Astronomy Colloquia at Caltech for 2018-19

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
3

Speaker: David Charbonneau
Institute: Harvard
Host: D. Mawet

The Terrestrial Planets of Other Stars

For the next decade, the only opportunity to study the atmospheres of terrestrial exoplanets will be scrutinize these worlds when they transit nearby small stars. There are 417 mid-to-late M-dwarfs within 15 parsecs, yet we know surprisingly little about them, let alone their attendant planets. I will discuss recent findings from the MEarth Project and TESS Mission, which seek to discover the most spectroscopically accessible terrestrial exoplanets. Our recent discovery of a several rocky worlds transiting the nearby small star LHS1140 provides an unprecedented opportunity to detect the molecules present in the atmosphere of a terrestrial exoplanet. In our planetary quest, MEarth observations have sharpened our understanding of the evolution of these low-mass stars, and hence the stellar environment in which these planets may wither or thrive.

10

Speaker: Caroline Morley
Institute: UT Austin
Host: Eve Lee

From Exotic to Familiar: Observing Exoplanet Atmospheres in the Coming Decade

Observations of exoplanets to date have used the Hubble and Spitzer Space Telescopes to reveal exotic exoplanet atmospheres, including significant effort to characterize planets with radii between Earth's and Neptune's -for which we have no counterparts in the solar system-that are accessible to current telescopes. Observations of their transmission spectra reveal a diversity of worlds, some shrouded in clouds and others with molecular features. I will discuss the types of clouds and hazes that can obscure transmission spectra, and show the effect that these thick hazes have on the thermal emission of small exoplanets. I will discuss some of my plans for new observations during the first cycle of JWST to measure the thermal emission of these planets. The new frontier of exoplanet atmosphere studies is characterizing the atmospheres of planets more familiar to Earthlings: cold gas giants and temperate Earths. I will discuss my current work to reveal the atmosphere of a cold free-floating giant planet, and my plans for detecting a host of interesting molecules in its atmosphere with JWST. We will soon be able to access Earth-sized, temperate worlds for the most favorable 3 systems orbiting the small stars. I will discuss the recent discoveries of Earth-sized planets around bright M dwarfs and how we might use JWST to detect their atmospheres. Lastly, I will discuss prospects with current and upcoming ground-based telescopes to detect exoplanet atmospheres, including some steps to take preceding the launch of JWST.

17

Speaker:  J. Xavier Prochaska
Institute: UC Santa Cruz
Host: Chris Martin

The Wolfe Disk: ALMA Discoveries of Distant, HI-selected Galaxies

I will review our series of successful programs to dissect the interstellar medium of distant, star-forming galaxies with the Atacama Large Millimeter Array (ALMA).  In particular, I will discuss surveys of the set of HI-selected galaxies known as the damped Lya systems (DLAs).  We resolve, in part, a decades old struggle to identify the galactic counterparts of these DLAs and thereby place them firmly in the modern picture of galaxy formation.  I will also highlight high spectral and spatial resolution observations of the Wolfe Disk,a z~4 galaxy with a Milky Way-like rotation curve.

24
Speaker: Brad Cenko
Institute: NASA
Host: M. Kasliwal

Recent Observational Puzzles from Tidal Disruption Flares: Towards Viable Probes in the LSST Era

I will present an overview of efforts across the electromagnetic spectrum to identify and study tidal disruption flares (TDFs), when a star wanders too close to a super-massive black hole and is torn apart by tidal forces. In particular I will focus on three unexpected surprises that challenge the most basic picture of these events: 1) large inferred radii for the optical/UV-emitting material, indicating either circularization of the bound debris at large distances and/or significant reprocessing of the radiation from the inner accretion disk; 2) the ubiquity of outflows, detected at radio, X-ray, and UV wavelengths, ranging from speeds of 100 km/s to near the speed of light; and, 3) the peculiar atomic abundances observed in the UV and optical spectra of these objects. Understanding the nature of the broadband emission will be critical if we wish to ultimately utilize these events as probes of black hole mass in distant quiescent galaxies in the LSST era. Finally I will provide an introduction to upcoming and proposed wide-field surveys that will help us address these issues in the coming years.

