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1
Petrovic, Jelena. "The evolution of massive binary systems." Serbian Astronomical Journal, no. 201 (2020): 1–13. http://dx.doi.org/10.2298/saj2001001p.
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The evolution of massive stars in close binary systems is significantly different from single star evolution due to a series of interactions between the two stellar components. Such massive close binary systems are linked to various astrophysical phenomena, for example Wolf-Rayet stars, supernova type Ib and Ic, X-ray binaries and gamma-ray bursts. Also, the emission of gravitational waves, recently observed by the LIGO-Virgo detectors, is associated with mergers in binary systems containing compact objects, relics of massive stars - black holes and neutron stars. Evolutionary calculations of massive close binary systems were performed by various authors, but many aspects are not yet fully understood. In this paper, the main concepts of massive close binary evolution are reviewed, together with the most important parameters that can influence the final outcome of the binary system evolution, such as rotation, magnetic fields, stellar wind mass loss and mass accretion efficiency during interactions. An extensive literature overview of massive close binary models in the light of exciting observations connected with those systems is presented.
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Fuller, Jim, and Wenbin Lu. "The spins of compact objects born from helium stars in binary systems." Monthly Notices of the Royal Astronomical Society 511, no. 3 (February 4, 2022): 3951–64. http://dx.doi.org/10.1093/mnras/stac317.
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ABSTRACT The angular momentum (AM) content of massive stellar cores helps us to determine the natal spin rates of neutron stars and black holes. Asteroseismic measurements of low-mass stars have proven that stellar cores rotate slower than predicted by most prior work, so revised models are necessary. In this work, we apply an updated AM transport model based on the Tayler instability to massive helium stars in close binaries, in which tidal spin-up can greatly increase the star’s AM. Consistent with prior work, these stars can produce highly spinning black holes upon core-collapse if the orbital period is less than $P_{\rm orb} \lesssim \! 1 \, {\rm d}$. For neutron stars, we predict a strong correlation between the pre-explosion mass and the neutron star rotation rate, with millisecond periods ($P_{\rm NS} \lesssim 5 \, {\rm ms}$) only achievable for massive ($M \gtrsim 10 \, M_\odot$) helium stars in tight ($P_{\rm orb} \lesssim 1 \, {\rm d}$) binaries. Finally, we discuss our models in relation to type Ib/c supernovae, superluminous supernove, gamma-ray bursts, and LIGO/Virgo measurements of black hole spins. Our models are roughly consistent with the rates and energetics of these phenomena, with the exception of broad-lined Ic supernovae, whose high rates and ejecta energies are difficult to explain.
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Mirabell, I. F. "Microquasars and ULXS: Fossils of GRB Sources." International Astronomical Union Colloquium 194 (2004): 14–17. http://dx.doi.org/10.1017/s0252921100151735.
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AbstractGamma-ray bursts (GRBs) of long duration probably result from the core-collapse of massive stars in binary systems. After the collapse of the primary star the binary system may remain bound leaving a microquasar or ULX source as remnant. In this context, microquasars and ULXs are fossils of GRB sources and should contain physical and astrophysical clues on their GRB-source progenitors. Here I show that the identification of the birth place of microquasars can provide constrains on the progenitor stars of compact objects, and that the runaway velocity can be used to constrain the energy in the explosion of massive stars that leave neutron stars and black holes. The observations show that the neutron star binaries LS 5039, LSI +61°303 and the low-mass black hole GRO J1655-40 formed in energetic supernova explosions, whereas the black holes of larger masses (M ≥ 10 M⊙) in Cygnus X-l and GRS 1915+105 formed promptly, in the dark or in underluminous supornovao. The association with clusters of massive stars of the microquasar LSI +61°303 and the magnetars SGR 1806-20 and SGR 1900+14, suggest that very massive stars (M ≥ 50 M⊙) may -in some cases- leave neutron stars rather than black holes. The models of GRB sources of long duration have the same basic ingredients as microquasars and ULXs: compact objects with accretion disks and relativistic jets in binary systems. Therefore, the analogies between microquasars and AGN may be extended to the sources of GRBs.
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Gruzinov, Andrei, Yuri Levin, and Christopher D. Matzner. "Negative dynamical friction on compact objects moving through dense gas." Monthly Notices of the Royal Astronomical Society 492, no. 2 (January 16, 2020): 2755–61. http://dx.doi.org/10.1093/mnras/staa013.
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ABSTRACT An overdense wake is created by a gravitating object moving through a gaseous medium, and this wake pulls back on the object and slows it down. This is conventional dynamical friction in a gaseous medium. We argue that if the object drives a sufficiently powerful outflow, the wake is destroyed and instead an extended underdense region is created behind the object. In this case the overall gravitational force is applied in the direction of the object’s motion, producing a negative dynamical friction (NDF). Black holes in dense gas drive powerful outflows and may experience the NDF, although extensive numerical work is probably needed to demonstrate or refute this conclusively. NDF may be important for stellar-mass black holes and neutron stars inside ‘common envelopes’ in binary systems, for stellar mass black holes inside active galactic nucleus discs, or for massive black holes growing through super-Eddington accretion in early Universe.
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Rastello, Sara, Michela Mapelli, Ugo N. Di Carlo, Giuliano Iorio, Alessandro Ballone, Nicola Giacobbo, Filippo Santoliquido, and Stefano Torniamenti. "Dynamics of binary black holes in low-mass young star clusters." Monthly Notices of the Royal Astronomical Society 507, no. 3 (August 16, 2021): 3612–25. http://dx.doi.org/10.1093/mnras/stab2355.
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ABSTRACT Young star clusters are dynamically active stellar systems and are a common birthplace for massive stars. Low-mass star clusters (∼300–103 M⊙) are more numerous than massive systems and are characterized by a two-body relaxation time-scale of a few Myr: the most massive stars sink to the cluster core and dynamically interact with each other even before they give birth to compact objects. Here, we explore the properties of black holes (BHs) and binary black holes (BBHs) formed in low-mass young star clusters, by means of a suite of 105 direct N-body simulations with a high original binary fraction (100 per cent for stars with mass >5 M⊙). Most BHs are ejected in the first ∼20 Myr by dynamical interactions. Dynamical exchanges are the main formation channel of BBHs, accounting for ∼40–80 per cent of all the systems. Most BBH mergers in low-mass young star clusters involve primary BHs with mass <40 M⊙ and low-mass ratios are extremely more common than in the field. Comparing our data with those of more massive star clusters (103 − 3 × 104 M⊙), we find a strong dependence of the percentage of exchanged BBHs on the mass of the host star cluster. In contrast, our results show just a mild correlation between the mass of the host star cluster and the efficiency of BBH mergers.
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García, Federico, Deborah N. Aguilera, and Gustavo E. Romero. "Conditions for jet formation in accreting neutron stars: the magnetic field decay." Proceedings of the International Astronomical Union 6, S275 (September 2010): 309–10. http://dx.doi.org/10.1017/s1743921310016248.
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AbstractAccreting neutron stars can produce jets only if they are weakly magnetized (B ~ 108 G). On the other hand, neutron stars are compact objects born with strong surface magnetic fields (B ~ 1012 G). In this work we study the conditions for jet formation in a binary system formed by a neutron star and a massive donor star once the magnetic field has decayed due to accretion. We solve the induction equation for the magnetic field diffusion in a realistic neutron star crust and discuss the possibility of jet launching in systems like the recently detected Supergiant Fast X-ray Transients.
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Sen, K., N. Langer, P. Marchant, A. Menon, S. E. de Mink, A. Schootemeijer, C. Schürmann, et al. "Detailed models of interacting short-period massive binary stars." Astronomy & Astrophysics 659 (March 2022): A98. http://dx.doi.org/10.1051/0004-6361/202142574.
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Context. The majority of massive stars are part of binary systems. In about a quarter of these, the companions are so close that mass transfer occurs while they undergo core hydrogen burning, first on the thermal and then on the nuclear timescale. The nuclear timescale mass transfer leads to observational counterparts: the semi-detached so-called massive Algol binaries. These systems may provide urgently needed tests of the physics of mass transfer. However, comprehensive model predictions for these systems are sparse. Aims. We use a large grid of detailed evolutionary models of short-period massive binaries and follow-up population synthesis calculations to derive probability distributions of the observable properties of massive Algols and their descendants. Methods. Our results are based on ∼10 000 binary model sequences calculated with the stellar evolution code MESA, using a metallicity suitable for the Large Magellanic Cloud (LMC), covering initial donor masses between 10 M⊙ and 40 M⊙ and initial orbital periods above 1.4 d. These models include internal differential rotation and magnetic angular momentum transport, non-conservative mass and angular momentum transfer between the binary components, and time-dependent tidal coupling. Results. Our models imply ∼30, or ∼3% of the ∼1000, core hydrogen burning O-star binaries in the LMC to be currently in the semi-detached phase. Our donor models are up to 25 times more luminous than single stars of an identical mass and effective temperature, which agrees with the observed Algols. A comparison of our models with the observed orbital periods and mass ratios implies rather conservative mass transfer in some systems, while a very inefficient one in others. This is generally well reproduced by our spin-dependent mass transfer algorithm, except for the lowest considered masses. The observations reflect the slow increase of the surface nitrogen enrichment of the donors during the semi-detached phase all the way to CNO equilibrium. We also investigate the properties of our models after core hydrogen depletion of the donor star, when these models correspond to Wolf-Rayet or helium+OB star binaries. Conclusions. A dedicated spectroscopic survey of massive Algol systems may allow to derive the dependence of the efficiency of thermal timescale mass transfer on the binary parameters, as well as the efficiency of semiconvective mixing in the stellar interior. This would be a crucial step towards reliable binary models up to the formation of supernovae and compact objects.
