When photons scatter, their angular distribution and energy shift reveal information about the structure of the scattering target. As a result, photon scattering has long been used to study materials at the atomic and molecular level. By substantially increasing the photon energy, experiments can also be used to measure electromagnetic properties of the proton and neutron -- properties which are sensitively related to the interactions among the constituent quarks and gluons. We will discuss experiments which measure the electric and magnetic polarizabilities of the nucleon, and present new results for the neutron.

 

Refreshments will be served in CP 179 at 3:15 PM

Details of the chemical composition of stars provide information about the formation and evolution of the galaxies in which they form. I will outline some of the connections and provide some results for our Milky Way Galaxy from the Sloan Digital Sky Survey (SDSS) Apache Point Observatory Galactic Evolution Experiment (APOGEE). APOGEE is providing maps of the abundances of stars across the Milky Way. These suggest different timescales for star formation in different locations, both radially and vertically within the disk of the Galaxy, and also suggest that movement of stars within the Galaxy, through a process knows as radial migration, is important.

Refreshments will be served in CP 179 at 3:15 PM

Twenty years ago, the Material Chip's invention allowed 10^3-10^4 materials with different compositions to be synthesized under the same conditions and characterized for physical properties in one experiment. Ten years ago, the development of the Materials Phase Diagram Chip allowed ternary phase diagrams at a constant synthesis temperature to be mapped in one experiment. Today, a complete phase diagram (a 3D contour with a 2D composition map and a temperature axis) can be mapped in one experiment with a single Materials Phase Diagram Chip, increasing the efficiency of phase diagram mapping by million-fold. The physics and implications of these chips will be discussed.

Refreshments will be served in CP 179 at 3:15 PM

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) will outfit the 10 m HET with an array of 150 integral-field fiber-coupled spectrographs covering 3500-5500A ̊ at ∼ 5A ̊ resolution. These are fed by 75 450-fiber IFUs distributed on a grid within a 20 arcmin field. This instrument, called VIRUS (Hill et al., 2014), will survey a 420 deg2 field in 3 years starting 2015. We will detect 0.8 million Lyman-α emitting (LAE) galaxies at 1.9 < z < 3.5 and more than one million [OII]-emitting galaxies at z < 0.5. The 3-D map of LAEs in a 9 Gpc3 volume will be used to measure the expansion history and the growth of structure at an early epoch (z ∼ 3). HETDEX is designed to provide a 3σ direct detection of dark energy at z ∼ 3 (for w = −1). HETDEX will constrain the evolution of dark energy and will also provide 0.1%-level accuracy on the curvature of the Universe, ten times better than current measurements; HETDEX will also provide competitive constraints on the total neutrino mass and on inflation models.

Refreshments will be served in CP 179 at 3:15 PM

As much as any science field, astronomy is about origins. Therefore, the origins of stars is a central question in the field. For more than a century, it has been known that stars form via gravitational contraction of clouds of interstellar gas and dust. And for more than a half century, it has been known that weak magnetic fields of uncertain origin can play a crucial role in the star formation process. Unfortunately, magnetic field strengths in interstellar space are notoriously difficult to measure. I will explain why magnetic fields are important to star formation, how we measure them, and what we now know about the interactions between gravity and magnetic fields during the star formation process. Curiously, magnetic fields in space can impede star formation, yet they are also essential to star formation. Without magnetic fields, there would be no Sun, no Earth, and no one to listen to this talk.

Refreshments will be served in CP 179 at 3:15 PM

Dr. Savvas Koushiappas (Brown University)

Searching for a WIMP signal in the gamma-ray sky: Current status, results and challenges.

Indirect detection of dark matter is extremely important because it probes the same physics that took place in the early universe leading to the observed relic abundance. I will focus on the current state of dark matter annihilation searches, and latest results. In addition, I will discuss on how these results fit in the broad picture of dark matter physics and what are the key outstanding issues in this endeavor.

From Voids to Clusters:Gas and Galaxy Evolution in the Local Universe

Our understanding of the formation and evolution of galaxies and their large scale structure has advanced enormously over the last decade, thanks to an impressive synergy between theoretical and observational efforts. While the growth of the dark matter component seems well understood, the physics of the gas, during its accretion, removal and/or depletion is less well understood. Increasingly large scale optical surveys are tracing out the cosmic web of filaments and voids. Mathematical tools have been developed to describe these structures and to identify galaxies located in specific environments. HI imaging surveys begin to answer the question: how do galaxies get and lose their gas? The best evidence for ongoing gas accretion is found in the lowest density environments, while removal of gas in the highest density environments stops star formation and reddens the galaxies.

Refreshments will be served in CP 177 at 3:15 PM