高红移耀变体4C 38.41光学多波段光变性质

4C 38.41是一颗红移为1.813、可分类为平谱射电类星体的耀变体,使用一台85 cm望远镜在2018年2月22日至26日期间对其进行了光学V和R波段测光观测,得到两个波段的准同时数据.基于这些数据分析了该源在不同光变时标下的光变特性.结果表明:这颗源在观测期间处于较弱的活动状态, V和R波段星等(V, R)总变化均约为0.20等.在天内时标下,其中3晚探测到了该源的天内光变,另有一晚可能存在天内光变.此外,通过色指数和时延分析发现4C 38.41在不同时标下都展现越亮越红行为,与大多数平谱射电类星体类似,但在最后一晚4C 38.41在颜色-星等图上呈现出v字形,即首先展现越亮越红行为,然后转变为越亮越蓝行为,这可能是由该源的辐射在吸积盘主导和喷流主导之间的转换造成的.此外在第2晚探测到了V、R波段之间的时延,这是首次在高红移耀变体中探测到不同光学波段光变之间的时延,可以用随机同步辐射小结构模型来解释.     

快速射电暴光学对应体在中国未来大视场望远镜中的可探测性分析

快速射电暴是近年来发展最快的天文学科之一. 理论上, 快速射电暴可能存在毫秒到小时时标的光学\lk对应体. 快速射电暴光学对应体有可能在中国未来大视场望远镜中探测到, 例如: 中国空间站工程巡天望远\lk镜(China Space Station Telescope, CSST)、中国科学技术大学和紫金山天文台合作的2.5m大视场巡天望远镜(Wide Field Survey Telescope, WFST)和地球2.0 (Earth 2.0, ET)等. 快速射电暴光学对应体通常分为毫秒时标光学对应体、小时时标光学对应体和光学余辉. 前两者可产生于快速射电暴的高能外延或是快速射电暴的射电辐射与高能电子的逆康普顿散射, 探测率与光学-射电流量比$\eta_\nu$关系密切. 对于毫秒时标光学对应体, 最理想情况下WFST、CSST和ET的探测率可以达到每年上百个. 当$\eta_\nu$~10^-3时, WFST、CSST的年探测率仅 为1个的量级, ET的年探测率为19.5个. 对于小时时标光学对应体, 最理想情况下超新星遗迹的年龄为5年且$\eta_\nu$约为10^-6时, 年探测率可到100以上. FRB 200428的X射线对应体表明, 快速射电暴可能产生相对论性外流并且与星际介质相互作用产生光学余辉. 结合快速射电暴的能量、在宇宙中的分布以及标准余辉模型, 可以对快速射电暴余辉的可探测性进行研究. 当总能量-射电能量比与FRB 200428类似(ζ = 10⁵)时, CSST、WFST和ET的 年探测率分别为1.3、1.0和67个.     

M型星AT Mic的X射线耀发统计研究

恒星耀发是剧烈的恒星活动过程,对恒星周围行星的大气构成和生命演化有重大影响.恒星耀发的辐射主要分布在光学和X射线波段,其中耀发时X射线波段流量可以增大数十至数百倍.M型耀星是最有可能存在类地行星的宿主恒星,因此,研究M型耀星的X射线耀发分布对寻找宜居的类地行星具有重要意义,并且也可以为即将发射的爱因斯坦探针卫星(Ein...     

W51M分子云中H和He复合线的观测研究

W51M (W51 Main)是一个和HⅡ区成协的大质量恒星形成区,在其中可以探测到众多的分子谱线和H、He射电复合线.中国科学院上海天文台基于天马65 m望远镜对W51M的观测数据,证认了主量子数在74–117之间的H、He复合发射线,其中主量子数在74–78之间的H和He的α复合线均被探测到.结合H和He复合线的多普勒致宽,算出该HⅡ区的电子温度约为7400 K, He+/H+的离子丰度比约为0.09,这与已有的研究基本吻合.考虑高信噪比的复合线,即H(n)α(74n78),计算得出W51M的平均湍动速度是13.767 km·s-1.通过确定W51M或其他HⅡ区中的复合线,获取电子温度、湍动速度以及其他物理参量,在电子数密度、元素丰度、恒星形成率等方面进行了探讨,对分子谱线以及其他波段的复合线研究具有借鉴意义.     

