W-type System Research Articles

Photometric study of the overcontact binary V826 Aur

We present BVRC differential photometry of an eclipsing binary system V826 Aur. A period analysis shows near constant period of 0.36 days across two decades of observation. The best fit models are consistent with a W-type W UMa overcontact binary consisting of a less massive G8 primary star and a more massive K0 secondary star. The modeled system properties are unremarkable with mass ratio (q=2.9), inclination (i=82°), fillout factor (f=0.094), and temperature ratio (T2/T1=0.96), all near the average for W-type systems. A very slight O’Connell effect is present and is analyzed. A cool spot is used to model the effect, resulting in fitted spot parameters of angular size (ρ=8.2°), temperature factor (κ=0.81), and longitude (λ=63°) while colatitude was fixed at 90°.

Is There a Substellar Object Orbiting the Solar-like Stable Contact Binary V2284 Cyg?

V2284 Cyg is a neglected W UMa-type binary star for photometric investigations. Monitored by the Kepler Space Telescope from 2009 to 2013, its light curves are continuously stable, suggesting that both components are inactive during this time interval. Based on the short-cadence observations, we determined the photometric solutions by using the 2013 version of the Wilson-Devinney code. These parameters reveal that V2284 Cyg is a W-type system with a degree of contact factor of f = 39.23% and a mass ratio of q = 2.90. Meanwhile, hundreds of times of minimum light were obtained and applied to analyze the orbital period changes. In the O-C diagram, a small-amplitude cyclic oscillation (A3 = 0.00030 days and T3 = 2.06 years) superimposed on a secular decreasing was found. The continuous decreasing may be a result from the mass transfer from the more massive component to the less massive one. With the long-term decreasing of the orbital period, this binary will evolve into a deeper contact system. Because the light curve is stable, the cyclic variation is plausibly explained as the light-travel time effect (LTTE) due to the presence of an additional body. The mass of the companion is . If the orbital plane inclination is a random distribution, it is a brown dwarf with 66.7% probability. Therefore, the companion of V2284 Cyg is possibly the first candidate of the brown dwarf orbiting around contact binary, where both component are sharing a common convective envelope.

First multi-colour photometric study of the short period K-type contact binary NSVS 2701634

We present the first CCD sets of complete light curves for the W Ursae Majoris W-type system NSVS 2701634. The observations were performed in the B, V and Ic bands using the 0.25 m telescope of the “Stazione Astronomica Betelgeuse” Italy, during 8 nights in April 2015.From our observations we were able to confirm and revise the short-period (0.24 days) variation found by Shaw and collaborators in their online list (http://physast.uga.edu/~jss/nsvs/) of periodic variable stars found in the Northern Sky Variability Survey.Using our 12 times of minimum light, the orbital period variations of NSVS 2701634 are studied for the first time. The general trend of the (O-C) curve reveals that its period is varying by a downward parabola that means that period is decreasing, this fact could be explained by a mass transfer between the components of the system.The light curves were modelled using the Wilson–Devinney code and the elements obtained from this analysis are used to compute the physical parameters of the system in order to study its evolutionary status.A reasonable fit of the synthetic light curves of the data indicated that NSVS 2701634 is an late-type (K3−K4+K6) contact binary system of W-Subtype of the W Ursae Majoris systems, with a mass ratio of q = 2.60, a degree of contact factor f = 15.3% and inclination i = 72°. The light curves show asymmetries at the maxima that are fitted adding an hot spot on the surface of the more massive star, known as inverse O’Connell effect.From an estimation of the absolute dimensions of the system and from the logM-logL diagram, it is seen that both components of NSVS 2701634 follow the general pattern of the W subtype W Ursae Majoris systems.

