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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 2017-18 committee members are Margaret Meixner (on Sabbatical), Jason Tumlinson (Co-chair), Alaina Henry, Brett Salmon, Ethan Vishniac (JHU Co-chair), Kevin Schlaufman (JHU), and David Nataf (JHU).

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

Date Speaker/Title
Feb. 07 Jennifer Johnson (Ohio State University)
Title: Better Stellar Ages Through Chemistry
Abstract: Reliable stellar ages hold the key to numerous questions of galaxy and stellar system formation. However, they have been frustratingly hard to measure for field stars. While Gaia will improve the situation markedly for nearby turnoff stars, determination of ages for giants will not benefit to the same degree. In this talk, I will discuss the calibration of chemical ages, based on [C/N], which tags the mass of the star, and [alpha/Fe], which tags the time since star formation began. I will use these ages to discuss outstanding problems in the Galaxy, including the amount of radial mixing through the disk, the prevalence of stellar mergers, and the inside-out formation of the Galaxy.
Host: Molly Peeples
Feb. 14 Suzanne Staggs (Princeton University)
Title: Probing the Universe with High-Resolution Cosmic Microwave Background Maps
Abstract: Famously, the rich angular power spectrum of the intensity of the cosmic microwave background (CMB) reveals the state of the universe a mere 10^{13} s after the big bang. In its fine-angular scale details, the CMB also encodes details of the CMB’s interactions with the rest of the universe in the subsequent 4^{17} s. The CMB is slightly polarized by Thomson scattering when there is any local quadrupolar anisotropy in the distribution of the scattering electron population. A primordial gravitational wave (PGW) background would imprint odd-parity polarizations patterns in the CMB polarization at very large angular scales, known as B-modes. Detection of PGWs would have an enormous impact on our understanding of the universe in its earliest instants (as early as 10^{-32} s): inflation is the only proposed primordial source for the as-yet undetected B-modes. At small angular scales, the CMB temperature and polarization maps provide fresh cosmological information, in part because of their sensitivity to the history of the growth rate of structures by gravitational collapse in the expanding universe. The Atacama Cosmology Telescope (ACT) is a special-purpose 6m telescope situated at 17,000 ft in the dry Atacama Desert of northern Chile, at a latitude of 23 degrees South. ACT’s millimeter-wave detectors measure both polarization and intensity at very fine angular scales (arcminutes). I will describe the ACT instrument and its data in the context of other ongoing and proposed CMB measurements, their scientific impact, and the potential discovery space.
Host: Tobias Marriage
Feb. 21 Vicky Kalogera (Northwestern University)
Title: The Dawn of Gravitational-Wave Astrophysics
Abstract: In the past two years the gravitational-wave detections enabled by the LIGO detectors have launched a new field in observational astronomy allowing us to study compact object mergers involving pairs of black holes and neutron stars. I will discuss what current results reveal about compact object astrophysics, from binary black hole formation and core-collapse of massive stars to short gamma-ray bursts and nuclear matter physics. I will also highlight what we can expect in the near future as detectors sensitivity improves and multi-messenger astronomy further advances.
Host: Andy Fruchter
Feb. 28 Kevin Schlaufman (JHU)
Title: The Maximum Mass of a Planet
Abstract: Which celestial bodies deserve to be classified as "planets" has been a source of controversy in astronomy for two hundred years. At the low-mass end, the discovery of numerous additional small bodies in the solar system lead to the International Astronomical Union's 2006 demotion of Pluto to "dwarf planet" status. At the high-mass end, the discovery of both giant planets and more-massive but still-not-stellar brown dwarfs orbiting stars like the Sun has focused attention on the upper limit for admission to the planet club. I'll describe the history of the controversy to this point and show that core accretion does not form objects more massive than about 10 times that of Jupiter. That inference can be used to infer the properties of protoplanetary disks and reveals that the Type I and Type II disk migration problems---two major issues for the modern model of planet formation---are not problems at all.
