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Staff Research
2017 Fall 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
Sept. 06 Geronimo Luis Villanueva (Goddard Space Flight Center)
Title: Is Mars Alive? Testing Current and Past Habitability
Abstract: We recently established that Mars lost an ocean’s worth of water, while the Curiosity rover has recently detected organics on the Martian surface and in the atmosphere. If Mars had a rich chemical and diverse past, how much of these biomarkers were lost to space, and how much are currently stored in the sub-surface? Are sub-surface habitable niches connecting now with the atmosphere? The answers to these fundamental questions of Mars evolution and habitability lie in robotic investigations of the planet’s surface and atmosphere. For instance, in the last decade we have obtained the most comprehensive search for organic material in the Martian atmosphere, permitting us to test for regions of active release and their evolution over time. We are preparing for the human exploration of Mars, and these recent insights about Mars’ past habitability are greatly assisting us in identifying the most promising research sites. In this talk, I will present the current frontiers in the exploration of planetary atmospheres and how the synergies between future space (e.g., ExoMars 2016, JWST) and ground astronomical assets (e.g., TMT, E-ELT) will transform our understanding of the composition, stability and evolution of the atmospheres in the Solar System and beyond.
Host: Bryan Holler
Sept. 13 Mark Devlin (University of Pennsylvania)
Title: The Cosmic Microwave Background:  Current Status and Future Prospects
Abstract: Researchers have been utilizing the measurements of the Cosmic Microwave Background (CMB) for the last several decades to study the birth and evolution of our Universe.  I will review the science behind the CMB and describe how we extract cosmological parameters from CMB maps.  I will conclude with the state of CMB measurements concentrating on the Atacama Cosmology Telescope.
Host: Tobias Marriage
Sept. 20 Raffaella Margutti (Northwestern University)
Title: Astronomical Transients That Defy All Classification Schemes
Abstract: Observations are drawing a complex picture of the latest stages of massive stars evolution and their explosions. In this seminar I concentrate on two among the least understood aspects of stellar evolution, adopting an observational perspective: How do massive stars loose a significant fraction of their mass in the years preceding the explosion? What powers the most luminous stellar explosions in our Universe? I address these questions by taking advantage from panchromatic observations of two remarkable transients: (i) the “normal” envelope-stripped SN2014C, which experienced a dramatic metamorphosis and evolved from Type I into Type II supernova over a timescale of a few months, thus violating the supernova classification scheme that hat has existed for decades. (ii) I will then describe the recent results from our efforts to constrain the energy source of Super-Luminous SNe, with a case study of the “bactrian” transient ASASSN-15lh, which might be the first element of an entirely new class of transients.
Host: Armin Rest and Gautham Narayan
Sept. 27 Bruce Draine (Princeton University)
Title: The Anomalous Microwave Emission: What Is It?
Abstract: The anomalous microwave emission (AME) is emission in the 20-60 GHz range that is correlated with interstellar dust. Discovered in 1996 by the COBE DMR experiment, the AME is a "foreground" that needs to be removed to study the CMB, but it is also an astrophysical puzzle: the emission mechanism remains uncertain.

I will review the observational status of the AME, and discuss the pros and cons of different possible emission mechanisms (e.g., spinning dust, thermal fluctuations in magnetic grain materials) that could be responsible for the AME, and future prospects.
Host: Ron Allen
Oct. 04 Megan Donahue (Michigan State University)
Title: How AGNs Regulate the Circumgalactic Gas: Feedback and Precipitation
Abstract: One of the biggest challenges to understanding how galaxies work is decoding the role of the central supermassive black hole. Without feedback from the black hole (“AGN feedback”), galaxy evolution models fail to produce realistic massive galaxies and galaxy clusters. Somehow, accretion of matter onto the central black hole of a massive galaxy is tuned so that it regulates radiative cooling and the condensation of gas in a volume of space many orders of magnitude larger than the zone of gravitational influence around a black hole. The effects of these black holes are most easily seen in the observations of the most massive galaxies in the universe, the central galaxies of galaxy clusters. Strong observational evidence now indicates the activity of the AGN is closely coupled to the thermodynamic state of the circumgalactic medium, where most of a galaxy’s baryons reside. I will discuss how this relationship could arise and how a feedback mechanism that maintains the circumgalactic medium in a marginally unstable state can regulate star formation within galaxies.
