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γ Leo is a long-period visual binary system consisting of K0 iii (A) and G7 iii (B) giants, in which particular interest is attracted by the brighter A since the discovery of a planet around it. While detailed spectroscopic comparative study of both components would be worthwhile (e.g., for probing any impact of planet formation on chemical abundances), such a research seems to have been barely attempted as most available studies tend to be biased toward A. Given this situation, the physical properties of A and B along with their differences were investigated based on high-dispersion spectra in order to establish their stellar parameters, evolutionary status, and surface chemical compositions. The following results were obtained. (1) The masses were derived as ∼ 1.7 M ⊙ and ∼ 1.6 M ⊙ for A and B, respectively, both of which are likely to be in the stage of red clump giants after He-ignition. The mass of the planet around A has also been revised as m p sin i p ≃ 10.7 M Jupiter (increased by ∼ 20 % ). (2) These are normal giants of subsolar metallicity ([Fe/H] ∼ − 0.4 ) belonging to the thin-disk population. (3) A as well as B show moderate C deficiency and N enrichment, which are in compatible with the prediction from the standard stellar evolution theory. (4) The chemical abundances of 26 elements are practically the same within ≲ 0.1 dex for both components, which implies that the surface chemistry is not appreciably affected by the existence of a planet in A. [ABSTRACT FROM AUTHOR]

The mass (M ) of a star can be evaluated from its spectroscopically determined effective temperature ( T eff ) and metallicity ([Fe/H]) along with the luminosity (L ; derived from parallax), while comparing them with grids of theoretical evolutionary tracks. It has been argued, however, that such a track-based mass ( M trk ) may tend to be overestimated for the case of red giants. Meanwhile, there is an alternative approach of evaluating mass ( M gLT ) directly from surface gravity (g ), L , and T eff . The practical reliability of M gLT was examined for ∼ 100 benchmark giants in the Kepler field, for which atmospheric parameters are already determined and the reliable mass ( M seis ) along with the evolutionary status are known from asteroseismology. In addition, similar check was also made for the accuracy of M trk for comparison. It turned out that, while a reasonable correlation is seen between M gLT and M seis almost irrespective of the stellar property, its precision is rather insufficient because log (M gLT / M seis) distributes rather widely within ∼ ± 0.2 –0.3 dex. In contrast, the reliability of M trk was found to depend on the evolutionary status. Although M trk and M seis are satisfactorily consistent with each other (typical dispersion of log (M trk / M seis) is within ∼± 0.1 dex) for H-burning red giants as well as He-burning 2nd clump giants of higher mass, M trk tends to be considerably overestimated as compared to M seis by up to ≲ 0.4 dex for He-burning 1st clump giants of lower mass. Accordingly, M gLT and M trk are complementary with each other in terms of their characteristic merit and demerit. [ABSTRACT FROM AUTHOR]

We have shown the simultaneous generation of macroscale fast flows and strong magnetic fields in the two-temperature relativistic electron–ion plasmas of astrophysical objects due to the Unified Reverse Dynamo/Dynamo mechanism. The resulting dynamical magnetic-field amplification and/or flow acceleration is directly proportional to the initial turbulent kinetic/magnetic (magnetic) energy; the process is very sensitive to the relativistically hot electron–ion fraction temperature and the magnetofluid coupling. It is shown that for realistic physical parameters of White Dwarfs accreting hot astrophysical flow /Binary systems there always exists such a real solution of the dispersion relation for which the formation of dispersive strong super-Alfvénic macroscale flow/outflow with Alfvén–Mach number > 10 6 and/or generation of superstrong magnetic fields is guaranteed. [ABSTRACT FROM AUTHOR]

We have shown the generation/amplification of fast macro-scale plasma flows in the degenerate two-fluid astrophysical systems with initial turbulent (micro-scale) magnetic/velocity fields due to the Unified Reverse Dynamo/Dynamo mechanism. This process is simultaneous with and complementary to the micro-scale unified dynamo. It is found that the generation of macro-scale flows is an essential consequence of the magneto-fluid coupling; the generation of macro-scale fast flows and magnetic fields are simultaneous, they grow proportionately. The resulting dynamical flow acceleration is directly proportional to the initial turbulent magnetic (kinetic/magnetic) energy in degenerate e-i (degenerate e-p) astrophysical plasma; the process is very sensitive to both the degeneracy level of the system and the magneto-fluid coupling. In case of degenerate e-p plasma, for realistic physical parameters, there always exists such a real solution of dispersion relation for which the formation of strong macro-scale flow/outflow is guaranteed; the generated/accelerated locally super-Alfvénic flows are extremely fast with Alfvén Mach number > 10 3 as observed in a variety of astrophysical outflows. [ABSTRACT FROM AUTHOR]

