Fill-out Factor Research Articles

Search for dormant black holes in ellipsoidal variables I. Revisiting the expected amplitudes of the photometric modulation

ABSTRACT Ellipsoidal variables present light-curve modulations caused by stellar distortion, induced by tidal interaction with their companions. An analytical approximated model of the ellipsoidal modulation is given as a discrete Fourier series by Morris & Naftilan. Based on numerical simulations using the phoebe code, we present here updated amplitudes of the first three harmonics of the model. The expected amplitudes are given as a function of the mass ratio and inclination of the binary system and the fillout factor of the primary – the ratio between the stellar radius and that of its Roche lobe. The corrections can get up to 30 per cent relative to the Morris & Naftilan model for fillout factors close to unity. The updated model can be instrumental in searching for short-period binaries with compact-object secondaries in large data sets of photometric light curves. As shown in one OGLE light-curve example, the minimum mass ratio can be obtained by using only the amplitudes of the three harmonics and an estimation of the stellar temperature. High enough amplitudes can help to identify binaries with mass ratios larger than unity, some of which might have compact companions.

Distribution of physical parameters for 380 contact binaries in the Kepler field

Abstract We present the physical parameters (p, T, q, i, f) of 380 Kepler contact binary systems (hereafter called CBs). A statistical study on the CBs is carried out based on a Kepler photometric database. Our samples were selected from the Kepler Eclipsing Binary Catalogue of EW-type eclipsing binaries with periods around 0.2–1 d and amplitudes greater than $5\%$. The physical parameters were obtained by fitting the Kepler light curves with the Wilson–Devinney eclipsing binary modeling program. Our sample of CBs contains 160 A-type and 220 W-type CBs. The fill-out factor distribution indicated that CBs generally have shallow fill-out; the proportion of CBs with fill-out factors less than $30\%$ is around $70\%$, which may be related to the formation and evolution of the CBs. The period–temperature relationship of CBs is consistent with previous studies, which is the well-known period–color relationship. The distribution between mass ratio and fill-out factor can provide some information for studying the deep, low-mass ratio contact binaries and CBs which have a large mass ratio. The mass–radius diagram shows that there is a similar linear relationship between the primary and secondary stars while the primary stars are located almost on the ZAMS line; this could be related to the internal nuclear reaction within the primary and secondary stars.

The first light curve solutions and period study of two contact binary systems: V1370 Tau and QQ Boo

The first light curve solutions of the binary systems V1370 Tau and QQ Boo are presented. The periodic changes are calculated, and a new ephemeris presented for each of these two binary systems. O-C analysis is performed using the MCMC method in OCFit code. The changing rate of period was measured as dP/dt= 0.2423 days/year for V1370 Tau and dP/dt= -0.1363 days/year for QQ Boo. The light curve solutions suggest that V1370 Tau is a weak-contact eclipsing binary system with a photometric mass ratio q = 0.829, and that the corresponding fillout factor is 11.06%. Furthermore, it is suggested that the QQ Boo binary system is also a weak-contact W UMa eclipsing binary with a photometric mass ratio q = 0.831, and that its fillout factor equals 10.26%. The light curve solutions require cold spots. Utilizing the Wilson-Devinney code the photometric and geometric parameters of the systems are determined. The distance of both V1370 Tau and QQ Boo are calculated according to the estimated absolute parameters as 159.95 ± 23 pc and 309.03 ± 25 pc, respectively, which are in a good agreement with the distance values derived from the Gaia DR2 parallax within one standard deviation. Moreover, the positions of their components on the H-R diagram are represented.