31
Speaker: Jason Rhodes
Institute: JPL
Host: D. Mawet

NASA's Next Astrophysics Flagship: The Wide Field Infrared Survey Telescope (WFIRST)

The top recommendation for a large space mission in the US 2010 Decadal Survey was the Wide Field Infrared Survey Telescope (WFIRST).  Similarities in hardware requirements between proposed dark energy, exoplanet microlensing, and near infrared surveyor missions allowed for a single mission that would accomplish all three goals.  The gift of an existing 2.4 meter telescope to NASA by another US government agency allowed for the addition of a coronagraph that will take images and spectra of nearby exoplanets; this instrument will be a technological stepping stone to imaging other Earths in the 2030s.  I will give an overview of WFIRST's proposed instrumentation, science goals, and implementation plan. I will delve into the details of a number of scientific and technical efforts in Pasadena that are paving the way for this ambitious and exciting mission.


NOVEMBER
7
Speaker: Decker French
Institute:  Carnegie Observatories
Host: A. Faisst

Bold Nuclei in Old Galaxies

Galaxies evolving through the post-starburst (or E+A) phase are in the midst of drastic changes in their stellar populations, morphologies, and gas content. They are likely experiencing periods of AGN-driven feedback, alongside a high rate of tidal disruption events (TDEs), and are thus good laboratories to explore how these nuclear processes depend on and affect the rest of the galaxy. While post-starburst galaxies have stopped forming new stars, we have discovered that many have significant reservoirs of molecular gas remaining, which are depleted only after the starburst had already ended. Young post-starburst galaxies have molecular gas reservoirs similar to normal star-forming galaxies, which decline to the levels of early type galaxies within 1-2 Gyr. This rate of gas depletion is too rapid to be explained by the low star formation rates in these galaxies, so AGN feedback may be responsible. Recent ALMA observations show these galaxies have low dense gas fractions, and the mechanisms which deplete the gas after the starburst may be the same as those which suppress the collapse of gas into denser states. We have also found that post-starburst galaxies host a disproportionate number of TDEs, in which a star is accreted onto the black hole. I will present recent work on what the cause of the TDE rate enhancement during this phase may be and how this host galaxy preference can be used as a tool for identifying new TDEs.

14
Speaker: Tamas Budavari
Institute: John Hopkins Univ
Host: M. Graham

Computational Optics for Astronomy Surveys

We will discuss recent efforts to extract more information from time-domain imaging surveys. Our approach is to model the latent image behind the turbulent atmosphere which blurs all observations to varying degrees - making the stars twinkle. If we can infer the image of the sky behind the atmosphere, all observational studies will simultaneously benefit. Advanced statistical modeling and computational methodology promise reliable solutions. In simulations using the software stack of the Large Synoptic Survey Telescope, we study the subtle prism effect of the atmosphere which shifts sources around depending on their spectral energy distribution and the angle of the telescope's pointing. Expected improvements include not only subband color estimates within the broadband filters, but also better determination of sky coordinates and shape measurements, which ultimately yield better maps of the Universe.

28

Speaker: Ken Shen
Institute: Berkeley
Host: J. Fuller

A Revolution in Our Understanding of Type Ia Supernovae

Despite the wide-ranging role Type Ia supernovae (SNe Ia) play throughout astrophysics, we lack a firm theoretical understanding of how they arise.  For decades, the "single-degenerate" scenario, in which an accreting white dwarf reaches the Chandrasekhar mass, held sway.  However, spurred by recent observational and theoretical advances, researchers have begun exploring alternative progenitor channels.  In this talk, I will show why some of us were drawn to the "dynamically driven double-degenerate double-detonation" (D6) scenario, and how it makes unique predictions for surviving hypervelocity companions that were confirmed by the Gaia satellite earlier this year.  These stars, perhaps the fastest unbound stars in the Milky Way, represent the first ever detections of SN Ia survivors and have brought the D6 scenario to the forefront of the field as the only known SN Ia progenitor scenario to succeed in nature.