FIRST PHOTOMETRIC INVESTIGATION OF THE SOLAR-TYPE CONTACT BINARY GSC 1537–1557

By analyzing R-c and I-c light curves of the short-period solar-type eclipsing binary GSC 1537-1557 we discovered that it is a shallow contact binary with a degree of contact factor of f = (8.10 +/- 1.79)%. Photometric solutions reveal that GSC 1537-1557 is a W-type system with a mass ratio of q = M-2/M-1 = 2.645 where the less massive component (the primary star) is about 110 K hotter than the more massive one (the secondary star). The asymmetry and variation of the light curves were explained as the activity of spots on the solar-type component stars. By investigating all of the available times of light minima, we found that the observed-calculated (O-C) curve shows a cyclic variation with a small amplitude of 0.00335 days and a period of 8.1 years. The small-amplitude cyclic change in the O - C curve was analyzed for the light-travel time effect via the presence of an extremely cool stellar companion. The mass of the third body was determined to be M-3 sin i' =(0.19 +/- 0.01) M-circle dot when M-1 + M-2 = 1.31 M-circle dot is adopted for GSC 1537-1557. The semimajor axis of the outer obit is a' sin i' =(4.58 +/- 0.33) AU.

The first photometric investigation of the neglected close binary star AQ Com

AQ Com is a W UMa-type binary star with a period of 0.28133days that was discovered about fifty years ago. However, it was neglected for photometric investigation. Complete light curves in Rc and Ic bands are presented that show a positive O’Conell effect. The light maxima following the primary minima are higher than the other ones in both bands. Photometric solutions obtained with the W–D (Wilson and Devinney) method suggest that AQ Com is a contact binary with a contact degree of f=21.4(±6.2)%. It is found that the contact binary is a W-type system with a mass ratio of q=2.86 where the less massive component is hotter than the more massive one in a common convective envelope. The asymmetries of the light curves are explained by two dark spots on the more massive component. By combining several determined times of light minimum with the others compiled from the literature, it is detected that the Observed-Calculated (O-C) curve may display a cyclic change with a period of 8.5years and an amplitude of 0.0016days. The cyclic oscillation may be caused by the presence of a cool third stellar object at an orbital separation of about ∼4.2AU. However, more data are needed to confirm the existence of the third body.

First photometric study of W UMa binary star LU Lac

LU Lac is a neglected W UMa binary star in photometric investigations. In this paper, we present BVRI CCD photometric light curves obtained on one night in 2012. The first photometric solutions of this system are computed by using the Wilson–Devinney code. It is shown that LU Lac is a marginal contact W-type system with a degree of contact factor of f=8.9%, a mass ratio of q=2.085 and a high inclination of i=82°.20. From the first analyses of orbital period changes, we found the period variation of the system includes an oscillation (A3=0.0125 days and T3=51.92 years). The cyclic change may be attributed to the light-travel time effect through the presence of a third body.

FIRST PHOTOMETRIC INVESTIGATION OF THE NEWLY DISCOVERED W UMa-TYPE BINARY STAR MR Com

By analyzing multi-color light curves of the newly discovered W UMa-type binary, MR Com, we discovered that it is a shallow-contact binary with a degree of contact factor of f = 10.0% +/- 2.1%. Photometric solutions reveal that MR Com is a W-type system with a mass ratio of q = 3.9 where the less massive component is about 90 K hotter than the more massive one. By investigating all of the available times of minimum light, we found that the general trend of the Observed-Calculated (O - C) curve shows a downward parabolic variation while it undergoes a cyclic variation with a small amplitude of 0.0031 days and a period of 10.1 yr. The downward parabolic change corresponds to a long-term decrease in the orbital period at a rate of (P) over dot = -5.3 x 10(-7) days yr(-1) that may be caused by a combination of a mass transfer and an angular momentum loss (AML) via magnetic braking. Among the 16 shallow-contact systems with a decreasing orbital period, MR Com has the lowest mass ratio (e.g., 1/q = 0.26). The shallow-contact configuration, the low-mass ratio, and the long-term period decrease all suggest that systems similar to MR Com are on the AML-controlled stage of the evolutionary scheme proposed by Qian. They will oscillate around a critical mass ratio and evolve into a deep contact with a higher mass ratio. The small-amplitude cyclic change in the O - C curve was analyzed for the light-travel time effect via the presence of an extremely cool stellar companion.

