Found 10 talks width keyword binary evolution

Tuesday July 6, 2021
Prof. Norbert Langer
University of Bonn


Massive stars are generally fast rotators, however, with significant dispersion. We discuss the hypothesis that all OB stars are all born with very similar spins, with slower and faster rotators being produced by close binary evolution. We review supporting evidence from recent observations of young and rich star clusters, from OB star surveys, and from dense grids of detailed binary evolution models. We connect the OB star spins with the likelihood of evolved/compact binary companions, and with the variety of the explosive end states of massive stars.



Thursday March 11, 2021
Dr. Tomer Shenar


"Classical Wolf-Rayet (WR) stars" represent a class of hot, hydrogen-depleted stars wtih powerful stellar winds and are prominent progenitors of black holes. Next to their unparalleled radiative and mechanical energy feedback, they offer unique probes of massive-star evolution at the upper-mass end. To become a classical WR star, single stars require substantial mass-loss to strip their outer, hydrogen-rich layers, implying that only very massive stars could enter the WR phase. However, mass-transfer in binaries can further aid in the stripping of stars and form Wolf-Rayet stars, or more generally helium stars, at lower masses.  Due to the decrease of mass-loss with metallicity, it has been predicted that WR stars at low metallicity tend to form in binaries. However, this has so far not been supported by observations.

In my talk, I will give an overview on our current knowledge of the properties of Wolf-Rayet populations in the Galaxy and the Magellanic Clouds based on exhaustive spectral analyses. I will illustrate why binary formation does not necessarily dominate the evolution of WR stars at low metallicity, and highlight important discrepancies between theory and observations of WR stars. I will discuss the observed rarity of intermediate mass helium stars, and present recent reports of unique helium stars in the exotic binaries LB-1 and HR 6819.


Tuesday February 23, 2021
Dr. Athira Menon
University of Amsterdam


The majority of massive stars are born in close binary systems with orbital periods of a few days. At some point during their core-hydrogen burning phase, both members of these close binaries inevitably overflow their Roche lobes simultaneously and get bound by a common equipotential surface. The characteristics of this `contact phase’ will determine the fate of the binary system: whether the stars will merge on the main sequence or evolve further towards becoming potential gravitational-wave progenitors. Although data is available for several of these massive contact binaries in the Magellanic Clouds and the Milky Way, there has not been a dedicated study of these systems so far. In this talk, I will present the first set of detailed binary models covering a wide range of initial masses (20-80 Msun) and initial periods (0.6-2 days), focusing especially on the properties of the contact phase. We find that our models can approximately reproduce the period-mass ratio trend of the observed binaries although for the higher masses of our grid, our model predictions do not match with what is observed. We also find that those binary models which are in contact over nuclear timescales evolve towards equal masses before ultimately merging on the main sequence. This first study of massive contact binaries has allowed us to gain insights into the physics of massive contact systems and also provide reasonable predictions for the final fate of close massive binary stars.

Tuesday July 21, 2020
Dr. Joris Vos
University of Potsdam


Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes of stable mass transfer from evolved red giants. The orbits of these binaries show a strong correlation between their orbital periods and mass ratios. The origins of this correlation have, so far, been lacking a conclusive explanation.
We have performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA. We have used a standard model for binary mass loss and a standard Galactic metallicity history.  We have achieved an excellent match to the observed period - mass ratio correlation without explicitly fine-tuning any parameters. Furthermore, our models produce a good match to the observed period - metallicity correlation.
We demonstrate, for the first time, how the metallicity history of the Milky Way is imprinted in the properties of the observed post-mass transfer binaries. We show that Galactic chemical evolution is an important factor in binary population studies of interacting systems containing at least one evolved low-mass (Mi < 1.6 Msol) component. Finally, we provide an observationally supported model of mass transfer from low-mass red giants onto main-sequence stars.

Zoom link:

Tuesday February 12, 2019
Dr. Hans Zinnecker
Univ. Autónoma de Chile, Severo Ochoa senior researcher



In this talk, I will review some highlights of my
studies of star formation in the past 35 years.

I started my PhD thesis on the theory of the stellar IMF
in 1977 at MPE in Garching and completed it in 1981.
I studied two different models: (a) hierarchical
cloud fragmentation (star formation as a random
multiplicative process) and (b) competitive accretion
in a protostellar cluster. The first model predicted a
log-normal stellar mass distribution (down to substellar
masses) while the second model produced a power law
(with a slope x = -1, close to the Salpeter slope). 
I will outline both models and discuss how they stood 
the test of time. 
Later, as a postdoc at ROE in Scotland (1983-87), I became 
an observer (mostly at UKIRT) and turned to near-infrared 
(J,H,K) observations of young embedded star clusters, 
such as the Orion Trapezium Cluster, using infrared arrays. 
We observed near-infrared stellar luminosity functions
and derived the corresponding stellar mass spectrum,
using time-dependent mass-luminosity relations based
on pre-Main Sequence evolutionary tracks (without accretion).
A key cluster we studied (with HST) in the near-IR was 
R136/30Dor in the LMC, and we proved the existence of a 
low-mass pre-Main Sequence population in this starburst cluster.
In the 1990s, we carried out the first direct imaging studies
of young low-mass pre-Main Sequence binary stars and also the
multiplicity of massive stars, using 2D speckle interferometry
and adaptive optics observations.
We also discovered the first molecular hydrogen (H2) jets
from deeply embedded low-mass protostars (HH211, HH212).  
Finally, time permitting, I will describe how I turned from a
near-infrared stellar astronomer to an interstellar
far-infrared astronomer, working with the B747SP
air-borne Stratospheric Observatory for Infrared
Astronomy (SOFIA) at NASA-Ames for the last 6 years.

