Orbital Period Changes Research Articles

Gravitational waves from disks around spinning black holes: Simulations in full general relativity.

We present fully general-relativistic numerical evolutions of self-gravitating tori around spinning black holes with dimensionless spin a/M = 0.7 parallel or antiparallel to the disk angular momentum. The initial disks are unstable to the hydrodynamic Papaloizou-Pringle instability which causes them to grow persistent orbiting matter clumps. The effect of black hole spin on the growth and saturation of the instability is assessed. We find that the instability behaves similarly to prior simulations with nonspinning black holes, with a shift in frequency due to spin-induced changes in disk orbital period. Copious gravitational waves are generated by these systems, and we analyze their detectability by current and future gravitational wave observatories for a large range of masses. We find that systems of 10 M ⊙-relevant for black hole-neutron star mergers-are detectable by Cosmic Explorer out to ~300 Mpc, while DECIGO (LISA) will be able to detect systems of 1000 M ⊙ (105 M ⊙)-relevant for disks forming in collapsing supermassive stars-out to cosmological redshift of z ~ 5 (z ~ 1). Computing the accretion rate of these systems we find that these systems may also be promising sources of coincident electromagnetic signals.

Departure from the Exact Location of Mean Motion Resonances Induced by the Gas Disk in Systems Observed by Kepler

Abstract The statistical results of transiting planets show that there are two peaks, around 1.5 and 2.0, in the distribution of orbital period ratios. A large number of planet pairs are found near the exact location of mean motion resonances (MMRs). In this work, we find that the depletion and structures of the gas disk play crucial roles in driving planet pairs out of the exact location of MMRs. Under such a scenario, planet pairs are trapped into exact MMRs during orbital migration first and keep migrating at the same pace. The eccentricities can be excited. Due to the existence of a gas disk, eccentricities can be damped, leading to a change in orbital period, which will make planet pairs depart from the exact location of MMRs. With depletion timescales larger than 1 Myr, near-MMR configurations are formed easily. Planet pairs have higher possibilities of escaping from MMRs with a higher disk aspect ratio. Additionally, with a weaker corotation torque, planet pairs can depart farther from the exact location of MMRs. The final location of the innermost planets in the systems are directly related to the transition radius from the optically thick region to the outer optically thin disk. While the transition radius is smaller than 0.2 au at the late stage of the star evolution process, the period of the inner planets can reach around 10 days. Our formation scenario is a possible mechanism for explaining the formation of near-MMR configurations with the innermost planet farther than 0.1 au.

Spectroscopic long-term monitoring of RZ Cas

Context. RZ Cas is a short-period Algol-type system showing episodes of mass transfer and δ Sct-like oscillations of its mass-gaining primary component. This system exhibits temporal changes in orbital period, v sin i, and the oscillation pattern of the primary component. Aims. We analyse high-resolution spectra of RZ Cas that we obtained during a spectroscopic long-term monitoring lasting from 2001 to 2017. In this first part we investigate the atmospheric parameters of the stellar components and the time variation of orbital period, v sin i, and radial velocities (RVs), searching for seasonal changes that could be related to episodes of mass exchange and to a possible activity cycle of the system triggered by the magnetic cycle of the cool companion. Methods. We used spectrum synthesis to analyse the spectra of both components of RZ Cas. The study of variations of the orbital period is based on published times of primary minima. We used the least-squares deconvolved (LSD) binary program to derive separated RVs and LSD profiles of the components. From the LSD profiles of the primary we determined its v sin i. Using Markov chain Monte Carlo simulations with the PHOEBE program, we modelled the RV variations of both components. Results. Spectrum analysis resulted in precise atmospheric parameters of both components, in particular in surface abundances below solar values. We find that the variation of orbital period is semi-regular and derive different characteristic timescales for different epochs of observation. We show that the RV variations with orbital phase can be modelled when including two cool spots on the surface of the secondary component. The modelling leads to very precise masses and separation of the components. The seasonal variation of several parameters, such as v sin i, rotation-orbit synchronisation factor, strength of the spots on the cool companion, and orbital period, can be characterised by a common timescale of the order of nine years. Conclusions. We interpret the timescale of nine years as the magnetic activity cycle of the cool companion. In particular the behaviour of the dark spots on the cool companion leads us to the interpretation that this timescale is based on an 18-yr magnetic dynamo cycle. We conclude that the mass-transfer rate is controlled by the variable depth of the Wilson depression in the magnetic spot around the Lagrangian point L1. In the result, based on available data, we observe a damped activity cycle of the star, starting with a high mass-transfer episode around 2001 with a calculated mass-transfer rate of 1.510−6 M⊙ yr−1, followed by quiet periods in 2006 and 2009, slightly higher activity around 2013 and 2014, and again followed by quiet periods in 2015 and 2016. However, owing to missing data for years 2010 and 2011, we cannot exclude that a second high mass-transfer episode occurred within this time span.