The V R I passbands light curves of V344 Lac were presented and analyzed by using the latest version of the W-D code. The observed spectrum reveals that V344 Lac is not an A3 type but would be a later F type star according to the yielded temperature. The results of solution show that V344 Lac is an A-subtype contact binary, with a moderate photometric mass ratio of 0.387 ± 0.003 and a moderate contact factor of 44.6 ± 3.0 % . Based on the parallax given by Gaia, the parameters of the components are estimated as: M 1 = 1.16 M ⊙ , M 2 = 0.45 M ⊙ , R 1 = 1.31 R ⊙ , R 2 = 0.88 R ⊙ , L 1 = 2.512 L ⊙ , L 2 = 1.057 L ⊙ . The period investigation indicates that V344 Lac may have an eccentric orbital oscillation, with P 3 = 12.4 ± 0.5 yr , A 3 = 0.0020 ± 0.0002 d , and e = 0.38 ± 0.16 . Analysis shows such oscillation would be caused by a magnetic activity which can be explained by the Applegate mechanism. Meanwhile, according to the value of l 3 and the estimated physical parameters of V344 Lac, the mass of the third companion may be 0.79 M ⊙ . This third body could be a wide company. [ABSTRACT FROM AUTHOR]

We carried out high-precision photometric observations of three eclipsing ultrashort-period contact binaries (USPCBs). Theoretical models were fitted to the light curves by means of the Wilson-Devinney code. The solutions suggest that the three targets have evolved to a contact phase. The photometric results are as follows: (a) 1SWASP J030749.87−365201.7, $q=0.439\pm0.003$ , $f=0.0\pm3.6\%$ ; (b) 1SWASP J213252.93−441822.6, $q=0.560\pm0.003$ , $f=14.2\pm1.9\%$ ; (c) 1SWASP J200059.78+054408.9, $q=0.436\pm0.008$ , $f=58.4\pm1.8\%$ . The light curves show O'Connell effects, which can be modeled by the assumed cool spots. The cool spots models are strongly supported by the night-to-night variations in the $I$ -band light curves of 1SWASP J030749.87−365201.7. For a comparative study, we collected the whole set of 28 well-studied USPCBs with $P < 0.24$ day. Thus, we found that most of them (17 of 28) are in shallow contact (i.e. fill-out factors $f<20\%$ ). Only four USPCBs have deep fill-out factors (i.e. $f>50\%$ ). Generally, contact binaries with deep fill-out factors are going to merge, but it is believed that USPCBs have just evolved to a contact phase. Hence, the deep USPCB 1SWASP J200059.78+054408.9 seems to be a contradiction, making it very interesting. Particularly, 1SWASP J030749.87−365201.7 is a zero contact binary in thermal equilibrium, implying that it should be a turn-off sample as predicted by the thermal relaxation oscillation (TRO) theory. [ABSTRACT FROM AUTHOR]

In this paper, we first discuss a series of important but puzzling physical mechanisms concerning the energy source, various kinds of core collapsed supernovae explosion mechanisms during central gravitational collapse in astrophysics. We also discuss the puzzle of possible association of $\gamma $ -ray burst with gravitational wave perturbation, the heat source for the molten interior of the core of the Earth and finally the puzzling problem of the cooling of white dwarfs. We then make use of the estimations for the space flux of magnetic monopoles (hereafter MMs) and nucleon decay induced by MMs (called the Rubakov-Callen (RC) effect) to obtain the luminosity due to the RC effect. In terms of the formula for this RC luminosity, we present a unified treatment for the heat source of the Earth's core, the energy source for the white dwarf interior, various kinds of core collapsed supernovae (Type II Supernova (SNII), Type Ib Supernova (SNIb), Type Ic Supernova (SNIc), Super luminous supernova (SLSN)), and the production mechanism for $\gamma $ -ray burst. This unified model can also be used to reasonably explain the possible association of the short $\gamma $ -ray burst detected by the Fermi $\gamma $ -ray Burst Monitoring Satellite (GBM) with the LIGO gravitational wave event GW150914 in September 2015. [ABSTRACT FROM AUTHOR]

We present the first light curves and pulsation analysis results for V729 Aql and two newly discovered eclipsing binaries, namely USNO-A2.0 0975-17281677 and USNO-A2.0 1200-03937339. Frequency search was applied on the residuals of their light curves and the results showed that their primary components pulsate in multiperiodic modes and lie well inside the frequency and temperature range of δ Scuti stars. Moreover, for USNO-A2.0 1200-03937339 two frequencies inside the γ Dor frequency range were also detected, but their origin is discussed. The photometric models of USNO-A2.0 1200-03937339 and V729 Aql are also presented, while their absolute parameters as well as the evolutionary status of their components were roughly estimated. [ABSTRACT FROM AUTHOR]

