ABSTRACT
We perform 3D hydrodynamical simulations of a common-envelope event involving a 12$\, \rm {M}_{\odot }$ red supergiant donor. Massive stars are expected to be qualitatively different from ...low-mass stars as their envelopes have significant support from radiation pressure, which increases both the final separation and amount of mass ejected through the common-envelope interaction. We perform adiabatic simulations that include radiation energy through the equation of state, which results in ejecting 60 per cent more mass (up to two thirds of the total envelope mass becoming unbound, or more) and yield a 10 per cent larger final separation compared to simulations that assume an ideal gas. When also including recombination energy, we find that at least three quarters of the envelope, and possibly the entire envelope, may be unbound. The final separation further increases by almost 20 per cent. The additional amount of ejected material is mainly due to energy injected from helium recombination. Hydrogen recombination plays a comparatively small role, as it mainly occurs in gas that has already become unbound. We conclude that the internal energy of the envelope can be a significant energy source for ejecting the common envelope, but ultimately radiation transport and convection need to be included.
Detecting double neutron stars with LISA Lau, Mike Y M; Mandel, Ilya; Vigna-Gómez, Alejandro ...
Monthly Notices of the Royal Astronomical Society,
03/2020, Volume:
492, Issue:
3
Journal Article
Peer reviewed
Open access
ABSTRACT
We estimate the properties of the double neutron star (DNS) population that will be observable by the planned space-based interferometer Laser Interferometer Space Antenna (LISA). By ...following the gravitational radiation-driven evolution of DNSs generated from rapid population synthesis of massive binary stars, we estimate that around 35 DNSs will accumulate a signal-to-noise ratio above 8 over a 4-yr LISA mission. The observed population mainly comprises Galactic DNSs (94 per cent), but detections in the LMC (5 per cent) and SMC (1 per cent) may also be expected. The median orbital frequency of detected DNSs is expected to be 0.8 mHz, and many of them will be eccentric (median eccentricity of 0.11). LISA is expected to localize these DNSs to a typical angular resolution of 2°. We expect the best-constrained DNSs to have eccentricities known to a few parts in a thousand, chirp masses measured to better than 1 per cent fractional uncertainty, and sky localization at the level of a few arcminutes. The orbital properties will provide insights into DNS progenitors and formation channels. The localizations may allow neutron star natal kick magnitudes to be constrained through the Galactic distribution of DNSs, and make it possible to follow up the sources with radio pulsar searches. LISA is also expected to resolve ∼104 Galactic double white dwarfs, many of which may have binary parameters that resemble DNSs; we discuss how the combined measurement of binary eccentricity, chirp mass, and sky location may aid the identification of a DNS.
Abstract
The role of recombination during a common-envelope event has been long debated. Many studies have argued that much of hydrogen recombination energy, which is radiated in relatively cool and ...optically thin layers, might not thermalize in the envelope. On the other hand, helium recombination contains ≈30 per cent of the total recombination energy, and occurs much deeper in the stellar envelope. We investigate the distinct roles played by hydrogen and helium recombination in a common-envelope interaction experienced by a 12 $\, \rm {M}_{\odot }$ red supergiant donor. We perform adiabatic, 3D hydrodynamical simulations that (i) include hydrogen, helium, and H2 recombination, (ii) include hydrogen and helium recombination, (iii) include only helium recombination, and (iv) do not include recombination energy. By comparing these simulations, we find that the addition of helium recombination energy alone ejects 30 per cent more envelope mass, and leads to a 16 per cent larger post-plunge-in separation. Under the adiabatic assumption, adding hydrogen recombination energy increases the amount of ejected mass by a further 40 per cent, possibly unbinding the entire envelope, but does not affect the post-plunge separation. Most of the ejecta becomes unbound at relatively high (>70 per cent) degrees of hydrogen ionisation, where the hydrogen recombination energy is likely to expand the envelope instead of being radiated away.
Abstract
Compact Object Mergers: Population Astrophysics and Statistics (COMPAS;
https://compas.science
) is a public rapid binary population synthesis code. COMPAS generates populations of isolated ...stellar binaries under a set of parameterized assumptions in order to allow comparisons against observational data sets, such as those coming from gravitational-wave observations of merging compact remnants. It includes a number of tools for population processing in addition to the core binary evolution components. COMPAS is publicly available via the GitHub repository
https://github.com/TeamCOMPAS/COMPAS/
, and is designed to allow for flexible modifications as evolutionary models improve. This paper describes the methodology and implementation of COMPAS. It is a living document that will be updated as new features are added to COMPAS; the current document describes COMPAS v02.21.00.
Abstract Accreting main-sequence stars expand significantly when the mass accretion timescale is much shorter than their thermal timescales. This occurs during mass transfer from an evolved giant ...star onto a main-sequence companion in a binary system and is an important phase in the formation of compact binaries including X-ray binaries, cataclysmic variables, and gravitational-wave sources. In this study, we compute 1D stellar models of main-sequence accretors with different initial masses and accretion rates. The calculations are used to derive semianalytical approximations to the maximum expansion radius. We assume that mass transfer remains fully conservative as long as the inflated accretor fits within its Roche lobe, leading stars to behave like hamsters, stuffing excess material behind their expanding cheeks. We suggest a physically motivated prescription for the mass growth of such “hamstars,” which can be used to determine mass-transfer efficiency in rapid binary population synthesis models. With this prescription, we estimate that progenitors of high-mass X-ray binaries and gravitational-wave sources may have experienced highly nonconservative mass transfer. In contrast, for low-mass accretors, the accretion timescale can exceed the thermal timescale by a larger factor without causing significant radial expansion.
