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From birth associations to field stars: mapping the small-scale orbit distribution in the Galactic disc

Coronado, Johanna and Rix, Hans-Walter and Trick, Wilma H. and El-Badry, Kareem and Rybizki, Jan and Xiang, Maosheng (2020) From birth associations to field stars: mapping the small-scale orbit distribution in the Galactic disc. Monthly Notices of the Royal Astronomical Society, 495 (4). pp. 4098-4112. ISSN 0035-8711. doi:10.1093/mnras/staa1358.

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Stars born at the same time in the same place should have formed from gas of the same element composition. But most stars subsequently disperse from their birth siblings, in orbit and orbital phase, becoming ‘field stars’. Here, we explore and provide direct observational evidence for this process in the Milky Way disc, by quantifying the probability that orbit-similarity among stars implies indistinguishable metallicity. We define the orbit similarity among stars through their distance in action-angle space, Δ(J, θ), and their abundance similarity simply by Δ[Fe/H]. Analysing a sample of main-sequence stars from Gaia DR2 and LAMOST, we find an excess of pairs with the same metallicity (Δ[Fe/H] < 0.1) that extends to remarkably large separations in Δ(J, θ) that correspond to nearly 1 kpc distances. We assess the significance of this effect through a mock sample, drawn from a smooth and phase-mixed orbit distribution. Through grouping such star pairs into associations with a friend-of-friends algorithm linked by Δ(J,θ), we find 100s of mono-abundance groups with ≥3 (to ≳20) members; these groups – some clusters, some spread across the sky – are over an order-of-magnitude more abundant than expected for a smooth phase-space distribution, suggesting that we are witnessing the ‘dissolution’ of stellar birth associations into the field.

Item Type:Article
Related URLs:
URLURL TypeDescription
Coronado, Johanna0000-0001-6629-0731
Rix, Hans-Walter0000-0003-4996-9069
Trick, Wilma H.0000-0002-2806-3738
El-Badry, Kareem0000-0002-6871-1752
Rybizki, Jan0000-0002-0993-6089
Xiang, Maosheng0000-0002-5818-8769
Additional Information:© 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( We thank the anonymous referee for their helpful comments that improved the quality of this manuscript. Additionally, we thank Eleonora Zari, Harshil Kamdar, and Charlie Conroy for useful discussions. This project was developed in part at the 2019 Santa Barbara Gaia Sprint, hosted by the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara. JC acknowledges support from the International Max Planck Research School for Astronomy and Cosmic Physics at Heidelberg University (IMPRS-HD) and the SFB 881 program (A3). HWR received support from the European Research Council under the European Union’s Seventh Framework Programme (FP 7) ERC Grant Agreement no. [321035]. JR was funded by the DLR (German space agency) via grant 50 QG 1403. This work has made use of data from the European Space Agency (ESA) mission Gaia,1 processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
Funding AgencyGrant Number
Max Planck Research School for Astronomy and Cosmic PhysicsUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)SFB 881
European Research Council (ERC)321035
Deutsches Zentrum für Luft- und Raumfahrt (DLR)50 QG 1403
Gaia Multilateral AgreementUNSPECIFIED
Issue or Number:4
Record Number:CaltechAUTHORS:20230105-894291000.23
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118703
Deposited By: George Porter
Deposited On:18 Jan 2023 20:42
Last Modified:18 Jan 2023 20:42

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