New and complete multi-band light curves of the oEA stars QY Aql, BW Del, TZ Dra, BO Her and RR Lep were obtained and analysed with the Wilson-Devinney code. The light curves residuals were further analysed with the Fourier method in order to derive the pulsation characteristics of the oscillating components. All the reliable observed times of minimum light were used to examine orbital period irregularities. The orbital period analyses revealed secular changes for QY Aql and BW Del, while the Light-Time Effect seems to be the best explanation for the cyclic period changes in TZ Dra and BO Her. RR Lep has a rather steady orbital period. Light curve solutions provided the means to calculate the absolute parameters of the components of the systems, which subsequently were used to make an estimate of their present evolutionary status. [ABSTRACT FROM AUTHOR]

The location of the lower Main Sequence in the Colour Magnitude Diagram, the magnitude of the Red Clump and the magnitude of the tip of the Red Giant Branch are three popular stellar distance indicators. With the present observational capabilities they can be applied to reach distances ranging from the Galactic Disk and Halo populations, to galaxies beyond the Local Group. The techniques devised to exploit these distance indicators are presented, together with a discussion of their calibration, the main sources of systematic errors and the predicted impact of the results from the GAIA mission. [ABSTRACT FROM AUTHOR]

RR Lyrae variables play an important role in several fields of stellar evolution and cosmology, moreover, they are the most popular primary standard candles for Population II stellar systems. In this paper, their properties are examined within the framework of modern computations of stellar evolution and pulsation models in order to discuss their use as distance indicators. The comparison between selected observed data and predicted relations, for the determination of both apparent and intrinsic distance moduli, is also presented. [ABSTRACT FROM AUTHOR]

New complete light and radial velocities curves were obtained for the eclipsing binaries CC Her and CM Lac. The data are analysed with modern techniques in order to derive the physical parameters of the systems and study their present evolutionary status. We found that CC Her is a classical Algol type binary, while CM Lac is a detached system with two Main Sequence stars in asynchronous orbit. [ABSTRACT FROM AUTHOR]

Advances in stellar interior modeling are being driven by new data from large-scale surveys and high-precision photometric and spectroscopic observations. Here we focus on single stars in normal evolutionary phases; we will not discuss the many advances in modeling star formation, interacting binaries, supernovae, or neutron stars. We review briefly: (1) updates to input physics of stellar models; (2) progress in two and three-dimensional evolution and hydrodynamic models; (3) insights from oscillation data used to infer stellar interior structure and validate model predictions (asteroseismology). We close by highlighting a few outstanding problems, e.g., the driving mechanisms for hybrid γ Dor/ δ Sct star pulsations, the cause of giant eruptions seen in luminous blue variables such as η Car and P Cyg, and the solar abundance problem. [ABSTRACT FROM AUTHOR]

We describe the content and properties of UV source catalogs from GALEX's All-Sky Imaging Survey (AIS, 5 σ depth ≈19.9(FUV)/20.8(NUV) mag, in the AB system) and Medium-depth Imaging Survey (MIS, 5 σ depth ≈22.6(FUV)/22.7(NUV) mag), constructed by Bianchi L., et al.: Mon. Not. R. Astron. Soc. (, in press). The catalogs contain 65.3/12.6 million (AIS/MIS) unique UV sources with photometric error in NUV less than 0.5 mag, over 21 435(AIS)/1579(MIS) square degrees. Matched optical data from GSC-II provide additional B, R, I photometry for the brightest sources, and SDSS provides u g r i z photometry over 7325(AIS)/1103(MIS) square degrees overlap areas. We discuss statistical properties that are relevant for understanding sample selection biases and completeness, in potential science applications of these catalogs. The FUV (1344-1786 Å) and NUV (1771-2831 Å) photometry uniquely enable selection of the hottest stellar objects, in particular hot white dwarfs (WD), which are elusive at optical wavelengths because of their hot temperatures and faint luminosities. From the GALEX-SDSS matched sources we selected ∼40 000 Milky Way (MW) stars hotter than about 18 000 K (FUV-NUV < −0.13). Their density increases towards low Galactic latitudes, but drops in the MW disk due to dust extinction. The hot-WD density at different Galactic latitudes, analyzed with Milky Way models, constrains the Initial-Final Mass Relation (IFMR), relevant for understanding the yield of chemical elements from intermediate-mass stars and the chemical enrichment of the Galaxy. [ABSTRACT FROM AUTHOR]

We present new ultraviolet spectra of the hottest known, peculiar white dwarf H1504+65, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. H1504+65 is the hottest known white dwarf ( T=200 000 K) and has an atmosphere mainly composed by carbon and oxygen, augmented with high amounts of neon and magnesium. This object is unique and the origin of its surface chemistry is completely unclear. We probably see the naked core of either a C-O white dwarf or even a O-Ne-Mg white dwarf. In the latter case, this would be the first proof that such white dwarfs can be the outcome of single-star evolution. The new observations were performed to shed light on the origin of this mysterious object. [ABSTRACT FROM AUTHOR]

