Research Paper J. Astron. Space Sci. 29(2), 151-161 (2012) http://dx.doi.org/10.5140/JASS.2012.29.2.151 Stars,Technical Companions, Paper and their Interactions: A Memorial to Robert H. Koch J. Astron. Space Sci. 28(4), 345-354 (2011) V700http://dx.doi.org/10.5140/JASS.2011.28.4.345 Cygni: A Dynamically Active W UMa-type Binary Star II

† Chun-HweyImplementation Kim1,2 and and Jang Validation Hae Jeong1,2 of Earth Acquisition Algorithm for 1Department of Astronomy and Space Science, Chungbuk National University, Cheongju 361-763, Korea 2Communication,Chungbuk National University Ocean Observatory, and Chungbuk Meteorological National University, Satellite Cheongju 361-763, Korea

Sang-wook Park1, Young-ran Lee1, Byoung-Sun Lee2, Yoola Hwang2, and Un-seob Lee1† An1Ground intensive Systems analysis Division, of 148 Satrec timings Initiative, of V700 Daejeon Cyg 305-811,was performed, Korea including our new timings and 59 timings calculated from2Satellite the System super Researchwide angle Team, search Electronics for planets and Telecommunications (SWASP) observations, Research and Institute, the dynamical Daejeon evidence305-700, Korea of the W UMa W subtype binary was examined. It was found that the orbital period of the system has varied over approximately 66y in two complicated cyclical components superposed on a weak upward parabolic path. The orbital period secularly increasedEarth acquisition at a rate is to ofsolve +8.7 when (±3.4) earth × can10-9 be day/year, visible from which satellite is one after order Sun acquisition of magnitude during lower launch than and earlythose opera obtained- by previoustion period investigators. or on-station The satellite small anomaly. secular Inperiod this paper, increase the isalgorithm interpreted and testas a result combination of the Communication, of both angular Ocean momentum lossand Meteorological(due to magnetic Satellite braking) (COMS) and Earth mass-transfer acquisition from are presented the less massivein case of component on-station satellite to the moreanomaly massive status. component. The Onealgorithms cyclical for componentthe calculation had of a Earth-pointing 20.y3 period withattitude an controlamplitude parameters of 0.d0037, including and thethose other attitude had directiona 62.y8 period vector, with an amplituderotation matrix, of 0. andd0258. maneuver The components time and duration had an are approximate based on COMS 1:3 relation configuration between (Eurostar their periods3000 bus). and The a coordinate1:7 ratio between theirsystem amplitudes. uses the reference Two plausible initial frame. mechanisms The constraint (i.e., calculatingthe light-time available effects time-slot [LTEs] tocaused perform by thethe earth presence acquisition of additional bodiesconsiders and eclipse, the Applegate angular separation, model) solarwere local considered time, and as infra-red possible earth explanations sensor blinding for conditions.the cyclical The components. results of Elec Based- on tronics and Telecommunications Research Institute (ETRI) are compared with that of the Astrium software to validate the the LTE interpretation, the minimum masses of 0.29 M⊙ for the shorter period and 0.50 M⊙ for the longer one were calculated.implemented The ETRI total software. light contributions were within 5%, which was in agreement with the 3% third-light obtained from the light curve synthesis performed by Yang & Dai (2009). The Applegate model parameters show that the root meanKeywords: square Earth luminosity acquisition, variations attitude control (relative parameter, to the luminosities time-slot, communication, of the eclipsing ocean components) and meteorological are 3 times satellite smaller than the nominal value (∆L/Lp,s ≈ 0.1), indicating that the variations are hardly detectable from the light curves. Presently, the LTE interpretation (due to the third and fourth stars) is preferred as the possible cause of the two cycling period changes.1. INTRODUCTION A possible evolutionary implication for the V700 Cygsun acquisitionsystem is discussed. is completed, the position of the earth is kept in the vision of the satellite by adjusting the three- KeCommunication,ywords: W UMa-type Ocean star, and V700 Meteorological Cyg, period change, Satellite light-time axis effects,attitude ofmagnetic the satellite activities with reference to the relative (COMS, Chollian) was launched on July 26, 2010 and is position of the sun and the satellite. When the initial at- now in operation successfully (Lee et al. 2011). COMS titude of the satellite is stabilized, the normal attitude is Satellite Ground Control System (SGCS) is developed by kept by obtaining the field of view (FOV) toward the earth 1. INTRODUCTION star is 374K cooler than the less massive 0.60 M⊙ star with a Electronics and Telecommunications Research Institute by means of the earth observation sensor. temperature of 5770 K. The fill-out factor is approximately (ETRI), and the algorithm of parameters and events for This paper describes mainly the earth acquisition pro- The eclipsing nature of V700 Cyg (OV 26, 2MASS 27% in moderate contact with one another. The O-C COMS satellite configuration is developed according cess after the sun acquisition in case that the status of J20310525 + 3847006, CCDM J20311 + 3847A, WDS J20311 diagram with the light elements (C = HJD 2445163.4896 + to the document provided from Astrium to ETRI (Laine COMS changes from on-station to abnormal. Based on + 3847A) was discovered by Whitney (1952) who classified 0.d340045602 E) by Niarchos et al. (1997) showed a short- 2006). the orbit information for the COMS earth acquisition, the d it asIn athe W launchUMa-type and binaryearly operation star with period a period (LEOP) of 0. or340048. in articleterm describes period instability. the method A close to search physical the propercompanion time that was m Thethe situation first photoelectric where the attitudeBV light ofcurves a satellite with isan not O ’Connellnor- periodsapproximately considering 1.4 the fainter constraints in the forV bandpass calculating than the V700 Cyg effectmal, the (Max satellite II fainter attitude than is notMax known I) were and secured thus it byshould Niarchos appropriatewas noted time by when Eggen the (1967). earth acquisitionV700 Cyg was can later be per catalogued- etbe al.fixed (1997) to a specific who studied direction global in order photometric to acquire properties the nor- of formedas CCDMfollowing J20311+3847A the sun acquisition. (Dommanget In case of & perform Nys 2002)- and themal systemattitude. through The position light curve of the synthesis sun is used as wellas the as ref period- ing theWDS earth J20311+3847A acquisition for(Mason COMS et at al. the 2001). selected The one earlier of history study.erences According to fix the satellite to those attitude authors, in aV700 specific Cyg direction. is a W UMa the calculatedwas well summarized time period, by the Niarchos algorithm et andal. (1997). simulation W-subtypeThe sun acquisition binary star refers with to thethe process spectral to type fix the of satelG5V- and result forIn attituderecent years, maneuver V700 process, Cyg was maneuver revisited time by Qian and (2003), lite attitude with reference to the solar position. Once the duration is verified. The actually realized earth acquisi- an orbital inclination of 79.9°. The more massive 0.92 M⊙ Molik & Wolf (2004), Xiang et al. (2009) and Yang & Dai