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Li, Xinyu, Philip Chang, Yuri Levin, Christopher D. Matzner, and Philip J. Armitage. "Simulation of a compact object with outflows moving through a gaseous background." Monthly Notices of the Royal Astronomical Society 494, no. 2 (April 9, 2020): 2327–36. http://dx.doi.org/10.1093/mnras/staa900.
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ABSTRACT A compact object moving relative to surrounding gas accretes material and perturbs the density of gas in its vicinity. In the classical picture of Bondi–Hoyle–Lyttleton accretion, the perturbation takes the form of an overdense wake behind the object, which exerts a dynamical friction drag. We use hydrodynamic simulations to investigate how the accretion rate and strength of dynamical friction are modified by the presence of outflow from the compact object. We show that the destruction of the wake by an outflow reduces dynamical friction, and reverses its sign when the outflow is strong enough, in good quantitative agreement with analytic calculations. For a strong isotropic outflow, the outcome on scales that we have simulated is a negative dynamical friction, i.e. net acceleration. For jet-like outflows driven by reprocessed accretion, both the rate of accretion and the magnitude of dynamical friction drop for more powerful jets. The accretion rate is strongly intermittent when the jet points to the same direction as the motion of the compact object. The dynamical effects of outflows may be important for the evolution of compact objects during the common envelope phase of binary systems, and for accreting compact objects and massive stars encountering active galactic nucleus discs.
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Schneider, F. R. N., Ph Podsiadlowski, and B. Müller. "Pre-supernova evolution, compact-object masses, and explosion properties of stripped binary stars." Astronomy & Astrophysics 645 (December 21, 2020): A5. http://dx.doi.org/10.1051/0004-6361/202039219.
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The era of large transient surveys, gravitational-wave observatories, and multi-messenger astronomy has opened up new possibilities for our understanding of the evolution and final fate of massive stars. Most massive stars are born in binary or higher-order multiple systems and exchange mass with a companion star during their lives. In particular, the progenitors of a large fraction of compact-object mergers, and Galactic neutron stars (NSs) and black holes (BHs) have been stripped of their envelopes by a binary companion. Here, we study the evolution of single and stripped binary stars up to core collapse with the stellar evolution code MESA and their final fates with a parametric supernova (SN) model. We find that stripped binary stars can have systematically different pre-SN structures compared to genuine single stars and thus also different SN outcomes. These differences are already established by the end of core helium burning and are preserved up to core collapse. Consequently, we find that Case A and B stripped stars and single and Case C stripped stars develop qualitatively similar pre-SN core structures. We find a non-monotonic pattern of NS and BH formation as a function of CO core mass that is different in single and stripped binary stars. In terms of initial mass, single stars of ≳35 M⊙ all form BHs, while this transition is only at about 70 M⊙ in stripped stars. On average, stripped stars give rise to lower NS and BH masses, higher explosion energies, higher kick velocities, and higher nickel yields. Within a simplified population-synthesis model, we show that our results lead to a significant reduction in the rates of BH–NS and BH–BH mergers with respect to typical assumptions made on NS and BH formation. Therefore, our models predict lower detection rates of such merger events with for example the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) than is often considered. Further, we show how certain features in the NS–BH mass distribution of single and stripped stars relate to the chirp-mass distribution of compact object mergers. Further implications of our findings are discussed with respect to the missing red-supergiant problem, a possible mass gap between NSs and BHs, X-ray binaries, and observationally inferred nickel masses from Type Ib/c and IIP SNe.
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Rose, Sam, Casey Y. Lam, Jessica R. Lu, Michael Medford, Matthew W. Hosek, Natasha S. Abrams, Emily Ramey, and Sergiy S. Vasylyev. "The Impact of Initial–Final Mass Relations on Black Hole Microlensing." Astrophysical Journal 941, no. 2 (December 1, 2022): 116. http://dx.doi.org/10.3847/1538-4357/aca09d.
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Abstract Uncertainty in the initial–final mass relation (IFMR) has long been a problem in understanding the final stages of massive star evolution. One of the major challenges of constraining the IFMR is the difficulty of measuring the mass of nonluminous remnant objects (i.e., neutron stars and black holes). Gravitational-wave detectors have opened the possibility of finding large numbers of compact objects in other galaxies, but all in merging binary systems. Gravitational lensing experiments using astrometry and photometry are capable of finding compact objects, both isolated and in binaries, in the Milky Way. In this work we improve the Population Synthesis for Compact object Lensing Events (PopSyCLE) microlensing simulation code in order to explore the possibility of constraining the IFMR using the Milky Way microlensing population. We predict that the Roman Space Telescope’s microlensing survey will likely be able to distinguish different IFMRs based on the differences at the long end of the Einstein crossing time distribution and the small end of the microlensing parallax distribution, assuming the small (π E ≲ 0.02) microlensing parallaxes characteristic of black hole lenses are able to be measured accurately. We emphasize that future microlensing surveys need to be capable of characterizing events with small microlensing parallaxes in order to place the most meaningful constraints on the IFMR.
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Shenar, T., D. P. Sablowski, R. Hainich, H. Todt, A. F. J. Moffat, L. M. Oskinova, V. Ramachandran, et al. "The Wolf–Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud." Astronomy & Astrophysics 627 (July 2019): A151. http://dx.doi.org/10.1051/0004-6361/201935684.
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Context. Massive Wolf–Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z ≈ 0.5 Z⊙), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf–Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45 ± 30% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only ≈12 ± 7% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises ≈4% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L ≈ 5.2 [L⊙], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (veq ≲ 250 km s−1) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.
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Pulley, D., G. Faillace, D. Smith, A. Watkins, and S. von Harrach. "The quest for stable circumbinary companions to post-common envelope sdB eclipsing binaries." Astronomy & Astrophysics 611 (March 2018): A48. http://dx.doi.org/10.1051/0004-6361/201731125.
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Context. Period variations have been detected in a number of eclipsing close compact binary subdwarf B stars (sdBs) and these have often been interpreted as being caused by circumbinary massive planets or brown dwarfs. According to canonical binary models, the majority of sdB systems are produced from low mass stars with degenerate cores where helium is ignited in flashes. Various evolutionary scenarios have been proposed for these stars, but a definite mechanism remains to be established. Equally puzzling is the formation of these putative circumbinary objects which must have formed from the remaining post-common envelope circumbinary disk or survived its evolution.Aim. In this paper we review the eclipse time variations (ETVs) exhibited by seven such systems (EC 10246-2707, HS 0705+6700, HS 2231+2441, J08205+0008, NSVS 07826147, NSVS 14256825, and NY Vir) and explore whether there is conclusive evidence that the ETVs observed over the last two decades can reliably predict the presence of one or more circumbinary bodies.Methods. We report 246 new observations of the seven sdB systems made between 2013 September and 2017 July using a worldwide network of telescopes. We combined our new data with previously published measurements to analyse the ETVs of these systems.Results. Our data show that period variations cannot be modelled simply on the basis of circumbinary objects. This implies that more complex processes may be taking place in these systems. These difficulties are compounded by the secondary star not being spectroscopically visible. From ETVs, it has historically been suggested that five of the seven binary systems reported here had circumbinary objects. Based on our recent observations and analysis, only three systems remain serious contenders. We find agreement with other observers that at least a decade of observations is required to establish reliable ephemerides. With longer observational baselines it is quite conceivable that the data will support the circumbinary object hypothesis of these binary systems. Also, we generally agree with other observers that higher values of (O–C) residuals are found with secondary companions of spectral type M5/6 (or possibly earlier as a result of an Applegate type mechanism).
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Antoniadis, John, David R. Aguilera-Dena, Alejandro Vigna-Gómez, Michael Kramer, Norbert Langer, Bernhard Müller, Thomas M. Tauris, Chen Wang, and Xiao-Tian Xu. "Explodability fluctuations of massive stellar cores enable asymmetric compact object mergers such as GW190814." Astronomy & Astrophysics 657 (January 2022): L6. http://dx.doi.org/10.1051/0004-6361/202142322.
