- ID:
- ivo://CDS.VizieR/J/A+A/557/A106
- Title:
- Evolution and CNO yields of Z=10^-5^ stars
- Short Name:
- J/A+A/557/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our main goals are to get a deeper insight into the evolution and final fates of intermediate-mass, extremely metal-poor (EMP) stars. We also aim to investigate the C, N, and O yields of these stars. Using the Monash University Stellar Evolution code MONSTAR we computed and analysed the evolution of stars of metallicity Z=10^-5^ and masses between 4 and 9M_{sun}_, from their main sequence until the late thermally pulsing (super)asymptotic giant branch, TP-(S)AGB phase.
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- ID:
- ivo://CDS.VizieR/J/ApJ/797/44
- Title:
- Evolution and nucleosynthesis of AGB stars
- Short Name:
- J/ApJ/797/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar evolutionary tracks and nucleosynthetic predictions for a grid of stellar models of low- and intermediate-mass asymptotic giant branch (AGB) stars at Z=0.001 ([Fe/H]=-1.2). The models cover an initial mass range from 1 M_{sun}_ to 7 M_{sun}_. Final surface abundances and stellar yields are calculated for all elements from hydrogen to bismuth as well as isotopes up to the iron group. We present the first study of neutron-capture nucleosynthesis in intermediate-mass AGB models, including a super-AGB model, of [Fe/H]=-1.2. We examine in detail a low-mass AGB model of 2 M_{sun}_ where the ^13^C({alpha},n)^16^O reaction is the main source of neutrons. We also examine an intermediate-mass AGB model of 5 M_{sun}_ where intershell temperatures are high enough to activate the ^22^Ne neutron source, which produces high neutron densities up to ~10^14^ n/cm^3^. Hot bottom burning is activated in models with M>=3 M_{sun}_. With the 3 M_{sun}_ model, we investigate the effect of varying the extent in mass of the region where protons are mixed from the envelope into the intershell at the deepest extent of each third dredge-up. We compare the results of the low-mass models to three post-AGB stars with a metallicity of [Fe/H]~-1.2. The composition is a good match to the predicted neutron-capture abundances except for Pb and we confirm that the observed Pb abundances are lower than what is calculated by AGB models.
- ID:
- ivo://CDS.VizieR/J/ApJ/696/797
- Title:
- Evolution and yields of low-mass AGB stars
- Short Name:
- J/ApJ/696/797
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The envelope of thermally pulsing asymptotic giant branch (TP-AGB) stars undergoing periodic third dredge-up (TDU) episodes is enriched in both light and heavy elements, the ashes of a complex internal nucleosynthesis involving p, {alpha}, and n captures over hundreds of stable and unstable isotopes. In this paper, new models of low-mass AGB stars (2M_{sun}_), with metallicity ranging between Z=0.0138 (the solar one) and Z=0.0001, are presented. Main features are (1) a full nuclear network (from H to Bi) coupled to the stellar evolution code, (2) a mass loss-period-luminosity relation, based on available data for long-period variables, and (3) molecular and atomic opacities for C- and/or N-enhanced mixtures, appropriate for the chemical modifications of the envelope caused by the TDU. For each model, a detailed description of the physical and chemical evolutions is presented; moreover, we present a uniform set of yields, comprehensive of all chemical species (from hydrogen to bismuth).
- ID:
- ivo://CDS.VizieR/J/A+A/647/A13
- Title:
- Evolutionary models for main-sequence phase
- Short Name:
- J/A+A/647/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The identification of stellar-mass black-hole mergers with up to 80M_{sun}_ as powerful sources of gravitational wave radiation led to increased interest in the physics of the most massive stars. The largest sample of possible progenitors of such objects, very massive stars (VMS) with masses up to 300M_{sun}_, have been identified in the 30 Dor star-forming region in the Large Magellanic Cloud (LMC). In this young starburst analogue, VMS were found to dominate stellar feedback. Despite their importance, the physics and evolution of VMS is highly uncertain, mainly due to their proximity to the Eddington limit. In this work, we investigate the two most important effects that are thought to occur near the Eddington limit: enhanced mass loss through optically thick winds and the formation of radially inflated stellar envelopes. We compute evolutionary models for VMS at LMC metallicity and perform a population synthesis of the young stellar population in 30 Dor. We adjust the input physics of our models to match the empirical properties of the single-star population in 30 Dor as derived in the framework of the VLT-Flames Tarantula Survey (VFTS). Enhanced mass loss and envelope inflation near the Eddington limit have a dominant effect on the evolution of the most massive stars. While the observed mass-loss properties and the associated surface He-enrichment are well described by our new models, the observed O-star mass-loss rates are found to cover a much larger range than theoretically predicted, with particularly low mass-loss rates for the youngest objects. Also, the (rotational) surface enrichment in the O-star regime appears to not be well understood. The positions of the most massive stars in the Hertzsprung-Russell diagram (HRD) are affected by mass loss and envelope inflation. For instance, the majority of luminous B supergiants in 30 Dor, and the lack thereof at the highest luminosities, can be explained through the combination of envelope inflation and mass loss. Finally, we find that the upper limit for the inferred initial stellar masses in the greater 30 Dor region is significantly lower than in its central cluster, R 136, implying a variable upper limit for the masses of stars. The implementation of mass-loss and envelope physics in stellar evolution models turns out to be essential for the modelling of the observable properties of young stellar populations. While the properties of the most massive stars (>~100M_{sun}_) are well described by our new models, the slightly less massive O stars investigated in this work show a much more diverse behaviour than previously thought, which has potential implications for rotational mixing and angular momentum transport. While the present models are a big step forward in the understanding of stellar evolution in the upper HRD, more work is needed to understand the mechanisms that regulate the mass-loss rates of OB stars and the physics of fast-rotating stars.