This isis anan Open open Access Access article article distributed distributed under under the termsthe terms of the of the ReceivedReceived Nov 15, May 2011 20, Revised 2012 Revised Nov 23, May 2011 26, Accepted 2012 Accepted Nov 25, 2011May 28, 2012 Creative Commons Commons Attribution Attribution Non-Commercial Non-Commercial License License (http://cre (http://- †Corresponding†Corresponding Author Author creativecommons.org/licenses/by-nc/3.0/)ativecommons.org/licenses/by-nc/3.0/) which which permits premits unrestricted unrestricted non-commercial use, use, distribution, distribution, and and reproduction reproduction in any in medium,any medium, E-mail:E-mail: [email protected] [email protected] provided thethe originaloriginal work work is is properly properly cited. cited. Tel: +82-42-365-7919Tel: +82-43-261-3139 Fax: +82-42-365-7500 Fax: +82-43-274-2312

Copyright © The Korean Space Science Society 345 http://janss.kr pISSN: 2093-5587 eISSN: 2093-1409 Copyright © The Korean Space Science Society 151 http://janss.kr plSSN: 2093-5587 elSSN: 2093-1409 J. Astron. Space Sci. 29(2), 151-161 (2012)

(2009). Qian (2003) obtained new light elements (C = HJD is a discussion of the implications of existing working 2449999.3003 + 0.d29063148 E) and noted that the short- hypotheses. term period instability detected by Niarchos et al. (1997) is not real but is caused by the use of an incorrect longer period. They also suggested that the orbital period varied 2. OBSERVATIONS AND TIMES OF MINIMA in a cyclical manner with a period of 40y and an amplitude of 0.d0095, which was superposed on a secular period The CCD photometric observations of V700 Cyg for the increasing at a rate of +8.41 × 10-8 d/yr. Molik & Wolf (2004) purpose of timing determination were made on the nights independently analyzed the times of minima that were of November 4 and 12 in 2008 with the 35 cm campus available to them and found only a cyclic period change station reflector at the Chungbuk National University of 46y without any secular change. Yang & Dai (2009) Observatory in Korea. The telescope was equipped with confirmed the result of Qian’s (2003) period study and an SBIG ST-8 CCD imaging system and electrically cooled obtained a cyclic period of 54y, with an amplitude of 0.d0212 with a 19' × 12'field of view. No filters were used in our longer than those identified by Qian (2003) and Molik observations. GSC 3152-527 and GSC 3153-193 were & Wolf (2004). Yang & Dai (2009) derived the rate of the chosen as the comparison and check stars, respectively. secular period increase as +2.89 × 10-8 d/yr, 3 times smaller The instrumentation used and reduction method for the than that of Qian (2003). In addition, new symmetric VR raw CCD frames have been described in detail by Kim et light curves showing no O’Connell effect were secured by al. (2006). The resultant standard error of our observations Yang & Dai (2009). Their analyses of the light curves with the (check minus comparison) was approximately ±0.m009. The Wilson-Devinney binary model (Wilson & Devinney 1971) light curves for the observations are shown in Fig. 1. showed a temperature difference of ΔT = 503K between the From our observations using the conventional Kwee & components, a mass ratio of 0.544, an inclination of 84.o1 van Woerden (1956, KW) method, two times of minimum and a fill-out factor of 15.1%. These values are larger than light were determined. In addition, we researched whether ΔT = 374K, smaller than 0.652, 79.o9 and 27%, respectively, according to Niarchos et al. (1997). Although the reasons for the differences between the two investigators are currently unknown, it is true that the differences cannot be negligible and must be solved with new photometric and spectroscopic observations. Xiang et al. (2009) also conducted a period study by using the times of minima available to them and found a period of 39.y1 for the cyclic term with an amplitude of 0.d0197; a secular period increase of +2.8 × 10-8 d/yr was derived. Xiang et al. (2009) suggested an additional cyclic oscillation with a period of approximately 25.y0 and a small amplitude of 0.d0031 in the residuals from the first cyclic term. Surveying the historical period studies performed by the investigators above, we note the following: 1) even concurrent studies (Xiang et al. 2009, Yang & Dai 2009) made with nearly the same times of minima do not show consistency for the period of the seemingly cyclic change; and 2) numerous timings before and after the recent period studies of Xiang et al. (2009) and Yang & Dai (2009) have been published (e.g., see Table 1 and the references therein). In this paper, we perform an intensive reanalysis of all the published timings available to us, including our new two timings and 59 others calculated from the super wide angle search for planets (SWASP) observations. Two cyclic changes superposed on a weakly constrained Fig. 1. The observed eclipse light curves of V700 Cyg and the check upward parabolic variation are suggested. The following star (GSC 3153-193) relative to the comparison star (GSC 3152-527). http://dx.doi.org/10.5140/JASS.2012.29.2.151 152 Chun-Hwey Kim & Jang Hae Jeong V700 Cygni, A dynamically active binary II

