List of Past Astronomy Colloquia : 01-Sep-2019 to 31-Dec-2019

Date:   Wednesday 11-Sep-2019
Speaker:   Dr. Kimberly Griffin (University of Maryland)
Title:  Understanding and Improving our Developmental Relationships

While mentoring is often recommended and relied upon as a way to support and train students and junior scholars, these relationships are often misunderstood and engaged in ways that are ineffective and unsatisfying. As a result, the positive outcomes associated with mentoring are often unrealized, and many faculty and students are dissatisfied with their relationships. This talk presents mentoring theory and research that can promote stronger relationships, unpacking common misunderstandings and offering key dimensions of effective mentor-mentee interactions.

Date:   Wednesday 18-Sep-2019
Speaker:   Dr. Robert Leamon (GSFC)
Title:  Terminators: the death of solar cycles: Implications in 2020 for Cosmic Rays, Gamma Rays, Stellar Dynamos and our Atmosphere

Sunspots are a canonical marker of the Sun's internal magnetic field which flips polarity every ~22 yr. The principal variation of sunspots, an ~11 yr variation, modulates the amount of the magnetic field that pierces the solar surface and drives significant variations in our star's radiative, particulate, and eruptive output over that period, and modulation of incoming cosmic rays. When the incoming hadronic cosmic rays interact with solar gas, the sun becomes a bright source of multi-GeV gamma rays. We will present observations from the Solar and Heliospheric Observatory and Solar Dynamics Observatory indicating that the 11 yr sunspot variation is intrinsically tied to the spatio-temporal overlap of the activity bands belonging to the 22 yr magnetic activity cycle. Using a systematic analysis of ubiquitous coronal brightpoints and the magnetic scale on which they appear to form, we show that the landmarks of sunspot cycles 23, 24 (and 25!) can be explained by considering the evolution and interaction of the overlapping activity bands of the longer-scale variability. We will also show how the activity band model can explain shorter cycles of activity, geomagnetic storms ("Space Weather"), and even drive climatic changes with real world consequences, such as hurricanes and agriculture.

Along the way we will discuss how I got to looking at things as seemingly disparate as gamma rays and crop prices, meandering through scientific disciplines, around the world, and through academia and government service.

Date:   Wednesday 25-Sep-2019
Speaker:   Dr. David Bennett (GSFC)
Title:  All the Cool Planets Are Found by Microlensing

NASA's Kepler mission has led a revolution in our understanding of extrasolar planetary systems, and TESS is just beginning to find a wealth of nearby exoplanets that can be studied in detail by JWST. However, these missions are not sensitive to cooler planets that form beyond the snow line, where planet formation is thought to be most efficient. In fact, analogs of the planets in our own Solar System are invisible to these missions. The Astro2010 decadal survey selected the WFIRST exoplanet microlensing survey to fill this gap in our understanding of the cool planets using ~25% of the total WFIRST observing time. WFIRST will complement the exoplanet statistics from Kepler with sensitivity to planets below an Earth masses at separations ranging from the habitable zone of FGK stars to infinity (i.e. unbound planets). This demographic data will be crucial for the understanding of the planet formation process, including the delivery of water to planets in the habitable zone. I present recent results from ground based microlensing observations that challenge a key aspect of the core accretion theory, and I also present results from Keck adaptive optics and Hubble Space Telescope imaging that are being used to develop the exoplanet and host star mass measurement method that will be used by WFIRST.

Date:   Wednesday 02-Oct-2019
Speaker:   Dr. Kate Alexander (Northwestern University)
Title:  Cosmic Extremes: Probing Energetic Transients with Radio Observations

Time-domain astrophysics provides a unique opportunity to study the most extreme physical processes in the Universe, including the deaths of massive stars, the destruction and creation of compact objects like neutron stars and black holes, and the tidal disruption of stars by supermassive black holes (SMBHs). Some transient events, in particular gamma-ray bursts (GRBs) and tidal disruption events (TDEs), launch relativistic jets and outflows that can be explored with radio observations. In these high-energy laboratories, the longer timescale of radio emission allows for extensive followup and characterization of the event energies and the densities of surrounding material, probing models of SMBH growth and accretion (TDEs) and stellar evolution models (GRBs). I will present high-cadence broadband radio and millimeter studies of GRB afterglows and TDEs undertaken with the goal of learning more about their physical properties, the physics underlying the formation and growth of relativistic jets and outflows, and the environments in which these events occur. The insights derived from these studies will be invaluable for designing and interpreting the results from future radio transient surveys.

Date:   Wednesday 09-Oct-2019
Speaker:   Dr. Joe Pesce (NSF)
Title:  Astronomy at the National Science Foundation

In this talk we will explore the National Science Foundation as a funder of fundamental scientific research. In particular, the focus will be on the Division of Astronomical Sciences (AST) within the Directorate of Mathematical and Physical Sciences. AST funds individual researchers and ground-based astronomical facilities. Opportunities, statistics, and future challenges (for AST, NSF and the astronomical community in general) will be discussed.

