Elsevier

New Astronomy

Volume 31, August 2014, Pages 65-68
New Astronomy

First photometric study of W UMa binary star LU Lac

https://doi.org/10.1016/j.newast.2014.03.002Get rights and content

Highlights

  • The first BVRI CCD photometric light curves were presented.

  • The first photometric solutions and orbital period analyses for LU Lac.

  • The photometric solutions suggest LU Lac is a marginal contact W-type system.

  • Orbital period analyses suggest it may be a triple system.

Abstract

LU Lac is a neglected W UMa binary star in photometric investigations. In this paper, we present BVRI CCD photometric light curves obtained on one night in 2012. The first photometric solutions of this system are computed by using the Wilson–Devinney code. It is shown that LU Lac is a marginal contact W-type system with a degree of contact factor of f=8.9%, a mass ratio of q=2.085 and a high inclination of i=82°.20. From the first analyses of orbital period changes, we found the period variation of the system includes an oscillation (A3=0.0125 days and T3=51.92 years). The cyclic change may be attributed to the light-travel time effect through the presence of a third body.

Introduction

LU Lac is a very short period binary system with an orbital period of 0.29880110 days (Kreiner, 2004). According to the General Catalogue of Variable Stars (Samus et al., 2007-2012), the apparent magnitude of LU Lac is B = 14.6–15.45 mag. Miller and Wachmann (1971) discovered the light variations of LU Lac and pointed out it is a W UMa type eclipsing binary with a period shorter than 0.3 days. The first light ephemeris was given by them. LU Lac was included in 58th Name-list of variable stars by Kukarkin et al. (1972). After that, Hoffmann (1981) observed it using five nights between different seasons, the B photoelectric light curve and three times of light minimum were obtained. Since then, some times of light minimum are available. Up to now, no light-curve solution has been published; therefore, LU Lac was put into our observational list. In this paper, the first complete BVRI light curves of LU Lac are presented. Then, the orbital period changes are analyzed and a photometric solution is obtained. Finally, the triplicity is discussed.

Section snippets

New CCD photometric observations

The first multi-color CCD photometric light curves of LU Lac were observed on 2012 August 22 with the PI 512×512 TE CCD photometric system attached to the 85 cm telescope at the Xinglong Station of National Astronomical Observatories of China (NAOC). The effective field of view is 14.5×14.5. The filter system is a standard Johnson-Cousins-Bessel multicolor CCD photometric system mounted on the primary focus (Zhou et al., 2009). The exposure time for each image was set as 30 s for the B band, 20 

Orbital period changes

LU Lac has been neglected for period study. By using our data together with those collected from the literature (e.g., from (O-C) gateway, http://var.astro.cz/ocgate/), the (O-C)1 values with respect to the following linear ephemeris were computed and the corresponding (O-C)1 curve is plotted in the upper panel of Fig. 2, with the period given by Kreiner (2004).MinI=2456162.13588+0d.2988011×E.It is revealed in the Fig. 2 that the (O-C)1 diagram of LU Lac is variable as expected. During fit of

Photometric solutions

Using the 2003 version of the W-D program (Wilson and Devinney, 1971, Wilson, 1990, Wilson, 1994, Wilson, 2003), photometric model fitting to the BVRI light curves of LU Lac was simultaneously done. According to the value of B-V=0.741, the temperature for Star 1 was fixed to T1=5310 K (Cox, 2000). Gravity-darkening coefficient of g1,2=0.32 (Lucy, 1976), and the bolometric albedo of A1,2=0.5 (Ruciński, 1969), were used because of

Discussions and conclusions

Based on our one-night BVRI light curves, the first photometric solutions for LU Lac are derived in the previous section. It is suggested that LU Lac is a marginal contact W-type W UMa system with a degree of contact of f=8.9%, a mass ratio of q=M2/M1=2.085. The effective temperature of the more massive component is lower than of the less massive one. The high orbital inclination of 82.20 (±0.25) indicates that the system is a total-eclipsing binary. Therefore, the derived photometric solutions

Acknowledgments

This work is partly supported by the Chinese Natural Science Foundation (Nos. 11133007, 11325315), West Light Foundation of the Chinese Academy of Sciences, and Key Laboratory Foundation of Chinese Academy of Sciences).

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