Due to the up/down asymmetry caused by stratification, overshooting above differs from overshooting below a convection zone. The flux of kinetic energy, frequently used as a proxy of overshooting below a convection zone, cannot be used for the upward problem.

The chemical abundances of the very metal poor double-enhanced stars are excellent information to set new constraints on models of neutron-capture processes at low metallicity. There have been many theoretical studies of s-process nucleosynthesis in low-mass AGB stars. Using the parametric approach based on the radiative s-process nucleosynthesis model, we calculate the following five parameters for a series of metal-poor stars. They are: the mass fraction of 13C pocket q, the overlap factor r, the neutron exposure per interpulse Δτ, and the component coefficients that correspond to relative contribution from the s-process and the r-process. We find that the mass fraction of 13C pocket q deduced for the Pb stars is comparable to the overlap factor r, which is about 10 times larger than normal AGB model; q ~ 0.05; and the neutron exposure per interpulse Δτ for all Pb stars are about 10 times smaller than the ST case (Δτ ~ 7.0mb−1). Although the two fundamental parameters Δτ and q obtained for the Pb stars are very different from the AGB stellar model, the results of the larger value of q and the smaller value of Δτ can also explain the abundance distribution of the Pb stars. This suggest that the q change to larger than that of normal AGB model. Then, this factor will result in the descent of the density of 13C in the nuclear synthesis region directly. So, the neutron exposure Δτ will also decrease to the same extent. Although the neutron number density in the larger initial mass AGB stars (m > 3M⊙) is high, the neutron irradiation time is shorter, obviously the neutron exposure per interpulse in the AGB stars should be smaller. It is noteworthy that the total amount of 13C in metal poor condition is close to the ST case, which is consistent with the primary nature of the neutron source.

Planetary nebulae are formed by an interacting winds process where the remnant of the AGB wind is compressed and accelerated by a later-developed fast wind from the central star. One-dimensional dynamical models have successfully explained the multi-shell (bubble, shell, crown, haloes) structures and the kinematics of planetary nebulae. However, the origin of the diverse asymmetric morphology of planetary nebulae is still not understood. Recent observations in the visible, infrared, and the submillimeter have suggested that the AGB mass loss becomes aspherical in the very late stages, forming an expanding torus around the star. A fast, highly collimated wind then emerges in the polar directions and carves out a cavity in the AGB envelope to form a bipolar nebula. Newly discovered structures such as concentric arcs, 2-D rings, multiple lobes, and point-symmetric structures suggest that both the slow and fast winds may have temporal and directional variations, and precession can play a role in the shaping of planetary nebulae. In this paper, we review the latest observations of planetary nebulae and proto-planetary nebulae and discuss the various physical mechanisms (rotation, binary, magnetic field, etc) that could lead to the observed morphologies.

It has long been clear that most, if not all, of the mass loss experienced by stars from 0.8 to 8 solar masses occurs near the tip of the AGB and/or the RGB. Evolutionary studies have incorporated empirical mass loss laws but theoretical models suggest quite different dependence of mass loss rate on stellar parameters. We are combining evolutionary model calculations with ISUEVO with mass loss modeling using the Bowen code in a systematic study of final stages of stellar evolution. We mapped the RGB (without steady mass loss) to the “Death Zone” as a function of mixing length, mass, and metallicity. We compared these results with observation data from Origlia. We are investigating a possible mass loss mechanism through companions as a complement to mass loss through pulsation. By the end of the project we expect to provide a reliable prescription for AGB mass loss.

We present the results of binary population simulations of carbon-enhanced metal-poor (CEMP) stars. We show that nitrogen and fluorine are useful tracers of the origin of CEMP stars, and conclude that the observed paucity of very nitrogen-rich stars puts strong constraints on possible modifications of the initial mass function at low metallicity. The large number fraction of CEMP stars may instead require much more efficient dredge-up from low-metallicity asymptotic giant branch stars.

Observations tend to select mass loss rates near the critical rate, Ṁcrit = M/L. There are two reasons for this. In some situations, such as near the tip of the AGB, the mass loss rate is very sensitive to stellar parameters. In this case, stars with Ṁ ≪ Ṁcrit have dust-free, hard-to-measure mass loss rates while stars with Ṁ ≫ Ṁcrit do not survive very long and thus make up a small fraction of any sample. Selection effects dominate the fitting of empirical formulae; observations of mass loss rates tell us more about which stars are losing mass than about how a star loses mass. In other situations, such as for some of the stars along the RGB, a steady state situation occurs where the loss of mass leads to a decrease in mass loss rate while the evolutionary changes lead to an increase; the result is a steady state with Ṁ = Ṁcrit. To determine the envelope mass and composition at the end of a phase of intensive mass loss requires stellar evolution models capable of responding on a time scale ~ tKH and thus, a new generation of stellar modeling codes.

