Keywords

We have developed a general statistical procedure for analysis of 2D and 3D finite patterns, which is applied to the data from recently released Gaia-ESA catalog DR2. The 2D analysis clearly confirms our former results on the presence of binaries in the former DR1 catalog. Our main objective is the statistical 3D analysis of DR2. For this, it is essential that the DR2 catalog includes parallaxes and data on the proper motion. The analysis allows us to determine for each pair of stars the probability that it is the binary star. This probability is represented by the function $\beta \left({\rm{\Delta }}\right)$ depending on the separation. Furthermore, a combined analysis of the separation with proper motion provides a clear picture of binaries with two components of the motion: parallel and orbital. The result of this analysis is an estimate of the average orbital period and mass of the binary system. The catalog we have created involves 80,560 binary candidates.

We describe a star cluster formation model that includes individual star formation from self-gravitating, magnetized gas, coupled to collisional stellar dynamics. The model uses the Astrophysical Multi-purpose Software Environment to integrate an adaptive-mesh magnetohydrodynamics code (FLASH) with a fourth order Hermite N-body code (ph4), a stellar evolution code (SeBa), and a method for resolving binary evolution (multiples). This combination yields unique star-formation simulations that allow us to study binaries formed dynamically from interactions with both other stars and dense, magnetized gas subject to stellar feedback during the birth and early evolution of stellar clusters. We find that for massive stars, our simulations are consistent with the observed dynamical binary fractions and mass ratios. However, our binary fraction drops well below observed values for lower mass stars, presumably due to unincluded binary formation during initial star formation. Further, we observe a buildup of binaries near the hard-soft boundary that may be an important mechanism driving early cluster contraction.

We present the results of a binary population study in the Orion Nebula Cluster (ONC) using archival Hubble Space Telescope (HST) data obtained with the Advanced Camera for Surveys in Johnson V filter (HST Proposal 10246, PI M. Robberto). Young clusters and associations hold clues to the origin and properties of multiple star systems. Binaries with separations <100 au are useful as tracers of the initial binary population because they are not as likely to be destroyed through dynamical interactions. Low-mass, low stellar density, star-forming regions such as Taurus–Auriga, reveal an excess of multiples compared to the Galactic field. Studying the binary population of higher mass, higher stellar density star-forming regions like the ONC provides useful information concerning the origin of the Galactic field star population. In this survey, we characterize the previously unexplored (and incomplete) separation parameter space of binaries in the ONC (15–160 au) by fitting a double-point-spread function (PSF) model built from empirical PSFs. We identified 14 candidate binaries (11 new detections) and find that ${8}_{-2 \% }^{+4 \% }$ of our observed sample are in binary systems, complete over mass ratios and separations of 0.6 < q < 1.0 and 30 < a < 160 au. This is consistent with the Galactic field M-dwarf population over the same parameter ranges, 6.5% ± 3%. Therefore, high-mass star-forming regions like the ONC would not require further dynamical evolution for their binary population to resemble the Galactic field, as some models have hypothesized for young clusters.

We propose that the inner engine of a type I binary-driven hypernova (BdHN) is composed of Kerr black hole (BH) in a non-stationary state, embedded in a uniform magnetic field B₀ aligned with the BH rotation axis and surrounded by an ionized plasma of extremely low density of 10⁻¹⁴ g cm⁻³. Using GRB 130427A as a prototype, we show that this inner engine acts in a sequence of elementary impulses. Electrons accelerate to ultrarelativistic energy near the BH horizon, propagating along the polar axis, θ = 0, where they can reach energies of ∼10¹⁸ eV, partially contributing to ultrahigh-energy cosmic rays. When propagating with $\theta \ne 0$ through the magnetic field B₀, they produce GeV and TeV radiation through synchroton emission. The mass of BH, M = 2.31M_⊙, its spin, α = 0.47, and the value of magnetic field B₀ = 3.48 × 10¹⁰ G, are determined self consistently to fulfill the energetic and the transparency requirement. The repetition time of each elementary impulse of energy ${ \mathcal E }\sim {10}^{37}$ erg is ∼10⁻¹⁴ s at the beginning of the process, then slowly increases with time evolution. In principle, this "inner engine" can operate in a gamma-ray burst (GRB) for thousands of years. By scaling the BH mass and the magnetic field, the same inner engine can describe active galactic nuclei.

We investigate the role of the Keplerian tidal field generated by a supermassive black hole (SMBH) on the three-body dynamics of stellar mass black holes. We consider two scenarios occurring close to the SMBH: the breakup of unstable triples and three-body encounters between a binary and a single. These two cases correspond to the hard and soft binary cases, respectively. The tidal field affects the breakup of triples by tidally limiting the system, so that the triples break earlier with lower breakup velocity, leaving behind slightly larger binaries (relative to the isolated case). The breakup direction becomes anisotropic and tends to follow the shape of the Hill region of the triple, favoring breakups in the radial direction. Furthermore, the tidal field can torque the system, leading to angular momentum exchanges between the triple and its orbit around the SMBH. This process changes the properties of the final binary, depending on the initial angular momentum of the triple. Finally, the tidal field also affects binary-single encounters: binaries tend to become both harder and more eccentric with respect to encounters that occur in isolation. Consequently, single-binary scattering in a deep Keplerian potential produces binaries with shorter gravitational wave merger timescales.

