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Colloquium Series

All talks are held on Wednesdays in the STScI John N. Bahcall Auditorium at 3:00 p.m. preceded by tea at 2:45 p.m.

Please direct questions or comments to the colloquium committee. The 2018-19 committee members are Jason Tumlinson (Chair), Alaina Henry, Lea Hagen, Ethan Vishniac (JHU Co-chair), Kevin Schlaufman (JHU), and Kate Rowlands (JHU).

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

Date Speaker/Title
Feb. 13 George Ricker (Massachusetts Institute of Technology)
Title: Searching Near and Far: Exoplanet Transits and Astrophysical Transients from TESS
Abstract: Successfully launched in April 2018, the Transiting Exoplanet Survey Satellite (TESS) is well on its way to discovering thousands of exoplanets in orbit around the brightest stars in the sky. During its two-year prime survey mission, TESS will monitor more than 200,000 bright stars in the solar neighborhood for temporary drops in brightness caused by planetary transits. This first-ever spaceborne all-sky transit survey will identify planets ranging in size from Earth-sized to gas giants, orbiting a wide variety of host stars, ranging from cool M dwarfs to hot O/B giants. TESS stars are typically 30–100 times brighter than those surveyed by the Kepler satellite; thus, TESS planets will be far easier to characterize with follow-up observations. For the first time it will be possible to study the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars. An additional data product from the TESS mission is its full frame images (FFIs) with a cadence of 30 minutes. These FFIs provide precise photometric information for every object within the 2300 square degree instantaneous field of view of the TESS cameras. In total, nearly 100 million objects brighter than magnitude I= +16 will be precisely photometered during the two-year prime mission. As TESS’s limiting magnitude for stacked FFIs extends to fainter than I= +19, we anticipate the discovery of a wealth of galactic and extragalactic transients during the prime mission, as well as numerous asteroids and NEOs. The initial TESS all-sky survey is well underway, covering 13 observation sectors in the Southern Ecliptic Hemisphere in Year 1, and 13 observation sectors in Year 2. A concurrent deep survey by TESS of regions surrounding the North and South Ecliptic Poles will provide prime exoplanet targets for characterization with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes coming online in the next two decades. The status of the TESS mission after the first seven observation sectors will be reviewed. The opportunities enabled by TESS’s unique lunar-resonant orbit for an extended mission lasting more than a decade will also be presented.
Host: TBD
Feb. 18 Natalie Batalha - Bahcall Lecture (University of California, Santa Cruz)
Title: Lava Worlds to Living Worlds: A Retrospective of NASA’s Kepler Mission
Abstract: 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.
Host: Director's Office/SMO
Feb. 27 Kristen McQuinn (Rutgers University)
Title: What’s Happening in the Smallest of Star-forming Galaxies?
Abstract: Small galaxies are key tools for understanding structure formation and galaxy evolution. Traditionally defined as galaxies below a mass threshold of ~10^9 Msun, they have long been used to study the individual components of galaxies (stars, gas, chemical elements) and as archeological records of the conditions in the early Universe. Now we are finding gas-rich, star-forming galaxies in the 10^5-10^7 Msun mass regime. Due to their low-masses, these systems act as boundary conditions for baryon physics in cosmological simulations and may provide the most stringest tests for dark matter physics. The physical properties of these extremely low-mass systems lie below below many thresholds from theoretical predictions and allow us to explore numerous questions about galaxy formation, survival, and evolution. In this talk, I will show how we are moving to the next frontier in low-mass galaxy research with the discovery and characterization of systems hovering at the brink of what we call a galaxy.
Host: Elena Sabbi
Mar. 06 Jennifer van Saders (University of Hawaii)
Title: Making Sense of Stellar Rotation Observed with Kepler: Gyrochronology, Magnetism, and a Sun in Transition
Abstract: Stellar rotation carries a wealth of information about stellar populations. In particular, the technique of gyrochronology was developed to utilize the spin-down of stars as a function of time as an indicator of stellar age. Gyrochronology has the potential to yield precise ages for large samples of stars, providing unprecedented chronological information for studies of the Milky Way and extrasolar planets. However, the technique is in its adolescence: it has been tested and validated under limited scenarios, but its weaknesses and limitations have hitherto been largely unexplored. With time-domain data from the Kepler mission, precision astrometry from Gaia, and lightcurves from the ongoing TESS mission, we can address these gaps: we now have access to datasets of rotation periods and distances for tens of thousands of stars, as well as independent asteroseismic ages and rotation periods for a few hundred old (main sequence) stars. I will discuss my comparisons of theoretical rotation models to these rotation data, which have yielded unexpected insights into the rotational and magnetic lives of stars (and the Sun!), as well as a better understanding of the power and peril of gyrochronology as a tool.
