We present a new stellar evolution code and a set of results, demonstrating its capability at calculating full evolutionary tracks for a wide range of masses and metallicities. The code is fast and efficient, and is capable of following through all evolutionary phases, without interruption or human intervention. It is meant to be used also in the context of modeling the evolution of dense stellar systems, for performing live calculations for both normal star models and merger-products.
The code is based on a fully implicit, adaptive-grid numerical scheme that solves simultaneously for structure, mesh and chemical composition. Full details are given for the treatment of convection, equation of state, opacity, nuclear reactions and mass loss.
Results of evolutionary calculations are shown for a solar model that matches the characteristics of the present sun to an accuracy of better than 1%; a 1 Msun model for a wide range of metallicities; a series of models of stellar populations I and II, for the mass range 0.25 to 64 Msun, followed from pre-main-sequence to a cool white dwarf or core collapse. An initial final-mass relationship is derived and compared with previous studies. Finally, we briefly address the evolution of non-canonical configurations, merger-products of low-mass main-sequence parents.
We present a database of the latest stellar models of the $Y^2$ (Yonsei-Yale) collaboration. This database contains the stellar evolutionary tracks from the pre-main-sequence birthline to the helium core flash that were used to construct the $Y^2$ isochrones. We also provide a simple interpolation routine that generates stellar tracks for given sets of parameters (metallicity, mass, and $α$-enhancement).
This is the second in a series of papers presenting an analytical model for the evolution of FRII radio sources. In this paper we evaluate the expected radio emission from a radio source incorporating energy loss processes for the relativistic electrons. By combining these results with our earlier dynamical model we calculate evolutionary tracks through the Power-Linear size diagram. These tracks are in good agreement with the observed distribution of sources in this diagram. The effects of different forms for the evolution of the magnetic field in the cocoon, the redshift of the source, the e…
Evolutionary tracks are of key importance for the understanding of star formation. Unfortunately, tracks published by various groups differ so that it is fundamental to have observational tests. In order to do this, we intend to measure the masses of the two components of the Pre-Main Sequence binary HD113449 by combining radial velocity measurements taken with HARPS, with infrared interferometric data using AMBER on the VLTI. The spectroscopic orbit that has already been determined, combined with the first AMBER measurement, allows us to obtain a very first estimation of the inclination of th…
We present a large grid of stellar evolutionary tracks, which are suitable to modelling star clusters and galaxies by means of population synthesis. The tracks are presented for the initial chemical compositions [Z=0.0004, Y=0.23], [Z=0.001, Y=0.23], [Z=0.004, Y=0.24], [Z=0.008, Y=0.25], [Z=0.019, Y=0.273] (solar composition), and [Z=0.03, Y=0.30]. They are computed with updated opacities and equation of state, and a moderate amount of convective overshoot. The range of initial masses goes from 0.15 M_sun to 7 M_sun, and the evolutionary phases extend from the zero age main sequence (ZAMS) til…
We complement our study of alpha/Fe enhanced stellar population models of Lick absorption indices (Thomas et al. 2003) by comparing two sets of alpha/Fe enhanced models. In both models the impact on Lick indices due to alpha/Fe enhancement is accounted for through a modification of the stellar absorption line-strengths using the response functions of Tripicco & Bell (1995). One set of models, however, uses solar-scaled, the other alpha/Fe enhanced stellar evolutionary tracks. Since the alpha/Fe enhanced tracks are hotter than the solar-scaled ones (Salasnich et al. 2000), the correspondent ste…
We present four large sets of evolutionary tracks for stars with initial chemical compositions [Y=0.250, Z=0.008], [Y=0.273, Z=0.019], [Y=0.320, Z=0.040] and [Y=0.390, Z=0.070] and enhancement of alpha elements with respect to the solar pattern. The major improvement with respect to previous similar calculations is that we use consistent opacities - i.e. computed with the same chemical composition as adopted in the stellar models - over the whole relevant range of temperatures. For the same initial chemical compositions [Y,Z] and otherwise identical input physics we present also new evolutiona…
