Calendar

Speaker: Andrea Bonfanti (Austrian Academy of Sciences, Graz, Austria)
Title: Insights into the M-dwarf radius and density valley
Abstract
M dwarfs are quite attractive in the domain of exoplanetology: Because of their low mass and small
radius, it is easier to detect low-mass planets with the transit method and the radial velocity (RV)
technique. In addition, it is more likely that the hosted planets are within the so-called habitable
zone (HZ). In fact, the HZ around M dwarfs is located closer to the host star than in stars of earlier
spectral type, and it is well known that both the transit method and the RV technique preferentially
detect close-in planets.
The first part of my talk will focus on the case of TOI-732, an M dwarf orbited by an ultra-short
period super-Earth and an outer mini-Neptune likely rich in volatiles. I will specifically show you
the full characterisation of the system with the determination of the stellar parameters followed by a
MCMC joint analysis of ground- and space-based lightcurves and RV time series. In particular, the
analysed dataset contain CHEOPS, TESS, and MAROON-X observations, among others.
TOI-732 is an interesting system also because its planets are located on the two opposite sides of
the so called radius valley. The nature of the radius valley has been deeply investigated in the
literature by mainly focusing on FGK stars, while only a few works specifically drew attention to
low-mass stars. These considerations open the second part of my talk, where I will compare both
evolution and formation mechanisms in shaping the M-dwarf radius valley. By complementing the
results of TOI-732 with literature data of well characterised M-dwarf exoplanets, I will explore the
topology of both the radius and the density valleys using a support vector machine procedure. I will
show you that the formation likely shapes the radius and density gaps more strongly than the
evolution mechanisms.

Speaker Dominique Meyer (Institute of Space Sciences ICE, CSIC, Campus UAB, Barcelona, Spain)

Titolo: “Supernova remnants of massive stars”

Abstract: Stars more massive than our Sun by at least a factor of ten are rare but seminal objects in galaxies such our Milky Way. Their powerful radiation, stellar winds, and explosive deaths are dominant engines driving the cycle of matter in the interstellar medium by ionizing and chemically enriching it, inducing turbulence, and producing cosmic rays. The direct surroundings of massive stars (circumstellar medium) appear as gaseous nebulae visible accross the electromagnetic spectrum.  The shapes of the nebulae and their physical charcteristics are the important fingerprints of past stellar evolution and the ambient medium properties. However, to understand how massive stars interact with their surrownding during their lives and after their deaths the sophysitacted multi-dimensional magneto-hydrodynamical and radiative transfer numerical simulations are required. In this talk we will take a journey throughout the lives of massive stars, from their infant to defunct evolutionary phases. We will employ some of the most complex numeric models exisiting to date to discover how interstellar medium morphology is sculptured by massive stars and what does it tell us about stellar feedback in galaxies. Particularly, we will present simulations tailored to the surroundings of evolved massive stars like the red supergiant Betelgeuse and Wolf-Rayet stars, to constrain their past evolution. Finally, we will explore what the asymmetries in non-thermal remnants left behind massive stars which died in a supernova explosion, like the Cygnus Loop nebula and pulsar wind nebulae, tell us about stellar lives.