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Research
Colloquium Series

All talks are held on Wednesdays in the STScI John N. Bahcall Auditorium at 3:30 p.m. preceded by tea at 3:15 p.m.

Please direct questions or comments to the colloquium committee. The 2015-16 committee members are Peter McCullough (chair), Jennifer Lotz, and Laura Watkins.

STScI presents live and archived webcasting of talks and Colloquium Series.

Date Speaker/Title
Feb. 03 (No Colloquium: JWST Meeting)
Feb. 10 Julianne Dalcanton (University of Washington)
Title: The Panchromatic Hubble Andromeda Treasury: Science from 117 Million Stars
Abstract: The Panchromatic Hubble Andromeda Treasury is an HST multicycle program to image the north east quadrant of M31 to deep limits in the UV, optical, and near-IR. The HST imaging has resolved the galaxy into over 150 million stars (comparable to ~1/2 the number of stars in SDSS), all with common distances and foreground extinctions. As its legacy, this survey adds M31 to the Milky Way and Magellanic Clouds as a fundamental calibrator of stellar evolution and star-formation processes for understanding the stellar populations of distant galaxies. I will briefly describe the survey strategy, data reduction, and key data products. I will then highlight new work using the NIR stellar populations to constrain the large scale properties of the cold ISM, with 25 pc resolution. These new maps offer the highest resolution available in M31, and point to surprising challenges facing models of dust emission.
Host: Erik Tollerud
Feb. 17 Mark Voit (Michigan State University)
Title: Waterfalls or Rain: How Does Gas Get Into Galaxies?
Abstract: Galaxies are commonly thought to acquire much of the gas that fuels star formation through streams of cold gas that flow along filaments of larger-scale structure: waterfalls. However, the universe\'s largest galaxies appear to have a different gas supply: precipitation of cold clouds out of hot circumgalactic gas via thermal instability. I will present both observational and theoretical support for the precipitation mode in large galaxies and show how the precipitation model can be applied to galaxies of all masses. One of the attractive features of the precipitation model is that it makes observationally testable predictions about the state of the circumgalactic medium, if most star-forming galaxies are indeed in a precipitating state.
Host: Brad Whitmore
Feb. 24 Catherine Pilachowski (Indiana University)
Title: Odd Elements in the Milky Way: What can they tell us about nucleosynthesis in stars?
Abstract: The spectra of cool stars provide access to the (nearly) full pattern of light element and isotopic abundances from C through Ti in stellar populations. The observed abundance patterns can be compared with nucleosynthesis and chemical evolution models to identify the specific contributors to light element abundances in three stellar populations (thin disk, thick disk, and Bulge); to constrain the relative contributions of different types of supernovae, massive stars and AGB stars; and to explore exotic nucleosynthesis processes that may occur during explosive nucleosynthesis. Diagnostics include not only specific element ratios, but matching the full pattern of abundances, including the amplitude of the odd-even effect and the slope of abundance vs. atomic number for both even and odd elements. Key to understanding the origin of the light elements is the determination of the abundances of the rarer odd light elements, including fluorine, phosphorus, and chlorine, and stable rare isotopes from carbon through titanium. Such an analysis is the next step in precision needed to understand the chemical evolution of Galactic stellar populations, using not just [element/Fe] ratios but a more holistic approach to examine the patterns of element abundances in stellar populations.
Host: Paul Goudfrooij
Mar. 02 (No Colloquium: JWST Meeting)
Mar. 09 Eddie Schlafly (LBNL)
Title: The Optical-Infrared Extinction Curve and its Variation in the Milky Way
Abstract: The dust extinction curve is a critical component of many observational programs and an important diagnostic of the physics of the interstellar medium. In this talk, I will present new measurements of the dust extinction curve and its variation towards tens of thousands of stars, a hundred-fold larger sample than in existing detailed studies. We use data from the APOGEE spectroscopic survey in combination with ten-band photometry from Pan-STARRS1, 2MASS, and WISE. Our data and analysis have revealed two new aspects of Galactic extinction: first, we find significant, wide-area variations in the shape of the extinction curve throughout the Galactic plane. These variations are on scales much larger than individual molecular clouds, posing a challenge to existing paradigms of dust formation and processing: the extinction curve must be tracing much more than just grain growth in dense molecular regions. Indeed, we find no correlation between the extinction curve shape and and dust column density up to E(B-V) ~ 2. Second, we discover a strong relationship between shape of the extinction curve and the far-infrared dust emissivity, an important new constraint on models of dust physics.
Host: Joshua Peek
Mar. 16 Hiranya Peiris (University College -London)
Title: Towards Fundamental Physics from Cosmological Surveys
Abstract: TBS
Host: Armin Rest
Mar. 23 Diana Buchwald (California Institute of Technology)
Title: Living on Paper: Einstein's Manuscripts 100 Years after GR
Abstract: The anniversary of the theory of general relativity, completed by Albert Einstein (1879-1955) in late 1915, provides an opportunity to reflect not only on the significant changes in theoretical physics and astronomy over the past century, but also on the changes in our understanding of the historical development of modern science. Einstein’s massive written legacy reveals how Einstein and his generation traversed theory and experiment on the path from classical physics to relativity and quantum theory, and also how they responded and were shaped by the social, political, and institutional transformations that have led to our current scientific culture.
Host: Van Dixon
Mar. 30 Ewine van Dishoeck (Leiden Observatory); Bahcall Lecturer
Title: Zooming In On the Planet-Forming Zones of Disks: Sweet Results from ALMA
Abstract: Protoplanetary disks are the birthplaces of planets, and have been beautifully revealed by iconic HST images. However, the spatial resolution at long wavelengths has so far been insufficient to resolve the critical 5-30 AU region and probe the bulk of the highly obscured disk material. ALMA now allows us to zoom in to nearby disks and determine the physical and chemical structure associated with planet formation. This talk will provide an overview of recent work on observations and models of protoplanetary disks around young stars in various stages of evolution. Early ALMA results include evidence for rotationally supported disks in the deeply embedded stage, the detection of organic molecules (including sugar) and water in forming disks, and the first images of the CO snowline in mature disks.

