118856665
The binary merger channel for the progenitor of the fastest rotating O-type star VFTS 102
VFTS 102 has a projected rotational velocity (>500 km s(-1)) and would appear to be the fastest rotating O-type star. We show that its high rotational velocity could be understood within the framework of the binary merger. In the binary merger channel, the progenitor binary of VFTS 102 would evolve into contact while two components are still on the main sequence, and then merge into a rapidly rotating single star. Employing Eggleton's stellar evolution code, we performed binary stellar evolution calculations and mapped out the initial parameters of the progenitor of VFTS 102 in the orbital period-mass ratio (P-q) plane. We found that the progenitor binary of VFTS 102 with initial mass ratio q(0) less than or similar to 0.7 should have an initial orbital period shorter than 3.76-4.25 d, while above this mass ratio it should have an initial orbital period shorter than 1.44-1.55 d. The progenitor of VFTS 102 would evolve into contact during the rapid mass transfer phase or during the subsequent slow mass transfer phase, and might ultimately merge into a rapidly rotating massive star. In addition, we performed Monte Carlo simulations to investigate the binary merger channel. We estimated the fraction of binaries that would merge into single stars and the fraction of single stars that might be produced from the binary merger channel. It is found that about 8.7 per cent of binaries would evolve into contact and merge into rapidly rotating single stars, and about 17.1 per cent of single stars might be produced from the binary merger channel and should have similar properties to VFTS 102. This suggests that the binary merger channel might be one of the main channels for the formation of rapidly rotating massive stars like VFTS 102.
17434779
Evolutionary population synthesis for binary stellar populations
We present integrated colours, integrated spectral energy distributions, and absorption-line indices, for instantaneous burst solar-metallicity binary stellar populations with ages in the range $1 {-} 15\,$Gyr. By comparing the results for populations with and without binary interactions we show that the inclusion of binary interactions makes the appearance of the population substantially bluer – this is the case for each of the quantities we have considered. This effect raises the derived age and metallicity of the population. Therefore it is necessary to consider binary interactions in order to draw accurate conclusions from evolutionary population synthesis work.
14270541
Structure and evolution of low-mass W UMa-type systems
The structure and evolution of low-mass W UMa-type contact binaries are discussed by employing Eggleton's stellar evolution code. Assuming that these systems completely satisfy Roche geometry for contact binaries with every kind of mass ratio (0.02-1.0) we calculate the relative radii (R-1.2/A, where R-1.2 are the radii of both stars and A is the orbital separation) of both components of contact binaries with different contact depths between inner and outer Roche lobes. We obtain a radius grid of contact binaries and can ensure the surfaces of two components lying on an equipotential surface by interpolation using this radius grid when we follow the evolution of the contact binaries. There are serious uncertainties concerning mainly the transfer of energy in these systems, i.e. it is unclear how and where the energy is transferred. We assume that the energy transfer takes place in different regions of the common envelope to investigate the effects of the region of energy transfer on the structure and evolution of contact binaries. We find that the region of energy transfer has a significant influence on the structure and evolution of contact binaries, and conclude that the energy transfer may occur in the outermost layers of the common convective envelope for W-type systems, and that this transfer takes place in the deeper layers of the common envelope for A-type systems. Meanwhile, if we assume that the energy transfer takes place in the outermost layers for our model with low total mass, and find that our model steadily evolves towards a system with a smaller mass ratio and a deeper envelope, suggesting that some A-type W UMa systems with low total mass could be considered as the later evolutionary stages of W-subtype systems, and that the surface temperature of the secondary exceeds that of the primary during the time when the primary expands rapidly, or the secondary contracts rapidly, suggesting that W-subtype systems may be caused by expansion of the primary, or by the contraction of the secondary.
197491146
Structure and evolution of low-mass W UMa type systems -- II. with angular momentum loss
119229638
The short-period limit of contact binaries
The stability of mass transfer is important in the formation of contact binaries from detached binaries when the primaries of the initially detached binaries fill their Roche lobes. Using Eggletons stellar evolution code, we investigate the formation and the short-period limit of contact binaries by considering the effect of the instability of mass transfer. It is found that with decreasing initial primary mass from 0.89 to 0.63 M?, the range of the initial mass ratio decreases for detached binaries that experience stable mass transfer and evolve into contact. If the initial primary mass is less than 0.63 M?, detached binaries would experience dynamically unstable mass transfer when the primaries of detached binaries fill their Roche lobes. These systems would evolve into a common envelope situation and probably then to a complete merger of two components on a quite short time-scale. This results in a low mass limit at about 0.63 M? for the primary mass of contact binaries, which might be the main reason why the period distribution of contact binaries has a short limit of about 0.22 d. By comparing the theoretical period distribution of contact binaries with the observational data, it is found that the observed contact binaries are above the low mass limit for the primary mass of contact binaries and no observed contact binaries are below this limit. This suggests that the short-period limit of contact binaries can be explained by the instability of the mass transfer that occurs when the primaries of the initially detached binaries fill their Roche lobes.
116828727
Effects of Binary interactions and metallicity on the calibrations of star formation rate
Using the Yunnan evolutionary population synthesis (EPS) models with and without binary interactions, we present the LHa, L[OII], Li,UV and LFIR for burst, E, S0, Sa-Sd and Irr galaxies at Z =0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02 and 0.03, present the conversion coefficients between star formation rate (SFR) and these diagnostics, and discuss the effects of binary interactions and metallicity on these SFR calibrations. 
The inclusion of binary interactions can lower the SFR versus LHa and SFR versus L[OII] conversion factors (CHa, C[OII]) by 0.1-0.2 dex, C1500 by 0.1 dex and C2800 by 0.2-0.1 dex, but raise CFIR by 0.05 dex. The differences in the CHa, C[OII] and C2800 caused by binary interactions are dependent of metallicity and those in the C1500 and CFIR are independent of metallicity. The higher is the metallicity, the larger are the differences in the CHa and C[OII], however, the smaller is the difference in the C2800 . 
