J/AJ/153/231 BVR photometry of EPIC 211957146 (Sriram+, 2017)
A study of the Kepler K2 variable EPIC 211957146 exhibiting a variable
O' Connell effect.
Sriram K., Malu S., Choi C.S., Vivekananda Rao P.
<Astron. J., 153, 231-231 (2017)>
=2017AJ....153..231S 2017AJ....153..231S (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, eclipsing ; Photometry, UBVRI
Keywords: binaries: close - binaries: eclipsing - stars: activity -
stars: evolution - stars: general - stars: individual: EPIC 211957146
Abstract:
We present the multi-band photometric and spectroscopic study of an
over-contact binary system, EPIC211957146. The light curves exhibit a
variable O' Connell effect, confirmed from our observational data and
the Kepler K2 data. The best photometric solution incorporating a dark
spot over the primary component unveils that the system has a low-mass
ratio (q∼0.17) and a high inclination (i∼85°). To confirm the
solution and constrain the uncertainty, Monte-Carlo simulations are
performed and the results are reported. Based on the O-C diagram
analysis, we see that the variable shows a period increase at the rate
of dP/dt∼1.06x10-6days/yr, which is higher than the theoretically
predicted value. Presence of a third body having a period of
∼16.23years is evident from the O-C diagram. No filled-in effect is
observed in the Hα line, while the effect is vividly present in
the Na line. From the Kepler K2 data, we found that the primary and
secondary minima exhibit an anti-correlated O-C variation followed by
an erratic behavior. This is possibly caused by the longitudinal
motion of the spot, and hence, we set a lower limit of ∼40days for the
spot modulation. We also observe a possibly associated photometric
difference in the primary depth by comparing our light curves with
Kepler K2 normalized light curves. This system has a low-mass ratio
and a high fill-out factor, and, theoretically, such a physical
configuration would lead to a merger.
Description:
Photometric observations of the variable EPIC 211957146 in the R band
were taken using the IUCAA-Girawali Observatory (IGO) 2m telescope
from 2015 February 5-22, for 5 nights (specifications of IGO 2m
telescope CCD are as discussed in Sriram et al. 2016AJ....151...69S 2016AJ....151...69S).
An exposure time of 20-30s was given for imaging. B and V band
observations were taken from the JCBT 1.3m telescope at Vainu Bappu
Observatory (VBO) during 2016 February 3-8 and 2016 March 25-April 3
for a total of 7 nights.
The JCBT 1.3m DFM telescope at VBO uses a 2K*4K UKATC CCD having a
gain of 0.745e-/ADU and a read out noise of 4.2e-. The plate scale
is 0.3arcsec/pixel resulting in an image of 10'*20' and images of the
source in the B and V bands were taken with an integration time of
120s. Differential photometry was performed on the variable, with the
comparison and check stars (of similar brightness) lying close to the
variable.
This source was also observed by the Kepler K2 mission Campaign 5, and
the data were acquired from the MAST portal and the NASA Exoplanet
Archive. K2 campaign 5 monitored the sky for a duration of ∼74days and
was fixed upon a single boresight position of 08h40m38s,
+16°49'47'' starting from 2015 April 27 to July 10.
Spectroscopic observation of the variable was performed during the
nights of 2016 January 29-30 using the 2m Himalaya Chandra Telescope
(HCT, IAO) equipped with the Himalaya Faint Object Spectrograph Camera
(HFOSC) having a 2K*4K CCD. Spectra were obtained with an exposure
time of 1800-2700s for both variable and spectrophotometric standard
stars (BD+08 2015). A few spectra were also taken on 2016 February 1
using the Optomechanics Research spectrograph mounted on the 2.3m
Vainu Bappu Telescope using a 1K*1K CCD. A 600lines/mm grating
spanning a wavelength range of 2000-8000Å with a dispersion of
2.6Å/pixel and a resolution of ∼5.3Å was used. The same
spectrophotometric standard as before was used for observation, and an
exposure time of 2700s was given to both the variable and the
standard.
Objects:
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RA (ICRS) DE Designation(s) (Period)
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08 45 54.23 +19 34 57.38 EPIC 211957146 = NSVS 10126046 (P=0.355018)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
figure1.dat 38 868 BVR band light curve data behind Figure 1
table2.dat 47 372 Observed times of minima for variable EPIC 211957146
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See also:
B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013)
J/AJ/135/907 : Variables in Praesepe identified with KELT (Pepper+, 2008)
Byte-by-byte Description of file: figure1.dat
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Bytes Format Units Label Explanations
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1 A1 --- Band [BVR] Band of observation (either B, V, or R)
3- 19 F17.9 d HJD ? Heliocentric Julian Date
21- 29 F9.6 --- Phase [-0.285/1]? Phase
31- 38 F8.6 --- NFlux [0.6/1.01]? Normalized light units
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 F10.5 d HJD Heliocentric Julian Date (HJD-2450000)
12- 18 F7.5 d e_HJD [0.00013/0.00898] Uncertainty in HJD
20- 27 F8.1 --- Epoch [-17388/8.5] Number of the cycle
29- 36 F8.5 d O-C1 [-0.042/0.02] (O-C) residual (obtained from
the linear ephemeris)
38- 45 F8.5 d O-C2 [-0.036/0.032] (O-C) residual, quadratic
ephemeris+LIght-travel Time Effect (LITE)
47 I1 --- Ref [1/5] Reference (1)
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Note (1): Reference codes are defined as follows:
1 = Northern Sky Variability Survey (NSVS) database;
2 = Pepper et al. 2008 (Cat. J/AJ/135/907);
3 = All Sky Automated Survey (ASAS) database;
4 = Our observations;
5 = Kepler K2 database.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 10-Aug-2017