Found 25 talks width keyword massive stars

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

Abstract

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.


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Thursday January 21, 2021
Prof. Corinne Charbonnel
University of Geneva

Abstract

Globular clusters (GCs) are fascinating objects nearly as old as the Universe that provide insight on a large variety of astrophysical and cosmological processes. However, their formation and their early and long-term evolution are far from being understood. In particular, the classical paradigm describing GCs as large systems of coeval stars formed out of chemically homogeneous material has been definitively swept away by recent high-precision spectroscopic and deep photometric observations. These data have provided undisputed evidence that GCs host multiple stellar populations, with very peculiar chemical properties. In this talk, I will review the properties of these multiple populations, before presenting the different scenarios that have been proposed to describe their formation. I will focus on the (many) current theoretical issues and open questions. 


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Tuesday July 16, 2019
Dr. Danny Lennon
IAC

Abstract

The existence of apparently isolated massive stars has been recognized for some time, and various explanations have been proposed to explain these ranging from isolated star formation to variouscluster ejection mechanisms. In this talk I will present recent results from Gaia and Hubble on stellar dynamics within the Tarantula Nebula/30 Doradus region of the Large Magellanic Cloud. I will discuss how these complementary datasets have improved our knowledge of this nearby mini-starburst. The first results indicate the existence of a few stars in the region with masses ~100 solar masses that have been ejected from the central dense cluster R136. Ejection velocities appear torange from a few 10s of km/s to ~100 km/s. Given the extreme youth of R136 it is therefore likely that the mechanism of ejection was via the dynamical interaction channel rather than the binary supernova ejection scenario.


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Thursday February 28, 2019
Prof. Alex Fullerton
Space Telescope Science Institute

Abstract

The growth of astrophysical understanding typically results fromthe constructive interplay between theoretical ideas andobservational insights, with each mode of exploration drivingprogress at different times. The result is invariably a morecomplicated but richer picture of the phenomenon than initiallyenvisaged, as well as deeper appreciation of the behavior ofcomplex systems.In this talk, I will use the development of our understanding ofthe structure of outflows from massive O- and B-type stars toillustrate this collaborative “dance”. Starting from the smooth,spherically symmetric models for radiatively driven windsdeveloped in the late 1960s, our view of these outflows hasevolved to include the growth of inhomogeneities on a variety ofspatial scales. Explanations for the origin of this structure havein turn prompted the realization that non-radiative processesmust also shape the emergence of the wind from the stellarphotosphere. Consequently, O- and B-type stars are morecomplicated – and interesting! – objects than often thought.While many fruitful avenues of research remain to be explored,the current paradigm provides a (mostly) self-consistent pictureof massive stars and their outflows.


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Monday November 5, 2018
Dr. Rainer Kuschnig
Graz University of Technology, Graz, Austria

Abstract

BRITE-Constellation (BRight Target Explorer) consists of six nano-satellites aiming to study of variability of the brightest stars in the sky. Austria, Poland, and Canada contribute two spacecraft each all launched into low earth orbits. The satellites have the same structure: they are 20 cm cubes, 7kg mass, with a CCD photometer fed by 3 cm aperture telescopes. The main difference between pairs of satellites is the instrument passband which set to blue (400-450nm) or red (550-700nm). The core scientific objective is to obtain high precision two color photometry, with a time base of up to 180 days, of stars brighter than 4.5 mag in order to study stellar pulsations, spots, and granulation, eclipsing binaries, search for planets and more.
Since the launch of the first two BRITE satellites in February 2013 more than 5 and a half years of experiences in space have been gathered to run the mission and a summary of lessons learned will be presented.  By now more than 20 peer-reviewed scientific articles have been published based on data collected by BRITE-Constellation satellites in space and most results presented therein benefitted greatly from supplementary spectroscopy by meter size telescopes obtained on ground.


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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.


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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.


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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.

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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.


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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.


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