Embedded Files
Second Semester 2020/21
Second Semester 2020/21
III seminario del II semestre 16 giugno 2021 h. 16:00 CEST
III seminario del II semestre 16 giugno 2021 h. 16:00 CEST
Title: ``Mass transfer in binary systems"
Title: ``Mass transfer in binary systems"
Mathieu Renzo
Mathieu Renzo
Flatiron Research Fellow, Center for Computational Astrophysics
Flatiron Research Fellow, Center for Computational Astrophysics
Columbia University
Columbia University
Abstract:
Abstract:
Most binaries, especially massive ones, will experience one or more phases of mass transfer during their evolution. Each results in significant changes in the evolution and appearance of _both_ stars and their orbit, with consequences for the final fate of the system. Mass transfer can be dynamically stable (Roche lobe overflow) or unstable (common envelope), depending on the reaction to the change in mass of the stellar and Roche lobe radii.
Most binaries, especially massive ones, will experience one or more phases of mass transfer during their evolution. Each results in significant changes in the evolution and appearance of _both_ stars and their orbit, with consequences for the final fate of the system. Mass transfer can be dynamically stable (Roche lobe overflow) or unstable (common envelope), depending on the reaction to the change in mass of the stellar and Roche lobe radii.
I will first discuss massive binaries experiencing stable Roche lobe overflow with particular focus on the accreting stars. These can be compared to observations of the nearest O-type star to Earth, the runaway star $\zeta$ Ophiuchi. With standard assumption, most properties of the stars can be reasonably reproduced and the models reveal important differences between accretor stars in binaries and single fast-rotating stars, especially in terms of their core rotation and density structure.
I will first discuss massive binaries experiencing stable Roche lobe overflow with particular focus on the accreting stars. These can be compared to observations of the nearest O-type star to Earth, the runaway star $\zeta$ Ophiuchi. With standard assumption, most properties of the stars can be reasonably reproduced and the models reveal important differences between accretor stars in binaries and single fast-rotating stars, especially in terms of their core rotation and density structure.
Then I will discuss how future gravitational wave detectors in the milli-Hertz range might provide insight in the physics of common envelope evolution. The possible target systems are Galactic low mass binaries (especially at the second common envelope before the formation of a double white dwarf) -- provided common envelope goes through a phase of self-regulated slow inspiral at short orbital separations.
Then I will discuss how future gravitational wave detectors in the milli-Hertz range might provide insight in the physics of common envelope evolution. The possible target systems are Galactic low mass binaries (especially at the second common envelope before the formation of a double white dwarf) -- provided common envelope goes through a phase of self-regulated slow inspiral at short orbital separations.
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II seminario del II semestre 3 giugno 2021 h. 16:00 CEST
II seminario del II semestre 3 giugno 2021 h. 16:00 CEST
Title: ``Understanding the formation of jet streams and storms on Saturn and Jupiter using 3D convection simulations"
Title: ``Understanding the formation of jet streams and storms on Saturn and Jupiter using 3D convection simulations"
Rakesh K. Yadav
Rakesh K. Yadav
Dept. of Earth and Planetary Sciences, Harvard University
Dept. of Earth and Planetary Sciences, Harvard University
Abstract:
Abstract:
Decades of observations have painted a rich picture of the atmosphere of Saturn and Jupiter. Both planets have jet streams which circulate unabated around the entire planet, along with numerous storms which could be even larger than the Earth. All these features are striking examples of turbulent self-organization of fluid flows. However, the exact physics behind the formation of these features is still uncertain. Using three simulation cases, I will discuss how rotating convection may form such features: The first simulation shows how rotating convection spontaneously forms jet streams with polygonal shapes, helping to shed light on how Saturn's famous hexagonal jet forms; The second generates several alternating jet streams, as well as numerous storms, similar to what we see on Jupiter; And, the third demonstrates how gigantic storms may form on these planets. I will discuss what we can learn from these cases about the fluid dynamics of Saturn and Jupiter.
Decades of observations have painted a rich picture of the atmosphere of Saturn and Jupiter. Both planets have jet streams which circulate unabated around the entire planet, along with numerous storms which could be even larger than the Earth. All these features are striking examples of turbulent self-organization of fluid flows. However, the exact physics behind the formation of these features is still uncertain. Using three simulation cases, I will discuss how rotating convection may form such features: The first simulation shows how rotating convection spontaneously forms jet streams with polygonal shapes, helping to shed light on how Saturn's famous hexagonal jet forms; The second generates several alternating jet streams, as well as numerous storms, similar to what we see on Jupiter; And, the third demonstrates how gigantic storms may form on these planets. I will discuss what we can learn from these cases about the fluid dynamics of Saturn and Jupiter.
