Astrophysics

Title: Convection in Cool Stars, as Revealed through Stellar Brightness Variations

Speaker: Fabienne Bastien, Pennsylvania State University

Host: Aaron Geller

Abstract: As a result of the high precision and cadence of surveys like MOST, CoRoT, and Kepler, we may now directly observe the very low-level light variations arising from stellar granulation in cool stars. Here, we discuss how this enables us to more accurately determine the physical properties of Sun-like stars, to understand the nature of surface convection and its connection to magnetic activity, and to better determine the properties of planets around cool stars. Indeed, such sensitive photometric "flicker" variations are now within reach for thousands of stars, and we estimate that upcoming missions like TESS will enable such measurements for ~100 000 stars. We present recent results that tie “flicker” to granulation and enable a simple measurement of stellar surface gravity with a precision of ~0.1 dex. We use this, together and solely with two other simple ways of characterizing the stellar photometric variations in a high quality light curve, to construct an evolutionary diagram for Sun-like stars from the Main Sequence on towards the red giant branch. We discuss further work that correlates “flicker” with stellar density, allowing the application of astrodensity profiling techniques used in exoplanet characterization to many more stars. We also present results suggesting that the granulation of F stars must be magnetically suppressed in order to fit observations. Finally, we show that we may quantitatively predict a star's radial velocity jitter from its brightness variations, permitting the use of discovery light curves to help prioritize follow-up observations of transiting exoplanets.

Keywords: Physics, Astronomy, Astrophysics


Title: Formation and stability of planetary systems

Speaker: Hanno Rein, University of Toronto

Host: Ben Nelson

Abstract: 

The diverse population of extrasolar planets keeps challenging theories of planet formation. Multi-planetary systems are of particular interest as their dynamical architectures allow us to constrain an otherwise unobservable formation phase.

I'll show how a simple stability requirement together with machine learning tools can be used to constrain orbital parameters of planetary systems such as HL-Tau and Trappist-1. Some of the dynamical properties we find in the these systems can be explained by a turbulent protoplanetary disk and stochastic planet migration. Saturn's rings can be thought of as a small scale version and test bed of the early Solar System. I'll show evidence that stochastic migration can be directly observed in moonlets around Saturn.

I'll finally talk about some of the numerical challenges when running accurate long term simulations of planetary systems. Even though we are solving differential equations that have been known since Newton's time, several breakthroughs were made only very recently with the help of clever numerical algorithms. Among these is the discovery that one percent of all realization of the Solar System lead to collisions between planets within the life-time of the Sun.

Keywords: Physics, Astronomy, Astrophysics


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TBD:

October 17, 2017, 4:00 PM - 5:00 PM

Title: 

Speaker: TBD

Host: Wen-fai Fong

Abstract: 

Keywords: Physics, Astronomy, Astrophysics


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Susan Clark: "TBA"

October 24, 2017, 4:00 PM - 5:00 PM

Title: 

Speaker: Susan Clark, Institute for Advanced Study

Host: Fabio Santos

Abstract: 

Keywords: Physics, Astronomy, Astrophysics


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Frank van den Bosch: "TBA"

October 31, 2017, 4:00 PM - 5:00 PM

Title: 

Speaker: Frank van den Bosch, Yale University   

Host: Sarah Wellons

Abstract: 

Keywords: Physics, Astronomy, Astrophysics


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Gregg Hallinan: "TBA"

November 7, 2017, 4:00 PM - 5:00 PM

Title: 

Speaker: Gregg Hallinan, Caltech 

Host: Deanne Coppejans

Abstract: 

Keywords: Physics, Astronomy, Astrophysics