S. Toonen

S. Toonen
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Solar and Stellar Astrophysics (17)
 
High Energy Astrophysical Phenomena (10)
 
Astrophysics of Galaxies (4)
 
Astrophysics (3)
 
Earth and Planetary Astrophysics (2)
 
General Relativity and Quantum Cosmology (1)

Publications Authored By S. Toonen

We consider the formation of binary black hole mergers through the evolution of field massive triple stars. In this scenario, favorable conditions for the inspiral of a black hole binary are initiated by its gravitational interaction with a distant companion, rather than by a common-envelope phase invoked in standard binary evolution models. We use a code that follows self-consistently the evolution of massive triple stars, combining the secular triple dynamics (Lidov-Kozai cycles) with stellar evolution. Read More

White dwarfs (WDs) are powerful tools to study the evolutionary history of stars and binaries in the Galaxy. But do we understand their multiplicity from a theoretical point of view? This can be tested by a comparison with the sample of WDs within 20 pc, which is minimally affected by selection biases. From the literature, we compile the available information of the local WD sample with a particular emphasis on their multiplicity, and compare this to synthetic models of WD formation in single stars and binaries. Read More

Even though Type Ia supernovae (SNIa) play an important role in many fields in astronomy, the nature of the progenitors of SNIa remain a mystery. One of the classical evolutionary pathways towards a SNIa explosion is the single degenerate (SD) channel, in which a carbon-oxygen white dwarf accretes matter from its non-degenerate companion until it reaches the Chandrasekhar mass. Constraints on the contribution from the SD channel to the overall SNIa rate come from a variety of methods, e. Read More

Double white dwarf (DWD) binaries are expected to be very common in the Milky Way, but their intrinsic faintness challenges the detection of these systems. Currently, only a few tens of detached DWDs are know. Such systems offer the best chance of extracting the physical properties that would allow us to address a wealth of outstanding questions ranging from the nature of white dwarfs, over stellar and binary evolution to mapping the Galaxy. Read More

Field stars are frequently formed in pairs, and many of these binaries are part of triples or even higher-order systems. Even though, the principles of single stellar evolution and binary evolution, have been accepted for a long time, the long-term evolution of stellar triples is poorly understood. The presence of a third star in an orbit around a binary system can significantly alter the evolution of those stars and the binary system. Read More

Binary mass transfer is at the forefront of some of the most exciting puzzles of modern astrophysics, including Type Ia supernovae, gamma-ray bursts, and the formation of most observed exotic stellar populations. Typically, the evolution is assumed to proceed in isolation, even in dense stellar environments such as star clusters. In this paper, we test the validity of this assumption via the analysis of a large grid of binary evolution models simulated with the SeBa code. Read More

The theoretical and observed populations of pre-cataclysmic variables (pre-CVs) are dominated by systems with low-mass white dwarfs (WDs), while the WD masses in CVs are typically high. In addition, the space density of CVs is found to be significantly lower than theoretical models. We investigate the influence of nova outbursts on the formation and (initial) evolution of CVs. Read More

Aims. We model the present-day population of 'classical' low-mass X-ray binaries (LMXBs) with neutron star accretors, which have hydrogen-rich donor stars. Their population is compared with that of hydrogen-deficient LMXBs, known as ultracompact X-ray binaries (UCXBs). Read More

Aims: We study single and binary white dwarfs in the inner halo of the Milky Way in order to learn more about the conditions under which the population of halo stars was born, such as the initial mass function (IMF), the star formation history, or the binary fraction. Methods: We simulate the evolution of low-metallicity halo stars at distances up to ~ 3 kpc using the binary population synthesis code SeBa. We use two different white dwarf cooling models to predict the present-day luminosities of halo white dwarfs. Read More

White dwarfs (WDs) can increase their mass by accretion from companion stars, provided the mass-accretion rate is high enough to avoid nova eruptions. The accretion regimes that allow growth of the WDs are usually calculated assuming constant mass-transfer rates. However, it is possible that these systems are influenced by effects that cause the rate to fluctuate on various timescales. Read More

Binary population synthesis (BPS) modelling is a very effective tool to study the evolution and properties of close binary systems. The uncertainty in the parameters of the model and their effect on a population can be tested in a statistical way, which then leads to a deeper understanding of the underlying physical processes involved. To understand the predictive power of BPS codes, we study the similarities and differences in the predicted populations of four different BPS codes for low- and intermediate-mass binaries. Read More