- ID:
- ivo://CDS.VizieR/J/A+A/487/1129
- Title:
- Evolutionary models of binaries
- Short Name:
- J/A+A/487/1129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The observed distribution of orbital periods of Algols with a B-type primary at birth agrees fairly well with the prediction from conservative theory. Conservative evolution fails, however, to produce the rather large fraction of Algols observed with a high mass-ratio. In order to keep Algols for a longer time with a higher mass-ratio without disturbing the distribution of orbital periods too much, interacting binaries have to lose a significant fraction of their total mass without losing much angular momentum before or during Algolism. We propose a mechanism that meets both requirements. In the case of direct impact the gainer spins up: sometimes up to critical velocity. Equatorial material on the gainer is therefore less bound. A similar statement applies to material located at the edge of an accretion disc. The incoming material moreover creates a hot spot in the area of impact. The sum of the rotational and radiative energy of hot spot material depends on the mass- transfer-rate. The sum of both energies overcomes the binding energy at a well defined critical value of the mass-transfer-rate. As long as the transfer-rate is smaller than this critical value RLOF happens conservatively. But as soon as the critical rate is exceeded the gainer will acquire no more than the critical value and RLOF runs into a liberal era.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A85
- Title:
- Evolutionary models of cold and low-mass planets
- Short Name:
- J/A+A/623/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Future instruments like the Near Infrared Camera (NIRCam) and the Mid Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) or the Mid-Infrared E-ELT Imager and Spectrograph (METIS) at the European Extremely Large Telescope (E-ELT) will be able to image exoplanets that are too faint (because they have a low mass, and hence a small size or low effective temperature) for current direct imaging instruments. On the theoretical side, core accretion formation models predict a significant population of low-mass and/or cool planets at orbital distances of ~10-100au. Evolutionary models predicting the planetary intrinsic luminosity as a function of time have traditionally concentrated on gas-dominated giant planets. We extend these cooling curves to Saturnian and Neptunian planets. We simulated the cooling of isolated core-dominated and gas giant planets with masses of 5M_{earth}_ to 2M_{jup}_. The planets consist of a core made of iron, silicates, and ices surrounded by a H/He envelope, similar to the ice giants in the solar system. The luminosity includes the contribution from the cooling and contraction of the core and of the H/He envelope, as well as radiogenic decay. For the atmosphere we used grey, AMES-Cond, petitCODE, and HELIOS models. We considered solar and non-solar metallicities as well as cloud-free and cloudy atmospheres. The most important initial conditions, namely the core-to-envelope ratio and the initial (i.e. post formation) luminosity are taken from planet formation simulations based on the core accretion paradigm. We first compare our cooling curves for Uranus, Neptune, Jupiter, Saturn, GJ 436b, and a 5M_{earth}_ planet with a 1% H/He envelope with other evolutionary models. We then present the temporal evolution of planets with masses between 5M_{earth}_ and 2M_{jup}_ in terms of their luminosity, effective temperature, radius, and entropy. We discuss the impact of different post formation entropies. For the different atmosphere types and initial conditions, magnitudes in various filter bands between 0.9 and 30 micrometer wavelength are provided. Using blackbody fluxes and non-grey spectra, we estimate the detectability of such planets with JWST. We found that a 20(100)M_{earth}_ planet can be detected with JWST in the background limit up to an age of about 10(100)Myr with NIRCam and MIRI, respectively.
