Low Mass Ratio Overcontact Research Articles

New photometric studies for two deep, low-mass ratio overcontact binaries: Y Sex and V1363 Ori

We present new photometry for two contact binaries, Y Sex and V1363 Ori, which were observed by three small telescopes in China. By using the W-D method, the absolute parameters are updated from new BVR light curves and previous radial velocity curves. Results identify that two binaries are deep, low-mass ratio (DLMR) overcontact binaries with q ⩽ 0.25 and f ⩾ 50%. From the temperature-luminosity diagram, the primary components are slightly evolved main-sequence stars, whose evolutionary ages are ∼2.51 Gyr for Y Sex and ∼3.56 Gyr for V 1363 Ori, respectively. From the (O − C) curves, it is found that the orbital periods may be undergoing secular increase with cyclic variations, which may be interpreted either by magnetic activity cycles or by the light-time orbit effect. With period increasing, this kind of DLMR overcontact binaries, such as Y Sex and V1363 Ori, will evolve into the rapid-rotating single stars.

Observations and light curve solutions of a selection of middle-contact W UMa binaries

Photometric observations in Sloan g′ and i′ bands of W UMa binaries NSVS 4340949, T-Dra0–00959, GSC 03950–00707, NSVS 4665041, NSVS 4803568, MM Peg, MM Com and NSVS 4751449 are presented. The light curve solutions revealed that the components of each target are of G and K spectral types. The binaries of the sample have middle-contact configurations whose fillout factors are within the range 0.2–0.4. The only exception is NSVS 4751449 which is in deeper contact (fillout factor of 0.55). It precisely obeys the relation between mass ratio and fillout factor for deep, low mass ratio overcontact binaries. One of the eclipses of almost all targets (except MM Peg) is an occultation and their photometric mass ratios and solutions could be accepted with confidence. We found that the target components have almost equal temperatures but differ considerably in size and mass. The components of the partially-eclipsed MM Peg have close parameters. Our solutions reveal that NSVS 4340949, T-Dra0–00959, NSVS 4803568 and MM Com are of W subtype while GSC 03950–00707, NSVS 4665041, MM Peg and NSVS 4751449 are of A subtype. This subclassification is well-determined for all totally-eclipsed binaries. The targets confirm the trends in which W-subtype systems have smaller periods and lower temperatures than A subtype binaries.

Long-term photometric study of a faint W UMa binary in the direction of M31

We carry out a re-analysis of the photometric data in bands which were taken during the Nainital Microlensing Survey from 1998 to 2002 with the aim to detect gravitational micro lensing events in the direction of M31. Here, we do photometric analysis of a faint W UMa binary identified in the target field. The orbital period of this star is found to be 0.266402±0.000018 d. The photometric mass ratio, q, is found to be . The photometric light curves are investigated using the Wilson-Devinney (WD) code and absolute parameters are determined using empirical relations which provide masses and radii of the binary as , and , respectively based on Rc band data. Quite similar values are found by analyzing Ic band data. From the photometric light curve examination, the star is understood to be a low mass-ratio overcontact binary of A-subtype with a high fill-out factor of about 47%. The binary system is found to be located approximately at a distance of having a separation of between the two components.

