The Binary Fraction of Milky Way Field Stars in DESI: Dependence on Chemical Abundance

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The gist

The binary fraction of Milky Way field stars in DESI depends primarily on chemical abundance, specifically [Fe/H], with secondary influences from [Mg/Fe] and Galactic position <ref:2610.111025, fb is

In short

The study used multi-epoch radial velocity variations from DESI data to find how often stars in the Milky Way are binary systems. The main finding is that this binary fraction primarily increases as metallicity ([Fe/H]) decreases. This dependence on chemical abundance is more significant than Galactic position or other factors, suggesting star formation conditions strongly influence binary system prevalence.

Key concepts

Binary Fraction ($f_b$)
$f_b$ represents the proportion of field main-sequence turn-off stars in the Milky Way that are currently in a binary system. The researchers used statistical methods on stellar velocity variations to estimate this number, showing it is strongly linked to how chemically enriched the stars are.
[Fe/H]
$[ ext{Fe}/ ext{H}]$ is a measure of a star's metallicity, indicating the abundance of iron relative to hydrogen. The study found that $f_b$ systematically increases as $[ ext{Fe}/ ext{H}]$ becomes lower (more metal-poor), suggesting that chemical composition plays the dominant role in determining binary status.
[Mg/Fe]
$[ ext{Mg}/ ext{Fe}]$ is a secondary chemical abundance ratio used to explore other influences. While it shows a modest increase in $f_b$ for more metal-rich stars, the primary trend is driven by $[ ext{Fe}/ ext{H}]$. This suggests that while magnesium abundance has some effect, iron abundance is the main driver of binary fraction variation.
Multi-epoch LOSV Variations
This statistical technique involves measuring changes in a star's line-of-sight velocity over multiple observations. By modeling these variations for both binary and nonbinary stars using Monte Carlo simulations, researchers can constrain the true binary fraction with high precision.

Terminology used across episodes

This episode discusses

The paper

The Binary Fraction of Milky Way Field Stars in DESI: Dependence on Chemical Abundance · Read on arXiv

Tian Qiu, Wenting Wang, Sergey E. Koposov, Songting Li, Nathan Sandford, Ting S. Li, Joan Najita, Jessica Nicole Aguilar, Steven Ahlen, Davide Bianchi

Department of Astronomy, School of Physics and Astronomy, and Key Laboratory for Particle Astrophysics and Cosmology (MOE)/Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University · State Key Laboratory of Dark Matter Physics, School of Physics and Astronomy, Shanghai Jiao Tong University · Institute for Astronomy, University of Edinburgh · Institute of Astronomy, University of Cambridge · Department of Astronomy & Astrophysics, University of Toronto · NSF NOIRLab · Lawrence Berkeley National Laboratory · Department of Physics, Boston University · Dipartimento di Fisica “Aldo Pontremoli”, Università degli Studi di Milano INAF-Osservatorio Astronomico di Brera, Department of Physics & Astronomy, University College London Instituto de Astrofísica de Canarias Instituto de Astrofísica de Canarias, Departamento de Astrofísica Universidad de La Laguna (ULL), Instituto de Física Universidad Nacional Autónoma de México Departamento de Física Universidad Nacional Autónoma Metropolitana · Institute of Cosmology and Gravitation University of Portsmouth · University of Virginia Department of Astronomy · Fermi National Accelerator Laboratory · Department of Physics Southern Methodist University Sorbonne Université CNRS/IN2P3 Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Institute de Física d’Altes Energies The Barcelona Institute of Science and Technology Institució Catalana de Recerca i Estudis Avançats · Observatorio Astronómico Universidad Autónoma de Madrid Instituto de Astrofísica de Andalucía CSIC · Departament de Física EEBE Universitat Politècnica de Catalunya Max Planck Institute for Extraterrestrial Physics

