International Journal of Application or Innovation in Engineering & Management (IJAIEM) Web Site: www.ijaiem.org Email: [email protected] Volume 3, Issue 5, May 2014 ISSN 2319 - 4847

Spectroscopic Analysis of Eclipsing Binary

Bushra Q. AL-Abudi1 and Rossul A. Abdulkareem 2

1,2University of Baghdad, College of Science, Astronomy and Space Department, Baghdad-Iraq

ABSTRACT In this paper, spectroscopic analysis of two eclipsing binaries systems ER Vul and BX And is presented. New orbital parameters were obtained by performing three computer modeling. The first model is software package PHOEBE based on the Wilson– Devinney method, the second is Binary Maker 3 (BM3) and the third is Spectroscopic binary solver (SBS). Our results are in good agreement with those obtained using the same modeling.

Key words: Eclipsing binaries, Spectroscopic, PHOEBE package, Binary Maker 3 and spectroscopic binary solver.

1. INTRODUCTION The study of binary stars is vitally important in astronomy because it is only by carefully measuring the interactions between stars that we can accurately determine their absolute characteristics such as mass, , and radius. In this paper, we will be discussed three computer modeling PHOEBE, Binary Maker 3(BM3) and spectroscopic binary solver (SBS) for analysis the of eclipsing binaries systems ER Vul and BX And of the short period group RS CVn binaries.

ER Vulpeculae (HD 200391, BD+27° 3952, HIP 103833, V = 7. 36ᵐ, P = ) is a double-lined spectroscopic binary, its was first determined by Northcott and Bakos (1956,1967)[1]. The spectroscopic orbit of the ER Vul was determined by McLean (1982) and several other radial velocity studies have been performed in recent e.g. Hall et al. 1990; Gunn et al. 1996 [2]. Hall (1976) classified ER Vul as a member of the short-period group of RS CVn systems, with main sequence components in a detached configuration. The RV of both components of ER Vul has been the subject of intense studies over many decades by several researchers. The first radial velocity curves of both components of ER Vul, based on an average of a dozen lines, which are taken between1949–1951 at David Dunlap Observatory, were published by Northcott and Bakos (1956). They found a systemic velocity of -25.2 km⁄sec and derived RV curve semi- amplitudes of 138.5 and 149.3 for the primary and secondary component, respectively. Alexandru and Călin detected a periodicity in the O–C curve of ER Vul and proved its detectability. They investigated the standard mechanisms for modulation and they emphasized a statistically significant increase of the orbital period of ER Vul. They proposed a methodology for estimating the detectability of periodic signals [3]. The orbital phases have been calculated with the following ephemeris: HJD (MinI) = 2 449 564.31173+ × E In this paper, we used this observation for analysis the radial velocity. Figure 1 shows the radial velocity of this binary [2].

Figure 1: Radial velocity of ER Vul

Ronald et.al observed the short-period eclipsing binary system BX And on five nights in 1976 at the Morgan Monroe station of the Goethe link Observatory of Indiana University. They found that BX And binary system consists of an F type primary component and a K secondary component [4]. The first radial velocity data and absolute dimensions of the system were obtained by Bell et. al. [5], where the data were phased according to the ephemeris: HJD (MinI) = 2446705.49310 0.00012 + E.0.61011258

In this paper, we used this observation for analysis the radial velocity. Figure 2 shows the radial velocity of this binary [5].

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Figure 2: Radial velocity of BX And This paper is organized as follows. We analyzed spectroscopic data in section 2. Section 2 .1 analyzed the radial velocities using PHOEBE and the physical parameters for the systems are calculated. Section 2 .2 analyzed the radial velocities using Binary maker 3 .Section 2 .3 analyzed the radial velocities using Spectroscopic Binary Solver (SBS). Section 3 is devoted to conclusions.

2. DATA ANALYSIS In order to modeling the radial velocities of eclipsing binaries ER Vul and BX And, we applied three different models: the first is PHOEBE (Prša and Zwitter 2005)[6] which is released under the GNU public license., it is modeling software for eclipsing binaries which uses the Wilson- Devinney code. The second is Binary maker 3 (BM3) and the third is Spectroscopic binary solver (SBS).

