小质量密近双星Case A演化和几乎相接双星的形成

计算了总质量为3.9M,具有不同初始质比和两子星间距的一组模型在总质量、总角动量守恒假设下的Case A演化,以探求Case A演化与几乎相接双星(NCS)可能的联系.结果表明确实存在经过Case A质量交流演化为NCS系统的途径。并且这样形成的NCS系统其随后的演化有两种前景:一种随即演化为相接系统;另一种则经由慢速质量交流成为较稳定的半接或不接系统.但能够演化为NCS状态的初始模型范围极为狭窄,本文大致确定了它们的初始质比、子星间距等参量范围. 结合模型计算结果,对已知29个NCS系统作了统计研究,结果表明NCS系统与相接双星在演化上有很密切的联系.     

The contribution to population in ellipticals of blue stragglers: A test of their origin

An observational test of the binary hypothesis for the origin of the blue straggler (BS) stars has been performed y searching for radial velocity variables among 27 BS in five galactic clusters. The significance of the BS phenomenon for the interpretation of evolutionary synthesis models and the spectra of elliptical galaxies is briefly discussed.     

Inclusion of binaries in evolutionary population synthesis

Using evolutionary population synthesis we present integrated colours, integrated spectral energy distributions and absorption-line indices defined by the Lick Observatory image dissector scanner (referred to as the Lick/IDS) system, for an extensive set of instantaneous-burst binary stellar populations with and without binary interactions. The ages of the populations are in the range 1–15 Gyr and the metallicities are in the range 0.0001–0.03. By comparing the results for populations with and without binary interactions we show that the inclusion of binary interactions makes the integrated U – B , B – V , V – R and R – I colours and all Lick/IDS spectral absorption indices (except for H_β) substantially smaller. In other words, binary evolution makes a population appear bluer. This effect raises the derived age and metallicity of the population.
We calculate several sets of additional solar-metallicity binary stellar populations to explore the influence of the binary evolution algorithm input parameters (the common-envelope ejection efficiency and the stellar wind mass-loss rate) on the resulting integrated colours. We also look at the dependence on the choice of distribution functions used to generate the initial binary population. The results show that variations in the choice of input model parameters and distributions can significantly affect the results. However, comparing the discrepancies that exist between the colours of various models, we find that the differences are less than those produced between the models with and those without binary interactions. Therefore it is very necessary to consider binary interactions in order to draw accurate conclusions from evolutionary population synthesis work.     

Revision of the photometric parameters of BS Cassiopeiae

Seven charge-coupled device(CCD)photometric times of light minimum of the overcontact binary BS Cas which were obtained from 2007 August to November and one CCD light curve in the R band which was observed on 2007 September 24 and October 15,are presented.It is found that the light curve of BS Cas has characteristics like a typical EW-type light variation.The light curve obtained by us is symmetric and shows total eclipses,which is very useful for determining photometric parameters with high precision.Photometric solutions were derived by using the 2003 version of the Wilson-Devinney code.It shows that BS Cas is a W-subtype overcontact binary(f = 27.5% ± 0.4%)with a mass ratio of q = 2.7188 ± 0.0040.The temperature difference between the two components is 190 K.Analysis of the O-C curve suggests that the period of AE Phe shows a long-term continuous decrease at a rate of dP/dt=-2.45 × 10-7 dyr-1.The long-time period decrease can be explained by mass transfer from the primary to the secondary.     

The influence of binary interactions on infrared passbands of populations

In our evolutionary population synthesis models, samples of binaries are reproduced by a ' patched ' Monte Carlo simulation and the stellar masses, integrated   J ,  H ,  K ,  L ,  L 2  and M magnitudes, mass-to-light ratios and broad colours involving infrared bands are presented for an extensive set of instantaneous-burst binary stellar populations. In addition, the fluctuations in the integrated colours, which have been given by Zhang et al., are reduced.
By comparing the results for binary stellar populations with (Model A) and without (Model B) binary interactions, we show that the inclusion of binary interactions makes the stellar mass of a binary stellar population smaller (  ∼3.6–4.5  per cent during the past 15 Gyr), magnitudes greater (except   U , ∼ 0.18 mag  at the most), colours bluer (∼0.15 mag for   V − K   at the most) and mass-to-light ratios greater (∼0.06 for K band) except those in the U and B passbands at higher metallicities. Binary interactions make the V magnitude less sensitive to age, and R and I magnitudes more sensitive to metallicity.
Given an age, the absolute values of the differences in the stellar mass, magnitudes and mass-to-light ratios (except those in the U and B bands) between Models A and B reach a maximum at   Z = 0.0001  , i.e. the effects of binary interactions on these parameters reach a maximum, while the differences in some colours reach a maximum at   Z ∼ 0.01–0.0004  . In contrast, the absolute value of the difference in the stellar mass is minimal at   Z = 0.03  ; those in the   U ,  B ,  V   magnitudes and the mass-to-light ratios in the U and B bands reach a minimum at   Z ∼ 0.01–0.004  .     

