Orbital period correction and light curve modeling of the W-subtype shallow contact binary OWLeo
aa r X i v : . [ a s t r o - ph . S R ] J u l Research in Astron. Astrophys. Vol.0 (200x) No.0, 000–000 http: // // / journals / raa R esearchin A stronomyand A strophysics Orbital period correction and light curve modeling of theW-subtype shallow contact binary OW Leo
Xiao Zhou , , and Shengbang Qian , , , Yunnan Observatories, Chinese Academy of Sciences (CAS), P.O. Box 110, 650216 Kunming, P. R.China [email protected] Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences,P. O. Box 110, 650216 Kunming, P. R. China Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, ChaoyangDis-trict, Beijing, 100012, P. R. China University of the Chinese Academy of Sciences, Yuquan Road 19
Abstract
Orbital period and multi-color light curves’ investigation of OW Leo are pre-sented for the first time. The orbital period of OW Leo is corrected from P = . P = . q = . f = . M = . M ⊙ , M = . M ⊙ , R = . R ⊙ , R = . R ⊙ , L = . L ⊙ and L = . L ⊙ .The evolutionary status show that the more massive star is less evolved than the less mas-sive star. OW Leo has very low metal abundance, which means its formation and evolutionare hardly influenced by any additional component. It is formed from an initially detachedbinary systems through nuclear evolution and angular momentum loss via magnetic brak-ing, and have passed a very long time of main sequence evolution. Key words: techniques: photometric – binaries: eclipsing – stars: evolution
Contact binaries, both inside and outside our Galaxy, have been proved to be powerful tools for study-ing a wide spectrum of astrophysical problems. They usually consist of F, G and K type stars and thecomponent stars are embedded in a common envelope. Due to the strong interactions between the com-ponent stars, the formation and evolution scenario for contact binaries are entirely and totally di ff erentfrom those of single stars, and still remains to be an open issue. A few years ago, many contact binarieshave been observed by photometric method. However, only very few targets have spectral informationdue to the low e ffi ciency of spectroscopic observations. Owe to the Large Sky Area Multi-Object FibreSpectroscopic Telescope (LAMOST) (Cui et al. 2012; Zhao et al. 2012), hundreds of thousands of con-tact binaries are provided with stellar atmospheric parameters, which makes it a better time to investigatecontact binaries (Qian et al. 2017, 2018).OW Leo, also named GSC 01443-00087 or NSVS 10352593, is a newly reported EW-type binary(Diethelm 2010). Its period was given as P = . Zhou et al. (VSX) (Watson et al. 2006). The binary system was observed by the LAMOST project for two times,which were on March 24, 2013 and February 6, 2018. The low resolution spectra gave out two sets ofstellar atmospheric parameters, which were listed in Table 1. There is no radial velocity curve publishedfor the target and its light curves haven’t been analysed yet. In the present work, we will state ourphotometric observation on OW Leo in Section 2. Then, all available mid-eclipse times are gathered toinvestigate the orbital period changes of OW Leo in Section 3, and our observational light curves andlight curve from All-Sky Automated Survey for SuperNovae (ASAS-SN) are modeled to get its physicalparameters in Section 4. Finally, the formation and evolution theory of OW Leo will be discussed inSection 5.
Table 1
Stellar atmospheric parameters of OW Leo.
