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Using the Bayesian Analysis of Stellar Evolution-9 code and Gaia DR3, Pan-STARRS, and 2MASS data, we identify photometric binaries in 35 open clusters (OCs) and constrain their masses. We find a strong correlation between the binary fraction and cluster dynamical age and an even stronger correlation between core binary fraction and cluster dynamical age. We find that the binary mass-ratio (q) distribution of dynamically young OCs is statistically distinct from that of the old OCs. On average, dynamically young OCs display multimodalqdistributions rising toward unity and toward our detection limit ofq= 0.5 while more dynamically evolved clusters display more uniformqdistributions, often with a peak nearq= 1. Interestingly, the uniformqdistribution with a peak nearq= 1 is consistent with binaries in the field. We also observe a similar transition from multimodal to unimodalqdistributions when comparing low-mass to high-mass OCs in our sample. Finally, we find a correlation between the medianqof the binary population in a cluster and the cluster dynamical age. We interpret these results as an indication that dynamical encounters tend to increase the fraction of high-mass-ratio binaries within a given cluster—in particular within the cluster’s core, where stellar dynamics are likely more important. This may be the result of stellar exchanges that tend to produce binaries with largerqand/or the preferential disruption or evaporation of lower-qbinaries. 

We identify observational signatures suggesting a history of dynamical instability in 26 out of 34 M-dwarf multi-planet systems containing no large planets. These systems may have primarily formed in a gas-rich environment, potentially hosted more planets, and were more compact. We extend previous simulations of the formation of the TRAPPIST-1 system to 100 Myr to test the stability of these systems without gas. We find that the absence of a strong mean motion resonance in the innermost planet pair and the absence of three-body resonances throughout the system are likely to result in the merging and ejection of planets after the gas disk disperses. The runs that experience such an instability tend to produce final systems with lower multiplicities, period ratios larger than two, increased orbital spacings, higher planetary angular momentum deficits, and slightly smaller mass ratios between adjacent planets. Remarkably, we find these same trends in the observations of M-dwarf multi-planet systems containing no large planets. Our work allows us to identify specific systems that may have experienced an instability, and it suggests that only  ∼25% of these systems formed in their current observed state, while most systems were likely more compact and multiplicitous earlier in time. Previous research indicates that planets that have experienced a late-stage giant impact may potentially be more habitable than those that did not. With this in mind, we suggest systems around M-dwarfs that contain period ratios larger than two be given priority in the search for habitable worlds. 

Abstract We present Hubble Space Telescope far-ultraviolet (FUV) spectra of a blue lurker–white dwarf (BL–WD) binary system in the 4 Gyr open cluster M67. We fit the FUV spectrum of the WD, determining it is a C/O WD with a mass of $0.72_{-0.04}^{+0.05}$ M_⊙and a cooling age of ~400 Myr. This requires a WD progenitor of ~3M_⊙, significantly larger than the current cluster turnoff mass of 1.3M_⊙. We suggest the WD progenitor star formed several hundred megayears ago via the merger of two stars near the turnoff of the cluster. In this scenario, the original progenitor system was a hierarchical triple consisting of a close, near-equal-mass inner binary, with a tertiary companion with an orbit of a few thousand days. The WD is descended from the merged inner binary, and the original tertiary is now the observed BL. The likely formation scenario involves a common envelope while the WD progenitor is on the AGB, and thus the observed orbital period of 359 days requires an efficient common envelope ejection. The rapid rotation of the BL indicates it accreted some material during its evolution, perhaps via a wind prior to the common envelope. This system will likely undergo a second common envelope in the future and thus could result in a short-period double WD binary or merger of a 0.72M_⊙C/O WD and a 0.38M_⊙helium WD, making this a potential progenitor of an interesting transient such as a sub-Chandrasekhar Type Ia supernova. 

Abstract Motivated by measurements of the rotation speed of accretor stars in post-mass-transfer (post-MT) systems, we investigate how magnetic braking affects the spin-down of individual stars during binary evolution with theMESAbinarymodule. Unlike the conventional assumption of tidal synchronization coupled with magnetic braking in binaries, we first calculate whether tides are strong enough to synchronize the orbit. Subsequently, this influences the spin-down of stars and the orbital separation. In this study, we apply four magnetic braking prescriptions to reduce the spin angular momentum of the two stars throughout the entire binary evolution simulation. Our findings reveal that despite magnetic braking causing continuous spin-down of the accretor, when the donor begins to transfer material onto the accretor, the accretor can rapidly spin up to its critical rotation rate. After MT, magnetic braking becomes more important in affecting the angular momentum evolution of the stars. Post-MT accretor stars thus serve as a valuable test bed for observing how the magnetic braking prescriptions operate in spinning down stars from their critical rotation, including the saturation regimes of the magnetic braking. The rotation rate of the accretor star, combined with its mass, could provide age information since the cessation of MT. By comparing the models against observations, the magnetic braking prescription by Garraffo et al. is found to better align with the rotation data of post-MT accretors. 