CCD photometry of W UMa-type contact binaries in the old open cluster Berkeley 39

We present the combined BVI multicolor photometric solutions of seven EW variables in the old open cluster Berkeley 39. The observations were carried out in the B and V passbands from the 2 m telescope at the IUCAA-Girawali Observatory in India. The analysis is done using the 2003 version of the Wilson-Devinney code and the fitted light curves are presented. The light curves appear to be symmetric in all the passbands. The photometric solutions suggest that the variables are W-type systems. The new ephemeris indicates that the orbital periods of the studied variables have not changed during the timespan of observations. Revised orbital period, absolute mass, radius and luminosity of the respective variables are presented. The absolute physical parameters of the variables follow the trend of field EW stars. Comparing the results obtained with the other theoretical works, we suggest that there is an excess loss of mass and angular momentum in these systems which may be due to their short period and relatively young age, possibly due to the presence of a third component or the initial detached period being less than 2 d.

Angular momentum and mass evolution of contact binaries

Various scenarios of contact binary evolution have been proposed in the past, giving hints of (sometimes contradictory) evolutionary sequences connecting A- and W-type systems. As the components of close detached binaries approach each other and contact binaries are formed, following evolutionary paths transforms them into systems of two categories: A-type and W-type. The systems evolve in a similar way but under slightly different circumstances. The mass/energy transfer rate is different, leading to quite different evolutionary results. An alternative scenario of evolution in contact is presented and discussed, based on the observational data of over one hundred low-temperature contact binaries. It results from the observed correlations among contact binary physical and orbital parameters. Theoretical tracks are computed assuming angular momentum loss from a system via stellar wind, accompanied by mass transfer from an advanced evolutionary secondary to the main-sequence primary. A good agreement is seen between the tracks and the observed graphs. Independently of details of the evolution in contact and a relation between A- and W-type systems, the ultimate fate of contact binaries involves the coalescence of both components into a single fast rotating star.

RT Leonis Minoris: Does It Belong to an A- or W-Type Overcontact Binary System?

Abstract New photometric observations and analyses of the W UMa-type binary system RT Leonis Minoris are presented. A period study with our four times of light minimum, including other eclipse times from the literature, suggests that the orbital period of the binary star is variable. The O – C curve can be explained as a cyclic variation with an amplitude of 0:d0049 and a period of 46.7 yr. Photometric solutions were derived by using the 2003 version of the Wilson–Devinney method (1971, ApJ, 166, 605), and absolute parameters of the system were determined. The results indicate that RT LMi is an ambiguous W UMa-type overcontact system for the following reasons: (i) the depths of both minima are nearly equal, which makes it very difficult to distinguish whether it belongs to an A- or W-type system; (ii) the primary minima in Hoffmann’s light curves are an occultation, indicating a W-type system, while the primary minimum in our light curve is a transit, suggesting an A-type light variation; and (iii) though our light curve shows an A-type variation, the photometric solutions indicate a higher secondary temperature of T2 = 6513 K (T1 = 6400 K), making the binary system, surprisingly, of W-type. These may indicate that Binnendijk’s classification based on the shape of the light curve cannot reveal the physical properties of W UMa-type binary stars of this kind.

Masses and angular momenta of contact binary stars

Abstract Results are presented on component masses and system angular momenta for over 100 low-temperature contact binaries. It is found that the secondary components in close binary systems are very similar in mass. Our observational evidence strongly supports the argument that the evolutionary process goes from near-contact binaries to A-type contact binaries, without any need of mass loss from the system. Furthermore, the evolutionary direction of A-type into W-type systems with a simultaneous mass and angular momentum loss is also discussed. The opposite direction of evolution seems to be unlikely, since it requires an increase of the total mass and the angular momentum of the system.

