DN Bootis: A low mass-ratio W UMa-type contact binary

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New Astronomy 13 (2008) 468–472 www.elsevier.com/locate/newast

DN Bootis: A low mass-ratio W UMa-type contact binary _ O ¨ zavcı a, S.O. Selam a, B. Albayrak a H.V. S ß enavcı a,*, R.H. Nelson b, I. a

Ankara University, Faculty of Science, Department of Astronomy and Space Sciences, TR-06100 Tandog˘an-Ankara, Turkey b 1393 Garvin Street, Prince George, BC, Canada V2M 3Z1 Received 7 November 2007; accepted 5 January 2008 Available online 11 January 2008 Communicated by E.P.J. van den Heuvel

Abstract New photoelectric BVR light curves and radial velocity curves were obtained for the HIPPARCOS discovery DN Boo at the 1 _ ¨ BITAK TU National Observatory of Turkey (TUG) and Dominion Astrophysical Observatory (DAO), respectively, to determine physical nature of the variable. The character of the obtained light curves and double-lined spectroscopic structures in the obtained spectra are revealed that DN Boo is a genuine EW type eclipsing binary. During the analysis of our new observations a simultaneous solution were derived for the photometric and spectroscopic data by using the Wilson–Devinney code and orbital parameters with absolute dimensions of the system were determined for the first time. Finally, the importance of very low mass-ratio contact binaries in the late stages of close binary evolution was discussed. Ó 2008 Elsevier B.V. All rights reserved. PACS: 97.10.Nf; 97.10.Pg; 97.80.Fk; 97.80.Hn Keywords: Binaries: close; Binaries: eclipsing; Stars: individual (DN Boo); Stars: fundamental parameters

1. Introduction The light variability of DN Boo (HIP 67657 = BD + 15°2636 = PPM 130126) was discovered by HIPPARCOS Satellite (ESA, 1997). Its type of variability was denoted as ‘‘P” (indicating the periodic variables but the nature of the light variability can not be determined) with an automated classification procedure by HIPPARCOS mission. Kazarovets et al. (1999) mentioned that it can be classified as a W UMa type (EW) system. DN Boo is also included in a recent eclipsing binary catalogue by Malkov et al. (2006) with the type of variability of EW marked by an uncertainity flag. These two clues made this variable star one of the *

Corresponding author. Tel.: +90 312 212 6720/1366; fax: +90 312 223 2395. E-mail addresses: [email protected] (H.V. S ß enavcı), _ [email protected] (R.H. Nelson), [email protected] (I. ¨ zavcı), [email protected] (S.O. Selam), albayrak@asO tro1.science.ankara.edu.tr (B. Albayrak). 1 _ ¨ BITAK: TU The Scientific and Technical Research Council of Turkey. 1384-1076/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.newast.2008.01.001

potential canditates of W UMa type contact binaries. In this study the ground-based radial velocity and light curves of the system were obtained for the first time and the type of variability of the system became definite after the analysis. 2. Observations New photoelectric observations of DN Boo in Johnson _ ¨ BITAK B, V, R bands were obtained at the TU National Observatory of Turkey (TUG) on the nights of 11, 12, and 13 March 2005, by using SSP-5A photometer attached to the 0.4 m Cassegrain telescope. BD + 15°2638 and BD + 15°2639 were chosen as comparison and check star, respectively. The relevant catalogue data for the observed stars are given in Table 1. A total of 320, 301, and 293 observations were obtained in B, V, and R passbands, respectively. The nightly extinction coefficients for each band were determined from the observations of the comparison star. The probable error of a single observation

H.V. S ß enavcı et al. / New Astronomy 13 (2008) 468–472 Table 1 The catalogue information for DN Boo, the comparison and check stars Parameter

DN Boo

Comparison

Check

GSC PPM a2000 d2000 BT VT BV

00906-00521 130126 13h 51m 42s.0 0 00 +14° 18 05 .9 m 11 .60 11m.30 0.3

00906-00700 130136 13h 52m 14s.6 0 00 +14° 20 27 .9 m 10 .98 10m.50 0.48

00906-00898 130142 13h 52m 52s.7 0 00 +14° 53 53 .0 m 10 .87 10m.14 0.73

point was estimated to be 0.014, 0.011 and 0.028 for B, V, and R bands, respectively. The differential B, V, R band light and B–V, V–R colour curves are given in Fig. 1. Our observations cover two minima, the timings of which were calculated by using the method of Kwee and van Woerden (1956) as MinI = 2453443.4726(3) and MinII = 2453442.3540(3). The photometric phases of the light and colour curves were calculated with the below given light elements which are corrected by using recent photoelectric times of minima (Note that the period value is about the twice of the value given in the HIPPARCOS Catalogue.): HJDMinI ¼ 2453443:4726ð4Þ þ 0:d 447568ð2Þ  E:

