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Transiting planets in multiple-star systems, especially high-order multiples, make up a small fraction of the known planet population but provide unique opportunities to study the environments in which planets would have formed. Planet-hosting binaries have been shown to have an abundance of systems in which the stellar orbit aligns with the orbit of the transiting planet, which could give insights into the planet formation process in such systems. We investigate here if this trend of alignment extends to planet-hosting triple-star systems. We present long-term astrometric monitoring of a novel sample of triple-star systems that host Kepler transiting planets. We measured orbit arcs in 21 systems, including 12 newly identified triples, from a homogeneous analysis of our Keck adaptive optics data and, for some systems, Gaia astrometry. We examine the orbital alignment within the nine most compact systems (⁠|$\lesssim 500$|  au), testing if either (or both) of the stellar orbits align with the edge-on orbits of their transiting planets. Our statistical sample of triple systems shows a tendency toward alignment, especially when assessing the alignment probability using stellar orbital inclinations computed from full orbital fits, but is formally consistent with isotropic orbits. Two-population tests where half of the stellar orbits are described by a planet-hosting-binary-like moderately aligned distribution give the best match when the other half (non-planet-hosting) has a Kozai-like misaligned distribution. Overall, our results suggest that our sample of triple-star planet-hosting systems are not fully coplanar systems and have at most one plane of alignment. [ABSTRACT FROM AUTHOR]

Context. Dual-field interferometric observations with VLTI/GRAVITY sometimes require the use of a binary calibrator. This is a binary star whose individual components remain unresolved by the interferometer, with a separation between 400 and 2000 mas for observations with the Unit Telescopes (UTs), or 1200–3000 mas for the Auxiliary Telescopes (ATs). The separation vector also needs to be predictable to within 10 mas for a proper pointing of the instrument. Aims. No list of properly vetted calibrators was available so far for dual-field observations with VLTI/GRAVITY on the UTs. Our objective is to compile such a list and make it available to the community. Methods. We identified a list of candidates from the Washington Double Star (WDS) catalogue, all with appropriate separations and brightness, scattered over the southern sky. We observed them as part of a dedicated calibration programme, determined whether these objects were true binaries (excluding higher multiplicities resolved interferometrically, but unseen by imaging), and extracted measurements of the separation vectors. We combined these new measurements with those available in the WDS to determine updated orbital parameters for all our vetted calibrators. Results. We compiled a list of 13 vetted binary calibrators for observations with VLTI/GRAVITY on the UTs, and we provide orbital estimates and astrometric predictions for each of them. We show that our list guarantees that there are always two binary calibrators at least at an airmass < 2 in the sky over the Paranal observatory at any point in time. Conclusions. Any principal investigator wishing to use the dual-field mode of VLTI/GRAVITY with the UTs can now refer to this list to select an appropriate calibrator. We encourage the use of whereistheplanet to predict the astrometry of these calibrators, which seamlessly integrates with p2Gravity for VLTI/GRAVITY dual-field observing material preparation. [ABSTRACT FROM AUTHOR]

Aims. We report the confirmation of a new transiting exoplanet orbiting the star TOI-5076. Methods. We present our vetting procedure and follow-up observations which led to the confirmation of the exoplanet TOI-5076b. In particular, we employed high-precision TESS photometry, high-angular-resolution imaging from several telescopes, and high-precision radial velocities from HARPS-N. Results. From the HARPS-N spectroscopy, we determined the spectroscopic parameters of the host star: Teff = (5070±143) K, log 푔 = (4.6±0.3), [Fe/H] = (+0.20±0.08), and [α/Fe] = 0.05±0.06. The transiting planet is a warm sub-Neptune with a mass mp = (16±2) M⊙, a radius rp =(3.2±0.l) R⊙ yielding a density ρp = (2.8±0.5) g cm−3. It revolves around its star approximately every 23.445 days. Conclusions. The host star is a metal-rich, K2V dwarf, located at about 82 pc from the Sun with a radius of R⋆ = (0.78±0.01) R⊙ and a mass of M⋆ = (0.80±0.07) M⊙. It forms a common proper motion pair with an M-dwarf companion star located at a projected separation of 2178 au. The chemical analysis of the host-star and the Galactic-space velocities indicate that TOI-5076 belongs to the old population of thin-to-thick-disk transition stars. The density of TOI-5076b suggests the presence of a large fraction by volume of volatiles overlying a massive core. We found that a circular orbit solution is marginally favored with respect to an eccentric orbit solution for TOI-5076b. [ABSTRACT FROM AUTHOR]

Context. The past few years have seen a revolution in the study of circumstellar disks. New instrumentation in the near-infrared and (sub)millimeter regimes have allowed us to routinely spatially resolve disks around young stars of nearby star-forming regions. As a result, we have found that substructures with scales of ~10 au in disks are common. We have also revealed a zoo of different morphologies, sizes, and luminosities that is as complex as the diversity of architectures found in evolved exoplanet systems. Aims. We study disk evolutionary trends as they appear in scattered light observations. Scattered light traces the micron-sized particles at the disk surface that are well coupled to the gas. This means that scattered light observations can be used to trace the distribution of the disk gas and its interaction with embedded perturbers. Methods. We used VLT/SPHERE to observe 20 systems in the Cha I cloud in polarized scattered light in the near-infrared. We combined the scattered light observations with existing literature data on stellar properties and with archival ALMA continuum data to study trends with system age and dust mass. We also connected resolved near-infrared observations with the spectral energy distributions of the systems. Results. In 13 of the 20 systems included in this study we detected resolved scattered light signals from circumstellar dust. For the CR Cha, CT Cha, CV Cha, SY Cha, SZ Cha, and VZ Cha systems we present the first detailed descriptions of the disks in scattered light. The observations found typically smooth or faint disks, often with little substructure, with the notable exceptions of SZ Cha, which shows an extended multiple-ringed disk, and WW Cha, which shows interaction with the cloud environment. New high S/N K-band observations of the HD 97048 system in our survey reveal a significant brightness asymmetry that may point to disk misalignment and subsequent shadowing of outer disk regions, possibly related to the suggested planet candidate in the disk. We resolve for the first time the stellar binary in the CS Cha system. Multiple wavelength observations of the disk around CS Cha have revealed that the system contains small, compact dust grains that may be strongly settled, consistent with numerical studies of circumbinary disks. We find in our sample that there is a strong anti-correlation between the presence of a (close) stellar companion and the detection of circumstellar material with five of our seven nondetections located in binary systems. We also find a correlation between disk mass, as inferred from millimeter observations, and the detection of scattered light signal. Finally, we find a tentative correlation between relative disk-to-star brightness in scattered light and the presence of a dust cavity in the inner (unresolved) disk, as traced by the system spectral energy distribution. At the same time, faint disks in our sample are generally younger than 2 Myr. [ABSTRACT FROM AUTHOR]

