The Observational Quest for Transiting Exomoons

David Kipping

Assistant Professor, Columbia University

Cool Worlds Lab website

With thousands of known transiting exoplanets, many as small as the Earth, our detection capabilities are beginning to border on that necessary to detect the largest moons found in our solar system. Exomoons would offer new opportunities to understand the origins of planetary systems, as well as potentially playing an important role in the search for life. I will discuss the various methods proposed to identify such objects, the state of our knowledge based on present observations, and the potential for new discoveries via upcoming observations (such as JWST), as well as new methodological developments. The exomoon candidates Kepler-1625b-i and 1708b-i will also be discussed, exploring their current status and follow-up potential. Going forward, it is suggested that the statistical validation of exomoons may enter the fray, akin to many of Kepler’s exoplanets, but JWST could present far more compelling detections should it be used for exomoon hunting.

The Path to Direct Imaging and Spectroscopy of Habitable Exoplanets with Large Ground-based Telescopes

Olivier Guyon

Subaru Telescope/University of Arizona/NINS Astrobiology Center

Direct imaging and spectroscopy of exoplanets is key to characterizing their atmospheres. Current 5-10m class telescopes equipped with adaptive optics and coronagraphy can image young giant gas planets in thermal emission in the near-IR (λ ≳ 1μm). Upcoming 30m class telescope will provide the angular resolution and collecting area to image Earth-size habitable planets in reflected light around nearby stars and probe their atmospheres for signs of biological activity. The best targets will be the nearest M-type stars, for which the planet-to-star reflected light contrast is two orders of magnitude milder than Earth-Sun analogs. I will describe the technical challenges that must be overcome to realize this goal. I will provide an overview of collaborative R&D activities at the Subaru Telescope to advance and prototype technical solutions, and focus on particularly promising approaches.

Machine Learning & Astronomy

Brice Ménard

Professor, Johns Hopkins University

The young field of Machine learning has changed the ways we interact with data. Neural networks have made us appreciate the potential of working with millions of parameters. Interestingly, the vast majority of scientific discoveries today, especially in astronomy, are not based on these new techniques. I will discuss the contrast between these two regimes and I will show how a new intermediate approach can provide promising tools for scientific research. I will show some applications in astrophysics and oceanography.

Planet- and Moon-Formation—Connecting Hydrodynamic Simulations of Planet Formation with Observations

Judit Szulágyi

Computational Astrophysics Group Lead, ETH Zurich

Computational Astrophysics Group website

Planets born in circumstellar disks create various disk substructures, such as gaps, rings, spirals, vortices. Similar structures are observed widely with ALMA, SPHERE and similar instruments. At least some of these disk features are likely due to forming planets, however there are also other mechanisms to explain them. Carrying out high resolution, 3D hydrodynamic simulations with radiative transfer already included, allow us to create realistic “mock observations” or “synthetic images” for a given instrument & telescope combination. These mock observations can be compared with already existing real data, or prepare for future observational proposals. We use them to understand how massive forming planets could be observed with the different instruments, how the planet-disk interactions look like on various wavelengths and what planet-generated features we can observe with the current & near-future instrumentation. I review our findings for near- and mid-infrared, sub-millimeter and radio wavelengths, and identify what are the best wavelengths and instruments for hunting for forming planets.

Transforming the LBTI into a Mid-Infrared Habitable-Zone Exoplanet Imager

Kevin Wagner

NASA Sagan Fellow, University of Arizona

Website

The Large Binocular Telescope Interferometer (LBTI) is a prototype instrument for the next class of large ground-based telescopes. With two 8.4m mirrors on a common mount, the effective imaging resolution of a 23-m telescope can be achieved with Fizeau interferometry. In the mid-infrared (specifically at 10-12 µm), this opens the possibility of imaging the habitable zones of several nearby sun-like stars in the Northern hemisphere–including Tau Ceti and Epsilon Eridani, the two closest single sun-like stars. This talk will describe our technical approach to upgrade the mid-infrared capabilities of LBTI for exoplanet imaging. Our planned upgrades include a new coronagraph designed for dual-aperture observations, and the commissioning of a new class of 10 µm detectors for ground-based astronomy. With these upgrades planned to be completed in the next two years, we anticipate that long (~100 hour) exposures will achieve sensitivity levels sufficient to image nearby habitable-zone super-Earths around Tau Ceti, Epsilon Eridani, and several other stars. With a similar instrument on a 30-m-class telescope, it will be possible to image these same planets in a single night–enabling detailed studies of their orbits and atmospheres.

Exoplanet Imaging: From Planet Formation to Exo-Earths

Kevin Wagner

Sagan Postdoctoral Fellow, University of Arizona

Website

High-contrast imaging has enabled the direct detection of over a dozen young exoplanets. Like the broader population of exoplanets at an earlier stage, the rate of discovery of new directly imaged planets is following a path of exponential growth. Young super-Jovian exoplanets, whose residual heat of recent formation raises their temperature and brightness in the infrared, were the first to be discovered (and on surprisingly wide orbits). Being the case that younger planets are easier to detect, some planets have even been imaged in the midst of their formation–with protoplanetary disks and accreting protoplanets imaged in concert. This talk will review the scientific direction and recent advancements of exoplanet imaging, and then will discuss prospects for the future of the field: in particular imaging exo-Earths around nearby stars. To do this, techniques that were developed in the near-infrared will need to be extended to both shorter wavelengths (for reflected light) and longer wavelengths (for thermal emission). Both are necessary in order to fully characterize nearby Earth-like planets, including fundamental properties such as their temperatures, radii, and albedos. With these properties established, in the next decades it will be possible to observe more intricate details of these nearby planets: such as land covering fractions, atmosphere and cloud properties, and even planetary-scale ecosystems.

