Spatial Curvature, Dark Energy Dynamics, Neither, or Both?
Bharat Ratra, Kansas State University
Clues to Globular Cluster Formation
David Nataf, Johns Hopkins University
Globular clusters are now well-established to host “Second-generation” stars, which show anomalous abundances in some or all of He, C, N, O, Na, Al, Mg, etc. The simplest explanations for these phenomena typically require the globular clusters to have been ~20x more massive at birth, and to have been enriched by processes which are not consistent with the theoretical predictions of massive star chemical synthesis models. The library of observations is now a vast one, yet there has been comparatively little progress in understanding how globular clusters could have formed and evolved. In this talk I discuss two new insights into the matter. First, I report on a meta-analysis of globular cluster abundances that combined APOGEE and literature data for 28 globular clusters, new trends with globular cluster mass are identified. I discuss the chemical properties of former globular cluster stars that are now part of the field population, and what can be learned.
The Magdalena Ridge Observatory Interferometer: Design Details and Progress towards First Light with UT#1
Michelle Creech-Eakman, New Mexico Tech
The Magdalena Ridge Observatory Interferometer (MROI), a 10-telescope optical/near-IR interferometer in central NM, has been conceived to be the most ambitious optical interferometric array under construction to date. With baselines ranging from 7.8 to 347 meters, and limiting magnitudes of 14 at H band, it will be able to assess many thousands of astronomical targets on spatial scales of 10’s to 0.1’s of milliarcseconds. This is achieved through several careful design choices and trade-offs which should allow the MROI to reach 4-5 magnitudes deeper than similar facilities can achieve today. After over a decade of funding from NRL and the major partner institutions (NM Tech and Cambridge University), new funding was obtained in late 2015 via a Cooperative Agreement between NM Tech and the Air Force Research Lab (AFRL) to bring the facility to a three-interferometer system capable of observing geosynchronous satellites. However, we still maintain an exciting and compelling astronomical portfolio which will produce statistical samples of: YSOs and their surrounding disks, systems dominated by mass-loss and mass-transfer, pulsating stars and binary star systems, and images of the environs of AGN in nearby galaxies. An overview of the major design components of this ambitious imaging machine, recent progress, and plans for MROI for the next 3 years under the AFRL Cooperative Agreement will be presented.
Understanding How Galaxies Reionized the Universe
Sanchayeeta Borthakur, Arizona State University
Identifying the population of galaxies that was responsible for the reionization of the universe is a long-standing quest in astronomy. While young stars can produce large amounts of ionizing photons, the mechanism behind the escape of Lyman continuum photons (wavelength < 912 A) from star-forming regions has eluded us. To identify such galaxies and to understand the process of the escape of Lyman continuum, we present an indirect technique known as the residual flux technique. Using this technique, we identified (and later confirmed) the first low-redshift galaxy that has an escape fraction of ionizing flux of 21%. This leaky galaxy provides us with valuable insights into the physics of starburst-driven feedback. In addition, since direct detection of ionizing flux is impossible at the epoch of reionization, the residual flux technique presents a highly valuable tool for future studies to be conducted with the upcoming large telescopes such as the JWST.
How to Take Pictures of Baby Planets
Kate Follette, Amherst College
Of the thousands of known extrasolar planets, why are the dozen or so directly imaged exoplanets among the most important despite their apparently anomalous properties within the general exoplanet population (>10 astronomical units, >2x the mass of Jupiter)? What are the prospects for (and recent successes in) detecting younger, lower-mass and/or closer-in planets via direct imaging? I will discuss the current state of the art in the field of high-contrast imaging of extrasolar planets and the disks of gas and dust from which planets form (“circumstellar disks”). I will place particular emphasis on a subset of objects that host both disks and (likely) planets – the so-called “transitional disks”. These young circumstellar disks are almost certainly actively undergoing planet formation, and yet the presence of disk material complicates our ability to isolate light from planets and/or protoplanets embedded within them. I will end by discussing recent results from the Giant Accreting Protoplanet Survey (GAPplanetS) of 15 southern-hemisphere transition disks. The GAPlanetS survey aims to find protoplanets embedded in transitional disks through a distinctive signature at hydrogen wavelengths, and has so far discovered: 2-3 planets, 1 accreting M-dwarf stellar companion, and 1 disk feature masquerading as a planet.
Rethinking the Fundamentals of Classical Nova Explosions
Laura Chomiuk, MSU
Over the past few years, a revolution has been taking place in our understanding of classical novae, largely driven by the discovery of GeV gamma-rays emanating from these garden-variety explosions. These gamma-rays hint that shocks are energetically important—perhaps even dominant—in novae. I will present our burgeoning understanding of shocks in novae, from both multi-wavelength observational and theoretical perspectives, and illustrate how novae can be used as testbeds to understand other shock-powered explosions.
Starless clumps and the earliest phases of high-mass star formation in the Milky Way
Brian Svoboda, NRAO Jansky Fellow
High-mass stars are key to regulating the interstellar medium, star formation activity, and overall evolution of galaxies, but their formation remains an open problem in astrophysics. In order to understand the physical conditions during the earliest phases of high-mass star formation, I will present observational studies we have carried out on dense starless clump candidates (SCCs) that show no signatures of star formation activity. We identify 2223 SCCs from the 1.1 mm Bolocam Galactic Plane Survey, systematically analyse their physical properties, and show that the starless phase is not represented by a single timescale, but evolves more rapidly with increasing clump mass. To investigate the sub-structure in SCCs at high spatial resolution, we investigate the 12 most high-mass SCCs within 5 kpc using ALMA. We find previously undetected low-luminosity protostars in 11 out of 12 SCCs, fragmentation equal to the thermal Jeans length of the clump, and no starless cores exceeding 30 solar masses. While uncertainties remain concerning the star formation efficiency in this sample, these observational facts are consistent with models where high-mass stars form from initially low- to intermediate-mass protostars that accrete most of their mass from the surrounding clump. I will also present on-going research studying gas inflow signatures with GBT/Argus and ALMA, and the dense core mass function with the JVLA.
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Solving the Puzzles of the Moon
Shun Karato, Yale University
After 50 years from the first landing of men on the Moon, about 380 kg of samples were collected by the Apollo mission. Chemical analyses of these samples together with a theory of planetary formation led to a “giant impact” paradigm (in mid 1970s). In this paradigm, the Moon was formed in the later stage of Earth formation (not the very late stage, though), when the proto-Earth was hit by an impactor with a modest size (~ Mars size) at an oblique angle. Such an impact is a natural consequence of planetary formation from a proto-planetary nebula. This collision may have kicked out mantle materials from the proto-Earth to form the Moon. This model explains mostly rocky composition of the Moon and the large angular momentum of the Earth-Moon system. High temperatures caused by an impact likely removed much of the volatile components such as water.
However, two recent geochemical observations cast doubt about the validity of such a paradigm. They include (i) not-so-dry Moon suggested from the analysis of basaltic inclusions in olivine, and (ii) the high degree of similarities in many isotopes. The first observation is obviously counter-intuitive, but the second one is also hard to reconcile with the standard model of a giant impact, because many models show that a giant impact produces the Moon mostly from the impactor. In this presentation, I will show how one can solve these puzzles by a combination of physics/chemistry of materials with some basic physics of a giant impact.