- ID:
- ivo://CDS.VizieR/J/A+A/507/1409
- Title:
- Models for dynamically dissolving star clusters
- Short Name:
- J/A+A/507/1409
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The dynamical escape of stars from star clusters affects the shape of the stellar mass function (MF) in these clusters, because the escape probability of a star depends on its mass. This is found in N-body simulations and has been approximated in analytical cluster models by fitting the evolution of the MF. Both approaches are naturally restricted to the set of boundary conditions for which the simulations were performed. The objective of this paper is to provide and to apply a simple physical model for the evolution of the MF in star clusters for a large range of the parameter space. It should also offer a new perspective on the results from N-body simulations. A simple, physically self-contained model for the evolution of the stellar MF in star clusters is derived from the basic principles of two-body encounters and energy considerations. It is independent of the adopted mass loss rate or initial mass function (IMF), and contains stellar evolution, stellar remnant retention, dynamical dissolution in a tidal field, and mass segregation. The evolution of the MF affects the integrated properties of star clusters. This data catalogue provides such quantities and also lists the evolution of the MF slope in certain mass ranges.
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- ID:
- ivo://CDS.VizieR/J/A+A/581/A15
- Title:
- Models for massive low-Z rotating single stars
- Short Name:
- J/A+A/581/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A good understanding of low-metallicity environments requires a detailed theoretical comprehension of the evolution of their massive stars. Our models can be used to interpret observations of local star-forming dwarf galaxies and high-redshift galaxies, as well as the metal-poor components of our Milky Way and its globular clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A132
- Title:
- Models for massive stars in the SMC
- Short Name:
- J/A+A/625/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of massive stars is strongly influenced by internal mixing processes such as semiconvection, convective core overshooting, and rotationally induced mixing. None of these processes are currently well constrained. We investigate models for massive stars in the Small Magellanic Cloud (SMC), for which stellar-wind mass loss is less important than for their metal-rich counterparts. We aim to constrain the various mixing efficiencies by comparing model results to observations. For this purpose, we use the stellar-evolution code MESA to compute more than 60 grids of detailed evolutionary models for stars with initial masses of 9...100M_{sun}_, assuming different combinations of mixing efficiencies of the various processes in each grid. Our models evolve through core hydrogen and helium burning, such that they can be compared with the massive main sequence and supergiant population of the SMC. We find that for most of the combinations of the mixing efficiencies, models in a wide mass range spend core-helium burning either only as blue supergiants, or only as red supergiants. The latter case corresponds to models that maintain a shallow slope of the hydrogen/helium (H/He) gradient separating the core and the envelope of the models. Only a small part of the mixing parameter space leads to models that produce a significant number of blue and red supergiants, which are both in abundance in the SMC. Some of our grids also predict a cut-o in the number of red supergiants above logL/L_{sun}_=5...5.5. Interestingly, these models contain steep H/He gradients, as is required to understand the hot, hydrogen-rich Wolf-Rayet stars in the SMC. We find that unless it is very fast, rotation has a limited effect on the H/He profiles in our models. While we use specific implementations of the considered mixing processes, they comprehensively probe the two firstorder structural parameters, the core mass and the H/He gradient in the core-envelope interface. Our results imply that in massive stars, mixing during the main-sequence evolution leads to a moderate increase in the helium core masses, and also that the H/He gradients above the helium cores become very steep. Our model grids can be used to further refine the various mixing efficiencies with the help of future observational surveys of the massive stars in the SMC, and thereby help to considerably reduce the uncertainties in models of massive star evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/553/A24
- Title:
- Models for rotating stars
- Short Name:
- J/A+A/553/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- B-type stars are known to rotate at various velocities, including very fast rotators near the critical velocity as the Be stars. In this paper, we provide stellar models covering the mass range between 1.7 to 15M_{sun}_, which includes the typical mass of known Be stars, at Z=0.014, 0.006 and 0.002 and for an extended range of initial velocities on the zero-age main sequence. We use the Geneva stellar-evolution code including the effects of shellular rotation and with a numerical treatment that has been improved in order for the code to track in a precise way the variation of the angular momentum content of the star as it changes under the influence of radiative winds and/or mechanical mass loss. We discuss the impact of the initial rotation rate on the tracks in the Hertzsprung-Russell diagram, the main-sequence (MS) lifetimes, the evolution of the surface rotation and abundances, as well as on the ejected masses of various isotopes. Among the new results obtained from the present grid we have that: 1) fast rotating stars with initial masses around 1.7M_{sun}_ present at the beginning of the core hydrogen-burning phase quite small convective cores with respect to their slowly rotating counterparts. This fact may be interesting to keep in mind in the frame of the asteroseismic studies of such stars; 2) the contrast between the core and surface angular velocity is higher in slower rotating stars. The values presently obtained are quite in the range of the very few values obtained for B-type stars from asteroseismology; 3) at Z=0.002, the stars in the mass range of 1.7 to 3M_{sun}_ with a mean velocity on the MS of the order of 150km/s show N/H enhancement superior to 0.2dex at mid-MS, and superior to 0.4dex at the end of the MS phase. At solar metallicity the corresponding values are below 0.2dex at any time in the MS. An extended database of stellar models containing 270 evolutionary tracks is provided to the community.