2.1 ANALYSIS with PHOEBE In order to analysis the radial velocities of these eclipsing binaries using PHOEBE, we added the experimental data in arrange consists of two columns the first column represents the independent variables, in this cause is phase, Then we plotted the synthetic and the experimental radial velocities of ER Vul and BX And as shown in figure 3 and figure 4, respectively.

Figure 3: Synthetic and plotted radial velocity curve of eclipsing binary ER Vul

Figure 4: Synthetic and plotted radial velocity curves of eclipsing binary BX And Volume 3, Issue 5, May 2014 Page 42

International Journal of Application or Innovation in Engineering & Management (IJAIEM) Web Site: www.ijaiem.org Email: [email protected] Volume 3, Issue 5, May 2014 ISSN 2319 - 4847

In this paper, we concentrated on the specific parameters identified in table 1.

Table 1: List of geometric and physical parameters in PHOEBE Parameters Description q Mass ratio i Inclination of orbit TAVH Temperature K effect of primary in TAVC Temperature effect of secondary star in K SMA Semi - major axis VGA Center of mass velocity in km/s Ω Non-dimensional surface potential K1 Semi amplitude of the primary component K2 Semi amplitude of the secondary component Systematic velocity

In order to obtain the physical and geometric parameters of the binary components, we adjusted a numerical eclipsing binary model to the observations; the mass-ratio of ER Vul and BX And were fixed at the values of 0.96 and 0.49, respectively and we fixed the values of the of the primary component (T1) ;these values are 6050 and 6600 for ER Vul and BX And binaries, respectively . This model and for a given q has the following adjustable parameters: the (i), the non-dimensional potentials ( 1 and 2 ), the effective temperature of the secondary component (T2). After some iteration we get the best match between the synthetic and the experimental radial velocity curve of the eclipsing binaries ER Vul and BX And as shown in the figure 5 and figure 6, respectively. The radial velocity curves residuals windows plot the difference between experimental and synthetic radial velocity curves verses the phase; Figure 7 and figure 8 show the residuals of both binaries. Table 2 presents the physical and orbital parameters of ER Vul and BX And from using PHOEBE model.

Figure: 5 The best match between the synthetic and the experimental radial velocity curve of binary ER Vul

Figure 6: The best match between the synthetic and the experimental radial velocity curve of binary BX And

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Figure 7: Residuals obtained from fitting routine of eclipsing binary ER Vul

Figure 8: Residuals obtained from fitting routine of eclipsing binary BX And

Table 2: The physical and orbital parameters of ER Vul and BX And Using PHOEBE parameters ER Vul Cakırli et.al. [2] BX And Bell et.al.[5] Mass 1 1.11 1.09 1.63 1.52  0.05 Mass 2 1.06 1.06 0.81 0.75  0.03 TAVH 6050 6010 6600 6800  200 TAVC 6016 5883 5362 4500  200 R1 1.05 1.16 1.78 1.78  0.03 R2 0.88 1.18 1.40 1.30  0.03 Ω(L1) 3.68 - 2.87 - Ω(L2) 3.16 - 2.57 - Mbol 1 4.87 4.28 4.36 2.79  0.13 Mbol 2 4.47 4.31 3.98 5.26  0.20 Inclination 67.138 ° 66.32° 76.35° 75.50° PHSV 5.06 - 2.95 - PCSV 5.69 - 2.81 - SMA 4.29 4.27 4.21 4.32

VGA -24.95 −25.2 -45.36 -45.11

2.2 ANALYSIS with BINARY MAKER 3 After providing experimental radial velocity curve data to the Binary Maker 3 we added input parameters to construct meaningful binary models. Binary Maker 3 was used to determine a preliminary solution to the radial velocity curves. To create the synthetic radial velocity curves of eclipsing binaries ER Vul and BX And, we pressed the Render button at the bottom of the User Input dialog and the radial velocity curves are plotted in the radial velocity curve window as shown in figures 9 and 10, respectively. Tables 3 and 4 show the output from binary maker for ER Vul and BX And eclipsing binary stars respectively.

