L.-Y. Zhu

Detection of a planetary system orbiting the eclipsing polar HU Aqr

Using the precise times of mid-egress of the eclipsing polar HU Aqr, we discovered that this polar is orbited by two or more giant planets. The two planets detected so far have masses of at least 5.9 and 4.5M(Jup). Their respective distances from the polar are 3.6 and 5.4 au with periods of 6.54 and 11.96 yr, respectively. The observed rate of decrease of period derived from the downward parabolic change in the observed - calculated (O - C) curve is a factor of 15 larger than the value expected for gravitational radiation. This indicates that it may be only a part of a long-period cyclic variation, revealing the presence of one more planet. It is interesting to note that the two detected circumbinary planets follow the Titus-Bode law of solar planets with n = 5 and 6. We estimate that another 10 yr of observations will reveal the presence of the predicted third planet.

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 Binnendijks 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.

AD Cancri: A shallow contact solar-type eclipsing binary and evidence for a dwarf third component and a 16 year magnetic cycle

CCD photometric observations of AD Cancri obtained from 2000 March 7 to 2004 December 20 are presented. Variations of the light levels at the primary minimum and both maxima are found. Uniform solutions of four sets of photometric data were derived by using the Wilson-Devinney method. The solutions suggest that AD Cancri is a shallow W-type contact binary (f 8.3% +/- 1.3%) with a highmass ratio of 1/q = 0.770 +/- 0.002. The long-term variation of the light curve is explained by variable dark-spot models of the more massive component star with a possible 17 yr cycle. Our 13 times of light minimum over 5 years, including others collected from the literature, have been used for the period study. The complex period changes can be sorted into a long-term period increase at rate of dP/dt +(4.94 +/- 0.16) x 10(-7) days yr(-1), a 16.2 yr periodic component (A(3) = 0.0155 days), and a very small amplitude period oscillation (A(4) = 0.0051 days, P-4 = 6.6 yr). The existence of third light may indicate that there is a tertiary component in the binary system. Solving the four-band light curves of Samec & Bookmyer, it is found that the contribution of the tertiary component to the total light of the triple system increases with wavelength, which suggests that it is very cool and may be a very red main-sequence star. The small-amplitude period oscillation may be caused by the light-time effect of the cool tertiary component (M-3 similar to 0.41 M-circle dot). The 16.2 yr periodic component in the orbital period and the 17 yr cyclic activity of the dark spot on the more massive component both may reveal that the more massive component displays solar-type magnetic activity with a cycle length of about 16 yr.

BI VULPECULAE: A SIAMESE TWIN WITH TWO VERY SIMILAR COOL STARS IN SHALLOW CONTACT

BI Vul is a cool eclipsing binary star (Sp. = K3 V) with a short period of 0.2518 days. The first charge-coupled device (CCD) light curves of the binary in the BVRI obtained on 2012 August 21 are presented and are analyzed using the Wilson-Devinney code. It is discovered that BI Vul is a marginal contact binary system (f = 8.7%) that contains two very similar cool components (q = 1.037). Both the marginal contact configuration and the extremely high mass ratio suggest that it is presently evolving into contact with little mass transfer between the components and it is at the beginning stage of contact evolution. By using all available times of minimum light, the variations in the orbital period are investigated for the first time. We find that the observed - calculated (O - C) curve of BI Vul shows a cyclic change with a period of 10.8 yr and an amplitude of 0.0057 days, while it undergoes a downward parabolic variation. The cyclic oscillation is analyzed for the light-travel time effect that arises from the gravitational influence of a possible third stellar object. The mass and orbital separation of the third body are estimated asM(3) similar to 0.30 M-circle dot and similar to 4.9 AU, respectively. The downward parabolic change reveals a long-term period decrease at a rate of (P) over dot = -9.5 x 10(-8) days yr(-1). The period decrease may be caused by angular momentum loss via magnetic stellar wind and/or it is only a part of a long-period (longer than 32 yr) cyclic variation, which may reveal the presence of another stellar companion in a wider orbit. These observational properties indicate that the formation of the Siamese twin is driven by magnetic braking and the third stellar companion should play an important role by removing angular momentum from the central binary.

