Binary Parameters Research Articles

Astrophysical and relativistic modeling of the recoiling black hole candidate in quasar 3C 186

The compact object in quasar 3C 186 is one of the most promising recoiling black hole candidates, exhibiting both an astrometric displacement between the quasar and the host galaxy as well as a spectroscopic shift between broad and narrow lines. 3C 186 also presents a radio jet that, when projected onto the plane of the sky, appears to be perpendicular to the quasar-galaxy displacement. Assuming a gravitational-wave kick is indeed responsible for the properties of 3C 186 and using state-of-the-art relativistic modeling, we show that current observations allow for exquisite modeling of the recoiling black hole. Most notably, we find that the kick velocity and the black hole spin are almost collinear with the line of sight and the two former vectors appear perpendicular to each other only because of a strong projection effect. The targeted configuration requires substantial fine-tuning: while there is a region in the black hole binary parameter space that is compatible with 3C 186, the observed system appears to be a rare occurrence. Using archival radio observations, we explored different strategies that could potentially confirm or rule out our interpretation. In particular, we developed two observational tests that rely on the brightness ratio between the approaching and receding jet as well as the asymmetry of the jet lobes. While the available radio data provide loose constraints, deeper observations have the unique potential of unveiling the nature of 3C 186.

A new pulsar timing model for scalar-tensor gravity with applications to PSR J2222-0137 and pulsar-black hole binaries

Context. Scalar-tensor gravity (STG) theories are well-motivated alternatives to general relativity (GR). One class of STG theories, Damour–Esposito–Farèse (DEF) gravity, has a massless scalar field with two arbitrary coupling parameters. We are interested in this theory because, despite its simplicity, it predicts a wealth of different phenomena, such as dipolar gravitational wave emission and spontaneous scalarisation of neutron stars (NSs). These phenomena of DEF gravity can be tested by timing binary radio pulsars. In the methods used so far, intermediate phenomenological post-Keplerian (PK) parameters are measured by fitting the corresponding timing model to the timing data whose values are then compared to the predictions from the alternative theory being tested. However, this approach loses information between intermediate steps and does not account for possible correlations between PK parameters. Aims. We aim to develop a new binary pulsar timing model ‘DDSTG’ (called after Damour, Deruelle and STG) to enable more precise tests of STG theories based on a minimal set of binary parameters. The expressions for PK parameters in DEF gravity are self-consistently incorporated into the model. PK parameters depend on two masses which are now directly fitted to the data without intermediate steps. The new technique takes into account all possible correlations between PK parameters naturally. Methods. Grids of physical parameters of NSs were calculated in the framework of DEF gravity for a set of 11 equations of state. Automatic differentiation (AutoDiff) technique was employed, which aids in the calculation of gravitational form factors of NSs with a higher precision than in previous works. The pulsar timing program TEMPO was selected as a framework for the realisation of the DDSTG model. The implemented model is applicable to any type of pulsar companions. We also simulated realistic future radio-timing datasets for a number of large radio observatories for the binary pulsar PSR J2222-0137 and three generic pulsar-black hole (PSR-BH) systems. Results. We applied the DDSTG model to the most recently published observational data for PSR J2222-0137. The obtained limits on DEF gravity parameters for this system confirm and improve previous results. New limits are also the most reliable because DEF gravity is directly fitted to the data. We argue that future observations of PSR J2222-0137 can significantly improve the limits and that PSR-BH systems have the potential to place the tightest limits in certain areas of the DEF gravity parameter space.