Host: N/A
March 07 Alexandra Pope (University of Massachusetts)
Title: Rise of Dust: Decoding Hidden Star Formation and Black Hole Growth over Cosmic Time
Abstract: The prominent peak in the history of star formation and black hole accretion at cosmic noon suggests strong evolution in the mechanisms that grow stars and black holes in galaxies over time. Infrared observations can uniquely quantify the energy balance between star formation and active galactic nuclei (AGN) activity, and constrain the composition and conditions of the gas and dust available to form new stars. In order to understand the enhanced activity at cosmic noon, we measure the interstellar medium (ISM) conditions in high redshift galaxies by combining diagnostics from mid-IR spectroscopy, far-IR/(sub)mm continuum and CO molecular lines. While ground-based facilities such as ALMA and the Large Millimeter Telescope (LMT) probe the cold ISM, JWST will be crucial for measuring the warm ISM and small dust grains. Looking to the future, a cold infrared telescope like the Origins Space Telescope is needed to decode galaxy growth over all cosmic time.
Host: Jen Lotz
March 12 Professor Garth Illingworth, Bahcall Lecture (University of California Santa Cruz)
Title: Galaxies at Cosmic Dawn: Exploring the First Billion Years with Hubble and Spitzer — Implications for JWST
Abstract: Hubble has revolutionized the discovery and study of the earliest galaxies through its exploration of the universe in the first billion years after the Big Bang. I will discuss what we have learned about galaxies during that epoch at redshift z>6 from the remarkable HST and Spitzer imaging surveys (e.g., GOODS, HUDF/XDF, HUDF09/12 and CANDELS), as well as surveys of lensing galaxy clusters (e.g., the Hubble Frontier Fields - HFF). Lensing clusters provide extraordinary opportunities for characterizing the faintest earliest galaxies, but also present extraordinary challenges. Analysis of early galaxies found in the HFF images reveal compact star-forming regions that, remarkably, can be as small as today's globular clusters and dwarf galaxies. The results from deep surveys with Hubble, combined with the recent results from Planck, indicate that galaxies dominated the UV ionizing flux that reionized the universe. One of the greatest surprises came from the discovery of very luminous galaxies at redshifts z~11 to z~8, just 400 to 650 million years after the Big Bang. Hubble and Spitzer recently encroached on JWST territory by looking back through 97% of all time to confirm a z~11.1 galaxy. This is far beyond what we ever expected Hubble and Spitzer could do. Twenty years of astonishing progress with Hubble and Spitzer leave me looking to JWST to provide even more remarkable exploration of the realm of the first galaxies. I will discuss how the latest Hubble and Spitzer results on the sizes of star-forming regions in distant galaxies, on the star formation rate at redshift z~10, and from Planck indicating that reionization began around z~10, together have significant implications for the detectability of the "first galaxies" with JWST.
Host: N/A
March 14 Andy Howell (Las Cumbres Observatory)
Title: Kilonovae, Pair Instability Supernovae, and the Progenitors of Type Ia Supernovae: Surprises from Las Cumbres Observatory
Abstract: We were one of six groups to first detect and characterize the kilonova associated with the gravitational wave signal GW170817. Using our global network of telescopes at Las Cumbres Observatory we were then able to observe the supernova approximately every 8 hours over the first few days.  I will discuss this and recent results from the Global Supernova Project. One of these includes the supernova iPTF14hls, a hard to understand supernova that has been luminous for years. It has a lightcurve with at least five peaks and spectra that evolve about 8 times slower than other supernovae.  It may be the first example of the theorized class of supernovae associated with stars in the 100 solar mass range: pulsational pair instability supernovae.
Host: Armin Rest
March 21 Kathrin Altwegg (Universität Bern )
Title: Rosetta at Comet 67P: Deciphering the Origin of the Solar System, the Earth and Life
Abstract: After more than 12 years the Rosetta spacecraft crash-landed on comet Churyumov-Gerasimenko on September 30, 2016. It has traveled billions of kilometers, just to study a small (4 km diameter) , black boulder named 67P/Churyumov-Gerasimenko. The results of this mission now seem to fully justify the time and money spent in the last decades on this endeavor. In the talk I will look back on the craziest mission ever flown by the European Space Agency and point out its technical challenges and scientific highlights. I will show how the results of this mission change our understanding about the formation of the solar system, the Earth and finally life itself.
