The Carbon-to-oxygen Ratio in Cool Brown Dwarfs and Giant Exoplanets. I. The Benchmark Late-T Dwarfs GJ 570D, HD 3651B, and Ross 458C

Measurements of the C/O ratio in brown dwarfs are lacking, in part due to past models adopting solar C/O only. We have expanded the ATMO 2020 atmosphere model grid to include nonsolar metallicities and C/O ratios in the T dwarf regime. We change the C/O ratio by altering either the carbon or oxygen...
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Gespeichert in:

Autor*in:	Mark W. Phillips [verfasserIn] Michael C. Liu [verfasserIn] Zhoujian Zhang [verfasserIn]

Format:	E-Artikel
Sprache:	Englisch

Erschienen:	2024

Schlagwörter:	Brown dwarfs T dwarfs Spectroscopy Near infrared astronomy Exoplanet atmospheres

Übergeordnetes Werk:	In: The Astrophysical Journal - IOP Publishing, 2022, 961(2024), 2, p 210
Übergeordnetes Werk:	volume:961 ; year:2024 ; number:2, p 210

Links:	Link aufrufen Link aufrufen Link aufrufen Journal toc

DOI / URN:	10.3847/1538-4357/ad06ba

Katalog-ID:	DOAJ096404442

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callnumber-first	Q - Science
author	Mark W. Phillips
spellingShingle	Mark W. Phillips misc QB460-466 misc Brown dwarfs misc T dwarfs misc Spectroscopy misc Near infrared astronomy misc Exoplanet atmospheres misc Astrophysics The Carbon-to-oxygen Ratio in Cool Brown Dwarfs and Giant Exoplanets. I. The Benchmark Late-T Dwarfs GJ 570D, HD 3651B, and Ross 458C
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topic_title	QB460-466 The Carbon-to-oxygen Ratio in Cool Brown Dwarfs and Giant Exoplanets. I. The Benchmark Late-T Dwarfs GJ 570D, HD 3651B, and Ross 458C Brown dwarfs T dwarfs Spectroscopy Near infrared astronomy Exoplanet atmospheres
topic	misc QB460-466 misc Brown dwarfs misc T dwarfs misc Spectroscopy misc Near infrared astronomy misc Exoplanet atmospheres misc Astrophysics
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title	The Carbon-to-oxygen Ratio in Cool Brown Dwarfs and Giant Exoplanets. I. The Benchmark Late-T Dwarfs GJ 570D, HD 3651B, and Ross 458C
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title_sort	carbon-to-oxygen ratio in cool brown dwarfs and giant exoplanets. i. the benchmark late-t dwarfs gj 570d, hd 3651b, and ross 458c
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title_auth	The Carbon-to-oxygen Ratio in Cool Brown Dwarfs and Giant Exoplanets. I. The Benchmark Late-T Dwarfs GJ 570D, HD 3651B, and Ross 458C
abstract	Measurements of the C/O ratio in brown dwarfs are lacking, in part due to past models adopting solar C/O only. We have expanded the ATMO 2020 atmosphere model grid to include nonsolar metallicities and C/O ratios in the T dwarf regime. We change the C/O ratio by altering either the carbon or oxygen elemental abundances, and we find that nonsolar abundances of these elements can be distinguished based on the shapes of the H and K bands. We compare these new models with medium-resolution ( R ≈ 1700), near-infrared (0.8–2.4 μ m) Gemini Near-Infrared Spectrograph (GNIRS) spectra of three benchmark late-T dwarfs, GJ 570D, HD 3651B, and Ross 458C. We find solar C/O ratios and best-fitting parameters ( T _eff , $\mathrm{log}(g)$ , Z ) broadly consistent with other analyses in the literature based on low-resolution ( R ∼ 100) data. The model-data discrepancies in the near-infrared spectra are consistent across all three objects. These discrepancies are alleviated when fitting the Y , J , H , and K bands individually, but the resulting best-fit parameters are inconsistent and disagree with the results from the full spectrum. By examining the model atmosphere properties we find this is due to the interplay of gravity and metallicity on H _2 –H _2 collisionally induced absorption. We therefore conclude that there are no significant issues with the molecular opacity tables used in the models at this spectral resolution. Instead, deficiencies are more likely to lie in the model assumptions regarding the thermal structures. Finally, we find a discrepancy between the GNIRS, SpeX, and other near-infrared spectra in the literature of Ross 458C, indicating potential spectroscopic variability.