Date:   Wednesday 16-Oct-2019
Speaker:   Dr. Dr. Klaus Pontoppidan (STSCI)
Title:  The Cauldron of Planet Formation: Understanding our Origins with Infrared Spectroscopy

The origins of the elemental carbon, nitrogen, oxygen and hydrogen that form life can be traced back to a massive reservoir of prestellar ices, which accretes onto planet-forming disks before they take part in the formation of planetesimals and ultimately planetary atmospheres. Their chemical evolution determines the compositions of planets, including those destined to orbit in a habitable zone. Yet the path from the interstellar medium to planets is one fraught with complexity and twists, making multi-wavelength observations critical to constrain theoretical predictions for planetary chemistry. In the past decade, great progress has been made in observing protoplanetary chemistry, not least in measuring the molecular composition in protoplanetary disks. In particular the warm molecular gas and dust in the planet-forming region of young disks are often probed in the near- to far-infrared. I will tell the current story of planet-forming chemistry, and argue that the James Webb Space Telescope, SOFIA, and future infrared observatories will play a fundamental role in our quest to understand our place in the Universe.

Date:   Wednesday 23-Oct-2019
Speaker:   Dr. Derek C. Richardson (University of Maryland)
Title:  "Earth Strikes Back: The DART Mission to Impact an Asterioid"

Date:   Wednesday 30-Oct-2019
Speaker:   Dr. Susan Clark (Institute for Advanced Study)
Title:  The magnetic interstellar medium in three dimensions

The Milky Way is magnetized. Magnetic fields thread the Galaxy, influencing interstellar physics from cosmic ray propagation to star formation. The magnetic interstellar medium (ISM) is also a formidable foreground for observational cosmology, particularly for the quest to find signatures of inflation in the polarized cosmic microwave background (CMB). Despite its importance across scientific realms, the structure of the Galactic magnetic field is not well understood. Observational tracers like polarized dust emission yield only sky-projected, distance-integrated measurements of the three-dimensional magnetic structure. I will discuss new ways to probe the magnetic ISM in three dimensions, by combining high-resolution observations of Galactic neutral hydrogen (HI) with recent insights into how HI morphology encodes properties of the ambient magnetic field. This allows the construction of 3D HI-based Stokes parameter maps: a new tool for studying the structure of the Galactic magnetic field, the ISM, and the polarized foreground to the CMB.

Date:   Wednesday 06-Nov-2019
Speaker:   Ms. Thankful Cromartie (NRAO)
Title:  High Mass Neutron Stars for Fun and Profit

The central densities of neutron stars are the highest known in the Universe, so measurements of pulsars -- like their masses and radii -- can give us unique insights into the physics of matter at extreme densities. High-precision timing measurements in the radio have provided several extremely constraining mass measurements, including iron-clad results that pulsars can be >2 Msun. Such systems strongly constrain the equation of state of neutron star matter and a variety of other topics in physics/astrophysics -- and additionally allow us to conduct unique tests of general relativity and search for nHz gravitational waves. New radio telescopes like MeerKAT, FAST, the SKA, and the ngVLA will soon provide many new pulsars and possibilities for many new masses and tests of basic physics.

Date:   Wednesday 13-Nov-2019
Speaker:   JSI Meeting
Title:  TBA

Date:   Wednesday 20-Nov-2019
Speaker:   Dr. Tuguldur Sukhbold (Ohio State University)
Title:  Islands of Explosions in a Sea of Implosions

The wealth of observational data on light curves, compact object masses, and chemical abundances hold critical clues on how massive stars live and die. However, the utility of these observables were severely hampered due to our limited understanding of the explosion mechanism in core-collapse supernovae. We address this problem by developing a novel and efficient method of simulating supernovae through calibrated neutrino-driven explosions. Instead of the usual arbitrary mass cuts and tuned energies, we employ neutrino-transport along with a proto-neutron star contraction model. In this talk, I will review some of the most exciting results we have found from the application of this approach to a population of single massive stars, including possible physical explanations to the "Red Supergiant Problem", and the birth mass function of black holes and neutron stars. I will end the talk by presenting new results from its application to massive stars in binary systems that have lost their envelope to its companion. Surprisingly, it turns out the explosions of stripped stars do not make enough Nickel-56 to explain the observed Type Ib/c light curves, which goes against the decades long assumption that their optical displays are powered by radioactivity.

Date:   Wednesday 04-Dec-2019
Speaker:   Dr. David Sing (Johns Hopkins University)
Title:  Hubble's Panchromatic Comparative View of Exoplanet Atmospheres

To date, Hubble has played the definitive role in the characterization of exoplanet atmospheres. From the first planets available, we have learned that their atmospheres are incredibly diverse. With HST, JWST, and TESS a new era of atmospheric studies is opening up, where wide scale comparative planetology is now possible. Such studies can provide insight into the underlying physical process through comparative studies. Hubble's full spectroscopic capabilities are now being used to produce the first large-scale, simultaneous UVOIR comparative study of 20 exoplanets ranging from super-Earth to Neptune and Jupiter sizes. With full UV to infrared wavelength coverage, an entire planet's atmosphere can be probed simultaneously and with sufficient numbers of planets, it will be possible to statistically compare their features with physical parameters. The panchromatic treasury program aims at build a lasting HST legacy, providing the UV and blue-optical exoplanet spectra which will be unavailable to JWST, providing key insights into clouds and mass loss. I will review the highlights of the program to date, which include atmospheric water resolved in emission and new absorption features seen in transmission such as escaping ionized metals. I will also present the latest findings from the ongoing Hubble Treasury program and discuss synergies with JWST.

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