Host: Ben Sargent
March 28 Jay Strader (Michigan State University)
Title: Black Holes in Globular Clusters
Abstract: Hundreds of stellar-mass black holes form in the early lifetime of a typical globular star cluster. But, unlike the case for neutron stars, no bright X-ray binaries containing black holes have been observed in globular clusters, which led to theoretical predictions that most or all of the black holes should be efficiently ejected through dynamical interactions. I will highlight results from our ongoing survey using deep radio continuum and X-ray data to search for accreting black holes in Milky Way globular clusters, presenting evidence that black holes may indeed be common in globular clusters. I will discuss implications for the dynamical formation of binary black holes observable as gravitational wave sources.
Host: Laura Watkins
April 04 Victoria Meadows (University of Washington)
Title: The Habitability of M Dwarf Planets
Abstract: TBS
Host: Jason Tumlinson
April 11 Steve Kawaler (Iowa State University)
Title: Connecting Highly Evolved Stars with Their Younger Selves through Space-based Asteroseismology
Abstract: By awakening us to the amazing abundance of other planetary systems, the Kepler mission was a landmark in advancing our understanding of the Universe. The mission (and its follow-on, K2) produced extremely accurate brightness measurements of nearly 200,000 stars, with continuous light curves spanning months to years. Beyond planet hunting, Kepler was also an "asteroseismology machine," revealing the subtle seismic vibrations of the stars. Through  asteroseismology, the data has exposed the internal structure of hundreds of main sequence stars, thousands of red giants, and dozens of white dwarfs - providing an exquisite record of the behavior of stars from birth to old age. In this talk I’ll discuss the contributions that asteroseismology has been able to make in tracing the evolution of stellar interiors, and plans for asteroseismology with new missions such as TESS and PLATO.
Host: David Soderblom
April 18 Melissa Ness (MPIA)
Title: Mapping the Milky Way's Assembly with Data Driven Spectroscopy
Abstract: I will present the most up to date results for the ages and precision abundances for hundreds of thousands of Milky Way stars, derived using the data-driven approach to spectroscopy, The Cannon. The Cannon is a new method for deriving fundamental diagnostics of galaxy formation and as I will show, also an efficient tool to enable data-driven discovery science. With new high precision methodologies like The Cannon to derive information from stellar spectra, combined with the distance and stellar motion measurements that will be delivered by the Gaia mission, we are coming into the era where we have both the data and tools to build the ultimate synthesis of Galactic information. I will highlight recent work that quantifies the prospects for chemical tagging of the Milky Way and discuss the opportunities for understanding our Galaxy's formation in the Gaia era.
Host: David Nataf
April 25 No Colloquium
May 02 Nitya Kallivayalil (University of Virginia)
Title: Milky Way Cosmology: Towards Full 6-D Dynamical Mapping of the Nearby Universe
Abstract: TBS
Host: Annalisa Calamida and Tony Sohn
May 09 Suvrath Mahavedan (Pennsylvania State University)
Title: High Precision Near-infrared and Optical Radial Velocities: Challenges, Progress, & Promise
Abstract: TBS
Host: Kevin Schlaufman
May 16 Alan Dressler (Carnegie Institution for Science)
Title: Late Bloomers: What ELSE Influences Star Formation Histories of Galaxies?
Abstract: Measuring the star formation histories (SFHs) and stellar mass growth of individual galaxies is challenging because stellar populations older than 2 Gyr have largely degenerate spectrophotometric properties. For this reason, the SFHs of present-epoch galaxies are largely obscured: the ubiquitous "tau-model" of explonential decline of the the star formation rate is a result of that insensitivity. In contast, the study of galaxies between 5 and 7 Gyr in lookback time allows a reliable measure of individual SFHs from z~1 to z ~ 0.5 and secure comparison to star formation before z~1. From this better vantage point, we have found a great diversity of SFHs in our photometric/spectroscopic study of ~8000 galaxies of 10^10-11 to 10^11 Msun. In particular, our group has identified a ~20% population of "late bloomers"--Milky Way mass galaxies that formed most of their stellar mass between z~1 and z~0.5. This discovery could have important implications for popular models where quasi-universal SFHs derived by abundance matching or integrating SFR scaling laws are "quenched" later in life, if not for the utility of linking stellar mass to dark matter halo growth, in general.
Host: Marc Rafelski
May 23 Sheperd Doeleman (Harvard University)
Title: The Event Horizon Telescope: Imaging and Resolving a Black Hole
Abstract: TBS
Host: TBS