Stellar multiplicity is a key aspect of exoplanet diversity, as the presence of more than one star in a planetary system can have both devastating and positive effects on its formation and evolution. In this paper, we present the results of a Lucky Imaging survey of 212 exoplanet host stars performed with AstraLux at the 2.2 m telescope of the Centro Astronómico Hispano en Andalucía. The survey includes data from seven observing epochs between August 2015 and September 2020, and data for individual targets from four earlier observing epochs. The targets of this survey are nearby, bright, solar-like stars with high proper motions. In total, we detected 46 co-moving companions of 43 exoplanet host stars. Accordingly, this survey shows that the minimum multiplicity rate of exoplanet host stars is |$20 \pm 3~{\rm per\ cent}$|⁠. In total, 33 binary and 10 hierarchical triple star systems with exoplanets have been identified. All companions were found to have a common proper motion with the observed exoplanet host stars, and with our astrometry we even find evidence of orbital motion for 28 companions. For all targets, we determine the detection limit and explore the detection space for possible additional companions of these stars. Based on the reached detection limit, additional co-moving companions beyond the detected ones can be excluded around all observed exoplanet host stars. The increasing number of exoplanets discovered in multiple stellar systems suggests that the formation of planets in such systems is by no means rare, but common. Therefore, our study highlights the need to consider stellar multiplicity in future studies of exoplanet habitability. [ABSTRACT FROM AUTHOR]

Detailed chemical composition of stars is of prime interest for a range of topics in modern stellar astrophysics, such as the chemical evolution of the Galaxy or the formation, composition, and structure of exoplanets. In this work, we derive the C and O abundances and update Sc, V, Mn, and Co abundances considering hyperfine structure effects and correcting for non-local thermodynamical equilibrium for a sample of 196 late-F, G-, and early-K stars with wide resolved M-dwarf companions. We accomplished this by employing the equivalent width method and high-resolution spectroscopic data. Furthermore, we investigated the distributions of [X/Fe] ratios and [C/O] as a function of metallicity ([Fe/H]) and kinematic population. The observed trends are consistent with previous findings reported in the literature. Additionally, we searched for confirmed exoplanets around our primary stars in the literature and found 24 exoplanets in 17 systems, while none of the M-dwarf companions in our sample presented confirmed exoplanets. In conclusion, our study provides homogeneous abundances from high-resolution spectra for a large sample of FGK primary stars, paving the way for further research on stellar abundances of the M secondaries and exoplanetary science. [ABSTRACT FROM AUTHOR]

We conduct a survey, which explores the data releases of the European Space Agency (ESA)– Gaia mission, in order to investigate the multiplicity of exoplanet hosts at distances of less than 625 pc around the Sun. With the accurate Gaia astrometry we are able to detect stellar and substellar companions of exoplanet hosts by proving the equidistance and common proper motion of these objects. Furthermore, by using the astro- and photometric data provided by the ESA– Gaia mission, we characterize the nature of the identified companions (substellar, stellar, main-sequence, or evolved), determine their properties (mass, effective temperature, and projected separation to the associated exoplanet host), and verify their orbital stability. In addition to main-sequence stars, the companions detected in this study include several brown and white dwarfs. So far in the course of our survey, the multiplicity of more than 2200 exoplanet hosts could be investigated, yielding a multiplicity rate of about 16 per cent (increased to about 19 per cent including published detections from other surveys). Finally, the derived physical properties of the companions were used to investigate the impact of the stellar multiplicity on the properties of the exoplanets and their hosts. In general, there are significant differences in the properties of these objects, dependent on the multiplicity status of their host system, e.g. higher masses of both planets and exoplanet hosts in multiple star systems. Furthermore, the masses and orbital eccentricities of multiple star planets significantly depend on the gravitational impact, induced by the companion star of the exoplanet host. [ABSTRACT FROM AUTHOR]

Located at less than two pc away, Luhman 16 AB (WISE J104915.57-531906.1) is the closest pair of brown dwarfs and the third closest "stellar" system to Earth. An exoplanet candidate in the Luhman 16 binary system was reported in 2017 based on a weak astrometric signature in the analysis of 12 HST epochs. An additional epoch collected in 2018 and re-analysis of the data with more advanced methods further increased the significance level of the candidate, consistent with a Neptune-mass exoplanet orbiting one of the Luhman 16 brown dwarf components. We report the joint analysis of these previous data together with two new astrometric HST epochs we obtained to confirm or disprove this astrometric signature. Our new analysis rules out the presence of a planet orbiting one component of the Luhman 16 AB system for masses 1.5 M (Neptune masses) and periods between 400 and 5000 days. However, the presence of third bodies with masses 3 M and periods between 2 and 400 days (~1.1 years) cannot be excluded. Our measurements make significant improvements to the characterization of this sub-stellar binary, including its mass-ratio 0.8305±0.0006, individual component masses 35.4±0.2M and 29.4±0.2M (Jupiter masses), and parallax distance 1.9960 pc ± 50 AU. Comparison of the masses and luminosities of Luhman 16 AB to several evolutionary models shows persistent discrepancies in the ages of the two components, but strengthens the case that this system is a member of the 510±95 Myr Oceanus Moving Group. [ABSTRACT FROM AUTHOR]

We present results from a Hubble Space Telescope imaging search for low-mass binary and planetary companions to 33 nearby brown dwarfs with spectral types of T8–Y1. Our survey provides new photometric information for these faint systems, from which we obtained model-derived luminosities, masses, and temperatures. Despite achieving a deep sensitivity to faint companions beyond 0.2–0.5 arcsec, down to mass ratios of 0.4–0.7 outside ∼5 au, we find no companions to our substellar primaries. From our derived survey completeness, we place an upper limit of |$f \lt 4.9~{{\ \rm per\ cent}}$| at the 1σ level (<13.0 per cent at the 2σ level) on the binary frequency of these objects over the separation range 1–1000 au and for mass ratios above q  = 0.4. Our results confirm that companions are extremely rare around the lowest mass and coldest isolated brown dwarfs, continuing the marginal trend of decreasing binary fraction with primary mass observed throughout the stellar and substellar regimes. These findings support the idea that if a significant population of binaries exist around such low-mass objects, it should lie primarily below 2–3 au separations, with a true peak possibly located at even tighter orbital separations for Y dwarfs. [ABSTRACT FROM AUTHOR]

We conduct a line-by-line differential analysis of a sample of 125 co-moving pairs of stars (dwarfs and subgiants near solar metallicity). We obtain high-precision stellar parameters with average uncertainties in effective temperature, surface gravity, and metallicity of 16.5 K, 0.033 and 0.014 dex, respectively. We classify the co-moving pairs of stars into two groups, chemically homogeneous (conatal; |Δ[Fe/H]| ≤ 0.04 dex) and inhomogeneous (non-conatal), and examine the fraction of chemically homogeneous pairs as a function of separation and effective temperature. The four main conclusions from this study are (1) A spatial separation of Δ s  = 106 au is an approximate boundary between homogeneous and inhomogeneous pairs of stars, and we restrict our conclusions to only consider the 91 pairs with Δ s  ≤ 106 au; (2) There is no trend between velocity separation and the fraction of chemically homogeneous pairs in the range Δ v  ≤ 4 km s−1; (3) We confirm that the fraction of chemically inhomogeneous pairs increases with increasing T eff and the trend matches a toy model of that expected from planet ingestion; (4) Atomic diffusion is not the main cause of the chemical inhomogeneity. A major outcome from this study is a sample of 56 bright co-moving pairs of stars with chemical abundance differences ≤ 0.02 dex (5 per cent) which is a level of chemical homogeneity comparable to that of the Hyades open cluster. These important objects can be used, in conjunction with star clusters and the Gaia 'benchmark' stars, to calibrate stellar abundances from large-scale spectroscopic surveys. [ABSTRACT FROM AUTHOR]

