| 1. |
- Bobrick, Alexey
(författare)
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Interacting Giants and Compact Stars
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on four papers dealing with various aspects of interactions in binary stars. Interactions between stars occur at nearly all stages of their evolution and can take many forms. For example, stars may lose material to a binary companion, merge, interact with groups of other stars in star clusters and explode in binary systems, among other interactions.The first paper in this thesis, Bobrick et al. (2017) (Paper I), models how white dwarfs interact with neutron stars as they spiral into contact due to gravitational wave emission. Through the use of hydrodynamic simulations with the Oil-on-Water code, we investigated the process of mass transfer in such binaries. We found that early phases of interactions in these systems lead to significant loss of angular momentum, driving systems to merge more often than previously expected. The third paper in the thesis, Bobrick et al. (2021a) (Paper III), describes the subsequent evolution of the white dwarf-neutron star binaries containing a massive white dwarf after they merge. In this case, the white dwarf gets shredded into a disc, reaching high temperatures leading to nuclear reactions. These nuclear reactions in the disc produce nickel-56 that gets ejected with the rest of the material from the vicinity of the neutron star. As the ejected material expands, the radioactive nickel-56 heats the material, causing it to glow and become observable as a supernova-like transient event. We used hydrodynamic simulations based on the Water code and a nuclear processing code Torch to study nucleosynthesis in the disc, and a supernova spectral synthesis code SuperNu to model how these events may be observed. Unlike papers I and III, which dealt with compact objects, papers II and IV focussed on interactions involving giant stars. In the second paper, Vos et al. (2020) (Paper II), we modelled how mass transfer between red giants and main-sequence stars can give rise to subdwarf B stars. These subdwarf B stars are remnant cores of the red giants that ignited helium while losing mass. By performing a population study based on detailed stellar structure code MESA, we found that the orbits of such subdwarf B binaries bear imprints of the chemical history of our Galaxy. The fact that the Milky Way had changed its metal content over time allowed us to explain the orbital periods of the known subdwarf B binaries. In our fourth study, Bobrick et al. (2021b) (Paper IV), we investigated the formation history of Betelgeuse, which is a red supergiant visible to the naked eye. It has been recently realised that Betelgeuse is likely an outcome of a merger between two stars that were ejected from their birth environment. To test this scenario, we used the FewBody code together with a Monte Carlo-based model of dynamical interactions in the Milky Way star clusters and synthesised a population of stars which may lead to the formation of Betelgeuse. We have confirmed that a stellar merger is indeed a likely mechanism behind the formation of Betelgeuse.
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| 2. |
- Bobrick, Alexey, et al.
(författare)
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Mass transfer in compact binaries
- 2012
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Ingår i: Mass transfer in compact binaries.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Bobrick, Alexey, et al.
(författare)
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Mass transfer in white dwarf-neutron star binaries
- 2017
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 467:3, s. 3556-3575
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Tidskriftsartikel (refereegranskat)abstract
- We perform hydrodynamic simulations of mass transfer in binaries that contain a white dwarf and a neutron star (WD-NS binaries), and measure the specific angular momentum of material lost from the binary in disc winds. By incorporating our results within a long-term evolution model, we measure the long-term stability of mass transfer in these binaries. We find that only binaries containing helium white dwarfs (WDs) with masses less than a critical mass of M-WD, (crit) = 0.2 M-circle dot undergo stable mass transfer and evolve into ultracompact X-ray binaries. Systems with higher mass WDs experience unstable mass transfer, which leads to tidal disruption of the WD. Our low critical mass compared to the standard jet-only model of mass-loss arises from the efficient removal of angular momentum in the mechanical disc winds, which develop at highly super-Eddington mass-transfer rates. We find that the eccentricities expected for WD-NS binaries when they come into contact do not affect the loss of angular momentum, and can only affect the long-term evolution if they change on shorter time-scales than the mass-transfer rate. Our results are broadly consistent with the observed numbers of both ultracompact X-ray binaries and radio pulsars with WD companions. The observed calcium-rich gap transients are consistent with the merger rate of unstable systems with higher mass WDs.
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| 4. |
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| 5. |
- Bobrick, Alexey, et al.
(författare)
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Transients from ONe white dwarf - neutron star/black hole mergers
- 2022
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 510:3, s. 3758-3777
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Tidskriftsartikel (refereegranskat)abstract
- We conduct the first 3D hydrodynamic simulations of oxygen-neon white dwarf-neutron star/black hole mergers (ONe WD-NS/BH mergers). Such mergers constitute a significant fraction, and may even dominate, the inspiral rates of all WD-NS binaries. We post-process our simulations to obtain the nuclear evolution of these systems and couple the results to a supernova spectral synthesis code to obtain the first light curves and spectra for these transients. We find that the amount of 56Ni synthesized in these mergers grows as a strong function of the WD mass, reaching typically 0.05 and up to 0.1M⊙ per merger. Photodisintegration leads to similar amounts of 4He and about a ten times smaller amount of 1H. The nuclear yields from these mergers, in particular those of 55Mn, may contribute significantly to Galactic chemical evolution. The transients expected from ONe WD-NS mergers are dominantly red/infrared, evolve on month-long time-scales and reach bolometric magnitudes of up to -16.5. The current surveys must have already detected these transients or are, alternatively, putting strong constraints on merger scenarios. The properties of the expected transients from WD-NS mergers best agree with faint type Iax supernovae. The Vera Rubin Observatory (LSST) will be detecting up to thousands of merging ONe WD-NS systems per year. We simulate a subset of our models with 2D axisymmetric FLASH code to investigate why they have been challenging for previous studies. We find that the likely main challenge has been effectively modelling the nuclear statistical equilibrium regime in such mergers.
