Authors: Waggoner, Abygail R., Cleeves, L. Ilsedore, Loomis, Ryan A., Aikawa, Yuri, Bae, Jaehan, Bergner, Jennifer B., Booth, Alice S., Calahan, Jenny K., Cataldi, Gianni, Law, Charles J., Le Gal, Romane, Long, Feng, Öberg, Karin I., Teague, Richard, Wilner, David J.

Abstract: Theoretical models and observations suggest that the abundances of molecular ions in protoplanetary disks should be highly sensitive to the variable ionization conditions set by the young central star. We present a search for temporal flux variability of HCO+ J=1-0, which was observed as a part of the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program. We split out and imaged the line and continuum data for each individual day the five sources were observed (HD 163296, AS 209, GM Aur, MWC 480, and IM Lup, with between 3 to 6 unique visits per source). Significant enhancement (>3\sigma) was not observed, but we find variations in the spectral profiles in all five disks. Variations in AS 209, GM Aur, and HD 163296 are tentatively attributed to variations in HCO+ flux, while variations in IM Lup and MWC 480 are most likely introduced by differences in the \textit{uv} coverage, which impact the amount of recovered flux during imaging. The tentative detections and low degree of variability are consistent with expectations of X-ray flare driven HCO+ variability, which requires relatively large flares to enhance the HCO+ rotational emission at significant (>20%) levels. These findings also demonstrate the need for dedicated monitoring campaigns with high signal to noise ratios to fully characterize X-ray flare driven chemistry. 

Citation: Waggoner, A. R., et al. 2023, ApJ, 956, 103

Paper Link: ApJ, ArXiv

Authors: Abygail R. Waggoner, Ilsedore L. Cleeves

Abstract: Young stars are highly variable in the X-ray regime. In particular, bright X-ray flares can substantially enhance ionization in the surrounding protoplanetary disk. Since disk chemical evolution is impacted by ionization, X-ray flares have the potential to fundamentally alter the chemistry of planet forming regions. We present 2D disk chemical models that incorporate a stochastic X-ray flaring module, named \xgen, and examine the flares' overall chemical impact compared to models that assume a constant X-ray flux. We examine the impact of 500 years of flaring events and find global chemical changes on both short time scales (days) in response to discrete flaring events and long time-scales (centuries) in response to the cumulative impact of many flares. Individual X-ray flares most strongly affect small gas-phase cations, where a single flare can temporarily enhance the abundance of species such as H3+, HCO+, CH3+, and C+. We find that flares can also drive chemistry out of "steady state" over longer time periods, where the disk-integrated abundance of some species, such as O and O2, changes by a few percent over the 500 year model. We also explore whether the specific history of X-ray flaring events (randomly drawn but from the same energy distribution) impacts the chemical evolution and find that it does not. Finally, we examine the impact of X-ray flares on the electron fraction. While most molecules modeled are not highly sensitive to flares, certain species, including observable molecules, are very reactive to the dynamic environment of a young star. 

Citation: Waggoner, A. R. & Cleeves, L. I., 2022, ApJ, 928, 46, doi: 10.3847/1538-4357/ab3d38

Paper Link: Astrophysical Journal, ArXiv

Authors: Abygail R. Waggoner, Yahya Abdulrahman, Alexis J. Iverson, Ethan P. Gibson, Mark A. Buckles, James S. Poole

Abstract: The regioselectivity of hydroxyl radical reactions with alkylarenes was investigated using a nuclear magnetic resonance (NMR)-based methodology capable of trapping and quantifying addition and hydrogen abstraction products of the initial elementary step of the oxidation process. Abstraction products are relatively minor components of the product mixtures (15–30 mol%), depending on the magnitude of the overall rate coefficient and the number of available hydrogens. The relative reactivity of addition at a given position on the ring depends on its relation to the methyl substituents on the hydrocarbons under study. The reactivity enhancements for disubstituted and trisubstituted rings are approximately additive under the conditions of this study.