Study of Eclipsing Binaries: Light Curves & O-C Diagrams Interpretation

The continuous improvement in observational methods of eclipsing binaries, EBs, yield more accurate data, while the development of their light curves, that is magnitude versus time, analysis yield more precise results. Even so, and in spite the large number of EBs and the huge amount of observational data obtained mainly by space missions, the ways of getting the appropriate information for their physical parameters etc. is either from their light curves and/or from their period variations via the study of their (O-C) diagrams. The latter express the differences between the observed, O, and the calculated, C, times of minimum light. Thus, old and new light curves analysis methods of EBs to obtain their principal parameters will be considered, with examples mainly from our own observational material, and their subsequent light curves analysis using either old or new methods. Similarly, the orbital period changes of EBs via their (O-C) diagrams are referred to with emphasis on the use of continuous methods for their treatment in absence of sudden or abrupt events. Finally, a general discussion is given concerning these two topics as well as to a few related subjects.

New insights on the massive interacting binary UU Cassiopeiae

We present the results of our study of the close binary UU Cassiopeiae based on previously published multiwavelength photometric and spectroscopic data. Based on eclipse timings from the last 117 years, we find an improved orbital period of Po = 8.d519296(8). In addition, we find a long cycle of length T ∼ 270 d in the Ic-band data. There is no evidence for orbital period change over the last century, suggesting that the rate of mass loss from the system or mass exchange between the stars is small. Sporadic and rapid brightness drops of up to ΔV = 0.3 mag are detected throughout the orbital cycle, and infrared photometry clearly suggests the presence of circumstellar matter. We model the orbital light curve of 11 published datasets, fixing the mass ratio and cooler star temperature from previous spectroscopic work: q = 0.52 and Tc = 22 700 K. We find a system seen at an angle of 74° with a stellar separation of 52 R⊙, a temperature for the hotter star of Th = 30 200 K and, for the hotter and cooler stars, respectively, stellar masses of 17.4 and 9 M⊙, radii of 7.0 and 16.9 R⊙, and surface gravities log g = 3.98 and 2.94. We find an accretion disk surrounding the more massive star that has a radius of 21 R⊙ and a vertical thickness at its outer edge of 6.5 R⊙; the disk nearly occults the hotter star. Two active regions hotter than the surrounding disk are found, one located roughly in the expected position where the stream impacts the disk and the other on the opposite side of the disk. Changes are observed in parameters of the disk and spots in different datasets.

A revisit of PSR J1909−3744 with 15-yr high-precision timing

ABSTRACT We report on a high-precision timing analysis and an astrophysical study of the binary millisecond pulsar, PSR J1909−3744, motivated by the accumulation of data with well improved quality over the past decade. Using 15 yr of observations with the Nançay Radio Telescope, we achieve a timing precision of approximately 100 ns. We verify our timing results by using both broad-band and sub-band template matching methods to create the pulse time-of-arrivals. Compared with previous studies, we improve the measurement precision of secular changes in orbital period and projected semimajor axis. We show that these variations are both dominated by the relative motion between the pulsar system and the Solar system barycentre. Additionally, we identified four possible solutions to the ascending node of the pulsar orbit, and measured a precise kinetic distance of the system. Using our timing measurements and published optical observations, we investigate the binary history of this system using the stellar evolution code mesa, and discuss solutions based on detailed WD cooling at the edge of the WD age dichotomy paradigm. We determine the 3D velocity of the system and show that it has been undergoing a highly eccentric orbit around the centre of our Galaxy. Furthermore, we set up a constraint over dipolar gravitational radiation with the system, which is complementary to previous studies given the mass of the pulsar. We also obtain a new limit on the parametrized post-Newtonian parameter, $\left| \hat\alpha_1 \right|$ < 2.1 × 10−5 at 95 per cent confidence level, which is fractionally better than previous best published value and achieved with a more concrete method.