Calculation of tidal-evolution constants for close binary systems

Tidal torque constants are calculated for each component of 112 close eclipsing binaries of the DMS type (detached components located within the main sequence) from the catalogue by Svechnikov and Perevozkina (1999) on the basis of the evolutionary models by Claret (2004), which are the first to present constants for investigation of tidal effects in close binaries. This study applies conversion of a grid of model tracks into that of isochrones with an arbitrarily small time step based on optimal nonlinear interpolation. The small time-step criterion guarantees application of the linear interpolation procedure to estimate the age of the DMS components and find an individual set of tidal-evolution constants for the close binary under study that refers to the estimated time point. The theoretical values of the apsidal motion period calculated from the individual internal structure constants for each close binary are well consistent with the observations. This confirms the validity of the evolutionary stellar models by Claret and the numerical algorithm proposed here.     

Population synthesis of gamma-ray bursts with precursor activity and the spinar paradigm

We study statistical properties of long gamma-ray bursts (GRBs) produced by the collapsing cores of WR stars in binary systems. Fast rotation of the cores enables a two-stage collapse scenario, implying the formation of a spinar-like object. A burst produced by such a collapse consists of two pulses, whose energy budget is enough to explain observed GRBs. We calculate models of spinar evolution using results from a population synthesis of binary systems (done by the 'Scenario Machine') as initial parameters for the rotating massive cores. Among the resulting bursts, events with a weaker first peak, namely precursor, are identified, and the precursor-to-main-pulse time separations fully agree with the range of the observed values. The calculated fraction of long GRBs with precursor (about 10 per cent of the total number of long GRBs) and the durations of the main pulses are also consistent with observations. Precursors with lead times greater by up to one order of magnitude than those observed so far are expected to be about a factor of 2 less numerous. Independently of the GRB model assumed, we predict the existence of precursors that arrive up to  ≳10³ s  in advance of the main events of GRBs.     

A review of early-type close binary systems

This is a review of close binary systems with very early spectral types (B, O, Of, and WR stars). We limit our selection to systems with Roche model photometric solution only. There are 10 contact systems known at present. Three of them (V701 Sco, BH Cen, and RZ Pyx) are located in the vicinity of the zero-age contact (ZC) according to a Spectral Type — Period diagram. Only the first two systems have absolute dimensions available. Both of these fall into the ZC zone in the logP-logm diagram and the logm-logR diagram. The system TU Mus was thought to be a ZC system is located in the evolved contact zone (EC) in the above diagrams. Both V701 Sco and BH Cen were thought to be having mass ratios about unity. With the much improved light curves of BH Cen and new analysis the mass ratio has been revised to 0.84! This result may favor Shu's model for early-type zero-age contact systems. The evolved systems might be undergone Case A mass exchange except for two systems (V729 Cyg and RY Sct) which might be from Case B. The systems V367 Cyg was classified by Plavec as a W Ser system may be a evolved contact system.It is interesting to note that V729 Cyg (O7f+OfIa), UW CMa(O7f+O) and CQ Cep(WN7+O) are all highly evolved contact systems. The Max II of UW CMa and CQ Cep are displaced to 0.78 and 0.80 phase, respectively. The displacement for V729 Cyg is not known due to poor coverage at this phase. The most distinct feature going from Of to Wolf-Rayet stars is the increasing domination of emission lines. It is suspected that this phaseshifts reflect the increasing activity of mass-flow in the common envelope.There are 8 semidetached systems with reliable absolute dimensions. It is believed that 6 of them are derived from Case A while the remaining 2 are from Case B mass exchange.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80, on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

Atmospheric analysis of the M/L and M/T dwarf binary systems LHS 102 and Gliese 229