Development of a consistent geochemical model of the Mg(OH)2–MgCl2–H2O system from 25°C to 120°C

The formation of magnesium chloride-hydroxide salts (magnesium hydroxychlorides) has implications for many geochemical processes and technical applications. For this reason, a thermodynamic database for evaluating the Mg(OH)2–MgCl2–H2O ternary system from 0 °C–120 °C has been developed based on extensive experimental solubility data. Internally consistent sets of standard thermodynamic parameters (ΔGf°, ΔHf°, S°, and CP) were derived for several solid phases: 3 Mg(OH)2:MgCl2:8H2O, 9 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2: 2H2O(s), brucite (Mg(OH)2), bischofite (MgCl2:6H2O), and MgCl2:4H2O. First, estimated values for the thermodynamic parameters were derived using a component addition method. These parameters were combined with standard thermodynamic data for Mg2+(aq) consistent with CODATA (Cox et al., 1989) to generate temperature-dependent Gibbs energies for the dissolution reactions of the solid phases. These data, in combination with values for MgOH+(aq) updated to be consistent with Mg2+-CODATA, were used to compute equilibrium constants and incorporated into a Pitzer thermodynamic database for concentrated electrolyte solutions. Phase solubility diagrams were constructed as a function of temperature and magnesium chloride concentration for comparisons with available experimental data. To improve the fits to the experimental data, reaction equilibrium constants for the Mg-bearing mineral phases, the binary Pitzer parameters for the MgOH+ — Cl− interaction, and the temperature-dependent coefficients for those Pitzer parameters were constrained by experimental phase boundaries and to match phase solubilities. These parameter adjustments resulted in an updated set of standard thermodynamic data and associated temperature-dependent functions. The resulting database has direct applications to investigations of magnesia cement formation and leaching, chemical barrier interactions related to disposition of heat-generating nuclear waste, and evaluation of magnesium-rich salt and brine stabilities at elevated temperatures.

Calculations of solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in aqueous solutions with accurate thermodynamic models

Determining solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in aqueous solutions is essential for various applications of noble gases in geological processes and for understanding the migration and accumulation of helium. This study developed two thermodynamic models for calculations of solubilities of five pure noble gases (i.e. He, Ne, Ar, Kr, and Xe) and He–CO2/CH4/N2 gas mixtures in water and in aqueous NaCl solution. The first model is constructed by extending the improved SAFT-LJ equation of state (EOS) to five binary H2O-noble gas systems and four ternary systems (i.e. H2O–He–NaCl, H2O–He–CO2, H2O–He–CH4, and H2O–He–N2). Both the non-ideality of aqueous phase and that of vapor phase of these systems were described using the improved SAFT-LJ EOS (φ-φ model). The second model is developed by modifying the gas solubility model proposed by Duan and his coworkers (one type of γ-φ model). The Pitzer theory was used to describe the non-ideality of aqueous phase and the improved SAFT-LJ EOS was used to describe the non-ideality of vapor phase. Both binary adjustable parameters of the improved SAFT-LJ EOS and parameters of the modified solubility model for pure gas were evaluated from experimental solubility data for pure gas. Both models are predictive for solubilities of gas mixtures since there is no need to evaluate their parameters from solubility data of gas mixtures.Comparisons of calculations of two models with experimental data show that both models can well represent solubilities and Henry's coefficients of five noble gases in pure water, as well as the solubility of He in aqueous NaCl solutions over a wide P-T range (273–600 K, 1–2000 bar for the solubility of He in water). The absolute average deviation of the improved SAFT-LJ EOS from experimental solubility data for five noble gases in pure water is 3.14% and that of the modified solubility model is 2.21%. Predictions of the improved SAFT-LJ EOS for Henry's coefficients for He in the He–CO2–H2O system are consistent with available experimental data. According to predictions of the improved SAFT-LJ EOS, Henry's coefficient for He in the He–CO2–H2O system is always lower than that in the He–H2O system at the same depth. Within 0–5 km depth, He solubility of He–CO2 gas mixture is much greater than that of pure He at the same depth and He partial pressure, He solubility of He–N2 mixture is a little greater than that of pure He, and He solubility of He–CH4 mixture is between that of He–CO2 mixture and that of He–N2 mixture. A computer program for calculations of solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in pure water and in aqueous NaCl solutions can be obtained from the corresponding author via email.

