TRO Theory Research Articles

Chromospheric activity and period variations of the contact binary EE Cet from TESS

From the 100-day TESS observations, we comprehensively studied the variations of the light curve and orbital period for EE Cet. It is found that an 83.2-day oscillation occurs in the differences between two light maxima, which identifies the existence of chromospheric activity. Using the 2016-version Wilson–Devinney code, we obtained three sets of photometric solutions from TIC1432, TIC2449 and TIC2495. Results imply a dark spot immigrating from longitude 217.9(±2.2)∘ in BJD 2459449 into longitude 61.6(±0.7)∘ in BJD 2459495. From the eclipse timing residuals (i.e., observed minus computed), the orbital period of EE Cet may be undergoing a long-term period increase with a periodic variation. The 15.95-yr periodic oscillation with A=0.0038(1) d may result from the light-time effect due to the third body. Meanwhile, the orbital period increases at a rate of dP/dt=1.74(±0.02)×10−7dyr−1, which may result from the conserved mass transfer from the less massive component to the more massive one. With mass transferring, EE Cet will evolve into the broken-contact configuration, as predicted by the TRO theory.

Extremely Low Mass-ratio Semi-detached Binaries: KIC 2719436 and KIC 4245897

We present two semi-detached binaries with extremely low mass-ratio (<0.1). The total eclipse feature on the light curves greatly improves the reliability of the binary light analysis results. Combining the photometric and spectral data, both the relative and the absolute parameters were obtained based on two methods. The masses and radii are M1 = 1.21 ± 0.45M⊙, M2 = 0.116 ± 0.044M⊙, R1 = 1.89 ± 0.25R⊙, and R2 = 0.76 ± 0.1R⊙ for KIC 2719436, and M1 = 1.58 ± 0.49M⊙, M2 = 0.153 ± 0.051M⊙, R1 = 1.9 ± 0.28R⊙, and R2 = 5.14 ± 0.79R⊙ for KIC 4245897. The binaries with extremely low mass-ratios provide a laboratory to study the binary outcomes as well as the extremely low-mass stars with complete physical properties. KIC 2719436 is an abnormal semi-detached binary system for its primary radius is much larger than that of the evolved secondary star who fills its own Roche Lobe. Excessive mass transfer leads to this situation on account of the effective angular momentum loss probably by the magnetic braking. KIC 2719436 is possible the closest target to the end as a single star that predicted by the TRO theory.

Mass Transfer and Intrinsic Light Variability in the Contact Binary MT Cas

First CCD photometry for the contact binary MT Cas is performed in 2013 in December. The spectral type of F8V is determined from the low-precision spectrum observed on 2018 Oct 22. With Wilson-Devinney code, the photometric solutions are deduced from VRc light curves (LCs) and AAVSO’s and ASAS-SN’s data, respectively. The results imply that MT Cas is a W-type weak-contact binary with a mass ratio of q=2.365(±0.005) and a fill-out factor of f=16.6(±1.2)%, respectively. The asymmetric LCs in 2013 are modeled by a dark spot on the more massive component. By analyzing the (O-C) curve, it is discovered that the orbital period may be undergoing a secular increase at a rate of dP/dt=1.12(±0.09)×10-8d yr-1, which may result from mass transfer from the less massive component to the more massive one. With mass transferring, MT Cas may evolve into a broken-contact configuration as predicted by TRO theory.

First R and I Lights and Their Photometric Analyses of GSC 02393–00680

Abstract We obtained complete $R$ and $I$ light curves of GSC 02393$-$00680 in 2008 and analyzed them with the 2003 version of the W–D code. It has been shown that GSC 02393$-$00680 is a W-type shallow contact binary system with a high mass ratio, $q =$ 1.600, and a degree of contact factor, $f =$ 5.0% ($\pm$1.3%). It will be a good example to check up on the TRO theory. A period investigation based on all available data suggests that the system has a small-amplitude period oscillation ($A_3 =$ 0$.^{\rm d}$0030; $T_3 =$ 1.92 years). This may indicate that it has a moderate-mass close third body, which is similar to XY Leo.

A New Photometric Study for the Weak-Contact Binary V700 Cygni

Abstract We present a new charge-coupled device (CCD) photometry for the weak-contact binary V700 Cygni. From our light curves in the VR bands, a photometric solution was deduced by the 2003 version of the W – D program. The results show that V700 Cyg is a W-subtype binary with $q$$=$ 0.5437($\pm$0.0018) and $f$$=$ 15.1%($\pm$0.3%). The contributions of the third light to the total light are $l_{3V}$$=$ 2.59%($\pm$0.10%) and $l_{3R}$$=$ 2.64%($\pm$0.10%) for the VR bands, respectively. Based on all available light-minimum times from 1946 to 2008, a detailed period analysis reveals that there exists a long-term period increase with a periodic oscillation. This cyclic variation, with $P_3$$=$ 54.0($\pm$2.0)yr, $A$$=$ 0.$^{\rm d}$0185 ($\pm$0.$^{\rm d}$0012 d), and $e{}^\prime$$=$ 0.2117($\pm$0.0059) from equation (3), may result from a light-time effect via the third body, identified by the third light in the photometric solution. If an additional body exists, V700 Cyg may be a triple star system. This kind of tertiary component may remove angular momentum from the central system, which may play an important role in the formation and evolution of the binary. A continuous period increase at a rate of $dP/dt$$=$$+$0.33($\pm$0.08) $\times$ 10$^{-7}$dyr$^{-1}$ can be interpreted as being mass transfer from the less-massive component to the more-massive one. With mass transferring, the orbital period increases and the separation between both components becomes wider. Finally, the contact configuration will break, as predicted by TRO theory. Therefore, this kind of weak-contact binary with a secular period increase will evolve into a broken-contact configuration.

