The evolution of massive binaries in a dense stellar cluster environment

Massive stars are among the most important objects in the Universe and many (most?) of them are formed in binaries. A selection of observational and theoretical facts that illustrate the importance of binaries and the evolution of massive and very massive stars in clusters with special emphasis on massive binaries have been summarized in two recent review papers (Vanbeveren, 2009, 2010). The present paper can be considered as an addendum of both reviews.Comment: 6 pages, 1 figure; to be published in the proceedings of the conference 'Binary star evolution: mass loss, accretion, and mergers', June 22-25, Mykono

A comparison between observed Algol-type double stars in the Solar neighborhood and evolutionary computations of galactic case A binaries with a B-type primary at birth

We first discuss a large set of evolutionary calculations of close binaries with a B-type primary at birth and with a period such that the Roche lobe overflow starts during the core hydrogen burning phase of the primary (intermediate mass and massive case A binaries). The evolution of both components is followed simultaneously allowing us to check for the occurrence of contact binaries. We consider various models to treat a contact system and the influence of these models on the predicted Algol-type system population is investigated. We critically discuss the available observations of Algol-type binaries with a B-type primary at birth. Comparing these observations with the predictions allows us to put constraints on the contact star physics. We find that mass transfer in Algols is most probably not conservative, that contact during this phase does not necessarily lead to a merger, and that angular momentum loss must be moderate.Comment: 8 pages, 9 figures, accepted for publication in A&A; accepted versio

The delayed time distribution of massive double compact star mergers

In order to investigate the temporal evolution of binary populations in general, double compact star binaries and mergers in particular within a galactic evolution context, a most straightforward method is obviously the implementation of a detailed binary evolutionary model in a galactic chemical evolution code. To our knowledge, the Brussels galactic chemical evolution code is the only one that fully consistently accounts for the important effects of interacting binaries on the predictions of chemical evolution. With a galactic code that does not explicitly include binaries, the temporal evolution of the population of double compact star binaries and mergers can be estimated with reasonable accuracy if the delayed time distribution (DTD) for these mergers is available. The DTD for supernovae type Ia has been studied extensively the last decade. In the present paper we present the DTD for merging double neutron star binaries and mixed systems consisting of a neutron star and a black hole. The latter mergers are very promising sites for the production of r-process elements and the DTDs can be used to study the galactic evolution of these elements with a code that does not explicitly account for binaries.Comment: 7 pages, 5 figures, accepted for publication in A&A; accepted versio

Massive double compact object mergers: gravitational wave sources and r-process-element production sites

With our galactic evolutionary code that contains a detailed intermediate mass and massive binary population model, we study the temporal evolution of the galactic population of double neutron star binaries, mixed systems with a neutron star and black hole component and double black hole binaries. We compute the merger rates of these relativistic binaries and we translate them into LIGO II detection rates. We demonstrate that accounting for the uncertainties in the relation 'initial mass-final mass' predicted by massive close binary evolution and due to the possible effect of large stellar wind mass loss during the luminous blue variable phase of a star with initial mass larger than 30-40 Mo and during the red supergiant phase of a star with initial mass smaller than 30-40 Mo when such a star is a binary component, the double black hole merger rate may be very small, contrary to predictions made by other groups. Hydrodynamic computations of r-process chemical yields ejected during the relativistic binary merger process have recently become available. With our galactic code that includes binaries it is then straightforward to calculate the temporal galactic evolution of the r-process elements ejected by these mergers. We conclude that except for the earliest evolutionary phase of the Galaxy (~the first 100 Myr) double compact star mergers may be the major production sites of r-process elements and it is probable that the mixed systems dominate this production over double neutron star binary mergers.Comment: 12 pages, 7 figures, accepted for publication in A&A; accepted versio

Massive star population synthesis with binaries

We first give a short historical overview with some key facts of massive star population synthesis with binaries. We then discuss binary population codes and focus on two ingredients which are important for massive star population synthesis and which may be different in different codes. Population simulations with binaries is the third part where we consider the initial massive binary frequency, the RSG/WR and WC/WN and SNII/SNIbc number ratio's, the probable initial rotational velocity distribution of massive stars.Comment: 5 pages, 1 figure, review paper to appear in the conference proceedings of the June 2015 Potsdam Wolf-Rayet workshop, edited by W.-R. Hamann, A. Sander, and H. Tod

Binary populations and stellar dynamics in young clusters

We first summarize work that has been done on the effects of binaries on theoretical population synthesis of stars and stellar phenomena. Next, we highlight the influence of stellar dynamics in young clusters by discussing a few candidate UFOs (unconventionally formed objects) like intermediate mass black holes, Eta Carinae, Zeta Puppis, Gamma Velorum and WR 140.Comment: Contributed paper IAU 250: Massive Stars as Cosmic Engine

The Chemical Evolution of the Solar Neighbourhood: the Effect of Binaries

In this paper we compute the time evolution of the elements (4He, 12C, 14N, 16O, 20Ne, 24Mg, 28Si, 32S, 40Ca and 56Fe) and of the supernova rates in the solar neighbourhood by means of a galactic chemical evolutionary code that includes in detail the evolution of both single and binary stars. Special attention is payed to the formation of black holes. Our main conclusions: in order to predict the galactic time evolution of the different types of supernovae, it is essential to compute in detail the evolution of the binary population, the observed time evolution of carbon is better reproduced by a galactic model where the effect is included of a significant fraction of intermediate mass binaries, massive binary mass exchange provides a possible solution for the production of primary nitrogen during the very early phases of galactic evolution, chemical evolutionary models with binaries or without binaries but with a detailed treatment of the SN Ia progenitors predict very similar age-metallicity relations and very similar G-dwarf distributions whereas the evolution of the yields as function of time of the elements 4He, 16O, 20Ne, 24Mg, 28Si, 32S and 40Ca differ by no more than a factor of two or three, the observed time evolution of oxygen is best reproduced when most of the oxygen produced during core helium burning in ALL massive stars serves to enrich the interstellar medium. This can be used as indirect evidence that (massive) black hole formation in single stars and binary components is always preceded by a supernova explosion.Comment: 59 page

Binaries, cluster dynamics and population studies of stars and stellar phenomena

The effects of binaries on population studies of stars and stellar phenomena have been investigated over the past 3 decades by many research groups. Here we will focus mainly on the work that has been done recently in Brussels and we will consider the following topics: the effect of binaries on overall galactic chemical evolutionary models and on the rates of different types of supernova, the population of point-like X-ray sources where we distinguish the standard high mass X-ray binaries and the ULXs, a UFO-scenario for the formation of WR+OB binaries in dense star systems. Finally we critically discuss the possible effect of rotation on population studies.Comment: 8 pages, 1 figure, to appear in the proceedings of Interacting Binaries: Accretion, Evolution and Outcomes, eds. Antonelli et a