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1. Stability-enhanced AP IMEX-LDG schemes for linear kinetic transport equations under a diffusive scaling

   https://doi.org/10.1016/j.jcp.2020.109485  

   Peng, Zhichao ; Cheng, Yingda ; Qiu, Jing-Mei ; Li, Fengyan ( August 2020 , Journal of Computational Physics)
2. Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology

   https://doi.org/10.1093/mnras/stz1633  

   Hey, Daniel R ; Holdsworth, Daniel L ; Bedding, Timothy R ; Murphy, Simon J ; Cunha, Margarida S ; Kurtz, Donald W ; Huber, Daniel ; Fulton, Benjamin ; Howard, Andrew W ( June 2019 , Monthly Notices of the Royal Astronomical Society)
3. Engaging Black Female Students in a Year-Long Preparatory Experience for AP CS Principles

   https://doi.org/10.1145/3408877.3432560  

   Escobar, Martha ; Gray, Jeff ; Haynie, Kathleen ; Qazi, Mohammed A. ; Rawajfih, Yasmeen ; McClendon, Pamela ; Tucker, Donnita ; Johnson, Wendy ( March 2021 , Proceedings of ACM Technical Symposium on Computer Science Education (SIGCSE’21))

   null (Ed.)

   In 2020, over 116,000 students took the Advanced Placement Computer Science Principles (AP CSP) Exam. Although Black female students have participated in AP CSP at higher rates than for the AP CSA course, their representation is still disproportionately lower than the school population of Black females. In this Experience Report, we present the early results of an NSF-sponsored effort that provides an AP CSP preparatory experience and CS career awareness to Black female students from rural, urban, and suburban communities in the state of Alabama. At the project’s core is a peer-learning community (PLC) facilitated by Black female teachers with deep knowledge of AP CSP. An intensive summer experience prepares students for the AP CSP course through culturally-responsive, project-based learning experiences designed to connect advanced computing concepts to the students’ personal lives and career aspirations. Interactions and support continue throughout the academic year to facilitate AP exam readiness. Online interactions among the PLC members serve to mitigate the barriers that young women of color typically encounter when pursuing CS education, increasing their persistence and success in CS. We examined whether students’ project participation enhances self-efficacy and perceived competency in CS, increases positive attitudes, awareness, and desire to pursue CS studies and careers, and mitigates perceived socio-cultural barriers to pursue studies and careers in CS. Our initial findings include AP CSP examination qualifying rates (87.5%) that exceed the 2019 national/statewide rates for all subgroups (including Alabama White male students), increased perceptions of Black females as belonging in CS, and gains in computing self-efficacy throughout the academic year. 

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4. Benchmarking the fundamental parameters of Ap stars with optical long-baseline interferometric measurements

   https://doi.org/10.1051/0004-6361/202038753  

   Perraut, K. ; Cunha, M. ; Romanovskaya, A. ; Shulyak, D. ; Ryabchikova, T. ; Hocdé, V. ; Nardetto, N. ; Mourard, D. ; Meilland, A. ; Morand, F. ; et al ( October 2020 , Astronomy & Astrophysics)

   null (Ed.)

   Context. The variety of physical processes at play in chemically peculiar stars makes it difficult to determine their fundamental parameters. In particular, for the magnetic ones, called Ap stars, the strong magnetic fields and the induced spotted stellar surfaces may lead to biased effective temperatures when these values are derived through spectro-photometry. Aims. We propose to benefit from the exquisite angular resolution provided by long-baseline interferometry in the visible to determine the accurate angular diameters of a number of Ap stars, and thus estimate their radii by a method that is as independent as possible of atmospheric models. Methods. We used the visible spectrograph VEGA at the CHARA interferometric array to complete the sample of Ap stars currently observable with this technique. We estimated the angular diameter and radius of six new targets. We estimated their bolometric flux based solely on observational spectroscopic and photometric data to derive nearly model-independent luminosities and effective temperatures. Results. We extend to 14 the number of Ap stars for which interferometric angular diameters have been measured. The fundamental parameters we derived for the complete Ap sample are compared with those obtained through a self-consistent spectroscopic analysis. Based on a model fitting approach of high-resolution spectra and spectro-photometric observations over a wide wavelength range, this method takes into account the anomalous chemical composition of the atmospheres and the inhomogeneous vertical distribution for different chemical elements. Regarding both the radii and the effective temperatures, the derived values from our interferometric observations and from self-consistent modelling are consistent within better than 2 σ for nine targets out of ten. We thus benchmark nine Ap stars for effective temperatures ranging from 7200 and 9100 K, and luminosities ranging between 7 L ⊙ and 86 L ⊙ . Conclusions. These results will be key for the future derivation of accurate radii and other fundamental parameters of fainter peculiar stars for which both the sensitivity and the angular resolution of the current interferometers are not sufficient. Within the context of the observations of Ap stars with the Transiting Exoplanet Survey Satellite (TESS), these interferometric measurements are crucial for testing the mechanism of pulsation excitation at work in these peculiar stars. In particular, our interferometric measurements provide accurate locations in the Hertzsprung-Russell diagram for hot Ap stars among which pulsations may be searched for with TESS, putting to test the blue edge of the theoretical instability strip. These accurate locations could be used to derive masses and ages of these stars through a specific grid of models, and to test correlations between the properties of these peculiar stars and their evolutionary state. 

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5. Fundamental properties of a selected sample of Ap stars: Inferences from interferometric and asteroseismic constraints

   https://doi.org/10.1051/0004-6361/202040234  

   Deal, M. ; Cunha, M. S. ; Keszthelyi, Z. ; Perraut, K. ; Holdsworth, D. L. ( June 2021 , Astronomy & Astrophysics)

   null (Ed.)

   Context. Magnetic fields influence the formation and evolution of stars and impact the observed stellar properties. magnetic A-type stars (Ap stars) are a prime example of this. Access to precise and accurate determinations of their stellar fundamental properties, such as masses and ages, is crucial to understand the origin and evolution of fossil magnetic fields. Aims. We propose using the radii and luminosities determined from interferometric measurements, in addition to seismic constraints when available, to infer fundamental properties of 14 Ap stars préviously characterised. Methods. We used a grid-based modelling approach, employing stellar models computed with the CESTAM stellar evolution code, and the parameter search performed with the AIMS optimisation method. The stellar model grid was built using a wide range of initial helium abundances and metallicities in order to avoid any bias originating from the initial chemical composition. The large frequency separations (Δ ν ) of HR 1217 (HD 24712) and α Cir (HD 128898), two rapidly oscillating Ap stars of the sample, were used as seismic constraints. Results. We inferred the fundamental properties of the 14 stars in the sample. The overall results are consistent within 1 σ with previous studies, however, the stellar masses inferred in this study are higher. This trend likely originates from the broader range of chemical compositions considered in this work. We show that the use of Δ ν in the modelling significantly improves our inferences, allowing us to set reasonable constraints on the initial metallicity which is, otherwise, unconstrained. This gives an indication of the efficiency of atomic diffusion in the atmospheres of roAp stars and opens the possibility of characterising the transport of chemical elements in their interiors. 

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