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Surveying for Close Binaries among Lithium-rich Giants

  • Jesús Torres
  • Sebastián Vilaza-Dallago
  • Julio Chanamé
  • Rafael Brahm
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Abstract

One of the possible scenarios usually considered to explain the existence of low-mass red giants with anomalously high lithium (Li) abundances requires the interaction with a close binary companion. If dominant, this enrichment channel predicts a significantly enhanced binary fraction among Li-rich giants relative to Li-normal ones. We aim to constrain the binary interaction hypothesis by using multi-epoch radial velocities (RVs) to measure the close binary fraction of a statistically robust sample of Li-rich giants. We are surveying both red clump (RC) and first ascent red giant (RGB) targets, which allows us to examine potential differences in the binary fraction as a function of evolutionary stage. We are monitoring 70 targets (40 RC and 30 RGB, all Li-rich) using ESPRESSO at the VLT, 57 of which (32 RC + 25 RGB) already have 4 or more visits over a ∼7 month baseline; the analysis in this paper is based on the latter. For the targets with RV variation larger than that expected for intrinsic jitter, we use a Monte Carlo analysis to estimate the probability that the observed RV variation is due to a stellar (PSB) or sub-stellar (PSS) companion. Discounting the 38 targets consistent with stellar jitter, we are left with 11 RC and 8 RGB stars (34% and 32% of the respective sub-samples) with RV variability consistent with the presence of a close companion with an orbital period shorter than 3000 days. Of these 19, 3 can be confirmed as stellar-mass companions. The distributions of PSB and PSS are statistically indistinguishable between the RC and RGB samples. We thus find no evidence so far in our current data for a binary fraction for Li-rich giants (in either evolutionary stage) larger than that expected for a Li-normal population. Extending the RV baseline to probe longer orbital periods will be important to keep exploring the plausibility of this scenario.

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Cite

BibTeXRIS
BibTeX
@misc{torres2026surveying,
  title = {{Surveying for Close Binaries among Lithium-rich Giants}},
  author = {Jesús Torres and Sebastián Vilaza-Dallago and Julio Chanamé and Rafael Brahm},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.38320},
  eprint = {2609.38320},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.38320},
}
RIS
TY  - UNPB
TI  - Surveying for Close Binaries among Lithium-rich Giants
AU  - Jesús Torres
AU  - Sebastián Vilaza-Dallago
AU  - Julio Chanamé
AU  - Rafael Brahm
PY  - 2026
DA  - 2026/09/29
PB  - arXiv
DO  - 10.48550/arxiv.2609.38320
UR  - https://arxiv.org/abs/2609.38320
AB  - One of the possible scenarios usually considered to explain the existence of low-mass red giants with anomalously high lithium (Li) abundances requires the interaction with a close binary companion. If dominant, this enrichment channel predicts a significantly enhanced binary fraction among Li-rich giants relative to Li-normal ones. We aim to constrain the binary interaction hypothesis by using multi-epoch radial velocities (RVs) to measure the close binary fraction of a statistically robust sample of Li-rich giants. We are surveying both red clump (RC) and first ascent red giant (RGB) targets, which allows us to examine potential differences in the binary fraction as a function of evolutionary stage. We are monitoring 70 targets (40 RC and 30 RGB, all Li-rich) using ESPRESSO at the VLT, 57 of which (32 RC + 25 RGB) already have 4 or more visits over a ∼7 month baseline; the analysis in this paper is based on the latter. For the targets with RV variation larger than that expected for intrinsic jitter, we use a Monte Carlo analysis to estimate the probability that the observed RV variation is due to a stellar (P_SB) or sub-stellar (P_SS) companion. Discounting the 38 targets consistent with stellar jitter, we are left with 11 RC and 8 RGB stars (34% and 32% of the respective sub-samples) with RV variability consistent with the presence of a close companion with an orbital period shorter than 3000 days. Of these 19, 3 can be confirmed as stellar-mass companions. The distributions of P_SB and P_SS are statistically indistinguishable between the RC and RGB samples. We thus find no evidence so far in our current data for a binary fraction for Li-rich giants (in either evolutionary stage) larger than that expected for a Li-normal population. Extending the RV baseline to probe longer orbital periods will be important to keep exploring the plausibility of this scenario.
ER  -