We analyse pre-Main Sequence evolutionary tracks for low mass stars with masses $m \le 1.4 \msol$ based on the Baraffe et al. (1998) input physics. We also extend the recent Chabrier et al. (2000) evolutionary models based on dusty atmosphere to young brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to molecular line lists, convection and initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages $\simle$ 1 Myr. We find a significant sensitivity of atmosphere profiles to the treatment of convection at low gravi…
We present new photometric and spectroscopic measurements for the unique, young, low-mass evolutionary track calibrator AB Dor C. While the new Ks photometry is similar to that previously published in Close et al. (2005) the spectral type is found to be earlier. Based on new H & K IFS spectra of AB Dor C (Thatte et al. 2007; paper 1) we adopt a spectral type of M5.5+/-1.0 for AB Dor C. This is considerably earlier than the M8+/-1 estimated in Close et al. (2005) and Nielsen et al. (2005) yet is consistent with the M6+/-1 independently derived by Luhman & Potter (2005). However, the spectrum pr…
We present an astrometric/spectroscopic orbital solution for the pre-main-sequence binary NTT 045251+3016. Our measurements for the primary and secondary masses are 1.45 +/- 0.19 M_sun and 0.81 +/- 0.09 M_sun, respectively, and 145 +/- 8 pc for the distance of the system, consistent with prior estimates for the Taurus-Auriga star-forming region. The evolutionary tracks of D'Antona & Mazzitelli (1997), Baraffe et al. (1998), and Palla & Stahler (1999) are tested against these dynamical mass measurements. Due to the intrinsic color/T_eff variation within the K5 spectral class, each pre-main-sequ…
We report the discovery of a double-lined, spectroscopic, eclipsing binary in the Orion star-forming region. We analyze the system spectroscopically and photometrically to empirically determine precise, distance-independent masses, radii, effective temperatures, and luminosities for both components. The measured masses for the primary and secondary, accurate to ~1%, are 1.01 Msun and 0.73 Msun, respectively; thus the primary is a definitive pre-main-sequence solar analog, and the secondary is the lowest-mass star yet discovered among pre-main-sequence eclipsing binary systems. We use these fun…
The time evolution of `fiducial' radio sources derived from fitting the dynamical model of Kaiser et al. (1997) is compared with the observational data for the `clan' sources found in the sample of giant and normal-size FRII-type sources published Paper I (Machalski et al. 2004). Each `clan' comprises 3, 4 or 5 sample sources having similar values of the two basic physical parameters: the jet power Q_{0} and central density of the galaxy nucleus rho_{0} (determined in Paper I) but different ages, radio luminosities and axial ratios. These sources are considered as the `same' source observed at…
Using the Hipparcos data, absolute magnitudes and thus the evolutionary status for the group of lambda Bootis stars were derived. The origin of this small group of non-magnetic, chemically peculiar stars, still remains a matter of debate. Using new evolutionary tracks, an age determination could be provided to distinguish between the two competing theories - the diffusion/mass-loss and the accretion. The results establish the members of this group as objects which are very close to the Main Sequence. This is supported by Pre-Main Sequence evolutionary tracks as well as by observational results…
Seventy-two grids of stellar evolutionary tracks, along with the capability to generate isochrones and luminosity/color functions from them, are presented in this investigation. Sixty of them extend (and encompass) the sets of models reported by VandenBerg et al. (2000, ApJ, 532, 430) for 17 [Fe/H] values from -2.31 to -0.30 and alpha-element abundances corresponding to [alpha/Fe] = 0.0, 0.3, and 0.6 (at each iron abundance) to the solar metallicity and to sufficiently high masses (up to ~2.2 solar masses) that isochrones may be computed for ages as low as 1 Gyr. The remaining grids contain tr…
Three binary systems in the Hyades open cluster (51 Tau, V818 Tau, and $θ^2$ Tau}, with known metallicity and good Johnson photometric data are used to test the validity of three independent sets of stellar evolutionary tracks. A statistical method is described and applied to the colour-magnitude diagram of the six selected components, giving rise to $χ^2$-contours in the metallicity--age plane. The effects of the Hipparcos parallaxes on these confidence regions are studied in detail for these binaries through a comparison with very accurate but older orbital parallaxes. There are no significa…
Ranging from track interpolation techniques through model atmospheres to the stochastic nature of the IMF, there are many uncertainties which need to be taken into account when modelling HR diagrams or performing population synthesis, particularly if comparison with actual data is sought. In this paper, we highlight (1) the problem of discontinuities along evolutionary tracks of massive stars (M> 8 Mo), showing that inconsistencies appear in the computation of the corresponding isochrones, and (2) the sampling fluctuations produced by the stochastic nature of the IMF, presenting a statistical …