Host: Molly Peeples
Oct. 11 Caitlin Casey (University of Texas)
Title: The Obscured Universe: From Peak Star-Formation to Reionization
Abstract: Although rare in the nearby Universe, galaxies with extraordinary star-formation rates (100-1000x the Milky Way at >100 Msun/year) represent the typical massive galaxy in the early Universe ~10 billion years ago. These galaxies’ high star-formation rates are predominantly obscured by dust which re-radiates >95% of the energy from young stars in the (sub)millimeter/far-infrared, hence they are often called dusty star-forming galaxies (DSFGs). Thanks to facilities like the Herschel Space Observatory, we have successfully mapped the contribution of such DSFGs to cosmic star-formation from z~0 back to z~2, where it appears they are factors of 1000x more common than they are locally and indeed appear to dominate. I will discuss the next steps in mapping the obscured Universe beyond z~2 towards the Reionization Era, what the implications might be for surveys conducted in the near-IR by HST, JWST, and WFIRST, and how we can use dust and gas tracers in such extreme galaxies as novel constraints on the assembly history of large-scale structure.
Host: Nadia Zakamska
Oct. 18 Ortwin Gerhard (Max-Planck-Institut für Extraterrestrische Physik)
Title: Dynamical and Chemo-Dynamical Models for the Barred Inner Galaxy
Abstract: The Milky Way has a cylindrically rotating, strongly peanut-shaped bulge which is the inner, three-dimensional part of a longer, flatter bar, as also seen in external galaxies and N-body simulations.  Dynamical models based on NIR star counts and kinematic measurements from several surveys determine best values for the bar pattern speed and for the stellar masses of the bulge, bar, and inner disk, many within 10% accuracy. The bar region contains the major fraction of the Galaxy's stellar mass, emphasizing the importance of the Milky Way bar for Galactic evolution. The models find a dark matter density profile which flattens to a shallow cusp or core in the bulge region, and have been used to infer the IMF from the time-scale distribution of bulge microlensing events.  Separate dynamical models for different metallicity components in the Galactic bulge/bar show the different spatial and orbital distributions of the stellar populations. This gives a vivid illustration of the complexity that is likely to result from the hierarchical formation history of galaxies in general.
Host: Rosie Wyse
Oct. 25 Ian Roederer (University of Michigan)
Title: Heavy Metals from the First Stars to Today
Abstract: NASA's Cosmic Origins program aims to address the question, "How did we get here?" My work addresses this question through three broad themes: the nature of the first stars, the formation and evolution of the Milky Way and Local Group, and the origin of the elements. I study dwarf galaxies, globular clusters, and stars in the halo using optical and ultraviolet high-resolution spectroscopic data from various telescopes on the ground and the Hubble Space Telescope (HST). I will present observations of heavy elements that change our understanding of when and how they were first produced in the early Universe, including perhaps by the first stars. Observations of heavy elements in a recently-discovered low-luminosity galaxy, Reticulum II, reveal that the r-process---one of the fundamental ways that stars produce heavy elements---may occur in mergers of neutron stars. I will highlight our collaborations with the nuclear astrophysics community, the important contributions of HST, and the sizable impact that future UV spectrographs in space could have on our understanding of nucleosynthesis and galactic formation.
Host: Kevin Schlaufman
Nov. 01 Blakesley Burkhart (Harvard-Smithsonian Center for Astrophysics)
Title: New Diagnostics of MHD Turbulence in the Multiphase Interstellar Medium
Abstract: Our current view of the interstellar medium (ISM) is as a multiphase environment where turbulence affects many key processes. These include star formation, cosmic ray acceleration, and the evolution of structure in the diffuse ISM. It is therefore essential to study and quantify interstellar turbulence using the strengths of numerical simulations in concert with observational studies. In this talk, I shall discuss progress in the development of new techniques for comparing observational data with numerical MHD simulations in the molecular medium, in neutral gas as traced by HI, and warm ionized gas as traced by synchrotron polarization. I will show how a confluence of simulations and novel multiwavelength measurements have taught us that: 1) The ISM in our Galaxy and nearby galaxies is supersonic in both the diffuse and molecular media, 2) Turbulence is primarily driven at scales larger than 100 parsecs, and 3) the magnetic field is a critical regulator of star formation. I will demonstrate how these measurements open up new avenues for studying star formation, cosmic ray acceleration and the formation of molecules in the ISM.
