Found 10 talks width keyword binaries
The MAGIC telescopes are a stereoscopic system
of two 17m mirror diameter Cherenkov telescopes for gamma-ray observations, in operation since many years on the island of
La Palma at the Observatorio del Roque de los Muchachos.
A new installation allows us to use those telescopes as optical
intensity interferometer which enables us to measure the size of bright
objects in the range of 0.6-1.5 milli-arcsec and other physical
parameters. In this presentation the setup is explained, our physics
targets, first results and also a future outlook of this project
with respect to the Cherenkov telescope array (CTA) currently
Massive stars are often found to be in pairs. This configuration is both a blessing and a curse. From it, we can estimate their exact properties such as their masses but the interactions that result during their life considerably affect the way that the stars evolve.
Here, we provide an overview of progresses made through a number of medium and large surveys. These results provide new insights on the observed and intrinsic multiplicity properties of massive stars through a large range of masses and at different metallicities. Furthermore, to understand how the stars evolve when they are in pair and what are the effects of these interactions on the stellar properties, we undertook a large study of more than 60 massive binaries at Galactic and LMC metallicities using spectral disentangling, atmosphere modelling and light curve fitting to determine their stellar parameters, and surface abundances. This unique dataset is the largest sample of binaries composed of at least one O-type star to be studied in such a homogeneous way. It allows us to give strong observational constraints to test theoretical binary evolutionary tracks, to probe rotational and tidal mixings and mass transfer episodes.
About half of the stars in our Galaxy are born in binary systems meaning that their evolution might be affected by the presence of a companion. Many aspects of binary interaction are still unknown so understanding the products that result from interacting systems is crucial to unravel the physical mechanisms involved. A prototypical example of such post-interaction binary systems in the low- and intermediate-mass regime are Barium (Ba) stars. Ba stars are main-sequence or giant stars which show an enhancement of chemical elements that should not yet be overabundant at these evolutionary stages. Currently, it is widely accepted that these chemicals were transferred from a more evolved companion during a phase of mass transfer and that this companion evolved into a cool white dwarf. Understanding the orbital properties of these systems, as well as the stellar properties of the Ba star and its polluter, is the key to the system’s interaction history.
In the last years, the synergy between Gaia data, of unprecedented quality, high-resolution spectroscopy, long-term radial-velocity monitoring programmes, and state-of-the-art stellar and binary evolution models has contributed to a better understanding of the properties of Ba stars and provided new observational constraints to theoretical studies. The new Hertzsprung-Russell diagrams of Ba stars allowed us to accurately determine their evolutionary status and their masses. Additionally, we have recently determined the orbital properties of many main-sequence Ba stars, much less studied until now than their giant counterparts, which led to a thorough comparison of the properties of the two samples. The comparison between the distributions of masses, periods and eccentricities that resulted from this analysis allowed us to investigate the evolution of Ba-star systems between these two phases. Our models show that a second stage of binary interaction, this time between the main-sequence Ba star and its white-dwarf companion, also takes place in some systems, affecting the distribution of orbits observed among Ba giants.
Zoom link: https://rediris.zoom.us/j/96557655189
In symbiotic stars, two different physical regimes of circumstellar
material exist side by side. Around the donor red giant star, there is a
cool and dense conical region of neutral wind. During quiescent phases,
the rest of the wind from the donor is ionized by its companion, in most
cases, a very hot and luminous white dwarf powered by accretion from the
giant's wind. Mass outflow from the majority of cool components in
symbiotic binaries is still not understood well. Some information about
the distribution of circumstellar matter can be obtained by measuring the
neutral hydrogen column densities from Rayleigh scattering along the
multiple lines of sight. I will present the wind velocity profiles derived
from the measured column densities of neutral hydrogen for two quiet
high-inclination symbiotic systems, EG And and SY Mus. The column density
models indicate the wind focusing towards the orbital plane and allow to
investigate the origin of the asymmetric UV continuum light curve profiles
of symbiotic stars.
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.
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.
The improvement on the Imaging Air Cherenkov Technique led to the discovery of a new class of compact binaries: the gamma-ray binaries. This small class consist of only five members, all of them composed by a massive star and a compact object. The nature of the compact object is unknown for all of them but PSR B1259-63, which contains a pulsar. It is crucial to study and monitor these systems not only to understand their behavior, the scenario accounting for the gamma-ray emission and their nature but also to comprehend why we have not detected more sources of this exclusive family. In this presentation, I will review the state-of-the-art of this field and I will present the observations performed with the MAGIC telescopes in order to unveil the nature of gamma-ray binaries.
The theory of stellar evolution is well developed over the past decades, and in particular the predictions of one dimensional numerical models have passed basic observational tests. With the advent of high precision astronomical observations, these tests can now be improved to fine tune the physics of the models. In particular, the combination of exploiting binary properties with the information obtained from asteroseismology, proves to provide a promising test framework. However, both binarity and seismology increase the complexity of the observational models and their relation to the stellar evolutionary model, and therefore require as many independent tests as possible.
Spectroscopic analysis of stellar populations is widely used to understand the history of many systems including globular clusters, nuclear star clusters, dwarf galaxies through to giant galaxies over a wide range of redshifts. In this talk I first explore aspects of stellar population fitting, focussing on the effects of interacting binary stars on the yields and hence the spectra of early-type galaxies. The second part of the talk concentrates on what we know about supernovae type Ia and the importance of understanding their contributions to the chemical evolution of galaxies and stellar populations.
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