arXiv subjects

S. Toonen

Publications and source records attributed to S. Toonen.

At least 19 recordsLinked to original sources

arXiv2026

Triple-induced mergers of black hole binaries: A comprehensive look at the role of stellar evolution, dynamical stability, and spin evolution

Mergers of black holes (BHs) have been shown to be a ubiquitous phenomenon in the Universe. However, uncertainties remain in our theoretical understanding of the evolution of the BHs prior to their merger. Black hole progenitors are seemingly born primarily in triples or higher-order multiples, and the presence of a tertiary object can perturb a black hole binary (BHB) enough to precipitate a merger. We used population synthesis coupled with orbit-averaged descriptions of triple dynamics to evolve a population of triples with initially wide orbits and massive progenitors. Wide orbits were chosen to avoid stellar interaction prior to BH formation. Systems that remain bound and form an inner BHB were evolved using a direct n-body code with post-Newtonian terms up to an order of 2.5. We also simulated the precession of the BH spin vectors by coupling the n-body solver with the differential equations for the spins. For the dynamically stable triples with inner BHBs, mergers occur with an estimated rate density of $\sim 5$ Gpc$^{-3}$ yr$^{-1}$. Mergers also occur in triples that become dynamically unstable at a rate of $\sim 1.4$ Gpc$^{-3}$ yr$^{-1}$. At the point of entering the 10 Hz gravitational wave frequency band, the merging inner binaries exhibit eccentricities between $10^{-4}$ and $10^{-2}$. The final effective spin of a BHB that merges through this channel can display a wide range of values between $-1$ and $1$, with a slight tendency towards $\chi_\text{eff} \approx 0$. This is a result of the strong three-body dynamics experienced by the merging triples before the inner binary begins to shrink due to GW emission. The inner angular momentum can explore the full phase space before the binary rapidly shrinks and decouples from the tertiary, effectively freezing out the effective spin to its value at the time of the highest inner eccentricity.

astro-ph.SR↗

arXiv2026

Multiplicity of Massive Stars at Low Metallicity: Early Results from the BLOeM Campaign

Massive stars at low metallicity (Z) play a central role in shaping the high-redshift Universe, yet their multiplicity remains poorly constrained. The Binarity at Low Metallicity (BLOeM) campaign is a two-year survey of 929 stars in the Small Magellanic Cloud with the Fibre Large Array Multi Element Spectrograph (FLAMES) instrument at ESO's Very Large Telescope, providing the first large-scale spectroscopic monitoring of massive stars at low Z (1/5 solar). Analysis of the initial nine epochs reveals high intrinsic binary fractions (>70%) on the main sequence and a steep decline in evolved objects. Analysis of the full dataset will yield orbital solutions, identify black-hole companions, and allow a derivation of the initial mass function for single and binary stars at low Z.

physics.gen-ph↗

arXiv2026

Southern Massive Stars at High Angular Resolution (SMaSH+): Properties of hierarchical massive triples

While massive stars are frequently found in triple architectures, the lack of observed parameter distributions has long remained a bottleneck for statistical models of their evolution. We compile the first representative set of physical and orbital distributions for main-sequence hierarchical massive triples. We present a homogeneous analysis of 26 O-type hierarchical triples identified in the SMaSH+ survey by combining spectroscopic data for inner binaries with interferometric and aperture masking detections of tertiary companions within $\sim$200 au. We derive the distributions of masses, mass ratios, and separations, and investigate their joint probability density functions. We assess the dynamical stability of these systems and estimate the relative importance of secular processes by comparing the von Zeipel-Kozai-Lidov (ZKL) timescale to the general relativistic precession timescale for five systems with well-constrained orbital solutions. Finally, we evaluate the observational completeness. The sample is dominated by strongly hierarchical configurations, consisting primarily of tight inner spectroscopic binaries(a_in< 1 au) and wider tertiaries (a_out/a_in $>$ 70 for most systems). We find no significant correlation between tertiary mass and either inner-binary mass or outer separation, indicating a broad diversity of system architectures. Ten systems host relatively massive tertiaries (q_out>0.5), especially at closer outer separations (a_out$\lesssim$30 au). For two to four systems out of five, general relativistic precession dominates over ZKL oscillations in their current configuration. These results provide the first observationally grounded distributions of key parameters for massive hierarchical triples and offer important constraints for population synthesis and evolutionary models, particularly regarding the role of tertiary companions in shaping binary evolution.