Thursday May 17, 2018
Dr. Henri M. J. Boffin
ESO, Garching


Binarity and mass transfer appear to play a key role in the shaping and, most likely, in the formation of planetary nebulae (PNe), thereby explaining the large fraction of axisymmetric morphologies. I present the binary hypothesis for PNe and its current status. Recent discoveries have led to a dramatic increase in the number of post-common envelope binary central stars of PNe, thereby allowing us to envisage statistical studies. Moreover, these binary systems let us study in detail the mass transfer episodes before and after the common envelope, and I present the evidences for mass transfer - and accretion - prior to the common envelope phase.

Tuesday January 16, 2018
Dr. Carlos del Burgo


We employ a Bayesian method to infer stellar parameters from the PARSEC  v1.2S library of stellar evolution models and test the accuracy of these theoretical predictions. Detached eclipsing binaries are ideal for testing. We employ a compilation of 165 detached eclipsing binary systems of our galaxy and the Magellanic clouds with reliable metallicities and measurements for the mass and radius to 2 per cent precision for most of them. We complement the analysis with 107 stars that are closer than 300 pc, for which we adopted solar metallicity. The applied Bayesian analysis relies on a prior for the initial mass function and flat priors for age and metallicity, and it takes on input the effective temperature, radius, and metallicity, and their uncertainties, returning theoretical predictions for other stellar parameters of the binaries. Our research is mainly based on the comparison of dynamical masses with the theoretical predictions for the selected binary systems. We determine the precision of the models. Also, we derive distances for the binaries, which are compared with trigonometric parallaxes whenever possible. We discuss the effects of evolution and the challenges associated with the determination of theoretical stellar ages.

Wednesday March 6, 2013
Dr. Jesús Corral Santana


X-ray transients are binary systems composed by a 'normal' star which is transfering mass onto a compact object (either a black hole or a neutron star) through Roche lobe overflow. These systems show sporadic outburst episodes and long quiescence states, being ideal systems to search for stellar-mass black holes. Different studies predict a Galactic population of ~10^3-10^4 X-ray transients, however, there are only 18 stellar-mass black holes dynamically confirmed (and other ~32 candidates whichc share similar timing and spectral properties).

In this talk I'll present the case of Swift J1357.2-0933, a new X-ray transient discovered in 2011. Our analysis shows that Swift J1357.2-0933 is the first black hole transient seen at a large inclination (>75º). High time resolution lightcurves show dips or eclipses produced by a vertical structure present in the inner accretion rather than the companion star. Some dips display up to ~50% reduction of flux in ~2min (~30% reduction of flux in 7s). Moreover, the dips present a recurrence period of a few minutes which increases with time. This can only be explained by the expansion of the obscuring structure outward in the accretion. Swift J1357.2-0933 could be the prototype of an hytherto Galactic population of black hole transients with large inclinations.

Friday November 20, 2009
Dr. Robert Williams
Space Telescope Science Institute, USA


Spectroscopic observations of novae date back a century, and the fundamental nature of the outburst has been understood for 50 years. Yet, recent observations suggest possible major modifications to the standard nova paradigm. A high-resolution spectroscopic survey of novae has revealed short-lived heavy element absorption systems near maximum light consisting of Fe-peak and s-process elements. The absorbing gas is circumbinary and it must pre-exist the outburst. Its origin appears to be mass ejection from the secondary star, implying large episodic mass transfer events from the secondary that initiate the nova outburst. The spectroscopic evolution of novae is interpreted in terms of two distinct interacting gas systems in which the bright continuum is produced by the outburst ejecta but absorption and emission lines originate in gas ejected by the secondary star in a way that may explain dust formation and X-ray emission from novae.

Friday November 20, 2009
Dr. Pasi Hakala
Tuorla Observatory, University of Turku, Finland


I present some recent results from our Optical and NIR studies of five short period low-mass X-ray binaries (LMXB's; X1822-371, X1957+115, UW CrB, X1916-05 and X0614+091). Optical photometry and spectroscopy reveal some surprising results on the geometry and evolution of accretions discs in LMXB's. Based on our data, it is increasingly clear that accretion discs in these systems are far from being stable and must undergo substantial precession and/or warping behaviour on timescales less than a day in case of the shortest period systems.

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