We present the latest results of our ongoing multiplicity study of (Community) TESS Objects of Interest, using astrometric and photometric data from the ESA‐Gaia mission to detect stellar companions of these stars and characterize their properties. A total of 134 binary, 6 hierarchical triple, and two quadruple star systems are identified among 1106 targets whose multiplicity is investigated in the course of our survey, located at distances closer than about 500 pc around the Sun. The detected companions and targets are at the same distance and have a common proper motion, as expected for components of gravitationally bound stellar systems, as demonstrated by their accurate Gaia DR3 astrometry. The companions have masses from about 0.11 to 2 M⊙$$ {M}_{\odot } $$ and are most abundant in the mass range between 0.2 and 0.5 M⊙$$ {M}_{\odot } $$. The companions have projected separations from the targets between about 50 and 9700 au. Their frequency is the highest and constant from about 300 up to 750 au, decreasing at larger projected separations. In addition to main sequence stars, four white dwarf companions are detected in this study, whose true nature is revealed by their photometric properties. [ABSTRACT FROM AUTHOR]

Disintegrating multiple systems have been previously discovered from kinematic studies of the Hipparcos catalogue. They are presumably the result of dynamical encounters taking place in the Galactic disc between single/multiple systems. In this paper, we aim to expand the search for such systems, to study their properties, as well as to characterize possible low-mass ejecta (i.e. brown dwarfs and planets). We have assembled a list of 15 candidate systems using astrometry from the Tycho-Gaia astrometric solution (later upgraded with Gaia DR3), and here we present the discovery and follow-up of five of them. We have obtained DECam imaging for all five systems and by combining near-infrared photometry and proper motion, we searched for ultracool ejected components. We find that the system consisting of TYC 7731-1951-1, TYC 7731-2128 AB, and TYC 7731-1995-1ABC?, contains one very promising ultracool dwarf candidate. Using additional data from the literature, we have found that three out of five disintegrating system candidates are likely to be true disintegrating systems. [ABSTRACT FROM AUTHOR]

V* PX Vir is a nearby single-lined spectroscopic binary with the primary being a variable of a BY Dra-type star. It has a period of ∼216 d and the components of the system are two low-mass pre-main-sequence stars. By a simultaneous least-squares fit to the radial velocities, the relative positions, and the revised Hipparcos intermediate astrometric data, the complete orbital solution is derived and the precision is improved significantly. In addition, the Hipparcos parallax is revised as 46.06±0.69 mas. Taking advantage of the resulting orbital elements and parallax, the component masses are calculated to be 0.74±0.06  M ⊙ and 0.47±0.02  M ⊙, respectively. The absolute magnitudes in the K and H bands are determined as 4.32±0.14, 4.42±0.03 for the primary and 5.63±0.46, 6.08±0.03 for the secondary, respectively. According to the derived physical parameters, the two components of the system lie very close to the same isochrone age 0.1–0.14 Gyr by comparison with pre-main-sequence evolution tracks. [ABSTRACT FROM AUTHOR]

VHS J1256−1257 AB is an ultracool dwarf binary that hosts a wide-separation planetary-mass companion that is a key target of the JWST Exoplanet Early Release Science programme. Using Keck adaptive optics imaging and aperture masking interferometry, we have determined the host binary's orbit (a = 1.96 ± 0.03 au, P = 7.31 ± 0.02 yr, e = 0.883 ± 0.003) and measured its dynamical total mass (0.141 ± 0.008 M⊙). This total mass is consistent with VHS J1256−1257 AB being a brown dwarf binary or pair of very low-mass stars. In addition, we measured the orbital motion of VHS J1256−1257 b with respect to the barycentre of VHS J1256−1257 AB, finding that the wide companion's orbit is also eccentric (⁠|$e=0.68^{+0.11}_{-0.10}$|⁠), with a mutual inclination of 115○ ± 14○ with respect to the central binary. This orbital architecture is consistent with VHS J1256−1257 b attaining a significant mutual inclination through dynamical scattering and thereafter driving Kozai–Lidov cycles to pump the eccentricity of VHS J1256−1257 AB. We derive a cooling age of 140 ± 20 Myr for VHS J1256−1257 AB from low-mass stellar/substellar evolutionary models. At this age, the luminosity of VHS J1256−1257 b is consistent with both deuterium-inert and deuterium-fusing evolutionary tracks. We thus find a bimodal probability distribution for the mass of VHS J1256−1257 b, either 12.0 ± 0.1  M Jup or 16 ± 1  M Jup, from these models. Future spectroscopic data to measure isotopologues such as HDO and CH3D could break this degeneracy and provide a strong test of substellar models at the deuterium-fusion mass boundary. [ABSTRACT FROM AUTHOR]

We present a high-contrast imaging survey of intermediate-mass (1.75–4.5 M⊙) stars to search the most extreme stellar binaries, i.e. for the lowest mass stellar companions. Using adaptive optics at the Lick and Gemini observatories, we observed 169 stars and detected 24 candidates companions, 16 of which are newly discovered, and all but three are likely or confirmed physical companions. Despite obtaining sensitivity down to the substellar limit for 75 per cent of our sample, we do not detect any companion below 0.3 M⊙, strongly suggesting that the distribution of stellar companions is truncated at a mass ratio of q min ≳ 0.075. Combining our results with known brown dwarf companions, we identify a low-mass companion desert to intermediate-mass stars in the range 0.02 ≲ q ≲ 0.05, which quantitatively matches the known brown dwarf desert among solar-type stars. We conclude that the formation mechanism for multiple systems operates in a largely scale-invariant manner and precludes the formation of extremely uneven systems, likely because the components of a protobinary accrete most of their mass after the initial cloud fragmentation. Similarly, the mechanism to form 'planetary' (q ≲ 0.02) companions likely scales linearly with stellar mass, probably as a result of the correlation between the masses of stars and their protoplanetary discs. Finally, we predict the existence of a sizable population of brown dwarf companions to low-mass stars and of a rising population of planetary-mass objects towards |${\approx}1\,M_\mathrm{Jup}$| around solar-type stars. Improvements on current instrumentation will test these predictions. [ABSTRACT FROM AUTHOR]

Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic, or parabolic passages (a so-called 'fly-by'), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared polarized light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems: AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarized intensity and put particular attention to the presence of multiple light sources in these systems. The local angle of linear polarization indicates the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show that the polarized intensity from scattering with multiple relevant light sources results from an incoherent summation of the individuals' contribution. This can produce nulls of polarized intensity in an image, as potentially observed in AS 205. We discuss the geometry and content of the systems by comparing the polarized light observations with other data at similar resolution, namely with ALMA continuum and gas emission. Collective observational data can constrain the systems' geometry and stellar trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction. [ABSTRACT FROM AUTHOR]