astro-ph.SR↗

arXiv2026

Reframing the Wide Eccentric Binary Problem: Eccentricity as a Probe of Mass-transfer Physics

Observations of wide post-interaction binaries show an unexpected feature; orbital eccentricity, which is not understood theoretically. A promising resolution to this long-standing puzzle is eccentric mass transfer (MT). Here the first complete framework for MT in orbits with arbitrary eccentricity, the general mass-transfer (GeMT) model, is confronted with the latest observations of hot subdwarfs of spectral type B (sdB) with main-sequence (MS) companions in wide orbits. SdBs are excellent benchmarks for binary evolution models, since their progenitors provide unique constraints on their formation histories. We isolate the effects of eccentric MT from other physical process and we show that it explains the observed orbital-parameter distributions and their correlations seen in wide sdB+MS binaries. To quantitatively constrain their orbital parameters, stellar evolution and tides should be included in future studies, yet it is encouraging that the GeMT model provides the first mechanism that qualitatively reproduces the observed distributions. We further demonstrate that post-MT eccentricities depend directly on key MT parameters, including transferred mass, accretion efficiency, and angular momentum loss. Given the multitude of eccentric post-MT binaries with components ranging from low- to high-mass stars to compact objects, we propose that post-MT eccentricities offer a new window onto binary evolution, presenting a powerful tool to constrain highly uncertain binary-evolution parameters and mass-transfer formation histories across diverse populations. Post-MT eccentricity should therefore be embraced as a key observable, rather than treated as a problem to be corrected.

astro-ph.SR↗

arXiv2025

Rethinking mass transfer: a unified semianalytical framework for circular and eccentric binaries. II. Orbital evolution due to nonconservative mass transfer

Although mass transfer (MT) has been studied primarily in circular binaries, observations show that it also occurs in eccentric systems. We investigate orbital evolution during nonconservative MT in eccentric orbits, a process especially relevant for binaries containing compact objects (COs). We examined four angular momentum loss (AML) modes: Jeans, isotropic reemission, orbital-AML, and $L_2$ mass loss, with the last mode being the most efficient AML mode. For a fixed AML mode and accretion efficiency, orbital evolution is correlated: orbits either widen while becoming more eccentric, or shrink while circularizing. Jeans mode generally yields orbital widening and eccentricity pumping, whereas $L_2$ mass loss typically leads to orbital shrinkage and eccentricity damping. Isotropic reemission and orbital-AML show an intermediate behavior. Adopting isotropic reemission, we demonstrate that eccentric MT produces compact binaries that merge via gravitational waves (GW) within a Hubble time, whereas the same systems would instead merge during MT under traditional modeling. We further show that, in eccentric orbits, the gravitational potential at $L_2$ becomes lower than at $L_1$ across a wide range of mass ratios and eccentricities, naturally linking eccentricity to $L_2$ mass loss. Eccentric MT may therefore lead to the formation of the circumbinary disks observed around eccentric post-red-giant-branch and post-asymptotic-giant-branch systems. Since interacting binaries containing COs are frequently eccentric, $L_2$ mass loss offers a new robust pathway to orbital tightening during eccentric MT, contributing to the formation rate of GW sources. This model can treat orbital evolution due to conservative and nonconservative MT in arbitrary eccentricities, with applications ranging from MT on the main sequence to GW progenitors.

