Calendar

Speaker: Emanuele Greco (INAF)
Titolo: Jitter radiation as an alternative for the nonthermal filaments in Supernova Remnants
Abstract: Synchrotron radiation from relativistic electrons is usually invoked as the responsible for the nonthermal emission observed in Supernova Remnants (SNRs). Diffusive shock acceleration (DSA) is the most popular mechanism to explain the process of particles acceleration and within its framework a crucial role is played by the turbulent magnetic-field. However, the standard models commonly used to fit X-ray synchrotron emission do not take into account the effects of turbulence in the shape of the resulting photon spectra. An alternative mechanism that properly includes such effects is the jitter radiation, that provides for an additional power-law beyond the classical synchrotron cutoff. In this talk, i will show the results of applying the jitter spectral model to various X-ray observations of Cassiopeia A and found that it describes the X-ray soft-to-hard range better than any of the standard cutoff models. I will also show what relevant turbulence and electrons’ parameters can be measured from the spectra in the jitter radiation framework.

Speaker: Konstantina Anastasopoulou (INAF)
Titolo: EWOCS: The X-ray properties of the Wolf-Rayet stars in the young massive star cluster Westerlund 1

Abstract: Wolf-Rayet (WR) stars are the latest stage in the evolution of very massive stars, before they finally explode as supernovae (SN) or possibly gamma-ray bursts. They exhibit dense and powerful stellar winds that, along with their ultimate death as core-collapse SN, dominate the feedback to the local interstellar medium in star-forming galaxies. Studying in more detail the properties of the short-lived WR phase, will advance our understanding on star-formation processes and will test stellar evolutionary predictions. The best laboratory to study the WR phase is the massive young star cluster Westerlund 1. It is the closest massive star cluster to the Sun, and it contains an impressive large sample of coeval massive stars including the largest population (24) of WR stars in our Galaxy. In this talk, I will present the first results of the EWOCS  (Extended Westerlund 1 and 2 Open Clusters Survey) project on the WR stars in Westerlund 1 based on a 1Msec Chandra/ACIS-I Large Project. With this very deep Chandra survey we are able to unravel the X-ray spectral, colour, and timing properties of the entire WR population and retrieve insights on their X-ray production mechanism. I will discuss these results in the context of different spectral subtypes of WR stars, as well as binarity since the majority of them show clear signs of very hot plasma created in the colliding-wind region of a binary system.

Speaker: Kevin France (University of Colorado at Boulder)

Title:  Exploring Extreme Exoplanets and Stellar Activity with Small Satellite Missions

Abstract: Atmospheric escape is a process that affects the structure, composition, and evolution of many planets.  Atmospheric escape rates depend critically on the extreme-ultraviolet (EUV) and far-ultraviolet (FUV) photon fluxes from the host star.  Owing to high levels of EUV and FUV irradiance from their nearby parent stars, the signatures of rapid atmospheric escape are detectable on close-in, gaseous exoplanets transiting bright stars.  In this talk, I will present current and future small satellite missions designed to directly observe atmospheric escape from exoplanets and to investigate the EUV luminosity and energy partition of EUV flares on nearby stars. The majority of the talk will focus on the Colorado Ultraviolet Transit Experiment (CUTE), a 6U CubeSat mission designed to take advantage of the near-ultraviolet (250 – 330 nm) stellar brightness distribution to conduct novel observations of the extended atmospheres of nearby close-in planets.  CUTE is NASA’s first dedicated exoplanet spectroscopy mission and has collected 6 – 11 transits of each of seven short-period exoplanets.  I will present an overview of the CUTE mission, including its development path and on-orbit observations of excess NUV absorption on ultra-hot Jupiters.  I will conclude the talk by describing the upcoming Monitoring Activity from Nearby sTars with uv Imaging and Spectroscopy (MANTIS) mission, a 12U CubeSat that will make simultaneous observations of nearby stars in four spectral bands from the EUV through the optical (~10 – 1000 nm).  MANTIS will conduct two surveys over its planned two-year mission lifetime: deep EUV observations of nearby stars and contemporaneous stellar characterization data in support of James Webb Space Telescope exoplanet spectroscopy observations.

Referente: Ileana Chinnici