The study of the stellar constituents of star-forming sites in a wide variety of conditions yields the key to interpreting wide-field UV-optical imaging of extended nearby galaxies, and of distant galaxies. We obtained six-band imaging (from far-UV to I) with HST-WFPC2 of 67 sites of recent star formation in eight Local Group galaxies. HST pointings were selected from GALEX wide-field FUV imaging, which traces the young stellar populations. The HST observations were optimized to characterize the hottest, most massive stars in these regions. From the HST photometry, analyzed with stellar model colors, we derived the physical parameters of the massive stars in each field, and of the extinction by interstellar dust. The HST results are used to interpret GALEX UV measurements of SF across the entire galaxies. Our comprehensive photometric study at HST resolution (sub-pc scale in these galaxies) also provides an ideal selection of targets for follow-up spectroscopy with large ground-based telescopes, and in the UV with HST- or WSO-class telescopes, to clarify the influence of metallicity on the properties and the evolution of massive stars. [ABSTRACT FROM AUTHOR]

We obtained several epochs of light minima and a complete R light curve of the W-type contact binary V1128 Tau in 2009. Two cool spots on the massive component are used to model the photometric light curve. Using all available data we find evidence for a long-term period variation with an amplitude of 0.0050±0.0012 days and a period of 16.7±0.9 years. Using parameters derived from a photometric model of the 2009 light curve we show that this period change could be explained by the Applegate mechanism on one of the components. [ABSTRACT FROM AUTHOR]

ording to the prevenient theoretical study, the minimum mass ratio for tidal stability of W Ursae Majoris (W UMa) systems is q=( M/ M)∼0.071-0.078. However, the mass ratios of some observed W UMa binaries are smaller than the theoretical minimum mass ratio. Using Eggleton's stellar evolution code, we study the effects of metallicity and evolution on the minimum mass ratio of W UMa systems ( M=1.2 M). We assume that $k_{1}^{2}=k_{2}^{2}$ for the component's dimensionless gyration radii and that the contact degree is about 70 per cent. We find that the dynamical stability of W UMa binaries depends on the metallicity of W UMa systems. For the W UMa systems at age = 0 Gyr, the distribution of the minimum mass ratio has a fairly wide range, from 0.083 to 0.064, with the metallicity range from Z=0.0001 to 0.03. W UMa systems with Z=0.01 have the smallest value of the minimum mass ratio, which is about 0.064. The existence of low- q systems can be explained partly by the dependence of the dimensionless gyration radius on the metallicity. In addition, the dependence of the minimum mass ratio on the evolution, as suggested by previously work, is confirmed. [ABSTRACT FROM AUTHOR]

Employing Eggleton's stellar evolution code with the optically thick wind assumption, we have systematically studied the WD + He star channel of Type Ia supernovae (SNe Ia), in which a carbon-oxygen WD accretes material from a He main-sequence star or a He subgiant to increase its mass to the Chandrasekhar mass. We mapped out the parameter spaces for producing SNe Ia. According to a detailed binary population synthesis approach, we find that the Galactic SN Ia birthrate from this channel is ∼0.3×10 yr, and that this channel can produce SNe Ia with short delay times (∼45-140 Myr). We also find that the surviving companion stars in this channel have a high spatial velocity (>400 km/s) after the SN explosion, which could be an alternative origin for hypervelocity stars (HVSs), especially for HVSs such as US 708. [ABSTRACT FROM AUTHOR]

Roche-lobe overflow and common envelope evolution are very important in binary evolution, which is believed to be the main evolutionary channel to hot subdwarf stars. The details of these processes are difficult to model, but adiabatic expansion provides an excellent approximation to the structure of a donor star undergoing dynamical time scale mass transfer. We can use this model to study the responses of stars of various masses and evolutionary stages as potential donor stars, with the urgent goal of obtaining more accurate stability criteria for dynamical mass transfer in binary population synthesis studies. As examples, we describe here several models with the initial masses equal to 1 M and 10 M, and identify potential limitations to the use of our results for giant-branch stars. [ABSTRACT FROM AUTHOR]

In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undiscovered population of substellar companions to apparently single subdwarf B stars might exist. Following this serendipitous discovery, the EXOTIME () monitoring program has been set up to follow the pulsations of a number of selected rapidly pulsating subdwarf B stars on time scales of several years with two immediate observational goals: These sets of data should therefore, at the same time, on the one hand be useful to provide extra constraints for classical asteroseismological exercises from the $\dot{P}$ (comparison with 'local' evolutionary models), and on the other hand allow one to investigate the preceding evolution of a target in terms of possible 'binary' evolution by extending the otherwise unsuccessful search for companions to potentially very low masses. While timing pulsations may be an observationally expensive method to search for companions, it samples a different range of orbital parameters, inaccessible through orbital photometric effects or the radial velocity method: the latter favours massive close-in companions, whereas the timing method becomes increasingly more sensitive toward wider separations. In this paper we report on the status of the on-going observations and coherence analysis for two of the currently five targets, revealing very well-behaved pulsational characteristics in HS 0444+0458, while showing HS 0702+6043 to be more complex than previously thought. [ABSTRACT FROM AUTHOR]

In this contribution I will review the present knowledge about helium and metal diffusion efficiency in the Sun and in old cluster stars and the influence of the uncertainties still present on these mechanisms concerning the stellar characteristics in different evolutionary phases. I will also discuss the relevance of the current uncertainties on the assumed chemical composition for the main evolutionary features of population II stars. [ABSTRACT FROM AUTHOR]

For models of the Sun and Sun-like stars, a high-quality equation of state is crucial. In addition, helioseismic and asteroseismic observations also put constraints on the physical formalisms. Thus, they effectively turn the Sun and the stars into laboratories for dense plasmas. Currently, the main astrophysical beneficiary of a good equation of state is the determination of the chemical composition. Here, seismic data have supplemented spectroscopic information. Recently, there has been theoretical progress in the equation of state, thanks to renewed rigorous and phenomenological approaches. [ABSTRACT FROM AUTHOR]

Stellar evolutionary models are essential for the determination of stellar masses and ages. Several parameters can be used to characterize the structure of subgiant stars. Amongst others we can find: the helium and metal abundances, mixing length and core overshooting. In many cases, these parameters are scaled taking into account the solar values. Yet, the universality of such scalings has been put to question. As shown here, by allowing some freedom to these parameters we end up with a degeneracy of model solutions. This puts serious limitations on the determination of mass and age. Asteroseismology may provide a valuable help to break such a degeneracy. This is illustrated with an application to the subgiant star μ Her. [ABSTRACT FROM AUTHOR]

We point out a strong time evolution of the mass-to-light conversion factor, η, commonly used to estimate masses of unresolved star clusters from observed cluster spectrophotometric measures. We present a series of gas-dynamical models, coupled with the Cambridge stellar evolution tracks, to compute line-of-sight velocity dispersions and half-light radii weighted by the luminosity. We explore a range of initial conditions, varying in turn the cluster mass and/or density, and the stellar population’s initial mass function. We find that η, and hence the estimated cluster mass, may increase by as much as a factor of three over time-scales of 50 million yr. We apply these results to an hypothetic cluster mass distribution function (d.f.), and show that the d.f. shape may be strongly affected at the low-mass end by this effect. Fitting truncated isothermal (Michie–King) models to the projected light profile leads to over-estimates of the concentration parameter, c, of δ c≈0.3 compared to the same functional fit applied to the projected mass density. [ABSTRACT FROM AUTHOR]

Stellar population models are a very useful tool to derive the stellar cluster age and luminosity mass from its integrated light. Evolutionary synthesis models depend on the stellar evolutionary tracks and the stellar libraries used to predict the spectral energy distribution of the stellar populations. In this review, I briefly comment on the new models that have incorporated the new evolutionary tracks with rotation and new computations for the evolutionary tracks of the TP-AGB. A more extended summary is also given of the current status of the most recent high-resolution stellar libraries at optical wavelengths and their implementation in evolutionary synthesis models. A comparison of the results obtained fitting the optical spectra of LMC and SMC stellar clusters with different high spectral resolution evolutionary synthesis models is also presented. [ABSTRACT FROM AUTHOR]

With more and more exoplanets being detected, it is paid closer attention to whether there are lives outside solar system. We try to obtain habitable zones and the probability distribution of terrestrial planets in habitable zones around host stars. Using Eggleton’s code, we calculate the evolution of stars with masses less than 4.00 M⊙. We also use the fitting formulae of stellar luminosity and radius, the boundary flux of habitable zones, the distribution of semimajor axis and mass of planets and the initial mass function of stars. We obtain the luminosity and radius of stars with masses from 0.08 to 4.00 M⊙, and calculate the habitable zones of host stars, affected by stellar effective temperature. We achieve the probability distribution of terrestrial planets in habitable zones around host stars. We also calculate that the number of terrestrial planets in habitable zones of host stars is 45.5 billion, and the number of terrestrial planets in habitable zones around K type stars is the most, in the Milky Way. [ABSTRACT FROM AUTHOR]

