Abstract
Stellar chemical compositions can be altered by ingestion of planetary material1,2 and/or planet formation, which removes refractory material from the protostellar disk3,4. These ‘planet signatures’ appear as correlations between elemental abundance differences and the dust condensation temperature3,5,6. Detecting these planet signatures, however, is challenging owing to unknown occurrence rates, small amplitudes and heterogeneous star samples with large differences in stellar ages7,8. Therefore, stars born together (that is, co-natal) with identical compositions can facilitate the detection of planet signatures. Although previous spectroscopic studies have been limited to a small number of binary stars9,10,11,12,13, the Gaia satellite14 provides opportunities for detecting stellar chemical signatures of planets among co-moving pairs of stars confirmed to be co-natal15,16. Here we report high-precision chemical abundances for a homogeneous sample of ninety-one co-natal pairs of stars with a well defined selection function and identify at least seven instances of planetary ingestion, corresponding to an occurrence rate of eight per cent. An independent Bayesian indicator is deployed, which can effectively disentangle the planet signatures from other factors, such as random abundance variation and atomic diffusion17. Our study provides evidence of planet signatures and facilitates a deeper understanding of the star–planet–chemistry connection by providing observational constraints on the mechanisms of planet engulfment, formation and evolution.
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Data availability
The spectral data underlying this article are available in Keck Observatory Archive (https://koa.ipac.caltech.edu/cgi-bin/KOA/nph-KOAlogin) and the European Southern Observatory Science Archive Facility (http://archive.eso.org/eso/eso_archive_main.html). They can be accessed with Keck Program ID W244Hr (semester: 2021B, principal investigator F.L.) and European Southern Observatory Programme ID 108.22EC.001 (principal investigator D.Y.), respectively. The spectra from the Magellan Telescope can be shared upon request to the corresponding author. The rest of data underlying this article are available in the article and its Supplementary Information.
Code availability
The stellar line analysis program MOOG is available at https://www.as.utexas.edu/~chris/moog.html. The stellar model atmospheres are available at http://kurucz.harvard.edu/grids.html. The code for equivalent width measurements is very similar to REvIEW, which is provided in https://github.com/madeleine-mckenzie/REvIEW. The Bayesian modelling program DYNESTY is available at https://github.com/joshspeagle/dynesty.
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Acknowledgements
This paper includes data gathered with the 6.5 metre Magellan Telescope located at Las Campanas Observatory, Chile. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 108.22EC.001. This research were supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. Y.-S.T. acknowledges financial support from the Australian Research Council through DECRA Fellowship DE220101520. M.T.M. acknowledges the support of the Australian Research Council through Future Fellowship grant FT180100194. B.B. thanks the European Research Council (ERC Starting Grant 757448-PAMDORA) for their financial support. M.J. gratefully acknowledges funding of MATISSE: Measuring Ages Through Isochrones, Seismology, and Stellar Evolution, awarded through the European Commission’s Widening Fellowship. This project has received funding from the European Union’s Horizon 2020 research and innovation programme. We thank A. Ji for offering advice on data collection and preparation; and S. Campbell, A. Mustill and Q. Sun for discussions. The C3PO programme is made possible through the Carnegie Observatories’ support and allocation of observation time on the Magellan Telescope. We recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
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F.L. led and played a part in all aspects of the observations and data analysis for this study, and wrote and developed the paper. Y.-S.T. initiated the C3PO program, carried out the Magellan observations and contributed to the statistical analysis of the research. D.Y. carried out the observations and part of spectroscopic analysis of the Magellan and the VLT data, and contributed to designing this study. B.B., M.J., and A.D. contributed to the theoretical interpretations of the observational results. A.K., M.T.M. and F.D. contributed to the development and writing of the paper. All authors read, commented and agreed on the paper.
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Extended data figures and tables
Extended Data Fig. 1 A portion of the reduced spectra of an example co-moving pair of stars (HD 185726/185689; Pair 124).
