667 research outputs found
The rate of WD-WD head-on collisions in isolated triples is too low to explain standard type Ia supernovae
Type Ia supernovae (Ia-SNe) are thought to arise from the thermonuclear
explosions of white dwarfs (WDs). The progenitors of such explosions are still
highly debated; in particular the conditions leading to detonations in WDs are
not well understood in most of the suggested progenitor models. Nevertheless,
direct head-on collisions of two WDs were shown to give rise to detonations and
produce Ia-SNe - like explosions, and were suggested as possible progenitors.
The rates of such collisions in dense globular clusters are far below the
observed rates of type Ia SNe, but it was suggested that quasi-secular
evolution of hierarchical triples could produce a high rate of such collisions.
Here we used detailed triple stellar evolution populations synthesis models
coupled with dynamical secular evolution to calculate the rates of WD-WD
collisions in triples and their properties. We explored a range of models with
different realistic initial conditions and derived the expected SNe total mass,
mass-ratio and delay time distributions for each of the models. We find that
the SNe rate from WD-WD collisions is of the order of 0.1% of the observed
Ia-SNe rate across all our models, and the delay-time distribution is almost
uniform in time, and is inconsistent with observations. We conclude that SNe
from WD-WD collisions in isolated triples can at most provide for a small
fraction of Ia-SNe, and can not serve as the main progenitors of such
explosions.Comment: 13 pages, 4 figures, submitted to A&
Binary black hole mergers from field triples: properties, rates and the impact of stellar evolution
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. After a black hole triple is
formed, its dynamical evolution is computed using either the orbit-averaged
equations of motion, or a high-precision direct integrator for triples with
weaker hierarchies for which the secular perturbation theory breaks down. Most
black hole mergers in our models are produced in the latter non-secular
dynamical regime. We derive the properties of the merging binaries and compute
a black hole merger rate in the range (0.3- 1.3) Gpc^{-3}yr^{-1}, or up to
~2.5Gpc^{-3}yr^{-1} if the black hole orbital planes have initially random
orientation. Finally, we show that black hole mergers from the triple channel
have significantly higher eccentricities than those formed through the
evolution of massive binaries or in dense star clusters. Measured
eccentricities could therefore be used to uniquely identify binary mergers
formed through the evolution of triple stars. While our results suggest up to
~10 detections per year with Advanced-LIGO, the high eccentricities could
render the merging binaries harder to detect with planned space based
interferometers such as LISA.Comment: Accepted for publication in ApJ. 10 pages, 6 figure
PopCORN: Hunting down the differences between binary population synthesis codes
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. We investigate
whether the differences are caused by different assumptions made in the BPS
codes or by numerical effects. To simplify the complex problem of comparing BPS
codes, we equalise the inherent assumptions as much as possible. We find that
the simulated populations are similar between the codes. Regarding the
population of binaries with one WD, there is very good agreement between the
physical characteristics, the evolutionary channels that lead to the birth of
these systems, and their birthrates. Regarding the double WD population, there
is a good agreement on which evolutionary channels exist to create double WDs
and a rough agreement on the characteristics of the double WD population.
Regarding which progenitor systems lead to a single and double WD system and
which systems do not, the four codes agree well. Most importantly, we find that
for these two populations, the differences in the predictions from the four
codes are not due to numerical differences, but because of different inherent
assumptions. We identify critical assumptions for BPS studies that need to be
studied in more detail.Comment: 13 pages, +21 pages appendix, 35 figures, accepted for publishing in
A&A, Minor change to match published version, most important the added link
to the website http://www.astro.ru.nl/~silviato/popcorn for more detailed
figures and informatio
Progenitors of Supernovae Type Ia
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. We determine the theoretical rates and delay time
distribution of SNIa progenitors and in particular study how assumptions affect
the predicted rates.Comment: 6 pages, 6 figures, appeared in proceedings for "The 18th European
White Dwarf Workshop
The evolution of hierarchical triple star-systems
Stars and planetary system
The evolution of hierarchical triple star-systems
Stars and planetary system
- β¦