T (K) Log (g) [Fe / H] Date5605 4.131 -0.734 March 24, 20135724 4.250 -0.606 February 6, 2018
The multi-color light curves of OW Leo were obtained on January 5 and 8, 2019 with the Xinglong85cm optical telescope of National Astronomical Observatories, Chinese Academy of Sciences. Thetelescope was equipped with a 2K ×
2K CCD Camera, and its field of view (FOV) was 32.8 squarearc-minutes (Zhou et al. 2009; Zhang et al. 2018). Four filters ( B , V , R C and I C ) from Johnson-Cousins’filters systems were chosen for the observations and the observational images were processed with theImage Reduction and Analysis Facility (IRAF) (Tody 1986). UCAC4 546-051376 and UCAC4 546-051360 in the same field of view were chosen as the Comparison (C) star and Check (Ch) star since weused the di ff erential photometry method to obtain the light variations of OW Leo. Their coordinates inJ2000.0 epoch and magnitudes in V band are listed in Table 2. Finally, we got the light variations of OWLeo and the observational light curves were plotted in Fig. 1. Table 2
Coordinates and V band magnitudes. Target α δ V ma g OW Leo 11 h m s . + ◦ ′ ′′ . . h m s . + ◦ ′ ′′ . . h m s . + ◦ ′ ′′ . . As shown in Fig. 1, we got the primary minimum (Left of Fig. 1 ) and secondary minimum (Rightof Fig. 1) of the eclipsing binary system. Then, parabola fit were applied on the observed light minimacurves and the mid-eclipse times were determined, which were listed in Table 3.
Table 3
New CCD times of mid-eclipse times.
JD (Hel.) Error (days) p / s Filter Date2458488.3337 ± . B V R C I C January 5, 20192458491.4265 ± . B V R C I C January 8, 2019
Orbital period variations are quite common among close binary systems due to the possible angularmomentum loss (ALM) from binary systems or mass transfer between the primary or secondary stars -subtype shallow contact binary of OW Leo 3 m ag HJD-2458400 m ag Fig. 1
The light curves obtained on January 5 are plotted in the left panel of Fig. 1 and thelight curves obtained on January 8 are displayed in the right. The blue, green, yellow and redcolors refer to light curves observed with B , V , R C and I C filters, respectively. The magnitudedi ff erences between the Variable star (OW Leo) and Comparison star (UCAC4 546-051376)are plotted with solid circles and the magnitude di ff erences between the Comparison star(UCAC4 546-051376) and Check star (UCAC4 546-051360) are plotted with open circles.(Zhang et al. 2018; Liu et al. 2018). Thus, the O - C method was widely used in correcting orbitalperiod or calculating orbital period variations of close binaries (Pi et al. 2017; He & Wang 2019). Foranalysis the orbital period of OW Leo, all available mid-eclipse times are gathered and listed Table 4.The descriptions for each column of Table 4 are:Column 1 - the observed mid-eclipse times in HJD;Column 2 - primary (p) or secondary (s) light minima;Column 3 - cycle numbers calculated from Equation 1;Column 4 - the calculated O − C values basing on Equation 1;Column 5 - observational errors;Column 6 - the references;The O − C values listed in Column 4 of Table 4 are calculated with the linear equation: Min . I ( HJD ) = . + d . × E . (1)As displayed in Fig. 2, linear fit is performed on the observed O - C curve, which means the orbitalperiod of OW Leo should be corrected from 0.325545days to 0.32554052days. The new ephemeris isdetermined to be: Min . I = . ± . + d . ± . × E (2) Zhou et al.
Table 4
Mid-eclipse times and O − C values of OW Leo. JD(Hel.) p / s Epoch O − C Error Ref.(2400000 + ) (days) (days)53175.509 p 0 0 155269.7211 p 6433 -0.0189 0.0005 155604.8643 s 7462.5 -0.0243 0.0006 255973.8650 p 8596 -0.0288 0.0007 356041.7390 s 8804.5 -0.0310 0.0021 358488.3337 p 16320 -0.0697 0.0002 458491.4265 s 16329.5 -0.0696 0.0001 4 Reference: (1) Diethelm (2010); (2) Diethelm (2011); (3) Diethelm (2012); (4) the present work. -0.08-0.07-0.06-0.05-0.04-0.03-0.02-0.010.000.01 0 2000 4000 6000 8000 10000 12000 14000 16000-0.0050.0000.005 O - C ( da ys ) R e s i dua l ( da ys ) E Fig. 2
The black dots in the upper panel refer to observational O - C values calculated fromEquation 1 and the red line represents theoretical O - C curve based on Equation 2. The fittingresiduals are shown in the lower panel of Fig. 2.