Context: The nature of the progenitors of type Ia supernova (SN) progenitors remains unclear. While it is usually agreed that single-degenerate progenitor systems would be luminous supersoft X-ray sources (SSSs), it was recently suggested that double-degenerate progenitors might also go through a SSS phase. Aims: We aim to examine the possibility of double-degenerate progenitor systems being SSSs, and place stringent upper limits on the maximally possible durations of any SSS phases and expected number of these systems in a galactic population. Read More

Context. An important ingredient in binary evolution is the common-envelope (CE) phase. Although this phase is believed to be responsible for the formation of many close binaries, the process is not well understood. Read More

[abridged] Aims. We model the number and properties of ultracompact X-ray binaries (UCXBs) in the Galactic Bulge. The objective is to learn about the formation of UCXBs and their evolution, such as the onset of mass transfer and late-time behavior. Read More

There is general agreement that supernovae Ia correspond to the thermonuclear runaway of a white dwarf that is part of a compact binary, but the details of the progenitor systems are still unknown and much debated. One of the proposed progenitor theories is the single-degenerate channel in which a white dwarf accretes from a companion, grows in mass, reaches a critical mass limit, and is then consumed after thermonuclear runaway sets in. However, there are major disagreements about the theoretical delay time distribution and the corresponding time-integrated supernova Ia rate from this channel. Read More

Despite the significance of Type Ia supernovae (SNeIa) in many fields in astrophysics, SNeIa lack a theoretical explanation. The standard scenarios involve thermonuclear explosions of carbon/oxygen white dwarfs approaching the Chandrasekhar mass; either by accretion from a companion or by a merger of two white dwarfs. We investigate the contribution from both channels to the SNIa rate with the binary population synthesis (BPS) code SeBa in order to constrain binary processes such as the mass retention efficiency of WD accretion and common envelope evolution. Read More

Despite the significance of type Ia supernovae (SNeIa) in many fields in astrophysics, SNeIa lack a theoretical explanation. We investigate the potential contribution to the SNeIa rate from the most common progenitor channels using the binary population synthesis (BPS) code SeBa. Using SeBa, we aim constrain binary processes such as the common envelope phase and the efficiency of mass retention of white dwarf accretion. Read More

We compare the results of three binary population synthesis codes to understand the differences in their results. As a first result we find that when equalizing the assumptions the results are similar. The main differences arise from deviating physical input. Read More

The study of Type Ia supernovae (SNIa) has lead to greatly improved insights into many fields in astrophysics, however a theoretical explanation of the origin of these events is still lacking. We investigate the potential contribution to the SNIa rate from the population of merging double carbon-oxygen white dwarfs. We aim to develope a model that fits the observed SNIa progenitors as well as the observed close double white dwarf population. Read More

We briefly discuss the method of population synthesis to calculate theoretical delay time distributions of type Ia supernova progenitors. We also compare the results of the different research groups and conclude that although one of the main differences in the results for single degenerate progenitors is the retention efficiency with which accreted hydrogen is added to the white dwarf core, this cannot explain all the differences. Read More

An update is presented to the software package SeBa for simulating single star and binary evolution in which new stellar evolution tracks have been implemented. SeBa is applied to study the population of close double white dwarf and the delay time distribution of double white dwarf mergers that may lead to Supernovae Type Ia. Read More

Stars on eccentric orbits around a massive black hole (MBH) emit bursts of gravitational waves (GWs) at periapse. Such events may be directly resolvable in the Galactic centre. However, if the star does not spiral in, the emitted GWs are not resolvable for extra-galactic MBHs, but constitute a source of background noise. Read More

The Fabry-Perot interferometer FaNTOmM was used at the 3.6m Canada France Hawaii Telescope and the 1.6m Mont Megantic Telescope to obtain data cubes in H-alpha of 9 nearby spiral galaxies from which maps in integrated intensity, velocity, and velocity dispersion were derived. Read More

We study the two-dimensional kinematics of the H-alpha-emitting gas in the nearby barred Scd galaxy, NGC 6946, in order to determine the pattern speed of the primary m=2 perturbation mode. The pattern speed is a crucial parameter for constraining the internal dynamics, estimating the impact velocities of the gravitational perturbation at the resonance radii, and to set up an evolutionary scenario for NGC 6946. Our data allows us to derive the best fitting kinematic position angle and the geometry of the underlying gaseous disk, which we use to derive the pattern speed using the Tremaine-Weinberg method. Read More

We study the kinematics of the barred spiral galaxy NGC 6946 by investigating the velocity field from H-alpha Fabry-Perot observations, determined the pattern speed of the bar by using the Tremaine-Weinberg method, and find a main pattern speed of 21.7 (+4.0,-0. Read More