Gravity-sensitive Spectral Indices in Ultracool Dwarfs: Investigating Correlations with Metallicity and Planet Occurrence using SpeX and FIRE Observations
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| Format: | Preprint |
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2025
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| author | Davoudi, Fatemeh Rackham, Benjamin V. de Wit, Julien Toomlaid, Jan Gillon, Michaël Triaud, Amaury H. M. J. Burgasser, Adam J. Theissen, Christopher A. |
| author_facet | Davoudi, Fatemeh Rackham, Benjamin V. de Wit, Julien Toomlaid, Jan Gillon, Michaël Triaud, Amaury H. M. J. Burgasser, Adam J. Theissen, Christopher A. |
| contents | We present a near-infrared spectroscopic analysis (0.9--2.4~$μ$m) of gravity indices for 56 ultracool dwarfs (M5.5--L0), including exoplanet hosts SPECULOOS-2, SPECULOOS-3, and LHS 3154, with 59 spectra from SpeX and FIRE and literature data for TRAPPIST-1. Using gravity-sensitive spectral features (FeH at 0.99, 1.20, and 1.55~$μ$m; VO at 1.06~$μ$m; the H-band continuum; KI at 1.17 and 1.25$μ$m), we investigate links between gravity classification, metallicity, and planet occurrence. All four planet hosts show intermediate-gravity signatures despite field-age indicators. A volume-corrected logistic regression finds no significant association between gravity class and planet occurrence. Among individual indices, FeH_z (0.99~$μ$m) is the most promising tracer of planet-hosting status, with a tentative $2σ$ correlation that may reflect observational biases. More robustly, FeH_z shows a $3.3σ$ anti-correlation with [Fe/H]. A Kruskal--Wallis test finds no metallicity difference across gravity classes, suggesting the FeH_z--[Fe/H] trend is not due to bulk metallicity. We propose this relation reflects the interplay of age, gravity, and composition, with higher-metallicity objects being systematically younger and lower-gravity, reducing FeH absorption. While only hinting at a connection between gravity-sensitive features and planet occurrence among late-M dwarfs, these results highlight the need for caution when using spectral diagnostics to interpret ultracool dwarf planet hosts. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2506_19928 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Gravity-sensitive Spectral Indices in Ultracool Dwarfs: Investigating Correlations with Metallicity and Planet Occurrence using SpeX and FIRE Observations Davoudi, Fatemeh Rackham, Benjamin V. de Wit, Julien Toomlaid, Jan Gillon, Michaël Triaud, Amaury H. M. J. Burgasser, Adam J. Theissen, Christopher A. Earth and Planetary Astrophysics Solar and Stellar Astrophysics We present a near-infrared spectroscopic analysis (0.9--2.4~$μ$m) of gravity indices for 56 ultracool dwarfs (M5.5--L0), including exoplanet hosts SPECULOOS-2, SPECULOOS-3, and LHS 3154, with 59 spectra from SpeX and FIRE and literature data for TRAPPIST-1. Using gravity-sensitive spectral features (FeH at 0.99, 1.20, and 1.55~$μ$m; VO at 1.06~$μ$m; the H-band continuum; KI at 1.17 and 1.25$μ$m), we investigate links between gravity classification, metallicity, and planet occurrence. All four planet hosts show intermediate-gravity signatures despite field-age indicators. A volume-corrected logistic regression finds no significant association between gravity class and planet occurrence. Among individual indices, FeH_z (0.99~$μ$m) is the most promising tracer of planet-hosting status, with a tentative $2σ$ correlation that may reflect observational biases. More robustly, FeH_z shows a $3.3σ$ anti-correlation with [Fe/H]. A Kruskal--Wallis test finds no metallicity difference across gravity classes, suggesting the FeH_z--[Fe/H] trend is not due to bulk metallicity. We propose this relation reflects the interplay of age, gravity, and composition, with higher-metallicity objects being systematically younger and lower-gravity, reducing FeH absorption. While only hinting at a connection between gravity-sensitive features and planet occurrence among late-M dwarfs, these results highlight the need for caution when using spectral diagnostics to interpret ultracool dwarf planet hosts. |
| title | Gravity-sensitive Spectral Indices in Ultracool Dwarfs: Investigating Correlations with Metallicity and Planet Occurrence using SpeX and FIRE Observations |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2506.19928 |