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

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 superflares.Using 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 days.This result supports the earlier conclusion by others that the Sun may possibly undergo a surprise superflare.Moreover,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,respectively.No large-amplitude flares were detected in A,F or K main sequence stars.Here we present preliminary analysis of these cases.The superflare detection,i.e.,an estimation of flare energy,is based on a more accurate method compared to previous studies.We fit an exponential decay function to flare light curves and study the relation between e-folding decay time,τ,versus flare amplitude and flare energy.We find that for slowly rotating Sun-like stars,large values ofτcorrespond to small flare energies and small values ofτcorrespond to high flare energies considered.Similarly,τis large for small flare amplitudes andτis small for large amplitudes considered.However,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.

Optical flare events on the RS Canum Venaticorum star UX Arietis

Based on long-term high-resolution spectroscopic observations obtained during five observing runs from 2001 to 2004, we study optical flare events and chromospheric activity variability of the very active RS CVn star UX Ari. By means of the spectral subtraction technique, several optical chromospheric activity indicators （including the He IDa, Na I D1, D2 doublet, Ha and Ca II IRT lines） covered in our echelle spectra were analyzed. Four large optical flare events were detected on UX Ari during our observations, which show prominent He I D3 line emission together with great enhancement in emission of the Ha and Ca II IRT lines and strong filled-in or emission reversal features in the Na ! D1, D2 doublet lines. The newly detected flares are much more energetic than previous discoveries, especially for the flare identified during the 2002 December observing run. Optical flare events on UX Ari are more likely to be observed around two quadratures of the system, except for our optical flares detected during the 2004 November observing run. Moreover, we have found rotational modulation of chromospheric activity in the Ha and Ca II IRT lines, which suggests the presence of chromospherically active longitudes over the surface of UX Ari. The change in chromospherically active longitudes among our observing runs, as well as the variation in chromospheric activity level from 2001 to 2004, indicates a long-term evolution of active regions.

Three X-ray flares near primary eclipse of the RS CVn binary XY UMa

We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa （Porb≈0.48 d）. In two Chandra ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly （〈 0.125 Porb） after a primary eclipse, and the other two happening shortly （〈 0.05/9orb） before a primary eclipse. Two flares occurred within roughly one orbital period （△Ф≈ 1.024 Porb） of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales during both quiescence and flares, as well as the timing of the flares. We explore the possibility that the flares are orbit-induced by introducing a small orbital eccentricity, which is quite challenging for this close binary.

Photometric and spectroscopic study of flares on Ross 15

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 work.We give the energy range of the B-band flare(1029.5-1031.5 erg) and the flare frequency distribution(FFD) for the star.Within 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> M6.We 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 sample.The 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.

An active M star with X-ray double flares disguised as an ultra-luminous X-ray source

Here we present research on an ultra-luminous X-ray source （ULX） candidate 2XMM J 140229.91＋542118.8. The X-ray light curves of this ULX candidate in M 101 exhibit features of a flare star. More importantly, the Chandra light curve displays unusual X-ray double flares, which is comprised of two close peaks. The X-ray （0.3-11.0 keV） flux of the first peak was derived from the two-temperature APEC model as ～ 1.1 ±0.1× 10-12 ergcm-2 s-1. The observed flux at its first peak increased by about two orders of magnitude in X-ray as compared to quiescence. The slope of the second fast decay phase is steeper than the slope of the first fast decay phase, indicating that the appearance of a second flare accelerated the cooling of the first flare in a way we do not understand yet. We also observed its optical counterpart using a 2.16 m telescope administered by National Astronomical Observatories, Chinese Academy of Sciences. By optical spectral fitting, it is confirmed to be a late type dMe2.5 star. According to the spectral type and apparent magnitude of its optical counterpart, we estimate the photometric distance to be ～ 133.4 ±14.2 pc. According to the X-ray spectral fitting, a possible explanation is provided. However, more similar close double flares are needed to confirm whether this accelerated cooling event is a unique coincidence or a common physical process during double flaring.

