Multicolor-photometric Investigation Of W UMa Type Contact Binary AL Cas

W Urase Majoris?W UMa?contact binary is a special type of ecliptic binary which their primary and secondary components have filled Roche lobes and shared a common envelope,this can result in frequently material and energy exchange between primary component and sec-ondary component.Light curves of W UMa binary systems are generally EW-type?the primary eclipsing deep is nearly equal to the secondary?and the orbital period is generally no more than one day.They probably are some progenitors for some important objects?e.g.,blue stragglers and cataclysmic binary?and can also be used as standard candle for distance determinations.Therefore,studying W UMa binaries has a very important value and significance.AL Cas is a W UMa contact binary,which its eclipsing light curves have nearly equal depth and the orbital period of 0.5005555 days.We used Nanshan One-meter Wide-field Tele-scope?NOWT?to obtain complete-multicolor light curves in 2016 and 2017,in the mean time,6 new times of light minimum are also obtained.We apply Wilson-Devinney?W-D?code to analyse the light curves,the result indicates that contact degree?f?,mass ratio?q?and effective temperature difference??T?is 35.7±0.9%,0.6399±0.0230 and 78 K,respectively.It is unex-pected that AL Cas is an A-type contact binary.Based on 74 times of light minimum from literatures and 6 new times of light minimum,we adopt the?O-C?method to study variations of the orbital period of AL Cas.Concretely,we update the linear ephemeris with the orbital period as P_orb=0.50055593 days.In addition,we confirm the orbital period of AL Cas exits a cyclic variation with a period of 81.25 yr and an amplitude of 0.01415 days.This cyclic change would be caused by the light-travel time effect from a third body.Finally,combined with PAR-SEC model and optical observations?i.e.,analysis of the light curves?,we apply two method to gain mass of AL Cas.In other words,by the DCWD method,masses of two components are determined as M₁=1.22±0.26 M_?with M₂=0.78±0.20 M_?;and by the DCRL,masses of the components are determined as M₁=1.19±0.23 M_?with M₂=0.76±0.18 M_?.