Astronomy Colloquia at Caltech for 2019-2020

Colloquia are held every Wednesday during the academic year at 4pm in the Cahill Hameetman auditorium.
Wine and cheese will be served in the Cahill Foyer from 5-5:30pm.

Month
Date
Speaker

Talk Title
OCTOBER
 2

Speaker:  Gregory Herczeg
Institute:  KIAA/Peking University
Host:        Lynne Hillenbrand

Title:  From Protostars to Adolescence: A Tour of Young Stellar Systems

Abstract:  While the stages in the formation of stellar systems are now well charted, uncertainties in the initial conditions and evolution lead to stellar systems with a diverse array of architectures.  In this talk, I will discuss the major stages in the evolution of your stellar objects, starting from the young protostars and ending in stars that have dispersed all circumstellar material.  At each step, I will describe insights into some of the relevant processes that are being obtained from ongoing observational programs.  For protostars, we are pursuing the first long-term monitoring program in the sub-mm to establish the role of accretion variability during the main phase of stellar growth.  The next stage, protoplanetary disks, is now being revolutionized by exquisite ALMA images of substructures, which point to the presence of hidden planets.  Finally, once the star, better descriptions of stellar properties is needed to fulfill the promise of Gaia in revealing the recent star formation in our local neighborhood.

9

Speaker:   Josiah Schwab
Institute:   UCSC
Host:         Sterl Phinney

Title:  Modules for Experiments in Stellar Astrophysics (MESA)

Abstract:  MESA is an open-source stellar evolution software instrument that is now entering its second decade of development.  MESA has become a widely-used tool in both research and education with ~1000 users distributed around the globe.  I will briefly summarize some of the key capabilities of MESA and describe how its usage and development is driven by the interaction of theory, modeling, and simulation with ongoing, rapid observational progress in stellar astrophysics.  I will also discuss how the capabilities of MESA enable some of my own work studying the fates of accreting and merging white dwarfs.

16

Speaker:   Evan Kirby
Institute:   Caltech
Host:        Andrew Howard

Title:  Galactic Archaeology:  Galaxy Formation and Nucleosynthesis

Abstract:  Galactic archaeology is the use of the velocities and abundances of stars to learn about the history of galaxy formation and nucleosynthesis.  I will tell three stories of galactic archaeology with three different groups of elements: alpha elements, the iron peak, and the r-process.  All of these measurements were made with the Keck/DEIMOS multi-object spectrograph.

First, I will present detailed abundances of individual stars in the dwarf satellites, stellar streams, and smooth halo of M31.  The evolution of [alpha/Fe] in these stars supports the hierarchical assembly paradigm of galaxy formation.

Second, I will present abundances of manganese and nickel in dwarf satellite galaxies of the Milky Way.  These abundances are best explained by a strong contribution of sub-Chandrasekhar-mass Type Ia supernovae.

Third, I will present measurements of barium abundances in the globular cluster M15.  The constancy of barium from the main sequence to the red giant branch indicates that the stars in M15 were born with their unusually large dispersion of r-process elements rather than acquiring it from an external source.

23
Speaker:  Steven Furlanetto
Institute:  UCLA
Host:        Andrew Howard

Title:  Hints of the Earliest Galaxies

Abstract:  The earliest generations of galaxies in our Universe constitute one of the last frontiers of cosmology.  Observations are beginning to probe many aspects of this era - from the reionization of intergalactic hydrogen about one billion years after the Big Bang to the first onset of star formation in our Universe, and new instruments promise to revolutionize our understanding of this era over the next several years.  I will discuss how multi-wavelength observations, from low-frequency radio measurements to near-infrared surveys, are essential to providing a complete view of these earliest luminous structures and their effects on baryons in the Universe.

30
Speaker:  Alexander Ji
Institute:  Carnegie Observatories
Host:        Evan Kirby

Title:  Near Field Cosmology with the Rapid Neutron-Capture Process

Abstract:  Detailed elemental abundances of surviving old stars provide an archaeological window to the first stars and galaxies. Using these measurements requires building up our understanding of the nuclear and stellar astrophysics that produce different elements and connecting them to galaxy formation and cosmology. I will show how stellar abundances of metal-poor stars have shaped our current understanding of the rapid neutron-capture process (r-process), including how they inform future multi-messenger observations of kilonovae. The r-process can in turn be used to build our understanding of the high-redshift universe, including galaxy formation in the faintest dwarf galaxies and the hierarchical assembly of our Milky Way's stellar halo.

NOVEMBER
6

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13
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20

Speaker:  Pawan Kumar
Institute:  University of Texas
Host:        Wenbin Lu

Title:  Physics of Enigmatic Fast Radio Bursts

Abstract:  Fast radio bursts (FRBs) are millisecond duration transient events of unknown physical origin that were discovered at GHz radio frequency in 2007 (the data was collected by the Parkes telescope in 2001). It is now well established that many of these bursts are located at a distance of several billion lightyears. And therefore the energy release in the radio band in these events is quite large. Using very general arguments, I will show that the radio emission is coherent, the magnetic field strength associated with the source of these events should be 10^{14}Gauss or more, and the electric field is of order 10^{10} esu. I will describe my recent work that magnetic field distortions (Alfven waves) are responsible for the strong electric field and the coherent radiation produced in these enigmatic events. I will also address polarization properties of the well known repeater. Reasons for believing that these transients are associated with young magnetars will also be described.


  27

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DECEMBER
4

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11

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  18

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JANUARY 8

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No Colloquium - AAS week

15

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22

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29

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FEBRUARY
5

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12

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19

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26

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MARCH
4

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11

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18

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25

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No Colloquium - Spring Break

APRIL
1

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Kingsley



8

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Greenstein



15

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Biard



22

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  29

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MAY
6

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13

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20

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27

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JUN
3

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10

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Neugebauer Lecture



Information for Speakers

Previous Astronomy Colloquia:


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