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Incontro con studenti a seguito della presentazione della
Incontro con studenti a seguito della presentazione della
Laurea Magistrale in Astronomia & Astrofisica: 18 maggio 2021 h. 11:00
Laurea Magistrale in Astronomia & Astrofisica: 18 maggio 2021 h. 11:00
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I seminario del II semestre 25 marzo 2021 h. 14:00 CEST
I seminario del II semestre 25 marzo 2021 h. 14:00 CEST
Title: ``Galactic Archæology in the Gaia era: unveiling the formation of the Milky Way with extremely metal-poor stars"
Title: ``Galactic Archæology in the Gaia era: unveiling the formation of the Milky Way with extremely metal-poor stars"
Federico Sestito, Post Doctoral Fellow, University of Victoria, Canada
Federico Sestito, Post Doctoral Fellow, University of Victoria, Canada
Abstract:
Abstract:
One of the goals of astrophysics is to understand the formation of the first stars and large structures in the early Universe and their physical properties, and this embraces several open questions. How did first stars form and what was their mass distribution? What are the channels to produce heavy elements? What is the amount of stellar, gas, and dark matter content in the first galaxies? There are two ways to investigate the answers for these questions. One is to observe at high redshift and, therefore, look back in time, when the Universe was a few billions of years old. The other way is to look at the chemistry and kinematics of stars formed in the early Universe that are still living and observable nowadays in the Milky Way and its satellites. This latter field is the so-called Galactic Archæology. Since these stars formed in the early and unpolluted Universe, they must be low-mass, and among the oldest and most metal-poor. From their chemical abundances it is possible to reconstruct the fossil record of the first generation of stars and their formation sites, while the kinematics of the most metal-poor stars might carry the imprints of the assembly and accretion history of the Milky Way. In the first part of the talk, I will describe the expected chemodynamical properties of the most metal-poor stars, the Pristine survey as leading in the investigation of this population of stars, and the revolution started with the Gaia satellite in synergy with ground-based surveys. In the second part, I will summarise my contribution to the field of Galactic Archæology. I will focus on the kinematical investigation of the most metal-poor stars using both observations and high-resolution cosmological simulations. I will show that, at odds with expectations, a fraction of the most metal-poor stars is inhabiting the Galactic plane, posing new questions on the formation of our Galaxy.
One of the goals of astrophysics is to understand the formation of the first stars and large structures in the early Universe and their physical properties, and this embraces several open questions. How did first stars form and what was their mass distribution? What are the channels to produce heavy elements? What is the amount of stellar, gas, and dark matter content in the first galaxies? There are two ways to investigate the answers for these questions. One is to observe at high redshift and, therefore, look back in time, when the Universe was a few billions of years old. The other way is to look at the chemistry and kinematics of stars formed in the early Universe that are still living and observable nowadays in the Milky Way and its satellites. This latter field is the so-called Galactic Archæology. Since these stars formed in the early and unpolluted Universe, they must be low-mass, and among the oldest and most metal-poor. From their chemical abundances it is possible to reconstruct the fossil record of the first generation of stars and their formation sites, while the kinematics of the most metal-poor stars might carry the imprints of the assembly and accretion history of the Milky Way. In the first part of the talk, I will describe the expected chemodynamical properties of the most metal-poor stars, the Pristine survey as leading in the investigation of this population of stars, and the revolution started with the Gaia satellite in synergy with ground-based surveys. In the second part, I will summarise my contribution to the field of Galactic Archæology. I will focus on the kinematical investigation of the most metal-poor stars using both observations and high-resolution cosmological simulations. I will show that, at odds with expectations, a fraction of the most metal-poor stars is inhabiting the Galactic plane, posing new questions on the formation of our Galaxy.
Giovedi' 18 Marzo 2021 h. 14:00 CEST
Giovedi' 18 Marzo 2021 h. 14:00 CEST
Students can meet the group of astrophysics at the University of Pisa.
