scholarly journals snapshot: connections between internal and surface properties of massive stars

2020 ◽  
Vol 495 (4) ◽  
pp. 4659-4680
Author(s):  
Eoin J Farrell ◽  
Jose H Groh ◽  
Georges Meynet ◽  
J J Eldridge ◽  
Sylvia Ekström ◽  
...  
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Strong Dependence ◽  
Stellar Structure ◽  
Binary Interaction ◽  
Analytical Relationship ◽  
Core Mass ◽  
Core Composition ◽  
Wide Range ◽  
Mass Fractions

ABSTRACT We introduce snapshot, a technique to systematically compute stellar structure models in hydrostatic and thermal equilibrium based on three structural properties – core mass Mcore, envelope mass Menv, and core composition. This approach allows us to connect these properties of stellar interiors to the luminosity and effective temperature Teff in a more systematic way than with stellar evolution models. We compute core-H burning models with total masses of Mtotal = 8–60 M⊙ and central H mass fractions from 0.70 to 0.05. Using these, we derive an analytical relationship between Mcore, Mtotal, and central H abundance that can be readily used in rapid stellar evolution algorithms. In contrast, core-He burning stars can have a wide range of combinations of Mcore, Menv, and core compositions. We compute core-He burning models with Mcore = 2–9 M⊙, Menv = 0–50 M⊙, and central He mass fractions of 0.50 and 0.01. Models with Mcore/Mtotal from 0.2 to 0.8 have convective envelopes, low Teff and will appear as red supergiants (RSGs). For a given Mcore, they exhibit a small variation in luminosity (0.02 dex) and Teff ($\sim 400\, \mathrm{K}$) over a wide range of Menv ($\sim$2–20 M⊙). This means that it is not possible to derive RSG masses from luminosities and Teff alone. We derive the following relationship between Mcore and the total luminosity of an RSG during core He burning: log Mcore ≃ 0.44log L/L⊙ − 1.38. At Mcore/Mtotal ≈ 0.2, our models exhibit a bistability and jump from an RSG to a BSG structure. Our models with Mcore/Mtotal > 0.8, which correspond to stripped stars produced by mass-loss or binary interaction, show that Teff has a strong dependence on Menv, Mcore, and the core composition. We constrain the mass of one of these stripped stars in a binary system, HD 45166, and find it to be less than its estimated dynamical mass. When a large observational sample of stripped stars becomes available, our results can be used to constrain their Mcore, Menv, mass-loss rates, and the physics of binary interaction.

scholarly journals Is GW190521 the merger of black holes from the first stellar generations?

2020 ◽  
Author(s):  
Eoin J Farrell ◽  
Jose H Groh ◽  
Raphael Hirschi ◽  
Laura Murphy ◽  
Etienne Kaiser ◽  
...  
Keyword(s):  
Black Holes ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Stars ◽  
Compact Star ◽  
Binary Interaction ◽  
Core Mass ◽  
Convective Mixing ◽  
Low Metallicity ◽  
Instability Regime

Abstract GW190521 challenges our understanding of the late-stage evolution of massive stars and the effects of the pair-instability in particular. We discuss the possibility that stars at low or zero metallicity could retain most of their hydrogen envelope until the pre-supernova stage, avoid the pulsational pair-instability regime and produce a black hole with a mass in the mass gap by fallback. We present a series of new stellar evolution models at zero and low metallicity computed with the Geneva and MESA stellar evolution codes and compare to existing grids of models. Models with a metallicity in the range 0 – 0.0004 have three properties which favour higher BH masses. These are (i) lower mass-loss rates during the post-MS phase, (ii) a more compact star disfavouring binary interaction and (iii) possible H-He shell interactions which lower the CO core mass. We conclude that it is possible that GW190521 may be the merger of black holes produced directly by massive stars from the first stellar generations. Our models indicate BH masses up to 70-75 M⊙. Uncertainties related to convective mixing, mass loss, H-He shell interactions and pair-instability pulsations may increase this limit to ∼85M⊙.

scholarly journals The Wolf–Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud

2019 ◽  
Vol 627 ◽  
pp. A151 ◽  
Author(s):  
T. Shenar ◽  
D. P. Sablowski ◽  
R. Hainich ◽  
H. Todt ◽  
A. F. J. Moffat ◽  
...  
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Stars ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Binary Interaction ◽  
Evolutionary Status ◽  
X Ray ◽  
Composite Spectra ◽  
The Impact