The Stellar Initial Mass Function in MASSIVE Early-Type Galaxies

Meng Gu

Postdoctoral Fellow, Carnegie Observatories

Website

The initial mass function (IMF) is fundamental to measuring important galaxy properties such as stellar mass and star formation history. I will present the stellar IMF in the center of nearby early-type galaxies in the MASSIVE survey based on high-quality Magellan/LDSS-3 spectroscopy and detailed stellar population synthesis modeling. I will focus on the relations among stellar IMF, global galaxy properties, and stellar populations and discuss the implications for the physical processes driving the global stellar IMF variation. I will share recent progress in measuring IMF gradients and the relation between IMF and local stellar population properties. I will discuss the implications for star formation histories and mass measurement.

Stellar Populations and Assembly Histories of Early-type Galaxies Near and Far

Meng Gu

Postdoctoral Fellow, Carnegie Observatories

Website

Reconstructing the formation and assembly history of galaxies is critical to astrophysics. Early-type galaxies (ETGs) give us a unique window to achieve this goal. Recent progress in stellar population synthesis (SPS) models has pushed us far beyond the “age and metallicity” era. Detailed element abundance patterns and initial mass function (IMF) extracted from the integrated light of ETGs significantly deepen our understanding of the star formation and assembly history of ETGs, the essential stellar mass measurement, and their dark matter content. I will present stellar population studies of massive galaxies and their surrounding environments, focusing on the scaling relations between stellar mass and stellar population properties from observation and simulation sides with implications for the connection between the environments and the growth and quenching of surrounding galaxies. I will discuss how low surface brightness observation, equipped with modern SPS, can probe galaxy formation and assembly at low mass regimes that are challenging to constrain. I will present novel measurements on the global and local stellar IMF in nearby massive galaxies in the MASSIVE survey. I will preview lookback studies that will soon be feasible with the new facilities, such as the Prime Focus Spectrograph (PFS) and the James Webb Space Telescope (JWST).

Bridging Theory and Observations in Time Domain Astronomy

Abigail Polin

Postdoctoral Fellow, Carnegie Observatories/Caltech

Website

We are entering a golden age of time domain astronomy. Technological advancements allow us to design observatories and surveys that probe transient phenomena like never before. The new push toward high cadence observing allows for surveys like ZTF, ASAS-SN, and ATLAS to resolve the earliest features of supernovae (SNe) hours after explosion. Currently we observe of order a thousand supernovae per year, and upcoming surveys like the LSST at the Vera Rubin Observatory will increase the number of observed transients by an order of magnitude.

This upcoming generation of transient science is being developed concurrently with advancements in computing technologies as supercomputers enter the Exascale and soon Petascale regimes, allowing theorists to model parts of the explosion physics for the first time.

In this talk I will discuss time domain astronomy from a theory perspective and describe what observations can be made throughout the lifetime of a supernova, from first light through the remnant phase, to uncover the physics driving the explosion.

How Rich is Rich? Modeling [Ca II] Emission Nebular Phase Supernovae

Abigail Polin

Postdoctoral Fellow, Carnegie Observatories/Caltech

Website

Nebular [Ca II] emission can show up in the spectra of just about every type of supernovae (SNe): SNe Type Ia, core collapse SNe and of course the elusive Ca-rich transients. But what this emission can tell us, beyond there being some (how much?) calcium in the ejecta, is not well understood. I will present ongoing work to quantify this phenomena using NLTE radiative transport methods on simple SN ejecta models. We aim to understand exactly what a [Ca II] emission line can tell us about abundances in SNe ejecta and when it can dominate a spectrum. Lastly, we relate our findings to the topic of Ca-rich transients in the attempt to answer the question that plagues us all: how rich in calcium are they really?

Probing Planet Formation with the Most Extreme Cases

Fei Dai

NASA Sagan Fellow, Caltech

Website

Thousands of exoplanets have been discovered in the past ~30 years. Kepler has shown us close-in, sub-Neptune exoplanets are extremely common in our Galaxy: with every Sun-like star having an order of unity chance of hosting them. The TESS mission is currently conducting an all-sky survey to discover the closest and brightest planet hosts amenable to detailed characterizations using the James Webb Space Telescope. With LUVOIR/HabEx and GMT/TMT recommended by the 2020 Decadal Survey, the detection of biosignatures, the holy grail of the exoplanet community, may be just a few decades ahead of us. However, there are still major gaps of knowledge in our understanding of planet formation, evolution, and habitability. The most extreme exoplanets are ideal for isolating, magnifying, and resolving the existing gaps of knowledge. In this talk, I will highlight three archetypal extreme planetary systems.

At the hottest extreme of planet formation are the ultra-short-period planets (USP, orbital period ~1 day, <2R_Earth) which seem impossible to have formed in situ. Yet, they are the most observationally favorable rocky planets for mass measurement, phase curves, and mass loss studies. I will demonstrate how USPs help us understand the composition, surface mineralogy, and formation pathways of terrestrial planets. The “super-puffs” (planets with anomalously low density, <0.1 g cm^-3) are susceptible to rapid atmospheric erosion with a timescale that is much shorter than the system’s age. I will introduce a scenario that involves ongoing atmospheric erosion and dust entrainment to explain the “super-puffs”. “Super-puffs”, with their ongoing atmospheric erosion, are ideal testbeds to investigate early hydrodynamical mass loss which is not seen on any solar system planets, yet important for understanding planet habitability. Finally, I will showcase a multi-planet system that is perhaps the most dynamically quiet that we know of. TOI-1136 has 6 transiting planets in a chain of mean-motion resonances. The orbital period ratios deviate from exact commensurability by merely a few parts in 10^-4. This 700 Myr-old system is likely a fossil record of the orbital architecture produced by convergent disk migration before dynamical processes could disrupt the resonant configuration.