We present  0.9–2.5 μm  spectroscopy with   R ∼800  and  1.12–1.22 μm  spectroscopy with   R ∼5800  for the M dwarfs Gl 229A and LHS 102A, and for the L dwarf LHS 102B. We also report IZJHKL ' photometry for both components of the LHS 102 system, and L ' photometry for Gl 229A. The data are combined with previously published spectroscopy and photometry to produce flux distributions for each component of the kinematically old disc M/L dwarf binary system LHS 102 and the kinematically young disc M/T dwarf binary system Gliese 229. The data are analysed using synthetic spectra generated by the latest 'AMES-dusty' and 'AMES-cond' models by Allard & Hauschildt. Although the models are not able to reproduce the overall slope of the infrared flux distribution of the L dwarf, most likely because of the treatment of dust in the photosphere, the data for the M dwarfs and the T dwarf are well matched. We find that the Gl 229 system is metal-poor despite having kinematics of the young disc, and that the LHS 102 system has solar metallicity. The observed luminosities and derived temperatures and gravities are consistent with evolutionary model predictions if the Gl 229 system is very young  (age∼30 Myr)  with masses (A,B) of (0.38,≳0.007) M_⊙, and the LHS 102 system is older, aged  1–10 Gyr  with masses (A,B) of (0.19,0.07) M_⊙.     

Simultaneous measurements of Martian plasma boundaries by Rosetta and Mars Express

We present the first two-spacecraft near-simultaneous observations of the Martian bow shock (BS), magnetic pileup boundary (MPB) and photo-electron boundary (PEB) obtained by the plasma instruments onboard Rosetta and Mars Express during the Rosetta Mars flyby on February 25, 2007. Our observations are compared with shape models for the BS and MPB derived from previous statistical studies. The MPB is found at its expected position but the BS for this event is found significantly closer to the planet than expected for the rather slow and moderately dense solar wind. Cross-calibration of the density measurements on the two spacecraft gives a density profile through the magnetosheath, indicating an increasing solar wind flux during the Rosetta passage which is consistent with the multiple BS crossings at the Rosetta exit.     

On the roche constants for Main-Sequence binaries

The ratiosC ₁/C ₂ of the constants defining the equipotential surfaces which describe the external forms of the components of a close binary system have been calculated on the basis of evolutionary models. Theoretical systems have been considered allowing for a wide range of input parameters (masses and separation) and taking into account the evolutionary effects on the radii of the stars during their Main-Sequence lifetime. The systems have not undergone any transfer of matter and are representative of detached binaries with Main-Sequence components. The ratios of the constants are confined in limited intervals and, for the highest values of the mass-ratio, they are clustered around the unit.     

Isolated versus common envelope dynamos in planetary nebula progenitors

The origin, evolution and role of magnetic fields in the production and shaping of proto-planetary nebulae (PPNe) and planetary nebulae (PNe) are a subject of active research. Most PNe and PPNe are axisymmetric with many exhibiting highly collimated outflows; however, it is important to understand whether such structures can be generated by isolated stars or require the presence of a binary companion. Towards this end, we study a dynamical, large-scale α−Ω interface dynamo operating in a 3.0 M_⊙ Asymptotic Giant Branch (AGB) star in both an isolated setting and a setting in which a low-mass companion is embedded inside the envelope. The back reaction of the fields on the shear is included and differential rotation and rotation deplete via turbulent dissipation and Poynting flux. For the isolated star, the shear must be resupplied in order to sufficiently sustain the dynamo. Furthermore, we investigate the energy requirements that convection must satisfy to accomplish this by analogy to the Sun. For the common envelope case, a robust dynamo results, unbinding the envelope under a range of conditions. Two qualitatively different types of explosion may arise: (i) magnetically induced, possibly resulting in collimated bipolar outflows and (ii) thermally induced from turbulent dissipation, possibly resulting in quasi-spherical outflows. A range of models is presented for a variety of companion masses.     

Orbital Parameters of the Binary Companion in o and Using Spectrum Disentangling

o And is one of the most frequently observed Be stars, both in photometry and spectroscopy. It is a multiple system of at least four stars (a Be star, a close binary of spectral types B7 and B8, and an A star). For over a century, numerous observers report a highly variable spectrum, photometric changes, and a substantial range of radial velocity. The star has changed back and forth between a shell-type and a normal B-type star. The last emission phase started in 1992 and ended in 2000. Analysis of the dynamical spectra at spectral lines Mg II 4481 Å and He I 6678 Å and radial velocity curves shows that the two binary components can be resolved. We decomposed the triple star spectra and computed orbital parameters of the binary companion using the KOREL code for spectrum disentangling.     