Context. Massive Wolf–Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z ≈ 0.5 Z⊙), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf–Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45  ±  30% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only ≈12  ±  7% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises ≈4% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L ≈ 5.2 [L⊙], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (veq ≲ 250 km s−1) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.

scholarly journals Carbon in the Envelopes of White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 188-191
Author(s):  
Francesca D’Antona
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Current Theory ◽  
Core Mass ◽  
Maximum Extension ◽  
Nuclear Burning ◽  
Remnant Mass

Current theory of stellar evolution predicts that stars of initial masses up to 4-6 M⊙ evolve into Carbon-Oxygen White Dwarfs surrounded by a Helium envelope and, possibly, by a Hydrogen envelope. It also predicts that the mass of the Helium envelope which remains on the star at the end of its double shell burning evolution is a function of the Carbon-Oxygen core mass (Paczynski 1975). It can be shown that this mass can be reduced – but only slightly – during the following evolution of the star towards the White Dwarf region, either by nuclear burning or by mass loss (D’Antona and Mazzitelli 1979). During the White Dwarf stage, Helium convection grows into White Dwarfs having Helium atmospheres. The maximum extension of Helium convective mass is a function of the mass of the star (Fontaine and Van Horn 1976; D’Antona and Mazzitelli 1975,1979). It turns out that the Helium envelope remnant mass is always at least three orders of magnitude larger than the maximum Helium convective mass, whatever the mass of the star may be. This statement is unlikely to be changed by refinements either in the theory of double shell burning or in the theory of White Dwarf envelope convection.

scholarly journals Stochastic gravitational wave background anisotropies in the mHz band: astrophysical dependencies

2019 ◽  
Vol 493 (1) ◽  
pp. L1-L5
Author(s):  
Giulia Cusin ◽  
Irina Dvorkin ◽  
Cyril Pitrou ◽  
Jean-Philippe Uzan
Keyword(s):  
Black Hole ◽  
Power Spectrum ◽  
Gravitational Wave ◽  
Stellar Evolution ◽  
Strong Dependence ◽  
Angular Power Spectrum ◽  
Orbital Parameters ◽  
Wide Range ◽  
Self Consistent ◽  
Gravitational Wave Background

ABSTRACT We show that the anisotropies of the astrophysical stochastic gravitational wave background in the mHz band have a strong dependence on the modelling of galactic and sub-galactic physics. We explore a wide range of self-consistent astrophysical models for stellar evolution and for the distribution of orbital parameters, all calibrated such that they predict the same number of resolved mergers to fit the number of detections during LIGO/Virgo O1 + O2 observations runs. We show that different physical choices for the process of black hole (BH) collapse and cut-off in the BH mass distribution give fractional differences in the angular power spectrum of anisotropies of up to 50 per cent on all angular scales. We also point out that the astrophysical information which can be extracted from anisotropies is complementary to the isotropic background and individual mergers. These results underline the interest in the anisotropies of the stochastic gravitational wave background as a new and potentially rich field of research, at the cross-road between astrophysics and cosmology.

scholarly journals Recent Advances in Convection Theory and Modelling

1995 ◽  
Vol 10 ◽  
pp. 433-434
Author(s):  
S. Sofia
Keyword(s):  
Stellar Evolution ◽  
Numerical Models ◽  
Spatial Scales ◽  
Stellar Structure ◽  
Wave Number ◽  
The Sun ◽  
Mixing Length ◽  
Number Range ◽  
Wide Range ◽  
Non Locality