The modeling of OW Leo’s light curves have been left out since the eclipsing binary system was discov-ered. We are going to modeling its light curves with the Wilson-Devinney program (Wilson & Devinney1971). The target have been observed by the LAMOST sky survey project for two times and the low res-olution spectra show that OW Leo is an solar-type binary system. The averaged temperature of 5665Kwas assumed to the component star. The gravity-darkening coe ffi cients are correspondingly assumed tobe g = g = . ffi cients are assumed to be A = A = . ffi cients are chosen accordingly (Van Hamme 1993). Thephased light curves are calculated from the linear ephemeris equation: -subtype shallow contact binary of OW Leo 5 Min . I ( HJD ) = . + d . × E . (3) As displayed in Fig. 3, the observed light curves are EW-type. Thus, Mode 3 for contact binary, Mode 4and Mode 5 for semi-contact binary are chosen to modeling the observational light curves. Since there isno radial velocity curves published, the q-search method is used to get the initial mass ratio (Zhou et al.2018). At first, the temperature of 5665K was assumed to the primary star ( T ), and the adjustableparameters are orbital inclination ( i ), modified dimensionless surface potential of the two componentstars ( Ω , Ω ), mean surface temperature of the secondary star ( T ), bandpass luminosity of the twocomponent stars ( L , L ). Then, we find that the light curves of OW Leo converged in Mode 3 and itsmass ratio ( M / M ) should be larger than 1, which mean that OW Leo is a W-subtype contact binarysystem. Therefore, the temperature of 5665K is assumed to the secondary star ( T ). The correspondingq-search diagram are shown in Fig.4. Then, the initial mass ratio is given to be q = .
05 and set as afree parameter to run the Wilson-Devinney program again. Finally, the physical parameter of the binarysystem are determined, which are listed in Table 5. The synthetic light curves are also plotted in Fig. 3. Itshould be pointed out that we also try to set third light ( l ) as a free parameter, but the light contributionfrom a tertiary component is not detected. Table 5
Photometric results of OW Leo
Parameters Values T ( K ) 5665(assumed)q ( M / M ) 3.05( ± . i ( ◦ ) 68.2( ± . T ( K ) 5885( ± ∆ T ( K ) 220( ± L / ( L + L ) ( B ) 0.3169( ± . L / ( L + L ) ( V ) 0.3041( ± . L / ( L + L ) ( R c ) 0.2981( ± . L / ( L + L ) ( I c ) 0.2937( ± . r ( pole ) 0.2731( ± . r ( side ) 0.2852( ± . r ( back ) 0.3220( ± . r ( pole ) 0.4540( ± . r ( side ) 0.4883( ± . r ( back ) 0.5157( ± . Ω = Ω ± . f . ± Σ ω ( O − C ) OW Leo was also observed by the All-Sky Automated Survey for SuperNovae (ASAS-SN)(Shappee et al. 2014; Jayasinghe et al. 2018) from January 25, 2013 to November 28, 2018. The datafrom the ASAS-SN was plotted in Fig. 5 (a). To modeling the data, we converted it to phased light curve.The light curve in Fig. 5 (b) was calculated basing on the original orbital period P = . P = . Zhou et al. R C I C V m ag Phase B
Fig. 3
The black dots are observational light curves obtained with the Xinglong 85cm opticaltelescope. The red lines are synthetic light curves from the Wilson-Devinney program. qq min = 3.05 Fig. 4
The q-search diagram. -subtype shallow contact binary of OW Leo 7 M ag HJD - 2456300 M ag Phase
Phase (c)(b) (a)
Fig. 5
Observational and synthetic light curves from ASAS-SN.
