Hindawi Publishing Corporation Journal of Astrophysics Volume 2015, Article ID 590673, 8 pages http://dx.doi.org/10.1155/2015/590673 Research Article An Extensive Photometric Investigation of the W UMa System DK Cyg M. M. Elkhateeb,1,2 M. I. Nouh,1,2 E. Elkholy,1,2 and B. Korany1,3 1 Astronomy Department, National Research Institute of Astronomy and Geophysics, Helwan, Cairo 11421, Egypt 2Physics Department, College of Science, Northern Border University, Arar 1321, Saudi Arabia 3Physics Department, Faculty of Applied Science, Umm Al-Qura University, Makkah 715, Saudi Arabia Correspondence should be addressed to M. I. Nouh; abdo [email protected] Received 25 August 2014; Revised 14 December 2014; Accepted 17 December 2014 Academic Editor: Theodor Pribulla Copyright © 2015 M. M. Elkhateeb et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. DK Cyg ( = 0.4707) is a contact binary system that undergoes complete eclipses. All the published photoelectric data have been collected and utilized to reexamine and update the period behavior of the system. A significant period increase with rate of −11 12.590 × 10 days/cycle was calculated. New period and ephemeris have been calculated for the system. A long term photometric solution study was performed and a light curve elements were calculated. We investigated the evolutionary status of the system using theoretical evolutionary models. 1. Introduction period and short durations of night, it is bound to remain ill- observed [9]. Only four complete light curves by Binnendijk The eclipsing binary DK Cyg (BD +330 4304, 10.37–10.93 mv) [6], Paparo et al. [10], Awadalla [9], and Baran et al. [11] isawellknowncontactbinarysystemwithaperiodofabout arepublished.Photoelectricobservationsandnewtimesof 0.4707 days. It was discovered as variable star earlier by Guth- minima have been carried out by many authors: Borkovits nick and Prager [1], so their epoch of intensive observations et al. [12], SarounovaandWolf[´ 13], Drozdz and Ogloza [14], is very long. The earliest photographic light curve classified Hubscheretal.[¨ 15], Dogru et al. [16], Hubscher et al. [17], the system as a W Ursae Majoris type. Rucinski and Lu [2] Hubscher et al. [18], Erkan et al. [19], Diethelm [20], Dogru carried out the first spectroscopic observations and estimated et al. [21], Simmons [22], Diethelm [23], and Diethelm [24]. = 0.325 the mass ratio as and classified the system as an In the present paper we are going to perform comprehen- A-subtype contact system with spectral type of A8V. Visual sive photometric study for the system DK Cyg. The structures light curves were published by Piotrowski [3]andTsesevitch of the paper are as follows: Section 2 deals with the period [4]fromKlepikova’sobservations. change, Section 3 is devoted to the light curve modeling, and First photoelectric observations for the system were car- Section 4 presents the discussion and conclusion reached. ried out by Hinderer [5], while Binnendijk [6]observedthe system photoelectrically in B- and V-bands and derived least 2. Period Change squares orbital solution. The system DK Cyg was classified in the General Catalogue of Variable Stars as A7V [7], while Although the period variation of contact binary systems Binnendijk [6] adopted it as A2. Mochnacki and Doughty [8] of the W UMa-type is a controversial issue of binary star showed that the color index of the system judged its spectral astrophysics, the cause of the variations (long as well as short type and found that the spectral type of the system is more term) is still a mystery for a discussion of possible physical likely to be about F0 to F2. Because the system DK Cyg is mechanisms [25]. Magnetic activity cycle is one of the main a summer object in the Northern hemisphere with 11.5-hour mechanisms that caused a period variation together with 2 Journal of Astrophysics the mass exchange between the components of each system. 0.14 Kaszas et al. [26] stated that the long term period variation 0.12 may be interpreted by a perturbation of the third companion or surface activity of the system components. 0.1 Observations by Binnendijk [6]showedachangeofthe 0.08 secondary minimum depth and a new linear light element 0.06 was derived. Period study by Paparo et al. [10]showedthat 0.04 the orbital period of the system DK Cyg increases and the first (O − C) parabolic light elements were calculated, which confirmed 0.02 thelightcurvevariability.Kissetal.