The first light curve solutions and period changes of EW Psc and HN Psc

The first light curve solutions of the stars EW and HN in the Pisces constellation are presented. Photometry, and its’ periodic changes are calculated and discussed. The analysis of the O-C diagram is done by the MCMC approach in the OCFit code and a new ephemeris is provided for the two binary systems. The results show that EW Psc is a near contact eclipsing binary system with a photometric mass ratio q = 0.587, and the fillout factor is -0.034 and -0.018 for the primary and secondary components, respectively. The solution results also show that the system HN Psc is a weak-contact W UMa eclipsing binary with a photometric mass ratio q = 0.853, and with a fillout factor of 5.6%. The light curves solutions required a cold spot to account for the O'Connell effect.

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.

First study of a low-amplitude eclipsing binary KIC11496078

We investigate a low-amplitude W UMa binary KIC 11496078 based on Kepler photometric data, and the diagrams of OC maxima and minima of light curves are plotted. The anti-correlated nature of the curves indicates that KIC 11496078 is a binary. We use short cadence mode (SC) data for analyzing the light curve. By performing some analyses, the parameters of the system are determined. The results show that this system has a low mass ratio (q ~ 0.065) and a small fill-out factor (f ~ 0.026). By using the empirical relations, the masses of the two components are estimated to be M1=1.207M⊙ andM2=0.075M⊙. In the second stage, we fit a quadratic function to the minima of the eclipses and use coefficients of this function to calculate the rate of orbital periodic changes P˙∼3.76×10−9dayyear. By assuming mass conservation, we obtain a mass transfer rate of 4.2×10−8M⊙year from the secondary component to the primary one. We apply the auto-correlation function to the difference between the maxima to calculate the spot rotation period of the system (0.3002937±2.81368E−6); this target shows subsynchronous rotation, which is due to the differential rotation.

First photometric investigation of two short-period eclipsing binaries NSVS 7377756 and for UCAC3 276-106147

We present the first CCD sets of complete light curves for two W Ursae Majoris Systems, UCAC3 276-106147 and NSVS 7377756. These light curves are here analyzed and modelled using the latest version of the Wilson-Devinney Code. We found that UCAC3 276-106147 is a W-subtype shallow-contact eclipsing binary (fill-out factor 7.5%), with a mass ratio of q = 2.88 (1/q = 0.347), a small temperature difference between the components of about ΔT =200K. NSVS 7377756 is an H-subtype binary system with a high mass ratio of q = 1.09 (1/q = 0.947), a weak degree of contact factor f = 3.8% and a temperature difference between the components of ΔT = 398 K. The light curves of both the systems appear to be unspotted. By using our 4 and 7 times of minimum light and the 30 and 104 ToMs extract from the SWASP observations, respectively for UCAC3 276-106147 and NSVS 7377756, the orbital periods are here revised. The elements obtained from this analysis are used to compute the physical parameters of the systems combining our photometric solution with the 3-D correlation obtained for contact binaries by Gazeas (2009). Based on these estimated parameters the evolutionary state of the components of the systems is investigated and discussed.

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.

New multi-color photometric investigations of solar-like contact binary V680 Per

High-precision CCD photometric observations of the contact binary V680 Per were obtained in 2016. Its symmetric multi-color light curves were analyzed by using the Wilson–Devinney (2013) program. These photometric solutions suggest that V680 Per is an A-type W UMa contact binary with the mass ratio of q = 0.693 and a fill-out factor of f = 18.84% with a small temperature difference of 101 K. Based on all minimum times, the O − C curve was analyzed for the first time in this study. A cyclic oscillation (A3 = 0.00093 d, T3 = 4.92 yr) superimposed on a secular decrease (dP/dt = −8.16 × 10−8 d yr−1) was identified. The continuous decrease in period is possibly a result of mass transfer from the more massive component to the less massive one, or angular momentum loss due to a magnetic stellar wind. Because of this secular decrease, it is predicted that the degree of contact will become higher, and V680 Per will evolve into a deeper overcontact binary.

