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The Physical Properties and starspot activity of the Triple System KIC 6525196

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Research in Astronomy and Astrophysics 2022年第7期22卷 214-223页

作者： Yang Pan Jian-Ning Fu Xiao-Bin Zhang Jia-Xin Wang Chun-Qian Li School of Physics and Astronomy China West Normal UniversityNanchong 637002China Department of Astronomy Beijing Normal UniversityBeijing 100875China Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China School of Science Chongqing University of Posts and TelecommunicationsChongqing 400065China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China

We present the results of photometric and spectroscopic analyses for the triple-lined system KIC 6525196,an eclipsing binary accompanied by a third *** modeling the Kepler light curves and radial velocities from LAMOST and HIDES observations,absolute parameters of the system are *** components of the eclipsing binary are found to be solar-like stars with masses and radii of M= 1.0286 ± 0.0026 M,R= 1.127 ± 0.008 *** M=0.9667 ± 0.0024 M,R=0.963 ± 0.007 *** mass of the third star is determined to be M= 0.772 ± 0.010 *** the out-of-eclipse light residuals,we measure rotation period and decay timescale of an active region by using the autocorrelation *** comparison to the Sun,the activity level of the system is significantly *** addition,a possible short photometric activity cycle of~244 days is detected.

关键词： stars:activity (stars:)binaries:eclipsing (stars:)binaries:spectroscopic

Spectral Behavior and Flaring activity ofⅡPeg in the Ultraviolet

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Research in Astronomy and Astrophysics 2022年第8期22卷 191-197页

作者： M.R.Sanad Astronomy Department National Research Institute of Astronomy and GeophysicsHelwanCairoEgypt

We have studied the spectral behavior of theⅡPeg binary system in the ultraviolet band by using International Ultraviolet Explorer(IUE)observations over the period *** ultraviolet observations reveal indication of flare activity in both chromosphere and transition region with their enhanced emission *** and after the flare activity the ultraviolet emission lines show low,intermediate and high *** spectral behavior is compared with previous *** detect prominent flare activity in 1989,1990 and *** and after this period there is a gradual clear decrease in the level of *** reddening ofⅡPeg was determined from a 2200?absorption feature to be E(B-V)=0.10±*** ascertained the average mass loss rate to be≈1×10^(-8)M_(☉)yr^(-1),and an average ultraviolet luminosity to be≈6×10^(29)erg s^(-1).We attributed the spectral variations to a cyclic behavior of the underlying magnetic dynamo and the prominent activity can be interpreted by the model of a two-ribbon flare.

关键词： line:profiles magnetic fields stars:activity stars:flare ultraviolet:stars

Optical and X-Ray Studies of Marginal Contact Binary RW Dor Using TESS and XMM-Newton Observatories

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Research in Astronomy and Astrophysics 2023年第11期23卷 183-197页

作者： K.Sriram G.Mamatha Rani Department of Astronomy Osmania University 500007India

Marginal short-period contact binaries are important to understand as they pose a different physical scenario than the predicted theoretical model based on the thermal relaxation oscillation mechanism due to their shallow degree of *** we present the optical and X-ray studies of a contact binary source RW Dor using the Transiting Exoplanet Survey Satellite(TESS)and XMM-Newton *** the first time we report the varying O'Connell effect and explain the asymmetry with a spot *** on the new times of minima,we make a robust estimate of the orbital period of the third body at 47.01~0.52 yr with an eccentricity e=*** show that the period-decreasing trend observed in O-C variation can be explained by both conservative mass transfer from primary to secondary and AML via stellar *** X-ray luminosity exhibited by RW Dor did not vary significantly on three different occasions and was found to be about 3.34×10~(29)erg s~(-1).Assuming that the quiescent X-ray emission is emitted from an undisturbed loop structure,the loop size is estimated to be 0.6-1×10~(10)cm which is≤Alfvén radius r_A~8×10~(10)cm.

