Search

Abstract: Orbital period changes of the near-contact binary (NCB) system, HL Aurigae, are analyzed based upon all the published CCD and photoelectric times of light minimum. It is found that the period of HL Aurigae shows a small-amplitude cyclic oscillation with a period of 6.5 years and an amplitude of 0. d 0058 while it undergoes a secular decrease at a rate of dP/dt =−1.08×10−7 days/year. The cyclic period oscillation can be interpreted either by the light-time effect of a third body or by magnetic activity cycles of the components. Since the third-body assumption is in agreement with the presence of a large amount of third light in the system discovered by , we think that HL Aurigae may be a true triple system. In order to deduce a G2-type third companion as proposed by , the orbital inclination of the third body should be i′=40°, which is much smaller than that of the eclipsing pair (i =85.°7). This suggests that the third companion is not coplanar with the eclipsing binary. This may indicate that the solar-mass component may be captured by the eclipsing binary system in some previous stages of its formation and evolution. HL Aurigae is a short-period NCB with a F1V-type primary and a G9V-type secondary component and both of the components are filling or nearly filling their Roche lobes. As the period is decreasing, the shrinking of the Roche lobe will finally cause it to evolve into a contact binary system in the timescale of ∼2.1×106 years. The period decrease may be caused by mass transfer or/and by angular momentum loss via magnetic braking. [Copyright &y& Elsevier]

Abstract: Orbital period variation of the W UMa-type eclipsing binary, V899 Herculis, discovered by the Hipparcos satellite was investigated based on all available photoelectric and CCD times of light minimum. It is discovered that the orbital period of the binary shows a cyclic change with an amplitude of 0.0117 days. The cyclic period change can be explained as the light-travel time orbit of a tertiary component in the system, which is in agreement with the spectroscopic result obtained by Lu et al. [Lu, W., Rucinski, S.M., Ogloza, W., 2001. AJ 122, 402] who found that the system, of which V899 Herculis is a fainter component (B), is a triple, even quadruple and with the photometric result obtained by Özdemir et al. [Özdemir, S., Demircan, O., Erdem, A., Cicek, C., Bulut, I., Soydugan, E., Soydugan, F., 2002. A&A 387, 240] who reported a large amount of third light (L 3 ∼0.68) of the system. The third body (A) rotates around the eclipsing pair in a period of 3.7 years. Lu et al. [Lu, W., Rucinski, S.M., Ogloza, W., 2001. AJ 122, 402] reported that the tertiary component is F5-type main-sequence star. However, the present analysis shows that the mass of the third component is no less than 2.8 M ⊙, which is larger than the mass of an F5-type main-sequence star suggesting that the tertiary component may be a non-eclipsing close binary. Therefore, the system may be a possible unsolved quadruple system containing double close binary stars. It is a good astrophysical laboratory to study the formation and evolution of binary and multiple system. The timescale for the formation of the G-type overcontact binary (V899 Herculis) via AML should be shorter than the main-sequence time of an F5-type star. [Copyright &y& Elsevier]