天宫2号POLAR探测器的低能X射线在轨定标

伽马暴偏振探测仪(POLAR)是天宫2号实验室上搭载的一个γ射线偏振仪,于2016年9月15日搭载在天宫2号进入低轨运行,主要用于探测在50-500 keV能区的硬X射线辐射的线偏振.POLAR由25个模块组成,每个模块有64个塑料闪烁体棒,总计有1600个塑料闪烁体棒,具有较大的有效探测面积和视场.在轨运行期间探测到多个小耀斑,它们的硬X射线光子能量通常小于50 keV,无法直接使用在轨和地面的高能定标结果来进行能谱分析.结合拉马第太阳高能光谱成像探测器(RHESSI)对耀斑SOL2016112907能谱的观测和蒙特卡洛模拟,对耀斑期间被激活的闪烁体棒进行能量低于50 keV的低能相对定标.虽然定标得到的能量阈值(～10 keV)和转换因子相对稳定,但是和高能定标给出的结果相比有显著差异,并且不同闪烁体棒显示出的差异没有明显的规律性.     

Heiles星光偏振源表的距离更正

星光偏振是研究星际介质磁场的有力工具之一.Heiles源表收集了9286颗恒星的偏振信息,是目前最大的光学波段星光偏振源表,被广泛使用.但该表中恒星的距离参数是以前的测光距离,很不确定.把Heiles源表和Gaia第2次数据释放(DR2)源表进行交叉证认,以位置和星等作为判据,匹配了7613颗恒星,并获得了这些恒星的三角视差距离和误差,超过90%的恒星距离相对误差小于20%.基于新的距离,展示了星光偏振在银河系内的分布并讨论了可能的应用.     

探测到气体的碎片盘统计研究

碎片盘通常被描述为贫气盘, 其气尘比显著低于原行星盘, 因此很少在碎片盘中探测到气体. 得益于各种灵敏的望远镜, 探测到气体的碎片盘的数量正在不断增加, 寻找更多的含有气体的碎片盘成为碎片盘研究的重点课题. 然而大范围的搜寻非常耗时且低效, 因而为了更快更好地遴选探测的目标, 需要根据这类源的特性择选更小范围样本. 通过统计探测到气体的碎片盘及其宿主恒星的参数总结出这些源的总体特性. 为此搜集了已经发表的探测到气体的碎片盘的文献, 总计找到37个源, 包括探测到CO等冷气体的12个源、CaII等热气体的14个源以及冷热气体共存的11个源. 通过统计其宿主恒星的光谱类型、年龄、离地球距离和碎片盘的相对光度、气体质量、尘埃质量等信息, 得出了主要结论: 宿主恒星多为B型和A型恒星, 年龄大部分都小于50Myr, 相对光度分布相比于已知碎片盘更为集中, 在$10^{ - 5     

耀变体在射电波段的偏振研究

利用UMRAO数据库22个耀变体源的偏振数据,根据LazarianPogosyan理论模型分析研究了耀变体射电波段的偏振随波长的变化,得出不同类的耀变体偏振随波长变化的原因。结果表明,与LazarianPogosyan理论模型吻合较好。由此得出如下结论:(1)反常去偏振耀变体源中反常法拉第旋光起主导作用,反常去偏振相对较少;(2)热辐射与同步辐射混合作用,高频波段的偏振度小于低频波段的偏振度(反常去偏振);(3)当被观测波段波长小于吸积盘热辐射对应的维恩波长时,高频波段的偏振度大于低频波段的偏振度(常规去偏振)。     

快速射电暴寄主星系色散量的估计

定位快速射电暴(Fast Radio Burst, FRB)以及确认其寄主星系至今仍是一个具有挑战性的难题,截至2021年4月已确认13个快速射电暴的寄主星系,其中只有3个重复暴,其余都是非重复暴.快速射电暴的寄主星系对快速射电暴起源的探索起着非常重要的作用,约束着快速射电暴前身星模型.对这些已确认寄主星系的FRB进行研究,发现FRB寄主星系对色散量(Dispersion Measure, DM)的贡献在一定范围内波动(0–240 pc·cm-3),并且寄主星系对DM的贡献与寄主星系的性质(恒星形成率、金属丰度)也可能具有关联性.寄主星系恒星形成率、金属丰度与色散量的统计关系对FRB邻近环境的研究有着重要意义.     

