Spring 2015 Colloquium Schedule

The Astronomy Department colloquia generally meet Thursdays at 4:00 pm in PAA A102 (the classroom part of the Physics/Astronomy Building complex) during the fall, winter, and spring when UW classes are in session. Talks given on days other than Thursday, or in locations other than PAA A102, are noted in red.

Additional talks will be added throughout the quarter. Please check back often.

Note: You may request quarterly email notification by sending a brief email message to office@astro.washington.edu.

For general disability accommodation requests, contact the Disability Services Office 10 days in advance of the event at: 206-543-6450 (voice), 206-543-6452 (TTY), 206-685-7264 (fax), or via email at dso@uw.edu.

Colloquium schedules at
Thu, Apr 02
4:00 A102
Victoria Meadows
University of Washington/NASA Astrobiology institute
"The Virtual Planetary Laboratory and the Search for Life Beyond the Solar System"

In the coming decades, the search for life outside our Solar System will be undertaken using astronomical observations of extrasolar terrestrial planets. The NASA Astrobiology Institute's Virtual Planetary Laboratory teamuses an interdisciplinary suite of computer models, coupled with input from observations, field data and laboratory work, to explore the factors that affect planetary habitability and to identify key signs of habitability and life to be sought in exoplanet observations. This talk will highlight VPL results to date, including methods to detect oceans on distant worlds, aspects of planetary habitability for stars orbiting M dwarfs, potential signs of life from alternative biospheres, the generation of false positives for life in planetary atmospheres, and future prospects for the characterization of potentially habitable exoplanets.

Thu, Apr 09
4:00 A102
Julie Lutz
University of Washington
"Fifty Years of UW Astronomy: 1965-2015"

In 1965 George Wallerstein and Paul Hodge joined Theodor Jacobson to formthe University of Washington Department of Astronomy. Since that time thedepartment has developed vibrant graduate and undergraduate programs, participated in many collaborations to build facilities and tocarry out multi-wavelength and multi-disciplinary astronomical research programs, gained considerable national and international recognition and developed strong outreach programs. Needless to say, there has been a lot of fun (and a few mishaps) to be had along the way. This presentation will review some highlights of UW Astronomy's past and present.

Thu, Apr 16
4:00 A102
Matthew Walker
"Let's Figure Out What Dark Matter Is"

I will discuss efforts to use astronomical observations to understand the nature of dark matter. First I will summarize recent results, and present new ones, regarding the structure of dark matter halos on the smallest galactic scales. Then I will explain why cosmological+hydrodynamical simulations can help to resolve long-standing controversies in this field (disclaimer: I do not know how to run cosmological+hydrodynamical simulations). Finally, I will show how observations of the nearest dwarf galaxies convey information about dark matter's particle interactions -- and perhaps even a detection.

Thu, Apr 23
4:00 A102
Rory Barnes
"Exoplanet Habitability"

The discovery of an inhabited exoplanet is a primary goal of modern astronomy. Identifying habitable planets begins with locating the planet's orbit relative to its star's "habitable zone." However, thehabitable zone is only a zeroeth order approximation for planetary habitability, i.e rocky worlds with liquid water. Many phenomena impact the stability and longevity of surface water, including processes that are negligible on Earth. Planets in the habitable zones of M dwarfs are subjected to tidal forces, which in some cases can produce tidal heating strong enough to preclude life. Planets in mean motion resonances, in which two orbital periods are close to a ratio of small integers, can lead to wild eccentricity and inclination swings that can sterilize a planet. Or, for more modest orbital evolution, can induce obliquity fluctuations that suppress ice sheet growth and permit habitability at larger star-planet separations thanfor planets with static obliquities like Earth. Results such as these reveal the need for a broader definition of planetary habitability that includes all relevant factors. I will describe new tools thatenable the fast modeling of habitability in any planetary system, prioritization of exoplanets for biosignature detection, and the engagement of students at all levels.

Thu, Apr 30
4:00 A102
Samantha Lawler
University of Victoria
"Fomalhaut b as a Dust Cloud: Frequent Collisions within the Fomalhaut Debris Disk"

Fomalhaut hosts a beautiful debris disk ring and a directly imaged planet candidate, Fomalhaut b, which seems to continually defy expectations. Originally thought to be a Jovian-mass planet constraining the ring, its unexpected spectral properties and highly eccentric, possibly ring-crossing orbit have completely ruled out that possibility. In this talk I will discusssome of the many theories to explain the weird properties of Fomalhaut b, including a large circumplanetary ring, a system of irregular satellites, and a recent small body collision. I will expand on the last theory, discussing my recent collisional probability simulations of the Fomalhaut debris disk, based on the structure of our Kuiper belt, which show the catastrophic disruption rate of d~100 km bodies in the high-eccentricity scattering component is several per decade. This model paints a picture of the Fomalhaut system as having recently (with ~10-100 Myr) experienced a dynamical instability within its planetary system, which scattered a massive number of planetesimals onto large, high eccentricity orbits similar to that of Fom b. If Fomalhaut b is indeed a dust cloud produced by such a collision, we should soon see another appear, while Fomalhaut b will expand until it is either resolved or becomes too faint to be seen.

