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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 (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). 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: ------------------------------------------------------------------------- RA (ICRS) DE Designation(s) (Period) ------------------------------------------------------------------------- 08 45 54.23 +19 34 57.38 EPIC 211957146 = NSVS 10126046 (P=0.355018) ------------------------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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)
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.
History: From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 10-Aug-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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