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

Speaker:  Hagai Perets
Institute:  Technion - IIT
Host:        Sterl Phinney

Title:  The Origins of Type Ia Supernovae (And What Does Darwin Have To Do With It)

Abstract:  Type Ia supernovae (SNe) are thought to originate from the thermonuclear explosions of carbon-oxygen (CO) white dwarf (WD) stars. They produce most of the iron-peak elements in the universe, and bright type Ia SNe serve as important "standard candle" cosmological distance indicators. The proposed progenitors of standard type Ia SNe have been studied for decades, and can be, generally, divided into explosions of CO WDs accreting material from stellar non-degenerate companions (single-degenerate; SD models), and those arising from the explosive interaction of two CO WDs (double-degenerate; DD models). However, current models for the progenitors of such SNe fail to reproduce the diverse properties of the observed explosions, nor do they explain the inferred rates and the characteristics of the observed populations of type Ia SNe and their expected progenitors. In the talk I'll discuss new results from our studies on the little explored mergers of CO-WDs with hybrid Helium-CO (He-CO) WDs.  We find that such He-enriched mergers give rise to double detonations, first catalyzed by Helium and the second in the carbon-oxygen core of the CO-WD. We find that the observable properties of the explosions produced from such mergers resemble those of observed type Ia SNe, and in particular they can produce a wide range of peak luminosities, consistent with those observed for normal type Ia SNe. Moreover, our population synthesis models show that, together with the contribution from mergers of massive double CO-WDs (producing the more luminous SNe), they can potentially reproduce the full range of type Ia SNe, their rate and delay-time distribution. Furthermore, mergers with low-mass CO WDs give rise to a wide variety of partial explosions that might reproduce the properties of sub-luminous types of type Ia SNe. We therefore suggest the mergers of hybrid WDs could play a key role in explaining the origins of of both normal and peculiar type Ia supernovae. I'd also mention what does Darwin has to do with all of this...

13
Speaker:  Heather Knutson
Institute:  Caltech
Host:        Andrew Howard

Title:  Exploring the Mysterious Origins of Super-Earths and Mini-Neptunes

Abstract:  Nearly a decade has passed since the discovery that planets with sizes intermediate between that of the Earth and Neptune ("super-Earths or mini-Neptunes", depending on their densities) dominate the observed population of close-in exoplanets.  These planets have no solar system analogue, yet 30% of Sun-like stars appear to have at least one (and often more) interior to Mercury's orbit.  Did these planets form in situ, or did they migrate inward from a more distant formation?  Either way, the implications for our understanding of planet formation are bound to be significant.  In my talk I will describe current efforts to address this question by characterizing the bulk densities and compositions of these planets and searching for outer gas giant companions.



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

Speaker:
Institute:
Host:

NO COLLOQUIUM - THANKSGIVING WEEK

DECEMBER






11

Speaker: Rosemary Wyse
Institute: Johns Hopkins Univ
Host:       Judy Cohen 

Title: Science with the Subaru Prime Focus Spectrogragph: The Local Group

Abtract:
The Subaru Prime Focus Spectrograph (PFS) will provide the unique capability of a wide-field (1.3 degree) massively multiplexed (2394 reconfigurable fibers) spectrograph on an 8-m telescope. The PFS team is developing a five-year, 360-night survey to be proposed as a Subaru Strategic Program, to address fundamental questions of cosmic evolution and the dark sector. We will investigate the formation and evolution of structure, from cosmological scales to the Local Group of galaxies. I will describe the motivation for the planned observations of faint stars in the Milky Way, in its satellite galaxies and in M31,and the insight we hope to gain into how galaxies form and evolve.

 





JANUARY 8

Speaker:
Institute:
Host:

No Colloquium - AAS week

15

Speaker:
Institute: 
Host:



22

Speaker:  Nathan Smith
Institute:  University of Arizona
Host:        Mansi Kasliwal

TBD

29

Speaker:  
Institute:
Host:


FEBRUARY
5

Speaker:  Feryal Ozel
Institute:  University of Arizona
Host:        Mansi Kasliwal

TBD

12

Speaker:   Richard Ellis
Institute:   Univ College London    
Host:         Tom Soifer

TBD

19

Speaker:    Ramesh Narayan           
Institute:    Harvard University
Host:          Mansi Kasliwal       

TBD

26

Speaker:    Harish Vedantham
Institute:    ASTRON
Host:          Vikram Ravi

TBD


MARCH
4

Speaker:   
Institute:
Host:



11

Speaker:
Institute:
Host:


18

Speaker:
Institute:
Host:





25

Speaker:
Institute:
Host:

No Colloquium - Spring Break

APRIL
1

Speaker:
Institute:
Host:





8

Speaker:   Heino Falcke
Institute:   Radbound University
Host:         Shri Kulkarni

TBD



15

Speaker:
Institute:
Host:





22

Speaker:
Institute:
Host:





  29

Speaker:
Institute:
Host:



MAY
6

Speaker:
Institute:
Host:



13

Speaker:   Joss Bland-Hawthorn
Institute:   University of Sydney
Host:         Mansi Kasliwal

TBD

20

Speaker:
Institute:
Host:



27

Speaker:
Institute:
Host:





JUN
3

Speaker:
Institute:
Host:




10

Speaker:
Institute:
Host:





Information for Speakers

Previous Astronomy Colloquia:


Updated: