Thermal Relaxation Oscillation Research Articles

Optical and X-Ray Studies of Marginal Contact Binary RW Dor Using TESS and XMM-Newton Observatories

Marginal short-period contact binaries are important to understand as they pose a different physical scenario than the predicted theoretical model based on the thermal relaxation oscillation mechanism due to their shallow degree of contact. Here we present the optical and X-ray studies of a contact binary source RW Dor using the Transiting Exoplanet Survey Satellite (TESS) and XMM-Newton telescopes. For the first time we report the varying O’Connell effect and explain the asymmetry with a spot model. Based on the new times of minima, we make a robust estimate of the orbital period of the third body at 47.01 ∼ 0.52 yr with an eccentricity e = 0.21. We show that the period-decreasing trend observed in O − C variation can be explained by both conservative mass transfer from primary to secondary and AML via stellar wind. The X-ray luminosity exhibited by RW Dor did not vary significantly on three different occasions and was found to be about 3.34 × 1029 erg s−1. Assuming that the quiescent X-ray emission is emitted from an undisturbed loop structure, the loop size is estimated to be 0.6–1 × 1010 cm which is ≤Alfvén radius r A ∼ 8 × 1010 cm.

A new look at the YY CrB binary system

This study presented a new analysis for the TESS-observed W Ursae Majoris (W UMa) binary star YY Coronea Borealis (YY CrB). The light curve was analyzed by the PHysics Of Eclipsing BinariEs (PHOEBE) Python version together with the Markov chain Monte Carlo (MCMC) method. The light curve solutions required a hot spot and l3. New eclipse times from the TESS observations were extracted, and the O-C curve of primary and secondary minima showed an anti-correlated manner. In order to study the O-C curve of minima, minima times between 1991 and 2023 were collected. This investigation reported a new linear ephemeris and by fitting a quadratic function to the O-C curve of minima, calculated the orbital period rate of Ṗ≈5.786×10−8dayyear. Assuming mass conservation, a mass exchange rate of Ṁ2=2.472×10−8 calculated from the more massive component to the less massive one. Then, by using the light travel time function, the possible third body was determined in the binary and derived the mass of the third body as 0.498M⊙ with a period of ≃7351.018 days. The O-C curve analysis and the quantity of mass indicate that the presence of a third body is unlikely. This binary is expected to evolve into a broken-contact phase and is a good case to support the thermal relaxation oscillation model.

Evidence of a Third Body and Photometric Solutions of a High Temperature Marginal Contact Binary CW Aqr

Marginal contact binary systems are an important class of binary systems in exploited by astronomers to understand various astrophysical phenomena as they bridge both semi-detached and overcontact stages. We studied the photometric data of CW Aqr using the JCB 1.3 m telescope (JCBT), Kepler, and TESS to understand the period variations and constrain the light curve solutions. We noted that the period of CW Aqr is increasing with a mass transfer rate of = 7.53 × 10−8 M ⊙ yr−1 from the secondary to the primary component. We also ascertained cyclic deviations along with a parabolic trend in the O − C diagram. The residuals displayed a sinusoidal trend which was fitted with an LTTE, indicating the presence of a third body with an orbital period of P 3 ∼10 yr and e = 0.10. We fitted the JCBT, Kepler, and TESS photometric normalized light curves and noted the mass ratio to be q ∼ 0.32 for both contact and semi-detached configurations. We identified a temperature difference between the primary and secondary components of ∼2500 K. No activity signatures were found in the observed light curves which were also evident from the Hα line studies where the filled-in effect was not seen. Overall our study suggests that CW Aqr is a marginal contact binary with a low mass ratio evolving toward a semi-detached configuration. However, it may merge if the period increases due to ongoing mass transfer accompanied by a lowering in the mass ratio and later oscillate back to the period-decreasing trend due to angular momentum loss over a few cycles of thermal relaxation oscillations followed by instability.

OT UMa and 2MASS J09251388+6424488: Two active contact eclipsing binary systems

In this paper, new photometric light curves (LCs) of OT UMa and 2MASS J09251388+6424488 (=NSVS 2497620, hereafter NSVS 2497) in BVRcIc-bands are presented and analyzed by using the 2015 version of the Wilson–Devinney (W–D) code. We found that both of them are active contact eclipsing binaries (CEBs) . At the same time, we estimated masses and radii of OT UMa and NSVS 2497 by using our photometric parameters. Then, we also studied the orbital period changes of them by using the O−C method via collecting all available times of light minimum for the first time, and new linear ephemerides are obtained. Besides, the formation and evolution of these two targets are discussed, and we thought that OT UMa could be undergoing thermal relaxation oscillations.

Mass-ratio distribution of contact binary stars

The mass ratio q of a contact binary star evolves through mass transfer, magnetic braking, and thermal relaxation oscillations to low values until it crosses a critical threshold qmin. When this occurs, the binary undergoes the tidal Darwin instability, leading to a rapid coalescence of the components and to an observable brightening of the system. The distribution of q has not been measured on a sufficiently large population of contact binary stars so far because determining q for a single contact binary usually requires spectroscopy. As was shown previously, however, it is possible to infer the mass-ratio distribution of the entire population of contact binaries from the observed distribution of their light-curve amplitudes. Employing Bayesian inference, we obtained a sample of contact binary candidates from the Kepler Eclipsing Binary Catalog combined with data from Gaia and estimates of effective temperatures. We assigned a probability of being a contact binary of either late or early type to each candidate. Overall, our sample includes about 300 late-type and 200 early-type contact binary candidates. We modeled the amplitude distribution assuming that mass ratios are described by a power law with an exponent b and a cutoff at qmin. We find qmin = 0.087−0.015+0.024 for late-type contact binaries with periods longer than 0.3 days. For late-type binaries with shorter periods, we find qmin = 0.246−0.046+0.029, but the sample is small. For early-type contact binary stars with periods shorter than one day, we obtain qmin = 0.030−0.022+0.018. These results indicate a dependence of qmin on the structure of the components, and they are broadly compatible with previous theoretical predictions. We do not find any clear trends in b. Our method can easily be extended to large samples of contact binaries from TESS and other space-based surveys.

The First Photometric and Spectroscopic Study of Contact Binary V2840 Cygni

The first photometric, spectroscopic and period variation studies of neglected short-period eclipsing binary V2840 Cygni are presented. High mass ratio contact binaries (HMRCBs), especially those in the weak-contact configuration, are vital when probing the evolutionary models of contact binaries (CBs) using stellar parameters. The photometric solutions reveal the weak-contact nature of V2840 Cygni with a high mass ratio (∼1.36), motivating us to investigate the nature of such binaries. The period variation study of V2840 Cygni spanning 15 yr shows a secular period decrease at a rate of ∼5.5 × 10−7 day yr−1, indicating mass transfer between the components. The superimposed cyclic variation provides a basic understanding of the possible third body (P 3 ∼ 8 yr, m 3 ∼ 0.51 M ⊙). Following the derived parameters, the evolution of the system is discussed based on the thermal relaxation oscillation (TRO) model. It is found that V2840 Cygni falls in a special category of HMRCBs, which validates TRO. To characterize the nature of HMRCBs, a catalog of 59 CBs with high mass ratios has been compiled along with their derived parameters from the literature. For all the HMRCBs in the study, a possible correlation between their contact configuration and observed period variations for relative log J rel is discussed. The spectroscopic study of V2840 Cygni provides evidence of the presence of magnetic activity in the system and the existence of ongoing mass transfer which is additionally deduced from the period variation study. The LAMOST spectra of 17 HMRCBs are collected to interpret the stellar magnetic activity in such systems.

The first photometric investigation of the poor-thermal contact binary V749 Aurigae

Abstract The multi-filter light curve analysis of V749 Aurigae (thereinafter V0749 Aur) is conducted for the first time. Its orbital period is improved from P = 0.409873 to 0.409890 d in this work. The photometric data from the All-Sky Automated Survey for SuperNovae (ASAS-SN) were utilized to examine the revised orbital period. Then, the phased multi-filter light curves were computed with the new period, and analyzed with the Wilson–Devinney (W-D) code. The results reveal that V0749 Aur is a marginal contact binary with a large temperature difference of about ΔT = 1600 K. It is a poor thermal contact binary, the light curves of which depart from EW-type and show EB-type light variations. Thus, V0749 Aur belongs to a particular group of binaries, named B-type binaries, predicted by the Thermal Relaxation Oscillation (TRO) theory. In addition, the amplitude differences in different bands of the light curves, imply the existence of a third light. The contribution of the third light detected by the light curve analysis is consistent with the contribution of a visual star, which is in the same line of sight as V0749 Aur but at a different distance. With its marginal contact and short period properties, V0749 Aur merits further attention as a potential transitional sample in binary evolution.

A Photometric Study of Two Contact Binaries: CRTS J025408.1+265957 and CRTS J012111.1+272933

We performed new photometric observations for two contact binaries (i.e., CRTS J025408.1+265957 and CRTS J012111.1+272933), which were observed by the 1.0 m telescope at Xingjiang Astronomical Observatory. From our light curves and several survey data, we derived several sets of photometric solutions. We found that CRTS J025408.1+265957 and CRTS J012111.1+272933 were A- and W-type W UMa, respectively. The results imply that the spot migrates or disappears in the two contact binaries, which were identified by chromospheric activity emissions (e.g., H α emission) from LAMOST spectra. From the O−C curves, the orbital periods of the two contact binaries may be increasing, which is interpreted by the mass transfer from the less massive component to the more massive one. With mass transferring, the two contact binaries may evolve from the contact configurations to semi-detached ones as predicted by the theory of thermal relaxation oscillation.

V505 Cyg: A Mass-transferring Marginal Contact Binary

High-precision photometric data of V505 Cyg from TESS and one spectrum observed by us are presented in this work, and the stellar atmospheric parameters of the primary component were derived via spectral fitting. Applying the Wilson–Devinney code, the photometric elements were computed for the first time. The results show V505 Cyg is a near contact binary with the primary filling its Roche Lobe and the secondary a little under-filling, along with the temperature difference of about ΔT = 1900 K between the two components. The eclipse is total and lasts for about 90 minutes, which is about 0.1 phase, so the photometric results are reliable. This system belongs to near-contact binaries with the light curves enhanced around the left shoulder of the secondary minimum, which can be explained by a hot spot on the secondary components due to mass transfer, via a stream from the primary components hitting the facing surface of the secondary components. Meanwhile, we conducted an orbital period investigation of it in detail. The orbital period study based on all times of minimum including 230 new ones determined by us reveals a secular period decreasing at the rate of dP/dt = −2.31 × 10−7 d · yr−1. The decrease of the orbital period can be the result of mass transfer between the components, agreeing well with the configuration and the asymmetric light curves of V505 Cyg. V505 Cyg is therefore another rare example of mass transferring marginal contact binary lying on the rapid evolutionary stage predicted by the Thermal Relaxation Oscillation theory. With the orbital period decrease, V505 Cyg will evolve into an overcontact binary.

V0644 Ser: An Active Ultrashort Period Contact Binary Star

The photometric solutions of the ultrashort period close binary V0644 Ser based on our new complete BVRI light curves are derived by the Wilson–Devininney code. The results show that V0644 Ser is a W-type shallow contact binary, and the third light was found in the R and I bands. Compared with the light curves in 2011, the amplitude variation of the secondary maximum can be explained by the temperature change from hot to cold in the local region of the star surface caused by magnetic activity or convective instability. Combined with the Gaia parallax, the absolute parameters of this system are obtained: M 1 = 0.29(4) M ⊙, M 2 = 0.56(9) M ⊙, R 1 = 0.48(3) R ⊙, R 2 = 0.65(3) R ⊙, L 1 = 0.11(2) L ⊙, L 2 = 0.16(2) L ⊙. To study the period variation, we fitted the SuperWASP, CSS, ASAS-SN and ZTF survey timing data to obtain light minima times spanning 14 yr. Through O − C analysis, we find that the orbital period of this system has a long-term period decrease and periodic oscillation. The long-term period decrease can be explained by the mass transfer from more-massive component to less one and angular momentum loss via magnetic stellar wind. With the period decrease, this system is evolving from the present shallow contact phase to a relatively deeper stage predicted by the thermal relaxation oscillation theory. Periodic oscillation can be explained by the light-time effect of the cool third body. This third body may play an important role in the early formation and evolution of the binary system by removing angular momentum.

Conservative mass transfer on eclipsing binary AE Phe from O-C diagram analysis

Eclipsing binary is an edge-on binary system where the components appear to be eclipsing one another. Eclipsing binaries therefore give a lot of information on the systems’ behavior, one of them from their period change. O-C diagram exhibits the deviation of the observed time of minimum from the calculated ones and its analysis will reveal the responsible mechanism, such as a hidden third component, apsidal motion, and mass transfer. AE Phe (V = 8.15 mag and spectral class G0V) is a W UMa W-type binary. Previous studies of its degree of contact have revealed AE Phe to be a shallow-contact binary. Photometric data were taken using PROMPT (Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes), CTIO on October 4th, 2013 on four filters: B, V, R, and I. The Kwee and van Woerden (1956) method was also used to determine AE Phe’s time of minimum. Analysis of the O-C diagram (taken from 1975 toward our observation) suggest that the period of AE Phe shows a long-term continuous increase. These period increase and degree of contact suggest that AE Phe is undergoing thermal relaxation oscillation (TRO) and is evolving to a broken-contact phase, with a possibility of angular momentum loss (AML) through magnetic braking.

CSS J075415.6+191052 and NW Leo: Two Contact Binaries at Different Evolutionary Stages

Multi-color light curves of CSS J075415.6+191052 and NW Leo are presented and the photometric solutions suggest that CSS J075415.6+191052 is an A-subtype contact binary with low mass ratio (q = 0.178) while NW Leo has a high mass ratio (q = 0.707). For CSS J075415.6+191052, the RI light curves show weakening around the left shoulder of the secondary minimum, which indicates that there may be a dark spot on the secondary component. However, the light curves of BV bands are totally symmetric. It is unreasonable if the dark spot is caused by magnetic activity or mass transfer between the two components. Therefore, weakening of the light curves in this contact binary is caused by something else. A possible explanation is mass transferring from the primary component to the common convective envelope through the inner Lagrangian point, and this part of the mass, for some reason, weakens the RI bands of light from the secondary component. O − C analysis of NW Leo reveals a cyclic period change with a modulation period of 4.7 yr, which may be caused by the light travel time effect of a third body. The positions of CSS J075415.6+191052 and NW Leo in the P–J′orb diagram indicate that CSS J075415.6+191052 mainly abides by the angular momentum loss theory while NW Leo is dominated by the thermal relaxation oscillation theory.

First photometric and orbital period investigations of the total-eclipse contact binary V0339 Com

We presented the first photometric and orbital period investigation for the W UMa-type binary V0339 Com. The multi-bands light curves were obtained and analyzed with the Wilson–Devinney Code. The photometric solutions suggested that V0339 Com is an A-subtype shallow contact binary with a degree of contact f=12.0%. The total eclipse of V0339 Com gives a reliable mass ratio of 0.304. The asymmetry light curves are well modeled by a cool spot on either the secondary or primary. With the empirical relation derived from a catalog of individually studied contact binaries and the photometric solutions, we determined the absolute parameters of V0339 Com. Combining the eclipse timings determined from our observations and several surveys’ data with those reported in the literature, we revealed that the orbital period of V0339 Com is undergoing a secular increase at a rate of Ṗ=5.45×10−7 d⋅yr−1. The secular period increase implies a continuous mass transfer from the less massive secondary to the more massive primary. Based on the conservative mass transfer, the observed period increase and the Roche-lobe model, we analyzed the evolutionary status of V0339 Com and found that it may be just at the stage predicted by the thermal relaxation oscillation theory, and be involving from the current contact state to the broken-contact one.

