We present a new grid of presupernova models of massive stars extending in mass between 13 and 120 , covering four metallicities (i.e., Fe/H = 0, −1, −2, and −3) and three initial rotation velocities ...(i.e., 0, 150, and 300 km s−1). The explosion has been simulated following three different assumptions in order to show how the yields depend on the remnant mass−initial mass relation. An extended network from H to Bi is fully coupled to the physical evolution of the models. The main results can be summarized as follows. (a) At solar metallicity, the maximum mass exploding as a red supergiant (RSG) is of the order of 17 in the nonrotating case, with the more massive stars exploding as Wolf-Rayet (WR) stars. All rotating models, conversely, explode as WR stars. (b) The interplay between the core He-burning and the H-burning shell, triggered by the rotation-induced instabilities, drives the synthesis of a large primary amount of all the products of CNO, not just . A fraction of them greatly enriches the radiative part of the He core (and is responsible for the large production of F), and a fraction enters the convective core, leading therefore to an important primary neutron flux able to synthesize heavy nuclei up to Pb. (c) In our scenario, remnant masses of the order of those inferred from the first detections of gravitational waves (GW 150914, GW 151226, GW 170104, GW 170814) are predicted at all metallicities for none or moderate initial rotation velocities.
We present a fine grid of solar metallicity models of massive stars (320 in the range 12 ≤ M( ) ≤ 27.95), extending from the main sequence up to the onset of the collapse, in order to quantitatively ...determine how their compactness 2.5, defined by O'Connor & Ott, scales with the carbon-oxygen core mass at the beginning of core collapse. We find a well defined, nonmonotonic (but not scattered) trend of the compactness with the carbon-oxygen core mass that is strictly (and mainly) correlated to the behavior, i.e., birth, growth, and disappearance, of the various carbon convective episodes that follow one another during the advanced evolutionary phases. Though both the mass size of the carbon-oxygen core and the amount of 12C left by the central He burning play a major role in sculpting the final mass-radius relation, it is the abundance of 12C that is ultimately responsible for the final degree of compactness of a star, because it controls the ability of the carbon-burning shell to advance in mass before the final collapse.
We investigate the impact of stellar rotation on the formation of black holes (BHs) by means of our population synthesis code sevn. Rotation affects the mass function of BHs in several ways. In ...massive metal-poor stars, fast rotation reduces the minimum zero-age main sequence (ZAMS) mass for a star to undergo pair instability and pulsational pair instability. Moreover, stellar winds are enhanced by rotation, peeling off the entire hydrogen envelope. As a consequence of these two effects, the maximum BH mass we expect from the collapse of a rotating metal-poor star is only ∼45 M , while the maximum mass of a BH born from a nonrotating star is ∼60 M . Furthermore, stellar rotation reduces the minimum ZAMS mass for a star to collapse into a BH from ∼18-25 M to ∼13-18 M . Finally, we have investigated the impact of different core-collapse supernova (CCSN) prescriptions on our results. While the threshold value of compactness for direct collapse and the fallback efficiency strongly affect the minimum ZAMS mass for a star to collapse into a BH, the fraction of the hydrogen envelope that can be accreted onto the final BH is the most important ingredient in determining the maximum BH mass. Our results confirm that the interplay between stellar rotation, CCSNe and pair instability plays a major role in shaping the BH mass spectrum.
Abstract We present the evolution and the explosion of two massive stars, 15 and 25 M ⊙ , spanning a wide range of initial rotation velocities (from 0 to 800 km s −1 ) and three initial ...metallicities: Z = 0 (Fe/H = −∞), 3.236 × 10 −7 (Fe/H = −5), and 3.236 × 10 −6 (Fe/H = −4). A very large nuclear network of 524 nuclear species extending up to Bi has been adopted. Our main findings may be summarized as follows: (a) rotating models above Z = 0 are able to produce nuclei up to the neutron closure shell N = 50, and in a few cases up to N = 82; (b) rotation drastically inhibits the penetration of the He convective shell in the H-rich mantle, a phenomenon often found in zero metallicity nonrotating massive stars; (c) vice versa, rotation favors the penetration of the O convective shell in the C-rich layers with the consequence of significantly altering the yields of the products of the C, Ne, and O burning; (d) none of the models that reach the critical velocity while in H burning lose more the 1 M ⊙ in this phase; (e) conversely, almost all models able to reach their Hayashi track exceed the Eddington luminosity and dynamically lose almost all their H-rich mantle. These models suggest that rotating massive stars may have contributed significantly to the synthesis of the heavy nuclei in the first phase of enrichment of the interstellar medium, i.e., at early times.
Abstract We present an extension of the set of models published in Limongi & Chieffi (2018) at metallicity 2 times solar, i.e., Fe/H = 0.3. The key physical properties of these models at the onset of ...core collapse are mainly due to the higher mass loss triggered by the higher metallicity: the supersolar metallicity (SSM) models reach core collapse with smaller He- and CO-core masses, while the amount of 12 C left by the central He burning is higher. These results are valid for all the rotation velocities. The yields of the neutron-capture nuclei expressed per unit mass of oxygen (i.e., the X/O) are higher in the SSM models than in the SM ones in the nonrotating case, while the opposite occurs in the rotating models. The trend shown by the nonrotating models is the expected one, given the secondary nature of the neutron-capture nucleosynthesis. Vice versa, the counterintuitive trend obtained in the rotating models is the consequence of the higher mass loss present in the SSM models, removes the H-rich envelope faster than in the SM models while the stars are still in central He burning, dumping out the entanglement (activated by the rotation instabilities) and therefore conspicuous primary neutron-capture nucleosynthesis.
