Tracing Accretion and Inner-Disk Gas Evolution in the Orion Nebula via Br-alpha and CO

Konstantin V. Getman; Maria Claudia Ramirez-Tannus; Jenny Frediani; Kevin L. Luhman; Eric D. Feigelson; Bayron Portilla-Revelo; Christian Rab; Valentin Brunn; Jan Forbrich; Thomas J. Haworth; Rens Waters; Arjan Bik; Charles J. Law; Andrew J. Winter; Vladimir S. Airapetian; Abygail R. Waggoner; Michael A. Kuhn; L. Ilsedore Cleeves; Sergio A. Dzib; Marco Padovani

arXiv · 2610.19244

Tracing Accretion and Inner-Disk Gas Evolution in the Orion Nebula via Br-alpha and CO

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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.

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Konstantin V. Getman, Maria Claudia Ramirez-Tannus, Jenny Frediani, Kevin L. Luhman, Eric D. Feigelson, Bayron Portilla-Revelo, Christian Rab, Valentin Brunn, Jan Forbrich, Thomas J. Haworth, Rens Waters, Arjan Bik, Charles J. Law, Andrew J. Winter, Vladimir S. Airapetian, Abygail R. Waggoner, Michael A. Kuhn, L. Ilsedore Cleeves, Sergio A. Dzib, Marco Padovani. 2026-10-13. Tracing Accretion and Inner-Disk Gas Evolution in the Orion Nebula via Br-alpha and CO. https://arxiv.org/abs/2610.19244

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