Particle Swarm Optimization Based Feature Selection Using Factorial Design

Feature selection, a common and crucial problem in current scientific research, is a crucial data preprocessing technique and a combinatorial optimization task. Feature selection aims to select a subset of informative and appropriate features from the original feature dataset. Therefore, improving performance on the classification task requires processing the original data using a feature selection strategy before the learning process. Particle swarm optimization, one of the metaheuristic algorithms that prevents the growth of computing complexity, can solve the feature selection problem satisfactorily and quickly with appropriate classification accuracy since it has local optimum escape strategies. There are arbitrary trial and error approaches described separately in the literature to determine the critical binary particle swarm optimization parameters, which are the inertial weight, the transfer function, the threshold value, and the swarm size, that directly affect the performance of the binary particle swarm optimization algorithm parameters used in feature selection. Unlike these approaches, this paper enables us to obtain scientific findings by evaluating all binary particle swarm optimization parameters together with the help of a statistically based factorial design approach. The results show how well the threshold and the transfer function have statistically affected the binary particle swarm optimization algorithm performance.

Bayesian Synthesis of Astrometric Wobble and Total Light Curves in Close Binary Supermassive Black Holes

We test the potential of Bayesian synthesis of upcoming multi-instrument data to extract orbital parameters and individual light curves of close binary supermassive black holes (CB-SMBH) with subparsec separations. Next-generation interferometers, will make possible the observation of astrometric wobbles in CB-SMBH. Combining them with periodic variable time-domain data from surveys like the Vera C. Rubin Legacy Survey of Space and Time, allows for more information on CB-SMBH candidates compared to standalone observational methods. Our method reliably determines binary parameters and component fluxes from binary total flux across long-term, intermediate, and short-term binary dynamics and observational configurations, assuming 10 annual observations, even in short period “q-accrete” objects. Expected CB-SMBH astrometric wobbles constructed from binary dynamical parameters might serve in refining observational strategies for CB-SMBH. Combination of inferred mass ratio, light curves of binary components, and observed photocenter wobbles can be a proxy for the activity states of CB-SMBH components.

Cubic-two-state equation of state for modeling liquid-liquid and vapor-liquid equilibria of nitriles + hydrocarbons or water mixtures

The cubic-two-state (CTS) equation of state (EoS) was employed for modeling the liquid-liquid and vapor-liquid equilibria of nitriles + hydrocarbons (alkanes and aromatics) or water mixtures. For nitriles, the five pure compound parameters were determined by fitting the model simultaneously to experimental saturation pressure, density of saturated liquid, enthalpy of vaporization and liquid-liquid equilibrium data when mixed with n-dodecane. For alkanes, the pure parameters were those determined from conventional corresponding states correlations for Soave-Redlich-Kwong EoS. The van der Waals mixing and combining rules were applied for dispersive parameter and covolume, with a temperature-dependent binary parameter. In the case of nitrile mixtures with aromatics and water, cross-association were considered with the previously published CTS combining rules, and no association binary parameters were required. The correlations were very good in all cases. The model was also able to predict selective extraction of sulfur compounds (benzothyophene and benzothyophene 1,1-oxide) from alkanes. Because of its simplicity, therefore, the CTS EoS is a very attractive option for process simulation involving this class of mixtures.

Transgender Women Exhibit a Distinct Stress Echocardiography Profile Compared With Age-Matched Cisgender Counterparts: The Mayo Clinic Women’s Heart Clinic Experience