New Data on the Eclipsing Binary V1848 Ori and Improved Orbital and Light Curve Solutions

Abstract New observations of the eclipsing binary system V1848 Ori were carried out using the V filter resulting in a determination of new times of minima and new ephemeris were obtained. We presented the first complete analysis of the system’s orbital period behavior and analysis of O-C diagram done by the GA and MCMC approaches in OCFit code. The O-C diagram demonstrates a sinusoidal trend in the data; this trend suggests a cyclic change caused by the LITE effect with a period of 10.57 years and an amplitude of 7.182 minutes. It appears that there is a third body with mass function of f (m 3) = 0.0058 M⊙ in this binary system. The light curves were analyzed using the Wilson-Devinney code to determine some geometrical and physical parameters of the system. These results show that V1848 Ori is a contact W UMa binary system with the mass ratio of q = 0.76 and a weak fillout factor of 5.8%. The O’Connell effect was not seen in the light curve and there is no need to add spot.

Photometric investigation on the W-subtype contact binary V1197 Her

Multi-color light curves of V1197 Her were obtained with the 2.4 meter optical telescope at the Thai National Observatory and the Wilson-Devinney (W-D) program was used to model the observational light curves. The photometric solutions reveal that V1197 Her is a W-subtype shallow contact binary system with a mass ratio of q = 2.61 and a fill-out factor of f = 15.7%. The temperature difference between the primary star and secondary star is only 140 K in spite of the low degree of contact, which means that V1197 Her is not only in geometrical contact configuration but is also already under thermal contact status. The orbital inclination of V1197 Her is as high as i = 82.7°, and the primary star is completely eclipsed at the primary minimum. The totally eclipsing characteristic implies that the determined physical parameters are highly reliable. The masses, radii and luminosities of the primary star (star 1) and secondary star (star 2) are estimated to be M1 = 0.30(1) M⊙, M2 = 0.77(2) M⊙, R1 = 0.54(1) R⊙, R2 = 0.83(1) R⊙, L1 = 0.18(1) L⊙ and L2 = 0.38(1) L⊙. The evolutionary statuses of the two component stars are drawn in the Hertzsprung-Russell diagram, showing that the less massive but hotter primary star is more evolved than the secondary star. The period of V1197 Her is decreasing continuously at a rate of dP/dt = −2.58 × 10−7 day · year−1, which can be explained by mass transfer from the more massive star to the less massive one at a rate of year−1. The light curves of V1197 Her are reported to show the O'Connell effect. Thus, a cool spot is added to the more massive star to model the asymmetry in the light curves.

UY Ursae Majoris: An A-Subtype W UMa System with a Very Large Fill-Out Factor and an Extreme Mass Ratio

We present new BVRI light curves of UY UMa with no O’Connell effect and a flat bottom secondary eclipse. Light curve synthesis with the Wilson-Devinney code gives a new solution, which is quite different from the previous study: UY UMa is an A-subtype over-contact binary with a small mass ratio of q = 0.21, a high inclination of 81°.4, a small temperature difference of ΔT = 18°, a large fill-out factor of f = 0.61, and a third light of approximately 10% of the total systemic light. The absolute dimensions were newly determined. Seventeen new times of minimum light have been calculated from our observations. The period study indicates that the orbital period has intricately varied in a secular period increase in which two cyclical terms with periods of 12y.0 and 46y.3 are superposed. The secular period increase was interpreted to be due to a conservative mass transfer of 2.68 × 10–8 M⊙/yr from the less massive to the more massive star. The cyclical components are discussed in terms of double-light time contributions from two additional bound stars. The statistical relations of Yang & Qian (2015) among the physical parameters of 45 deep, low mass ratio contact binaries were revisited by using the physical parameters of UY UMa and 25 Kepler contact binaries provided by Şenavci et al. (2016).