ABSTRACT
At least one in five of all planetary nebulae are the product of a common envelope (CE) interaction, where the companion in-spirals into the envelope of an asymptotic giant branch (AGB) star ...ejecting the nebula and leaving behind a compact binary. In this work we carry out 3D smoothed particle hydrodynamics simulations of the CE interaction between a 1.7 M⊙ AGB star and a 0.6 M⊙ companion. We model the AGB structure using a 1D stellar model taken at the seventh thermal pulse. The interaction takes place when the giant is on the expanding phase of the seventh thermal pulse and has a radius of 250 R⊙. The post-CE orbital separations varies between 20 and 31 R⊙, with the inclusion of recombination energy resulting in wider separations. Based on the observed short in-spiral time-scales, we suggest that thermal pulses can trigger CEs, extending the ability of AGB stars to capture companions into CEs, that would lead to the prediction of a larger population of post-AGB, post-CE binaries. Simulations that include a tabulated equation of state unbind a great deal more gas, likely unbinding the entire envelope on short time-scales. The shape of the CE after the in-spiral is more spherical for AGB than red giant branch stars, and even more so if recombination energy is included. We expect that the planetary nebula formed from this CE will have different features compared to those formed from red giant branch stars.
COVID toe in an adolescent boy: a case report Wong, J S C; Wong, T S; Chua, G T ...
Hong Kong medical journal = Xianggang yi xue za zhi,
04/2022, Volume:
28, Issue:
2
Journal Article
Peer reviewed
Open access
The appearance of chilblain-like lesions was not thought to be associated with a poor disease outcome.2 3 A major limitation of these reports is that only 11% of cases hospitalised tested positive ...for SARS-CoV-2 by polymerase chain reaction (PCR), with the remainder untested or testing negative. Another systematic review also concluded that some, but not all paediatric cases, who developed chilblain-like lesions during the COVID-19 pandemic had positive SARS-CoV-2 PCR, serology or viral particles confirmed in electron microscopy.5 Larger-scale epidemiological study is needed to confirm an association between these chilblain-like lesions and COVID-19 infection. Joshua SC Wong 1 †; TS Wong 1 †; Gilbert T Chua 2 †; Christy Wan 1; SH Lau 1; Samuel CS Ho 1; Jaime S Rosa Duque 2; Ian CK Wong 3,4; Kelvin KW To 5; Winnie WY Tso 2; Christine S Wong 6; Marco HK Ho 2; Janette Kwok 7; CB Chow 1; Paul KH Tam 8,9; Godfrey CF Chan; 2; WH Leung 2; YL Lau 2; Patrick Ip 2; Mike YW Kwan; CUHK 1 1 Department of Paediatrics and Adolescent Medicine, Princess Margaret Hospital, Hong Kong 2 Department of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong 3 Centre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy, The University of Hong Kong, Hong Kong 4 Research Department of Practice and Policy, UCL School of Pharmacy, University College London, United Kingdom 5 Department of Microbiology, Carol Yu Centre for Infection, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong 6 Dermatology Division, Department of Medicine, Queen Mary Hospital, Hong Kong 7 Division of Transplantation and Immunogenetics, Department of Pathology, Queen Mary Hospital, Hong Kong 8 Division of Paediatric Surgery, Department of Surgery, The University of Hong Kong, Hong Kong 9 Dr Li Dak-Sum Research Centre, The University of Hong Kong–Karolinska Institutet Collaboration in Regenerative Medicine, The University of Hong Kong, Hong Kong † Co-first authors
The SARS-CoV-2 pandemic poses the greatest global public health challenge in a century. Neutralizing antibody is a correlate of protection and data on kinetics of virus neutralizing antibody ...responses are needed. We tested 293 sera from an observational cohort of 195 reverse transcription polymerase chain reaction (RT-PCR) confirmed SARS-CoV-2 infections collected from 0 to 209 days after onset of symptoms. Of 115 sera collected ≥61 days after onset of illness tested using plaque reduction neutralization (PRNT) assays, 99.1% remained seropositive for both 90% (PRNT
) and 50% (PRNT
) neutralization endpoints. We estimate that it takes at least 372, 416 and 133 days for PRNT
titres to drop to the detection limit of a titre of 1:10 for severe, mild and asymptomatic patients, respectively. At day 90 after onset of symptoms (or initial RT-PCR detection in asymptomatic infections), it took 69, 87 and 31 days for PRNT
antibody titres to decrease by half (T
) in severe, mild and asymptomatic infections, respectively. Patients with severe disease had higher peak PRNT
and PRNT
antibody titres than patients with mild or asymptomatic infections. Age did not appear to compromise antibody responses, even after accounting for severity. We conclude that SARS-CoV-2 infection elicits robust neutralizing antibody titres in most individuals.
PDF
