Astrophysics Science Division
Astrophysics Science Division Colloquium Series Schedule: Spring 2019

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) - Magnetic Phenomena from Low-mass Stars to Brown Dwarfs
Apr 09 Stella Kafka (AAVSO) - 100+ years of Citizen Science: The AAVSO supporting NASA projects
Apr 16 Jon Pratt (NIST) - "For all times, For all people" the eternal quest for universal measures
Apr 23 Special Location: Building 34, Room W120A/B
Shelley Wright (UCSD) - Extending Technosignature Searches to Optical and Infrared Wavelengths
Apr 30 Cullen Blake (U Penn) - Next-generation Doppler Spectrometers


May 07 Special Location: Building 34, Room W305
Lutz Wisotzki (AIP) - The circumgalactic medium of high redshift galaxies in emission
May 14 Brenda Dingus (LANL) - Surveying the TeV Sky with HAWC
May 21 Neelima Sehgal (Stony Brook University) - Mapping Dark Matter on Large and Small Scales with the Cosmic Microwave Background
May 28 Special Location: Building 34, Room W120A/B
Lindy Blackburn (Harvard) - Imaging a black hole with the Event Horizon Telescope


Jun 04 Paul T. O'Brien (Leicester) - THESEUS - the Transient High Energy Survey and Early Universe Surveyor
Jun 11 Special Location: Building 34, Room W120A/B
Adam Mantz (Stanford) - Cosmology with clusters of galaxies
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.

Magnetic Phenomena from Low-mass Stars to Brown Dwarfs
Sebastian Pineda
Tuesday, Apr 02, 2019


The continued search for habitable worlds beyond the solar system has generated great interest in the study of low-mass red dwarfs, which will host many of the best planetary targets for atmospheric characterization with the James Webb Space Telescope. However, the atmospheres of these planets and their prospects for habitability depend on the magnetic processes powering high-energy stellar radiation, flares, and particle fluxes, which can have a strong impact on atmospheric mass loss and photochemistry. Understanding how this activity changes with stellar properties remains a critical question in low-mass stellar astrophysics. I will discuss our current efforts to characterize these emissions and their underlying magnetic processes going from M-dwarf stars to the substellar regime of brown dwarfs, where there are fundamental changes in stellar structure, atmospheric behavior, and magnetism. Our initiatives include: (1) the Far Ultraviolet M-dwarf Evolution Survey (FUMES) to assess the rotational and age evolution of the UV emissions of early-to-mid M-dwarfs with the Hubble Space Telescope. (2) A Transiting Exoplanet Survey Satellite (TESS) guest investigator program looking at photometric variability in very-low mass stars, including flares and rotational spot modulations. (3) The fundamental characterization of brown dwarf aurorae, including the possibility of significant magnetic star-planet interactions as the mechanism powering the observed radio emissions. These endeavors will be key to incorporating stellar activity in assessments of planetary habitability, and using brown dwarf magnetism as a stepping stone toward characterizing exoplanetary magnetic fields.

100+ years of Citizen Science: The AAVSO supporting NASA projects
Stella Kafka
Tuesday, Apr 09, 2019


The AAVSO was formed in 1911 as a group of US-based amateur observers obtaining data in support of professional astronomy projects. As such, this is the first International Astronomical Association that was focusing on citizen science, enabling observers worldwide to acquire, analyze and communicate scientific data. In its current form, the AAVSO is an International Organization with members and observers from both the professional and non-professional astronomical community, contributing photometry to a public photometric database of more than 30,000 variable objects, and using it for research projects. Very frequently, AAVSO observers are called to support NASA missions in optical, IR, x-rays and the UV, ensuring that citizens actively participate in NASA’s science and are engaged members of the scientific process. I will present the main aspects of the association and how it has evolved with time to become a premium resource for variable star researchers. I will also discuss the various means that the AAVSO is using to support cutting-edge variable star science, the core of the AAVSO’s program and databases and how it engages its members in projects, building a stronger international astronomical community.