astro-ph.SR↗

arXiv2025

Binary imposters: Mergers in massive hierarchical triple stars

Massive stars are often born in triples, where gravitational dynamics and stellar interactions play a crucial role in shaping their evolution. One such pathway includes the merger of the inner binary, transforming the system to a binary with a distinct formation history. Therefore, the interpretation of observed binary properties and their inferred formation history may require the consideration of a potential triple origin. We aim to investigate the population of stellar mergers in massive hierarchical triples. Specifically, we assess how frequently mergers occur, and characterise the properties of the post-merger binaries and their subsequent evolution. We combine the triple population synthesis code TRES, which self-consistently models stellar evolution, binary interaction, and gravitational dynamics, with the binary population synthesis code SeBa to simulate 10^5 dynamically stable, massive triples from the zero-age main sequence through merger and post-merger evolution. We explore the effects of a range of physical models for the initial stellar properties, mass transfer, and merger. We find that stellar mergers are a common outcome, occurring in 20-32% of massive triples. Most mergers happen relatively early in the evolution of the system and involve two main-sequence (MS) stars, producing rejuvenated merger remnants that can appear significantly younger than their tertiary companions. Consequently, we predict that 2-10% of all wide MS+MS binaries (P>100 days) have a measurable age discrepancy, and serve as a promising way to identify merged stars. The post-merger systems preferentially evolve into wide, eccentric binaries, with ~80% avoiding further interaction. However, a notable fraction (16-22%) undergoes a second mass-transfer phase, which may result in the formation of high-mass X-ray binaries or mergers of compact objects that spiral in via gravitational-wave emission.

astro-ph.SR↗

arXiv2025

A high fraction of close massive binary stars at low metallicity

At high metallicity, a majority of massive stars have at least one close stellar companion. The evolution of such binaries is subject to strong interaction processes, heavily impacting the characteristics of their life-ending supernova and compact remnants. For the low-metallicity environments of high-redshift galaxies constraints on the multiplicity properties of massive stars over the separation range leading to binary interaction are crucially missing. Here we show that the presence of massive stars in close binaries is ubiquitous, even at low metallicity. Using the Very Large Telescope, we obtained multi-epoch radial velocity measurements of a representative sample of 139 massive O-type stars across the Small Magellanic Cloud, which has a metal content of about one fifth of the solar value. We find that 45% of them show radial velocity variations which demonstrate that they are members of close binary systems, and predominantly have orbital periods shorter than one year. Correcting for observational biases indicates that at least 70[+11:-6]% of the O stars in our sample are in close binaries, and that at least 68[+7:-8]% of all O stars interact with a companion star during their lifetime. We found no evidence supporting a statistically significant trend of the multiplicity properties with metallicity. Our results indicate that multiplicity and binary interactions govern the evolution of massive stars and determine their cosmic feedback and explosive fates.

astro-ph.SR↗

arXiv2025

Rethinking mass transfer: a unified semi-analytical framework for circular and eccentric binaries. I. Orbital evolution due to conservative mass transfer

Mass transfer (MT) is a fundamental process in stellar evolution. While MT in circular orbits is well studied, observations indicate that it also occurs in eccentric ones, where theoretical models are limited. We present a new semi-analytic framework for the secular orbital evolution of mass-transferring binaries, treating stars either as point-masses or as extended bodies. For the first time, a MT model is applicable to both circular and eccentric orbits and accommodates conservative and non-conservative MT across a broad range of mass ratios and stellar spins. We derive secular, orbit-averaged equations describing the orbital evolution by treating MT, mass loss, and angular momentum (AM) loss as perturbations to the general two-body problem. Assuming conservative MT, we compare our results to previous models and validate them against numerical integrations. Our model predicts eccentric post-MT systems in wider orbits than classical results. Compared to other eccentric MT frameworks we find a broader parameter space for orbital widening and eccentricity pumping. Accounting for extended bodies yields stronger semimajor axis and eccentricity growth at a given mass ratio, and further broadens the parameter space for orbital widening and eccentricity pumping. Whether extended bodies are considered or not, eccentric MT naturally predicts higher eccentricities at longer orbital periods, a correlation observed in numerous post-MT systems, providing a robust mechanism for their formation. Our model can be integrated into binary evolution and population synthesis codes to consistently treat conservative and non-conservative MT in arbitrarily eccentric orbits with applications ranging from MT on the main sequence to gravitational-wave progenitors.

