Supernovae are not the only extremely high-energy events linked to the binary star evolution. Supernovae of type Ia are a product of a binary star evolution (Whelan & Iben 1973 Tutukov & Yungelson 1981 Iben & Tutukov 1984 Webbink 1984 Maoz, Mannucci & Nelemans 2014), and several other subtypes are also suspected to be (Podsiadlowski et al. Barkana & Loeb 2001 Abel, Bryan & Norman 2002 Heger & Woosley 2002 Stacy, Greif & Bromm 2010 Stanway, Eldridge & Becker 2016). At high redshifts, multiplicity of the first stellar systems stipulates how the mass is apportioned between the Population III stars and thus controls the ionizing radiation and metal enrichment, which in turn define the subsequent growth of structure in the Universe (e.g. Bate, Bonnell & Price 1995 Bate, Bonnell & Bromm 2003 McKee & Ostriker 2007). As a channel to study fragmentation processes at the birth sites, it informs the theory of star formation (see e.g. 2018 Andrews, Breivik & Chatterjee 2019)Ĭonstraining the statistics of opposite ends of the companion mass function as well as everything in between is crucial to our understanding of stellar multiplicity which forms one of the foundations of astrophysics. 2014) and dark remnants such as black holes (Breivik, Chatterjee & Larson 2017 Mashian & Loeb 2017 Kinugawa & Yamaguchi 2018 Yalinewich et al. Inspired by this, the community has understandably focused on stellar companions that are tricky to observe otherwise such as exosolar planets (Lattanzi et al. 2001 Gaia Collaboration 2016) have offered a much improved chance of discovering small wobbles in the stellar motion due to multiplicity. Space-based astrometric missions such as Hipparcos (Perryman et al. ![]() ![]() Better still, the motion of the centre of light can be straightforwardly interpreted, placing constraints on the properties of the unseen companion (see van de Kamp 1975). This was first demonstrated almost a century ago (see Reuyl 1936 Lippincott 1955). Unresolved stellar companions induce photocentre wobble, giving us a chance to detect binary systems via astrometry. Finally, we point out a hint of evidence for the existence of additional companions to the hosts of extrasolar hot Jupiters.īinaries: general, stars: evolution, stars: general 1 INTRODUCTIONĪ star’s path in the sky is often wiggled, but not always due to its parallax. We also illustrate how unresolved hierarchical triples inflate the relative velocity signal in wide binaries. We highlight the elevated binary fraction for the nearby blue stragglers and blue horizontal branch stars. The observed incidence of unresolved companions is high for massive young stars and drops steadily with stellar mass, reaching its lowest levels for white dwarfs. We apply this technique to the Gaia DR2 data and show how the binary fraction evolves across the Hertzsprung–Russell diagram. We test this idea on a sample of known spectroscopic binaries and demonstrate that the amplitude of the centroid perturbation scales with the binary period and the mass ratio as expected. We convert RUWE into the amplitude of the image centroid wobble, which, if scaled by the source distance, is proportional to the physical separation between companions (for periods up to several years). We show that such stars can be easily detected with the reduced χ 2 statistic, or renormalized unit weight error (RUWE), provided as part of Gaia DR2. For stars with unresolved companions, motions of the centre of light and that of mass decouple, causing a single-source astrometric model to perform poorly.
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