Department Events

Colloquium by Vicky Kalogera

Mon, July 27, 2020


Fundamental Stellar Astrophysics in the Gaia Era: A New Understanding of Local Stellar Populations

Mon, July 20, 2020

We begin with an overview of the precision stellar astrophysics enabled by the confluence of Gaia parallaxes with large-scale photometric and spectroscopic surveys. We then give examples of the new understanding of local Galactic structure that this has enabled, including in particular the detailed history of canonical star-forming regions, and the discovery of "stellar strings" reflecting the local conditions of recent star formation. We conclude with the example of a newly discovered, young, triple star system including an eclipsing binary, that provides prima facie evidence supporting the new "stellar strings" paradigm.


How do you form a binary black hole?

Mon, June 29, 2020

When an isolated binary black hole merges in the field of a galaxy, its gravitational-wave story is complete. But when black holes merge in a dense star cluster, their merger products can remain in the cluster, where they continue to participate in dynamical encounters, form binaries, and potentially merge again. In this talk I will describe the production of repeated mergers in globular clusters, and how the rate of mergers depends on the initial properties (e.g. spin) of black holes formed from stars. I will show how these "second-generation" black holes differ from black holes formed from stellar collapse, and how Advanced LIGO and Virgo can already distinguish these unique astrophysical populations.


Constraining Planet Formation with Spectroscopy of Direct Imaged Planets

Mon, June 22, 2020

In the past decade, several new jovian exoplanets at wide separations have been revealed using ground based telescopes equipped with adaptive optics systems. These planets, with masses between ~2-14 MJup, remain a puzzle for both major planet formation models. At the same time, they offer a powerful tool in the hunt for observational constraints of formation, as they can be characterized with both imaging and spectroscopy. I will describe our recent efforts to push beyond the discovery phase into the realm of detailed characterization of these planetary systems. Using OSIRIS at Keck, we have been targeting known directly imaged planetary systems for detailed mapping of their atmospheres at R~4000. I will describe our findings, including the atmospheric abundance measurements for these planets, which can potentially be used as a diagnostic of formation. I will describe upcoming instrumentation efforts that will improve our ability to obtain spectra for directly imaged planets, including spectrographs in the planning phases for Keck and the future Thirty Meter Telescope, and the discuss prospects for direct exoplanet spectroscopy in the next two decades from the ground.


Supermassive Black Hole Feedback in Massive Galaxies and Clusters

Mon, June 15, 2020

The centers of massive galaxies and galaxy clusters contain hot plasma that loses its energy rapidly through radiation of X-ray photons. The energy loss is thought to be compensated by the energy input from the supermassive black holes (SMBHs) in the centers of these systems, via a process often termed as “AGN feedback”. In this talk, I will review the state of the field, and discuss what we have learned from numerical simulations in the past few years, including how AGN jets deposit their energy to the surrounding medium, and how they affect cooling and star formation. I will also talk about my recent analysis of optical and ALMA observations of multiphase filaments in cluster centers, which not only improves our understanding of AGN feedback, but also puts unprecedented constraints on microscopic transport processes in the weakly-collisional, magnetized intracluster plasma.


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