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Figure 9: : The synthetic and the experimental radial velocity curves of binary ER Vul

Figure 10: The synthetic and the experimental radial velocity curves of binary BX And

Table 3: The output from Binary Maker of eclipsing ER Vul Ω1= 5.070 Ω 2 = 4.824 Mean radius 1 = 0.245 Mean radius 2 = 0.125 inclination = 68.300 Eccentricity = 0.000 mass ratio input = 0.961[7] Period = 0.698 temperature 1 = 6050 temperature 2 = 6016 K1 = 139.5 K2 = 145.8 V0= -24.6

Table 4: The output from Binary Maker of eclipsing binary star BX And Ω1= 2.864 Ω2= 2.864 Mean radius 1 = 0.442 Mean radius 2 = 0.320 inclination = 75.500 Eccentricity = 0.000 mass ratio input = 0.497[7] Period = 0.610 temperature 1 = 6600 temperature 2 = 4800 K1 = 105.5 K2 =212.3 V0= -45.1

2.3 Analysis with Spectroscopic Binary Solver (SBS)

The radial velocity of star in a binary system is defined as follows [8]: V=  Kcos( )  ecos………..(1) where  is the systematic velocity, K is the semi-amplitude of the velocity curve and  ,, e are the angular polar coordinate (true anomaly), the longitude of periastron and the eccentricity, respectively . The quantities θ and ω are measured from the periastron point and the spectroscopic reference line (plane of sky), respectively. The mass-ratio q can be determined from the ratio of the semi-amplitudes q = K2/K1. Also the semi-amplitude of the velocity curve may also be determined by 2 a sin i K  ……………...(2) P 1- e2 Volume 3, Issue 5, May 2014 Page 45

International Journal of Application or Innovation in Engineering & Management (IJAIEM) Web Site: www.ijaiem.org Email: [email protected] Volume 3, Issue 5, May 2014 ISSN 2319 - 4847 where a is the semi axis of the orbit around the center of mass, P is the period of motion, and inclination i is the angle between the line of sight and the normal of the orbital plane. Thus, since we know P, e and K, we can determine a sin i – but we cannot determine a or i separately. According to definition of the center of mass, the mass ratio in the system is obtained as: M a sin i 2  1 ………………(3) M 1 a2 sin i According to Kepler’s third law and equation 3 , the following relation is obtained 2 3  a1 sin i  a2 sin i  M1 sin i  a2 sin i  ………..(4)  P  A similar relation is obtained for the secondary component only by replacing 1 with 2 and vice versa, in the equation 4. We adopted the mass ratio q = M2/M1 = 0.96 for ER Vul and 0.49 for BX And from our radial velocity . The Root Mean Square (RMS) can be calculated from the following equation [8]: RMS = ………....(5)

Where Vobs represents observed radial velocity,Vcalc represents numerical calculated velocity, and N represents the number of iterations where a few iterations often produce a reasonably good fit to the observed radial velocity data. We note that the best fit is achieved when the calculated RMS value is minimized. In this work, we used Spectroscopic Binary Solver software (SBS) [9] to calculate the orbital parameters of a binary star system based on observed radial velocities relevant to equation 1.For spectroscopic binaries where both components radial velocities are measurable, it is possible to determine the spectroscopic orbital solution. After providing experimental radial velocity curve data to the (SBS), we added input parameters to construct meaningful binary models, then we begin the analysis by clicking on the Read File button to select data file containing radial velocity observations per star. Each line of data must consist of an observation time (in decimal days) and a measured radial velocity (in km/s or m/s) separated by either spaces or tabs. After providing experimental radial velocity curve data to the SBS, we make some iteration by clicking on solve button till we get the less value of Root Mean Square. Figures 11 and 12 show the Synthetic and observation data radial velocity curves for both binaries while figures 13 and 14 show orbital parameters fitted to the observation data radial velocity curves for ER Vul and BX And, respectively. The orbital parameters and a comparison are given in tables 5 and 6 for both binaries.

Figure 11: Synthetic and observation data radial velocity curves of eclipsing binary ER Vul.

Figure 12: Synthetic and observation data radial velocity curves of eclipsing binary BX And Volume 3, Issue 5, May 2014 Page 46

International Journal of Application or Innovation in Engineering & Management (IJAIEM) Web Site: www.ijaiem.org Email: [email protected] Volume 3, Issue 5, May 2014 ISSN 2319 - 4847

Figure13: The best match between the synthetic and the experimental radial velocity curve of eclipsing binary ER Vul

Figure 14: The best match between the synthetic and the experimental radial velocity curve of eclipsing binary BX And