Host: Rachel Osten
Mar. 13 Sarah Horst (Johns Hopkins University)
Title: Planets in a Bottle: Exploring Planetary Atmospheres in the Lab
Abstract: From exoplanets, with their surprising lack of spectral features, to Titan and its characteristic haze layer, numerous planetary atmospheres may possess photochemically produced particles of "haze". With few exceptions, we lack strong observational constraints (in situ or remote sensing) on the size, shape, density, and composition of these particles. Photochemical models, which can generally explain the observed abundances of smaller, gas phase molecules, are not well suited for investigations of much larger, solid phase particles. Laboratory investigations of haze formation in planetary atmospheres therefore play a key role in improving our understanding of the formation and composition of haze particles. I will discuss a series of experiments aimed at improving our understanding of the physical and chemical properties of planetary atmospheric hazes on Titan, Pluto, super-Earths, and mini-Neptunes.
Host: David Soderblom
Mar. 20 No Colloquium - JHU Spring Break
Mar. 27 No Colloquium - Hubble Fellows Symposium
Apr. 03 Evan Kirby (Caltech)
Title: Nucleosynthesis in Degenerate Objects
Abstract: Although thermonuclear (Type Ia) supernovae and neutron star mergers are some of the most important astrophysical events, our understanding of these explosions is vague. I will present abundance measurements of elements across the periodic table (Mg, Fe, Ni, Ba, and others) that address the nature of both types of explosions. The measurements are based on Keck/DEIMOS spectroscopy of red giants in dwarf galaxies, which experienced a large number of Type Ia supernovae. The iron-peak elemental abundances strongly suggest that the majority of Type Ia supernovae in dwarf galaxies exploded below the Chandrasekhar mass, i.e., the double-degenerate model or the single-degenerate, double-detonation model. The DEIMOS spectra also reveal that barium comes from the r-process and appears in the dwarf galaxies on a timescale similar to iron (at least 100 Myr). Therefore, the mostly likely origin is not supernovae but neutron star mergers. The evolution of the [Ba/Fe] ratio indicates a neutron star merger rate consistent with results from LIGO.
Host:Molly Peeples and Kevin Schlaufman
Apr. 10 TBD
Title: TBS
Abstract: TBS
Host: TBD
Apr. 17 Scott Sheppard (Carnegie Institution for Science)
Title: The Solar System Beyond Pluto
Abstract: The Kuiper Belt, which has Pluto as the largest member, is a region of comet-like objects just beyond Neptune. This belt of objects has an outer edge, which we are only now able to explore in detail with new wide-field imagers on the world’s largest telescopes. For the past few years, our team has been performing the largest and deepest survey ever attempted to search for distant solar system objects. The ongoing search has discovered the object with the most distant orbit known in our solar system and some of the largest known trans-Neptunian objects. The uniform survey has shown that the most extremely distant objects are strangely grouped closely together in orbital space, which suggests a yet unobserved Super-Earth or larger planet is shepherding them into similar orbits that some have called Planet X or Planet Nine. I will discuss the most recent discoveries at the fringe of our solar system.