If you have any question you can add it here . During the meeting we will answer your questions
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First Semester 2020/21
First Semester 2020/21
9 Dicembre 2020 h. 16:00 CEST
9 Dicembre 2020 h. 16:00 CEST
M.Cantiello - CCA, Flatiron Institute and Princeton University:
M.Cantiello - CCA, Flatiron Institute and Princeton University:
``The new era of stellar physics''
``The new era of stellar physics''
Stellar astrophysics is undergoing a renaissance driven by new observational and theoretical capabilities. Wide-field time-domain surveys have uncovered new classes of stellar explosions, helping to understand how stars evolve and end their lives. Gravitational-wave astronomy is providing exciting insights into the properties of the final remnants of massive stars. Asteroseismology, the study of waves in stars, is also producing dramatic breakthroughs in stellar structure and evolution. Thanks to space astrometry, accurate distances are now available for an unprecedented number of galactic stars. From a theoretical standpoint, it is increasingly possible to study aspects of the three-dimensional structure of stars using targeted numerical simulations. These studies can then be used to develop more accurate models of these physics in one-dimensional stellar evolution codes. I will review some of the most important results in stellar physics of the last few years, and highlight what are the most relevant puzzles that still need to be solved. I will put particular emphasis on the physics of massive stars, which are the progenitors of core-collapse supernovae, gamma-ray bursts and the massive compact remnants observed by LIGO.
2 Dicembre 2020 h. 16:00 CEST
2 Dicembre 2020 h. 16:00 CEST
Edward F. Guinan - Villanova University:
Edward F. Guinan - Villanova University:
``Antics of Betelguese''
``Antics of Betelguese''
Betelgeuse (Yad al-Jauzā; alpha Ori) is the brightest red supergiant (RSG) and one of nearest core-collapse supernova progenitors. Evolution models indicate that this beloved star may be nearing the end of its short (but brilliant) life. Betelgeuse is destined “to go supernova” sometime in the next 100,000 yrs. (the sooner the better!). From over 180 years of observations Betelgeuse has been a well-behaved semi-regular variable RSG. This includes 100-yrs of _AAVSO_observations, and for the last ~25-yrs, Villanova V-band and TiO/near-IR solid-state photometry. But this dramatically changed during 2019/20 when the star underwent a surprising 1.0 mag “_fainting_”. by mid-February 2020, fading to V~1.62 mag. It is not well known how core-collapse SN II stars behave prior to exploding. This unprecedented behavior triggered speculations that Betelgeuse was about to explode (so far unfulfilled). The reports of the unusual fading led to intensive observations using many instruments (e.g., Chandra, HST, VLT/SPHERE, SOFIA, e-Merlin, STELLA, STEREO, and several others.) covering X-ray to the radio wavelengths. I will discuss what has been learned about the star and the 2019/20 “Great Dimming”. Also discussed is what to expect when Betelgeuse becomes a supernova.
26 Novembre 2020 h. 16:00 CEST
26 Novembre 2020 h. 16:00 CEST
Jeff Scargle - Astrobiology and Space Science Division. NASA Ames Research Center:
Jeff Scargle - Astrobiology and Space Science Division. NASA Ames Research Center:
``The Dynamic Universe: Adventures in Astronomical Time Series Analysis''
``The Dynamic Universe: Adventures in Astronomical Time Series Analysis''
Welcome to a tour of the dynamic, highly active Universe — far different from earlier serene ``clockwork''visions. We start nearby in the solar system, then pass by exploding stars, merging black holes, active galaxies, and gamma-ray bursts. Modern data analysis techniques have illuminated the accretion and explosive dynamical processes animating these systems. New frequency-domain and time-domain methods will be illustrated using high-energy time series data from the Crab Nebula, gamma-ray bursts, sources of gravitational waves, and active galactic nuclei. At least one spin-off of these methods will change the way you carry out elementary statistical data analysis.
28 ottobre 2020 h. 16:00 CEST
28 ottobre 2020 h. 16:00 CEST
Lee Hartmann - University of Michigan:
Lee Hartmann - University of Michigan:
``Mass and angular momentum addition in star formation''
``Mass and angular momentum addition in star formation''
The initial mass function of stars - the number of stars N formed per interval of mass M - has long been known to be a power law, with d log N/d log M = 𝛤 = -1.3. Many explanations of this distribution have been advanced over the years, including fractal dimensions of star-forming molecular clouds and/or self-similar grouping of clouds. I will discuss simplified numerical simulations of star formation which show that gravitational accretion onto initial seed masses generates a power law mass distribution approaching 𝛤 → -1 asymptotically, irrespective of complications of cloud structure. This mechanism can also explain the mass function of young star clusters, which also has a power law distribution with 𝛤 = -1. Finally, I will describe preliminary results concerning the origin of protostellar cloud angular momenta, including magnetic fields, with implications for the properties of protoplanetary disks that result from cloud collapse.
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