A photometric study of the high-mass-ratio contact binary AV Puppis

The multi-color photometric light curves for contact binary AV Puppis (AV Pup) in VRcIc bandpasses are presented and analyzed by using the 2013 version of the Wilson-Devinney (W-D) code. The solutions suggest that AV Pup is a peculiar A-subtype W UMa contact binary with a high mass ratio (q = m2/m1 = 0.896) and a low fill-out factor (f = 10%). Combining our newly determined times of minimum with those collected from literatures, the orbital period changes of this system are investigated. The O – C analysis indicates that the orbital period of AV Pup is increasing at a rate of dP/dt = 4.83 × 10−7 days yr−1, which can be explained by mass transfer from the less massive component to the more massive one.

V752 Cen - A triple-lined spectroscopic contact binary with sudden and continuous period changes

Abstract V752 Cen is a triple-lined spectroscopic contact binary. Its multi-colour light curves were obtained in the years 1971 and 2018, independently. Photometric analyses reveal that the two sets of light curves produce almost consistent results. It contains a W-subtype totally eclipsing binary, and its mass ratio and fill-out factor are q = 3.35(1) and $f = 29(2)\, {{\ \rm per\ cent}}$. The absolute elements of its two component stars were determined to be M1 = 0.39(2)M⊙, M2 = 1.31(7)M⊙, R1 = 0.77(1)R⊙, R2 = 1.30(2)R⊙, L1 = 0.75(3)L⊙ and L2 = 2.00(7)L⊙. The period of V752 Cen is 0.37023198 day. The 0.37-d period remained constant from its first measurement in 1971 until the year 2000. However, it changed suddenly around the year 2000 and has been increasing continuously at a rate of dP/dt = +5.05 × 10−7day · year−1 since then, which can be explained by mass transfer from the less massive component star to the more massive one with a rate of $\frac{dM_{2}}{dt}=2.52\times {10^{-7}}M_\odot /year$. The period variation of V752 Cen over the 48 years in which the period has been monitored is really unusual, and is potentially related to effects from the possible presence of a nearby third star or of a pair of stars in a second binary.

YZ Phoenicis: a very short period K-type contact binary with variation of the O’Connell effect and orbital period change

Abstract YZ Phe is a very short-period contact binary (Sp. = K2 V) with an orbital period of 0.2347 d near the short period limit (0.22 d). We present the complete light curves which photometric data were obtained from the 60 cm telescope of PROMPT-8 at CTIO in Chile during 2016 June to October and 2017 August. The photometric solutions were determined by using the Wilson & Devinney code and the results reveal that YZ Phe is a W-subtype shallow contact binary ($f\sim 10\,$, q = 2.635, or 1/q = 0.379 for W subtype) with rotational motion of a large hot spot on the more massive component, showing a strong O’Connell effect with variation of maxima in photometric time series at period of 4.20 yr and stellar cycle at period of 1.28 yr. By compiling all available eclipse times, the result shows a long-term period decrease at a rate of dP/dt = −2.64(±0.02) × 10−8 d yr−1, superimposed on a cyclic variation (A3 = 0.0081 d and P3 = 40.76 yr). This variation cannot be explained by the Applegate mechanism. Thus, the cyclic change may be interpreted as the light-travel time effect via the presence of a cool third body. Based on photometric solutions, the third light was detected as $2\,$ of the total light in V and I bands. These results support the existence of a third body. The long-term period decrease can be explained by mass transfer from the more massive component ($M_2 \sim 0.74\, M_{\odot }$) to the less massive one ($M_1 \sim 0.28\, M_{\odot }$) or plus angular momentum loss (AML) via magnetic braking. With 1/q < 0.4 and long-term period decrease, all factors suggest that YZ Phe is on the AML-controlled state and its fill-out factor will increase, as well as the system evolving into a deeper normal contact binary.

IU Cancri: a solar-type contact binary with mass transfer

We present new CCD photometry of the solar-type contact binary IU Cnc, which was observed from November 2017 to March 2018 with three small telescopes in China. BV light curves imply that IU Cnc is a W-type contact binary with total eclipses. The photometric solution indicates that the mass ratio and fill-out factor are q = 4.104 ± 0.004 and f = 30.2% ± 0.3%, respectively. From all available light minimum times, the orbital period may increase at a rate of dP/dt = +6.93(4) × 10−7 d yr−1, which may result from mass transfer from the secondary component to the primary one. With mass transferring, IU Cnc may evolve from a contact configuration into a semi-detached configuration.