V700 Cyg has been observed in survey works such as the all 3. PERIOD STUDY sky automated survey (ASAS) and the SWASP. Fortunately, V700 Cyg is identified as 1SWASP + J203105.27 + 384701.8 in To investigate the period variation of V700 Cyg, a total of the SWASP public archive that is available at the Web1 and 148 (9 visual, 14 plate, 7 photographic, and 118 photoelectric managed by the SWASP community. Using the SWASP data and CCD) times of minimum light (including ours and those observed from June 14 to October 25 in 2007, we calculated from the SWASP) were collected from a modern database a total of 59 timings (27 for the primary timing and 32 for the (Kreiner et al. 2001) and from the recent literature. Table 1 secondary timing) by the KW method. lists only the photoelectric and CCD minima, which were not compiled by Yang & Dai (2009) or published after their

1http://www.wasp.le.ac.uk/public/lc/index.php study.

Table 1. The CCD times of minima of V700 Cyg not listed in Yang & Dai (2009) or published after their study.

a HJD Error Type Cycle (O-Clinear) (O-Cfull) Reference (2400000+) 51770.5449 0.0005 I 22582.0 +0.0185 +0.0003 Agerer & Hübscher (2002) 51770.3994 0.0003 II 22581.5 +0.0183 +0.0001 Agerer & Hübscher (2002) 52859.5331 0.0001 I 26329.0 +0.0134 -0.0001 Kotkova & Wolf (2006) 53894.4692 - I 29890.0 +0.0136 +0.0001 Brát et al. (2007) 53963.3488 0.0001 I 30127.0 +0.0137 -0.0006 Xiang et al. (2009) 54034.2627 0.0001 I 30371.0 +0.0137 -0.0004 Brát et al. (2007) 54210.9659 0.0004 I 30979.0 +0.0135 +0.0004 Nelson (2008) 54246.4226 0.0003 I 31101.0 +0.0132 +0.0004 Brát et al. (2007) 54279.5543 0.0003 I 31215.0 +0.0130 +0.0004 This paper (SWASP) 54280.5715 0.0002 II 31218.5 +0.0130 +0.0004 This paper (SWASP) 54281.5884 0.0002 I 31222.0 +0.0127 +0.0001 This paper (SWASP) 54282.6058 0.0003 II 31225.5 +0.0129 +0.0003 This paper (SWASP) 54283.6232 0.0002 I 31229.0 +0.0131 +0.0005 This paper (SWASP) 54284.6402 0.0002 II 31232.5 +0.0129 +0.0003 This paper (SWASP) 54285.6575 0.0002 I 31236.0 +0.0130 +0.0004 This paper (SWASP) 54286.5296 0.0001 I 31239.0 +0.0132 +0.0006 This paper (SWASP) 54286.6745 0.0001 II 31239.5 +0.0128 +0.0002 This paper (SWASP) 54287.5472 0.0003 II 31242.5 +0.0136 +0.0010 This paper (SWASP) 54287.6920 0.0004 I 31243.0 +0.0131 +0.0005 This paper (SWASP) 54288.5637 0.0002 I 31246.0 +0.0129 +0.0003 This paper (SWASP) 54288.7089 0.0002 II 31246.5 +0.0128 +0.0002 This paper (SWASP) 54289.5812 0.0002 II 31249.5 +0.0132 +0.0006 This paper (SWASP) 54291.6154 0.0002 II 31256.5 +0.0130 +0.0004 This paper (SWASP) 54292.4869 0.0005 II 31259.5 +0.0126 +0.0000 This paper (SWASP) 54292.6326 0.0001 I 31260.0 +0.0129 +0.0004 This paper (SWASP) 54297.7176 0.0002 II 31277.5 +0.0119 -0.0006 This paper (SWASP) 54298.5904 0.0002 II 31280.5 +0.0128 +0.0003 This paper (SWASP) 54307.4544 0.0002 I 31311.0 +0.0126 +0.0002 This paper (SWASP) 54307.6001 0.0003 II 31311.5 +0.0130 +0.0006 This paper (SWASP) 54308.4721 0.0002 II 31314.5 +0.0131 +0.0007 This paper (SWASP) 54308.6171 0.0002 I 31315.0 +0.0128 +0.0004 This paper (SWASP) 54313.5574 0.0003 I 31332.0 +0.0123 -0.0000 This paper (SWASP) 54314.4281 0.0004 I 31335.0 +0.0111 -0.0012 This paper (SWASP) 54316.6092 0.0002 II 31342.5 +0.0125 +0.0002 This paper (SWASP) 54318.6434 0.0002 II 31349.5 +0.0123 -0.0000 This paper (SWASP) 54333.4654 0.0004 II 31400.5 +0.0121 -0.0001 This paper (SWASP) 54334.4825 0.0001 I 31404.0 +0.0120 -0.0002 This paper (SWASP) 54335.4995 0.0001 II 31407.5 +0.0118 -0.0004 This paper (SWASP) 54337.3890 0.0001 I 31414.0 +0.0122 +0.0000 This paper (SWASP) 54337.5341 0.0002 II 31414.5 +0.0120 -0.0002 This paper (SWASP) 54338.4059 0.0002 II 31417.5 +0.0119 -0.0003 This paper (SWASP) 54338.5513 0.0002 I 31418.0 +0.0120 -0.0002 This paper (SWASP) 54339.4231 0.0001 I 31421.0 +0.0119 -0.0003 This paper (SWASP) 54339.5685 0.0003 II 31421.5 +0.0120 -0.0002 This paper (SWASP) 54340.4397 0.0003 II 31424.5 +0.0113 -0.0009 This paper (SWASP) 54340.5854 0.0002 I 31425.0 +0.0117 -0.0005 This paper (SWASP) 54341.4579 0.0002 I 31428.0 +0.0123 +0.0001 This paper (SWASP) 54344.5096 0.0002 II 31438.5 +0.0124 +0.0002 This paper (SWASP) 54345.5262 0.0001 I 31442.0 +0.0118 -0.0004 This paper (SWASP) 54346.5428 0.0003 II 31445.5 +0.0111 -0.0010 This paper (SWASP)

