Articles

 

Long–term photometric and spectroscopic observations of the near–contact binary KR CYGNI¹

 

E. Sipahi, C. İbanoğlu, and Ö. Çakirli

 

Ege University, Science Faculty, Astronomy and Space Sciences Dept., 35100 Bornova, İzmir, Turkey. (esin.sipahi@mail.ege.edu.tr, cafer.ibanoglu@mail.ege.edu.tr, omur.cakirli@gmail.com).

 

Received 2012 February 23.
Accepted 2012 September 5.

 

RESUMEN

Presentamos curvas de luz en varios colores y velocidades radiales obtenidas a lo largo de cinco años para la binaria en cuasi–contacto KR Cyg. Obtenemos para las masas de las componentes 2.88 ± 0.20 M_Θ y 1.26 ± 0.07 M_Θ, y para los radios 2.59 ±0.06 R_Θ y 1.80 ±0.04 R_Θ. También investigamos las determinaciones empíricas del albedo y la temperatura efectiva de la estrella más fría y menos masiva de KR Cyg, y de otras dos binarias en cuasi–contacto similares, AK CMi y DO Cas. Los residuos entre los flujos observados y los calculados se atribuyen al efecto de la iluminación mutua, la cual calienta las capas superficiales de la estrella iluminada y hace que varíe no sólo el albedo bolométrico, sino también el coeficiente del ennegrecimiento al limbo y el exponente del abrillantamiento por gravedad. Los albedos efectivos son generalmente menores que los esperados para la envolvente de una estrella convectiva. Nuestros resultados son preliminares y especulativos.

 

ABSTRACT

We present the multi–color, five–year light curves and the radial velocities of the near–contact binary system KR Cyg. We derived the masses of the components as 2.88 ± 0.20 M_Θ and 1.26 ± 0.07 M_Θ and the radii as 2.59 ± 0.06 R_Θ and 1.80 ± 0.04 R_Θ. We also searched for the empirical determination of albedo and effective temperature of the cooler, less massive star of KRCyg, and of two similar near contact binaries AK CMi, and DO Cas. The residuals between the observed and computed fluxes are attributed to the effect of mutual illumination which heats the surface layers of the illuminated star and does vary not only its bolometric albedo but also its limb–darkening coefficient and gravity–brightening exponent. The effective albedos are generally smaller than that expected from an envelope of convective star. These results are preliminary and speculative.

Key Words: binaries: close — binaries: eclipsing — binaries: general — binaries: spectroscopic — stars: individual (KRCyg, AKCMi, DO Cas).

 

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ACKNOWLEDGMENTS

We thank the Turkish Scientific and Technical Research Council (TÜBİTAK) for a partial support with Project number 109T708 and EBİLTEM Ege University Science Foundation Project No:2011/BİL/007. We also thank TÜBİTAK National Observatory (TUG) for a partial support in using RTT150 and T100 telescopes with project numbers 10ARTT150–483–0, 11ARTT150–123–0 and 10CT100–101. We also thank the persons responsible for the Bakirlitepe observing station for their warm hospitality. This research has made use of the ADS and CDS databases, operated by the CDS, Strasbourg, France and TÜBİTAK ULAKBİM Süreli Yayinlar Kataloĝu.

 

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NOTE

¹ Based on observations collected at TUBITAK National Observatory (Antalya, Turkey).