Table5: New Orbital parameters of ER Vul Present Paper Cakırli et.al. [2] Period 0.6980  0.00e 0.6982  0.00e  (km s-1) -26.6  0.000 −28.3  3.3 -1 K1( km s ) 141.5  0.000 139.3  4.6 -1 K2 (km s ) 149.8  0.000 144.3  5.2 35.42 _ 1 () 180.0 _ 2 () a1sin i (km) 1.329e + 06  0.00e 1.92  0.07 a2sin i (km ) 1.433e + 06  0.00e 1.99  0.08 3 M1 sin i (M ) 8.943e - 01  0.00e 0.84  0.07 3 M2 sin i (M ) 8.296e -01  0.00e 0.81  0.06 e 0.000 _

q= M2 /M1 0.93  0.00e 0.96  0.05

Table6: New Orbital parameters of BX And Present Paper Bell et.al.[5] Period 0.631  0.00e 0.610  (km s-1) -45.6  0.00 -45.1  2.7 -1 K1( km s ) 106.0  0.00 105.5  1.9 -1 K2 (km s ) 212.3  0.00 212.3  4.0

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0.0  0.0 _ 1 () 180.0 0.0 _ 2 ()  a1sin i (km) 8.893e+05  0.00 1.272  0.022 a2sin i (km ) 1.7811e+06  0.00 2.559  0.048 3 M1 sin i (M ) 1.359e  0.00 1.358  0.045 3 M2 sin i (M ) 6.788e-01  0.00 0.675  0.022 e 0.0 0.0

q= M2 /M1 0.497  0.00 0.497  0.013

3. CONCLUSIONS In this paper, the results from a radial velocity analysis of the eclipsing binaries ER Vul and BX And are presented and discussed. The analysis of spectroscopic data of both eclipsing binaries using PHOEBE, BM3 and SBS models has allowed us to determine the orbital parameters of the component stars. By iterative adjustment parameters best fitting to experimental data are established. PHOEBE, BM3 and SBS programs plotted the radial velocity curves for each system. 3 3 New orbital parameters such as systematic velocity, semi amplitude, a1sin i, a2sin i, M1 sin i, and M2 sin i are determined. Our numerical calculations show that the results obtained for the orbital parameters are in good agreement with those obtained by other researchers.

References [1] K. Olah, E. Budding, H. I. Kim, and P.B. Etzel, “The active close binary system ER Vulpeculae”, Astronomy and Astrophysics Journal 8 June 1994. [2] O. Cakırli, C. Ibanoglu, A. Frasca, and S. Catalano, “Hα variations of the RS CVn type binary ER Vulpeculae”, Astronomy & Astrophysics Journal, 17 December 2002 [3] Alexandru, P. and Călin V."Orbital period modulation of the eclipsing binary system ER Vulpeculae: Real or not?", New Astronomy Journal, Vol. 23, October 2013 [4] G. Ronald , Fuller R. E., and R.H. Kaitchuck, ” BX Andromedae : A shallow contact system with a large temperature difference”, The Astronomical Journal, Vol 97, no. 4 ,April 1989 [5] S. A. Bell, P.P. Rainger, G. Hill and R.W. Hilditich, “ A Photometric and Spectroscopic study of BX Andromedea”, University Observatory, 23 October 1989 [6] A. Prša ,"PHOEBE Scientific Reference", villanova university, college of arts and sciences, dept. of astronomy and astrophysics, PHOEBE version 0.30,2011. [7] G. Dryomova, E. Perevozkina and M. Svechnikov," Catalogue of the orbital elements, masses, and for short-periodic RS CVn-type eclipsing systems" A&A 437, 375–381,2005. [8] K. Karami and R. Mohebi1" Velocity Curve Analysis of the Spectroscopic Binary Stars PV Pup, HD 141929, EE Cet and V921 Her by Nonlinear Regression" J. Astrophys. Astr. 28, 217–230, 2007. [9] D.O. Johnson,” Spectroscopy Binary Solver”, The Astronomical Journal, Data 10, 2004

Authors Bushra Q. Al-Abudi received Ph.D. degree in Astronomy in 2002 from University of Baghdad, College of Science, Astronomy and Space Department. Currently she is professor in Astronomy and Space department and her research interests include spectroscopy and photometry analysis of binary stars.

Rossul A. Abdulkareem received B.Sc. degrees in Astronomy in 2012 from university of Baghdad, College of Science, Astronomy and Space Department. Currently she is M.Sc. student in Astronomy and Space Department. Department.

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