153 http://janss.kr J. Astron. Space Sci. 29(2), 151-161 (2012)

Table 1. (Continued)

a HJD Error Type Cycle (O-Clinear) (O-Cfull) Reference (2400000+) 54347.5606 0.0001 I 31449.0 +0.0117 -0.0004 This paper (SWASP) 54361.3659 0.0001 II 31496.5 +0.0121 +0.0001 This paper (SWASP) 54362.3832 0.0002 I 31500.0 +0.0122 +0.0002 This paper (SWASP) 54363.4002 0.0002 II 31503.5 +0.0120 -0.0000 This paper (SWASP) 54364.4177 0.0002 I 31507.0 +0.0123 +0.0003 This paper (SWASP) 54371.3923 0.0002 I 31531.0 +0.0117 -0.0002 This paper (SWASP) 54371.5375 0.0005 II 31531.5 +0.0116 -0.0003 This paper (SWASP) 54372.4104 0.0003 II 31534.5 +0.0126 +0.0007 This paper (SWASP) 54373.4273 0.0002 I 31538.0 +0.0123 +0.0004 This paper (SWASP) 54374.4444 0.0003 II 31541.5 +0.0122 +0.0003 This paper (SWASP) 54393.3349 0.0002 II 31606.5 +0.0117 -0.0001 This paper (SWASP) 54394.3524 0.0001 I 31610.0 +0.0120 +0.0002 This paper (SWASP) 54395.3692 0.0001 II 31613.5 +0.0116 -0.0002 This paper (SWASP) 54396.3857 0.0007 I 31617.0 +0.0109 -0.0009 This paper (SWASP) 54397.4033 0.0003 II 31620.5 +0.0113 -0.0005 This paper (SWASP) 54398.4207 0.0004 I 31624.0 +0.0115 -0.0003 This paper (SWASP) 54399.4383 0.0004 II 31627.5 +0.0119 +0.0001 This paper (SWASP) 54293.5051 0.0004 I 31263.0 +0.0136 +0.0010 Brát et al. (2007) 54405.3960 0.0001 I 31648.0 +0.0116 -0.0001 Brát et al. (2008) 54597.4997 0.0003 I 32309.0 +0.0084 -0.0018 Brát et al. (2008) 54707.5050 0.0007 II 32687.5 +0.0100 +0.0007 Hübscher et al. (2010a) 54774.9294 0.0002 II 32919.5 +0.0081 -0.0007 This paper (CbNUO) 54782.9218 0.0001 I 32947.0 +0.0082 -0.0006 This paper (CbNUO) 55050.5908 0.0009 I 33868.0 +0.0063 -0.0004 Hübscher et al. (2010b) 55050.4457 0.0009 II 33867.5 +0.0065 -0.0002 Hübscher et al. (2010b) 55073.5506 0.0007 I 33947.0 +0.0062 -0.0002 Hübscher et al. (2010b) 55073.4063 0.0004 II 33946.5 +0.0073 +0.0008 Hübscher et al. (2010b) 55398.4750 0.0029 I 35065.0 +0.0055 +0.0016 Hübscher (2011) 55456.3091 0.0014 I 35264.0 +0.0041 +0.0006 Brát et al. (2011) 55456.3082 0.0022 I 35264.0 +0.0032 -0.0003 Brát et al. (2011) 55463.2841 0.0002 I 35288.0 +0.0040 +0.0006 Brát et al. (2011) 55463.2838 0.0002 I 35288.0 +0.0037 +0.0003 Brát et al. (2011) 56013.0066 0.0002 II 37179.5 -0.0015 -0.0007 The Nelson web pageb aI: primary eclipse, II: secondary eclipse. bHttp://www.aavso.org/bob-nelsons-o-c-files.