ASAS J083241+2332.4: A NEW EXTREME LOW MASS RATIO OVERCONTACT BINARY SYSTEM

ABSTRACT We present the R- and V-band CCD photometry and Hα line studies of an overcontact binary ASAS J083241+2332.4. The light curves exhibit totality along with a trace of the O’Connell effect. The photometric solution indicates that this system falls into the category of extreme low-mass ratio overcontact binaries with a mass ratio, q ∼ 0.06. Although a trace of the O’ Connell effect is observed, constancy of the Hα line along various phases suggest that a relatively higher magnetic activity is needed for it to show a prominent fill-in effect. The study of O–C variations reveals that the period of the binary shows a secular increase at the rate of dP/dt ∼ 0.0765 s years−1, which is superimposed by a low, but significant, sinusoidal modulation with a period of ∼8.25 years. Assuming that the sinusoidal variation is due to the presence of a third body, orbital elements have been derived. There exist three other similar systems, SX Crv, V857 Her, and E53, which have extremely low mass ratios and we conclude that ASAS J083241+2332.4 resembles SX Crv in many respects. Theoretical studies indicate that at a critical mass ratio range, q critical = 0.07–0.09, overcontact binaries should merge and form a fast rotating star, but it has been suggested that q critical can continue to fall up to 0.05 depending on the primary's mass and structure. Moreover, the obtained fill-out factors (50%–70%) indicate that mass loss is considerable and hydrodynamical simulations advocate that mass loss from L 2 is mandatory for a successful merging process. Comprehensively, the results indicate that ASAS J083241+2332.4 is at a stage of merger. The pivotal role played by the subtle nature of the derived mass ratio in forming a rapidly rotating star has been discussed.

THE FIRST PHOTOMETRIC ANALYSIS OF THE OVERCONTACT BINARY MQ UMa WITH AN ADDITIONAL COMPONENT

The first V Rc Ic bands light curves of MQ UMa are presented and analyzed using the Wilson-Devinney (W-D) program. It is discovered that MQ UMa is an A-subtype contact binary with a high fill-out (f=82 %) and a low mass ratio (q = 0:195), which indicates that it is in the late evolutionary stage of latetype tidal-locked binary stars. The mass of the primary and secondary stars are estimated and the evolutionary status of the two components are placed in the H-R diagram. The W-D solutions also indicates that MQ UMa may be a triple system with an F5V type additional component. A sample of sixteen high fillout, low mass ratio overcontact binaries are collected and their possible evolution scenarios are discussed. Using the five times of light minimum recently observed together with those collected from literatures, the authors find that the observedcalculate (O-C) curve exhibits a cyclic period variation. The cyclic period change also reveals the presence of a tertiary component, which may play an important role in the formation and evolution of this binary system by drawing angular momentum from the central system.

Discovery of a deep, low mass ratio overcontact binary GSC 03517–00663**Supported by the National Natural Science Foundation of China.

When observing blazars, we identified a new eclipsing binary named GSC 03517–00663. The light curves of GSC 03517–00663 are typical of EW-type light curves. Based on the observation using the 1 m telescope at the Weihai Observatory of Shandong University, complete VRI light curves were determined. Then, we analyzed the multiple light curves using the Wilson-Devinney program. It was found that GSC 03517–00663 has a mass ratio of q = 0.164 and a degree of contact of f = 69.2%. GSC 03517–00663 is a deep, low mass ratio overcontact binary. The light curves of GSC 03517–00663 show a strong O'Connell effect, which was explained by employing a dark spot on the secondary component.

DEEP, LOW MASS RATIO OVERCONTACT BINARY SYSTEMS. XIII. DZ PISCIUM WITH INTRINSIC LIGHT VARIABILITY

New multi-color photometry for the eclipsing binary DZ Psc was performed in 2011 and 2012 using the 85 cm telescope at the Xinglong Station of the National Astronomical Observatories of China. Using the updated Wilson-Devinney (W-D) code, we deduced two sets of photometric solutions. The overcontact degree is f = 89.7(+/- 1.0)%, identifying DZ Psc as a deep, low mass ratio overcontact binary. The asymmetric light curves (i.e., LC2 in 2012) were modeled by a hot spot on the primary star. Based on all of the available light minimum times, we discovered that the orbital period of DZ Psc may be undergoing a secular period increase with a cyclic variation. The modulated period and semi-amplitude of this oscillation are P-mod = 11.89(+/- 0.19) yr and A = 0.0064(+/- 0.0006) days, which may be possibly attributed to either cyclic magnetic activity or light-time effect due to the third body. The long-term period increases at a rate of dP/dt = +7.43(+/- 0.17) x 10(-7) days yr(-1), which may be interpreted as conserved mass transfer from the less massive component to the more massive one. With mass transferring, DZ Psc will finally merge into a rapid-rotation single star when J(spin)/J(orb) > 1/3.

