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52 pages, 10192 KiB

Open AccessReview

Broad Observational Perspectives Achieved by the Accreting White Dwarf Sciences in the XMM-Newton and Chandra Eras

by Şölen Balman, Marina Orio and Gerardo J. M. Luna

Universe 2025, 11(4), 105; https://doi.org/10.3390/universe11040105 - 21 Mar 2025

Viewed by 1473

Accreting white dwarf binaries (AWDs) comprise cataclysmic variables (CVs), symbiotics, AM CVns, and other related systems that host a primary white dwarf (WD) accreting from a main sequence or evolved companion star. AWDs are a product of close binary evolution; thus, they are important for understanding the evolution and population of X-ray binaries in the Milky Way and other galaxies. AWDs are essential for studying astrophysical plasmas under different conditions along with accretion physics and processes, transient events, matter ejection and outflows, compact binary evolution, mergers, angular momentum loss mechanisms, and nuclear processes leading to explosions. AWDs are also closely related to other objects in the late stages of stellar evolution, with other accreting objects in compact binaries, and even share common phenomena with young stellar objects, active galactic nuclei, quasars, and supernova remnants. As X-ray astronomy came to a climax with the start of the Chandra and XMM-Newton missions owing to their unprecedented instrumentation, new excellent imaging capabilities, good time resolution, and X-ray grating technologies allowed immense advancement in many aspects of astronomy and astrophysics. In this review, we lay out a panorama of developments on the study of AWDs that have been accomplished and have been made possible by these two observatories; we summarize the key observational achievements and the challenges ahead. Full article

(This article belongs to the Special Issue X-ray Astronomy Steps into the 21st Century: Chandra and XMM-Newton at 25)

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15 pages, 414 KiB

Open AccessArticle

Prospects of Searching for Type Ia Supernovae with 2.5-m Wide Field Survey Telescope

by Maokai Hu, Lei Hu, Ji-an Jiang, Lin Xiao, Lulu Fan, Junjie Wei and Xuefeng Wu

Universe 2023, 9(1), 7; https://doi.org/10.3390/universe9010007 - 22 Dec 2022

Cited by 13 | Viewed by 2359

Abstract

Type Ia supernovae (SNe Ia) are thermonuclear explosions of carbon-oxygen white dwarfs (WDs) and are well-known as a distance indicator. However, it is still unclear how WDs increase their mass near the Chandrasekhar limit and how the thermonuclear runaway happens. The observational clues associated with these open questions, such as the photometric data within hours to days since the explosion, are scarce. Thus, an essential way is to discover SNe Ia at specific epochs with optimal surveys. The 2.5 m Wide Field Survey Telescope (WFST) is an upcoming survey facility deployed in western China. In this paper, we assess the detectability of SNe Ia with mock observations of the WFST. Followed by the volumetric rate, we generate a spectral series of SNe Ia based on a data-based model and introduce the line-of-sight extinction to calculate the brightness from the observer. By comparing with the detection limit of the WFST, which is affected by the observing conditions, we can count the number of SNe Ia discovered by mock WFST observations. We expect that the WFST can find more than

3.0 \times 10^{4}

pre-maximum SNe Ia within one year of running. In particular, the WFST could discover about 45 bright SNe Ia, 99 early phase SNe Ia, or

1.1 \times 10^{4}

well-observed SNe Ia with the hypothesized Wide, Deep, or Medium modes, respectively, suggesting that the WFST will be an influential facility in time-domain astronomy. Full article

(This article belongs to the Special Issue Supernovae Observations and Researches)

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8 pages, 1625 KiB

Open AccessArticle

An Elementary Model for a Self-Accelerating Outward Propagating Flame Subject to the Rayleigh–Taylor Instability: Transition to Detonation

by Leonid Kagan and Gregory Sivashinsky

Fluids 2020, 5(4), 196; https://doi.org/10.3390/fluids5040196 - 31 Oct 2020

Cited by 5 | Viewed by 2096

Abstract

Within the Boussinesq approximation, an elementary model for the deflagration-to-detonation transition triggered by self-acceleration of an expanding flame is formulated and explored. The self-acceleration is sustained by the intrinsic Rayleigh–Taylor instability until the Deshaies–Joulin deflagrability threshold is reached, followed by an abrupt transition to detonation. Emergence of the threshold is caused by positive feedback between the accelerating flame and the flame-driven pressure shock that results in the thermal runaway when the flame speed reaches a critical level. The model offers a simple mechanism that may be responsible for the transition to detonation in thermonuclear supernovae. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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