"For all times, For all people" the eternal quest for universal measures
Jon Pratt
Tuesday, Apr 16, 2019


The International System of Units, or SI, will undergo a profound change on World Metrology Day, May 20, 2019. From that day forward, more than 60 countries accounting for 98% of global GDP have agreed that all standards of measure will be derived from a collection of fundamental quantities and constants. These quantities include the hyperfine splitting frequency of a Cesium atom, the speed of light, the quantum of action, the fundamental charge, and the Boltzmann and Avogadro constants, all of which are now accepted as fixed, physical invariants of the universe, having exact numerical values in terms of our existing units of measure. This audacious move shuns physical standards to embrace completely conceptual references teased from the standard model of physics. The move would no doubt have pleased the originators of the metric system, who were striving for nothing less than to "sign up the universe", as Napoleon derisively mocked in his memoirs. "For all times, For all people" was the rallying cry in 1790, and in this talk I will examine some of the historical, philosophical, and technical aspects of this pivot point for humanity, when measurement might be released from earthly limitations to become truly universal.

Extending Technosignature Searches to Optical and Infrared Wavelengths
Shelley Wright
Tuesday, Apr 23, 2019


How common is life in the universe? Is there other intelligent life? For over 50 years, astronomers have been conducting the search for extraterrestrial intelligence (SETI). These searches have been primarily focused at radio wavelengths, but in the last decade astronomers are thinking critically about new ways to conduct technosignature searches at optical and infrared wavelengths. Our team has been operating the first SETI instrument to search for nanosecond pulsed signals at near-infrared wavelengths. Now our team is developing an "all-sky" optical and wide-field near-infrared pulsed technosignature and fast-transient experiment, called PANOSETI, that is capable of imaging >8,500 sq. degrees of the sky instantaneously. The optical component of PANOSETI will cover a solid angle 3 million times larger than previous targeted SETI searches, while also increasing dwell time per source by a factor of 10,000. One primary goal of PANOSETI is to implement detection methods for pulsed transients and variable sources over 10 decades: nanosecond to seconds. I will discuss the current and future landscape of technosignature searches and instrumentation. Optical and infrared SETI experiments that explores the very fast time domain, especially with large sky coverage, offers a prime opportunity for new discoveries that complement Multimessenger and time domain astrophysics.

Next-generation Doppler Spectrometers
Cullen Blake
U Penn
Tuesday, Apr 30, 2019


The Doppler technique is a key tool for discovering and characterizing planets orbiting other stars. By measuring the reflex motion of the host star as the star and planet orbit a common center of mass, “extrasolar” planets can be discovered and, in some cases, the masses of those planets directly measured. Over the past three decades, advances in technology have enabled some spectrometers to achieve 1 m/s radial velocity precision for Sun-like stars. However, detecting analogs of any of the terrestrial planets in our solar system will require substantially better precision - Earth induces a 10 cm/s motion in the Sun. It has been a long-term goal in the community to achieve Doppler measurement precision sufficient to detect an Earth analog, but a host of astrophysical and instrumental noise sources become important below 1 m/s. I will describe two upcoming Doppler spectrometers designed for detecting and characterizing small planets – NEID, which will be deployed this year to the WIYN telescope at Kitt Peak in Arizona, and MINERVA-Red, which will also be deployed this year to Mt. Hopkins in Arizona.

The circumgalactic medium of high redshift galaxies in emission
Lutz Wisotzki
Leibniz-Institut für Astrophysik Potsdam (AIP)
Tuesday, May 7, 2019


I present observations with the MUSE instrument at the ESO-VLT that reveal the ubiquitous presence of extended Ly-alpha emitting envelopes around individual normal (non-AGN) galaxies at redshifts z > 3. These haloes are larger by factors of ~3-20 than the corresponding rest-frame UV continuum sources as seen by HST. Between ~20% and >~95% of the observed total Ly-alpha flux comes from the extended halo component. At the sensitivity level provided by MUSE, a large fraction of the field of view is actually covered with Lya emission from redshifts 3 < z < 6. The corresponding cross-sections are comparable to those of high-column density hydrogen absorbers, suggesting that most atomic hydrogen at these redshifts has now also been detected in emission. Our observations provide direct insights into the spatial distribution of at least partly neutral gas in the circumgalactic medium of low mass galaxies at z > 3. I also discuss some implications for the demographics of high-redshift galaxies.

Surveying the TeV Sky with HAWC
Brenda Dingus
Tuesday, May 14, 2019


The High Altitude Water Cherenkov (HAWC) observatory is a continuously operating (>95% on-time), wide field-of-view (~2 sr) TeV gamma-ray detector located at 14000’ above sea level in Puebla, Mexico. HAWC has detected nearly 50 Galactic sources at TeV energies of which ~1/4 were not previously known. Notable among these are the microquasar SS433 and the nearby extended pulsar wind nebula Geminga. Within the region surveyed by HAWC are many dark matter rich objects, such as dwarf spheroidal galaxies, and these HAWC data place the strongest constraints to date on annihilating or decaying dark matter with masses >10 TeV. HAWC has also strongly detected the two extragalactic sources Mrk 421 and Mrk 501 which are monitored daily and observed to be variable. The HAWC data are searched in real time for other transient sources. HAWC monitors the same sky as gamma-ray satellites (Fermi), gravity-wave (LIGO) detectors and neutrino observatories (IceCube) allowing for multi-wavelength and multi-messenger observations. In this talk I will discuss my favorite HAWC sources and the implications of the HAWC observations.

Mapping Dark Matter on Large and Small Scales with the Cosmic Microwave Background
Neelima Sehgal
Stony Brook University
Tuesday, May 21, 2019


In this talk I will discuss the next frontier of research on the Cosmic Microwave Background (CMB): precisely measuring the gravitational lensing of the CMB. This CMB lensing signal encodes a wealth of statistical information about the distribution of matter in the Universe, which is sensitive to the total mass of the neutrinos and the particle properties of dark matter. I will discuss recent progress on measuring the neutrino mass using existing CMB data and forecasts for upcoming datasets. I will also discuss a novel and powerful way to probe dark matter particle properties using deep, high-resolution CMB lensing measurements. These measurements can distinguish between cold dark matter and alternative dark matter models that can explain observational puzzles of small-scale structure. I will discuss a new experiment being developed, called CMB-HD, that can achieve this science and also open new windows on the early Universe, gas and galaxy evolution, planetary studies, and the transient sky.

Imaging a black hole with the Event Horizon Telescope
Lindy Blackburn
Tuesday, May 28, 2019


The Event Horizon Telescope (EHT) has captured the first image of the shadow of a black hole, a result of the processing and interpretation of petabytes of signal data recorded simultaneously at several locations spanning the globe using the technique of very-long-baseline interferometry. The radio image, taken at a wavelength of 1.3 mm (230 GHz) matches that of lensed photons from relativistic magnetized plasma surrounding a 6.5 billion solar mass black hole at the center of M87. I will introduce the EHT instrument and first results, highlighting the challenges in processing, calibrating, and fitting images and models to the massive amounts of data from the heterogeneous EHT array. I will also discuss next steps for the EHT, including the possibility of higher resolution and faster imaging with the addition of antennas in space.

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.

Cosmology with clusters of galaxies
Adam Mantz
Tuesday, Jun 11, 2019


The gas mass fractions and the distribution in mass and redshift of the galaxy cluster population provide powerful probes of cosmology, constraining the cosmic matter density, the amplitude of the matter power spectrum, properties of dark energy, and the mass of neutrinos, among other parameters. Improvements in cluster data on several fronts have yielded significant gains in the last decade, notably the maturation of weak gravitational lensing as a probe of total mass and the steady expansion of cluster surveys at all wavelengths. I will review the current state of the two leading cluster cosmology tests, and comment on some of the exciting prospects for the next decade.

Past Colloquia Schedules