Colloquia: Fall 2022
Host: A. Boogert
Host: F. Bresolin
SIGNALS: Learning About the Birth of Stars with SITELLE
University of Oxford
Host: I. Szapudi
University of New Mexico
Host: R. Jedicke
Sam Barden & Andy Sheinis
MSE / CFHT
Host: E. Baxter
Host: J. van Saders
Host: J. van Saders
Host: B. Shappee
Host: D. Huber
Host: D. Simons
Host: S. Habbal
Host: I. Szapudi
Host: M. Liu
American Museum of Natural History
Host: M. Hon
White Dwarf Research Corporation
Host: J. van Saders
All colloquia are held at 11:45 am HST unless otherwise noted.
Probing the jet-disk connection using infrared observations of protostellar jets
Dr. Jessica Erkal
Observational Astrochemistry Postdoctoral Fellow, UH IfA
Protostellar jets are extended columns of high velocity material moving away from the star-disk plane, and they are observed emerging from the youngest Class 0 stars to more evolved Class II stars in nearby star-forming regions. While protostellar jets were not initially anticipated by star formation models, we now believe they play a crucial role in star formation by providing a way to remove excess angular momentum which allows accretion to continue onto the star. In this talk, I present the results of three studies using high-resolution observations to investigate the role of protostellar jets. In a case study of the bipolar jet from the Class II source DO Tau, we observe asymmetries in the morphology and kinematics lending support to the idea that magnetic fields can aid the launching of the jet and the jet collimation. Jet axis wiggling observed in the DO Tau jet is consistent with jet precession which may be due to a companion in the disk or the launching of a disk wind. In a study of four Class 0/I jets (HH 1, HH 34, HH 46 and HH 111), we also observe jet axis wiggling consistent with jet precession, and for HH 111 with the presence of a companion in the disk. These two studies reveal a new potential avenue to identify newly forming substellar companions in the inner disk. Finally, we investigate the accretion and ejection connection using observations of the He I 1 micron line in a sample of over 100 stars in the Lupus and Upper Scorpius star forming regions. We find variations in the line profile which point to an evolution of the accretion and ejection signatures over time, and with source properties, confirming the results of past works and supporting the idea that the winds traced by the He I line are accretion powered. Each of these three studies highlight the link between the jet and the central source, and how high-resolution observations are a critical tool in understanding the role of protostellar jets in star formation.
Testing the Cosmological Principle
Dr. Subir Sarkar
Professor of Physics, University of Oxford
In the ΛCDM cosmological model the universe is assumed to be statistically isotropic and homogeneous when averaged on large scales. That the CMB has a dipole anisotropy is supposedly due to our peculiar motion because of local inhomogeneity. There should then be a similar dipole in the sky distribution of high redshift sources. Using catalogues of radio sources and quasars we find that this standard expectation is rejected at >5σ. This undermines the standard practice of boosting to the ‘CMB frame’ to analyse cosmological data, in particular for inferring an isotropic acceleration of the Hubble expansion rate which is interpreted as due to Λ.
Explosions in the Sky and Fire on the Ground: The Physics of Cosmic Airbursts
Dr. Mark Boslough
University of New Mexico
On February 15, 2013, an asteroid exploded without warning near the Siberian city of Chelyabinsk. It was quickly reported by the Russian media as a UFO. Videos were shared on social media, and ordinary people became aware of it before NASA officials did. By contrast, the June 30, 1908 Tunguska airburst—10 times larger—was not immediately reported or studied. In the 1990s a piece of enigmatic glass had been identified in a scarab that adorned a breastplate found in King Tut’s tomb. It appeared to be the product of an impact event, but the mechanism for its formation was not understood. Simulations now support the hypothesis that the glass was created by heating and ablation of sandstone and sand near ground zero from a 100 megaton or larger airburst. The explosion was similar to the Chelyabinsk and Tunguska airbursts, but so big that the white-hot asteroid vapor cloud formed a jet of fire that descended all the way to the ground. Models of these events form the basis our understanding of the physics of airbursts and their contribution to impact risk. To improve and test our models, we need more observational data by discovering the next death plunge asteroid before it strikes.
Dr. Mark Boslough is a physicist who received his BS from Colorado State University in 1977 and PhD from Caltech in 1983. He worked at Sandia National Laboratories from 1983 until 2017. He is now a Research Professor at University of New Mexico, physicist at Los Alamos National Laboratory, and chair of the Asteroid Day Expert Panel. His research topics have included Comet Shoemaker-Levy 9, Libyan Desert Glass, the 1908 Tunguska explosion, the 2008 TC3 airburst over Sudan, and Jupiter impacts of 2010 and 2012. He coauthored the US National Academies report “Defending Planet Earth” in 2010. His simulations of the 2013 Chelyabinsk airburst were featured in a NOVA documentary and appeared on the covers of Nature and Physics Today. He has contributed impact simulations for disaster-planning exercises and has appeared in dozens of science documentaries with location filming in Siberia, the Sahara Desert, and elsewhere. Asteroid 73520 Boslough (2003 MB1) was named after him.