[abridged] We have assembled a database of stars having both masses determined from measured orbital dynamics and sufficient spectral and photometric information for their placement on a theoretical HR diagram. Our sample consists of 115 low mass (M < 2.0 Msun) stars, 27 pre-main sequence and 88 main sequence. We use a variety of available pre-main sequence evolutionary calculations to test the consistency of predicted stellar masses with dynamically determined masses. Despite substantial improvements in model physics over the past decade, large systematic discrepancies still exist between emp…
Any stellar system with a star formation history (SFH) more extended than a massive star's lifetime will be composite in metallicity. Our method of chemically consistent evolutionary synthesis tries to account for the increasing initial metallicity of successive generations of stars. Using various sets of input physics for a range of metallicities $10^{-4} \leq Z \leq 0.05$ we keep track of the ISM enrichment and follow successive generations of stars using stellar evolutionary tracks, yields, model atmosphere spectra, index calibrations, etc., appropriate for their respective initial metallic…
The rates at which mass accumulates into protostellar cores can now be predicted in numerical simulations. Our purpose here is to develop methods to compare the statistical properties of the predicted protostars with the observable parameters. This requires (1) an evolutionary scheme to convert numerically-derived mass accretion rates into evolutionary tracks and (2) a technique to compare the tracks to the observed statistics of protostars. Here, we use a 3D-Kolmogorov-Smirnov test to quantitatively compare model evolutionary tracks and observations of Class0 protostars. We find that the wide…
Two problems about the faintest Small Magellanic Cloud (SMC) Cepheids are addressed. On one hand evolutionary tracks fail to cross the Cepheid Instability Strip for the highest magnitudes (i.e. I-mag~17) where Cepheids are observed; Mass-Luminosity relations (ML) obtained from evolutionary tracks disagree with Mass-Luminosity relations derived from observations. We find that the above failures concern models built with standard input physics as well as with non-standard ones. The present work suggests that towards highest magnitudes, Cepheids stars undergo a selection effect caused by evolutio…
A parameter study of the spectral evolution of a typical post-AGB star, with particular emphasis on the evolution of the infrared colours, is presented. The models are based on the latest evolutionary tracks for hydrogen burning post-AGB stars. For such tracks the evolutionary rate is very dependent on the assumed mass loss rate as a function of time. We investigate this effect by modifying the mass loss prescription. The newly calculated evolutionary rates and density distributions are used to model the spectral evolution of a post-AGB star with the photo-ionization code Cloudy, including dus…
The Teff location of Pre-Main Sequence (PMS) evolutionary tracks depends on the treatment of over-adiabaticity. Since the convection penetrates into the stellar atmosphere, also the treatment of convection in the modeling of stellar atmospheres will affect the location of the Hayashi tracks. We present new non-grey PMS tracks for Teff>4000 K. We compute several grids of evolutionary tracks varying: 1. the treatment of convection: either the Mixing Length Theory (MLT) or Canuto et al. (1996, CGM) treatment; 2.the atmospheric boundary conditions: we use the new Vienna grids of ATLAS9 atmospheres…
We expand upon the results of Close et al. 2005 regarding the young, low-mass object AB Dor C and its role as a calibration point for theoretical tracks. We present an improved spectral reduction and a new orbital solution with two additional epochs. Our improved analysis confirms our spectral type of M8 (+/- 1) and mass of 0.090+/-0.003 solar masses for AB Dor C. Comparing the results for AB Dor C with other young, low-mass objects with dynamical masses we find a general trend where current evolutionary models tend to over-predict the temperature (or under-predict the mass) for low mass stars…
We present a new set of theoretical evolutionary synthesis models, PopStar. This grid of Single Stellar Populations covers a wide range in both, age and metallicity. The models use the most recent evolutionary tracks together with the use of new NLTE atmosphere models for the hot stars (O, B, WR, post-AGB stars, planetary nebulae) that dominate the stellar cluster's ionizing spectra. The results of the models in VO format can be used through VOSpec.