Towards a more complete understanding of planet formation

Fei Dai

NASA Sagan Fellow, Caltech

Website

In this talk, I will tackle three open questions in planet formation.

1. How lossy is the process of planet formation?  Recent discoveries of 1I/’Oumuamua and 2I/Borisov reveal a large number density of interstellar interlopers roaming in our galaxy.  Consequently, a significant number of planetesimals in protoplanetary disks must be left over from planet formation and subsequently ejected from their home system or get engulfed by the host star.  We leverage detailed abundance studies of comoving binaries to gauge the frequency of planet(esimal) engulfment.
2. Could planet formation be starved out in a metal-poor environment?  So far, exoplanet discovery has focused on solar-type stars in the solar neighborhood.  With TESS’s full sky coverage and ground-based medium resolution surveys, we examined whether planet formation is suppressed for metal-poor host stars (-1<[Fe/H]<-0.5).  Preliminary results suggest that sub-Neptune planets form readily in this environment: possibly hinting at the early inward drift of solids in protoplanetary disks.  Moreover, the orbital architecture and dominant mineralogy may be different for the metal-poor planetary systems.
3. What is the connection between inner terrestrial planets and outer gas giants?  The Nice model and Grand Tack model suggest that the gas giants may be the guardians of the terrestrial planets as was originally thought (e.g. Shoemaker-Levy 9).  Instead, they are often responsible for generating the dynamical hazard in the first place.  Using the Keck Planet Finder (radial velocity, Rossiter McLaughlin effect) and the Gaia (astrometry), we will constrain the 3-D orbital architecture of planetary systems and the dynamical implications.

Preparing for the Time-Domain Revolution with the Young Supernova Experiment

David Jones

Assistant Astronomer, Gemini Observatory

Website

Time-domain science has undergone a revolution over the past decade; tens of thousands of new supernovae (SNe) are now discovered each year and the rate will soon increase even further with the advent of the Rubin Observatory. However, several observational domains, including SNe within days or hours of explosion and faint, red transients, are just beginning to be explored. Here, I will present recent work on the Young Supernova Experiment (YSE), a novel optical time-domain survey on the Pan-STARRS telescopes. Our survey is designed to obtain well-sampled griz light curves for thousands of transient events up to z ≍ 0.2. This large sample of transients with four-band light curves will lay the foundation for the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope, providing a critical preparatory data set in similar filters and a well-calibrated low-redshift anchor of cosmologically useful SNe Ia to benefit dark energy science. As the name suggests, YSE complements and extends other ongoing time-domain surveys by discovering fast-rising SNe within a few hours to days of explosion. I will present an overview of YSE, including science goals, survey characteristics, and a summary of our transient discoveries to date, and I will discuss how our team is using these data to prepare for the next decade of time-domain astronomy.

The need for magnetic field constraints in radiative hydrodynamic modeling of solar flares

Jeffrey Reep

Astrophysicist, United States Naval Research Laboratory

Solar flares are driven by magnetic reconnection, a restructuring of the magnetic field topology that causes the conversion of magnetic energy to thermal and kinetic energy. A large fraction of the energy thermalizes newly-formed coronal loops, heating and filling the plasma there, driving a sharp increase in intensity across the electromagnetic spectrum. Radiative hydrodynamic modeling of these flaring loops is used to tightly constrain the details of the physics, notably the transport of energy across the various layers of the solar atmosphere and the resultant radiative output. Unfortunately, the details of the magnetic field strength and geometry in the solar corona have remained poorly constrained to date, leading to poor assumptions that may require reexamination of many previous results. The recent advent of the Daniel K. Inouye Solar Telescope (DKIST) and two of its IfA-led instruments, however, will significantly strengthen our understanding of the coronal magnetic field by giving direct measurements of the field across multiple heights in the atmosphere. I will discuss the basics of the modeling, our current limitations, and our future prospects with DKIST and other observations.

Alfvénic Wave Dissipation in the Chromosphere as a Source of Thermal Runaway

Jeffrey Reep

Astrophysicist, United States Naval Research Laboratory

Coronal rain is thought to form due to localized condensations of plasma, where a localized increase in the density drives a thermal runaway. To date, simulations of rain have focused on the thermal nonequilibrium (TNE) process, where extremely long duration, quasi-steady footpoint heating leads to the gradual buildup of these condensations—a thermal equilibrium cannot form. Coronal rain is observed not only in quiescent active regions, but also in extremely impulsive flares, where such long duration heating is not likely. In previous work, we showed that the “standard” flare heating due to an electron beam is wholly incapable of directly producing coronal rain. In this work, we examine the resistive dissipation of Alfvén waves in the chromosphere. The waves are strongly damped by ion-neutral collisions (ambipolar diffusion), causing a negative feedback: as the plasma is heated and ionized, the waves dissipate less effectively. Because of this limitation, it is likely that waves, too, cannot drive coronal rain, but measurements of their properties in the chromosphere are necessary to reach a definitive conclusion. This leaves open an important question: what physical mechanism can heat footpoints long enough to cause rain or TNE?