Stress echocardiographic (SE) testing is an important modality in cardiovascular risk stratification and obstructive coronary artery disease assessment. Binary sex-based parameters are classically used for the interpretation of these studies, even among transgender women (TGW). Coronary artery disease is a leading cause of morbidity and mortality in this population. Yet, it remains unclear whether TGW exhibit a distinct stress testing profile from their cisgender counterparts. Using a matched case-control study design, the authors compared the echocardiographic stress testing profiles of TGW (n=43) with those of matched cisgender men (CGM; n=84) and cisgender women (CGW; n=86) at a single center. Relevant data, including demographics, comorbidities, and cardiac testing data, were manually extracted from the patients' charts. The prevalence of hypertension and dyslipidemia was similar between TGW and CGW and lower than that of CGM (P=.003 and P=.009, respectively). The majority of comorbidities and laboratory values were similar. On average, TGW had higher heart rates than CGM (P=.002) and had lower blood pressures than CGM and CGW (P<.05). TGW's double product and metabolic equivalents were similar to those among CGW and lower than those of CGM (P=.016 and P=.018, respectively). On echocardiography, left ventricular end-diastolic and end-systolic diameters among TGW were similar to those of CGW but lower than those of CGM (P=.023 and P=.018, respectively). Measures of systolic and diastolic function, except for exercise mitral valve E/e' ratio, which was lower in TGW than CGW (P=.029), were largely similar among the three groups. There was no difference in the wall motion score index, and therefore, no difference in the percentage of positive SE test results. This study shows, for the first time, that TGW have a SE profile that is distinct from that of their cisgender counterparts. Larger, multicenter, prospective studies are warranted to further characterize the SE profile of TGW.

Diffusion coefficients and atomic mobilities in the BCC phase of the Al–Nb–V system

Diffusion coefficients in the BCC phase of the Al–Nb–V ternary system are studied for the first time, including an assessment of the atomic mobilities. Ternary interdiffusion coefficients are obtained from the intersecting diffusion paths of several sets of diffusion couples that are annealed at both 1100 °C and 1200 °C. Existing experimental data from the pertinent binary systems are also employed for the assessments of atomic mobilities using the 1-parameter Z-Z-Z binary diffusion coefficient model developed by Zhong et al [1]. Interdiffusion coefficients in the BCC region of the Al–V system are also extracted through a forward-simulation analysis and incorporated into the mobility modeling. A complete description of diffusion in the BCC phase of the Al–Nb–V system is presented following the Binary and Cross-Binary Parameters Only (BCBPO) model developed by Zhong and Zhao [2]. Our data will be valuable input to diffusion-related simulation of refractory high entropy alloys containing aluminum.

A comprehensive X-ray analysis of the massive O-type binary HD 93250 over two decades

Massive star winds are known to be responsible for X-ray emission arising from wind plasma heated by the strong shocks up to temperatures of 10$^6$--10$^7$ K in the case of colliding wind binaries. The investigation of X-ray emission from massive stars thus constitutes a valuable tool for identifying binaries, which is otherwise a difficult task using classical techniques. We investigated thermal and nonthermal X-ray emission from the massive O-type star HD\,93250 to unveil its binary orbital parameters independently. To meet our goal, we analyzed X-ray data obtained with European Photon Imaging Camera on board XMM-Newton spanning over sim 19 years. Additionally, we analyzed NuSTAR observations of HD\,93250 taken at various epochs. We determine the variability timescale of the X-ray emission to be 193.8pm 1.3\,d, in full agreement with the 194.3pm 0.4\,d period derived from the astrometric orbit. The X-ray spectrum of HD\,93250 is well explained by a three-temperature thermal plasma emission model with temperatures of 0.26, 1.0, and 3.3 keV. The resulting X-ray flux varies in compliance with the typical colliding wind emission from eccentric massive binaries where it enhances near periastron passage and decreases gradually close to apastron in proportion to the inverse of the binary separation. The periastron-to-apastron X-ray emission ratio points to an eccentricity range of 0.20-0.25, once again in agreement with the previously determined astrometric orbit. Finally, we do not detect any hard X-ray emission attributable to nonthermal emission above 10 keV. Given the derived plasma temperature, the strong phase-locked variability, and the significant over-luminosity in X-rays, we establish that the X-ray emission from HD\,93250 is dominated by the colliding-wind region. Our results lend support to the idea that X-ray time analysis of massive stars constitutes a relevant tool for investigating their multiplicity and for extracting relevant information on their basic orbital parameters ---such as period and eccentricity--- independently of any orbital solution derived from classical techniques.