[25]updatedthelinear 0 ephemeris of DK Cyg, while Awadalla [9]recalculatedanew − quadratic element for the system and confirmed the light 0.02 curve variability suggested by Paparo et al. [10]. Wolf et al. −0.04 [27] used a set of 101 published times of minimum covering 0 40000 30000 20000 10000 10000 20000 30000 40000 50000 the interval between 1926 and 2000 in order to update the − − − − quadratic element calculated by Awadalla [9]. They showed E −11 Integer cycle ( ) that the period increases by the rate 11.5 × 10 days/cycle. Borkovits et al. [28] follow the period behavior of the system Figure 1: Period behavior of DK Cyg. using set of published minima from HJD 2424760 to HJD 2453302. In this paper we studied the orbital period behavior of the 0.04 ( − ) system DK Cyg using the diagram based on more 0.02 complete data set collected from the literatures and databases of BAV, AAVSO, and BBSAG observers. Part of our collected 0 data set was given by Kreiner et al. [29]; unpublished Hippar- (O − C)q −0.02 cos observations and main part were downloaded from web- site (http://astro.sci.muni.cz/variables/ocgate/); Table 1 listed −0.04 only those minima not listed on the mentioned websites. A total of 195 minima times were incorporated in our analysis −0.06 0 covering about 86 years (66689 orbital revolutions) from 40000 30000 20000 10000 20000 40000 10000 30000 50000 1927 to 2013. It is clear that our set of data added about − − − − 94 of new minima and increases the interval limit of the Integer cycle (E) orbital period study about 13 years more than the data of Wolf et al. [27], which may give more accurate insight on Figure 2: Calculated residuals from the quadratic ephemeris. the period behavior of the system. The different types of the collected minima (i.e., photographic, visual, photoelectric, andCCD)wereweightedaccordingtotheirtype.Theresidual The rate of period increasing resulting from the quadratic / = 12.568 ×10−11 ( − )’s were computed using Binnendijk [6] ephemeris (1) elements (3) is days/cycle or 9.746 × 10−8 and represented in Figure 1. No distinction has been made days/year or 0.84 seconds/century. More future between primary and secondary minima: systematic and continuous photometric observations are needed to follow a continuous change in the orbital period of Min = 2437999.5838 + 0.47069055 ∗. (1) the system DK Cyg which may show a periodic behavior. The fourth column of Table 1 represents the quadratic residuals Itcanbeseenfromthefigurethatthebehavioroftheorbital ( − ) calculated using the new element of (2) and period of the system DK Cyg shows a parabolic distribution represented in Figure 2. All published linear and quadratic which is generally interpreted by the transfer of mass from elements together with that resulting from our calculations one component to the other of binary. Reasonable linear least are listed in Table 2. It is noted from the table that the squaresfitofthedataavailableimprovedthelightelements quadratic term resulting from our calculations has slightly given in (1) to higher value than that calculated by Awadalla [9], Wolf et al. [27], and Borkovits et al. [28]. This can be interpreted by the Min = 2437999.5961 +0 .47069206 ∗ . (2) ±0.0192 ±0.0243 increasing of the set of minima in our study compared to the =0.47069206 onetheyused(nearlydouble);alsowecoveredaninterval The linear element yields a new period of larger than the one they used. dayswhichislongerby0.13secondswithrespecttothevalue given by Binnendijk [6]. Quadratic least squares fit gives 3. Light Curve Modeling Min = 2437999.5803 +0 .47069064 ∗ ±0.0192 ±0.0237 Light curve modeling for the system DK Cyg by Mochnacki (3) + 6.284 × 10−11 ×2. and Doughty [8] using Binnendijk [6]observationsinV- ±2.5654×10−12 band showed nonmatching between the theoretical curve and Journal of Astrophysics 3 Table 1: Times of minimum light for DK Cyg. HJD Method ( − ) ( −) References HJD Method ( − ) ( −) References 2434179.4690 Vis −8116 0.00970 0.00971 1 2451749.4450 pe 29212 0.04885 −0.00370 3 2447758.4352 Pe 20733 0.02423 −0.00099 2 2451777.6740 ccd 29272 0.03642 −0.01636 5 2447790.4437 Pe 20801 0.02577 0.00037 2 2452163.6590 ccd 30092 0.05517 −0.00074 5 2447963.6620 Pe 21169 0.02995 0.00354 3 2452245.5592 ccd 30266 0.05521 −0.00137 5 2447963.8960 Pe 21169.5 0.02860 0.00220 3 2452253.5613 ccd 30283 0.05557 −0.00108 5 2448265.1380 Pe 21809.5 0.02865 0.00046 4 2452441.8384 ccd 30683 0.05645 −0.00176 5 2448265.1382 Pe 21809.5 0.02885 0.00066 4 2452512.4415 pe 30833 0.05597 −0.00284 7 2448272.1987 Pe 21824.5 0.02899 0.00076 4 2452525.6231 ccd 30861 0.05824 −0.00069 5 2448297.6160 Pe 21878.5 0.02900 0.00062 3 2452526.5644 ccd 30863 0.05816 −0.00078 5 2448302.7930 Pe 21889.5 0.02841 −0.00001 3 2452811.8062 ccd 31469 0.06148 0.00013 5 2448308.2078 Pe 21901 0.03027 0.00182 4 2453223.4286 ccd 32343.5 0.06500 −0.00006 8 2448308.2079 Pe 21901 0.03037 0.00192 4 2453228.3681 ccd 32354 0.06225 −0.00274