18 research outputs found
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