The spectra of HD 185726 and HD 185689 are plotted in dark green and orange, respectively. The stellar parameters of these two stars are: [Teff = 6271 K; \(\log \,g\) = 4.2 cm s−2; [Fe/H] = −0.364 dex] for HD 185726, and [Teff = 6132 K; \(\log \,g\) = 4.36 cm s−2; [Fe/H] = −0.207 dex] for HD 185689. Representative lines of oxygen, iron, silicon, and nickel adopted in this analysis are marked out. It demonstrates that even at the level of a few percent, the differences in line strengths (for different elements) between two stars can be clearly revealed, if they exist.
Extended Data Fig. 2 Comparison of abundance results.
a. The deviations in differential abundances (Δ[X/H]) as a function of atomic number for seven pairs with multiple observations. Different colours represent the deviations in Δ[X/H] for different pairs, as specified in the legend. The dashed lines mark out the 1 σ range around zero. b. Δ[X/H] as a function of atomic number for a common pair HD 133131A/B between this study and31. Black circles and blue rectangles represent the abundance results from two independent observations. They demonstrate that the pairwise differences are nearly zero with the standard deviation of ≈ 0.02 dex. We note that two pairs (38 and 108) exhibit slightly larger differences (still within 0.03–0.04 dex for most elements) between the two observations, possibly due to different instruments (for Pair 38) and varying S/N achieved (100–150 versus 200 for Pair 108).
Extended Data Fig. 3 The distributions of differences in Bayesian evidence Δln(Z) between the planetary ingestion and the flat models.
Red: the control sample of far co-moving pairs (Δs ≥ 106 AU); blue: the target sample of close, co-natal co-moving pairs (Δs < 106 AU); grey: the mock noise sample; orange: the mock signal sample. The distributions, unlike that of Tcond trends, are distinguishable between different samples, indicating that we can effectively disentangle the potential planet signatures in the 91 co-natal pairs from the control sample of far pairs, as well as from the mock sample representing realistic noise and pure signal.
Extended Data Fig. 4 Differences in Bayesian evidence Δln(Z)atom between the planetary ingestion and the atomic diffusion models as a function of spatial separations Δs.
The red and blue circles represent the far and close co-moving pairs, respectively. The dashed line marks out our selection criterion for Δln(Z)atom. It demonstrates that the far co-moving pairs (non co-natal sample) are distinctively affected by atomic diffusion (possibly due to larger differences in the relative stellar parameters such as ΔTeff), when compared to the close, co-natal co-moving pairs.
Extended Data Fig. 5 Total accreted mass of Earth material (from the best-fitting model) as a function of Δln(Z) between the planetary ingestion and the flat models for the 91 close, co-natal co-moving pairs.
The dashed line marks out our selection criterion for Δln(Z). The data are colour-coded with the mass fraction of convection zone (fCZ), indicating that stars with larger Δln(Z) tend to have larger accreted mass, while the exact amount of accretion is determined by fCZ.
Extended Data Fig. 6 Abundance differences (Δ[X/H]) in our candidate pairs.
Same as Fig. 1a, but for: a. Pair 69; and b. Pair 74. The error bars are 1 σ uncertainties of the observed abundances.
Extended Data Fig. 7 Abundance differences (Δ[X/H]) in our candidate pairs.
Same as Fig. 1a, but for: a. Pair 77; and b. Pair 79. The error bars are 1 σ uncertainties of the observed abundances.
Extended Data Fig. 8 Abundance differences (Δ[X/H]) in our candidate pairs.
Same as Fig. 1a, but for: a. Pair 112; and b. Pair 116. The error bars are 1 σ uncertainties of the observed abundances.
Supplementary information
Supplementary Table 1
The spectral line list used in this study, along with atomic data and equivalent width measurements.
Supplementary Table 2
The adopted elemental abundance differences (Δ[X/H]) and the associated uncertainties for each co-moving pair of stars in this study.
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Liu, F., Ting, YS., Yong, D. et al. At least one in a dozen stars shows evidence of planetary ingestion. Nature 627, 501–504 (2024). https://doi.org/10.1038/s41586-024-07091-y
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DOI: https://doi.org/10.1038/s41586-024-07091-y
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