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The first three observing runs with Advanced LIGO and Virgo have resulted in the detection of binary black hole (BBH) mergers with highly unequal mass components, which are difficult to reconcile with standard formation paradigms. The most representative of these is GW190814, a highly asymmetric merger between a 23 M⊙ black hole (BH) and a 2.6 M⊙ compact object. Here, we explore recent results, suggesting that a sizable fraction of stars with pre-collapse carbon-oxygen core masses above 10 M⊙, and extending up to at least 30 M⊙, may produce objects inside the so-called lower mass gap that bridges the division between massive pulsars and BHs in Galactic X-ray binaries. We demonstrate that such an explosion landscape would naturally cause a fraction of massive binaries to produce GW190814-like systems instead of symmetric-mass BBHs. We present examples of specific evolutionary channels leading to the formation of GW190814 and GW200210, a 24 + 2.8 M⊙ merger discovered during the O3b observing run. We estimate the merger-rate density of these events in our scenario to be 𝒪(5%) of the total BBH merger rate. Finally, we discuss the broader implications of this formation channel for compact object populations, and its possible relevance to less asymmetric merger events such as GW200105 and GW200115.
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Petrovic, Jelena. "The influence of initial orbital period on helium and carbon-oxygen core masses in massive case a binary systems with low accretion efficiency." Serbian Astronomical Journal, no. 205 (2022): 45–51. http://dx.doi.org/10.2298/saj2205045p.
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The evolutionary models of 33 massive Case A binary systems in mass range from 30M? to 40M? with initial orbital periods of 3, 4 and 5 days, accretion efficiency of 10% and at the solar metallicity are presented. The models are obtained with the MESA (Modules for Experiments in Stellar Astrophysics) numerical code. The evolution is followed from a double O-type star, through Case A and Case mass transfer, to the formation of a carbon-oxygen (CO) core in the primary. The evolution of the secondary star in each binary system is further modeled with the same numerical code in an approximation of a single star, also to the formation of a carbon-oxygen core. The resulting helium core masses are in the range of 7.94M? - 13.19M? and 12.30M? and 19.12M? for primary and secondary stars, respectively. The carbon-oxygen core masses are between 5.26M? and 10M? for primaries and between 8.96M? and 15.32M? for secondaries. A clear influence of the initial orbital period on the resulting helium and CO core masses is demonstrated: primary stars in binary systems with initial orbital periods of 3, 4 and 5 days have on average about 15%, 8% and 2.5% smaller CO cores than single stars with the same initial masses. On the other hand, it was found that the correlation between the CO and helium core mass does not depend on the initial orbital period and can be approximated with the same linear fit for all binary systems. The CO/helium core mass ratio is found to be larger in binary systems than for single stars. It is also shown that the black hole formation limit for primary stars depends on the initial orbit and is between 33M? - 34M?, 32M? - 33M? and 30M? - 31M?, for the initial orbital periods of 3, 4 and 5 days, respectively. The resulting double compact objects are of two types: mixed neutron star - black hole systems (6 models) and double black holes (27 models). The resulting black hole masses are estimated to be in the range of 5M? to 17M?.
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Klencki, J., M. Moe, W. Gladysz, M. Chruslinska, D. E. Holz, and K. Belczynski. "Impact of inter-correlated initial binary parameters on double black hole and neutron star mergers." Astronomy & Astrophysics 619 (November 2018): A77. http://dx.doi.org/10.1051/0004-6361/201833025.
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The distributions of the initial main-sequence binary parameters are one of the key ingredients in obtaining evolutionary predictions for compact binary (BH–BH/BH–NS/NS–NS) merger rates. Until now, such calculations were done under the assumption that initial binary parameter distributions were independent. For the first time, we implement empirically derived inter-correlated distributions of initial binary parameters primary mass (M1), mass ratio (q), orbital period (P), and eccentricity (e). Unexpectedly, the introduction of inter-correlated initial binary parameters leads to only a small decrease in the predicted merger rates by a factor of ≲2–3 relative to the previously used non-correlated initial distributions. The formation of compact object mergers in the isolated classical binary evolution favours initial binaries with stars of comparable masses (q ≈ 0.5–1) at intermediate orbital periods (log P (days) = 2–4). New distributions slightly shift the mass ratios towards lower values with respect to the previously used flat q distribution, which is the dominant effect decreasing the rates. New orbital periods (∼1.3 more initial systems within log P (days) = 2–4), together with new eccentricities (higher), only negligibly increase the number of progenitors of compact binary mergers. Additionally, we discuss the uncertainty of merger rate predictions associated with possible variations of the massive-star initial mass function (IMF). We argue that evolutionary calculations should be normalized to a star formation rate (SFR) that is obtained from the observed amount of UV light at wavelength 1500 Å (an SFR indicator). In this case, contrary to recent reports, the uncertainty of the IMF does not affect the rates by more than a factor of ∼2. Any change to the IMF slope for massive stars requires a change of SFR in a way that counteracts the impact of IMF variations on compact object merger rates. In contrast, we suggest that the uncertainty in cosmic SFR at low metallicity can be a significant factor at play.
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Mata Sánchez, Daniel, Mark R. Kennedy, Colin J. Clark, Rene P. Breton, and Vikhram S. Dhillon. "Astrophysical entomology: dissecting the black widow population through multi-band light curve modelling." Proceedings of the International Astronomical Union 16, S363 (June 2020): 324–26. http://dx.doi.org/10.1017/s1743921322001077.
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AbstractThe population of black widows, binary systems containing a millisecond pulsar and a very low-mass companion star exposed to the high-energy pulsar wind, has grown exponentially in the past few years. The number of black widow candidates is now over 30 systems, but only 14 have been confirmed so far. Their relevance in analysing the extremes of the neutron stars properties led to multiwavelength dedicated studies that revealed a rich phenomenology. In this work, we provide a glimpse into the black widow class through modelling of high-cadence multi-band light curves of 6 systems, accounting for almost half of the confirmed population. A better understanding of the black widow population, which hosts some of the most massive and fastest spinning neutron stars, will ultimately benefit future modelling of compact object mergers.
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Vynatheya, Pavan, and Adrian S. Hamers. "How Important Is Secular Evolution for Black Hole and Neutron Star Mergers in 2+2 and 3+1 Quadruple-star Systems?" Astrophysical Journal 926, no. 2 (February 1, 2022): 195. http://dx.doi.org/10.3847/1538-4357/ac4892.
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Abstract Mergers of black holes (BHs) and neutron stars (NSs) result in the emission of gravitational waves that can be detected by LIGO. In this paper, we look at 2+2 and 3+1 quadruple-star systems, which are common among massive stars, the progenitors of BHs and NSs. We carry out a detailed population synthesis of quadruple systems using the Multiple Stellar Evolution code, which seamlessly takes into consideration stellar evolution, binary and tertiary interactions, N-body dynamics, and secular evolution. We find that, although secular evolution plays a role in compact object (BH and NS) mergers, (70–85)% (depending on the model assumptions) of the mergers are solely due to common envelope evolution. Significant eccentricities in the LIGO band (higher than 0.01) are only obtained with zero supernova (SN) kicks and are directly linked to the role of secular evolution. A similar outlier effect is seen in the χ eff distribution, with negative values obtained only with zero SN kicks. When kicks are taken into account, there are no systems that evolve into a quadruple consisting of four compact objects. For our fiducial model, we estimate the merger rates (in units of Gpc−3 yr−1) in 2+2 quadruples (3+1 quadruples) to be 10.8 ± 0.9 (2.9 ± 0.5), 5.7 ± 0.6 (1.4 ± 0.4), and 0.6 ± 0.2 (0.7 ± 0.3) for BH–BH, BH–NS, and NS–NS mergers, respectively. The BH–BH merger rates represent a significant fraction of the current LIGO rates, whereas the other merger rates fall short of LIGO estimates.
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Quast, M., N. Langer, and T. M. Tauris. "Mass transfer on a nuclear timescale in models of supergiant and ultra-luminous X-ray binaries." Astronomy & Astrophysics 628 (July 29, 2019): A19. http://dx.doi.org/10.1051/0004-6361/201935453.
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Context. The origin and number of the Galactic supergiant X-ray binaries is currently not well understood. They consist of an evolved massive star and a neutron star or black-hole companion. X-rays are thought to be generated from the accretion of wind material donated by the supergiant, while mass transfer due to Roche-lobe overflow is mostly disregarded because the high mass ratios of these systems are thought to render this process unstable. Aims. We investigate how the proximity of supergiant donor stars to the Eddington limit, and their advanced evolutionary stage, may influence the evolution of massive and ultra-luminous X-ray binaries with supergiant donor stars (SGXBs and ULXs). Methods. We constructed models of massive stars with different internal hydrogen and helium gradients (H/He gradients) and different hydrogen-rich envelope masses, and exposed them to slow mass-loss to probe the response of the stellar radius. In addition, we computed the corresponding Roche-lobe overflow mass-transfer evolution with our detailed binary stellar evolution code, approximating the compact objects as point masses. Results. We find that a H/He gradient in the layers beneath the surface, as it is likely present in the well-studied donor stars of observed SGBXs, can enable mass transfer in SGXBs on a nuclear timescale with a black-hole or a neutron star accretor, even for mass ratios in excess of 20. In our binary evolution models, the donor stars rapidly decrease their thermal equilibrium radius and can therefore cope with the inevitably strong orbital contraction imposed by the high mass ratio. We find that the orbital period derivatives of our models agree well with empirical values. We argue that the SGXB phase may be preceded by a common-envelope evolution. The envelope inflation near the Eddington limit means that this mechanism more likely occurs at high metallicity. Conclusion. Our results open a new perspective for understanding that SGBXs are numerous in our Galaxy and are almost completely absent in the Small Magellanic Cloud. Our results may also offer a way to find more ULX systems, to detect mass transfer on nuclear timescales in ULX systems even with neutron star accretors, and shed new light on the origin of the strong B-field in these neutron stars.
