arXiv subjects

W. -P. Liao

Publications and source records attributed to W. -P. Liao.

9 recordsLinked to original sources

arXiv2025

Reconsidering The Bailey Diagrams of ab-type RR Lyrae Stars, Metallicity-Mediated Evolution as the Direct Cause of the Oosterhoff Phenomenon

We re-examine the Bailey diagrams of fundamental mode RR Lyrae stars from the perspective of horizontal branch (HB) evolution, identifying evolutionary effects as the probable direct cause of the Oosterhoff dichotomy. By establishing empirical relationships between pulsation amplitude and average effective temperature, and utilizing pulsation period relations from nonlinear models, we transform theoretical HB evolutionary parameters into pulsation space and map them onto Bailey diagrams. We find that all pulsating Zero-Age Horizontal Branch stars fall within the Oosterhoff type I (OoI) region, with a pronounced period shift effect observed for relatively metal-rich samples ([Fe/H] > -1). Evolutionary tracks confirm that OoI stars are predominantly early-stage HB stars, while Oosterhoff type II stars are highly evolved objects entering the instability strip late in their HB phase from the blue side. Crucially, metallicity plays a dual role: it directly influences pulsation periods through the period relation, but more fundamentally acts as the first parameter influencing HB morphology. This morphology statistically determines whether HB stars predominantly enter the instability strip during early or late evolutionary stages. Consequently, while evolutionary effects directly govern an individual star's position in the Bailey diagram, the population-level Oosterhoff phenomenon emerges from the interplay between these effects and the metallicity-dependent HB morphology. Our study confirms that evolutionary effects are the direct drivers of the period difference and underscores metallicity's vital role in the statistical emergence of Oosterhoff groups. Continued study of this phenomenon offers key insights into the formation history of the Milky Way and nearby dwarf galaxies.

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arXiv2023

Comparative study of TESS photometry and radial velocities on six early K-type contact binaries with similar periods around 0.268 days

High-precision light curves were extracted from TESScut images. Together with APOGEE and LAMOST medium resolution spectra, a joint study was made for six early K-type contact binary candidates selected unbiasedly with orbital periods around 0.268 days. It is found that all of them (RV CVn, EK Com, V384 Ser, V1038 Her, EH CVn, and CSS$\_$J125403.7+503945) are W-subtype shallow contact systems though with different mass ratios ($1/q$ = 0.27--0.62). The effective temperature differences between binary components are around a few hundred Kelvins. The original definition of A- and W-subtypes were compared with the customarily used methods which rely on the shape or on the photometric solutions of light curves. The latter two methods are not always reliable and therefore the radial velocity analysis is strongly recommended. Through a collection of all available K-type contact binaries with both photometric and spectroscopic measurements, it is found that almost all of them are W-subtype systems, except a few objects which have nearly identical temperatures for binary components. This W-subtype phenomenon for K-type contact binaries should be further checked with more samples in the future. Finally, the physical parameters of the targets were determined with joint data analysis and the multiplicity is discussed for these targets. V384 Ser and RV CVn are confirmed very likely to be triple systems from comprehensive analysis, while V1038 Her is a candidate of a triple system based on photometric and spectroscopic solutions.

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arXiv2023

V606 Cen: A Newly Formed Massive Contact Binary in a Hierarchical Triple System

V606 Centauri (V606 Cen) is an early B-type close binary with an orbital period of 1.4950935\,d and the complete light curves are very difficult to be observed on the ground. By analyzing the unbroken and continuous light curve obtained by TESS, we found that it is a marginal contact binary with a very low fill-out factor of about 2\%. The O-C diagram of V606 Cen is constructed for the first time based on the 118.8-years eclipse times. It is found that the O-C diagram shows a downward parabolic change together with a cyclic oscillation with an amplitude of 0.0544\, d and a period of 88.8\, yr. The downward parabolic variation reveals a linear period decrease at a rate of $dP/dt = -2.06 \times{10^{-7}} d \cdot yr^{-1}$ that can be explained by the mass transfer from the more massive component to the less massive one. Both the marginal contact configuration and the continuous period decrease suggest that V606 Cen is a newly formed contact binary via Case A mass transfer. Meanwhile, the cyclic change in the O-C diagram can be explained by the Light-Travel Time Effect via the presence of a third body. The lowest mass of the tertiary companion is determined as M$_{3}$ = 4.51($\pm0.38$)M$_{\odot}$ that is orbiting around the central eclipsing binary in a nearly circular orbit (e=0.32). All the results indicate that V606 Cen is a newly formed massive contact binary and just reaches the contact configuration during the mass transfer in a hierarchical triple system.

