197491146
Structure and evolution of low-mass W UMa type systems -- II. with angular momentum loss
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.
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.
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.
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.
122993825
Field measurement of PEP-II LER dipoles and quadrupoles at IHEP
The field measurement of 209 dipoles and 320 quadrupoles for PEP-II LER will be finished at IHEP in June 1997. This paper covers the details of the magnetic measurement devices developed to measure these magnets as well as the results of the measurements.
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.
11692409
Electromagnetic energy for a charged Kerr black hole in a uniform magnetic field
With the Komar mass formula we calculate the electromagnetic energy for a charged Kerr black hole in a uniform magnetic field. We find that the total electromagnetic energy takes the minimum when the Kerr black hole possesses a nonzero net charge $Q=2\ensuremath{\xi}{B}_{0}{J}_{H}$ where ${B}_{0}$ is the strength of the magnetic field, ${J}_{H}$ is the angular momentum of the black hole, and $\ensuremath{\xi}$ is a dimensionless parameter determined by the spin of the black hole. However, the Wald state with ${Q=2B}_{0}{J}_{H}$ does not minimize the electromagnetic energy.
119221579
Observation of Single Top Quark Production at D0
This paper presents the observation of the electroweak production of single top quarks in the D0 detector at the Fermilab Tevatron pp Collider at a center‐of‐mass energy of 1.96 TeV. Events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks are used to measure a cross section for single top‐quark production of σ(pp→tb+X,tqb+X) = 3.94±0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5×10−7, corresponding to a 5.0 standard deviation significance.
15779981
Can Temperature Be Quantized
It is shown that the temperature may be quantized in some spacetime due to the periodically topological structure of the Euclidean section. The quanta of the temperature is the Hawking-Unruh temperature.