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Su, Yubo, and Dong Lai. "Dynamical tides in eccentric binaries containing massive main-sequence stars: analytical expressions." Monthly Notices of the Royal Astronomical Society 510, no. 4 (December 21, 2021): 4943–51. http://dx.doi.org/10.1093/mnras/stab3698.
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ABSTRACT Tidal evolution of eccentric binary systems containing at least one massive main-sequence (MS) star plays an important role in the formation scenarios of merging compact-object binaries. The dominant dissipation mechanism in such systems involves tidal excitation of outgoing internal gravity waves at the convective-radiative boundary and dissipation of the waves at the stellar envelope/surface. We have derived analytical expressions for the tidal torque and tidal energy transfer rate in such binaries for arbitrary orbital eccentricities and stellar rotation rates. These expressions can be used to study the spin and orbital evolution of eccentric binaries containing massive MS stars, such as the progenitors of merging neutron star binaries. Applying our results to the PSR J0045-7319 system, which has a massive B-star companion and an observed, rapidly decaying orbit, we find that for the standard radius of convective core based on non-rotating stellar models, the B-star must have a significant retrograde and differential rotation in order to explain the observed orbital decay rate. Alternatively, we suggest that the convective core may be larger as a result of rapid stellar rotation and/or mass transfer to the B-star in the recent past during the post-MS evolution of the pulsar progenitor.
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Hamers, Adrian S., Antti Rantala, Patrick Neunteufel, Holly Preece, and Pavan Vynatheya. "Multiple Stellar Evolution: a population synthesis algorithm to model the stellar, binary, and dynamical evolution of multiple-star systems." Monthly Notices of the Royal Astronomical Society 502, no. 3 (February 3, 2021): 4479–512. http://dx.doi.org/10.1093/mnras/stab287.
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ABSTRACT In recent years, observations have shown that multiple-star systems such as hierarchical triple and quadruple-star systems are common, especially among massive stars. They are potential sources of interesting astrophysical phenomena such as compact object mergers, leading to supernovae, and gravitational wave events. However, many uncertainties remain in their often complex evolution. Here, we present the population synthesis code Multiple Stellar Evolution (mse), designed to rapidly model the stellar, binary, and dynamical evolution of multiple-star systems. mse includes a number of new features not present in previous population synthesis codes: (1) an arbitrary number of stars, as long as the initial system is hierarchical, (2) dynamic switching between secular and direct N-body integration for efficient computation of the gravitational dynamics, (3) treatment of mass transfer in eccentric orbits, which occurs commonly in multiple-star systems, (4) a simple treatment of tidal, common envelope, and mass transfer evolution in which the accretor is a binary instead of a single star, (5) taking into account planets within the stellar system, and (6) including gravitational perturbations from passing field stars. mse, written primarily in the C++ language, will be made publicly available and has few prerequisites; a convenient python interface is provided. We give a detailed description of MSE and illustrate how to use the code in practice. We demonstrate its operation in a number of examples.
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Garofali, Kristen, and Benjamin F. Williams. "Using High-Mass X-ray binaries to probe massive binary evolution: The age distribution of High-Mass X-ray binaries in M33." Proceedings of the International Astronomical Union 14, S346 (August 2018): 322–31. http://dx.doi.org/10.1017/s1743921318007470.
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AbstractHigh-mass X-ray binaries (HMXBs) provide an exciting window into the underlying processes of both binary as well as massive star evolution. Because HMXBs are systems containing a compact object accreting from a high-mass star at close orbital separations they are also likely progenitors of gamma-ray bursts and gravitational wave sources. We present classification and age measurements for HMXBs in M33 using a combination of deep Chandra X-ray imaging, and archival Hubble Space Telescope data. We constrain the ages of the HMXB candidates by fitting the color-magnitude diagrams of the surrounding stars, which yield the star formation histories of the surrounding region. Unlike the age distributions measured for HMXB populations in the Magellanic Clouds, the age distribution for the HMXB population in M33 contains a number of extremely young (<5 Myr) sources. We discuss these results the context of the effect of host galaxy properties on the observed HMXB population.
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Levesque, Emily M., Philip Massey, Anna N. Żytkow, and Nidia Morrell. "Discovery of a Thorne-Żytkow object candidate in the Small Magellanic Cloud." Proceedings of the International Astronomical Union 9, S307 (June 2014): 57–63. http://dx.doi.org/10.1017/s1743921314006279.
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AbstractThorne-Żytkow objects (TŻOs) are a theoretical class of star in which a compact neutron star is surrounded by a large, diffuse envelope. Supergiant TŻOs are predicted to be almost identical in appearance to red supergiants (RSGs), with their very red colors and cool temperatures placing them at the Hayashi limit on the H-R diagram. The only features that can be used at present to distinguish TŻOs from the general RSG population are the unusually strong heavy-element and lithium lines present in their spectra. These elements are the unique products of the stars fully convective envelope linking the photosphere with the extraordinarily hot burning region in the vicinity of the neutron star core. We have recently discovered a TŻO candidate in the Small Magellanic Cloud. It is the first star to display the distinctive chemical profile of anomalous element enhancements thought to be characteristic of TŻOs; however, up-to-date models and additional observable predictions (including potential asteroseismological signatures) are required to solidify this discovery. The definitive detection of a TŻO would provide the first direct evidence for a completely new model of stellar interiors, a theoretically predicted fate for massive binary systems, and never-before-seen nucleosynthesis processes that would offer a new channel for heavy-element and lithium production in our universe.
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Olejak, A., K. Belczynski, T. Bulik, and M. Sobolewska. "Synthetic catalog of black holes in the Milky Way." Astronomy & Astrophysics 638 (June 2020): A94. http://dx.doi.org/10.1051/0004-6361/201936557.
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Aims. We present an open-access database that includes a synthetic catalog of black holes (BHs) in the Milky Way, divided by the components disk, bulge, and halo. Methods. To calculate the evolution of single and binary stars, we used the updated population synthesis code StarTrack. We applied a new model of the star formation history and chemical evolution of Galactic disk, bulge, and halo that was synthesized from observational and theoretical data. This model can be easily employed for other studies of population evolution. Results. We find that at the current Milky Way (disk+bulge+halo) contains about 1.2 × 108 single BHs with an average mass of about 14 M⊙, and 9.3 × 106 BHs in binary systems with an average mass of 19 M⊙. We present basic statistical properties of the BH population in three Galactic components such as the distributions of BH masses, velocities, or the numbers of BH binary systems in different evolutionary configurations. Conclusions. The metallicity of a stellar population has a significant effect on the final BH mass through the stellar winds. The most massive single BH in our simulation of 113 M⊙ originates from a merger of a BH and a helium star in a low-metallicity stellar environment in the Galactic halo. We constrain that only ∼0.006% of the total Galactic halo mass (including dark matter) can be hidden in the form of stellar origin BHs. These BHs cannot be detected by current observational surveys. We calculated the merger rates for current Galactic double compact objects (DCOs) for two considered common-envelope models: ∼3–81 Myr−1 for BH-BH, ∼1–9 Myr−1 for BH-neutron star (NS), and ∼14–59 Myr−1 for NS-NS systems. We show the evolution of the merger rates of DCOs since the formation of the Milky Way until the current moment with the new star formation model of the Galaxy.
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Broekgaarden, Floor S., Stephen Justham, Selma E. de Mink, Jonathan Gair, Ilya Mandel, Simon Stevenson, Jim W. Barrett, Alejandro Vigna-Gómez, and Coenraad J. Neijssel. "stroopwafel: simulating rare outcomes from astrophysical populations, with application to gravitational-wave sources★." Monthly Notices of the Royal Astronomical Society 490, no. 4 (September 27, 2019): 5228–48. http://dx.doi.org/10.1093/mnras/stz2558.