Citation: Waggoner, A. R., Abdulrahman, Y., Iverson, A. J., Gibson, E. P., Buckles, M. A., Poole, J. S. Reaction of hydroxyl radical with arenes in solution -- on the importance of benzylic hydrogen abstraction. 2021, Journal of Physical Organic Chemistry, e4278.

Paper Link: Journal of Physical Organic Chemistry 

Authors: Briley L. Lewis, Abygail R. Waggoner, Emma Clarke, Alison L. Crisp, Mark Dodici, Graham M. Doskoch, Michael M. Foley, Ryan Golant, Katya Gozman, Sahil Hegde, Macy J. Huston, Charles J. Law, Roel R. Lefever, Ishan Mishra, Mark Popinchalk, Sabina Sagynbayeva, Wei Yan, Kaitlin L. Ingraham Dixie, K. Supriya

Abstract: Astrobites is an international collaboration of graduate students that aims to make astronomy more accessible through daily journal article summaries and other educational and professional resources. Among these resources is a set of open-source lesson plans designed to help educators incorporate Astrobites articles and resources into their classrooms. In this study, we aim to determine the effectiveness of these lesson plans at increasing students' perceived understanding of and confidence in astronomy. During the 2022-2023 academic year twelve faculty members incorporated our lesson plans into their classes, surveyed their students before and after the activities, and participated in follow-up interviews at the end of their classes. Quantitative survey data clearly show that students' perceptions of their abilities with jargon, identifying main takeaways of a paper, conceptual understanding of physics and astronomy, and communicating scientific results all improved with use of the Astrobites lesson plans. Additionally, students show some evidence of increased confidence and sense of belonging within astronomy after exposure to these lessons. These findings suggest that incorporating current research in the undergraduate classroom through accessible, scaffolded resources like Astrobites may increase students' ability to engage with research literature, as well as their preparation for participation in research and applied careers.

Citation: (to be added once paper is published)

Links: ArXiv, submitted to the Journal of Science Education and Technology 

Authors: Karin I. Öberg, Viviana V. Guzmán, Catherine Walsh, Yuri Aikawa, Edwin A. Bergin, Charles J. Law, Ryan A. Loomis, Felipe Alarcon, Sean M. Andrews, Jaehan Bae, Jennifer B. Bergner, Yann Boehler, Alice S. Booth, Arthur D. Bosman, Jenny K. Calahan, Gianni Cataldi, L. Ilsedore Cleeves, Ian Czekala, Kenji Furuya, Jane Huang, John D. Ilee, Nicolas T. Kurtovic, Romane Le Gal, Yao Liu, Feng Long, Francois Menard, Hideko Nomura, Laura M. Perez, Chunhua Qi, Kamber R. Schwarz, Anibal Sierra, Richard Teague, Takashi Tsukagoshi, Yoshihide Yamato, Merel L. R. van 't Hoff, Abygail R. Waggoner, David J. Wilner, Ke Zhang

Abstract: Planets form and obtain their compositions in dust and gas-rich disks around young stars, and the outcome of this process is intimately linked to the disk chemical properties. The distributions of molecules across disks regulate the elemental compositions of planets, including C/N/O/S ratios and metallicity (O/H and C/H), as well as access to water and prebiotically relevant organics. Emission from molecules also encodes information on disk ionization levels, temperature structures, kinematics, and gas surface densities, which are all key ingredients of disk evolution and planet formation models. The Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program was designed to expand our understanding of the chemistry of planet formation by exploring disk chemical structures down to 10 au scales. The MAPS program focuses on five disks - around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480 - in which dust substructures are detected and planet formation appears to be ongoing. We observed these disks in 4 spectral setups, which together cover ~50 lines from over 20 different species. This paper introduces the ApJS MAPS Special Issue by presenting an overview of the program motivation, disk sample, observational details, and calibration strategy. We also highlight key results, including discoveries of links between dust, gas, and chemical sub-structures, large reservoirs of nitriles and other organics in the inner disk regions, and elevated C/O ratios across most disks. We discuss how this collection of results is reshaping our view of the chemistry of planet formation. 

