Variability of Young Stellar Objects in the Perseus Molecular Cloud

We present an analysis of 288 young stellar objects(YSOs)in the Perseus molecular cloud that have well defined g and r-band lightcurves from the Zwicky Transient Facility.Of the 288 YSOs,238 sources(83%of our working sample)are identified as variables based on the normalized peak-to-peak variability metric,with variability fraction of 92%for stars with disks and 77%for the diskless populations.These variables are classified into different categories using the quasiperiodicity(Q)and flux asymmetry(M)metrics.Fifty-three variables are classified as strictly periodic objects that are well phased and can be attributed to spot modulated stellar rotation.We also identify 22 bursters and 25 dippers,which can be attributed to accretion burst and variable extinction,respectively.YSOs with disks tend to have asymmetric and non-repeatable lightcurves,while the YSOs without disks tend to have(quasi)periodic lightcurves.The periodic variables have the steepest change in g versus g-r,while bursters have much flatter changes than dippers in g versus g-r.Periodic and quasiperiodic variables display the lowest variability amplitude.Simple models suggest that the variability amplitudes of periodic variables correspond to changes of the spot coverage of 30%-40%,burster variables are attributed to accretion luminosity changes in the range of L_(acc)/L_(*)=0.1-0.3,and dippers are due to variable extinction with A_(V)changes in the range of 0.5-1.3 mag.

恒星黑子对恒星视星等颜色和视锂丰度的影响

发展了一种简单的双温模型用于研究黑子对活动星的视星等、颜色和视Li丰度的影响.在适当的黑子覆盖因子下,恒星黑子能产生可观的活动星的视星等(V星等约±0.2星等)、颜色(B-V颜色约-0.1星等)和Li I λ6708 (?)谱线等值宽度(约-0.2-0.3 dex)的变化.与非活动的正常恒星相比,表面被黑子覆盖的活动星有更蓝的B-V颜色,它们的Li I λ6708 (?)谱线的等值宽度也变窄.根据观测到的活动星黑子引起的光变变幅,估计视圆面黑子覆盖率的变化范围△Fs从百分之几到约0.2.视圆面黑子覆盖率不太可能超过0.3.

Spot and Facula Activity Variations of the Eccentric Detached Eclipsing Binary KIC 8098300 Based on the Time-series Orbital Solutions

The LAMOST spectra and Kepler light curves are combined to investigate the detached eclipsing binary KIC 8098300,which shows the O’Connell effect caused by spot/facula modulation.The radial velocity(RV)measurements are derived by using the tomographic spectra disentangling technology.The mass ratio q=K1/K2=0.812±0.007,and the orbital semimajor axis a sin i=14.984±0.048 R_(⊙)are obtained by fitting the RV curves.We optimize the binary model concerning the spot/facula activity with the code PHOEBE and obtain precise parameters of the orbit including the eccentricity e=0.0217±0.0008,the inclination i=87°.71±0°.04,and the angle of periastronω=284°.1±0°.5.The masses and radii of the primary and secondary star are determined as M_(1)=1.3467±0.0001 M_(⊙),R_(1)=1.569±0.003 R_(⊙),and M_(2)=1.0940±0.0001 M_(⊙),R_(2)=1.078±0.002 R_(⊙),respectively.The ratio of temperatures of the two component stars is r_(teff)=0.924±0.001.We also obtain the periastron precession speed of 0.000024±0.000001 day cycle-l.The residuals of out-of-eclipse are analyzed using the auto-correlation function and the discrete Fourier transform.The spot/facula activity is relatively weaker,but the lifetime is longer than that of most single main sequence stars in the same temperature range.The average rotation period of the spots P_(rot)=4.32 days is slightly longer than the orbital period,which may be caused by either the migration of spots/faculae along the longitude or the latitudinal differential rotation.The activity may be spot-dominated for the secondary star and facula-dominated for the primary star.The method of this work can be used to analyze more eclipsing binaries with the O’Connell effect in the Kepler field to obtain the precise parameters and investigate the difference of spot behavior between binaries and single stars.It is helpful for a deeper understanding of the stellar magnetic activity and dynamo theory.

KIC 10417986:Spectroscopic Confirmation of the Nature of the Binary System with aδScuti Component

KIC 10417986 is a short orbital period(0.0737 day)ellipsoidal variable star with aδSct andγDor hybrid pulsation component discovered by Kepler.The ground-based spectroscopic observations were carried out in the winters of 2020 and 2021 to investigate the binary nature of this star.We derive the orbital parameters using the rvfit code with a result of K_(1)=29.7±1.5 km s^(-1),γ=-18.7±1.7 km s^(-1),and confirm an orbital period of 0.84495 day instead of the result given by Kepler.The atmospheric parameters of the primary are determined by the synthetic spectral fitting technique with the estimated values of T_(eff)=7411±187 K,log g=4.2±0.3 dex,[M/H]=0.08±0.09 dex and vsini=52±11 km s^(-1).KIC 10417986 is a circular orbit binary system.From the single-lined nature and mass function of the star,the derived orbital inclination is 26°±6°,and the mass of the secondary is 0.52_(-0.09)^(+0.18)M_(⊙),which should be a late-K to early-M type star.Fourteen frequencies are extracted from Kepler light curves,of which six independent frequencies in the high-frequency region are identified as the p-mode pulsations ofδSct star,and one independent frequency in the low-frequency region(f_(2)=1.3033 cd^(-1))is probably the rotational frequency due to the starspots rather than the ellipsoidal effect.