DEEP, LOW-MASS RATIO OVERCONTACT BINARY SYSTEMS. XII. CK BOOTIS WITH POSSIBLE CYCLIC MAGNETIC ACTIVITY AND ADDITIONAL COMPANION

We present precision CCD photometry, a period study, and a two-color simultaneous Wilson code solution of the short-period contact binary CK Bootis. The asymmetric light curves were modeled by a dark spot on the primary component. The result identifies that CK Boo is an A-type W UMa binary with a high fillout of f = 71.7(+/- 4.4)%. From the O-C curve, it is found that the orbital period changes in a complicated mode, i.e., a long-term increase with two sinusoidal variations. One cyclic oscillation with a period of 10.67(+/- 0.20) yr may result from magnetic activity cycles, which are identified by the variability of Max. I - Max. II. Another sinusoidal variation (i.e., A = 0.0131 days(+/- 0.0009 days) and P-3 = 24.16(+/- 0.64) yr) may be attributed to the light-time effect due to a third body. This kind of additional companion can extract angular momentum from the central binary system. The orbital period secularly increases at a rate of dP/dt = +9.79(+/- 0.80) x 10(-8) days yr(-1), which may be interpreted by conservative mass transfer from the secondary to the primary. This kind of deep, low-mass ratio overcontact binaries may evolve into a rapid-rotating single star, only if the contact configuration do not break down at J(spin) > (1/3)J(orb).

A statistical analysis of deep low-mass ratio overcontact binaries

Based on the observations of 30 deep low-mass ratio overcontact binaries, some important results were discovered as follows: (1) The relationships of M-L and M-R imply that due to its evolution and expansion the luminosity of this kind of binary decreases and its radius increases, which suggests that it is in the final stage of its evolution. (2) The relationship between M total and J total shows when the mass ratio decreases, the total angular momentum per mass also correspondingly decreases. Therefore, the mass and angular momentum for this kind of binaries are continuously lossing in the process from the contact configuration to the merged configuration. (3) From the relationships of q-f and q-J spin/ J orb, the minimum mass-ratio for the overcontact binary may be determined as 0.0439?0.0465. It is a key challenge for us to bring forward the evoluionary theory and the merged mechanism of the binary. The observed minimum mass-ratio binary is V857 Her up to now. The merged timescale is around 1.07 Ga through the conservated mass transfer from the more massive component to the less massive one.

DEEP, LOW MASS RATIO OVERCONTACT BINARY SYSTEMS. IX. V345 GEMINORUM WITH A BRIGHT VISUAL PAIR

CCD photometric observations of the visual binary, V345 Geminorum, obtained from 2007 January 24 to 2009 March 22, are presented. When comparing the light curves in 2007 and 2008, it is found that there appears to be an O'Connell effect in the light curves of 2008. From those observations, two sets of photometric solutions were deduced using the 2003 version of the W-D program. The results indicated that V345 Gem is a low mass ratio overcontact binary with f = 72.9%(+/- 3.1%). The asymmetric light curves in 2008 may be attributed to the activity of starspot, whose area is up to 1.55% of the area of the more massive component. The contributions of the third light to the total light are approximately 20% in the BVR bands. The absolute physical parameters for V345 Gem were obtained first. From the log L-log M diagram of the binary-star evolution, the primary component is an evolved star. From the O-C curve for V345 Gem, it is discovered that there exists a long-term period increase with a cyclic variation. The period and amplitude of the cyclic variation are P(3) = 646.7(+/- 0.7) day and A = 0(d).0019(+/- 0(d).0002), which may be caused by the light-time effect via the assumed third body. If it is true, the visual binary V345 Gem may be a quadruple star. The kind of additional component may remove angular momentum from the central system, which may play an important role for the formation and evolution of the binary. The secular period increases at a rate of dP/dt = +5.88 x 10(-8) d yr(-1), indicating that the mass transfers from the less massive component to the more massive component. With mass transferring, the orbital angular momentum decreases while the spin angular momentum increases. When J(spin)/J(orb) > 1/3, this kind of deep, low mass ratio overcontact binary with secular period increase may evolve into a rapid-rotating single star.

