Period investigation of Algol systems TZ Eri and TU Her

Res. Astron. Astrophys.

2020

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The new complete BVRcIc light curves and spectra of the short-period eclipsing binary XZ CMi are presented. The results from the combined analysis based on the photometric and spectroscopic data show that XZ CMi is a near contact binary with the secondary component filling its critical Roche lobe while the primary filling 91% of its Roche lobe. The investigation of the O – C diagram reveals that its orbital period is continuously increasing, which is consistent with the derived configuration and caused by the mass transfer from the less massive star to the more massive one. In addition, an obvious periodic modulation with the amplitude of0.0187(±0.0016) d and a high eccentric of 0.86(±0.04) is detected, which could be the results of the light time effect as a third star with the mass no less than 0.42(±0.09) M ⊙ orbiting around the central eclipsing binary once every 95.7(±2.1) yr. Furthermore, we found a visual companion star at 2.4” east by south of this system at a much greater distance by direct image. The large third light contribution found from the light curve analysis could be well explained by the existence of the third star and the fourth visual one. The similar parallax and proper motion imply that the components of this hierarchical quadruple system might be bounded by gravitation. Spectroscopic observations for two visual components were carried out by the LAMOST and 2.16 m telescopes, respectively. Their different values of [Fe/H] suggest that they were not born from the same origin. Thus, XZ CMi system is an interesting and important target to study the formation of the multiple stars.

Section: Orbital Period Evolutionmentioning

confidence: 99%

Eclipsing binary XZ CMi in a hierarchical quadruple system

Res. Astron. Astrophys.

2020

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Is the eclipsing binary RR Dra dancing with a hidden tertiary black hole candidate?

Monthly Notices of the Royal Astronomical Society

2021

Analysis of timing variation of the eclipsing binary RR Dra implies the existence of an additional object with mass of no less than 3.5(±0.2) M⊙. This third object is orbiting around the central eclipsing pair once every 98(±1) years, making the whole a hierarchical triple system. However, reliable photometric solutions based on light curves from TESS and WASP show that contribution of the third-light takes only about 2% of the total luminosity. It could photometrically be attributed to other unrelated star located within the aperture. The tertiary component is thus a massive object but invisible in optical wavelengths. Besides, evidence of misalignment between the barycenter and the center of light of the system is also found. This strengthen the existence of a hidden black hole candidate in the form of the third body. The potential black hole may play an essential role in extracting angular momentum from the central binary pair, forming the current state. As a good laboratory, RR Dra is an interesting system that can help to study stellar-mass black hole under the circumbinary case.

Evolutionary inference and statistical constraints on Algols including SD2-type near contact binaries

Monthly Notices of the Royal Astronomical Society

Yue

2022

Algol-type binaries (Algols) have aroused extensive interests due to the idiosyncratic evolutionary stages of both components. To better understand the evolutionary properties of such characteristic population, we collected mostly double-lined samples and performed systematic work concentrated on their physical constraints. It is found that orbital period cut-off for the OB and AF type Algols are P(OB) >0.482 d, P(AF) >0.358 d; constraints on mean density and surface gravity of the secondary components are $\overline{\rho }_2$(OB) < 0.144 ρ⊙, $\overline{\rho }_2$(AF) < 0.26 ρ⊙, log g2(OB) < 4.719 cgs and log g2(AF) < 4.517 cgs. Limitations of a(OB) >3.48 R⊙ and a(AF) >2.29 R⊙ have been deduced from the a - P relation. Moreover, statistical analysis of secular period changes reveal that Algols with higher f1 and relevant shorter period generally show weak period change. It hints that there is some connections between f1 and orbital evolution. Systems with lower f1 have the chance to evolve from classic Algols to SD2-type near contact binaries; systems with higher f1 obey the evolutionary channel from SD2-type near contact binaries to contact binaries. However, it seems that SD2-type near contact binaries could not evolve toward classic Algols. As a natural lab Algols are producing peculiar stellar experimental samples via complicated astrophysical processes, which will enhance our understanding on the physical properties and evolution of such binary populations.