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Abstract We present a catalog of ∼10,000 resolved triple star systems within 500 pc of the Sun, constructed using Gaia data. The triples include main-sequence, red giant, and white dwarf components spanning separations of 10–50,000 au. A well-characterized selection function allows us to constrain intrinsic demographics of the triple star population. We find that (a) all systems are compatible with being hierarchical and dynamically stable; (b) mutual orbital inclinations are isotropic for wide triples but show modest alignment as the systems become more compact; (c) primary masses follow a Kroupa initial mass function weighted by the triple fraction; (d) inner binary orbital periods, eccentricities, and mass ratios mirror those of isolated binaries, including a pronounced twin excess (mass ratios greater than 0.95) out to separations of 1000+ au, suggesting a common formation pathway; (e) tertiary mass ratios follow a power-law distribution with slope −1.4; (f) tertiary orbits are consistent with a log-normal period distribution and thermal eccentricities, subject to dynamical stability. Informed by these observations, we develop a publicly available prescription for generating mock triple star populations. Finally, we estimate the catalog’s completeness and infer the intrinsic triple fraction, which rises steadily with primary mass: from 5% at ≲0.5M_⊙to 35% at 2M_⊙. The public catalog provides a robust testbed for models of triple star formation and evolution. 

Abstract The formation of cataclysmic variables (CVs) has long been modeled as a product of common envelope evolution (CEE) in isolated binaries. However, a significant fraction of intermediate-mass stars—the progenitors of the white dwarfs (WDs) in CVs—are in triples. We therefore investigate the importance of triple star dynamics in CV formation. Using Gaia astrometry and existing CV catalogs, we construct a sample of ∼50 CVs in hierarchical triples within 1 kpc of the Sun, containing main-sequence and WD tertiaries at separations of 100–30,000 au. We infer that at least 10% of CVs host wide tertiaries. To interpret this discovery, we evolve a population of 2000 triples using detailed three-body simulations, 47 of which become CVs. We predict that 20% of CVs in triples form without ever experiencing CEE, where the WD and donor are brought together by the eccentric Kozai-Lidov mechanism after the formation of the WD. These systems favor larger donor stars and longer birth orbital periods (8–20 hr) than typical CVs. Among systems that do undergo CEE, about half would not have interacted without the presence of the tertiary. Triple formation channels both with and without CEE require initially wide inner orbits (≳1 au), which in turn require larger tertiary separations to be stable. Consistent with this prediction, we find that the observed Gaia CV triples have wider separations on average than normal wide binaries selected in the same way. Our work underscores the importance of triples in shaping interacting binary populations including CVs, ultracompact binaries, and low-mass X-ray binaries. 

Abstract Five self-lensing binaries (SLBs) have been discovered with Kepler light curves. They contain white dwarfs (WDs) in AU-scale orbits that gravitationally lens solar-type companions. Forming SLBs likely requires common envelope evolution when the WD progenitor is an AGB star and has a weakly bound envelope. No SLBs have yet been discovered with data from the Transiting Exoplanet Survey Satellite (TESS), which observes far more stars than Kepler did. Identifying self-lensing in TESS data is made challenging by the fact that TESS only observes most stars for  ∼25 days at a time, so only a single lensing event will be observed for typical SLBs. TESS’s smaller aperture also makes it sensitive only to SLBs a factor of  ∼100 brighter than those to which Kepler is sensitive. We demonstrate that TESS has nevertheless likely already observed  ∼4 times more detectable SLBs than Kepler. We describe a search for non-repeating self-lensing signals in TESS light curves and present preliminary candidates for which spectroscopic follow-up is ongoing. We calculate the sensitivity of our search with injection and recovery tests on TESS and Kepler light curves. Based on the 5 SLBs discovered with Kepler light curves, we estimate that (1.1 ± 0.6)% of solar-type stars are orbited by WDs with periods of 100–1000 days. This implies a space density of AU-scale WD + main sequence (MS) binaries a factor of 20–100 larger than that of astrometrically identified WD + MS binaries with orbits in Gaia DR3. We conclude that the Gaia sample is still quite incomplete, mainly because WD + MS binaries can only be unambiguously identified as such for high mass ratios. 