Deep, Low Mass Ratio Overcontact Binary Systems. VI. AH Cancri in the Old Open Cluster M67

CCD photometric light curves in the B and V bands obtained in 2001 and in the V band obtained in 2002 of AH Cnc in the old open cluster M67 are presented. It is shown that AH Cnc is a total-eclipsing binary and its light curves correspond to a typical A type according to Binnendijk's classification. The variations of the light curve around the primary minimum and second maximum were found. Our nine epochs of light minimum monitored from 2001 to 2005, including others collected from the literature, were used to create the first study of the period changes of the binary system. A cyclic oscillation with a period of 36.5 yr and an amplitude of 0.0237 days was discovered to be superposed on a continuous period increase (dP/dt = 3: 99; 10(-7) days yr(-1)). Weak evidence indicates that there exists another small-amplitude period oscillation (A(4) = 0: 0035 days, P-4 = 7.75 yr). The symmetric light curves in the B and V bands obtained in 2001 were analyzed with the 2003 version of the Wilson-Devinney code. It is confirmed that AH Cnc is a deep overcontact binary system with a high degree of overcontact f = 58.5%+/- 4.5% and a low mass ratio of q = 0.1682 +/- 0.0012. The existence of the third light and the cyclic period oscillation both may suggest that AH Cnc is a triple system containing an unseen third body. The tertiary component may have played an important role in the origin of the overcontact binary star by removing angular momentum from the central system, which would cause it to have a short initial orbital period and thus evolve into an overcontact configuration by angular momentum loss. The long-term period increase can be interpreted as a mass transfer from the less massive component to the more massive one. As the orbital period increases, the decrease of the mass ratio will cause it finally to evolve into a single rapid-rotating star when the system meets the more familiar criterion that the orbital angular momentum be less than 3 times the total spin angular momentum. Therefore, AH Cnc may be a progenitor of the blue straggler stars in M67.

Deep, Low Mass Ratio Overcontact Binary Systems. III. CU Tauri and TV Muscae

New CCD photometric light curves in the B and V bands of the neglected W UMa - type eclipsing variable star CU Tauri are presented. The O'Connell effect in the V light curve obtained in 2001 by Yang and Liu was about Delta V = +0.015, but it vanished in our 2004 observations. The variations in the levels of bothminima were seen. Our two epochs of light minimum and others compiled from the literature were used for the period study. It is shown that the types of some eclipse times were incorrect and the values of the period obtained by previous investigators were aliases that prevented formation of a plausible O - C curve. A new linear ephemeris was derived, and it is discovered that the orbital period of CU Tau shows a continuous decrease at a rate of dP/dt = - 1.81 x 10(-6) days yr(-1). The present symmetric light curves were solved with the 2003 version of the Wilson-Devinney (W-D) code. Both our solutions and those derived by Yang and Liu reveal that CU Tau is a deep ( f = 50.1% +/- 3.2%), low mass ratio (q = 0.1770 +/- 0.0017) overcontact binary system. Meanwhile, the photoelectric light curves in the B, V, R, and I bands of TV Muscae published by Hilditch and coworkers were reanalyzed with the 2003 version of the W-D code. It is shown that the low mass ratio binary turns out to be a deep overcontact system with f = 74.3% +/- 11.3%. A period analysis with all collected times of light minimum revealed a combination of a long-term period decrease (dP/dt = - 2.16 x 10(-7) days yr(-1)) and a possible cyclic change with a period of 29.1 yr. The rapid long-term period decreases of both systems can be explained as a combination of the mass transfer from the more massive component to the less massive one and the angular momentum loss due to mass outflow from the L2 point. In that way, the overcontact degrees of the two systems will become deeper as their periods decrease, and finally they will evolve into a single rapid-rotation star. However, for CU Tau, the rate of the secular period decrease is very large when compared with the other systems of the same type. This suggests that the long-term period decrease may be part of a long-period periodic change, which we need more data to check.