Abstract
We present a simple criterion to predict the explodability of massive stars based on the density and entropy profiles before collapse. If a pronounced density jump is present near the ...Si/Si–O interface, the star will likely explode. We develop a quantitative criterion by using ∼1300 1D simulations where
ν
-driven turbulence is included via time-dependent mixing-length theory. This criterion correctly identifies the outcome of the supernova more than 90% of the time. We also find no difference in how this criterion performs on two different sets of progenitors, evolved using two different stellar evolution codes: FRANEC and KEPLER. The explodability as a function of mass of the two sets of progenitors is very different, showing: (i) that uncertainties in the stellar evolution prescriptions influence the predictions of supernova explosions; (ii) the most important properties of the pre-collapse progenitor that influence the explodability are its density and entropy profiles. We highlight the importance that
ν
-driven turbulence plays in the explosion by comparing our results to previous works.
Abstract
According to a standard initial mass function, stars in the range 7–12
M
⊙
constitute ∼50% (by number) of the stars more massive than ∼7
M
⊙
, but in spite of this, their evolutionary ...properties, and in particular their final fate, are still scarcely studied. In this paper, we present a detailed study of the evolutionary properties of solar metallicity nonrotating stars in the range 7–15
M
⊙
, from the pre-main-sequence phase up to the presupernova stage or an advanced stage of the thermally pulsing phase, depending on the initial mass. We find that (1) the 7.00
M
⊙
star develops a degenerate CO core and evolves as a classical asymptotic giant branch (AGB) star in the sense that it does not ignite the C-burning reactions, (2) stars with initial mass
M
≥ 9.22
M
⊙
end their lives as core-collapse supernovae, (3) stars in the range 7.50 ≤
M
/
M
⊙
≤ 9.20 develop a degenerate ONeMg core and evolve through the thermally pulsing super-AGB phase, (4) stars in the mass range 7.50 ≤
M
/
M
⊙
≤ 8.00 end their lives as hybrid CO/ONeMg or ONeMg WDs, and (5) stars with initial mass in the range 8.50 ≤
M
/
M
⊙
≤ 9.20 may potentially explode as electron-capture supernovae.
ABSTRACT
Carbon-enhanced metal-poor (CEMP) stars are the living fossils holding records of chemical enrichment from early generations of stars. In this work, we perform a set of numerical simulations ...of the enrichment from a supernova (SN) of a first generation of metal-free (Pop III) star and the gravitational collapse of the enriched cloud, considering all relevant cooling/heating processes and chemical reactions as well as the growth of dust grains. We adopt faint SN models for the first time with progenitor masses MPopIII = 13–$80 \ {\rm M_{\bigodot }}$, which yield C-enhanced abundance patterns (C/Fe = 4.57–4.75) through mixing and fallback of innermost layers of the ejecta. This model also considers the formation and destruction of dust grains. We find that the metals ejected by the SN can be partly re-accreted by the same dark matter minihalo, and carbon abundance of the enriched cloud A(C) = 3.80–5.06 is lower than the abundance range of observed CEMP stars (A(C) ≳ 6) because the mass of the metals ejected by faint SNe is smaller than normal core-collapse SNe due to extensive fallback. We also find that cloud fragmentation is induced by gas cooling from carbonaceous grains for $M_{\rm Pop III}= 13 \ {\rm M_{\bigodot }}$ even with the lowest iron abundance Fe/H ∼ −9. This leads to the formation of low-mass stars, and these ‘giga metal-poor’ stars can survive until the present-day Universe and may be found by future observations.
ABSTRACT
The relative importance of metals and dust grains in the formation of the first low-mass stars has been a subject of debate. The recently discovered Galactic halo star SDSS J102915+172927 ...has a mass less than 0.8 M⊙ and a metallicity of Z= 4.5 × 10−5 Z⊙. We investigate the origin and properties of this star by reconstructing the physical conditions in its birth cloud. We show that the observed elemental abundance trend of SDSS J102915+172927 can be well fitted by the yields of core-collapse supernovae (SNe) with metal-free progenitors of 20 and 35 M⊙. Using these selected SN explosion models, we compute the corresponding dust yields and the resulting dust depletion factor taking into account the partial destruction by the SN reverse shock. We then follow the collapse and fragmentation of a star-forming cloud enriched by the products of these SN explosions at the observed metallicity of SDSS J102915+172927. We find that 0.05-0.1 M⊙ mass fragments, which then lead to the formation of low-mass stars, can occur provided that the mass fraction of dust grains in the birth cloud exceeds 0.01 of the total mass of metals and dust. This, in turn, requires that at least 0.4 M⊙ of dust condense in the first SNe, allowing for moderate destruction by the reverse shock. If dust formation in the first SNe is less efficient or strong dust destruction does occur, the thermal evolution of the SDSS J102915+172927 birth cloud is dominated by molecular cooling, and only ≥8 M⊙ fragments can form. We conclude that the observed properties of SDSS J102915+172927 support the suggestion that dust must have condensed in the ejecta of the first SNe and played a fundamental role in the formation of the first low-mass stars.
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