DECEMBER
5
Speaker: Jessie Christiansen
Institute: Caltech
Host: D. Mawet

Ten Thousand Pieces of Blue Sky: Building towards the complete picture of exoplanet demographics

The NASA Kepler mission has provided its final planet candidate catalogue, the K2 mission has contributed another four years’ worth of data, and the NASA TESS mission has just started producing planet candidates of its own. The demographics of the exoplanet systems probed by these transiting exoplanet missions are complemented by the demographics probed by other techniques, including radial velocity, microlensing, and direct imaging. I will walk through the progress of the Kepler occurrence rate calculations, including some of the outstanding issues that are being tackled. I will demonstrate how K2 and TESS are able to push the stellar parameter space in which we can explore occurrence rates beyond that examined by Kepler, and progress to that end. Finally, I will highlight some of the pieces of the larger demographics puzzle - occurrence rate results from the other techniques that probe different stellar and exoplanet regimes - and how we can start joining those pieces together.

12

Speaker: Smadar Naoz
Institute: UCLA
Host:  Jim Fuller

Mergers and Disruptions in Extreme Gravitational Potentials

Nuclear star clusters around supermassive black holes are likely the most collisional stellar systems in the Universe and are also embedded in extremely deep gravitational potential. Consequently, unique stellar dynamical processes and interactions are expected to take place. For example, collisions and mergers between stars and compact objects are likely to happen in this environment. I will explore these collisions and mergers and their product and will connect between them and some of the observed puzzles in galactic nuclei and in particular our own Galactic Center. Specifically, I will offer possible connections between those merger products and (1) the perplexing population of young stars that are isotropically distributed (S-stars) in a region that is hostile to star formation, (2)  the new class of cold stars in this same region that are two orders of magnitude larger than typical stars (e.g., the "gas-like cloud" G2), (3) stellar black hole-black hole binary mergers and LIGO observations, and (4) supermassive black-hole merger with a stellar-mass compact objects and future LISA observations. Recent developments in our understanding of the underlining physics of three- to few- body dynamics offer the opportunity to address puzzles at these extreme places in our Universe.

JANUARY 9

Speaker:
Institute:
Host:

No Colloquium - AAS week

16

Speaker: Jenny Greene
Institute:  Princeton
Host: P. Hopkins

TBD

23

Speaker: Alex Szalay
Institute: John Hopkins
Host: Mansi Kasliwal

TBD

30

Speaker: Yanqin Wu
Institute: Univ of Toronto
Host: Eve Lee

TBD

FEBRUARY
6

Speaker: Suvi Gezari
Institute: Univ of Maryland
Host: M. Graham

TBD

13

Speaker: Sandro Tacchella
Institute: Harvard
Host: A. Faisst

TBD

20

Speaker: Eliot Quataert
Institute: UC Berkeley
Host: M. Kasliwal

TBD

27

Speaker: Felix Aharonian
Institute: MPIK, Germany
Host: Gregg Hallinan

TBD

MARCH
6

Speaker: Ariel Goobar
Institute: Stockholm University
Host: M. Kasliwal

TBD

13

Speaker: Maxwell Moe
Institute:Univ of Arizona, Tucson
Host: J. Fuller

TBD

20

Speaker: Matthew Povich
Institute: Cal Poly Pomona
Host: Matthew Graham

TBD

27

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No Colloquium - Spring Break

APRIL
3

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10

Speaker: Jocelyn Bell Burnell
Institute: Oxford University
Host: Mansi Kasliwal

TBD


17

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24

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MAY
1

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8

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15

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22

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29

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JUN
5

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Information for Speakers

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