astro-ph.SR↗

arXiv2025

Eclipsing white dwarf from the Zwicky Transient Facility: II. Seven eclipsing double white dwarfs

In a systematic search for eclipsing white dwarfs using Zwicky transient facility (ZTF) data, we found seven eclipsing double white dwarfs with orbital periods ranging from 45 minutes to 3 hours. We collected high-speed light curves, archival multi-wavelength data, and optical spectra for all systems and determined the binary parameters for each of them. We show that six of the systems are low-mass, double helium-core white dwarf binaries, with the last one a carbon-oxygen -- helium core white dwarf binary. These binaries slowly spiral inwards due to gravitational wave energy losses and are expected to merge within 36Myr--1.2Gyr, and we predict that the shortest orbital period binary will show a measurable eclipse arrival time delay within a decade. The two longest systems show a delay in the arrival time of the secondary eclipse, which we attribute to a small eccentricity of $\approx 2\times10^{-3}$. This is the first time that a non-zero eccentricity is measured in a compact double white dwarf binary. We suggest that these systems emerged from the common envelope with this small eccentricity, and because of the relatively long orbital period, gravitational wave emission has not yet circularised the binaries. Finally, we predict that relativistic apsidal precession will result in a change in the delay of the secondary eclipse that is measurable within a decade.

astro-ph.SR↗

arXiv2025

A systematic method to identify runaways from star clusters produced from single-binary interactions: A case study of M67

One hypothesis for runaway stars (RSs) is that they are ejected from star clusters with high velocities relative to the cluster center-of-mass motion. There are two competing mechanisms for their production: supernova-based ejections in binaries, where one companion explodes, leaves no remnant, and launches the other companion at the instantaneous orbital velocity, and the disintegration of triples (or higher-order multiples), which produces a recoiled runaway binary (RB) and an RS. We search for RS candidates using data from the Gaia DR3 survey with a focus on triple disintegration since in this case the product is always a binary and a single star that should be moving in opposite directions. We created a systematic methodology to look for candidate RS-RB runaway pairs produced from the disintegration of bound three-body systems formed from single-binary interactions based on momentum conservation and causality. The method we use is general and can be applied to any cluster with a 5D kinematic data set. We used our criteria to search for these pairs in a 150 pc circular field of view surrounding the open cluster M67, which we used as a benchmark cluster to test the robustness of our method. Our results reveal only one RS-RB pair that is consistent with all of our selection criteria out of an initial sample of $10^8$ pairs.

astro-ph.SR↗

arXiv2025

Binarity at LOw Metallicity (BLOeM): Enhanced multiplicity of early B-type dwarfs and giants at $Z=0.2\,{\rm Z}_\odot$