Light curve solution and orbital period analysis of the contact binary V842 Herculis

New photoelectric BV light curves were obtained for the neglected eclipsing binary V842 Her at the TUBITAK National Observatory (TUG) and studied for the first time in detail to determine the orbital parameters and geometry of the system. The solutions obtained simultaneously for the new light curves and the radial velocity curves in the literature by using the Wilson-Devinney code reveal a typical W-type contact system. The light curves exhibit the so-called O'Connell effect which the level of the primary maxima being higher than that of the secondary ones in both pass-bands. The O'Connell effect in the light curves is explained in terms of a dark-spot located on the more massive component which makes the more massive larger component slightly cooler than the less massive smaller one. The O – C diagram constructed for all available times of minima of V842 Her exhibits a cyclic character superimposed on a quadratic variation. The quadratic character yields a orbital period increase with a rate of dP /dt = 7.76 × 10–7 days yr–1 which can be attributed to the mass exchange/loss mechanism in the system. By assuming the presence of a gravitationally bound third body in the system, the analysis of the cyclic nature in the O – C diagram revealed a third body with mass of 0.4M⊙ orbiting around the eclipsing pair. The possibility of magnetic activity cycle effect as a cause for the observed cyclic variation in the O – C diagram was also discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure and evolution of low-mass W UMa-type systems

The structure and evolution of low-mass W UMa-type contact binaries are discussed by employing Eggleton's stellar evolution code. Assuming that these systems completely satisfy Roche geometry for contact binaries with every kind of mass ratio (0.02–1.0) we calculate the relative radii (R1,2/A, where R1,2 are the radii of both stars and A is the orbital separation) of both components of contact binaries with different contact depths between inner and outer Roche lobes. We obtain a radius grid of contact binaries and can ensure the surfaces of two components lying on an equipotential surface by interpolation using this radius grid when we follow the evolution of the contact binaries. There are serious uncertainties concerning mainly the transfer of energy in these systems, i.e. it is unclear how and where the energy is transferred. We assume that the energy transfer takes place in different regions of the common envelope to investigate the effects of the region of energy transfer on the structure and evolution of contact binaries. We find that the region of energy transfer has a significant influence on the structure and evolution of contact binaries, and conclude that the energy transfer may occur in the outermost layers of the common convective envelope for W-type systems, and that this transfer takes place in the deeper layers of the common envelope for A-type systems. Meanwhile, if we assume that the energy transfer takes place in the outermost layers for our model with low total mass, and find that our model steadily evolves towards a system with a smaller mass ratio and a deeper envelope, suggesting that some A-type W UMa systems with low total mass could be considered as the later evolutionary stages of W-subtype systems, and that the surface temperature of the secondary exceeds that of the primary during the time when the primary expands rapidly, or the secondary contracts rapidly, suggesting that W-subtype systems may be caused by expansion of the primary, or by the contraction of the secondary.

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.

A possible relation between the period change and the mass ratio for W-type contact binaries