One-minute colloquium

Presented by the IfA Community

Participants will have a single slide and one (1) minute [60 seconds!] to present their research.

For newcomers, this is a great introduction to what goes on at IfA. For those who might’ve been kicking around since before ‘Oumuamua entered the solar system, it’s always interesting to see what your peers have been up to for the past year.

Plus, witness the ruthless truncation as the presentation auto-advances slides after exactly 60 seconds!

Rebuilding Type Ia Supernova Distance Measurements with the SALT3 Model

David O. Jones

Assistant Astronomer, Gemini Observatory

Website

Recent measurements of the Hubble constant (H₀) and the dark energy equation of state (w) have substantially reduced their statistical and systematic uncertainties. However, a 5σ tension between H₀ measurements measured locally versus predicted by CMB data—under the assumption of ΛCDM—requires us to re-examine our assumptions and methodologies as we examine the evidence for new physics. A leading candidate for unrecognized systematic errors in cosmological parameter measurements is the industry standard SN distance measurement model itself, SALT2, as its code base and training data had not been significantly changed in the last 15 years.

Over the last three years, I led a small team of junior scientists to re-build this model in open-source Python from the ground up, and in the process we yielded

1. more precise distance measurements from SNe Ia,
2. an extension of the model to the near-infrared that reduces systematic uncertainties caused by dust extinction,
3. an exhaustive exploration of systematic uncertainties in the model training process, and
4. a rigorous spectroscopic and phase-dependent model of the relationship between SNe Ia and their host galaxy masses for the first time.

This model (SALT3) is predicted to yield a 20% increase in usable observations from the Roman Space Telescope SN survey. In the coming years, our open-source model-training framework will be used with new SN photometry and spectra—including data from UKIRT, Gemini, PanSTARRS, and the UH88—to continually improve the SN model fidelity as Rubin Observatory and Roman Space Telescope data transform our understanding of cosmology.

A young quasar forming in a dust-enshrouded starburst in the early Universe

Seiji Fujimoto

NASA Hubble Fellow, University of Texas

Website

Understanding how super-massive black holes (SMBHs) form and grow in the early universe has become a major challenge since the discovery of luminous quasars only 700 million years after the Big Bang. Simulations indicate an evolutionary sequence of dust-reddened quasars emerging from heavily dust-obscured starbursts that then transition to unobscured luminous quasars by expelling gas and dust. Although the last phase has been identified out to redshift z = 7.6, a transitioning quasar has not been found at similar redshifts due to their faintness at optical and near-infrared wavelengths. In this talk, I will report our recent discovery of an ultraviolet (UV) compact object, GNz7q, associated with a dust-enshrouded starburst at a redshift of z = 7.1899 ± 0.0005, recently published by Nature. The host galaxy is more luminous in dust emission than any other known object at this epoch, forming 1,600 solar masses of stars per year within a central radius of 480 pc. A red point source in the far-UV is identified in deep, high-resolution imaging and slitless spectroscopy. GNz7q is extremely faint in X-rays, indicating the emergence of a Compton-thick super-Eddington black hole accretion disk at the dusty starburst core. The observed properties are consistent with predictions from cosmological simulations and suggest GNz7q is an antecedent to unobscured luminous quasars at later epochs. Remarkably, the latest JWST observations have routinely identified similarly red compact objects at z ~ 5-8, despite its small survey areas, which may lead to renovating our understanding of the abundance of the quasar population and their contribution to cosmic Reionization.

Exploring visible and obscured sides of the early Universe—Today and Beyond

Seiji Fujimoto

NASA Hubble Fellow, University of Texas

Website

Understanding galaxy formation and evolution in the Epoch of Reionization (EoR; z ≳ 6) is essential, as they are the key probe for fundamental cosmological questions (e.g., cosmic Reionization, large-scale structure formation). In this context, the baryon cycle is one of the most important mechanisms regulating galaxy evolution, but its direct observation is still difficult at EoR. I conduct deep ALMA and HST observations for EoR galaxies and find 10-kpc scale cold carbon gas halos surrounding star-forming galaxies at z ≳ 6. The carbon halo is ~5 times larger than the stellar continuum, evidence of outflow remnants in the early galaxies but challenging current galaxy evolution models. To gain a better understanding of the early baryon cycle and address the “formation” of galaxies, I will also present my vision in the next few to 10s years. A unique ensemble of ~120 hrs PI JWST, ALMA, and MUSE programs targeting strongly lensed galaxies at z = 6-7 forms the cornerstone of my plan. I will comprehensively characterize 1) chemical enrichment, 2) mass (star, dust, gas, and dark matter) assembly, and 3) kinematics down to physical scales of ~20-80 pc in the lensed galaxies. Then, the insight and experience of JWST x ALMA joint analysis will be smoothly applied to other JWST-observed galaxies at z > 6-12 by leading immediate ALMA follow-up in multiple co-I JWST treasury programs to search for the first emergence of stellar light and dust in the universe. I will also overview my recent successful achievements of the joint JWST x ALMA analyses in the last 6 months, now exploring the earliest epoch of the universe out to z ~ 17.

Increasing the diversity of exoplanet discoveries—How and why?