Early B-type stars ($M_i=8-15$ M$_\odot$) are frequently in multiple systems, as evidenced by spectroscopic campaigns in the Milky Way (MW) and the Large Magellanic Cloud (LMC). Previous studies have shown no strong metallicity dependence in the close-binary (a>10 au) fraction or orbital-period distributions between the MW's solar metallicity (Z$_\odot$) and that of the LMC (Z=0.5 Z$_\odot$). However, similar analyses in more metal-poor environments are still scarce. We focus on 309 early B-type stars (luminosity classes III-V) from the Binarity at LOw Metallicity campaign in the Small Magellanic Cloud (SMC, Z=0.2 Z$_\odot$) using VLT/FLAMES multi-epoch spectroscopy. By applying binary detection criteria consistent with previous works, we identify 153 stars (91 SB1, 59 SB2, 3 SB3) exhibiting significant radial-velocity (RV) variations, resulting in an observed multiplicity fraction of $f^{obs}_{mult}=50\pm3\%$. Using Monte Carlo simulations to account for observational biases, we infer an intrinsic close-binary fraction of $f_{mult}=80\pm8\%$. A Markov chain Monte Carlo analysis of the peak-to-peak RV distribution ($\Delta{\rm RV}_{\rm max}$) confirms a high multiplicity fraction of $f_{mult}=78\pm5\%$. These findings suggest a possible anti-correlation between metallicity and the fraction of close B-type binaries, with the SMC multiplicity fraction significantly exceeding previous measurements in the LMC and MW. The enhanced fraction of close binaries at SMC's low metallicity may have broad implications for massive-star evolution in the early Universe. More frequent mass transfer and envelope stripping could boost the production of exotic transients, stripped supernovae, gravitational-wave progenitors, and sustained UV ionising flux, potentially affecting cosmic reionisation. Theoretical predictions of binary evolution under metal-poor conditions will provide a key test of our results.

astro-ph.SR↗

arXiv2025

Binarity at Low Metallicity (BLOeM) -- Multiplicity properties of Oe and Be stars

Rapidly rotating classical OBe stars have been proposed as the products of binary interactions, and the fraction of Be stars with compact companions implies that at least some are. However, to constrain the interaction physics spinning up the OBe stars, a large sample of homogeneously analysed OBe stars with well-determined binary characteristics and orbital parameters are required. We investigate the multiplicity properties of a sample of 18 Oe, 62 Be, and two Of?p stars observed within the BLOeM survey in the Small Magellanic Cloud. We analyse the first nine epochs of spectroscopic observations obtained over approximately three months in 2023. Radial velocities (RVs) of all stars are measured. Applying commonly-used binarity criteria we classify objects as binaries, binary candidates, and apparently single (RV stable) objects. We further inspect the spectra for double-lined spectroscopic binaries and cross-match with catalogues of X-ray sources and photometric binaries. We classify 14 OBe stars as binaries, and an additional 11 as binary candidates. The two Of?p stars are apparently single. Two more objects are most likely currently interacting binaries. Without those, the observed binary fraction for the OBe sample (78 stars) is f_OBe_obs=0.18+/-0.04 (f_obs_cand=0.32+/-0.05 including candidates). This fraction is less than half of that measured for OB stars in BLOeM. Combined with the lower fraction of SB2s, this suggests that OBe stars have indeed fundamentally different binary properties than OB stars. We find no evidence for OBe binaries with massive compact companions, in contrast to expectations from binary population synthesis. Our results support the binary scenario as an important formation channel for OBe stars, as post-interaction binaries may have been disrupted or the stripped companions of OBe stars are harder to detect.

astro-ph.SR↗

arXiv2025

Binarity at LOw Metallicity (BLOeM): The multiplicity properties and evolution of BAF-type supergiants

Given the uncertain evolutionary status of blue supergiant stars, their multiplicity properties hold vital clues to better understand their origin and evolution. As part of The Binarity at LOw Metallicity (BLOeM) campaign in the Small Magellanic Cloud we present a multi-epoch spectroscopic survey of 128 supergiant stars of spectral type B5--F5, which roughly correspond to initial masses in the range 6 to 30 solar masses. The observed binary fraction for the B5-9 supergiants is 25+/-6 % (10+/-4 %) and 5+/-2 % (0 %) for the A-F stars, using a radial velocity (RV) variability threshold of 5 kms (10 kms) as a criterion for binarity. Accounting for observational biases we find an intrinsic multiplicity fraction of less than 18% for the B5-9 stars and 8$^{+9}_{-7}$% for the AF stars, for the orbital periods up to 10$^{3.5}$day and mass-ratios (q) in the range 0.1 < q < 1. The large stellar radii of these supergiant stars prevent short orbital periods but we demonstrate that this effect alone cannot explain our results. We assess the spectra and RV time series of the detected binary systems and find that only a small fraction display convincing solutions. We conclude that the multiplicity fractions are compromised by intrinsic stellar variability such that the true multiplicity fraction may be significantly smaller. Our main conclusions from comparing the multiplicity properties of the B5-9 and AF supergiants to that of their less evolved counterparts is that such stars cannot be explained by a direct evolution from the main sequence. Furthermore, by comparing their multiplicity properties to red supergiant stars we conclude that the AF supergiant stars are neither progenitors nor descendants of red supergiants.

