Magnetic Activities And Physical Parameters Of Late-type Stars Based On Big Data From Domestic And Foreign Sky Surveys

The study of starspots,flares,and chromospheric activity lines emission of late-type stars play an important role in understanding the formation and evolution of stellar magnetic fields and exploring extraterrestrial civilization.With the LAMOST spectral survey and Kepler photometric survey and other projects,a large amount of astronomical observation data has been released,allowing us to use astronomical big data to study the magnetic activity of late-type stars.This thesis mainly analyzes the magnetic activities of M-type stars,X-ray stars and red giants through LAMOST spectra and Kepler photometric data,and analyzes the physical parameters and magnetic activities of the four W UMa-type eclipsing binaries(UV Lyn,V781Tau,NSVS 4484038,2MASS J15471055+5302107)by combining LAMOST spectra and photometric data from ground-based small telescopes in the world.The research results are as follows:?.We perform a statistical study of magnetic activities of M-type stars by combining the spectra of LAMOST DR5 with photometric data from the Kepler and K2 missions.We obtain 516,688 M-type stellar spectra from LAMOST DR5 and calculate their equivalent widths of magnetic activity lines(H?,H?,H?,H?,Ca ? H&K,and He ? D3).The analysis result shows that the activity ratio of these magnetic activity lines gradually increased between the spectral types M0 to M3.Using the H?line,40,464 spectra of 38,417 M-type stars show magnetic activity,and 1791 of these 5499 M-type stars with repeated observations have H?variability.In addition,through cross-matching 516,688 LAMOST low-dispersion spectra with Kepler and K2 databases,the long-cadence photometric data of 8964 M-type stars were obtained.By using the method of reducing the background light curve plus visual inspection,we obtain 17,432 stellar flares from 4143 M-type stars.In addition,we also use the least-square spectral analysis method to search for the rotation period of these M-type stars.The results of spectral analysis and photometric analysis of M-type stars show that:1.The flare frequency of M-type stars is also a function of spectral type in M0–M3.2.The equivalent width of H?and Ca ? H lines are closely related to the stellar flare amplitude.3.The equivalent width of the magnetic activity lines(H?,Ca ? H,He ? D3)gradually decrease with the increase of the rotation period,and the flare amplitude also gradually decreases with the increase of the rotation period.In addition,we found that using the H?equivalent width equal to 0.75(?)and using the rotation period equal to 10 days as the threshold for the M-type stellar flare time frequency are almost equivalent.?.We cross-match the X-ray stellar catalogue(12254 X-ray stars)from ARXA with LAMOST DR3,and obtain 984 good spectra from 713 X-ray sources.By calculating the equivalent width of H?lines in these spectra,we found that 203 LAMOST low-dispersion spectra of 145 X-ray stars with H?line emission,and the proportion of H?line emission of the X-ray stars shows a gradually increasing trend in the spectral type FGKM.Of the 145 X-ray stars,10 are novae,2 are planetary nebulae,6 are OB type stars,7 are cataclysmic variables(CVs),76 are FGKM type Classical T Tauri stars(CTTs),and 44 are late-type stars with magnetic activity.In addition,we analyze the H?variability of 53 X-ray stars that observed multiple times.Among them,37 CTTs show H?variability,which may be produced by magnetospheric accretion from a thick and dense circumstellar disk.There are 5 CVs with H?variability,which may be caused by the accretion disks surrounding the white dwarf.There are 8 late-type stars with H?variability,which may be caused by the existence of magnetic activity in the photosphere and chromosphere.We also analyze the Ca ? IRT lines emission of 18 X-ray stars.Finally,we discuss the relationships between the equivalent width of H?line and X-ray flux.?.We present new photometric data and LAMOST spectra for four W UMa binaries:UV Lyn,V781 Tau,NSVS 4484038 and 2MASS J15471055+5302107.First,we use the least square method to update the ephemeris of the four W UMa eclipsing binaries and analyze their orbital period changes,and then use the Wilson-Devinney program to obtain the orbital and starspot parameters of the four binaries through the least square method.Comparing the starspot parameters at different time,there are magnetic activities in these four binaries.The orbital period of UV Lyn is increasing at a rate of dP/dt=+8.9(5)×10^-8days/year,which may be due to mass transfer from the less massive component to the more massive component at a rate of d M₁/dt=-6.4×10^-8M_?/year.The period variation of 2MASS J15471055+5302107 is also increasing at a rate of dP/dt=+6.0(4)×10^-7days/year,which can be explained by mass transfer from the less component to the more massive component at a rate of d M₁/dt=-2.8×10^-7M_?/year.The period variation of V781 Tau presents the downward parabola superimposed the cyclic oscillation.The period of V781 Tau is decreasing at a rate of dP/dt=-3.2(4)×10^-8days/year,which can be explained by mass transfer from the more massive component to the less massive component at a rate of d M₂/dt=-2.2×10^-8M_?/year.The cyclic oscillation may be due to the magnetic activity with a period of 30.8(5)years.The period variation of NSVS 4484038 also shows the cyclic oscillation,which could be explained by the magnetic activity with 10.8(1)years or a black hole candidate with a minimum mass of 5.015M_?.It is necessary to carry out continuous multi-band observation and verification in the future.?.We use LAMOST DR5 low-dispersion spectra to study the magnetic activities of red giants and use back-propagation neural networks to build the red giant age estimation model.We analyze the magnetic activities of 5349 LAMOST low-dispersion spectra of 3539 red giants by calculating equivalent width of magnetic activity lines(H?,H?,H?,H?,Ca ? H&K and Ca ? IRT).Combining LAMOST spectral parameters(Teff,log,[Fe/H]),asteroseismic parameters(?_max,??),and equivalent widths of the magnetic activity lines,an attempt was made to estimate the age of red giants using back-propagation neural networks.By using the neural networks to select the input parameters,we get the best age estimation of the red giants with the input parameters‘Teff',‘[Fe/H]',‘logg',‘?_max'and‘??'.The average value of the relative error between the estimated age and the isochronous age is 22.4%.The age estimation was not improved by adding the equivalent widths of more magnetic activity lines.This indicates that the equivalent widths of these spectral lines are not directly related to the age of the red giants.The reason for this might be that the dynamo operating in the outer layers of the red giants has shut off at the end of core-hydrogen-burning.The absence of emission in all the magnetic activity lines of the 5349 LAMOST spectra also confirms this conclusion.In addition,the results indicate that the equivalent widths of the magnetic activity lines are more related to the stellar effective temperature.