The formation of close binaries has been an open question for decades. A large fraction of close binaries are in triple systems, suggesting that their formation may be associated with the Kozai–Lidov mechanism. However, this picture remains under debate because the configurations of many observed triples are unlikely to trigger the Kozai–Lidov mechanism. In this paper, we use the close binary samples, including eclipsing, spectroscopic, and astrometric binaries, from Gaia Data Release 3 to investigate the mysterious connection between inner binaries and their wide tertiaries. We show that the wide tertiary (at 103–104 au) fraction increases with decreasing orbital periods of the inner binaries. The wide tertiary fraction of eclipsing binaries (a median orbital period of 0.41 d) is 2.33 ± 0.11 times higher than the field wide binary fraction. Furthermore, there is a tentative excess at ∼104 au for tertiaries of eclipsing binaries. Using the v − r angle distributions, we show that wide tertiaries have isotropic orientations with respect to the inner binaries, and the co-planar orbits can be ruled out. The inferred eccentricity distribution of wide tertiaries is consistent (<1σ) with being thermal (f (e) ∝  e), similar to wide binaries at similar separations. The dynamical unfolding scenario is disfavoured because it predicts highly eccentric wide tertiaries, which is inconsistent with our findings. For the Kozai–Lidov mechanism to be effective for wide tertiaries at >103 au, the initial separations of the inner binaries need to be >3 au. Future theoretical investigations are needed to explore the parameter space at these large initial separations and large tertiary separations. [ABSTRACT FROM AUTHOR]

Future Gaia and Legacy Survey of Space and Time data releases, together with wide area spectroscopic surveys, will deliver large samples of resolved binary stars with phase space coordinates, albeit with low-cadence. Given an eccentricity law f (ϵ), we derive properties of (i) the velocity distribution |$v/\sqrt{G M/r}$| normalized by the value for a circular orbit at the measured separation r ; (ii) the astrometric acceleration distributions a /(GM / r 2) again normalized to the circular orbit value. Our formulation yields analytic predictions for the full statistical distribution for some commonly used eccentricity laws, if the time-scale of data sampling is comparable to or exceeds the binary period. In particular, the velocity distribution for the linear eccentricity law is surprisingly simple. With Bayesian analysis, we suggest a method to infer the eccentricity distribution based on the measured velocity distribution. [ABSTRACT FROM AUTHOR]

A total of 3350 objects from the Sixth Catalog of Orbits of Visual Binary Stars (ORB6) are investigated to validate Gaia Early Data Release 3 (EDR3) parallaxes and provide mass estimates for the systems. We show that two-thirds of binaries with a separation of 0.2–0.5 arcsec are left without a parallax solution in EDR3. Special attention is paid to 521 pairs with the parallax known separately for each component. We find 16 entries that are deemed to be chance alignments of unrelated stars. First we show examples of high-confidence binary systems with significant differences in the reported parallaxes of their components. Next we conclude that the reported Gaia EDR3 parallax errors are underestimated, by at least a factor of 3, for sources with a large renormalized unit-weight error (RUWE). Parallaxes are needed to estimate stellar masses. Because nearly 30 per cent of ORB6 entries lack a 5- or 6-parameter solution in EDR3, we attempt to enrich the astrometric data. Distant companions of ORB6 entries are revealed in EDR3 by the analysis of stellar proper motions and Hipparcos parallaxes. Notably, in 28 cases, intrinsic EDR3 parallaxes of the binary components appear to be less reliable than the parallax of the outer companions. Gaia DR2, The Tycho-Gaia Astrometric Solution (TGAS) and Hipparcos parallaxes are used when EDR3 data are unavailable. A synthetic mass–luminosity relationship in the G band for main-sequence stars is obtained to provide mass estimates along with dynamical masses calculated via Kepler's third law. [ABSTRACT FROM AUTHOR]

The long-period giant planet HR 5183 b has one of the most extreme orbits among exoplanets known to date, and represents a test for models of their dynamical evolution. In this work, we use Hipparcos – Gaia astrometry to measure the orbital inclination of this planet for the first time and find |$i=89.9^{+13.3\circ }_{-13.5}$|⁠ , fully consistent with edge-on. The long orbital period and high eccentricity of HR 5183 b are supported by our results, with |$P=102^{+84}_{-34}$| yr and e = 0.87 ± 0.04. We confirm that HR 5183 forms a physically bound binary with HIP 67291 at a projected separation of 15 400 AU, and derive new constraints on the orbit of this pair. We combine these results to measure the mutual inclination between the planetary and binary orbits; we observe significant evidence for misalignment, which remains even after accounting for bias of the prior towards high mutual inclinations. However, our results are too imprecise to evaluate a recent prediction that the mutual inclination should reflect the formation history of HR 5183 b. Further observations, especially the release of the full Gaia astrometric data, will allow for improved constraints on the planet-binary mutual inclination. |$52 \pm 16\ \hbox{per cent}$| of known planets with eccentricities e ≥ 0.8 are found in multiple star systems, a rate that we find to be greater than for the overall planet population to moderate significance (p = 0.0075). This supports the hypothesis that dynamical interactions with wide stellar companions plays an important role in the formation of highly eccentric exoplanets. [ABSTRACT FROM AUTHOR]

Based on high-contrast images obtained with the Gemini Planet Imager (GPI), we report the discovery of two point-like sources at angular separations ρ ∼ 0.18 and 0.80 arcsec from the stars HD 29992 and HD 196385. A combined analysis of the new GPI observations and images from the literature indicates that the source close to HD 29992 could be a companion to the star. Concerning HD 196385, the small number of contaminants (∼0.5) suggests that the detected source may be gravitationally bound to the star. For both systems, we discarded the presence of other potential companions with m > 75 MJup at ρ ∼ 0.3–1.3 arcsec. From stellar model atmospheres and low-resolution GPI spectra, we derive masses of ∼0.2–0.3 M⊙ for these sources. Using a Markov-chain Monte Carlo approach, we performed a joint fit of the new astrometry measurements and published radial velocity data to characterize the possible orbits. For HD 196385B, the median dynamic mass is in agreement with that derived from model atmospheres, whilst for HD 29992B the orbital fit favours masses close to the brown dwarf regime (∼0.08 M⊙). HD 29992 and HD 196385 might be two new binary systems with M-type stellar companions. However, new high angular resolution images would help to confirm definitively whether the detected sources are gravitationally bound to their respective stars, and permit tighter constraints on the orbital parameters of both systems. [ABSTRACT FROM AUTHOR]

Improving direct detection capability close to the star through improved star subtraction and post-processing techniques is vital for discovering new low-mass companions and characterizing known ones at longer wavelengths. We present results of 17 binary star systems observed with the Magellan adaptive optics system (MagAO) and the Clio infrared camera on the Magellan Clay Telescope using binary differential imaging (BDI). BDI is an application of reference differential imaging (RDI) and angular differential imaging (ADI) applied to wide binary star systems (2 arcsec <Δρ < 10 arcsec) within the isoplanatic patch in the infrared. Each star serves as the point spread function (PSF) reference for the other, and we performed PSF estimation and subtraction using principal component analysis. We report contrast and mass limits for the 35 stars in our initial survey using BDI with MagAO/Clio in L ′ and 3.95 µm bands. Our achieved contrasts varied between systems, and spanned a range of contrasts from 3.0 to 7.5 magnitudes and a range of separations from 0.2 to 2 arcsec. Stars in our survey span a range of masses, and our achieved contrasts correspond to late-type M-dwarf masses down to ∼10  M Jup. We also report detection of a candidate companion signal at 0.2 arcsec (18 au) around HIP 67506 A (SpT G5V, mass ∼1.2 M⊙), which we estimate to be |$\sim 60-90 \, \rm{M_{Jup}}$|⁠. We found that the effectiveness of BDI is highest for approximately equal brightness binaries in high-Strehl conditions. [ABSTRACT FROM AUTHOR]

