13861127
Evolutionary population synthesis for binary stellar population at high spectral resolution: integrated spectral energy distributions and absorption-feature indices
Using evolutionary population synthesis, we present high-resolution (0.3 angstrom) integrated spectral energy distributions from 3000 to 7000 angstrom and absorption-line indices defined by the Lick Observatory Image Dissector Scanner (Lick/IDS) system, for an extensive set of instantaneous-burst binary stellar populations with binary interactions. The ages of the populations are in the range 1-15 Gyr and the metallicities are in the range 0.004-0.03. These high-resolution synthesis results can satisfy the needs of modern spectroscopic galaxy surveys, and are available on request. By comparing the synthetic continuum of populations at high and low resolution, we show that there is good agreement for solar metallicity and tolerable disagreement for non- solar metallicity. The strength of the Balmer lines at high spectral resolution is greater than that at low resolution for all metallicities. The comparison of Lick/IDS absorption-line indices at low and high resolution, both of which are obtained by the fitting functions, shows that the discrepancies in all indices except for TiO1 and TiO2 are insignificant for populations with Z = 0.004 and 0.02. The high-resolution Ca4227, Fe5015 and Mg-b indices are redder than the corresponding low-resolution ones for populations with Z = 0.01 and 0.03; this effect lowers the derived age and metallicity of the population. The high-resolution Mg-1, Fe5709 and Fe5782 indices are bluer than those at low resolution; this effect raises the age and metallicity. The discrepancy in these six indices is greater for populations with Z = 0.03 in comparison to Z = 0.01. At high resolution we compare the Lick/IDS spectral absorption indices obtained by using the fitting functions with those measured directly from the synthetic spectra. We find that the Ca4455, Fe4668, Mg-b and Na D indices obtained by the use of the fitting functions are redder for all metallicities, Fe5709 is redder at Z = 0.03 and becomes bluer at Z = 0.01 and 0.004, and the other indices are bluer for all metallicities than the corresponding values measured directly from the synthetic spectra.
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.
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.
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.
119107827
Holographic thermalization and gravitational collapse in a spacetime dominated by quintessence dark energy
In this paper, the thermalization has been studied holographically. Explicitly in the gravity side, we consider the gravitational collapse of a thin shell of dust in a spacetime dominated by quintessence dark energy. With the thermalization probes such as the normalized geodesic length and minimal area surface, we study the effect of the state parameter for the quintessence dark energy on the thermalization. Our results show that the smaller the state parameter of quintessence is, the harder the plasma to thermalize. We also investigate the thermalization velocity and thermalization acceleration. We hope our results here can shed light on the nature of the quintessence dark energy.
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.
10120589
The nonhomologous nature of solar diameter variations
We show in this Letter that the changes of the solar diameter in response to variations of large-scale magnetic fields and turbulence are not homologous. For the best current model, the variation at the photospheric level is over 1000 times larger than the variation at a depth of 5 Mm, which is about the level at which f-mode solar oscillations determine diameter variations. This model is supported by observations that indicate larger diameter changes for high-degree f-modes than for low-degree f-modes, since the energy of the former is concentrated at shallower layers than the latter.
118472204
Binary Stellar Population Synthesis Model
Using Yunnan evolutionary population synthesis (EPS) models, we present integrated colours, integrated spectral energy distributions (ISEDs) and absorption-line indices defined by the Lick Observatory image dissector scanner (Lick/IDS) system, for an extensive set of instantaneous-burst binary stellar populations (BSPs) with interactions. By comparing the results for populations with and without interactions we show that the inclusion of binary interactions makes the appearance of the population substantially bluer. This effect raises the derived age and metallicity of the population. To be used in the studies of modern spectroscopic galaxy surveys at intermediate/high spectral resolution, we also present intermediate- (3A) and high-resolution (~0.3A) ISEDs and Lick/IDS absorption-line indices for BSPs. To directly compare with observations the Lick/IDS absorption indices are also presented by measuring them directly from the ISEDs.
118660988
Inclusion of sdBs in evolutionary population synthesis for binary stellar populations and the application: the determination of photo-z and galaxy morphology
Subdwarf B stars (sdBs) can significantly change the ultraviolet spectra of populations at age t∼1 Gyr, and have been even included in the evolutionary population synthesis (EPS) models by Han et al. (Mon. Not. R. Astron. Soc. 380:1098, 2007). In this study we present the spectral energy distributions (SEDs) of binary stellar populations (BSPs) by combining the EPS models of Han et al. (Mon. Not. R. Astron. Soc. 380:1098, 2007) and those of the Yunnan group (Zhang et al. in Astron. Astrophys. 415:117, 2004; Mon. Not. R. Astron. Soc. 357:1088, 2005), which have included various binary interactions (except sdBs) in EPS models. This set of SEDs is available upon request from the authors.Using this set of SEDs of BSPs we build the spectra of Burst, E, S0–Sd and Irr types of galaxies by using the package of Bruzual and Charlot (Mon. Not. R. Astron. Soc. 344:1000, 2003). Combined with the photometric data (filters and magnitudes), we obtain the photometric redshifts and morphologies of 1502 galaxies by using the Hyperz code of Bolzonella et al. (Astron. Astrophys. 363:476, 2000). This sample of galaxies is obtained by removing those objects, mismatched with the SDSS/DR7 and GALEX/DR4, from the catalogue of Fukugita et al. (Astron. J. 134:579, 2007). By comparison the results with the SDSS spectroscopic redshifts and the morphological index of Fukugita et al. (Astron. J. 134:579, 2007), we find that the photo-z fluctuate with the SDSS spectroscopic redshifts, while the Sa–Sc galaxies in the catalogue of Fukugita et al. (Astron. J. 134:579, 2007) are classified earlier as Burst-E galaxies.