Stars that Move Together Were Born Together

Abstract

It is challenging to reliably identify stars that were born together outside of actively star-forming regions and bound stellar systems. However, co-natal stars should be present throughout the Galaxy, and their demographics can shed light on the clustered nature of star formation and the dynamical state of the disk. In previous work we presented a set of simulations of the Galactic disk that followed the clustered formation and dynamical evolution of 4 billion individual stars over the last 5 Gyr. The simulations predict that a high fraction of co-moving stars with physical and 3D velocity separation of ∆r < 20 pc and ∆v < 1.5 km s −1 are co-natal. In this Letter, we use Gaia DR2 and LAMOST DR4 data to identify and study co-moving pairs. We find that the distribution of relative velocities and separations of pairs in the data is in good agreement with the predictions from the simulation. We identify 111 co-moving pairs in the Solar neighborhood with reliable astrometric and spectroscopic measurements. These pairs show a strong preference for having similar metallicities when compared to random field pairs. We therefore conclude that these pairs were very likely born together. The simulations predict that co-natal pairs originate preferentially from high-mass and relatively young (< 1 Gyr) star clusters. Gaia will eventually deliver well-determined metallicities for the brightest stars, enabling the identification of thousands of co-natal pairs due to disrupting star clusters in the solar neighborhood.

Stellar clustering shapes the architecture of planetary systems

“…These long-lived phase space overdensities originate mostly from the most massive clusters. This finding is observationally supported by the fact that co-moving stellar pairs (and ‘networks’ of such pairs, that is, groups) are common even at separations of tens of parsecs 48 and that the vast majority of these pairs exhibit similar metallicities 38 . Observationally, dynamical heating mechanisms appear to affect stars in the Milky Way on timescales of about 4.5 Gyr (ref.…”

“…We interpret stars in an overdensity as phase space neighbours and plausible members of such groups. It is likely that at least some of the stars in an overdensity were born together 38 . By contrast, stars occupying an environment of low phase space density are the least likely to have neighbours with which they were born.…”

Very wide companion fraction from Gaia DR2: A weak or no enhancement for hot Jupiter hosts, and a strong enhancement for contact binaries

“…Here we propose another scenario where the enhanced occurrence rate of dual systems is due to the co-chemical (components have similar metallicities) and the co-eval (components have similar ages) nature of the components of wide binaries. Andrews et al (2018) show that the components of wide binaries with separations < 4 × 10 4 AU have similar metallicities and elemental abundances within measurement uncertainties (see Kamdar et al 2019 for larger separations). Therefore, if we find a wide companion around a hot jupiter host, then because hot jupiter hosts tend to have higher metallicities (Gonzalez 1997;Santos et al 2004;Fischer & Valenti 2005) and the components of wide binaries have similar metallicities (Andrews et al 2018), we would expect that the wide companion of a hot jupiter host also has a higher metallicity and therefore a higher chance of hosting a hot jupiter, resulting in an enhanced occurrence rate of dual hot jupiter hosts.…”

Extended stellar systems in the solar neighborhood

“…Stripped cluster members cannot be identified with the classical approach of locating overdensities with respect to the background population. Instead, kinematic and chemical information must be used to identify stellar siblings reliably (Kamdar et al 2019). While elemental abundances are only now becoming available in moderately sufficient quantities, the Gaia mission has ushered kinematic measurements into the age of big data.…”