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.

RW Doradus: A solar-type shallow contact binary with a new orbital period investigation

Abstract New CCD photometric light curves of the short-period (P = 0.285 d) eclipsing binary RW Dor are presented. The observations were performed with the PROMPT-8 robotic telescope at CTIO in Chile between 2015 March and 2017 March. Other eclipse timings were obtained from the 2.15 m JS telescope at CASLEO, San Juan, Argentina in 2011 December. Based on a light curve analysis, it is found that RW Dor is a W-type shallow contact binary with a fill-out factor f ∼ 11% and a high mass ratio q ∼ 1.587 (1/q = 0.63), where the hotter component is the less massive one (M1 ∼ 0.52 M⊙ and M2 ∼ 0.82 M⊙). For orbital-period investigation, 15 new eclipse times and those previously published were compiled. O − C analysis with very weak evidence suggests that a long-term decrease in period with a rate of dP/dt = −9.61 × 10−9 d yr−1 is superimposed on a cyclic variation (A3 = 0.0054 d and P3 = 49.9 yr). The long-term decrease can be interpreted as mass transfer from the more massive component to the less massive one, or combined with angular momentum loss via magnetic braking. In addition, the marginal contact phase, high mass ratio (1/q > 0.4), and long-term decrease in period all suggest that RW Dor is a newly formed contact binary via Case A mass transfer, and it will evolve into a deeper normal contact binary. If the cyclic change is correct, the light travel-time effect via the presence of a cool third body will be a more plausible explanation for this.

Two Massive Twins in a Deep-contact Binary with a Black Hole Candidate

Abstract New light curves in B, V, R, and I bands for the B-type contact binary V593 Cen were obtained, and another V-band light curve was collected from All Sky Automated Survey data. We analyzed these two sets of light curves using the Wilson–Devinney code. It was found that V593 Cen is a deep-contact binary with a fill-out factor of more than 45%. The mass ratio, derived to be nearly one from light curves, indicates that this system contains two twin components. Together with the higher temperature of the less-massive component, it is inferred that the system has just passed the mass-reversal stage during the mass-transfer evolution. Therefore, at present it has the shortest period and deepest-contact configuration. By analyzing all available eclipse times, it is found that the O − C curve of V593 Cen shows a cyclic variation with a period of 50.9 yr. This can be explained as the light-travel time effect via the presence of a third body. The mass of the third body is derived to be larger than 4.3 (±0.3) M ⊙, and it should contribute to the total light of the system. However, no third light is detected during the photometric analyses. This indicates that it may be a black hole candidate orbiting the central mass-transferring binary in a triple system. During the evolution of this hierarchical triple-star system, the “eccentric Kozai–Lidov” mechanism may play a major role in the formation of the inner contact binary. This system seems a perfect candidate to be one of “merged” systems mentioned by Naoz & Fabrycky.

Starspots in contact and semi-detached binary systems

AbstractWe investigated the statistical properties of both cool and hot starspots in eclipsing binary stars. The starspot and binary parameters for contact and semi-detached systems were collected from literature, determined on the basis of synthetic light-curve analysis. We examined associations between these parameters. It was found that the cool spots in W-type binaries show properties similar to those of sunspots and starspots generated by dynamos, which differs from those of the cool spots in A-type binaries.The properties of hotspots also differ between the W- and A-type samples. From the physical properties of A- and W-type binaries, we infer that mass transfer is a dominant process for forming the hotspots in A-type binaries, and that both mass transfer and magnetic activity can contribute to the formation of the hotspots in W-type binaries. Our results also indicate that the hotspot size in the A-type sample is correlated with the temperature of spotted stars, orbital period, mass ratio, and fill-out factor.