The orbital period and light curves of OW Leo are investigated for the first time, which reveal that itsorbital period should be corrected from P = . P = . q = . f = . M = . M ⊙ basing on its e ff ective temperature of T = K (Cox 2000). Then, the other absolute parameters of the two component stars are calculated and listed inTable 6. And the orbital semi-major axis is calculated to be a = . ± . R ⊙ according to the kepler’sthird law. Table 6
Absolute parameters of the component stars in OW Leo
Parameters Primary star Secondary star M . ± . M ⊙ . ± . M ⊙ R . ± . R ⊙ . ± . R ⊙ L . ± . L ⊙ . ± . L ⊙ Although the researches on contact binaries have a very long history, the formation and evolu-tion theory of contact binaries are still incomplete. Webbink (1976) proposed that contact binaries areevolved from initially detached binary systems. The more massive component in a binary system ex-panded first and filled its critical Roche lobe, and then transfer masses to the less massive companionstar through the inner Lagrangian point of the binary system. In recent years, more and more contact
Zhou et al. binaries were reported to have additional components orbiting around the central binaries (Yang et al.2019; Zhou & Soonthornthum 2019; Zhang et al. 2020). The additional components may be ejectedfrom the center of initially multiple star system and pump out angular momentum from the multiplestar system, and left out a tight binary system, which will evolve to a contact binary system finally,especially for the formation of M-type contact binaries (Goodwin et al. 2004; Qian et al. 2015). Basingon the statistical research of stellar atmospheric parameters of EW-type binaries from the LAMOST,Qian et al. (2019) pointed out that the metal abundance of over 80 % EW-type binaries are lower thanthe Sun, which means that they are old population stars. They may evolve from initially detached binarysystems through nuclear evolution and angular momentum loss via magnetic braking.According to the stellar atmospheric parameters in Table 1, we can see that OW Leo is a shallowcontact binary with very low metal abundance. Thus, it may have not contaminate by material from anadditional component. It should be evolved from an initially detached binary systems through a verylong time of main sequence evolution. And the absolute parameters of several more W-subtype shallowcontact binaries are collected and listed in Table 7. Their evolutionary status are shown in Fig. 6. We cansee that the less massive stars have already evolved away from the terminal-age main sequence(TAMS),while most of more massive stars are still stay in the main sequence belt. For W-subtype shallow contactbinaries, the more massive stars expand and fill the critical Roche lobe on its way evolving to the redgiant branch (RGB), and transfer masses to the less evolved component stars. The transferred massesalso filled the critical Roche lobe of the less massive star and formed the thin common envelope withthe two component star embedded inside. Therefore, the less massive stars will seem more evolved thanthe more massive components.
Table 7
The W-subtype shallow contact binaries.
Target M M R R L L Ref.V1007 Cas 0 . M ⊙ . M ⊙ . R ⊙ . R ⊙ . L ⊙ . L ⊙ . M ⊙ . M ⊙ . R ⊙ . R ⊙ . L ⊙ . L ⊙ . M ⊙ . M ⊙ . R ⊙ . R ⊙ . L ⊙ . L ⊙ + . M ⊙ . M ⊙ . R ⊙ . R ⊙ . L ⊙ . L ⊙ + . M ⊙ . M ⊙ . R ⊙ . R ⊙ . L ⊙ . L ⊙ . M ⊙ . M ⊙ . R ⊙ . R ⊙ . L ⊙ . L ⊙ Reference: (1) Li et al. (2018); (2) Li et al. (2019); (3) Zhou & Soonthornthum (2020); (4) Li et al. (2020); (5) Shokry et al.(2020)
Acknowledgements
This research was supported by the National Natural Science Foundation ofChina (Grant No. 11703080, 11703082 and 11873017), the Joint Research Fund in Astronomy (GrantNo. U1931101) under cooperative agreement between the National Natural Science Foundation ofChina and Chinese Academy of Sciences, and the Yunnan Fundamental Research Projects (Grant No.2018FB006). We acknowledge the support of the sta ff of the Xinglong 85cm telescope. This workwas partially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories, Chinese Academy of Sciences. Guoshoujing Telescope (theLarge Sky Area Multi-Object Fiber Spectroscopic Telescope LAMOST) is a National Major ScientificProject built by the Chinese Academy of Sciences. Funding for the project has been provided by theNational Development and Reform Commission. LAMOST is operated and managed by the NationalAstronomical Observatories, Chinese Academy of Sciences. References
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