ð1Þ

The light levels were estimated by averaging the data around the maxima and minima (by taking D/ ¼ 0:02 phase interval) and listed in Table 2 along with their differences. New radial velocity observations of DN Boo were obtained at the Dominion Astrophysical Observatory (DAO), in Victoria, BC, Canada to reveal the double-lined spectroscopic binary nature and more specifically, to determine its precise mass-ratio. Observations were made on five nights from 17 to 25 April 2006, by using the high resolu˚ /mm) spectrograph in the Cassegrain focus of tion (10 A 1.8 m Plaskett telescope. HD102870, HD122693, HD089449, HD122693, HD149803, and HD140913 were chosen as radial velocity standard stars. Initial pre-processing included cosmic ray removal, aperture setting and sum-

Fig. 1. Differential B, V, R band light and B–V, V–R colour curves of DN Boo.

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Table 2 The light levels and their differences in the light curves of DN Boo

Maximum light at / = 0.25 Maximum light at / = 0.75 Minimum light at / = 0.00 Minimum light at / = 0.50 Dmax (m0.25–m0.75) Dmin (m0.00–m0.50) Depth of minimum I Depth of minimum II

DB

DV

DR

0.426 ± 0.007

0.633 ± 0.007

0.711 ± 0.008

0.425 ± 0.010

0.627 ± 0.006

0.713 ± 0.012

0.630 ± 0.014

0.825 ± 0.004

0.901 ± 0.007

0.629 ± 0.015

0.820 ± 0.010

0.903 ± 0.010

0.001 0.001 0.204 0.204

0.006 0.050 0.192 0.192

0.003 0.002 0.190 0.189

mation to one-dimensional, and finally calibration from arc spectra were made by using the RAVERE software developed by RHN (see Nelson, 2005). The velocity determinations of DN Boo were done using software BROAD developed by RHN (Nelson, 2005) using the broadening functions of Rucinski (2004) (see Nelson et al., 2006 for more details). Our estimate of the spectral type is F8 V and the spectroscopic elements V c ; K 1 and K 2 were determined as 11.4(4) km/s, 26.2(8) km/s and 254.2(12) km/ s, respectively. From the velocity amplitudes of the components ðK i Þ the spectroscopic mass ratio of the system were calculated as qsp ¼ 0:103ð3Þ. The radial velocity observations were given in Table 3 and represented graphically in Fig. 2.

Table 3 Radial velocity observations of DN Boo HJD

Phase

V1

DV1

V2

DV2

2453847.7714 2453848.8188 2453848.8679 2453850.8933

0.342 0.682 0.792 0.317

29.10 18.61 13.95 33.58

1.98 1.21 1.74 0.86

202.02 243.74 262.57 212.59

2.74 3.00 1.77 1.50

Fig. 2. Radial velocity curves for the components of DN Boo.

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3. The light curves analysis Our new photoelectric light and radial velocity curves were analysed simultaneously with the WD-2003 light curve analysis programme by Wilson and Devinney (1971) to obtain the physical and orbital parameters of DN Boo. During the analysis, instead of the often used and somewhat questionable practice of forming normal points, the original observational data is used in order to avoid negative influences of such normalization. The gravity darkening coefficients and the bolometric albedos of the component stars were fixed to their theoretical values according to their known physical nature as g1 ¼ g2 ¼ 0:32 (Lucy, 1967) and A1 ¼ A2 ¼ 0:5 (Rucinski, 1969), respectively. The mass-ratio (q = 0.103) and the velocity of the center of mass (V c ¼ 11:4 km/s) determined in this study were set to the corresponding values and kept constant during the analysis. The effective temperature of the primary component ðT 1 Þ was adopted from effective temperature calibration for dwarf stars by Popper (1980) according to the spectral type F8V determined in this study. Linear-cosine law limb-darkening coefficients x1 , x2 and x3 were interpolated from van Hamme’s (1993) tables. The orbital inclination (i), the surface potentials of

the both components ðX1;2 Þ, the effective temperature of the secondary component ðT 2 Þ, the orbital semi-major axis in units of solar radius (a) and the relative monochromatic

Fig. 3. Observational and theoretical light curves with the O–C residuals of DN Boo in B-Band.

