CygX—1硬态高能光子的时延

硬X射线和软射线光子的时延时研究主能辐射的一个重要方面，傅里叶交叉谱常常被用于教育处硬软光子之间的时延，但是交叉说示能在高于30Hz的傅里叶频率上从CygX-1测量到有统计意义的快速光变，由李惕培在时域上发展的交叉相关函方法能有效测量不同时间尺度上的时延，利用此交叉相关分析方法，讨论了不同观测时期CygX-1硬态高能光子时延 的性质，分析结果表明，CygX-1硬态在短的尺度（＜0．1秒）上存存在有意义的时间延迟，并将短时间尺度上的观测结果和各种CygX-1硬态模型进行了比较讨论。     

A warped m= 2 water maser disc in V778 Cyg?

The silicate carbon star V778 Cyg is a source of 22-GHz water maser emission which was recently resolved by MERLIN. Observations revealed an elongated     -like structure along which the velocities of the maser features show a linear dependence on the impact parameter. This is consistent with a doubly warped   m = 2  disc observed edge-on. Water masers and silicate dust emission (detected by the Infrared Astronomical Satellite and Infrared Space Observatory ) have a common origin in O-rich material and are likely to be co-located in the disc. We propose a detailed self-consistent model of a masing gas–dust disc around a companion to the carbon star in a binary system, which allows us to estimate the companion mass of  1.7 ± 0.1 M_⊙  , the disc radius of  40 ± 3  au and the distance between companions of ∼80 au. Using a dust–gas coupling model for water masing, we calculate the maser power self-consistently, accounting for both the gas and the dust energy balances. Comparing the simulation results with the observational data, we deduce the main physical parameters of the masing disc, such as the gas and dust temperatures and their densities. We also present an analysis of the stability of the disc.     

Low frequency flickering of TT arietis: Hard and soft X-ray emission region

Using archival ASCA observations of TT Arietis, X-ray energy spectra and power spectra of the intensity time series are presented for the first time. The energy spectra are well-fitted by a two continuum plasma emission model with temperatures 1 keV and 10 keV. A coherent feature at 0.643 mHz appeared in the power spectra during the observation.     

Clumped structure of WR wind derived from IR observations of WR+O binaries: some comments on the light curve solution for V444 Cygni

Strong increasing of the width and the depth of the secondary minimum of the light curve of V444 Cyg Wolf-Rayet eclipsing binary discovered by Cherepashchuk and Khaliullin (1973, 1975) from simultaneous narrow band continuum observations (4244–7512 Å) have been confirmed by new quasi-simultaneous UJK observations. This increasing of the width and the depth of the secondary minimum implies strong increasing of the radius of the extended atmosphere of the WN5 star with wavelength, which cannot be explained be the theory of homogeneous WR wind. These data can be understood in the model of WR wind proposed by Cherepashchuk et al. (1984). New data, supporting the reliability of the light curve solution for V444 Cyg of Cherepashchuk (1975) are presented.     

X-ray spectroscopy of stellar coronae

Summary From the early discovery in 1948 of X-rays from the Solar corona, X-ray spectroscopy has proven to be an invaluable tool in studying hot astrophysical and laboratory plasmas. Because the emission line spectra and continua from optically thin plasmas are fairly well known, high-resolution X-ray spectroscopy has its most obvious application in the measurement of optically thin sources such as the coronae of stars. In particular X-ray observations with theEINSTEIN observatory have demonstrated that soft X-ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable exception of single very cool giant and supergiant stars and A-type dwarfs. Observations with the spectrometers aboardEINSTEIN andEXOSAT have shown that data of even modest spectral resolution (/ = 10–100) permit the identification of coronal material at different temperatures whose existence may relate to a range of possible magnetic loop structures in the hot outer atmospheres of these stars. The higher spectral resolution of the next generation of spectrometers aboard NASA'sAXAF and ESA'sXMM will allow to fully resolve the coronal temperature structure and to enable velocity diagnostics and the determination of coronal densities, from which the loop geometry (i.e. surface filling factors and loop lengths) can be derived. In this paper various diagnostic techniques are reviewed and the spectral results fromEINSTEIN andEXOSAT are discussed. A number of spectral simulations forAXAF andXMM, especially high-resolution iron K-shell, L-shell, and2s-2p spectra in the wavelength regions around 1.9 Å, 10 Å, and 100 Å, respectively, are shown to demonstrate the capabilities for temperature, density, and velocity diagnostics. Finally, iron K-shell spectra are simulated for various types of detectors such as microcalorimeter, Nb-junction, and CCD.     