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ABSTRACT Gravitational-wave observations of double compact object (DCO) mergers are providing new insights into the physics of massive stars and the evolution of binary systems. Making the most of expected near-future observations for understanding stellar physics will rely on comparisons with binary population synthesis models. However, the vast majority of simulated binaries never produce DCOs, which makes calculating such populations computationally inefficient. We present an importance sampling algorithm, stroopwafel, that improves the computational efficiency of population studies of rare events, by focusing the simulation around regions of the initial parameter space found to produce outputs of interest. We implement the algorithm in the binary population synthesis code compas, and compare the efficiency of our implementation to the standard method of Monte Carlo sampling from the birth probability distributions. stroopwafel finds ∼25–200 times more DCO mergers than the standard sampling method with the same simulation size, and so speeds up simulations by up to two orders of magnitude. Finding more DCO mergers automatically maps the parameter space with far higher resolution than when using the traditional sampling. This increase in efficiency also leads to a decrease of a factor of ∼3–10 in statistical sampling uncertainty for the predictions from the simulations. This is particularly notable for the distribution functions of observable quantities such as the black hole and neutron star chirp mass distribution, including in the tails of the distribution functions where predictions using standard sampling can be dominated by sampling noise.
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Ciolfi, Riccardo. "Short gamma-ray burst central engines." International Journal of Modern Physics D 27, no. 13 (October 2018): 1842004. http://dx.doi.org/10.1142/s021827181842004x.
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Growing evidence connects the progenitor systems of the short-hard subclass of gamma-ray bursts (GRBs) to the merger of compact object binaries composed of two neutron stars (NSs) or of an NS and a black hole (BH). The recent observation of the binary NS (BNS) merger event GW170817 associated with GRB 170817A brought a great deal of additional information and provided further support to the above connection, even though the identification of this burst as a canonical short GRB (SGRB) remains uncertain. Decades of observational constraints and theoretical models consolidated the idea of a jet origin for the GRB prompt emission, which can also explain the multiwavelength afterglow radiation observed in most of the events. However, the mechanisms through which a BNS or NS–BH merger remnant would power a collimated outflow are much less constrained. Understanding the properties of the remnant systems and whether they can provide the right conditions for jet production has been a main driver of the great effort devoted to study BNS and NS–BH mergers, and still represents a real challenge from both the physical and the computational points of view. One fundamental open question concerns the nature of the central engine itself. While the leading candidate system is a BH surrounded by a massive accretion disk, the recent observation of plateau-shaped X-ray afterglows in some SGRBs would suggest a longer-lived engine, i.e. a metastable (or even stable) massive NS, which would also exclude NS–BH progenitors. Here we elaborate on this key aspect, considering three different scenarios to explain the SGRB phenomenology based on different hypotheses on the nature of the merger remnant. Then, we discuss the basic properties of GRB 170817A and how this event would fit within the different frameworks of the above scenarios, under the assumption that it was or was not a canonical SGRB.
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Rueda, J. A., R. Ruffini, and Y. Wang. "Induced Gravitational Collapse, Binary-Driven Hypernovae, Long Gramma-ray Bursts and Their Connection with Short Gamma-ray Bursts." Universe 5, no. 5 (May 9, 2019): 110. http://dx.doi.org/10.3390/universe5050110.
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There is increasing observational evidence that short and long Gamma-ray bursts (GRBs) originate in different subclasses, each one with specific energy release, spectra, duration, etc, and all of them with binary progenitors. The binary components involve carbon-oxygen cores (CO core ), neutron stars (NSs), black holes (BHs), and white dwarfs (WDs). We review here the salient features of the specific class of binary-driven hypernovae (BdHNe) within the induced gravitational collapse (IGC) scenario for the explanation of the long GRBs. The progenitor is a CO core -NS binary. The supernova (SN) explosion of the CO core , producing at its center a new NS ( ν NS), triggers onto the NS companion a hypercritical, i.e., highly super-Eddington accretion process, accompanied by a copious emission of neutrinos. By accretion the NS can become either a more massive NS or reach the critical mass for gravitational collapse with consequent formation of a BH. We summarize the results on this topic from the first analytic estimates in 2012 all the way up to the most recent three-dimensional (3D) smoothed-particle-hydrodynamics (SPH) numerical simulations in 2018. Thanks to these results it is by now clear that long GRBs are richer and more complex systems than thought before. The SN explosion and its hypercritical accretion onto the NS explain the X-ray precursor. The feedback of the NS accretion, the NS collapse and the BH formation produce asymmetries in the SN ejecta, implying the necessity of a 3D analysis for GRBs. The newborn BH, the surrounding matter and the magnetic field inherited from the NS, comprises the inner engine from which the GRB electron-positron ( e + e − ) plasma and the high-energy emission are initiated. The impact of the e + e − on the asymmetric ejecta transforms the SN into a hypernova (HN). The dynamics of the plasma in the asymmetric ejecta leads to signatures depending on the viewing angle. This explains the ultrarelativistic prompt emission in the MeV domain and the mildly-relativistic flares in the early afterglow in the X-ray domain. The feedback of the ν NS pulsar-like emission on the HN explains the X-ray late afterglow and its power-law regime. All of the above is in contrast with a simple GRB model attempting to explain the entire GRB with the kinetic energy of an ultrarelativistic jet extending through all of the above GRB phases, as traditionally proposed in the “collapsar-fireball” model. In addition, BdHNe in their different flavors lead to ν NS-NS or ν NS-BH binaries. The gravitational wave emission drives these binaries to merge producing short GRBs. It is thus established a previously unthought interconnection between long and short GRBs and their occurrence rates. This needs to be accounted for in the cosmological evolution of binaries within population synthesis models for the formation of compact-object binaries.
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Arun, Kenath. "Some Aspects of Binary Compact Astrophysical Objects." Mapana - Journal of Sciences 7, no. 1 (May 31, 2008): 64–70. http://dx.doi.org/10.12723/mjs.12.6.
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This paper shall look into the systems of compact astrophysical objects (black holes, neutron stars and white dwarfs) concerning mainly with binary systems. Determination of the orbital periods, velocities, etc, for such systems and also, the energy lost from the system through gravitational waves has been made, From the concept of energy loss, the merger of the two black holes in the system has been considered and the typical time required for the merger is calculated.
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Kalogera, V. "Close Binaries with Two Compact Objects." International Astronomical Union Colloquium 177 (2000): 579–84. http://dx.doi.org/10.1017/s0252921100060668.
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AbstractThe coalescence of close binary systems with two compact objects (neutron stars and black holes) are considered to be promising sources of gravitational waves for the currently built laser interferometers. Here, I review the current Galactic coalescence estimates derived both theoretically and empirically. I discuss the uncertainties involved as well as ways of obtaining an upper limit to the coalescence rate of two neutron stars.
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Deng, Yangyang, Zhongmu Li, and Wen Chen. "Simulation of Formation of Binary Compact Objects in Globular Cluster." Journal of Physics: Conference Series 2068, no. 1 (October 1, 2021): 012049. http://dx.doi.org/10.1088/1742-6596/2068/1/012049.
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Abstract Binary compact objects are the special binary systems, which were composed of compact objects (i.e., white dwarf, neutron star and black hole). They contribute a lot to the sources of gravitational waves. The study of binary compact objects in star clusters and galaxies can provide a theoretical guidance for gravitational wave detection and improve the probability of detection effectively. We simulate the formation and fraction of binary compact objects in a small globular cluster, via NBODY6++GPU, an efficient N-body simulation code. We obtain the fractions of white dwarf binaries and neutron star binaries at different ages. The results show that the dynamic interactions among stars can also result in some binary compact objects besides binary evolution.
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Mahy, L., H. Sana, M. Abdul-Masih, L. A. Almeida, N. Langer, T. Shenar, A. de Koter, et al. "The Tarantula Massive Binary Monitoring." Astronomy & Astrophysics 634 (February 2020): A118. http://dx.doi.org/10.1051/0004-6361/201936151.
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Context. Accurate stellar parameters of individual objects in binary systems are essential to constrain the effects of binarity on stellar evolution. These parameters serve as a prerequisite to probing existing and future theoretical evolutionary models. Aims. We aim to derive the atmospheric parameters of the 31 double-lined spectroscopic binaries in the Tarantula Massive Binary Monitoring sample. This sample, composed of detached, semi-detached and contact systems with at least one of the components classified as an O-type star, is an excellent test-bed to study how binarity can impact our knowledge of the evolution of massive stars. Methods. In the present paper, 32 epochs of FLAMES/GIRAFFE spectra are analysed by using spectral disentangling to construct the individual spectra of 62 components. We then apply the CMFGEN atmosphere code to determine their stellar parameters and their helium, carbon, and nitrogen surface abundances. Results. Among the 31 systems that we study in the present paper, we identify between 48 and 77% of them as detached, likely pre-interacting systems, 16% as semi-detached systems, and between 5 and 35% as systems in or close to contact phase. Based on the properties of their components, we show that the effects of tides on chemical mixing are limited. Components on longer-period orbits show higher nitrogen enrichment at their surface than those on shorter-period orbits, in contrast to expectations of rotational or tidal mixing, implying that other mechanisms play a role in this process. For semi-detached systems, components that fill their Roche lobe are mass donors. They exhibit higher nitrogen content at their surface and rotate more slowly than their companions. By accreting new material, their companions spin faster and are likely rejuvenated. Their locations in the N − v sin i diagram tend to show that binary products are good candidates to populate the two groups of stars (slowly rotating, nitrogen-enriched objects and rapidly rotating non-enriched objects) that cannot be reproduced through single-star population synthesis. Finally, we find no peculiar surface abundances for the components in (over-)contact systems, as has been suggested by evolutionary models for tidal mixing. Conclusions. This sample, consisting of 31 massive binary systems, is the largest sample of binaries composed of at least one O-type star to be studied in such a homogeneous way by applying spectral disentangling and atmosphere modelling. The study of these objects gives us strong observational constraints to test theoretical binary evolutionary tracks.