The ratio of the difference in the conversion factor caused by metallicity to the [Fe/H] range, Delta_{case,Z}/Delta_{[Fe/H]}, reaches 0.2 for LHa and L[OII], 0.1 for Li,UV and 0.1-0.2 for LFIR. The dC_{case,Z}/d[Fe/H] is different within different [Fe/H] ranges and reaches the maximum value near the solar metallicity. At last, the Li,UV is not suitable to linear calibration of SFR at low metallicities. 
We also obtain the LHa, L[OII], Li,UV and LFIR for burst, E, S0, Sa-Sd and Irr galaxies by using the EPS models of BC03 (0.0001<Z<0.05), SB99 (0.0004<Z<0.05), PEGASE (0.0001<Z<0.1) and POPSTAR (0.0001<Z<0.05), present the conversion coefficients between SFR and these diagnostics, discuss the effects of the initial mass function and metallicity on these conversion coefficients, and compare the conclusions with those from our models.
15336878
Hot subdwarfs from the stable Roche lobe overflow channel
Context. Hot subdwarfs are core-helium-burning stars with extremely thin envelopes. We discuss the formation and evolution of hot subdwarfs formed through the stable Roche lobe overflow (RLOF) channel of intermediate-mass binaries, although their formation channels are various. Aims. In this study, we concentrate on the formation and evolution of hot subdwarfs binaries through the stable RLOF channel of intermediate-mass binaries. We aim at setting out the properties of hot subdwarfs and their progenitors, so that we can understand the formation and evolution of hot subdwarfs. Methods. Employing Eggleton's stellar evolution code, we have computed conservative and nonconservative population I binary evolution sequences. The initial mass of the primary ranges from 2.2 to 6.3 M(circle dot), spaced by approximately 0.1 in log M, the initial mass ratio q(i) = M(1)/M(2) is between 1.1 and 4.5, and the Roche lobe overflow begins at the main sequence, the Hertzsprung gap and the first giant branch. In nonconservative binary evolution, we assume that 50 percent of the mass lost from the primary leaves the system, carrying away the specific angular momentum of the primary, and the remaining mass is accreted on to the secondary during the RLOF. Also, we have studied the distributions of the mass and orbital periods of hot subdwarfs using the population synthesis approach. Results. We have obtained the ranges of the initial parameters of progenitor binaries and the properties of hot subdwarfs through the stable RLOF channel of intermediate-mass binaries, e. g. mass, envelope mass and age of hot subdwarfs. We have found that hot subdwarfs could be formed through stable Roche lobe overflow at the main sequence and Hertzsprung gap. We have also found that some subdwarf B or OB stars have anomalously high mass (similar to 1 M(circle dot)) with a thick envelope (similar to 0.07 M(circle dot)-similar to 0.16) in our models. By comparing our theoretical results with observations on the hot subdwarfs in open clusters, we suggest that more hot subdwarfs in binary systems might be found in open clusters in the future.
118607128
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, L2 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 (similar to 3.6-4.5 per cent during the past 15 Gyr), magnitudes greater (except U, similar to 0.18 mag at the most), colours bluer (similar to 0.15 mag for V - K at the most) and mass-to-light ratios greater (similar to 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 similar to 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 similar to 0.01-0.004.
118371809
The Laser Beacon: A survey system for the torsion-free alignment and monitoring of the L3 Muon Spectrometer octants
Given the small sagitta of a few millimeters of high energetic muons in the L3 Muon Spectrometer at LEP (CERN) and the enormous dimensions (75 m2 × 14 m) of this instrument, it is evident that alignment is the most critical task for its proper evaluation. In the chambers of each of the sixteen modules (“octants”), which form the spectrometer, wire planes are precisely positioned with respect to the front side and the rear side centerlines. A novel system - the Laser Beacon System - allows to make these centerlines coplanar within 25 μ rad by the aid of a reference plane defined by a sweeping laser beam. This restricts a possible torsion induced systematic momentum error for a 50 GeV/c muon to 0.25%. The main design and production features of the Laser Beacon System are described. Results of measurements in test assemblies and in the octants are given.
3091361
Transient Events from Neutron Star Mergers
Mergers of neutron stars (NS + NS) or neutron stars and stellar-mass black holes (NS + BH) eject a small fraction of matter with a subrelativistic velocity. Upon rapid decompression, nuclear-density medium condenses into neutron-rich nuclei, most of them radioactive. Radioactivity provides a long-term heat source for the expanding envelope. A brief transient has a peak luminosity in the supernova range, and the bulk of radiation in the UV-optical domain. We present a very crude model of the phenomenon, and simple analytical formulae that can be used to estimate the parameters of a transient as a function of poorly known input parameters. The mergers may be detected with high-redshift supernova searches as rapid transients, many of them far away from the parent galaxies. It is possible that the mysterious optical transients detected by Schmidt et al. are related to neutron star mergers, since they typically have no visible host galaxy.
119297362
Holographic forced fluid dynamics in non-relativistic limit
We study the thermodynamics and non-relativistic hydrodynamics of the holographic fluid on a finite cutoff surface in the Gauss-Bonnet gravity. It is shown that the isentropic flow of the fluid is equivalent to a radial component of gravitational field equations. We use the non-relativistic fluid expansion method to study the Einstein-Maxwell-dilaton system with a negative cosmological constant, and obtain the holographic incompressible forced Navier-Stokes equations of the dual fluid at AdS boundary and at a finite cutoff surface, respectively. The concrete forms of external forces are given. (c) 2012 Elsevier B.V. All rights reserved.