LO And: an A-subtype contact binary with a very cool third component

Despite the intensive investigations since the discovery of LO And approximately 60 yr ago, its evolutionary status and subtype are still a matter of controversy. By simultaneously modeling the radial-velocity curves and new light curves with the Wilson-Devinney code, we present new geometric, photometric and absolute parameters for this system. The simultaneous solution suggests that LO And is an A-subtype contact binary with a contact degree of 32.4%. The absolute parameters are modified to become M 1 = 1.409 M ⊙, M 2 = 0.449 M ⊙, R 1 = 1.36 R ⊙ and R 2 = 0.83 R ⊙. From our observations and data from surveys, we determined 334 eclipse timings. The O – C diagram, constructed from the new eclipse timings and those reported in the literature, reveals a secular increase and a cyclic variation in its orbital period. The former is caused by conservative mass transfer from the secondary component with less mass to the primary one with more mass. The latter may be explained by either the cyclic magnetic activity on the two components or the light-time effect due to a third body. With the absolute physical parameters, we investigated its evolutionary status, and find that LO And is an unevolved contact binary undergoing thermal relaxation oscillation, which will eventually coalesce into a single star with rapid rotation.

Investigation of the shortest period Am type eclipsing binary TYC 6408–989–1

The first BV bands photometric observations and the low-resolution spectrum of the shortest period Am type eclipsing binary TYC 6408–989–1 have been obtained. The stellar atmospheric parameters of the primary star were obtained through the spectral fitting as follows: T eff = 6990 ± 117 K, log g = 4.25 ± 0.26 cm s−2, [Fe/H] = −0.45 ± 0.03 dex. The original spectra obtained by European Southern Observatory (ESO) were processed with an IRAF package by us. Based on the ESO blue-violet spectra, TYC 6408–989–1 was concluded as a marginal Am (Am:) star with a spectral type of kA3hF1mA5 IV-V identified through the MKCLASS program. The observed light curves were analyzed through the Wilson-Devinney code. The final photometric solutions show that TYC 6408–989–1 is a marginal contact binary with a low mass ratio (q = 0.27). The temperature of the secondary component derived through the light curve analysis is significantly higher than main sequence stars. In addition, TYC 6408–989–1 is a poor thermal contact binary. The temperature differences between the two components is about 1800 K. TYC 6408–989–1 should be located in the oscillation stage predicted by the thermal relaxation oscillations theory (TRO) and will evolve into the shallow contact stage eventually. The very short period (less than one day), marginal Am peculiarity and quite large rotational velocity (v sin i ≃ 160 km s−1) make TYC 6408–989–1 become a challenge to the cut-off of rotation velocities and periods of Am stars. We have collected the well known eclipsing Am binaries with absolute parameters from the literature.

The Energy Transport Induced by Horizontal Turbulence in Rotating W-type W UMa Contact Binaries

Abstract The aim of this paper is to investigate the impact of energy transfer on the evolution of contact binaries. Horizontal turbulence is triggered by the differential rotation induced by meridional circulation, which is a direct consequence of nonuniform heating at the inner critical Roche lobes because of strong rotational and tidal distortions. Thermal energy is transferred by the horizontal turbulence from the more massive star to the less massive one, and horizontal turbulence can be responsible for the redistribution of what is a significant fraction of the total core luminosity. The secondary becomes overluminous and oversized owing to energy transfer from the companion star, whereas the primary shifts toward smaller luminosity and is undersized. The convective regions for primaries are enlarged by the improved radiative temperature gradient. The main region for energy transport is located at the bottom of the common envelope because of a higher local density and enthalpy difference. One can find that thermal structure can be disturbed and display periodic thermal relaxation oscillations between the semidetached stage and the contact stage. W-type W UMa contact binaries acquire efficient energy transfer, which can cause the temperature of secondaries to exceed that of the primaries. However, angular momentum loss owing to nonconservative mass transfer can make the system maintain shallow contact and not evolve from overcontact to semidetached configurations, and the system may appear as an A-type W UMa contact binary.

The first photometric investigation of the contact binary OQ Cam

The first charge-coupled device photometric light curves in B, V, Rc , and Ic bands of the short-period contact binary star OQ Cam are presented. Through analyzing the light curves with the Wilson-Devinney code, it is found that OQ Cam is a W-type shallow contact binary star with a contact degree of f = 20.2%. Based on the O – C analyzing, the orbit period displays a long term increasing with a rate of dP/dt = 4.40 × 10−7 d yr−1. The increasing in orbit period can be interpreted by mass transfer from the less massive component to the more massive one. As the orbit period increases, OQ Cam would evolve from the present shallow contact configuration to a non-contact stage. So it may be a potential candidate to confirm the thermal relaxation oscillation theory.