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Mas-Hesse, J. Miguel, and Miguel Cerviño. "Evolutionary population synthesis: the effect of binary systems." Symposium - International Astronomical Union 193 (1999): 550–58. http://dx.doi.org/10.1017/s0074180900206268.
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We present in this contribution our set of multi-wavelength synthesis models including the evolution of single and binary stars. The main results we have obtained can be summarized as follows: (a) massive close-binary systems will start to experience mass transfer episodes after the first 4Myr of the starburst evolution; (b) as a result of these mass transfer processes, stars of relatively low initial mass can lose completely their envelope and become a Wolf-Rayet star. In this way, the formation of WR stars is extended over longer than 15 Myr, and does not stop at 6Myr as predicted by models including only single stars; (c) WR stars can thus be coeval with red supergiants, which peak at around 10 Myr for solar metallicities; (d) the accretion of mass will originate relatively massive stars at ages for which they should have already disappeared; these stars, together with the WR stars formed in rather evolved clusters, increase the production of ionizing photons, so that the Hβ equivalent width will not drop as rapidly as predicted by models considering only individual stars; and (e) the mass transfer to compact companions will produce an additional source of high-energy radiation in the form of high-mass X-ray binaries, not predicted either by standard synthesis models.
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Taam, Ronald E. "The Formation and Evolution of Compact Stars in Binaries." International Astronomical Union Colloquium 194 (2004): 81–84. http://dx.doi.org/10.1017/s0252921100152005.
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AbstractThe stellar evolutionary processes responsible for the formation of compact objects in interacting binary systems and their evolution are described. The common envelope phase plays a crucial role in their formation and angular momentum losses associated with magnetic braking and/or mass loss are important for their evolution. An application of these processes provides the evolutionary link between classes of interacting binary systems.
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de Grijs, Richard, Chengyuan Li, and Aaron M. Geller. "The dynamical importance of binary systems in young massive star clusters." Proceedings of the International Astronomical Union 12, S316 (August 2015): 222–27. http://dx.doi.org/10.1017/s1743921315009096.
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AbstractCharacterization of the binary fractions in star clusters is of fundamental importance for many fields in astrophysics. Observations indicate that the majority of stars are found in binary systems, while most stars with masses greater than 0.5M⊙ are formed in star clusters. In addition, since binaries are on average more massive than single stars, in resolved star clusters these systems are thought to be good tracers of (dynamical) mass segregation. Over time, dynamical evolution through two-body relaxation will cause the most massive objects to migrate to the cluster center, while the relatively lower-mass objects remain in or migrate to orbits at greater radii. This process will globally dominate a cluster’s stellar distribution. However, close encounters involving binary systems may disrupt ‘soft’ binaries. This process will occur more frequently in a cluster’s central, dense region than in its periphery, which may mask the effects of mass segregation. Using high resolution Hubble Space Telescope observations, combined with sophisticated N-body simulations, we investigate the radial distributions of the main-sequence binary fractions in massive young Large Magellanic Cloud star clusters. We show that binary disruption may play an important role on very short timescales, depending on the environmental conditions in the cluster cores. This may lead to radial binary fractions that initially decline in the cluster centers, which is contrary to the effects expected from dynamical mass segregation.
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Belkus, Houria, Joris Van Bever, and Dany Vanbeveren. "The Formation and Evolution of Very Massive Stars in Dense Stellar Systems." Proceedings of the International Astronomical Union 3, S246 (September 2007): 357–58. http://dx.doi.org/10.1017/s1743921308015925.
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AbstractThe early evolution of dense stellar systems is governed by massive single star and binary evolution. Core collapse of dense massive star clusters can lead to the formation of very massive objects through stellar collisions (M≥ 1000M⊙). Stellar wind mass loss determines the evolution and final fate of these objects, and determines whether they form black holes (with stellar or intermediate mass) or explode as pair instability supernovae, leaving no remnant. We present a computationally inexpensive evolutionary scheme for very massive stars that can readily be implemented in an N-body code. Using our new N-body code ‘Youngbody’ which includes a detailed treatment of massive stars as well as this new scheme for very massive stars, we discuss the formation of intermediate mass and stellar mass black holes in young starburst regions. A more detailed account of these results can be found in Belkus, Van Bever & Vanbeveren (2007).
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Mota, Clésio E., Luis C. N. Santos, Franciele M. da Silva, César V. Flores, Tiago J. N. da Silva, and Débora P. Menezes. "Anisotropic compact stars in Rastall–Rainbow gravity." Classical and Quantum Gravity 39, no. 8 (March 24, 2022): 085008. http://dx.doi.org/10.1088/1361-6382/ac5a13.
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Abstract In this work, we investigate anisotropic effects on the equations of state (EoS) used to describe neutron and quark stars in the framework of Rastall–Rainbow gravity. All our calculations are computed using two different EoS to describe the matter contained within the star: the MIT bag model for quark stars and the IU-FSU parameterisation for the standard hadronic matter. From the values of masses and radii obtained, we can conclude that anisotropic pressure has significant consequences on the structure of compact objects. Specifically, when anisotropy is considered within general relativity, it significantly modifies the maximum stellar mass. On the other hand, when Rastall–Rainbow gravity and anisotropy are simultaneously considered, they provide the best results for the masses and radii of some important astrophysical objects such as the low-mass x-ray binary (LMXB) NGC 6397 and the extremely massive millisecond pulsating source of radio (PSR) J0740 + 6620, for instance. Radii results inferred from the Lead Radius EXperiment (PREX-2) and the compact object in the mass-gap of GW190814 event can also be described for certain values of the Rastall–Rainbow and anisotropy parameters.
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Fragos, Tassos, Jeff J. Andrews, Simone S. Bavera, Christopher P. L. Berry, Scott Coughlin, Aaron Dotter, Prabin Giri, et al. "POSYDON: A General-purpose Population Synthesis Code with Detailed Binary-evolution Simulations." Astrophysical Journal Supplement Series 264, no. 2 (February 1, 2023): 45. http://dx.doi.org/10.3847/1538-4365/ac90c1.
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Abstract Most massive stars are members of a binary or a higher-order stellar system, where the presence of a binary companion can decisively alter their evolution via binary interactions. Interacting binaries are also important astrophysical laboratories for the study of compact objects. Binary population synthesis studies have been used extensively over the last two decades to interpret observations of compact-object binaries and to decipher the physical processes that lead to their formation. Here, we present POSYDON, a novel, publicly available, binary population synthesis code that incorporates full stellar structure and binary-evolution modeling, using the MESA code, throughout the whole evolution of the binaries. The use of POSYDON enables the self-consistent treatment of physical processes in stellar and binary evolution, including: realistic mass-transfer calculations and assessment of stability, internal angular-momentum transport and tides, stellar core sizes, mass-transfer rates, and orbital periods. This paper describes the detailed methodology and implementation of POSYDON, including the assumed physics of stellar and binary evolution, the extensive grids of detailed single- and binary-star models, the postprocessing, classification, and interpolation methods we developed for use with the grids, and the treatment of evolutionary phases that are not based on precalculated grids. The first version of POSYDON targets binaries with massive primary stars (potential progenitors of neutron stars or black holes) at solar metallicity.
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van den Heuvel, Edward P. J. "High-Mass X-ray Binaries: progenitors of double compact objects." Proceedings of the International Astronomical Union 14, S346 (August 2018): 1–13. http://dx.doi.org/10.1017/s1743921319001315.
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AbstractA summary is given of the present state of our knowledge of High-Mass X-ray Binaries (HMXBs), their formation and expected future evolution. Among the HMXB-systems that contain neutron stars, only those that have orbital periods upwards of one year will survive the Common-Envelope (CE) evolution that follows the HMXB phase. These systems may produce close double neutron stars with eccentric orbits. The HMXBs that contain black holes do not necessarily evolve into a CE phase. Systems with relatively short orbital periods will evolve by stable Roche-lobe overflow to short-period Wolf-Rayet (WR) X-ray binaries containing a black hole. Two other ways for the formation of WR X-ray binaries with black holes are identified: CE-evolution of wide HMXBs and homogeneous evolution of very close systems. In all three cases, the final product of the WR X-ray binary will be a double black hole or a black hole neutron star binary.
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Koumpia, E., K. M. Ababakr, W. J. de Wit, R. D. Oudmaijer, A. Caratti o Garatti, P. Boley, H. Linz, S. Kraus, J. S. Vink, and J. B. Le Bouquin. "Resolving the MYSO binaries PDS 27 and PDS 37 with VLTI/PIONIER." Astronomy & Astrophysics 623 (March 2019): L5. http://dx.doi.org/10.1051/0004-6361/201834624.
