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| Main Authors: | , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2512.03456 |
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| _version_ | 1866910089110093824 |
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| author | Shridharan, B Manoj, P Pathak, Vinod Chandra Garatti, Alessio Caratti O Banerjee, Bihan Henning, Th. Kamp, I. van Dishoeck, E. Tyagi, H. Arun, R. Mathew, B. Güdel, M. Lagage, P. -O. |
| author_facet | Shridharan, B Manoj, P Pathak, Vinod Chandra Garatti, Alessio Caratti O Banerjee, Bihan Henning, Th. Kamp, I. van Dishoeck, E. Tyagi, H. Arun, R. Mathew, B. Güdel, M. Lagage, P. -O. |
| contents | We present a comprehensive study of mid-infrared neutral hydrogen (H~\textsc{i}) emission lines in 79 nearby (d $<$ 200 $pc$) young stars using JWST/MIRI. We aim to identify mid-infrared H~\textsc{i} transitions that can serve as reliable accretion diagnostics in young stars, and evaluate their utility in deriving physical conditions of the accreting gas. We identify and measure 22 H~\textsc{i} transitions in the MIRI wavelength regime (5-28 $μm$) and perform LTE slab modelling to remove the H\textsubscript{2}O contribution from selected H~\textsc{i} transitions. We find that mid-IR H~\textsc{i} line emission is spatially compact, even for sources with spatially extended [Ne~\textsc{ii}] and [Fe~\textsc{ii}] jets, suggesting minimal contamination from extended jet. Although Pfund~$α$ (H~\textsc{i}~6--5) and Humphreys~$α$ (H~\textsc{i}~7--6) are the strongest lines, they are blended with H$_2$O transitions. This blending necessitates additional processing to remove molecular contamination, thereby limiting their use as accretion diagnostics. Instead, we identify the H~\textsc{i}~(8--6) at 7.502 $μm$ and H~\textsc{i}~(10--7) at 8.760 $μm$ transitions as better alternatives, as they are largely unaffected by molecular contamination and offer a more reliable means of measuring accretion rates from MIRI spectra. We provide updated empirical relations for converting mid-IR H~\textsc{i} line luminosities into accretion luminosity for 6 different H~\textsc{i} lines in the MIRI wavelength range. Moreover, comparison of observed line ratios with theoretical models shows that MIR H~\textsc{i} lines offer robust constraints on the hydrogen gas density in accretion columns, $n_\mathrm{H} = $10$^{10.6}$ to 10$^{11.2}$ cm$^{-3}$ in most stars, with some stars exhibiting lower densities ($<10^{10}$~cm$^{-3}$), approaching the optically thin regime. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_03456 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Improving Accretion Diagnostics for Young Stellar Objects with Mid-infrared Hydrogen lines from JWST/MIRI Shridharan, B Manoj, P Pathak, Vinod Chandra Garatti, Alessio Caratti O Banerjee, Bihan Henning, Th. Kamp, I. van Dishoeck, E. Tyagi, H. Arun, R. Mathew, B. Güdel, M. Lagage, P. -O. Solar and Stellar Astrophysics Earth and Planetary Astrophysics Astrophysics of Galaxies We present a comprehensive study of mid-infrared neutral hydrogen (H~\textsc{i}) emission lines in 79 nearby (d $<$ 200 $pc$) young stars using JWST/MIRI. We aim to identify mid-infrared H~\textsc{i} transitions that can serve as reliable accretion diagnostics in young stars, and evaluate their utility in deriving physical conditions of the accreting gas. We identify and measure 22 H~\textsc{i} transitions in the MIRI wavelength regime (5-28 $μm$) and perform LTE slab modelling to remove the H\textsubscript{2}O contribution from selected H~\textsc{i} transitions. We find that mid-IR H~\textsc{i} line emission is spatially compact, even for sources with spatially extended [Ne~\textsc{ii}] and [Fe~\textsc{ii}] jets, suggesting minimal contamination from extended jet. Although Pfund~$α$ (H~\textsc{i}~6--5) and Humphreys~$α$ (H~\textsc{i}~7--6) are the strongest lines, they are blended with H$_2$O transitions. This blending necessitates additional processing to remove molecular contamination, thereby limiting their use as accretion diagnostics. Instead, we identify the H~\textsc{i}~(8--6) at 7.502 $μm$ and H~\textsc{i}~(10--7) at 8.760 $μm$ transitions as better alternatives, as they are largely unaffected by molecular contamination and offer a more reliable means of measuring accretion rates from MIRI spectra. We provide updated empirical relations for converting mid-IR H~\textsc{i} line luminosities into accretion luminosity for 6 different H~\textsc{i} lines in the MIRI wavelength range. Moreover, comparison of observed line ratios with theoretical models shows that MIR H~\textsc{i} lines offer robust constraints on the hydrogen gas density in accretion columns, $n_\mathrm{H} = $10$^{10.6}$ to 10$^{11.2}$ cm$^{-3}$ in most stars, with some stars exhibiting lower densities ($<10^{10}$~cm$^{-3}$), approaching the optically thin regime. |
| title | Improving Accretion Diagnostics for Young Stellar Objects with Mid-infrared Hydrogen lines from JWST/MIRI |
| topic | Solar and Stellar Astrophysics Earth and Planetary Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2512.03456 |