Young M-type binaries are particularly useful for precise isochronal dating by taking advantage of their extended pre-main sequence evolution. Orbital monitoring of these low-mass objects becomes essential in constraining their fundamental properties, as dynamical masses can be extracted from their Keplerian motion. Here, we present the combined efforts of the AstraLux Large Multiplicity Survey, together with a filler sub-programme from the SpHere INfrared Exoplanet (SHINE) project and previously unpublished data from the FastCam lucky imaging camera at the Nordical Optical Telescope (NOT) and the NaCo instrument at the Very Large Telescope (VLT). Building on previous work, we use archival and new astrometric data to constrain orbital parameters for 20 M-type binaries. We identify that eight of the binaries have strong Bayesian probabilities and belong to known young moving groups (YMGs). We provide a first attempt at constraining orbital parameters for 14 of the binaries in our sample, with the remaining six having previously fitted orbits for which we provide additional astrometric data and updated Gaia parallaxes. The substantial orbital information built up here for four of the binaries allows for direct comparison between individual dynamical masses and theoretical masses from stellar evolutionary model isochrones, with an additional three binary systems with tentative individual dynamical mass estimates likely to be improved in the near future. We attained an overall agreement between the dynamical masses and the theoretical masses from the isochrones based on the assumed YMG age of the respective binary pair. The two systems with the best orbital constrains for which we obtained individual dynamical masses, J0728 and J2317, display higher dynamical masses than predicted by evolutionary models. [ABSTRACT FROM AUTHOR]

We report spectroscopic observations of the nearby, 19.5-yr binary system GJ 67AB spanning more than 35 yr. We carry out a global orbital solution combining our radial-velocity measurements with others from the literature going back more than a century, and with all other available astrometric observations. The latter include measurements of the relative position as well as the Hipparcos intermediate data and photographic observations tracing the motion of the photocentre. We derive masses for the primary and the M-dwarf secondary of 0.95 ± 0.11 and 0.254 ± 0.019 M⊙, respectively, as well as a more accurate trigonometric parallax of 79.08 ± 0.63 mas, which accounts for the orbital motion. We provide evidence suggesting that the much smaller parallax from Gaia DR3 is biased. The precision in the masses remains limited mainly by the still few measurements of the relative position. [ABSTRACT FROM AUTHOR]

The last decade of direct imaging (DI) searches for sub-stellar companions has uncovered a widely diverse sample that challenges the current formation models, while highlighting the intrinsically low occurrence rate of wide companions, especially at the lower end of the mass distribution. These results clearly show how blind surveys, crucial to constrain the underlying planet and sub-stellar companion population, are not an efficient way to increase the sample of DI companions. It is therefore becoming clear that efficient target selection methods are essential to ensure a larger number of detections. We present the results of the COPAINS Survey conducted with SPHERE/VLT, searching for sub-stellar companions to stars showing significant proper motion differences (Δμ) between different astrometric catalogues. We observed 25 stars and detected ten companions, including four new BDs: HIP 21152 B, HIP 29724 B, HD 60584 B, and HIP 63734 B. Our results clearly demonstrate how astrometric signatures, in the past only giving access to stellar companions, can now thanks to Gaia reveal companions well in the sub-stellar regime. We also introduce FORECAST (Finely Optimised REtrieval of Companions of Accelerating STars), a tool which allows to check the agreement between position and mass of the detected companions with the measured Δμ. Given the agreement between the values of the masses of the new sub-stellar companions from the photometry with the model-independent ones obtained with FORECAST, the results of COPAINS represent a significant increase in the number of potential benchmarks for BD and planet formation and evolution theories. [ABSTRACT FROM AUTHOR]

The latest results from our ongoing multiplicity study of (Community) TESS Objects of Interest are presented, using astro‐ and photometric data from the ESA‐Gaia mission, to detect stellar companions of these stars and characterize their properties. A total of 124 binary and 7 hierarchical triple star systems were detected among 2175 targets, whose multiplicity was investigated in the course of our survey, which are located at distances closer than about 500 pc around the Sun. The detected companions and the targets are located at the same distance and share a common proper motion, as expected for components of gravitationally bound stellar systems, as proven with their accurate Gaia EDR3 astrometry. The companions have masses in the range between about 0.09 and 2.5 M⊙$$ {M}_{\odot } $$ and are most frequently found in the mass range between 0.15 and 0.8 M⊙$$ {M}_{\odot } $$. The companions exhibit projected separations to the targets between about 50 to 9700 au and their frequency is the highest and constant up to about 500 au, while it decreases for larger projected separations. In addition to mainly mid M to early K dwarfs, 4 white dwarf companions were also detected in this survey, whose true nature could be identified with their photometric properties. [ABSTRACT FROM AUTHOR]

The relative Rectilinear motion of optical double stars provides an important clue to the relationship of the components. We provide an objective method of confirming the optical status of double stars, and of obtaining unbiased rectilinear elements solely on data obtained from the HIPPARCOS and Gaia DR2 space missions. We apply this technique to determine the rectilinear elements of 14 optical double stars from the southern double star catalogue of James Dunlop. The resultant uncertainties are, on average, an order of magnitude smaller than the method currently used. [ABSTRACT FROM AUTHOR]

We have developed a new, fast method of estimating the orbital properties of a binary or triple system using as few as two epochs of astrometric data. fobos (Few Observation Binary Orbit Solver) uses a flat prior brute force Monte Carlo method to produce probability density functions of the likely orbital parameters. We test the code on fake observations and show that it can (fairly often) constrain the semi-major axis to within a factor of 2–3, and the inclination to within ∼20° from only two astrometric observations. We also show that the 68 and 95 per cent confidence intervals are statistically reliable. Applying this method to triple systems allows the relative inclination of the secondary and tertiary star orbits to be constrained. fobos can usually find a statistically significant number of possible matches in CPU minutes for binary systems, and CPU hours for triple systems. [ABSTRACT FROM AUTHOR]

We present follow‐up imaging and spectroscopic observations of the exoplanet host star γ Cep A, and of its low‐mass stellar companion γ Cep B. We used the lucky‐imager AstraLux at the Calar Alto observatory to follow the orbital motion of the companion around its primary, whose radial velocity (RV) was determined with spectra of the star, taken with the Échelle spectrograph FLECHAS at the University Observatory Jena. We measured the astrometry of the companion relative to the exoplanet host star in all AstraLux images and determined its apparent SDSS i′‐band photometry, for which we obtained i′=9.84±0.17 mag. Using stellar evolutionary models and the Gaia parallax of the exoplanet host star, we derived the mass of γ Cep B to be 0.39 ± 0.03 M⊙. This is in good agreement with the mass of the companion that we derived from its near‐infrared photometry given in the literature. With the detection limit reached in our AstraLux images, we explored the detection space of potential additional companions in the γ Cep binary system. In the background limited region at angular separations larger than 5 arcsec (or 69 au of projected separation) companions down to 0.11 M⊙ are detectable around the bright exoplanet host star. The radial field of view, fully covered by our AstraLux observations, exhibits a radius of 11.2 arcsec. This allows the detection of companions with projected separations up to 155 au. However, except for γ Cep B, no additional companions could be imaged with AstraLux around the exoplanet host star. We redetermined the orbital solution of the γ Cep binary system with the new AstraLux astrometry of γ Cep B and the additional radial velocities of γ Cep A, obtained from our FLECHAS spectroscopy of the star, combined with astrometric and RV data from the literature. The determined Keplerian orbital elements were used to derive the system parameters and to calculate specific future ephemeris for this intriguing exoplanet host binary star system. [ABSTRACT FROM AUTHOR]

