Astronomy Colloquium
Wednesday, May 10th 3:30 pm - 5 pm Nat Sciences Annex 101

Jen van Saders – Carnegie Observatories
Making Sense of Stellar Rotation Observed with Kepler: Gyrochronology, Magnetism, and a Sun in Transition
Stellar rotation carries a wealth of information about stellar populations. In particular, the technique of gyrochronology was developed to utilize the spin-down of stars as a function of time as an indicator of stellar age. Gyrochronology has the potential to yield precise ages for large samples of stars, providing unprecedented chronological information for studies of the Milky Way and extrasolar planets. However, the technique is in its adolescence: it has been tested and validated under limited scenarios, but its weaknesses and limitations have hitherto been largely unexplored. With time-domain data from the Kepler mission we can address these gaps: we now have access to datasets of rotation periods for tens of thousands of stars, as well as independent asteroseismic ages and rotation periods for a few hundred old (main sequence) stars.  I will discuss my comparisons of theoretical rotation models to theseKepler data, which have yielded unexpected insights into the rotational and magnetic lives of stars (and the Sun!), as well as a better understanding of the power and peril of

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gyrochronology as a tool. 

Physics Colloquium

Thursday, May 11th, 3:45 pm - 4:55 pm, Nat Sci

Annex 101

Steve Boggs - UC San Diego

Exploring New Directions in Gamma Ray Astrophysics with COSI

The Compton Spectrometer and Imager (COSI) wide-field gamma-ray telescope (0.2-5 MeV) is designed to probe the origins of Galactic positrons, uncover sites of nucleosynthesis in the Galaxy, and perform pioneering studies of gamma-ray polarization. COSI is the first science payload designed to fly on NASA’s 18 MCF superpressure balloon. COSI underwent a successful 46-day science flight in 2016, the first science payload to launch from New Zealand. I will discuss the science goals and status of results of COSI, the technological advances of the instrument, future goals for the COSI program, and the potential of NASA’s superpressure balloon program.


Friday, May 12th, 12:30 pm, ISB 102

Diana Powell – UC Santa Cruz

Protoplanetary Disks and Exoplanet Clouds: A Microphysical Perspective

In this talk I will discuss two subjects that I approach from the perspective of microphysics.

First, I will present a novel method for determining the surface density of protoplanetary disks through consideration of disk ‘dust lines’ that indicate the observed disk radial scale at different observational wavelengths. This method relies on the assumption that the microphysical processes of particle growth and drift control the radial scale of the disk at late stages of evolution. I will discuss an initial proof of concept of this method through an application to the disk TW Hya and will provide further observational diagnostics.

Second, I will present the first application of a self-consistent, one-dimensional microphysical and vertical transport model (CARMA) to determine the size distribution of cloud particles for hot Jupiters. This first principles approach to cloud modeling will help to inform our observational interpretations as well as allow us to test assumptions made in other cloud modeling work.