Duplicity amongst HIPPARCOS stars

Stars observed by the astrometry satellite Hipparcos may be unknown double stars. A subsample of those are dangerous for the extragalactic link of Hipparcos proper motions by long-term photographic proper motions, if the time base of Hipparcos is too short to detect the orbital motion. The probability of these cases and the typical size of the photocentric orbital motion are estimated by Monte Carlo simulations for the sample of 33 stars used in the Bonn extragalactic link. Both are found to be considerable: about 16% and 9 mas/yr respectively.     

Stream formation in W Serpentis-type binaries

By the method proposed by Nazarenko (1993) and using observational data obtained by different authors, the physical conditions in the stream in the neighbourhood of the inner Lagrangian point L₁ were calculated for three interacting binary systems of W Ser-type: β Lyr, V367 Cyg, RY Sct. It is shown, that as a result of the evolutional expansion of the mass losing component the deep layers of its atmosphere reach the neighbourhood of the first Lagrangian point L₁ and a stream of axial symmetric shape is formed. Its radius is comparable to the dimension of the mass losing component. The rate of the mass transfer increases up to 10⁻⁵ M_⊙/yr. The calculated parameters of the stream in the neighbourhood of the point L₁ explain the main observational properties of the investigated systems (existence of extended circumstellar matter with a developed structure, high mass transfer rate).     

More than two hundred and fifty thousand spectroscopic binary or variable star candidates discovered by LAMOST

About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than10 km s^-1 and they are possible spectroscopic binary or variable candidates(SBVCs). It is shown that most SBVCs are slightly metal poorer than the Sun. There are two peaks in the temperature distribution of SBVCs around 5760 K and 4870 K, while there are three peaks in the distribution of the gravitational acceleration at 2.461, 4.171 and 4.621 cm s^-2. The locations of SBVCs on the [Fe/H]-T, [Fe/H]-log g, log g-T and H-R diagrams are investigated. It is found that the detected SBVCs could be classified into four groups. The first group has higher log g～4.621 and lower T ～ 4870 K which are mainly cool red dwarf binaries. The second group of SBVCs has logg around 4.171 cm s^-2 that includes binaries and pulsating stars such as δSet and γ Dor variables. The gravitational accelerations of the third group of SBVCs are higher and some of them are below the zero-age main sequence. They may be contact binaries in which the primary components are losing energy to the secondaries in the common envelopes and are at a special stellar evolutionary stage.The last group is composed of giants or supergiants with log g around 2.461 cm s^-2 that may be evolved pulsating stars. One target(C134624.29+333921.2) is confirmed as an eclipsing binary with a period of 0.65 days. A preliminary analysis suggests that it is a detached binary with a mass ratio of 0.46. The primary fills its critical Roche lobe by about 89%, indicating that mass transfer will occur between the two components.     

Preface: Modern studies of variable stars

In this Mini-Volume, seven papers written on the basis of talks selected from those presented at the scientific conference "Modern studies of variable stars," commemorating Prof. M. A. Svechnikov(1933–2011), are published. The conference covered a variety of variable-star topics; the papers in this Mini-Volume deal with close, mainly eclipsing, binaries, Herbig Be stars and stellar molecular masers, with an accent on stellar catalogs of different kinds. We briefly review the contents of these papers.     

IU Cancri:a solar-type contact binary with mass transfer

We present new CCD photometry of the solar-type contact binary IU Cnc, which was observed from November 2017 to March 2018 with three small telescopes in China. BV light curves imply that IU Cnc is a W-type contact binary with total eclipses. The photometric solution indicates that the mass ratio and fill-out factor are q = 4.104 ± 0.004 and f = 30.2%± 0.3%, respectively. From all available light minimum times, the orbital period may increase at a rate of dP/dt =+6.93(4)× 10^-7 d yr^-1, which may result from mass transfer from the secondary component to the primary one. With mass transferring,IU Cnc may evolve from a contact configuration into a semi-detached configuration.