Colloquium

The Graduating Student Colloquium

This special colloquium will feature talks by this year's graduating students: Stephanie Douglas, Miao Li, Maria Charisi, Susan Clark, and Andrea Petri.

Stephanie Douglas: Open clusters as laboratories for stellar spin-down and magnetic activity decay

Abstract: Open clusters are collections of stars with a single, well-determined age, and can be used to investigate the connections between angular-momentum evolution and magnetic activity over a star’s lifetime. I will discuss my study of the 650 Myr-old Hyades and Praesepe clusters, which, as two of the oldest nearby clusters, are particularly important benchmarks. My measurements of rotation in these clusters have enabled new tests of models describing the evolution of stellar rotation; discrepancies with these models imply that we still do not fully understand how magnetic fields and binary companions affect stellar-spin down.

Andrea Petri: Non-Gaussian information in cosmology with Weak Lensing

Weak Lensing (WL) is becoming a popular observational technique to constrain parameters in the Standard Model of cosmology. The WL effect is sensitive to the late time evolution of the Universe, in which structures are non--linear. Because of this, WL observations cannot be treated as Gaussian random fields and statistical information on cosmology leaks from quadratic correlations into more complicated, higher order, image features. I will present the main results obtained during my graduate work, showing that higher order features in WL observations help tightening the constraints on the equation of state of dark energy. I will also discuss the computational, statistical and WL systematic issues we had to address in order to come to this conclusion.

Maria Charisi: "Quasars with periodic variability as sub-parsec supermassive black hole binary candidates"

Supermassive black hole binaries (SMBHBs) should be fairly common in galactic nuclei as a result of galaxy mergers. At sub-parsec separations, where individuals black holes cannot be resolved, SMBHBs may be recognized by the periodic modulation of their brightness. I will discuss the detection of a population of quasars with significant periodic variability from a systematic search in the Palomar Transient Factory.

Susan Clark: Magnetic fields in the interstellar medium

The Milky Way is magnetized. Invisible magnetic fields thread the Galaxy on all scales and play a vital but still poorly understood role in regulating flows of gas in the interstellar medium and the formation of stars. I will present highlights from my thesis work on magnetic fields in the diffuse interstellar gas. At high Galactic latitudes, diffuse neutral hydrogen is organized into an intricate network of slender linear features. I will show that these neutral hydrogen “fibers” are extremely well aligned with the ambient magnetic field as traced by both starlight polarization and Planck 353 GHz polarized dust emission. The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. Because the orientation of neutral hydrogen is an independent predictor of the local dust polarization angle, our work provides a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination.

Miao Li: Supernova feedback in galaxy formation

Abstract: I will describe how we use high-resolution simulations to understand the nature and impacts of supernova feedback, as well as its observational implications.

Followed by wine and cheese i

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