Models of α Centauri A and B with and without seismic constraints: time dependence of the mixing-length parameter

The α Centauri (α Cen) binary system is a well-known stellar system with very accurate observational constraints on the structure of its component stars. In addition to the classical non-seismic constraints, there are also seismic constraints for the interior models of α Cen A and B. These two types of constraint give very different values for the age of the system. While we obtain 8.9 Gyr for the age of the system from the non-seismic constraints, the seismic constraints imply that the age is about 5.6–5.9 Gyr. There may be observational or theoretical reasons for this discrepancy, which can be found by careful consideration of similar stars. The α Cen binary system, with its solar-type components, is also suitable for testing the stellar mass dependence of the mixing-length parameter for convection derived from the binaries of Hyades. The values of the mixing-length parameter for α Cen A and B are 2.10 and 1.90 for the non-seismic constraints. If we prioritize the seismic constraints, we obtain 1.64 and 1.91 for α Cen A and B, respectively. By taking into account these two contrasting cases for stellar mass dependence of the mixing-length parameter, we derive two expressions for its time dependence, which are also compatible with the mass dependence of the mixing-length parameter derived from the Hyades stars. For assessment, these expressions should be tested in other stellar systems and clusters.     

Powerful CMD:a tool for color-magnitude diagram studies

We present a new tool for color-magnitude diagram(CMD) studies, Powerful CMD. This tool is built based on the advanced stellar population synthesis(ASPS) model, in which single stars, binary stars, rotating stars and star formation history have been taken into account. Via Powerful CMD, the distance modulus, color excess, metallicity, age, binary fraction, rotating star fraction and star formation history of star clusters can be determined simultaneously from observed CMDs. The new tool is tested via both simulated and real star clusters. Five parameters of clusters NGC 6362, NGC 6652, NGC 6838 and M67 are determined and compared to other works. It is shown that this tool is useful for CMD studies, in particular for those utilizing data from the Hubble Space Telescope(HST). Moreover, we find that inclusion of binaries in theoretical stellar population models may lead to smaller color excess compared to the case of single-star population models.     

HD 9770, a southern active-chromosphere system

The visual triple system HD 9770 (BB Scl) has been the subject of a four-year programme of UVB ( RI )_C photometry and H α échelle spectroscopy. Analysis of the data obtained over that period shows that star B, and probably also star A, of HD 9770 is a binary. The A system comprises a K1V star, which may be in a binary system with another K dwarf. The B system is an eclipsing binary of the BY Dra type in which both stars are chromospherically active. An orbital period of 0.476 525±0.000 013 d has been derived from the light curve in V . Physical parameters derived from analysis of the light curves in UBV ( RI )_C are presented.     

The temperature anisotropy and adiabatic cooling of the protons in the solar wind

A simple theoretical expression for the mean kinetic temperature of the protons in a steady state as a function of heliocentric distance is derived. The basic assumption is that the temperature anisotropy of the protons is invariant in space where binary encounters are rare. For an assumed base temperature of 5 × 10⁵K at a distance of 0.05 AU, the calculated temperature at a distance of 1 AU is in the range (2–4) × 10⁴K for an average anisotropy factor of 3: this range of temperatures is close to the observed average value under so-called ‘quiet’ conditions. Measurement of the anisotropy factor at different heliocentric distances is required to test the basis of the model.     

Secular dynamics of S-type planetary orbits in binary star systems: applicability domains of first- and second-order theories

We analyse the secular dynamics of planets on S-type coplanar orbits in tight binary systems, based on first- and second-order analytical models, and compare their predictions with full N-body simulations. The perturbation parameter adopted for the development of these models depends on the masses of the stars and on the semimajor axis ratio between the planet and the binary. We show that each model has both advantages and limitations. While the first-order analytical model is algebraically simple and easy to implement, it is only applicable in regions of the parameter space where the perturbations are sufficiently small. The second-order model, although more complex, has a larger range of validity and must be taken into account for dynamical studies of some real exoplanetary systems such as \(\gamma \) Cephei and HD 41004A. However, in some extreme cases, neither of these analytical models yields quantitatively correct results, requiring either higher-order theories or direct numerical simulations. Finally, we determine the limits of applicability of each analytical model in the parameter space of the system, giving an important visual aid to decode which secular theory should be adopted for any given planetary system in a close binary.     

NGC 3603星团中的大质量逃逸双星

非团环境中的大质量恒星以及大质量双星的起源是理解大质量恒星形成和演化的关键问题之一. 年轻大质量星团内的动力学交会过程是产生大质量逃逸星的重要途径之一. 选取了银河系内年轻大质量星团NGC 3603外围的两个碰撞星风系统候选体MTT68A和MTT71作为研究对象, 通过分析\emphChandra X射线观测以及\emphGaia第2批数据发布(DR2)中的天体测量结果, 研究它们作为相互作用的大质量双星系统的起源. X射线数据的分析表明, 它们的X射线能谱中存在Fe XXV发射线成分; 相较于普通O型星, 以双温等离子体模型拟合得到偏高的高温成分温度($\gtrsim$2.0keV), 并且X射线光度与热光度的比值也较高($\gtrsim10^{-5.8