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Cooling Models for the Most Massive White Dwarfs
Schwab, Josiah
We present a set of ultramassive white dwarf models, focused on masses above 1.3 M⊙. Given the uncertainties about the formation and compositions of such objects, we construct parameterized model sequences, guided by evolutionary calculations including both single star and double white dwarf merger formation channels. We demonstrate tha…
Particle-In-Cell Simulations of Electrostatic Solitary Waves in Asymmetric Magnetic Reconnection
Wang, Shui; Lu, Quanming; Gao, Xinliang +5 more
Electrostatic solitary waves (ESWs) are ubiquitously observed in magnetic reconnection. In this study, two-dimensional (2-D) particle-in-cell (PIC) simulations are performed to investigate the characteristics of ESWs in asymmetric magnetic reconnection. ESWs with bipolar structures of the parallel electric field can be generated near the separatri…
Similar but different: the varied landscape of Onfp/Oef stars variability
Nazé, Yaël; Rauw, Gregor
The Oef category gathers rapidly rotating and evolved O-stars displaying a centrally reversed He II λ 4686 emission line. The origin of the variability of their photospheric and wind spectral lines is debated, with rotational modulation or pulsations as the main contenders. To shed new light on this question, we analysed high-quality and high-cade…
The ACTIONFINDER: An Unsupervised Deep Learning Algorithm for Calculating Actions and the Acceleration Field from a Set of Orbit Segments
Famaey, Benoit; Ibata, Rodrigo; Monari, Giacomo +1 more
We introduce the ACTIONFINDER, a deep learning algorithm designed to transform a sample of phase-space measurements along orbits in a static potential into action and angle coordinates. The algorithm finds the mapping from positions and velocities to actions and angles in an unsupervised way, by using the fact that points along the same orbit have…
Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-poor K Dwarf
Butler, R. Paul; Gorjian, Varoujan; López-Morales, Mercedes +35 more
Using radial-velocity measurements from four instruments, we report the mass and density of a 2.043 ±0.069 R ⊕ sub-Neptune orbiting the quiet K-dwarf Wolf 503 (HIP 67285). In addition, we present improved orbital and transit parameters by analyzing previously unused short-cadence K2 campaign 17 photometry and conduct a joint radial-velo…
Thermodynamics of the Magnetotail Current Sheet Thinning
Petrukovich, A. A.; Nakamura, R.; Artemyev, A. V. +1 more
Substorm growth phase in the magnetotail is characterized by formation of a thin current sheet (CS) becomes unstable due to external or internal drivers. Such instability results in magnetic field line reconnection, the substorm onset. The CS thinning, as a key process of substorm dynamics, has been included into many global and local simulations …
A deep search for faint Chandra X-ray sources, radio sources, and optical counterparts in NGC 6752
Anderson, Jay; Strader, Jay; Heinke, Craig O. +6 more
We report the results of a deep search for faint Chandra X-ray sources, radio sources, and optical counterparts in the nearby, core-collapsed globular cluster, NGC 6752. We combined new and archival Chandra imaging to detect 51 X-ray sources (12 of which are new) within the 1.9 arcmin half-light radius. Three radio sources in deep ATCA 5 and 9 GHz…
The Mass and Age Distribution of Halo White Dwarfs in the Canada-France Imaging Survey
Gwyn, Stephen D. J.; McConnachie, Alan W.; Cuillandre, Jean-Charles +6 more
We present optical spectroscopy for 18 halo white dwarfs identified using photometry from the Canada-France Imaging Survey and Pan-STARRS1 DR1 3π survey combined with astrometry from Gaia DR2. The sample contains 13 DA, 1 DZ, 2 DC, and 2 potentially exotic types of white dwarf. We fit both the spectrum and the spectral energy distribution in order…
Deriving the bulk properties of solar wind electrons observed by Solar Orbiter. A preliminary study of electron plasma thermodynamics
Lewis, G. R.; Kataria, D. O.; Owen, C. J. +8 more
Context. We demonstrate the calculation of solar wind electron bulk parameters based on recent observations by Solar Wind Analyser - Electron Analyser System on board Solar Orbiter. We use our methods to derive the electron bulk parameters in a time interval spanning several hours. We attempt a preliminary examination of the polytropic behavior of…
2019 International Women's Day event. Two-step solar flare with multiple eruptive signatures and low Earth impact
Magdalenić, J.; Temmer, M.; Veronig, A. M. +7 more
Context. We present a detailed analysis of an eruptive event that occurred on 2019 March 8 in the active region AR 12734, which we refer as the International Women's Day event. The event under study is intriguing based on several aspects: (1) low-coronal eruptive signatures come in `pairs', namely, there is a double-peaked flare, two coronal dimmi…