Eccentricity of wide binaries is difficult to measure due to their long orbital periods. With Gaia 's high-precision astrometric measurements, eccentricity of a wide binary can be constrained by the angle between the separation vector and the relative velocity vector (the v - r angle). In this paper, by using the v - r angles of wide binaries in Gaia Early Data Release 3, we develop a Bayesian approach to measure the eccentricity distribution as a function of binary separations. Furthermore, we infer the eccentricities of individual wide binaries and make them publicly available. Our results show that the eccentricity distribution of wide binaries at 102 AU is close to uniform and becomes superthermal at >103 AU, suggesting two formation mechanisms dominating at different separation regimes. The close binary formation, most likely disc fragmentation, results in a uniform eccentricity distribution at <102 AU. The wide binary formation that leads to highly eccentric wide binaries at >103 AU may be turbulent fragmentation and/or the dynamical unfolding of compact triples. With Gaia , measuring eccentricities is now possible for a large number of wide binaries, opening a new window to understanding binary formation and evolution. [ABSTRACT FROM AUTHOR]

Planet formation is often considered in the context of one circumstellar disc around one star. Yet, stellar binary systems are ubiquitous, and thus a substantial fraction of all potential planets must form and evolve in more complex, dynamical environments. We present the results of a 5 yr astrometric monitoring campaign studying 45 binary star systems that host Kepler planet candidates. The planet-forming environments in these systems would have literally been shaped by the binary orbits that persist to the present day. Crucially, the mutual inclinations of star–planet orbits can only be addressed by a statistical sample. We describe in detail our sample selection and Keck/NIRC2 laser guide star adaptive optics observations collected from 2012 to 2017. We measure orbital arcs, with a typical accuracy of ∼0.1 mas yr−1, that test whether the binary orbits tend to be aligned with the edge-on transiting planet orbits. We rule out randomly distributed binary orbits at 4.7σ, and we show that low mutual inclinations are required to explain the observed orbital arcs. If the stellar orbits have a field binary-like eccentricity distribution, then the best match to our observed orbital arcs is a distribution of mutual inclinations ranging from 0° to 30°. We discuss the implications of such widespread planet–binary alignment in the theoretical context of planet formation and circumstellar disc evolution. [ABSTRACT FROM AUTHOR]

We present a strongly interacting quadruple system associated with the K2 target EPIC 220204960. The K2 target itself is a Kp = 12.7-mag star at Teff ≃ 6100 K, which we designate as 'B-N' (blue northerly image). The host of the quadruple system, however, is a Kp ≃ 17-mag star with a composite M-star spectrum, which we designate as 'R-S' (red southerly image). With a 3.2-arcsec separation and similar radial velocities and photometric distances, 'B-N' is likely physically associated with 'R-S', making this a quintuple system, but that is incidental to our main claim of a strongly interacting quadruple system in 'R-S'. The two binaries in 'R-S' have orbital periods of 13.27 and 14.41 d, respectively, and each has an inclination angle of ≳89°. From our analysis of radial-velocity (RV) measurements, and of the photometric light curve, we conclude that all four stars are very similar with masses close to 0.4M⊙. Both of the binaries exhibit significant eclipse-timing variations where those of the primary and secondary eclipses 'diverge' by 0.05 d over the course of the 80-d observations. Via a systematic set of numerical simulations of quadruple systems consisting of two interacting binaries, we conclude that the outer orbital period is very likely to be between 300 and 500 d. If sufficient time is devoted to RV studies of this faint target, the outer orbit should be measurable within a year.

Stellar multiplicity is among the oldest and richest problems in astrophysics. Binary stars are a cornerstone of stellar mass and radius measurements that underpin modern stellar evolutionary models. Binaries are the progenitors of many of the most interesting and exotic astrophysical phenomena, ranging from type Ia supernovae to gamma ray bursts, hypervelocity stars, and most detectable stellar black holes. They are also ubiquitous, accounting for about half of all stars in the Universe. In the era of gravitational waves, wide-field surveys, and open-source stellar models, binaries are coming back stronger than a nineties trend. Much of the progress in the last decade has been enabled by the Gaia mission, which provides high-precision astrometry for more than a billion stars in the Milky Way. The Gaia data probe a wider range of binary separations and mass ratios than most previous surveys, enabling both an improved binary population census and discovery of rare objects. I summarize recent results in the study of binary stars brought about by Gaia , focusing in particular on developments related to wide (a ≳ 100 au) binaries, evidence of binarity from astrometric noise and proper motion anomaly, astrometric and radial velocity orbits from Gaia DR3, and binaries containing non-accreting compact objects. Limitations of the Gaia data, the importance of ground-based follow-up, and anticipated improvements with Gaia DR4 are also discussed. [ABSTRACT FROM AUTHOR]

In 1829 James Dunlop published the first southern double star catalogue of some 253 double stars. The accuracy of this catalogue has been determined by using Aladin to cross-match them with Gaia DR2 and estimate their positional (right ascension, declination, position angle, and separation) and magnitude accuracy. Seven per cent could not be identified using Aladin and 14 were single stars. We found 13 double stars (5 per cent) not currently listed in the Washington Double Star Catalog. The catalogue equinox was determined as B1826.0. Overall, 1σ uncertainties in right ascension were within 1 sidereal minute and declinations within 10 arcmin. We also identified and corrected a number of Quadrant errors in the position angles and quantified the separations. Apparent visual magnitude estimates were generally within 1 mag. Dunlop's overall uncertainties were larger than those of his contemporaries, nevertheless the little known catalogue remains valuable as the earliest source of over 200 double star astrometric and visual magnitude estimates. [ABSTRACT FROM AUTHOR]

WR22 = HD 92740 is a bright (V  = 6.4 mag), intrinsically luminous, double-line WN7h  + O9III-V binary exhibiting one sharp 8 per cent deep eclipse near periastron in its elliptical (e  = 0.6) 80-day orbit, when the WR-star passes in front of the O star, with no secondary eclipse. We apply two models (L96, A13) to probe the optical space-based light curves from BRITE-Constellation , including three separate, complete eclipses, that show increased (o-c) scatter compared to the rest of the observations outside the eclipses, likely due to O-star light encountering WR wind-clumps. L96 is a simple atmospheric-eclipse model, often applied to close WR + O binaries, where the O-star is considered a point-source. A13 considers a finite-disk O-star and allows for atmospheric, photospheric and reflection components to the eclipse, permitting a better characterization of its shape through a more physically realistic description of the structures for both stars in WR22. Nevertheless, A13 is still susceptible to uncertainties in the luminosity of the O-star before unique values for the orbital inclination and WR mass-loss rate can be estimated. We present solutions for the two extremes of the O-star, O9V and O9III. As photometry alone cannot allow us to discriminate between these, we compared our results to the spectral models found in the literature and determined the correct solution to be O9V. Our best-fitting A13 Model 1 gives i  = 83.5 ± 0.4°, with |$\dot{M}_{\rm WR} = (1.86 \pm 0.2) \times 10^{-5} \dot{M}_{\odot }/yr$|⁠. The flux ratio in the red BRITE band in this model is F O/ F WR = 0.064 ± 0.002. [ABSTRACT FROM AUTHOR]

