A VLT/CRIRES+ study of helium 1.083μm absorption features towards the inner Orion Nebula
Abstract
JWST NIRCam F115W observations towards the inner Orion Nebula revealed a diverse array of previously unknown dark features. The most likely cause was absorption or suppressed emission of the helium 1.083μm triplet which lies in that filter. We have obtained VLT/CRIRES+ high-resolution spectrographic observations over a selection of different dark targets, confirming that the features are indeed explained by a reduction in the flux of the helium 1.083μm triplet, a reduction that is fairly uniform across the line. The Orion Nebula is a blister HII region, with a dense, bright ionised layer on the far side from the observer near the Orion A molecular cloud and lower density gas elsewhere. Using a simple radiative transfer model, we show that dark features arise when emission from the dense layer is absorbed by intermediate density helium (e.g. in clumps, globules, or winds from objects like proplyds) on the near side of the dense layer.
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BibTeX
@misc{haworth2026vltcrires,
title = {{A VLT/CRIRES+ study of helium 1.083$μ$m absorption features towards the inner Orion Nebula}},
author = {Thomas J. Haworth and Mark McCaughrean and Mario van den Ancker and James E. Owen and John Bally and Samuel Pearson},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.00215},
eprint = {2611.00215},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.00215},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A VLT/CRIRES+ study of helium 1.083μm absorption features towards the inner Orion Nebula
AU - Thomas J. Haworth
AU - Mark McCaughrean
AU - Mario van den Ancker
AU - James E. Owen
AU - John Bally
AU - Samuel Pearson
PY - 2026
DA - 2026/11/01
PB - arXiv
DO - 10.48550/arxiv.2611.00215
UR - https://arxiv.org/abs/2611.00215
AB - JWST NIRCam F115W observations towards the inner Orion Nebula revealed a diverse array of previously unknown dark features. The most likely cause was absorption or suppressed emission of the helium 1.083μm triplet which lies in that filter. We have obtained VLT/CRIRES+ high-resolution spectrographic observations over a selection of different dark targets, confirming that the features are indeed explained by a reduction in the flux of the helium 1.083μm triplet, a reduction that is fairly uniform across the line. The Orion Nebula is a blister HII region, with a dense, bright ionised layer on the far side from the observer near the Orion A molecular cloud and lower density gas elsewhere. Using a simple radiative transfer model, we show that dark features arise when emission from the dense layer is absorbed by intermediate density helium (e.g. in clumps, globules, or winds from objects like proplyds) on the near side of the dense layer.
ER -