Two CCD epochs of light minimum and a complete R light curve of SS Ari are presented. The light curve obtained in 2007 was analyzed with the 2003 version of the W-D code. It is shown that SS Ari is a shallow contact binary system with a mass ratio q=3.25 and a degree of contact factor f=9.4%(±0.8%). A period investigation based on all available data shows that there may exist two distinct solutions about the assumed third body. One, assuming eccentric orbit of the third body and constant orbital period of the eclipsing pair, results in a massive third body with M3=1.73 M⊙ and P3=87.0 yr. On the contrary, assuming continuous period changes of the eclipsing pair the orbital period of tertiary is 37.75 yr and its mass is about 0.278 M⊙. Both of the cases suggest the presence of an unseen third component in the system. [ABSTRACT FROM AUTHOR]

We review and discuss horizontal branch (HB) stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC—an argument which, due to its strong reliance on the ancient RR Lyrae stars, is essentially independent of the chemical evolution of these systems after the very earliest epochs in the Galaxy’s history. Convenient analytical fits to isochrones in the HB type–[Fe/H] plane are also provided. In this sense, a rediscussion of the second-parameter problem is also presented, focusing on the cases of NGC 288/NGC 362, M13/M3, the extreme outer-halo globular clusters with predominantly red HBs, and the metal-rich globular clusters NGC 6388 and NGC 6441. The recently revived possibility that the helium abundance may play an important role as a second parameter is also addressed, and possible constraints on this scenario discussed. We critically discuss the possibility that the observed properties of HB stars in NGC 6388 and NGC 6441 might be accounted for if these clusters possess a relatively minor population of helium-enriched stars. A technique is proposed to estimate the HB types of extragalactic globular clusters on the basis of integrated far-UV photometry. The importance of bright type II Cepheids as tracers of faint blue HB stars in distant systems is also emphasized. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyr, is also revisited. Taking into due account the evolutionary status of RR Lyr, the derived relation implies a true distance modulus to the LMC of ( m– M)0=18.44±0.11. Techniques providing discrepant slopes and zero points for the M V(RRL)–[Fe/H] relation are briefly discussed. We provide a convenient analytical fit to theoretical model predictions for the period change rates of RR Lyrae stars in globular clusters, and compare the model results with the available data. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are also investigated. [ABSTRACT FROM AUTHOR]

The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell region. Thus, the photospheric element abundances of these stars allow us to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We compare predicted element abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. A good qualitative and quantitative agreement is found for many species (He, C, N, O, Ne, F, Si, Ar) but discrepancies for others (P, S, Fe) point at shortcomings in stellar evolution models for AGB stars. Almost all of the chemical trace elements in these hot stars can only be identified in the UV spectral range. The Far Ultraviolet Spectroscopic Explorer and the Hubble Space Telescope played a crucial role for this research. [ABSTRACT FROM AUTHOR]

The stellar evolution code YREC is outlined with emphasis on its applications to helio- and asteroseismology. The procedure for calculating calibrated solar and stellar models is described. Other features of the code such as a non-local treatment of convective core overshoot, and the implementation of a parametrized description of turbulence in stellar models, are considered in some detail. The code has been extensively used for other astrophysical applications, some of which are briefly mentioned at the end of the paper. [ABSTRACT FROM AUTHOR]

We summarize the main physical assumptions and numerical procedures adopted by the FRANEC code to compute stellar models in all the evolutionary phases at hydrostatic and thermal equilibrium. An application to the Standard Solar Model is also briefly presented. [ABSTRACT FROM AUTHOR]

This paper presents the Geneva stellar evolution code with special emphasis on the modeling of solar-type stars. The basic input physics used in the Geneva code as well as the modeling of atomic diffusion is first discussed. The physical description of rotation is then presented. Finally, the modeling of magnetic instabilities and transport of angular momentum by internal gravity waves is briefly summarized. [ABSTRACT FROM AUTHOR]

The present paper provides a description of the oscillation code filou, its main features, type of applications it can be used for, and some representative solutions. The code is actively involved in CoRoT/ESTA exercises (this volume) for the preparation for the proper interpretation of space data from the CoRoT mission. Although CoRoT/ESTA exercises have been limited to the oscillations computations for non-rotating models, the main characteristic of filou is, however, the computation of radial and non-radial oscillation frequencies in presence of rotation. In particular, filou calculates (in a perturbative approach) adiabatic oscillation frequencies corrected for the effects of rotation (up to the second order in the rotation rate) including near degeneracy effects. Furthermore, filou works with either a uniform rotation or a radial differential rotation profile (shellular rotation), feature which makes the code singular in the field. [ABSTRACT FROM AUTHOR]

A short presentation of the Nice OScillations Code (NOSC) and of its general properties is given here. We described the physics and the various numerical tools, that we have developed to check the validity and the internal consistency of the frequency calculations for a given model. We present different examples of adiabatic calculations, with an estimation of the achieved internal consistency and numerical accuracy. [ABSTRACT FROM AUTHOR]

