Colloquium

Colloquium: Balancing the Cluster Baryon Budget

The deep gravitational potential wells of clusters of galaxies should capture fair samples of the total baryon fraction of the Universe, unless other physical processes drive baryons out of clusters. Thus precision measurements of the baryon fraction, particularly as a function of cluster mass, can reveal the history of baryon flux into and out of clusters. How those baryons are then apportioned between stars and intracluster gas---the star formation efficiency---informs models of cluster assembly and massive galaxy evolution, as well as efforts to use the cluster gas fraction to constrain the mass density and dark energy equation of state parameters. Even the partitioning of the stellar baryons alone, in and out of galaxies, tests models of cluster galaxy evolution, as intracluster stars are the final, unambiguous signature of stars stripped from cluster galaxies during tidal encounters. We have discovered that intracluster stars are a significant part of the stellar baryons in clusters and poorer groups of galaxies. I will present new work characterizing the properties of this previously unexplored component, as well as the consequences for the cluster baryon budget and its relationship to the Universal value.

Date: 
Friday, October 20, 2017 - 3:30pm to 4:30pm
Location: 
CP 155
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Colloquium

Date: 
Friday, April 28, 2017 - 3:30pm to 4:30pm
Location: 
CP155
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The Proton and the Future of Particle Physics

The Proton and the Future of Particle Physics by Richard Hill, University of Chicago.

Topological Insulators 101

Dr. Ganpathy Murthy University of Kentucky We thought we knew all there was to know about band insulators back in the 1930s. However, in the last 10 years we have learnt that there distinct types of band insulators in 2 and 3 dimensions. The distinction between these types is "topological", a term I will explain. I will introduce the idea of band topology in detail in 2D. I will then use the example of the integer quantum Hall effects to show that a topological insulator has edge states that are robust to disorder. Next I will introduce time-reversal invariance, which puts powerful constraints on band insulators. Once again, edge modes will prove to be extremely useful in characterizing the different types of band insulators. I will end up by talking about 3D topological insulators and some of the phenomenology associated with them.

Enhancing Exoplanet Discovery and Characterization through Stellar Photometric “Flicker”

Dr. Fabienne Bastien Pennsylvania State University 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 activity, and to better determine theproperties 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 characterizationto 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 RV jitter using our evolutionary diagram, permitting the use of discovery light curves to help prioritize follow-up observations of transiting exoplanets.

Muonium, Positronium, Proton Radius, and all that

Dr. Michael Eides University of Kentucky I will discuss physics of exotic muonium and positronium atoms, high precision quantum electrodynamic calculations of energy levels, and determination of the electron-muon mass ratio. I'll introduce the proton radius puzzle, discuss briefly the experimental data on muonic hydrogen, deuterium, and helium, and explain the status of the respective theory.

Topological Insulators 101

 

 

Dr. Ganpathy Murthy University of Kentucky We thought we knew all there was to know about band insulators back in the 1930s. However, in the last 10 years we have learnt that there distinct types of band insulators in 2 and 3 dimensions. The distinction between these types is "topological", a term I will explain. I will introduce the idea of band topology in detail in 2D. I will then use the example of the integer quantum Hall effects to show that a topological insulator has edge states that are robust to disorder. Next I will introduce time-reversal invariance, which puts powerful constraints on band insulators. Once again, edge modes will prove to be extremely useful in characterizing the different types of band insulators. I will end up by talking about 3D topological insulators and some of the phenomenology associated with them.

 

 

Enhancing Exoplanet Discovery and Characterization through Stellar Photometric “Flicker”

 

 

Dr. Fabienne Bastien Pennsylvania State University 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 activity, and to better determine theproperties 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 characterizationto 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 RV jitter using our evolutionary diagram, permitting the use of discovery light curves to help prioritize follow-up observations of transiting exoplanets.

 

 

Muonium, Positronium, Proton Radius, and all that

Dr. Michael Eides University of Kentucky I will discuss physics of exotic muonium and positronium atoms, high precision quantum electrodynamic calculations of energy levels, and determination of the electron-muon mass ratio. I'll introduce the proton radius puzzle, discuss briefly the experimental data on muonic hydrogen, deuterium, and helium, and explain the status of the respective theory.

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