Thu, May 07
4:00 A102
Jason Kalirai
"Frontier Science with the James Webb Space Telescope"

The James Webb Space Telescope (JWST) will be the most powerful space telescopethat astronomers have ever constructed, and it is a critical step towards answering the top science questions outlined in the Astronomy & Astrophysics 2010 and 2020 Decadal Surveys. The spring of 2015 is the 2.5 year mark before the JWST Cycle 1 Call for Proposals. The conversation is now changing from development progress to science planning. In this presentation, I will describethe plans for creating a community defined zero proprietary time "Early ReleaseScience Program" for JWST, for releasing an innovative 3D Exposure Time Calculator, for developing simulators to predict JWST imaging and spectroscopicperformance, and for organizing future workshops and science meetings to plan collaborative programs and learn how to reduce JWST data. The talk will also include a summary of the current status of the JWST project and a few of the fundamental science cases that are uniquely enabled by JWST's unprecedented sensitivity (10 minute exposures will detect M dwarfs with V = 30 at S/N = 5) and superb resolution (diffraction limited at 2, 4, and 7+ microns). These include core science drivers such as the measurement of the first galaxies in the Universe and the tracing of galaxy growth through our cosmic history, aswell as the first high-resolution exquisite spectroscopic characterization of dense environments in the Milky Way galaxy. I will also discuss entirely new scientific frontiers with JWST, such as the potential to characterize the atmospheres of nearby habitable zone rocky exoplanets.

Thu, May 14
4:00 A102
Aaron Boley
"Planet formation theory in the era of exoplanets: moving bricks and houses"

Our understanding of planet formation has been strongly influenced by the Solar System. Now, with about 2000 confirmed exoplanets among nearly 5000 candidates, we are able to look at many different types of planetary system architectures and to examine critically the gaps in planet formation theory, while also revisiting the early history of the Solar System itself. Of particular interest is a subclass of multi-planet configurations that I refer to as Systems with Tightly-packed Inner Planets (STIPs). STIPs are characterized as having multiple planets with periods less than 100 days (Mercury orbits the Sun in about 88 days). Their large abundance (which may include >10% of stars) suggests that they are one of the principal outcomes of planet formation. The range of planetary types among STIPs is vast, and the total system mass of many STIPs may be too large to be consistent with their formation from only local disc material. A number of disc processes have been identified that may be able to transport disc solids or even entire planets to short orbital periods. As such, a significant challenge in planet formation theory is to determine which processes are dominant in various environments. Moreover, we must ask why does the Solar System seem to look so different, how might it be related to STIPs, and what processes in Solar System formation theory are generally applicable to planet formation? In this talk, I will discuss some of these challenges and present several of the proposed ideas in understanding the origins of planetary system architectures.

Wed, May 20
4:30 A118
P.J.E. Peebles
Princeton University
"A Walk Through the Tangled Discovery of Remnants of the Big Bang"

Our tested and established theory of the expanding universe grew out of a tangled web of serendipitous discoveries, paths not taken, and brilliant insights. The confusion is familiar in natural science. Unusual here is that relatively few people were involved and they liberally expressed themselves in the literature, offering an accessible look at what people were thinking and doing. I report my impressions.

Thu, May 28
4:00 A102
Zack Berta-Thompson
"In Search of New and Better Sunsets"

Transmission spectroscopy of exoplanet atmospheres has provided us with glimpses of the color of sunset on diverse worlds. However, the spectra gathered to date paint a rather confusing picture, with few measurements matching initial theoretical predictions. Solving this problem will require both deeper observations of well-studied types of planets and broader observations of new types of planets. In one attempt to clarify these murky waters, I will present precise new measurements of the transmission spectrum of a recently discovered, easy-to-observe hot Jupiter, and discuss what these and other observations of known planets can tell us about puffy planets' atmospheres. Looking forward, I will provide a sketch of the landscape for exoplanet atmospheric characterization in the near future, discussing the new easy-to-characterize planets we can expect to discover with the upcoming Transiting Exoplanet Survey Satellite (TESS) and with other ongoing projects.

Thu, Jun 04
4:00 A102
Allen Shafter
"Recurrent Novae in M31"

Novae are among the most violent explosions in the Universe, behind only Supernovae and GRBs in the energetics of their eruptions. In this talk I will discuss the role that observations of extragalactic novae play in our understanding of overall nova properties. I'll begin with a brief introduction of classical novae as compact binary stars, followed by a discussion of nova rates and properties in the nearby Andromeda galaxy, M31. I'll conclude with a discussion of the recurrent nova population in M31, including the remarkable recurrent nova and possible SN Ia progenitor M31N 2008-12a, which has a recurrence time of only a year.