We describe the Garching Stellar Evolution Code. General features, treatment of the microphysics, details of the numerical solution, handling and particularities are discussed. The standard solar model serves as the most basic benchmark to test the accurateness of the code and is presented, too. [ABSTRACT FROM AUTHOR]

In this paper we present a grid of stellar evolution models, computed with an up-to-date physical description of the internal structure, using the Code d’Évolution Stellaire Adaptatif et Modulaire ( cesam). The evolutionary sequences span from the pre-main sequence to the beginning of the Red Giant Branch and cover an interval of mass typical for low and intermediate mass stars. The chemical composition (both helium and metal abundance) is the solar one. The frequencies of oscillation, computed for specific stellar models of the grid using the Porto Oscillations Code ( posc), are also provided. This work was accomplished in order to support the preparation of the CoRoT mission within the Evolution and Seismic Tools Activity (CoRoT/ESTA). On the other hand, the grid can also be used, more generally, to interpret the observational properties of either individual stars or stellar populations. The grids (data and documentation) can be found at . [ABSTRACT FROM AUTHOR]

We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT. [ABSTRACT FROM AUTHOR]

We compare the predictions of the FRANEC and CESAM stellar evolutionary codes for selected physical quantities used as input parameters in current asteroseismological calculations. The agreement is satisfactory but the effect of the remaining small discrepancies on the predicted oscillation frequencies should be carefully evaluated. [ABSTRACT FROM AUTHOR]

We present grids of stellar models and their associated oscillation frequencies that have been used by the CoRoT Seismology Working Group during the scientific preparation of the CoRoT mission. The stellar models have been calculated with the CESAM stellar internal structure and evolution code while the oscillation frequencies have been obtained from the CESAM models by means of the ADIPLS adiabatic oscillation programme. The grids cover a range of masses, chemical compositions and evolutionary stages corresponding to those of the CoRoT primary targets. The stellar models and oscillation frequencies are available on line through the Evolution and Seismic Tools Activity (ESTA) web site. [ABSTRACT FROM AUTHOR]

The forthcoming data expected from space missions such as CoRoT require the capacity of the available tools to provide accurate models whose numerical precision is well above the expected observational errors. In order to secure that these tools meet the specifications, a team has been established to test and, when necessary, to improve the codes available in the community. The CoRoT Evolution and Seismic Tool Activity (ESTA) has been set up with this mission. Several groups have been involved. The present paper describes the motivation and the organisation of this activity, providing the context and the basis for the presentation of the results that have been achieved so far. This is not a finished task as future even better data will continue to demand more precise and complete tools for asteroseismology. [ABSTRACT FROM AUTHOR]

A first part gives a summary of the main conclusions stemmed from the different comparisons reported in this book. One main conclusion is: with some care in the computations, one is able to obtain frequency differences between different computations which are smaller than required by Corot challenges. This is true for high frequency modes. Small frequency differences are much less easily obtained for low frequencies around the fundamental radial mode frequency. Care here means: having the same physics, same constants of physics, same input stellar parameters, computing models and oscillations with enough self numerical consistent accuracy. The ESTA group has built reference grids of models and associated oscillation frequencies and made them available to the community. In a second part of the present paper, a study case is considered in order to show the need and the use of such reference grids. Finally some perspectives concerning the remaining tasks are suggested. [ABSTRACT FROM AUTHOR]

The cesam code is a consistent set of programs and routines which perform calculations of 1D quasi-hydrostatic stellar evolution including microscopic diffusion of chemical species and diffusion of angular momentum. The solution of the quasi-static equilibrium is performed by a collocation method based on piecewise polynomials approximations projected on a B-spline basis; that allows stable and robust calculations, and the exact restitution of the solution, not only at grid points, even for the discontinuous variables. Other advantages are the monitoring by only one parameter of the accuracy and its improvement by super-convergence. An automatic mesh refinement has been designed for adjusting the localisations of grid points according to the changes of unknowns. For standard models, the evolution of the chemical composition is solved by stiffly stable schemes of orders up to four; in the convection zones mixing and evolution of chemical are simultaneous. The solution of the diffusion equation employs the Galerkin finite elements scheme; the mixing of chemicals is then performed by a strong turbulent diffusion. A precise restoration of the atmosphere is allowed for. [ABSTRACT FROM AUTHOR]

We present a grid of stellar models, obtained with the CLÉS evolutionary code, following the specification of ESTA-Task1, and the corresponding seismic properties, computed with the LOSC code. We provide a complete description of the corresponding files that will be available on the ESTA web-pages. [ABSTRACT FROM AUTHOR]