The observed orbits of emission-line stars may be affected by systematics owing to their broad emission lines being formed in complex and extended environments. This is problematic when orbital parameter probability distributions are estimated assuming radial-velocity data are solely comprised of Keplerian motion plus Gaussian white noise, leading to overconfident and inaccurate orbital solutions, with implications for the inferred dynamical masses and hence evolutionary models. We present a framework in which these systems can be meaningfully analysed. We synthesize benchmark data sets, each with a different and challenging noise formulation, for testing the performance of different algorithms. We make these data sets freely available with the aim of making model validation an easy and standardized practice in this field. Next, we develop an application of Gaussian processes to model the radial-velocity systematics of emission-line binaries, named marginalized |$\mathcal {GP}$|⁠. We benchmark this algorithm, along with current standardized algorithms, on the synthetic data sets and find our marginalized |$\mathcal {GP}$| algorithm performs significantly better than the standard algorithms for data contaminated by systematics. Finally, we apply the marginalized |$\mathcal {GP}$| algorithm to four prototypical emission-line binaries: Eta Carinae, GG Carinae, WR 140, and WR 133. We find systematics to be present in several of these case studies; and consequently, the predicted orbital parameter distributions, and dynamical masses, are modified from those previously determined. [ABSTRACT FROM AUTHOR]

Speckle observations of binary stars were performed in the 900–1600 nm infrared range at the 6‒m telescope using the commercially available CCD camera SWIR Snake-640 with InGaAs 640 × 512 pixels sensitive area. Peltier cooling of the sensor allows reaching –30°C temperature of the CCD. The thermal noise of the CCD remains significantly high under such temperature. That limits the speckle interferometric application of the camera to approximately 9th magnitude under moderate seeing conditions. To estimate other characteristics of the camera for interferometric application in the near-IR, we used it to measure separations, position angles and magnitude differences of some well-studied binary stars. Diffraction-limited angular resolution was achieved for each of the reconstructed images. [ABSTRACT FROM AUTHOR]

Abstract—We present the study of the multiple system HD 52721 by means of speckle interferometry in 2019–2020 at the 6-m telescope of the SAO RAS. Formerly, HD 52721 was known as triple ( (B2V + B2V; ) + ; ). In our work, the system is resolved as a speckle interferometric triple system, i.e., the total system multiplicity increased up to four components ( (B2Ve; )+ (B9VХ, ); ). We have used the reference-dependent and reference-independent methods for measuring positional parameters and magnitude differences between the components. The obtained measurements of the brightness differences agree with the observed light curve of the eclipsing pair. [ABSTRACT FROM AUTHOR]

We present the latest results of our ongoing multiplicity study of (Community) TESS Objects of Interest, using astro‐ and photometric data from the ESA‐Gaia mission, to detect stellar companions of these stars and to characterize their properties. In total, 107 binary, 5 hierarchical triple star systems, as well as one quadruple system were detected among 585 targets surveyed, which are all located at distances closer than about 500 pc around the Sun. As proven with their accurate Gaia EDR3 astrometry, the companions and the targets are located at the same distance and share a common proper motion, as it is expected for components of gravitationally bound stellar systems. The companions exhibit masses in the range between about 0.09 M⊙ and 4.5 M⊙ and are most frequently found in the mass range between 0.15 and 0.6 M⊙. The companions are separated from the targets by about 120 up to 9,500 au and their frequency is the highest and constant within about 500 au while it continually decreases for larger separations. Beside mainly early to mid M dwarfs, also five white dwarf companions were identified in this survey, whose true nature was revealed by their photometric properties. [ABSTRACT FROM AUTHOR]

We have used WFPC2 on board the Hubble Space Telescope to obtain images of 47 members of the Taurus and Chamaeleon I star-forming regions that have spectral types of M6-L0 (M ∼ 0.01-0.1 M ). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. In these images, we have identified promising candidate companions to 2MASS J04414489+2301513 (ρ = 0.″105/15 AU), 2MASS J04221332+1934392 (ρ = 0.″05/7 AU), and ISO 217 (ρ = 0.″03/5 AU). We reported the first candidate in a previous study, showing that it has a similar proper motion as the primary in images from WFPC2 and Gemini adaptive optics. We have collected an additional epoch of data with Gemini that further supports that result. By combining our survey with previous high-resolution imaging in Taurus, Chamaeleon I, and Upper Sco (τ ∼ 10 Myr), we measure binary fractions of 14/93 = for M4-M6 (M ∼ 0.1-0.3 M ) and 4/108 = for >M6 (M ≲ 0.1 M ) at separations of >10 AU. Given the youth and low density of these regions, the lower binary fraction at later types is probably primordial rather than due to dynamical interactions among association members. The widest low-mass binaries (>100 AU) also appear to be more common in Taurus and Chamaeleon I than in the field, which suggests that the widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or that field brown dwarfs have been born predominantly in denser clusters where wide systems are disrupted or inhibited from forming. © 2014. The American Astronomical Society. All rights reserved..

We present results from a near-infrared (NIR) adaptive optics (AO) survey of pre-main-sequence stars in the Lupus molecular cloud with NACO at the Very Large Telescope (VLT) to identify (sub)stellar companions down to ∼20-au separation and investigate the effects of multiplicity on circumstellar disc properties. We observe for the first time in the NIR with AO a total of 47 targets and complement our observations with archival data for another 58 objects previously observed with the same instrument. All 105 targets have millimetre Atacama Large Millimetre/sub-millimetre Array (ALMA) data available, which provide constraints on disc masses and sizes. We identify a total of 13 multiple systems, including 11 doubles and 2 triples. In agreement with previous studies, we find that the most massive (M dust > 50 M⊕) and largest (R dust > 70 au) discs are only seen around stars lacking visual companions (with separations of 20–4800 au) and that primaries tend to host more massive discs than secondaries. However, as recently shown in a very similar study of >200 PMS stars in the Ophiuchus molecular cloud, the distributions of disc masses and sizes are similar for single and multiple systems for M dust < 50 M⊕ and radii R dust < 70 au. Such discs correspond to ∼80–90 per cent of the sample. This result can be seen in the combined sample of Lupus and Ophiuchus objects, which now includes more than 300 targets with ALMA imaging and NIR AO data, and implies that stellar companions with separations >20 au mostly affect discs in the upper 10 |${{\ \rm per\ cent}}$| of the disc mass and size distributions. [ABSTRACT FROM AUTHOR]

The intermediate-mass Herbig Ae star V1787 Ori is a member of the L1641 star-forming region in the Orion A molecular cloud. We report the detection of an M-type companion to V1787 Ori at a projected separation of 6.66 arcsec (corresponding to 2577 au), from the analysis of VLT/NACO adaptive optics K s-band image. Using astrometric data from Gaia DR2, we show that V1787 Ori A and B share similar distance (d ∼ 387 pc) and proper motion, indicating that they are physically associated. We estimate the spectral type of V1787 Ori B to be M5 ± 2 from colour–spectral type calibration tables and template matching using SpeX spectral library. By fitting PARSEC models in the Pan-STARRS colour–magnitude diagram, we find that V1787 Ori B has an age of 8.1 |$^{+1.7}_{-1.5}$| Myr and a mass of 0.39 |$^{+0.02}_{-0.05}$| M⊙. We show that V1787 Ori is a pre-main-sequence wide binary system with a mass ratio of 0.23. Such a low-mass ratio system is rarely identified in Herbig Ae/Be binary systems. We conclude this work with a discussion on possible mechanisms for the formation of V1787 Ori wide binary system. [ABSTRACT FROM AUTHOR]