Orbital period changes of eight W-type contact binaries (TY Boo, BH Cas, AD Cnc, TX Cnc, RZ Com, LS Del, BB Peg and AA UMa) are presented based on the analysis of their O–C curves. It is found that the periods of the five systems TY Boo, TX Cnc, RZ Com, LS Del and AA UMa show secular increase. For BB Peg, its period increase rate has been revised. For AD Cnc, weak evidence also shows that its orbital period is increasing. For the remaining BH Cas, the three times of light minimum given by Agerer & Hubscher indicate that, recently, its period has been increasing. However, the properties of the period need further study. The mass ratios of all the systems are larger than 0.4. The period increases of the systems may suggest that the W-type W UMa stars with high mass ratio usually show their period increase. In order to check this conclusion, secular period changes of 30 W-type contact binaries have been collected from the literature. It is found that systems showing period increase usually have a higher mass ratio , and the periods of low-mass ratio systems are varying in a secular decrease. This strongly suggests that a relation between the orbital period variation and the mass ratio for W-type contact binaries may exist. If the secular period change is caused by conservative mass transfer between the components, this relation may suggest that the evolution of the W-type systems is oscillation around a critical mass ratio . However this is highly speculative. On the other hand, the relation may be potentially strong observational evidence for Rahunen's conclusion that angular momentum loss (AML) may enable the components of a contact binary to remain in good contact throughout the thermal relaxation oscillation (TRO) cycle. This connection could be explained by the combination of the TRO and the variable AML via the change of depth of contact, which needs further studies observationally and theoretically.

V 700 Cygni and AW Virginis: Two W-type W UMa systems with spotted components

A photometric analysis of the W UMa systems V 700 Cyg and AW Vir, based on photoelectric B and V light curves, is presented. Since no spectroscopic mass-ratio is available, the q -search method was applied to find the preliminary range of the mass-ratio in order to search for the final solution. First, an unspotted solution was carried out by using the unperturbed parts of the light curves and applying the DC program of the WD code. The final spotted solution was made by adopting spot models for the two systems. In the case of V 700 Cyg, two cool spots were placed on the primary (more massive, larger and cooler) component to explain the O'Connell effect ( fainter than ) and a small deficit of light just before . In the case of AW Vir, one cool spot was placed on the primary component to explain the relatively large O'Connell effect. Both objects are W-type systems with partial eclipses; V 700 Cyg is fairly evolved while AW Vir is rather unevolved.

TU Bootis: An ambiguous W Ursae Majoris system

The W UMa system TU Boo has a period of 0.32438 days and a spectral type G3. We present here the first photometric analysis, based on photoelectric B and V light curves. The q -search method was used to find the preliminary range of the mass-ratio in order to search for the final solution. The unspotted solution was found by using the unperturbed part of the light curve and applying the DC program of the WD code. Spot models were computed, a one-spot model to explain the O'Connell effect ( fainter than ) by introducing a cool spot on the larger component, and a two-spot model to explain both the O'Connell effect and the small excess of light just after by assuming, in addition, a bright region on the smaller component near the neck region of the common envelope. TU Boo is an A-type W UMa system with complete eclipses, the secondary minimum being an occultation. However, the derived physical parameters of the system and its light curve anomalies are more common for slightly evolved W-type systems.

Almost-contact semidetached EP Cep in NGC 188

The photomectic observations of EP Cep, from Kaluzny and shara (1987), were analyzed by the Wilson and Devinney method. The appropriate value of the mass ratio of this system was found after extensive searches. EP Cep has a semi-detached configuration where the lower-mass component is in contact with its respective Roche surface. The higher-mass component very nearly fills its Roche lobe. It is very close to being a critical configuration. The mass ratio of the system is about 1.292 and the inclination is 66.°942. EP Cep has the characteristic of a W-type WUMa system. The absolute dimensions for the primary and secondary of this system were calculated from its spectral types and by combining the photometric solution with inferred component radial velocities (Baliunas and Guinan, 1985).

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.

Radial velocities of the contact binary system RW Doradus

Radial velocities are reported for both components of the short-period contact binary RW Dor. Although the data set is limited to nine observations of one half of the orbital cycle, and two observations of the other half, the mass ratio and the minimum masses are determined to precisions of 5 per cent. These results are then combined with those from wide-ranging analyses of extensive photometric observations by Kaluzny & Caillault (1989, Acta Astr., 39) and Marton et al. (1989, MNRAS, 240) to establish the masses and other astrophysical parameters of the system for the first time. The system is confirmed to be a W-type contact binary composed of two K-type stars. It is therefore one of the lowest mass W-type systems known and has properties typical of such contact binaries