- ID:
- ivo://CDS.VizieR/VI/65
- Title:
- Evolutionary models of evolved stars
- Short Name:
- VI/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Tables are given for all of the evolutionary tracks in the paper, which represent the evolution from the Zero-Age Horizontal Branch to a point either late in the AGB evolution, or in many cases to a point on the white dwarf cooling sequences. There are sequences for 8 different compositions. The original grid of tracks comprises several tens of thousands of models. In order to make this grid easy to use while not seriously compromising the representation of the evolution, much shorter tables have been derived for the general user. The data given here have been derived from these original calculations by linear and quadratic interpolation routines. For the HB phase, the evolution is represented at a fixed set of core helium values. After core exhaustion, the table points are at fixed intervals along the evolutionary path. The compositions in the tables are denoted as follows: -------------------------------------------------- Filename YHB [Fe/H] [O/Fe] Mc -------------------------------------------------- g14.dat 0.245 -2.26 0.50 0.495 e64.dat 0.247 -1.48 0.60 0.485 j63.dat 0.257 -0.47 0.23 0.475 z22.dat 0.288 +0.00 0.00 0.469 z42.dat 0.292 +0.39 0.00 0.464 z62.dat 0.289 +0.58 0.00 0.458 yz42.dat 0.356 +0.43 0.00 0.454 yz62.dat 0.459 +0.71 0.00 0.434 ------------------------------------------------- The columns give respectively: 1 Age in Myr since ZAHB 2 Central helium fraction 3 log Te (effective temperature, Kelvin) 4 log L (surface luminosity) in solar units 5 log g (surface gravity, cgs units) 6 log R (radius, cm) 7 Mass at peak energy production rate of hydrogen burning shell (solar units) 8 log Tc (central Temperature, Kelvin) 9 log rho_c (central density cgs units) The fortran format for the data tables is: '(f10.5,8(2x,f7.4))' for the first header line the format is: '("Track: ",i4,"lines Mass = ",f5.3," [Fe/H] = ",f5.2," [O/Fe] = ", f5.2," Y = ", f5.3)' while the second header line containing the column titles can of course be read as a character string ( format = '(a)' ). More specialized data is available in some cases from the first author, who should be contacted if other data are needed (see AAS directory for current address.)
- ID:
- ivo://CDS.VizieR/VI/113
- Title:
- Evolutionary models of Population II stars
- Short Name:
- VI/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The models are calculated for different chemical compositions both without overshooting (standard models, including microscopic diffusion of He and heavy elements) and with different overshooting efficiency. Each set of models can be found in a different sub-directory. It is possible to get all the content for each chemical composition, the content of each selected sub-directory or just a given file. In each directory there are evolutionary tracks (TRACKS), isochrones (ISOCHRONES), horizontal branch models together with a table of the ZAHB characteristics (HB) and files with some relevant physical values of selected models (STRUCTURES). Models with overshooting are calculated for masses higher than 1M_{sun}_ to avoid the unobserved presence of the overall contraction feature in 1M_{sun}_ stars. Thus isochrones for ages higher than about 5Gyr are the same as in the standard case and thus are not included in the overshooting directories. Models with overshooting does not include microscopic diffusion because for masses higher than about 1M_{sun}_ the effect of this mechanism is almost negligible. Models with overshooting are calculated for masses higher than 1M_{sun}_ to avoid the unobserved presence of the overall contraction feature in 1M_{sun}_ stars. Thus isochrones for ages higher than about 5Gyr are the same as in the standard case and thus are not included in the overshooting directories. Models with overshooting does not include microscopic diffusion because for masses higher than about 1M_{sun}_ the effect of this mechanism is almost negligible. All the tracks and isochrones have been transformed in the observation plane by adopting the model atmospheres by Castelli (1999A&A...346..564C), see also Castelli, Gratton & Kurucz (1997A&A...318..841C). For convenience, all tracks and isochrones have been grouped in 4 tables tracks.dat, struct.dat, hb.dat and isochron.dat
- ID:
- ivo://CDS.VizieR/J/ApJ/745/174
- Title:
- Evolutionary models of young gas-giant planets
- Short Name:
- J/ApJ/745/174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gas-giant planets that form via core accretion might have very different characteristics from those that form via disk instability. Disk-instability objects are typically thought to have higher entropies, larger radii, and (generally) higher effective temperatures than core-accretion objects. In this paper, we provide a large set of models exploring the observational consequences of high-entropy (hot) and low-entropy (cold) initial conditions, in the hope that this will ultimately help to distinguish between different physical mechanisms of planet formation. However, the exact entropies and radii of newly formed planets due to these two modes of formation cannot, at present, be precisely predicted. It is possible that the distribution of properties of core-accretion-formed planets and the distribution of properties of disk-instability-formed planets overlap. We, therefore, introduce a broad range of "warm-start" gas-giant planet models. Between the hottest and the coldest models that we consider, differences in radii, temperatures, luminosities, and spectra persist for only a few million to a few tens of millions of years for planets that are a few times Jupiter's mass or less. For planets that are ~five times Jupiter's mass or more, significant differences between hottest-start and coldest-start models persist for on the order of 100 Myr. We find that out of the standard infrared bands (J, H, K, L', M, N) the K and H bands are the most diagnostic of the initial conditions. A hottest-start model can be from ~4.5 mag brighter (at Jupiter's mass) to ~9 mag brighter (at 10 times Jupiter's mass) than a coldest-start model in the first few million years. In more massive objects, these large differences in luminosity and spectrum persist for much longer than in less massive objects. Finally, we consider the influence of atmospheric conditions on spectra, and find that the presence or absence of clouds, and the metallicity of an atmosphere, can affect an object's apparent brightness in different bands by up to several magnitudes.
- ID:
- ivo://CDS.VizieR/VI/96
- Title:
- Evolutionary Sequences
- Short Name:
- VI/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The tracks cover the mass interval from 0.6 to 120M_{sun}_, for 7 different metallicities The isochrones are derived from the evolutionary tracks listed in the item above.