Part 1: Dr. Barden. Exploration of a 14-meter, 1.5-degree field of view, quad-mirror anastigmatic telescope concept for wide-field spectroscopy and imaging for MSE
The baseline MSE telescope was a prime focus system allowing about ~4000 fiber probes across the 1.5 square degree field of view. Optical ghosting within the proposed corrector led us to explore alternative telescope concepts. MSE is now doing a trade off between a 2 mirror (the Dual-Mirror, D-M concept) Cassegrain configuration and a Paul-Baker 3-mirror plus fold (the Quad-Mirror, Q-M concept). The Q-M concept offers a Nasmyth mounted focal station which would permit considerable enhancement in capability over the original and D-M designs where the instrument package must ride on the telescope, the first notable aspect being a second Nasmyth port for other instrumentation. Both the D-M and Q-M concepts allow a larger physical focal surface, due to the slower focal ratios, in which a higher density of fiber probes can be implemented. With upwards of 20,000 fiber probes across the 1.5 square degree field, more ambitious faint target surveys are realizable for Pan-STARRS and Rubin followup.
Part 2: Dr. Sheinis. Multi-object spectroscopic capability at the Canada France Hawaii telescope: The MSE pathfinder
MSE/CFHT plan to develop an end-to-end Pathfinder for the Maunakea Spectroscopic Explorer (MSE). The goal of the Pathfinder will be to retire many of the high-level technical risks for MSE by demonstrating on-sky the ability of the major components of MSE in parallel with producing a community-shared science product. The science goals include time-domain astrophysics, specifically spectroscopic follow-up of transients identified by facilities such as Rubin Observatory and Zwicky Transient Factory Facility; Galactic archeology; and stellar abundance and stellar evolution studies. The end-to-end Pathfinder will be a multi-object spectrograph fed at prime focus from CFHT. It will utilize the same visible and NIR MSE spectrograph design with a multiplexing of ~1000 fibers using the same fiber positioner technology as MSE as well as a separate IFU at cassegrain focus. The Pathfinder will prototype the software architecture MSE including scheduling; targeting; data reduction and analysis; and data management, archiving, and database manipulation.
Searching for Signposts of Failed White Dwarf Supernovae
Dr. JJ Hermes
Type Ia supernovae involve the thermonuclear detonation of white dwarf stars, and are an essential tool allowing us to study the Universe on vast scales. However, Type Ia supernovae are not the only byproducts of the mergers at the endpoints of binaries. I will discuss the growing number of observational signposts that can distinguish populations of white dwarf stars that descend from failed Type Ia supernovae. I will also discuss how space-based missions like Gaia, Kepler, and TESS have allowed us better select merger byproducts among the population of typical stellar remnants, allowing us to better characterize the fossils in our nearby stellar graveyard.
New Methods for Seismic Analysis with Gravitoacoustic Mixed Modes
Dr. Joel Ong
Hubble Fellow, UH IfA
Studies of the Sun’s interior through the analysis and interpretation of its p-mode oscillations — helioseismology — constitute our gold standard in the study of stellar interiors in general. Aside from the Sun, measurements of solar-like p-modes are easiest for post-main-sequence stars; subgiants and red giants now constitute the majority of our seismic observations. However, foundational assumptions underlying helioseismology cease to be applicable for these evolved stars, on account of their different internal structures, rendering them impenetrable to much analysis of a similar kind. Whereas the helioseismic techniques in question borrow heavily from the quantum mechanics of atomic systems, I demonstrate that oscillations in these giants which possess mixed p-mode and g-mode character behave like acoustic “molecules”, rather than atoms, and therefore demand the adaptation of techniques from quantum chemistry instead. I describe two applications of this construction to constraining stellar properties by forward modeling — both in terms of their structure, and also regarding their internal rotational dynamics.
Reverberation Mapping Black Hole Accretion Flows
Dr. Erin Kara
Assistant Professor of Physics, Massachusetts Institute of Technology
Most of the power from an Active Galactic Nucleus is released close to the black hole, and thus studying the inner accretion flow, at the intersection of inflow and outflow, is essential for understanding how black holes grow and affect galaxy evolution. In the past decade, we have had a breakthrough in how we probe the inner accretion flow, through the discovery of X-ray Reverberation Mapping, where X-rays produced close to the black hole reverberate off inflowing gas. By measuring reverberation time delays, we can quantify the effects of strongly curved space time and the black hole spin, which is key for understanding how efficiently energy can be tapped from the accretion process. In this talk, I will give an overview of this field, and show how extending these spectral-timing techniques to transient accretion events like Tidal Disruption Events and black hole X-ray binaries is helping us probe the formation of X-ray coronae, jets and other relativistic outflows.
