IP Lyn:A Totally Eclipsing Contact Binary with an Extremely Low Mass Ratio

We present the first photometric and orbital period investigations for a neglected totally eclipsing contact binary IP Lyn.The photometric solutions derived from both ground-based and several surveys'observations suggest that it is a shallow contact binary with an extremely low mass ratio of 0.055.The weak asymmetry observed in our multiple band light curves can be interpreted as a result of an active cool spot on the primary.The absolute physical parameters were determined with the Gaia-distance-based method and checked by an empirical relation.Combining the eclipse timings collected from the literature and those derived from our and variable surveys'observations,we find that IP Lyn has been undergoing a secular orbital period increase for the past two decades,implying a mass transfer from the less massive secondary to the primary.By comparing the current parameters with the critical instability ones,we infer that IP Lyn is currently stable in spite of its relatively low mass ratio and orbital angular momentum.Finally,from a catalog of 117 extremely low mass ratio contact binaries,we find that their orbital angular momenta are significantly lower than those of the contact binaries with a relatively high mass ratio,suggesting they should be at the late evolutionary stage of a contact binary.

Orbital period changes of the W UMa binary YY Eri

Orbital period changes of the W UMa-type binary YY Eri are analyzed by using all photoelectric and ccd times of light minimum. The results show that its orbital period is undergo- ing a secular increase superposed on two cyclic oscillations. The continuous increase at the rate of dP/dt = 6.3806 × 10^-8 d yr^-1 may be accounted for by mass transfer from the less massive com- panion to the more massive one. Two periodic variations with periods of 38.6192 and 22.3573 yr may be attributed to the light-time effect of a faint third star and the cyclic magnetic activity of the system, respectively.

Mass transfer and possible third-body effect on the period variations of the near-contact binary CN And

We present a period analysis of the near-contact binary CN And using all available times of light minima. It is revealed that the orbital period exhibits a long-term decrease as well as a small-amplitude cyclic oscillation. This result suggests that the secular period decrease at the rate of d P/dt =-1.4017 ×10-7 d yr-1 is caused by a combination of mass transfer and angular momentum loss due to magnetic braking. The periodic variation with an amplitude of A = 0.0036 d and a period of Pmod = 28.3542 yr should be rooted in the light-time effect of a third body, rather than cyclic magnetic activity.

HT Lyn and IR Lyn:Two Semi-detached-type Near-contact Binaries with Stable Orbital Period

We presented the first photometric and orbital period investigations for two near-contact binaries:HT Lyn and IR Lyn.The light-curves solutions derived from both our ground-based and various surveys’observations suggested that HT Lyn and IR Lyn are two semi-detached-type near-contact binaries with the secondary and primary components filling the Roche lobe.Combining the eclipse timings derived from several surveys’data and our observations with those reported in the literature,we modified the orbital periods and revealed that their orbital periods were stable for the last two decades.The absolute physical parameters were well determined by using the empirical relations and the Gaia-distance-based method.Similar to other near-contact binaries,the primary components of HT Lyn and IR Lyn are evolving at the main-sequence stage,while their less-massive secondary components show the over-sized and over-luminosity features and should be more evolved than their primary ones.Combining the stable orbital period with the semi-detached configurations,we infer that the two near-contact binaries may be just located in the critical phase and evolving from the current semi-detached phase to the detached or contact one.

The orbital period variations of AH Virginis

Abstract We present a study of orbital period changes in AH Virginis. We perform a careful literature search for all available minima times, from which we derived a new linear ephemeris and constructed an O - C curve. We found that the orbital period of AH Virginis shows a long-term increase, dP/dt = （2.1869 ± 0.0161） × 10^-7 d yr^-1, and a small periodic variation with a period of 37.19 yr. Since AH Virginis is an over- contact system and the primary component shows strong Ha and Mg II emission lines, we discuss the possible connection between mass transfer, magnetic activity and or- bital period changes.

Reanalysis of the orbital period variations of two DLMR overcontact binaries:FG Hya and GR Vir

We investigate orbital period changes of two deep, low mass ratio（DLMR） overcontact W UMa-type binaries, FG Hya and GR Vir. It is found that the orbital period of FG Hya shows a cyclic change with a period of Pmod= 54.44 yr. The cyclic oscillation may be due to a third body in an eccentric orbit, while the orbital period of GR Vir shows a periodic variation with a period of Pmod= 28.56 yr and an amplitude of A = 0.0352 d. The periodic variation of GR Vir can be interpreted as a result of either the light-time effect of an unseen third body or the magnetic activity cycle.

LO And:an A-subtype contact binary with a very cool third component

Despite the intensive investigations since the discovery of LO And approximately 60 yr ago,its evolutionary status and subtype are still a matter of controversy.By simultaneously modeling the radialvelocity curves and new light curves with the Wilson-Devinney code,we present new geometric,photometric and absolute parameters for this system.The simultaneous solution suggests that LO And is an A-subtype contact binary with a contact degree of 32.4%.The absolute parameters are modified to become M_(1)=1.409 M⊙,M_(2)=0.449 M⊙,R_(1)=1.36 R⊙and R_(2)=0.83 R⊙.From our observations and data from surveys,we determined 334 eclipse timings.The O−C diagram,constructed from the new eclipse timings and those reported in the literature,reveals a secular increase and a cyclic variation in its orbital period.The former is caused by conservative mass transfer from the secondary component with less mass to the primary one with more mass.The latter may be explained by either the cyclic magnetic activity on the two components or the light-time effect due to a third body.With the absolute physical parameters,we investigated its evolutionary status,and find that LO And is an unevolved contact binary undergoing thermal relaxation oscillation,which will eventually coalesce into a single star with rapid rotation.