Orbital parameters and period variation studies of the short-period eclipsing binaries FG Sct, VZ Lib and VZ Psc

We present eight sets of new light curves for binaries FG Sct,VZ Lib and VZ Psc,which are all contact eclipsing binaries with short orbital periods.We carried out our observations from 2016 to 2017 using the 60-cm telescope administered by National Astronomical Observatories,Chinese Academy of Sciences,the Holcomb Observatory at Butler University and the SARA-CT telescope in Chile.We firstly determined the orbital parameters of FG Sct using the O-C method and obtained photometric solutions utilizing the updated W-D program.We also studied its period variation and discovered that its orbital period is decreasing at a rate of 6.39(±0.24)×10^-8 d yr-1,which was likely caused by mass transfer from the primary component to the secondary component or angular momentum interchange between the two components via magnetic interactions.For VZ Lib and VZ Psc,we simultaneously analyzed their BV RI light curves in conjunction with the published radial velocities.In order to obtain the orbital parameters of VZ Lib,we also analyzed its period variation and revised cyclic change,which could be attributed to either the light-time effect due to a tertiary companion or magnetic activity cycle mechanism.We derived the periods of the tertiary component of VZ Lib to be 48.7(±0.1) yr or magnetic cycle to be 46.9(±1.9) yr.Strong emission lines at Ca II H+K,Hα,Hβ,Hγ and Ca II IRT were detected in the LAMOST spectra of VZ Psc,which imply chromospheric activities in this binary system.

Stellar activity cycles as revealed by long-term beat-like patterns from light curves of Kepler

Stellar activity cycles have been found on many stars through different methods.Although in debate,an empirical relation has been found where a period of stellar activity cycle Pcyc is positively correlated with rotation period Prot along some segregated branches.In this work,we built a systematic process to search for the Kepler objects that are analogous to the long-term solar brightness variations and investigate their possible origins.After a rigorous selection,we obtained 43 objects that all exhibit clear long-term beat-like patterns and their variability(amplitude of rotational modulation)periods and rotation periods were derived.Due to the 4-year duration of the Kepler mission,our targets are located in the region where the cycle periods are longer than~1 yr and shorter than~2.5 yr.However,all of our targets exhibit clear and notable quasi-periodic variations in variability,yet we cannot confirm any linear trends that were predicted by previous research independently.This may suggest that in the Kepler realm of the Pcyc-Prot diagram,these relations would mix with each other or the beat-like patterns may not be related to the stellar cycle unless other evidence is provided.

AD Cancri: A Contact Binary with Components in Poor Thermal Contact

We present the light curve and photometric solutions of the contact binary AD Cnc. The light curve appears to exhibit a typical O'Connell effect, with Maximum I brighter than Maximum II by 0.010 mag. in V. From 1987 to 2000, the light curve showed changes of shape: the depth of the primary eclipse increased by about 0.056m while that of the secondary eclipse decreased by about 0.032m, so the difference between the primary and the secondary eclipses increased by about 0.088m, while there was no obvious variation in the O'Connell effect. Using the present and past times of minimum light, the changes in the orbital period of the system are analyzed. The result reveals that the orbital period of AD Cnc has continuously increased at a rate of dp/dt=4.4 × 10-7day yr-1. The light curve is analyzed by means of the latest version of the Wilson-Devinney code. The results show that AD Cnc is a W-subtype contact binary with a small mass ratio of 0.267 and the two components are in poor thermal contact. AD Cnc has a component temperature difference exceeding 500 K, and exhibits a shallow contact of 3.6%. The asymmetry of the light curves is explained by the star spot model.

Kalman滤波算法在高精度星点定位中的应用

空间巡天相机稳像系统的控制精度要求高,对导航星传感器提出了更高的要求。为提高导航星传感器的精度和带宽,提出了一种采用预测开窗和Kalman滤波相结合的星点定位方法。利用陀螺测量的三轴角速度信息,推导建立星点粗位置预测方程,得到星点的粗位置,在CMOS探测器上以预测点为中心的较小邻域范围内开窗,可提高运算速度。利用Kalman滤波算法对星点位置进行校正,最终得到高精度的星点位置。仿真实验结果表明,相比于传统的质心法,平均每帧图像处理时间从59ms减少到27ms,定位结果的标准差从0.1pixel减小到0.04pixel。提出的方法是一条提高星点定位运算速度和精度的有效途径,可为我国巡天相机导航星系统的研制提供一定参考。