3.05 kW, 13.7 GHz linewidth fiber amplifier based on PRBS phase modulation for SBS suppression

In this paper, we establish a multi-stage fiber amplifier with pseudo-random binary sequence (PRBS) phase modulation. The stimulated Brillouin gain spectra of the main amplifier with both the unmodulated and pseudo-random binary sequence phase modulated configuration are measured (with corresponding output power), and the stimulated Brillouin scattering (SBS) threshold is investigated experimentally and theoretically. The pseudo-random binary sequence phase modulation parameters are optimized by theoretical simulation. With a two-stage preamplifier chain and a counter-pumping main amplifier stage, a maximum 3.05 kW output power with a slope efficiency of 85.9% is obtained experimentally. The central wavelength of the fiber amplifier is 1050 nm, associated with a full-width at half-maximum linewidth of 13.7 GHz. The stimulated Brillouin scattering reflectivity is below 0.01% at 3.05 kW at 13.7 GHz, which indicates that stimulated Brillouin scattering can be suppressed efficiently at this power and linewidth level.

Detection of Contact Binary Candidates Observed By TESS Using the Autoencoder Neural Network

A contact binary may be the progenitor of a red nova that eventually produces a merger event and have a cut-off period of around 0.2 days. Therefore, a large number of contact binaries is needed to search for the progenitor of red novae and to study the characteristics of short-period contact binaries. In this paper, we employ the Phoebe program to generate a large number of light curves based on the fundamental parameters of contact binaries. Using these light curves as samples, an autoencoder model is trained, which can reconstruct the light curves of contact binaries very well. When the error between the output light curve from the model and the input light curve is large, it may be due to other types of variable stars. The goodness of fit (R 2) between the output light curve from the model and the input light curve is calculated. Based on the thresholds for global goodness of fit (R 2), period, range magnitude, and local goodness of fit (R 2), a total of 1322 target candidates were obtained.

TESS Photometry of AM Her and AR UMa: Binary Parameters, Cyclotron Emission Modeling, and Mass Transfer Duty Cycles

Transiting Exoplanet Survey Satellite (TESS) photometry of the polars AM Herculis (AM Her) and AR Ursae Majoris (AR UMa) is presented, along with high-speed photometry. AM Her shows a variety of high states with frequent transitions between them. TESS photometry of AR UMa in the low state reveals no evidence of accretion, while the McDonald 2.1 m telescope caught AR UMa in its high accretion state. Roche-lobe overflow is shut off during low states of AR UMa, while accretion often still takes place during low states of AM Her. We derive inclinations of 50° and 70° for AM Her and AR UMa respectively. To model the high-state light curves of AM Her, we employ a self-organized map light-curve classification scheme to establish common accretion configurations. The cyclotron radiation properties then allow the production of emission region maps on the surface of the white dwarf. The accretion geometry of AM Her is most consistent with a multipolar field structure. The high-state photometry of AR UMa has stochastic accretion flaring, which we attribute to magnetically buffeted mass transfer through the inner Lagrangian point L1. To consider this possibility, we examine the magnetism of both stars and argue that the local magnetic field near L1 can initiate short-lived accretion events and affect transitions between high and low accretion states in both AM Her and AR UMa. In particular, AR UMa has the low state as its default, while AM Her and most other active polars are in the high state by default.

