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.
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.
117833563
A Library of Lick/IDS Indices for Binary Stellar Populations
Using EPS we present 13 refined Lick/IDS absorption-line indices for an extensive set of instantaneous-burst binary stellar populations (BSPs) at high resolution (0.3 \AA) of various age and metallicity (1-15Gyr, 0.004-0.03), and 38 indices at intermediate resolution (3 \AA). These indices are obtained by two methods: (1) obtain them by using the empirical fitting functions (FFs method); (2) measure them directly from the synthetic spectra (DC method). Together with our previous paper a database of Lick/IDS spectral absorption-line indices for BSPs at high and intermediate resolutions is provided. This set of indices includes 21 indices of Worthey et al., four Balmer indices defined by Worthey & Ottaviani and 13 indices with the new passband definitions of Trager et al. The full set of synthetic indices and the integrated pseudo-continuum are listed in the Appendix, which is only available online or from our website (this http URL com/), or on request from the first author. Moreover, the ISEDs can be obtained from our website. 
We compare the synthetic Lick/IDS indices obtained by FFs method and those by DC method, and find that the discrepancies are significant: Ca4455 (index 6), Fe4668 (8), Mg_b (13), Fe5709 (17), NaD (19), TiO_1 (20) and TiO_2 (21, except for Z=0.02) in the W94 system, Ca4455^T (6^T), C_2 4668^T (8^T), NaD^T (19^T), TiO_1^T (20^T) and TiO_2^T (21^T, except for Z=0.02) in the T98 system obtained by DC method are less (bluer) than the corresponding ones obtained by FFs method for all metallicities. Ca4227 (index 3), Fe5782 (18),Ca4227^T (3^T) and Fe5782^T (18^T) are greater at Z=0.03 and become to be bluer at Z=0.004, Fe5709^T (17^T) index is less at Z=0.03 and becomes to be redder at Z=0.004 than the corresponding ones obtained by FFs method.
15936992
Integrated spectral energy distributions and absorption-feature indices of single stellar populations
Using evolutionary population synthesis, we present integrated spectral energy distributions and absorption-line indices defined by the Lick Observatory image dissector scanner (referred to as Lick/IDS) system, for an extensive set of instantaneous burst single stellar populations (SSPs). The ages of the SSPs are in the range 1 Gyrless than or equal totauless than or equal to19 Gyr and the metallicities are in the range -2.3less than or equal to[Fe/H]less than or equal to+0.2. Our models use the rapid single stellar evolution algorithm of Hurley, Pols and Tout for the stellar evolutionary tracks, the empirical and semi-empirical calibrated BaSeL-2.0 model of Lejeune, Cuisinier and Buser for the library of stellar spectra and the empirical fitting functions of Worthey, Faber, Gonzalez and Burstein for the Lick/IDS spectral absorption-feature indices. Applying our synthetic Lick/IDS absorption-line indices to the merit function, we obtain the age and the metallicity of the central region of M32, which can be well explained by an instantaneous SSP with an age of similar to6.5 Gyr and a metallicity similar to solar. Applying the derived age and the metallicity from the merit function to a number of index-index diagrams, we find that the plots of H-beta-Fe5015 and H-beta-Fe5782 are the best index-index diagrams from which we can directly obtain reasonable age and metallicity.
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.
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.
12246797
The molecular emissions and the infall motion in the high-mass young stellar object G8.68−0.37
We present a multi-wavelength observational study towards the high-mass young stellar object G8.68−0.37. A single massive gas-and-dust core is observed in the (sub)millimetre continuum and molecular line emissions. We fitted the spectral energy distribution (SED) from the dust continuum emission. The best-fitting SED suggests the presence of two components with temperature of T_d = 20 and 120 K, respectively. The core has a total mass of up to 1.5 × 10^3 M_⊙ and a bolometric luminosity of 2.3 × 10^4 L_⊙. Both the mass and luminosity are dominated by the cold component (T_d= 20 K). The molecular lines of C^(18)O, C^(34)S, DCN and thermally excited CH_(3)OH are detected in this core. Prominent infall signatures are observed in the ^(12)CO (1 − 0) and (2 − 1). We estimated an infall velocity of 0.45 km s^(−1) and a mass infall rate of 7 × 10^(−4) M_⊙ yr^(−1). From the molecular lines, we have found a high DCN-to-HCN abundance ratio of 0.07. The overabundant DCN may originate from a significant deuteration in the previous cold pre-protostellar phase. And the DCN should now be rapidly sublimated from the grain mantles to maintain the overabundance in the gas phase.
16866447
Interpreting Helioseismic Structure Inversion Results of Solar Active Regions
Helioseismic techniques such as ring-diagram analysis have often been used to determine the subsurface structural differences between solar active and quiet regions. Results obtained by inverting the frequency differences between the regions are usually interpreted as the sound-speed differences between them. These in turn are used as a measure of temperature and magnetic-field strength differences between the two regions. In this paper we first show that the “sound-speed” difference obtained from inversions is actually a combination of sound-speed difference and a magnetic component. Hence, the inversion result is not directly related to the thermal structure. Next, using solar models that include magnetic fields, we develop a formulation to use the inversion results to infer the differences in the magnetic and thermal structures between active and quiet regions. We then apply our technique to existing structure inversion results for different pairs of active and quiet regions. We find that the effect of magnetic fields is strongest in a shallow region above 0.985R⊙ and that the strengths of magnetic-field effects at the surface and in the deeper (r<0.98R⊙) layers are inversely related (i.e., the stronger the surface magnetic field the smaller the magnetic effects in the deeper layers, and vice versa). We also find that the magnetic effects in the deeper layers are the strongest in the quiet regions, consistent with the fact that these are basically regions with weakest magnetic fields at the surface. Because the quiet regions were selected to precede or follow their companion active regions, the results could have implications about the evolution of magnetic fields under active regions.
118518653
Constraining fast radio burst progenitors with gravitational lensing
Fast Radio Bursts (FRBs) are new transient radio sources discovered recently. Because of the angular resolution restriction in radio surveys, no optical counter part has been identified yet so it is hard to determine the progenitor of FRBs. In this paper we propose to use radio lensing survey to constrain FRB progenitors. We show that, different types of progenitors lead to different probabilities for a FRB to be gravitationally lensed by dark matter halos in foreground galaxies, since different type progenitors result in different redshift distributions of FRBs. For example, the redshift distribution of FRBs arising from double stars shifts toward lower redshift than of the FRBs arising from single stars, because double stars and single stars have different evolution timescales. With detailed calculations, we predict that the FRB sample size for producing one lensing event varies significantly for different FRB progenitor models. We argue that this fact can be used to distinguish different FRB models and also discuss the practical possibility of using lensing observation in radio surveys to constrain FRB progenitors.
12639048
Towards complete phase diagrams of a holographic p-wave superconductor model
A bstractWe study in detail the phase structure of a holographic p-wave superconductor model in a five dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. To construct complete phase diagrams of the model, we consider both the soliton and black hole backgrounds. In both two cases, there exist second order, first order and zeroth order phase transitions, and the so-called “retrograde condensation” also happens. In particular, in the soliton case with the mass of the vector field being beyond a certain critical value, we find a series of phase transitions happen such as “insulator/superconductor/insulator/superconductor”, as the chemical potential continuously increases. We construct complete phase diagrams in terms of temperature and chemical potential and find some new phase boundaries.
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.