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1699 Publications visible to you, out of a total of 1699
Contact tracing of binary stars: Pathways to stellar mergers

Abstract (Expand)

Stellar mergers are responsible for a wide variety of phenomena such as rejuvenated blue stragglers, highly magnetised stars, spectacular transients, iconic nebulae, and stars with peculiar surface … chemical abundances and rotation rates. Before stars merge, they enter a contact phase. Here, we investigate which initial binary-star configurations lead to contact and classical common-envelope (CE) phases and assess the likelihood of a subsequent merger. To this end, we computed a grid of about 6000 detailed 1D binary evolution models with initial component masses of 0.5 − 20.0 M⊙ at solar metallicity. Both components were evolved, and rotation and tides were taken into account. We identified five mechanisms that lead to contact and mergers: runaway mass transfer, mass loss through the outer Lagrange point L2, expansion of the accretor, orbital decay because of tides, and non-conservative mass transfer. At least 40% of mass-transferring binaries with initial primary-star masses of 5 − 20 M⊙ evolve into a contact phase; > 12% and > 19% likely merge and evolve into a CE phase, respectively. Because of the non-conservative mass transfer in our models, classical CE evolution from late Case-B and Case-C binaries is only found for initial mass ratios qi < 0.15 − 0.35. For larger mass ratios, we find stable mass transfer. In early Case-B binaries, contact occurs for initial mass ratios qi < 0.15 − 0.35, while in Case-A mass transfer, this is the case for all qi in binaries with the initially closest orbits and qi < 0.35 for initially wider binaries. Our models predict that most Case-A binaries with mass ratios of q < 0.5 upon contact mainly get into contact because of runaway mass transfer and accretor expansion on a thermal timescale, with subsequent L2-overflow in more than half of the cases. Thus, these binaries likely merge quickly after establishing contact or remain in contact only for a thermal timescale. On the contrary, Case-A contact binaries with higher mass ratios form through accretor expansion on a nuclear timescale and can thus give rise to long-lived contact phases before a possible merger. Observationally, massive contact binaries are almost exclusively found with mass ratios q > 0.5, confirming our model expectations. Because of non-conservative mass transfer with mass transfer efficiencies of 15 − 65%, 5 − 25%, and 25 − 50% in Case-A, -B, and -C mass transfer, respectively (for primary-star masses above 3 M⊙), our contact, merger, and classical CE incidence rates are conservative lower limits. With more conservative mass transfer, these incidences would increase. Moreover, in most binaries, the non-accreted mass cannot be ejected, raising the question of the further evolution of such systems. The non-accreted mass may settle into circumstellar and circumbinary disks, but could also lead to further contact systems and mergers. Overall, contact binaries are a frequent and fascinating result of binary mass transfer of which the exact outcomes still remain to be understood and explored further.

Authors: J. Henneco, F. R. N. Schneider, E. Laplace

Date Published: 1st Feb 2024

Publication Type: Journal

The role of heparin in spike SARS-CoV-2 infection: From a model for heparan sulfates to a starting structure for antivirals

Abstract

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Authors: Giulia Paiardi, Maria Milanesi, Matheus Ferraz, Liv Zimmermann, Chiara Urbinati, Pasqua Oreste, Francesca Caccuri, Petr Chlanda, Marco Rusnati, Rebecca C. Wade

Date Published: 1st Feb 2024

Publication Type: Journal

General relativistic moving-mesh hydrodynamic simulations with AREPO and applications to neutron star mergers

Abstract

Not specified

Authors: Georgios Lioutas, Andreas Bauswein, Theodoros Soultanis, Rüdiger Pakmor, Volker Springel, Friedrich K. Röpke

Date Published: 1st Feb 2024

Publication Type: Journal

Quantification and Prediction of Multiple Sequence Alignment Difficulty

Abstract

Not specified

Authors: Luc Mercatoris, Alexandros Stamatakis

Date Published: 1st Feb 2024

Publication Type: Master's Thesis

Convective-core overshooting and the final fate of massive stars

Abstract

Not specified

Authors: D. Temaj, F. R. N. Schneider, E. Laplace, D. Wei, Ph. Podsiadlowski

Date Published: 1st Feb 2024

Publication Type: Journal

Validating CESU-8 Encoded Text Utilising SIMD Instructions

Abstract

Not specified

Authors: Marco Schröder, Stefan Machmeier, Suyeon Maeng, Vincent Heuveline

Date Published: 1st Feb 2024

Publication Type: Journal

Examining quasar absorption-line analysis methods: the tension between simulations and observational assumptions key to modelling clouds

Abstract (Expand)

ABSTRACT A key assumption in quasar absorption-line studies of the circumgalactic medium (CGM) is that each absorption component maps to a spatially isolated ‘cloud’ structure that has single valued …ure that has single valued properties (e.g. density, temperature, metallicity). We aim to assess and quantify the degree of accuracy underlying this assumption. We used adaptive mesh refinement hydrodynamic cosmological simulations of two z = 1 dwarf galaxies and generated synthetic quasar absorption-line spectra of their CGM. For the Si ii λ1260 transition, and the C iv λλ1548, 1550 and O vi λλ1031, 1037 fine-structure doublets, we objectively determined which gas cells along a line of sight (LOS) contribute to detected absorption. We implemented a fast, efficient, and objective method to define individual absorption components in each absorption profile. For each absorption component, we quantified the spatial distribution of the absorbing gas. We studied a total of 1302 absorption systems containing a total of 7755 absorption components. 48  per cent of Si ii, 68  per cent of C iv, and 72  per cent of O vi absorption components arise from two or more spatially isolated ‘cloud’ structures along the LOS. Spatially isolated ‘cloud’ structures were most likely to have cloud–cloud LOS separations of 0.03Rvir (1.3 kpc), 0.11Rvir (4.8 kpc), and 0.13Rvir (5.6 kpc) for Si ii, C iv, and O vi, respectively. There can be very little overlap between multiphase gas structures giving rise to absorption components. If our results reflect the underlying reality of how absorption lines record CGM gas, they place tension on current observational analysis methods as they suggest that component-by-component absorption-line formation is more complex than is assumed and applied for chemical-ionization modelling.

Authors: Rachel Marra, Christopher W Churchill, Glenn G Kacprzak, Nikole M Nielsen, Sebastian Trujillo-Gomez, Emmy A Lewis

Date Published: 1st Feb 2024

Publication Type: Journal

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