(1)

The (O-C1) diagram is shown in Fig. 2 where different symbols in size and shape are used according to the observational method and the type of eclipse for each of the timings. As shown in Fig. 2, it is clear that the variation y y pattern of the observed (O-C1) residuals from 1946 to 2012 is complex. The orbital period before about 2008y seemed to be globally sinusoidal; however, there is a large gap of about 12 years between 1982y and 1994y. This fact was noticed by Qian (2003), Xiang et al. (2009) and Yang & Dai (2009). These authors made intensive period studies of V700 Cyg and adopted a quadratic plus sine ephemeris to explain the (O-C) residuals constructed with their available timings. Fig. 2. The (O-C) diagram of V700 Cyg drawn together with the non- linear terms (solid and dashed lines) of Eq. (2). The recent residuals from Note that the initial epoch (HJD 2449999.3003) used by Eq. (2) at the bottom deviate remarkably from the non-linear terms of Eq. (2). Qian (2003) and Yang & Dai (2009) is not a primary epoch representing a deeper eclipse, rather it is a secondary epoch and the eclipse types of the timings in Table 3 from the The (O-C) residuals of all the timings were calculated with Yang & Dai (2009) study were listed reversely. The primary the linear ephemeris of Kreiner et al. (2001) as follows: timings in the Yang & Dai (2009) Table 3 should be changed http://dx.doi.org/10.5140/JASS.2012.29.2.151 154 Chun-Hwey Kim & Jang Hae Jeong V700 Cygni, A dynamically active binary II

Table 2. The Final solutions of Eqs. (3) and (4). Parameter Eq.(3) Eq.(4) Unit

T0 2445207.5007 (20) 2445207.5039 (39) HJD P 0.29063051 (39) 0.29063070 (15) day A -3.5 (4.7) × 10-12 +3.5 (1.6) × 10-12 day/P 3rd-body (j = 3) 3rd-body (j = 3) 4th-body (j = 4) 8 8 8 aj sin ij 8.86 (11) × 10 2.19 (13) × 10 6.69 (57) ×10 km 5.92 (70) 1.47 (8) 4.47 (37) AU

ωj 333 (34) 15 (11) 33 (16) degree

ej 0.532 (41) 0.934 (95) 0.068 (28) -

Pj 73.9 (3.7) 20.3 (2) 62.8 (2.4) year

Tj 2443231 (68) 2446478 (8) 2445974 (91) HJD

Kj 0.0301 (37) 0.0037 (3) 0.0258 (21) day

to secondary timings and vice-versa. Xiang et al. (2009) used the ephemeris (Eq. 1) from Kreiner et al. (2001) and improved it as follows:

(2)

The dashed and solid lines in Fig. 2 denote the linear (plus quadratic) and full terms, respectively, from Eq. (2). The residuals from Eq. (2) were plotted at the bottom of Fig. 2 where the recent timings (since 2007y) have been clearly deviating from the ephemeris, which implies that Eq. (2) should be revised and/or the period change of V700 Cyg may be more complicated. Fig. 3. The (O-C) diagram of V700 Cyg drawn together with the non- To understand the general period change behavior, we linear terms (solid and dashed lines) of Eq. (3) and Table 2. The recent residuals from Eq. (3) at the bottom show a small oscillatory pattern. tried to fit all of the times of minima to a quadratic plus LTE ephemeris described as: lines representing the quadratic and LTE terms, respectively. , (3) The residuals from the full terms were plotted in the bottom of Fig. 3. where τ3 is the light-time due to the assumed third body and As shown in Fig. 3, Eq. (3) provides a more satisfactory includes the five orbital parameters (a12 sin i12, e12, ω12, P12, fit to the observed timings than Eq. (2). The cyclic period y y y y y T12) for the mass center of the eclipsing pair around the mass is calculated as 73. 9 (±3. 7), which is 27. 9, 34. 8 and 19. 2 center of the triple system. The parametric and differential longer than those provided by Molik & Wolf (2004), Xiang et forms of the orbital elements for the light-time orbit were al. (2009) and Yang & Dai (2009), respectively. Note that the taken from Irwin (1952, 1959). The Levenberg-Marquardt photoelectric and CCD residuals at the bottom of Fig. 3 are method (Press et al. 1992) was used to solve Eq. (3) distributed in an oscillatory pattern with a small amplitude simultaneously. As shown in the 2nd column of Table 2, the of about 0.d003 and with a short period of about 20y. The final solution was quickly derived. In this and subsequent standard deviation for the photoelectric and CCD residuals calculations, we assigned different weights to the data is σ = ±0.d0019, which is 4 times larger than the nominal according to the inverse values of the scatters observed for error (±0.d0005) of the modern photoelectric and CCD the observational methods: 30 to the photoelectric or CCD timing observations. The coefficient of the quadratic term observations and 1 to the photographic, plate and visual has a value smaller than its standard error (with a negative data. The resultant (O-C) diagram with the linear term in sign), which is contrary to the findings of Xiang et al. (2009) Table 2 was drawn in Fig. 3, which shows dashed and solid and Yang & Dai (2009). This result implies that the secular

155 http://janss.kr J. Astron. Space Sci. 29(2), 151-161 (2012)

variation is not well constrained by the present timing data because the quasi-sinusoidal variation is dominant and also because the secondary oscillatory pattern is not considered in Eq. (3). To find the variation characteristics of the small oscillation in Fig. 3, we used two LTEs ephemeris, which are

expressed by simply adding τ4 to Eq. (3) as follows:

