Found 20 talks width keyword massive stars

Video
Thursday September 29, 2016
Dr. Fabian Schneider
Univeristy of Oxford

Abstract

Approximately 10 per cent of massive OBA main-sequence (MS) and pre-MS stars harbour strong, large-scale magnetic fields. At the same time, there is a dearth of magnetic stars in close binaries. A process generating strong magnetic fields only in some stars must be responsible and several channels for the formation of magnetic massive stars have been proposed. In this talk, I will present recent results on the origin and evolution of such strong surface magnetic fields. Regarding the origin, mergers of MS and pre-MS stars have been proposed to form magnetic stars and I will highlight a method to probe this hypothesis observationally. Applying this new method to two magnetic massive stars, we find that they are indeed consistent with being MS merger products. Utilising a large sample of magnetic and non-magnetic OB stars, I will show that there is a dearth of evolved magnetic stars that suggests that magnetic fields disappear over time. I will argue that this is most likely caused by decaying magnetic fields.


Video
Tuesday October 6, 2015
Prof. Norbert Langer
Univ. of Bonn

Abstract

It is often assumed that when stars reach their Eddington limit, strong outflows are initiated, and that this happens only for extreme stellar
masses. I will show that in realistic models of stars up to 500 Msun, the Eddington limit is not reached at the stellar surface. Instead, I will argue that the Eddington limit is exceeded inside the stellar envelope, in hydrogen-rich stars above about 1 ... 30 Msun, and in Wolf-Rayet stars above 7 Msun, with drastic effects for their structure and stability. I will discuss the observational evidence for this, and outline evolutionary consequences.


Video
Thursday September 10, 2015
Prof. Noah Soker
Physics Department TECHNION, Israel

Abstract

I will describe the roles of jets in several quite different astrophysical systems. These include exploding core collapse supernovae, expelling common envelopes, and heating gas in clusters of galaxies. Hot bubbles inflated by jets seem to be a key ingredient in the interaction of jets with the ambient gas. The understanding that jets can efficiently interact with the ambient gas leads to new notions, such as the jittering jets model to explode massive stars, and the grazing envelope evolution(GEE) that can replace the common envelope evolution in some cases.

Video
Thursday November 27, 2014
Dr. Melanie Godart
IAC

Abstract

Massive stars shape and drive our Universe. Many issues such as their formation, their stability and the mass loss effects for example, are nowadays far for being completely understood. To improve our understanding, asteroseismology provides a powerful tool and excellent results have been obtained over the last years. Recent ground-based and space observations have shown the presence of pulsations in massive main sequence and post-main sequence stars, such as acoustic and gravity modes excited by the kappa-mechanism and even solar-like oscillations. Theoretical studies emphasized the presence of strange modes in massive models, excited by the strange mode instability mechanism. Moreover, recent theoretical analyses have shown that hot supergiants can also pulsate in oscillatory convective modes propagating in the superficial layers of these stars. I will expose here the instability domains of massive stars as well as their excitation mechanisms and present the latest results in the domain.


Video
Wednesday November 19, 2014
Dr. Cyril Georgy
Keele University

Abstract

We will start by recalling the effects of rotation on stellar evolution and briefly explain its implementation in a stellar evolution code. We will present a set of various grids of massive stars models, and then show some recent results obtained by our new SYCLIST toolbox, which is able (among other things) to generate synthetic stellar clusters, including various physical ingredients, such as initial rotation and angle of view distributions, gravity and limb darkening, etc.


Video
Thursday July 10, 2014
Dr. Geroges Meynet
Univ. of Geneve

Abstract

In the early Universe, massive stars played a key role in the early chemical evolution of galaxies and in injecting important amount of ionising radiation in their environments. The first question that will be addressed in this seminar is the following one: can we infer some properties of the first stellar generations in the Universe by studying the surface composition of very metal poor stars in the halo of our Galaxy? The talk will focus on both the regular halo stars and the so-called Carbon Enhanced Metal Poor (CEMP) stars. The second topic that will be addressed in this talk deals with a much more recent event, the birth of the Solar System. Here the question will be: what do the presence of short lived radioactive elements in the proto-solar nebula tell us about the stellar environment of the Sun 4.56 billion years ago? The talk will focus on the discussion of the origin of 26Al and 60Fe in the proto-solar nebula.