Absolute parameters and observed flares in the M-type detached eclipsing binary 2MASS J04100497+2931023

The eclipsing binary 2 MASS J04100497+2931023(J04100497+2931023) is classified its spectral type of M0±2 V on basis of a low-resolution spectral survey by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST). The low-resolution spectra exhibit strong single-peak emission in the Hα line. We obtained the radial velocities of this binary by means of the Cross-Correlation Function method from the LAMOST medium-resolution spectra. Both components of J04100497+2931023 indicate strong emissions in the Hα line. We performed follow-up photometric observations of J04100497+2931023 using the Xinglong 85 cm telescope of National Astronomical Observatories, Chinese Academy of Sciences. We obtained its full light curve in V RI filters. We first determined their absolute parameters from simultaneously radial velocity and light curves by the Wilson-Devinney program. From our new light curves, we detected three flares for the first time, including one convective flare. The amplitudes,durations, energies, and spectral indices of three flares were also determined. J04100497+2931023 was monitored for approximately 29 h, which indicates that the flare rate is 0.1 flare per hour. We conclude that J04100497+2931023 is a low-mass detached eclipsing binary with strong magnetic activity.

Magnetar giant flare originating from GRB 200415A:transient GeV emission, time-resolved E_(p)-L_(iso) correlation and implications

Giant flares(GFs)are unusual bursts from soft gamma-ray repeaters(SGRs)that release an enormous amount of energy in a fraction of a second.The afterglow emission of these SGR-GFs or GF candidates is a highly beneficial means of discerning their composition,relativistic speed and emission mechanisms.GRB 200415A is a recent GF candidate observed in a direction coincident with the nearby Sculptor galaxy at 3.5 Mpc.In this work,we searched for transient gamma-ray emission in past observations by Fermi-LAT in the direction of GRB 200415A.These observations confirm that GRB 200415A is observed as a transient GeV source only once.A pure pair-plasma fireball cannot provide the required energy for the interpretation of GeV afterglow emission and a baryonic poor outflow is additionally needed to explain the afterglow emission.A baryonic rich outflow is also viable,as it can explain the variability and observed quasi-thermal spectrum of the prompt emission if dissipation is happening below the photosphere via internal shocks.Using the peak energy(Ep)of the time-resolved prompt emission spectra and their fluxes(Fp),we found a correlation between Ep and Fp or isotropic luminosity Liso for GRB 200415A.This supports the intrinsic nature of Ep-Liso correlation found in SGRs-GFs,hence favoring a baryonic poor outflow.Our results also indicate a different mechanism at work during the initial spike,and that the evolution of the prompt emission spectral properties in this outflow would be intrinsically due to the injection process.

The 6.7 keV Line Emission from the Stellar Flare of Algol

We present spectral analysis of Algol stellar flare data. The 2-day observation of Algol in our Galaxy was done by Suzaku Satellite. Algol binary system consists of two component stars that eclipse one another periodically. The stellar magnetic field activities and Roche Lobe overflow/mass transfer mechanisms during rapid rotation of the component stars generate an X-ray emission. The variation in brightness of the stellar flare from epoch to epoch provides useful information of stellar properties of the component stars. The atomic physics of the Kα line emission process in the vicinities of chromospherically active and X-ray flare stars, and binaries is well understood. The photo ionization/collisional excitation in the Algol’s corona produces 6.7 keV line emission. The accumulated spectra in X-ray Imaging Spectrometer (XIS) sensors fitted combined with bremsstrahlung model and Gaussian line show a strong fixed X-ray energy of 6.7 keV.

High Energy Emission from Magnetar Due to Giant Flare

We propose a theoretical model for magnetar giant flare to explain the flaring activity on 2004 December 27 from SGR1806-20 comprehensively. A global rearrangement is expected by the magnetic reconnection that requires explaining the giant SGR flares. In this paper we propose two regions of flares: preflare on the surface of magnetar and main burst at a distance of light cylinder radius. Acquiring the maximum potential drop on the magnetar surface, adopting space charge limited flow model, and using magnetic field B ≈ 1015 G, the luminosities of flare energies release for the preflare phase and main burst phase are found to be in the order of 1041 erg·sˉ1 and 1044 erg·sˉ1 respectively, conforming to magnetar burst energy and flare temperature is determined by considering black body radiation.

The Formation and Evolution of the Sun and the Source of Star Energy as Well as the Sunspots and Flares of the Sun

Nebula theory is the most widely accepted hypothesis about the formation and evolution of the Solar System. This theoryholds that the Sun is formed from a collapsed gas cloud 4.57 billion years ago;when the core temperature of the gas cloud rises to 10million K, the thermonuclear reaction of hydrogen fusion into helium is ignited, then the Sun become a star;once the hydrogen in thecore is exhausted, the life of the star will end. But the limited hydrogen element obviously cannot satisfy such a long-termthermonuclear reaction, in order to sustain long-term thermonuclear reactions, a steady stream of fuel must be obtained from space.So the existing hypothesis about the formation and evolution of the Solar System has serious defects. Thus the author has studied theformation of the Moon, the Earth and the Sun, and discovered the formation of the Sun and the real source of star energy. The authorcould also explain many solar activity phenomena such as sunspots, flares, prominences, etc.

