Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main-Sequence Stars

By S. Wolk, E. Flaccomio, G. Micela, F. Favata, A. Glassgold, H. Shang, Eric D. Feigelson. 2005

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In 2003 January, the Chandra Orion Ultradeep Project (COUP) detected about 1400 young stars during a 13.2 day observation of the Orion Nebula Cluster (ONC). This paper is a study of the X-ray properties of a well-defined sample of 28 solar-mass ONC stars based on COUP data. Our goals are to characterize the magnetic activity of analogs of the young Sun and thereby to improve understanding of the effects of solar X-rays on the solar nebula during the era of planet formation. Given the length of the COUP observation we are able to clearly distinguish characteristic and flare periods for all stars. We find that active young suns spend 70% of their time in a characteristic state with relatively constant flux and magnetically confined plasma with temperatures kT2 ≃ 2.1 × kT1. During characteristic periods, the 0.5-8 keV X-ray luminosity is about 0.03% of the bolometric luminosity. One or two powerful flares per week with peak luminosities log LX ~ 30-32 ergs s-1 are typically superposed on this characteristic emission accompanied by heating of the hot plasma component from ≃2.4 to ≃7 keV at the flare peak. The energy distribution of flares superposed on the characteristic emission level follows the relationship dN/dE ∝ E-1.7. The flare rates are consistent with the production of sufficiently energetic protons to spawn a spallogenic origin of some important short-lived radionuclides found in ancient meteorites. The X-rays can ionize gas in the circumstellar disk at a rate of 6 × 10-9 ionizations per second at 1 AU from the central star, orders of magnitude above cosmic-ray ionization rates. The estimated energetic particle fluences are sufficient to account for many isotopic anomalies observed in meteoritic inclusions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/b29aa4f46ad157f85810c0e753d5607055ed7717

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Citations in the corpus

X-ray emission from T Tauri stars and the role of accretion: inferences from the XMM-Newton extended survey of the Taurus molecular cloud (2006, background): “Also, frequent flaring in TTS (Wolk et al. 2005; Stelzer et al. 2007; Franciosini et al. 2007) clearly points to a coronal (or magnetospheric) origin of the X-ray emission.”
Bright X-Ray Flares in Orion Young Stars from COUP: Evidence for Star-Disk Magnetic Fields? (2005, methodology): “The MLB approach identifies (as discussed by Wolk et al. 2005) a ‘‘characteristic’’ level, essentially a quiescent level during the observation, as well as blocks that are significantly above this level and during which the X-ray luminosity is constant.”
The Sun in Time: Activity and Environment (2007, background): “Wolk et al. (2005) studied frequency and properties of flares in the Orion Nebula cluster, concluding that the median peak luminosity of their sample was log LX = 30.97, with extremely hard spectra at peak time.”
EXCLUSION OF COSMIC RAYS IN PROTOPLANETARY DISKS: STELLAR AND MAGNETIC EFFECTS (2013, background): “…has been observed that objects with high stellar X-ray luminosity (LXR & 1031 erg s−1) typically have harder X-ray spectra at energies exceeding 2 keV, characteristic of emission contribution from stellar flares (Carkner et al. 1996; Imanishi et al. 2001; Wolk et al. 2005; Preibisch et al. 2005).”
The Origin of T Tauri X-Ray Emission: New Insights from the Chandra Orion Ultradeep Project (2005, background): “Wolk et al. (2005) empirically establish a proxy for the quiescent emission levels by determining a ‘‘characteristic level’’ in each light curve, which is essentially defined as the average count rate over periods where the count rate is not significantly elevated.”