J/AJ/147/98 Times of minimum light for EQ Tau (Li+, 2014) ================================================================================ The triple binary star EQ Tau with an active component. Li K., Qian S.-B., Hu S.-M., He J.-J. =2014AJ....147...98L ================================================================================ ADC_Keywords: Binaries, eclipsing Keywords: binaries: close - binaries: eclipsing - stars: individual: EQ Tau Abstract: New photometric data of EQ Tau observed in 2010 and 2013 are presented. Light curves obtained in 2000 and 2004 by Yuan & Qian and 2001 by Yang & Liu, together with our two newly determined sets of light curves, were analyzed using the Wilson-Devinney code. The five sets of light curves exhibit very obvious variations, implying that the light curves of EQ Tau show a strong O'Connell effect. We found that EQ Tau is an A-type shallow contact binary with a contact degree of f=11.8%; variable dark spots on the primary component of EQ Tau were also observed. Using 10 new times of minimum light, together with those collected from the literature, the orbital period change of EQ Tau was analyzed. We found that its orbital period includes a secular decrease (dP/dt=-3.63x10^-8^days/yr) and a cyclic oscillation (A_3_=0.0058 days and P_3_=22.7 yr). The secular increase of the period can be explained by mass transfer from the more massive component to the less massive one or/and angular momentum loss due to a magnetic stellar wind. The Applegate mechanism cannot explain the cyclic orbital period change. A probable transit-like event was observed in 2010. Therefore, the cyclic orbital period change of EQ Tau may be due to the light time effect of a third body. Description: The CCD photometric observations of EQ Tau were first carried out using the 60cm telescope at Yunnan Observatory from 2009 to 2012, during which some new times of minimum light were determined. Then, EQ Tau was observed using the 1m telescope at Yunnan Observatory on 2010 October 30 and November 1, and complete V, R, and I light curves were derived. Finally, EQ Tau was observed by using the 85cm telescope at Xinglong station of the National Astronomical Observatories of China (NAOC) on 2013 January 8 and 11, and complete B, V, R, and I light curves were obtained. All telescopes were equipped with the standard Johnson-Cousin-Bessel UBVRI CCD photometric system. Objects: ------------------------------------------------------------ RA (ICRS) DE Designation(s) ------------------------------------------------------------ 03 48 13.43 +22 18 50.9 V* EQ Tau = V* EQ Tau = CSV 347 ------------------------------------------------------------ File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 32 23 Newly determined times of minimum light for EQ Tau table2.dat 62 272 Times of minimum light for EQ Tau refs.dat 115 66 References -------------------------------------------------------------------------------- See also: B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013) J/MNRAS/381/602 : BV differential light curves of EQ Tau (Yuan+, 2007) J/AJ/132/960 : V(RI)c light-curves of EQ Tauri (Hrivnak+, 2006) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 F12.4 d HJD Heliocentric Julian Date 14- 19 F6.4 d e_HJD Uncertainty in HJD 21 A1 --- Type [ps] Minimum type (p=primary, s=secondary) 23- 27 A5 --- Flt Filter (B, V, R, I, Clear) 29- 32 A4 --- Tel Telescope (1) -------------------------------------------------------------------------------- Note (1): Telescope codes defined as follows: 1m = 1m telescope at Yunnan Observatory; 60cm = 60cm telescope at Yunnan Observatory; 85cm = 85cm telescope at Xinglong station of the National Astronomical Observatories of China (NAOC). -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 F12.4 d HJD Heliocentric Julian Date 14- 15 A2 --- Type Miminum type (I or II) 17- 19 A3 --- Meth Observation method (ccd=charge-coupled device, pe=photoelectric, pg=photographic) 21- 26 F6.4 d e_HJD Error in the time of light minimum (1) 28- 35 F8.1 --- E Epoch (cycle) 37- 43 F7.4 d O-C1 The (O-C)_1_ value (2) 45- 51 F7.4 d O-C2 The (O-C)_2_ value (2) 53- 59 F7.4 d Res Residual (2) 61- 62 I2 --- Ref Reference code; in refs.dat file -------------------------------------------------------------------------------- Note (1): Some references do not show the errors of the times of light minimum. We set the errors of pe and CCD data as 0.0010 and the errors of pg data as 0.0100. Note (2): The different resoiduals are: * (O-C)_1_ is calculated from 2440213.325+0.341347E (top panel of Fig.4), which can be fitted by Eq.(2). * (O-C)_2_ represents the residuals after removal of the secular decrease of 3.63x10^-8^d/yr (middle panel of Fig.4). * Res represents the residuals after both the secular decrease and the periodic variation (P_3_=8305d) -------------------------------------------------------------------------------- Byte-by-byte Description of file: refs.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 2 I2 --- Ref Reference identifier 4- 22 A19 --- BibCode Bibliographic code 24- 43 A20 --- Aut Author's name 45-115 A71 --- Com Comments -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 12-Sep-2014