, (4)

where τ4 is the light-time due to the assumed fourth body

and also includes the five orbital parameters (a123 sin i123,

e123, ω123, P123, T123) from the mass-center of the eclipsing pair as well as the third-body revolving around the mass center Fig. 4. The (O-C) diagram of V700 Cyg drawn together with the non- linear terms (solid and dashed lines) of Eq. (4) and Table 2. of the quadruple system. The Levenberg-Marquardt method was used again to solve Eq. (4) simultaneously. Thirteen parameters were adjusted in Eq. (4). The results are listed in the 3rd and 4th columns of Table 2. The quality of the final solution represented by Eq. (4) can be judged by Fig. 4, which plots the (O-C) residuals with the linear term of Eq. (4); the dashed and solid lines represent the quadratic and full terms of Eq. (4), respectively. As shown at the bottom of Fig. 4, the standard deviation for the photoelectric and CCD residuals from the full terms of Eq. (4) is σ = ±0.d0006, which is compatible with the nominal, modern photoelectric and CCD timing accuracy. Figs. 5 and 6 show two cyclic (O-C) diagrams phased with each of their periods; the continuous lines were drawn with the solution parameters in Table 2. The residuals from the linear and full terms of Eq. (4) are listed in the fifth and sixth columns of Table 2, respectively. Fig. 5. The (O-C) diagram of V700 Cyg phased with the longer period of 63.y4 in Table 2. The arrows marked as ‘a’ and ‘b’ represent the phases that From the coefficient (A) of the quadratic term in Table 2, correspond to the light curves secured by Niarchos et al. (1997) and Yang a secularly increasing rate of the period is calculated as +8.7 & Dai (2009), respectively. (±4.0) × 10-9 day/year, which is approximately one order of magnitude lower than the results obtained by Xiang et al. (2009) and Yang & Dai (2009). The secular period increase is not convincingly revealed with the present timing data.

4. TWO CYCLIC PERIOD CHANGES

In the above section, we have decoupled two cyclic terms via Eq. (4) from the observed (O-C) residuals shown in Figs. 4-6. One LTE orbit with the longer period of 62.y8 d (Pout) has a semi-amplitude of 0. 0258 (Kout) and a relatively

small eccentricity of 0.067 (eout) while the LTE orbit with the y d shorter period of 20. 3 (Pin) has a semi-amplitude of 0. 0037

(Kin) and a remarkably large eccentricity of 0.934 (ein). There Fig. 6. The (O-C) diagram of V700 Cyg phased with the shorter period y of 20. 4 in Table 2. The arrows marked as ‘a’ and ‘b’ represent the phases is a commensurable relationship of 1:3 between Pin and Pout, corresponding to the light curves secured by Niarchos et al. (1997) and 1:7 between K and K and 14:1 between e and e . Yang & Dai (2009), respectively. in out in out Two rival theories may explain these cyclic period http://dx.doi.org/10.5140/JASS.2012.29.2.151 156 Chun-Hwey Kim & Jang Hae Jeong V700 Cygni, A dynamically active binary II

Table 3. The basic parameters for the hypothetical third and fourth mean that the additional bodies revolve around the mass bodies in the V700 Cyg system. center of the system in planes nearly coplanar with the Parameter Shorter period Longer period Unit orbital plane of the eclipsing pair. (20.y3) (62.y8) The Applegate (1992) model can alternatively explain the Mass function 0.0076 (21) 0.0227 (59) M⊙ Mass cyclical components of the period variability. According i´ = 30˚ 0.66 (3) 1.30 (33) M⊙ to this theory, the cyclic changes in the magnetic dynamo i´ = 60˚ 0.34 (4) 0.60 (2) M ⊙ activity of tidally locked cool stars in binary systems can i´ = 90˚ 0.293 (2) 0.495 (11) M⊙ Luminosity produce small cyclic orbital period modulations. Using the i´ = 30˚ 0.25 (11) 3.24 (56) L ⊙ modulation periods and amplitudes listed in Table 2 and i´ = 60˚ 0.021 (8) 0.17 (7) L⊙ i´ = 90˚ 0.011 (5) 0.080 (32) L⊙ adopting the absolute dimensions explained above, the Luminosity ratio model parameter variations needed to change the orbital (l /(l1 + l2 + l3 + l4)) i´ = 30˚ 0.05 (2) 0.64 (9) - period for V700 Cyg can be obtained from the formula i´ = 60˚ 0.012 (2) 0.096 (5) - provided by Applegate (1992). The calculations were made i´ = 90˚ 0.007 (4) 0.048 (3) - with the assumption that two cyclical period changes are produced by both components. Table 4 lists the resultant changes: 1) The LTEs are caused by additional third and Applegate parameters where the root mean square (RMS) fourth bodies in the V700 Cyg system; or 2) the Applegate luminosities converted to magnitude scale were calculated (1992) mechanism, which was improved by Lanza et al. with the formula provided by Kim et al. (1997). The (1998). If the LTEs are assumed to be the mechanism to parameters in Table 4 show that the Applegate mechanism produce two cyclic period changes, then mass functions, could operate well in both the primary and secondary masses and bolometric luminosities for different components for both cyclic period changes, although the inclinations of two tertiary bodies were calculated by using RMS luminosity variations relative to the luminosities of the absolute dimension (M1 = 0.92 M⊙, M2 = 0.60 M⊙, R1 the primary and secondary stars are 3 times smaller than