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

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 data.The said study also considered how the statistics change with stellar rotation period,which in turn,had to be determined.Using 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)<1 day).On one hand,previous studies have revealed short 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 stars.On the other hand,extensive studies exist which establish an empirical connection between a star's activity cycle and rotation periods.In this study,we compile all available Kepler data with P_(rot)<1 day,and rely on an established empirical relation between P_(cyc)and P_(rot)with the aim to provide predictions for very short 5.09≤P_(cyc)≤38.46 day cases in a tabular form.We propose an observation to measure P_(cyc)using a monitoring program of stellar 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 test.We also propose an alternative method for measuring very short P_(cyc),using flare-detection algorithms applied to future space mission data.

XMM-Newton observation of the eclipsing binary Algol

We present an XMM-Newton observation of the eclipsing binary Algol which contains an X-ray dark B8V primary and an X-ray bright K2IV secondary. The observation covered the optical secondary eclipse and captured an X-ray flare that was eclipsed by the B star. The XMM-Newton European Photon Imaging Camera and Reflection Grating Spectrometer spectra of Algol in its quiescent state are described by a two-temperature plasma model. The cool component has a temperature around 6.4× 106 K while that of the hot component ranges from 2 to 4.0× 107 K. Coronal abundances of C, N, O, Ne, Mg, Si and Fe were obtained for each component for both the quiescent and the flare phases, generally with upper limits for S and Ar, and upper limits for C, N, and O from the hot component. F-tests show that the abundances do not need to be different between the cool and the hot component and between the quiescent and the flare phase with the exception of Fe. Although the Fe abundance of the cool component remains constant at -0.14, the hot component shows an Fe abundance of -0.28, which increases to -0.44 during the flare. This increase is expected from the chromospheric evaporation model. The absorbing column density NH of the quiescent emission is 2.5 - 1020 cm-2, while that of the flare-only emission is significantly lower and consistent with the column density of the interstellar medium. This observation substantiates earlier suggestions of the presence of X-ray absorbing material in the Algol system.

Spectral Behavior and Flaring Activity ofⅡPeg in the Ultraviolet

We have studied the spectral behavior of theⅡPeg binary system in the ultraviolet band by using International Ultraviolet Explorer(IUE)observations over the period 1979-1993.The ultraviolet observations reveal indication of flare activity in both chromosphere and transition region with their enhanced emission lines.Before and after the flare activity the ultraviolet emission lines show low,intermediate and high flux.The spectral behavior is compared with previous studies.We detect prominent flare activity in 1989,1990 and 1992.Before and after this period there is a gradual clear decrease in the level of activity.The reddening ofⅡPeg was determined from a 2200?absorption feature to be E(B-V)=0.10±0.02.We 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.

Temperature Analysis of Flaring(AR 11283)and Non-flaring(AR 12194)Coronal Loops

Here,we study the temperature structure of flaring and non-flaring coronal loops,using extracted loops from images taken in six extreme ultraviolet channels recorded by Atmospheric Imaging Assembly/Solar Dynamics Observatory.We use data for loops of an X2.1-class-flaring active region(AR 11283)during 22:10 UT until 23:00 UT,on 2011 September 6;and a non-flaring active region(AR 12194)during 08:00:00 UT until 09:00:00 UT on2014 October 26.By using the spatially synthesized Gaussian differential emission measure(DEM)forward-fitting method,we calculate the peak temperatures for each strip of the loops.We apply the Lomb–Scargle method to compute the oscillation periods for the temperature series of each strip.The periods of the temperature oscillations for the flaring loops ranged from 7 to 28.4 minutes.These temperature oscillations show very close behavior to the slow-mode oscillation.We observe that the temperature oscillations in the flaring loops started at least around10 minutes before the transverse oscillations and continue for a long time duration even after the transverse oscillations ended.The temperature amplitudes increased during the flaring time(20 minutes)in the flaring loops.The periods of the temperatures obtained for the non-flaring loops ranged from 8.5 to 30 minutes,but their significances are less(below 0.5)in comparison with the flaring ones(near to one).Hence the detected temperature periods for the non-flaring loops’strips are less probable in comparison with the flaring ones,and maybe they are just fluctuations.Based on our confined observations,it seems that the flaring loops’periods show more diversity and their temperatures have wider ranges of variation than the non-flaring ones.More accurate commentary in this respect requires more extensive statistical research and broader observations.