Citation: Öberg, K. I., Guzmán, V. V., Walsh, C., + MAPS Team. 2021 ApJS, 257, 1, doi: 10.3847/1538-4365/ac1432

Links: ArXiv, ALMA Science Portal

Authors: Ian Czekala, Ryan A. Loomis, Richard Teague, Alice S. Booth, Jane Huang, Gianni Cataldi, John D. Ilee, Charles J. Law, Catherine Walsh, Arthur D. Bosman, Viviana V. Guzmán, Romane Le Gal, Karin I. Öberg, Yoshihide Yamato, Yuri Aikawa, Sean M. Andrews, Jaehan Bae, Edwin A. Bergin, Jennifer B. Bergner, L. Ilsedore Cleeves, Nicolas T. Kurtovic, François Ménard, Hideko Nomura, Laura M. Pérez, Chunhua Qi, Kamber R. Schwarz, Takashi Tsukagoshi, Abygail R. Waggoner, David J. Wilner, Ke Zhang

Abstract: The Molecules with ALMA at Planet-forming Scales large program (MAPS LP) surveyed the chemical structures of five protoplanetary disks across more than 40 different spectral lines at high angular resolution (0.15" and 0.30" beams for Bands 6 and 3, respectively) and sensitivity (spanning 0.3 - 1.3 mJy/beam and 0.4 - 1.9 mJy/beam for Bands 6 and 3, respectively). In this article, we describe our multi-stage workflow -- built around the CASA tclean image deconvolution procedure -- that we used to generate the core data product of the MAPS LP: the position-position-velocity image cubes for each spectral line. Owing to the expansive nature of the survey, we encountered a range of imaging challenges; some are familiar to the sub-mm protoplanetary disk community, like the benefits of using an accurate CLEAN mask, and others less well-known, like the incorrect default flux scaling of the CLEAN residual map first described in Jorsater & van Moorsel 1995 (the "JvM effect"). We distill lessons learned into recommended workflows for synthesizing image cubes of molecular emission. In particular, we describe how to produce image cubes with accurate fluxes via the "JvM correction," a procedure that is generally applicable to any image synthesized via CLEAN deconvolution but is especially critical for low S/N emission. We further explain how we used visibility tapering to promote a common, fiducial beam size and contextualize the interpretation of signal to noise ratio when detecting molecular emission from protoplanetary disks. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement. 

Citation: Czekala, I., Loomis, R. A., Teague, R., + MAPS Team. 2021, ApJS, 257, 2, doi: 10.3847/1538-4365/ac1430

Links: ArXiv,  ALMA Science Portal

Authors: Erica M. Johnson, Abygail R. Waggoner, Shijing Xia, Hoi Ling Luk, Christopher M. Hadad, and James S. Poole

Abstract: The effect of ring substitution on the kinetics of reaction of arenes, heterocycles, and alkenes with hydroxyl radical is investigated in terms of reactivity and selectivity, using laser flash photolysis (LFP) in acetonitrile solution. The LFP data indicate that charge-transfer contributions in the transition state play an important role in dictating reactivity, and there is a correlation between the experimental and calculated ionization potentials of the arenes and alkenes and their respective reactivities. The reactivity observed for arenes in acetonitrile exhibits a much greater sensitivity toward substitution on the ring than in water, and therefore aqueous data cannot be used to predict reactivity in nonaqueous environments. Nonaqueous solution data may be predictable from gas phase data, and vice versa.

Citation: Johnson, E. M.,Waggoner, A. R., Xia, S., Luk, H. L., Hadad, C. M., Poole, J. S. Reactivity of hydroxylradical in nonaqueous phases: addition reactions. 2018, J. Phys. Chem. A, 122, 42, 8326-8335

Paper Link: Here