David Martin

NASA Sagan Fellow, Ohio State University

Website

Two outstanding questions in astronomy are 1) How do solar systems form and evolve; and 2) Are we alone in the universe? Through the relatively new field of exoplanets we are beginning to answer these questions. However, the majority of discoveries have been limited to planets on short-period orbits around single, main sequence, Sun-like stars. Narrow discoveries breed a narrow understanding. I will outline a path to greater exoplanet diversity, including planet hosts across the H-R diagram and multi-star systems. I will demonstrate an end-to-end approach that combines theory with data from existing and upcoming observatories. Through this we can gain a broader understanding of the lives of planets and the stars that host them, and forge a path towards habitable worlds.

Low-mass stars—Nature’s gift or curse for exoplanets?

David Martin

NASA Sagan Fellow, Ohio State University

Website

M-dwarfs are the most common stars in the galaxy. They are popular targets for exoplanet hunters because of a short-period habitable zone that is easier to observe. This has directed recent transit surveys (e.g., TESS, MEarth & TRAPPIST), motivated the construction of new redder spectrographs (e.g., KPF & MAROON-X), and has provided prime targets for atmospheric characterization (e.g., JWST & ARIEL). However, there remain fundamental challenges with these low-mass stars. M-dwarfs are highly active, which may be devastating for the “habitable” worlds orbiting them. Fundamental stellar parameters of mass, radius, temperature, and metallicity are often poorly constrained, which hurts stellar models and hinders exoplanet characterization. Finally, questions remain about how the planet formation process scales with stellar mass. I will demonstrate our recent and upcoming work to solve these problems, and show how we assist the burgeoning field of M-dwarf exoplanets in the 2020s.

Spectroscopic observations and modeling of solar flares and energetic events

Vanessa Polito

Research Scientist, Bay Area Environmental Research Institute

Website

Solar flares are our solar system’s largest explosive events, capable of releasing a very large amount of energy in the form of radiation, ejection of hot plasma and particles. Solar flares, together with the solar wind—a constant outflow of solar material that streams out from the Sun—can severely influence our space environment. While the details behind the physical processes driving these energetic events are not fully understood, significant progress has been made in recent years thanks to the advent of high-resolution observatories and advanced modelling. In this talk, I will describe some of my research in the area of solar flares, active region heating and connection with the slow solar wind. In particular, I will show how constraints between competing models of solar flares and energetic events can be obtained by combining spectroscopic and imaging observations from current space-based telescopes with predictions from radiative hydrodynamic models. I will also provide an outlook on my future research utilizing current and upcoming solar spectroscopic observatories.

Solar flare heating mechanisms: Diagnostics from UV spectral lines

Vanessa Polito

Research Scientist, Bay Area Environmental Research Institute

Website

In this talk, I will describe in more detail two topics that have been the focus of my recent research in the field of solar flares. In particular, I will discuss my research addressing the origin of non-thermal broadening in high-temperature spectral lines during flares, which remains a long-standing unsolved question. I will also present recent work focusing on high-resolution spectroscopic observations of flare ribbons in the lower solar atmosphere. These results demonstrate the importance of combining high-resolution observations and modelling to distinguish between energy deposition mechanisms in solar flares.

A Massive Star Is Born: How Stellar Feedback Limits Accretion Onto Massive Stars

Anna Rosen

NSF/UC Chancellor’s Postdoctoral Fellow, UC San Diego

Website

Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium (ISM) with their intense radiation fields and fast, isotropic radiatively-driven winds dwarfs the contribution by their vastly more numerous low-mass cousins. This stellar feedback influences star and galaxy formation, and drives the dynamical and chemical evolution of galaxies. Massive stars form from the gravitational collapse of magnetized, dense, and turbulent molecular gas located within Giant Molecular Clouds (GMCs). Feedback from their radiation fields, collimated protostellar outflows, and stellar winds may limit their growth by accretion, necessitating detailed radiation magnetohydrodynamic (RMHD) simulations to understand how these feedback processes may impact their formation.

In this talk, I will present results from a series of RMHD simulations modeling the formation of massive stars and show that stellar feedback can quench accretion onto ~30 M_☉ stars that form in isolation. My results imply that stars more massive than this must form via large-scale, high ram-pressure dynamical inflows within GMCs, consistent with observations. This highlights the need for future studies to follow the gravitational collapse of GMCs in order to trace large-scale inflows to the birth sites of massive stars. I will conclude by discussing my plans to use state-of-the-art high-resolution RMHD simulations that are capable of resolving individual star formation on GMC scales, to study star cluster formation and assess the importance of stellar feedback, including how stellar winds enrich the ISM and contribute to the chemical evolution of galaxies.

Gone with the Wind: Assessing the Importance of Stellar Wind Feedback in Star Cluster Formation

Anna Rosen

NSF/UC Chancellor’s Postdoctoral Fellow, UC San Diego

Website

Massive star clusters (M_★ ≳ 10³ M_☉; MSCs) contain numerous hot stars that launch fast stellar winds. These winds collide with the interstellar medium (ISM) and the winds of nearby stars, producing shock-heated (T~10⁷ K) tenuous gas that adiabatically expands and may ultimately leave the cluster. This process pushes out dense gas that might otherwise be converted into stars. The integrated kinetic energy carried by these winds is comparable to that delivered by supernova explosions, suggesting that at early times, winds could be an important form of feedback on the surrounding cold material from which the star cluster formed. A common signature of stellar wind feedback in MSCs is the diffuse, thermal soft X-ray emission that fills the surrounding HII region. However, the observed diffuse X-ray emission from MSCs is far weaker than predicted by theoretical models, suggesting that wind feedback may be dynamically unimportant. In this talk, I will discuss how the integrated stellar wind energy produced by MSCs can be lost through various physical mechanisms and motivate why future theoretical studies, including numerical simulations of the formation of massive star clusters, are necessary to determine the spatial and temporal importance of stellar wind feedback in MSC formation.