Binary populations encode information about the physical conditions of star formation and the subsequent evolution of stellar populations. Adopting a statistical method based on multi-epoch line-of-sight velocity variations, we constrain the binary fraction, f b, of field main-sequence turn-off stars in the Milky Way using data from the second data release of the DESI Milky Way Survey. f b is found to primarily increase with lower [Fe/H]. At [Fe/H] -1.3, f b shows a modest increase with increasing [Mg/Fe], whereas no clear trend is detected at lower [Fe/H]. The apparent variations of f b with angular momentum and Galactic height are largely explained by their underlying [Fe/H] distributions, while the remaining variations broadly follow differences in [Mg/Fe]. Within overlapping regions of the [Fe/H]--[Mg/Fe] plane, the thin disk, thick disk, stellar halo and GSE populations exhibit no significant differences in their binary fractions. Thus, our measurements indicate that the variation in f b is dominated by chemical abundance, which could be explained by the metallicity-dependent gas cooling efficiency and fragmentation. The weaker [Mg/Fe] dependence at fixed [Fe/H] might be associated with the formation conditions of stars, with higher [Mg/Fe] stars generally forming earlier under a more gas-rich and turbulent environment.

Transcript

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "The Binary Fraction of Milky Way Field Stars in DESI".

Jocelyn: The binary fraction of Milky Way field stars in DESI depends primarily on chemical abundance, specifically

Fe/H: , with secondary influences from

Mg/Fe: and Galactic position <ref:2610.111025,

Vera: First, who's behind it and why it matters.

Paper summary: Vera: So we started by looking at how to constrain this binary fraction using multi-epoch line-of-sight velocity variations from the DESI Milky Way Survey data. The authors used a statistical method based on those velocity variations to find the binary fraction, f b, of field main-sequence turn-off stars in the Milky Way.

Jocelyn: They found that this binary fraction, f b, primarily increases with lower

Fe/H: , and they also noted that at

Fe/H: -one point three, f b shows a modest increase with increasing

Mg/Fe: , while no clear trend is seen at lower

Fe/H: <ref:2610.11102#pg2,shows a modest increase with increasing Mg/Fe>.

Subrahmanyan: The core claim of the paper is that the apparent variations we see in f b with angular momentum and Galactic height are largely explained by their underlying

Fe/H: distributions, while the remaining variations broadly follow differences in

Mg/Fe: .

Vera: And they conclude that within overlapping regions of the

Fe/H: –

Mg/Fe: plane, populations like the thin disk, thick disk, stellar halo and GSE populations exhibit no significant differences in their binary fractions.

Jocelyn: The main conclusion they draw is that the variation in f b is dominated by chemical abundance, which they suggest could be explained by the metallicity-dependent gas cooling efficiency and fragmentation.

Subrahmanyan: And they offer a physical interpretation for why there's that weaker

Mg/Fe: dependence at fixed

Fe/H: ; it might be associated with the formation conditions of stars, with higher

Mg/Fe: stars generally forming earlier under a more gas-rich and turbulent environment.

Vera: So, to put it simply, they are saying that metallicity is the key observable here for understanding binary populations in our galaxy.

Jocelyn: And that this dependence on

Fe/H: , especially the increase toward lower

Fe/H: , is consistent with results from several independent methods and surveys.

Conclusion: Vera: So looking at the full picture, this paper by Qiu et al., Wang et al., Koposov et al., Li et al., Sandford, Li, Aguilar, Ahlen, Bianchi, Brooks, Rosell, Claybaugh and others is really telling us that we need to look at chemical abundance when we talk about the binary fraction in the DESI MSTO sample.

Jocelyn: They found that

Fe/H: is the primary observable associated with the binary fraction in this DESI MSTO sample, and they noted an inverse relation between f b and

Fe/H: .

Subrahmanyan: That inverse relation is consistent with results from other studies, like those using LAMOST or APOGEE radial-velocity studies which have reported higher binary fractions among metal-poor solar-type stars.

Vera: So, the implication for us is that metallicity really does influence the binary population, particularly for the close-binary systems that spectroscopic surveys are probing.

Jocelyn: The paper also touches on how metallicity affects cooling through competing processes, and radiation-hydrodynamical simulations suggest metal-poor gas can cool more efficiently at high densities due to less dust.

Subrahmanyan: This enhanced cooling promotes fragmentation on smaller spatial scales, which leads to a larger close-binary fraction among low-mass stars with a semi-major axis of about zero point five astronomical units.

Vera: So the overall picture is that the paper shows how chemical abundance, specifically

Fe/H: , dictates the binary fraction in our field stars, and this has implications for understanding star formation in the early universe where metal-poor environments could have produced different binary populations.

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