We investigate the formation of neutral and singly ionized scandium lines in the solar photospheres. Extensive statistical equilibrium calculations were carried out for a model atom, which comprises 92 terms for Sc I and 79 for Sc II. Synthetic line profiles calculated from the level populations according to the NLTE departure coefficients were compared with the observed solar spectral atlas. Abundance determinations using the ODF model lead to a solar Sc abundance of between log ϵ⊙ = 3.07 and 3.13, depending on the choice of f values.

More than about 50% stars are in binaries, but the effects of binary evolution were not taken into account in most previous stellar population synthesis studies. In fact, binaries can affect the integrated peculiarities such as spectral energy distributions (SEDs), colours, and line-strength indices of populations. With the effects of binary stars taken into account, some new results for stellar population studies will be shown. We discuss how binaries affect the colours and Lick indices of simple stellar populations, and the measurement of stellar ages and metallicities.

We describe our work on the development and application of a stellar structure code to compute model sequences representing donor stars in interacting binaries subject to rapid (adiabatic) mass-loss. The donor star is assumed to remain in hydrostatic equilibrium, but no heat flow is allowed. These sequences can be used to define bifurcation sequences in close binary evolution, and to circumscribe possible survivors of common envelope evolution.

The Yonsei-Yale Isochrones have been widely used since its birth in 2001. We announce a major upgrade mainly making varieties of helium values available. The recent works on the globular clusters with extreme helium abundances have called for such a need. The new version of the Y2 Isochrones are available for [α/Fe] = 0 through 0.6, ΔY/ΔZ = 1.5 through 3.0, and extreme helium abundances (Y = normal 0.05, 0.1, 0.15, 0.2), and for 11 metallicity grids, with full capability of interpolation. The database will be powerful for making population models. Besides, the accuracy of the models on the lower main sequence has been substantially improved. We illustrate the major upgrades and demonstrate the power of the new grids.

We present the spectral properties of a large sample of nearly face-on low surface brightness (LSB) disk galaxies selected from the SDSS-DR4 main galaxy sample. About 12,282 LSB galaxies have been selected from the photometry database with their B-band central surface brightness μ0(B) ranging from 22 to 24.5 mag arcsec−2. About 7000 of such LSBGs have measured emission lines ([OII]3727, [OIII]5007, Hβ, Hα, [NII]6583) with the S/N ratio greater than 5σ. Their spectral diagnostic diagram of [NII]/Hα vs. [OIII]/Hβ shows that ~89% of them are star-forming galaxies, and ~11% could be classified as AGNs. The relations of μ0(B) vs. 12+log(O/H) and μ0(B) vs. stellar masses M* of these star-forming LSB galaxies show that their O/H and M* increase following the increasing μ0(B). The majority of these LSBGs are on the higher branch of metallicity.

Turbulent convection models (TCM) provide a better way to study convection in stars than the MLT. Improving numerical method, we adopted larger diffusion parameters and smaller dissipation parameters in order to further correct the p-mode oscillation frequencies of TCM models. The density gradient reversing is discussed.

KZ Hya is a short-period high amplitude metal pool population II pulsating variable. Its spectral type is B9-A7 III/IV. Its average effective temperature is 7640K. But its mass is only 0.97 solar mass. From normal stellar evolution and H-R diagram, we can not get such a solar mass star at post main sequence stage with so high effective temperature and so early type spectra. We observe this star since 1984 till now, 23years past. Finally we prove it is inside a binary with at least 2 unseen companions. The most massive companion has mass larger than 0.76 solar mass, mostly may be 0.99 to 3.99 solar mass. That means this companion must be a massive white dwarf. The distance between tow companions is about 10 AU. If the companion is white dwarf, this binary are fairly inside the nebula. This system is very old, older than 7.59 billion years. The nebula should be already diluted to very low density so that we can see the nebula directly. As its spectra type is B9III/VI at some time of maximum light and the visual absolute magnitude is 2.78, about 2 magnitudes higher than our sun. We can image that at the end of AGB stage of the companion, the strong fast winds from hot central core push away the outer atmosphere of KZ Hya. Later KZ Hya absorbed a part of Helium rich material from the companion. This will cause hydrogen content X decrease from 0.75 to about 0.62. Then KZ Hya looks like a hot post main sequence star