We analyze with hydrodynamical simulations the evolution of galaxy clusters in a cosmological environment. Power ratios (Buote \& Tsai 1995) are used to quantitatively relate cluster morphologies to their dynamical states. The simulated clusters follow the same ``evolutionary track'' obeyed by a sample of low-redshift $(z<0.2)$ ROSAT PSPC clusters (Buote \& Tsai 1996) indicating that the detailed evolution of individual simulated clusters is consistent with observed clusters. However, the distribution of simulated clusters (for $Ω=1$ standard Cold Dark Matter) along the evolutionary track at t…
Evolutionary population synthesis models for a wide range of metallicities, ages, star formation histories, and Horizontal Branch morphologies, including blue morphologies at high metallicity, are computed. The energetics of the post Main Sequence evolutionary phases are evaluated with the fuel consumption theorem. The impact on the models of the stellar evolutionary tracks is assessed. We find modest differences in synthetic broad-band colours as induced by the use of different tracks in our code (e.g. d(V-K) ~ 0.08 mag; d(B-V) ~ 0.03 mag). These differences are smaller than the scatter among…
Stellar models have been computed for stars having [Fe/H] = 0.0 and -2.0 to determine the effects of using boundary conditions derived from the latest MARCS model atmospheres. The latter were fitted to the interior models at both the photosphere and at tau = 100, and at least for the 0.8-1.0 solar mass stars considered here, the resultant evolutionary tracks were found to be nearly independent of the chosen fitting point. Particular care was taken to treat the entire star as consistently as possible; i.e., both the interior and atmosphere codes assumed the same abundances and the same treatmen…
Aims. Determination of the present evolutionary state and the restrictions on the initial mass ratios of RZ Cas, KO Aql and S Equ. Methods. Comparison of mass gaining stars with evolutionary models of single stars with the same mass and subsequent comparison with accretion tracks from simultaneous conservative binary evolution. Results. The gainers are in an early main sequence stage (Xc greater than 0.5), with KO Aql being almost unevolved (assuming quasi-thermal equilibrium). The initial donor/gainer mass ratios Mdi/Mgi must be larger than three to obtain the present mass and luminosity of t…
We analyze the robustness of H--deficient post--AGB tracks regarding previous evolution of their progenitor stars and the constitutive physics of the remnants. Our motivation is a recent suggestion of Werner & Herwig (2006) that previous evolution should be important in shaping the final post--AGB track and the persisting discrepancy between asteroseismological and spectroscopical mass determinations. This work is thus complementary to our previous work (Miller Bertolami & Althaus 2006) and intends to shed some light on the uncertainty behind the evolutionary tracks presented there. We compute…
We present the Pre-Main-Sequence (PMS) evolutionary tracks of stars with 0.0065~5.0Ms. The models were evolved from the PMS stellar birthline to the onset of hydrogen burning in the core. The convective turnover timescales which enables an observational test of theoretical model, particulary in the stellar dynamic activity, are also calculated. All models have Sun-like metal abundances, typically considered as the stars in the Galactic disk and the star formation region of Population I star. The convection phenomenon is treated by the usual mixing length approximation. All evolutionary tracks …
We derive detailed theoretical models for 1074 nearby stars from the SPOCS (Spectroscopic Properties of Cool Stars) Catalog. The California and Carnegie Planet Search has obtained high-quality echelle spectra of over 1000 nearby stars taken with the Hamilton spectrograph at Lick Observatory, the HIRES spectrograph at Keck, and UCLES at the Anglo Australian Observatory. A uniform analysis of the high-resolution spectra has yielded precise stellar parameters, enabling systematic error analyses and accurate theoretical stellar modeling. We have created a large database of theoretical stellar evol…
Various scenarios of contact binary evolution have been proposed in the past, giving hints of (sometimes contradictory) evolutionary sequence connecting A-type and W-type systems. As the components of close detached binaries approach each other and contact binaries are formed, following evolutionary paths transform them into systems of two categories: A-type and W-type. The systems evolve in a similar way but under slightly different circumstances. The mass/energy transfer rate is different, leading to quite different evolutionary results. An alternative scenario of evolution in contact is pre…