- ID:
- ivo://CDS.VizieR/J/MNRAS/425/1696
- Title:
- Models of a young star cluster ejecta
- Short Name:
- J/MNRAS/425/1696
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have computed with a fine time grid the evolution of the elemental abundances of He, C, N and O ejected by young (t<20Myr) and massive (M=10^6^M_{sun}_) coeval stellar cluster with a Salpeter initial mass function (IMF) over a wide range of initial abundances. Our computations incorporate the mass loss from massive stars (M>=30M_{sun}_) during their wind phase including the Wolf-Rayet phase and the ejecta from the core-collapse supernovae. We find that during the Wolf-Rayet phase (t<5Myr) the cluster ejecta composition suddenly becomes vastly overabundant in N for all initial abundances and in He, C and O for initial abundances higher than one-fifth of the solar. The C and O abundances in the cluster ejecta can reach over 50 times the solar value with important consequences for the chemical and hydrodynamical evolution of the surrounding interstellar medium.
- ID:
- ivo://CDS.VizieR/J/A+AS/126/39
- Title:
- Models of circumstellar dust shells
- Short Name:
- J/A+AS/126/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Main properties of the steady state hydrodynamical models of circumstellar gas/dust shells around late type giants, computed for different stellar parameters (mass, luminosity, effective temperature) and dust composition (astronomical silicates, graphite, or amorphous carbon, with properties given in Tab.1 and Fig.1). Each table lists the results as a function of the adopted mass loss rate for fixed stellar parameters and dust properties. Tables 2 - 11 are related to Figures 2 - 11: Each of the figures shows the velocity structure and the resulting spectral energy distribution for a subset of models listed in the respective table.
- ID:
- ivo://CDS.VizieR/J/ApJ/690/20
- Title:
- Models of the AGN and black hole populations
- Short Name:
- J/ApJ/690/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct evolutionary models of the populations of active galactic nuclei (AGNs) and supermassive black holes, in which the black hole mass function grows at the rate implied by the observed luminosity function, given assumptions about the radiative efficiency and the luminosity in Eddington units. We draw on a variety of recent X-ray and optical measurements to estimate the bolometric AGN luminosity function and compare to X-ray background data and the independent estimate of Hopkins et al. to assess remaining systematic uncertainties. The integrated AGN emissivity closely tracks the cosmic star-formation history, suggesting that star formation and black hole growth are closely linked at all redshifts.
