Found 25 talks width keyword stellar evolution

Tuesday September 20, 2022
Dr. Asif ud-Doula
Penn State University


Massive stars (at least eight times as massive as the Sun) possess strong stellar winds driven by radiation. With the advent of the so called MiMeS collaboration, an increasing number of these massive stars have been confirmed to have global magnetic fields. Such magnetic fields can have significant influence on the dynamics of these stellar winds which are strongly ionized. Such interaction of the wind and magnetic field can generate copious amount of X-rays, they can spin the star down, they can also help form large scale disk-like structures. In this presentation I will discuss the nature of such radiatively-driven winds and how they interact with magnetic fields.

Tuesday May 31, 2022
Dr. Orlagh Creevey
Observatoire Cote d'Azur (France)


Gaia Data Release 3 (13 June 2022) contains astrophysical parameters for up to 1.5 billion sources derived from the low resolution BP and RP prism spectra, the high resolution RVS spectra, photometry and astrometry.

These include object classifications (star, galaxy, stellar spectral type,...), unresolved galaxies and quasar redshifts (~6 million), outlier objects, interstellar medium characterisation (extinction and DIBs), and spectroscopic and evolutionary parameters (~470 million) for a large variety of stellar types from ultra-cool dwarfs to hot OB stars.

In this talk, I will present an overview of the astrophysical parameter content of Gaia DR3 that was derived using the Astrophysical Parameters Inference System (Apsis) software. I will first give a brief description of the data, models and methods that were employed, and then I will focus on describing what type of parameters you can find in the archive and where to find them among the 30+ new tables. I will then describe the overall performance and present some pre-Gaia DR3 highlights.

Thursday February 24, 2022
Dr. Diego Godoy-Rivera


Rotation plays an important role in the life of stars and offers a potential diagnostic to infer their ages and that of their planets. This idea is known as gyrochronology, and if properly calibrated, its applications to Galactic, stellar, and exoplanetary astrophysics would be far-reaching. Nevertheless, while potentially fruitful over a wide range of ages and masses, recent results have raised concerns regarding gyrochronology’s applicability. In this talk, I will present the opportunities that the Gaia astrometry has opened to address these issues. First, regarding rotation’s classical calibrators, I will illustrate the impact that removing the non-member contamination has on the rotational sequences of open clusters. Second, I will present a novel method that tests the state-of-the-art gyrochronology relations in under-explore domains using wide binary stars. Finally, I will discuss the prospects for expanding the existing rotational constraints in unprecedented regimes using data from the TESS mission.

Tuesday January 25, 2022
Drs. Sarah Martell
Australian National University


The field of Galactic archaeology has been very active in recent years, with a major influx of data from the Gaia satellite and large spectroscopic surveys. The major science questions in the field include Galactic structure and dynamics, the accretion history of the Milky Way, chemical tagging, and age-abundance relations. I will give an overview of GALAH as a large spectroscopic survey, and describe how it is complementary to other ongoing and future survey projects. I will also discuss recent science highlights from the GALAH team and compelling questions for future work.

Tuesday December 14, 2021
Dr. Santi Cassisi


Galactic globular clusters have always been at the crossroad of several investigations
in both Stellar and Galactic Astrophysics. For long time, they have been considered
the prototypes of Simple Stellar Populations, and hence used for testing and calibrating
stellar evolutionary models as well as population synthesis tools. Nowadays, after the 
discovery of the presence of multiple stellar populations in almost all Galactic GCs, we know
that this assumption is no longer valid. The process(es) of formation and early evolution 
of these star clusters is (are) very far to be understood, and any scenario so far envisaged is
severely challenged by the pletora of empirical evidence collected till now. In the same time,
thanks to the availability of an impressive observational framework - collected by combining
kinematic measurements from Gaia mission, with data provided by large spectroscopic and 
photometric surveys -, GCs are playing a crucial role for our understanding of the
assembly history of the Milky Way.
We will review our present knowledge about these important stellar systems, discussing the 
several, open issues related to their formation/evolution, and discuss how we can use them
in our effort to depict the Milky Way assembly history.

Tuesday November 23, 2021
Dr. Dainis Dravins
Lund Observatory (Sweden)


The new generation of spectrometers designed for extreme precision radial velocities enable correspondingly precise stellar spectroscopy. It is now fruitful to theoretically explore what the information content would be if stellar spectra could be studied with spectral resolutions of a million or more, and to deduce what signatures remain at lower resolutions. Hydrodynamic models of stellar photospheres predict how line profiles shapes, asymmetries, and convective wavelength shifts vary from disk center to limb. Corresponding high-resolution spectroscopy across spatially resolved stellar disks is now practical using differential observations during exoplanet transits, thus enabling the testing of such models. A most demanding task is to understand and to model spectral microvariability toward the radial-velocity detection of also low-mass planets in Earth-like orbits around solar-type stars. Observations of the Sun-as-a-star with extreme precision spectrometers now permit searches for spectral-line modulations on the level of a part in a thousand or less, feasible to test against hydrodynamic models of various solar features.

Tuesday November 23, 2021
Dr. Eva Villaver


Planetary systems have been found systematically orbiting main sequence stars and red giants. But the detection of planets per se during the white dwarf phase has been more elusive with only 3 systems.  We have, however, ample indirect evidence  of the existence of planetary debris around these systems in the form of material acreted onto the white dwarf, disks and even planetesimals. In this talk, I will review how we can put the pieces together: how we can reconcile what we see in white dwarfs with what we can infer regarding the evolution of planetary systems from the main sequence phase.


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.


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


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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