Host: Kevin Schlaufman
Apr. 24 No Colloquium - Spring Symposium
May 01 Or Graur (CfA Harvard University)
Title: Rage Against the Dying of the Light: The Progenitors of Type Ia Supernovae
Abstract: Type Ia supernovae (SNe Ia) have famously been used as standard candles, a use that led to the discovery that the expansion of the Universe was accelerating under the influence of a mysterious new phenomenon called "dark energy." And yet, we still do not have a clear picture of the progenitors of SNe Ia, i.e., what types of star systems end up exploding as these supernovae. For obvious reasons, most observers study these supernovae when they are young and at their brightest. In my talk, I will present recent results from studies of SN Ia rates, from non-detections of SNe Ia in different types of observations, and from SN Ia observations taken thousands of days after explosion. I will specifically emphasize how Hubble Space Telescope observations of old SNe Ia, great then 1000 days after explosion, reveal a possible new correlation between the intrinsic luminosity of the SNe and the way their luminosity fades at these late times. If confirmed, this correlation could provide a brand new diagnostic of SN Ia progenitor, explosion, and nebular physics.
Host: Lou Strolger
May 08 Evgenya Shkolnik (Arizona State University)
Title: Exploring Exoplanets and their Stars with the UV Space Telescopes of the Past, Present and Future
Abstract: Roughly seventy-five billion low-mass stars (a.k.a. M dwarfs) in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs. Knowing the UV environments of M dwarf planets of all sizes will is crucial to understand their atmospheric composition and evolution, providing the needed context for measured exoplanet spectra; while for HZ terrestrial planet, characterization of the UV provides a key parameter in a planet’s potential to be habitable and discriminating between biological and abiotic sources for observed biosignatures. Our efforts to study the UV photometrically and spectroscopically of such planetary systems employ past, present and future space telescopes: the Galaxy Evolution Explorer (GALEX), the Hubble Space Telescope (HST), and the upcoming NASA-funded Star-Planet Activity Research CubeSat (SPARCS), due for launch at the end of 2021. SPARCS will be a 6U CubeSat completely devoted to continuous photometric monitoring of M stars, measuring their variability, flare rates and evolution, while also being a pathfinder for much-needed UV small satellites.
Host: Jason Tumlinson
May 15 Karoline Gilbert (STScI)
Title: The Progress and Promise of Stellar Halo Studies: Fossil Records of Hierarchical Galaxy Formation
Abstract: Stellar halos provide a record of the earliest stages of a galaxy’s formation as well as the mass growth of later epochs. All stages of accretion are represented in the halo: fully phase-mixed stars accreted at early times, stars in distinct tidal streams, and stars in satellite galaxies that will eventually be tidally incorporated into the halo. Stellar halos are also expected to include a population of stars formed within the host galaxy itself. Deciphering a stellar halo's detailed formation history requires measurements in multiple observational dimensions. Our near neighbor, the Andromeda galaxy, provides a unique opportunity to study the global properties of a stellar halo with detailed measurements of individual stars. I will present the global properties of Andromeda’s stellar halo, derived from a large spectroscopic survey of stars throughout the Andromeda system and discuss the limits of such analyses for deciphering the detailed formation history of the halo. A promising new avenue is the use of chemical abundances, which encode information about the environment in which a star formed. I will present first results from a new survey to measure the relative abundances of iron and alpha elements in fields throughout the Andromeda system. I will also briefly discuss future prospects for increasing the observed phase space of stellar halos in Andromeda and beyond.
Host: TBD
May 22 Laura Sales (University of California, Riverside)
Title: Dwarfs and Their Tiny Satellites as Extreme Probes to the LCDM Model
Abstract: Dwarfs come in all forms, from rotationally-supported star-forming disks to spheroidal stellar systems with no star-formation and negligible rotation. We use cosmological hydrodynamical simulations to show that environment plays a significant role on the assembly history, star formation and globular cluster population of these dwarfs, solving a long-standing issue on the origin of dwarf ellipticals in galaxy clusters. But as observations push deeper into fainter and fainter galaxies, the theoretical predictions become most extreme. LCDM makes two clear predictions: i) fainter objects should become increasingly more dark-matter dominated as we move to lower masses and ii) galaxies of any size should be surrounded by a wealth of dark-matter subhalos, many of them massive enough to host their own stars. I will use cosmological simulations to address these predictions and compare them to available observational constraints for the Baryonic Tully-Fisher relation and distribution of dwarfs in the Local Volume. The recent detection of several potential dwarfs associated to the Large Magellanic Cloud by the DES survey is an exciting discovery that cries for new observational campaigns able push the detection of very faint galaxies beyond the limits of our own backyard.
Host: Katey Alatalo and Erik Tollerud