= 1.04 R⊙, R2 = 0.86 R⊙, L1 = 0.83 L⊙, L2 = 0.74 L⊙) of the the nominal value (∆L/Lp,s ≈ 0.1) that the Applegate model eclipsing pair, which was provided by Niarchos et al. (1997). requires. These small RMS luminosity variations correspond The results are listed in Table 3. In Table 3, the minimum to ±0.m01, and they may be hardly detectable from any of masses (i’ = 90˚) of 0.29 M⊙ for the third-body and 0.50 the light curves measured during the suggested modulation

M⊙ for the fourth body would contribute small fractions of periods (because of the dominant light variations caused approximately 0.7% and 5% lights, respectively, to the total by the spot activities involved). We made a morphology luminosity (lt = l1 + l2 + l3 + l4). From their VR light curves investigation of historical light curves secured at two synthesis, Yang & Dai (2009) derived a third light of about different epochs by Niarchos et al. (1997) and Yang & Dai 3% that shows a good agreement with our value. If the third (2009). The BV photoelectric light curves of Niarchos et and fourth bodies (at least one additional body) in the V700 al. (1997) show an O’Connell effect for both light curves. Cyg system are assumed to be real, the small contribution of However, the VR CCD light curves of Yang & Dai (2009) are their lights to the total light of the quadruple system would perfectly symmetrical within their observational errors.

Table 4. The Applegate model parameters for the shorter and longer periods. Parameter Shorter period (20.y3) Longer period (62.y8) Unit

Primary star Secondary star Primary star Secondary star

∆P 0.07860 0.07860 0.1775 0.1775 s ∆P/P 3.13 × 10-6 4.20 × 10-6 7.07 × 10-6 7.07 × 10-6 - ∆J 5.58 × 1046 1.90 × 1047 1.26 × 1047 9.48 × 1046 (g cm2 s-1) 53 53 53 53 2 Is 6.39 × 10 2.85 × 10 6.39 × 10 2.85 × 10 (g cm ) ∆Ω 8.73 × 10-8 1.47 × 10-7 1.97 × 10-7 3.33 × 10-7 s ∆Ω/Ω 3.49 × 10-4 5.89 × 10-4 7.88 × 10-4 1.33 × 10-3 - ∆E 9.75 × 1039 1.24 × 1040 4.97 × 1040 6.31 × 1040 erg s 31 31 31 32 ∆Lrms 4.78 × 10 6.07 × 10 7.88 × 10 1.00 × 10 erg s

0.012 0.016 0.021 0.026 L⊙

0.015 0.021 0.025 0.035 Lp,s ±0.009 ±0.011 ±0.014 ±0.018 mag B 6.58 × 103 7.59 × 103 5.62 × 103 6.48 × 103 gauss

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The observation epochs of light curves by Niarchos et al. & Guinan 1994, Maceroni & van’t Veer 1991, Stepien 1995, (1997) and Yang & Dai (2009) are marked as ‘a’ and ‘b’ with 2006, Demircan 1999). Mass and energy exchanges through an arrow in Figs. 5 and 6, respectively. As shown in Fig. 5, the connecting neck between the two components are also the light curves from Niarchos et al. (1997) were obtained possible, resulting in a thermal relaxation oscillation (TRO; from a position somewhat distant from the ascending Lucy 1976, Flannery 1976, Robertson & Eggleton 1977). If nodal point in the 63.y4 sinusoidal curve, but Yang & Dai’s we assume that the two mechanisms occur concurrently (2009) obtained their light curves just near the descending in any contact binary system and that the size of the period nodal point. Because the two epochs are near nodal points decreasing rate predicted by the AML is slightly smaller than and the Applegate RMS brightness variation calculation that of the increase rate caused by a mass transfer from the is small, the expectation is that the light curves at the two less massive component to the more massive component, epochs are symmetrical, but the reality described above is then a weak secular period increase could possibly be different. In Fig. 6, we see that the light curves of Niarchos observed (as in the V700 system). Under this assumption, et al. (1997) and Yang & Dai (2009) were observed near the an observed secular period rate can be formulated as the bottom and top, respectively, of the highly quasi-sinusoidal sum of the period change rates of the two mechanisms as curve with the 20.y4 shorter period. If the Applegate follows: mechanism is assumed to be a cause of the shorter period modulation, then any light curves at the positions should , (5) show as asymmetrical because of the highly enhanced magnetic activities, but the perfect symmetric light curves from Yang & Dai (2009) defy that explanation. Based on where the first and second terms in the right side represent these discussions, the preferred explanation is that the the period variation rates due to magnetic braking (mb) geometrical LTEs (due to the third and fourth stars) cause and mass transfer (mt), respectively. In the case of V700 the two cyclic period variations, although the Applegate Cyg, the decreasing period rate caused by the magnetic mechanism cannot be ruled out based on the presently braking was determined to be -5.8 × 10-8 day/year with the available insufficient data (light curves and timings). formula provided by Bradstreet & Guinan (1994). Therefore, the secular period increase by a mass transfer from the less massive star to the more massive one is calculated with Eq. 5. DISCUSSION AND CONCLUSION (5) as +6.7× 10-8 day/year, which is comparable to those of other W UMa contact binaries (e.g., Wolf et al. 2000, Qian To understand the dynamical picture of this active W 2003, Kim et al. 2003, Lee et al. 2008). If this picture is true UMa binary system in detail, we analyzed a total of 148 of V700 Cyg, then the system is on an evolutionary phase timings of V700 Cyg, including our two timings and 59 in that the increasing period rate by a secular mass transfer others that were calculated from the SWASP observations. from the less massive hot star to the more massive cool It was found that the orbital period of the system has varied one is comparable to or slightly larger than the decreasing over about 66y in two cyclical components superposed on rate by a secular AML (due to magnetic braking). Future a weakly constrained upward parabola. Three decoupled timings are important in resolving whether this conjecture components of the period variability were investigated. is realistic. The secular period increase of +8.7 (±4.0) × 10-9 day/ In addition to the secular period increase, the complex year is one order of magnitude lower than those obtained period variations of V700 Cyg were decoupled into two previously (Xiang et al. 2009, Yang & Dai 2009), indicating cyclical components via two LTE ephemeris. The inner y y that the secular period increase over 66 is not convincingly orbit has a period of 20. 3 (Pin), a small semi-amplitude of d revealed with the present timing data. The weak secular 0. 0037 (Kin) and a remarkably large eccentricity of 0.934 y period increase of V700 Cyg may be a special feature in (ein), while the outer orbit has a longer period of 62. 8 (Pout), d that the secular period increases (or decreases) of most a semi-amplitude of 0. 0258 (Kout) and a small eccentricity of of W UMa contact binaries are approximately one or two 0.067 (eout). Some commensurable relations between these orders of magnitude larger than that of V700 Cyg (e.g., Wolf elements seem to exist such as Pin:Pout ≈ 1:3, Kin:Kout ≈ 1:7, et al. 2000, Qian 2003, Kim et al. 2003, Lee et al. 2008). In and ein:eout ≈ 14:1. Our investigation shows that these types general, W UMa binaries are known to suffer from a secular of commensurabilities, particularly between periods, exist period decrease via angular momentum loss (AML) due to possibly in some eclipsing binary stars with orbital periods magnetic braking (van’t Veer 1979, Rucinski 1982, Bradstreet that have been reported to suffer from two sinusoidal period http://dx.doi.org/10.5140/JASS.2012.29.2.151 158 Chun-Hwey Kim & Jang Hae Jeong V700 Cygni, A dynamically active binary II

