A Period Study and Spot Model for the Eclipsing Binary TU Bootis

Abstract

ABSTRACT. We present the photometric properties of the eclipsing binary TU Boo from detailed studies of the period and light variations, based on our new BVR observations and historical data collected from the literature. A total of 349 times of minimum light over 80 yr, including our four timings, were used for the period study. An analysis of the resulting diagram reveals that the orbital period of TU Boo has varied in a quasi-sinusoidal O-C way superposed on a long-term period decrease. The secular variation presumably indicates that mass is thermally transferred from the more massive primary star to its companion at a rate of about 7.24 # 10 Ϫ8 M , yr Ϫ1 . The period and semiamplitude of the cyclical variation are 54.5 yr and 0.0177 days, respectively, which could be produced by either a light-time effect or a magnetic activity cycle. Our light curves are asymmetrical, with max I about 0.02-0.03 mag brighter than max II. Among possible spot models, the light variations were bestfit by using a two-spot model with both a cool spot and a hot spot on the secondary star. These may be formed by a combination of effects from a magnetic dynamo and mass transfer. We suggest that TU Boo is probably a triple system, consisting of a massive primary star with a spectral type of G3, a secondary component of spectral type G5-6, and a low-mass M-type tertiary companion with a minimum mass of about p 0.34 M , . M 3

A Photometric Study of the Short-Period Close Binary V432 Persei and Its Implications for the Star's Evolution

“…However, we failed to find any connection between the luminosity variation and the period change. V432 Per is the third of six cool binaries on our program which does not conform to a prediction of Applegate's mechanism (Kim et al 1997(Kim et al , 2003a(Kim et al , 2003bLee et al 2004Lee et al , 2007b. Hence, the sinusoidal component of the period variability most likely arises from the light-time effect due to a dM tertiary companion gravitationally bound to the V432 Per system.…”

“…We can see that a large, dark spot on the primary star and its variability has been sufficient for the light-curve representations of V432 Per at the two different times. It is possible that the intrinsic light variations of the binary system could be caused by the simultaneous existence of the magnetic cool spot on the primary star and a hot spot due to mass transfer between the components (e.g., TU Boo, Lee et al 2007b). However, separate trials for such spot configurations did not give a better fit than our single, cool-spot model.…”

New Photometric Investigations of G-type Contact Binary TU Boo

“…The magnitude differences of the comparison star (C) minus that of the check star (CH) are shown in the lower part of Figure 1. The distortions and O'Connell effect (Niarchos et al 1996;Lee et al 2007;Coughlin 2010) have been variable in the past, therefore we look forward to much more variations to investigation on the magnetic activities. However, the upper points of Figure 1 display the height of light curves in 2020 and 2021 are nearly the same and symmetric with total eclipse, maybe the activities on the surface of the components are weak.…”

“…The effective temperature of the secondary component is 5805 K, slightly higher than the primary component 5800 K. According to the definitions of A-subtype and W-subtype (Binnendijk 1970), although the difference of temperature is very small, the primary one should be the hotter stars for A-type contact binaries. Lee et al (2007) also made the same way to reveal that it is an typical A-type system with q = 0.508, T 1 = 5800 K, T 2 = 5737 K. However, via the fitting of UBVRI-band light curves, Coughlin (2010) suggested that TU Boo is a near-contact or barely semidetached system with q = 0.481, T 1 = 5821 K, T 2 = 5691 K. In these investigations, their asymmetric light curves were fitting with the different spot. Did the spot make influence on the structure?…”

“…Due to the ambiguity of two subtypes, the investigators had paid attention to this system. Lee et al (2007) carried out BVR-band observations, which were with positive O'Connell effect. Their solutions suggest that TU Boo is an A-type system, and the fill-out factor of 17% is about 2 times smaller than 32% (Niarchos et al 1996), it is unreasonable for the obvious variation of the degrees of contact within about 20 yr. Also, during the studies on the orbital period, they found that a quasi-sinusoidal term is superposed on a long-term decrease.…”