As a tool to interpret nearby and high redshift galaxy data from optical to K-band we present our chemically consistent spectrophotometric evolutionary synthesis models. These models take into account the increasing initial metallicity of successive stellar generations using recently published metallicity dependent stellar evolutionary tracks, stellar yields and model atmosphere spectra. The influence of the metallicity is analysed. Dust absorption is included on the basis of gas content and abundance as it varies with time and galaxy type. We compare our models with IUE template spectra and a…
Depending on the outcome of pre-CV formation, mass transfer may set in under thermally unstable conditions in a significant number of systems. Full computations have shown that such an early phase of thermal-timescale mass transfer usually leads to ordinary looking CVs, but these do also show some unusual properties (e.g. chemical anomalies in later stages). Rather than investigating the common envelope evolution leading to pre-CVs, we study the properties of multiple evolutionary tracks starting with a phase of thermal-timescale mass transfer. Apart from fitting unusual CVs (like AE Aqr), glo…
We construct evolutionary synthesis models for simple stellar populations using the evolutionary tracks from the Padova group (1993, 1994), theoretical colour calibrations from Lejeune et al., and fit functions for stellar atmospheric indices from Worthey et al.. A Monte-Carlo technique allows us to obtain a smooth time evolution of both broad band colours in UBVRIK and a series of stellar absorption features for Single Burst Stellar Populations ({\bf SSPs}). We present colours and indices for SSPs with ages from $1 \cdot 10^9$ yrs to $1.6 \cdot 10^{10}$ yrs and metallicities $[M/H]$ = -2.3, -…
We supplement current evolutionary computations concerning Magellanic Cloud stars by exploring the evolutionary behavior of canonical stellar models (i.e.,with inefficient core overshooting) with metallicities suitable for stars in the Clouds. After discussing the adequacy of the adopted evolutionary scenario, we present evolutionary sequences as computed following a selected sample of stellar models in the mass range 0.8-8 Mo from the Main Sequence till the C ignition or the onset of thermal pulses in the advanced Asymptotic Giant Branch phase. On this basis, cluster isochrones covering the r…
We supplement recent evolutionary computations of canonical stellar models (i.e. with inefficient core overshooting) with Z=0.0002, 0.0004, 0.0006, 0.001, 0.004, 0.008 and suitable assumptions about the original He content. Evolutionary results have been compared with observational data in order to properly calibrate the efficiency of the surface convection. On this basis, we follow the evolution of stellar models in the mass range 0.6 to 11 M$_{\odot}$ from the Main Sequence (MS) until C ignition or the onset of thermal pulses, presenting cluster isochrones covering the range of ages from 20 …
We present a library of 1654 high-resolution stellar spectra, with a sampling of 0.3 A and covering the wavelength range from 3000 A ~ to 7000 A The library was computed with the latest improvements in stellar atmospheres, incorporating non-LTE line-blanketed models for hot, massive (Teff >= 27500 K) and line-blanketed models for cool (3000 K =< Teff =< 4500 K) stars. The total coverage of the grid is 3000 K =< Teff =< 55000 K and -0.5 =< log g =< 5.5, for four chemical abundance values: twice solar, solar, half solar and 1/10 solar. Evolutionary synthesis models using this library are present…
We present seven evolutionary tracks for low-mass white dwarfs with helium cores, ranging in mass from 0.179 to 0.414 Msol. We generated the pre-white dwarf models from a 1 Msol sequence extending up to the tip of its red-giant branch by applying high mass-loss rates at appropriate positions, and we followed their evolution across the Hertzsprung-Russell diagram and down the cooling path. We discuss the internal structures and cooling properties of these new models and compare them with those of recently published models for low-mass white dwarfs which are based on simplified initial configura…
We have developed a new evolutionary synthesis code, which incorporates the output from chemical evolution models. We compare results of this new code with other published codes, and we apply it to the irregular galaxy NGC 1560 using sophisticated chemical evolution models. The code makes important contributions in two areas: a) the building of synthetic populations with time-dependent star formation rates and stellar populations of different metallicities; b) the extension of the set of stellar tracks from the Geneva group by adding the AGB phases for $m_i/M_\odot \geq 0.8$ as well as the ver…
