Radio stars observed in the LAMOST spectral survey

Radio stars have attracted astronomers＇ attention for several decades. To better understand the physics behind stellar radio emissions, it is important to study their optical behaviors. The LAMOST survey provides a large database for researching stellar spectroscopic properties of radio stars. In this work, we concentrate on their spectroscopic properties and infer physical properties from their spectra, such as stellar activity and variability. We mined big data from the LAMOST spectral survey Data Release 2 （DR2）, published on 2016 June 30, by cross-matching them with radio stars from FIRST and other surveys. We obtained 783 good stellar spectra with high signal to noise ratio for 659 stars. The criteria for selection were positional coincidence within 1.5＂ and LAMOST objects classified as stars. We calculated the equivalent widths （EWs） of the Ca II H＆K, HS, H＇7, H/3, Ha and Ca II IRT lines by integrating the line profiles. Using the EWs of the Ha line, we detected 147 active stellar spectra of 89 objects having emissions above the Ha continuum. There were also 36 objects with repeated spectra, 28 of which showed chromospheric activity variability. Furthermore, we found 14 radio stars emitting noticeably in the Ca II IRT lines. The low value of the EWs542/EWsags ratio for these 14 radio stars possibly alludes to chromospheric plage regions.

The Remnant of Neutron Star-White Dwarf Merger and the Repeating Fast Radio Bursts

Fast radio bursts (FRBs) at cosmological distances still hold concealed physical origins. Previously Liu (2018) proposes a scenario that the collision between a neutron star (NS) and a white dwarf (WD) can be one of the progenitors of non-repeating FRBs and notices that the repeating FRBs can also be explained if a magnetar formed after such NS-WD merger. In this paper, we investigate this channel of magnetar formation in more detail. We propose that the NS-WD post-merger, after cooling and angular momentum redistribution, may collapse to either a black hole or a new NS or even remains as a hybrid WDNS, depending on the total mass of the NS and WD. In particular, the newly formed NS can be a magnetar if the core of the WD collapsed into the NS while large quantities of degenerate electrons of the WD compressed to the outer layers of the new NS. A strong magnetic field can be formed by the electrons and positive charges with different angular velocities induced by the differential rotation of the newborn magnetar. Such a magnetar can power the repeating FRBs by the magnetic reconnections due to the crustal movements or starquakes.

Intensity distribution function and statistical properties of fast radio bursts

Fast Radio Bursts （FRBs） are intense radio flashes from the sky that are characterized by mil- lisecond durations and Jansky-level flux densities. We carried out a statistical analysis on FRBs that have been discovered. Their mean dispersion measure, after subtracting the contribution from the interstellar medium of our Galaxy, is found to be ~ 660 pc cm-3, supporting their being from a cosmological origin. Their energy released in the radio band spans about two orders of magnitude, with a mean value of ~ 10-39 erg. More interestingly, although the study of FRBs is still in a very early phase, the published collection of FRBs enables us to derive a useful intensity distribution function. For the 16 non-repeating FRBs detected by the Parkes telescope and the Green Bank Telescope, the intensity distribution can be described as dN/dFobs = （4.1± 1.3） × 103 F-obs1.1±0.2 sky-1 d-l, where Fobs is the observed radio obs fluence in units of Jy ms. Here the power-law index is significantly flatter than the expected value of 2.5 for standard candles distributed homogeneously in a flat Euclidean space. Based on this intensity distribution function, the Five-hundred-meter Aperture Spherical radio Telescope （FAST） is predicted to be able to detect about five FRBs for every 1000 h of observation time.

Morphology and kinematics of the gas envelope of the variable AGB star π^1 Gruis

Observations of the ^12CO（3–2） emission from the circumstellar envelope（CSE） of the variable star π1Gru using the compact array of the ALMA observatory have been recently made accessible to the public. An analysis of the morphology and kinematics of the CSE is presented with a result very similar to that obtained earlier for ^12CO（2–1） emission using the Submillimeter Array. A quantitative comparison is made using their flared disk model. A new model is presented that provides a significantly better description of the data, using radial winds and smooth evolutions of the radio emission and wind velocity from the stellar equator to the poles.

Evidence of Evolution in the Dense Cores in Massive Star Forming Regions

The excitation of H2O masers usually needs very high density gas,hence it can serve as a marker of dense gas in HⅡ region. We selected a sample of H2O maser sources from Plume et al. （four with, and four without detected CS（J = 7 - 6） emission）, and observed them in ^13CO（J=1-0） and C^18O （J=1-0）. C^18O （J=1-0） emission was detected only in three of the sources with detected CS（J=7-6） emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.