An all-sky sample of 1227 visual binaries based on Washington Double Star catalogue is constructed to infer the initial mass function (IMF), mass ratio, and projected distance distribution with a dedicated population synthesis model. Parallaxes from Gaia DR2 and Hipparcos are used to verify the distance distribution. The model is validated on the single-star Tycho-2 sample and successfully reproduces the observed magnitudes and angular separations. The projected separation distribution follows f (s) ∼ s −1.2 in 102–2 × 103   au range for 1–4.5 m ⊙ primary stars. Several algorithms are explored as pairing functions. Random pairing is confidently rejected. Primary-constrained pairing (PCP) and split-core pairing (SCP), the scenarios adopting primary component's or total system's mass as fundamental, are considered. The preferred IMF slope is α ∼ 2.8 either way. A simple power-law mass ratio distribution is unlikely, but the introduction of a twin excess provides a favourable result. PCP with f (q) ∼ q −1 is preferred with a tiny twin fraction, models with f (q) ∼ q −1.5 are acceptable when a larger twin excess is allowed. SCP is similar to PCP when a larger slope of the power law is adopted: f (q) ∼ q β + 0.7. [ABSTRACT FROM AUTHOR]

In this work, the orbital elements are improved and the total masses of the three close visual binary systems CVBSs: HIP 11352, HIP 70973, and HIP 72479 are precisely calculated. The calculations were performed based on an assessment of the latest Gaia DR2 and Hipparcos trigonometric parallax measurements. The morphology and kinematics of orbits are fitted to the observational data available in the Fourth Catalogue of Interferometric Measurements of Binary Stars, and compared with the earlier orbits published in the Sixth Catalog of Orbits of Visual Binary Stars. The computation of orbital elements allows the determination and estimation of the mass sums for the three systems as: 1.81 ± 0.17 M⊙, 1.83 ± 0.07 M⊙, and 1.61 ± 0.26 M⊙ for HIP 11352, HIP 70973, and HIP 72479 respectively. This suggests that these systems belong to the main sequence stars for both components. This will provide valuable insights into the evolution paths of these systems. [ABSTRACT FROM AUTHOR]

The first results of a new survey, which explores the second data release of the ESA‐Gaia mission, are reported in order to search for stellar companions of (Community) TESS Objects of Interest and to characterize their properties. In total, 193 binary and 15 hierarchical triple star systems are presented, detected among 1,391 target stars, which are located at distances closer than about 500 pc around the Sun. The companions and the targets are equidistant and share a common proper motion, as is expected for gravitationally bound stellar systems, proven with their accurate Gaia astrometry. The companions exhibit masses in the range between about 0.08 M⊙ and 3M⊙ and are most frequently found in the mass range between 0.13 and 0.6M⊙. The companions are separated from the targets by about 40 up to 9,900 au, and their frequency continually decreases with increasing separation. While most of the detected companions are late K to mid M dwarfs, also five white dwarf companions were identified in this survey, whose true nature is revealed by their photometric properties. [ABSTRACT FROM AUTHOR]

Context. Recent surveys indicate that planets in binary systems are more abundant than previously thought, which is in agreement with theoretical work on disc dynamics and planet formation in binaries. So far, most observational surveys, however, have focused on short-period planets in binaries, thus little is known about the occurrence rates of planets on longer periods (≥10 au). Aims. In order to measure the abundance and physical characteristics of wide-orbit giant exoplanets in binary systems, we have designed the "VIsual Binary Exoplanet survey with Sphere" (VIBES) to search for planets in visual binaries. It uses the SPHERE instrument at VLT to search for planets in 23 visual binary and four visual triple systems with ages of <145 Myr and distances of <150 pc. Methods. We used the IRDIS dual-band imager on SPHERE to acquire high-contrast images of the sample targets. For each binary, the two components were observed at the same time with a coronagraph masking only the primary star. For the triple star, the tight components were treated as a single star for data reduction. This enabled us to effectively search for companions around 50 individual stars in binaries and four binaries in triples. Results. We derived upper limits of <13.7% for the frequency of sub-stellar companions around primaries in visual binaries, <26.5% for the fraction of sub-stellar companions around secondaries in visual binaries, and an occurrence rate of <9.0% for giant planets and brown dwarfs around either component of visual binaries. We have combined our observations with literature measurements to astrometrically confirm, for the first time, that 20 binaries and two triple systems, which were previously known, are indeed physically bound. Finally, we discovered a third component of the binary HD 121336. Conclusions. The upper limits we derived are compatible with planet formation through the core accretion and the gravitational instability processes in binaries. These limits are also in line with limits found for single star and circumbinary planet search surveys. [ABSTRACT FROM AUTHOR]

Context. The angle between the stellar spin-axis and the orbital plane of a stellar or planetary companion has important implications for the formation and evolution of such systems. A study by Hale (1994, AJ, 107, 306) found that binaries with separations a ≲ 30 au are preferentially aligned while binaries on wider orbits are frequently misaligned. Aims. We aim to test the robustness of the Hale study results by reanalysing the sample of visual binaries with measured rotation periods using independently derived stellar parameters and a Bayesian formalism. Methods. Our analysis is based on a combination of data from the Hale study and newly obtained spectroscopic data from the Hertzsprung SONG telescope, combined with astrometric data from Gaia DR2 and the Washington Double Star Catalog. We combine measurements of stellar radii and rotation periods to obtain stellar rotational velocities v. Rotational velocities v are combined with measurements of projected rotational velocities v sin i to derive posterior probability distributions of stellar inclination angles i. We determine line-of-sight projected spin-orbit angles by comparing stellar inclination angles with astrometric orbital inclination angles. Results. We find that the precision of the available data is insufficient to make inferences about the spin-orbit alignment of visual binaries. The data are equally compatible with alignment and misalignment at all orbital separations. Conclusions. We conclude that the previously reported trend that binaries with separations a ≲ 30 au are preferentially aligned is spurious. The spin-orbit alignment distribution of visual binaries is unconstrained. Based on simulated observations, we predict that it will be difficult to reach the sufficient precision in v sin i, rotation periods, and orbital inclination required to make robust statistical inferences about the spin-orbit alignment of visual binaries. [ABSTRACT FROM AUTHOR]

We present the results from an integral field spectroscopy study of seven close visual binary pairs of young M-dwarf multiple systems. The target systems are part of the astrometric monitoring AstraLux programme, surveying hundreds of M-dwarf systems for multiplicity and obtaining astrometric epochs for orbital constraints. Our new VLT/SINFONI data provides resolved spectral type classifications in the J, H, and K bands for seven of these low-mass M-dwarf binaries, which we determine by comparing them to empirical templates and examining the strength of water absorption in the K band. The medium resolution K-band spectra also allows us to derive effective temperatures for the individual components. All targets in the survey display several signs of youth, and some have kinematics similar to young moving groups, or low surface gravities which we determined from measuring equivalent widths of gravity sensitive alkali lines in the J band. Resolved photometry from our targets is also compared with isochrones from theoretical evolutionary models, further implying young ages. Dynamical masses will be provided from continued monitoring of these systems, which can be seen as emblematic binary benchmarks that may be used to calibrate evolutionary models for low-mass stars in the future. [ABSTRACT FROM AUTHOR]