- ID:
- ivo://CDS.VizieR/J/A+A/558/A131
- Title:
- Model spectra of hot stars at the pre-SN stage
- Short Name:
- J/A+A/558/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the fundamental properties of core-collapse Supernova (SN) progenitors from single stars at solar metallicity. We combine Geneva stellar evolutionary models with initial masses of Mini=20-120M_{sun}_ with atmospheric/wind models using CMFGEN. We provide synthetic photometry and high-resolution spectra of hot stars at the pre-SN stage. For Mini=9-20M_{sun}_, we supplement our analysis using publicly available MARCS model atmospheres of RSGs. We employ observational criteria of spectroscopic classification and find that massive stars, depending on Mini and rotation, end their lives as red supergiants (RSG), yellow hypergiants (YHG), luminous blue variables (LBV), and Wolf-Rayet (WR) stars of the WN and WO spectral types. For rotating models, we obtain the following types of SN progenitors: WO1-3 (Mini<=32M_{sun}_), WN10-11 (25<Mini< 32M_{sun}_), LBV (20<=Mini<25M_{sun}_), G1 Ia+ (18<Mini<20M_{sun}_), and RSGs (9<=Mini<=18M_{sun}_). For non-rotating models, we find spectral types WO1-3 (Mini>40M_{sun}_), WN7-8 (25<Mini<=40M_{sun}_), WN11h/LBV (20<Mini<=25M_{sun}_), and RSGs (9<=Mini<=20M_{sun}_). Our rotating models indicate that SN IIP progenitors are all RSG, SN IIL/b progenitors are 56% LBVs and 44% YHGs, SN Ib progenitors are 96% WN10-11 and 4% WOs, and SN Ic progenitors are all WO stars. We find that not necessarily the most massive and luminous SN progenitors are the brighter ones in a given filter. We show that SN IIP progenitors (RSGs) are bright in the RIJHK_S filters and faint in the UB filters. SN IIL/b progenitors (LBVs and YHGs), and SN Ib progenitors (WNs) are relatively bright in optical/IR filters, while SN Ic progenitors (WOs) are faint in all optical filters. We argue that SN Ib and Ic progenitors from single stars should be undetectable in the available pre-explosion images with the current magnitude limits, in agreement with observational results.
- ID:
- ivo://CDS.VizieR/J/A+A/463/455
- Title:
- Nearby early-type gal. with ionized gas. III.
- Short Name:
- J/A+A/463/455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper is devoted to the study of the underlying stellar population of a sample of 62 nearby early-type galaxies, predominantly located in low density environments, a large fraction of which showing emission lines. Ages, metallicities and [{alpha}/Fe] ratios have been derived through the comparison of Lick indices measured at different galacto-centric distances (7 apertures and 4 gradients) with new Simple Stellar Population (SSP) models which account for the presence of alpha/Fe-enhancement. The SSPs cover a wide range of ages (10^8^-16x10^9^yr), metallicities (0.0004<=Z<=0.05) and [{alpha}/Fe] ratios (0-0.8). To derive the stellar population parameters we use an algorithm that provides, together with the most likely solution in the (age, Z, [{alpha}/Fe]) space, also the probability density function along the age-metallicity degeneracy. We derive a large spread in age, with SSP-equivalent ages ranging from a few to 15Gyrs. Age does not show any significant trend with central velocity dispersion sigma_c_ but E galaxies appear on average older than lenticulars.
- ID:
- ivo://CDS.VizieR/J/A+A/440/647
- Title:
- New grids of stellar models. II.
- Short Name:
- J/A+A/440/647
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New stellar models spefically designed for the Small Magellanic Cloud are presented in this paper. In order to take into account the uncertainties in the metal content we computed two grids with different metallicities: Z=0.002 and Z=0.004. The covered mass range is from 0.8 up to 125M_{sun} and the models are followed until the exhaustion of carbon in the core, for the more massive ones. We have introduced a recent measurement of the nuclear rate ^14^N(p,{gamma})^15^O. A comparison among models with the old and new rate was carried out revealed that the former are slightly hotter than the first ones. Such differences depend on the mass range. The opacities, the equation of state, the remaining nuclear reactions rates, the core overshooting parameterization and the convective transport of energy are the same as discussed previously by us. We also give, besides the classical evolutionary models outputs, the internal structure constants needed to investigate apsidal motion and tidal evolution in close binaries. This aspect acquires importance in the light of recent investigations on circularization and synchronization levels in binary systems belonging to the Magellanic Clouds. The role of rotation can also be investigated through the gravity-darkening exponents which allow us to compute the brightness distribution of a given stellar surface.
