ASD Colloquium Series - Spring 2019

ASD Colloquium Series - Spring 2019

The Astrophysics Science Division colloquia occur on Tuesdays at 3:45 pm, with an opportunity to meet the speaker at 3:30 pm, in building 34, room W150 (unless otherwise noted). Schedules from past colloquium seasons are available.

Contact: Knicole Colon


Feb 5 David Ciardi (Caltech/IPAC-NExScI) - Exoplanets From Space and From the Ground: Coupling Our Resources to Find Our Place in the Universe
Feb 12 Ralph Kraft (Harvard/SAO) - Mergers, gas dynamics and the viscosity of the Intracluster Medium: X-ray observations and simulations of early-type galaxies inflating into the Virgo and Fornax clusters
Feb 19 Special Location: B3 Auditorium - Joint Scientific/ASD Colloquium/The John Bahcall Lecture
Natalie Batalha (UC Santa Cruz) - Lava Worlds to Living Worlds: a Retrospective of NASA's Kepler Mission
Feb 26 Padi Boyd (Goddard Space Flight Center) - The Transiting Exoplanet Survey Satellite (TESS) Early Science Results


Mar 5 David Bennett (Goddard Space Flight Center) - Microlensing and WFIRST Find the Cool Planets
Mar 12 Felix Aharonian (DIAS, Dublin) - Toward the solution of the origin of Galactic Cosmic Rays
Mar 19 Special Location: Building 34, Room W305
Meredith MacGregor (Carnegie) - Exploring Planet Formation and Habitability
Mar 26 Special Location: Building 34, Room W120A/B
Christopher Berry (Northwestern) - The unique potential of gravitational-wave astronomy with extreme-mass-ratio inspirals


Apr 02 Special Location: Building 34, Room W305
Sebastian Pineda (Colorado/LASP)
Apr 09 Stella Kafka (AAVSO)
Apr 16 Jon Pratt (NIST)
Apr 23 Special Location: Building 34, Room W120A/B
Shelley Wright (UCSD)
Apr 30 Cullen Blake (U Penn)


May 07 Lutz Wisotzki (AIP)
May 14 Brenda Dingus (LANL)
May 21 Neelima Sehgal (Stony Brook University)
May 28 No Colloquium - Memorial Day


Jun 04 Paul T. O'Brien (Leicester) - THESEUS - the Transient High Energy Survey and Early Universe Surveyor
Jun 11 Adam Mantz (Stanford)
Jun 18 Special Location: Building 34, Room W120A/B
Chanda Prescod-Weinstein (University of New Hampshire)

Exoplanets From Space and From the Ground: Coupling Our Resources to Find Our Place in the Universe

David Ciardi


Tuesday, Feb 5, 2019


Since the discovery of the first planetary systems around stars other than the Sun only three decades ago, we have discovered more than 3000 planetary systems. Initially, all of the discoveries were made from the ground but in the early-2000s, spacecraft were starting to be used to characterize these planets and discover new exoplanetary systems. With the launch of Kepler in 2009, the majority of known exoplanets were, for the first time, discovered from a space platform, and now that TESS has launched in 2018, the number of exoplanet discoveries from space is expected to increase by almost an order of magnitude. However, none of these discoveries could have been made without the coupling of ground-based observations with the space-based detections. Both Kepler and TESS have an extensive community wide ground program to confirm the planetary candidates as bona fide planetary systems. As we move from the era of planetary discovery to the era of planetary characterization, the coupling of space-based and ground-based observations will become even more important as march towards our ultimate goal of finding habitable (and perhaps inhabited) worlds beyond our Solar System.

Mergers, gas dynamics and the viscosity of the Intracluster Medium: X-ray observations and simulations of early-type galaxies inflating into the Virgo and Fornax clusters

Ralph Kraft


Tuesday, Feb 12, 2019


We present results from deep Chandra and XMM-Newton observations of the massive early-type galaxies NGC 4552 and NGC 1404 falling into the nearby Virgo and Fornax clusters. We combine these observations with specifically-tailored viscous and inviscid hydrodynamic simulations for an unprecedented view of the gas dynamics in these nearby clusters. We detect a remnant tail in NGC 4552 behind the stripped gas core, but find no evidence of X-ray emission from the deadwater or far wake regions of the tail. Our viscous simulations of the infall of this galaxy into the Virgo cluster suggest that if the ICM viscosity were a significant fraction of the Spitzer viscosity, this long, cold tail would be easily visible. We therefore conclude that to the extent that one can characterize the transport processes in terms of a classical viscosity, the viscosity must be many orders of magnitude below the Spitzer value and the flow turbulent. In the Fornax cluster, we detect four sloshing fronts in the cluster ICM. Based on our numerical simulations, all four of these fronts can plausibly be attributed to the infall of the early-type galaxy NGC 1404 into the cluster potential. We argue that the presence of these sloshing cold fronts, the lack of its own extended gas halo, and the approximately transonic infall velocity indicate that this must be at least the second core passage for NGC 1404. Additionally, there is virtually no stripped tail of cool gas behind NGC 1404, conclusively demonstrating that the stripped gas is efficiently mixed with the cluster ICM. This mixing most likely occurs via small-scale Kelvin-Helmholtz instabilities formed in the high Reynolds number flow. Finally, we will outline future work, and briefly describe the potential of deep observations with the future generation of X-ray observatories.

Lava Worlds to Living Worlds: a Retrospective of NASA's Kepler Mission

Natalie Batalha

UC Santa Cruz

Tuesday, Feb 19, 2019


In November, engineers transmitted the Goodnight Sequence to power down the Kepler spacecraft thereby initiating mission closeout. The end of Kepler is the end of an exciting chapter in exoplanet exploration. We'll pay homage to the mission by playing back some of its science highlights. We'll also consider Kepler's exoplanet legacy -- what it leaves behind and what role it will play in the chapters being written now by TESS and in the near future by JWST.

The Transiting Exoplanet Survey Satellite (TESS) Early Science Results

Padi Boyd

Goddard Space Flight Center

Tuesday, Feb 26, 2019


TESS’s primary science goal is to discover planets smaller than Neptune orbiting nearby bright stars. It does so by monitoring millions of stars with high time resolution, high accuracy, long time-baseline time series data (light curves) in a wide bandpass optimized for nearby small, cool M-stars. Launched in April 2018, TESS is now more than halfway through the first year of its 2-year near-all-sky survey.

The unprecedented time domain astronomical dataset that will result from the TESS survey allows identification and study of numerous additional types of astronomical phenomena, from comets and asteroids in our own solar system, starspots, flares and oscillations on stars, to supernovae in nearby galaxies and monitoring the brighter active galaxies.

In this talk, I will give an overview of the TESS mission status, discuss some early science results including confirmed small planets, flaring behavior in small stars, and supernovae on the rise, and discuss the many ways in which the scientific and general community are jumping in and making quick progress, with the focus on maximizing the science impact of this innovative survey mission.

TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. George Ricker of MIT’s Kavli Institute for Astrophysics and Space Research serves as principal investigator for the mission. Additional partners include Orbital ATK, NASA’s Ames Research Center, the Harvard-Smithsonian Center for Astrophysics, and the Space Telescope Science Institute. The TESS science instruments were jointly developed by MIT’s Kavli Institute for Astrophysics and Space Research and MIT’s Lincoln Laboratory. More than a dozen universities, research institutes, and observatories worldwide are participants in the mission.

Microlensing and WFIRST Find the Cool Planets

David Bennett

Goddard Space Flight Center

Tuesday, Mar 5, 2019


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. The WFIRST exoplanet microlensing survey is based on the Microlensing Planet Finder mission concept that was developed at Goddard, and it will complement the exoplanet statistics 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 and describe the mass measurement method being developed by Goddard’s microlensing group that will be used to find the masses of most of the exoplanets found by WFIRST.