关键词： (stars:)binaries(including multiple):close X-rays:binaries stars:activity

The Dependence of Stellar activity Cycles on Effective Temperature

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Research in Astronomy and Astrophysics 2022年第12期22卷 198-210页

作者： Leonid Kitchatinov Institute of Solar-Terrestrial Physics SB RAS Lermontov Str.126AIrkutsk 664033Russia

This paper proposes the idea that the observed dependence of stellar activity cycles on rotation rate can be a manifestation of a stronger dependence on the effective temperature. Observational evidence is recalled and theoretical arguments are given for the presence of cyclic activity in the case of sufficiently slow rotation only. Slow rotation means proximity to the observed upper bound on the rotation period of solar-type stars. This maximum rotation period depends on temperature and shortens for hotter stars. The maximum rotation period is interpreted as the minimum rotation rate for operation of a large-scale dynamo. A combined model for differential rotation and the dynamo is applied to stars of different mass rotating with a rate slightly above the threshold rate for the *** show shorter dynamo cycles for hotter stars. As the hotter stars rotate faster, the computed cycles are also shorter for faster rotation. The observed smaller upper bound for rotation period of hotter stars can be explained by the larger threshold amplitude of the α-effect for onset of their dynamos: a larger α demands faster rotation. The amplitude of the(cycling) magnetic energy in the computations is proportional to the difference between the rotation period and its upper bound for the dynamo. stars with moderately different rotation rates can differ significantly in super-criticality of their dynamos and therefore in their magnetic activity, as observed.

关键词： dynamo stars:activity stars:magnetic field stars:solar-type stars:rotation

Prediction of Short Stellar activity Cycles using Derived and Established Empirical Relations between activity and Rotation Periods

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Research in Astronomy and Astrophysics 2023年第11期23卷 125-135页

作者： A.K.Althukair D.Tsiklauri Department of Physics and Astronomy School of Physical and Chemical SciencesQueen Mary University of LondonMile End RoadLondonE14NSUK Physics Department College of SciencesPrincess Nourah Bint Abdulrahman UniversityRiyadhP.O.Box 84428Saudi Arabia

In our previous work,we investigated the occurrence rate of super-flares on various types of stars and their statistical properties,with a particular focus on G-type dwarfs,using entire Kepler *** said study also considered how the statistics change with stellar rotation period,which in turn,had to be *** such new data,as a by-product,we found 138 Kepler IDs of F-and G-type main sequence stars with rotation periods less than a day(P_(rot)activity cycles in F-type and G-type stars and the question investigated was whether or not short-term activity cycles are a common phenomenon in these *** the other hand,extensive studies exist which establish an empirical connection between a star's activity cycle and rotation *** this study,we compile all available Kepler data with P_(rot)activity(e.g.,activity-related chromospheric emission S-index)or a similar means for the Kepler IDs found in this study in order put the derived empirical relations between P_(cyc)and P_(rot)derived here to the *** also propose an alternative method for measuring very short P_(cyc),using flare-detection algorithms applied to future space mission data.

关键词： stars:activity stars:flare stars:rotation stars:solar-type stars:statistics Sun:flares

New Cases of Superflares on Slowly Rotating Solar-type stars and Large Amplitude Superflares in G-and M-type Main Sequence stars

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Research in Astronomy and Astrophysics 2023年第10期23卷 308-323页

In our previous work,we searched for superflares on different types of stars while focusing on G-type dwarfs using entire Kepler data to study statistical properties of the occurrence rate of *** these new data,as a byproduct,we found 14 cases of superflare detection on 13 slowly rotating Sun-like stars with rotation periods of24.5–44 *** result supports the earlier conclusion by others that the Sun may possibly undergo a surprise ***,we found 12 and seven new cases of detection of exceptionally large amplitude superflares on six and four main sequence stars of G-and M-type,*** large-amplitude flares were detected in A,F or K main sequence *** we present preliminary analysis of these *** superflare detection,i.e.,an estimation of flare energy,is based on a more accurate method compared to previous *** fit an exponential decay function to flare light curves and study the relation between e-folding decay time,τ,versus flare amplitude and flare *** find that for slowly rotating Sun-like stars,large values ofτcorrespond to small flare energies and small values ofτcorrespond to high flare energies ***,τis large for small flare amplitudes andτis small for large amplitudes ***,there is no clear relation between these parameters for large amplitude superflares in the main sequence G-and M-type stars,as we could not establish clear functional dependence between the parameters via standard fitting algorithms.

