Found 4 talks width keyword mass loss

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 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.


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.


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