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.Comment: 2 pages 2 figure

The Effect of Binary Interactions in Infrared Passbands

We present the integrated J, H, K, L, M and N magnitudes and the colours involving infrared bands, for an extensive set of instantaneous-burst binary stellar populations (BSPs) by using evolutionary population synthesis (EPS). By comparing the results for BSPs WITH and WITHOUT binary interactions we show that the inclusion of binary interactions makes the magnitudes of populations larger (fainter) and the integrated colours smaller (bluer) for t > 1Gyr. Also, we compare our model magnitudes and colours with those of Bruzual & Charlot (2003, hereafter BC03) and Maraston (2005, hereafter M05). At last, we compare these model broad colours with Magellanic Clouds globular clusters (GCs) and Milky Way GCs. In (V-R)-[Fe/H] and (V-I)-[Fe/H] diagrams it seems that our models match the observations better than those of BC03 and M05.Comment: 2 page 3 figure

Binary interactions and UV photometry on photometric redshift

Using the Hyperz code (Bolzonella et al. 2000) we present photometric redshift estimates for a random sample of galaxies selected from the SDSS/DR7 and GALEX/DR4, for which spectroscopic redshifts are also available. We confirm that the inclusion of ultraviolet photometry improves the accuracy of photo-zs for those galaxies with g*-r* < 0.7 and z_spec < 0.2. We also address the problem of how binary interactions can affect photo-z estimates, and find that their effect is negligible.Comment: 2 pages 1 figure

Subdwarf B stars from the common envelope ejection channel

From the canonical binary scenario, the majority of sdBs are produced from low-mass stars with degenerate cores where helium is ignited in a way of flashes. Due to numerical difficulties, the models of produced sdBs are generally constructed from more massive stars with non-degenerate cores, leaving several uncertainties on the exact characteristics of sdB stars. Employing MESA, we systematically studied the characteristics of sdBs produced from the common envelope (CE) ejection channel, and found that the sdB stars produced from the CE ejection channel appear to form two distinct groups on the effective temperature-gravity diagram. One group (the flash-mixing model) almost has no H-rich envelope and crows at the hottest temperature end of the extremely horizontal branch (EHB), while the other group has significant H-rich envelope and spreads over the whole canonical EHB region. The key factor for the dichotomy of the sdB properties is the development of convection during the first helium flash, which is determined by the interior structure of the star after the CE ejection. For a given initial stellar mass and a given core mass at the onset of the CE, if the CE ejection stops early, the star has a relatively massive H-rich envelope, resulting in a canonical sdB generally. The fact of only a few short-orbital-period sdB binaries being in the flash-mixing sdB region and the lack of He-rich sdBs in short-orbital-period binaries indicate that the flash mixing is not very often in the products of the CE ejection. A falling back process after the CE ejection, similar to that happened in nova, is an appropriate way of increasing the envelope mass, then prevents the flash mixing.Comment: accepted by A&A 12 pages, 11 figure

Pseudogap and Fermi-arc Evolution in the Phase-fluctuation Scenario

Pseudogap phenomena and the formation of Fermi arcs in underdoped cuprates are numerically studied in the presence of phase fluctuations that are simulated by an XY model. Most importantly the spectral function for each Monte Carlo sample is calculated directly and efficiently by the Chebyshev polynomials without having to diagonalize the fermion Hamiltonian, which enables us to handle a system large enough to achieve sufficient momentum/energy resolution. We find that the momentum dependence of the energy gap is identical to that of a pure d-wave superconductor well below the KT-transition temperature ($T_{KT}$), while displays an upturn deviation from $\cos k_x - \cos k_y$ with increasing temperature. An abrupt onset of the Fermi arcs is observed above $T_{KT}$ and the arc length exhibits a similar temperature dependence to the thermally activated vortex excitations.Comment: 5 pages, 4 figure

Orbital-transverse density-wave instabilities in iron-based superconductors

Besides the conventional spin-density-wave (SDW) state, a new kind of orbital-transverse density-wave (OTDW) state is shown to exist generally in multi-orbital systems. We demonstrate that the orbital character of Fermi surface nesting plays an important role in density responses. The relationship between antiferromagnetism and structural phase transition in LaFeAsO (1111) and BaFe$_2$As$_2$ (122) compounds of iron-based superconductors may be understood in terms of the interplay between the SDW and OTDW with a five-orbital Hamiltonian. We propose that the essential difference between 1111 and 122 compounds is crucially determined by the presence of the two-dimensional $d_{xy}$-like Fermi surface around (0,0) being only in 1111 parent compounds.Comment: several parts were rewritten for clarity. 6 pages, 3 figures, 1 tabl