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.
17105580
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) 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.
15791171
Energy transfer and its effects on the secondaries in W Ursae Majoris type contact binaries
Based on the physical parameters of 133 W Ursae Majoris (W UMa) type contact binaries, energy transfer and its effects on the secondaries in W UMa contact binaries are investigated. Relations are given between the mass ratio (q) for W UMa contact binaries and the relative energy transfer rates, i.e. U(1), the ratio of the transferred luminosity to the surface luminosity of the primary, and U(2), the ratio of the transferred luminosity to the nuclear luminosity of the secondary. The theoretical curves(U(1) versus q and U(2) versus q) are derived based on various assumptions: that the two components in each W UMa system are nearly identical in effective temperature and just fill their inner Roche lobes, and the primaries are zero-age main-sequence stars. Although these curves can reflect the distribution of U(1) and U(2) versus q, some observational systems deviate significantly from these curves. This results mainly from the difference in effective temperatures of the components of W UMa systems. The radius and the density of the secondary are related to the relative energy transfer rate U(2): the higher U(2), the greater the expansion and the lower the density of the secondary in a W UMa system. In addition, it is found that the temperature difference of W UMa binary components is correlated with the relative energy transfer rate U(1) and decreases with increasing U(1). This might suggest that there is a thermal coupling between the two components in W UMa contact binaries, and that the classification of W UMa contact binaries into A or W types depends on the energy transfer from the primary to the secondary. The temperature difference of W UMa binary components is poorly correlated with the mass of the primary. This suggests that the properties of the common envelope of a W UMa contact binary might not have a significant effect on the energy transfer between the two components.
1551177
The dynamical stability of W Ursae Majoris-type systems
Theoretical study indicates that a contact binary system would merge into a rapidly rotating single star due to tidal instability when the spin angular momentum of the system is more than a third of its orbital angular momentum. Assuming that W Ursae Majoris (W UMa) contact binary systems rigorously comply with the Roche geometry and the dynamical stability limit is at a contact degree of about 70 per cent, we obtain that W UMa systems might suffer Darwin's instability when their mass ratios are in a region of about 0.076-0.078 and merge into the fast-rotating stars. This suggests that the W UMa systems with mass ratio q <= 0.076 cannot be observed. Meanwhile, we find that the observed W UMa systems with a mass ratio of about 0.077, corresponding to a contact degree of about 86 per cent would suffer tidal instability and merge into the single fast-rotating stars. This suggests that the dynamical stability limit for the observed W UMa systems is higher than the theoretical value, implying that the observed systems have probably suffered the loss of angular momentum due to gravitational wave radiation (GR) or magnetic stellar wind (MSW).
123917430
ON KAON CONDENSATION IN DENSE NUCLEAR MATTER
The properties of kaons and antikaons in dense nuclear matter are investigated within the framework of relativistic mean-field theory including delta degrees of freedom. The couplings of kaon-baryon Interactions are determined by the chiral models. We find that the effective masses and energies of kaons and antikaons are reduced on account of the delta resonance in the nuclear matter. This mechanism may enhance the possibility of the existence of kaon condensation.
16252430
Universal Crossover in Perturbation Theory with a Large Field Cutoff
For lambda phi^4 models, the introduction of a large field cutoff improves significantly the accuracy that can be reached with perturbative series but the calculation of the modified coefficients remains a challenging problem. We show that this problem can be solved numerically, and in the limits of large and small field cutoffs, for the ground state energy of the anharmonic oscillator. For the two lowest orders, the approximate formulas obtained in the large field cutoff limit extend unexpectedly far in the low field cutoff region. For the higher orders, the transition between the small field cutoff regime and the large field cutoff regime can be described in terms of a universal function.
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.
24114301
Discovery of a selective inhibitor of oncogenic B-Raf kinase with potent antimelanoma activity
BRAFV600E is the most frequent oncogenic protein kinase mutation known. Furthermore, inhibitors targeting “active” protein kinases have demonstrated significant utility in the therapeutic repertoire against cancer. Therefore, we pursued the development of specific kinase inhibitors targeting B-Raf, and the V600E allele in particular. By using a structure-guided discovery approach, a potent and selective inhibitor of active B-Raf has been discovered. PLX4720, a 7-azaindole derivative that inhibits B-RafV600E with an IC50 of 13 nM, defines a class of kinase inhibitor with marked selectivity in both biochemical and cellular assays. PLX4720 preferentially inhibits the active B-RafV600E kinase compared with a broad spectrum of other kinases, and potent cytotoxic effects are also exclusive to cells bearing the V600E allele. Consistent with the high degree of selectivity, ERK phosphorylation is potently inhibited by PLX4720 in B-RafV600E-bearing tumor cell lines but not in cells lacking oncogenic B-Raf. In melanoma models, PLX4720 induces cell cycle arrest and apoptosis exclusively in B-RafV600E-positive cells. In B-RafV600E-dependent tumor xenograft models, orally dosed PLX4720 causes significant tumor growth delays, including tumor regressions, without evidence of toxicity. The work described here represents the entire discovery process, from initial identification through structural and biological studies in animal models to a promising therapeutic for testing in cancer patients bearing B-RafV600E-driven tumors.
15868166
Variation of the Amati relation with cosmological redshift: a selection effect or an evolution effect?
Because of the limit in the number of gamma-ray bursts (GRBs) with available redshifts and spectra, all current investigations on the correlation among GRB variables use burst samples with redshifts that span a very large range. The evolution and selection effects have thus been ignored, which might have important influence on the results. In this Letter, we divide the 48 long-duration GRBs in Amati (2006, 2007) into four groups with redshift from low to high, each group contains 12 GRBs. Then we fit each group with the Amati relation log Eiso = a + blog Epeak, and check if the parameters a and b evolve with the GRB redshift. We find that a and b vary with the mean redshift of the GRBs in each group systematically and significantly. Monte-Carlo simulations show that there is only � 4 percent of chance that the variation is caused by the selection effect arising from the fluence limit. Hence, our results may indicate that GRBs evolve strongly with the cosmological redshift.