Massive close binaries II

In the present review we summarize direct and indirect evidence that the massive close binary frequency is very large. We then discuss the binary evolutionary processes and we present a general massive close binary evolutionary scheme. Finally, we highlight the importance of massive close binaries for population number synthesis and the chemical evolution of galaxies.Comment: 21 pages, 6 figures, to appear in "Massive Stars: Formation, Evolution, Internal Structure and Environnement", eds. M. Heydari-Malayeri and J.-P. Zah

Close Pairs as Probes of the Galaxy's Chemical Evolution

Understanding the galaxy in which we live is one of the great intellectual challenges facing modern science. With the advent of high quality observational data, the chemical evolution modeling of our galaxy has been the subject of numerous studies in the last years. However, all these studies have one missing element which is the evolution of close binaries. Reason: their evolution is very complex and single stars only perhaps can do the job. (Un)Fortunately at present we know that a significant fraction of the observed intermediate mass and massive stars are members of a binary or multiple system and that certain objects can only be formed through binary evolution. Therefore galactic studies that do not account for close binaries may be far from realistic. We implemented a detailed binary population in a galactic chemical evolutionary model. Notice that this is not something simple like replacing chemical yields. Here we discuss three topics: the effect of binaries on the evolution of 14N, the evolution of the type Ia supernova rate and the effects on the G-dwarf distribution, the link between the evolution of the r-process elements and double neutron star mergers (candidates of short gamma-ray burst objects).Comment: 10 pages, 5 figures, Invited paper at IAUS240, IAUXXVI GA Pragu

Two distributions shedding light on supernova Ia progenitors: delay times and G-dwarf metallicities

Using a population number synthesis code with detailed binary evolution, we calculate the distribution of the number of type Ia supernovae as a function of time after starburst. This is done for both main progenitor scenarios (single degenerate and double degenerate), but also with various evolutionary assumptions (such as mass transfer efficiency, angular momentum loss, and common envelope description). The comparison of these theoretically predicted delay time distributions with observations in elliptical galaxies then allows to constrain the evolutionary scenarios and parameters. From the morphological shape of the distributions, we conclude that all supernovae Ia cannot be produced through the single degenerate scenario alone, with the best match being obtained when both scenarios contribute. Within the double degenerate scenario, most systems go through a phase of quasi-conservative, stable Roche lobe overflow. We propose stellar rotation as a possible solution for the underestimation of the observed absolute number of events, as is the case in many theoretical population synthesis studies. A brief comparison with these other studies is made, showing good correspondence under the nontrivial condition of equivalent assumptions. We also investigate the influence of different supernova Ia progenitors and evolutionary parameters on the theoretical distribution of the iron abundance of G-type dwarfs in the Galactic disk. These stars are good indicators of the entire chemical history of the Galaxy, and their predicted metallicity distribution can also be compared to the observational ones. This again limits the number of acceptable combinations of assumptions. Supporting previous results, the best correspondence is found in the case where both the single and double degenerate scenario contribute.Comment: 4 pages, 3 figures, to appear in proceedings of "IAUS 281: Binary Paths to Type Ia Supernovae Explosions

The evolution of massive and very massive stars in clusters

The present paper reviews massive star (initial mass smaller than 120 M0) and very massive star (initial mass larger than 120 M0) evolution. I will focus on evolutionary facts and questions that may critically affect predictions of population and spectral synthesis of starburst regions. We discuss the ever-lasting factor 2 or more uncertainty in the stellar wind mass loss rates. We may ask ourselves if stellar rotation is one of the keys to understand the universe, why so many massive stars are binary components and why binaries are ignored or are considered as the poor cousins by some people? And finally, do ultra luminous X-ray sources harbor an intermediate mass black hole with a mass of the order of 1000 M0?Comment: 16 pages, 7 figures, Review talk presented at the conference From Taurus to the Antennae, Sheffield 4-8th August 200

Stellar dynamics in young clusters: the formation of massive runaways and very massive runaway mergers

In the present paper we combine an N-body code that simulates the dynamics of young dense stellar systems with a massive star evolution handler that accounts in a realistic way for the effects of stellar wind mass loss. We discuss two topics: 1. The formation and the evolution of very massive stars (with a mass >120 Mo) is followed in detail. These very massive stars are formed in the cluster core as a consequence of the successive (physical) collison of 10-20 most massive stars of the cluster (the process is known as runaway merging). The further evolution is governed by stellar wind mass loss during core hydrogen burning and during core helium burning (the WR phase of very massive stars). Our simulations reveal that as a consequence of runaway merging in clusters with solar and supersolar values, massive black holes can be formed but with a maximum mass of 70 Mo. In small metallicity clusters however, it cannot be excluded that the runaway merging process is responsible for pair instability supernovae or for the formation of intermediate mass black holes with a mass of several 100 Mo. 2. Massive runaways can be formed via the supernova explosion of one of the components in a binary (the Blaauw scenario) or via dynamical interaction of a single star and a binary or between two binaries in a star cluster. We explore the possibility that the most massive runaways (e.g., zeta Pup, lambda Cep, BD+433654) are the product of the collision and merger of 2 or 3 massive stars.Comment: Updated and final versio

Can Neutron Star Mergers Alone Explain the r-process Enrichment of the Milky Way?

© 2023. The Author(s). Published by the American Astronomical Society. This is an open access article under the terms of the Creative Commons Attribution License, https://creativecommons.org/licenses/by/4.0/Comparing Galactic chemical evolution models to the observed elemental abundances in the Milky Way, we show that neutron star mergers can be a leading r-process site only if at low metallicities such mergers have very short delay times and significant ejecta masses that are facilitated by the masses of the compact objects. Namely, black hole–neutron star mergers, depending on the black hole spins, can play an important role in the early chemical enrichment of the Milky Way. We also show that none of the binary population synthesis models used in this Letter, i.e., COMPAS, StarTrack, Brussels, ComBinE, and BPASS, can currently reproduce the elemental abundance observations. The predictions are problematic not only for neutron star mergers, but also for Type Ia supernovae, which may point to shortcomings in binary evolution models.Peer reviewe