Planets result from a series of processes within a circumstellar disk. Evidence comes from the near planar orbits in the Solar System and other planetary systems, observations of newly formed disks around young stars, and debris disks around main-sequence stars. As planet-hunting techniques improve, we approach the ability to detect systems like the Solar System, and place ourselves in context with planetary systems in general. Along the way, new classes of planets with unexpected characteristics are discovered. One of the most recent classes contains super Earth-mass planets orbiting a few AU from low-mass stars. In this contribution, we outline a semi-analytic model for planet formation during the pre-main sequence contraction phase of a low-mass star. As the star contracts, the “snow line”, which separates regions of rocky planet formation from regions of icy planet formation, moves inward. This process enables rapid formation of icy protoplanets that collide and merge into super-Earths before the star reaches the main sequence. The masses and orbits of these super-Earths are consistent with super-Earths detected in recent microlensing experiments. [ABSTRACT FROM AUTHOR]

The formations of the blue straggler stars and the FK Com-type stars are unsolved problems in stellar astrophysics. One of the possibilities for their formations is from the coalescence of W UMa-type overcontact binary systems. Therefore, deep ( f > 50%), low-mass ratio ( q < 0.25) overcontact binary stars are a very important source to understand the phenomena of Blue Straggler/FK Com-type stars. Recently, 12 W UMa-type binary stars, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, V410 Aur, XY Boo, SX CrV, QX And, GSC 619-232, and AH Cnc, were investigated photometrically. Apart from TV Mus, XY boo, and GSC 619-232, new observations of the other 9 binaries were obtained. Complete light curves of the 10 systems, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, GSC 619-232, V410 Aur, XY Boo, and AH Cnc, were analyzed with the 2003 version of the W-D code. It is shown that all of those systems are deep ( f > 50%), low-mass ratio ( q < 0.25) overcontact binary stars. We found that the system GSC 619-232 has the highest degree of overcontact ( f = 93.4%). The derived photometric mass ratio of V857 Her, q = 0.0653, indicates that it is the lowest-mass ratio system among W UMa-type binaries. Of the 12 sample stars, long-term period changes of 11 systems were found. About 58% (seven) of the sample binaries show cyclic period oscillation. No cyclic period changes were discovered for the other 5 systems, which may be caused by the short observational time interval or by insufficient observations. Therefore, we think that all W UMa-type binary stars may contain cyclic period variations. By considering the long-term period changes (both increase and decrease) of those binary stars, we proposed two evolutionary scenarios evolving from deep, low-mass ratio overcontact binaries into Blue Straggler/FK Com-type stars. [ABSTRACT FROM AUTHOR]

A review is presented of the progress that has been made in the last 3 years towards quantifying the properties of high-mass detached and semi-detached eclipsing binaries in Local Group galaxies. Comparisons between these observational results on masses, radii, temperatures and luminosities for stars in detached binaries and evolution models for single stars at the appropriate metallicity are found to be very good. New evolution models for interacting binaries passing through case A mass exchange are being calculated, and indicate a requirement for some mass loss to find agreement with the observational data. The observational data on such semi-detached systems show similar properties to those in the Milky Way galaxy. The directly-determined distances to all these eclipsing binaries are proving to be most valuable for strengthening the distance scale amongst the Local Group galaxies. [ABSTRACT FROM AUTHOR]

We present new population synthesis calculations of close young neutron stars. In comparison with our previous investigation we use a different neutron star mass spectrum and different initial spatial and velocity distributions. The results confirm that most of ROSAT dim radioquiet isolated neutron stars had their origin in the Gould Belt. We predict that about several tens of young neutron stars can be identified in ROSAT All Sky Survey data at low galactic latitudes. Some of these sources also can have counterparts among EGRET unidentified sources. [ABSTRACT FROM AUTHOR]

AA Dor is an eclipsing, close, post common-envelope binary (PCEB) consisting of a sdOB primary star and an unseen secondary with an extraordinary small mass (M2 ≈ 0.066 M⊙)—formally a brown dwarf. The brown dwarf may have been a former planet which survived a common envelope (CE) phase and has even gained mass. A recent determination of the components' masses from results of NLTE spectral analysis and subsequent comparison to evolutionary tracks shows a discrepancy compared to masses derived from radial-velocity and the eclipse curves. Phase-resolved high-resolution and high-SN spectroscopy was carried out in order to investigate this problem. We present results of a NLTE spectral analysis of the primary, an analysis of its orbital parameters, and discuss possible evolutionary scenarios. [ABSTRACT FROM AUTHOR]

Horizontal branch stars should show significant differential rotation with depth. Models that assume systematic angular momentum exchange in the convective envelope and local conservation of angular momentum in the core produce HB models that preserve a rapidly rotating core. A direct probe of core rotation is available. The nonradial pulsations of the EC14026 stars frequently show rich pulsation spectra. Thus their pulsations probe the internal rotation of these stars, and should show the effects of rapid rotation in their cores. Using models of sdB stars that include angular momentum evolution, we explore this possibility and show that some of the sdB pulsators may indeed have rapidly rotating cores. [ABSTRACT FROM AUTHOR]