Abstract We search for mass segregation in the intermediate-aged open cluster NGC 6819 within a carefully identified sample of probable cluster members. Using photometry from Gaia, Pan-STARRS, and the Two Micron All Sky Survey as inputs for a Bayesian statistics software suite, BASE-9, we identify a rich population of (photometric) binaries and derive posterior distributions for the cluster age, distance, metallicity, and reddening, as well as star-by-star photometric membership probabilities, masses, and mass ratios (for binaries). Within our entire sample, we identify 2632 cluster members and 777 binaries. We then select a main-sequence “primary sample” with 14.85 <G< 19.5, containing 1342 cluster members and 250 binaries with mass ratiosq> 0.5, to investigate mass segregation. Within this primary sample, we find the binary radial distribution is significantly shifted toward the cluster center as compared to the single stars, resulting in a binary fraction that increases significantly toward the cluster core. Furthermore, we find that within the binary sample, more massive binaries have more centrally concentrated radial distributions than less massive binaries. The same is true for the single stars. We verify the expectation of mass segregation for this stellar sample in NGC 6819 through both relaxation time arguments and by investigating a sophisticatedN-body model of the cluster. Importantly, this is the first study to investigate mass segregation of the binaries in the open cluster NGC 6819. 

Abstract Wind Roche-lobe overflow (WRLOF) is a mass-transfer mechanism proposed by Mohamed and Podsiadlowski for stellar binaries wherein the wind acceleration zone of the donor star exceeds its Roche-lobe radius, allowing stellar wind material to be transferred to the accretor at enhanced rates. WRLOF may explain characteristics observed in blue lurkers and blue stragglers. While WRLOF has been implemented in rapid population synthesis codes, it has yet to be explored thoroughly in detailed binary models such asMESA(a 1D stellar evolution code), and over a wide range of initial binary configurations. We incorporate WRLOF accretion inMESAto investigate wide low-mass binaries at solar metallicity. We perform a parameter study over the initial orbital periods and stellar masses. In most of the models where we consider angular momentum transfer during accretion, the accretor is spun up to the critical (or breakup) rotation rate. Then we assume the star develops a boosted wind to efficiently reduce the angular momentum so that it could maintain subcritical rotation. Balanced by boosted wind loss, the accretor only gains ∼2% of its total mass, but can maintain a near-critical rotation rate during WRLOF. Notably, the mass-transfer efficiency is significantly smaller than in previous studies in which the rotation of the accretor is ignored. We compare our results to observational data of blue lurkers in M67 and find that the WRLOF mechanism can qualitatively explain the origin of their rapid rotation, their location on the H-R diagram, and their orbital periods. 

Abstract We study the effects of general relativity (GR) on the evolution and alignment of circumbinary disks around binaries on all scales. We implement relativistic apsidal precession of the binary into the hydrodynamics codephantom. We find that the effects of GR can suppress the stable polar alignment of a circumbinary disk, depending on how the relativistic binary apsidal precession timescale compares to the disk nodal precession timescale. Studies of circumbinary disk evolution typically ignore the effects of GR, which is an appropriate simplification for low-mass or widely separated binary systems. In this case, polar alignment occurs, provided that the disks initial misalignment is sufficiently large. However, systems with a very short relativistic precession timescale cannot polar align and instead move toward coplanar alignment. In the intermediate regime where the timescales are similar, the outcome depends upon the properties of the disk. Polar alignment is more likely in the wavelike disk regime (where the disk viscosity parameter is less than the aspect ratio,α<H/r), since the disk is in good radial communication. In the viscous disk regime, disk breaking is more likely. Multiple rings can destructively interact with one another, resulting in short disk lifetimes and the disk moving toward coplanar alignment. Around main-sequence star or stellar mass black hole binaries, polar alignment may be suppressed far from the binary, but in general, the inner parts of the disk can align to polar. Polar alignment may be completely suppressed for disks around supermassive black holes for close binary separations. 

Abstract We present Firefly, a new browser-based interactive tool for visualizing 3D particle data sets. On a typical personal computer, Firefly can simultaneously render and enable real-time interactions with ≳10 million particles, and can interactively explore data sets with billions of particles using the included custom-built octree render engine. Once created, viewing a Firefly visualization requires no installation and is immediately usable in most modern internet browsers simply by visiting a URL. As a result, a Firefly visualization works out-of-the-box on most devices including smartphones and tablets. Firefly is primarily developed for researchers to explore their own data, but can also be useful to communicate results to researchers and/or collaborators and as an effective public outreach tool. Every element of the user interface can be customized and disabled, enabling easy adaptation of the same visualization for different audiences with little additional effort. Creating a new Firefly visualization is simple with the provided Python data preprocessor that translates input data to a Firefly-compatible format and provides helpful methods for hosting instances of Firefly both locally and on the internet. In addition to visualizing the positions of particles, users can visualize vector fields (e.g., velocities) and also filter and color points by scalar fields. We share three examples of Firefly applied to astronomical data sets: (1) the FIRE cosmological zoom-in simulations, (2) the SDSS galaxy catalog, and (3) Gaia Data Release 3. A gallery of additional interactive demos is available at alexbgurvi.ch/Firefly .