Video
Tuesday April 29, 2014
Dr. Sergio Simon
IAC

Abstract

The application of the Fourier transform (FT) technique to high resolution spectra of OB-type stars has challenged our previous knowledge about stellar rotation in stars in the upper region of the HRD. The FT is an old and powerful tool that has being widely used in the case of cool stars, but only very recently applied to massive stars in a systematic way. In this talk I will present the results of the line-broadening characterization of ~250 Galactic OB-type stars (including dwarfs, giants and supergiants with spectral types O4-B9) from the IACOB spectroscopic database. I will show how these analyses have led to a downward revision of previously determined projected rotational velocities in these stars, and have definitely confirmed the presence of a non-negligible extra line-broadening contribution (commonly called macroturbulent broadening) in the whole OB star domain. I will also provide some notes about the importance of these findings on the evolution of massive stars and the detection of stellar oscillations along the lifetime of these important astrophysical objects.


Video
Wednesday November 13, 2013
Prof. Rudolf Kudritzki
Institute for Astronomy, University of Hawaii at Manoa

Abstract

The determination of chemical composition and distances of galaxies is crucial for constraining the theory of galaxy formation and evolution in a dark energy and cold dark matter dominated universe. However, the standard technique using HII regions to determine the metallicity of star forming galaxies, nearby and at high redshift, is subject to large systematic uncertainties that are poorly understood and the determinination of accurate distances using Cepheids suffers from uncertainties caused by the metallicity dependence of the period luminosity relationship and extinction and crowding corrections. Multi-object spectroscopy of blue and red supergiant stars - the brightest stars in the universe at visual and NIR wavelengths - provides an attractive alternative. I will present results accumulated over recent years for galaxies in the Local Group and beyond out to a distance of 8 Mpc and will discuss the potential of future work with TMT and E-ELT. Combining the photon collecting power of these next generation telescopes with Adaptive Optics we will be able to study individual supergiant stars in galaxies as distant as the Coma cluster. With spectroscopy of the integrated light of young very massive Star Super Clusters and simple population synthesis techniques we can reach out ten times further.


Video
Thursday February 21, 2013
Prof. Sally Oey
University of Michigan

Abstract

The fate of ionizing radiation from massive stars has fundamental consequences on scales ranging from the physics of circumstellar disks to the ionization state of the entire universe. On galactic scales, the radiative feedback from massive stars is a major driver for the energetics and phase balance of the interstellar medium in star-forming galaxies. While even starburst galaxies appear to be largely optically thick in the Lyman continuum, ionization-parameter mapping shows that significant populations of HII regions within galaxies are optically thin, powering the diffuse, warm ionized medium. I will discuss our multi-faceted work to clarify our understanding of radiative feedback in star-forming galaxies from the Magellanic Clouds to starbursts.


Video
Tuesday May 29, 2012
Dr. Sebastián Ramírez Alegría
Instituto de Astrofísica de Canarias, Spain

Abstract

I am going to present the new massive and obscured cluster Masgomas-1. This cluster, discovered by our group formed by astronomers from the IAC and CEFCA, is the
first candidate derived from the preliminary version of our systematic search algorithm for obscured (and young) massive clusters, and part of the MASGOMAS project  (MAssive Stars in Galactic Obscured MAssive clusterS). In this talk I will present the spectrophotometric observations obtained with LIRIS at William Herschel Telescope (ORM), which allowed the physical characterization of the massive stellar population of Masgomas-1, and the confirmation of the  cluster's massive nature
(i.e. Mcl > 10^4 Msun).


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