Stellar activity on the young suns of orion: Coup observations of K5-7 pre-main-sequence stars

S. J. Wolk, F. R. Harnden, E. Flaccomio, G. Micela, F. Favata, H. Shang, E. D. Feigelson

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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 kT 2 ≃ 2.1 × kT 1. 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 L X ∼ 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 radio-nuclides 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.

Original languageEnglish (US)
Pages (from-to)423-449
Number of pages27
JournalAstrophysical Journal, Supplement Series
Issue number2
StatePublished - Oct 2005

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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