Special attention will be given to transitional disks, which are a subset of disks with evidence for sharp-rimmed cavities (gaps or holes) in their inner part but with otherwise normal outer disks. These disks are called 'transitional' because they are thought to represent the evolutionary phase from the gas-rich protoplanetary disk to the gas-poor debris disk stage. They are the best candidate sources for harboring just-formed giant planets. ALMA allows imaging of both the gas and dust in these disks, with gas cavities found to be significantly smaller than those of the dust, providing constraints on the properties of the young planets. The surprising discovery of huge asymmetric dust traps ('planetesimal or Kuiper-Belt factory') will be highlighted. Future prospects for JWST will be discussed.
Host: I. Neill Reid
April 06 (No Colloquium: HST Phase I Deadline Week)
April 13 Claire Max (University of California -Santa Cruz)
Title: Black Holes and Outflows in Nearby ULIRGS
Abstract: TBS
Host: Nino Cucchiara
April 20 Klaus Pontoppidan (Space Telescope Science Institute)
Title:Toward a Comparative Inventory of Volatile Molecules in Protoplanetary Disks, Comets and Primordial Ice
Abstract: TBS
Host: N/A
April 27 (No Colloquium: Spring Symposium)
May 04 (No Colloquium: JWST Meeting)
May 11 Tracy Webb (McGill University)
Title: The Growth of the Most Massive Galaxies in the Highest Density Regions: Evidence for In-Situ Star Formation in SpARCS Brightest Cluster Galaxies
Abstract: TBS
Host: Jennifer Lotz
May 18 Nicholas Suntzeff (Texas A&M University)
Title: From Calán/Tololo to HZT to the Carnegie Supernova Project: Thirty Years of Watching Stars Explode
Abstract: Starting in 1986, Mark Phillips, Mario Hamuy, and I began the study of the properties of nearby supernovae, and were the first to produce a light curve based on CCD data. With Jose Maza, in 1989, we began the concentrated study of nearby supernovae called the Calan/Tololo Survey, which led to discoveries including the establishment of Type Ia supernovae as standardizable candles, the deeper understanding of reddening and temperature effects in light curves and spectra, and with the HST calibration of distances to nearby host galaxies of these SNe, the modern value of the Hubble constant based on the quiet Hubble flow defined by supernovae. In 1994, Brian Schmidt and I founded the High-Z Supernova Team utilizing the Calán/Tololo results and MLCS techniques developed by Riess et al. The image subtraction software was developed by Schmidt and later Tonry. These techniques underlie the discovery by both the HZT and the Supernova Cosmology Project of Saul Perlmutter et al (who developed independent software) of the apparent accelerated expansion of the Universe. All these discoveries rest on the rickety photometric system astronomers have organically developed over the last 70 years. With the improvement in the fundamental calibration system led by HST astronomers, and a reanalysis of astronomical photometric techniques by Stubbs and Tonry, we now see the results of supernova cosmology are limited by the systematic errors in how we do photometry. We founded the Carnegie Supernova Project to create a new and precisely calibrated set of nearby supernovae to dig into these systematic effects and to anchor the acceleration results. In this talk, I will present our recently completed ten year survey of exploding stars in the nearby Universe.
Host: D. Soderblom and Adam Riess
May 25 J. J. Eldridge (University of Auckland)
Title: What's the Link Between Superluminous Supernovae and Gamma-Ray Bursts?
Abstract: TBS
Host: Andy Fruchter