26 1143 UKIRT Wide Field Camera Transit Survey (WTS)
J-band photometry of binary WTS 19g-4-02069
table2b.dat 30 135 Isaac Newton Telescope (INT) i-band differential
follow-u photometry of WTS 19g-4-02069
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Byte-by-byte Description of file: table2a.dat
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Bytes Format Units Label Explanations
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1- 11 F11.6 d HJD Heliocentric Julian date (HJD-2454000)
13- 19 F7.4 mag Jmag WTS J magnitude (1)
21- 26 F6.4 mag e_Jmag rms uncertainty on JWTS (2)
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Note (1): Quoted magnitudes in the WFCAM system can be converted to other
photometric systems as described in Hodgkin et al. (2009MNRAS.394..675H 2009MNRAS.394..675H).
Note (2): The J-band errors are estimated using a noise model including Poisson
noise, sky noise, readout noise and errors in the background estimation.
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Byte-by-byte Description of file: table2b.dat
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Bytes Format Units Label Explanations
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1 A1 --- Event [ps] primary or secondary eclipse
3- 13 F11.6 d HJD Heliocentric Julian date (HJD-2454000)
15- 22 F8.5 mag Dimag Differential INT i magnitude
24- 30 F7.5 mag e_Dimag rms uncertainty on Dimag
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 18-Jun-2014