GR Virginis: A Deep Overcontact Binary

Orbital period variations of the low-mass ratio (q = 0.122) overcontact binary system, GR Vir, were investigated by using two new CCD times of minimum light and other photoelectric data compiled from literatures. It is found that the O-C residuals of GR Vir show a cyclic variation with a period of 19.3 yr and an amplitude of 0.0140 days while they are undergoing a long-term decrease (dP/dt = 4.32 x 10(-7) days yr(-1)). Meanwhile, the 1988 photoelectric observations from Cereda et al. were analyzed using the Wilson-Devinney method. Like some low-mass ratio overcontact binary stars (e.g., AW UMa), GR Vir is an A-type overcontact binary with a high degree of overcontact (f = 78.6%). By combining the spectroscopic solutions with the photometric elements, the absolute parameters of the system are determined as follows: M-1 = 1.36 M-circle dot, M-2 = 0.17 M-circle dot, a = 2.40 R-circle dot, R-1 = 1.42 R-circle dot, R-2 = 0.61 R-circle dot, L-1 = 2.87 L-circle dot, and L-2 = 0.48 L-circle dot. The long-term period decrease is interpreted as the result of mass transfer from the more massive component to the less massive one in combination with the angular momentum loss due to mass outflow from the L-2 point. The conditions in GR Vir resemble those in AW UMa. Both systems show a high degree of overcontact, low mass ratios, and secular shrinking of their orbits. As their orbital periods decrease, the shrinking of the inner and outer critical Roche lobes will cause the common convective envelope to become deeper, until finally the formation of single, rapid-rotation stars is inevitable. The period oscillation may by caused either by the presence of an unseen tertiary component (e.g., a white dwarf) or by magnetic activity on the part of the primary component.

Are overcontact binaries undergoing thermal relaxation oscillation with variable angular momentum loss?

Orbital period variations of five W-type overcontact binaries, GW Cep, VY Cet, V700 Cyg, EM Lac and AW Vir, are presented based on the analysis of all available times of light minimum. It is discovered that the period of GW Cep is decreasing at a rate of dP/dt = -6.62 x 10(-8) d yr(-1). For VY Cet and V700 Cyg, a cyclic oscillation is found superimposed on a secular period increase, which can be explained either by the light-time effect of an assumed third body or by magnetic activity cycles. For the other two, EM Lac and AW Vir, the periods show a secular increase. GW Cep is a low mass ratio system with q = 0.37, while the others are high mass ratio systems (q = 0.67, 0.65, 0.63 and 0.76, respectively). The period changes of the five sample stars are in good agreement with Qian's conclusion that low mass ratio overcontact binaries usually show a decreasing period, while the periods of high mass ratio systems are increasing. Based on the period variations of 59 overcontact binaries, a statistical investigation of period change is given. It is confirmed that the period change of a W UMa-type binary star is correlated with the mass ratio (q) and with the mass of the primary component (M-1). Meanwhile, some statistical relations (M-1-P, J(s)-M-1, J(s)-M-2 and J(s)-P) for overcontact binaries are presented using the absolute parameters of 78 systems. From these relations, the following results may be drawn: (i) free mass transfer in both directions exists between the components, which is assumed by thermal relaxation oscillation (TRO) theory; (ii) angular momentum loss (AML) can make a W UMa-type star maintain shallow overcontact and not evolve from overcontact to semidetached configurations as proposed by Rahunen; (iii) the evolution of the W UMa-type systems may be oscillation around a critical mass ratio, while the critical mass ratio varies with the mass of the primary component. These results can be plausibly explained by the combination of the TRO and the variable AML via a change of depth of the overcontact, which is consistent with the X-ray and IUE observations.