Eclipsing Binaries in Dynamically Interacting Close, Multiple Systems

Close, compact, hierarchical, and multiple stellar systems, i.e., multiples having an outer orbital period from months to a few years, comprise a small but continuously growing group of the triple and multiple star zoo. Many of them consist of at least one eclipsing pair of stars and, therefore, exhibit readily observable short-term dynamical interactions among the components. Thus, their dynamical and astrophysical properties can be explored with high precision. In this paper we present an overview of the history of the search for additional components around eclipsing binaries from the first serendipitous discoveries to more systematic recent studies. We describe the different observational detection methods and discuss their connections to the different kinds of astrophysical and dynamical information that can be mined from different datasets. Moreover, the connection amongst the observable phenomena and the long-term dynamics of such systems is also discussed.

A Nascent Tidal Dwarf Galaxy Forming within the Northern H i Streamer of M82

We identify a ∼600 pc wide region of active star formation located within a tidal streamer of M82 via Hα emission (F Hα ∼ 6.5 × 10−14 erg s−1 cm−2), using a pathfinder instrument based on the Dragonfly Telephoto Array. The object is kinematically decoupled from the disk of M82 as confirmed via Keck/LRIS spectroscopy and is spatially and kinematically coincident with an overdensity of H i and molecular hydrogen within the “northern H i streamer” induced by the passage of M81 several hundred Myr ago. From H i data, we estimate that ∼5 × 107 M ⊙ of gas is present in the specific overdensity coincident with the Hα source. The object’s derived metallicity (12+ log ( O / H ) ≃ 8.6 ), position within a gas-rich tidal feature, and morphology (600 pc diameter with multiple star-forming clumps), indicate that it is likely a tidal dwarf galaxy in the earliest stages of formation.

The Census of Exoplanets in Visual Binaries: Population Trends from a Volume-Limited Gaia DR2 and Literature Search

We present results from an extensive search in the literature and Gaia DR2 for visual co-moving binary companions to stars hosting exoplanets and brown dwarfs within 200 pc. We found 218 planet hosts out of the 938 in our sample to be part of multiple-star systems, with 10 newly discovered binaries and 2 new tertiary stellar components. This represents an overall raw multiplicity rate of 23.2 ± 1.6 % for hosts to exoplanets across all spectral types, with multi-planet systems found to have a lower stellar duplicity frequency at the 2.2-σ level. We found that more massive hosts are more often in binary configurations, and that planet-bearing stars in multiple systems are predominantly observed to be the most massive component of stellar binaries. Investigations of the multiplicity of planetary systems as a function of planet mass and separation revealed that giant planets with masses above 0.1 MJup are more frequently seen in stellar binaries than small sub-Jovian planets with a 3.6-σ difference, a trend enhanced for the most massive (>7 MJup) short-period (<0.5 AU) planets and brown dwarf companions. Binarity was however found to have no significant effect on the demographics of low- mass planets (<0.1 MJup) or warm and cool gas giants (>0.5 AU). While stellar companion mass appears to have no impact on planet properties, binary separation seems to be an important factor in the resulting structure of planetary systems. Stellar companions on separations <1000 AU can play a role in the formation or evolution of massive, close-in planets, while planets in wider binaries show similar properties to planets orbiting single stars. Finally, our analyses indicate that numerous stellar companions on separations smaller than 1–3 arcsec likely remain undiscovered to this date. Continuous efforts to complete our knowledge of stellar multiplicity on separations of tens to hundreds of AU are essential to confirm the reported trends and further our understanding of the roles played by multiplicity on exoplanets.

White dwarf–main sequence star collisions from wide triples in the field

ABSTRACT Multiple star systems interact strongly with galactic field stars when the outer semi-major axis of a triple or multiple star is >103 AU. Stable triples composed of two white-dwarfs (WD) and a low-mass main sequence (MS) star in a wide outer orbit can thus be destabilized by gravitational interactions with random field stars. Such interactions excite the eccentricity of the distant third star sufficiently so that it begins to interact significantly with the inner binary. When this occurs, the triple undergoes multiple binary-single resonant encounters. These encounters may result either in a collision between the non-degenerate component and a WD, or the breakup of the triple into a compact binary and a third object which is ejected. The compact binary can be either a MS–WD pair which survives, or collides or a double WD (DWD), which may inspiral through gravitational wave emission. We calculate the collision rate between a MS and WD star, and the merger rate of DWDs. Additionally, we describe the prospects of detectability of such a collision, which may resemble a sub-luminous supernovae event.

Multiple Stellar Evolution: a population synthesis algorithm to model the stellar, binary, and dynamical evolution of multiple-star systems

ABSTRACT In recent years, observations have shown that multiple-star systems such as hierarchical triple and quadruple-star systems are common, especially among massive stars. They are potential sources of interesting astrophysical phenomena such as compact object mergers, leading to supernovae, and gravitational wave events. However, many uncertainties remain in their often complex evolution. Here, we present the population synthesis code Multiple Stellar Evolution (mse), designed to rapidly model the stellar, binary, and dynamical evolution of multiple-star systems. mse includes a number of new features not present in previous population synthesis codes: (1) an arbitrary number of stars, as long as the initial system is hierarchical, (2) dynamic switching between secular and direct N-body integration for efficient computation of the gravitational dynamics, (3) treatment of mass transfer in eccentric orbits, which occurs commonly in multiple-star systems, (4) a simple treatment of tidal, common envelope, and mass transfer evolution in which the accretor is a binary instead of a single star, (5) taking into account planets within the stellar system, and (6) including gravitational perturbations from passing field stars. mse, written primarily in the C++ language, will be made publicly available and has few prerequisites; a convenient python interface is provided. We give a detailed description of MSE and illustrate how to use the code in practice. We demonstrate its operation in a number of examples.