DART mission determination of momentum transfer: Model of ejecta plume observations

The NASA Double Asteroid Redirection Test (DART) spacecraft will impact the secondary member of the [65803] Didymos binary in order to perform the first demonstration of asteroid deflection by kinetic impact. Determination of the momentum transfer to the target body from the kinetic impact is a primary planetary defense objective, using ground-based telescopic observations of the orbital period change of Didymos and imaging of the DART impact ejecta plume by the LICIACube cubesat, along with modeling and simulation of the DART impact. LICIACube, contributed by the Italian Space Agency, will perform a flyby of Didymos a few minutes after the DART impact, to resolve the ejecta plume spatial structure and to study the temporal evolution. LICIACube ejecta plume images will help determine the vector momentum transfer from the DART impact, by determining or constraining the direction and the magnitude of the momentum carried by ejecta. A model is developed for the impact ejecta plume optical depth, using a point source scaling model of the DART impact. The model is applied to expected LICIACube plume images and shows how plume images enable characterization of the ejecta mass versus velocity distribution. The ejecta plume structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given time. The evolution of the plume optical depth profiles determined from LICIACube images can distinguish between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity distributions. LICIACube plume images discriminate the differences in plume structure and evolution that result from different target physical properties, mainly strength and porosity, thereby allowing inference of these properties to improve the determination of momentum transfer.

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.

The binary evolution of SAX J1808.4−3658: implications of an evolved donor star

ABSTRACT Observations of the accretion powered millisecond pulsar SAX J1808.4−3658 have revealed an interesting binary evolution, with the orbit of the system expanding at an accelerated rate. We use the recent finding that the accreted fuel in SAX J1808.4−3658 is hydrogen depleted to greatly refine models of the progenitor and prior evolution of the binary system. We constrain the initial mass of the companion star to 1.0–1.2 M⊙, more massive than previous evolutionary studies of this system have assumed. We also infer the system must have undergone strongly non-conservative mass transfer in order to explain the observed orbital period changes. We include mass loss due to the pulsar radiation pressure on the donor star, inducing an evaporative wind which is ejected at the inner Lagrangian point of the binary system. The resulting additional loss of angular momentum resolves the discrepancy between conservative mass transfer models and the observed orbital period derivative of this system. We also include a treatment of donor irradiation due to the accretion luminosity, and find this has a non-negligible effect on the evolution of the system.

The First Light Curve Modeling and Orbital Period Change Investigation of Nine Contact Binaries around the Short-period Cutoff

Abstract In this paper, we present the first light curve synthesis and orbital period change analysis of nine contact binaries around the short-period limit. It is found that all these systems are W-subtype contact binaries. One of them is a medium contact system while the others are shallow contact ones. Four of them manifest obvious O’Connell effect explained by a dark spot or hot spot on one of the component stars. Third light was detected in three systems. By investigating orbital period variations, we found that four of the targets display a secular period decrease while the others exhibit a long-term period increase. The secular period decrease is more likely caused by angular-momentum loss while the long-term period increase is due to mass transfer from the less massive component to the more massive one. Based on the statistic of 19 ultrashort-period contact binaries with known orbital period changes, we found that seven of them display long-term decrease (three of them also exhibit cyclic variations), ten of them manifest long-term increase while two of them only show cyclic variation, and that most of them are shallow contact binaries supporting the long timescale angular-momentum loss theory suggested by Stepien. For the three deep contact systems, we found that they are probably triple systems. The tertiary companion plays an essential role during their formation and evolution.

A unified theory of cataclysmic variable evolution from feedback-dominated numerical simulations

The envelopes accreted by white dwarf stars from their hydrogen-rich companions1 experience thermonuclear-powered runaways2,3 observed as classical nova eruptions4,5 peaking at 105–106 solar luminosities6–9. Virtually all nova progenitors—‘nova-like variables’—exhibit high mass transfer rates to their white dwarfs before and after an eruption10. Surprisingly, 10–1,000 times lower mass transfer rate11 binaries, exhibiting accretion-powered ‘dwarf nova’ outbursts12, exist at identical orbital periods. Nova shells surrounding dwarf novae13–16 demonstrate that at least some novae metamorphize into dwarf novae17,18, though the mechanisms and timescales governing mass transfer rate variations are poorly understood. Here, we report simulations of the multi-Gyr evolution of novae modelling every eruption’s thermonuclear runaway, mass and angular momentum losses, feedback due to irradiation and variable mass transfer rate, and orbital size and period changes. These feedback-dominated simulations reproduce the observed range of mass transfer rates at a given orbital period, with large and cyclic kyr–Myr timescale changes. They also demonstrate Myr-long deep hibernation (complete stoppage of mass transfer), but only in short-period binaries; that initially different binaries converge to become nearly identical systems; low-mass-transfer-rate dwarf novae occasionally generate novae; and that the masses of white dwarfs decrease monotonically, but only slightly while their red dwarf companions are consumed. Cataclysmic variables—a binary pairing of a white dwarf and a hydrogen-rich donor star—experience mass transfer and other complex interactions. This numerical simulation by Hillman et al. models in particular the feedback between the stellar pair, and succeeds in reproducing many of the observed characteristics of cataclysmic variables.