基于PSP观测的行星际Ⅲ型射电爆发的研究进展

与太阳射电爆发相比,通常认为频率较低的行星际射电爆发产生于远离低日冕的行星际空间.地球电离层的截止导致地基设备无法对其进行观测.美国国家航空航天局(National Aeronautics and Space Administration, NASA)发射的帕克太阳探测器(Parker Solar Probe, PSP)是迄今为止距离太阳最近的空间探测器.其搭载的射电频谱仪能够对10 k Hz–19.17 MHz频段范围内的射电辐射进行观测. PSP能够靠近甚至可能穿越行星际III型射电爆发的辐射源区,因此使用PSP对行星际射电爆发进行观测具有前所未有的优势.简要介绍了目前为止使用PSP的射电观测数据对行星际III型射电爆发的多方面研究,包括爆发的发生率、偏振、散射、截止频率、可能的辐射机制和相关的辐射源区等方面的研究进展,并讨论了其未来的研究前景.     

Polarization Observation Experiments for Radio Flares of Stars at the 6 cm Band

We have performed radio polarization observation experiments of the stars V772 Her and β Per with the Urumqi 25 m radio telescope at the 6 cm waveband, and obtained light curves of the stars after data processing and calibration. A radio ?are from the star V772 Her was detected on 2011 April 13. The degree of linear polarization of this ?are is about 30%, and the polarization angle is about 4°. We have detected also the slowly-varying component of the radio radiation from β Per, as well as a short ?are superposed on it, which has a very weak linear polarization.     

The magnetic SW Sextantis star RX J1643.7+3402

We present time-resolved spectroscopy and circular spectropolarimetry of the SW Sex star RX J1643.7+3402. We find significant polarization levels exhibiting a variability at a period of  19.38 ± 0.39  min. In addition, emission-line flaring is found predominantly at twice the polarimetric period. These two findings are strong evidences in favour of the presence of a magnetic white dwarf in the system. We interpret the measured periodicities in the context of our magnetic accretion model for SW Sex stars. In contrast with LS Pegasi – the first SW Sex star discovered to have modulated circular polarization – the polarization in RX J1643.7+3402 is suggested to vary at  2(ω−Ω)  , while the emission lines flare at  (ω−Ω)  . However, a  2ω/ω  interpretation cannot be ruled out. Together with LS Peg and V795 Her, RX J1643.7+3402 is the third SW Sex star known to exhibit modulated circular polarization.     

Polarimetry of stellar active regions and flares

Observations of regular and irregular polarimetric variability in late-type stars are reviewed, and the related physical and geometrical effects are discussed. There are indications that the irregular part of the variability could be caused by transient events, possibly associated with flares. Polarimetric observations during flares are reviewed, and preliminary results of new observations of a well-known flare star, YY Geminorum, are presented. The results show that the small flare in YY Gem did not cause any significant variations in linear polarization, while the binary eclipse evidently causes an enhancement in the polarization. The reasons for the difficulties in stellar flare polarimetry are discussed. Finally, future prospects for the observations of flaring stars and for the utilization of linear polarimetry as a complementary method to other techniques of surface imaging of stellar activity and flares are presented.     

Pulsating microwave emission from the star AD Leo

We have performed a spectral analysis of the quasi-periodic low-frequency modulation of microwave emission from a flare on the star AD Leo. We used the observations of the May 19, 1997 flare in the frequency range 4.5–5.1 GHz with a total duration of the burst phase of about 50 s obtained in Effelsberg with a time resolution of 1 ms. The time profile of the radio emission was analyzed by using the Wigner-Ville transformation, which yielded the dynamic spectrum of low-frequency pulsations with a satisfactory frequency-time resolution. In addition to the noise component, two regular components were found to be present in the low-frequency modulation spectrum of the stellar radio emission: a quasi-periodic component whose frequency smoothly decreased during the flare from ～2 to ～0.2 Hz and a periodic sequence of pulses with a repetition rate of about 2 Hz, which was approximately constant during the flare. We consider the possibility of the combined effect of MHD and LCR oscillations of the radio source on the particle acceleration in the stellar atmosphere and give estimates of the source’s parameters that follow from an analysis of the low-frequency modulation spectra.     

A flare in the mira X oph

Before the observation of the 1974 U Ori eruption, it was considered that the Mira stars had only some regular OH variations. With this eruption, we realized that sometimes flares can occur in this type of star. In the course of an OH Mira star monitoring programme with the Nançay radio telescope, we have discovered a new eruptive type of OH maser emission in several sources. Especially, in early 1992, we observed a quickly rising 1665 Mhz emission in the Mira X Oph. The main characteristics of this flare were: large flux variations independent of the light curve; large degree of circular polarization; radial velocity emission close to the stellar velocity.     