Abstract Using data from Gaia DR3, we construct a sample of 14,791 gravitationally bound wide pairs in which one of the components is an unresolved binary with an astrometric orbital or acceleration solution. These systems are hierarchical triples, with inner binary separations of order 1 au, and outer separations of 100–100,000 au. Leveraging the fact that the inner binary and outer tertiary should have nearly identical parallaxes, we use the sample to calibrate the parallax uncertainties for orbital and acceleration binary solutions. We find that the parallax uncertainties of orbital solutions are typically underestimated by a factor of 1.3 atG> 14, and by a factor of 1.7 atG= 8–14. The true parallax uncertainties are nevertheless a factor of ∼10 smaller than those of the single-star astrometric solutions for the same sources. The parallax uncertainties of acceleration solutions are underestimated by larger factors of 2–3 but still represent a significant improvement compared to the sources’ single-star solutions. We provide tabulated uncertainty inflation factors for astrometric binary solutions and make the catalog of hierarchical triples publicly available. 

Recent observations have found a growing number of hypervelocity stars with speeds of ≈1500 − 2500 km s⁻¹that could have only been produced through thermonuclear supernovae in white dwarf binaries. Most of the observed hypervelocity runaways in this class display a surprising inflated structure: their current radii are roughly an order of magnitude greater than they would have been as white dwarfs filling their Roche lobe. While many simulations exist studying the dynamical phase leading to supernova detonation in these systems, no detailed calculations of the long-term structure of the runaways have yet been performed. We used an existing AREPOhydrodynamical simulation of a supernova in a white dwarf binary as a starting point for the evolution of these stars with the one-dimensional stellar evolution code MESA. We show that the supernova shock is not energetic enough to inflate the white dwarf over timescales longer than a few thousand years, significantly shorter than the 10^5 − 6year lifetimes inferred for observed hypervelocity runaways. Although they experience a shock from a supernova less than ≈0.02 R_⊙away, our models do not experience significant interior heating, and all contract back to radii of around 0.01 R_⊙within about 10⁴years. Explaining the observed inflated states requires either an additional source of significant heating or some other physics that is not yet accounted for in the subsequent evolution. 

Abstract We measure the mass distribution of main-sequence (MS) companions to hot subdwarf B stars (sdBs) in post-common envelope binaries (PCEBs). We carried out a spectroscopic survey of 14 eclipsing systems (“HW Vir binaries”) with orbital periods of 3.8 < P_orb < 12 hr, resulting in a well-understood selection function and a near-complete sample of HW Vir binaries withG < 16. We constrain companion masses from the radial velocity curves of the sdB stars. The companion mass distribution peaks atM_MS ≈ 0.15M_⊙and drops off atM_MS > 0.2M_⊙, with only two systems hosting companions above the fully convective limit. There is no correlation betweenP_orbandM_MSwithin the sample. A similar drop-off in the companion mass distribution of white dwarf (WD) + MS PCEBs has been attributed to disrupted magnetic braking (MB) below the fully convective limit. We compare the sdB companion mass distribution to predictions of binary evolution simulations with a range of MB laws. Because sdBs have short lifetimes compared to WDs, explaining the lack of higher-mass MS companions to sdBs with disrupted MB requires MB to be boosted by a factor of 20–100 relative to MB laws inferred from the rotation evolution of single stars. We speculate that such boosting may be a result of irradiation-driven enhancement of the MS stars’ winds. An alternative possibility is that common envelope evolution favors low-mass companions in short-period orbits, but the existence of massive WD companions to sdBs with similar periods disfavors this scenario.