A New CCD Photometric Investigation of the Short-Period Close Binary AP Leonis

New CCD photometric light curves in the B, V, and R bands of the short-period close binary AP Leonis are presented. A photometric analysis with our symmetric light curves suggests that AP Leo is an overcontact binary with a degree of overcontact of 24.9%. Since the O - C values of photographic and visual times of light minimum showed a large scatter (up to 0.06 days), all of the period changes proposed for the eclipsing binary by previous investigators are not reliable. In this paper the orbital period changes of AP Leo are analyzed based on all published CCD and photoelectric eclipse times. A small-amplitude cyclic oscillation, with a period of 22.4 yr and an amplitude of 0.0049 days, is discovered to be superposed on a secular period decrease at a rate of dP/dt = - 1:08; 10(-7) days yr(-1). The continuous period decrease may be caused by angular momentum loss or a combination of the mass transfer from the primary to the secondary and angular momentum loss. The cyclic period change may indicate that AP Leo is a triple system containing a cool dwarf third component. If this is true, it is possible that this third component plays an important role in the origin and evolution of the overcontact system by removing angular momentum from the central system, and that it makes the eclipsing pair have a low angular momentum and a short initial orbital period ( e. g., P < 5 days). In that case, the initially detached system evolves into an overcontact configuration via magnetic torques from stellar winds. On the other hand, the rapid rotation of the solar-type components (spectral type G0) and the variations of the light curve indicate a high degree of magnetic activity from the spin-up of the components. Both the long-term period decrease and the oscillation can plausibly be interpreted by magnetic activity (i.e., enhanced magnetic stellar wind and activity cycles).

Deep, low mass ratio overcontact binary systems. v. the lowest mass ratio binary V857 herculis

Charge-coupled device (CCD) photometric light curves in the B, V, and R bands of the complete eclipsing binary star V857 Her are presented. It is shown that the light curves of the W UMa-type binary are symmetric and of A type according to Binnendijks classification. Our four epochs of light minimum along with others compiled from the literature were used to revise the period and study the period change. Weak evidence indicates that the orbital period of V857 Her may show a continuous increase at a rate of dP/dt = +2.90 x 10(-7) days yr(-1). The photometric parameters of the system were determined with the 2003 version of the Wilson-Devinney code. It is shown that V857 Her is a deep overcontact binary system with f = 83.8% +/- 5.1%. The derived mass ratio of q = 0.06532 +/- 0.0002 suggests that it has the lowest mass ratio among overcontact binary systems. As the orbital period increases, the decrease of the mass ratio will cause it to evolve into a single rapidly rotating star when it meets the more familiar criterion that the orbital angular momentum be less than 3 times the total spin angular momentum. To understand the evolutionary state of the system, long-term photometric monitoring and spectroscopic observations will be required.

Deep, low mass ratio overcontact binary systems. IV. V410 Aurigae and XY Bootis

The complete charge-coupled device (CCD) light curves in the V, R, and I bands for the eclipsing binary V410 Aur were observed at the Yunnan Observatory in China. Four new light minimum times of V410 Aur were derived from new observations. The photometric solution for V410 Aur was obtained for the first time, while the orbital elements for XY Boo ( observed by Binnendijk in 1971) were reanalyzed by using the latest Wilson-Devinney code. The third light contributions to the total lights of the two binaries are obtained. The results reveal that both systems are A-subtype W UMa binaries with low mass ratios and deep degrees of overcontact (i.e., q(ph) = 0.1428 and f = 52.4% for V410 Aur, and q(ph) = 0.1855 and f = 55.9% for XY Boo). The photometric mass ratios of the two binaries are very consistent with the spectroscopic mass ratios. By combining the spectroscopic elements with our photometric solutions, the absolute photometric parameters for V410 Aur and XY Boo are ( re) determined. Analyzing the orbital periods of the two binaries, it is discovered that their orbital periods show continuous period increases, suggesting that the systems are undergoing mass transfer from the less massive component to the more massive one through the inner Lagrangian point L-1. This kind of binary, with a low mass ratio, a deep degree of overcontact, and a continuous period increase, may coalesce into a rapidly rotating single star due to tidal instability.