astro-ph.SR↗

arXiv2024

BH-BH mergers with & without EM counterpart: A model for stable tertiary mass transfer in hierarchical triple systems

Triple stars are prevalent within the population of observed stars. Their evolution, compared to binaries, is notably more complex, influenced by unique dynamical, tidal, and mass transfer processes. Understanding these phenomena is essential for a comprehensive insight into multistar evolution and the formation of energetic transients, including gravitational-wave mergers. Our study probes the evolution of triple star systems when the tertiary fills its Roche lobe and transfers mass to the inner binary, potentially forming GW sources with distinct properties. We develop an analytical model for hierarchical triples undergoing stable mass transfer from the tertiary. Using population synthesis simulations, we investigate triples with a Roche-lobe filling tertiary and an inner binary black hole. These systems originate from inner binaries undergoing chemically homogeneous evolution. Our analysis includes populations with metallicities of Z=0.005 and Z=0.0005, focusing on primary components with initial masses of 20 to 100 M_sun, and inner and outer orbital separations up to 40 R_sun and 10^5 R_sun, respectively. Our results show that mass transfer predominantly leads to orbital shrinkage of the inner binary, non-zero eccentricities, and expansion of the outer orbit. Among systems with CHE inner binaries, 9.5% result in mass transfer from the tertiary onto an inner BBH. We predict high formation efficiency of GW mergers, ranging from 85.1% to 100% at Z=0.005 and 100% at Z=0.0005, with short delay times. Local merger rates are projected to be between 0.69 to 1.74 Gpc^-3 yr^-1. A fraction of these BBH mergers, entering the LISA and aLIGO frequency bands, may still be accreting gas, potentially producing a strong electromagnetic counterpart. EM signals vary significantly based on model assumptions, ranging from less than 0.03% to 46.8% of all mergers if circumbinary disk formation is allowed.

astro-ph.SR↗

arXiv2024

Massive stellar triples on the edge: A numerical study of the evolution and final outcomes of destabilized massive triples

Massive stars reside predominantly in triples or higher-order multiples. Their lives can be significantly affected by three-body interactions, making it an important area of study in the context of massive star evolution. In this study we provide a statistical overview of the lives and final outcomes of destabilized massive triples. A population of initially stable triples with a massive primary star are evolved from the zero-age main sequence using the code TRES, which combines stellar evolution with orbit-averaged dynamics. The triples that become unstable are transferred to a direct N-body code where they are simulated until the system disintegrates. This excludes systems undergoing mass transfer, such that the instability is caused by stellar winds or supernovae. Two suites of N-body simulations are performed; one with gravity as the only interaction, and one with stellar evolution included. We find that collisions occur in 35 - 40% of systems, with the variation coming from whether stellar evolution is included. The collisions mainly involve two main sequence stars (70 - 78%) or a main sequence and post-main sequence star (13 - 28%). We estimate a Galactic rate of collisions due to massive triple destabilization at 1.1 - 1.3 events per Myr. Furthermore, we find that the process of destabilization often ends in the ejection of one of the stellar bodies, specifically for 31 - 40% of systems. The ejected bodies have typical velocities of around 6 km/s, with a tail stretching to 102 km/s. If we assume that 20% of massive stars are runaway stars, then 0.1% of runaways originate from triple destabilization. Overall, our simulations show that triple instability affects approximately 2% of massive triples. However, we estimate that up to ten times as many systems can become unstable due to mass transfer in the inner binary, and these system may end up ejecting bodies at higher velocities.