The nature of classical symbiotic stars

The results of the optical and infrared observations of classical symbiotic stars Z and, CI Cyg, BF Cyg, AG Dra, AX Per, V443 Her, and YY Her are summarized. It is shown that the hot component of most classical symbiotic stars is a hot subdwarf and not a Main-Sequence star with an accretion disc. The energy source of its outbursts is the gravitational energy of the matter accreted from the cool component's surface. The cool component is a red giant filling the Roche lobe and having class II luminosity. In the intervals between outbursts the hot component's luminosity may be determined by its own energy sources. It is probable that among classical symbiotic stars there are-in an insignificant quantity-systems in which the hot component is a Main-Sequence star with an accretion disc. In such systems eclipses of the hot source of radiation by the red giant must without fail occur and the hot component must be a yellow or red dwarf. The transition from a symbiotic nova (V1016 Cyg, HM Sge, and RR Tel) to a classical symbiotic nova takes place at the moment when the cool component's size is approaching the size of the Roche lobe, resulting in a sharp increase of the accretion rate of its matter onto the hot component. The nonstationarity of this process leads to the appearance of nova-like outbursts on classical symbiotic stars' light curves.     

Simultaneous photoelectric and spectral observations of the star EV Lac

We discuss the results of simultaneous photoelectric and spectral observations of the flare star EV Lac. The observations of EV Lac were carried out at the National Astronomical Observatory of the Bulgarian Academy of Sciences in August 1986. The photoelectric observations were conducted in the U-color with 1 sec time integration on a 60cm telescope. The effective time of photoelectric observations was 13 hours. The spectral observations were carried out on a two-meter telescope. During one night 35 spectrograms of the star EV Lac were obtained, each of which lasted 2 minutes. The equivalent widths of the H emission line were measured. During the photoelectric observations 6 flares were recorded. One of the two comparison stars, C₂ showed variable brightness.Translated fromAstrofizika, Vol. 37, No. 4, 1994.The authors consider it their pleasant duty to thank Professor L. V. Mirzoyan for valuable advice and the staff of the Rozhen Observatory of the Bulgarian Academy of Sciences for assistance during the observations.     

Photometric Studies of Twelve Deep, Low-mass Ratio Overcontact Binary Systems

The formations of the blue straggler stars and the FK Com-type stars are unsolved problems in stellar astrophysics. One of the possibilities for their formations is from the coalescence of W UMa-type overcontact binary systems. Therefore, deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars are a very important source to understand the phenomena of Blue Straggler/FK Com-type stars. Recently, 12 W UMa-type binary stars, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, V410 Aur, XY Boo, SX CrV, QX And, GSC 619-232, and AH Cnc, were investigated photometrically. Apart from TV Mus, XY boo, and GSC 619-232, new observations of the other 9 binaries were obtained. Complete light curves of the 10 systems, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, GSC 619-232, V410 Aur, XY Boo, and AH Cnc, were analyzed with the 2003 version of the W-D code. It is shown that all of those systems are deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars. We found that the system GSC 619-232 has the highest degree of overcontact (f = 93.4%). The derived photometric mass ratio of V857 Her, q = 0.0653, indicates that it is the lowest-mass ratio system among W UMa-type binaries.Of the 12 sample stars, long-term period changes of 11 systems were found. About 58% (seven) of the sample binaries show cyclic period oscillation. No cyclic period changes were discovered for the other 5 systems, which may be caused by the short observational time interval or by insufficient observations. Therefore, we think that all W UMa-type binary stars may contain cyclic period variations. By considering the long-term period changes (both increase and decrease) of those binary stars, we proposed two evolutionary scenarios evolving from deep, low-mass ratio overcontact binaries into Blue Straggler/FK Com-type stars.     

Simultaneous photometric and spectral analysis of a new outburst of V1686 Cyg

We present an analysis of the optical observations of Herbig Ae/Be(HAeBe) star V1686 Cyg,which is associated with a small isolated star-forming region around HAeBe star BD+40?4124. We observed this star as a part of our project investigating young eruptive stars. Observations were conducted on the 2.6-m telescope of Byurakan Observatory from 2015 to 2017. In this period, we obtained direct images of V1686 Cyg and 14 medium-and low-resolution spectra. In the course of observations, we noticed that this star underwent an atypical brightness outburst. After data reduction, we found that the full rise and decline in the brightness of V1686 Cyg had an amplitude of almost 3 magnitudes and lasted about 3 months.We were also able to track changes in the stellar spectrum during the outburst, which are correlated with the photometric variations.     

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.