A Search for Star-Disk Interaction Among the Strongest X-ray Flaring Stars in the Orion Nebula Cluster

TL;DR

This study investigates whether energetic X-ray flares in young stars are caused by magnetic interactions with circumstellar disks, finding that up to 40% of flaring stars may have such interactions, while others have large stellar magnetic loops.

Contribution

It provides detailed modeling of spectral energy distributions to assess the presence and proximity of circumstellar disks in flaring stars, revealing new insights into star-disk magnetic interactions.

Findings

Up to 40% of flaring stars show evidence of star-disk magnetic interaction.

Most stars lack disk material within reach of large magnetic loops.

Large magnetic loops can be anchored solely to the stellar surface in many cases.

Abstract

The Chandra Orion Ultradeep Project observed hundreds of young, low-mass stars undergoing highly energetic X-ray flare events. The 32 most powerful cases have been modeled with the result that the magnetic structures responsible for these flares can be many stellar radii in extent. In this paper, we model the observed spectral energy distributions of these 32 stars in order to determine, in detail for each star, whether there is circumstellar disk material situated in sufficient proximity to the stellar surface for interaction with the large magnetic loops inferred from the observed X-ray flares. Our spectral energy distributions span the wavelength range 0.3-8 um (plus 24 um for some stars), allowing us to constrain the presence of dusty circumstellar material out to >10 AU from the stellar surface in most cases. For 24 of the 32 stars in our sample the available data are sufficient to constrain the location of the inner edge of the dusty disks. Six of these (25%) have spectral energy distributions consistent with inner disks within reach of the observed magnetic loops. Another four stars may have gas disks interior to the dust disk and extending within reach of the magnetic loops, but we cannot confirm this with the available data. The remaining 14 stars (58%) appear to have no significant disk material within reach of the large flaring loops. Thus, up to ~40% of the sample stars exhibit energetic X-ray flares that possibly arise from a magnetic star-disk interaction, and the remainder are evidently associated with extremely large, free-standing magnetic loops anchored only to the stellar surface.