Performance of the 37-element solar adaptive optics for the 26 cm solar fine structure telescope at Yunnan Astronomical Observatory

A 37-element solar adaptive optics system, which consists of a fine tracking loop with a tip/tilt mirror and a correlation tracker, and a high-order correction loop with a 37-element deformable mirror, a correlating Shack-Hartmann wavefront sensor, and a real-time controller, was built and installed at the 26 cm solar fine structure telescope of the Yunnan Astronomical Observatory in 2009. In this system, the absolute difference algorithm is used. A new architecture with field-programmable gate array (FPGA) and digital signal processor (DSP) for the real-time controller based on systolic array and pipeline was developed. The computational latencies of the fine tracking loop and high-order correction loop are about 35 and 100 mu s, respectively. The tracking residual root-mean-square error is less than 0.1 arcsec, and the wavefront residual root-mean-square error is about 0.05 wavelengths (lambda = 550 nm) after correction. The observational results show that the contrast and resolution of the solar images are improved after the correction by this adaptive optics system

OPTICAL FLARES AND A LONG-LIVED DARK SPOT ON A COOL SHALLOW CONTACT BINARY

W UMa-type stars are contact systems where both cool components fill the critical Roche lobes and share a common convective envelope. Long and unbroken time-series photometry is expected to play an important role in their origin and activity. The newly discovered short-period W UMa-type star, CSTAR 038663, was monitored continuously by Chinese Small Telescope ARray (CSTAR) in Antarctica during the winters of 2008 and 2010. There were 15 optical flares recorded in the i band during the winter of 2010. This was the first time such flares were detected from a W UMa-type star. By analyzing the nearly unbroken photometric data from 2008, it is discovered that CSTAR 038663 is a W-type shallow contact binary system (f = 10.6(+/- 2.9)%) with a high mass ratio of q = 1.12(+/- 0.01), where the less massive component is slightly hotter than the more massive one. The asymmetric light curves are explained by the presence of a dark spot on the more massive component. Its temperature is about 800 K lower than the stellar photosphere and it covers 2.1% of the total photospheric surface. The lifetime of the dark spot is longer than 116 days. Using 725 eclipse times, we found that the observed-calculated (O-C) curve may show a cyclic variation that is explained by the presence of a close-in third body. Both the shallow contact configuration and the extremely high mass ratio suggest that CSTAR 038663 is presently evolving into a contact system with little mass transfer. The formation and evolution is driven by the loss of angular momentum via magnetic braking, and the close-in companion star is expected to play an important role, removing angular momentum from the central eclipsing binary.

Deep, Low Mass Ratio Overcontact Binary Systems. VII. QX Andromedae in the Intermediate-Age Open Cluster NGC 752

QX Andromedae is a short- period eclipsing binary in the intermediate- age open cluster NGC 752. Charge- coupled device photometric observations of the close binary system obtained from 2004 November 13 to 2006 November 18 are presented. It is confirmed that the light curves show partial eclipses, and night-to- night intrinsic variations are seen. As in the case of AH Cancri in the old open cluster M67, the light curve of QX And seems to change between A and W types. Both the short- and long-term light variations suggest that QX And shows strong magnetic activity, which is in agreement with its X- ray observations. The symmetric light curves in B and V bands obtained the night of 2004 November 13 were analyzed with the new version of the W- D code. It is found that QX And is a deep overcontact binary system with a high degree of overcontact of f = 55.9% and a low mass ratio of q = 0.2327, suggesting that it is in the late stage of overcontact evolution. Based on our 23 times of light minimum, including four recently published eclipse times, the orbital period of the eclipsing binary was revised. It was discovered that the orbital period shows a continuous period increase at a rate of dP/dt =+2.48x10(-7) days yr(-1), which can be interpreted as a mass transfer from the less massive component to the more massive one. As the period increases, the mass ratio of the system will decrease. It may finally evolve into a rapid- rotating single star when it meets the more familiar criterion that the orbital angular momentum is less than 3 times the total spin angular momentum. The existence of QX And in the late evolutionary stage of an overcontact binary in the intermediate- age open cluster NGC 752 indicates that it may undergo strong cluster stellar interaction. This means it had a very short initial orbital period and could have evolved into the present evolutionary state within the cluster age. By comparing with the evolutionary state of TX Cnc in M44, it is estimated that the lifetime of overcontact binaries may be no less than 1 Gyr.