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arXiv · 2404.19676

The Nature of X-Rays from Young Stellar Objects in the Orion Nebula Cluster -- A Chandra HETGS Legacy Project

Norbert S. Schulz·David P. Huenemoerder·David A. Principe·Marc Gagne·Hans Moritz Günther·Joel Kastner·Joy Nichols·Andrew Pollock·Thomas Preibisch·Paola Testa·Fabio Reale·Fabio Favata·Claude R. Canizares
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Abstract

The Orion Nebula Cluster (ONC) is the closest site of very young ($\sim$ 1 Myrs) massive star formation. The ONC hosts more than 1600 young and X-ray bright stars with masses ranging from $\sim$ 0.1 to 35 $M_\odot$. The Chandra HETGS Orion Legacy Project observed the ONC with the Chandra high energy transmission grating spectrometer (HETGS) for $2.1\,$Ms. We describe the spectral extraction and cleaning processes necessary to separate overlapping spectra. We obtained 36 high resolution spectra which includes a high brilliance X-ray spectrum of $\theta^1$ Ori C with over 100 highly significant X-ray lines. The lines show Doppler broadening between 300 and $400\;\mathrm{km}\;\mathrm{s}^{-1}$. Higher spectral diffraction orders allow us to resolve line components of high Z He-like triplets in $\theta^1$ Ori C with unprecedented spectral resolution. Long term light curves spanning $\sim$20 years show all stars to be highly variable, including the massive stars. Spectral fitting with thermal coronal emission line models reveals that most sources show column densities of up to a few times $10^{22}\,$cm$^{-2}$ and high coronal temperatures of 10 to 90 MK. We observe a bifurcation of the high temperature component where some stars show a high component of 40 MK, while others show above 60 MK indicating heavy flaring activity. Some lines are resolved with Doppler broadening above our threshold of $\sim200\;\mathrm{km}\;\mathrm{s}^{-1}$, up to $500\;\mathrm{km}\;\mathrm{s}^{-1}$. This data set represents the largest collection of HETGS high resolution X-ray spectra from young pre-MS stars in a single star-forming region to date.

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Norbert S. Schulz, David P. Huenemoerder, David A. Principe, Marc Gagne, Hans Moritz Günther, Joel Kastner, Joy Nichols, Andrew Pollock, Thomas Preibisch, Paola Testa, Fabio Reale, Fabio Favata, Claude R. Canizares. 2024-04-30. The Nature of X-Rays from Young Stellar Objects in the Orion Nebula Cluster -- A Chandra HETGS Legacy Project. https://arxiv.org/abs/2404.19676

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