astro-ph.SR↗

arXiv2024

Binarity at LOw Metallicity (BLOeM): a spectroscopic VLT monitoring survey of massive stars in the SMC

Surveys in the Milky Way and Large Magellanic Cloud revealed that the majority of massive stars will interact with companions during their lives. However, knowledge of the binary properties of massive stars at low metallicity, which approaches the conditions of the Early Universe, remains sparse. We present the Binarity at LOw Metallicity (BLOeM) campaign - an ESO large programme designed to obtain 25 epochs of spectroscopy for 929 massive stars in the SMC - the lowest metallicity conditions in which multiplicity is probed to date (Z = 0.2 Zsun). BLOeM will provide (i) the binary fraction, (ii) the orbital configurations of systems with periods P < 3 yr, (iii) dormant OB+BH binaries, and (iv) a legacy database of physical parameters of massive stars at low metallicity. The stars are observed with the LR02 setup of the giraffe instrument of the Very Large Telescope (3960-4570A, resolving power R=6200; typical signal-to-noise ratio S/N=70-100). This paper utilises the first 9 epochs obtained over a three-month time. We describe the survey and data reduction, perform a spectral classification of the stacked spectra, and construct a Hertzsprung-Russell diagram of the sample via spectral-type and photometric calibrations. The sample covers spectral types from O4 to F5, spanning the effective temperature and luminosity ranges 6.5<Teff/kK<45 and 3.7<log L/Lsun<6.1 and initial masses 8<Mini/Msun<80. It comprises 159 O-type stars, 331 early B-type (B0-3) dwarfs and giants (luminosity classes V-III), 303 early B-type supergiants (II-I), and 136 late-type supergiants. At least 82 stars are Oe/Be stars: 20 O-type and 62 B-type (13% and 11% of the respective samples). In addition, it includes 4 high-mass X-ray binaries, 3 stars resembling luminous blue variables, 2 bloated stripped-star candidates, 2 candidate magnetic stars, and 74 eclipsing binaries.

astro-ph.SR↗

arXiv2023

The 40 pc sample of white dwarfs from Gaia

We present a comprehensive overview of a volume-complete sample of white dwarfs located within 40 pc of the Sun, a significant proportion of which were detected in Gaia Data Release 3 (DR3). Our DR3 sample contains 1076 spectroscopically confirmed white dwarfs, with just five candidates within the volume remaining unconfirmed (more than 99 per cent spectroscopic completeness). Additionally, 28 white dwarfs were not in our initial selection from Gaia DR3, most of which are in unresolved binaries. We use Gaia DR3 photometry and astrometry to determine a uniform set of white dwarf parameters, including mass, effective temperature, and cooling age. We assess the demographics of the 40 pc sample, specifically magnetic fields, binarity, space density and mass distributions.

astro-ph.SR↗

arXiv2023

Triage of the Gaia DR3 astrometric orbits. II. A census of white dwarfs

The third data release of Gaia was the first to include orbital solutions assuming non-single stars. Here, we apply the astrometric triage technique of Shahaf et al. to identify binary star systems with companions that are not single main-sequence stars. Gaia's synthetic photometry of these binaries is used to distinguish between systems likely to have white-dwarf companions and those that may be hierarchical triples. The study uncovered a population of nearly 3200 binaries, characterised by orbital separations on the order of an astronomical unit, in which the faint astrometric companion is probably a white dwarf. This sample increases the number of orbitally solved binary systems of this type by about two orders of magnitude. Remarkably, over 110 of these systems exhibit significant ultraviolet excess flux, confirming this classification and, in some cases, indicating their relatively young cooling ages. We show that the sample is not currently represented in synthetic binary populations, and is not easily reproduced by available binary population synthesis codes. Therefore, it challenges current binary evolution models, offering a unique opportunity to gain insights into the processes governing white-dwarf formation, binary evolution, and mass transfer.

astro-ph.SR↗