J/AJ/149/194 Differential BVR light curves of DK Cyg (Lee+, 2015) ================================================================================ The physical nature and orbital behavior of the eclipsing system DK Cygni. Lee J.W., Youn J.-H., Park J.-H., Wolf M. =2015AJ....149..194L ================================================================================ ADC_Keywords: Binaries, eclipsing ; Photometry, UBVRI ; Photometry, CCD Keywords: binaries: close - binaries: eclipsing - stars: individual: DK Cyg - starspot Abstract: New CCD photometry is presented for the hot overcontact binary DK Cyg together with reasonable explanations for the light and period variations. Historical light and velocity curves from 1962 to 2012 were simultaneously analyzed with the Wilson-Devinney (W-D) synthesis code. The brightness disturbances were satisfactorily modeled by applying a magnetic cool spot on the primary star. Based on 261 times of minimum light that include 116 new timings and span more than 87 years, a period study reveals that the orbital period has varied due to a periodic oscillation superimposed on an upward parabola. The period and semi-amplitude of the modulation are about 78.1years and 0.0037days, respectively. This detail is interpreted as a light-travel-time effect due to a circumbinary companion with a minimum mass of M_3_=0.065M_{sun}_, within the theoretical limit of ~0.07M_{sun}_ for a brown dwarf star. The observed period increase at a fractional rate of +2.74x10^-10^ is in excellent agreement with that calculated from our W-D synthesis. Mass transfer from the secondary to the primary component is mainly responsible for the secular period change. We examined the evolutionary status of the DK Cyg system from the absolute dimensions. Description: We carried out CCD photometry of DK Cyg on nine nights from 2012 September 20 through October 21 in order to obtain new multiband light curves. The observations were taken with a PIXIS: 2048B CCD camera and a BVR filter set attached to the 61 cm reflector at Sobaeksan Optical Astronomy Observatory (SOAO) in Korea. Objects: ------------------------------------------------------------------- RA (ICRS) DE Designation(s) (Period) ------------------------------------------------------------------- 21 35 02.67 +34 35 45.4 V* DK Cyg = HIP 106574 (P=0.4706906) ------------------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 65 1478 CCD photometric observations of DK Cyg observed at Sobaeksan Optical Astronomy Observatory (SOAO) table6.dat 57 234 Observed photoelectric and CCD times of minimum light for DK Cyg refs.dat 110 58 References -------------------------------------------------------------------------------- See also: B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013) J/AJ/145/100 : Differential BVR light curves of EP And (Lee+, 2013) J/A+A/289/137 : DK Cygni light curve (Awadalla, 1994) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 13 F13.5 d HJD-B Heliocentric Julian Date of B band observation 15- 21 F7.4 mag DBmag Differential B band magnitude (1) 23- 35 F13.5 d HJD-V ? Heliocentric Julian Date of V band observation 37- 43 F7.4 mag DVmag ? Differential V band magnitude (1) 45- 57 F13.5 d HJD-R ? Heliocentric Julian Date of R band observation 59- 65 F7.4 mag DRmag ? Differential R band magnitude (1) -------------------------------------------------------------------------------- Note (1): TYC 2712-1372-1 was chosen as a comparison star. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table6.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 11 F11.5 d HJD Heliocentric Julian Date (HJD-2400000) 13- 23 F11.5 d HJED Heliocentric Julian Ephemeris Date in the Terrestrial Time (TT) scale (HJED-2400000) 25- 31 F7.5 d e_HJD ? Error in HJD 33- 39 F7.1 --- E [-4753/39989] Epoch (cycle) 41- 48 F8.5 d O-C [-0.005/0.004] The (O-C) residual 50- 51 A2 --- Min Minimum type (I or II) 53- 57 A5 --- Ref Reference; in refs.dat file -------------------------------------------------------------------------------- Byte-by-byte Description of file: refs.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 A5 --- Ref Reference identifier 7- 25 A19 --- BibCode Bibliographic code 27- 51 A25 --- Aut Author's name 53-110 A58 --- Com Comments -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 11-Jun-2015