Thunder and Lightning: New Frontiers in Time-domain Astronomy

Ben Margalit

Theoretical Astrophysics Center Postdoctoral Fellow, UC Berkeley

Website

Advances in multi-messenger and time-domain astronomy provide a fresh view of the dynamic Universe and herald a new era in astrophysics. Through gravitational waves and across the electromagnetic spectrum, transient astrophysical phenomena hold enormous potential as probes of extreme physics and cosmic scales. In this talk I will give an overview of recent developments in time-domain astronomy. Focusing on two frontier research areas—neutron star mergers and fast radio bursts—I will illustrate how transients can be harnessed to study fundamental open questions with far-reaching implications. I will conclude by briefly discussing the future of the field and the opportunities ahead.

The “Explosion” of Transients Across the Electromagnetic Spectrum

Ben Margalit

Theoretical Astrophysics Center Postdoctoral Fellow, UC Berkeley

Website

Time-domain astronomy is undergoing a revolution. In radio, optical, and X-rays, puzzling new transients are being discovered at an increasing rate and requiring theoretical interpretation. In this talk, I will present recent advances in modeling emission from explosive transients across the electromagnetic spectrum. Focusing on shocks as a unifying theme, I will discuss the diverse signatures of astrophysical blast waves in different physical regimes, with application to neutron star mergers, gamma-ray bursts, fast blue optical transients, and a new predicted class of X-ray transients. The close interplay between these theoretical advances and recent observations will be highlighted along the way, and future opportunities will be discussed.

Probing the Circumgalactic Medium at high redshifts using Gamma-ray Bursts

Pradip Gatkine

NASA Hubble Fellow, Caltech

Website

How did the galaxies enrich the universe with the elements of life? This is a major unsolved question in astronomy. The circumgalactic medium (CGM) resides at the nexus of galactic inflows and outflows, and acts as a reservoir of metals and baryons. Hence, CGM plays an important role in the cosmic metal enrichment. The low-mass galaxies at high redshifts (z > 2) are likely a major player in the cosmic metal enrichment given their shallow potential wells. However, it is extremely difficult to probe their CGM and galactic flows using conventional methods such as using quasar sightlines.

In this talk, I will discuss a new technique of using spectra of gamma-ray burst (GRB) afterglows to investigate the CGM of low-mass galaxies before cosmic noon (z > 2, i.e. > 10 billion years ago). In particular, I will discuss the finding of ubiquitous outflows and how the outflows relate to the galaxy properties. We find a tantalizing CGM-galaxy co-evolution over 10 billion years, suggesting a self-regulation. I will highlight my ongoing efforts to further examine these outflows in 2D. To conclude, I will outline new directions to perform detailed investigation of the multiphase CGM-galaxy connection with multi-wavelength observations to create a complete picture of the cosmic baryon cycle and metal enrichment.

Measuring cosmic dynamics with Astrophotonics: Getting ready for the next-generation telescopes

Pradip Gatkine

NASA Hubble Fellow, Caltech

Website

Astrophotonics is a new system-on-chip approach for astronomical instrumentation to yield compact, modular, and novel ways to manipulate the photons from one or more telescopes on a chip. The photonic platform of guided light in fibers and waveguides has opened the doors to next-generation instrumentation for both ground- and space-based telescopes. With their compact form factor, on-chip astrophotonic spectrographs offer a transformative approach for building ultra-high-resolution (R ~ 100,000) and high-stability spectrometers. Astrophotonic devices are critical for enabling some of the most exciting high-precision science cases, such as constraining exoplanet masses, directly measuring the cosmic acceleration, and probing the multiphase galactic flows that enrich the universe with elements of life.

In this talk, I will highlight the latest results from my efforts to build high-throughput on-chip astrophotonic spectrometers approaching R ~ 100,000 in the near-IR. I will further outline strategies for achieving the aforesaid challenging measurements (from exoplanets to extragalactic to cosmological), at an unprecedented precision using Astrophotonics.

Effects of turbulent fluctuations on space plasmas

Riddhi Bandyopadhyay

Associate Research Scholar, Princeton University

Website

The solar wind consists of the ionized and magnetized plasma that flows from the Sun’s corona into interplanetary space. Interaction of the solar wind with other objects in space, such as the Earth’s magnetosphere, gives rise to “space weather”. Extreme space weather events can damage space satellites and even shut down our electric transmission grids.

Like many other plasmas within and beyond the solar system, the solar wind and planetary magnetospheres exhibit strong fluctuations, including waves and turbulence. These fluctuations play a key role in the evolution of the solar wind and variability of space weather, yet the underlying characteristics are not well understood. In this talk, I will discuss how the data obtained from various space missions and simulations help to characterize the effects of turbulence on the large-scale behavior of the solar wind. I will start with NASA’s Magnetospheric MultiScale (MMS) mission and present its contributions to understanding the fundamental physics of solar-wind magnetosphere coupling. Then, I will proceed with some recent discoveries of the Parker Solar Probe (PSP) mission near the solar corona. Finally, I will discuss the prospect of using multi-spacecraft coordinated studies to track the evolution of the solar wind plasma throughout the heliosphere.