GSC3658-0076: A Binary System at the Beginning of Mass Transfer

Photometric data of the new discovered binary GSC3658-0076 observed by [Gonzalez-Rojas et al.: 2003, IBVS, No. 5437.] were analyzed using the latest Wilson-Devinney code. The system turns out to be a detached binary system with the primary component almost filling its Roche lobe, while the secondary one is detached from the critical Roche lobe. According to the mass-radius relation of unevolved (ZAMS) detached binaries given by [Demircan and Kahraman: 1991, Ap & SS 181, 313.], the primary component is more evolved. These properties reveal that GSC3658-0076 may be at the beginning of the mass transfer phase and may evolve from the present detached system into a contact binary or be in the broken-contact phase predicted by TRO theory.

A study of the EB-type eclipsing binary GR Tauri with mass transfer

In this paper, new CCD BV light curves of the EB-type eclipsing binary GR Tau, which were obtained in 1999, are analyzed by means of the Wilson-Devinney program. The photometric solution of this system is obtained, and its absolute parameters are also derived. Our study has demonstrated that GR Tau is a near-contact binary system with an almost-contact semidetached configuration in which the primary fills its Roche lobe, and both components are main-sequence stars. The asymmetric shape of the light curves can be explained by a hot spot on the surface of the secondary, which is created by the mass transfer from the primary to the secondary. GR Tau belongs to the V 1010 Oph subclass of near-contact binaries, and is a good example of a system in the broken-contact phase predicted by the TRO theory.

A period investigation of the overcontact binary system V417 Aquilae

A detailed orbital period investigation of the short-period () W UMa type star, V417 Aql, is presented based on the analysis of its O–C data. It is shown that the period change of the binary system is continuous. A periodic variation, with a period of 42.4 years and an amplitude of , is found superimposed on a long-term period decrease ( days/year). The period oscillation can be explained either by the light-time effect via the presence of an unseen third body or by magnetic activity cycles of the components. V417 Aql is a W-type overcontact binary system with a low mass ratio of . The long-term period variation is in agreement with the conclusion of Qian ([CITE]b) that a low-mass ratio W-type system usually shows a secular period decrease. This suggests that V417 Aql is on the AML-controlled stage of the evolutionary scheme proposed by Qian ([CITE]b). Meanwhile, the light-curve paradox encountered by TRO theory is discussed.

The variations in light and color curves and possible short period oscillations of the binary AU Serpentis

We have photometrically monitored AU Ser for five years, It is considered to be a binary in poor thermal contact (Kaluzny 1986) or in detachment (Djurasevic 1993), The addition of new minimum times slightly modified the light ephemeris of Binnendijk (1972). The value and sign of the O'Connell effect have been changing with time. A remarkable Variation of the difference between minimum depths in light. curves has taken place in the period from 1991 to 1995. These variations in light curves are not expected by TRO theory but reminiscent of the situation in VW Cep, Our data, along with Binnendijk's, show a variation in color curves especially for 1995 observations. The variations in light and color curves might be straightforwardly explained by the distortion of starspot(s), Possible oscillations with short periods and shortly coherent times have been detected, which is unusual for such a binary.

The interaction between the secondary and the common convective envelope in a contact binary

It has been suggested that a contact system almost certainly cannot exist in static equilibrium undergoing periodic thermal relaxation oscillation. The energy transfer in a common convective envelope (CCE) makes the secondary have a complex structure, so the interaction between the secondary and CCE may play an important role in the structure and evolution of the contact system. The present paper tests the TRO theory and investigates this interaction with polytropic stellar model from the observational datum of 22 contact systems directly. It shows that the A-type systems are expanding with a velocity of 25.04 m yr−1, and the W-type systems are contracting at velocity of 3.10 m yr−1 by the calculations about these contact systems. Also, we calculate the ratio of energy transfer and the interaction coefficient for them. The HS (hot secondary) model is supported by our calculations. These results may help to understand the TRO theory and the W-phenomenon.

Evolutionary Effects in Contact Binaries

The structure and evolution of contact binaries is an extremely difficult problem in theoretical astrophysics.Several attempts have been made to set up a satisfactory model, see e.g. Lucy,1976, Flannery, 1976, Shu, Lubow and Anderson, 1976, Robertson and Eggleton, 1977, Rahunen and Vilhu, 1977 and others. There are, roughly, two lines of sight: Shu, Lubow and Anderson postulate the existence of a contact discontinuity in one of the two components of a contact binary (DSC Theory); in this case age zero models in thermal equilibrium are possible. The other authors find that unevolved contact binaries cannot achieve thermal equilibrium; therefore, relaxation oscillations on a thermal time scale are expected (TRO Theory). For a detailed discussion of the different effects see Lucy and Wilson,1979.

The Physical Status of VW Cephei

The decreasing period of VW Cep, interpreted on conservative case mass transfer, implies mass flow from primary to secondary. The TRO theory then predicts semi-detached status. The system b-v color is the same at the two minima, to within observational error. This is in marginal disagreement with a hot secondary. It also implies close thermal contact, in disagreement with the postulated semi-detached status.