Long-term Photometry and Orbital Period Change of the W UMa–type Binary v0599 Aur: Evidence of about 11 yr Magnetic-activity Cycle

Abstract Combining all available photometric data from various surveys and literature with our observations, we present 10 sets of light curves for the eclipsing binary V0599 Aur covering a timescale of 20 yr. During the last two decades, the O’Connell effect continuously varied and went through at least two flips between positive and negative effects. The photometric solutions from our two sets of multicolored light curves show that V0599 Aur is a W-type shallow contact binary with an active spot on the secondary. Its absolute parameters are determined by combining the Gaia distance with the photometric solutions. The period investigation reveals a secular decrease and a cyclic variation in its orbital period. The former mainly originates from the mass transfer from the more massive secondary to the less massive primary. The latter can be preferentially explained as a result of cyclic magnetic activity of the secondary, with three observational supports: (1) the existence and evolution of an active spot suggested by the long-term photometry, (2) periodic variation in both the O’Connell effect and relative luminosity, and (3) weak correlations between O’Connell effect/relative luminosity changes and cyclic period variation. Together with the cyclic period variation and its theoretical reasonability by Applegate’s mechanism, we suggest that the secondary of V0599 Aur is a solar-type magnetic-activity star with an approximately 11 yr active cycle. Furthermore, by combining the secular period decrease with the Roche-lobe model, we infer that V0599 Aur is evolving from the marginal contact state controlled by thermal relaxation oscillation theory to the overcontact state.

ASAS J174406+2446.8 is identified as a marginal-contact binary with a possible cool third body

ASAS J174406+2446.8 was originally found as a δ Scuti-type pulsating star with the period P = 0.189068 d by ASAS survey. However, the LAMOST stellar parameters reveal that it is far beyond the red edge of pulsational instability strip on the log g − T diagram of δ Scuti pulsating stars. To understand the physical properties of the variable star, we observed it by the 1.0-m Cassegrain reflecting telescope at Yunnan Observatories. Multi-color light curves in B, V, Rc and Ic bands were obtained and are analyzed by using the W-D program. It is found that this variable star is a shallow-contact binary with an EB-type light curve and an orbital period of 0.3781 d rather than a δ Scuti star. It is a W-subtype contact binary with a mass ratio of 1.135(± 0.019) and a fill-out factor of 10.4%(± 5.6)%. The situation of ASAS J174406+2446.8 resembles those of other EB-type marginal-contact binaries such as UU Lyn, II Per and GW Tau. All of them are at a key evolutionary phase from a semi-detached configuration to a contact system predicted by the thermal relaxation oscillation theory. The linear ephemeris was corrected by using 303 new determined times of light minimum. It is detected that the O – C curve shows a sinusoidal variation that could be explained by the light-travel-time effect via the presence of a cool red dwarf. The present investigation reveals that some of the δ Scuti-type stars beyond the red edge of pulsating instability strip on the log g – T diagram are misclassified eclipsing binaries. To understand their structures and evolutionary states, more studies are required in the future.

Photometric light curve solutions of three ultra-short period eclipsing binaries

We present the results of our study of the eclipsing binary systems CSS J112237.1+395219, LINEAR 1286561 and LINEAR 2602707 based on new CCD B, V, Rc and Ic complete light curves. The ultra-short period nature of these stars, as reported by Drake et al., is confirmed and the system’s periods are revised. The light curves were modeled using the 2003 version of the Wilson-Devinney code. When necessary, cool spots on the surface of the primary component were introduced to account for asymmetries in the light curves. As a result, we found that CSS J112237.1+395219 is a W UMa type contact binary system belonging to W subclass with a mass ratio of q = 1.61 and a shallow degree of contact of 14.8% where the primary component is hotter than the secondary one by 500 K. LINEAR 1286561 and LINEAR 2602707 are detached binary systems with mass ratios q = 3.467 and q = 0.987 respectively. These detached systems are low-mass M-type eclipsing binaries with similar temperatures. The marginal contact, fill-out factor and temperature difference between components of CSS J112237.1+395219 suggest that this system may be at a key evolutionary state predicted by thermal relaxation oscillation (TRO) theory. From the estimated absolute parameters, we conclude that our systems share common properties with other ultra-short period binaries.