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arXiv2018

RW Dor: A G-type shallow contact binary with new orbital period investigation

New CCD photometric light curves of short period (P=0.285d) eclipsing binary RW Dor are presented. The observations performed with the PROMPT-8 robotic telescope at CTIO in Chile from March 2015 to March 2017. The other eclipse timings were obtained from the 2.15-m JS telescope at CASLEO, San Juan, Argentina in December 2011. By light-curve analysis, it is found that RW Dor is a W-type shallow contact binary with a fill-out factor $f \sim 11\%$ and high mass ratio $q \sim 1.587$ (1/q = 0.63), where the hotter component is the less massive one ($M_1 \sim 0.52M_{\odot}$ and $M_2 \sim 0.82M_{\odot}$). For orbital period investigation, the new fifteen eclipse times and those in previous published were compiled. Based on $O-C$ analysis with very weak evidence suggests that a long-term period decrease with a rate of $\mathrm{d}P/\mathrm{d}t = -9.61\times10^{-9}$ d $\textrm{yr}^{-1}$ is superimposed on a cyclic variation ($A_3$ = 0.0054 days and $P_3$ = 49.9 yrs). The long-term period decrease can be interpreted as mass transfer from the more massive component to the less massive one or combine with the angular momentum loss (AML) via magnetic braking. In addition, with the marginal contact phase, high mass ratio (1/q $>$ 0.4) and the long-term period decrease, all suggest that RW Dor is a newly formed contact binary via a Case A mass transfer and it will evolve into a deeper normal contact binary. If the cyclic change is correct, the light-travel time effect via the presence of a cool third body will be more plausible to explain for this.

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arXiv2017

A New Stellar Outburst Associated with the Magnetic Activities of the K-type Dwarf in a White-dwarf Binary

1SWASP\,J162117.36$+$441254.2 was originally classified as an EW-type binary with a period of 0.20785\,days. However, it was detected to have undergone a stellar outburst on June 3, 2016. Although the system was latter classified as a cataclysmic variable (CV) and the event was attributed as a dwarf-nova outburst, the physical reason is still unknown. This binary has been monitored photometrically since April 19, 2016 and many light curves were obtained before, during and after the outburst. Those light and color curves observed before the outburst indicate that the system is a special CV. The white dwarf is not accreting material from the secondary and there are no accretion disks surrounding the white dwarf. By comparing the light curves obtained from April 19 to September 14, 2016, it was found that magnetic activity of the secondary is associated with the outburst. We show strong evidence that the $L_1$ region on the secondary was heavily spotted before and after the outburst and thus quench the mass transfer, while the outburst is produced by a sudden mass accretion of the white dwarf. These results suggest that J162117 is a good astrophysical laboratory to study stellar magnetic activity and its influences on CV mass transfer and mass accretion.

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arXiv2016

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.

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arXiv2012

Optical flares and flaring oscillations on the M-type eclipsing binary CU Cnc

We report here the discovery of an optical flare observed in R band from the red-dwarf eclipsing binary CU Cnc whose component stars are at the upper boundary of full convection (M1=0.43 and M2=0.4M0, M0 is the solar mass). The amplitude of the flare is the largest among those detected in R band (~0.52mag) and the duration time is about 73 minutes. As those observed on the Sun, quasi-periodic oscillations were seen during and after the flare. Three more R-band flares were found by follow up monitoring. In total, this binary was monitored photometrically by using R filter for 79.9 hours, which reveals a R-band flare rate about 0.05 flares per hour. These detections together with other strong chromospheric and coronal activities, i.e., very strong H_alpha and H_beta emission features and an EUV and X-ray source, indicate that it has very strong magnetic activity. Therefore, the apparent faintness (~1.4 magnitude in V) of CU Cnc compared with other single red dwarfs of the same mass can be plausibly explained by the high coverage of the dark spots.

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arXiv2011

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 4.5\,M_{Jup}. Their respective distances from the polar are 3.6 AU and 5.4 AU with periods of 6.54 and 11.96 years, respectively. The observed rate of period decrease derived from the downward parabolic change in O-C curve is a factor 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 years of observations will reveal the presence of the predicted third planet.

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arXiv2008

Evidence of a Massive Black Hole Companion in the Massive Eclipsing Binary V Puppis

Up to now, most stellar-mass black holes were discovered in X-ray emitting binaries, in which the black holes are formed through a common-envelope evolu tion. Here we give evidence for the presence of a massive black hole candidate as a tertiary companion in the massive eclipsing binary V Puppis. We found that the orbital period of this short-period binary (P=1.45 days) shows a periodic variation while it undergoes a long-term increase. The cyclic period oscillation can be interpreted by the light-travel time effect via the presence of a third body with a mass no less than 10.4 solar mass. However, no spectral lines of the third body were discovered indicating that it is a massive black hole candidate. The black hole candidate may correspond to the weak X-ray source close to V Puppis discovered by Uhuru, Copernicus, and ROSAT satellites produced by accreting materials from the massive binary via stellar wind. The circumstellar matter with many heavy elements around this binary may be formed by the supernova explosion of the progenitor of the massive black hole. All of the observations suggest that a massive black hole is orbiting the massive close binary V Puppis with a period of 5.47 years. Meanwhile, we found the central close binary is undergoing slow mass transfer from the secondary to the primary star on a nuclear time scale of the secondary component, revealing that the system has passed through a rapid mass-transfer stage.

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