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| 6. |
- Church, Ross, et al.
(författare)
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Interacting Compact Binaries: Modeling Mass Transfer in Eccentric Systems
- 2012
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Ingår i: Advances in Computational Astrophysics: methods, tools, and outcomes. - 9781583817889 ; 453, s. 175-178
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Konferensbidrag (refereegranskat)abstract
- We discuss mass transfer in eccentric binaries containing a white dwarf and a neutron star (WD-NS binaries). We show that such binaries are produced from field binaries following a series of mass transfer episodes that allow the white dwarf to form before the neutron star. We predict the orbital properties of binaries similar to the observed WD-NS binary J1141+6545, and show that they will undergo episodic mass transfer from the white dwarf to the neutron star. Furthermore, we describe oil-on-water, a two-phase SPH formalism that we have developed in order to model mass transfer in such binaries.
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| 7. |
- Church, Ross P., et al.
(författare)
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Formation Constraints Indicate a Black Hole Accretor in 47 Tuc X9
- 2017
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 851:1
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Tidskriftsartikel (refereegranskat)abstract
- The luminous X-ray binary 47 Tuc X9 shows radio and X-ray emission consistent with a stellar-mass black hole (BH) accreting from a carbon-oxygen white dwarf. Its location, in the core of the massive globular cluster 47 Tuc, hints at a dynamical origin. We assess the stability of mass transfer from a carbon-oxygen white dwarf onto compact objects of various masses, and conclude that for mass transfer to proceed stably, the accretor must, in fact, be a BH. Such systems can form dynamically by the collision of a stellar-mass BH with a giant star. Tidal dissipation of energy in the giant's envelope leads to a bound binary with a pericenter separation less than the radius of the giant. An episode of common-envelope evolution follows, which ejects the giant's envelope. We find that the most likely target is a horizontal-branch star, and that a realistic quantity of subsequent dynamical hardening is required for the resulting binary to merge via gravitational wave emission. Observing one binary like 47 Tuc X9 in the Milky Way globular cluster system is consistent with the expected formation rate. The observed 6.8-day periodicity in the X-ray emission may be driven by eccentricity induced in the ultra-compact X-ray binary's orbit by a perturbing companion.
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| 8. |
- Grishin, Evgeni, et al.
(författare)
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Supernova explosions in active galactic nuclear discs
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 507:1, s. 156-174
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Tidskriftsartikel (refereegranskat)abstract
- Active galactic nuclei (AGNs) are prominent environments for stellar capture, growth, and formation. These environments may catalyse stellar mergers and explosive transients, such as thermonuclear and core-collapse supernovae (SNe). SN explosions in AGN discs generate strong shocks, leading to unique observable signatures. We develop an analytical model that follows the evolution of the shock propagating in the disc until it eventually breaks out. We derive the peak luminosity, bolometric light curve, and breakout time. The peak luminosities may exceed 1045 erg s−1 and last from hours to days. The brightest explosions occur in regions of reduced density: either off-plane, or in discs around low-mass central black holes (∼106 M⊙), or in starved subluminous AGNs. Explosions in the latter two sites are easier to observe due to a reduced AGN background luminosity. We perform suites of 1D Lagrangian radiative hydrodynamics snec code simulations to validate our results and obtain the luminosity in different bands, and 2D axisymmetric Eulerian hydrodynamics code hormone simulations to study the morphology of the ejecta and its deviation from spherical symmetry. The observed signature is expected to be a bright blue, UV or X-ray flare on top of the AGN luminosity from the initial shock breakout, while the subsequent red part of the light curve will largely be unobservable. We estimate the upper limit for the total event rate to be R≲100 yr−1 Gpc−3 for optimal conditions and discuss the large uncertainties in this estimate. Future high-cadence transient searches may reveal these events. Some existing tidal disruption event candidates may originate from AGN SNe.
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| 9. |
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| 10. |
- Jacobson-Galán, Wynn V., et al.
(författare)
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Late-time Observations of Calcium-rich Transient SN 2019ehk Reveal a Pure Radioactive Decay Power Source
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 908:2
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Tidskriftsartikel (refereegranskat)abstract
- We present multiband Hubble Space Telescope imaging of the calcium-rich supernova (SN) SN 2019ehk at 276-389 days after explosion. These observations represent the latest B-band to near-IR photometric measurements of a calcium-rich transient to date and allow for the first opportunity to analyze the late-time bolometric evolution of an object in this observational SN class. We find that the late-time bolometric light curve of SN 2019ehk can be described predominantly through the radioactive decay of 56Co for which we derive a mass of M(56Co) = (2.8 ± 0.1) × 10-2 M o. Furthermore, the rate of decline in bolometric luminosity requires the leakage of γ-rays on timescale t γ = 53.9 ± 1.30 days, but we find no statistical evidence for incomplete positron trapping in the SN ejecta. While our observations cannot constrain the exact masses of other radioactive isotopes synthesized in SN 2019ehk, we estimate a mass ratio limit of M(57Co)/M(56Co) ≤ 0.030. This limit is consistent with the explosive nucleosynthesis produced in the merger of low-mass white dwarfs, which is one of the favored progenitor scenarios in early-time studies of SN 2019ehk.
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