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Context. Binarity and multiplicity appear to be a common outcome in star formation. In particular, the binary fraction of massive (OB-type) stars can be very high. In many cases, the further stellar evolution of these stars is affected by binary interactions at some stage during their lifetime. The origin of this high binarity and the binary parameters are poorly understood because observational constraints are scarce, which is predominantly due to a dearth of known young massive binary systems. Aims. We aim to identify and describe massive young binary systems in order to fill in the gaps of our knowledge of primordial binarity of massive stars, which is crucial for our understanding of massive star formation. Methods. We observed the two massive young stellar objects (MYSOs) PDS 27 and PDS 37 at the highest spatial resolution provided by VLTI/PIONIER in the H-band (1.3 mas). We applied geometrical models to fit the observed squared visibilities and closure phases. In addition, we performed a radial velocity analysis using published VLT/FORS2 spectropolarimetric and VLT/X-shooter spectroscopic observations. Results. Our findings suggest binary companions for both objects at 12 mas (30 au) for PDS 27 and at 22–28 mas (42–54 au) for PDS 37. This means that they are among the closest MYSO binaries resolved to date. Conclusions. Our data spatially resolve PDS 27 and PDS 37 for the first time, revealing two of the closest and most massive (>8 M⊙) YSO binary candidates to date. PDS 27 and PDS 37 are rare but great laboratories to quantitatively inform and test the theories on formation of such systems.
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De, K., M. M. Kasliwal, E. O. Ofek, T. J. Moriya, J. Burke, Y. Cao, S. B. Cenko, et al. "A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary." Science 362, no. 6411 (October 11, 2018): 201–6. http://dx.doi.org/10.1126/science.aas8693.
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Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 1050ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.
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Cardoso, Vitor, Caio F. B. Macedo, Kei-ichi Maeda, and Hirotada Okawa. "ECO-spotting: looking for extremely compact objects with bosonic fields." Classical and Quantum Gravity 39, no. 3 (January 31, 2022): 034001. http://dx.doi.org/10.1088/1361-6382/ac41e7.
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Abstract Black holes are thought to describe the geometry of massive, dark compact objects in the Universe. To further support and quantify this long-held belief requires knowledge of possible, if exotic alternatives. Here, we wish to understand how compact can self-gravitating solutions be. We discuss theories with a well-posed initial value problem, consisting in either a single self-interacting scalar, vector or both. We focus on spherically symmetric solutions, investigating the influence of self-interacting potentials into the compactness of the solutions, in particular those that allow for flat-spacetime solutions. We are able to connect such stars to hairy black hole solutions, which emerge as a zero-mass black hole. We show that such stars can have light rings, but their compactness is never parametrically close to that of black holes. The challenge of finding black hole mimickers to investigate full numerical-relativity binary setups remains open.
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Bodensteiner, J., T. Shenar, and H. Sana. "Investigating the lack of main-sequence companions to massive Be stars." Astronomy & Astrophysics 641 (September 2020): A42. http://dx.doi.org/10.1051/0004-6361/202037640.
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Context. About 20% of all B-type stars are classical Be stars – stars whose spectra imply the presence of a circumstellar decretion disk. The disk phenomenon is strongly correlated with rapid rotation, the origin of which remains unclear. It may be rooted in single- or binary-star evolution. In the framework of the binary channel, the initially more massive star transfers mass and angular momentum to the original secondary, which becomes a Be star. The system then evolves into a Be binary with a post-main-sequence companion, which, depending on the companion mass, may later be disrupted in a supernova event. Hence, if the binary channel dominates the formation of Be stars, one may expect a strong lack of close Be binaries with main sequence (MS) companions. Aims. We want to test the prediction of the binary channel. Through an extensive, star-by-star review of the literature of a magnitude-limited sample of Galactic early-type Be stars, we investigate whether Be binaries with MS companions are known to exist. Methods. Our sample is constructed from the BeSS database and cross-matched with all available literature on the individual stars. Archival and amateur spectra are used to verify the existing literature when conflicting reports are found. Results. Out of an initial list of 505 Be stars, we compile a final sample of 287 Galactic Be stars earlier than B1.5 with V ≤ 12 mag. Out of those, 13 objects were reported as Be binaries with known post-MS companions (i.e., compact objects or helium stars) and 11 as binaries with unknown, uncertain or debated companions. We find no confirmed reports of Be binaries with MS companions. For the remaining 263 targets, no significant reports of multiplicity exist in the literature, implying that they are either Be binaries with faint companions, or truly single. Conclusions. The clear lack of reported MS companions to Be stars, which stands in contrast to the high number of detected B+B MS binaries, strongly supports the hypothesis that early-type Be stars are binary interaction products that spun up after mass and angular momentum transfer from a companion star. Taken at face value, our results may suggest that a large majority of the early-type Be stars have formed through binary mass-transfer.
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Niemela, Virpi S., Roberto Gamen, Nidia I. Morrell, and Sixto Giménez Benítez. "Wolf-Rayet binaries: old friends and new acquaintances." Symposium - International Astronomical Union 193 (1999): 26–37. http://dx.doi.org/10.1017/s0074180900204890.
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Observations of WR stars in binary systems are discussed, emphasizing constraints on our knowledge of the binary frequency of WR stars, and of WR stars as a distinctive class of objects. Radial velocity orbits of newly discovered binaries, e.g., WR 29, a short period WN7+OB binary in our Galaxy, and SMC/AB 7, a massive WN+O7 binary in the Small Magellanic Cloud, are presented. New spectroscopic observations of binary systems with previously known orbits are also reported, showing in the case of WR 21 evidence of change of the orbital elements as derived from different spectral lines. An elliptic orbit for CV Ser is also illustrated.
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Kaper, L., A. Van der Meer, and A. H. Tijani. "High-Mass X-Ray Binaries and OB Runaway Stars." International Astronomical Union Colloquium 191 (August 2004): 128–31. http://dx.doi.org/10.1017/s0252921100008617.
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AbstractHigh-mass X-ray binaries (HMXBs) represent an important phase in the evolution of massive binary systems and provide fundamental information on the properties of the OB-star primaries and their compact secondaries (neutron star, black hole). Recent observations indicate that the neutron stars in some of these systems (Vela X-1, 4U 1700-37) are more massive than the canonical mass of 1.35 M⊙. These observations have important consequences for the equation of state at supranuclear densities and the formation mechanism(s) of neutron stars and black holes: supernovae and gamma-ray bursts. As a consequence of the supernova explosion that produced the compact star in these systems, HMXBs have high space velocities and thus are runaways. Alternatively, OB-runaway stars can be ejected from a cluster through dynamical interactions. Observations obtained with the Hipparcos satellite indicate that both scenarios are at work.
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Fragione, Giacomo, and Fabio Antonini. "Massive binary star mergers in galactic nuclei: implications for blue stragglers, binary S-stars, and gravitational waves." Monthly Notices of the Royal Astronomical Society 488, no. 1 (June 21, 2019): 728–38. http://dx.doi.org/10.1093/mnras/stz1723.
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ABSTRACT Galactic nuclei are often found to contain young stellar populations and, in most cases, a central supermassive black hole (SMBH). Most known massive stars are found in binaries or higher multiplicity systems, and in a galactic nucleus the gravitational interaction with the SMBH can affect their long-term evolution. In this paper, we study the orbital evolution of stellar binaries near SMBHs using high precision N-body simulations, and including tidal forces and post-Newtonian corrections to the motion. We focus on the Lidov–Kozai (LK) effect induced by the SMBH on massive star binaries. We investigate how the properties of the merging binaries change with varying the SMBH mass, the slope of the initial mass function, the distributions of the binary orbital parameters, and the efficiency in energy dissipation in dissipative tides. We find that the fraction of merging massive binary stars is in the range ∼4–$15{{\ \rm per\ cent}}$ regardless of the details of the initial distributions of masses and orbital elements. For a Milky Way-like nucleus, we find a typical rate of binary mergers $\Gamma \approx 1.4\times 10^{-7} {\, \rm yr}^{-1}$. The merger products of massive binaries can be rejuvenated blue-straggler stars, more massive than each of their original progenitors, and G2-like objects. Binary systems that survive the LK cycles can be source of X-rays and gravitational waves, observable with present and upcoming instruments.
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Warner, Brian. "Cataclysmic Variable Stars." Highlights of Astronomy 11, no. 1 (1998): 16–27. http://dx.doi.org/10.1017/s1539299600019924.