Characterization of the sub-Alfvénic Solar Corona Observed by the Parker Solar Probe

Riddhi Bandyopadhyay

Associate Research Scholar, Princeton University

Website

The solar wind consists of the ionized and magnetized plasma that flows from the Sun’s corona into interplanetary space. In the lower solar coronal regions, where the magnetic field is dominant, the Alfvén speed is much higher than the wind speed. In contrast, the near-Earth solar wind is strongly super-Alfvénic, i.e., the wind speed greatly exceeds the Alfvén speed. The transition between these regimes occurs in a region classically described as the “Alfvén surface”. In late 2021, NASA’s Parker Solar Probe (PSP) spacecraft entered this surface, as it follows a series of orbits that gradually approach more closely to the Sun. During its 8th and 9th solar encounters, at a distance of about 16 solar radii from the Sun, PSP sampled four extended periods in which the solar wind speed was measured to be smaller than the local Alfvén speed. These are the first in situ detections of sub-Alfvénic solar wind in the inner heliosphere by PSP. In this talk, I will discuss the properties of these recently observed sub-Alfvénic solar wind, which may provide important previews of the physical processes operating at lower altitude.

Deciphering the Origin of Nonthermal Particles with First Principles Modeling of Plasma Turbulence

Luca Comisso

Associate Research Scientist, Columbia University

Website

Understanding the origin of nonthermal particles and radiation that are commonly observed from a variety of astrophysical sources represents the most promising opportunity to uncover the physics of these astrophysical systems. In systems such as the Sun’s corona or accretion disk coronae, the dissipation of large reservoirs of magnetic energy provides the most likely path toward particle acceleration and high energy radiation. In view of the enormous scale separation between the energy-carrying scale and the plasma kinetic scales, turbulence is a natural candidate for converting the available magnetic energy into particle kinetic energy and radiation. In this talk, I will outline recent developments in our understanding of the physics underlying particle acceleration in turbulent plasmas, including the role of magnetic reconnection. I will also highlight the most important implications for understanding the nonthermal emission from the solar corona and accretion disk coronae of supermassive black holes. Lastly, I will briefly highlight the future prospects of this research program.

The Importance of Turbulence and Reconnection in the Formation of Suprathermal Seed Populations for Solar Energetic Particle Events

Luca Comisso

Associate Research Scientist, Columbia University

Website

Solar Energetic Particle (SEP) events, namely high-energy ions coming from the Sun with energies ranging from a few tens of keV to several GeV, have historically been classified into two main types: impulsive and gradual. It is generally believed that impulsive SEP events are associated with flares and gradual SEP events are caused by particle acceleration at coronal mass ejection (CME) driven shocks. To accelerate particles to the observed high energy in the gradual SEP events, it is required that suprathermal seed particles are injected with energies far exceeding the typical thermal energy of particles in the solar corona and the solar wind. However, the mechanisms responsible for generating suprathermal particles and determining their energy distribution have remained elusive over the years. During this talk, I will demonstrate how plasma turbulence and magnetic reconnection, which are naturally expected to occur in the solar corona, can provide an efficient mechanism for the necessary particle injection and help address this long-standing issue. I will discuss the latest findings from numerical simulations and theoretical models that explore the interplay between turbulence and magnetic reconnection in the solar corona. I will also discuss the implications of these results for our understanding of particle acceleration in the solar corona and how they can inform future observational and modeling efforts.

Transcending the Limits of Astrostatistics with Machine Learning Methods

Yuan-Sen Ting

Associate Professor, Australian National University

Website

Astronomy has undergone a profound transformation in recent years, as the acquisition of ever-growing amounts of data through increasingly powerful instruments has opened up a wealth of new avenues of exploration. However, this boon is not without its own set of challenges, as astronomical observations are often multi-dimensional in nature, encompassing the most meticulous imaging of weak lensing, reionization, and protoplanetary disks at their finest details, as well as the comprehensive characterization of complex galaxy mergers throughout cosmic history. In this realm, conventional astrostatistical methods falter.

To address this challenge, I will expound upon two different machine learning approaches for characterizing these complex astronomical systems. Firstly, the Mathematics of Information: I will explore how machine learning can refine the compression of information and extract higher-order moments in stochastic processes. Secondly, a Generative Paradigm: I will delve into how generative models, such as normalizing flows and diffusion models, permit us to model astronomical data sets with exactitude, furthering the study of complicated astronomical systems within their observational domain.

Cosmic variance in cosmological N-body simulations

Gábor Rácz

NASA Postdoctoral Program Fellow, JPL

Website

Cosmic variance is a fundamental limitation to the accuracy of cosmological simulations, which arises from the finite size of the simulated volume. In this talk, we will review the sources and effects of cosmic variance in N-body simulations of the large scale structure of the Universe.

In the first half of this talk, I will describe a new method for estimating and reducing this source of error. In this novel technique, simulations are run in matching pairs, and the average statistical properties of a pair of such simulations have greatly suppressed variance. Using this new method can significantly reduce the computational costs of predicting the properties of cosmic structures for a given cosmological model by enabling the use of smaller simulated volumes without compromising the precision.

In the remaining time, I will present a novel cosmological N-body simulation technique, the StePS (STEreographically Projected cosmological Simulations) method. In this, the infinite spatial extent of the Universe is compactified into a finite hypersurface of a four dimensional sphere with isotropic boundary conditions to follow the evolution of the large-scale structure. Cosmic variance has a strong effect in StePS topology, and reducing this is crucial during the analysis of these simulations.