Sudden and steady orbital period changes across the classical nova eruptions of DQ Her and BT Mon

ABSTRACT I report two new measures of the sudden change in the orbital period (P) across the nova eruption (ΔP) and the steady period change in quiescence ($\dot{P}$) for classical novae (CNe) DQ Her and BT Mon. The fractional changes (ΔP/P) in parts per million (ppm) are −4.46 ± 0.03 for DQ Her and +39.6 ± 0.5 for BT Mon. For BT Mon, the ΔP/P value is not large enough (i.e. >1580 ppm) to allow for hibernation in this system. The negative ΔP/P for DQ Her is a confident counterexample of the hibernation model for the evolution of cataclysmic variables. Further, published models of period changes by nova eruptions do not allow for such a negative value, so some additional mechanism is required, with this perhaps being due to asymmetric ejection of material. My program has also measured the first long-term $\dot{P}$ for CNe, with 0.00 ± 0.02 for DQ Her and −2.3 ± 0.1 for BT Mon, all with units of 10−11 d cycle−1. These can be directly compared to the predictions of the magnetic braking model, where the long-term average $\dot{P}$ is a single universal function of P. The predicted values are −0.027 for DQ Her and −0.33 for BT Mon. For both novae, the measured $\dot{P}$ is significantly far from the predictions for magnetic braking. Further, the observed ΔP for BT Mon imposes an additional positive period change of +0.60 × 10−11 d cycle−1 when averaged over the eruption cycle, so this system actually has a long-term rise in P.

Sudden and steady orbital period changes across six classical Nova Eruptions: the end of hibernation and two serious challenges for the magnetic braking model of cataclysmic variable evolution

ABSTRACT I report on two new measures of the sudden change in the orbital period (P) across the nova eruption (ΔP) and the steady period change in quiescence ($\dot{P}$) for classical novae (CNe) RR Pic and HR Del, bringing a total of six such measures for CNe, all in a final report of my large and long observing program. The fractional changes (ΔP/P) in parts-per-million (ppm) are −290.71 ± 0.28 (QZ Aur), −472.1 ± 4.8 (HR Del), −4.46 ± 0.03 (DQ Her), +39.6 ± 0.5 (BT Mon), −2003.7 ± 0.9 (RR Pic), and −273 ± 61 (V1017 Sgr). These results are in stark opposition to the Hibernation Model for the evolution of cataclysmic variables (CVs), which requires ΔP/P> + 1000 ppm to get the required drop in the accretion rate to produce hibernation. The hibernation model cannot be salvaged in any way. My program has also measured the first long-term $\dot{P}$ for CNe, with −2.84 ± 0.22 (QZ Aur), +4.0 ± 0.9 (HR Del), +0.00 ± 0.02 (DQ Her), −2.3 ± 0.1 (BT Mon), and +1.25 ± 0.01 (RR Pic) in units of 10−11 d per cycle. These can be directly compared to the predictions of the magnetic braking model, where the long-term average $\dot{P}$ is a single universal function of P. The measured values are +5.3, −94, 0.00, +6.9, and −190 times that predicted by the model, so the predictions are always greatly wrong. Further, the effects of the ΔP averaged over the eruption cycle are usually much larger than the magnetic braking effects. To get a realistic model of CV evolution, we must add the physics of the ΔP and $\dot{P}$ variations.

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.

A photometric study of the short-period eclipsing binary 1SWASP J204932.94-654025.8, showing strong third light

1SWASP J204932.94-654025.8 (hereafter J2049) is a newly discovered eclipsing binary system with an orbital period of 0.2299103 days. BVRc light curves (LCs) are presented and analyzed by using the 2013 version of the Wilson–Devinney (W–D) program. Because the observed LCs are asymmetric, a hot star-spot was employed on the secondary component during our analysis. We found that J2049 is a W-subtype shallow contact eclipsing binary system with an orbit inclination of 62∘.69 ± 0∘.95 and a mass ratio of q =1.326 ± 0.056. More importantly, we found the presence of a strong third light, with an average luminosity contribution of 31.3% of the total light. Based on times of the light minima, the orbital period changes of J2049 are studied for the first time, and there is no evidence for any significant dp/dt now. Considering the presence of the third light and the short time span of the eclipse times, more observations are needed in the future.

