n-Jia Li

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.

DETECTION OF A TERTIARY BROWN DWARF COMPANION IN THE sdB-TYPE ECLIPSING BINARY HS 0705+6700

HS 0705+6700 is a short-period (P = 2.3 hr), close binary containing a hot sdB-type primary and a fully convective secondary. We have monitored this eclipsing binary for more than two years and as a result, 32 times of light minimum were obtained. Based on our new eclipse times together with these compiled from the literature, it is discovered that the observed-calculated curve of HS 0705+6700 shows a cyclic variation with a period of 7.15 years and a semiamplitude of 92.4 s. The periodic change was analyzed for the light-travel time effect that may be due to the presence of a tertiary companion. The mass of the third body is determined to be M3 sin i = 0.0377(+/- 0.0043) M(circle dot) when a total mass of 0.617 M(circle dot) for HS 0705+6700 is adopted. For orbital inclinations i >= 32.degrees 8, the mass of the tertiary component would be below the stable hydrogen-burning limit of M(3) similar to 0.072M(circle dot), and thus it would be a brown dwarf. The third body is orbiting the sdB-type binary at a distance shorter than 3.6 AU. HS 0705+6700 was formed through the evolution of a common envelope after the primary becomes a red giant. The detection of a substellar companion in HS 0705+6700 system at this distance from the binary could give some constraints on stellar evolution in such systems and the interactions between red giants and their companions.

MAGNETIC BRAKING AND THE EVOLUTION OF THE HW VIR-LIKE BINARY STARS

HW Vir-like close binaries are thought to be the progenitors of cataclysmic variables. However, how this type of peculiar stars evolve into cataclysmic variables is an unsolved problem in astrophysics. Here we report the variations of the orbital period of HW Vir, the prototype of this group of systems. A long-term period decrease is discovered to be superimposed on the well-known cyclic change reported by previous investigators. It is suggested that the continuous decrease can be plausibly interpreted by angular momentum loss via magnetic braking of the completely convective star. This is driving the shrink of the orbit and will result in mass transfer between both components. We found that the binary will be undergoing mass transfer long before the sdB primary star evolves into a white dwarf. This conclusion suggests that HW Vir-like binaries do not directly evolve into cataclysmic variables through angular momentum loss as astronomers previously thought. On the other hand, if the observed period decrease is only part of a long-period cyclic variation, it may reveal the presence of another substellar companion in a wide orbit. This makes HW Vir an important system for future study of the formation and evolution of substellar objects.

HIGH FILL-OUT, EXTREME MASS RATIO OVERCONTACT BINARY SYSTEMS. VIII. EM PISCIUM

CCD photometric observations of the newly discovered close binary, EM Piscium, obtained from 2006 December 4 to 2008 January 7, are presented. The light curves are symmetric and show complete eclipses with an eclipse duration of 54 minutes. When comparing the present light curves with those published by Gonzalez-Rojas et al., it is found that the depths of the two minima of the light curve have been interchanged, and the positive OConnell effect has disappeared. The symmetric light curves in R and I bands were analyzed with the 2003 version of the W - D code. It is found that EM Piscium is a high fill-out overcontact binary system (f = 95.3 +/- 2.7%) with an extreme mass ratio of q = 0.1487, suggesting that it is on the late evolutionary stage of late-type tidal-locked binaries. Based on the nine instances of light minimum that we determined and those published by previous investigators, it is discovered that the orbital period shows a cyclic period variation with a period of 3.3 years, while it undergoes a continuously rapid increase at a rate of d P/dt = +3.97 x 10(-6) days year(-1). The cyclic period reveals the presence of a tertiary companion, which may play an important role for the formation and evolution of the overcontact binary by drawing angular momentum from the central system via Kozai oscillation or a combination of Kozai cycle and tidal friction. The high fill-out, the extreme mass ratio, and the rapid period increase may suggest that the binary system is quickly evolving into a rapid-rotating single star.

Pulsar wind model for the spin-down behavior of intermittent pulsars

Intermittent pulsars are part-time radio pulsars. They have higher slow down rates in the on state (radio-loud) than in the off state (radio-quiet). This gives evidence that particle wind may play an important role in pulsar spindown. The effect of particle acceleration is included in modeling the rotational energy loss rate of the neutron star. Applying the pulsar wind model to the three intermittent pulsars (PSR B1931+24, PSR J1841–0500, and PSR J1832+0029) allows their magnetic fields and inclination angles to be calculated simultaneously. The theoretical braking indices of intermittent pulsars are also given. In the pulsar wind model, the density of the particle wind can always be the Goldreich-Julian density. This may ensure that different on states of intermittent pulsars are stable. The duty cycle of particle wind can be determined from timing observations. It is consistent with the duty cycle of the on state. Inclination angle and braking index observations of intermittent pulsars may help to test different models of particle acceleration. At present, the inverse Compton scattering induced space charge limited flow with field saturation model can be ruled out.

IS WX CEN A POSSIBLE TYPE Ia SUPERNOVA PROGENITOR WITH WIND-DRIVEN MASS TRANSFER?

WX Cen is one of a few compact binary supersoft X-ray sources (CBSS) in the Galaxy that is a possible Type Ia supernova (SN Ia) progenitor. The supersoft X-ray radiation is explained as hydrostatic nuclear burning on the surface of the white dwarf component that is accreting hydrogen from a stellar companion at a high rate. If the mass donor in this system has a low mass, as has been suggested in the literature, one would expect a high wind-driven mass transfer rate. In that case, the orbital period of the system should increase. To test this theoretical prediction, we have monitored the system photometrically since 2010. By using four newly determined eclipse timings together with those collected from the literature, we discovered that the orbital period is decreasing at a rate of dP/dt = -5.15 x 10(-7) days yr(-1). The long-term decrease in the orbital period is contrary to the prediction that the system is powered by wind-driven accretion. It therefore seems plausible that the mass donor could be more massive than the white dwarf, and that the mass transfer is driven by the thermal instability of the donor star. This finding suggests that WX Cen is a key object to check the physical mechanisms of mass accretion in CBSS. The corresponding timescale of the period change is about P/P. similar to 0.81 x 10(6) yr, indicating that WX Cen may evolve into an SNe Ia within one million years in the Galaxy.

High amplitude δ Scuti star BO Lyn with evidence of a late A-type companion in an elliptical orbit

We present 145 times of light maximum for high amplitude δ Scuti star BO Lyn based on several sky surveys (CRTS, DASCH, NSVS, OMC and SuperWASP) and our photometric observations. Combining with the data in literature, a total of 179 times of light maximum are used to analyze the O − C diagram of BO Lyn. We find that it can be described by an upward parabolic component and a periodic variation with a period of 34.5 ± 0.1 yr. The latter could be caused by the light travel time effect as a result of an additional companion orbiting in a highly elliptical orbit ( e = 0.64 ± 0.03). Our study indicates that the companion’s luminosity cannot be ignored, and it should be a late A-type main-sequence star. The long-term period change of BO Lyn is also detected, and its value, 1.52 ± 0.26 × 10 −3 d Myr −1 , is consistent with evolutionary models. We suggest that more spectroscopic and photometric observations are needed in the future to confirm the nature of the BO Lyn system.

Multi-color light curves and orbital period research of eclipsing binary V1073 Cyg

New Multi-color

Lunar-based Ultraviolet Telescope study of the well-known Algol-type binary TW Dra

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