OHANA NUI: Using quantum optics to measure astrophysical quantum degeneracy in Sirius B

Olivier Lai

Researcher, Observatoire de la Côte d’Azur

Between 1999 and 2012, a collaboration of Observatories strived to connect telescopes at the summit of Maunakea with single mode optical fibres into a kilometric baseline interferometer to operate at near infrared wavelengths; it was the OHANA project, (Optical Hawaiian Array for Nanoradian Astronomy), with all the telescopes operating as a family. We achieved some success, first injecting starlight into single mode fibres (at CFHT, Keck, and Gemini in 2001, 2002, and 2003 respectively) and then succeeding in coherently transporting light from the two Kecks through fibres and measuring stellar fringes in 2005. Unfortunately, luck was not with us and adverse weather conditions prevented us from performing astronomical observations of YSOs and AGNs at Keck until 2009. The ‘OHANA-Iki experiment was developed around the same time in preparation for a CFHT-Gemini baseline, to demonstrate the interferometric chain using 8” telescopes, from acquisition and fringe capture to reduced data for outdoor fiber links. At that time, the lengths of the fibers were not servoed and this was clearly identified as an issue that would need to be addressed for effective fibered links between telescopes for coherent detection in the future. The project came to an end in 2012, leaving some of us feeling that we had been young and foolish to embark on such an ambitious project.

Now that we are older and presumably wiser, we propose to revive the idea of interferometric connection of the Maunakea telescopes, but this time in the visible and using quantum optics. The technique of intensity interferometry, developed by Hanbury-Brown and Twiss in the 1950s and used with great success in the 1960s at the Narrabri Interferometer, fell into neglect with the advent of amplitude interferometry, pioneered by Antoine Labeyrie in the 1970s. But technological progress driven by quantum optics and telecommunications has led to the development of new components (SPADs, SNSPDS) which have allowed to extend the sensitivity of the technique by orders of magnitude. We have developed a collaboration between quantum optics physicist and astronomers at Université Côte d’Azur since 2016 and have demonstrated the promise of the technique using our 1m telescopes to achieve original and meaningful astrophysical measurements. One of the main advantages of the technique, besides being insensitive to atmospheric turbulence, is that it requires no physical link between the telescopes, making it ideally suited for implementation on a site such as Maunakea, with no impact on the mountain whatsoever.

The longest baselines on the mountain would allow to obtain a visibility measurement in one night of integration on Sirius B, the closest known white dwarf. These exotic objects are supported by Fermi electron degeneracy, and their diameter is estimated from their luminosity; such a measurement would uniquely constrain the diameter and demonstrate quantum mechanics at work on an astrophysical size object!

The Search for Other Earths

Megan Bedell

Associate Research Scientist, Flatiron Institute

Website

Detecting a true Earth twin exoplanet (an Earth-mass planet orbiting a Sun-like star within the habitable zone) has recently become feasible for the first time thanks to advances in observational technology. I will give an overview of the motivations and challenges in achieving this goal, and in discovering new exoplanets more generally. In particular, I’ll focus on the Terra Hunting Experiment, an upcoming radial velocity (RV) survey dedicated to the search for Earth twins. I will also present recent work on designing surveys and developing statistical tools for measuring sub-meter-per-second amplitude motions in distant stars.

Black holes across cosmic history: How did they get so big?

Duncan Farrah

Assistant Specialist, UH IfA/UH Mānoa Department of Physics & Astronomy

Observations across multiple domains have shown that black holes are often more massive than can readily be explained. This includes the black hole mergers observed with LIGO, which challenge canonical stellar synthesis, and the supermassive black holes in the most distant quasars, which are very hard to form via accretion and mergers alone. In this talk I will present results on another domain in which black holes seem to be more massive, and grow faster, than is easily explainable via traditional galaxy assembly pathways—the SMBHs in passively evolving red-sequence elliptical galaxies at z < 1. I will then propose a solution that may help to resolve tensions in black hole mass measurements across multiple domains, and which has some further, broader consequences.

The 20 April 2023 Total Solar Eclipse and How Miracles Can Happen

Shadia Habbal

Astronomer, UH IfA

Website

The 20 April 2023 total solar eclipse presented several challenges, among which: 1) As a hybrid, it was at most 60 seconds long; and 2) The path of totality intercepted land in only a few places, notably the very small North West Cape peninsula in Australia; East Timor; and a few tiny islands along the way. However, the predicted ideal weather prospects and the occurrence of totality almost at maximum solar activity were reasons enough to make it worth the effort to transport over 400 kg of instrumentation across the Pacific and then the Australian continent. In this fun talk, I will share with you the trials and tribulations of the Solar Wind Sherpas and the few miracles they encountered along the way.

The 20 April 2023 Total Solar Eclipse and How Miracles Can Happen

Lucy Lu

Postdoc, Columbia University

Galactic Archaeology aims to understand the formation history of the Milky Way (MW). Observations from large spectroscopic and photometric surveys over the last decade have revolutionized this field. Many substructures and stellar populations have been discovered thanks to full sky surveys, such as Gaia, suggesting the MW is out of equilibrium. However, with numerous missions providing high-quality spectra and photometric time series for billions of stars, it has become increasingly difficult to interpret multidimensional data. One way to address the challenge of large data ensembles is to convey multidimensional information in a more compact way. This can be done by constructing a set of key summary statistics. In my talk, I will talk about how I use photometric and abundance data to obtain the ages and birth radii of stars in the MW. These two physical quantities of stars, along with stellar abundances and kinematic measurements provide a “Galactic timetable” that marks the locations and times of occurrence of different events including mergers and enhancements in the star formation rate.