This Joint Discussion (Number 13), took place on August 22, 1994 at The Hague, in connection with the XXII General Assembly of the IAU. At the one-day long meeting, there were presentations by 15 invited speakers and 15 posters.The Joint Discussions had been organized in response to the considerable progress made in this field of research during the previous decade. Although it had long been known that the prevailing mixing length theory (MLT), used extensively and very successfully in Astrophysics for several decades had become needlessly limited, until recently it was impractical to contemplate more realistic approaches. The situation has changed recently as a consequence of advances in numerical techniques and computational capabilities, and thus JD 13 was organized to discuss the advances, and perhaps to understand the strengths and weaknesses of each approach.There were two presentations which addressed the main issues in convection theory (E. Schatzman), and the astrophysical implications (P. Demarque). Several talks covered current numerical codes, which included deep convection in a rotating reference frame (K. Chan), convection in the presence of magnetic fields (P. Fox), and shallower solar convection simulations on a wide range of spatial scales (A. Nordlund). Although these approaches have enriched (and are continuing to enrich) our understanding of the physics of convective fluids, they are much too detailed (both in space and in time) to be integrated in the study of stellar evolution. To overcome this shortcoming, S. Sofia described a technique developed together with Lydon and Fox to use relationships between dynamical and thermodynamic properties of convective flows derived in numerical models to be applied in stellar structure and evolution codes by performing small modifications of the standard MLT formalism. The advantage of this technique is that it does not contain a mixing length or any other arbitrary parameter, and it was used successfully in modeling the evolution of the Sun and other solar analogues. V. Canuto also presented a formulation of convection both amenable to be used in stellar evolution studies, and not requiring an arbitrary mixing length-like parameter. His formulation uses the Reynolds stress method, which has the advantage of modeling the full eddy spectrum of the turbulence, rather than the narrow wave number range for energy containing eddies assumed in the MLT. Additionally, this technique can address the problems of non-locality and overshoot. M. Stix also addressed non-locality and overshoot by presenting results of a non-local mixing length model of the Sun derived from the Shaviv and Salpeter model.

scholarly journals Evolution and Mass Loss of Cool Aging Stars: A Daedalean Story

2021 ◽  
Vol 59 (1) ◽  
Author(s):  
Leen Decin
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Binary Interaction ◽  
Annual Review ◽  
Publication Date ◽  
Driving Mechanism ◽  
Chemical Enrichment ◽  
Dust Seeds

A multitude of phenomena—such as the chemical enrichment of the Universe, the mass spectrum of planetary nebulae, white dwarfs and gravitational wave progenitors, the frequency distribution of supernovae, the fate of exoplanets, etc.—are highly regulated by the amounts of mass that stars expel through a powerful wind. For more than half a century, these winds of cool aging stars have been interpreted within the common interpretive framework of 1D models. I here discuss how that framework now appears to be highly problematic. • Current 1D mass-loss rate formulae differ by orders of magnitude, rendering contemporary stellar evolution predictions highly uncertain. These stellar winds harbor 3D complexities that bridge 23 orders of magnitude in scale, ranging from the nanometer up to thousands of astronomical units. We need to embrace and understand these 3D spatial realities if we aim to quantify mass loss and assess its effect on stellar evolution. We therefore need to gauge the following: • The 3D life of molecules and solid-state aggregates: The gas-phase clusters that form the first dust seeds are not yet identified. This limits our ability to predict mass-loss rates using a self-consistent approach. • The emergence of 3D clumps: They contribute in a nonnegligible way to the mass loss, although they seem of limited importance for the wind-driving mechanism. • The 3D lasting impact of a (hidden) companion: Unrecognized binary interaction has biased previous mass-loss rate estimates toward values that are too large. Only then will it be possible to drastically improve our predictive power of the evolutionary path in 4D (classical) spacetime of any star. Expected final online publication date for the Annual Review of Astronomy and Astrophysics, Volume 59 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals Unveiling the Planet Population at Birth

2020 ◽  
Author(s):  
James Rogers ◽  
James Owen
Keyword(s):  
Mass Loss ◽  
Mass Fraction ◽  
Planet Formation ◽  
Evolution Model ◽  
Inference Model ◽  
Core Mass ◽  
Core Composition ◽  
New Information ◽  
Loss Mechanisms

<p>Recent Kepler data has shown that the radius distribution of small, close-in exoplanets is bimodal. Such bimodality was expected from photoevaporation models of close-in super-Earths, where some planets are stripped of their primordial H/He atmospheres, whilst others retain them. We present a hierarchical inference model on the distribution of Kepler planets using the photoevaporation evolution model. This approach is used to place key constraints on the planetary distributions for core composition, core mass and initial envelope mass-fraction, as well as test other models of planet evolution such as core-powered mass-loss. This new information has interesting implications on planet formation models and also hints at additional atmopsheric mass-loss mechanisms.</p>

scholarly journals Supernovae from Wolf-Rayet Stars

1991 ◽  
Vol 143 ◽  
pp. 566-566
Author(s):  
Norbert Langer ◽  
Stanford E. Woosley
Keyword(s):  
Mass Loss ◽  
Initial Mass ◽  
Surface Mass ◽  
Final Mass ◽  
Wide Range ◽  
Mass Fractions ◽  
Star Surface ◽  
Mass Dependent

