Tracing Accretion and Inner-Disk Gas Evolution in the Orion Nebula via Br-alpha and CO
Abstract
We present a systematic spectroscopic study of hydrogen Brackett-alpha (Br-alpha) and carbon monoxide (CO) fundamental-band (4.3-5.2 micron) emission from a homogeneous sample of 0.2-1.5 Msun pre-main-sequence (PMS) stars in the Orion Nebula observed with JWST/NIRSpec-MOS as part of our Chandra-JWST project. Using 73 Br-alpha and 46 CO spectra, we investigate correlations between warm-gas emission, stellar properties, accretion, and environment with censored correlation and regression analyses accounting for multiple testing. Br-alpha luminosity correlates strongly with accretion luminosity (Lacc), even after excluding sources within 2' of Theta1 Ori C, the nebula's main ionizing O-type star, whose radiation may bias proplyd Lacc estimates. This supports Br-alpha as a robust empirical tracer of accretion in PMS stars. Br-alpha also correlates with visual extinction (Av) and more weakly with stellar bolometric luminosity and mass. CO fundamental-band luminosities likewise correlate positively with Lacc and Av, relationships that persist in a larger combined JWST/NIRSpec+MIRI sample spanning multiple star-forming regions. In contrast to Br-alpha, CO luminosity shows no significant dependence on basic stellar properties, suggesting that warm molecular gas is governed primarily by accretion and local disk conditions. The weaker correlations of the Spitzer/IRAC spectral slope with Lacc and Av suggest that warm inner-disk gas may evolve or disperse faster than optically thick dust. Overall, the CO results tentatively indicate declining warm-gas emission as disks evolve, modulated by accretion-powered thermal and ultraviolet excitation, although variations in emitting area inherited from natal core conditions may also contribute.
Related
- A VLT/CRIRES+ study of helium 1.083μm absorption features towards the inner Orion Nebula
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- X-shooter survey Across Regions and Ages to probe Disk Evolution (ARADE): Accretion properties in Orion A and their relation with disk masses
- A Hectospec Spectroscopic Census of Kinematic Members in the Orion Nebula Cluster
- A Hectospec Spectroscopic Census of Kinematic Members in the Orion Nebula Cluster
BibTeX
@misc{getman2026tracing,
title = {{Tracing Accretion and Inner-Disk Gas Evolution in the Orion Nebula via Br-alpha and CO}},
author = {Konstantin V. Getman and Maria Claudia Ramirez-Tannus and Jenny Frediani and Kevin L. Luhman and Eric D. Feigelson and Bayron Portilla-Revelo and Christian Rab and Valentin Brunn and Jan Forbrich and Thomas J. Haworth and Rens Waters and Arjan Bik and Charles J. Law and Andrew J. Winter and Vladimir S. Airapetian and Abygail R. Waggoner and Michael A. Kuhn and L. Ilsedore Cleeves and Sergio A. Dzib and Marco Padovani},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.19244},
eprint = {2610.19244},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.19244},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Tracing Accretion and Inner-Disk Gas Evolution in the Orion Nebula via Br-alpha and CO
AU - Konstantin V. Getman
AU - Maria Claudia Ramirez-Tannus
AU - Jenny Frediani
AU - Kevin L. Luhman
AU - Eric D. Feigelson
AU - Bayron Portilla-Revelo
AU - Christian Rab
AU - Valentin Brunn
AU - Jan Forbrich
AU - Thomas J. Haworth
AU - Rens Waters
AU - Arjan Bik
AU - Charles J. Law
AU - Andrew J. Winter
AU - Vladimir S. Airapetian
AU - Abygail R. Waggoner
AU - Michael A. Kuhn
AU - L. Ilsedore Cleeves
AU - Sergio A. Dzib
AU - Marco Padovani
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.19244
UR - https://arxiv.org/abs/2610.19244
AB - We present a systematic spectroscopic study of hydrogen Brackett-alpha (Br-alpha) and carbon monoxide (CO) fundamental-band (4.3-5.2 micron) emission from a homogeneous sample of 0.2-1.5 Msun pre-main-sequence (PMS) stars in the Orion Nebula observed with JWST/NIRSpec-MOS as part of our Chandra-JWST project. Using 73 Br-alpha and 46 CO spectra, we investigate correlations between warm-gas emission, stellar properties, accretion, and environment with censored correlation and regression analyses accounting for multiple testing. Br-alpha luminosity correlates strongly with accretion luminosity (Lacc), even after excluding sources within 2' of Theta1 Ori C, the nebula's main ionizing O-type star, whose radiation may bias proplyd Lacc estimates. This supports Br-alpha as a robust empirical tracer of accretion in PMS stars. Br-alpha also correlates with visual extinction (Av) and more weakly with stellar bolometric luminosity and mass. CO fundamental-band luminosities likewise correlate positively with Lacc and Av, relationships that persist in a larger combined JWST/NIRSpec+MIRI sample spanning multiple star-forming regions. In contrast to Br-alpha, CO luminosity shows no significant dependence on basic stellar properties, suggesting that warm molecular gas is governed primarily by accretion and local disk conditions. The weaker correlations of the Spitzer/IRAC spectral slope with Lacc and Av suggest that warm inner-disk gas may evolve or disperse faster than optically thick dust. Overall, the CO results tentatively indicate declining warm-gas emission as disks evolve, modulated by accretion-powered thermal and ultraviolet excitation, although variations in emitting area inherited from natal core conditions may also contribute.
ER -