Toward the solution of the origin of Galactic Cosmic Rays

Felix Aharonian

DIAS, Dublin

Tuesday, Mar 12, 2019


Over recent years, impressive progress has been achieved in the precision and quality of Cosmic Ray (CR) measurements. It includes the detection of a substantial hardening of the energy spectrum of protons and nuclei above 100 GeV/amu; the extension of the electron spectrum to the energy of 20 TeV, the discovery of anomalously high content of secondary positrons and antiprotons, etc. I will discuss the implications of these results in the context of the current paradigm of Galactic CRs, in particular in relation to the potential CR factories revealed by the high/very-high-energy gamma-ray observations. I will argue that supernova remnants remain the prime candidates as major sources of galactic cosmic rays, however, presumably with a reduced role at highest energies. I will discuss the clusters of young massive stars and the supermassive black hole in the Galactic Center as alternative suppliers of PeV particles to galactic cosmic rays.

Exploring Planet Formation and Habitability

Meredith MacGregor


Tuesday, Mar 19, 2019


More than 20% of nearby main sequence stars are surrounded by debris disks, where planetesimals, larger bodies similar to asteroids and comets in our own Solar System, are ground down through collisions. The resulting dusty material is directly linked to any planets in the system, providing an important probe of the processes of planet formation and subsequent dynamical evolution. I will present highlights from ongoing work that explores how planetary systems form and evolve by (1) probing the grain properties of material in debris disks, (2) connecting debris disk structure to sculpting planets, and (3) understanding the impact of stellar flares on planetary habitability. Measurements of the long wavelength spectral index determine the grain size distribution in circumstellar disks, informing constraints on composition and collision processes. Detailed modeling of ALMA millimeter observations constrains the properties of possible planets responsible for sculpting nearby debris disk systems. Resolved imaging of debris disks also detects the host stars in many cases, yielding additional insights into the radiation environment of these planetary systems. Together these results provide an exciting foundation to investigate the evolution of planetary systems through multi-wavelength observations.

The unique potential of gravitational-wave astronomy with extreme-mass-ratio inspirals

Christopher Berry


Tuesday, Mar 26, 2019


The inspiral of a stellar-mass compact object into a massive (~10^4–10^7 solar mass) black hole produces an extreme mass ratio inspiral and a gravitational-wave signal that could be observed by LISA. These are detectable out to redshift of ~3–4, and we predict ~1–10^4 events per year. Extreme mass ratio inspirals complete tens of thousands of orbits, most of them in the strong-field region of the massive black hole, making the signals extremely intricate. This enables precision measurements of the source parameters: redshifted masses, massive black hole spin and orbital eccentricity can be determined with fractional errors ~1/10^4–1/10^6. The results can be used to perform tests of the Kerr nature of the massive black hole, and map out the population of massive black holes. The unique information encoded in extreme mass ratio inspirals makes them a valuable target for future space-based gravitational-wave observatories.

THESEUS - the Transient High Energy Survey and Early Universe Surveyor

Paul T. O'Brien


Tuesday, Jun 04, 2019


We are entering a new era for high energy astrophysics with the use of new technology to increase our ability to both survey and monitor the sky. I will discuss THESEUS, which is under Phase A study by ESA for its M5 mission. THESEUS will carry two large area monitors utilising Lobster-eye and coded-mask technologies respectively, and an optical-IR telescope to provide redshift estimates using imaging and spectroscopy. This combination, on a rapid response spacecraft, will locate and characterise thousands of GRBs and other transients. These data will facilitate an exploration of the earliest phase of star formation and come at a time when multi-messenger astronomy has begun to provide a new window on the universe. High-energy observations provide a unique probe of compact objects which are the most likely sources of detectable gravitational waves and cosmic neutrinos. THESEUS will also provide key targets for other observing facilities, such as Athena and 30m class ground-based telescopes.

Past Colloqia Schedules

2019: Spring
2018: Fall, Spring
2017: Fall, Spring
2016: Fall, Spring
2015: Fall, Spring
2014: Fall, Spring
2013: Fall, Spring, Summer
2012: Fall, Spring
2011: Fall, Spring
2010: Fall, Spring

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