Table 4 Results derived from the simultaneous light and radial velocity curve modelling of DN Boo in MOD-03 of the WD code Parameter

Value ± Error

Fixed parameters A1 = A2 g1 = g2 Vc (km s1) q(m2/m1) T1 (K) x1 (B,V,R) x2 (B,V,R)

0.5 0.32 11.4 0.103 6095 0.696, 0.563, 0.462 0.701, 0.565, 0.463

Adjusted parameters i° X1 = X2 T2 (K) L1/L1 + L2(B) L1/L1 + L2(V) L1/L1 + L2(R) L2/L1 + L2(B) L2/L1 + L2(V) L2/L1 + L2(R)

60.02 ± 0.63 1.925 ± 0.055 6071 ± 52 0.875 ± 0.053 0.875 ± 0.041 0.874 ± 0.036 0.125 0.125 0.126

Roche geometry related dimensions r1 (pole) r1 (side) r1 (back) r2 (pole) r2 (side) r2 (back)

0.55 ± 0.01 0.61 ± 0.02 0.64 ± 0.03 0.21 ± 0.02 0.22 ± 0.02 0.28 ± 0.08

RðO  CÞ2B

0.06

RðO  CÞ2V

0.03

RðO  CÞ2R

0.05

The parameters without errors are coupled to the other parameters or fixed.

Fig. 4. Same as in Fig. 3, but for V-Band.

Fig. 5. Same as in Fig. 3, but for R-Band.

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Table 5 Absolute dimensions of DN Boo Parameter

Value

a(R) d [pc] R1 [R] R2 [R] M1 [M] M2 [M] L1 [L] L2 [L] Log g1[cgs] Log g2[cgs] Mbol,1 Mbol,2

2.863 ± 0.018 416 ± 17 1.710 ± 0.067 0.670 ± 0.110 1.428 ± 0.039 0.148 ± 0.006 3.750 ± 0.280 0.560 ± 0.170 4.127 ± 0.006 3.962 ± 0.009 3.355 ± 0.085 5.417 ± 0.395

Fig. 6. The geometrical configuration of DN Boo seen at phase 0.25.

luminosity of the primary component ðL1 Þ were chosen as adjustable parameters. We have performed the analysis in MODE-03 of the WD code according to the over-contact configuration of the system. The results derived from our simultaneous light and radial velocity curve modelling of DN Boo are given in Table 4 and represented graphically in B, V, and R bands with Figs. 3–5, respectively. The Roche geometry of the system seen at orbital phase 0.25 was also presented in Fig. 6. Figs. 3–5 are also containing O–C residuals from the model at the bottom of each light curve for visual inspections about the goodness of the fits. 4. Results and conclusions New B, V, R light and radial velocity curves of DN Boo were obtained for the first time and analysed simultaneously with the revised version of Wilson–Devinney (WD-2003) code. The first spectroscopic observations of the system obtained in this study allows us to determine the spectral type of the system more accurately. Additionally, the double-lined spectra revealed the binary nature of the variable in no doubt and lead to determine a precise mass-ratio for the system. Moreover, we were able to calculate accurate absolute dimensions (see Table 5) for DN Boo system by simultaneously analysing the light and radial velocity curves. The analysis results indicate that DN Boo is a typical low mass-ratio A-type W UMa system with a DT = 24 K surface temperature difference between the component stars and no appreciable light curve asymmetry. The computed absolute parameters of DN Boo are used to estimate the evolutionary status of the system by using the evolutionary tracks and isochrones given by Girardi et al. (2000), on mass-radius, mass-luminosity and HR diagrams (see Figs. 7–9). The components of DN Boo and eight selected low mass-ratio A-type W UMa’s (q < 0.15, see Table 6) are plotted on these diagrams for comparison. The high degree of overcontact (f = 0.64) of DN Boo is in

Fig. 7. The positions of the components of DN Boo and other selected low mass-ratio W UMa’s on mass-luminosity diagram. The circles and triangles represent the primary and secondary components, respectively.

Fig. 8. The positions of the components of DN Boo and other selected low mass-ratio W UMa’s on mass-radius diagram. The circles and triangles represent the primary and secondary components, respectively.

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H.V. S ß enavcı et al. / New Astronomy 13 (2008) 468–472

Fig. 9. The positions of the components of DN Boo and other selected low mass-ratio W UMa’s on H–R diagram. The circles and triangles represent the primary and secondary components, respectively.