abstractGer	Measurements of the C/O ratio in brown dwarfs are lacking, in part due to past models adopting solar C/O only. We have expanded the ATMO 2020 atmosphere model grid to include nonsolar metallicities and C/O ratios in the T dwarf regime. We change the C/O ratio by altering either the carbon or oxygen elemental abundances, and we find that nonsolar abundances of these elements can be distinguished based on the shapes of the H and K bands. We compare these new models with medium-resolution ( R ≈ 1700), near-infrared (0.8–2.4 μ m) Gemini Near-Infrared Spectrograph (GNIRS) spectra of three benchmark late-T dwarfs, GJ 570D, HD 3651B, and Ross 458C. We find solar C/O ratios and best-fitting parameters ( T _eff , $\mathrm{log}(g)$ , Z ) broadly consistent with other analyses in the literature based on low-resolution ( R ∼ 100) data. The model-data discrepancies in the near-infrared spectra are consistent across all three objects. These discrepancies are alleviated when fitting the Y , J , H , and K bands individually, but the resulting best-fit parameters are inconsistent and disagree with the results from the full spectrum. By examining the model atmosphere properties we find this is due to the interplay of gravity and metallicity on H _2 –H _2 collisionally induced absorption. We therefore conclude that there are no significant issues with the molecular opacity tables used in the models at this spectral resolution. Instead, deficiencies are more likely to lie in the model assumptions regarding the thermal structures. Finally, we find a discrepancy between the GNIRS, SpeX, and other near-infrared spectra in the literature of Ross 458C, indicating potential spectroscopic variability.
abstract_unstemmed	Measurements of the C/O ratio in brown dwarfs are lacking, in part due to past models adopting solar C/O only. We have expanded the ATMO 2020 atmosphere model grid to include nonsolar metallicities and C/O ratios in the T dwarf regime. We change the C/O ratio by altering either the carbon or oxygen elemental abundances, and we find that nonsolar abundances of these elements can be distinguished based on the shapes of the H and K bands. We compare these new models with medium-resolution ( R ≈ 1700), near-infrared (0.8–2.4 μ m) Gemini Near-Infrared Spectrograph (GNIRS) spectra of three benchmark late-T dwarfs, GJ 570D, HD 3651B, and Ross 458C. We find solar C/O ratios and best-fitting parameters ( T _eff , $\mathrm{log}(g)$ , Z ) broadly consistent with other analyses in the literature based on low-resolution ( R ∼ 100) data. The model-data discrepancies in the near-infrared spectra are consistent across all three objects. These discrepancies are alleviated when fitting the Y , J , H , and K bands individually, but the resulting best-fit parameters are inconsistent and disagree with the results from the full spectrum. By examining the model atmosphere properties we find this is due to the interplay of gravity and metallicity on H _2 –H _2 collisionally induced absorption. We therefore conclude that there are no significant issues with the molecular opacity tables used in the models at this spectral resolution. Instead, deficiencies are more likely to lie in the model assumptions regarding the thermal structures. Finally, we find a discrepancy between the GNIRS, SpeX, and other near-infrared spectra in the literature of Ross 458C, indicating potential spectroscopic variability.
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container_issue	2, p 210
title_short	The Carbon-to-oxygen Ratio in Cool Brown Dwarfs and Giant Exoplanets. I. The Benchmark Late-T Dwarfs GJ 570D, HD 3651B, and Ross 458C
url	https://doi.org/10.3847/1538-4357/ad06ba https://doaj.org/article/2a9642978de4432d822602927119cc4b https://doaj.org/toc/1538-4357
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By examining the model atmosphere properties we find this is due to the interplay of gravity and metallicity on H _2 –H _2 collisionally induced absorption. We therefore conclude that there are no significant issues with the molecular opacity tables used in the models at this spectral resolution. Instead, deficiencies are more likely to lie in the model assumptions regarding the thermal structures. 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The Carbon-to-oxygen Ratio in Cool Brown Dwarfs and Giant Exoplanets. I. The Benchmark Late-T Dwarfs GJ 570D, HD 3651B, and Ross 458C

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