changes. For example, there is a 40:11 relationship between the primary and secondary stars are 3 times smaller than the m the shorter and longer periods in the OO Aql system nominal value (∆L/Lp,s ≈ 0.1), which corresponds to ±0. 01 (Albayrak et al. 2005), 13:5 in the VW Cep system (Zasche & and may be hardly detectable from the light curves because Wolf 2007), 7:2 in the WZ Cep system (Jeong & Kim 2011), 7:1 of the spot activities involved. The historical light curves in the AH Cep (Kim et al. 2005), 2:1 in the SZ Her system (Lee at different epochs do not seem to follow the mechanism, et al. 2012), 11:3 in the T LMi system (Zasche et al. 2006), although the Applegate mechanism cannot be ruled out 41:7 in the SW Lyn system (Kim et al. 2010), and 5:2 in the based on the evidence currently available. V508 Oph system (Albayrak et al. 2005). Similar relationships are also found in other eclipsing binary systems, which are known to have sub-stellar companions (see Lee et al. 2012). ACKNOWLEDGMENTS If these commensurable relationships are truly produced by additional bodies in the systems, they would be interpreted This paper is dedicated to the late Robert H. Koch who as a stable orbital resonances produced by a long-term remains in our memories as an admirable teacher and best gravitational interaction between two tertiary bodies in the friend. We are also grateful for his major contributions to systems (Peale 1976, Kley et al. 2004). If so, it is important to close binary stars. This study used the Simbad database question their origin and evolution. Are the tertiary bodies maintained at CDS, Strasbourg, France. Photometric data captured dynamically during the long evolutionary path of from the WASP public archive were used in this paper. a close binary or are they formed primordially as a multiple The WASP consortium is comprised of the University of system? At the moment, these questions are difficult to Cambridge, Keele University, University of Leicester, the answer. However, observational evidence supports the Open University, Queen’s University in Belfast, St. Andrews latter question (Tokovinin et al. 2006, Rucinski et al. 2007, University, and the Isaac Newton Group. Funding for WASP Eggleton & Tokovinin 2008). Eggleton (2012) suggested a comes from the consortium universities and from the UK series of evolutionary sequences in a global manner, which Science and Technology Facilities Council. This work was may provide a good answer to the latter question. According supported by the research grant of the Chungbuk National to Eggleton (2012), the primordial triple systems in which University in 2010. the inner and outer orbits have a high mutual inclination secularly evolve through Kozai (1962) cycles and induced tidal frictions into close binaries within 10-day periods. Due REFERENCES to magnetic braking, the late type close binaries can further evolve into contact binaries with common envelopes via Agerer F, Hübscher J, Photoelectric minima of selected AML. After suffering from many TRO processes, the contact eclipsing binaries and maxima of pulsating stars, IBVS, binaries emerge into single stars because of violent Darwin 5296, 1-16 (2002). instability. Finally, wide binaries consisting of emerged Albayrak BA, Period study of the close binary V508 single stars and relatively unchanged components remain. If Ophiuchi, PASA, 22, 311-314 (2005). http://dx.doi. this scenario is correct, then the additional bodies we have org/10.1071/AS05014 suggested in the V700 Cyg system may be evidence that Applegate JH, A mechanism for orbital period modulation strongly supports the scenario. The minimum masses for in close binaries, ApJ, 385, 621-629 (1992). http:// the inner and outer bodies of V700 Cyg were derived as 0.29 dx.doi.org/10.1086/170967

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