Table 6 Physical parameters of other selected low mass-ratio W UMa binaries which were taken from Yakut and Eggleton (2005) except V776 Cas from Djurasˇevic´ et al. (2004) Name

q

T(1, 2)

M(1, 2)

L(1, 2)

R(1, 2)

CK Boo  CrA SX Crv FG Hya TV Mus AW UMa GR Vir V776 Cas

0.106 0.128 0.080 0.111 0.138 0.078 0.124 0.130

6200, 6291 7100, 6640 6340, 6160 5900, 6012 5980, 6088 7175, 7022 6300, 6163 6890, 6620

1.42, 0.15 1.72, 0.22 1.25, 0.10 1.44, 0.16 0.94, 0.13 1.79, 0.14 1.37, 0.17 1.63, 0.21

2.89, 0.48 10.27, 1.34 2.50, 0.25 2.20, 0.41 2.27, 0.43 8.60, 1.01 2.90, 0.50 5.81, 0.89

1.48, 0.59 2.12, 0.88 1.31, 0.44 1.42, 0.59 1.41, 0.59 1.90, 0.68 1.43, 0.62 1.73, 0.74

agreement with those of A-type W UMa binaries (Rucinski, 1985). The primary component of the system lying near the TAMS in mass-radius, mass-luminosity and HR diagrams indicates a typical A-type primary component that is predominantly more evolved than their W-type counterparts (see Lucy and Wilson, 1979). The position of the primary component also agrees well with the position of the primaries of deeper contact low mass-ratio A-type systems that they all have substantially larger radii than expected for their ZAMS masses (Yakut et al., 2004). The secondary component is larger and brighter than its expected ZAMS mass in mass-radius, mass-luminosity diagrams. This can be explained as a result of luminosity transfer from the primary to secondary component as already suggested by Hilditch et al. (1988) and it is in agreement for the A-type contact binary systems. The final stages of the evolution of late-type contact binaries are still not well understood. There are several

clues that they can be the progenitors of rapidly-rotating single giants (Blue Stragglers and FK Com type stars) by coalescence of two components through continuing angular momentum loss (AML). A very first scenario of such evolution was proposed by Webbink (1976) and the consistency of this scenario was discussed by several authors (e.g. see Rucinski, 1993 and references therein). In principle, this scenario has still wide acceptance and put the over-contact, very low mass-ratio contact binaries, like DN Boo, into a very important place in the context of final stages of the close binary evolution. According to the scenario, they are all to be expected to show secular orbital period decrease (Qian et al., 2006) as a consequence of AML and this can be easily followed by observations. The coalescence theories on producing rapidly-rotating single giants still needs a good sample of very low mass-ratio contact binary systems that their observational aspects (i.e. absolute dimensions and orbital period variations) are followed for a long time. So, we need as many systems as DN Boo which are sufficiently observed and have well determined parameters to clarify the possible link between the evolved contact binaries and rapidly-rotating single giants. References Djurasˇevic´, G., Albayrak, B., Selam, S.O., Erkapic´, S., S ß enavcı, H.V., 2004. NewA 9, 425. European Space Agency, 1997. The HIPPARCOS and TYCHO Catalogues SP-1200. Girardi, L., Bressan, A., Bertelli, G., Chiosi, C., 2000. A&AS 141, 371. Hilditch, R.W., King, D.T., McFarlane, T.M., 1988. MNRAS 231, 341. Kazarovets, A.V., Samus, N.N., Durlevich, O.V., Frolov, M.S., Antipin, S.V., Kireeva, N.N., Pastukhova, E.N., 1999. IBVS No. 4659. Kwee, K.K., van Woerden, H., 1956. BAN 12, 327. Lucy, L.B., 1967. ZA 65, 89. Lucy, L.B., Wilson, R.E., 1979. ApJ 231, 502. Malkov, O.Yu., Oblak, E., Snegireva, E.A., Torra, J., 2006. A&Ap 446, 785. Nelson, R.H., 2005. Software by Bob Nelson, http://members.shaw.ca/ bob.nelson/software1.htm. Nelson, R.H., Terrell, D., Gross, J., 2006. IBVS No. 5715. Popper, D.M., 1980. ARA&A 18, 115. Qian, S., Yang, Y., Zhu, L., He, J., Yuan, J., 2006. ApSS 304, 25. Rucinski, S.M., 1969. AcA 19, 245. Rucinski, S.M., 1985. In: Pringle, J.E., Wade, R.A. (Eds.), Contact Binaries: Theory. Cambridge University Press, p. 113. Rucinski, S.M., 1993. In: Sahade, J., McCluskey, G.E., Jr., Kondo, J. (Eds.), The Realm of Interacting Binary Stars. Kluwer Acad. Publ., Dordrecht, The Netherlands, p. 111. Rucinski, S.M., 2004. IAU Symp. No. 215. In: Meader, A., Eenens, P. (Eds.), Advantages of the Broadening Function (BF) Over the CrossCorrelation Function (CCF), ASP Conf. Series, p. 17. van Hamme, W., 1993. AJ 106, 2096. Webbink, R.F., 1976. ApJ 209, 829. Wilson, R.E., Devinney, E.J., 1971. ApJ 166, 605. _ ˘ lu, C., 2004. A&A 417, 725. Yakut, K., Kalomeni, B., Ibanog Yakut, K., Eggleton, P.P., 2005. ApJ 629, 1055.