Analysis of the Parameters of Pre-Cataclysmic Binaries with sdB-subdwarfs: V1828 Aql

Analysis of the Parameters of Pre-Cataclysmic Binaries with sdB-subdwarfs: V1828 Aql

Beyond the Background: Gravitational-wave Anisotropy and Continuous Waves from Supermassive Black Hole Binaries

Pulsar timing arrays have found evidence for a low-frequency gravitational-wave background (GWB). Assuming that the GWB is produced by supermassive black hole binaries (SMBHBs), the next gravitational-wave (GW) signals astronomers anticipate are continuous waves (CWs) from single SMBHBs and their associated GWB anisotropy. The prospects for detecting CWs and anisotropy are highly dependent on the astrophysics of SMBHB populations. Thus, information from single sources can break degeneracies in astrophysical models and place much more stringent constraints than the GWB alone. We simulate and evolve SMBHB populations, model their GWs, and calculate their anisotropy and detectability. We investigate how varying components of our semianalytic model, including the galaxy stellar mass function, the SMBH–host galaxy relation (M BH–M bulge), and the binary evolution prescription, impact the expected detections. The CW occurrence rate is greatest for few total binaries, high SMBHB masses, large scatter in M BH–M bulge, and long hardening times. The occurrence rate depends most on the binary evolution parameters, implying that CWs offer a novel avenue to probe binary evolution. The most detectable CW sources are in the lowest frequency bin for a 16.03 yr PTA, have masses from ∼109 to 1010 M ⊙, and are ∼1 Gpc away. The level of anisotropy increases with frequency, with the angular power spectrum over multipole modes ℓ varying in low-frequency C ℓ>0/C 0 from ∼5 × 10−3 to ∼2 × 10−1, depending on the model; typical values are near current upper limits. Observing this anisotropy would support SMBHB models for the GWB over cosmological models, which tend to be isotropic.

The X-Ray Emission Reveals the Coronal Activities of Semi-detached Binaries

X-ray emission is an important tracer of stellar magnetic activity. We carried out a systematic correlation analysis for the X-ray luminosity logLX , bolometric luminosity logLbol , and X-ray activity level log(LX /L bol) versus the binary parameters including orbital period P, Rossby number R O, effective temperature T eff, metallicity [Fe/H], the surface gravity logg , stellar mass M, and radius R, by assembling a large sample of semi-detached (EB-type) binaries with X-ray emission (EBXs). The fact that both logLX and logLbol change in accordance with logP indicates that X-ray emission originates from the convection zone, while logLX is proportional to the convection zone area. We found that EBXs with main-sequence components exhibit an upward and then a downward trend in both the logTeff – logLX and M– logLX relations, which is different from the monotonically decreasing trend shown by EBXs containing sub-giant and giant components. The magnetic activity level is negatively correlated with logTeff and stellar mass. Based on the magnetic dynamo model, the variations in the size and thickness of the surface convection zones can explain the observed relations. EBXs with main-sequence components have a similar R O– log(LX/Lbol) relationship to that of the binaries in the clusters as Praesepe and Hyade. We compared the X-ray radiation properties of EBXs with those of the X-ray-emitting contact binaries and found that EBXs have broader value ranges for logLX and log(LX /L bol).

An Estimate of the Binary Star Fraction among Young Stars at the Galactic Center: Possible Evidence of a Radial Dependence

We present the first estimate of the intrinsic binary fraction of young stars across the central ≈0.4 pc surrounding the supermassive black hole (SMBH) at the Milky Way Galactic center (GC). This experiment searched for photometric variability in 102 spectroscopically confirmed young stars, using 119 nights of 10″ wide adaptive optics imaging observations taken at W. M. Keck Observatory over 16 yr in the K′ -[2.1 μm] and H-[1.6 μm] bands. We photometrically detected three binary stars, all of which are situated more than 1″ (0.04 pc) from the SMBH and one of which, S2-36, is newly reported here with spectroscopic confirmation. All are contact binaries or have photometric variability originating from stellar irradiation. To convert the observed binary fraction into an estimate of the underlying binary fraction, we determined the experimental sensitivity through detailed light-curve simulations, incorporating photometric effects of eclipses, irradiation, and tidal distortion in binaries. The simulations assumed a population of young binaries, with stellar ages (4 Myr) and masses matched to the most probable values measured for the GC young star population, and underlying binary system parameters (periods, mass ratios, and eccentricities) similar to those of local massive stars. As might be expected, our experimental sensitivity decreases for eclipses narrower in phase. The detections and simulations imply that the young, massive stars in the GC have a stellar binary fraction ≥71% (68% confidence), or ≥42% (95% confidence). This inferred GC young star binary fraction is consistent with that typically seen in young stellar populations in the solar neighborhood. Furthermore, our measured binary fraction is significantly higher than that recently reported by Chu et al. based on radial velocity measurements for stars ≲1″ of the SMBH. Constrained with these two studies, the probability that the same underlying young star binary fraction extends across the entire region is <1.4%. This tension provides support for a radial dependence of the binary star fraction, and therefore, for the dynamical predictions of binary merger and evaporation events close to the SMBH.