Mapping the Milky Way with Asteroseismology
Dr. Daniel Hey
Variable Stars Postdoctoral Fellow, UH IfA
Galactic astronomy has entered a golden era, driven by the combination of large scale multi-object spectroscopic surveys and the exquisite all-sky view provided by the ESA Gaia Mission. Since its third data release, Gaia has enabled spectacular breakthroughs in our understanding of Galactic dynamics, driven primarily by the all-sky map of hundreds of thousands of individual stars. However, the range of this map is limited to a relatively nearby region within 5-10 kpc from the Sun. There is presently no viable means of deriving distances to large, population independent samples of stars in the outer Galaxy. Current methods rely on exploiting the period-luminosity relation of Cepheid and RR Lyrae variables, which, despite being highly precise distance indicators, are relatively rare. In this talk, I will discuss recent efforts in using variable M-giant stars as viable distance indicators from ground-based photometry missions. M-giants are both common throughout our galaxy, and extremely luminous, making them excellent targets for ground-based surveys.
Euclid: The ESA cosmology mission
Dr. Jean-Gabriel Cuby
Executive Director, CFHT
Euclid is an ESA cosmology mission to be launched in 2023 and positioned at L2. Euclid will map the large-scale structures of the Universe up to redshift 2 to characterize the effects of dark energy. The mission will perform a wide-field imaging and spectroscopic (slitless) survey of 15,000 square degrees down to AB magnitudes of 24.5 (10σ) and 24 (5σ) in the visible and near-infrared respectively. The mission will also observe about 50 square degrees at a depth 2 magnitudes deeper. Euclid will make extensive use of ancillary data, including data acquired by telescopes located in Hawaiʻi on Maunakea and Haleakalā. I will describe the mission, its instruments and the planned survey.
The “Missing Stellar CME Conundrum”: Lessons from the Sun
Dr. Xudong Sun
Assistant Astronomer, UH IfA
Despite the frequent detection of stellar super flares, reports on stellar coronal mass ejections (CMEs) are rare. This is in contrast with the Sun, where almost all large flares are accompanied by a CME. In this talk, I will review observational constraints on this “missing stellar CME conundrum”. I will describe our effort at applying lessons from the Sun to more active late-type stars. We argue that the torus instability, a leading mechanism for solar CME, tends to be suppressed in stellar magnetic environment. Contributing factors include larger spots, stronger global dipole field, and more closed magnetic topology compared to the Sun. Their confining effect will induce “failed eruptions” with flare emission but no plasmatic ejecta.
JWST: from First Light to First Science
Dr. Marshall Perrin
Associate Astronomer, Space Telescope Science Institute
After decades of development by a globe-spanning team, JWST is now providing an unprecedented view of the cosmos. I will describe our experience thus far operating this new great observatory: from mission development, to prelaunch preparations, to launch and commissioning, and now into the first of many years of science operations. I will provide a first-hand look at the processes and teamwork we used to deploy the observatory and align its optics, and discuss some of the surprises (both challenges and good news) encountered along the way. From early in telescope commissioning, this observatory’s power and sensitivity were already apparent with spectacular images and spectra. Now during science operations, we continue to learn more about observatory hardware performance and calibrations; this is still early days in our adventure with JWST.
I’ll close with a look at (a small fraction of) some of the early science results with JWST, particularly some of our early observations of nearby exoplanetary systems.
The Galactic Museum of Natural History
Dr. Joel Zinn
Postdoctoral Fellow, American Museum of Natural History
Decades after the first evidence of a bimodality in the distribution of stellar alpha element abundances, the field of Galactic archaeology has still not reached a consensus model to explain it. This so-called alpha bimodality is closely linked with the formation and evolution of the Galactic disc, and so any model of the evolution of the Galaxy needs to explain not only the resulting chemical distribution of the two alpha populations, but also their ages. In this talk, I will discuss how asteroseismic ages, when combined with kinematic and spectroscopic information, are informing our understanding of the alpha bimodality and the evolution of the Galactic disc. I will also touch on how asteroseismology is helping to reveal the history of the Galaxy’s stellar halo. In order to reconstruct a more complete timeline for the disc and stellar halo, however, I will show why it is necessary to recalibrate our asteroseismic tools and will present promising techniques for assessing ages for the most metal-poor and distant populations with asteroseismology.
Magnetic Stellar Evolution and Planetary Habitability
Dr. Travis Metcalfe
Senior Research Scientist, White Dwarf Research Corporation
Over the past several years, evidence has emerged that something unexpected occurs in the evolution of rotation and magnetism near the middle of a star’s main-sequence lifetime. For solar-type stars the transition begins near the age of the Sun, when rotation becomes too slow to imprint Coriolis forces on the global convective patterns, reducing the shear induced by differential rotation, and disrupting the production of large-scale magnetic fields by the global dynamo. Combining asteroseismology from NASA’s Kepler and TESS missions with spectropolarimetry from the Large Binocular Telescope and other facilities, the Sun appears to have entered this phase a few hundred million years ago, just as life was emerging from the well-shielded oceans onto land. Younger stars bombard their planets with radiation and charged particles that are hostile to the development of complex life, but older stars appear to quiet down substantially and provide a more stable environment. I will summarize the evidence for this unexpected transition, outline our current understanding of its likely origin, and speculate on the implications for planetary habitability beyond stellar middle-age.