The complete evolution of a star with an initial mass of 60 M⊙ and Z = Z⊙ (i.e. a typical W R progenitor) from the ZAMS through the supernova phase has been investigated. Mass loss in the different evolutionary stages, especially mass dependent W R mass loss, leads to a WO star (surface mass fractions {He,C,O} = {0.14, 0.38, 0.48}; cf. Fig. 1) of 4 . 2 M⊙ as pre-SN configuration. The low final mass may be typical for a wide range of initial masses (cf. Langer, 1989, Astr. Ap. 220, 135).

scholarly journals Size Evolution of Close-in Super-Earths through Giant Impacts and Photoevaporation

2021 ◽  
Vol 923 (1) ◽  
pp. 81
Author(s):  
Yuji Matsumoto ◽  
Eiichiro Kokubo ◽  
Pin-Gao Gu ◽  
Kenji Kurosaki
Keyword(s):  
Radial Profile ◽  
Analytical Models ◽  
Core Mass ◽  
Outer Planets ◽  
The Core ◽  
Size Evolution ◽  
Wide Range ◽  
Mass Fractions ◽  
Giant Impacts ◽  
Impact Phase

Abstract The Kepler transit survey with follow-up spectroscopic observations has discovered numerous super-Earth sized planets and revealed intriguing features of their sizes, orbital periods, and their relations between adjacent planets. For the first time, we investigate the size evolution of planets via both giant impacts and photoevaporation to compare with these observed features. We calculate the size of a protoplanet, which is the sum of its core and envelope sizes, by analytical models. N-body simulations are performed to evolve planet sizes during the giant impact phase with envelope stripping via impact shocks. We consider the initial radial profile of the core mass and the initial envelope mass fractions as parameters. Inner planets can lose their whole envelopes via giant impacts, while outer planets can keep their initial envelopes, because they do not experience giant impacts. Photoevaporation is simulated to evolve planet sizes afterward. Our results suggest that the period-radius distribution of the observed planets would be reproduced if we perform simulations in which the initial radial profile of the core mass follows a wide range of power-law distributions and the initial envelope mass fractions are ∼0.1. Moreover, our model shows that the adjacent planetary pairs have similar sizes and regular spacings, with slight differences from detailed observational results such as the radius gap.

scholarly journals Formation of GW190521 from stellar evolution: the impact of the hydrogen-rich envelope, dredge-up and 12C(α, γ)16O rate on the pair-instability black hole mass gap

2020 ◽  
Author(s):  
Guglielmo Costa ◽  
Alessandro Bressan ◽  
Michela Mapelli ◽  
Paola Marigo ◽  
Giuliano Iorio ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Reaction Rate ◽  
Primary Component ◽  
Mass Reduction ◽  
Black Hole Mass ◽  
Core Mass ◽  
The Core ◽  
Mass Gap ◽  
M Stars ◽  
The Impact

Abstract Pair-instability (PI) is expected to open a gap in the mass spectrum of black holes (BHs) between ≈40 − 65 M⊙ and ≈120 M⊙. The existence of the mass gap is currently being challenged by the detection of GW190521, with a primary component mass of $85^{+21}_{-14}$ M⊙. Here, we investigate the main uncertainties on the PI mass gap: the 12C(α, γ)16O reaction rate and the H-rich envelope collapse. With the standard 12C(α, γ)16O rate, the lower edge of the mass gap can be 70 M⊙ if we allow for the collapse of the residual H-rich envelope at metallicity Z ≤ 0.0003. Adopting the uncertainties given by the starlib database, for models computed with the 12C(α, γ)16O rate −1 σ, we find that the PI mass gap ranges between ≈80 M⊙ and ≈150 M⊙. Stars with MZAMS > 110 M⊙ may experience a deep dredge-up episode during the core helium-burning phase, that extracts matter from the core enriching the envelope. As a consequence of the He-core mass reduction, a star with MZAMS = 160 M⊙ may avoid the PI and produce a BH of 150 M⊙. In the −2 σ case, the PI mass gap ranges from 92 M⊙ to 110 M⊙. Finally, in models computed with 12C(α, γ)16O −3 σ, the mass gap is completely removed by the dredge-up effect. The onset of this dredge-up is particularly sensitive to the assumed model for convection and mixing. The combined effect of H-rich envelope collapse and low 12C(α, γ)16O rate can lead to the formation of BHs with masses consistent with the primary component of GW190521.

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