LL Com: A Near-contact Total Eclipsing Binary at a Key Stage of Evolution

Abstract Despite the discovery of LL Com, a Lyrae-type eclipsing binary system, approximately 60 yr ago, little has been found concerning its detailed photometry and orbital-period change until now. In this paper, we present the first multi-band charge-coupled-device photometric light curves, from which a significant luminosity reduction around the primary eclipse is revealed. Based on LAMOST data, we first determined LL Com’s spectrum as F1V and then analyzed the light curves with the 2015 version of the Wilson-Devinney code. The fact that LL Com is a near-contact binary system with a semi-detached configuration, where the secondary component only fills its Roche lobe and the primary component fills more than 95% of its Roche lobe, is suggested through the photometric solution. In addition, according to archival photometry and previously published times of minima, a secular period increase at a rate of was found, which implies a continuous mass transfer from the secondary to the primary. Utilizing the photometric solution and the simulations of single-particle trajectories, we propose the existence of a cool spot on the surface of the primary component. This cool spot can be naturally produced by the impacts that occur during mass flow, and it also successfully interprets the luminosity reduction in the light curves. Finally, with the combination of thermal relaxation oscillation theory and the Roche-Lobe model, we conclude that LL Com is transitioning from the semi-detached to the detached phase.

Period investigation of Algol systems TZ Eri and TU Her

TZ Eri and TU Her are both classic Algol-type systems (Algols). By observing and collecting times of minimum light, we constructed the O – C curves for the two systems. The long-time upward and downward parabolas shown in these diagrams are considered to be the result of the combination of mass transfer and angular momentum loss. The secular orbital period change rates are dP/dt = 4.74(± 0.12) × 10−7 d yr−1 and dP/dt = −2.33(± 0.01)× 10−6 d yr−1, respectively. There are also cyclic variations in their O – C curves which might be caused by the light-travel time effect (LTTE). A circumbinary star may exist in the TZ Eri system with a mass of at least 1.34 M⊙, while there are possibly two celestial bodies that almost follow a 2 : 1 resonance orbit around the TU Her binary pair. Their masses are at least 2.43 M⊙ and 1.27 M⊙.

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.

Origin of the orbital period change in contact binary stars

The evolution of contact binary star systems in mass asymmetry (transfer) coordinate is considered. The orbital period changes are explained by an evolution in mass asymmetry towards the symmetry (symmetrization of binary system). It is predicted that decreasing and increasing orbital periods are related, respectively, with the nonoverlapping and overlapping stage of the binary star during its symmetrization. A huge amount of energy [Formula: see text][Formula: see text]J is converted from the potential energy into internal energy of the stars during the symmetrization. As shown, the merger of stars in the binary systems, including KIC 9832227, is energetically an unfavorable process. The sensitivity of the calculated results to the values of total mass and orbital angular momentum is analyzed.

Physical Properties of the Close-in Tertiary in the Southern Triple-lined System VZ Lib

Abstract VZ Lib is a southern triple-lined system. By analyzing all available times of light minima, orbital period changes are revisited in detail. We discovered that the observed–calculated (O − C) curve shows a long-term period decrease at a rate of , revealing a mass transfer from the more massive component to the less massive one. A cyclic variation covering more than three cycles was discovered, which was analyzed for the light-travel-time effect via the presence of the tertiary companion. The cyclic variation has a short period of 2.96 (±0.04) yr and a small semiamplitude of 0.0039 (±0.0004) days. The mass of the third body was determined to be M ⊙ and an orbital semimajor axis shorter than au was obtained. Orbital properties of this close-in companion should provide valuable information on the formation of close binaries and stellar dynamical interaction. New complete light curves of VZ Lib were obtained and modeled with the Wilson–Devinney code. The light curves show a small but significant O’Connell effect that was not detectable in 1981 and 2007 but in 2004, so we derived a new photometric solution with assuming spot and a third light in the system. It is found that the light-curve subtype changed from A-type to W-type, which was possibly caused by a dark spot on the massive component. Our photometric solutions are in agreement with the spectroscopic results given by previous authors.