ASD Colloquium Series - Fall 2020

ASD Colloquium Series - Fall 2020

The Astrophysics Science Division colloquia occur virtuallly on Tuesdays at 3:45 pm. Schedules from past colloquium seasons are available.

Contact: Knicole Colon


Aug 25 Virtual Colloquium
Robert Stein (DESY Zeuthen) - A high-energy neutrino coincident with a Tidal Disruption Event


Sep 1 No Colloquium
Sep 8 Virtual Colloquium
Keivan G. Stassun and Marina Kounkel (Vanderbilt University, Western Washington University) - Fundamental Stellar Astrophysics in the Gaia Era: A New Understanding of Local Stellar Populations
Sep 15 Virtual Colloquium
Andrey Kravtsov (University of Chicago) - Gaseous halos of galaxies as a key testing ground for galaxy formation models
Sep 22 No Colloquium
Sep 29 No Colloquium


Oct 6 Virtual Colloquium
Valeriya Korol (University of Birmingham) - Galactic Astronomy with LISA
Oct 13 Virtual Colloquium
Steven Finkelstein (University of Texas at Austin)
Oct 20 Virtual Colloquium
Tiziana DiMatteo (Carnegie Mellon University)
Oct 27 Virtual Colloquium
Joern Wilms (Dr. Karl Remeis-Observatory and Erlangen Centre for Astroparticle Physics)


Nov 03 Virtual Colloquium
Jessica Gaskin (NASA MSFC)
Nov 10 Virtual Colloquium
Thomas Siegert (University of California, San Diego)
Nov 17 Virtual Colloquium
Fred Adams (University of Michigan)
Nov 24 No Colloquium - Thanksgiving Week


Dec 01 Virtual Colloquium
David Sibeck & Scott Porter (GSFC)
Dec 08 Virtual Colloquium
Xavier Siemens (University of Wisconsin-Milwaukee)
Dec 15 Virtual Colloquium
Kate Follette (Amherst College)

A high-energy neutrino coincident with a Tidal Disruption Event

Robert Stein

DESY Zeuthen

Tuesday, Aug 25, 2020


IceCube discovered a diffuse flux of high-energy neutrinos in 2013, and recently identified the flaring blazar TXS 0506+056 as a likely neutrino source. However, a combined analysis of many similar blazars revealed no significant population excess, leaving the vast majority of the neutrino flux unexplained. I will discuss the identification of a second likely neutrino source, the Tidal Disruption Event (TDE) AT2019dsg, found as part of a systematic search for optical counterparts to high-energy neutrinos using the Zwicky Transient Facility. The probability of finding such a TDE with our follow-up program by chance is just 0.2%. Our multi-wavelength observations reveal the presence of a central engine powering particle acceleration in AT2019dsg, and confirm that this object can satisfy all necessary conditions for PeV neutrino production.

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

Keivan G. Stassun and Marina Kounkel

Vanderbilt University, Western Washington University

Tuesday, Sep 08, 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.

Gaseous halos of galaxies as a key testing ground for galaxy formation models

Andrey Kravtsov

University of Chicago

Tuesday, Sep 15, 2020


Presence of diffuse extended gaseous halos - or circumgalactic medium (CGM) - around galaxies is indicated by observations and is generally predicted by galaxy formation models. Properties of these halos should bear imprint of the key processes driving galaxy formation, such as accretion history of gas and outflows driven by feedback. I will briefly review what we currently know about CGM properties and the evidence that CGM has complex multiphase structure quite different from gaseous halos of group- and cluster-sized systems. I will present results of recent studies of gaseous halos in cosmological galaxy formation simulations that show that multiphase structure arises due to thermal instability seeded by the nonlinear density perturbations arising during gas accretion from IGM and winds from both the central and satellite galaxies.

Galactic Astronomy with LISA

Valeriya Korol

University of Birmingham

Tuesday, Oct 06, 2020


White dwarf stars are a well-established tool for studying Galactic stellar populations. Two white dwarfs in a tight orbit forming a double white dwarf (DWD) binary offer us an additional messenger - gravitational waves - for exploring the Milky Way and its immediate surroundings. Gravitational waves produced by DWDs can be detected by the future Laser Interferometer Space Antenna (LISA). I will discuss what we will learn about our Galaxy from the LISA sample of DWDs. In particular, I will demonstrate how well the density distribution of DWDs constrains scale parameters of the Milky Way's bulge, disc and central bar. Finally, I will show that massive Galactic satellites can be seen on gravitational wave sky and I will present which of their properties we will be able to investigate with LISA.

Past Colloqia Schedules

2020: Spring
2019: Fall, Spring
2018: Fall, Spring
2017: Fall, Spring
2016: Fall, Spring
2015: Fall, Spring
2014: Fall, Spring
2013: Fall, Spring, Summer
2012: Fall, Spring
2011: Fall, Spring
2010: Fall, Spring

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