CoBiToM project – I. Contact binaries towards merging

ABSTRACT Binary and multiple stellar systems are numerous in our solar neighbourhood with 80 per cent of the solar-type stars being members of systems with high order multiplicity. The Contact Binaries Towards Merging (CoBiToM) Project is a programme that focuses on contact binaries and multiple stellar systems, as a key for understanding stellar nature. The goal is to investigate stellar coalescence and merging processes, as the final state of stellar evolution of low-mass contact binary systems. Obtaining observational data of approximately 100 eclipsing binaries and multiple systems and more than 400 archival systems, the programme aspires to give insights for their physical and orbital parameters and their temporal variations, e.g. the orbital period modulation, spot activity etc. Gravitational phenomena in multiple-star environments will be linked with stellar evolution. A comprehensive analysis will be conducted, in order to investigate the possibility of contact binaries to host planets, as well as the link between inflated hot Jupiters and stellar mergers. The innovation of CoBiToM Project is based on a multimethod approach and a detailed investigation, that will shed light for the first time on the origin of stellar mergers and rapidly rotating stars. In this work, we describe the scientific rationale, the observing facilities to be used and the methods that will be followed to achieve the goals of CoBiToM Project and we present the first results as an example of the current research on evolution of contact binary systems.

Dynamical influence of a wide binary companion on giant planet migration

<p>About half of the Sun-like stars are part of multiple-star systems. To date more than 100 planets are known moving around one stellar component of a binary star (S-type planets), with diverse eccentricities. These discoveries raise the question of their formation and long-term evolution, since the stellar companion can strongly affect the planet formation process. Here we study the dynamical influence of a wide binary companion on the (Type-II) migration of a single giant planet in the protoplanetary disk. Using a modified version of an N-body integrator adapted for binary star systems and adopting eccentricity and inclination damping formulae (derived from hydrodynamical simulations) to properly model the influence of the disk, we carried out more than 3500 numerical simulations with different initial configurations and study the dynamics of the systems up to 100 Myr. Particular attention is paid to the Lidov-Kozai resonance whose role is determinant for the evolution of the giant planet, although initially embedded in the disk, when the stellar companion is highly inclined. We highlight the high probability for the planet of experiencing, during the disk phase, a scattering event or an ejection due to the presence of the binary companion. We also show that a capture of the migrating planet in the Lidov-Kozai resonance is far from being automatic even when the binary companion is highly inclined, since only 10% of the systems actually end up in the resonance. Nevertheless, using a simplified quadrupolar hamiltonian approach, we point out that, for highly inclined binary companions, the dynamical evolutions are strongly affected by the Lidov-Kozai resonance islands, which create the pile-ups observed around – but not centred on – the pericenter values of 90° and 270° in the final distribution of the giant planets. The influence of the self-gravity of the disk on the previous results is finally discussed.</p>

Analysis of eclipsing binaries in multiple stellar systems: the case of V1200 Centauri

ABSTRACT We present a new analysis of the multiple-star V1200 Centauri based on the most recent observations for this system. We used the photometric observations from the Solaris network and the Transiting Exoplanet Survey Satellite telescope, combined with the new radial velocities from the CHIRON spectrograph and those published in the literature. We confirmed that V1200 Cen consists of a 2.5-d eclipsing binary orbited by a third body. We derived the parameters of the eclipsing components, which are $M_{\mathrm{ Aa}} = 1.393\pm 0.018\,$M⊙, $R_{\mathrm{ Aa}} = 1.407\pm 0.014\,$R⊙, and $T_{{\rm eff},\mathrm{ Aa}} = 6588\pm 58\,$K for the primary, and $M_{\mathrm{ Ab}} = 0.8633\pm 0.0081\,$M⊙, $R_{\mathrm{ Ab}} = 1.154\pm 0.014\,$R⊙, and $T_{{\rm eff},\mathrm{ Ab}} = 4475\pm 68\,$K for the secondary. Regarding the third body, we obtained significantly different results than those previously published. The period of the outer orbit is found to be 180.4 d, implying a minimum mass of $M_\mathrm{ B} = 0.871\pm 0.020\,$M⊙. Thus, we argue that V1200 Cen is a quadruple system with a secondary pair composed of two low-mass stars. Finally, we determined the ages of each eclipsing component using two evolution codes, namely mesa and cestam. We obtained ages of 16–18.5 and 5.5–7 Myr for the primary and the secondary, respectively. In particular, the secondary appears larger and hotter than that predicted at the age of the primary. We concluded that dynamical and tidal interactions occurring in multiples may alter the stellar properties and explain the apparent non-coevality of V1200 Centauri.