Host: Ethan Vishniac
Nov. 08 Mariska Kriek (University of California - Berkeley)
Title: Reconstructing the Formation Histories of Massive Galaxies
Abstract: In past years, large and deep photometric and spectroscopic surveys have significantly advanced our understanding of galaxy growth, from the most active time in the universe (z~2) to the present day. In particular, the evolution in stellar mass, star formation rate, and structure of complete galaxy samples have provided independent and complementary insights into their formation histories. In addition, detailed studies of the properties of individual distant galaxies have led to a better apprehension of the physical processes which govern galaxy growth. Nonetheless, many outstanding questions remain. In this talk I will give an overview of our current picture of galaxy growth over the past 11 billion years, discuss current challenges and outstanding questions, and introduce new and ongoing efforts to further unravel the formation histories of massive galaxies.
Host: Iva Momcheva
Nov. 15 Wendy Freedman (University of Chicago)
Title: Resolving the Tension in the Hubble Constant
Abstract: The accuracy with which we can measure the Hubble constant, Ho has been steadily increasing over the past decade. The direct and traditional means to measure Ho is based on measurement of distances and velocities to galaxies in the local universe; for example, using Cepheid variables and Type Ia supernovae. A model-dependent Ho can be inferred from applying a cosmological model to measurements of anisotropies in the cosmic microwave background. Recently, these two precise techniques have yielded values of Ho that disagree at more than 3-sigma. This disagreement may be signaling errors in one or both techniques. Alternatively, it could be signaling new physics not currently included in the standard model of cosmology. The Chicago-Carnegie Hubble Program is undertaking a completely independent calibration of the Hubble constant using red giant stars in the nearby universe. These stars are proving to be both more precise and more accurate than the traditional Cepheid variables. Moreover, with the imminent launch of the James Webb Space Telescope and new geometric parallaxes measured by Gaia, they will provide a means of measuring Ho to both a precision and accuracy of 2%.
Host: Adam Riess
Nov. 22 No Colloquium
Nov. 29 Victoria Kaspi (McGill University)
Title: Fast Radio Bursts
Abstract: Fast Radio Bursts (FRBs) are a newly discovered astrophysical phenomenon consisting of short (few ms) bursts of radio waves. FRBs occur roughly 1000 times per sky per day. From their dispersion measures, these events are clearly extragalactic and possibly generally at cosmological distances. One FRB is known to repeat and indeed has been localized to a dwarf galaxy at redshift 0.2. Nevertheless, the origin of FRBs, whether repeating or not, is presently unknown. In this talk I will review FRB properties as well as highlight efforts to find FRBs, including a new Canadian radio telescope, CHIME, that is predicted to make major progress on the FRB problem.
Host: Rachel Osten
Dec 06 Mark Vogelsberger (Massachusetts Institute of Technology)
Title: Simulating Galaxy Formation: IllustrisTNG and Beyond
Abstract: In my talk I will describe recent efforts to model the large-scale distribution of galaxies with cosmological hydrodynamics simulations. I will focus on the Illustris simulation, and our new simulation campaign, the IllustrisTNG project. After demonstrating the success of these simulations in terms of reproducing an enormous amount of observational data, I will also talk about directions for further improvements over the next couple of years.
Host: Alaina Henry
Dec 13 Gilles Fontaine (University of Montreal)
Title: Asteroseismology As Probe of Internal Rotation in Pulsating White Dwarf Stars
Abstract: A few years ago, Charpinet, Fontaine, & Brassard (2009, Nature, 461, 501) developed a new approach to test for solid body rotation (and deviations thereof) in pulsating stars. The method was successfully applied to the prototype of the GW Vir class of pulsating white dwarfs, PG 1159-035, for which the internal rotation profile was mapped over 99% of its mass (92% of its radius), a much better coverage than can currently be achieved from either helioseismology or asteroseismology of normal or giant stars. Similar results were obtained since for the four other GW Vir pulsators with available and suitable seismic rotational data. These stars are all found to rotate rigidly but, more importantly, to rotate extremely slowly, not only at the surface but *globally*. Since the internal rotation profile is available over 99% of the mass of each of these pulsators, it is possible to compute the global rotation energy as well as the total angular momentum in each case. This leads to ratios of the global rotation energy to the internal thermal energy ranging from 1.E-08 to 1.E-06, and to total angular momentum that is 200 to 25 times smaller than that of the actual Sun. In essence, these post-AGB objects have lost *all* of their initial angular momentum. This finding has a direct impact on the question of angular momentum transfer that must exist between the radiative core and the convective envelope in the red giant phases of stellar evolution. While the distribution of rotation kernels is exceptionally favorable for mapping the full structure of a GW Vir star, mode confinement below the outer envelope can also help in probing an unexpectedly large fraction of the mass in some cooler, more degenerate pulsating white dwarfs of the V777 Her and ZZ Ceti types.
Host: Annalisa Calamida