关键词： stars:activity stars:flare stars:rotation stars:solar-type stars:statistics Sun:flares

A study of the global magnetic activity of the star Kepler-17 using light curve inversion with bipartite regularization

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Research in Astronomy and Astrophysics 2021年第4期21卷 173-192页

作者： Tao Luo Yan-Yan Liang Wing-Huen Ip Hao-Zhi Huang Xu-Xin Lin State Key Laboratory of Lunar and Planetary Sciences Macao University of Science and TechnologyMacaoChina Faculty of Information Technology Macao University of Science and TechnologyMacaoChina Institute of Astronomy “National Central University”ZhongliTaoyuan

A new method of light curve inversion with bipartite regularization(LIBR),which is complementary to the previous treatments by Bonomo and Lanza and Estrela and Valio,is used to reconstruct the physical properties of star spots on the solar-type star Kepler-17 by using the full Q1-Q17 data *** Markov Chain Monte Carlo(MCMC)method was applied to find the best profile of the reconstructed *** known value of the rotation inclination of Kepler-17 allows the generation of a star spot model in a sequence of stellar rotation with a period of 12.26 *** of the nature of the light curve inversion,the spot model is limited to the equatorial *** also investigated the starspot lifetimes of Kepler-17 utilizing the MCMC *** with the LIBR inversion results,it was found that the star spots typically last from one to several stellar *** the time evolution of the spot size,a magnetic cycle period of 437 d can be *** value is comparatively shorter than the solar cycle which might be a consequence of the younger age(~1.78 Gyr)of *** light curve of Kepler-17 is characterized by the presence of large-amplitude variation caused by star spots but no superflare *** interesting possibility is that the magnetic energy stored in the star spot regions could have been constantly dissipated by electrodynamic interaction between the central star and the hot Jupiter,Kepler-17 b,via a lower-level energy release process.

关键词： stars:activity stars:imaging stars:spots

Photometric and spectroscopic study of flares on Ross 15

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Research in Astronomy and Astrophysics 2021年第1期21卷 67-74页

作者： Jian-Ying Bai Ali Esamdin Xing Gao Yan Yan Juan-Juan Ren Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China University of Chinese Academy of Sciences Beijing 100049China National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China CAS Key Laboratory of Solar activity National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China

We conducted photometric and spectroscopic observations of Ross 15 in order to further study the flare properties of this less observed flare star.A total of 28 B-band flares are detected in 128 hr of photometric observations,leading to a total flare rate of 0.22-0.040.04 h-1,more accurate than that provided by previous *** give the energy range of the B-band flare(1029.5-1031.5 erg) and the flare frequency distribution(FFD) for the *** the same energy range,the FFD is lower than that of GJ 1243(M4)and YZ CMi(M4.5),roughly in the middle of those of three M5-type stars and higher than the average FFDs of spectral types> *** performed,for the first time for Ross 15,simultaneous high-cadence spectroscopic and photometric observations,resulting in detection of the most energetic flare in our *** intensity enhancements of the continuum and Balmer lines with significant correlations between them are detected during the flare,which is the same as those of other deeply studied flare stars with similar spectral type.

关键词： stars:flare stars:activity stars:late-type

Gaia calibrated UV luminous stars in LAMOST

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Research in Astronomy and Astrophysics 2018年第12期18卷 123-130页

作者： Yu Bai Ji-Feng Liu Song Wang Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences College of Astronomy and Space Sciences University of Chinese Academy of Sciences

We take advantage of Gaia Data Release 2 to present 275 and 1774 ultraviolet luminous stars in the far ultraviolet(FUV) and near ultraviolet(NUV), *** stars exceed their expected values by 5σ with respect to over one million ultraviolet stars in the log g *** extinction is corrected with a 3 D dust *** order to limit the Lutz-Kelker bias to an insignificant level, we select stars with relative uncertainties in luminosity less than 40% and trigonometric parallaxes less than 20%.We cross-identified our sample with the catalogs of RR Lyr stars and possible white dwarf main-sequence binaries, and find they compose ～62% and ～16% of our sample in the FUV and NUV, *** catalog provides a unique sample to study stellar activity, spectrally unresolved compact main-sequence binaries and variable stars.

关键词： stars:activity stars:general ultraviolet:stars