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Stars in an open cluster are assumed to have formed from a broadly homogeneous distribution of gas, implying that they should be chemically homogeneous. Quantifying the level to which open clusters are chemically homogeneous can therefore tell us about ISM pollution and gas-mixing in progenitor molecular clouds. Using SDSS-V Milky Way Mapper and SDSS-IV APOGEE DR17 abundances, we test this assumption by quantifying intrinsic chemical scatter in up to 20 different chemical abundances across 26 Milky Way open clusters. We find that we can place 3σ upper limits on open cluster homogeneity within 0.02 dex or less in the majority of elements, while for neutron capture elements, as well as those elements having weak lines, we place limits on their homogeneity within 0.2 dex. Finally, we find that giant stars in open clusters are ~0.01 dex more homogeneous than a matched sample of field stars.
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This content will become publicly available on March 24, 2027
The chemical homogeneity of single-lined spectroscopic binaries in open clusters
ABSTRACT Using SDSSṇV DR19 Milky Way Mapper APOGEE data, we measure the impact that close binarity has on surface chemistry across the Hertzsprung–Russell diagram in a broad set of abundances by studying single-lined spectroscopic binaries (SB1s) in open clusters. We derive binary membership and orbital parameters for 103 SB1s by analysing APOGEE radial velocities with the joker and ultranest. We perform a detailed abundance analysis with bacchus to derive abundances in fourteen chemical species: Si, Fe, C, N, O, Na, Mg, Al, Ca, Ti, Cr, Ni, Ce, and Nd. Leveraging the assumptions of chemical homogeneity in open clusters, we compare the surface abundances of SB1s to non-binary stars at similar evolutionary states. We find that a subset of binaries with significant UV excess have a $$\Delta$$[C/N] that is 0.2–0.5 dex higher than expected, resulting in overestimated [C/N]-based ages for those stars. This points to pollution from an evolved companion and has implications for [C/N]-based age studies of the broader Milky Way. At the population level, we find that SB1s in our sample can be treated as statistically chemically homogeneous with their single-star counterparts, and we find no connection between orbital separation and chemical enrichment or depletion. We show that at separations up to 5 pc, co-eval stars can be considered chemically homogeneous with one another within current abundance precisions, regardless of multiplicity.
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- PAR ID:
- 10705571
- Publisher / Repository:
- Monthly Notices of the Royal Astronomical Society
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 547
- Issue:
- 4
- ISSN:
- 0035-8711
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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