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The evolution of single stars on and away from the main sequence is well understood. A degenerate core is formed in a star as the star leaves the main sequence and expands to a giant with a radius typically 50 - 500 Ro . Observationally it is known that most stars are members of binary systems, and among these many have orbital periods less than 100 y. It can happen, therefore, that the expanding envelope of the primary of a binary system can reach to the secondary. As this happens, the primary fills its Roche tidal lobe and transfers matter to the secondary; if the primary has a radiative envelope the rate at which this occurs exceeds the Eddington limit of the secondary, which therefore repels the incoming gas, forming a common envelope around the two stars. Friction within the envelope causes the stars to spiral towards each other until the energy and angular momentum extracted from the binary orbit and transferred to the envelope are sufficient to eject the common envelope as a planetary nebula, leaving a short period binary comprising a white dwarf and a main sequence star.This mechanism of producing short period binaries containing white dwarfs, proposed by Ostriker and by Paczynski (1976), is the probable origin of the class of objects known as Cataclysmic Variable Stars (CVs), which encompass the classical novae, dwarf novae, novalike variables and a variety of related objects. Evidence has been accumulating for forty years (Crawford & Kraft 1956, Warner 1995a) that every CV consists of a secondary star (usually a dwarf, but a few systems contain giants) filling its Roche lobe and transferring mass to a white dwarf primary. In systems of normal chemical composition the orbital periods lie between 75 mins and ~250 d, with the majority having . A few hydrogen-free systems are known for which 17 mins < Porb < 50 mins. It should be noted that CVs are very compact binary systems: for h such a binary would fit inside the Sun.
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Mermilliod, Jean-Claude, and Beatriz García. "Spectroscopic Binaries in Young Open Clusters." Symposium - International Astronomical Union 200 (2001): 191–98. http://dx.doi.org/10.1017/s0074180900225217.
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We have analysed the binarity and multiplicity characteristics of 120 O-type stars in 22 very young open clusters and found marked differences between the “rich” (N ≥ 6 O-type stars and primaries) and “poor” (N = 1) clusters. In the rich clusters, the binary frequencies vary between 14% (1 SB among 7 stars) and 80% (8 SBs among 10 stars). Multiple systems seem not to be frequent and stars are spread all over the cluster area. In poor clusters, the binary frequency of the O-type objects is nearly 100%, with orbital periods around 3 days. Several binaries are also eclipsing. Additional companions are always present. They form either hierarchical multiple stars or trapezium systems. These massive multiple systems are generally found close to the cluster center, although there are exceptions.
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Lagos, F., M. R. Schreiber, S. G. Parsons, B. T. Gänsicke, and N. Godoy. "Most EL CVn systems are inner binaries of hierarchical triples." Monthly Notices of the Royal Astronomical Society: Letters 499, no. 1 (October 21, 2020): L121—L125. http://dx.doi.org/10.1093/mnrasl/slaa164.
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ABSTRACT In spite of their importance for modern astronomy, we do not fully understand how close binary stars containing at least one white dwarf form from main-sequence binary stars. The discovery of EL CVn binaries, close pre-white dwarfs with A/F main-sequence star companions, offers now the unique possibility to test models of close compact binary star formation. Binary evolution theories predict that these EL CVn stars descend from very close main-sequence binaries with orbital periods shorter than 3 d. If this is correct, nearly all EL CVn stars should be inner binaries of hierarchical triples because more than 95 per cent of very close main-sequence binaries (the alleged progenitor systems) are found to be hierarchical triples. We here present SPHERE/IRDIS observations of five EL CVn binaries, finding in all of them tertiary objects, as predicted. We conclude that EL CVn systems are inner binaries of hierarchical triples and indeed descend from very close main-sequence binaries that experience stable mass transfer.
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Bodensteiner, J., D. Baade, J. Greiner, and N. Langer. "Infrared nebulae around bright massive stars as indicators for binary interactions." Astronomy & Astrophysics 618 (October 2018): A110. http://dx.doi.org/10.1051/0004-6361/201832722.
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Context. Recent studies show that more than 70% of massive stars do not evolve as effectively single stars, but as members of interacting binary systems. The evolution of these stars is thus strongly altered compared to similar but isolated objects. Aims. We investigate the occurrence of parsec-scale mid-infrared nebulae around early-type stars. If they exist over a wide range of stellar properties, one possible overarching explanation is non-conservative mass transfer in binary interactions, or stellar mergers. Methods. For ∼3850 stars (all OBA stars in the Bright Star Catalogue (BSC), Be stars, BeXRBs, and Be+sdO systems), we visually inspect WISE 22 μm images. Based on nebular shape and relative position, we distinguish five categories: offset bow shocks structurally aligned with the stellar space velocity, unaligned offset bow shocks, and centered, unresolved, and not classified nebulae. Results. In the BSC, we find that 28%, 13%, and 0.4% of all O, B, and A stars, respectively, possess associated infrared (IR) nebulae. Additionally, 34/234 Be stars, 4/72 BeXRBs, and 3/17 Be+sdO systems are associated with IR nebulae. Conclusions. Aligned or unaligned bow shocks result from high relative velocities between star and interstellar medium (ISM) that are dominated by the star or the ISM, respectively. About 13% of the centered nebulae could be bow shocks seen head- or tail-on. For the rest, the data disfavor explanations as remains of parental disks, supernova remnants of a previous companion, and dust production in stellar winds. The existence of centered nebulae also at high Galactic latitudes strongly limits the global risk of coincidental alignments with condensations in the ISM. Mass loss during binary evolution seems a viable mechanism for the formation of at least some of these nebulae. In total, about 29% of the IR nebulae (2% of all OBA stars in the BSC) may find their explanation in the context of binary evolution.
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Mahy, L., C. Lanthermann, D. Hutsemékers, J. Kluska, A. Lobel, R. Manick, B. Miszalski, M. Reggiani, H. Sana, and E. Gosset. "Multiplicity of Galactic luminous blue variable stars." Astronomy & Astrophysics 657 (December 20, 2021): A4. http://dx.doi.org/10.1051/0004-6361/202040062.
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Context. Luminous blue variables (LBVs) are characterised by strong photometric and spectroscopic variability. They are thought to be in a transitory phase between O-type stars on the main sequence and the Wolf-Rayet stage. Recent studies also evoked the possibility that they might be formed through binary interaction. Only a few are known in binary systems so far, but their multiplicity fraction is still uncertain. Aims. We derive the binary fraction of the Galactic LBV population. We combine multi-epoch spectroscopy and long-baseline interferometry to probe separations from 0.1 to 120 mas around confirmed and candidate LBVs. Methods. We used a cross-correlation technique to measure the radial velocities of these objects. We identified spectroscopic binaries through significant radial velocity variability with an amplitude larger than 35 km s−1. We also investigated the observational biases to take them into account when we established the intrinsic binary fraction. We used CANDID to detect interferometric companions, derive their flux fractions, and their positions on the sky. Results. From the multi-epoch spectroscopy, we derive an observed spectroscopic binary fraction of 26−10+16%. Considering period and mass ratio ranges from log(Porb) = 0 − 3 (i.e. from 1 to 1000 days), q = 0.1 − 1.0, and a representative set of orbital parameter distributions, we find a bias-corrected binary fraction of 62−24+38%. Based on data of the interferometric campaign, we detect a binary fraction of 70 ± 9% at projected separations between 1 and 120 mas. Based on the derived primary diameters and considering the distances of these objects, we measure for the first time the exact radii of Galactic LBVs to be between 100 and 650 R⊙. This means that it is unlikely that short-period systems are included among LBV-like stars. Conclusions. This analysis shows for the first time that the binary fraction in the Galactic LBV population is large. If they form through single-star evolution, their orbit must be large initially. If they form through a binary channel, the implication is that either massive stars in short binary systems must undergo a phase of fully non-conservative mass transfer to be able to sufficiently widen the orbit to form an LBV, or that LBVs form through merging in initially binary or triple systems. Interferometric follow-up would provide the distributions of orbital parameters at more advanced stages and would serve to quantitatively test the binary evolution in massive stars.
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Meurs, E. J. A., and E. P. J. van den Heuvel. "The galactic number of Wolf-Rayet stars produced via close binary evolution." Symposium - International Astronomical Union 163 (1995): 329–30. http://dx.doi.org/10.1017/s0074180900202246.
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Wolf-Rayet stars may have evolved from massive close binary systems, as a result of the mass transfer processes in such systems. A substantial fraction of all WR stars known is, indeed, found in close binaries, with massive early-type companions. After the outer layers of the initial primary have been removed during Roche Lobe Over-Flow, the remaining stellar core may be a helium-burning helium star, classified observation ally as a WR star. The fraction of such evolved binaries among main-sequence stars can be computed, following recipes from stellar- and galactic evolution and assuming steady, standard-IMF star formation over the last ∼ 109 yr in our Galaxy. Combining these results with the stellar PMF yields the total galactic number of such objects, or alternatively the number expected within, e.g., 3 kpc from the Sun. Comparison with observed numbers shows that the close binary produced WR stars should constitute a significant fraction of all WR stars, the exact fraction being dependent on the lower mass limit for WR star production (and also the duration of WR characteristics in the helium star's lifetime). The mass transfer processes in close binary systems probably allow this limit to be lower than in the case of a single WR star. Another favourable comparison regards the computed and observed numbers of persistent strong, massive X-ray binaries. Finally, second-phase WR stars are likely to comprise 5 — 10 % of the number of normal, first-stage WR binaries.