The Transition from Giant Planets to Brown Dwarfs beyond 1 au from the Stellar Metallicity Distribution
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866908699008696320 |
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| author | Giacalone, Steven Howard, Andrew W. Gilbert, Gregory J. Van Zandt, Judah Petigura, Erik A. Handley, Luke B. |
| author_facet | Giacalone, Steven Howard, Andrew W. Gilbert, Gregory J. Van Zandt, Judah Petigura, Erik A. Handley, Luke B. |
| contents | Giant planets and brown dwarfs are thought to form via a combination of pathways, including bottom-up mechanisms in which gas is accreted onto a solid core and top-down mechanisms in which gas collapses directly into a gravitationally-bound object. One can distinguish the prevalence of these mechanisms using host star metallicities. Bottom-up formation thrives in metal-rich environments, whereas top-down formation is weakly dependent on ambient metal content. Using a hierarchical Bayesian model and the results of the California Legacy Survey (CLS), a low-bias and homogeneously analyzed radial velocity survey, we find evidence for a transition in the stellar metallicity distribution at a companion mass of $γ= 27_{-8}^{+12} \, M_{\rm Jup}$ for companions with orbital separations between $1-50$ au. Companions below and above this threshold tend to orbit stars with higher ($\rm{[Fe/H]} = 0.17 \pm 0.12$ dex) and lower ($\rm{[Fe/H]} = -0.03 \pm 0.10$ dex) metallicities, respectively. Previous studies of relatively close-in companions reported evidence of a lower transition mass of $\leq 10 \, {\rm M_{\rm Jup}}$. When applied to the CLS sample, our model predicts the probability of a transition in the stellar metallicity distribution at or below $10 \, { M_{\rm Jup}}$ to be $< 1 \%$. We compare our results to estimates of $γ$ gleaned from other observational metrics and discuss implications for planet formation theory. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_11818 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Transition from Giant Planets to Brown Dwarfs beyond 1 au from the Stellar Metallicity Distribution Giacalone, Steven Howard, Andrew W. Gilbert, Gregory J. Van Zandt, Judah Petigura, Erik A. Handley, Luke B. Earth and Planetary Astrophysics Solar and Stellar Astrophysics Giant planets and brown dwarfs are thought to form via a combination of pathways, including bottom-up mechanisms in which gas is accreted onto a solid core and top-down mechanisms in which gas collapses directly into a gravitationally-bound object. One can distinguish the prevalence of these mechanisms using host star metallicities. Bottom-up formation thrives in metal-rich environments, whereas top-down formation is weakly dependent on ambient metal content. Using a hierarchical Bayesian model and the results of the California Legacy Survey (CLS), a low-bias and homogeneously analyzed radial velocity survey, we find evidence for a transition in the stellar metallicity distribution at a companion mass of $γ= 27_{-8}^{+12} \, M_{\rm Jup}$ for companions with orbital separations between $1-50$ au. Companions below and above this threshold tend to orbit stars with higher ($\rm{[Fe/H]} = 0.17 \pm 0.12$ dex) and lower ($\rm{[Fe/H]} = -0.03 \pm 0.10$ dex) metallicities, respectively. Previous studies of relatively close-in companions reported evidence of a lower transition mass of $\leq 10 \, {\rm M_{\rm Jup}}$. When applied to the CLS sample, our model predicts the probability of a transition in the stellar metallicity distribution at or below $10 \, { M_{\rm Jup}}$ to be $< 1 \%$. We compare our results to estimates of $γ$ gleaned from other observational metrics and discuss implications for planet formation theory. |
| title | The Transition from Giant Planets to Brown Dwarfs beyond 1 au from the Stellar Metallicity Distribution |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2511.11818 |