Type IIb supernovae (SNe) are important candidates to understand mechanisms that drive the stripping of stripped-envelope (SE) supernova (SN) progenitors. While binary interactions and their high incidence are generally cited to favor them as SN IIb progenitors, this idea has not been tested using models covering a broad parameter space. In this paper, we use non-rotating single- and binary-star models at solar and low metallicities spanning a wide parameter space in primary mass, mass ratio, orbital period, and mass transfer efficiencies. We find that our single- and binary-star models contribute to roughly equal, however small, numbers of SNe IIb at solar metallicity. Binaries only dominate as progenitors at low metallicity. We also find that our models can account for less than half of the observationally inferred rate for SNe IIb at solar metallicity, with computed rates ≲4% of core-collapse (CC) SNe. On the other hand, our models can account for the rates currently indicated by observations at low metallicity, with computed rates as high as 15% of CC SNe. However, this requires low mass transfer efficiencies (≲0.1) to prevent most progenitors from entering contact. We suggest that the stellar wind mass-loss rates at solar metallicity used in our models are too high. Lower mass-loss rates would widen the parameter space for binary SNe IIb at solar metallicity by allowing stars that initiate mass transfer earlier in their evolution to reach CC without getting fully stripped.

The parameter distribution of binaries is a fundamental knowledge of the stellar systems. A statistical study on the binary stars is carried out based on the LAMOST spectral and Kepler photometric database. We presented a catalog of 1320 binary stars with plentiful parameters, including period, binary subtype, atmosphere parameters (T_eff, [Fe/H], and $\mathrm{log}g$), and the physical properties, such as mass, radius, and age, for the primary component stars. Based on this catalog, the unbiased distribution, rather than the observed distribution, was obtained after the correction of selection biases by the Monte Carlo method considering comprehensive affecting factors. For the first time, the orbital eccentricity distribution of the detached binaries is presented. The distribution differences between the three subtypes of binaries (detached, semidetached, and contact) are demonstrated, which can be explained by the generally accepted evolutional scenarios. Many characteristics of the binary stars, such as huge mass transfer on semidetached binaries, period cutoff on contact binaries, period–temperature relationship of contact binaries, and the evolved binaries, are reviewed by the new database. This work supports a common evolutionary scenario for all subtypes of binary stars.

Aluminium-26 is a short-lived radionuclide with a half-life of 0.72 Myr, which is observed today in the Galaxy via γ-ray spectroscopy and is inferred to have been present in the early solar system via analysis of meteorites. Massive stars are considered the main contributors of ²⁶Al. Although most massive stars are found in binary systems, the effect, however, of binary interactions on the ²⁶Al yields has not been investigated since Braun & Langer. Here we aim to fill this gap. We have used the MESA stellar evolution code to compute massive (10 M_⊙ ≤ M ≤ 80 M_⊙) nonrotating single and binary stars of solar metallicity (Z = 0.014). We computed the wind yields for the single stars and for the binary systems where mass transfer plays a major role. Depending on the initial mass of the primary star and orbital period, the ²⁶Al yield can either increase or decrease in a binary system. For binary systems with primary masses up to ∼35–40 M_⊙, the yield can increase significantly, especially at the lower mass end, while above ∼45 M_⊙ the yield becomes similar to the single-star yield or even decreases. Our preliminary results show that compared to supernova explosions, the contribution of mass loss in binary systems to the total ²⁶Al abundance produced by a stellar population is minor. On the other hand, if massive star mass loss is the origin of ²⁶Al in the early solar system, our results will have significant implications for the identification of the potential stellar, or stellar population, source.

We report the first-time use of the Aqueye+ and Iqueye instruments to record lunar occultation events. High time resolution recordings in different filters have been acquired for several occultations taken from 2016 January through 2018 January with Aqueye+ at the Copernicus telescope and Iqueye at the Galileo telescope in Asiago, Italy. Light curves with different time bins were calculated in post-processing and analyzed using a least-square model-dependent method. A total of nine occultation light curves were recorded, including one star for which we could measure for the first time the size of the chromosphere (μ Psc) and one binary star for which discrepant previous determinations existed in the literature (SAO 92922). A disappearance of Alf Tau shows an angular diameter in good agreement with literature values. The other stars were found to be unresolved, at the milliarcsecond level. We discuss the unique properties of Aqueye+ and Iqueye for these kind of observations, namely the simultaneous measurement in up to four different filters thanks to pupil splitting, and the unprecedented time resolution well exceeding the microsecond level. This latter makes Aqueye+ and Iqueye suitable to observe not just occultations by the Moon, but also much faster events such as, e.g., occultations by artificial screens in low orbits. We provide an outlook of future possible observations in this context.

Binary stars are common. While only those with small separations may exchange gas with one another, even the widest binaries interact with their gaseous surroundings. Drag forces and accretion rates dictate how these systems are transformed by these interactions. We perform three-dimensional hydrodynamic simulations of Bondi–Hoyle–Lyttleton flows, in which a binary moves supersonically relative to a homogeneous medium, using the adaptive mesh refinement code FLASH. We simulate a range of values of the initial semimajor axis of the orbit relative to the gravitational focusing impact parameter of the pair. When the binary separation is less than the gravitational focusing impact parameter, the pair orbits within a shared bow shock. When the pair is wider, each object has an individual bow shock structure. The long-term evolution of the binary is determined by the timescales for accretion, slowing of the center of mass, and orbital inspiraling. We find a clear hierarchy of these timescales; a binary's center-of-mass motion is slowed over a shorter timescale than the pair inspirals or accretes. In contrast to previous analytic predictions, which assume an unperturbed background medium, we find that the timescale for orbital inspiraling is proportional to the semimajor axis to the 0.19 ± 0.01 power. This positive scaling indicates that gaseous drag forces can drive binaries either to coalescence or to the critical separation at which gravitational radiation dominates their further evolution. We discuss the implications of our results for binaries embedded in the interstellar medium, active galactic nuclei disks, and common envelope phases.