| 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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| 11. |
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| 12. |
- Roy, Niranjan C., et al.
(författare)
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3D Hydrodynamical Simulations of Helium-ignited Double-degenerate White Dwarf Mergers
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 932:2
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Tidskriftsartikel (refereegranskat)abstract
- The origins of Type Ia supernovae (SNe Ia) are still debated. Some of the leading scenarios involve a double detonation in double white dwarf (WD) systems. In these scenarios, helium shell detonation occurs on top of a carbon-oxygen (CO) WD, which then drives the detonation of the CO core, producing an SN Ia. Extensive studies have been done on the possibility of a double helium detonation, following a dynamical helium mass-transfer phase onto a CO-WD. However, 3D self-consistent modeling of the double-WD system, the mass transfer, and the helium shell detonation have been little studied. Here we use 3D hydrodynamical simulations to explore this case in which a helium detonation occurs near the point of Roche lobe overflow of the donor WD and may lead to an SN Ia through the dynamically driven double-degenerate double-detonation (D6) mechanism. We find that the helium layer of the accreting primary WD does undergo a detonation, while the underlying CO core does not, leading to an extremely rapid and faint nova-like transient instead of a luminous SN Ia event. This failed core detonation suggests that D6 SNe Ia may be restricted to the most massive CO primary WDs. We highlight the nucleosynthesis of the long-lived radioisotope 44Ti during explosive helium burning, which may serve as a hallmark both of successful as well as failed D6 events, which subsequently detonate as classical double-degenerate mergers.
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| 13. |
- Vos, Joris, et al.
(författare)
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Looking into the cradle of the grave: J22564-5910, a potential young post-merger hot subdwarf
- 2021
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 1432-0746 .- 0004-6361. ; 655
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Tidskriftsartikel (refereegranskat)abstract
- Context. We present the discovery of J22564-5910, a new type of hot subdwarf (sdB) which shows evidence of gas present in thesystem and it has shallow, multi-peaked hydrogen and helium lines which vary in shape over time. All observational evidence pointstowards J22564-5910 being observed very shortly after the merger phase that formed it.Aims. Using high-resolution, high signal-to-noise spectroscopy, combined with multi-band photometry, Gaia astrometry, and TESSlight curves, we aim to interpret these unusual spectral features.Methods. The photometry, spectra, and light curves were all analysed, and their results were combined in order to support ourinterpretation of the observations: the likely presence of a magnetic field combined with gas features around the sdB. Based onthe triple-peaked H lines, the magnetic field strength was estimated and, by using the shellspec code, qualitative models of gasconfigurations were fitted to the observations.Results. All observations can either be explained by a magnetic field of ∼650 kG, which enables the formation of a centrifugalmagnetosphere, or a non-magnetic hot subdwarf surrounded by a circumstellar gas disc or torus. Both scenarios are not mutuallyexclusive and both can be explained by a recent merger.Conclusions. J22564-5910 is the first object of its kind. It is a rapidly spinning sdB with gas still present in the system. It is thefirst post-merger star observed this early after the merger event, and as such it is very valuable system to test merger theories. If themagnetic field can be confirmed, it is not only the first magnetic sdB, but it hosts the strongest magnetic field ever found in a pre-whitedwarf object. Thus, it could represent the long sought-after immediate ancestor of strongly magnetic white dwarfs.
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| 14. |
- Vos, Joris, et al.
(författare)
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Observed binary populations reflect the Galactic history. Explaining the orbital period-mass ratio relation in wide hot subdwarf binaries.
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 1432-0746 .- 0004-6361.
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Tidskriftsartikel (refereegranskat)abstract
- Context. Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes of stable mass transfer from evolved red giants. The orbits of these binaries show a strong correlation between their orbital periods and mass ratios. The origins of this correlation have, so far, been lacking a conclusive explanation. Aims. We aim to find a binary evolution model which can explain the observed correlation. Methods. Radii of evolved red giants, and hence the resulting orbital periods, strongly depend on their metallicity. We performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA. We used a standard model for binary mass loss and a standard metallicity history of the Galaxy. The resulting sdB systems were selected based on the same criteria as was used in observations and then compared with the observed population. Results. We have achieved an excellent match to the observed period-mass ratio correlation without explicitly fine-tuning any parameters. Furthermore, our models produce a very good match to the observed period-metallicity correlation. We predict several new correlations, which link the observed sdB binaries to their progenitors, and a correlation between the orbital period, metallicity, and core mass for subdwarfs and young low-mass helium white dwarfs. We also predict that sdB binaries have distinct orbital properties depending on whether they formed in the Galactic bulge, thin or thick disc, or the halo. Conclusions. We demonstrate, for the first time, how the metallicity history of the Milky Way is imprinted in the properties of the observed post-mass transfer binaries. We show that Galactic chemical evolution is an important factor in binary population studies of interacting systems containing at least one evolved low-mass (Minit < 1.6 M⊙) component. Finally, we provide an observationally supported model of mass transfer from low-mass red giants onto main-sequence stars.
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| 15. |
- Zenati, Yossef, et al.
(författare)
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Faint Rapid Red Transients from Neutron Star - CO White Dwarf Mergers
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 493:3, s. 3956-3965
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Tidskriftsartikel (refereegranskat)abstract
- Mergers of neutron stars (NS) and white dwarfs (WD) may give rise to observable explosive transientevents. We use 3D hydrodynamical (SPH) simulations, as well as 2D hydrodynamical-thermonuclearsimulations (using the FLASH AMR code) to model the disruption of CO-WDs by NSs, whichproduce faint transient events. We post-process the simulations using a large nuclear network andmake use of the SuperNu radiation-transfer code to predict the observational signatures and detailedproperties of these transients. We calculate the light-curves (LC) and spectra for five models of NS -CO-WD mergers. The small yields of56Ni (few×10−3M) result in faint, rapidly-evolving reddenedtransients (RRTs) with B (R) - peak magnitudes of at most∼−12 (−13) to∼−13 (−15), muchshorter and fainter than both regular and faint/peculiar type-Ia SNe. These transients are likely to beaccompanied by several months-long, 1–2 mag dimmer red/IR afterglows. We show that the spectraof RRTs share some similarities with rapidly-evolving transients such as SN2010x, although RRTsare significantly fainter, especially in the I/R bands, and show far stronger Si lines. We estimate thatthe upcoming Large Synoptic Survey Telescope could detect RRTs at a rate of up to∼10−70 yr−1,through observations in the R/I bands. The qualitative agreement between the SPH and FLASHapproaches supports the earlier hydrodynamical studies of these systems.
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