Algorithmic Pulsar Timer for Binaries

Pulsar timing is a powerful tool that, by accounting for every rotation of a pulsar, precisely measures the spin frequency, spin frequency derivatives, astrometric position, binary parameters when applicable, properties of the interstellar medium, and potentially general relativistic effects. Typically, this process demands fairly stringent scheduling requirements for monitoring observations as well as deep domain knowledge to “phase connect” the timing data. We present an algorithm that automates the pulsar-timing process for binary pulsars, whose timing solutions have an additional level of complexity, although the algorithm works for isolated pulsars as well. Using the statistical F-test and the quadratic dependence of the reduced χ 2 near a minimum, the global rotation count of a pulsar can be determined efficiently and systematically. We have used our algorithm to establish timing solutions for two newly discovered binary pulsars, PSRs J1748−2446aq and J1748−2446at, in the globular cluster Terzan 5, using ∼70 Green Bank Telescope observations from the last 13 yr.

Probing Supermassive Black Hole Seed Scenarios with Gravitational-wave Measurements

The process whereby the supermassive black holes (SMBHs) populating the centers of galaxies have been assembled remains to be established, with the relative importance of seeds provided by collapsed Population III stars, black holes formed in nuclear star clusters via repeated mergers, or direct collapses of protogalactic disks yet to be determined. In this paper we study the prospects for casting light on this issue by future measurements of gravitational waves emitted during the inspirals and mergers of pairs of intermediate-mass black holes (IMBHs), discussing in particular the roles of prospective measurements by LISA and the proposed atom interferometers AION and AEDGE. We find that the expected number of detectable IMBH binaries is O(100) for LISA and AEDGE and O(10) for AION in low-mass seeds scenarios and goes down to O(10) for LISA and below one for AEDGE and AION in high-mass seed scenarios. This allows all of these observatories to probe the parameters of the seed model, in particular, if at least a fraction of the SMBHs arises from a low-mass seed population. We also show that the measurement accuracy of the binary parameters is, in general, best for AEDGE, which sees very precisely the merger of the binary.

Binary origin of blue straggler stars in Galactic star clusters

Building on the recent release of a new Gaia -based blue straggler star catalog in Galactic open star clusters (OCs), we explored the properties of these stars in a cluster sample spanning a wide range in fundamental parameters. We employed Gaia EDR3 to assess the membership of any individual blue or yellow straggler to their parent cluster. We then made use of the ASteCA code to estimate the fundamental parameters of the selected clusters, in particular, the binary fraction. With all this at hand, we critically revisited the relation of the blue straggler population and the latter. For the first time, we found a correlation between the number of blue stragglers and the host cluster binary fraction and binaries. This supports the hypothesis that binary evolution is the most viable scenario of straggler formation in Galactic star clusters. The distribution of blue stragglers in the Gaia color-magnitude diagram was then compared with a suite of composite evolutionary sequences derived from binary evolutionary models that were run by exploring a range of binary parameters: age, mass ratio, period, and so forth. The excellent comparison between the bulk distribution of blue stragglers and the composite evolutionary sequences loci further supports the binary origin of most stragglers in OCs and paves the way for a detailed study of individual blue stragglers.