Quark nova model for fast radio bursts

Fast radio bursts （FRBs） are puzzling, millisecond, energetic radio transients with no discernible source; observations show no counterparts in other frequency bands. The birth of a quark star from a parent neutron star experiencing a quark nova - previously thought undetectable when born in isolation - provides a natural explanation for the emission characteristics of FRBs. The generation of unstable r-process elements in the quark nova ejecta provides millisecond exponential injection of electrons into the surrounding strong magnetic field at the parent neutron star＇s light cylinder via β-decay. This radio synchrotron emission has a total duration of hundreds of milliseconds and matches the observed spectrum while reducing the inferred dispersion measure by approximately 200 cm-3 pc. The model allows indirect measurement of neutron star magnetic fields and periods in addition to providing astronomical measurements of β-decay chains of unstable neutron rich nuclei. Using this model, we can calculate expected FRB average energies （- 1041 erg） and spectral shapes, and provide a theoretical framework for determining distances.

周期性重复快速射电暴双星模型再研究

在椭圆轨道的致密双星模型作为周期性重复快速射电暴(Fast Radio Bursts,FRBs)起源的基础上,考虑引力辐射对快速射电暴周期性行为的影响。这个双星系统包含一个具有强偶极磁场的中子星和一个磁化的白矮星。当白矮星充满它的洛希瓣时,物质将通过内拉格朗日点转移到中子星表面。由于角动量守恒,白矮星可能在一次爆发之后被踢开,接着在演化过程中由于引力辐射再次充满洛希瓣,实现再次爆发。这种情况下,快速射电暴的周期对应于双星轨道周期P_(orb),而它与两次质量转移时间间隔Δt之间的关系是能否显现周期性行为的关键因素。很明显,Δt≈P_(orb)或者Δt<P_(orb)是周期性行为显现的必要条件。反之,如果Δt>>P_(orb),周期性将很难观测到。结果表明,只有相对较长周期的快速射电暴才能显示周期性行为,这表明目前仅有的两个周期性快速射电暴都对应于较长的周期是合理的。

利用测地观测中搭载式相位参考模式观测射电星Del Lib和HR 1099

基于盖亚(Gaia)天体测量数据建立的盖亚天体参考系(Gaia Celestial Reference Frame,GCRF)与基于甚长基线干涉测量(Very Long Baseline Interferometry,VLBI)建立的国际天球参考系(International Celestial Reference Frame,ICRF)具有一定的系统差异,需要对盖亚的数据进行外部的独立评估,以建立光学和射电参考架连接。国际上对参考架的连接普遍采用在光学和射电波段都有辐射的天体,在暗端(星等G≥15)使用类星体,在亮端(G≤13)使用射电星。由于普通VLBI观测申请批准的周期长,难度大,因此,我们尝试将一部分射电星的观测转向数量较多的测地观测,在测地观测中搭载相位参考模式来观测射电星。为了测试这种观测的可行性,我们在IVS(The International VLBI Service for Geodesy and Astrometry)和LBA(Large Baseline Array)的测地观测中搭载相位参考观测,选取Del Lib和HR 1099作为实验的目标源。观测得到了这两颗射电星的VLBI图像、流量和单历元坐标,且坐标精度高于前人;同时结合前人的数据,对这两颗射电星进行了视差和自行拟合,结果与前人和盖亚的结果相符,且部分精度更高。验证了测地模式中搭载相位参考观测射电星的可行性,为后续丰富射电星VLBI天体测量样本,连接光学与射电参考架奠定了一定的基础。

深空测控系统跟踪接收机射电星校相的可行性分析

在深空测控系统的实际应用中,由于其天线口径大等原因,面临着角跟踪系统和差通道相位一致性需要在无塔条件下校准的关键技术难题。基于利用射电星校相的解决思路,首先通过分析确定了设计实现方案,并针对射电星信号的特点,结合具体的设计实现对其进行了理论分析,最后给出了实验验证结果。实验证明了射电星校相的可行性,这将对深空测控系统的应用具有非常重要的指导意义。

射电星与射电源的光学定位

用佘山40厘米望远镜,在AGK3和SAO星表系统中,确定了85颗射电星和3颗射电源的光学位置.其平均精度在赤经和赤纬上分别为0(?)13和0(?)11.所得结果和其它射电星表作了比较.