重新审查昴星团成员星锂丰度的弥散

重新审查了昴星团成员星的活动性和在同一颜色处Li丰度的弥散。发现大多数的研究者低估了昴星团恒星的活动性.重新研究了恒星的活动性(包括黑子活动)和星团中恒星的不均匀红化效应对Li丰度弥散的影响.得到的主要结论是:没有坚实的证据说明观测到的Li丰度弥散是代表具相同有效温度星团成员大气Li丰度存在真实的差异.相反,假若不是全部,其大部的视Li丰度弥散是活动星的大气效应所致.Li丰度-恒星自转关联很可能只是Li丰度-恒星活动性关联的一种反映.

疏散星团中的耀星及其演化学意义

耀星是红矮星早期演化的一个必经阶段，这个阶段的持续时间取决于恒星的质量。在年轻和比较年轻的疏散星团（和星协）中，都含有大量耀星，它们的光度分布是疏散星团（或星协）年龄的标志。在昂星团中已发现大星耀星，对它们的自行、测光和分光资料进行深入的统计研究，对于解决疏散星团及矮星起源和演化问题，有着极其重要的价值。

昂星团天区耀星成员性和相对数量的再讨论

本文通过统计比较，并用更完善的模型作成员概率的最大似然估计，对昂星团天区耀星的成员性进行了新的细致的讨论，指出Ｍｉｒｚｏｙａｎ等根据Ｊｏｎｅｓ的自行成员概率估计得出的非成员耀星呈现向团心集中强烈趋势的现象，是由于Ｊｏｎｅｓ对成员星成员概率的普遍低估以及对外围恒星成员概率的一定程度高估加上在中心附近观测误差和错误显著增加而造成的．本文根据Ｓｔａｕｆｆｅｒ等对更完整的样本估计的成员概率，以其中成员概率大于０．５的星为成员星，重新计算了昂星团内成员耀星在红矮星中占的比例（相对数量），表明了相对数量在ＭＶ＜８．０时随星等变暗而增大，而ＭＶ≈８．０时开始稳定在６４％左右，直至样本完整性的极限（ＭＶ≈１１．５）．因此，昂星团内无明显耀发活动的红矮星占该星团内红矮星总数的１／３左右或更少．

A Possible Mechanism for the Origin of Ultrastrong Magnetic Field of Magnetars

Growing observations reveal that soft gamma-ray repeaters and anomalous x-ray pulsars are magnetars. Their magnetic fields may achieve 10^14 - 10^15G. We explore the origin of the superstrong magnetic field by considering the magnetization of the ^3P2 superfluid neutrons inside neutron stars （NSs）. By solving the Tolman-Oppenheimer-Volkov equations together with the equation of state adopted by Elgaroy it et al. [Phys. Rev. Lett. 77 （1996） 1428] in the calculation of the neutron pairing gap, we specifically calculate the NS internal structure, the permissible region for ^3P2 superfluid neutrons inside the NS, and the total magnetic moment contributed by the orderly arranged neutron vortexes. The result shows that the induced magnetic field may cover a wide range, which is consistent with the magnetic field predicted by the standard magnetic dipole radiation for pulsar spindown.

太阳的形成与恒星能量的来源及太阳的黑子与耀斑

星云说是最广为接受的太阳形成与演化假说,该假说认为太阳是在45.7亿年前由一片坍缩的气体云形成的,当气体云核心温度上升到1000万K时,氢聚变成氦的热核反应就被点燃,太阳便成了恒星;一旦核心的氢消耗殆尽,恒星的生命就将结束。但有限的氢元素显然无法满足如此长期的热核反应,要维持长期的热核反应必须从太空中源源不断地获得燃料,所以现有的太阳形成假说存在严重缺陷。于是,作者重新研究了月球、地球和太阳的形成过程,发现了太阳的形成规律和恒星能量的真正来源,并能科学地解释诸如太阳黑子、耀斑、日珥等太阳活动现象。

类太阳恒星耀斑光变轮廓特征分析

太阳耀斑是由于在太阳黑子附近磁场能量的突然释放所引起的爆发现象.人们发现在许多类太阳恒星上也有类似的耀斑(称类太阳恒星耀斑)出现.主要采用开普勒太空望远镜获取的数据,从中选取SC(Short Cadence)数据进行分析,找出类太阳恒星上耀斑光变轮廓的特征参数并做统计,总结耀斑的活动特点.分析结果表明:类太阳恒星耀斑的光变轮廓和爆发的特征时间与太阳耀斑的相似,这可以说明两种耀斑的物理机制相同.