We report on an ongoing investigation into a seismic calibration of solar models designed for estimating the main-sequence age and a measure of the chemical abundances of the Sun. Only modes of low degree are employed, so that with appropriate modification the procedure could be applied to other stars. We have found that, as has been anticipated, a separation of the contributions to the seismic frequencies arising from the relatively smooth, glitch-free, background structure of the star and from glitches produced by helium ionization and the abrupt gradient change at the base of the convection zone renders the procedure more robust than earlier calibrations that fitted only raw frequencies to glitch-free asymptotics. As in the past, we use asymptotic analysis to design seismic signatures that are, to the best of our ability, contaminated as little as possible by those uncertain properties of the star that are not directly associated with age and chemical composition. The calibration itself, however, employs only numerically computed eigenfrequencies. It is based on a linear perturbation from a reference model. Two reference models have been used, one somewhat younger, the other somewhat older than the Sun. The two calibrations, which use BiSON data, are more-or-less consistent, and yield a main-sequence age t⊙ = 4.68 ± 0.02 Gy, coupled with a formal initial heavy-element abundance Z = 0.0169 ± 0.0005. The error analysis has not yet been completed, so the estimated precision must be taken with a pinch of salt.

We investigate the weakness of the present turbulence model with the nonlocal treatment of dissipation rate. A revised version is well tested for the solar convection. The suggestion of constant mixing length parameter of MLT could not hold any more if we refer to the nonlocal description of the dissipation rate, especially in the region of overshooting zone.

We discuss the role of mass loss for the evolution of the most massive stars, highlighting the role of the predicted bi-stability jump that might be relevant for the evolution of rotational velocities during or just after the main sequence. This mechanism is also proposed as an explanation for the mass-loss variations seen in the winds from Luminous Blue Variables (LBVs). These might be relevant for the quasi-sinusoidal modulations seen in a number of recent transitional supernovae (SNe), as well as for the double-throughed absorption profile recently discovered in the Hα line of SN 2005gj. Finally, we discuss the role of metallicity via the Z-dependent character of their winds, during both the initial and final (Wolf-Rayet) phases of evolution, with implications for the angular momentum evolution of the progenitor stars of long gamma-ray bursts (GRBs).

A two-fluid model to OB stars is investigated, in which the flow is described by a set of two components, One for the dense clumps and the other for the smooth gas. The two components are coupled by friction drag. The velocity structure of clumps is assumed to be beta law, thus, the velocity structure of the second component could be attained by shooting method. The result is compared with the X-ray observations.

We have carried out a detailed study of the single-degenerate channel for the progenitors of type Ia supernovae (SNe Ia). In the model, a carbon-oxygen white dwarf (CO WD) accretes hydrogen-rich material from an unevolved or a slightly evolved non-degenerate companion to increase its mass to Chandrasekhar mass limit. Incorporating the prescription of Hachisu et al. (1999a) for the accretion efficiency into Eggleton's stellar evolution code and assuming that the prescription is valid for all metallicities, we performed binary stellar evolution calculations for more than 25,000 close WD binary systems with various metallicities. The initial parameter spaces for SNe Ia are presented in an orbital period-secondary mass (log Pi, M2i) plane for each Z.

Adopting the results above, we studied the birth rate of SNe Ia for various Z via binary population synthesis. From the study, we see that for a high Z, SNe Ia occur systemically earlier and the peak value of the birth rate is larger if a single starburst is assumed. The Galactic birth rate from the channel is lower than (but comparable to) that inferred from observations.

We also showed the distributions of the parameters of the binary systems at the moment of supernova explosion and the distributions of the properties of companions after supernova explosion. The former provides physics input to simulate the interaction between supernova ejecta and its companion, and the latter is helpful for searching the companions in supernova remnants.

With two stellar sample A and B, the age-metallicity relation (AMR) in the Galactic thin disk is investigated. The results show two different AMRs: one is a nearly flat AMR from photometric analysis of sample A, the other is an obvious AMR derived from spectroscoipic analysis of sample B.

We present 3-D hydrodynamical simulations of the extended turbulent convective envelope of a low-mass red giant star. These simulations, computed with the ASH code, aim at understanding the redistribution of angular momentum and heat in extended turbulent convection zones of these giant stars. We focus our study on the effects of turbulence and of the rotation rate on the convective patterns and on the distribution of angular momentum within the inner 50% of the convective envelope of such stars.