口面天线无塔校相方法

单脉冲跟踪体制下测控设备需要进行校相,传统校相依赖于标校塔。针对这个局限性开展了无塔校相方法研究。从和差双通道角度跟踪原理出发,介绍了无塔校相研究的最新进展,总结了三种无塔校相方法以及各种方法的应用条件。试验证明了这些方法的可行性,并且有些方法已进入工程应用阶段。

我国卫星导航系统相关技术发展分析

卫星导航系统应用广泛,有利于促进国民经济的快速发展。本文在介绍国内卫星导航系统及其国内市场状况基础上,结合北斗卫星导航相关产业发展趋势,从组合导航、增强系统、时钟同步和定向解算等方面分析了北斗卫星导航系统的技术成果,并讨论了有助于提高北斗卫星导航系统精度的相关辅助技术的发展情况。最后结合我国国情和国内卫星导航系统相关技术特点,给出我国第二代卫星导航定位系统发展的若干建议。

利用射电星噪声的无塔校相方法

提出了射电星幅射的射电噪声信号用作单脉冲角跟踪和、差通道幅、相校准的信标源的校相方法。介绍了其跟踪和校准原理,分析了与正弦标校信号的区别,讨论了其在宽带跟踪和窄带跟踪中的不同应用。

深空测控系统中的射电星校相方法

深空测控系统要求具有角度自跟踪功能,而和差双通道跟踪体制下测控设备在任务前需要进行校相。传统校相依赖标校塔,深空测控系统天线口径大,无法建造满足远场条件的标校塔,从而只能采用其他校相方案。本文通过分析校相过程的机理,并结合射电星具有全天候、分布广、星历精确已知的特点,得到了利用射电星校相的方法。通过前期大量试验证明了该方法的可行性,并已确定应用于深空测控系统的研制。

利用射电星校准13m测控天线指向误差及测试结果

分析了利用射电星校准13m测控天线指向精度的方法,综合利用射电星和光标测试数据,采用简化的天线误差模型,计算出天线误差系数,经过误差修正后天线的指向精度达到设计要求。

飞行器三轴姿态测量方法

介绍了到目前为止常用飞行器三轴姿态测量敏感器 .详述了这些姿态敏感器的工作原理 .根据这些原理分析了它们的优缺点 ,并比较了它们的性能指标 .

IRAS 19227+1700:富碳星还是富氧星?

IRAS 19227+1700作为富碳星列于新版碳星星表中,然而该星在IRAS红外双色图上处于典型的有较厚富氧拱星包层区域中,而不处于硅酸盐碳星通常所处的区域,而且有证据表明该星不但有主线和伴线羟基脉泽发射,还有靠近中心星的水脉泽发射,其IRAS LRS谱在9-12μm范围有尘埃发射特征,近红外的观测又证实它确实存在热的拱星包层,因此IRAS 19227+1700的拱星包层应该全是富氧性质的,它的中心星是富氧的可能性也极大。

惯性/卫星/天文组合导航仿真研究

研究组合导航系统优化导航的精度,针对星敏感器和卫星导航数据难以获取。为了对惯性/卫星/天文组合导航系统优化分析,同时克服物理实验缺少飞行轨迹信息的不足,深入研究了组合导航系统半物理仿真系统。提出了利用分布式子系统仿真模拟器,通过外部接口传输导航数据的仿真方法,便于进行子系统的单独验证以及组合导航仿真研究。通过对各子系统的仿真以及利用联邦滤波结构的组合导航算法仿真,结果表明,改变导航参数后的表现与理想结果一致,证明系统能够完成设定的导航任务,并为设计提供了参考。

地面测控系统校相方法综述

地面测控系统中,常用的跟踪体制为比幅单脉冲跟踪体制,不论是单脉冲单通道还是单脉冲双通道跟踪体制,其首先要解决的是校相问题,通过校相保证和、差通道相位一致性,才能实现对目标的稳定跟踪。本文主要介绍了应用于地面测控系统中的校相技术,包括对塔校相、对星校相、对射电星校相、近场校相等方法以及无人机在校相技术中的应用,总结了各种方法的基本原理及使用方法。

晚型巨星FK Com的射电观测研究

本文作者使用美国ＶＬＡ，对快速目转的晚型巨星ＦＫＣｏｍ在３．６、６、１８、２０厘米波长上进行了射电观测，探测到ｍＪｙ量级的射电辐射，而没有探测到圆偏振。我们用热模型对射电频谱进行了拟合，结果都不成功。当发射体内电子密度为９×１０８ｃｍ－３，温度为５×１０７Ｋ时，半径为１２０Ｒ⊙．可获得较为接近的流量，但１０９量级的电子密度不大可能扩展到如此大的范围。这样的发射体用热模型得到的Ｘ射线光度比Ｅｉｎｓｔｅｉｎ天文台所观测到的值大两个数量级。ＦＫＣｏｍ的射电光度和Ｘ射线光度与ＲＳＣＶｎ双星系统相近，如果ＦＫＣｏｍ的射电发射也是由相对论电子在中等强度的磁场中作加速运动产生的话，则在１０高斯磁场中半径为３Ｒ⊙左右的发射区在相应波段即可达到观测的流量值。